Efficacy of propofol-supplemented cardioplegia on biomarkers of organ injury in patients having cardiac surgery using cardiopulmonary bypass: A protocol for a randomised controlled study (ProMPT2).

INTRODUCTION: Cardiac surgery with cardiopulmonary bypass and cardioplegic arrest is known to be responsible for ischaemia and reperfusion organ injury. In a previous study, ProMPT, in patients undergoing coronary artery bypass or aortic valve surgery we demonstrated improved cardiac protection when supplementing the cardioplegia solution with propofol (6 mcg/ml). The aim of the ProMPT2 study is to determine whether higher levels of propofol added to the cardioplegia could result in increased cardiac protection. METHODS AND ANALYSIS: The ProMPT2 study is a multi-centre, parallel, three-group, randomised controlled trial in adults undergoing non-emergency isolated coronary artery bypass graft surgery with cardiopulmonary bypass. A total of 240 patients will be randomised in a 1:1:1 ratio to receive either cardioplegia supplementation with high dose of propofol (12 mcg/ml), low dose of propofol (6 mcg/ml) or placebo (saline). The primary outcome is myocardial injury, assessed by serial measurements of myocardial troponin T up to 48 hours after surgery. Secondary outcomes include biomarkers of renal function (creatinine) and metabolism (lactate). ETHICS AND DISSEMINATION: The trial received research ethics approval from South Central - Berkshire B Research Ethics Committee and Medicines and Healthcare products Regulatory Agency in September 2018. Any findings will be shared though peer-reviewed publications and presented at international and national meetings. Participants will be informed of results through patient organisations and newsletters. TRIAL REGISTRATION: ISRCTN15255199. Registered in March 2019.

Endothelial glycocalyx is damaged in diabetic cardiomyopathy: angiopoietin 1 restores glycocalyx and improves diastolic function in mice.

AIMS/HYPOTHESIS: Diabetic cardiomyopathy (DCM) is a serious and under-recognised complication of diabetes. The first sign is diastolic dysfunction, which progresses to heart failure. The pathophysiology of DCM is incompletely understood but microcirculatory changes are important. Endothelial glycocalyx (eGlx) plays multiple vital roles in the microcirculation, including in the regulation of vascular permeability, and is compromised in diabetes but has not previously been studied in the coronary microcirculation in diabetes. We hypothesised that eGlx damage in the coronary microcirculation contributes to increased microvascular permeability and hence to cardiac dysfunction. METHODS: We investigated eGlx damage and cardiomyopathy in mouse models of type 1 (streptozotocin-induced) and type 2 (db/db) diabetes. Cardiac dysfunction was determined by echocardiography. We obtained eGlx depth and coverage by transmission electron microscopy (TEM) on mouse hearts perfusion-fixed with glutaraldehyde and Alcian Blue. Perivascular oedema was assessed from TEM images by measuring the perivascular space area. Lectin-based fluorescence was developed to study eGlx in paraformaldehyde-fixed mouse and human tissues. The eGlx of human conditionally immortalised coronary microvascular endothelial cells (CMVECs) in culture was removed with eGlx-degrading enzymes before measurement of protein passage across the cell monolayer. The mechanism of eGlx damage in the diabetic heart was investigated by quantitative reverse transcription-PCR array and matrix metalloproteinase (MMP) activity assay. To directly demonstrate that eGlx damage disturbs cardiac function, isolated rat hearts were treated with enzymes in a Langendorff preparation. Angiopoietin 1 (Ang1) is known to restore eGlx and so was used to investigate whether eGlx restoration reverses diastolic dysfunction in mice with type 1 diabetes. RESULTS: In a mouse model of type 1 diabetes, diastolic dysfunction (confirmed by echocardiography) was associated with loss of eGlx from CMVECs and the development of perivascular oedema, suggesting increased microvascular permeability. We confirmed in vitro that eGlx removal increases CMVEC monolayer permeability. We identified increased MMP activity as a potential mechanism of eGlx damage and we observed loss of syndecan 4 consistent with MMP activity. In a mouse model of type 2 diabetes we found a similar loss of eGlx preceding the development of diastolic dysfunction. We used isolated rat hearts to demonstrate that eGlx damage (induced by enzymes) is sufficient to disturb cardiac function. Ang1 restored eGlx and this was associated with reduced perivascular oedema and amelioration of the diastolic dysfunction seen in mice with type 1 diabetes. CONCLUSIONS/INTERPRETATION: The association of CMVEC glycocalyx damage with diastolic dysfunction in two diabetes models suggests that it may play a pathophysiological role and the enzyme studies confirm that eGlx damage is sufficient to impair cardiac function. Ang1 rapidly restores the CMVEC glycocalyx and improves diastolic function. Our work identifies CMVEC glycocalyx damage as a potential contributor to the development of DCM and therefore as a therapeutic target.

Nrf2-Keap-1 imbalance under acute shear stress induces inflammatory response in venous endothelial cells.

Vascular endothelial cell stimulation is associated with the activation of different signalling pathways and transcription factors. Acute shear stress is known to induce different pro-inflammatory mediators such as IL-8. Nrf2 is activated by prolonged high shear stress promoting an antiinflammatory and athero-protective environment. However, little is known about the impact of acute shear stress on Nrf2 and Keap1 function and its role in IL-8 regulation. We aimed to examine Nrf2-Keap1 complex activation in-vitro and its role in regulating IL-8 transcripts under acute arterial shear stress (12 dyn/cm2) in venous endothelial cells (ECs). We note that acute high shear stress caused a significant upregulation of Nrf2 target genes, HO-1 and GCLM and an increased IL-8 upregulation at 90 and 120 minutes. Mechanistically, acute high shear did not affect Nrf2 nuclear translocation but resulted in reduced nuclear Keap1, suggesting that the reduction in nuclear Keap1 may result in increased free nuclear nrf2 to induce transcription. Consistently, the suppression of Keap1 using shRNA (shKeap1) resulted in significant upregulation of IL-8 transcripts in response to acute shear stress. Interestingly; the over expression of Nrf2 using Nrf2-Ad-WT or Sulforaphane was also associated with significant upregulation of IL-8 compared to controls. This study highlights the role of Keap1 in Nrf2 activation under shear stress and indicates that activation of Nrf2 may be deleterious in ECs in the context of acute haemodynamic injury.

Cardioprotection of Immature Heart by Simultaneous Activation of PKA and Epac: A Role for the Mitochondrial Permeability Transition Pore.

Metabolic and ionic changes during ischaemia predispose the heart to the damaging effects of reperfusion. Such changes and the resulting injury differ between immature and adult hearts. Therefore, cardioprotective strategies for adults must be tested in immature hearts. We have recently shown that the simultaneous activation of protein kinase A (PKA) and exchange protein activated by cAMP (Epac) confers marked cardioprotection in adult hearts. The aim of this study is to investigate the efficacy of this intervention in immature hearts and determine whether the mitochondrial permeability transition pore (MPTP) is involved. Isolated perfused Langendorff hearts from both adult and immature rats were exposed to global ischaemia and reperfusion injury (I/R) following control perfusion or perfusion after an equilibration period with activators of PKA and/or Epac. Functional outcome and reperfusion injury were measured and in parallel, mitochondria were isolated following 5 min of reperfusion to determine whether cardioprotective interventions involved changes in MPTP opening behaviour. Perfusion for 5 min preceding ischaemia of injury-matched adult and immature hearts with 5 µM 8-Br (8-Br-cAMP-AM), an activator of both PKA and Epac, led to significant reduction in post-reperfusion CK release and infarct size. Perfusion with this agent also led to a reduction in MPTP opening propensity in both adult and immature hearts. These data show that immature hearts are innately more resistant to I/R injury than adults, and that this is due to a reduced tendency of MPTP opening following reperfusion. Furthermore, simultaneous stimulation of PKA and Epac causes cardioprotection, which is additive to the innate resistance.

Inhibition of Cardiac RIP3 Mitigates Early Reperfusion Injury and Calcium-Induced Mitochondrial Swelling without Altering Necroptotic Signalling.

Receptor-interacting protein kinase 3 (RIP3) is a convergence point of multiple signalling pathways, including necroptosis, inflammation and oxidative stress; however, it is completely unknown whether it underlies acute myocardial ischemia/reperfusion (I/R) injury. Langendorff-perfused rat hearts subjected to 30 min ischemia followed by 10 min reperfusion exhibited compromised cardiac function which was not abrogated by pharmacological intervention of RIP3 inhibition. An immunoblotting analysis revealed that the detrimental effects of I/R were unlikely mediated by necroptotic cell death, since neither the canonical RIP3-MLKL pathway (mixed lineage kinase-like pseudokinase) nor the proposed non-canonical molecular axes involving CaMKIIδ-mPTP (calcium/calmodulin-dependent protein kinase IIδ-mitochondrial permeability transition pore), PGAM5-Drp1 (phosphoglycerate mutase 5-dynamin-related protein 1) and JNK-BNIP3 (c-Jun N-terminal kinase-BCL2-interacting protein 3) were activated. Similarly, we found no evidence of the involvement of NLRP3 inflammasome signalling (NOD-, LRR- and pyrin domain-containing protein 3) in such injury. RIP3 inhibition prevented the plasma membrane rupture and delayed mPTP opening which was associated with the modulation of xanthin oxidase (XO) and manganese superoxide dismutase (MnSOD). Taken together, this is the first study indicating that RIP3 regulates early reperfusion injury via oxidative stress- and mitochondrial activity-related effects, rather than cell loss due to necroptosis.

Consecutive Isoproterenol and Adenosine Treatment Confers Marked Protection against Reperfusion Injury in Adult but Not in Immature Heart: A Role for Glycogen.

Consecutive treatment of adult rat heart with isoproterenol and adenosine (Iso/Aden), known to consecutively activate PKA/PKC signaling, is cardioprotective against ischemia and reperfusion (I/R). Whether this is cardioprotective in an immature heart is unknown. Langendorff-perfused hearts from adult and immature (60 and 14 days old) male Wistar rats were exposed to 30 min ischemia and 120 min reperfusion, with or without prior perfusion with 5 nM Iso for 3 min followed by 30 µM Aden for 5 min. Changes in hemodynamics (developed pressure and coronary flow) and cardiac injury (Lactate Dehydrogenase (LDH) release and infarct size) were measured. Additional hearts were used to measure glycogen content. Iso induced a similar inotropic response in both age groups. Treatment with Iso/Aden resulted in a significant reduction in time to the onset of ischemic contracture in both age groups whilst time to peak contracture was significantly shorter only in immature hearts. Upon reperfusion, the intervention reduced cardiac injury and functional impairment in adults with no protection of immature heart. Immature hearts have significantly less glycogen content compared to adult. This work shows that Iso/Aden perfusion confers protection in an adult heart but not in an immature heart. It is likely that metabolic differences including glycogen content contribute to this difference.

From basic mechanisms to clinical applications in heart protection, new players in cardiovascular diseases and cardiac theranostics: meeting report from the third international symposium on "New frontiers in cardiovascular research".

In this meeting report, particularly addressing the topic of protection of the cardiovascular system from ischemia/reperfusion injury, highlights are presented that relate to conditioning strategies of the heart with respect to molecular mechanisms and outcome in patients' cohorts, the influence of co-morbidities and medications, as well as the contribution of innate immune reactions in cardioprotection. Moreover, developmental or systems biology approaches bear great potential in systematically uncovering unexpected components involved in ischemia-reperfusion injury or heart regeneration. Based on the characterization of particular platelet integrins, mitochondrial redox-linked proteins, or lipid-diol compounds in cardiovascular diseases, their targeting by newly developed theranostics and technologies opens new avenues for diagnosis and therapy of myocardial infarction to improve the patients' outcome.

Homocysteine Exposure Impairs Myocardial Resistance to Ischaemia Reperfusion and Oxidative Stress.

BACKGROUND/AIMS: Hyperhomocysteinaemia is recognised as a strong independent risk factor for developing cardiovascular disease. This study investigated how an acute homocysteine dose affected cardiac performance during ischaemia reperfusion and cardiomyocyte contractility and morphology under normal conditions and during oxidative stress. METHODS: Cardiac function was measured in isolated and perfused rat hearts before and after 40 minutes' global normothermic ischaemia. Where used, 0.1 mM L-homocysteine was present prior to, and throughout ischaemia, before wash out after 10 minutes' reperfusion. Calcium transients under normal conditions and changes in contractile synchronicity during oxidative stress (exposure to 0.2 mM H2O2) were measured in freshly isolated rat cardiomyocytes incubated for 60 minutes ± 0.1 mM L-homocysteine. RESULTS: During ischaemia reperfusion 0.1 mM L-homocysteine significantly reduced the rate pressure product during reperfusion (10,038 ± 749 vs. 5955 ± 567 mmHg bpm, p < 0.001), but did not affect time to ischaemic contracture. Incubation of freshly isolated cardiomyocytes with 0.1 mM L-homocysteine significantly decreased the amplitude of the calcium transient and slowed the time to half relaxation. CONCLUSIONS: These findings suggest that homocysteine exposure affected myocardial recovery from ischaemia and contractile homeostasis although the exact mechanisms for these changes remain to be determined.

Remote ischemic conditioning: from experimental observation to clinical application: report from the 8th Biennial Hatter Cardiovascular Institute Workshop.

In 1993, Przyklenk and colleagues made the intriguing experimental observation that 'brief ischemia in one vascular bed also protects remote, virgin myocardium from subsequent sustained coronary artery occlusion' and that this effect'... may be mediated by factor(s) activated, produced, or transported throughout the heart during brief ischemia/reperfusion'. This seminal study laid the foundation for the discovery of 'remote ischemic conditioning' (RIC), a phenomenon in which the heart is protected from the detrimental effects of acute ischemia/reperfusion injury (IRI), by applying cycles of brief ischemia and reperfusion to an organ or tissue remote from the heart. The concept of RIC quickly evolved to extend beyond the heart, encompassing inter-organ protection against acute IRI. The crucial discovery that the protective RIC stimulus could be applied non-invasively, by simply inflating and deflating a blood pressure cuff placed on the upper arm to induce cycles of brief ischemia and reperfusion, has facilitated the translation of RIC into the clinical setting. Despite intensive investigation over the last 20 years, the underlying mechanisms continue to elude researchers. In the 8th Biennial Hatter Cardiovascular Institute Workshop, recent developments in the field of RIC were discussed with a focus on new insights into the underlying mechanisms, the diversity of non-cardiac protection, new clinical applications, and large outcome studies. The scientific advances made in this field of research highlight the journey that RIC has made from being an intriguing experimental observation to a clinical application with patient benefit.

Stimulation of ICa by basal PKA activity is facilitated by caveolin-3 in cardiac ventricular myocytes.

L-type Ca channels (LTCC), which play a key role in cardiac excitation-contraction coupling, are located predominantly at the transverse (t-) tubules in ventricular myocytes. Caveolae and the protein caveolin-3 (Cav-3) are also present at the t-tubules and have been implicated in localizing a number of signaling molecules, including protein kinase A (PKA) and ß2-adrenoceptors. The present study investigated whether disruption of Cav-3 binding to its endogenous binding partners influenced LTCC activity. Ventricular myocytes were isolated from male Wistar rats and LTCC current (ICa) recorded using the whole-cell patch-clamp technique. Incubation of myocytes with a membrane-permeable peptide representing the scaffolding domain of Cav-3 (C3SD) reduced basal ICa amplitude in intact, but not detubulated, myocytes, and attenuated the stimulatory effects of the ß2-adrenergic agonist zinterol on ICa. The PKA inhibitor H-89 also reduced basal ICa; however, the inhibitory effects of C3SD and H-89 on basal ICa amplitude were not summative. Under control conditions, myocytes stained with antibody against phosphorylated LTCC (pLTCC) displayed a striated pattern, presumably reflecting localization at the t-tubules. Both C3SD and H-89 reduced pLTCC staining at the z-lines but did not affect staining of total LTCC or Cav-3. These data are consistent with the idea that the effects of C3SD and H-89 share a common pathway, which involves PKA and is maximally inhibited by H-89, and suggest that Cav-3 plays an important role in mediating stimulation of ICa at the t-tubules via PKA-induced phosphorylation under basal conditions, and in response to ß2-adrenoceptor stimulation.

Switching back to normal diet following high-fat diet feeding reduces cardiac vulnerability to ischaemia and reperfusion injury.

BACKGROUND: We have recently shown that hearts of mice fed high-fat diet exhibit increased vulnerability to ischaemia and reperfusion (I/R) in parallel to changes in catalase protein expression, mitochondrial morphology and intracellular diastolic Ca(2+). AIMS: To determine whether switching from high-fat back to normal diet alters vulnerability to I/R and to investigate cardiac cellular remodelling in relation to the mechanism(s) underlying I/R injury. METHODS AND RESULTS: Male C57BL/6J mice were fed a high-fat diet for 19-22 weeks; after which a subset of mice was switched back to normal diet for 4-6 weeks. Hearts from mice switched back to normal diet were more resistant to reperfusion injury compared to hearts from mice fed only high-fat diet. This was associated with a significant reversal in catalase expression (western blotting) and recovery of size and density of mitochondria (electron microscopy). In contrast, switching back to normal diet did not alter cardiomyocyte contractility or Ca(2+) transients compared to high-fat diet. CONCLUSION: This study shows for the first time that switching the diet from high-fat back to normal reduces vulnerability to I/R. This effect is associated with changes in catalase levels and mitochondrial morphology without altering cardiomyocyte contractility or Ca(2+) transients.

Clinically-relevant consecutive treatment with isoproterenol and adenosine protects the failing heart against ischaemia and reperfusion.

BACKGROUND: Consecutive treatment of normal heart with a high dose of isoproterenol and adenosine (Iso/Ade treatment), confers strong protection against ischaemia/reperfusion injury. In preparation for translation of this cardioprotective strategy into clinical practice during heart surgery, we further optimised conditions for this intervention using a clinically-relevant dose of Iso and determined its cardioprotective efficacy in hearts isolated from a model of surgically-induced heart failure. METHODS: Isolated Langendorff-perfused rat hearts were treated sequentially with 5 nM Iso and 30 µM Ade followed by different durations of washout prior to 30 min global ischaemia and 2 hrs reperfusion. Reperfusion injury was assessed by measuring haemodynamic function, lactate dehydrogenase (LDH) release and infarct size. Protein kinase C (PKC) activity and glycogen content were measured in hearts after the treatment. In a separate group of hearts, Cyclosporine A (CsA), a mitochondria permeability transition pore (MPTP) inhibitor, was added with Iso/Ade. Failing hearts extracted after 16 weeks of ligation of left coronary artery in 2 months old rats were also subjected to Iso/Ade treatment followed by ischaemia/reperfusion. RESULTS: Recovery of the rate pressure product (RPP) in Iso/Ade-treated hearts was significantly higher than in controls. Thus in Iso/Ade treated hearts with 5 nM Iso and no washout period, RPP recovery was 76.3±6.9% of initial value vs. 28.5±5.2% in controls. This was associated with a 3 fold reduction in LDH release irrespective to the duration of the washout period. Hearts with no washout of the drugs (Ade) had least infarct size, highest PKC activity and also showed reduced glycogen content. Cardioprotection with CsA was not additive to the effect of Iso/Ade treatment. Iso/Ade treatment conferred significant protection to failing hearts. Thus, RPP recovery in failing hearts subjected to the treatment was 69.0±16.3% while in Control hearts 19.7±4.0%. LDH release in these hearts was also 3 fold lower compared to Control. CONCLUSIONS: Consecutive Iso/Ade treatment of normal heart can be effective at clinically-relevant doses and this effect appears to be mediated by glycogen depletion and inhibition of MPTP. This intervention protects clinically relevant failing heart model making it a promising candidate for clinical use.

The effect of disease on human cardiac protein expression profiles in paired samples from right and left ventricles.

BACKGROUND: Cardiac diseases (e.g. coronary and valve) are associated with ventricular cellular remodeling. However, ventricular biopsies from left and right ventricles from patients with different pathologies are rare and thus little is known about disease-induced cellular remodeling in both sides of the heart and between different diseases. We hypothesized that the protein expression profiles between right and left ventricles of patients with aortic valve stenosis (AVS) and patients with coronary artery disease (CAD) are different and that the protein profile is different between the two diseases. Left and right ventricular biopsies were collected from patients with either CAD or AVS. The biopsies were processed for proteomic analysis using isobaric tandem mass tagging and analyzed by reverse phase nano-LC-MS/MS. Western blot for selected proteins showed strong correlation with proteomic analysis. RESULTS: Proteomic analysis between ventricles of the same disease (intra-disease) and between ventricles of different diseases (inter-disease) identified more than 500 proteins detected in all relevant ventricular biopsies. Comparison between ventricles and disease state was focused on proteins with relatively high fold (±1.2 fold difference) and significant (P < 0.05) differences. Intra-disease protein expression differences between left and right ventricles were largely structural for AVS patients and largely signaling/metabolism for CAD. Proteins commonly associated with hypertrophy were also different in the AVS group but with lower fold difference. Inter-disease differences between left ventricles of AVS and CAD were detected in 9 proteins. However, inter-disease differences between the right ventricles of CAD and AVS patients were associated with differences in 73 proteins. The majority of proteins which had a significant difference in one ventricle compared to the other pathology also had a similar trend in the adjacent ventricle. CONCLUSIONS: This work demonstrates for the first time that left and right ventricles have a different proteome and that the difference is dependent on the type of disease. Inter-disease differential expression was more prominent for right ventricles. The finding that a protein change in one ventricle was often associated with a similar trend in the adjacent ventricle for a large number of proteins suggests cross-talk proteome remodeling between adjacent ventricles.

Metabolic derangement and cardiac injury early after reperfusion following intermittent cross-clamp fibrillation in patients undergoing coronary artery bypass graft surgery using conventional or miniaturized cardiopulmonary bypass.

Myocardial ischemic stress and early reperfusion injury in patients undergoing coronary artery bypass grafting (CABG) operated on using intermittent cross-clamp fibrillation (ICCF) are not presently known. The role of mini-cardiopulmonary bypass (mCPB) versus conventional CPB (cCPB) during ICCF has not been investigated. These issues have been addressed as secondary objective of randomised controlled trial (ISRCTN30610605) comparing cCPB and mCPB. Twenty-six patients undergoing primary elective CABG using ICCF were randomised to either cCPB or mCPB. Paired left ventricular biopsies collected from 21 patients at the beginning and at the end of CPB were used to measure intracellular substrates (ATP and related compounds). Cardiac troponin T (cTnT) and CK-MB levels were measured in plasma collected from all patients preoperatively and after 1, 30, 60, 120, and 300 min after institution of CPB. ICCF was associated with significant ischemic stress as seen by fall in energy-rich phosphates early after reperfusion. There was also a fall in nicotinamide adenine dinucleotide (NAD(+)) indicating cardiomyocyte death which was confirmed by early release of cTnT and CK-MB during CPB. Ischemic stress and early myocardial injury were similar for cCPB and mCPB. However, the overall cardiac injury was significantly lower in the mCPB group as measured by cTnT (mean ± SEM: 96 ± 14 vs. 59 ± 8 µg/l, p = 0.02), but not with CK-MB. ICCF is associated with significant metabolic derangement and early myocardial injury. This early outcome was not affected by the CPB technique. However, the overall cardiac injury was lower for mCPB only when measured using cTnT.

Local inhibition of microRNA-24 improves reparative angiogenesis and left ventricle remodeling and function in mice with myocardial infarction.

Myocardial infarction (MI) is the leading cause of death worldwide. MicroRNAs regulate the expression of their target genes, thus mediating a plethora of pathophysiological functions. Recently, miRNA-24 emerged as an important but controversial miRNA involved in post-MI responses. Here, we aimed at clarifying the effect of adenovirus-mediate intra-myocardial delivery of a decoy for miRNA-24 in a mouse MI model and to investigate the impact of miRNA-24 inhibition on angiogenesis and cardiovascular apoptosis. After MI induction, miRNA-24 expression was lower in the peri-infarct tissue and its resident cardiomyocytes and fibroblasts; while it increased in endothelial cells (ECs). Local adenovirus-mediated miRNA-24 decoy delivery increased angiogenesis and blood perfusion in the peri-infarct myocardium, reduced infarct size, induced fibroblast apopotosis and overall improved cardiac function. Notwithstanding these beneficial effects, miRNA-24 decoy increased cardiomyocytes apoptosis. In vitro, miRNA-24 inhibition enhanced ECs survival, proliferation and networking in capillary-like tubes and induced cardiomyocyte and fibroblast apoptosis. Finally, we identified eNOS as a novel direct target of miR-24 in human cultured ECs and in vivo. Our findings suggest that miRNA-24 inhibition exerts distinct biological effects on ECs, cardiomyocytes and fibroblasts. The overall result of post-infarction local miRNA-24 inhibition appears to be therapeutic.

Corrigendum: Patterns of cytokine release and association with new onset of post-cardiac surgery atrial fibrillation.

[This corrects the article DOI: 10.3389/fsurg.2023.1205396.].

The effect of cardioplegic supplementation with sildenafil on cardiac energetics in a piglet model of cardiopulmonary bypass and cardioplegic arrest with warm or cold cardioplegia.

Cardioplegic cardioprotection strategies used during paediatric open-heart surgery remain suboptimal. Sildenafil, a phosphodiesterase 5 (PDE-5) inhibitor, has been shown to be cardioprotective against ischemia/reperfusion injury in a variety of experimental models and this study therefore tested the efficacy of supplementation of cardioplegia with sildenafil in a piglet model of cardiopulmonary bypass and arrest, using both cold and warm cardioplegia protocols. Piglets were anaesthetized and placed on coronary pulmonary bypass (CPB), the aorta cross-clamped and the hearts arrested for 60 min with cardioplegia with or without sildenafil (10 nM). Twenty minutes after removal of cross clamp (reperfusion), attempts were made to wean the pigs from CPB. Termination was carried out after 60 min reperfusion. Throughout the protocol blood and left ventricular tissue samples were taken for analysis of selected metabolites (using HPLC) and troponin I. In both the cold and warm cardioplegia protocols there was evidence that sildenafil supplementation resulted in faster recovery of ATP levels, improved energy charge (a measure of metabolic flux) and altered release of hypoxanthine and inosine, two purine catabolites. There was no effect on troponin release within the studied short timeframe. In conclusion, sildenafil supplementation of cardioplegia resulted in improved cardiac energetics in a translational animal model of paediatric CPB surgery.

Propofol improves recovery of the isolated working hypertrophic heart from ischaemia-reperfusion.

The general anaesthetic propofol shows promise in protecting normal hearts against various cardiac insults, but little is known about its cardioprotective potential in hypertrophic hearts. This study tested the hypothesis that propofol at a clinically relevant dose would enhance functional recovery in hypertrophic hearts following ischaemia. Hypertrophic hearts from spontaneously hypertensive rats and hearts from their normotensive controls, Wistar Kyoto Rats, were equilibrated in the working mode prior to global normothermic ischaemia. Reperfusion commenced with 10 min in Langendorff mode, followed by 30-min working reperfusion. Functional performance was measured throughout the working mode, whilst reperfusion damage was assessed from myocardial troponin I release during Langendorff reperfusion. Where used, 4 µg/ml propofol was added 10 min before ischaemia and was washed out 10 min into working reperfusion. An additional protocol investigated recovery of hearts protected by normothermic hyperkalaemic cardioplegic arrest. Following 20-min ischaemia, reperfusion damage was significantly worse in hypertrophic hearts compared to normal hearts, whilst addition of propofol to hypertrophic hearts significantly improved the aortic flow (31 ± 5.8 vs. 11.6 ± 2.0 ml/min, n = 6-7 ± SE, p < 0.05). Propofol also conferred significant protection following 30-min ischaemia where the recovery of cardiac output and stroke volume was similar to that for cardioplegia alone. Incubation with propofol improved the NADH/NAD(+) ratio in freshly isolated cardiomyocytes from hypertrophic hearts, suggesting possible improvements in metabolic flux. These findings suggest that propofol at the clinically relevant dose of 4 µg/ml is as effective as cardioplegic arrest in protecting hypertrophic hearts against ischaemia-reperfusion.

Interplay of Oxidative Stress and Necrosis-like Cell Death in Cardiac Ischemia/Reperfusion Injury: A Focus on Necroptosis.

Extensive research work has been carried out to define the exact significance and contribution of regulated necrosis-like cell death program, such as necroptosis to cardiac ischemic injury. This cell damaging process plays a critical role in the pathomechanisms of myocardial infarction (MI) and post-infarction heart failure (HF). Accordingly, it has been documented that the modulation of key molecules of the canonical signaling pathway of necroptosis, involving receptor-interacting protein kinases (RIP1 and RIP3) as well as mixed lineage kinase domain-like pseudokinase (MLKL), elicit cardioprotective effects. This is evidenced by the reduction of the MI-induced infarct size, alleviation of myocardial dysfunction, and adverse cardiac remodeling. In addition to this molecular signaling of necroptosis, the non-canonical pathway, involving Ca2+/calmodulin-dependent protein kinase II (CaMKII)-mediated regulation of mitochondrial permeability transition pore (mPTP) opening, and phosphoglycerate mutase 5 (PGAM5)-dynamin-related protein 1 (Drp-1)-induced mitochondrial fission, has recently been linked to ischemic heart injury. Since MI and HF are characterized by an imbalance between reactive oxygen species production and degradation as well as the occurrence of necroptosis in the heart, it is likely that oxidative stress (OS) may be involved in the mechanisms of this cell death program for inducing cardiac damage. In this review, therefore, several observations from different studies are presented to support this paradigm linking cardiac OS, the canonical and non-canonical pathways of necroptosis, and ischemia-induced injury. It is concluded that a multiple therapeutic approach targeting some specific changes in OS and necroptosis may be beneficial in improving the treatment of ischemic heart disease.

Determination of Agrin and Related Proteins Levels as a Function of Age in Human Hearts.

Background: Mature cardiomyocytes are unable to proliferate, preventing the injured adult heart from repairing itself. Studies in rodents have suggested that the extracellular matrix protein agrin promotes cardiomyocyte proliferation in the developing heart and that agrin expression is downregulated shortly after birth, resulting in the cessation of proliferation. Agrin based therapies have proven successful at inducing repair in animal models of cardiac injury, however whether similar pathways exist in the human heart is unknown. Methods: Right ventricular (RV) biopsies were collected from 40 patients undergoing surgery for congenital heart disease and the expression of agrin and associated proteins was investigated. Results: Agrin transcripts were found in all samples and their levels were significantly negatively correlated to age (p = 0.026), as were laminin transcripts (p = 0.023), whereas no such correlation was found for the other proteins analyzed. No significant correlations for any of the proteins were found when grouping patients by their gender or pathology. Immunohistochemistry and western blots to detect and localize agrin and the other proteins under analysis in RV tissue, confirmed their presence in patients of all ages. Conclusions: We show that agrin is progressively downregulated with age in human RV tissue but not as dramatically as has been demonstrated in mice; highlighting both similarities and differences to findings in rodents. Our results lay the groundwork for future studies exploring the potential of agrin-based therapies in the repair of damaged human hearts.