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G Assmann

Publications and source records attributed to G Assmann.

At least 397 records · Page 22Linked to original sources
PubMed1983

Quantification of high-density-lipoprotein cholesterol by precipitation with phosphotungstic acid/MgCl2.

We evaluated the use of a modified phosphotungstic acid/MgCl2 precipitation procedure for the precipitation of apolipoprotein B-containing lipoproteins. Precipitation of these lipoproteins [very-low- and low-density lipoproteins, and lipoprotein (a)] is complete, with negligible coprecipitation of high-density lipoprotein subfractions (HDL1, HDL2, HDL3), even in hypertriglyceridemic sera. In comparison with ultracentrifugation, the precipitation method yields, on the average, values that are 0.17 mmol/L lower for cholesterol values but almost identical for apolipoprotein A-I and phosphatidylcholine. Looking for delta 3,5-cholestadiene formed from cholesterol in the precipitation residue, we used "high-performance" liquid chromatography and "high-performance" thin-layer chromatography and found none.

Apolipoproteins↗
PubMed1983

Densitometry of phosphatidylcholine and sphingomyelin in high-density lipoproteins.

We describe the quantitative densitometric determination of phosphatidylcholine (PC) and sphingomyelin (SP) in human serum after precipitation with phosphotungstic acid/MgCl2 and use of thin-layer chromatography. After development, chromatographic plates were charred with methanolic sulfuric acid and MnCl2 and scanned by direct reflectance densitometry in an automated densitometric system interfaced to a basic programmable computing integrator. The method is sensitive enough to detect abnormally low concentrations of PC and SP in high-density lipoproteins. The accuracy of the method was tested either with the Bartlett phosphorus assay or with enzymatic methods for PC and SP; correlations of the described method with the enzymatic determinations were r = 0.93 and 0.88, respectively. Day-to-day precision (CV) for the phospholipid determination was 8.6% for PC and 12.2% for SP. The major advantage of this inexpensive technique is that native plasma or serum or the serum supernate after precipitation can be used without prior delipidation. With this technique serum high-density lipoproteins had PC values of 1.08 (SD 0.32) mmol/L in men (n = 158) and 1.12 (SD 0.37) mmol/L in women (n = 192); similarly, SP values were 0.23 (SD 0.07) mmol/L in the men and 0.23 (SD 0.08) mmol/L in the women. The differences by sex are not significant.

Adult↗
PubMed1983

[Candidate selected method for the enzymatic determination of total cholesterol in serum].

An enzymatic method is described for the determination of total cholesterol in serum using a single aqueous reagent which can easily be prepared from commercial substrates and enzymes. The determination is carried out manually, the resulting stable chromogen is measured at a wavelength of 500-550 nm. The cholesterol concentration may be calculated either using a primary cholesterol standard or a constant factor for a given wavelength. The reliability of the method is reported: Data for the imprecision are given on the basis of a survey in 3 laboratories, the accuracy is established by comparison with a definitive and a reference method. Analytical and biological interferances are briefly discussed and results with this enzymatic method are reported concerning the reference values for serum cholesterol.

Cholesterol↗
PubMed1982

Dissociation of apolipoprotein AI from apoprotein-lipid complexes and from high-density lipoproteins. A fluorescence study.

The dissociation of the apoprotein AI (apoAI) from the apoAI-dimyristoylglycerophosphocholine complex and from human high-density lipoproteins (HDL), was induced by incubation with guanidinium hydrochloride at concentrations between 0 M and 7 M. The kinetics and extent of denaturation were followed by monitoring both the fluidity of the lipid phase by fluorescence polarization measurements and the protein conformation by measuring the tryptophanyl fluorescence emission. The association with lipids protects apoAI against denaturation both in HDL and in the apoAI-phospholipid complex. The results of the kinetic and end-point measurements suggest that the denaturing effect of guanidine hydrochloride on the apoAI-lipid complex and on HDL is a two-step process. It involves the dissociation of the apoAI-phospholipid bond, as evidenced by fluidity measurements: this effect is maximal between 3 M and 4 M guanidine hydrochloride. The conformational change of the apoAI protein into a randomly coiled structure with the tryptophanyl residues exposed to the solvent is maximal between 4 M and 6 M guanidine hydrochloride. HDL and the apoAI-phospholipid complex have a closely similar behaviour towards denaturation by guanidine hydrochloride indicating that the phospholipid-apoAI association in HDL is primarily responsible for the stability of the lipoprotein molecule.

Apolipoprotein A-I↗
PubMed1982

Preparation of high-density lipoproteins labelled exclusively at the cholesteryl ester moiety.

The in vitro preparation of HDL radiolabelled at the cholesteryl ester moiety was determined by incubating different serum fractions with [3H]cholesteryl linoleate or cholesteryl [14C]oleate dissolved in dimethylsulfoxide (DMSO) and subsequent re-isolation of HDL from the incubation mixture by ultracentrifugation. Using the supernatant obtained by precipitation of apolipoprotein B-containing lipoproteins with phosphotungstate/MgCl2 or using the greater than 1.075 kg/l fraction of sera, the bulk of the added radioactivity could be recovered in the re-isolated HDL fraction, as demonstrated by density gradient ultracentrifugation or by gel chromatography. Incubation experiments using whole sera or the greater than 1.063 kg/l fraction of sera resulted in the preferential association of the labelled cholesteryl linoleate with apolipoprotein B-containing lipoproteins.

Apolipoproteins↗
PubMed1982

The role of lecithin: cholesterol acyltransferase in high density lipoprotein3/high density lipoprotein2 interconversion.

Serum was incubated in vitro with and without inhibition of lecithin:cholesterol acyltransferase (LCAT, EC 2.3.1.43). High density lipoprotein2 (HDL2) and high density lipoprotein3 (HDL3) were separated by zonal ultracentrifugation and analysed for lipid and apoprotein contents. The incubation of fresh sera resulted in a time-dependent decrease in HDL3 and an increase in HDL2. At the end of 24 h incubation HDL3 disappeared completely and the HDL2 peak had reached its maximum. The newly formed HDL2 was relatively enriched in total protein (apoprotein A-I, C-apoproteins) and cholesteryl esters, and depleted in phosphatidylcholine. Its migration in polyacrylamide gel electrophoresis was identical with HDL2 contained in fresh serum or HDL2 isolated from serum by zonal ultracentrifugation. The generated HDL2 particles exhibited the same electron microscopical characteristics as reference HDL2 samples prior to incubation. Addition of Ellman's reagent to the incubation mixture or heat inactivation of the samples prior to incubation resulted in a complete inhibition of HDL3/HDL2 interconversion, whereas addition of 1 mol/l NaCl had no detectable influence. There was also a substantial increase in HDL2 when VLDL-deficient serum was incubated at 37 degrees C. Similarly, in fresh serum from a patient affected with familial lipoprotein lipase deficiency, HDL3 was completely converted to HDL2. Our experiments demonstrate that LCAT promotes HDL3/HDL2 interconversion in native serum irrespective of the presence or absence of triglyceride-rich lipoproteins and lipoprotein lipase.

Adult↗
PubMed1982

Apolipoprotein A-IV polymorphism in man.

In man, apolipoprotein A-IV is characterized by a genetically determined polymorphism controlled by two codominant alleles. Two isoforms of this apolipoprotein, designated A-IV-1 and A-IV-2, can be identified by isoelectric focusing. Among 1000 healthy factory workers participating in an epidemiological study, A-IV-1 (genotype 1-1) was observed in 85%; A-IV-2 (genotype 2-2), in 0.5%; and A-IV-1 in combination with A-IV-2 (genotype 1-2), in 14%. In four nonrelated subjects, an apolipoprotein A-IV variant (A-IV-Münster), characterized by a slightly more basic isoelectric focusing behavior than A-IV-2, was detected in combination either with A-IV-1 or A-IV-2. Mendelian inheritance of this variant could be demonstrated.

Apolipoproteins↗
PubMed1982

The delayed effects of prolonged physical exercise and physical training on cholesterol level.

The delayed effects of prolonged physical exercise on total and high-density lipoprotein (HDL) cholesterol were studied before and after a training period of 8 weeks. In 15 subjects, 1 and 2 days after a 3 h running test, total cholesterol was significantly lower than 1 day before and 8 days after the end of the exercise. One day post-exercise, HDL-cholesterol was significantly higher compared with 1 day before and 8 days afterwards. In ten subjects participating in the training program, decreased total cholesterol values were again found on the first day after the post-training exercise test. Total and HDL cholesterol levels were not significantly affected by 8 weeks of training.

Adult↗
PubMed1982

The relationship of HDL-apolipoprotein A-I and HDL-Cholesterol to risk factors of coronary heart disease: initial results of the prospective epidemiological study in company employees in Westfalia.

In a prospective epidemiologic study in company employees in Westfalia aimed at improving early diagnosis of coronary heart disease in 3069 men and 1387 women, concentrations of HDL-apolipoprotein A-I and HDL-cholesterol were measured and the results were correlated with several risk factors of coronary heart disease. A negative correlation between hypertriglyceridaemia and HDL-cholesterol (r = 0.25 male;-0.27 female;p less than 0.001) and between relative body weight and HDL-cholesterol (r=-0.21 male;-0.20 female;p less than 0.001) could be shown but not between hypertriglyceridaemia and HDL-apolipoprotein A-I and between relative body weight and HDL-apolipoprotein A-I. In cigarette smokers HDL-apolipoprotein A-I as well as HDL-cholesterol were found to be lower than in non-smokers. On the other hand HDL-apolipoprotein A-I but not HDL-cholesterol was positively correlated with systolic and diastolic blood pressure.

Aging↗
PubMed1982

The influence of a 100 km run on the composition of HDL.

In 26 male patients in a 100 km run, concentrations of the HDL constituents cholesterol, apolipoprotein A-I, phosphatidyl choline and sphingomyelin were determined before and immediately after the run. Before running, the values for HDL cholesterol were higher in the participants than in a control population. However, the HDL sphingomyelin, HDL phosphatidyl choline and HDL apolipoprotein A-I values for the participants did not differ from the values in a control population. After the 100 km run only the HDL cholesterol values were increased whereas the other HDL constituents were not affected by the run. It is concluded, that the single exposure to prolonged heavy exercise produces a change in HDL composition which is characterized by an exclusive increase in the cholesterol content of the HDL.

Adult↗
PubMed1982

[The enzymatic analysis of sphingomyelin in HDL (author's transl)].

A simple method is described for the enzymatic determination of sphingomyelin in the apolipoprotein B-free supernatants prepared by precipitation of blood sera with phosphotungstate/MgCl2. The analysis is based on the enzymatic hydrolysis of sphingomyelin, by sphingomyelinase from B. cereus, into phosphorylcholine and N-acylsphingosine, and subsequent hydrolysis of phosphorylcholine by alkaline phosphatase. The choline formed is determined by choline kinase in an optical test. The results from this method were in good agreement with those obtained by the conventional chemical sphingomyelin determination. Furthermore, there was a good correlation between the sphingomyelin concentrations obtained from the HDL fractions isolated by ultracentrifugation (1.063-1.21 kg/l) and those obtained from the apolipoprotein B free supernatants after phosphotungstate/mgCl2 precipitation of sera.

Bacillus cereus↗
PubMed1982

One-step screening method for the polymorphism of apolipoproteins A-I, A-II, and A-IV.

Apolipoprotein A-I exhibits a polymorphism that can be easily investigated in native serum by a simple method involving incubation of serum in the presence of decylsulfate and beta-mercaptoethanol and subsequent isoelectric focusing. From six to eight proteins can be separated in a pH gradient from 4 to 6 and thus patients with apolipoprotein A-I variants can be distinguished from normal persons. This method also permits monitoring for polymorphic forms of apoA-II and apoA-IV as well as detection of C apolipoproteins. To verify the identity of the different apolipoproteins, a two-dimensional electrophoresis technique was applied, with an SDS system for the second dimension. In addition, monospecific antibodies for apolipoproteins A-I, A-II, and A-IV were used for the immunological identification. The method described here led to the discovery of three different familial apolipoprotein A-I variants.

Apolipoprotein A-I↗
PubMed1982

Influence of triglyceride-rich lipoproteins on nephelometry of apolipoprotein A-I.

Measurement of apolipoprotein A-I in native human sera by endpoint or rate nephelometry may give falsely high results for sera that have a high triglyceride content. Such erroneous determinations of apolipoprotein A-I can be avoided if one instead assays supernates of sera from which apolipoprotein B-containing particles have been precipitated with phosphotungstic acid and MgCl2. A high triglyceride concentration in serum does not impair the completeness of the precipitation of apolipoprotein B-containing lipoproteins or the analytical recovery of apolipoprotein A-I. In a prospective epidemiologic study, by using rate nephelometry we found that there were different mean concentrations for apolipoprotein A-I in supernates of sera from men (1.36 g/L) and women (1.49 g/L). Furthermore, the known risk factors for atherosclerosis showed different correlations with apolipoprotein A-I than with high-density lipoprotein cholesterol.

Adolescent↗
PubMed1982

Isolation of human serum HDL1 by zonal ultracentrifugation.

High density lipoprotein subfraction-1 (HDL(1)) is thought to interact with the high-affinity apoprotein B, E receptors of peripheral cells and may act as a modulator of LDL binding and uptake. In the present study the concentration and composition of HDL(1) in normal and hypercholesterolemic sera were studied using zonal ultracentrifugation. To permit separation of the HDL(1) from VLDL, LDL, and Lp(a), the apoB-containing lipoproteins were first precipitated from serum using the phosphotungstic acid/magnesium chloride (PTA/MgCl(2)) method after which the supernatant fraction was subjected to zonal ultracentrifugation. It could be demonstrated that following PTA/MgCl(2) precipitation HDL(1) floats as a single peak at d 1.08-1.09 g/ml (NaBr) and is sufficiently separated from high density lipoprotein-2 (HDL(2)) and high density lipoprotein-3 (HDL(3)). The HDL(2)/HDL(3) subfraction pattern was not affected by the precipitation method. As previously described, in vitro incubation of serum leads to the LCAT-dependent interconversion of HDL(3) or HDL(2). Using the technique described here, it was discovered that a simultaneous elevation of HDL(1) occurred. This increase in HDL(1) concentration could not be observed when LCAT was inhibited by heat inactivation or addition of Ellman's reagent. In normal fresh serum only a small HDL(1) peak could be detected, but in patients with familial hypercholesterolemia (apoB, E receptor deficiency) HDL(1) was elevated five to tenfold compared to normal values and further increased in concentration upon incubation of serum. On the other hand, in sera of patients with familial HDL deficiency (Tangier disease), HDL(1) was undetectable. Analysis of the HDL fractions in serum of a patient with abetalipoproteinemia revealed that following in vitro incubation there was formation of HDL(1) despite the lack of apoprotein B-containing lipoproteins. These data support the concept that HDL(1) formation occurs during LCAT-mediated HDL(3)/HDL(2) interconversion in vitro.-Schmitz, G., and G. Assmann. Isolation of human serum HDL(1) by zonal ultracentrifugation.

Apolipoproteins↗
PubMed1981

In vitro interaction of human HDL with human apolipoprotein A-II. Synthesis of apolipoprotein A-II-rich HDL.

The aim of this study was to define the specific affinity of human apolipoproteins A-I and A-II for HDL lipids and to investigate the possible transfer of apolipoproteins from the HDL molecule. For this purpose we incubated human HDL with increasing amounts of isolated apolipoprotein A-II. After incubation the reaction products were separated by gel chromatography and apolipoproteins A-I and A-II were quantified separately by immunonephelometry and HDL lipids by thin-layer chromatography. According to our results, apolipoprotein A-II progressively displaces apolipoprotein A-I to generate an HDL-like particle with identical lipid composition, hydrodynamic properties and lipid fluidity. These data indicate that apolipoprotein A-II is able to displace quantitatively apolipoprotein A-I from HDL in vitro, and that such a mechanism might contribute to the regulation of the HDL2 in equilibrium or formed from HDL3 distribution in plasma.

Apolipoprotein A-I↗