The effect of mercuric chloride on renal brush border membrane

Effect of potassium dichromate on renal brush border membrane enzymes and phosphate transport in rats

Chromium is widely used in industry but exposure to chromium compounds in the workplace can result in nephrotoxicity. Various nephrotoxicants affect the brush border membrane (BBM) lining the epithelial cells of the proximal tubule, but there have been no studies regarding the effect of potassium dichromate (K2Cr2O7), a hexava-lent chromium compound, on renal BBM. In the present work, the effect of administering a single intraperitoneal dose (15 mg/kg body weight) of K2Cr2O7 on rat renal BBM enzymes and inorganic phosphate (Pi) transport was studied. The animals were administered normal saline (control) or K2Cr2O7 and sacrificed 1, 2, 4 and 8 days after treatment. K2Cr2O7 induced reversible damage to the rat kidney function as indicated by serum creatinine (Scr) and urea nitrogen levels. The activities of BBM marker enzymes were significantly decreased in isolated BBM vesicles (BBMV) and homogenates of cortex and medulla on 1, 2 and 4 days after administration of K2Cr2O7with complete recovery to control values after 8 days. The decrease in the activities of the enzymes was mainly due to changes in maximum velocity (Vmax) values, while the Michaelis constant (Km) remained unchanged. The sodium dependent Pi transport across BBMV was reduced by 50% after treatment with K2Cr2O7. Thus, the administration of a single dose of K2Cr2O7 leads to impairment in the functions of renal BBM. These results suggest that the nephrotoxicity of K2Cr2O7 may be mediated, at least in part, by its effect on renal BBM.

Protective effects of 2,3-dimercaptopropane-1-sulfonate on mercuric chloride-induced acute inhibition of enzymes from rat duodenal mucosa and kidney cortex

Acute inhibitory effects of mercuric chloride on the activities of several enzymes from rat duodenal mucosa and kidney cortex and the protection provided by 2,3-dimercaptopropane-1-sulfonate (DMPS) were examined. Activities of carbonic anhydrase in homogenate, brush border and cytosol and of Mg(2+)-dependent, HCO3-stimulated ATPase in homogenate and brush border of duodenal mucosa and kidney cortex and activities of kidney microsomal Mg(2+)-dependent, Na(+)-K(+)-stimulated ATPase were all decreased following administration of HgCl2 (1-3 mg Hg/kg body weight s.c. once daily for 3 days). Decreases occurred generally in a dose-dependent manner and went back to near normal or normal levels by the combined administration of 20 and 30 mg DMPS/kg per day for 3 days. The concentration of serum urea nitrogen was increased about 8 times by the administration of 2 mg Hg/kg and restored to normal by the concomitant administration of 30 mg DMPS/kg. After the administration of 2 mg Hg/kg per day for 3 days, about half of the renal cortical proximal tubuli were necrotic. Administration of 30 mg DMPS/kg restored these changes to almost normal. The results suggest that DMPS is useful in mitigating acute Hg poisoning and that part of the protective effect of DMPS on enzyme damage induced by Hg poisoning may be due to its chelating action.

Effectiveness of N-acetylcysteine in protecting against mercuric chloride-induced nephrotoxicity

Mercuric chloride (HgCl2)-induced nephrotoxicity, as measured by functional and biochemical parameters was evaluated in rats at different kidney non-protein sulfhydryls (NPS) levels. Diethylmaleate (DEM) induced a 75% of NPS diminution 1 h after the administration. Renal function (clearance) and biochemical measurements (gamma-glutamyltranspeptidase activity in urine, and lipoperoxides in kidney tissue) were impaired when the animals were HgCl2-treated. Values were highly impaired when the kidneys were NPS-depleted and were improved when NPS pools were previously increased although they were not similar to control values. DEM treatment promoted a higher accumulation of HgCl2 in both kidney and liver while NAC-treatment reduced significantly the metal content in these organs. These data are in favour of a positive relationship among mercury content and organ injury. On the other hand, mercury content increased while NPS levels diminished. NPS might play a role in the HgCl2 detoxification and thus avoids mercury accumulation and mercury effects.

The implication of renal glutathione levels in mercuric chloride nephrotoxicity

The effects of renal glutathione (GSH) depletion on renal injury following a single injection of mercuric chloride (HgCl2) were evaluated in the rat. Animals were injected with different doses of HgCl2 and the renal function were studied 1 h later. Diethylmaleate (DEM) (4 mmol/kg body wt, i.p.) induced a significant depletion of GSH by reducing renal GSH levels to 25% of control values. This effect lasted for 6 h. HgCl2-induced nephrotoxicity, as measured by fractional excretion of glucose, lithium, sodium, potassium and water was increased in rats treated with DEM. The time course of HgCl2 nephrotoxicity was also investigated by determining the renal function at different times after HgCl2 and HgCl2 plus DEM injection. Renal impairment was significantly more marked in rat depleted of GSH.