Sympathetic neural mechanisms in human hypertension

Activation of Cannabinoid Type 2 Receptor in Microglia Reduces Neuroinflammation through Inhibiting Aerobic Glycolysis to Relieve Hypertension

BACKGROUND

Studies have shown that the chronic use of cannabis is associated with a decrease in blood pressure. Our previous studies prove that activating the cannabinoid type 2 (CB2) receptor in the brain can effectively reduce blood pressure in spontaneously hypertensive rats; however, the exact mechanism has not been clarified. The objective of this study is to demonstrate that activation of microglial CB2 receptors can effectively reduce the levels of TNF-α, IL-1β, and IL-6 in the paraventricular nucleus (PVN) through inhibiting aerobic glycolysis, thereby relieving hypertension.

METHODS

AngiotensinII (AngII) was administered to BV2 cells and C57 mice to induce hypertension and the release of proinflammatory cytokines. The mRNA and protein expression of the CB2 receptor, TNF-α, IL-1β, IL-6, and the PFK and LDHa enzymes were detected using RT-qPCR and Western blotting. The Seahorse XF Energy Metabolism Analyzer was used to measure the oxidative phosphorylation and aerobic glycolysis metabolic pathways in BV2 cells. The long-term effects of injecting JWH133, a selective CB2 receptor agonist, intraperitoneally on blood pressure were ascertained. ELISA was used to measure norepinephrine and lactic acid levels while immunofluorescence labeling was used to locate the CB2 receptor and c-Fos. By injecting pAAV-F4/80-GFP-mir30shRNA (AAV2-r-CB2shRNA) into the lateral cerebral ventricle, the CB2 receptor in microglia was specifically knocked down.

RESULTS

Activation of CB2 receptors by the agonist JWH133 suppressed TNF-α, IL-1β, and IL-6 by inhibiting PFK and LDHa enzymes involved in glycolysis, as well as lactic acid accumulation, along with a reduction in glycoPER levels (marks of aerobic glycolysis) in AngII-treated BV2 cells. In AngII-treated mice, the administration of JWH133 specifically activated CB2 receptors on microglia, resulting in decreased expression levels of PFK, LDHa, TNF-α, IL-1β, and IL-6, subsequently leading to a decrease in c-Fos protein expression within PVN neurons as well as reduced norepinephrine levels in plasma, ultimately contributing to blood pressure reduction.

CONCLUSION

The results suggest that activation of the microglia CB2 receptor decreases the neuroinflammation to relieve hypertension; the underlying mechanism is related to inhibiting aerobic glycolysis of microglia.

Modulation of Sympathetic Overactivity to Treat Resistant Hypertension

PURPOSE OF REVIEW

To review the role and evidence for sympathetic overactivity in resistant hypertension and review the therapies that have been studied to modulate the sympathetic nervous system to treat resistant hypertension, with a focus on non-pharmacologic therapies such as renal denervation, baroreflex activation therapy, and carotid body ablation.

RECENT FINDINGS

Based on the two best current techniques available for assessing sympathetic nerve activity, resistant hypertension is characterized by increased sympathetic nerve activity. Several device therapies, including renal denervation baroreflex activation therapy and carotid body ablation, have been developed as non-pharmacologic means of reducing blood pressure in resistant hypertension. With respect to renal denervation, the technologies for renal denervation have evolved since the unfavorable results from the HTN-3 study, and the revised technologies are being actively studied. Data from the first phase of the SPYRAL HTN Clinical Trial Program have been published. Results from the SPYRAL HTN-OFF MED trial suggest that ablating renal nerves can reduce blood pressure in patients with untreated mild-to-moderate hypertension. The SPYRAL HTN-ON MED trial demonstrated the safety and efficacy of catheter-based renal denervation in patients with uncontrolled hypertension on antihypertensive treatment. Interestingly, there was a high rate of medication non-adherence among patients with hypertension in this study. One attractive alternative to radiofrequency ablation is the use of ultrasound for renal denervation. Proof of concept data for the Paradise endovascular ultrasound renal denervation system was recently published in the RADIANCE-HTN SOLO trial. The results of this trial indicate that, among patients with mild to moderate hypertension on no medications, renal denervation with the Paradise system results in a greater reduction in both SBP and DBP at 2months compared with a sham procedure. Overall reductions were similar in magnitude to those noted in the SPYRAL HTN-OFF MED study. With respect to carotid body ablation, there is an ongoing proof of concept study that is investigating the safety and feasibility of ultrasound-based endovascular carotid body ablation in 30 subjects with treatment-resistant hypertension outside of the USA. The sympathetic nervous system is an important contributor to resistant hypertension. Modulation of sympathetic overactivity should be an important goal of treatment. Innovative therapies using non-pharmacologic means to suppress the sympathetic nervous system are actively being studied to treat resistant hypertension.

Role of cannabinoid receptor type 1 in rostral ventrolateral medulla in high-fat diet-induced hypertension in rats

BACKGROUND

Stimulation of cannabinoid type 1 (CB1) receptor in the rostral ventrolateral medulla (RVLM) increases renal sympathetic activity (RSNA) and blood pressure (BP) in rats. Thus, we hypothesized that CB1 receptor in the RVLM may play a critical role in the development of obesity-induced hypertension.

METHODS

To this end, we evaluated the levels of endocannabinoids and CB1 receptors in the RVLM in high-fat diet (HFD)-induced hypertensive rats. We then used pharmacological and molecular methods to examine the role of RVLM CB1 receptors in regulation of BP, heart rate (HR), and RSNA in obesity-induced hypertensive rats.

RESULTS

We found that HFD-fed rats exhibited higher basal BP, HR, and RSNA than standard diet-fed rats, which were associated with increased levels of endocannabinoids and CB1 receptor expression in the RVLM. Furthermore, unilateral intra-RVLM microinjections of AM251 (0, 100, or 500 nM/0.5 μl/site) dose-dependently decreased BP, HR, and RSNA to a greater extent in HFD-fed rats than in standard diet-fed rats. Finally, siRNA-mediated knockdown of CB1 receptor expression in the RVLM robustly decreased BP, HR, and RSNA in HFD-fed rats.

CONCLUSION

Taken together, our results suggested that enhanced CB1 receptor-mediated neurotransmissions in the RVLM may play a role in the development of obesity-induced hypertension.

Overactivation of cannabinoid receptor type 1 in rostral ventrolateral medulla promotes cardiovascular responses in spontaneously hypertensive rats

OBJECTIVE

Stimulation of cannabinoid type 1 (CB1) receptor in the rostral ventrolateral medulla (RVLM) increases renal sympathetic nerve activity (RSNA) and blood pressure (BP) in rats. Thus, we hypothesized that abnormal expression of CB1 receptor in the RVLM may play a critical role in the pathogenesis of essential hypertension.

METHODS

We evaluated the effects of intra-RVLM infusions of arachidonyl-2'-chloroethylamide (ACEA), selective CB1 receptor agonist, with or without AM251, selective CB1 receptor antagonist, on BP, heart rate (HR), and RSNA in spontaneously hypertensive rats and wild-type rats. We also assessed the protein level and surface expression of CB1 receptor in the RVLM in these rats.

RESULTS

We found that spontaneously hypertensive rats exhibited higher basal BP, HR, and RSNA than wild-type rats. Furthermore, unilateral intra-RVLM microinjections ACEA (0, 10, or 100 nM/0.5 μl/site) increased BP, HR, and RSNA to a greater extent in spontaneously hypertensive rats than in wild-type rats. These effects were abolished by co-administrations of AM251 (500 nM/0.5 μl/site) into the RVLM. In addition, the protein level of CB1 receptor in the RVLM was robustly increased in spontaneously hypertensive rats, which is correlated with ACEA-induced maximum changes of RSNA, and this was also associated with reduced expression of β-arrestin 2 in the RVLM in spontaneously hypertensive rats. Finally, overexpression of β-arrestin 2 in the RVLM in spontaneously hypertensive rats attenuated BP, HR and RSNA.

CONCLUSION

Taken together, our results suggested that alterations of CB1 receptor desensitization in the RVLM may play a role in the pathogenesis of essential hypertension.

Effect of Strength Training on Oxidative Stress and the Correlation of the Same with Forearm Vasodilatation and Blood Pressure of Hypertensive Elderly Women: A Randomized Clinical Trial

The aim of the study was to evaluate the effect of strength training on oxidative stress and the correlation of the same with forearm vasodilatation and mean blood pressure of hypertensive elderly women, at rest (basal) and during a static handgrip exercise. Insufficiently active hypertensive elderly women (N = 25; mean age = 66.1 years) were randomized into a 10 week strength training group (n = 13) or control (n = 12) group. Plasma malondialdehyde (MDA), total antioxidant capacity (TAC), plasma nitrite (NO2-), forearm blood flow (FBF), mean blood pressure (MBP) and vascular conductance ([FBF / MBP] x 100) were evaluated before and after the completion of the interventions. The strength training group increased the TAC (pre: Median = 39.0; Interquartile range = 34.0-41.5% vs post: Median = 44.0; Interquartile range = 38.0-51.5%; p = 0.006) and reduced the MDA (pre: 4.94 ± 1.10 μM vs post: 3.90 ± 1.35 μM; p = 0.025; CI-95%: -1.92 --0.16 μM). The strength training group increased basal vascular conductance (VC) (pre: 3.56 ±0.88 units vs post: 5.21 ±1.28 units; p = 0.001; CI-95%: 0.93-2.38 units) and decreased basal MBP (pre: 93.1 ±6.3 mmHg vs post: 88.9 ±5.4 mmHg; p = 0.035; CI-95%: -8.0 --0.4 mmHg). Such changes were also observed during static handgrip exercise. A moderate correlation was observed between changes in basal VC and MBP with changes in NO2- (ΔVC → r = -0.56, p = 0.047; ΔMBP → r = -0.41, p = 0.168) and MDA (ΔVC → r = 0.64, p = 0.019; ΔMBP → r = 0.31, p = 0.305). The strength training program reduced the oxidative stress of the hypertensive elderly women and this reduction was moderately correlated with their cardiovascular benefits.

TRIAL REGISTRATION

ensaiosclinicos.gov.br RBR-48c29w.

Sumac as a novel adjunctive treatment in hypertension: a randomized, double-blind, placebo-controlled clinical trial

Sumac; a novel adjunctive treatment in Blood Pressure.

Effects of different doses of dexmedetomidine on heart rate and blood pressure in intensive care unit patients

The aim of the present study was to observe and compare the sedative effect of different doses of DEX on heart rate (HR) and blood pressure (BP) in critically ill patients admitted to intensive care units (ICUs). The study included patients that were retained in ICUs and required sedation between January and March 2014. Patients were excluded if they had a BP of >200 mmHg, a HR of <60 bpm or were in a state of shock. The included patients were randomized into three groups: Group A, 1.0 µg/kg/10 min DEX; group B, 0.5 µg/kg/10 min DEX; and group C, 0.4 µg/kg/h DEX. After receiving these initial designated doses of DEX via an intravenous (IV) infusion pump for 10 min, the patients were maintained continuously at an identical dose of 0.4 µg/kg/h DEX. Ramsay score, HR, systolic blood pressure (SBP), diastolic blood pressure (DBP), breathing rate (BR) and peripheral capillary oxygen saturation (SpO₂) were recorded prior to the IV pump infusion and at 2, 4, 6, 8, 10, 60, 120, 180 and 240 min following infusion. Patients in groups A and B achieved sedation more rapidly compared with those in group C (P<0.05). HR decreased more significantly at 8 and 60 min after the initial IV pump infusion with DEX in groups A and B compared with group C (P<0.05). SBP decreased significantly at 10 min after IV pump infusion in group A compared with groups B and C (P<0.05). No significant difference existed in the SBP reduction trend between the three groups during the maintenance period. Therefore, the routine dose of DEX (0.4 µg/kg/h) provides an ideal sedative effect in ICU patients. The recommended loading dose for a more rapid sedation is 0.5 µg/kg/h. High loading doses of DEX via IV pump infusion should be avoided in elderly individuals, patients with acute exacerbation of chronic obstructive pulmonary disease and anemic patients, in whom combination medication, such as midazolam or propofol, may be considered when necessary.

The sympathetic nervous system as a target for the treatment of hypertension and cardiometabolic diseases

The regulation of blood pressure by the sympathetic nervous system is reviewed with an emphasis on the role of the sympathetic nervous system in the development and maintenance of hypertension. Evidence from patients and animal models is summarized. Because it is clear that there is a neural contribution to many types of human hypertension and other cardiometabolic diseases, the case is presented for a renewed emphasis on the development of sympatholytic approaches for the treatment of hypertension and other conditions associated with hyperactivity of the sympathetic nervous system.

Receptor tyrosine kinase Ephb6 regulates vascular smooth muscle contractility and modulates blood pressure in concert with sex hormones

Eph kinases constitute the largest receptor tyrosine kinase family, and their ligands, ephrins (Efns), are also cell surface molecules. Our study is the first to assess the role of Ephb6 in blood pressure (BP) regulation. We observed that EphB6 and all three of its Efnb ligands were expressed on vascular smooth muscle cells (VSMC) in mice. We discovered that small arteries from castrated Ephb6 gene KO males showed increased contractility, RhoA activation, and constitutive myosin light chain phosphorylation ex vivo compared with their WT counterparts. Consistent with this finding, castrated Ephb6 KO mice presented heightened BP compared with castrated WT controls. In vitro experiments in VSMC revealed that cross-linking Efnbs but not Ephb6 resulted in reduced VSMC contractions, suggesting that reverse signaling through Efnbs was responsible for the observed BP phenotype. The reverse signaling was mediated by an adaptor protein Grip1. Additional experiments demonstrated decreased 24-h urine catecholamines in male Ephb6 KO mice, probably as a compensatory feedback mechanism to keep their BP in the normal range. After castration, however, such compensation was abolished in Ephb6 KO mice and was likely the reason why BP increased overtly in these animals. It suggests that Ephb6 has a target in the nervous/endocrine system in addition to VSMC, regulating a testosterone-dependent catecholamine compensatory mechanism. Our study discloses that Ephs and Efns, in concert with testosterone, play a critical role in regulating small artery contractility and BP.

Switch to glutamate receptor 2-lacking AMPA receptors increases neuronal excitability in hypothalamus and sympathetic drive in hypertension

Glutamatergic synaptic input in the hypothalamic paraventricular nucleus (PVN) plays a critical role in regulating sympathetic outflow in hypertension. GluR2-lacking AMPA receptors (AMPARs) are permeable to Ca(2+), and their currents show unique inward rectification. However, little is known about changes in the AMPAR composition and its functional significance in hypertension. In this study, we found that AMPAR-mediated EPSCs (AMPAR-EPSCs) of retrogradely labeled spinally projecting PVN neurons exhibited a linear current-voltage relationship in Wistar-Kyoto (WKY) rats. However, AMPAR-EPSCs of labeled PVN neurons in spontaneously hypertensive rats (SHR) displayed inward rectification at positive holding potentials, which were not altered by lowering blood pressure with celiac ganglionectomy. Blocking GluR2-lacking AMPARs with 1-naphthyl acetyl spermine (NAS) caused a greater reduction in the AMPAR-EPSC amplitude and firing activity of PVN neurons in SHR than in WKY rats. Furthermore, blocking NMDA receptors and inhibition of calpain or calcineurin abolished inward rectification of AMPAR-EPSCs of PVN neurons in SHR. The GluR2 protein level was significantly less in the plasma membrane but greater in the cytosolic vesicle fraction in SHR than in WKY rats. In addition, microinjection of NAS into the PVN decreased blood pressure and lumbar sympathetic nerve activity in SHR but not in WKY rats. Our study reveals that increased GluR2-lacking AMPAR activity of PVN neurons results from GluR2 internalization through NMDA receptor-calpain-calcineurin signaling in hypertension. This phenotype switch in synaptic AMPARs contributes to increased excitability of PVN presympathetic neurons and sympathetic vasomotor tone in hypertension.

Vasopressin V1a receptor polymorphism and interval walking training effects in middle-aged and older people

We assessed whether single nucleotide polymorphism rs1042615 of the vasopressin V1a receptor altered the indices of lifestyle-related diseases in middle-aged and older people (mean+/-SD: 64+/-7 years), and, if so, whether it also altered the effects of interval walking training (IWT). CC, CT, and TT carriers of rs1042615 (42, 118, and 64 men, respectively; 113, 263, and 154 women, respectively) performed IWT. We included 5 sets of 3-minute fast walking at > or =70% peak aerobic capacity for walking and 3-minute slow walking at 40% peak aerobic capacity per day for > or =4 days per week for 5 months. Before IWT, the body mass index and diastolic blood pressure (DBP) for men were 25.1+/-0.3 kg/m(2) (mean+/-SE) and 84+/-1 mm Hg in TT, higher than the 23.6+/-0.4 kg/m(2) and 78+/-1 mm Hg in CC, respectively (P<0.01), differences that disappeared after IWT despite similar training achievement between groups (P>0.6). After IWT, body mass index and DBP decreased in TT (-0.9+/-0.1 kg/m(2) and -5+/-1 mm Hg, respectively), more than in CC (-0.5+/-0.1 kg/m(2) and 1+/-1 mm Hg, respectively; P<0.05), with a greater decrease in low-density lipoprotein cholesterol in TT than CC carriers (P<0.01). The decreases in DBP and low-density lipoprotein cholesterol were still greater in TT carriers even after adjustment for their pretraining values. On the other hand, for women, these parameters before IWT and their changes after IWT were similar among CC, CT, and TT carriers. Thus, polymorphism rs1042615 of the V1a receptor altered body mass index and DBP in middle-aged and older men and the training-induced responses of DBP and low-density lipoprotein cholesterol, whereas women did not show any of these responses.

Phosducin influences sympathetic activity and prevents stress-induced hypertension in humans and mice

Hypertension and its complications represent leading causes of morbidity and mortality. Although the cause of hypertension is unknown in most patients, genetic factors are recognized as contributing significantly to an individual's lifetime risk of developing the condition. Here, we investigated the role of the G protein regulator phosducin (Pdc) in hypertension. Mice with a targeted deletion of the gene encoding Pdc (Pdc-/- mice) had increased blood pressure despite normal cardiac function and vascular reactivity, and displayed elevated catecholamine turnover in the peripheral sympathetic system. Isolated postganglionic sympathetic neurons from Pdc-/- mice showed prolonged action potential firing after stimulation with acetylcholine and increased firing frequencies during membrane depolarization. Furthermore, Pdc-/- mice displayed exaggerated increases in blood pressure in response to post-operative stress. Candidate gene-based association studies in 2 different human populations revealed several SNPs in the PDC gene to be associated with stress-dependent blood pressure phenotypes. Individuals homozygous for the G allele of an intronic PDC SNP (rs12402521) had 12-15 mmHg higher blood pressure than those carrying the A allele. These findings demonstrate that PDC is an important modulator of sympathetic activity and blood pressure and may thus represent a promising target for treatment of stress-dependent hypertension.