Role of human flavin-containing monooxygenase (FMO) 5 in the metabolism of nabumetone: Baeyer–Villiger oxidation in the activation of the intermediate metabolite, 3-hydroxy nabumetone, to the active metabolite, 6-methoxy-2-naphthylacetic acid in vitro

Abstract

1. Nabumetone (NAB) is a non-steroidal anti-inflammatory drug used clinically, and its biotransformation includes the major active metabolite 6-methoxy-2-naphthylacetic acid (6-MNA). One of the key intermediates between NAB and 6-MNA may be 3-hydroxy nabumetone (3-OH-NAB).

2. The aim of the present study was to investigate the role of flavin-containing monooxygenase (FMO) isoform 5 in the formation of 6-MNA from 3-OH-NAB. To elucidate the biotransformation of 3-OH-NAB to 6-MNA, an authentic standard of 3-OH-NAB was synthesised and used as a substrate in an incubation with human liver samples or recombinant enzymes.

3. The formation of 3-OH-NAB was observed after the incubation of NAB with various cytochrome P450 (CYP) isoforms. However, 6-MNA itself was rarely detected from NAB and 3-OH-NAB. Further experiments revealed a 6-MNA peak derived from 3-OH-NAB in human hepatocytes. 6-MNA was also detected in the extract obtained from 3-OH-NAB by a combined incubation of recombinant human FMO5 and human liver S9.

4. We herein demonstrated that the reaction involves carbon-carbon cleavage catalyzed by the Baeyer–Villiger oxidation (BVO) of a carbonyl compound, the BVO substrate, such as a ketol, by FMO5. Further in vitro inhibition experiments showed that multiple non-CYP enzymes are involved in the formation of 6-MNA from 3-OH-NAB.

Keywords:

• Nabumetone
• 3-hydroxy nabumetone
• 6-methoxy-2-naphthylacetic acid (6-MNA)
• flavin-containing monooxygenase 5 (FMO5)
• Baeyer–Villiger oxidation (BVO)

Acknowledgments

The authors are indebted to Kentaro Hori, Shimadzu Techno-Research, Inc., for his help with the operation of the triple quadruple liquid chromatograph mass spectrometer (LC-MS/MS, LCMS-8060, Shimadzu, Kyoto, Japan).

Ethical approval

This material is the authors’ own original work, which has not been previously published elsewhere. This article reflects the authors’ own research and analyses in a truthful and complete manner and does not violate any code of ethics.

Disclosure statement

The authors report no declarations of interest.