Comparative disposition of the nephrotoxicant N-(3, 5-dichlorophenyl)succinimide and the non-nephrotoxicant N-(3, 5-difluorophenyl)succinimide in Fischer 344 rats.

Disposition of the nephrotoxicant N-(3,5-dichlorophenyl)succinimide (NDPS) was compared with that of a nontoxic analog, N-(3, 5-difluorophenyl)succinimide (DFPS). Male Fischer 344 rats were administered 0.2 or 0.6 mmol/kg [14C]NDPS or [14C]DFPS (i.p. in corn oil). Plasma concentrations were determined from blood samples obtained through the carotid artery. Urine samples were analyzed for metabolite content by HPLC. Rats were sacrificed at 3 h (DFPS) or 6 h (NDPS) and tissue radiolabel content and covalent binding were determined. [14C]NDPS-derived plasma radioactivity levels were 6- to 21-fold higher and peaked later than those from [14C]DFPS. Six hours after dosing, NDPS was 40% eliminated in the urine compared with approximately 90% for DFPS. By 48 h, only 67% of the NDPS dose was eliminated in urine. In contrast, DFPS excretion was virtually complete within 24 h. NDPS underwent oxidative metabolism to a slightly greater extent than DFPS. Distribution of [14C]NDPS-derived radioactivity into the kidneys was 3- to 6-fold higher than that into the liver or heart, and was more extensive than with [14C]DFPS. NDPS also covalently bound to plasma, renal, and hepatic proteins to a greater extent than DFPS. In summary, NDPS achieves higher tissue and plasma concentrations, covalently binds to a greater extent, and is eliminated more slowly than DFPS. Differences in the lipid solubility of NDPS metabolites and DFPS metabolites may help explain these results. The overall greater tissue exposure of NDPS and its metabolites may contribute to differential toxicity of these analogs.

The effect of aromatic fluorine substitution on the nephrotoxicity and metabolism of N-(3,5-dichlorophenyl)succinimide in Fischer 344 rats.

N-(3,5-Difluorophenyl)succinimide (DFPS) is a non-toxic analogue of the nephrotoxic fungicide N-(3,5-dichlorophenyl)succinimide (NDPS). Although NDPS must be metabolized to produce renal damage, the metabolic fate of DFPS is unknown. These studies were therefore designed to examine the nephrotoxic potential of putative DFPS metabolites and to determine if DFPS is metabolized differently from NDPS. Male Fischer-344 rats were administered (1.0 mmol/kg. i.p. in corn oil) DFPS, N-(3,5-difluorophenyl)succinamic acid (DFPSA), N-(3,5-difluorophenyl)-2-hydroxysuccinimide (DFHS), N-(3,5-difluorophenyl)-2- or -3-hydroxysuccinamic acids (2- and 3-DFHSA, respectively), N-(3,5-difluoro-4-hydroxyphenyl)succinimide (DFHPS). N-(3,5-difluoro-4-hydroxyphenyl) succinamic acid (DFHPSA) or corn oil only (1.2 ml/kg). Although some of the compounds produced changes in renal function and histology, these alterations were not indicative of irreversible kidney damage. DFPSA, 2-DFHSA, 3-DFHSA and DFHPSA were detected in the urine of rats 3 h after administration of 0.2 mmol/kg [14C]DFPS. The same metabolites were produced by isolated rat hepatocytes, but not by renal proximal tubule cells. Formation of the oxidative metabolites in vitro was prevented by the cytochrome P450 inhibitor 1-aminobenzotriazole. It appears that DFPS undergoes hepatic biotransformation similar to NDPS and that some of its metabolites have reversible effects on renal proximal tubules.

In vitro metabolism of the nephrotoxicant N-(3,5-dichlorophenyl)succinimide in the Fischer 344 rat and New Zealand white rabbit.

1. The nephrotoxicant N-(3,5-dichlorophenyl)succinimide (NDPS) underwent nonenzymatic hydrolysis to N-(3,5-dichlorophenyl)succinamic acid (NDPSA) in buffer, rat liver and kidney homogenates, and rabbit liver homogenates. 2. In the presence of NADPH, rat liver homogenates converted NDPS to NDPSA and N-(3,5-dichlorophenyl)-2-hydroxysuccinamic acid (2-NDHSA). 3. Using liver homogenates from the phenobarbital (PB)-pretreated rat, 2-NDHSA production was increased 5-fold, and the metabolites N-(3,5-dichlorophenyl)-2-hydroxysuccinimide (NDHS) and N-(3,5-dichlorophenyl)-3-hydroxysuccinamic acid (3NDHSA) were also detected. Formation of these latter metabolites was suppressed by CO or omission of NADPH. No hydroxylated metabolites were detected when NDPSA was incubated with PB-induced rat liver homogenates. 4. Oxidative metabolites were not produced when NDPS was incubated with kidney homogenates from the control or PB-pretreated rat. 5. NDHS underwent rapid hydrolysis in buffer to yield 2-NDHSA and 3-NDHSA. 6. Rabbit liver homogenates converted NDPS to NDPSA, 3,5-dichloroaniline (DCA), and succinic acid (SA). Production of DCA and SA was inhibited by the amidase inhibitor bis-p-nitrophenyl phosphate. Oxidative metabolism did not occur in rabbit tissue. 7. These experiments demonstrate that a PB-inducible form of rat liver P450 converts NDPS to NDHS, which then undergoes hydrolysis to 2-NDHSA and 3-NDHSA. An alternative route of production for 2-NDHSA and 3-NDHSA, via hydroxylation of NDPSA, does not occur. In rabbit liver NDPS metabolism was primarily amidase-mediated.

Potential metabolism and cytotoxicity of N-(3,5-dichlorophenyl)succinimide and its hepatic metabolites in isolated rat renal cortical tubule cells.

N-(3,5-Dichlorophenyl)succinimide (NDPS) is an agricultural fungicide and antimicrobial agent that produces nephrotoxicity in rats. The contribution of the kidney, if any, to the mechanism of toxicity of NDPS is not known. Therefore, the ability of isolated renal cortical tubule cells to metabolize NDPS and some of its known hepatic metabolites was studied. The cytotoxic potential of these compounds was also assessed. Renal cortical tubule cells were isolated by collagenase digestion and were incubated with the test compounds (2 mM) for 3 h. Metabolite formation was monitored by reversed phase HPLC and cell viability was assessed using trypan blue exclusion. The isolated kidney cells do not appear to metabolize NDPS or any of its known hepatic metabolites. In addition, none of these compounds were directly cytotoxic to the renal cells. However, the cells were susceptible to mercuric chloride (1 mM) and chloroform (125 or 200 mM). Intracellular glutathione levels were unaltered by the presence of NDPS in the incubations. These results suggest that NDPS and its metabolites are not directly toxic to the kidney and are not converted into the ultimate nephrotoxic species by the kidney. Extrarenal metabolism may, therefore, be critical to the expression of NDPS-induced nephrotoxicity.