Evidence for the Formation of Dinor Isoprostanes E1from α-Linolenic Acid in Plants

Stefanie Parchmann,Martin J Mueller

doi:10.1074/jbc.273.49.32650

Abstract

The free radical oxidation of arachidonic acid is known to generate complex metabolites, termed isoprostanes, that share structural features of prostaglandins and exert potent receptor-mediated biological activities. In the present study, we show that alpha-linolenic acid can undergo a similar oxidation process, resulting in a series of isomeric dinor isoprostanes E1. E-ring dinor isoprostane formation from linolenate was found to be catalyzed by soybean lipoxygenase. The main enzymatic products were 13- and 9-hydroperoxylinolenate but in addition, two dinor isoprostane E1 regioisomers were formed with a yield of 0.31%. Identification and quantification of two dinor isoprostane E1 regioisomers in plant cell cultures was achieved by a negative chemical ionization gas chromatography-mass spectrometry method using [18O]dinor isoprostanes E1 as internal standards. Endogenous levels of these compounds were determined in four taxonomically distant plant species and found to be in the range of 4.5 to 60.9 ng/g of dry weight. Thus analogous pathways in animals and plants exist, each leading to a family of prostaglandin-like compounds derived from polyunsaturated fatty acids. It remains to be shown whether the dinor isoprostanes exert biological activities in plants as has been demonstrated for their C20 congeners in mammals.

Highlights

Identification and quantification of two dinor isoprostane E1 regioisomers in plant cell cultures was achieved by a negative chemical ionization gas chromatographymass spectrometry method using [18O]dinor isoprostanes E1 as internal standards
As early as the 1960s, it was shown by Nutgeren et al (7) that prostaglandin-like compounds could be formed by autoxidation of 8,11,14-eicosatrienoic acid
In Negative Ion Chemical Ionization (NCI) GC-MS, the carboxylate anions of [18O]iPB1 type I and type II compounds were detected at m/z 381, whereas unlabeled reference compounds were detected at m/z 379, indicating the presence of one 18O atom/molecule labeled with

Summary

Introduction

Identification and quantification of two dinor isoprostane E1 regioisomers in plant cell cultures was achieved by a negative chemical ionization gas chromatographymass spectrometry method using [18O]dinor isoprostanes E1 as internal standards. A crude mixture of [18O]dinor-iPE1s labeled with three 18O atoms was obtained by eluting the column with 500 ml of diethyl ether/acetone/acetic acid (7:3:0.1, v/v).

Results

Conclusion