Hyaluronic acid: structure of the macromolecule in the connective tissue matrix

Hyaluronic acid: molecular conformation and interactions in the tetragonal form of the potassium salt containing extended chains

X-ray diffraction data were used to determine the detailed crystal structure of a tetragonal form of potassium hyaluronate containing relatively extended 4-fold helical chains (rise per disaccharide h = 0.95 nm). The polysaccharide chains are left-handed (4(3] helices. Two antiparallel chains pack in a tetragonal unit cell (a = b = 0.996 nm, c = 3.788 nm) with P4(3)2(1)2 space group symmetry. The chain conformations are stabilized intramolecularly by O4-O5 hydrogen bonds across the beta(1 leads to 3) linkage and by a pair of intermolecular hydrogen bonds per disaccharide between adjacent antiparallel chains. Fourier difference synthesis revealed one potassium ion and two water molecules per disaccharide. Six polyanion oxygen atoms from three neighboring chains together with one of these water molecules form the co-ordination polyhedra. Further stability is brought about through inter- and intrachain water bridges involving both water molecules. The probable reason for the stability of this extended allomorph is discussed in terms of the preferred co-ordination geometry of the potassium ion.

Amvisc in extracapsular cataract extraction

Amvisc, a purified fraction of sodium hyaluronate, was evaluated and compared with Healon in cataract extraction and primary intraocular lens implantation. Both visco-elastic solutions are valuable adjuncts to intraocular surgery. A number of patients had moderately elevated IOP after these solutions had been used in the anterior chamber. This moderate elevation was observed less frequently with Amvisc than with Healon, and may be attributed to the lower viscosity of Amvisc. Both visco-elastic solutions provide good endothelial protection as evidenced by the minimal corneal edema seen in both groups. Postoperative anterior chamber inflammation was minimal in all patients in this study.

A new chromatographic method for the fractionation of hyaluronic acid

Sodium hyaluronate from rooster comb, umbilical cord, bovine vitreous and a special commercial hyaluronic acid preparation, "HealonR" have been fractionated at 4 degrees C on DEAE-Sephacel columns using salt gradients from 0 leads to 0.4M NaCl. All samples examined displayed a high degree of polydispersity. The number of well separated fractions observed in these chromatograms ranges from 10-30 depending on the source of the material. A molecular weight distribution effect does not seem to be the main factor controlling this fractionation as no differences could be observed when the limiting viscosity numbers (eta) for numerous fractions isolated from the same sample were compared with each other. As no galactosamine, sulfate or phosphate is found directly linked to these fractions, it is suggested that disaggregation of an hyaluronate molecular aggregate could be the basis for this fractionation.

Studies on hyaluronic acid. V. Relationship between the protein content and viscosity of rooster comb dermis hyaluronic acid

Protein accounted for an average of 8.7% w/w of the hyaluronic acid obtained from rooster comb dermis extracts and three types of peptide constituents appeared to be present. A few collagen-like fibers were closely associated with the hyaluronic acid when samples were examined in the electron microscope and collagenase treatment decreased the intrinsic viscosity from 7000-5000 ml/g to 3900-2700 ml/g. The quantities of collagen present, however, were too small to detect chemically with the methods employed. The major peptide consituent was readily separated from the hyaluronic acid by fractionation in a cesium chloride gradient or by treatment with pronase. The viscosity was decreased by the density gradient procedure but not by the pronase digestion. Repeated fractionation in a cesium chloride gradient decreased the intrinsic viscosity still further and a small peptide constituent with a high glycine and serine content remained associated with a hyaluronic acid. The data suggest that an interaction or entanglement with collagen fibers is responsible for the high viscosity of hyaluronic acid in this tissue extract and that the viscosity of purified hyaluronic acid preparations is dependent upon interactions between adjacent polysaccharide chains. Interactions between the major peptide constituent and polysaccharide chains or the small residual peptide component remaining with hyaluronic acid after extensive purification procedures, however, appear to be involved in some organized structure because the presence of the major peptide constituent minimized the decrease in viscosity that occurred when hyaluronic acid samples were lyophilized.

Studies on the structure of hyaluronic acid. Characterization of the product formed when hyaluronic acid is treated with ascorbic acid

Physical and chemical methods were used to characterize hyaluronic acid before (fraction HAIIBI) and after (fraction HA-AA) treatment with ascorbic acid. Fraction HA-AA was recovered with an almost quantitative yield and was shown to be chemically identical with fraction HAIIBI by all the methods used. These two materials, however, differed markedly in their molecular sizes and degree of polydispersity. By using sedimentation, diffusion and sedimentation-equilibrium analyses, weight-average molecular weights of about 1.2x10(6) and 6.5x10(4) respectively were obtained for fractions HAIIBI and HA-AA. It is concluded from these results that hyaluronic acid has a molecular weight of about 65000 and that the polysaccharide chain of this molecule is not depolymerized by ascorbic acid. It is further proposed that hyaluronic acid molecules in the matrix of connective tissues are present either in an aggregated form or as subunits of heterogeneous macromolecules, and that it is the linkages responsible for the organization of these structures which are broken by ascorbic acid.