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Biomedical subjects

G Assmann

Publications and source records attributed to G Assmann.

At least 37 records · Page 2Linked to original sources
PubMed1991

Apolipoprotein C-III(Lys58----Glu). Identification of an apolipoprotein C-III variant in a family with hyperalphalipoproteinemia.

Apolipoprotein C-III is a major protein constituent of triglyceride rich lipoproteins and HDL. It occurs in plasma in three isoforms differing by their sialic acid content. Apo C-III putatively inhibits lipolysis and the apo E mediated hepatic uptake of remnants from triglyceride rich particles. We identified a heterozygous carrier of an apolipoprotein C-III variant by the presence of additional bands after isoelectric focusing (IEF) of VLDL. Structural analysis of the variant protein by HPLC, time-of-flight secondary ion mass spectrometry, and automated gas phase sequencing revealed a lysine to glutamic acid replacement in position 58. The underlying A to G exchange was verified by direct sequencing subsequent to amplification by polymerase chain reaction of exon 4 of the apo C-III gene. Family studies revealed vertical transmission of this defect. The two variant carriers exhibited plasma concentrations of HDL cholesterol and apo A-I above the 95th percentiles of sex matched controls whereas the unaffected father and sister showed normal values. The plasma concentrations of apo C-III in the two variant carriers were decreased by 30-40% compared with those of the two unaffected family members and to random controls. Using two-dimensional immunoelectrophoresis as well as IEF and subsequent scanning densitometry, we found that the low serum concentration of apo C-III was a consequence of diminished concentrations of the variant apo C-III isoproteins in both VLDL (15% of normal) and HDL (25% of normal). Apo C-III(Lys58----Glu) heterozygotes possessed unusual HDL as demonstrated by nondenaturing gradient gel electrophoresis. They consisted mainly of HDL2b and contained a proportion of atypically large particles, enriched in apo E, with a Stokes diameter of 13-18 nm and resembling HDLc. In conclusion, heterozygosity for a structural apo C-III variant--apo C-III(Lys58----Glu)--was identified in two hyperalphalipoproteinemic subjects characterized by the presence of low plasma apo C-III concentrations and atypically large HDL.

Adult↗
PubMed1991

Using mutagenic polymerase chain reaction primers to detect carriers of familial defective apolipoprotein B-100.

Familial defective apolipoprotein (apo) B-100 is a genetic trait characterized by an Arg----Gln substitution in position 3500 of the apo B sequence. This genetic defect is associated with greatly increased concentrations of plasma cholesterol and may thus increase the risk of developing premature atherosclerotic disease. We describe here the use of mutagenic polymerase chain reaction primers, which greatly facilitate identification of carriers of this mutation. Moreover, we demonstrate that this method may also be used for determining the phase between two polymorphic sites. Using apo B-100 as an example we located on different chromosomes the defect in codon 3500 and a mutation in codon 3611, which produces another Arg----Gln change in the encoded apo B-100 amino acid sequence, in two probands heterozygous for both mutations.

Adolescent↗
PubMed1991

Site-specific methionine sulfoxide formation is the structural basis of chromatographic heterogeneity of apolipoproteins A-I, C-II, and C-III.

ApoA-I and apoC-II are eluted in two isoforms and apoC-III2 is eluted in three isoforms by reversed phase high performance liquid chromatography (HPLC). The structural basis of these nongenetic heterogeneities was unravelled using HPLC of proteolytic peptides and time-of-flight secondary ion mass spectrometry (TOF-SIMS). In apoA-I, the chromatographic microheterogeneity was caused by the formation of methionine sulfoxides (MetSO). However, only residues Met112 and Met148 were found oxidized, whereas Met86 was unaffected and also resistant towards artificial oxidation. To assess whether and to what extent amino acid substitutions in apoA-I might affect methionine sulfoxidation, the tryptic peptides of 13 different mutant apoA-I proteins from 24 heterozygous apoA-I variant carriers were analyzed by HPLC. In normal apoA-I, the ratios MetSO112/Met112 and MetSO148/Met148 were highly variable. By contrast, the relative ratio of oxidation of methionine residues 112 and 148 was constant. The amino acid changes Lys107----Met, Lys107----O, Glu139----Gly, Glu147----Val, and Pro165----Arg resulted in the preferential oxidation of Met112, and Asp103----Asn resulted in a preferential oxidation of Met148; whereas Pro3----Arg, Pro3----His, Pro4----Arg, Asp89----Glu, Ala158----Asp, Glu198----Lys, and Asp213----Gly had no impact. ApoC-II and apoC-III isoforms differed by the oxidation of the two methionine residues in these proteins. Whereas in apoC-II both methionine residues were oxidized in parallel, in apoC-III the two methionine residues differed in their susceptibility towards oxidation. We conclude that the formation of MetSO depends on the molecular microenvironment within a protein.

Amino Acid Sequence↗
PubMed1991

Relationship of lipoprotein(a) to variables of coagulation and fibrinolysis in a healthy population.

In the Prospective Cardiovascular Münster (PROCAM) study, serum lipoprotein(a) [Lp(a)] and its relationship to pro- and anticoagulatory as well as fibrinolytic indices were determined in a large group of employees: 864 men (m) and 373 women (f), ages 16-65 years. Univariate statistical analysis showed Lp(a) concentration to be associated with fibrinogen concentrations in both sexes (m: r = 0.08, P less than 0.05; f: r = 0.20, P less than 0.001), but not with euglobulin fibrinolysis activity, tissue-type plasminogen activator, plasminogen activator inhibitor type 1 (PAI-1), or the split products of cross-linked fibrin (d-dimer). In women only, Lp(a) was significantly correlated with antithrombin III (r = 0.15, P less than 0.01) and Protein C (r = 0.17, P less than 0.01). Further sex-related differences were seen in the relationship between Lp(a) and age (m: r = 0.05; f: r = 0.23, P less than 0.001) and body mass index (m: r = 0.01; f: r = 0.19, P less than 0.001), primarily as a consequence of remarkable differences of Lp(a) concentrations between postmenopausal (mean = 79.4 mg/L) and premenopausal women (mean = 51.5 mg/L, P = 0.001). Multiple-regression analysis demonstrated a significant negative correlation of Lp(a) to PAI-1 (m: beta = -0.12, P less than 0.01; f: beta = -0.14, P less than 0.05) and a positive correlation to cholesterol (m: beta = 0.18, P less than 0.001; f: beta = 0.17, P less than 0.01) and systolic blood pressure (m: beta = 0.08, P less than 0.05; f: beta = 0.11, P less than 0.05).

Adolescent↗
PubMed1991

Structural and functional properties of reconstituted high density lipoprotein discs prepared with six apolipoprotein A-I variants.

Six apolipoprotein A-I (apoA-I) variants containing the following amino acid changes: Pro3----Arg, Pro4----Arg, Lys107----0 (Lys deletion) Lys107----Met, Pro165----Arg, and Glu198----Lys, and the corresponding normal allele products, were isolated by preparative isoelectric focusing from heterozygous individuals. The apoA-I samples were reconstituted with palmitoyloleoyl phosphatidylcholine (POPC) or dipalmitoyl phosphatidylcholine (DPPC), and small amounts of cholesterol, into discoidal high density lipoprotein (HDL) complexes in order to examine their lipid binding and structural properties as well as their ability to activate lecithin:cholesterol acyltransferase (LCAT). Starting with initial molar ratios around 100:5:1 for phosphatidylcholine-cholesterol-apolipoprotein, all the normal and variant apoA-Is were completely incorporated into reconstituted HDL (rHDL). The rHDL particle sizes and their distributions were examined by nondenaturing gradient gel electrophoresis, before and after incubation with LDL, to assess the folding of apoA-I in the complexes. Intrinsic Trp fluorescence properties of the rHDL were measured, as a function of temperature and guanidine hydrochloride concentration, to detect conformational differences in the apoA-I variants. In addition, the LCAT reaction kinetics were measured with all the rHDL, and the apparent kinetic constants were compared. In terms of the structure of the rHDL particles, all the normal variant apoA-Is had similar sizes (94, 96 A) and size distributions, and indistinguishable fluorescence properties, with the exception of the Lys107----0 mutant. This variant formed slightly larger particles that were resistant to rearrangements in the presence of LDL, and had an altered apoA-I conformation in the vicinity of the Trp residues. The kinetic experiments with LCAT indicated that the apoA-I variants, Lys107----0 and Pro165----Arg, in rHDL particles had statistically different (30 to 90%) kinetic constants from the corresponding normal allele products; however, the variability in the kinetic constants among the normal apoA-I products was even greater (40 to 430%). Therefore, we conclude that the effects of these six mutations in apoA-I on the activation of LCAT are minor, and that the structural effects on rHDL, and possibly native HDL, are insignificant with the exception of the Lys107----0 mutation.

Amino Acid Sequence↗
PubMed1990

Structural analysis of human apolipoprotein A-I variants. Amino acid substitutions are nonrandomly distributed throughout the apolipoprotein A-I primary structure.

In the course of an electrophoretic mutation screening program of 32,000 dried blood samples from newborns, 17 genetic variants of apolipoprotein A-I (apoA-I) were found and structurally analyzed. The following defects were identified by the combined use of high performance liquid chromatography, time-of-flight secondary ion mass spectrometry, and sequence analysis: Pro3----Arg (1 x), Pro4----Arg (1 x), Asp89----Glu (1 x), Lys107----0 (4 x), Lys107----Met (2 x), Glu139----Gly (2 x), Glu147----Val (1 x), Pro165----Arg (4 x), and Glu198----Lys (1 x). The distribution of point mutations in the apoA-I gene leading to these 9 and 11 other variants of apoA-I reported previously was statistically analyzed. Substitutions are overrepresented in the 10 amino-terminal amino acids (p less than 0.001, chi 2-test) and in residues 103-177 (p less than 0.025, chi 2-test) or residues 103-198 (p less than 0.05, chi 2-test), respectively. We further noted the following. (i) Prolines were substituted by arginine or histidine residues at a frequency much higher than expected on the basis of random nucleotide substitutions (5 out of 18 "electrically non-neutral" amino acid substitutions, p less than 0.001, chi 2-test). These substitutions are the result of transversions of cytosines contained within stretches of at least 5 consecutive cytosines in the apoA-I gene. The observed hypervariability of the apoA-I amino terminus, therefore, might be caused by a hot spot for mutation formed by the 7 subsequent cytosines in codons 3, 4, and 5. (ii) CpG dinucleotides were overrepresentatively affected by C----T transitions (5 out of 18 electrically nonneutral amino acid substitution, p less than 0.001, chi 2-test). The hypervariability of the apoA-I alpha-helical domain might therefore be caused by CpG dinucleotides predominantly occurring in codons 120-208 of apoA-I (82 out of 125). (iii) Comparison of mutation sites in the human apoA-I gene with sites of nonsynonymous substitutions revealed that amino acid substitutions found in human apoA-I were predominantly localized in areas that were little conserved during mammalian evolution. These regions may therefore represent areas of less structural constraint for the function of apoA-I.

Amino Acid Sequence↗
PubMed1990

At what levels of total low- or high-density lipoprotein cholesterol should diet/drug therapy be initiated? European guidelines.

The control of coronary artery disease depends primarily on its prevention at an early stage. Researchers generally agree that early prevention depends on the elimination or treatment of known risk factors, among which hyperlipidemia occupies a central position. Two European Consensus Conferences have concluded that therapy of hyperlipidemia should always start with dietary counseling. First, subjects with body mass indexes (weight/height) greater than 27 should lose weight. Second, the lipid-lowering diet should provide 55% of calories from carbohydrates; 10 to 15% from protein; and up to 30% from fat comprising 10% each of saturated, monounsaturated and polyunsaturated fatty acids; less than 300 mg/day cholesterol; 35 g/day of fiber derived largely from legumes and other vegetables; and fruit. Further reduction of fat consumption (to 20 to 25% of total energy) and of cholesterol (to less than 150 mg/day) may be attempted when patients respond inadequately to the standard diet. The goal of treatment is to minimize the risk of coronary artery disease and of pancreatitis. Where possible, a low-density lipoprotein cholesterol level of 135 mg/dl (3.5 mmol/liter) should be the goal in hypercholesterolemic patients with multiple or severe risk factors and a level of 155 mg/dl (4 mmol/liter) in the absence of other risk factors. Also, high-density lipoprotein cholesterol greater than 35 mg/dl and triglycerides less than 200 mg/dl are considered important goals of treatment. Some patients with hyperlipidemia do not respond adequately to diet and correction of underlying causes; drug treatment should then be instituted, but careful attention to diet should be continued.

Cholesterol, HDL↗
PubMed1990

Genes and dyslipoproteinaemias.

The Prospective Cardiovascular Münster (PROCAM) Study clearly demonstrated that low levels of high density lipoprotein (HDL)-cholesterol are a powerful predictor of subsequent coronary heart disease (CHD) and that both exogenous factors (cigarette smoking, physical inactivity, obesity) and genetic factors (dyslipidaemia, diabetes mellitus) affect serum concentrations of HDL-cholesterol. In case-control studies, the apoprotein (apo) B/apo A-I ratio was found to be more meaningful than the lipoprotein lipid ratio in predicting risk of CHD in a group of young myocardial infarction (MI) survivors. Screening of young (less than or equal to 45 years) MI survivors did not show an increased prevalence of apo A-I variants compared with controls and newborns, thus apo A-I variants probably do not contribute substantially to low HDL-cholesterol levels and the risk of CHD in the general population. Genetic anomalies causing HDL-cholesterol depletion or apo A-I deficiency probably do not relate to structural anomalies of apo A-I but rather to regulatory anomalies in the production of HDL apolipoproteins or to catabolic or intracellular events that are important in the homeostasis of plasma HDL-cholesterol.

Apolipoproteins↗
PubMed1990

Modelling the Helsinki Heart Study by means of risk equations obtained from the PROCAM Study and the Framingham Heart Study.

Data from the Prospective Cardiovascular Münster (PROCAM) study have been used to develop a mathematical model that accurately predicts the outcome of treatment in a primary prevention study (the Helsinki Heart Study). The PROCAM study identified 8 major risk factors for coronary heart disease: age, total plasma cholesterol level, plasma high density lipoprotein (HDL)-cholesterol level, systolic blood pressure, smoking, diabetes, angina pectoris, and a family history of myocardial infarction. A single risk factor such as total plasma cholesterol level is not sufficiently sensitive to identify individuals at high risk of coronary heart disease. The total cholesterol:HDL-cholesterol ratio is recommended for clinical use. On the basis of these data, a primary prevention strategy for coronary heart disease in West Germany has been proposed to optimise the cost-effectiveness of such treatment. Future research should focus on the identification of feasible and sensitive risk factors for coronary heart disease. Fibrinogen and apolipoproteins have already attracted interest in this regard but more definitive studies are required to confirm their role as risk factors for coronary heart disease.

Coronary Disease↗
PubMed1990

Primary prevention of coronary heart disease in the Federal Republic of Germany. Analysis of cost-effectiveness.

The cost-effectiveness of a primary prevention strategy for coronary heart disease is reviewed in this paper. Five subgroups were identified, depending on the degree of medical intervention required to achieve a target low density lipoprotein (LDL)-cholesterol level of less than 4.15 mmol/L. One group required no intervention and, apart from initial screening costs, no further treatment costs were incurred. The cost-effectiveness of medical intervention in the other groups was calculated by use of mathematical models to predict the incidence of coronary heart disease. According to this analysis, life-years saved per 1000 individuals and cost per life-years saved increased as the intensity of intervention increased. In individuals in whom a reduction in total cholesterol was required, life expectancy did not improve substantially, but the onset of coronary heart disease was deferred until an older age. Cholesterol-lowering interventions are unlikely to result in important savings to the health care system, as the benefit of treatment is rather reflected in terms of reduced mortality and improved quality of life. Total costs (in Deutschmarks [DM]) per life-year saved in this analysis were DM30,000-40,000 in men and DM86,000-110,000 in women.

Coronary Disease↗
PubMed1990

HDL metabolism and atherosclerosis.

Epidemiologic studies of recent years have demonstrated an association between low plasma high-density lipoprotein (HDL) cholesterol levels and the development of atherosclerosis. The PROCAM (Prospective Cardiovascular Münster) study has identified HDL cholesterol as the single parameter predictor with the highest potency. Also, in multiple logistic function analysis of these data, which included the eight best independent predictors, HDL cholesterol contributed the largest portion to the overall predictive power of the algorithm. Further evidence for the important role of HDL in the atherosclerotic process was provided by the Helsinki Heart Study, in which the lipid-lowering and HDL-increasing drug gemfibrozil was effective in reducing CAD incidences. In cohort studies, we have shown that HDL cholesterol concentrations largely differ between CAD patients and sex- and age-matched unaffected controls and that this difference increases with age. The reverse cholesterol transport hypothesis is the most widely used to explain the biochemistry of HDL-mediated atherosclerosis. In fact, it has been shown that HDL mediates the disposal of excess cellular cholesterol. There is evidence for the existence of two different mechanisms by which HDL can take up cellular cholesterol: both involve specific cellular recognition sites and probably also different HDL subpopulations. At least two different mechanisms have been identified by which the HDL cholesterol is finally targeted to the liver: attachment of apolipoprotein E for direct recognition by liver receptors or lipid transfer to lipoproteins of lower density that are subsequently also recognized by internalizing liver receptors. This knowledge gives rise to many different candidate genes for the formation of HDL deficiencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Arteriosclerosis↗
PubMed1990

Normolipemic dysbetalipoproteinemia and hyperlipoproteinemia type III in subjects homozygous for a rare genetic apolipoprotein E variant (apoE1).

A family with three heterozygote and two homozygote carriers of the rare apolipoprotein E1 isoform was detected by isoelectric focusing. One of the homozygous patients had type III hyperlipidemia, while the other showed normolipemic dysbetalipoproteinemia. Restriction fragment length analysis as well as allele specific oligonucleotides were used to identify the structural alterations forming the abnormal epsilon 1 genotype. Comparison with the most common epsilon 3 allele showed that two base exchanges A for G in codon 127 and T for G in codon 158 (Asp for Gly and Cys for Arg, respectively) are responsible for the amino acid substitution which causes the charge shift observed in isoelectric focusing. The same defects have been described in the only previously characterized apoE1 (Weisgraber et al. 1984. J. Clin. Invest. 73: 1024-1033). In addition to the study by Weisgraber and coworkers, who reported on a heterozygous patient, we here describe the metabolic and clinical consequences of a homozygosity for this rare allele. Changes in lipoprotein metabolism, as well as in clinical phenotypes, were exactly identical to those seen in patients homozygous for the epsilon 2 allele, which has in common with the epsilon 1 allele the mutation in codon 158, but lacks the substitution in codon 127. In addition, lipoprotein profiles of the epsilon 3/epsilon 1 heterozygotes were indistinguishable from those of epsilon 3/epsilon 2 heterozygotes. Therefore, we conclude that the additional mutation in codon 127 that characterizes the epsilon 1 allele is of no functional importance in vivo.

Adolescent↗
PubMed1990

Lipoprotein(a) is an independent risk factor for myocardial infarction at a young age.

We quantified lipoprotein(a) [Lp(a)] immunochemically in young (less than 46 y) male survivors of myocardial infarction and in age-matched controls recruited from participants of the Prospective Cardiovascular Münster (PROCAM) study. We further determined apolipoprotein E polymorphism and measured triglycerides, total cholesterol, high- and low-density lipoprotein cholesterol (HDL and LDL), and apolipoproteins AI, AII, and B in the serum of these subjects. Lp(a) concentrations in serum were not correlated with other well-recognized risk factors for early myocardial infarction such as apolipoproteins AI and B, LDL cholesterol, and HDL cholesterol. Apolipoprotein E polymorphism did not affect Lp(a) concentrations, but had a major influence on apolipoprotein B concentration. Lp(a) concentrations were not influenced by age. Our data suggest that (a) an increased concentration of Lp(a) constitutes an independent risk factor for early myocardial infarction and (b) the concentrations of Lp(a) and LDL cholesterol (apolipoprotein B) in serum are under separate metabolic control.

Age Factors↗
PubMed1989

Diabetes mellitus and hypertension in the elderly: concomitant hyperlipidemia and coronary heart disease risk.

Age is an important factor in predicting risk of myocardial infarction (MI). Age is currently treated as an independent variable in assessing risk, but it is also related to other major risk factors including hyperlipidemia, hypertension and diabetes, all of which increase in prevalence with age. Current evidence indicates that a combination of 2 or more of the major risk factors predisposes a person to a high risk of MI. In the experience of the Prospective Cardiovascular Munster study, patients with diabetes alone have twice the risk of MI, but those with diabetes and hyperlipidemia have about a 15-fold increased risk. Similarly, patients with hypertension alone have twice the risk of MI, but those with hypertension combined with hyperlipidemia have approximately a 15-fold increased risk.

Adult↗
PubMed1989

European lipid guidelines: therapeutic recommendations. European Atherosclerosis Society.

The European Consensus Conference has classified persons with hyperlipidemia into 5 groups on the basis of cholesterol and triglyceride levels. Plasma cholesterol concentration alone is not sufficient for the assessment of myocardial infarction risk; other risk factors must be considered for a more sensitive prediction. Guidelines for risk assessment of coronary heart disease and treatment regimens for each of the 5 hyperlipidemia groups, as outlined in the Policy Statement on coronary heart disease of the European Atherosclerosis Society, are described. It is emphasized that therapeutic goals for patients with hyperlipidemia depend to some extent on the presence or absence of other risk factors; plasma cholesterol and low-density lipoprotein cholesterol target levels may be lower in those with associated risk factors.

Age Factors↗