DIETARY-FAT SATURATION IN RHESUS-MONKEYS AFFECTS LDL CONCENTRATIONS BY MODULATING THE INDEPENDENT PRODUCTION OF LDL APOLIPOPROTEIN-B

In a recent study from this laboratory, rhesus monkeys fed a 90% palm oil/10% soybean oil-containing diet (PS), rich in 16:0 and 18:1 fatty acids, had decreased total and LDL cholesterol concentrations compared to monkeys fed a 90% coconut oil/10% soybean oil-containing diet (CS), rich in 12:0 and 14:0 fatty acids. To investigate the metabolic basis of these changes, homologous I-125-VLDL and I-131-LDL were injected simultaneously into eight monkeys (four per dietary group). Analysis of apo B specific activity curves revealed that PS monkeys had an increased pool size of VLDL apo B (P < 0.02), a 3-fold increase in the total VLDL apo B transport rate (P < 0.001), a decreased pool size of LDL apo B (P < 0.01) and a 2-fold decrease in the total transport rate of LDL apo B (P < 0.001), while the irreversible FCR for VLDL apo B and LDL apo B was similar between dietary groups. PS monkeys derived a greater percentage of LDL apo B from VLDL catabolism resulting in a greater transport rate of LDL apo B from VLDL catabolism (P < 0.055), in comparison to CS monkeys. For CS monkeys the proportion as well as the amount of LDL apo B derived from VLDL-independent catabolism (i.e., LDL apo B derived from sources other than VLDL catabolism) was higher (P < 0.001) than the values obtained in PS monkeys. In both dietary groups the proportion of VLDL apo B converted to LDL apo B was similar, although the absolute amount was higher for the PS monkeys (P < 0.06). The proportion of VLDL apo B directly removed from the circulation was similar for both dietary groups, with the absolute amount being higher for the PS monkeys (P < 0.001). Consistent with the lower pool size of LDL apo B and the higher pool size of VLDL apo B observed in PS monkeys, plasma and LDL cholesterol concentrations tended to be lower, whereas plasma triacylglycerol and VLDL cholesterol concentrations tended to be higher, but these changes were not statistically significant. Although total apo B and VLDL apo B transport rates were increased 2-3-fold in PS monkeys, LDL apo B concentration was reduced by 40% (P < 0.02) attributed to a significant reduction in the mass and proportion of LDL apo B derived independent of VLDL catabolism. The current study indicates that the saturation of dietary fat has distinct affects on VLDL-dependent and VLDL-independent transport of LDL apo B in the rhesus.