Development of resistance against hexachlorobutadiene in the proximal tubules of young male rat.

Hexachlorobutadiene (HCBD) is a potent nephrotoxin in rodents that can cause degeneration, necrosis and regeneration in renal tubular epithelial cells. Its toxicity is due to its conjugation by glutathione (GSH) to form glutathione S-conjugate, by the enzyme glutathione S-transferase and finally to the related cysteine-conjugate. This metabolite is then actively taken up by kidney and cleared in the renal tubular epithelial cells, rich in beta-lyase, to a reactive thiol derivative that covalently binds to the macromolecules. In this study, different groups of 28-day male Wistar albino (W/A) rats were dosed daily with 25 mg/kg HCBD for 2, 3, 4 and 7 days; control group dosed with corn oil. Data showed that in the 2- and 3-day treated groups there was substantial necrosis to the straight portion of the proximal tubules (pars recta or S3 segment), rich in glutamine transaminase K (GTK/beta-lyase). In the 4-day treated group, the renal proximal tubules had regenerated and showed a basophilic appearance. In animals treated for 7 days, it was observed that the kidney appeared to have returned to normal and had become resistant to further doses of HCBD. To define the time for the kidney to regain susceptibility to HCBD, 18- and 25-day studies with both low (25 mg/kg) and high (100 mg/kg) doses of HCBD (following two initial doses of 25 mg/kg) were performed. In the 18-day study, histopathological examination of the kidneys in animals of this group and also animals in the 25-day study, which received two further doses of HCBD, showed that the severity of kidney damage is much less than in the 2-day treated animals, a clear indication that the tubular cells were still resistant to the low dose of HCBD. Concentration of blood urea nitrogen, as a marker of kidney damage, in these two groups also confirmed the results. In animals re-exposed to the high dose of HCBD, data showed that the susceptibility to HCBD was starting to return.