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.