Lactic acid bacteria strains reduce in vitro mercury toxicity on the intestinal mucosa

A bicameral model consisting of Caco-2 and HT29-MTX intestinal epithelial cells and THP-1-derived macrophages has been used to test the ability of two strains of Lactobacillus to protect from damage caused by mercury. Exposure to 1 mg/ml mercury [Hg(II) or methyl-Hg] for seven days in this model resulted in an inflammatory and pro-oxidant response mainly driven by macrophages. This led to an impairment in the intestinal barrier, defective tight-junctions, increased permeability and mucus hypersecretion. In addition, the wound-healing capacity of the epithelial monolayer was also diminished. However, the presence of heat-killed Lactobacillus intestinalis or Lactobacillus johnsonii cells during Hg exposure reverted these effects, and most of the parameters recovered values similar to control cells. Both lactobacilli showed the capacity to bind Hg(II) and methyl-Hg under the cell culture conditions. This points to Hg sequestration as a likely mechanism that counteracted Hg toxicity. However, differences in the Hg binding capacity and in the effects between both strains suggest that other probiotic-mediated mechanisms may play a role in the alleviation of the damage elicited by Hg. These results show the potential of the bicameral intestinal epithelial model for screening of effective strains for their use in later in vivo studies.