Reduced Cell Excitability of Cardiac Postganglionic Parasympathetic Neurons Correlates With Myocardial Infarction-Induced Fatal Ventricular Arrhythmias in Type 2 Diabetes Mellitus

Hydrogen Peroxide-Induced Re-Expression of Repressor Element 1-Silencing Transcription Factor Contributes to Cardiac Vagal Dysfunction in Type 2 Diabetes Mellitus

Diabetes mellitus, especially type 2 diabetes mellitus (T2DM), is a major health problem worldwide and has become a leading cause of mortality. As a common complication of patients with T2DM, cardiac autonomic dysfunction (including sympathetic overactivation and reduced vagal tone) is associated with a higher risk of arrhythmia-related sudden cardiac death. Our previous study found that T2DM-elevated hydrogen peroxide (H2O2) levels in atrioventricular ganglion (AVG) neurons contribute to the decrease in cardiac vagal function and ventricular arrhythmogenesis through inhibition of N-type Ca2+ channels (Cav2.2). In the present study, treatment with exogenous H2O2 in differentiated NG108-15 cells increased REST expression and decreased Cav2.2-α expression. Adenoviral catalase gene transfection into the AVG neurons significantly reduced the REST levels elevated by a high-fat diet plus streptozotocin-induced T2DM. Lentiviral REST shRNA transfection markedly increased Cav2.2-α expression in the AVG neurons from T2DM rats. REST shRNA also activated N-type Ca2+ channels and increased cell excitability of AVG neurons in T2DM rats. Additionally, REST shRNA markedly improved cardiac vagal activation in T2DM rats. The present study suggests that the H2O2-REST-Cav2.2 channel signaling axis could be a potential therapeutic target to normalize cardiac vagal dysfunction and its related cardiac complications in T2DM.

Altered leptin signaling and attenuated cardiac vagal activity in rats with type 2 diabetes

Introduction

The leading cause of death in type 2 diabetes mellitus (T2DM) patients is cardiovascular-related events, including myocardial infraction-induced ventricular arrhythmia. Previous studies have shown that T2DM-induced functional remodeling of cardiac vagal postganglionic (CVP) neurons contributes to ventricular arrhythmogenesis. As leptin resistance is common in T2DM patients, and CVP neurons are located in epicardial adipose pads, a tissue that secretes leptin, in this study we aimed to elucidate a correlation between leptin resistance and CVP neuronal dysfunction in T2DM.

Methods

A high fat-diet/low dose streptozotocin-induced T2DM rat model was used in this study to characterize T2DM-induced alterations in cardiac parasympathetic tone, determined by changes in baroreflex sensitivity and CVP neuronal excitability. The impact of leptin resistance on CVP neurons was also studied by examining the expression of leptin in epicardial adipose pads, and leptin receptors and uncoupling protein 2 (UCP2) in CVP neurons.

Results

T2DM rats exhibited diminished baroreflex sensitivity, and decreased CVP neuronal excitability, demonstrated by a reduced frequency of action potentials, diminished nAChR currents, and an attenuated response to nicotine stimulation. Additionally, compared to sham animals, the expression of leptin receptors and UCP2 in CVP neurons was reduced as early as 4 weeks post-T2DM although the leptin levels in epicardial adipose pads was increased during the progression of T2DM, which demonstrated the occurrence of leptin resistance in T2DM CVP neurons.

Conclusion

Cardiac parasympathetic dysfunction in T2DM rats is due, in part, to functional remodeling of CVP neurons. As leptin resistance develops as early as 4 weeks post-T2DM induction, diminished leptin receptors-UCP2 signaling may contribute to CVP neuronal dysregulation.

Remodeling of the Intracardiac Ganglia During the Development of Cardiovascular Autonomic Dysfunction in Type 2 Diabetes: Molecular Mechanisms and Therapeutics

Type 2 diabetes mellitus (T2DM) is one of the most significant health issues worldwide, with associated healthcare costs estimated to surpass USD 1054 billion by 2045. The leading cause of death in T2DM patients is the development of cardiovascular disease (CVD). In the early stages of T2DM, patients develop cardiovascular autonomic dysfunction due to the withdrawal of cardiac parasympathetic activity. Diminished cardiac parasympathetic tone can lead to cardiac arrhythmia-related sudden cardiac death, which accounts for 50% of CVD-related deaths in T2DM patients. Regulation of cardiovascular parasympathetic activity is integrated by neural circuitry at multiple levels including afferent, central, and efferent components. Efferent control of cardiac parasympathetic autonomic tone is mediated through the activity of preganglionic parasympathetic neurons located in the cardiac extensions of the vagus nerve that signals to postganglionic parasympathetic neurons located in the intracardiac ganglia (ICG) on the heart. Postganglionic parasympathetic neurons exert local control on the heart, independent of higher brain centers, through the release of neurotransmitters, such as acetylcholine. Structural and functional alterations in cardiac parasympathetic postganglionic neurons contribute to the withdrawal of cardiac parasympathetic tone, resulting in arrhythmogenesis and sudden cardiac death. This review provides an overview of the remodeling of parasympathetic postganglionic neurons in the ICG, and potential mechanisms contributing to the withdrawal of cardiac parasympathetic tone, ventricular arrhythmogenesis, and sudden cardiac death in T2DM. Improving cardiac parasympathetic tone could be a therapeutic avenue to reduce malignant ventricular arrhythmia and sudden cardiac death, increasing both the lifespan and improving quality of life of T2DM patients.

A New Scoring System for Predicting Ventricular Arrhythmia Risk in Patients with Acute Myocardial Infarction

Objective

In this study, a risk score for ventricular arrhythmias (VA) were evaluated for predicting the risk of ventricular arrhythmia (VA) of acute myocardial infarction (AMI) patients.

Methods

Patients with AMI were divided into two sets according to whether VA occurred during hospitalization. Another cohort was enrolled for external validation. The area under the curve (AUC) of receiver operating characteristic (ROC) was calculated to evaluate the accuracy of the model.

Results

A total of 1493 eligible patients with AMI were enrolled as the training set, of whom 70 (4.7%) developed VA during hospitalization. In-hospital mortality was significantly higher in the VA set than in the non-VA set (31.4% vs 2.7%, P=0.001). The independent predictors of VA in patients with AMI including Killip grade ≥3, STEMI patients, LVEF <50%, frequent premature ventricular beats, serum potassium <3.5 mmol/L, type 2 diabetes, and creatinine level. The AUC of the model for predicting VT/VF in the training set was 0.815 (95% CI: 0.763-0.866). A total of 1149 cases were enrolled from Xuzhou Center Hospital as the external validation set. The AUC of the model in the external validation set for predicting VT/VF was 0.755 (95% CI: 0.687-0.823). Calibration curves indicated a good consistency between the predicted and the observed probabilities of VA in both sets.

Conclusion

We have established a clinical prediction risk score for predicting the occurrence of VA in AMI patients. The prediction score is easy to use, performs well and can be used to guide clinical practice.

Hydrogen Peroxide Scavenging Restores N-Type Calcium Channels in Cardiac Vagal Postganglionic Neurons and Mitigates Myocardial Infarction-Evoked Ventricular Arrhythmias in Type 2 Diabetes Mellitus

Objective

Withdrawal of cardiac vagal activity is associated with ventricular arrhythmia-related high mortality in patients with type 2 diabetes mellitus (T2DM). Our recent study found that reduced cell excitability of cardiac vagal postganglionic (CVP) neurons is involved in cardiac vagal dysfunction and further exacerbates myocardial infarction (MI)-evoked ventricular arrhythmias and mortality in T2DM. However, the mechanisms responsible for T2DM-impaired cell excitability of CVP neurons remain unclear. This study tested if and how elevation of hydrogen peroxide (H2O2) inactivates CVP neurons and contributes to cardiac vagal dysfunction and ventricular arrhythmogenesis in T2DM.

Methods and Results

Rat T2DM was induced by a high-fat diet plus streptozotocin injection. Local in vivo transfection of adenoviral catalase gene (Ad.CAT) successfully induced overexpression of catalase and subsequently reduced cytosolic H2O2 levels in CVP neurons in T2DM rats. Ad.CAT restored protein expression and ion currents of N-type Ca2+ channels and increased cell excitability of CVP neurons in T2DM. Ad.CAT normalized T2DM-impaired cardiac vagal activation, vagal control of ventricular function, and heterogeneity of ventricular electrical activity. Additionally, Ad.CAT not only reduced the susceptibility to ventricular arrhythmias, but also suppressed MI-evoked lethal ventricular arrhythmias such as VT/VF in T2DM.

Conclusions

We concluded that endogenous H2O2 elevation inhibited protein expression and activation of N-type Ca2+ channels and reduced cell excitability of CVP neurons, which further contributed to the withdrawal of cardiac vagal activity and ventricular arrhythmogenesis in T2DM. Our current study suggests that the H2O2-N-type Ca2+ channel signaling axis might be an effective therapeutic target to suppress ventricular arrhythmias in T2DM patients with MI.