Simultaneous determination of short-chain fatty acids and tryptophan metabolites by a propyl chloroformate-...

Short-chain fatty acids (SCFAs) and tryptophan metabolites, serve as key mediators of host-microbiota crosstalk, influencing physiological and pathological processes. Their interconnected roles necessitate simultaneous quantification to fully elucidate the potential mechanism of gut microbiota in metabolic diseases. However, they are difficult to be detected simultaneously due to differences in content or different polarity which contain specific carboxylic group, amino group or phenolic hydroxyl groups. In current study, our primary goal is to establish a rapid and sensitive quantitative measurement for SCFAs and tryptophan metabolites by using propyl chloroformate-(PCF) derivatization based on gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) analysis. Then, we applied the established method in measurement of serum samples from healthy subjects and metabolic associated fatty liver disease (MAFLD) patients. First, we optimized the reaction conditions including PCF volume, reaction time, extraction reagent ratio, and alkaline reagent concentration, enabling the simultaneous detection of acetic acid, propionic acid, isobutyric acid, butyric acid, isovaleric acid, valeric acid, 2-methylvaleric acid, hexanoic acid, indole, succinic acid, quinolinic acid, indole acetic acid, glutamine, indole butyric acid, 3-hydroxyanthranilic acid, melatonin, kynurenine, tyrosine, and tryptophan. 2-chloro-L-phenylalanine was set as the internal standard. The optimized condition showed good linearity, and the intra/inter-day precision achieved in the range from 0.81% to 14.88%. The recovery ranged from 85.68% to 114.50% and the matrix effect ranged from 85.81% to 113.42%. In addition, the influence of different storage conditions on sample stability was also acceptable. Finally, the quantitation result of serum samples indicated that isovaleric acid, quinolineic acid, indoleacetic acid, glutamine, melatonin, tyrosine, and tryptophan had significant difference between healthy subjects and MAFLD patients. The levels of isovaleric acid, indoleacetic acid, glutamine, tyrosine, and tryptophan had significant correlations with clinical indicators such as ALT, AST, Cap, Cr and TG, supporting their potential for further translational studies. In summary, this improved method is applicable for quantitative measurement of SCFAs and tryptophan metabolites, as well as those endogenous metabolites containing carboxylic, amino and phenolic hydroxyl groups.