Evolution of antioxidant defence mechanisms

The metabolic strengths, weakness, opportunities and threats of the metabolic ability to split water brought about a proliferation of biological systems, produced a toxic oxygenic environment, and were responsible for the development of antioxidant defence mechanisms. Evolution is driven by heritable adaptions which improve environmental ‘fit’. Hence aerobic respiration, using oxygen as a nutrient, came to predominate in biological systems, and antioxidant defence mechanisms which prevent and neutralise toxic oxygen intermediates have become widespread, varied, coordinated and effective. Antioxidant defences are nor infallible however. In humans, reactive oxygen species-induced damage is associated with the ageing process, and with chronic diseases including cancer and coronary heart disease. Interestingly, some important antioxidants, including ascorbic acid and the tocopherols, cannot be synthesised by humans and must be taen in the diet. Another antioxidant, uric acid, is found in much higher concentrations in humans than in other mammals, and levels are also affected by diet. In humans, therefore, antioxidant defence against toxic oxygen intermediates is species specific and heavily influenced by nutrition.