Mouse Peritoneal Macrophage Prostaglandin E1 Synthesis is Altered by Dietary Gamma-Linolenic Acid

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Abstract
The ability of dietary gamma-linolenic acid [18:3(n-6)] to modulate prostaglandin biosynthesis in mouse resident peritoneal macrophages was determined. Mice were fed diets containing corn oil, borage oil or evening primrose oil or a mixture of borage and fish oils. After 2 wk, resident peritoneal macrophages were isolated and stimulated with unopsonized zymosan to induce prostaglandin synthesis. Borage oil, primrose oil and fish-borage oil mixture dietary groups (containing 25.6, 11.9 and 19.5 g γ-linolenic acid/100 g fatty acids, respectively) had significantly (P < 0.05) enhanced prostaglandin E1 synthesis (39.7, 29.4 and 73.0 nmol prostaglandin E1/mg protein, respectively) compared with corn oil-fed (containing 1/mg protein. Borage oil- and fish-borage oil mixture-fed mice had the highest biosynthetic ratio of prostaglandin E1/prostaglandin E2 (E1/E2 ≈ 0.2). Macrophages from borage oil-fed mice synthesized the lowest amount of prostacyclin (198.7 nmol 6-keto-prostaglandin F1α/mg protein) compared with corn oil-, primrose oil- and fish-borage oil mixture-fed mice (379.7, 764.8 and 384.2 nmol 6-keto-prostaglandin F1α/mg protein, respectively). In addition, borage oil-, primrose oil- and fish-borage oil mixture-fed mice had significantly (P < 0.05) higher levels of dihomo-γ-linolenic acid [20:3(n-6)] in membrane phospholipids (5.5, 3.5 and 5.7 mol/100 mol, respectively) relative to corn oil-fed mice (2.0 mol/100 mol). These results indicate that mouse peritoneal macrophages elongate dietary γ-linolenic acid to dihomo-γ-linolenic acid, and upon stimulation, convert dihomo-γ-linolenic acid to prostaglandin E1, an eicosanoid with anti-aggregatory, anti-inflammatory properties.