NEW THERAPEUTIC STRATEGY TO CONTRAST INFLAMMATION AND LUNG REMODELLING PROCESSES IN A MURINE MODEL OF CHRONIC OBSTRUCTIVE PULMONARY DISEASE

Chronic obstructive pulmonary disease (COPD) is characterized by chronic and abnormal lung inflammation leading to progressive and irreversible airflow obstruction. According to the latest World Health Organization (WHO) estimates, 64 million people currently have moderate to severe COPD, and WHO predicts that COPD will become the third leading cause of death worldwide by 2030. Since COPD is a multifactorial disease, it is difficult to reproduce a valid animal model that is able to express all the phenotypical features clinically observed in patients. The main experimental protocols used so far require genetic approaches or the exposure of animals to noxious stimuli, such as tobacco smoke and irritant agents. In the literature to date no protocol has considered chronic treatment with multiple risk factors. The aim of this study was to develop a model of COPD, exposing animals to environmental conditions similar to those of patients with COPD in order to reproduce a chronic inflammatory state, emphysema and bronchial remodelling. The validation of this model was useful for therapy studies. Mice were exposed for 1, 3 or 6 weeks to the main COPD risk factors: cigarette smoke; lipopolysaccharide to mimic bacterial exacerbations of the disease and particulate matter (PM-10) from urban pollution. The first week of exposure is able to induce an increase in inflammatory cytokines, which progressively reduce in the following weeks. Real time PCR has shown, from the third week, an increase in gene expression of TGFbeta and αSMA (key factors in the remodelling pathway) and proteolytic enzymes, with a peak in the sixth week of exposure, confirmed by immunochemistry and Western blot. Histological analysis showed a progressive thickening of the bronchial wall, destruction of lung tissue, enlargement of air spaces (emphysema) and the formation of lymphoid follicles, in particular in the sixth week of combined treatment. Thus, the use of this new experimental protocol is able to trigger inflammatory processes which, in the later stages of exposure, induce destruction of the lung parenchyma and airway remodelling (bronchial wall thickening, goblet cell hyperplasia and B-cell follicles), which are irreversible after treatment cessation. This demonstrates that the pathogenesis observed in mice reflects the natural history of COPD. The therapeutic goal of COPD treatment, in addition to clinical improvement, is the modification of the natural history of the disease, reducing mortality. Nevertheless, all available therapies are essentially symptomatic and contribute to improving the quality of life, without counteracting the progressive decline of the lung function. In contrast to current GOLD guidelines, which provide the use of inhaled corticosteroids in advanced stages of COPD (when tissue remodelling has already been occurred), the aim of this study was to test the hypothesis that a combination of bronchodilators and anti-inflammatory treatment is able to influence the progression of COPD only in early stages of pathogenesis, when tissue damage is less relevant and bronchial structural changes are still reversible. Mice with COPD-like phenotype were treated with a combination of antinflammatory (fluticasone) and bronchodilators (salmeterol and tiotropium) drugs, at different times: - mice early treated (treatment started at the first week of exposure to risk factors, for 4 weeks); - mice late treated (treatment started at the sixth week of exposure to risk factors, for 4 weeks). Pharmacological treatment significantly decreases level of cytokines in a group early treated compared to untreated. No significant effects were observed in groups treated later, since levels of cytokines resulted similar between group untreated and those treated. Early therapy was able to attenuate the activation of remodelling processes (bronchial wall thickening, goblet cell hyperplasia, formation of B cell follicles). Moreover, therapy in the first stage of the disease was able to reduce the degree of lung tissue destruction (emphysema). No significant effects on bronchial remodelling were observed in groups treated later. These data confirmed that a bronchodilator and antinflammatory therapy began too late is not able to counteract tissue changes, despite effective action on gene and tissue expression of remodelling factors. Instead, an early pharmacological treatment reduced the peak of inflammation contributing to attenuate bronchial alterations that are still reversible. Thus, the addition of an anti-inflammatory drug to bronchodilator therapy in the early stages could be a useful new therapeutic strategy to reduce the extent of bronchial obstruction and to effectively counteract the progression of the disease.