A. Lau

Antioxidants protect from atherosclerosis by a heme oxygenase-1 pathway that is independent of free radical scavenging

Oxidative stress is implicated in atherogenesis, yet most clinical trials with antioxidants, particularly vitamin E, have failed to protect against atherosclerotic diseases. A striking exception is probucol, which retards atherosclerosis in carotid arteries and restenosis of coronary arteries after angioplasty. Because probucol has in vitro cellular-protective effects independent of inhibiting lipid oxidation, we investigated the mode of action of probucol in vivo. We used three models of vascular disease: apolipoprotein E–deficient mice, a model of atherosclerosis; rabbit aortic balloon injury, a model of restenosis; and carotid injury in obese Zucker rats, a model of type 2 diabetes. Unexpectedly, we observed that the phenol moieties of probucol were insufficient, whereas its sulphur atoms were required for protection. Probucol and its sulphur-containing metabolite, but not a sulphur-free phenolic analogue, protected via cell-specific effects on inhibiting macrophage accumulation, stimulating reendothelialization, and inhibiting vascular smooth muscle cell proliferation. These processes were mediated via induction of heme oxygenase-1 (HO-1), an activity not shared by vitamin E. Our findings identify HO-1 as the molecular target of probucol. They indicate 2-electron rather than radical (1-electron) oxidants as important contributors to atherogenesis, and point to novel lead compounds for therapeutic intervention against atherosclerotic diseases.

Probucol Promotes Functional Reendothelialization in Balloon-Injured Rabbit Aortas

Background—Probucol remains the only conventional drug that reduces restenosis after coronary angioplasty. Apart from its weak cholesterol-lowering effect, probucol has antioxidant properties, but it remains unclear how this drug inhibits restenosis. Methods and Results—Aortic balloon-injured New Zealand White rabbits were fed 2% (wt/wt) cholesterol-enriched or normal chow, with 0.75% (wt/wt) probucol (P) or without (controls, C) for 6 weeks. Endothelial denudation of the abdominal aorta was performed at week 3 with a 3F Fogarty embolectomy catheter. The arteries were harvested after week 6 and analyzed for histology, lipids and antioxidants, and endothelial regeneration and function. Probucol significantly decreased aortic intima-to-media ratio (cholesterol-fed: C, 1.10±0.08 versus P, 0.70±0.10; normal: C, 0.89±0.02 versus P, 0.83±0.05;P <0.05) and the numbers of proliferating intimal smooth muscle cells and lowered serum cholesterol without altering the proportion of aortic lipids that was oxidized. Probucol promoted endothelial regeneration in the injured aorta in cholesterol-fed rabbits (25% increase in reendothelialization, P <0.05) and in those on normal chow (37% increase, P <0.01). This was associated with both improved endothelial function as assessed by enhanced aortic ring relaxation and cGMP production in response to acetylcholine and decreased intimal thickening. Conclusions—Probucol inhibits intimal thickening in balloon-damaged arteries of rabbits by promoting the regeneration of functional endothelium, without affecting the proportion of aortic lipids that was oxidized. This novel in vivo finding helps explain how probucol inhibits restenosis after coronary angioplasty and highlights potential new targets for therapeutic intervention.

The roles of myeloperoxidase in coronary artery disease and its potential implication in plaque rupture.

ABSTRACT Atherosclerosis is the main pathophysiological process underlying coronary artery disease (CAD). Acute complications of atherosclerosis, such as myocardial infarction, are caused by the rupture of vulnerable atherosclerotic plaques, which are characterized by thin, highly inflamed, and collagen-poor fibrous caps. Several lines of evidence mechanistically link the heme peroxidase myeloperoxidase (MPO), inflammation as well as acute and chronic manifestations of atherosclerosis. MPO and MPO-derived oxidants have been shown to contribute to the formation of foam cells, endothelial dysfunction and apoptosis, the activation of latent matrix metalloproteinases, and the expression of tissue factor that can promote the development of vulnerable plaque. As such, detection, quantification and imaging of MPO mass and activity have become useful in cardiac risk stratification, both for disease assessment and in the identification of patients at risk of plaque rupture. This review summarizes the current knowledge about the role of MPO in CAD with a focus on its possible roles in plaque rupture and recent advances to quantify and image MPO in plasma and atherosclerotic plaques.

Systematic review of cardiac electrical disease in Kearns-Sayre syndrome and mitochondrial cytopathy.

Kearns-Sayre syndrome (KSS) is a mitochondrial disorder characterised by onset before the age of 20years, progressive external ophthalmoplegia, and pigmentary retinopathy, accompanied by either cardiac conduction defects, elevated cerebrospinal fluid protein or cerebellar ataxia. 50% of patients with KSS develop cardiac complications. The most common cardiac manifestation is conduction disease which may progress to complete atrioventricular block or bradycardia-related polymorphic ventricular tachycardia (PMVT). The management of cardiac electrical disease associated with KSS and mitochondrial cytopathy is systematically reviewed including the case of a 23year-old female patient with KSS who developed a constellation of cardiac arrhythmias including rapidly progressive conduction system disease and monomorphic ventricular tachycardia with myocardial scarring. The emerging role of cardiac magnetic resonance imaging (CMR) in detecting subclinical cardiac involvement is also highlighted. This review illustrates the need for cardiologists to be informed about this rare but emerging condition.

Equivalent lipid oxidation profiles in advanced atherosclerotic lesions of carotid endarterectomy plaques obtained from symptomatic type 2 diabetic and nondiabetic subjects.

Type 2 diabetes (T2D) increases the risk for cardiovascular disease and is thought to be associated with increased oxidative stress, a contributor to atherogenesis. Surprisingly, however, there is little direct evidence that T2D-associated oxidative stress results in increased lipid oxidation and/or decreased antioxidant capacity in human atherosclerotic lesions. The aim of this study was to measure vascular lipid oxidation and antioxidants in T2D. The arterial content of oxidized lipid and antioxidants in carotid endarterectomy specimens obtained from diabetic and normoglycemic patients was determined using high-performance liquid chromatography (HPLC), stable isotope dilution gas chromatography-mass spectrometry (GC/MS), and gas-liquid chromatography techniques. The concentrations of hydroxyoctadecanoic acid, F(2)-isoprostanes, and 7-ketocholesterol, as well as alpha-tocopherol, ascorbate, and urate were not different in the two patient groups, whether expressed per unit protein or as a ratio per parent compound. Unexpectedly, a significant decrease in the level of arterial lipid hydroperoxide was found in diabetic patients. Our results do not support the notion that advanced atherosclerotic lesions from T2D patients contain more oxidized lipids than corresponding lesions from nondiabetic subjects.

Coenzyme Q10 supplementation inhibits aortic lipid oxidation but fails to attenuate intimal thickening in balloon-injured New Zealand white rabbits

Oxidized lipoproteins are implicated in atherosclerosis, and some antioxidants attenuate the disease in animals. Coenzyme Q(10) (CoQ(10)) in its reduced form, ubiquinol-10, effectively inhibits lipoprotein oxidation in vitro and in vivo; CoQ(10) supplements also inhibit atherosclerosis in apolipoprotein E gene knockout (apoE-/-) mice. Here we tested the effect of dietary CoQ(10) supplements on intimal proliferation and lipoprotein lipid oxidation in balloon-injured, hypercholesterolemic rabbits. Compared to nonsupplemented chow, CoQ(10) supplementation (0.5% and 1.0%, w/w) significantly increased the plasma concentration of CoQ(10) and the resistance of plasma lipids to ex vivo oxidation. CoQ(10) supplements also increased the content of CoQ(10) in the aorta and liver, but not in the brain, skeletal muscle, kidney, and heart. Surprisingly, CoQ(10) supplementation at 1% increased the aortic concentrations of all lipids, particularly triacylglycerols, although it significantly inhibited the proportion of triacylglycerols present as hydroperoxides by > 80%. The observed increase in vessel wall lipid content was reflected in elevated plasma concentrations of cholesterol, cholesteryl esters and triacylglycerols, and hepatic levels of mRNA for 3-hydroxy-3-methylglutaryl-coenzyme A reductase. CoQ(10) supplements did not attenuate lesion formation, assessed by the intima-to-media ratio of injured aortic vessels. Thus, like in apoE-/- mice, a high dose of supplemented CoQ(10) inhibits lipid oxidation in the artery wall of balloon-injured, hypercholesterolemic rabbits. However, unlike its antiatherosclerosis activity in the mice, CoQ(10) does not inhibit intimal hyperplasia in rabbits, thereby dissociating this disease process from lipid oxidation in the vessel wall.

Protective effects of probucol in two animal models of atherosclerosis.

Abstract Lipid oxidation is widely accepted to be critical in the initiation of atherosclerosis,1 the major cause of death in industrialized countries. The use of antioxidants to improve health in non-deficient individuals, however, remains contentious as randomized trials of antioxidant supplementation in patients with established coronary disease have shown conflicting results.2–4 The potential role for antioxidants in earlier stages of atherosclerosis remains untested. Probucol, a cholesterol-lowering antioxidant, has generated much interest as it decreases restenosis after coronary angioplasty.5 Studies using probucol in animal models of atherosclerosis have, however, shown conflicting results, including inhibitory,6 neutral7 or promoting8 effects. Furthermore, the mechanisms of action of probucol in vivo remain unclear.