Genetic Deficiency of Flavin-Containing Monooxygenase 3 ( Fmo3 ) Protects Against Thrombosis but Has Only a Minor Effect on Plasma Lipid Levels—Brief Report

Abstract

Objective— FMO (flavin-containing monooxygenase) 3 converts bacterial-derived trimethylamine to trimethylamine N-oxide (TMAO), an independent risk factor for cardiovascular disease. We generated FMO3 knockout (FMO3KO) mouse to study its effects on plasma TMAO, lipids, glucose/insulin metabolism, thrombosis, and atherosclerosis. Approach and Results— Previous studies with an antisense oligonucleotide (ASO) knockdown strategy targeting FMO3 in LDLRKO (low-density lipoprotein receptor knockout) mice resulted in major reductions in TMAO levels and atherosclerosis, but also showed effects on plasma lipids, insulin, and glucose. Although FMO3KO mice generated via CRISPR/Cas9 technology bred onto the LDLRKO background did exhibit similar effects on TMAO levels, the effects on lipid metabolism were not as pronounced as with the ASO knockdown model. These differences could result from either off-target effects of the ASO or from a developmental adaptation to the FMO3 deficiency. To distinguish these possibilities, we treated wild-type and FMO3KO mice with control or FMO3 ASOs. FMO3-ASO treatment led to the same extent of lipid-lowering effects in the FMO3KO mice as the wild-type mice, indicating off-target effects. The levels of TMAO in LDLRKO mice fed an atherogenic diet are very low in both wild-type and FMO3KO mice, and no significant effect was observed on atherosclerosis. When FMO3KO and wild-type mice were maintained on a 0.5% choline diet, FMO3KO showed a marked reduction in both TMAO and in vivo thrombosis potential. Conclusions— FMO3KO markedly reduces systemic TMAO levels and thrombosis potential. However, the previously observed large effects of an FMO3 ASO on plasma lipid levels appear to be due partly to off-target effects.

Transcriptome analysis of Klf15‑mediated inhibitory functions in a mouse deep venous thrombosis model

“…The present study demonstrated that host hepatic FMO3, the final product of the metaorganismal TMAO pathway, participates in diet-and gut microbiota-dependent changes in both platelet responsiveness and thrombosis potential in vivo (37). Shih et al (39) treated WT and FMO3KO mice with control or FMO-3 ASOs. FMO-3-ASO treatment led to the same extent of lipid-lowering effects in the FMO3KO mice as it did in the WT mice, indicating off-target effects.…”

Alisma orientalis Beverage Treats Atherosclerosis by Regulating Gut Microbiota in ApoE-/- Mice

“…In humans and rodents, gut microbial enzymes convert choline and L-carnitine present in high-fat food into a toxic gas labeled as TMA. TMA travels to the liver through the portal blood circulation where it is oxidized by FMO3 into TMAO (Tang et al, 2013;Shih et al, 2019). When TMAO enters the circulation, it triggers low-grade chronic systemic inflammation.…”

“…Serum TMAO is primarily formed by the transformation of hepatic FMO3 from TMA into the liver (Shih et al, 2019). So, we examined if AOB modifies the FMO3 liver expression.…”

“…Dietary molecules are transformed into trimethylamine (TMA) through the action of gut microbiota, and TMA is then transformed into trimethylamine N-oxide (TMAO) by hepatic flavin monooxygenase (FMO). FMO3 is a major member of the FMO family, and inhibition of FMO3 can significantly decrease TMAO levels and AS (Shih et al, 2019). TMAO as a gut microbiota-derived metabolite, which is also related to the Western diets (Barrea et al, 2019a).…”

Gut microbiota in atherosclerosis: focus on trimethylamine N‐oxide

“…FMO3 deficiency and antisense‐mediated silence of FMO3 can reduce TMAO levels, while overexpression of hepatic FMO3 can enhance TMAO generation (). FMO3 knockout mice showed decreased TMAO levels, coinciding with reduced platelet activation and thrombogenic potential (). Besides, FMO3 expression is affected by sex hormones via regulation of farnesoid X receptor (FXR) in vivo.…”