Identification of endocannabinoids and related compounds in human fat cells

Objective: Recently, an activation of the endocannabinoid system during obesity has been reported. More particularly, it has been demonstrated that hypothalamic levels of both endocannabinoids, 2‐arachidonoylglycerol and anandamide (N‐arachidonoylethanolamine), are up‐regulated in genetically obese rodents. Circulating levels of both endocannabinoids were also shown to be higher in obese compared with lean women. Yet, the direct production of endocannabinoids by human adipocytes has never been demonstrated. Our aim was to evaluate the ability of human adipocytes to produce endocannabinoids. Research Methods and Procedures: The production of endocannabinoids by human adipocytes was investigated in a model of human white subcutaneous adipocytes in primary culture. The effects of leptin, adiponectin, and peroxisome proliferator‐activated receptor (PPAR)‐γ activation on endocannabinoid production by adipocytes were explored. Endocannabinoid levels were determined by high‐performance liquid chromatography (HPLC)‐atmospheric pressure chemical ionization (APCI)‐mass spectrometry (MS) analysis, leptin and adiponectin secretion measured by enzyme‐linked immunosorbent assay (ELISA), and PPAR‐γ protein expression examined by Western blotting. Results: We show that 2‐arachidonoylglycerol, anandamide, and both anandamide analogs, N‐palmitoylethanolamine and N‐oleylethanolamine, are produced by human white subcutaneous adipocytes in concentrations ranging from 0.042 ± 0.004 to 0.531 ± 0.048 pM/mg lipid extract. N‐palmitoylethanolamine is the most abundant cannabimimetic compound produced by human adipocytes, and its levels are significantly down‐regulated by leptin but not affected by adiponectin and PPAR‐γ agonist ciglitazone. N‐palmitoylethanolamine itself does not affect either leptin or adiponectin secretion or PPAR‐γ protein expression in adipocytes. Discussion: This study has led to the identification of human adipocytes as a new source of endocannabinoids and related compounds. The biological significance of these adipocyte cannabimimetic compounds and their potential implication in obesity should deserve further investigations.