Liquid Chromatography–Tandem Mass Spectrometry Method for Simultaneous Quantification of Four Endocannabinoids and Endocannabinoid-Like Substances in Plasma: Application in an HIV—Hepatitis C Virus Coinfected Population

Background: The endocannabinoid system regulates immune function, inflammation, and metabolism and has gained increasing attention in clinical research. However, the instability, low abundance, and physicochemical complexity of endocannabinoids (ECs) and EC-like substances (EC-like) make their quantification in plasma analytically challenging. Objective and methods: The authors developed and validated a liquid chromatography–tandem mass spectrometry method for the simultaneous quantification of N-arachidonoylethanolamide (AEA), 2-arachidonoylglycerol, and its isomer 1-arachidonoylglycerol (2-AG/1-AG), oleoylethanolamide (OEA), and palmitoylethanolamide (PEA) in human plasma. Results: Extraction was performed using liquid–liquid extraction combined with liquid chromatography–tandem mass spectrometry. The method achieved lower limits of quantification of 0.1 mcg/L for AEA, 0.2 mcg/L for 2-AG/1-AG, and 0.5 mcg/L for OEA and PEA, with calibration curves showing high linearity (R 2 ≥ 0.995). Intra-assay and interassay accuracy and precision were both within 15%. Additional validation parameters, including selectivity, recovery, carryover, matrix suitability, and dilution integrity, fulfilled regulatory criteria. Preanalytical handling significantly influenced concentrations: Delayed centrifugation and postthaw storage increased AEA, OEA, and PEA levels. The validated method was applied to plasma samples from patients coinfected with HIV and hepatitis C virus, enabling reproducible quantification of ECs and EC-like substances in a clinically relevant cohort. Conclusions: The study demonstrates that biological and technical factors markedly affect plasma EC and EC-like concentrations. Standardized preanalytical processing is therefore essential for accurate measurement, and the proposed method provides a robust tool for clinical and pharmacological research.