Optimal pH 8.5 to 9 for the hydrolysis of vixotrigine and other basic substrates of carboxylesterase-1 in human liver microsomes
Creators: name: Johnson, Joshua L.
name: Huang, Jiansheng
name: Rooney, Michael
name: Gu, Chungang
Publisher: name: Taylor & Francis
Year: 2022
Subjects: subject: Biochemistry
subject: Molecular Biology
subject: Physiology
subject: FOS: Biological sciences
subject: Pharmacology
subject: Biotechnology
subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: Ecology
subject: Sociology
subject: FOS: Sociology
subject: Immunology
subject: FOS: Clinical medicine
subject: 69999 Biological Sciences not elsewhere classified
subject: Cancer
subject: 110309 Infectious Diseases
subject: FOS: Health sciences

description: Vixotrigine is a voltage- and use-dependent sodium channel blocker under investigation for the potential treatment of neuropathic pain. One of the major <i>in vivo</i> metabolic pathways of vixotrigine in humans is the hydrolysis of the carboxamide to form the carboxylic acid metabolite M14.The <i>in vitro</i> formation of M14 in human hepatocytes was inhibited by the carboxylesterase (CES) inhibitor Bis(4-nitrophenyl) phosphate in a concentration-dependent manner. The hydrolysis reaction was identified to be catalysed by recombinant human CES1b.Initial observation of only trace level formation of M14 in human liver microsomes at pH 7.4 caused us to doubt the involvement of CES1, an enzyme localised at the endoplasmic reticulum and the dominant carboxylesterase in human liver. Further investigation has revealed that optimal pH for the hydrolysis of vixotrigine and two other basic substrates of CES1, methylphenidate and oseltamivir, in human liver microsomes was pH 8.5–9 which is higher than their respective pK<sub>a(base),</sub> suggesting that neutral form of basic substrates is probably preferred for CES1 catalysis in liver microsomes. Vixotrigine is a voltage- and use-dependent sodium channel blocker under investigation for the potential treatment of neuropathic pain. One of the major <i>in vivo</i> metabolic pathways of vixotrigine in humans is the hydrolysis of the carboxamide to form the carboxylic acid metabolite M14. The <i>in vitro</i> formation of M14 in human hepatocytes was inhibited by the carboxylesterase (CES) inhibitor Bis(4-nitrophenyl) phosphate in a concentration-dependent manner. The hydrolysis reaction was identified to be catalysed by recombinant human CES1b. Initial observation of only trace level formation of M14 in human liver microsomes at pH 7.4 caused us to doubt the involvement of CES1, an enzyme localised at the endoplasmic reticulum and the dominant carboxylesterase in human liver. Further investigation has revealed that optimal pH for the hydrolysis of vixotrigine and two other basic substrates of CES1, methylphenidate and oseltamivir, in human liver microsomes was pH 8.5–9 which is higher than their respective pK<sub>a(base),</sub> suggesting that neutral form of basic substrates is probably preferred for CES1 catalysis in liver microsomes.