Validation of a tandem mass spectrometry method using combined extraction of 37 oxylipins and 14 endocannabinoid-related compounds including prostamides from biological matrices

• Novel method for endocannabinoid, prostamide and oxylipin detection by UPLC–ESI-MS/MS.
• Using combined solid phase extraction for endocannabinoid, prostamide and oxylipin.
• Facilitates discovery of tissue and species specificity of eicosanoid levels.

There is a clinical need for more relevant coverage of bioactive lipids using smaller sample volumes. Therefore, we have validated a tandem mass spectrometry method for combined solid phase extraction of 37 compounds in the oxylipin (OxL) and 14 in the endocannabinoid (eCB) metabolome, as well as prostamides. The limits of quantification (LOQ) for compounds in the eCB metabolome were in the range 0.5–1000 fg on column, intraday accuracy and precision ranges (%) were 83–125 and 0.3–17, respectively, and interday accuracy and precision ranges (%) were 80–119 and 1.2–20, respectively, dependent upon the compound and the concentration studied. Corresponding values for OxL were 0.5 fg–4.2 pg on column (LOQ), 85–115% (inter- and intraday accuracy) and <5% (precision). The combined extraction method was successfully applied to tissues, cell extracts, human plasma and milk samples. A deeper study of levels in elk, pig and cow brain, as well as cow heart and liver revealed tissue and species-specific elevation of eicosanoids: arachidonate diols, 20-HETE and 12(S)-HEPE (cow liver), LTB4 (cow brain), and monohydroxy metabolites (HETEs), epoxides and 5-oxo-ETE in elk brain, which might be caused by factors of stress and/or post-mortem reactions in the tissues.

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