What Are Dextrans?

Dextran is a polysaccharide comprised of d-glucopyranose (d-glucose) repeating units linked through glycosidic linkages. It is biocompatible, biodegradable, and presents antithrombotic and anti-inflammatory properties. Dextran functional hydroxyl (–OH) groups offer an easy point for chemical conjugation with other materials. As an example, dextran can be modified with hydrophobic moieties in order to form dextran-based amphiphiles. These amphiphilic materials can encapsulate poorly water-soluble chemotherapeutics through hydrophobic interactions and self-assemble into nanocarriers. What Are the Chemical Structure and Properties of Dextrans? Dextran consists of α(1,6)-linked glucan with side chains attached to the C-3 position of the backbone (Figure 1). It is synthesized from sucrose by certain lactic acid bacteria, such as leuconostoc mesenteroides. The molecular weight of natural dextran has a wide range (9–200 × 106). From periodate and methylation analysis, the degree of branching is estimated to be 5%. Most of the side chains contain one or two glucose units. Dextran exhibits an extendable coil structure in solution, due mainly to its flexible α(1,6)-glycosidic linkage. It has high solubility in water and many organic solvents, such as methyl sulfoxide, formamide, ethylene glycol, glycerol, 4-methylmorpholine-4-oxide, and hexamethylphosphoramide. What Is the Function of Dextran? Dextran is a versatile compound with many clinical applications in medicine, ranging from anesthesiology and surgery to radiology and ophthalmology. In the operating room and intensive care unit settings, dextran is used osmotically as a colloid to treat hypovolemia and/or hemorrhage from trauma, burns, surgeries, or other causes if ABO compatibility tests are not possible in time. Labeled with technetium Tc-99m, clinicians use intravenous dextran during radiographic imaging such as nuclear medicine, MRI, or scintigraphy, and as a contrast agent to detect and diagnose conditions such as ventricular aneurysms and pericardial effusions. Dextran may be employed for its antithrombotic effect to prevent postoperative venous thrombosis. Finally, dextran has several ophthalmic applications as solutions for relieving ocular irritation or xerophthalmia. Outside of medicine, it is used widely in the food and chemical industries. How Are Dextrans Used for Drug Carriers? Dextran is attached to the drug molecules for the formation of a prodrug using various techniques like direct linkage, attachment through intercalated spacer arm, use of modulator ligand and tissue specific receptor ligand. In the direct linkage model of dextran the drug is directly linked to dextran, which will release the active agent in a predictable manner. The regeneration of the parent drug would be exclusively governed by the pH dependent hydrolysis, as the bulky dextran matrix would be inaccessible to enzymatic attack. The active drug is released from the dextran prodrug by the cleavage of the covalent bond existing between drug and the carrier moiety dextran, enzyme or pH. If the drug contains a hydrolyzable chemical bond, it might deteriorate even attached to the polymer backbone. The ability of the bulky dextran molecule to suppress catabolism of the attached drug/enzyme has been exploited extensively.