Opposing effects of methylmercury and n‐3 long‐chain polyunsaturated fatty acids on oxidative status

Abstract

The objective was to assess interactive effects of methylmercury (MeHg) and n‐3 long‐chain polyunsaturated fatty acids (LCPUFA) on oxidative status of animals exposed chronically to MeHg and fed a diet with (+) or (−) without n‐3 LCPUFA. Female rats (n=8/grp) were exposed for 1 yr to 0, 0.5, & 5 ppm MeHg in water and consumed a diet containing palm, safflower, soybean and either coconut in (−) n−3 diet or fish oil in (+) n‐3 diet. The expression of the pro‐oxidative enzyme NADPH oxidase (OX) and antioxidant enzymes glutathione peroxidase (GSH‐Px), catalase (CAT), and superoxide dismutase (SOD) were determined using RT‐PCR. Protein oxidation was assessed by measuring protein carbonyl content. The (+) n−3 groups had significantly lower gene expression of OX than (−) n−3 groups (P ≤ 0.001) in both heart and liver. A mercury effect was observed for this enzyme in the liver (P = 0.01), with increased prooxidant activity with MeHg. The n‐3 fed animals without MeHg have decreased oxidized protein content in heart by 35% compared to (−) n−3 group. No overall diet effect was observed in gene expression of any of the antioxidant enzymes. In the liver, presence of MeHg decreased antioxidant activity as reflected in gene expression of GSH‐Px (P = 0.05) and CAT (P = 0.005). The opposing effect of environmental contaminant, MeHg, and n‐3 LCPUFA in fish may be explained, in part, through changes in oxidative status. (Funded by AAES 13–014)