Sympathoexcitation by oxidative stress in the brain mediates arterial pressure elevation in obesity-induced hypertension

Sestrin2 in POMC neurons modulates energy balance and obesity related metabolic disorders via mTOR signaling

Sestrin2 is a highly conserved protein that can be induced under various stress conditions. Researches have revealed that the signaling pathway of the mammalian target of rapamycin (mTOR) is essential in modulating both glucose and lipid metabolism. However, the precise involvement of Sestrin2 in the hypothalamus, particularly in pro-opiomelanocortin (POMC) neurons, in control of energy homeostasis remains uncertain. In this study, we aimed to investigate the functional role of Sestrin2 in hypothalamic POMC neurons in regulation of energy balance, as well as revealing the underlying mechanisms. Therefore, cre-dependent AAV virus encoding or silencing Sestrin2 was injected into the hypothalamic ARC of pomc-cre transgenic mice. The results demonstrated that Sestrin2 overexpression in POMC neurons ameliorated high-fat diet (HFD)-induced obesity and increased energy expenditure. Conversely, Sestrin2 deficiency in POMC neurons predisposed mice to HFD induced obesity. Additionally, the thermogenesis of brown adipose tissue and lipolysis of inguinal white adipose tissue were both enhanced by the increased sympathetic nerve innervation in Sestrin2 overexpressed mice. Further exploration revealed that Sestrin2 overexpression inhibited the mTOR signaling pathway in hypothalamic POMC neurons, which may account for the alleviation of systematic metabolic disturbance induced by HFD in these mice. Collectively, our findings demonstrate that Sestrin2 in POMC neurons plays a pivotal role in maintaining energy balance in a context of HFD-induced obesity by inhibiting the mTOR pathway, providing new insights into how hypothalamic neurons respond to nutritional signals to protect against obesity-associated metabolic dysfunction.

Salt-Sensitive Hypertension and the Kidney

Salt-sensitive hypertension (SS-HT) is characterized by blood pressure elevation in response to high dietary salt intake and is considered to increase the risk of cardiovascular and renal morbidity. Although the mechanisms responsible for SS-HT are complex, the kidneys are known to play a central role in the development of SS-HT and the salt sensitivity of blood pressure (SSBP). Moreover, several factors influence renal function and SSBP, including the renin-angiotensin-aldosterone system, sympathetic nervous system, obesity, and aging. A phenotypic characteristic of SSBP is aberrant activation of the renin-angiotensin system and sympathetic nervous system in response to excessive salt intake. SSBP is also accompanied by a blunted increase in renal blood flow after salt loading, resulting in sodium retention and SS-HT. Obesity is associated with inappropriate activation of the aldosterone mineralocorticoid receptor pathway and renal sympathetic nervous system in response to excessive salt, and mineralocorticoid receptor antagonists and renal denervation attenuate sodium retention and inhibit salt-induced blood pressure elevation in obese dogs and humans. SSBP increases with age, which has been attributed to impaired renal sodium handling and a decline in renal function, even in the absence of kidney disease. Aging-associated changes in renal hemodynamics are accompanied by significant alterations in renal hormone levels and renal sodium handling, resulting in SS-HT. In this review, we focus mainly on the contribution of renal function to the development of SS-HT.

Non-Invasive Blood Pressure Tracking of Spontaneous Hypertension Rats Using an Electronic Nose

Traditional noninvasive blood pressure measurement methods in experimental animals are time consuming and difficult to operate, particularly for large numbers of animals. In this study, the possibility of sensing fecal odor to estimate the blood pressure status of spontaneous hypertension rats (SHRs) was explored with the aim of establishing a new method for non-invasive monitoring of blood pressure. The body weight and blood pressure of SHRs kept increasing with growth, and the odor information monitored using an E-nose varied with the blood pressure status, particularly for sensors S6 and S7. The fecal information was analyzed using principal component analysis, canonical discriminant analysis and multilayer perception neural networks (MLP) to discriminate SHRs from normal ones, with a 100% correct classification rate. For better prediction of blood pressure, the model built using multiple linear regression analysis, partial least squares regression analysis and multilayer perceptron neural network analysis were used, with coefficients of determination (R2) ranging from 0.8036 to 0.9926. Moreover, the best prediction model for blood pressure was established using MLP analysis with an R2¬ higher than 0.91. Thus, changes in blood pressure levels can be tracked non-invasively, and normotension can be distinguished from hypertension or even at different hypertension levels based on the odor information of rat feces, providing a foundation for non-invasive health monitoring. This work might provide potential instructions for functional food research aimed at lowering blood pressure.

The causal associations of non-alcoholic fatty liver disease with blood pressure and the mediating effects of cardiometabolic risk factors: A Mendelian randomization study

BACKGROUND AND AIMS

Non-alcoholic fatty liver disease (NAFLD) is prevalent in hypertensive people, but the causal effect remains unclear. We employed Mendelian randomization (MR) approach to assess the causality between NAFLD and different blood pressure (BP) parameters.

METHOD AND RESULTS

Instrumental variables for genetically predicted NAFLD, including chronically elevated serum alanine aminotransferase levels (cALT) and imaging and biopsy-confirmed NAFLD, were obtained from a genome-wide association study (N = 164,197). Multiple MR methods were implemented, including Inverse variance weighted, MR-Egger, Maximum likelihood, Weighted median, Simple median, Penalised weighted median, MR-RAPS, and cML-MA. Outliers were detected using MR-PRESSO, and pleiotropy was assessed using MR-Egger intercept and Phenoscanner. Heterogeneity was quantified using Cochran's Q and Rucker's Q' tests. Potential shared risk factors were analyzed to reveal the mediating effect. A higher genetic predisposition to cALT was causally associated with an increased risk of elevated BP levels, resulting in 0.65 mmHg (95% CI, 0.42-0.87), 0.38 mmHg (95% CI, 0.25-0.50) and 0.33 mmHg (95% CI, 0.22-0.44) higher for systolic BP, diastolic BP and pulse pressure, respectively. When more stringent criteria were used, imaging and biopsy-confirmed NAFLD showed a 1.12 mmHg (95% CI, 0.94-1.30) increase in SBP and a 0.55 mmHg (95% CI, 0.39-0.70) increase in DBP. Risk factor and mediation analyses suggested type 2 diabetes and fasting insulin levels might mediate the causal relationship between NAFLD and BP.

CONCLUSION

The two-sample MR analyses showed robust causal effects of genetically predicted NAFLD on 3 different BP indices. The shared genetic profile between NAFLD and BP may suggest important therapeutic targets and early interventions for cardiometabolic risk factors.

Clarification of hypertension mechanisms provided by the research of central circulatory regulation

Sympathoexcitation, under the regulatory control of the brain, plays a pivotal role in the etiology of hypertension. Within the brainstem, significant structures involved in the modulation of sympathetic nerve activity include the rostral ventrolateral medulla (RVLM), caudal ventrolateral medulla (CVLM), nucleus tractus solitarius (NTS), and paraventricular nucleus (paraventricular). The RVLM, in particular, is recognized as the vasomotor center. Over the past five decades, fundamental investigations on central circulatory regulation have underscored the involvement of nitric oxide (NO), oxidative stress, the renin-angiotensin system, and brain inflammation in regulating the sympathetic nervous system. Notably, numerous significant findings have come to light through chronic experiments conducted in conscious subjects employing radio-telemetry systems, gene transfer techniques, and knockout methodologies. Our research has centered on elucidating the role of NO and angiotensin II type 1 (AT1) receptor-induced oxidative stress within the RVLM and NTS in regulating the sympathetic nervous system. Additionally, we have observed that various orally administered AT1 receptor blockers effectively induce sympathoinhibition by reducing oxidative stress via blockade of the AT1 receptor in the RVLM of hypertensive rats. Recent advances have witnessed the development of several clinical interventions targeting brain mechanisms. Nonetheless, Future and further basic and clinical research are needed.

Hypertension Related to Obesity: Pathogenesis, Characteristics and Factors for Control

The World Health Organization (WHO) refers to obesity as abnormal or excessive fat accumulation that presents a health risk. Obesity was first designated as a disease in 2012 and since then the cost and the burden of the disease have witnessed a worrisome increase. Obesity and hypertension are closely interrelated as abdominal obesity interferes with the endocrine and immune systems and carries a greater risk for insulin resistance, diabetes, hypertension, and cardiovascular disease. Many factors are at the interplay between obesity and hypertension. They include hemodynamic alterations, oxidative stress, renal injury, hyperinsulinemia, and insulin resistance, sleep apnea syndrome and the leptin-melanocortin pathway. Genetics, epigenetics, and mitochondrial factors also play a major role. The measurement of blood pressure in obese patients requires an adapted cuff and the search for other secondary causes is necessary at higher thresholds than the general population. Lifestyle modifications such as diet and exercise are often not enough to control obesity, and so far, bariatric surgery constitutes the most reliable method to achieve weight loss. Nonetheless, the emergence of new agents such as Semaglutide and Tirzepatide offers promising alternatives. Finally, several molecular pathways are actively being explored, and they should significantly extend the treatment options available.

Maternal High-Fat Diet and Offspring Hypertension

The incidence of hypertension has increased to epidemic levels in the past decades. Increasing evidence reveals that maternal dietary habits play a crucial role in the development of hypertension in adult offspring. In humans, increased fat consumption has been considered responsible for obesity and associated diseases. Maternal diets rich in saturated fats have been widely employed in animal models to study various adverse offspring outcomes. In this review, we discussed current evidence linking maternal high-fat diet to offspring hypertension. We also provided an in-depth overview of the potential mechanisms underlying hypertension of developmental origins that are programmed by maternal high-fat intake from animal studies. Furthermore, this review also presented an overview of how reprogramming interventions can prevent maternal high-fat-diet-induced hypertension in adult offspring. Overall, recent advances in understanding mechanisms behind programming and reprogramming of maternal high-fat diet on hypertension of developmental origins might provide the answers to curtail this epidemic. Still, more research is needed to translate research findings into practice.

Biomarkers of high salt intake

High salt intake is associated with hypertension, which is a leading modifiable risk factor for cardiovascular disease (CVD) and chronic kidney disease (CKD). International Guidelines recommend a large reduction in the consumption of sodium to reduce blood pressure, organ damage, and mortality. In its early stages, the symptoms of CKD are generally not apparent. CKD proceeds in a "silent" manner, necessitating the need for urinary biomarkers to detect kidney damage at an early stage. Since traditional renal biomarkers, such as serum creatinine, are not sufficiently sensitive, difficulties are associated with detecting kidney damage induced by a high salt intake, particularly in normotensive individuals. Several new biomarkers for renal tubular damage, such as neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), vanin-1, liver-type fatty acid-binding protein (L-FABP), and monocyte chemotactic protein-1 (MCP-1), have recently been identified. However, few studies have investigated early biomarkers for CKD progression associated with a high salt diet. This chapter provides insights into novel biomarkers for CKD in normo- and hypertensive individuals with a high salt intake. Recent studies using spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) fed a high salt diet identified urinary vanin-1 and NGAL as early biomarkers for renal tubular damage in SHR and WKY, whereas urinary KIM-1 was a useful biomarker for salt-induced renal injury in SHR only. Clinical studies are needed to confirm these findings.

Kidney and epigenetic mechanisms of salt-sensitive hypertension

Dietary salt intake increases blood pressure (BP) but the salt sensitivity of BP differs between individuals. The interplay of ageing, genetics and environmental factors, including malnutrition and stress, contributes to BP salt sensitivity. In adults, obesity is often associated with salt-sensitive hypertension. The children of women who experience malnutrition during pregnancy are at increased risk of developing obesity, diabetes and salt-sensitive hypertension as adults. Similarly, the offspring of mice that are fed a low-protein diet during pregnancy develop salt-sensitive hypertension in association with aberrant DNA methylation of the gene encoding type 1A angiotensin II receptor (AT_1AR) in the hypothalamus, leading to upregulation of hypothalamic AT_1AR and renal sympathetic overactivity. Ageing is also associated with salt-sensitive hypertension. In aged mice, promoter methylation leads to reduced kidney production of the anti-ageing factor Klotho and a decrease in circulating soluble Klotho. In the setting of Klotho deficiency, salt-induced activation of the vascular Wnt5a-RhoA pathway leads to ageing-associated salt-sensitive hypertension, potentially as a result of reduced renal blood flow and increased peripheral resistance. Thus, kidney mechanisms and aberrant DNA methylation of certain genes are involved in the development of salt-sensitive hypertension during fetal development and old age. Three distinct paradigms of epigenetic memory operate on different timescales in prenatal malnutrition, obesity and ageing.

Dietary potassium and the kidney: lifesaving physiology

Potassium often has a negative connotation in Nephrology as patients with chronic kidney disease (CKD) are prone to develop hyperkalaemia. Approaches to the management of chronic hyperkalaemia include a low potassium diet or potassium binders. Yet, emerging data indicate that dietary potassium may be beneficial for patients with CKD. Epidemiological studies have shown that a higher urinary potassium excretion (as proxy for higher dietary potassium intake) is associated with lower blood pressure (BP) and lower cardiovascular risk, as well as better kidney outcomes. Considering that the composition of our current diet is characterized by a high sodium and low potassium content, increasing dietary potassium may be equally important as reducing sodium. Recent studies have revealed that dietary potassium modulates the activity of the thiazide-sensitive sodium-chloride cotransporter in the distal convoluted tubule (DCT). The DCT acts as a potassium sensor to control the delivery of sodium to the collecting duct, the potassium-secreting portion of the kidney. Physiologically, this allows immediate kaliuresis after a potassium load, and conservation of potassium during potassium deficiency. Clinically, it provides a novel explanation for the inverse relationship between dietary potassium and BP. Moreover, increasing dietary potassium intake can exert BP-independent effects on the kidney by relieving the deleterious effects of a low potassium diet (inflammation, oxidative stress and fibrosis). The aim of this comprehensive review is to link physiology with clinical medicine by proposing that the same mechanisms that allow us to excrete an acute potassium load also protect us from hypertension, cardiovascular disease and CKD.

Review of the health benefits of habitual consumption of miso soup: focus on the effects on sympathetic nerve activity, blood pressure, and heart rate

High salt intake increases blood pressure, and dietary salt intake has been clearly demonstrated to be associated with hypertension incidence. Japanese people consume higher amounts of salt than Westerners. It has been reported that miso soup was one of the major sources of daily salt intake in Japanese people. Adding salt is indispensable to make miso, and therefore, in some cases, refraining from miso soup is recommended to reduce dietary salt intake. However, recent studies using salt-sensitive hypertensive models have revealed that miso lessens the effects of salt on blood pressure. In other word, the intake of miso dose not increase the blood pressure compared to the equivalent intake of salt. In addition, many clinical observational studies have demonstrated the absence of a relationship between the frequency of miso soup intake and blood pressure levels or hypertension incidence. The mechanism of this phenomenon seen in the subjects with miso soup intake has not been fully elucidated yet. However, in basic studies, it was found that the ingredients of miso attenuate sympathetic nerve activity, resulting in lowered blood pressure and heart rate. Therefore, this review focused on the differences between the effects of miso intake and those of the equivalent salt intake on sympathetic nerve activity, blood pressure, and heart rate.

Impact of sex and age on metabolism, sympathetic activity, and hypertension

In this brief review, we summarize the current knowledge on the complex interplay between metabolism, sympathetic activity and hypertension with a focus on sex differences and changes with age in humans. Evidence suggests that in premenopausal women, sex hormones, particularly estrogen exerts a profound cardioprotective effect which may be associated with favorable metabolic profiles, as well as lower sympathetic activity and blood pressure at rest and any given physiological and environmental stimuli compared with men of a similar age. Along this line, premenopausal women seem to be generally protected from obesity-induced metabolic and cardiovascular complications. However, postmenopausal estrogen deprivation during midlife and older age has a detrimental impact on metabolism, may lead to adipose tissue redistribution from the subcutaneous to abdominal area, and augments sympathetic activity. All these changes could contribute significantly to the higher prevalence of hypertension and greater cardiometabolic risk in older women than older men. It is proposed that obesity-related hypertension has a neurogenic component which is characterized by sympathetic overactivity, but the impact of sex and age remains largely unknown. Understanding sex and age-specific differences in obesity and sympathetic neural control of blood pressure is important in the prevention and/or risk reduction of cardiometabolic disorders for both men and women.

The role of oxidative stress in cardiovascular disease caused by social isolation and loneliness

Loneliness and social isolation are common sources of chronic stress in modern society. Epidemiological studies have demonstrated that loneliness and social isolation increase mortality risk as much as smoking or alcohol consumption and more than physical inactivity or obesity. Loneliness in human is associated with higher blood pressure whereas enhanced atherosclerosis is observed in animal models of social isolation. Loneliness and social isolation lead to activation of the hypothalamic-pituitary-adrenocortical (HPA) axis, enhanced sympathetic nerve activity, impaired parasympathetic function and a proinflammatory immune response. These mechanisms have been implicated in the development of cardiovascular disease conferred by social isolation although a causal relationship has not been established so far. There is evidence that oxidative stress is likely to be a key molecular mechanism linking chronic psychosocial stress to cardiovascular disease. NADPH oxidase-mediated oxidative stress in the hypothalamus has been shown to be required for social isolation-induced HPA axis activation in socially isolated rats. Oxidative stress in the rostral ventrolateral medulla is also a key regulator of sympathetic nerve activity. In the vasculature, oxidative stress increases vascular tone and promote atherogenesis through multiple mechanisms. Thus, preventing oxidative stress may represent a therapeutic strategy to reduce the detrimental effects of social stress on health.

Superoxide anions modulate the effects of alarin in the paraventricular nucleus on sympathetic activity and blood pressure in spontaneously hypertensive rats

Neuropeptides are involved in the regulation of the sympathetic activity and blood pressure in the paraventricular nucleus of the hypothalamus (PVN). The present study was designed to determine how alarin modulates the renal sympathetic nerve activity (RSNA), arterial blood pressure and mean arterial pressure (MAP) in the PVN, and whether superoxide anions regulate the effects of alarin in the PVN of spontaneously hypertensive rats (SHRs). Acute experiment was carried out with male Wistar-Kyoto rats (WKY) and SHRs under anesthesia. RSNA, systolic blood pressure (SBP), diastolic blood pressure (DBP), and MAP were measured. Alarin microinjection into the PVN increased RSNA (7.8 ± 1.8 vs. 14.8 ± 2.3%), SBP (5.9 ± 1.4 vs. 12.1 ± 1.6 mmHg), DBP (5.1 ± 0.8 vs. 10.0 ± 1.1 mmHg), and MAP (5.4 ± 1.2 vs. 10.7 ± 1.3 mmHg) in WKY rats and SHRs,. Alarin antagonist ala6-25 Cys decreased RSNA, SBP, DBP, and MAP in SHRs, and inhibited the effects of alarin. The alarin level was increased in the PVN of SHR compared to WKY rats. (29.7 ± 4.9 vs. 14.6 ± 2.4 pg/mg protein). PVN microinjection of superoxide anion scavengers tempol and tiron, or NAD(P)H oxidase inhibitor apocynin, decreased RSNA, SBP, DBP, and MAP in SHRs, and inhibited the effects of alarin, but the superoxide dismutase inhibitor diethyldithiocarbamic acid potentiated the effects of alarin. Superoxide anions and NAD(P)H oxidase activity levels in the PVN were increased by alarin, but decreased by alarin antagonist ala6-25 Cys. The alarin-induced increases in superoxide anions and NAD(P)H oxidase activity levels were abolished by pre-treatment with ala6-25 Cys. The results suggest that alarin in the PVN increases sympathetic outflow and blood pressure. The enhanced activity of endogenous alarin in the PVN contributes to sympathetic activation in hypertension, and the superoxide anion is involved in these alarin-mediated processes in the PVN.

Obesity-induced sympathoexcitation is associated with Nrf2 dysfunction in the rostral ventrolateral medulla

Increases in sympathetic nerve activity (SNA) have been implicated in obesity-induced risk for cardiovascular diseases, especially hypertension. Previous studies indicate that oxidative stress in the rostral ventrolateral medulla (RVLM), a key brain stem region that regulates sympathetic outflow to peripheral tissues, plays a pathogenic role in obesity-mediated sympathoexcitation. However, the molecular mechanisms underlying this phenomenon are not clear. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that regulates the expression of antioxidant and anti-inflammatory genes and confers cytoprotection against oxidative stress. The present study was designed to investigate whether Nrf2 dysfunction was associated with obesity-induced oxidative stress in the RVLM and sympathoexcitation. C57BL/6J mice were fed with chow or a high-fat diet (HFD) for 16 wk. Blood pressure parameters were assessed by radiotelemeters in conscious freely moving mice. SNA was measured by heart rate variability analysis and also through assessment of depressor response to ganglionic blockade. The RVLM was microdissected for gene expression and protein analysis (Western blot analysis and activity assay) related to Nrf2 signaling. Our results showed that HFD-induced obesity resulted in significant increases in SNA, although we only observed a mild increase in mean arterial pressure. Obesity-induced oxidative stress in the RVLM was associated with impaired Nrf2 signaling marked by decreased Nrf2 activity, downregulation of Nrf2 mRNA, its target genes [NAD(P)H quinone dehyrogenase 1 (Nqo1) and superoxide dismutase 2 (Sod2)], and inflammation. Our findings suggest that obesity results in Nrf2 dysfunction, which likely causes maladaptation to oxidative stress and inflammation in the RVLM. These mechanisms could potentially contribute to obesity-induced sympathoexcitation.

Evaluation of the pathophysiological mechanisms of salt-sensitive hypertension

The currently available data have indicated that dietary salt is directly correlated with blood pressure (BP) and the occurrence of hypertension. However, the salt sensitivity of BP is different in each individual. Genetic factors and environmental factors influence the salt sensitivity of BP. Obesity, stress, and aging are strongly associated with increased BP salt sensitivity. Indeed, a complex and interactive genetic and environmental system can determine an individual's BP salt sensitivity. However, the genetic/epigenetic determinants leading to salt sensitivity of BP are still challenging to identify primarily because lifestyle-related diseases, including hypertension, usually become a medical problem during adulthood, although their causes may be attributed to the earlier stages of ontogeny. The association between distinct developmental periods involves changes in gene expression, which include epigenetic phenomena. The role of epigenetic modification in the development of salt-sensitive hypertension is presently under investigation. Recently, we identified aberrant DNA methylation in the context of prenatally programmed hypertension. In this review, we summarize the existing knowledge regarding the pathophysiological mechanisms of salt-sensitive hypertension. Additionally, we discuss the contribution of epigenetic mechanisms in the development of salt-sensitive hypertension.

Involvement of Vanin-1 in Ameliorating Effect of Oxidative Renal Tubular Injury in Dahl-Salt Sensitive Rats

In salt-sensitive hypertension, reactive oxygen species (ROS) play a major role in the progression of renal disease partly through the activation of the mineralocorticoid receptor (MR). We have previously demonstrated that urinary vanin-1 is an early biomarker of oxidative renal tubular injury. However, it remains unknown whether urinary vanin-1 might reflect the treatment effect. The objective of this study was to clarify the treatment effect for renal tubular damage in Dahl salt-sensitive (DS) rats. DS rats (six weeks old) were given one of the following for four weeks: high-salt diet (8% NaCl), high-salt diet plus a superoxide dismutase mimetic, tempol (3 mmol/L in drinking water), high-salt diet plus eplerenone (100 mg/kg/day), and normal-salt diet (0.3% NaCl). After four-week treatment, blood pressure was measured and kidney tissues were evaluated. ROS were assessed by measurements of malondialdehyde and by immunostaining for 4-hydroxy-2-nonenal. A high-salt intake for four weeks caused ROS and histological renal tubular damages in DS rats, both of which were suppressed by tempol and eplerenone. Proteinuria and urinary N-acetyl-β-D-glucosaminidase exhibited a significant decrease in DS rats receiving a high-salt diet plus eplerenone, but not tempol. In contrast, urinary vanin-1 significantly decreased in DS rats receiving a high-salt diet plus eplerenone as well as tempol. Consistent with these findings, immunohistochemical analysis revealed that vanin-1 was localized in the renal proximal tubules but not the glomeruli in DS rats receiving a high-salt diet, with the strength attenuated by tempol or eplerenone treatment. In conclusion, these results suggest that urinary vanin-1 is a potentially sensitive biomarker for ameliorating renal tubular damage in salt-sensitive hypertension.

Brain renin-angiotensin system in broiler chickens with cold-induced pulmonary hypertension

1. The relative expression of angiotensinogen (AGT), renin, angiotensin-converting enzyme (ACE) and angiotensin II type 1 receptor (AT₁R) was determined using quantitative real-time PCR on tissue from the brain (forebrain, midbrain and hindbrain) to investigate the effect of cold-induced pulmonary hypertension syndrome (PHS) in broilers aged 42 days. Brain angiotensin II (Ang II) and AT₁R levels were measured using enzyme immunoassay. 2. The right ventricle/total ventricles (RV/TV) ratio of the heart was increased in broilers exposed to cold stress (PHS group) at the end of the experiment. 3. ACE and renin transcripts in three parts of the brain were significantly increased in the PHS group at 42 d of age compared to controls while AGT transcript was significantly increased only in the hindbrain of PHS birds. The amount of AT1R transcript did not differ between control and PHS groups. 4. The amount of Ang II significantly decreased only in the midbrain of PHS birds compared with controls while the amounts of AT₁R were not different between treatments in the three segments of the brain. 5. It was concluded that brain gene expression of AGT (in the hindbrain), renin, and ACE was upregulated in broilers with PHS whereas Ang II and AT1R levels were not changed. These results provided evidence of diminished involvement of the renin-angiotensin system in the pathogenesis of chicken pulmonary hypertension.

Central ANG-(1-7) infusion improves blood pressure regulation in antenatal betamethasone-exposed sheep and reveals sex-dependent effects on oxidative stress

Fetal exposure to betamethasone (BMX) as a consequence of glucocorticoid administration to women threatening premature delivery may lead to long-term deleterious effects on the cardiovascular system and dysregulation of blood pressure in exposed adults. Indeed, adult offspring of BMX sheep exhibit increased mean arterial pressure (MAP) and attenuated baroreflex sensitivity (BRS) that are associated with lower medullary and cerebrospinal fluid (CSF) angiotensin-(1-7) [(ANG-(1-7)] content. Thus we determined the effects of ANG-(1-7) supplementation in the CSF on MAP, BRS, blood pressure (BPV) and heart rate variability (HRV) in conscious animals. The peptide or artificial CSF (aCSF) was infused continuously into the lateral ventricle (intracerebroventricular) of 4-mo-old male and female BMX sheep for 2 wk. Analysis of data from males and females combined revealed that intracerebroventricular ANG-(1-7) significantly lowered MAP and heart rate and improved BRS as compared with baseline; intracerebroventricular aCSF did not change these indexes. Similar patterns were observed for altered hemodynamics and autonomic function produced by intracerebroventricular ANG-(1-7) in both sexes. Oxidative stress and MAP kinase (MAPK) activation were lower in tissues from the dorsomedial medulla (DMM) of ANG-(1-7)-treated males but were unchanged in the treated females, when assessed at the end of the treatment period. We conclude that in the face of ANG-(1-7) deficiency in CSF and medullary tissue in BMX sheep intracerebroventricular supplementation of ANG-(1-7) lowers MAP and restores the impaired autonomic function to a similar degree in both males and females; however, the attenuation of MAPK and oxidative stress within the DMM was evident only in males. NEW & NOTEWORTHY We demonstrate that intracerebroventricular angiotensin-(1-7) [(ANG-(1-7)] treatment for 2 wk in antenatal betamethasone-exposed sheep provides beneficial effects on blood pressure and autonomic function. The physiological improvements are accompanied by an attenuation of oxidative stress in males but not females. The finding that ANG-(1-7) supplementation lowers blood pressure and restores the impaired autonomic function in a model of fetal programming previously shown to exhibit a deficiency in cerebrospinal fluid and brain tissue illustrates the potential for new therapeutic strategies for reducing cardiovascular dysfunction arising from prenatal events.

Sex differences in sympathetic activity in obesity and its related hypertension

The prevalence of obesity is rapidly increasing in the United States, particularly among women. Approximately 60-70% of hypertension in adults may be directly attributed to obesity. In addition, maternal obesity is a major risk factor for hypertensive disorders during pregnancy. The underlying mechanisms for the association between obesity and cardiovascular risk are multifactorial, but activation of the sympathetic nervous system is one significant contributing factor. This brief review summarizes the current knowledge on sex differences in sympathetic activity in obesity and its related hypertension, with a focus on studies in humans. Evidence suggests that abdominal visceral fat, rather than subcutaneous fat, is related to augmented sympathetic activity regardless of sex. Race/ethnicity may affect the relationship between obesity and sympathetic activity. Obesity-related hypertension has an important neurogenic component, which is characterized by sympathetic overactivity. However, sex may influence the association between hypertension and sympathetic overactivity in obese people. Finally, both body weight and sympathetic overactivity seem to be involved in the development of gestational hypertensive disorders in women. Chronic hyperinsulinemia due to insulin resistance, high plasma levels of leptin, and/or obstructive sleep apnea may be responsible for sympathetic overactivity in obesity-related hypertension.

Sympathetic nervous system as a target for aging and obesity-related cardiovascular diseases

Chronic sympathetic nervous system overactivity is a hallmark of aging and obesity and contributes to the development of cardiovascular diseases including hypertension and heart failure. The cause of this chronic sympathoexcitation in aging and obesity is multifactorial and centrally mediated. In this mini-review, we have provided an overview of the key and emerging central mechanisms contributing to the pathogenesis of sympathoexcitation in obesity and healthy aging, specifically focusing on hypertension. A clear understanding of these mechanisms will pave way for targeting the sympathetic nervous system for the treatment of cardiovascular diseases in obesity and aging.

Aberrant DNA methylation of hypothalamic angiotensin receptor in prenatal programmed hypertension

Maternal malnutrition, which causes prenatal exposure to excessive glucocorticoid, induces adverse metabolic programming, leading to hypertension in offspring. In offspring of pregnant rats receiving a low-protein diet or dexamethasone, a synthetic glucocorticoid, mRNA expression of angiotensin receptor type 1a (Agtr1a) in the paraventricular nucleus (PVN) of the hypothalamus was upregulated, concurrent with reduced expression of DNA methyltransferase 3a (Dnmt3a), reduced binding of DNMT3a to the Agtr1a gene, and DNA demethylation. Salt loading increased BP in both types of offspring, suggesting that elevated hypothalamic Agtr1a expression is epigenetically modulated by excessive glucocorticoid and leads to adult-onset salt-sensitive hypertension. Consistent with this, dexamethasone treatment of PVN cells upregulated Agtr1a, while downregulating Dnmt3a, and decreased DNMT3a binding and DNA demethylation at the Agtr1a locus. In addition, Dnmt3a knockdown upregulated Agtr1a independently of dexamethasone. Hypothalamic neuron-specific Dnmt3a-deficient mice exhibited upregulation of Agtr1a in the PVN and salt-induced BP elevation without dexamethasone treatment. By contrast, dexamethasone-treated Agtr1a-deficient mice failed to show salt-induced BP elevation, despite reduced expression of Dnmt3a. Thus, epigenetic modulation of hypothalamic angiotensin signaling contributes to salt-sensitive hypertension induced by prenatal glucocorticoid excess in offspring of mothers that are malnourished during pregnancy.

Molecular and elemental effects underlying the biochemical action of transcranial direct current stimulation (tDCS) in appetite control

Recent studies highlight that obesity may alter the electric activity in brain areas triggering appetite and craving. Transcranial direct current brain stimulation (tDCS) has recently emerged as a safe alternative for treating food addiction via modulating cortical excitability without any high-risk surgical procedure to be utilized. As for anodal-type tDCS (atDCS), we observe increased excitability and spontaneous firing of the cortical neurons, whilst for the cathodal-type tDCS (ctDCS) a significant decrease is induced. Unfortunately, for the method to be fully used in a clinical setting, its biochemical action mechanism must be precisely defined, although it is proposed that molecular remodelling processes play in concert with brain activity changes involving the ions of: Na, Cl, K and Ca. Herein, we proposed for the first time Fourier transform infrared (FTIR) and synchrotron X-ray fluorescence (SRXRF) microprobes for a combined molecular and elemental analysis in the brain areas implicated appetite control, upon experimental treatment by either atDCS or ctDCS. The study, although preliminary, shows that by stimulating the prefrontal cortex in the rats fed high-caloric nutrients, the feeding behavior can be significantly changed, resulting in significantly inhibited appetite. Both, atDCS and ctDCS produced significant molecular changes involving qualitative and structural properties of lipids, whereas atDCS was found with a somewhat more significant effect on protein secondary structure in all the brain areas investigated. Also, tDCS was reported to reduce surface masses of Na, Cl, K, and Ca in almost all brain areas investigated, although the atDCS deemed to have a stronger neuro-modulating effect. Taken together, one can report that tDCS is an effective treatment technique, and its action mechanism in the appetite control seems to involve a variety of lipid-, protein- and metal/non-metal-ion-driven biochemical changes, regardless the current polarization.

Macrophage-dependent impairment of α2-adrenergic autoreceptor inhibition of Ca2+ channels in sympathetic neurons from DOCA-salt but not high-fat diet-induced hypertensive rats

DOCA-salt and obesity-related hypertension are associated with inflammation and sympathetic nervous system hyperactivity. Prejunctional α₂-adrenergic receptors (α₂ARs) provide negative feedback to norepinephrine release from sympathetic nerves through inhibition of N-type Ca²⁺ channels. Increased neuronal norepinephrine release in DOCA-salt and obesity-related hypertension occurs through impaired α₂AR signaling; however, the mechanisms involved are unclear. Mesenteric arteries are resistance arteries that receive sympathetic innervation from the superior mesenteric and celiac ganglia (SMCG). We tested the hypothesis that macrophages impair α₂AR-mediated inhibition of Ca²⁺ channels in SMCG neurons from DOCA-salt and high-fat diet (HFD)-induced hypertensive rats. Whole cell patch-clamp methods were used to record Ca²⁺ currents from SMCG neurons maintained in primary culture. We found that DOCA-salt, but not HFD-induced, hypertension caused macrophage accumulation in mesenteric arteries, increased SMCG mRNA levels of monocyte chemoattractant protein-1 and tumor necrosis factor-α, and impaired α₂AR-mediated inhibition of Ca²⁺ currents in SMCG neurons. α₂AR dysfunction did not involve changes in α₂AR expression, desensitization, or downstream signaling factors. Oxidative stress impaired α₂AR-mediated inhibition of Ca²⁺ currents in SMCG neurons and resulted in receptor internalization in human embryonic kidney-293T cells. Systemic clodronate-induced macrophage depletion preserved α₂AR function and lowered blood pressure in DOCA-salt rats. HFD caused hypertension without obesity in Sprague-Dawley rats and hypertension with obesity in Dahl salt-sensitive rats. HFD-induced hypertension was not associated with inflammation in SMCG and mesenteric arteries or α₂AR dysfunction in SMCG neurons. These results suggest that macrophage-mediated α₂AR dysfunction in the mesenteric circulation may only be relevant to mineralocorticoid-salt excess. NEW & NOTEWORTHY Here, we identify a contribution of macrophages to hypertension development through impaired α₂-adrenergic receptor (α₂AR)-mediated inhibition of sympathetic nerve terminal Ca²⁺ channels in DOCA-salt hypertensive rats. Impaired α₂AR function may involve oxidative stress-induced receptor internalization. α₂AR dysfunction may be unique to mineralocorticoid-salt excess, as it does not occur in obesity-related hypertension.

Factors Responsible for Obesity-Related Hypertension

PURPOSE OF REVIEW

The major health issue of being overweight or obese relates to the development of hypertension, insulin resistance and diabetic complications. One of the major underlying factors influencing the elevated blood pressure in obesity is increased activity of the sympathetic nerves to particular organs such as the kidney.

RECENT FINDINGS

There is now convincing evidence from animal studies that major signals such as leptin and insulin have a sympathoexcitatory action in the hypothalamus to cause hypertension. Recent studies suggest that this may involve 'neural plasticity' within hypothalamic signalling driven by central actions of leptin mediated via activation of melanocortin receptor signalling and activation of brain neurotrophic factors. This review describes the evidence to support the contribution of the SNS to obesity related hypertension and the major metabolic and adipokine signals.

Inhibition of NADPH Oxidase-Dependent Oxidative Stress in the Rostral Ventrolateral Medulla Mediates the Antihypertensive Effects of Acupuncture in Spontaneously Hypertensive Rats

Oxidative stress in the rostral ventrolateral medulla (RVLM), where the sympathetic nervous control center is located, contributes to neural mechanisms of hypertension. Acupuncture was previously reported to favorably affect high blood pressure. However, little is known about the effect of acupuncture on oxidative stress-modulated mechanisms in hypertension. This study was designed to evaluate the hypothesis that acupuncture exerts an antihypertensive effect via ameliorating oxidative stress and the redox-sensitive pathway in the RVLM of spontaneously hypertensive rats. Two weeks of acupuncture reduced blood pressure and sympathetic nervous system activity in spontaneously hypertensive rats. Oxidative stress in the RVLM was alleviated by acupuncture, accompanied by a decrease in nicotinamide adenine dinucleotide phosphate oxidase activity and expression of its subunits. Acupuncture significantly altered the mitogen-activated protein kinases signaling pathway as assessed by pathway enrichment analysis in a gene chip assay. The phosphorylation of p38 mitogen-activated protein kinases and extracellular signal-regulated protein kinase 1/2, but not Jun N-terminal kinase, was downregulated by acupuncture. Microinjection bilaterally of the superoxide dismutase mimetic tempol, nicotinamide adenine dinucleotide phosphate oxidase inhibitor apocynin, or diphenyleneiodonium chloride into the RVLM mimicked the antihypertensive effect of acupuncture. In contrast, the nicotinamide adenine dinucleotide phosphate oxidase agonist tetrabromocinnamic acid abolished the beneficial effects of acupuncture. Furthermore, injection of capsaicin or surgical sectioning of the sciatic nerve abolished the antihypertensive effect of acupuncture. We conclude that acupuncture decreases high blood pressure and nicotinamide adenine dinucleotide phosphate oxidase in the RVLM of spontaneously hypertensive rats. The mitogen-activated protein kinases and the sciatic nerve are involved in the mechanism of acupuncture's amelioration of hypertension.

Short hairpin RNA interference targeting interleukin 1 receptor type I in the paraventricular nucleus attenuates hypertension in rats

Blood pressure is controlled by tonic sympathetic activities, excessive activation of which contributes to the pathogenesis and progression of hypertension. Interleukin (IL)-1β in the paraventricular nucleus (PVN) is involved in sympathetic overdrive and hypertension. Here, we investigated the therapeutic effects of IL-1 receptor type I (IL-1R1) gene silencing in the PVN on hypertension. Recombinant lentivirus vectors expressing a short hairpin RNA (shRNA) targeting IL-1R1 (Lv-shR-IL-1R1) or a control shRNA were microinjected into PVN of spontaneously hypertensive rats (SHRs) and normotensive WKY rats. The fluorescence of green fluorescent protein-labelled vectors appeared at 2 weeks after injection and persisted for at least 8 weeks. IL-1R1 protein expression in the PVN was reduced 4 weeks after Lv-shR-IL-1R1 injection in SHRs. IL-1R1 interference also reduced basal sympathetic activity, cardiac sympathetic afferent reflex in SHRs. Depressor effects were observed from week 2 to 10 after Lv-shR-IL-1R1 treatment in SHRs, with the most prominent effects seen at the end of week 4. Furthermore, Lv-shR-IL-1R1 treatment decreased the ratio of left ventricular weight to body weight and cross-sectional areas of myocardial cells in SHRs. Additionally, Lv-shR-IL-1R1 treatment prevented an increase in superoxide anion and pro-inflammatory cytokines (PICs, TNF-α and IL-1β) in the PVN of SHR, and upregulated anti-inflammatory cytokine (AIC, IL-10) expression. These results indicate that shRNA interference targeting IL-1R1 in the PVN decreases arterial blood pressure, attenuates excessive sympathetic activity and cardiac sympathetic afferent reflex, and improves myocardial remodelling in SHRs by restoring the balance between PICs and AICs to attenuate oxidative stress.

Salt sensitivity and its implication in clinical practice

Hypertension (HTN) is a complex multi-factorial disease and is considered one of the foremost modifiable risk factors for stroke, heart failure, ischemic heart disease and renal dysfunction. Over the past century, salt and its linkage to HTN and cardiovascular (CV) mortality has been the subject of intense scientific scrutiny. There is now consensus that different individuals have different susceptibilities to blood pressure (BP)-raising effects of salt and this susceptiveness is called as salt sensitivity. Several renal and extra-renal mechanisms are believed to play a role. Blunted activity of the renin–angiotensin–aldosterone system (RAAS), adrenal Rac1-MR-Sgk1-NCC/ENaC pathway, renal SNS-GR-WNK4-NCC pathway, defect of membrane ion transportation, inflammation and abnormalities of Na⁺/Ca²⁺ exchange have all been implicated as pathophysiological basis for salt sensitive HTN. While salt restriction is definitely beneficial recent observation suggests that treatment with Azilsartan may improve salt sensitivity by selectively reducing renal proximal tubule Na⁺/H⁺ exchange. This encourages the future potential benefits of recognizing and therapeutically addressing the salt sensitive phenotype in humans.

Obesity-Induced Hypertension: Brain Signaling Pathways

Obesity greatly increases the risk for cardiovascular, metabolic, and renal diseases and is one of the most significant and preventable causes of increased blood pressure (BP) in patients with essential hypertension. This review highlights recent advances in our understanding of central nervous system (CNS) signaling pathways that contribute to the etiology and pathogenesis of obesity-induced hypertension. We discuss the role of excess adiposity and activation of the brain leptin-melanocortin system in causing increased sympathetic activity in obesity. In addition, we highlight other potential brain mechanisms by which increased weight gain modulates metabolic and cardiovascular functions. Unraveling the CNS mechanisms responsible for increased sympathetic activation and hypertension and how circulating hormones activate brain signaling pathways to control BP offer potentially important therapeutic targets for obesity and hypertension.

Obesity-associated extracellular mtDNA activates central TGFβ pathway to cause blood pressure increase

Hypothalamic inflammation was recently found to mediate obesity-related hypertension, but the responsible upstream mediators remain unexplored. In this study, we show that dietary obesity is associated with extracellular release of mitochondrial DNA (mtDNA) into the cerebrospinal fluid and that central delivery of mtDNA mimics transforming growth factor-β (TGFβ) excess to activate downstream signaling pathways. Physiological study reveals that central administration of mtDNA or TGFβ is sufficient to cause hypertension in mice. Knockout of the TGFβ receptor in proopiomelanocortin neurons counteracts the hypertensive effect of not only TGFβ but also mtDNA excess, while the hypertensive action of central mtDNA can be blocked pharmacologically by a TGFβ receptor antagonist or genetically by TGFβ receptor knockout. Finally, we confirm that obesity-induced hypertension can be reversed through central treatment with TGFβ receptor antagonist. In conclusion, circulating mtDNA in the brain employs neural TGFβ pathway to mediate a central inflammatory mechanism of obesity-related hypertension.

Deletion of p22phox-dependent oxidative stress in the hypothalamus protects against obesity by modulating 3-adrenergic mechanisms

A role for oxidative stress in the brain has been suggested in the pathogenesis of diet-induced obesity (DIO), although the underlying neural regions and mechanisms remain incompletely defined. We tested the hypothesis that NADPH oxidase-dependent oxidative stress in the paraventricular nucleus (PVN), a hypothalamic energy homeostasis center, contributes to the development of DIO. Cre/LoxP technology was coupled with selective PVN adenoviral microinjection to ablate p22^phox , the obligatory subunit for NADPH oxidase activity, in mice harboring a conditional p22^phox allele. Selective deletion of p22^phox in the PVN protected mice from high-fat DIO independent of changes in food intake or locomotor activity. This was accompanied by β₃-adrenoceptor-dependent increases in energy expenditure, elevations in brown adipose tissue thermogenesis, and browning of white adipose tissue. These data reveal a potentially novel role for brain oxidative stress in the development of DIO by modulating β₃-adrenoceptor mechanisms and point to the PVN as an underlying neural site.

The Role of Acute Intermittent Hypoxia in Neutrophil-Generated Superoxide, Sympathovagal Balance, and Vascular Function in Healthy Subjects

Introduction: Recurrent hypoxia (HPX), a hallmark of the obstructive sleep apnea (OSA), impairs autonomic balance, and increases arterial blood pressure (BP). Oxidative stress is one of the mechanisms involved in these alterations. The cumulative effect of acute intermittent HPX and the chronicity may determine whether the response crosses the threshold from having protective value to pathology. However, the impact of acute intermittent HPX–reoxygenation on markers of oxidative stress in healthy individuals remains to be fully understood.

Objective: To analyze the effects of the acute intermittent HPX on the generation of neutrophil-derived superoxide, sympathovagal balance, and vascular function in healthy subjects.

Methods: We applied six cycles of intermittent HPX (10% O₂ and 90% N₂) for 5 min followed by 2 min of room-air in 15 healthy volunteers (34 ± 2 years; 22.3 ± 0.46 kg/m²), without OSA (polysomnography), during wakefulness. During the experimental protocol, we recorded O₂ saturation, end-tidal CO₂, heart rate (HR), systolic, and diastolic BP, cardiac output (CO) and peripheral resistance (PR). Cardiac sympathovagal balance was determined by HR variability analysis (low frequency and high frequency bands, LF/HF). Superoxide generation in polymorphonuclear neutrophil cells were established using relative luminescence units (PMNs RLU) at baseline (pre-HPX) and immediately after hypoxia induction (post-HPX6).

Results: The studied subjects had normal levels of BP, plasma glucose, lipid profile, and inflammatory marker (C-reactive protein). Acute intermittent HPX increased HR, systolic BP, CO, and decreased PR. Additionally, acute intermittent HPX increased PMNs RLU, measured post-HPX6 (470 ± 50 vs. 741 ± 135, P < 0.05). We found a similar increase in LF/HF post-HPX6 (0.91 ± 0.11 vs. 2.85 ± 0.40, P < 0.05). PR was diminished from pre-HPX to post-HPX6 (1.0 ± 0.03 vs. 0.85 ± 0.06, P < 0.05). Further analysis showed significant association between O₂ saturation and PMNs RLU (R = −0.62, P = 0.02), and with LF/HF (R = −0.79, P = 0.02) post-HPX6. In addition, an association was found between PMNs RLU and PR post-HPX6 (R = 0.58, P = 0.04).

Conclusion: Acute exposure to intermittent HPX not only increased superoxide generation in neutrophils, but also impaired cardiac sympathovagal balance in healthy subjects. These data reinforce the role of intermittent HPX in superoxide generation on neutrophils, which may lead to an impairment in peripheral vascular resistance.

Renal sympathetic denervation attenuates hypertension and vascular remodeling in renovascular hypertensive rats

Li P, Huang P, Yang Y, Liu C, Lu Y, Wang F, Sun W, Kong X. Renal sympathetic denervation attenuates hypertension and vascular remodeling in renovascular hypertensive rats. J Appl Physiol 122: 121–129, 2017. First published October 14, 2016; doi: 10.1152/japplphysiol.01019.2015 .—Sympathetic activity is enhanced in patients with essential or secondary hypertension, as well as in various hypertensive animal models. Therapeutic targeting of sympathetic activation is considered an effective antihypertensive strategy. We hypothesized that renal sympathetic denervation (RSD) attenuates hypertension and improves vascular remodeling and renal disease in the 2-kidney, 1-clip (2K1C) rat model. Rats underwent 2K1C modeling or sham surgery; then rats underwent RSD or sham surgery 4 wk later, thus resulting in four groups (normotensive-sham, normotensive-RSD, 2K1C-sham, and 2K1C-RSD). Norepinephrine was measured by ELISA. Echocardiography was used to assess heart function. Fibrosis and apoptosis were assessed by Masson and TUNEL staining. Changes in mean arterial blood pressure in response to hexamethonium and plasma norepinephrine levels were used to evaluate basal sympathetic nerve activity. The 2K1C modeling success rate was 86.8%. RSD reversed the elevated systolic blood pressure induced by 2K1C, but had no effect on body weight. Compared with rats in the 2K1C-sham group, rats in the 2K1C-RSD group showed lower left ventricular mass/body weight ratio, interventricular septal thickness in diastole, left ventricular end-systolic diameter, and left ventricular posterior wall thickness in systole, whereas fractional shortening and ejection fraction were higher. Right kidney apoptosis and left kidney hypertrophy were not changed by RSD. Arterial fibrosis was lower in animals in the 2K1C-RSD group compared with those in the 2K1C-sham group. RSD reduced plasma norepinephrine and basal sympathetic activity in rats in the 2K1C-RSD group compared with rats in the 2K1C-sham group. These results suggest a possible clinical efficacy of RSD for renovascular hypertension.

NEW & NOTEWORTHY The effects of renal sympathetic denervation (RSD) on hypertension, cardiac function, vascular fibrosis, and renal apoptosis were studied in the 2K1C rat model. Results showed that RSD attenuated hypertension, improved vascular remodeling, and reduced vascular fibrosis through decreased sympathetic activity in the 2K1C rat model, but it did not change the kidney size, renal apoptosis, or renal caspase-3 expression. These results could suggest possible clinical efficacy of RSD for renovascular hypertension.

Neural Control of Non-vasomotor Organs in Hypertension

Hypertension affects over 25 % of the population with the incidence continuing to rise, due in part to the growing obesity epidemic. Chronic elevations in sympathetic nerve activity (SNA) are a hallmark of the disease and contribute to elevations in blood pressure through influences on the vasculature, kidney, and heart (i.e., neurogenic hypertension). In this regard, a number of central nervous system mechanisms and neural pathways have emerged as crucial in chronically elevating SNA. However, it is important to consider that "sympathetic signatures" are present, with differential increases in SNA to regional organs that are dependent upon the disease progression. Here, we discuss recent findings on the central nervous system mechanisms and autonomic regulatory networks involved in neurogenic hypertension, in both non-obesity- and obesity-associated hypertension, with an emphasis on angiotensin-II, salt, oxidative and endoplasmic reticulum stress, inflammation, and the adipokine leptin.

The Role of CNS in the Effects of Salt on Blood Pressure

Sympathetic nerve activity is involved in the pathogenesis of salt-sensitive hypertension. The central nervous system, which regulates sympathetic nerve activity and blood pressure, plays a pivotal role. Central sympathoexcitation is deeply involved in the pathogenesis of salt-sensitive hypertension, although the precise mechanisms have not been fully elucidated because of their complexity. The role of brain oxidative stress in sympathoexcitation has been suggested in some types of hypertensive animal models. We have shown that increased brain oxidative stress may elevate arterial pressure through central sympathoexcitation in salt-sensitive hypertension. Several other factors such as mineralocorticoid receptors, aldosterone, corticosterone, epithelial sodium channels, and angiotensin II also play important roles in central sympathetic activation, some of which can be associated with brain oxidative stress. Furthermore, brain paraventricular nucleus Gαi2-protein-mediated transduction has been recently reported as a candidate for the molecular mechanism countering the development of salt-sensitive hypertension.

The Role of Aldosterone in Obesity-Related Hypertension

Obese subjects often have hypertension and related cardiovascular and renal diseases, and this has become a serious worldwide health problem. In obese subjects, impaired renal-pressure natriuresis causes sodium retention, leading to the development of salt-sensitive hypertension. Physical compression of the kidneys by visceral fat and activation of the sympathetic nervous system, renin-angiotensin systems (RAS), and aldosterone/mineralocorticoid receptor (MR) system are involved in this mechanism. Obese subjects often exhibit hyperaldosteronism, with increased salt sensitivity of blood pressure (BP). Adipose tissue excretes aldosterone-releasing factors, thereby stimulating aldosterone secretion independently of the systemic RAS, and aldosterone/MR activation plays a key role in the development of hypertension and organ damage in obesity. In obese subjects, both salt sensitivity of BP, enhanced by obesity-related metabolic disorders including aldosterone excess, and increased dietary sodium intake are closely related to the incidence of hypertension. Some salt sensitivity-related gene variants affect the risk of obesity, and together with salt intake, its combination is possibly associated with the development of hypertension in obese subjects. With high salt levels common in modern diets, salt restriction and weight control are undoubtedly important. However, not only MR blockade but also new diagnostic modalities and therapies targeting and modifying genes that are related to salt sensitivity, obesity, or RAS regulation are expected to prevent obesity and obesity-related hypertension.

Oxidant and enzymatic antioxidant status (gene expression and activity) in the brain of chickens with cold-induced pulmonary hypertension

To evaluate oxidant and antioxidant status of the brain (hindbrain, midbrain, and forebrain) in chickens with cold-induced pulmonary hypertension, the measurements of lipid peroxidation, protein oxidation, antioxidant capacity, enzymatic activity, and gene expression (for catalase, glutathione peroxidase, and superoxide dismutases) were done. There were high lipid peroxidation/protein oxidation and low antioxidant capacity in the hindbrain of cold-induced pulmonary hypertensive chickens compared to control (P < 0.05). In the hypertensive chickens, superoxide dismutase activity was decreased (forebrain, midbrain, and hindbrain), while catalase activity was increased (forebrain and midbrain) (P < 0.05). Glutathione peroxidase activity did not change. Relative gene expression of catalase and superoxide dismutases (1 and 2) was downregulated, while glutathione peroxidase was upregulated in the brain of the cold-induced pulmonary hypertensive chickens. Probably, these situations in the oxidant and antioxidant status of the brain especially hindbrain may change its function at cardiovascular center and sympathetic nervous system to exacerbate pulmonary hypertension.

Alpha lipoic acid supplementation attenuates reactive oxygen species in hypothalamic paraventricular nucleus and sympathoexcitation in high salt-induced hypertension

AIMS

High salt-induced oxidative stress plays an important role in the development of hypertension. Alpha lipoic acid (ALA) is extensively recognized as having a powerful superoxide inhibitory property. In this study, we determined whether ALA supplementation attenuates oxidative stress in hypothalamic paraventricular nucleus (PVN), decreases the sympathetic activity and arterial pressure in high salt-induced hypertension by cross-talking with renin-angiotensin system (RAS) and pro-inflammatory cytokines (PICs).

METHODS

Male Wistar rats were administered a normal-salt diet (NS, 0.3% NaCl) or a high-salt diet (HS, 8.0% NaCl) for 8 weeks. These rats received ALA (60mg/kg) dissolved in vehicle (0.9% saline) or an equal voleme of vehicle, by gastric perfusion for 9 weeks.

RESULTS

High salt intake resulted in higher renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP). These rats also had higher levels of superoxide, gp91(phox), gp47(phox) (subunits of NAD(P)H oxidase), angiotensin-converting enzyme (ACE), angiotensin II type1 receptor (AT1-R), interleukin-1beta (IL-1β), interleukin-6 (IL-6), and lower levels of interleukin-10 (IL-10) and copper/zinc superoxide dismutase (Cu/Zn-SOD) than control animals. Treatment with ALA significantly attenuated the levels of superoxide, gp91(phox), gp47(phox), ACE, AT1-R, IL-1β and IL-6, increased the levels of IL-10 and Cu/Zn-SOD, and decreased MAP and RSNA compared with high-salt induced hypertensive rats. The mRNA expression of gp47(phox) and gp91(phox) are in accordance with their protein expression.

CONCLUSION

These findings suggest that supplementation of ALA obviously decreases the sympathetic activity and arterial pressure in high salt-induced hypertension by improving the superoxide inhibitory property, suppressing the activation of RAS and restoring the balance between pro- and anti-inflammatory cytokines in the PVN.

Chronic estrogen exposure affects gene expression in the rostral ventrolateral medulla of young and aging rats: Possible role in hypertension

BACKGROUND

Chronic exposure to estradiol-17β (E2) in adult female rats increases mean arterial pressure by stimulating superoxide production in the rostral ventrolateral medulla (RVLM). However the mechanisms behind this phenomenon are unknown. We hypothesized that E2 exposure induces the gene expression of cytokines, chemokines and NADPH oxidase (Nox) in the RVLM that promotes superoxide production and aging would exacerbate this effect.

METHODS

Young adult (3-4 month old) and middle-aged (6-8 month old) female Sprague Dawley rats were sham-implanted (YS and MS respectively) or implanted s.c. with slow-release E2 pellets (20 ng of E2/day for 90 days; YE and ME respectively). Blood pressure (BP) was measured during the last 3 weeks of exposure in a separate set of rats. At the end of treatment, the animals were sacrificed and RVLM was isolated from the brainstem. PCR array and Quantitative RT-PCR were performed with the tissue to quantify genes associated with hypertension and superoxide production. Superoxide dismutase (SOD) activity was also measured in the RVLM from a different set of animals.

RESULTS

E2 exposure increased mean arterial pressure in both YE and ME animals. Inflammatory genes such as interleukin-1β, interleukin-6 and monocyte chemoattractant protein-1 were significantly up-regulated in the RVLM of ME treated female rats compared to YS rats, but not in YE rats. Endothelin-1 (ET-1) gene was up-regulated in the RVLM of both YE and ME rats that were exposed to E2. Furthermore, chronic E2 treatment increased the mRNA levels of Nox1 and Nox2 genes in the RVLM of YE but not ME animals. SOD activity was reduced in MA animals, compared to young animals. E2 treatment had no significant effect on SOD activity.

CONCLUSION

Chronic E2 exposure stimulates the expression of inflammatory genes in older animals and increases the expression of Nox subunits in the RVLM of younger animals. SOD activity was reduced in older animals. This suggests increased superoxide production in younger animals, but reduced superoxide elimination in older animals. On the other hand, E2 exposure stimulates ET-1 expression in both young and aging animals. These findings suggest that hypertension caused by chronic E2 exposure may involve different molecular mediators in young and aging animals, however ET-1 and superoxide could be common mediators for both age groups.

Restraint stress exacerbates cardiac and adipose tissue pathology via β-adrenergic signaling in rats with metabolic syndrome

Restraint stress stimulates sympathetic nerve activity and can affect adiposity and metabolism. However, the effects of restraint stress on cardiovascular and metabolic disorders in metabolic syndrome (MetS) have remained unclear. We investigated the effects of chronic restraint stress and β-adrenergic receptor (β-AR) blockade on cardiac and adipose tissue pathology and metabolic disorders in a rat model of MetS. DahlS.Z- Leprfa/ Leprfa (DS/obese) rats, derived from a cross between Dahl salt-sensitive and Zucker rats. Rats were exposed to restraint stress (restraint cage, 2 h/day) for 4 wk from 9 wk of age with or without daily subcutaneous administration of the β-AR blocker propranolol (2 mg/kg). Age-matched homozygous lean littermates of DS/obese rats (DahlS.Z- Lepr+ /Lepr+ rats) served as control animals. Chronic restraint stress exacerbated hypertension as well as left ventricular hypertrophy, fibrosis, diastolic dysfunction, and oxidative stress in a manner sensitive to propranolol treatment. Restraint stress attenuated body weight gain in DS/obese rats, and this effect tended to be reversed by propranolol ( P = 0.0682). Restraint stress or propranolol did not affect visceral or subcutaneous fat mass. However, restraint stress potentiated cardiac and visceral adipose tissue inflammation in DS/obese rats, and these effects were ameliorated by propranolol. Restraint stress also exacerbated glucose intolerance, insulin resistance, and abnormal lipid metabolism in a manner sensitive to propranolol. In addition, restraint stress increased urinary norepinephrine excretion, and propranolol attenuated this effect. Our results thus implicate β-ARs in the exacerbation of cardiac and adipose tissue pathology and abnormal glucose and lipid metabolism induced by restraint stress in this model of MetS.

Blockade of brain angiotensin II type 1 receptor inhibits the development of atrial fibrillation in hypertensive rats

BACKGROUND

Hypertension is a powerful risk factor of atrial fibrillation (AF). The pathophysiology of AF with hypertension is associated with sympathoexcitation or the renin-angiotensin system; however, current therapies cannot sufficiently prevent its development. We previously revealed that brain angiotensin II type 1 receptor (AT1R) blockade causes a depressor response via sympathoinhibition. Herein, we evaluated whether brain AT1R contributes to AF development in hypertensive rats.

METHODS

We divided the stroke-prone spontaneously hypertensive rats (SHRSP) treated with intracerebroventricular (ICV) infusion of vehicle, ICV infusion of losartan (S-LOS), or oral administration of hydralazine (S-HYD); and Wistar Kyoto rats treated with ICV S-VEH.

RESULTS

Two weeks later, systolic blood pressure was significantly lower in the S-LOS group than in the S-VEH group and was even lower in the S-HYD group. Urinary norepinephrine excretion for 24h, an indirect marker of sympathoexcitation, significantly reduced in the S-LOS group but increased in the S-HYD group despite depressor response. AF was induced by transesophageal burst pacing. AF duration was significantly shorter in the S-LOS group than in the S-VEH group (5.0±0.4 vs. 15.2±3.7 s; n = 8 each; P < 0.05). However, it was significantly longer in the S-HYD group than in the S-VEH group. Interstitial atrial fibrosis and echocardiographic parameters did not differ between the SHRSP groups.

CONCLUSIONS

Brain AT1R blockade suppresses AF inducibility and maintenance independent of depressor response in hypertensive rats.

Renal mechanisms of salt-sensitive hypertension: contribution of two steroid receptor-associated pathways

Although salt is a major environmental factor in the development of hypertension, the degree of salt sensitivity varies widely among individuals. The mechanisms responsible for this variation remain to be elucidated. Recent studies have revealed the involvement of two important signaling pathways in renal tubules that play key roles in electrolyte balance and the maintenance of normal blood pressure: the β2-adrenergic stimulant-glucocorticoid receptor (GR)-with-no-lysine kinase (WNK)4-Na+-Cl− cotransporter pathway, which is active in distal convoluted tubule (DCT)1, and the Ras-related C3 botulinum toxin substrate (Rac)1-mineralocorticoid receptor (MR) pathway, which is active in DCT2, connecting tubules, and collecting ducts. β2-Adrenergic stimulation due to increased renal sympathetic activity in obesity- and salt-induced hypertension suppresses histone deacetylase 8 activity via cAMP/PKA signaling, increasing the accessibility of GRs to the negative GR response element in the WNK4 promoter. This results in the suppression of WNK4 transcription followed by the activation of Na+-Cl− cotransporters in the DCT and elevated Na+ retention and blood pressure upon salt loading. Rac1 activates MRs, even in the absence of ligand binding, with this activity increased in the presence of ligand. In salt-sensitive animals, Rac1 activation due to salt loading activates MRs in DCT2, connecting tubules, and collecting ducts. Thus, GRs and MRs are independently involved in two pathways responsible for renal Na+ handling and salt-sensitive hypertension. These findings suggest novel therapeutic targets and may lead to the development of diagnostic tools to determine salt sensitivity in hypertensive patients.

Oxidative stress in obesity: a critical component in human diseases

Obesity, a social problem worldwide, is characterized by an increase in body weight that results in excessive fat accumulation. Obesity is a major cause of morbidity and mortality and leads to several diseases, including metabolic syndrome, diabetes mellitus, cardiovascular, fatty liver diseases, and cancer. Growing evidence allows us to understand the critical role of adipose tissue in controlling the physic-pathological mechanisms of obesity and related comorbidities. Recently, adipose tissue, especially in the visceral compartment, has been considered not only as a simple energy depository tissue, but also as an active endocrine organ releasing a variety of biologically active molecules known as adipocytokines or adipokines. Based on the complex interplay between adipokines, obesity is also characterized by chronic low grade inflammation with permanently increased oxidative stress (OS). Over-expression of oxidative stress damages cellular structures together with under-production of anti-oxidant mechanisms, leading to the development of obesity-related complications. The aim of this review is to summarize what is known in the relationship between OS in obesity and obesity-related diseases.

Exercise training attenuates sympathetic activation and oxidative stress in diet-induced obesity

It is known that excessive sympathetic activity and oxidative stress are enhanced in obesity. This study aimed to clarify whether exercise training (ET) attenuates sympathetic activation and oxidative stress in obesity. The obesity was induced by high-fat diet (HFD) for 12 weeks. Male Sprague-Dawley rats were assigned to four groups: regular diet (RD) plus sedentary (RD-S), RD plus ET (RD-ET), HFD plus sedentary (HFD-S), and HFD plus ET (HFD-ET). The rats in RD-ET and HFD-ET groups were trained on a motorized treadmill for 60 min/day, five days/week for 8 weeks. The sympathetic activity was evaluated by the plasma norepinephrine (NE) level. The superoxide anion, malondialdehyde and F2-isoprostanes levels in serum and muscles were measured to evaluate oxidative stress. The ET prevented the increases in the body weight, arterial pressure and white adipose tissue mass in HFD rats. The NE level in plasma and oxidative stress related parameters got lower in HFD-ET group compared with HFD-S group. We have found decreased mRNA and protein levels of toll-like receptor (TLR)-2 and TLR-4 by ET in HFD rats. These findings suggest that ET may be effective for attenuating sympathetic activation and oxidative stress in diet-induced obesity.

Telmisartan exerts sustained blood pressure control and reduces blood pressure variability in metabolic syndrome by inhibiting sympathetic activity

BACKGROUND

Accumulating evidence on blood pressure (BP) reduction with various angiotensin II receptor blockers (ARBs) show that the magnitudes and durations of BP control differ across ARBs. However, the mechanism of ARBs is unknown. This work was undertaken to compare telmisartan and valsartan in duration of BP control, BP variability, and effects on the autonomic nervous system.

METHODS

Using radiotelemetry combined with spectral analysis with a fast Fourier transformation algorithm, we compared the effects of various doses of telmisartan and valsartan on BP and its variability during dark (active phase) and light (inactive phase) periods over 5 weeks in SHR/NDmcr-cp(+/+)(SHRcp) rats, a model of metabolic syndrome. We also compared the effects of these ARBs on autonomic nervous system, central oxidative stress, and inflammation in SHRcp rats.

RESULTS

Telmisartan exerted a longer-lasting BP-lowering effect and greater attenuation of BP variability in SHRcp than valsartan. Telmisartan decreased low frequency power of systolic BP and increased spontaneous baroreflex gain in SHRcp during both the dark and light periods more than valsartan. Telmisartan reduced 24-hour urinary norepinephrine excretion more than valsartan. Furthermore, telmisartan attenuated oxidative stress and the numbers of gp91(phox)-positive cells and activated microglia and astrocytes in the rostral ventrolateral medulla of SHRcp rats more than valsartan.

CONCLUSIONS

The superiority of telmisartan over valsartan in sustained BP control and reduction of BP variability was attributed to more suppression of sympathetic activity and more improvement of baroreceptor reflex. The greater suppression of sympathetic activity by telmisartan appeared to be partially mediated by a stronger amelioration of central oxidative stress.

Role of Nitric Oxide Synthase Uncoupling at Rostral Ventrolateral Medulla in Redox-Sensitive Hypertension Associated With Metabolic Syndrome

Metabolic syndrome (MetS), which is rapidly becoming prevalent worldwide, is long known to be associated with hypertension and recently with oxidative stress. Of note is that oxidative stress in the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons reside, contributes to sympathoexcitation and hypertension. This study sought to identify the source of tissue oxidative stress in RVLM and their roles in neural mechanism of hypertension associated with MetS. Adult normotensive rats subjected to a high-fructose diet for 8 weeks developed metabolic traits of MetS, alongside increases in sympathetic vasomotor activity and blood pressure. In RVLM of these MetS rats, the tissue level of reactive oxygen species was increased, nitric oxide (NO) was decreased, and mitochondrial electron transport capacity was reduced. Whereas the protein expression of neuronal NO synthase (nNOS) or protein inhibitor of nNOS was increased, the ratio of nNOS dimer/monomer was significantly decreased. Oral intake of pioglitazone or intracisternal infusion of tempol or coenzyme Q 10 significantly abrogated all those molecular events in high-fructose diet–fed rats and ameliorated sympathoexcitation and hypertension. Gene silencing of protein inhibitor of nNOS mRNA in RVLM using lentivirus carrying small hairpin RNA inhibited protein inhibitor of nNOS expression, increased the ratio of nNOS dimer/monomer, restored NO content, and alleviated oxidative stress in RVLM of high-fructose diet–fed rats, alongside significantly reduced sympathoexcitation and hypertension. These results suggest that redox-sensitive and protein inhibitor of nNOS–mediated nNOS uncoupling is engaged in a vicious cycle that sustains the production of reactive oxygen species in RVLM, resulting in sympathoexcitation and hypertension associated with MetS.

Systemic and renal oxidative stress in the pathogenesis of hypertension: modulation of long-term control of arterial blood pressure by resveratrol

Hypertension affects over 25% of the global population and is associated with grave and often fatal complications that affect many organ systems. Although great advancements have been made in the clinical assessment and treatment of hypertension, the cause of hypertension in over 90% of these patients is unknown, which hampers the development of targeted and more effective treatment. The etiology of hypertension involves multiple pathological processes and organ systems, however one unifying feature of all of these contributing factors is oxidative stress. Once the body's natural anti-oxidant defense mechanisms are overwhelmed, reactive oxygen species (ROS) begin to accumulate in the tissues. ROS play important roles in normal regulation of many physiological processes, however in excess they are detrimental and cause widespread cell and tissue damage as well as derangements in many physiological processes. Thus, control of oxidative stress has become an attractive target for pharmacotherapy to prevent and manage hypertension. Resveratrol (trans-3,5,4'-Trihydroxystilbene) is a naturally occurring polyphenol which has anti-oxidant effects in vivo. Many studies have shown anti-hypertensive effects of resveratrol in different pre-clinical models of hypertension, via a multitude of mechanisms that include its function as an anti-oxidant. However, results have been mixed and in some cases resveratrol has no effect on blood pressure. This may be due to the heavy emphasis on peripheral vasodilator effects of resveratrol and virtually no investigation of its potential renal effects. This is particularly troubling in the arena of hypertension, where it is well known and accepted that the kidney plays an essential role in the long term regulation of arterial pressure and a vital role in the initiation, development and maintenance of chronic hypertension. It is thus the focus of this review to discuss the potential of resveratrol as an anti-hypertensive treatment via amelioration of oxidative stress within the framework of the fundamental physiological principles of long term regulation of arterial blood pressure.

Increased oxidative stress in obesity: implications for metabolic syndrome, diabetes, hypertension, dyslipidemia, atherosclerosis, and cancer

Obesity, especially of the abdominal type, is a health problem that constitutes metabolic syndrome and increases the incidence of various diseases, including diabetes, hypertension, dyslipidemia, atherosclerosis, and cancer. Various mechanisms linking obesity to these associated diseases have been postulated. One candidate is oxidative stress, which has been implicated in vascular complications of diabetes and in pancreatic -cell failure in diabetes. Notably, obese people without diabetes also display elevated levels of systemic oxidative stress. In addition, levels of oxidative stress are increased in the adipose tissue in obese mice. Treating obese mice with antioxidant agents attenuates the development of diabetes. In 3T3-L1 adipocytes, increases in reactive oxygen species (ROS) occur with lipid accumulation; the addition of free fatty acids elevates ROS generation further. Thus, adipose tissue represents an important source of ROS; ROS may contribute to the development of obesity-associated insulin resistance and type 2 diabetes. Moreover, the levels of oxidative stress present in several other types of cells or tis-sues, including those in the brain, arterial walls, and tumors, have been implicated in the pathogenesis associated with hypertension, atherosclerosis, and cancer. The increased levels of systemic oxidative stress that occur in obesity may contribute to the obesity-associated development of these diseases.