Formation of isoprostane F2-like compounds (phytoprostanes F1) from α-linolenic acid in plants

Isoprostanes F-2 are biologically active prostaglandin F-2-like compounds formed by free radical-catalyzed oxidation of arachidonic acid (C20:4). Here. we show that a series of diner isoprostanes F-1, which we term phytoprostanes F-1 (PPF(1)s), are formed by nonenzymatic oxidation of linolenate (C18:3) in plants. Identification and quantification of PPF(1)s were achieved by a negative ion chemical ionization gas chromotography-mass spectrometry method using oxygen 18-labeled PPF(1)s as internal standards. PPF(1)s were found in leaves, flowers, and roots of taxonomically distinct plant species at concentrations ranging from 43 to 1380 ng/g of dry weight. In addition, esterified PPF(1)s were found at 10- to 150-fold higher concentrations. During the drying and storage of various plant organs, endogenous PPF1 levels increased dramatically by 15- to 263-fold. Because the structurally related prostaglandin F-2 alpha and isoprostanes F-2 exert potent biological activities (i.e., broncho- and vasoconstriction) in the: nanomolar range, PPF(1)s could potentially exert similar biological activities. Notably, fresh birch pollen, which ran easily be inhaled, contains exceedingly high concentrations (32,440 ng/g) of free PPF(1)s. (C) 2000 Elsevier Science Inc.