Cardiac sympathoexcitation in heart failure

Muscarinic and nicotinic receptors stimulation by vagus nerve stimulation ameliorates trastuzumab-induced cardiotoxicity via reducing programmed cell death in rats

Despite its efficacy in human epidermal growth factor receptor 2 positive cancer treatment, trastuzumab-induced cardiotoxicity (TIC) has become a growing concern. Due to the lack of cardiomyocyte regeneration and proliferation in adult heart, cell death significantly contributes to cardiovascular diseases. Cardiac autonomic modulation by vagus nerve stimulation (VNS) has shown cardioprotective effects in several heart disease models, while the effects of VNS and its underlying mechanisms against TIC have not been found. Forty adult male Wistar rats were divided into 5 groups: (i) control without VNS (CSham) group, (ii) trastuzumab (4 mg/kg/day, i.p.) without VNS (TSham) group, (iii) trastuzumab + VNS (TVNS) group, (iv) trastuzumab + VNS + mAChR blocker (atropine; 1 mg/kg/day, ip, TVNS + Atro) group, and (v) trastuzumab + VNS + nAChR blocker (mecamylamine; 7.5 mg/kg/day, ip, TVNS + Mec) group. Our results showed that trastuzumab induced cardiac dysfunction by increasing autonomic dysfunction, mitochondrial dysfunction/dynamics imbalance, and cardiomyocyte death including apoptosis, autophagic deficiency, pyroptosis, and ferroptosis, which were notably alleviated by VNS. However, mAChR and nAChR blockers significantly inhibited the beneficial effects of VNS on cardiac autonomic dysfunction, mitochondrial dysfunction, cardiomyocyte apoptosis, pyroptosis, and ferroptosis. Only nAChR could counteract the protective effects of VNS on cardiac mitochondrial dynamics imbalance and autophagy insufficiency. Therefore, VNS prevented TIC by rebalancing autonomic activity, ameliorating mitochondrial dysfunction and cardiomyocyte death through mAChR and nAChR activation. The current study provides a novel perspective elucidating the potential treatment of VNS, thus also offering other pharmacological therapeutic promises in TIC patients.

Stellate Ganglia and Cardiac Sympathetic Overactivation in Heart Failure

Heart failure (HF) is a major public health problem worldwide, especially coronary heart disease (myocardial infarction)-induced HF with reduced ejection fraction (HFrEF), which accounts for over 50% of all HF cases. An estimated 6 million American adults have HF. As a major feature of HF, cardiac sympathetic overactivation triggers arrhythmias and sudden cardiac death, which accounts for nearly 50–60% of mortality in HF patients. Regulation of cardiac sympathetic activation is highly integrated by the regulatory circuitry at multiple levels, including afferent, central, and efferent components of the sympathetic nervous system. Much evidence, from other investigators and us, has confirmed the afferent and central neural mechanisms causing sympathoexcitation in HF. The stellate ganglion is a peripheral sympathetic ganglion formed by the fusion of the 7th cervical and 1st thoracic sympathetic ganglion. As the efferent component of the sympathetic nervous system, cardiac postganglionic sympathetic neurons located in stellate ganglia provide local neural coordination independent of higher brain centers. Structural and functional impairments of cardiac postganglionic sympathetic neurons can be involved in cardiac sympathetic overactivation in HF because normally, many effects of the cardiac sympathetic nervous system on cardiac function are mediated via neurotransmitters (e.g., norepinephrine) released from cardiac postganglionic sympathetic neurons innervating the heart. This review provides an overview of cardiac sympathetic remodeling in stellate ganglia and potential mechanisms and the role of cardiac sympathetic remodeling in cardiac sympathetic overactivation and arrhythmias in HF. Targeting cardiac sympathetic remodeling in stellate ganglia could be a therapeutic strategy against malignant cardiac arrhythmias in HF.

Cardiovascular variability and β-ARs gene expression at two stages of doxorubicin - Induced cardiomyopathy

Using comprehensive analysis of heart rate (HRV) and blood pressure (BPV) short-term variability we estimated the time course of changes of autonomic nervous system remodeling in two stages of doxorubicin-induced cardiomyopathy (DCM). We also investigated the level of gene expression of cardiac β-1 (β-1AR) and β-2 (β-2AR) adrenoceptors. Experiments were performed in adult male Wistar rats equipped with indwelling catheters for BP recording and blood withdrawal. A 15 mg/kg total cumulative dose of doxorubicin was injected i.p. to rats to induce DCM or saline for control (n=18). Rats were assessed for general toxicity, cardiovascular hemodynamic and echocardiography before treatment (n=6), 35 days (DOX35; n=6) and 70 days (DOX70; n=6) post-treatment. HRV was evaluated by spectral analysis, Poincaré plots, sample and approximate entropy. Expression of β-1AR and β-2AR mRNA was evaluated by RT-qPCR. Doxorubicin-treated rats exhibited poor general condition and lower survival than saline-treated rats. In DOX35 rats, there were no echocardiography signs of decompensation, no increase in serum cardiac troponins, but there was an increase of HRV and decrease of HR complexity. In these rats typical microscopic signs of cardiotoxicity were seen along with over-expression of β-1AR mRNA. 70 days post-treatment echocardiography revealed signs of decompensation and serum cardiac troponin T was increased. At this stage BPV decreased. In conclusion, HRV increase matches transient over-expression of cardiac β-1AR mRNA in compensate stage of DCM while decompensate stage of DCM is characterized by a decrease of BPV and no changes in β-1AR and β-2AR gene expression.

Clinical significance of respiratory compensation during exercise testing in cardiac patients

Ventilation (VE) increases linearly with the increase of carbon dioxide output (VCO2) during cardiopulmonary exercise testing. VE-VCO2 slope rises in parallel with exercise intensity, reaches a turning point (called the RC point), then steepens because of respiratory compensation for lactic acidosis. While this RC point can be identified universally, it is undetectable in some patients. In this study we evaluated whether the respiratory compensation during exercise testing has clinical significance in cardiac patients. In total, 152 cardiac patients with a respiratory exchange ratio at peak exercise (peak R) of between 1.10 and 1.20 were enrolled. Cardiopulmonary parameters were compared between patients who manifested the RC point (n = 118) and those who did not (n = 34). The peak R did not significantly differ between these two groups. Compared to the patients without the RC point, those with the RC point had a higher oxygen uptake at peak exercise (peak VO2) (20.2 ± 5.3 vs 13.6 ± 3.4 mL/min/kg, p < 0.001), higher anaerobic threshold (AT) (12.4 ± 3.2 vs 9.2 ± 2.3 mL/min/kg, p < 0.001), and lower VE-VCO2 slope (31.7 ± 5.8 vs 37.8 ± 9.6, p = 0.001). Brain natriuretic peptide (BNP) tended to be lower in the patients with the RC point (175.4 ± 364.7 vs 327.9 ± 381.1 pg/mL, p = 0.067). Peak VO2, the marker of cardiopulmonary function, was found to be the independent predictor of the presence of the RC point. The present findings suggest that the phenomenon of respiratory compensation during heavy exercise indicates better cardiopulmonary function in cardiac patients within a prescribed range of effort.

Carotid Body-Mediated Chemoreflex Drive in The Setting of low and High Output Heart Failure

Enhanced carotid body (CB) chemoreflex function is strongly related to cardiorespiratory disorders and disease progression in heart failure (HF). The mechanisms underlying CB sensitization during HF are not fully understood, however previous work indicates blood flow per se can affect CB function. Then, we hypothesized that the CB-mediated chemoreflex drive will be enhanced only in low output HF but not in high output HF. Myocardial infarcted rats and aorto-caval fistulated rats were used as a low output HF model (MI-CHF) and as a high output HF model (AV-CHF), respectively. Blood flow supply to the CB region was decreased only in MI-CHF rats compared to Sham and AV-CHF rats. MI-CHF rats exhibited a significantly enhanced hypoxic ventilatory response compared to AV-CHF rats. However, apnea/hypopnea incidence was similarly increased in both MI-CHF and AV-CHF rats compared to control. Kruppel-like factor 2 expression, a flow sensitive transcription factor, was reduced in the CBs of MI-CHF rats but not in AV-CHF rats. Our results indicate that in the setting of HF, potentiation of the CB chemoreflex is strongly associated with a reduction in cardiac output and may not be related to other pathophysiological consequences of HF.

Improvement of Myocardial Function Following Catheter-Based Renal Denervation in Heart Failure

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A porcine model of heart failure was induced by myocardial infarction followed by rapid ventricular pacing for 4 weeks.

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Catheter-based renal denervation was performed using an expandable basket with 4 electrodes to deliver radiofrequency energy. Histological examination showed significant denervation of the renal arteries after the procedure.

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Compared with the control group, animals that received renal denervation showed significant improvement of cardiac function as determined by LV ejection fraction, maximum rate of LV pressure rise normalized to instantaneous developed pressure, and reduction of myocardial and renal norepinephrine gradient at 10 weeks after procedure.

Renal denervation (RD) is a potential novel nonpharmacological therapy for heart failure (HF). We performed bilateral catheter-based RD in 10 adult pigs and compared them with 10 control subjects after induction of HF to investigate the long-term beneficial effects of RD on left ventricular (LV) function and regional norepinephrine gradient after conventional HF pharmacological therapy. Compared with control subjects, animals treated with RD demonstrated an improvement in LV function and reduction of norepinephrine gradients over the myocardium and kidney at 10-week follow-up. Our results demonstrated that effective bilateral RD decrease regional norepinephrine gradients and improve LV contractile function compared with medical therapy alone.

Cardiac sympathetic afferent reflex control of cardiac function in normal and chronic heart failure states

KEY POINTS

Cardiac sympathetic afferents are considered to be essential pathways for transmission of cardiac nociception to the central nervous system during myocardial ischaemia. However, a potential contribution of the CSAR control of cardiac dysfunction in both normal and chronic heart failure (CHF) states remains unknown. We found that activation of the CSAR evokes little increase in cardiac contractility with an exaggerated peripheral vasoconstriction in the CHF state. CSAR inhibition by epicardial lidocaine decreased cardiac contractility to a greater extent in CHF rats than sham rats. Furthermore, we also found that epicardial lidocaine paradoxically decreased left ventricular end-diastolic pressure (LVEDP) and left ventricular end-diastolic volume (preload) in CHF rats, which was not observed in sham rats. Chronic ablation of the CSAR by epicardial application of the afferent neurotoxin, RTX, selectively lowered diastolic blood pressure CHF rats. The observation suggests that CSAR has a differential effect on cardiac function in normal and CHF states. CSAR activation in normal state causes significant increase in cardiac contractility and cardiac output.

ABSTRACT

The enhanced 'cardiac sympathetic afferent reflex' (CSAR) critically contributes to the exaggerated global sympathetic tone in chronic heart failure (CHF). However, a potential contribution of the cardio-cardiac reflex control of cardiac function in both normal and CHF states remains unknown. In this study, we evaluated the effects of direct activation or inhibition of the CSAR on cardiac function by pressure-volume (P-V) loop analysis in ∼12-week sham-operated and myocardial infarcted (MI) rats. In sham rats, acute CSAR activation by epicardial application of bradykinin (BK) increased heart rate (HR), left ventricular systolic pressure (LVSP), the maximum first derivative of left ventricular pressure (dp/dt_max ), and the slope of the end-systolic P-V relationship (ESPVR), suggesting that acute CSAR activation in the normal state enhances myocardial contractility. CSAR activation also decreased left ventricular (LV) systolic and diastolic volumes with little effect on LV end-diastolic pressure (LVEDP) or the end-diastolic P-V relationship (EDPVR) in sham rats. Compared to sham, CHF rats exhibit a reduced increase in the slope of the ESPVR and dp/dt_max in response to BK, indicating a poor contractile response to CSAR activation. Interestingly, BK application in CHF rats increased cardiac systolic and diastolic volumes and further increased the elevated LVEDP, neither of which was seen in sham rats. Following CSAR inhibition by epicardial lidocaine, blood pressure, HR, LVSP, dp/dt, LVEDP and ESPVR decreased in CHF rats whereas lidocaine had little effect in sham rats, indicating that the CSAR is tonically active in CHF and contributes to cardiac dysfunction. Furthermore, we found that epicardial lidocaine paradoxically decreased LV end-diastolic volume (preload) in CHF rats, which was not observed in sham rats. The decreased preload by lidocaine in CHF rats may be due to a reduction in peripheral vascular resistance since epicardial lidocaine significantly lowered peripheral (renal) sympathetic nerve activity in CHF rats but not in sham rats. Furthermore, chronic ablation of CSAR by epicardial application of a selective afferent neurotoxin, resiniferatoxin, selectively lowered diastolic blood pressure both at daytime and night-time with less effect on systolic blood pressure in CHF rats. Our data suggest that there is an imbalance between cardiac and peripheral responses to CSAR in CHF animals compared to sham-operated controls.

Contribution of peripheral and central chemoreceptors to sympatho-excitation in heart failure

Chronic heart failure (CHF) is a major public health problem. Tonic hyper-activation of sympathetic neural outflow is commonly observed in patients with CHF. Importantly, sympatho-excitation in CHF exacerbates its progression and is strongly related to poor prognosis and high mortality risk. Increases in both peripheral and central chemoreflex drive are considered markers of the severity of CHF. The principal peripheral chemoreceptors are the carotid bodies (CBs) and alteration in their function has been described in CHF. Mainly, during CHF the CB chemosensitivity is enhanced leading to increases in ventilation and sympathetic outflow. In addition to peripheral control of breathing, central chemoreceptors (CCs) are considered a dominant mechanism in ventilatory regulation. Potentiation of the ventilatory and sympathetic drive in response to CC activation has been shown in patients with CHF as well as in animal models. Therefore, improving understanding of the contribution of the peripheral and central chemoreflexes to augmented sympathetic discharge in CHF could help in developing new therapeutic approaches intended to attenuate the progression of CHF. Accordingly, the main focus of this review is to discuss recent evidence that peripheral and central chemoreflex function are altered in CHF and that they contribute to autonomic imbalance and progression of CHF.

Brain-heart interactions: physiology and clinical implications

The brain controls the heart directly through the sympathetic and parasympathetic branches of the autonomic nervous system, which consists of multi-synaptic pathways from myocardial cells back to peripheral ganglionic neurons and further to central preganglionic and premotor neurons. Cardiac function can be profoundly altered by the reflex activation of cardiac autonomic nerves in response to inputs from baro-, chemo-, nasopharyngeal and other receptors as well as by central autonomic commands, including those associated with stress, physical activity, arousal and sleep. In the clinical setting, slowly progressive autonomic failure frequently results from neurodegenerative disorders, whereas autonomic hyperactivity may result from vascular, inflammatory or traumatic lesions of the autonomic nervous system, adverse effects of drugs and chronic neurological disorders. Both acute and chronic manifestations of an imbalanced brain-heart interaction have a negative impact on health. Simple, widely available and reliable cardiovascular markers of the sympathetic tone and of the sympathetic-parasympathetic balance are lacking. A deeper understanding of the connections between autonomic cardiac control and brain dynamics through advanced signal and neuroimage processing may lead to invaluable tools for the early detection and treatment of pathological changes in the brain-heart interaction.

Altered ENaC is Associated With Aortic Baroreceptor Dysfunction in Chronic Heart Failure

BACKGROUND

Abnormal baroreceptor function contributes to attenuated arterial baroreflex sensitivity in chronic heart failure (CHF). As a mechanosensor in mammalian nonepithelium, the epithelial sodium channel (ENaC) is an amiloride-sensitive and voltage-independent ion channel. The ENaC is thought to be a component of baroreceptor mechanosensitive ion channels in aortic baroreceptor cell bodies and nerve terminals. In this study, therefore, we measured the expression and activation of the ENaC in nodose neuronal cell bodies and aortic baroreceptor nerve terminals in sham and CHF rats.

METHODS AND RESULTS

CHF was induced by surgical ligation of left coronary artery. The development of CHF was confirmed by hemodynamic and morphological characteristics. The aortic baroreceptor sensitivity was blunted in anesthetized CHF rats, compared with that in sham rats. The data from immunostaining and western blot analysis showed that the protein of β- and γ-ENaC subunits was expressed in nodose neuronal cell bodies and aortic baroreceptor nerve terminals, whereas the protein of α-ENaC subunit was undetectable. CHF reduced protein expression of β- and γ-ENaC subunits in nodose neuronal cell bodies and aortic baroreceptor nerve terminals. Additionally, the data recorded by the whole cell patch-clamp technique demonstrated that ENaC currents in aortic baroreceptor neurons were lower in CHF rats than that in sham rats.

CONCLUSION

These results suggest that reduced protein expression of the ENaC decreases the ENaC activation, which could be involved in attenuation of the aortic baroreceptor sensitivity in the CHF state. Baroreceptors should be a potential therapeutic target for reducing mortality in CHF.

Glia, sympathetic activity and cardiovascular disease

NEW FINDINGS

What is the topic of this review? In this review, we discuss recent findings that provide a novel insight into the mechanisms that link glial cell function with the pathogenesis of cardiovascular disease, including systemic arterial hypertension and chronic heart failure. What advances does it highlight? We discuss how glial cells may influence central presympathetic circuits, leading to maladaptive and detrimental increases in sympathetic activity and contributing to the development and progression of cardiovascular disease. Increased activity of the sympathetic nervous system is associated with the development of cardiovascular disease and may contribute to its progression. Vasomotor and cardiac sympathetic activities are generated by the neuronal circuits located in the hypothalamus and the brainstem. These neuronal networks receive multiple inputs from the periphery and other parts of the CNS and, at a local level, may be influenced by their non-neuronal neighbours, in particular glial cells. In this review, we discuss recent experimental evidence suggesting that astrocytes and microglial cells are able to modulate the activity of sympathoexcitatory neural networks in disparate physiological and pathophysiological conditions. We focus on the chemosensory properties of astrocytes residing in the rostral ventrolateral medulla oblongata and discuss signalling mechanisms leading to glial activation during brain hypoxia and inflammation. Alterations in these mechanisms may lead to heightened activity of sympathoexcitatory CNS circuits and contribute to maladaptive and detrimental increases in sympathetic tone associated with systemic arterial hypertension and chronic heart failure.

Hyperventilation in normoxia following myocardial infarction in rats: a shift in the set point of the hypoxic ventilatory response

AIM

The peripheral chemoreflex is augmented in heart failure, and it may contribute to sympathoexcitation. This study aimed to investigate both the chemoreflex and the cardiac sympathetic nerve activity in the acute-stage post-myocardial infarction.

METHODS

Myocardial infarction was induced in male adult Sprague-Dawley rats by permanent ligation of the left anterior descending coronary artery. Within-animal repeated measure assessment of normoxic and hypoxic ventilation patterns was determined with whole-body plethysmography and compared to sham-operated controls. Cardiac function, morphology and cardiac sympathetic nerve activity were determined 14 days later.

RESULTS

Infarction induced increases in normoxic ventilation through increases in tidal volume within 3 days. At the same time points, the hypoxic ventilatory response to short durations (10 min) of hypoxia (8, 10 and 12% inspired O2 ) was blunted. At the end of the experiment (D14), increases in nerve activity, specifically through increased firing rate, and significant cardiac dysfunction (ejection fraction 43%) were observed in myocardial infarction (MI) group.

CONCLUSIONS

An augmentation of normoxic ventilation caused by myocardial infarction occurs before the amplification of the hypoxic ventilatory response. It occurs much earlier following myocardial injury than previously demonstrated and may have a role in initiating cardiac sympathoexcitation. The difference in the augmentation of hypoxic response between early and late stages post-myocardial infarction suggest that the initial change in the chemoreflex is an alteration to the operating point of chemoreflex.

Heart rate dynamics in doxorubicin-induced cardiomyopathy

The clinical use of doxorubicin, an effective chemotherapeutic is hampered by the development of irreversible cardiotoxicity. Here we test time-frequency analysis of heart rate (HR) variability (HRV) for early detection of doxorubicin-induced cardiotoxicity. Experiments were conducted in adult male Wistar rats treated for 15 days with doxorubicin (DOXO, total dose 15 mg kg(-1), i.p.) or saline (CONT). DOXO rats exhibited cardiotoxicity confirmed by histological examination without developing heart failure as estimated by echocardiography. However, HR variability increase reflected subtle microscopic changes of cardiac toxicity in DOXO rats. The results recommend time-frequency analysis of HRV for early detection of doxorubicin-induced cardiomyopathy.

Exercise training prevents the deterioration in the arterial baroreflex control of sympathetic nerve activity in chronic heart failure patients

Arterial baroreflex control of muscle sympathetic nerve activity (ABRMSNA) is impaired in chronic systolic heart failure (CHF). The purpose of the study was to test the hypothesis that exercise training would improve the gain and reduce the time delay of ABRMSNA in CHF patients. Twenty-six CHF patients, New York Heart Association Functional Class II-III, EF ≤ 40%, peak V̇o2 ≤ 20 ml·kg(-1)·min(-1) were divided into two groups: untrained (UT, n = 13, 57 ± 3 years) and exercise trained (ET, n = 13, 49 ± 3 years). Muscle sympathetic nerve activity (MSNA) was directly recorded by microneurography technique. Arterial pressure was measured on a beat-to-beat basis. Time series of MSNA and systolic arterial pressure were analyzed by autoregressive spectral analysis. The gain and time delay of ABRMSNA was obtained by bivariate autoregressive analysis. Exercise training was performed on a cycle ergometer at moderate intensity, three 60-min sessions per week for 16 wk. Baseline MSNA, gain and time delay of ABRMSNA, and low frequency of MSNA (LFMSNA) to high-frequency ratio (HFMSNA) (LFMSNA/HFMSNA) were similar between groups. ET significantly decreased MSNA. MSNA was unchanged in the UT patients. The gain and time delay of ABRMSNA were unchanged in the ET patients. In contrast, the gain of ABRMSNA was significantly reduced [3.5 ± 0.7 vs. 1.8 ± 0.2, arbitrary units (au)/mmHg, P = 0.04] and the time delay of ABRMSNA was significantly increased (4.6 ± 0.8 vs. 7.9 ± 1.0 s, P = 0.05) in the UT patients. LFMSNA-to-HFMSNA ratio tended to be lower in the ET patients (P < 0.08). Exercise training prevents the deterioration of ABRMSNA in CHF patients.

Time and technology will tell: the pathophysiologic basis of neurohormonal modulation in heart failure

The central roles of neurohormonal abnormalities in the pathobiology of heart failure have been defined in recent decades. Experiments have revealed both systemic involvement and intricate subcellular regulation by circulating effectors of the sympathetic nervous system, the renin-angiotensin-aldosterone system, and others. Randomized clinical trials substantiated these findings, establishing neurohormonal antagonists as cornerstones of heart failure pharmacotherapy, and occasionally offering further insight on mode of benefit. This review discusses the use of β-blockers, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and aldosterone receptor antagonists in the treatment of heart failure, with particular attention to the pathophysiologic basis and mechanisms of action.

Central exogenous nitric oxide decreases cardiac sympathetic drive and improves baroreflex control of heart rate in ovine heart failure

Heart failure (HF) is associated with increased cardiac and renal sympathetic drive, which are both independent predictors of poor prognosis. A candidate mechanism for the centrally mediated sympathoexcitation in HF is reduced synthesis of the inhibitory neuromodulator nitric oxide (NO), resulting from downregulation of neuronal NO synthase (nNOS). Therefore, we investigated the effects of increasing the levels of NO in the brain, or selectively in the paraventricular nucleus of the hypothalamus (PVN), on cardiac sympathetic nerve activity (CSNA) and baroreflex control of CSNA and heart rate in ovine pacing-induced HF. The resting level of CSNA was significantly higher in the HF than in the normal group, but the resting level of RSNA was unchanged. Intracerebroventricular infusion of the NO donor sodium nitroprusside (SNP; 500 μg · ml(-1)· h(-1)) in conscious normal sheep and sheep in HF inhibited CSNA and restored baroreflex control of heart rate, but there was no change in RSNA. Microinjection of SNP into the PVN did not cause a similar cardiac sympathoinhibition in either group, although the number of nNOS-positive cells was decreased in the PVN of sheep in HF. Reduction of endogenous NO with intracerebroventricular infusion of N(ω)-nitro-l-arginine methyl ester decreased CSNA in normal but not in HF sheep and caused no change in RSNA in either group. These findings indicate that endogenous NO in the brain provides tonic excitatory drive to increase resting CSNA in the normal state, but not in HF. In contrast, exogenously administered NO inhibited CSNA in both the normal and HF groups via an action on sites other than the PVN.