INVESTIGATIONS ON THE NEPHROTOXICITY AND HEPATOTOXICITY OF TRIVALENT AND HEXAVALENT CHROMIUM COMPOUNDS

In contrast to trivalent chromium (Cr(III)) compounds, hexavalent chro mium ((Cr(VI)) compounds are oxidizing agents capable of directly indu cing tissue damage and possessing carcinogenic, mutagenic and teratoge nic potency. After oral or dermal absorption of Cr(VI), the kidney is the main target organ for chromium accumulation, which might result in acute tubular necrosis in humans, In contrast, an acute toxic effect of Cr(VI) on the liver has not yet been described. Therefore, we used two established epithelial cell lines from the kidney (Opossum kidney cells) and the liver (Hep G2 cells) to design an in vitro-assay which is able to examine acute toxic effects of chromium compounds. Cells of both cell lines were treated with various concentrations of Cr(III) a nd Cr(VI) ranging from 0.01 mu mol/l to 1 mmol/l for 24 h. Thereafter, cell morphology, organization of the intracellular cytoskeleton, numb er of viable cells and mean cell volume were examined. The results sho w that Cr(VI), but not Cr(III), has an acute cytotoxic effect and caus es a dose-dependent loss in cell viability. The effective dose that ca used 50% of cell death was 5 mu mol/l for kidney epithelial cells and 50 mu mol/l for liver epithelial cells. This means that kidney epithel ial cells are 10 times more sensitive towards Cr(VI) treatment than li ver epithelial cells and this might explain the known nephrotoxicity i n vive. The loss in cell viability was accompanied by a rounding and d etachment of the cells and a marked reduction of intracellular F-actin -containing stress fibers. Microtubules and intermediate-sized filamen ts were observed to be unaffected. Only in the case of kidney epitheli al cells, a dose-dependent cell volume increase was observed after Cr( VI) treatment at concentrations up to 50 mu mol/l. At higher concentra tions, the cell volume decreased due to the high number of cells under going lysis and the appearance of cellular fragments. Various chloride channel blockers with different specifities, molecular structures and inhibitory potentials were tested for their ability to prevent Cr(VI) -induced cell damage. None of the channel blockers was able to inhibit cell damage, suggesting that the uptake of Cr(VI) through the general anion transport system of the cell membrane might be only one facet o f cellular uptake and toxification. The data presented here not only c onfirm the different organ-specific effects of Cr(III) and Cr(VI), but also provide a basis for future experiments on the understanding of a cute toxicity of Cr(VI) compounds. Moreover, the results demonstrate t hat the designed in vitro-assay might be a useful tool to prove whethe r non-toxic Cr(III) can be oxidized to Cr(VI) under specific industria l conditions (for example, in the leather or chrome industry).