Biomedical subjects

B Rosengren

Publications and source records attributed to B Rosengren.

At least 19 recordsLinked to original sources

PubMed2001

Elevated levels of small, low-density lipoprotein with high affinity for arterial matrix components in patients with rheumatoid arthritis: possible contribution of phospholipase A2 to this atherogenic profile.

OBJECTIVE: This work studied the presence of inflammatory and atherogenic lipoprotein markers that could explain the high incidence of cardiovascular disease (CVD) reported in rheumatoid arthritis (RA) patients. METHODS: Inflammatory markers were 1) soluble adhesion molecules (intercellular adhesion molecule [ICAM] and vascular cell adhesion molecule [VCAM]), 2) C-reactive protein (CRP), 3) fibrinogen (Fb), 4) cytokines (interferon-gamma [IFNgamma], tumor necrosis factor alpha [TNFalpha]), and 5) secretory group IIA phospholipase A2 (sPLA2-IIA). Atherogenic lipoprotein markers were 1) the size distribution of plasma lipoprotein subclasses, and 2) the binding affinity of low-density lipoprotein (LDL) to chondroitin 6-sulfate glycosaminoglycan (GAG). RESULTS: RA patients (n = 31) and matched controls (n = 28) had similar plasma concentrations of total cholesterol, triglycerides, Apo B, Apo A-I, very low-density lipoprotein, intermediate-density lipoprotein, and high-density lipoprotein (HDL). RA patients had significantly higher plasma levels of sPLA2-IIA, ICAM, CRP, Fb, TNFalpha, and IFNgamma compared with controls. RA patients also had significantly higher levels of small, dense LDL-1 (P < 0.05) and lower levels of small HDL-2 particles (P < 0.001) compared with controls. In addition, LDL from RA patients had a significantly higher binding affinity (Kd) to GAG (mean +/- SD Kd 204+/-22.4 nM Apo B) than did LDL from control subjects (Kd 312+/-36 nM Apo B) (P < 0.05). This Kd value showed a significant negative correlation with the plasma levels of LDL-1 (r = -0.566, P < or = 0.004). In RA patients, a significant positive correlation was obtained between sPLA2-IIA and CRP, ICAM, and LDL-1. HDL-2 showed a negative correlation with sPLA2-IIA. CONCLUSION: These atherogenic lipoprotein factors combined with the presence of chronic inflammation may contribute to the high CVD-related mortality in RA patients.

Adult↗

PubMed2000

Interferon-gamma induces secretory group IIA phospholipase A2 in human arterial smooth muscle cells. Involvement of cell differentiation, STAT-3 activation, and modulation by other cytokines.

Increased expression of secretory non-pancreatic phospholipase A(2) (sPLA(2)-IIA) could be part of the inflammatory reaction in atherosclerosis. However, the factors controlling sPLA(2)-IIA production in human vascular cells are unknown. We investigated regulation of sPLA(2)-IIA expression and secretion by human arterial smooth muscle cells in culture (HASMC). SPLA(2)-IIA was induced after 3-14 days of culture in non-proliferating conditions. SPLA(2)-IIA was co-expressed with heavy caldesmon, a cytoskeleton protein, and p27, a G(1) cyclin inhibitor, proteins characteristically expressed by differentiated cells. Further incubation with 50-500 units/ml of interferon (IFN)-gamma significantly increased sPLA(2)-IIA mRNA and secretion. IFN-gamma-induced sPLA(2)-IIA was found to be active in cell media and associated with cell membrane proteoglycans. IFN-gamma induced sPLA(2)-IIA expression was antagonized by tumor necrosis factor (TNF)-alpha and interleukin (IL)-10. TNF-alpha added individually induced a significant but transient (4 h) increase in sPLA(2)-IIA secretion. IL-10 by itself did not affect sPLA(2)-IIA expression and secretion. IFN-gamma-stimulated sPLA(2)-IIA transcription involved STAT-3 protein. Interestingly, IL-6 but not IFN-gamma up-regulated the sPLA(2)-IIA expression in HepG2 cells, thus sPLA(2)-IIA induction by IFN-gamma response appears to be cell specific. In summary, conditions leading to cell differentiation induced sPLA(2)-IIA expression in HASMC and further exposure to IFN-gamma can up-regulate sPLA(2)-IIA transcription and secretion. This IFN-gamma stimulatory effect can be modulated by other cytokines.

Arteries↗

PubMed1999

CD44, a cell surface chondroitin sulfate proteoglycan, mediates binding of interferon-gamma and some of its biological effects on human vascular smooth muscle cells.

Several cytokines and growth factors act on cells after their association with the glycosaminoglycan (GAG) moiety of cell surface proteoglycans (PGs). Interferon-gamma (IFN-gamma) binds to GAG; however, the relevance of this interaction for the biological activity of IFN-gamma on human cells remains to be established. Human arterial smooth muscle cells (HASMC), the main cells synthesizing PG in the vascular wall, respond markedly to IFN-gamma. We found that treatment of HASMC with chondroitinase ABC, an enzyme that degrades chondroitin sulfate GAG, reduced IFN-gamma binding by more than 50%. This treatment increased the affinity of 125I-IFN-gamma for cells from a Kd value of about 93 nM to a Kd value of about 33 nM. However, the total binding was reduced from 9. 3 +/- 0.77 pmol/microg to 3.0 +/- 0.23 pmol/mg (n = 4). Interestingly, pretreatment with chondroitinase ABC reduced significantly the cellular response toward IFN-gamma. The interaction of IFN-gamma with chondroitin sulfate GAG was confirmed by affinity chromatography of isolated cell-associated 35S-, 3H-labeled PG on a column with immobilized IFN-gamma. The cell-associated PG that binds to IFN-gamma was a chondroitin sulfate PG (CSPG). This CSPG had a core protein of approximately 110 kDa that was recognized by anti-CD44 antibodies on Western blots. High molecular weight complexes between IFN-gamma and chondroitin 6-sulfate were observed in gel exclusion chromatography. Additions of chondroitin 6-sulfate to cultured HASMC antagonized the antiproliferative effect and expression of major histocompatibility complex II antigens induced by IFN-gamma. These results indicate that IFN-gamma binds with low affinity to the chondroitin sulfate GAG moiety of the cell surface CSPG receptor CD44. This interaction may increase the local concentration of IFN-gamma at the cell surface, thus facilitating its binding to high affinity receptors and modulating the ability of IFN-gamma to signal a cellular response.

Animals↗

PubMed1998

Hemin binding and oxidation of lipoproteins in serum: mechanisms and effect on the interaction of LDL with human macrophages.

Most models of lipoprotein oxidation by free radicals have excluded macromolecular plasma components from the system. This limits their biological significance because oxidation of lipoproteins appears to occur in the intima in the presence of a plasma ultrafiltrate. Hemin, a product of in vivo hemoglobin degradation, binds and oxidizes purified lipoproteins. However, it is not known whether this occurs in the presence of plasma components that may sequester hemin. We found that hemin in serum diluted to protein levels of the extracellular fluid (10-30%) binds to low and high density lipoproteins (LDL, HDL) with association constants in the nmol/L range. In the presence of H2O2, hemin oxidizes both lipoproteins in diluted serum with formation of conjugated dienes, thiobarbituric acid reacting substances, and F2-isoprostanes. This appeared to be caused by the high affinity of hemin with LDL and by the Fe3+ liberated that remains associated with the particles after hemin is degraded. Spectrophotometric and fluorescence experiments and electrophoresis of porphyrins complex with LDL indicated that the heme ring is buried in the lipoprotein surface-monolayer with the carboxylic groups in contact with positive regions of the protein and the solvent. Human macrophages associated and degraded 3- to 4-times more hemin-oxidized LDL in diluted serum than native LDL. It is possible then that at sites of LDL, accumulation in the extracellular intima, hemin and H2O2 production could cause oxidation with potential atherogenic consequences for cellular lipoprotein processing. This may occur even when other macromolecules of the extracellular fluid are present.

Biological Transport↗

PubMed1997

Neoadjuvant chemotherapy with cisplatin and 5-fluorouracil in advanced squamous cell carcinoma of the head and neck: a randomized phase III study.

BACKGROUND AND PURPOSE: In 1986 a prospective, randomized, multi-centre trial for evaluation of neoadjuvant chemotherapy with cisplatin and 5-fluorouracil in the treatment of advanced squamous cell carcinoma of the head and neck was initiated. As survival in this group of patients is poor the purpose was to find a possible survival benefit of the chemotherapy in addition to radiotherapy compared to radiotherapy only. METHODS: Four-hundred sixty-one patients from Denmark, Norway and Sweden with tumors in oral cavity, oropharynx, hypopharynx and larynx were randomized to receive either standard treatment (radiotherapy or radiotherapy followed by surgery) or neoadjuvant chemotherapy followed by standard treatment. Chemotherapy included three courses of cisplatin 100 mg/m2 i.v. infusion on day 1 followed by 5-fluorouracil 1000 mg/m2 per day continuous i.v. infusion for 120 hours. Radiotherapy 64-70 Gy in 2 Gy per fraction, 5 times/week, was given to patients in both treatment arms. RESULTS: Response rate was 71% for patients randomized to chemotherapy-radiotherapy and 66% for patients randomized to standard treatment (not statistically significant). Residual tumors were excised if possible. After surgery 62% of the patients randomized to chemotherapy-radiotherapy and 60% of the patients in the standard treatment group were clinically tumor free. CONCLUSIONS: No statistically significant benefit in survival was observed for patients treated with neoadjuvant chemotherapy followed by radiotherapy. Nor was there any impact of chemotherapy on the number of patients achieving loco-regional tumor control after primary treatment.

Adult↗

PubMed1997

Localization of nonpancreatic secretory phospholipase A2 in normal and atherosclerotic arteries. Activity of the isolated enzyme on low-density lipoproteins.

Secretory nonpancreatic type II phospholipase A2 (snpPLA2) hydrolyzes fatty acids at the sn-2 position in phospholipids releasing free fatty acids (FFAs) and lysophospholipids. These products may act as intracellular second messengers or can be further metabolized into proinflammatory lipid mediators. The presence of snpPLA2 in extracellular fluids and serum during inflammation has suggested a role of the enzyme in this process. However, the presence of snpPLA2 in a variety of normal tissues suggests that snpPLA2 may also have physiological functions. Atherosclerosis appears to have an inflammatory component. Here we report on the snpPLA2 localization in normal and atherosclerotic lesions and on the properties of the isolated enzyme. A strong snpPLA2 immunoreactivity was observed in the arterial media that was colocalized with alpha-actin-positive vascular smooth muscle cells (SMCs) in both normal and atherosclerotic vessels. In aortic atherosclerotic lesions, snpPLA2 was observed colocalized with CD68-positive macrophages and HHF-35-positive SMCs and extracellularly in the lipid core. snpPLA2 was isolated from human normal arteries and from aorta with lesions. The enzyme was isolated by acid extraction of normal arterial tissues followed by immunoaffinity chromatography. The purified snpPLA2 had an expected molecular weight of 14 kD by polyacrylamide gel electrophoresis and appeared as a single band in immunoblotting. The enzymatic activity was followed by measuring release of fatty acids from phospholipid liposomes or LDL as substrates. The enzymatic activity was inhibited with two specific inhibitors for human snpPLA2: (1) monoclonal antibody 187 and (2) LY311727, a synthetic selective inhibitor. The mRNA for snpPLA2 was detected with reverse transcriptase polymerase chain reaction. These results indicate that snpPLA2 is present in human arteries and that it is able to hydrolyze phospholipids in LDL. The results support the hypothesis that snpPLA2 can release proinflammatory lipids at places of LDL deposition in the arterial wall.

Adult↗

PubMed1996

Binding of human phospholipase A2 type II to proteoglycans. Differential effect of glycosaminoglycans on enzyme activity.

Phospholipase A2 acting on low density lipoproteins in the extracellular arterial intima may form proinflammatory lipid mediators. Human nonpancreatic secretory phospholipase A2 has three regions that may associate with sulfated glycosaminoglycans. The apoB-100 molecule in low density lipoproteins also has glycosaminoglycan binding regions that could mediate its retention in the arterial intima. Here we report that human nonpancreatic phospholipase A2 isolated from a transfected cell line binds to glycosaminoglycans secreted by cultured human arterial smooth muscle cells. A gel mobility shift assay showed that the affinity of phospholipase A2 for glycosaminoglycans from a heparan sulfate/chondroitin sulfate proteoglycan was higher than for chondroitin sulfate glycosaminoglycans from a larger versican-like proteoglycan. Affinity chromatography confirmed these results. All glycosaminoglycans tested, at concentrations up to 100 microM, increased the activity of phospholipase A2 toward phosphatidylcholine liposomes. Above this concentration, heparan sulfate and heparin inhibited the enzyme. Heparin and chondroitin 6-sulfate increased phospholipase A2 activity on low density lipoproteins up to 4-fold at 100 microM, whereas heparan sulfate had no effect. The results indicate that human nonpancreatic secretory phospholipase A2 interacts with proteoglycans via their glycosaminoglycan moiety and that the enzyme activity may be modulated by the association of the enzyme and its substrate to the sulfated polysaccharides.

Chondroitin Sulfates↗

PubMed1995

Interferon gamma binds to extracellular matrix chondroitin-sulfate proteoglycans, thus enhancing its cellular response.

The amino acid sequence of interferon gamma (IFN-gamma) has basic amino acid clusters similar to the heparin-binding consensus sequences found in other proteins that bind to proteoglycans (PGs). We investigated whether recombinant human IFN-gamma could bind to extracellular matrix (ECM) PGs secreted by human arterial smooth muscle cells (HASMCs) in vitro and whether the interaction affected the cellular response to IFN-gamma. As an in vitro model of ECM we used the basement membrane from HASMCs in culture. The binding of 125I-IFN-gamma to ECM was reduced significantly by pretreatment of ECM with chondroitinase ABC, an enzyme that degrades chondroitin-sulfate glycosaminoglycans. IFN-gamma binding to ECM was reduced by increasing concentrations of chondroitin-6-sulfate. 125I-IFN-gamma (0.05 to 2 ng/mL) binding data indicated an apparent Kd of 2 x 10(-11) mol/L and a maximum binding of 1.6 x 10(6) IFN-gamma molecules bound per square millimeter of ECM. Experiments with synthetic peptides suggested that residues 127 through 135 (AKTGKRKRS) are involved in the binding. The binding to chondroitin-sulfate PGs was confirmed by affinity chromatography of isolated [35S]chondroitin-sulfate PGs from ECM and cell-culture medium on immobilized IFN-gamma. The binding was abolished by treatment with chondroitinase ABC. ECM-bound IFN-gamma was more effective in inducing the expression of class II major histocompatibility antigens such as HLA-DR in HASMCs and human arterial endothelial cells than soluble IFN-gamma. These results suggest a role for chondroitin-sulfate PGs in immobilizing IFN-gamma in the ECM compartment and enhancing the cellular response to IFN-gamma.

Amino Acid Sequence↗

PubMed1993

Binding of low density lipoproteins by proteoglycans synthesized by proliferating and quiescent human arterial smooth muscle cells.

Chondroitin sulfate-rich proteoglycans secreted by arterial intima smooth muscle cells appear involved in low density lipoprotein entrapment and modification. Hypothetically, such a process may contribute to atherogenesis. We compared composition and size of those proteoglycans synthesized by proliferating and resting human arterial smooth muscle cells for which low density lipoprotein had affinity. Lipoprotein-binding proteoglycans secreted by proliferating cells were larger than those of resting cells (M(r) = 1.1 x 10(6) versus 0.8 x 10(6). This was primarily caused by increased M(r) of the chondroitin sulfate chains (6 x 10(4) versus 3.5 x 10(4)). The glycosaminoglycan chains of the proteoglycans from both cells were made of more than 90% chondroitin 6-sulfate and chondroitin 4-sulfate in a 6:4 ratio. Affinity chromatography indicated that low density lipoprotein had a higher affinity with the proteoglycans synthesized by proliferating cells than those from resting cells. Measured with gel mobility shift assay, the apparent affinity constant of low density lipoproteins for proteoglycans from proliferating cells was 3-fold higher than that for proteoglycans from resting cells. This increased affinity appeared related to the higher relative proportion of proteoglycans with longer glycosaminoglycan chains secreted by the proliferating cells than those secreted by the resting cells.

Arteries↗

PubMed1993

Lipoprotein oxidation and measurement of thiobarbituric acid reacting substances formation in a single microtiter plate: its use for evaluation of antioxidants.

Transition metals catalyze free radical-mediated oxidation of lipids and lipoproteins. This process is currently studied because of its potential relevance to pathological processes like atherosclerosis. Formation of thiobarbituric acid-reacting substances from polyenoic fatty acids is frequently used to follow oxidation of lipids and plasma lipoproteins. We describe here how Cu(II)- and Fe(III)-catalyzed oxidation of human low density lipoprotein or soy bean phospholipids and the photometric evaluation of the thiobarbituric acid-reaching substances formed can be conducted in the same 96-well microtiter plate. The procedure showed a correlation of 0.98 with conventional two-stage fluorimetric and spectrophotometric methods and also showed better reproducibility. The plate method can handle up to one plate per hour with considerably less labor than the test tube assays. The plate procedure required small volumes of diluted samples of lipoproteins lipids and reagents. The method was suitable for testing the concentration-dependent antioxidant potency of substances like probucol, butylated hydroxytoluene, and alpha-tocopherol. The method can also be used to follow the kinetics of oxidation of lipoproteins.

Antioxidants↗

PubMed1993

Backscatter radiation at tissue-titanium interfaces. Biological effects from diagnostic 65 kVp x-rays.

The induced secondary electrons from a metal surface by diagnostic x-rays are thought to contribute to cell damage near the tissue-metal boundaries of metal implants. Titanium implants are becoming increasingly more popular for tissue reconstructions and it is rather often desirable to take radiographs of the operated area. In this study we compared the biological effects of radiation on cultured mammalian test cells grown on titanium plates with the radiation effects on cells that were grown on plastic control plates. In order to study the acute radiation effects on cell growth it was necessary to work with rather high radiation doses (0.7-5 Gy). Photon energies, suitable for diagnostic radiography in odontology, 65 kV, were applied. We found that the cells grown on titanium plates were, in terms of the applied dose in the surrounding culture medium, more sensitive to the irradiations than the cells growing on plastic plates. The survival curve for the cells on titanium had a steeper slope, showed no shoulder in the low-dose region and looked like curves normally obtained for high LET radiation. It was not possible to resolve to what degree the titanium-dependent changes were due to an increased dose near the titanium surface or to a change in the radiobiological effectiveness. Although there was a significant decrease in cellular survival near the metal, postoperative intraoral radiography after titanium implantations need not be excluded. The maximal doses given in odontological x-ray examinations are less than 1 mGy and, if the results in this study are applied, the biological effects near the titanium implant will correspond to biological effects in soft tissue of doses less than 20 mGy which is lower than the doses that give acute effects. The risk of acute healing disturbances are significant only at much higher radiation doses.

Animals↗

PubMed1992

Bleomycin/cis-platin as neoadjuvant chemotherapy before radical radiotherapy in localized, inoperable carcinoma of the esophagus. A prospective randomized multicentre study: the second Scandinavian trial in esophageal cancer.

Survival and swallowing function were studied in a randomized trial of 97 patients with inoperable, localized esophageal carcinoma. Radical radiotherapy was given to 51 patients, while 46 patients had two courses of bleomycin/cisplatin before radiotherapy. The survival was 29% after one year, and 6% after 3 years in the radiotherapy group. The survival in the combined treatment group was 18 and 0%, respectively; p = 0.1895. The number of patients who could swallow any food increased from 6% before treatment to 38% after 3 months in the radiotherapy group, and from 0% to 23% in the combined group. No benefit was found by combining bleomycin/cisplatin with radiotherapy.

Aged↗

PubMed1992

Effect of arterial proteoglycans and glycosaminoglycans on low density lipoprotein oxidation and its uptake by human macrophages and arterial smooth muscle cells.

The reversible interaction of low density lipoprotein (LDL) with arterial chondroitin sulfate proteoglycans (CSPGs) or glycosaminoglycans (GAGs) selects LDL particles with a high affinity for sulfated GAGs and also induces modifications in apolipoprotein B (apo B) and the lipid organization of the lipoprotein. In the present work we studied the effect that the reversible interaction with sulfated polysaccharides has on the susceptibility of LDL to in vitro oxidation. For this purpose soluble, nonaggregated CSPG- or GAG-treated LDL was subjected to oxidation in the presence of 5 microM CuSO4 for as long as 48 hours. The rate of formation of thiobarbituric acid-reactive substances, the decrease in isoelectric point, the increase in relative electrophoretic mobility of LDL, the higher degradation rate by human macrophages, and the lower degradation rate by human arterial smooth muscle cells showed that LDLs exposed to CSPGs and GAGs were significantly more susceptible to oxidation than native LDL. Results from competition experiments indicate that C6S-treated LDL after 4 hours of oxidation is taken up via the acetylated LDL receptor in human macrophages. Coincubation of lipoproteins with human macrophages or human arterial smooth muscle cells for 24 hours also indicated that C6S-treated LDL was more susceptible to cell-induced modifications than native LDL. The occurrence in vivo of similar processes may contribute to focal retention, increased rate oxidation of LDL in the arterial intima, and foam cell formation during atherogenesis.

Arteries↗

PubMed1991

Modifications of low-density lipoprotein induced by arterial proteoglycans and chondroitin-6-sulfate.

Association of low-density lipoproteins (LDL) with arterial chondroitin sulfate proteoglycans (CSPG) appears to contribute to their deposition in the extracellular intimal compartment and to its internalization by macrophages. CSPG and LDL interact by ionic bridges with formation of soluble and insoluble complexes. We studied the alterations on LDL structure induced by its association with arterial CSPG and other glycosaminoglycans (GAG). In soluble complexes, at low and at physiological ionic strength, arterial CSPG and sulfated GAG modify the kinetics of apoB-100 proteolysis by trypsin. However, less marked alterations in the peptide patterns were observed with proteinase V8 and almost none with thermolysin. This is indirect evidence that the presence of CSPG and GAG modified the exposure of polar regions of apoB-100 in LDL. Competitive binding experiments with agarose-bound heparin and soluble GAG also suggest that after formation of insoluble complexes with arterial CSPG and resolubilization the exposure of Lys, Arg-rich segments of apoB-100 is increased. Results from differential scanning calorimetry and differential thermal spectrophotometry showed that the CSPG and GAG-induced modifications reduced the thermal stability of the surface and core in LDL. If present in vivo, the structural alterations of polar segments of the LDL protein moiety may influence the outcome of its interaction with the arterial mesenchyma.

Apolipoprotein B-100↗

PubMed1991

Anticipatory nausea and vomiting in cancer patients.

The present study reports on a mediating mechanism for anticipatory nausea and vomiting (ANV) in cancer chemotherapy. ANV is usually explained as a classically conditioned response. However, conditioning models have failed to explain individual variation in ANV susceptibility. On the basis of the positive correlation between degree of autonomic reactivity (AR) and conditionability, it is proposed that individual AR is predictive of ANV development. Of the 31 patients who participated in the study, 74% experienced postinfusion nausea and vomiting (PNV). Of the 23 patients who experienced PNV, 52% developed ANV. AR was recorded in a habituation paradigm before chemotherapy treatment was initiated. The patients in the ANV group showed significantly increased sympathetic reactivity as compared with the no-ANV group, implying that AR is a mediator of ANV development.

Adolescent↗

PubMed1991

Backscatter radiation at tissue-titanium interfaces. Analyses of biological effects from 60Co and protons.

It has been claimed that implanted metals can cause backscatter radiation in radiation therapy with a dose enhancement at the bone-metal and tissue-metal interfaces on the beam entrance side. Theoretical calculations and experimental measurements with ionization chambers have indicated that such effects might be significant. Titanium implants are increasingly used in oral and maxillo-facial surgery for reconstruction purposes. A more detailed knowledge of backscatter-induced effects is therefore desired when head and neck cancers in patients with implants are treated with radiotherapy. We have made comparisons of cell survival after irradiation of two types of cultured cells grown directly on titanium metal and on plastic control supports. The cell cultures were irradiated with either 60Co photons or range modulated protons. No significant differences in the colony-forming capacity were found between the irradiated cells grown on titanium and those grown on plastic control supports. This was the case for both radiation types and the results were also observed to be dose-independent. The only observed phenomena were that the two cell-lines differed in radiosensitivity and that protons gave higher biological effects than gamma radiation. The results show that there were no significant changes in cell survival at the interface between the tissue equivalent medium and titanium support indicating that a dose increase induced by backscatter radiation, which possibly could demolish the osseointegration or induce osteoradionecrosis, are minimal when high energy photons or range modulated protons are applied.

Animals↗

PubMed1991

Modification of copper-catalyzed oxidation of low density lipoprotein by proteoglycans and glycosaminoglycans.

Chondroitin sulfate proteoglycans (CSPG) appear to contribute to retention of low density lipoproteins (LDL) in atherosclerotic lesions. In vitro, CSPG and glycosaminoglycans (GAG) modify LDL structure and increase its uptake by macrophages. This latter effect appears related to increased exposure of arginine- and lysine-rich segments of apoB-100. We explored whether alterations of LDL induced by human arterial CSPG and purified GAG alter the lipoprotein susceptibility to transition metals-catalyzed oxidation. Human LDL was complexed with human arterial CSPG and dissociated by raising the ionic strength. The nonaggregated, CSPG- and GAG-treated LDL was subjected to oxidation by micromolar amounts of Cu+, Cu2+, Fe2+, and Fe3+. This treatment increased LDL susceptibility to Cu2+ oxidation 3- to 5-times, as indicated by the degradation rate of phospholipids and cholesteryl esters and formation rates of dienes and thiobarbituric acid-reacting substances (TBARS). Also, human macrophages degraded the CSPG-treated, Cu2+-oxidized LDL 3- to 6-times faster than native LDL similarly treated. No enhancement of oxidation was observed with Fe2+, Fe3+, and Cu+. Quenching of the LDL intrinsic fluorescence by Cu2+ showed that heparin, CSPG, and chondroitin-6-SO4 pretreatment increased the access of Cu2+ to hydrophobic chromophores, probably tryptophan, 6- to 7-, 3- to 4-, and 2- to 3-fold, respectively. Also, the affinity constant (Ka) of LDL for Cu2+ was increased from 0.12 microM to 0.20 microM by the treatment with CSPG and GAG. These results and evaluation of the fraction of surface-accessible LDL chromophores to acrylamide quenching suggest that the increased susceptibility to oxidation may be associated with an increase in the access of Cu2+ to hydrophobic regions in LDL caused by treatment with CSPG and GAG. This effect was not detected with Cu+, Fe2+, or Fe3+. The phenomenon may contribute to acceleration of the oxidative modifications of LDL in cell culture models and in vivo.

Aorta↗

PubMed1990

Molecular basis of the association of arterial proteoglycans with low density lipoproteins: its effect on the structure of the lipoprotein particle.

Modifications of low density lipoproteins (LDL) that enter the arterial intima appear to be responsible for their eventual extracellular and intracellular accumulation during atherogenesis. Some of these modifications seem to be the result of LDL association with intimal chondroitin sulphate-rich proteoglycans (CSPG). We have used frontal elution affinity chromatography, binding and competition experiments with synthetic segments of apoB-100 to better define the ligand regions for the LDL-CSPG complexes. The minimum structural requirement for recognition by the CSPG appears to be a hydrophilic nine-residue amino-acid segment with five lysine and arginine residues. Analysis of other similar regions in apoB-100 and other glycosaminoglycan-binding proteins suggest that besides a cluster of positively charged amino-acids, the presence of hydroxyl-containing residues favours the association with sulphated proteoglycans. With controlled proteolytic hydrolysis, we found that the interaction of LDL with CSPG modifies the surface accessibility of a apoB-100 segments containing arginine and lysine. Because these apoB-100 domains may also be involved in cell-receptor binding, the CSPG-induced modifications could be the structural explanation for the observed increase in cellular uptake of proteoglycan-modified LDL.

Amino Acid Sequence↗