Effect of dietary supplementation with n-3 polyunsaturated fatty acids on physical properties and metabolism of low density lipoprotein in humans

Abstract

The effects of marine n-3 polyunsaturated fatty acids were investigated in relation to the chemical and physical properties of low density lipoprotein (LDL) and how these changes affected LDL metabolism in humans. The subjects received supplements of six capsules daily, each capsule containing 1g of either highly concentrated ethyl esters of n-3 fatty acids (85% eicosapentaenoic acid and docosahexaenoic acid) (n=12) or corn oil (56% linoleic and 26% oleic acid) (n=11). After 4 months of oil supplementation, the following changes were observed in the lipid moiety of the n-3-enriched LDL particles compared with LDL from the corn oil group: LDL choiesteryl ester, as well as the amount of total lipids of LDL, was significantly lower (0.97±0.12 versus 1.19±0.23 mg/mg protein and 1.88±0.40 versus 2.45±0.31 mg/mg, respectively; mean±SD, n=6, p<0.05); the amount of eicosapentaenoic and docosahexaenoic acids and the unsaturation index increased (104.0 versus 29.4 μg/mg protein and 6.64 versus 5.49, respectively); and differential scanning calorimetry showed that LDL cholesteryl ester melting temperature was lowered by 2°C (27.6±0.8° versus 29.5±0.2°C). The only effect observed on the protein moiety was an increase in the ratio of apolipoprotein (apo) B to cholesterol (0.66±0.17 versus 0.82±0.14 mg/mg cholesterol; p<0.05). Circular dichroism spectra of LDL indicated an α-helix content of 46±5% in apo B from both groups. No difference was observed by 13C nuclear magnetic resonance spectroscopy in the ratio of "active" to "normal" lysine residues of apo B. No detectable differences in the size of n-3 fatty acid-enriched LDL particles versus control LDL could be measured by either electron microscopy of negatively stained LDL (24.5±2.0 versus 25.0±1.5 nm) or dynamic light scattering (24.9±0.9 versus 24.9±0.4 nm). LDL from the fish oil and corn oil groups showed similar susceptibility to Cu2+-catalyzed lipid peroxidation, as indicated by the amount of lipid peroxides formed during the oxidation time, and degradation of oxidatively modified LDL in J774 macrophages as a function of Cu2+ oxidation time. No effect of n-3 fatty acids was observed on LDL metabolism. Specific uptake and degradation of n-3 fatty acid-enriched LDL were similar to those for control LDL in HepG2 cells as well as in human skin fibroblasts, and they showed the same ability to stimulate cholesteryl ester synthesis. Peripheral blood mononuclear cells from the two supplementation groups were able to take up a similar amount of LDL regardless of the source of LDL. No difference was observed with respect to the amount of mRNA specific for the LDL receptor, LDL receptor-related protein, and 3-hydroxy-3-methylglutaryl coenzyme A reductase in the peripheral blood mononuclear cells. We conclude that marine n-3 polyunsaturated fatty acids induced some changes in the lipid moiety of LDL; however, these changes had no measurable effect on the cellular metabolism of LDL. (Arteriosclerosis and Thrombosis 1992;12:369-379).