Inactivation of the elastase inhibitory activity of alpha 1 antitrypsin in fresh samples of synovial fluid from patients with rheumatoid arthritis

Site-Specific Conjugation of a Selenopolypeptide to Alpha-1-antitrypsin Enhances Oxidation Resistance and Pharmacological Properties

Human alpha-1-antitrypsin (A1AT), a native serine-protease inhibitor that protects tissue damage from excessive protease activities, is used as an augmentation therapy to treat A1AT-deficienct patients. However, A1AT is sensitive to oxidation-mediated deactivation and has a short circulating half-life. Currently, there is no method that can effectively protect therapeutic proteins from oxidative damage in vivo. Here we developed a novel biocompatible selenopolypeptide and site-specifically conjugated it with A1AT. The conjugated A1AT fully retained its inhibitory activity on neutrophil elastase, enhanced oxidation resistance, extended the serum half-life, and afforded long-lasting protective efficacy in a mouse model of acute lung injury. These results demonstrated that conjugating A1AT with the designed selenopolymer is a viable strategy to improve its pharmacological properties, which could potentially further be applied to a variety of oxidation sensitive biotherapeutics.

Serpins in cartilage and osteoarthritis: what do we know?

Serpins (serine proteinase inhibitors) are an ancient superfamily of structurally similar proteins, the majority of which use an elegant suicide inhibition mechanism to target serine proteinases. Despite likely evolving from a single common ancestor, the 36 human serpins have established roles regulating diverse biological processes, such as blood coagulation, embryonic development and extracellular matrix (ECM) turnover. Genetic mutations in serpin genes underpin a host of monogenic disorders — collectively termed the ‘serpinopathies’ — but serpin dysregulation has also been shown to drive pathological mechanisms in many common diseases. Osteoarthritis is a degenerative joint disorder, characterised by the progressive destruction of articular cartilage. This breakdown of the cartilage is driven by the metalloproteinases, and it has long been established that an imbalance of metalloproteinases to their inhibitors is of critical importance. More recently, a role for serine proteinases in cartilage destruction is emerging; including the activation of latent matrix metalloproteinases and cell-surface receptors, or direct proteolysis of the ECM. Serpins likely regulate these processes, as well as having roles beyond serine proteinase inhibition. Indeed, serpins are routinely observed to be highly modulated in osteoarthritic tissues and fluids by ‘omic analysis, but despite this, they are largely ignored. Confusing nomenclature and an underappreciation for the role of serine proteinases in osteoarthritis (OA) being the likely causes. In this narrative review, serpin structure, biochemistry and nomenclature are introduced, and for the first time, their putative importance in maintaining joint tissues — as well as their dysregulation in OA — are explored.

Post-Translational Modifications of Circulating Alpha-1-Antitrypsin Protein

Alpha-1-antitrypsin (AAT), an acute-phase protein encoded by the SERPINA1 gene, is a member of the serine protease inhibitor (SERPIN) superfamily. Its primary function is to protect tissues from enzymes released during inflammation, such as neutrophil elastase and proteinase 3. In addition to its antiprotease activity, AAT interacts with numerous other substances and has various functions, mainly arising from the conformational flexibility of normal variants of AAT. Therefore, AAT has diverse biological functions and plays a role in various pathophysiological processes. This review discusses major molecular forms of AAT, including complex, cleaved, glycosylated, oxidized, and S-nitrosylated forms, in terms of their origin and function.

Context-Specific and Immune Cell-Dependent Antitumor Activities of α1-Antitrypsin

α1-antitrypsin (AAT), a circulating glycoprotein that rises during acute phase responses and healthy pregnancies, exhibits immunomodulatory properties in several T-cell-dependent immune pathologies. However, AAT does not directly interfere with T-cell responses; instead, it facilitates polarization of macrophages and dendritic cells towards M2-like and tolerogenic cells, respectively. AAT also allows NK cell responses against tumor cells, while attenuating DC-dependent induction of autoimmune NK cell activities. Since AAT-treated macrophages bear resemblance to cancer-promoting tumor-associated macrophages (TAMs), it became imperative to examine the possible induction of tumor permissive conditions by AAT. Here, AAT treatment is examined for its effect on tumor development, metastatic spread, and tumor immunology. Systemic AAT treatment of mice inoculated with B16-F10 melanoma cells resulted in significant inhibition of tumor growth and metastatic spread. Using NK cell-resistant RMA cells, we show that AAT interferes with tumor development in a CD8+ T-cell-dependent manner. Unexpectedly, upon analysis of tumor cellular composition, we identified functional tumor-infiltrating CD8+ T-cells alongside M1-like TAMs in AAT-treated mice. Based on the ability of AAT to undergo chemical modifications, we emulated conditions of elevated reactive nitrogen and oxygen species. Indeed, macrophages were stimulated by treatment with nitrosylated AAT, and IFNγ transcripts were significantly elevated in tumors extracted soon after ischemia-reperfusion challenge. These context-specific changes may explain the differential effects of AAT on immune responses towards tumor cells versus benign antigenic targets. These data suggest that systemically elevated levels of AAT may accommodate its physiological function in inflammatory resolution, without compromising tumor-targeting immune responses.

Oxidized alpha-1 antitrypsin as a predictive risk marker of opisthorchiasis-associated cholangiocarcinoma

The oxidized alpha-1 antitrypsin (ox-A1AT) is one modified form of A1AT, generated via oxidation at its active site by free radicals released from inflammatory cells which subsequently are unable to inhibit protease enzymes. The presence of ox-A1AT in human serum has been used as oxidative stress indicator in many diseases. As oxidative/nitrative damage is one major contributor in opisthorchiasis-driven cholangiocarcinogenesis, we determined A1AT and ox-A1AT expression in human cholangiocarcinoma (CCA) tissue using immunohistochemical staining and measured serum ox-A1AT levels by ELISA. A1AT and ox-A1AT were found to be expressed in the tumor of CCA patients. The group with high expression has a significant poor prognosis. Serum levels of ox-A1AT were also significantly higher in groups of patients with heavy Opisthorchis viverrini infection, advanced periductal fibrosis (APF) and CCA when compared with healthy controls (P < 0.001). Odds ratio (OR) analysis implicated high ox-A1AT levels as a risk predictor for APF and CCA (P < 0.001; OR = 140.5 and 22.0, respectively). In conclusion, as APF may lead to hepatobiliary diseases and an increased risk of CCA development, our results identified ox-A1AT as a potential risk indicator for opisthorchiasis-associated CCA. This marker could now be explored for screening of subjects living in endemic areas where the prevalence of opisthorchiasis still remains high.

Assessment of some tools for the characterization of the human osteoarthritic cartilage proteome

Since the proteome of osteoarthritic articular cartilage has been poorly investigated as yet, we adapted proteomic technologies to the study of the proteins secreted or released by fresh human osteoarthritic cartilage in culture. Fresh cartilage explants were obtained from three donors undergoing surgery for knee joint replacement. The explants were dissected out, minced, and incubated in serum-free culture medium. After 48 h, proteins in the medium were identified by two-dimensional or off-gel electrophoresis coupled to tandem mass spectrometry, or by using an antibody-based protein microarray designed to detect angiogenic factors, growth factors, chemokines, and cytokines. We identified a series of 43 proteins. Some of these proteins were already described as secretion products of chondrocytes, such as YKL-39 or osteoprotegerin, while several other were known proteins but have never been reported previously in cartilage, such as the serum amyloid P-component, the vitamin D binding protein, the pigment epithelium derived factor, the pulmonary and activation-regulated chemokine, lyl-1, thrombopoietin, fibrinogen, angiogenin, gelsolin, and osteoglycin/mimecan. While this study enabled the identification of novel proteins secreted or released by human osteoarthritic cartilage, the goal of the present work was essentially to describe the technical approach necessary for a systematic study of osteoarthritic cartilages from a large population of donors, in order to be able to select the good markers and/or targets for this poorly explored disease.

Anti-oxidant therapy: does it have a role in the treatment of human disease?

Free radical oxidative stress has been implicated in the pathogenesis of a variety of human diseases. Natural anti-oxidant defences have also been found to be defective in many of the same diseases. Many researchers have concluded that, if the imbalance between the oxidative stresses and anti-oxidant defence can be corrected by supplementing natural anti-oxidant defences, it may be possible to prevent or retard disease progression. Potential anti-oxidant therapies include natural anti-oxidant enzymes and vitamins or synthetic agents with anti-oxidant activity. Diseases where anti-oxidant therapy may be beneficial can be divided into those involving acute intervention, such as reperfusion injury or inflammation, and those involving chronic preventative therapy, such as atherosclerosis, carcinogenesis and diabetic vascular disease. The pharmaceutical considerations are different in each case. The principles guiding the development, use and assessment of anti-oxidant therapies are discussed in this review.

Ambroxol inhibits peroxynitrite-induced damage of alpha1-antiproteinase and free radical production in activated phagocytic cells

The present study examined the effect of ambroxol on toxic action of peroxynitrite and the respiratory burst in activated phagocytic cells. Ambroxol decreased the inactivation or destruction of alpha1-antiproteinase induced by peroxynitrite (ONOO-) or hypochlorous acid (HOCl), which was similar to penicillamine and glutathione and was greater than diclofenac sodium and naproxen sodium. Ambroxol significantly decreased ONOO--mediated tyrosine nitration and iron plus EDTA-mediated degradation of 2-deoxy-D-ribose. Ambroxol significantly attenuated the production of superoxide, hydrogen peroxide, HOCl, and nitric oxide in fMLP- or IL-1-activated phagocytic cells, while the inhibitory effects of antiinflammatory and thiol compounds were only observed in HOCl production. Ambroxol and antiinflammatory drugs did not show a cytotoxic effect on macrophages. The results suggest that ambroxol protects tissue components against oxidative damage by an action different from antiinflammatory drugs. Ambroxol may interfere with oxidative damage of alpha1-antiproteinase through a scavenging action on ONOO- and HOCl and inhibition of the respiratory burst of phagocytic cells.

Evaluation of oxidized alpha-1-antitrypsin in blood as an oxidative stress marker using anti-oxidative alpha1-AT monoclonal antibody

BACKGROUND

alpha1-AT is a 52-kDa acute-phase protein and a typical serine proteinase inhibitor, which is present in human serum. In vivo, the inhibitor prevents tissue damage by inactivating proteinases, such as elastase, that are released from activated neutrophils in the presence of inflammation.

METHODS

We obtained a monoclonal antibody against oxidized alpha1-AT(3F4) using chloramine T-oxidized alpha1-AT as the antigen.

RESULTS

This antibody did not react with either the native alpha1-AT or the elastase-alpha1-AT complex. However, it reacted with alpha1-AT oxidized by various oxidants and peroxide lipid. The oxidized alpha1-AT is a polymer with a molecular mass of 100-200 kDa in addition to the 52-kDa protein that corresponds to the native alpha1-AT in sera. In vitro evaluations reveal that fatty acids are involved in the polymerization. Furthermore, the concentrations of oxidized alpha1-AT in the sera of patients with inflammatory and rheumatoid diseases were higher than those in healthy subjects.

CONCLUSIONS

We considered that 3F4 is an effective antibody that can specifically recognize oxidized alpha1-AT, a marker of oxidative stress.

In vivo complex formation of oxidized alpha(1)-antitrypsin and LDL

An inactivated form of alpha(1)-antitrypsin (AT) and LDL coelutes in gel permeation chromatography. To characterize and to quantify the amount of this fraction of AT, a monoclonal antibody was established against chloramine T-oxidized AT and named OxAT-4. OxAT-4 recognized the oxidatively modified AT, including hexylaldehyde- or 4-hydroxy-2-nonenal-modified AT, but neither normal active AT nor trypsin/AT complex. Comigration of apoB and oxidized AT was demonstrated by Western blotting analysis of AT-LDL by means of anti-apoB monoclonal antibody and OxAT-4. A complex of oxidized AT and LDL (AT-LDL) was isolated from human plasma LDL by affinity column with an OxAT-4 antibody-coated carrier. AT-LDL was degraded 4 times more effectively by mouse peritoneal macrophages, but this was not mediated by scavenger receptor class A type I. Localization of AT-LDL was detected in human atherosclerotic lesions of the coronary artery, but distribution of it was not completely identical to that of macrophages. In situ hybridization revealed AT expression by macrophages, which were present in intimal layers of the coronary artery. From these findings, we concluded that AT is produced and oxidized by macrophages, then attached to LDL in the intimal layer of the arterial wall. Although AT-LDL that escapes into the blood stream can be cleared by hepatocytes, the remaining AT-LDL may be taken up by macrophages and contribute to the lipid accumulation in arterial wall cells as the early stage of atherogenesis.

Conformational properties of serine proteinase inhibitors (serpins) confer multiple pathophysiological roles

Serine proteinase inhibitors (Serpins) are irreversible suicide inhibitors of proteases that regulate diverse physiological processes such as coagulation, fibrinolysis, complement activation, angiogenesis, apoptosis, inflammation, neoplasia and viral pathogenesis. The molecular structure and physical properties of serpins permit these proteins to adopt a number of variant conformations under physiological conditions including the native inhibitory form and several inactive, non-inhibitory forms, such as complexes with protease or other ligands, cleaved, polymerised and oxidised. Alterations of a serpin which affect its structure and/or secretion and thus reduce its functional levels may result in pathology. Serpin dysfunction has been implicated in thrombosis, emphysema, liver cirrhosis, immune hypersensitivity and mental disorders. The loss of inhibitory activity of serpins necessarily results in an imbalance between proteases and their inhibitors, but it may also have other physiological effects through the generation of abnormal concentrations of modified, non-inhibitory forms of serpins. Although these forms of inhibitory serpins are detected in tissues and fluids recovered from inflammatory sites, the important questions of which conditions result in generation of different molecular forms of serpins, what biological function these forms have, and which of them are directly linked to pathologies and/or may be useful markers for characterisation of disease states, remain to be answered. Elucidation of the biological activities of non-inhibitory forms of serpins may provide useful insights into the pathogenesis of diseases and suggest new therapeutic strategies.

Regulation of cell function by methionine oxidation and reduction

Reactive oxygen species (ROS) are generated during normal cellular activity and may exist in excess in some pathophysiological conditions, such as inflammation or reperfusion injury. These molecules oxidize a variety of cellular constituents, but sulfur-containing amino acid residues are especially susceptible. While reversible cysteine oxidation and reduction is part of well-established signalling systems, the oxidation and the enzymatically catalysed reduction of methionine is just emerging as a novel molecular mechanism for cellular regulation. Here we discuss how the oxidation of methionine to methionine sulfoxide in signalling proteins such as ion channels affects the function of these target proteins. Methionine sulfoxide reductase, which reduces methionine sulfoxide to methionine in a thioredoxin-dependent manner, is therefore not only an enzyme important for the repair of age- or degenerative disease-related protein modifications. It is also a potential missing link in the post-translational modification cycle involved in the specific oxidation and reduction of methionine residues in cellular signalling proteins, which may give rise to activity-dependent plastic changes in cellular excitability.

Activation of primary human monocytes by the oxidized form of alpha1-antitrypsin

The oxidation of methionine residues in many proteins, including the serine proteinase inhibitor alpha1-antitrypsin (AAT), can result in functional inactivation. In this study we investigated the pro-inflammatory properties of oxidized AAT (oxAAT), specifically its ability to activate human monocytes in culture. Monocytes stimulated with oxAAT at concentrations up to 0.2 mg/ml for 24 h showed significant elevation in monocyte chemoattractant protein-1, cytokine interleukin-6, and tumor necrosis factor-alpha expression and increased NADPH oxidase activity. Monocytes activated with oxAAT showed surprising effects on lipid metabolism. Expression of low density lipoprotein (LDL) receptors increased by up to 76% compared with controls but was not accompanied by any changes in (125)I-labeled LDL binding and, paradoxically, decreased LDL uptake, degradation, and intracellular cholesterol synthesis. oxAAT also down-regulated the scavenger receptor CD36, which takes up and is up-regulated by oxidized LDL and is down-regulated by cholesterol efflux. As a by-product of oxidative events accompanying inflammation, oxAAT has multiple effects on cytokine expression, generation of reactive oxygen species, and on intracellular lipid metabolism. The up-regulation of monocyte-derived reactive oxygen by oxAAT could potentially result in self-amplification of AAT oxidation and, thereby, the other effects deriving from it. This implies that there are as yet unidentified regulatory processes that control this cycle.

Expression of the thioredoxin-thioredoxin reductase system in the inflamed joints of patients with rheumatoid arthritis

OBJECTIVE

To examine the expression of the thioredoxin (TRX)-thioredoxin reductase (TR) system in patients with rheumatoid arthritis (RA) and patients with other rheumatic diseases.

METHODS

Levels of TRX in plasma and synovial fluid (SF) were measured using enzyme-linked immunosorbent assay. Cellular distribution of TRX was determined by flow cytometry and histochemistry. Cellular expression of TR was studied by in situ messenger RNA (mRNA) hybridization. The effect of oxidative stress and tumor necrosis factor alpha (TNF alpha) on TRX expression by cultured rheumatoid fibroblast-like synoviocytes was studied.

RESULTS

Significantly increased TRX levels were found in the SF from 22 patients with RA, when compared with plasma levels in the same patients (P < 0.001) and compared with SF TRX levels in 15 patients with osteoarthritis (P < 0.001), 13 patients with gout (P < 0.05), and 9 patients with reactive arthritis (P < 0.0001). The presence of TRX could be demonstrated within the SF-derived mononuclear cells and synovial tissue (ST) of RA patients. Concordantly, expression of TR mRNA was observed in the ST of these patients. Stimulation of synovial fibroblast-like synoviocytes with either H2O2 or TNF alpha induced an increase in the production of TRX.

CONCLUSION

The data demonstrate significantly increased concentrations of TRX in the SF and ST of RA patients when compared with the levels in patients with other joint diseases. Evidence is presented that the local environment in the rheumatic joint contributes to increased TRX production. Based on its growth-promoting and cytokine-like properties, it is proposed that increased expression of TRX contributes to the disease activity in RA.

Modulation of peroxynitrite- and hypochlorous acid-induced inactivation of alpha1-antiproteinase by mercaptoethylguanidine

1. Peroxynitrite is a cytotoxic species that can be formed, among other mechanisms, by the rapid reaction of superoxide with nitric oxide. Peroxynitrite formation has been implicated in a wide range of neurodegenerative and chronic inflammatory diseases, as has the formation of hypochlorous acid by myeloperoxidase. 2. There is considerable interest in the development of peroxynitrite scavengers as therapeutic agents. The thiol compound mercaptoethylguanidine has been suggested to fulfil this role since it has recently been shown to be not only a potent inhibitor of inducible nitric oxide synthase but also a scavenger of peroxynitrite. Indeed, it has been shown to be protective in some experimental models of circulatory shock and inflammation at plasma levels in the approximate range 100-300 microM. 3. One protein inactivated by peroxynitrite is the major inhibitor of serine proteinases in human body fluids, alpha1-antiproteinase. At high (250-1000 microM) concentrations, mercaptoethylguanidine was found to be effective in preventing peroxynitrite-mediated tyrosine nitration and alpha1-AP inactivation. 4. By contrast, lower concentrations of mercaptoethylguanidine (1-60 microM) enhanced the inactivation of alpha1-antiproteinase by peroxynitrite. 5. At all concentrations tested (1-1000 microM), mercaptoethylguanidine decreased the inactivation of alpha1-antiproteinase by hypochlorous acid. 6. We suggest that products of reaction of mercaptoethylguanidine with peroxynitrite or peroxynitrite-derived products could cause damage to alpha1-antiproteinase, and possibly other proteins in vivo, whereas scavenging of hypochlorous acid by mercaptoethylguanidine could contribute to its anti-inflammatory action in vivo.

Destruction of articular cartilage by alpha 2 macroglobulin elastase complexes: role in rheumatoid arthritis

OBJECTIVE

Neutrophil elastase accounts for the ability of some fresh rheumatoid synovial fluids to degrade cartilage matrix in vitro. The aim of this study was to determine if enzyme activity could result from depletion of synovial fluid inhibitors or protection of the enzyme from inhibition.

METHODS

The ability of synovial fluids to inhibit porcine pancreatic elastase was investigated together with chemical pretreatments capable of inactivating alpha 1 protease inhibitor (alpha 1PI) or preventing formation of alpha 2 macroglobulin (alpha 2M) elastase complexes. Subsequently, complexes of human neutrophil elastase with alpha 2M were prepared and applied to frozen sections of cartilage. Proteoglycan loss was quantified by alcian blue staining and scanning and integrating microdensitometry. Parallel studies were carried out using a low molecular weight chromogenic elastase substrate. The effects of alpha 1PI and SF on these systems were investigated. Finally, synovial fluids were subjected to gel filtration and the fractions assayed for elastase activity. High molecular weight fractions were pooled, concentrated, and tested for their ability to degrade cartilage sections.

RESULTS

All synovial fluids reduced the activity of porcine pancreatic elastase, the inhibition mainly being attributable to alpha 1PI, whereas remaining activity resulted from complexes of elastase with alpha 2M. Complexes of human neutrophil elastase with alpha 2M were shown to cause proteoglycan degradation in frozen sections of human articular cartilage. Alpha 1PI prevented alpha 2M elastase complexes from degrading cartilage but not the chromogenic substrate. The data suggested that alpha 1PI does not inhibit elastase bound to alpha 2M but sterically hinders the complex. However, only one of five synovial fluids was able to completely block the actions of alpha 2M elastase complexes against cartilage. Gel filtration of rheumatoid synovial fluids showed elastase and cartilage degrading activity to be associated with fractions that contained alpha 2M, and not with fractions expected to contain free enzyme.

CONCLUSIONS

The data suggest that synovial fluid alpha 2M elastase complexes can degrade cartilage matrix in rheumatoid arthritis.

Antioxidant properties of the decarboxylated dimer of aminoethylcysteine ketimine: assessment of its ability to scavenge peroxynitrite

The natural sulfur compound aminoethylcysteine ketimine decarboxylated dimer (AECK dimer) has been investigated for its ability to act as peroxynitrite scavenger. It has been found that the product efficiently protects against the nitration of tyrosine and the inactivation of alpha1-antiproteinase by peroxynitrite. The tyrosine nitration can be completely prevented by 100 microM AECK dimer which appears as effective as the antioxidants glutathione and N-acetylcysteine. The AECK dimer was also found to limit surface charge alteration of low density lipoprotein induced by peroxynitrite. These findings indicate that the AECK dimer is a strong protective agent against peroxynitrite damage and that it could play an important role in the defence against oxidative stress in human diseases.

Thiols and disulphides can aggravate peroxynitrite-dependent inactivation of alpha1-antiproteinase

Peroxynitrite (ONOO-) is a cytotoxic species formed in vivo. There is considerable interest in the development of ONOO- 'scavengers' as therapeutic agents; several thiols have been suggested to fulfil this role. One protein inactivated by ONOO- is alpha1-antiproteinase (alpha1AP), the major inhibitor of serine proteinases in human body fluids. At low thiol:ONOO- concentration ratios, several thiols (captopril, penicillamine, cysteine, cystine and penicillamine disulphide) aggravated inactivation of alpha1AP by ONOO- , whereas GSH, GSSG, homocysteine, ergothioneine, N-acetylcysteine, lipoate and dihydrolipoate did not. We suggest that sulphur-containing radicals are produced by reaction of certain thiols/disulphides with ONOO- or ONOO- -derived products and could mediate biological damage, including inactivation of alpha1AP. This must be considered in attempts to use thiols as 'peroxynitrite scavengers'.

Prevention of peroxynitrite-dependent tyrosine nitration and inactivation of alpha1-antiproteinase by antibiotics

Peroxynitrite, formed by reaction of superoxide and nitric oxide, appears to be an important tissue damaging species generated at sites of inflammation. In this paper, we compare the abilities of several antibiotics to protect against peroxynitrite-dependent inactivation of alpha1-antiproteinase, and to inhibit tyrosine nitration by peroxynitrite, in vitro. Tetracycline, minocycline, doxycycline, rifamycin and rifampicin were highly protective in both assay systems, whereas several other antibiotics tested were not. The possibility that antibiotics could affect tissue injury at sites of inflammation by scavenging peroxynitrite is discussed.

Thiourea and dimethylthiourea inhibit peroxynitrite-dependent damage: nonspecificity as hydroxyl radical scavengers

Thiourea and, more recently, dimethylthiourea, have been used as hydroxyl radical (OH.) scavengers in experiments both in vitro and in vivo. We show that both compounds can inhibit nitration of the amino acid tyrosine on addition of peroxynitrite, and also the inactivation of alpha1-antiproteinase by peroxynitrite. Hence, protective effects of (dimethyl) thiourea could be due to inhibition of peroxynitrite-dependent damage as well as to OH. scavenging, and these compounds must not be regarded as specific OH. scavengers.

Protection against peroxynitrite-dependent tyrosine nitration and alpha 1-antiproteinase inactivation by ascorbic acid. A comparison with other biological antioxidants

Peroxynitrite, formed by reaction of superoxide and nitric oxide, appears to be an important tissue-damaging species generated at sites of inflammation. In this paper, we compare the abilities of several biological antioxidants to protect against peroxynitrite-dependent inactivation of alpha 1-antiproteinase, and to inhibit tyrosine nitration upon addition of peroxynitrite. GSH and ascorbate protected efficiently in both systems. Uric acid inhibited tyrosine nitration but not alpha 1-antiproteinase inactivation. The possibility that ascorbic acid is an important scavenger of reactive nitrogen species in vivo is discussed.

The inhibitory effects of antirheumatic drugs on the activity of human leukocyte elastase and cathepsin G

The serine proteinases elastase and cathepsin G from polymorphonuclear granulocytes play a critical role in articular cartilage degradation, not only as proteolytic enzymes able to degrade the extracellular matrix but also by additionally modulating the level of active matrix metalloproteinases, key enzymes of the proteolytic destruction of cartilage during rheumatoid arthritis. The aim of our study was to examine whether anti-inflammatory drugs and selected compounds inhibited elastase and cathepsin G, and also to determine whether it is necessary to use a highly purified elastase preparation to screen drugs for their ability to block the activity of this enzyme. Eglin C and the glycosaminoglycan-peptide complex DAK-16, at concentrations ranging from 10(-9) to 10(-4) M, dose-dependently inhibited elastase and cathepsin G while the nonsteroidal anti-inflammatory drugs oxyphenbutazone, phenylbutazone, sulfinpyrazone and diclofenac-Na required high concentrations to demonstrate some inhibitory effects on the activity of both enzymes. None of the other anti-inflammatory drugs tested at a concentration of 10(-4) M such as acetylsalicylic acid, dexamethasone, indomethacin, ketoprofen, naproxen, oxaceprol, pirprofen and tiaprofenic acid demonstrated any marked inhibitory activity on either of these proteinases. Only a few drugs, when dosed therapeutically, achieved synovial fluid concentrations sufficient to inhibit the activities of both proteinases. The antirheumatic drugs demonstrated similar inhibition profiles in purified or partially purified elastase preparations. Thus the leukocyte extract containing the partially purified elastase and cathepsin G which can be rapidly and easily prepared at low costs appears to be an efficient mean of screening potentially new therapeutic agents for their ability to inhibit leukocyte elastase and cathepsin G.

Protection against peroxynitrite dependent tyrosine nitration and alpha 1-antiproteinase inactivation by some anti-inflammatory drugs and by the antibiotic tetracycline

OBJECTIVE

To examine in vitro the ability of several drugs to protect against deleterious effects of peroxynitrite, a cytotoxic agent formed by reaction of nitric oxide with superoxide radical, that may be generated in the rheumatoid joint and could cause joint damage.

METHODS

The ability of several drugs to protect against such possible toxic actions of peroxynitrite as inactivation of alpha 1-antiproteinase and nitration of tyrosine was evaluated.

RESULTS

Most non-steroidal anti-inflammatory drugs were moderately (indomethacin, diclofenac, naproxen, tolmetin) or only weakly (sulindac, ibuprofen, aurothioglucose, flurbiprofen, sulphasalazine, salicylate, penicillamine disulphide) effective in preventing tyrosine nitration and alpha 1-antiproteinase inactivation by peroxynitrite, but 5-aminosalicylate and penicillamine were much more effective, as was the antibiotic tetracycline (but not ampicillin). Phenylbutazone and flufenamic acid protected effectively against tyrosine nitration, but could not be tested in the alpha 1-antiproteinase system. The analgesic paracetamol was highly protective in both assay systems.

CONCLUSION

Many drugs used in the treatment of rheumatoid arthritis are unlikely to act by scavenging peroxynitrite. The feasibility of peroxynitrite scavenging as a mechanism of penicillamine, 5-aminosalicylate, and paracetamol action in vivo is discussed.

Inactivation of tissue inhibitor of metalloproteinase-1 by peroxynitrite

Peroxynitrite (ONOO-) has recently been implicated in connective tissue destruction in vivo. We have studied the effect of ONOO- on the activity of tissue inhibitor of metalloproteinase-1 (TIMP-1) in vitro. The inactivation of TIMP-1 by ONOO- was dose dependent with 50 microM ONOO- reducing the inhibitory activity of TIMP-1 towards gelatinase-A by 50%. High concentrations of ONOO- (500 microM-5 mM) caused protein fragmentation whilst lower concentrations (<250 microM) inactivated TIMP-1 without altering the molecular weight. Inactivation could be blocked by ONOO- scavengers but not by hydroxyl radical scavengers. Our results show that ONOO- is capable of inactivating TIMP-1, a process which could potentiate metalloproteinase-mediated tissue breakdown.

Characterization of drugs as antioxidant prophylactics

There is growing interest in the evaluation of drugs (prescription only medicines and over-the-counter medicines) as antioxidant prophylactics. Although free radical mechanism in human degenerative diseases is now generally recognised, the mechanisms of tissue injury in humans are very complex and it may not be possible to clearly identify the role played by free radicals in the process. This review examines the current evidence to support the notion that drugs for a particular therapeutic category might possess useful antioxidant capacity hence minimising tissue injury due to free radicals.

The chemical modification of glycosaminoglycan structure by oxygen-derived species in vitro

The effect of reactive oxygen species (ROS) on the chemical structure of glycosaminoglycans (GAG) was studied in order to consider their role in connective tissue damage during an inflammatory disease state such as periodontal disease. GAG were exposed to a radical generating system for 1 h and analysed by gel filtration for fragmentation and chemically with respect to uronic acid, hexosamine and sulfate content. Non-sulfated GAG, hyaluronan and chondroitin, were most susceptible to depolymerisation and chemical modification of uronic acid and hexosamine residues by ROS. Depolymerisation and chemical modification of sulfated GAG, chondroitin 4-sulfate, dermatan sulfate and heparan sulfate was significantly less than for non-sulfated GAG. The highly sulfated GAG heparin showed minimal depolymerisation by ROS, but uronic acid residues were readily modified. Analysis of the ROS-exposed residues suggests that uronic acid is capable of degrading to a 3-carbon aldehyde, malondialdehyde. Chondroitin sulfate exposed to ROS resulted in marginal desulfation. The results suggest that the presence of sulfate on the GAG chain may protect the molecule against ROS attack. However, chemical modification of GAG may affect proteoglycan function and be of importance in considering connective tissue destruction in a variety of pathological situations, including periodontal disease.

Promotion of oxidative damage to arachidonic acid and alpha 1-antiproteinase by anti-inflammatory drugs in the presence of the haem proteins myoglobin and cytochrome C

A mixture of myoglobin and hydrogen peroxide (H2O2) causes peroxidation of arachidonic acid. This peroxidation is greatly accelerated by adding phenylbutazone, which is effective even in the absence of H2O2. A wide range of other drugs was examined for their ability to exert similar pro-oxidant effects. We found that meclofenamic acid and flufenamic acid stimulated myoglobin-dependent lipid peroxidation, but only in the presence of H2O2. Ascorbic acid inhibited peroxidation both in the presence and in the absence of these drugs. Phenylbutazone, meclofenamic acid and flufenamic acid could also cause damage to proteins (as measured by inactivation of alpha 1-antiproteinase) in the presence of myoglobin and H2O2. The mitochondrial protein cytochrome c can also stimulate lipid peroxidation in the presence of H2O2. Phenylbutazone and meclofenamic acid, but not flufenamic acid, enhanced the peroxidation, which was again inhibited by ascorbic acid. However, only phenylbutazone caused inactivation of alpha 1-antiproteinase in the presence of cytochrome c and H2O2. Since respiring mitochondria generate superoxide radicals and H2O2, catalysis of lipid peroxidation and of the formation of drug-derived radicals by cytochrome c could be a mechanism contributing to mitochondrial damage by drugs.

Relationship between alpha 1-antitrypsin inactivation and tumor necrosis factor alpha concentration in the synovial fluid of patients with rheumatoid arthritis

OBJECTIVE

To examine the relationship between alpha 1-antitrypsin (alpha 1AT) specific activity and tumor necrosis factor alpha (TNF alpha) concentration in synovial fluid from 48 patients with rheumatoid arthritis.

METHODS

The specific activity of alpha 1AT was calculated from the measurement of alpha 1AT concentration (by rocket immunoelectrophoresis) and elastase inhibitory capacity. TNF alpha was detected by enzyme-linked immunosorbent assay.

RESULTS

TNF alpha concentrations correlated with the extent of alpha 1AT inactivation.

CONCLUSION

Our findings are consistent with a role of elastase in TNF alpha release within the inflamed joint.

Thrombin in inflammation and healing: relevance to rheumatoid arthritis

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Reactivity of an active center analog of Cu2Zn2superoxide dismutase in murine model of acute and chronic inflammation

The antiinflammatory efficacy of CuPu(Py)2 ([[N,N'-bis(2-pyridylmethylene)-1,4-butanediamine] (N,N',N'',N''')]-Cu2+), a serum stable active center analog of Cu2Zn2superoxide dismutase (SOD), was tested in vitro and in vivo in male Wistar rats suffering from potassium peroxochromate-induced inflammation. Parameters including 99mTc gamma-scintigraphic imaging, the arthritis score, the plasma superoxide dismutase activity, the inhibition of plasma sulfhydryl depletion as well as mitogenic and phagocytic responses were used to quantify the disease activity. All parameters improved impressively during the treatment with CuPu(Py)2 and resembled those of healthy animals after 21 days. The arthritis score was inhibited by 80% (P > 0.001) and the plasma SOD activity enhanced by 380% (P > 0.001). The depletion of plasma sulfhydryls and the leukocytic responses to concanavalin A, tetradecanoylphorbolacetate, and lipopolysaccharide were significantly reduced (P > 0.001) and correlated well with the arthritis score. The collapse of antioxidant defenses in human plasma as well as the depolymerization of hyaluronic acid was mimicked in vitro and successfully inhibited by CuPu(Py)2. Oxidant-induced injury of plasma components during the aqueous decay of potassium peroxochromate were demonstrated to activate the oxidative burst of phagocytes in human blood. The role of impaired pro- and antioxidant balances in the etiology of inflammatory and autoimmune rheumatic diseases is discussed.

Inactivation of synovial fluid alpha 1-antitrypsin by exercise of the inflamed rheumatoid joint

alpha 1-Antitrypsin (alpha 1AT) is known to be oxidised by reactive oxygen species both in vitro and in vivo, leading to its inactivation. We report here that synovial fluid (SF) alpha 1AT is inactivated during exercise of the knee-joints of rheumatoid arthritis (RA) patients. Sequential SF sampling from exercised RA patients showed a marked decrease in the mean activity of alpha 1AT after exercise with no change in the molecular forms of alpha 1AT. No such inactivation was found in the control (continuously resting) RA patients. We suggest that oxidation may contribute to alpha 1AT inactivation as a consequence of 'hypoxic-reperfusion' injury after exercise of the inflamed joint.

Doxycycline in the protection of serum alpha-1-antitrypsin from human neutrophil collagenase and gelatinase

The concentration of doxycycline required to inhibit 50% (50% inhibitory concentration for serpinase activity) of alpha-1-antitrypsin degradation by purified neutrophil collagenase was found to be approximately 20 microM, a value similar to the 50% inhibitory concentration of doxycycline required to inhibit collagen degradation by neutrophil collagenase. Doxycycline also efficiently inhibited phorbol myristate acetate-triggered neutrophil-mediated degradation of alpha-1-antitrypsin. This suggests that doxycycline can protect alpha-1-antitrypsin from collagenase and gelatinase in the presence of other proteases and biologically active molecules that are released by triggered neutrophils. The protection of a body's alpha-1-antitrypsin shield from serpinolytic activity of collagenase and matrix metallproteinases can result in inhibition of serine proteases such as neutrophil elastase. Tetracyclines may thus protect matrix constituents from a wider spectrum of neutral proteases than previously recognized, not just from the matrix metalloproteinases collagenase and gelatinase.

Inhibition of neutrophil superoxide production by human plasma alpha 1-antitrypsin

We report here that human plasma alpha 1-antitrypsin (alpha 1-AT) inhibited human neutrophil O2.- release elicited by a variety of stimulants. In comparison, the inhibitory capacities of two serine protease inhibitors, L-1-tosylamide 2-phenylethyl chloromethyl ketone (TPCK) and soybean trypsin inhibitor (SBTI), and the human recombinant alpha 1-AT mutant, alpha 1-AT-Arg358 were in the order: alpha 1-AT = TPCK much greater than alpha 1-AT-Arg358 greater than SBTI when cells were stimulated with concanavalin A plus cytochalasin E. These data suggest that, in human inflammatory fluids containing relatively high concentrations of alpha 1-AT (such as rheumatoid arthritis synovial fluid), (i) alpha 1-AT may down-regulate the inflammatory process by inhibiting the neutrophil respiratory burst and (ii) serpin oxidation by neutrophil-released reactive oxygen species is unlikely to occur.