Estimation of reference intervals of five endocannabinoids and endocannabinoid related compounds in human plasma by two dimension-LC/MS/MS.

The elucidation of the role of endocannabinoids in physiological and pathological conditions and the transferability of the importance of these mediators from basic evidence into clinical practice is still hampered by the indefi niteness of their circulating reference intervals. In this work, we developed and validated a two-dimensional LC/ MS/MS method for the simultaneous measurement of plasma endocannabinoids and related compounds such as arachidonoyl-ethanolamide, palmitoyl-ethanolamide, and oleoyl-ethanolamide, belonging to the N-acyl-ethanolamide (NAE) family, and 2-arachidonoyl-glycerol and its inactive isomer 1-arachidonoyl-glycerol from the monoacyl-glycerol (MAG) family. We found that several pitfalls in the endocannabinoid measurement may occur, from blood withdrawal to plasma processing. Plasma extraction with toluene followed by on-line purifi cation was chosen, allowing highthroughput and reliability. We estimated gender-specifi c reference intervals on 121 healthy normal weight subjects fulfi lling rigorous anthropometric and hematic criteria. We observed no gender differences for NAEs, whereas signifi - cantly higher MAG levels were found in males compared with females. MAGs also signifi cantly correlated with triglycerides. NAEs increased with age in females, and arachidonoyl- ethanolamide correlated with adiposity and metabolic parameters in females. This work paves the way to the establishment of defi nitive reference intervals for circulating endocannabinoids to help physicians move from the speculative research field into the clinical fiel