Preparation of insoluble collagen from human cartilage

Pre-crosslinked polymeric collagen in 3-D models of mechanically stiff tissues: blended collagen polymer hydrogels for rapid layer fabrication

Currently one factor hindering the development of collagen hydrogel constructs for tissue engineering is the mismatch between initial cellularity and mechanical strength. The main advantage of collagen hydrogel tissue constructs is their ability to support interstitially seeded cells. However, cells are sensitive to their environment, in particular, substrate stiffness, which cannot easily be replicated within hydrogels without cytotoxic cross-linking treatment. In this study, pre-crosslinked polymeric collagen fibrils are introduced as a starting material, thereby avoiding artificial cross-linking. Shear aggregation of this material in solution results in fibril alignment, but cell addition is only possible when polymeric collagen is blended with its monomeric counterparts to slow the aggregation of collagen fibrils. The hydrogel can then be brought to physiological collagen density by plastic compression. Interstitially seeded fibroblasts were supported for 14days. Although compression of blended gels resulted in some cell death due to increased rate of fluid expulsion, not normally seen in conventional collagen hydrogels, the surviving cell population recovers during subsequent culture. Importantly, the compression process can be controlled and customized to limit cell damage. This is the first report of native polymeric collagen used in a tissue engineering context, for the rapid production of a stiff collagen-cell constructs.

Glucose Oxidase Incorporated Collagen Matrices for Dermal Wound Repair in Diabetic Rat Models: A Biochemical Study

Impaired wound healing in diabetes is a well-documented phenomenon. Emerging data favor the involvement of free radicals in the pathogenesis of diabetic wound healing. We investigated the beneficial role of the sustained release of reactive oxygen species (ROS) in diabetic dermal wound healing. In order to achieve the sustained delivery of ROS in the wound bed, we have incorporated glucose oxidase in the collagen matrix (GOIC), which is applied to the healing diabetic wound. Our in vitro proteolysis studies on incorporated GOIC show increased stability against the proteases in the collagen matrix. In this study, GOIC film and collagen film (CF) are used as dressing material on the wound of streptozotocin-induced diabetic rats. A significant increase in ROS ( p < 0.05) was observed in the fibroblast of GOIC group during the inflammation period compared to the CF and control groups. This elevated level up regulated the antioxidant status in the granulation tissue and improved cellular proliferation in the GOIC group. Interestingly, our biochemical parameters nitric oxide, hydroxyproline, uronic acid, protein, and DNA content in the healing wound showed that there is an increase in proliferation of cells in GOIC when compared to the control and CF groups. In addition, evidence from wound contraction and histology reveals faster healing in the GOIC group. Our observations document that GOIC matrices could be effectively used for diabetic wound healing therapy.

Interactions of elastin and aorta with sugars in vitro and their effects on biochemical and physical properties

Stiffening of blood vessel walls occurs in the early stages of atherosclerosis, and this process is known to occur earlier in diabetic subjects. The effect could be due, in part, to glycation. Although collagen is responsible for ensuring the ultimate tensile strength of the tissue, elastin largely determines the compliance of the vessel wall in the normal physiological range of pressures and this appears to be closely matched to haemodynamic requirements. Changes in elastin are therefore likely to affect optimal function of the tissue. We have investigated the susceptibility of elastin to glycation and effects of glycation on its mechanical and physicochemical properties. We found that purified elastin and a collagen-elastin preparation from the porcine thoracic aorta rapidly incorporated glucose and ribose, the extent increasing linearly with increasing concentration and reaching a maximum after 7 days at 37 degrees C. Biochemical analysis showed that about one of the five lysines available per elastin monomer was glycated after 12 days incubation at a sugar concentration of 250 mmol/l. In long-term incubations glycation was associated with the appearance of the advanced glycation end products, the fluorescent cross-link pentosidine and the non-fluorescent putative cross-link NFC-1. In both purified elastin and the whole elastin-collagen matrix the slope of the force-extension curve increased significantly with glycation. The greatest increase in stiffness was observed in the elastin-collagen preparation after ribose incubation (250 mmol/l for 1 month), where the slope, at large strain, increased by 56 +/- 19% (mean +/- SD, n = 12). The diameter of the tissue at 1 N force also changed: for elastin there was an increase in length of approximately 5%, but for the elastin-collagen there was a decrease of similar magnitude indicating that glycation introduces differential strains within the fibrous protein matrix. Potentiometric titration demonstrated that glycation was associated both with loss of basic groups and shifts in pK of the acidic groups, which indicated changes in the environment of the charge groups due to conformational rearrangements. Changes in ion binding were dependent on pH, and were consistent with a reduction in effective anionic charge. Calcium binding to elastin was increased at acid pH, but decreased at higher pH. We suggest that these effects are not only due to changes in the charge profile, but also in the conformation of the molecule resulting from glycation of the charged lysine and arginine side-chain residues.

Quantitative analysis of chondroitin sulphate retention by tannic acid during preparation of specimens for electron microscopy

The ability of tannic acid to enhance binding of glycosaminoglycans to purified collagen was analysed in an in vitro system using amino sugar analysis on an amino acid analyser, transmission electron microscopy, and scanning electron microscopy. Collagen was purified by digestion with trypsin, papain, and hyaluronidase. Purified collagen was incubated with hyaluronic acid or with chondroitin sulphate glycosaminoglycan and then treated with tannic acid. Tannic acid was found to enhance retention during preparation for electron microscopy of either of the glycosaminoglycans onto collagen fibres. The ability of tannic acid to enhance binding of collagen and glycosaminoglycans might explain, at least in part, its structural reinforcement effect on resected synovial joint-apposing surfaces during preparation for scanning electron microscopy.

Intrinsic fibre architecture and attachments of the human epiglottis and their contributions to the mechanism of deglutition

Two mechanisms have been proposed which address the downfolding of the epiglottis during swallowing. The passive mechanism (Fink et al. 1979) focuses on passive mechanical forces transmitted through the median hyoepiglottic ligament and pre-epiglottic adipose tissue to the epiglottis. The active mechanism (Ekberg & Sigurjonsson, 1982) expands the passive mechanism to include active contributions from the aryepiglotticus and thyroepiglotticus muscles. By means of laryngeal microdissection and whole mount orcein staining, distinct bands of fascial condensations were identified running from the lateral edge of the epiglottis just superior to the attachment of the median hyoepiglottic ligament to the hyoid bone near the ends of the greater horns. Neither the proposed active nor the passive mechanisms address the possible contribution of these paired lateral hyoepiglottic ligaments to epiglottic downfolding. Computer image analysis of videofluoroscopic examinations of swallowing was then used to assess the dynamic movements of the larynx during swallowing. It was observed that the downfolding of the epiglottis occurred in the same video frame as initiation of anterior displacement of the hyoid bone and thyrohyoid approximation. Based on the anatomical and dynamic relationship of the epiglottis to other laryngeal structures, we propose that as the larynx elevates and the hyoid bone moves anteriorly, these lateral ligaments exert traction preferentially on the upper third of the epiglottis to bring it to a position below the horizontal.

Light and electron microscopic morphology of the temporomandibular joint in growing and mature crab-eating monkeys (Macaca fascicularis): the condylar articular layer

In an attempt to establish maturational alterations in the morphology of the articular tissue layer, mandibular condyles of four immature and four mature male monkeys (Macaca fascicularis) were studied using light microscopy as well as scanning and transmission electron microscopy. Specimens were fixed in situ by perfusion in the presence of ruthenium red to stabilize proteoglycans. Preparations intended for observation in the scanning electron microscope were first dehydrated and sputtered for the examination of articular surfaces, and afterwards treated with trypsin to expose the spatial arrangement of collagen fibrils. Gross anatomical relations between joint components indicated that the anterior and central, but not the posterior region of the condylar articular surface can be subject to compressional load. Load-bearing and non-load-bearing regions differed with respect to the morphology of the articular layer. Load-bearing surfaces were covered by a prominent articular surface lamina similar to that observed on articular cartilage. This lamina seemed to constitute an integral part of the articular layer, distinct from the lining of synovial fluid, and to be composed largely of proteoglycans. It was unaffected by maturation. The subjacent, load-bearing articular layer differed markedly in structure, both from articular cartilage, and between immature and mature animals. Articular cells of immature animals were classified as fibroblastlike, but unlike typical fibroblasts, were surrounded by a thin, often incomplete halo of fibril-free pericellular matrix, presumably consisting of proteoglycans. In mature animals, articular cells closely resembled chondrocytes, but exhibited prominent nuclear fibrous laminae, which usually are found only in fibroblasts. Thus, the load-bearing part of the articular layer seems to undergo a maturation-dependent metaplastic conversion, from a dense connective tissue with some features of fibrocartilage, to a fibrocartilage-like tissue containing chondrocyte-like cells with some features of fibroblasts. This conversion might reflect an adaptation to a maturation-associated increase in articular stress.

Scanning electron microscope observations on collagen fibers in human dentin and pulp

Human permanent teeth were examined in the scanning electron microscope after demineralization and exposure to preparative procedures based on hydrogen peroxide, trypsin, and EDTA. These substances removed the inorganic material, the cellular structures, the homogeneous connective tissue ground substance, and interfibrillar matrix. The remaining tissue components comprised a network of distinct collagen fibers whose organization was related to the type of tissue in which these were incorporated. A similar or identical method has not been developed or applied to teeth previously. Dentin and predentin comprised a compact mass of fibers which basically were parallel to the continuously growing interior surface of the predentin, or arranged at an acute angle to this plane. Collagen fibers in the pulp were numerous, but lacked any particular orientation in most areas. Interodontoblastic fibers crossed the odontoblastic zone at a right angle to the pulp chamber wall and mingled with collagen fibers in predentin. When previously published findings of ours are taken into account, it is possible to conclude that other factors than the organization of the collagen fibers are responsible for the stainability of these fibers in predentin and in interglobular dentin with silver methenamine, and that aldehyde groups on collagen fibers in predentin may be actively and directly involved in the mineralization of the dentin.

Extrafibrillar proteoglycans osmotically regulate the molecular packing of collagen in cartilage

The molecular packing density of collagen and hence the intrafibrillar water content appears to be regulated in cartilage by the osmotic pressure gradient existing between the extrafibrillar and the intrafibrillar compartments.

The role of calcium in the mechanical behaviour of bone

Plugs of fresh post mortem human patellar subchondral bone were soaked for three weeks in an organic solvent (ethanol) which contained a chelating agent (EDTA). This technique selectively removes the calcified inorganic component without disrupting the structure of the remaining bone matrix. These plugs, together with untreated plugs as controls, were treated in unconfined compression at a fixed strain rate and allowed to relax to evaluate the contribution made by the calcium component to the physical and time-dependent properties of subchondral bone.

Chemical composition and swelling of normal and osteoarthrotic femoral head cartilage. II. Swelling

Studies of the equilibrium, partition, and diffusion of tritiated water were carried out on normal and osteoarthrotic cartilage as well as on cartilage from which proteoglycans had been extracted chemically. All the water was found to be freely exchangeable in both normal and degenerate specimens. The diffusiviity of the water was equal to about 40% of the value in free solution, with an activation energy equal to that in free solution. It was concluded that the swelling of degenerate tissue is not due to any changes in the state of the water, but to a failure of the damaged collagen network to oppose the swelling pressure of the proteoglycans. Swelling similar to that observed in fibrillated cartilage was also found in initially normal specimens treated with collagenase.

Osteoarthrotic articular cartilage lesions of the femoral head observed in the scanning electron microscope

A topographical study of the articular surface of 21 femoral heads removed for surgery of osteoarthrosis was made using the scanning electron microscope. Sections of degenerate cartilage were pretreated with H2O2 and trypsin to reveal the collagenous framework. Torn and frayed collagen bundles were evident on all the specimens studied, the length of these bundles varying from 20 to 150 micron. The frequency of the bundles over the degenerate fibrous areas varied considerably, and bundle sizes ranged from 20 to 70 micron. The topography of a single femoral head removed from a rheumatoid arthritic was very much smoother, with torn fibre ends ruptured at the same level. Although the exposed bone was considerably "smoother" than the residual fibrocartilage, ruptured osteons and trabeculae revealed large voids in the surface which would presumably alter the lubrication and fluid flow characteristics of the functioning joint. The effects of these changes on joint tension and lubrication are discussed.

Chemical composition and swelling of normal and osteoarthrotic femoral head cartilage. I. Chemical composition

Radiochemical and biochemical methods were used to characterize post-mortem and osteoarthrotic femoral head cartilage. Fixed charge density measurements were correlated with glycosaminoglycan content as estimated by uronic acid and hexosamine analyses. In post-mortem cartilage water content decreased from a maximum at the surface to a minimum in the deep zones. In the osteoarthrotic specimens water content was greatest in the middle zones. Glycosaminoglycan content increased with depth and in the osteoarthrotic specimens was reduced throughout the depth of the cartilage. With increasing degeneration there was an increase in water content and decrease in glycosaminoglycan content. The difference in the water content profile in osteoarthrotic cartilage was explained in terms of damage to the collagen network. In osteoarthrosis the latter is no longer capable of restraining the swelling pressure produced by the glycosaminoglycans and swelling is greatest in the midzones, where glycosaminoglycan content is highest.

The collagen fibril organization in human articular cartilage

In this scanning electron microscopic study blocks of collagen fibrils were prepared from human articular cartilage, using two techinques which selectively removed either the proteoglycans alone, or both the proteoglycans and the collagen fibrils, of the non-calcified cartilage layer. Amino acid analysis of the fibrils confirmed the purity of the collagen after proteoglycan extraction. The cartilage was scanned in four different ways: (1) normal to the articular surface, (2) in superficial sections, (3) on surfaces of blocks which had been broken in planes parallel to artificial splits make by the insertion of a pin, and (4) on fracture surfaces which traversed the calcified cartilage and the subchondral bone. Five features of the organization of the collagen fibrils were specially noted: (1) Individual fibrils within the trabeculae joined to form small fibre bundles which became grouped into larger bundles at the calcified/uncalcified interface. (2) Fibrils in the deep and middle zones which, exhibiting the characteristic surface periodicity of collagen, were generally oriented towars the articular surface in large bundles approximately 55 micronm across. (3) In the superficial zone, fibrils ran parallel to the surface. (4) The surface fibrils had random orientation, even at the bases of empty lacunae vacated by chondrocytes during specimen preparation. (5) The collagen fibrils of the lacunar walls appeared to be thinner and more closely packed than thos between the lacunae. The fine collagen fibrils associated with the lacunar walls were frequently observed to pass through a large lacunar space, resulting in the formation of two or more compartments, each of which was presumably filled with a chondrocyte in the living cartilage.

Biochemical and physiochemical characterization of pepsin-solubilized type-II collagen from bovine articular cartilage

Solubilization of collagen from bovine articular with pepsin requires the preliminary extraction of proteoglycans from the ground substance. Biochemical and physiochemical properties of this pepsin-solubilized collagen are independent of the pretreatment (extraction with 1.5M-CaCl2, 5M-guanidinium chloride or 0.2M-NaOH) and of the age range (2-4-year-old and 2-month-old animals). Characterization of the de-natured components, of the CNBr peptides and of the amino acid and cross-link composition shows that the collagen of the hyaline cartilage is all type II. Electrical birefringence measurements showed the presence of tropocollagen molecules (length 280nm) and molecules whose length is slightly less than twice that of the tropocollagen molecules. This latter molecule may be a dimer composed of two monomers linked by intermolecular head-to-tail bonds and whose theoretical length (530nm), according to the quarter-stagger theory, is in good agreement with our measured values (510-530nm). We have verified that the beta-components of this collagen are formed of two alpha-chains linked by the stable intermolecular bond, dehydrodihydroxylysinonorleucine. These dimeric molecules are absent from solutions of skin collagen whose beta-components possess only aldol-type intramolecular cross-links. Although reconstituted fibres from solutions of skin and cartilage collagen are similar, the segment-long spacing crystallites formed with pepsin-solubilized cartilage collagen present a symmetrical and dimeric form corresponding to the lateral aggregation of two monomers with an overlap (90nm) of the C-terminal ends.

[The change of hyaluronic acid of the vitreous humour by oxidation-reduction-systems (author's transl)]

Purified hyaluronic acid of ox vitreous humour was isolated treating the acetone precipitate of a vitreous humour homogenate with 1 M NaCl solution and thereafter with cetylpyridiniumchloride. Both disc-electrophoresis and hydroxyproline content proved the absence of collagen in the purified hyaluronic acid. FeSO4, ascorbate, and cysteine changed the hyaluronic acid molecule and lowered the viscosity of the hyaluronic acid solution, EDTA alone did not affect the viscosity but enhanced the effectiveness of iron ions or ascorbate on the viscosity of the solution. Catalase prevented the reduction of the viscosity by the above mentioned substances. Therefore, it is suggested that H2O2 and free radicals are generated during the reaction. The free radicals produced are responsible for the change of the hyaluronic acid molecule.

[The attack of different proteases on isolated zonular fibers (author's transl)]

Some proteases, i.e. trypsin, alpha-chymotrypsin, thermolysin, proteinase K, alpha-amylase, collagenase, and papain were investigated on their effect on isolated zonular fibers. All these enzymes but collagenase were zonulolytic active. An attack on the ground substance of the fibers by substances solving glycosaminoglycans and proteoglycans (hyaluronidase, EDTA, guanidinium chloride, H2O2) showed an increased effect of the enzymes used. These results suggest that the interfibrillar matrix has a protective function on the zonular fibers.

Indoluble collagen II. The use of fluorescein labelled polymeric collagen fibrils in a very sensitive assay procedure for enzymes degrading insoluble collagen

98% of the collagen in mature connective tissue is in the form of insoluble collagen fibers, consisting of bundles of polymeric collagen (PC) fibrils. The enzymes concerned in connective tissue remodeling degrade PC rather than tropocollagen (TC). TC is the most usual substrate for collagenase assays, and we believe it is essential to employ PC in any study of the activity of collagenolytic enzymes. In order to facilitate the study of enzymic degradation of PC we have labelled PC with fluorescein iso-thiocyanate to produce F-PC fibrils, containing 5 fluorescein labelled epilson-NH2 groups of lysine per TC molecule within the PC. The fluorescent F-PC is degraded at the same rate as PC with the release of hydroxyprolyl peptides but has the great advantage that the solubilised F-peptides can be quantitated by their fluorescent emission. The technique is described in detail employing bacterial collagenase and mammalian collagenase preparations to illustrate the methodology. The advantages of the fluorescent technique over the collagenolytic assay methods currently in use are outlined.