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PubMed1997

alpha-Trinositol prevents increased negativity of interstitial fluid pressure in rat skin and trachea induced by dextran anaphylaxis.

The new anti-inflammatory agent alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate), is suggested to act on the cellular adhesion receptor towards extracellular matrix components, the beta1-integrins, and may therefore represent a novel principle for therapy of the phenomena associated with acute inflammation. Increased negativity of interstitial fluid pressure (p(if)) is a major driving force for the rapid edema formation in trachea and skin associated with dextran anaphylaxis in the rat. We therefore used this experimental model to study the effect of alpha-trinositol in skin and trachea of pentobarbital anesthetized rats. p(if) was measured with sharpened glass capillaries (3-7 microm) connected to a servocontrolled counterpressure system. alpha-Trinositol (10 mg) was given before or after dextran. Circulatory arrest was induced 2 min after i.v. dextran to limit the increased capillary fluid filtration associated with the anaphylactic reaction. This increased filtration will otherwise raise interstitial volume and thereby p(if) and cause an underestimation of a potential increased negativity of p(if). In the trachea, p(if) was 0.0 +/- 1.0 mmHg (S.D.) and -1.4 +/- 0.5 mmHg in controls given saline vehicle and alpha-trinositol (P > 0.05), respectively, and fell to -8.5 +/- 2.7 mmHg after dextran (P < 0.01). alpha-Trinositol given 2 min prior to or after dextran resulted in p(if) of -1.7 +/- 1.2 mmHg (P > 0.05 versus control, P < 0.01 versus dextran) and -4.7 +/- 3.0 mmHg (P < 0.01 versus control and dextran), respectively. In skin, i.v. dextran caused p(if) to fall from -0.6 +/- 0.5 to -4.6 +/- 1.9 mmHg (P < 0.001). When alpha-trinositol was given prior to dextran the corresponding figures were -0.4 +/- 0.8 and -0.9 +/- 1.1 mmHg, respectively (P > 0.05). Subdermal administration of alpha-trinositol after i.v. dextran and circulatory arrest normalized p(if) in concentration of 100, 10 and partly at 1 mg/ml. Thus, alpha-trinositol prevented the increased negativity of p(if) induced by dextran anaphylaxis when administered prior to as well as after dextran showing that the alpha-trinositol also could influence an already started inflammatory reaction.

Anaphylaxis↗

PubMed1996

Do low molecular weight heparin and dextran increase the blood loss in transurethral resection of the prostate?

OBJECTIVE: To evaluate whether the use of dextran or the combination of low molecular weight heparin and dextran increases the blood loss in elective transurethral resection for benign prostatic hyperplasia. PATIENTS AND METHODS: This open randomized controlled study included 198 patients operated under spinal anaesthesia who were allocated to four groups differing in the combination of prophylactic treatment used for thrombosis and for the substitution of blood loss. The prophylactic treatment was either dalteparin sodium, continued each day until mobilization, or 3% Ringer dextran-60 just before operation and continued with 6% dextran-70 for 2 days post-operatively, and the volume substitute was Ringer dextran or Ringer's acetate. Thus, the four treatments (by prophylaxis and volume substitute, respectively) were dalteparin and Ringer's acetate, dalteparin and dextran, dextran and Ringer's acetate, and dextran and dextran. The haemoglobin lost to the irrigation fluid was measured and used to calculate blood loss. RESULTS: Patients receiving dextran had a larger post-operative and total blood loss than those who did not. The need for transfusion did not differ between the treatment groups. CONCLUSION: The combination of dalteparin and dextran was not associated with an increased blood loss above that with dextran alone.

Aged↗

PubMed1973

Regulation of immunoglobulin synthesis by dextran.

Dextran, of the variety commonly used as plasma expander, markedly altered antibody synthesis to an unrelated antigenic stimulus, SRBC, in two animal species, guinea pig and mouse. The time at which dextran was administered relative to antigen was found to be most critical for increasing or decreasing the number of IgM and IgG PFC. Furthermore, these times differed for the two species studied. Typically, when given to guinea pigs 6 h before SRBC, dextran caused a 20-fold rise in IgM-producing cells but had little effect upon IgG synthesis. However, if dextran preceded antigen by 24 h the same magnitude of increase was seen in IgG-forming cells while a decrease in IgM-producing cells occurred. In mice, a short 2 h interval between dextran and antigen favored cells synthesizing IgG and not those producing IgM. A longer 6 to 24 h lapse between dextran and antigen resulted again in an inverted pattern, i.e., an increase in IgM and a decrease in IgG-producing cells. In both species, if dextran was given 48 h before antigen, synthesis of IgG markedly decreased. At the cellular level dextran activated those B cells already in the vascular compartment. In stimulating the IgM response to SRBC, dextran appears either to substitute for T cells or to amplify the effects of that small number of T cells still present in bone marrow preparations. Dextran-altered mouse B cells synthesized SRBC-specific IgG in the presence of normal T cells at an earlier time than did normal B and T cells. However, dextran was unable to cause blastogenesis in vitro of guinea pig lymph node cells or mouse B, T, and spleen cells. The data suggest at least two effects that T cells exert upon B cells. One is to stimulate more B cells to produce IgM, a function accomplished by endotoxins, PWM, PPD, and the simple polysaccharide dextran. The other is to trigger shifts in synthesis of immunoglobulins M and G. Our observations are compatible with the view that a single cell is capable of synthesizing both of these immunoglobulins and that the stimulating factor for one may cause cessation of the other.

Animals↗

PubMed2000

Effects of dextran sulfate on tracheal mucociliary velocity in dogs.

We have shown that low molecular weight dextran, as a potential mucolytic agent, reduced the viscoelasticity and spinnability of cystic fibrosis (CF) sputum and improved its ciliary transportability in vitro; it also reduced viscoelasticity of healthy dog mucus in in vitro testing. In anesthetized dogs, dextran administered by aerosol at 65 mg/mL increased tracheal mucus velocity, but this increase was not sustained for higher concentrations. The purpose of the present study is to evaluate whether low mol. wt. dextran sulfate, a charged oligosaccharide, exhibits similar effects to previously tested neutral dextran when administered by aerosol to anesthetized dogs in terms of mucus rheology and mucociliary clearance rate. Healthy mongrel dogs were anesthetized with pentobarbital and intubated. Aerosols of Ringer's solution or dextran sulfate (m.w. 5000) dissolved in Ringer's were generated by Pari LC STAR nebulizer, and delivered during 30-min periods of spontaneous breathing. Tracheal transepithelial potential difference (PD, using agar filled electrodes) and tracheal mucociliary velocity (TMV, by charcoal marker particle transport) were measured under bronchoscopic control, and mucus for viscoelasticity analysis by magnetic rheometry was collected by the endotracheal tube method. We performed experiments in seven dogs, involving 30-min administrations of aerosol, separated by 30-min periods of no aerosol. All dogs received inhalations of 6.5 mg/mL, 20 mg/mL, and 65 mg/mL dextran sulfate. Tracheal mucus viscoelasticity (average log G* over 1-100 rad/s) decreased progressively with increasing dose of dextran sulfate; for the highest concentration (65 mg/mL), log G* decreased by a factor of 2.61 (p = 0.021). A modest increase in the TMV was observed for the first dose of dextran sulfate (128% of baseline at 6.5 mg/mL, p = 0.066); thereafter TMV was stable. PD increased significantly at each concentration of dextran sulfate compared with Ringer control; however, there was no additional change between the three groups. The solids content of collected airway fluid (%SC) was gradually increased during successive 30-min dextran sulfate aerosols, indicating a significant residence time for the dextran in the mucus, and correlating with the decrease in viscoelasticity. These results suggest that dextran sulfate may be potentially of therapeutic value as a mucolytic agent, assisting mucus clearance by cough and physiotherapy, although whether it stimulates mucociliary clearance remains to be proven.

Aerosols↗

PubMed1993

Binding, internalization and excretion of TGF alpha-dextran associated radioactivity in cultured human glioma cells.

Conjugates based on transforming growth factor alpha, TGF alpha, or epidermal growth factor, EGF, are candidates for targeted radiotherapy against EGF-receptor rich tumours such as gliomas or squamous carcinomas. In this study, binding, internalization and excretion of radiolabelled TGF alpha and TGF alpha-dextran conjugates was analysed in an EGF-receptor rich human glioma cell line. The binding of 125I-TGF alpha was EGF-receptor specific and the binding pattern was similar to that of 125I-EGF. The TGF alpha-dextran conjugate also bound specifically but gave maximum binding for a longer time during continuous incubation compared to when only TGF alpha was used. The excretion pattern of internalized radioactivity was somewhat slower for 125I-TGF alpha-dextran, with 125I-labelling on the TGF alpha part, as compared to 125I-TGF alpha although most of the radioactivity in both cases was excreted within 4 hours. The fate of the dextran part of the conjugate, as followed by means of 125I-labelling of the dextran, was different since all radioactivity in that case remained cell-associated for at least up to 22 hours. Furthermore, by comparison with previously published results, it was seen that the radioactivity delivered through the TGF alpha part of TGF alpha-dextran was retained for a shorter period of time by the cells than when delivered by EGF in EGF-dextran conjugates. However, when the radioactivity was delivered by the dextran part of the conjugates, the radioactivity seemed to be retained equally well or even better when TGF alpha-dextran was applied. It is concluded that TGF alpha-dextran, as well as EGF-dextran, have interesting properties for targeting against EGF-receptors and that the dextran part is well retained in the cells and therefore might be a suitable carrier for toxic agents such as radionuclides. It is of high interest to continue with toxicological and pharmacological in vivo studies of the conjugates.

Binding Sites↗

PubMed2005

Benchmarking iron dextran sensitivity: reactions requiring resuscitative medication in incident and prevalent patients.

BACKGROUND: Reliable information on the incidence of severe reactions to iron dextran is limited. Administration of agents of resuscitation in acute anaphylaxis may serve as a marker to quantify life-threatening adverse drug reactions. METHODS: To determine the incidence of the most serious reactions to intravenous (i.v.) iron dextran, we searched the Gambro Healthcare US medical database for evidence of same-day administration of both i.v. iron dextran and parenteral adrenaline, corticosteroids or antihistamines. We confirmed each case as an iron dextran sensitivity reaction by direct inquiry. We also determined the total reported number of suspected adverse iron dextran reactions. RESULTS: During the 16 month study period, we determined that 1,066,099 doses of i.v. iron dextran were given to 48,509 patients, including 20,213 patients who had not previously received iron dextran (iron dextran naïve). We identified seven patients who experienced reactions requiring resuscitative agents, all in response to a test dose (five patients) or first therapeutic dose (two patients), and therefore all in the iron-naïve (incident) group. Thus, we found the incidence of iron dextran reactions requiring resuscitative agents to be 0.035% (7 out of 20,213). No reaction was fatal. In a combined group of incident and prevalent patients, we found 337 total reports of suspected adverse reactions to iron dextran, without regard to severity of reaction, yielding an overall per patient adverse drug event (ADE) rate of 0.69% (337 out of 48,509) and per exposure rate of 0.03% (337 out of 1,066,099). CONCLUSIONS: The incidence of reactions to iron dextran requiring resuscitative medications, per exposure or per patient, is approximately 0.035%. Reactions of this severity occur after either the test dose or first dose of iron dextran.

Adrenal Cortex Hormones↗

PubMed1993

Clinical efficacy of aspirin and dextran for thromboprophylaxis in geriatric hip fracture patients.

The clinical efficacy of thromboprophylaxis with aspirin and dextran 40 was compared in a prospective review of 530 geriatric hip fracture patients treated surgically. All patients were also treated with early mobilization with weight bearing as tolerated and above-knee elastic stockings. In addition to clinical efficacy in preventing thromboembolic complications [deep vein thrombosis (DVT), pulmonary embolism (PE)], safety and cost-effectiveness were also assessed. The overall incidence of clinical thromboembolic disease was 2.8% (DVT = 0.4%, PE = 2.4%). The incidence of DVT (0.5%) and PE (2.6%) in the aspirin group was essentially the same as the incidence of DVT (0.3%) and PE (2.4%) in the dextran group. The inhospital mortality rate (aspirin 4.6%, dextran 3.8%), wound drainage (aspirin 1.5%, dextran 0.9%), deep wound infection (aspirin 0.5%, dextran 0.3%), gastrointestinal bleeding (aspirin 2.1%, dextran 1.5%), and congestive heart failure (aspirin 2.6%, dextran 1.8%) did not differ significantly between the two groups. The intraoperative transfusion rate was similar in both groups (aspirin .65 units, dextran .55 units). However, postoperatively, the transfusion rate was significantly higher in the dextran group (aspirin .26 units, dextran .41 units, p < .05). The treatment of thromboembolic complications was the same for each group and therefore represents similar treatment costs. However, the cost of prophylaxis with dextran was $309 per patient and with aspirin was $1.79 per patient. Our findings suggest that, based on clinical diagnostic criteria, aspirin and dextran are equally effective thromboembolic prophylactic agents in geriatric hip fracture patients. The safety, cost, and ease of administration of aspirin may make its use more desirable.

Aged↗

PubMed1998

Dextran-70 inhibits equine platelet aggregation induced by PAF but not by other agonists.

Dextrans of mean molecular weight 70 kDa (dextran-70) have had clinical use as anti-thrombotics in man. A major part of the anti-thrombotic action is mediated via inhibition of platelet function. Greatorex (1975, 1977) treated thromboembolic colic in horses with infusions of dextran-70 and reported a 90% recovery rate, but this treatment is nonetheless rarely used. We have used an in vitro method to examine the effect of dextran-70 on equine platelet suspensions, in the hope that understanding the mechanism of action of dextran-70 might lead to the development of alternative therapeutic agents. The effects of dextran-70 on equine platelets occurred immediately in vitro with an initial activation and shape change. Subsequent assessment of aggregation revealed a dose-dependent specific inhibition of platelet-activating factor (PAF)-induced aggregation, significant in rate of aggregation at dextran-70 concentrations >40 g/l (P<0.05) and in extent of aggregation at dextran-70 concentrations >50 g/l (P<0.05). Pre-incubation with 60 g/l dextran-70 significantly inhibited the rate and extent of aggregation in response to PAF (1 nmol/l) (P<0.001 and P = 0.003, respectively) but this was not dependent on the duration of pre-incubation (from 0 to 150 min). No effects were seen when the agonist was adenosine 5'-diphosphate (200 nmol/l), collagen (10 mg/l), 5-hydroxytryptamine (100 micromol/l) or U44069 (600 nmol/l) (all P>0.1). Analysis of PAF concentration-aggregation curves after pre-incubation with 60 g/l dextran-70 indicated significant noncompetitive inhibition by dextran-70 (P<0.001 for rate and extent of aggregation). The ability of dextran-70 to inhibit responses of equine platelets to PAF is probably an important component of its beneficial effect as an anti-thrombotic in colic cases.

Adenosine Diphosphate↗

PubMed1969

Dextran-induced agglutination of Streptococcus mutans, and its potential role in the formation of microbial dental plaques.

Glucose-grown washed cells of streptococci similar to Streptococcus mutans, which contain cell-bound dextransucrase, have been observed to agglutinate upon the addition of high molecular weight dextran. Low molecular weight dextran or unrelated polysaccharides were ineffective. Agglutination also occurred upon addition of sucrose, which can be converted into dextran, but not with other mono- and disaccharides. Other bacteria, including species capable of synthesizing dextrans, were not observed to exhibit this phenomenon. Cells of S. mutans agglutinated upon addition of dextran over a wide pH range, but maximal sensitivity to dextran occurred at pH 8.5. At this pH, such cells can be used for a simple, specific, and exquisitely sensitive qualitative assay for high molecular weight dextran, for addition of 6 ng of dextran with a molecular weight of 2 x 10(6) (i.e., approximately three molecules per cell) caused detectable agglutination. High concentrations of glucose, levan, and dextran of molecular weight of 2 x 10(4) inhibited the reaction. Fluorescein-labeled cells of S. mutans were observed to adhere to dextran-containing plaques and dextran-treated teeth, suggesting that this phenomenon may be of importance in the formation of streptococcal dental plaques. The mechanism responsible for dextraninduced agglutination appears to involve the affinity of a receptor site, possibly dextransucrase, on the surface of several cells for common dextran molecules.

Agglutination↗

PubMed1985

Urinary excretion characteristics of a polymeric prodrug of mitomycin C, mitomycin C-dextran conjugate.

Urinary excretion characteristics of a polymeric prodrug of mitomycin C (MMC), mitomycin C-dextran conjugate (MMC-D), following intravenous administration was studied in rats. Three types of MMC-D, conjugates with dextrans of molecular weights of 10000, 70000 and 500000, were tested and urine concentration of MMC, dextran and spacer were determined by three analytical methods, i.e., bioassay, anthrone method and radioactivity counting. MMC was assayed separately as a free form and conjugated form based on antimicrobiological activity. MMC administered as a free form was excreted rapidly into urine but only a small amount of MMC was excreted following the administration of MMC-D. The excreted amount of MMC in a conjugated form varied with the size of carrier dextran while similar sustained excretion was observed regardless of the carrier size. The excretion of carrier dextran determined by anthrone method was confined as the molecular weight was increased. The effect of molecular weight was also observed in the case of spacer-introduced dextran (dextran-C6 spacer) and original dextran. Compared with neutral dextran, cationic MMC-D and anionic dextran-C6 spacer exhibited diminished excretion, indicating the effect of charge on urinary excretion. The urinary recovery of radioactivity was almost in accordance with that of carrier dextran. However, the urinary recovery of MMC based on biological activity was considerably lower than that of carrier dextran. It was suggested that MMC-D underwent inactivation to a great extent before releasing active MMC in the body. The effect of physicochemical properties such as molecular weight and electric charge on the urinary excretion of the polymeric prodrug was thus elucidated.

Animals↗

PubMed2002

Effect of dextrans on cryopreservation of goat cauda epididymal spermatozoa using a chemically defined medium.

Experiments were carried out to investigate the cryoprotecting potential of dextrans (ranging from 10 to 2000 kDa) using a synthetic model system developed recently in this laboratory. Goat spermatozoa from the cauda epididymidis were extracted in a chemically defined medium (modified Ringer's solution) and assayed for motility using a phase-contrast microscope. The sperm cells were subjected to a freezing protocol in a computer-controlled biofreezer (cooling at 0.25 degrees C min(-1) to 5 degrees C; 5 degrees C min(-1) to -20 degrees C; 20 degrees C min(-1) to -100 degrees C) and plunged into liquid nitrogen. The frozen cells were thawed rapidly at 37 degrees C in a thermostatic waterbath. In the absence of dextran, all the spermatozoa lost their motility. The cryoprotecting efficacy of each dextran was found to be biphasic in nature. Initially, as the concentration of dextran was increased, the recovery of sperm motility also increased and reached an optimum value; however, with further increases in dextran concentration, the recovery of motility decreased sharply. Of all the sugar polymers tested, 10 kDa dextran showed the highest cryoprotecting efficacy, whereas the 2000 kDa sugar polymer was the least active. Dextrans of 10, 40, 73, 173, 252, 500 and 2000 kDa offered maximum cryorecovery of forward motility to the extent of approximately 23%, 21%, 19%, 18%, 16%, 15% and 8%, respectively. Optimum concentrations of these dextrans for cryoprotection of sperm motility were 8.42, 2.50, 1.09, 0.37, 0.31, 0.10 and 0.04 mmol l(-1), respectively. It thus appears that each dextran has a characteristic cryoprotection profile. The data show that the cryoprotecting efficacy and optimum cryoprotecting concentrations of dextrans are inversely related to their molecular mass. Dextran also served as a significant cryoprotectant in the presence of glycerol (0.87 mol l(-1)) and dimethyl sulphoxide (0.76 mol l(-1)), which are well known cryoprotectants; the action of the combined cryoprotectants was almost additive. The presence of glycerol or glycerol plus dimethyl sulphoxide caused a significant reduction (from 8.42 to 6.27 mmol l(-1)) in the optimum concentration of dextran. In the presence of the three cryoprotectants, recovery of sperm motility was as high as 58% (forward motility) and 60% (total motility).

Animals↗

PubMed1987

Dextrans.

Dextrans were first used in clinical practice in 1947. Raw dextran is produced by bacterial conversion of sucrose to a branched chain structure which is heterogeneous in composition. Further refinement is carried out by hydrolysis and fractionation. Clinically useful dextrans form only 1 percent of the total molecular spectrum of raw dextran. The two most frequently used dextrans are Dextran 40 and Dextran 70. These have molecular weights of 40,000 and 70,000 respectively. The use of average molecular weight to describe dextrans is generally unsatisfactory since an infinite variety of dextrans could meet a particular weight specification. Categorization of dextrans will be discussed in detail. Clinical uses include plasma expansion, antithrombogenesis and haemodilution. Major efforts to reduce the antigenically active components of clinically used dextrans have been made and manufacturers have identified the principal factors responsible for allergic responses. However, major allergic responses to dextran still cause clinicians great concern and the problem is by no means resolved.

Dextrans↗

PubMed1981

Pharmacokinetics of low molecular (monovalent) dextran (Dx 1) in volunteers.

Dextran-induced side effects were attributed to preformed antibodies that cross-react with dextran. These antibodies can be blocked by monovalent haptens (dextrans 1) in animals. Dextran 1 is also well tolerated in humans. Plasma levels and renal excretion of monovalent dextran (dextran 1, molecular weight around 1,000) were measured in five volunteers after intravenous administration of 20 ml 15% dextran 1 (3 g), and in one volunteer after intravenous administration of 50 ml (7.5 g). Measurements could be satisfactorily described by a two-compartment open model with elimination from the central compartment only: mean half-life for the beta phase of 1.9 h, a mean cumulative asymptotic elimination of dextran in the urine of 75%, and a mean renal clearance of 137 ml/min with a mean total clearance of 187 ml/min were estimated. The terminal half-life of dextran 60 (Macrodex) was 24 h (median). In volunteers with dextran antibodies no anaphylactoid symptoms were observed after Dx 1. In conclusion, the intravenous preinjection of dextran 1, owing to its pharmacokinetic behavior, should prevent antibody-mediated side effects after infusions with clinical dextrans (e.g., Macrodex, Rheomacrodex).

Administration, Oral↗

PubMed1993

[Severe dextran-induced anaphylactic/anaphylactoid reaction despite preventive hapten administration].

Dextran-60 is widely used as a colloid volume substitute and for thromboprophylaxis. In order to avoid the most dangerous complication associated with dextran, the dextran-induced anaphylactic/anaphylactoid reaction (DIAR), hapten dextran is infused before starting the first application of dextran. We report of a 60-year-old man with multiple trauma, who received a dextran infusion for thromboprophylaxis because of high risk for thrombosis due to a severe thrombocytosis developing in the late postoperative period. Despite prophylaxis with monovalent hapten dextran, an anaphylactic reaction occurred. Although a serum sample drawn prior to the reaction is lacking, the causal relationship to dextran can be classified as likely, due to the close time relationship to the dextran-60 infusion. In addition, there were high titers of dextran-reactive antibodies in the blood drawn immediately after the reaction occurred. It is concluded that even after correct application of monovalent hapten dextran, dextran infusions carry the risk of severe anaphylactic reactions. They should therefore only be administered if clinical observation of the patient and the possibility of resuscitation are guaranteed.

Anaphylaxis↗

PubMed2024

Mannose receptor (MRC1) mediates uptake of dextran in macrophages via receptor-mediated endocytosis.

UNLABELLED: Macrophages maintain surveillance of their environment using receptor-mediated endocytosis and pinocytosis. Receptor-mediated endocytosis allows macrophages to recognize and internalize specific ligands whereas macropinocytosis non-selectively internalizes extracellular fluids and solutes. Here, CRISPR/Cas9 whole-genome screens were used to identify genes regulating constitutive and growth factor-stimulated dextran uptake in murine bone-marrow derived macrophages (BMDM). The endocytic mannose receptor c-type 1 ( Mrc1 , also known as CD206) was a top hit in the screen. Targeted gene disruptions of Mrc1 reduced dextran uptake but had little effect on uptake of Lucifer yellow, a fluid-phase marker. Other screen hits also differentially affected the uptake of dextran and Lucifer yellow, indicating the solutes are internalized by different mechanisms. We further deduced that BMDMs take up dextran via MRC1-mediated endocytosis by showing that competition with mannan, a ligand of MRC1, as well as treatment with Dyngo-4a, a dynamin inhibitor, reduced dextran uptake. Finally, we observed that IL4-treated BMDM internalize more dextran than untreated BMDM by upregulating MRC1 expression. These results demonstrate that dextran is not an effective marker for the bulk uptake of fluids and solutes by macropinocytosis since it is internalized by both macropinocytosis and receptor-mediated endocytosis in cells expressing MRC1. This report identifies numerous genes that regulate dextran internalization in primary murine macrophages and predicts cellular pathways and processes regulating MRC1. This work lays the groundwork for identifying specific genes and regulatory networks that regulate MRC1 expression and MRC1-mediated endocytosis in macrophages. SIGNIFICANCE STATEMENT: Macrophages constantly survey and clear tissues by specifically and non-specifically internalizing debris and solutes. However, the molecular mechanisms and modes of regulation of these endocytic and macropinocytic processes are not well understood. Here, CRISPR/Cas9 whole genome screens were used to identify genes regulating uptake of dextran, a sugar polymer that is frequently used as a marker macropinocytosis, and compared with Lucifer yellow, a fluorescent dye with no known receptors. The authors identified the mannose receptor as well as other proteins regulating expression of the mannose receptor as top hits in the screen. Targeted disruption of Mrc1 , the gene that encodes mannose receptor, greatly diminished dextran uptake but had no effect on cellular uptake of Lucifer yellow. Furthermore, exposure to the cytokine IL4 upregulated mannose receptor expression on the cell surface and increased uptake of dextran with little effect on Lucifer yellow uptake. Studies seeking to understand regulation of macropinocytosis in macrophages will be confounded by the use of dextran as a fluid-phase marker. MRC1 is a marker of alternatively activated/anti-inflammatory macrophages and is a potential target for delivery of therapeutics to macrophages. This work provides the basis for mechanistic underpinning of how MRC1 contributes to the receptor-mediated uptake of carbohydrates and glycoproteins from the tissue milieu and distinguishes genes regulating receptor-mediated endocytosis from those regulating the bona fide fluid-phase uptake of fluids and solutes by macropinocytosis.

Journal Article↗

PubMed1982

Induction of metallothionein in liver and changes of essential metal levels in selected tissues by three dextran derivatives.

Three dextran derivatives (dextran sulfate, DEAE-dextran and Dextran T500) were injected intraperitoneally into mice to study the induction of zinc-thionein in the liver, and the changes of essential metal levels in the liver, kidneys and spleen. The former was investigated with a high performance liquid chromatograph equipped with an atomic absorption spectrophotometer, and the latter with an inductively coupled plasma-atomic emission spectrometer. Dextran sulfate and DEAE-dextran induced a large amount of hepatic zinc-thionein dose-dependently, while Dextran T500 did not induce metallothionein substantially at the doses studied 20, 40 and 60 mg/kg body wt). The injection of dextran sulfate resulted in a significant increase of spleen weight, with a transitory increase of calcium concentration in the three tissues and a significant decrease of iron level in the spleen. In accord with the induction of zinc-thionein by dextran sulfate and DEAE-dextran, zinc concentration in the liver also increased transitionally after both injections and the time-course of the hepatic zinc level in dextran sulfate showed a close resemblance to that of the calcium one.

Animals↗

PubMed1980

An assessment of the potential use of anionic dextrans as a plasma substitute.

Several problems exist when dextrans are used as plasma substitutes. High molecular weight dextrans can cause red cell aggregation and increased blood viscosity. Low molecular weight dextrans, although shown to improve circulation and promote flow, are removed rather rapidly from the circulation due to high premeation rates across capillary walls. In the present study, a small anionic charge is introduced onto the dextran to make it electrostatically negative. Since capillary walls have been shown to retain negatively charged solutes in preference to neutral solutes, the anionic dextran should retain its effectiveness for longer periods of time compared to similar sized neutral dextran. Studies were done on eight unanaesthetized dogs to compare the relative disappearance rates of dextran and anionic dextran (carboxymethyl dextran) from the circulation. It was shown that anionic dextrans do remain in the circulation over a longer period of time compared to neutral dextrans.

Animals↗

PubMed2002

Agarose-dextran gels as synthetic analogs of glomerular basement membrane: water permeability.

Novel agarose-dextran hydrogels were synthesized and their suitability as experimental models of glomerular basement membrane was examined by measuring their Darcy (hydraulic) permeabilities (kappa). Immobilization of large dextran molecules in agarose was achieved by electron beam irradiation. Composite gels were made with agarose volume fractions (phi(a)) of 0.04 or 0.08 and dextran volume fractions (phi(d)) ranging from 0 to 0.02 (fiber volume/gel volume), using either of two dextran molecular weights (500 or 2000). At either agarose concentration and for either size of dextran, kappa decreased markedly as the amount of dextran was increased. Statistically significant deviations from the value of kappa for pure agarose were obtained for remarkably small volume fractions of dextran: phi(d) > or = 0.0003 for phi(a) = 0.04 and phi(d) > or = 0.001 for phi(a) = 0.08. The Darcy permeabilities were much more sensitive to phi(d) than to phi(a), and were as much as 26 times smaller than those of pure agarose. Although phi(d) was an important variable, dextran molecular weight was not. The effects of dextran addition on kappa were described fairly well using simple structural idealizations. At high agarose concentrations, the dextran chains behaved as fine fibers interspersed among coarse agarose fibrils, whereas, at low concentrations, the dextran molecules began to resemble spherical obstacles embedded in agarose gels. The ability to achieve physiologically relevant Darcy permeabilities with these materials (as low as 1.6 nm2) makes them an attractive experimental model for glomerular basement membrane and possibly other extracellular matrices.

Biophysical Phenomena↗