Targeting oxidant-dependent pathways to treat cardiovascular comorbidities in chronic obstructive pulmonary disease (COPD)
Creators: name: BRASSINGTON, Kurt
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 320103
subject: Respiratory diseases

description: Chronic obstructive pulmonary disease (COPD) is defined as a persistent airflow limitation and lung inflammation which causes a progressive decline in lung function. COPD is the 4th leading cause of death globally with ~50% of these patients dying from a cardiovascular event (1, 2) . The respiratory symptoms associated with this disease are caused by abnormalities to both the airway and the alveoli, due to exposure to noxious gases and particles such as cigarette smoke (CS). The reduced lung function seen in COPD is caused by structural damage to the lung parenchyma (emphysema) and the small airways, promoting hypoxia (3). Increased oxidative stress has been shown to cause both acute and chronic pulmonary inflammation. The spill over of pro-inflammatory mediators from the lungs into the systemic circulation, causes a persistent systemic inflammatory response that drives vascular dysfunction and contributes to cardiovascular disease onset and progression.<br><br>
The increased oxidative burden and associated inflammation in COPD, has been shown to alter blood vessel structure, through driving vascular remodelling, arterial stiffness and promoting atherosclerosis (4). Circulating oxygen levels play a pivotal role in maintaining the secretion of endothelial derived vasoactive substances, such as Nitric oxide and various prostaglandins, all of which control vascular tone. Under hypoxic conditions, like those seen in patients with COPD, the regulation of these vasoactive substances may be altered due to oxidative damage to the vascular endothelial cells, thus promoting vascular dysfunction in these patients. The research project at hand will observe the effects of antioxidant treatments and their ability to reduce the effects of oxidative stress induced systemic inflammation, through regulating the key oxidative-stress related enzyme (GPX). By limiting ROS production, reductions should be seen in both systemic and pulmonary inflammatory responses as well as endothelial oxidative damage, causing subsequent reductions in the instance or severity of cardiovascular outcomes in patients with COPD.<br><br>
In this thesis, a pre-established preclinical smoke exposure model of COPD was used to investigate the effects of cigarette smoking on comorbid CVD and to assess the effectiveness of a novel antioxidant therapy using ebselen. Through the use of ebselen, we aimed to determine if targeting the oxidant-dependent mechanisms which drive COPD and its various comorbidities would provide some beneficial results on both the pulmonary and extra-pulmonary manifestations associated with this disease, particularly cardiovascular disease. Through using this model of COPD, we were able to induce the hallmark features of COPD in mice, including both pulmonary and systemic inflammation, vascular dysfunction as well as defining the underlying mechanism driving CVD onset and progression in both stable and viral exacerbated COPD.<br><br>

Initially, we set out to observe if there were in fact any alterations to vascular function in response to cigarette smoke. In Chapter 3, we investigated the effects of acute CS exposure on vascular function, which showed that, as little as 4-days of CS exposure was enough to induce vascular dysfunction in vivo. We then sought to investigate if this was worsened in our established model of COPD, with 2-months CS exposure inducing significant immune cell recruitment, enhanced pulmonary inflammation and oxidative stress, systemic inflammation and a clear CVD phenotype. Immunohistochemistry and immunofluorescent staining was then completed on aortic sections which provided valuable insight into the oxidative mechanism driving CVD in COPD.<br><br>

In chapter 4, ebselen was used to mimic the activity of GPX, as well as prevent P47phox subunit binding to the NADPH oxidase 2 (NOX-2) enzyme. Based on the data obtained in Chapter 3, it was clear that the vascular dysfunction observed was the result of enhanced oxidative stress. Administration of ebselen proved to be effective in the treatment of both the pulmonary and extra-pulmonary manifestations in this model. Ebselen successfully reduced pulmonary inflammation (neutrophilic) and completely preserved vascular function in vivo. Upon histological staining, it was discovered that ebselen ablated vascular oxidative stress and thus led to the preservation of endothelial nitric oxide synthase (eNOS) expression, which is responsible for nitric oxide dependent vasodilation. Through targeting oxidant dependent mechanisms, we were able to effectively preserve vascular function, highlighting the importance of novel therapeutic development.<br><br>

In Chapter 5, we investigated the effect of viral exacerbations in COPD in regard to cardiovascular disease, as patients whom experience AECOPD are at a heightened risk of CVD-associated mortality. Upon inoculation with the influenza A virus, there was a significant increase in immune cell recruitment into the BALF and worsened pulmonary inflammation observed. We also demonstrated that during a viral exacerbation at d3 there is a significant worsening of vascular endothelial dysfunction, however at d10 (resolution phase) this is not evident. It was later shown that this worsened vascular dysfunction was the result of enhanced oxidative stress, reduced eNOS expression and a localised inflammatory effect induced by CD3+ T-cell recruitment into the aortic wall in response to viral infection.<br><br>

In Chapter 6, we used our validated model of AECOPD to investigate the effectiveness of antioxidant treatment with ebselen following viral infection. We demonstrated that prophylactic administration of ebselen was sufficient in modulating pulmonary neutrophilic recruitment whilst completely preventing the worsened vascular endothelial dysfunction observed in our AECOPD model. Ebselen was able to completely preserve vascular endothelial dysfunction in both stable and viral exacerbated COPD, through the modulation of vascular oxidative stress, eNOS preservation and preventing CD3+ T-cell recruitment into the aortic wall in response to viral infection. This thesis highlights that ebselen may be a novel, lifesaving therapeutic for the treatment of both the pulmonary and cardiovascular manifestations associated with both COPD and AECOPD. Additionally, this study also validated methods that can be used for the investigating the mechanisms driving the onset and progression of comorbid CVD, providing a valuable outline that may be used in future studies.