Dextran

Description

Dextran, a glucose polymer composed predominantly of ol-1,6-glucopyranosidic linkages, is produced from sucrose by Leuconostoc mesenteroides and related organisms and from dextrins by other bacteria.
Dextran is used in a bead form to aid in bioreactor applications, some size-exclusion chromatography matrices and in osmotic stress technique study involved in biological molecules. It can be used as a stabilizing coating to protect metal nanoparticles from oxidation.
Dextrans are long-chain glucose polysaccharides of various relative molecular masses. Dextran 70 (relative molecular mass 70 000) is retained in the intravascular space where, like albumin, it contributes to the colloid oncotic pressure of plasma. Unlike albumin, dextran 70, when given in large amounts, prevents platelet aggregation and facilitates fibrinolysis.

Dextran Structure

Dextran is an α-D-1,6-glucose-linked glucan with side-chains 1-3 linked to the backbone units of the Dextran biopolymer. The degree of branching is approximately 5%. The branches are mostly 1-2 glucose units long.
Dextran can be obtained from fermentation of sucrose-containing media by Leuconostoc mesenteroides B512F.
A fragment of the Dextran structure is illustrated in Figure 1.

Fig. 1: Dextran is a glucose polymer in which the linkages are predominantly of the α(1,6) type. The degree of α(1,3) branching is generally less than 5% and decreases with decreasing molecular weight

History

In the early 1940's, at the same time as Stacey and his associates in Birmingham were studying bacterial dextrans and Hehre and colleagues in the USA were pursuing the dextran producing activity of cell-free extracts of Leuconostoc , a young Swedish biochemist, B. Ingelman, at the Department of Biochemistry and Physical Chemistry, University of Uppsala began probing the polysaccharides and proteins of sugar beet juice.
One of the critical episodes was the discovery of dextran in an infected sample of the juice. This initiated a series of investigations on the polysaccharide. At the end of 1942, a recently qualified M.D., A. Grönwall, joined the laboratory to study tuberculin. Considerable effort was being devoted at the time to the freeze-drying of blood plasma for military medicine. Within the space of months, Ingelman and Grönwall had stumbled on the idea of using a hydrolyzed dextran as a plasma substitute. After studies on the partial hydrolysis, fractionation, and extensive biological studies, a Swedish pharmaceutical company adopted the project in 1943, and later that year, preliminary clinical trials began. In 1944, under the direction of the surgeon, G. Bohmansson, extensive clinical trials were started at the Regional Hospital in Örebro. The dextran used at that time was derived from Leuconostoc mesenteroides , strain 7E, and was slightly more branched than the present one. By 1947, about four years after the innovation, a 6% solution of a dextran fraction had been approved for clinical use in Sweden and, shortly thereafter, in the U.K., an achievement that would be inconceivable under the present regulatory climate.The product was gradually improved and was designated Dextran 70. Samples of the Swedish product were soon tested clinically in the USA.
Dextran 70 is generally marketed as a 6% solution in normal saline and as such continues to maintain its position worldwide as the plasma volume expander of choice. It is recommended for the treatment of shock or impending shock due, for example, to hemorrhage, burns, surgery or trauma. Dextran 70 also reduces the risk for thrombosis and numerous studies testify to its value in significantly reducing the risk of post-operative fatal pulmonary emboli.

Uses

1. The demand for technical dextrans from industry has shown a significant increase in the past decade. Since household sucrose, fruits or fruit beverages could be contaminated with traces of dextrans, ingestion of dextrans, albeit in small amounts, may not be uncommon. Dextran is degraded by dextran-splitting bacteria in the human gut and most of the hydrolysis products can be absorbed to produce a rapid increase in blood sugar and liver glycogen
2. However, in the food industry, where innumerable applications of dextrans in foodstuffs were patented in the 50's and 60's, no application appears to have been pursued and the mandatory toxicological studies to gain FDA approval were not performed. Hence in 1977, the GRAS (generally recognized as safe) status of dextrans was deleted. Dextrans are not permitted in the UK or Europe as foodstuff additives, and dextrans do not seem to have been considered by the Joint FAO/WHO Expert Committee on Foodstuff Additives (JECFA). Dextrans are, however, considered as safe as components of food packaging materials.
3. Dextran fractions do not appear to be included in the lists of permitted additives (ingredients) for pharmaceutical formulations such as ointments and creams for topical use and tablets and capsules for oral use. However, providing the appropriate documentation is presented, there are no a priori reasons why they may not be used. Indeed several products in which a dextran fraction is used as a non-active ingredient are on the market.
4. Purified dextran fractions with high clarity and low chloride levels find extensive applications in the photographic industry. Addition of low concentrations of dextran to the silver emulsion is found to enhance significantly the quality of the images. The effect is presumably attributable to the effect of dextran on the conformation of the gelatin molecules.
5. Since Albertsson revealed the enormous potential of 2-phase polymer systems, especially dextran-PEG systems, for the partition of sub-cellular particles and macromolecules, an immense number of applications has evolved. These systems offer a means of fractionation beyond the range of conventional techniques. Some recent applications are: the separation of peripheral blood cells, distinguishing erythrocytes from multiple sclerosis patients, the separation of enzymes, for example pullulanase, from Klebsiella pneumoniae cells, and the partitioning of murine lymphoblasts.
6. Dextran has been recommended as a cryoprotective agent for human, animal and plant cells. Thus a mixture of 5% methyl sulphoxide and 9% Dextran 70 was found to afford optimal cryoprotection of human bone marrow committed stem cells.
7. The effect of dextrans as adjuvants for prolonging local anesthetic block has been a matter of some debate. Early results had proved somewhat contradictory. Recent reexamination by Hassan and colleagues has revealed that the prolongation of the effect of anesthetic is dependent on the anesthetic used, the MW of the dextran, and the type of dextran derivative used. A prolongation of up to 350% has been obtained.

Specification

Dextran 70 powder Pharmaceutical grade (for injections)

Diverse Applications

1. Dextran has traditionally been used in infusion fluid and volume expander products. However, dextran has a very diverse application area ranging from vaccines over ophthalmic use to stabilizer of biological components. Some of the uses in life sciences.
2. Vaccines: Dextran can be part of vaccines as a carrier, a back-bone and/or as a stabilizer of the antigen or other subunits. Derivatives of dextran in particular DEAE-dextran are often also used.
3. Eye Drops or Similar Solutions: Dextran is often used in eye drops or similar solution for ophthalmic application. Dextran can be used as the active ingredient in eye drops due to its lubricating nature or as tear-replacement. This application is used to relieve dry, irritated eyes. Common causes for dry eyes include wind, sun, heating/air conditioning, computer use/reading, and certain medications. Furthermore dextran can also be used in eye drops with a medicating component.
4. Protein Stabilization: The dextran molecule is known to benefit on structural stability of freeze-dried products, protein stability and the recovery of enzyme activity after freeze-drying.
5. Excipient in Lyophilization (freeze-drying): Lyophilization is a commonly used technique for formulation development of small molecules, proteins and vaccines which are unstable in aqueous medium and/or are thermolabile in nature. Lyophilization of drug alone, however, presents certain formulation development challenges, which may be overcome by incorporation of excipients in the formulation. Dextran is often used as excipient during lyophilization as a bulking agent and/or a collapse temperature modifier.
6. Cryo-Protectant: Dextran can be used as a cryo-protectant in combination with DSMO, glycerol etc. Dextrans can be used to cryo-preserve cell lines, stem cell preparations and biological samples in general. It is believed these cryo-protectants contributes to a more controlled formation of ice crystals which leads to lesser damage to cell membranes and organelles.
7. Storing Organs for Transplantation: Dextran is widely accepted as solution for storing and preparing organs for transplantation. Traditionally Corneas has been stored and/or prepared for transplantation dextran, but now a multitude of different organs and tissues are being stored in dextran solution for increased longevity or dextran are used in preparation prior to transplantation.
8. Oral Products: Dextran has a wide use in oral pharmaceuticals. Dextran is applied for solidity and consistency of substance during processing e.g. freeze drying. Dextran can also be used to alter the dissolution profile of drug formulations.
9. Blood Cell Separation: Dextran can be applied in the reversible aggregation of human red blood cells, yet the mechanistic details governing the process are still being explored. The process is useful for separation of red blood cells from other cells and components of the blood.
10. Blood Volume Expander: Intravenous solutions with dextran function both as volume expanders and means of parenteral nutrition. Such a solution provides an osmotically neutral fluid that once in the body is digested by cells into glucose and free water.

Production Methods

Dextran for clinical and technical products is produced in most developed countries throughout the world. In the West, most producers use the Leuconostoc mesenteroides NRRL B-512(F) or B-512 strain for the fermentation. In other parts of the world, alternative strains appear to be used.
Most major producers of dextran employ a process based on the batchwise culture of Leuconostoc in the presence of sucrose. The viscous culture fluid is then precipitated in ethanol or methanol, whereafter the native dextran obtained is hydrolyzed in dilute acid and the desired dextran is isolated by fractionation. Although the present state of the art offers alternative methods of producing defined fractions, most producers are still operating a procedure introduced about 35 years ago. In introducing any change, a producer must be convinced that, not only must the new process be more efficient in man-power and materials, but the final product must conform in every respect with the medical requirements for safety and efficacy.
The organism, Leuconostoc mesenteroides NRRL B-512(F), is a member of the Lactobacillaceae family, genus Leuconostoc and species mesenteroides (134). The organism produces spherical or ovoid cells and classifies as a gram-positive facultative anaerobe. Apart from dextran and lactic acid, it produces, inter alia , carbon dioxide, ethanol, mannitol and acetic acid.

Dextran Safety

Dextran has been used in numerous products for human use for decades
Products include both IV, IM, oral, and topical administration. These products have typically been used globally including US and Europe. Examples include Dextran use for plasma volume expansion, in numerous eyes drops, and oral products like Spasfon and Opalmon.
For decades Dextran has had the Generally Recognized As Safe (GRAS) label from the US FDA, which was renewed in 2013. (Link to article).
The established use of dextran through decades of human use in numerous products with different administration forms clearly establishes the low risk profile of Dextran.
This is well known to competent authorities around the world, and it is taken into consideration when the regulatory authorities are establishing their toxicological, preclinical and clinical requirements.

Description

Dextrans are glucose polymers produced by bacteria linked in an α-1,6 chain and having an α-1,3 or α-1,4 branch about every fifth residue. The specific positioning of the branching varies by the bacterium producing it. The molecular weights of these chains generally are 40 or 70 kDa (dextran-40 and dextran-70, respectively), and the compounds work via an osmotic gradient similar to the colloids and hypertonic crystalloid solutions.
Dextrans have a longer intravascular residence time than albumin, which limits interstitial edema. As with the crystalloids and other colloids, the dextrans have no oxygen-carrying capacity. Furthermore, because they are bacterial products, the dextrans have the potential to be potent antigens and induce anaphylaxis.

Chemical Properties

white crystals or powder

Originator

LMD 10%,Abbott,US,1967

Uses

antiinflammatory veterinary drug

Uses

dextran is a polysaccharide with water-binding properties. It is also used to control product viscosity. Some studies indicate a capacity to enhance the anti-aging activity of formulations containing weak acids, as well as to reduce possible skin irritation arising from such acids.

Uses

also available in pharma grade

Uses

exhibit borad spectrum of biological activities, with very low anticoagulant capacity: they activate lipoprotein elimination by lipase stimulation, inhibit cell proliferation in vascular wall, regulate transport of plasmatic proteins and inhibit depositi

Uses

Dextran is a polysaccharide composed of glucose molecules used as an antithrombotic to reduce blood viscosity and as a volume expander in anemia. Studies show that it inhibits the mannose receptor-med iated clearance of tissue-type plasminogen activator (t-PA).

Definition

dextran: A glutinous glucose polymerproduced by certain bacteria. Itcan be made by fermenting sucrose(cane sugar) and is used as a thickeningagent, as a stabilizer in ice cream,and as a substitute for plasma inblood transfusions. Esters with sulphuricacid yield sodium salts thatare employed as anticoagulant drugs.

Manufacturing Process

Sucrose is subjected to the action of the bacterium Leuconosfoc mesenteroides B 512 and the crude, high-molecular weight dextran thus formed is hydrolyzed and fractionated to an average molecular weight of about 40,000 as measured by light-scattering techniques.

brand name

Gentran 40 (Baxter Healthcare).

Therapeutic Function

Plasma extender

General Description

Dextrans are polysaccharides with molecular weights ≥1,000 Dalton, with a linear backbone of α-linked D-glucopyranosyl repeating units. Dextrans are found as bacterial extracellular polysaccharides. They are synthesized from sucrose by Leuconostoc mesenteroides and Lactobacillus brevis. Bacteria employ dextran in biofilm formation or as a protective coating to evade host phagocytes in the case of pathogenic bacteria.
Dextran from Leuconostoc mesenteroides (Mw: 12,000) may be used as an analytical standard to calibrate the column for gel permeation chromatography (GPC).

Biochem/physiol Actions

Dextran is a branched glucan composed of linear a(1→6) linked glucose units and a (1→3) link initiated branches. Dextran ranges in size from 10,000 to 150,000 Kd. Dextrans are used in many applications as volume extenders, stabilizers, matrix components, binding platforms, lubricants and physical structure components.

Mechanism of action

Safety Profile

Suspected carcinogen with experimental carcinogenic data. When heated to decomposition it emits acrid smoke and fumes. See also other DEXTRANS.

Veterinary Drugs and Treatments

Dextran 70 is a relatively low cost colloid for the adjunctive treatment of hypovolemic shock. Hetastarch is the more commonly employed synthetic colloid used today.

Purification Methods

Solutions of dextran keep indefinitely at room temperature if 0.2mL of Roccal (10% alkyldimethylbenzylammonium chloride) or 2mg phenyl mercuric acetate are added per 100mL solution. This inhibits mould growth. [Scott & Melvin Anal Biochem 25 1656 1953.]