Exercise benefits cardiovascular health in hyperlipidemia rats correlating with changes of the cardiac vagus nerve

Time-domain heart rate dynamics in the prognosis of progressive atherosclerosis

BACKGROUND AND AIM

The regular uptake of a high-fat diet (HFD) with changing lifestyle causes atherosclerosis leading to cardiovascular diseases and autonomic dysfunction. Therefore, the current study aimed to investigate the correlation of autonomic activity to lipid and atherosclerosis markers. Further, the study proposes a support vector machine (SVM) based model in the prediction of atherosclerosis severity.

METHODS AND RESULTS

The Lead-II electrocardiogram and blood markers were measured from both the control and the experiment subjects each week for nine consecutive weeks. The time-domain heart rate variability (HRV) parameters were derived, and the significance level was tested using a one-way Analysis of Variance. The correlation analysis was performed to determine the relation between autonomic parameters and lipid and atherosclerosis markers. The statistically significant time-domain values were used as features of the SVM. The observed results demonstrated the reduced time domain HRV parameters with the increase in lipid and atherosclerosis index markers with the progressive atherosclerosis severity. The correlation analysis revealed a negative association between time-domain HRV parameters with lipid and atherosclerosis parameters. The percentage accuracy increases from 86.58% to 98.71% with the increase in atherosclerosis severity with regular consumption of HFD.

CONCLUSIONS

Atherosclerosis causes autonomic dysfunction with reduced HRV. The negative correlation between autonomic parameters and lipid profile and atherosclerosis indexes marker revealed the potential role of vagal activity in the prognosis of atherosclerosis progression. The support vector machine presented a respectable accuracy in the prediction of atherosclerosis severity from the control group.

Exercise Attenuates Myocardial Ischemia-Reperfusion Injury by Regulating Endoplasmic Reticulum Stress and Mitophagy Through M2 Acetylcholine Receptor

Aims: Adaptive changes in the heart by exercise have been shown to reduce the risk of cardiovascular disease, and M2 Acetylcholine receptor (M2AChR), a receptor abundantly present on cardiac parasympathetic nerves, is closely associated with the development of cardiovascular disease. The present study intends to investigate whether exercise can regulate endoplasmic reticulum stress (ERS) and mitophagy through M2AChR to resist myocardial ischemia-reperfusion (I/R) injury and to elucidate its mechanism of action. Results: Exercise enhanced parasympathetic nerve function and increased myocardial M2AChR protein expression in I/R rats. In addition, it promoted the protein expression of MFN2 and inhibited the expression of Drp1, Chop, PINK1/Parkin, and PERK/eIF2α/ATF4 signaling pathways, effectively reducing mitophagy, ERS, and apoptosis. At the cellular level, 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) reduced hypoxia/reoxygenation (H/R)-induced ERS through the downregulated expression of PERK/eIF2α/ATF4 pathway proteins in H9C2 cardiomyocytes. When intervened with M2AChR inhibitors, the levels of ERS and phosphorylation levels of the PERK/eIF2α/ATF4 pathway were increased in H/R cells. Innovation and Conclusion: Exercise intervention activated the parasympathetic state in rats. It inhibited myocardial mitophagy and ERS levels, and reduced myocardial apoptosis through M2AChR, thereby resisting I/R-induced myocardial injury and improving cardiac function. Antioxid. Redox Signal. 40, 209-221.

Resveratrol and regular exercise may attenuate hypertension-induced cardiac dysfunction through modulation of cellular stress responses

AIMS

Hypertension is one of the major causes of cardiac damage. In this study, the effects of resveratrol supplementation and regular exercise on hypertension-induced cellular stress responses of myocardium were compared.

MAIN METHODS

Hypertension was induced in male Wistar rats by deoxycorticosterone-acetate + salt administration for 12 weeks. Resveratrol and regular exercise were applied for the last six weeks. In addition to biochemical and molecular examinations, isoprenaline, phenylephrine and, acetylcholine-mediated contractions and sinus rate were recorded in the isolated cardiac tissues.

KEY FINDINGS

Resveratrol and regular exercise reduced systolic blood pressure in hypertensive rats. The altered adrenergic and cholinergic responses of the right atrium and left papillary muscles in hypertension were separately improved by resveratrol and regular exercise. Resveratrol and regular exercise decreased plasma and cardiac total antioxidant capacity and, augmented the expression of antioxidant genes in hypertensive rats. While regular exercise restored the increase in p-PERK expression associated with endoplasmic reticulum stress and decrease in mitophagic marker PINK1 expression, resveratrol only ameliorated PINK1 expression in hypertensive rats. Resveratrol and exercise training suppressed hypertension-induced NLRP3 inflammasome activation by reversing the increase in NLRP3, p-NF-κB expression and the mature-IL-1β/pro-IL-1β and cleaved-caspase-1/pro-caspase-1 ratio. Resveratrol and exercise enhanced mRNA expression of caspase-3, bax, and bcl-2 involved in the apoptotic pathway, but attenuated phosphorylation of stress-related mitogenic proteins p38 and JNK induced by hypertension.

SIGNIFICANCE

Our study demonstrated the protective effect of resveratrol and exercise on hypertension-induced cardiac dysfunction by modulating cellular stress responses including oxidative stress, ER stress, mitophagy, NLRP3 inflammasome-mediated inflammation, and mitogenic activation.

Aerobic exercise ameliorates cardiac hypertrophy by regulating mitochondrial quality control and endoplasmic reticulum stress through M2 AChR

Aerobic exercise increases M2 AChR, which thus improves cardiac function in cardiovascular disease (CVD) rats. This study aimed to determine whether aerobic exercise could ameliorate pressure overload-induced heart hypertrophy through M2 AChR, and to elucidate the underlying mechanisms of action. Mice were used to establish the myocardial hypertrophy model by transverse aortic constriction (TAC), and subjected to 2, 4, and 8 weeks of moderate-intensity aerobic exercise and choline intervention (14 mg/kg/day). Our results showed that 4 and 8 weeks of exercise and choline intervention reduced excessive mitochondrial fission and autophagy of myocardial mitochondria, thereby improving the ultrastructure and function of mitochondria after TAC. Moreover, 8-week exercise and choline intervention have enhanced parasympathetic function and promoted the expression of M2 AChR. In addition, 8-week exercise and choline intervention also inhibited the protein expression of myocardial MFN2, PERK/eIF2α/ATF4, and NLRP3/caspase-1/IL-1β signaling pathways, thereby effectively reducing mitochondrial fusion, endoplasmic reticulum stress, and inflammation. Taken together, these data suggest that pressure overload led to cardiac hypertrophy, cardiac dysfunction, and decreased parasympathetic function in cardiac tissues. Aerobic exercise attenuated cardiac dysfunction by modulating the expression of proteins involved in mitochondrial quality control, and induced endoplasmic reticulum stress and inflammation, thereby reducing cardiac hypertrophy and improving cardiac function in impaired heart tissues following TAC, which was likely mediated by M2 AChR activation.

Pharmacological Modulation of Vagal Nerve Activity in Cardiovascular Diseases

Cardiovascular diseases are life-threatening illnesses with high morbidity and mortality. Suppressed vagal (parasympathetic) activity and increased sympathetic activity are involved in these diseases. Currently, pharmacological interventions primarily aim to inhibit over-excitation of sympathetic nerves, while vagal modulation has been largely neglected. Many studies have demonstrated that increased vagal activity reduces cardiovascular risk factors in both animal models and human patients. Therefore, the improvement of vagal activity may be an alternate approach for the treatment of cardiovascular diseases. However, drugs used for vagus nerve activation in cardiovascular diseases are limited in the clinic. In this review, we provide an overview of the potential drug targets for modulating vagal nerve activation, including muscarinic, and β-adrenergic receptors. In addition, vagomimetic drugs (such as choline, acetylcholine, and pyridostigmine) and the mechanism underlying their cardiovascular protective effects are also discussed.

The Influence of Environmental Enrichment on Cardiovascular and Behavioral Responses to Social Stress

OBJECTIVE

Stress is linked to negative cardiovascular consequences and increases in depressive behaviors. Environmental enrichment (EE) involves exposure to novel items that provide physical and cognitive stimulation. EE has behavioral, cognitive, and neurobiological effects that may improve stress responses in humans and animal models. This study investigated the potential protective effects of EE on behavior and cardiovascular function in female prairie voles after a social stressor.

METHODS

Radiotelemetry transmitters were implanted into female prairie voles to measure heart rate (HR) and heart rate variability (HRV) throughout the study. All females were paired with a male partner for 5 days, followed by separation from their partner for 5 additional days, and a 10-day treatment period. Treatment consisted of continued isolation, isolation with EE, or re-pairing with the partner (n = 9 per group). After treatment, animals were observed in the forced swim test (FST) for measures of stress coping behaviors.

RESULTS

Isolation elevated HR and reduced HRV relative to baseline for all groups (p < .001). HR and HRV returned to baseline in the EE and re-paired groups, but not in the continued isolation group (p < .001). Animals in the EE and re-paired groups displayed significantly lower immobility time (p < .001) and HR (p < .03) during the FST, with a shorter latency for HR to return to baseline levels after the FST, relative to the continued isolation group (p < .001).

CONCLUSIONS

EE and re-pairing reversed the negative behavioral and cardiovascular consequences associated with social isolation.

Vagal Modulation of the Inflammatory Response in Sepsis

The vagus nerve can sense peripheral inflammation and transmit action potentials from the periphery to the brainstem. Vagal afferent signaling is integrated in the brainstem, and efferent vagus nerves carry outbound signals that terminate in spleen and other organs. Stimulation of efferent vagus nerve leads to the release of acetylcholine in these organs. In turn, acetylcholine interacts with members of the nicotinic acetylcholine receptor (nAChR) family, particularly with the alpha7 nicotinic acetylcholine receptor (α7nAChR), which is expressed by macrophages and other cytokine-producing cells. Ultimately, the production of proinflammatory cytokines is markedly inhibited. This neuroimmune communication is termed "the inflammatory reflex". The uncontrolled inflammation as a result from sepsis can lead to multiple organ failure, and even death. Experimental data show that regulation of the inflammatory reflex appears to be a useful interventional strategy for septic response. Herein, we review recent advances in the understanding of the inflammatory reflex and discuss potential therapeutics that vagal modulation of the immune system for the treatment of severe sepsis and septic shock.

Novel strategies and underlying protective mechanisms of modulation of vagal activity in cardiovascular diseases

Cardiovascular disease remains a major cause of disability and death worldwide. Autonomic imbalance, characterized by suppressed vagal (parasympathetic) activity and increased sympathetic activity, correlates with various pathological conditions, including heart failure, arrhythmia, ischaemia/reperfusion injury and hypertension. Conventionally, pharmacological interventions, such as β-blocker treatment, have primarily targeted suppressing sympathetic over-activation, while vagal modulation has always been neglected. Emerging evidence has documented the improvement of cardiac and vascular function mediated by the vagal nerve. Many investigators have tried to explore the effective ways to enhance vagal tone and normalize the autonomic nervous system. In this review, we attempt to give an overview of these therapeutic strategies, including direct vagal activation (electrical vagal stimulation, ACh administration and ACh receptor activation), pharmacological modulation (adenosine, cholinesterase inhibitors, statins) and exercise training. This overview provides valuable information for combination therapy, contributing to establishment of a comprehensive system on vagal modulation from the aspects of clinical application and lifestyle improvement. In addition, the mechanisms contributing to the benefits of enhancing vagal tone are diverse and have not yet been fully defined. We endeavour to outline the recent findings that advance our knowledge regarding the many favourable effects exerted by vagal activation: anti-inflammatory pathways, modulation of NOS and NO signalling, regulation of redox state, improvement of mitochondrial biogenesis and function, and potential calcium regulation. This review may help to develop novel therapeutic strategies targeting enhancing vagal activity for the treatment of cardiovascular diseases.

Exercise training reduces insulin resistance in postmyocardial infarction rats

Myocardial infarction (MI) induces cardiac dysfunction and insulin resistance (IR). This study examines the effects of MI-related IR on vasorelaxation and its underlying mechanisms, with a specific focus on the role of exercise in reversing the impaired vasorelaxation. Adult male Sprague-Dawley rats were divided into three groups: Sham, MI, and MI+Exercise. MI+Exercise rats were subjected to 8 weeks of treadmill training. Cardiac contraction, myocardial and arterial structure, vasorelaxation, levels of inflammatory cytokines, expression of eNOS and TNF-α, and activation of PI3K/Akt/eNOS and p38 mitogen-activated protein kinase (p38 MAPK) were determined in aortas. MI significantly impaired endothelial structure and vasodilation (P < 0.05-0.01), as indicated by decreased arterial vasorelaxation to ACh and insulin. MI also attenuated the myocardial contractile response, decreased aortic PI3K/Akt/eNOS expression and phosphorylation by insulin, and increased IL-1β, IL-6, and TNF-α expression and p38 MAPK activity (P < 0.05-0.01). Exercise improved insulin sensitivity in aortas, facilitated myocardial contractile response and arterial vasorelaxation to ACh and insulin, and increased arterial PI3K/Akt/eNOS activity. Moreover, exercise markedly reversed increased p38 MAPK activity and normalized inflammatory cytokines in post-MI arteries. Inhibition of PI3K with LY-294002, and eNOS with L-NAME significantly blocked arterial vasorelaxation and PI3K/Akt/eNOS phosphorylation in response to insulin. In conclusion, these results demonstrate that endothelial dysfunction in response to insulin plays an important role in MI-related IR. The reversal of IR by exercise is most likely associated with normalizing inflammatory cytokines, increasing the activation of PI3K/Akt/eNOS, and reducing the activation of p38 MAPK.

Exercise training starting at weaning age preserves cardiac pacemaker function in adulthood of diet-induced obese rats

Peripheral sympathetic overdrive in young obese subjects contributes to further aggravation of insulin resistance, diabetes, and hypertension, thus inducing worsening clinical conditions in adulthood. Exercise training has been considered a strategy to repair obesity autonomic dysfunction, thereby reducing the cardiometabolic risk. Therefore, the aim of this study was to assess the effect of early exercise training, starting immediately after weaning, on cardiac autonomic control in diet-induced obese rats. Male Wistar rats (weaning) were divided into four groups: (i) a control group (n = 6); (ii) an exercise-trained control group (n = 6); (iii) a diet-induced obesity group (n = 6); and (iv) an exercise-trained diet-induced obesity group (n = 6). The development of obesity was induced by 9 weeks of palatable diet intake, and the training program was implemented in a motor-driven treadmill (5 times per week) during the same period. After this period, animals were submitted to vein and artery catheter implantation to assess cardiac autonomic balance by methylatropine (3 mg/kg) and propranolol (4 mg/kg) administration. Exercise training increased running performance in both groups (p < 0.05). Exercise training also prevented the increased resting heart rate in obese rats, which seemed to be related to cardiac pacemaker activity preservation (p < 0.05). Additionally, the training program preserved the pressure and bradycardia responses to autonomic blockade in obese rats (p < 0.05). An exercise program beginning at weaning age prevents cardiovascular dysfunction in obese rats, indicating that exercise training may be used as a nonpharmacological therapeutic strategy for the treatment of cardiometabolic diseases.

Exercise improves the dilatation function of mesenteric arteries in postmyocardial infarction rats via a PI3K/Akt/eNOS pathway-mediated mechanism

Myocardial infarction (MI) has been shown to induce endothelial dysfunction in peripheral resistance arteries and thus increase peripheral resistance. This study was designed to investigate the underlying mechanisms of post-MI-related dysfunctional dilatation of peripheral resistance arteries and, furthermore, to examine whether exercise may restore dysfunctional dilatation of peripheral resistance arteries. Adult male Sprague-Dawley rats were divided into three groups: sham-operated, MI, and MI + exercise. Ultrastructure and relaxation function of the mesenteric arteries, as well as phosphatidylinositol-3 kinase (PI3K), Akt kinases (Akt), endothelial nitric oxide synthase (eNOS) activity, and phosphorylation of PI3K, Akt, and eNOS by ACh were determined. Post-MI rats exhibited pronounced ultrastructural changes in mesenteric artery endothelial cells and endothelial dysfunction. In addition, the activities of PI3K, Akt, and eNOS, and their phosphorylation by ACh were significantly attenuated in mesenteric arteries (P < 0.05-0.01). After 8 wk of exercise, not only did endothelial cells appeared more normal in structure, but also ameliorated post-MI-associated mesenteric arterial dysfunction, which were accompanied by elevated activities of PI3K, Akt, and eNOS, and their phosphorylation by ACh (P < 0.05-0.01). Importantly, inhibition of either PI3K or eNOS attenuated exercise-induced restoration of the dilatation function and blocked PI3K, Akt, and eNOS phosphorylation by ACh in the mesenteric arteries. These data demonstrate that MI induces dysfunctional dilation of peripheral resistance arteries by degradation of endothelial structural integrity and attenuating PI3K-Akt-eNOS signaling. Exercise may restore dilatation function of peripheral resistance arteries by protecting endothelial structural integrity and increasing PI3K-Akt-eNOS signaling cascades.