Hui-Ming Guo

Oxidative Stress in Hypoxic-Ischemic Encephalopathy: Molecular Mechanisms and Therapeutic Strategies

Hypoxic-ischemic encephalopathy (HIE) is one of the leading causes of morbidity and mortality in neonates. Because of high concentrations of sensitive immature cells, metal-catalyzed free radicals, non-saturated fatty acids, and low concentrations of antioxidant enzymes, the brain requires high levels of oxygen supply and is, thus, extremely sensitive to hypoxia. Strong evidence indicates that oxidative stress plays an important role in pathogenesis and progression. Following hypoxia and ischemia, reactive oxygen species (ROS) production rapidly increases and overwhelms antioxidant defenses. A large excess of ROS will directly modify or degenerate cellular macromolecules, such as membranes, proteins, lipids, and DNA, and lead to a cascading inflammatory response, and protease secretion. These derivatives are involved in a complex interplay of multiple pathways (e.g., inflammation, apoptosis, autophagy, and necrosis) which finally lead to brain injury. In this review, we highlight the molecular mechanism for oxidative stress in HIE, summarize current research on therapeutic strategies utilized in combating oxidative stress, and try to explore novel potential clinical approaches.

Alpha1 catalytic subunit of AMPK modulates contractile function of cardiomyocytes through phosphorylation of troponin I

AIMS The specific role of AMPKα1 or AMPKα2 in mediating cardiomyocyte contractile function remains elusive. The present study investigated how AMPK activation modulates the contractility of isolated cardiomyocytes. MAIN METHODS Mechanical properties and intracellular Ca(2+) properties were measured in isolated cardiomyocytes. The stress signaling was evaluated using western blot and immunoprecipitation analysis. KEY FINDINGS AMPK activator, A-769662 induced maximal velocity of shortening (+dL/dt) and relengthening (-dL/dt), peak height and peak shortening (PS) amplitude in both WT and AMPKα2 KO cardiomyocytes, but did not affect time-to-90% relengthening (TR90). AMPK KD cardiomyocytes demonstrated contractile dysfunction compared with cardiomyocytes from WT and AMPKα2 KO hearts. However, the rise of intracellular Ca(2+) levels as well as intracellular ATP levels has no significant difference among WT, AMPKα2 KO and AMPK KD groups with and without the presence of A-769662. Besides, WT, AMPKα2 KO and AMPK KD group displayed a phosphorylated AMPK and downstream acetyl-CoA carboxylase (ACC) phosphorylation. Interestingly, A-769662 also triggered troponin I (cTnI) phosphorylation at Ser(149) site which is related to contractility of cardiomyocytes. Furthermore, the immunoprecipitation analysis revealed that AMPKα1 of cardiomyocytes was phosphorylated by A-769662. SIGNIFICANCE This is the first study illustrating that activation of AMPK plays a significant role in mediating the contractile function of cardiomyocytes using transgenic animal models. AMPK activator facilitates the contractility of cardiomyocytes via activating AMPKα1 catalytic subunit. The phosphorylation of cTnI by AMPK could be a factor attributing to the regulation of contractility of cardiomyocytes.

The protective effect of trimetazidine on myocardial ischemia/reperfusion injury through activating AMPK and ERK signaling pathway

INTRODUCTION Trimetazidine (TMZ) is an anti-anginal drug that has been widely used in Europe and Asia. The TMZ can optimize energy metabolism via inhibition of long-chain 3-ketoacyl CoA thiolase (3-KAT) in the heart, with subsequent decrease in fatty acid oxidation and stimulation of glucose oxidation. However, the mechanism by which TMZ aids in cardioprotection against ischemic injury has not been characterized. AMP-activated protein kinase (AMPK) is an energy sensor that controls ATP supply from substrate metabolism and protects heart from energy stress. TMZ changes the cardiac AMP/ATP ratio by modulating fatty acid oxidation, thereby triggering AMPK signaling cascade that contributes to the protection of the heart from ischemia/reperfusion (I/R) injury. METHODS The mouse model of in vivo regional ischemia and reperfusion by the ligation of the left anterior descending coronary artery (LAD) was used for determination of myocardial infarction. The infarct size was compared between C57BL/6J WT mice and AMPK kinase dead (KD) transgenic mice with or without TMZ treatment. The ex vivo working heart perfusion system was used to monitor the effect of TMZ on glucose oxidation and fatty acid oxidation in the heart. RESULTS TMZ treatment significantly stimulates cardiac AMPK and extracellular signal-regulated kinase (ERK) signaling pathways (p<0.05 vs. vehicle group). The administration of TMZ reduces myocardial infarction size in WT C57BL/6J hearts, the reduction of myocardial infarction size by TMZ in AMPK KD hearts was significantly impaired versus WT hearts (p<0.05). Intriguingly, the administration of ERK inhibitor, PD98059, to AMPK KD mice abolished the cardioprotection of TMZ against I/R injury. The ex vivo working heart perfusion data demonstrated that TMZ treatment significantly activates AMPK signaling and modulating the substrate metabolism by shifting fatty acid oxidation to glucose oxidation during reperfusion, leading to reduction of oxidative stress in the I/R hearts. Therefore, both AMPK and ERK signaling pathways mediate the cardioprotection of TMZ against ischemic injury. The metabolic benefits of TMZ for angina patients could be due to the activation of energy sensor AMPK in the heart by TMZ administration.

Natural Antioxidant-Isoliquiritigenin Ameliorates Contractile Dysfunction of Hypoxic Cardiomyocytes via AMPK Signaling Pathway

Isoliquiritigenin (ISL), a simple chalcone-type flavonoid, is derived from licorice compounds and is mainly present in foods, beverages, and tobacco. Reactive oxygen species (ROS) is a critical factor involved in modulating cardiac stress response signaling during ischemia and reperfusion. We hypothesize that ISL as a natural antioxidant may protect heart against ischemic injury via modulating cellular redox status and regulating cardioprotective signaling pathways. The fluorescent probe H2DCFDA was used to measure the level of intracellular ROS. The glucose uptake was determined by 2-deoxy-D-glucose-3H accumulation. The IonOptix System measured the contractile function of isolated cardiomyocytes. The results demonstrated that ISL treatment markedly ameliorated cardiomyocytes contractile dysfunction caused by hypoxia. ISL significantly stimulated cardioprotective signaling, AMP-activated protein kinase (AMPK), and extracellular signal-regulated kinase (ERK) signaling pathways. The ROS fluorescent probe H2DCFDA determination indicated that ISL significantly reduced cardiac ROS level during hypoxia/reoxygenation. Moreover, ISL reduced the mitochondrial potential (Δψ) of isolated mouse cardiomyocytes. Taken together, ISL as a natural antioxidant demonstrated the cardioprotection against ischemic injury that may attribute to the activation of AMPK and ERK signaling pathways and balance of cellular redox status.

Influence of sirolimus-induced TGF-β secretion on mouse Treg cell proliferation

We examined the effects of co-culturing CD4+ CD25+ Treg cells with sirolimus or cyclosporin A on Treg cell proliferation and differentiation and on transforming growth factor-β (TGF-β) and Foxp3 expression. CD4+ CD25+ Treg cells were harvested from mononuclear cells of spleens of C57BL/6 mice using immunomagnetic beads and divided into control, sirolimus, and cyclosporine groups. Following a 96-h co-culture, Treg cells were assayed by flow cytometry. FoxP3 and TGF-β mRNA levels and secretion were assayed by reverse transcription polymerase chain reaction and enzyme-linked immunosorbent assay. Smad protein of the TGF-β signaling pathway was assayed by western blot and its effect on CD4+ CD25+ FoxP3+ Treg cell proliferation was determined. Sirolimus-promoted differentiation and proliferation was examined using a TGF-β neutralizing antibody. Sirolimus-treated CD4+ T cell TGF-β secretion increased 2.5X over control levels (P < 0.01), but that of the cyclosporine group decreased marginally (P > 0.05). The CD4+ cell proportion decreased significantly (41.25 vs 69.22%, P < 0.01) and slightly (65.21 vs 69.22, P > 0.05) in the cyclosporine and sirolimus groups, respectively. T cell Foxp3 mRNA expression was significantly higher in the sirolimus-treated than in the cyclosporine (53.7 vs 40.2%, P < 0.05) and control groups (P < 0.01), but was significantly lower in the cyclosporine group than in controls (23.6 vs 40.2%, P < 0.01). Overall, sirolimus promoted CD4+ CD25+ Treg cell proliferation and growth in vitro, whereas cyclosporin A inhibited proliferation. Sirolimus might promote CD4+ CD25+ FoxP3+ regulatory T cell proliferation by inducing TGF-β secretion in vivo.

Effect of low temperatures on BAX and BCL2 proteins in rats with spinal cord ischemia reperfusion injury.

We evaluated changes in BAX and BCL2 expression levels after spinal cord ischemia/reperfusion injury (SCII) and hypothermia during operations in rats. Eighty rats were divided into four groups: Group A (N = 20, 18°C); Group B (N = 20, 28°C); Group C (N = 20, room temperature); and Group D (N = 20, sham operation control). Spinal cord ischemia was induced for 90 min. Hypothermia was induced 15 min before, and maintained during ischemia, followed by heating to normothermia for 30 min after reperfusion. Motor function of the lower limbs was evaluated according to the Tarlov score at 72 and 168 h. For each rat, spinal cord samples were taken at 6, 24, 72 h, and 1 week to evaluate the histopathological changes, neuronal apoptosis, and BAX and BCL2 expression levels. Compared with normothermia, hypothermia significantly improved hind limb function; Group B achieved a higher score than Group A. Group D showed no neurologic deficiency, while the other groups showed various degrees. Group C exhibited greater neuronal apoptosis, higher BAX expression, but lower BCL2 expression than the other groups. Compared with Group A, BAX was expressed less and BCL2 more in Group B, and there was less apoptosis in Group B. Hypothermia preserves hind limb motor function and reduces neuronal death, thereby protecting rats from SCII. The spinal cord may be protected from SCII by inhibition of BAX and activation of BCL2. However, deep hypothermia may inhibit the expression of BCL2, resulting in a worse outcome than mild hypothermia.

Long-Term Clinical Outcomes of the Carpentier-Edwards Perimount Pericardial Bioprosthesis in Chinese Patients with Single or Multiple Valve Replacement in Aortic, Mitral, or Tricuspid Positions

Objectives: To report the safety and efficacy results of a 9- to 15-year follow-up investigation among patients who had received Carpentier-Edwards Perimount (CE-P) bovine pericardial bioprostheses (Edwards Lifesciences, Irvine, CA, USA) for valve replacement. Methods: This retrospective study investigated freedom from structural valve deterioration (SVD) as well as survival and reoperation among different age and etiology groups in patients who were implanted with a CE-P bioprosthesis at Guangdong General Hospital between 2001 and 2007. Kaplan-Meier survival analysis and multivariate Cox proportional hazards regression were performed. Results: The mean age of the patients (N = 225) was only 61.2 ± 11.5 years at valve replacement. More than half of the patients (55.1%) had rheumatic heart disease. The survival rates were 86.46, 81.58, and 74.42% at 5 years, 64.39, 66.19, and 55.85% at 10 years, and 48.37, 57.33, and 46.54% at 15 years for the groups with mitral valve replacement (MVR), aortic valve replacement (AVR), and double valve replacement (DVR), respectively. The median time to freedom from SVD was 12.5, 13.2, and 11.2 years, respectively, for patients with MVR, AVR, and DVR. A higher age at valve replacement was a significant risk factor for SVD in all patients (p < 0.01). Conclusions: Good long-term clinical results of CE-P valves have been demonstrated in Chinese patients >60 years.

Giant Left Ventricular Myxoma With Obstruction of the Left Ventricular Outflow Tract

A rare case of giant left ventricular (LV) myxoma with obstruction of the left ventricular outflow tract (LVOT) was found incidentally on echocardiography in an asymptomatic 21-year-old woman. The tumor was successfully resected through transatrial septal access.

Surgical ablation for persistent atrial fibrillation in concomitant cardiac surgery: mid-long-term result

OBJECTIVES Surgical ablation is an option for patients with atrial fibrillation (AF) undergoing concomitant cardiac surgery. This study aims to evaluate the outcome of surgical ablation during concomitant cardiac surgery and to identify the independent predictors for a primary end-point consisting of AF or atrial flutter (AFL) recurrence, death, permanent pacemaker implantation and necessity for anti-arrhythmic drugs and the effects of reintervention for AF/AFL recurrence. METHODS A retrospective analysis was performed for 1028 patients who underwent surgical ablation during concomitant cardiac surgery from October 2004 to April 2015. Nine hundred and twenty-seven of 1017 (91.2%) discharged patients were followed up. Sixty-three recurrent patients received reintervention. Predictors of ablation failure were identified using univariate analysis and the Cox regression model. RESULTS The mean follow-up length was 29.0 ± 22.7 months. The New York Heart Association class, ejection fraction, left atrial and right atrial diameters and left ventricular end-diastolic diameter were improved at follow-up compared with the preoperative status. The rate of freedom from the primary end-point at 1, 2 and 3 years was 86.8, 79.4 and 68.3%. Independent predictors of reaching the primary end-point were AF/AFL at discharge, preoperative right atrial diameter, hypertension, diabetes and smoking. The rate of sinus rhythm without anti-arrhythmic drugs at 12, 24 and 36 months after reintervention was 78.3, 62.8 and 49.9%, respectively. CONCLUSIONS Surgical ablation has a high success rate and may improve cardiac function postoperatively. AF/AFL at discharge, preoperative right atrial diameter, hypertension, diabetes and smoking are the major independent predictors for ablation failure. Reintervention in AF/AFL recurrent patients can achieve a favourable clinical outcome.

Surgical Treatment of Giant Left Atrial Diverticulum in an Adult

Giant left atrial diverticulum is a rare congenital abnormality that is most commonly diagnosed in childhood. Here, we report the case of an 18-year-old woman who presented with chest tightness. Contrast-enhanced computed tomography imaging revealed a 12-cm×7-cm left atrial diverticulum. After transesophageal echocardiography was used to exclude left atrial thrombus and mitral regurgitation, an isolated left atrial diverticulum resection was performed. The patient had an uneventful recovery.