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

[EN] 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 Dicentrarchus labrax growth and total DNTB- and thioredoxin-reductase (TrxR) activities and the transcription of four redox genes (txn1, gpx1, txnrd3, and txnrd2) 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 txn1, gpx1, and txnrd2. Feeding 6.7 mg Hg/kg for 53 days downregulated the genes of the thioredoxin system (txn1, txnrd3, and txnrd2) but upregulated gpx1, 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. ; The work was supported by grants from the Spanish MINECO (RTC-2014–2837-2- “SELATUN: Minimización de la problemática del mercurio del atún y valorización del atún como alimento saludable, Programa Retos-Colaboración 2014” and CTM2012-40203-C02-01- “BMW: Biomarcadores estándar de base científica en mejillón para diagnosticar y monitorizar los efectos biológicos de la polución en el Golfo de Bizkaia: implementación de la DEME”), Euskampus Fundazioa- Campus of International Excellence (307615SAA2), and from the Basque Government Elkartek Grant KK-2016/00057- “MAROMEGA: Nuevas alternativas para la producción de omega-3 a partir de recursos marinos.” The funding sources had no involvement in the preparation of this manuscript.