Thimerosal positivities: patch testing to methylmercury chloride in subjects sensitive to ethylmercury chloride

The aim of this paper was to evaluate whether methylmercury chloride (MeHgC l) aq., when patch tested in a group of thimerosal-positive subjects reacti ng to ethylmercury chloride (EtMgCl), might be a reliable model for the bet ter understanding of interactions between alkylmercury compounds and the sk in. 19 out of 21 consecutive patients who previously had given positive pat ch-test reactions to both ethylmercury chloride 0.0165% eth.(EtHgCl, 0.615 mM) and MeHgCl 0.031% aq.(1.23 mM), and negative reactions to thiosalicylic acid 0.05% (3.24 mM) aq./eth. 50/50, were repatch tested to 8 mu l of MeHg Cl 0.031% aq. and to 8 mu l of aq. solutions containing MeHgCl mixed with c ysteine, glutathione, ZnSO4, Mg SO4 Mn SO4, ZnCl2, MgCl2 and Mn Cl-2 respec tively The results showed that cysteine, glutathione and Zn(IT) salts were able to abolish the positive reactions, demonstrating the role played by bo th thiol groups and Zn(II) itself. Patch tests concomitantly carried out in 16 out of 19 patients to 8 mu l of aqueous MeHgCl and to 8 mu l of aqueous solutions containing MeHgCl and MeHgCl mixed to fragment 56-61 of metallot hionein I (MT I), MT I and MT II-Zn, respectively, revealed that all the MT s tested were able to reduce or to inhibit the reactions, demonstrating the effect of the thiol groups. Due to the close chemical similarities to EtHg Cl and to its water solubility, MeHgCl seems to be a suitable model for eva luating the reactivity of alkylmercury compounds in the skin. We speculate that both EtHg- and MeHg-derivatives are xenobiotics with similar reactivit y. However, the lack of clinical relevance of the reactions to both alkyl c ompounds lead us to conclude that, since environmental exposure does not se em to play a pivotal role, they probably have mostly to do with compounds i ncluded in in the standard series, and are elicited by reduced function of physiological SH chelators.