Vitamin E protection in the biochemical adaptation of marine organisms to cold-water environments

Vitamin E is one of the most important lipid-soluble antioxidants to occur in plants and animals for cellular protection against lipid peroxidation. An essential adaptation to low temperature is the elaboration of high levels of unsaturated fatty acids in the composition of cellular membranes, which is necessary to maintain functional membrane fluidity. Increasing the content of lipid unsaturation, however, occurs at the expense of enhancing the vulnerability of cellular membranes to oxidative damage. First isolated from salmon eggs, cold-water marine organisms were found to produce, or acquire, a specific vitamin E homologue, named "marine-derived tocopherol" (MDT), having an unusual methylene unsaturation at its isoprenoid-chain terminus. In this overview we compare the antioxidant composition of tropical, temperate and polar fishes, present provisional evidence that MDT is produced at the primary food chain, and provide empirical confirmation that the enhanced reactivity of MDT at low temperature is attributed to its greater rate of diffusion in viscous lipids at low temperatures. This claim of biochemical adaptation is supported by a unique model of diffusion-limited reactivity that mimics changes in the ratio of the MDT/alpha-tocopherol rate constants at diminishing levels of radical flux in viscous media at low temperature. We offer in conclusion future outlooks to research on antioxidant protection in cold-water ectotherms.