ATLA::Alternatives to Laboratory Animals

Volume 30, Number 1

A comparative study of the toxicity of mercury dichloride and methylmercury, assayed by the frog embryo teratogenesis assay-Aenopus (FETAX).

Mariangela Prati¹, Rosalba Gornati¹, Patrizia Boracchi², Elia Biganzoli³, Salvador Fortaner⁴, Romano Pietra⁴, Enrico Sabbioni⁴ and Giovanni Bernardini¹

¹Department of Structural and Functional Biology, Universitá dell'Insubria, 3 Via Dunant, 21100 Varese, Italy; ²1nstitute of Medical Statistics and Biometry, Universitá di Milano, 1 Via Venezian, 20133 Milan, Italy; ³Unit of Medical Statistics and Biometry, Istituto Nazionale per lo Studio e la Cura dei Tumori, 1 Via Venezian, 20133 Milan, Italy; ⁴ECVAM, Institute for Health & Consumer Protection, European Commission Joint Research Centre, Ispra 21020 (VA), Italy<

SUMMARY

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 0.313 µM and a median teratogenic concentration [TC50] of 0.236 µM, showed a higher toxicity than HgCl₂, with estimated LC50 and TC50 values of 0.601 µM and 0.513 µM, 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.

Keywords: arsenic, FETAX hormesis, mercury, neutron activation analysis, selenium, zinc