Abstract

UDP-glycosyltransferases (UGTs) are an important group of enzymes that participate in phase II metabolism of xenobiotics and use the cofactor UDP-glucuronic acid for the production of glucuronides. When acting on molecules bearing a carboxylic acid they can form acyl glucuronides, a group of metabolites that has gained significant interest in recent years because of concerns about their potential role in drug toxicity. In contrast, reports about the production of drug acyl glucosides (which might also display high reactivity) have been scarce. In this study, we discovered the formation of acyl glycoside metabolites of R- and S-ibuprofen (Ibu) by human liver microsomes supplied with the cofactor UDP-glucose. Subsequently, human UGT2B7*1 and UGT2B7*2 recombinantly expressed in fission yeast Schizosaccharomyces pombe could be shown to catalyze these reactions. Moreover, we could enhance the glucoside production rate in fission yeast by overexpressing the fission yeast gene SPCC1322.04, a potential UDP-glucose pyrophosphorylase (UGPase), but not by overexpression of SPCC794.10, and therefore suggest to name this gene fyu1 for fission yeast UGPase1. It was interesting to note that pronounced differences between the two polymorphic UGT2B7 variants were observed with respect to acyl glucoside production. Finally, using the metabolic precursor [¹³C₆]glucose, we demonstrated the production of stable isotope-labeled reference standards of Ibu acyl glucoside and Ibu acyl glucuronide by whole-cell biotransformation in fission yeast.