Joanne L. Wright

Animal models of chronic obstructive pulmonary disease

The mechanisms involved in the genesis of chronic obstructive pulmonary disease (COPD) are poorly defined. This area is complicated and difficult to model because COPD consists of four separate anatomic lesions (emphysema, small airway remodeling, pulmonary hypertension, and chronic bronchitis) and a functional lesion, acute exacerbation; moreover, the disease in humans develops over decades. This review discusses the various animal models that have been used to attempt to recreate human COPD and the advantages and disadvantages of each. None of the models reproduces the exact changes seen in humans, but cigarette smoke-induced disease appears to come the closest, and genetically modified animals also, in some instances, shed light on processes that appear to play a role.

Mechanisms of cigarette smoke-induced COPD: insights from animal models.

Cigarette smoke-induced animal models of chronic obstructive pulmonary disease support the protease-antiprotease hypothesis of emphysema, although which cells and proteases are the crucial actors remains controversial. Inhibition of either serine or metalloproteases produces significant protection against emphysema, but inhibition is invariably accompanied by decreases in the inflammatory response to cigarette smoke, suggesting that these inhibitors do more than just prevent matrix degradation. Direct anti-inflammatory interventions are also effective against the development of emphysema, as are antioxidant strategies; the latter again decrease smoke-induced inflammation. There is increasing evidence for autoimmunity, perhaps directed against matrix components, as a driving force in emphysema. There is intriguing but controversial animal model evidence that failure to repair/failure of lung maintenance also plays a role in the pathogenesis of emphysema. Cigarette smoke produces small airway remodeling in laboratory animals, possibly by direct induction of fibrogenic growth factors in the airway wall, and also produces pulmonary hypertension, at least in part through direct upregulation of vasoactive mediators in the intrapulmonary arteries. Smoke exposure causes goblet cell metaplasia and excess mucus production in the small airways and proximal trachea, but these changes are not good models of either chronic bronchitis or acute exacerbations. Emphysema, small airway remodeling, pulmonary hypertension, and mucus production appear to be at least partially independent processes that may require different therapeutic approaches.

Effect of an MMP-9/MMP-12 inhibitor on smoke-induced emphysema and airway remodelling in guinea pigs

Background: Matrix metalloproteases (MMPs) are believed to be important in the pathogenesis of cigarette smoke-induced emphysema, but this hypothesis has only been proved in the mouse and its applicability to other species, particularly humans, is uncertain. The role of MMPs in smoke-induced small airway remodelling is unknown. Methods: The effects of a dual MMP-9/MMP-12 inhibitor, AZ11557272, on the development of anatomical and functional changes of chronic obstructive pulmonary disease (COPD) in guinea pigs exposed daily to cigarette smoke for up to 6 months were examined. Results: At all times, smoke-induced increases in lavage inflammatory cells, lavage desmosine (a marker of elastin breakdown) and serum tumour necrosis factor α (TNFα) were completely abolished by AZ11557272. At 6 months there was an increase in lung volumes and airspace size. AZ11557272 returned the pressure- volume curve to control levels, decreased smoke-induced increases in total lung capacity, residual volume and vital capacity by about 70%, and also reversed smoke-induced airspace enlargement by about 70%. There was a very strong correlation between surface to volume ratio and both lavage desmosine and serum TNFα levels. AZ11557272 protected against smoke-mediated increases in small airway wall thickness but did not prevent smoke-induced increases in mean pulmonary artery pressure. Conclusions: An MMP-9/MMP-12 inhibitor can substantially ameliorate morphological emphysema, small airway remodelling and the functional consequences of these lesions in a non-murine species. These findings strengthen the idea that MMPs are important mediators of the anatomical changes behind COPD in humans, and suggest that MMP-9 and MMP-12 may be potential intervention targets.

Acute exacerbation (acute lung injury of unknown cause) in UIP and other forms of fibrotic interstitial pneumonias

Acute exacerbation of usual interstitial pneumonia (UIP) is a condition in which patients with UIP, and occasionally other forms of fibrotic interstitial lung disease, develop rapid respiratory failure, accompanied by extensive radiologic infiltrates. The pathologic features of this condition are ill-defined in the literature and the outcome is unclear. We report 12 such patients, 9 with underlying UIP, 2 with underlying fibrotic nonspecific interstitial pneumonia, and 1 with underlying chronic hypersensitivity pneumonitis, who underwent surgical lung biopsy for diagnosis. High-resolution computed tomography data were available in 11 cases and showed the presence of extensive bilateral ground-glass opacities, sometimes accompanied by focal consolidation, superimposed on underlying fibrosis. Three microscopic patterns of acute lung injury were seen: diffuse alveolar damage (DAD), organizing pneumonia (OP), and a pattern of numerous very large fibroblast foci superimposed on underlying fibrosis. After the biopsy, all patients were treated with steroids, in some instances accompanied by cyclophosphamide or azathioprine. Ten patients survived the acute episode and were discharged with survival times of 1 to 11 months; of these cases, 6 showed a pattern of OP or OP plus extensive fibroblast foci; 2 a pattern of extensive fibroblast foci only; and 2 a pattern of DAD. Both patients who died had histologic DAD. We conclude that acute exacerbation of UIP and other fibrotic lung diseases produces a variety of pathologic patterns on biopsy, and that patients with OP or extensive fibroblast foci as the acute pattern seem to do better than those with DAD. Our data also imply that survival (of the acute episode) may be better than the literature suggests.

Pulmonary hypertension in chronic obstructive pulmonary disease: current theories of pathogenesis and their implications for treatment

The development of pulmonary hypertension is a poor prognostic sign in patients with chronic obstructive pulmonary disease (COPD), affecting both mortality and quality of life. Although pulmonary hypertension in COPD is traditionally viewed as a result of emphysematous destruction of the vascular bed and/or hypoxia, recent studies indicate that neither of these factors correlates very well with pulmonary artery pressures. New human and animal experimental data are beginning to show that pulmonary hypertension in this setting is probably a result of the direct effect of tobacco smoke on the intrapulmonary vessels with abnormal production of mediators that control vasoconstriction, vasodilatation, and vascular cell proliferation, ultimately leading to aberrant vascular remodelling and aberrant vascular physiology. These changes are in many ways similar to those seen in other forms of pulmonary hypertension and suggest that the treatments used for primary pulmonary hypertension may be beneficial in patients with COPD.

The Role of Interleukin-1β in Murine Cigarette Smoke–Induced Emphysema and Small Airway Remodeling

Interleukin-1beta (IL-1beta), a proinflammatory cytokine, is elevated in cigarette smokers. To determine whether IL-1beta plays a role in the pathogenesis of cigarette smoke-induced emphysema and small airway remodeling, IL-1 receptor knockout (IL1RKO), TNF-alpha receptor knockout (TNFRKO), or C57Bl/6 (control) mice were exposed to cigarette smoke acutely or for up to 6 months. With a single acute exposure, smoke elevated IL-1beta in C57Bl/6 mice. IL1RKO mice were protected against acute smoke-mediated increases in lavage inflammatory cells and matrix breakdown. In C57Bl/6 mice, acute smoke-mediated increases in inflammatory cells, serum IL-1beta, and serum TNF-alpha were blocked by z-VAD-fmk, a pan-caspase inhibitor, or z-WEHD-fmk, a caspase-1 (IL-1-converting enzyme, [ICE]) inhibitor. With 6 months of exposure, IL-1beta was no longer increased, but IL-18 was elevated. After 6 months of exposure, IL1RKO mice were 65% protected against emphysema, whereas TNFRKO mice were 83% protected. Both strains were completely protected against small airway remodeling. Lavage desmosine, hydroxyproline, and hyaluronan, matrix breakdown markers, were elevated in C57 but not IL1RKO mice. We conclude that IL-1beta plays a significant role in induction of murine emphysema and small airway remodeling, and is comparable to TNF-alpha in its effects. The protective effects of caspase inhibitors appear to be related to inhibition of ICE and raise the question of whether models that ameliorate emphysema with caspase inhibitors are really blocking IL-1beta (and IL-18) activation rather than blocking apoptosis.

Chronic hypersensitivity pneumonitis.

Hypersensitivity pneumonitis (HP) is traditionally divided on clinical grounds into acute, subacute, and chronic stages. Most biopsy specimens come from patients in the subacute stage, in which there is a relatively mild, usually peribronchiolar, chronic interstitial inflammatory infiltrate, accompanied in most cases by poorly formed interstitial granulomas or isolated giant cells. However, the pathologic features in the chronic, ie, fibrotic stage, are poorly defined in the literature. These features are important to recognize because the chronic stage of HP is often associated with a poor prognosis. We reviewed 13 cases of chronic HP. Where information was available, exposures to the sensitizing agent had generally occurred over a long period of time. Three patterns of fibrosis were seen: 1) predominantly peripheral fibrosis in a patchy pattern with architectural distortion and fibroblast foci resembling, microscopically, usual interstitial pneumonia (UIP); 2) relatively homogeneous linear fibrosis resembling fibrotic nonspecific interstitial pneumonia (NSIP); and 3) irregular predominantly peribronchiolar fibrosis. In some instances, mixtures of the UIP-like and peribronchiolar patterns were found. In all cases, the presence of scattered poorly formed granulomas, or isolated interstitial giant cells, or sometimes only Schaumann bodies indicated the correct diagnosis. In 7 cases, areas of typical subacute HP were present as well. High-resolution CT scans showed variable patterns ranging from severe fibrosis, in some instances with an upper zone predominance, to predominantly ground glass opacities with peripheral reticulation. We conclude that, at the level of morphology, chronic HP may closely mimic UIP or fibrotic NSIP. If no areas of subacute HP are evident, the presence of isolated giant cells, poorly formed granulomas, or Schaumann bodies is crucial to arriving at the correct diagnosis, and the finding of peribronchiolar fibrosis may be helpful. Despite the presence of extensive fibrosis, some patients responded to removal from exposure and steroid therapy.

Alpha-1-Antitrypsin and a Broad Spectrum Metalloprotease Inhibitor, RS113456, Have Similar Acute Anti-Inflammatory Effects

There is increasing evidence that antiproteases are able to affect the inflammatory response. To further examine this question, we administered human α-1-antitrypsin (α1AT) or a synthetic metalloprotease inhibitor (RS113456) to C57 mice followed by a single intratracheal dose of quartz, a dust that evokes a marked, lasting, polymorphonuclear leukocyte (PMN) infiltrate. At 2 hours after dust administration, both antiproteases completely suppressed silica-induced PMN influx into the lung and macrophage inflammatory protein-2 (MIP-2)/monocyte chemotactic protein-1 (MCP-1) (neutrophil/macrophage chemoattractant) gene expression, partially suppressed nuclear transcription factor κB (NF-κB) translocation, and increased inhibitor of NF-κB (IκB) levels. By 24 hours, PMN influx and connective tissue breakdown measured as lavage desmosine or hydroxyproline were still at, or close to, control levels after antiprotease treatment, and increases in NF-κB translocation and MIP-2/MCP-1 gene expression were variably suppressed. At both time points, neither agent prevented silica-induced increases in amount of whole lung MIP-2 or MCP-1 protein, but both did prevent increases in whole lung intercellular adhesion molecule-1 (ICAM-1) at 24 hours. Inactivating the α1AT by oxidation to the point that it no longer possessed antiproteolytic properties did not affect its ability to suppress inflammation. Both antiproteases also prevented the silica-induced acute inflammatory response in mice with knocked out genes for macrophage metalloelastase (MME −/−), mice that develop inflammation, but not connective tissue breakdown, and the pattern of α1AT breakdown fragments was identical in control and MME −/− animals. These findings suggest that, in this model of acute PMN mediated inflammation, a serine protease inhibitor and a metalloprotease inhibitor have similar anti-inflammatory properties, that inflammation is not mediated by proteolysis with generation of chemotactic matrix fragments, and that classic antiproteolysis (complexing of protease to antiprotease) probably does not play a role in suppression of inflammation. The antiproteolytic effects of these agents do not seem to be mediated by protection of endogenous α1AT.

Proteases and emphysema

Purpose of review The protease-antiprotease theory of emphysema is widely accepted, but exactly which cells/proteases play a role continues to be a controversial subject. Recent findings Reports in humans show increased metalloproteinase activity in emphysema, but the exact role of metalloproteinases remains unclear. In laboratory animals, neutrophils turn out to be crucial, and neutrophil influx correlates well with measurements of matrix destruction. Neutrophil influx is linked to metalloproteinase activity, and in mice MMP12-induced release of tumor necrosis factor-α drives neutrophil infiltration. Serine elastase inhibitors, knockout of neutrophil elastase, and interference with tumor necrosis factor-α signaling all provide significant protection against smoke-induced emphysema, but metalloproteinase inhibitors may yield greater protection. In genetically modified mice, emphysema can be produced by overexpression of mediators such as tumor necrosis factor-α, interferon-γ, or interleukin-13, and these models show evidence of metalloproteinase, cysteine protease, and serine protease attack with complicated relationships among these mediators. Collagen breakdown also appears to be important in the genesis of emphysema. Pro-apoptotic agents produce emphysema as well, possibly via an elastolytic pathway. Summary The idea that a single protease or a single type of inflammatory cell is responsible for human emphysema is unlikely to be true; rather, there are complex interactions among proteases, and between proteases and other mediators. The problem at this time is attempting to sort out the numerous candidate effector agents and to determine which of the animal models are relevant to human disease, since there may be considerable discrepancies in the types of proteases and their roles between laboratory animals and humans. There is now good evidence from animal models that antiproteolytic therapy can be of benefit in ameliorating cigarette smoke-induced emphysema.

α1-Antitrypsin monotherapy induces immune tolerance during islet allograft transplantation in mice

Human pancreatic islet transplantation offers diabetic patients tight glucose control but has low graft survival rates. The immunosuppressive drugs that are administered to graft recipients lack the antiinflammatory benefits of corticosteroids because of their diabetogenic effects. The serum protease inhibitor α1-antitrypsin (AAT) possesses antiinflammatory properties and reduces cytokine-mediated islet damage. In the present study, diabetic mice were grafted with allogeneic islets and treated with AAT monotherapy (n = 24). After 14 days of treatment, mice remained normoglycemic and islet allografts were functional for up to 120 treatment-free days. After graft removal and retransplantation, mice accepted same-strain islets but rejected third-strain islets, thus confirming that specific immune tolerance had been induced. Explanted grafts exhibited a population of T regulatory cells in transplant sites. According to RT-PCR, grafts contained high levels of mRNA for foxp3, cytotoxic T lymphocyte antigen-4, TGF-β, IL-10, and IL-1 receptor antagonist; expression of proinflammatory mediators was low or absent. After implantation of skin allografts, AAT-treated mice had greater numbers of foxp3-positive cells in draining lymph nodes (DLNs) compared with control treatment mice. Moreover, dendritic cells in DLNs exhibited an immature phenotype with decreased CD86 activation marker. Although the number of CD3 transcripts decreased in the DLNs, AAT did not affect IL-2 activity in vitro. Thus, AAT monotherapy provides allografts with antiinflammatory conditions that favor development of antigen-specific T regulatory cells. Because AAT treatment in humans is safe, its use during human islet transplantation may be considered.