THE MOLECULAR BASIS FOR MERCURY TOXICITY

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The high toxicity of mercury compounds is well known, but the mechanisms of toxicity remain largely obscure. Human exposure to mercury comes from many sources, including predatory marine fish and from vaccines, where Thimerosal (ethylmercurithiosalicylate), a commonly-added fungicide and bactericide, has been implicated in autism and Asperger's syndrome. The nature and development of the toxic effects are critically dependent upon the chemical form of the mercury, but very little is known about the chemical fate of the metal after it has been ingested. One major reason for this is a lack of good in situ probes for mercury. X-ray absorption spectroscopy can provide information on the chemical environment of metals and metalloids in situ. We propose to apply Hg L-edge XAS to develop an understanding of the chemical toxicology of mercury in rats, as a model for human exposure. The ultimate goal of this work is to provide the chemical basis for effective chelation therapy treatment of mercury poisoning in humans. Current mercury chelation therapy drugs are not very effective. A striking illustration of their inadequacy is provided by the tragic case of a chemist at Dartmouth College, who was accidentally exposed to a small quantity of dimethylmercury and died ten months later despite intensive chelation therapy. The drugs currently used for mercury chelation therapy - dimercapto propanesulfonic acid, and dimercapto succinic acid - have their origins in antidotes for arsenic war agents such as Lewisite. While mercury is well known for its affinity for thiols, these viscinal dithiols are poorly suited as ligands for Hg due to their inability to coordinate the metal linearly. A knowledge of the chemical forms of mercury in tissues is an essential prerequisite for chelation therapy design, and we plan to use the information obtained from XAS, together with computational chemistry, to this end.