Assessment of coronary microcirculation alterations in a porcine model of no-reflow using ultrasound localization microscopy: a proof of concept study.

BACKGROUND: Coronary microvascular obstruction also known as no-reflow phenomenon is a major issue during myocardial infarction that bears important prognostic implications. Alterations of the microvascular network remains however challenging to assess as there is no imaging modality in the clinics that can image directly the coronary microvascular vessels. Ultrasound Localization Microscopy (ULM) imaging was recently introduced to map microvascular flows at high spatial resolution (∼10 µm). In this study, we developed an approach to image alterations of the microvascular coronary flow in ex vivo perfused swine hearts. METHODS: A porcine model of myocardial ischemia-reperfusion was used to obtain microvascular coronary alterations and no-reflow. Four female hearts with myocardial infarction in addition to 6 controls were explanted and placed immediately in a dedicated preservation and perfusion box manufactured for ultrasound imaging. Microbubbles (MB) were injected into the vasculature to perform Ultrasound Localization Microscopy (ULM) imaging and a linear ultrasound probe mounted on a motorized device was used to scan the heart on multiple slices. The coronary microvascular anatomy and flow velocity was reconstructed using dedicated ULM algorithms and analyzed quantitatively. FINDINGS: We were able to image the coronary microcirculation of ex vivo swine hearts at a resolution of tens of microns and measure flow velocities ranging from 10 mm/s in arterioles up to more than 200 mm/s in epicardial arteries. Under different aortic perfusion pressures, we measured in large arteries of a subset of control hearts an increase of flow velocity from 31 ± 11 mm/s at 87 mmHg to 47 ± 17 mm/s at 132 mmHg (N = 3 hearts, P < 0.05). This increase was compared with a control measurement with a flowmeter in the aorta. We also compared 6 control hearts to 4 hearts in which no-reflow was induced by the occlusion and reperfusion of a coronary artery. Using average MB velocity and average density of MB per unit of surface as two ULM quantitative markers of perfusion, we were able to detect areas of coronary no-reflow in good agreement with a control anatomical pathology analysis of the cardiac tissue. In the no-reflow zone, we measured an average perfusion of 204 ± 305 MB/mm2 compared to 3182 ± 1302 MB/mm2 in the surrounding re-perfused area. INTERPRETATION: We demonstrated this approach can directly image and quantify coronary microvascular obstruction and no-reflow on large mammal perfused hearts. This is a first step for noninvasive, quantitative and affordable assessment of the coronary microcirculation function and particularly coronary microvascular anatomy in the infarcted heart. This approach has the potential to be extended to other clinical situations characterized by microvascular dysfunction. FUNDING: This study was supported by the French National Research Agency (ANR) under ANR-21-CE19-0002 grant agreement.

Isolated Mitochondria State after Myocardial Ischemia-Reperfusion Injury and Cardioprotection: Analysis by Flow Cytometry.

RATIONALE: Mitochondria are key organelles involved in cell survival and death during the acute phenomena of myocardial ischemia-reperfusion (i.e., myocardial infarction). To investigate the functions of isolated mitochondria such as calcium retention capacity, oxidative phosphorylation, and reactive oxygen species (ROS) production, already established methods are based on extramitochondrial measurements of the whole mitochondria population. OBJECTIVE: The aim of this study was to develop a reliable and well-characterized method for multiparametric analysis of isolated single mitochondrion by flow cytometry (FC) in the context of myocardial infarction. The advantage of FC is the possibility to give a simultaneous analysis of morphological parameters (side and forward scatters: SSC and FSC) for each mitochondrion, combined with intramitochondrial measurements of several biological markers, such as ROS production or membrane potential (Δφm), using specific fluorescent probes. METHODS AND RESULTS: For this study, a rat model of ischemia-reperfusion and a protective approach of post-conditioning using low reperfusion pressure was used. Thanks to the use of specific probes (NAO, MTR, TMRM, DilC1, and DHR123) combined with flow cytometry, we propose a method: (i) to identify mitochondrial populations of interest based on quality criteria (NAO/TMRM double staining); (ii) to monitor their morphological criteria, especially during swelling due to calcium overload; and (iii) to compare mitochondrial functions (membrane potential and ROS production) in different experimental groups. Applied to mitochondria from ischemic hearts, these measurements revealed that individual mitochondria are altered and that cardioprotection by low-pressure reperfusion reduces damage, as expected. CONCLUSIONS: Our results highlight FC as a reliable and sensitive method to investigate changes in mitochondrial functions and morphology in pathological conditions that disrupts their activity such as the case in ischemia-reperfusion. This methodological approach can be extended to other pathologies involving mitochondrial dysfunctions. Moreover, FC offers the possibility to work with very small amounts of isolated mitochondria, a factor that may limit the use of classical methods.

Postconditioning by Delayed Administration of Ciclosporin A: Implication for Donation after Circulatory Death (DCD).

Heart transplantation is facing a shortage of grafts. Donation after Circulatory Death (DCD) would constitute a new potential of available organs. In the present work, we aimed to evaluate whether Postconditioning (ischemic or with ciclosporin-A (CsA)) could reduce ischemia-reperfusion injury in a cardiac arrest model when applied at the start of reperfusion or after a delay. An isolated rat heart model was used as a model of DCD. Hearts were submitted to a cardiac arrest of 40 min of global warm ischemia (37 °C) followed by 3 h of 4 °C-cold preservation, then 60 min reperfusion. Hearts were randomly allocated into the following groups: control, ischemic postconditioning (POST, consisting of two episodes each of 30 s ischemia and 30 s reperfusion at the onset of reperfusion), and CsA group (CsA was perfused at 250 nM for 10 min at reperfusion). In respective subgroups, POST and CsA were applied after a delay of 3, 10, and 20 min. Necrosis was lower in CsA and POST versus controls (p < 0.01) whereas heart functions were improved (p < 0.01). However, while the POST lost its efficacy if delayed beyond 3 min of reperfusion, CsA treatment surprisingly showed a reduction of necrosis even if applied after a delay of 3 and 10 min of reperfusion (p < 0.01). This cardioprotection by delayed CsA application correlated with better functional recovery and higher mitochondrial respiratory index. Furthermore, calcium overload necessary to induce mitochondrial permeability transition pore (MPTP) opening was similar in all cardioprotection groups, suggesting a crucial role of MPTP in this delayed protection of DCD hearts.

Quantitative stiffness assessment of cardiac grafts using ultrasound in a porcine model: A tissue biomarker for heart transplantation.

BACKGROUND: Heart transplantation is the definitive treatment for many cardiovascular diseases. However, no ideal approach is established to evaluate heart grafts and it mostly relies on qualitative interpretation of surgeon based on the organ aspect including anatomy, color and manual palpation. In this study we propose to assess quantitatively the Shear Wave Velocity (SWV) using ultrasound as a biomarker of cardiac viability on a porcine model. METHODS: The SWV was assessed quantitatively using a clinical ultrasound elastography device (Aixplorer, Supersonics Imagine, France) linked to a robotic motorized arm (UR3, Universal Robots, Denmark) and the elastic anisotropy was obtained using a custom ultrasound research system. SWV was evaluated as function of time in two porcine heart model during 20h at controlled temperature (4°C). One control group (N = 8) with the heart removed and arrested by cold cardioplegia and immerged in a preservation solution. One ischemic group (N = 6) with the organ harvested after 30 min of in situ warm ischemia, to mimic a donation after cardiac death. Hearts graft were revived at two preservation times, at 4 h (N = 11) and 20 h (N = 10) and the parameters of the cardiac function evaluated. FINDINGS: On control hearts, SWV remained unchanged during the 4h of preservation. SWV increased significantly between 4 and 20h. For the ischemic group, SWV was found higher after 4h (3.04 +/- 0.69 vs 1.69+/-0.19 m/s, p = 0.007) and 20h (4.77+/-1.22 m/s vs 3.40+/-0.75 m/s, p = 0.034) of preservation with significant differences. A good correlation between SWV and cardiac function index was found (r2=0.88) and manual palpation score (r2=0.81). INTERPRETATION: Myocardial stiffness increase was quantified as a function of preservation time and harvesting conditions. The correlation between SWV and cardiac function index suggests that SWV could be used as a marker of graft viability. This technique may be transposed to clinical transplantation for assessing the graft viability during transplantation process. FUNDING: FRM PME20170637799, Agence Biomédecine AOR Greffe 2017, ANR-18-CE18-0015.

Cooling Uncouples Differentially ROS Production from Respiration and Ca2+ Homeostasis Dynamic in Brain and Heart Mitochondria.

Hypothermia provides an effective neuro and cardio-protection in clinical settings implying ischemia/reperfusion injury (I/R). At the onset of reperfusion, succinate-induced reactive oxygen species (ROS) production, impaired oxidative phosphorylation (OXPHOS), and decreased Ca2+ retention capacity (CRC) concur to mitochondrial damages. We explored the effects of temperature from 6 to 37 °C on OXPHOS, ROS production, and CRC, using isolated mitochondria from mouse brain and heart. Oxygen consumption and ROS production was gradually inhibited when cooling from 37 to 6 °C in brain mitochondria (BM) and heart mitochondria (HM). The decrease in ROS production was gradual in BM but steeper between 31 and 20 °C in HM. In respiring mitochondria, the gradual activation of complex II, in addition of complex I, dramatically enhanced ROS production at all temperatures without modifying respiration, likely because of ubiquinone over-reduction. Finally, CRC values were linearly increased by cooling in both BM and HM. In BM, the Ca2+ uptake rate by the mitochondrial calcium uniporter (MCU) decreased by 2.7-fold between 25 and 37 °C, but decreased by 5.7-fold between 25 and 37 °C in HM. In conclusion, mild cold (25-37 °C) exerts differential inhibitory effects by preventing ROS production, by reverse electron transfer (RET) in BM, and by reducing MCU-mediated Ca2+ uptake rate in BM and HM.

Comparison Between Multiline Transmission and Diverging Wave Imaging: Assessment of Image Quality and Motion Estimation Accuracy.

High frame rate imaging is particularly important in echocardiography for better assessment of the cardiac function. Several studies showed that diverging wave imaging (DWI) and multiline transmission (MLT) are promising methods for achieving a high temporal resolution. The aim of this study was to compare MLT and compounded motion compensation (MoCo) DWI for the same transmitted power, same frame rates [image quality and speckle tracking echocardiography (STE) assessment], and same packet size [tissue Doppler imaging (TDI) assessment]. Our results on static images showed that MLT outperforms DW in terms of resolution (by 30% on average). However, in terms of contrast, MLT outperforms DW only for the depth of 11 cm (by 40% on average), the result being reversed at a depth of 4 cm (by 27% on average). In vitro results on a spinning phantom at nine different velocities showed that similar STE axial errors (up to 2.3% difference in median errors and up to 2.1% difference in the interquartile ranges) are obtained with both ultrafast methods. On the other hand, the median lateral STE estimates were up to 13% more accurate with DW than with MLT. On the contrary, the accuracy of TDI was only up to ~3% better with MLT, but the achievable DW Doppler frame rate was up to 20 times higher. However, our overall results showed that the choice of one method relative to the other is therefore dependent on the application. More precisely, in terms of image quality, DW is more suitable for imaging structures at low depths, while MLT can provide an improved image quality at the focal point that can be placed at higher depths. In terms of motion estimation, DW is more suitable for color Doppler-related applications, while MLT could be used to estimate velocities along selected lines of the image.

Mesenchymal stem cells sense mitochondria released from damaged cells as danger signals to activate their rescue properties.

Mesenchymal stem cells (MSCs) protect tissues against cell death induced by ischemia/reperfusion insults. This therapeutic effect seems to be controlled by physiological cues released by the local microenvironment following injury. Recent lines of evidence indicate that MSC can communicate with their microenvironment through bidirectional exchanges of mitochondria. In particular, in vitro and in vivo studies report that MSCs rescue injured cells through delivery of their own mitochondria. However, the role of mitochondria conveyed from somatic cells to MSC remains unknown. By using a co-culture system consisting of MSC and distressed somatic cells such as cardiomyocytes or endothelial cells, we showed that mitochondria from suffering cells acted as danger-signaling organelles that triggered the anti-apoptotic function of MSC. We demonstrated that foreign somatic-derived mitochondria were engulfed and degraded by MSC, leading to induction of the cytoprotective enzyme heme oxygenase-1 (HO-1) and stimulation of mitochondrial biogenesis. As a result, the capacity of MSC to donate their mitochondria to injured cells to combat oxidative stress injury was enhanced. We found that similar mechanisms - activation of autophagy, HO-1 and mitochondrial biogenesis - occurred after exposure of MSC to exogenous mitochondria isolated from somatic cells, strengthening the idea that somatic mitochondria alert MSC of a danger situation and subsequently promote an adaptive reparative response. In addition, the cascade of events triggered by the transfer of somatic mitochondria into MSC was recapitulated in a model of myocardial infarction in vivo. Specifically, MSC engrafted into infarcted hearts of mice reduced damage, upregulated HO-1 and increased mitochondrial biogenesis, while inhibition of mitophagy or HO-1 failed to protect against cardiac apoptosis. In conclusion, our study reveals a new facet about the role of mitochondria released from dying cells as a key environmental cue that controls the cytoprotective function of MSC and opens novel avenues to improve the effectiveness of MSC-based therapies.

Unacylated ghrelin analog prevents myocardial reperfusion injury independently of permeability transition pore.

Reperfusion injury is responsible for an important part of myocardial infarct establishment due notably to triggering cardiomyocytes death at the first minutes of reperfusion. AZP-531 is an optimized analog of unacylated ghrelin currently in clinical development in several metabolic diseases. We investigated a potential cardioprotective effect of AZP-531 in ischemia/reperfusion (IR) and the molecular underlying mechanism(s) involved in this protection. In vivo postconditioning with AZP-531 in C57BL6 mouse IR model decreased infarct size. Western blot analysis on areas at risk from the different mouse groups showed that AZP-531 activates Akt, ERK1-2 as well as S6 and 4EBP1, mTORC1 effectors. We also showed an inhibition of caspase 3 cleavage and Bax translocation to the mitochondria. AZP-531 also stimulated the expression of antioxidants and was capable of decreasing mitochondrial H2O2 production, contributing to the reduction of ROS accumulation. AZP-531 exhibits cardioprotective effect when administrated for postconditioning in C57BL6 mouse IR model. Treatment with AZP-531 rescued the myocardium from cell death at early reperfusion by stimulating protein synthesis, inhibiting Bax/caspase 3-induced apoptosis as well as ROS accumulation and oxidative stress-induced necrosis. AZP-531 may prove useful in the treatment of IR injury.

Delayed low pressure at reperfusion: A new approach for cardioprotection.

OBJECTIVES: The aims of this study were to evaluate whether the delayed application of low-pressure reperfusion could reduce lethal reperfusion injury and whether the inhibition of the opening of the mitochondrial permeability transition pore is involved in this protection. METHODS: Isolated rat hearts (n = 120) underwent 40 minutes of global ischemia followed by 60 minutes of reperfusion. Hearts were randomly assigned to the following groups: control, postconditioning (comprising 2 episodes of 30 seconds of ischemia and 30 seconds of reperfusion), and low-pressure reperfusion (using a reduction of perfusion pressure at 70 cm H2O for 10 minutes). In additional groups, postconditioning and low-pressure reperfusion were applied after a delay of 3, 10, and 20 minutes after the initial 40-minute ischemic insult. RESULTS: As expected, infarct size (triphenyltetrazolium chloride staining) and lactate dehydrogenase release were significantly reduced in low-pressure reperfusion and postconditioning versus controls (P < .01), whereas functional parameters (coronary flow, rate pressure product) were improved (P < .01). Although delaying postconditioning by more than 3 minutes resulted in a loss of protection, low-pressure reperfusion still significantly reduced infarct size when applied as late as 20 minutes after reperfusion. This delayed low-pressure reperfusion protection was associated with an improved mitochondrial respiration, lower reactive oxygen species production, and enhanced calcium retention capacity, related to inhibition of permeability transition pore opening. CONCLUSIONS: We demonstrated for the first time that low-pressure reperfusion can reduce lethal myocardial reperfusion injury even when performed 10 to 20 minutes after the initiation of reperfusion.

Cardiac fibroblasts protect cardiomyocytes against lethal ischemia-reperfusion injury.

Roles of cardiac fibroblasts (CFs) in the regulation of myocardial structure and function have been emphasized in the last decade. Their implications in pathophysiological aspects of chronic heart diseases such as myocardial remodeling and fibrosis are now well established; however their contribution to the acute phase of ischemia-reperfusion injury still remains elusive. We hypothesized that CF may contribute to cardiomyocyte (CM) protection against ischemia-reperfusion injuries. Experiments performed on isolated neonatal rat CF and CM demonstrated that the presence of CF in co-cultures increases CM viability (58 ± 2% versus 30 ± 2% in control) against hypoxia-reoxygenation injury, in a paracrine manner. It was confirmed by a similar effect of hypoxic CF secretome alone on CM viability (51 ± 9% versus 31 ± 4% in untreated cells). These findings were corroborated by in vivo experiments in a mice model of myocardial infarction in which a 25% infarct size reduction was observed in CF secretome treated mice compared to control. Tissue inhibitor of metalloproteinases-1 (TIMPs-1) alone, abundantly detected in CF secretome, was able to decrease CM cell death (35%) and experiments with pharmacological inhibitors of PI3K/Akt and ERK1/2 pathways provided more evidence that this paracrine protection is partly mediated by these signaling pathways. In vivo experiments strengthened that TIMP-1 alone was able to decrease infarct size (37%) and were validated by depletion experiments demonstrating that CF secretome cardioprotection was abolished by TIMP-1 depletion. Our data demonstrated for the first time that CFs participate in cardioprotection during the acute phase of ischemia-reperfusion via a paracrine pathway involving TIMP-1.

In vitro and in vivo models of cerebral ischemia show discrepancy in therapeutic effects of M2 macrophages.

THE INFLAMMATORY RESPONSE FOLLOWING ISCHEMIC STROKE IS DOMINATED BY INNATE IMMUNE CELLS: resident microglia and blood-derived macrophages. The ambivalent role of these cells in stroke outcome might be explained in part by the acquisition of distinct functional phenotypes: classically (M1) and alternatively activated (M2) macrophages. To shed light on the crosstalk between hypoxic neurons and macrophages, an in vitro model was set up in which bone marrow-derived macrophages were co-cultured with hippocampal slices subjected to oxygen and glucose deprivation. The results showed that macrophages provided potent protection against neuron cell loss through a paracrine mechanism, and that they expressed M2-type alternative polarization. These findings raised the possibility of using bone marrow-derived M2 macrophages in cellular therapy for stroke. Therefore, 2 million M2 macrophages (or vehicle) were intravenously administered during the subacute stage of ischemia (D4) in a model of transient middle cerebral artery occlusion. Functional neuroscores and magnetic resonance imaging endpoints (infarct volumes, blood-brain barrier integrity, phagocytic activity assessed by iron oxide uptake) were longitudinally monitored for 2 weeks. This cell-based treatment did not significantly improve any outcome measure compared with vehicle, suggesting that this strategy is not relevant to stroke therapy.

Volatile anaesthetics and cardioprotection: lessons from animal studies.

Volatile anaesthetics emerged as important cardioprotective agents in both animal models of ischaemia/reperfusion injury and humans with coronary artery disease. Their administration before a prolonged ischaemic episode is known as anaesthetic preconditioning, whereas when given at the very onset of reperfusion, the strategy is termed anaesthetic postconditioning. Both types of anaesthetic conditioning reduce, albeit not to the same degree, the extent of myocardial injury. They share similar, albeit not identical, intracellular signal transduction pathways with their widely investigated counterparts, ischaemic pre- and postconditioning. Despite a wealth of preclinical evidence for cardioprotection for anaesthetic conditioning strategies, their translation into clinical therapy has been rather disappointing. This review highlights the major findings on the cardioprotective effects of volatile anaesthetics in experimental settings. It explores hypotheses that may explain the lack of efficacy observed in several past clinical studies paving the way for future preclinical and translational studies.

Determination of the myocardial area at risk with pre- versus post-reperfusion imaging techniques in the pig model.

The purpose of this study was to compare the accuracy of post-reperfusion cardiac magnetic resonance (CMR) and pre-reperfusion multidetector computed tomography (MDCT) imaging to measure the size of the area at risk (AAR), using pathology as a reference technique in a porcine acute myocardial infarction model. Fifteen pigs underwent balloon-induced coronary artery occlusion for 40 min followed by reperfusion. The AAR was assessed with arterial enhanced MDCT performed during occlusion, while two different T2 weighted (T2W) CMR imaging sequences and the contrast-enhanced (ce-) CMR endocardial surface length (ESL) were performed after 90 min of reperfusion. Animals were euthanized and the AAR was assessed by pathology. Additional measurements of the myocardial water content in the AAR, remote and the AAR border zones were performed. AAR by pathology best correlated with measurements made by MDCT (R(2) = 0.88; p < 0.001) with little bias on Bland-Altman plots (bias 2.5%, SD 6.1% LV area). AAR measurements obtained by T2W STIR, T2W ACUTE sequences or the ESL on ce-CMR showed a fair correlation with pathology (R(2) = 0.72, R(2) = 0.65 and R(2) = 0.69, respectively; all p ≤ 0.001), but significantly overestimated the size of the AAR with important bias (17.4 ± 10.8% LV area; 11.7 ± 11.0% LV area; 13.0 ± 10.3% LV area, respectively). The myocardial water content in the AAR border zones was significantly higher than the remote (82.8 vs. 78.8%; p < 0.001). Our data suggest that post-reperfusion imaging methods overestimated the AAR likely due to the presence of edema outside of the boundaries of the AAR. Pre-reperfusion arterial enhanced MDCT showed the greatest accuracy for the assessment of the AAR.

Brain death provokes very acute alteration in myocardial morphology detected by echocardiography: preventive effect of beta-blockers.

Our objective was to evaluate immediate acute changes in myocardial function during the autonomic storm of brain death (BD). Wistar rats were divided into four groups (n = 8/group): controls without any treatment, ß-blocker (Esmolol®, 10 mg/kg), calcium channel blocker (Diltiazem®, 10 mg/kg), or alpha-blocker (Prazosin®, 0.3 mg/kg). Treatments were administered intravenously 5 min before BD induction. Echocardiography (ATL-5000, 8 MHz) was performed to measure left ventricular (LV) dimensions and fractional shortening at baseline, during BD induction and 5 min and 15 min after BD. In controls, BD was immediately associated with an increase in wall thickness and a decrease in LV cavity dimension. This myocardial wall hypertrophy was completely prevented by ß-blockers, but not with calcium- and alpha-blockers. Extensive myocardial interstitial edema was found in all groups, except in the ß-blocker group. Myocardial wall hypertrophy was also prevented during a longer follow-up of 180 min after BD in ß-blocker group as opposed to controls. In conclusion, BD is associated with an immediate and severe myocardial damage related to an important interstitial edema which is prevented by ß-blockers.

Mesenchymal stem cell conditioned media attenuates in vitro and ex vivo myocardial reperfusion injury.

BACKGROUND: Previous studies have suggested that implantation of mesenchymal stem cells (MSC) or their conditioned media (MSC CM) improves heart function after myocardial infarction. We sought to determine whether MSC and MSC CM added at the onset of reperfusion attenuates myocardial reperfusion injury. METHODS: Rat MSC and neonatal rat cardiomyocytes (NRC) were isolated and cultured separately. NRC were subjected to simulated in vitro ischemia/reperfusion (I/R). At the onset of reperfusion, NRC received either fresh medium (control group) or one of the following treatments: MSC in fresh medium; MSC CM alone (without MSC); MSC CM + inhibitors of PI3K (LY294002 or Wortmannin); MSC CM + antibodies neutralizing IGF-1 or VEGF; MSC + inhibitors of PI3K; or cyclosporine. Cell injury was assessed by LDH activity and MTT staining at the end of reperfusion. VEGF, IGF-1 and HGF were measured in each experimental treatment preparation. Ex vivo experimentation on isolated rat hearts subjected to I/R were performed to evaluate the protective effects of MSC CM on myocardial reperfusion injuries measured through CK release and infarct size after TTC staining. RESULTS: In vitro cell injury was significantly reduced by MSC, MSC CM and CsA. PI3K inhibitors significantly attenuated the protection afforded by MSC CM but not growth factor inhibitors. Ex vivo experimentation showed that MSC CM significantly reduced myocardial I/R injury. CONCLUSION: Our data suggest that MSC CM added at the onset of reperfusion can protect myocardium from I/R injury. In vitro data suggest a protection mediated by paracrine activation of the PI3K pathway.

[Improving donor heart preservation ex vivo]. / Amélioration de la prêservation des greffons cardiaques avant transplantation.

There is a shortage of heart donors. Some available organs are lost through deterioration prior to transplantation. Indeed, from the moment of brain death until reperfusion in the recipient, cardiac grafts (and also kidney, lung and liver grafts) can undergo irreversible damage due to cardioplegia, the harvesting procedure, and hypothermic transport. The noxious phenomena occurring during cold ischaemia and myocardial reperfusion have been studied for more than 40 years. It was long believed that only the ischaemic phase was harmful, through depletion of energy stores, ionic imbalance, and metabolic disruption. We now know that the heart graft can also be damaged during the reperfusion phase, through calcium overload, free radical production, and mitochondrial changes. Preconditioning and post-conditioning procedures are being developed to protect the ischemic organ.

Post-conditioning protects from cardioplegia and cold ischemia via inhibition of mitochondrial permeability transition pore.

BACKGROUND: The aim of this study was to evaluate the role of the mitochondrial permeability transition pore (MPTP) in the protection achieved by post-conditioning of hearts submitted to hypothermic cardioplegia and ischemia. METHODS: Isolated rat hearts (n = 30) underwent cold cardioplegia (4 degrees C, Celsior solution) and 8 hours of ischemia at 4 degrees C, followed by a 60-minute Langendorff reperfusion. Hearts were randomly assigned to one of two groups: post-conditioning (post-C, consisting of episodes of 30-second ischemia and 30-second reperfusion at onset of reperfusion) or control (no intervention). A sham group was added for which hearts were harvested and immediately reperfused without ischemia. Coronary flow, heart rate, dP/dt and rate-pressure product were measured. Infarct size was assessed by triphenyltetrazolium chloride (TTC) staining and lactate dehydrogenase (LDH), creatine phosphokinase (CPK) and troponin I release analysis. After reperfusion, heart mitochondria were isolated and calcium overload necessary to induce MPTP opening was measured. From the onset of reperfusion, all functional parameters were significantly improved in post-C vs control hearts. RESULTS: Infarct size, measured both by TTC staining and LDH, and CPK and troponin I leakage were lower in post-C hearts (p < 0.01). Mean calcium load needed to induce MPTP opening was higher in post-C mitochondria vs controls (p < 0.01). CONCLUSIONS: Post-conditioning protects the rat heart against cold ischemia-reperfusion injury. Our data suggest that this protection involves inhibition of MPTP opening.

Brain death does not change epicardial action potentials and their response to ischemia-reperfusion in open-chest pigs.

BACKGROUND: It is debated whether brain death (BD) causes transient functional ischemia. In this investigation we used monophasic action potential (AP) recording during BD as a sensitive means to assess: (i) whether ischemia was present; and (ii) the effect of BD on a subsequent ischemia-reperfusion challenge. METHODS: In Period 1, BD was induced (BD group, 6 pigs) or not induced (sham maneuver, control [C] group, 6 pigs), and effects were followed for 3 hours. In Period 2, left anterior descending (LAD) coronary artery ligation ischemia was applied for 20 minutes to all hearts, followed by 60-minute reperfusion. RESULTS: In Period 1, plasma norepinephrine was 3.1-, 6.3- and 5-fold greater in BD than in C at 1, 120 and 180 minutes, respectively, and systolic blood pressure was 26% greater at 1 minute and 35% at 120 minutes. The arteriovenous difference in lactate was similar or lower in BD than in C. In both groups, at all time-points, the action potential recording had a rectangular plateau shape and action potential duration (APD50) had a linear relationship to the cardiac inter-beat (RR) interval (R2 = 0.89 and 0.73, slope = 0.42 +/- 0.02 and 0.46 +/- 0.06 in BD and C, respectively). In Period 2, ischemia caused a similar (50%) APD shortening in BD and C. Restoration of the APD upon reperfusion was complete in both groups. CONCLUSIONS: Our findings suggest that BD does not cause direct cardiac ischemia and does not change the response of the heart to subsequent ischemia-reperfusion challenge.

PI 3-kinase regulates the mitochondrial transition pore in controlled reperfusion and postconditioning.

OBJECTIVE: We investigated whether phosphatidylinositol 3-kinase (PI3K) might regulate mitochondrial permeability transition pore (mPTP) opening in hearts reperfused with either low pressure or postconditioning. METHODS: Male Wistar rat hearts (n=72) were perfused according to the Langendorff technique, exposed to 30 min of ischemia, and assigned to one of the following groups: (1) reperfusion with normal pressure (NP; 100 cm H2O), (2) reperfusion with low pressure (LP; 70 cm H2O), or reperfusion with postconditioning, i.e. 3 episodes of 30 s reperfusion followed by 30 s of ischemia (PostC). Hearts received either the PI3K inhibitors wortmannin or LY294002, or vehicle at the onset of the 60 min reperfusion. Postischemic functional recovery was assessed by rate-pressure product (RPP), and irreversible injury by lactate dehydrogenase (LDH), creatine kinase (CK) and troponin I (TnI) release. Mitochondria were isolated from the reperfused myocardium, and Ca2+-induced mPTP opening was measured using a potentiometric method. RESULTS: Functional recovery was significantly improved in LP and PostC hearts with RPP averaging 13,880+/-810 (LP) and 17,130+/-900 mm Hgxbeats/min (PostC) versus 6450+/-500 mm Hgxbeats/min in NP hearts (p<0.01). LDH release averaged 230+/-30 and 145+/-15 IU/h/g of myocardial tissue in LP and PostC versus 340+/-10 IU/h/g in NP (p<0.05). Wortmannin and LY294002 prevented both RPP improvement and decrease in LDH, CK, and TnI release in LP and PostC groups. The Ca2+ load required to induce mPTP opening averaged 58+/-3 and 52+/-1 nmol/mg mitochondrial proteins in LP and PostC groups, respectively, versus 35+/-4 nmol/mg in the NP group (p<0.01). Wortmannin and LY294002 prevented the beneficial effect in both the LP and PostC groups. CONCLUSION: These results suggest that PI3K regulates the opening of the mitochondrial permeability transition pore in rat hearts reperfused with low pressure or postconditioning.

Non-beating HL-1 cells for confocal microscopy: application to mitochondrial functions during cardiac preconditioning.

HL-1, the first cell line with a cardiac phenotype for biological experiments, displays spontaneous electrophysiological and mechanical regular activity, and cyclic calcium movements. We isolated a derived line, devoid of transient movements, for confocal microscopy experiments. These cells do express cardiac proteins: connexin 43, the cardiac isoform of dihydropyridine receptors, desmin, and developmental myosin but have no sarcomeric arrangement. They still possess the electrophysiological characteristics and ionic currents of cardiac cells, among them the cardiac potassium current IKr. We also found diazoxide and glibenclamide sensitive potassium channels with properties similar to IK(ATP) in adult cardiac myocytes. The pacemaker current I(f) was not observed, in agreement with the cells showing excitability but lacking in pacemaker activity. The absence of movement is an advantage for studies which include changes of media in order to follow morphological changes under continuous perfusion. We observed however a basal spontaneous movement of mitochondria and we developed a method to quantify its amplitude using confocal microscopy. No mitochondrial depolarization could be detected when the membrane potential was measured by using very low light photomultiplier and confocal fluorescence imaging under the K(ATP) channel opener diazoxide. Thus cardiac pharmacological preconditioning by K(ATP) channel openers might involve other routes than mitochondrial K channels targeting.