Time-dependent uptake, distribution and biotransformation of chromium(VI) in individual and bulk human lung cells: application of synchrotron radiation techniques.
Chromium(VI) is a human carcinogen, primarily affecting the respiratory tract probably via active transport into cells, followed by the reduction to Cr(III) with the formation of DNA-damaging intermediates. Distribution of Cr and endogenous elements within A549 human lung adenocarcinoma epithelial cells, following treatment with Cr(VI) (100 microM, 20 min or 4 h) were studied by synchrotron-radiation-induced X-ray emission (SRIXE) of single freeze-dried cells. After the 20-min treatment, Cr was confined to a small area of the cytoplasm and strongly co-localized with S, Cl, K, and Ca. After the 4-h treatment, Cr was distributed throughout the cell, with higher concentrations in the nucleus and the cytoplasmic membrane. This time-dependence corresponded to approximately 100% or 0% clonogenic survival of the cells following the 20-min or 4-h treatments, respectively, and could potentially be explained by a new cellular protective mechanism. Such processes may also be important in reducing the potential hazards of Cr(III) dietary supplements, for which there is emerging evidence that they exert their anti-diabetic effects via biological oxidation to Cr(VI). The predominance of Cr(III) was confirmed by micro-XANES spectroscopy of intracellular Cr hotspots. X-ray absorption spectroscopy (XANES and EXAFS, using freeze-dried cells after the 0-4-h treatments) was used to gain insight into the chemical structures of Cr(III) complexes formed during the intracellular reduction of Cr(VI). The polynuclear nature of such complexes (probably with a combination of carboxylato and hydroxo bridging groups and O-donor atoms of small peptides or proteins) was established by XAFS data analyses.
Harris
Hugh H
HH
Centre for Heavy Metals Research, and Centre for Structural Biology and Structural Chemistry, School of Chemistry, University of Sydney, NSW, Australia.
Levina
Aviva
A
Dillon
Carolyn T
CT
Mulyani
Irma
I
Lai
Barry
B
Cai
Zhonghou
Z
Lay
Peter A
PA
D001711:Biotransformation; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D002857:Chromium / Q000378:metabolism*; D006801:Humans; D008168:Lung / Q000166:cytology* / Q000378:metabolism*; D046911:Macromolecular Substances / Q000378:metabolism; D015394:Molecular Structure; D013052:Spectrometry, X-Ray Emission; D013057:Spectrum Analysis / Q000379:methods; D017356:Synchrotrons; D013997:Time Factors; D014965:X-Rays
D046911:Macromolecular Substances; D002857:Chromium