Oleamide activates peroxisome proliferator-activated receptor gamma (PPARγ) in vitro

Background: Oleamide (ODA) is a fatty acid primary amide first identified in the cerebrospinal fluid of sleep-deprived cats, which exerts effects on vascular and neuronal tissues, with a variety of molecular targets including cannabinoid receptors and gap junctions. It has recently been reported to exert a hypolipidemic effect in hamsters. Here, we have investigated the nuclear receptor family of peroxisome proliferator-activated receptors (PPARs) as potential targets for ODA action. Results: Activation of PPAR alpha, PPAR beta and PPAR gamma was assessed using recombinant expression in Chinese hamster ovary cells with a luciferase reporter gene assay. Direct binding of ODA to the ligand binding domain of each of the three PPARs was monitored in a cell-free fluorescent ligand competition assay. A well-established assay of PPAR. activity, the differentiation of 3T3-L1 murine fibroblasts into adipocytes, was assessed using an Oil Red O uptake-based assay. ODA, at 10 and 50 mu M, was able to transactivate PPAR alpha, PPAR beta and PPAR gamma receptors. ODA bound to the ligand binding domain of all three PPARs, although complete displacement of fluorescent ligand was only evident for PPAR gamma, at which an IC50 value of 38 mu M was estimated. In 3T3-L1 cells, ODA, at 10 and 20 mu M, induced adipogenesis. Conclusions: We have, therefore, identified a novel site of action of ODA through PPAR nuclear receptors and shown how ODA should be considered as a weak PPAR gamma ligand in vitro.