Depletion of alpha-tocopherol and astaxanthin in Atlantic salmon (Salmo salar) affects autoxidative defense and fatty acid metabolism

Duplicate groups of Atlantic salmon post-smelts were fed four purified diet s supplemented with both vitamin E and the carotenoid astaxanthin (Ax) (+E, +Ax), or supplemented with either vitamin E or Ax (-E, +Ax and +E, -Ax) or deficient in both vitamin E and Ax (-E, -Ax) for 22 wk. There were no effe cts of diet on growth rate, but an extensive lipoid liver degenerative lesi on was observed in 15% of fish fed diets deficient in vitamin E. Tissue vit amin E concentrations varied in accordance with dietary vitamin E in liver, muscle, heart, plasma, brain and eye; levels were reduced to similar to 3% in liver but only to 40% in eye of fish fed diets deficient in vitamin E c ompared with those fed diets supplemented with vitamin E. An interactive sp aring of Ax supplementation on tissue vitamin E concentration was observed, but only in brain. Dietary deficiency of both vitamin E and Ax significant ly increased the recovery of desaturated and elongated products of both [1- C-14] 18:3(n-3) and [1-C-14] 20:5(n-3) in isolated hepatocytes, suggesting that conversion of fatty acids to their long-chain highly unsaturated produ cts can be stimulated by a deficiency of lipid-soluble antioxidants. The an tioxidant synergism of vitamin E and Ax was supported by their ability to r educe malondialdehyde formation in an in vitro stimulation of microsomal li pid peroxidation and to reduce plasma levels of 8-isoprostane. The results of this study suggest that both vitamin E and the carotenoid Ax have antiox idant functions in Atlantic salmon.