Biosynthesis of 5,6-dihydroxyprostaglandin E 1, and F 1α from 5,6-dihydroxyeicosatrienoic acid by ram seminal vesicles

Abstract

cis-5(6)Epoxy- cis-8,11,14-eicosatrienoic acid was recently found to be metabolized by ram seminal vesicles to 5-hydroxyprostaglandin I 1α and 5-hydroxyprostaglandin I 1β,5(6)epoxyprostaglandin E 1 and 5,6-dihydroxyprostaglandin E 1 The epoxide can be hydrolyzed by epoxide hydrolases to 5,6-dihydroxy-8,11,14-eicosatrienoic acid. The latter was incubated with microsomes of ram seminal vesicles for 2 min at 37°C and the polar metabolites were purified by reversed phase HPLC and analyzed by capillary column gas chromatography-mass spectrometry. The major metabolite was identified as 5,6-dihydroxyprostaglandin F 1α. In the presence of glutathione (1 mM), 5,6-dihydroxyprostaglandin E 1 was also formed. The 3H-labelled vicinal diol and the 3H-labelled epoxide were metabolized to polar products to a similar extent, but the formation of prostaglandin E compounds in the presence of glutathione was lower from the diol than from the epoxide or from arachidonic acid. The likely prostaglandin endoperoxide intermediates in the metabolism of the diol (5,6-dihydroxyprostaglandin G 1 and 5,6-dihydroxyprostaglandin H 1) thus appear to be less prone to be isomerized to prostaglandin E compounds than prostaglandins G 2 and H 2 and their 5(6)epoxy counterparts. 5(6)Epoxyprostaglandin E 1 and 5,6-dihydroxyprostaglandin E 1 can be chemically transformed into 5,6-dihydroxyprostaglandin B 1. The latter can be analyzed by HPLC or by mass fragmentography, and a simple chemical synthesis of 5,6-dihydroxyprostaglandin b 1 from prostaglandin E 2 is described.