Author:

Abstract:

Chronic obstructive pulmonary disease (COPD) affects millions of people and is the third leading cause of mortality worldwide. COPD is an irreversible lung disease characterized by a progressive airflow limitation with persistent respiratory symptoms. Almost 50% of the cigarette smokers in industrialized countries will eventually develop COPD, making cigarette smoking the main risk factor for COPD. COPD is a heterogenous disease where causality is difficult to investigate in humans and in in vitro models. Therefore, in vivo models of cigarette smoke (CS) exposure are commonly used as approach to investigate human COPD features. However, a heterogenous diversity in CS-exposure mouse models exists, with the most used CS exposure delivery systems being the nose-only and whole-body systems. Although these systems represent an appropriate way in mimicking COPD features, a standardized protocol to allow comparison of these two systems was lacking. We suggested that sensitization to CS can happen through the skin or gastro-intestinal tract. Namely, whole-body CS-exposure resulted in a higher uptake of CS and an increased adaptive immune activation in lung and adjacent airway lymph nodes compared to the nose-only system. On the other hand, the nose-only CS exposure system allowed for a better controllability on the amount of CS inhaled and circumvents the influence of skin absorption. Therefore, most of the experiments in this dissertation were explored using an established nose-only CS exposure mouse model. Vitamin D deficiency (VDD) is highly prevalent among COPD patients and correlates with disease severity. Clinical studies reported VDD as a risk factor for frequent upper and lower respiratory tract infections, one of the key features in triggering an acute exacerbation in COPD. AECOPD is a temporally flare-up of the disease that worsens the overall prognosis of COPD patients with a severe loss of functional status, impaired quality of life, worsening of respiratory symptoms and even hospitalization with a high risk for mortality. Non-typeable Haemophilus influenzae (NTHi) is one of these pathogens, that is often isolated during acute exacerbations and was used as a trigger to mimic AECOPD in this dissertation. However, it is still unclear whether VDD would worsen a bacterial airway infection while reducing bacterial clearance and enhancing airway inflammation exaggerating thereby lung destruction. Surprisingly, VDD, irrespective of CS exposure eradicated NTHi faster from the lungs with a rapid resolution of inflammation. The upregulation of CRAMP might have contributed to eradication of the NTHi infection, but more importantly we found an imbalanced expression of MMP9/TIMP1 and MMP12/TIMP1 ratio, that is likely to promote ECM breakdown in the lungs during AECOPD. Frequent exacerbators (>2 exacerbations per year) also exist and can be found in all COPD severity classes in whom, according to observational studies, severe VDD can be highly prevalent. Frequent exacerbators have a steeper annual decline of FEV1 compared to infrequent exacerbators, but the impact of VDD on frequent exacerbations is unclear. We explored the role of VDD on repeated NTHi infections, mimicking frequent exacerbators (³ 2 exacerbations per year) during CS-exposure. We used a chronic CS exposure mouse model combined with three consecutive NTHi infections. We demonstrated that VDD, irrespective of CS exposure in mice, promoted NTHi-specific and auto-antibodies both pre- and post-NTHi-infections, expediting the NTHI clearance but also promoting lung destruction. Serum samples acquired from COPD patients before and 1 year after supplementation with vitamin D3, showed an increase in total IgG and anti-NTHi IgG in VDD and for the latter also in vitamin D insufficient patients, suggesting a protective role of vitamin D3 supplementation against exacerbations in this patient population, without affecting autoimmunity. The repercussions of exacerbations are severe in COPD as they threaten patient's health, lung function and quality of life. Currently, they are managed by inhaled bronchodilators, corticosteroids and antibiotics, however, some patients remain unresponsive to such treatment. There is, therefore, a need to find better treatments for AECOPD. An attractive approach would be local delivery of 1a,25(OH)2D directly to the lungs, knowing that both the bronchial epithelial layer and immune cells express vitamin D receptor (VDR) and the metabolic CYP enzymes (CYP27B1 and CYP24A1). In vitro, vitamin D can regulate oxidative stress, inflammation, T-cell development, antimicrobial peptide production and lung remodeling, which support the concept that 1a,25(OH)2D can suppress lung inflammation. We demonstrated that local administration of 1a,25(OH)2D into the lungs using a micro-spray reduced acute LPS-induced inflammation in vitamin D sufficient (VDS) mice while this strategy prevented epithelial barrier leakage and damage in lung of VDD mice. We found that 1a,25(OH)2D locally administered into the lungs could be an efficient strategy and alternative to current treatments to reduce infiltration of neutrophils but also to maintain the epithelial barrier integrity in severe VDD without inducing hypercalcemia. Taken together, our data demonstrate an important role for the vitamin D pathway in AECOPD and support the concept that local administration of 1a,25(OH)2D into the lungs represents an attractive strategy to minimize lung inflammation.