PGE2 production is suppressed by chemically-synthesized Δ7-eicosatrienoic acid in macrophages through the competitive inhibition of COX-2

Δ7-Eicosatrienoic acid (Δ7-ETrA; Δ7,11,14-20:3), an elongation metabolite of pinolenic acid (PNA; Δ5,9,12-18:3), is a rare polyunsaturated fatty acid (PUFA) originally from pine seeds. Incorporation of PNA and Δ7-ETrA into murine macrophages inhibited lipopolysaccharide (LPS)-stimulated prostaglandin E2 (PGE2) production. Due to the lack of availability of the naturally-occurring fatty acid, we synthesized Δ7-ETrA and demonstrated it was capable of suppressing PGE2 production. Using laboratory synthetic techniques involving 2-carbon elongation and argentated column chromatography, Δ7-ETrA was synthesized and isolated. Its identity and purity (>98%) were confirmed by gas chromatography (GC)/GC-mass spectroscopy. Incubation of murine RAW264.7 cells or rat primary peritoneal macrophages with Δ7-ETrA reduced PGE2 production by up to 84%, but slightly down-regulated type-2 cyclooxygenase (COX-2) expression. Δ7-ETrA blocked nuclear factor-kappa B (NF-κB) translocation into nucleus and inactivated mitogen-activated protein kinases (MAPK), however, these results might not directly account for its inhibitory effect. Furthermore, PGE2 production reduced by Δ7-ETrA was highly correlated with the extent of Δ7-ETrA incorporation into cellular phospholipids and appeared to be the result of competition between this unusual fatty acid and arachidonic acid (AA) for COX-2. In conclusion, Δ7-ETrA incorporation suppresses PGE2 production by macrophages through competition between Δ7-ETrA and AA for COX-2.