Intermediate Density Lipoprotein Fractions Research Articles

Increased cholesterol concentration in intermediate density lipoprotein fraction of normolipidemic non-insulin-dependent diabetics

There is increasing agreement about the atherogenicity of intermediate density lipoprotein (IDL). In order to determine whether normocholesterolemic diabetics are at a higher risk of atherosclerosis, cholesterol concentrations in three subclasses of triglyceride-rich lipoprotein fraction ( S f 12–400) were examined. Their plasma triglyceride and cholesterol levels were limited to below 150 and 250 mg/dl, respectively. They were divided into 3 groups according to their treatment: insulin injection (group I), sulphonylurea (group S) and diet alone (group D). Age-matched healthy normolipidemic non-obese subjects served as controls (group C). Triglyceride-rich lipoproteins were separated by ultracentrifugation: very low density lipoprotein (VLDL), S f 60–400; intermediate density lipoprotein, (IDL 1), S f 20–60; IDL 2; S f 12–20. Cholesterol concentrations in total plasma, VLDL, IDL 2 and high density lipoprotein (HDL) were all identical in every group. A significant increase in cholesterol concentration was found in IDL 1 of groups S and D. Low density lipoprotein-cholesterol of group I was also increased. These findings indicate an increased risk factor in normolipidemic diabetics.

Increased factor VII coagulant activity in the rabbit following diet-induced hypercholesterolaemia: Evidence for increased conversion of VII to αVII a a and higher flux within the coagulation pathway

Factor VII coagulant activity (VIII) is considerably higher in rabbits fed a 1% cholesterol-supplemented diet than in rabbits fed a standard diet. This increase was statistically significant 4–6 days from the beginning of treatment and rose to about 300% during the 100 days of treatment. Treatment is also associated with a 20-fold increase in plasma cholesterol concentration with the major fraction of excess cholesterol associated with the very low and intermediate density lipoprotein fractions. In both groups of rabbits, the direction and extent of variation in VIII generally coincided with variation in cholesterol. so that over time there were significant and positive correlations between plasma cholesterol concentration in both the rabbits fed the standard diet and the rabbits fed the cholesterol-supplemented diet. The increase in VIIc was due to a higher proportion of the more active aVIIin the plasma of hypercholesterolaemic rabbits rather than to an increase in the concentration of the single-chain protein. The plasma concentration of factor X and prothrombin had increased in the hypercholesterolaemic rabbits by 10 days from the beginning of treatment and both proteins were maintained at 150–200% of the concentrations in the plasma of rabbits fed the standard diet. However, these differences were only seen when the factor X and prothrombin were assayed using synthetic substrates. The specific coagulation assays for these two factors revealed no differences between the groups of animals up to 100 days.

Lipoprotein levels in genetically selected mice with increased susceptibility to atherosclerosis.

Male mice of two inbred strains, C57BR/cdJ and CBA/J, were maintained either on an atherogenic diet rich in cholesterol (5%) and saturated fat (30%) or on a control Purina Laboratory Chow diet. After 3 weeks on a 90% atherogenic/10% chow diet, the C57BR/cdJ mice showed a fivefold increase in plasma total cholesterol levels, while the CBA/J strain indicated only a twofold increase. On the atherogenic diet, both groups of animals showed marked increases in a lipoprotein of a broad density spectrum (1.006 greater than d less than 1.063) with prebeta and beta mobility on agarose gel electrophoresis, but the C57BR/cdJ strain showed a greater increase than the CBA/J strain. The very low density lipoprotein (VLDL) contained predominantly lipoprotein of prebeta mobility, while intermediate density lipoprotein (IDL) and low density lipoprotein (LDL) contained lipoprotein of beta-mobility. In both strains, the major lipid component in this lipoprotein was cholesteryl ester and both strains showed large amounts of an apoprotein (apo) with E mobility as defined for known apoproteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis or by isoelectric focusing on polyacrylamide-urea disc gels. The phosphatidylcholine/free cholesterol ratio of the VLDL, IDL, and LDL fractions isolated from the C57BR/cdJ mice on the atherogenic diet (0.76 to 0.95) was noticeably lower than that (1.10 to 1.19) from the CBA/J mice maintained on the same diet. There was a marked decrease in the high density lipoprotein (HDL) fraction in both strains of mice on the atherogenic diet, but a greater reduction in the HDL level of the C57BR/cdJ strain with a 50% decrease in the phosphatidylcholine/free cholesterol ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of protein and carbohydrate type on serum and liver lipids and lipoprotein cholesterol in rabbits.

The non-lipid portions of semi-synthetic diets appear to be important determinants of hypercholesterolemia and atherosclerosis in the rabbit. Serum and liver lipid concentrations were determined in rabbits which had been pair-fed various protein (casein or soy protein isolate) and carbohydrate (sucrose or dextrose) sources as part of low fat, low cholesterol, semi-synthetic diets. It was verified that casein-containing diets render rabbits hypercholesterolemic, while soy protein caused a degree of hypocholesterolemia. Additionally, sucrose, when fed in conjunction with casein, appears to augment this hypercholesterolemic effect. The distribution of total cholesterol among lipoprotein subclasses was increased in both the intermediate density lipoprotein (IDL) (1.006-1.019 g/ml) and low density lipoprotein (LDL) (1.019-1.063 g/ml) fractions and decreased in the high density lipoprotein (HDL) (1.063-1.21 g/ml) fraction when casein is fed. Soy protein feeding caused relatively more cholesterol to appear only in the IDL fraction when compared with commercial chow fed rabbits. Reasons for these differences may involve the saturation or suppression of endogenous lipoprotein hepatic receptors.

Serum lipids, “double pre-beta lipoproteinemia,” and distribution of the apo-very-low-density (VLDL) lipoprotein peptides in hypothyroid patients before and after substitution therapy

Thirty-six hypothyroid patients had total thyroidectomy for cancer. Thirty of them were studied before and during hormone replacement therapy, 1-1 .1 μg/kg triiodothyronine (T 3) per day. Mean treatment period was 90 days. During treatment mean serum total cholesterol (TC), triglycerides (TG), the ratio of TC to TG in very-low-density lipoprotein and the prevalence of the “double pre-beta VLDL lipoproteinemia” (Double-PBL) were significantly reduced as compared to the pretreatment values. The VLDL peptides were separated by isoelectric focusing (IEF) in polyacrylamide gel. The relative content of apolipoprotein E (arginine-rich apoprotein) and the E C-peptides ratio were significantly reduced after T 3 therapy. On the contrary, the content of C II peptide was significantly increased. Apoprotein E was positively correlated with serum TC. The proportion of the intermediate density lipoprotein fraction, evaluated by agarose gel electrophoresis, consistently decreased after treatment. The results of our study suggest that thyroid hormones affect the metabolism of remnant lipoproteins.