Methods for the study of the glycoproteins and proteoglycans of bone using bacterial collagenase. Determination of bone sialoprotein and chondroitin sulphate

An in vitro model for the pathological degradation of articular cartilage in osteoarthritis

The objective of this study was to develop an in vitro cartilage degradation model that emulates the damage seen in early-stage osteoarthritis. To this end, cartilage explants were collagenase-treated to induce enzymatic degradation of collagen fibers and proteoglycans at the articular surface. To assess changes in mechanical properties, intact and degraded cartilage explants were subjected to a series of confined compression creep tests. Changes in extracellular matrix structure and composition were determined using biochemical and histological approaches. Our results show that collagenase-induced degradation increased the amount of deformation experienced by the cartilage explants under compression. An increase in apparent permeability as well as a decrease in instantaneous and aggregate moduli was measured following collagenase treatment. Histological analysis of degraded explants revealed the presence of surface fibrillation, proteoglycan depletion in the superficial and intermediate zones and loss of the lamina splendens. Collagen cleavage was confirmed by the Col II-3/4Cshort antibody. Degraded specimens experienced a significant decrease in proteoglycan content but maintained total collagen content. Repetitive testing of degraded samples resulted in the gradual collapse of the articular surface and the compaction of the superficial zone. Taken together, our data demonstrates that enzymatic degradation with collagenase can be used to emulate changes seen in early-stage osteoarthritis. Further, our in vitro model provides information on cartilage mechanics and insights on how matrix changes can affect cartilage's functional properties. More importantly, our model can be applied to develop and test treatment options for tissue repair.

Collagen synthesis and mineralization in the early phase of distraction bone healing

Corticotomy of the distal radius followed by gradual distraction by external fixation was performed on three sheep. Collagen synthesis and mineral deposition were analysed from sequential biopsies obtained from the center of the distraction area during the first 4 weeks of distraction. The whole distraction area was rapidly filled with organic matrix the amount of which, due to fluctuation in its nonprotein component, initially decreased from 88 to 66% of the level in control bone but gained its initial level in 4 weeks. Total protein in the matrix represented 70% of that in the control bone during the 4-week follow up period while the proportion of collagen of the total protein increased from 53 to 88%, a level comparable with the unoperated bone. Determination of the type of fibrillar collagen by characterization of their cyanogen bromide peptides showed that in the distraction area production of type II collagen does not occur but the heteropolymer type I (alpha 1(I)2 alpha 2(I)1) collagen represents almost totally the collagen synthesized. Deposition of mineral into the distraction gap was detectable already after 2 weeks and increased rapidly after 3 weeks of distraction. The results suggest that unlike in other processes, e.g., direct osteonal and callus-type bone repair, in distraction bone healing gradual distraction of osteotomized bone leads directly to synthesis of mature fibrous organic matrix of bone followed by its rapid mineralization.

Studies on EDTA extracts and collagenase digests from osteoporotic cancellous bone of the femoral head

Using EDTA extraction and collagenase digestion, cancellous bone of the femoral heads from 10 normal and 9 osteoporotic subjects were analyzed for their contents of collagen, sialoprotein, proteoglycan and carbohydrate. The percentage of extracted matrix proteins of the osteoporotic bone in EDTA was significantly decreased, as was the collagenase-resistant fraction (p less than 0.05). The sialic acid level in osteoporotic bone matrix was lower than in controls (p less than 0.05). The alterations found in bone matrix constituents in osteoporotic bone relative to controls suggest that in osteoporosis and fractures, not only bone mass changes, but also bone quality changes play a role in bone strength.

Noncollagenous proteins in normal and pathological human bone

The concentrations of alpha 2HS-glycoprotein, albumin, and sialic acid were measured in the bone of 28 normal individuals and 6 patients with osteogenesis imperfecta, 3 patients with Paget's disease, and 4 patients with either renal osteodystrophy, osteoporosis, osteomalacia, or osteopetrosis. The concentration of alpha 2HS-glycoprotein in neonatal bone was 3 X higher than in bone from children and 7 X higher than in adult bone. The concentrations of albumin and sialic acid in neonatal bone were 1.5 X higher that in bone from children and twice the levels in adult bone. The concentrations of alpha 2HS-glycoprotein, albumin and sialic acid were above the normal mean values in the patients with osteogenesis imperfecta, and 4 patients had significantly raised levels of one or more of these proteins. The concentrations of these noncollagenous proteins were also significantly raised in Paget's disease, and the alpha 2HS-glycoprotein was significantly raised in renal osteodystrophy. The lowest level of alpha 2HS-glycoprotein was in osteopetrotic bone and the lowest levels of albumin and sialic acid were in osteoporotic bone. The results of this study suggest that the concentrations of alpha 2HS-glycoprotein, albumin, and sialic acid in bone are related to the rate of bone turnover.

Extraction from bone powder: collagen, calcium and phosphate

A method for the estimation of the extraction rate is shown and exemplified by preliminary data from extraction of collagen, calcium and phosphate with EDTA and neutral salt solution. The initial extraction rate was high, even with neutral salt solution, and optimal extraction efficiency was obtained within 24 h.

Chemical composition of normal and osteoarthrotic cancellous bone of the femoral head. Studies of EDTA extracts and collagenase digests

Using EDTA extraction and collagenase digestion, cancellous bone from the femoral heads of ten normal and eight osteoarthrotic individuals was analyzed for its content of collagen, sialoprotein, proteoglycan, and carbohydrate. The EDTA extractability of the matrix proteins of the osteoarthrotic bone was significantly increased (P less than 0.001), as was the soluble collagenase-resistant fraction (SCRF). EDTA residues, bone matrix size, the collagenase-resistant fraction (CRF), and the insoluble collagenase-resistant fraction (ICRF) of the osteoarthrotic cases were not different from those of the controls. The amounts of carbohydrate and proteoglycans were considerably elevated in the bone matrix of the osteoarthrotic bone (P less than 0.01 and P less than 0.001, respectively). In the EDTA extracts, sialoprotein and proteoglycan contents were found in significant higher amounts (P less than 0.05 and P less than 0.01, respectively) in the osteoarthrotic cases. In the SCRF, the hexose and sialic acid contents were higher in the osteoarthrotic bone (P less than 0.01), while in the ICRF all the analyses were significantly increased in the osteoarthrotic bone (P less than 0.001). The ratios of collagen to non-collagenous components were lower in the osteoarthrotic than in normal bones. The quantitative and qualitative variations in cancellous bone proteins from the femoral head in osteoarthrosis found in this study suggest that alterations in subchondral bone play a role in the pathophysiology of cartilage degeneration in osteoarthrosis.

Chemical composition of human bone

The mineral and non-collagenous organic components of normal human femoral cortex were examined following powdering, demineralization with EDTA and digestion with bacterial collagenase. The protein, hexose, sialic acid and uronic acid contents of the matrix were determined. Neonatal bone had lower levels of mineral and calcium and higher levels of organic material and sialic acid than adult bone, suggesting increased glycoprotein content in neonatal bone. The soluble non-collagenous matrix of human femoral cortex was examined by gel filtration on Sephadex G100 and by ion-exchange chromatography on DEAE-cellulose. Four fractions were eluted off Sephadex-G100: a large molecular weight fraction, a shoulder on the descending portion of this, both of which contained sialic acid and two smaller molecular weight fractions. The material eluted off DEAE-cellulose was separated into 6 fractions which were similar to those found for beef and rabbit bone matrix. Human bone matrix appeared more resistant to collagenase digestion than beef bone, soluble collagen eluted later off DEAE-cellulose than beef bone; sialic acid gave 3 peaks: a major and two lesser ones. The sialic acid-containing material in the fifth fraction was probably bound to proteoglycan. Rabbit bone has 2 to 3 sialic acid peaks whereas beef bone has one, indicating species differences in cortical bone matrix.

Analysis of the heterogeneity of human collagens by two-dimensional polyacrylamide-gel electrophoresis

The heterogeneity of the CNBr-cleavage peptides of human types I, II, III and V collagens were studied by using two-dimensional electrophoresis combining non-equilibrium pH-gradient-gel electrophoresis and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Specific 'maps' were produced by the peptides obtained from the chains of each type of collagen, and most peptides had at least three charged forms of the same molecular weight. Specific 'maps' were also produced by the peptides of types I, III and V collagens from insoluble dermis and the peptides of types I and V collagens from decalcified bone. The alpha 1(I) CB7 and alpha 1(I) CB8 and the alpha 2 CB4 peptides obtained from the type I collagens of these tissues contained the same number of charged components, but there was a relative increase in the more basic components in bone. Some aspects of the involvement of the alpha 1(I) CB6 and the alpha 1(III) CB9 peptides in cross-linkages were also studied. The recovery of the alpha 1(I) CB6 peptide from bone and dermis was decreased and the alpha 1(III) CB9 peptide was not detected in dermis. Additional peptides, which were probably cross-linked peptides involving the alpha 1(I) CB6 peptide, were also observed.

Non-collagenous proteins of rat dentin. Evidence that phosphoprotein is not covalently bound to collagen

The non-collagenous proteins of rat dentin that remain firmly bound to the matrix after demineralization were studied in order to ascertain if they are covalently linked to insoluble dentin collagen. After solubilization with CNBr or with bacterial collagenase, unusually small amounts of dentin phosphoprotein were detected in the matrix. The phosphoprotein obtained by CNBr digestion of the matrix was separated from collagen peptides using two chromatographic steps. Thus even this small quantity of phosphoprotein found in decalcified rat dentin matrix was not covalently bound to collagen.

Ca2+-binding glycoprotein in avian bone induced by estrogen

The discovery in calcifying cartilage of a glycoprotein, endowed with high calcium affinity and alkaline phosphatase activity, has prompted the investigation of the presence of this compound in other calcified tissues. From medullary bone, a tissue which is highly mineralized under estrogen stimulus, a glycoprotein has been extracted which had the properties described. Besides the high calcium affinity (KD = 10(-7)M), this protein shows phosphatase activity and rate of hydrolysis of ATP, GTP and pyrophosphate was measured. Analysis of the chemical composition of the matrix of the medullary bone indicates that proteoglycans are present in large amounts. The calcium binding glycoprotein appears to be a compound present in different calcified tissues.