Biomedical subjects

H Vlassara

Publications and source records attributed to H Vlassara.

At least 109 records · Page 6Linked to original sources

PubMed1986

Reduced plasma lipoprotein lipase activity in patients with malignancy-associated weight loss.

Post-heparin plasma lipoprotein lipase activity was measured in 28 cancer patients with varying degrees of weight loss, and in 16 normal volunteers. Total lipoprotein lipase activity was decreased by 35.4% (P less than 0.001) in the cancer group. The component lipase activities, hepatic (HLPL), and peripheral (PLPL), were decreased by 40% (P less than 0.001) and 38% (P less than 0.005) respectively. In addition, the level of total peripheral lipoprotein lipase correlated well with the percent body weight lost by these patients (r = 0.6, P less than 0.01). Regardless of extent of disease, patients with lung cancer showed the lowest enzyme activity (mean 191 mU/ml +/- 30 SEM, P less than 0.001) and the greatest percent of weight loss (mean 16%), while patients with breast cancer had nearly normal lipase activity (mean 315 mU/ml +/- 50 SEM, normal 340 mU/ml +/- 22 SEM, P less than 0.10) and minimal weight loss (mean 8.4%). Fasting serum triglycerides were significantly elevated in the patient group (mean 120 mg/dl +/- 9.7 SEM) as compared to normal (mean 71 mg/dl +/- 7 SEM, P less than 0.001). The mean fasting insulin level was elevated in the patient group (13 mU/ml +/- 3.0 SEM), although in the majority of the patients it was found within the normal range (4-24 mU/ml). We conclude that the significant decrease in the total LPL activity may be responsible in part for the characteristic hypertriglyceridemia present in cancer patients.

Adult↗

PubMed1986

Trapped immunoglobulins on peripheral nerve myelin from patients with diabetes mellitus.

Diabetic peripheral neuropathy is characterized by endoneurial capillary closure and by segmental demyelination and axonal degeneration in a spatial pattern consistent with ischemic damage. The increased permeability of human diabetic endoneurial capillaries to plasma proteins may contribute to the pathogenesis of these structural changes in peripheral nerve by further accelerating the rate at which plasma proteins are trapped by reactive nonenzymatic glycosylation products on long-lived proteins such as myelin. We have measured trapped immunoglobins (Ig) G and M on peripheral nerve myelin from diabetic and nondiabetic patients by an enzyme-linked immunosorbent assay to determine whether plasma proteins accumulate on nerves as they do in the glomerular matrix of diabetics. The amount of trapped IgG on brain myelin from these subjects was also determined. Peripheral nerve myelin from diabetics had on average greater than 14 times the amount of trapped IgM found in identically prepared samples from nondiabetics (0.90 +/- 0.2 vs. 0.06 +/- 0.004 OD/micrograms myelin protein) and greater than 4 times the amount of trapped IgG (6.40 +/- 1.92 vs. 1.5 +/- 0.25 OD/micrograms myelin protein). In contrast, no significant trapping of IgG was detected in any samples of brain myelin. This most likely reflects effective exclusion of IgG by the blood-brain barrier. These data suggest that excessive trapping of Igs and other plasma proteins by diabetic peripheral nerve myelin may contribute to the development of peripheral nerve damage, whereas the lack of such trapping by brain myelin may partly explain the rarity of diabetic central neuropathy.

Adult↗

PubMed1986

Nonenzymatic glycosylation: role in the pathogenesis of diabetic complications.

Prolonged hyperglycemia is the primary metabolic abnormality responsible for the development of irreversible tissue damage in chronic diabetes. However, patients with similar levels of chronic hyperglycemia can differ markedly in their susceptibility to diabetic complications. Among the mechanisms by which hyperglycemia may lead to tissue damage, nonenzymatic glycosylation involves excessive chemical attachment of glucose to proteins without the involvement of enzymes. The early Amadori products, resembling hemoglobin A1c, slowly give rise to complex irreversible glycosylation adducts. Only these post-Amadori products accumulate in diabetic tissues over long periods. However, early nonenzymatic glycosylation or Amadori product formation can alter such physiological processes as enzyme activity or binding of regulatory molecules. Advanced glycosylation end products can covalently trap extravasated serum proteins to the extravascular matrix, and thus may contribute to capillary closure in the retina and glomerulus, and to arterial narrowing in the coronary, cerebral, and peripheral circulation. Although a macrophage receptor system may antagonize this glycosylation-mediated accumulation of proteins by recognizing and ingesting those proteins with advanced glycosylation end products, excessive formation of those proteins in diabetes may saturate the capacity of the macrophage removal system.

Blood Glucose↗

PubMed1985

Protein glycosylation and the pathogenesis of atherosclerosis.

This review summarizes the progress of research in nonenzymatic glycosylation that is of potential relevance to atherosclerosis and relates this knowledge to the accelerated large-vessel disease observed in diabetics through a hypothetical model based on current concepts of atherogenesis. Critical new information has recently been obtained about complex glycosylation adducts, which form very slowly through a series of further reactions and rearrangements from the initial Amadori product. These adducts, called advanced glycosylation end products (AGE), are not reversible like the Amadori product. Thus, they continue to accumulate indefinitely on long-lived molecules such as collagen and nucleic acids. AGE covalently trap soluble plasma proteins, act as signals for macrophage recognition and uptake, and induce mutations in double-stranded plasmid DNA. Covalent trapping of low-density lipoproteins by AGE on collagen may promote excessive lipid accumulation in the arterial walls of diabetics, whereas trapping of von Willebrand factor by AGE may increase platelet adhesion and aggregation, leading to smooth muscle cell proliferation in the arterial intima. Recognition and uptake of AGE-protein derivatives by scavenging macrophages may further contribute to the process of atherogenesis by stimulating the release of such macrophage secretory products as macrophage-derived growth factor. Accumulation of AGE on smooth muscle cell DNA may also enhance proliferation of arterial smooth muscle cells by increasing the rate of mutations that affect growth control.

Arteriosclerosis↗

PubMed1985

High-affinity-receptor-mediated uptake and degradation of glucose-modified proteins: a potential mechanism for the removal of senescent macromolecules.

Proteins that have been modified by long-term exposure to glucose accumulate advanced glycosylation end products (AGE) as a function of protein age. In these studies, we have characterized the interaction of AGE-protein with mouse peritoneal macrophages, using AGE-modified bovine serum albumin (AGE-BSA, prepared by incubation with glucose) as a probe. AGE-BSA was specifically bound to cells at 4 degrees C and was taken up and degraded at 37 degrees C; these processes were concentration dependent and saturable. Competition experiments with AGE-BSA, BSA incubated with phosphate-buffered saline rather than glucose, and yeast mannan demonstrated that macrophages specifically recognize AGE on proteins by a receptor that is completely distinct from the mannose/fucose receptor. Scatchard analysis of AGE-BSA binding data indicated that there are approximately 1.06 X 10(5) receptors per macrophage, with an affinity constant of 1.75 X 10(-11) M. Specific binding of AGE-BSA to the macrophage receptor was competitively inhibited by BSA that had been chemically coupled to a synthetic analogue of the specific AGE, 2-(2-furoyl)-4(5)-(2-furanyl)-1H-imidazole (FFI-BSA). FFI-BSA was also taken up by macrophages in a concentration-dependent, saturable manner. Prior incubation of macrophages with AGE-BSA failed to influence the subsequent uptake and degradation of added AGE-BSA. Thus, the AGE receptor does not appear to be down-regulated by exposure to AGE-proteins. Results from these studies suggest that AGE could act in vivo as a specific signal for recognition and degradation of senescent macromolecules. Incomplete removal of AGE-proteins by macrophages may ultimately give rise to some of the physiologic changes that occur with normal aging.

Aging↗

PubMed1985

Recognition and uptake of human diabetic peripheral nerve myelin by macrophages.

Macrophages recognize and ingest several human proteins whose amino groups have been modified in vitro by specific chemical reagents. Because amino groups of human peripheral nerve myelin proteins become covalently modified in vivo by products of nonenzymatic glycosylation, we examined myelin/macrophage interactions using peripheral nerve myelin prepared from diabetic and nondiabetic patients. Intracellular accumulation of diabetic myelin increased with concentration in an apparently saturable fashion, reaching levels 3-4 times higher than those of age-matched nondiabetic samples. Low-temperature inhibition of cellular myelin accumulation further suggested that diabetic myelin uptake was associated with adsorptive endocytosis. Macrophage recognition and accumulation of nondiabetic myelin glycosylated in vitro increased with duration of sugar incubation, to a level nearly nine times that of the same sample incubated in buffer alone. Data from competition experiments with albumin and myelin glycosylated in vitro showed that recognition of human peripheral nerve myelin proteins by macrophages is specific for protein-bound products of nonenzymatic glycosylation. In vivo, such macrophage recognition of and interaction with nonenzymatic glycosylation products on diabetic peripheral nerve myelin could contribute to the pathogenesis of segmental demyelination.

Adult↗

PubMed1985

Nonenzymatic glycosylation products on collagen covalently trap low-density lipoprotein.

Advanced nonenzymatic glycosylation products capable of cross-linking proteins accumulate on collagen in vivo in proportion to time-averaged blood glucose concentration. In this report, we have evaluated the ability of advanced nonenzymatic glycosylation products formed on collagen in vitro to covalently bind low-density lipoprotein (LDL) in a manner similar to that which occurs in human atherosclerotic lesions. At constant LDL concentration, covalent trapping increased linearly with the extent of advanced glycosylation product formation, from 1.42 +/- 0.15 to 4.46 +/- 0.36 micrograms LDL protein/mg collagen. At a constant level of collagen advanced glycosylation product, LDL binding increased as a function of increasing LDL concentration. At an LDL-cholesterol level of 103 mg/dl, covalent trapping of LDL by nonenzymatic glycosylation products on collagen averaged 3.2 times as much as control (P less than 0.01). These data indicate that LDL is bound specifically by reactive products generated by nonenzymatic glycosylation of collagen, and suggest that excessive LDL trapping by hyperglycemia-induced advanced glycosylation endproducts may contribute to the accelerated development of atherosclerosis in patients with diabetes mellitus.

Animals↗

PubMed1984

Accumulation of diabetic rat peripheral nerve myelin by macrophages increases with the presence of advanced glycosylation endproducts.

We have previously shown that increased nonenzymatic glycosylation occurs in peripheral nervous tissue of diabetic humans and animals, primarily on the PO-protein of peripheral nerve myelin. The pathophysiologic mechanism by which this biochemical alteration leads to myelin breakdown and removal is not as yet understood. In the present study we show that advanced glycosylation end-product (AGE) adducts that form during long-term exposure of peripheral nerve myelin proteins to glucose in vitro and in vivo markedly alter the way in which myelin interacts with elicited macrophages. In this interaction, macrophages appear to specifically recognize AGEs on myelin, since AGE-BSA competes nearly as effectively as AGE-myelin, while neither unmodified BSA nor unmodified myelin compete. The failure of yeast mannan to interfere with macrophage recognition of AGE-myelin suggests that the mannose/fucose receptor does not mediate this process. Recognition of AGE-protein by macrophages is associated with endocytosis, as demonstrated by resistance of cell-associated radioactivity to removal by trypsin action, and by low temperature inhibition of ligand accumulation in the cellular fraction. 125I-labeled myelin that had been incubated in vitro with 50 mM glucose for 8 wk reached a steady state accumulation within thioglycolate-elicited macrophages that was five times greater than that of myelin incubated without glucose. Similarly, myelin isolated from rats having diabetes for 1.5-2.0 years duration had a steady state level that was 9 times greater than that of myelin from young rats, and 3.5 times greater than that of myelin from age-matched controls. In contrast, myelin isolated from rats having diabetes for 4-5 wk had the same degree of accumulation observed with myelin of age-matched normal rats. These data suggest that the amount of increased nonenzymatic glycosylation observed in the myelin of short-term diabetic rats had not yet resulted in the significant accumulation of AGE-myelin present both in vitro and in the long-term diabetic rats. The disappearance of acid-insoluble radioactivity from within the cells and the appearance of acid-soluble radioactivity released into the medium were very similar for the two groups, suggesting that the striking difference in accumulation seen between normal myelin and AGE-myelin is due primarily to increased uptake. Formation of irreversible AGE-adducts on myelin appears to promote the recognition and uptake of the modified myelin by macrophages. This interaction between AGE-myelin and macrophages may initiate or contribute to the segmental demyelination associated with diabetes and the normal aging of peripheral nerve.

Aging↗

PubMed1984

Association of insulin pump therapy with raised serum amyloid A in type I diabetes mellitus.

Serum concentrations of serum amyloid A protein, the high-density-lipoprotein-associated tissue amyloid A precursor, were determined in 29 diabetic patients receiving insulin by subcutaneous injection and in 50 receiving subcutaneous infusion pump therapy. Insulin delivered by continuous subcutaneous pumps stimulated serum amyloid A production to levels nearly six times those in normal subjects, nearly twice as much as insulin given by subcutaneous injection. 85% of patients with serum amyloid A levels greater than or equal to 10(4) ng/ml were being treated with insulin pump therapy. The relation between insulin aggregation and amyloid A in diabetes was evaluated in 1 patient; treatment with syringe-aggregated insulin resulted in a nearly 300% increase in serum amyloid A levels. The use of high-potency non-aggregating insulins in the pump treatment of type I diabetic patients may be necessary for optimum therapy.

Adolescent↗

PubMed1984

Inhibition of heparin-catalyzed human antithrombin III activity by nonenzymatic glycosylation. Possible role in fibrin deposition in diabetes.

The effect of nonenzymatic glycosylation on the biologic function of human antithrombin III was evaluated using a chromogenic thrombin substrate assay in the presence of catalytic amounts of heparin. Experimental conditions that increased the rate of nonenzymatic protein glycosylation were associated with decreases in the thrombin-inhibiting activity of antithrombin III. This glycosylation-induced inhibition of heparin-catalyzed antithrombin III activity was completely reversible by preassay incubation with excess sodium heparin. These observations provide a biochemical explanation for the heparin-reversible, accelerated fibrinogen disappearance rate induced by hyperglycemia in diabetic patients. Defective inhibition of the coagulation cascade induced by excessive nonenzymatic glycosylation of antithrombin III in vivo could contribute to accumulation of fibrin in various diabetic tissues.

Antithrombin III↗

PubMed1984

Nonenzymatic glycosylation and the pathogenesis of diabetic complications.

Glucose chemically attaches to proteins and nucleic acids without the aid of enzymes. Initially, chemically reversible Schiff base and Amadori product adducts form in proportion to glucose concentration. Equilibrium is reached after several weeks, however, and further accumulation of these early nonenzymatic glycosylation products does not continue beyond that time. Subsequent reactions of the Amadori product slowly give rise to nonequilibrium advanced glycosylation end-products which continue to accumulate indefinitely on longer-lived molecules. Excessive formation of both types of nonenzymatic glycosylation product appears to be the common biochemical link between chronic hyperglycemia and a number of pathophysiologic processes potentially involved in the development of long-term diabetic complications. The major biological effects of excessive nonenzymatic glycosylation include: inactivation of enzymes; inhibition of regulatory molecule binding; crosslinking of glycosylated proteins and trapping of soluble proteins by glycosylated extracellular matrix (both may progress in the absence of glucose); decreased susceptibility to proteolysis; abnormalities of nucleic acid function; altered macromolecular recognition and endocytosis; and increased immunogenicity.

Blood Glucose↗

PubMed1983

Excessive nonenzymatic glycosylation of peripheral and central nervous system myelin components in diabetic rats.

The amount of nonenzymatic glycosylation present in normal and diabetic rat peripheral nerve myelin, whole brain, brain myelin, and individual myelin protein components was determined using NaB3H4 reduction followed by either boronic acid affinity chromatography or SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Diabetic peripheral nerve myelin (PNS-M) showed a 5.2-fold increase over normal, indicating that myelin is the major peripheral nerve component undergoing excessive glycosylation in diabetes. SDS-PAGE of diabetic and normal PNS-M showed no differences in the pattern of protein bands or in the distribution of glycosylated adducts. However, in the diabetic, the amount of incorporated radioactivity was 3.74 times greater in the P0 protein and 2.8 times greater in the high-molecular-weight material that did not enter the gel. In whole brain, a 2.4-fold increase in the amount of nonenzymatic glycosylation was observed when diabetic was compared with normal, while diabetic brain myelin (CNS-M) was 3.8 times more glycosylated than normal brain myelin. SDS-PAGE of diabetic and normal CNS-M, like that of PNS-M, showed no differences in the pattern of protein bands or in the distribution of glycosylated adducts. The amount of incorporated radioactivity, however, was 3.18 times greater in the proteolipid region, 2.37 times greater for basic myelin protein, and 2.9 times greater for the high-molecular-weight proteins that did not enter the gel. This excessive nonenzymatic glycosylation of the main peripheral and central nervous system myelin components may contribute to the functional abnormalities of myelinated neurons associated with diabetes.

Animals↗

PubMed1983

Nonenzymatic glycosylation reduces the susceptibility of fibrin to degradation by plasmin.

The effect of nonenzymatic glycosylation on the susceptibility of fibrin to degradation by the specific fibrinolytic enzyme plasmin was evaluated using both a fibrin plate assay and a fluorogenic synthetic plasmin substrate assay. Data from both types of experiments demonstrate that nonenzymatic glycosylation reduces the susceptibility of fibrin to plasmin degradation. Acetylation and carbamylation have qualitatively similar effects, indicating that chemical modification of lysine amino groups is the underlying phenomenon responsible for the observed degradative defect produced by glucose. Experimental conditions that increased the rate of nonenzymatic protein glycosylation (higher monosaccharide concentration, glucose-6-phosphate) were associated with correspondingly greater degrees of resistance to degradation by plasmin. Such reduced degradation of nonenzymatically glycosylated proteins in vivo may contribute to the accumulation of fibrin and several other proteins observed in those tissues most frequently affected by the complications of diabetes.

Binding Sites↗

PubMed1982

Assessment of diabetic control by measurement of urinary glycopeptides.

The relationship between improvement in diabetic control and changes in levels of glycosylated urinary peptides was investigated. Eight poorly controlled Type 1 (insulin-dependent) diabetic patients were studied as optimal metabolic control was achieved. Mean daily blood glucose values and weekly haemoglobin A1 levels were determined simultaneously. Urinary glycosylated peptide levels fell 50% in 15 days, compared with 23 days for haemoglobin A1. Levels of glycosylated urinary peptides were sensitive to increased mean blood glucose concentrations of 9.72 mmol/l and increased linearly up to 20.0 mmol/l (r = 0.98) when compared with mean blood glucose levels obtained 8-9 days earlier. A similar correlation was found with haemoglobin A1 levels. Levels of glycosylated urinary peptides before and after optimal control were compared, and a decrease of 40% was observed (pre-control: 269 +/- 44 mumol/day, optimal control: 162 +/- 45 mumol/day, mean +/- SEM). The lag time between the fall in mean blood glucose level and the parallel fall in glycosylated urinary peptides was 8-9 days, suggesting that measurement of these compounds may become a useful clinical laboratory technique for monitoring short-term integrated glycaemia in diabetic patients.

Adolescent↗

PubMed1981

Nonenzymatic glycosylation of peripheral nerve protein in diabetes mellitus.

A new affinity chromatography system that selectively retains glycosylated amino acids has been utilized to determine the amount of nonenzymatic glycosylation present in peripheral nerve from diabetic and control rats and dogs. The mean value for glycosylated amino acids in diabetic rats was 2.8 times greater than the mean value in normal rats (P less than 0.001). In diabetic dogs, mean values were 2.15 times greater than normal values (P less than 0.05). Amino acid analysis of reduced, glycosylated amino acids previously isolated by affinity chromatography showed that glycosylated lysine and its hydrolysis rearrangement products were the major borohydride-reducible adduct present. In addition, another glycosylated product was noted to be present in major proportions. This radioactive product did not chromatograph with any of the available glycosylated amino acid standards. The finding that diabetes results in a nearly 3-fold increase of peripheral nerve glycosylation is consistent with a number of previous investigations in which glycosylation was measured in hemoglobin, serum albumin, and urinary amino acids and peptides from diabetics and normals. The results reported here provide evidence that increased nonenzymatic glycosylation is occurring in a tissue where physiological, morphological, and clinical degeneration characteristically develop as a result of diabetes mellitus.

Animals↗

PubMed1980

Measurement of glycosylated amino acids and peptides from urine of diabetic patients using affinity chromatography.

An affinity chromatography system has been developed that retains glycosylated amino acids and peptides. Using this system, synthetic 14C-glycosylated lysine (reduced with NaB3H4) was completely separated from a mixture of reduced 14C-glycosylated lysine and unmodified 3H-lysine. Amino acid analysis of the retained peak from hydrolyzed human diabetic hemoglobin previously reduced with NaB3H4 revealed an equimolar mixture of glycosylated valine and glycosylated lysine, in agreement with previously published data obtained using other methodologies. These data demonstrate that in alkaline solution, the NaB3H4-reducible breakdown products of nonenzymatically glycosylated proteins are adsorbed to m-aminophenyl boronic acid immobilized on Bio-Gel P-6, while nonglycosylated amino acids are not. This affinity chromatography system should facilitate the rapid evaluation of nonenzymatic glycosylation in a large number of diabetic tissues. Levels of retained compounds in urine from diabetic and normal patients were determined by measuring ninhydrin-positive material. Amino acid analysis of NaB3H4-reduced hydrolysates of these peaks showed that glycosylated lysine was the major borohydride-reducible adduct present (67%--86%). Linear regression analysis showed that the quantity of excreted compounds in normals correlated with body weight (r = 0.63). The mean level (mumol leucine-equivalent/24 h/kg body weight) in diabetics was over 1.5 times that found in urine from normal subjects (P < 0.005).

Carbon Radioisotopes↗

PubMed1977

Nonenzymatic glycosylation of hemoglobin.

The incubation of dialyzed hemoglobin A with a number of phosphorylated glycolytic intermediates leads to the formation of covalent hemoglobin adducts that co-chromatograph with hemoglobin AIb. Phosphorylated hexoses (glucose-6-P, fructose-6-P, fructose-1,6-P2) and trioses (glyceraldelyde-3-P, dihydroxyacetone-P) containing a free aldehyde or ketone can glycosylate hemoglobin A nonenzymatically. From 7 to 12% of the hemoglobin can be modified after a 72-h incubation of an equimolar mixture of hemoglobin A and the phosphorylated intermediate. No significant formation of adduct was seen with a sugar alone (glucose, fructose) or glycolytic intermediate which had a blocked aldehyde (glucose-1-P, glucose-1,6-P2, UDP-glucose). The addition of an equimolar amount of 2,3-diphosphoglycerate reduced adduct formation. Evidently, the phosphate is needed to orient and stabilize the intermediate in the bisphosphoglycerate pocket of hemoglobin so that the addition reaction can proceed. All of the hemoglobin A adducts were indistinguishable form hemoglobin AIb by ion exchange chromatography and isoelectric focusing. The hemoglobin A-glucose-6-P adduct and hemoglobin AIb had a NaB3H4-reducible linkage in the beta chain. The concentration of hemoglobin AIb is elevated in patients with diabetes mellitus. This presumably reflects the increased concentrations of glycolytic intermediates (glucose-6-P, fructose-6-P, fructose-1,6-P2, dihydroxyacetone-P) which were found to be significantly elevated in the red cells of diabetic patients as compared with normal controls.

Adult↗

PubMedDate not supplied

The AGE-receptor in the pathogenesis of diabetic complications.

Native glucose-derived glycation derivatives (advanced glycation end products, AGE) in vascular, renal and neuronal tissues contribute to organ damage. Glycation derivatives include a number of chemically and cell-reactive substances, also termed glycoxidation products or glycotoxins (GT). Cell-associated AGE-specific receptors (AGE-Rs), AGE-R1-3, RAGE, as well as the scavenger receptors ScR-II and CD-36 that are present on vascular, renal, hemopoietic, and neuronal/glial cells, serve in the regulation of AGE uptake and removal. AGE-Rs also modulate cell activation, growth-related mediators, and cell proliferation, consequently influencing organ structure/function. This occurs via oxidant stress triggered via receptor-dependent or -independent pathways, and leads to signal activation pathways, resulting in pro-inflammatory responses. In susceptible individuals, the AGE-R expression/function may be subject to environmental or gene-related modulation, which in turn may influence tissue-specific gene functions. In this context, altered expression and activity of AGE-R components has recently been found in both mouse diabetes models and humans with diabetic complications. Although several gene polymorphisms are detected in most AGE-R components, no significant correlation to diabetic complications has as yet been found. Further investigation is underway to define whether primary or secondary genetic links of pathogenic significance exist in this system. Various AGE-binding peptides or soluble receptors have emerged as potential sequestering agents for toxic AGEs as potential therapies for diabetic complications.

Diabetic Nephropathies↗