COINCUBATION OF RAT RENAL PROXIMAL TUBULES WITH HEPATIC SUBCELLULAR-FRACTIONS POTENTIATES THE EFFECTS OF PARAAMINOPHENOL

Treatment of rats with para-aminophenol (PAP) (300 mg/kg ip) produced decreases in renal nonprotein sulfhydryl (NPSH) content, oxygen consum ption, and adenine nucleotide concentrations 2-4 hr following administ ration. In contrast, incubation of rat renal tubules with up to 1 mM P AP for 4 hr produced inconsistent changes in renal tubules. This discr epancy suggested that extrarenal metabolism of PAP may be involved in PAP bioactivation and nephrotoxicity. We designed the present studies to test the hypothesis that hepatic metabolism of PAP potentiates the effects of PAR on renal tubules. Incubation of renal tubules with 0.5 mM PAP and 10 mg protein from hepatic postmitochondrial supernatant (S 9 fraction) in the absence of glutathione (GSH) for 4 hr did not alter renal oxygen consumption or adenine nucleotide metabolite concentrati ons. We observed no changes when we incubated tubules with 0.5 mM PAP and 1 mM GSH in the absence of hepatic S9 fraction. However, incubatio n of renal tubules with 0.5 mM PAP, 1 mM GSH, and 10 mg hepatic S9 pro tein for 4 hr significantly decreased renal oxygen consumption and ade nosine triphosphate and total nucleotide concentrations. These data su ggest that the effects of PAP in renal tubules may be potentiated by e nzymatic metabolism of PAP, possibly involving oxidation and GSH conju gation. From experiments using hepatic microsomes or cytosol instead o f S9 fraction, we found that changes were produced when we incubated t ubules with PAP in the presence of hepatic microsomes, but not cytosol . These data suggest that hepatic microsomal metabolism of PAP may con tribute to the production of changes in renal tubules in vitro. PAR-in duced changes in renal proximal tubules were prevented when we include d a beta-nicotinamide adenine dinucleotide phosphate (NADPH) generatin g system in the incubation medium. The protective effect of NADPH pers isted when microsomes were inactivated by incubation With 1-aminobenzo triazole, a cytochrome P450 inhibitor. These data suggest that cytochr ome P450-dependent oxidation is not involved in the production or prev ention of PAP-induced changes in renal tubules. The enzyme(s) responsi ble for PAP bioactivation and the mechanism(s) by which NADPH protects renal tubules from PAP-induced decrements in oxygen consumption and a denine nucleotide concentrations are currently unclear. (C) 1997 Socie ty of Toxicology.