Chronic obstructive pulmonary disease (COPD) is the collective term describing two separate chronic lung disease diseases: emphysema and chronic bronchitis (1). Initial clinical symptoms are shortness of breath and occasional cough. As the disease progresses difficulties in breathing becomes more pronounced, the cough more persistent and becomes associated with production of a clear sputum. In severe cases there are additional heart complications. The major risk factor for COPD is cigarette smoking. Between 1980 and 1990 there was a 22% increase in the occurrence of the disease with attributed 84,000 deaths in 1990 in the USA (www.nhlbi.nih.gov/health). Current therapies address the symptoms and range from bronchodilators, corticosteroids to oxygen. While there are no effective cures, although the disease can be prevented and progress slowed in many cases by removing the principal risk factor: cigarette smoking. Progression of the disease is associated with degradation of elastin in the walls of the alveoli, resulting in the functional destruction of the these organs. The net increase in proteolytic activity leading to this loss of alveoli function is a growing focus of pharmaceutical efforts for identification of a therapy for the amelioration of this disease. Of specific interest for this review has been the potential roles of members of the MMP family in both the destruction of elastin and the aberrant remodeling of damaged alveoli. An example of such a MMP is Metalloelastase. Metalloelastase (MMP-12) is (as the name suggests) capable of degrading elastin, as well as other extra-cellular matrix components. It is produced predominantly by infiltrating macrophages and appears essential for macrophage migration through extra-cellular matrix (2). Mouse metalloelastase knock-out studies implicate this enzyme as a key mediator in the pathology associated with cigarette smoke induced emhysema (3). There is also associative evidence from human genetic and animal studies suggesting a pathological link with other MMPs, such as MMPs 1,2,3,8& 9. The evidence for the role of these MMPs in the pathological processes associated with COPD and prospects for MMP inhibitors as the basis for future therapies will be addressed in this review.

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Two low-molecular-mass inhibitors of matrix metalloproteinases (MMPs), CT1166, a concentration-dependent selective inhibitor of gelatinases A and B, and Ro 31-7467, a concentration-dependent selective inhibitor of collagenase, were examined for their effects on bone resorption and type-I collagenolysis. The test systems consisted of measuring (1) the release of [3H]proline from prelabelled mouse calvarial explants; (2) the release of 14C from prelabelled type-I collagen films by mouse calvarial osteoblasts; and (3) lacunar resorption by isolated rat osteoclasts cultured on ivory slices. In 24 h cultures, CT1166 and Ro 31-7467 inhibited both interleukin-1 alpha- (IL-1 alpha; 10(-10) M) and 1,25-dihydroxyvitamin D3 (10(-8) M)-stimulated bone resorption in cultured neonatal mouse calvariae at concentration selective for the inhibition of gelatinase (10(-9) M for CT1166) and collagenase (10(-8) M for Ro 31-7467) respectively. For each compound the inhibition was dose-dependent, reversible, and complete at a 10(-7) M concentration. However, CT1166 (10(-9) M) and Ro 31-7467 (10(-8) M) in combination were required to completely abolish IL-1 alpha-stimulated bone resorption in mouse calvariae throughout a 96 h culture period. Neither of the inhibitors affected protein synthesis, DNA synthesis nor the IL-1 alpha-stimulated secretion of the lysosomal enzyme, beta-glucuronidase. Both CT1166 and Ro 31-7467 partially inhibited IL-1 alpha-stimulated lacunar resorption by isolated osteoclasts, but were without effect on unstimulated lacunar resorption. Rodent osteoclasts produced collagenase and gelatinases-A and -B activity. In contrast the substrate used to assess osteoclast lacunar resorption contained no detectable collagenase or gelatinase activity. Both compounds dose-dependently inhibited 1,25-dihydroxyvitamin D3 (10(-8) M)-stimulated degradation of type-I collagen by mouse calvarial osteoblasts; however, complete inhibition of collagenolysis was only achieved at concentrations at which CT1166 and Ro 31-7467 act as general MMP inhibitors. This study demonstrates that collagenase and gelatinases A and/or B participate in bone resorption. While these MMPs may be primarily involved in osteoid removal, we conclude that they may also be released by osteoclasts, where they participate in bone collagen degradation within the resorption lacunae.

, p.o., inhibited degradation of articular cartilage in a rat monoarthritis model induced by an intra-articular injection of Propionibacterium acnes. 6 Ro 32-3555 is a potential therapy for the treatment of the chronic destruction of articulating cartilage in both rheumatoid and osteoarthritis.

Ro 32-3555, a collagenase selective inhibitor, inhibits both the cartilage and bone changes in this mouse model of OA, and thus shows great potential as a treatment of OA in humans.

N-terminal analysis of aggrecan fragments lost from bovine nasal cartilage cultured in the presence of recombinant human interleukin 1alpha revealed a predominant ARGSVIL sequence with an additional ADLEX sequence. Production of the ARGSVIL-containing fragments has been attributed to the action of a putative proteinase, aggrecanase. The minor sequence (ADLEX) corresponds to a new reported cleavage product; comparison of this sequence with the available partial sequence of bovine aggrecan indicates that this is the product of a cleavage occurring towards the C-terminus of the protein. Matrix metalloproteinase (MMP) inhibitors inhibited aggrecan loss from bovine nasal explants incubated in the presence of recombinant human interleukin 1alpha. A strong correlation between inhibition of aggrecan metabolism and inhibition of stromelysin 1 (MMP 3) (r=0.93) suggests a role for stromelysin or a stromelysin-like enzyme in cartilage aggrecan metabolism. However, the compounds were approx. 1/1000 as potent in inhibiting aggrecan loss from the cartilage explants as they were in inhibiting stromelysin. There was little or no correlation between inhibition of aggrecan metabolism and inhibition of gelatinase B (MMP 9) or inhibition of collagenase 1 (MMP 1). Studies with collagenase inhibitors with a range of potencies showed a correlation between inhibition of collagenase activity and inhibition of collagen degradation in the cartilage explant assay. This indicates that in interleukin 1alpha-driven bovine nasal cartilage destruction, stromelysin (or a closely related enzyme) is involved in aggrecan metabolism, whereas collagenase is principally responsible for collagen degradation.

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The clinical efficacy of anti-TNF-alpha therapies have highlighted the apparently central role that TNF-alpha plays in the pathology of rheumatoid arthritis, particularly the inflammatory component. Recent identification of a metalloproteinase from the metzincin superfamily responsible for the production of the soluble form of this cytokine, has generated a large amount of pharmaceutical interest and presents the prospect of a metalloproteinase inhibitor as an anti-inflammatory drug. However, the traditional focus of metzincin inhibitor research has been the identification of inhibitors of matrix metalloproteinases; enzymes associated with matrix destruction, a feature common to both rheumatoid arthritis and osteoarthritis. Inhibitors of this class of metalloproteinase are now in clinical evaluation in patients. This review summarises the current development status of metalloproteinase inhibitors in arthritic diseases and discusses some of the issues that have arisen during their progress to become clinical treatments for these diseases.