Sodium hyaluronate
Sodium hyaluronate or hyaluronic acid (HA) is a straight-chain polysaccharide with a high molecular weight which is an alternating copolymer of N-acetyl-D-glucosamine and D-glucuronic acid. Chemically, hyaluronic acid is formed by straight polymer chains having a molecular weight ranging from hundreds thousand to millions dalton, including repeated disaccharid units constituted by N-acetyl glucosamine and glucoronic acid bound to each other by glucosidic bonds. Hyaluronic acid is present in various connective tissues of animals, such as skin and cartilage. Some organs are specifically rich in hyaluronic acid, such as the umbilical cord, synovial fluid, the vitreous humor and rooster combs. In addition, hyaluronic acid is produced by various microorganisms, such as streptococci Type A and C. Hyaluronic acid plays a fundamental role in tissue repair processes, especially in the first stages of the process of the formation of granulation tissue, by stabilizing the coagulation matrix and controlling its degradation, favoring the recruitment of inflammatory cells, such as polymorphonucleocytes and monocytes, of mesenchymal cells, such as fibroblasts and endothelial cells, and directing the subsequent migration of epithelial cells. In skin and cartilage, the role of hyaluronic acid is to bind water and retain the tonicity and elasticity of the tissue. In joint fluids, the viscous hyaluronic acid solution serves as a lubricant to provide a protective environment to the cells. A solution of ultrapure hyaluronic acid from rooster combs has been in use for several years as a supportive medium in opthalmic surgery. Hyaluronic acid is a critical component of connective tissue and typically exists in a state of strong association with proteins and other glycosoamino glycans (GAGs) such as heparin and chondroitin sulfate. Hyaluronic acid has the capacity of binding high amounts of water coming from the capillary network, necessary to keep in a solution form the catabolites, electrolytes and gases that spread from the capillaries to the cells and vice-versa, through the interstitial fluid. This phenomenon is of the essential to maintain the skin elastic and in a gelatinous physical condition. Sodium hyaluronate and hyaluronic acid are collectively referred to as hyaluronan. Hyaluronan molecules have differing molecular weights due to the fact that the number of repeating disaccharide units in each molecule is variable. Sodium hyaluronate occurs naturally in cellular surfaces, in the basic extracellular substances of the connective tissues of vertebrates, in the synovial fluid of joints, in the vitreous humor of the eye, and in the tissue of umbilical cord. Sodium hyaluronate acts as a regulator of viscosity, tissue hydration, lubrication, and repair, and is involved in cell mobility, cell differentiation, wound healing, and cancer metastasis. Sodium hyaluronate (NaHA) viscoelastic compositions have been employed extensively in certain ophthalmological procedures such as cataract surgery. In these procedures, the composition may be placed in the anterior chamber of the eye to facilitate surgical manipulations. Hyaluronan solutions and cross-linked hyaluronan gels can be used as drug delivery systems.
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