title: Metabolism of prostaglandin glycerol esters and prostaglandin ethanolamides in vitro and in vivo.
abstract: Prostaglandin glycerol esters (PG-Gs) and prostaglandin ethanolamides (PG-EAs) are generated by the action of cyclooxygenase-2 on the endocannabinoids 2-arachidonylglycerol (2-AG) and arachidonylethanolamide, respectively. These novel eicosanoids may have unique pharmacological properties and/or serve as latent sources of prostaglandins at sites remote from their tissue of origin. Therefore, we investigated the metabolism of PG-Gs and PG-EAs in vitro and in vivo. PGE(2)-G was rapidly hydrolyzed in rat plasma to generate PGE(2) (t(1/2) = 14 s) but was only slowly metabolized in human plasma (t(1/2) > 10 min). An intermediate extent of metabolism of PGE(2)-G was observed in human whole blood (t(1/2) approximately 7 min). The parent arachidonylglycerol, 2-AG, and the more stable regioisomer, 1-AG, also were much more rapidly metabolized in rat plasma compared with human plasma. PGE(2)-EA was not significantly hydrolyzed in plasma, undergoing slow dehydration/isomerization to PGB(2)-EA. Both PGE(2)-G and PGE(2)-EA were stable in canine, bovine, and human cerebrospinal fluid. Human 15-hydroxyprostaglandin dehydrogenase, the enzyme responsible for the initial step in PG inactivation in vivo, oxidized both PGE(2)-G and PGE(2)-EA less efficiently than the free acid. The sterically hindered glyceryl prostaglandin was the poorest substrate examined in the E series. Minimal 15-hydroxyprostaglandin dehydrogenase oxidation of PGF(2 alpha)-G was observed. PGE(2)-G and PGE(2)-EA pharmacokinetics were assessed in rats. PGE(2)-G was not detected in plasma 5 min following an intravenous dose of 2 mg/kg. However, PGE(2)-EA was detectable up to 2 h following an identical dose, displaying a large apparent volume of distribution and a half-life of over 6 min. The results suggest that endocannabinoid-derived PG-like compounds may be sufficiently stable in humans to exert actions systemically. Furthermore, these results suggest that the rat is not an adequate model for investigating the biological activities of 2-arachidonylglycerol or glyceryl prostaglandins in humans.
authors.affiliation: Department of Biochemistry and Chemistry, Vanderbilt-Ingram Cancer Center and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
authors.forename: K R
authors.initials: KR
authors.lastname: Kozak
authors.forename: B C
authors.initials: BC
authors.lastname: Crews
authors.forename: J L
authors.initials: JL
authors.lastname: Ray
authors.forename: H H
authors.initials: HH
authors.lastname: Tai
authors.forename: J D
authors.initials: JD
authors.lastname: Morrow
authors.forename: L J
authors.initials: LJ
authors.lastname: Marnett
mesh_terms: D000818:Animals; D063385:Cannabinoid Receptor Modulators; D015232:Dinoprostone / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics; D004355:Drug Stability; D004952:Esters / Q000378:metabolism; D004983:Ethanolamines / Q000378:metabolism* / Q000493:pharmacokinetics; D005989:Glycerides / Q000378:metabolism* / Q000493:pharmacokinetics; D006801:Humans; D006911:Hydroxyprostaglandin Dehydrogenases / Q000378:metabolism; D008297:Male; D010949:Plasma / Q000378:metabolism; D011453:Prostaglandins / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D063385:Cannabinoid Receptor Modulators; D004952:Esters; D004983:Ethanolamines; D005989:Glycerides; D011453:Prostaglandins; C518978:prostaglandin E2 glyceryl ester; D006911:Hydroxyprostaglandin Dehydrogenases; C035859:15-hydroxyprostaglandin dehydrogenase; D015232:Dinoprostone