Astaxanthin and canthaxanthin do not induce liver or kidney xenobiotic-metabolizing enzymes in rainbow trout (Oncorhynchus mykiss Walbaum)

This study was designed to assess the effects of dietary carotenoid supplementation on liver and kidney xenobiotic-metabolizing enzymes in the rainbow trout. Twelve rainbow trout (mean weight 266+/-10 g) were assigned to each of three replicate tanks for each of four dietary treatments; astaxanthin, canthaxanthin, negative control and positive control using beta-naphthoflavone, at a target dietary inclusion of 100 mg kg(-1) for each additive. Fish were fed for 3 weeks at a level of 1.2% body wt. day(-1). Serum carotenoid levels were used as indicators of exposure and were not significantly different (P>0.05) between carotenoid-fed trout. Livers and kidney were frozen separately in liquid N(2) by immersion and microsomal fractions from pooled samples (n=3) assayed for xenobiotic-metabolizing enzyme (cytochrome P450 monoxygenase) activities including ethoxyresorufin O-deethylase; methoxyresorufin O-demethylase; pentoxyresorufin O-dealkylase; benzoxyresorufin O-dearylase; and the conjugating enzymes glucuronosyl transferase; and glutathione-s-transferase. Results revealed that carotenoid treatment did not significantly (P>0.05) induce any enzyme system examined. Results are discussed in the context of metabolism of absorbed carotenoids.