Direct speciation analysis of arsenic in sub-cellular compartments using micro-X-ray absorption spectroscopy

Identification of arsenic chemical species at a sub-cellular level is a key to understanding the mechanisms involved in arsenic toxicology and antitumor pharmacology When performed with a microbeam, X-ray absorption near-edge structure (mu-XANES) enables the direct speciation analysis of arsenic in sub-cellular compartments avoiding cell fractionation and other preparation steps that might modify the chemical species. This methodology couples tracking of cellular organelles in a single cell by confocal or epifluorescence microscopy with local analysis of chemical species by mu-XANES. Here we report the results obtained with a mu-XANES experimental setup based on Kirkpatrick-Baez X-ray focusing optics that maintains high flux of incoming radiation (> 10(11) ph/s) at micrometric spatial resolution (15 x 4.0 mu m(2)) This original experimental setup enabled the direct speciation analysis of arsenic in sub-cellular organelles with a 10(-15)g detection limit. mu-XANES shows that inorganic arsenite, As(OH)3, is the main form of arsenic in the cytosol, nucleus, and mitochondrial network of cultured cancer cells exposed to As2O3. On the other hand, a predominance of As(III) species is observed in HepG2 cells exposed to As(OH)(3) with, in some cases, oxidation to a pentavalent form in nuclear structures of HepG2 cells The observation of intra-nuclear mixed redox states suggests an inter-individual variability in a cell population that can only be evidenced with direct sub-cellular speciation analysis (C) 2009 Elsevier Inc All rights reserved