2-Arachidonoylglycerol, an Endogenous Cannabinoid Receptor Ligand, Induces Accelerated Production of Chemokines in HL-60 Cells

2-Arachidonoylglycerol is an endogenous ligand for the cannabinoid receptors (CB1 and CB2). Previously, we provided evidence that 2-arachidonoylglycerol, but not anandamide (N-arachidonoylethanolamine), is the true natural ligand for the cannabinoid receptors. In the present study, we examined in detail the effects of 2-arachidonoylglycerol on the production of chemokines in human promyelocytic leukemia HL-60 cells. We found that 2-arachidonoylglycerol induced a marked acceleration in the production of interleukin 8. The effect of 2-arachidonoylglycerol was blocked by treatment of the cells with SR144528, a cannabinoid CB2 receptor antagonist, indicating that the effect of 2-arachidonoylglycerol is mediated through the CB2 receptor. Augmented production of interleukin 8 was also observed with CP55940, a synthetic cannabinoid, and an ether-linked analog of 2-arachidonoylglycerol. On the other hand, neither anandamide nor the free arachidonic acid induced the enhanced production of interleukin 8. A similar effect of 2-arachidonoylglycerol was observed in the case of the production of macrophage-chemotactic protein-1. The accelerated production of interleukin 8 by 2-arachidonoylglycerol was observed not only in undifferentiated HL-60 cells, but also in HL-60 cells differentiated into macrophage-like cells. Noticeably, 2-arachidonoylglycerol and lipopolysaccharide acted synergistically to induce the dramatically augmented production of interleukin 8. These results strongly suggest that the CB2 receptor and its physiological ligand, i.e., 2-arachidonoylglycerol, play important regulatory roles such as stimulation of the production of chemokines in inflammatory cells and immune-competent cells. Detailed studies on the cannabinoid receptor system are thus essential to gain a better understanding of the precise regulatory mechanisms of inflammatory reactions and immune responses.