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.

Porphyran is an agar-like polysaccharide with a linear backbone consisting of 3 linked β-D-galactosyl units alternating with either 4-linked α-L-galactosyl 6-sulphate or 3-6-anhydro-α-L-galactosyl units.The composition includes 6-O-sulphated L-galactose, 6-O-methylated D-galactose, L-galactose, 3,6-anhydro-L-galactose, 6-O-methyl D-galactose and ester sulphate. Some of the ester is present as 1,4-linked L-galactose 6-sulphate. The precise composition of porphyran shows seasonal and environmental variations. Porphyran is not used commercially, but the seaweed, Porphyra umbilicalis, is edible and is consumed in Wales (Laver). It is also made into a delicacy called Laverbread. The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.

Chondroitin sulfate A sodium salt is a glycosaminoglycan that is derived from chondroitin. It is a complex carbohydrate with a high molecular weight and an average MW of 10,000 to 50,000 Da. The synthesis of the monosaccharide units in chondroitin sulfate A sodium salt occurs by Methylation, Click modification, Polysaccharide, or Fluorination. Chondroitin sulfate A sodium salt can be custom synthesized according to customer specifications and can be ordered as a CAS No. 39455-18-0 with high purity.

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.

Laminaran is a polysaccharide that co-occurs with fucoidan and alginate in brown seaweeds such as Laminaria digitata, Laminaria cloustoni, Eisenia bicyclis and Thallus laminariae. It is a β-1,3-linked glucan which it is claimed stimulates the immune system in mammals and fish. The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.

Laminaran is a polysaccharide that co-occurs with fucoidan and alginate in brown seaweeds such as Laminaria digitata, Laminaria cloustoni, Eisenia bicyclis and Thallus laminariae. It is a β-1,3-linked glucan which it is claimed stimulates the immune system in mammals and fish. The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.

Isolichenan is a cold-water soluble (1,3)-(1,4)-α-D-glucan isolated from lichen Cetraria islandica to have MW of about 6-8 kDa. Lichens produce isolichenan-type polysaccharides with considerable variation in linkage ratios as well as MW, even within the same species. Occasionally these α-glucans can be branched at O2, O3 or O6. The immunomodulating 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’.

Sodium polymannuronate is produced from alginates by partial hydrolysis and chromatography of brown algae such as Laminaria digitata, Ascophyllum nodosum and Fucus spp. The image was kindly provided by Prof Mike Guiry from Cork who runs ‘The Seaweed Site’.

Chondroitin sulphate is the most abundant glycosaminoglycan in mammalian tissues and occurs both in skeletal and soft connective tissue. The disaccharide repeat unit consists of N-acetyl galactosamine sulphate linked β1,4 to glucuronic acid.

In their simplest forms, xylans are linear homopolymers of β-1,4-xylose residues. In nature they are partially substituted by acetyl, 4-O-methyl-D-glucuronosyl and α-1,3 L-arabinofuranosyl residues, forming complex heterogenous and polydispersed glycans. An example of this is in the L-arabino (methyl-D-glucurono) xylan from corn cob.

Low calcium heparin is a glycosaminoglycan, which occurs in many mammalian tissues and has important anticoagulant and thrombolytic properties. The chemical structure is composed mainly of two disaccharide repeating units A and B. A is L-iduronic acid 2-suplhate linked α-(1,4) to 2-deoxy-2-sulfamido-D-galactose 6-sulphate, while B is D-glucuronic acid β-(1,4) linked to 2-deoxy-2-sulfamido-D-glucose 6-sulphate.

In addition to the β-glucans from cereals, another group of β-glucans are found in the cell walls of yeast (Saccharomyces cerevisiae), bacteria and fungi, with significantly differing physicochemical properties dependent on source. Typically these β-glucans form a linear backbone with 1,3 β-glycosidic bonds but vary with respect to molecular mass, solubility, viscosity, branching structure, and gelation properties, causing diverse physiological effects in animals.  They are structural components in the cell walls of Saccharomyces cerevisiae and to provide stability, they have a few b-1,6 branch points that lock into other cell wall components (1 in 5 glucose residues). So in any extraction you get a few 1,6 linked glucose residues ~5%. The yeast and fungal β-glucans have been investigated for their ability to modulate the immune system. They are also used in various nutraceutical and cosmetic products, as texturing agents, and as fibre supplements. Their detailed molecular structures are key to the physical properties that they exhibit, such as water solubility, viscosity, gelation properties and physiological functions. The image was kindly provided by Dr. Chris Lawson.

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.

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 (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 has many similarities to human inflammatory bowel disease.

Dextran is α-(1,6)-linked α-D-glucan with α-(1,3)-linked glucose branch points produced by fermentation of Leuconostoc mesenteroides via the action of the enzyme dextransucrase on sucrose.  The main use for native dextran is as an extender in blood transfusions and products having a range of sharp cut-off molecular weights are produced commercially for this and other applications.  A complex of Iiron with dextran, known as iron dextran, is used as a source of iron for baby piglets which are often anaemic at birth.

Gycosaminoglycan in many organs; joint lubricant and shock absorber

Welan gum is a microbial polysaccharide produced by a species of Alcaligenes and shows interesting rheological properties of use in the oil and agricultural industries. The structure is similar to gellan based on repeating glucose, rhamnose and glucuronic acid units but with a single side chain of either an α-L-rhamnopyranosyl or an α-L-mannopyranosyl unit linked (1,3) to the 4-O-substituted β-D-glucopyranosyl unit in the backbone.

Amylopectin is composed of between 2,000 to 200,000 glucose residues linked α (1→4) with α (1→6) branching. The molecule is highly branched, every 24 to 30 glucose units, resulting in a soluble molecule with many terminal residues. Starch is made of about 70% amylopectin by weight, though it varies depending on the source (higher in medium-grain rice to 100% in glutinous rice, waxy potato starch, waxy corn, and lower in long-grain rice, amylomaize, and russet potatoes).