title: Quantification of endocannabinoids in biological systems by chromatography and mass spectrometry: a comprehensive review from an analytical and biological perspective.
abstract: The endocannabinoids anandamide (arachidonoyl ethanolamide, AEA) and 2-arachidonoyl glycerol (2AG) are physiologically occurring, biologically active compounds on CB(1) and CB(2) receptors with multiple physiological functions. AEA and 2AG have been identified and quantified in many mammalian biological fluids and tissues, such as human plasma, adipocytes, tissues and tissue microdialysates, at concentrations in the picomolar-to-nanomolar range under basal conditions. In this article, recently published chromatographic and mass spectrometric analytical methods, i.e., HPLC with fluorescence or ultraviolet detection, LC-MS, LC-MS/MS, GC-MS and GC-MS/MS, are reviewed and discussed, notably from the quantitative point of view. We focus on and emphasize the particular importance of blood sampling, sample storage and work-up including solvent and solid-phase extraction and derivatization procedures, matrix-effects, and stability of analytes. As 2AG spontaneously isomerizes to its CB(1)/CB(2) receptors biologically inactive 1-arachidonoyl glycerol (1AG) by acyl migration, this phenomenon and its particular importance for accurate quantification of 2AG are discussed in detail. Due to the electrical neutrality of AEA and 2AG their solvent extraction by toluene offers the least matrix-effect and minimum isomerization. LC-MS/MS is the most frequently used analytical technique for AEA and 2AG. At present, the utility of the GC-MS/MS methodology seems to be limited to AEA measurement in human plasma, bronchoalveolar liquid (BAL) and microdialysate samples. Despite great instrumental advances in the LC-MS/MS methodology, sampling and sample treatment remains one of the most crucial analytical steps in 2AG analysis. Extension of the LC-MS/MS methodology, for instance to microdialysate and BAL samples from clinical studies, is a big analytical challenge in endocannabinoid analysis in clinical settings. Currently available LC-MS/MS and GC-MS/MS methods should be useful to investigate the metabolism of AEA and 2AG beyond hydrolysis, i.e., by β- and ω-oxidation pathways.
authors.affiliation: Hannover Medical School, Hannover, Germany. zoerner.alexander@mh-hannover.de
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Zoerner
authors.forename: Frank-Mathias
authors.initials: FM
authors.lastname: Gutzki
authors.forename: Sandor
authors.initials: S
authors.lastname: Batkai
authors.forename: Marcus
authors.initials: M
authors.lastname: May
authors.forename: Christin
authors.initials: C
authors.lastname: Rakers
authors.forename: Stefan
authors.initials: S
authors.lastname: Engeli
authors.forename: Jens
authors.initials: J
authors.lastname: Jordan
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Tsikas
mesh_terms: D053000:Analytic Sample Preparation Methods; D063385:Cannabinoid Receptor Modulators / Q000032:analysis* / Q000737:chemistry; D011232:Chemical Precipitation; D063388:Endocannabinoids; D006801:Humans; D013058:Mass Spectrometry / Q000379:methods*; D017551:Microdialysis
chemical_list: D063385:Cannabinoid Receptor Modulators; D063388:Endocannabinoids