A comparative study of the low-molecular mass serine proteinase inhibitors of human connective tissues

A Retrospective Analysis of the Cartilage Kunitz Protease Inhibitory Proteins Identifies These as Members of the Inter-α-Trypsin Inhibitor Superfamily with Potential Roles in the Protection of the Articulatory Surface

Aim: The aim of this study was to assess if the ovine articular cartilage serine proteinase inhibitors (SPIs) were related to the Kunitz inter-α-trypsin inhibitor (ITI) family. Methods: Ovine articular cartilage was finely diced and extracted in 6 M urea and SPIs isolated by sequential anion exchange, HA affinity and Sephadex G100 gel permeation chromatography. Selected samples were also subjected to chymotrypsin and concanavalin-A affinity chromatography. Eluant fractions from these isolation steps were monitored for protein and trypsin inhibitory activity. Inhibitory fractions were assessed by affinity blotting using biotinylated trypsin to detect SPIs and by Western blotting using antibodies to α1-microglobulin, bikunin, TSG-6 and 2-B-6 (+) CS epitope generated by chondroitinase-ABC digestion. Results: 2-B-6 (+) positive 250, 220,120, 58 and 36 kDa SPIs were detected. The 58 kDa SPI contained α1-microglobulin, bikunin and chondroitin-4-sulfate stub epitope consistent with an identity of α1-microglobulin-bikunin (AMBP) precursor and was also isolated by concanavalin-A lectin affinity chromatography indicating it had N-glycosylation. Kunitz protease inhibitor (KPI) species of 36, 26, 12 and 6 kDa were autolytically generated by prolonged storage of the 120 and 58 kDa SPIs; chymotrypsin affinity chromatography generated the 6 kDa SPI. KPI domain 1 and 2 SPIs were separated by concanavalin lectin affinity chromatography, domain 1 displayed affinity for this lectin indicating it had N-glycosylation. KPI 1 and 2 displayed potent inhibitory activity against trypsin, chymotrypsin, kallikrein, leucocyte elastase and cathepsin G. Localisation of versican, lubricin and hyaluronan (HA) in the surface regions of articular cartilage represented probable binding sites for the ITI serine proteinase inhibitors (SPIs) which may preserve articulatory properties and joint function. Discussion/Conclusions: The Kunitz SPI proteins synthesised by articular chondrocytes are members of the ITI superfamily. By analogy with other tissues in which these proteins occur we deduce that the cartilage Kunitz SPIs may be multifunctional proteins. Binding of the cartilage Kunitz SPIs to HA may protect this polymer from depolymerisation by free radical damage and may also protect other components in the cartilage surface from proteolytic degradation preserving joint function.

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.

The proteinase-antiproteinase theory of emphysema: a speculative analysis of recent advances into the pathogenesis of emphysema

This review concerns the reasons why only an estimated 10-15% of patients with alpha-1-antitrypsin (A1AT) deficiency develop the destructive lung disease known as emphysema. The arguments presented revolve around the proteinase-antiproteinase balance in the 'microenvironment' of the epithelial space of the lung. Attention is focused on the balance between destructive enzymes such as neutrophil elastase and protective proteins such as A1AT, secretory leucocyte proteinase inhibitor (SLPI), human elastase inhibitor (HEI) and elafin. When neutrophil elastase is already attached to the elastin fibres the smaller molecules SLPI and elafin appear to be better inhibitors of this enzyme than larger inhibitors such as A1AT and HEI. Furthermore, SLPI and elafin may provide the first line of defence against proteinase attack from neutrophil elastase. In trying to explain the variability in the clinical expression of A1AT-deficiency and the development of emphysema, the importance of changes to A1AT, SLPI and elafin molecules induced by smoking and/or oxygen free radicals has been considered. It is possible that emphysema only develops in patients who have SLPI/elafin deficiency as well as A1AT deficiency.

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.

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.

Regulation of proteolytic activity in tissues

Degradation of tissue proteins is controlled by multiple means. These include regulation of the synthesis of proteinases, activation of the zymogen forms, the activity of the mature proteinase, and the degradation of these enzymes and the substrates. Mature proteinases can be controlled by pH, calcium ions, ATP, lipids and the formation of complexes with other proteinases, proteoglycans, and inhibitors.

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.

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.