Polysaccharides

Dextran sulphate is a dextran derivative whose ulcer (colitis) -causing properties were first reported in hamsters and extrapolated a few years later to mice and rats. The exact mechanisms through which dextran sulphate induces intestinal inflammation are unclear but may be the result of direct damage of the monolayer of epithelial cells in the colon, leading to the crossing of intestinal contents (for e.g. commensal bacteria and their products) into underlying tissue and therefore induction of inflammation.  The dextran sulphate sodium-induced ulceration model in laboratory animals has some advantages when compared to other animal models of colitis due to its simplicity and similarities to human inflammatory bowel disease.  MW is in the range of 40,000Da

Starch is an energy storing polysaccharide produced by higher plants and some algae. Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol. It consists of two types of polysaccharide: the linear and helical amylose (α-1,4-linked glucose) and the branched amylopectin (α-1,4 and α-1,6-linked glucose). Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin by weight.

Xylan is the most abundant noncellulosic polysaccharide present in both hardwoods and annual plants. Xylan is found mainly in the secondary cell wall as part of the hemicellulose fraction and is considered to form an interface between lignin and other polysaccharides. In their simplest forms, xylans are linear homopolymers of β-1,4-xylose residues but can also form complex heterogenous and polydispersed glycans.

Glycogen is a highly branched polysaccharide of glucose that serves as a form of energy storage in animals and fungi. It is the main storage form of glucose in the body.  In humans, glycogen is made and stored primarily in liver and muscle cells and functions as the second most important energy storage molecule to fat which is held in adipose tissue. Glycogen is analogous to starch and has a structure similar to amylopectin, but is more extensively branched and compact than starch. It occurs as granules in the cytosol/cytoplasm in many cell types, and plays an important role in the glucose cycle.

In water, hydroxypropyl cellulose forms liquid crystals with many mesophases depending on concentration. These mesophases include isotropic, anisotropic, nematic and cholesteric, the latter resulting in many colors such as violet, green and red. Pharmaceutical applications include treatments for medical conditions such as dry eye syndrome (keratoconjunctivitis sicca), recurrent corneal erosions, decreased corneal sensitivity, exposure and neuroparalytic keratitis. It is also used as a binder in tablets. Hydroxypropylcellulose is also used as a thickener, a binder and emulsion stabiliser in foods with E number E463.  HPC is used as a support matrix for DNA separations by capillary and microchip electrophoresis.

Starch consists of two polysaccharides, amylose and amylopectin and represents approximately 20-25% of the total polysaccharide content in starch. Amylose molecules consist of single mostly unbranched chains of 500-20,000 α-(1->4)-D-glucose residues dependent on source (e.g. wheat, rice, potato, tapioca, etc). Amylose can form an extended shape (hydrodynamic radius 7-22 nm) but generally tends to wind up into a rather stiff left-handed single helix or form even stiffer parallel left-handed double helical junction zones. Hydrogen bonding between aligned chains causes retrogradation and releases some of the bound water (syneresis). The aligned chains may then form double stranded crystallites that are resistant to amylases. These possess extensive inter- and intra-strand hydrogen bonding, resulting in a fairly hydrophobic structure of low solubility. The amylose content of starches is thus the major cause of resistant starch formation.

Cellulose is a linear polysaccharide of β 1-4 linked glucose residues. The polysaccharide chains are bundled as microfibrils in cell walls and provide the essential structural components within growing plants. Each microfibril exhibits a high degree of three-dimensional internal bonding resulting in a crystalline structure that is insoluble in water, resistant to reagents and very strong.

A linear polyuronide obtained from the brown seaweeds (e.g. Laminaria hyperborea, Fucus vesiculosus, Ascophyllum nodosum). In the free acid form, the chemical structure consists of protonated blocks of (1,4) linked-β-D-polymannuronic acid (poly M), (1,4) linked-α-L-polyguluronic acid (poly G) and alternating blocks of the two uronic acids (poly MG).

Psyllium seed gum comes from plants of the Plantago genus and is cultivated mainly in the Mediterranian and in India. Psyllium has been used for many years medical applications and more recently there has been a resurgency of interest because it has been seen as a soluble dietary fibre. The proposed structure is of a backbone of D-xylopyranosyl units linked (1,4) and (1,3) with the 4-linked units bearing side chains. The side chains consist of α-L-arabinofuranosyl units linked (1,3) and (1,2) and β-D-xylopyranosyl units linked (1,3) and (1,2) and the α-D-GalAρ-(1,2)-α-L-Rhaρ aldobiuronic acid units linked (1,2) to the main chain.

Porcine mucosal heparin derivative; no anti-coagulant activity

Arabinoxylans consist of α-L-arabinofuranose residues attached as branch-points to β-(1,4)-linked D-xylopyranose main chains. These may be 2- or 3-substituted or 2- and 3- di-substituted. The arabinose residues may also be linked to other groups attached such as glucuronic acid residues, ferulic acid cross links and acetyl groups. Arabinoxylans generally consist of between 1500 - 5000 residues.