An economically viable stable isotope-enhanced multiple reaction monitoring method for total fatty acid analysis in a mouse model of non-alcoholic fatty liver disease

The complex pathological mechanisms of non-alcoholic fatty liver disease (NAFLD) are closely related to dysregulated lipid metabolism, and the therapeutic effects of the traditional Chinese medicine Zexie-Baizhu Decoction (AA) on NAFLD have been gaining increasing attention. However, research into altered lipid metabolism, especially fatty acids, in NAFLD and the intervention of AA faces technical challenges, especially in the precise quantitative analysis of fatty acids in biological samples. The high complexity of biological matrices, particularly after drug intervention, greatly increases the difficulty of detection. Therefore, this study innovatively developed a simple and economical stable isotope derivatization technique by synthesizing d₆N,N-dimethylethylenediamine (d₆-DMED) in the laboratory, establishing a simple and economical method for fatty acid quantification. This method employs a chemical reaction under low-temperature conditions to ensure the efficient synthesis of d₆-DMED. Using ultra-high performance liquid chromatography-triple quadrupole mass spectrometry technique (UHPLC-MS/MS), combined with optimized chromatographic separation conditions and dynamic multiple reaction monitoring mode, the study established a highly sensitive detection method for 35 fatty acid derivatives. Methodological evaluation showed that the limits of quantification ranged from 0.002 to 0.060 μM, with high linearity of R² > 0.995. Additionally, the relative recovery rates were between 93.14% and 106.63%. To further demonstrate the feasibility of this method for fatty acid quantification, it was applied to measure fatty acids in multiple tissues in a mouse NAFLD model, as well as the effects of AA intervention on fatty acid metabolism. This rapid, simple, and cost-effective detection method not only enhances the understanding of NAFLD mechanisms but also provides a new strategy for evaluating the biological complex system after drug intervention.