Anandamide Oxidation by Wild-Type and Polymorphically Expressed CYP2B6 and CYP2D6□S

Anandamide is an arachidonic acid-derived endogenous cannabi-noid that regulates normal physiological functions and pathophys-iological responses within the central nervous system and in the periphery. Several cytochrome P450 (P450) isoforms metabolize anandamide to form hydroxylated and epoxygenated products. Human CYP2B6 and CYP2D6, which are expressed heteroge-neously throughout the brain, exhibit clinically significant polymor-phisms and are regulated by external factors, such as alcohol and smoking. Oxidative metabolism of anandamide by these two P450s may have important functional consequences for endocannabinoid system signaling. In this study, we investigated the metabolism of anandamide by wild-type CYP2B6 (2B6.1) and CYP2D6 (2D6.1) and by their common polymorphic mutants 2B6.4, 2B6.6, 2B6.9, and 2D6.34. Major differences in anandamide metabolism by the two isoforms and their mutants were found in vitro with respect to the formation of 20-hydroxyeicosatetraenoic acid ethanolamide (20-HETE-EA) and 14,15-epoxyeicosatetraenoic acid ethanolamide (14,15-EET-EA). Pharmacological studies showed that both 20-HETE-EA and 14,15-EET-EA bind to the rat brain cannabinoid CB1 receptor with lower affinities relative to that of anandamide. In addition, both products are degraded more rapidly than anand-amide in rat brain homogenates. Their degradation occurs via different mechanisms involving either fatty acid amide hydrolase (FAAH), the major anandamide-degrading enzyme, or epoxide hy-drolase (EH). Thus, the current findings provide potential new in-sights into the actions of inhibitors FAAH and EH, which are being developed as novel therapeutic agents, as well as a better under-standing of the interactions between the cytochrome P450 mono-oxygenases and the endocannabinoid system