The endocannabinoid anandamide is a precursor for the signaling lipid N-arachidonoyl glycine by two distinct pathways.
BACKGROUND
N-arachidonoyl glycine (NAGly) is an endogenous signaling lipid with a wide variety of biological activity whose biosynthesis is poorly understood. Two primary biosynthetic pathways have been proposed. One suggests that NAGly is formed via an enzymatically regulated conjugation of arachidonic acid (AA) and glycine. The other suggests that NAGly is an oxidative metabolite of the endogenous cannabinoid, anandamide (AEA), through an alcohol dehydrogenase. Here using both in vitro and in vivo assays measuring metabolites with LC/MS/MS we test the hypothesis that both pathways are present in mammalian cells.


RESULTS
The metabolic products of deuterium-labeled AEA, D4AEA (deuterium on ethanolamine), indicated that NAGly is formed by the oxidation of the ethanolamine creating a D2NAGly product in both RAW 264.7 and C6 glioma cells. Significantly, D4AEA produced a D0NAGly product only in C6 glioma cells suggesting that the hydrolysis of AEA yielded AA that was used preferentially in a conjugation reaction. Addition of the fatty acid amide (FAAH) inhibitor URB 597 blocked the production of D0NAGly in these cells. Incubation with D8AA in C6 glioma cells likewise produced D8NAGly; however, with significantly less efficacy leading to the hypothesis that FAAH-initiated AEA-released AA conjugation with glycine predominates in these cells. Furthermore, the levels of AEA in the brain were significantly increased, whereas those of NAGly were significantly decreased after systemic injection of URB 597 in rats and in FAAH KO mice further supporting a role for FAAH in endogenous NAGly biosynthesis. Incubations of NAGly and recombinant FAAH demonstrated that NAGly is a significantly less efficacious substrate for FAAH with only ~50% hydrolysis at 30 minutes compared to 100% hydrolysis of AEA. Co-incubations of AEA and glycine with recombinant FAAH did not, however, produce NAGly.


CONCLUSIONS
These data support the hypothesis that the signaling lipid NAGly is a metabolic product of AEA by both oxidative metabolism of the AEA ethanolamine moiety and through the conjugation of glycine to AA that is released during AEA hydrolysis by FAAH.
Bradshaw
Heather B
HB
The Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA. hbbradsh@indiana.edu
Rimmerman
Neta
N
Hu
Sherry Shu-Jung
SS
Benton
Valery M
VM
Stuart
Jordyn M
JM
Masuda
Kim
K
Cravatt
Benjamin F
BF
O'Dell
David K
DK
Walker
J Michael
JM
D000581:Amidohydrolases / Q000037:antagonists & inhibitors / Q000172:deficiency; D000818:Animals; D001095:Arachidonic Acids / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D001549:Benzamides / Q000494:pharmacology; D001921:Brain / Q000187:drug effects / Q000201:enzymology; D001923:Brain Chemistry; D002219:Carbamates / Q000494:pharmacology; D045744:Cell Line, Tumor; D063388:Endocannabinoids; D005998:Glycine / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D050356:Lipid Metabolism; D008297:Male; D053858:Metabolic Networks and Pathways; D051379:Mice; D018345:Mice, Knockout; D010084:Oxidation-Reduction; D053284:Polyunsaturated Alkamides / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D000099252:Fatty Acid Amide Hydrolases
D000581:Amidohydrolases; D001095:Arachidonic Acids; D001549:Benzamides; D002219:Carbamates; D063388:Endocannabinoids; D005998:Glycine; D053284:Polyunsaturated Alkamides; D011994:Recombinant Proteins; D000099252:Fatty Acid Amide Hydrolases; C465623:N-arachidonylglycine; C500528:cyclohexyl carbamic acid 3'-carbamoylbiphenyl-3-yl ester; C078814:anandamide