Linoleic acid peroxidation products are metabolized by hydrogenation in porcine liver tissue

Abstract

Homogenization of mammalian tissue activates enzymes which cause degradation. This effect was used to elucidate the metabolism of 13-S-hydroxy-9,11-octadecadienoic acid (13-S-HODE) and 9-S-hydroxy-10,12-octadecadienoic acid (9-S-HODE), physiologically active products of lipid peroxidation (LPO) processes, by electron ionization GC/MS. 13-S-HODE was added to a porcine liver homogenate, samples withdrawn at timed intervals and extracts of polar fatty acids then subjected to GC/MS analysis, after methylation and trimethylsilylation, to give mass spectra of derivatised hydroxy acids that showed that degradation starts with the hydrogenation of one double bond. The position of the remaining double bond was determined by reacting the hydroxyoctadecenoic acid thus obtained with osmium tetroxide to give a trihydroxystearic acid. After appropriate derivatization (methylation, trimethylsilylation), the mass spectrum unambiguously demonstrated the presence of a 9,10,13-trihydroxystearic acid derivative and hence the double bond in the precursor molecule is located in position 9. Enzymatic hydrogenation of 13-S-HODE is enhanced by the addition of NADH and, to an even greater extent, by NADPH. Similarly, 9-S-HODE is metabolized to 9-S-hydroxy-12-octadecenoic acid.