Enzymatic formation of prostamide F2α from anandamide involves a newly identified intermediate metabolite, prostamide H2

Prostaglandin F-2 alpha 1-ethanolamide (prostamideF(2 alpha)) is a potent ocular hypotensive agent in animals and represents a new class of fatty acid amide compounds. Accumulated evidence indicated that anandamide, an endogenous bioactive ligand for cannabinoid receptors, may serve as a common substrate to produce all prostamides, including prostamide F-2 alpha. After incubation of anandamide with cyclooxygenase 2 (COX-2), the reaction mixture was profiled by HPLC and an intermediate metabolite was discovered and characterized as a cyclic endoperoxide ethanolamide using HPLC-tandem mass spectrometry. Formation of prostamide F-2 alpha was also demonstrated when the intermediate metabolite was isolated and incubated with prostaglandin F synthase (PGF synthase). These results suggest that the biosynthesis of prostamide F-2 alpha proceeds in two consecutive steps: oxidation of anandamide to form an endoperoxide intermediate by COX-2, and reduction of the endoperoxide intermediate to form prostamide F-2 alpha by PGF synthase. This endoperoxide ethanolamide intermediate has been proposed as prostamide H-2.