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.

A fucan sulphate found in brown marine algae (Phaeophyta-typically Fucus serratus, Ascophyllum nodosum, Laminaria digitata (illustrated) and Macrocystis pyrifyra) and has been shown to have anticoagulant activity. The main constituents are α-1,4 and α-1,2 linked L-fucose sulphates although galactose also occurs and there are many variations of the basic structure found in different species of Phaeophyta.
The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.

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.

Lichenin, the poly β-D-Glucan of Cetraria islandica (Iceland moss), is found by enzymic degradation to differ in fine structure from the poly β-D-glucans of cereal grains. Thus, the basic structure of lichenin is a tetrameric unit in which two adjacent 1,4 linkages alternate with an isolated 1,3 linkage; occasionally four consecutive monomers are linked by 1,4 bonds. The immunomodulatory activity of isolichenan was tested in in vitro phagocytosis and anti-complementary assays, and proved to be active in both cases.
The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.

Chitosan is the deacetylated form of chitin.  The polysaccharide is deacetylated in order to render it soluble, which is then possible at pH values of less than 7 (normally in dilute acid).  This then allows the material to be used in a number of industrial applications as a binder and film former.

Hydroxypropyl methylcellulose (HPMC or hypromellose) is a semisynthetic, inert and viscoelastic polymer that is used as eye drops and as semi-synthetic substitute for tear-films. When applied, a hypromellose solution acts to swell and absorb water, by increasing the thickness of the tear-film, resulting in decreased eye irritation.  In addition to its use in ophthalmic liquids, hypromellose has been used as an excipient in oral tablet and capsule formulations, where, depending on the grade, it functions as controlled-release agent. It is also used as a binder and as a component of tablet coatings.  Hypromellose in aqueous solution, unlike methylcellulose, exhibits thermal gelation properties. HPMC is approved as a food additive, emulsifier, thickening and suspending agent, and as an alternative to animal gelatin (Codex Alimentarius code (E number) is E464).