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PubMed1982

Effect of dextran on platelet activation by polymerizing fibrin.

Dextran has been shown to alter the mechanical properties and lysability of fibrin. The present study was undertaken to determine whether it would also influence the ability of polymerizing fibrin to activate platelets. Human fibrinogen, with or without the presence of dextran, was incubated with either human thrombin or reptilase at 37 C. Macroscopically evident fibrils first appeared at 7 1/2 to 8 minutes in fibrinogen solution not containing dextran and at 2 1/2 to 3 minutes in solution containing dextran. Both solutions caused aggregation of washed human platelets, but the one containing dextran was less potent (P less than 0.005). Similarly, polymerizing fibrin, under the influence of dextran, was a less potent stimulator of platelet release of labeled serotonin. Scanning electron microscopy showed decreased platelet adhesion to fibrin polymerized in the presence of dextran. Inclusion of dextran in plasminogen-rich bovine fibrin clots facilitated their lysis by urokinase. Apparently, dextran not only increases the lysability of fibrin but also alters the platelet-activating activity of polymerizing fibrin.

Animals↗

PubMed1995

Partitioning of proteins in dextran/hydrophobically modified dextran aqueous two-phase systems.

Partitioning of proteins was studied in aqueous two-phase systems composed of the polymers dextran and hydrophobically modified dextran. The modified dextrans were benzoyl dextran with a degree of substitution of 0.17 and valeryl dextran with a degree of substitution of 0.20. Phase diagrams for the systems of dextran/benzoyl dextran and dextran/valeryl dextran were determined at room temperature. The proteins studied were beta-galactosidase, bovine serum albumin, beta-lactoglobulin, lysozyme, myoglobin and cytochrome C. The partition coefficients of a series of salts were determined in dextran/benzoyl dextran two-phase systems. The addition of salts had strong effect on the partitioning of proteins. This effect was related to protein net charge and the position of the ions in the Hofmeister series. Cross partitioning of bovine serum albumin was studied in a dextran/benzoyl dextran aqueous two-phase system.

Animals↗

PubMed1996

Influence of dextrans on lung preservation: is the molecular weight important?

BACKGROUND: The addition of dextran with a molecular weight of 40,000 Dalton in pulmonary preservation solutions has proved to be beneficial. However, dextrans of other size have not yet been investigated. Therefore, it is unclear whether dextran 40,000 represents the optimal additive for lung preservation solutions. METHOD: In a working rat heart-lung model, lung were preserved with regular Euro-Collins solution or with Euro-Collins solution containing 5% dextran of different sizes: 40,000 Dalton molecular weight; 70,000 Dalton molecular weight; 160,000 Dalton molecular weight. After 2 hours of ischemia functional (oxygenation; pulmonary vascular resistance) and structural (wet/dry-ratio, light microscopy) data were assessed and the amount of dextran in the lung tissue was measured. RESULTS: Lungs preserved with Euro-Collins solution 70,000 Dalton molecular weight or Euro-Collins solution 160,000 Dalton molecular weight exhibited superior functional and structural results when compared with Euro-Collins solution and Euro-Collins solution 40,000 Dalton molecular weight. Additionally, the least amount of dextran in the lung tissue was found in organs preserved with Euro-Collins solution 160,000 Dalton molecular weight after ischemia and reperfusion. CONCLUSIONS: Dextrans are useful additives for lung preservation solutions. However, the size of the molecules is important because dextrans of 160,000 Dalton molecular weight were superior to dextrans of lower molecular weight in our study.

Animals↗

PubMed1999

Structural Change in Dextran: Mechanism of Insolubilization by Adsorption on the Air-Liquid Interface.

To clarify the insolubilization mechanism of water-soluble dextran, the association of dextran in water was studied by dynamic light scattering measurements and a surface chemical approach. Dynamic light scattering measurements indicated that insolubilization of dextran is accompanied by a structural change in dextran. Surface tension data for dextran molecules revealed a structural change in dextran molecules at the air-liquid interface. These results suggest that insolubilization of dextran molecules occurred through an adsorption process at the air-liquid interface. Insolubilization of dextran molecules can be reduced by inhibition of this structural change in dextran molecules. The presence of boron as an impurity was found to trigger precipitation based on inductively coupled plasma mass spectrometry measurements and precipitation tests. Copyright 1999 Academic Press.

Journal Article↗

PubMed1985

[Production of aldosterone and its precursor steroids by the adrenal zona glomerulosa in dextran sulfate-treated rats].

Heparin and heparinoids are known to produce selective aldosterone deficiency in man and experimental animals. To assess the nature of the hypoaldosteronism caused by heparin and heparinoids, we investigated the production of aldosterone and its precursor steroids in response to angiotensin II (AII), ACTH or potassium in adrenal zona glomerulosa cells from dextran sulfate-treated rats compared with that in the cells from vehicle-treated rats. Dextran sulfate-treated rats had a decrease in plasma aldosterone and a reduction in the width of the zona glomerulosa 4 weeks after the treatment (40 mg/day, intramuscularly). In these rats, PRA and plasma AII tended to be high, and plasma corticosterone was normal. Basal aldosterone production, when corrected to a uniform number of cells per group, was similar in cells from dextran sulfate- and vehicle-treated rats. The cells from dextran sulfate-treated rats had a less sensitive and lower response of aldosterone production to AII; an increase by 4 orders of magnitude in the threshold dose for AII and a decrease in the maximal AII-stimulated level. The maximal AII-stimulated levels, but not the basal levels, of pregnenolone, corticosterone and 18-hydroxycorticosterone production were low in the cells from dextran sulfate-treated rats. ACTH produced a similar stimulatory effect on aldosterone production in the cells from dextran sulfate- and vehicle-treated rats. The cells from dextran sulfate-treated rats had a less sensitive and lower response of aldosterone production to potassium; an increase by one order of magnitude in the threshold dose for potassium and a decrease in the maximum potassium-stimulated level, presumably because of the glomerulosa hyporesponsiveness to AII. These results suggest that long-term treatment with dextran sulfate in rats produces selective impairment of adrenal zona glomerulosa cells, involving the specific receptors and the aldosterone biosynthesis, to AII in addition to a reduction in the glomerulosa width.

Adrenal Cortex↗

PubMed1984

Depression of cytochrome P-450-dependent drug biotransformation in hepatocytes after the activation of the reticuloendothelial system by dextran sulfate.

Cytochrome P-450 and aryl hydrocarbon hydroxylase were depressed in microsomes prepared from the livers of mice treated with dextran sulfate. Unlike some other immune modulating drugs which decrease cytochrome P-450, dextran sulfate did not induce interferon production in the serum of these animals. Dextran sulfate had no effect on cytochrome P-450 when incubated with isolated hepatocytes alone but with mixtures of hepatocytes and Kupffer cells both cytochrome P-450 and aryl hydrocarbon hydroxylase were significantly depressed. Kupffer cells were then incubated at 37 degrees C for 30 min with dextran sulfate. After centrifugation the resulting cell-free supernatant decreased cytochrome P-450 and aryl hydrocarbon hydroxylase when incubated with hepatocytes. These experiments suggest that dextran sulfate stimulates the release of a factor by Kupffer cells which can decrease cytochrome P-450 in hepatocytes. This was confirmed by incubating cells in a membrane partitioned double-chambered Marbrook vessel to separate cell types and prevent passage of dextran sulfate. When dextran sulfate was added to the chamber containing Kupffer cells a factor was released which crossed a semipermeable membrane and depressed cytochrome P-450 levels in the hepatocytes in the other chamber. It is concluded that dextran sulfate depresses drug biotransformation in the liver via a factor which is released from Kupffer cells.

Animals↗

PubMed1991

Binding of epidermal growth factor-dextran conjugates to cultured glioma cells.

Some gliomas, melanomas and squamous carcinomas have large numbers of EGF receptors which could, in these cases, be used for targeting with toxic agents. We investigated whether EGF could be conjugated to dextran, which is a suitable carrier for toxic agents, without losing its ability to bind to the receptor. Dextran of 20 kDa molecular weight was activated with I-cyano-4-dimethylamino pyridinium tetrafluoroborate (CDAP) yielding highly active pyridinium-isourea derivatives. EGF was coupled to the activated dextran through the amino terminus and glycine was added to block residual activity. The EGF-dextran conjugate was, after purification on Sephadex G25 and Sephacryl 200 columns, tested for its receptor binding properties on human malignant glioma, U343MGaC12:6, cells. The conjugate inhibited binding of 125I-EGF in a competitive assay, showing that the binding was receptor-specific. Dextran conjugated with glycine, without EGF, had no inhibitory effect. The conjugate was radio-labelled either on the EGF part with 125I or on the dextran part with 3H-glycine, and the internalization patterns were compared to the internalization of 125I-EGF. The radioactivity of the conjugates remained cell-associated for more than 20 hr, regardless of whether the radioactivity was on the EGF or on the dextran part, while the radioactivity of unconjugated EGF rapidly disappeared from the cells. Most of the cell-associated radioactivity was, at all analysed time intervals, located intracellularly. Thus, it seems promising to use dextran, conjugated with EGF, as a carrier of, for example, toxic radioactive nuclides.

Dextrans↗

PubMed2002

Heparin and non-heparin-like dextrans differentially modulate endothelial cell proliferation: in vitro evaluation with soluble and crosslinked polysaccharide matrices.

Proliferation of endothelial cells (ECs) is a cellular step of particular importance for implanted cardiovascular biomaterials. Heparin and some synthetic water-soluble non-anticoagulant polysaccharides derived from dextran and bearing anionic carboxymethyl and hydrophobic benzylamine groups were first investigated for their effects on EC proliferation in vitro. The results assessed by cell counting, 3H-thymidine uptake, and flow cytometry analysis, showed that the derivatized dextran-bearing hydrophobic groups stimulated the EC growth in the presence of serum, whereas native dextran or dextran-bearing anionic carboxymethyl groups were inactive and heparin was slightly inhibitory. Then, we showed that the derivatized dextran enhanced EC proliferation by potentiation of the mitogenic activities of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF-2), two potent EC growth factors. In the presence of 2 nM of derivatized dextran, a 3-fold and 13-fold increase of 3H-thymidine uptake was obtained with VEGF and FGF-2, respectively. Finally, proliferation of ECs was investigated on crosslinked gels made of polysaccharides. It is of interest that EC proliferation was higher on gels containing the derivatized dextran than on plain hydrogels, and heparinized gels inhibited cell proliferation. From the obtained results, we propose that the synthetic non-heparin-like dextran may be of interest as a coating for the endothelialization of cardiovascular biomaterials.

Anticoagulants↗

PubMed1993

A novel approach to the production of clinical-grade dextran.

Efficient unit operations for the production and purification of the enzyme dextransucrase and the biosynthesis and fractionation of dextrans have been developed and tested. An alternative process for the production of clinical-grade dextran has been proposed by integrating these processes to achieve improved dextran product yield and the recovery of fructose as a valuable by-product. The enzyme dextransucrase, which synthesizes dextran from sucrose, has been produced either by non-aerated fed-batch or continuous fermentations, purified by continuous ultracentrifugation and ultrafiltration and used in a bioreactor-separator stage for the biosynthesis of dextran. High molecular weight dextrans have been biosynthesized on continuous counter-current chromatographic bioreactor-separator systems. Membrane filtration and size exclusion continuous chromatography were used for the fractionation of the native dextran and production of clinical-grade dextran. The advantages of the proposed process over the conventional process are related to cost reduction due to the elimination of ethanol usage and recovery, improved product quality control and the production and recovery of fructose as a by-product.

Dextrans↗

PubMed1995

Gadolinium and dysprosium chelates of DTPA-amide-dextran: synthesis, 1H NMR relaxivity, and induced 23Na NMR shift.

In this study the conjugated macromolecular ligand, diethylenetriaminepentaacetic acid (DTPA)-amide-dextran, was synthesized by attaching DTPA to the dextran macromolecule (M(r) approximately 6000) by a covalent amide bond. Subsequently, DTPA-amide-dextran was complexed with either of the two lanthanide metal ions dysprosium (Dy) or gadolinium (Gd). The paramagnetic 23Na NMR shift induced by Dy(DTPA-amide-dextran) and the relaxivity (rho 1) induced by Gd(DTPA-amide-dextran) were characterized. Dy(DTPA-amide-dextran) induced a 25% larger 23Na NMR shift than that induced by Dy(DTPA). Neither the shift induced by Dy(DTPA-amide-dextran) nor the shift induced by Dy(DTPA) was affected by increasing levels of calcium ions in the solution. offDTPA-amide-dextran) exhibited an in vitro rho 1 of 8.4 (mM s)-1 at a 0.23 T magnetic field and 9.3 (mM s)-1 at a 0.47 T magnetic field, thus indicating a positive magnetic field dependence.

Amides↗

PubMed1993

In vitro stimulation of human endothelial cells by derivatized dextrans.

Derivatized dextrans exert a stimulatory effect on the in vitro growth of human umbilical vein endothelial cells (HUVEC). Measurements of growth were monitored by [3H]thymidine uptake and cell numbers. Our results show that some derivatized dextrans at 4 micrograms/ml (88 nM) increase the [3H]thymidine incorporation, whereas starting dextran (40,000 Da), dextran sulfate, and carboxymethyl dextran have no effect. In addition, heparin under similar experimental conditions shows a slight inhibitory effect on the HUVEC growth. The stimulatory effect of derivatized dextrans was also found when HUVEC grew during 7 days in medium containing 2% fetal bovine serum. We also observed that derivatized dextrans had no effect on the mitogenic activity of acidic fibroblast growth factor, a mitogenic factor for several cell types including HUVEC. By assessment of [3H]thymidine uptake at 48 h without serum, we concluded that the exogenous growth factors were not involved in the proliferative activity of these components. The stimulatory effects are related to the chemical nature and the proportion of substituents on the synthetic polysaccharides. The data indicate that benzylamide sulfonated groups play a key role in the stimulation of HUVEC growth. Neither carboxyl nor sulfate groups alone exhibit this effect. Thus, the stimulatory capacity of dextran derivatives depends strongly on the respective ratios of the functional groups.

Carbohydrate Sequence↗

PubMed1981

Dextran is resistant to lysosomal digestion in kidney tubules.

Low molecular weight dextran (Rheomacrodex) was infused into dextran resistant rats in a dose of 5 g/kg body weight. The kidneys were studied by electron microscopy at different time intervals after infusion using a special fixative for the demonstration of dextran. The lysosomes of proximal tubule cells gradually accumulated dextran which remained in small amounts even after 10 days. In separate kidney slice experiments the ability of dextran-loaded proximal tubule lysosomes to digest absorbed proteins was determined using 125I-labelled lysozyme. There were no changes in lysosomal protein digestion. Labelled dextran was resistant to digestion in vitro by homogenates of rat or rabbit kidney cortex or isolated rat lysosomal enzymes. It is concluded that the protein absorption pathway and lysosomal protein catabolism is unchanged after tubular uptake of dextran despite pronounced ultrastructural alterations to the lysosomal system and that dextran is resistant to lysosomal digestion in renal proximal tubules.

Animals↗

PubMed2006

The mechanism of the dextran-induced red blood cell aggregation.

In order to clarify the mechanism of dextran-induced aggregation, the effect of the ionic strength (I) on the minimal shear stress (tau(c)) required to rupture RBC doublets was studied for suspensions with the external media containing 76 and 298 kDa dextrans. At low and high ionic strengths, tau(c) increases with increasing I, whereas at intermediate I values, tau(c) versus I dependencies reveal a plateau step. The non-monotonous shape of these curves disagrees with the depletion model of RBC aggregation and is consistent with the predictions of the bridging mechanism. Literature reports point out that elastic behavior of dextran molecules in low and high I regions is fairly typical of Hookean springs and hence predict an increase in tau(c) with increasing I. A plateau step is accounted for by the enthalpic component of the dextran elasticity due to the shear-induced chair-boat transition of the dextran's glucopyranose rings. A longer plateau step for suspensions with a higher molecular weight dextran is explained by a larger contribution of the enthalpic component to the dextran elasticity. Thus, the results reported in this study provide evidence that RBC aggregation is caused by the formation of dextran bridges between the cells.

Blood Viscosity↗

PubMed1998

Red blood cell rouleaux formation in dextran solution: dependence on polymer conformation.

The velocity of rouleaux formation (RF), as previously shown, increases with increasing dextran concentration up to a critical concentration (Ca), beyond which the addition of dextran reduces the RF velocity (RFV). de Gennes' model for polymer solutions suggests that dextrans exist in two conformations: a coil structure at low concentrations, which changes to a network beyond a critical concentration (C*). In the present study we examined the relation between Ca and C* for dextrans of different molecular weight, and found that they coincide. This suggests that the change in dextran behavior, from increasing to decreasing RFV, occurs when their conformation changes from coil to network. In addition, it has been reported that in dilute dextran solutions the intercellular distance (D) between RBC in rouleaux increases with the molecular weight of the dextran. We found that D correlates with Rf, the end-to-end distance of the polymer molecule, and for all dextrans D < or = 1.5 Rf. In accord with de Gennes' Model for polymers between surfaces, this corresponds to intercellular interaction with two overlapping surface-associated polymer layers, which may extend "tails" to interact with the opposing cells.

Dextrans↗

PubMed1982

The prevention of postoperative pelvic adhesions: an animal study comparing barrier methods with dextran 70.

There are two major approaches to the prophylaxis for adhesions: chemical methods (e.g., dextran) and barrier methods. Theoretically, dextran prevents the formation of adhesions by a surface-coating or hydroflotation effect, whereas the barrier methods either prevent the formation of or mask adhesions by covering and isolating the injured area with an inert substance. This study compared the efficacy of two different concentrations of dextran 70 and various barriers in preventing the formation of adhesions in the female rabbit pelvis. Symmetrical cut and scrape lesions were made on both sides of each rabbit's uterus; for the barrier-treated animals, the lesions on one side were covered with a barrier, and the contralateral side served as a control. The barriers tested were: Gelfilm, Surgicel, Silastic, Gelfoam paste, amnion, peritoneum, and omentum (five rabbits per subgroup). The same cut and scrape lesions were induced in 16 additional rabbits in the chemical group. These rabbits were subsequently treated with 10 ml/kg of intraperitoneal 6% dextran 70 (five rabbits), and 32% dextran 70 (five rabbits), and were compared with six external control rabbits. The severity of the adhesions that formed was graded by a numerical scoring system. The barrier methods tested resulted, generally, in an increased formation of adhesions when a comparison was made with control and with dextran-treated animals. The degree of formation of adhesions in the dextran-treated rabbits did not differ from that in the control animals. The data suggest that the barrier methods actually promote the formation of adhesions whereas the findings with dextran 70 were inconclusive.

Amnion↗

PubMedDate not supplied

Electrophoresis of human red blood cells and platelets. Evidence for depletion of dextran.

A theoretical description of polymer depletion layers near smooth and hairy surfaces is developed and used for interpretation of experiments. Electrophoretic mobility measurements of human red blood cells and platelets in aqueous electrolyte solutions were performed in the presence of dextran (MW = 70 kD) to study the interaction of dextran with the cell surface. The electrophoretic mobility in the presence of dextran was considerably larger than expected from the viscosity. This behavior was interpreted as evidence for the existence of a polymer depletion layer. Depending on ionic strength, depletion layer thicknesses ranging from 2.9 to 4.4 nm were found. The dextran concentration at the outer border of the glycocalyx was only 10% of the bulk value. One cannot exclude the possibility that this small amount reflected adsorption. In the case of platelets, the degree of the mobility reduction depended on ionic strength. Depletion of dextran from the platelet surface apparently became smaller with decreasing ionic strength. This indicated a more complex pattern of interaction of dextran with the platelet surface than with the RBC surface. Both adsorption and polymer penetration into the glycocalyx were discussed quantitatively. It was concluded that ionic strength-dependent penetration of dextran into the hairy layer is more likely than ionic strength dependent adsorption changes. As in the case of red cells, some adsorption of dextran might be present.

Adsorption↗

PubMed1984

The effect of altering the external calcium concentration and a calcium channel blocker, verapamil, on microvascular leaky sites and dextran clearance in the hamster cheek pouch.

The role of calcium in contractile mechanisms has been well documented. Since the formation of intraendothelial gaps may be due to a contractile process, these studies were initiated to describe the effects of altering the external calcium concentration and a calcium blocker, verapamil, on the development of leaky sites and clearance of dextran in the hamster cheek pouch under normal and histamine-stimulated conditions. Adult Syrian hamsters were anesthetized and tracheostomized, and the femoral vein was cannulated for injecting the FITC-Dextran-70K. In all hamsters, a removable plastic chamber was placed in the cheek pouch to observe and collect suffusate from the microvasculature. In one series of experiments, suffusion was begun with either "normal" calcium (1.5 mM) or a calcium-free, Ringer's bicarbonate (pH 7.4, 36 degrees) buffer. After a 30-min period, fluorescein-labeled dextran (FITC-Dextran-70K) was given intravenously and the number of leaky sites and dextran clearance determined for 30-45 min. Two 5-min periods of stimulation with histamine (10(-7) and 10(-6) M) followed by a 30-min equilibration were completed while the above measurements were repeated. Then, the suffusate was switched to the opposite calcium buffer and the same sequence repeated. A similar protocol was followed using either the "normal" buffer or a high (4.5 mM)-calcium buffer. In another series of experiments, similar measurements were completed with and without verapamil (10(-4) M) using a "normal" calcium buffer and histamine-stimulated conditions. In the control, nonstimulated state, there was a significant increase in the leaky sites while suffusing with low-calcium buffer; however, there were no changes in leaky sites while suffusing with the high-calcium buffer. In the histamine-stimulated state, the increase in the number of leaky sites and dextran clearance was attenuated with the low-calcium buffer and potentiated with the high-calcium buffer. While suffusing with the verapamil buffer, there was an increase in the control number of leaky sites and in the histamine-stimulated state there was an attenuation of the histamine-stimulated response. These results indicate that external calcium influences and modulates microvascular leaky sites in normal and stimulated states and that the formation of leaky sites and dextran clearance after histamine stimulation require the transmembrane flux of calcium. Also, the formation of leaky sites was coupled directly to the clearance of dextran.

Animals↗

PubMed1987

Immune response of carps (Cyprinus carpio L.) against dextran.

In carps no antibodies could be evoked by immunization with soluble high molecular weight dextran using doses of 1-5000 mg dextran per kg body weight. On the other hand, an immune response against dextran could be elicited by immunization with a vaccine of Leuconostoc mesenteroides B512 as well as a dextran-BSA-conjugate. These carp anti-dextran antibodies showed precipitating and agglutinating activities with specificity against alpha linked dextran determined by the almost complete inhibition of the dextran-anti-dextran reaction by isomaltodecaose.

Animals↗