HgS and Zuotai differ from HgCl₂ and methyl mercury in intestinal Hg absorption, transporter expression and gut...

Mercury (Hg) is generally considered as a toxic metal; yet the biological outcomes of Hg-containing compounds are highly dependent upon their chemical forms. We hypothesize that mercury sulfide (HgS) is different from HgCl₂ and methylmercury (MeHg) in producing intestinal Hg absorption and disruption of gut microbiome. To test this hypothesis, mice were given orally with HgS (α-HgS, 30 mg/kg), Zuotai (β-HgS, 30 mg/kg), HgCl₂ (33.6 mg/kg, equivalent Hg as HgS), or MeHg (3.1 mg/kg, 1/10 Hg as HgS) for 7 days. Accumulation of Hg in the duodenum and ileum after HgCl₂ (30-40 fold) and MeHg (10-15 fold) was higher than HgS and Zuotai (~2-fold). HgCl₂ and MeHg decreased intestinal intake peptide transporter-1 and Ost-β, and increased ileal bile acid binding protein and equilibrative nucleoside transporter-1. The efflux transporters ATP-binding cassette sub-family C member-4 (Abcc4), Abcg2, Abcg5/8, and Abcb1b were increased by HgCl₂ and to a lesser extent by MeHg, while HgS and Zuotai had minimal effects. Bacterial DNA was extracted and subjected to 16S rDNA sequencing. Operational taxonomic unit (OTU) results showed that among the 10 phyla, HgS increased Firmicutes, Proteobacteria, while HgCl₂ increased Bacteroidetes, Cyanobacteria and decreased Firmicutes; among the 79 families, HgS increased Rikenellaceae, Lactobacillaceae, Helicobacteraceae, and decreased Prevotellaceae, while HgCl₂ increased Odoribacteraceae, Porphyromonadaceae, and decreased Lactobacillaceae; among the 232 genus/species, HgS and Zuotai affected gut microbiome quite differently from HgCl₂ and MeHg. qPCR analysis with 16S rRNA confirmed sequencing results. Thus, chemical forms of mercury are a major determinant for intestinal Hg accumulation, alterations in transporters and disruption of microbiome.