Chronic Low-Level Vagus Nerve Stimulation Improves Long-Term Survival in Salt-Sensitive Hypertensive Rats

Autonomic neuromodulation for cardiomyopathy associated with metabolic syndrome - Prevention of precursors for heart failure with preserved ejection fraction

Metabolic syndrome (MetS) induces a systemic inflammatory state which can lead to cardiomyopathy, manifesting clinically as heart failure (HF) with preserved ejection fraction (HFpEF). MetS components are intricately linked to the pathophysiologic processes of myocardial remodeling. Increased sympathetic nervous system activity, which is noted as an upstream factor of MetS, has been linked to adverse myocardial structural changes. Since renal denervation and vagus nerve stimulation have a sympathoinhibitory effect, attention has been paid to the cardioprotective effects of autonomic neuromodulation. In this review, the pathophysiology underlying the relationship between MetS and HF is elucidated, and the evidence regarding autonomic neuromodulation in HFpEF is summarized.

Autonomic Nervous System: A Therapeutic Target for Cardiac End-Organ Damage in Hypertension

More than 1.5 billion people worldwide have arterial hypertension. Hypertension increases the risks of death and cardiovascular disease, such as atrial fibrillation and heart failure. The autonomic nervous system plays an essential role in hypertension development and disease progression. While lifestyle factors, such as obesity and obstructive sleep apnea, predispose to hypertension by increasing sympathetic activity, hypertension itself maintains the autonomic nervous imbalance, providing the substrate for atrial fibrillation and heart failure. Therefore, autonomic nervous system modulation either by direct targeting or indirect treatment of comorbidities has the potential to treat both hypertension and related atrial and ventricular end-organ damage. We discuss interventions for the modulation of the autonomic nervous system for hypertension and related cardiac end-organ damage, including pharmacological adrenergic beta-receptor blockade, renal denervation, carotid baroreceptor stimulation, low-level vagal stimulation, and ablation of ganglionated plexuses. In summary, the literature suggests that targeting the autonomic nervous system potentially represents a therapeutic approach to prevent atrial and ventricular end-organ damage in patients with hypertension. However, clinical trials specifically designed to test the effect of autonomic modulation on hypertension-mediated cardiac end-organ damage are scarce.

Bioelectronic modulation of carotid sinus nerve to treat type 2 diabetes: current knowledge and future perspectives

Bioelectronic medicine are an emerging class of treatments aiming to modulate body nervous activity to correct pathological conditions and restore health. Recently, it was shown that the high frequency electrical neuromodulation of the carotid sinus nerve (CSN), a small branch of the glossopharyngeal nerve that connects the carotid body (CB) to the brain, restores metabolic function in type 2 diabetes (T2D) animal models highlighting its potential as a new therapeutic modality to treat metabolic diseases in humans. In this manuscript, we review the current knowledge supporting the use of neuromodulation of the CSN to treat T2D and discuss the future perspectives for its clinical application. Firstly, we review in a concise manner the role of CB chemoreceptors and of CSN in the pathogenesis of metabolic diseases. Secondly, we describe the findings supporting the potential therapeutic use of the neuromodulation of CSN to treat T2D, as well as the feasibility and reversibility of this approach. A third section is devoted to point up the advances in the neural decoding of CSN activity, in particular in metabolic disease states, that will allow the development of closed-loop approaches to deliver personalized and adjustable treatments with minimal side effects. And finally, we discuss the findings supporting the assessment of CB activity in metabolic disease patients to screen the individuals that will benefit therapeutically from this bioelectronic approach in the future.

Vagus nerve stimulation as immunomodulatory therapy for stroke: A comprehensive review

Stroke is a devastating cerebrovascular pathology with high morbidity and mortality. Inflammation plays a central role in the pathophysiology of stroke. Vagus nerve stimulation (VNS) is a promising immunomodulatory method that has shown positive effects in stroke treatment, including neuroprotection, anti-apoptosis, anti-inflammation, antioxidation, reduced infarct volume, improved neurological scores, and promotion of M2 microglial polarization. In this review, we summarize the current knowledge about the vagus nerve's immunomodulatory effects through the cholinergic anti-inflammatory pathway (CAP) and provide a comprehensive assessment of the available experimental literature focusing on the use of VNS in stroke treatment.

2023 update and perspectives

Total 276 manuscripts were published in Hypertension Research in 2022. Here our editorial members picked up the excellent papers, summarized the current topics from the published papers and discussed future perspectives in the sixteen fields. We hope you enjoy our special feature, 2023 update and perspectives in Hypertension Research.

The Changes of Cardiovascular Neurotransmitter Levels under Low-Intensity Focused Ultrasound Stimulation of the Vagus Nerve

BACKGROUND

Our previous study has shown that stimulation of the vagus nerve with low-intensity focused ultrasound could modulate blood pressure (BP), but the underlying mechanisms remain unclear. This study investigated the changes of cardiovascular neurotransmitter levels to indirectly evaluate the responses of the autonomic nervous system and renin-angiotensin system under low-intensity focused ultrasound stimulation (FUS) of the vagus nerve.

METHODS

Cardiovascular neurotransmitter levels of epinephrine (EPI), norepinephrine (NE), and angiotensin II (ANGII) were measured and compared before and after the FUS in seven spontaneously hypertensive rats; and were also measured and compared between a target stimulation group (FUS, n = 6) and non-target stimulation group (Control, n = 5) after stimulation to exclude the influence of potential confounding factors.

RESULTS

The t-test results showed that the levels of EPI, NE, and ANGII were significantly decreased (P < 0.05) after stimulation compared to before stimulation. Additionally, the levels of NE and EPI were significantly lower (P < 0.05) in the FUS group than in the Control group after stimulation, indicating that the activities of the sympathetic nervous system and renin-angiotensin system of the vagus nerve might be inhibited by FUS of the vagus nerve.

CONCLUSION

These findings reveal the mechanism of BP lowing in response to FUS of the vagus nerve.Clinical Relevance-This study revealed the mechanism of BP lowering in response to focused ultrasound stimulation of the vagus nerve through analyzing the changes of cardiovascular neurotransmitter levels.

Autonomic modulation by low-intensity focused ultrasound stimulation of the vagus nerve

Objective.Our previous study has shown that low-intensity focused ultrasound stimulation (FUS) of the vagus nerve could modulate blood pressure (BP), but its underlying mechanisms remain unclear. We hypothesized that low-intensity FUS of the vagus nerve would regulate autonomic function and thus BP.Approach.17 anesthetized spontaneously hypertensive rats were treated with low-intensity FUS of the left vagus nerve for 15 min each trial. Continuous BP, heart rate, respiration rate (RR), and core body temperature were simultaneously recorded to evaluate the effects on BP and other physiological parameters. Heart rate variability (HRV), systolic BP variability, and baroreflex sensitivity were computed to evaluate the autonomic modulation function. A Control-sham group without stimulation and another Control-FUS group with non-target stimulation were also examined to exclude the influence of potential confounding factors on autonomic modulation.Main results.A prolonged significant decrease in BP, pulse pressure, RR, the normalized low-frequency power of HRV, and the low-to-high frequency power ratio of HRV were found after the low-intensity FUS of the left vagus nerve in comparison with the baseline and those of the control groups, demonstrating that activities of the sympathetic nervous system were inhibited. The prolonged significant increase of the normalized high-frequency power of HRV suggested the activation of parasympathetic activity.Significance.Low-intensity FUS of the left vagus nerve effectively improved the autonomic function by activating parasympathetic efferent and inhibiting sympathetic efferent, which contributes to BP reduction. The findings shed light on the hypotensive mechanism underlying FUS.

Strategies for precision vagus neuromodulation

The vagus nerve is involved in the autonomic regulation of physiological homeostasis, through vast innervation of cervical, thoracic and abdominal visceral organs. Stimulation of the vagus with bioelectronic devices represents a therapeutic opportunity for several disorders implicating the autonomic nervous system and affecting different organs. During clinical translation, vagus stimulation therapies may benefit from a precision medicine approach, in which stimulation accommodates individual variability due to nerve anatomy, nerve-electrode interface or disease state and aims at eliciting therapeutic effects in targeted organs, while minimally affecting non-targeted organs. In this review, we discuss the anatomical and physiological basis for precision neuromodulation of the vagus at the level of nerve fibers, fascicles, branches and innervated organs. We then discuss different strategies for precision vagus neuromodulation, including fascicle- or fiber-selective cervical vagus nerve stimulation, stimulation of vagal branches near the end-organs, and ultrasound stimulation of vagus terminals at the end-organs themselves. Finally, we summarize targets for vagus neuromodulation in neurological, cardiovascular and gastrointestinal disorders and suggest potential precision neuromodulation strategies that could form the basis for effective and safe therapies.

Effect of Vagus Nerve Stimulation on Attention and Working Memory in Neuropsychiatric Disorders: A Systematic Review

BACKGROUND

It has been suggested that vagus nerve stimulation (VNS) may enhance attention and working memory. The neuromodulator effects of VNS are thought to activate the release of neurotransmitters involving cognition and to promote neuronal plasticity. Therefore, VNS has been studied for its effects on attention and working memory impairment in neuropsychiatric disorders.

OBJECTIVES

This study aimed to assess the effects of VNS on attention and working memory among patients with neuropsychiatric disorders, examine stimulation parameters, provide mechanistic hypotheses, and propose future studies using VNS.

MATERIALS AND METHODS

We conducted a systematic review using electronic databases MEDLINE (Ovid), Embase (Ovid), Cochrane library, and PsycINFO (Ovid). Narrative analysis was used to describe the therapeutic effects of VNS on attention and working memory, describe stimulation parameters, and propose explanatory mechanisms.

RESULTS

We identified 20 studies reporting VNS effects on attention and working memory in patients with epilepsy or mood disorders. For epilepsy, there was one randomized controlled trial from all 18 studies. It demonstrated no statistically significant differences in the cognitive tasks between active and control VNS. From a within-subject experimental design, significant improvement of working memory after VNS was demonstrated. One of three nonrandomized controlled trials found significantly improved attentional performance after VNS. The cohort studies compared VNS and surgery and found attentional improvement in both groups. Nine of 12 pretest-posttest studies showed improvement of attention or working memory after VNS. For mood disorders, although one study showed significant improvement of attention following VNS, the other did not.

CONCLUSIONS

This review suggests that, although we identified some positive results from eligible studies, there is insufficient good-quality evidence to establish VNS as an effective intervention to enhance attention and working memory in persons with neuropsychiatric disorders. Further studies assessing the efficacy of such intervention are needed.

An ASIC System for Closed-Loop Blood Pressure Modulation through Right Cervical Vagus Nerve Stimulation

OBJECTIVE

Heart disease is the leading cause of death worldwide. Hypertension is an important precursor and the most common risk factor to heart failure. While some patients can control their high blood pressure with pharmaceuticals, many suffer from resistant hypertension, where antihypertensive medications do not achieve the desired outcome. Electrical stimulation is an emerging therapy to modulate blood pressure and integrating it with closed-loop feedback can improve blood pressure control.

METHODS

We design and fabricate two application-specific integrated circuits (ASICs) for stimulation and pressure sensing using TSMC's 180 nm MS RF G process. We create a closed-loop system by integrating the ASICs with a microscale pressure sensor and a custom-built Python script and test the full system in six Long Evans rats using vagus nerve stimulation.

RESULTS

After calibration and benchtop verification, we prove the functionality of the system in lowering, and maintaining a desired blood pressure in vivo. The system effectively monitors pressure and stimulates when that pressure exceeds the user-determined threshold.

CONCLUSION

By combining this stimulation therapy with a pressure sensor, we present a novel closed-loop, electroceutical system that has the potential to monitor and modulate blood pressure.

SIGNIFICANCE

We present a drug-free, potentially side-effect-free electroceutical therapeutic for managing resistant hypertension.

Therapeutic targeting of inflammation in hypertension: from novel mechanisms to translational perspective

Both animal models and human observational and genetic studies have shown that immune and inflammatory mechanisms play a key role in hypertension and its complications. We review the effects of immunomodulatory interventions on blood pressure, target organ damage, and cardiovascular risk in humans. In experimental and small clinical studies, both non-specific immunomodulatory approaches, such as mycophenolate mofetil and methotrexate, and medications targeting T and B lymphocytes, such as tacrolimus, cyclosporine, everolimus, and rituximab, lower blood pressure and reduce organ damage. Mechanistically targeted immune interventions include isolevuglandin scavengers to prevent neo-antigen formation, co-stimulation blockade (abatacept, belatacept), and anti-cytokine therapies (e.g. secukinumab, tocilizumab, canakinumab, TNF-α inhibitors). In many studies, trial designs have been complicated by a lack of blood pressure-related endpoints, inclusion of largely normotensive study populations, polypharmacy, and established comorbidities. Among a wide range of interventions reviewed, TNF-α inhibitors have provided the most robust evidence of blood pressure lowering. Treatment of periodontitis also appears to deliver non-pharmacological anti-hypertensive effects. Evidence of immunomodulatory drugs influencing hypertension-mediated organ damage are also discussed. The reviewed animal models, observational studies, and trial data in humans, support the therapeutic potential of immune-targeted therapies in blood pressure lowering and in hypertension-mediated organ damage. Targeted studies are now needed to address their effects on blood pressure in hypertensive individuals.

Systemic administration of choline acetyltransferase decreases blood pressure in murine hypertension

Acetylcholine (ACh) decreases blood pressure by stimulating endothelium nitric oxide-dependent vasodilation in resistance arterioles. Normal plasma contains choline acetyltransferase (ChAT) and its biosynthetic product ACh at appreciable concentrations to potentially act upon the endothelium to affect blood pressure. Recently we discovered a T-cell subset expressing ChAT (TChAT), whereby genetic ablation of ChAT in these cells produces hypertension, indicating that production of ACh by TChAT regulates blood pressure. Accordingly, we reasoned that increasing systemic ChAT concentrations might induce vasodilation and reduce blood pressure. To evaluate this possibility, recombinant ChAT was administered intraperitoneally to mice having angiotensin II-induced hypertension. This intervention significantly and dose-dependently decreased mean arterial pressure. ChAT-mediated attenuation of blood pressure was reversed by administration of the nitric oxide synthesis blocker L-nitro arginine methyl ester, indicating ChAT administration decreases blood pressure by stimulating nitic oxide dependent vasodilation, consistent with an effect of ACh on the endothelium. To prolong the half life of circulating ChAT, the molecule was modified by covalently attaching repeating units of polyethylene glycol (PEG), resulting in enzymatically active PEG-ChAT. Administration of PEG-ChAT to hypertensive mice decreased mean arterial pressure with a longer response duration when compared to ChAT. Together these findings suggest further studies are warranted on the role of ChAT in hypertension.

The Role of Short-Chain Fatty Acids of Gut Microbiota Origin in Hypertension

Hypertension is a significant risk factor for cardiovascular and cerebrovascular diseases, and its development involves multiple mechanisms. Gut microbiota has been reported to be closely linked to hypertension. Short-chain fatty acids (SCFAs)-the metabolites of gut microbiota-participate in hypertension development through various pathways, including specific receptors, immune system, autonomic nervous system, metabolic regulation and gene transcription. This article reviews the possible mechanisms of SCFAs in regulating blood pressure and the prospects of SCFAs as a target to prevent and treat hypertension.

Benefits of pharmacological and electrical cholinergic stimulation in hypertension and heart failure

Systemic arterial hypertension and heart failure are cardiovascular diseases that affect millions of individuals worldwide. They are characterized by a change in the autonomic nervous system balance, highlighted by an increase in sympathetic activity associated with a decrease in parasympathetic activity. Most therapeutic approaches seek to treat these diseases by medications that attenuate sympathetic activity. However, there is a growing number of studies demonstrating that the improvement of parasympathetic function, by means of pharmacological or electrical stimulation, can be an effective tool for the treatment of these cardiovascular diseases. Therefore, this review aims to describe the advances reported by experimental and clinical studies that addressed the potential of cholinergic stimulation to prevent autonomic and cardiovascular imbalance in hypertension and heart failure. Overall, the published data reviewed demonstrate that the use of central or peripheral acetylcholinesterase inhibitors is efficient to improve the autonomic imbalance and hemodynamic changes observed in heart failure and hypertension. Of note, the baroreflex and the vagus nerve activation have been shown to be safe and effective approaches to be used as an alternative treatment for these cardiovascular diseases. In conclusion, pharmacological and electrical stimulation of the parasympathetic nervous system has the potential to be used as a therapeutic tool for the treatment of hypertension and heart failure, deserving to be more explored in the clinical setting.

Nitric Oxide Alleviated High Salt-Induced Cardiomyocyte Apoptosis and Autophagy Independent of Blood Pressure in Rats

The present study aimed to explore whether high-salt diet (HSD) could cause cardiac damage independent of blood pressure, and whether nitric oxide (NO) could alleviate high-salt-induced cardiomyocyte apoptosis and autophagy in rats. The rats received 8% HSD in vivo. H9C2 cells or primary neonatal rat cardiomyocytes (NRCM) were treated with sodium chloride (NaCl) in vitro. The levels of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2, LC3 II/LC3 I, Beclin-1 and autophagy related 7 (ATG7) were increased in the heart of HSD rats with hypertension (HTN), and in hypertension-prone (HP) and hypertension-resistant (HR) rats. Middle and high doses (50 and 100 mM) of NaCl increased the level of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2, LC3 II/LC3 I, Beclin-1, and ATG7 in H9C2 cells and NRCM. The endothelial NO synthase (eNOS) level was increased, but p-eNOS level was reduced in the heart of HSD rats and H9C2 cells treated with 100 mM NaCl. The level of NO was reduced in the serum and heart of HSD rats. NO donor sodium nitroprusside (SNP) reversed the increases of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2 induced by NaCl (100 mM) in H9C2 cells and NRCM. SNP treatment attenuated the increases of cleaved-caspase 3/caspase 3, Bax/Bcl2, LC3 II/LC3 I, Beclin-1, and ATG7 in the heart, but had no effect on the blood pressure of HSD rats with HR. These results demonstrated that HSD enhanced cardiac damage independently of blood pressure. Exogenous NO supplementarity could alleviate the high salt-induced apoptosis and autophagy in cardiomyocytes.

Development and characterization of a chronic implant mouse model for vagus nerve stimulation

Vagus nerve stimulation (VNS) suppresses inflammation and autoimmune diseases in preclinical and clinical studies. The underlying molecular, neurological, and anatomical mechanisms have been well characterized using acute electrophysiological stimulation of the vagus. However, there are several unanswered mechanistic questions about the effects of chronic VNS, which require solving numerous technical challenges for a long-term interface with the vagus in mice. Here, we describe a scalable model for long-term VNS in mice developed and validated in four research laboratories. We observed significant heart rate responses for at least 4 weeks in 60-90% of animals. Device implantation did not impair vagus-mediated reflexes. VNS using this implant significantly suppressed TNF levels in endotoxemia. Histological examination of implanted nerves revealed fibrotic encapsulation without axonal pathology. This model may be useful to study the physiology of the vagus and provides a tool to systematically investigate long-term VNS as therapy for chronic diseases modeled in mice.

Bioelectronic medicine for the autonomic nervous system: clinical applications and perspectives

Bioelectronic medicine (BM) is an emerging new approach for developing novel neuromodulation therapies for pathologies that have been previously treated with pharmacological approaches. In this review, we will focus on the neuromodulation of autonomic nervous system (ANS) activity with implantable devices, a field of BM that has already demonstrated the ability to treat a variety of conditions, from inflammation to metabolic and cognitive disorders. Recent discoveries about immune responses to ANS stimulation are the laying foundation for a new field holding great potential for medical advancement and therapies and involving an increasing number of research groups around the world, with funding from international public agencies and private investors. Here, we summarize the current achievements and future perspectives for clinical applications of neural decoding and stimulation of the ANS. First, we present the main clinical results achieved so far by different BM approaches and discuss the challenges encountered in fully exploiting the potential of neuromodulatory strategies. Then, we present current preclinical studies aimed at overcoming the present limitations by looking for optimal anatomical targets, developing novel neural interface technology, and conceiving more efficient signal processing strategies. Finally, we explore the prospects for translating these advancements into clinical practice.

Blood Pressure Modulation With Low-Intensity Focused Ultrasound Stimulation to the Vagus Nerve: A Pilot Animal Study

Objective

For hypertensive individuals, their blood pressure (BP) is often managed by taking medications. However, antihypertensive drugs might cause adverse effects such as congestive heart failure and are ineffective in significant numbers of the hypertensive population. As an alternative method for hypertension management, non-drug devices-based neuromodulation approaches such as functional electrical stimulation (FES) have been proposed. The FES approach requires the implantation of a stimulator into the body. One recently emerging technique, called low-intensity focused ultrasound stimulation (FUS), has been proposed to non-invasively modulate neural activities. In this pilot study, the feasibility of adopting low-intensity FUS neuromodulation for BP regulation was investigated using animal models.

Methods

A FUS system was developed for BP modulation in rabbits. For each rabbit, the low-intensity FUS with different acoustic intensities was used to stimulate its exposed left vagus nerve, and the BP waveform was synchronously recorded in its right common carotid artery. The effects of the different FUS intensities on systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MAP), and heart rate (HR) were extensively examined from the BP recordings.

Results

The results demonstrated that the proposed FUS method could successfully induce changes in SBP, DBP, MAP, and HR values. When increasing acoustic intensities, the values of SBP, DBP, and MAP would tend to decrease more substantially.

Conclusion

The findings of this study suggested that BP could be modulated through the FUS, which might provide a new way for non-invasive and non-drug management of hypertension.

Advances in understanding mechanisms and therapeutic targets to treat comorbid depression and cardiovascular disease

Chronic or repeated social stress exposure often precipitates the onset of depression and cardiovascular disease (CVD). Despite a clear clinical association between CVD and depression, the pathophysiology underlying these comorbid conditions is unclear. Chronic exposure to social stress can lead to immune system dysregulation, mitochondrial dysfunction, and vagal withdrawal. Further, regular physical exercise is well-known to exert cardioprotective effects, and accumulating evidence demonstrates the antidepressant effect of exercise. This review explores the contribution of inflammation, mitochondrial dysfunction, and vagal withdrawal to stress-induced depression and CVD. Evidence for therapeutic benefits of exercise, anti-inflammatory therapies, and vagus nerve stimulation are also reviewed. Benefits of targeted therapeutics of mitochondrial agents, anti-inflammatory therapies, and vagus nerve stimulation are discussed. Importantly, the ability of exercise to impact each of these factors is also reviewed. The current findings described here implicate a new direction for research, targeting the shared mechanisms underlying comorbid depression-CVD. This will guide the development of novel therapeutic strategies for the prevention and treatment of these stress-related pathologies, particularly within treatment-resistant populations.

A rodent model for long-term vagus nerve stimulation experiments

Aim: Investigations into the benefits of vagus nerve stimulation (VNS) using rodents have led to promising findings for treating clinical disorders. However, the majority of research has been limited to acute timelines. We developed a rodent model for longitudinal assessment of VNS and validated it with a long-term experiment incorporating continuous physiological monitoring. While the primary aim was not to investigate the effects of VNS on the cardiovascular system, we analyzed cardiovascular parameters to demonstrate the model's capabilities in a long-term stimulation-and-recording setup. Materials & methods: Rats were implanted with a cuff electrode around the cervical vagus nerve and electrocardiogram monitoring devices were implanted in the peritoneal cavity. We also designed a connector mount for seamless access to the cuff electrode for VNS in awake-behaving rats. Results & conclusion: Results signified easy-to-interface VNS system, electrode robustness and discernible physiological signals in a long-term setup. Analysis of the cardiovascular parameters revealed some transient effects during VNS. Our proposed model enables long-term VNS experiments along with physiological monitoring in unanesthetized rats.