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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Arsenic Toxicity and HSP70 Expression in Xenopus laevis Embryos

Rosalba Gornati, Claudio Monetti, Davide Vigetti, Stefano Bosisio, Salvador Fortaner, Enrico Sabbioni, Giovanni Bernardini and Mariangela Prati

The evaluation of the effect of trace metals on health can be difficult, because of their presence in the environment in various chemical forms. Exposure to arsenic compounds is an example of this complexity, as it can be present in the environment in inorganic and organic forms. The effects of arsenic in vertebrates are complicated by several variables, such as speciation of the element, the exposure route, and the susceptibility of the particular animal species. The embryotoxicity and teratogenicity of three arsenic species - sodium arsenite (NaAsO2), disodium hydrogen arsenate (Na2HAsO4) and dimethylarsinic acid [(CH3)2AsOOH] - were evaluated by the modified frog embryo teratogenic assay on Xenopus (FETAX). We also show how the classical FETAX endpoints, based on morphological and morphometrical analysis, can conveniently be integrated with the study of molecular markers. Possible changes in the expression of the mRNA for the heat-shock protein HSP70, following exposure to NaAsO2, were examined by using the reverse transcriptase polymerase chain reaction. HSP70 mRNA is strongly induced by arsenic.
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Platinum Toxicity and Gene Expression in Xenopus Embryos: Analysis by FETAX and Differential Display

Claudio Monetti, Giovanni Bernardini, Davide Vigetti, Mariangela Prati, Salvador Fortaner, Enrico Sabbioni and Rosalba Gornati

Since the level of platinum in the environment is destined to increase, because of its use in vehicle catalytic converters, the toxicity of platinum needs further investigation. In this study, the frog embryo teratogenesis assay–Xenopus (FETAX) was used to compare the embryotoxicity and teratogenicity of two common platinum species, (NH4)2PtCl4 and (NH4)2PtCl6. The uptake rates of the two platinum species were studied, and also their effects on the expression of genes encoding metallothionein and heat-shock protein 70, which are known to be induced by several stress factors. In addition, the differential display technique was used to search for genes that were specifically induced by platinum. A gene for the type I collagen α-chain and a novel gene were identified.
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