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PubMed2002

Surface activity and emulsification properties of hydrophobically modified dextrans.

Neutral polymeric surfactants were synthesized by covalent attachment of hydrophobic groups (aromatic rings) onto a polysaccharide backbone (dextran). By changing the conditions of the modification reaction, the number of grafted hydrophobic groups per 100 glucopyranose units (substitution ratio) was varied between 7 and 22. In aqueous solution, these polymers behaved like classical associative polymers as demonstrated by viscometric measurements. The associative behavior was more pronounced when the substitution ratio increased. The surface-active properties of the modified dextrans were evidenced by surface tension (air/water) and interfacial tension (dodecane/water) measurements. In each case the surface or interfacial tension leveled down above a critical polymer concentration, which was attributed to the formation of a dense polymer layer at the liquid-air or liquid-liquid interface. Dodecane-in-water emulsions were prepared using the polymeric surfactants as stabilizers, with oil volume fractions ranging between 5 and 20%. The oil droplet size (measured by dynamic light scattering) was correlated to the amount of polymer in the aqueous phase and to the volume of emulsified oil. The thickness of the adsorbed polymer layer was estimated thanks to zeta potential measurements coupled with size measurements. This thickness increased with the amount of polymer available for adsorption at the interface. The dextran-based surfactants were also applied to emulsion polymerization of styrene and stable polystyrene particles were obtained with a permanent adsorbed dextran layer at their surface. The comparison with the use of an unmodified dextran indicated that the polymeric surfactants were densely packed at the surface of the particles. The colloidal stability of the suspensions of polystyrene particles as well as their protection against protein adsorption (bovine serum albumin, BSA, used as a test protein) were also examined.

Journal Article↗
PubMed2005

Iloprost to improve surfactant function in porcine pulmonary grafts stored for twenty-four hours in low-potassium dextran solution.

OBJECTIVES: The optimal strategy for pulmonary graft preservation remains elusive. Experimental work and initial clinical experience support low-potassium dextran solutions as lung perfusates. We have previously shown a protective effect of prostaglandin E 1 on ischemia-reperfusion injury in lung transplantation by a shift from proinflammatory to anti-inflammatory cytokines in a rat lung transplantation model. In this study, we tested the hypothesis that the addition of a prostacyclin analog (iloprost) to low-potassium dextran might lead to improved surfactant and ultimately graft function. METHODS: In a randomized, blinded study with a porcine left single-lung transplantation model, donor lungs were flushed with 1 L of either low-potassium dextran solution or low-potassium dextran solution modified by the addition of 250 microg iloprost (n = 6 in each group). Grafts were stored at 4 degrees C for 24 hours. After transplantation, the right bronchus and pulmonary artery were clamped, and the animals remained dependent on the graft. Posttransplantation graft function was assessed throughout a 7-hour observation period by measuring oxygenation (30-minute intervals), different pulmonary and systemic hemodynamic parameters, and wet/dry lung weight ratios. Bronchoalveolar lavage fluid was obtained before and 2 hours after reperfusion. Surfactant function was measured from bronchoalveolar lavage fluid with a pulsating bubble surfactometer. Neutrophil sequestration was assessed by a myeloperoxidase assay performed on lung tissue specimens taken at the end of the observation period. RESULTS: Pulmonary vascular resistance remained lower in the iloprost group than in the control group (P < .05). Tissue water content after 7 hours of reperfusion remained lower in the iloprost group (P < .05). In addition, significantly reduced myeloperoxidase tissue activity was observed in the iloprost group (P < .05). Although there was no difference in degradation of surface active surfactant large aggregates to small aggregates, the surface tension measured at minimal bubble diameter was lower in the iloprost group (P < .05). CONCLUSIONS: Modification of low-potassium dextran solution with the prostacyclin analog iloprost resulted in a significant amelioration of ischemia-reperfusion injury and improved preservation of surfactant function in transplanted lungs. This intriguing approach merits further evaluation with respect to the mechanisms involved and, ultimately, potential introduction into clinical lung transplantation.

Animals↗
PubMed1980

Dextran alpha-(1 yields 2)-debranching enzyme from Flavobacterium Sp. M-73. Properties and mode of action.

The general properties and specificity of a dextran alpha-(1 yields 2)-debranching enzyme from Flavobacterium have been examined in order to apply this enzyme to the structural analysis of highly branched dextrans. The optimum pH range and temperature were pH 5.5-6.5, and 45 degrees, respectively. The enzyme was stable up to 40 degrees on heating for 10 min, and over a pH range of 6.5-9.0 on incubation at 4 degrees for 24 h. The effects of various metal ions and chemical reagents have also been examined. The debranching enzyme has a strict specificity for the (1 yields 2)-alpha-D-glucosidic linkage at branch points of dextrans and related branched oligosaccharides, and produces D-glucose as the only reducing sugar. The degree of hydrolysis of the dextrans by this enzyme and the Km value (mg/mL) were as follows: B-1298 soluble, 25.2%, 0.21; B-1299 soluble, 31.5%, 0.27; and B-1397, 11.8%, 0.91. the debranching enzyme thus has a novel type of specificity as a dextranhydrolase. We have termed this enzyme as dextran alpha-(1 yields 2)-debranching enzyme, and its systematic name is also discussed.

Cations↗
PubMed2006

Induced phase separation in low-ionic-strength cellulose nanocrystal suspensions containing high-molecular-weight blue dextrans.

Spontaneous entropic phase separation phenomena occur in a wide range of systems containing highly anisotropic colloidal particles. Among these are aqueous suspensions of negatively charged cellulose I nanocrystals produced by sulfuric acid hydrolysis of native cellulose, which phase separate into isotropic and chiral nematic liquid-crystalline phases. Phase separation of an isotropic phase from a completely ordered nanocrystal suspension may be induced by the addition of salts or nonadsorbing macromolecules. In previous work (Edgar, C. D.; Gray, D. G. Macromolecules 2002, 35, 7400-7406), an isotropic phase was found to form over a period of several days when blue dextran (a sulfonated triazine dye, Cibacron blue 3G-A, covalently attached to high-molecular-weight dextran chains) was added to initially ordered suspensions. Here we report work showing that the observed phase separation was associated with the charged dye molecules attached to the dextran. The Cibacron blue 3G-A dye attached to blue dextran was found to induce greater phase separation than free (unbound) dye; at increasing ionic strength, depletion attractions due to the blue dextran increasingly contribute to the phase separation.

Journal Article↗
PubMed2000

Controlled release of liposomes from biodegradable dextran microspheres: a novel delivery concept.

PURPOSE: To design liposome-loaded microspheres, which release the liposomes in a time-controlled manner and in intact form. METHODS: Liposomes were encapsulated in biodegradable dextran-based microspheres, which were prepared using an aqueous two phase system consisting of poly(ethylene glycol) and methacrylated dextran. The effects of liposome size and membrane fluidity, microsphere water content, degree of methacrylate substitution, and type of dextran derivative used, on encapsulation efficiency, release, and integrity of the liposomes were investigated. RESULTS: Liposomes were entrapped in dextran-based microspheres quantitatively and with full preservation of their integrity. Liposomes with a low, as well as with a high membrane fluidity, were released from the microspheres in their intact form and with preservation of their size. Release kinetics depended only on the degradation rate of the microspheres. For rapidly degrading systems, pulsed release was observed and the time after which the pulse occurred (from 5 until 25 days) could be tailored by the gel characteristics such as initial water content, degree of methacrylate substitution, and type of hydrolytically sensitive spacer present in the cross-links. This delay time was not dependent on the size of the liposomes in the range studied (0.1-0.2 microm). Microspheres which degraded more slowly showed, after a certain delay time, sustained release of the liposomes extended up to 100 days. CONCLUSIONS: A novel drug delivery concept based on the encapsulation of liposomes in biodegradable dextran-based microspheres was designed. The system released the liposomes in intact form in a controlled way after a prolonged period of time.

Calorimetry, Differential Scanning↗
PubMed2005

Diffusion exchange NMR spectroscopic study of dextran exchange through polyelectrolyte multilayer capsules.

Diffusion exchange of dextran with molecular weights 4.4 and 77 kDa through polyelectrolyte multilayer (PEM) hollow capsules consisting of four bilayers of polystyrene sulfonate/polydiallyldimethylammonium chloride has been investigated using two-dimensional nuclear-magnetic-resonance methods: diffusion-diffusion exchange spectroscopy (DEXSY) and diffusion-relaxation correlation spectroscopy (DRCOSY). Results obtained in DRCOSY experiments show that the diffusion process of dextran 77 kDa exhibits an observation time dependence suggesting a diffusion behavior restricted by confinement. We find evidence for both single capsule and capsule aggregate states, with a partitioning of the 77-kDa dextran between the free and capsule states much larger than that suggested by volume fraction alone. Results from DEXSY experiments show that dextran 77 kDa is in diffusive exchange through the capsules with an exchange time of around 1 s. In contrast, the capsules have no detectable influence on the diffusion process of the dextran 4.4 kDa. This quantitative information may be used in designing PEM capsules as drug carriers.

Journal Article↗
PubMed1990

Dextran sulfate disposition in the rat.

Comparative studies of oral and intravenous administration of tritiated dextran sulfate in rats showed markedly different distribution patterns. Following IV dosing about 50 per cent of the radioactivity was recovered in feces and urine within 24 h. The major portion of the recoverable dose was eliminated in the urine as dextran sulfate within 3 h after administration. In orally treated rats only about 32 per cent of the 3H was recovered in the feces and urine, the major fraction being associated with unabsorbed dextran sulfate in the feces. The remainder of the dose in both treatment groups has apparently distributed throughout the rat body with some accumulation in the liver, kidney and spleen. Consequently, the disposition of about 67 per cent or the oral dose could not be fully accounted for by these excretion routes. However, separation with Sephadex columns showed similarities in the 24 h plasma and urine profiles of the IV and orally dosed rats which suggest that while the oral dose was absorbed as dextran sulfate, it underwent rapid metabolism to small molecular weight products prior to entering the systemic circulation which were then widely distributed within the rat.

Administration, Oral↗
PubMed1981

Strain-specific aggregation of enterovirus by dextran sulfate.

Dextran sulfate aggregates several enteroviruses depending not only on the pH, the ionic strength of the medium, but also on the protein content of the fluids and on strain specificities of the viruses. The aggregation effect was measured by filtration experiments, by sedimentation in the ultracentrifuge and by electron microscopy. The well known inhibiting effect of dextran sulfate on plaque formation may be due to its aggregating effect: A very strong inhibition of the release of matured virions from the infected cells is observed in medium containing dextran sulfate, whereas the adsorption process is inhibited much less compared with PBS controls. The maximal effect on virus aggregation, plaque size and virus release is observed at the same concentration of dextran sulfate.

Cytopathogenic Effect, Viral↗
PubMed1988

Apheretic treatment of severe familial hypercholesterolemia: comparison of dextran sulfate cellulose and double membrane filtration methods for low density lipoprotein removal.

The two more widely available techniques for the extracorporeal removal of low density lipoproteins (LDL), dextran sulfate cellulose column and double membrane filtration, were comparatively tested in severe familial hypercholesterolemic patients, both acutely and during a continued 3-month treatment. The selective dextran sulfate procedure removed close to 60% of LDL and 16% of high density lipoproteins (HDL) upon each apheresis, vs. 42% and 32%, respectively, in the case of the semi-selective double membrane filtration. Upon long term biweekly treatments, LDL-cholesterol (LDL-C) decreased, with the selective procedure, from a pre-treatment level of 406.0 +/- 40.7 mg/dl to a value fluctuating between 295.4 +/- 33.8 mg/dl and 116.9 +/- 22.0 mg/dl (highest vs. lowest levels) whereas, in the case of double membrane filtration, LDL-C levels ranged between 334.8 +/- 39.8 mg/dl and 192.3 +/- 49.9 mg/dl. HDL-cholesterol levels were somewhat raised, to a higher extent with dextran sulfate apheresis. The LDL/HDL-cholesterol "atherogenic ratio", decreased from a pre-treatment value of 10.27 +/- 3.04 to values ranging between 3.61 and 6.82 with dextran sulfate and between 6.70 and 7.68 with double membrane plasmapheresis.

Adult↗
PubMed1987

Investigation on the fate of orally administered DEAE-dextran in rats.

The breakdown of the carbohydrates by the colonic bacterial flora can cause intestinal symptoms, such as meteorism, abdominal pain and diarrhoea. The ability of digestive enzymes and colonic bacterial flora to break down the DEAE-dextran, a new lipid lowering resin, was investigated in rats. DEAE-dextran appeared to be unaffected by either enzyme activity in the small intestine or bacterial flora in the large intestine. This may be important when dealing with the pharmacological activity of DEAE-dextran and estimating its side effects. Small intestinal transit rate appeared to be accelerated by oral DEAE-dextran in rats.

Administration, Oral↗
PubMed1984

Purification and biological property of heparin cofactor II: activation of heparin cofactor II and antithrombin III by dextran sulfate and various glycosaminoglycans.

Heparin cofactor II (HC II) has been purified from human plasma by a modification of the method described by Tollefsen et al. (J. Biol. Chem., 257, 2162, 1982) and abilities of dextran sulfate and various glycosaminoglycans to activate the antithrombin activities of HC II and antithrombin III (AT III) were studied. By the purification method described here, highly purified HC II with the same specific activity as reported by Tollefsen et al. was obtained with a higher yield and in a shorter purification time. Heparin, dextran sulfate and chondroitin polysulfates 1 and 5 activated both HC II and AT III, while dermatan sulfate activated only HC II. Dextran sulfate was almost as active as heparin in the activation of HC II and AT III, indicating that in the interactions of heparin with HC II and AT III, sulfate groups of heparin are more important than carboxyl groups. When mixed with thrombin in the presence of dermatan sulfate, normal human plasma showed antithrombin activity which was not due to AT III but to HC II only. HC II did not inhibit factor Xa or plasmin in the presence of any glycosaminoglycans or dextran sulfate, suggesting that HC II would be a specific inhibitor of thrombin.

Antithrombin III↗
PubMed1984

Abolition by dextran sulfate of the heparin-accelerated antithrombin III/thrombin reaction.

Dextran sulfate did not inhibit the amidolytic activity of thrombin on Boc-Val-Pro-Arg-4-methylcoumaryl-7-amide, but abolished inhibition of the enzyme with antithrombin III (AT III) in the presence of heparin. Dextran sulfate did not bind to AT III and had less affinity than immobilized heparin for the protein. Dextran sulfate bound strongly to thrombin and had higher affinity than immobilized heparin for the enzyme. These findings indicate that binding of dextran sulfate to a site other than the active site of thrombin to prevent the approach of AT III in the presence of heparin.

Animals↗
PubMed1982

Glomerular permeability to neutral and anionic dextrans in experimental diabetes.

Renal clearances of polydispersed neutral and anionic dextrans were measured in diabetic rats. In addition, urinary protein and albumin excretion rates were determined. Measurements were performed 3 months after the induction of diabetes (i.v. alloxan 50 to 55 mg/kg of body wt) in rats which were either untreated or which received supplemental insulin (6 U of NPH daily) and were compared to those in age-matched SHAM-treated rats. Fractional clearances (relative to inulin) of neutral dextrans remained unchanged in insulin-supplemented rats and were slightly but significantly increased in untreated rats. The application of an isoporous model of the glomerular filtration barrier permitted the conclusion that the size-selective characteristics of the barrier were unaltered in diabetic rats. Fractional clearances of anionic dextrans were significantly reduced 50 to 60% in both diabetic groups suggesting an increase in the negative charge density of the filtration barrier and potentially an increase in restriction to the glomerular filtration of anionic proteins. However, urinary and albumin excretions tended to increase in both groups of diabetic rats, including a 164% increase in albumin excretion in untreated rats. This apparent discrepancy between reduced dextran sulfate clearances and increased protein excretions suggests that factors other than charge-selectivity may be of major importance in determining the filtration of proteins. The marked increase in albumin excretion observed in our diabetic rats appears to be a result of decreased tubular reabsorption rather than increased filtration of albumin.

Albuminuria↗
PubMed1987

The autoactivation of factor XII (Hageman factor) induced by low-Mr heparin and dextran sulphate. The effect of the Mr of the activating polyanion.

Human Factor XII is known to undergo autoactivation in the presence of dextran sulphate of Mr 500,000. We have now studied the dependence of this reaction on the Mr of the dextran sulphate by using fractions resolved by gel filtration. We have found that autoactivation can be induced by dextran sulphate fractions with Mr as low as 3000, and there is a marked dependence of the rate constant of autoactivation on the Mr value. Fractions with Mr below 8000 gave very low rates of autoactivation; there was a sharp increase in the rate obtained when the Mr of the dextran sulphate was greater than 10,000. Various preparations of heparin were also able to support the autoactivation of Factor XII and gave a very similar relationship between molecular size and reaction rate. The data provide support for the hypothesis that the mechanism by which the 'surface' acts in contact activation involves the presence, on the same particle, of multiple binding sites for the proteins.

Binding Sites↗
PubMed1980

Artifactual reduction of high-density lipoprotein cholesterol estimates after dextran sulfate--Mg2+ precipitation.

Estimates of serum or plasma high-density lipoprotein (HDL) concentrations are usually accomplished by measuring the residual cholesterol after polyanionic precipitation of the very low and low-density lipoproteins. A comparison was made of the HDL cholesterol values obtained using both heparin--MnCl2 and dextran sulfate--Mg2+ as precipitating agents. Enzymatic cholesterol determinations showed that the dextran sulfate--Mg2+ method led to gross underestimation of the serum HDL cholesterol concentration (approximately -25%), a difference that was even greater when ultracentrifugally isolated HDL concentrations were assayed rather than serum. Immunochemical determinations of the A-I and B apolipoproteins demonstrated that the discrepancy was attributable neither to incomplete precipitation of the lower density lipoproteins by heparin--MnCl2 nor to precipitation of HDL by dextran sulfate--Mg2+. Incubation of sera with reagents at 37 C, however, minimized or eliminated the differences in results. These findings indicate that temperature is a critical factor when enzymatic quantification of HDL cholesterol is performed after dextran sulfate--Mg2+ precipitation.

Chemical Precipitation↗
PubMed1982

HDL cholesterol quantitation by phosphotungstate-Mg2+ and by dextran sulfate-Mn2+-polyethylene glycol precipitation, both with enzymic cholesterol assay compared with the lipid research method.

Two methods using commercial kits for high density lipoprotein (HDL) cholesterol quantitation were compared with the Lipid Research Clinics (LRC) procedures. HDL cholesterol quantitations on 50 patient specimens by the Lancer HDL cholesterol Rapid Stat Kit (Lancer) with phosphotungstate-Mg2+ precipitation and enzymic cholesterol assay averaged 424 mg/L, and by a method with dextran sulfate-Mn2+-polyethylene glycol (dextran sulfate) precipitation and enzymic cholesterol assay averaged 474 mg/L. By comparison, the LRC method (heparin-Mn2+ precipitation combined with a Liebermann-Burchard reagent cholesterol assay) averaged 478 mg/L. Supernates obtained by the three precipitation methods had similar cholesterol values when analyzed by the LRC assay, suggesting that the observed differences were primarily due to differences between the cholesterol assays. Results were consistent with underestimation by the enzymic assay of cholesterol in the supernates, offset by a positive interference of Mn2+ in the dextran sulfate-produced supernates. Among-day CVs of 4-5% were observed for the Lancer method, and 6-7% for the dextran sulfate method. Sedimentation of precipitates in hypertriglyceridemic specimens was excellent by both methods.

Chemical Precipitation↗
PubMed1962

Inhibitory effects of carbohydrates on histamine release and mast cell disruption by dextran.

Alloxan diabetic rats failed to show the skin reaction (blue spot) evoked by dextran, whereas the effects produced by histamine and compound 48/80 were not altered. When dextran and glucose were injected simultaneously into the skin the reaction was inhibited. In vitro, mast cell alterations produced by dextran occurred simultaneously with histamine release; both processes were inhibited by glucose, other carbohydrates related to glucose, and inhibitors of anaphylaxis. These experiments suggest that dextran releases histamine by a mechanism similar to that found with 48/80 and anaphylaxis in the rat. The inhibitory effect of carbohydrates may be understood on the basis of a competitive mechanism.

Alloxan↗
PubMed1963

PLASMA VOLUME EXPANSION BY RAPID INFUSION OF A LOW MOLECULAR WEIGHT DEXTRAN.

Large infusions of a 10% solution of dextran of molecular weight 40,000 were given to dogs during 3 min using a specially designed apparatus. The initial expansion of plasma volume was about twice the volume of solution injected. Plasma volume then fell rapidly (with a half life of about 2 hr), more rapidly than the fall in dextran concentration (half-life of about 4.5 hr). Fluctuations in plasma volume and protein concentration were repeatedly observed during the return towards normal values. At 5 to 6 hr renal excretion accounted for 40% of the infused dextran, about 20% was intravascular and the remaining 40% was presumably extravascular. No dextran was found in the cerebrospinal fluid.

Animals↗