Characterization of trimethylamine metabolic pathways using pseudo-targeted metabolomics

Trimethylamine (TMA) metabolism comprises choline-containing compounds' metabolization, TMA production and trimethylamine N-oxide (TMAO) generation. However, the presence of numerous compounds in the carnitine and phosphatidylcholine (PC) pool compositions complicates profiling work significantly. This study is aimed at developing an efficient method for profiling TMA metabolic pathways, including quantifying known compounds and semi-quantifying the differential metabolites in the carnitine and PC pool compositions. Pseudo-targeted metabolomics is applicable for characterization. Firstly, multivariate statistics were performed to identify valuable metabolites (variable importance in the projection ＞1) from quality control biological samples. Given that TMA metabolism involved in host-gut microbiota interaction, co-metabolites were defined as the intersections of valuable metabolites from different biological samples (serum, liver, and intestinal contents) and further screened. Finally, alterations in TMA metabolism were observed in dextran sulfate sodium-induced colitis, with semi-quantitative analysis for excavated co-metabolites including 11 PCs, 6 lyso-phosphatidylcholines, and 2 acylcarnitines and quantitative analysis for 10 known metabolites. The findings revealed increased TMA production and accumulation of choline-containing compounds in the gut during ulcerative colitis exacerbation. Correspondingly, the circulating level of TMAO was elevated in the colitis group. A comprehensive understanding of TMA metabolism can contribute to disease differential diagnoses and potential mechanism studies.