Retardation of atherogenesis and other effects of a fish oil additive to a hyperlipidemic diet for swine

Effect of n-3 fatty acids on the composition and binding properties of lipoproteins in hypertriglyceridemic patients

BACKGROUND

Treatment of hyperlipidemic patients with fish oil results in an increase in plasma LDL cholesterol despite a marked decrease in the LDL precursor, VLDL.

OBJECTIVE

We studied the relation between VLDL composition and LDL concentrations.

DESIGN

Fourteen hypertriglyceridemic patients were treated with encapsulated fish oil (containing 1.45 g eicosapentaenoic acid and 1. 55 g docosahexaenoic acid/d) for 4 wk. Venous blood samples were collected before and after treatment. Eleven normolipidemic subjects served as a control group.

RESULTS

Fish oil effectively lowered plasma lipid and apolipoprotein (apo) E concentrations in the hypertriglyceridemic patients, whereas apo B concentrations increased. The lipid and apolipoprotein content of VLDL decreased, whereas LDL cholesterol and LDL apo B increased. Fractionation of VLDL by heparin-affinity chromatography showed that before treatment hypertriglyceridemic patients had more VLDL in the 0.05-mol NaCl/L subfraction and less in the 0.20-mol/L subfraction than did control subjects (P < 0.05), whereas the subfraction distribution pattern was normalized after fish-oil treatment. Nevertheless, plasma concentrations of the 0.05-mol NaCl/L subfraction were decreased and those of the 0.20-mol/L subfraction were increased in hypertriglyceridemic patients after fish-oil treatment (P < 0.05). Fish-oil treatment both enhanced VLDL binding and lowered LDL binding to fibroblasts.

CONCLUSION

Treatment of hypertriglyceridemic patients with fish oil caused differential effects on VLDL subfractions and decreased LDL binding to fibroblast receptors, which may have contributed to the paradoxical increase in LDL-cholesterol concentrations.

Increased n-3 polyunsaturated fatty acid content of red blood cells from fish oil-fed rabbits increases in vitro lipid peroxidation, but decreases hemolysis

In view of a possible relationship between fish oil, lipid peroxidation, and atherosclerosis, the in vitro lipid peroxidation susceptibility of red blood cells (RBCs) from rabbits on conventional (-FO) and fish oil-enriched diets (+FO) was investigated. The diet caused substantial increases in the RBC concentrations of n-3 polyunsaturated fatty acids (PUFAs), in combination with decreases in the concentration of oleic acid (18:1) and linoleic acid (18:2). Cumene hydroperoxide-induced oxidative stress led to increased overall fatty acid peroxidation in +FO RBCs compared with with -FO RBCs, as quantitated by GLC fatty acid analysis. However, the increased overall susceptibility to lipid peroxidation of +FO RBCs was not reflected in increased peroxidation of every individual fatty acid. This was observed for endogenous arachidonic acid (20:4) as well as, in separate experiments, for exogenously added parinaric acid (PnA). The increased cumene hydroperoxide-induced PUFA oxidation in +FO RBCs was accompanied by a lesser extent of hemolysis. To account for these observations, it is proposed that the increased n-3 PUFA content of +FO RBCs serves as an oxidizable buffer. The present data suggest that oxidation of fatty acids can occur until a critically low level of intact phospholipid in the RBC membrane is reached, after which the membrane destabilizes and hemolysis occurs. At the same time, the PUFA buffer in +FO RBCs could also prevent oxidative damage to specific membrane proteins, which could also help prevent cell lysis.