Effect of dietary fat saturation and cholesterol on low density lipoprotein degradation by mononuclear cells of Cebus monkeys.

The mechanism by which dietary unsaturated fatty acids lower low density lipoprotein (LDL) cholesterol is unknown. Unsaturated fatty acids incorporated into the cell membrane can increase membrane fluidity and, as a result, dramatically alter membrane-dependent cell functions. Therefore, we examined the effect of long-term dietary consumption of corn oil and coconut oil with and without cholesterol in amounts equivalent to those of a typical Western diet on the degradation of human LDL by peripheral blood mononuclear cells in Cebus albifrons monkeys. Cellular LDL degradation was dramatically enhanced in the mononuclear cells isolated from animals fed corn oil in comparison with those from animals fed coconut oil. The addition of cholesterol to the diets resulted in a slight attenuation of LDL degradation in the corn oil group while no effect was noted in the coconut oil group. Crossover LDL binding and degradation experiments with LDL isolated from animals fed corn oil diets and coconut oil diets demonstrated increased binding and degradation of LDL in mononuclear cells from animals fed corn oil diets. Enhanced mononuclear cell LDL degradation was accompanied by increased cellular cis-unsaturated fatty acyl content, increased membrane fluidity, and decreased plasma cholesterol. Increased cellular cis-unsaturated fatty acyl content with its concomitant increase in membrane fluidity mirrored the dietary lipid profile of the host animal. A linear relationship was observed between cellular LDL degradation and both cellular cis-unsaturated fatty acyl content and membrane fluidity. These observations parallel results noted in whole-animal LDL catabolic studies with these same animals described elsewhere. These data suggest a novel mechanism by which dietary unsaturated fatty acids exert their LDL-lowering effect.