Endocannabinoid-Related Enzymes as Drug Targets with Special Reference to N-Acylphosphatidylethanolamine-Hydrolyzing Phospholipase D

Anandamide (N-arachidonoylethanolamine) is the first discovered endocannabinoid (endogenous ligand of cannabinoid receptors). In animal tissues, anandamide is principally formed together with other bioactive long-chain N-acylethanolamines from membrane glycerophospholipid by two enzyme reactions. The first reaction is the transfer of a fatty acyl chain from the sn-1 position of glycerophospholipid to phosphatidylethanolamine by calcium-dependent N-acyltransferase, resulting in the generation of Nacylphosphatidylethanolamine (NAPE). The second reaction is catalyzed by a phosphodiesterase of the phospholipase D (PLD)-type, which releases N-acylethanolamines from their corresponding NAPEs. The produced N-acylethanolamines are hydrolyzed to fatty acids and ethanolamine by fatty acid amide hydrolase or an amidase acting exclusively at acidic pH. Our recent cDNA cloning of the NAPE-hydrolyzing PLD (NAPEPLD) from mouse, rat and human revealed that NAPE-PLD is a novel enzyme which has no homology with any known PLD enzymes, but belongs to the zinc metallo-hydrolase family of the β-lactamase fold. The recombinant enzyme hydrolyzed various NAPEs, including the anandamide precursor Narachidonoylphosphatidylethanolamine at similar rates, but was inactive with phosphatidylcholine and phosphatidylethanolamine. Considering cannabimimetic activities of anandamide, the enzymes involved in the biosynthesis and degradation of anandamide, including NAPE-PLD, may be promising targets for therapeutic agents.