Scavenging superoxide selectively in mouse forebrain is associated with improved cardiac function and survival following myocardial infarction

Extracellular Vesicles Regulate Sympatho-Excitation by Nrf2 in Heart Failure

BACKGROUND

Chronic heart failure (CHF) is associated with redox imbalance. Downregulation of Nrf2 (nuclear factor [erythroid-derived 2]-like 2) plays important roles in disrupting myocardial redox homeostasis and mediating sympathetic nerve activity in the setting of CHF. However, it is unclear if circulating extracellular vesicles (EVs) elicit sympathetic excitation in CHF by disrupting central redox homeostasis. We tested the hypothesis that cardiac-derived EVs circulate to the presympathetic rostral ventrolateral medulla and contribute to oxidative stress and sympathetic excitation via EV-enriched microRNA-mediated Nrf2 downregulation.

METHODS

Data were collected on rats with CHF post-myocardial infarction (MI) and on human subjects with ischemic CHF. EVs were isolated from tissue and plasma, and we determined the miRNAs cargo that related to targeting Nrf2 translation. We tracked the distribution of cardiac-derived EVs using in vitro labeled circulating EVs and cardiac-specific membrane GFP+ transgenic mice. Finally, we tested the impact of exogenously loading of antagomirs to specific Nrf2-related miRNAs on CHF-EV-induced pathophysiological phenotypes in normal rats (eg, sympathetic and cardiac function).

RESULTS

Nrf2 downregulation in CHF rats was associated with an upregulation of Nrf2-targeting miRNAs, which were abundant in cardiac-derived and circulating EVs from rats and humans. EVs isolated from the brain of CHF rats were also enriched with Nrf2-targeting miRNAs and cardiac-specific miRNAs. Cardiac-derived EVs were taken up by neurons in the rostral ventrolateral medulla. The administration of cardiac-derived and circulating EVs from CHF rats into the rostral ventrolateral medulla of normal rats evoked an increase in renal sympathetic nerve activity and plasma norepinephrine compared with Sham-operated rats, which were attenuated by exogenously preloading CHF-EVs with antagomirs to Nrf2-targeting miRNAs.

CONCLUSIONS

Cardiac microRNA-enriched EVs from animals with CHF can mediate crosstalk between the heart and the brain in the regulation of sympathetic outflow by targeting the Nrf2/antioxidant signaling pathway. This new endocrine signaling pathway regulating sympathetic outflow in CHF may be exploited for novel therapeutics.

Resolving inflammatory links between myocardial infarction and vascular dementia

Myocardial infarction is associated with increased risk for vascular dementia. In both myocardial infarction and vascular dementia, there is evidence that elevated inflammatory biomarkers are associated with worsened clinical outcomes. Myocardial infarction leads to a systemic inflammatory response, which may contribute to recruitment or activation of myeloid cells, including monocytes, microglia, and perivascular macrophages, within the central nervous system. However, our understanding of the causative roles for these cells linking cardiac injury to the development and progression of dementia is incomplete. Herein, we provide an overview of inflammatory cellular and molecular links between myocardial infarction and vascular dementia and discuss strategies to resolve inflammation after myocardial infarction to limit neurovascular injury.

Oral ascorbic acid 2-glucoside prevents coordination disorder induced via laser-induced shock waves in rat brain

Oxidative stress is considered to be involved in the pathogenesis of primary blast-related traumatic brain injury (bTBI). We evaluated the effects of ascorbic acid 2-glucoside (AA2G), a well-known antioxidant, to control oxidative stress in rat brain exposed to laser-induced shock waves (LISWs). The design consisted of a controlled animal study using male 10-week-old Sprague-Dawley rats. The study was conducted at the University research laboratory. Low-impulse (54 Pa•s) LISWs were transcranially applied to rat brain. Rats were randomized to control group (anesthesia and head shaving, n = 10), LISW group (anesthesia, head shaving and LISW application, n = 10) or LISW + post AA2G group (AA2G administration after LISW application, n = 10) in the first study. In another study, rats were randomized to control group (n = 10), LISW group (n = 10) or LISW + pre and post AA2G group (AA2G administration before and after LISW application, n = 10). The measured outcomes were as follows: (i) motor function assessed by accelerating rotarod test; (ii) levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), an oxidative stress marker; (iii) ascorbic acid in each group of rats. Ascorbic acid levels were significantly decreased and 8-OHdG levels were significantly increased in the cerebellum of the LISW group. Motor coordination disorder was also observed in the group. Prophylactic AA2G administration significantly increased the ascorbic acid levels, reduced oxidative stress and mitigated the motor dysfunction. In contrast, the effects of therapeutic AA2G administration alone were limited. The results suggest that the prophylactic administration of ascorbic acid can reduce shock wave-related oxidative stress and prevented motor dysfunction in rats.

Molecular Hydrogen Prevents Social Deficits and Depression-Like Behaviors Induced by Low-Intensity Blast in Mice

Detonation of explosive devices creates blast waves, which can injure brains even in the absence of external injuries. Among these, blast-induced mild traumatic brain injury (bmTBI) is increasing in military populations, such as in the wars in Afghanistan, Iraq, and Syria. Although the clinical presentation of bmTBI is not precisely defined, it is frequently associated with psycho-neurological deficits and usually manifests in the form of poly-trauma including psychiatric morbidity and cognitive disruption. Although the underlying mechanisms of bmTBI are largely unknown, some studies suggested that bmTBI is associated with blood-brain barrier disruption, oxidative stress, and edema in the brain. The present study investigated the effects of novel antioxidant, molecular hydrogen gas, on bmTBI using a laboratory-scale shock tube model in mice. Hydrogen gas has a strong prospect for clinical use due to easy preparation, low-cost, and no side effects. The administration of hydrogen gas significantly attenuated the behavioral deficits observed in our bmTBI model, suggesting that hydrogen application might be a strong therapeutic method for treatment of bmTBI.

Cardiovascular injury induced by tobacco products: assessment of risk factors and biomarkers of harm. A Tobacco Centers of Regulatory Science compilation

Although substantial evidence shows that smoking is positively and robustly associated with cardiovascular disease (CVD), the CVD risk associated with the use of new and emerging tobacco products, such as electronic cigarettes, hookah, and heat-not-burn products, remains unclear. This uncertainty stems from lack of knowledge on how the use of these products affects cardiovascular health. Cardiovascular injury associated with the use of new tobacco products could be evaluated by measuring changes in biomarkers of cardiovascular harm that are sensitive to the use of combustible cigarettes. Such cardiovascular injury could be indexed at several levels. Preclinical changes contributing to the pathogenesis of disease could be monitored by measuring changes in systemic inflammation and oxidative stress, organ-specific dysfunctions could be gauged by measuring endothelial function (flow-mediated dilation), platelet aggregation, and arterial stiffness, and organ-specific injury could be evaluated by measuring endothelial microparticles and platelet-leukocyte aggregates. Classical risk factors, such as blood pressure, circulating lipoproteins, and insulin resistance, provide robust estimates of risk, and subclinical disease progression could be followed by measuring coronary artery Ca2+ and carotid intima-media thickness. Given that several of these biomarkers are well-established predictors of major cardiovascular events, the association of these biomarkers with the use of new and emerging tobacco products could be indicative of both individual and population-level CVD risk associated with the use of these products. Differential effects of tobacco products (conventional vs. new and emerging products) on different indexes of cardiovascular injury could also provide insights into mechanisms by which they induce cardiovascular harm.

Implications of disturbances in circadian rhythms for cardiovascular health: A new frontier in free radical biology

Cell autonomous circadian "clock" mechanisms are present in virtually every organ, and generate daily rhythms that are important for normal physiology. This is especially relevant to the cardiovascular system, for example the circadian mechanism orchestrates rhythms in heart rate, blood pressure, cardiac contractility, metabolism, gene and protein abundance over the 24-h day and night cycles. Conversely, disturbing circadian rhythms (e.g. via shift work, sleep disorders) increases cardiovascular disease risk, and exacerbates cardiac remodelling and worsens outcome. Notably, reactive oxygen species (ROS) are important contributors to heart disease, especially the pathophysiologic damage that occurs after myocardial infarction (MI, heart attack). However, little is known about how the circadian mechanism, or rhythm desynchrony, is involved in these key pathologic stress responses. This review summarizes the current knowledge on circadian rhythms in the cardiovascular system, and the implications of rhythm disturbances for cardiovascular health. Furthermore, we highlight how free radical biology coincides with the pathogenesis of myocardial repair and remodelling after MI, and indicate a role for the circadian system in the oxidative stress pathways in the heart and brain after MI. This fusion of circadian biology with cardiac oxidative stress pathways is novel, and offers enormous potential for improving our understanding and treatment of heart disease.

Blood-borne interleukin-1β acts on the subfornical organ to upregulate the sympathoexcitatory milieu of the hypothalamic paraventricular nucleus

We previously reported that microinjection of the proinflammatory cytokine interleukin-1β (IL-1β) into the subfornical organ (SFO) elicits a pressor response accompanied by increases in inflammation and renin-angiotensin system (RAS) activity in the SFO and hypothalamic paraventricular nucleus (PVN). The present study sought to determine whether blood-borne IL-1β induces similar neurochemical changes in the SFO and PVN and, if so, whether increased inflammation and RAS activity at the SFO level orchestrate the sympathoexcitatory response to circulating IL-1β. In urethane-anesthetized male Sprague-Dawley rats, intravenous injection of IL-1β (500 ng) increased blood pressure, heart rate, renal sympathetic nerve activity, and mRNA for angiotensin-converting enzyme, angiotensin II type 1a receptor, cyclooxygenase-2, tumor necrosis factor-α, and IL-1β, as well as the tumor necrosis factor-α p55 receptor and the IL-1 receptor, in the SFO and PVN. Pretreatment with SFO microinjections of the angiotensin II type 1a receptor blocker losartan (1 µg), the angiotensin-converting enzyme inhibitor captopril (1 µg), or the cyclooxygenase-2 inhibitor NS-398 (2 µg) attenuated expression of these excitatory mediators in the SFO and downstream in the PVN and the IL-1β-induced pressor responses. An SFO lesion minimized the IL-1β-induced expression of inflammatory and RAS components as well as c-Fos, an indicator of neuronal excitation, in the PVN. These studies demonstrate that circulating IL-1β, which increases in cardiovascular disorders such as hypertension and heart failure, acts on the SFO to increase inflammation and RAS activity in the SFO and PVN and that intervening in these neurochemical processes in the SFO can significantly reduce the sympathetic response.

Overexpression of copper/zinc superoxide dismutase in the median preoptic nucleus improves cardiac function after myocardial infarction in the rat

Previous reports indicate that overexpression of copper/zinc superoxide dismutase (CuZnSOD), an intracellular superoxide (O2 (•-) ) scavenging enzyme, in the brain subfornical organ improves cardiac function in a mouse model of heart failure (HF). A downstream hypothalamic site, the MnPO, may act as a relay centre for O2 (•-) to serve as a mediator in the pathophysiology of HF. To test the hypothesis that elevated O2 (•-) in the MnPO contributes to the pathophysiology of HF and decreased cardiac function, we injected adenovirus encoding CuZnSOD (AdCuZnSOD, n=7) or control empty adenovirus vector (AdEmpty, n=7) into the MnPO of normal rats. Subsequently, rats were subjected to coronary artery ligation to create a myocardial infarct (MI) of the left ventricle. Cardiac function was monitored via echocardiography. Upon completion, rat brains were examined for CuZnSOD expression in MnPO via immunofluorescence and histopathological analyses of cardiac infarct size were conducted. Baseline (EF) ejection fractions (%) of AdCuZnSOD and AdEmpty rats were 73 ± 1 and 71 ± 1, respectively. Two weeks after MI, EF was significantly decreased in both groups of rats (AdCuZnSOD: 51 ± 3, AdEmpty: 46 ± 1). In contrast, by 4 weeks post MI, EF had improved to 64 ± 2 in AdCuZnSOD rats, yet was only 52 ± 1 in AdEmpty rats, and this was accompanied by lower plasma noradrenaline levels in AdCuZnSOD rats (0.49 ± 0.19 ng/mL) compared to AdEmpty rats (1.20 ± 0.32 ng/mL). In conclusion, despite decreases in EF early after MI, overexpression of CuZnSOD in the MnPO was related to an improvement in left ventricular function and concomitant decreased plasma noradrenaline levels 4 weeks post MI.

Circulating angiotensin II deteriorates left ventricular function with sympathoexcitation via brain angiotensin II receptor

Sympathoexcitation contributes to the progression of heart failure. Activation of brain angiotensin II type 1 receptors (AT₁R) causes central sympathoexcitation. Thus, we assessed the hypothesis that the increase in circulating angiotensin II comparable to that reported in heart failure model affects cardiac function through the central sympathoexcitation via activating AT₁R in the brain. In Sprague-Dawley rats, the subcutaneous infusion of angiotensin II for 14 days increased the circulating angiotensin II level comparable to that reported in heart failure model rats after myocardial infarction. In comparison with the control, angiotensin II infusion increased 24 hours urinary norepinephrine excretion, and systolic blood pressure. Angiotensin II infusion hypertrophied left ventricular (LV) without changing chamber dimensions while increased end-diastolic pressure. The LV pressure–volume relationship indicated that angiotensin II did not impact on the end-systolic elastance, whereas significantly increased end-diastolic elastance. Chronic intracerebroventricular infusion of AT₁R blocker, losartan, attenuated these angiotensin II-induced changes. In conclusion, circulating angiotensin II in heart failure is capable of inducing sympathoexcitation via in part AT₁R in the brain, subsequently leading to LV diastolic dysfunction.

Central nervous system circuits modified in heart failure: pathophysiology and therapeutic implications

The pathophysiology of heart failure (HF) is characterized by an abnormal activation of neurohumoral systems, including the sympathetic nervous and the renin-angiotensin-aldosterone systems, which have long-term deleterious effects on the disease progression. Perpetuation of this neurohumoral activation is partially dependent of central nervous system (CNS) pathways, mainly involving the paraventricular nucleus of the hypothalamus and some regions of the brainstem. Modifications in these integrative CNS circuits result in the attenuation of sympathoinhibitory and exacerbation of sympathoexcitatory pathways. In addition to the regulation of sympathetic outflow, these central pathways coordinate a complex network of agents with an established pathophysiological relevance in HF such as angiotensin, aldosterone, and proinflammatory cytokines. Central pathways could be potential targets in HF therapy since the current mainstay of HF pharmacotherapy aims primarily at antagonizing the peripheral mechanisms. Thus, in the present review, we describe the role of CNS pathways in HF pathophysiology and as potential novel therapeutic targets.

Effects of β-adrenoceptor subtypes on cardiac function in myocardial infarction rats exposed to fine particulate matter (PM 2.5)

The pathophysiological mechanisms of heart failure (HF) stems were mainly from longstanding overactivation of the sympathetic nervous system and renin-angiotensin-aldosterone system. Recent studies highlighted the potential benefits of β1-adrenoceptor (β1-AR) blocker combined with β2-adrenergic receptor (β2-AR) agonist in patients with HF. Long-term exposure to fine particulate air pollution, such as particulate matter ≤ 2.5 μm in diameter (PM_2.5), has been found associated with acute myocardial infarction (AMI) which is the most common cause of congestive HF. In this study, we have investigated the effect of combined metoprolol and terbutaline on cardiac function in a rat model of AMI exposed to PM_2.5. Our results demonstrated that short-term exposure to PM_2.5 contributes to aggravate cardiac function in rats with myocardial infarction. The combined use of β1-AR blocker and β2-AR agonist is superior to β1-AR blocker alone for the treatment of AMI rats exposed to PM_2.5. The combination of β1-AR blocker and β2-AR agonist may decrease the mortality of patients with myocardial infarction who have been exposed to PM_2.5.

Cardiac macrophages and apoptosis after myocardial infarction: effects of central MR blockade

After myocardial infarction (post-MI), inflammation and apoptosis contribute to progressive cardiac remodeling and dysfunction. Cardiac mineralocorticoid receptor (MR) and β-adrenergic signaling promote apoptosis and inflammation. Post-MI, MR activation in the brain contributes to sympathetic hyperactivity and an increase in cardiac aldosterone. In the present study, we assessed the time course of macrophage infiltration and apoptosis in the heart as detected by both terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and active caspase-3 immunostaining in both myocytes and nonmyocytes, as well as the effects of central MR blockade by intracerebroventricular infusion of eplerenone at 5 μg/day on peak changes in macrophage infiltration and apoptosis post-MI. Macrophage numbers were markedly increased in the infarct and peri-infarct zones and to a minor extent in the noninfarct part of the left ventricle at 10 days post-MI and decreased over the 3-mo study period. Apoptosis of both myocytes and nonmyocytes was clearly apparent in the infarct and peri-infarct areas at 10 days post-MI. For TUNEL, the increases persisted at 4 and 12 wk, but the number of active caspase-3-positive cells markedly decreased. Central MR blockade significantly decreased CD80-positive proinflammatory M1 macrophages and increased CD163-positive anti-inflammatory M2 macrophages in the infarct. Central MR blockade also reduced apoptosis of myocytes by 40-50% in the peri-infarct and to a lesser extent of nonmyocytes in the peri-infarct and infarct zones. These findings indicate that MR activation in the brain enhances apoptosis both in myocytes and nonmyocytes in the peri-infarct and infarct area post-MI and contributes to the inflammatory response.

Attenuation of microglial and neuronal activation in the brain by ICV minocycline following myocardial infarction

Following myocardial infarction, microglia, the immune cells in the central nervous system, become activated in the hypothalamic paraventricular nucleus (PVN) suggesting inflammation in this nucleus. Little is known about other brain nuclei. In the present study, we investigated whether the rostral ventrolateral medulla (RVLM), the nucleus tractus solitarius (NTS) and the periaqueductal grey (PAG), regions known to have important cardiovascular regulatory functions, also show increased microglial activation and whether this coincides with increased neuronal activity. We also investigated whether minocycline inhibited microglial activation and whether this also affected neuronal activity and cardiac function. Compared to controls there was a significant increase in the proportion of activated microglia and neuronal activation in the PVN, RVLM, NTS and PAG, 12weeks following myocardial infarction (P<0.001). Intracebroventricular infusion of minocycline (beginning one week prior to infarction) significantly attenuated the increase in microglial activation by at least 50% in the PVN, RVLM, PAG and NTS, and neuronal activation was significantly reduced by 50% in the PVN and virtually abolished in the PAG, RVLM and NTS. Cardiac function (percent fractional shortening) was significantly reduced by 55% following myocardial infarction but this was not ameliorated by minocycline treatment. The results suggest that following myocardial infarction, inflammation occurs in brain nuclei that play key roles in cardiovascular regulation and that attenuation of this inflammation may not be sufficient to ameliorate cardiac function.

Hypothalamic paraventricular nucleus activation contributes to neurohumoral excitation in rats with heart failure

Heart failure (HF) is a serious cardiovascular disease and is characterized by exaggerated sympathetic activity. In this paper, we review these limited studies, with particular emphasis on examining the role of the paraventricular nucleus (PVN) in the neurohumoral excitation in HF. The PVN is an important neuroendocrine and preautonomic output nucleus, and is considered as the important central site for integration of sympathetic nerve activity. Accumulating evidences demonstrate that a number of neurohumoral processes are involved in the pathophysiology of HF, such as renin-angiotensin system (RAS), proinflammatory cytokines (PICs), neurotransmitters, and reactive oxygen species (ROS). Recent studies about neurohumoral regulation indicate that angiotensin II type1 receptor (AT₁-R) is the important product mediated by cytoplasmic nuclear factor-kappa B (NF-κB) which is up-regulated along with elevated PICs and angiotensin II (ANG II) in the PVN of HF rats. These findings suggest that the NF-κB mediates the cross-talk between RAS and PICs in the PVN in HF. The further studies indicate that the interaction between AT₁-R and NF-κB in the PVN contributes to oxidative stress and sympathoexcitation by modulating neurotransmitters in heart failure, and the superoxide activates NF-κB in the PVN and contributes to neurohumoral excitation. In conclusion, the neurohumoral excitation in HF is based on the interaction of RAS, PICs, ROS, NF-κB and neurotransmitters in the PVN; and the activated NF-κB in the PVN modulates the neurotransmitters and contributes to sympathoexcitation in rats with heart failure.

Subfornical organ mediates sympathetic and hemodynamic responses to blood-borne proinflammatory cytokines

Proinflammatory cytokines play an important role in regulating autonomic and cardiovascular function in hypertension and heart failure. Peripherally administered proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), act on the brain to increase blood pressure, heart rate, and sympathetic nerve activity. These molecules are too large to penetrate the blood-brain barrier, and so the mechanisms by which they elicit these responses remain unknown. We tested the hypothesis that the subfornical organ (SFO), a forebrain circumventricular organ that lacks a blood-brain barrier, plays a major role in mediating the sympathetic and hemodynamic responses to circulating proinflammatory cytokines. Intracarotid artery injection of TNF-α (200 ng) or IL-1β (200 ng) dramatically increased mean blood pressure, heart rate, and renal sympathetic nerve activity in rats with sham lesions of the SFO (SFO-s). These excitatory responses to intracarotid artery TNF-α and IL-1β were significantly attenuated in SFO-lesioned (SFO-x) rats. Similarly, the increases in mean blood pressure, heart rate, and renal sympathetic nerve activity in response to intravenous injections of TNF-α (500 ng) or IL-1β (500 ng) in SFO-s rats were significantly reduced in the SFO-x rats. Immunofluorescent staining revealed a dense distribution of the p55 TNF-α receptor and the IL-1 receptor accessory protein, a subunit of the IL-1 receptor, in the SFO. These data suggest that SFO is a predominant site in the brain at which circulating proinflammatory cytokines act to elicit cardiovascular and sympathetic responses.

Mitochondrial-localized NADPH oxidase 4 is a source of superoxide in angiotensin II-stimulated neurons

Angiotensin II (ANG II) plays an important role in the central regulation of systemic cardiovascular function. ANG II-mediated intraneuronal signaling has been shown to be predicated by an increase in mitochondrial superoxide (O₂∙-), yet the source of this reactive oxygen species (ROS) production remains unclear. NADPH oxidase 4 (Nox4), a member of the NADPH oxidase family, has been reported to be localized in mitochondria of various cell types and has been implicated in brain angiotensinergic signaling. However, the subcellular localization and function of Nox4 in neurons has not been fully elucidated. In this study, we hypothesized that Nox4 is expressed in neuron mitochondria and is involved in ANG II-dependent O₂∙--mediated intraneuronal signaling. To query this, Nox4 immunofluorescent staining and mitochondrial enrichment were performed in a mouse catecholaminergic neuronal cell model (CATH.a). Nox4 was shown to be present in neuron mitochondria as evidenced by colocalization with both the mitochondrial-localized protein manganese superoxide dismutase (MnSOD) and dye MitoTracker Red. Moreover, Nox4 expression was significantly increased in enriched mitochondrial fractions compared with whole cell lysates. Additionally, adenoviral-encoded small interfering RNA for Nox4 (AdsiNox4) caused a robust knockdown in Nox4 mRNA and protein levels, which led to the attenuation of ANG II-induced mitochondrial O₂∙- production. Finally, in the subfornical organ (SFO) of the brain, Nox4 not only demonstrated mitochondrial localization but was induced by chronic, peripheral infusion of ANG II. Collectively, these data suggest that Nox4 is a source of O₂∙- in neuron mitochondria that contributes to ANG II intraneuronal signaling.

Antioxidant-based therapies for angiotensin II-associated cardiovascular diseases

Cardiovascular diseases, including hypertension and heart failure, are associated with activation of the renin-angiotensin system (RAS) and increased circulating and tissue levels of ANG II, a primary effector peptide of the RAS. Through its actions on various cell types and organ systems, ANG II contributes to the pathogenesis of cardiovascular diseases by inducing cardiac and vascular hypertrophy, vasoconstriction, sodium and water reabsorption in kidneys, sympathoexcitation, and activation of the immune system. Cardiovascular research over the past 15-20 years has clearly implicated an important role for elevated levels of reactive oxygen species (ROS) in mediating these pathophysiological actions of ANG II. As such, the use of antioxidants, to reduce the elevated levels of ROS, as potential therapies for various ANG II-associated cardiovascular diseases has been intensely investigated. Although some antioxidant-based therapies have shown therapeutic impact in animal models of cardiovascular disease and in human patients, others have failed. In this review, we discuss the benefits and limitations of recent strategies, including gene therapy, dietary sources, low-molecular-weight free radical scavengers, polyethylene glycol conjugation, and nanomedicine-based technologies, which are designed to deliver antioxidants for the improved treatment of cardiovascular diseases. Although much work has been completed, additional research focusing on developing specific antioxidant molecules or proteins and identifying the ideal in vivo delivery system for such antioxidants is necessary before the use of antioxidant-based therapies for cardiovascular diseases become a clinical reality.

Central Rho kinase inhibition restores baroreflex sensitivity and angiotensin II type 1 receptor protein imbalance in conscious rabbits with chronic heart failure

The small GTPase RhoA and its associated kinase ROCKII are involved in vascular smooth muscle cell contraction and endothelial NO synthase mRNA destabilization. Overactivation of the RhoA/ROCKII pathway is implicated in several pathologies, including chronic heart failure (CHF), and may contribute to the enhanced sympathetic outflow seen in CHF as a result of decreased NO availability. Thus, we hypothesized that central ROCKII blockade would improve the sympathovagal imbalance in a pacing rabbit model of CHF in an NO-dependent manner. CHF was induced by rapid ventricular pacing and characterized by an ejection fraction of ≤45%. Animals were implanted with an intracerbroventricular cannula and osmotic minipump (rate, 1 μL/h) containing sterile saline, 1.5 µg/kg per day fasudil (Fas, a ROCKII inhibitor) for 4 days or Fas+100 µg/kg per day Nω-Nitro-l-arginine methyl ester hydrochloride, a NO synthase inhibitor. Arterial baroreflex control was assessed by intravenous infusion of sodium nitroprusside and phenylephrine. Fas infusion significantly lowered resting heart rate by decreasing sympathetic and increasing vagal tone. Furthermore, Fas improved baroreflex gain in CHF in an NO-dependent manner. In CHF Fas animals, the decrease in heart rate in response to intravenous metoprolol was similar to Sham and was reversed by Nω-Nitro-l-arginine methyl ester hydrochloride. Fas decreased angiotensin II type 1 receptor and phospho-ERM protein expression and increased endothelial NO synthase expression in the brain stem of CHF animals. These data strongly suggest that central ROCKII activation contributes to cardiac sympathoexcitation in the setting of CHF and that central Fas restores vagal and sympathetic tone in an NO-dependent manner. ROCKII may be a new central therapeutic target in the setting of CHF.

Neurohumoral stimulation

The temporal relationship between the development of heart failure and activation of the neurohumoral systems involved in chronic heart failure (CHF) has not been precisely defined. When a compensatory mechanism switches to a deleterious contributing factor in the progression of the disease is unclear. This article addresses these issues through evaluating the contribution of various cardiovascular reflexes and cellular mechanisms to the sympathoexcitation in CHF. It also sheds light on some of the important central mechanisms that contribute to the increase in sympathetic nerve activity in CHF.

Peroxisome proliferator-activated receptor-γ regulates inflammation and renin-angiotensin system activity in the hypothalamic paraventricular nucleus and ameliorates peripheral manifestations of heart failure

Activation of peroxisome proliferator-activated receptor (PPAR)-γ, a nuclear transcription factor, has been shown to inhibit the production of proinflammatory cytokines and, in peripheral tissues, to downregulate the renin-angiotensin system. PPAR-γ is expressed in key brain areas involved in cardiovascular and autonomic regulation. We hypothesized that activation of central PPAR-γ would reduce sympathetic excitation and ameliorate peripheral manifestations of heart failure (HF) by inhibiting central inflammation and brain renin-angiotensin system activity. Two weeks after coronary artery ligation, HF rats received an intracerebroventricular infusion of the PPAR-γ agonist pioglitazone or vehicle for another 2 weeks. PPAR-γ expression in the paraventricular nucleus of hypothalamus, an important cardiovascular region, was unchanged in HF compared with sham-operated rats. However, PPAR-γ DNA binding activity was reduced, nuclear factor-κB activity was increased, and expression of proinflammatory cytokines and angiotensin II type-1 receptor was augmented in the HF rats. Mean blood pressure response to ganglionic blockade was greater; plasma norepinephrine levels, lung/body weight, right ventricle/body weight, and left ventricular end-diastolic pressure were increased; and maximal left ventricular dP/dt was decreased. All of these findings were ameliorated in HF rats treated with intracerebroventricular pioglitazone, which increased PPAR-γ expression and DNA binding activity in the paraventricular nucleus of hypothalamus. The results demonstrate that cardiovascular and autonomic mechanisms leading to heart failure after myocardial infarction can be modulated by activation of PPAR-γ in the brain. Central PPAR-γ may be a novel target for treatment of sympathetic excitation in myocardial infarction-induced HF.

Brain-selective overexpression of angiotensin-converting enzyme 2 attenuates sympathetic nerve activity and enhances baroreflex function in chronic heart failure

Angiotensin-converting enzyme 2 (ACE2) has been suggested to be involved in the central regulation of autonomic function. During chronic heart failure (CHF), elevated central angiotensin II signaling contributes to the sustained increase of sympathetic outflow. This is accompanied by a downregulation of ACE2 in the brain. We hypothesized that central overexpression of ACE2 decreases sympathetic outflow and enhances baroreflex function in CHF. Transgenic mice overexpressing human ACE2 selectively in the brain (SYN-hACE2 [SA]) and wild-type littermates (WT) were used. CHF was induced by permanent coronary artery ligation. Four weeks after coronary artery ligation, both WT and SA mice exhibited a significant decrease in left ventricular ejection fraction (<40%). A slight decrease in mean arterial pressure was found only in SA mice. Compared with WT mice with CHF, brain-selective ACE2 overexpression attenuated left ventricular end-diastolic pressure; decreased urinary norepinephrine excretion; baseline renal sympathetic nerve activity (WT CHF: 71.6±7.6% max versus SA CHF: 49.3±6.1% max); and enhanced baroreflex sensitivity (maximum slope: WT sham: 1.61±0.16%/mm Hg versus SA CHF: 1.51±0.17%/mm Hg). Chronic subcutaneous blockade of mas receptor increased renal sympathetic nerve activity in SA mice with CHF (A779: 67.3±5.8% versus vehicle: 46.4±3.6% of max). An upregulation in angiotensin II type 1 receptor expression was detected in medullary nuclei in WT CHF mice, which was significantly attenuated in SA mice with CHF. These data suggest that central ACE2 overexpression exerts a potential protective effect in CHF through attenuating sympathetic outflow. The mechanism for this effect involves angiotensin (1-7) mas signaling, as well as a decrease in angiotensin II type 1 receptor signaling in the medulla.

NADPH oxidases in cardiovascular disease: insights from in vivo models and clinical studies

NADPH oxidase family enzymes (or NOXs) are the major sources of reactive oxygen species (ROS) that are implicated in the pathophysiology of many cardiovascular diseases. These enzymes appear to be especially important in the modulation of redox-sensitive signalling pathways that underlie key cellular functions such as growth, differentiation, migration and proliferation. Seven distinct members of the family have been identified of which four (namely NOX1, 2, 4 and 5) may have cardiovascular functions. In this article, we review our current understanding of the roles of NOX enzymes in several common cardiovascular disease states, with a focus on data from genetic studies and clinical data where available.

Angiotensin II and angiotensin-1-7 redox signaling in the central nervous system

Reactive oxygen species (ROS) are important intra-neuronal signaling intermediates in angiotensin II (AngII)-related neuro-cardiovascular diseases associated with excessive sympathoexcitation, including hypertension and heart failure. ROS-sensitive effector mechanisms, such as modulation of ion channel activity, indicate that elevated levels of ROS increase neuronal activity. Nitric oxide, which may work to counter the effects of ROS, particularly superoxide, has been identified as a signaling molecule in angiotensin-1-7 (Ang-(1-7)) stimulated neurons. This review focuses on recent studies that have revealed details on the AngII-activated sources of ROS, the downstream redox-sensitive effectors, Ang-(1-7)-stimulated increase in nitric oxide, and the neuro-cardiovascular (patho)physiological responses modulated by these reactive species. Understanding these intra-neuronal signaling mechanisms should provide insight for the development of new redox-based therapeutics for the improved treatment of angiotensin-dependent neuro-cardiovascular diseases.

AT2 receptor signaling and sympathetic regulation

There is a growing consensus that the balance between Angiotensin Type 1 (AT1R) and Angiotensin Type 2 (AT2R) signaling in many tissues may determine the magnitude and, in some cases the direction, of the biological response. Sympatho-excitation in cardiovascular diseases is mediated by a variety of factors and is, in part, dependent on Angiotensin II signaling in the central nervous system. Recent data have provided evidence that the AT2R can modulate sympatho-excitation in animals with hypertension and heart failure. The evidence for this concept is reviewed and a model is put forward to support the rationale that therapeutic targeting of the central AT2R may be beneficial in the setting of chronic heart failure.

Renal denervation modulates angiotensin receptor expression in the renal cortex of rabbits with chronic heart failure

Excessive sympathetic drive is a hallmark of chronic heart failure (HF). Disease progression can be correlated with plasma norepinephrine concentration. Renal function is also correlated with disease progression and prognosis. Because both the renal nerves and renin-angiotensin II system are activated in chronic HF we hypothesized that excessive renal sympathetic nerve activity decreases renal blood flow in HF and is associated with changes in angiotensin II type 1 receptor (AT1R) and angiotensin II type 2 receptor (AT2R) expression. The present study was carried out in conscious, chronically instrumented rabbits with pacing-induced HF. We found that rabbits with HF showed a decrease in mean renal blood flow (19.8±1.6 in HF vs. 32.0±2.5 ml/min from prepace levels; P<0.05) and an increase in renal vascular resistance (3.26±0.29 in HF vs. 2.21±0.13 mmHg·ml(-1)·min in prepace normal rabbits; P<0.05) while the blood flow and resistance was not changed in HF rabbits with the surgical renal denervation. Renal AT1R expression was increased by ∼67% and AT2R expression was decreased by ∼87% in rabbits with HF; however, kidneys from denervated rabbits with HF showed a near normalization in the expression of these receptors. These results suggest renal sympathetic nerve activity elicits a detrimental effect on renal blood flow and may be associated with alterations in the expression of angiotensin II receptors.

Pluronic-modified superoxide dismutase 1 attenuates angiotensin II-induced increase in intracellular superoxide in neurons

Overexpressing superoxide dismutase 1 (SOD1; also called Cu/ZnSOD), an intracellular superoxide (O(2)(*-))-scavenging enzyme, in central neurons inhibits angiotensin II (AngII) intraneuronal signaling and normalizes cardiovascular dysfunction in diseases associated with enhanced AngII signaling in the brain, including hypertension and heart failure. However, the blood-brain barrier and neuronal cell membranes impose a tremendous impediment for the delivery of SOD1 to central neurons, which hinders the potential therapeutic impact of SOD1 treatment on these diseases. To address this, we developed conjugates of SOD1 with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer (Pluronic) (SOD1-P85 and SOD1-L81), which retained significant SOD1 enzymatic activity. The modified SOD1 effectively scavenged xanthine oxidase/hypoxanthine-derived O(2)(*-), as determined by HPLC and the measurement of 2-hydroxyethidium. Using catecholaminergic neurons, we observed an increase in neuronal uptake of SOD1-Pluronic after 1, 6, or 24h, compared to neurons treated with pure SOD1 or PEG-SOD1. Importantly, without inducing neuronal toxicity, SOD1-Pluronic conjugates significantly inhibited AngII-induced increases in intraneuronal O(2)(*-) levels. These data indicate that SOD1-Pluronic conjugates penetrate neuronal cell membranes, which results in elevated intracellular levels of functional SOD1. Pluronic conjugation may be a new delivery system for SOD1 into central neurons and therapeutically beneficial for AngII-related cardiovascular diseases.

The attenuation of central angiotensin II-dependent pressor response and intra-neuronal signaling by intracarotid injection of nanoformulated copper/zinc superoxide dismutase

Adenoviral-mediated overexpression of the intracellular superoxide (O(2)(*-)) scavenging enzyme copper/zinc superoxide dismutase (CuZnSOD) in the brain attenuates central angiotensin II (AngII)-induced cardiovascular responses. However, the therapeutic potential for adenoviral vectors is weakened by toxicity and the inability of adenoviral vectors to target the brain following peripheral administration. Therefore, we developed a non-viral delivery system in which CuZnSOD protein is electrostatically bound to a synthetic poly(ethyleneimine)-poly(ethyleneglycol) (PEI-PEG) polymer to form a polyion complex (CuZnSOD nanozyme). We hypothesized that PEI-PEG polymer increases transport of functional CuZnSOD to neurons, which inhibits AngII intra-neuronal signaling. The AngII-induced increase in O(2)(*-), as measured by dihydroethidium fluorescence and electron paramagnetic resonance spectroscopy, was significantly inhibited in CuZnSOD nanozyme-treated neurons compared to free CuZnSOD- and non-treated neurons. CuZnSOD nanozyme also attenuated the AngII-induced inhibition of K(+) current in neurons. Intracarotid injection of CuZnSOD nanozyme into rabbits significantly inhibited the pressor response of intracerebroventricular-delivered AngII; however, intracarotid injection of free CuZnSOD or PEI-PEG polymer alone failed to inhibit this response. Importantly, neither the PEI-PEG polymer alone nor the CuZnSOD nanozyme induced neuronal toxicity. These findings indicate that CuZnSOD nanozyme inhibits AngII intra-neuronal signaling in vitro and in vivo.

Silencing nox4 in the paraventricular nucleus improves myocardial infarction-induced cardiac dysfunction by attenuating sympathoexcitation and periinfarct apoptosis

RATIONALE

Myocardial infarction (MI)-induced heart failure is characterized by central nervous system-driven sympathoexcitation and deteriorating cardiac function. The paraventricular nucleus (PVN) of the hypothalamus is a key regulator of sympathetic nerve activity and is implicated in heart failure. Redox signaling in the PVN and other central nervous system sites is a primary mechanism of neuro-cardiovascular regulation, and excessive oxidant production by activation of NADPH oxidases (Noxs) is implicated in some neuro-cardiovascular diseases.

OBJECTIVE

We tested the hypothesis that Nox-mediated redox signaling in the PVN contributes to MI-induced sympathoexcitation and cardiac dysfunction in mice.

METHODS AND RESULTS

Real-time PCR revealed that Nox4 was the most abundantly expressed Nox in PVN under basal conditions. Coronary arterial ligation (MI) caused a selective upregulation of this homolog compared to Nox1 and Nox2. Adenoviral gene transfer of Nox4 (AdsiNox4) to PVN (bilateral) attenuated MI-induced superoxide formation in this brain region (day 14) to the same level as that produced by PVN-targeted gene transfer of cytoplasmic superoxide dismutase (AdCu/ZnSOD). MI mice treated with AdsiNox4 or AdCu/ZnSOD in the PVN showed marked improvement in cardiac function as assessed by echocardiography and left ventricular hemodynamic analysis. This was accompanied by significantly diminished sympathetic outflow and apoptosis in the periinfarct region of the heart.

CONCLUSIONS

These results suggest that MI causes dysregulation of Nox4-mediated redox signaling in the PVN, which leads to sympathetic overactivation and a decline in cardiac function. Targeted inhibition of oxidant signaling in the PVN could provide a novel treatment for MI-induced heart failure.

Circulating signals as critical regulators of autonomic state--central roles for the subfornical organ

To maintain homeostasis autonomic control centers in the hypothalamus and medulla must respond appropriately to both external and internal stimuli. Although protected behind the blood-brain barrier, neurons in these autonomic control centers are known to be influenced by changing levels of important signaling molecules in the systemic circulation (e.g., osmolarity, glucose concentrations, and regulatory peptides). The subfornical organ belongs to a group of specialized central nervous system structures, the circumventricular organs, which are characterized by the lack of the normal blood-brain barrier, such that circulating lipophobic substances may act on neurons within this region and via well-documented efferent neural projections to hypothalamic autonomic control centers, influence autonomic function. This review focuses on the role of the subfornical organ in sensing peripheral signals and transmitting this information to autonomic control centers in the hypothalamus.

Sympathetic nervous system overactivity and its role in the development of cardiovascular disease

This review examines how the sympathetic nervous system plays a major role in the regulation of cardiovascular function over multiple time scales. This is achieved through differential regulation of sympathetic outflow to a variety of organs. This differential control is a product of the topographical organization of the central nervous system and a myriad of afferent inputs. Together this organization produces sympathetic responses tailored to match stimuli. The long-term control of sympathetic nerve activity (SNA) is an area of considerable interest and involves a variety of mediators acting in a quite distinct fashion. These mediators include arterial baroreflexes, angiotensin II, blood volume and osmolarity, and a host of humoral factors. A key feature of many cardiovascular diseases is increased SNA. However, rather than there being a generalized increase in SNA, it is organ specific, in particular to the heart and kidneys. These increases in regional SNA are associated with increased mortality. Understanding the regulation of organ-specific SNA is likely to offer new targets for drug therapy. There is a need for the research community to develop better animal models and technologies that reflect the disease progression seen in humans. A particular focus is required on models in which SNA is chronically elevated.

Superoxide scavenging and Akt inhibition in myocardium ameliorate pressure overload-induced NF-κB activation and cardiac hypertrophy

Recent studies from our laboratory and others have shown that increases in cytoplasmic superoxide (O(2)(·-)) levels and Akt activation play a key role in agonist-stimulated NF-κB activation and cardiomyocyte hypertrophy in vitro. In this study, we tested the hypothesis that adenovirus (Ad)-mediated intramyocardial gene transfer of cytoplasmic superoxide dismutase (AdCu/ZnSOD) or a dominant-negative form of Akt (AdDNAkt) in mice would attenuate pressure overload-induced increases in activation of the redox-sensitive transcription factor NF-κB and cardiac hypertrophy. Adult C57BL/6 mice were subjected to thoracic aortic banding (TAB) or sham surgery, and intramyocardial injections of viral vectors (AdCu/ZnSOD, AdDNAkt, or control) were performed. There was robust transgene expression in the heart, which peaked 6-7 days after injection and then declined to undetectable levels by 12-14 days. In mice injected with AdBgL II, TAB caused a significant increase in O(2)(·-) generation and cardiac mass at 1 wk, and these responses were markedly attenuated by AdCu/ZnSOD. In addition, TAB induced time-dependent activation of NF-κB in the myocardium as measured longitudinally by in vivo bioluminescent imaging of NF-κB-dependent luciferase expression. This was also abolished by intracardiac AdCu/ZnSOD or AdDNAkt, but not the control vector. The inhibition of Akt and O(2)(·-)-mediated NF-κB activation in TAB hearts was associated with an attenuation of cardiac hypertrophy. Since a direct cause-and-effect relationship between NF-κB activation and cardiomyocyte hypertrophy has been established previously, our data support the hypothesis that increased O(2)(·-) generation and Akt activation are key signaling intermediates in pressure overload-induced activation of NF-κB and cardiac hypertrophy.

Brain renin–angiotensin–aldosterone system and ventricular remodeling after myocardial infarct: a reviewThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research

After a myocardial infarct (MI), a variety of mechanisms contribute to progressive cardiac remodeling and dysfunction. Progressive activation of central sympathoexcitatory pathways appears to depend on a neuromodulatory pathway, involving local production of aldosterone and release of endogenous ouabain-like compounds (‘ouabain’) possibly from magnocellular neurons in the supraoptic and paraventricular nuclei. ‘Ouabain’ may lower the membrane potential of neurons and thereby enhance activity of angiotensinergic pathways. These central pathways appear to coordinate progressive activation of several peripheral mechanisms such as sympathetic tone and circulating and cardiac renin–angiotensin–aldosterone system (RAAS). Central blockade of aldosterone production, mineralocorticoid receptors, ‘ouabain’ activity, or AT1 receptors similarly prevents activation of these peripheral mechanisms. Cardiac remodeling after MI involves progressive left ventricular dilation, fibrosis, and decrease in contractile performance. Central blockade of this neuromodulatory pathway causes a marked attenuation of the remodeling and dysfunction, presumably by inhibiting increases in (cardiac) sympathetic activity and RAAS. At the cellular level, these systems may contribute to the cardiac remodeling by activating proinflammatory cytokines and cardiac myocyte apoptosis. New therapeutic approaches, specifically preventing activation of this brain neuromodulatory pathway, may lead to more optimal and specific approaches to the prevention of heart failure after MI.

Regulation of central angiotensin type 1 receptors and sympathetic outflow in heart failure

Angiotensin type 1 receptors (AT(1)Rs) play a critical role in a variety of physiological functions and pathophysiological states. They have been strongly implicated in the modulation of sympathetic outflow in the brain. An understanding of the mechanisms by which AT(1)Rs are regulated in a variety of disease states that are characterized by sympathoexcitation is pivotal in development of new strategies for the treatment of these disorders. This review concentrates on several aspects of AT(1)R regulation in the setting of chronic heart failure (CHF). There is now good evidence that AT(1)R expression in neurons is mediated by activation of the transcription factor activator protein 1 (AP-1). This transcription factor and its component proteins are upregulated in the rostral ventrolateral medulla of animals with CHF. Because the increase in AT(1)R expression and transcription factor activation can be blocked by the AT(1)R antagonist losartan, a positive feedback mechanism of AT(1)R expression in CHF is suggested. Oxidative stress has also been implicated in the regulation of receptor expression. Recent data suggest that the newly discovered catabolic enzyme angiotensin-converting enzyme 2 (ACE2) may play a role in the modulation of AT(1)R expression by altering the balance between the octapeptide ANG II and ANG- (1-7). Finally, exercise training reduces both central oxidative stress and AT(1)R expression in animals with CHF. These data strongly suggest that multiple central and peripheral influences dynamically alter AT(1)R expression in CHF.

Chronic central versus systemic blockade of AT(1) receptors and cardiac dysfunction in rats post-myocardial infarction

In rats, both central and systemic ANG II type 1 (AT(1)) receptor blockade attenuate sympathetic hyperactivity, but central blockade more effectively attenuates left ventricular (LV) dysfunction post-myocardial infarction (MI). In protocol I, we examined whether functional effects on cardiac load may play a role and different cardiac effects disappear after withdrawal of the blockade. Wistar rats were infused for 4 wk post-MI intracerebroventricularly (1 mg.kg(-1).day(-1)) or injected subcutaneously daily (100 mg x kg(-1) x day(-1)) with losartan. LV dimensions and function were assessed at 4 wk and at 6 wk post-MI, i.e., 2 wk after discontinuing treatments. At 4 and 6 wk post-MI, LV dimensions were increased and ejection fraction was decreased. Intracerebroventricular but not subcutaneous losartan significantly improved these parameters. At 6 wk, LV peak systolic pressure (LVPSP) and maximal or minimal first derivative of change in pressure over time (dP/dt(max/min)) were decreased and LV end-diastolic pressure (LVEDP) was increased. All four indexes were improved by previous intracerebroventricular losartan, whereas subcutaneous losartan improved LVEDP only. In protocol II, we evaluated effects of oral instead of subcutaneous administration of losartan for 4 wk post-MI. Losartan ( approximately 200 mg x kg(-1) x day(-1)) either via drinking water or by gavage similarly decreased AT(1) receptor binding densities in brain nuclei and improved LVEDP but further decreased LVPSP and dP/dt(max). These results indicate that effects on cardiac load by peripheral AT(1) receptor blockade or the pharmacokinetic profile of subcutaneous versus oral dosing do not contribute to the different cardiac effects of central versus systemic AT(1) receptor blockade post-MI.