In Vitro Assessment of the Reactivity of Acyl Glucuronides

Methodology is described to evaluate the reactivity of acyl glucuronides of carboxylic acid-containing compounds. In this chapter, zomepirac is presented as an example where the reactivity is determined in two complimentary ways: (1) Acyl glucuronides are prepared with UDPGA-fortified microsomes and 1-O-β acyl glucuronide is established based on its sensitivity to hydrolysis by β-glucuronidase. The chemical degradation of 1-O-β isomer in 0.1 M phosphate buffer at pH 7.4 is monitored over time for acyl migration by LC-MS/MS analyses. Half-life of disappearance of 1-O-β acyl glucuronide is used as an index of reactivity. (2) Another index of reactivity of acyl glucuronide is from covalent binding to a protein. Acyl glucuronides are incubated with human serum albumin for 2 h. After pelleting and extensively washing the protein pellets, covalent binding is determined by quantitation of the released aglycone from alkaline hydrolysis.