Dietary Ratio of (n-6)/(n-3) Polyunsaturated Fatty Acids Alters the Fatty Acid Composition of Bone Compartments and Biomarkers of Bone Formation in Rats

Abstract

The effects of dietary polyunsaturated fatty acids (PUFA) on ex vivo bone prostaglandin E₂ (PGE₂) production and bone formation rate were evaluated in rats. Weanling male Sprague-Dawley rats were fed AIN-93G diet containing 70 g/kg of added fat for 42 d. The dietary lipid treatments were formulated with safflower oil and menhaden oil to provide the following ratios of (n-6)/(n-3) fatty acids: 23.8 (SMI), 9.8 (SMII), 2.6 (SMIII), and 1.2 (SMIV). Ex vivo PGE₂ production in liver homogenates and bone organ cultures (right femur and tibia) were significantly lower in rats fed diets with a lower dietary ratio of (n-6)/(n-3) fatty acids than in those fed diets with a higher dietary ratio. Regression analysis revealed a significant positive correlation between bone PGE₂ and the ratio of arachidonic acid (AA)/eicosapentaenoic acid (EPA), but significant negative correlations between bone formation rate and either the ratio of AA/EPA or PGE₂ in bone. Activities of serum alkaline phosphatase isoenzymes, including the bone-specific isoenzyme (BALP), were greater in rats fed a diet high in (n-3) or a low ratio of (n-6)/(n-3), further supporting the positive action of (n-3) fatty acids on bone formation. These results demonstrated that the dietary ratio of (n-6)/(n-3) modulates bone PGE₂ production and the activity of serum BALP in growing rats.