Alteration of structural and mechanical properties of the temporomandibular joint disc following elastase digestion

The temporomandibular joint disc is a fibrocartilaginous structure, composed of collagen fibers, elastin fibers, and proteoglycans. Despite the crucial role of elastin fibers in load‐bearing properties of connective tissues, its contribution in temporomandibular joint disc biomechanics has been disregarded. This study attempts to characterize the structural–functional contribution of elastin in the temporomandibular joint disc. Using elastase, we selectively perturbed the elastin fiber network in porcine temporomandibular joint discs and investigated the structural, compositional, and mechanical regional changes through: (a) analysis of collagen and elastin fibers by immunolabeling and transmission electron microscopy; (b) quantitative analysis of collagen tortuosity, cell shape, and disc volume; (c) biochemical quantification of collagen, glycosaminoglycan and elastin content; and (d) cyclic compression test. Following elastase treatment, microscopic examination revealed fragmentation of elastin fibers across the temporomandibular joint disc, with a more pronounced effect in the intermediate regions. Also, biochemical analyses of the intermediate regions showed significant depletion of elastin (50%), and substantial decrease in collagen (20%) and glycosaminoglycan (49%) content, likely due to non‐specific activity of elastase. Degradation of elastin fibers affected the homeostatic configuration of the disc, reflected in its significant volume enlargement accompanied by remarkable reduction of collagen tortuosity and cell elongation. Mechanically, elastase treatment nearly doubled the maximal energy dissipation across the intermediate regions while the instantaneous modulus was not significantly affected. We conclude that elastin fibers contribute to the restoration and maintenance of the disc resting shape and actively interact with collagen fibers to provide mechanical resilience to the temporomandibular joint disc.

The dynamic mechanical viscoelastic properties of the temporomandibular joint disc: The role of collagen and elastin fibers from a perspective of polymer dynamics

The temporomandibular joint disc is a structure, characterized as heterogeneous fibrocartilage, and is composed of macromolecular biopolymers. Despite a large body of characterization studies, the contribution of matrix biopolymers on the dynamic viscoelastic behavior of the disc is poorly understood. Given the high permeability and low concentration of glycosaminoglycans in the disc, it has been suggested that poro-elastic behavior can be neglected and that the intrinsic viscoelastic nature of solid matrix plays a dominant role in governing its time-dependent behavior. This study attempts to quantify the contribution of collagen and elastin fibers to the viscoelastic properties of the disc. Using collagenase and elastase, we perturbed the collagen and elastin fibrillar network in porcine temporomandibular joint discs and investigated the changes of dynamic viscoelastic properties in five different regions of the disc. Following both treatments, the storage and loss moduli of these regions were reduced dramatically up to the point that the tissue was no longer mechanically heterogeneous. However, the proportion of changes in storage and loss moduli were different for each treatment, reflected in the decrease and increase of the loss tangent for collagenase and elastase treated discs, respectively. The reduction of storage and loss moduli of the disc correlated with a decrease of biopolymer length. The present study indicates that the compositional and structural changes of collagen and elastin fibers alter the viscoelastic properties of the disc consistent with polymer dynamics.

Pathogenic stromal cells as therapeutic targets in joint inflammation

Knowledge of how the joint functions as an integrated unit in health and disease requires an understanding of the stromal cells populating the joint mesenchyme, including fibroblasts, tissue-resident macrophages and endothelial cells. Knowledge of the physiological and pathological mechanisms that involve joint mesenchymal stromal cells has begun to cast new light on why joint inflammation persists. The shared embryological origins of fibroblasts and endothelial cells might shape the behaviour of these cell types in diseased adult tissues. Cells of mesenchymal origin sustain inflammation in the synovial membrane and tendons by various mechanisms, and the important contribution of newly discovered fibroblast subtypes and their associated crosstalk with endothelial cells, tissue-resident macrophages and leukocytes is beginning to emerge. Knowledge of these mechanisms should help to shape the future therapeutic landscape and emphasizes the requirement for new strategies to address the pathogenic stroma and associated crosstalk between leukocytes and cells of mesenchymal origin.

Serine proteinases in the turnover of the cartilage extracellular matrix in the joint: implications for therapeutics

Cartilage destruction is a key characteristic of arthritic disease, a process now widely established to be mediated by metzincins such as MMPs. Despite showing promise in preclinical trials during the 1990s, MMP inhibitors for the blockade of extracellular matrix turnover in the treatment of cancer and arthritis failed clinically, primarily due to poor selectivity for target MMPs. In recent years, roles for serine proteinases in the proteolytic cascades leading to cartilage destruction have become increasingly apparent, renewing interest in the potential for new therapeutic strategies that utilize pharmacological inhibitors against this class of proteinases. Herein, we describe key serine proteinases with likely importance in arthritic disease and highlight recent advances in this field. LINKED ARTICLES: This article is part of a themed section on Translating the Matrix. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.1/issuetoc.

Stroma: fertile soil for inflammation

Biological therapies for the management of immune mediated inflammatory diseases such as rheumatoid arthritis have proven to be extremely successful in recent years. Despite these successes, even the most effective of therapies do not lead to cure. Why chronic inflammation persists indefinitely within the rheumatoid synovium despite an absence of continuous stimulation, and why some patients with early synovitis progress to persistent disease whilst others do not, has remained unexplained. In contrast to the paradigm that stromal cells are biochemically active but immunologically passive, there is now growing evidence that stromal components from the rheumatoid synovium play a crucial part in the immunopathology of rheumatoid arthritis. Stromal cells play a central role in the transformation of an acute, resolving to a chronic inflammatory process, and to the persistence of synovial inflammation and joint destruction through a variety of immune mechanisms. Therapeutic manipulation of the stroma is a largely unexplored, yet potentially vital area of research. Targeting pathogenic stromal cells has the potential to provide a cure for chronic inflammatory disorders such as rheumatoid arthritis.

Adiponectin and its globular fragment differentially modulate the oxidative burst of primary human phagocytes

Adiponectin (Acrp30) belongs to the family of C1q/tumor necrosis factor α (TNFα)-related proteins. Acrp30 circulates as multimers of high, middle, and low molecular weight. In this study, we detected Acrp30 and its globular fragment (gAcrp30) in synovial fluid from rheumatoid arthritis patients. Intriguingly, the LMW form was more abundant in synovial fluid than in serum from both rheumatoid arthritis patients and healthy subjects. We also investigated the effects of Acrp30 and gAcrp30 on reactive oxygen species (ROS) production via the phagocytic NADPH oxidase. Acrp30 inhibited fMLF-induced ROS production by human phagocytes, whereas gAcrp30 enhanced it. gAcrp30's effect is additive with TNFα, whereas Acrp30 inhibited TNFα-induced priming. gAcrp30 enhanced NOX-2 expression at the plasma membrane, with a concomitant increase in p47(phox) phosphorylation. Selective inhibitors of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase 1 (ERK1)/2 abrogated p47(phox) phosphorylation by gAcrp30. In contrast, p47(phox) phosphorylation was inhibited by Acrp30 in association with increased AMP-activated protein kinase (AMPK) phosphorylation in phagocytes. These results suggest that human phagocyte ROS production is regulated by different mechanisms selective for Acrp30 versus gAcrp30. An imbalance between gAcrp30 and higher molecular weight isoforms of Acrp30 might contribute to chronic inflammation by regulating NADPH oxidase.

Cathepsin B and cystatin C play an inflammatory role in gouty arthritis of the knee

BACKGROUND

To relate the expression of the matrix degrading proteinase cathepsin B and its endogenous inhibitor cystatin C in the synovial fluid (SF) to the clinical and laboratory variables of joint inflammation in gouty arthritis of the knee.

METHODS

Thirty-nine SF samples were obtained from inflamed knees of patients with acute gout. The levels of cathepsin B, cystatin C, urokinase-type plasminogen activator (uPA), soluble uPA receptor (suPAR) and PA inhibitor type-1 (PAI-1), activities of matrix metalloproteinase-2 (MMP-2) and MMP-9, and cell counts as well as local arthritis activity scores (LAS) were examined.

RESULTS

The increases of cathepsin B levels correlated with increased leukocyte and neutrophil counts, latent MMP-9 (pro-MMP-9) activities, uPA, suPAR and PAI-1 levels, and uPA/PAI-1 ratios. Increased cystatin C levels corresponded closely with increased LAS, leukocyte and neutrophil counts, pro-MMP-9 activities, uPA, suPAR and PAI-1 levels, and uPA/PAI-1 ratios. Moreover, there was a correlation between cathepsin B and cystatin C levels.

CONCLUSIONS

These results show a high correlation between the cathepsin B/cystatin C system and markers of joint inflammation in acute gout of the knee, demonstrating the pathologic role of cathepsin B and cystatin C in inflammation.

Environmental effects on charge densities of biologically active molecules: do molecule crystal environments indeed approximate protein surroundings?

In the present paper, we investigate whether crystal and enzyme environments influence the electron density (ED) of active compounds in a similar manner. This supposition is essential for high-resolution X-ray studies, which use the EDs obtained from crystals of the pure active compound as approximations for the ED of the active compound in its complex with the target enzyme. The EDs of such complexes determine the molecular recognition process between the targeted enzyme and active compound and are, hence, extremely useful tools for rational drug design. The approximation of such EDs by data obtained from crystals of the pure active compound is needed since high-resolution X-ray experiments of the target-ligand complexes are still extremely demanding. Quantum mechanical/molecular mechanical (QM/MM) and pure QM calculations are employed to determine the EDs of two inhibitors, the reversible trans-4-(aminomethyl)cyclohexane-1-carboxylic acid (AMCHA) and the irreversible E64c in four different environments (the enzyme-inhibitor complex, crystals of the pure compounds, a continuum solvation model, and the gas phase). Our investigation shows that the environment inside of the crystal of the pure active compound generally influences the ED of an active compound in a very similar way as the enzyme surrounding in the complex between the active compound and target enzyme. However, this does not hold any more if the geometrical arrangement of the inhibitor in the enzyme differs significantly from that in the crystal. While EDs computed for gas-phase environments deviate strongly from those in crystal and protein surroundings, polar solvent environments provide rather similar electron distributions. Thus, such continuum solvation models are very well suited to compute density databases which are to be employed for the determination of the ED of macromolecules.

The importance of the active site histidine for the activity of epoxide- or aziridine-based inhibitors of cysteine proteases

In the present study the importance of the active site histidine residue (His) for the activity of epoxide- or aziridine-based cysteine protease inhibitors is examined theoretically. To account for all important effects, QM/MM hybrid approaches are employed which combine quantum mechanical (QM) methods that are necessary to describe bond-breaking and formation processes, with molecular mechanics (MM) methods that incorporate the influence of the protein environment. Using various model systems, the computations exclude a direct proton shift from the active site His residue to the inhibitor, but show that one water molecule is sufficient to establish a very efficient relay system. This relay system allows an easy proton transfer from the active site His residue to the inhibitor and is thus essential for the activity of both types of inhibitors. Differences between the epoxides and the aziridines are discussed, along with some implications for the rational design of optimized inhibitors. The work presented herein represents the first QM/MM study into the mode of action of these important inhibitor classes.

On the origin of the stabilization of the zwitterionic resting state of cysteine proteases: a theoretical study

Papain-like cysteine proteases are ubiquitous proteolytic enzymes. The protonated His199/deprotonated Cys29 ion pair (cathepsin B numbering) in the active site is essential for their proper functioning. The presence of this ion pair stands in contrast to the corresponding intrinsic residue p K a values, indicating a strong influence of the enzyme environment. In the present work we show by molecular dynamics simulations on quantum mechanical/molecular mechanical (QM/MM) potentials that the ion pair is stabilized by a complex hydrogen bond network which comprises several amino acids situated in the active site of the enzyme and 2-4 water molecules. QM/MM reaction path computations for the proton transfer from His199 to the thiolate of the Cys29 moiety indicate that the ion pair is about 32-36 kJ mol (-1) more stable than the neutral form if the whole hydrogen bonding network is active. Without any hydrogen bonding network the ion pair is predicted to be significantly less stable than the neutral form. QM/MM charge deletion analysis and QM model calculations are used to quantify the stabilizing effect of the active-site residues and the L1 helix in favor of the zwitterionic form. The active-site water molecules contribute about 30 kJ mol (-1) to the overall stabilization. Disruption of the hydrogen bonding network upon substrate binding is expected to enhance the nucleophilic reactivity of the thiolate.

The Examination of Rheumatoid Factor and Other Serum Markers in Rheumatoid Arthritis

Rheumatoid factor (IgM-RF) has been widely used to diagnose rheumatoid arthritis (RA) in clinical practice. We investigated the RA diagnostic performances of anti-cyclic citrullinated peptide antibody (anti-CCP), matrix metalloproteinase-3 (MMP-3), anti-agalactosyl IgG antibody (CA*RF), and anti-calpastatin antibody (ACA) in comparison with IgM-RF. Among 68 RA patients, IgM-RF was positive in 31 (45.6%) and negative in 37 (54.4%). In the IgM-RF-positive group, positivity in anti-CCP, CA*RF, and ACA was 97%, 100%, and 97%, respectively, although that in MMP-3 (74%) was inferior to the others. On the other hand, in the IgM-RF-negative group, positivity in anti-CCP, MMP-3, and ACA was 73%, 81%, and 86%, respectively, although that in CA*RF was only 59%. We conclude that the combination of IgM-RF and anti-CCP/ACA will provide an accurate diagnosis of RA in clinical practice.

Quantification of protease activities in synovial fluid from rheumatoid and osteoarthritis cases: comparison with antioxidant and free radical damage markers

We have compared (using the same series of experimental samples) the levels of activity of a comprehensive range of cytoplasmic, lysosomal and matrix protease types, together with the levels of free radical-induced protein damage (determined as protein carbonyl derivative) in synovial fluid from rheumatoid (RA) and osteoarthritis (OA) cases. Many protease types showed significantly increased activity (typically by a factor of 2-3-fold) in RA compared to OA cases. Protease activity levels (including those enzyme types putatively involved in the immune response, such as dipeptidyl aminopeptidase IV) in plasma were not significantly different in RA and control cases. The level of free radical induced damage to synovial fluid proteins was approximately 2-fold higher in RA compared to OA, although there was no significant difference in total antioxidant status in synovial fluid or plasma between RA, OA or control cases. We conclude from the above that activation of proteolytic enzymes and free radicals (occurring specifically within synovial tissues) are likely to be of equal potential importance as protein damaging agents in the pathogenesis of RA, and the development of novel therapeutic strategies for the latter disorder should include both protease inhibitory and free radical scavenging elements. In addition, the protease inhibitory element should be designed to inhibit the action of a broad range of enzymic mechanistic types (cysteine, serine, metallo proteinases and peptidases).

Inhibition of papain with 2-benzyl-3,4-epoxybutanoic acid esters. Mechanistic and stereochemical probe for cysteine protease catalysis

Papain, a prototypic cysteine protease was inactivated by methyl and benzyl esters of (2S,3S)-2-benzyl-3,4-epoxybutanoic acid. On the other hand, methyl ester of (2S,3R)-2-benzyl-3,4-epoxybutanoic acid was shown to be a competitive inhibitor for the enzyme. It was inferred from the inactivation stereochemistry that in the papain catalytic reaction the nucleophilic attack of the side chain thioalkoxide of Cys-25 on the scissile peptide bond of substrates occurs in the 're' fashion. The papain inactivating potency of (2S,3S)-2-benzyl-3,4-epoxybutanoic acid methyl ester was enhanced over three-fold in a pH 8.0 solution compared with in the neutral solution. This together with our previous observation with alpha-chymotrypsin and the recent theoretical treatment of the enzymic reaction of papain, suggest that in the inactivation of papain by oxirane containing inhibitors, the oxirane does not need to be activated by prior protonation as thought previously. The oxirane ring is sufficiently labile that the unprotonated oxirane moiety can undergo an electrophilic reaction with the Cys-25 thiolate.

Leishmania major: comparison of the cathepsin L- and B-like cysteine protease genes with those of other trypanosomatids

Cysteine proteases play important roles in the pathogenesis of several parasitic infections and have been proposed as targets for the structure-based strategy of drug design. As a first step toward applying this strategy to design inhibitors as antiparasitic agents for leishmaniasis, we have isolated and sequenced the full-length clones of two cysteine protease genes from Leishmania major. One of the genes is structurally similar to the cathepsin L-like family and the other is similar to the cathepsin B-like family of cysteine proteases. The L. major cathepsin L-like sequence has a proregion that shares high sequence similarity with other cathepsin L sequences but not cathepsin B sequences and has a proline/threonine-rich C-terminal extension. The cathepsin L-like gene occurs in multiple copies, whereas there may be only one copy of the cathepsin B-like gene. Northern blot analyses show that both genes are expressed in the promastigote and amastigote stages, and pulse field gel electrophoresis revealed that the cathepsin L- and B-like genes are each found on two nonhomologous chromosomes. The L. major L-like amino acid sequence is 75% identical to the L. mexicana sequence, 74% identical to the L. pifanoi sequence, 47% identical with the Trypanosoma cruzi sequence, 47% identical with the T. congolense sequence, and 45% identical with the T. brucei sequence. L. major is one of two trypanosomatid species for which a cathepsin B-like gene has been identified and sequenced; its amino acid sequence is 82% identical to the one from L. mexicana. Tree inference based on distance and parsimony methods of kinetoplastid cathepsin L proteins yielded independent support for phylogenetic hypotheses inferred from analyses of ribosomal RNA genes. Because the cathepsin L locus has a high level of phylogenetic signal with respect to trypanosomatid taxa, this locus has great potential utility for investigating the evolutionary history of trypanosomatids and related organisms.

Proteoglycan degrading activity in granulomatous inflammation: comparison between the C57b1/6 and C57bg/bg mouse

OBJECTIVE AND DESIGN

Proteoglycan (GAG) and collagen are lost from cartilage juxtaposed to murine granulomatous tissue in both control and C57bg/bg (elastase deficient mice). The objective was to extract and characterise proteoglycan degrading activity within granulomas of both strains.

MATERIALS

15 animals (female C57b1/6 and C57bg/bg mice) per group were used.

TREATMENT

Cotton-wrapped rat femoral head cartilages were implanted subcutaneously into the dorsum of the mice and the granulomas excised fourteen days later.

METHODS

Granuloma and granuloma cell-granule preparations were fractionated within a detergent-based buffer and tested for their abilities to degrade cartilage in vitro in the presence and absence of enzyme inhibitors. Elastase and cathepsin G activities were also assessed using specific substrates. Statistical significance was calculated using Student's t-test.

RESULTS

Extracts from both strains induced the loss of cartilage GAG. This was correlated with cathepsin G activity (r = 0.96) and was inhibited by a specific cathepsin-G inhibitor (95%, p < 0.001), but not specific elastase or metalloproteinase inhibitors. Elastase activity but not that of cathepsin G was absent in the beige mice, whilst both enzymes were active in the controls.

CONCLUSIONS

It appears that neutrophil cathepsin G may play an important role in the degradation of cartilage proteoglycan in the murine cotton-pellet granuloma in both C57b1/6 and C57bg/bg.

Mechanistic studies on the inactivation of papain by epoxysuccinyl inhibitors

Analogs of the epoxysuccinyl peptide cysteine proteinase inhibitor, EP-475 (2a), in which the free carboxylate has been replaced by hydroxamic acid, amide, methyl ketone, hydroxyl, and ethyl ester functionalities, have been synthesized. Individual rate constants of inhibition of papain were determined for these inhibitors. The results show that a carbonyl-containing functionality is necessary for good activity. The pH dependence of the inhibition of papain was determined for a nonionizable EP-475 (2a) analog; inhibition was found to depend on two acidic ionizations (pKas of 3.93 and 4.09) of papain. Implications for the mechanism of action of epoxysuccinyl peptides with papain are discussed.

Convenient fluorometric assay for matrix metalloproteinase activity and its application in biological media

Matrix metalloproteinases (MMPs) are involved in physiological tissue remodeling and pathological conditions like tumour metastasis and joint destruction. Until now, no convenient and sensitive MMP-activity assay in crude media like synovial fluid has been available. Therefore, the highly soluble fluorogenic substrate TNO211 (Dabcyl-Gaba-Pro-Gln-Gly-Leu-Glu(EDANS)-Ala-Lys-NH2), containing the MMP cleavable Gly-Leu bond and EDANS/Dabcyl as fluorophore/quencer combination, was synthesized and characterized as an MMP specific substrate. We show that the fluorogenic assay using TNO211 is sensitive and can detect MMP activity in culture medium from endothelial cells and untreated synovial fluid (SF) from RA and OA patients, and control subjects. MMP activity in SF significantly increased in the order C < OA < RA, thus the frequent use of OA samples as control in studies on RA is debatable.

Cathepsin B in gingival crevicular fluid of adult periodontitis patients: identification by immunological and enzymological methods

Cathepsin B (EC 3.4.22.1), a typical lysosomal cysteine proteinase was identified immunologically with anti-human cathepsin B antibody in inflammatory exudate, gingival crevicular fluid (GCF) of adult periodontitis patients. The sensitive enzyme immunoassay (EIA) system initially developed, was rarely influenced by the presence of endogenous cysteine proteinase inhibitors, cystatin(s), indicating that it is possible to quantify the gross amount of cathepsin B including free enzyme forms and enzyme-inhibitor complex forms using this EIA system. The cathepsin B levels in GCF as determined by EIA and the activity measured with Z-Arg-Arg-MCA showed positive and significant correlation with various clinical parameters. Immunoblotting analysis revealed that the molecular form was a 29 kDa mature enzyme. More than 95% of Z-Arg-Arg-MCA hydrolytic activity in each GCF sample was inhibited by CA-074, specific inhibitor of cathepsin B. These results strongly suggested that the gross amount of cathepsin B in GCF as well as its activity level is closely associated with the severity of the disease and that cathepsins B play an important role in the pathogenesis of periodontitis.

Cathepsin B in osteoarthritis: zonal variation of enzyme activity in human femoral head cartilage

OBJECTIVES

To determine the quantitative topographical distribution of cathepsin B in human femoral head cartilage by measuring the zonal variation of enzyme activity in specimens taken from various anatomical regions of normal and osteoarthritic (OA) tissues, and to correlate this parameter with the severity of the OA lesions.

METHODS

OA articular cartilage was obtained at surgery for total hip replacement and control cartilage obtained at postmortem. Cylinders of full thickness cartilage with underlying bone were retrieved with a biopsy trephine. Sections of cartilage were produced by cryocutting the tissue as slices parallel to the articular surface and assayed for cathepsin B with a specific, highly sensitive fluorogenic substrate. The severity of the OA lesions was graded according to the histopathological-histochemical method of Mankin.

RESULTS

Zonal cathepsin B activity of normal cartilage was uniform and low in all regions of the femoral head. In apparently intact OA cartilage and in severely degraded tissue the zonal distribution and the amounts of enzyme were similar to control values. At sites with active disease, cathepsin B activity was much greater than in controls and its irregular zonal distribution correlated with tissue degeneration, hypercellularity, or cloning of chondrocytes as determined histochemically. Particularly high enzyme levels were observed at sites with regenerating cartilage, where some zonal peaks attained 20-fold activity with respect to controls.

CONCLUSION

Cathepsin B may play a role in sustaining the chronicity of OA, not as an initiator, but rather as a perpetuator of the disease and as an antagonist of regeneration.

In vitro embryotoxicity of the cysteine proteinase inhibitors benzyloxycarbonyl-phenylalanine-alanine-diazomethane (Z-Phe-Ala-CHN2) and benzyloxycarbonyl-phenylalanine-phenylalanine-diazomethane (Z-Phe-Phe-CHN2)

This study makes use of whole embryo culture to investigate the potential embryotoxicity of benzyloxycarbonyl-phenylalanine-alanine-diazomethane (Z-Phe-Ala-CHN2) and benzyloxycarbonyl-phenylalanine-phenylalanine-diazomethane (Z-Phe-Phe-CHN2), two low molecular weight, active site-directed and irreversible inhibitors of the lysosomal cysteine proteinases. Peptidyl diazomethanes are the most specific inhibitors available for lysosomal cysteine proteinases and can be hypothesized to interrupt visceral yolk sac (VYS)-mediated nutrition during early organogenesis. When added directly to the culture medium of gestational day 10-11 rat conceptuses, both compounds inhibited lysosomal cysteine proteinase activity in the VYS in a concentration-dependent fashion that correlated with the degree of embryotoxicity observed. Z-Phe-Ala-CHN2 and Z-Phe-Phe-CHN2 were also found to increase the protein content of the VYS, even though all other conceptual growth parameters decreased. This effect was dependent on the serum content of the culture medium and the exposure time. Histological examination of Z-Phe-Ala-CHN2-treated conceptuses revealed a dramatic increase in the size and number of vacuoles in the VYS endoderm epithelium, suggestive of inhibition of VYS proteolysis. At the same time, excessive cell death was observed throughout the neuroepithelium and in specific regions of the mesenchyme of the corresponding embryos. This cell death manifested morphological characteristics of apoptosis and could be detected by supravital staining with Nile Blue Sulphate. These findings provide additional evidence in support of the hypothesis that lysosomal cysteine proteinases play a critical role in VYS-mediated histiotrophic nutrition and suggest that peptidyl diazomethanes may be useful in further characterization of these enzymes. The possible direct effects of these inhibitors on embryonic cells and the relationships between interruption of VYS-mediated nutritional processes and embryonic cell death are discussed.

Stimulation of the secretion of latent cysteine proteinase activity by tumor necrosis factor alpha and interleukin-1

OBJECTIVE

Cultured synovial fibroblast-like cells from 3 patients with rheumatoid arthritis (RA) and 3 patients with osteoarthritis (OA) were evaluated for their potential to secrete cysteine proteinases spontaneously and after stimulation by tumor necrosis factor alpha (TNF alpha) or interleukin-1 (IL-1).

METHODS

Culture media and cell lysates were analyzed before and after high performance liquid chromatography (HPLC) using the enzymatic substrate, Z-Phe-Arg-AMC, and by immunoblotting with anti-cathepsin B antiserum. Immunolocalization of cathepsin B was studied on cell monolayers.

RESULTS

Latent cysteine proteinase activity was found to be secreted spontaneously by cultured synovial fibroblast-like cells. This activity was increased after treatment with either TNF alpha or IL-1. Stimulated protease activity was eluted by HPLC at a peak coincident with that of purified cathepsin B. By immunoblot, cell supernatants contained a 43-kd form of cathepsin B, while cell lysates contained a 30-kd form, consistent, respectively, with cathepsin B before and after cleavage of its propeptide. An intracellular increase in cathepsin B after treatment with TNF alpha was also seen with immunohistochemical studies.

CONCLUSION

TNF alpha (in the 6 cases studied) and IL-1 (in 4 cases) stimulated the secretion of a latent cysteine proteinase activity from synovial fibroblast-like cells, which appears to represent primarily cathepsin B.