Depletion of cytochrome P-450 and alterations in activities of drug metabolizing enzymes induced by cephaloridine in the rat kidney cortex

Impact of cephaloridine on glutathione and related enzymes: comparison of in vivo and in vitro rat models

The aim of this study was to investigate the early effects of cephaloridine (CPH) on glutathione-dependent phase II detoxification in the rat proximal tubular cell and to find an in vitro alternative to the in vivo model. The in vivo study was conducted in three groups of rats which received CPH at doses of 250, 500 or 750 mg/kg per day for 3 days, while another group received 500 mg/kg as a single dose. For the in vitro study, rat renal proximal tubular cultured cells were exposed to CPH at concentrations of 0.3, 0.6, 1, 1.7 mM for 24, 48 and 72 h. Glutathione-dependent detoxification was evaluated in vivo and in vitro on the basis of total intracellular glutathione (GSH), glutathione S-transferase (GST) and glutathione peroxidase (GPX). Glutathione reductase (GRED) and GST mRNA levels were also determined. Results of in vivo and in vitro models were comparable in terms of the early increase of GSH, GST and GRED. This increase had a bell-shaped dose-response with a maximum at 500 mg/kg in vivo and 1 mM in vitro. Beyond these doses, GSH and its dependent enzyme levels decreased, associated with cytotoxicity in vitro and renal insufficiency in vivo. The increased GST activity was associated with an increased level of GST7 in vivo and a markedly increased level of GST1-2 in vitro. We concluded that the in vitro model can be used as an alternative to animal experimentation to study glutathione-dependent detoxication. Low cytotoxic doses of CPH induced an early increase of glutathione phase II-dependent detoxification enzymes.

Renal cell type specificity of cephalosporin-induced cytotoxicity in suspensions of isolated proximal tubular and distal tubular cells

We have developed an in vitro model for investigation of nephron heterogeneity and cell type-specific patterns of renal injury. To further validate our model and to study biochemical mechanisms of cephalosporin-induced injury, cytotoxicity of three cephalosporins was studied in freshly isolated proximal tubular (PT) and distal tubular (DT) cells from rat kidney. The three cephalosporins [cephaloridine (CPH), cephalexin (CXN), cephalothin (CTN)] were chosen because they exhibit varying degrees of nephrotoxicity in vivo and contain different functional groups. CPH produced greater amounts of lactate dehydrogenase release from PT cells than either CXN or CTN, indicating greater toxicity of CPH, which agrees with in vivo observations. DT cells were not affected by any of the cephalosporins. Thus, the cephem ring is sufficient to produce PT cell injury but the presence of other functional groups modifies toxicity. SKF-525A and alpha-tocopherol protected PT cells from both CPH and CTN, suggesting involvement of cytochrome P-450 metabolism and oxidative stress. Both PT and DT cells exhibited transport of CPH or CXN and transport of CPH into PT cells was inhibitable by probenecid, consistent with action of a specific carrier. Transport alone, therefore, cannot account for the cell type specificity pattern in vitro. Effects on intracellular glutathione status, malondaldehyde formation, and uncoupler-stimulated respiration were also investigated, and these generally correlated with cell type specificity patterns but not always with degree of cytotoxicity. These results validate further the isolated PT and DT cells as in vitro models to study cell type-specific renal injury and show a role for oxidative stress, cytochrome P-450 bioactivation, and mitochondrial dysfunction in cephalosporin-induced PT cell injury.

Interactions among nephrotoxicants: N-(3,5-dichlorophenyl)succinimide and cephaloridine

Numerous studies have demonstrated the interactive potential between nephrotoxicants. The purpose of this study was to examine the interactive potential between two model nephrotoxicants, N-(3,5-dichlorophenyl)succinimide (NDPS) and cephaloridine (CPH). Male Fischer 344 rats (4 rats per group) were administered an intraperitoneal (i.p.) injection of CPH (500 mg/kg), NDPS (0.2 mmol/kg) or the appropriate vehicle 1 h prior to administration of an i.p. injection of NDPS (0.2, 0.4, or 1.0 mmol/kg), CPH (500, 750 or 1000 mg/kg) or the appropriate vehicle. Renal function was monitored at 24 and 48 h. Combination of non-nephrotoxic doses of CPH (500 mg/kg) and NDPS (0.2 mmol/kg) did not result in nephrotoxicity, regardless of which compound was administered first. NDPS (0.2 mmol/kg) weakly enhanced the nephrotoxicity observed following CPH (1000 mg/kg) injection but had little effect on CPH (750 mg/kg)-induced renal effects. However, CPH (500 mg/kg) markedly attenuated NDPS (0.4 or 1.0 mmol/kg)-induced nephrotoxicity. These results demonstrate that prior NDPS exposure has little effect on the outcome of CPH-induced renal effects, but prior CPH exposure can markedly alter the renal response to NDPS administration.

Increased reduced glutathione and glutathione S-transferase activity in chronic cephaloridine nephrotoxicity studies in the rat

The effect of repeated cephaloridine treatment on renal glutathione and related enzymes has been investigated in young adult male and female Sprague-Dawley rats. Animals were given intraperitoneally daily doses of either 750 mg/kg for two weeks or 500 or 750 mg/kg for three months. Measurement of blood and urinary parameters (electrolytes, urea, creatinine) did not reveal any renal function impairment and histological examination confirmed the absence of renal damage. By contrast, an increase in reduced glutathione (2 to 3-fold) and glutathione S-transferase activity (1.5 to 2-fold) was observed. These results are consistent with the development of an adaptative phenomenon to cephaloridine subchronic treatment in the rat, leading to a tolerance to high repeated doses.

Specific alterations of rat renal microsomal proteins induced by cephaloridine

In order to elucidate the molecular mechanisms of cephaloridine (CPH) nephrotoxicity, the effect of cephaloridine treatment on the protein composition of different subcellular fractions from rat kidney cortex was investigated. After intravenous treatment of male Wistar rats with 250-1200 mg/kg/d CPH for 1-3 days, kidneys were removed and the homogenate from renal cortex was separated into lysosomal, cytosolic and microsomal fractions. The polypeptide composition of the different subfractions was analyzed by one-dimensional SDS-gel electrophoresis and quantified by densitometry. Significant differences in the polypeptide composition between treated and non-treated animals were seen in the microsomal fraction. CPH-treatment induced a polypeptide with an apparent molecular weight of 44,000 and decreased the content of cytochrome P-450 isoenzymes in the microsomal fraction. Solubilization experiments showed that the CPH-induced microsomal polypeptide of molecular weight 44,000 is a peripheral membrane protein rather than an integral membrane protein. The induction of this protein by CPH was dose- and time-dependent. Preliminary experiments using the kidney slice technique indicate that the induction of this polypeptide correlates with the nephrotoxicity measured as decrease in renal cortical accumulation of organic ions. Thus, the results of the present study indicate that treatment of rats with CPH resulted in the induction of a microsomal polypeptide of molecular weight 44,000 which could be a sensitive parameter of cephaloridine nephrotoxicity.