Human platelets and polymorphonuclear leukocytes synthesize oxygenated derivatives of arachidonylethanolamide (anandamide): their affinities for cannabinoid receptors and pathways of inactivation.
Arachidonylethanolamide (AEA), the putative endogenous ligand of the cannabinoid receptor, has been shown to be a substrate for lipoxygenase enzymes in vitro. One goal of this study was to determine whether lipoxygenase-rich cells metabolize AEA. [14C]AEA was converted by human polymorphonuclear leukocytes (PMNs) to two major metabolites that comigrated with synthetic 12(S)- and 15(S)-hydroxy-arachidonylethanolamide (HAEA). Human platelets convert [14C]AEA to 12(S)-HAEA. 12(S)-HAEA binds to both CB1 and CB2 receptors with approximately the same affinity as AEA. 12(R)-HAEA, which is not produced by PMNs, has 2-fold lower affinity for the CB1 receptor and 10-fold lower affinity for the CB2 receptor than 12(S)-HAEA. 15-HAEA has a lower affinity than AEA for both receptors, with Ki values of 738 and >1000 nM for CB1 and CB2 receptors, respectively. The addition of a hydroxyl group at C20 of AEA resulted in a ligand with the same affinity for the CB1 receptor but a 4-fold lower affinity for the CB2 receptor than AEA. 12(S)-HAEA and 15-HAEA are poor substrates for AEA amidohydrolase and do not bind to the AEA uptake carrier. In conclusion, the addition of a hydroxyl group at C12 of the arachidonate backbone of AEA does not affect binding to CB receptors but is likely to increase its half-life. The addition of hydroxyl groups at other positions affects ligand affinity for CB receptors; both the position of the hydroxyl group and the configuration of the remaining double bonds are determinants of affinity.
Edgemond
W S
WS
Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
Hillard
C J
CJ
Falck
J R
JR
Kearn
C S
CS
Campbell
W B
WB
D000581:Amidohydrolases / Q000378:metabolism; D000818:Animals; D001092:Arachidonate 12-Lipoxygenase / Q000378:metabolism; D001093:Arachidonate 15-Lipoxygenase / Q000378:metabolism; D001095:Arachidonic Acids / Q000096:biosynthesis* / Q000378:metabolism; D001792:Blood Platelets / Q000201:enzymology / Q000378:metabolism*; D063388:Endocannabinoids; D006801:Humans; D008297:Male; D009474:Neurons / Q000378:metabolism; D009504:Neutrophils / Q000201:enzymology / Q000378:metabolism*; D053284:Polyunsaturated Alkamides; D051381:Rats; D017207:Rats, Sprague-Dawley; D043885:Receptor, Cannabinoid, CB2; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000378:metabolism*; D013379:Substrate Specificity
D001095:Arachidonic Acids; C469526:Cnr2 protein, rat; D063388:Endocannabinoids; D053284:Polyunsaturated Alkamides; D043885:Receptor, Cannabinoid, CB2; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; D001092:Arachidonate 12-Lipoxygenase; D001093:Arachidonate 15-Lipoxygenase; D000581:Amidohydrolases; C078814:anandamide