Collagen

Collagen is the foremost constituent of the extracellular matrix that is abundant fibrous structural protein in all higher entities^[1]. It is mostly found in fibrous tissues such as skin, ligament and tendon in the form of elongated fibrils and is also abundant in cornea, blood vessels, bone, cartilage, intervertebral disc and the gut. These are the most abundant protein in mammals constituting over 30% of the total proteins in animal body^[2]. All proteins that have a structure based on three helix polypeptide chains belonging to the collagen family, being identified 26 types until now^{[10, 11]}. The unique structure of collagen is responsible for its fibrous nature that is very hard to degrade^[3]. Until now, the molecule has been classified in 26 different types that are grouped into eight families depending on its structure, chain bonding, and position in the human body. Among the classifications, it can be found the fibril-forming, basement membrane, microfibrillar, anchoring fibrils, hexagonal network-forming, fibril-associated collagens with interrupted triple helix [FACIT], transmembrane, and multiplexins^[4].

Collagen fibers are commonly white, opaque, and readily recognized in tissues. It is considered as a viscoelastic material that possesses high tensile strength and low extensibility. Its isoelectric point is around pH 5.816; and in terms of temperature, the shrinkage temperature[Ts] of most mammalian fibrils is between 62°C and 65°C, whereas fish fibrils Ts ranges from 38°C to 54°C. On the other hand, the denaturation temperature Tm is less by 25°C 30°C than Ts^[5]. It is known that collagen is a molecule with low immunogenicity, diminishing the possibilities of not being accepted when ingested or injected to a foreign body. The only fractions capable of occasioning immune response are located in the helical region of the chains and in the telo-peptide region^[6]. Even though this molecule has low antigenicity, it can be modified to eliminate any immune response. An alternative can be carried out by the elimination of banded structure through heat or chemical treatment degradation of non-helical section by proteinases or cross-linking^{[7, 8]}.

Three identical or non-identical polypeptide chains form the distinct structure of collagen. Each chain is composed of around 1000 amino acids or more in length in some collagen types^[9]. Super coiling of three polypeptide chains in a left handed manner around a common axis, with staggering of one residue between the adjacent chains leads to a single extended right-handed triple helical conformation. Glycine is the only amino acid that can be accommodated in the interior part of the triple helix without chain distortion. The close packing of three chains around a common axis leads to a steric constraint on every third residue. N, C-telopeptides are the non-helical terminals of triple helix that perform a significant role in the formation of micro-fibril and fibril. The arrangement of amino acids in a unique fashion leads to formation of triple-helical structure of collagen. Glycine is having the smallest side group and is repeated at every third location in the order; it permits close packaging of the chains into a helix and leaves very minute space for residues in the core. In the repeating unit of Gly-X-Y, around 35% of the non-glycine positions are engaged by proline which is almost exclusively found in the X-position while Y-positions are predominantly occupied by 4-hydroxyproline. Prolyl hydroxylase converts proline of into hydroxyproline by post-translational hydroxylation^[10]. Hydroxyproline comprises around 10% of the amino acid composition of collagen that can be readily used for the quantification of collagen or its degraded products in the presence of other proteins^[11]. Along with hydroxyproline collagen also have the presence of unusual amino acid hydroxylysine. Hydroxylysine is formed from lysine by enzymatic hydroxylation through lysyl-hydroxylase; which is exactly similar to the conversion of proline to hydroxyproline. Hydroxylysyl residues provide the attachment of sugar components that is very vital for the formation of triple-helical structure of the collagen molecule^[12].

Collagen and gelatin are different forms of the same macromolecule. Gelatin is a soluble protein obtained by partial hydrolysis of collagen. In recent times applications of collagen and gelatin in the field of food, cosmetic, photographic, medicine and cell cultures have increased. Most of the times the collagen and gelatin used in the industrial products are obtained from mammalian sources[bovine and porcine] whereas; production of collagen and gelatin from the fish waste has received considerable attention in recent years^[13].
Nature sources
Collagen sources can be obtained from animal and vegetable sources. From animal sources, the most common are bovine, porcine, human collagen, and marine organism such as scale fish and fish skin^{[4, 14-16]}. Among these animal sources, bovine collagen is commonly used as a temporary cover for extra-oral wounds^[17] and also for the burns on the body. It has large applications because of its helpfulness and biocompatibility^[18]. Porcine collagen matrices, on the contrary, have the potential to be useful for grafting of soft tissues^[19]. It provides a biocompatible surgical material as an alternative to an autogenous transplant^[20]. Animal terrestrial sources comprise from chicken, kangaroo tail, rat tail tendons, duck feet, equine tendon, alligators bon/skin, bird’s feet, sheepskin, and frog skin. Types I and II come from equine skin, cartilage, and flexor. Types I, II, III, and V come from chicken neck. Type IX is found in chicken embryo sternal cartilage, I and III from skin, and IV from muscular tissue^[21].
Synthetic sources
Collagen is widely used to help blood clotting, healing, and tissue remodeling. Animal-derived[natural] collagen is used in many clinical applications, but there are some concerns with respect to its role in inflammation, batch-to-batch variability, and possible disease transfection^[6]. To avoid immune problems, some synthetic sources have been found, for example, the material commercially named KOD. This is a synthetic protein made of 36 amino acids that self-assemble into triple-helix nanofibers and hydrogels; it mimics natural collagen and it could improve upon commercial sponges or therapies based on naturally derived collagen. The sequence of the peptide is[Pro-Lys-Gly][Pro-Hyp-Gly][Asp-HypGly], and in single-letter amino acid, abbreviation is[P-K-G][P-OG][D-O-G], giving it the name KOD^[6]. This material presents theoretical analogues to native collagen in protein structure and folding, as well as pro-coagulatory fractions that could promote platelet activation and adhesion^[6]. It can be used as a hemostat or a clotting agent thanks to its capacity to trap red blood cells to stop bleeding. It also binds and activates platelets to form clots and promote healing without promoting inflammation^[22].
Another synthetic source for collagen has been developed using recombinant technology to produce high quality and animal-derived contaminant-free collagens. These recombinant collagens have been produced in mammalian cells, insect cell cultures, yeast, and mostly in plant cell culture. The production of plant-derived recombinant collagen has been reported using tobacco, transgenic maize seed, and barley^[23].

Supplementation of collagen in food enhances there nutritive as well as functional property that ultimately results in improved health benefits^[24]. Synthesis of collagen decreases with aging that can be gained by consuming collagen supplemented food products. The metabolites of collagen attract fibroblasts and they help in the synthesis of new collagen that then assembles bone, skin and ligaments^[25]. Collagen supplements helps to fulfill the collagen requirement of the body. Hence, the food products supplemented with collagen may have tremendous potential and health benefits^[26]. Recently in the food industry they are extensively used in products as foaming agents, emulsifiers, stabilizers, microencapsulating agents and biodegradable film-forming materials^[27]. Collagens have tremendous industrial applications; majorly of which lies in pharmaceutical and food industries. Collagen has been considered as an excellent biomaterial for the development of wound dressing systems and tissue engineering constructs due to its exceptional biocompatibility, low antigenic and high direct cell adhesion ability^{[2, 24]}. For medical applications; collagens are reported to be processed into various forms such as sheets, scaffolds, tubes, films, sponges, membranes, composites, fleeces, injectable solutions and dispersions^[28-33]. Collagen has been also applied for delivery of the drug in numerous applications such as ophthalmology, wound and burn dressing, tumor treatment and tissue engineering. Applications of collagen were also suggested in functional food, drinks, dietary supplements, confectionery and desserts^{[24, 34-36]}. It has also been used as a food additive that subsequently showed the improvement in rheological properties of foodstuffs^[37]. Collagen films or coatings help to extend the shelf life of the products and also function as carriers of active substances^{[38, 39]}. The collagen mediated delivery systems in the form of mini pellets and tablets are used for drug delivery^[40].

1. Sweeney, S.M., Orgel, J.P., Fertala, A., McAuliffe, J.D., Turner, K.R., Di Lullo, G.A., Forlino, A., 2008. J. Biol. Chem. 283, 21187–21197.
2. Pati, F., Adhikari, B., Dhara, S., 2010. Bioresour. Technol. 101, 3737–3742.
3. Suzuki, Y., Tsujimoto, Y., Matsui, H., Watanabe, K., 2006. J. Biosci. Bioeng. 102, 73–81.
4. Gelse K, Poschl E, Aigner T. Adv Drug Deliv Rev. 2003;55:1531-1546.
5. Rajini K. Physical properties of collagen, at Intra and Inter Molecular Levels. 2001:2.
6. Kumar V, Taylor N, Jalan A, Hwang L, Wang B, Hartgerink J. Biomacromol. 2014;15:1484-1490.
7. Park J. Biomaterials: An Introduction. 3rd ed. Springer; 2007.
8. Chanjuan D, Yonggang L. Polymers. 2016;8:42.
9. Friess, W., 1998. Eur. J. Pharm. Biopharm. 45, 113–136.
10. Kucharz, E.J., 1992. The Collagens: Biochemistry and Pathophysiology. Springer, Berlin Heidelberg, pp. 31–53[Biosynthesis of collagen].
11. Woessner, J.F., 1961. Arch. Biochem. Biophys. 93, 440–447.
12. Piez, K., 1984. In: Piez, K.A., Reddi, A.H.[Eds.], Extracellular Matrix Biochemistry. Elsevier, London, pp. 1–40.
13. Bhagwat, P.K., Jhample, S.B., Jalkute, C.B., Dandge, P.B., 2016. RSC Adv. 6, 65222–65231.
14. Ivipriya K, Kumar K, Bhat A, Kumar D, John A, Lakshmanan P. J App Pharm Sci. 2015;5:123-127.
15. Fan J. Nutrients. 2013;5:223-233.
16. Sibilla S, Godfrey M, Brewer S, Budh-Raja A, Genovese L. Open Neutraceutical J. 2015;8:29-42.
17. Sowjanya N, Rao N, Bushan S, Krishnan G. J Clin Diagn Res. 2016;10:ZC30-ZC33.
18. Karsdal M. Biochemistry of Collagens Structure, Function and Biomarkers. London, United Kingdom: Academic Press; 2016.
19. Herford A, Akin L, Cicciu M, Maiorana C, Boyne P. J Oral Maxillofac Surg. 2010;68:1463-1470.
20. Brinckmann JCBC, Notbohm H, M€uller PK, B€achinger HP. Collagen: Primer in Structure, Processing and Assembly. Berlin, Germany: Springer; 2005:56.
21. Gupta R, Canerdy T, Skaggs P, et al. Vet Pharmacol Ther. 2009;32:577-584.
22. Williams M. Synthetic collagen promotes natural clotting. Rice University News & Media. http://news.rice.edu/2014/04/09/synthetic-collagen-promotes-natural-clotting/. Published 2014
23. Xu X, Gan Q, Clough R, et al. BMC Biotechnol. 2011;11:69.
24. Bilek, S.E., Bayram, S.K., 2015. J. Funct. Foods 14, 562–569.
25. King’Ori, A.M., 2011. Int. J. Poult. Sci. 10, 908–912.
26. Antoniewski, M.N., Barringer, S.A., 2010. Crit. Rev. Food Sci. Nutr. 50, 644–653.
27. Herpandi, N.H., Rosma, A., Wan Nadiah, W.A., 2011. Compr. Rev. Food Sci. Food Saf. 10, 195–207.
28. Alberti, K.A., Hopkins, A.M., Tang-Schomer, M.D., Kaplan, D.L., Xu, Q., 2014. Biomaterials 35, 3551–3557.
29. Campbell, J.J., Husmann, A., Hume, R.D., Watson, C.J., Cameron, R.E., 2017. Biomaterials 114, 34–43.
30. Fu, J.H., Zhao, M., Lin, Y.R., Tian, X.D., Wang, Y.D., Wang, Z.X., Wang, L.X., 2017. Heart Lung Circ. 26, 94–100.
31. Zirk, M., Fienitz, T., Edel, R., Kreppel, M., Dreiseidler, T., Rothamel, D., 2016. Oral. Maxillofac. Surg. 20, 249–254.
32. Moreira, C.D., Carvalho, S.M., Mansur, H.S., Pereira, M.M., 2016. Mater. Sci. Eng. C 58, 1207–1216.
33. Mottahedi, M., Han, H.C., 2016. J. Mech. Behav. Biomed. Mater. 60, 515–524.
34. Clark, K.L., Sebastianelli, W., Flechsenhar, K.R., Aukermann, D.F., Meza, F., Millard, R.L., Deitch, J.R., Sherbondy, P.S., Albert, A., 2008. Curr. Med. Res. Opin. 24, 1485–1496.
35. Cai, L., Feng, J., Regenstein, J., Lv, Y., Li, J., 2017. Food Hydrocoll. 67, 157–165.
36. Li, L., Kim, J.H., Jo, Y.J., Min, S.G., Chun, J.Y., 2015. J. Food Sci. Res. 35, 156–163.
37. Baziwane, D., He, Q., 2003. Gelatin: the paramount food additive. Food Rev. Int. 19, 423–435.
38. Bonilla, J., Atares, L., Vargas, M., Chiralt, A., 2012. J. Food Eng. 110, 208–213
39. Galus, S., Kadzinska, J., 2015. Trends Food Sci. Technol. 45, 273–283.
40. Jeevithan, E., Qingbo, Z., Bao, B., Wu, W., 2013. J. Nutr. Ther. 2, 218–227.

Collagen is a protein that is the principal constituent of connective tissue and bones of vertebrates; it can be converted to gelatin and glue by boiling in water.

collagen is very popular in skin care formulations for its strong hydration potential and its ability to bind and retain many times its weight in water. This water-binding and retention ability makes collagen effective for use in skin moisturizers as a skin-protecting agent. It will not leave a feeling of tackiness or dryness on the skin, especially when used in hydrolyzed or soluble forms. As a film former, collagen aids in reducing natural moisture loss, thereby helping hydrate the skin. In skin care preparations, it enhances the humectancy of a topical product, contributes sheen, builds viscosity, and leaves the skin smooth and soft. It is not water soluble, and has been very popular in cosmetic formulations for more than 30 years. Collagen is rich in proline and hydroxyproline, and is considered a “commercially pure” protein. originally derived from animal connective tissue, which is similar to the collagen produced by the body in the skin and bones, today for cosmetic use it is either synthetically derived or bioengineered. Also considered an anti-irritant, collagen does not cause allergic reactions when used on the skin. It is very stable, bland in odor, and light in color. This is one of the most effective and economical proteins available to cosmetic formulators.

collagen (soluble) demonstrates enhanced moisture uptake and, therefore, is more effective than collagen. This is a clear liquid form of collagen preferred for use in cosmetics because, when incorporated into a formulation, it does not separate as regular collagen can. When incorporated into detergents, soluble collagen significantly reduces the amount of amino acids extracted from the skin when washing with the detergents and water. Soluble collagen is perhaps the most widely used and recognized high molecularweight protein in skin care formulations.

collagen: An insoluble fibrous proteinfound extensively in the connectivetissue of skin, tendons, andbone. The polypeptide chains of collagen(containing the amino acidsglycine and proline predominantly)form triple-stranded helical coils that are bound together to form fibrils,which have great strength and limitedelasticity. Collagen accounts forover 30% of the total body protein ofmammals.

Collagen solution is derived by dissolving collagen molecules in an aqueous solution. Collagen type Iα1 (COL1A1) is encoded by the gene that is located on human chromosome 17q21.33. It is the most abundant extracellular matrix (ECM) protein in humans. Type 1 collagen is the major structural protein of bone, tendon, skin and cornea. The encoded protein is a heterotrimer consisting of two α1-chains and one α2-chain.

Collagen is an insoluble fibrous protein found extensively in the connective tissue of skin, tendons and bones. Polypeptide chains of collagen predominantly contain glycine and proline. These form triple-stranded, helical coils to form fibrils, which have strength and elasticity. Collagen accounts for over 30% of the total body protein in mammals.

Collagen provides extracellular support for multicellular animals. Collagen type I offers mechanical stability, strength and toughness to a range of tissues from tendons and ligaments, to skin, cornea, bone and dentin.