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G Camejo

Publications and source records attributed to G Camejo.

At least 55 records · Page 3Linked to original sources
PubMed1991

Molecular parameters that control the association of low density lipoprotein apo B-100 with chondroitin sulphate.

The association of low density lipoprotein (LDL) with proteoglycans of the arterial intima, in particular chondroitin 6-sulphate proteoglycans, may contribute to LDL accumulation during atherogenesis. We studied the interactions of apolipoprotein B-100 (apo B-100) peptide segments and model peptides with chondroitin 6-sulphate. The ability of these peptides to inhibit complex formation between LDL and chondroitin 6-sulphate was used as a measurement of the interaction. Results from earlier studies suggest that surface located segments of apo B-100 are responsible for the interaction of LDL with heparin and chondroitin sulphate-rich arterial proteoglycans. Therefore 16 hydrophilic apo B-100 peptides were selected for studies and synthesized with a peptide synthesizer. These synthetic peptides were 7 to 26 amino acids long. Four of the peptides inhibited the association of LDL with chondroitin 6-sulphate, namely apo B segments 4230-4254, 3359-3377, 3145-3157 and 2106-2121. The 3359-3377 segment was the most efficient. A common feature between the interacting peptides was an excess of positively charged side chains and based on these results we synthesized nine model peptides that shared sequence characteristics with the interacting apo B-100 peptides. Five of these: RSGRKRSGK, RSSRKRSGK, RGGRKRGGK, RSRSRSRSR and RGRGRGRGR were shown to block the LDL-chondroitin-6-sulphate association, RSRSRSRSR being the most effective. The results suggest that the optimal association of the peptides with chondroitin 6-sulphate is obtained with a minimal chain length of nine amino acids and a minimum of five positive charges and that flexibility in the binding region is important.

Amino Acid Sequence↗
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

Modification of low density lipoprotein association with the arterial intima. A possible environment for the antiatherogenic action of beta-blockers.

The accumulation of lipoproteins and lipids associated with the progression of atherosclerotic lesions appears to be a sequential process involving interactions with the intimal extracellular matrix and, subsequently, with cells. Apolipoprotein B-containing lipoproteins appear first to be retained and modified focally by proteoglycans of the extracellular matrix. The association with the extracellular matrix may lead to further modifications. In vitro resident macrophages take up the modified apolipoprotein B lipoproteins via a nonsaturable mechanism that may contribute to their transformation into foam cells characteristic of the atherosclerotic lesion. The affinity of low density lipoprotein (LDL) for arterial proteoglycans in vitro is related to the charge and triglyceride content. Small, triglyceride-poor, cholesterol-rich particles interact more efficiently with proteoglycans and are taken up faster by cultured macrophages than larger triglyceride-rich ones. beta-Blockers increase the relative triglyceride content of circulating LDL, and in vitro this LDL has a lower affinity for arterial proteoglycans. These results suggest that some of the experimental antiatherogenic actions of beta-blockers may be related to a reduced LDL affinity for extracellular intima components associated with the small changes induced by the drugs in the lipoprotein structure. Hypothetically, this reduced affinity could diminish the focal accumulation of LDL in lesion-prone sites.

Adrenergic beta-Antagonists↗
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↗
PubMed1991

Uptake and degradation of low density lipoproteins in atherosclerotic rabbit aorta: role of local LDL modification.

The uptake of native and modified low density lipoprotein (LDL) in foam cells in atherosclerotic tissue was studied in an in vitro perfusion system for rabbit aorta. Experimental atherosclerosis was induced in rabbits by a combination of cholesterol feeding and mechanical injury. The aorta was perfused in an incubation chamber. A trace-label, radioiodinated tyramine-cellobiose, was used to study cellular uptake of lipoproteins. After perfusion, the tissue was digested and cells were isolated by centrifugation in a density gradient. About 40 times more LDL per cell was accumulated in the foam cell fraction than in the smooth muscle cell fraction. When the cellular uptake of LDL and acetylated LDL (AcLDL) was compared, about 4 times more AcLDL than LDL was taken up by the foam cells, suggesting that the scavenger receptor is expressed in these cells. In a competition experiment, the uptake of LDL into foam cells was reduced by 70% when a tenfold excess of AcLDL was added. This experiment suggests that native LDL is taken up by the same mechanism as AcLDL. The accumulation of radiolabeled LDL in plaques and in foam cells was reduced by 30-55% by adding vitamin E (0.1 mg/ml) to the system. These studies show an uptake of LDL by foam cells in the atherosclerotic tissue. Furthermore, these cells seem to express the scavenger receptor. The competition experiment would suggest that native LDL is taken up by the scavenger receptor. The observation that an antioxidant, vitamin E, may decrease this uptake suggests that oxidative modification of LDL is of importance for this process.

Acetylation↗
PubMed1990

Effect of short-term beta blockade on serum lipid levels and on the interaction of LDL with human arterial proteoglycans.

In view of conflicting evidence suggesting that beta-blockers have an anti-atherogenic effect as well as induce a potentially atherogenic lipoprotein profile, the effects of a short term beta-blockade on serum lipoproteins were studied in 39 healthy volunteers. Because the interaction of LDL with arterial proteoglycans appears to play a role in lipoprotein accumulation during atherogenesis, the effects of metoprolol and atenolol on low density lipoprotein interaction with human aortic proteoglycans were included in the study. We could confirm that the beta-blockers caused a decrease in HDL cholesterol and an increase in triglycerides, both potentially undesirable effects. In addition, however they induced a significant decrease in the in vitro LDL affinity for arterial proteoglycans. Since there appears to be a strong association between LDL reactivity with proteoglycans and risk for myocardial infarction, this effect of the beta-blockers may be an anti-atherogenic effect which overrides other effects on the lipoprotein pattern.

Adult↗
PubMed1990

Transfer of lipoproteins from plasma to the cell populations of the normal and atherosclerotic arterial tissue.

It appears that retention of lipoproteins rather than increased influx is the basis for lipoprotein deposition in arterial tissue during atherogenesis. Binding of lipoproteins to arterial proteoglycans is mediated by a peptide sequence considered to be involved in the interaction between the lipoproteins and the lipoprotein receptor. Consequently, in the presence of an excess of arterial proteoglycan, receptor-mediated cellular uptake of LDL is inhibited. However, LDL which has been precipitated by proteoglycan and subsequently resolubilized is taken up more avidly than native LDL, both in macrophages and in smooth muscle cells. This appears to be due to selection by the proteoglycans of a more reactive fraction of LDL. This fraction has a smaller molecular size and less surface phospholipids. As smaller LDL particles also have a higher transfer rate into the arterial tissue they may be particularly atherogenic. Low density lipoproteins appear to be taken up with higher affinity by arterial macrophages than by smooth muscle cells. The selective transfer of the LDL to macrophages can be inhibited by alpha-tocopherol, suggesting that oxidative modification may be involved in this process. The role of foam cells in atherogenesis is discussed in the context of the energy requirements of the arterial wall.

Animals↗
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↗
PubMed1990

Interaction of LDL with human arterial proteoglycans stimulates its uptake by human monocyte-derived macrophages.

The aim of this work was to investigate the possible mechanisms for uptake by human monocyte-derived macrophages (HMDM) of low density lipoprotein (LDL) pretreated with human arterial chondroitin-6-SO4-rich proteoglycan (LDL-PG). HMDM were incubated with 125I-labeled tyramine cellobiose-labeled LDL-PG, native LDL, and acetylated LDL (Ac-LDL). The results showed that two to four times more LDL-PG than LDL was bound and internalized by the HMDM. Competition experiments showed that LDL-PG competed with native LDL for the apoB,E (LDL) receptor, but not for the Ac-LDL scavenger receptor. Both the LDL and LDL-PG uptake were reduced after preincubation of the macrophages with unlabeled native LDL, though to a lesser extent with LDL-PG. The specific binding of 125I-labeled LDL and 125I-labeled LDL-PG at 4 degrees C was both saturable and concentration-dependent. The dissociation constant (Kd) for binding was 8.6 x 10(-9) M for LDL and 9.4 x 10(-9) M for LDL-PG, but the maximum binding (Bmax) was 1.5-times higher for LDL-PG. Cholesterol derived from LDL-PG was less effective than native LDL in suppressing HMG-CoA reductase activity. The results indicate that the uptake of LDL-PG is mediated not only by the LDL-receptor, but also by another unspecific pathway, which may not be subjected to regulation. These results provide further support for the hypothesis that LDL modifications induced by arterial PG may contribute to the formation of foam cells.

Acetylation↗
PubMed1990

Hyperlipoproteinemia type I in a patient with active lipoprotein lipase in adipose tissue and indications of defective transport of the enzyme.

This paper presents a case of typical hyperlipoproteinemia type I in a young woman. Her serum triglycerides varied between 2 and 90 mmol/l and she had substantial amounts of apolipoprotein B-48 in fasting plasma. She had no detectable lipoprotein lipase (LPL) activity in post-heparin plasma (less than 0.2 percent of normal). Southern blot analysis suggested no major defect in her LPL gene and Northern blot analysis of adipose tissue RNA showed normal-sized LPL-mRNA. A 2-h [35S]methionine incorporation experiment with adipose tissue pieces in vitro showed that she produced normal-sized LPL and had LPL catalytic activity in the tissue. The amounts were, however, only 5-10% of control. No detectable LPL radioactivity or catalytic activity was released from patient tissue even in the presence of heparin in the incubations. Immunofluorescent staining of adipose tissue biopsies from the patient showed LPL immunoreactivity only in adipocytes and little or none within the capillaries. Treatment of immunoprecipitated labeled LPL with endoglycosidase H showed that the oligosaccharide chains on her enzyme were of the high-mannose type and not processed as in controls. Taken together the data suggest that the patient synthesizes a relatively normal LPL protein which is core-glycosylated and folded into active enzyme as in normal subjects, but is not effectively transported via the Golgi to the cell surface.

Adipose Tissue↗
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

Agarose isoelectric focusing of plasma low and very low density lipoproteins using the PhastSystem.

Human plasma lipoproteins, fractionated by density gradient ultracentrifugation, and very low density lipoproteins, subfractionated by cumulative rate centrifugation, were subjected to agarose isoelectric focusing in small format thin gels prepared in the laboratory for the commercially available PhastSystem (Pharmacia). From preparation of the gels to their staining, the procedure took less than 3 h. The pH gradient was found reproducible and the apparent average pI of individual low density lipoproteins could be measured with a coefficient of variation of less than 5% between and less than 2% within the same run. The method appears especially suitable for the exploration of charge properties of multiple lipoprotein samples, or other large macromolecules as low density lipoproteins and very low density lipoproteins, with considerable economy of time and reagents.

Cholesterol, LDL↗
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

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↗
PubMed1988

Lipoprotein structural abnormalities in chronic renal failure with and without hemodialysis.

Nine patients with chronic renal failure in maintenance hemodialysis (CRF-HD) and nine without hemodialysis (CRF) showed similar modifications in the structure and composition of VLDL and LDL isolated by density gradient centrifugation as compared to normal controls. In very low density lipoproteins (VLDL), the ratios of triglycerides to protein and of cholesterol to protein were strongly correlated. All patients, independently of their cholesterol and triglyceride levels, presented a "beta-VLDL" caused by an increment in the isoelectric point of the particles in the density range 1.006-1.019 g/ml. This was probably due to the augmented proportion of apoB in them and is not associated with the E2 phenotype. The results indicate that the structural modifications of VLDL and low density lipoprotein (LDL), present in chronic renal failure, are not changed by maintenance hemodialysis and that they are not necessarily associated with hyperlipidemia.

Adult↗
PubMed1987

Effect of arterial proteoglycans on the interaction of LDL with human monocyte-derived macrophages.

The effect of human arterial proteoglycans (PG1) on the interaction of low density lipoprotein (LDL) with cultured human monocyte-derived macrophages (HMDM) was studied. LDL was insolubilized by treatment with chondroitin-6-sulfate-rich, partially purified PG1. The LDL, resolubilized in culture medium, was added to HMDM. The PG1 pretreated LDL induced lipid accumulation in the HMDM, converting them into foam cells. Mass determination of lipids by spectrophotometric and chromatographic procedures showed a 2-4-fold accumulation of triglycerides, phospholipids, unesterified cholesterol and cholesterol esters in 48 h, in the HMDM incubated with PG pretreated LDL, when compared to those incubated with native LDL. Incorporation of [14C]oleic acid into the HMDM lipid esters correlated with the accumulation. Association of 125I-labeled LDL and of fluorescent labeled LDL (3,3-octadecyl indocarbocyanine) to HMDM also indicated that the PG1-pretreatment of LDL increased its uptake. Density gradient centrifugation, isoelectric focusing and electron microscopy showed that, when added to the cells, the PG1 pretreated LDL was not aggregated or altered in its surface charge. However, controlled trypsin treatment and polypeptide pattern analysis indicate that the accessibility of apoB has been altered. The results suggest that changes in the surface of LDL, induced by the arterial PG1, lead to increased endocytosis of the lipoprotein and stimulation of lipid synthesis in the macrophages. The possibility that a similar process may cause lipid accumulation in arterial macrophages is discussed.

Cells, Cultured↗
PubMed1987

Effect of prazosin and propranolol on lipoproteins of hypertensive patients.

A comparative study between prazosin and propranolol with twenty male patients with mild to moderate essential hypertension was used to study the effects of these antihypertensive agents on plasma lipoproteins, and more specifically high density lipoproteins-2 and Apo A-I. After 4 weeks on placebo, the patients were randomly assigned to prazosin therapy (Group A) and other ten patients to propranolol therapy (Group B) for 8 weeks. Doses required for normalization of blood pressure ranged between 1 to 8 mg/day for prazosin and 20 to 240 mg/day for propranolol. The mean blood pressure was lowered to normal by both drugs. The results indicate that prazosin has no adverse effects on plasma lipids and lipoproteins separated by density gradient centrifugation. In contrast, propranolol increased total plasma triglycerides and decreased high density lipoprotein-2 apoprotein A-I and cholesterol levels by 50% in the group of ten patients. Since low levels of high density lipoproteins have been found to be associated with an increased incidence of coronary artery disease, the data obtained suggest that propranolol may induce significant, potentially atherogenic changes on lipid metabolism in hypertensive patients.

Adult↗