T his review so far has considered the role of vascular cells in the generation of reactive oxygen species (ROS) and novel approaches to their detection in integrated systems such as animal models of vascular disease and humans. We now turn attention to evidence consistent with a role for ROS in models of human disease and in discrete patient populations. We also briefly comment on the outcomes of clinical trials of antioxidants. Mainly, these have been disappointing. However, it is premature to conclude that the oxidation hypothesis of disease causality has been adequately tested.
ROS and Vascular Disease: Animal StudiesAnimal studies, for the most part, support a fundamental role for ROS in cardiovascular disease. Any controversy could in part reflect the use of ineffective antioxidants and the selection of models in which ROS generation is of marginal relevance to the measured outcome. Both of these issues require a quantitatively accurate measurement of drug effect (ie, antioxidant capacity) before hypotheses relating to the role of oxidant stress can be addressed rationally. These issues pertain to clinical trials also, as we will discuss. However, animal studies permit administration of much more powerful antioxidants (eg, rate constant for interaction of superoxide dismutase (SOD) with O 2 ·Ϫ Ϸ1.6ϫ10 9 · mol/L Ϫ1 · s Ϫ1 ) than is possible in humans (eg, rate constant for vitamin E Ϸ0.59 mol/L Ϫ1 · s Ϫ1 ) or, like in the case of vitamin E, doses of the antioxidant in excess of those usually applied in clinical research.
AtherosclerosisAnimal models of atherosclerosis have documented that all the constituents of the plaque produce and use ROS. Lesion formation is associated with the accumulation of lipid peroxidation products 1,2 and induction of inflammatory genes, 3 inactivation of NO · resulting in endothelial dysfunction, 4,5 activation of matrix metalloproteinases, 6 and increased smooth muscle cell growth. 7 Atherogenesis in rodents is accompanied by increasing lipid peroxidation in vivo. Thus, levels of the F 2 isoprostane (iP), iPF 2␣ -IV, are increased in both urine and aortic tissue as atherosclerosis evolves in both apolipoprotein E (ApoE)-and low-density lipoprotein (LDL) receptor-knockout mice. 8,9 Evidence exists for and against the efficacy of vitamin E in limiting atherogenesis. 10 -12 However, a rational basis for selection of the interventional regimens, or indeed the possibility of comparing treatment regimens across models and species by anything other than weight-corrected dosing, does not exist, pointing to the need for a much more rigorous approach to the development, application, and testing of antioxidant therapies. If a dosing regimen of vitamin E is selected on the basis of its ability to suppress elevated urinary iPF 2␣ -VI in atherosclerotic ApoE mice, vitamin E will retard atherosclerosis by Ϸ50% while leaving hypercholesterolemia unaffected. 8 However, administration of much lower doses of vitamin E to the same model failed to detect an impact on atherogenesis. 10 It is notew...