Purification and characterization of an elastase inhibitor derived from hyaline cartilage

Articular cartilage has the ability to retard the invasiveness of inflammatory cells such as leucocytes. This resistance is in part due to the avascular nature, organization, and composition of the extracellular matrix. Extractable components (anti-invasion factors, [AIF]) within the matrix have been shown to be responsible for protecting the tissue against proteases produced by invading leucocytes. In the present study, AIF is examined for leucocyte elastase inhibitory activity using both analytical and preparative electrophoretic and chromatographic techniques. A specific leucocyte elastase inhibitor was isolated and identified as a 15,000 dalton protein on SDS-PAGE. The inhibitor is distinct from aprotinin (Trasylol) in size, electrophoretic pattern, and comparative peptide maps. The inhibitor exhibited a highly cationic (pI greater than 9.5) as well as a strong hydrophobic character. These properties of primary structure were confirmed by amino acid composition and sequence of the amino-terminal residues. The amino-terminal sequence showed no homologies to other proteins or known protease inhibitors. This matrix-derived protease inhibitor may be an important mediator in the regulation of and protection against cartilage destruction.