Inhibition of mitochondrial reactive oxygen species improves coronary endothelial function after cardioplegic hypoxia/reoxygenation

OBJECTIVE

Cardioplegic ischemia-reperfusion and diabetes mellitus are correlated with coronary endothelial dysfunction and inactivation of small conductance calcium-activated potassium channels. Increased reactive oxidative species, such as mitochondrial reactive oxidative species, may contribute to oxidative injury. Thus, we hypothesized that inhibition of mitochondrial reactive oxidative species may protect coronary small conductance calcium-activated potassium channels and endothelial function against cardioplegic ischemia-reperfusion-induced injury.

METHODS

Small coronary arteries and endothelial cells from the hearts of mice with and without diabetes mellitus were isolated and examined by using a cardioplegic hypoxia and reoxygenation model to determine whether the mitochondria-targeted antioxidant Mito-Tempo could protect against coronary endothelial and small conductance calcium-activated potassium channel dysfunction. The microvessels or mouse heart endothelial cells were treated with or without Mito-Tempo (0-10 μM) 5 minutes before and during cardioplegic hypoxia and reoxygenation. Microvascular function was assessed in vitro by vessel myography. K+ currents of mouse heart endothelial cells were measured by whole-cell patch clamp. The levels of intracellular cytosolic free calcium (Ca2+) concentration, mitochondrial reactive oxidative species, and small conductance calcium-activated potassium protein expression of mouse heart endothelial cells were measured by Rhod-2 fluorescence staining, MitoSox, and Western blotting, respectively.

RESULTS

Cardioplegic hypoxia and reoxygenation significantly attenuated endothelial small conductance calcium-activated potassium channel activity, caused calcium overload, and increased mitochondrial reactive oxidative species of mouse heart endothelial cells in both the nondiabetic and diabetes mellitus groups. In addition, treating mouse heart endothelial cells with Mito-Tempo (10 μM) reduced cardioplegic hypoxia and reoxygenation-induced Ca2+ and mitochondrial reactive oxidative species overload in both the nondiabetic and diabetes mellitus groups, respectively (P < .05). Treatment with Mito-Tempo (10 μM) significantly enhanced coronary relaxation responses to adenosine 5'-diphosphate and NS309 (P < .05), and endothelial small conductance calcium-activated potassium channel currents in both the nondiabetic and diabetes mellitus groups (P < .05).

CONCLUSIONS

Administration of Mito-Tempo improves endothelial function and small conductance calcium-activated potassium channel activity, which may contribute to its enhancement of endothelium-dependent vasorelaxation after cardioplegic hypoxia and reoxygenation.

Effect of cardioplegic arrest and reperfusion on left and right ventricular proteome/phosphoproteome in patients undergoing surgery for coronary or aortic valve disease

Our earlier work has shown inter‑disease and intra‑disease differences in the cardiac proteome between right (RV) and left (LV) ventricles of patients with aortic valve stenosis (AVS) or coronary artery disease (CAD). Whether disease remodeling also affects acute changes occuring in the proteome during surgical intervention is unknown. This study investigated the effects of cardioplegic arrest on cardiac proteins/phosphoproteins in LV and RV of CAD (n=6) and AVS (n=6) patients undergoing cardiac surgery. LV and RV biopsies were collected during surgery before ischemic cold blood cardioplegic arrest (pre) and 20 min after reperfusion (post). Tissues were snap frozen, proteins extracted, and the extracts were used for proteomic and phosphoproteomic analysis using Tandem Mass Tag (TMT) analysis. The results were analysed using QuickGO and Ingenuity Pathway Analysis softwares. For each comparision, our proteomic analysis identified more than 3,000 proteins which could be detected in both the pre and Post samples. Cardioplegic arrest and reperfusion were associated with significant differential expression of 24 (LV) and 120 (RV) proteins in the CAD patients, which were linked to mitochondrial function, inflammation and cardiac contraction. By contrast, AVS patients showed differential expression of only 3 LV proteins and 2 RV proteins, despite a significantly longer duration of ischaemic cardioplegic arrest. The relative expression of 41 phosphoproteins was significantly altered in CAD patients, with 18 phosphoproteins showing altered expression in AVS patients. Inflammatory pathways were implicated in the changes in phosphoprotein expression in both groups. Inter‑disease comparison for the same ventricular chamber at both timepoints revealed differences relating to inflammation and adrenergic and calcium signalling. In conclusion, the present study found that ischemic arrest and reperfusion trigger different changes in the proteomes and phosphoproteomes of LV and RV of CAD and AVS patients undergoing surgery, with markedly more changes in CAD patients despite a significantly shorter ischaemic period.

Revising ventricular septal defect residual shunts without aortic re-cross-clamping: a safe and effective surgical procedure

Background

The conventional approach to revising a residual shunt following ventricular septal defect (VSD) closure is to re-occlude the aorta and repair the residual shunt under cardioplegic arrest. The present study evaluated the safety and effectiveness of a new approach for revising residual shunts following VSD repair without re-occluding the aorta. This approach is known as on beating heart surgery.

Methods

This retrospective study included 80 pediatric patients who underwent surgical closure of a simple VSD. Residual shunts larger than 2 mm were intraoperatively detected by transesophageal echocardiography (TEE) and these patients received immediate reintervention. Of the patients, 37 received on beating heart surgery without aortic cross-clamping (Group A) and 43 patients were operated on with aortic cross-clamping and cardioplegia (Group B).

Results

Residual VSD closures were successfully performed in all patients. Group A had significantly shorter aortic cross-clamp times (P<0.0001), significantly shorter CPB times (P<0.01), a lower incidence of prolonged ventilation (>6 hours) (P=0.04), a lower incidence of prolonged intensive care unit (ICU) stay (ICU stay >1 day) (P=0.02), and reduced in-hospital expenses (P<0.0001) compared with Group B. There was no significant difference in the incidence of recurrent residual shunts (P=0.96), prolonged postoperative hospital stay (>5 days) (P=0.24), or the incidence of perioperative complications (P=0.81) between the groups.

Conclusions

On beating heart surgery is a safe and effective approach for the closure of residual VSDs and is significantly associated with a lower incidence of prolonged ventilation, a lower incidence of prolonged ICU stay, and reduced in-hospital expenses.

Cardioprotective Effects of Sphingosine-1-Phosphate Receptor Immunomodulator FTY720 in a Clinically Relevant Model of Cardioplegic Arrest and Cardiopulmonary Bypass

Objective: FTY720, an immunomodulator derived from sphingosine-1-phosphate, has recently demonstrated its immunomodulatory, anti-inflammatory, anti-oxidant, anti-apoptotic and anti-inflammatory properties. Furthermore, FTY720 might be a key pharmacological target for preconditioning. In this preclinical model, we have investigated the effects of FTY720 on myocardium during reperfusion in an experimental model of cardioplegic arrest (CPA) and cardiopulmonary bypass.

Methods: 30 Sprague–Dawley rats (300–350 g) were randomized into two groups: Group-A, treated with FTY720 1 mg/kg via intravenous cannulation, and Group-B, as control. After 15 min of treatment, rats underwent CPA for 30 min followed by initiation of extracorporeal life support for 2 h. Support weaning was done, and blood and myocardial tissues were collected for analysis. Hemodynamic parameters, inflammatory mediators, nitro-oxidative stress, neutrophil infiltration, immunoblotting analysis, and immunohistochemical staining were analyzed and compared between groups.

Results: FTY720 treatment activated the Akt/Erk1/2 signaling pathways, reduced the level of inflammatory mediators, activated antiapoptotic proteins, and inhibited proapoptotic proteins, leading to reduced nitro-oxidative stress and cardiomyocyte apoptosis. Moreover, significant preservation of high-energy phosphates were observed in the FTY720-treated group. This resulted in improved recovery of left ventricular systolic and diastolic functions.

Conclusion: The cardioprotective mechanism in CPA is associated with activation of prosurvival cell signaling pathways that prevents myocardial damage. FTY720 preserves high-energy phosphates attenuates myocardial inflammation and oxidative stress, and improves cardiac function.

Left ventricular dysfunction after two hours of polarizing or depolarizing cardioplegic arrest in a porcine model

INTRODUCTION

This experimental study compares myocardial function after prolonged arrest by St. Thomas' Hospital polarizing cardioplegic solution (esmolol, adenosine, Mg²⁺) with depolarizing (hyperkalaemic) St. Thomas' Hospital No 2, both administered as cold oxygenated blood cardioplegia.

METHODS

Twenty anaesthetized pigs on tepid (34°C) cardiopulmonary bypass (CPB) were randomised to cardioplegic arrest for 120 min with antegrade, repeated, cold, oxygenated, polarizing (STH-POL) or depolarizing (STH-2) blood cardioplegia every 20 min. Cardiac function was evaluated at Baseline and 60, 150 and 240 min after weaning from CPB, using a pressure-conductance catheter and epicardial echocardiography. Regional tissue blood flow, cleaved caspase-3 activity and levels of malondialdehyde were evaluated in myocardial tissue samples.

RESULTS

Preload recruitable stroke work (PRSW) was increased after polarizing compared to depolarizing cardioplegia 150 min after declamping (73.0±3.2 vs. 64.3±2.4 mmHg, p=0.047). Myocardial tissue blood flow rate was high in both groups compared to the Baseline levels and decreased significantly in the STH-POL group only, from 60 min to 150 min after declamping (p<0.005). Blood flow was significantly reduced in the STH-POL compared to the STH-2 group 240 min after declamping (p<0.05). Left ventricular mechanical efficiency, the ratio between total pressure-volume area and blood flow rate, gradually decreased after STH-2 cardioplegia and was significantly reduced compared to STH-POL cardioplegia after 150 and 240 min (p<0.05 for both).

CONCLUSION

Myocardial protection for two hours of polarizing cardioplegic arrest with STH-POL in oxygenated blood is non-inferior compared to STH-2 blood cardioplegia. STH-POL cardioplegia alleviates the mismatch between myocardial function and perfusion after weaning from CPB.

A rabbit model of antegrade selective cerebral perfusion with cardioplegic arrest

OBJECTIVE

Due to the weak ascending aorta, it is extremely challenging to establish an anterograde selective cerebral perfusion (ASCP) model in rabbits, especially when cardioplegic arrest is required. Herein, the aim of this study was to establish a rabbit ASCP model with cardiac arrest being easily performed and being similar to the clinical scenario.

MATERIALS AND METHODS

Twenty-two adult New Zealand white rabbits were selected for ASCP model establishment and another 22 rabbits were utilized for blood donation. The cardiopulmonary bypass (CPB) circuit consisted of a roller pump, a membrane oxygenator, a heat-cooler system and a blood reservoir, which were connected by silicone tubing. The total priming volume of the circuit was 70 ml. Cannulations on the right and left subclavian arteries were used for arterial inflow and cardioplegia perfusion, respectively. Venous drainage was conducted through the right atrial appendage. ASCP was initiated by clamping the innominate artery; the flow rate was maintained 10 ml/kg/minute and sustained for 60 minutes. After 120 minutes of reperfusion, the rabbits were sacrificed. The mean arterial pressure, heart rate, electrocardiogram and urine output were monitored. Arterial blood samples were analyzed at the following time points: after anesthesia, immediately after CPB, after aorta cross-clamping and cardioplegia perfusion, 5 min after the re-opening of the aorta and at CPB termination.

RESULTS

ASCP modeling was performed successfully on 18 rabbits and 4 rabbits unsuccessfully. Vital signs and blood gas indictors changed in an acceptable range throughout the experiments. One rabbit had ventricular fibrillation after re-opening of the ascending aorta. Obvious hemodilution occurred after the perfusion of cardioplegia, but the hematocrit improved after CPB termination.

CONCLUSION

By using cannulation of the subclavian artery rather than the aorta and with a low priming volume, we established a modified rabbit model of ASCP with cardioplegic arrest. The model has excellent repeatability and operability, which is similar to the clinic process and is suitable for the study of cerebral, cardiac and renal protection.