Dietary Fructooligosaccharides Reduce Mercury Levels in the Brain of Mice Exposed to Methylmercury

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Methylmercury (MeHg) exposure during pregnancy is a concern because of its potential health risks to fetuses. Intestinal microbiota has important roles in the decomposition and fecal excretion of MeHg. We investigated the effect of nondigestible saccharides on the accumulation and excretion of Hg after MeHg exposure. Female BALB/cByJ mice were fed a basal diet or the same diet supplemented with 5% fructooligosaccharides (FOS) or 2.5% glucomannan. Six weeks after feeding, mice were administered MeHg chloride (4 mg Hg/kg, per os (p.o.)), and urine and feces were collected for 28 d. FOS-fed mice had lower total Hg levels in all tissues (including the brain) compared with that of controls. The glucomannan diet had no effect on tissue Hg levels. No differences in tissue concentrations of inorganic Hg among groups were found. Fecal Hg excretion was markedly higher in FOS-fed mice than that in controls, but urinary Hg excretion was similar. FOS-fed mice had a higher proportion of inorganic Hg in feces than that of controls, with a significant increase in fecal Hg excretion. Analysis of fecal bacterial population showed the relative abundance of Bacteroides in FOS-fed mice to be higher than that in controls. The results suggest that FOS enhanced fecal Hg excretion and decreased tissue Hg levels after MeHg administration, possibly by accelerating MeHg demethylation by intestinal bacteria (the candidate genus Bacteroides). This demethylation also reduces MeHg absorption in the large intestine. In conclusion, daily FOS intake may decrease tissue Hg levels in animals and humans exposed to MeHg.