The degradation of cartilage proteoglycans by tissue proteinases. Proteoglycan structure and its susceptibility to proteolysis

Distribution pattern and functional state of alpha 1-antichymotrypsin in plaques and vascular amyloid in Alzheimer's disease. A immunohistochemical study with monoclonal antibodies against native and inactivated alpha 1-antichymotrypsin

Monoclonal antibodies (mAbs) were raised against inactivated alpha 1-antichymotrypsin (ACT) to study the presence and functional state of the serine protease inhibitor alpha 1-antichymotrypsin in cerebral amyloid deposits in Alzheimer's disease. A panel of seven different mAbs was obtained; six of them were directed against neoepitopes that are expressed on ACT after interaction with proteases (inactivated ACT) and one mAb was directed against an epitope that is exposed both on native and inactivated ACT. The mAbs against neoepitopes could discriminate native ACT from complexed and inactivated ACT in vitro as shown in binding experiments in the presence of either native or inactivated ACT. With the mAbs against ACT we found that: (a) besides classical congophilic plaques, amorphous noncongophilic beta/A4-positive plaques were stained; (b) amorphous and classical plaques reacted with both types of mAbs against ACT indicating that this ACT was either complexed to a protease or proteolytically inactivated; (c) vascular amyloid was not stained for ACT. The presence of ACT in amorphous and classical plaques and its absence in vascular amyloid may indicate differences in the proteolytic degradation of preamyloid into amyloid fibrils. Our study strongly suggests that ACT is biologically active in amyloid plaques from an early stage.

Monitoring of elastase in plasma of burned patients in relation to other inflammation parameters

Twenty burned patients divided in three groups according to the severity of the lesions were investigated at 1- or 2-day intervals for up to 5 weeks after injury. Plasma elastase levels were elevated during the first day after injury and were correlated with the area of the burns. However, plasma elastase was rapidly bound and inactivated by protease inhibitors. Leucocyte counts, fever and the concentration of alpha-1-proteinase inhibitor were not correlated with the extent of the burn. The rise of plasma elastase was not accompanied by consumption of the elastase inhibitory capacity (EIC) of plasma, which increased to a plateau around day 5. The EIC values were in accord with the rise of alpha-1-proteinase inhibitor, the major anti-elastase agent in plasma. Studies of blister fluid in eight patients showed that the elastase content was higher than that of corresponding plasma, while the concentration of alpha 1-proteinase inhibitor and the EIC were comparable with those of plasma. Measurements of the levels of tumour necrosis factor released by stimulated macrophages in five patients with major burns showed no significant increase compared with controls.

Structural characterization of human alveolar bone proteoglycans

Proteoglycans were extracted from EDTA-demineralized human alveolar bone under dissociative conditions using 4 M guanidinium chloride in the presence of protease inhibitors. The extract was further purified by anion-exchange chromatography on DEAE-Sephacel, using a step-wise salt gradient. The proteoglycan-rich fraction was analysed for carbohydrate, protein and amino acid composition and molecular size by SDS-PAGE. Glycosaminoglycan content was determined by cellulose acetate electrophoresis after proteolysis. The sulphate isomers of the glycosaminoglycans were confirmed by Fourier-transformed infra-red spectroscopy. Two chondroitin sulphate-proteoglycan species were identified with molecular weights of 79 and 55-65 kDa, respectively. The core proteins had molecular weights of 49 kDa for both proteoglycans, with the amino acid content rich in glycine, leucine, glutamate and aspartate. The chondroitin sulphate chains were mainly as the 4-sulphate isomer forms although low but detectable amounts of 6-sulphate isomer were also present.

Cathepsin B and cysteine protease inhibitors in human osteoarthritis

The aim of this study was to determine the involvement of cathepsin B and its inhibitors in the proteolytic degradation of human osteoarthritic (OA) tissue. The characteristics of the cathepsin B found in both normal and OA cartilage and synovium were similar to those of the lysosomal cathepsin B. Two inhibitors of cysteine proteases were found with a molecular weight of 67,000 and 16,000 Da. The cartilage cathepsin B level of OA specimens (54.8 +/- 7.3 units/micrograms of DNA) was greater than the controls (39.8 +/- 3.2 units/micrograms of DNA). Mild-moderate graded samples (78.1 +/- 12.0 units/micrograms of DNA) had significantly higher levels of enzyme activity than the severely graded ones (31.4 +/- 3.9 units/micrograms of DNA, p less than 0.001) and controls (p less than 0.01). Compared to controls (2.3 +/- 0.4 units/mg of tissue w.w.), cysteine protease inhibitory activity in OA cartilage was decreased in specimens with severe lesions (1.5 +/- 0.2 units/mg of tissue). This was particularly noted in patients who had not received steroid injections (1.2 +/- 0.3 units/mg of tissue, p less than 0.05). In OA synovia, the cathepsin B level was greater (40.7 +/- 7.4 units/mg of tissue w.w., p less than 0.02) than in the controls (13.6 +/- 3.7 units/mg of tissue). The cysteine protease inhibitory activity was similar in OA synovium (1.7 +/- 0.2 units/mg of tissue w.w.) and in controls (1.5 +/- 0.3 units/mg of tissue). This data demonstrated an imbalance between the levels of cathepsin B and cysteine protease inhibitors in OA tissue. A decrease of specific inhibitors could be an important contributing factor, particularly in more severe lesions.

Histologic and histochemical changes in articular cartilages of immature beagle dogs dosed with difloxacin, a fluoroquinolone

The histologic and histochemical features of quinolone-induced arthropathy were studied using 14 skeletally immature Beagle dogs (3 to 4 months old) dosed orally with difloxacin at 300 mg/kg body weight once daily for 1, 2, 5, or 7 days. A placebo was given to eight other age-matched Beagle dogs that served as controls. A scoring technique that included lesion size and histologic features was used to determine the progression of lesions. Articular-epiphyseal cartilage complexes on the femoral and humeral heads and tibial tarsal bone were identified as predilection sites. Within predilection sites on femoral and humeral heads, lesions developed in specific areas. Lesions appeared within 2 days of the onset of treatment, and lesion scores increased with time. Grossly, the lesions were raised, fluid-filled vesicles on the articular surface. Histologic changes included vesicle formation with loss of proteoglycan, clumping of unmasked collagen, and degeneration and necrosis of chondrocytes. In lesions with higher scores, chondrocytes were often in clusters or they were undergoing metaplasia toward spindle-shaped cells. Although dissolution of matrix and necrosis of chondrocytes were typical of all lesions, smaller lesions had histologically normal chondrocytes adjacent to small vesicles. In sections stained with toluidine blue, proteoglycan was aggregated with collagen fibrils or was absent from the matrix adjacent to vesicles. Unique features, such as biomechanical forces, may predispose specific areas of articular cartilage to develop lesions.

Determination of cathepsins B and H in sera and synovial fluids of patients with different joint diseases

Synovial fluids and sera of patients with inflammatory and metabolic joint diseases contain different cysteine proteinases. The quantities of cathepsins B and H were determined by newly developed specific enzyme-linked immunoassay tests (ELISA), with detection limits of 0.5 microgram/l for cathepsin B and 3 micrograms/l for cathepsin H. The values of cathepsin B in normal sera ranged from 0.6 microgram/l to 2 micrograms/l, whereas in sera of patients with joint diseases they ranged from 1.7 micrograms/l to 18 micrograms/l. Cathepsin H was not found in sera (values below 3 micrograms/l), but was measurable in patients' synovial fluids. Patients with rheumatoid arthritis have on average the highest values of cathepsin B in synovial fluids, whereas patients with undifferentiated arthritis have the highest values of cathepsin H. The results show that cathepsins B and H are present in arthritic synovial fluids, where they may be implicated in destructive processes. There is yet no clear correlation between the quantity of each cathepsin released in synovia and the clinical diagnosis or the stage of the disease.

Cartilage proteoglycan aggregate is degraded more extensively by cathepsin L than by cathepsin B

The degradative actions of cathepsins L and B on human articular-cartilage proteoglycan aggregates were examined. Cathepsin L was found to be much more extensive than cathepsin B in degrading proteoglycan aggregates. It released products with size similar to that of single chondroitin sulphate chains, and a series of degraded link-protein fragments in the digestion mixtures. These proteolytically modified link-protein components (Mr 25,000 and 33,000) have similar Mr values to those of fragments observed in adult human cartilage. In contrast, cathepsin B exhibited a much more limited degradation on both proteoglycan subunits and link-protein components. Both cathepsins L and B generate multiple but distinct cleavage sites on human link proteins, and the hydrolysed bonds have been identified in the region between residues 18 and 29. Protein sequencing analysis of these modified link-protein components also provided evidence for the location of a second N-linked glycosylation site at residue 41 in human link proteins, in addition to that previously described at residue 6 on a proportion of the link proteins. Furthermore, it allows us to report the sequence of human link protein up to residue 65.

Collagen degradation in ischaemic rat hearts

Myocardial extracellular matrix is organized into a complex arrangement of intercellular and pericellular fibres and fibrils that serves as a supporting framework for contracting cells. Recent evidence suggests that changes in ventricular shape and function occurring after ischaemic injury may be related to alterations of this matrix. In this report we describe the rapid and extensive loss of collagen in myocardial infarction produced by ligating the left anterior descending coronary artery of the rat for 1-3 h. The total collagen content in the myocardial infarct zones after 1, 2 and 3 h of ligation was 75 +/- 8%, 65 +/- 7% and 50 +/- 10% respectively (mean +/- S.D.) of that of either the non-infarcted tissue controls or of the same regions in sex- and age-matched normal left ventricles. A marked decrease also occurred in the residual collagens which were not extractable with 6 M-guanidine hydrochloride, suggesting that rapid degradation of insoluble collagen fibres may also occur. The decreased collagen content in the 3 h myocardial infarct coincided with the appearance of several enzyme activities. Collagenase, other neutral proteinase and presumed lysosomal serine proteinase activities were increased by 3, 3 and 2 times the control values respectively. These results suggest that the increased activities of collagenase and other neutral proteinases may be responsible for the rapid degradation of extracellular matrix collagen in myocardial infarct.

Isolation and characterisation of a neutral proteinase from the canine intervertebral disc

A neutral proteinase of 94 kDa capable of degrading gelatin, canine disc proteoglycan, and L-lysine and L-arginine peptide substrates has been isolated from the greyhound intervertebral disc. Strong inhibition of this proteinase with class-specific inhibitors, such as APMSF, TLCK and benzamidine indicated a 'serine'-type specificity. Metallo, aspartyl- and cysteine proteinase inhibitors were devoid of significant action. Degradation of the resident canine disc proteoglycan monomer by the disc proteinase was shown to occur at the hyaluronic acid binding region, thereby diminishing its ability to aggregate with hyaluronic acid. The hydrodynamic size of the proteoglycan degradation products was only slightly less than that of the intact disc proteoglycan subunits.

Drug-induced inhibition of proteoglycanase activity in the Hulth-Telhag model

Evidence has accumulated that there are increased degradative enzymes in osteoarthritis responsible for joint destruction. These enzymes are metal-dependent, and inhibited by EDTA. EDTA was administered intra-articularly to rabbits in an experimental model of osteoarthritis. There was a 25% reduction in neutral proteoglycanase activity and 75% of the animals had a reduction in the severity of the arthritis as measured on a histologic-histochemical grading system. It is suggested that future chemotherapeutic studies on arthritis might focus on enzyme inhibition.

Structure, function, and control of neutrophil proteinases

Elastase and cathepsin G are two of the major enzymes present in and secreted by human neutrophils. These proteinases can rapidly degrade connective tissue proteins. However, they also may be involved in other processes, including the activation or inactivation of protein hormones and the inactivation of plasma proteinase inhibitors. Neutrophil elastase has been implicated in the development of pulmonary emphysema, although a function for cathepsin G has not yet been elucidated. Both enzymes are normally tightly controlled by plasma proteinase inhibitors. However, this proteinase-proteinase inhibitor balance can be perturbed in favor of free enzyme by several methods, with resulting tissue damage. The use of inhibitors from several sources should be helpful in augmenting natural levels so that homeostasis can be maintained.

Structure, function, and control of neutrophil proteinases

Elastase and cathepsin G are two of the major enzymes present in and secreted by human neutrophils. These proteinases can rapidly degrade connective tissue proteins. However, they also may be involved in other processes, including the activation or inactivation of protein hormones and the inactivation of plasma proteinase inhibitors. Neutrophil elastase has been implicated in the development of pulmonary emphysema, although a function for cathepsin G has not yet been elucidated. Both enzymes are normally tightly controlled by plasma proteinase inhibitors. However, this proteinase-proteinase inhibitor balance can be perturbed in favor of free enzyme by several methods, with resulting tissue damage. The use of inhibitors from several sources should be helpful in augmenting natural levels so that homeostasis can be maintained.

Immunochemical identification of the serine protease inhibitor alpha 1-antichymotrypsin in the brain amyloid deposits of Alzheimer's disease

Two approaches--molecular cloning and immunochemical analysis--have identified one of the components of Alzheimer's disease amyloid deposits as the serine protease inhibitor alpha 1-antichymotrypsin. An antiserum against isolated Alzheimer amyloid deposits detected immunoreactivity in normal liver. The antiserum was then used to screen a liver cDNA expression library, yielding three related clones. DNA sequence analysis showed that these clones code for alpha 1-antichymotrypsin. Antisera against purified alpha 1-antichymotrypsin stained Alzheimer amyloid deposits, both in situ and after detergent extraction from brain. The anti-amyloid antiserum recognizes at least two distinct epitopes in alpha 1-antichymotrypsin, further supporting the presence of this protein in Alzheimer amyloid deposits. In addition to being produced in the liver and released into the serum, alpha 1-antichymotrypsin is expressed in Alzheimer brain, particularly in areas that develop amyloid lesions. Models by which alpha 1-antichymotrypsin could contribute to the development of Alzheimer amyloid deposits are discussed.

Degradation of rat chondrosarcoma proteoglycans by a neutral metalloprotease from rabbit chondrocytes

Rat chondrosarcoma proteoglycan aggregate with radiolabeled core protein was digested with a chondrocyte metalloprotease (CMP) or clostripain (CP) at neutral pH. The rates of product formation and the sizes and antigenicities of the products were studied using column chromatography and monoclonal antibodies. Sixteen percent of [35S]methionine label and 17-18% of [3H]serine label in core protein were freed from glycosaminoglycan bound peptides by 50 U/ml (760 micrograms/ml) of CP or 10 micrograms/ml (estimated) of CMP in 180 min. The CP reaction was almost complete at 5 minutes while the CMP reaction proceeded slowly from 5 to 180 min. The chondroitin-sulfate rich fragments were smaller after CP than CMP treatment. The 180 min CMP digest contained protein that migrated in 2 peaks on Sepharose CL6B. These two peaks corresponded to the peaks where hyaluronic acid binding region produced by CP and link protein migrate. Metalloenzyme inhibitors inhibited CMP with IC50s of 5 x 10(-5)M, 1 x 10(-3)M, and 80 micrograms/ml for phenanthroline, EDTA, and alpha 2-macroglobulin, respectively.

Interaction of polymorphonuclear leukocytes with cartilage in vitro. Catabolic effects of serine proteases and oxygen radicals

The ability of purified PMN serine proteases as well as oxygen-derived free radicals (ODFR) generated by activated phagocytes to damage cartilage matrix has been thoroughly investigated in vitro. The question in the present study was the extent to which enzymatic and ODFR-mediated mechanisms can contribute to the degradation of bovine cartilage slices by zymosan-stimulated PMN. Tissue destruction as assessed by mechanical parameters of stability as well as by liberation of uronic acids from matrix proteoglycans was not inhibitable by the radical scavengers superoxide dismutase (SOD) and catalase (CAT), while serine protease inhibitors led to a significant reduction of matrix degradation. Thus an enzymatic mechanism may play a major part in PMN-induced cartilage damage. Besides this predominant role of especially serine proteases a direct, non-zymosan-dependent stimulatory effect of cartilage matrix on PMN to release elastase into the incubation medium was detected. Hence an as-yet unknown mechanism of PMN activation is indicated, while unspecific effects by bacterial contamination, complement factors, or endotoxin could be excluded as an explanation for the observed phenomenon.

The glycosaminoglycan constituents of alveolar and basal bone of the rabbit

Proteoglycan was extracted from alveolar and basal bone of New Zealand White rabbits using a sequential extraction procedure. Proteoglycans not associated with the bone mineral represented 1% of the total organic matrix whereas proteoglycans associated with the mineral represented 20% of the alveolar organic matrix and 12% of the basal organic matrix. Chondroitin-4-sulphate and keratan sulphate were identified in both alveolar and basal bone following protease treatment of the proteoglycan extracts and enzymic digestion with chondroitinase AC, ABC and keratanase. Differences were observed in the percentage of each glycosaminoglycan (GAG) in the total organic matrix. In alveolar bone samples, keratan sulphate and chondroitin-4-sulphate is present in equal proportions. In basal bone chondroitin-4-sulphate represents approximately half the value found in alveolar bone and keratan sulphate about a quarter. The extracts were examined by gel filtration on Sepharose 4B under associative conditions. The 280 nm absorbance profiles of proteoglycan from alveolar and basal bone were essentially similar with three main peaks evident, including molecular weight material in excess of 2 X 10(6). The bulk of the bone GAG appeared in the medium molecular weight range with trace amounts in lower molecular weight fractions.

The immunologic detection and characterization of cartilage proteoglycan degradation products in synovial fluids of patients with arthritis

Antibodies were used in radioimmunoassays with gel chromatography to detect the hyaluronic acid-binding region, core protein, and keratan sulfate of human cartilage proteoglycan in the synovial fluids of patients with rheumatoid arthritis, juvenile rheumatoid arthritis, and osteoarthritis. All fluids contained proteoglycan that was mainly included on Sepharose CL-4B; this result indicates cleavage of proteoglycan (which is normally excluded). The hyaluronic acid-binding region was the smallest and most commonly detected fragment. It was relatively free of keratan sulfate and core protein, and it could sometimes bind to hyaluronic acid. Other larger fragments containing core protein and/or keratan sulfate were detected in every fluid.

Primary structure of human neutrophil elastase

The complete amino acid sequence of human neutrophil elastase has been determined. The protein consists of 218 amino acid residues, contains two asparagine-linked carbohydrate side chains, and is joined together by four disulfide bonds. Comparison of the sequence to other serine proteinases indicates only moderate homology with porcine pancreatic elastase (43.0%) or neutrophil cathepsin G (37.2%). In particular, many of the residues suggested to play important roles in the mechanism by which the pancreatic elastase functions are significantly changed in the neutrophil enzyme, indicating alternative types of binding with the human proteinase.

Biochemical changes in periodontal ligament ground substance associated with short-term intrusive loadings in adult monkeys (Macaca Fascicularis)

Proteoglycan-like fractions (PG) were isolated from the ligaments of teeth undergoing various degrees of intrusive loadings. The PG were characterized by their molecular-size profiles on Sepharose 4B, the presence of uronic acid in the separated fractions and by the electrophoretic detection of constituent glycosaminoglycans including heparan sulphate, hyaluronic acid, dermatan sulphate and chondroitin-4-sulphate. The high molecular-weight fraction, peak i (estimated minimum size, 2 X 10(6) daltons) of the normal-functioning (stressed) ligament was reduced approx. 70 per cent, compared with ligament undisturbed for 3 h. There was a decrease in peak-i size between 0.25 and 1 N loadings of approx. 72 per cent. The 4 N loadings produced a further decrease followed by an increase during a 3 h undisturbed recovery phase. Thus changes in the chemistry and properties of the ground-substance components of the periodontal ligament could partly explain changes in tooth mobility.

Isolation, characterization, and amino-terminal amino acid sequence analysis of human neutrophil cathepsin G from normal donors

Human neutrophil cathepsin G from normal donors has been purified 82-fold using an isolation procedure which included sequential sodium chloride extraction, Aprotonin-Sepharose affinity chromatography, CM-cellulose ion-exchange chromatography, and AcA44 gel filtration chromatography. The inclusion of this last purification step was crucial for separating inactive lower molecular weight species from the active forms of neutrophil cathepsin G and resulted in a higher specific activity of the final preparation. SDS polyacrylamide gradient gel electrophoresis of the purified reduced protein demonstrated three discrete polypeptides of Mr 31,000, 30,000, and 29,500. Peptide analysis of tryptic digests indicated that these three polypeptides are structurally related to each other and represent microheterogeneity of the purified protein. The cathepsin G peptide maps were distinctly different from the peptide maps of neutrophil elastase. The apparent isoelectric points of these forms as determined by two-dimensional electrophoresis was approximately 8.0. Utilizing microsequencing techniques, the first 25 residues of normal neutrophil cathepsin G have been determined and shown to be identical (except for residue 11) with the sequence of 21 residues of cathepsin G isolated from leukemic myeloid cells. A high degree of homology was found when the amino-terminal regions of neutrophil cathepsin G, rat mast cell protease II (65%) and two human serine proteinases, factor D (52%) and neutrophil elastase (48%), were compared. A precipitating monospecific antiserum to cathepsin G was produced by repeated immunizations of guinea pigs. This antiserum has been used in immunoblotting experiments to demonstrate that the intracellular form(s) of this enzyme is the same approximate Mr as the purified enzyme, and to develop a solid-phase radioimmunoassay for measuring neutrophil cathepsin G in the range 5-50 ng/ml.

The effect of chronic inflammation on gingival connective tissue proteoglycans and hyaluronic acid

Proteoglycans have been isolated and analysed from extracts of normal and chronically inflamed human gingiva in order to determine the effects of chronic inflammation on these important soft connective tissue extracellular macromolecules. The uronic acid content of glycosaminoglycans isolated by papain digestion of normal and inflamed gingiva did not differ significantly. Likewise, electrophoretic analysis revealed that the content of hyaluronic acid, heparan sulfate, dermatan sulfate and chondroitin sulfate was similar. The sulfated glycosaminoglycans from both sources eluted from a Sepharose C1-6B column with a Kav of 0.45 (approximate Mr 25,000). However, hyaluronic acid from normal gingiva was predominantly of a large size eluting in the void volume of a Sepharose. CL-6B column, while that isolated form inflamed tissue was mostly a small molecular weight species which eluted in the included volume of a Sepharose CL-6B column. Using dissociative conditions, intact proteoglycans could be more readily extracted from inflamed tissues (90% of the total tissue uronic acid) than from normal tissues where only 80% of the total tissue uronic acid was extractable. Even though DEAE-Sephacel ion-exchange chromatography revealed no differences in charge between normal and inflamed gingival proteoglycans, Sepharose CL-4B chromatography revealed more molecular size polydispersity in samples from inflamed tissue than from normal tissue. Taken together, these results indicate that while hyaluronic acid is depolymerized in inflamed tissue, no evidence of sulfated glycosaminoglycan degradation was found. Therefore, the most likely cause for disruption to the molecular integrity of the proteoglycans is via proteolytic alteration to the proteoglycan core protein.

Isolation, characterization, and amino-terminal amino acid sequence analysis of human neutrophil elastase from normal donors

Human neutrophil elastase from normal donors has been purified using an isolation procedure which included sequential sodium chloride extraction, Aprotinin-Sepharose affinity chromatography, CM-cellulose ion-exchange chromatography, and AcA44 gel filtration chromatography. The inclusion of this last purification step was crucial for separating inactive lower molecular weight species from the active forms of neutrophil elastase and resulted in a higher specific activity of the final preparation. Sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis of the reduced purified protein demonstrated three polypeptides of Mr 31,000, 28,000, and 27,500. Four polypeptides were resolved on acid gel electrophoresis; each of the four possessed amidolytic activity. Furthermore, peptide analysis of Staphylococcus aureus V8 protease digests indicated that these polypeptides are structurally related to each other and represent microheterogeneity of the purified protein. The apparent isoelectric points of these four forms as determined by two-dimensional electrophoresis range from 6.1 to 6.7. By utilizing microsequencing techniques, the first 40 residues of neutrophil elastase have been determined and compared with the reported sequence of elastase isolated from leukemic myeloid cells. In addition, a high degree of homology was found within the amino-terminal regions of neutrophil elastase and the serine proteinases porcine elastase, bovine chymotrypsin, human factor D, and the beta chain of plasmin.

Resolution of cartilage proteoglycan and its proteolytic degradation products by high-performance liquid chromatography using a gel filtration system

Cartilage proteoglycan subunits are resolved from their various-size proteolytic degradation products by a gel filtration high-performance liquid chromatography system using a Bio-Gel TSK-60 column in tandem with a Bio-Gel TSK-50 column. Molecules ranging in size from the intact proteoglycan to single chondroitin sulfate chains are eluted in the included volume. Each analysis takes less than 30 min to complete, and with purified samples as little as 20 micrograms of proteoglycan is required. The method can be applied to the measurement of proteoglycan in mixtures, such as tissue culture media, by monitoring effluent fractions using the dimethylmethylene blue dye-binding assay.

Human leukocyte cathepsin G. Subsite mapping with 4-nitroanilides, chemical modification, and effect of possible cofactors

The extended substrate binding site of cathepsin G from human leukocytes has been mapped by using a series of peptide 4-nitroanilide substrates. The enzyme has a significant preference for substrates with a P1 Phe over those with the other aromatic amino acids Tyr and Trp. The S2 subsite was mapped with the substrates Suc-Phe-AA-Phe-NA where AA was 13 of the 20 amino acid residues commonly found in proteins. The best residues were Pro and Met. The S3 subsite was mapped with the sequence Suc-AA-Pro-Phe-NA by using 14 different amino acid residues for AA. The two best residues were the isosteric Val and Thr. No significant improvement in reactivity was obtained by extending the substrate to include seven different P4 residues. The kinetic parameters for cathepsin G are significantly slower than those for many other serine proteases. Changes in the reaction conditions and addition of possible cofactors or ligands were in general found to have little effect on the enzymatic activity, while chemical modifications and proteolysis destroyed the activity of cathepsin G. Cathepsin G hydrolyzed peptides containing model desmosine residues and prefers the hydrophobic picolinoyllysine derivative over lysine by substantial margins at both the S4 and S2 subsites but will not tolerate it at S3. Substrates with sequences related to the cathepsin G cleavage site in angiotensin I and angiotensinogen, and the reactive site of alpha 1-antichymotrypsin, were hydrolyzed effectively by enzyme, but with unexceptional rates. Our results indicate that the natural substrate(s) and function(s) of cathepsin G still remain to be discovered.

Evaluation of the extent of heterogeneity in the Glycera dibranchiata monomer haemoglobin fraction by the use of n.m.r. and ion-exchange chromatography

The coelomic haemoglobin of Glycera dibranchiata is known to be separable into monomeric and higher-Mr fractions. Although exhibiting homogeneity with respect to Mr, the extent of haemoglobin heterogeneity for the monomer fraction has never been adequately assayed. In the present paper we demonstrate that there exists in the monomer haemoglobin fraction reproducibly detectable heterogeneity regardless of the presence or absence of proteinase inhibitors during the isolations. These results show that, considered on the same time scale as previous preparations used for amino acid sequencing, crystallography and kinetics, the monomer haemoglobin fraction is highly heterogeneous. Application of ion-exchange chromatography and ion-filtration methods resulted in the isolation of four resolvable haem protein components from the Glycera monomer haemoglobin fraction. Three of these components were isolated in sufficient quantity to employ proton n.m.r. as a successful analytical tool for discriminating the individual haemoglobins. These results are not surprising. Several previous studies indicated less extensive heterogeneity in the monomer fraction. Moreover, the ability of the Glycera monomer haemoglobin to bind oxygen at even quite low partial pressures has been attributed to functional diversity originating in multiple haemoglobin components. The present work reveals the extent of the haemoglobin heterogeneity. The results show that it is more extensive than previously believed. Examination of this monomer fraction is particularly important, since crystallography indicates that one of the components of the monomer fraction lacks the E-7 (distal) histidine residue. As a consequence, the identification of such extensive heterogeneity is important to many previously published ligand-binding studies.

Chondrocyte-mediated depletion of articular cartilage proteoglycans in vitro

The degradation of proteoglycan was examined in cultured slices of pig articular cartilage. Pig leucocyte catabolin (10 ng/ml) was used to stimulate the chondrocytes and induce a 4-fold increase in the rate of proteoglycan loss from the matrix for 4 days. Material in the medium of both control and depleted cultures was mostly a degradation product of the aggregating proteoglycan. It was recovered as a very large molecule slightly smaller than the monomers extracted with 4M-guanidinium chloride and lacked a functional hyaluronate binding region. The size and charge were consistent with a very limited cleavage or conformational change of the core protein near the hyaluronate binding region releasing the C-terminal portion of the molecule intact from the aggregate. The 'clipped' monomer diffuses very rapidly through the matrix into the medium. The amount of proteoglycan extracted with 4M-guanidinium chloride decreased during culture from both the controls and depleted cartilage, and the average size of the molecules initially remained the same. However, the proportion of molecules with a smaller average size increased with time and was predominant in explants that had lost more than 70% of their proteoglycan. All of this material was able to form aggregates when mixed with hyaluronate, and glycosaminoglycans were the same size and charge as normal, indicating either that the core protein had been cleaved in many places or that larger molecules were preferentially released. A large proportion of the easily extracted and non-extractable proteoglycan remained in the partially depleted cartilage and the molecules were the same size and charge as those found in the controls. There was no evidence of detectable glycosidase activity and only very limited sulphatase activity. A similar rate of breakdown and final distribution pattern was found for newly synthesized proteoglycan. Increased amounts of latent neutral metalloproteinases and acid proteinase activities were present in the medium of depleted cartilage. These were not thought to be involved in the breakdown of proteoglycan. Increased release of proteoglycan ceased within 24h of removal of the catabolin, indicating that the effect was reversible and persisted only while the stimulus was present.

Redox status of cultured fibroblasts. Possible relations with specific catabolic rates of proteoglycans

In cultured embyonic rat fibroblast the cytoplasmic NAD/NADH ratio was determined from the lactate/pyruvate ratio under acidic, hypoxic and lactic acid-rich conditions.

RESULTS AND CONCLUSIONS

The NAD/NADH ratio is reduced when the lactate concentration increases at pH 7.4 with and without hypoxia. At pH 6.6 this ratio is not reduced by lactate in normoxia: Conditions of aerobic glycolysis did not increase NADH. The NAD/NADH ratio was strongly lowered at pH 6.6 by lactate plus hypoxia. At low cell density this condition of hypoxic glycolysis is correlated with the increase of the specific activities of CS- and DS-proteoglycans (DS much greater than CS). But only the CS concentration was increased. Conditions of aerobic glycolysis at low cell density caused a moderate increase of both the specific activity and concentration of DS. The different regulation of the turnover of CS- and DS-proteoglycans is suggested to be based on their different synthetic capacities (CS greater than DS) on the one side and on the effect of specifically acting proteoglycanases on the other side. Maximal degradation of proteoglycans seems to be stimulated by NADH-activated proteases, supposedly thiol proteases. Lower degradation seems to be effectuated under non-reductive acidic conditions. Both these types of degradation seem stronger to affect DS-proteoglycan. Some neutral proteases seem stronger to affect CS-proteoglycan. Improved oxygen supply might reduce the CS concentration in proliferating tissue, such as in chronic inflammation, and thus reduce this process.

Radioimmunoassay of proteoglycans

Human articular cartilage proteoglycan monomers (PG) were purified and used for developing a radioimmunoassay. Its analytical sensitivity is 0.6 ng/tube and its clinical sensitivity is 20 microliter/tube for serum and 0.12 microliter/tube for synovial fluid. The intra- and between-assay variation coefficient are less than 10 and 20%, respectively, in the linear part of the curve. There is a complete cross reaction with costal, vertebral disk and tracheal cartilage PGs and the PGs extracted from vein and artery. Concerning the latter, inhibition curves are not parallel. No cross reaction exists with PGs from various fetal tissues and small PGs from bone. However, large PGs from bone produce a weak cross reaction. Furthermore, the assay is species specific since cartilage PGs from dog, rat, chicken and calf embryos either do not or weakly cross react in the assay. Other constituents of cartilage: type II collagen, fibronectin, chondroitin sulfate and hyaluronic acid do not interfere with the assay. The antigenic determinants are localized on the protein core of the PG, as shown by the lack of cross reaction with glycosaminoglycans and PG treatment with various enzymes.

Partial purification and characterization of a proteoglycan-degrading neutral protease from bovine epiphyseal cartilage

Degradation of the proteoglycan matrix is considered an essential step in the process of calcification in the growth plate. This laboratory has just described the presence of a protease in human growth plate cartilage that degrades proteoglycan at neutral pH. We report here the isolation, partial purification, and characterization of these proteoglycan-degrading neutral proteases of bovine epiphyseal cartilage. It appears that there is more than a single enzyme active at neutral pH. These enzymes are of low molecular weight (below 30,000), poorly charged, and inhibited by metal chelating agents. Activity is best restored in the presence of zinc. This represents the first characterization of this important enzyme group.

Comparative rates of proteoglycan synthesis and size of proteoglycans in normal and osteoarthritic chondrocytes

Normal human and osteoarthritic cells were isolated from cartilage with clostridial collagenase. The cells were grown in media as a suspension culture in the presence of 35SO4. Osteoarthritic cartilage of moderate histologic grade (4-8) yielded chondrocytes which incorporated 35SO4 at a rate 3-4 times greater than did normal chondrocytes. The rate of incorporation, however, decreased to normal levels with chondrocytes isolated from mild (grade 0-3) or more advanced (grade 9-13) stages of the disease. These results corroborate those obtained in earlier studies using organ cultures and show that when osteoarthritic cells are isolated from their matrix environment, they continue to synthesize macromolecules at an increased rate. Analysis of the material synthesized by the isolated cells on sizing column demonstrated an inverse relationship between the size of the 35SO4 containing molecules and the severity of the disease.

Inhibition of cartilage breakdown by hydrocortisone in a tissue culture model of rheumatoid arthritis

Bovine nasal cartilage discs cocultured with human rheumatoid synovial membrane or synovial-membrane-conditioned media release proteoglycan largely as a result of cartilage breakdown. We assessed the effects of hydrocortisone on proteoglycan distribution between cartilage and culture medium, and on cartilage breakdown expressed as the release of either proteoglycan or 35S-products from prelabelled discs. The presence of synovial membrane inhibited the capacity for net proteoglycan synthesis, preventing its accumulation in cartilage; this was little affected by hydrocortisone. The major response to pharmacological concentrations of hydrocortisone was suppression of both spontaneous and synovial-membrane-induced cartilage breakdown. The autolysis of synovial protein that normally occurred during culture was similarly prevented by comparable doses of corticosteroid. Changes in chromatographic distribution of the 35S-labelled degradation products released from cartilage conformed with a corticosteroid-induced inhibition of endogenous lysosomal or related proteinase activity. Additionally, inhibition of the early events in synovial membrane that are responsible for chondrocyte-mediated breakdown of cartilage may contribute significantly to the overall corticosteroid effect.

Tumor invasion and host extracellular matrix

In this review some of the major mechanistic pathways by which tumor cells are thought to invade host tissues are discussed. Tumor invasion has been conceived to be the result of pathological, close-range interactions between malignant cells and host stroma. The sequence of events that characterize invasion can be summarized as follows: (a) Tumor cell clusters break from the confinement of the primary tumor. Loss of intercellular junctions (desmosomes), alterations in the chemical composition and physical properties of the cell surface coat (loss of fibronectin and heparan sulfate; excessive amounts of hyaluronate), and loosening of cell-substrate interactions (loss of hemidesmosomes, fibronectin, and heparan sulfate), are among the most frequently listed causes of tumor cell shedding. (b) Increased proteolytic activities at the invasion front cause focal alterations in the surrounding extracellular matrix, thereby changing its physical properties. Collagenases and cathepsins, as well as elastase and other neutral proteinases are the enzymes most frequently associated with matrix destruction and invasion. In some tissues this process is effectively regulated by inhibitors of matrix-degrading, proteolytic enzymes. (c) Tumor cells migrate into the altered matrix, possibly moving as aggregates along guidance tracks provided by host structures (blood vessels, lymphatics, nerves) or matrix macromolecules (collagen and fibronectin tracks). Migration seems to be preceded by increased swelling of glycosaminoglycan (i.e., hyaluronate) in the matrix, ahead of the migrating cell population. Various host cell types (mast cells, fibroblasts, endothelial cells, macrophages, etc.) may participate in these events.

Extracellular matrix destruction by invasive tumor cells

The invasion of normal tissues and penetration of basement membranes by malignant cells is likely to require the active participation of hydrolytic enzymes. The four major groups of connective tissue proteins, glycoproteins, proteoglycans, collagen and elastin, vary in their quantitative distributions between different tissues. With the exception of elastin, they also vary qualitatively within each class, so that there are no 'typical' connective tissue barriers to tumor cell penetration. The matrix constituents are stabilized and organized by a variety of covalent and noncovalent interactions between the connective tissue proteins. These interactions play important roles in matrix integrity and may alter the susceptibilities of the constituents to degradative enzymes. It is likely that the complete degradation of the matrix will require the action of more than one enzyme because of differing susceptibilities to tissue proteinases. Primary and transplantable tumors produce well-characterized enzymes which may participate in invasion. These enzymes may also be involved in connective tissue turnover in other normal and pathological situations. The use of long-term tumor cell cultures has verified that tumor cells themselves are capable of producing these enzymes. However, there are many potential modulating influences operative in vivo which are absent in culture so that details of actual mechanisms and control of digestion of complex substrates are not well understood. Recent work on the degradation by tumor cells of extracellular matrices previously produced by cultured cells is likely to shed more light on pathways of tissue destruction in vivo. Experiments with tumor cell variants of defined metastatic potentials will also be useful, but invasive and metastatic abilities are not necessarily correlated. It is unlikely that simple correlations can be drawn between the production of one particular degradative enzyme by all tumor cells and the complex biological mechanisms operative during tumor invasion.

The properties of the neutral proteinase released by primary chondrocyte cultures and its action on proteoglycan aggregate

The enzymatic mechanism of proteoglycan breakdown is of major interest, since it has been proposed that osteoarthritis involves increased proteolytic breakdown of proteoglycans. This paper describes the properties of the proteoglycan-degrading enzymes released into the extracellular milieu by chondrocyte cultures that produce cartilage-specific type II collagen but no detectable type I collagen. Attention has been focused on enzymes active at neutral pH, since the pH of the extracellular matrix is around neutrality. Biogel P-60 chromatography of concentrated culture medium showed a major peak of enzyme activity on proteoglycan monomer entrapped in polyacrylamide beads as well as on native proteoglycan aggregates. The enzyme yields a specific limit digestion peptide from the aggregate of approximately 55,000 daltons (in the presence of SDS). This limit peptide is probably derived from the hyaluronic acid-binding region of proteoglycan. The proteolytic enzyme is latent but can be activated by aminophenylmercuric acetate or trypsin. The molecular weight of both the active and latent forms, determined by gel filtration, is approximately 33,000. The activity is not inhibited by phenylmethylsulfonyl fluoride or pepstatin but is completely inhibited by o-phenanthroline; the activity is restored by Zn or Co ions in the presence of calcium chloride. Removal of calcium by dialysis results in a reversible loss of activity. The release of such a metalloproteinase by chondrocytes into the extracellular milieu, its activity at physiological pH and its ability to degrade native proteoglycans are consistent with a role of the enzyme in proteoglycan metabolism.

Proteoglycans from normal and degenerate cartilage of the adult human tibial plateau

Proteoglycans were extracted from normal and degenerate cartilage of the human tibial plateau. Both areas possessed proteoglycans of similar chemical composition, though the degenerate cartilage contained a greater proportion of molecules of lower buoyant density and enriched in keratan sulfate. There was no evidence for the changes in glycosaminoglycan synthesis that have been described for clinically osteoarthritic cartilage, or for changes in the ability to aggregate with hyaluronic acid.

A direct simultaneous plate assay of proteoglycan and collagen degradation by cells in culture and its application to synovial cells

1. A radiochemical plate assay is presented that allows a simultaneous evaluation of the capacity of cells in culture to degrade proteoglycan and collagen. Its principle consists of monitoring the release of soluble radioactive degradation products from Multiwell culture plates coated with dried reconstituted 3H-labelled-proteoglycan/14C-labelled-collagen mixed gels. The plates can also be used for the assay of proteolytic activities within enzyme solutions. 2. When cultured on the plates, rabbit synovial cells degrade collagen and proteoglycan almost simultaneously, owing to the secretion of collagenase and of a proteoglycan-degrading metal-dependent neutral proteinase.

Lysosomal elastase: effect on mechanical and biochemical properties of normal cartilage, inhibition by polysulfonated glycosaminoglycan, and binding to chondrocytes

Rheumatic joint destruction usually starts with the destabilisation of cartilage. Lysosomal elastase is a candidate effector of this process, since this enzyme is found at the site of cartilage erosion by rheumatoid synovial tissue. In order to prove this hypothesis we assessed the mechanical stability of cartilage during treatment by this enzyme in vitro. An indentation apparatus was used for this purpose and biochemical as well as microscopic techniques were used to supplement the results thus obtained. Our findings show that elastase irreversibly impairs the stability of cartilage by lysis of matrix proteoglycans without the help of additive enzymes. Collagen fragmentation played no significant role during elastase-induced destabilisation, while specific collagenase attacked the collagen network within the matrix only subsequent to the removal of proteoglycans. These findings suggest that elastase is a leading enzyme during proteolytic cartilage degradation. In addition polysulfonated glycosaminoglycan was found to reduce the mechanical effect of elastase on normal cartilage. It is therefore concluded that local inhibition of elastase promises therapeutic benefit during rheumatic cartilage degradation. Upon treatment of cartilage with elastase we observed this enzyme not only within the matrix under destruction but also bound to chondrocytes. These findings support the hypothesis that elastase plays a role on the matrix not only by direct degradation, but also by an indirect effect mediated through living chondrocytes.