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Biomedical subjects

H Dieplinger

Publications and source records attributed to H Dieplinger.

At least 73 records · Page 4Linked to original sources
PubMed1992

Apo(a) isoforms predict risk for coronary heart disease. A study in six populations.

Elevated concentrations of lipoprotein(a) (Lp[a]) in plasma are associated with premature coronary heart disease (CHD). Lp(a) levels are largely determined by alleles at the hypervariable apolipoprotein(a) (apo[a]) gene locus, but other genetic and environmental factors as well as diseases also affect plasma Lp(a) concentrations. It is therefore unclear whether Lp(a) is a primary genetic risk factor or whether Lp(a) levels are elevated secondary to disease in CHD patients. We have analyzed apo(a) phenotypes that represent a stable genetic trait in subjects with CHD and control subjects from different populations representing a variety of ethnic groups (Tyrol, Germany, Wales, Israel, Singapore Chinese, and Singapore Indian). Despite differences in sampling design and disease definition in this multipopulation case-control study, those apo(a) isoforms associated with high Lp(a) plasma concentrations (B, S1, and S2) were more frequent in the CHD patients in each ethnic group. These differences were significant in three of the studied populations and highly significant (p < 0.001) in the pooled (total) group. Lp(a) concentrations were also measured in all groups except Germans and were found to be consistently higher in cases than in control subjects in each ethnic group. For all but one population (Israeli) the differences were significant. The effects of the apo(a) size polymorphism on Lp(a) levels were similar in CHD patients and control subjects from different populations. The data demonstrate that alleles at the apo(a) locus determine the risk for CHD through their effects on Lp(a) concentrations across multiple populations with large differences in CHD frequency and risk factor profiles.

Adult↗
PubMed1990

[Plasma concentration of lipoprotein(a) and distribution of its subtypes in the healthy population of Hungary].

Authors determined the plasma levels of total cholesterol, HDL-cholesterol, apoprotein B-100 (apo B-100), apoprotein A-I (apo A-I) and lipoprotein(a) in 202 (139 female and 63 male) randomized blood donors. The phenotypes of lipoprotein(a) were detected by SDS-polyacrylamide gelelectrophoresis and Western blotting. The average plasma total cholesterol concentration of this Hungarian population was 5.7 +/- 1.1 mmol/l. The other lipoprotein parameters were HDL-cholesterol: 1.36 +/- 0.04 mmol/l; and the apoprotein B-100 concentration: 70 +/- 17.4 mg/dl. In these parameters no difference between males and females could be found. The average plasma apoprotein A-I in females was 156.3 +/- 23.6 mg/dl and in males 143.8 +/- 26.8 mg/dl and the difference was statistically significant (p less than 0.01). The average lipoprotein(a) concentration of this population was 10.5 +/- 13.5 mg/dl and there was no significant difference between males and females (9.0 +/- 10.7 and 13.9 +/- 17.7 mg/dl, respectively). The distribution of plasma Lp(a) was highly skewed in the direction of low concentration values. In females a moderate bimodial distribution could be demonstrated. Documented by several authors lipoprotein(a) level higher than 30 mg/dl serves as an independent risk factor for atherosclerosis. In this population only 9.4% of subjects had lipoprotein(a) concentrations over this limit (5.9% female and 3.5% male). The relative alle frequency of different phenotypes showed the following distribution: B 0.007, S1 0.015, S2 0.154, S3 0.231, S4 0.230 and null 0.362. In this population the F phenotype could not be detected.

Arteriosclerosis↗
PubMed1990

Abetalipoproteinemia with an ApoB-100-lipoprotein(a) glycoprotein complex in plasma. Indication for an assembly defect.

Patients with autosomal recessive abetalipoproteinemia (ABL) lack in their plasma all lipoproteins containing apolipoprotein (apo)B-100 or B-48. Previous studies have suggested that this is due to the complete absence of apoB. We have investigated whether such patients (n = 10) are able to secrete the lipoprotein(a) (Lp(a] glycoprotein (apo(a] which, in normal plasma, exists as a complex with low density lipoproteins containing apoB-100 (Lp(a) lipoprotein). All 10 patients had reduced but detectable apo(a) levels in plasma (mean, 0.49 mg/dl; range, 0.2-2.03 mg/dl) but no Lp(a) lipoprotein. However, we also detected small amounts (0.2-2.8 mg/dl) of apoB in all patients with ABL. The apoB in the ABL patients had the size of apoB-100 and occurred as a lipid-poor complex with the Lp(a) glycoprotein in a fraction of density 1.22 g/ml. This material may represent partially assembled Lp(a) lipoprotein. There was also uncomplexed apo(a) and apoB-100 in the ABL plasma. The distribution and relative concentration of both proteins in the density fraction greater than 1.06 g/ml varied among patients. The data suggest that in ABL, the assembly of apoB-containing lipoproteins is defective and that apoB-100 may be secreted without its full lipid complement when complexed with apo(a).

Abetalipoproteinemia↗
PubMed1990

Lecithin cholesterol acyl transferase deficiency: molecular analysis of a mutated allele.

The enzyme, lecithin cholesterol acyltransferase (LCAT), is responsible for the esterification of plasma cholesterol mediating the transfer of an acyl group from lecithin to the 3-hydroxy group of cholesterol. Deficiency of the enzyme is a well-known syndrome with a widespread geographic occurrence. We have cloned an allele from a patient homozygous for the LCAT deficiency. The only change that we could detect is a C to T transition in the fourth exon of the gene; this causes a substitution of Arg for Trp at position 147 of the mature protein. The functional significance of such a substitution with respect to the enzyme defect was demonstrated by transfecting the mutated LCAT gene in the cell line COS-1.

Alleles↗
PubMed1990

Frequency and effect of human apolipoprotein A-IV polymorphism on lipid and lipoprotein levels in an Icelandic population.

Human apolipoprotein A-IV (apo A-IV) exhibits a genetic polymorphism with two common alleles, A-IV1 and A-IV2, in Caucasian populations. We have investigated this polymorphism in the Icelandic population. The frequencies of the two alleles are significantly different from middel European populations with a higher frequency of the A-IV2 allele (0.117 versus 0.077) occurring in Iceland. The alleles at the apo A-IV locus have significant effects on plasma high density lipoprotein cholesterol (HDL-C) and triglyceride levels. The average effect of the A-IV2 allele is to raise HDL-C by 4.9 mg/dl and to lower triglyceride levels by 19.4 mg/dl. We estimate that the genetic variability at the apo A-IV gene locus accounts for 3.1% of the total variability of HDL-C and for 2.8% of the total variability of triglycerides in the population from Iceland. This confirms and extends our previous observations on apo A-IV allele effects in Tyroleans in an independent population.

Alleles↗
PubMed1989

Defects in the low density lipoprotein receptor gene affect lipoprotein (a) levels: multiplicative interaction of two gene loci associated with premature atherosclerosis.

The lipoprotein (a) [Lp(a)] contains two nonidentical protein species, apolipoprotein (apo) B-100 and a specific high molecular weight glycoprotein, apo(a). Lp(a) represents a continuous quantitative genetic trait, the genetics of which are only poorly understood. Genetic variation at the apo(a) locus affects plasma Lp(a) levels and explains at least 40% of the variability of this trait. Lp(a) levels were found to be elevated 3-fold in the plasma from patients with the heterozygous form of familial hypercholesterolemia who have one mutant low density lipoprotein receptor gene. This elevation was not due to a higher frequency of those apo(a) types that are associated with high Lp(a) levels in familial hypercholesterolemia patients. Rather Lp(a) levels were elevated for each of the apo(a) phenotypes examined. The effects of the apo(a) and low density lipoprotein receptor genes on Lp(a) levels are not additive but multiplicative. This is a situation not commonly considered in quantitative human genetics. We conclude that Lp(a) levels in plasma may be determined by variation at more than one gene locus.

Arteriosclerosis↗
PubMed1988

Quantification of human apolipoprotein A-IV by "sandwich"-type enzyme-linked immunosorbent assay.

A specific and sensitive "sandwich"-type enzyme-linked immunosorbent assay (ELISA) has been developed for quantifying human apo A-IV. Using apo A-IV immunosorbent columns, we isolated monospecific anti-apo A-IV antibodies for coating the ELISA plates and for preparing peroxidase-antibody conjugate. The assay can detect as little as 0.20 ng of apo A-IV, with mean intra- and interassay CVs of 3.6% and 8.2%, respectively. The apoA-IV concentrations in normolipemic and hyperlipemic plasma were unaffected by either delipidation or treatment with detergents or urea. To validate the ELISA assay we compared it with an immunoelectrophoretic technique. ApoA-IV concentrations in plasma from normo- and dyslipemic subjects compared well by the two assays (r = 0.89). The mean apo A-IV concentration, measured by ELISA in plasma from 50 normolipemic subjects, was 143 (SD 52) mg/L; values for dyslipemic subjects were not significantly different. We also used this new assay to monitor apo A-IV profiles of normolipemic and hypertriglyceridemic plasma after chromatographic fractionation.

Apolipoproteins A↗
PubMed1987

In vitro formation of HDL-2 from HDL-3 and triacylglycerol-rich lipoproteins by the action of lecithin:cholesterol acyltransferase and cholesterol ester transfer protein.

In order to study the factors responsible for the formation of high-density lipoprotein subfraction-2 (HDL-2), very-low-density lipoproteins (VLDL) and HDL-3 were mixed and incubated with purified bovine milk lipoprotein lipase, human serum lecithin:cholesterol acyltransferase, cholesteryl ester transfer protein and mixtures thereof. The results can be summarized as follows: Incubation of HDL-3 and VLDL for 24 h at 37 degrees C without enzymes did not cause any significant change in the protein:lipid ratio or in the flotation constant of the HDL. Cholesteryl ester transfer protein treatment caused only an exchange of part of the HDL cholesteryl esters with VLDL triacylglycerols. Lipoprotein lipase caused a slight shift of HDL-hydrated density to lower values; HDL-2b, however, was not formed. Incubation of HDL-3 and VLDL with lecithin:cholesterol acyltransferase or mixtures of lecithin:cholesterol acyltransferase and lipoprotein lipase reduced the HDL-protein:lipid ratio and increased the HDL-flotation rate. The newly formed HDL resembled that of native HDL-2a. The incubation of HDL-3 and VLDL with lecithin:cholesterol acyltransferase and cholesteryl ester transfer protein caused a shift of the HDL-3 into an HDL-2b-like fraction. Particles resembling HDL-2b in the analytical ultracentrifuge were also formed if VLDL + HDL-3 were incubated with lipoprotein lipase or lipoprotein lipase + cholesteryl ester transfer protein in a medium containing low amounts of albumin, insufficient for binding all liberated fatty acids during hydrolysis. The incubation of mixtures of HDL-3 and chylomicrons enriched with apoAI in the presence of lecithin:cholesterol acyltransferase and cholesteryl ester transfer protein caused the formation of HDL-2-like particles which resembled those of native HDL-2 also with respect to the apoAI/AII ratio.

Carrier Proteins↗
PubMed1987

The role of LCAT and cholesteryl ester transfer proteins for the HDL and LDL structure and metabolism.

Since the early detection of LCAT by Glomset, a great deal of research has been conducted for establishing the role of this enzyme in the Lp metabolism. It became apparent that LCAT produces more than 3/4 of the CE found in plasma. LCAT acts primarily on Lp with high PC/FC contents and high PC/FC ratios. For expression of the full activity, apo-Lp cofactors such as apo-AI, -CI, -AIV and -E are necessary. Although it was believed for a long time that HDL are the only substrate for LCAT we could demonstrate that LDL and even apoA/C/E free LpB is utilized by LCAT. The CE formed in PC/FC rich Lp are transferred to VLDL and LDL by specific proteins, which also promote the exchange of CE against TG. TG in these particles are hydrolyzed by liver lipase providing new space in the core for further cholesterol esterification. Thus LCAT exerts its physiological role in concert with other enzymes e.g. LPL, hepatic lipase and possibly phospho-lipases as well as with exchange and transfer processes partly catalyzed by specific exchange/transfer proteins. The main function of LCAT without doubt is the reverse cholesterol transport from periphery to liver counteracting the accumulation of CE in reticulo endothelial cells by the scavenger pathway. Metabolic studies revealed that the cholesterol clearance from the circulation proceeds in the same order of magnitude as the esterification by LCAT takes place. This possibly implies that LCAT might be the rate limiting enzyme for cholesterol catabolism from blood.

Animals↗
PubMed1986

Cloning and expression of human lecithin-cholesterol acyltransferase cDNA.

cDNA and genomic cloning has been used to determine the mRNA and amino acid sequence of human plasma lecithin-cholesterol acyltransferase (LCATase; EC 2.3.1.43). The mature protein was found to contain 416 amino acid residues with a hydrophobic leader sequence of 24 amino acids. An unusual feature of the message is that the poly(A) signal AATAAA overlaps the COOH-terminal glutamic acid and stop codons, and the 3' untranslated region is only 23 bases. The protein itself is distinguished by a number of extended sequences of hydrophobic amino acids, one of which contains a hexapeptide identical with the interfacial binding segment of the active site of pancreatic lipase and is similar to the same site of lingual lipase. The cloned cDNA allows the expression of active LCATase by transfected tissue culture cells.

Amino Acid Sequence↗
PubMed1986

Plasma cholesterol metabolism in end-stage renal disease. Difference between treatment by hemodialysis or peritoneal dialysis.

Plasma cholesterol metabolism was investigated in normotriglyceridemic patients with end-stage renal disease treated by hemo- or continuous ambulatory peritoneal dialysis (CAPD), and compared with that in a control group with normal renal function. A reversed net transport of free cholesterol from plasma to cultured fibroblasts, as well as greatly reduced levels of plasma cholesterol esterification and cholesterol ester transfer rates to low and very low density lipoproteins (LDL and VLDL), was found in the hemodialysis group compared to the controls. The LDL and VLDL contained increased amounts of free cholesterol and inhibited cholesterol ester transfer when recombined with control plasma. The LDL triglyceride content was doubled in the hemodialysis group, whereas cholesterol esters were decreased. Patients treated by CAPD, in marked contrast, had cholesterol metabolic rates that were within the normal range, as well as normal lipoprotein composition.

Apolipoprotein A-I↗
PubMed1985

Altered metabolism of low density lipoprotein in humans after prolonged incubation in plasma.

Lecithin: cholesterol acyltransferase (LCAT) in combination with exchange and transfer proteins is known to alter the composition of all plasma lipoprotein fractions. Human plasma from healthy donors was incubated for 24 h at 37 degrees C in the absence and at 4 degrees C and at 37 degrees C in the presence of the LCAT inhibitors sodium iodoacetate (5 mmol/l), and the low density lipoprotein fractions (LDL) were isolated. LDL isolated from LCAT-active plasma (LDL-a) exhibited pronounced alterations in their surface material: the relative content of phospholipids and of free cholesterol was reduced and the content of tetramethylurea-soluble apolipoproteins was increased. LDL isolated from plasma incubated at 37 degrees C with or without sodium iodoacetate showed significantly increased triglyceride concentrations. The LDL fractions from LCAT-active and LCAT-inactive (LDL-i) incubates were iodinated with 125I and 131I respectively, and their metabolic behaviour was studied in humans. LDL-a was cleared from circulation at a slower rate as compared with LDL-i (t 1/2 = 3.17 +/- 0.47 vs 2.88 +/- 0.45 days). The apparent fractional catabolic rate of LDL-a, calculated according to a two-pool model, was reduced by 22.2 +/- 3.1%. Comparing LDL-a with LDL isolated from LCAT-inactive plasma which had been incubated at 37 degrees C, the changes in the metabolic variables were less pronounced. It is concluded that physiological alterations of the chemical compositions, caused by LCAT and exchange/transfer proteins, influence the metabolism of LDL.

Adult↗
PubMed1985

The in vitro formation of HDL2 during the action of LCAT: the role of triglyceride-rich lipoproteins.

We examined the effects of lecithin:cholesterol acyl transferase (LCAT) and of lipoprotein lipase (LPL) on the conversion of high density lipoproteins (HDL) towards fractions of lower densities using the analytical ultracentrifuge. Freshly isolated whole plasma was incubated for 24 h at 37 degrees C in the presence or absence of active enzyme systems. In some cases, lipoproteins were removed by selective precipitations; alternatively, we added triglyceride-rich lipoproteins (TGRLP) or Intralipid to the incubations. The results are as follows. 1) The incubation of whole plasma containing active LCAT leads to a conversion of HDL3 to a fraction of lower density, notably HDL2a. If LCAT is inhibited, the conversion is far less pronounced. 2) If very low and low density lipoproteins are removed by phosphotungstate precipitation and the supernatant is incubated with LCAT, HDL3 shifts towards higher densities. 3) The presence of phosphatidylcholine/cholesterol liposomes or the presence of blood cells as a source of additional LCAT substrate had only little influence on the HDL conversion in our system. 4) The addition of TGRLP or of Intralipid at minimal ratios of 2.5:1 caused an almost complete conversion of HDL3 to HDL2b. This conversion was dependent on active LCAT. 5) LPL also caused a shift of HDL3 to HDL2a if TGRLP was present. HDL2b, however, was not formed by LPL unless LCAT was active.

Cholesterol↗
PubMed1984

The low-density-lipoprotein pathway of native and chemically modified low-density lipoproteins isolated from plasma incubated in vitro.

Normal fasting human plasma was incubated for 24 h at 37 degrees C in the presence or absence of lecithin:cholesterol acyltransferase (LCAT) inhibitors. The low-density lipoprotein (LDL) fractions of incubated plasma (control LDL and LCAT-modified LDL) were studied with respect to their chemical and functional properties. LCAT-modified LDL differed from control LDL by a decreased phospholipid and free-cholesterol content, but increased cholesteryl esters. Furthermore, an increase of the relative protein content in LDL by 16-20% was found. Apolipoproteins of LCAT-modified LDL exhibited a 10-fold increase of apo AI, a 4-5-fold increase of apo E, and a 2-fold increase of apo C. All these apolipoproteins resided together with apo B on the same particles. LCAT-modified LDL displayed a higher electrophoretic mobility, a higher hydrated density, a decreased flotation constant and a smaller diameter. Cultured human fibroblasts bound and internalized LCAT-modified LDL to a lower extent than control LDL. The degradation, however, was faster. Modified LDL suppressed 3-hydroxy-3-methylglutaryl-CoA reductase activity to a lower extent than did control LDL. Our results demonstrate that LCAT action, together with lipid transfer and exchange processes, markedly alters the chemical and physiochemical properties of LDL. This in turn significantly influences LDL catabolism in vitro.

Cells, Cultured↗
PubMed1984

In vitro modification of the chemical composition of human plasma low density lipoproteins: effects of morphology and thermal properties.

The effects of enzymatic action on human low density lipoproteins (LDL) occurring during in vitro incubation of plasma have been studied by chemical analysis, analytical ultracentrifugation, negative stain electron microscopy and X-ray small angle scattering. Chemically, the action of cholesteryl ester exchange and transfer proteins(s) (CEPT) leads to a relative increase in trigylcerides at the expense of cholesteryl esters. Morphologically, the particles maintain their characteristic features detectable by X-ray small angel scattering. Additional action of lecithin/cholesterol acyl transferase (LCAT) causes mainly a decrease in polar lipid contents and a reduction in particle size. The associated changes in the thermotropic transition were found to be strongly correlated to the triglyceride/cholesteryl ester ratio.

Carrier Proteins↗
PubMed1983

Apolipoproteins (A-I, A-II, B), Lp(a) lipoprotein and lecithin: cholesterol acyltransferase activity in diabetes mellitus.

Concentrations of HDL cholesterol, apolipoprotein (apo) A-I and apo A-II were found to be significantly decreased in patients with insulin-dependent diabetes (IDD) and non-insulin-dependent diabetes (NIDD) compared with carefully selected controls matched for sex, age and body weight. LDL cholesterol and apo B levels did not differ significantly between diabetics and controls. Concentrations of lipoprotein Lp(a), an independent risk factor for coronary artery disease in non-diabetics, were above 20 mg/dl in only 14% of diabetics and in 5% of controls. LCAT activity was normal in diabetics, irrespective of type of diabetes, sex and age of patients. No correlation between HbA1 and either HDL cholesterol or A-I and A-II was found in IDD and NIDD. A positive correlation between HbA1 and either triglyceride or VLDL triglyceride was noted in IDD and NIDD. There was also a positive correlation between insulin dosage in IDD and HDL cholesterol, apolipoprotein A-I and A-II.

Adolescent↗