Vagal nerve stimulation in prevention and management of coronary heart disease

Spatiotemporally specific roles of TLR4, TNF, and IL-17A in murine endotoxin-induced inflammation inferred from analysis of dynamic networks

Background

Bacterial lipopolysaccharide (LPS) induces a multi-organ, Toll-like receptor 4 (TLR4)-dependent acute inflammatory response.

Methods

Using network analysis, we defined the spatiotemporal dynamics of 20, LPS-induced, protein-level inflammatory mediators over 0–48 h in the heart, gut, lung, liver, spleen, kidney, and systemic circulation, in both C57BL/6 (wild-type) and TLR4-null mice.

Results

Dynamic Network Analysis suggested that inflammation in the heart is most dependent on TLR4, followed by the liver, kidney, plasma, gut, lung, and spleen, and raises the possibility of non-TLR4 LPS signaling pathways at defined time points in the gut, lung, and spleen. Insights from computational analyses suggest an early role for TLR4-dependent tumor necrosis factor in coordinating multiple signaling pathways in the heart, giving way to later interleukin-17A—possibly derived from pathogenic Th17 cells and effector/memory T cells—in the spleen and blood.

Conclusions

We have derived novel, systems-level insights regarding the spatiotemporal evolution acute inflammation.

The Role of Cardiac Ganglia in the Prevention of Coronary Atherosclerosis: An Analytical Examination of Cholesterol-fed Rabbits

Background

The heart is innervated by the autonomic nervous system, which contributes to the control of the heart’s rhythm and coronary circulation. It has been suggested that the cardiac fibers of the vagus nerve play important roles in controlling circulatory functions and in protecting against atherosclerotic pathologies in coronary arteries.

Aims

To investigate the presence of atherosclerotic differences in the coronary arteries of cholesterol-fed rabbits by measuring the density of cardiac ganglia neurons.

Study Design

Animal experiment.

Methods

This study was conducted using 45 male rabbits. Over a period of 16 weeks, they were kept on an atherogenic diet of water ad libitum and high fat (8.6%) containing saturated fatty acids with 205 mg/kg of cholesterol (1%) per day. Then, their hearts were removed and examined by histopathological methods. Atherosclerotic plaques of the main coronary arteries were examined using the Cavalieri method. Atherosclerosis index values (AIVs) were estimated as the wall surface area/plaque surface area, and the results were analyzed with the Kruskal-Wallis and Mann-Whitney U tests.

Results

While the average atherosclerosis index value was estimated to be ≤8% in 21 animals, the atherosclerosis index value was 9-20% in animals with minor plaque detection (n=11) and ≥20% in animals with major plaque detection (n=10). Increased atherosclerosis index values were more common in animals with low neuron densities than in animals with high neuron densities (p<0.017).

Conclusion

The low neuron density of the cardiac ganglia in cholesterol-fed rabbits is associated with an increased atherosclerotic plaque incidence and volume.

Breath of Life: The Respiratory Vagal Stimulation Model of Contemplative Activity

Contemplative practices, such as meditation and yoga, are increasingly popular among the general public and as topics of research. Beneficial effects associated with these practices have been found on physical health, mental health and cognitive performance. However, studies and theories that clarify the underlying mechanisms are lacking or scarce. This theoretical review aims to address and compensate this scarcity. We will show that various contemplative activities have in common that breathing is regulated or attentively guided. This respiratory discipline in turn could parsimoniously explain the physical and mental benefits of contemplative activities through changes in autonomic balance. We propose a neurophysiological model that explains how these specific respiration styles could operate, by phasically and tonically stimulating the vagal nerve: respiratory vagal nerve stimulation (rVNS). The vagal nerve, as a proponent of the parasympathetic nervous system (PNS), is the prime candidate in explaining the effects of contemplative practices on health, mental health and cognition. We will discuss implications and limitations of our model.

A review of vagus nerve stimulation as a therapeutic intervention

In this review, we provide an overview of the US Food and Drug Administration (FDA)-approved clinical uses of vagus nerve stimulation (VNS) as well as information about the ongoing studies and preclinical research to expand the use of VNS to additional applications. VNS is currently FDA approved for therapeutic use in patients aged >12 years with drug-resistant epilepsy and depression. Recent studies of VNS in in vivo systems have shown that it has anti-inflammatory properties which has led to more preclinical research aimed at expanding VNS treatment across a wider range of inflammatory disorders. Although the signaling pathway and mechanism by which VNS affects inflammation remain unknown, VNS has shown promising results in treating chronic inflammatory disorders such as sepsis, lung injury, rheumatoid arthritis (RA), and diabetes. It is also being used to control pain in fibromyalgia and migraines. This new preclinical research shows that VNS bears the promise of being applied to a wider range of therapeutic applications.

Vagus Nerve Stimulation Modulates Complexity of Heart Rate Variability Differently during Sleep and Wakefulness

Progressive loss of heart rate variability (HRV) and complexity are associated with increased risk of mortality in patients with cardiovascular disease and are a candidate marker for patients at risk of sudden cardiac death. HRV is influenced by the cardiac autonomic nervous system (ANS), although it is unclear which arm of the ANS (sympathetic or parasympathetic) needs to be perturbed to increase the complexity of HRV. In this case–control study, we have analyzed the relation between modulation of vagus nerve stimulation (VNS) and changes in complexity of HRV as a function of states of vigilance. We hypothesize that VNS – being a preferential activator of the parasympathetic system – will decrease the heart rate (HR) and increase the complexity of HRV maximum during sleep. The electrocardiogram (EKG) obtained from a 37-year-old, right-handed male with known intractable partial epilepsy and left therapeutic VNS was analyzed during wakefulness and sleep with VNS ON and OFF states. Age-matched control EKG was obtained from five participants (three with intractable epilepsy and two without epilepsy) that had no VNS implant. The study demonstrated the following: (1) VNS increased the complexity of HRV during sleep and decreased it during wakefulness. (2) An increase in parasympathetic tone is associated with increased complexity of HRV even in the presence of decreased HR. These results need to be replicated in a larger cohort before developing patterned stimulation using VNS to stabilize cardiac dysautonomia and prevent fatal arrhythmias.

Autonomic boundary conditions for ventricular fibrillation and their implications for a novel defibrillation technique

The sympathetic and parasympathetic divisions of the autonomic nervous system modulate cardiac rhythm and the probability of arrhythmia occurrence. Both increased sympathetic drive and hypoxia increase the likelihood for ventricular fibrillation (VF). Vagus nerve stimulation (VNS) can protect from fatal arrhythmias via cholinergic and nitrergic action. We sought to determine boundary conditions for VF and defibrillation by autonomic manipulations accompanied or not by hypoxic changes in urethane-anesthetized rats. VF was induced with (1) vagotomy, (2) systemic high-dose (>15 mg/kg) isoproterenol, and (3) hypoxemia. When VNS (50 Hz) produced cardiac standstill, it converted every VF episode (59/59). A nitric oxide synthase inhibitor did not reduce VNS efficacy (13/14 episodes converted), but addition of atropine reduced VNS efficacy (11/27 episodes converted). VF can be induced by autonomic derangements only under constrained conditions, including sympathetic over-activation, reduced parasympathetic input, and hypoxemia. VNS can provide an alternative method to defibrillate via its cholinergic action.

Chronic inflammatory diseases are stimulated by current lifestyle: how diet, stress levels and medication prevent our body from recovering

Serhan and colleagues introduced the term "Resoleomics" in 1996 as the process of inflammation resolution. The major discovery of Serhan's work is that onset to conclusion of an inflammation is a controlled process of the immune system (IS) and not simply the consequence of an extinguished or "exhausted" immune reaction. Resoleomics can be considered as the evolutionary mechanism of restoring homeostatic balances after injury, inflammation and infection. Under normal circumstances, Resoleomics should be able to conclude inflammatory responses. Considering the modern pandemic increase of chronic medical and psychiatric illnesses involving chronic inflammation, it has become apparent that Resoleomics is not fulfilling its potential resolving capacity. We suggest that recent drastic changes in lifestyle, including diet and psycho-emotional stress, are responsible for inflammation and for disturbances in Resoleomics. In addition, current interventions, like chronic use of anti-inflammatory medication, suppress Resoleomics. These new lifestyle factors, including the use of medication, should be considered health hazards, as they are capable of long-term or chronic activation of the central stress axes. The IS is designed to produce solutions for fast, intensive hazards, not to cope with long-term, chronic stimulation. The never-ending stress factors of recent lifestyle changes have pushed the IS and the central stress system into a constant state of activity, leading to chronically unresolved inflammation and increased vulnerability for chronic disease. Our hypothesis is that modern diet, increased psycho-emotional stress and chronic use of anti-inflammatory medication disrupt the natural process of inflammation resolution ie Resoleomics.