Sulfation and glucuronidation as competing pathways in the metabolism of hydroxamic acids: the role of N,O-sulfonation in chemical carcinogenesis of aromatic amines.

Aromatic amines can be metabolized by N-acetylation and N-hydroxylation to hydroxamic acids; these subsequently are conjugated to form the N,O-sulfonate and N,O-glucuronide conjugates. The N,O-sulfonates are highly labile metabolites that generate reactive intermediates involved in the covalent binding of the parent compound to protein, RNA and DNA, as well as to low molecular compounds like glutathione. This paper discusses methods used to decrease sulfation in vivo, and thereby to enhance the formation of the more stable N,O-glucuronides from N-hydroxy-2-acetylaminofluorene and N-hydroxy-4-acetylamino-4'-fluorobiphenyl. Acetaminophen pretreatment decreases the sulfate availability, but results in many side effects that complicate the analysis of the results. An 8% casein diet reduces the sulfate availability in the rat to approximately 20% of control and thus offers an effective approach to decrease sulfation. The most effective selective inhibition of sulfation is by pentachlorophenol, which very strongly reduces N,O-sulfonation of both hydroxamic acids, and selectively inhibits the formation of DNA adducts that have retained the N-acetyl group. This inhibitor and the related 2,6-dichloro-4-nitrophenol can be employed to study the role of sulfation of hydroxamic acids in initiation and promotion of tumor formation by aromatic amines.