Polyacrylamide gels of increasing concentration gradient for the electrophoresis of lipoproteins

Fractionation of bovine serum lipoproteins and their characterization by gradient gel electrophoresis

Bovine serum lipoproteins were fractionated by precipitation with dextran sulphate followed by ultracentrifugation and were examined by paper electrophoresis and by disk electophoresis in acrylamide gels. Gels containing concentration gradients of both sucrose and acrylamide gave better resolution of lipoproteins than did gels of uniform composition or gels with a concentration gradient of sucrose and a uniform concentration of acrylamide.

The densities of the lipoprotein classes isolated (listed in order of increasing mobility on electrophoresis in acrylamide gels) were as follows:

I, d < 1·019; II, 1·039 <d<1·050;

III, 1·019 <d<1·039; IVa and IVb, d > 1·050.

Lipoproteins of classes I, II and III were precipitated by dextran sulphate. On paper electrophoresis, lipoproteins of class II had β mobility and lipoproteins of classes IVa and IVb had α mobility. Lipoproteins of class I remained at the origin.

The lipoprotein classes of bovine sera resembled those of sheep and goat sera in that class IV predominated. In contrast, the sera of several non-ruminant species showed a predominance of lipoprotein classes of low electrophoretic mobility.

Low-density-lipoprotein peak particle size in a Mediterranean population

BACKGROUND

The predominance of small, dense low-density lipoprotein (LDL) particles ('LDL phenotype B') has been associated with a three-fold increased risk of myocardial infarction, but the feasibility of the identification of small, dense LDL as independent predictors of coronary artery disease risk in population studies remains questioned. Design We evaluated the LDL peak particle size and its relation with other established risk factors for coronary heart disease in a group of 156 randomized subjects living on the Mediterranean island of Ustica (71 males and 85 women, range of age 20-69 years), representing approximately 30% of the total population.

RESULTS

The prevalence of LDL phenotype B subjects was low (approximately 15% in both men and women) and there was a clear trend for both genders in reducing the LDL peak particle size with age. Moreover, LDL phenotype B subjects had higher BMI values, prevalence of diabetes and plasma triglyceride (TG) levels and lower plasma HDL-C concentrations in comparison with LDL phenotype A individuals; in a multivariate analysis, plasma TG levels were the only variable independently associated with LDL peak particle size.

CONCLUSIONS

In this population, which appears to be somewhat protected by premature coronary artery disease, a low prevalence of the LDL pattern B was found in both men and women, and plasma TG could have a key role in regulating the LDL peak particle size. The follow up, still ongoing, will provide useful information on the predictive role of LDL peak particle size on cardiovascular risk, at least in a low-risk population.

Advances in agarose gel electrophoresis of serum lipoproteins

Agarose gel electrophoresis has been extensively employed by researchers to gain a greater understanding of lipoprotein biology and its relationship to cardiovascular disease. Advances in this technique have been made in the visualization and quantitation of separated lipoproteins, in the use of agarose gel electrophoresis for detection and quantitation of apolipoproteins of the separated lipoproteins, and in the detection of lipoprotein heterogeneity. Agarose gel electrophoresis has been employed for two-dimensional electrophoretic analysis of lipoproteins as well as in several different methods which probe the immunological properties of lipoproteins. Agarose gel electrophoresis has thus become an important tool in the study of serum lipoproteins in both clinical and basic science laboratories.

Gradient acrylamide/agarose gels for electrophoretic separation of intact human very low density lipoproteins, intermediate density lipoproteins, lipoprotein a, and low density lipoproteins

An exponential gradient gel with 0-10% acrylamide and 0.5% agarose was developed for electrophoresis of intact high molecular weight lipoproteins. This system resolves very low density lipoproteins, intermediate density lipoproteins, lipoprotein a, and low density lipoproteins in a size-dependent fashion. The characteristic relative mobility of these species can be determined in relation to protein and colloidal gold reference materials. Electron microscopy of selected lipoprotein fractions confirmed that relative mobility was related to apparent lipoprotein diameter. The composite gel medium can be used with prestained lipoproteins and permits immunoelectroblotting for qualitative analysis of apolipoprotein constituents.

Monitoring of detergent binding to amphiphilic proteins by means of micelles containing the hydrophobic dye Sudan Black B

A simple method for detecting micellar binding of Triton X-100 to amphiphilic proteins is described. The hydrophobic dye Sudan Black B is incorporated into Triton micelles. Binding of the coloured micelles to serum apoliproteins, as well as to amphiphilic proteins, or erythrocyte and fat globule membranes renders these visible as dark bands after sucrose density gradient centrifugation. In contrast, the hydrophilic proteins present in lipoprotein-free serum do not show detergent binding. The method does not permit accurate quantification of detergent binding, but may serve as a pilot procedure for initial detection of amphiphilic proteins and for monitoring their isolation from crude solubilized membrane material. The sensitivity of the assay corresponds to that obtained with [3H]Triton X-100.

The separation of plasma lipoproteins using gel electrofocusing and polyacrylamide gradient gel electrophoresis

Polyacrylamide gel electrofocusing and gradient electrophoresis have been used to separate the lipoproteins in whole plasma and in fractions prepared by sequential flotation in the ultracentrifuge and by precipitation with dextran sulphate and manganous chloride. After the two-dimensional separation, high density lipoproteins appear as a zone showing noticeable heterogeneity with respect to both isoelectric point and molecular weight. Low density lipoproteins are resolved as a compact spot while very low density lipoproteins are visible as a long horizontal streak across the top of the electrophoresis gel. The implications of the technique for the analysis of lipoprotein patterns in pathological plasmas are discussed.

Lipoprotein pre-staining: comparison of nitroblue tetrazolium and Sudan Black B

Nitroblue tetrazolium and Sudan Black B have been compared as pre-staining agents for human serum lipoproteins, using acrylamide gel gradients. Results from Nitroblue tetrazolium staining should be used with caution for low and very low density lipoproteins, and further work appears necessary on the reaction with alpha-lipoproteins.

Familial hyper-HDL-(a)-cholesterolemia

In one family the mother, two children and a maternal aunt showed a hypercholesterolemic state characterized by a unusually high percentage of cholesterol in ultracentrifugally-recovered HDL-(a)-LP. An intensely stained a-band was present in all these subjects both in plasma and in ultracentrifugal fraction, with d greater than 1063. Symptoms or signs due to the hypercholesterolemic state were not present. The father was affected by Type IIA hypercholesterolemia. This lipid defect was also present in one of the two children.

Type 3 hyperlipoproteinaemia

Eighteen patients with type III hyperlipoproteinaemia, diagnosed on the basis of skin lesions, serum lipids, and lipoprotein electrophoresis, have been fully investigated over a period of 15 years. The incidence of coronary artery disease was only slightly increased, and was not increased at all among first-degree relatives. Peripheral occlusive arterial disease was probably more common. An increased incidence of carbohydrate intolerance was found in neither the patients nor their relatives. The effects of treatment on the skin were uniformly good.