PubMed Health⌕ Search

Biomedical subjects

J J Reynolds

Publications and source records attributed to J J Reynolds.

At least 37 records · Page 2Linked to original sources
PubMed1995

Immunolocalisation studies on six matrix metalloproteinases and their inhibitors, TIMP-1 and TIMP-2, in synovia from patients with osteo- and rheumatoid arthritis.

OBJECTIVE: To assess the likely importance of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) in the arthritic process. METHODS: Synovial samples from seven joints with rheumatoid arthritis and three osteoarthritic joints were analysed by indirect immunofluorescence microscopy. Using specific human antisera, we documented the frequencies and distributions of collagenase, stromelysins 1 and 2, matrilysin, gelatinases A and B, TIMP-1, and TIMP-2. RESULTS: Stromelysin 1 was found in all synovia, bound to extracellular matrix, within cells, or both, indicating stromelysin synthesis. Matrilysin was present in only one active inflammatory synovium, and focal synthesis of collagenase and gelatinase A was seen in four synovia. Stromelysin 2 and TIMP-2 were not observed, but TIMP-1 synthesis was seen in five synovia, and in two active synovia the distribution of TIMP-1 positive cells was more widespread than that of MMPs. CONCLUSIONS: The presence of stromelysin 1 in all synovia clearly implicates this enzyme in joint damage. Collagenase, gelatinase A and matrilysin may also have a role in rheumatoid arthritis, but are not significant in osteoarthritis. However, marked regional variations were found in the synthesis of these MMPs, indicating not only that these diseases are episodic but that control of enzyme synthesis is focal. Only TIMP-1 may be considered an inhibitory factor.

Adult↗
PubMed1995

Osteoblasts mediate insulin-like growth factor-I and -II stimulation of osteoclast formation and function.

Insulin-like growth factor-I (IGF-I) and IGF-II have powerful, well defined effects on osteoblastic cells, stimulating their proliferation and inducing collagen synthesis, but the role of IGF-I and -II in modulating osteoclast differentiation and activity remains unclear. We first examined the bone-resorptive effects of IGF-I and IGF-II by assessing 45Ca2+ release from neonatal mouse calvarial bones. Both IGFs dose dependently stimulated bone resorption, with an EC50 of 8 x 10(-9) M for IGF-I and 2 x 10(-8) M for IGF-II. We then tested the effects of the IGFs on bone resorption by rat isolated osteoclasts cultured on ivory slices. Neither IGF-I nor IGF-II stimulated isolated osteoclast activity. However, in the presence of either primary mouse osteoblasts or human osteosarcoma MG 63 cells, both IGFs enhanced osteoclast resorptive activity, with an EC50 of 5 x 10(-10) M for IGF-I and 10(-9) M for IGF-II. Stimulation was not mediated by BALB/c/3T3 cells, a nonosteoblastic cell line. The effects of the IGFs were blocked by alpha IR-3, an antibody to the type I IGF receptor, but not by beta-galactosidase, a lysosomal enzyme that competes with IGF-II for the type II IGF receptor. We then examined the effects of the IGFs on the formation of osteoclast-like multinucleate cells (MNCs) in mouse bone marrow cultures. IGF-I and -II dose dependently increased the number of tartrate-resistant acid phosphatase (TRAP)-positive MNCs, although their effects were less than that of 1,25-dihydroxyvitamin D3 (a hormone that induces osteoclast differentiation). No TRAP-positive MNCs appeared in the absence of these hormones. Like authentic osteoclasts, the TRAP-positive MNCs formed in response to IGF-I and -II bound [125I]salmon calcitonin. When mouse bone marrow cells were cultured on ivory slices in the presence of either IGF-I or IGF-II for 10 days, numerous resorption lacunae were formed. beta-Galactosidase had no effect on IGF-mediated osteoclast formation. These results are strong evidence that both IGF-I and IGF-II stimulate bone resorption in vitro by enhancing osteoclast formation and function. Our data also suggest that the IGFs act through the intermediary of osteoblastic cells to stimulate osteoclast activity and that the type I, but not the type II, IGF receptor is involved in their responses. We propose that the local production of IGF-I and IGF-II may modulate both osteoblast-osteoclast interactions and osteoclast formation and play an important role in bone remodeling.

Acid Phosphatase↗
PubMed1994

Cell surface-mediated activation of progelatinase A: demonstration of the involvement of the C-terminal domain of progelatinase A in cell surface binding and activation of progelatinase A by primary fibroblasts.

We report that the isolated C-terminal domain of progelatinase A is inhibitory to the activation of this proenzyme by primary skin fibroblast plasma membranes but is unable to inhibit organomercurial-induced self-cleavage and activation. Ligand binding studies demonstrate that fibroblasts stimulated with concanavalin A to activate progelatinase A have a significantly enhanced level of cell surface-associated progelatinase A. Tissue inhibitor of metalloproteinases-2 (TIMP-2), an effective inhibitor of membrane-mediated progelatinase A activation, is able to abolish the enhanced level of cell surface-associated progelatinase A that occurs following stimulation. TIMP-1, a poor inhibitor of membrane activation, is unable to inhibit the cell surface binding of progelatinase A. The enhancement in the binding of 125I-progelatinase A to fibroblasts following concanavalin A stimulation can be blocked by the inclusion of excess C-terminal gelatinase A but not by a truncated form of gelatinase A lacking the C-terminal domain. Scatchard analysis of the binding of 125I-progelatinase A to concanavalin A-stimulated fibroblasts has identified 950,000 gelatinase binding sites per cell with a Kd of 1.3 x 10(-8) M. Analysis of non-stimulated fibroblasts has identified 500,000 sites per cell with a Kd of 2.6 x 10(-8) M. We propose that membrane-mediated activation of progelatinase A involves binding of the proenzyme through its C-terminal domain to the cell surface and that TIMP-2 can inhibit activation by interaction with progelatinase A through the C-terminal domain, thus preventing binding of the proenzyme.

Amino Acid Sequence↗
PubMed1994

The purification and partial characterization of bone resorptive polypeptides from bovine bone matrix.

Matrix proteins were extracted from bovine cortical bone with EDTA/Tris-HCl under non-dissociative conditions at neutral pH. Four distinct bone resorptive proteins with molecular masses of 14, 25, 29 and 40 kDa were purified and partially characterized using an in vitro neonatal mouse calvarial assay and a growth factor assay using BALB/c/3T3 cells. The 14 kDa protein was purified by anion exchange chromatography (Mono Q) and gel filtration (Superdex 75HR) using FPLC (fast protein liquid chromatography); this factor stimulated the proliferation of MCF-7 human breast cancer cells, a bioassay which is specific for the insulin-like growth factors (IGFs). The 25, 29 and 40 kDa proteins were purified by sequential chromatography as follows: anion-exchange (Mono Q), heparin-Sepharose, hydroxyapatite, concanavalin A-Sepharose, phenyl-Superose, reversed phase high performance liquid chromatography (HPLC) and sodium dodecylsulfate polyacrylamide gelelectrophoresis (SDS-PAGE). The 25 kDa protein was identified as TGF-beta by its inhibitory effect on the proliferation of mink lung cells. The 40 kDa protein enhanced the formation of multinucleate tartrate-resistant acid phosphatase positive cells in a murine bone marrow differentiation assay, but was without effect in an isolated osteoclast assay and had no growth factor activity; this protein is likely to be a colony stimulating factor. The 29 kDa protein was also without growth factor activity; it was, however, able to stimulate bone resorption in the isolated osteoclast assay, suggesting a direct action in osteoclast function. The 29 and 40 kDa proteins may be osteoblast gene products that have been sequestrated by the bone matrix in a similar fashion to TGF-beta and the IGFs. This is the first report of proteins isolated from bone matrix which directly stimulate osteoclast differentiation and activity.

Animals↗
PubMed1994

Rabbit calvarial osteoblasts in culture constitutively synthesize progelatinase-A, and TIMP-1 and TIMP-2.

Defining the TIMPs (tissue inhibitors of metalloproteinases) produced by non-human bone cells is important because animal models and cells are used extensively for research on bone resorption, and because TIMP-2 can bind to and prevent activation of progelatinase-A. By zymography we show that rabbit calvarial osteoblasts in culture constitutively synthesize TIMP-2 in addition to TIMP-1 and progelatinase-A. Previously we found that human osteoblasts produced only low levels of TIMP-2 under any conditions. We also show that stimulated rabbit osteoblasts can degrade a type I collagen film even though both TIMPs are being synthesized.

Animals↗
PubMed1994

Inhibition of bone resorption by selective inactivators of cysteine proteinases.

Inactivators of cysteine proteinases (CPs) were tested as inhibitors of bone resorption in vitro and in vivo. The following four CP inactivators were tested: Ep475, a compound with low membrane permeability which inhibits cathepsins B, L, S, H, and calpain; Ep453, the membrane-permeant prodrug of Ep475; CA074, a compound with low membrane permeability which selectively inactivates cathepsin B; and CA074Me, the membrane-permeant prodrug of CA074. The test systems consisted of 1) monitoring the release of radioisotope from prelabelled mouse calvarial explants and 2) assessing the extent of bone resorption in an isolated osteoclast assay using confocal laser microscopy. Ep453, Ep475, and CA074Me inhibited both stimulated and basal bone resorption in vitro while CA074 was without effect; the inhibition was reversible and dose dependent. None of the inhibitors affected protein synthesis, DNA synthesis, the PTH-enhanced secretion of beta-glucuronidase, and N-acetyl-beta-glucosaminidase, or the spontaneous release of lactate dehydrogenase. Ep453, Ep475, and CA074Me dose-dependently inhibited the resorptive activity of isolated rat osteoclasts cultured on bone slices with a maximal effect at 50 microM. The number of resorption pits and their mean volume was reduced, whilst the mean surface area remained unaffected. Again, CA074 was without effect. Ep453, Ep475, and CA074Me, but not CA074, when administered subcutaneously at a dose of 60 micrograms/g body weight inhibited bone resorption in vivo as measured by an in vivo/in vitro assay, by about 20%. This study demonstrates that cathepsins B, L, and/or S are involved in bone resorption in vitro and in vivo. Whilst cathepsin L and/or S act extracellularly, and possibly intracellularly, cathepsin B mediates its effects intracellularly perhaps through the activation of other proteinases involved in subosteoclastic collagen degradation.

Animals↗
PubMed1994

Metalloproteinase production by rabbit articular cartilage: comparison of the effects of interleukin-1 alpha in vitro and in vivo.

To assess the effects of interleukin-1 on intact To assess the effects of interleukin-1 on intact articular cartilage in vitro, explants from young and adult rabbits were cultured with interleukin-1 and the distributions of the matrix metalloproteinases and tissue inhibitor of metalloproteinases (TIMP-1) were investigated by indirect immunofluorescence microscopy. One to 2-week-old cartilage chondrocytes synthesized collagenase in response to pure or crude interleukin-1 (monocyte conditioned medium), with subarticular cells most responsive. Collagenase synthesis was not stimulated in adult articular chondrocytes when explants were treated with either pure or crude interleukin-1. Stromelysin, gelatinase and TIMP-1 could not be demonstrated within any zone of the cartilage, indicating that their synthesis was not stimulated by either pure or crude interleukin-1. The addition of fibroblast growth factors, either alone or in combination with interleukin-1, did not modify these responses. These results contrast markedly with observations on cultured chondrocyte monolayers, where interleukin-1 treatment induces near co-ordinate expression of metalloproteinases. To assess the effects of interleukin-1 in vivo, it was injected into adult rabbit knee joint spaces and the articular cartilage subsequently analysed for evidence of altered metalloproteinase production by immunocytochemistry. No significant increase in metalloproteinase or TIMP-1 synthesis by chondrocytes was detected, although the cartilage matrix showed a marked loss of toluidine blue metachromasia. We conclude that metalloproteinases are not involved in the rapid loss of proteoglycan from cartilage matrix in these situations.

Animals↗
PubMed1994

Effect of poly DL-lactide--co-glycolide implants and xenogeneic bone matrix-derived growth factors on calvarial bone repair in the rabbit.

Polymer implant discs composed of 50:50 poly DL-lactide-co-glycolide (molecular weight about 9000) were used to repair 5 mm calvarial defects in 2 kg rabbits and osseous repair compared to spontaneous healing (control). After 4 weeks the implants had undergone substantial degradation with little evidence of residual polymer. The extent to which the defects had been replaced by bone showed individual variation. In some animals a layer of bone with normal cancellous architecture had bridged the defect, but at no time was bone observed in intimate contact with the polymer matrix, suggesting that the material had acted as a tissue spacer rather than an osteoconductive substrate. Non-osseous tissue consisted of a highly vascular fibrous connective tissue containing variable numbers of inflammatory cells. In some sites numerous macrophages and multinucleate giant cells were observed, the majority of which were shown by immunocytochemistry to be MHC class II-positive. Histomorphometric analysis demonstrated no statistically significant difference in osseous repair between control and polymer implant groups after 1, 2 or 3 months. Incorporation of bone matrix proteins extracted from bovine cortical bone into the discs, however, provoked a cellular and humoral immune response which had a significant inhibitory effect on osseous repair. These data suggest, first, that while synthetic polymers have potential as bone graft substitutes, improvements in their performance in vivo are needed and, second, it is advisable to use allogeneic proteins in rabbit models of bone regeneration.

Animals↗
PubMed1994

Immunolocalization of matrix metalloproteinases and TIMP-1 (tissue inhibitor of metalloproteinases) in human gingival tissues from periodontitis patients.

The matrix metalloproteinases (MMPs) collagenase, gelatinase A (72 kDa gelatinase), stromelysin, and their specific inhibitor TIMP-1 (tissue inhibitor of metalloproteinases), were immunolocalized using specific polyclonal antisera in gingival tissues from 21 patients with chronic inflammatory periodontal disease. Monoclonal antibodies against macrophages (Leu-M5), B cells (Leu-14), helper T cells (OKT4), suppressor T cells (OKT8) and the HLA-DR epitope were also used to identify leukocyte subsets. MMPs were observed in connective tissues at sites that histologically showed signs of remodelling. The number and distribution of positive cells varied widely, however, not only between individual biopsy specimens, but also within the same specimen. The same was true for the composition and distribution of the inflammatory cell infiltrate. Moreover, although there was a positive correlation between the number of MMP-producing cells and the severity of inflammation in some specimens, for others with comparable leukocyte subset scoring the number was reduced and sometimes absent altogether. Cells secreting MMPs were fibroblasts, macrophages and epithelial cells. It was not possible to determine unequivocally whether a MMP-positive cell within the connective tissue was a fibroblast or a macrophage, since the antisera recognise both fibroblast and macrophage MMPs and the different fixation requirements for MMPs (4% paraformaldehyde) and Leu-M5 (acetone) precluded co-localization on the same section. TIMP-1 was immunolocalized within connective tissue cells at sites of tissue remodelling. Our results support the hypothesis that tissue-derived MMPs may be involved in tissue remodelling in periodontal disease and conclusively demonstrate that epithelial cells may be involved as well as connective tissue cells.

Antibodies, Monoclonal↗
PubMed1994

Connective tissue degradation in health and periodontal disease and the roles of matrix metalloproteinases and their natural inhibitors.

Connective tissue remodeling is essential for normal growth and development, and many diseases have long been associated with the breakdown of the collagenous matrix of bone, cartilage, and related tissues. Recent work has established that members of the family of matrix metalloproteinases (MMPs) are key enzymes in matrix degradation. They function at neutral pH and can digest synergistically all the matrix macromolecules. Biochemical and cloning studies indicate that there are three major groups, collagenases, gelatinases, and stromelysins. Naturally occurring inhibitors, TIMPs (Tissue Inhibitors of MetalloProteinases), are important controlling factors in the actions of MMPs, and tissue destruction in disease processes often correlates with an imbalance of MMPs over TIMPs. The major inhibitor is TIMP-1 (or TIMP), a 30-kDa glycoprotein that is synthesized by most cells. The expression of MMPs and TIMPs by cells is regulated by many cytokines (particularly interleukin-1, IL-1), growth factors, and hormones, some of which are specific to cell type and others that are ubiquitous (e.g., transforming growth factor beta, TGF-beta). One way in which pathogenic organisms might mediate tissue degradation in periodontal diseases is through the ability of cell wall antigens to stimulate cytokine production by circulating mononuclear cells. These would then induce MMP synthesis by resident gingival cells, thereby initiating degradative events. Direct in vivo evidence for the source of collagenase and other MMPs in periodontal tissues is limited. By using specific polyclonal antibodies and indirect immunofluorescence, we could demonstrate the presence of collagenase, stromelysin-1, gelatinase A, and TIMP in human gingival biopsy specimens.(ABSTRACT TRUNCATED AT 250 WORDS)

Connective Tissue↗
PubMed1994

The effects of selective inhibitors of matrix metalloproteinases (MMPs) on bone resorption and the identification of MMPs and TIMP-1 in isolated osteoclasts.

We have compared the effects of a general matrix metalloproteinase (MMP) inhibitor (CT435) with those of a concentration-dependent specific gelatinase inhibitor (CT543; Ki < 20 nM) on bone resorption in vitro. The test systems consisted of measuring: (i) the release of 45Ca2+ from prelabelled mouse calvarial explants; (ii) the release of 45Ca2+ from prelabelled osteoid-free calvarial explants co-cultured with purified chicken osteoclasts; and (iii) lacunar resorption by isolated rat osteoclasts cultured on ivory slices. Both CT435 and CT543 dose-dependently inhibited the release of 45Ca2+ from neonatal calvarial bones stimulated by either parathyroid hormone or 1,25-dihydroxyvitamin D3. Moreover, CT543 produced a 40% inhibition at a concentration (10(-8) M) selective for the inhibition of human gelatinases A and B. CT435 (10(-5) M) and CT543 (10(-5) M) partially inhibited the release of 45Ca2+ from osteoid-free calvarial explants by chicken osteoclasts with a maximum of approximately 25% for unstimulated cultures, and approximately 36% for cultures stimulated by interleukin-1 alpha (IL-1 alpha; 10(-10) M). Neither inhibitor prevented lacunar resorption on ivory by unstimulated rat osteoclasts, but the compounds produced a partial reduction in both the number and total surface area of lacunae in IL-1 alpha-stimulated cultures, with maximal action at 10(-5) M. Neither of the inhibitors affected protein or DNA synthesis, nor the IL-1 alpha-stimulated secretion of the lysosomal enzyme beta-glucuronidase. Immunocytochemistry demonstrated that isolated rabbit osteoclasts constitutively expressed gelatinase A and synthesized gelatinase B, collagenase and stromelysin, as well as the tissue inhibitor of matrix metalloproteinases-1 (TIMP-1) following IL-1 alpha stimulation. These experiments have shown that in addition to collagenase, gelatinases A and B are likely to play a significant role in bone resorption. They further suggest that MMPs produced by osteoclasts are released into the sub-osteoclastic resorption zone where they participate in bone collagen degradation.

Animals↗
PubMed1994

Regional and temporal changes in the synthesis of matrix metalloproteinases and TIMP-1 during development of the rabbit mandibular condyle.

Connective tissues synthesise and secrete a family of matrix metalloproteinases (MMPs; collagenases, gelatinases and stromelysins) capable of degrading all the components of connective tissue matrices at physiological pH. We document the patterns of synthesis and distribution of MMPs and the tissue inhibitor of metalloproteinases-1 (TIMP-1) within the developing rabbit mandibular condyle using immunofluorescence microscopy. MMPs and TIMP-1 were detected both as bright intracellular accumulations within Golgi vesicles and also as diffuse matrix-bound extracellular deposits. Cells in the articular zone, proliferative zone, condylar cartilage and bone of the mandibular ramus were shown to produce all 3 classes of MMPs and TIMP-1 with the exception of stromelysin, which was not synthesised by cells of the bone of spongiosum. Temporal synthesis of MMPs and TIMP-1 within these regions varied during the period 18 d postcoitum to 14 d postnatum. Our results document unique patterns of MMP and TIMP-1 synthesis during embryonic and early postnatal development of condylar cartilage and support the concept that cells synthesise and secrete MMPs and TIMP-1 before undergoing proliferation and hypertrophy. A comparison of these results with data in the rabbit growth plate show many similarities, but some differences exist that probably reflect differences in the modes of growth of the 2 cartilages.

Animals↗
PubMed1993

Inhibition of stimulated bone resorption in vitro by TIMP-1 and TIMP-2.

Recombinant human TIMP-1 and TIMP-2 (tissue inhibitors of metalloproteinases) inhibited bone resorption induced by either parathyroid hormone or 1,25-dihydroxyvitamin D3 in cultured neonatal mouse calvariae. The inhibition was reversible, dose-dependent and complete at 1 microgram/ml inhibitor concentration. TIMP-2 was more potent than TIMP-1. TIMP-1 and TIMP-2 also inhibited basal bone resorption. Neither metalloproteinase inhibitor affected protein synthesis, DNA synthesis, the PTH-enhanced secretion of beta-glucuronidase or the spontaneous release of lactate dehydrogenase. These results suggest that endogenous TIMPs play a central role in regulating both physiological and pathological bone resorption.

Animals↗
PubMed1993

Bone-derived growth factor release from poly(alpha-hydroxy acid) implants in vitro.

Matrix proteins were extracted from bovine cortical bone and polymer implant discs (13 mm x 2 mm composed of 50:50 poly DL-lactide-co-glycolide; mol. wt. approximately 9000) prepared by compression moulding granules with lyophilized bone matrix extracts (BMX) 10.1 (w/w). BMX-containing polymers were cultured for 5 wk in either serum-free Dulbecco's modification of Eagle's medium (DMEM) or phosphate buffer, and growth factor activity released into the media assayed by its ability to stimulate the proliferation of murine fibroblast BALB/c/3T3 cells. Approximately 60-75% of the biological activity was released during the first week of culture; however, less than half of the growth factor units originally incorporated into the implants retained biological activity. Scanning electron microscopy revealed the development of significant internal porosity by week 2; the size of the channels, pores and surface openings suggested they were of the right order for bone ingrowth. These preliminary findings suggest that poly(alpha-hydroxy acid) polymers containing bone-derived growth factors could have potential for stimulating osseous regeneration in vivo.

3T3 Cells↗
PubMed1993

The expression of matrix metalloproteinases and their inhibitors by pig synovial cells and their regulation by combinations of cytokines and growth factors.

1. Pig synovial fibroblasts in culture were studied to determine if they were an easily reproducible model system for studying the actions of cytokines and growth factors on human synovial cells. The biochemical analyses were conducted by activity assays, enzymography and Northern blot. 2. Human recombinant interleukin-1 alpha, basic fibroblast growth factor and transforming growth factor-beta 1 were studied in combinations because of their known involvement in controlling tissue remodelling. 3. The response of pig fibroblasts to these agents, in terms of the expression of matrix metalloproteinases (collagenase, gelatinase and stromelysin) and their inhibitors (TIMPs), show that they behave similarly enough to human cells for use when supplies of human primary cells are unavailable.

Animals↗
PubMed1993

Rabbit models of arthritis: immunolocalization of matrix metalloproteinases and tissue inhibitor of metalloproteinase in synovium and cartilage.

The distribution of the matrix metalloproteinases, collagenase, stromelysin, gelatinases A and B, and the tissue inhibitor of metalloproteinases in cartilage and synovium removed from rabbits up to 27 days after induction of two models of arthritis was investigated by immunolocalization. Following intra-articular injection of poly-D-lysine/hyaluronic acid coacervate, collagenase and stromelysin were found bound to cartilage matrix, but there was little increase in chondrocyte synthesis of these enzymes. The synovium underwent a complex wound healing response involving invagination and encapsulation of the coacervate and inflammatory cell debris, during which all four metalloproteinases and tissue inhibitor of metalloproteinase could be immunolocalized. The second model, intra-articular injection of ovalbumin into sensitized rabbits, caused considerable chondrocyte necrosis; collagenase was found bound to cartilage matrix on day 13, although again there was little evidence of synthesis by chondrocytes. Inflammatory cell infiltration of meniscoid synovia took place initially, followed by fibrosis involving macrophagelike cells secreting gelatinase A. In both models there was rapid loss of glycosaminoglycan metachromasia from the cartilage matrix. These results are discussed in relation to current knowledge of metalloproteinase involvement in the chronic rheumatoid synovial pannus erosion of cartilage in humans. The data suggest that there are considerable differences between rheumatoid arthritis and these models, and their use must therefore be carefully defined.

Animals↗
PubMed1992

Cell-mediated degradation of type IV collagen and gelatin films is dependent on the activation of matrix metalloproteinases.

The ability of normal rabbit dermal fibroblasts to degrade films of type IV collagen and gelatin when stimulated by phorbol ester was shown to be dependent on the induction, secretion and activation of 95 kDa gelatinase B and the secretion and activation of 72 kDa gelatinase A and stromelysin. Degradation was inhibited by exogenous human recombinant tissue inhibitor of metalloproteinases-1, specific antibodies to gelatinase and stromelysin and by the reactive-oxygen-metabolite inhibitor catalase. We discuss the various pathways for activation of matrix metalloproteinases in this model system and conclude that, although plasmin may play a key role in the activation of gelatinase B and stromelysin, gelatinase A is activated by a mechanism which has yet to be elucidated. The involvement of oxygen radicals in the direct activation of matrix metalloproteinases in this model is thought to be unlikely.

Animals↗