Inhibition of contractile activity during postconditioning enhances cardioprotection by restoring sarcolemmal dystrophin through phosphatidylinositol 3-kinase

Essential roles of the dystrophin-glycoprotein complex in different cardiac pathologies

The dystrophin-glycoprotein complex (DGC), situated at the sarcolemma dynamically remodels during cardiac disease. This review examines DGC remodeling as a common denominator in diseases affecting heart function and health. Dystrophin and the DGC serve as broad cytoskeletal integrators that are critical for maintaining stability of muscle membranes. The presence of pathogenic variants in genes encoding proteins of the DGC can cause absence of the protein and/or alterations in other complex members leading to muscular dystrophies. Targeted studies have allowed the individual functions of affected proteins to be defined. The DGC has demonstrated its dynamic function, remodeling under a number of conditions that stress the heart. Beyond genetic causes, pathogenic processes also impinge on the DGC, causing alterations in the abundance of dystrophin and associated proteins during cardiac insult such as ischemia-reperfusion injury, mechanical unloading, and myocarditis. When considering new therapeutic strategies, it is important to assess DGC remodeling as a common factor in various heart diseases. The DGC connects the internal F-actin-based cytoskeleton to laminin-211 of the extracellular space, playing an important role in the transmission of mechanical force to the extracellular matrix. The essential functions of dystrophin and the DGC have been long recognized. DGC based therapeutic approaches have been primarily focused on muscular dystrophies, however it may be a beneficial target in a number of disorders that affect the heart. This review provides an account of what we now know, and discusses how this knowledge can benefit persistent health conditions in the clinic.

The Protective Effect of Cx43 Protein-Mediated Phosphocreatine on Myocardial Ischemia/Reperfusion Injury

Objectives

To verify the protective effect of phosphocreatine on myocardium in an ischemic model and the possible mechanism of action.

Methods

The model of myocardial ischemia/reperfusion (I/R) was established by the ligation balloon method. 30 SD rats were randomly divided into three groups, n = 10 in each group. Sham operation group: the coronary artery was not blocked and observed for 120 minutes. The ischemia/reperfusion (I/R) group was given ischemia for 30 minutes and ischemia reperfusion for 90 minutes. Phosphocreatine (PCr) group: after 30 minutes of ischemia, the rats were intraperitoneally injected with PCr (200 mg/kg) for 90 minutes. The animal groups of myocardial ischemia/reperfusion model in vitro were the same as those in vivo. The heart was removed by thoracotomy and washed immediately in H-K buffer solution. Then, the heart was installed on the Langendorff instrument. The concentration of PCr perfusion fluid in the PCr group was 10 mmol/L. The changes in coronary blood flow in isolated myocardium were recorded. The heart rate and electrocardiogram were recorded by RM6240BT. At the end of the experiment, myocardial pathological sections and Cx43 immunofluorescence staining were made, and the contents of malondialdehyde (MDA) in myocardial tissue were detected.

Results

Phosphocreatinine treatment improved the myocardial ischemia model, performance in electrocardiogram (ECG) changes (ST segment apparent), and histological changes (decrease in necrotic myocardial cells, inflammatory cell infiltration, and a reduction in myocardial edema). At the same time, MDA decreased, while coronary blood flow and Cx43 expression significantly improved.

Conclusions

Phosphocreatine can improve the electrocardiogram and restore histologic changes in ischemic myocardium and coronary blood flow. The postulated mechanism is by inhibiting the generation of free oxygen radicals and restoring the expression of Cx43 protein.

Protective effects of phosphocreatine administered post-treatment combined with ischemic post-conditioning on rat hearts with myocardial ischemia/reperfusion injury

Background

The aim of the study was to investigate the effects of phosphocreatine (PCr) post-treatment combined with ischemic post-conditioning on myocardial ischemia/reperfusion (I/R) injury in a rat model.

Methods

Forty Sprague-Dawley rats that had undergone 30 minutes ischemia and 120 minutes reperfusion were randomly divided into four groups (n = 10 in each group): the I/R group, the ischemia post-conditioning (IPost) group, the PCr group, and the IPost + PCr group. The activities of serum creatine kinase (CK), myeloperoxidase (MPO), and lactate dehydrogenase (LDH) were measured after 120 minutes of reperfusion. At the end of the experiment, serum levels of nuclear factor (NF)-κB and tumor necrosis factor (TNF)-α were detected, myocardial infarct size (IS) was measured by triphenyltetrazolium chloride staining, and myocardial expression of Bcl-2 and phosphorylated Akt (p-Akt) was determined by western blot.

Results

The IPost, PCr, and PCr + IPost groups had significantly lower IS than the I/R group (P < 0.05). The reductions in CK, LDH, and MPO release were consistent with the decrease in the myocardial IS (P < 0.05). Serum concentrations of TNF-α and NF-κB in the IPost, PCr, and PCr + IPost groups were significantly lower than those in the I/R group (P < 0.05). The levels of p-Akt and Bcl-2 in the IPost, PCr, and PCr + IPost groups were greater than those in the I/R group (P < 0.05). CK, LDH, MPO, NF-κB, TNF-α, p-Akt, Bcl-2 and IS were further enhanced in the IPost + PCr group (P < 0.05).

Conclusions

Post-treatment with PCr enhanced the protective effect of IPost on rat myocardium affected by I/R injury, possibly by inhibiting the inflammatory response and activating the phosphatidylinositol 3-kinase (PI-3K)/Akt/Bcl-2 signaling pathway.

Fluopsin C induces oncosis of human breast adenocarcinoma cells

AIM

Fluopsin C, an antibiotic isolated from Pseudomonas jinanesis, has shown antitumor effects on several cancer cell lines. In the current study, the oncotic cell death induced by fluopsin C was investigated in human breast adenocarcinoma cells in vitro.

METHODS

Human breast adenocarcinoma cell lines MCF-7 and MD-MBA-231 were used. The cytotoxicity was evaluated using MTT assay. Time-lapse microscopy and transmission electron microscopy were used to observe the morphological changes. Cell membrane integrity was assessed with propidium iodide (PI) uptake and lactate dehydrogenase (LDH) assay. Flow cytometry was used to measure reactive oxygen species (ROS) level and mitochondrial membrane potential (Δψm). A multimode microplate reader was used to analyze the intracellular ATP level. The changes in cytoskeletal system were investigated with Western blotting and immunostaining.

RESULTS

Fluopsin C (0.5-8 μmol/L) reduced the cell viability in dose- and time-dependent manners. Its IC50 values in MCF-7 and MD-MBA-231 cells at 24 h were 0.9 and 1.03 μmol/L, respectively. Fluopsin C (2 μmol/L) induced oncosis in both the breast adenocarcinoma cells characterized by membrane blebbing and swelling, which was blocked by pretreatment with the pan-caspase inhibitor Z-VAD-fmk. In MCF-7 cells, fluopsin C caused PI uptake into the cells, significantly increased LDH release, induced cytoskeletal system degradation and ROS accumulation, decreased the intracellular ATP level and Δψm. Noticeably, fluopsin C exerted comparable cytotoxicity against the normal human hepatocytes (HL7702) and human mammary epithelial cells with the IC50 values at 24 h of 2.7 and 2.4 μmol/L, respectively.

CONCLUSION

Oncotic cell death was involved in the anticancer effects of fluopsin C on human breast adenocarcinoma cells in vitro. The hepatoxicity of fluopsin C should not be ignored.

Absence of glucose transporter 4 diminishes electrical activity of mouse hearts during hypoxia

Insulin resistance, which characterizes type 2 diabetes, is associated with reduced translocation of glucose transporter 4 (GLUT4) to the plasma membrane following insulin stimulation, and diabetic patients with insulin resistance show a higher incidence of ischaemia, arrhythmias and sudden cardiac death. The aim of this study was to examine whether GLUT4 deficiency leads to more severe alterations in cardiac electrical activity during cardiac stress due to hypoxia. To fulfil this aim, we compared cardiac electrical activity from cardiac-selective GLUT4-ablated (G4H-/-) mouse hearts and corresponding control (CTL) littermates. A custom-made cylindrical 'cage' electrode array measured potentials (Ves) from the epicardium of isolated, perfused mouse hearts. The normalized average of the maximal downstroke of Ves ( (|d Ves/dt(min)|na), which we previously introduced as an index of electrical activity in normal, ischaemic and hypoxic hearts, was used to assess the effects of GLUT4 deficiency on electrical activity. The |d Ves/dt(min)|na of G4H −/− and CTL hearts decreased by 75 and 47%, respectively (P < 0.05), 30 min after the onset of hypoxia. Administration of insulin attenuated decreases in values of |d Ves/dt(min)|na in G4H −/− hearts as well as in CTL hearts, during hypoxia. In general, however, G4H −/− hearts showed a severe alteration of the propagation sequence and a prolonged total activation time. Results of this study demonstrate that reduced glucose availability associated with insulin resistance and a reduction in GLUT4-mediated glucose transport impairs electrical activity during hypoxia, and may contribute to cardiac vulnerability to arrhythmias in diabetic patients.

Intracoronary followed by intravenous administration of the short-acting β-blocker landiolol prevents myocardial injury in the face of elective percutaneous coronary intervention

BACKGROUND

Myocardial injury during elective percutaneous coronary intervention (PCI) is associated with higher subsequent cardiac events and mortality. β-Blockers have been used to reduce myocardial injury during ischemia and reperfusion. We investigated whether intracoronary followed by intravenous administration of the short-acting β-blocker landiolol prevents myocardial injury in the face of elective PCI.

METHODS AND RESULTS

Patients undergoing elective PCI (n=70) were randomly assigned to the landiolol (n=35) or control (n=35) group. Landiolol or saline was administered into target vessels through a balloon catheter for 1min before and after first balloon inflation followed by continuous intravenous administration for 6h after PCI. The incidence of myocardial injury defined by cardiac troponin-I (cTnI) >/=0.05 ng/ml was 79% of the patients in the control group compared to 56% in the landiolol group (p=0.04). The cTnI level at 24h after PCI tended to be lower in the landiolol group (0.57 ± 1.14 versus 1.27 ± 2.48 ng/ml; p=0.07), while the CK-MB level was not significantly different between the landiolol and control groups. The incidence of peri-procedural myocardial infarction defined by cTnI >/=0.12 ng/ml was significantly (p=0.02) lower in the landiolol group (41%) compared to the control group (70%). There was no incidence of coronary spasm, hypotension, bradycardia or heart failure during and after PCI in the two groups.

CONCLUSIONS

Brief intracoronary followed by continuous intravenous administration of landiolol is safe and effective for myocardial protection in the face of elective PCI.

Heart rate limitation and cardiac unloading in sevoflurane post-conditioning

BACKGROUND

Sevoflurane post-conditioning (SePost) has been found to alleviate ischemic myocardial reperfusion injury through the activation of prosurvival kinases. Lowered myocardial oxygen demand from reduced cardiac work may also contribute to cardioprotection, and is much less well-studied. Our aim was to examine the simultaneous effects of SePost on cardiac work (here, rate-pressure product, RPP) and myocardial infarct size in a porcine model.

METHODS

Anesthetized 25 kg pigs were randomly allocated to two groups and underwent 45 min regional coronary artery balloon occlusion and subsequent 2 h reperfusion. SePost (n = 10) was given as sevoflurane 1.5-3% end-tidal concentration during reperfusion while controls (n = 12) were untreated. Aortic blood pressure was measured directly, while mixed-venous oxygen saturation and cardiac output were measured in the pulmonary artery. Cardiac work was determined as RPP. Post-mortem, histologic myocardial infarct size (IS), and area at risk were determined in transverse heart slices after tetrazolium stain.

RESULTS

Myocardial infarct size was reduced from (control) 55.0 (mean) ± 13.6% (standard deviation) to 32.5 ± 13.4% in group SePost (P = 0.0009). During reperfusion, SePost resulted in lower heart rate (P = 0.0003), cardiac output (P = 0.0123), mixed-venous oxygen saturation (P = 0.0103), blood pressure, and RPP (P < 0.0001). RPP was highly correlated to IS (P = 0.0055).

CONCLUSION

SePost (1.5-3%) reduced infarct size after regional myocardial ischemia in vivo and reduced cardiac work was significantly correlated to myocardial salvage.

Costameric proteins: from benchside to future translational cardiovascular research

Costameres encircle the myocyte perpendicular to its long axis, and comprise two protein complexes: the dystrophin-glycoprotein complex (DGC) and the vinculin-talin-integrin system. They participate in signaling functions and protect muscle cells from damage induced by workload. The behaviour of those proteins has been a focus of study starting from skeletal and smooth muscle cells to cardiomyocytes, and still represents a topical subject for cardiovascular translational research. This review summarizes the past and present novel approaches of our and other groups of work on this subject of research.