Evidence for the formation of dinor isoprostanes E-1 from alpha-linolenic acid in plants

The free radical oxidation of arachidonic acid is known to generate complex metabolites, termed isoprostanes, that share structural features of prosta glandins and exert potent receptor-mediated biological activities. In the p resent study, we show that alpha-linolenic acid can undergo a similar oxida tion process, resulting in a series of isomeric dinor isoprostanes E-1. E-r ing dinor isoprostane formation from linolenate was found to be catalyzed b y soybean lipoxygenase, The main enzymatic products were 13- and 9-hydroper oxylinolenate but in addition, two dinor isoprostane E-1 regioisomers were formed with a yield of 0.31%. Identification and quantification of two dinor isoprostane E-1 regioisomers in plant cell cultures was achieved by a negative chemical ionization gas chromatography-mass spectrometry method using [O-18]dinor isoprostanes E-1 as internal standards. Endogenous levels of these compounds were determined in four taxonomically distant plant species and found to be in the range o f 4.5 to 60.9 ng/g of dry weight. Thus analogous pathways in animals and plants exist, each leading to a fami ly of prostaglandin-like compounds derived from polyunsaturated fatty acids . It remains to be shown whether the dinor isoprostanes exert biological ac tivities in plants as has been demonstrated for their C20 congeners in mamm als.