Human neutrophil and mast cell proteases implicated in inflammation

Neutrophil proteinase 3 acts on protease-activated receptor-2 to enhance vascular endothelial cell barrier function

OBJECTIVE

The principle role of the vascular endothelium is to present a semi-impermeable barrier to soluble factors and circulating cells, while still permitting the passage of leukocytes from the bloodstream into the tissue. The process of diapedesis involves the selective disruption of endothelial cell junctions, which could compromise vascular integrity. It is therefore somewhat surprising that neutrophil transmigration does not significantly impair endothelial barrier function. We examined whether neutrophils might secrete factors that promote vascular integrity during the latter stages of neutrophil transmigration, in particular, the role of neutrophil serine proteinase 3 (PR3).

METHODS AND RESULTS

Endothelial cells were treated with PR3 either in its soluble form or in a complex form with cell surface NB1. We observed that PR3 mediated the enhancement of endothelial cell junctional integrity and that this required its proteolytic activity, as well as endothelial cell expression of the protease-activated receptor-2. Importantly, PR3 suppressed the vascular permeability changes and disruption of junctional proteins induced by the action of protease-activated receptor-1 agonists.

CONCLUSIONS

These findings establish the potential for neutrophil-derived PR3 to play a role in reestablishing vascular integrity after leukocyte transmigration and in protecting endothelial cells from protease-activated receptor-1-induced permeability changes that occur during thrombotic and inflammatory events.

Neutrophil serine proteases fine-tune the inflammatory response

Neutrophil serine proteases are granule-associated enzymes known mainly for their function in the intracellular killing of pathogens. Their extracellular release upon neutrophil activation is traditionally regarded as the primary reason for tissue damage at the sites of inflammation. However, studies over the past several years indicate that neutrophil serine proteases may also be key regulators of the inflammatory response. Neutrophil serine proteases specifically process and release chemokines, cytokines, and growth factors, thus modulating their biological activity. In addition, neutrophil serine proteases activate and shed specific cell surface receptors, which can ultimately prolong or terminate cytokine-induced responses. Moreover, it has been proposed that these proteases can impact cell viability through their caspase-like activity and initiate the adaptive immune response by directly activating lymphocytes. In summary, these studies point to neutrophil serine proteases as versatile mediators that fine-tune the local immune response and identify them as potential targets for therapeutic interventions.

Neutrophil serine proteases: specific regulators of inflammation

Neutrophils are essential for host defence against invading pathogens. They engulf and degrade microorganisms using an array of weapons that include reactive oxygen species, antimicrobial peptides, and proteases such as cathepsin G, neutrophil elastase and proteinase 3. As discussed in this Review, the generation of mice deficient in these proteases has established a role for these enzymes as intracellular microbicidal agents. However, I focus mainly on emerging data indicating that, after release, these proteases also contribute to the extracellular killing of microorganisms, and regulate non-infectious inflammatory processes by activating specific receptors and modulating the levels of cytokines.

Impaired immunity and enhanced resistance to endotoxin in the absence of neutrophil elastase and cathepsin G

While the critical role of reactive oxygen intermediates (ROI) in the microbicidal activity of polymorphonuclear granulocytes is well established, the function of the nonoxidative effector mechanisms in vivo remains unclear. Here we show that mice deficient in the neutrophil granule serine proteases elastase and/or cathepsin G are susceptible to fungal infections, despite normal neutrophil development and recruitment. The protease deficiencies but not the absence of ROI leads to enhanced resistance to the lethal effects of endotoxin LPS, although normal levels of TNFalpha are produced. The data demonstrate a critical role of the nonoxidative effector mechanisms of neutrophils in host immunity and immunopathology and identify elastase and cathepsin G as effectors in the endotoxic shock cascade downstream of TNFalpha.

Synthetic peptides derived from the sequence of human C-reactive protein inhibit the enzymatic activities of human leukocyte elastase and human leukocyte cathepsin G

Peptides derived from the primary sequence of the acute phase reactant C-reactive protein (CRP) are shown to inhibit in vitro the enzymatic activities of human leukocyte elastase (hLE) and human leukocyte cathepsin G (hCG), which are associated with tissue damage occurring in the course of several chronic inflammatory conditions. CRP-derived peptides were synthesized based on their sequence similarity to domains within the natural inhibitors of hLE and hCG. The octapeptide Val89-Thr-Val-Ala-Pro-Val-His-Ile96 (CRP 89-96) is shown to inhibit hLE and hCG to a larger extent than peptides of similar chain lengths corresponding to the active sites of their natural inhibitors, alpha 1-protease inhibitor and alpha-antichymotrypsin, respectively. Several additional peptides containing this core sequence were synthesized and shown to be inhibitors, in contrast to peptides derived from other regions of CRP as well as the intact protein, which are totally inactive. The inhibitory capability of CRP-derived peptides, which may be generated in vivo by neutrophil-mediated proteolysis as part of a complex regulatory homeostatic mechanism, may now be used as a basis for the design of novel therapeutic substances. The present finding may shed some light on the enigmatic physiological functions of CRP.

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.

Peptide boronic acids. Versatile synthetic ligands for affinity chromatography of serine proteinases

Peptide boronic acids are potent transition-state analogue inhibitors of serine proteinases. We prepared the peptide boronic acids Ala-Ala-boroPhe (AAbF), targeted at chymotrypsin-like proteinases, and Ala-Ala-boroVal (AAbV), targeted at elastolytic enzymes. Analogues protected on the N-terminus with the carbonylbenzyloxy (Cbz) group were powerful inhibitors of human neutrophil elastase (HNE) and human cathepsin G (CatG), as well as the non-human counterparts, porcine pancreatic elastase (PPE) and bovine alpha-chymotrypsin (ChT) Removal of N-Cbz protecting groups and immobilization with Sepharose 6B provided affinity matrices. Columns consisting of the AAbF or AAbV affinity matrix separated a mixture of PPE and ChT. PPE was specifically retained by the AAbV column and ChT was specifically retained by the AAbF column. HNE and CatG were not separated using the AAbF matrix, but were separated with the AAbV matrix. To demonstrate the practical utility of these affinity ligands, HNE was isolated from crude human neutrophil extracts, resulting in an 18-fold purification in one chromatographic step, with a 41% recovery of elastolytic activity. Because peptide boronic acids can be synthesized having specificity for a wide range of target enzymes, this method is readily adaptable as a general procedure for isolation and purification of serine proteinases.

Efficacy of systemically administered acetylsalicylic acid plus scaling on periodontal health and elastase-alpha 1-proteinase inhibitor in gingival crevicular fluid

The purpose of this proof of principle trial was to assess whether conventional periodontal therapy and systemically administrated acetylsalicylic acid (ASA) are functionally synergistic when combined in the treatment of periodontitis. A total of 30 patients with untreated moderate to severe adult periodontitis were enrolled into the study and were given placebo q.i.d. between the baseline and 6-week examination, and acetylsalicylic acid (ASA) 500 mg q.i.d. between the 6-week and 12-week examinations. In addition, they received supra- and subgingival scaling in 1 quadrant after baseline examination and in 2 further randomly selected quadrants after the 6-week examination. The study design resulted in the following 4 therapies: (1) scaling plus ASA 500 mg q.i.d.; (2) scaling plus placebo q.i.d.; (3) ASA 500 mg q.i.d. alone; (4) placebo q.i.d. alone. Two-way analysis of variance showed functional synergism of ASA and scaling, resulting in a therapeutic efficacy approximately equivalent to the sum of each individual therapeutic efficacy (i.e., ASA alone and scaling alone) in reducing gingival inflammation and pocket probing depth over the 6-week observation period (interaction: p > 0.05). Only the effect of ASA was significant in reducing the concentration of elastase-alpha 1-proteinase inhibitor in gingival crevicular fluid (GCF E-alpha 1-PI) (p < 0.001), reduction in GCF E-alpha 1-PI concentrations by ASA may indicate a decreased risk in periodontal disease progression. The results suggest that the combination of therapies and their different mechanisms of action, i.e., reduction of bacterial plaque and inhibition of destructive components of the immune responses, may result in functionally synergistic therapeutic efficacies in patients with untreated adult periodontitis.

Studies on inhibition of neutrophil cathepsin G by alpha 1-antichymotrypsin

alpha 1-Antichymotrypsin, a member of the serpin family of serine proteinase inhibitors, has been reported to inhibit chymotrypsin by a modified version of the suicide substrate reaction mechanism operative for other serpins. To investigate if this mechanism is also applicable to the inhibition of cathepsin G by this serpin, the effect of temperature on the reaction between cathepsin G and alpha 1-antichymotrypsin has been examined by SDS-PAGE and stoichiometric titrations. At 0 degree C, a cathepsin G-alpha 1-antichymotrypsin complex of M(r) 89,250 is formed which, at 38 degrees C, was cleaved by free enzyme to give a stable complex of M(r) 80,250. The reaction stoichiometry at 0 degree C was 1.53, which decreased to 1.30 at 38 degrees C, consistent with an decrease in the substrate pathway. These data are compatible with the modified suicide substrate reaction scheme. The formation of three products (cleaved inhibitor and two forms of complex) from the reaction and the potential for differential product formation suggests that modulation of the suicide substrate mechanism may play a role in the regulation of inflammatory processes mediated by cathepsin G.

Neutrophil lysosomal nonoxidative microbicidal proteins in early-onset periodontitis

The purpose of this study was to evaluate whether the reduced microbicidal activity of polymorphonuclear leukocytes (neutrophils) in patients with early-onset periodontitis is associated with a deficiency of nonoxidative microbicidal proteins. Neutrophils from 10 patients with early-onset periodontitis and 8 healthy control subjects were assessed for elastase isozymes 1 through 4, cathepsin G isozymes 1 through 4 and defensins (HNP-1, HNP-2 and HNP-3) using cationic and acid urea polyacrylamide gel electrophoresis. The results showed that both the total content and the relative distribution of elastase and cathepsin G isozymes was normal in neutrophils of patients with early-onset periodontitis. However, the HNP-3 content was significantly reduced in neutrophils from patients with generalized early-onset periodontitis. These findings indicate that the impaired microbicidal activities of neutrophils in patients with early-onset periodontitis does not appear to be based on an elastase or cathepsin G abnormality in neutrophils. Due to the high variability of HNP-1 + 2 and HNP-3 in neutrophils of control subjects, the reduced HNP-3 content in neutrophils probably plays a minor role in the pathogenesis of generalized early-onset periodontitis.

Alpha-enolase: a novel cytosolic autoantigen in ANCA positive vasculitis

Anti-neutrophil cytoplasmic antibodies (ANCA) in sera from patients with clinically proven vasculitis have been described as reacting with proteins present in the granules of human neutrophils. We have studied sera from 59 ANCA positive patients to further characterize the antibody response. In addition to the antigens previously identified in the vasculitic syndromes (myeloperoxidase and serine proteinase 3) the majority of these sera contained antibodies that reacted with a cytosolic extract of neutrophils on Western blots. Nearly 40% of these sera had antibodies directed against a cytosolic protein(s) of molecular mass 48 kD. This protein was purified from neutrophil cytosol by ammonium sulphate fractionation, anion exchange and reverse phase chromatography. Amino acid sequence analysis of a proteolytic fragment of this protein identified it as alpha enolase. The anti-enolase antibodies only recognized the alpha isoform and were present in sera giving either a pANCA or cANCA staining pattern by indirect immunofluorescence. Antibodies to alpha enolase were also found in sera from patients with systemic lupus erythematosus, particularly those with renal disease. We conclude that the antibody response in ANCA positive vasculitis is not restricted to neutrophil granule proteins.

Experimental evaluation of a collagen-coated vicryl mesh as a dural substitute

Dural substitutes must provide immediate restitution of a membranous covering for the brain without inducing any adverse reaction in the host or provoking adhesions to underlying nervous tissues. Ideally, the material should disappear completely and be replaced by tissues similar to the dura mater. In this study, parietal dural defects were created in 12 beagle dogs and closed with a vicryl mesh prosthesis made watertight by a film of bovine collagen. Clinical and biological tolerances were satisfactory. There was one case of early local infection. Gross and microscopic examinations performed between 7 days and 9 months after implantation showed degradation of the prosthetic mesh and connective tissue growth into the implant mimicking dura mater as early as 15 days after implantation. There was no attendant inflammatory reaction or cortical adhesions or other adverse reactions. The authors conclude that collagen-embedded vicryl mesh provides satisfactory biological function and compatibility when used as a substitute for dura mater in the dog.

Rat granulosa cells produce a novel trypsin-like protease in response to gonadotropin treatment

Rat ovaries produce a novel ovarian trypsin-like protease that is regulated during follicular development. The protease extracted from the ovaries of immature gonadotropin-treated female rats was unstable to denaturation, but was recoverable after non-denaturing electrophoresis. The activity was inhibited by synthetic serine protease inhibitors but not by aprotinin or soybean trypsin inhibitor, thus distinguishing the enzyme from pancreatic trypsin. Treatment with pregnant mare's serum gonadotropin (PMSG) significantly increased the levels of enzyme in the ovarian granulosa cells (Control, 0.0027 units/10(6) cells; PMSG-treated, 0.0062 units/10(6) cells) which was also secreted by these cells. The novel enzyme described here may be important for matrix remodelling during follicular growth.