Utilization of dihomo-gamma-linolenic acid (8,11,14-eicosatrienoic acid) by murine peritoneal macrophages

This study examined the metabolism of dihomo-gamma-linolenic acid (20:3(n-6] in casein-elicited murine peritoneal macrophages. Cells were incubated with [14C]20:3(n-6) in the presence of 1% fetal bovine serum (FBS) or 0.025% bovine serum albumin (BSA), and the distribution and identity of membrane-bound and soluble products were determined. Approx. 70-80% of the [14C]20:3(n-6) was recovered in membrane phospholipids. The distribution of radiolabel in individual cellular phospholipids revealed a time-dependent (6 vs. 16 h) increase in the percentage of radiolabel esterified to phosphatidylethanolamine (PE). Analysis of cellular total lipids following transmethylation indicated that approx. 4, 2 and 9% of the incorporated 20:3(n-6), respectively, had been desaturated and elongated into 20:4(n-6), 22:4(n-6) and 22:3(n-6). When cells prelabeled for 16 h were incubated in the presence of the divalent cation ionophore, A23187, or zymosan for 30-60 min, two radiolabeled metabolites were isolated in the incubation supernatant. These metabolites were identified as 12-hydroxy-8,10,14- and 15-hydroxy-8,11,13-eicosatrienoic acids, as determined by reverse-phase and normal-phase high-performance liquid chromatography. The generation of monohydroxy fatty acids was notably absent in prelabeled quiescent cells and A23187-stimulated cells incubated with BW755C, a dual cyclooxygenase and lipoxygenase inhibitor. We conclude that casein-elicited murine peritoneal macrophages can extensively metabolize 20:3(n-6) through delta 5-desaturase, elongase and oxygenation reactions.