Uptake and incorporation of pinolenic acid reduces n-6 polyunsaturated fatty acid and downstream prostaglandin formation in murine macrophage

Many reports have shown the beneficial effects of consumption of pine seeds and pine seed oil. However, few studies have examined the biological effect of pinolenic acid (PNA; δ5,9,12-18:3), the main fatty acid in pine seed oil. In this study, using murine macrophage RAW264.7 cells as a model, we examined the effect of PNA on polyunsaturated fatty acid (PUFA) metabolism, prostaglandin (PG) biosynthesis and cyclooxygenase-2 (COX-2) expression. Results showed that PNA was readily taken up, incorporated and elongated to form eicosatrienoic acid (ETrA, δ7,11,14-20:3) in macrophage cells. A small portion of this elongated metabolite was further elongated to form δ9,13,16-22:3. The degree of incorporation of PNA and its metabolites into cellular phospholipids varied with the length of incubation time and the concentration of PNA in the medium. Incubation of PNA also modified the fatty acid profile of phospholipids: the levels of 18- and 20-carbon PUFA were significantly decreased, whereas those of 22-carbon fatty acids increased. This finding suggests that PNA enhances the elongation of 20-carbon fatty acids to 22-carbon fatty acids. The syntheses of PGE₁ from dihomo-γ-linolenic acid (DGLA, δ8,11,14-20:4) and PGE₂ from arachidonic acid (ARA, δ5,8,11,14-20:4) were also suppressed by the presence of PNA and its metabolite. As the expression of COX-2 was not suppressed, the inhibitory effect of PNA on PG activity was attributed in part to substrate competition between the PNA metabolite (i.e., δ7,11,14-20:3) and DGLA (or ARA).