Nox2 deficiency prevents hypertension-induced vascular dysfunction and hypertrophy in cerebral arterioles

Advanced Magnetic Resonance Imaging to Define the Microvascular Injury Driven by Neuroinflammation in the Brain of a Mouse Model of Hypertension

BACKGROUND

Hypertension is one of the main risk factors for dementia and cognitive impairment.

METHODS

We used the model of transverse aortic constriction to induce chronic pressure overload in mice. We characterized brain injury by advanced translational applications of magnetic resonance imaging. In parallel, we analyzed peripheral target organ damage induced by chronic pressure overload by ultrasonography. Microscopical characterization of brain vasculature was performed as well, together with the analysis of immune and inflammatory markers.

RESULTS

We identified a specific structural, microstructural, and functional brain injury. In particular, we highlighted a regional enlargement of the hypothalamus, microstructural damage in the white matter of the fimbria, and a reduction of the cerebral blood flow. A parallel analysis performed by confocal microscopy revealed a correspondent tissue damage evidenced by a reduction of cerebral capillary density, paired with loss of pericyte coverage. We assessed cognitive impairment and cardiac damage induced by hypertension to perform correlation analyses with the brain injury severity. At the mechanistic level, we found that CD8+T cells, producing interferon-γ, infiltrated the brain of hypertensive mice. By neutralizing this proinflammatory cytokine, we obtained a rescue of the phenotype, demonstrating their crucial role in establishing the microvascular damage.

CONCLUSIONS

Overall, we have used translational tools to comprehensively characterize brain injury in a mouse model of hypertension induced by chronic pressure overload. We have identified early cerebrovascular damage in hypertensive mice, sustained by CD8+IFN-γ+T lymphocytes, which fuel neuroinflammation to establish the injury of brain capillaries.

Health position paper and redox perspectives - Disease burden by transportation noise

Transportation noise is a ubiquitous urban exposure. In 2018, the World Health Organization concluded that chronic exposure to road traffic noise is a risk factor for ischemic heart disease. In contrast, they concluded that the quality of evidence for a link to other diseases was very low to moderate. Since then, several studies on the impact of noise on various diseases have been published. Also, studies investigating the mechanistic pathways underlying noise-induced health effects are emerging. We review the current evidence regarding effects of noise on health and the related disease-mechanisms. Several high-quality cohort studies consistently found road traffic noise to be associated with a higher risk of ischemic heart disease, heart failure, diabetes, and all-cause mortality. Furthermore, recent studies have indicated that road traffic and railway noise may increase the risk of diseases not commonly investigated in an environmental noise context, including breast cancer, dementia, and tinnitus. The harmful effects of noise are related to activation of a physiological stress response and nighttime sleep disturbance. Oxidative stress and inflammation downstream of stress hormone signaling and dysregulated circadian rhythms are identified as major disease-relevant pathomechanistic drivers. We discuss the role of reactive oxygen species and present results from antioxidant interventions. Lastly, we provide an overview of oxidative stress markers and adverse redox processes reported for noise-exposed animals and humans. This position paper summarizes all available epidemiological, clinical, and preclinical evidence of transportation noise as an important environmental risk factor for public health and discusses its implications on the population level.

Redox Switches in Noise-Induced Cardiovascular and Neuronal Dysregulation

Environmental exposures represent a significant health hazard, which cumulatively may be responsible for up to 2/3 of all chronic non-communicable disease and associated mortality (Global Burden of Disease Study and The Lancet Commission on Pollution and Health), which has given rise to a new concept of the exposome: the sum of environmental factors in every individual’s experience. Noise is part of the exposome and is increasingly being investigated as a health risk factor impacting neurological, cardiometabolic, endocrine, and immune health. Beyond the well-characterized effects of high-intensity noise on cochlear damage, noise is relatively well-studied in the cardiovascular field, where evidence is emerging from both human and translational experiments that noise from traffic-related sources could represent a risk factor for hypertension, ischemic heart disease, diabetes, and atherosclerosis. In the present review, we comprehensively discuss the current state of knowledge in the field of noise research. We give a brief survey of the literature documenting experiments in noise exposure in both humans and animals with a focus on cardiovascular disease. We also discuss the mechanisms that have been uncovered in recent years that describe how exposure to noise affects physiological homeostasis, leading to aberrant redox signaling resulting in metabolic and immune consequences, both of which have considerable impact on cardiovascular health. Additionally, we discuss the molecular pathways of redox involvement in the stress responses to noise and how they manifest in disruptions of the circadian rhythm, inflammatory signaling, gut microbiome composition, epigenetic landscape and vessel function.

Animal Models of Hypertension: A Scientific Statement From the American Heart Association

Hypertension is the most common chronic disease in the world, yet the precise cause of elevated blood pressure often cannot be determined. Animal models have been useful for unraveling the pathogenesis of hypertension and for testing novel therapeutic strategies. The utility of animal models for improving the understanding of the pathogenesis, prevention, and treatment of hypertension and its comorbidities depends on their validity for representing human forms of hypertension, including responses to therapy, and on the quality of studies in those models (such as reproducibility and experimental design). Important unmet needs in this field include the development of models that mimic the discrete hypertensive syndromes that now populate the clinic, resolution of ongoing controversies in the pathogenesis of hypertension, and the development of new avenues for preventing and treating hypertension and its complications. Animal models may indeed be useful for addressing these unmet needs.

The importance of comorbidities in ischemic stroke: Impact of hypertension on the cerebral circulation

Comorbidities are a hallmark of stroke that both increase the incidence of stroke and worsen outcome. Hypertension is prevalent in the stroke population and the most important modifiable risk factor for stroke. Hypertensive disorders promote stroke through increased shear stress, endothelial dysfunction, and large artery stiffness that transmits pulsatile flow to the cerebral microcirculation. Hypertension also promotes cerebral small vessel disease through several mechanisms, including hypoperfusion, diminished autoregulatory capacity and localized increase in blood-brain barrier permeability. Preeclampsia, a hypertensive disorder of pregnancy, also increases the risk of stroke 4-5-fold compared to normal pregnancy that predisposes women to early-onset cognitive impairment. In this review, we highlight how comorbidities and concomitant disorders are not only risk factors for ischemic stroke, but alter the response to acute ischemia. We focus on hypertension as a comorbidity and its effects on the cerebral circulation that alters the pathophysiology of ischemic stroke and should be considered in guiding future therapeutic strategies.

Oxidation of cysteine 117 stimulates constitutive activation of the type Iα cGMP-dependent protein kinase

The type I cGMP-dependent protein kinase (PKG I) is an essential regulator of vascular tone. It has been demonstrated that the type Iα isoform can be constitutively activated by oxidizing conditions. However, the amino acid residues implicated in this phenomenon are not fully elucidated. To investigate the molecular basis for this mechanism, we studied the effects of oxidation using recombinant WT, truncated, and mutant constructs of PKG I. Using an in vitro assay, we observed that oxidation with hydrogen peroxide (H₂O₂) resulted in constitutive, cGMP-independent activation of PKG Iα. PKG Iα C42S and a truncation construct that does not contain Cys-42 (Δ53) were both constitutively activated by H₂O₂ In contrast, oxidation of PKG Iα C117S maintained its cGMP-dependent activation characteristics, although oxidized PKG Iα C195S did not. To corroborate these results, we also tested the effects of our constructs on the PKG Iα-specific substrate, the large conductance potassium channel (K_Ca 1.1). Application of WT PKG Iα activated by either cGMP or H₂O₂ increased the open probabilities of the channel. Neither cGMP nor H₂O₂ activation of PKG Iα C42S significantly increased channel open probabilities. Moreover, cGMP-stimulated PKG Iα C117S increased K_Ca 1.1 activity, but this effect was not observed under oxidizing conditions. Finally, we observed that PKG Iα C42S caused channel flickers, indicating dramatically altered K_Ca 1.1 channel characteristics compared with channels exposed to WT PKG Iα. Cumulatively, these results indicate that constitutive activation of PKG Iα proceeds through oxidation of Cys-117 and further suggest that the formation of a sulfur acid is necessary for this phenotype.

Cerebral Vascular Disease and Neurovascular Injury in Ischemic Stroke

The consequences of cerebrovascular disease are among the leading health issues worldwide. Large and small cerebral vessel disease can trigger stroke and contribute to the vascular component of other forms of neurological dysfunction and degeneration. Both forms of vascular disease are driven by diverse risk factors, with hypertension as the leading contributor. Despite the importance of neurovascular disease and subsequent injury after ischemic events, fundamental knowledge in these areas lag behind our current understanding of neuroprotection and vascular biology in general. The goal of this review is to address select key structural and functional changes in the vasculature that promote hypoperfusion and ischemia, while also affecting the extent of injury and effectiveness of therapy. In addition, as damage to the blood-brain barrier is one of the major consequences of ischemia, we discuss cellular and molecular mechanisms underlying ischemia-induced changes in blood-brain barrier integrity and function, including alterations in endothelial cells and the contribution of pericytes, immune cells, and matrix metalloproteinases. Identification of cell types, pathways, and molecules that control vascular changes before and after ischemia may result in novel approaches to slow the progression of cerebrovascular disease and lessen both the frequency and impact of ischemic events.

The Pathophysiological Role of NOX2 in Hypertension and Organ Damage

NADPH oxidases (NOXs) represent one of the major sources of reactive oxygen species in the vascular district. Reactive oxygen species are responsible for vascular damage that leads to several cardiovascular pathological conditions. Among NOX isoforms, NOX2 is widely expressed in many cells types, such as cardiomyocytes, endothelial cells, and vascular smooth muscle cells, confirming its pivotal role in vascular pathophysiology. Studies in mice models with systemic deletion of NOX2, as well as in transgenic mice overexpressing NOX2, have demonstrated the undeniable involvement of NOX2 in the development of hypertension, atherosclerosis, diabetes mellitus, cardiac hypertrophy, platelet aggregation, and aging. Of note, the inhibition of NOX2 has been found to be protective for cardiovascular homeostasis. Here, we review the evidence demonstrating that the modulation of NOX2 activity is able to improve vascular physiology, suggesting that NOX2 may be a potential target for therapeutic applications.

Cerebral Small Vessel Disease: Targeting Oxidative Stress as a Novel Therapeutic Strategy?

Cerebral small vessel disease (SVD) is a major contributor to stroke, and a leading cause of cognitive impairment and dementia. Despite the devastating effects of cerebral SVD, the pathogenesis of cerebral SVD is still not completely understood. Moreover, there are no specific pharmacological strategies for its prevention or treatment. Cerebral SVD is characterized by marked functional and structural abnormalities of the cerebral microcirculation. The clinical manifestations of these pathological changes include lacunar infarcts, white matter hyperintensities, and cerebral microbleeds. The main purpose of this review is to discuss evidence implicating oxidative stress in the arteriopathy of both non-amyloid and amyloid (cerebral amyloid angiopathy) forms of cerebral SVD and its most important risk factors (hypertension and aging), as well as its contribution to cerebral SVD-related brain injury and cognitive impairment. We also highlight current evidence of the involvement of the NADPH oxidases in the development of oxidative stress, enzymes that are a major source of reactive oxygen species in the cerebral vasculature. Lastly, we discuss potential pharmacological strategies for oxidative stress in cerebral SVD, including some of the historical and emerging NADPH oxidase inhibitors.

Microvascular Dysfunction and Cognitive Impairment

The impact of vascular risk factors on cognitive function has garnered much interest in recent years. The appropriate distribution of oxygen, glucose, and other nutrients by the cerebral vasculature is critical for proper cognitive performance. The cerebral microvasculature is a key site of vascular resistance and a preferential target for small vessel disease. While deleterious effects of vascular risk factors on microvascular function are known, the contribution of this dysfunction to cognitive deficits is less clear. In this review, we summarize current evidence for microvascular dysfunction in brain. We highlight effects of select vascular risk factors (hypertension, diabetes, and hyperhomocysteinemia) on the pial and parenchymal circulation. Lastly, we discuss potential links between microvascular disease and cognitive function, highlighting current gaps in our understanding.

NADPH Oxidase Activity in Cerebral Arterioles Is a Key Mediator of Cerebral Small Vessel Disease-Implications for Prevention

Cerebral small vessel disease (SVD), a common feature of brain aging, is characterized by lacunar infarcts, microbleeds, leukoaraiosis, and a leaky blood-brain barrier. Functionally, it is associated with cognitive decline, dementia, depression, gait abnormalities, and increased risk for stroke. Cerebral arterioles in this syndrome tend to hypertrophy and lose their capacity for adaptive vasodilation. Rodent studies strongly suggest that activation of Nox2-dependent NADPH oxidase activity is a crucial driver of these structural and functional derangements of cerebral arterioles, in part owing to impairment of endothelial nitric oxide synthase (eNOS) activity. This oxidative stress may also contribute to the breakdown of the blood-brain barrier seen in SVD. Hypertension, aging, metabolic syndrome, smoking, hyperglycemia, and elevated homocysteine may promote activation of NADPH oxidase in cerebral arterioles. Inhibition of NADPH oxidase with phycocyanobilin from spirulina, as well as high-dose statin therapy, may have potential for prevention and control of SVD, and high-potassium diets merit study in this regard. Measures which support effective eNOS activity in other ways-exercise training, supplemental citrulline, certain dietary flavonoids (as in cocoa and green tea), and capsaicin, may also improve the function of cerebral arterioles. Asian epidemiology suggests that increased protein intakes may decrease risk for SVD; conceivably, arginine and/or cysteine-which boosts tissue glutathione synthesis, and can be administered as N-acetylcysteine-mediate this benefit. Ameliorating the risk factors for SVD-including hypertension, metabolic syndrome, hyperglycemia, smoking, and elevated homocysteine-also may help to prevent and control this syndrome, although few clinical trials have addressed this issue to date.

The role of oxidative stress and autophagy in atherosclerosis. Oxid Med Cell Longev. 2015;2015:130315. [PMID: 25866599 PMCID: PMC4381688 DOI: 10.1155/2015/130315]

Atherosclerosis is a multifactorial, multistep disorder of large- and medium-sized arteries involving, in addition to age, gender and menopausal status, a complex interplay between lifestyle and genetic risk factors. Atherosclerosis usually begins with the diffusion and retention of atherogenic lipoproteins into the subendothelial space of the artery wall where they become oxidized by local enzymes and accumulate, leading to the formation of a cushion called atheroma or atheromatous or fibrofatty plaque, composed of a mixture of macrophages, lymphocytes, smooth muscle cells (SMCs), cholesterol cleft, necrotic debris, and lipid-laden foam cells. The pathogenesis of atherosclerosis still remains incompletely understood but emerging evidence suggests that it may involve multiple cellular events, including endothelial cell (EC) dysfunction, inflammation, proliferation of vascular SMCs, matrix (ECM) alteration, and neovascularization. Actually, a growing body of evidence indicates that autophagy along with the chronic and acute overproduction of reactive oxygen species (ROS) is integral to the development and progression of the disease and may represent fruitful avenues for biological investigation and for the identification of new therapeutic targets. In this review, we give an overview of ROS and autophagy in atherosclerosis as background to understand their potential role in this vascular disease.

Melatonin receptor and KATP channel modulation in experimental vascular dementia

Cerebrovascular and cardiovascular diseases are stated as important risk factors of vascular dementia (VaD) and other cognitive disorders. In the central nervous system, melatonin (MT1/MT2) as well as serotonin subtype 2C (5-HT2C) receptors is pharmacologically associated with various neurological disorders. Brain mitochondrial potassium channels have been reported for their role in neuroprotection. This study has been structured to investigate the role of agomelatine, a melatonergic MT1/MT2 agonist and nicorandil, a selective ATP sensitive potassium (KATP) channel opener in renal artery ligation (two-kidney-one-clip: 2K1C) hypertension induced endothelial dysfunction, brain damage and VaD. 2K1C-renovascular hypertension has increased mean arterial blood pressure (MABP), impaired memory (elevated plus maze and Morris water maze), endothelial function, reduced serum nitrite/nitrate and increased brain damage (TTC staining of brain sections). Furthermore, 2K1C animals have shown high levels of oxidative stress in serum (increased thiobarbituric acid reactive species-TBARS with decreased levels of glutathione-GSH, superoxide dismutase-SOD and catalase-CAT), in the aorta (increased aortic superoxide anion) and in the brain (increased TBARS with decreased GSH, SOD and CAT). 2K1C has also induced a significant increase in brain inflammation (myeloperoxidase-MPO levels), acetylcholinesterase activity (AChE) and calcium levels. Impairment in mitochondrial complexes like NADH dehydrogenase (complex-I), succinate dehydrogenase (complex-II) and cytochrome oxidase (complex-IV) was also noted in 2K1C animals. Administration of agomelatine, nicorandil and donepezil significantly attenuated 2K1C-hypertension induced impairments in memory, endothelial function, nitrosative stress, mitochondrial dysfunction, inflammation and brain damage. Therefore, modulators of MT1/MT2 receptors and KATP channels may be considered as potential agents for the management of renovascular hypertension induced VaD.

The L-arginine pathway in acute ischemic stroke and severe carotid stenosis: temporal profiles and association with biomarkers and outcome

BACKGROUND

Endothelial dysfunction is associated with increased levels of asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) resulting in a decreased production of nitric oxide, which regulates the vascular tone.

METHODS

Patients with acute ischemic stroke (AIS, n = 55) and asymptomatic significant carotid stenosis (AsCS, n = 44) were prospectively investigated. L-arginine, ADMA, SDMA, S100 B, and high-sensitivity C-reactive protein (hsCRP) were serially measured within 6 hours after the onset of stroke, at 24 and 72 poststroke hours. All markers were compared with healthy subjects (n = 45). The severity of AIS was daily assessed by National Institute of Health Stroke Scale scoring.

RESULTS

Even within 6 hours after the onset of stroke, L-arginine, ADMA, and SDMA were significantly higher in patients with AIS compared with both AsCS and healthy subjects. S100 B reflecting infarct size, positively correlated with the level of SDMA at 72 poststroke hours; changes in concentration of S100 B positively correlated with changes in the concentration of ADMA by 72 hours. Change in concentration of both ADMA and SDMA correlated with the change in concentration of hsCRP. Concentrations of L-arginine and hsCRP at 72 poststroke hours, respectively, were independent predictors of poststroke infection. S100 B level measured within 6 hours after the onset of AIS and hsCRP at 72 poststroke hours were independent predictors of death.

CONCLUSIONS

Metabolites of the L-arginine pathway were elevated in the very acute phase of ischemic stroke indicating a more pronounced endothelial dysfunction compared with AsCS. An increased basal L-arginine level in patients with AIS might be an adaptive mechanism; such transient elevation of the L-arginine/ADMA ratio at 24 poststroke hours may suggest that a temporary increase of L-arginine along with decrease of ADMA might be related to the protective role of L-arginine. Changes in the L-arginine pathway are predictive of poststroke infections.

Mitochondrial regulation of NADPH oxidase in hindlimb unweighting rat cerebral arteries

Exposure to microgravity results in post-flight cardiovascular deconditioning and orthostatic intolerance in astronauts. Vascular oxidative stress injury and mitochondrial dysfunction have been indicated in this process. To elucidate the mechanism for this condition, we investigated whether mitochondria regulated NADPH oxidase in hindlimb unweighting (HU) rat cerebral and mesenteric arteries. Four-week HU was used to simulate microgravity in rats. Vascular superoxide generation, protein and mRNA levels of Nox2/Nox4, and the activity of NADPH oxidase were examined in the present study. Compared with control rats, the levels of superoxide increased in cerebral (P<0.001) but not in mesenteric vascular smooth muscle cells. The protein and mRNA levels of Nox2 and Nox4 were upregulated significantly (P<0.001 and P<0.001 for Nox2, respectively; P<0.001 and P<0.001 for Nox4, respectively) in HU rat cerebral arteries but not in mesenteric arteries. NADPH oxidases were activated significantly by HU (P<0.001) in cerebral arteries but not in mesenteric arteries. Chronic treatment with mitochondria-targeted antioxidant mitoTEMPO attenuated superoxide levels (P<0.001), decreased the protein and mRNA expression levels of Nox2/Nox4 (P<0.01 and P<0.05 for Nox2, respectively; P<0.001 and P<0.001 for Nox4, respectively) and the activity of NADPH oxidase (P<0.001) in HU rat cerebral arteries, but exerted no effects on HU rat mesenteric arteries. Therefore, mitochondria regulated the expression and activity of NADPH oxidases during simulated microgravity. Both mitochondria and NADPH oxidase participated in vascular redox status regulation.