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Biomedical subjects

O Wiklund

Publications and source records attributed to O Wiklund.

At least 37 records · Page 2Linked to original sources
PubMed1990

Differential uptake of proteoglycan-selected subfractions of low density lipoprotein by human macrophages.

Macrophages and arterial chondroitin sulfate proteoglycans (CSPG) are probably associated with extracellular and intracellular lipoprotein deposition during atherogenesis. We found that human arterial CSPG can be used to select subclasses from low density lipoprotein (LDL) with different structural properties and capacities to interact with human monocyte-derived macrophages (HMDM). Four subclasses, LDL(PG)1 to LDL(PG)4, in order of decreasing CSPG-complexing capacity, were prepared and characterized in terms of their ability to interact with HMDM. The LDL subclasses with highest avidity for CSPG, LDL(PG)1 and LDL(PG)2, were bound, internalized, and degraded more efficiently than those of lower avidity for CSPG. From LDL(PG)1 to LDL(PG)4, the gradual decrease in uptake by HMDM and decreasing avidity for CSPG were associated with a gradual decrease in isoelectric point (from 5.93 to 5.68) and an augmented ratio of surface polar lipid to core nonpolar components (from 0.35 to 0.54). Competition experiments indicated that the proteoglycan-selected subfractions shared the binding sites and uptake mechanisms of native LDL. The results suggest the existence of a structurally related gradation in the avidity of LDL subpopulations for cells and matrix components. The presence within LDL subpopulations of a differential capacity to interact with intimal extracellular and cellular elements could be associated with a similar heterogeneity in their atherogenic potential.

Binding Sites↗
PubMed1989

Apolipoprotein B in human aortic biopsies in relation to serum lipids and lipoproteins.

A total of 46 patients, aged 39-71 years (mean 57.7), were studied. Forty-eight percent of the patients were hyperlipidemic and 63% had earlier suffered a myocardial infarction. Biopsies from aorta were obtained during coronary bypass surgery. Apo B was extracted from the intima by incubation of the tissue in buffer, followed by collagenase digestion. Intimal apo B was quantified in an immunoradiometric assay. There were significant correlations between total or collagenase-extractable apo B and serum cholesterol (rs = 0.39, P less than 0.01), serum triglycerides (rs = 0.33, P less than 0.05), LDL cholesterol (rs = 0.33, P less than 0.05) and serum apo B (rs = 0.37, P less than 0.05). The correlations were strongest for the collagenase-extractable apo B, while no correlations were observed for the buffer-extractable intimal apo B. No significant correlations were found between intimal apo B and serum HDL, apo A-I, smoking habits, history of hypertension or sustained myocardial infarction. Follow-up data were available for 42 of the patients, with a mean follow-up period of 35.1 months. The patients were classified according to symptoms of angina pectoris at the time of follow-up. There were significantly lower levels of serum apo A-I in the patients with poorer clinical prognosis. In a linear multiple stepwise regression analysis, apo A-I and serum LDL were significantly and independently related to clinical prognosis (R2 = 0.31).

Adult↗
PubMed1989

Binding parameters and concentration modulate formation of complexes between LDL and arterial proteoglycans in serum.

The interactions of LDL with extracellular matrix proteoglycans apparently contribute to the accumulation of apo B-lipoproteins in atherogenesis. Serum LDL forms insoluble complexes with human arterial chondroitin sulfate proteoglycans (CSPG). While the amount of insolubilized LDL varies, serum from survivors of myocardial infarcts and ischaemic subjects shows higher values of CSPG-insolubilized LDL than serum from controls. In this study, we explored the relationship between the formation of LDL-CSPG complexes in serum and some LDL properties, using binding isotherms and characterization of isolated LDL from 12 healthy controls and 12 young myocardial infarct survivors. The amount of LDL insolubilized in serum from solutions of CSPG was found to be a function of the product Bt (total binding) x the amount of serum LDL-cholesterol. Furthermore, the Bt values for the isolated LDL from controls and patients could be predicted with more than 70% certainty by using a multiple regression model which included the cholesterol/protein ratio, protein/triglyceride ratio, isoelectric point and the affinity coefficient of the lipoprotein for CSPG. The results indicate that LDL-CSPG measurements in serum are dependent upon both LDL concentration and structural properties which are related to its tendency to form complexes with arterial CSPG.

Adult↗
PubMed1989

Lack of correlation between the apolipoprotein B XbaI polymorphism and blood lipid levels in a Swedish population.

The possible connections between the apolipoprotein B (apo B) XbaI polymorphism and the serum levels of total cholesterol, triglycerides, LDL, HDL and apo B have been investigated among 187 randomly selected subjects from Gothenburg, Sweden. The interferences of age and sex on the serum lipoproteins and apo B concentrations were considered. Using multiple regression analysis, we compared the different lipid levels and the levels of apo B with the genotypes X1X1, X1X2 and X2X2 (X1 = without the XbaI restriction site, X2 = with the site), with age and with sex and with those factors combined with each other. A significantly higher concentration of serum cholesterol and LDL among men than among women was found and total serum cholesterol, LDL and apo B were positively correlated with age. The allele frequency of the XbaI polymorphism in the sample was 0.45 for the allele without the XbaI restriction site. No correlation was found between the apo B genotypes and the levels of serum lipoproteins or apo B.

Adult↗
PubMed1989

Affinity of LDL to a human arterial proteoglycan among male survivors of myocardial infarction.

In the present study, the hypothesis that the affinity of LDL to arterial proteoglycans might discriminate myocardial infarction patients from controls were tested. The patients were 52 men who had sustained a myocardial infarction at an age of 50 years or less and the controls, selected from a random population sample, were matched to the patients for age and sex. Serum cholesterol, triglycerides, LDL-cholesterol, HDL-cholesterol and apoB discriminated patients from controls. In addition, LDL reactivity with arterial proteoglycans was significantly higher in patients than in controls. In a multiple regression analysis, with patient or control as the dependent variable, apoB levels, LDL proteoglycan reactivity and serum triglycerides appeared as independent contributors to the regression. These observations indicate that LDL reactivity with arterial proteoglycans is a new, highly significant factor which discriminates between young myocardial infarction patients and controls.

Adult↗
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↗
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

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

Turnover and tissue sites of degradation of glucosylated low density lipoprotein in normal and immunized rabbits.

Immunological mechanisms have been implicated in the atherogenic process since immunoglobulins are frequently found in the atherosclerotic aorta. We have previously shown that modifications of homologous low density lipoproteins (LDL) make it immunogenic. In particular we have demonstrated that immunization with homologous nonenzymatically glucosylated LDL (glcLDL) results in the generation of antibodies specific to the derivatized lysine residue, and that such antibodies do not react with native LDL epitopes. In the present study we immunized rabbits with reductively glucosylated rabbit LDL and then determined the effects of the circulating antibodies on the rates of plasma clearance and on the sites of degradation of LDL in which varying degrees of glucosylation had been achieved. In normal chow-fed animals, the plasma clearance of glcLDL was retarded in proportion to the extent of lysine derivatization. In contrast, in immunized animals the clearance of glcLDL was greatly accelerated. When 10% or more of lysine residues were derivatized, clearance of glcLDL was accelerated 50- to 100-fold. Even when only 5% of lysines were derivatized, plasma clearance was accelerated 2- to 3-fold. Cholesterol feeding inhibited LDL clearance from plasma and decreased LDL uptake of LDL receptor-rich tissues. In a similar manner, glucosylation of LDL inhibited its ability to bind to the LDL receptor and redirected sites of LDL degradation away from LDL receptor-rich tissues. Thus degradation of glcLDL by liver and adrenal was markedly diminished. The presence of antibodies to glcLDL also redirected sites of degradation of the modified LDL, primarily to the reticuloendothelial cells of the liver. There was no evidence for specific targeting of glcLDL-immunoglobulin complexes to the aorta; instead they were targeted to the liver. These data suggest that the presence of humoral antibodies to modified LDL acts to rapidly remove such LDL from plasma and specifically targets such complexes to reticuloendothelial cells, primarily in the liver. In this manner such antibodies may serve a useful purpose.

Adrenal Glands↗
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

Stoichiometric binding of apolipoprotein B-specific monoclonal antibodies to low density lipoproteins.

The structure of apolipoprotein B and its stoichiometry on plasma lipoproteins has been a major issue and one refractory to a variety of analyses. Immunochemical analyses represent an independent approach. Examinations of apolipoprotein B (apo-B) epitopes on human plasma low density lipoproteins (LDL) using monoclonal antibodies have consistently revealed the existence of extensive apo-B heterogeneity. In the present study, we have addressed the solution of the stoichiometry problem using quantitative analysis of the maximum number of identical antibodies that can be bound per LDL particle in which we take into account this ligand heterogeneity. We have estimated the molecular weight of apo-B by quantifying the number of times a given apo-B epitope is expressed on the surface of LDL. The quantitative binding of eight previously characterized monoclonal antibodies was measured in a fluid phase radioimmunoassay. The results were analyzed by Scatchard analysis and expressed on the basis of independent measurements of the maximum amount of LDL that could be bound by each antibody. Affinity constants for each of the eight antibodies varied between 8.5 X 10(7) and 80 X 10(7) M-1. For these same antibodies, the concentration of maximally bound antibody at a normalized LDL concentration of 1000 ng/ml was estimated to be 0.9-1.8 nM with a mean of 1.23 nM. Adopting a molecular mass from physicochemical analysis for LDL apo-B of 550,000 daltons, the molar ratio between bound antibody and LDL varied between 0.5 and 1.2 (mean 0.75 +/- 0.15). The results supported the hypothesis that apo-B is present as a single large molecular weight polypeptide in LDL.

Antibodies, Monoclonal↗