Phenotyping analysis of the Japanese Kampo medicine maoto in healthy human subjects using wide-targeted plasma metabolomics

•Traditional herbal medicines consist of a vast number of compounds and are assumed to exert their activity by affecting various sites in the body.•Plasma metabolomics was used for phenotype analysis of the Japanese kampo medicine maoto in a human clinical study.•Maoto influenced plasma amino acids and lipid mediators.•Primary compounds in maoto such as ephedrine, prunasin, cinnamic acid, and glyccyrhetinic acid were absorbed in the bloodstream.•Alteration of branched-chain amino acid levels by maoto administration is likely caused by ephedrine and its analogues. Traditional herbal medicine (THM) consists of a vast number of compounds that exert pharmacological effects throughout the body. Comprehensive phenotyping analysis using omics is essential for understanding the nature of THM in detail. We previously reported that the Japanese Kampo medicine maoto ameliorated flu-like symptoms in a rat infection model and dynamically changed plasma metabolites as indicated by metabolome analysis. The aim of this study was to apply wide-targeted plasma metabolomics with quantitative analysis of maoto compounds in a human clinical trial to evaluate the effect of maoto on plasma metabolites. Four healthy human subjects were recruited. Plasma samples were collected before and 0.25, 0.5, 1, 2, 4 and 8 h after maoto treatment. Wide-targeted metabolomics and quantitative analysis of the main chemical constituents of maoto were then performed. Plasma metabolome analysis revealed that maoto administration decreased essential amino acids including branched-chain amino acids (BCAAs) and increased various kinds of ω-3 fatty acids including eicosapentaenoic acid and docosahexaenoic acid, consistent with previous studies in rats. Fifteen of the major compounds in maoto were identified in the systemic circulation. Finally, the correlation between endogenous metabolites and maoto compounds in plasma was analyzed and the results indicated that the decrease in plasma BCAAs might be caused by ephedrines present in maoto. The present study demonstrated that plasma metabolomic studies of endogenous and exogenous metabolites are useful for elucidating the mechanism of action of THM.