Antioxidant activities and selenogene transcription in the European sea bass (Dicentrarchus labrax) liver depend, in a non-linear manner, on the Se/Hg molar ratio of the feeds

Abstract

Feeding 3.9 and 6.7 mg Hg/kg (Se/Hg molar ratios of 0.8 and 0.4, respectively) for 14 days negatively affected <i>Dicentrarchus labrax</i> growth and total DNTB- and thioredoxin-reductase (TrxR) activities and the transcription of four redox genes (<i>txn1</i>, <i>gpx1</i>, <i>txnrd3</i>, and <i>txnrd2</i>) in the liver, but a diet with 0.5 mg Hg/kg (Se/Hg molar ratio 6.6) slightly increased both reductase activities and the transcription of <i>txn1</i>, <i>gpx1</i>, and <i>txnrd2</i>. Feeding 6.7 mg Hg/kg for 53 days downregulated the genes of the thioredoxin system (<i>txn1</i>, <i>txnrd3</i>, and <i>txnrd2</i>) but upregulated <i>gpx1</i>, confirming the previously proposed complementarity among the antioxidant systems. Substitution of 20% of the feed by thawed white fish (hake) slightly counteracted the negative effects of Hg. The effects were not statistically significant and were dependent, in a non-linear manner, on the Se/Hg molar ratio of the feed but not on its Hg concentration. These results stress the need to consider the Se/Hg molar ratio of the feed/food when evaluating the toxicity of Hg.