Studies on the oxidation of ω-hydroxyprostaglandins by an NAD-dependent dehydrogenase from mammalian liver cytosol

Abstract

The oxidation of 12-hydroxylauric acid methyl ester (12-OH-L-Me) and of ω-hydroxy-prostaglandins (ω-OH-PGs) such as 20-OH-PGB 1 and 20-OH-PGE 1, was demonstrated with liver cytosol from rat, rabbit, and guinea pig in the presence of NAD; however, NADP did not support this oxidation. (ω-1)-Hydroxy-compounds (11-OH-laurate and 19-OH-PGB 1) and PGE 1, PGF 1α, and PGB 1, all lacking the terminal (ω)-hydroxyl, did not reduce NAD. However, at pH 10, PGE 1 slightly enhanced NAD reduction, suggesting that at this pH PGE 1, could be a substrate for 15-hydroxy-PG dehydrogenase (PGDH). The oxidation products from incubations of 12-OH-L-Me, 20-OH-PGB 1-Me, and 20-OH-PGE 1 with guinea pig liver cytosol were isolated and identified by gas chromatography/mass fragmentation spectrometry as being the corresponding dicarboxylic acids. In contrast to the liver cytosol, guinea pig kidney cytosol had only a minimal effect on NAD reduction by 12-OH-L-Me but nevertheless did support the stimulation of NAD reduction by PGE 1, and PGF 1α, but not by PGB 1, indicating the participation of kidney cytosolic PGDH in PGE 1 and PGF 1α oxidation and demonstrating that the oxidation of ω-OH to the carboxylic acid is not mediated by PGDH. Though the in vivo rate of oxidation of ω-OH-PGs has not been established, these results suggest that the urinary dicarboxylic-PG metabolites involve a multiple sequentialstep oxidation of PGs involving ω-hydroxylation by an NADPH-cytochrome P-450 system in the endoplasmic reticulum and the subsequent oxidation of the ω-OH by an NAD-dependent dehydrogenase in the cytosol.