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Biomedical subjects

R R Frants

Publications and source records attributed to R R Frants.

At least 181 records · Page 10Linked to original sources
PubMed1992

Heparan sulphate proteoglycans are involved in the lipoprotein lipase-mediated enhancement of the cellular binding of very low density and low density lipoproteins.

We found that LPL enhances the binding to HepG2 cells and fibroblasts of both VLDL and apoE free LDL. In the presence of 1.7 micrograms/ml of purified bovine LPL, the binding of LDL and VLDL was up to 60 fold increased as compared to the control binding. In addition, LPL enhances the binding in LDL-receptor negative fibroblasts to the same extent as it does in normal fibroblasts. The presence of 10 mM of EGTA could not prevent the LPL-mediated enhancement of the binding of both LDL and VLDL to fibroblasts, indicating that the binding is calcium independent. Furthermore, up- and down regulation of the LDL receptor did not influence the binding of these lipoproteins in the presence of LPL. Strikingly, we found that the enhancing effect of LPL on the binding of LDL and VLDL to HepG2 cells could be abolished by preincubation of the cells with heparinase, suggesting that heparan sulphate proteoglycans are involved in the LPL-mediated stimulation. We hypothesize that the enhancement of the cellular binding of LDL and VLDL in the presence of LPL is caused by an LPL-bridging between proteoglycans present on the plasma membrane and the lipoproteins, and that the LDL receptor and LRP are not involved.

Cell Membrane↗
PubMed1992

Absence of mutations in the promoter region of the low density lipoprotein receptor gene in a large number of familial hypercholesterolaemia patients as revealed by denaturing gradient gel electrophoresis.

Denaturing gradient gel electrophoresis (DGGE) was used in combination with the polymerase chain reaction (PCR) to detect sequence variations in the promoter region of the low density lipoprotein receptor (LDLR) gene. On the basis of calculated predictive melting properties we designed primers to amplify a 447-bp fragment of the promoter region from position -512 to -66, containing previously identified regulatory sequences. Using a primer with a GC-clamp in combination with restriction enzyme digestion, two melting domains could be analysed simultaneously. By oligonucleotide-directed mutagenesis artificial mutants were generated to optimize the conditions and to test the sensitivity of the method. All mutants were readily detected by electrophoresis in a 9% polyacrylamide gel containing a 10%-60% linear denaturing gradient. Using this method, we analysed DNA samples of 350 heterozygous familial hypercholesterolaemia (FH) patients. No mutations were detected, suggesting that mutations in the regulatory elements of the promoter sequence do not play a significant role in the etiology of FH.

Base Sequence↗
PubMed1992

Protease inhibitor (Pi) locus, fertility and twinning.

In a sample of 160 Dutch twin pairs and their parents, we found that mothers of dizygotic twins had frequencies of the S and Z alleles at the protease inhibitor (Pi) locus that were 3 times higher than a control sample. Mothers of identical twins also had a higher frequency of S than controls. The S allele may thus both increase ovulation rate and enhance the success of multiple pregnancies. There was also an increased frequency of the S allele in fathers of dizygotic twins; however, this may be a secondary effect of assortative mating for family size (indicating by the number of siblings of the parents), for which a correlation of 0.2 was observed. Parents of dizygotic twins came from larger families than parents of monozygotic twins, but no effect of Pi type on family size was seen.

Alleles↗
PubMed1992

Familial dysbetalipoproteinemia: a genetically heterogenous disease caused by mutations of the ligand apolipoprotein E.

Apolipoprotein E is present on the surface of very-low-density lipoprotein (VLDL) and chylomicron-remnants and is essential for the receptor mediated endocytosis of these particles via hepatic receptors. Several types of mutations of the apoE can cause a deficiency in the clearance of these remnant particles. An accumulation of lipoprotein-remnant particles may occur and familial dysbetalipoproteinemia (FD) develops. Genotyping of the various apoE variants and relation of these mutations with their effect on the lipoprotein-remnant removal have provided more insight in the structure-relationship of apoE ligand-receptor interactions. It is postulated that the apoE2 (Arg158----Cys) mutation is just outside the binding domain and that its deficient binding can be stimulated by exogenous factors. This hypothesis can explain why apoE2/E2 homozygosity can only induce FD under certain circumstances. ApoE mutations that occur in the binding domain, e.g., apoE2 (Lys146----Gln) have a direct effect on the ligand-receptor binding and, in these individuals, FD is inherited in an autosomal dominant way. Finally, apoE3-Leiden has an arginine residue at 112 and has a repeat of seven extra amino acid residues just outside the binding domain. Because of this repeat, conformational changes of the binding domain can ensue. Due to the fact that in apo E3-Leiden the arginine residue is present at 112, apoE3 Leiden is predominantly present on chylomicron and VLDL remnants. In these persons FD is also inherited in an autosomal dominant way.

Apolipoproteins E↗
PubMed1992

Lipoprotein profile of a Greenland Inuit population. Influence of anthropometric variables, Apo E and A4 polymorphism, and lifestyle.

Previously it has been reported that Greenland Inuit (Eskimos) from the Uummannaq district display low levels of plasma cholesterol and triglycerides and relatively high levels of high density lipoprotein (HDL) when compared with healthy Danish control subjects (Lancet 1971;1:1143-1146). Here we present data obtained in 1989 that show the following. In a group of 133 healthy adult Greenland Inuit from Nanortalik, the levels of plasma cholesterol and low density lipoprotein (LDL) cholesterol (6.39 and 4.39 mmol/l, respectively) were slightly higher than "normal" values found in western societies, whereas the HDL cholesterol level was markedly higher (1.64 mmol/l). Compared with most Caucasian populations, the Inuit population we studied exhibits a high apolipoprotein (APO)E*4 allele frequency (0.229), whereas the APOE*2 allele frequency was extremely low (0.015). In contrast to Caucasian populations, in the Inuit population the apoE polymorphism showed only a minor influence on the plasma lipid and (apo)lipoprotein levels, as evaluated by multiple regression analysis, with the exception of apoE levels. This absence of an effect could be explained by the low very low density lipoprotein (VLDL) plus intermediate density lipoprotein (IDL) cholesterol levels. The contributions of eicosapentaenoic acid and linoleic acid to the total amount of fatty acids in plasma cholesterol esters differed markedly from those reported in 1971 for another Greenland Inuit population (3.2% versus 15.8% and 49.5% versus 20.4%, respectively), thereby resembling values now found in the average western population. Even in those Inuit who reported exclusive consumption of the traditional Inuit diet (13% of the population), the fatty acid composition of the plasma cholesterol esters closely resembled the values measured in western populations.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

The familial hypercholesterolemia (FH)-North Karelia mutation of the low density lipoprotein receptor gene deletes seven nucleotides of exon 6 and is a common cause of FH in Finland.

A mutation of the LDL receptor gene very common among Finnish patients with heterozygous familial hypercholesterolemia (FH) was identified. This mutation, designated as FH-North Karelia, deletes seven nucleotides from exon 6 of the LDL receptor gene, causes a translational frameshift, and is predicted to result in a truncated receptor protein. Only minute quantities of mRNA corresponding to the deleted gene were detected. Functional studies using cultured fibroblasts from the patients revealed that the FH-North Karelia gene is associated with a receptor-negative (or binding-defective) phenotype of FH. Carriers of the FH-North Karelia gene showed a typical xanthomatous form of FH, with mean serum total and LDL cholesterol levels of 12 and 10 mmol/liter, respectively. This mutation was found in 69 (34%) out of 201 nonrelated Finnish FH patients and was especially abundant (prevalence 79%) in patients from the eastern Finland. These results, combined with our earlier data on another LDL receptor gene deletion (FH-Helsinki), demonstrate that two "Finnish-type" mutant LDL receptor genes make up about two thirds of FH mutations in this country, reflecting a founder gene effect. This background provides good possibilities to examine whether genetic heterogeneity affects the clinical presentation or responsiveness to therapeutic interventions in FH.

Alleles↗
PubMed1992

Immunological discrimination between the human apolipoprotein E2(Arg158----Cys) and E3 isoforms.

A specific anti-apoE2(Arg158----Cys) monoclonal antibody was raised by means of immunization of mice with a variant specific synthetic peptide. The peptide sequences used were homologous to apolipoprotein E of human and mouse. Consequently, the mouse immune system was tolerant to most of the selected sequences. Immunization with only one of selected peptides (amino acids 154-172) evoked an anti-peptide and anti-native protein response. Surprisingly, this peptide was predicted to have a low antigenicity index, in contrast to the other used peptides. The variant specific anti-peptide MAb that was generated with this sequence, recognizes apoE2(Arg158----Cys) and not apoE3. We here describe a sensitive, time saving, and simple immunoblot assay to detect apoE2(Arg158----Cys) in human sera without prior isoelectric focusing of serum proteins.

Amino Acid Sequence↗
PubMed1991

Detection of allele-specific transcripts by the polymerase chain reaction (AST-PCR).

We have applied the polymerase chain reaction to detect differences in relative amount of allele-specific transcripts of the low density lipoprotein receptor gene in individuals with heterozygous familial hypercholesterolemia (FH). This method is based on detection of loss of heterozygosity of exon-specific restriction fragment length polymorphisms present in amplified mRNA fragments as compared to amplified genomic DNA fragments. We detected loss of allele-specific mRNA in 20% of informative FH patients. In principle, this method enables the analysis of relative allele-specific transcript levels of any expressed gene and can thus be generally applied to study processes involving differential gene expression.

Alleles↗
PubMed1991

Apolipoprotein E polymorphism affects plasma levels of lipoprotein(a).

In a group of 303 healthy Caucasian adults of both sexes we studied the influence of the apolipoprotein E (apo E) polymorphism on plasma levels of Lipoprotein(a) (Lp(a). The APOE*2 allele was found to decrease the mean plasma Lp(a) level by 24.8%, whereas the APOE*4 allele increased the mean Lp(a) level by 25.7%. These effects were parallel to the effect of apo E polymorphism on plasma cholesterol and low density lipoprotein (LDL)-cholesterol. For the Lp(a) levels, the genetic variance associated with the APOE locus contributed about 4% to the total phenotypic variance. For plasma cholesterol and LDL-cholesterol this contribution was 4.5 and 6.3%, respectively. We also found a significant positive correlation between LDL-cholesterol and Lp(a) levels. Since the apo E polymorphism effects LDL-receptor activity, we conclude that, at least in healthy normolipidemic individuals, plasma levels of Lp(a) are modulated by the LDL-receptor activity.

Alleles↗
PubMed1991

Interpretation of polymorphic DNA patterns in the human alpha-amylase multigene family.

Previous molecular studies have clearly shown that the human amylase locus has a very complicated structure. Multiple salivary and pancreatic amylase genes are present on haplotypes with variable numbers of genes. To study the population heterogeneity, human genomic DNA from family members and random individuals was digested with a number of different restriction enzymes and hybridized with probes representing various parts of the human pancreatic amylase cDNA. The complex patterns obtained were, in most cases, compatible with predictions from the restriction enzyme maps of cloned human amylase genes. With some enzymes deviations from the predicted intensities of the bands associated with the pancreatic amylase gene AMY2A were observed. These findings can be explained by unequal homologous crossovers between AMY2A and AMY1A, resulting in haplotypes with one gene less or one gene more than the haplotypes described thus far. Moreover, a very complicated TaqI polymorphism was found that can be explained by homologous crossovers between different salivary amylase genes. Because some salivary amylase genes have an inverted orientation with respect to the others, these data provide evidence for the occurrence of intrachromosomal, homologous crossovers, as proposed by us previously (P. C. Groot et al., 1990, Genomics 8: 97-105).

Blotting, Southern↗
PubMed1991

Familial dysbetalipoproteinemia associated with apolipoprotein E3-Leiden in an extended multigeneration pedigree.

By the careful screening of familial dysbetalipoproteinemic (FD) patients, five probands showing heterozygosity for the APOE*3-Leiden allele were found. Genealogical studies revealed that these probands share common ancestry in the 17th century. In a group of 128 family members, spanning three generations, 37 additional heterozygous APOE*3-Leiden gene carriers were detected. Although with a variable degree of severity, all carriers exhibited characteristics of FD such as (a) elevated levels of cholesterol in the very low density lipoprotein (VLDL) and intermediate density lipoprotein (IDL) fractions, (b) elevated ratios of cholesterol levels in these density fractions over total plasma levels of triglycerides, and (c) strongly increased plasma levels of apolipoprotein E (apoE). Multiple linear regression analysis revealed that most of the variability in expression of FD in APOE*3-Leiden allele carriers can be explained by age. Body mass index showed a less significant influence on the expression of FD. Gender had no effect on the expression in E*3-Leiden allele carriers, nor did it influence the age of onset of FD. In the group of APOE*3-Leiden allele carriers, we found that the E*2 allele enhances the expression of FD, whereas the E*4 allele had the opposite effect. Isoelectric focusing of plasma and of isolated VLDL, IDL, and high density lipoprotein density fractions showed that in E*3-Leiden allele carriers the apoE3-Leiden variant largely predominates over its normal apoE counterpart, especially in the VLDL and IDL density fractions. We conclude that in APOE*3-Leiden allele carriers FD is dominantly inherited with a high rate of penetrance, i.e., the presence of normally functioning apoE molecules in the plasma does not prevent the age-related expression of this disease.

Adolescent↗
PubMed1990

Location of facioscapulohumeral muscular dystrophy gene on chromosome 4.

The autosomal dominant disorder facioscapulohumeral muscular dystrophy (FSHD) is the last of the major progressive muscular dystrophies in which the gene had not been located. In linkage analysis on ten Dutch families with this disorder a lod score of 6.34 at a recombination fraction of 0.13 was obtained with the microsatellite marker Mfd 22 (D4S171). This maps the FSHD gene to chromosome 4. Only one family was uninformative for this marker. We found no evidence of genetic heterogeneity.

Adult↗