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PubMed1974

Mechanism of adherence of Streptococcus mutans to smooth surfaces. II. Nature of the binding site and the adsorption of dextran-levan synthetase enzymes on the cell-wall surface of the streptococcus.

The mechanism of adsorption of the Streptococcus mutans enzymes responsible for the synthesis of insoluble dextran-levan to the S. mutans cell-wall binding sites has been studied. Certain characteristics of these binding sites are presented. The adsorption of these enzymes to the cell surface occurred rapidly without the addition of a source of energy and over a pH range of 3 to 11. The adsorption was inhibited by soluble dextran, probably due to the strong affinity of the polymer to the enzyme. All other polymers and sugars studied showed little or no inhibition. The adsorption was also inhibited by antibody globulin to the a-d immunologically specific group antigen surface polysaccharide of S. mutans and by anti-dextran globulin. The inhibition by anti-a-d globulin is considered to be due to a restriction of access of enzyme to the binding site of the enzyme which may be located in close proximity to the group antigen. On the other hand, anti-dextran globulin appeared to directly inhibit the adsorption by covering the binding site. Dextranase destroyed the binding site and released glucose from the S. mutans cells. These data indicate that S. mutans grown in media containing glucose possesses a small amount of dextran on the cell surface, and that this dextran is, or is a part of, the binding site for enzymes which synthesize the insoluble dextran-levan polymer. Trypsin inhibited the synthesis of insoluble polysaccharide and the adherence of cells. It is not clear in this case that destruction of the binding sites occurred. These data present a partial explanation of the processes which may be concerned in the formation of dental plaque on the smooth surfaces of teeth.

Adsorption↗

PubMed1974

Streptococcus mutans dextransucrase: requirement for primer dextran.

Dextran stimulation (priming) of the dextransucrase (EC 2.4.1.5) from Streptococcus mutans strain 6715 was studied. The dextransucrase activity in supernatant fluids from glucose-grown cultures was shown to be partially primer dependent. During extended storage at 4 C the enzyme retained its activity. However, the ability to make dextran became increasingly primer dependent. Hydroxylapatite-chromatographed enzyme preparations were completely dependent upon added dextran for rapid synthesis of methanol-insoluble glucan from sucrose. Half-maximal stimulation of new dextran synthesis occurred with dextran at a concentration of 2 to 3 muM and with a molecular weight of about 2,600. Neither glycogen, amylose, inulin, nor isomaltose functioned as primer. Studies with the dextransucrase activities detectable by in situ assay in polyacrylamide gels subjected to electrophoresis under nondenaturing conditions revealed that the major activity was detectable in the presence of sucrose alone and was stimulated by addition of primer dextran. The minor activity was only detected when primer dextran was present. Homogeneous preparations of both enzymes contained 30 to 40% carbohydrate.

Autoradiography↗

PubMed1983

Determination of glomerular permselectivity to neutral dextrans in the dog.

The multiple-indicator-dilution (MID) technique was used to separate solute flux (Js) across the glomerular and postglomerular capillaries in vivo. Anesthetized mongrel dogs (n = 20) during mannitol diuresis received a pulse of extracellular indicators including 125I-albumin (plasma reference), [14C]inulin (glomerular reference), creatinine (interstitial reference), and a neutral [3H]dextran (specific mol wt between 10,000 and 24,000 dalton) in the left renal artery. Left renal venous and ureteric outflows were rapidly sampled. 3H-labeled dextrans 10,000-15,500 had renal vein mean transit times (t) greater than those of 125I-albumin, indicating postglomerular extraction. 3H-labeled dextrans greater than 15,500 had t values identical to those of 125I-albumin, indicating only unidirectional glomerular extraction. The glomerular fractional dextran extractions relative to simultaneously injected [14C]inulin (ED/Ei) were calculated from urine and renal vein outflow curves and ranged from 0.98 +/- 0.02 to 0.33 +/- 0.12 (SD) for mol wt 10,000 +/- 24,000. ED/Ei values were quantitatively identical to constant-infusion fractional clearances of the same dextrans. Renal plasma flow (RPF) was then deliberately reduced two-to threefold in the same dog. ED/Ei as measured by the MID technique remained unchanged during graded reduction in RPF. In constant-infusion experiments RPF was reduced from 5.78 to 2.77 ml X s-1 X 100 g-1 and GFR from 50.4 to 36.3 ml X min-1, but the fractional neutral dextran clearances remained constant. The predominance of convective solute flux across the dog glomerulus permitted calculation of glomerular reflection coefficients 0.03 +/- 0.06 to 0.85 +/- 0.03 (SD) for neutral 3H-labeled dextrans 10,000-24,000 dalton.

Animals↗

PubMed1998

Anomalous decrease in dextran sulfate clearance in the diabetic rat kidney.

The anomalous increase in charge selectivity as previously observed with reduced dextran sulfate clearances in diabetic rats (L. D. Michels, M. Davidman, and W. F. Keane. Kidney Int. 21: 699-705, 1982) was confirmed in 4-wk streptozotocin (STZ) diabetic Sprague-Dawley rats using the isolated perfused kidney technique. The apparent charge selectivity in both control and diabetic rats could be abolished by increasing the dextran sulfate concentration to 200 micrograms/ml in the perfusate. This was demonstrated by a high rate of processing of dextran sulfate (approximately 1,700 ng.min-1.kidney-1) by glomeruli in both control and diabetic kidneys and by the fact that charge interaction could not explain the concentration dependence. The amount of urinary desulfation of dextran sulfate was also found to be significantly less in the diabetic kidney as was glomerular sulfatase activity compared with controls. Dextran sulfate glomerular processing is therefore altered in the STZ diabetic rat kidney but could be rationalized in terms of previous models of endothelial cell receptor-mediated uptake of dextran sulfate. The results are consistent with recent work demonstrating that there is little or no electrostatic charge interaction operating on dextran sulfate or other negatively charged molecules at the glomerular capillary wall.

Animals↗

PubMed1976

Studies on passive transfer of anti-dextran and anti-egg albumin reactivity in the rat.

We were unable, passively, to transfer reactivity against dextran to the skin or peritoneal mast cells of non-dextran-reactive rats, by using serum or material eluted at pH 3 from mast cells of spontaneously dextran-reactive rats. When the dextran-reactive donor rats had also been immunized against egg albumin (EA) with pertussis vaccine (inducing IgE anti-EA antibody), passive sensitivity against EA (but not against dextran) could easily be transferred. The results indicated that the anti-dextran reactivity is not due to IgE antibody. Systemic reactions against dextran and EA differed in pattern, supporting the concept that the two substances acted through different mechanisms.

Anaphylaxis↗

PubMed1981

Appearance of dextrans and antidextran antibodies in human sera.

The serologically active moiety of an antigen detected occasionally in pathologic sera by double-diffusion gel precipitation tests, referred to in earlier studies as ubiquitous tissue antigen, was identified as a dextran composed predominantly, if not exclusively, of a(1 leads to 6)-linked glycopyranoses. By means of an enzyme immunoassay, dextran or dextran-like material, which inhibited the binding of antidextran serum to dextran, was detected in sera of several patients with various gastrointestinal (GI) diseases, especially GI ulcers (7/10), and also often in sera of aged people (9/21). However, 2 of 50 normal blood donor sera and a few sera from almost every disease group studied contained low quantities of dextran-like material. The levels of antidextran antibodies of the IgG class were also often elevated among patients with GI diseases and aged people as demonstrated by enzyme immunoassay with dextran T-500 as the solid phase antigen. OD values exceeding the mean plus 2.5 SD of 106 normal blood donor sera were recorded in ;69% of patients with gastric and duodenal ulcers, 40% with ulcerative colitis, 29% with Crohn's disease, 20% with colorectal carcinomas, and in 21% with rheumatoid arthritis. None of 23 children, but 9 of 23 aged people (35%) had elevated antibody levels. It is suggested that absorption of dextrans from food or their production by intestinal bacteria may be facilitated in various GI diseases.

Adult↗

PubMed2000

Lung delivery of aerosolized dextran.

The ability of nebulizers to deliver dextran (nominal molecular mass, 4,000 g/mol) to the lung as an inhaled aerosol is evaluated by in vitro experimental methods and mathematical models. Dextran in isotonic saline was aerosolized by four nebulizer types (Pari LC STAR, Hudson T-Updraft II, Acorn II, and Sonix 2000) at dextran concentrations </= 400 mg/ml and with 2.5- and 4-ml volume fills. Aerosols inhaled during breath simulation were characterized by in-line phase Doppler anemometry, filter collection, osmometry, and gravimetry. Mathematical models were used to estimate amounts of the characterized aerosols depositing in the different regions of lung models, and mathematical models of mucous thickness were then developed to estimate initial concentrations of the depositing dextran in the mucus of each conducting airway generation. Models of three subjects (4 yr old, 8 yr old, and adult) were used. The high viscosity of the dextran solutions tested (up to seven times that of water) negatively impacts nebulization, and results in poor performance with most delivery systems tested. Our results suggest that airway mucosal dextran concentrations associated with efficacy in previous animal and in vitro models are achievable with reasonable delivery times (</= 12 min) with only one of the delivery systems/formulations tested: the Pari LC STAR nebulizer, using a 2. 5-ml volume fill and a dextran concentration of 200 mg/ml.

Administration, Inhalation↗

PubMed1976

Permselectivity of of the glomerular capillary wall. Studies of experimental glomerulonephritis in the rat using neutral dextran.

Polydisperse [3h] dextran was infused into eight Munich-Wistar rats in the early autologous phase of nephrotoxic serum nephritis (NSN), thereby permitting direct measurements of pressures and flows in surface glomeruli and fractional clearances for dextrans [(U/P) dextran/(U/P) inulin] ranging in radius from 18 to 42 A. Despite glomerular injury, evidenced morphologically and by a marked reduction in the glomerular capillary ultrafiltration coefficient, the glomerular filtration rate remained normal because of a compensating increase in the mean net ultrafiltration pressure. In NSN rats, as in normal controls, inulin was found to permeate the glomerular capillary wall without measurable restriction, and dextrans were shown to be neither secreted nor reabsorbed. For dextran radii of 18, 22, 26, 30, 34, 38, and 42 A, (U/P) dextran/(U/P) inulin in NSN and control rats, respectively, averaged 0.90 vs. 0.99, 0.81 vs. 0.97, 0.63 vs. 0.83, 0.38 vs 0.55, 0.20 vs. 0.30, 0.08 vs. 0.11, and 0.02 vs. 0.03. Using a theory based on macromolecular transport through pores, the results indicate that in NSN rats, effective pore radius is the same as in controls, approximately 50 A. In NSN, however, the ratio of total pore surface area to pore length, a measure of the number of pores, is reduced to approximately 1/3 that of control, probably due to a reduction in capillary surface area. These results suggest that proteinuria in glomerular disease is not due simply to increases in effective pore radius or number of pores, as previously believed. Using a second theoretical approach, based on the Kedem-Katchalsky flux equations, dextran permeability across glomerular capillaries was found to be slightly lower, and reflection coefficient slightly higher in NSN than in control rats.

Animals↗

PubMed1994

Dextran sulphates protect porcine arterial endothelial cells from free radical injury.

1. The ability of dextran sulphate to protect cultured porcine arterial endothelial cells injured by addition of xanthine and xanthine oxidase (X/XO) or hydrogen peroxide to cell medium was examined using a variety of drug preparations. Cell damage was assessed by determining cell viability (by trypan blue exclusion) and release of lactate dehydrogenase into the medium. 2. Dextran sulphates of average molecular weight (M(r)) 5000, 8000 (hydrogenated or unhydrogenated) at 0.05, 0.5, 5 and 50 micrograms ml-1 medium, added 24 h prior to X/XO, protected cells, whereas dextran sulphate M(r) 500,000 was protective only at 0.5 microgram ml-1. 3. None of the dextran sulphates used showed any toxic effect on cells in concentrations up to 500 micrograms ml-1 medium. 4. When the duration of pretreatment with dextran sulphate M(r) 8000 was varied, 6 h was required for a protective effect on cells damaged by X/XO, which was enhanced with durations of 16 and 24 h. 5. Dextran sulphates had a similar protective effect on cells damaged by hydrogen peroxide. 6. This study suggest that dextran sulphates may prevent conditions resulting from free radical injury.

Animals↗

PubMed2001

Effect of FITC-dextran molecular weight on its release from floating cetyl alcohol and HPMC tablets.

The release mechanism of high molecular weight fluorescein isothiocyanate dextrans (FITC-dextrans) from HPMC hydrogel matrices was studied. An anomaly was noted in the release behaviour of a series of high molecular weight FITC-dextrans from a tablet formulation designed to float in stomach contents. The tablets contained sodium bicarbonate and hydroxypropylmethyl cellulose (HPMC) in a cetyl alcohol matrix. When hydrated in an acid medium, this tablet consisted of a mixed solid with a viscous surface layer containing carbon dioxide bubbles through which the active ingredient (FITC-dextran) was released into the aqueous environment. However, it was observed that, above a critical molecular weight (approx. 65 kDa), the FITC-dextran was only released into the medium by an erosion-type mechanism, whereas, below this value, both diffusion and erosion processes took place. The key constraint appeared to be the apparent gel pore-size of the hydrated HPMC that was approximately 12 nm in diameter, irrespective of the molecular weight of the HPMC samples evaluated. It was concluded that FITC-dextran release was controlled by both FITC-dextran molecular weight and the HPMC hydrogel structure.

Dextrans↗

PubMed1984

The effect of insulin-dextran complexes on the protein synthesis in the primary monolayer culture of adult rat hepatocytes.

The purpose of the present study was to investigate the mechanisms of the long-term effects of insulin on protein synthesis in rat liver parenchymal cells. Three kinds of soluble and stable insulin-dextran complexes (I: Mr 150,000; II: Mr 450,000; III: Mr 2,000,000) were prepared. The effects of insulin or insulin-dextran complexes on protein synthesis were evaluated in the primary monolayer culture of adult rat liver. To avoid the effects of serum factors, the primary monolayer culture of adult rat liver in serum free medium was established. The cultured hepatocytes well maintained the metabolic and morphological characteristics of the adult rat liver. The incorporation of [14C]-leucine into trichloroacetic acid insoluble proteins and immunoprecipitates by anti-rat albumin serum were measured in cultured hepatocytes prepared either from the control or streptozotocin-induced rats. An addition of insulin-dextran complexes to the culture medium of the hepatocytes from diabetic rats stimulated the protein synthesis as well as the native insulin. The maximal effect of insulin-dextran complex (I) on protein synthesis was comparable to native insulin. However, insulin-dextran complex (II) caused a 67% stimulation of native insulin. Insulin-dextran complexes (III) induced only a slight increase of protein synthesis. Furthermore, an addition of insulin-dextran complexes into the medium caused a more tight cellular attachment to the dish and more extensive spreading. These results favor the view that the stimulation by insulin of protein synthesis in rat hepatocytes does not require the entry of insulin into cells.

Albumins↗

PubMed1990

Size determination of red blood cell aggregates induced by dextran using ultrasound backscattering phenomenon.

Different methods are commonly used to study the red blood cell aggregation phenomenon. The major interest of the ultrasonic method presently discussed is to assess the mean size of red blood cell (RBC) aggregates by measuring ultrasonic intensity backscattered by blood. Applying Rayleigh theory of sound to blood medium, one can show that the scattered ultrasonic intensity is proportional to the 6th power of the size of the RBC aggregates. The ultrasonic method is used to evaluate the mean size of RBC aggregates induced by dextrans. RBCs are suspended at various hematocrits H, in solution of dextrans of different molecular weights M and at different weight concentrations Cw. Results are presented by using the ultrasonic backscattering coefficient chi which is a relevant quantity in a scattering experiment. For suspensions of RBCs aggregated with dextran of molecular weight 70,000 dalton (dextran 70) at concentration Cw = 40 g/l, variations of chi as a function of H are similar to those obtained for normal blood. At a fixed hematocrit, variation of chi versus Cw for dextran 70 exhibits a maximum at 40 g/l. In the case of RBCs suspended at hematocrit 20% and aggregated with dextrans of molecular weight M, 70,000 less than or equal to M less than or equal to 2,000,000, the variations of chi versus molar concentration Cm are similar to those of the microscopic aggregation index defined by Chien (1). Finally, a statistical model of the blood structure previously described (2) is applied to evaluate the mean size of the aggregates. According to this model, the mean size of aggregates is independent of hematocrit for H less than or equal to 40% and independent of the molecular weight of dextran for M greater than or equal to 150,000 dalton.

Dextrans↗

PubMed1991

Assessment of red blood cell aggregation with dextran by ultrasonic interferometry.

Aggregation of human red blood cells (RBCs) induced by dextrans of various molecular weight has been studied by using a new ultrasonic interferometry method. This method, based on A-mode echography, allowed for the measurement of the accumulation rate of particles on a solid plate which is related to their sedimentation rate (i.e., to their mean size). The initial aggregation process, the mean and the maximum sedimentation rate of aggregates and the packing of the sedimented RBCs have been investigated. Effects of hematocrit, molecular weight of dextrans and inhibition by dextran 40 on the RBC aggregation induced by dextran of higher molecular weight have been determined by analysing variations of the aggregate size. Results obtained confirm the aggregation effect of dextrans of molecular weights equal or higher than 70,000 dalton and disaggregation effect of dextran 40,000 dalton on aggregation by dextrans of higher molecular weight.

Dextrans↗

PubMed1998

Conjugate chemistry, iodination and cellular binding of mEGF-dextran-tyrosine: preclinical tests in preparation for clinical trials.

A conjugate with specific binding to the epidermal growth factor receptor, EGFR, and of interest for clinical tests was prepared using mouse epidermal growth factor, mEGF, and dextran. The mEGF was first coupled to dextran by reductive amination in which the free amino group on the N-terminal of mEGF was reacted with the aldehyde group on the reductive end of the dextran chain. The end-end coupled intermediate was further activated by the cyanopyridinium agent CDAP and tyrosines introduced to the dextran part of the conjugate. The mEGF-dextran-tyrosine conjugate was, with high efficiency, iodinated with the chloramine-T method. Approximately 25-35% of the radioactivity could be removed from the conjugate after exposure to protease K while 65-75% of the radioactivity could be removed after exposure to dextranase. Thus, the largest amount of the iodine was on the dextran part of the conjugate. The iodinated mEGF-dextran-tyrosine had EGFR specific binding since the binding to an EGFR rich human glioma cell line could be displaced by an excess of non-radioactive mEGF. The conjugate was to a large extent internalized in these cells and the administrated radioactivity was thereby retained inside the cells for at least up to 50 h.

Animals↗

PubMed2000

Reduction of background activity through radiolabeling of antifibrin Fab' with 99mTc-dextran.

UNLABELLED: Scintigraphic detection of occult disease is limited by background activity in the blood and in the extravascular space that reduces target-specific contrast. To lower nonspecific background activity, we have studied the in vivo biodistribution kinetics of a clot-targeting molecule (MH1 Fab') attached to (99m)Tc-dextran. We tested the hypothesis that the complex will have better background clearance than the directly radiolabeled clot-targeting molecule. METHODS: Fab' fragments of MH1 Fab' antifibrin antibody were coupled to (99m)Tc-sulfhydryl dextran through disulfide exchange, and clot binding bioreactivity was tested in vitro and in vivo in a rabbit jugular vein thrombus model. To assess the background clearance kinetics and extravascular leakage, we studied (99m)Tc-dextran, (99m)Tc-MH1 Fab', and the (99m)Tc-dextran-labeled MH1 Fab' complexes in rats. RESULTS: (99m)Tc-radiolabeled dextran derivatives were radiochemically stable and retained clot-binding bioreactivity in vivo. In the rat model, blood and tissue clearance of the (99m)Tc-dextran MH1 Fab' constructs was substantially improved relative to directly radiolabeled MH1 Fab'. At 1 h, total and extravascular tracer localizations in lung and muscle were significantly lower for 99mTc-dextranradiolabeled MH1 Fab' than for (99m)Tc-MH1 Fab' (P < 0.05). CONCLUSION: The study observations suggest that radiolabeling through a (99m)Tc-dextran moiety may improve the detection of pulmonary emboli and other clinically important fixed intravascular targets by lowering nonspecific background activity.

Animals↗

PubMed2002

EGF and dextran-conjugated EGF induces differential phosphorylation of the EGF receptor.

Dextran-conjugated EGF (EGF-dextran) has a potential use for targeted radionuclide therapy of tumors that overexpress the epidermal growth factor receptor (EGFR). There are plans to treat both bladder carcinomas and malignant gliomas with local injections of radiolabeled EGF-dextran since these tumors often express high levels of EGFR. In this report we show that EGF and EGF-dextran differentially activate the EGFR. In the human glioma cell line U-343, activation of the serine/threonine kinases Erk and Akt is identical upon stimulation with EGF or EGF-dextran. However, the effect on phospholipase Cgamma1 (PLCgamma1) phosphorylation differs. In cells stimulated with EGF-dextran, the PLCgamma1 phosphorylation is lower than in cells stimulated with EGF. This observation could be explained by the fact that the PLCgamma1 association sites in the EGFR, tyrosine residues 992 and 1173, were phosphorylated to a lower degree when the receptor was stimulated with EGF-dextran as compared to with EGF.

Dextrans↗

PubMed2001

[Effect of dextran combination with flurosemide on nephrotic syndrome].

OBJECTIVE: To compare the diuretic effect of coadministration of dextran and flurosemide with that of coadministration of Albumin and flurosemide on primary nephrotic syndrome. METHODS: In a double-blind placebo-controlled study, eighteen primary nephrotic syndrome patients on standard sodium chloride intake, random by divided into three groups and received by intravenous administration for 60 minutes for three days (a) FU (1 mg.kg-1) combination with a sham infusion, (b) FU (1 mg.kg-1) combination with 50 ml of 20% solution of Albumin, or (c) FU (1 mg/kg) combination with 250 ml dextran 40. Urinary volume, sodium and plasma atrial nartiuretic peptide concentration were assessed. RESULTS: The results showed that administration of FU alone increased mean cumulative urinary sodium and volume excretion as compared with the administration of sham infusion without treatment (P < 0.05). The administration of FU and albumin or FU and dextran 40 caused an even more marked increase of urinary sodium and volume excretion (P < 0.01), as compared with the administration of sham infusion without treatment. Plasma ANP increased significantly on both albumin infusion days and dextran 40 infusion days (P < 0.05). CONCLUSION: Coadministration of albumin and FU or dextran 40 and FU can increase the urinary volume and urinary Na and ANP significantly, dextran 40 can take the place of albumin because there was no difference between the administration of FU and albumin and FU and dextran in UV, Una and ANP.

Adolescent↗

PubMed1992

Inhibition by heparin and derivatized dextrans of Staphylococcus aureus adhesion to fibronectin-coated biomaterials.

Recent data on cardiovascular device-centered infections suggest that some plasma and extracellular matrix proteins contribute to bacterial adhesion and colonization on biomaterials. We previously developed an in vitro assay to study the Staphylococcus aureus adhesion-promoting effect of surface-adsorbed fibronectin on flat PMMA coverslips coated with a monolayer amount of fibronectin. We screened the potential anti-adhesive properties of a group of substituted dextrans, previously shown to exhibit potent anticoagulant and anticomplementary activities. In comparison to unsubstituted dextran which showed no significant (< 20%) adhesion inhibition at 1 mg/ml, dextrans increasingly substituted with carboxylic and benzylamide groups (CMBD) exhibited increasing anti-adhesive activities. Three CMBD derivatives showing an increasing proportion (5-14%) of benzylamide groups showed inhibition of bacterial adhesion increasing from 33 to 51% at 1 mg/ml. Another category of substituted dextrans having a variable proportion (2-26%) of sulfonated benzylamide groups (CMBDS) produced active inhibition of S. aureus adhesion. In comparison to these heparin-like dextran derivatives, native heparin produced inhibition values of S. aureus adhesion which were intermediate between those of CMBD and CMBDS compounds. Furthermore, the anti-adhesive activity was still expressed when substituted dextrans were preincubated with fibronectin-coated PMMA but washed away at the time when radiolabeled bacteria were added to the adhesion assay. This indicates that the anti-adhesive effects of CMBDS could be exerted at the level of the S. aureus binding site of fibronectin. In conclusion, S. aureus adhesion on fibronectin-coated biomaterials can be efficiently blocked in vitro by soluble compounds such as dextran derivatives.

Adsorption↗