Selective oxygenation of the endocannabinoid 2-arachidonylglycerol by leukocyte-type 12-lipoxygenase

The endogenous cannabinoid system appears to serve vascular, neurological, immunological, and reproductive functions. The identification of 2-arachido nylglycerol (2-AG) as an endogenous ligand for the central (CB1) and periph eral (CB2) cannabinoid receptors has prompted interest in enzymes capable o f modifying or inactivating this endocannabinoid. Porcine leukocyte 12-liop oxygenase (12-LOX) oxygenated 2-AG to the 2-glyceryl ester of 12(S)-hydrope roxyeicosa-5,8,10,14-tetraenoic acid (12-HPETEG). The k(cat)/dK(M) for oxyg enation of 2-AG was 40% of the value for arachidonic acid. In contrast to t he results with leukocyte 12-LOX, 2-AG oxygenation was not detected with pl atelet-type 12-LOX. Among a series of structurally related arachidonyl este rs, 2-AG served as the preferential substrate for leukocyte 12-LOX. 12(S)-H ydroxyeicosa-5,8,10,14-tetraenoic acid glyceryl ester (12-HETE-G) was produ ced following addition of 2-AC to COS-7 cells transiently transfected with leukocyte 12-LOX. These results demonstrate that leukocyte-type 12-LOX effi ciently oxidizes 2-AG in vitro and in intact cells, suggesting a role for t his oxygenase in the endogenous cannabinoid system.