Identification and characterization of two chloramphenicol glucuronides from the in vitro glucuronidation of chloramphenicol in human liver microsomes

Abstract

This study reports the development of a specific and sensitive liquid chromatography coupled with tandem mass spectrometry detection (LC-MS/MS) assay for the quantification of the in vitro O-glucuronidation of chloramphenicol (CP), the determination of the kinetic parameters for the O-glucuronidation of CP in pooled human liver microsomes (HLM), the biosynthesis of the CP glucuronides (CPGlu), and identification of the structures of CPGlu by ¹H-nuclear magnetic resonance (NMR) and MS. Two glucuronyl derived metabolites of CP were obtained from the incubation of alamethicin-activated HLM with CP and uridine 5′-diphosphoglucuronic acid (UDPGA) in pH 7.4 TRIS buffer. Their identification and structural confirmation were achieved by β-glucuronidase hydrolysis, in the presence and absence of UDPGA, and by ¹H-NMR and LC-MS/MS. These two metabolites were biosynthesized, isolated, and purified using high-performance liquid chromatography (HPLC). Their structures were further identified as the 1-O-CPGlu (the minor glucuronide formed at the secondary alcohol of CP) and 3-O-CPGlu (the major glucuronide formed at the primary alcohol of CP) by LC-MS/MS and two-dimensional NMR. The enzymatic kinetic parameters K_m and V_max in HLM for the 3-O-CPGlu were determined to be 650 µM and 0.26 nmoles min⁻¹ mg⁻¹, respectively, and for the 1-O-CPGlu to be 301 µM and 0.014 nmoles min⁻¹ mg⁻¹, respectively. This study also provides a sensitive and specific method for the measurement of in vitro CP-UDP-glucuronosyltransferase (UGT) activity.

Key Words::

• Chloramphenicol
• human liver microsomes
• glucuronidation
• enzyme kinetics
• chloramphenicol O-glucuronides
• liquid chromatography coupled with tandem mass spectrometry detection (LC-MS/MS)

Acknowledgements

The authors thank Dr Xiaoyong Sun, Dr Christopher Brummel, Dr Caroline Decker, Dr Eric Gangle, Dr Hongying Gao, Dr Christopher Lepre (NMR analysis), Dr Ronghua Wang, and Dr Tiansheng Wang for their assistance and helpful discussions.