ATALAY, M., D. E. LAAKSONEN, S. KHANNA, E. KALISTE-KORHONEN, O. HÄNNINEN, and C. K. SEN. Vitamin E regulates changes in tissue antioxidants induced by fish oil and acute exercise. Med. Sci. Sports Exerc., Vol. 32, No. 3, pp. 601–607, 2000.
Purpose: Prooxidant effects of fish oil supplementation could unfavorably affect the cardiovascular benefits of fish oil. We tested the effects of 8 wk vitamin E cosupplementation with fish oil on antioxidant defenses at rest and in response to exhaustive exercise in rats.
Methods: Rats (N = 80) were divided into fish oil, fish oil and vitamin E (FOVE), soy oil, and soy oil and vitamin E (SOVE) supplemented groups. For the vitamin E supplemented rats, corresponding groups (FOVE-Ex and SOVE-Ex) performed an acute bout of exhaustive exercise after the supplementation period.
Results: Fish oil supplementation increased the activity of catalase, glutathione peroxidase, and glutathione-S-transferase in the liver and red gastrocnemius (RG) muscle. Fish oil decreased liver total glutathione (TGSH) levels. Vitamin E supplementation decreased antioxidant enzyme activities to levels at or near those in SOVE in a tissue specific pattern. Vitamin E increased TGSH in liver, heart, and RG. Regression analysis showed TGSH to be a negative determinant of protein oxidative damage as measured by protein carbonyl levels in both liver and RG. Catalase activity was associated with liver lipid peroxidation as measured by thiobarbituric acid–reacting substances. The exercise-induced decrease in hepatic TGSH tended to be less in FOVE versus SOVE. Exhaustive exercise also modulated tissue antioxidant enzymes.
Conclusions: Vitamin E supplementation markedly decreased fish oil induced antioxidant enzyme activities in all tissues. Sparing of glutathione may be an important mechanism by which vitamin E decreased tissue protein oxidative damage.
Fish oil–induced oxidative stress could reduce the purported cardiovascular benefits of fish oil (17,23,28). Diets high in fish have not been conclusively shown to decrease cardiovascular morbidity or mortality (4). Although fish oil may decrease serum triglyceride levels, increase membrane fluidity, and decrease platelet thromboxane production, it may also cause oxidative stress. Oxidative stress is believed to play a major role in atherosclerosis (32) and many other diseases. Physical exercise also acutely induces oxidative stress (26,30).
The high degree of unsaturation of the (n-3) fatty acids making up fish oil may predispose to oxidative stress (17,23,28). Fish oils have also been shown to induce peroxisomal β-oxidation, in which fatty-acyl oxidation gives hydrogen peroxide as a normal byproduct (9). We recently showed in rats that, even with high dose supplementation of the lipophilic chain breaking antioxidant vitamin E with fish oil, liver lipid peroxidation as measured by thiobarbituric acid–reacting substances (TBARS) remained higher compared with supplementation of vitamin E with soy oil (28), in agreement with previous studies (17). Protein oxidative damage as measured by protein carbonyl levels in most of tissues examined was not affected by fish oil supplementation, although vitamin E strongly decreased protein carbonyl levels in all tissues measured (28).
As a compensatory mechanism against the prooxidant properties of fish oil, fish oil supplementation has also been shown to markedly induce activity of antioxidant enzymes such as glutathione peroxidase (GPX), glutathione-S-transferase (GST), and catalase (11,35), in addition to variable effects on glutathione (10). Glutathione is an ubiquitous cytosolic antioxidant tripeptide that regenerates vitamin E and ascorbate and protects against protein oxidative damage by maintaining protein thiols (22,34) in addition to direct free radical- and GPX-dependent hydrogen peroxide and peroxyl radical scavenging. GST catalyzes the reaction between the -SH group and potential alkylating agents, rendering them more water soluble and suitable for transport out of the cell (18). GST can also use peroxides as a substrate (3). Catalase is a hydrogen peroxide scavenging enzyme mainly localized to peroxisomes or microperoxisomes (21). These antioxidants and antioxidant enzymes work independently and in concert to protect against oxygen toxicity (27).
Many studies have shown that even moderate exercise may result in oxidative damage (2,28). Increased exercise-induced oxidative stress could reduce the beneficial effects of regular exercise (27). This may be particularly concerning to groups predisposed to oxidative stress, such as those who consume large amounts of fish or take fish oil supplements. We recently found that, despite higher hepatic lipid peroxidation at rest in fish oil and vitamin E supplemented (FOVE) rats compared with soy oil and vitamin E supplemented (SOVE) animals, FOVE rats tended to be relatively less susceptible to exercise-induced oxidative stress as measured by vitamin E depletion and protein carbonyl and TBARS formation (28). A possible mechanism for decreased susceptibility to exercise-induced oxidative stress may be because mitochondrial β-oxidation, hypothesized to be a primary source of exercise-induced oxidative stress, undergoes a marked increase during exercise, in apparent contrast to peroxisomal β-oxidation. Thus, the role of peroxisomal β-oxidation as a cause of oxidative stress appears to decrease during exercise relative to mitochondrial oxidation. Also, fish oil has potent antiinflammatory effects (8,13,16), which could contribute to decreased susceptibility to exercise-induced oxidative stress. The effect of fish oil and vitamin E supplementation on tissue antioxidant defenses during physical exercise has not been studied.
The aims of this study were 1) to assess the effect of fish oil supplementation alone and with vitamin E on physiological antioxidant defenses in liver, heart, and skeletal muscle at rest and after exhaustive exercise, and 2) to assess the determinants of previously reported (28) lipid and protein indices of oxidative stress in liver and skeletal muscle in an experimental rat model using soy oil, high in (n-6) fatty acid content, for comparison.