Hydrolysis of conjugated metabolites of buprenorphine.: I.: The quantitative enzymatic hydrolysis of buprenorphine-3-β-D-glucuronide in human urine

Buprenorphine, which is a powerful analgesic, a substitution drug for opioids widely used in Europe, and a promising new drug currently undergoing clinical trials in the treatment of opioid dependence in the U.S., is excreted in human urine mainly as glucuronide conjugates. In gas chromatographic-mass spectrometric analysis, the urine specimens must be first hydrolyzed to release buprenorphine from its glucuronide conjugates. In order to evaluate the existing hydrolysis methods and to find the optimal hydrolysis conditions, buprenorphine-3-β-D-glucuronide (B3G) was synthesized. Urine fortified with synthetic B3G was hydrolyzed using acid, base, and β-glucuronidases from different source species, including Helix pomatia, Escherichia coli, and Patella vulgata. Glusulase®, a preparation containing both β-glucuronidase (H. pomatia) and sulfatase, was also tested. Whereas both acidic and basic hydrolysis were ineffective, quantitative hydrolysis could be achieved by using β-glucuronidases under appropriate conditions. However, we found that there was a marked difference in the reactivity of these enzymes (E. coli>H. pomatia≫P. vulgata). The optimal incubation conditions for enzymatic hydrolysis of B3G were 2 h at 37°C for E. coli and 4 h at 60°C or 16 h at 37°C for H. pomatia. Using 1000 Fishman units of either of these two enzymes, effective hydrolysis could be achieved even when the B3G concentration was as high as 2000 ng/mL. Glusulase was equally effective toward B3G if the fortified urine samples were incubated with 25 μL of this enzyme for 1 h at 60°C.