A simple LC-MS/MS method for the simultaneous quantification of endocannabinoids in biological samples

The arachidonic acid derivatives N-arachidonoylethanolamine (anandamide; AEA), 2-arachidonoylglycerol (2-AG), N-arachidonoyldopamine (NADA), 2-arachidonoylglycerol ether (noladin ether; 2-AGE) and O-arachidonoylethanolamine (virodhamine; VA) were identified as physiological components of the endocannabinoid (EC) system. In order to gain further profound knowledge about the different EC-induced physiological and pathophysiological effects, appropriate analytical methods are required. The method described here uses liquid chromatography in combination with positive electrospray ionization mass spectrometry (LC-MS/MS) to quantify the concentrations of the above-mentioned EC compounds in cells. Sample preparation prior to LC-MS/MS analysis was performed by means of two liquid extractions with ethyl acetate. The method has been validated according to the bioanalytical guidelines of the Food and Drug Administration (FDA). The lower limits of quantification were 0.03 ng/mL for AEA, 2 ng/mL for 2-AG, 0.03 ng/mL for NADA, 0.3 ng/mL for 2-AGE and 0.15 ng/mL for VA. Linearity was demonstrated up to 10 ng/mL (AEA, NADA, 2-AGE and VA) and 50 ng/mL (2-AG). The values for intra- and inter-day precision and accuracy were within the guideline recommended acceptance criteria for assay validation. Low matrix effects and good recovery were found for AEA, 2-AG and 2-AGE, while a higher matrix effect was observed for NADA and VA. Extraction yields were lowest for VA. The method was used for EC measurement in different cell lines and in mouse brains.