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. 2022 Jan 27;11:e76554. doi: 10.7554/eLife.76554

Figure 7. Graphical summary depicting the proposed role of trimethylamine (TMA) in the progression of alcohol-associated liver disease (ALD).

Figure 7.

Gut microbiota can elicit both metabolism-dependent and metabolism-independent effects in ALD. Relevant to this manuscript, intestinal microbes metabolize dietary L-carnitine, choline, or phosphatidylcholine (PC) to form TMA, which is a volatile compound that originates exclusively from gut bacterial metabolism and is elevated in ALD. Importantly, TMA can also be converted to trimethylamine N-oxide (TMAO) by hepatic flavin monooxygenase 3 (FMO3), and TMAO has recently been linked to cardiovascular disease (CVD) promotion in humans. Metabolism-independent effects are the result of gut hyperpermeability (leaky gut), allowing bacterial cell wall products such as lipopolysaccharide (LPS) and peptidoglycans to enter into the blood stream and engage with host pattern recognition receptors (PRR) to promote hepatic inflammation. Collectively, metabolism-dependent pathways such as TMA production as well as metabolism-independent pathways provide multiple bacterially derived ‘hits’ to promote ALD progression. The small molecule bacterially targeted CutC/D inhibitors iodomethylcholine (IMC) and fluoromethylcholine (FMC) can effectively blunt ethanol-induced liver injury in mice.