Efferent duct toxicity with secondary testicular changes in rats following administration of a novel leukotriene A4 hydrolase inhibitor.

The efferent ducts represent an important site of toxicity in the male reproductive tract but are not routinely examined in toxicity studies. This article describes a primary efferent duct toxicity that resulted in secondary testicular changes in rats. Male rats were administered LTI-1, a leukotriene A4 hydrolase inhibitor, at doses up to 250 mg/kg/d for 3 month or 150 mg/kg/d for 6 month. At the highest dose levels, testicular changes were predominantly unilateral and characterized by diffuse dilation or atrophy of the seminiferous tubules. These testicular changes correlated with granulomatous inflammation in the corresponding efferent ducts, suggesting that the mechanism for the testicular changes involves obstruction and impaired fluid reabsorption in the efferent ducts. Subsequent buildup in fluid volume and back-pressure upstream of the blockage cause dilation of the seminiferous tubules, which, in its late stages, progress to tubular atrophy. There are important differences in efferent duct anatomy between rats and larger mammals, including humans, such that the latter are less susceptible to testicular injury by this mechanism. Because of the limited relevance of this rat-specific finding to humans, it is important to distinguish testicular changes secondary to efferent duct toxicity from primary drug-induced testicular toxicity.

Analysis of DNA adducts in rats exposed to pentachlorophenol.

Pentachlorophenol (PCP) is a widely used biocide that has been reported to be hepatocarcinogenic in mice. Its effects in rats are equivocal, but the liver clearly is not a target organ for carcinogenesis. The carcinogenic effects of PCP in mice may relate to reactive oxygen species generated during metabolism. PCP is known to increase the hydroxyl radical-derived DNA lesion, 8-oxodeoxyguanosine (ohdG), in the liver of exposed mice. To investigate whether the generation of oxidative DNA damage and direct DNA adducts may explain the species difference in carcinogenicity, we have analyzed ohdG in hepatic DNA from PCP-exposed rats. Rats were exposed acutely to PCP for 1 or 5 days. Tissues also were obtained from a 27 week interim sacrifice of the 2 year National Toxicology Program carcinogenesis bioassay. We used HPLC with electrochemical array detection for ohdG analysis. Single or 5 day exposure to PCP (up to 120 or 60 mg/kg/day, respectively) did not increase ohdG. Dietary exposure to 1000 p.p.m. PCP (equivalent to 60 mg/kg/day) for 27 weeks induced a 2-fold increase in ohdG (1.8 versus 0.91x10(-6) in controls). In parallel, formation of direct DNA adducts was analyzed by 32P-post-labeling following nuclease P1 adduct enrichment. We detected two major DNA adducts with relative adduct labeling of 0.78x10(7) adducts per total nucleotides. One of these adducts was found to co-migrate with the adduct induced by the metabolite, tetrachloro-1,4-benzoquinone. We observed differences in DNA adduct formation between acute and chronic studies, with acute studies not inducing any detectable amount of DNA adducts. These results indicated that chronic, but not acute exposure to PCP increased ohdG and direct adducts in hepatic DNA. As the same exposure conditions that enhanced ohdG did not produce liver cancer in rats, the generation of reactive oxygen species, oxidative DNA damage and direct DNA adducts is not sufficient for the induction of hepatocarcinogenesis by PCP in the rat.

Methods for measuring DNA adducts and abasic sites II: methods for measurement of DNA adducts.

This unit contains protocols for analyzing DNA adducts separated from the DNA backbone. HPLC is used to quantify total guanine or ribo- or deoxynucleotides as well as methods for analyzing specific adducts. These methods include HPLC with electrochemical detection, immunoaffininty chromatography to enrich for specific adducts, and gas and liquid chromatography in combination with HPLC and mass spectrometry.