Lack of Correlation betweenpara-Aminophenol Toxicityin Vivoandin Vitroin Female Sprague–Dawley Rats

Abstract

The present study was designed to test the hypothesis thatpara-aminophenol (PAP) nephrotoxicity is due to autooxidation. We compared renal functional responses following PAP administration to female Sprague–Dawley rats and following incubation of renal proximal tubules with PAP. The concentrations of PAP selected forin vitroincubations produced cytotoxicity (for example, a decrease in oxygen consumption or adenine nucleotide concentration) in rat renal epithelial cells or rabbit proximal tubule suspensions. In rats, PAP (300 mg/kg ip) caused proximal tubular necrosis within 24 hr. Changes in renal function 24 hr following PAP administration included increased kidney weight and blood urea nitrogen concentration and decreased renal glutathione (GSH) content and adenine nucleotide concentrations. PAP did not cause hepatic damage. Within 2–4 hr following PAP administration, renal GSH content and adenine nucleotide concentrations were significantly decreased. In renal cortical slices prepared from PAP-treated rats, oxygen consumption and accumulation of organic ions (para-aminohippurate and tetraethylammonium) were significantly decreased compared with renal cortical slices prepared from control rats. In liver, GSH content was significantly decreased from 1 to 4 hr following PAP administration. In contrast to the effects of PAPin vivo,renal proximal tubules showed little evidence of injury when incubated with 0.1 or 0.5 mMPAP for up to 4 hr in the presence or absence of amino acids in the incubation medium. When tubules were incubated with 1 mMPAP for 4 hr in the presence of amino acids, GSH content, AMP concentration, and TEA uptake were significantly decreased. When amino acids were removed from the incubation medium, 1 mMPAP caused decreases in oxygen consumption and ATP concentration after 4 hr of incubation. Functional changes observed during incubation with PAPin vitrowere not consistent with functional changes observedin vivo.The discrepancy between PAP toxicityin vivoandin vitrosuggests that autooxidation is unlikely to be responsible for PAP nephrotoxicity and that nephrotoxicityin vivois primarily mediated by extrarenal bioactivation. Further, depletion of hepatic GSH content prior to changes in renal function suggests that PAP or a PAP metabolite may conjugate with hepatic GSH. These observations suggest that PAP nephrotoxicity may be mediated by PAP–GSH conjugates rather than autooxidation of PAP in the kidney.