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Biomedical subjects

G Assmann

Publications and source records attributed to G Assmann.

At least 361 records · Page 20Linked to original sources
PubMed1985

Tangier disease: a disorder of intracellular membrane traffic.

The interaction of human high density lipoproteins (HDL) with isolated human monocytes from control and Tangier patients was studied in tissue culture experiments. It was observed that normal monocytes, similar to mouse peritoneal macrophages, bind HDL to a cell surface receptor, internalize the bound HDL particles, transport the internalized HDL intracellularly through the cytoplasmic compartment without significant degradation, and ultimately resecrete intact HDL. The cellular interaction of Tangier monocytes with normal HDL was markedly different from control monocytes. HDL binding to Tangier monocytes was moderately increased and cell-associated HDL radioactivity was 6- to 10-fold enhanced in Tangier monocytes. The bulk of the internalized HDL, however, was detected in secondary lysosomes. Only minor amounts of the internalized HDL were resecreted from the Tangier monocytes, and most of this was degraded. These data suggest that the cellular metabolism of HDL is abnormal in Tangier monocytes. It is postulated that Tangier disease may be a disorder of intracellular membrane traffic in which HDL is diverted into the lysosomal compartment and degraded instead of being secreted through its regular transcellular route.

Adolescent↗
PubMed1985

Observations of HDL components in female probands following an ultra-long distance run of 100 miles.

The serum concentrations of total cholesterol and triglycerides as well as the cholesterol, phosphatidyl choline, and apolipoprotein components of HDL were tested in 19 participants immediately before and immediately after a 100-mile run. After the run, taking into account any alterations in total protein, the following changes were observed: a decrease in total cholesterol (p less than 0.001), as well as in triglycerides (p less than 0.05), and an increase in HDL cholesterol (p less than 0.05), and HDL phosphatidyl choline (p less than 0.01). The concentrations of HDL apolipoprotein A-I and HDL apolipoprotein A-II were not affected. The results indicate a change in composition of HDL following extreme prolonged physical exercise in women.

Apolipoprotein A-I↗
PubMed1985

VLDL apolipoprotein B determination in blood serum following precipitation of LDL with polyvinylsulphate.

A method is described for the determination of VLDL apolipoprotein B by radial immunodiffusion (RID) in serum supernatants following precipitation of LDL with polyvinylsulphate. The measurement of VLDL apolipoprotein B is based on the incubation of the polyvinylsulphate supernatant with triglyceride lipase (330 kU/l end concentration) for 12-24 hours at 37 degrees C. A good measure of agreement was found for the corresponding VLDL apolipoprotein B values measured by RID in the polyvinylsulphate supernatants (y) and VLDL apolipoprotein B values calculated as tetramethylurea-insoluble protein in the d less than 1.006 kg/l serum fraction (x) (r = 0.88, y = 0.96x + 0.004, n = 54). Within the tested range of 1.2 mmol/l to 6.7 mmol/l triglycerides, the concentration of apolipoprotein B measured in the polyvinylsulphate supernatant showed a linear relationship. Correlation analysis of VLDL apolipoprotein B values and serum triglycerides and VLDL cholesterol, respectively, showed a good correlation (r = 0.77 and r = 0.75, respectively, n = 54). In the determination of VLDL apolipoprotein B measured in polyvinylsulphate supernatant, a variation coefficient of 4.3% (means = 10.1 mmol/l, n = 20) was found in relation to the precision in the series, and a variation coefficient of 11.4% (means = 5.3 mmol/l, n = 15) in relation to day to day precision.

Apolipoproteins B↗
PubMed1985

Turbidimetric assay of apolipoprotein A-II.

A turbidimetric assay for the quantification of apolipoprotein A-II in serum is described. Its adaptation for the Cobas Bio Analyser (Hoffmann La Roche) is reported. Regression analysis of apolipoprotein A-II values measured by turbidimetry revealed a good measure of agreement with the data obtained by radial immunodiffusion (RID) (r = 0.90, y = 0.97x + 0.021, n = 100) as well as with data obtained by immunonephelometry (r = 0.838, y = 0.925x + 0.029, n = 34). A variation coefficient of 3.2% (n = 18) was found in relation to the precision in the series and a variation coefficient of 3.5% (n = 36) in relation to day to day precision.

Antibodies↗
PubMed1985

Characterization of very low density lipoproteins and intermediate density lipoproteins of normo- and hyperlipidemic apolipoprotein E-2 homozygotes.

Triglyceride-rich lipoproteins derived from ten normo- and hyperlipidemic apoE-2 homozygotes were analyzed for their composition, beta-VLDL content, and their ability to induce cholesteryl ester storage in macrophages. In six of these probands apoE sequence analysis revealed that the cysteine residues were at positions 112 and 158 of the amino acid sequence (Rall et al. 1983. J. Clin. Invest. 71: 1023-1031). ApoE-2 of these six and the other four patients was further analyzed by SDS electrophoresis to exclude the presence of apoE-2* (Rall et al. 1982. Proc. Natl. Acad. Sci. USA. 79: 4696-4700). The relative serum concentrations of free and esterified cholesterol transported in the d less than 1.006 g/ml and d 1.006-1.019 g/ml lipoproteins of the apoE-2 homozygotes was significantly higher as compared to controls. Compositional analysis of these lipoproteins revealed a relative reduction of triglycerides and a relative increase of cholesteryl esters as compared to controls. In most patients, with increasing serum triglyceride levels the cholesteryl ester concentration increased in d less than 1.006 g/ml and d 1.006-1.019 g/ml lipoproteins. However, in three patients with a low content of beta-VLDL, the increase in the d less than 1.006 g/ml fraction cholesterol was mostly due to free cholesterol and not due to cholesteryl esters. The degree of the macrophage cholesteryl ester accumulation induced by d less than 1.006 g/ml lipoproteins was mostly dependent on the concentration of the beta-migrating fraction (beta-VLDL). The amount of beta-VLDL and pre-beta-VLDL contained in the d less than 1.006 g/ml fraction was determined densitometrically after electrophoretic separation. It could be demonstrated that the beta-VLDL content in the d less than 1.006 g/ml fraction of the apoE-2 homozygous patients was largely independent of serum triglyceride and serum cholesterol levels. When macrophages were incubated with the IDL fraction (d 1.006-1.019 g/ml) from the apoE-2 patients, no significant increase in cellular cholesteryl esters above control levels was observed. Studies with purified lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) clearly revealed that both enzymes interacted with apoE-2 VLDL (binding, hydrolysis) to a lesser degree compared to control preparations. However, the apoE-2 VLDL preparations containing a low content of beta-VLDL were better substrates for LPL and HTGL than those containing a high beta-VLDL content. It is concluded from our studies that the plasma beta-VLDL content in apoE-2 homozygotes is a major determinant for cholesteryl ester accumulation in macrophages.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1984

Abnormal lecithin:cholesterol acyltransferase activation by a human apolipoprotein A-I variant in which a single lysine residue is deleted.

An apolipoprotein (apo) A-I variant that has a relative charge of -1 compared to normal apo-A-I on isoelectric focusing gels has been identified in five unrelated families as a result of screening a large number of individuals. The cause of the electrophoretic abnormality has been examined by analyzing the variant apo-A-I structure. The evidence suggests that a single amino acid, lysine 107, has been deleted in the variant apo-A-I of all affected individuals studied from these families, with the remainder of the variant apo-A-I sequence being unaffected. The deletion of this single basic amino acid residue is sufficient to account for the charge difference between the variant and normal apo-A-I as seen on isoelectric focusing gels. This variant, previously referred to as A-I-Marburg or A-I-Münster-2, can now be designated by the structural abnormality apo-A-I(Lys107----0). The evidence from extensive pedigree analysis suggests the likelihood that the deletion mutant gene is allelic to the normal apo-A-I gene. At the same time, the kindred analyses have failed to yield a lipid abnormality that can be unequivocally related to the presence of this deletion mutant of apo-A-I. However, all subjects expressing apo-A-I(Lys107----0) also express normal apo-A-I, so that any abnormality caused by the variant apo-A-I might be adequately compensated for by the normal apo-A-I. To examine directly the functional consequence of the lysine deletion, the isolated variant was tested in vitro for its ability to activate lecithin:cholesterol acyltransferase, the principal cholesterol-esterifying enzyme in plasma. It was found that apo-A-I(Lys107----0) is deficient in its ability to activate lecithin:cholesterol acyltransferase, having only 40-60% of the cofactor activity of normal apo-A-I. The cofactor activity of the pro-apo-A-I component of the variant was also reduced to about 60% of either normal A-I or normal pro-apo-A-I. The functional defect is probably related to a disruption in the secondary and/or tertiary structure of the protein caused by the deletion of lysine 107 in the primary structure.

Adult↗
PubMed1984

A quantitative densitometric method for the rapid separation and quantitation of the major tissue and lipoprotein lipids by high-performance thin-layer chromatography. I. Sample preparation, chromatography, and densitometry.

A rapid method for the separation and quantitation of the major lipids of tissues and lipoproteins by automated high-performance thin-layer chromatography is presented. Solvent systems for one-dimensional separation of neutral lipids, of cholesteryl esters, and of phospholipids are described. Separated lipids are measured following treatment with methanolic sulphuric acid containing manganese chloride and scanned in fluorescence or absorption mode. Absolute quantitation is obtained by the use of an internal standard and by references to standards for each lipid run on the same plates as samples. The method described here is particularly suitable for the rapid quantitation of small amounts of lipid (0.01-0.02 nmol per sample), for example in tissue culture studies; 100 micrograms of fibroblast or macrophage protein are sufficient for complete lipid analysis. The coefficients of variation due to the sample preparation, application to the plates and densitometry are in the range 7.2-9.1%. The method was compared with enzymatic determinations for cholesterol and gave correlation coefficients of 0.95 for total cholesterol and 0.91 for unesterified cholesterol. Phospholipid estimation was compared with large-plate thin-layer chromatography and phosphorus analysis and gave correlation coefficients of 0.90 for phosphatidylcholine and 0.89 for sphingomyelin.

Animals↗
PubMed1984

A quantitative densitometric method for the rapid separation and quantitation of the major lipids of tissues and lipoproteins by high-performance thin-layer chromatography. II. Reduction of the densitometric data.

A BASIC program is described for acquisition of data and data reduction for an automated densitometric system for quantitation of lipids separated by high-performance thin-layer chromatography. The program allows calculation of mass of samples from log/log calibration curves computed from standards. The calculated masses are reported as nmol/volume or nmol/mg protein. The program contains a flexible dialog system which permits its use for a variety of applications in addition to the system described for quantitation of lipids.

Autoanalysis↗
PubMed1984

Human apolipoprotein A-I polymorphism. Identification of amino acid substitutions in three electrophoretic variants of the Münster-3 type.

Variant forms of apolipoprotein A-I (apo-A-I) have been shown to exist in the human population. One mutant form, referred to as apo-A-I-Münster-3, is one charge unit more basic than normal apo-A-I on isoelectric focusing gels. This variant has the same immunologic characteristics and molecular weight as normal apo-A-I. The apo-A-I-Münster-3 from subjects in three unrelated families (in two of which the trait has been shown to be transmitted as an autosomal co-dominant) has been analyzed by partial amino acid sequencing to define the cause of the electrophoretic abnormality. In the apo-A-I of family A, the abnormality was shown to occur in the smallest cyanogen bromide fragment, CB-2 (residues 87-112), and amino acid sequencing revealed asparagine instead of the usual aspartic acid at residue 103. Subjects with this mutant form have shown no signs of dyslipoproteinemia. The NH2-terminal cyanogen bromide fragment (CB-1, residues 1-86) from the apo-A-I of family B was shown to differ electrophoretically from normal CB-1, and amino acid sequencing revealed that a substitution of arginine for proline at residue 4 was responsible for this variant form. Analysis of the plasma lipids of one affected family B member demonstrated that the percentage of the total cholesterol that was esterified was somewhat lower than that normally observed. In a third family, family C, a variant having the same electrophoretic abnormality as the other two was determined to have an amino acid substitution at yet a different position. In this variant, histidine was found at residue 3 in the apo-A-I sequence, rather than the usual proline. In all three cases, the substitution could account for the electrophoretic abnormality. It is proposed that these three apo-A-I-Münster-3 variants be designated apo-A-I(Asp103----Asn), apo-A-I(Pro4----Arg), and apo-A-I(Pro3----His), respectively, to indicate the substitution that accounts for the abnormality in isoelectric focusing gels.

Amino Acids↗
PubMed1984

Changes of plasma lipids and lipoprotein levels during danazol treatment for endometriosis.

Previous data of lipid and lipoprotein level changes with the application of danazol, an isoxazol derivative of 17-alpha-ethinyl testosterone, have been conflicting. We measured cholesterol, triglycerides, low density lipoproteins and high density lipoproteins, estradiol and progesterone in 62 patients treated for endometriosis with danazol 600 mg daily. The fasting blood samples were taken before, every month during danazol medication, and 4, 12 and 24 weeks after cessation of therapy. Inconsistent changes in total cholesterol and triglyceride levels were observed. The data showed a constant, though not significant increase of the mean LDL levels. Plasma HDL decreased approximately 45% during the first two months of danazol influence and remained constantly low for the rest of the treatment. The atherogenic ratio (LDL:HDL) was doubled by-danazol. Five patients developed a reversible type IIa hyperlipoproteinemia. The plasma levels of estradiol decreased, but showed normal midfollicular values during the treatment period. In contrast, the plasma levels of progesterone fell significantly and were sometimes undetectable. These findings demonstrate an atherogenic potential of danazol, especially when long term treatment is taken into consideration.

Adult↗
PubMed1984

Changes in HDL composition in female subjects following a 100-km run.

In 12 female subjects participating in a 100-km run, the concentrations of cholesterol and triglycerides as well as those of HDL components (total cholesterol, cholesteryl ester, unesterified cholesterol, phosphatidyl choline, apolipoprotein A-I, and apolipoprotein A-II) were measured before and after the run. The concentrations of HDL unesterified cholesterol, HDL phosphatidyl choline, and HDL apolipoprotein A-I of the participants of the 100-km run were higher than the corresponding values of a control group of female company employees, whereas there was no difference in triglycerides, total cholesterol. HDL cholesterol, and HDL apolipoprotein A-II. Values of triglycerides and total cholesterol ascertained after the run were clearly decreased when compared to pre-exercise values (by 70% and 10%, respectively). Also, total protein content of the serum was marginally reduced after the run. Considering the reduction in protein level. HDL cholesterol and HDL apolipoprotein A-I values were raised after the run (P less than 0.01, P less than 0.05, respectively) while HDL phosphatidyl choline values decreased irrespective of the reduction in total protein (P less than 0.01). The quotients HDL cholesterol / total cholesterol as well as HDL cholesterol / HDL phosphatidyl choline were clearly higher after the run than before (P less than 0.01). The HDL apolipoprotein A-II level did not change post-exercise. These results indicate a change in the structure of HDL following a 100-km run in female athletes.

Adult↗
PubMed1984

Topography and dynamics of receptors for acetylated and malondialdehyde-modified low-density lipoprotein in the plasma membrane of mouse peritoneal macrophages as visualized by colloidal gold in conjunction with surface replicas.

The topography and dynamics of receptors for acetylated (acetyl) and malondialdehyde-modified (MDA) low-density lipoprotein (LDL) in the plasma membrane of cultured mouse peritoneal macrophages were investigated using a new technique. Modified LDL labeled with gold particles was used to visualize LDL receptors in the plane of the plasma membrane in platinum-carbon surface replicas of critical point-dried cells. It was found that the native distribution of unoccupied acetyl-LDL receptors is diffuse, whereas unoccupied MDA-LDL receptors are preclustered in the plasma membrane. Competition and double labeling experiments suggest the existence of two distinct classes of receptor sites for acetyl-LDL and MDA-LDL.

Acetylation↗
PubMed1984

Determination of LDL cholesterol and LDL apolipoprotein B following precipitation of VLDL in blood serum with phosphotungstic acid/MgCl2.

A method is described for the selective precipitation of VLDL in blood serum using phosphotungstic acid/MgCl2. The method allows for the calculation of LDL apolipoprotein B as well as for the calculation of LDL cholesterol (following the additional determination of HDL cholesterol). Dependent on the triglyceride and the cholesterol content of the serum, three different procedures were developed using phosphotungstic acid and MgCl2 in different concentrations in the precipitation assay. Within the tested range of 3-10 mmol/l total cholesterol and 1-4 mmol/l triglyceride in blood serum the VLDL were nearly completely precipitated with negligible coprecipitation of LDL and HDL, but 40-50% coprecipitation of Lp(a). Regression analysis of the cholesterol values obtained by precipitation with phosphotungstic acid/MgCl2 (= serum cholesterol - LDL cholesterol), and the cholesterol values obtained by ultracentrifugation (d greater than 1.006 kg/l) revealed a good measure of agreement (r = 0.97, y = 0.93 X + 0.35, n = 76). An equally good measure of agreement was found for the corresponding apolipoprotein B values (r = 0.96, y = 1.03 X - 0.2, n = 61). In the determination of LDL cholesterol a variation coefficient of 4.3% (n = 20) was found in relation to the precision in the series, and a variation coefficient of 4.8% (n = 25) in relation to day to day precision.

Apolipoproteins↗
PubMed1984

Precipitation of LDL with sulphopolyanions: a comparison of two methods for LDL cholesterol determination.

Two commercially available tests for the determination of LDL cholesterol were compared. The determination principle lies in the precipitation of LDL using heparin (Merck, Darmstadt test) or using polycyclic surface activated anions (bioMérieux test), as well as ascertaining LDL cholesterol by subtracting cholesterol in the supernatant from total cholesterol (Merck, Darmstadt test) or the direct determination of cholesterol in the redissolved precipitate (bioMérieux test). Regression analysis of the LDL cholesterol values obtained by precipitation and the LDL cholesterol values obtained by the combination of ultracentrifugation and HDL cholesterol determination (cholesterol in the d greater than 1.006 kg/l ultracentrifugation fraction- HDL cholesterol) resulted in a good correlation (precipitation using polycyclic surface activated anions: r = 0.95, y = 1.01x - 0.14, n = 34; heparin precipitation: r = 0.94, y = 0.86x + 0.10, n = 28). In sera containing triglycerides ranging from 2.28 mmol/l to 10.9 mmol/l there was an adequate agreement between the values obtained by precipitation with polycyclic surface activated anions and those of the reference method (r = 0.94, y = 0.9x + 0.47, n = 51), whereas the data obtained by heparin precipitation clearly deviated from the data of the reference method (r = 0.69, y = 0.75x + 0.003, n = 32).

Anions↗
PubMed1984

Multicentre study of a new enzymatic method of cholesterol determination.

A new enzymatic method for the determination of cholesterol in serum and plasma was evaluated in 8 separate laboratories in comparison with routine and reference methods. Investigation of the analytical reliability in the 2-26 mmol/l measurement range showed the following results: At the set reading points (10 min at 25 degrees C and 5 min at 37 degrees C) the reaction shows complete substrate conversion. The colour complex is stable over a period of 60 min. The response to cholesterol is linear up to 26 mmol/l. Precision within the series was 0.6-2.8% in 20 determinations (coefficient of variation). Day to day precision was 0.5-3.3% in triple determinations of 10 days (coefficient of variation). Accuracy was studied with 2 samples (assigned value: 3.52 and 6.70 mmol/l respectively). In the case of sample 1 the mean for the 8 laboratories was 3.44, with a median of 3.44; for sample 2 the values were 6.68 and 6.72. The results demonstrate an excellent transferability. In comparison with other enzymatic procedures, the values found with the new test were 5-10% higher; these results agree at all concentration ranges with the reference methods of Abell & Kendall and with those from mass spectrometry.

Cholesterol↗