A Comparative Study of the Toxicity of Mercury Dichloride and Methylmercury, Assayed by the Frog Embryo Teratogenesis Assay–Xenopus (FETAX)

Mariangela Prati, Rosalba Gornati, Patrizia Boracchi, Elia Biganzoli, Salvador Fortaner, Romano Pietra, Enrico Sabbioni and Giovanni Bernardini

The Frog Embryo Teratogenesis Assay–Xenopus (FETAX) is a powerful and flexible bioassay that makes use of the embryos of the anuran amphibian Xenopus laevis. The FETAX can detect xenobiotics that affect embryonic development, when mortality, teratogenicity and growth inhibition are used as endpoints. The FETAX was used to compare the embryotoxic and teratogenic potentials of two chemical species of mercury: inorganic mercury(II) chloride (HgCl2) and organic methylmercury chloride (MeHgCl). MeHgCl, with an estimated median lethal concentration [LC50] of 0.313μM and a median teratogenic concentration [TC50] of 0.236μM, showed a higher toxicity than HgCl2, with estimated LC50 and TC50 values of 0.601μM and 0.513μM, respectively. On the basis of these results, HgCl2 and MeHgCl can be classified as “slightly teratogenic compounds”, as the ratio of LC50/TC50 is less than 1.5. There was a significant deviation from the commonly described monotonic behaviour of the concentration–response curves, suggesting a hormetic effect of both species of mercury. Uptake experiments, followed by neutron activation analysis, showed a higher incorporation of mercury in embryos exposed to MeHgCl compared with those exposed to HgCl2. Interestingly, Hg-exposed embryos showed a higher content of selenium and zinc than did control embryos.
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Responses of Human Gingival and Periodontal Fibroblasts to a Low-Zinc Environment

Emil Rudolf and Miroslav Červinka

Morphology, motility, proliferation rate and markers of oxidative stress in primary human gingival fibroblasts (GF) and periodontal ligamental fibroblasts (PDL-F) grown in zinc-deficient cultivation medium (ZDM), were studied over a 5-week culture period. A low-zinc environment effectively reduced the total, as well as the free, intracellular zinc content in both cell types, over the course of the experiment. Decreased intracellular zinc content resulted in altered cellular morphology, reduced motility, and rearrangement of actin and tubulin in the cytoskeleton. In addition, fibroblasts with low zinc content exhibited decreased proliferation, accompanied by changes in cell cycle distribution, expression of specific biochemical markers, increased oxidative stress and the activation of caspase-3. Supplementation of ZDM with exogenous zinc prevented the loss of intracellular zinc, while also restoring the morphology, cell proliferation and mitogenic signalling of the cultured cells. Moreover, such supplemented cells were protected against oxidative stress and cell death. Of the two primary cell cultures examined, GF were more sensitive to decreased intracellular zinc content, when compared to PDL-F. The results obtained suggest that the human primary cell cultures can be useful for the longer-term evaluation of the effects of nutritional factors originating from the environment.
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