Sex differences in hexachlorobutadiene biotransformation and nephrotoxicity.

ABSTRACT

Hexachlorobutadiene is nephrotoxic in rats, causing damage to the proximale tubules. Renal toxicity is presumed to be due to bioactivation by glutathione S-conjugate formation. Hexachlorobutadiene is conjugated with glutathione to S-(1,2,3,4,4-pentachlorobutadienyl)glutathione and further transformed to S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine (PCBC), which is N-acetylated in the liver to form N-acetyl-S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine (N-ac-PCBC). N-ac-PCBC is accumulated in the kidney. Renal acylases cleave N-ac-PCBC to PCBC, which is a substrate for renal cysteine conjugate beta-lyase and transformed to a reactive thioketene. Binding of this intermediate to renal macromolecules is most likely responsible for the nephrotoxicity of hexachlorobutadiene. In this study, we administered [14C]HCBD (200 mg/kg, per gavage) to male and female Wistar rats and compared the distribution and biotransformation. No significant differences in the disposition and rates of excretion of [14C]hexachlorobutadiene-derived radioactivity were observed between male and female rats. A portion of the dose (15.6 +/- 4.2) was excreted in the feces and 3.1% ( +/- 0.7) in the urine of male rats, and 11.1% ( +/- 3.8) of the dose was excreted in the feces and 4.5% ( +/- 1.5) in the urine of female rats. The major metabolite excreted by female rats was N-ac-PCBC, while small amounts of PCBC were also detected. In the urine of male rats, in addition to small amounts of PCBC and N-ac-PCBC, N-acetyl-S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine sulfoxide and [14C]hexachlorobutadiene were identified. Formation of the electrophile N-ac-PCBC sulfoxide must be considered as an alternative, beta-lyase-independent, bioactivation pathway for hexachlorobutadiene-derived S-conjugates. In isolated rat renal tubular cells, N-ac-PCBC sulfoxide induced a significantly more marked loss in cell viability than N-ac-PCBC. After identical doses of hexachlorobutadiene, the extent of necrosis to the pars recta of the proximal tubules was increased in male rats compared to the necrotic changes in female rats. While female animals showed a normal liver histology, male rats revealed slight toxic centrilobular liver changes in addition to the renal necroses. In vitro, only liver microsomes from male rats catalyzed the formation of N-ac-PCBC sulfoxide from N-ac-PCBC. Our results describe a new pathway of hexachlorobutadiene biotransformation in male rats, the formation of a mercapturic acid sulfoxide. The formation of this Michael acceptor may contribute to sex differences in hexachlorobutadiene nephrotoxicity.