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G Assmann

Publications and source records attributed to G Assmann.

At least 343 records · Page 19Linked to original sources
PubMed1986

Role of the high density lipoprotein-receptor cycle in macrophage-cholesterol metabolism.

The intracellular catabolism of lipids and the blood cholesterol level are known to have an essential impact on the onset and progress of atherosclerosis. As lipoprotein receptors can influence the co-operation of macrophages, high density lipoproteins and enzymes of lipid metabolism, the contribution of these receptors to transport and intracellular processing of cholesterol are investigated by means of biochemical analysis and electron microscopy. Taking the effect of second messenger systems into consideration, a model for impaired lipoprotein receptor function affecting the cholesterol metabolism is developed.

Animals↗
PubMed1986

Apolipoprotein B determination in the dissolved precipitate obtained after precipitation of LDL with polyvinylsulphate. An alternative method for the determination of LDL apolipoprotein B without using ultracentrifugation.

Using a commercially available test for LDL cholesterol (Boehringer Mannheim), a method was developed for determination of LDL apolipoprotein B without using ultracentrifugation. The infranatant obtained by precipitation of serum with polyvinylsulphate was redissolved in a saline citrate solution and incubated with phospholipase A2, phospholipase C, phospholipase D or triglyceride lipase, respectively. When the saline-citrate redissolved precipitate was monitored by electron microscopy, it appeared as a fibriform network. The additional incubation with phospholipase A2, C, D, or triglyceride lipase resulted in a molecularization of LDL particles. By electron microscopy these particles could not be distinguished from LDL particles isolated by ultracentrifugation. In radial immunodiffusion tests, the additional incubation of the redissolved precipitate with phospholipase C or phospholipase D resulted in a total loss of the slight immunoreactivity observed before phospholipase incubation. However, additional incubation with triglyceride lipase resulted in a significant increase in immunoreactivity. Only the additional incubation of the redissolved precipitate with phospholipase A2 resulted in an immunoprecipitation reaction comparable to that with LDL particles isolated by ultracentrifugation. Using a resolubilized and phospholipase A2-incubated precipitate of a pool serum as apolipoprotein B standard, a good correlation was obtained between apolipoprotein B values measured in this dissolved precipitate and those measured in the d greater than 1.006 kg/l fraction isolated by ultracentrifugation (r = 0.95; y = 0.95x + 0.018; n = 44).

Apolipoproteins B↗
PubMed1986

HDL apolipoprotein A-I and HDL apolipoprotein A-II concentrations in male company employees in Westphalia aged 40 years and older.

The major structural components of high density lipoproteins were determined in the sera of 638 male employees aged 40 years and older. It was demonstrated that the HDL apolipoprotein A-I/HDL cholesterol ratio as well as the HDL apolipoprotein A-II/HDL cholesterol ratio are similarly correlated to a cumulative score of established risk factors for atherosclerosis. Most important, however, is the finding that the correlation of these ratios to the risk factor rating of atherosclerosis is found in subgroups with normal or elevated HDL cholesterol values. Furthermore, it is shown that the relative content of apolipoproteins A-I and A-II in individual HDL is partly dependent on the plasma concentration of HDL cholesterol and triglycerides. It is concluded that HDL composition may have an additional predictive significance for the development of atherosclerosis.

Adult↗
PubMed1986

Polymorphisms in the apolipoprotein AI-CIII gene complex.

We report the presence of five restriction fragment length polymorphisms in the apolipoprotein AI-CIII (apo AI-CIII) gene complex as well as their respective allelic frequencies in a German population (pi) that we studied: an SstI (BanII) polymorphism in the 3' non-coding region of apo CIII q1(pi) = 0.13); an MspI polymorphism in the third intron of apo AI (q2(pi) = 0.12); a PvuII polymorphism in the first intron of apo CIII (q3(pi) = 0.30); and two XmnI polymorphisms in the 5' side of apo AI (q4(pi) = 0.20 and q5(pi) = 0.05).

Apolipoprotein A-I↗
PubMed1986

High performance liquid chromatography and time-of-flight secondary ion mass spectrometry: a new dimension in structural analysis of apolipoproteins.

We report the isolation and characterization of an apolipoprotein A-I mutant using a new technique for structural analysis of apolipoproteins based upon the combined techniques of protein isolation by isoelectric focusing in immobilized pH-gradients, reversed-phase HPLC of tryptic peptides, and subsequent molecular weight analysis of isolated peptides by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The particular advantages of the TOF-SIMS procedure in the characterization of proteolytic peptides are the detection limits in the picomole range, the accuracy of molecular weight determination (up to 3000 +/- 1 D), the speed of analysis, and the wide range of applications for involatile biomolecules. The described procedure for the analysis of apolipoproteins requires only 2 ml of serum as starting material. This method can be used to monitor for genetic polymorphisms and posttranslational modifications on a microscale basis. Applying these techniques, we characterized a new apolipoprotein A-I mutant with an amino acid exchange arginine177 by histidine.

Apolipoprotein A-I↗
PubMed1986

Association of apolipoprotein E polymorphism, low-density lipoprotein cholesterol, and coronary artery disease.

We determined the frequencies of genetic apolipoprotein E isoforms in 570 survivors of myocardial infarction, all with demonstrable coronary heart disease, as compared with 624 healthy persons. In controls, E-4/E-3 heterozygosity was associated with total cholesterol concentrations of 1985 (SD 364) mg/L and low-density lipoprotein (LDL)-cholesterol concentrations of 1306 (SD 332) mg/L. Significantly lower values, 1811 (SD 312) mg/L and 1121 (SD 274) mg/L, respectively, were observed for E-3/E-2 heterozygous persons. In survivors of myocardial infarction, the respective values were significantly higher than in controls, differing between E-4/E-3 and E-3/E-2 heterozygous patients by 233 and 220 mg/L, respectively. Moreover, E-4/E-3 heterozygosity was accompanied by earlier age of myocardial infarction (48.8 +/- 7.4 years) as compared with E-3/E-2 heterozygosity (53.4 +/- 6.9 years) and E-3/E-3 homozygosity (51.2 +/- 7.7 years). Evidently, apolipoprotein E polymorphism can contribute to total and LDL-cholesterol concentrations in serum, thereby affecting risk of coronary heart disease and myocardial infarction.

Age Factors↗
PubMed1986

Detection of apolipoprotein E variants by an oligonucleotide "melting" procedure.

An oligonucleotide "melting" procedure was developed whereby we can monitor for a sequence heterogeneity in the gene for apolipoprotein E production. Two oligonucleotides were synthesized, one recognizing the common epsilon 3 allele but not the common epsilon 2 allele, the other recognizing the epsilon 2 allele but not the epsilon 3 allele. Samples from 15 subjects with different apolipoprotein E phenotypes as classified by isoelectric focusing were analyzed by this method for the presence of an Arg----Cys substitution in position 158 of the apolipoprotein E amino acid sequence. In 14 of these subjects the genotype determined by oligonucleotide melting agreed with the phenotype identified by isoelectric focusing. In one patient, however, whose phenotype was E2/2 by isoelectric focusing, the DNA hybridized with both oligonucleotides. We conclude that this patient has a mutation in one of his alleles for apolipoprotein E that differs from the frequently seen Arg----Cys change. The apolipoprotein E gene may thus be more heterogeneous than previously anticipated.

Alleles↗
PubMed1985

Epidemiological study on factor VII, factor VIII and fibrinogen in an industrial population--II. Baseline data on the relation to blood pressure, blood glucose, uric acid, and lipid fractions.

In a preceding paper the baseline data in the Münster Arteriosclerosis Study (PROCAM study) of the levels of fibrinogen, factor VIIc and factor VIIIc were described, and their correlation of age, body weight, smoking, alcohol, pill-using and menopause discussed. In this part the relationship of these coagulation factors to blood pressure, blood glucose, uric acid and lipid parameters, which were examined in 4186 apparently healthy individuals, is presented. The correlations are described using two different statistical models, first the Pearson correlation coefficients after allowing each clotting factor for the effects of age, cigarette and alcohol consumption, body weight, menopausal state, pill using and the other clotting factors, and secondly by a multiple regression analysis. The data suggest that there are multiple interrelationships between hemostatic factors and the variables under consideration. The most striking positive correlations were found for factor VIIc to blood glucose and triglycerides in men and women and to HDL-cholesterol in women.

Age Factors↗
PubMed1985

Analytical capillary isotachophoresis: a routine technique for the analysis of lipoproteins and lipoprotein subfractions in whole serum.

A capillary isotachophoretic separation technique was developed for lipoproteins in native serum which, compared with previous electrophoretic techniques, has negligible molecular sieve effects, does not need gel casting, is suitable for whole serum and has a high discriminative power for lipoprotein subfractions. The technique is based on pre-staining whole serum lipoproteins for 30 min at 4 degrees C before separation of 0.5 microliter of the sample in a free-flow capillary system (0.5 mm I.D.) with discontinuous buffer system. In normolipidaemic sera, high-density (HDL) and low-density lipoproteins (VLDL) are separated into two major subpopulations according to their net electric mobility. The identification of these fractions was confirmed by substitution with ultracentrifugally isolated lipoproteins and by their complete absence from Tangier and abetalipoproteinaemic serum. Triglyceride-rich very low-density lipoproteins (VLDL) revealed a defined zone between the HDL and LDL subpopulations. Our preliminary results indicate that the separation of human whole serum lipoproteins by capillary isotachophoresis is a promising method for the determination of lipoprotein subfractions.

Abetalipoproteinemia↗
PubMed1985

Interaction of high density lipoproteins with cholesteryl ester-laden macrophages: biochemical and morphological characterization of cell surface receptor binding, endocytosis and resecretion of high density lipoproteins by macrophages.

Morphological and biochemical experiments were carried out to investigate the interaction of human serum high density lipoproteins (HDL) with mouse peritoneal macrophages. It is demonstrated that resident mouse peritoneal macrophages express HDL receptors. Subsequent to receptor-mediated binding, HDL are internalized and intracellularly transported into endosomes. These endosomes do not fuse with the lysosomal compartment but interact with the margin of intracellular plasma lipid droplets. Macrophages do not degrade, but rather resecrete internalized HDL particles as described for the transferrin-receptor pathway. HDL binding to freshly isolated macrophages is saturable at a concentration of approximately 320 ng HDL-protein/mg cell protein and a Scatchard plot indicates the presence of some 130 000-190 000 receptors/cell with a Kd of approximately 9 X 10(-7) M. Binding of HDL on the macrophage surface is significantly enhanced in cholesterol-laden macrophages, whereas the increase in the rate of uptake and secretion is less pronounced. Within the HDL fraction the HDL2 subclass showed higher binding, uptake and secretion activity as compared with HDL3. From these experimental data we postulate that cholesterol uptake from macrophages is mediated by HDL particles which interact with these cells via a receptor-mediated retroendocytosis pathway.

Animals↗
PubMed1985

Regulation of high density lipoprotein receptors in cultured macrophages: role of acyl-CoA:cholesterol acyltransferase.

The interaction of human serum high density lipoproteins (HDL) with mouse peritoneal macrophages and human blood monocytes was studied. Saturation curves for binding of apolipoprotein E-free [125I]HDL3 showed at least two components: non-specific binding and specific binding that saturated at approximately 40 micrograms HDL protein/ml. Scatchard analysis of specific binding of apo E-free [125I]-HDL3 to cultured macrophages yielded linear plots indicative of a single class of specific binding sites. Pretreatment of [125I]HDL3 with various apolipoprotein antibodies (anti apo A-I, anti apo A-II, anti apo C-II, anti apo C-III and anti apo E) and preincubation of the cells with anti-idiotype antibodies against apo A-I and apo A-II prior to the HDL binding studies revealed apolipoprotein A-I as the ligand involved in specific binding of HDL. Cellular cholesterol accumulation via incubation with acetylated LDL led to an increase in HDL binding sites as well as an increase in the activity of the cytoplasmic cholesterol esterifying enzyme acyl-CoA:cholesterol acyltransferase (ACAT). Incubation of the cholesterol-loaded cells in the presence of various ACAT inhibitors (Sandoz 58.035, Octimibate-Nattermann, progesterone) revealed a time- and dose-dependent amplification in HDL binding and HDL-mediated cholesterol efflux. It is concluded that the homeostasis of cellular cholesterol in macrophages is regulated in part by the number of HDL binding sites and that ACAT inhibitors enhance HDL-mediated cholesterol efflux from peripheral cells.

Animals↗
PubMed1985

Severe polyneuropathy in Tangier disease mimicking syringomyelia or leprosy. Clinical, biochemical, electrophysiological, and morphological evaluation, including electron microscopy of nerve, muscle, and skin biopsies.

Polyneuropathy in Tangier disease can be divided into three clinical types. The most severe form (type III) with a syringomyelia-like syndrome has been described in three cases only. Here, a fourth case of this type is presented. Because of unusual trophic disturbances even leprosy was suspected. Electrodiagnostic findings, including evoked cerebral potentials in this case, were suggestive of a generalized neuropathy with some degree of primary or secondary demyelination and implied possible impairment of central structures. Sural nerve biopsy, including electron microscopy and quantitative analysis, revealed a predominant reduction of smaller myelinated and unmyelinated fibres. The main morphological feature was the abundance of abnormal non-membrane-bound vacuoles in Schwann cells, mostly of the unmyelinated type, and in some endoneurial fibroblasts, macrophages and perineurial cells. There was no inverse relationship between lipid vacuoles and axons in Schwann cell complexes as suspected by others. An excess of endoneurial collagen as well as an increased fascicular area were obvious. In five skin biopsy specimens of different regions typical vacuoles were noted in Schwann cells, histiocytes, nevus cells, and rarely in perineurial cells.

Adult↗