Formation of isoprostane F(2)-like compounds (phytoprostanes F(1)) from alpha-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 dinor 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 chromatography-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 PPF(1) levels increased dramatically by 15- to 263-fold. Because the structurally related prostaglandin F(2alpha) 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 can easily be inhaled, contains exceedingly high concentrations (32,440 ng/g) of free PPF(1)s.