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    • br Materials and methods br Results br Discussion Chronic in

    2021-06-19


    Materials and methods
    Results
    Discussion Chronic inflammation is central to COPD and plays a critical role in the disease pathogenesis and progression. Among the various inflammatory cells, neutrophils are the key players in COPD pathogenesis. Their numbers are raised in airspaces and lung secretions from patients with COPD, which further correlates with the decline in lung functions [50], [51]. These cells are a major source of ROS, proteases, cytokines, and their degranulation results in lung tissue damage [50]. Recent studies have shown that these cells are also involved in induction of steroid resistance in airway diseases [52], [53], [54], [55]. Plumb et al. reported that increased numbers of airway neutrophils with reduced expression of glucocorticoid receptors might contribute to glucocorticoid resistance in patients with COPD patients [53]. Additionally, it is reported that neutrophils’ extracellular enzymes like neutrophil elastase and MPO, contribute to the disease [56]. Apart from this, aberrant neutrophils functions like excessive protease, ROS production and an enhanced chemotactic mobility, have been reported in patients of COPD [56], [57], [58]. Thus targeting neutrophilic inflammation might help us in alleviating various COPD associated features. Interestingly, our data strongly suggest that PARP-1 inhibition significantly mitigate elastase induced neutrophilic inflammation. MPO, a microbicidal peroxidase, is abundantly expressed in azurophilic granules of neutrophils [59]. The enzyme catalyzes the formation of hypochlorous acid; thus, can induce oxidative stress at the site of inflammation [60]. Owing to neutrophilic inflammation, increased activity of the enzyme has been reported in lung tissues and sputum of patients with COPD, which correlates well with the disease progression [61], [62]. Our results confirm that the reduced number of neutrophils upon PARP inhibition was associated with suppressed MPO activity in lungs after elastase administration. Furthermore, we tested the effectiveness of dexamethasone (corticosteroid), in our model and data showed that drug reduced the number of neutrophils effectively at a very high dose (10 mg/kg b.wt). It is important to mention that dexamethasone mitigates OVA induced inflammation in our mouse model of acute IL-4, murine recombinant at a much lower dose i.e. 0.5 mg/kg b.wt. (data not shown). Overall, our findings underline the potential of PARP inhibiting drugs in suppression of airway inflammation in conditions where steroid does not work very well. Oxidative stress is long known for its crucial role in COPD pathogenesis. Persistent inflammatory conditions, neutrophils accumulation, cigarette smoke are the primary sources for ROS in lungs, which in turn cause redox imbalance and consequent damage to lipids, proteins, and nucleic acids [48]. MDA, a product of fatty acid peroxidation, is widely used as a marker of oxidative stress. Different studies have shown that MDA levels are increased in serum and sputum of patients with COPD, and correlate well with disease progression [63], [64]. Our observation that PARP-1 inhibition restores the levels of ROS and MDA in lungs towards normal corroborates earlier reported role of PARP inhibition in normalization of redox status potentially by curbing recruitment of inflammatory cells [30], [31], [65]. Along with the raised levels of oxidants, altered antioxidant potential has also been reported in patients with COPD [66], [67], [68]. Restoration of GSH level towards normal provides additional support on the ability of the drug in potentiating antioxidant systems in the tissue. Increased DNA damage due to enhanced oxidative stress has been reported in patients with COPD. Ceylan et al. and Maluf et al. reported that DNA damage is increased in the PBMCs from patients with COPD as compared to healthy individuals [69], [70]. Similar results were found in a study involving lung tissue samples from patient with COPD. It was reported that double strand DNA breaks were higher in alveolar type I, II cells, and endothelial cells in the COPD patients when compared to asymptomatic smokers and nonsmokers [24]. In consideration of increased DNA damage in COPD, the concomitant elevation in the activity of DNA repair enzyme, PARP-1, has also been reported. Hageman et al. reported the systemic activation of PARP-1 as the percentage of PAR positive lymphocyte was found to be significantly higher in the patients with COPD when compared to the healthy individuals [27]. Recently it has been reported that levels of the DNA damage, PARP-1 activity, and PARP-1 mRNA expression in PBMCs correlate well with progression as well as exacerbation of COPD [26]. Our data also strongly suggest that reduction in lung inflammation and oxidative stress in the tissue by olaparib was closely associated with the suppression of PARP activity.