Replacing Dietary Palmitic Acid with Elaidic Acid (t-C18:1Δ9) Depresses HDL and Increases CETP Activity in Cebus Monkeys

Abstract

The question whether dietary trans fatty acids affect lipoprotein metabolism similarly to specific saturated fatty acids was investigated in 11 normolipemic cebus monkeys by exchanging 5% dietary energy (%en) between elaidic (t-C18:1 delta9) and palmitic acid (16:0) in two test diets (30%en fat + 100 mg cholesterol/1000 kcal diet) conforming to the American Heart Association (AHA) Step 1 guidelines. These were compared with a normal control diet rich in saturated fat and cholesterol (38%en fat + 180 mg cholesterol/1000 kcal diet). The control diet was fed initially for 14 wk, followed by each of the the two test diets in a crossover design. Plasma lipid concentrations were determined four times between the 6th and 14th wk. Turnover studies (using 125I-HDL and 131I-LDL) were conducted after 9 wk in each dietary period. Relative to the control diet, both test diets significantly reduced plasma total cholesterol (TC), HDL cholesterol (HDL-C) and VLDL plus LDL cholesterol (LDL-C) concentrations; triglyceride (TG) concentrations tended to be lower. However, the trans diet resulted in a significantly greater reduction in HDL-C than the palmitate diet (124 +/- 17, 117 +/- 18 and 106 +/- 13 mg/dL for the control, palmitate and trans diets, respectively). The palmitate diet significantly decreased the TC/HDL-C ratio by 11% when compared with the control diet (1.68 +/- 0.17 vs. 1.89 +/- 0.30), whereas the trans diet had no effect (1.81 +/- 0.20 vs. 1.89 +/- 0.30). Kinetic studies revealed that, relative to the control diet, both test diets significantly lowered the LDL apolipoprotein B (apoB) pool size, principally reflecting an increase in the LDL apoB fractional catabolic rate (FCR) related to the reduced cholesterol intake. Between the two test diets, no significant differences in LDL kinetic parameters were observed. Both test diets significantly decreased HDL apoA1 concentrations in comparison with the control diet, which was partly explained by an increase in the fractional catabolic rate of HDL. Of the two test diets, the trans diet was associated with a 9.5% greater HDL FCR than the palmitate diet (P < 0.08) and a significant increase in plasma cholesteryl ester transfer protein (CETP) activity (% transfer 114 +/- 7 vs. 91 +/- 7; P < 0.03). Thus, palmitic acid- and elaidic acid-rich diets produced identical effects on LDL metabolism in normocholesterolemic cebus monkeys fed diets with low levels of cholesterol, whereas elaidic acid depressed HDL-C, attributable to both increased CETP activity and HDL clearance.