Effect of dietary fish oil on development and selected functions of murine inflammatory macrophages.

Inflammatory macrophages from mice fed diets containing menhaden fish oil (MFO) have a reduced capacity for cytotoxicity of mastocytoma cells upon activation with interferon-gamma (IFN gamma) and lipopolysaccharide due to an altered responsiveness to IFN gamma. In an effort to elucidate further how dietary MFO effects macrophage function, we have studied the maturation of inflammatory macrophages from mice fed MFO compared with mice fed safflower oil (SFO) using several processes that serve as markers of the activational state. No significant differences in the recruitment or percentage of peritoneal exudate cells as macrophages after thioglycollate injection and no differences in spreading, binding, or phagocytosis of sheep erythrocytes or phagocytosis of yeast by inflammatory macrophages were observed when the dietary groups were compared. However, MFO macrophages had an altered capacity for peroxide release when stimulated with unopsonized zymosan (10-200 micrograms/ml). Furthermore, to elucidate how MFO feeding could alter IFN gamma-induced responses of inflammatory macrophages, we assessed phorbol-12-myristate-13-acetate-induced hydrogen peroxide production and expression of class II MHC determinants (Ia). There were no differences between macrophages from mice fed the two diets with respect to the production of peroxide when they were preincubated with 0.1-10 U/ml of IFN gamma. However, MFO macrophages had greater peroxide production after enhancement with 100 U/ml of IFN gamma. With respect to Ia induction, the percentage of macrophages responding to IFN gamma was not altered by diet, and there were no differences in expression of Ia induced by 24 hr exposure to IFN gamma. Thus the differential effect of MFO compared with SFO is probably mediated not by an alteration in the maturation of inflammatory macrophages but rather through the alteration of IFN gamma-induced functions such as peroxide production.

Dietary manipulation of macrophage phospholipid classes: selective increase of dihomogammalinolenic acid.

Because alterations in the dietary content of fatty acids are an important method for modulating macrophage eicosanoid production, we have quantitated the levels of n-6 and n-3 polyunsaturated fatty acids in peritoneal macrophage individual phospholipids from mice fed diets (3 wk) with either safflower oil (SAF), predominantly containing 18:2n-6, borage (BOR) containing 18:2n-6 and 18:3n-6, fish (MFO) containing 20:5n-3 and 22:6n-3, and borage/fish mixture (MIX) containing 18:2n-6, 18:3n-6, 20:5n-3 and 22:6n-3. Dietary n-3 fatty acids were readily incorporated into macrophage phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI). The increase in n-3 fatty acid levels was accompanied by a decrease in the absolute levels of 18:2n-6, 20:4n-6 and 22:4n-6 in PC, PE and PS. Interestingly, PI 20:4n-6 levels were not significantly lowered (P greater than 0.05) in MIX and MFO macrophages relative to SAF and BOR. These data demonstrate the unique ability of this phospholipid to selectively maintain its 20:4n-6 levels. In BOR and MIX animals, 20:3n-6 levels were significantly increased (P less than 0.05) in all phospholipids relative to SAF and MFO. The combination of borage and fish oils (MIX diet) produced the highest 20:3n-6/20:4n-6 ratio in all phospholipids. These data show that the macrophage eicosanoid precursor levels of 20:3n-6, 20:4n-6 and n-3 acids can be selectively manipulated through the use of specific dietary regimens. This is noteworthy because an increase in phospholipid levels of 20:3n-6 and 20:5n-3, while concomitantly reducing 20:4n-6, may have therapeutic potential in treating inflammatory disorders.

Fatty acid composition of macrophage phospholipids in mice fed fish or borage oil.

The polyunsaturated fatty acid (PUFA) composition of murine peritoneal macrophage phospholipids was dramatically altered in vivo following the four-wk feeding of specific dietary oils. Fish oil (containing 20:5n-3 and 22:6n-3) feeding significantly increased macrophage 20:5n-3, 22:5n-3, and 22:6n-3 (P less than 0.05), while borage oil (containing 18:2n-6 and 18:3n-6) increased (P less than 0.05) the macrophage 20:3n-6/20:4n-6 ratio, relative to safflower oil (containing 18:2n-6) and hydrogenated coconut oil (containing 12:0)-fed animals. The macrophage phospholipid PUFA profiles were compared with those of the liver, lung and spleen. The significance of the PUFA alterations is discussed.