Synthesis of prostaglandin F ethanolamide by prostaglandin F synthase and identification of Bimatoprost as a potent inhibitor of the enzyme: new enzyme assay method using LC/ESI/MS

Prostaglandin (PG) D-2 ethanolamide (prostamide D-2) was reduced to 9alpha, 11beta-PGF(2) ethanolamide (9alpha, 11beta-prostamide F-2) by PGF synthase, which also catalyzes the reduction of PGH(2) and PGD(2) to PGF(2alpha) and 9alpha11beta-PGF(2), respectively. These enzyme activities were measured by a new method, the liquid chromatographic-electrospray ionization-mass spectrometry (LC/ESI/MS) technique, which could simultaneously detect the substrate and all products. PGF(2alpha), 9alpha,l lbeta-PGF(2), PGD(2), PGH(2), 9alpha,11beta-prostamide F-2, and prostamide D-2 were separated on a TSKgel ODS 80Ts column, ionized by electrospray, and detected in the negative mode. Selected ion monitoring (SIM) of m/z 353 ([M-H](-)), 353 ([M-H](-)), 351 ([M-H](-)) 333 ([M-H-H2O](-)) 456 ([M+59](-)), and m/z 358 ([M-37](-)) was used for quantifying PGF(2alpha), 9alpha,11beta-PGF(2), PGD(2), PGH(2), 9alpha,11beta-prostamide F-2, and prostamide D-2, respectively. The detection limit for PGF(2alpha) and 9alpha,11beta-PGF(2) was 0.01 pmol, that for PGH(2) and PGD(2), 0.1 pmol; and that for prostamide D-2 and 9alpha,11beta-prostamide F-2, 0.5 and 0.03 pmol, respectively. The LC/ESI/MS technique for measuring PGF synthase activity showed higher sensitivity than other methods. Using this method, we found that Bimatoprost, the ethyl amide analog of 17-phenyl-trinor PGF(2alpha) and an anti-glaucoma agent, inhibited all three reductase activities of PGF synthase when used at a low concentration. These results suggest that Bimatoprost also behaves as a potent PGF synthase inhibitor in addition to having prostamide-like activity. (C) 2004 Elsevier Inc. All rights reserved.