Mass spectrometry-based metabolomics to identify taurine-modified metabolites in heart

Taurine is an abundant beta-amino acid found in high concentration in mammalian tissues. Taurine possesses many beneficial functions in mammalian cells. There are also a variety of taurine-conjugated products formed between taurine and bile acids, fatty acids, chloramine, mitochondrial tRNA, etc., and some of these have been identified as functional compounds. In the present study, we identified taurine-conjugated metabolites using LC-MS-based metabolome analysis of heart extracts prepared from hearts of wild-type and taurine transporter-knockout (TauTKO) mice, the latter being severely taurine deficient. Comparison analysis of metabolites identified taurine-containing dipeptides, including glutamyltaurine, aspartyltaurine, isoleucyltaurine, and leucyltaurine, which are present in wild-type but not TauTKO hearts. Acyltaurines (taurine-conjugated fatty acids) and taurine-conjugated bile acids were also detected, with levels unchanged in the TauTKO heart in comparison to the wild-type heart. These results demonstrate that taurine exists not only in the standard free form within the heart, but also in multiple conjugated forms, whose functions in the heart remain to be discovered.