The TMAO-Generating Enzyme Flavin Monooxygenase 3 Is a Central Regulator of Cholesterol Balance

Abstract

SUMMARY Circulating levels of the gut microbe-derived metabolite trimethylamine-N-oxide (TMAO) have recently been linked to cardiovascular disease (CVD) risk. Here we performed transcriptional profiling in mouse models of altered reverse cholesterol transport (RCT), and serendipitously identified the TMAO-generating enzyme flavin monooxygenase 3 (FMO3) as a powerful modifier of cholesterol metabolism and RCT. Knockdown of FMO3 in cholesterol-fed mice alters biliary lipid secretion, blunts intestinal cholesterol absorption, and limits the production of hepatic oxysterols and cholesteryl esters. Furthermore, FMO3 knockdown stimulates basal and liver X receptor (LXR)-stimulated macrophage RCT, thereby improving cholesterol balance. Conversely, FMO3 knockdown exacerbates hepatic ER stress and inflammation in part by decreasing hepatic oxysterol levels and subsequent LXR activation. FMO3 is thus identified as a central integrator of hepatic cholesterol and triacylglycerol metabolism, inflammation, and ER stress. These studies suggest that the gut microbiota-driven TMA/FMO3/TMAO pathway is a key regulator of lipid metabolism and inflammation.

New Insight into the Dietary Cause of Atherosclerosis: Implications for Pharmacology

“…After absorption, TMA is N-oxidized mainly by FMO3 Warrier et al, 2015). Congenital absence of FMO3 leads to "fish odor syndrome," a result of the inability to metabolize TMA; TMA smells like rotting fish .…”

“…However, beginning in 2011, investigators in the Cleveland Clinic and other venues published a series of groundbreaking papers suggesting TMAO formed from dietary TMA-containing nutrients, especially animal products, might, in fact, be the "toxic" metabolite, a prime cause of atherosclerosis (Wang et al, 2011;Koeth et al, 2013;Tang et al, 2013;Jonsson and Bäckhed, 2015;Shih et al, 2015;Troseid et al, 2015;Wang et al, 2015;Warrier et al, 2015). Basically, what these investigators have shown is that the TMA covalently incorporated in lecithin, choline, betaine, or carnitine can be metabolized in gut by bacterial lyases to release TMA, a gas.…”

“…This hypothesis, described in detail below, has recently been supported by substantial evidence in animals and humans (Wang, et al, 2011;Koeth et al, 2013;Tang et. al., 2013;Jonsson and Bäckhed;Troseid, et al, 2015;Wang et al, 2015;Warrier, et al, 2015). Briefly, trimethylamine (TMA)-containing dietary compounds, found mainly in meat, milk, some fish, and other animal foods (e.g., lecithin, choline, betaine, carnitine) are converted by TMA lyases (lyases) in gut bacteria to TMA, which is absorbed and then oxidized by hepatic flavin mono-oxygenase 3 (FMO3) to the toxic trimethylamine N-oxide (TMAO).…”

Nutrigenomics, the Microbiome, and Gene-Environment Interactions: New Directions in Cardiovascular Disease Research, Prevention, and Treatment

“…257 TMAO is formed from trimethylamine via hepatic flavin mono-oxygenase 3. 258 Mechanistic studies in mice have identified that modulation of flavin mono-oxygenase 3 levels affect TMAO levels and glucose and lipid metabolism, 259,260 further complicating the identification of the precise mechanism by which TMAO affects CVD. The microbiome plays an obligate role in the formation of trimethylamine (from the trimethylamine-containing nutrients choline and carnitine), and antibiotic knockdown studies clearly show that TMAO is not formed in the absence of the microbiome.…”

High mass accuracy assay for trimethylamine N-oxide using stable-isotope dilution with liquid chromatography coupled to orthogonal acceleration time of flight mass spectrometry with multiple reaction monitoring

“…It is also being investigated in other diseases where the aetiology is thought to be related to a perturbance of the gut microbiome, including colorectal cancer [4], diabetes [5] and renal disease [6] as well as being a putative central mediator in cholesterol balance [7]. Described methods for detecting TMAO are centred on the use of liquid chromatographytandem mass spectrometry with multiple reaction monitoring (LC-MS/MS-MRM), often utilising a stable isotopically labelled standard for quantitation [e.g.…”