Natural and synthetic inhibitors of UDP-glucuronosyltransferase.

Glucuronidation is a major detoxification pathway in vertebrates. The reaction is catalyzed by a family of UDP-glucuronosyltransferases (UGTs) and involves conjugation of many endobiotic and xenobiotic substances with glucuronic acid, forming inactive water-soluble glucuronides. UGT prevents the accumulation of potentially toxic compounds and/or their subsequent bioactivation to more toxic intermediates, although biologically active glucuronides are also known. Impairment of UGTs may have important toxicological consequences. Substances found to inhibit or down-regulate UGT activity include endogenous compounds, a wide range of clinically used drugs, environmental contaminants, and natural toxic substances present in the diet. The development of selective, active-site-directed UGT inhibitors greatly enables the study of various UGT isoenzymes. A promising approach offers the design of transition-state analogs of the glucuronidation reaction.