Role of cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP) and p38 mitogen activated protein kinase (p38 MAPK) in preconditioning of the ischaemic myocardium

[摘要] ENGLISH ABSTRACT:Ischaemic preconditioning (PC) is the phenomenon whereby a short episode ofcoronary occlusion followed by reperfusion protects the myocardium against asubsequent period of prolonged (also called index or sustained) ischaemia. Eventhough the exact mechanism of PC remains to be established, it implies that the hearthas an endogenous protective mechanism against ischaemia which, if identified, mayhave important clinical implications. The importance of establishing the mechanism ofPC lies in the potential to convert this biological phenomenon into a therapeutic modalityto be used clinically. If mediated by certain components of a signal transductionpathway, such a goal will be achievable.Several triggers and signal transduction pathways have been implicated in the mechanismof protection induced by PC: for example, receptor-dependent endogenous triggers (suchas adenosine and opioids) and receptor-independent endogenous triggers (such as freeradicals and calcium). However, the involvement of both the ~-adrenergic signallingpathway as well as nitric oxide (NO) in PC has not been defined.It has been suggested that all triggers are linked to a common final pathway, forexample, activation of protein kinase C (PKC) and/or the mitogen-activated kinases(MAPKs), in particular p38 MAPK. However, the role of the latter is still controversial.The aim of this study was to:(A) characterize changes in the cyclic nucleotides, cAMP and cGMP, and p38 MAPKoccurring during the entire experimental procedure in an attempt to gain insights intothe possible mechanisms involved in ischaemie PC (Chapter 3);(8) establish the significance of the changes observed in cAMP and cGMP bypharmacological manipulation of their respective pathways (Chapters 4 and 5);(C) establish the role of p38 MAPK in ischaemie PC: trigger or mediator involvement(Chapter 6).Isolated perfused working rat hearts were preconditioned by 3 x 5 min global ischaemia,interspersed by 5 min reperfusion, followed by 25 min global ischaemia and 30 minreperfusion. Functional recovery during reperfusion was used as end-point. Heartswere freeze-clamped at different times during the PC protocol, sustained ischaemia, as well as during reperfusion. Tissue cyclic nucleotides (cAMP and cGMP), cyclicnucleotide phosphodiesterase (cAMP- and cGMP-PDE) activities, adenylyl cyclase andprotein kinase A activities and p-adrenergic receptor characteristics were determined.p38 MAPK activation was also assessed by Western blotting, using dual phospho-p38MAPK (Thr180ITyr182) antibody as well as activating transcription factor 2 (ATF2)activation. In addition, to evaluate the role of p38 MAPK in PC protection, the effect ofinhibition of p38 MAPK activation, by 8B203580, was determined in adult isolated ratcardiomyocytes as well as in isolated perfused rat hearts.Based on the results obtained, it is proposed that during a multi-cycle ischaemie PCprotocol triggers (presumably endogenous catecholamines and NO) are released whichinduce cyclic changes in cyclic nucleotides, cAMP and cGMP. Both these cyclicnucleotides transiently activate the downstream stress kinase, p38 MAPK, which maytrigger further downstream adaptive processes.Furthermore, the sustained ischaemic period of PC hearts was characterized byattenuated cAMP and elevated cGMP levels, as well as attenuated activation of p38MAPK, which was associated with cardioprotection. In addition, pharmacologicalattenuation of p38 MAPK activation during sustained ischaemia led to functional recovery.It is concluded that the cardioprotection of PC is due to attenuation of ischaemia-inducedp38 MAPK activation. Pharmacological manipulation of this kinase should be consideredas a therapeutic modality in the future.

[发布机构] Stellenbosch University