Analysis of Oxidative Stress and Wound-Inducible Dinor Isoprostanes F(1) (Phytoprostanes F(1)) in Plants

Isoprostanes F(2) are arachidonate autoxidation products in mammals that have been shown to be induced during several human disorders associated with enhanced free-radical generation. Isoprostanes F(2) represent not only extremely reliable markers of oxidative stress in vivo, but they also exert potent biological effects. Therefore, it has been postulated that isoprostanoids are mediators of oxidant injury in vivo. Higher plants, however, do not synthesize arachidonic acid or isoprostanes. Here we show that a series of isoprostane F(2) analogs termed phytoprostanes F(1) (previously dinor isoprostanes F(1)) are formed by an analogous pathway from α-linolenate in plants. High-performance liquid chromatography and gas chromatography-mass spectrometry methods using [(18)O](3)phytoprostanes F(1) as internal standard have been developed to quantify phytoprostanes F(1). In fresh peppermint (Mentha piperita) leaves, phytoprostanes F(1) were found in free form (76 ng/g of dry weight) and at about 150-fold higher levels esterified in lipids. It is notable that these levels of phytoprostanes F(1) are more than two orders of magnitude higher than the basal levels of isoprostanes F(2) in mammalian tissues. Furthermore, wounding, as well as butyl hydroperoxide or cupric acetate stress triggered a dramatic increase of free and esterified phytoprostanes F(1). Thus phytoprostanes F(1) may represent a sensitive measure of oxidative damage in plants similar to isoprostanes in mammals. However, one of the most exciting issues to be clarified is the possibility that linolenate-derived phytoprostanes F(1) exert biological activities in plants and/or animals.