Mechanism of chloroform nephrotoxicity: IV. Phenobarbital potentiation of in vitro chloroform metabolism and toxicity in rabbit kidneys

Metabolism of chloroform (CHCl₃) by a cytochrome P-450-dependent process to a reactive metabolite may be required to elicit hepatic and renal toxicities. Specific inducers or inhibitors of cytochrome P-450 have been employed frequently as tools to demonstrate this relationship between metabolism and toxicity in the liver. The experiments reported herein were designed to identify the relationship between metabolism and toxicity of CHCl₃ in the kidney of rabbits, a species in which renal cytochrome P-450 is induced by phenobarbital. Pretreatment with phenobarbital enhanced the toxic response of renal cortical slices to CHCl₃in vitro as indicated by decreased p-aminohippurate and tetraethylammonium accumulation. Phenobarbital pretreatment also potentiated in vitro¹⁴CHCl₃ metabolism to ¹⁴CO₂ and covalently bound radioactivity in rabbit renal cortical slices and microsomes. Addition of l-cysteine significantly reduced covalent binding in renal microsomes from both phenobarbital-treated and control rabbits and was associated with the formation of the radioactive phosgene-cysteine conjugate 2-oxothiazolidine-4-carboxylic acid (OTZ). Formation of OTZ was enhanced in renal microsomes from phenobarbital-pretreated rabbits. Thus, this in vitro model supports the hypothesis that the kidney metabolizes CHCl₃ to the nephrotoxic metabolite, phosgene.