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Biomedical subjects

H B Nader

Publications and source records attributed to H B Nader.

At least 19 recordsLinked to original sources
PubMed1992

Interaction of heparin with myosin ATPase: possible involvement with the hemorrhagic activity and a correlation with antithrombin III high affinity-heparin molecules.

Up to 50% of [35S]-heparin molecules prepared from rat skin bind to rabbit muscle myosin ATPase, in a concentration dependent manner, producing a stable complex with a dissociation constant of 3 x 10(-7) M. The [35S]-heparin in the complex has a distinct electrophoretic behaviour and is precipitated by TCA together with myosin. Other [35S]-glycosaminoglycans, namely, heparan sulfate, dermatan sulfate and chondroitin sulfate also prepared from rat tissues are unable to form complexes with the enzyme. Among the sulfated glycosaminoglycans obtained from different sources only heparin is able to displace the bound [35S]-heparin from the ATPase. Heparin with high affinity for antithrombin III, prepared by antithrombin-affinity chromatography, dislodges up to 90% of the bound [35S]-heparin. Furthermore, antithrombin III-high affinity heparin shows a high affinity for myosin ATPase when compared to antithrombin III-low affinity heparin which shows a low affinity for the enzyme. It is also shown that myosin ATPase inhibits the "in vitro" plasma anticoagulant activity of heparin. These are suggestive that the special structure of the heparin molecules needed for the binding to antithrombin and myosin ATPase bears important similarities. The mechanism of the hemorrhagic effect of heparin is discussed in view of these interactions.

Adenosine Triphosphate↗
PubMed1992

Effect of monensin on the sulfation of heparan sulfate proteoglycan from endothelial cells.

Monensin is a monovalent metal ionophore that affects the intracellular translocation of secretory proteins at the level of trans-Golgi cisternae. Exposure of endothelial cells to monensin results in the synthesis of heparan sulfate and chondroitin sulfate with a lower degree of sulfation. The inhibition is dose dependent and affects the ratio [35S]-sulfate/[3H]-hexosamine of heparan sulfate from both cells and medium, with no changes in their molecular weight. By the use of several degradative enzymes (heparitinases, glycuronidase, and sulfatases) the fine structure of the heparan sulfate synthesized by control and monensin-treated cells was investigated. The results have shown that among the six heparan sulfate disaccharides there is a specific decrease of the ones bearing a sulfate ester at the 6-position of the glucosamine moiety. All other biosynthetic steps were not affected by monensin. The results are indicative that monensin affects the hexosamine C-6 sulfation, and that this sterification is the last step of the heparan sulfate biosynthesis and should occur at the trans-Golgi compartment.

Animals↗
PubMed1992

Effects of vitamin A administration on collagen and sulfated glycosaminoglycans contents in the livers of rats treated with carbon tetrachloride.

We have investigated the effects of nontoxic doses of vitamin A on the hepatic contents of collagen and sulfated glycosaminoglycans (SGAGs) in rats chronically treated with CCl4. When the animals were treated with this retinoid before the intoxication with CCl4, liver collagen level was significantly reduced as compared with that in rats that received only CCl4 (3.31 +/- 0.40 vs 5.00 +/- 0.61 mg/gm wet liver, mean +/- SD, respectively), although no significant differences were found for the relative proportion of type III collagen related to type I collagen. The absolute increment in the total amount of liver SGAG in the vitamin A--pretreated group was followed by a more important increase in the concentration of dermatan sulfate as compared with the CCl4 group (dermatan sulfate-to-heparan sulfate ratio: 1.15 for the CCl4 group vs 1.70 for the vitamin A--pretreated group). A significant proportion of the dermatan sulfate from this last group was of higher molecular weight when compared with the dermatan sulfate found in the liver of rats that received only CCl4. Our results indicate that the pretreatment with vitamin A modifies hepatic collagen and SGAG deposition and can inhibit or delay the development of liver cirrhosis in rats chronically treated with CCl4. We speculate that this effect could be due to the changes in the fat-storing (Ito) cells phenotype induced by vitamin A.

Animals↗
PubMed1991

Characterization of a heparan sulfate and a peculiar chondroitin 4-sulfate proteoglycan from platelets. Inhibition of the aggregation process by platelet chondroitin sulfate proteoglycan.

A high molecular weight chondroitin sulfate proteoglycan (Mr 240,000) is released from platelet surface during aggregation induced by several pharmacological agents. Some details on the structure of this compound are reported. beta-Elimination with alkali and borohydride produces chondroitin sulfate chains with a molecular weight of 40,000. The combined results indicate a proteoglycan molecule containing 5-6 chondroitin sulfate chains and a protein core rich in serine and glycine residues. Degradation with chondroitinase AC shows that a 4-sulfated disaccharide is the only disaccharide released from this chondroitin sulfate, characterizing it as a chondroitin 4-sulfate homopolymer. It is shown that this proteoglycan inhibits the aggregation of platelets induced by ADP. Analysis of the sulfated glycosaminoglycans not released during aggregation revealed the presence of a heparan sulfate in the platelets. Degradation by heparitinases I and II yielded the four disaccharide units of heparan sulfates: N,O-disulfated disaccharide, N-sulfated disaccharide, N-acetylated 6-sulfated disaccharide, and N-acetylated disaccharide. The possible role of the sulfated glycosaminoglycans on cell-cell interaction is discussed in view of the present findings.

Adenosine Diphosphate↗
PubMed1991

Decrease in sulphated glycosaminoglycans in aortic dissection--possible role in the pathogenesis.

STUDY OBJECTIVE: The aim was to investigate alterations in sulphated glycosaminoglycans in aortic dissection. DESIGN: Aortic fragments were taken from 10 patients within the first 3 d after onset of symptoms of aortic dissection and from nine age matched patients with no aortic disease. Sulphated glycosaminoglycans were analysed and quantified by agarose gel electrophoresis and densitometry after degradation with specific enzymes. MEASUREMENTS AND MAIN RESULTS: The amount of chondroitin sulphate was similar (7.14 v 7.60 mg.g-1 of dry tissue, n = 10, p greater than 0.5) in patients with dissection and in the control group. Total sulphated glycosaminoglycan content was decreased (11.51 v 14.26 mg.g-1 of dry tissue, n = 10, p less than 0.001). This difference was due to heparan sulphate (1.79 v 2.48 mg.g-1 of dry tissue, n = 10, p less than 0.05) and mainly to dermatan sulphate (2.58 v 4.18 mg.g-1 of dry tissue, n = 10, p less than 0.001). The ratio of 6-/4-sulphated disaccharides after chondroitinase ABC digestion was increased in the affected group. No correlation between these biochemical results and a histological evaluation of mucoid content was found. On the other hand, a significant increase in chondroitin sulphate could be observed related to aging. CONCLUSIONS: The diminution in sulphated glycosaminoglycans and its possible relationship with fat, collagen, and other extracellular matrix molecules could lead to a weakness in the aortic wall related to the dissection.

Adult↗
PubMed1991

Dependence of the C-6 sulfate of the glucosamine moiety and 1----4 glycosidic linkage of heparin disaccharides for production of hemorrhage: reversal of the antihemostatic activity of heparin and their fragments by adenosine triphosphate and myosin.

Topical application or intraperitoneal injection of heparin and heparin oligosaccharides produces a potent inhibition of skin hemostasis. Studies conducted with disaccharides derived from heparin, heparan sulfate, and chondroitin sulfates have shown that delta-4,5-uronyl-(1----4)-glucosamine, bearing a sulfate at the C-6 position of the glucosamine residue, is the minimum structure for the antihemostatic activity. The disaccharides with this basic structure produce uncontrollable hemorrhage from small blood vessels, similar to that observed for heparin. The finding that other sulfated disaccharides, with the same sulfate to hexosamine to uronic acid ratios but with the sulfate at a different position (C-2) or with a different glycosidic linkage (1----3), were inactive as inhibitors of hemostasis indicates that a specific structure is needed to produce the effect. The inhibitory activity of the normal hemostatic process produced by heparin and its products could be reversed either by ATP or myosin. Molecular models show that part of the disaccharide inhibitors and ATP have a similar structural conformation.

Adenosine Triphosphate↗
PubMed1990

Sequential degradation of chondroitin sulfate in molluscs. Desulfation of chondroitin sulfate without prior depolymerization by a novel sulfatase from Anomalocardia brasiliana.

A sulfatase acting upon chondroitin sulfate polymers, free of beta-glucuronidase and beta-N-acetylhexosaminidases, was isolated from extracts of the mollusc Anomalocardia brasiliana. The enzyme totally desulfates both chondroitin 4- and 6-sulfates without concomitant depolymerization of the compounds. It has no activity upon heparan sulfate, heparin, dermatan sulfate, and chondroitin sulfate disaccharides. It shows a pH of 5.0 and a temperature of 37 degrees C for optimum activity with a Km of 4 x 10(-5) M. The sulfatase is inhibited by sulfate and phosphate ions and HgCl2. The latter inhibition is reverted by sodium tetrathionate. Contrary to the sulfatases described so far the enzyme is activated by the lactone of D-saccharic acid when in the presence of beta-glucuronidase and beta-N-acetylgalactosaminidase. Several experiments indicate that the sulfatase is the first enzyme in the sequential degradation of chondroitin sulfate in the mollusc. This differs from the pathway of degradation of this compound in vertebrates and bacteria.

Animals↗
PubMed1990

Purification and substrate specificity of heparitinase I and heparitinase II from Flavobacterium heparinum. Analyses of the heparin and heparan sulfate degradation products by 13C NMR spectroscopy.

The purification of two heparitinases and a heparinase, in high yields from Flavobacterium heparinum was achieved by a combination of molecular sieving and cation-exchange chromatography. Heparinase acts upon N-sulfated glucosaminido-L-iduronic acid linkages of heparin. Substitution of N-sulfate by N-acetyl groups renders the heparin molecule resistant to degradation by the enzyme. Heparitinase I acts on N-acetylated or N-sulfated glucosaminido-glucuronic acid linkages of the heparan sulfate. Sulfate groups at the 6-position of the glucosamine moiety of the heparan sulfate chains seem to be impeditive for heparitinase I action. Heparitinase II acts upon heparan sulfate producing disulfated, N-sulfated and N-acetylated-6-sulfated disaccharides, and small amounts of N-acetylated disaccharide. These and other results suggest that heparitinase II acts preferentially upon N,6-sulfated glucosaminido-glucuronic acid linkages. The total degradation of heparan sulfate is only achieved by the combined action of both heparitinases. The 13C NMR spectra of the disaccharides formed from heparan sulfate and a heparin oligosaccharide formed by the action of the heparitinases are in accordance to the proposed mode of action of the enzymes. Comparative studies of the enzymes with the commercially available heparinase and heparitinase are described.

Carbohydrate Sequence↗
PubMed1990

Impaired sulphated glycosaminoglycan metabolism in a patient with GM-2 gangliosidosis (Tay-Sachs disease).

An abnormal urinary excretion of sulphated glycosaminoglycans in a patient with GM-2 gangliosidosis (Tay-Sachs disease) is described. Besides the accumulation of GM-2 ganglioside in liver and lack of hexosaminidase A, the patient shows an abnormal urinary excretion of an iduronic acid-rich low molecular weight heparan sulphate. Also, no dermatan sulphate could be detected in the urine, whereas this compound was the main sulphated glycosaminoglycan in the liver of the patient. Heparan sulphate was the main glycosaminoglycan of normal liver. The total amount of sulphated glycosaminoglycans in the urine and liver of the patient did not differ significantly from the amounts found in the liver and urine of normal subjects. Several plasma glycosidases have been assayed and the activities did not differ significantly from the values obtained for the plasma of normal subjects.

Dermatan Sulfate↗
PubMed1989

Antihemostatic activity of heparin disaccharides and oligosaccharides obtained by chemical and enzymatic fragmentation: reversal of the hemorrhagic activity by ATP and myosin.

Heparin and its fragments, namely, trisulfated disaccharide, pentasulfated tetrasaccharide, octasulfated hexasaccharide and an oligosaccharide (M.W. 6,300) prepared by enzymatic fragmentation and an oligosaccharide (M.W. 4,500) prepared by chemical fragmentation are potent inhibitors of skin hemostasis when applied topically. All the heparin fragments tested are 10 to 20 times more active than heparin itself on a weight basis in disrupting the normal hemostatic mechanism. As heparin, the fragments produce a residual antihemostatic effect which persists after extensive washing of the preparation with isotonic solutions. This residual effect could be removed either by ATP or myosin ATPase.

Adenosine Triphosphate↗
PubMed1989

Heparin stimulates the synthesis and modifies the sulfation pattern of heparan sulfate proteoglycan from endothelial cells.

Heparin stimulates 2-3-fold, in a concentration-dependent manner, the synthesis of heparan sulfate secreted by cultured endothelial cells. The increase in synthetic rate takes place immediately after exposure of the cells to heparin, affects only heparan sulfate, and is specific for the endothelial cell. No stimulation by other glycosaminoglycans was observed. Analysis of the disaccharide products formed by the action of heparitinases reveals a higher degree of sulfation of the uronic acid residues in the heparan sulfate of cells exposed to heparin.

Animals↗
PubMed1989

Heparin in molluscs: chemical, enzymatic degradation and 13C and 1H n.m.r. spectroscopical evidence for the maintenance of the structure through evolution.

The structural features and anticoagulant activity of heparins isolated from three species of molluscs (Anomalocardia brasiliana, Donnax striatus and Tivela mactroides) are reported. It is shown by chemical analyse, type of products formed by action of heparinase and heparitinase II, anticoagulant activity, 13C and 1H n.m.r. spectroscopy, that the mollusc heparins are virtually indistinguishable from heparins present in mammalian tissues. These data, taken as a whole, suggest that heparin has maintained its main structural features through evolution. The implications of these findings are discussed.

Animals↗
PubMed1989

Structural requirements of heparin disaccharides responsible for hemorrhage: reversion of the antihemostatic effect by ATP.

Topically applied heparin and heparan sulfate disaccharides, with the basic structure delta-4,5 uronyl-(1----4)-glucosamine and bearing a sulfate at the C-6 position of the glucosamine residue, are antihemostatics as potent as heparin, producing uncontrollable hemorrhage from small blood vessels. The finding that other sulfated disaccharides with the same sulfate:hexosamine:uronic acid ratios but with the sulfate at a different position (C-2), or with different glycosidic linkage (1----3), were inactive as inhibitors of hemostasis indicates that a specific structure is needed to produce the effect. The inhibitory activity of the normal hemostatic process could be reversed by ATP. Molecular models show that part of the disaccharide inhibitors and ATP hold a similar structural conformation.

Adenosine Triphosphate↗
PubMed1988

Inhibition of synthesis of heparan sulfate by selenate: possible dependence on sulfation for chain polymerization.

Selenate, a sulfation inhibitor, blocks the synthesis of heparan sulfate and chondroitin sulfate by cultured endothelial cells. In contrast, selenate does not affect the production of hyaluronic acid, a nonsulfated glycosaminoglycan. No differences in molecular weight, [3H]glucosamine/[35S]sulfuric acid ratios, or disaccharide composition were observed when the heparan sulfate synthesized by selenate-treated cells was compared with that of control cells. The absence of undersulfated chains in preparations from cultures exposed to selenate supports the concept that, in the intact cell, the polymerization of heparan sulfate might be dependent on the sulfation of the saccharide units added to the growing glycosaminoglycan chain.

Animals↗
PubMed1987

N-glycansulfated fibronectin: one of the several sulfated glycoproteins synthesized by endothelial cells in culture.

N-glycanase, an endoglycosidase that cleaves the bond between asparagine and glucosamine, releases oligosaccharides with various degree of sulfation from endothelial cell fibronectin. As shown by analysis by polyacrylamide gel electrophoresis of culture medium conditioned by cells exposed to [35S]sulfate, endothelial cell fibronectin is one of a number of glycoproteins bearing sulfated oligosaccharides, synthesized by this cell type.

Cell Line↗
PubMed1987

Structure and antithrombin-binding properties of heparin isolated from the clams Anomalocardia brasiliana and Tivela mactroides.

Heparin with high anticoagulant activity was isolated from the two marine clam species Anomalocardia brasiliana and Tivela mactroides. A large portion of the polysaccharide chains of both preparations bound with high affinity to immobilized antithrombin. Titrations monitored by tryptophan fluorescence showed that clam polysaccharide chains with Mr approximately 22,500 contained up to three binding sites for antithrombin and that the binding constants for the interaction of these chains with antithrombin were higher than those reported for mammalian heparin of comparable size. Structural analysis of clam heparin fractions and subfractions of clam heparin with differing affinity for immobilized antithrombin revealed the presence of large amounts (up to 25-30% of the total disaccharide units) of the 3-O-sulfated saccharide sequences (-GlcNSO3)-GlcA-GlcNSO3(3-OSO3)- and (-GlcNSO3)-GlcA-GlcNSO3(3,6-di-OSO3)-, previously identified as unique markers for the antithrombin-binding region of heparin. The content of these saccharide sequences was found to increase with increasing affinity of the parent polysaccharide for antithrombin. Structural analysis of the clam heparins also demonstrated the occurrence of a novel saccharide sequence, tentatively identified as (-GlcNSO3)-IdA-GlcNSO3(3,6-di-OSO3)-, that has not previously been found in heparin or related polysaccharides. The contents of this latter sequence, at most 3-4% of the total disaccharide units, showed no correlation with the affinity for antithrombin.

Animals↗