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Biomedical subjects

G Bondjers

Publications and source records attributed to G Bondjers.

At least 91 records · Page 5Linked to original sources
PubMed1989

XbaI restriction fragment length polymorphism of apolipoprotein B in Swedish myocardial infarction patients.

Apolipoprotein B (apoB) is a major importance to the metabolism of lipoproteins, and there is also evidence which suggests that apoB plays a central role in atherogenesis. In order to study whether there is a link between one of the mutations of the apoB gene and premature coronary heart disease, the frequency of the XbaI RFLP for the apoB gene was analysed in 52 male myocardial infarction patients. These were compared with a control group matched for age and sex (n = 52), and a random population sample of middle-aged men (n = 106). Two alleles were identified by the presence (X2) or the absence (X1) of an XbaI cleavage site. A somewhat higher frequency of the X2 allele was seen among the patients, however there was no significant difference between patients and controls regarding the genotypes or allele frequencies. This observation does not confirm one earlier report where a higher frequency of the X1 allele was seen in myocardial infarction patients. Differences between the studied populations or epidemiological designs of the studies might explain the diverging results. Further studies are evidently needed to fully resolve the relation between the XbaI RFLP and risk of atherosclerotic disease or lipoprotein metabolism.

Adult↗
PubMed1989

Differential effects of continuous versus intermittent administration of growth hormone to hypophysectomized female rats on serum lipoproteins and their apoproteins.

The effects of the plasma pattern of GH on serum and lipoprotein levels of total cholesterol, triglycerides, apolipoprotein A-I (apo A-I), apolipoprotein B 48/100 (apo B), and apolipoprotein E (apo E) were studied in hypophysectomized female Sprague-Dawley rats, which had been given replacement therapy with L-T4 and hydrocortisone. Bovine GH (1 mg/kg.day) was administered sc either continuously by means of osmotic minipumps or by two daily injections. Serum lipoproteins were separated by sequential ultracentrifugation into very low density lipoproteins [density (d) less than 1.006 g/ml], low density lipoproteins (LDL; d 1.006-1.063 g/ml) and high density lipoproteins (HDL; d 1.063-1.21 g/ml). The content of total cholesterol and triglycerides were then determined. Apo A-I, apo B, and apo E were isolated from rat serum and antibodies raised in rabbits. In serum and in lipoprotein fractions, the content of apo A-I, apo-B, and apo E were determined by electroimmunoassay. After hypophysectomy, there occurred a decrease in serum cholesterol and serum levels of apo A-I and apo E, in spite of replacement therapy with T4 and cortisone. Similar changes were also observed in HDL. In contrast, apo B, cholesterol, and triglycerides were increased in LDL. Estradiol treatment had no effect on these changes. Continuous infusion of GH resulted in an increase in cholesterol and apo E in serum and HDL to the levels of intact females. In contrast, GH given twice daily had no effect. Therefore, the sexually dimorphic secretion of GH may be important for the regulation of sex differences in apo E and HDL cholesterol levels. There were no consistent effects of GH treatment on the levels of apo A-I in serum or HDL, but GH treatment resulted in a decrease in apo B and triglycerides in both serum and LDL, regardless of the mode of administration. This suggests that GH regulates the serum and LDL levels of apo B and triglycerides independently of the secretory pattern.

Animals↗
PubMed1988

Studies on the assembly of apo B-100-containing lipoproteins in HepG2 cells.

The relationship between apoB-100 and the membrane of the endoplasmic reticulum (ER) has been studied by a combination of pulse-chase methodology and subcellular fractionation. HepG2 cells were pulse-labeled with [35S]methionine for 3 min and chased with cold methionine for periods between 0 and 20 min. ApoB-100 and albumin, present in the membrane as well as in the luminal content of the ER vesicles, were isolated after each chase period. The results indicated that apoB-100 was cotranslationally bound to the membrane of the ER, and from this membrane-bound form, was transferred to the lumen after a delay of 10-15 min. Albumin was, as could be expected for a typical secretory protein, cotranslationally sequestered in the lumen of the ER. Apo-B-100-containing lipoproteins present in the microsomal lumen were analyzed by ultracentrifugation in a sucrose gradient. ApoB-100 occurred on rounded particles in three density regions: (i) d 1.1065-1.170 g/ml (Fraction I), (ii) d 1.011-1.045 g/ml (Fraction II), and (iii) d less than 1.011 g/ml (Fraction III). Fraction I, isolated from cells cultured in the absence of oleic acid, contained a homogenous population of particles with a mean diameter of approximately 200 A. Fraction I isolated from cells cultured in the presence of oleic acid was slightly more heterogeneous and had a mean diameter of approximately 250 A. Fractions II and III had mean diameters of 300 and 500 A, respectively. Cholesterol esters and triacylglycerol were the quantitatively dominating lipid constituents of all three fractions. Pulse-chase experiments indicated that Fraction I contained the newly assembled lipoproteins. With increasing chase time, the apoB-100 radioactivity was redistributed from Fraction I to Fractions II and III, indicating that Fraction I is converted into Fractions II and III during the intracellular transfer. Particles corresponding to Fractions II and III were by far the most abundant lipoproteins found in the medium. The results presented support the possibility of a sequential assembly of apoB-100-containing lipoproteins.

Albumins↗
PubMed1988

Human arterial smooth muscle cells in culture. Effects of platelet-derived growth factor and heparin on growth in vitro.

Human arterial smooth muscle cells (hASMC) were cultured from explants of the inner media of uterine arteries obtained at hysterectomy. The presence of alpha-actin and smooth muscle-specific actin isoforms and the microscopic appearance of the cells in secondary culture established their smooth muscle origin. The hASMC were diploid and had no signs of transformation. Plasma-derived serum failed to stimulate their proliferation in vitro. Their rate of proliferation was, however, proportional to the concentration of whole blood serum in the medium. Anti-PDGF IgG at high concentrations inhibited the stimulatory effect of whole blood serum on cell proliferation. This suggests that hASMC depend on exogenous PDGF for their growth. In PDS or bovine serum albumin cell numbers remained constant for 7 days in culture and the thymidine index was below 1% per 24 h. When reexposed to whole blood serum these cells started to proliferate within 2 days. This indicates that hASMC when deprived of PDGF enter a quiescent state that is fully reversible upon rexposure to the mitogen. Heparin is a powerful growth inhibitor for SMC. In our system, heparin caused a dose-dependent inhibition of cell proliferation despite optimal concentrations of whole blood serum. This inhibition was reversible upon withdrawal of heparin. At heparin concentrations which caused a half-maximal inhibition it was also competed for by increasing concentrations of whole blood serum. Quiescent hASMC expressed the PDGF receptor on their surface as judged from immunofluorescence with a monoclonal antibody. This was true irrespective of whether growth arrest was achieved by serum depletion or by the addition of heparin to serum-containing medium. Cells growing in the presence of whole blood serum did not, however, express the receptor antigen. These observations suggest that heparin may interfere with PDGF or with its binding and further processing at the level of the cell-surface receptor.

Arteries↗
PubMed1988

Atherosclerosis in rabbits identified as high and low responders to an atherogenic diet and the effect of treatment with a beta 1-blocker.

In order to investigate whether initial plasma lipid concentrations could be used to distinguish between high and low responders to an atherogenic diet, rabbits were divided into 3 groups according to their plasma concentrations of cholesterol and phospholipids after 4 weeks on a standard rabbit diet. Plasma cholesterol and phospholipid levels were less than 0.5 mM, less than 1.1 mM, respectively, in group 1 (n = 17), greater than 0.5 mM, less than 1.1 mM, in group 2 (n = 13), and greater than 0.5 mM, greater than or equal to 1.1 mM, in group 3 (n = 14). After 7 weeks on a diet containing 0.25% cholesterol and 3% coconut oil, animals in groups 1 and 2 had a lower increase in their plasma lipid levels compared with group 3. Half of each group was then treated with the beta 1-adrenoceptor antagonist metoprolol during the next 14 weeks on the atherogenic diet. At the end of the study, the extent of atherosclerosis both in the aortas and in the coronary arteries of the control animals showed a positive correlation to plasma cholesterol and to plasma phospholipid concentrations integrated over time. The metoprolol-treated animals in groups 1 and 2 had a reduction of atherosclerosis compared with their respective controls. We conclude that subpopulations of rabbits that react differently on an atherogenic diet can be identified by their initial plasma lipid levels, and that metoprolol treatment of low responders to an atherogenic diet significantly reduces atherosclerotic lesions of the aorta.

Animals↗
PubMed1988

Aortic intimal lipid content and serum lipoproteins in patients undergoing coronary by-pass surgery as related to clinical prognosis.

Intimal lipid concentrations were determined in aortic biopsies obtained during coronary by-pass surgery. In addition serum lipoprotein and apolipoprotein levels were quantitated and their relationships to aortic intimal lipid concentrations were analysed. The possibility to use aortic intimal lipid and serum lipoprotein or apolipoprotein concentrations to predict clinical prognosis following the coronary by-pass operation was also evaluated. Intimal cholesterol, cholesterol ester, phosphatidylcholine and sphingomyelin were intercorrelated, whereas none of these lipid fractions correlated to aortic intimal triglyceride levels. Patients with hypertension had higher aortic intimal cholesterol ester levels than normotensive patients. There was a positive correlation between the number of stenosed coronary arteries and serum apo B or triglyceride levels. In addition there was a negative correlation between the number of stenosed arteries and HDL-cholesterol. Prognosis after the operation was inversely correlated to serum apo A-I levels. Our data do not, however, support the notion that aortic intimal lipid levels can be used to evaluate prognosis after coronary by-pass surgery.

Adult↗
PubMed1988

Quantification of plasma lipids and apolipoproteins in British Halflop rabbits. A comparison between normocholesterolemic rabbits, hypercholesterolemic rabbits (modified WHHL rabbits) and rabbits fed an atherogenic diet.

We have established isolation methods and developed electroimmunoassays for rabbit apolipoprotein A-I (apo A-I), apo B, apo C-III and apo E. The assays were used to characterize a hyperlipidemic strain of the British Halflop rabbits (BHL rabbits), obtained after cross-breeding with WHHL rabbits and referred to as modified WHHL rabbits, and to investigate the changes in the apolipoprotein levels induced by feeding normal BHL rabbits an atherogenic diet (0.25% cholesterol and 3% coconut oil). The modified WHHL rabbits were characterized by increased levels of apo B, apo C-III and apo E as well as cholesterol, phospholipids and triacylglycerol as compared to chow-fed BHL rabbits, while the apo A-I levels were only half of those found in the chow-fed animals. The modified WHHL rabbits had virtually no low density lipoprotein (LDL) receptor activity and a low fractional catabolic rate (FCR) of LDL. These results indicate that the modified WHHL rabbit has the homozygous form of the LDL receptor deficiency. The BHL rabbits fed the atherogenic diet showed increased levels of cholesterol, triacylglycerol, apo B, apo C-III and apo E, as compared to those of the chow-fed BHL rabbits. The apo E and apo C-III reached levels in the range of or even higher than those of the modified WHHL rabbits. The apo A-I levels on the other hand did not differ from those of the chow-fed rabbits. Feeding an atherogenic diet led to a decrease in the FCR of LDL to a level similar to that found in the modified WHHL rabbits.

Animals↗
PubMed1987

Structure and biosynthesis of apolipoprotein B.

Apolipoprotein (apo) B100 copy deoxyribonucleic acid (cDNA) has been cloned and sequenced. The total sequence of apo B100 messenger ribonucleic acid has been revealed by the work from our group, as well as other groups. The sequence spans 13,689 nucleotides from the initiation to the stop codon. Thus the messenger has the capacity to code for 4563 amino acids corresponding to a molecular weight of approximately 510,000. Computer analyses revealed the presence of regions with amphipathic alpha-helix and of hydrophobic regions with a high probability of beta-structure. Regions of the molecule are characterized by continuous variations between hydrophillic and hydrophobic sequences, the latter coinciding with a high probability of beta-structure. It is suggested that this beta-structure is involved, together with the amphipathic alpha-helix, in the binding of apo B100 to the lipid. Pulse-chase studies in Hep G2 cells showed that apo B100 is synthesized as one protein, with a translation time of 14 minutes. The protein is transferred through the cell and secreted within 30 minutes without undergoing any major change in molecular mass. The residence kinetics in the endoplasmic reticulum (ER) is characterized by an increase during the first 10 to 15 minutes of chase followed by an almost linear decrease with a decay rate of 6%/min. The transfer through the ER to the Golgi apparatus accounts for one third of the time needed for the intracellular transfer of apo B100, whereas two thirds of the time is required for the transfer through the later part of the secretory pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1987

Apolipoprotein B: structure, biosynthesis and role in the lipoprotein assembly process.

The complete amino acid sequence of the liver-synthesized apolipoprotein B (apoB) species, apoB 100, has been derived from cloned cDNA. The protein consists of 4536 amino acids (+ a 27 amino acid signal sequence). Cysteine is clustered in the N-terminal 1/10 of the protein, suggesting the presence of a stabilized tertiary structure in this part of the molecule. Three types of structure are suggested to be of importance for the binding of the protein to lipids; (i) hydrophobic sequences with a high probability for beta-sheet structure, (ii) strict amphipathic beta-sheets, and (iii) amphipathic alfa-helices. An apoB 100 molecule is completed within 10-14 min and secreted after approximately 30 min, 1/3 of which is due to the transfer through the endoplasmic reticulum (ER), while 2/3 is spent in the Golgi apparatus. ApoB 100 is co-translationally N-glycosylated and 25% of the oligosaccharide chains is processed in the Golgi compartment. Other posttranslational modifications that have been discussed include covalent acylation and phosphorylation. It has also been suggested that the lipid moiety of the apoB 100 lipoproteins are modified during the passage through the Golgi apparatus. The site of lipoprotein assembly is suggested to be separated from the site of apoB 100 synthesis, and apoB 100 appears to be co-translationally bound to the ER membrane and from this transferred to the ER lumen. Based on these observations a model for the assembly of apoB 100 lipoproteins is discussed in this paper. The intestinal derived apoB species, apoB 48, has a molecular mass of 210 kDa and appears to correspond to the N-terminal 48% of apoB 100. The mechanism by which apoB 48 is formed is still not known. Available data indicate that the protein is formed within the intestinal cells, these data also argue against the possibility that apoB 48 is formed by posttranslational proteolysis of apoB 100. The formation of a separate apoB 48 mRNA by alternative splicing has been suggested, based on the observation of a 7 kb mRNA which corresponds to the 5' portion of the apoB 100 mRNA. However, the most abundant apoB mRNA species found in the intestine have a size that corresponds to that of the apoB 100 mRNA, furthermore the observation that apoB 48 appears to terminate in a 7.5 kb exon that appears to lack alternative splice sites, does not favour the possibility of alternative splicing.

Amino Acid Sequence↗
PubMed1987

Lipoprotein lipase in atherosclerosis: its presence in smooth muscle cells and absence from macrophages.

The localization of lipoprotein lipase (LPL) in human atherosclerotic lesions was studied with immunocytochemical techniques. In the fibrous cap and surrounding intima of the plaque, where the smooth muscle cell is the dominating cell type, a high number of cells reacted with anti-LPL. A much lower number of stained cells was seen in the central lipid core region where the macrophages dominate. Further characterization of the LPL-containing cells in tissue sections showed that most of them were smooth muscle cells. Only a minor fraction of the macrophages in the plaque contained the enzyme. The results were confirmed on isolated cells from atherosclerotic tissue. Lipoprotein lipase was also detected in smooth muscle cells of non-atherosclerotic arteries. These findings suggest that the smooth muscle cells are the major source of LPL in the vascular wall. However, the enzyme was not present in some of the smooth muscle cells in the atherosclerotic lesion. This may imply that LPL synthesis is down-regulated in the atherosclerotic plaque.

Aged↗
PubMed1986

Pulse-chase studies of the synthesis and intracellular transport of apolipoprotein B-100 in Hep G2 cells.

The synthesis and secretion of apolipoprotein B-100 (apoB-100) have been studied in a human hepatoma cell line, the Hep G2 cells. The time needed for the synthesis of apoB-100 was estimated to be 14 min, which corresponds to a translation rate of approximately 6 amino acids/s. ApoB-100 was compared with albumin and alpha 2-macroglobulin as to the distribution between the membrane and the luminal content in the endoplasmic reticulum (ER) and the Golgi apparatus. The results suggested that apoB-100 approximately followed the distribution of these secretory proteins in the Golgi, while the ratios between the percent membrane-bound apoB-100 and percent membrane-bound albumin or alpha 2-macroglobulin were 3-4:1 in the ER. This may suggest that apoB-100 occurs in a membrane-associated form in ER prior to the integration in the lipoproteins. Pulse-chase studies combined with subcellular fractionation was used to investigate the kinetics for the intracellular transfer of apoB-100. A 3-min pulse of [35S]methionine was followed by an increase in apoB-100 radioactivity in the ER during the first 10-15 min of chase. The following 10-15 min of chase were characterized by linear decrease in apoB-100 radioactivity with a decay rate of approximately 6%/min. The residence kinetics for apoB-100 in the ER differed from that of transferrin and probably also from that of albumin. By comparing the time for the pulse maximum in ER with that in the denser Golgi fractions the time needed for the transfer between ER and Golgi could be estimated to be 10 min. The time needed for the secretion of newly synthesized apoB-100 was estimated to be 30 min. This indicates that the transfer of the protein through the Golgi apparatus to the extracellular space requires 20 min.

Apolipoprotein B-100↗
PubMed1986

A new microimmunoassay for apolipoprotein B in arterial tissue. Studies on peroperative human biopsies.

An immuno-radiometric assay (IRMA) for determination of apolipoprotein B (apo B) in arterial intima is described. Intima was dissected from aortic biopsies obtained peroperatively. The tissue was first incubated in buffer to release a 'buffer extractable' pool of apo B. A 'tightly bound' fraction was then released by incubating the tissue in collagenase for 6 h. 'Buffer extractable' and 'tightly bound' apo B were then determined with IRMA. The IRMA is an immunological method based on the primary reaction between antigen and antibody, and it was found to be reproducible and sensitive enough for determination of apo B even in small tissue samples. In aortic intimal specimens without obvious atherosclerotic lesions, total apo B content was found to be 223 +/- 213.2 micrograms/g wet weight or 30 +/- 32.8 micrograms/mm2 intimal area (mean +/- SD). The majority of the biopsies contained 100-300 micrograms/g wet weight of apo B. This concentration corresponds to approximately 25% of the serum concentration. Duplicate tissue samples were obtained from 26 patients. The 2 samples were analysed separately and there was a highly significant correlation between apo B content in the 2 biopsies (rs = +0.89). About 20% of the tissue apo B was buffer extractable, and there was a strong positive correlation between buffer extractable and tightly bound apo B (rs = +0.76). The total amount of apo B found in non-atherosclerotic intima, is considerably lower than in previous reports. This difference might at least partly be due to different quantitation techniques but may also be due to differences between autopsy material and peroperatively obtained biopsies. The lower level reported here is more in agreement with studies on the kinetics of apo B into the arterial wall, as well as reported levels of apo B in interstitial fluid and in lymph.

Apolipoproteins B↗
PubMed1985

Molecular cloning of human apolipoprotein B cDNA.

In this paper we describe the isolation of cDNA clones which code for parts of apolipoprotein B (apoB). The clones were obtained by immunoscreening of an expression library (lambda gt 11) derived from a human hepatoma cell line (Hep G2). The relationship between positive clones and apoB was established with immunochemical techniques using polyclonal as well as monoclonal antibodies. Recombinants, expressing nonoverlapping regions of apoB are described, all hybridizing with a very large mRNA (approximately 20,000 bases long). The nucleotide sequence obtained predicts a primary protein structure with a composition suitable for the formation of stretches of an amphipatic alpha-helix.

Amino Acid Sequence↗
PubMed1985

Pulse-chase studies of the synthesis of apolipoprotein B in a human hepatoma cell line, Hep G2.

We have used pulse-chase methodology to study the synthesis of apolipoprotein B in a human hepatoma-derived cell line, the Hep G2 cells. A 2-min pulse with [35S]methionine was followed by a chase period varying from 5-90 min. A protein of large molecular mass (estimated molecular mass: 312 +/- 41 kDa, mean +/- SD, n = 8) could be immunoprecipitated from the cells at all chase periods between 5 min and 60 min with both monoclonal antibodies to a narrow density cut of the low density lipoprotein LDL-2 (density: 1.030-1.055 g/ml) and polyclonal antibodies to the apolipoprotein B apo B 100 or to a narrow density cut of LDL-2 (density: 1.030-1.055 g/ml). In addition to this large molecular mass protein, nascent polypeptides could be precipitated after 5, 10 and 15 min of chase. The apolipoprotein B molecules that had been labelled during the pulse disappeared from the cells after 60-90 min of chase, while they started to appear in the medium after 30-35 min of chase. The results obtained indicate (a) that apolipoprotein B is synthesized as one polypeptide with a large molecular mass, (b) that newly synthesized apolipoprotein B molecules are secreted after a delay of 30-35 min, (c) that no intracellular accumulation of apolipoprotein B occurs, and (d) that apolipoprotein B is recovered in the density fraction less than 1.21 g/ml of the medium suggesting that it is secreted in lipoprotein form.

Apolipoproteins B↗
PubMed1984

Evidence for a structural relationship between apoB75kDa and human plasma apolipoprotein B 100, from translation of human liver mRNA in vitro and immunochemical studies with monoclonal and polyclonal antibodies.

We have investigated the relation between an 80-kDa protein synthesized in vitro in protein-synthesizing system programmed with human liver mRNA [Olofsson, S.-O., Elias, P., Boström, K., Lundholm, K., Norfeldt, P.-I., Wiklund, O., Fager, G., and Bondjers, G. (1983) FEBS Lett. 156, 63-66] and a 70-80-kDa protein, apoB75kDa, isolated from the low-density lipoproteins-2 (LDL-2) [Olofson, S.-O., Boström, K., Svanberg, U., and Bondjers, G. (1980) Biochemistry 19, 1059-1064]. Five monoclonal antibodies directed against LDL-2 as well as polyclonal antibodies against a narrow density cut of LDL-2 (d = 1.030 - 1.055) were used to precipitate apoB-related proteins synthesized in vitro in a protein-synthesizing system programmed with human liver mRNA (or total RNA fraction). With all monoclonal antibodies as well as the polyclonal antibodies, a protein with an estimated molecular mass of 80 +/- 1.3 kDa (mean +/- SD, n = 12) could be precipitated. The observation that all monoclonal antibodies used reacted with apoB75kDa indicates a close immunological relation between this 80-kDa protein and apoB75kDa. Limited proteolysis of the 80-kDa protein (synthesized in the presence of [35S]-methionine) with Staphylococcus aureus V8 protease generated six [35S]-methionine-containing bands that could be separated on a polyacrylamide gradient gel (12-20%). All these radioactive bands corresponded to major protein-stained bands obtained after limited proteolysis of apoB75kDa. This observation suggests a structural relation between the two proteins. Taken together, our results indicate that a protein corresponding to apoB75kDa is synthesized in vitro in a protein synthesizing system programmed with human liver mRNA (or total RNA fraction). We have also compared apoB75kDa and the major component of apoLDL-2, apoB100 [Kane, J. P., Hardman, D.A., and Paulus, H.E. (1980) Proc. Natl Acad. Sci USA 77, 2465-2469] by immunochemical methods. We could demonstrate that six monoclonal antibodies directed against four to six different epitopes on LDL-2, as well as polyclonal antibodies to apoB100 and apoB75kDa, all reacted with apoB75kDa and apoB100. These observations indicate a close immunological relation between the two proteins. Taken together our results support the hypothesis that apoB100 has a subunit structure. We therefore suggest that apoB75kDa is a subunit of apoB100 synthesized in human liver.

Animals↗
PubMed1983

Human liver RNA-programmed in vitro synthesis of a polypeptide related to human apolipoprotein B.

In an in vitro synthesizing system programmed with RNA from human liver a polypeptide with an estimated Mr of 80 000 (80 kDa) +/- 1400 (mean +/- SD, n = 5) was synthesized. This polypeptide could be precipitated with antiserum to a narrow density cut of LDL (d = 1.030-1.055) or antiserum against the high-Mr form of apoB (apoB 100 [4]). The synthesized protein is immunologically related to a 75 kDa protein isolated from LDL. We suggest that the 80 kDa protein represents a primary translation product of apoB synthesized in human liver.

Animals↗