Angiotensin-II-derived reactive oxygen species on baroreflex sensitivity during hypertension: new perspectives

Potential Mechanisms Underlying COVID-19-Mediated Central and Peripheral Demyelination: Roles of the RAAS and ADAM-17

Demyelination is among the most conspicuous neurological sequelae of SARS-CoV-2 infection (COVID-19) in both the central (CNS) and peripheral (PNS) nervous systems. Several hypotheses have been proposed to explain the mechanisms underlying demyelination in COVID-19. However, none have considered the SARS-CoV-2's effects on the renin-angiotensin-aldosterone system (RAAS). Therefore, our objective in this review is to evaluate how RAAS imbalance, caused by direct and indirect effects of SARS-CoV-2 infection, could contribute to myelin loss in the PNS and CNS. In the PNS, we propose that demyelination transpires from two significant changes induced by SARS-CoV-2 infection, which include upregulation of ADAM-17 and induction of lymphopenia. Whereas, in the CNS, demyelination could result from RAAS imbalance triggering two alterations: (1) a decrease in angiotensin type II receptor (AT2R) activity, responsible for restraining defense cells' action on myelin; (2) upregulation of ADAM-17 activity, leading to impaired maturation of oligodendrocytes and myelin formation. Thus, we hypothesize that increased ADAM-17 activity and decreased AT2R activity play roles in SARS-CoV-2 infection-mediated demyelination in the CNS.

The interplay of p38 MAPK signaling and mitochondrial metabolism, a dynamic target in cancer and pathological contexts

Mitochondria play a crucial role in cellular metabolism and bioenergetics, orchestrating various cellular processes, including energy production, metabolism, adaptation to stress, and redox balance. Besides, mitochondria regulate cellular metabolic homeostasis through coordination with multiple signaling pathways. Importantly, the p38 mitogen-activated protein kinase (MAPK) signaling pathway is a key player in the intricate communication with mitochondria, influencing various functions. This review explores the multifaced interaction between the mitochondria and p38 MAPK signaling and the consequent impact on metabolic alterations. Overall, the p38 MAPK pathway governs the activities of key mitochondrial proteins, which are involved in mitochondrial biogenesis, oxidative phosphorylation, thermogenesis, and iron homeostasis. Additionally, p38 MAPK contributes to the regulation of mitochondrial responses to oxidative stress and apoptosis induced by cancer therapies or natural substances by coordinating with other pathways responsible for energy homeostasis. Therefore, dysregulation of these interconnected pathways can lead to various pathologies characterized by aberrant metabolism. Consequently, gaining a deeper understanding of the interaction between mitochondria and the p38 MAPK pathway and their implications presents exciting forecasts for novel therapeutic interventions in cancer and other disorders characterized by metabolic dysregulation.

Rosuvastatin, but not atorvastatin, enhances the antihypertensive effect of cilostazol in an acute model of hypertension

PURPOSE

Hypertensive emergency, a sudden and severe increase in blood pressure, necessitates immediate intervention to avoid end-organ damage. Cilostazol, a selective phosphodiesterase-III inhibitor, has vasodilator effect. Here, we investigated the effect of two commonly used statins, atorvastatin or rosuvastatin, on cilostazol antihypertensive activity in acute model of hypertension.

METHODS

Hypertensive emergency was induced via angiotensin II intravenous infusion (120 ng.kg-1.min-1). Rats were subjected to real-time arterial hemodynamics and electrocardiogram recording while investigated drugs were injected slowly at cumulative doses 0.5, 1, and 2 mg.kg-1, individually or in combination, followed by baroreflex sensitivity (BRS) analysis and serum electrolytes (Na+ and K+) and vasomodulators (norepinephrine (NE), and nitric oxide (NO)) assessment.

RESULTS

Cilostazol reduced systolic blood pressure (SBP), while co-injection with rosuvastatin augmented cilostazol SBP-reduction up to 30 mmHg. Compared to atorvastatin, rosuvastatin boosted the cilostazol-associated reduction in peripheral resistance, as evidenced by further decrease in diastolic, pulse, and dicrotic-notch pressures. Rosuvastatin co-injection prevented cilostazol-induced changes of ejection and non-ejection durations. Additionally, rosuvastatin coadministration produced better restoration of BRS, with an observed augmented increase in BRS indexes from spectral analysis. Greater reduction in sympathetic/parasympathetic ratio and serum NE upon rosuvastatin coadministration indicates further shift in sympathovagal balance towards parasympathetic dominance. Additionally, rosuvastatin coinjection caused a greater decrease in serum sodium, while more increase in NO indicating augmented reduction of extracellular volume and endothelial dysfunction.

CONCLUSION

Rosuvastatin boosted cilostazol's antihypertensive actions through effects on peripheral resistance, BRS, sympathovagal balance, endothelial dysfunction, and electrolytes balance, while atorvastatin did not demonstrate a comparable impact.

Inflammation of some visceral sensory systems and autonomic dysfunction in cardiovascular disease

The sensitization and hypertonicity of visceral afferents are highly relevant to the development and progression of cardiovascular and respiratory disease states. In this review, we described the evidence that the inflammatory process regulates visceral afferent sensitivity and tonicity, affecting the control of the cardiovascular and respiratory system. Some inflammatory mediators like nitric oxide, angiotensin II, endothelin-1, and arginine vasopressin may inhibit baroreceptor afferents and contribute to the baroreflex impairment observed in cardiovascular diseases. Cytokines may act directly on peripheral afferent terminals that transmit information to the central nervous system (CNS). TLR-4 receptors, which recognize lipopolysaccharide, were identified in the nodose and petrosal ganglion and have been implicated in disrupting the blood-brain barrier, which can potentiate the inflammatory process. For example, cytokines may cross the blood-brain barrier to access the CNS. Additionally, pro-inflammatory cytokines such as IL-1β, IL-6, TNF-α and some of their receptors have been identified in the nodose ganglion and carotid body. These pro-inflammatory cytokines also sensitize the dorsal root ganglion or are released in the nucleus of the solitary tract. In cardiovascular disease, pro-inflammatory mediators increase in the brain, heart, vessels, and plasma and may act locally or systemically to activate/sensitize afferent nervous terminals. Recent evidence demonstrated that the carotid body chemoreceptor cells might sense systemic pro-inflammatory molecules, supporting the novel proposal that the carotid body is part of the afferent pathway in the central anti-inflammatory reflexes. The exact mechanisms of how pro-inflammatory mediators affects visceral afferent signals and contribute to the pathophysiology of cardiovascular diseases awaits future research.

The effect of vitamin C on nitroglycerin-mediated vasodilation in individuals with and without the aldehyde dehydrogenase 2 polymorphism

AIMS

To mediate its pharmacodynamic effects, glyceryl trinitrate (GTN) requires bioactivation, by which it releases nitric oxide or a nitric oxide moiety. The exact mechanism of GTN bioactivation remains uncertain. Mitochondrial aldehyde dehydrogenase (ALDH-2) has been proposed as the primary enzyme responsible for this bioactivation process. Evidence for the importance of ALDH-2 in GTN bioactivation has been inconsistent, particularly in human models. An alternative hypothesis suggests that decreased ALDH-2 activity leads to accumulation of reactive cytotoxic aldehydes, which either inhibit the vasoactive product(s) of GTN or impair other enzymatic pathways involved in the bioactivation of GTN. We investigated the effect of supplemental vitamin C on vascular responses to GTN in healthy volunteers of East Asian descent, of whom 12 with and 12 without the ALDH-2 polymorphism participated.

METHODS

Subjects underwent 2 sequential brachial artery infusions of GTN at rates of 5, 11 and 22 nmol/min, separated by a 30-min washout period. The GTN infusions were carried out in the presence and absence of vitamin C using a randomized, crossover design. Venous occlusion plethysmography was used to measure forearm blood flow responses to GTN.

RESULTS

Compared to subjects with functional ALDH-2, the variant group exhibited blunted hemodynamic responses to intra-arterial GTN infusions, although this reduction in response was not statically significant. Contrary to our hypothesis, vitamin C had an inhibitory effect on GTN mediated vasodilation as compared to GTN during saline in both groups.

CONCLUSION

We conclude that vitamin C did not augment the acute vascular response to GTN in those with the ALDH-2 polymorphism.

SARS-CoV-2 and Hypertension: Evidence Supporting Invasion into the Brain Via Baroreflex Circuitry and the Role of Imbalanced Renin-Angiotensin-Aldosterone-System

Hypertension is considered one of the most critical risk factors for COVID-19. Evidence suggests that SARS-CoV-2 infection produces intense effects on the cardiovascular system by weakening the wall of large vessels via vasa-vasorum. In this commentary, we propose that SARS-CoV-2 invades carotid and aortic baroreceptors, leading to infection of the nucleus tractus solitari (NTS) and paraventricular hypothalamic nucleus (PVN), and such dysregulation of NTS and PVN following infection causes blood pressure alteration at the central level. We additionally explored the hypothesis that SARS-CoV-2 favors the internalization of membrane ACE2 receptors generating an imbalance of the renin-angiotensin-aldosterone system (RAAS), increasing the activity of angiotensin II (ANG-II), disintegrin, and metalloproteinase 17 domain (ADAM17/TACE), eventually modulating the integration of afferents reaching the NTS from baroreceptors and promoting increased blood pressure. These mechanisms are related to the increased sympathetic activity, which leads to transient or permanent hypertension associated with SARS-CoV-2 invasion, contributing to the high number of deaths by cardiovascular implications.

Hinokitiol for hypertensive emergencies: effects on peripheral resistance, cardiac load, baroreflex sensitivity, and electrolytes balance

Hinokitiol, a natural monoterpenoid, has been shown previously to possess a potent vasodilating activity in vitro in both control and hypertensive aortae. Here, the antihypertensive and cardioprotective effects of an intravenous hinokitiol injection were fully investigated in angiotensin II-induced hypertensive emergency in rats. Hinokitiol intravenous injection was prepared in the form of self-nanoemulsifying drug delivery system. Rat's arterial and ventricular hemodynamics were measured in real-time recordings in addition to surface electrocardiogram while slow injection of cumulative doses of hinokitiol or vehicle as well as time control. Hinokitiol at dose 10 mg/kg showed a considerable reduction in the raised systolic blood pressure (30 mmHg) within only 30 min. The decrease in blood pressure seems to be mediated through a reduction in peripheral resistance, as appears from the decreases in diastolic pressure, dicrotic notch pressure, and pulse pressure. In addition, hinokitiol injection reduced heart load due to the decrease in heart rate, increases in cycle duration (particularly the non-ejection duration) and diastolic duration, and decreases in end-diastolic pressure. An effect most likely mediated via prolongation of ventricular repolarization as appears from the increases in PR, QTc, and JT intervals. However, acute intravenous injection of hinokitiol neither affected the baroreflex sensitivity nor sodium/potassium balance. In conclusion, acute hinokitiol intravenous injection markedly reduced severe hypertension in rats. This effect seems to be mediated through decreasing peripheral resistance and decreasing cardiac load, suggesting that it is an effective treatment in hypertensive emergencies after clinical evaluation.

Renin-angiotensin-system increases phosphorylated tau and Reactive Oxygen Species in human cortical neuron cell line

Alzheimer's Disease (AD) is the most common cause of dementia. AD patients had increased extracellular amyloid β plaques and intracellular hyperphosphorylated tau (p-tau) in neurons. Recent studies have shown an association between the Renin-Angiotensin System (RAS) and AD. The involvement of RAS has been mediated through Angiotensin II (AngII), which is overexpressed in aging brains. However, the exact mechanism of how AngII contributes to AD is unknown. Thus, we hypothesize that AngII increases p-tau by activating its kinases, CDK5 and MAPK. In the human cortical neuron cell line, HCN2, treatment with AngII upregulated the gene expression of CDK5 (2.9 folds, p < 0.0001) and MAPTK (1.9 folds, p < 0.001). The AT1R antagonist, Losartan, blocked the changes in tau kinases. Also, AngII-induced the MAPK activation, increasing its phosphorylation by 400% (p < 0.0001), an increase that was also blocked by Losartan. An increase in p-tau by AngII was observed using fluorescent microscopy. We then quantified Reactive Oxygen Species (ROS) production, and it was significantly increased by AngII (p < 0.01), and treatment with Losartan blunted their production (p < 0.05). The data obtained demonstrated that AngII might contribute to the pathogenesis of AD.

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Angiotensin II increases CDK5 and MAPK gene expression in human cortical neuron cell line.

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Angiotensin II increases tau phosphorylation in human cortical neuron cell line.

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Angiotensin II increases Reactive Oxygen Species production in human cortical neuron cell line.

Association of dietary intake of saturated fatty acids with hypertension: 1999-2018 National Health and Nutrition Examination Survey

Objective

This study aimed to assess the relationship between the dietary intake of saturated fatty acids (SFAs) and its subtypes (C4:0, C6:0, C8:0, C10:0, C12:0, C14:0, C16:0, and C18:0) and hypertension.

Design participants and methods

Adults aged 20 years and older based used the U.S. Health and Nutrition Survey (1999-2018) were used as participants. Two averages of 24 h dietary recall data were obtained for weight-adjusted continuous cross-sectional analysis. Two 24-h recall interview data means were obtained for weight-adjusted continuous cross-sectional analysis. A logistic regression model was used to estimate the weighted odds ratio (OR) and its 95% confidence interval (CI) for hypertension.

Results

The study included 7,222 respondents over 20 years of age with a hypertension prevalence of 23.2% and a significant difference in the dietary intake of carbohydrates among patients with hypertension. Dietary intake of nutrients was more in men than in women with hypertension. After adjusting for confounders, adjusting for nutrients, and reducing covariance among nutrients, the OR (95% CI) for women's dietary intake of SFAs, C14:0, C16:0, C18:0 fourth quartile, and C14:0 third quartile were 0.57 (0.34, 0.95), 0.57 (0.34, 0.95), 0.57 (0.34, 0.95), 0.57 (0.34, 0.95), and 0.57 (0.34, 0.95), respectively, which may be a risk factor for hypertension. In older (≥65, years) respondents, the OR (95% CI) for dietary intake of SFAs, C4:0, C14:0, C16:0 fourth quartile, and C12:0 third quartile were 0.42 (0.21, 0.86), 0.46 (0.22, 0.95), 0.39 (0.18, 0.85), 0.38 (0.17, 0.84), and 0.45 (0.20, 0.99), respectively, which may be a protective factor for hypertension.

Conclusion

The study was based on the American Health and Nutrition Examination Survey, and a strong correlation was found between dietary intake of SFAs, C14:0, C16:0, and C18:0 and hypertension in women (dietary intake of SFAs, C4:0, C12:0, C14:0, and C16:0) and middle-aged and older adults (dietary intake of SFAs, C4:0, C12:0, C14:0, and C16:0). In addition, dietary nutrient intake should be carefully selected for the rational prevention of hypertension.

Theories and Molecular Basis of Vascular Aging: A Review of the Literature from VascAgeNet Group on Pathophysiological Mechanisms of Vascular Aging

Vascular aging, characterized by structural and functional alterations of the vascular wall, is a hallmark of aging and is tightly related to the development of cardiovascular mortality and age-associated vascular pathologies. Over the last years, extensive and ongoing research has highlighted several sophisticated molecular mechanisms that are involved in the pathophysiology of vascular aging. A more thorough understanding of these mechanisms could help to provide a new insight into the complex biology of this non-reversible vascular process and direct future interventions to improve longevity. In this review, we discuss the role of the most important molecular pathways involved in vascular ageing including oxidative stress, vascular inflammation, extracellular matrix metalloproteinases activity, epigenetic regulation, telomere shortening, senescence and autophagy.

Rutin Modulates MAPK Pathway Differently from Quercetin in Angiotensin II-Induced H9c2 Cardiomyocyte Hypertrophy

Rutin is a flavonoid with antioxidant property. It has been shown to exert cardioprotection against cardiomyocyte hypertrophy. However, studies regarding its antihypertrophic property are still lacking, whether it demonstrates similar antihypertrophic effect to its metabolite, quercetin. Hence, this study aimed to investigate the effects of both flavonoids on oxidative stress and mitogen-activated protein kinase (MAPK) pathway in H9c2 cardiomyocytes that were exposed to angiotensin II (Ang II) to induce hypertrophy. Cardiomyocytes were exposed to Ang II (600 nM) with or without quercetin (331 μM) or rutin (50 μM) for 24 h. A group given vehicle served as the control. The concentration of the flavonoids was chosen based on the reported effective concentration to reduce cell hypertrophy or cardiac injury in H9c2 cells. Exposure to Ang II increased cell surface area, intracellular superoxide anion level, NADPH oxidase and inducible nitric oxide synthase activities, and reduced cellular superoxide dismutase activity and nitrite level, which were similarly reversed by both rutin and quercetin. Rutin had no significant effects on phosphorylated proteins of extracellular signal-related kinases (ERK1/2) and p38 but downregulated phosphorylated c-Jun N-terminal kinases (JNK1/2), which were induced by Ang II. Quercetin, on the other hand, had significantly downregulated the phosphorylated proteins of ERK1/2, p38, and JNK1/2. The quercetin inhibitory effect on JNK1/2 was stronger than the rutin. In conclusion, both flavonoids afford similar protective effects against Ang II-induced cardiomyocyte hypertrophy, but they differently modulate MAPK pathway.

Activation of the Cholinergic Anti-inflammatory Pathway Attenuated Angiotension II-Dependent Hypertension and Renal Injury

Background: Angiotensin II (AngII) induces renal fibrosis, characterized by fibroblast proliferation, inflammatory cell infiltration and excessive extracellular matrix deposition, all of which was relevant closely to hypertension. The vagus nerve-related cholinergic anti-inflammatory pathway (CAP) modulates local and systemic inflammatory responses. The aim of present study was to determine the effect of CAP on renal inflammation and fibrosis.

Methods and Results: AngII-induced hypertension was induced in vivo by 14-days low-dose AngII infusion from osmotic minipumps. We used GTS-21 dihydrochloride, a selective nicotinic acetylcholine receptor agonist. Daily intraperitoneal GTS-21 injection and/or vagotomy started after hypertension was confirmed and continued for 4 weeks. The elevated blood pressure caused by AngII was significantly attenuated by GTS-21. Improved baroreflex sensitivity was observed after GTS-21 administration. Masson stain and immunoblotting revealed that deposition of excessive fibrosis and overexpression of inflammatory cytokines induced by AngII was reduced by GTS-21. To determine the role of autonomic control in CAP, unilateral vagotomy was performed. Vagotomy weakened the effect of CAP on AngII-induced hypertension. In vitro, GTS-21 suppressed NF-κB activation, attenuated AngII-induced epithelial-mesenchymal transition and reduced inflammation and fibrosis in NRK-52E cells; α-bungarotoxin (α-Bgt, an α7-nAChR selective antagonist) partly inhibited these effects.

Conclusion: CAP protected against AngII-induced hypertension via improvement in autonomic control, suppression of NF-κB activation, and reduction of renal fibrosis and inflammatory response.

Cross Talk between COVID-19 and Breast Cancer

Cancer patients are more susceptible to COVID-19; however, the prevalence of COVID-19 in different types of cancer is still inconsistent and inconclusive. Here, we delineate the intricate relationship between breast cancer and COVID-19. Breast cancer and COVID-19 share the involvement of common comorbidities, hormonal signalling pathways, gender differences, rennin- angiotensin system (RAS), angiotensin-converting enzyme-2 (ACE-2), transmembrane protease serine 2 (TMPRSS2) and dipeptidyl peptidase-IV (DPP-IV). We also shed light on the possible effects of therapeutic modalities of COVID-19 on breast cancer outcomes. Briefly, we conclude that breast cancer patients are more susceptible to COVID-19 in comparison with their normal counterparts. Women are more resistant to the occurrence and severity of COVID-19. Increased expressions of ACE2 and TMPRSS2 are correlated with occurrence and severity of COVID-19, but higher expression of ACE2 and lower expression of TMPRSS2 are prognostic markers for overall disease free survival in breast cancer. The ACE2 inhibitors and ibuprofen therapies for COVID-19 treatment may aggravate the clinical condition of breast cancer patients through chemo-resistance and metastasis. Most of the available therapeutic modalities for COVID-19 were also found to exert positive effects on breast cancer outcomes. Besides drugs in clinical trend, TMPRSS2 inhibitors, estrogen supplementation, androgen deprivation and DPP-IV inhibitors may also be used to treat breast cancer patients infected with SARS-CoV-2. However, drug-drug interactions suggest that some of the drugs used for the treatment of COVID-19 may modulate the drug metabolism of anticancer therapies which may lead to adverse drug reaction events.

Overexpression of Central ACE2 (Angiotensin-Converting Enzyme 2) Attenuates the Pressor Response to Chronic Central Infusion of Ang II (Angiotensin II): A Potential Role for Nrf2 (Nuclear Factor [Erythroid-Derived 2]-Like 2)

We investigated the mechanism by which ACE2 (angiotensin-converting enzyme 2) overexpression alters neurohumoral outflow and central oxidative stress. Nrf2 (nuclear factor [erythroid-derived 2]-like 2) is a master antioxidant transcription factor that regulates cytoprotective and antioxidant genes. We hypothesized that upregulation of central ACE2 inhibits the pressor response to Ang II (angiotensin II) by reducing reactive oxygen species through a Nrf2/antioxidant enzyme-mediated mechanism in the rostral ventrolateral medulla. Synapsin human Angiotensin Converting Enzyme 2 positive (SynhACE2^+/+) mice and their littermate controls synhACE2^-/- were used to evaluate the consequence of intracerebroventricular infusion of Ang II. In control mice, Ang II infusion evoked a significant increase in blood pressure and norepinephrine excretion, along with polydipsia and polyuria. The pressor effect of central Ang II was completely blocked in synhACE2^+/+ mice. Polydipsia, norepinephrine excretion, and markers of oxidative stress in response to central Ang II were also reduced in synhACE2^+/+ mice. The MasR (Mas receptor) agonist Ang 1-7 and blocker A779 had no effects on blood pressure. synhACE2^+/+ mice showed enhanced expression of Nrf2 in the rostral ventrolateral medulla which was blunted following Ang II infusion. Ang II evoked nuclear translocation of Nrf2 in cultured Neuro 2A (N2A) cells. In synhACE2^-/- mice, the central Ang II pressor response was attenuated by simultaneous intracerebroventricular infusion of the Nrf2 activator sulforaphane; blood pressure was enhanced by knockdown of Nrf2 in the rostral ventrolateral medulla in Nrf2 floxed (Nrf2^f/f) mice. These data suggest that the hypertensive effects of intracerebroventricular Ang II are attenuated by selective overexpression of brain synhACE2 and may be mediated by Nrf2-upregulated antioxidant enzymes in the rostral ventrolateral medulla.

Angiotensin II-mediated nondipping during sleep in healthy humans: effects on baroreflex function at subsequent daytime

Blood pressure dipping at night is mediated by sleep-inherent, active downregulation of sympathetic vascular tone. Concomitantly, activity of the renin-angiotensin system is reduced, which might contribute to the beneficial effect of baroreflex downward resetting on daytime blood pressure homeostasis. To evaluate whether experimental nondipping mediated by angiotensin II during sleep would alter blood pressure and baroreflex function the next day in healthy humans, angiotensin-II or placebo (saline) was infused for a 7-h period at night, preventing blood pressure dipping in 11 sleeping normotensive individuals (5 males, balanced, crossover design). Baroreflex function was assessed about 1 h upon awakening and stop of infusion via microneurographic recordings of muscle sympathetic nerve activity (MSNA), showing that resting MSNA was significantly increased following angiotensin II nondipping compared with placebo ( P = 0.029), whereas blood pressure and heart rate remained unchanged. Baroreflex sensitivity in response to vasoactive drug challenge was preserved, and neuroendocrine markers of fluid balance and electrolytes did not differ between conditions. Ambulatory blood pressure during subsequent daytime was not altered. Data were compared with analog experiments previously performed within the same subjects during awake daytime (ANCOVA). We conclude that angiotensin-II mediated nocturnal nondipping did not induce blood pressure elevation at subsequent daytime in healthy humans but was linked to increased vasoconstrictive sympathetic activity. This is in contrast to a prolonged increase in blood pressure in corresponding daytime experiments of the same individuals. Evidently, sleep strongly preserves normotensive blood pressure homeostasis in healthy humans.

Counter-regulatory renin-angiotensin system in cardiovascular disease

The renin-angiotensin system is an important component of the cardiovascular system. Mounting evidence suggests that the metabolic products of angiotensin I and II - initially thought to be biologically inactive - have key roles in cardiovascular physiology and pathophysiology. This non-canonical axis of the renin-angiotensin system consists of angiotensin 1-7, angiotensin 1-9, angiotensin-converting enzyme 2, the type 2 angiotensin II receptor (AT₂R), the proto-oncogene Mas receptor and the Mas-related G protein-coupled receptor member D. Each of these components has been shown to counteract the effects of the classical renin-angiotensin system. This counter-regulatory renin-angiotensin system has a central role in the pathogenesis and development of various cardiovascular diseases and, therefore, represents a potential therapeutic target. In this Review, we provide the latest insights into the complexity and interplay of the components of the non-canonical renin-angiotensin system, and discuss the function and therapeutic potential of targeting this system to treat cardiovascular disease.

Effect of (-)-epicatechin on the modulation of progression markers of chronic renal damage in a 5/6 nephrectomy experimental model

Aims

To evaluate the effects of (-)-epicatechin (Epi) in the progression of kidney damage.

Material and methods

We assessed the effects of Epi [0.01-20 mg/kg of body weight/day] during 14 days, in a 5/6 nephrectomy model in mice.

Key findings

Nephrectomy-induced systolic arterial hypertension was significantly reduced in a dose dependent manner with Epi treatment. Increased serum creatinine and urea were reduced almost to normal values. The concentration of tetrahydrobiopterin (BH4), used as subrogate of endothelial dysfunction, decreased in nephrectomyzed animals, Epi treatment increased BH4 levels almost reaching normal values. The expression of angiotensin II receptor (AT₁-R) and NADPH oxidase-4 (NOX-4) and 3-nitrotyrosine levels increased with nephrectomy and were reduced with Epi treatment. Renal tissue morphology in the remaining tissue was conserved with Epi treatment in a dose dependent manner.

Significance

Chronic kidney disease (CKD) is an independent cardiovascular risk factor associated with a mortality rate 10 to 20 times higher than that of the general population. High blood pressure, endothelial dysfunction and oxidative stress are important factors determining kidney damage progression. Findings of this study indicate that Epi is able to counteract the deleterious effects of subtotal nephrectomy and the structural and functional changes in the remnant kidney tissue, decreasing the progression of CKD. These results warrant the possibility of implement clinical trials to limit the progression of CKD in humans.

Evaluation of Pathological Association between Stroke-Related QTL and Salt-Induced Renal Injury in Stroke-Prone Spontaneously Hypertensive Rat

The stroke-prone spontaneously hypertensive rat (SHRSP) suffers from severe hypertension and hypertensive organ damage such as cerebral stroke and kidney injury under salt-loading. By a quantitative trait locus (QTL) analysis between SHRSP and SHR (the stroke-resistant parental strain of SHRSP), two major QTLs for stroke susceptibility were identified on chromosomes 1 and 18 of SHRSP, which were confirmed in congenic strains constructed between SHRSP and SHR. As the progression of renal dysfunction was suggested to be one of the key factors inducing stroke in SHRSP, we examined effects of the stroke-related QTLs on kidney injury using two congenic strains harboring either of SHRSP-derived fragments of chromosomes 1 and 18 in the SHR genome. The congenic strains were challenged with 1% NaCl solution for 4 weeks; measurement of systolic blood pressure and urinary isoprostane level (a marker for oxidative stress) and evaluation of renal injury by quantification of genetic marker expression and histological examination were performed. We found that the congenic rats with SHRSP-derived fragment of chromosome 18 showed more severe renal damage with higher expression of Col1α-1 (a genetic marker for renal fibrosis) and higher urinary isoprostane level. In contrast, the fragment of chromosome 1 from SHRSP did not give such effects on SHR. Blood pressure was not greater in either of the congenic strains when compared with SHR. We concluded that the QTL region on chromosome 18 might deteriorate salt-induced renal injury in SHR through a blood pressure-independent mechanism.

The renin-angiotensin system in cardiovascular autonomic control: recent developments and clinical implications

Complex and bidirectional interactions between the renin-angiotensin system (RAS) and autonomic nervous system have been well established for cardiovascular regulation under both physiological and pathophysiological conditions. Most research to date has focused on deleterious effects of components of the vasoconstrictor arm of the RAS on cardiovascular autonomic control, such as renin, angiotensin II, and aldosterone. The recent discovery of prorenin and the prorenin receptor have further increased our understanding of RAS interactions in autonomic brain regions. Therapies targeting these RAS components, such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers, are commonly used for treatment of hypertension and cardiovascular diseases, with blood pressure-lowering effects attributed in part to sympathetic inhibition and parasympathetic facilitation. In addition, a vasodilatory arm of the RAS has emerged that includes angiotensin-(1-7), ACE2, and alamandine, and promotes beneficial effects on blood pressure in part by reducing sympathetic activity and improving arterial baroreceptor reflex function in animal models. The role of the vasodilatory arm of the RAS in cardiovascular autonomic regulation in clinical populations, however, has yet to be determined. This review will summarize recent developments in autonomic mechanisms involved in the effects of the RAS on cardiovascular regulation, with a focus on newly discovered pathways and therapeutic targets for this hormone system.

Alteration in Brain Functional and Effective Connectivity in Subjects With Hypertension

To reveal the physiological mechanism of the cognitive decline in subjects with hypertension, the functional connectivity (FC) was assessed by using the wavelet phase coherence (WPCO), and effective connectivity (EC) was assessed by using the coupling strength (CS) of near-infrared spectroscopy (NIRS) signals. NIRS signals were continuously recorded from the prefrontal cortex, sensorimotor cortex, and occipital lobes of 13 hypertensive patients (hypertension group, 70 ± 6.5 years old) and 16 elderly healthy subjects (control group, 71 ± 5.5 years old) in resting and standing periods. WPCO and CS were calculated in four frequency intervals: I, 0.6–2; II, 0.145–0.6; III, 0.052–0.145; and IV, 0.021–0.052 Hz. CS quantifies coupling amplitude. In comparison with the control group, the hypertension group showed significantly decreased (p < 0.05) WPCO and CS in intervals III and IV and in the resting and standing states. WPCO and CS were significantly decreased in the resting state compared with those in the standing state in the hypertension group (p < 0.05). Decreased WPCO and CS indicated a reduced network interaction, suggesting disturbed neurovascular coupling in subjects with hypertension. Compared with the control group, the hypertension group showed significantly lower Mini-Mental State Examination (MMSE) (p = 0.028) and Montreal Cognitive Assessment (MoCA) scores (p = 0.011). In the hypertension group, correlation analysis showed that WPCO and CS were significantly positively correlated with MMSE and MoCA scores, respectively. These findings may provide evidence of impaired cognitive function in hypertension and can enhance the understanding on neurovascular coupling.

Inhibition of PDE5 Restores Depressed Baroreflex Sensitivity in Renovascular Hypertensive Rats

Renal artery stenosis is frequently associated with resistant hypertension, which is defined as failure to normalize blood pressure (BP) even when combined drugs are used. Inhibition of PDE5 by sildenafil has been shown to increase endothelial function and decrease blood pressure in experimental models. However, no available study evaluated the baroreflex sensitivity nor autonomic balance in renovascular hypertensive rats treated with sildenafil. In a translational medicine perspective, our hypothesis is that sildenafil could improve autonomic imbalance and baroreflex sensitivity, contributing to lower blood pressure. Renovascular hypertensive 2-kidney-1-clip (2K1C) and sham rats were treated with sildenafil (45 mg/Kg/day) during 7 days. At the end of treatment, BP and heart rate (HR) were recorded in conscious rats after a 24-h-recovery period. Spontaneous and drug-induced baroreflex sensitivity and autonomic tone were evaluated; in addition, lipid peroxidation was measured in plasma samples. Treatment was efficient in increasing both spontaneous and induced baroreflex sensitivity in treated hypertensive animals. Inhibition of PDE5 was also capable of ameliorating autonomic imbalance in 2K1C rats and decreasing systemic oxidative stress. Taken together, these beneficial effects resulted in significant reductions in BP without affecting HR. We suggest that sildenafil could be considered as a promising alternative to treat resistant hypertension.

Reactive Oxygen Species in the Paraventricular Nucleus of the Hypothalamus Alter Sympathetic Activity During Metabolic Syndrome

The paraventricular nucleus of the hypothalamus (PVN) contains heterogeneous populations of neurons involved in autonomic and neuroendocrine regulation. The PVN plays an important role in the sympathoexcitatory response to increasing circulating levels of angiotensin II (Ang-II), which activates AT1 receptors in the circumventricular organs (OCVs), mainly in the subfornical organ (SFO). Circulating Ang-II induces a de novo synthesis of Ang-II in SFO neurons projecting to pre-autonomic PVN neurons. Activation of AT1 receptors induces intracellular increases in reactive oxygen species (ROS), leading to increases in sympathetic nerve activity (SNA). Chronic sympathetic nerve activation promotes a series of metabolic disorders that characterizes the metabolic syndrome (MetS): dyslipidemia, hyperinsulinemia, glucose intolerance, hyperleptinemia and elevated plasma hormone levels, such as noradrenaline, glucocorticoids, leptin, insulin, and Ang-II. This review will discuss the contribution of our laboratory and others regarding the sympathoexcitation caused by peripheral Ang-II-induced reactive oxygen species along the subfornical organ and paraventricular nucleus of the hypothalamus. We hypothesize that this mechanism could be involved in metabolic disorders underlying MetS.

Role of autonomic reflex arcs in cardiovascular responses to air pollution exposure

The body responds to environmental stressors by triggering autonomic reflexes in the pulmonary receptors, baroreceptors, and chemoreceptors to maintain homeostasis. Numerous studies have shown that exposure to various gases and airborne particles can alter the functional outcome of these reflexes, particularly with respect to the cardiovascular system. Modulation of autonomic neural input to the heart and vasculature following direct activation of sensory nerves in the respiratory system, elicitation of oxidative stress and inflammation, or through other mechanisms is one of the primary ways that exposure to air pollution affects normal cardiovascular function. Any homeostatic process that utilizes the autonomic nervous system to regulate organ function might be affected. Thus, air pollution and other inhaled environmental irritants have the potential to alter both local airway function and baro- and chemoreflex responses, which modulate autonomic control of blood pressure and detect concentrations of key gases in the body. While each of these reflex pathways causes distinct responses, the systems are heavily integrated and communicate through overlapping regions of the brainstem to cause global effects. This short review summarizes the function of major pulmonary sensory receptors, baroreceptors, and carotid body chemoreceptors and discusses the impacts of air pollution exposure on these systems.

Prolonged blood pressure elevation following continuous infusion of angiotensin II-a baroreflex study in healthy humans

ANG II interacts with the sympathetic nervous system at central nervous blood pressure-regulating structures, including the baroreflex. It is unknown whether prolonged BP elevation mediated by high ANG II plasma levels could induce a persistent shift of the central nervous baroreflex setpoint, lasting beyond the short ANG II plasmatic half time of a few seconds, thereby consolidating elevated BP and/or increased SNA in healthy humans. In a blinded crossover design, ANG II or placebo (saline) was infused for a 6-h period in 12 resting normotensive students (6 males, 6 females) raising BP to borderline hypertensive levels. Between 60 and 120 min after the infusion period, muscle sympathetic nerve activity (MSNA) was assessed microneurographically and correlated with oscillometric BP measurements and heart rate at supine rest (baseline) and during pharmacologic baroreceptor challenge. Infusion of ANG II increased BP to borderline-hypertensive levels, as intended, whereas heart rate remained unaltered. At baroreflex assessment (i.e., 60-120 min after end of infusion period), systolic BP was significantly higher compared with placebo (Δ8.4 ± 3.1 mmHg; P < 0.05), whereas diastolic values were nearly equal between conditions. Baseline MSNA was neither decreased nor increased, and baroreflex sensitivity to vasoactive drug challenge was not altered. Our results show that elevation of ANG II plasma levels over 6 h was able to increase systolic, but not diastolic, BP far beyond blood-mediated ANG II effects. MSNA or heart rate did not counter-regulate this BP elevation, indicating that ANG II had sustainably reset the central nervous BP threshold of sympathetic baroreflex function to accept elevated BP input signals without counter-regulatory response.

The use of angiotensin II receptor antagonists to increase the efficacy of radiotherapy in cancer treatment

Angiotensin II receptor antagonists inhibit various signaling pathways involved in the regulation of inflammation, apoptosis and angiogenesis. Radiation-induced activation of a proinflammatory cytokine network has been shown to mediate normal tissue injury induced by ionizing radiation in cancer patients, resulting in serious side effects. Hence, not only do angiotensin II receptor antagonists block inflammatory signaling both in cancer cells and in normal cells, but they are also effective in the treatment of cancer by inhibiting tumor progression, vascularization and metastasis. This review addresses the role of angiotensin II inhibitors in cancer therapy, and their potential to increase therapeutical index by protecting normal cells and sensitizing tumor cells to radiotherapy.

Coconut oil supplementation and physical exercise improves baroreflex sensitivity and oxidative stress in hypertensive rats

The hypothesis that oral supplementation with virgin coconut oil (Cocos nucifera L.) and exercise training would improve impaired baroreflex sensitivity (BRS) and reduce oxidative stress in spontaneously hypertensive rats (SHR) was tested. Adult male SHR and Wistar Kyoto rats (WKY) were divided into 5 groups: WKY + saline (n = 8); SHR + saline (n = 8); SHR + coconut oil (2 mL·day(-1), n = 8); SHR + trained (n = 8); and SHR + trained + coconut oil (n = 8). Mean arterial pressure (MAP) was recorded and BRS was tested using phenylephrine (8 μg/kg, intravenous) and sodium nitroprusside (25 μg·kg(-1), intravenous). Oxidative stress was measured using dihydroethidium in heart and aorta. SHR + saline, SHR + coconut oil, and SHR + trained group showed higher MAP compared with WKY + saline (175 ± 6, 148 ± 6, 147 ± 7 vs. 113 ± 2 mm Hg; p < 0.05). SHR + coconut oil, SHR + trained group, and SHR + trained + coconut oil groups presented lower MAP compared with SHR + saline group (148 ± 6, 147 ± 7, 134 ± 8 vs. 175 ± 6 mm Hg; p < 0.05). Coconut oil combined with exercise training improved BRS in SHR compared with SHR + saline group (-2.47 ± 0.3 vs. -1.39 ± 0.09 beats·min(-1)·mm Hg(-1); p < 0.05). SHR + saline group showed higher superoxide levels when compared with WKY + saline (774 ± 31 vs. 634 ± 19 arbitrary units (AU), respectively; p < 0.05). SHR + trained + coconut oil group presented reduced oxidative stress compared with SHR + saline in heart (622 ± 16 vs. 774 ± 31 AU, p < 0.05). In aorta, coconut oil reduced oxidative stress in SHR compared with SHR + saline group (454 ± 33 vs. 689 ± 29 AU, p < 0.05). Oral supplementation with coconut oil combined with exercise training improved impaired BRS and reduced oxidative stress in SHR.

The Effects of Hydroalchoholic Extract of Teucrium polium L. on Hypertension Induced by Angiotensin II in Rats

BACKGROUND

Antispasmodic and vasorelaxant effects of Teucrium polium L. (TP) were mentioned in former studies, so we attempted to evaluate the eventual preventive effect of TP in an acute experimental model of hypertension induced by angiotensin II (Ang II).

METHODS

Forty-eight male Wistar rats were divided randomly into six groups (n = 8); control Group (C), which received only saline, group Ang II; which received Ang II (300 ng/min, IV), group losartan (Los); which received Los (10 mg/kg, IV) before Ang II injection, three groups of TP 100, TP 200, and TP 400; which received different doses of TP extract (100, 200 and 400 mg/kg, IP, respectively) before Ang II application. After cannulation of the femoral artery, mean arterial blood pressure (MAP) and heart rate (HR) was continuously measured and recorded during the experiments. Comparisons were performed using t-test with SPSS software, version 16 (SPSS, Chicago, IL).

RESULTS

MAP and HR in Ang group were significantly higher than the control group (P < 0.001), MAP in group Los significantly was lower than Ang group (P < 0.001) and pretreatment with three doses of TP extract also inhibited increasing of MAP after Ang II injection (P < 0.001). Los also inhibited the increase of HR due to Ang II (P < 0.001), but none of three doses of TP extract had a protective effect on tachycardia induced by Ang II.

CONCLUSIONS

It seems TP extract could be effective in preventing of high blood pressure induced by Ang II pathway activation but could not have remarkable efficacy for improving the created tachycardia.