Microglia, autonomic nervous system, immunity and hypertension: Is there a link?

Causal associations between hypertension and abnormal brain cortical structures: Insights from a bidirectional Mendelian randomization study

Background

Observational studies suggest that hypertension affects brain cortical structure. However, the potential causal association has yet to be entirely determined. Thus, we aim to assess the causality between hypertension and abnormal cortical structure.

Methods

We conducted a bidirectional Mendelian randomization (MR) study to estimate their relationship. Genome-wide association study summary statistics of hypertension (n = 484,598) and brain cortical (surface area and thickness) (n = 51,665) were derived from publicly available databases. Sensitivity analyses were applied to ensure the robustness of the results.

Results

The study showed that hypertension was associated with a decline in total brain cortical thickness [β, -0.0308 mm; 95 % confidence interval (CI), -0.0610 to -0.0007; p = 0.045] and the insula thickness [β, -0.0415 mm; 95 % CI, -0.0772 to -0.0057; p = 0.023]. A null association was observed between hypertension and other brain regions. In the reverse MR analysis, the total cortical surface area (per 1 SD increase) significantly decreased the incidence of hypertension [odds ratio (OR), 0.976; 95 % CI, 0.963 to 0.990; p = 5.15E-04]. The caudal anterior cingulate cortex thickness (per 1 SD increase) was significantly associated with an increased risk of hypertension [OR, 1.057; 95 % CI, 1.034 to 1.082; p = 1.08E-06]. Moreover, we found several nominally associated gyri, including cuneus, isthmus cingulate, middle temporal, para hippocampal, posterior cingulate, superior temporal, and medial orbitofrontal, influence the incidence of hypertension.

Conclusion

Our study showed causal relationships between hypertension and changes in specific brain cortical, providing new evidence for the heart-brain axis theory.

Irisin Attenuates Neuroinflammation Targeting the NLRP3 Inflammasome

Neuroinflammation is defined as an immune response involving various cell types, particularly microglia, which monitor the neuroimmune axis. Microglia activate in two distinct ways: M1, which is pro-inflammatory and capable of inducing phagocytosis and releasing pro-inflammatory factors, and M2, which has anti-inflammatory properties. Inflammasomes are large protein complexes that form in response to internal danger signals, activating caspase-1 and leading to the release of pro-inflammatory cytokines such as interleukin 1β. Irisin, a peptide primarily released by muscles during exercise, was examined for its effects on BV2 microglial cells in vitro. Even at low concentrations, irisin was observed to influence the NLRP3 inflammasome, showing potential as a neuroprotective and anti-inflammatory agent after stimulation with lipopolysaccharides (LPSs). Irisin helped maintain microglia in their typical physiological state and reduced their migratory capacity. Irisin also increased Arg-1 protein expression, a marker of M2 polarization, while downregulating NLRP3, Pycard, caspase-1, IL-1β, and CD14. The results of this study indicate that irisin may serve as a crucial mediator of neuroprotection, thus representing an innovative tool for the prevention of neurodegenerative diseases.

Improvement of the Immunity System Through Sports: Novel Regulatory Mechanisms for Hypertension

Hypertension and its resulting target organ damage is a complex process associated with a range of physiological and molecular factors, including immune regulation. The profound effects of exercise on normal immune system function and the development and progression of hypertension are well known. This review aims to create new avenues for preventing and treating hypertension and its associated target organ damage. This narrative review emphasizes the role of exercise training in the prevention/treatment of hypertension development through immune response modulation and presents current perspectives on the available scientific evidence. Several studies have shown that exercise regulates hypertension by altering immune cells, which is partly attributable to the anti-inflammatory effects of exercise training. Regular exercise modifies immune modulation and could represent a new mechanism for regulating hypertension. Although the utilization of exercise training and the immune system in conjunction for treating and preventing hypertension is still in its early stages, current scientific literature indicates numerous potential physiological links between exercise training, the immune system, and hypertension.

Angiotensin II, blood-brain barrier permeability, and microglia interplay during the transition from pre-to hypertensive phase in spontaneously hypertensive rats

Background

Hypertension is characterized by upregulation of the renin-angiotensin system, increased blood-brain barrier (BBB) permeability, microglia activation within autonomic nuclei, and an intense sympathoexcitation. There is no information on the interplay of these events during the development of neurogenic hypertension. We sought to identify the interaction and time-course changes of Ang II availability, barrier dysfunction, microglia activation, and autonomic imbalance within autonomic areas during the development of neurogenic hypertension.

Methods

Sequential changes of hemodynamic/autonomic parameters, BBB permeability, microglia structure/density (IBA-1), and angiotensin II (Ang II) immunofluorescence were evaluated within the paraventricular hypothalamic nucleus, nucleus of the solitary tract, and rostral ventrolateral medulla of Wistar and spontaneously hypertensive rats (SHRs) aged 4 weeks, 5 weeks, 6 weeks, 8 weeks, and 12 weeks. The somatosensory cortex and hypoglossal nucleus were also analyzed as non-autonomic control areas.

Results

Increased brain Ang II availability (4th-5th week) was the first observed change, followed by the incipient BBB leakage and increased microglia density (6th week). From the 5th-6th weeks on, BBB leakage, Ang II, and IBA-1 densities increased continuously, allowing a parallel increase in both Ang II-microglia colocalization and the transition of microglial cells from highly ramified in the basal surveillant condition (4th-5th week) to shorter process arbors, fewer endpoints, and enlarged soma in the disease-associate condition (6th week to the 12th week). Simultaneously with increased Ang II-microglia colocalization and microglia morphologic phenotypic changes, sympathetic activity and pressure variability increased, autonomic control deteriorated, and blood pressure increased. These responses were not specific for autonomic nuclei but also occurred at a lower magnitude in the somatosensory cortex and hypoglossal nucleus, indicating the predominance of hypertension-induced effects on autonomic areas. No changes were observed in age-matched controls where Ang II density did not change.

Conclusion

Brain Ang II density is the initial stimulus to drive coordinated changes in BBB permeability and microglial reactivity. Increased BBB dysfunction allows access of plasma Ang II and increases its local availability and the colocalization and activation of microglial cells. It is a potent stimulus to augments vasomotor sympathetic activity, autonomic imbalance, and pressure elevation during the establishment of hypertension.

Microglia in the hypothalamic paraventricular nucleus sense hemodynamic disturbance and promote sympathetic excitation in hypertension

Hypertension is usually accompanied by elevated sympathetic tonicity, but how sympathetic hyperactivity is triggered is not clear. Recent advances revealed that microglia-centered neuroinflammation contributes to sympathetic excitation in hypertension. In this study, we performed a temporospatial analysis of microglia at both morphological and transcriptomic levels and found that microglia in the hypothalamic paraventricular nucleus (PVN), a sympathetic center, were early responders to hypertensive challenges. Vasculature analyses revealed that the PVN was characterized by high capillary density, thin vessel diameter, and complex vascular topology relative to other brain regions. As such, the PVN was susceptible to the penetration of ATP released from the vasculature in response to hemodynamic disturbance after blood pressure increase. Mechanistically, ATP ligation to microglial P2Y12 receptor was responsible for microglial inflammatory activation and the eventual sympathetic overflow. Together, these findings identified a distinct vasculature pattern rendering vulnerability of PVN pre-sympathetic neurons to hypertension-associated microglia-mediated inflammatory insults.

Examination of the Relationship Between Sensory Processing Skills, Kinesiophobia and Fear of Falling in Older Adults with Hypertension and Normotension

OBJECTIVES

The aim of the study was to investigate fear of falling, kinesiophobia, and sensory processing in older adults with hypertension and normotension.

METHODS

Older adults, 62 with hypertension and 62 with normotension, aged 65-84 years were included in the study. The assessment of fear of falling was conducted using the Tinetti Falls Efficacy Scale, kinesiophobia was evaluated with the Tampa Kinesiophobia Scale, and sensory processing skills were analyzed with the Adolescent/Adult Sensory Profile.

RESULTS

Significant differences were found between the groups in terms of vestibular processing, visual processing and activity level, fear of falling and kinesiophobia (p < .05). No significant differences were found between the groups with respect to taste/smell, tactile, and auditory processing skills. The findings revealed that older adults with hypertension exhibited diminished vestibular and visual processing abilities, reduced activity levels, and heightened concerns about falling and a tendency to experience kinesiophobia. Fear of falling and kinesiophobia were found to increase with decreasing vestibular processing skills and activity levels in both groups (p < .05). Regression analysis revealed that age, kinesiophobia, vestibular processing, and activity levels were significant determinants of fear of falling (p < .05).

CONCLUSION

It is recommended that older adults with hypertension be assessed in terms of sensory, functional, and mental health, with the objective of planning appropriate intervention approaches.

Dynamic dysregulation of transcriptomic networks in brainstem autonomic nuclei during hypertension development in the female spontaneously hypertensive rat

Neurogenic hypertension stems from an imbalance in autonomic function that shifts the central cardiovascular control circuits toward a state of dysfunction. Using the female spontaneously hypertensive rat and the normotensive Wistar-Kyoto rat model, we compared the transcriptomic changes in three autonomic nuclei in the brainstem, nucleus of the solitary tract (NTS), caudal ventrolateral medulla, and rostral ventrolateral medulla (RVLM) in a time series at 8, 10, 12, 16, and 24 wk of age, spanning the prehypertensive stage through extended chronic hypertension. RNA-sequencing data were analyzed using an unbiased, dynamic pattern-based approach that uncovered dominant and several subtle differential gene regulatory signatures. Our results showed a persistent dysregulation across all three autonomic nuclei regardless of the stage of hypertension development as well as a cascade of transient dysregulation beginning in the RVLM at the prehypertensive stage that shifts toward the NTS at the hypertension onset. Genes that were persistently dysregulated were heavily enriched for immunological processes such as antigen processing and presentation, the adaptive immune response, and the complement system. Genes with transient dysregulation were also largely region-specific and were annotated for processes that influence neuronal excitability such as synaptic vesicle release, neurotransmitter transport, and an array of neuropeptides and ion channels. Our results demonstrate that neurogenic hypertension is characterized by brainstem region-specific transcriptomic changes that are highly dynamic with significant gene regulatory changes occurring at the hypertension onset as a key time window for dysregulation of homeostatic processes across the autonomic control circuits.NEW & NOTEWORTHY Hypertension is a major disease and is the primary risk factor for cardiovascular complications and stroke. The gene expression changes in the central nervous system circuits driving hypertension are understudied. Here, we show that coordinated and region-specific gene expression changes occur in the brainstem autonomic circuits over time during the development of a high blood pressure phenotype in a rat model of human essential hypertension.

Induced Relaxation Enhances the Cardiorespiratory Dynamics in COVID-19 Survivors

Most COVID-19 survivors report experiencing at least one persistent symptom after recovery, including sympathovagal imbalance. Relaxation techniques based on slow-paced breathing have proven to be beneficial for cardiovascular and respiratory dynamics in healthy subjects and patients with various diseases. Therefore, the present study aimed to explore the cardiorespiratory dynamics by linear and nonlinear analysis of photoplethysmographic and respiratory time series on COVID-19 survivors under a psychophysiological assessment that includes slow-paced breathing. We analyzed photoplethysmographic and respiratory signals of 49 COVID-19 survivors to assess breathing rate variability (BRV), pulse rate variability (PRV), and pulse-respiration quotient (PRQ) during a psychophysiological assessment. Additionally, a comorbidity-based analysis was conducted to evaluate group changes. Our results indicate that all BRV indices significantly differed when performing slow-paced breathing. Nonlinear parameters of PRV were more appropriate for identifying changes in breathing patterns than linear indices. Furthermore, the mean and standard deviation of PRQ exhibited a significant increase while sample and fuzzy entropies decreased during diaphragmatic breathing. Thus, our findings suggest that slow-paced breathing may improve the cardiorespiratory dynamics of COVID-19 survivors in the short term by enhancing cardiorespiratory coupling via increased vagal activity.

Intermittent Lead Exposure Induces Behavioral and Cardiovascular Alterations Associated with Neuroinflammation

The nervous system is the primary target for lead exposure and the developing brain appears to be especially susceptible, namely the hippocampus. The mechanisms of lead neurotoxicity remain unclear, but microgliosis and astrogliosis are potential candidates, leading to an inflammatory cascade and interrupting the pathways involved in hippocampal functions. Moreover, these molecular changes can be impactful as they may contribute to the pathophysiology of behavioral deficits and cardiovascular complications observed in chronic lead exposure. Nevertheless, the health effects and the underlying influence mechanism of intermittent lead exposure in the nervous and cardiovascular systems are still vague. Thus, we used a rat model of intermittent lead exposure to determine the systemic effects of lead and on microglial and astroglial activation in the hippocampal dentate gyrus throughout time. In this study, the intermittent group was exposed to lead from the fetal period until 12 weeks of age, no exposure (tap water) until 20 weeks, and a second exposure from 20 to 28 weeks of age. A control group (without lead exposure) matched in age and sex was used. At 12, 20 and 28 weeks of age, both groups were submitted to a physiological and behavioral evaluation. Behavioral tests were performed for the assessment of anxiety-like behavior and locomotor activity (open-field test), and memory (novel object recognition test). In the physiological evaluation, in an acute experiment, blood pressure, electrocardiogram, and heart and respiratory rates were recorded, and autonomic reflexes were evaluated. The expression of GFAP, Iba-1, NeuN and Synaptophysin in the hippocampal dentate gyrus was assessed. Intermittent lead exposure induced microgliosis and astrogliosis in the hippocampus of rats and changes in behavioral and cardiovascular function. We identified increases in GFAP and Iba1 markers together with presynaptic dysfunction in the hippocampus, concomitant with behavioral changes. This type of exposure produced significant long-term memory dysfunction. Regarding physiological changes, hypertension, tachypnea, baroreceptor reflex impairment and increased chemoreceptor reflex sensitivity were observed. In conclusion, the present study demonstrated the potential of lead intermittent exposure inducing reactive astrogliosis and microgliosis, along with a presynaptic loss that was accompanied by alterations of homeostatic mechanisms. This suggests that chronic neuroinflammation promoted by intermittent lead exposure since fetal period may increase the susceptibility to adverse events in individuals with pre-existing cardiovascular disease and/or in the elderly.

Adrenoceptors as potential target for add-on immunomodulatory therapy in multiple sclerosis

This review summarizes recent findings related to the role of the sympathetic nervous system (SNS) in pathogenesis of multiple sclerosis (MS) and its commonly used experimental model - experimental autoimmune encephalomyelitis (EAE). They indicate that noradrenaline, the key end-point mediator of the SNS, acting through β-adrenoceptor, has a contributory role in the early stages of MS/EAE development. This stage is characterized by the SNS hyperactivity (increased release of noradrenaline) reflecting the net effect of different factors, such as the disease-associated inflammation, stress, vitamin D hypovitaminosis, Epstein-Barr virus infection and dysbiosis. Thus, the administration of propranolol, a non-selective β-adrenoceptor blocker, readily crossing the blood-brain barrier, to experimental rats before the autoimmune challenge and in the early (preclinical/prodromal) phase of the disease mitigates EAE severity. This phenomenon has been ascribed to the alleviation of neuroinflammation (due to attenuation of primarily microglial activation/proinflammatory functions) and the diminution of the magnitude of the primary CD4+ T-cell autoimmune response (the effect associated with impaired autoantigen uptake by antigen presenting cells and their migration into draining lymph nodes). The former is partly related to breaking of the catecholamine-dependent self-amplifying microglial feed-forward loop and the positive feedback loop between microglia and the SNS, leading to down-regulation of the SNS hyperactivity and its enhancing influence on microglial activation/proinflammatory functions and the magnitude of autoimmune response. The effects of propranolol are shown to be more prominent in male EAE animals, the phenomenon important as males (like men) are likely to develop clinically more severe disease. Thus, these findings could serve as a firm scientific background for formulation of a new sex-specific immune-intervention strategy for the early phases of MS (characterized by the SNS hyperactivity) exploiting anti-(neuro)inflammatory and immunomodulatory properties of propranolol and other relatively cheap and safe adrenergic drugs with similar therapeutic profile.

Clinical outcomes in COVID-19 among patients with hypertension in the Philippine CORONA Study

OBJECTIVE

To describe the association between hypertension and clinical outcomes in a cohort of patients with coronavirus disease 2019 (COVID-19).

DESIGN

Retrospective cohort study.

SETTING

Thirty-seven (37) hospitals in the Philippines.

PATIENTS

10,881 patients admitted for COVID-19 from February to December 2020.

MEASUREMENTS AND MAIN RESULTS

Among the 10,881 patients included in the Philippine CORONA Study, 3647 (33.5%) had hypertension. On regression analysis adjusted for confounders (age group, sex, smoking history, diabetes, chronic cardiac disease, chronic kidney disease, chronic respiratory disease, chronic neurologic disease, chronic liver disease, HIV/AIDS, and malignancy), patients with hypertension had significantly greater odds of in-hospital mortality (OR 1.33, 95% CI 1.17-1.52), respiratory failure (OR 1.99, 95% CI 1.75-2.28), ICU admission (OR 2.16, 95% CI 1.90-2.45) and severe/critical disease (OR 1.57, 95% CI 1.41-1.75), compared to patients without hypertension. The time-to-event analysis with confounder adjustment also showed that hypertension was significantly associated with shorter time-to-event outcomes of in-hospital mortality (HR 1.13, 95% CI 1.01-1.26), respiratory failure (HR 1.86, 95% CI 1.65-2.10), and ICU admission (HR 1.99, 95% CI 1.76-2.23).

CONCLUSIONS

Our analysis of nationwide data confirmed previous findings that hypertension is an independent risk factor for worse clinical outcomes among patients hospitalized for COVID-19, with increased odds of in-hospital mortality, respiratory failure, ICU admission, and severe/critical COVID-19. More specific studies should be done to elucidate the impact of hypertension characteristics, such as chronicity, severity, drug therapy, and level of control on these clinical outcomes.

Role of inflammation, immunity, and oxidative stress in hypertension: New insights and potential therapeutic targets

Hypertension is regarded as the most prominent risk factor for cardiovascular diseases, which have become a primary cause of death, and recent research has demonstrated that chronic inflammation is involved in the pathogenesis of hypertension. Both innate and adaptive immunity are now known to promote the elevation of blood pressure by triggering vascular inflammation and microvascular remodeling. For example, as an important part of innate immune system, classically activated macrophages (M1), neutrophils, and dendritic cells contribute to hypertension by secreting inflammatory cy3tokines. In particular, interferon-gamma (IFN-γ) and interleukin-17 (IL-17) produced by activated T lymphocytes contribute to hypertension by inducing oxidative stress injury and endothelial dysfunction. However, the regulatory T cells and alternatively activated macrophages (M2) may have a protective role in hypertension. Although inflammation is related to hypertension, the exact mechanisms are complex and unclear. The present review aims to reveal the roles of inflammation, immunity, and oxidative stress in the initiation and evolution of hypertension. We envisage that the review will strengthen public understanding of the pathophysiological mechanisms of hypertension and may provide new insights and potential therapeutic strategies for hypertension.

Microglia-mediated inflammatory destruction of neuro-cardiovascular dysfunction after stroke

Stroke, a serious systemic inflammatory disease, features neurological deficits and cardiovascular dysfunction. Neuroinflammation is characterized by the activation of microglia after stroke, which disrupts the cardiovascular-related neural network and the blood-brain barrier. Neural networks activate the autonomic nervous system to regulate the cardiac and blood vessels. Increased permeability of the blood-brain barrier and the lymphatic pathways promote the transfer of the central immune components to the peripheral immune organs and the recruitment of specific immune cells or cytokines, produced by the peripheral immune system, and thus modulate microglia in the brain. In addition, the spleen will also be stimulated by central inflammation to further mobilize the peripheral immune system. Both NK cells and Treg cells will be generated to enter the central nervous system to suppress further inflammation, while activated monocytes infiltrate the myocardium and cause cardiovascular dysfunction. In this review, we will focus on microglia-mediated inflammation in neural networks that result in cardiovascular dysfunction. Furthermore, we will discuss neuroimmune regulation in the central-peripheral crosstalk, in which the spleen is a vital part. Hopefully, this will benefit in anchoring another therapeutic target for neuro-cardiovascular dysfunction.

Targeting autonomic nervous system as a biomarker of well-ageing in the prevention of stroke

Stroke prediction is a key health issue for preventive medicine. Atrial fibrillation (AF) detection is well established and the importance of obstructive sleep apneas (OSA) has emerged in recent years. Although autonomic nervous system (ANS) appears strongly implicated in stroke occurrence, this factor is more rarely considered. However, the consequences of decreased parasympathetic activity explored in large cohort studies through measurement of ANS activity indicate that an ability to improve its activity level and equilibrium may prevent stroke. In support of these observations, a compensatory neurostimulation has already proved beneficial on endothelium function. The available data on stroke predictions from ANS is based on many long-term stroke cohorts. These data underline the need of repeated ANS evaluation for the general population, in a medical environment, and remotely by emerging telemedicine digital tools. This would help uncovering the reasons behind the ANS imbalance that would need to be medically adjusted to decrease the risk of stroke. This ANS unbalance help to draw attention on clinical or non-clinical evidence, disclosing the vascular risk, as ANS activity integrates the cumulated risk from many factors of which most are modifiable, such as metabolic inadaptation in diabetes and obesity, sleep ventilatory disorders, hypertension, inflammation, and lack of physical activity. Treating these factors may determine ANS recovery through the appropriate management of these conditions. Natural aging also decreases ANS activity. ANS recovery will decrease global circulating inflammation, which will reinforce endothelial function and thus protect the vessels and the associated organs. ANS is the whistle-blower of vascular risk and the actor of vascular health. Such as, ANS should be regularly checked to help draw attention on vascular risk and help follow the improvements in response to our interventions. While today prediction of stroke relies on classical cardiovascular risk factors, adding autonomic biomarkers as HRV parameters may significantly increase the prediction of stroke.

Angiotensin II differentially affects hippocampal glial inflammatory markers in young adult male and female mice

Hypertension is a risk factor for neurodegenerative disorders involving inflammation and inflammatory cytokine-producing brain cells (microglia and astrocytes) in the hippocampus and medial prefrontal cortex (mPFC). Here we investigated the effect of slow-pressor angiotensin II (AngII) on gliosis in the hippocampus and mPFC of young adult (2-mo-old) male and female mice. In males, AngII induced hypertension, and this resulted in an increase in the density of the astrocyte marker glial fibrillary acidic protein (GFAP) in the subgranular hilus and a decrease in the density of the microglial marker ionized calcium binding adapter molecule (Iba-1) in the CA1 region. Females infused with AngII did not show hypertension but, significantly, showed alterations in hippocampal glial activation. Compared with vehicle, AngII-infused female mice had an increased density of Iba-1 in the dentate gyrus and CA2/3a region. Like males, females infused with AngII exhibited decreased Iba-1 in the CA1 region. Neither male nor female mice showed differences in GFAP or Iba-1 in the mPFC following AngII infusion. These results demonstrate that the hippocampus is particularly vulnerable to AngII in young adulthood. Differences in gonadal hormones or the sensitivity to AngII hypertension may account for divergences in GFAP and Iba-1 in males and females.

The gut-brain axis and sodium appetite: Can inflammation-related signaling influence the control of sodium intake?

Sodium is the main cation present in the extracellular fluid. Sodium and water content in the body are responsible for volume and osmotic homeostasis through mechanisms involving sodium and water excretion and intake. When body sodium content decreases below the homeostatic threshold, a condition termed sodium deficiency, highly motivated sodium seeking, and intake occurs. This is termed sodium appetite. Classically, sodium and water intakes are controlled by a number of neuroendocrine mechanisms that include signaling molecules from the renin-angiotensin-aldosterone system acting in the central nervous system (CNS). However, recent findings have shown that sodium and water intakes can also be influenced by inflammatory agents and mediators acting in the CNS. For instance, central infusion of IL-1β or TNF-α can directly affect sodium and water consumption in animal models. Some dietary conditions, such as high salt intake, have been shown to change the intestinal microbiome composition, stimulating the immune branch of the gut-brain axis through the production of inflammatory cytokines, such as IL-17, which can stimulate the brain immune system. In this review, we address the latest findings supporting the hypothesis that immune signaling in the brain could produce a reduction in thirst and sodium appetite and, therefore, contribute to sodium intake control.

The Putative Role of Astaxanthin in Neuroinflammation Modulation: Mechanisms and Therapeutic Potential

Neuroinflammation is a protective mechanism against insults from exogenous pathogens and endogenous cellular debris and is essential for reestablishing homeostasis in the brain. However, excessive prolonged neuroinflammation inevitably leads to lesions and disease. The use of natural compounds targeting pathways involved in neuroinflammation remains a promising strategy for treating different neurological and neurodegenerative diseases. Astaxanthin, a natural xanthophyll carotenoid, is a well known antioxidant. Mounting evidence has revealed that astaxanthin is neuroprotective and has therapeutic potential by inhibiting neuroinflammation, however, its functional roles and underlying mechanisms in modulating neuroinflammation have not been systematically summarized. Hence, this review summarizes recent progress in this field and provides an update on the medical value of astaxanthin. Astaxanthin modulates neuroinflammation by alleviating oxidative stress, reducing the production of neuroinflammatory factors, inhibiting peripheral inflammation and maintaining the integrity of the blood-brain barrier. Mechanistically, astaxanthin scavenges radicals, triggers the Nrf2-induced activation of the antioxidant system, and suppresses the activation of the NF-κB and mitogen-activated protein kinase pathways. With its good biosafety and high bioavailability, astaxanthin has strong potential for modulating neuroinflammation, although some outstanding issues still require further investigation.

Low-Intensity Resistance Exercise Combined With Blood Flow Restriction is More Conducive to Regulate Blood Pressure and Autonomic Nervous System in Hypertension Patients-Compared With High-Intensity and Low-Intensity Resistance Exercise

Background: The effect of resistance exercise on the autonomic nervous system of patients with hypertension has not been identified.

Objective: To explore a suitable resistance training method for hypertension patients to regulate blood pressure (BP) and autonomic nervous system function.

Method: Forty-five hypertension patients aged between 55 and 70 years were randomly equally divided into three groups: the high-intensity resistance exercise (HE) group, the low-intensity resistance exercise combined with blood flow restriction (LE-BFR) group, and the low-intensity resistance exercise (LE) group. All patients performed quadriceps femoris resistance exercise. The exercise intensity of HE, LE-BFR and LE group was 65, 30 and 30% of one repetition maximum (1RM), respectively. The LE-BFR group used pressure cuffs to provide 130% of systolic pressure to the patient’s thighs during resistance exercise. The training program was 20 times/min/set with a 1-min break after each set, and was conducted five sets/day and 3 days/week, lasting for 12 weeks. The heart rate (HR), BP, root-mean-square of difference-value of adjacent RR intervals (RMSSD), low frequency (LF) and high frequency (HF) were evaluated before and after the first training and the last training.

Result: Significant differences in HR were observed in both recovery states after the first and last training (p < 0.01). After 12 weeks of training, the recovery speed of HR in the LE-BFR group increased significantly (p < 0.01). The systolic blood pressures in the HE and LE-BFR group were significantly reduced (p < 0.05 and p < 0.01), and the differences among groups were significant (p < 0.01). In the last recovery state, the RMSSD of the LE group was significantly lower than that in the first recovery state (p < 0.01). The LF/HF ratios of the HE and LE groups in the resting and recovery states were increased significantly (all p < 0.01). LF/HF ratios in the LE-BFR group in the resting and recovery state were decreased significantly (both p < 0.01).

Conclusion: Compared to HE and LE, LE-BFR could effectively decrease systolic pressure and regulate the autonomic nervous system function in hypertension patients.

Gut Microbiome and Neuroinflammation in Hypertension

Hypertension is a worldwide problem with major impacts on health including morbidity and mortality, as well as consumption of health care resources. Nearly 50% of American adults have high blood pressure, and this rate is rising. Even with multiple antihypertensive drugs and aggressive lifestyle modifications, blood pressure is inadequately controlled in about 1 of 5 hypertensive individuals. This review highlights a hypothesis for hypertension that suggests alternative mechanisms for blood pressure elevation and maintenance. A better understanding of these mechanisms could open avenues for more successful treatments. The hypothesis accounts for recent understandings of the involvement of gut physiology, gut microbiota, and neuroinflammation in hypertension. It includes bidirectional communication between gut microbiota and gut epithelium in the gut-brain axis that is involved in regulation of autonomic nervous system activity and blood pressure control. Dysfunction of this gut-brain axis, including dysbiosis of gut microbiota, gut epithelial dysfunction, and deranged input to the brain, contributes to hypertension via inflammatory mediators, metabolites, bacteria in the circulation, afferent information alterations, etc resulting in neuroinflammation and unbalanced autonomic nervous system activity that elevates blood pressure. This in turn negatively affects gut function and its microbiota exacerbating the problem. We focus this review on the gut-brain axis hypothesis for hypertension and possible contribution to racial disparities in hypertension. A novel idea, that immunoglobulin A-coated bacteria originating in the gut with access to the brain could be involved in hypertension, is raised. Finally, minocycline, with its anti-inflammatory and antimicrobial properties, is evaluated as a potential antihypertensive drug acting on this axis.

Renal denervation: basic and clinical evidence

Renal nerves have critical roles in regulating blood pressure and fluid volume, and their dysfunction is closely related with cardiovascular diseases. Renal nerves are composed of sympathetic efferent and sensory afferent nerves. Activation of the efferent renal sympathetic nerves induces renin secretion, sodium absorption, and increased renal vascular resistance, which lead to increased blood pressure and fluid retention. Afferent renal sensory nerves, which are densely innervated in the renal pelvic wall, project to the hypothalamic paraventricular nucleus in the brain to modulate sympathetic outflow to the periphery, including the heart, kidneys, and arterioles. The effects of renal denervation on the cardiovascular system are mediated by both efferent denervation and afferent denervation. The first half of this review focuses on basic research using animal models of hypertension and heart failure, and addresses the therapeutic effects of renal denervation for hypertension and heart failure, including underlying mechanisms. The second half of this review focuses on clinical research related to catheter-based renal denervation in patients with hypertension. Randomized sham-controlled trials using second-generation devices, endovascular radiofrequency-based devices and ultrasound-based devices are reviewed and their results are assessed. This review summarizes the basic and clinical evidence of renal denervation to date, and discusses future prospects and potential developments in renal denervation therapy for cardiovascular diseases.

The Bidirectional Signal Communication of Microbiota-Gut-Brain Axis in Hypertension

Hypertension is a critical risk factor of cardiovascular diseases. A new concept of microbiota-gut-brain axis has been established recently, mediating the bidirectional communication between the gut and its microbiome and the brain. Alterations in bidirectional interactions are believed to be involved in the blood pressure regulation. Neuroinflammation and increased sympathetic outflow act as the descending innervation signals from the brain. Increased sympathetic activation plays a recognized role in the genesis of hypertension. The present evidence demonstrates that gut dysbiosis is associated with central nervous system neuroinflammation. However, how the gut influences the brain remains unclear. We reviewed the roles of neuroinflammation and gut microbiota and their interactions in the pathogenesis of hypertension and described the ascending signaling mechanisms behind the microbiota-gut-brain axis in detail. Additionally, the innovative prohypertensive mechanisms of dietary salt through the microbiota-gut-brain axis are summarized. The bidirectional communication mechanisms were proposed for the first time that the descending signals from the brain and the ascending connections from the gut form a vicious circle of hypertension progression, acting as a premise for hypertension therapy.

Hypothalamic inflammation in metabolic disorders and aging

The hypothalamus is a critical brain region for the regulation of energy homeostasis. Over the years, studies on energy metabolism primarily focused on the neuronal component of the hypothalamus. Studies have recently uncovered the vital role of glial cells as an additional player in energy balance regulation. However, their inflammatory activation under metabolic stress condition contributes to various metabolic diseases. The recruitment of monocytes and macrophages in the hypothalamus helps sustain such inflammation and worsens the disease state. Neurons were found to actively participate in hypothalamic inflammatory response by transmitting signals to the surrounding non-neuronal cells. This activation of different cell types in the hypothalamus leads to chronic, low-grade inflammation, impairing energy balance and contributing to defective feeding habits, thermogenesis, and insulin and leptin signaling, eventually leading to metabolic disorders (i.e., diabetes, obesity, and hypertension). The hypothalamus is also responsible for the causation of systemic aging under metabolic stress. A better understanding of the multiple factors contributing to hypothalamic inflammation, the role of the different hypothalamic cells, and their crosstalks may help identify new therapeutic targets. In this review, we focus on the role of glial cells in establishing a cause-effect relationship between hypothalamic inflammation and the development of metabolic diseases. We also cover the role of other cell types and discuss the possibilities and challenges of targeting hypothalamic inflammation as a valid therapeutic approach.

PLIN2 Mediates Neuroinflammation and Oxidative/Nitrosative Stress via Downregulating Phosphatidylethanolamine in the Rostral Ventrolateral Medulla of Stressed Hypertensive Rats

Purpose

Oxidative/nitrosative stress, neuroinflammation and their intimate interactions mediate sympathetic overactivation in hypertension. An immoderate inflammatory response is characterized not only by elevated proinflammatory cytokines (PICs) but by increases in mitochondrial dysfunction, reactive oxygen species (ROS), and nitric oxide (NO). Recent data pinpoint that both the phospholipid and lipid droplets (LDs) are potent modulators of microglia physiology.

Methods

Stress rats underwent compound stressors for 15 days with PLIN2-siRNA or scrambled-siRNA (SC-siRNA) administrated into the rostral ventrolateral medulla (RVLM). Lipids were analyzed by mass spectroscopy-based quantitative lipidomics. The phenotypes and proliferation of microglia, LDs, in the RVLM of rats were detected; blood pressure (BP) and myocardial injury in rats were evaluated. The anti-oxidative/nitrosative stress effect of phosphatidylethanolamine (PE) was explored in cultured primary microglia.

Results

Lipidomics analysis showed that 75 individual lipids in RVLM were significantly dysregulated by stress [PE was the most one], demonstrating that lipid composition changed with stress. In vitro, prorenin stress induced the accumulation of LDs, increased PICs, which could be blocked by siRNA-PLIN2 in microglia. PLIN2 knockdown upregulated the PE synthesis in microglia. Anti-oxidative/nitrosative stress effect of PE delivery was confirmed by the decrease of ROS and decrease in 3-NT and MDA in prorenin-treated microglia. PLIN2 knockdown in the RVLM blocked the number of iNOS⁺ and PCNA⁺ microglia, decreased BP, alleviated cardiac fibrosis and hypertrophy in stressed rats.

Conclusion

PLIN2 mediates microglial polarization/proliferation via downregulating PE in the RVLM of stressed rats. Delivery of PE is a promising strategy for combating neuroinflammation and oxidative/nitrosative stress in stress-induced hypertension.

Role of Hypertension on the Severity of COVID-19: A Review

ABSTRACT

The novel coronavirus disease (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly evolved into a global pandemic. The substantial morbidity and mortality associated with the infection has prompted us to understand potential risk factors that can predict patient outcomes. Hypertension has been identified as the most prevalent cardiovascular comorbidity in patients infected with COVID-19 that demonstrably increases the risk of hospitalization and death. Initial studies implied that renin-angiotensin-aldosterone system inhibitors might increase the risk of viral infection and aggravate disease severity, thereby causing panic given the high global prevalence of hypertension. Nonetheless, subsequent evidence supported the administration of antihypertensive drugs and noted that they do not increase the severity of COVID-19 infection in patients with hypertension, rather may have a beneficial effect. To date, the precise mechanism by which hypertension predisposes to unfavorable outcomes in patients infected with COVID-19 remains unknown. In this mini review, we elaborate on the pathology of SARS-CoV-2 infection coexisting with hypertension and summarize potential mechanisms, focusing on the dual roles of angiotensin-converting enzyme 2 and the disorders of renin-angiotensin-aldosterone system in COVID-19 and hypertension. The effects of proinflammatory factors released because of immune response and gastrointestinal dysfunction in COVID-19 are also discussed.

Assessment of sudomotor function in hypertensive with/without type-2 diabetes patients using SUDOSCAN: An electrophysiological study

Objective

Electrochemical skin conductance (ESC) test is a simple and non-invasive screening test can detect dysfunction of the peripheral sudomotor, and indirectly estimates the function of cardiac autonomic nerves. This study aimed to assess the ESC values in hypertensive patients with/without type-2 diabetes by using SUDOSCAN technology. Moreover, this study evaluated the role of cardiometabolic risk factors on the results of ESC test.

Methods

This cross-sectional study was carried on three groups of participants, including healthy subjects (Group I, n = 49), hypertensive without type-2 diabetes (Group II, n = 75) patients, and hypertensive with type-2 diabetes (Group III, n = 76) patients. Body mass index (BMI), blood pressure (systolic, diastolic and pulse pressure index), fasting serum glucose, and lipid profile were determined. ESC test as a measurement sudomotor function was determined by applying a small direct current at low voltage to hands and feet sensor plates through SUDOSCAN device.

Results

ESC values of the peripheral sudomotor nerves in the Group II and III patients were significantly lower than the corresponding values of Group I. SUDOSCAN results of Group II and III. Significant discriminators of cardiac autonomic neuropathy (≥30 score) that determined by the area under the curve (AUC) with 95% confidence interval (95% C.I.) were, duration of the disease, BMI, and mean blood pressure in Group II, while the duration of the disease and the BMI were significant discriminators in Group III.

Conclusions

SUDOSCAN is a simple, useful device, which can detect the impairment of peripheral autonomic small nerve fibers and the risk of cardiac autonomic neuropathy in hypertension. Moreover, the duration of the disease and the associated cardiometabolic risk factors are important predictors of significant SUDOSCAN findings.

Significance

ESC test is useful in detecting subclinical neuropathy in hypertensive patients as well as in type 2 diabetes.

Assessment of sudomotor function in hypertensive with/without type-2 diabetes patients using SUDOSCAN: An electrophysiological study

•

SUDOSCAN is a simple non-invasive device that can assess the sudomotor nerves.

•

Hypertensive patients have sub-clinical impairment of peripheral and autonomic nerve fibers function.

•

Cardio-metabolic risk factors are important discriminators of abnormal SUDOSCAN data.

Objective

Electrochemical skin conductance (ESC) test is a simple and non-invasive screening test can detect dysfunction of the peripheral sudomotor, and indirectly estimates the function of cardiac autonomic nerves. This study aimed to assess the ESC values in hypertensive patients with/without type-2 diabetes by using SUDOSCAN technology. Moreover, this study evaluated the role of cardiometabolic risk factors on the results of ESC test.

Methods

This cross-sectional study was carried on three groups of participants, including healthy subjects (Group I, n = 49), hypertensive without type-2 diabetes (Group II, n = 75) patients, and hypertensive with type-2 diabetes (Group III, n = 76) patients. Body mass index (BMI), blood pressure (systolic, diastolic and pulse pressure index), fasting serum glucose, and lipid profile were determined. ESC test as a measurement sudomotor function was determined by applying a small direct current at low voltage to hands and feet sensor plates through SUDOSCAN device.

Results

ESC values of the peripheral sudomotor nerves in the Group II and III patients were significantly lower than the corresponding values of Group I. SUDOSCAN results of Group II and III. Significant discriminators of cardiac autonomic neuropathy (≥30 score) that determined by the area under the curve (AUC) with 95% confidence interval (95% C.I.) were, duration of the disease, BMI, and mean blood pressure in Group II, while the duration of the disease and the BMI were significant discriminators in Group III.

Conclusions

SUDOSCAN is a simple, useful device, which can detect the impairment of peripheral autonomic small nerve fibers and the risk of cardiac autonomic neuropathy in hypertension. Moreover, the duration of the disease and the associated cardiometabolic risk factors are important predictors of significant SUDOSCAN findings.

Significance

ESC test is useful in detecting subclinical neuropathy in hypertensive patients as well as in type 2 diabetes.

Upregulation of Chemokines in the Paraventricular Nucleus of the Hypothalamus in Rats with Stress-Induced Hypertension

Background

The neuroinflammation of paraventricular nucleus (PVN) of the hypothalamus has been implicated in the development of hypertension. The promoted invasion of peripheral immune cells into PVN may be attributed to the upregulation of chemokines, then exacerbating neuroinflammation. We studied the expressions of chemokines, activation of microglial cells, and inflammatory mediators in PVN of rats with stress-induced hypertension (SIH).

Material/Methods

SIH was induced by electrical foot shock combined with noise for 2 h twice a day, at an interval of 4 h for 14 consecutive days. At the end of the 14th day, fresh PVN tissues were collected to measure the expressions of chemokines using the RayBiotech antibody array.

Results

We are the first to report that the expression of CXCL7 was extremely high in PVN of control rats, and was significantly lower in SIH rats. The expressions of CCL2 and CX3CL1 in PVN of SIH rats significantly exceeded those of control rats. The numbers of CX3CR1 (receptor of CX3CL1)-immunostained cells and oxycocin-42 (OX-42, marker of microglia)-positive cells increased in PVN of the SIH rats. The stress enhanced the protein expressions of proinflammatory cytokines IL-6 and IL-17 and reduced those of anti-inflammatory cytokines TGF-β and IL-10 in PVN.

Conclusions

In PVN of SIH rats, chronic stress induced neuroinflammation characterized by the activated microglia and upregulated proinflammatory cytokines. Expressions of chemokines CXCL7, CX3CL1, and CCL2 were altered. The causal link of chemokines to PVN neuroinflammation and hypertension remain to be determined.

Nox1/4 inhibition exacerbates age dependent perivascular inflammation and fibrosis in a model of spontaneous hypertension

Hypertension is associated with oxidative stress and perivascular inflammation, critical contributors to perivascular fibrosis and accelerated vascular ageing. Oxidative stress can promote vascular inflammation, creating options for potential use of NADPH oxidase inhibitors in pharmacological targeting of perivascular inflammation and its consequences.

Accordingly, we characterized age-related changes in oxidative stress and immune cell infiltration in normotensive (WKY) and spontaneously hypertensive rats (SHRs). Subsequently, we used pharmacological inhibitors of Nox1 (ML171) and Nox1/Nox4 (GKT137831; 60 mg/kg), to modulate NADPH oxidase activity at the early stage of spontaneous hypertension and investigated their effects on perivascular inflammation and fibrosis.

Results

Ageing was associated with a progressive increase of blood pressure as well as an elevation of the total number of leukocytes, macrophages and NK cells infiltrating perivascular adipose tissue (PVAT) in SHRs but not in WKY. At 1 month of age, when blood pressure was not yet different, only perivascular NK cells were significantly higher in SHR. Spontaneous hypertension was also accompanied by the higher perivascular T cell accumulation, although this increase was age independent. Aortic Nox1 and Nox2 mRNA expression increased with age only in SHR but not in WKY, while age-related increase of Nox4 mRNA in the vessels has been observed in both groups, it was more pronounced in SHRs. At early stage of hypertension (3-months) the most pronounced differences were observed in Nox1 and Nox4. Surprisingly, GKT137831, dual inhibitor of Nox1/4, therapy increased both blood pressure and perivascular macrophage infiltration. Mechanistically, this was linked to increased expression of proinflammatory chemokines expression (CCL2 and CCL5) in PVAT. This inflammatory response translated to increased perivascular fibrosis. This effect was likely Nox4 dependent as the Nox1 inhibitor ML171 did not affect the development of spontaneous hypertension, perivascular macrophage accumulation, chemokine expression nor adventitial collagen deposition.

In summary, spontaneous hypertension promotes ageing-associated perivascular inflammation which is exacerbated by Nox4 but not Nox1 pharmacological inhibition.

Light Emitting Diode Therapy Protects against Myocardial Ischemia/Reperfusion Injury through Mitigating Neuroinflammation

Background

Neuroinflammation plays a key role in myocardial ischemia-reperfusion (I/R) injury. Previous studies showed that light-emitting diode (LED) therapy might improve M2 microglia activation and brain-derived neurotrophic factor (BDNF) expression, thereby exerting anti-inflammatory effects. Therefore, we hypothesized that LED therapy might reduce myocardial I/R injury by neuroinflammation modulation.

Objective

To explore the effect of LED therapy on myocardial I/R-induced injury and seek the underlying mechanism.

Methods

Thirty rats were randomly divided into three groups: Control group (without LED treatment or myocardial I/R, n = 6), I/R group (with myocardial I/R only, n = 12), and LED+I/R group (with myocardial I/R and LED therapy, n = 12). Electrocardiogram was recorded continuously during the procedure. In addition, brain tissue was extracted for BDNF, Iba1, and CD206 analyses, and heart tissue for myocardial injury (ischemic size and infarct size), IL-4 and IL-10 mRNA analysis.

Results

In comparison with the I/R group, the ischemia size and the infarct size were significantly attenuated by LED therapy in the LED+I/R group. Meanwhile, the microglia activation induced by I/R injury was prominently attenuated by LED treatment either. And it is apparent that there was also an increase in the beneficial neuroinflammation markers (BDNF and CD206) in the paraventricular nucleus (PVN) in the LED+I/R group. Furthermore, the anti-inflammatory cytokines, IL-4 and IL-10, were greatly decreased by I/R while improved by LED treatment in myocardium.

Conclusion

LED therapy might reduce neuroinflammation in PVN and decrease myocardium injury by elevating BDNF and M2 microglia.

Salt-dependent hypertension and inflammation: targeting the gut-brain axis and the immune system with Brazilian green propolis

Systemic arterial hypertension (SAH) is a major health problem around the world and its development has been associated with exceeding salt consumption by the modern society. The mechanisms by which salt consumption increase blood pressure (BP) involve several homeostatic systems but many details have not yet been fully elucidated. Evidences accumulated over the last 60 decades raised the involvement of the immune system in the hypertension development and opened a range of possibilities for new therapeutic targets. Green propolis is a promising natural product with potent anti-inflammatory properties acting on specific targets, most of them participating in the gut-brain axis of the sodium-dependent hypertension. New anti-hypertensive products reinforce the therapeutic arsenal improving the corollary of choices, especially in those cases where patients are resistant or refractory to conventional therapy. This review sought to bring the newest advances in the field articulating evidences that show a cross-talking between inflammation and the central mechanisms involved with the sodium-dependent hypertension as well as the stablished actions of green propolis and some of its biologically active compounds on the immune cells and cytokines that would be involved with its anti-hypertensive properties.

High Salt Intake Lowers Behavioral Inhibition

Stress-related neuropsychiatric (e.g., anxiety, depression) and cardiovascular diseases are frequently comorbid, though discerning the directionality of their association has been challenging. One of the most controllable risk factors for cardiovascular disease is salt intake. Though high salt intake is implicated in neuropsychiatric diseases, its direct neurobehavioral effects have seldom been explored. We reported that elevated salt intake in mice augments neuroinflammation, particularly after an acute stressor. Here, we explored how high salt consumption affected behavioral responses of mice to mildly arousing environmental and social tests, then assessed levels of the stress-related hormone corticosterone. Unexpectedly, anxiety-related behaviors in the elevated plus maze, open field, and marble burying test were unaffected by increased salt intake. However, nest building was diminished in mice consuming high salt, and voluntary social interaction was elevated, suggesting reduced engagement in ethologically-relevant behaviors that promote survival by attenuating threat exposure. Moreover, we observed significant positive correlations between social preference and subsequent corticosterone only in mice consuming increased salt, as well as negative correlations between open arm exploration in the elevated plus maze and corticosterone selectively in mice in the highest salt condition. Thus, heightened salt consumption reduces behavioral inhibition under relatively low-threat conditions, and enhances circulating corticosterone proportional to specific behavioral shifts. Considering the adverse health consequences of high salt intake, combined with evidence that increased salt consumption impairs inhibition of context-inappropriate behaviors, we suggest that prolonged high salt intake likely promulgates maladaptive behavioral and cardiovascular responses to perceived stressors that may explain some of the prevalent comorbidity between cardiovascular and neuropsychiatric diseases.