Comparative effects of ω-3 and ω-6 polyunsaturated fatty acids on protein metabolism in rats bearing the mammary adenocarcinoma

Abstract

The comparative effects of diets containing 20% (wt/wt) of either fish oil (FO) or safflower oil (SO) on protein synthesis and catabolism were determined in rats bearing the 7,12-dimethylbenz(a)anthracene (DMBA) 13762 mammary adenocarcinoma in vivo using a 6-hour constant infusion of L-(1-14C)-leucine. Tumor-bearing animals fed FO had significantly lower tumor growth rate (36 ± 0.5 v 53 ± 0.7%/d, P < .05), total tumor protein synthesis (Ts) (1.25 ± 0.1 v 1.85 ± 0.1 μmol/h, P < .05), and tumor protein concentration (12.0 ± 0.5 v 14.0 ± 0.7%/d, P < 0.01). Tumor fractional synthetic rate and total protein breakdown rate of the tumor were unaffected by FO feeding. Both tumor-bearing and saline-control animals fed FO had significantly (P < .01) lower liver fractional synthetic rate and total protein breakdown rate, and higher liver total protein compared with SO-fed rats. Muscle protein kinetics were unaffected by either treatment or diet. Whole body protein kinetics were not affected by dietary treatment, but the presence of tumor significantly (P < .001) reduced whole body flux, synthesis, breakdown, and oxidation. Chronic FO feeding for 7 weeks significantly (P < .001) lowered ω-6 polyunsaturated fatty acids (ω-6 PUFAs) and significantly elevated ω-3 polyunsaturated fatty acids (ω-3 PUFAs) (P < .001) in both plasma phospholipid and triglycerides. The present study indicates that dietary FO can modulate mammary tumor growth in a manner that reflects changes in protein metabolism in both host and tumor tissues.