Isolation and properties of hyaluronic acid from bovine heart valves

Hyaluronan - a functional and structural sweet spot in the tissue microenvironment

Transition from homeostatic to reactive matrix remodeling is a fundamental adaptive tissue response to injury, inflammatory disease, fibrosis, and cancer. Alterations in architecture, physical properties, and matrix composition result in changes in biomechanical and biochemical cellular signaling. The dynamics of pericellular and extracellular matrices, including matrix protein, proteoglycan, and glycosaminoglycan modification are continually emerging as essential regulatory mechanisms underlying cellular and tissue function. Nevertheless, the impact of matrix organization on inflammation and immunity in particular and the consequent effects on tissue healing and disease outcome are arguably under-studied aspects of adaptive stress responses. Herein, we review how the predominant glycosaminoglycan hyaluronan (HA) contributes to the structure and function of the tissue microenvironment. Specifically, we examine the evidence of HA degradation and the generation of biologically active smaller HA fragments in pathological settings in vivo. We discuss how HA fragments versus nascent HA via alternate receptor-mediated signaling influence inflammatory cell recruitment and differentiation, resident cell activation, as well as tumor growth, survival, and metastasis. Finally, we discuss how HA fragmentation impacts restoration of normal tissue function and pathological outcomes in disease.

Tissue structure and macromolecular diffusion in umbilical cord. Immobilization of endogenous hyaluronic acid

Diffusion of endogenous hyaluronic acid and 125I-labelled albumin, monitored by desorption from umbilical cord (Wharton's jelly) slices, was studied in relation to tissue structure. Diffusion of hyaluronic acid was Fickian and some two orders of magnitude slower than that in free solution. After treatment of tissue with trypsin which removes proteoglycan(s) and degrades glycoprotein microfibrils, hyaluronic acid mobility through the collagen fibril network that remains is increased by an order of magnitude. These findings indicate that the mobility of hyaluronic acid in tissue is reduced both by the collagen network and by the presence of proteoglycan(s) and/or microfibrils. Estimates of the reduction in mobility due to physical entanglements with the fibrillar networks show that these play a major role. The mobility of hyaluronic acid found for intact tissue is sufficient for it to permeate the extracellular space within its metabolic turnover time. Labelled albumin diffusion is intact tissue, on the other hand, is reduced by only some 30% relative to free solution. This is consistent with the approximate 10% reduction found for the polysaccharide-free tissue (given by the excluded volume fraction) and the approximate 20% reduction expected for the polysaccharides in the interstitial fluid. Similar effects appear to be involved in the mobility of endogenous diffusible proteins in tissue.

The collagen of heart valve

A hydroxylysine-rich type I collagen has been isolated from pepsin-digested porcine heart valve. The ratio of alpha1 to alpha2 in the isolated molecule was 2:1. The component alpha chains exhibited unusual chromatographic behavior in comparison to corresponding chains from human dermis and lathyritic rat skin collagen. The composition of component cyanogen bromide peptides identified the alpha chains as authentic type I chains and demonstrated hydroxylysine enrichment throughout the length of the chain. delta6-Dehydro-5,5'dihydroxylysinonorleucine, a collagen cross-link derived from two hydroxylysyl residues and ordinarily found in hard tissue collagens was found to be the predominant cross-link in heart valve.

Structural investigation of loose connective tissue by using a series of dextran fractions as non-interacting macromolecular probes

The ability of the uncharged open-coil dextran molecules to penetrate tissue space, without coil-shape change, was utilized to probe (by partitioning experiments) the structural arrangement of the collagen-fibre network and the proteoglycan system. Hyaluronidase digests most of the proteoglycans away and enables the respective contributions to the exclusion volume to be evaluated by using a series of different-molecular-weight dextrans. It appears that the major part of the exclusion volume is due to the collagen-fibril as a rod and the dextran coil as an impenetrable sphere. The additional exclusion due to the proteoglycans could be accounted for by a set of points (regions of high proteoglycan-segment density) over which the dextran coild cannot pass. These points are an average of 50 nm apart and are indicative of local extensive entanglement of high-molecular-weight proteoglycans with each other. Reasons are given why these entanglements could not act as cross-links in long-term elastic loading of the tissue.

Aging and the interstitial content of loose connective tissue. A brief note

The concentration of hyaluronic acid which is the fixed loose connective tissue component determining water and other potentials in the interstitium remains constant with age. Since the collagen fiber network in the native tissue state is unstressed, changes in collagen fiber morphology and in collagen content with age have no influence.

Biochemical study of cardiac valvular tissue. Biosynthesis in vitro of hexosamine-containing substances in bovine heart valve

1. Two distinct hexosamine-containing substances have been obtained from bovine cardiac valvular tissue which was incubated with labelled glucosamine. These were identified as mucopolysaccharides and glycopeptides respectively, both by the elution pattern from a Sephadex G-50 column and by chemical analysis. 2. In the mucopolysaccharide fraction about 80% of both the total hexosamine and total radioactivity were present; the galactosamine/glucosamine ratio of the amounts was about 1.36. 3. The glycopeptide fractions had about 20% of both total hexosamine and total radioactivity; the galactosamine/glucosamine ratio of amounts was about 0.44. In this fraction, over 15% of radioactivity was present in sialic acid. 4. In contrast with the concentrations of the several chemical components, there were remarkable differences in the biosynthetic activities among the four valves; the tricuspid valve had highest specific radioactivity in all components of both substances, followed then in turn by mitral, aortic and pulmonary valves. 5. Glucosamine in mucopolysaccharides had a rapid rate of turnover, followed then in turn by turnover rates of both glucosamine and galactosamine in glycopeptides, and of galactosamine in mucopolysaccharides. The possible significance of these findings is discussed.

Isolation and properties of chondroitin sulphates from bovine heart valves

1. Several protein-polysaccharides were isolated from the soluble extracts of bovine heart valves by sedimentation equilibrium in a caesium chloride density gradient (Meyer, Preston & Lowther, 1969). 2. Compositional and structural studies indicated that the polysaccharide moiety was chondroitin sulphate. Differences in the protein content of the products were observed. There was no evidence suggesting the presence of keratan sulphate. 3. Sedimentation studies indicated that the molecular weights of the samples were between 4.2x10(4) and 6.5x10(4). The results are discussed in terms of a basic model for the protein-polysaccharides of two polysaccharide chains linked by a protein of variable size.