Rheology of hyaluronic acid

The dynamic viscoelastic properties of hyaluronic acid solutions have been measured over the frequency range 0.02–1.67 cps. The effects of varying temperature, hyaluronic acid concentration, pH, and ionic strength on the dynamic shear moduli were studied. The solutions exhibited a sharp transition from viscous to elastic behavior as the strain frequency increased. No entanglement coupling of the hyaluronic acid molecules was evident over the concentration range 2.0–4.0 mg./ml. Solutions at pH 2.5 showed a pronounced elastic behavior relative to both higher and lower pH's. This effect was attributed to a stiffening of the hyaluronic acid molecule at this pH.     

Characterization of proteoglycan and the proteoglycan--hyaluronic acid complex by electric birefringence.

An electric field causes partial alignment of macromolecules in a dilute solution. The accompanying changes in the solution birefringence offer a sensitive and quick means of monitoring the rates of particle orientation and hence the size of the solute molecules. Such measurements are reported for dilute solutions of proteoglycans in the absence and presence of added hyaluronic acid. The proteoglycan molecules are shown to be some 580 nm long. In the presence of hyaluronic acid they form aggregates that appear to be consistent with the model previously proposed in which the proteoglycans attach radially to the extended hyaluronic acid chain. The electric-birefringence relaxation rates indicate aggregates of similar length to that of the extended hyaluronic acid chain, with the proteoglycans spaced on average at 29nm intervals. A proteoglycan sample the cystine residues of which had been reduced and alkylated showed no evidence of aggregation with hyaluronic acid up to the concentrations of the acid corresponding to 1% of the total uronic acid content. The electric-birefringence method is shown to have a large potential in the study of associating polysaccharide solutions.     

The equilibrium sedimentation of hyaluronic acid and of two synthetic polymers

1. The method of equilibrium sedimentation has been investigated as an alternative to osmotic-pressure measurement for determining thermodynamic properties of polymer solutions at relatively high concentrations. 2. The simplifications that must be made in the theoretical treatment are discussed. 3. Measurements have been made on samples of polyethylene glycol, neutralized polymethacrylic acid and hyaluronic acid. With the first and third, values of the ;non-ideality coefficients' have been obtained that agree with those obtained from osmotic measurements on the same materials. 4. Evidence has been obtained of the presence in hyaluronic acid preparations of a fraction that has either a lower degree of thermodynamic non-ideality or a higher density increment than the bulk of the sample. This fraction is not protein.     

Cellulose derivative-hyaluronic acid-based microporous hydrogels cross-linked through divinyl sulfone (DVS) to modulate equilibrium sorption capacity and network stability

The aim of this work is to obtain a chemically cross-linked hydrogel from hyaluronic acid and cellulose derivatives that exhibits sensitivity to variation of the composition of the external absorbing medium and an equilibrium sorption capacity higher than a common hyaluronic acid-based hydrogel, in view of its potential use in prevention of postsurgical soft tissue adhesion. This has been achieved by chemical stabilization of hyaluronic acid (HA) and cellulose derivatives, hydroxyethylcellulose (HEC) and carboxymethylcellulose (CMCNa) through the difunctional cross-linker divinyl sulfone. Significant increase in sorption capacity, both in water and in water solutions at different ionic strength, has been observed for these samples in comparison with hydrogels obtained through chemical stabilization of hyaluronic acid. Moreover, different dehydration procedures adopted for the xerogel synthesis have been used, which resulted in a modulation of the equilibrium sorption capacity. Hyaluronic acid stability has been confirmed by means of NMR analysis.     

Hyaluronic acid: separation and biological implications

Hyaluronic acid (hyaluronan) is a ubiquitous extracellular matrix component, and present at high concentrations in skin, joints and cornea. In the skin, it is synthesized primarily by dermal fibroblasts and by epidermal keratinocytes. Hyaluronic acid usually exists as a high molecular mass (600,000-1,000,000) and non-sulfated glycosaminoglycan composed of a disaccharide unit of [bond]3GlcNAc beta 1[bond]4GlcA beta 1[bond]. Hyaluronic acid has been widely used not only for osteoarthritis and ophthalmology but also for cosmetics for skin care. To examine the biological activities of hyaluronic acid, we have to accurately determine the quantity and molecular masses in biological samples. We review recent development in the analysis of hyaluronic acid having various molecular sizes using electrophoretic and chromatographic techniques. Recently, interactions between hyaluronic acid oligomers and hyaluronic acid-binding proteins have attracted the interest for understanding the biological functions. We show some interesting reports on biological interactions of hyaluronic acid and its oligomers with some proteins.     

Dielectric changes in hyaluronate solutions at microwave frequencies as a function of concentration,system pH,and temperature

The dielectric response of human umbilical cord hyaluronic acid in various environments has been studied at microwave frquencies using a resonant microwave cavity as a probe. Both the real and imaginary parts of complex dielectric constant and the loss tangent for hyaluronate solutions are obtained by utilizing equations for perturbation of a resonant cavity. Dielectric changes at room temperature have been observed in aqueous solutions of hyaluronic acid as a function of concentration ranging from 0 to 350 mg/ml. The data indicate the existence of ordered phases in hyaluronate solutions at selective concentrations, that is, exhibiting lyotropic-type transitions. Hyaluronate solutions at 1.5 and 3 mg/ml concentrations have been studied at various pH in the range of 6–8 and at constant ionic strength 0.1. A temperature-dependent transition in hyaluronate solution of 120 mg/ml concentration has been observed at physiological temperature. It is shown that this temperature-dependent behavior can be related to the orientational polarizability term in the Debye theory of polar molecules in liquids.     

Identification of hyaluronic acid binding sites in the extracellular domain of CD44

CD44 is a polymorphic glycoprotein expressed on the surface of many tissues and cell lines which has been implicated in a number of cellular functions including lymphocyte homing to mucosal lymphoid tissue (Peyers patches), leukocyte activation, lymphopoiesis, and tumor metastasis. The predominant isoform found on human leukocytes, CD44H, is a receptor for hyaluronic acid. Because of the prominent role CD44 plays in diverse biological processes, we set out to identify the hyaluronic acid binding site(s) in the extracellular domain of CD44H. Using truncation and site-directed mutagenesis we identified two regions containing clusters of conserved basic residues which are important in hyaluronic acid binding. One of these regions is situated near the NH2 terminus and is homologous to other hyaluronic acid binding proteins including cartilage link protein. The other more membrane proximal region lies outside the link protein homologous domain. Mutagenesis of basic residues within these regions established their role as determinants in hyaluronic acid binding. Mutation of Arg 41, a position where a basic residue is conserved in all hyaluronic acid binding proteins, completely abolished binding suggesting that this residue plays a critical role in hyaluronic acid binding.     

Surface rheological properties of hyaluronic acid solutions

Using an oscillating ring surface rheometer, surface shear rheological studies of hyaluronic acid solutions at physiological pH have demonstrated the elastico-viscous nature of the surface films. The properties of these surface films change with time and are shown to be related to bulk concentration, ionic strength and pH. This ageing behaviour can be explained on the basis of molecular conformational changes and molecular segmental kinetics. The results are discussed in relation to the postulated function of hyaluronic acid in synovial fluid.     

In vitro reconstitution of fibrillar collagen type I assemblies at reactive polymer surfaces

The reconstitution of fibrillar collagen and its assemblies with heparin and hyaluronic acid was studied in vitro. Fibril formation kinetics were analyzed by turbidity and depletion measurements in solutions containing varied concentrations of collagen and glycosaminoglycans. Fibril-forming collagen solutions were further applied for the coating of planar substrates which had been modified with alternating maleic anhydride copolymer films before. The immobilized collagen assemblies were characterized with respect to the deposited amount of protein using ellipsometry and acidic hydrolysis/HPLC-based amino acid analysis, respectively. AFM, SEM, and cLSM were utilized to gain information on structural features and patterns formed by surface-attached fibrils depending on the initial solution concentrations of collagen. The results revealed that the addition of heparin and hyaluronic acid affected both the fibril dimensions and the meshwork characteristics of the surface-bound fibrils.     

Studies on the generation of hydrogen peroxide during some non-enzymic reactions changing the hyaluronic acid molecule.

The effect of catalase on non-enzymic-induced changes in the conformation of hyaluronic acid in a vitreous humour preparation was measured using viscometry. Ascorbate, heavy metal ions, riboflavin or EDTA all lowered the viscosity of hyaluronic acid solutions. These effects could be prevented by the addition of catalase. This suggested that H2 O2 is produced by these compounds and that the resulting change in conformation of hyaluronic acid may be due to peroxyl and hydroxyl attack by the free radicals thus generated.     

Influences of sulfated glycosaminoglycans on biosynthesis of hyaluronic acid in rabbit knee synovial membrane

The effect of various sulfated glycosaminoglycans on glycoconjugates syntheses in synovial membranes of rabbit knee joints in culture was investigated by two different approaches. In the first approach, synovial membranes isolated from rabbit knee joints were cultured in the presence of sulfated glycosaminoglycans and [14C]glucosamine. In the second approach, solutions of sulfated glycosaminoglycans were injected into rabbit knee joints and synovial membranes isolated from the joints were cultured in the presence of [14C]glucosamine. The major part of [14C]glucosamine-labeled glycoconjugates associated with the synovial membranes and secreted into culture medium was hyaluronic acid. Of the natural glycosaminoglycans tested, dermatan sulfate gave the maximum stimulation of hyaluronic acid synthesis followed by chondroitin 4- and 6-sulfate. Heparin, heparan sulfate, keratan sulfate, keratan polysulfate, and hyaluronic acid had no significant effect. Of the chemically polysulfated glycosaminoglycans, GAGPS (a persulfated derivative of chondroitin sulfate) gave high stimulation but N-acetylchitosan 3,6-disulfate had no effect. The effect of sulfated glycosaminoglycans on hyaluronic acid synthesis was the same in both experimental approaches. The increase in the amount of secreted hyaluronic acid in culture medium paralleled that in synovial membranes. The results indicate that the galactosamine-containing sulfated glycosaminoglycans have a specific stimulatory effect on hyaluronic acid synthesis. A high degree of sulfation of the molecules appeared to potentiate the stimulatory effect.     

The hydrodynamic resistance of hyaluronic acid: estimates from sedimentation studies

The problem of estimating the permeability of hyaluronic acid as a function of concentration has been examined. A previously known method of obtaining permeability from sedimentation studies has been employed, and the results have been compared to those obtained from convection studies, in which solvent is forced through the hyaluronic acid. The two sets of results were seen to be at variance, which could be explained by a flow-induced polarization of the hyaluronic acid in the convection studies. The polarization phenomenon was described in terms of a convection-associated compaction balancing the hyaluronic acid's intrinsic resistance to compression. Based on these results and other arguments, it was suggested that data from sedimentation studies provide a more accurate estimate of hyaluronic acid permeability than do convection experiments. The implications of this finding in a physiological context were briefly discussed.     

Studies on the generation of hydrogen peroxide during some non-enzymic reactions changing the hyaluronic acid molecule

The effect of catalase on non-enzymic-induced changes in the conformation of hyaluronic acid in a vitreous humour preparation was measured using viscometry. Ascorbate, heavy metal ions, riboflavin or EDTA all lowered the viscosity of hyaluronic acid solutions. These effects could be prevented by the addition of catalase. This suggested that H₂O₂ is produced by these compounds and that the resulting change in conformation of hyaluronic acid may be due to peroxyl and hydroxyl attack by the free radicals thus generated.     

The synthesis of hyaluronic acid by sheep and rabbit articular cartilage in vitro.

Standard methods of glycosaminoglycan separation were used to confirm the presence of hyaluronic acid in sheep and rabbit articular cartilage. During incubation of carilage in vitro in the presence of [1-14 C]acetate, cartilage cells synthesize this macromolecule and, under the conditions used, it appears to have a shorter turnover time than chondroitin suplhate in the same tissue. The possible functions of hyaluronic acid in cartilage are discussed.     

pH control of the third virial coefficient of hyaluronate solutions calculated from van der Waals forces by means of the Lifshitz-McLachlan susceptibility theory

Positive third virial coefficients and osmotic coefficients have been calculated for human umbilical cord hyaluronic acid solutions at pHs 6.0, 6.5, 7.0, 7.5, 8.0, and 8.5 and constant ionic strength 0.1. The calculations are based on experimental axial flow birefringence and radial linear dichroism data previously reported and the Lifshitz-McLachlan field theory of van der Waals forces. The second virial coefficients are negative, according to both this analysis and light scattering evidence, and reflect the tendency of hyaluronic acid to associate. This negativity denies the assumption of force additivity required by virial expansion theory.The results are in reasonable agreement with those of light scattering studies, and indicate the extreme nonideality of hyaluronate solutions with a high degree of pH control of osmotic pressure. The data are explained within the context of statistical mechanical and field theories of van der Waals forces, and the osmotic pressure of a solution is related to its optical properties. The numerical method used offers a way of exploring the applicability of modern interparticle force theory to biological systems.     

The composition and physicochemical properties of hyaluronic acids prepared from ox synovial fluid and from a case of mesothelioma

1. Materials containing hyaluronic acid have been prepared by filtration (Ogston & Stanier, 1950) from ox synovial fluid and from a protein-rich human mesothelioma fluid. The ox material has been deproteinized by treatment with chloroform and pentanol and by gradient elution on DEAE-Sephadex; several fractions were obtained by the latter method. These materials can be stored in solution at −20° without change of properties. The ox material contained 21% of protein; all other preparations contained less than 6% of protein. 2. The two materials have been compared by sedimentation and viscosity and shown to be closely similar. Treatment of the ox material with neuraminidase caused no change in its viscosity behaviour. 3. Information about the molecular configuration of the ox material has been obtained from measurements of light-scattering and viscosity. The results, though consistent with a highly extended configuration, are not consistent with a linear random-coil configuration. It is tentatively suggested that the structure may have some degree of branching and of cross-linking, which give it a rigidity with respect to expansion of the molecular domain that would not be possessed by a random coil. 4. The deproteinized material recovered from DEAE-Sephadex, though polydisperse, showed unchanged average molecular weight; however, the average radius of gyration was greater than before this treatment. 5. Acidification to approx. pH3 resulted in a contraction of the structure, with only a slight degree of expansion when the pH was restored to 6·8–7·0. 6. Measurements of optical rotatory dispersion qualitatively support a structure less simple than a linear random coil. 7. Colloid osmotic pressures of mixed solutions of bovine serum albumin and of hyaluronic acid prepared by filtration from ox synovial fluid have been measured. The results agree approximately with those of Laurent & Ogston (1963) but are in quantitative disagreement with the partition measurements of Ogston & Phelps (1960). The relationships between thermodynamic quantities in a quaternary system of electrolytes are discussed in Appendix 2. 8. Refractometric measurements have been made in connexion with light-scattering measurements, as the basis for a convenient method of determining the concentrations of solutions of hyaluronic acids, and to measure the partition of sodium chloride in dialysis experiments. The theory of the last use is discussed in Appendix 1. 9. Sedimentation measurements on the ox preparation have been made up to a concentration of 1·4×10⁻²g./ml. The form of the sedimentation coefficient–concentration relationship is discussed. The value of the sedimentation coefficient at higher concentration is the basis of an illustration of the likely effect of hyaluronic acid on the flow of water through narrow channels in connective tissue. 10. Available colorimetric methods have been shown to give low estimates for glucuronic acid when applied to highly polymerized materials, as compared with estimates by decarboxylation. A spectrophotometric titration with cetylpyridinium bromide has been shown to give estimates of carboxyl groups that agree well with those of decarboxylation when applied to preparations of hyaluronic acid under suitable conditions; the results are not affected by the presence of protein. 11. Estimates of glucosamine (Ogston, 1964) have been found to be low compared with those of total acetyl, independently of the presence of protein. The magnitude of the discrepancy is characteristically different for preparations from ox synovial fluid and from mesothelioma. 12. Sialic acid was estimated in several preparations. It is likely that this forms part of the protein. 13. Analyses of preparations for total nitrogen, amino acids, total acetyl, glucuronic acid (by decarboxylation) and ash account for at least 95·7% of the dry weight in terms of N-acetylglucosaminyl, glucuronyl, protein and metal ions. Previously published analyses of hyaluronic acids are reviewed. 14. The estimated molar ratios of glucuronic acid to glucosamine were all significantly greater than unity. 15. The analytical results are interpreted as agreeing with the physicochemical measurements in suggesting a more complex structure, for at least some hyaluronic acids, than that of an alternate linear copolymer in random-coil configuration.     

Hyaluronic acid bonded to cell culture surfaces inhibits the program of myogenesis

Primary isolates of chick leg muscle myoblasts cultured on hyaluronic acid substrates have been examined by transmission electron microscopy for evidence of myoblast fusion and subsequent differentiation. Even though these cells form close contacts, no evidence of multinucleated myotubes is found in these cultures. Two-dimensional SDS-polyacrylamide gel electrophoresis shows that the muscle macromolecular biosynthetic program is not initiated in these hyaluronic acid fusion-blocked cells. Further, these fusion-blocked myoblasts continue replicating while cultured on hyaluronic acid surfaces. The inhibition of both fusion and the myogenic expressional program is reversed by replating these myoblasts onto a denatured collagen (gelatin) substrate; both the synthesis of muscle-specific proteins and the formation of multinucleated myotubes are observed when these subcultured cells are introduced onto gelatin substrates. These observations indicate that the hyaluronic acid inhibition of fusion is not permanent and is manifested in a way different from other fusion blockers in that hyaluronic acid inhibits both fusion and the myogenic expressional program.     

Evaluating specific adhesion of Plasmodium falciparum-infected erythrocytes to immobilised hyaluronic acid with comparison to binding of mammalian cells

A feature of infection with Plasmodium falciparum is the ability of parasite-infected erythrocytes to adhere to vascular endothelial cells and accumulate in vital organs, associated with severe clinical disease. Hyaluronic acid was recently identified as a receptor for adhesion and has been implicated in mediating the accumulation of parasites in the placenta. Here, we report in vitro assays to measure specific adhesion of infected erythrocytes to hyaluronic acid that is distinct from binding to chondroitin sulphate A, another glycosaminoglycan implicated as a receptor in placental malaria. In this study, specific adhesion of mature stage infected erythrocytes to hyaluronic acid of high purity immobilised on plastic surfaces was abolished by pre-treating hyaluronic acid with a specific hyaluronate lyase from Streptomyces, whereas the same treatment of chondroitin sulphate A had little effect. Adhesion to hyaluronic acid could not be explained by the presence of chondroitin sulphate A or other glycosaminoglycans in the hyaluronic acid preparations. Chinese hamster ovary cells bound in a similar manner in the assays and confirmed that hyaluronic acid was appropriately immobilised for cell adhesion. In contrast to parasites, these cells did not adhere to chondroitin sulphate A. The adsorption of hyaluronic acid onto plastic surfaces was also confirmed by the use of a specific hyaluronic acid-binding protein. Fixing cells with glutaraldehyde at the completion of adhesion assays reduced the number of parasites remaining adherent to hyaluronic acid, but not to chondroitin sulphate A or CD36. These findings have important implications for understanding and evaluating interactions between P. falciparum and hyaluronic acid that may be involved in disease pathogenesis.     

Effect of trimethylcolchicinic acid on the synthesis and excretion of proteoglycans in tissue culture.

The action of trimethylcolchicinic acid on the synthesis and excretion of proteoglycans has been studied on the L cell strain. The incorporation of precursors has been measured, and proteoglycans produced in the culture medium have been extracted and their concentration determined. The mucopolysaccharide components have been studied by electrophoresis. Control cultures produce hyaluronic acid, dermatan sulfate and very low concentrations of chondroitin 4-sulphate or 6-sulphate. Cultures treated with trimethycolchicinic acid (4 mu g/ml) produce hyaluronic acid, very high concentrations of chondroitin 4-sulphate or 6-sulphate and only traces of dermatan sulphate. So, trimethylcolchicinic acid does not modify the synthesis of hyaluronic acid: it considerably increases the production of chondroitin 4-sulphate or 6-sulphate and inhibits the production of dermatan sulphate. Protein fraction of the proteoglycans is proportionally increased in treated cultures, but there is no marked difference between amino acid concentrations of proteoglycans extracted from control and treated cultures. A slight fall in the cystine concentrations was the only change in the amino acid content of proteoglycans extracted from treated cultures. A hypothesis to explain these results is discussed.     

Synthesis and partial characterization of hydrogels obtained via glutaraldehyde crosslinking of acetylated chitosan and of hyaluronan derivatives

Hydrophilic networks based on functionalized hyaluronic acid and on partially acetylated chitosan, respectively, have been obtained. In the case of hyaluronic acid (HA), primary amino functionalities have been introduced along the polysaccharide chains. The ensuing derivatives, i.e., HA-lysine (HA-K), HA-diamino pentane (HA-DAP), and HA-glycine-lysine (HA-GK), have been characterized by high field NMR spectroscopy. NMR 2D-DOSY experiments have allowed us to optimize the purification procedure. Chitosan was made soluble in water by partial acetylation. Cross-linking reactions have been performed using glutaraldehyde. The obtained networks have been qualitatively characterized by means of (13)C CP-MAS NMR technique. The hydrogels have been characterized also in terms of water uptake.