University  of  Nottingham    

School  of  Biosciences          

POLYSACCHARIDE  BIOTECHNOLOGY  ESSAY            

MODULE:  D24BT5  -­  POLYSACCHARIDE  AND  DRUG  DELIVERY  BIOTECHNOLOGY  

 MODULE  CONVENOR:  Stephen  E.  Harding  

     

Applied  Biopharmaceutical  and  Biotechnology  Entrepreneurship      

Student  ID:  4222466    

                   

       

April  29,  2015  

Introduction   The industrial impact of the polysaccharides in industrial applications is incredible important due to the possible applications. The wide possible applications of these water-soluble carbohydrate polymers are due to their physical and chemical properties. Chief among polysaccharide characteristics is their rheological properties this means the capability to modify the aqueous environment in where they are, they can form gels, films and membranes, they also can thicken, emulsify, chelate, stabilize, flocculate, suspend and swell. Polysaccharides are non toxic natural polymers obtained from renewable sources, other important features is their biocompatibility and biodegradability coupled with the wide availability and usually low cost there are an increasing use and exploitation in the formulation of products from biomedical, food and cosmetic industries. With polysaccharides one can have rod shape molecules like alginates, xanthans, and chitosans, polyanions such as alginate pectins, carrageenans, xanthans and hyaluronic acid, linear random coil type structures like dextrans and pullulans, branched structures like glycogen and amylopectin, neutral structures as guar, pullullan and dextran and finally also polycations as dextrans derivatives and chitosans. All of these molecules harvestable at low cost in large quantities (Harding et. Al 2002). At present many polysaccharides are used in non-modified or modified composition, despite their homopolymer block constitution they can form defined structures, even these simple structures can be further developed to create new polysaccharides, the modifications will enhance the capabilities of the actual industrial available polymer forms to serve pharmaceutical needs as carriers for controlled drug release. In the form of micro and nanoparticles, polysaccharides have been found to be useful in many diseases in different parts of the human body. There are a number of examples of micro and nanoparticles based on polysaccharides applied in the fields of ophthalmic, respiratory, renal, cardiovascular, digestive, immunologic diseases, cancer therapy, neurologic and endocrine pathology8. Carbohydrates containing dendrimers in biomedical applications are reviewed to underline their implications in drug and gene deliveries, synthetic vaccines and prevention of pathological processes caused by bacteria and viruses. Two main approaches of glycodendrimer syntheses - convergent and divergent - are described. Since glycopeptide dendrimers suppress lectin-carbohydrate interactions, glycodendrimeric libraries provide potent inhibitors of bacterial adhesion and biofilm formation. These and further applications is the main reason why I consider that polysaccharides are really complex substances with a broad application in industry and medical area, I will discuss further the issue and compare the feasibility and economic cost of production of cellulose, pectin, alginate, chitosan, cyclodextrins and pullulan polysaccharides.

Structural polysaccharides Cellulose is the world’s most abundant natural polymer with an estimated annual global production and decomposition of about 1.5 × 1012 t, which is of the same order as the finite reserves of the most important fossil and mineral resources. A versatile structuring of cellulose by mechanical and chemical modifications has led to its use in a number of applications.

The cellulose molecule consists of glucose units linked by β-1,4-glycosidic bonds. The glucose structure is a D-glucopyranose ring in 4C1-chair configuration, which exhibits the lowest energy conformation (Appendix 1).

In microbial fermentations, the cost of substrates normally accounts for up to 50–65 % of the total cost of production. BC production is not the exception, and thus in recent years much work has been devoted to find new low cost carbon sources. Recently, Castro et al. (2011) produced BC microfibrils (2.8 g/l of medium) from non-conventional sources such as pineapple peel juice and sugarcane juice by use of a strain from Gluconacetobacter swingsii sp. studied the feasibility of using low quality date syrup—a fruit largely produced in the hot arid regions of Southwest Asia and North Africa—, for the production of BC using G. xylinus, obtaining a yield of 43.5 g/l of fermentation medium.

Pectin are polymer of galacturonic acid linked by α(1-4) linked bonds and where the carboxil groups are methylated to varying degree. The linear galactoronan chain also contains a number of rhamnose residues throug α(1-2) links impose a bend in the chain (Appendix1). Commercial pectin is extracted from citrus, apple, or other higher plants, and is used as mentioned in the table. Pectin can be classified into natural pectin with a high molecular mass (Mm) or low Mm modified pectin according to the processing methods. Unextracted natural pectin found in fruits and vegetables is a food component, as well as a soluble dietary fiber (DF). DF is defined as a polysaccharide or resistant oligosaccharide with molecular masses ranging in the hundreds of kilo Daltons (kDas). Some commercial pectins are also designated as DF, suggesting their structures are similar to unextracted pectin. DF cannot be digested in the gastrointestinal tract; however, it can be degraded and fermented by colonic microbiota, which is helpful for reducing the risk of colon cancer (Wicker et . al, 2014).

Marine polysaccharides Alginates are isolated from brown seaweed using dilute alkaline extraction. The resulting solutions are treated with mineral acids and are subsequently converted to sodium alginate. Alginic acid is a linear polymer consisting of D-mannuronic acid and L-guluronic acid residues (Appendix 1). Alginic acid forms a high-viscosity acid gel in the presence of water, which is attributed to the hydration of the polymer chain and intermolecular hydrogen bonding. Alginate polymers form gelsin the presence of divalent and multivalent cations (except Mg2+) by cross-linking of the carboxylate groups on the polymer backbone (Tonnesen and Karlsen, 2002). Positively charged proteins (e.g., TGF b1) can react with the carboxylic acid groups of the alginates, which may result in protein denaturation. To prevent loss of activity, additives such as polyacrylic acid are often used. The protection of the protein has been attributed to the shielding effect of the polyacrylic acid from the low molecular fragments of the alginates (Mumper et al., 1994). Amsden et al. (1999) reported that protein diffusion was highest in alginate gels prepared from alginates with a low guluronic acid fraction, which was associated with greater flexibility of the alginate backbone. Chitin is a polysaccharide found in the outer skeleton of insects, crabs, shrimps and lobsters, whereas chitosan is deacetylated chitin. Chitin resembles cellulose in structure, but it has an

acetamid group instead of a hydroxyl group att he C-2 position of the backbone polymer chain. It is composed of 2-acetamido-2-deoxy-b-D-glucose attached with b (1/4) linkages (Appendix1) and is degraded by chitinase (Ravi Kumar,2000). To improve solubility, it is necessary to deacetylate chitin by 80–85% or higher, they’re by yielding chitosan. With further de acetylation, enhanced solubility is achieved. Both chitin and chitosan are biocompatible, biodegradable, non-toxic and have good adsorption properties, which make them suitable for various drug delivery applications. Chitosan is one of the few cationic polyelectrolytes found in nature (Takayanagi and Motomizu, 2006). Chitin and chitosan vary in composition depending on the origin and manufacturing process. Their use has been limited due to the relatively laborious isolation process, which can increase production costs.

Microbial polysaccharides Pullulan is a commercially available polysaccharide purified from the fermentation medium of the fungus-like yeast Aureobasidium pullulans . It was first described by Bauer in 1938 and its structure was investigated by Bender and coworkers and Wallenfels and co-workers, who named it pullulan. Hayashibara Company (Okayama, Japan) started its commercial production in 1976 and pullulan films were available in 1982. Pullulan has no carcinogenic, mutagenic and toxicological activities. Pullulan films are considered as edible packaging and have applications in food industry. As a biodegradable and biocompatible biopolymer, pullulan has achieved wide regulatory acceptance with its proven safety record. In the United States, pullulan has ‘Generally Regarded As Safe’ status. Pullulan is a unique biopolymer with many properties and hundreds of patented applications; however, its commercial underdevelopment might be due, in large part, to its relatively high price. A number of reviews on pullulan have been published in the last 15 years and we will mainly focus on the biomedical applications of pullulan after a brief introduction of its structure and rheological properties Cyclodextrins are truncated cone shaped oligosaccharides derived from starch, containing six or more α-D- glucopyranose units linked α-1,4 bonds8. They are termed α-cyclodextrins if the number of sugar units is six, β-cyclodextrins if they are seven and if its eight they are known as γ-cyclodextrins1 as shown in Appendix 1. Cyclodextrins molecule are hydrophilic on the outside but they conformation make them less hydrophilic on the inside due to the carbons and the acetal groups of the sugar units predominantly being located here. This local environment is favourable for complexation of poorly water-soluble drugs, hence improving their solubility, cyclodextrins complexes of drugs can be used to formulate poorly water-soluble drugs as solutions but also oral dosage forms including tablets and capsules8.

Polysaccharide Industrial applications Production cost

Chemical enzymatic

modification

Cellulose

Filler in building and coating materials, and for laminates, papers, textiles, optical films, sorption media, viscosity regulators and advanced functional materials for biomedical devices and enantioselective chromatography.

US $1500-1850 / Metric Ton

Yes

Pectin Stabilizer, thickener, gelling agent, emulsifier, and drug vehicle in the food and pharmaceutical industries

10 USD per kg Yes

Alginate Encapsulate drugs in microcapsules or for matrix-type drug delivery systems, gelling agent

US$12 per kg Yes

Chitosan Biomedical devices, gelling agent, wound-healing agent and a delivery vehicle for pharmaceuticals and genes

US $10 to $1,000 per kilogram depending on product quality

Yes

Pullulan

Filler for low-calorie food and beverages, in manufacturing for the production of adhesives, cosmetics, binders, thickeners and coating agents, in electronics and optics where it is used because of its film and fibre forming properties, in chromatography as a molecular weight standard and in pharmaceuticals. Similar to dextran, pullulan can be used as a plasma expander

US $30-120 / Kilogram

Yes

Cyclodextrins Increasing bioavailability, Cholesterol free products, Multifunctional dietary fiber, drug encapsulation

5 USD per kg. Yes

Table 1: Properties of Polysaccharides

Conclusions  Although synthetic polymers are used more extensively in the field of drug delivery, biopolymers and their derivatives are rapidly gaining in importance. This is mainly due to their intrinsic properties that render the appealing. In general, they are non-carcinogenic, muco adhesive, biocompatible and biodegradable. For example, chitosan has been used in oral and nasal delivery systems, where the muco adhesive property of the polymer plays an important role. Furthermore, the properties of the biopolymers can be tailored via chemical modification to further expand their functionality. For example, sodium carboxymethylcellulose has been used as a viscosity-building agent and as a binder in pharmaceutical formulations but does not show pH-dependent swelling behaviour. However, when it is esterified with acrymethacrylol chloride, it shows pH-dependents welling and becomes insoluble in water. Along with being biocompatible and non-carcinogenic, biopolymers are also ideal candidates for the development of matrices for tissue engineering and wound dressings, developed transparent starch hydrogels for use as a wound dressing. In tissue engineering, researchers are physically entrapping growth factors with in biopolymer matrices for the development of specific cells and tissues. In closing, the importance of biopolymers in the development of matrices for the controlled release of drugs and other bioactive compounds will continue to increase. Other than developments in the biomedical and pharmaceutical industries, it is likely that biopolymer usage will see rapid growth in the areas of cosmetology and nutraceutical delivery.

References

1.   Amsden, B. and Turner, N. (1999). Diffusion characteristics ofcalcium alginate gels. Biotechnol Bioengineering 65 (5),605–610.

2.   Annal, A. K., Bhopatkar, D., Tokura, S., Tamura, H., andStevens, W. F. (2003). Chitosan-alginate multilayer beadsfor gastric passage and controlled intestinal release ofprotein. Drug Development and Industrial Pharmacy 29,713–72.

3.   Brewster M E, Loftsson T (2007) Cyclodextrins as pharmaceutical solubilisers. Adv Drug Delivery Review 59: 645-666.

4.   Castro, Cristina, et al. "Structural characterization of bacterial cellulose produced by Gluconacetobacter swingsii sp. from Colombian agroindustrial wastes." Carbohydrate Polymers 84.1 (2011): 96-102.

5.   Kasapis, Stefan Norton, Ian T. Ubbink, Johan B. (2009). Modern Biopolymer Science - Bridging the Divide between Fundamental Treatise and Industrial Application. (pp. 595-604). Elsevier.

6.   Harding, Stephen E., and Gary G. Adams. An introduction to polysaccharide biotechnology. CRC Press, 2002.

7.   Mumper, Russell J., et al. "Calcium-alginate beads for the oral delivery of transforming growth factor-β 1 (TGF-β 1): stabilization of TGF-β 1 by the addition of polyacrylic acid within acid-treated beads." Journal of Controlled Release 30.3 (1994): 241-251.

8.   Perrie, Y., & Rades, T. (2012). FASTtrack-Pharmaceutics-: Drug Delivery and Targeting. Pharmaceutical Press.

9.   Ravi Kumar MNV (2000). A review of chitin and chitosanapplications. Reactive and Functional Polymers 46 (1), 1–27.Reverchon, E. and Antonacci, A. (2006). Chitosan micropar-ticles production by supercritical fuid processing. Indus-trial & Engineering Chemistry Research 45 (16), 5722–5728.

10.  kayanagi, T. and Motomizu, S. (2006). Chitosan asCationic Polyelectrolyte for the Modifcation of Electro-osmotic Flow and Its Utilization for the Separation ofInorganic Anions by Capillary Zone Electrophoresis.Analytical Sciences 22 (9), 1241–1244.

11.  Tønnesen, Hanne Hjorth, and Jan Karlsen. "Alginate in drug delivery systems." Drug development and industrial pharmacy 28.6 (2002): 621-630.

12.  Wicker, Louise, et al. "Pectin as a bioactive polysaccharide–Extracting tailored function from less." Food Hydrocolloids 42 (2014): 251-259.

13.  Z.M. Chi and S.Z. Zhao, Enzyme and Microbial Technology, 2003, 33, 2/3, 206

Appendix 1: Polysaccharides structures.  

Schematic representation of a cellulose molecule          

  Diagram of MP structure. MP has a less complex structure with shorter side-chains and a lower DE in contrast to natural pectin. Undefined structures may occur during modification. GS, such as RG-II and XGA, is thought to be significantly reduced.

Chemical structure of alginic acid

Chemical structure of (a) chitin and (b) chitosan

Schematic structure of pullulan. The monomer of pullulan is anhydroglucose. The numbers depict the position of the carbon atoms as defined by the nomenclature of carbohydrates

Chemical structures of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin, the three-dimensional shape of each molecule and cavity diameter are also shown.