Trimethylamine N-oxygenation in cynomolgus macaques genotyped for flavin-containing monooxygenase 3 (FMO3)

Polymorphic human and cynomolgus macaque flavin-containing monooxygenases (FMO) 3 are important oxygenation enzymes for nitrogen-containing drugs. Inter-animal variability of FMO3-dependent drug oxygenations in vivo is suspected in cynomolgus macaques because such variability is evident in humans. Therefore, this follow-up study was performed to investigate the pharmacokinetics of orally administered deuterium-labeled trimethylamine in three cynomolgus macaques genotyped for FMO3. Trimethylamine-d₉ was rapidly absorbed and attained plasma concentrations greater than the background levels of non-labeled trimethylamine. Trimethylamine-d₉ was then converted to trimethylamine-d₉N-oxide. The half-lives, maximum plasma concentrations, and areas under the curve for trimethylamine-d₉ and its N-oxygenated metabolite and the total clearance for orally administered trimethylamine-d₉ were not different among the heterozygote for Q506K FMO3, the heterozygote for V325I FMO3, and the heterozygote for both S99N and F510S FMO3. Trimethylamine N-oxygenation activities mediated by liver microsomes prepared from the same three animals were not substantially different. However, recombinant proteins of the corresponding cynomolgus FMO3 variants showed apparent reduced trimethylamine N-oxygenation activities compared with the wild-type proteins. This study suggests only limited polymorphic effects on the in vivo catalytic function of cynomolgus FMO3. These findings yield important insights in terms of both quantitative and qualitative variations of polymorphic FMO3 in cynomolgus liver.