Renal Protein Degradation: A Biochemical Target of Specific Nephrotoxicants

Abstract

Renal Protein Degradation: A Biochemical Target of Specific Nephrotoxicants. Cojocel, C., Smith, J.H., Maita, K., Sleight, S.D. and Hook, J.B. (1983). Fundam. Appl. Toxicol. 3: 278–284. Protein degradation in the kidney occurs mainly in lysosomes, organelles which may also accumulate nephrotoxic chemicals. The goal of this study was to evaluate the effects of intracellular accumulation of gentamicin, cephaloridine and cisplatin on lysosomal digestion of the protein lysozyme. Gentamicin (15 or 30 mg/kg/day for 3 or 5 days), cisplatin (2.5 or 5 mg/kg) or cephaloridine (500, 1000, 2000 or 2500 mg/kg) was administered ip to male Wistar rats. The main site of the nephrotoxic effects of these compounds was the proximal tubule where these agents differentially affected S1, S2 and/or S3 segments. A 2- and 4-fold increase of the excretion of N-acetyl-β-D-glucos-aminidase (NAG) was observed in the urine from cisplatinand gentamicin-treated rats, respectively; no change in enzyme excretion occurred after cephaloradine. One hour prior to sacrifice, rats were given 0.3 mg of unlabelled lysozyme in combination with 125I-lysozyme in 0.3 mL saline. Renal cortical slices were prepared and incubated for 15, 30, 60 and 90 min. Release of trichloroacetic acid (TCA)soluble radioactivity into the medium was assumed to quantify lysosomal degradation of lysozyme. Accumulation of p-amino-hippurate (PAH) in renal cortical slices and changes in blood urea nitrogen (BUN) concentration were used as indices of renal damage. TCA-soluble radioactivity increased in the medium from kidney slices from control rats to 50% of the total radioactivity after 90 min incubation. In gentamicin treated rats, lysozyme degradation was significantly decreased by doses of 15 and 30 mg/kg/day after 3 and 5 days of exposure in the absence of any changes in BUN or PAH accumulation. Increased BUN and decreased PAH accumulation was accompanied by reduced release of lysozyme degradation products from kidney slices of rats treated with both doses of cisplatin. Cephaloridine appeared to have no effect on renal catabolism of lysozyme at 500 and 1000 mg/kg; however at higher doses lysozyme degradation decreased and changes in BUN and PAH occurred. Thus, all three compounds used were effective in decreasing renal catabolism of lysozyme. Protein degradation was an early and sensitive indicator of aminoglycoside-induced nephrotoxicity since a decrease in protein degradation in kidney slices from gentamicin-treated rats was not associated with alterations in BUN or PAH accumulation but was associated with ultrastructural changes.