Publications

Nitroglycerin limits infarct size through S-nitrosation of Cyclophilin D: A novel mechanism for an old drug

August 27, 2018

Ioanna Andreadou

Aims
Nitroglycerin (NTG) given prior to an ischemic insult exerts cardioprotective effects. However, whether administration of an acute low dose of NTG in a clinically relevant manner following an ischemic episode limits infarct size, has not yet been explored.
Methods and Results
Adult mice were subjected to acute myocardial infarction in vivo and then treated with vehicle or low dose NTG prior to reperfusion. This treatment regimen minimized myocardial infarct size without affecting hemodynamic parameters, but the protective effect was absent in mice rendered tolerant to the drug. Mechanistically, NTG was shown to nitrosate and inhibit cyclophilin D (CypD), and NTG administration failed to limit infarct size in CypD knockout mice. Additional experiments revealed lack of the NTG protective effect following genetic (knockout mice) or pharmacological inhibition (L-NAME treatment) of the endothelial nitric oxide synthase (eNOS). The protective effect of NTG was attributed to preservation of the eNOS dimer. Moreover, NTG retained its cardioprotective effects in a model of endothelial dysfunction (ApoE knockout) by preserving CypD nitrosation. Human ischemic heart biopsies revealed reduced eNOS activity and exhibited reduced CypD nitrosation.
Conclusions
Low dose NTG given prior to reperfusion reduces myocardial infarct size by preserving eNOS function, and the subsequent eNOS-dependent S-nitrosation of cyclophilin D, inhibiting cardiomyocyte necrosis. This novel pharmacological action of NTG warrants confirmation in clinical studies, although our data in human biopsies provide promising preliminary results.

Cardioprotective reperfusion strategies differentially affect mitochondria:studies in an isolated rat heart model of donation after circulatory death (DCD)

July 18, 2018

Sarah L. Longnus

Donation after circulatory death (DCD) holds great promise for improving cardiac graft availability, however concerns persist regarding injury following warm ischemia, after donor circulatory arrest, and subsequent reperfusion. Application of pre-ischemic treatments is limited for ethical reasons, thus cardioprotective strategies applied at graft procurement (reperfusion) are of particular importance in optimizing graft quality. Given the key role of mitochondria in cardiac ischemia-reperfusion injury, we hypothesize that three reperfusion strategies: mild hypothermia, mechanical post-conditioning and hypoxia, when briefly applied at reperfusion onset, provoke mitochondrial changes that may underlie their cardioprotective effects. Using an isolated, working rat heart model of DCD, we demonstrate that all three strategies improve oxygen-consumption-cardiac-work coupling and increase tissue ATP content, in parallel with increased functional recovery. These reperfusion strategies, however, differentially affect mitochondria; mild hypothermia also increases phosphocreatine content, while mechanical post-conditioning stimulates mitochondrial complex I activity and reduces cytochrome c release (marker of mitochondrial damage), whereas hypoxia up-regulates the expression of Pgc-1α (regulator of mitochondrial biogenesis). Characterisation of the role of mitochondria in cardioprotective reperfusion strategies should aid in the identification of new, mitochochondrial-based therapeutic targets and the development of effective reperfusion strategies that could ultimately facilitate DCD heart transplantation.

Cardioprotection of ischaemic preconditioning is associated with inhibition of translocation of MLKL within the plasma membrane

June 19, 2018

Adriana Adameová

Necroptosis, a form of cell loss involving the RIP1‐RIP3‐MLKL axis, has been identified in cardiac pathologies while its inhibition is cardioprotective. We investigated whether the improvement of heart function because of ischaemic preconditioning is associated with mitigation of necroptotic signaling, and these effects were compared with a pharmacological antinecroptotic approach targeting RIP1. Langendorff‐perfused rat hearts were subjected to ischaemic preconditioning with or without a RIP1 inhibitor (Nec‐1s). Necroptotic signaling and the assessment of oxidative damage and a putative involvement of CaMKII in this process were analysed in whole tissue and subcellular fractions. Ischaemic preconditioning, Nec‐1s and their combination improved postischaemic heart function recovery and reduced infarct size to a similar degree what was in line with the prevention of MLKL oligomerization and translocation to the membrane. On the other hand, membrane peroxidation and apoptosis were unchanged by either approach. Ischaemic preconditioning failed to ameliorate ischaemia–reperfusion‐induced increase in RIP1 and RIP3 while pSer229‐RIP3 levels were reduced only by Nec‐1s. In spite of the additive phosphorylation of CaMKII and PLN because of ditherapy, the postischaemic contractile force and relaxation was comparably improved in all the intervention groups while antiarrhythmic effects were observed in the ischaemic preconditioning group only. Necroptosis inhibition seems to be involved in cardioprotection of ischaemic preconditioning and is comparable but not intensified by an anti‐RIP1 agent. Changes in oxidative stress nor CaMKII signaling are unlikely to explain the beneficial effects.

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