Tricks and Tracks in the Identification and Quantification of Endocannabinoids

Abstract

The endocannabinoid system serves pivotal roles in a diverse range of physiological and pathophysiological states, including behavior, pain, schizophrenia, obesity, Alzheimer disease, multiple sclerosis and cardiovascular disease. A number of endocannabinoids (eCBs) and their receptors have been characterised and identified in a plethora of biological matrices. The eCBs include N‐arachidonoyl ethanolamine (anandamide), 2‐arachidonoyl glycerol, 2‐arachidonoyl glyceryl ether (noladin ether), O‐arachidonoyl ethanolamine (virodhamine) and N‐arachidonoyl dopamine. Advanced targeted mass spectrometry methods, particularly the selected reaction monitoring, has facilitated sensitive quantification of eCBs owing particularly to minimisation of the complex and abundant lipid matrix, invariably accompanying the eCBs in biological extracts. In this article, state‐of‐the‐art analytical workflows for eCBs extraction and mass‐spectrometry identification and quantification are concisely reviewed. Challenges and considerations on the isolation and analytical conditions to prevent artificial interferences in the measurement of eCBs concentration will be highlighted.

Key Concepts:

  • Endocannabinoids are lipid signalling molecules with pivotal role in a plethora of physiological and pathophysiological states, including anxiety, fear, learning and memory, pain etc.

  • Imbalances in the ECS activity underlie various psychiatric, neurological, metabolic and immunological diseases, and thus ECS is emerging as an appealing therapeutic target.

  • Quantitative profiling of endocannabinoids in various biological tissues is imperative to discover their site of action and determine the reference and altered concentration values.

  • Chemical isomerisation of eCBs, as well as ex‐vivo degradation and synthesis can occur during biological matrix sampling and processing, leading to artificial changes in the endogenous levels of eCBs.

  • Conditions for biological matrix sampling, storage, transportation and eCBs extraction methods have to be tailored and standardised with respect to biological matrix to achieve a reliable determination of reference and disease or pathological state‐related altered concentrations of eCBs in tissues and bodily fluids.

  • LC–ESI/SRM is the method of choice for eCBs quantification owing to the increased selectivity, specificity, robustness, precision and accuracy of quantification.

  • Validation and standardisation of LC/MS assays, biological matrix sampling and processing from tissues and bodily fluids are pivotal to allow comparison of eCB levels across studies and for prospective clinical research.

Keywords: endocannabinoids; eCBs; eCB Extraction; SPE; LLE; eCB concentrations; Endocannabinoid system; targeted quantification; LC–SRM quantification

Figure 1. Chemical structure of eCBs.
Figure 2. Schematic representation of the quantification workflow of eCBs using solvent extraction and LC–SRM quantification. (a) A representative extracted ion chromatogram in SRM mode for AEA, 2‐AG and 1‐AG, is depicted. Chromatographic separation as obtained on a reversed phase C18 column is illustrated (sample preparation and LC–SRM conditions according to Wojtalla et al., ). Each peak is assigned with the corresponding retention time and analyte identity.
Figure 3. Chemical isomerisation of 2‐AG to 1‐AG.
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Further Reading

Fanelli F, Di Lallo VD, Belluomo I et al. (2012) Estimation of reference intervals of five endocannabinoids and endocannabinoid related compounds in human plasma by two dimensional‐LC/MS/MS. Journal of Lipid Research 53: 481–493.

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Piomelli D (2003) The molecular logic of endocannabinoid signalling. Nature Reviews Neurosciences 4: 873–884.

Zoerner AA, Gutzki FM, Batkai S et al. (2011) Quantification of endocannabinoids in biological systems by chromatography and mass spectrometry: A comprehensive review from an analytical and biological perspective. Biochimica et Biophysica Acta 1811: 706–723.

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Lerner, Raissa, Lutz, Beat, and Bindila, Laura(Sep 2013) Tricks and Tracks in the Identification and Quantification of Endocannabinoids. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0023407]