Dextran
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2008-07-02T13:12:28Z
Preacherdoc
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/* Laboratory uses */ Corrected capital
{{unreferenced|date=January 2008}}
'''Dextran''' is a complex, branched [[glucan]] ([[polysaccharide]]) made of many [[glucose]] molecules joined into chains of varying lengths (from 10 to 150 [[Atomic mass unit|kilodaltons]]), used as an [[Thrombosis|antithrombotic]] (anti-[[platelet]]), and to reduce blood [[viscosity]].
The straight chain consists of α1->6 [[glycosidic]] linkages between glucose molecules, while branches begin from α1->4 linkages (and in some cases, α1->2 and α1->3 linkages as well). (For information on the numbering of [[carbon]] [[atom]]s in glucose, see the [[glucose]] article.) Dextran is synthesized from sucrose by certain lactic-acid bacteria, the best-known being ''Leuconostoc mesenteroides'' and ''[[Streptococcus mutans]]''. [[Dental plaque]] is rich in dextrans. Dextran is also formed by the [[probiotic]] ''[[Lactobacillus brevis]]'' to create the crystals of [[tibicos]], or water kefir [[fermented beverage]] with reported health benefits.
==Uses==
===Microsurgery uses===
These agents are used commonly by microsurgeons to decrease vascular [[thrombosis]]. The antithrombotic effect of dextran is mediated through its binding of [[erythrocytes]], [[platelets]], and vascular [[endothelium]], increasing their [[electronegativity]] and thus reducing [[erythrocyte]] aggregation and [[platelet]] adhesiveness. Dextrans also reduce factor VIII-Ag [[Von Willebrand factor]], thereby decreasing platelet function. Clots formed after administration of dextrans are more easily lysed due to an altered thrombus structure (more evenly distributed platelets with coarser [[fibrin]]). By inhibiting α-2 antiplasmin, dextran serves as a [[plasminogen]] activator and therefore possesses [[thrombolytic]] features.
Outside from these features, larger dextrans, which do not pass out of the vessels, are potent osmotic agents, and thus have been used urgently to treat [[hypovolemia]]. The hemodilution caused by volume expansion with dextran use improves blood flow, thus further improving patency of microanastomoses and reducing thrombosis. Still, no difference has been detected in antithrombotic effectiveness in comparison of intraarterial and intravenous administration of dextran.
Dextrans are available in multiple molecular weights ranging from 10,000 Da to 150,000 Da. The larger dextrans are excreted poorly from the kidney and therefore remain in the blood for as long as weeks until they are metabolized. Subsequently, they have prolonged antithrombotic and [[colloidal]] effects. In this family, dextran-40 (MW: 40,000 Da), has been the most popular member for [[Anticoagulant|anticoagulation]] therapy. Close to 70% of dextran-40 is excreted in urine within the first 24 hours after intravenous infusion while the remaining 30% will be retained for several more days.
===Other medical uses===
* It is used in some [[eye drop]]s as a lubricant, and in certain intravenous fluids to solubilise other factors, e.g. iron (=iron dextran).
* Dextran in [[Intravenous therapy|intravenous]] solution provides an osmotically neutral fluid that once in the body is digested by cells into glucose and free water. It is occasionally used to replace lost [[blood]] in emergency situations, when replacement blood is not available, but must be used with caution as it does not provide necessary electrolytes and can cause [[hyponatremia]] or other [[electrolyte]] disturbances.
* It also increases [[blood sugar]] levels.
===Laboratory uses===
Dextran is used in the [[osmotic stress technique]] for applying [[osmotic pressure]] to biological molecules.
It is also used in some size-exclusion chromatography matrices; an example is [[Sephadex]]''''''.
Dextran has also been used in bead form to aid in bioreactor applications.
Dextran has been used in immobilization in Biosensors.
Dextran preferentially binds to early [[endosomes]]; fluorescently-labelled dextran can be used to visualize these endosomes under a fluorescent microscope.
Dextran can be used as a stabilising coating to protect metal nanoparticles from oxidation and improve biocompatibility.
==Side effects==
Although there are relatively few side-effects associated with dextran use, these side-effects can be very serious. These include [[anaphylaxis]], volume overload, [[pulmonary oedema]], [[cerebral oedema]], or platelet dysfunction. An uncommon but significant complication of dextran osmotic effect is [[acute renal failure]]. The pathogenesis of this renal failure is the subject of many debates with direct toxic effect on tubules and [[glomerulus]] versus intraluminal hyperviscosity being some of the proposed mechanisms. Patients with history of [[diabetes mellitus]], [[Renal failure|renal insufficiency]], or vascular disorders are most at risk. Brooks and others recommend the avoidance of dextran therapy in patients with [[Chronic kidney disease|chronic renal insufficiency]] and CrCl<40 cc per minute.
==External links==
*[http://www.dextran.net/dextran-properties.html Resource on dextran properties and structure of dextran polymers]
*[http://www.drugdigest.org/DD/DVH/Uses/0,3915,7971%7CDextran,00.html Dextran (Drug Digest)]
[[Category:Biotechnology products]]
[[Category:Polysaccharides]]
[[Category:Intravenous fluids]]
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