Hyaluronic Acid-protein Complex Research Articles

The influence of the acetabular labrum seal, intact articular superficial zone and synovial fluid thixotropy on squeeze-film lubrication of a spherical synovial joint

A model of synovial fluid (SF) filtration by articular cartilage (AC) in a step-loaded spherical synovial joint at rest is presented. The effects of joint pathology (such as a depleted acetabular labrum, a depleted cartilage superficial zone consistent with early osteoarthritis and an inflammatory SF) on the squeezed synovial film are also investigated. Biphasic mixture models for AC (ideal fluid and elastic porous transversely isotropic two-layer matrix) and for SF (ideal and thixotropic fluids) are applied and the following results are obtained. If the acetabular labrum is able to seal the pressurised SF between the articular surfaces (as in the normal hip joint), the fluid in the synovial film and in the cartilage within the labral ring is homogeneously pressurised. The articular surfaces remain separated by a fluid film for minutes. If the labrum is destroyed or absent and the SF can escape across the contact edge, the fluid pressure is non-homogeneous and with a small jump at the articular surface at the very moment of load application. The ensuing synovial film filtration by porous cartilage is lower for the normal cartilage (with the intact superficial zone) than if this zone is already depleted or rubbed off as in the early stage of primary osteoarthritis. Compared with the inflammatory (Newtonian) SF, the normal (thixotropic) fluid applies favourably in the squeezed film near the contact centre only, yielding a thicker SF film there, but not affecting the minimum thickness in the fluid film profile at a fixed time. For all that, in the unsealed case for both the normal and pathological joint, the macromolecular concentration of the hyaluronic acid–protein complex in the synovial film quickly increases due to the filtration in the greater part of the contact. A stable synovial gel film, thick on the order of 10 −7 m, protecting the articular surfaces from the intimate contact, is formed within a couple of seconds. Boundary lubrication by the synovial gel is established if sliding motion follows until a fresh SF is entrained into the contact. This theoretical prediction is open for experimental verifications.

The diffusion coefficient of caffeine through agar gels containing a hyaluronic acid-protein complex. A model system for the study of the permeability of connective tissues.

A hyaluronic acid-protein complex was embedded into agar gel. This gel complex resembles in some respects the physiological situation in connective tissue, but still permits precise physicochemical measurements to be made. The diffusion coefficient of caffeine into and from such gels has been measured as a function of both agar and hyaluronate concentration. The value for the diffusion coefficient of caffeine was also measured by using a Gouy type diffusiometer. From both types of measurement the value for D (Fick) for caffeine when extrapolated to zero caffeine and agar concentrations agreed at (6.79+/-0.01)x10(-6)cm(2).s(-1) at 25 degrees C. Although agar concentration had only a small effect on caffeine diffusion, hyaluronic acid caused a large decrease in caffeine diffusion co-efficient. The presence of the hyaluronic acid-protein complex within the gel tended to oppose gel syneresis, a concentration of 1.7mg/ml abolishing the effect and higher concentrations reversing it. The possible physiological implications of these results are discussed.

The rheology of synovial fluid

A review has been undertaken of the rheological properties of synovial fluid in which the viscosity of synovial fluid under single-shear and multi-shear rate conditions, and the visco-elastic behaviour in conditions of oscillatory shear rate have been described. Synovial fluid is a pseudo-plastic (shear-thinning) fluid, both in normal and pathological conditions. The fluid exhibits elasticity and a normal-force effect. The low friction in joints is associated with a full film of lubricant which separates the surfaces and high friction results from thin films of localised boundary friction due to asperity contacts. A series of experiments with varying types of cartilage and synovial fluid have suggested that the nature of the lubricating fluid and the articular surfaces are important in determining shear stress during reciprocating motion. Scanning electron microscopy has confirmed the suggestion that surface aggregation of hyaluronic acid-protein complex can give enhanced lubrication.

Mode of aggregation of hyaluronic acid protein complex on the surface of articular cartilage.

Mode of aggregation of hyaluronic acid protein complex on the surface of articular cartilage.

Isolation of hyaluronic acid by gel filtration on agarose

A method is described for preparing an undegraded, hyaluronic acid-protein complex from synovial fluid, and which gives, at the same time, a picture of molecular weight heterogeneity in the hyaluronic acid. The protein is shown to be firmly bound to the polysaccharide.

Fingerprinting the hyaluronic acid-protein complex of human vitreous humour

Hyaluronic acid-protein complexes have been separated from the free proteins present in human vitreous humour by passage down DEAE Sephadex. Cetyldimethylbenzylammonium chloride has been used to fingerprint the complexes in the form of their turbidity curves. Hyaluronic acid degraded by either testicular hyaluronidase or ascorbic acid has been similarly examined.

On the estimation of glucosamine in hyaluronic acid

In the estimation of glucosamine in complex material by the method of Elson and Morgan (1), it is shown that use of added glucosamine as an internal standard allows not only for loss of glucosamine during hydrolysis in acid but also for loss during the subsequent reaction with acetylacetone; the latter loss occurs to a serious extent if glucuronic acid or protein is present in the proportions found in the hyaluronic acid-protein complex of ox synovial fluid. In the analysis by Ogston and Stanier (2) of the hyaluronic acid-protein complex of ox synovial fluid only 93% of the total dry weight was accounted for in terms of acetylglucosamine, glucuronic acid, protein, and ash. Moggridge and Neuberger (3) and Johansen, Marshall, and Neuberger (4) have indicated that the liberation of glucosamine from polysaccharides may be a slow process owing to the stability of glycoside linkage after removal of N-acetyl by hydrolysis. However, prolonged heating with acid is known to cause loss of free glucosamine (5, 6). With the object of allowing for losses of glucosamine during hydrolysis, we have added known amounts of glucosamine to hyaluronic acid before hydrolysis; the final recovery of added glucosamine then provides an internal standard with which glucosamine liberated from the polysaccharide is compared. Use of this method has resulted in substantially higher estimates of glucosamine than when glucosamine is used, in the usual way, as an external standard. It has revealed that a substantial loss of glucosamine occurs also during reaction with acetylacetone, if protein or glucuronic acid is present in the original material, in addition to the loss during hydrolysis.

Mucopolysaccharides in Disease

Publisher Summary The chapter discusses mucopolysaccharides in disease. Meyer (M12) introduced the term mucopolysaccharide to describe “hexosamine-containing polysaccharides of animal origin, occurring either in a pure state or as protein salts. The chapter states that the prefix “muco” was chosen to denote the relationship of this type of substance with mucus, the physiological term for a viscous secretion. It is confined to a group of substances, including hyaluronic acid, the isomeric chondroitin sulfates, and heparin, which are conveniently termed acidic mucopolysacchurides. The chapter discusses that in most connective tissues of animals, the acidic mucopolysaccharides are complexed with protein or peptide residues. Little is known about the structure of these complexes, and the term mucopolysaccharide is therefore, best applied only to the pure polysaccharide. When the latter is complexed with protein, it has been suggested that a noncommittal term, such as hyaluronic acid-protein complex should be used. The chapter reviews the methods that are available for the isolation of pure mucopolysaccharides. Recent evidence suggests that the isolation of mucopolysaccharide-protein complexes is probably to be of increasing importance from a biological and medical viewpoint.

On the structure of hyaluronic acid-protein complex isolated from rous chicken sarcoma

A complex of the mucoid type containing hyaluronic acid and protein can be isolated from Rous chicken sarcoma and from normal sources (synovia, umbilical cord, comb). The protein is firmly bound to the polysaccharide, its amount depending on the source of the preparation. The polysaccharidic part of the complex from tumoral tissues consists of a repeating unit of glucuronic acid and glucosamine, hence its composition is similar to that of complexes from normal sources. The effects of proteolytic enzymes on the protein components of the complexes from tumoral and normal tissues are different.