Metabolism of xenobiotic carboxylic acids: focus on coenzyme A conjugation, reactivity, and interference with lipid metabolism.

While xenobiotic carboxylic acids (XCAs) have been studied extensively with respect to their enzymatic conversion to potentially reactive acyl glucuronides with implications to drug induced hepatotoxicity, the formation of xenobiotic-S-acyl-CoA thioesters (xenobiotic-CoAs) have been much less studied in spite of data indicating that such conjugates may be equally or more reactive than the corresponding acyl glucuronides. This review addresses enzymes and cell organelles involved in the formation of xenobiotic-CoAs, the reactivity of such conjugates toward biological macromolecules, and in vitro and in vivo methodology to assess consequences of such reactivity. Further, the propensity of xenobiotic-CoAs to interfere with endogenous lipid metabolism, e.g., inhibition of β-oxidation or depletion of the CoA or carnitine pools, adds to the complexity of the potential contribution of XCAs to hepatotoxicity by a number of mechanisms in addition to those in common with the corresponding acyl glucuronides. On the basis of our review of the literature on xenobiotic-CoA conjugates, there appear to be a number of gaps in our understanding of the bioactivation of XCA both with respect to the mechanisms involved and the experimental approaches to distinguish between the role of acyl glucuronides and xenobiotic-CoA conjugates. These aspects are focused upon and described in detail in this review.