Ipratropium bromide is a short-acting, non-selective, muscarinic antagonist frequently prescribed for the treatment of Chronic Obstructive Pulmonary Disease (COPD) and as an emergency adjunct therapy for acute asthma. Within the past decade, there has been an accumulating wealth of clinical evidence which indicates that anti-muscarinic drugs, such as ipratropium, are responsible for an increased risk of stroke or, an adverse cardiovascular outcome (including increasing the risk and severity of myocardial infarction (MI)). MI remains the highest risk factor of death for COPD patients due to the systemic co-morbidities associated with COPD, which includes ischaemic heart disease (IHD). Despite the knowledge that approximately 22% of COPD patients also suffer from underlying IHD, the cardiovascular safety of muscarinic antagonists, such as ipratropium, has not been tested in a non-clinical setting of IHD or MI. In order to address this, the current project was designed to investigate, for the first time, the effects of ipratropium on the myocardium in a non-clinical setting. It was identified that under normoxic conditions, ipratropium did not have a significant effect on cardiac myocyte viability or infarction, from 3 month Sprague Dawley rats. In addition to this, following simulated ischaemia, ipratropium also did not appear to exacerbate myocardial injury. However, when ipratropium was administered in the context of simulated ischaemia followed by reperfusion, there was a significant exacerbation in myocardial injury which was characterised by increases in infarction, apoptosis, necrosis and a loss of resilience of oxidative stress. In order to characterise the mechanism by which ipratropium exerts the observed cardio-toxic effects, it was investigated whether acetylcholine (ACh) or cyclosporin A (CsA) were capable of attenuating the ipratropium induced cardiotoxicity. Both agents showed significant limitation of injury when co-administered with ipratropium indicating that ipratropium exerts its cardio-toxic effect through a mechanism which links muscarinic signalling to the mitochondrial permeability transition pore (mPTP). This supports previously published work where the protective signalling of ACh has been shown to promote the phosphorylation of pro-survival kinases, such as Akt and Erk1/2 and that this provides inhibition of the mPTP. Western blotting was employed to identify whether there was an involvement of the pro-survival kinases Akt and Erk1/2, as well as the stress induced kinase JNK. Ipratropium significantly increased levels of phospho-Akt and phospho-Erk1/2. However, JNK levels appeared to be insignificantly altered in comparison with the control groups. Both ACh and CsA were capable of limiting these increases. Further to this, an aged study was carried out, which showed that, within the aged myocardium, ipratropium is capable of eliciting further injury in comparison with the 3 month age groups. The effect of ipratropium on tolerance of oxidative stress was not significant, but, also, ACh and CsA were shown as unable to protect. Significant levels of JNK were also observed in the aged animals in comparison with the 3 month groups. In combination, the results presented here demonstrate, for the first time, that ipratropium is capable of exacerbating ischaemia/reperfusion injury in in vitro models of myocardial ischaemia/reperfusion. In addition, ACh and CsA are capable of limiting this injury, implying a role for pro-survival kinases and the mPTP in ipratropium induced myocardial injury. In the aged study, ipratropium still exacerbated injury, however, ACh and CsA appeared unable to protect, therefore promoting previous work that cellular signalling is altered in the senescent myocardium. In conclusion, further studies must be carried out in order to fully characterise the cardio-vascular safety profile of ipratropium.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:681424 |
| Date | January 2015 |
| Creators | Harvey, K. |
| Publisher | Coventry University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://curve.coventry.ac.uk/open/items/f03ffc6e-3554-4062-99c2-1c243feb582a/1 |
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