Evaluating oxidation processes in relation to cardiovascular disease: a current review of oxidant/antioxidant methodology

Evidence has now been accumulated of the involvement of reactive oxygen species (ROS)(1) in the onset of several pathological conditions, including atherosclerosis (1, 2), cancer (3-5), cataract (6), postischemic reoxygenation injury (3), rheumatoid arthritis (7), and complications associated with aging (8). However, the implication of ROS in the above mentioned diseases has often been hypothesized on the basis of indirect observations, ie antioxidant supplementation contributing to the alleviation of certain diseases. Furthermore, negative results of clinical trials have been published, dampening enthusiasm and calling for a more cautious approach to antioxidant therapy (2, 9, 10). Intrinsic uncertainties in the selection of appropriate markers of ROS-mediated processes, related to diseases, as well as in the dosage and duration of treatments, make it difficult to plan interventional studies and to evaluate the results. ROS, such as hydroxyl (OH.), superoxide (O-2-), or peroxyl (RO2.) radicals, are produced in the body under physiological conditions or in response to external injuries and they become toxic when their levels exceed the antioxidant capacity of the body: it should be clear to the reader that a continuous production of free radicals and ROS is a perfectly physiological process (the human body can produce over 2 Kg of superoxide per year (11)) in addition to being a defense mechanism by which activated phagocytes destroy noxious invaders (12). Research concerning the antioxidant(2) activity of individual compounds, as well as of mixtures and of body fluids, should take at least three interdependent variables into account: (i) the substrate to be studied, (ii) the oxidative system(s) employed, and (iii) the parameters of oxidation to be evaluated. Individual substrates generate different products when exposed to different oxidative conditions ((12), Bellomo, unpublished data): the widest array of tests should thus be employed in antioxidant investigation. In addition, different ROS-generated markers may be differentially correlated with pathogenic processes. This review is an update of the approaches and methods used in the evaluation of ROS-mediated processes and it also attempts to outline some thought-provoking topics concerning the study of antioxidants as related to human pathology.