Abstract's Details

XAS and XRF Combined Yield New Insight into the in vivo Roles of Cr, Hg and Cu
Abstract ID	UMTG:3-2
Presenter	Hugh Harris
Presentation Type	SSRL/LCLS
Full Author List	H. H. Harris (1), A. Levina (2), S. Vogt (3), L. E. Wu (4), H. Eastgate (5), B. Lai (3), P. A. Lay (2)
Affiliations	(1) The University of Adelaide (2) The University of Sydney (3) Argonne National Labs (4) Garvan Institute of Medical Research (5) Eastmac Pty. Ltd.
Category	Bio/Life Sciences
Abstract	The wide applicability of X-ray absorption and fluorescence techniques to different sample types has allowed us to develop our understanding of the biological fate of metals that many of us expose ourselves to by choice. This presentation will cover some recent results from two separate projects that involve samples approaching the in vivo ideal. Chromium(III) compounds are highly popular dietary supplements that are used to enhance insulin action. By contrast, Cr(VI) species have well-established cytotoxic, genotoxic and carcinogenic activities. We have fitted XANES spectra from Cr(VI)-treated cultured mammalian cells with Cr model compound spectra to show that Cr is predominantly bound to carboxylato, amine and imidazole residues in high-molecular-mass (> 30 kDa) species. Cell lysis results in a significant redistribution of Cr(III) species and the formation of a low-molecular-mass fraction whose properties are very similar to the purported natural Cr(III)-containing factor, chromodulin, on whose existence the antidiabetic behaviour and dietary essentiality of Cr has been based. We have used XRF and micro-XANES to demonstrate biological oxidation of Cr(III) to Cr(VI) in a relevant mammalian in vitro cell model, providing an alternative explanation for the insulin potentiating effects of Cr(III), but also indicating potential health concerns for Cr dietary supplements. I will also briefly discuss XRF and XANES experiments on the distribution and identity of metal species in extracted human teeth, including migration of Hg from dental amalgams and the serendipitous identification of a link between Cu and tooth decay.
Footnotes
Funding Acknowledgement	We gratefully acknowledge financial support from the Australian Research Council, the Department of State and Regional Development of the Victorian State Government and the Australian Synchrotron Research Program. The use of both SSRL and APS facilities was supported by the US Department of Energy (OBES/OBER).