Free radicals, arachidonic acid metabolites, and nutrition

Oxygen reactive species are normally formed in cells and play an essential part of the bactericidal activity of phagocytic cells. The damaging effect of these oxygen reactive species is prevented by the endogenous scavengers SOD, glutathione peroxidase, catalase, circulating transferrin, ascorbic acid, and membrane-bound alpha-tocopherol. However, when excess amounts of oxygen radicals and hydrogen peroxide are formed, as in reperfusion injury or trauma, the endogenous scavengers are insufficient to react with these active molecules. Lipid peroxidation is an important part of the formation of oxygen reactive species. Lipid peroxidation, especially peroxidation of LDL, may have a significant role in atherosclerosis. Thus dietary manipulation of PG and TX formation through either feeding cold water fish oils or plant oils containing high amounts of polyunsaturated fatty acids may be a two-edged sword. Also, the dietary manipulation of arachidonic acid through increasing its precursor linoleate may cause a decrease in the immune response as seen in animal experiments. The marine oils may be regarded as a natural aspirin in that formation of PGs of the bisenoic series will be replaced by the PGs of the trienoic series. This results in the formation of TXA3, which is biologically inactive, and PGI3, which is biologically active like PGI2. This may have no physiologic consequences but it is used to illustrate a possible mechanism for the postulated beneficial cardiovascular effects of these oils. The issues and the mechanisms are controversial and frequently highly speculative. The subject is a boon for the lipid biochemist and nutritionist.(ABSTRACT TRUNCATED AT 250 WORDS)