Reactive oxygen species, NADPH oxidases, and hypertension

Angiotensin II-dependent hypertension requires cyclooxygenase 1-derived prostaglandin E2 and EP1 receptor signaling in the subfornical organ of the brain

Cyclooxygenase (COX)-derived prostanoids have long been implicated in blood pressure (BP) regulation. Recently prostaglandin E(2) (PGE(2)) and its receptor EP(1) (EP(1)R) have emerged as key players in angiotensin II (Ang II)-dependent hypertension (HTN) and related end-organ damage. However, the enzymatic source of PGE(2,) that is, COX-1 or COX-2, and its site(s) of action are not known. The subfornical organ (SFO) is a key forebrain region that mediates systemic Ang II-dependent HTN via reactive oxygen species (ROS). We tested the hypothesis that cross-talk between PGE(2)/EP(1)R and ROS signaling in the SFO is required for Ang II HTN. Radiotelemetric assessment of blood pressure revealed that HTN induced by infusion of systemic "slow-pressor" doses of Ang II was abolished in mice with null mutations in EP(1)R or COX-1 but not COX-2. Slow-pressor Ang II-evoked HTN and ROS formation in the SFO were prevented when the EP(1)R antagonist SC-51089 was infused directly into brains of wild-type mice, and Ang-II-induced ROS production was blunted in cells dissociated from SFO of EP(1)R(-/-) and COX-1(-/-) but not COX-2(-/-) mice. In addition, slow-pressor Ang II infusion caused a ≈3-fold increase in PGE(2) levels in the SFO but not in other brain regions. Finally, genetic reconstitution of EP(1)R selectively in the SFO of EP(1)R-null mice was sufficient to rescue slow-pressor Ang II-elicited HTN and ROS formation in the SFO of this model. Thus, COX 1-derived PGE(2) signaling through EP(1)R in the SFO is required for the ROS-mediated HTN induced by systemic infusion of Ang II and suggests that EP(1)R in the SFO may provide a novel target for antihypertensive therapy.

The link between angiotensin II-mediated anxiety and mood disorders with NADPH oxidase-induced oxidative stress

The renin-angiotensin system (RAS) and its active peptide angiotensin II (AngII) have major involvements not only in hypertension but also in mood and anxiety disorders. Substantial evidence supports the notion that AngII acts as a neuromodulator in the brain. In this review, we provide an overview of the link between the RAS and anxiety or mood disorders, and focus on recent advances in the understanding of AngII-linked, NADPH oxidase-derived oxidative stress in the central nervous system, which may underlie pathogenesis of mood and anxiety disorders.

Chronic exercise preserves renal structure and hemodynamics in spontaneously hypertensive rats

AIMS

Exercise training (ExT) is a recommended adjunct to many pharmaceutical antihypertensive therapies. The effects of chronic ExT on the development of hypertension-induced renal injury remain unknown. We examined whether ExT would preserve renal hemodynamics and structure in the spontaneously hypertensive rat (SHR), and whether these effects were mediated by improved redox status and decreased inflammation. Normotensive WKY rats and SHR underwent moderate-intensity ExT for 16 weeks. One group of SHR animals was treated with hydralazine to investigate the pressure-dependent/independent effects of ExT. Acute renal clearance experiments were performed prior to sacrifice. Tissue free radical production rates were measured by electron paramagnetic resonance; gene and protein expression were measured by real time RT-PCR and Western blot or immunofluorescence, respectively. Plasma angiotensin II levels and kidney antioxidants were assessed. Training efficacy was assessed by citrate synthase activity assay in hind-limb muscle.

RESULTS

ExT delayed hypertension, prevented oxidative stress and inflammation, preserved antioxidant status, prevented an increase in circulating AngII levels, and preserved renal hemodynamics and structure in SHR. In addition, exercise-induced effects, at least, in part, were found to be pressure-independent.

INNOVATION

This study is the first to provide mechanistic evidence for the renoprotective benefits of ExT in a model of hypertension. Our results demonstrate that initiation of ExT in susceptible patients can delay the development of hypertension and provide renoprotection at the functional and ultrastructural level.

CONCLUSION

Chronic ExT preserves renal hemodynamics and structure in SHR; these effects are partially mediated by improved redox status and decreased inflammation.

Asymmetric dimethylarginine and reactive oxygen species: unwelcome twin visitors to the cardiovascular and kidney disease tables

Plasma levels of asymmetric dimethylarginine or markers of reactive oxygen species are increased in subjects with risk factors for cardiovascular disease or chronic kidney disease. We tested the hypothesis that reactive oxygen species generate cellular asymmetric dimethylarginine that together cause endothelial dysfunction that underlies the risk of subsequent disease. Rat preglomerular vascular smooth muscle cells transfected with p22(phox) had increased NADPH oxidase activity, enhanced activity and expression of protein arginine methyltransferase, and reduced activity and protein expression of dimethylarginine dimethylaminotransferase and of cationic amino acid transferase 1 resulting in increased cellular levels of asymmetric dimethylarginine. Rats infused with angiotensin II had oxidative stress. The endothelial function of their mesenteric arterioles was changed from vasodilatation to vasoconstriction, accompanied by increased vascular asymmetric dimethylarginine. All of these changes were prevented by Tempol. In vivo silencing of dimethylarginine dimethylaminotransferase 1 increased plasma levels of asymmetric dimethylarginine, whereas silencing of dimethylarginine dimethylaminotransferase 2 impaired endothelial function. We suggest that initiation factors, such as angiotensin II, expressed in blood vessels or tissues of subjects with cardiovascular and kidney disease risk factors generate reactive oxygen species from NADPH oxidase that enhances cellular asymmetric dimethylarginine in an amplification loop. This leads to adverse changes in vascular and organ functions, as a consequence of reduced tissue levels of NO and increased reactive oxygen species. Thus, we conclude that reactive oxygen species and asymmetric dimethylarginine form a tightly coupled amplification system that translates cardiovascular/kidney risk into overt disease.

Differential roles of NADPH oxidases in vascular physiology and pathophysiology

Reactive oxygen species (ROS) are produced by all vascular cells and regulate the major physiological functions of the vasculature. Production and removal of ROS are tightly controlled and occur in discrete subcellular locations, allowing for specific, compartmentalized signaling. Among the many sources of ROS in the vessel wall, NADPH oxidases are implicated in physiological functions such as control of vasomotor tone, regulation of extracellular matrix and phenotypic modulation of vascular smooth muscle cells. They are involved in the response to injury, whether as an oxygen sensor during hypoxia, as a regulator of protein processing, as an angiogenic stimulus, or as a mechanism of wound healing. These enzymes have also been linked to processes leading to disease development, including migration, proliferation, hypertrophy, apoptosis and autophagy. As a result, NADPH oxidases participate in atherogenesis, systemic and pulmonary hypertension and diabetic vascular disease. The role of ROS in each of these processes and diseases is complex, and a more full understanding of the sources, targets, cell-specific responses and counterbalancing mechanisms is critical for the rational development of future therapeutics.

Increased oxidative stress, the renin-angiotensin system, and sympathetic overactivation induce hypertension in kidney androgen-regulated protein transgenic mice

Gender differences in the incidence and severity of hypertension have suggested the involvement of a sex-dependent mechanism. Transgenic (Tg) mice overexpressing kidney androgen-regulated protein (KAP) specifically in kidney showed hypertension associated with oxidative stress. Reactive oxygen species (ROS) are strongly implicated in the pathological signaling leading to hypertension in a framework that includes renin-angiotensin system (RAS) activation, increased sympathetic activity, and cardiac remodeling. In this report, we observed that plasma levels of angiotensin II and catecholamines were increased in KAP Tg mice, compared with wild-type animals. Systemic administration of Tempol, a membrane-permeative superoxide dismutase mimetic, reduced arterial pressure as well as urinary excretion of oxidative stress markers and reduced both angiotensin II and norepinephrine plasma levels in KAP Tg mice. Intracerebroventricular administration of Tempol also reduced arterial pressure in Tg mice. Moreover, administration of apocynin and DPI, inhibitors of NADPH oxidase, a major source of ROS, also reduced arterial pressure and both angiotensin II and norepinephrine plasma levels in Tg mice. Thus, we analyzed the involvement of the RAS and sympathetic nervous system in KAP Tg mouse hypertension. Both captopril and losartan reduced arterial blood pressure in Tg mice, as also occurred after β-adrenergic blockade with atenolol. Also, intracerebroventricular losartan administration reduced arterial pressure in KAP Tg mice. Our data demonstrate that hypertension in male KAP Tg mice is based on increased oxidative stress, increased sympathetic activity, and RAS activation. Moreover, our results suggest a role for increased oxidative stress in the CNS as a major cause of hypertension in these animals.

LOX-1 and angiotensin receptors, and their interplay

The renin-angiotensin system (RAS) plays an important role in regulating blood pressure, water-salt balance and the pathogenesis of cardiovascular diseases. Angiotensin II (Ang II) is the physiologically active mediator and mediates the main pathophysiological actions in RAS. Ang II exerts the effects by activating its receptors, primarily type 1 (AT1R) and type 2 (AT2R). Most of the known pathophysiological effects of Ang II are mediated by AT1R activation. The precise physiological function of AT2R is still not clear. Generally, AT2R is considered to oppose the effects of AT1R. Lectin-like oxidized low-density lipoprotein scavenger receptor-1 (LOX-1) is one of the major receptors responsible for binding, internalizing and degrading ox-LDL. The activation of LOX-1 has been known to be related to many pathophysiological events, including endothelial dysfunction and injury, fibroblast growth, and vascular smooth muscle cell hypertrophy. Many of these alterations are present in atherosclerosis, hypertension, and myocardial ischemia and remodeling. A growing body of evidence suggests the existence of a cross-talk between LOX-1 and Ang II receptors. Their interplays are embodied in the reciprocal regulation of their expression and activity. Their interplays are involved in a series of signals. Recent studies suggests that reactive oxygen species (ROS), nitric oxide (NO), protein kinase C (PKC) and mitogen activated protein kinases (MAPKs) are important signals responsible for their cross-talk. This paper reviews these aspects of dyslipidemia and RAS activation.

The mitochondrial paradigm for cardiovascular disease susceptibility and cellular function: a complementary concept to Mendelian genetics

While there is general agreement that cardiovascular disease (CVD) development is influenced by a combination of genetic, environmental, and behavioral contributors, the actual mechanistic basis of how these factors initiate or promote CVD development in some individuals while others with identical risk profiles do not, is not clearly understood. This review considers the potential role for mitochondrial genetics and function in determining CVD susceptibility from the standpoint that the original features that molded cellular function were based upon mitochondrial-nuclear relationships established millions of years ago and were likely refined during prehistoric environmental selection events that today, are largely absent. Consequently, contemporary risk factors that influence our susceptibility to a variety of age-related diseases, including CVD were probably not part of the dynamics that defined the processes of mitochondrial-nuclear interaction, and thus, cell function. In this regard, the selective conditions that contributed to cellular functionality and evolution should be given more consideration when interpreting and designing experimental data and strategies. Finally, future studies that probe beyond epidemiologic associations are required. These studies will serve as the initial steps for addressing the provocative concept that contemporary human disease susceptibility is the result of selection events for mitochondrial function that increased chances for prehistoric human survival and reproductive success.

Endothelial progenitor cells relationships with clinical and biochemical factors in a human model of blunted angiotensin II signaling

Angiotensin II (Ang II) is essential for endothelial progenitor cells (EPCs) function as Ang-II-induced oxidative stress causes senescence of EPCs and endothelial dysfunction and Ang II type 1 receptor blockers increase EPCs. Moreover, EPCs activity is dependent on nitric oxide (NO) and heme oxygenase (HO)-1 as these correlate with EPCs senescence and are reduced in hypertensives. Bartter's/Gitelman's syndrome patients (BS/GS), have increased Ang II yet normo/hypotension along with blunted Ang II signaling, reduced oxidative stress, increased NO and HO-1, thus presenting a unique system to explore EPC biology and its relationship with vascular clinical and biochemical correlates. Circulating EPCs, NO-dependent vasodilation (flow-mediated dilation (FMD)) and HO-1 gene expression were characterized in 10 BS/GS patients and in 10 normotensive subjects. EPCs defined by cell surface antigens CD34+kinase-insert domain receptor (KDR+), CD133+KDR+ and CD133+CD34+KDR+ cells were quantitiated via direct three-color flow-cytometry analysis, HO-1 gene expression by reverse transcription-PCR and FMD by B-mode echo scan of the right brachial artery. Correlation analysis was carried out regarding FMD and EPCs, FMD and HO-1 and EPCs and HO-1. In BS/GS, CD34+KDR+ cell numbers did not differ from controls while CD133+KDR+ and CD133+CD34+KDR+ cell numbers were higher. HO-1 gene expression, as well as FMD, was higher in BS/GS compared with controls. Both CD133+KDR+ and CD133+CD34+KDR+ strongly correlated with both FMD and HO-1. FMD and HO-1 were also strongly correlated. These results document in a human system that EPC numbers and specific populations are related to important clinical and biochemical factors involved in cardiovascular (CV) status and reaffirm the utility of BS/GS patients as a useful system to investigate EPC's role(s) in the pathophysiology of cardiovascular remodeling in humans.

Effect of olmesartan on oxidative stress in hypertensive patients: mechanistic support to clinical trials derived evidence

The role of oxidative stress in the pathophysiology of hypertension and target organ damage is widely recognized. Using a molecular biology approach, we report, in essential hypertensive patients, the effect of the angiotensin II type 1 receptor blocker olmesartan on the mononuclear cell (PBMC) protein expression of major elements in the oxidative stress and vascular remodeling-related pathways, p22(phox) and HO-1, along with the phosphorylation state of ERK1/2 and plasma oxidized low-density lipoproteins (oxLDL). Twenty untreated essential hypertensive patients (range blood pressure: 142?156/94?98 mmHg) were treated with olmesartan medoxomil (20 mg/day for 6 months) and blood samples collected at baseline, 3 and 6 months for PBMC p22(phox) and HO-1 protein expression, phosphorylation state of ERK1/2 (western blot) and oxLDL level (ELISA) evaluations. Olmesartan normalized blood pressure since the third month (149 ? 4.7/94.88 ? 1.9 mmHg vs 137.89 ? 2.08/88.44 ? 2.0 at 3 months and vs 135.44 ? 2.18/85.78 ? 1.2 at 6 months, analysis of variance: p < 0.001). p22(phox) protein level declined at 3 months (7.10 ? 2.61 vs 9.32 ? 2.43 densitometric units (d.u.; p < 0.001), further declining at 6 months (4.55 ? 1.26 d.u., p < 0.001). HO-1 levels increased at 3 months (10.87 ? 1.92 vs 7.70 ? 0.71 d.u., p = 0.001) and remained elevated (11.11 ? 1.89 d.u., p = 0.001), without further increase at 6 months. Phosphorylated ERK1/2 declined at 3 months (3.94 ? 1.44 vs 5.62 ? 1.11 d.u., p = 0.001), further declining at 6 months (1.94 ? 0.87, p < 0.001). oxLDL significantly declined at 3 and 6 months. These results demonstrate that olmesartan inhibits oxidative stress. Given the involvement of oxidative stress and its signaling in atherogenesis, and the available evidence of olmesartan's vasoprotective, anti-inflammatory and antiatherosclerotic effects derived from clinical trials in humans, the results of our study provide a mechanistic rationale for the omelsartan's antioxidant and anti-inflammatory potential translation, in the long term, toward the antiatherosclerotic and antiremodeling effects reported on the clinical ground.

Reactive oxygen species (ROS) from NADPH and xanthine oxidase modulate the cutaneous local heating response in healthy humans

Local cutaneous heating produces vasodilation that is largely nitric oxide (NO) dependent. We showed that angiotensin II (ANG II) attenuates this by an ANG II receptor, type 1 (AT1R)-dependent mechanism that is reversible with the antioxidant ascorbate, indicating oxidative stress. Reactive oxygen species (ROS) produced by ANG II employ NADPH and xanthine oxidase pathways. To determine whether these mechanisms pertain to skin, we measured cutaneous local heating with 10 μM ANG II, using apocynin to inhibit NADPH oxidase and allopurinol to inhibit xanthine oxidase. We also inhibited superoxide with tempol, and H(2)O(2) with ebselen. We heated the skin of the calf in 8 healthy volunteers (24.5-29.9 yr old) to 42°C and measured local blood flow to assess the percentage of maximum cutaneous vascular conductance. We remeasured while perfusing allopurinol, apocynin, ebselen, and tempol through individual microdialysis catheters. This was then repeated with ANG II combined with antioxidant drugs. tempol and apocynin alone had no effect on the heat response. Allopurinol enhanced the entire response (125% of heat alone), while ebselen suppressed the heat plateau (76% of heat alone). ANG II alone caused significant attenuation of the entire heat response (52%). When added to ANG II, Allopurinol partially reversed the ANG II attenuation. Heat with ebselen and ANG II were similar to heat and ANG II; ebselen only partially reversed the ANG II attenuation. Apocynin and tempol each partially reversed the attenuation caused by ANG II. This suggests that ROS, produced by ANG II via NADPH and xanthine oxidase pathways, modulates the response of skin to the application of heat, and thus contributes to the control of local cutaneous blood flow.

NAD(P)H oxidase and renal epithelial ion transport

A fundamental requirement for cellular vitality is the maintenance of plasma ion concentration within strict ranges. It is the function of the kidney to match urinary excretion of ions with daily ion intake and nonrenal losses to maintain a stable ionic milieu. NADPH oxidase is a source of reactive oxygen species (ROS) within many cell types, including the transporting renal epithelia. The focus of this review is to describe the role of NADPH oxidase-derived ROS toward local renal tubular ion transport in each nephron segment and to discuss how NADPH oxidase-derived ROS signaling within the nephron may mediate ion homeostasis. In each case, we will attempt to identify the various subunits of NADPH oxidase and reactive oxygen species involved and the ion transporters, which these affect. We will first review the role of NADPH oxidase on renal Na(+) and K(+) transport. Finally, we will review the relationship between tubular H(+) efflux and NADPH oxidase activity.