Purification of a serine-proteinase inhibitor from human articular cartilage. Identity with the acid-stable proteinase inhibitor of mucous secretions

Modulation of granulocyte-endothelium interactions by antileukoproteinase: inhibition of anti-type II collagen antibody-induced leukocyte attachment to the synovial endothelium

Antileukoproteinase (ALP) is a physiological inhibitor of granulocytic serine proteases that has been shown to have anti-inflammatory properties in addition to its antiproteolytic activity. On the basis of its potential to block anti-collagen type II (CII) antibody-induced arthritis (CAIA) and to suppress the conformational activation of β₂-integrins in leukocytes, the present study was undertaken to investigate its interference with leukocyte adherence to cytokine-activated endothelium. The potential of recombinant ALP to block the interactions of leukocytes with the endothelial lining was concomitantly investigated in vitro and in vivo. Thus, intravital fluorescence microscopic imaging of leukocyte rolling and firm adhesion to postcapillary venules were performed in the knee joints of DBA1/J mice after intravenous injection of anti-CII mAbs. An IL-1β-activated endothelial layer formed by a murine glomerular cell line (glEND.2) was used to assay the interaction with human leukocytes in vitro. Electromobility shift and luciferase reporter gene assays permitted the analysis of cytokine-induced activation of the NF-κB pathway. Fluorescence-activated cell sorting was applied to determine endothelial E-selectin expression. Leukocyte rolling and firm adhesion to the synovial endothelium in an early response to the anti-CII antibody transfer were significantly decreased in ALP-pretreated mice. Concomitantly, ALP suppressed the IL-1β-induced NF-κB activation and the upregulation of E-selectin expression in glEND.2 cells in vitro. These findings support the notion that the newly uncovered properties of ALP to interfere with cytokine signalling and upregulation of adhesion molecules in endothelial cells are likely to contribute to the therapeutic potential of ALP in immune-complex-induced tissue injury.

Antileukoproteinase: Modulation of neutrophil function and therapeutic effects on anti-type II collagen antibody-induced arthritis

OBJECTIVE

Antileukoproteinase (ALP) is a physiologic inhibitor of granulocytic serine proteases. The present study was undertaken to investigate its therapeutic benefit in an antibody-transfer model of erosive polyarthritis and to elucidate its potential to interfere with immune complex-dependent inflammatory pathways.

METHODS

Arthritis development was induced in male (BALB/c x B10.Q)F(1) mice by intravenous injection of two monoclonal antibodies specific for type II collagen and was quantified by clinical scoring and histopathology. Arthritis severity was assessed in a cohort of mice under systemic treatment with recombinant human ALP (daily doses of 0.1 mg for 5 days starting immediately after disease induction) in comparison with untreated controls. Concomitantly, functional assays (phagocytosis, oxidative burst, fluorescence-activated cell sorting analysis of integrin expression) were performed on neutrophils upon in vitro stimulation by IgG-coated latex beads.

RESULTS

ALP treatment reduced arthritis incidence and severity and had a protective effect against cartilage and bone erosion. ALP inhibited the conversion of the leukocyte beta2 integrins into an active conformation upon Fc receptor stimulation of granulocytes. ALP bound to the actin-bundling protein L-plastin and down-modulated filamentous actin assembly in response to stimulation with IgG-coated latex beads in granulocytes. ALP exerted additional inhibitory effects on neutrophil functions associated with cytoskeletal reorganization, such as phagocytosis and oxidative burst.

CONCLUSION

In addition to its antiprotease activity, ALP exerts a variety of blocking effects on neutrophil functions, probably due to modulation of cytoskeletal changes, that may contribute to this inhibitor's antiarthritis potential and qualify it as a multifunctional regulator of inflammatory responses.

Isolation of chymase complexed with physiological inhibitor similar to secretory leukocyte protease inhibitor (SLPI) from hamster cheek pouch tissues

A low molecular weight protein complexed with chymase was isolated from hamster cheek pouch tissues. This protein had an apparent molecular mass of about 10 kDa on SDS-PAGE and the N-terminal sequence showed some homology to secretory leukocyte protease inhibitor (SLPI), which is known as the predominant inhibitor of neutrophil elastase and cathepsin G. Remarkably enhanced inhibition of chymase activity was achieved in the presence of heparin, indicating that the functional property was also similar to SLPI. These findings suggest that this SLPI-like protein is a candidate for a physiological inhibitor of chymase.

Constitutive and regulated secretion of secretory leukocyte proteinase inhibitor by human intestinal epithelial cells

BACKGROUND & AIMS

Epithelial cells participate in immune regulation and mucosal integrity by generating a range of biologically active mediators. In the intestine, little is known about the potential endogenous anti-inflammatory molecules. Secretory leukocyte proteinase inhibitor (SLPI) is a major serine proteinase inhibitor, a potent antibiotic, and thus a potential anti-inflammatory molecule, although it is not known if it is secreted by intestinal epithelial cells.

METHODS

We show, by reverse-transcription polymerase chain reaction, the presence of SLPI messenger RNA in human model intestinal epithelial cell lines (Caco2-BBE, T84, and HT29-Cl.19A) and human jejunum and colon biopsy specimens. The polymerase chain reaction product was cloned and sequenced and is identical to that of SLPI isolated previously from the human parotid gland.

RESULTS

As analyzed by enzyme-linked immunosorbent assay, the constitutive secretion of SLPI occurs in a markedly polarized manner toward the apical surface and is enhanced by inflammatory mediators including tumor necrosis factor alpha and interleukin 1beta (approximately 3.5-fold increase over control value). SLPI release is also stimulated by activation of protein kinase C isoenzymes, but not by activation of adenosine 3',5'-cyclic monophosphate- or Ca(2+)-regulated signaling molecules. SLPI protein is detectable in intestinal lavage fluids collected from normal adult humans. Recombinant SLPI attenuates digestive enzyme (trypsin)- or leukocyte proteinase (elastase)-induced permeability alteration of a model epithelia in a dose-dependent manner. Moreover, SLPI exhibits an antibacterial activity against at least one major intestinal pathogen, Salmonella typhimurium. In contrast, SLPI does not influence epithelial barrier integrity as assessed by transepithelial conductance measurements or electrogenic ion transport.

CONCLUSIONS

These results establish that human intestinal epithelium expresses and apically secretes SLPI, a molecule that may significantly contribute to the protection against attack from inflammatory cells and digestive enzymes, as well as against microbial infection.

Secretory leukocyte protease inhibitor suppresses the inflammation and joint damage of bacterial cell wall-induced arthritis

Disruption of the balance between proteases and protease inhibitors is often associated with pathologic tissue destruction. To explore the therapeutic potential of secretory leukocyte protease inhibitor (SLPI) in erosive joint diseases, we cloned, sequenced, and expressed active rat SLPI, which shares the protease-reactive site found in human SLPI. In a rat streptococcal cell wall (SCW)-induced model of inflammatory erosive polyarthritis, endogenous SLPI was unexpectedly upregulated at both mRNA and protein levels in inflamed joint tissues. Systemic delivery of purified recombinant rat SLPI inhibited joint inflammation and cartilage and bone destruction. Inflammatory pathways as reflected by circulating tumor necrosis factor alpha and nuclear factor kappaB activation and cartilage resorption detected by circulating levels of type II collagen collagenase-generated cleavage products were all diminished by SLPI treatment in acute and chronic arthritis, indicating that the action of SLPI may extend beyond inhibition of serine proteases.

Inhibition of neutrophil cathepsin G by oxidized mucus proteinase inhibitor. Effect of heparin

Oxidation of mucus proteinase inhibitor (MPI) transforms Met73, the P'1 residue of its active center into methionine sulfoxide and lowers its affinity for neutrophil elastase [Boudier, C., and Bieth, J. G. (1994) Biochem. J. 303, 61-68]. Here, we show that the oxidized inhibitor has also a decreased affinity for neutrophil cathepsin G and pancreatic chymotrypsin. The Ki of the oxidized MPI-cathepsin G complex (1.2 microM) is probably too high to be compatible with significant inhibition of cathepsin G in inflammatory lung secretions. Stopped-flow kinetics shows that, within the inhibitor concentration range used, the mechanism of inhibition of cathepsin G and chymotrypsin by oxidized MPI is consistent with a one-step reaction, [equation in text] whereas the inhibition of elastase takes place in two steps, [equation in text]. Heparin, which accelerates the inhibition of the three proteinases by native MPI, also favors their interaction with oxidized MPI. Flow calorimetry shows that heparin binds oxidized MPI with Kd, Delta H degrees, and Delta S degrees values close to those reported for native MPI. In the presence of heparin, oxidized MPI inhibits cathepsin G via a two-step reaction characterized by Ki = 0.22 microM, k2 = 0.1 s-1, k-2 = 0.023 s-1, and Ki = 42 nM. Under these conditions, in vivo inhibition of cathepsin G is again possible. Heparin also improves the inhibition of chymotrypsin and elastase by oxidized MPI by increasing their kass or k2/Ki and decreasing their Ki. Our data suggest that oxidation of MPI during chronic bronchitis may lead to cathepsin G-mediated lung tissue degradation and that heparin may be a useful adjuvant of MPI-based therapy of acute lung inflammation in cystic fibrosis.

The cloning and characterization of a murine secretory leukocyte protease inhibitor cDNA

Human secretory leukocyte protease inhibitor (hSLPI) is produced by epithelial cells at mucosal surfaces, where it regulates both the neutrophil-mediated inflammation that characterizes inflammatory diseases, and pathogens themselves via both antiprotease and "defensin-like" activities. Additionally, hSLPI may regulate other processes such as cutaneous desquamation and placental invasiveness. To better understand the primary physiologic roles of SLPI, it will be important to establish a genetically tractable animal model, the most attractive candidate being the mouse. In this report, the cloning and characterization of murine (m) SLPI is described. mSLPI is encoded by a single copy gene, and appears structurally highly similar to hSLPI. At the same time, significant differences between mSLPI and hSLPI are presented, notably a difference in expression pattern, and a structural difference in the protease binding site that correlates with a difference in the spectrum of protease inhibiton. Such species-specific evolution of this protease inhibitor is notable given that species-specific structure-function differences have previously been reported for the alpha-1 antitrypsin family.

Use of secretory leukoprotease inhibitor to augment lung antineutrophil elastase activity

Physiologically, secretory leukoprotease inhibitor (SLPI) is the major antiprotease of the epithelium of the upper respiratory tract providing protection against neutrophil elastase (NE). The recombinant form of SLPI (rSLPI) has several advantages compared with alpha 1-antitrypsin that make it interesting as potential therapy. In vitro, rSLPI proves to be an excellent inhibitor of NE. When administered as an aerosol in vitro and in vivo, the structure and function of rSLPI remain intact. Using the aerosol route, the half-life of rSLPI in respiratory epithelial lining fluid is 12 h; thus, giving it twice daily should guarantee satisfactory levels in the lung. Following inhalation, rSLPI moves from the epithelium in an intact form into the interstitium of the lung. Following on from these in vitro and in vivo experiments, a short-term study in patients with cystic fibrosis was performed with aerosolized rSLPI. Promising results relative to NE level reduction and the consequences for the inflammatory process in the bronchi were achieved. rSLPI not only induced an increase of the anti-NE protective screen, but also improved the antioxidant protection by raising glutathione levels in the lung in sheep. rSLPI may therefore provide a unique opportunity for protecting the lung from the damage caused by inflammatory processes by giving a single drug.

Oxidized mucus proteinase inhibitor: a fairly potent neutrophil elastase inhibitor

N-chlorosuccinimide oxidizes one of the methionine residues of mucus proteinase inhibitor with a second-order rate constant of 1.5 M-1.s-1. Cyanogen bromide cleavage and NH2-terminal sequencing show that the modified residue is methionine-73, the P'1 component of the inhibitor's active centre. Oxidation of the inhibitor decreases its neutrophil elastase inhibitory capacity but does not fully abolish it. The kinetic parameters describing the elastase-oxidized inhibitor interaction are: association rate constant kass. = 2.6 x 10(5) M-1.s-1, dissociation rate constant kdiss. = 2.9 x 10(-3) s-1 and equilibrium dissociation constant Ki = 1.1 x 10(-8) M. Comparison with the native inhibitor indicates that oxidation decreases kass. by a factor of 18.8 and increases kdiss. by a factor of 6.4, and therefore leads to a 120-fold increase in Ki. Yet, the oxidized inhibitor may still act as a potent elastase inhibitor in the upper respiratory tract where its concentration is 500-fold higher than Ki, i.e. where the elastase inhibition is pseudo-irreversible. Experiments in vitro with fibrous human lung elastin, the most important natural substrate of elastase, support this view: 1.35 microM elastase is fully inhibited by 5-6 microM oxidized inhibitor whether the enzyme-inhibitor complex is formed in the presence or absence of elastin and whether elastase is pre-adsorbed on elastin or not.

A solid phase enzyme linked immunofiltration assay for secretory leucocyte proteinase inhibitor

A solid phase enzyme linked immunosorbent filtration assay (ELIFA) has been developed for secretory leucocyte proteinase inhibitor (SLPI) utilising polyclonal anti-recombinant SLPI (anti-rSLPI) and polyclonal anti-bronchial mucus proteinase inhibitor (anti-BLPI) IgG samples. Millipore HATF nitrocellulose 96-well plates were used as receptacles for the assay and a commercial goat anti-rabbit IgG alkaline phosphatase conjugate was used as a secondary antibody for quantitation of levels of primary antibodies bound to rSLPI in the plate wells. Antigen bound to the HATF plates efficiently and the washing/blocking steps were simplified by vacuum filtration of samples resulting in a rapid and convenient assay system. The ELIFA was also sensitive and a detection limit of 0.1 ng SLPI/well was achieved using either anti-SLPI or anti-BLPI as primary antibodies. This assay was used to demonstrate the production of SLPI at moderate levels (0.5-3 ng/ml media) by human articular chondrocytes grown in monolayer culture.

Secretory leucocyte proteinase inhibitor is produced by human articular cartilage chondrocytes and intervertebral disc fibrochondrocytes

The objective of this study was to examine the expression of the secretory leucocyte proteinase inhibitor (SLPI) gene by human articular cartilage chondrocytes and intervertebral disc fibrochondrocytes. RNA was extracted from human articular cartilage chondrocytes, synovial fibroblasts and fibrochondrocytes of the annulus fibrosus. Expression was analysed by Northern blotting and hybridisation to a SLPI RNA probe. SLPI was isolated from chondrocyte culture supernatant by gel-permeation and cation-exchange chromatography and examined by a solid-phase enzyme-linked immunofiltration assay for SLPI and by SDS/PAGE using Western blotting with polyclonal IgG samples against bronchial mucus leucocyte proteinase inhibitor and SLPI. This identified biochemically and immunologically the major serine proteinase inhibitory protein synthesised by chondrocytes as SLPI. Secretory leucocyte proteinase inhibitor mRNA was detected in RNA preparations from articular cartilage chondrocytes and annulus fibrosus fibrochondrocytes. The results presented here allowed us to deduce that human articular cartilage chondrocytes and intervertebral disc fibrochondrocytes synthesized SLPI whereas human synovial fibroblasts did not.

Characterization and gene sequence of the precursor of elafin, an elastase-specific inhibitor in bronchial secretions

Human bronchial mucous secretions have been shown to contain inhibitors of serine proteinases secreted by neutrophils. The role of these inhibitors is probably to control the enzymes secreted in the airways and in the lung interstitium. Three of these inhibitors have been identified and characterized: alpha 1-proteinase inhibitor, mucus proteinase inhibitor, and elafin. The elafin molecule, a 6.0 kD inhibitor of serine proteinases shows homology with mucus proteinase inhibitor. We recently isolated both molecules in bronchial secretions. In this report, we present evidence for the existence of a precursor of the elafin molecule. We have cloned and sequenced the gene for this precursor and show that it is composed of three exons. The coding information for a 117 amino acid precursor protein of elafin (inclusive of the signal peptide) is contained in the first two exons. This was confirmed at the mRNA and protein levels. By Northern Blot analysis we detected a 800 bp long product, and by immunoaffinity we detected in sputum and in cultured epithelial cell supernatant (NCI-H322 cell line) a 12 kD protein species cross-reacting with anti-elafin IgG. The finding of possible cross-linking function for the precursor in addition to its antiproteinase activity indicates a possible role for this molecule as a cross-linker agent in the extracellular matrix.

Comparison of the proteoglycanolytic activities of human leukocyte elastase and human cathepsin G in vitro and in vivo

In this study, we evaluated the in vitro and in vivo potency of human leukocyte elastase (HLE) and human cathepsin G (HCG) as proteoglycanases. In vitro evaluation was done using bovine nasal septum aggrecan and aggrecan/hyaluronan aggregate as substrates. Enzyme activity was assessed by the ability of the proteinases to abrogate the ability of aggrecan to aggregate with hyaluronan. In vivo activity of the proteinases was tested by injecting purified HLE and HCG intra-articularly into rabbit stifle joints and quantifying the levels of proteoglycan released into synovial fluids. On a molar basis, HCG was at least tenfold more potent than HLE as a proteoglycanase in vitro. Moreover, HCG was twofold more potent as a proteoglycanase in vivo. In contrast, HLE hydrolyzed elastin approximately 22-fold faster than HCG, but was only slightly more rapid than HCG when [3H]-transferrin was used as substrate. These data indicate that HCG is more potent than HLE as a proteoglycanase both in vitro and in vivo. Thus, HCG could be more important in the pathogenesis of rheumatoid arthritis than previously suspected.

The serine proteinase inhibitory proteins of the human intervertebral disc: their isolation, characterization and variation with ageing and degeneration

Serine proteinase inhibitory proteins (SPIs) were extracted from human disc tissues using 2 M GuHCl and subjected to CsCl density gradient ultracentrifugation. The SPIs recovered in the low buoyant density fractions (rho < or = 1.35 g/ml) were purified by a combination of gel-permeation, ion-exchange, trypsin affinity, and reverse-phase high performance chromatographies. Characterisation of the major disc SPI by polyacrylamide gel electrophoresis, isoelectric focussing, enzyme inhibition and pH stability studies indicated that this small molecular weight (12-14 kDa), highly basic (pI > 9.5), acid-stable but alkaline-labile protein possessed potent inhibitory activity against bovine pancreatic trypsin and chymotrypsin, and human leukocyte elastase and cathepsin G. Two-major and two-minor low molecular weight cationic SPI species were identified by reverse-phase HPLC. The predominant species was identical to a human articular cartilage SPI sharing amino terminal sequence homology with the mucus proteinase inhibitors (MPIs). It also cross-reacted with an antiserum to the MPIs and behaved identically to secretory leucocyte proteinase inhibitor (SLPI) when examined by reverse phase HPLC, and SDS PAGE. A higher molecular weight (54 kDa), anionic (pI approximately 4.6) SPI was also purified and identified as alpha 1-proteinase inhibitor (alpha 1-PI). Quantification of alpha 1-PI and the small molecular weight cationic disc inhibitors indicated that the latter were depleted in morphologically degenerate disc tissues while levels of alpha 1-PI were somewhat higher although a large proportion of the alpha 1-PI was inactive. A depletion of total SPI levels was evident overall in degenerate discs suggesting a functional role for these inhibitory proteins in the maintenance of IVD matrix homeostasis.

Development of an avidin-biotin competitive inhibition assay and validation of its use for the quantitation of human intervertebral disc serine proteinase inhibitory proteins

A simple convenient method has been developed for the quantitation of serine proteinase inhibitors (SPIs) in tissue extracts. The method is based on the competitive binding to trypsin and chymotrypsin immobilized using glutaraldehyde on 96-well microtiter plate wells of native SPIs and a biotinylated secretory proteinase inhibitor (SLPI) standard. The bound SLPI standard was visualized using an avidin-alkaline phosphatase conjugate and inhibition curves were determined using absorbancy measurements at 405 nm. The standard assay had a range between 0.02 and 1 microgram SLPI/well and a lower detection limit of 20 ng SLPI/well; an improved microassay had a detection limit of 2 ng SLPI/well. Only active free inhibitor was detected in the assay since denatured and/or enzyme-inhibitor complexes did not bind to the plates. A range of SPI species was demonstrable in human bronchial mucus and intervertebral disc SPI samples using this technique. Quantitation of SPI levels in a number of intervertebral disc samples indicated that the SPIs were depleted in degenerate discs compared to nondegenerate discs (P less than 0.05, n = 12). Since the immobilized trypsin and chymotrypsin microplates used in this assay may be prepared in advance (and are stable at 4 degrees C for at least 1 month) the remaining two steps of the assay (the inhibition step and visualization) may be completed in 2-3 h; thus the assay is simple, convenient, and fast. All reagents (other than the biotinylated SLPI standard) are readily available commercially, and in principle the assay could be adapted to other systems provided defined biotinylated standards were available.

The serine-protease inhibitor of cartilage matrix is not a chondrocytic gene product

Human articular cartilage contains significant amounts of antileukoprotease, a cationic low-molecular-mass serine-protease inhibitor, which was originally purified from mucous secretions (synonym: secretory leukocyte proteinase inhibitor). As it was not known whether the inhibitor molecule is also synthesized locally, we investigated antileukoprotease gene expression in chondrocytes. No antileukoprotease-specific mRNA was detected in adult or foetal human chondrocytes by in situ hybridization, Northern-blot analysis or polymerase chain reaction. Concurrently, the chondrocytes remained unstained on immunohistology, whereas immunoreactive antileukoprotease was demonstrated in the cartilage matrix. By Northern-blot analysis, the antileukoprotease message was detected in the promyelocytic cell line HL60, the myelomonocytic cell line U937 and even in mature polymorphonuclear leukocytes from the peripheral blood of healthy donors. Immunoperoxidase staining of polymorphonuclear leukocytes for the antileukoprotease protein indicated that this cell is likely to be the physiological source of the inhibitor in serum. The results further suggest an accumulation of the inhibitor in the cartilage matrix.

Cytotoxic effects of rheumatoid arthritis sera on chondrocytes

Human sera from patients with rheumatoid arthritis (RA) and also from healthy donors were found to be toxic to cultured chondrocytes. Immunoglobulins were found to bind to the surface of cultured cells and cells in chicken sternal cartilage, as detected by indirect immunofluorescence. In vitro, cell detachment from the substrate was caused by the incubation of chondrocyte monolayers with 5 per cent and less RA serum. Serum treatment caused cytotoxic degradation of the cells. This could be quantified by a chromium release assay. Heat inactivation of the serum abolished the cytotoxicity. The extent of the cytotoxic reaction was related to the complement content of the serum and also to the intensity of the disease, as determined by the Ritchie-index. Other cell types, as chondrosarcoma cells, normal fibroblasts and corneal epithelium, were not affected by RA sera.

Isolation and characterization of an abundant elastase inhibitor from NaCl extracts of bovine nasal septa and articular cartilage

Extracts of cartilage have been reported to inhibit many serine proteinases and metalloenzymes. Such inhibition may be important in protecting cartilage against degradation by chondrocytic proteinases such as collagenase, stromelysin and by leukocytic proteases, such as elastase. We report here isolation and partial characterization of a 17-kD elastase inhibitor from 0.5 M NaCl extracts of both nasal septum cartilage and articular cartilage, which inhibits elastase and represents 0.08% of the weight of nasal cartilage and 0.002% of the weight of articular cartilage. The protein was highly specific for elastase and did not inhibit cartilage metalloproteinases, suggesting that it may be mainly directed toward protecting cartilage against leukocytic proteases. The inhibitor had a blocked amino-terminus, was high in serine and glycine and lacked carbohydrate. The ease with which the inhibitor was extracted from cartilage suggests that it may function in vivo as a highly abundant elastase inhibitor which is secreted into synovial fluid from cartilage. The inhibitor was shown to be synthesized by bovine articular cartilage in explant culture and nearly all of the metabolically labeled material was secreted into the culture media. The inhibitor cross-reacted with polyclonal antibodies to bovine neck ligament alpha-elastin and antibodies to the inhibitor reacted with bovine neck ligament elastin. The properties of this inhibitor are different than those of any other reported cartilage derived inhibitor.