State-of-the-Art lecture. Role of angiotensin and oxidative stress in essential hypertension

Macula Densa Nitric Oxide Synthase 1β Protects against Salt-Sensitive Hypertension

Nitric oxide (NO) is an important negative modulator of tubuloglomerular feedback responsiveness. We recently found that macula densa expresses α-, β-, and γ-splice variants of neuronal nitric oxide synthase 1 (NOS1), and NOS1β expression in the macula densa increases on a high-salt diet. This study tested whether upregulation of NOS1β expression in the macula densa affects sodium excretion and salt-sensitive hypertension by decreasing tubuloglomerular feedback responsiveness. Expression levels of NOS1β mRNA and protein were 30- and five-fold higher, respectively, than those of NOS1α in the renal cortex of C57BL/6 mice. Furthermore, macula densa NO production was similar in the isolated perfused juxtaglomerular apparatus of wild-type (WT) and nitric oxide synthase 1α-knockout (NOS1αKO) mice. Compared with control mice, mice with macula densa-specific knockout of all nitric oxide synthase 1 isoforms (MD-NOS1KO) had a significantly enhanced tubuloglomerular feedback response and after acute volume expansion, significantly reduced GFR, urine flow, and sodium excretion. Mean arterial pressure increased significantly in MD-NOS1KO mice (P<0.01) but not NOS1flox/flox mice fed a high-salt diet. After infusion of angiotensin II, mean arterial pressure increased by 61.6 mmHg in MD-NOS1KO mice versus 32.0 mmHg in WT mice (P<0.01) fed a high-salt diet. These results indicate that NOS1β is a primary NOS1 isoform expressed in the macula densa and regulates the tubuloglomerular feedback response, the natriuretic response to acute volume expansion, and the development of salt-sensitive hypertension. These findings show a novel mechanism for salt sensitivity of BP and the significance of tubuloglomerular feedback response in long-term control of sodium excretion and BP.

NMDA Receptor Plasticity in the Hypothalamic Paraventricular Nucleus Contributes to the Elevated Blood Pressure Produced by Angiotensin II

Hypertension induced by angiotensin II (Ang II) is associated with glutamate-dependent dysregulation of the hypothalamic paraventricular nucleus (PVN). Many forms of glutamate-dependent plasticity are mediated by NMDA receptor GluN1 subunit expression and the distribution of functional receptor to the plasma membrane of dendrites. Here, we use a combined ultrastructural and functional analysis to examine the relationship between PVN NMDA receptors and the blood pressure increase induced by chronic infusion of a low dose of Ang II. We report that the increase in blood pressure produced by a 2 week administration of a subpressor dose of Ang II results in an elevation in plasma membrane GluN1 in dendrites of PVN neurons in adult male mice. The functional implications of these observations are further demonstrated by the finding that GluN1 deletion in PVN neurons attenuated the Ang II-induced increases in blood pressure. These results indicate that NMDA receptor plasticity in PVN neurons significantly contributes to the elevated blood pressure mediated by Ang II.

Vitamin D cell signalling in health and disease

Vitamin D deficiency has been linked to many human diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), hypertension and cardiovascular disease. A Vitamin D phenotypic stability hypothesis, which is developed in this review, attempts to describe how this vital hormone acts to maintain healthy cellular functions. This role of Vitamin D as a guardian of phenotypic stability seems to depend on its ability to maintain the redox and Ca(2+) signalling systems. It is argued that its primary action is to maintain the expression of those signalling components responsible for stabilizing the low resting state of these two signalling pathways. This phenotypic stability role is facilitated through the ability of vitamin D to increase the expression of both Nrf2 and the anti-ageing protein Klotho, which are also major regulators of Ca(2+) and redox signalling. A decline in Vitamin D levels will lead to a decline in the stability of this regulatory signalling network and may account for why so many of the major diseases in man, which have been linked to vitamin D deficiency, are associated with a dysregulation in both ROS and Ca(2+) signalling.

Mechanisms and consequences of endothelial nitric oxide synthase dysfunction in hypertension

Reduced nitric oxide bioavailability contributes to endothelial dysfunction and hypertension. The endothelial isoform of nitric oxide synthase (eNOS) is responsible for the production of nitric oxide within the endothelium. Loss of eNOS cofactor tetrahydrobiopterin to initial increase in oxidative stress leads to uncoupling of eNOS, in which the enzyme produces superoxide anion rather than nitric oxide, further substantiating oxidative stress to induce vascular pathogenesis. The current review focuses on recent advances on the molecular mechanisms and consequences of eNOS dysfunction in hypertension, and potential novel therapeutic strategies restoring eNOS function to treat hypertension.

Novel role for retinol-binding protein 4 in the regulation of blood pressure

Elevated levels of serum retinol-binding protein 4 (RBP4) contribute to insulin resistance and correlate with increased prevalence of hypertension and myocardial infarction. We sought to determine whether lowering RBP4 would improve blood pressure (BP) and protect against obesity- or angiotensin (Ang)-II-induced hypertension. Systolic and diastolic BP were lower in the RBP4-knockout (RBP4-KO) mice and higher in the RBP4-overexpressing (RBP4-Tg) mice compared with BP in the wild-type (WT) littermates. Carbachol-induced vasodilatation was increased in arteries from the RBP4-KO compared with the WT mice and was impaired in the RBP4-Tg mice. Aortic eNOS(Ser1177) phosphorylation was enhanced ∼50% in the RBP4-KO mice, with no change in total eNOS protein. Feeding a high-fat diet increased BP in the RBP4-KO mice only to the level in the WT mice fed chow and had no effect on aortic eNOS(Ser1177) phosphorylation. Ang-II infusion resulted in 22 mmHg lower systolic BP in the RBP4-KO than in the WT mice, although the relative BP increase over saline infusion was ∼30% in both. Ang-II treatment decreased aortic eNOS(Ser1177) phosphorylation in the WT and RBP4-KO mice, but phosphorylation remained higher in the RBP4-KO mice. Cardiac hypertrophy with Ang-II treatment was diminished by 56% in the RBP4-KO mice. Thus, elevated serum RBP4 raises BP and lack of RBP4 reduces it, with commensurate changes in aortic eNOS(Ser1177) phosphorylation. Lowering RBP4 may reduce BP through enhanced eNOS-mediated vasodilatation and may be a novel therapeutic approach for hypertension.

NLRP3 inflammasome: from a danger signal sensor to a regulatory node of oxidative stress and inflammatory diseases

IL-1β production is critically regulated by cytosolic molecular complexes, termed inflammasomes. Different inflammasome complexes have been described to date.

While all inflammasomes recognize certain pathogens, it is the distinctive feature of NLRP3 inflammasome to be activated by many and diverse stimuli making NLRP3 the most versatile, and importantly also the most clinically implicated inflammasome. However, NLRP3 activation has remained the most enigmatic. It is not plausible that the intracellular NLRP3 receptor is able to detect all of its many and diverse triggers through direct interactions; instead, it is discussed that NLRP3 is responding to certain generic cellular stress-signals induced by the multitude of molecules that trigger its activation.

An ever increasing number of studies link the sensing of cellular stress signals to a direct pathophysiological role of NLRP3 activation in a wide range of autoinflammatory and autoimmune disorders, and thus provide a novel mechanistic rational, on how molecules trigger and support sterile inflammatory diseases. A vast interest has created to unravel how NLRP3 becomes activated, since mechanistic insight is the prerequisite for a knowledge-based development of therapeutic intervention strategies that specifically target the NLRP3 triggered IL-1β production. In this review, we have updated knowledge on NLRP3 inflammasome assembly and activation and on the pyrin domain in NLRP3 that could represent a drug target to treat sterile inflammatory diseases. We have reported mutations in NLRP3 that were found to be associated with certain diseases. In addition, we have reviewed the functional link between NLRP3 inflammasome, the regulator of cellular redox status Trx/TXNIP complex, endoplasmic reticulum stress and the pathogenesis of diseases such as type 2 diabetes. Finally, we have provided data on NLRP3 inflammasome, as a critical regulator involved in the pathogenesis of obesity and cardiovascular diseases.

Differential transcriptional activity of kidney genes in hypertensive ISIAH and normotensive WAG rats

Transcriptional activity of the kidney genes was compared in hypertensive ISIAH and normotensive WAG rats using the oligonucleotide microarray technique. Most of differentially expressed genes were downregulated in ISIAH kidney both in renal cortex and medulla. According to functional annotation the kidney function in ISIAH rats is based on altered expression of many genes working in stress-related mode. The alterations in gene expression are likely related to both pathophysiological and compensatory mechanisms. The further studies of genes differentially expressed in ISIAH and WAG kidney will help to reveal new hypertensive genes and mechanisms specific for stress-induced arterial hypertension.

Postmenopausal hypertension and sodium sensitivity

It has been well established that women generally have lower incidence rates of hypertension than men at similar ages and these differences may vary with age. It also has been observed in many studies that after menopause, blood pressure (BP) increases in women to levels even higher than in men. The lack of estrogens may not be suggested as the only component involved in the development of postmenopausal hypertension. Thus, in this mini-review, the possible mechanisms by which sex hormones may influence the BP are discussed. This review also examines the renal regulatory mechanisms for gender differences in BP and explores the effects of salt intake on BP (salt-sensitivity) in pre and post-menopausal women.

Estrogen has been shown to stimulate nitric oxide (NO) production, thus female sex hormones have a beneficial effect on BP control. Evidences that angiotensin type 2 receptor (AT₂R) is up-regulated by estrogen support the favorable effects on BPs in women than men. The kidney plays an integral role in the regulation of arterial pressure through the mechanism of pressure-natriuresis, which has been shown to be modulated by the RAS. The prevalence of salt-sensitivity increases with age and low-salt diets has shown to help reduce systolic BP (SBP) and diastolic BP. While oral hormone replacement therapy has yielded only a neutral or minimal effect on the elevation of SBP, both the transdermal route replacement and a novel progestin with anti-aldosterone activity (drospirenone) has also shown to reduce SBP.

Circulating purine compounds, uric acid, and xanthine oxidase/dehydrogenase relationship in essential hypertension and end stage renal disease

Purine nucleotide liberation and their metabolic rate of interconversion may be important in the development of hypertension and its renal consequences. In the present study, blood triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP) breakdown pathway was evaluated in relation to uric acid concentration and xanthine dehydrogenase/xanthine oxidase (XDH/XO) in patients with essential hypertension, patients with chronic renal diseases on dialysis, and control individuals. The pattern of nucleotide catabolism was significantly shifted toward catabolic compounds, including ADP, AMP, and uric acid in patients on dialysis program. A significant fall of ATP was more expressed in a group of patients on dialysis program, compared with the control value (p<0.001), while ADP and AMP were significantly increased in both groups of patients compared with control healthy individuals (p<0.001), together with their final degradation product, uric acid (p<0.001). The index of ATP/ADP and ATP/uric acid showed gradual significant fall in both the groups, compared with the control value (p<0.001), near five times in a group on dialysis. Total XOD was up-regulated significantly in a group with essential hypertension, more than in a group on dialysis. The activity of XO, which dominantly contributes reactive oxygen species (ROS) production, significantly increased in dialysis group, more than in a group with essential hypertension. In conclusion, the examination of the role of circulating purine nucleotides and uric acid in pathogenesis of hypertension and possible development of renal disease, together with XO role in ROS production, may help in modulating their liberation and ROS production in slowing progression from hypertension to renal failure.

Disparate effects of single endothelin-A and -B receptor blocker therapy on the progression of renal injury in advanced renovascular disease

We hypothesized that chronic specific endothelin (ET)-A receptor blockade therapy would reverse renal dysfunction and injury in advanced experimental renovascular disease. To test this, unilateral renovascular disease was induced in 19 pigs and after 6 weeks, single-kidney hemodynamics and function was quantified in vivo using computed-tomography. All pigs with renovascular disease were divided such that 7 were untreated, 7 were treated with ET-A blockers, and 5 were treated with ET-B blockers. Four weeks later, all pigs were re-studied in vivo, then euthanized and ex vivo studies performed on the stenotic kidney to quantify microvascular density, remodeling, renal oxidative stress, inflammation, and fibrosis. RBF, GFR, and redox status were significantly improved in the stenotic kidney after ET-A but not ET-B blockade. Furthermore, only ET-A blockade therapy reversed renal microvascular rarefaction and diminished remodeling, which was accompanied by a marked decreased in renal inflammatory and fibrogenic activity. Thus, ET-A but not ET-B blockade ameliorated renal injury in pigs with advanced renovascular disease by stimulating microvascular proliferation and decreasing the progression of microvascular remodeling, renal inflammation and fibrosis in the stenotic kidney. These effects were functionally consequential since ET-A blockade improved single kidney microvascular endothelial function, RBF, and GFR, and decreased albuminuria.

Enhanced expression and activity of Nox2 and Nox4 in the macula densa in ANG II-induced hypertensive mice

NAD(P)H oxidase (Nox)2 and Nox4 are the isoforms of Nox expressed in the macula densa (MD). MD-derived superoxide (O₂⁻), primarily generated by Nox2, is enhanced by acute ANG II stimulation. However, the effects of chronic elevations in ANG II during ANG II-induced hypertension on MD-derived O₂⁻ are unknown. We infused a slow pressor dose of ANG II (600 ng·min⁻¹·kg⁻¹) for 2 wk in C57BL/6 mice and found that mean arterial pressure was elevated by 22.3 ± 3.4 mmHg (P < 0.01). We measured O₂⁻ generation in isolated and perfused MDs and found that O₂⁻ generation by the MD was increased from 9.4 ± 0.9 U/min in control mice to 34.7 ± 1.8 U/min in ANG II-induced hypertensive mice (P < 0.01). We stimulated MMDD1 cells, a MD-like cell line, with ANG II and found that O₂⁻ generation increased from 921 ± 91 to 3,687 ± 183 U·min⁻¹·10⁵ cells⁻¹, which was inhibited with apocynin, oxypurinol, or NS-398 by 46%, 14%, and 12%, respectively. We isolated MD cells using laser capture microdissection and measured mRNA levels of Nox. Nox2 and Nox4 levels increased by 3.7 ± 0.17- and 2.6 ± 0.15-fold in ANG II-infused mice compared with control mice. In MMDD1 cells treated with Nox2 or Nox4 small interfering (si)RNAs, ANG II-stimulated O₂⁻ generation was blunted by 50% and 41%, respectively. In cells treated with p22(phox) siRNA, ANG II-stimulated O₂⁻ generation was completely blocked. In conclusion, we found that a subpressor dose of ANG II enhances O₂⁻ generation in the MD and that the sources of this O₂⁻ are primarily Nox2 and Nox4.

Hypertension: physiology and pathophysiology

Despite major advances in understanding the pathophysiology of hypertension and availability of effective and safe antihypertensive drugs, suboptimal blood pressure (BP) control is still the most important risk factor for cardiovascular mortality and is globally responsible for more than 7 million deaths annually. Short-term and long-term BP regulation involve the integrated actions of multiple cardiovascular, renal, neural, endocrine, and local tissue control systems. Clinical and experimental observations strongly support a central role for the kidneys in the long-term regulation of BP, and abnormal renal-pressure natriuresis is present in all forms of chronic hypertension. Impaired renal-pressure natriuresis and chronic hypertension can be caused by intrarenal or extrarenal factors that reduce glomerular filtration rate or increase renal tubular reabsorption of salt and water; these factors include excessive activation of the renin-angiotensin-aldosterone and sympathetic nervous systems, increased formation of reactive oxygen species, endothelin, and inflammatory cytokines, or decreased synthesis of nitric oxide and various natriuretic factors. In human primary (essential) hypertension, the precise causes of impaired renal function are not completely understood, although excessive weight gain and dietary factors appear to play a major role since hypertension is rare in nonobese hunter-gathers living in nonindustrialized societies. Recent advances in genetics offer opportunities to discover gene-environment interactions that may also contribute to hypertension, although success thus far has been limited mainly to identification of rare monogenic forms of hypertension.

Salt-sensitive hypertension in mitochondrial superoxide dismutase deficiency is associated with intra-renal oxidative stress and inflammation

BACKGROUND

Renal interstitial inflammation and oxidative stress are invariably present and play a key role in the pathogenesis of hypertension in experimental animals. Mitochondria are the major source of reactive oxygen species (ROS). ROS generated in the mitochondria are normally contained by the mitochondrial antioxidant system including manganese superoxide dismutase (MnSOD). We have previously shown that a high salt diet causes hypertension in MnSOD-deficient (MnSOD(+/-)) mice but not in wild-type mice. The present study was undertaken to determine the effect of a high salt diet on oxidative and inflammatory pathways in the kidneys of MnSOD(+/-) mice compared to the wild-type mice.

METHODS

Wild-type (MnSOD(+/+)) and MnSOD(+/-) mice were randomized to receive a regular or a high salt diet for 4 months. Tail arterial pressure was measured and timed urine collection was obtained. The animals were then euthanized and the kidneys were harvested and processed for histological examination and Western blot analyses.

RESULTS

In confirmation of our earlier study, a high salt diet resulted in a significant rise in arterial pressure and urinary albumin excretion in MnSOD(+/-) mice. This was accompanied by upregulation of NAD(P)H oxidase subunits, activation of nuclear factor kappa B, and elevation of PAI-1, iNOS, oxidized LDL receptor, and CD36 in the kidneys of the MnSOD(+/-) mice fed the high salt diet. In contrast, consumption of a high salt diet did not significantly alter blood pressure, urine protein excretion, or the measured oxidative and inflammatory mediators in the wild-type mice.

CONCLUSION

Salt-induced hypertension in MnSOD(+/-) mice is associated with activation of intra-renal inflammatory and ROS generating pathways.

Effects of traditional Chinese medicine Xin-Ji-Er-Kang formula on 2K1C hypertensive rats: role of oxidative stress and endothelial dysfunction

Background

XinJiErKang (XJEK), a Chinese herbal formula, is identified as an effective preparation to treat coronary heart disease and myocarditis. The aim of the study is to investigate the anti-hypertensive effects of XJEK by oral administration and also to find out whether the drug has any role in oxidative stress and vascular endothelial function.

Methods

Clipping of the renal artery resulted in gradual elevation of the systolic blood pressure (SBP) which reached a plateau after 4 weeks of surgery. Treatment of hypertensive rats (20 mmHg higher than basic systolic blood pressure) with XJEK (6, 12, 24 g/kg/day) and fosinopril (15 mg/kg/day) respectively by intragastric administration started 4 weeks after surgery and continued for 4 weeks. The sham-operated (Sh-Op) controls received drinking water. BP was monitored weekly using tail-cuff apparatus. At the end of 8 wk, left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP), rate of rise of left ventricular pressure (±dp/dtmax) were examined (PowerLab 8/30, AD Instruments, Australia). The myocardial hypertrophy index was expressed as heart weight/body weight (HW/BW), the histological changes were investigated by hematoxylin and eosin (HE) and Van Gieson (VG) stain. Endothelium-dependent relaxations due to acetylcholine were observed in isolated rat thoracic aortic ring preparation. Superoxide dismutase (SOD) activity, malondialdehyde (MDA) and nitric oxide (NO) content in serum, contents of hydroxyproline (Hyp) in the ventricular tissue were assayed by xanthin oxidase method, thiobarbituric acid (TBA) method, Griess method and alkaline hydrolysis method, respectively. Angiotensin II (Ang II) content in serum was detected by radioimmunoasssay method.

Results

XJEK therapy potently improved cardiac function, inhibited myocardial hypertrophy, improved cardiac pathology change, decreased the myocardial cross-section area (CSA), collagen volume fraction (CVF) and perivascular circumferential collagen area (PVCA), reduced the content of Hyp in the left ventricular tissue, inhibited the decrease of SOD activity and increase of MDA, Ang II content in serum. Moreover, treatment with XJEK improved endothelial dysfunction (ED) manifested by promoting endothelial-dependent vasodilation of thoracic aortic rings and enhancing the NO activity in serum.

Conclusions

These findings suggest that administration of XJEK possess protective effects against 2K1C induced hypertension and cardiac remodeling in rats, preserve NO activity and endothelial function.

Increased Prevalence of Hypertension in Young Adults with High Heteroplasmy Levels of the MELAS m.3243A>G Mutation

BACKGROUND

The pathophysiology of hypertension in patients with mitochondrial diseases is different from that of the general population. Growing evidence exists linking mtDNA, its mutations, and mitochondrial dysfunction to the pathogenesis of hypertension. No reports on the prevalence of hypertension in late-onset mtDNA diseases have been described.

METHODS

We performed a retrospective chart review of adult patients with late-onset mtDNA diseases between January 1999 and January 2012 at our center. We grouped them into age categories to allow comparison with previously reported Canadian Health Measures Survey (CHMS) prevalence data.

RESULTS

Twenty-three subjects with hypertension were identified for a crude prevalence of 39.7 % (95 % CI 27-53 %) as compared to the CHMS age-predicted prevalence of 30.5 %. When analyzed by individual age group, there were no significant differences between the observed and the CHMS predicted prevalence rates in the 40 years and older cohorts (age category 40-59, p = 0.63; age category 60-79, p = 0.85). However, hypertension rates were significantly higher than predicted in the under 40 years cohort (55.6 vs. 2.8 %, p < 0.001, CI 21-86 %), in which hypertensive patients with the MELAS m.3243A>G mutation were significantly clustered (p < 0.01). This younger MELAS cohort (n = 4, mean age = 24 years) with hypertension had heteroplasmy levels (mean = 68 %) that were significantly higher than the levels found in the older non-hypertensive MELAS cohort (n = 8, mean age = 52 years, mean = 33 %) (p = 0.04).

CONCLUSION

Relative to age, gender, and mtDNA disease subtype, young adults with high heteroplasmy levels of the MELAS m.3243A>G mutation demonstrate an increased prevalence of hypertension. Further prospective data are needed to confirm this initial finding, which has potentially important treatment implications.

Role of cellular L-arginine uptake and nitric oxide production on renal blood flow and arterial pressure regulation

PURPOSE OF REVIEW

L-Arginine (L-Arg) is the substrate for nitric oxide (NO) formation. Reduced NO bioavailability, particularly within the renal circulation, has been identified as a key factor in the pathogenesis of hypertension. This review focuses on the pathogenic role of abnormal L-Arg transport, particularly within the kidney, in hypertension.

RECENT FINDINGS

Most recent studies have attempted to restore NO bioavailability in cardiovascular diseases with the use of antioxidants to reduce NO inactivation, but this approach has failed to provide beneficial effects in the clinical setting. We argue that this may be due to reduced NO formation in hypertension, which has largely been overlooked as a means of restoring NO bioavailability in cardiovascular diseases. Recent data indicate that renal L-Arg transport plays an important role in regulating both renal perfusion and function and the long-term set point of arterial pressure in health. Perturbations in the renal L-Arg transport system can give rise to abnormal renal perfusion and function, initiating hypertension and related renal damage.

SUMMARY

Accordingly, we propose that L-Arg transporters are a new treatment target in hypertension and in disease states where renal NO bioavailability is disturbed.

Prolonged fasting activates Nrf2 in post-weaned elephant seals

Elephant seals naturally experience prolonged periods of absolute food and water deprivation (fasting). In humans, rats and mice, prolonged food deprivation activates the renin-angiotensin system (RAS) and increases oxidative damage. In elephant seals, prolonged fasting activates RAS without increasing oxidative damage likely due to an increase in antioxidant defenses. The mechanism leading to the upregulation of antioxidant defenses during prolonged fasting remains elusive. Therefore, we investigated whether prolonged fasting activates the redox-sensitive transcription factor Nrf2, which controls the expression of antioxidant genes, and if such activation is potentially mediated by systemic increases in RAS. Blood and skeletal muscle samples were collected from seals fasting for 1, 3, 5 and 7 weeks. Nrf2 activity and nuclear content increased by 76% and 167% at week 7. Plasma angiotensin II (Ang II) and transforming growth factor β (TGF-β) were 5000% and 250% higher at week 7 than at week 1. Phosphorylation of Smad2, an effector of Ang II and TGF signaling, increased by 120% at week 7 and by 84% in response to intravenously infused Ang II. NADPH oxidase 4 (Nox4) mRNA expression, which is controlled by smad proteins, increased 430% at week 7, while Nox4 protein expression, which can activate Nrf2, was 170% higher at week 7 than at week 1. These results demonstrate that prolonged fasting activates Nrf2 in elephant seals and that RAS stimulation can potentially result in increased Nox4 through Smad phosphorylation. The results also suggest that Nox4 is essential to sustain the hormetic adaptive response to oxidative stress in fasting seals.

Angiotensin-(1-7) modulates renin-angiotensin system associated with reducing oxidative stress and attenuating neuronal apoptosis in the brain of hypertensive rats

Angiotensin-(1-7) [Ang-(1-7)] has beneficial effects against hypertension-induced damage in heart and kidney, but its effects in brain are not clear as yet. The present study aimed to investigate the protective effects of Ang-(1-7) on the physiopathologic changes caused by hypertension in brain of spontaneously hypertensive rats (SHRs). Wistar-Kyoto rats received intracerebroventricular (I.C.V.) infusion of artificial cerebrospinal fluid (aCSF) while SHRs received I.C.V. infusion of Ang-(1-7), Mas receptor antagonist A-779 and aCSF for 4 weeks. Brain tissues were collected and analyzed by western blot, enzyme immunoassay, spectrophotometric assays and terminal deoxynucleotidyl transferase-mediated dUTP end-labeling (TUNEL) staining. Our study showed that infusion of Ang-(1-7) for 4 weeks significantly reduced the expression of Angiotensin II and Angiotensin II type 1 receptors in SHR brain. Additionally, it decreased the levels of malondialdehyde and elevated total superoxide dismutase activity, which was accompanied by reductions of NADPH oxidase subunit gp91(phox) and inducible nitric oxide synthase in the brain of SHR. The increases of the percentage of TUNEL-positive neurons and Bax to Bcl-2 ratio in SHR brain were also attenuated by Ang-(1-7). The anti-oxidative and anti-apoptosis effects of Ang-(1-7) are independent of blood pressure reduction and can be partially abolished by A-779. These findings suggest that chronic treatment with Ang-(1-7) is beneficial to attenuate hypertension-induced physiopathologic changes in brain and may be helpful to prevent hypertension-related cerebrovascular diseases.

Quercetin improves baroreflex sensitivity in spontaneously hypertensive rats

Quercetin is a well-known antioxidant. Here, we investigated the effects of treatment with quercetin on mean arterial pressure (MAP), heart rate (HR) and baroreflex sensitivity (BRS) in spontaneously hypertensive rats (SHR). SHR and their controls (WKY) were orally treated with quercetin (2, 10 or 25 mg/kg/day) or saline for seven days. On the 8th day, MAP and HR were recorded. BRS was tested using phenylephrine (8 mg/kg, i.v.) and sodium nitroprusside (25 mg/kg, i.v.). Oxidative stress was measured by tiobarbituric acid reactive species assay. The doses of 10 (n = 8) and 25 mg/kg (n = 8) were able to decrease the MAP in SHR (n = 9) (163 ± 4 and 156 ± 5 vs. 173 ± 6, respectively, p < 0.05) but not in WKY (117 ± 1 and 118 ± 2 vs. 113 ± 1, respectively, p < 0.05). The dose of 25 mg/kg/day increased the sensitivity of parasympathetic component of the baroreflex (−2.47 ± 0.31 vs. −1.25 ± 0.8 bpm/mmHg) and decreased serum oxidative stress in SHR (2.04 ± 0.17 vs. 3.22 ± 0.37 nmol/mL, n = 6). Our data suggest that treatment with quercetin reduces hypertension and improves BRS in SHR via reduction in oxidative stress.

Hypertension in postmenopausal women

Blood pressure is typically lower in premenopausal women than in men. However, after menopause, the prevalence of hypertension in women is higher than it is in men. Hypertension is a major risk factor for cardiovascular disease in women and men, but cardiovascular disease is the leading cause of death in women. Furthermore, there is evidence that blood pressure may not be as well-controlled in women as in men, despite the fact that most women adhere better to their therapeutic regimens and medications than do men, and have their blood pressures measured more frequently than do men. This review describes possible mechanisms by which blood pressure may be increased in postmenopausal women.

Clinical and molecular characterization of a Han Chinese family with high penetrance of essential hypertension

Mutations in mitochondrial DNA are associated with cardiovascular diseases. We reported here molecular characterization of a three-generation Han Chinese family with maternally transmitted hypertension. Most strikingly, this family exhibited a high penetrance of hypertension. Sequence analysis of mitochondrial genome showed the presence of 12,338T>C mutation and 12,330A>G mutation and distinct sets of polymorphisms belonging to the Asian haplogroup F2b. Interestingly, the well-known 12,338T>C mutation, which caused a change of methionine in the translational initiation codon of ND5, also localized in two nucleotides adjacent to the 3' end of tRNA(Leu(CUN)), was implied to cause a decrease in ND5 mRNA level as well as to alter tRNA(Leu(CUN)) stability level. Moreover, the highly conserved 12,330A>G mutation, which disrupted the base pairing (6T-67A) in acceptor arm of tRNA(Leu(CUN)), may result in the failure of tRNA(Leu(CUN)) metabolism. Therefore, the combination of ND5 12,338T>C and tRNA(Leu(CUN)) 12,330A>G mutations may contribute to the high penetrance of hypertension in this Chinese family.

Hyperbilirubinemia, augmentation of endothelial function, and decrease in oxidative stress in Gilbert syndrome

BACKGROUND

Patients with Gilbert syndrome have mild unconjugated hyperbilirubinemia. It has been shown that bilirubin is an endogenous antioxidant. We evaluated the role of oxidative stress in endothelial function in patients with Gilbert syndrome under normal conditions without cardiovascular risk factors.

METHODS AND RESULTS

A total of 108 young men with Gilbert syndrome without cardiovascular risk factors and 108 age-matched healthy men (normal controls) were enrolled in this study. Serum concentrations of bilirubin were higher in patients with Gilbert syndrome than in control subjects (29.2±11.6 versus 9.4±2.7 μmol/L; P<0.001). Serum concentrations of malondialdehyde-modified low-density lipoprotein and urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OHdG), as indices of oxidative stress, were lower in patients with Gilbert syndrome than in control subjects (61.8±24.5 versus 72.5±21.8 U/L, P=0.034; 7.8±2.4 versus 10.4±3.2 ng/mg creatinine, P=0.001, respectively). Flow-mediated vasodilation was greater in patients with Gilbert syndrome than in normal control subjects (7.2±2.2% versus 5.9±1.7%; P<0.001). Vascular responses to nitroglycerine were not significantly different between the 2 groups. Flow-mediated vasodilation correlated with serum concentration of bilirubin (r=0.44, P<0.001), malondialdehyde-modified low-density lipoprotein (r=-0.25, P=0.01), and urinary excretion of 8-OHdG (r=-0.27, P=0.004) in patients with Gilbert syndrome but not in control subjects. In addition, serum concentration of bilirubin correlated with malondialdehyde-modified low-density lipoprotein (r=-0.20, P=0.04) and 8-OHdG (r=-0.21, P=0.02) in patients with Gilbert syndrome but not in control subjects.

CONCLUSIONS

Patients with Gilbert syndrome had low levels of oxidative stress associated with hyperbilirubinemia and enhancement of endothelium-dependent vasodilation.

CLINICAL TRIAL REGISTRATION

URL: http://www.umin.ac.jp. Unique identifier: UMIN000003409.

Virtual patients and sensitivity analysis of the Guyton model of blood pressure regulation: towards individualized models of whole-body physiology

Mathematical models that integrate multi-scale physiological data can offer insight into physiological and pathophysiological function, and may eventually assist in individualized predictive medicine. We present a methodology for performing systematic analyses of multi-parameter interactions in such complex, multi-scale models. Human physiology models are often based on or inspired by Arthur Guyton's whole-body circulatory regulation model. Despite the significance of this model, it has not been the subject of a systematic and comprehensive sensitivity study. Therefore, we use this model as a case study for our methodology. Our analysis of the Guyton model reveals how the multitude of model parameters combine to affect the model dynamics, and how interesting combinations of parameters may be identified. It also includes a "virtual population" from which "virtual individuals" can be chosen, on the basis of exhibiting conditions similar to those of a real-world patient. This lays the groundwork for using the Guyton model for in silico exploration of pathophysiological states and treatment strategies. The results presented here illustrate several potential uses for the entire dataset of sensitivity results and the "virtual individuals" that we have generated, which are included in the supplementary material. More generally, the presented methodology is applicable to modern, more complex multi-scale physiological models.

Erectile dysfunction and hypertension: impact on cardiovascular risk and treatment

Erectile dysfunction (ED) is a common complaint in hypertensive men and can represent a systemic vascular disease, an adverse effect of antihypertensive medication or a frequent concern that may impair drug compliance. ED has been considered an early marker of cardiovascular disease. The connection between both conditions seems to be located in the endothelium, which may become unable to generate the necessary dilatation in penile vascular bed in response to sexual excitement, producing persistent impairment in erection. On the other hand, the real influence of antihypertensive drugs in erectile function still deserves discussion. Therefore, regardless of ED mechanism in hypertension, early diagnosis and correct approach of sexual life represent an important step of cardiovascular evaluation which certainly contributes for a better choice of hypertension treatment, preventing some complications and restoring the quality of life.

Spontaneously hypertensive rats develop pronounced hepatic steatosis induced by choline-deficient diet: Evidence for hypertension as a potential enhancer in non-alcoholic steatohepatitis

AIM

  Patients with non-alcoholic steatohepatitis (NASH) frequently have many co-morbidities including essential hypertension, which is reported to increase vascular production of reactive oxygen species (ROS) and alter the hepatic anti-oxidant defense system. Since ROS play a role in the pathogenesis of NASH, it is hypothesized that hypertension modulates the hepatic oxidative status and influences the development of NASH. The aim of this study was to investigate the potential effects of hypertension on the progression of NASH.

METHODS

  Spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats as normotensive controls were fed choline-deficient (CD) diet for 5 weeks. Histological changes, messenger RNA (mRNA) expression and thiobarbituric acid reactive substances (TBARS) levels in the liver were assessed in each group.

RESULTS

  Choline-deficient diet led to pronounced hepatic steatosis in SHR with an 8-fold increase of the hepatic triglyceride content, while there was no significant increase in WKY. These changes in SHR were associated with significant reduction in the expression of mRNA for peroxisome proliferator activated receptor α, acyl-CoA oxidase, microsomal triglyceride transfer protein, and apolipoprotein B100. Consistent with the significant reduction of hepatic superoxide dismutase activity and marked downregulation of the gene expression of hepatic antioxidant enzymes, the hepatic TBARS level and the plasma level of alanine aminotransferase were only increased in SHR on CD diet.

CONCLUSIONS

  Spontaneously hypertensive rats receiving CD diet showed severe hepatic steatosis associated with reduction of hepatic anti-oxidant capacity, leading to increased hepatic oxidative stress and tissue damage. Accordingly, hypertension might have a potential effect on the progression of NASH.

A randomly-controlled study on the cardiac function at the early stage of return to the plains after short-term exposure to high altitude

High altitude acclimatization and adaptation mechanisms have been well clarified, however, high altitude de-adaptation mechanism remains unclear. In this study, we conducted a controlled study on cardiac functions in 96 healthy young male who rapidly entered the high altitude (3700 m) and returned to the plains (1500 m) after 50 days. Ninety eight healthy male who remained at low altitude were recruited as control group. The mean pulmonary arterial pressure (mPAP), left ventricular ejection fraction (LVEF), left ventricular fraction shortening (LVFS), cardiac function index (Tei index) were tested. Levels of serum creatine kinase isoform MB (CK-MB), lactate dehydrogenase isoenzyme-1 (LDH-1), endothelin-1 (ET-1), nitrogen oxide (NO), serum hypoxia-inducible factor-1α (HIF-1α), 8-iso-prostaglandin F_2α (8-iso PGF_2α), superoxide dismutase (SOD) and malonaldehyde (MDA) were measured at an altitude of 3700 m and 1500 m respectively. The results showed that after short-term exposure to high altitude mPAP and Tei index increased significantly, while LVEF and LVFS decreased significantly. These changes were positively correlated with altitude. On the 15^th day after the subjects returned to low altitude, mPAP, LVEF and LVFS levels returned to the same level as those of the control subjects, but the Tei index in the returned subjects was still significantly higher than that in the control subjects (P<0.01). We also found that changes in Tei index was positively correlated with mPAP, ET-1, HIF-1α and 8-iso PGF_2α levels, and negatively correlated with the level of NO, LVEF, LVFS, CK-MB and LDH-1. These findings suggest that cardiac function de-adapts when returning to the plains after short-term exposure to high altitude and the function recovery takes a relatively long time.

Antenatal nicotine induces heightened oxidative stress and vascular dysfunction in rat offspring

BACKGROUND AND PURPOSE

Antenatal nicotine exposure causes aberrant vascular reactivity and increased blood pressure in adult male rat offspring in a sex-dependent manner. The present study tested the hypothesis that maternal nicotine administration increases the production of reactive oxygen species resulting in the vascular hypertensive reactivity in male offspring.

EXPERIMENTAL APPROACH

Nicotine was administered to pregnant rats via subcutaneous osmotic minipumps throughout the gestation. The vascular oxidative damage and dysfunction were determined in 5-month-old male offspring. Contraction studies were performed on isolated aortas and their expression of NADPH oxidase (Nox2)/gp91 and nox4 determined by Western blot analysis. In addition, oxidative damage in the vessel wall was determined by measuring malondialdehyde concentrations, vascular superoxide production and SOD activity.

KEY RESULTS

Antenatal nicotine significantly increased angiotensin II-induced arterial contractions in the offspring. The exaggerated vascular contractions were inhibited by both apocynin (a Nox inhibitor) and tempol (a SOD mimetic) in a concentration-dependent manner. In addition, ACh-induced relaxations were impaired in aortas isolated from the nicotine-treated offspring, which were restored by both apocynin and tempol in a concentration-dependent manner. The nicotine treatment significantly decreased the superoxide dismutase activity and increased malondialdehyde, superoxide and nitrotyrosine protein levels in the vascular wall. Consistently, antenatal nicotine exposure significantly enhanced the protein expression of NADPH oxidase Nox2/gp91, but not Nox4 in the aorta.

CONCLUSIONS AND IMPLICATIONS

The present findings suggest that antenatal nicotine exposure results in the programming of heightened oxidative stress and vascular hypertensive reactivity via a Nox2-dependent mechanism, leading to an increased risk of hypertension in adult offspring.

Coping with physiological oxidative stress: a review of antioxidant strategies in seals

While diving, seals are exposed to apnea-induced hypoxemia and repetitive cycles of ischemia/reperfusion. While on land, seals experience sleep apnea, as well as prolonged periods of food and water deprivation. Prolonged fasting, sleep apnea, hypoxemia and ischemia/reperfusion increase oxidant production and oxidative stress in terrestrial mammals. In seals, however, neither prolonged fasting nor apnea-induced hypoxemia or ischemia/reperfusion increase systemic or local oxidative damage. The strategies seals evolved to cope with increased oxidant production are reviewed in the present manuscript. Among these strategies, high antioxidant capacity and the oxidant-mediated activation of hormetic responses against hypoxia and oxidative stress are discussed. In addition to expanding our knowledge of the evolution of antioxidant defenses and adaptive responses to oxidative stress, understanding the mechanisms that naturally allow mammals to avoid oxidative damage has the potential to advance our knowledge of oxidative stress-induced pathologies and to enhance the translative value of biomedical therapies in the long term.

Evaluation of oxidative stress in children with congenital heart defects

BACKGROUND

A significant cause of death and chronic illness in childhood is caused by cardiovascular diseases, including congenital heart disease (CHD). This study aims to investigate the oxidative stress status and to establish its association with CHD in children.

METHODS

The study involves measurements of malondialdehyde (MDA), protein carbonyl (PCO), total anti-oxidant capacity, high-sensitive C-reactive protein (hs-CRP), fibrinogen and cytokine (interleukin [IL-6] and tumor necrosis factor-α) levels in 43 children with CHD and 30 healthy age-matched children.

RESULTS

MDA, PCO, hs-CRP, fibrinogen, IL-6 and tumor necrosis factor-α were significantly elevated while total anti-oxidant capacity was significantly declined in patients compared with the controls. MDA was positively correlated with PCO, hs-CRP, Qp/Qs and systolic pulmonary artery pressure. PCO was positively correlated with hs-CRP, fibrinogen, IL-6 and systolic pulmonary artery pressure.

CONCLUSION

Oxidative stress and its association with other markers in children with CHD was established. To the best of our knowledge, this is the first time that PCO has been used as a biomarker in CHD and it may be employed as a new diagnostic biomarker in CHD and in the assessment of its severity.

Novel paramagnetic AT1 receptor antagonists

Novel paramagnetic selective angiotensin AT(1) receptor antagonists (sartans) bearing nitroxides (3, 4) have been prepared and their pharmacology evaluated in vitro as well as in vivo. Compounds 3, 4 proved to be effective sartans with pK(B) estimates in the range 6.2-9.1. In addition, the sodium salt (11) of 4 (R = Bu) is able to protect against vascular injury in hypertensive rats as determined by its ability to attenuate the development of intimal thickening caused by balloon injury of the carotid artery.

Different impacts of cardiovascular risk factors on oxidative stress

The objective of the study was to evaluate oxidative stress (OS) status in subjects with different cardiovascular risk factors. With this in mind, we have studied three models of high cardiovascular risk: hypertension (HT) with and without metabolic syndrome, familial hypercholesterolemia (FH) and familial combined hyperlipidemia (FCH) with and without insulin resistance. Oxidative stress markers (oxidized/reduced glutathione ratio, 8-oxo-deoxyguanosine and malondialdehide) together with the activity of antioxidant enzyme triad (superoxide dismutase, catalase, glutathione peroxidase) and activation of both pro-oxidant enzyme (NAPDH oxidase components) and AGTR1 genes, as well as antioxidant enzyme genes (CuZn-SOD, CAT, GPX1, GSR, GSS and TXN) were measured in mononuclear cells of controls (n = 20) and patients (n = 90) by assessing mRNA levels. Activity of some of these antioxidant enzymes was also tested. An increase in OS and pro-oxidant gene mRNA values was observed in patients compared to controls. The hypertensive group showed not only the highest OS values, but also the highest pro-oxidant activation compared to those observed in the other groups. In addition, in HT a significantly reduced antioxidant activity and mRNA induction of antioxidant genes were found when compared to controls and the other groups. In FH and FCH, the activation of pro-oxidant enzymes was also higher and antioxidant ones lower than in the control group, although it did not reach the values obtained in hypertensives. The thioredoxin system was more activated in patients as compared to controls, and the highest levels were in hypertensives. The increased oxidative status in the presence of cardiovascular risk factors is a consequence of both the activation of pro-oxidant mechanisms and the reduction of the antioxidant ones. The altered response of the main cytoplasmic antioxidant systems largely contributes to OS despite the apparent attempt of the thioredoxin system to control it.

Postmenopausal hypertension

Cardiovascular disease is the leading cause of morbidity and mortality in postmenopausal women. Hypertension is a major risk factor for cardiovascular disease. The mechanisms responsible for postmenopausal hypertension have not been completely elucidated. However, various mechanisms have been implicated to play a role. For example, there is evidence that changes in estrogen/androgen ratios favoring increases in androgens, activation of the renin-angiotensin and endothelin systems, activation of the sympathetic nervous system, metabolic syndrome and obesity, inflammation, increased vasoconstrictor eicosanoids, and anxiety and depression may be important in the pathogenesis of postmenopausal hypertension. There is also evidence that hypertension is less well controlled in aging women than in aging men, but the reasons for this gender difference is not clear. Postmenopausal hypertension is likely multifactorial. Future studies will be necessary to determine the contribution of these systems listed above in mediating postmenopausal hypertension and to design treatment strategies that encompass these mechanisms to improve the quality of life of postmenopausal women as they age.

The tRNAMet 4435A>G mutation in the mitochondrial haplogroup G2a1 is responsible for maternally inherited hypertension in a Chinese pedigree

Mutations in mitochondrial DNA (mtDNA) have been associated with hypertension in several pedigrees with maternal inheritance. However, the pathophysiology of maternally inherited hypertension remains poorly understood. We reported here clinical, genetic evaluations and molecular analysis of mtDNA in a three-generation Han Chinese family with essential hypertension. Eight of 17 matrilineal relatives exhibited a wide range of severity in essential hypertension, whereas none of the offsprings of the affected father had hypertension. The age-at-onset of hypertension in the maternal kindred varied from 31 to 65 years, with an average of 52 years. Sequence analysis of mtDNA in this pedigree identified the known homoplasmic 4435A>G mutation, which is located at immediately 3' end to the anticodon, corresponding to the conventional position 37 of tRNA(Met), and 41 variants belonging to the Asian haplogroup G2a1. In contrast, the 4435A>G mutation occurred among mtDNA haplogroups B5a, D, M7a2 and J. The adenine (A37) at this position of tRNA(Met) is extraordinarily conserved from bacteria to human mitochondria. This modified A37 was shown to contribute to the high fidelity of codon recognition, structural formation and stabilization of functional tRNAs. However, 41 other mtDNA variants in this pedigree were the known polymorphisms. The occurrence of the 4435A>G mutation in two genetically unrelated families affected by hypertension indicates that this mutation is involved in hypertension. Our present investigations further supported our previous findings that the 4435A>G mutation acted as an inherited risk factor for the development of hypertension. Our findings will be helpful for counseling families of maternally inherited hypertension.

Ginkgo biloba extract (EGb 761) normalizes hypertension in 2K, 1C hypertensive rats: role of antioxidant mechanisms, ACE inhibiting activity and improvement of endothelial dysfunction

The 2 kidney, 1-clip (2K, 1C) model of hypertension was used to investigate the potential antihypertensive effect of a standardized leaf extract of Ginkgo biloba (EGb 761). Clipping of the renal artery resulted in gradual elevation of the systolic blood pressure (SBP) reaching a plateau after 4 weeks of surgery. Treatment of hypertensive rats with EGb 761 (60, 90, 180 mg/kg/day orally) was therefore started 4 weeks after surgery and continued for 3 weeks. This led to a dose-dependent reduction in SBP with no significant change in heart rate. Control hypertensive rats showed a significant elevation of total protein thiols (Pr-SHs level) in both clipped and non-clipped kidneys as well as in the serum. However, glutathione peroxidase (GSH-Px) activity was decreased in the clipped kidneys but elevated in the non-clipped ones and in the blood. The malondialdehyde (MDA) level was raised in clipped kidneys but not in non-clipped ones nor in the serum. Nitric oxide (NO level) and angiotensin converting enzyme (ACE) activity were increased in both clipped and non-clipped kidneys but not in the serum. Endothelium-dependent and -independent relaxation of aortic rings towards acetylcholine (Ach) and sodium nitroprusside (SNP) were impaired. Treatment with EGb 761 (180 mg/kg/day for 3 weeks) was associated with recovery of GSH-Px activity in clipped kidneys, inhibition of ACE activity in both kidneys and a reduction in the elevated NO level of the non-clipped kidneys, decreased responsiveness to the vasoconstrictor NE and improvement of endothelial function as evidenced by restoration of endothelium-dependent vasorelaxation induced by Ach. The observed beneficial effects of the EGb 761 may be attributed to different factors, including ACE inhibition and maintenance of cellular antioxidant capacity as well as preserving vascular reactivity towards endothelium-dependent and -independent vasodilators while inhibiting responses to vasoconstrictors.

Mitochondrial aldehyde dehydrogenase prevents ROS-induced vascular contraction in angiotensin-II hypertensive mice

Mitochondrial aldehyde dehydrogenase (ALDH2) is an enzyme that detoxifies aldehydes to carboxylic acids. ALDH2 deficiency is known to increase oxidative stress, which is the imbalance between reactive oxygen species (ROS) generation and antioxidant defense activity. Increased ROS contribute to vascular dysfunction and structural remodeling in hypertension. We hypothesized that ALDH2 plays a protective role to reduce vascular contraction in angiotensin-II (AngII) hypertensive mice. Endothelium-denuded aortic rings from C57BL6 mice, treated with AngII (3.6 μg/kg/min, 14 days), were used to measure isometric force development. Rings treated with daidzin (10 μmol/L), an ALDH2 inhibitor, potentiated contractile responses to phenylephrine (PE) in AngII mice. Tempol (1 mmol/L) and catalase (600 U/mL) attenuated the augmented contractile effect of daidzin. In normotensive mice, contraction to PE in the presence of the daidzin was not different from control, untreated values. AngII aortic rings transfected with ALDH2 recombinant protein decreased contractile responses to PE compared with control. These data suggest that ALDH2 reduces vascular contraction in AngII hypertensive mice. Because tempol and catalase blocked the contractile response of the ALDH2 inhibitor, ROS generation by AngII may be decreased by ALDH2, thereby preventing ROS-induced contraction.

Polymorphisms of antioxidant enzymes, blood pressure and risk of hypertension

OBJECTIVE

To assess the association of single-nucleotide polymorphisms (SNPs) in genes codifying for antioxidant enzymes to blood pressure (BP) values and risk of hypertension.

METHODS

Population-based study including 1388 participants (704 women) older than 18 years in which 300 were untreated hypertensive patients. In 335 untreated hypertensive patients referred to one hypertension clinic, the study was replicated. Thirty-five SNP throughout 13 genes were analyzed using SNPlex. In a subgroup of hypertensive patients, the amount of 8-oxo-deoxyguanosine and GPX activity levels was measured in mononuclear cells.

RESULTS

In the general population, genotypes with the G allele of the c.172G>A polymorphism in the SOD3 gene and those with the T allele of the c.-20C>T polymorphism in the CAT gene were associated with significant lower values of BP. Likewise, these genotypes were associated with less risk for hypertension after adjusting for confounder variables. Haplotypes in both genes increased the strength of associations. In the hypertensive patients, the same alleles of the two polymorphisms were associated with lower BP values too. In addition, two others, the CT-TT genotypes of the c.891C>T polymorphism in the GPX1 gene and the CT-CC genotypes of the c.-793T>C polymorphism of the TXN gene were also significantly associated to lower BP values. Furthermore, the CC genotype of the c.891C>T polymorphism in the GPX1 gene was associated with higher values of 8-oxo-dG and GPX activity levels as compared to those for the CT-TT genotype.

CONCLUSIONS

The results of the present study support the influence of antioxidant enzyme genes in BP values and hypertension risk.

F2-isoprostanes as an indicator and risk factor for coronary heart disease

Coronary heart disease (CHD) is the leading single cause of death in the United States and most Western countries, killing more than 400,000 Americans per year. Although CHD often manifests suddenly as a fatal myocardial infarction, the atherosclerosis that gives rise to the infarction develops gradually and can be markedly slowed or even reversed through pharmacological and lifestyle interventions. These same atherosclerotic processes also drive related vascular diseases such as stroke and peripheral artery disease, and individuals surviving occlusive events often develop additional complications including ischemic cardiomyopathy and heart failure. Therefore, better detection of subclinical atherosclerosis, along with more effective treatments, could significantly reduce the rate of death from CHD and related vascular diseases in the United States. In recent years, oxidation of polyunsaturated fatty acids (PUFAs) in plasma lipoproteins has been postulated to be a critical step in the development of atherosclerosis. If so, then monitoring lipid peroxidation should be a useful indicator of disease risk and progression. This review focuses on the evidence that specific PUFA peroxidation products, the F(2)-isoprostanes, are useful biomarkers that could potentially be utilized as indicators of CHD.

Central Pressure and Biomarker Responses to Renin Inhibition with Hydrochlorothiazide and Ramipril in Obese Hypertensives: The ATTAIN Study

BACKGROUND/AIMS

In obese, hypertensive subjects, the renin-angiotensin system (RAS) is enhanced and natriuresis impaired, suggesting a role for combination RAS blockade with diuretics. Data suggest that renin inhibition may attenuate diuretic-induced RAS activation and oxidative stress.

METHODS

In this 8-week, double-blind study of 386 obese individuals (mean body mass index: 35.3) with stage 2 hypertension (mean age: 54.9 years; mean sitting systolic blood pressure, SBP: ≧160 but <200 mm Hg), we compared the efficacy of aliskiren + hydrochlorothiazide (HCTZ) in reducing blood pressure (BP), plasma renin activity (PRA), and a urinary marker of oxidative stress to ramipril. Subjects were randomized to aliskiren/HCTZ 150/12.5 mg or ramipril 5 mg for 1 week, and after the 1st week force titrated to aliskiren/HCTZ 300/25 mg or ramipril 10 mg for 7 weeks.

RESULTS

After 8 weeks, aliskiren/HCTZ provided greater reductions in office BP than ramipril (-28.1/-10.1 vs. -16.6/-3.6 mm Hg, p < 0.0001) as well as 24-hour ambulatory and central pressure measures. Aliskiren/HCTZ also lowered PRA (-45 vs. +83%) and the urinary F2-isoprostane/creatinine ratio (-18 vs. +7%) to a greater extent than ramipril. Adverse events (AEs) were similar in the two groups (35.8% with aliskiren/HCTZ vs. 37.3% on ramipril reporting at least one AE).

CONCLUSIONS

Our findings suggest that the aliskiren/HCTZ combination reduced BP, PRA, and isoprostanes to a greater extent than did ramipril in obese patients with stage 2 hypertension.

Vascular structure and oxidative stress in salt-loaded spontaneously hypertensive rats: effects of losartan and atenolol

BACKGROUND

Renin-angiotensin system (RAS) modulation by high dietary sodium may contribute to salt-induced hypertension, oxidative stress, and target organ damage. We investigated whether angiotensin II (Ang-II) type 1 (AT1)-receptor blockade (losartan) could protect the aorta and renal arteries from combined hypertension- and high dietary salt-related oxidative stress.

METHODS

Spontaneously hypertensive rats (3-month-old, n = 10/group) received tap water (SHR), water containing 1.5% NaCl (SHR+S), 1.5% NaCl and 30 mg losartan/kg/day (SHR+S+L), or 50 mg atenolol/kg/day (SHR+S+A). Atenolol was used for comparison. Ten Wistar-Kyoto rats (WKY) were controls. Systolic blood pressure (SBP) was determined by tail plethysmography. After 5 months of treatment, vascular remodeling and oxidative stress (superoxide production and NAD(P)H-oxidase activity (chemiluminescence), malondialdehyde (MDA) content (high-performance liquid chromatography), endothelial nitric oxide synthase (eNOS) activity [(14)C-arginine to (14)C citrulline], CuZn-SOD activity (spectrophotometry)) were studied.

RESULTS

In SHR, salt-loading significantly aggravated hypertension, urinary protein excretion, intraparenchymal renal artery (IPRArt) perivascular fibrosis, aortic and renal artery oxidative stress, and induced endothelial cell loss in IPRArts. In salt-loaded SHR, 5-month losartan and atenolol treatments similarly reduced SBP, but only losartan significantly prevented (i) urinary protein excretion increase, (ii) or attenuated hypertension-related vascular remodeling, (iii) aortic MDA accumulation, (iv) renal artery eNOS activity lowering, and (v) aortic and renal artery superoxide dismutase (SOD) activity reduction. In SHR+S, the contributions to aortic superoxide production were as follows: uncoupled eNOS > xanthine oxidase (XO) > NAD(P)H oxidase.

CONCLUSIONS

In this salt-sensitive genetic hypertension model, losartan protects from hypertension- and high dietary salt-related vascular oxidative stress, exceeding the benefits of BP reduction. Also, during salt overload, BP-independent factors contribute to vascular remodeling, at least part of which derive from AT1-receptor activation.

Angiotensin II induced cerebral microvascular inflammation and increased blood-brain barrier permeability via oxidative stress

Although hypertension has been implicated in the pathogenesis of vascular disease, its role in inflammatory responses, especially in brain, remains unclear. In this study we found key mechanisms by which angiotensin II (AngII) mediates cerebral microvascular inflammation. C57BL/6 male mice were subjected to slow-pressor dose of AngII infusion using osmotic mini-pumps at a rate of 400 ng/kg/min for 14 days. Vascular inflammation in the brain was evaluated by analysis of leukocyte-endothelial interaction and blood-brain barrier (BBB) permeability. Results from intravital microscopy of pial vessels in vivo, revealed a 4.2 fold (P<0.05, compared to vehicle) increase in leukocyte adhesion on day 4 of AngII infusion. This effect persisted through day 14 of AngII infusion, which resulted in a 2.6 fold (P<0.01, compared to vehicle) increase in leukocyte adhesion. Furthermore, evaluation of BBB permeability by Evans Blue extravasation showed that Ang II significantly affected the BBB, inducing 3.8 times (P<0.05, compared to vehicle) higher permeability. Previously we reported that AngII mediated hypertension promotes oxidative stress in the vasculature. Thus, we used the superoxide scavenger; 4-hydroxy-TEMPO (Tempol) to determine whether AngII via oxidative stress could contribute to higher leukocyte adhesion and increased BBB permeability. Tempol was given via drinking water (2 mmol) on day 4th following Ang II infusion, since oxidative stress increases in this model on day 4. Treatment with Tempol significantly attenuated the increased leukocyte/endothelial interactions and protected the BBB integrity on day 14 of AngII infusion. In conclusion, AngII via oxidative stress increases cerebral microvasculature inflammation and leads to greater immune-endothelial interaction and higher BBB permeability. This finding may open new avenues for the management of nervous system pathology involving cerebrovascular inflammation.

Role of reactive oxygen species in hyperadrenergic hypertension: biochemical, physiological, and pharmacological evidence from targeted ablation of the chromogranin a (Chga) gene

BACKGROUND

Oxidative stress, an excessive production of reactive oxygen species (ROS) outstripping antioxidant defense mechanisms, occurs in cardiovascular pathologies, including hypertension. In the present study, we used biochemical, physiological, and pharmacological approaches to explore the role of derangements of catecholamines, ROS, and the endothelium-derived relaxing factor nitric oxide (NO(•)) in the development of a hyperadrenergic model of hereditary hypertension: targeted ablation (knockout [KO]) of chromogranin A (Chga) in the mouse.

METHODS AND RESULTS

Homozygous ⁻(/)⁻ Chga gene knockout (KO) mice were compared with wild-type (WT, +/+) control mice. In the KO mouse, elevations of systolic and diastolic blood pressure were accompanied by not only elevated catecholamine (norepinephrine and epinephrine) concentrations but also increased ROS (H₂O₂) and isoprostane (an index of lipid peroxidation), as well as depletion of NO(•). Renal transcript analyses implicated changes in Nox1/2, Xo/Xdh, and Sod1,2 mRNAs in ROS elevation by the KO state. KO alterations in blood pressure, catecholamines, H₂O₂, isoprostane, and NO(•) could be abrogated or even normalized (rescued) by either sympathetic outflow inhibition (with clonidine) or NADPH oxidase inhibition (with apocynin). In cultured renal podocytes, H₂O₂ production was substantially augmented by epinephrine (probably through β₂-adrenergic receptors) and modestly diminished by norepinephrine (probably through α₁-adrenergic receptors).

CONCLUSIONS

ROS appear to play a necessary role in the development of hyperadrenergic hypertension in this model, in a process mechanistically linking elevated blood pressure with catecholamine excess, renal transcriptional responses, ROS elevation, lipid peroxidation, and NO(•) depletion. Some of the changes appear to be dependent on transcription, whereas others are immediate. The cycle could be disrupted by inhibition of either sympathetic outflow or NADPH oxidase. Because common genetic variation at the human CHGA locus alters BP, the results have implications for antihypertensive treatment as well as prevention of target-organ consequences of the disease. The results document novel pathophysiological links between the adrenergic system and oxidative stress and suggest new strategies to probe the role and actions of ROS within this setting.