Determination of total, free and esterified short-chain fatty acid in human serum by liquid chromatography-mass spectrometry

Background Short-chain fatty acids are primarily absorbed through the portal vein during lipid digestion, which is utilized as the energy source, as well as prevent type 2 diabetes and some cancers. However, reports on the determination of these short-chain fatty acids in human serum are limited. Methods Blood samples from human subjects (n = 547, male/female = 246/301, age 58.85 +/- 12.57) were collected. Saponification was applied to obtain total fatty acid. After derivatization by 2-nitrophenylhydrazine, fatty acid 4:0 and fatty acid 6:0 were measured by liquid chromatography-mass spectrometry. Results The developed method exhibited good linearity (R-2 = 0.9996 for both). All the coefficients of variation of reproducibility and accuracy for fatty acid 4:0 and fatty acid 6:0 ranged 3.0%-6.1%, with the average recoveries of 87.8%-102.4% and 92.2%-98.2%, respectively. In all the samples, the concentration of fatty acid 4:0 (162.4 +/- 76.4 mu mol/L) was significantly higher than fatty acid 6:0 (2.0 +/- 2.5 mu mol/L, P < 0.001). Furthermore, the esterified form was predominant in both fatty acid 4:0 and fatty acid 6:0 (98.2% and 82.4% of total fatty acids, respectively). Besides, short-chain fatty acids showed no significant differences with regard to sex or age differences. Conclusion This developed liquid chromatography-mass spectrometry method is convenient and reliable, which might be useful for monitoring the variations of short-chain fatty acids in blood.