Quantification of anandamide content in animal cells and tissues: the normalization makes the difference

Anandamide (N-arachidonoylethanolamine, AEA) is an endogenous lipid that binds to cannabinoid receptors in the central nervous system and in peripheral cells. Quantitative analysis of AEA is generally based on the normalization to the fresh weight of the samples. Here, we show that the normalization procedure of AEA content is such a critical factor, that it might introduce per se significant discrepancies in the quantification of AEA even in the same sample. We suggest that a rapid, accurate and most reliable reference to quantify AEA and congeners from different sources is the protein content, a common parameter to cells and tissues.