Roles and Mechanisms of Choline Metabolism in Nonalcoholic Fatty Liver Disease and Cancers

Choline participates in three major metabolic pathways: oxidation, phosphorylation, and acetylation. Through oxidation, choline is converted to betaine and contributes to methyl metabolism and epigenetic regulation. Through phosphorylation, choline participates in phospholipid metabolism, and serves as the precursor of phosphocholine, phosphatidylcholine, glycerophosphocholine, and other essential compounds, thereby modulating lipid metabolism and transport. Through acetylation, choline is transformed into acetylcholine in cholinergic neurons, playing a vital role in neurotransmission. Moreover, gut microbiota can metabolize choline into trimethylamine-N-oxide, and be involved in the pathogenesis of various diseases such as nonalcoholic fatty liver disease (NAFLD), cancer, cardiovascular disease, etc. Since choline metabolism is implicated in the development of NAFLD and diverse cancers, including liver cancer, it may serve as a therapeutic target for these diseases in the future. Currently, there are numerous therapeutic agents targeting choline metabolism to treat NAFLD and cancers, but most of them are ineffective and some even have adverse effects that lead to a series of complications. Therefore, further research and clinical validation are required to obtain safe and efficacious drugs. This review comprehensively summarizes the choline metabolic pathway and its regulatory mechanisms, elucidates the roles and mechanisms of choline metabolism in the aforementioned diseases, and provides a discussion of the current advances and immense potential of this field.