Impact of Diabetes and its pharmacological treatment on cardiovascular function: studies on ischaemia-reperfusion models
Year: 2011
Type: dissertation
Abstract: Cardiovascular diseases are the leading cause of death worldwide of which ischaemic heart disease plays a main role. A diminished supply of oxygen and nutrients is extremely detrimental for the cardiac tissue, which has a high energetic demand. Following ischaemia-reperfusion injury, cell death will occur to great extent. Dead tissue is replaced by scar tissue, resulting in an impairment of cardiac function and heart failure. Importantly, clinical studies have shown that diabetic patients are more prone to suffer from cardiovascular diseases and to have worse clinical outcomes after an ischaemia-reperfusion injury event. The need for pharmacological agents that target both cardiovascular diseases and diabetes is of extreme relevance. Recently, the UKPDS study suggested that diabetic patients treated with metformin would have better clinical outcomes after suffering a cardiovascular event. Metformin is the most prescribed anti-diabetic drug worldwide and is known to target the mitochondria and 5’AMP-activated kinase (AMPK). AMPK is a kinase that functions as the cellular energy sensor. It is activated upon events that reduce energy reserves, such as exercise and ischaemia and coordinates both metabolism and intracellular signalling events towards an effective use of ATP during energy depletion. Activation of AMPK is beneficial if it occurs during myocardial ischaemia, but is role during reperfusion is still controversial. We hypothesised that metformin could be cardioprotective against myocardial infarction when administered at reperfusion via AMPK activation with concomitant improvement of cardiac metabolism and signalling that would prevent the occurrence of mitochondrial permeability transition (MPT) and cell death. To verify this hypothesis, a Langendorff perfused rat heart model of regional ischaemia with myocardial infarction assessed as our primary endpoint. In addition, adult rat ventricular myocytes were exposed to laser induced oxidative stress and imaged using confocal microscopy to follow mitochondrial depolarization and occurence of MPT and Western blotting performed to verify the activation of protective kinases. To study the influence of diabetes upon ischaemia-reperfusion injury, a colony of Goto-Kakizaki (GK) rat was established and characterized as an animal model of type 2 diabetes. Metformin, when administered at the onset of reperfusion was cardioprotective due to a transient activation AMPK and associated enhanced nitric oxide production, stimulation of adenosine receptors and delayed opening of the MPT pore (MPTP), which prevented cell death. In addition, protection of the diabetic heart was obtained by administration of metformin 24 hours prior to the ischaemic insult, concomitant with AMPK activation prior to the ischaemic insult and with nitric oxide production at reperfusion, an effect similar the protection observed in delayed ischaemic preconditioning. Interestingly, the use of an AMPK inhibitor, compound C, either prior to or during ischaemia abolished the reduction of myocardial infarction in the diabetic heart afforded by ischaemic pre- and postconditioning, suggesting a pivotal role for AMPK for the susceptibility of the myocardium to be protected. These results represented a strong background for the second hypothesis investigated that endogenous AMPK activation during myocardial ischaemia above physiological levels would protect against ischaemia-reperfusion injury. The administration during ischaemia of a newly discovered AMPK activator, A-769662, to diabetic and non-diabetic rat hearts, significantly reduced myocardial infarct size in a concentration-dependent manner. The activation of AMPK associated with ischaemia, was significantly increased in the presence of A-769662 and associated with a reduction of infarction after 120 min of reperfusion. Interestingly, there were no changes in the activation of the Reperfusion Injury Salvage Kinase (RISK) pathway, in the Langendorff rat perfused heart model. Our data suggests that enhancing activation of AMPK during ischaemia may be a novel cardioprotective strategy for the ischaemic-reperfused heart. Moreover, A-769662 significantly delayed MPTP opening in adult ventricular myocytes from non-diabetic and diabetic hearts, when administered prior and during the laser-induced oxidative stress, in the same concentrations shown to reduce myocardial infarction. In summary, we have thus demonstrated that metformin can protect the diabetic heart when given prior or after ischaemia, by the activation of the AMPK-eNOS-NO axis that results in a significant delay of MPTP occurrence and cell death. Hence, more details about metformin’s cardioprotective mechanisms have been revealed as this drug seems to be a valuable cardioprotective agent for the diabetic heart. Furthermore, pharmacological activation of AMPK alone in the diabetic heart could constitute a novel cardioprotective strategy that should be further explored and eventually translated from bench side to the clinical setting.
Author: Marta Sofia Abreu Paiva
Language: English
Subfield: Cardiology and Cardiovascular Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2911637911