Role of oxidatively modified low density lipoproteins and anti-oxidants in atherothrombosis

Low-calorie cranberry juice supplementation reduces plasma oxidized LDL and cell adhesion molecule concentrations in men

Elevated circulating concentrations of oxidized LDL (OxLDL) and cell adhesion molecules are considered to be relevant markers of oxidative stress and endothelial activation which are implicated in the development of CVD. On the other hand, it has been suggested that dietary flavonoid consumption may be cardioprotective through possible favourable impacts on LDL particle oxidation and endothelial activation. The present study was undertaken to determine the effect of the daily consumption of low-calorie cranberry juice cocktail on plasma OxLDL, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin concentrations in men. Thirty men (mean age 51 (sd 10) years) were recruited and asked to consume increasing daily doses of cranberry juice cocktail (125, 250 and 500 ml/d) over three successive periods of 4 weeks. Plasma OxLDL and adhesion molecule concentrations were measured by ELISA before and after each phase. We noted a significant decrease in plasma OxLDL concentrations following the intervention (P < 0.0001). We also found that plasma ICAM-1 (P < 0.0001) and VCAM-1 (P < 0.05) concentrations decreased significantly during the course of the study. In summary, the present results show that daily cranberry juice cocktail consumption is associated with decreases in plasma OxLDL, ICAM-1 and VCAM-1 concentrations in men.

Molecular basis for susceptibility of plasma platelet-activating factor acetylhydrolase to oxidative inactivation

Platelet-activating factor acetylhydrolase (PAF-AH) is a phospholipase A2 that inactivates potent lipid messengers, such as PAF and modified phospholipids generated in settings of oxidant stress. The catalytic activity of PAF-AH is sensitive to oxidants, a feature that may have pathological consequences. We report that peroxynitrite, an oxidant species generated after cellular activation, mediates oxidative inactivation of PAF-AH. We found that peroxynitrite inactivated and derivatized the recombinant protein and obtained evidence supporting a role for a methionine and two tyrosine residues in this process. We employed interspecies comparisons and site-directed mutagenesis and identified a role for M-117, and a smaller contribution of Y-307 and Y-335 as targets of oxidant attack using free and lipoprotein-associated recombinant proteins. M-117 is adjacent to W-115 and L-116, which are essential for association of PAF-AH with LDL. Oxidation of LDL-associated PAF-AH partially dissociated the enzyme from the particles. Similarly, oxidation of the purified enzyme in the absence of lipoproteins prevented subsequent association with LDL. These results provide new insights into the molecular mechanisms that mediate inactivation of PAF-AH in settings of oxidant stress and the consequences of oxidation on the ability of this enzyme to associate with LDL.

Vitamin E and heart disease: basic science to clinical intervention trials

A review is presented of studies on the effects of vitamin E on heart disease, studies encompassing basic science, animal studies, epidemiological and observational studies, and four intervention trials. The in vitro, cellular, and animal studies, which are impressive both in quantity and quality, leave no doubt that vitamin E, the most important fat-soluble antioxidant, protects animals against a variety of types of oxidative stress. The hypothesis that links vitamin E to the prevention of cardiovascular disease (CVD) postulates that the oxidation of unsaturated lipids in the low-density lipoprotein (LDL) particle initiates a complex sequence of events that leads to the development of atherosclerotic plaque. This hypothesis is supported by numerous studies in vitro, in animals, and in humans. There is some evidence that the ex vivo oxidizability of a subject's LDL is predictive of future heart events. This background in basic science and observational studies, coupled with the safety of vitamin E, led to the initiation of clinical intervention trials. The three trials that have been reported in detail are, on balance, supportive of the proposal that supplemental vitamin E can reduce the risk for heart disease, and the fourth trial, which has just been reported, showed small, but not statistically significant, benefits. Subgroup analyses of cohorts from the older three trials, as well as evidence from smaller trials, indicate that vitamin E provides protection against a number of medical conditions, including some that are indicative of atherosclerosis (such as intermittent claudication). Vitamin E supplementation also produces an improvement in the immune system and protection against diseases other than cardiovascular disease (such as prostate cancer). Vitamin E at the supplemental levels being used in the current trials, 100 to 800 IU/d, is safe, and there is little likelihood that increased risk will be found for those taking supplements. About one half of American cardiologists take supplemental vitamin E, about the same number as take aspirin. In fact, one study suggests that aspirin plus vitamin E is more effective than aspirin alone. There are a substantial number of trials involving vitamin E that are in progress. However, it is possible, or even likely, that each condition for which vitamin E provides benefit will have a unique dose-effect curve. Furthermore, different antioxidants appear to act synergistically, so supplementation with vitamin E might be more effective if combined with other micronutrients. It will be extremely difficult to do trials that adequately probe the dose-effect curve for vitamin E for each condition that it might affect, or to do studies of all the possible combinations of other micronutrients that might act with vitamin E to improve its effectiveness. Therefore, the scientific community must recognize that there never will be a time when the science is "complete." At some point, the weight of the scientific evidence must be judged adequate; although some may regard it as early to that judgement now, clearly we are very close. In view of the very low risk of reasonable supplementation with vitamin E, and the difficulty in obtaining more than about 30 IU/day from a balanced diet, some supplementation appears prudent now.

Anti-oxidant therapy for the treatment of coronary artery disease

Coronary artery disease is the most common cause of death in developed countries. It may present in many different ways, but most frequently as a myocardial infarction, sudden death, angina or heart failure. Preventive measures in relation to coronary artery disease are particularly important because of its high incidence, high mortality and because most patients die outside hospital. Since the oxidation of low density lipoprotein cholesterol (LDL-C) is a critical early step in the process of atheroma formation, taking anti-oxidants to prevent LDL-C oxidation may prove a very effective means of reducing coronary artery disease mortality. However, the role of anti-oxidants in coronary artery disease prevention needs to be evaluated as part of an overall strategy that includes pharmacological and non-pharmacological measures, which are described in this review. In addition, a more structured and scientific approach to anti-oxidant therapy needs to be adopted. This requires that evidence for oxidative stress in a particular condition is obtained, the nature and severity determined and an appropriate anti-oxidant is administered, in an effective dose, which can be shown to correct the oxidative stress. When this is achieved, meaningful clinical trials should be possible, which will determine the place of anti-oxidant therapy for the specified condition.