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Involvement of Oxidation-Sensitive Mechanisms in the Cardiovascular Effects of Hypercholesterolemia

      Hypercholesterolemia is a common clinical metabolic and/or genetic disorder that promotes functional and structural vascular wall injury. The underlying mechanisms for these deleterious effects involve a local inflammatory response and release of cytokines and growth factors. Consequent activation of oxidation-sensitive mechanisms in the arterial wall, modulation of intracellular signaling pathways, increased oxidation of low-density lipoprotein cholesterol, and quenching of nitric oxide can all impair the functions controlled by the vascular wall and lead to the development of atherosclerosis. This cascade represents a common pathological mechanism activated by various cardiovascular risk factors and may partly underlie synergism among them as well as the early pathogenesis of atherosclerosis. Antioxidant intervention and restoration of the bioavailability of nitric oxide have been shown to mitigate functional and structural arterial alterations and improve cardiovascular outcomes. Elucidation of the precise nature and role of early transductional signaling pathways and transcriptional events activated in hypercholesterolemia in children and adults, including mothers during pregnancy, and understanding their downstream effects responsible for atherogenesis may help in directing preventive and interventional measures against atherogenesis and vascular dysfunction.
      CHD (coronary heart disease), eNOS (endothelial nitric oxide synthase), HMG-CoA (3-hydroxy-3-methylglutaryl coenzyme A), IL (interleukin), iNOS (inducible nitric oxide synthase), LAD (left anterior descending), LDL (low-density lipoprotein), NADPH (nicotine adenine dinucleotide phosphate), NFκB (nuclear factor κ B), NO (nitric oxide), NOS (nitric oxide synthase), ROS (reactive oxygen species)
      Progressive accumulation of evidence over the past 4 decades has shown that elevated plasma cholesterol is an independent risk factor for cardiovascular disease and increased mortality.
      • Smith GD
      • Shipley MJ
      • Marmot MG
      • Rose G
      Plasma cholesterol concentration and mortality: the Whitehall Study.
      Establishment of the National Cholesterol Education Program in 1985 substantially increased the awareness of the risks associated with an elevated cholesterol level and provided guidelines for lipid-lowering therapy.
      • Brown WV
      Hypercholesterolemia in the United States: how far have we come?.
      Despite a decline in mean serum cholesterol levels in the United States and the availability of therapeutic options, about 50% of middle-aged adults still have total cholesterol values higher than desirable,
      • Grundy SM
      Management of high serum cholesterol and related disorders in patients at risk for coronary heart disease.
      which likely contribute to atherosclerosis being one of the major causes of coronary heart disease (CHD) and premature death in the United States.
      • Ross R
      The pathogenesis of atherosclerosis: a perspective for the 1990s.
      Moreover, progressive lifestyle changes toward a Western diet with high-fat intake are increasing the incidence of hypercholesterolemia
      • Yamada M
      • Wong FL
      • Kodama K
      • Sasaki H
      • Shimaoka K
      • Yamakido M
      Longitudinal trends in total serum cholesterol levels in a Japanese cohort, 1958–1986.
      • Zhou B
      • Rao X
      • Dennis BH
      • PRC-USA Cardiovascular and Cardiopulmonary Research Group
      • et al.
      The relationship between dietary factors and serum lipids in Chinese urban and rural populations of Beijing and Guangzhou.
      and consequently CHD
      • Woo KS
      • Chook P
      • Raitakari OT
      • McQuillan B
      • Feng JZ
      • Celermajer DS
      Westernization of Chinese adults and increased subclinical atherosclerosis.
      in populations that previously had a relatively low risk for the disease.

      MECHANISMS UNDERLYING CARDIOVASCULAR EFFECTS OF HYPERCHOLESTEROLEMIA

      The increased availability of lipids in hypercholesterolemia promotes initiation and progression of atherogenesis in the arterial wall because the oxidative modification and uptake of lipids are not feedback controlled, thus facilitating their excessive uptake.
      • Gniwotta C
      • Morrow JD
      • Roberts II, LJ
      • Kühn H
      Prostaglandin F2-like compounds, F2-isoprostanes, are present in increased amounts in human atherosclerotic lesions.
      Indeed, angiographic trials have demonstrated that cholesterol-lowering therapy significantly reduced progression and increased regression of atherosclerotic coronary arterial lesions.
      • Brown BG
      • Zhao XQ
      • Sacco DE
      • Albers JJ
      Lipid lowering and plaque regression: new insights into prevention of plaque disruption and clinical events in coronary disease.
      Surprisingly, however, the marked reduction in clinical events far outweighed the relatively modest frequency and magnitude of lesion regression, which may be partly explained by local depletion of lipids and plaque stabilization, with an ensuing decrease in acute coronary events.
      • Brown BG
      • Zhao XQ
      • Sacco DE
      • Albers JJ
      Atherosclerosis regression, plaque disruption, and cardiovascular events: a rationale for lipid lowering in coronary artery disease.
      Furthermore, the increased incidence of cardiac events associated with hypercholesterolemia in the absence of significantly obstructive CHD has been partly attributed to functional alterations in the arterial wall, such as impaired coronary vascular responses
      • Suwaidi JA
      • Hamasaki S
      • Higano ST
      • Nishimura RA
      • Holmes Jr, DR
      • Lerman A
      Long-term follow-up of patients with mild coronary artery disease and endothelial dysfunction.
      to various stimuli, and to increased cardiac demand.
      • Kinlay S
      • Ganz P
      Role of endothelial dysfunction in coronary artery disease and implications for therapy.
      • Britten M
      • Schachinger V
      The role of endothelial function for ischemic manifestations of coronary atherosclerosis [in German].
      Indeed, over the past 2 decades it has become apparent that endothelium-dependent vascular relaxation is abnormal in various disease states, including hypercholesterolemia, atherosclerosis, diabetes mellitus, hypertension, and pre-eclampsia, and after heart transplantation.
      • Harrison DG
      • Ohara Y
      Physiologic consequences of increased vascular oxidant stresses in hypercholesterolemia and atherosclerosis: implications for impaired vasomotion.
      • Lerman LO
      • Nath KA
      • Rodriguez-Porcel M
      • et al.
      Increased oxidative stress in experimental renovascular hypertension.
      • Rodriguez-Porcel M
      • Krier JD
      • Lerman A
      • et al.
      Combination of hypercholesterolemia and hypertension augments renal function abnormalities.
      In 1986 Ludmer et al
      • Ludmer PL
      • Selwyn AP
      • Shook TL
      • et al.
      Paradoxical vasoconstriction induced by acetylcholine in atherosclerotic coronary arteries.
      first demonstrated that intra-coronary infusion of acetylcholine in humans with CHD caused coronary vasoconstriction. Altered vasomotor regulation by the endothelium has subsequently been shown to be an early development of atherogenesis
      • Lerman A
      • Burnett Jr, JC
      Intact and altered endothelium in regulation of vasomotion.
      involving both large vessels and the microcirculation
      • Cooper A
      • Heagerty AM
      Endothelial dysfunction in human intramyocardial small arteries in atherosclerosis and hypercholesterolemia.
      and to be at least partly reversible with lipid-lowering therapy,
      • Hamasaki S
      • Higano ST
      • Suwaidi JA
      • et al.
      Cholesterol-lowering treatment is associated with improvement in coronary vascular remodeling and endothelial function in patients with normal or mildly diseased coronary arteries.
      blockade of the renin-angiotensin system,
      • Pitt B
      The potential use of angiotensin-converting enzyme inhibitors in patients with hyperlipidemia.
      and/or antioxidant therapeutic strategies.
      • Harrison DG
      • Ohara Y
      Physiologic consequences of increased vascular oxidant stresses in hypercholesterolemia and atherosclerosis: implications for impaired vasomotion.
      Nonetheless, the abnormal regulation of vascular tone may reflect impairment in an array of functions controlled by the vascular wall, such as lipid breakdown, platelet function, coagulation, monocyte adhesion, inflammation, and vessel growth.
      • Luscher TF
      • Tanner FC
      • Noll G
      Lipids and endothelial function: effects of lipid-lowering and other therapeutic interventions.
      • Vogel RA
      • Corretti MC
      • Gellman J
      Cholesterol, cholesterol lowering, and endothelial function.
      The underlying mechanisms responsible for these abnormalities are likely multifactorial, but major contributors that appear to be enhanced during hypercholesterolemia and could be responsible for the early endothelial dysfunction include (1) uncoupling of receptors from G proteins, (2) increased production of oxygen radicals, and (3) decreased availability of L-arginine, a nitric oxide (NO) precursor, coupled with reduced NO production by the damaged endothelium (see subsequent discussion). Indeed, several such events may stem from activation of redox-sensitive mechanisms involved in cellular signaling
      • de Nigris F
      • Franconi F
      • Maida I
      • Palumbo G
      • Anania V
      • Napoli C
      Modulation by α- and ?-tocopherol and oxidized low-density lipoprotein of apoptotic signaling in human coronary smooth muscle cells.
      • de Nigris F
      • Youssef T
      • Ciafré S
      • et al.
      Evidence for oxidative activation of c-Myc-dependent nuclear signaling in human coronary smooth muscle cells and in early lesions of Watanabe heritable hyperlipidemic rabbits: protective effects of vitamin E.
      • Ignarro LJ
      • Cirino G
      • Casini A
      • Napoli C
      Nitric oxide as a signaling molecule in the vascular system: an overview.
      • Mercurio F
      • Manning AM
      Multiple signals converging on NF-kappaB.
      • Napoli C
      • Quehenberger O
      • de Nigris F
      • Abete P
      • Glass CK
      • Palinski W
      Mildly oxidized low density lipoprotein activates multiple apoptotic signaling pathways in human coronary cells.
      (such as nuclear factor κ B [NFκB]
      • Mercurio F
      • Manning AM
      Multiple signals converging on NF-kappaB.
      • Wilson SH
      • Caplice NM
      • Simari RD
      • Holmes Jr, DR
      • Carlson PJ
      • Lerman A
      Activated nuclear factor-κB is present in the coronary vasculature in experimental hypercholesterolemia.
      and c-Myc
      • de Nigris F
      • Lerman LO
      • Rodriguez-Porcel M
      • De Montis MP
      • Lerman A
      • Napoli C
      c-Myc activation in early coronary lesions in experimental hypercholesterolemia.
      ), increased levels, and subsequent oxidation of low-density lipoprotein (LDL) and oxidative degradation of NO.

      Reactive Oxygen Species

      A growing body of evidence suggests that numerous pathological conditions are associated with an increased vascular (and to a lesser extent plasma) production of reactive oxygen species (ROS) and other radicals,
      • Harrison DG
      • Ohara Y
      Physiologic consequences of increased vascular oxidant stresses in hypercholesterolemia and atherosclerosis: implications for impaired vasomotion.
      • Kojda G
      • Harrison D
      Interactions between NO and reactive oxygen species: pathophysiological importance in atherosclerosis, hypertension, diabetes and heart failure.
      the most prominent of which are superoxide and hydroxyl radical,
      • Griendling KK
      • Sorescu D
      • Lassegue B
      • Ushio-Fukai M
      Modulation of protein kinase activity and gene expression by reactive oxygen species and their role in vascular physiology and pathophysiology.
      and oxidants like hydrogen peroxide and peroxynitrite.
      • Ferdinandy P
      • Schulz R
      Peroxynitrite: toxic or protective in the heart?.
      This form of pro-oxidant shift in vascular redox status (the so-called oxidant stress), particularly interactions between NO and ROS, represents a common pathological mechanism activated by many cardiovascular risk factors.
      • Kojda G
      • Harrison D
      Interactions between NO and reactive oxygen species: pathophysiological importance in atherosclerosis, hypertension, diabetes and heart failure.
      Furthermore, ROS seem to serve important cellular signaling mechanisms responsible for many of the features of vascular dysfunction and atherogenic lesion formation.
      • de Nigris F
      • Youssef T
      • Ciafré S
      • et al.
      Evidence for oxidative activation of c-Myc-dependent nuclear signaling in human coronary smooth muscle cells and in early lesions of Watanabe heritable hyperlipidemic rabbits: protective effects of vitamin E.
      • Napoli C
      • Quehenberger O
      • de Nigris F
      • Abete P
      • Glass CK
      • Palinski W
      Mildly oxidized low density lipoprotein activates multiple apoptotic signaling pathways in human coronary cells.
      • Kojda G
      • Harrison D
      Interactions between NO and reactive oxygen species: pathophysiological importance in atherosclerosis, hypertension, diabetes and heart failure.
      Hypercholesterolemia per se may enhance formation of lipid peroxidative compounds, which are formed when ROS (and/or other radicals) react with increased levels of plasma and tissue lipids. The precipitating events in radical generation during the evolution of atherosclerosis appear to involve early injury to the vascular endothelial layer,
      • Hennig B
      • Chow CK
      Lipid peroxidation and endothelial cell injury: implications in atherosclerosis.
      which increases its adhesiveness, permeability, and procoagulation properties, and damage to the intima via formation of oxidized lipoproteins (see subsequent discussion).
      • Ross R
      Atherosclerosis—an inflammatory disease.
      Penetration and accumulation in the arterial wall of triglyceride-rich lipoproteins, including very LDL, chylomicrons, and their remnants, activate or induce the synthesis of factors that can initiate inflammatory responses. These include plasminogen activator inhibitor 1 (which may interfere with fibrinolysis), protein kinase C, mitogen-activated protein kinase, and NFκB, which has an important role in the phenotypic modulation of endothelial cells to a proinflammatory condition
      • Stemerman MB
      Lipoprotein effects on the vessel wall [editorial].
      In particular, LDL has numerous effects on the endothelium, including those on plasminogen activator inhibitor 1 and induction of adhesion molecule expression
      • Stemerman MB
      Lipoprotein effects on the vessel wall [editorial].
      Native LDL per se can induce the release of superoxide anion,
      • Pritchard Jr, KA
      • Groszek L
      • Smalley DM
      • et al.
      Native low-density lipoprotein increases endothelial cell nitric oxide synthase generation of superoxide anion.
      leading to formation of the potent oxidant peroxynitrite and triggering a vicious cycle of oxidation. Subsequent oxidation of LDL yields its oxidized form, which possesses greater efficacy in initiation of superoxide anion production and endothelial dysfunction.
      • Hein TW
      • Kuo L
      LDLs impair vasomotor function of the coronary microcirculation: role of superoxide anions.
      Thus, early injury induces the endothelium to have procoagulant properties; to form vasoactive molecules, cytokines, and growth factors; and to initiate a local inflammatory response that might continue indefinitely.
      • Ross R
      Atherosclerosis—an inflammatory disease.
      Release of cytokines and growth factors,
      • Ross R
      Atherosclerosis—an inflammatory disease.
      such as tumor necrosis factor α, interleukin (IL)-1ß, and interferon-gamma, may in turn stimulate ROS-producing enzymes like nicotine adenine dinucleotide phosphate (NADPH) oxidase, the major source of superoxide anion in vascular cells and myocytes,
      • Griendling KK
      • Sorescu D
      • Ushio-Fukai M
      NAD(P)H oxidase: role in cardiovascular biology and disease.
      xanthine oxidase,
      • Cardillo C
      • Kilcoyne CM
      • Cannon III, RO
      • Quyyumi AA
      • Panza JA
      Xanthine oxidase inhibition with oxypurinol improves endothelial vasodilator function in hypercholesterolemic but not in hypertensive patients.
      • Wolin MS
      Reactive oxygen species and vascular signal transduction mechanisms.
      NO synthase (NOS), cyclooxygenase, myeloperoxidase,
      • Berliner JA
      • Heinecke JW
      The role of oxidized lipoproteins in atherogenesis.
      and lipoxygenase.
      • Kunsch C
      • Medford RM
      Oxidative stress as a regulator of gene expression in the vasculature.
      This cascade may also involve local activation of the renin-angiotensin system,
      • Hoshida S
      • Yamashita N
      • Kuzuya T
      • Hori M
      Differential effects of long-term renin-angiotensin system blockade on limitation of infarct size in cholesterol-fed rabbits.
      which can promote oxidation via angiotensin II-induced stimulation of NADPH oxidase.
      • Rajagopalan S
      • Kurz S
      • Münzel T
      • et al.
      Angiotensin II-mediated hypertension in the rat increases vascular superoxide production via membrane NADH/NADPH oxidase activation: contribution to alterations of vasomotor tone.
      The vascular NADPH oxidase is similar in structure to the neutrophil NADPH oxidase,
      • Griendling KK
      • Sorescu D
      • Lassegue B
      • Ushio-Fukai M
      Modulation of protein kinase activity and gene expression by reactive oxygen species and their role in vascular physiology and pathophysiology.
      and it produces superoxide and hydrogen peroxide on stimulation by mechanical forces (eg, stretch and shear stress),
      • De Keulenaer GW
      • Chappell DC
      • Ishizaka N
      • Nerem RM
      • Alexander RW
      • Griendling KK
      Oscillatory and steady laminar shear stress differentially affect human endothelial redox state: role of a superoxide-producing NADH oxidase.
      hormonal stimulation,
      • Rajagopalan S
      • Kurz S
      • Münzel T
      • et al.
      Angiotensin II-mediated hypertension in the rat increases vascular superoxide production via membrane NADH/NADPH oxidase activation: contribution to alterations of vasomotor tone.
      or growth factors and cytokines.
      • Griendling KK
      • Sorescu D
      • Ushio-Fukai M
      NAD(P)H oxidase: role in cardiovascular biology and disease.
      In hypercholesterolemia an important role for increased production of ROS is also ascribed to xanthine oxidase,
      • White CR
      • Darley-Usmar V
      • Berrington WR
      • et al.
      Circulating plasma xanthine oxidase contributes to vascular dysfunction in hypercholesterolemic rabbits.
      which, due to an increase in plasma cholesterol, is released into the circulation where it binds to endothelial cells and sustains production of superoxide anion.
      • White CR
      • Darley-Usmar V
      • Berrington WR
      • et al.
      Circulating plasma xanthine oxidase contributes to vascular dysfunction in hypercholesterolemic rabbits.
      The cellular sources of these species include blood-borne phagocytic cells and infiltrating monocytes (Figure 1), in addition to cells within the vascular wall, such as smooth muscle cells, endothelial cells, and fibroblasts.
      • Griendling KK
      • Alexander RW
      Oxidative stress and cardiovascular disease [editorial].
      Notwithstanding the presence of macrophages and the postulated involvement of superoxide in atherogenesis, its NADPH oxidase-derived source may be from vascular cells because paucity of phagocytic NADPH oxidase does not decrease lesion size in apolipoprotein E- and gp91-phox subunit deficient knock-out mice.
      • Kirk EA
      • Dinauer MC
      • Rosen H
      • Chait A
      • Heinecke JW
      • LeBoeuf RC
      Impaired superoxide production due to a deficiency in phagocyte NADPH oxidase fails to inhibit atherosclerosis in mice.
      Although cells are normally protected from ROS by antioxidant defense mechanisms, such as the oxygen-radical scavenger enzymes catalase, superoxide dismutase, and glutathione per-oxidase, the rate of ROS formation can exceed the antioxidant defense capacity and thereby increase oxidant stress.
      • Kunsch C
      • Medford RM
      Oxidative stress as a regulator of gene expression in the vasculature.
      The precise mechanisms whereby cells in the arterial wall produce ROS are only presently coming to light and will almost certainly prove to be a primary focus of future therapeutic strategies.
      Figure thumbnail gr1
      Figure 1Oxidation-sensitive mechanisms activated in the arterial wall during hypercholesterolemia. Increased availability of native low-density lipoprotein (nLDL) cholesterol and release of reactive oxygen species (ROS) lead to production of “minimally” or “mildly” oxidized LDL (moxLDL) in association with a decrease in bioavailability of nitric oxide (NO). These alterations may interfere with the normal function of the blood vessel and thus induce endothelial dysfunction. Furthermore, increased uptake of moxLDL by the vascular wall results in further oxidation of LDL to an “extensively” modified (eoxLDL) form and subsequent accumulation and macrophage uptake of LDL, which in turn promote inflammatory responses and continued release of ROS. Pro-oxidant effects on endothelial and smooth muscle cells initiate a chain reaction of redox-sensitive transductional and transcriptional events (inset). Activation of both FAS and tumor necrosis factor receptors (TNFR) and the caspase, mitogen-activated protein (MAP) kinase, and JUN kinase pathways lead to stimulation of various oxidation-sensitive transcription factors that have the potential to increase the expression of various cell adhesion molecules and inflammatory gene products. Antioxidants can interfere with this pathophysiological scenario at several points by scavenging or blunting the release of ROS and by retarding LDL oxidation. AP = activator protein; ATF = activating transcription factor; CREB = cyclic adenosine monophosphate response element binding protein; E2F = elongation 2 factor; ELK = ets-like element kinase; IκB = inhibitor of κ B; NFκB = nuclear factor κ B.
      The ROS in turn initiate a chain reaction of redox-sensitive signaling events through which they influence vascular smooth muscle cell growth and migration, modulation of vascular function, expression of a proinflammatory phenotype, and modification of the extracellular matrix
      • Griendling KK
      • Sorescu D
      • Lassegue B
      • Ushio-Fukai M
      Modulation of protein kinase activity and gene expression by reactive oxygen species and their role in vascular physiology and pathophysiology.
      (Figure 1). The signaling pathways through which ROS exert these effects include activation of both Fas and tumor necrosis factor receptors,
      • Napoli C
      • Quehenberger O
      • de Nigris F
      • Abete P
      • Glass CK
      • Palinski W
      Mildly oxidized low density lipoprotein activates multiple apoptotic signaling pathways in human coronary cells.
      caspase, and the mitogen-activated protein kinase/Jun kinase pathways.
      • de Nigris F
      • Franconi F
      • Maida I
      • Palumbo G
      • Anania V
      • Napoli C
      Modulation by α- and ?-tocopherol and oxidized low-density lipoprotein of apoptotic signaling in human coronary smooth muscle cells.
      As a result, several redox-sensitive transcription factors are stimulated, such as activating transcription factor 2, ets-like element kinase-dependent 1, cyclic adenosine monophosphate response element binding protein, NFκB, activator protein 1 complex, p53, and c-Myc/Max complex and its binding factors elongation 2 factor and activator protein 2 complex
      • de Nigris F
      • Franconi F
      • Maida I
      • Palumbo G
      • Anania V
      • Napoli C
      Modulation by α- and ?-tocopherol and oxidized low-density lipoprotein of apoptotic signaling in human coronary smooth muscle cells.
      • de Nigris F
      • Youssef T
      • Ciafré S
      • et al.
      Evidence for oxidative activation of c-Myc-dependent nuclear signaling in human coronary smooth muscle cells and in early lesions of Watanabe heritable hyperlipidemic rabbits: protective effects of vitamin E.
      • Napoli C
      • Quehenberger O
      • de Nigris F
      • Abete P
      • Glass CK
      • Palinski W
      Mildly oxidized low density lipoprotein activates multiple apoptotic signaling pathways in human coronary cells.
      • Wilson SH
      • Caplice NM
      • Simari RD
      • Holmes Jr, DR
      • Carlson PJ
      • Lerman A
      Activated nuclear factor-κB is present in the coronary vasculature in experimental hypercholesterolemia.
      (Figure 1). This can lead to increased expression of various cell adhesion molecules and inflammatory gene products, such as vascular cell adhesion molecule 1, intercellular adhesion molecule 1, and monocyte chemo-attractant protein 1. The involvement of ROS in activation of these pathways is underscored by the successful attenuation of these components using antioxidants, both in vitro and in vivo,
      • de Nigris F
      • Franconi F
      • Maida I
      • Palumbo G
      • Anania V
      • Napoli C
      Modulation by α- and ?-tocopherol and oxidized low-density lipoprotein of apoptotic signaling in human coronary smooth muscle cells.
      • de Nigris F
      • Youssef T
      • Ciafré S
      • et al.
      Evidence for oxidative activation of c-Myc-dependent nuclear signaling in human coronary smooth muscle cells and in early lesions of Watanabe heritable hyperlipidemic rabbits: protective effects of vitamin E.
      • Kunsch C
      • Medford RM
      Oxidative stress as a regulator of gene expression in the vasculature.
      and oxygen-radical scavengers.
      • Napoli C
      • Quehenberger O
      • de Nigris F
      • Abete P
      • Glass CK
      • Palinski W
      Mildly oxidized low density lipoprotein activates multiple apoptotic signaling pathways in human coronary cells.
      Accumulating evidence also provides a compelling case for enhanced oxidative stress in vascular dysfunction, the most important manifestation of which is modulation of a set(s) of proinflammatory genes that are regulated directly or indirectly by ROS in the arterial wall.
      • Alexander RW
      Atherosclerosis as disease of redox-sensitive genes.
      Viewed in this perspective, LDL oxidation could be an important consequence of a generalized metabolic oxidation-related abnormality of the arterial wall in atherosclerosis, rather than a single core pathophysiological feature. The fact that hypercholesterolemia, hypertension, and advanced glycosylation end products formation linked to diabetes mellitus all activate similar redox-sensitive pro-inflammatory genes associated with the pathogenesis of atherosclerosis and decrease the bioavailability of NO provides the potential for the development of a unifying framework concerning the etiology of atherosclerotic disease.
      • Rodriguez-Porcel M
      • Krier JD
      • Lerman A
      • et al.
      Combination of hypercholesterolemia and hypertension augments renal function abnormalities.
      • Ross R
      Atherosclerosis—an inflammatory disease.
      • Lee RT
      • Libby P
      The unstable atheroma.
      • Libby P
      • Ridker PM
      Novel inflammatory markers of coronary risk: theory versus practice [editorial].
      The atherogenic effect of hypertension may be partly mediated via activation of the renin-angiotensin system, stimulation of NADPH oxidase,
      • Rajagopalan S
      • Kurz S
      • Münzel T
      • et al.
      Angiotensin II-mediated hypertension in the rat increases vascular superoxide production via membrane NADH/NADPH oxidase activation: contribution to alterations of vasomotor tone.
      and increased levels of proinflammatory genes in the vessel wall
      • Chen X-L
      • Tummala PE
      • Olbrych MT
      • Alexander RW
      • Medford RM
      Angiotensin II induces monocyte chemoattractant protein-1 gene expression in rat vascular smooth muscle cells.
      ; however, shear stress and vascular hemodynamic stress per se can also trigger redox-sensitive mechanisms and thus contribute to hypertension-induced atherogenesis.
      • De Keulenaer GW
      • Chappell DC
      • Ishizaka N
      • Nerem RM
      • Alexander RW
      • Griendling KK
      Oscillatory and steady laminar shear stress differentially affect human endothelial redox state: role of a superoxide-producing NADH oxidase.
      • Ishizaka N
      • De León H
      • Laursen JB
      • et al.
      Angiotensin II-induced hypertension increases heme oxygenase-1 expression in rat aorta.
      Diabetes mellitus and hyperglycemia also augment generation of superoxide anions and LDL peroxidation,
      • El-Swefy S
      • Schaefer EJ
      • Seman LJ
      • et al.
      The effect of vitamin E, probucol, and lovastatin on oxidative status and aortic fatty lesions in hyperlipidemic-diabetic hamsters.
      promote activation of redox-sensitive pathways,
      • Pieper GM
      • Riaz-ul-Haq
      Activation of nuclear factor-κB in cultured endothelial cells by increased glucose concentration: prevention by calphostin C.
      decrease bioavailability of NO,
      • Kakoki M
      • Hirata Y
      • Hayakawa H
      • et al.
      Effects of hypertension, diabetes mellitus, and hypercholesterolemia on endothelin type B receptor-mediated nitric oxide release from rat kidney.
      induce formation of advanced glycosylation end products, and induce endothelial dysfunction.
      • Posch K
      • Simecek S
      • Wascher TC
      • et al.
      Glycated low-density lipoprotein attenuates shear stress-induced nitric oxide synthesis by inhibition of shear stress-activated L-arginine uptake in endothelial cells.
      Indeed, activation of intracellular oxidative signals and modulation of vascular proinflammatory gene expression may provide a molecular mechanism underlying the synergism among cardiovascular risk factors and the early pathogenesis of atherosclerosis.
      • Kunsch C
      • Medford RM
      Oxidative stress as a regulator of gene expression in the vasculature.
      These concepts also underscore the potential of anti-oxidants as attractive therapeutic agents.
      • de Nigris F
      • Franconi F
      • Maida I
      • Palumbo G
      • Anania V
      • Napoli C
      Modulation by α- and ?-tocopherol and oxidized low-density lipoprotein of apoptotic signaling in human coronary smooth muscle cells.
      • de Nigris F
      • Youssef T
      • Ciafré S
      • et al.
      Evidence for oxidative activation of c-Myc-dependent nuclear signaling in human coronary smooth muscle cells and in early lesions of Watanabe heritable hyperlipidemic rabbits: protective effects of vitamin E.
      • Pryor WA
      Vitamin E and heart disease: basic science to clinical intervention trials.
      The effects of experimental hypercholesterolemia and oxidation-sensitive mechanisms on this cascade of events have been investigated in various animal models, such as murine
      • Carmeliet P
      • Moons L
      • Collen D
      Mouse models of angiogenesis, arterial stenosis, atherosclerosis and hemostasis.
      • Fuster V
      • Poon M
      • Willerson JT
      Learning from the transgenic mouse: endothelium, adhesive molecules, and neointimal formation [editorial].
      • Palinski W
      • Napoli C
      • Reaven PD
      Mouse models of atherosclerosis.
      and swine.
      • Shimokawa H
      • Vanhoutte PM
      Hypercholesterolemia causes generalized impairment of endothelium-dependent relaxation to aggregating platelets in porcine arteries.
      • Lerman A
      • Webster MWI
      • Chesebro JH
      • et al.
      Circulating and tissue endothelin immunoreactivity in hypercholesterolemic pigs.
      Experimental investigation of the development and progression of atherosclerosis has been greatly facilitated by the use of targeted mouse models of the disease, particularly those resulting from the absence of functional genes.
      • Knowles JW
      • Maeda N
      Genetic modifiers of atherosclerosis in mice.
      Mice are rapidly becoming a ubiquitous model of atherogenesis, and although wild-type mice are inherently resistant to hypercholesterolemia and atherogenesis, identification of genes determining the susceptibility to the disease and gene-knockout and transgene approaches have led to generation of the apolipoprotein E knockout mouse, LDL-receptor deficient mouse, and double-knockout mouse models that develop extensive atherosclerosis.
      • Carmeliet P
      • Moons L
      • Collen D
      Mouse models of angiogenesis, arterial stenosis, atherosclerosis and hemostasis.
      • Fuster V
      • Poon M
      • Willerson JT
      Learning from the transgenic mouse: endothelium, adhesive molecules, and neointimal formation [editorial].
      • Palinski W
      • Napoli C
      • Reaven PD
      Mouse models of atherosclerosis.
      The hypercholesterolemic mouse model also facilitated study of the “priming” phenomenon, which involves activation of NFκB-dependent genes in lesion-prone areas.
      • Hajra L
      • Evans AI
      • Chen M
      • Hyduk SJ
      • Collins T
      • Cybulsky MI
      The NF-κB signal transduction pathway in aortic endothelial cells is primed for activation in regions predisposed to atherosclerotic lesion formation.
      The pig model is appealing for studying human disease states because the anatomy and physiology of the pig heart are comparable to those of humans.
      • Bloor CM
      • White FC
      • Roth DM
      The pig as a model of myocardial ischemia and gradual coronary artery occlusion.
      In hypercholesterolemic pigs, coronary vasomotor dysfunction is associated with an increase in both the level
      • Lerman A
      • Webster MWI
      • Chesebro JH
      • et al.
      Circulating and tissue endothelin immunoreactivity in hypercholesterolemic pigs.
      and the vasoconstrictor effects
      • Mathew V
      • Cannan CR
      • Miller VM
      • et al.
      Enhanced endothelin-mediated coronary vasoconstriction and attenuated basal nitric oxide activity in experimental hypercholesterolemia.
      of endothelin-1, as well as decreased bioavailability of NO,
      • Mathew V
      • Cannan CR
      • Miller VM
      • et al.
      Enhanced endothelin-mediated coronary vasoconstriction and attenuated basal nitric oxide activity in experimental hypercholesterolemia.
      • Best PJM
      • Lerman LO
      • Romero JC
      • Richardson D
      • Holmes Jr, DR
      • Lerman A
      Coronary endothelial function is preserved with chronic endothelin receptor antagonism in experimental hyper-cholesterolemia in vitro.
      activation of NFκB,
      • Wilson SH
      • Caplice NM
      • Simari RD
      • Holmes Jr, DR
      • Carlson PJ
      • Lerman A
      Activated nuclear factor-κB is present in the coronary vasculature in experimental hypercholesterolemia.
      and priming of c-Myc.
      • de Nigris F
      • Lerman LO
      • Rodriguez-Porcel M
      • De Montis MP
      • Lerman A
      • Napoli C
      c-Myc activation in early coronary lesions in experimental hypercholesterolemia.
      Increased vasoconstrictor activity of oxidation byproducts in this model
      • Wilson SH
      • Best PJM
      • Lerman LO
      • Holmes Jr, DR
      • Richardson DM
      • Lerman A
      Enhanced coronary vasoconstriction to oxidative stress product, 8-epi-prostaglandinF, in experimental hypercholesterolemia.
      can be blunted by endothelin receptor blockade.
      • Hasdai D
      • Mathew V
      • Schwartz RS
      • et al.
      Enhanced endothelin-B-receptor-mediated vasoconstriction of small porcine coronary arteries in diet-induced hypercholesterolemia.
      • Best PJM
      • McKenna CJ
      • Hasdai D
      • Holmes Jr, DR
      • Lerman A
      Chronic endothelin receptor antagonism preserves coronary endothelial function in experimental hypercholesterolemia.
      These changes were associated with alterations in intramyocardial microvascular function
      • Möhlenkamp S
      • Lerman LO
      • Lerman A
      • et al.
      Minimally invasive evaluation of coronary microvascular function by electron beam computed tomography.
      and spatial density.
      • Rodriguez-Porcel M
      • Lerman A
      • Ritman EL
      • Wilson SH
      • Best PJM
      • Lerman LO
      Altered myocardial microvascular 3D architecture in experimental hypercholesterolemia.
      Indeed, we recently showed
      • Rodriguez-Porcel M
      • Lerman A
      • Best PJM
      • Krier JD
      • Napoli C
      • Lerman LO
      Hypercholesterolemia impairs myocardial perfusion and permeability: role of oxidative stress and endogenous scavenging activity.
      that in this model hypercholesterolemia was associated with blunted myocardial perfusion and increased vascular permeability responses to increased cardiac demand, accompanied by depletion of tissue endogenous radical scavengers and enhanced oxidizability of LDL, all of which were correctable with long-term antioxidant therapy. We subsequently showed that similar oxidation-sensitive mechanisms were activated in the systemic and renal circulation of the renovascular hypertensive pig model
      • Lerman LO
      • Nath KA
      • Rodriguez-Porcel M
      • et al.
      Increased oxidative stress in experimental renovascular hypertension.
      and markedly augmented by coexistence with hypercholesterolemia,
      • Rodriguez-Porcel M
      • Krier JD
      • Lerman A
      • et al.
      Combination of hypercholesterolemia and hypertension augments renal function abnormalities.
      paralleled by renal perfusion abnormalities. A growing bulk of evidence shows that coronary blood flow and myocardial perfusion are altered in humans with hypercholesterolemia
      • Schachinger V
      • Zeiher AM
      Alterations of coronary blood flow and myocardial perfusion in hypercholesterolaemia.
      • Zeiher AM
      • Drexler H
      • Wollschlager H
      • Just H
      Modulation of coronary vasomotor tone in humans: progressive endothelial dysfunction with different early stages of coronary atherosclerosis.
      • Hasdai D
      • Gibbons RJ
      • Holmes Jr, DR
      • Higano ST
      • Lerman A
      Coronary endothelial dysfunction in humans is associated with myocardial perfusion defects.
      • Hasdai D
      • Holmes Jr, DR
      • Higano ST
      • Burnett Jr, JC
      • Lerman A
      Prevalence of coronary blood flow reserve abnormalities among patients with nonobstructive coronary artery disease and chest pain.
      and are clinically consequential
      • Suwaidi JA
      • Hamasaki S
      • Higano ST
      • Nishimura RA
      • Holmes Jr, DR
      • Lerman A
      Long-term follow-up of patients with mild coronary artery disease and endothelial dysfunction.
      ; they also may be related to the concurrent oxidative stress.

      Oxidized LDL

      Susceptibility to atherosclerosis is associated with elevations in specific populations of apolipoprotein B–containing particles involving increased oxidation of LDL and associated changes in its biological properties.
      • Steinberg D
      Low density lipoprotein oxidation and its pathobiological significance.
      • Tribble DL
      Lipoprotein oxidation in dyslipidemia: insights into general mechanisms affecting lipoprotein oxidative behavior.
      Lipoprotein oxidation may be potentiated by the greater mass of oxidizable LDL substrates available in hypercholesterolemia, by a decrease of natural antioxidants bound on LDL, and by a greater intrinsic susceptibility for oxidation of the specific steric forms of LDL (eg, small dense LDL) that arise in these disorders.
      • Steinberg D
      Low density lipoprotein oxidation and its pathobiological significance.
      • Tribble DL
      Lipoprotein oxidation in dyslipidemia: insights into general mechanisms affecting lipoprotein oxidative behavior.
      Entrapment of the LDL particles within the arterial wall (Figure 1) results in progressive oxidation (to minimally and extensively oxidized forms) and internalization of this modified LDL by an entire family of scavenger receptors on macrophages and smooth muscle cells, which in turn lead to formation of lipid peroxides, activation of inflammatory cytokines, and a vicious cycle of inflammation and oxidation, eventuating in accumulation of lipid-laden foam cells and plaque formation.
      • Ross R
      Atherosclerosis—an inflammatory disease.
      The broad cascade of transduction and transcriptional events in the arterial wall induced by 2 forms of oxidized LDL is shown in Figure 1. These pathways activated by minimally and extensively oxidized LDL are probably largely similar to those activated by ROS and other radicals.
      • de Nigris F
      • Franconi F
      • Maida I
      • Palumbo G
      • Anania V
      • Napoli C
      Modulation by α- and ?-tocopherol and oxidized low-density lipoprotein of apoptotic signaling in human coronary smooth muscle cells.
      • Napoli C
      • Quehenberger O
      • de Nigris F
      • Abete P
      • Glass CK
      • Palinski W
      Mildly oxidized low density lipoprotein activates multiple apoptotic signaling pathways in human coronary cells.
      Obviously, several “intermediate” forms of oxidized LDL can be formed in the intima with different degrees of both lipid and protein oxidation. Considerable light has been shed on the mechanisms of interaction between hypercholesterolemia and hypertension with the recent discovery of LOX-1,
      • Sawamura T
      • Kume N
      • Aoyama T
      • et al.
      An endothelial receptor for oxidized low-density lipoprotein.
      a novel lectin-like receptor for oxidized LDL on vascular wall cells that is inducible by angiotensin II
      • Morawietz H
      • Rueckschloss U
      • Niemann B
      • et al.
      Angiotensin II induces LOX-1, the human endothelial receptor for oxidized low-density lipoprotein.
      and fluid shear stress,
      • Murase T
      • Kume N
      • Korenaga R
      • et al.
      Fluid shear stress transcriptionally induces lectin-like oxidized LDL receptor-1 in vascular endothelial cells.
      is up-regulated in both disease states,
      • Nagase M
      • Hirose S
      • Sawamura T
      • Masaki T
      • Fujita T
      Enhanced expression of endothelial oxidized low-density lipoprotein receptor (LOX-1) in hypertensive rats.
      • Chen M
      • Kakutani M
      • Minami M
      • et al.
      Increased expression of lectin-like oxidized low density lipoprotein receptor-1 in initial atherosclerotic lesions of Watanabe heritable hyperlipidemic rabbits.
      and may provide an additional link between hypertension and atherogenesis.
      • Kita T
      LOX-1, a possible clue to the missing link between hypertension and atherogenesis.
      Furthermore, the ability of oxidized LDL to up-regulate its own endothelial receptor
      • Li D
      • Mehta JL
      Upregulation of endothelial receptor for oxidized LDL (LOX-1) by oxidized LDL and implications in apoptosis of human coronary artery endothelial cells: evidence from use of antisense LOX-1 mRNA and chemical inhibitors.
      provides an additional route for the vicious cycle of pathophysiological events triggered in hypercholesterolemia.
      These facets of LDL oxidation are potentiated in several forms of dyslipidemia and, in view of both differences and similarities among these disorders, indicate that LDL oxidative behavior is determined by a complex array of physical, chemical, and metabolic factors.
      • Chait A
      • Brazg RL
      • Tribble DL
      • Krauss RM
      Susceptibility of small, dense, low-density lipoproteins to oxidative modification in subjects with the atherogenic lipoprotein phenotype, pattern B.
      • Napoli C
      • Ambrosio G
      • Scarpato N
      • et al.
      Decreased low-density lipoprotein oxidation after repeated selective apheresis in homozygous familial hypercholesterolemia.
      • Napoli C
      • Postiglione A
      • Triggiani M
      • et al.
      Oxidative structural modifications of low density lipoprotein in homozygous familial hypercholesterolemia.
      Moreover, long-term residence of circulating LDL and aging may increase LDL's susceptibility to further oxidative modification in the arterial wall.
      • Reaven PD
      • Napoli C
      • Merat S
      • Witztum JL
      Lipoprotein modification and atherosclerosis in aging.
      Oxidized LDL exerts profound effects on the vasomotor response of isolated arteries to various stimuli that closely mimic the vascular dysfunction associated with hypercholesterolemia and atherosclerosis in humans.
      • Steinberg D
      Low density lipoprotein oxidation and its pathobiological significance.
      • Cox DA
      • Cohen ML
      Effects of oxidized low-density lipoprotein on vascular contraction and relaxation: clinical and pharmacological implications in atherosclerosis.
      The inhibitory effect of oxidized LDL on vascular relaxation may be related to uncoupling of endothelial receptors from endothelial guanine nucleotide-binding regulatory (Gi) protein and interruption of Gi protein-dependent pathways.
      • Flavahan NA
      Lysophosphatidylcholine modifies G protein-dependent signaling in porcine endothelial cells.
      The beneficial effect of lipid-lowering therapy in restoring vascular function
      • Järvisalo MJ
      • Toikka JO
      • Vasankari T
      • et al.
      HMG CoA reductase inhibitors are related to improved systemic endothelial function in coronary artery disease.
      and greatly decreasing the frequency of cardiac events associated with atherosclerosis,
      • Shepherd J
      • Cobbe SM
      • Ford I
      • West of Scotland Coronary Prevention Study Group
      • et al.
      Prevention of coronary heart disease with pravastatin in men with hypercholesterolemia.
      combined with the ability of antioxidants to alleviate vasomotor disturbances in hypercholesterolemia and slow the progression of atherosclerosis, strongly supports a causative role of oxidized LDL in mediating vascular dysfunction in vivo and contributing to both preclinical and clinical sequelae of CHD.
      • Cox DA
      • Cohen ML
      Effects of oxidized low-density lipoprotein on vascular contraction and relaxation: clinical and pharmacological implications in atherosclerosis.
      Further research for a more complete understanding of the mechanisms of oxidized LDL formation and actions in vivo may reveal novel strategies to inhibit these pathophysiological events and may prove beneficial in the therapeutic management of atherosclerosis-related diseases.

      Nitric Oxide

      One of the main mechanisms underlying impaired endothelial function in hypercholesterolemia and other cardiovascular risk factors
      • Luscher TF
      • Tanner FC
      • Dohi Y
      Age, hypertension and hypercholesterolaemia alter endothelium-dependent vascular regulation.
      is decreased bioavailability of NO.
      • Ignarro LJ
      • Cirino G
      • Casini A
      • Napoli C
      Nitric oxide as a signaling molecule in the vascular system: an overview.
      Bioavailability of NO is probably impaired not by a single defect but by various mechanisms affecting both its synthesis and its breakdown,
      • Ignarro LJ
      • Cirino G
      • Casini A
      • Napoli C
      Nitric oxide as a signaling molecule in the vascular system: an overview.
      • John S
      • Schmieder RE
      Impaired endothelial function in arterial hypertension and hypercholesterolemia: potential mechanisms and differences.
      among which increased superoxide anion production and oxidative stress represent major mechanisms.
      Endogenous NO is generated by a family of 3 distinct calmodulin-dependent NOS enzymes. The endothelial (eNOS) and neuronal NOS isoforms are both constitutively expressed enzymes whose activities are stimulated by increases in intracellular calcium. In the endothelium, eNOS converts the amino acid L-arginine to L-citrulline and NO, a reaction that requires availability of both the substrate (L-arginine) and a cofactor, tetrahydrobiopterin, which couples L-arginine oxidation to NADPH consumption.
      • Vasquez-Vivar J
      • Kalyanaraman B
      • Martasek P
      • et al.
      Superoxide generation by endothelial nitric oxide synthase: the influence of cofactors.
      Tight control of NO signaling is largely regulated at the level of eNOS biosynthesis,
      • Bredt DS
      Endogenous nitric oxide synthesis: biological functions and pathophysiology.
      which can be achieved by modulation of eNOS gene expression (eg, by shear stress or cell proliferation) or activity (eg, by shear stress or stimulation of specific receptors to agonists). Various stimuli for eNOS also alter cellular redox state, suggesting that ROS might modulate eNOS expression.
      • Drummond GR
      • Cai H
      • Davis ME
      • Ramasamy S
      • Harrison DG
      Transcriptional and posttranscriptional regulation of endothelial nitric oxide synthase expression by hydrogen peroxide.
      Localization of eNOS to specialized plasma membrane invaginations (caveolae) seems to be required for its maximal activity,
      • Peterson TE
      • Poppa V
      • Ueba H
      • Wu A
      • Yan C
      • Berk BC
      Opposing effects of reactive oxygen species and cholesterol on endothelial nitric oxide synthase and endothelial cell caveolae.
      and phosphorylation and subcellular translocation (from caveolae to the cytoskeleton or cytosol) are probably involved in eNOS regulation.
      • Arnal JF
      • Dinh-Xuan AT
      • Pueyo M
      • Darblade B
      • Rami J
      Endothelium-derived nitric oxide and vascular physiology and pathology.
      Recent evidence indicates that, in hypercholesterolemia, increased cholesterol uptake by endothelial cells up-regulates the abundance of the structural protein and signal transduction regulator caveolin-1
      • Bucci M
      • Gratton JP
      • Rudic RD
      • et al.
      In vivo delivery of the caveolin-1 scaffolding domain inhibits nitric oxide synthesis and reduces inflammation.
      (a putative negative regulator of eNOS
      • Feron O
      • Dessy C
      • Desager J-P
      • Balligand J-L
      Hydroxy-methylglutaryl-coenzyme A reductase inhibition promotes endothelial nitric oxide synthase activation through a decrease in caveolin abundance.
      • Shah V
      • Toruner M
      • Haddad F
      • et al.
      Impaired endothelial nitric oxide synthase activity associated with enhanced caveolin binding in experimental cirrhosis in the rat.
      ) and stabilizes the inhibitory heterocomplex that it forms with eNOS.
      • Feron O
      • Dessy C
      • Desager J-P
      • Balligand J-L
      Hydroxy-methylglutaryl-coenzyme A reductase inhibition promotes endothelial nitric oxide synthase activation through a decrease in caveolin abundance.
      Similarly, ROS decrease both eNOS expression and association with caveolin.
      • Peterson TE
      • Poppa V
      • Ueba H
      • Wu A
      • Yan C
      • Berk BC
      Opposing effects of reactive oxygen species and cholesterol on endothelial nitric oxide synthase and endothelial cell caveolae.
      Furthermore, in the absence of either L-arginine or tetra-hydrobiopterin (eg, due to tetrahydrobiopterin oxidation by peroxynitrite), eNOS produces superoxide and hydrogen peroxide,
      • Heinzel B
      • John M
      • Klatt P
      • Bohme E
      • Mayer B
      Ca2+/calmodulin-dependent formation of hydrogen peroxide by brain nitric oxide synthase.
      a phenomenon termed NOS uncoupling.
      • Cai H
      • Harrison DG
      Endothelial dysfunction in cardiovascular diseases: the role of oxidant stress.
      In fact, eNOS uncoupling may contribute to increased oxidative stress by both decreasing generation of NO and increasing release of superoxide.
      Immune functions of NO are mediated by a calcium-independent inducible NOS (iNOS).
      • Bredt DS
      Endogenous nitric oxide synthesis: biological functions and pathophysiology.
      This isoform of the NOS enzyme is often involved in proinflammatory processes
      • Detmers PA
      • Hernandez M
      • Mudgett J
      • et al.
      Deficiency in inducible nitric oxide synthase results in reduced atherosclerosis in apolipoprotein E-deficient mice.
      ; is expressed in inflammatory, smooth muscle, and endothelial cells of human atherosclerotic lesions
      • Behr-Roussel D
      • Rupin A
      • Sansilvestri-Morel P
      • Fabiani JN
      • Verbeuren TJ
      Histochemical evidence for inducible nitric oxide synthase in advanced but non-ruptured human atherosclerotic carotid arteries.
      ; and is especially prominent in macrophages.
      • Luoma JS
      • Strålin P
      • Marklund SL
      • Hiltunen TP
      • Särkioja T
      • Ylä-Herttuala S
      Expression of extracellular SOD and iNOS in macrophages and smooth muscle cells in human and rabbit atherosclerotic lesions: colocalization with epitopes characteristic of oxidized LDL and peroxynitrite-modified proteins.
      Its role in atherogenesis is controversial because it appears that iNOS-derived NO can inhibit, have no effect, or enhance leukocyte rolling and adhesion depending on the type of inflammatory response.
      • Hickey MJ
      Role of inducible nitric oxide synthase in the regulation of leucocyte recruitment.
      Indeed, concurrent iNOS deficiency reduced the size of atherosclerotic lesions in atherosclerosis-susceptible apolipoprotein E–deficient mice,
      • Detmers PA
      • Hernandez M
      • Mudgett J
      • et al.
      Deficiency in inducible nitric oxide synthase results in reduced atherosclerosis in apolipoprotein E-deficient mice.
      and its inhibition limited progression of preexisting atherosclerosis in hypercholesterolemic rabbits
      • Behr-Roussel D
      • Rupin A
      • Simonet S
      • et al.
      Effect of chronic treatment with the inducible nitric oxide synthase inhibitor N-iminoethyl-L-lysine or with L-arginine on progression of coronary and aortic atherosclerosis in hypercholesterolemic rabbits.
      ; however, iNOS also counteracted progression of intimal thickening during periadventitial inflammation in rabbit carotid artery
      • De Meyer GR
      • Kockx MM
      • Cromheeke KM
      • Seye CI
      • Herman AG
      • Bult H
      Periadventitial inducible nitric oxide synthase expression and intimal thickening.
      and inhibited inflammatory cytokine-induced proliferative and vasospastic changes in porcine coronary artery in vivo.
      • Fukumoto Y
      • Shimokawa H
      • Kozai T
      • et al.
      Vasculoprotective role of inducible nitric oxide synthase at inflammatory coronary lesions induced by chronic treatment with interleukin-1β in pigs in vivo.
      Interestingly, iNOS-derived NO inhibits eNOS in rat kidney and provokes renal dysfunction consequent to lipopolysaccharide administration.
      • Schwartz D
      • Mendonca M
      • Schwartz I
      • et al.
      Inhibition of constitutive nitric oxide synthase (NOS) by nitric oxide generated by inducible NOS after lipopolysaccharide administration provokes renal dysfunction in rats.
      Further studies are needed to define more precisely the conditions under which iNOS exerts beneficial or detrimental effects on the development of atherosclerosis.
      Modulation of NO-dependent pathways could provide several benefits in negating atherosclerotic lesion formation and progression.
      • Napoli C
      • Ignarro LJ
      Nitric oxide and atherosclerosis.
      Among the normal functions of NO are inhibition of platelet adherence and aggregation, reduction in adherence of leukocytes to the endothelium, and suppression of vascular smooth muscle cell proliferation.
      • Cooke JP
      • Dzau VJ
      Nitric oxide synthase: role in the genesis of vascular disease.
      NO is a potent antioxidant, ROS scavenger, and modulator of inflammatory and signal transduction pathways, which can modulate lipid peroxidation and proinflammatory gene expression.
      • Gutteridge JM
      • Halliwell B
      Free radicals and antioxidants in the year 2000: a historical look to the future.
      • Wolin MS
      Interactions of oxidants with vascular signaling systems.
      However, NO and its products, such as reactive nitrogen species, may also exert pro-oxidant effects, like increase membrane and lipoprotein lipid oxidation and foam cell formation. This type of reaction depends on the relative concentrations of NO, ROS, and antioxidants, as well as on the aqueous-lipid solubility and relative rates of reaction of the participating reactive species. Hence, when endogenous tissue rates of oxidant production are accelerated or when tissue oxidant defenses are depleted, NO-derived oxidizing species can promote pro-atherogenic effects.
      • Bloodsworth A
      • O'Donnell VB
      • Freeman BA
      Nitric oxide regulation of free radical- and enzyme-mediated lipid and lipoprotein oxidation.
      Therefore, a decrease in the relative bioavailability of NO not only impairs endothelium-dependent vasodilation but also activates other mechanisms that have an important role in the pathogenesis of atherosclerosis.
      • Quyyumi AA
      Endothelial function in health and disease: new insights into the genesis of cardiovascular disease.
      Patients with hypercholesterolemia have impaired receptor- and endothelium-dependent vascular relaxation, which may predispose coronary arteries to vasoconstriction.
      • Zeiher AM
      • Drexler H
      • Wollschlager H
      • Just H
      Endothelial dysfunction of the coronary microvasculature is associated with coronary blood flow regulation in patients with early atherosclerosis.
      Loss of basal and flow-mediated NO production has been shown in the proximal segments of coronary arteries,
      • Tousoulis D
      • Tentolouris C
      • Crake T
      • Toutouzas P
      • Davies G
      Basal and flow-mediated nitric oxide production by atheromatous coronary arteries.
      while the vasorelaxant effect of nitroglycerin appears to be preserved,
      • Egashira K
      • Hirooka Y
      • Kai H
      • et al.
      Reduction in serum cholesterol with pravastatin improves endothelium-dependent coronary vasomotion in patients with hypercholesterolemia.
      although not in all vascular beds.
      • Feldstein A
      • Krier JD
      • Sarafov MH
      • et al.
      In vivo renal vascular and tubular function in experimental hypercholesterolemia.
      The physiological role of NO in the regulation of vascular tone by the endothelium is diminished in patients with hypercholesterolemia.
      • Casino PR
      • Kilcoyne CM
      • Quyyumi AA
      • Hoeg JM
      • Panza JA
      Investigation of decreased availability of nitric oxide precursor as the mechanism responsible for impaired endothelium-dependent vasodilation in hypercholesterolemic patients.
      Obviously, therapeutic strategies that aim to improve the bioavailability of NO in these patients are warranted.
      • Ignarro LJ
      • Cirino G
      • Casini A
      • Napoli C
      Nitric oxide as a signaling molecule in the vascular system: an overview.

      NOVEL TREATMENT STRATEGIES IN HYPERCHOLESTEROLEMIA

      Hypercholesterolemia plays a major causal role in atherogenesis, and therefore reduction of blood cholesterol is a primary therapeutic target. Progress has been substantial in identifying pathogenic mechanisms of atherosclerosis, in particular with regard to the role of apolipoproteins and scavenger receptors, adhesion molecules, growth factors, and interleukins.
      • Harrison DG
      • Ohara Y
      Physiologic consequences of increased vascular oxidant stresses in hypercholesterolemia and atherosclerosis: implications for impaired vasomotion.
      • Ross R
      Atherosclerosis—an inflammatory disease.
      • Libby P
      • Ridker PM
      Novel inflammatory markers of coronary risk: theory versus practice [editorial].
      • Brown MS
      • Goldstein JL
      A proteolytic pathway that controls the cholesterol content of membranes, cells, and blood.
      Both primary
      • Shepherd J
      • Cobbe SM
      • Ford I
      • West of Scotland Coronary Prevention Study Group
      • et al.
      Prevention of coronary heart disease with pravastatin in men with hypercholesterolemia.
      and secondary
      Randomised trial of cholesterol lowering in 4444 patients with coronary heart disease: the Scandinavian Simvastatin Survival Study (4S).
      • Sacks FM
      • Pfeffer MA
      • Moye LA
      • Cholesterol and Recurrent Events Trial Investigators
      • et al.
      The effect of pravastatin on coronary events after myocardial infarction in patients with average cholesterol levels.
      prevention trials have demonstrated unequivocally the decrease in coronary morbidity and mortality that can be achieved by lowering lipids in patients with hypercholesterolemia. To decrease the rate of cardiac events and mortality, the target goals of therapy are generally to achieve LDL levels of 100 mg/dL or lower in patients with established CHD and 130 mg/dL or lower in high-risk patients without established CHD. Conventional interventions include lifestyle modification (eg, reduced intake of saturated fatty acids and cholesterol and increased physical activity), addressing other concurrent cardiovascular risk factors (such as obesity, hypertension, diabetes, or post-menopause), and drug therapy.
      Lipid-lowering drugs include bile acid sequestrants, nicotinic acid, and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (“statins”), all of which have important roles in cholesterol-lowering therapy, alone or in combination.
      • Grundy SM
      Management of high serum cholesterol and related disorders in patients at risk for coronary heart disease.
      The agents with the greatest LDL cholesterol-lowering effect are the bile acid sequestrants, which up-regulate the LDL receptor by interruption of enterohepatic circulation of cholesterol-rich bile acids, and the statins, which interfere with the cholesterol biosynthesis pathway by inhibiting HMG-CoA reductase.
      • Farmer JA
      • Gotto AM
      Choosing the right lipid-regulating agent: a guide to selection.
      The greatest triglyceride-lowering effect is exerted by nicotinic acid, which decreases the production of very LDL cholesterol and reduces the availability of circulating free fatty acids, and the fibric acid derivatives, which activate hepatic peroxisome proliferator-activated receptor α-1 and lipoprotein lipase, thus improving the plasma transport rates of several lipoproteins, and inhibit inflammatory mediators.
      • Watts GF
      • Dimmitt SB
      Fibrates, dyslipoproteinaemia and cardiovascular disease.
      Among these, statins are the most commonly prescribed agents for the treatment of hypercholesterolemia because of their efficacy in reducing both LDL levels and event rates and because of their excellent tolerability and safety.
      • Maron DJ
      • Fazio S
      • Linton MF
      Current perspectives on statins.
      When this approach does not achieve desired goals in LDL levels, in rare circumstances (such as familial hypercholesterolemia), patients can undergo LDL apheresis, which has been associated with a decreased CHD event rate.
      • Ansell BJ
      • Watson KE
      • Fogelman AM
      An evidence-based assessment of the NCEP Adult Treatment Panel II guidelines: National Cholesterol Education Program.
      Remarkably, some of the conventional interventions exert their beneficial effects to some extent through attenuation of oxidation-sensitive mechanisms. For example, long-term exercise training may improve bioavailability of NO and endothelium-mediated vasorelaxation,
      • Griffin KL
      • Laughlin MH
      • Parker JL
      Exercise training improves endothelium-mediated vasorelaxation after chronic coronary occlusion.
      partly by increasing expression of CuZn superoxide dismutase
      • Rush JWE
      • Laughlin MH
      • Woodman CR
      • Price EM
      SOD-1 expression in pig coronary arterioles is increased by exercise training.
      ; however, this mechanism does not appear to have a major role in acute exercise-induced skin and muscle hyperemia.
      • Koller-Strametz J
      • Matulla B
      • Wolzt M
      • et al.
      Role of nitric oxide in exercise-induced vasodilation in man.
      Notwithstanding an evident need to decrease plasma cholesterol, novel strategies in recent years have attempted to target mechanisms responsible for the outcomes of hypercholesterolemia, with primary goals of both decreasing oxidant stress and increasing bioavailability of NO.

      Antioxidant Approaches

      The large body of evidence supporting the important contribution of endogenous oxidative stress to the development of early atherosclerosis in humans
      • Napoli C
      • D'Armiento FP
      • Mancini FP
      • et al.
      Fatty streak formation occurs in human fetal aortas and is greatly enhanced by maternal hypercholesterolemia: intimal accumulation of low density lipoprotein and its oxidation precede monocyte recruitment into early atherosclerotic lesions.
      • Napoli C
      • Glass CK
      • Witztum JL
      • Deutsch R
      • D'Armiento FP
      • Palinski W
      Influence of maternal hypercholesterolaemia during pregnancy on progression of early atherosclerotic lesions in childhood: Fate of Early Lesions in Children (FELIC) study.
      • Yla-Herttuala S
      • Rosenfeld ME
      • Parthasarathy S
      • et al.
      Gene expression in macrophage-rich human atherosclerotic lesions: 15-lipoxygenase and acetyl low density lipoprotein receptor messenger RNA colocalize with oxidation specific lipid-protein adducts.
      has led to the use of antioxidant therapy in an attempt to prevent functional and structural vascular damage. In vitro, cellular, and animal studies clearly demonstrate that vitamin E, the most important fat-soluble antioxidant, and vitamin C, a highly potent water-soluble antioxidant,
      • Fuller CJ
      • Grundy SM
      • Norkus EP
      • Jialal I
      Effect of ascorbate supplementation on low density lipoprotein oxidation in smokers.
      can retard LDL oxidation and protect animals against various types of oxidative stress,
      • de Nigris F
      • Youssef T
      • Ciafré S
      • et al.
      Evidence for oxidative activation of c-Myc-dependent nuclear signaling in human coronary smooth muscle cells and in early lesions of Watanabe heritable hyperlipidemic rabbits: protective effects of vitamin E.
      • Pryor WA
      Vitamin E and heart disease: basic science to clinical intervention trials.
      • Freyschuss A
      • Xiu RJ
      • Zhang J
      • et al.
      Vitamin C reduces cholesterol-induced microcirculatory changes in rabbits.
      and they can potentially interrupt the downstream sequence of atherogenic events. Clinical intervention trials with long-term antioxidant therapy support the notion that supplemental vitamin E can reduce the risk of myocardial infarction and heart disease,
      • Stephens NG
      • Parsons A
      • Schofield PM
      • Kelly F
      • Cheeseman K
      • Mitchinson MJ
      Randomised controlled trial of vitamin E in patients with coronary disease: Cambridge Heart Antioxidant Study (CHAOS).
      although results regarding improved cardiac outcomes in high-risk patients with atherosclerosis are occasionally conflicting.
      • Yusuf S
      • Dagenais G
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      which may underlie their capacity to improve vascular function
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      and plaque morphology
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      independent of lowering of lipids. Recent evidence indicates that statins also inhibit vascular smooth muscle cell growth
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      Short-term pravastatin mediates growth inhibition and apoptosis, independently of Ras, via the signaling proteins p27Kip1 and PI3 kinase.
      but activate the protein kinase AKT to promote new blood vessel growth,
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      which may serve as an additional beneficial mechanism to inhibit plaque formation.
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      Their capability to reduce the expression of IL-1β and IL-6, peroxisome proliferator-activated receptor α and γ, and the p22-phox and p47-phox subunits of NADPH oxidase underscores their beneficial anti-inflammatory and antioxidant attributes.
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      Moreover, vitamin E supplementation benefits endothelial function beyond that achieved with statins alone.
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      In extreme increases in blood cholesterol, LDL apheresis is a safe procedure for patients with homozygous familial hypercholesterolemia
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      or severe CHD.
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      During selective LDL apheresis, an increase in plasma glutathione concentrations was observed, which was unaccompanied by a significant reduction in the plasma activity of antioxidant enzymes, LDL, red blood cells, or granulocytes and may explain the lack of plasma lipid peroxidation shown during this kind of extracorporeal treatment.
      • Napoli C
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      • Schettler V
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      Review: the oxidant/antioxidant balance during regular low density lipoprotein apheresis.
      In addition, LDL isolated at the end of apheresis procedures is more resistant to oxidation.
      • Napoli C
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      Decreased low-density lipoprotein oxidation after repeated selective apheresis in homozygous familial hypercholesterolemia.

      Restoration of NO Bioavailability

      Endothelial dysfunction contributes to the pathogenesis of myocardial ischemia, and cholesterol-lowering therapy may restore vascular function.
      • van Boven AJ
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      • Paoletti R
      Endothelial dysfunction and dyslipidemia: possible effects of lipid lowering and lipid modifying therapy.
      Moreover, since depletion of L-arginine may contribute to endothelial dysfunction, infusion of L-arginine improves the forearm resistance vessel blood flow responses to methacholine in patients with hypercholesterolemia.
      • Creager MA
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      • et al.
      Impaired vasodilation of forearm resistance vessels in hypercholesterolemic humans.
      Administration of L-arginine partially restores endothelium-dependent vasodilation in patients with hypercholesterolemia
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      • Coleman SM
      • Dzau VJ
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      L-arginine improves endothelium-dependent vasodilation in hypercholesterolemic humans.
      • Drexler H
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      • Meinzer K
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      Correction of endothelial dysfunction in coronary microcirculation of hyper-cholesterolaemic patients by L-arginine.
      and dilates coronary stenoses in patients with CHD.
      • Tousoulis D
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      • Lerman A
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      Long-term L-arginine supplementation improves small-vessel coronary endothelial function in humans.
      and may be a therapeutic option for patients with coronary endothelial dysfunction and nonobstructive CHD.
      • Lerman A
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      • Holmes Jr, DR
      Long-term L-arginine supplementation improves small-vessel coronary endothelial function in humans.
      Indeed, oral L-arginine led to a significant clinical improvement in 70% of patients with intractable angina pectoris, in association with a significant decrease in cell adhesion molecule and proinflammatory cytokine levels,
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      suggesting that it may also have anti-inflammatory properties. The mechanisms by which NO bioavailability can be improved with any drug therapy remain to be elucidated and may provide further insights into the mechanisms involved in impaired endothelial function and atherogenesis.
      • Napoli C
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      Nitric oxide and atherosclerosis.

      EFFECTS OF HYPERCHOLESTEROLEMIA AND INCREASED OXIDATION ON EARLY ATHEROGENESIS IN HUMANS

      Until recently, atherogenesis was thought to begin during late childhood, although fatty streaks had occasionally been observed in younger children.
      • Pathobiological Determinants of Atherosclerosis in Youth (PDAY) Research Group
      Natural history of aortic and coronary atherosclerotic lesions in youth: findings from the PDAY Study.
      • Berenson GS
      • Srinivasan SR
      • Bao W
      • Newman III, WP
      • Tracy RE
      • Wattigney WA
      • Bogalusa Heart Study
      Association between multiple cardiovascular risk factors and atherosclerosis in children and young adults.
      However, a systematic morphometric analysis of the entire aorta of premature human fetuses demonstrated that formation of fatty streaks, the precursors of more advanced atherosclerotic lesions, is prevalent in all fetal aortas and that their number and size are markedly increased in fetuses whose mothers had hypercholesterolemia during pregnancy.
      • Napoli C
      • D'Armiento FP
      • Mancini FP
      • et al.
      Fatty streak formation occurs in human fetal aortas and is greatly enhanced by maternal hypercholesterolemia: intimal accumulation of low density lipoprotein and its oxidation precede monocyte recruitment into early atherosclerotic lesions.
      Fetal lesions contained typical components of early atherosclerotic lesions, such as native and oxidized LDL and macrophages, and their distribution reflected that of more advanced atherosclerosis seen in adults, ie, most extensive in the abdominal aorta, followed by the aortic arch. This suggests that, during the earlier stages of pregnancy, maternal hypercholesterolemia may promote early atherogenesis in the fetus.
      • Napoli C
      • Palinski W
      Maternal hypercholesterolemia during pregnancy influences the later development of atherosclerosis: clinical and pathogenic implications.
      • Palinski W
      • Napoli C
      Pathophysiological events during pregnancy influence the development of atherosclerosis in humans.
      The assumption that LDL oxidation is a contributor to atherogenesis in fetal arteries was also supported by a later study
      • Napoli C
      • Witztum JL
      • de Nigris F
      • Palumbo G
      • D'Armiento FP
      • Palinski W
      Intracranial arteries of human fetuses are more resistant to hypercholesterolemia-induced fatty streak formation than extracranial arteries.
      in which the middle cerebral and basilar arteries of fetuses contained significantly smaller lesions than the aorta and common carotid arteries. Determinations of the arterial activities of oxygen-radical scavengers, such as manganese superoxide dismutase, catalase, and glutathione peroxidase, indicated that overall intracranial arteries of human fetuses were better protected against oxidation than extracranial arteries.
      • Napoli C
      • Witztum JL
      • de Nigris F
      • Palumbo G
      • D'Armiento FP
      • Palinski W
      Intracranial arteries of human fetuses are more resistant to hypercholesterolemia-induced fatty streak formation than extracranial arteries.
      These results are consistent with the assumption that better protection against free radical–mediated oxidation may contribute to the greater resistance of intracranial arteries to hypercholesterolemia-induced atherogenesis and vascular dysfunction.
      • Napoli C
      • Paternò R
      • Faraci FM
      • Taguchi H
      • Postiglione A
      • Heistad DD
      Mildly oxidized low-density lipoprotein impairs responses of carotid but not basilar artery in rabbits.
      To investigate whether fetal lesions regress and/or whether they influence atherogenesis during childhood and adolescence, the Fate of Early Lesions in Children (FELIC) study was designed.
      • Napoli C
      • Glass CK
      • Witztum JL
      • Deutsch R
      • D'Armiento FP
      • Palinski W
      Influence of maternal hypercholesterolaemia during pregnancy on progression of early atherosclerotic lesions in childhood: Fate of Early Lesions in Children (FELIC) study.
      Atherosclerosis was established by computer-assisted image analysis in normocholesterolemic children and was found to progress much faster in children whose mothers had hypercholesterolemia during pregnancy than in children of normocholesterolemic mothers, despite normal lipid profiles in both groups of children. None of the risk factors of atherogenesis assessed in these children could account for the faster atherogenesis in children of hypercholesterolemic mothers. Although parental genetic differences are likely to contribute to the different susceptibility of children to the disease, we postulated that maternal-fetal hypercholesterolemia induced constitutive changes in gene expression in arterial cells, which were associated with a greater susceptibility to the disease later in life.
      • Napoli C
      • Palinski W
      Maternal hypercholesterolemia during pregnancy influences the later development of atherosclerosis: clinical and pathogenic implications.
      • Palinski W
      • Napoli C
      Pathophysiological events during pregnancy influence the development of atherosclerosis in humans.
      A recent study demonstrated that fetal lesions in the rabbit can be reduced with vitamin E or cholestyramine treatment of the hypercholesterolemic mothers during pregnancy.
      • Napoli C
      • Witztum JL
      • Calara F
      • de Nigris F
      • Palinski W
      Maternal hypercholesterolemia enhances atherogenesis in normocholesterolemic rabbits, which is inhibited by antioxidant or lipid-lowering intervention during pregnancy: an experimental model of atherogenic mechanisms in human fetuses.
      Maternal hypercholesterolemia during gestation should therefore be added to the list of risk factors determining the need for monitoring and for preventive therapy.
      • Cleeman JI
      • Grundy SM
      National Cholesterol Education Program recommendations for cholesterol testing in young adults: a science-based approach.
      Current clinical guidelines place great emphasis on early detection of hypercholesterolemia,
      • American Academy of Pediatrics
      National Cholesterol Education Program: report of the Expert Panel on Blood Cholesterol Levels in Children and Adolescents.
      although such screening would not detect an increased risk associated with maternal hypercholesterolemia in normocholesterolemic subjects. An intense lipid-lowering intervention may be a therapeutic option for children with several risk factors. As indicated by a recent meta-analysis of studies on the development of coronary artery disease in children and adolescents,
      • Duplaga BA
      Treatment of childhood hypercholesterolemia with HMG-CoA reductase inhibitors.
      an average reduction of LDL cholesterol by 25% can be obtained with statins in combination with a lipid-lowering diet. Statins are generally well tolerated in children and adolescents, and current data do not indicate adverse effects on growth and sexual development in male adolescents. In high-risk children, follow-up may need to include an attempt for an earlier than usual noninvasive diagnosis of atherosclerosis. Potential approaches include measurement of coronary flow velocity in the distal left anterior descending (LAD) coronary artery with transthoracic Doppler echocardiography,
      • Hozumi T
      • Yoshida K
      • Ogata Y
      • et al.
      Noninvasive assessment of significant left anterior descending coronary artery stenosis by coronary flow velocity reserve with transthoracic color Doppler echocardiography.
      determination of the degree of stenosis in the proximal LAD coronary artery by transesophageal Doppler study
      • Isaaz K
      • da Costa A
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      • Cerisier A
      • Lamaud M
      Use of the continuity equation for transesophageal Doppler assessment of severity of proximal left coronary artery stenosis: a quantitative coronary angiography validation study.
      or magnetic resonance imaging,
      • Hundley WG
      • Hamilton CA
      • Clarke GD
      • et al.
      Visualization and functional assessment of proximal and middle left anterior descending coronary stenoses in humans with magnetic resonance imaging.
      measurement of coronary flow reserve in the LAD coronary artery by contrast-enhanced transthoracic second harmonic echocardiography/Doppler study,
      • Caiati C
      • Montaldo C
      • Zedda N
      • et al.
      Validation of a new noninvasive method (contrast-enhanced transthoracic second harmonic echo Doppler) for the evaluation of coronary flow reserve: comparison with intracoronary Doppler flow wire.
      or quantification of coronary calcifications by electron beam computed tomography.
      • Budoff MJ
      • Georgiou D
      • Brody A
      • et al.
      Ultrafast computed tomography as a diagnostic modality in the detection of coronary artery disease: a multicenter study.
      • Guerci AD
      • Spadaro LA
      • Popma JJ
      • et al.
      Relation of coronary calcium score by electron beam computed tomography to arteriographic findings in asymptomatic and symptomatic adults.
      • Rumberger JA
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      Coronary artery calcium area by electron-beam computed tomography and coronary atherosclerotic plaque area: a histopathologic correlative study.
      Another clinical scenario that may involve dyslipidemia and oxidative stress is the pregnancy-related preeclampsia syndrome, the etiology and pathogenesis of which remain poorly understood.
      • Hubel CA
      Dyslipidemia, iron, and oxidative stress in preeclampsia: assessment of maternal and feto-placental interactions.
      Recent evidence points to a pro-oxidant shift in preeclampsia, and ROS and/or their metabolites have been hypothesized to ultimately compromise the vasodilatory, antiaggregatory, and barrier defense functions of the endothelium. Failure of flow-induced shear stress may contribute to the gestational hypertension of preeclampsia.
      • Cockell AP
      • Poston L
      Flow-mediated vasodilatation is enhanced in normal pregnancy but reduced in preeclampsia.
      Maternal dyslipidemia and altered iron kinetics in preeclampsia may potentially affect disease progression.
      • Hubel CA
      Dyslipidemia, iron, and oxidative stress in preeclampsia: assessment of maternal and feto-placental interactions.
      Oxidative stress as a result of interaction of fetoplacental and maternal factors and autoimmune reaction may lead to the manifestations of preeclampsia. For example, interaction of maternal neutrophils and oxidized lipids with placental cells and placenta-derived factors can engender a vicious cycle of oxidative stress that may ultimately cause widespread endothelial cell dysfunction and physiological perturbations downstream of cellular signaling. A randomized controlled trial recently showed that vitamin C and E supplementation may be beneficial in women with or at increased risk for preeclampsia,
      • Chappell LC
      • Seed PT
      • Briley AL
      • et al.
      Effect of antioxidants on the occurrence of pre-eclampsia in women at increased risk: a randomised trial.
      suggesting that the “primum movent” of the disease was increased lipid oxidation during pregnancy.

      CONCLUSIONS

      Hypercholesterolemia is a common clinical disorder that may begin early in life in humans, and it subsequently promotes atherogenesis by injuring the vascular wall, thereby impairing a multitude of functions and signaling pathways that it controls and leading to development of atheromatous plaques. The underlying mechanisms responsible for these abnormalities may emanate from activation of oxidation-sensitive mechanisms, increased oxidation of LDL cholesterol, and quenching of NO. This cascade of events can begin as early as during pregnancy, altering the complex framework of signaling network in the arterial wall. Novel treatment strategies that attempt to decrease oxidation and restore bioavailability of NO have the potential to decrease morphologic and functional arterial damage and improve cardiovascular outcomes in patients with hypercholesterolemia.

      Acknowledgments

      We dedicate this article to the memory of Dr Russell Ross who died on March 18, 1999. We thank Drs Wulf Palinski and Filomena de Nigris for valuable discussions in the field.

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      1. Randomised trial of cholesterol lowering in 4444 patients with coronary heart disease: the Scandinavian Simvastatin Survival Study (4S).