RENAL OXIDANT INJURY AND OXIDANT RESPONSE INDUCED BY MERCURY

The role of oxidative stress in mercuric chloride (HgCl2)-induced neph rotoxicity is uncertain and controversial. We demonstrate that LLC-PK1 cells, exposed to HgCl2, generate massive amounts of hydrogen peroxid e, the latter completely quenched by the hydrogen peroxide scavenger, pyruvate. HgCl2 exerts a dose-dependent cytotoxicity which is attenuat ed by pyruvate and catalase. Cellular generation of hydrogen peroxide arises, at least in part, from mitochondria since mitochondrial rates of generation of hydrogen peroxide increase in response to HgCl2; HgCl 2 also provokes a shift in absorbance spectra in rhodamine 123 loaded- mitochondria and stimulates mitochondrial state 4 respiration. HgCl2, applied for one hour, impairs cellular vitality as demonstrated by the MTT assay, an assay dependent in part on mitochondrial function. HgCl 2 impairs function in other organelles such as lysosomes that maintain a transmembrane proton gradient; these latter effects are partially a ttenuated by pyruvate. We complement these in vitro findings with in v ivo evidence demonstrating that HgCl2 stimulates renal generation of h ydrogen peroxide. The functional significance of such generation of hy drogen peroxide was evaluated in rats deficient in selenium and vitami n E, a nutrient deficiency that impairs the scavenging of hydrogen per oxide and promotes the toxicity of this oxidant. In these rats serum c reatinine values were significantly higher on sequential days followin g the administration of HgCl2. To probe the renal response to oxidativ e stress induced by HgCl2, we examined hydrogen peroxide-scavenging en zymes and redox-sensitive genes. Catalase activity was unaltered where as glutathione peroxidase activity was decreased, effects that may con tribute to the net renal generation of hydrogen peroxide. The redox se nsitive enzyme, heme oxygenase, was markedly up-regulated in the kidne y in response to HgCl2. HgCl2 also induced members of the bcl family, bcl2 and bclx, genes that protect against apoptosis and oxidant injury . In another model of oxidant-induced renal injury, the glycerol model , bcl2 mRNA was not induced at 6 and 24 hours after the administration of glycerol. In summary, we demonstrate vitro and in vivo and such ge neration of peroxide contributes to renal dysfunction in vitro and in vivo. We also demonstrate that in response to HgCl2, redox sensitive g enes are expressed including heme oxygenase and members of the bcl fam ily.