The interaction of chromium (VI) with macrophages : Depletion of glutathione and inhibition of glutathione reductase

There are reports of alterations in the number and functions of the cells of the immune system in patients with metal-on-metal (MOM) orthopaedic implants. These effects have been correlated with elevated chromium levels in the patients' blood. We have investigated the interactions of clinically relevant concentrations of Cr VI with macrophages in vitro, and the mechanisms responsible for its toxicity. Cr VI causes a concentration dependent decrease in macrophage viability above 1 microM as measured by the MTT and Neutral Red assays. This falls well within the range of circulating chromium serum concentrations measured in patients with MOM. Intracellular reduced glutathione (GSH) levels fall as a result, and most of the loss (86%) is accounted for by oxidation to the dimer, GSSG. Prior depletion of GSH does not sensitise the cells to Cr VI toxicity, implying that it is not involved in protecting the cells against the effects of Cr VI. During the metabolism of Cr VI, glutathione reductase activity is inhibited. In contrast, the activities of catalase and superoxide dismutase are not significantly altered. Prior inhibition of glutathione reductase activity protects against the toxicity of Cr VI to a significant extent, suggesting that it reduces Cr VI to a toxic metabolite