AbstractThe treatment of asthma still relies on primary therapy with bronchodilators; in particular b adrenergic receptor (bAR) agonists with a diverse range of short acting and long acting bARs available. An increase in the number of cardiovascular events with the use of bronchodilators have recently been reported including hypertrophy, heart failure, myocardial ischaemia and infarction. Several subtypes of bAR receptors exist including the b1 Adrenergic Receptor (b1AR) and b2 Adrenergic Receptor (b2AR), both located in the heart. The effects of selective b2AR agonists were investigated in the Langendorff model of myocardial ischaemia reperfusion injury, isolated perfused rat hearts underwent 35 minutes of ischaemia and 120 minutes of reperfusion.
The selective b2AR long acting b agonists Formoterol and Salmeterol had no significant effect on infarct to risk ratio or time taken to depolarisation and hypercontracture in isolated cardiomyocytes. The non-selective b1AR agonist Isoproterenol has been show to induce myocardial ischaemia and infarction in rat hearts previously, here we demonstrated Isoproterenol (0.5μM) significantly decreased time taken to depolarisation and hypercontracture in isolated cardiomyocytes. The short acting b2AR agonist Salbutamol (0.01μ-1μM) significantly increased infarct to risk ratio in the Langendorff in addition to significantly decreasing time to hypercontracture in cardiomyocytes in the oxidative stress model highlighting a potential role of the mitochondrial permeability transition pore (mPTP). Activation of phosphorylated Akt and phosphorylated Erk1/2 via the PI3K/Akt signalling pathway and p44/p42 MAPK pathway were investigated by western blot analysis. Salbutamol significantly elevated expression of p-Akt in rat hearts exposed to reperfusion for 20 and 120 minutes whilst reducing expression of p-Erk. Recorded elevated cleaved caspase 3 expression in Salbutamol treated hearts can be associated as a marker of increased in cardiomyocyte cell death.
The b1AR antagonist CGP 20712 was administered in the presence of Salbutamol with minimal reduction in infarct size in rat hearts recorded and no significant change in time taken to hypercontracture in isolated cardiomyocytes suggesting that Salbutamol mediated toxicity is via b2AR activation. Confirmation of this was verified with the b2AR antagonist ICI 118, 551. Significant decrease in infarct size was recorded in addition to a significant increase in time to hypercontracture in the oxidative stress model. Further to this, caspase 3 expression was significantly reduced in addition with p-Akt expression.
With a potential role of the mitochondria and the mPTP contributing to Salbutamol induced myocardial injury, the Cyclophilin D inhibitor Cyclosporin A was administered in hearts and cardiomyocytes in the presence of Salbutamol. Infarct size was significantly reduced whilst time taken to hypercontracture significantly increased, suggesting that CsA treatment inhibits Salbutamol mediated injury via Cyclophilin D inhibition of the mPTP.
To conclude, our results demonstrated that Salbutamol caused cardiotoxicity at tissue, cellular and protein level in conditions of ischaemia reperfusion injury. Further to this, inhibition of Cyclophilin D by CsA, or the use of the b2AR antagonist ICI 118, 551 inhibits Salbutamol induced toxicity.
|Date of Award||2016|
|Supervisor||Afthab Hussain (Supervisor), Helen Maddock (Supervisor) & Christopher Mee (Supervisor)|
- Reperfusion injury