Increased superoxide anion in rostral ventrolateral medulla contributes to hypertension in spontaneously hypertensive rats via interactions with nitric oxide

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.

Coenzyme Q10 effects in neurological diseases

Coenzyme Q10 (CoQ10), a lipophilic substituted benzoquinone, is present in animal and plant cells. It is endogenously synthetized in every cell and involved in a variety of cellular processes. CoQ10 is an obligatory component of the respiratory chain in inner mitochondrial membrane. In addition, the presence of CoQ10 in all cellular membranes and in blood. It is the only endogenous lipid antioxidant. Moreover, it is an essential factor for uncoupling protein and controls the permeability transition pore in mitochondria. It also participates in extramitochondrial electron transport and controls membrane physicochemical properties. CoQ10 effects on gene expression might affect the overall metabolism. Primary changes in the energetic and antioxidant functions can explain its remedial effects. CoQ10 supplementation is safe and well-tolerated, even at high doses. CoQ10 does not cause any serious adverse effects in humans or experimental animals. New preparations of CoQ10 that are less hydrophobic and structural derivatives, like idebenone and MitoQ, are being developed to increase absorption and tissue distribution. The review aims to summarize clinical and experimental effects of CoQ10 supplementations in some neurological diseases such as migraine, Parkinson´s disease, Huntington´s disease, Alzheimer´s disease, amyotrophic lateral sclerosis, Friedreich´s ataxia or multiple sclerosis. Cardiovascular hypertension was included because of its central mechanisms controlling blood pressure in the brainstem rostral ventrolateral medulla and hypothalamic paraventricular nucleus. In conclusion, it seems reasonable to recommend CoQ10 as adjunct to conventional therapy in some cases. However, sometimes CoQ10 supplementations are more efficient in animal models of diseases than in human patients (e.g. Parkinson´s disease) or rather vague (e.g. Friedreich´s ataxia or amyotrophic lateral sclerosis).

Sympathoinhibition and Vasodilation Contribute to the Acute Hypotensive Response of the Superoxide Dismutase Mimic, MnTnBuOE-2-PyP5+, in Hypertensive Animals

The pathogenesis of hypertension has been linked to excessive levels of reactive oxygen species (ROS), particularly superoxide (O2•-), in multiple tissues and organ systems. Overexpression of superoxide dismutase (SOD) to scavenge O2•- has been shown to decrease blood pressure in hypertensive animals. We have previously shown that MnTnBuOE-2-PyP5+ (BuOE), a manganese porphyrin SOD mimic currently in clinical trials as a normal tissue protector for cancer patients undergoing radiation therapy, can scavenge O2•- and acutely decrease normotensive blood pressures. Herein, we hypothesized that BuOE decreases hypertensive blood pressures. Using angiotensin II (AngII)-hypertensive mice, we demonstrate that BuOE administered both intraperitoneally and intravenously (IV) acutely decreases elevated blood pressure. Further investigation using renal sympathetic nerve recordings in spontaneously hypertensive rats (SHRs) reveals that immediately following IV injection of BuOE, blood pressure and renal sympathetic nerve activity (RSNA) decrease. BuOE also induces dose-dependent vasodilation of femoral arteries from AngII-hypertensive mice, a response that is mediated, at least in part, by nitric oxide, as demonstrated by ex vivo video myography. We confirmed this vasodilation in vivo using doppler imaging of the superior mesenteric artery in AngII-hypertensive mice. Together, these data demonstrate that BuOE acutely decreases RSNA and induces vasodilation, which likely contribute to its ability to rapidly decrease hypertensive blood pressure.

Rodent models of hypertension

Elevated blood pressure (BP), or hypertension, is the main risk factor for cardiovascular disease. As a multifactorial and systemic disease that involves multiple organs and systems, hypertension remains a challenging disease to study. Models of hypertension are invaluable to support the discovery of the specific genetic, cellular and molecular mechanisms underlying essential hypertension, as well as to test new possible treatments to lower BP. Rodent models have proven to be an invaluable tool for advancing the field. In this review, we discuss the strengths and weaknesses of rodent models of hypertension through a systems approach. We highlight the ways how target organs and systems including the kidneys, vasculature, the sympathetic nervous system (SNS), immune system and the gut microbiota influence BP in each rodent model. We also discuss often overlooked hypertensive conditions such as pulmonary hypertension and hypertensive-pregnancy disorders, providing an important resource for researchers.

Angiotensin-(1-7) Central Mechanisms After ICV Infusion in Hypertensive Transgenic (mRen2)27 Rats

Previous data showed hypertensive rats subjected to chronic intracerebroventricular (ICV) infusion of angiotensin-(1-7) presented attenuation of arterial hypertension, improvement of baroreflex sensitivity, restoration of cardiac autonomic balance and a shift of cardiac renin-angiotensin system (RAS) balance toward Ang-(1-7)/Mas receptor. In the present study, we investigated putative central mechanisms related to the antihypertensive effect induced by ICV Ang-(1-7), including inflammatory mediators and the expression/activity of the RAS components in hypertensive rats. Furthermore, we performed a proteomic analysis to evaluate differentially regulated proteins in the hypothalamus of these animals. For this, Sprague Dawley (SD) and transgenic (mRen2)27 hypertensive rats (TG) were subjected to 14 days of ICV infusion with Ang-(1-7) (200 ng/h) or 0.9% sterile saline (0.5 μl/h) through osmotic mini-pumps. We observed that Ang-(1-7) treatment modulated inflammatory cytokines by decreasing TNF-α levels while increasing the anti-inflammatory IL-10. Moreover, we showed a reduction in ACE activity and gene expression of AT1 receptor and iNOS. Finally, our proteomic evaluation suggested an anti-inflammatory mechanism of Ang-(1-7) toward the ROS modulators Uchl1 and Prdx1.

Different reactive species modulate the hypotensive effect triggered by angiotensins at CVLM of 2K1C hypertensive rats

Hypertension is associated with increased central activity of the renin-angiotensin system (RAS) and oxidative stress. Here, we evaluated whether reactive species and neurotransmitters could contribute to the hypotensive effect induced by angiotensin (Ang) II and Ang-(1-7) at the caudal ventrolateral medulla (CVLM) in renovascular hypertensive rats (2K1C). Therefore, we investigated the effect of Ang II, Ang-(1-7), and the Ang-(1-7) antagonist A-779 microinjected before and after CVLM microinjection of the nitric oxide (NO)-synthase inhibitor, (L-NAME), vitamin C (Vit C), bicuculline, or kynurenic acid in 2K1C and SHAM rats. Baseline values of the mean arterial pressure (MAP) in 2K1C rats were higher than in SHAM rats. CVLM microinjection of Ang II, Ang-(1-7), l-NAME, or bicuculline induced decreases in the MAP in SHAM and 2K1C rats. In addition, Vit C and A-779 produced decreases in the MAP only in 2K1C rats. Kynurenic acid increased the MAP in both SHAM and 2K1C rats. Only the Ang-(1-7) effect was increased by l-NAME and reduced by bicuculline in SHAM rats. L-NAME also reduced the A-779 effect in 2K1C rats. Only the Ang II effect was abolished by CVLM Vit C and enhanced by CVLM kynurenic acid in SHAM and 2K1C rats. Overall, the superoxide anion and glutamate participated in the hypotensive effect of Ang II, while NO and GABA participated in the hypotensive effect of Ang-(1-7) in CVLM. The higher hypotensive response of A-779 in the CVLM of 2K1C rats suggests that Ang-(1-7) contributes to renovascular hypertension.

Nanoformulation of the superoxide dismutase mimic, MnTnBuOE-2-PyP5+, prevents its acute hypotensive response

Scavenging superoxide (O₂^•-) via overexpression of superoxide dismutase (SOD) or administration of SOD mimics improves outcomes in multiple experimental models of human disease including cardiovascular disease, neurodegeneration, and cancer. While few SOD mimics have transitioned to clinical trials, MnTnBuOE-2-PyP⁵⁺ (BuOE), a manganese porphyrin SOD mimic, is currently in clinical trials as a radioprotector for cancer patients; thus, providing hope for the use of SOD mimics in the clinical setting. However, BuOE transiently alters cardiovascular function including a significant and precipitous decrease in blood pressure. To limit BuOE's acute hypotensive action, we developed a mesoporous silica nanoparticle and lipid bilayer nanoformulation of BuOE (nanoBuOE) that allows for slow and sustained release of the drug. Herein, we tested the hypothesis that unlike native BuOE, nanoBuOE does not induce an acute hypotensive response, as the nanoformulation prevents BuOE from scavenging O₂^•- while the drug is still encapsulated in the formulation. We report that intact nanoBuOE does not effectively scavenge O₂^•-, whereas BuOE released from the nanoformulation does retain SOD-like activity. Further, in mice, native BuOE, but not nanoBuOE, rapidly, acutely, and significantly decreases blood pressure, as measured by radiotelemetry. To begin exploring the physiological mechanism by which native BuOE acutely decreases blood pressure, we recorded renal sympathetic nerve activity (RSNA) in rats. RSNA significantly decreased immediately following intravenous injection of BuOE, but not nanoBuOE. These data indicate that nanoformulation of BuOE, a SOD mimic currently in clinical trials in cancer patients, prevents BuOE's negative side effects on blood pressure homeostasis.

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MnTnBuOE-2-PyP⁵⁺ (BuOE) induces a rapid and significant decrease in blood pressure.

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BuOE's hypotensive response is concomitant with reduced sympathetic nerve activity.

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Nanoformulated BuOE (nanoBuOE) release of active drug is slow and sustained.

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nanoBuOE prevents the BuOE-induced hypotensive and sympathoinhibition responses.

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.

Upregulating Nrf2 in the RVLM ameliorates sympatho-excitation in mice with chronic heart failure

Nuclear factor E2-related factor 2 (Nrf2) is a key transcription factor that maintains redox homeostasis by governing a broad array of antioxidant genes in response to oxidant stress. We hypothesized that overexpression of Nrf2 in the rostral ventrolateral medulla (RVLM) ameliorates sympatho-excitation in mice with coronary artery ligation-induced chronic heart failure (CHF). To address this, we overexpressed Nrf2 in the RVLM using an HIV-CamKIIa-Nrf2 lenti virus in C57BL/6 mice. In addition, we used a Lenti-Cre virus in Keap1^flox/flox mice to upregulate Nrf2 non-selectively in the RVLM. Arterial blood pressure (AP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded under conscious and anesthetized conditions, respectively. Protein expression was assayed using western blotting and immunofluorescence staining. We found that (1) Nrf2 and two target proteins, NQO1 and HO-1 in the RVLM were significantly lower in CHF compared to Sham mice. Nrf2 viral transfection of the RVLM upregulated Nrf2 protein. (2) Urinary NE excretion in CHF mice was markedly attenuated following Nrf2 upregulation (812 ± 133 vs 1120 ± 271 ng/24hr mean. ±SE, *p < 0.05, n = 8/group). (3) In the conscious state, CHF mice overexpressing Nrf2 exhibited an enhancement in spontaneous baroreflex gain and in phenylephrine-induced baroreflex control of HR. (4) Acute experiments under anesthetisa revealed a significant decrease in basal RSNA (44.0 ± 6.5 vs 64.7 ± 8.3% of Max. *P < 0.05 n = 8/group) and enhancement in baroreflex sensitivity (Maximal gain -1.8 ± 0.3 vs 1.1 ± 0.2 of mmHg. **p < 0.01. n = 6/group) in CHF mice that were virally transfected with Nrf2 compared with CHF mice transfected with Lenti-GFP. Finally, Lenti-Cre viral overexpression of Nrf2 in Keap1^flox/flox mice reduced Keap1 protein and increased Nrf2, NQO1, and HO-1 in the RVLM of Sham and CHF mice. CHF-Cre mice exhibited a significant decrease in baseline RSNA and plasma NE concentration (8.9 ± 1.1 vs 12.7 ± 0.9 ng/mL *P < 0.05 n = 6/group) as compared with CHF-GFP mice. Based on the above data, we conclude that upregulating Nrf2 selectively in the RVLM attenuates sympatho-excitation in CHF mice. Nrf2 may be an important central target for autonomic modulation in cardiovascular disease and during stress.

High fructose diet induces early mortality via autophagy factors accumulation in the rostral ventrolateral medulla as ameliorated by pioglitazone

High fructose ingestion enhances mortality which has been linked to autonomic dysregulation. However, the underlying mechanisms are still largely unknown. In the present study, we demonstrated that 3 months of high fructose diet (HFD) ingestion induced mortality in 18-week-old Wistar Kyoto rats (WKY) during anesthesia. Concurrently, the low frequency (LF) and the high frequency (HF) elements of the power spectral analyses of SBP were increased. Of note, the decreased ratio of LF and HF (LF/HF), an index of sympathetic and parasympathetic balance, suggested an autonomic imbalance. In the rostral ventrolateral medulla (RVLM), a center of sympathetic outflow, the levels of presynaptic (synaptophysin) and postsynaptic (postsynaptic density protein 95 and phospho-Ca²⁺/calmodulin-dependent protein kinase II) proteins were increased. The down-regulation of insulin receptor β and insulin receptor substrate 1 suggested the status of insulin desensitization. Moreover, the up-regulation of AMP-activated protein kinase and sirtuin 1 suggested the enhancement of energy sensing to activate autophagy. Simultaneously, the accumulations of Beclin-1, ATG12 and LC3B were increased in RVLM. Pioglitazone (PIO), an insulin sensitizer, effectively relieved the accumulation of Beclin-1 and ATG12 as well as the synaptic proteins synchronized with the reverses of insulin and energy sensing signals. Moreover, the autonomic dysregulation and anesthesia-associated mortality were intervened. Together, these results suggested that the HFD-induced, anesthesia-associated mortality rate was related to the autonomic abnormality derived from the RVLM synaptic alteration, which is strongly related to insulin desensitization-associated autophagy. PIO intervened the HFD-induced mortality via reversal of the above-mentioned molecules.

Differential impacts of brain stem oxidative stress and nitrosative stress on sympathetic vasomotor tone

Based on work-done in the rostral ventrolateral medulla (RVLM), this review presents four lessons learnt from studying the differential impacts of oxidative stress and nitrosative stress on sympathetic vasomotor tone and their clinical and therapeutic implications. The first lesson is that an increase in sympathetic vasomotor tone because of augmented oxidative stress in the RVLM is responsible for the generation of neurogenic hypertension. On the other hand, a shift from oxidative stress to nitrosative stress in the RVLM underpins the succession of increase to decrease in sympathetic vasomotor tone during the progression towards brain stem death. The second lesson is that, by having different cellular sources, regulatory mechanisms on synthesis and degradation, kinetics of chemical reactions, and downstream signaling pathways, reactive oxygen species and reactive nitrogen species should not be regarded as a singular moiety. The third lesson is that well-defined differential roles of oxidative stress and nitrosative stress with distinct regulatory mechanisms in the RVLM during neurogenic hypertension and brain stem death clearly denote that they are not interchangeable phenomena with unified cellular actions. Special attention must be paid to their beneficial or detrimental roles under a specific disease or a particular time-window of that disease. The fourth lesson is that, to be successful, future antioxidant therapies against neurogenic hypertension must take into consideration the much more complicated picture than that presented in this review on the generation, maintenance, regulation or modulation of the sympathetic vasomotor tone. The identification that the progression towards brain stem death entails a shift from oxidative stress to nitrosative stress in the RVLM may open a new vista for therapeutic intervention to slow down this transition.

Spontaneously hypertensive rats exhibit higher sensitivity to ethanol-induced hypotensive effects: Role of NMDA receptors and nitric oxide in rostral ventrolateral medulla

Intake of ethanol (alcohol) affects cardiovascular function. Acute ethanol intake has been shown to lower blood pressure (BP) in hypertensive patients. The present study was undertaken to examine the effects and mechanisms of acute administration of ethanol on BP in hypertensive and normotensive rats. Ethanol was given by intraperitoneal (i.p.) injection in male spontaneously hypertensive rats (SHRs) and the normotensive Wistar-Kyoto rats (WKYs). BP responses were measured in free-moving conscious rats or in urethane-anesthetized rats. Inhibitors were applied by bilateral microinjection into the rostral ventrolateral medulla (RVLM). Nitric oxide (NO•) levels and glutamate levels were determined by nitrate and nitrite (NOx) analyzer and HPLC-ECD, respectively. Intraperitoneal (i.p.) injection of ethanol (1.6 g/kg) caused a significant decrease in BP in free-moving or in anesthetized SHRs but not in WKYs. A higher dose (3.2 g/kg) of ethanol decreased BP in both SHRs and WKYs, although the depressor responses in SHRs occurred significantly earlier than those in WKYs. The blood ethanol concentrations 60 min after injection were similar in SHRs and WKYs. Bilateral microinjection of nitric oxide synthase (NOS) inhibitors or glutamatergic NMDA receptor antagonists into the RVLM 5 min after administration of ethanol significantly inhibited the ethanol-induced depressor effects in SHRs. The levels of NOx and glutamate release in the RVLM following ethanol administration and the NOx content in the RVLM areas 30 min after administration were significantly increased in SHRs, but not in WKYs. Our results showed that SHRs were more sensitive to ethanol-induced hypotensive effects than WKYs because of augmentation of ethanol-induced expression of the glutamatergic NMDA receptor/NO• signal in the RVLM of SHRs.

Redox Signaling and Persistent Pulmonary Hypertension of the Newborn

Reactive oxygen species (ROS) are redox-signaling molecules that are critically involved in regulating endothelial cell functions, host defense, aging, and cellular adaptation. Mitochondria are the major sources of ROS and important sources of redox signaling in pulmonary circulation. It is becoming increasingly evident that increased mitochondrial oxidative stress and aberrant signaling through redox-sensitive pathways play a direct causative role in the pathogenesis of many cardiopulmonary disorders including persistent pulmonary hypertension of the newborn (PPHN). This chapter highlights redox signaling in endothelial cells, antioxidant defense mechanism, cell responses to oxidative stress, and their contributions to disease pathogenesis.

Age-dependent redox status in the brain stem of NO-deficient hypertensive rats

BACKGROUND

The brain stem contains important nuclei that control cardiovascular function via the sympathetic nervous system (SNS), which is strongly influenced by nitric oxide. Its biological activity is also largely determined by oxygen free radicals. Despite many experimental studies, the role of AT1R-NAD(P)H oxidase-superoxide pathway in NO-deficiency is not yet sufficiently clarified. We determined changes in free radical signaling and antioxidant and detoxification response in the brain stem of young and adult Wistar rats during chronic administration of exogenous NO inhibitors.

METHODS

Young (4 weeks) and adult (10 weeks) Wistar rats were treated with 7-nitroindazole (7-NI group, 10 mg/kg/day), a specific nNOS inhibitor, with N^G-nitro-L-arginine-methyl ester (L-NAME group, 50 mg/kg/day), a nonspecific NOS inhibitor, and with drinking water (Control group) during 6 weeks. Systolic blood pressure was measured by non-invasive plethysmography. Expression of genes (AT1R, AT2R, p22phox, SOD and NOS isoforms, HO-1, MDR1a, housekeeper GAPDH) was identified by real-time PCR. NOS activity was detected by conversion of [3H]-L-arginine to [3H]-L-citrulline and SOD activity was measured using UV VIS spectroscopy.

RESULTS

We observed a blood pressure elevation and decrease in NOS activity only after L-NAME application in both age groups. Gene expression of nNOS (youngs) and eNOS (adults) in the brain stem decreased after both inhibitors. The radical signaling pathway triggered by AT1R and p22phox was elevated in L-NAME adults, but not in young rats. Moreover, L-NAME-induced NOS inhibition increased antioxidant response, as indicated by the observed elevation of mRNA SOD3, HO-1, AT2R and MDR1a in adult rats. 7-NI did not have a significant effect on AT1R-NADPH oxidase-superoxide pathway, yet it affected antioxidant response of mRNA expression of SOD1 and stimulated total activity of SOD in young rats and mRNA expression of AT2R in adult rats.

CONCLUSION

Our results show that chronic NOS inhibition by two different NOS inhibitors has age-dependent effect on radical signaling and antioxidant/detoxificant response in Wistar rats. While 7-NI had neuroprotective effect in the brain stem of young Wistar rats, L-NAME- induced NOS inhibition evoked activation of AT1R-NAD(P)H oxidase pathway in adult Wistar rats. Triggering of the radical pathway was followed by activation of protective compensation mechanism at the gene expression level.

Neuroinflammation contributes to autophagy flux blockage in the neurons of rostral ventrolateral medulla in stress-induced hypertension rats

BACKGROUND

Neuroinflammation plays hypertensive roles in the uninjured autonomic nuclei of the central nervous system, while its mechanisms remain unclear. The present study is to investigate the effect of neuroinflammation on autophagy in the neurons of the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons for the maintenance of vasomotor tone reside.

METHODS

Stress-induced hypertension (SIH) was induced by electric foot-shock stressors with noise interventions in rats. Systolic blood pressure (SBP) and the power density of the low frequency (LF) component of the SAP spectrum were measured to reflect sympathetic vasomotor activity. Microglia activation and pro-inflammatory cytokines (PICs (IL-1β, TNF-α)) expression in the RVLM were measured by immunoblotting and immunostaining. Autophagy and autophagic vacuoles (AVs) were examined by autophagic marker (LC3 and p62) expression and transmission electron microscopy (TEM) image, respectively. Autophagy flux was evaluated by RFP-GFP-tandem fluorescent LC3 (tf-LC3) vectors transfected into the RVLM. Tissue levels of glutamate, gamma aminobutyric acid (GABA), and plasma levels of norepinephrine (NE) were measured by using high-performance liquid chromatography (HPLC) with electrochemical detection. The effects of the cisterna magna infused minocycline, a microglia activation inhibitor, on the abovementioned parameters were analyzed.

RESULTS

SIH rats showed increased SBP, plasma NE accompanied by an increase in LF component of the SBP spectrum. Microglia activation and PICs expression was increased in SIH rats. TEM demonstrated that stress led to the accumulation of AVs in the RVLM of SIH rats. In addition to the Tf-LC3 assay, the concurrent increased level of LC3-II and p62 suggested the impairment of autophagic flux in SIH rats. To the contrary, minocycline facilitated autophagic flux and induced a hypotensive effect with attenuated microglia activation and decreased PICs in the RVLM of SIH rats. Furthermore, SIH rats showed higher levels of glutamate and lower level of GABA in the RVLM, while minocycline attenuated the decrease in GABA and the increase in glutamate of SIH rats.

CONCLUSIONS

Collectively, we concluded that the neuroinflammation might impair autophagic flux and induced neural excitotoxicity in the RVLM neurons following SIH, which is involved in the development of SIH.

Effects of propolis, caffeic acid phenethyl ester, and pollen on renal injury in hypertensive rat: An experimental and theoretical approach

The objective of this study was to evaluate the antioxidant effects of propolis, caffeic acid phenethyl ester (CAPE; active compound in propolis), and pollen on biochemical oxidative stress biomarkers in rat kidney tissue inhibited by N^ω -nitro-L-arginine methyl ester (L-NAME). The biomarkers evaluated were paraoxonase (PON1), oxidative stress index (OSI), total antioxidant status (TAS), total oxidant status (TOS), asymmetric dimethylarginine (ADMA), and nuclear factor kappa B (NF-κB). TAS levels and PON1 activity were significantly decreased in kidney tissue samples in the L-NAME-treated group (P < 0.05). The levels of TAS and PONI were higher in the L-NAME plus propolis, CAPE, and pollen groups compared with the L-NAME-treated group. TOS, ADMA, and NF-κB levels were significantly increased in the kidney tissue samples of the L-NAME-treated group (P < 0.05). However, these parameters were significantly lower in the L-NAME plus propolis, CAPE, and pollen groups (P < 0.05) compared with rats administered L-NAME alone (P < 0.05). Furthermore, the binding energy of CAPE within catalytic domain of glutathione reductase (GR) enzyme as well as its inhibitory mechanism was determined using molecular modeling approaches. In conclusion, experimental and theoretical data suggested that oxidative alterations occurring in the kidney tissue of chronic hypertensive rats may be prevented via active compound of propolis, CAPE administration.

Selective Nrf2 Gene Deletion in the Rostral Ventrolateral Medulla Evokes Hypertension and Sympathoexcitation in Mice

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master transcriptional regulator of redox homeostasis that impacts antioxidant gene expression. Central oxidative stress and reduced antioxidant enzyme expression in the rostral ventrolateral medulla (RVLM) contributed to sympathoexcitation in chronic heart failure. In the current study, we hypothesized that deletion of Nrf2 in the RVLM would increase sympathetic drive and blood pressure. Experiments were performed in Nrf2-floxed mice treated with microinjection of lentiviral-Cre-GFP or lentiviral-GFP into the RVLM. Two weeks after viral administration, Nrf2 message, protein, oxidative stress, cardiovascular function, and sympathetic outflow were evaluated. We found that (1) Nrf2 mRNA and protein in the RVLM were significantly lower in Cre mice compared with control GFP mice. Nrf2-targeted antioxidant enzymes were downregulated, whereas reactive oxygen species were elevated. (2) Blood pressure measurements indicated that Cre mice displayed a significant increase in blood pressure (mean arterial pressure, 123.7±3.8 versus 100.2±2.2 mm Hg; P<0.05, n=6), elevated urinary norepinephrine (NE) concentration (456.4±16.9 versus 356.5±19.9 ng/mL; P<0.05, n=6), and decreased spontaneous baroreflex gain (up sequences, 1.66±0.17 versus 3.61±0.22 ms/mm Hg; P<0.05, n=6; down sequences, 1.89±0.12 versus 2.98±0.19 ms/mm Hg; P<0.05, n=6). (3) Cre mice displayed elevated baseline renal sympathetic nerve activity and impaired inducible baroreflex function. These data suggest that Nrf2 gene deletion in the RVLM elevates blood pressure, increases sympathetic outflow, and impairs baroreflex function potentially by impaired antioxidant enzyme expression.

Angiotensin II induces interleukin-6 expression in astrocytes: Role of reactive oxygen species and NF-κB

Previously, we showed that the bio-peptide angiotensin (Ang) II induces interleukin-6 (IL-6) in cultured astrocytes; however, the mechanism(s) involved in this effect were unknown. In the current study, we determined in brainstem and cerebellum astrocytes from the spontaneously hypertensive rat (SHR), the effect of Ang II to induce IL-6 as well as reactive oxygen species (ROS) generation. Results from this study showed that Ang II significantly induced the differential expression of IL-6 mRNA and protein levels in astrocytes from both regions of Wistar and SHRs. There were differences in the ability of Ang II to induce IL-6 mRNA and protein levels, but these differences were not apparent at all time points examined. Ang II also induced ROS generation, but there were no significant differences between ROS generation in SHR samples as compared to the Wistar samples. Ang II-induced IL-6 levels were mediated via the AT₁/Nuclear Factor Kappa beta/ROS pathway. Overall, our findings suggest that there may be dysregulation in IL-6 production from astrocytes, contributing to differences observed in SHRs versus its normotensive control. Elucidating the mechanisms involved in Ang II pro-inflammatory effects in the central nervous system may lead to the development of novel therapeutic strategies that can be harnessed not just to treat hypertension, but other Ang II-mediated diseases as well.

Effects of high fructose intake on the development of hypertension in the spontaneously hypertensive rats: the role of AT1R/gp91PHOX signaling in the rostral ventrolateral medulla

Both genetic and dietary factors determine the development of hypertension. Whether dietary factor impacts the development of hereditary hypertension is unknown. Here, we evaluated the effect of daily high-fructose diet (HFD) on the development of hypertension in adolescent spontaneously hypertensive rats (SHR). Six-week-old SHR were randomly divided into two groups to receive HFD or normal diet (ND) for 3 weeks. The temporal profile of systolic blood pressure, alongside the sympathetic vasomotor activity, in the SHR-HFD showed significantly greater increases at 9-12 weeks of age compared with the age-matched SHR-ND group. Immunofluorescence was used to identify the distribution of reactive oxygen species (ROS), oxidants and antioxidants in rostral ventrolateral medulla (RVLM) where sympathetic premotor neurons reside. In RVLM of SHR-HFD, the levels of ROS accumulation and lipid peroxidation were elevated. The changes in protein expression were measured by Western blot. NADPH oxidase subunit gp91^phox and angiotensin II type I receptor were up-regulated in RVLM neuron. On the other hand, the expression of extracellular superoxide dismutase was suppressed. Both molecular and hemodynamic changes in the SHR-HFD were rescued by oral pioglitazone treatment from weeks 7 to 9. Furthermore, central infusion with tempol, a ROS scavenger, effectively ameliorated ROS accumulation in RVLM and diminished the heightened pressor response and enhanced sympathetic activity in the SHR-HFD. Together, these results suggest that HFD intake at adolescent SHR may impact the development of hypertension via increasing oxidative stress in RVLM which could be effectively attenuated by pioglitazone treatment.

Effect of p22phox depletion on sympathetic regulation of blood pressure in SHRSP: evaluation in a new congenic strain

Oxidative stress in the rostral ventrolateral medulla (RVLM), a sympathetic center in the brainstem, was implicated in the regulation of sympathetic activity in various hypertensive models including stroke-prone spontaneously hypertensive rats (SHRSP). In this study, we evaluated the role of the NADPH oxidases (NOX) in the blood pressure (BP) regulation in RVLM in SHRSP. The P22PHOX-depleted congenic SHRSP (called SP.MES) was constructed by introducing the mutated p22phox gene of Matsumoto Eosinophilic Shinshu rat. BP response to glutamate (Glu) microinjection into RVLM was compared among SHRSP, SP.MES, SHR and Wistar Kyoto (WKY); the response to Glu microinjection was significantly greater in SHRSP than in SP.MES, SHR and WKY. In addition, tempol, losartan and apocynin microinjection reduced the response to Glu significantly only in SHRSP. The level of oxidative stress, measured in the brainstem using lucigenin and dihydroethidium, was reduced in SP.MES than in SHRSP. BP response to cold stress measured by telemetry system was also blunted in SP.MES when compared with SHRSP. The results suggested that oxidative stress due to the NOX activation in RVLM potentiated BP response to Glu in SHRSP, which might contribute to the exaggerated response to stress in this strain.

ROS production is increased in the kidney but not in the brain of Dahl rats with salt hypertension elicited in adulthood

Enhanced production of superoxide radicals by nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase in the brain and/or kidney of salt hypertensive Dahl rats has been proposed to participate in the pathogenesis of this form of experimental hypertension. Most information was obtained in young Dahl salt-sensitive (DS) rats subjected to high salt intake prior to sexual maturation. Therefore, the aim of our study was to investigate whether salt hypertension induced in adult DS rats is also accompanied with a more pronounced oxidative stress in the brain or kidney as compared to Dahl salt-resistant (DR) controls. NADPH oxidase activity as well as the content of thiobarbituric acid-reactive substances (TBARS) and conjugated dienes (oxidative index), which indicate a degree of lipid peroxidation, were evaluated in two brain regions (containing either hypothalamic paraventricular nucleus or rostral ventrolateral medulla) as well as in renal medulla and cortex. High salt intake induced hypertension in DS rats but did not modify blood pressure in DR rats. DS and DR rats did not differ in NADPH oxidase-dependent production of ROS, TBARS content or oxidative index in either part of the brain. In addition, high-salt diet did not change significantly any of these brain parameters. In contrast, the enhanced NADPH oxidase-mediated ROS production (without significant signs of increased lipid peroxidation) was detected in the renal medulla of salt hypertensive DS rats. Our findings suggest that there are no signs of enhanced oxidative stress in the brain of adult Dahl rats with salt hypertension induced in adulthood.

Brain Angiotensin II Type 1 Receptor Blockade Improves Dairy Blood Pressure Variability via Sympathoinhibition in Hypertensive Rats

Abnormal blood pressure (BP) elevation in early morning is known to cause cardiovascular events. Previous studies have suggested that one of the reasons in abnormal dairy BP variability is sympathoexcitation. We have demonstrated that brain angiotensin II type 1 receptor (AT1R) causes sympathoexcitation. The aim of the present study was to investigate whether central AT1R blockade attenuates the excess BP elevation in rest-to-active phase in hypertensive rats or not. Stroke-prone spontaneously hypertensive rats (SHRSP) were treated with intracerebroventricular infusion (ICV) of AT1R receptor blocker (ARB), oral administration of hydralazine (HYD), or ICV of vehicle (VEH). Telemetric averaged mean BP (MBP) was measured at early morning (EM), after morning (AM), and night (NT). At EM, MBP was significantly lower in ARB to a greater extent than in HYD compared to VEH, though MBP at AM was the same in ARB and HYD. At NT, MBP was also significantly lower in ARB than in HYD. These results in MBP were compatible to those in sympathoexcitation and suggest that central AT1R blockade attenuates excess BP elevation in early active phase and continuous BP elevation during rest phase independent of depressor response in hypertensive rats.

Muscle mechanoreflex overactivity in hypertension: a role for centrally-derived nitric oxide

The cardiovascular response to exercise is abnormally large in hypertension. Over the past decade, it has become clear that the exercise pressor reflex (a peripheral feed-back mechanism originating in skeletal muscle) contributes significantly to the generation of this hyper-responsiveness. Further, it has been determined that overactivity of the mechanically (muscle mechanoreflex) and chemically (muscle metaboreflex) sensitive components of the exercise pressor reflex underpin its dysfunction. Given the recent attention in the literature, this review focuses upon the aberrant function of the muscle mechanoreflex in this disease. Evidence supporting a role for the mechanoreflex in the pathogenesis of the exaggerated cardiovascular response to physical activity is highlighted. The peripheral and central mechanisms that may be responsible for mechanoreflex overactivity in hypertension are likewise discussed. Particular attention is given to emerging evidence implicating a role for centrally-derived nitric oxide in this process.

Cardiac peroxisome proliferator-activated receptor-γ expression is modulated by oxidative stress in acutely infrasound-exposed cardiomyocytes

The aim of the present study was to examine the effects of acute infrasound exposure on oxidative damage and investigate the underlying mechanisms in rat cardiomyocytes. Neonatal rat cardiomyocytes were cultured and exposed to infrasound for several days. In the study, the expression of CAT, GPx, SOD1, and SOD2 and their activities in rat cardiomyocytes in infrasound exposure groups were significantly decreased compared to those in the various time controls, along with significantly higher levels of O₂⁻ and H₂O₂. Decreased cardiac cell viability was not observed in various time controls. A significant reduction in cardiac cell viability was observed in the infrasound group compared to the control, while significantly increased cardiac cell viability was observed in the infrasound exposure and rosiglitazone pretreatment group. Compared to the control, rosiglitazone significantly upregulated CAT, GPx, SOD1, and SOD2 expression and their activities in rat cardiomyocytes exposed to infrasound, while the levels of O₂⁻ or H₂O₂ were significantly decreased. A potential link between a significant downregulation of PPAR-γ expression in rat cardiomyocytes in the infrasound group was compared to the control and infrasound-induced oxidative stress. These findings indicate that infrasound can induce oxidative damage in rat cardiomyocytes by inactivating PPAR-γ.

An increase in adenosine-5'-triphosphate (ATP) content in rostral ventrolateral medulla is engaged in the high fructose diet-induced hypertension

Background

The increase in fructose ingestion has been linked to overdrive of sympathetic activity and hypertension associated with the metabolic syndrome. The premotor neurons for generation of sympathetic vasomotor activity reside in the rostral ventrolateral medulla (RVLM). Activation of RVLM results in sympathoexcitation and hypertension. Neurons in the central nervous system are able to utilize fructose as a carbon source of ATP production. We examined in this study whether fructose affects ATP content in RVLM and its significance in the increase in central sympathetic outflow and hypertension induced by the high fructose diet (HFD).

Results

In normotensive rats fed with high fructose diet (HFD) for 12 weeks, there was a significant increase in tissue ATP content in RVLM, accompanied by the increases in the sympathetic vasomotor activity and blood pressure. These changes were blunted by intracisternal infusion of an ATP synthase inhibitor, oligomycin, to the HFD-fed animals. In the catecholaminergic-containing N2a cells, fructose dose-dependently upregulated the expressions of glucose transporter 2 and 5 (GluT2, 5) and the rate-limiting enzyme of fructolysis, ketohexokinase (KHK), leading to the increases in pyruvate and ATP production, as well as the release of the neurotransmitter, dopamine. These cellular events were significantly prevented after the gene knocking down by lentiviral transfection of small hairpin RNA against KHK.

Conclusion

These results suggest that increases in ATP content in RVLM may be engaged in the augmented sympathetic vasomotor activity and hypertension associated with the metabolic syndrome induced by the HFD. At cellular level, the increase in pyruvate levels via fructolysis is involved in the fructose-induced ATP production and the release of neurotransmitter.

Brain stem NOS and ROS in neural mechanisms of hypertension

SIGNIFICANCE

There is now compelling evidence to substantiate the notion that by depressing baroreflex regulation of blood pressure and augmenting central sympathetic outflow through their actions on the nucleus tractus solitarii (NTS) and rostral ventrolateral medulla (RVLM), brain stem nitric oxide synthase (NOS) and reactive oxygen species (ROS) are important contributing factors to neural mechanisms of hypertension. This review summarizes our contemporary views on the impact of NOS and ROS in the NTS and RVLM on neurogenic hypertension, and presents potential antihypertensive strategies that target brain stem NOS/ROS signaling.

RECENT ADVANCES

NO signaling in the brain stem may be pro- or antihypertensive depending on the NOS isoform that generates this gaseous moiety and the site of action. Elevation of the ROS level when its production overbalances its degradation in the NTS and RVLM underlies neurogenic hypertension. Interventional strategies with emphases on alleviating the adverse actions of these molecules on blood pressure regulation have been investigated.

CRITICAL ISSUES

The pathological roles of NOS in the RVLM and NTS in neural mechanisms of hypertension are highly complex. Likewise, multiple signaling pathways underlie the deleterious roles of brain-stem ROS in neurogenic hypertension. There are recent indications that interactions between brain stem ROS and NOS may play a contributory role.

FUTURE DIRECTIONS

Given the complicity of action mechanisms of brain-stem NOS and ROS in neural mechanisms of hypertension, additional studies are needed to identify the most crucial therapeutic target that is applicable not only in animal models but also in patients suffering from neurogenic hypertension.

Statins and the autonomic nervous system

Statins (3-hydroxy-3-methylglutaryl-CoA reductase inhibitors) reduce plasma cholesterol and improve endothelium-dependent vasodilation, inflammation and oxidative stress. A ‘pleiotropic’ property of statins receiving less attention is their effect on the autonomic nervous system. Increased central sympathetic outflow and diminished cardiac vagal tone are disturbances characteristic of a range of cardiovascular conditions for which statins are now prescribed routinely to reduce cardiovascular events: following myocardial infarction, and in hypertension, chronic kidney disease, heart failure and diabetes. The purpose of the present review is to synthesize contemporary evidence that statins can improve autonomic circulatory regulation. In experimental preparations, high-dose lipophilic statins have been shown to reduce adrenergic outflow by attenuating oxidative stress in central brain regions involved in sympathetic and parasympathetic discharge induction and modulation. In patients with hypertension, chronic kidney disease and heart failure, lipophilic statins, such as simvastatin or atorvastatin, have been shown to reduce MNSA (muscle sympathetic nerve activity) by 12–30%. Reports concerning the effect of statin therapy on HRV (heart rate variability) are less consistent. Because of their implications for BP (blood pressure) control, insulin sensitivity, arrhythmogenesis and sudden cardiac death, these autonomic nervous system actions should be considered additional mechanisms by which statins lower cardiovascular risk.

Angiotensin-generated reactive oxygen species in brain and pathogenesis of cardiovascular diseases

SIGNIFICANCE

Overproduction of angiotensin II (Ang II) in brain contributes to the pathogenesis of cardiovascular diseases. One of the most promising theses that emerged during the last decade is that production of reactive oxygen species (ROS) and activation of redox-dependent signaling cascades underlie those Ang II actions. This review summarizes our status of understanding on the roles of ROS and redox-sensitive signaling in brain Ang II-dependent cardiovascular diseases, using hypertension and heart failure as illustrative examples.

RECENT ADVANCES

ROS generated by NADPH oxidase, mitochondrial electron transport chain, and proinflammatory cytokines activates mitogen-activated protein kinases and transcription factors, which in turn modulate ion channel functions and ultimately increase neuronal activity and sympathetic outflow in brain Ang II-dependent cardiovascular diseases. Antioxidants targeting ROS have been demonstrated to be beneficial to Ang II-induced hypertension and heart failure via protection from oxidative stress in brain regions that subserve cardiovascular regulation.

CRITICAL ISSUES

Intra-neuronal signaling and the downstream redox-sensitive proteins involved in controlling the neuronal discharge rate, the sympathetic outflow, and the pathogenesis of cardiovascular diseases need to be identified. The cross talk between Ang II-induced oxidative stress and neuroinflammation in neural mechanisms of cardiovascular diseases also warrants further elucidation.

FUTURE DIRECTIONS

Future studies are needed to identify new redox-based therapeutics that work not only in animal models, but also in patients suffering from the prevalent diseases. Upregulation of endogenous antioxidants in the regulation of ROS homeostasis is a potential therapeutic target, as are small molecule- or nanoformulated conjugate-based antioxidant therapy.

Pro-opiomelanocortin gene delivery suppresses the growth of established Lewis lung carcinoma through a melanocortin-1 receptor-independent pathway

BACKGROUND

Pro-opiomelanocortin (POMC) is the precursor of several neuropeptides, such as corticotropin, melanocyte-stimulating hormone and the endogenous opioid (β-endorphin). Our previous studies have indicated that POMC gene delivery inhibited the progression and metastasis of B16-F10 melanoma via the α- melanocyte-stimulating hormone/melanortin-1 receptor (MC-1R) pathway.

METHODS

In the present study, the therapeutic efficacy of POMC gene therapy was evaluated in mice bearing established Lewis lung carcinoma (LLC) models both in vitro and in vivo. We also investigated the MC-1R-independent mechanism underlying POMC gene therapy.

RESULTS

We found that POMC gene delivery significantly inhibited the growth and colony formation in MC-1R-deficient LLC cells. In addition, POMC gene transfer effectively suppressed the growth of established LLC in mice. The inhibitory mechanisms underlying POMC gene delivery were attibuted to be inhibition of proliferation and the induction of apoptosis. Moreover, POMC gene delivery attenuated tumor β-catenin signaling by reducing protein levels of β-catenin and its downstream proto-oncogenes, including cyclin D1 and c-myc. Lastly, POMC gene delivery induced a significant suppression of tumor vasculature.

CONCLUSIONS

These results support the existence of an MC-1R-independent pathway for POMC gene therapy, which further expands the therapeutic spectrum of POMC therapy for multiple types of cancer.

Decreases in manganese superoxide dismutase expression and activity contribute to oxidative stress in persistent pulmonary hypertension of the newborn

A rapid increase in the synthesis and release of nitric oxide (NO) facilitates the pulmonary vasodilation that occurs during birth-related transition. Alteration of this transition in persistent pulmonary hypertension of the newborn (PPHN) is associated with impaired function of endothelial nitric oxide synthase (eNOS) and an increase in oxidative stress. We investigated the hypothesis that a decrease in expression and activity of mitochondrial localized manganese superoxide dismutase (MnSOD) in pulmonary artery endothelial cells (PAEC) increases oxidative stress and impairs eNOS function in PPHN. We isolated PAEC and pulmonary arteries from fetal lambs with PPHN induced by prenatal ductus arteriosus ligation or sham ligation (control). We investigated MnSOD expression and activity, tyrosine nitration of MnSOD, and mitochondrial O(2)(-) levels in PAEC from control and PPHN lambs. We introduced exogenous MnSOD via an adenoviral vector (ad-MnSOD) transduction into PAEC and pulmonary arteries of PPHN lambs. The effect of ad-MnSOD was investigated on: mitochondrial O(2)(-) levels, MnSOD and eNOS expression and activity, intracellular hydrogen peroxide (H(2)O(2)) levels, and catalase expression in PAEC. MnSOD mRNA and protein levels and activity were decreased and MnSOD tyrosine nitration was increased in PPHN-PAEC. ad-MnSOD transduction of PPHN-PAEC increased its activity two- to threefold, decreased mitochondrial O(2)(-) levels, and increased H(2)O(2) levels and catalase expression. ad-MnSOD transduction improved eNOS expression and function and the relaxation response of PPHN pulmonary arteries. Our observations suggest that decreased MnSOD expression and activity contribute to the endothelial dysfunction observed in PPHN.

Oxidative stress in the brain causes hypertension via sympathoexcitation

Activation of the sympathetic nervous system (SNS) has an important role in the pathogenesis of hypertension, and is determined by the brain. Previous many studies have demonstrated that oxidative stress, mainly produced by angiotensin II type 1 (AT(1)) receptor and nicotinamide adenine dinucleotide phosphate (NAD (P) H) oxidase, in the autonomic brain regions was involved in the activation of the SNS of hypertension. In this concept, we have investigated the role of oxidative stress in the rostral ventrolateral medulla (RVLM), which is known as the cardiovascular center in the brainstem, in the activation of the SNS, and demonstrated that AT(1) receptor and NAD (P) H oxidase-induced oxidative stress in the RVLM causes sympathoexcitation in hypertensive rats. The mechanisms in which brain oxidative stress causes sympathoexcitation have been investigated, such as the interactions with nitric oxide (NO), effects on the signal transduction, or inflammations. Interestingly, the environmental factors of high salt intake and high calorie diet may also increase the oxidative stress in the brain, particularly in the RVLM, thereby activating the central sympathetic outflow and increasing the risk of hypertension. Furthermore, several orally administered AT(1) receptor blockers have been found to cause sympathoinhibition via reduction of oxidative stress through the inhibition of central AT(1) receptor. In conclusion, we must consider that AT(1) receptor and the related oxidative stress production in the brain cause the activation of SNS in hypertension, and that AT(1) receptor in the brain could be novel therapeutic target of the treatments for hypertension.

Nontranscriptional activation of PI3K/Akt signaling mediates hypotensive effect following activation of estrogen receptor β in the rostral ventrolateral medulla of rats

Background

Estrogen acts on the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons are located, to elicit vasodepressor effects via an estrogen receptor (ER)β-dependent mechanism. We investigated in the present study nontranscriptional mechanism on cardiovascular effects following activation of ERβ in the RVLM, and delineated the involvement of phosphatidylinositol 3-kinase (PI3K)/serine/threonine kinase (Akt) signaling pathway in the effects.

Methods

In male Sprague–Dawley rats maintained under propofol anesthesia, changes in arterial pressure, heart rate and sympathetic neurogenic vasomotor tone were examined after microinjection bilaterally into RVLM of 17β-estradiol (E2β) or a selective ERα or ERβ agonist. Involvement of ER subtypes and PI3K/Akt signaling pathway in the induced cardiovascular effects were studied using pharmacological tools of antagonists or inhibitors, gene manipulation with antisense oligonucleotide (ASON) or adenovirus-mediated gene transfection.

Results

Similar to E2β (1 pmol), microinjection of ERβ agonist, diarylpropionitrile (DPN, 1, 2 or 5 pmol), into bilateral RVLM evoked dose-dependent hypotension and reduction in sympathetic neurogenic vasomotor tone. These vasodepressive effects of DPN (2 pmol) were inhibited by ERβ antagonist, R,R-tetrahydrochrysene (50 pmol), ASON against ERβ mRNA (250 pmol), PI3K inhibitor LY294002 (5 pmol), or Akt inhibitor (250 pmol), but not by ERα inhibitor, methyl-piperidino-pyrazole (1 nmol), or transcription inhibitor, actinomycin D (5 or 10 nmol). Gene transfer by microinjection into bilateral RVLM of adenovirus encoding phosphatase and tensin homologues deleted on chromosome 10 (5 × 10⁸ pfu) reversed the vasodepressive effects of DPN.

Conclusions

Our results indicate that vasodepressive effects following activation of ERβ in RVLM are mediated by nongenomic activation of PI3K/Akt signaling pathway. This study provides new insight in the intracellular signaling cascades involved in central vasodepressive functions of estrogen.

Brain stem oxidative stress and its associated signaling in the regulation of sympathetic vasomotor tone

There is now compelling evidence from studies in humans and animals that overexcitation of the sympathetic nervous system plays an important role in the pathogenesis of cardiovascular diseases. An excellent example is neurogenic hypertension, in which central sympathetic overactivation is involved in the development, staging, and progression of the disease, and one of the underlying mechanisms involves oxidative stress in key brain stem sites that are engaged in the regulation of sympathetic vasomotor tone. Using the rostral ventrolateral medulla (RVLM) and nucleus tractus solitarii (NTS) as two illustrative brain stem neural substrates, this article provides an overview of the impact of reactive oxygen species and antioxidants on RVLM and NTS in the pathogenesis of neurogenic hypertension. This is followed by a discussion of the redox-sensitive signaling pathways, including several kinases, ion channels, and transcription factors that underpin the augmentation in sympathetic vasomotor tone. In addition, the emerging view that brain stem oxidative stress is also causally related to a reduction in sympathetic vasomotor tone and hypotension during brain stem death, methamphetamine intoxication, and temporal lobe status epilepticus will be presented, along with the causal contribution of the oxidant peroxynitrite formed by a reaction between nitric oxide synthase II (NOS II)-derived nitric oxide and superoxide. Also discussed as a reasonable future research direction is dissection of the cellular mechanisms and signaling cascades that may underlie the contributory role of nitric oxide generated by different NOS isoforms in the differential effects of oxidative stress in the RVLM or NTS on sympathetic vasomotor tone.

Sympathetic regulation of vascular function in health and disease

The sympathetic nervous system (SNS) is known to play a pivotal role in short- and long-term regulation of different functions of the cardiovascular system. In the past decades increasing evidence demonstrated that sympathetic neural control is involved not only in the vasomotor control of small resistance arteries but also in modulation of large artery function. Sympathetic activity and vascular function, both of which are key factors in the development and prognosis of cardiovascular events and disease, are linked at several levels. Evidence from experimental studies indicates that the SNS is critically influenced, at the central and also at the peripheral level, by the most relevant factors regulating vascular function, such as nitric oxide (NO), reactive oxygen species (ROS), endothelin (ET), the renin-angiotensin system. Additionally, there is indirect evidence of a reciprocal relationship between endothelial function and activity of the SNS. A number of cardiovascular risk factors and diseases are characterized both by increased sympathetic outflow and decreased endothelial function. In healthy subjects, muscle sympathetic nerve activity (MSNA) appears to be related to surrogate markers of endothelial function, and an acute increase in sympathetic activity has been associated with a decrease in endothelial function in healthy subjects. However, direct evidence of a cause-effect relationship from human studies is scanty. In humans large artery stiffness has been associated with increased sympathetic discharge, both in healthy subjects and in renal transplant recipients. Peripheral sympathetic discharge is also able to modulate wave reflection. On the other hand, large artery stiffness can interfere with autonomic regulation by impairing carotid baroreflex sensitivity.

Endothelin-1 in paraventricular nucleus modulates cardiac sympathetic afferent reflex and sympathetic activity in rats

Background

Cardiac sympathetic afferent reflex (CSAR) is a positive-feedback, sympathoexcitatory reflex. Paraventricular nucleus (PVN) is an important component of the central neurocircuitry of the CSAR. The present study is designed to determine whether endothelin-1 (ET-1) in the PVN modulates the CSAR and sympathetic activity, and whether superoxide anions are involved in modulating the effects of ET-1 in the PVN in rats.

Methodology/Principal Findings

In anaesthetized Sprague–Dawley rats with cervical vagotomy and sinoaortic denervation, renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded. The CSAR was evaluated by the responses of the RSNA and MAP to epicardial application of capsaicin. Microinjection of ET-1 into the bilateral PVN dose-dependently enhanced the CSAR, increased the baseline RSNA and MAP. The effects of ET-1 were blocked by PVN pretreatment with the ET_A receptor antagonist BQ-123. However, BQ-123 alone had no significant effects on the CSAR, the baseline RSNA and MAP. Bilateral PVN pretreatment with either superoxide anion scavenger tempol or polyethylene glycol-superoxide dismutase (PEG-SOD) inhibited the effects of ET-1 on the CSAR, RSNA and MAP. Microinjection of ET-1 into the PVN increased the superoxide anion level in the PVN, which was abolished by PVN pretreatment with BQ-123. Epicardial application of capsaicin increased superoxide anion level in PVN which was further enhanced by PVN pretreatment with ET-1.

Conclusions

Exogenous activation of ET_A receptors with ET-1 in the PVN enhances the CSAR, increases RSNA and MAP. Superoxide anions in PVN are involved in the effects of ET-1 in the PVN.

The effects of catalase inhibition into the fourth cerebral ventricle on the Bezold-Jarisch reflex in spontaneously hypertensive rats

Many studies have investigated the role of oxidative stress on cardiovascular system in the brainstem of spontaneously hypertensive rats (SHR). However, we do not know yet if catalase inhibition influences cardiopulmonary reflex (Bezol-Jarisch reflex). Thus, we aimed to evaluate the effects of central catalase inhibition on cardiopulmonary reflex in SHR. Males Wistar Kyoto (WKY) rats and SHR were implanted with a stainless steel guide cannula into the fourth cerebral ventricle (4th V). The femoral artery and vein were cannulated for mean arterial pressure (MAP) and heart rate (HR) measurement and drug infusion, respectively. The cardiopulmonary reflex was tested with phenylbiguanide (PBG, 8 μg/kg, bolus, i.v.). Cardiopulmonary reflex was evaluated before and 15 minutes after 3-amino-1,2,4-triazole (ATZ, 0.01 g/100 μL) injection into the 4th V. Vehicle treatment did not change basal MAP and HR and cardiopulmonary reflex responses in SHR and WKY rats. Central ATZ increased hypotensive (p=0.038) responses without influencing the bradycardic reflex (p=0.287) in WKY rats. In SHR, ATZ increased hypotension (p=0.0004) and bradycardic (p=0.04) responses to i.v. PBG. No changes were observed regarding basal MAP and HR after ATZ injection in SHR and WKY rats. We suggest central catalase inhibition affects cardiopulmonary reflex with more intensity in SHR compared to WKY rats.

Oxidative stress in the rostral ventrolateral medulla modulates excitatory and inhibitory inputs in spontaneously hypertensive rats

OBJECTIVES

The rostral ventrolateral medulla (RVLM) of the brainstem and the paraventricular nucleus (PVN) of the hypothalamus play crucial roles in central cardiovascular regulation. In hypertensive rats, an imbalance of excitatory and inhibitory inputs to the RVLM enhances central sympathetic outflow. Increased reactive oxygen species (ROS) in the RVLM also contribute to sympathoexcitation, leading to hypertension. The aim of the present study was to elucidate whether ROS in the RVLM modulate synaptic transmission via excitatory and inhibitory amino acids and influence the excitatory inputs to the RVLM from the PVN in spontaneously hypertensive rats (SHRs).

METHODS AND RESULTS

We transfected adenovirus vectors encoding the manganese superoxide dismutase (AdMnSOD) gene to scavenge ROS in the RVLM both in Wistar-Kyoto rats and SHRs. The decreases in blood pressure and renal sympathetic nerve activity (RSNA) evoked by injecting kynurenic acid, a glutamate receptor blocker, into the RVLM were attenuated, and the increases in blood pressure and RSNA evoked by injecting bicuculline, a γ-amino butyric acid (GABA) receptor blocker, into the RVLM were enhanced in AdMnSOD-transfected SHRs compared with adenovirus vectors encoding the β-galactosidase (AdLacZ) gene-transfected SHRs. Furthermore, the increases in blood pressure and RSNA evoked by injecting bicuculline into the PVN were attenuated in AdMnSOD-transfected SHRs compared with AdLacZ-transfected SHRs.

CONCLUSION

These findings suggest that ROS in the RVLM enhance glutamatergic excitatory inputs and attenuate GABAergic inhibitory inputs to the RVLM, thereby increasing sympathoexcitatory input to the RVLM from the PVN in SHRs.

Catalase inhibition into the fourth cerebral ventricle affects bradycardic parasympathetic response to increase in arterial pressure without changing the baroreflex

Exogenous catalase influences neural control of cardiovascular system; however, we do not know yet if its inhibition into the fourth cerebral ventricle (4(th) V) influences baroreflex regulation. We evaluated the effects of central catalase inhibition on baroreflex in conscious Wistar rats. We used males Wistar rats (320-370 g), which were implanted with a stainless steel guide cannula into 4(th) V. The femoral artery and vein were cannulated for mean arterial pressure (MAP) and heart rate (HR) measurement and drug infusion, respectively. After basal MAP and HR recordings, the baroreflex was tested with a pressor dose of phenylephrine (PHE, 8 μg/kg, bolus) and a depressor dose of sodium nitroprusside (SNP, 50 μg/kg, bolus). Baroreflex was evaluated before 5, 15, 30 and 60 minutes after 3-amino-1, 2, 4-triazole (ATZ, 0.001 g/100 μL) injection into the 4(th) V. Vehicle treatment did not change baroreflex responses. ATZ attenuated bradycardic peak and reduced HR range at 30 minutes. ATZ into the 4(th) V reduced bradycardic and tachycardic reflex responses to increase and decrease MAP, respectively (p<0.05) 30 minutes after its microinjection without significantly changing the basal MAP and HR. In conclusion, central catalase inhibition influenced the highest parasympathetic response to MAP increase in conscious Wistar rats without change baroreflex gain.

The sympathetic nervous system and blood pressure in humans: implications for hypertension

A neurogenic component to primary hypertension (hypertension) is now well established. Along with raised vasomotor tone and increased cardiac output, the chronic activation of the sympathetic nervous system in hypertension has a diverse range of pathophysiological consequences independent of any increase in blood pressure. This review provides a perspective on the actions and interactions of angiotensin II, inflammation and vascular dysfunction/brain hypoperfusion in the pathogenesis and progression of neurogenic hypertension. The optimisation of current treatment strategies and the exciting recent developments in the therapeutic targeting of the sympathetic nervous system to control hypertension (for example, catheter-based renal denervation and carotid baroreceptor stimulation) will be outlined.

Oxidative stress in the cardiovascular center has a pivotal role in the sympathetic activation in hypertension

Activation of the sympathetic nervous system has an important role in the pathogenesis of hypertension. However, the precise mechanisms involved are not fully understood. Oxidative stress may be important in hypertension as well as in other cardiovascular disorders. We investigated the role of oxidative stress, particularly in the rostral ventrolateral medulla (RVLM), which is known as the cardiovascular center in the brainstem, in the activation of the sympathetic nervous system in hypertension. We observed that the reactive oxygen species (ROS) production increases in the RVLM in hypertensive rats, thereby enhancing the central sympathetic outflow, which leads to hypertension. Furthermore, the environmental factors of high salt intake and a high-calorie diet may also increase the ROS production in the RVLM, thereby activating the central sympathetic outflow and increasing the risk of hypertension. The activation of the nicotinamide adenine dinucleotide phosphate oxidase via the angiotensin type 1 (AT1) receptors is suggested to be the major source of ROS production, and an altered downstream signaling pathway is involved in the activation of the RVLM neurons, leading to enhanced central sympathetic outflow and hypertension. Thus, the brain AT1 receptors may be novel therapeutic targets, and, in fact, oral treatment with angiotensin receptor blockers has been found to inhibit the central AT1 receptors, despite the blood-brain barrier.

Plasma reactive carbonyl species: Potential risk factor for hypertension

To study the role of oxidative stress in hypertension and pre-hypertension, this study analysed plasma levels of reactive carbonyl species (RCS) in 1204 Chinese Han adults. Results showed a statistically significant positive correlation (p < 0.001) between blood pressure and plasma RCS levels with or without being adjusted for covariates. Multivariate-adjusted odds ratio (OR) illustrated that, compared with the lowest quartile of plasma RCS levels, the highest quartile subjects had a 59% and a 130% increase in the risk for developing pre-hypertension and hypertension, respectively. The multi-interaction analysis manifested that the underlying mechanism of the increase of hypertensive risk or pre-hypertensive risk by overweight and unhealthy lifestyles might, at least in part, be through oxidative stress. In conclusion, these findings suggest that oxidative stress, as indicated by plasma RCS levels, are not the necessary consequence of pre-hypertension or hypertension, but reliable risk factors for developing pre-hypertension or hypertension in Chinese Han adults.