[Free radicals in the pathogenesis of selected diseases]

Free radicals are chemical substances which contain one or more unpaired electrons, which is the cause of their high reactivity with a series of biologically important substances such as fatty acids, DNA, RNA, amino acids. The source of radicals are immunological reactions and reactions in the endoplasmatic reticulum during detoxication of xenobiotics. Free radicals can act on the organism by a number of reactions, the most frequent on being lipid peroxidation when important toxic products are formed such as 4-hydroxy 2,3 trans-nonenal (4-HNE) and malondialdehyde. Direct assessment of free radicals due to their short life span is difficult in clinical practice. The majority of measurements is based on the assessment of substances which are formed by the reaction of free radicals in the organism. The most frequent method is assessment by means of thiobarbituric acid. Oxidative stress (the reaction produced by the action of free radicals) of tissues and cells is caused by the increased formation of free radicals and/or reduced capacity of antioxidant systems. Free radicals are involved in the process of ageing, cancerogenesis, inflammatory and degenerative diseases, atherogenesis, and play a part in the ischaemic and toxic damage of the organism. During evolution antioxidant defence mechanisms developed which under physiological conditions are sufficient to inactivate free radicals. Antioxidant systems can be divided into two groups--antioxidant enzymes (superoxide dismutase, glutathione peroxidase, catalase etc) and antioxidant substrates (tocopherols, carotenoids, ascorbic acid, glutathione, transferrin, ceruloplasmin etc).