Inactivation of alpha-1-proteinase inhibitor in serum by stimulated human polymorphonuclear leucocytes. Evidence for a myeloperoxidase-dependent mechanism

β2 integrin-mediated cell-cell contact transfers active myeloperoxidase from neutrophils to endothelial cells

Atherosclerosis and vasculitis both feature inflammation mediated by neutrophil-endothelial cell (EC) contact. Neutrophil myeloperoxidase (MPO) can disrupt normal EC function, although the mechanism(s) by which MPO is transferred to ECs are unknown. We tested the hypothesis that close, β2 integrin-dependent neutrophil-EC contact mediates MPO transfer from neutrophils to ECs. We used sensitive MPO assays and flow cytometry to detect MPO in ECs and demonstrate that ECs acquired MPO when contacted by neutrophils directly but not when ECs and neutrophils were separated in Transwells. The transfer was dependent on neutrophil number, exposure time, and incubation temperature. Transfer occurred in several EC types, increased with endotoxin, was not accompanied by MPO release into the medium, and was not abrogated by inhibiting degranulation to secretagogues. Confocal microscopy showed MPO internalization by ECs with cytoplasmic and nuclear staining. Neutrophils and ECs formed intimate contact sites demonstrated by electron microscopy. Blocking CD11b or CD18 β2 integrin chains, or using neutrophils from CD11b gene-deleted mice, reduced MPO transfer. EC-acquired MPO was enzymatically active, as demonstrated by its ability to oxidize the fluorescent probe aminophenyl fluorescein in the presence of a hydrogen peroxide source. The data suggest an alternative to EC uptake of soluble MPO, namely the cell contact-dependent, β2 integrin-mediated transfer from neutrophils. The findings could be of therapeutic relevance in atherosclerosis and vasculitis.

Neutrophil elastase, proteinase 3, and cathepsin G as therapeutic targets in human diseases

Polymorphonuclear neutrophils are the first cells recruited to inflammatory sites and form the earliest line of defense against invading microorganisms. Neutrophil elastase, proteinase 3, and cathepsin G are three hematopoietic serine proteases stored in large quantities in neutrophil cytoplasmic azurophilic granules. They act in combination with reactive oxygen species to help degrade engulfed microorganisms inside phagolysosomes. These proteases are also externalized in an active form during neutrophil activation at inflammatory sites, thus contributing to the regulation of inflammatory and immune responses. As multifunctional proteases, they also play a regulatory role in noninfectious inflammatory diseases. Mutations in the ELA2/ELANE gene, encoding neutrophil elastase, are the cause of human congenital neutropenia. Neutrophil membrane-bound proteinase 3 serves as an autoantigen in Wegener granulomatosis, a systemic autoimmune vasculitis. All three proteases are affected by mutations of the gene (CTSC) encoding dipeptidyl peptidase I, a protease required for activation of their proform before storage in cytoplasmic granules. Mutations of CTSC cause Papillon-Lefèvre syndrome. Because of their roles in host defense and disease, elastase, proteinase 3, and cathepsin G are of interest as potential therapeutic targets. In this review, we describe the physicochemical functions of these proteases, toward a goal of better delineating their role in human diseases and identifying new therapeutic strategies based on the modulation of their bioavailability and activity. We also describe how nonhuman primate experimental models could assist with testing the efficacy of proposed therapeutic strategies.

Release and activation of matrix metalloproteinase 8 from human neutrophils triggered by the leukotoxin of Actinobacillus actinomycetemcomitans

Matrix metalloproteinase 8 (MMP 8) degrades type I collagen and may be involved in the pathogenesis of periodontitis. Latent MMP 8 is stored in neutrophil granules and can be activated when released extracellularly. The periodontitis-associated bacterium Actinobacillus actinomycetemcomitans produces an RTX-toxin, leukotoxin, that degranulates and lyses human neutrophils. This study deals with the ability of leukotoxic A. actinomycetemcomitans to trigger the release and activation of MMP 8. Whole bacteria of three A. actinomycetemcomitans strains or leukotoxin purified from the highly toxic strain HK 1519 were incubated with human neutrophils. The extracellularly released latent and active forms of MMP 8 were detected by an immunoblot technique using specific antibodies against the protease. The activity of MMP 8 was determined by a collagen degradation assay. All strains induced release and activation of MMP 8. The effect was more pronounced under aerobic than anaerobic conditions and correlated with the leukotoxicity of the strains. Pure leukotoxin also induced MMP 8 release and activation in a concentration-dependent manner. Under aerobic conditions, oxidising substances formed by the neutrophils contributed to the rapid activation of the latent enzyme. Upon anaerobic incubation, the activation was slow and mainly caused by other proteases released during neutrophil degranulation. The activation was totally abolished in the presence of serum, probably due to the serum-protease inhibitors. Compared to the calcium ionophore A 23187, a well-known stimulus of neutrophil degranulation, leukotoxin was a more powerful inducer of MMP 8 release, since it triggered the process at a 1000-fold lower concentration. The present findings reveal a specific mechanism that can be induced by A. actinomycetemcomitans leukotoxin and which may contribute to the degradation of periodontal tissues under certain conditions.

Anti-proteinase 3 antibody activation of neutrophils can be inhibited by alpha1-antitrypsin

Wegener's granulomatosis (WG) is classically associated with the presence of cytoplasmic antineutrophil cytoplasmic autoantibodies (c-ANCA). Proteinase 3 (PR3), the target antigen for c-ANCA, is inhibited by the antiprotease alpha1-antitrypsin (A1AT), and recent studies have demonstrated that WG patients who are A1AT-deficient have a worse clinical course, suggesting that a protease-antiprotease imbalance may play a role in WG. We evaluated the effect of A1AT on anti-PR3 antibody-induced activation of neutrophils. The neutrophil was chosen because of its central role in the pathogenesis of WG. Isolated neutrophils from healthy controls were incubated with tumor necrosis factor (TNF)-alpha to induce surface expression of PR3. Subsequently, they were stimulated with a monoclonal antibody to PR3, resulting in a significant increase in respiratory burst. Addition of A1AT (1 mg/ml) to the TNF-alpha- primed cells before the addition of the anti-PR3 antibody resulted in a 47% reduction in anti-PR3 antibody-induced activation. A1AT mediated this inhibitory action by preventing anti-PR3 antibody binding to PR3 on the cell, thereby preventing the PR3-FcgammaR11a cross-linkage required for cell activation. Further, anti-PR3 antibody-induced activation of neutrophils from WG patients can be reduced by 56% with A1AT. These data suggest that protease-antiprotease interactions may play a pivotal role in neutrophil activation in WG.

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.

3-(Alkylthio)-N-hydroxysuccinimide derivatives: potent inhibitors of human leukocyte elastase

A series of 3-(alkylthio)-N-hydroxysuccinimide derivatives was synthesized and their inhibitory activity towards human leukocyte elastase (HLE) was investigated. The interaction of the compounds having a 3-alkylthioether side chain (compounds 1 and 2) with HLE was found to involve rapid acylation of the enzyme, followed by total regain of enzymatic activity within 3 h. Interestingly, compounds 3-8, having an oxidized thioether side chain, were found to be highly effective, time-dependent, irreversible inhibitors of the enzyme. The k(obs)/I values for compounds 3-8 ranged between 890 and 24,000 M-1 s-1. These findings demonstrate that, unlike the physiological inhibitor of HLE (alpha-1-proteinase inhibitor), which is inactivated upon oxidation, low-molecular-weight compounds retain and/or show enhanced inhibitory activity towards HLE upon oxidation of the thioether side chain and lay the groundwork for the development of compounds that embody proteinase inhibitory and antioxidant activity.

Oxidative inactivation of alpha 1-proteinase inhibitor by alveolar macrophages from healthy smokers requires the presence of myeloperoxidase

The aim of this work was to study the ability of human alveolar macrophages (AM) of 10 healthy smokers to inactivate alpha 1-proteinase inhibitor (alpha 1PI). Purified alpha 1PI was incubated for 45 min, with human alveolar macrophages before and after stimulation by phorbol myristate acetate (PMA) or opsonized zymosan. As a positive control, the same experiments were performed in parallel with blood human neutrophils (PMN). Results are expressed as percentage of inactivation of alpha 1PI as evaluated from its inhibitory activity against porcine pancreatic elastase. A strong correlation (r = 0.99) was shown when inhibitory activity of alpha 1PI was evaluated against porcine pancreatic elastase or human neutrophil elastase. Unstimulated AM (1.57 +/- 0.9%) as well as stimulated AM (PMA: 1 +/- 0.4%; zymosan: 3 +/- 0.6%) were unable to inactivate alpha 1PI. Gel electrophoresis of alpha 1PI demonstrated that AM before or after stimulation induced a slight proteolysis of alpha 1PI, whereas both cleaved and complexed alpha 1PI were found when alpha 1PI was incubated with activated PMN. Both unstimulated (22 +/- 2.6%) and activated PMN (PMA: 91.7 +/- 4.7%; zymosan: 90 +/- 5.5%) were responsible for a significant inactivation of alpha 1PI. Catalase, in contrast to superoxide dismutase, was responsible for a near complete protection of alpha 1PI inactivation by PMN. To better determine the role of PMN secretory products, especially myeloperoxidase (MPO), we also investigated the effect of zymosan-activated PMN supernatants or of purified MPO on the alpha 1PI-AM reaction. MPO assay in PMN supernatants demonstrated that activated neutrophils released significant amounts of MPO (16.8 +/- 4.1 U/ml), whereas MPO was undetectable in activated AM supernatants.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation between leukocyte-associated plasma proteins and white cell differential count

Prealbumin, albumin, orosomucoid (including the cellular variant orosomucoid2), alpha 1-antitrypsin, haptoglobin and transferrin were quantified in 107 cell samples from acute and chronic myeloid leukaemia, seven polycytaemia, seven normal blood marrow and 56 normal blood leukocytes by crossed immunoelectrophoresis. By statistical multivariate analyses, the individual plasma proteins and their combined protein patterns were correlated with the diagnoses and it was demonstrated that acute leukaemia cell samples contained significantly different protein patterns compared with the other diagnostic groups and normal controls. By comparison with the white blood cell differential count, in 78 samples of acute leukaemia, it was demonstrated that the protein patterns were significantly correlated with the specific cell types in the samples. In all, the differential counts accounted for about 29% of the variation in protein patterns. Alpha 1-antitrypsin was found significantly correlated with the myeloblasts and myelo-band cells. Orosomucoid2 and haptoglobin were significantly correlated with mature granulocytes and albumin was significantly correlated with lymphocytes. In some cell samples, after cytotoxic treatment of acute leukaemia, the granulocytes did not have orosomucoid2 despite normal morphology, suggesting defective maturation of these granulocytes. These results indicate that the mechanisms responsible for uptake of plasma proteins are highly specific for different cell types and in the case of myeloid cells specifically related to cell differentiation.

Aqueous cigarette tar extracts damage human alpha-1-proteinase inhibitor

The elastase inhibitory capacity (EIC) of human alpha-1-proteinase inhibitor (alpha 1PI) is severely compromised by aqueous cigarette tar extract (ACTE). An aqueous extract of the tar from two cigarettes causes a loss of EIC of at least 60% in 24 h at 37 degrees C (pH 7.4) and the damaging capability of the ACTE is retained for many hours. Hydrogen peroxide appears to be an essential component of the mechanism by which ACTE damages alpha 1 PI, since catalase substantially protects alpha 1PI from ACTE-mediated damage. Only mild protection is offered by 10 mM diethylenetriamine pentaacetic acid, indicating only a minor role for transition metal ions in the alpha 1PI-damaging process. Hydroxyl radicals are unlikely agents of alpha 1PI damage in the ACTE system, as judged from hydroxyl radical scavenger studies. Ascorbate and various thiols offer protection to different degrees, dependent on the incubation conditions. Of several amino acids tested, cysteine and methionine (but not methionine sulfoxide) are the only two that protect alpha 1PI. We suggest that components of cigarette smoke particulate matter extracted into the aqueous lung fluid environment may cause local deficiencies in alpha 1PI in smokers' lungs.

Stimulation of neutrophil elastase and myeloperoxidase release by IgG fragments

Human leucocyte elastase (HLE) cleaves IgG into Fab and Fc fragments. The Fc fragment bears an elastase-specific antigen and has previously been reported to be found in synovial fluid during rheumatoid arthritis. In addition, biological activity of elastase-specific Fc fragments has been described in modulating granulocyte oxidative metabolism. To investigate further regulatory effects of the elastase-induced IgG cleavage products, we tested the elastase and myeloperoxidase release of granulocytes. IgG fragments induce no enzyme release of unstimulated neutrophils. But elastase and myeloperoxidase release of cytochalasin b/FMLP-treated neutrophils is stimulated in a dose-dependent manner by the Fab fragments. The extent of stimulation depends on stimulus concentration and is at its maximum for low (e.g. 2.5 x 10(-8) M) FMLP concentration. Ten nanomoles Fab/4 x 10(6) PMN augment elastase release to 206% and myeloperoxidase release to 155% after pre-stimulation with 2.5 x 10(-8) M FMLP. Fc fragments stimulate elastase release to 162% but no MPO release. Untreated IgG1 and analog Fab and Fc fragments produced by papain cleavage react similarly. Elastase-generated IgG fragments may therefore up-regulate their concentration by simulating elastase release. The concomitantly stimulated release of myeloperoxidase may influence bactericidal activity and termination of oxidative burst.

Inhibition of neutrophil oxidative burst by elastase-generated IgG fragments

IgG1 is cleaved in vitro by granulocyte elastase into Fc, Fab and Fabc fragments. The cleaved products have been isolated by a series of chromatographic procedures and characterized with regard to molecular mass and isoelectric point. The Fc fragment has been previously shown to express at its N-terminal site a neoantigen which is specific for elastase (Kolb, G., Eckle, I., Heidtmann, H.-H., Neurath, F. & Havemann, K. (1988) Scand. J. Rheumatol. S75, 179-189). The production of superoxide radical anions in prestimulated neutrophils is inhibited dose-dependently by the elastase-generated Fc and Fabc fragments. Native IgG1 and Fab fragments show no inhibitory effect, nor do papain-generated Fc fragments. The degree of inhibition depends on the stimulus applied: half-maximal inhibition is obtained by 6 microM Fc after stimulation with 4 beta-phorbol and 2.4 microM after stimulation with fMet-Leu-Phe; neutrophils stimulated with serum-activated zymosan are not inhibited by IgG fragments. The effect of Fc is purely cellular; no inhibition of O2 generation can be produced by applying Fc to the xanthine oxidase/xanthine system. The fragments have no effect on the activation or activity of crude NADPH oxidase, which is the O2-forming enzyme system of neutrophils. Possible mechanisms are discussed by which Fc acts on stimulated neutrophils.

Apparent inactivation of alpha 1-antiproteinase by sulphur-containing radicals derived from penicillamine

alpha 1-Antiproteinase is the major inhibitor of proteolytic enzymes, such as elastase, in human plasma. Its elastase-inhibitory capacity can be inactivated by exposure to hydroxyl radicals (.OH) generated either by pulse radiolysis or by an Fe3+-EDTA/H2O2/ascorbic acid system. Inactivation of alpha 1-antiproteinase by radiolytically-generated .OH under anoxic conditions was decreased by adding a range of anti-inflammatory drugs to the reaction mixtures, including the thiol compound penicillamine. However, under conditions favouring formation of oxysulphur radicals, protection by thiols such as penicillamine was much decreased. It is proposed that sulphur-containing radicals resulting from attack of biologically-produced oxidants upon penicillamine in the presence of O2 can themselves inactivate alpha 1-antiproteinase, and that such radicals might contribute to the side-effects produced by penicillamine or gold thiol therapy in rheumatoid arthritis.

Antioxidant properties of conjugated bilirubin and biliverdin: biologically relevant scavenging of hypochlorous acid

Conjugated bilirubin at low micromolar concentrations strongly inhibits the luminol-enhanced chemiluminescence response of stimulated human polymorphonuclear leukocytes. In contrast, it does not inhibit either reduction of ferricytochrome c or lucigenin-mediated chemiluminescence of stimulated cells. Also, conjugated bilirubin and its metabolic precursor, biliverdin, do not inhibit the enzyme myeloperoxidase (MPO) since (i) the MPO-dependent oxidation of guaiacol is not affected by biliverdin and (ii) the spectral changes observed when conjugated bilirubin is oxidized by a MPO-H2O2-Cl(-)-system are very similar to those obtained with reagent HOCl. As judged from these spectroscopic studies, each molecule of conjugated bilirubin can scavenge one molecule of HOCl giving rise to an oxidation product that itself is capable of scavenging further molecules of HOCl. Importantly, at physiological pH, both bile pigments can efficiently protect the elastase-inhibitory capacity of alpha 1-antiprotease against inactivation by reagent HOCl.