Xiaorong Hu

Minocycline protects against myocardial ischemia and reperfusion injury by inhibiting high mobility group box 1 protein in rats

Minocycline has been shown to protect against myocardial ischemia and reperfusion injury. However, the mechanism remains unclear. This study was to investigate the role of high mobility group box 1 protein (HMGB1) in the cardioprotection of minocycline during myocardial ischemia and reperfusion in rats. Anesthetized male rats were once treated with minocycline (45 mg/kg, i.p.) 1h before ischemia, and then subjected to ischemia for 30 min followed by reperfusion for 4h. The lactate dehydrogenase (LDH), creatine kinase (CK) and infarct size were measured and the myocardial tissue apoptosis was assessed by TUNNEL assay. Neonatal rat ventricular myocytes were prepared and then cultured with recombinant HMGB1. Cell apoptosis was measured using an annexin V-FITC apoptosis detection kit. HMGB1 expression was assessed by immunoblotting. After 4h of reperfusion, minocycline could significantly decrease the infarct size, myocardium apoptosis and the levels of LDH and CK (all P<0.05). Meanwhile, minocycline could also significantly inhibit the HMGB1 expression during myocardial ischemia and reperfusion compared to that in ischemia and reperfusion group (P<0.05). In vitro, HMGB1 could significantly decrease the cell viability and promote the apoptosis of neonatal myocytes in a dose-dependent manner. The present study suggested that minocycline could protect against myocardial ischemia and reperfusion injury by inhibiting HMGB1 expression.

Increased serum HMGB1 is related to the severity of coronary artery stenosis

BACKGROUND High mobility group box 1 (HMGB1) protein has been identified as a novel pro-inflammatory cytokine in coronary artery disease (CAD). We investigated the relationship between serum HMGB1 level and the severity of coronary artery stenosis. METHODS Serum HMGB1 concentration in patients was measured by ELISA. All patients underwent coronary angiography and were assigned into groups according to the quartile of HMGB1 level. RESULTS HMGB1 level in USAP group was higher than that in control and SAP group. HMGB1 level in SAP group was higher than that in control group (p<0.05). Gensini scores in the highest quartile group (group IV), group III and group II were all significantly higher than that in the lowest quartile group (group I). There was significant correlation between angiographic Gensini score and serum level of HMGB1 (r=0.710, p<0.05). However, in subgroup analysis, we found that serum HMGB1 level was only correlated with angiographic Gensini score in SAP patients (r=0.786, p<0.05), but not USAP patients. CONCLUSIONS Serum HMGB1 level was markedly increased with the severity of coronary artery stenosis in patients with SAP and USAP, especially in SAP patients, which suggested that increased serum HMGB1 may involve in the pathogenesis of atherosclerotic CAD.

Low testosterone level in middle-aged male patients with coronary artery disease

BACKGROUND Endogenous testosterone has been shown to provide a protective role in the development of cardiovascular diseases in men. This study investigated the changes of testosterone level and its relationship to the severity of coronary artery stenosis in middle-aged men with coronary artery disease (CAD). METHODS Serum testosterone concentration was measured in 87 middle-aged men patients with CAD including stable angina pectoris (SAP), unstable angina pectoris (USAP) and acute myocardial infarction (AMI). All patients underwent coronary angiography and the severity of coronary stenosis was estimated by the Gensini coronary score. The patients with the severity of coronary artery stenosis of less than 50% served as control group. RESULTS The levels of testosterone in SAP group (488.2 ± 96.8ng/dl), USAP group (411.6 ± 128.6ng/dl) and AMI group (365.3 ± 116.6ng/dl) were significantly lower than that in control group (562.8 ± 110.2ng/dl) (all p<0.05). When compared with another group among SAP, USAP and AMI groups, the level of testosterone in the AMI group was the lowest, the USAP group was the median while the SAP group was the highest (all p<0.05). There was a significant correlation between angiographic Gensini score and testosterone level (n=87, r=-0.513, p<0.05). Multiple regression analysis found that testosterone and BMI were independent predictors for CAD (testosterone: odds ratio 0.311, 95% confidence interval 0.174-0.512; BMI: odds ratio 1.905, 95% confidence interval 1.116-2.973). CONCLUSION The present study showed that middle-aged male patients with CAD present a lower level of serum testosterone and the testosterone level was negatively correlated with the severity of coronary artery stenosis.

Effects of ganglionated plexi ablation on ventricular electrophysiological properties in normal hearts and after acute myocardial ischemia

BACKGROUND Ganglionated plexi (GP) ablation has been shown to play an important role in atrial fibrillation (AF) initiation and maintenance. Also, GP ablation increases chances for prevention of AF recurrence. This study investigated the effects of GP ablation on ventricular electrophysiological properties in normal dog hearts and after acute myocardial ischemia (AMI). METHODS Fifty anesthetized dogs were assigned into normal heart group (n=16) and AMI heart group (n=34). Ventricular dynamic restitution, effective refractory period (ERP), electrical alternans and ventricular fibrillation threshold (VFT) were measured before and after GP ablation in the normal heart group. In the AMI heart group, the incidence of ventricular arrhythmias and VFT were determined. RESULTS In the normal heart group, GP ablation significantly prolonged ERP, facilitated electrical alternans but did not increase ERP dispersion, the slope of restitution curves and its spatial dispersion. Also, GP ablation did not cause significant change of VFT. In the AMI heart group, the incidence of ventricular arrhythmias after GP ablation was significantly higher than that in the control group or the GP plus stellate ganglion (SG) ablation group (P<0.05). Spontaneous VF occurred in 8/12, 1/10 and 2/12 dogs in the GP ablation group, the GP plus SG ablation group and the control group, respectively (P<0.05). VFT in the GP ablation group showed a decreased trend though a significant difference was not achieved compared with the control or the GP plus SG ablation group. CONCLUSIONS GP ablation increases the risk of ventricular arrhythmias in the AMI heart compared to the normal heart.

Beta-1-adrenergic receptors mediate Nrf2-HO-1-HMGB1 axis regulation to attenuate hypoxia/reoxygenation-induced cardiomyocytes injury in vitro.

Backgroud/Aims: The aim of the study was to evaluate the effects of beta1-adrenergic receptors (β1-ARs) -mediated nuclear factor erythroid 2-related factor 2 (Nrf2)-heme oxygenase-1 (HO-1)-high mobility group box 1 protein (HMGB1) axis regulation in hypoxia/reoxygenation (H/R)-induced neonatal rat cardiomyocytes. Methods: The neonatal cultured cardiomyocytes were concentration-dependently pretreated by dobutamine (DOB), a selective β1-adrenergic receptor agonist, in the absence and/or presence of LY294002 (a phosphatidylinositol 3-kinase (PI3K) inhibitor), SB203580 (a p38mitogen-activated-protein kinase (p38MAPK) inhibitor), Nrf2siRNA and HO-1siRNA, respectively, and then treated by H/R. The effects and mechanisms by which H/R-induced cardiomyocytes injury were evaluated. Results: Significant increase of HO-1 was found in neonatal cultured cardiomyocytes treated with DOB, when compared to the control group. Significant change for Nrf2 translocation was also revealed in neonatal cultured cardiomyocytes treated with DOB. Insignificant decreases of NF-kappaB p65 activation and HMGB1 release were observed in H/R-induced neonatal cultured cardiomyocytes treated with DOB, when compared to the control group. Importantly, DOB treatment significantly increased the cell viability and decreased the levels of LDH and MDA in H/R-induced cardiomyocytes injury. However, DOB failed to increase HO-1, inhibit NF-kappaB p65 activation, prevent HMGB1 release and attenuate H/R-induced cardiomyocytes injury when the cultured cardiomyocytes were pretreated by Nrf2siRNA, HO-1siRNA, PI3K inhibitor (LY294002) and p38MAPK inhibitor (SB203580), respectively. Conclusions: β1-ARs-mediated Nrf2-HO-1-HMGB1 axis regulation plays a critical protective role in H/R-induced neonatal rat cardiomyocytes injury in vitro via PI3K/p38MAPK signaling pathway.

HMGB1: A potential therapeutic target for myocardial ischemia and reperfusion injury

Myocardial ischemia and reperfusion (I/R) injury is well known in therapy for acute coronary syndrome and open heart surgery. Although reperfusion therapy (such as thrombolysis and percutaneous coronary intervention) is essential for the survival of ischemic tissue, reperfusion itself causes additional cellular injury. I/R could cause local myocardial inflammation, accompanying with apoptosis, which could result in myocardial cell damage [1]. High mobility group box 1 protein (HMGB1), a highly conserved nuclear protein, could regulate gene transcription and maintain the nucleosome structure. HMGB1 could be passively released fromnecrotic cell, apoptotic cell or actively secreted by innate immune cells (such as macrophages and monocytes) [2,3]. Recently, a present study shows that HMGB1 acts as a novel early mediator of inflammation and participates in the pathogenesis of myocardial I/R injury, and HMGB1 could promote the release of tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6), whereas HMGB1 A box peptide (a specific HMGB1 antagonist) could reduce myocardial ischemia and reperfusion injury and inhibit the release of TNF-α and IL-6 [4]. Meanwhile, lots of drugs have been found to reduce myocardial I/R injury by inhibiting HMGB1 expression, including asperosaponin X [5], minocycline [6], ethyl pyruvate, [7] etc. These suggested that HMGB1 may play an important role in myocardial I/R injury and inhibiting HMGB1 could reduce myocardial I/R injury. There was a cross-talk between HMGB1 and other proinflammatory cytokines, such as TNF-α, IL-6 and C-reactive protein (CRP) [4,8,9]. Once released from necrotic cell, apoptotic cell or macrophages, HMGB1 functions as a proinflammatory stimulus that upregulates TNF-α, IL-6, CRP and macrophage inflammatory proteins (MIP-1α andMIP-1β) [8,9], indicating that this mechanism reinforced the inflammatory process. As inflammation plays a critical role in myocardial I/R injury [1]. Thus, inhibiting HMGB1 expression could suppress inflammation and reduce myocardial I/R injury. Jiang et al. [5] show that treatment of asperosaponin X could protect the rats from myocardial I/R injury and lower HMGB1 and other proinflammatory cytokines; meanwhile, asperosaponin X could attenuate hypoxia-induced cytotoxicity and block TNF-α-induced HMGB1 expression in vivo. These results further suggested that inhibiting HMGB1 expression by asperosaponin X could protect heart against myocardial I/R injury. In conclusion, HMGB1may be a critical mediator for myocardial I/R injury and a potential therapeutic target for myocardial I/R injury. Inhibiting HMGB1 expression may reduce myocardial I/R injury. This study was partially supported by a grant from the National Natural Science Foundation of China (No. 81100146), grant 111023 from the Fundamental Research Funds for the Central Universities and the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20110141120060). The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology (Shewan and Coats 2010; 144: 1–2).

Anti‑inflammatory effect of sodium butyrate preconditioning during myocardial ischemia/reperfusion

High mobility group box 1 protein (HMGB1) has an important role in myocardial ischemia/reperfusion (I/R) injury. Sodium butyrate, an inhibitor of histone deacetylase, has been shown to inhibit HMGB1 expression. In the present study, the effect of sodium butyrate on myocardial I/R injury in rats was investigated. Anesthetized male rats were intraperitoneally administered sodium butyrate (100 or 300 mg/kg) 30 min prior to the induction of ischemia. The rats were then subjected to ischemia for 30 min followed by reperfusion for 4 h. Infarct size, lactate dehydrogenase (LDH), creatine kinase (CK) and superoxide dismutase (SOD) activity and malondialdehyde (MDA) levels were then measured. The expression of HMGB1 was assessed using western blot analysis. The results demonstrated that pretreatment with sodium butyrate (300 mg/kg) significantly reduced the infarct size, as well as the levels of LDH and CK (P<0.05). In addition, sodium butyrate (300 mg/kg) was shown to significantly inhibit the I/R-induced increase in the level of MDA and reduction in the level of SOD (P<0.05). Furthermore, treatment with sodium butyrate (300 mg/kg) was found to significantly inhibit the expression of TNF-α, IL-6 and HMGB1 induced by I/R injury (P<0.05). In conclusion, the results from the present study suggest that preconditioning with sodium butyrate may attenuate myocardial I/R injury by inhibition of the expression of inflammatory mediators during myocardial I/R.

Preconditioning with high mobility group box 1 protein protects against myocardial ischemia–reperfusion injury

Abstract Objective To investigate whether preconditioning with high mobility group box 1 protein (HMGB1) could reduce myocardial ischemia–reperfusion (I/R) injury. Methods and results Infarct size, lactate dehydrogenase (LDH), creatine kinase (CK), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were assessed. HMGB1 preconditioning reduced significantly the infarct size induced by I/R. The LDH, CK, TNF-α and IL-6 levels were significantly decreased by HMGB1 preconditioning compared to those in the I/R group. Conclusion The present study suggested that preconditioning with HMGB1 could induce HMGB1 tolerance and protect against myocardial I/R injury.

Effects of Sympathetic Nerve Stimulation on Ischemia-induced Ventricular Arrhythmias by Modulating Connexin43 in Rats

BACKGROUND Increased cardiac sympathetic nerve activity is thought to contribute to ventricular tachyarrhythmias during acute myocardial ischemia (MI). However, the mechanism is not completely understood. This study investigated the effects of sympathetic nerve stimulation (SNS) on ventricular tachyarrhythmias and connexin43 (Cx43) during acute MI in rats. METHODS Ninety five male Wistar rats were randomly assigned into four groups receiving the following treatments: myocardial ischemia with sympathetic nerve stimulation (MI-SNS, n=25), sham-operation treated with sham stimulation (SO, n=20), myocardial ischemia with sham stimulation (MI, n=25), myocardial ischemia pretreated with sympathetic nerve stimulation (pSNS-MI, n=25). RESULTS During the 30-min ischemia, the incidence of ventricular tachyarrhythmias, i.e., ventricular tachycardia or ventricular fibrillation (VT/VF) was increased in the MI-SNS group and decreased in the pSNS-MI group compared to that in the MI group (p<0.05 for both). The total amount of Cx43 protein was significantly decreased in the MI-SNS group but not in the MI group and the pSNS-MI group. The amount of phosphorylated Cx43 in the MI-SNS group was significantly lower compared to that in the SO group and the MI group (p<0.05). However, the amount of phosphorylated Cx43 was significantly increased in the pSNS-MI group compared to that in the MI group and the MI-SNS group (p<0.05). CONCLUSIONS SNS promoted the degradation of Cx43 protein, especially the phosphorylated Cx43 protein, whereas pSNS inhibited the ischemia-induced loss of phosphorylated Cx43 during acute MI. These changes may be related to the pro- or anti-arrhythmic effect of SNS or pSNS during acute MI.

Exogenous High-Mobility Group Box 1 Protein Injection Improves Cardiac Function after Myocardial Infarction: Involvement of Wnt Signaling Activation

Exogenous high-mobility group box 1 protein (HMGB1) injection could prevent left ventricular remodeling and enhance left ventricular function during myocardial infarction (MI). However, the mechanism remains unclear. This paper was to investigate in the mechanism of cardioprotection of HMGB1 during MI in rats. Anesthetized male rats were treated once with HMGB1 (200 ng) 4 h after MI and then executed after 7 and 28 days, respectively. Cardiac function, collagen deposition, and dishevelled-1 and β-catenin protein expression were measured. After MI 7 days or 28 days, the left ventricular ejection fraction (LVEF) was significantly decreased compared to that of sham-operated control group (P < 0.05). However, the LVEF HMGB1-treated groups were significantly higher compared to those of the MI group in both 7 days and 28 days (P < 0.05). The collagen volume fraction was significantly reduced in the HMGB1-treated group in infarcted border zone. HMGB1 could activate the expression of dishevelled-1 and β-catenin proteins (P < 0.05). Our study suggested that exogenous high-mobility group box 1 protein injection improves cardiac function after MI, which may be involved in Wnt/β-catenin signaling activation.