Rhian M. Touyz

Correction of Arterial Structure and Endothelial Dysfunction in Human Essential Hypertension by the Angiotensin Receptor Antagonist Losartan

BACKGROUND Structural and functional alterations of the vasculature may contribute to complications of hypertension. Because angiotensin II may be pivotal in some of these vascular abnormalities, we tested the hypothesis that the angiotensin type 1 (AT(1)) receptor antagonist losartan, in contrast to the beta-blocker atenolol, would correct resistance artery abnormalities in patients with essential hypertension. METHODS AND RESULTS Nineteen untreated patients with mild essential hypertension (47+/-2 years, range 30 to 65 years; 57% male) were randomly assigned in double-blind fashion to losartan or atenolol treatment for 1 year. Nine age/sex-matched normotensive subjects were also studied. Both treatments reduced blood pressure to a comparable degree (losartan, from 149+/-4.1/101+/-1.6 to 128+/-3.6/86+/-2.2 mm Hg, P<0.01; atenolol, from 150+/-4.0/99+/-1.2 to 130+/-3.2/84+/-1.4 mm Hg, P<0.01). Resistance arteries (luminal diameter 150 to 350 microm) dissected from gluteal subcutaneous biopsies were studied on a pressurized myograph. After 1 year of treatment, the ratio of the media width to lumen diameter of arteries from losartan-treated patients was significantly reduced (from 8.4+/-0.4% to 6.7+/-0.3%, P<0.01). Arteries from atenolol-treated patients exhibited no significant change (from 8. 3+/-0.3% to 8.8+/-0.5% after treatment). Endothelium-dependent relaxation (acetylcholine-induced) was normalized by losartan (from 82.1+/-4.9% to 94.7+/-1.1%, P<0.01) but not by atenolol (from 80. 4+/-2.7% to 81.7+/-4.6%). Endothelium-independent relaxation (by sodium nitroprusside) was unchanged after treatment. CONCLUSIONS The AT(1) antagonist losartan corrected the altered structure and endothelial dysfunction of resistance arteries from patients with essential hypertension, whereas the beta-blocker atenolol had no effect.

Expression of a Functionally Active gp91phox-Containing Neutrophil-Type NAD(P)H Oxidase in Smooth Muscle Cells From Human Resistance Arteries Regulation by Angiotensin II

A major source of vascular smooth muscle cell (VSMC) superoxide is NAD(P)H oxidase. However, the molecular characteristics and regulation of this enzyme are unclear. We investigated whether VSMCs from human resistance arteries (HVSMCs) possess a functionally active, angiotensin II (Ang II)–regulated NAD(P)H oxidase that contains neutrophil oxidase subunits, including p22phox, gp91phox, p40phox, p47phox, and p67phox. mRNA expression of gp91phox homologues, nox1 and nox4, was also assessed in HVSMCs, human aortic smooth muscle cells, and rat VSMCs. HVSMCs were obtained from resistance arteries from gluteal biopsies of healthy subjects. gp91phox and nox4, but not nox1, were detected in HVSMCs. Nox1 and nox4, but not gp91phox, were expressed in human aortic smooth muscle cells and rat VSMCs. All NAD(P)H oxidase subunits were present in HVSMCs as detected by reverse transcriptase–polymerase chain reaction and immunoblotting. Ang II increased NAD(P)H oxidase subunit abundance. These effects were inhibited by cycloheximide. Acute Ang II stimulation (10 to 15 minutes) increased p47phox serine phosphorylation and induced p47phox and p67phox translocation. This was associated with NAD(P)H oxidase activation. In cells transfected with gp91phox antisense oligonucleotides, Ang II–mediated actions were abrogated. NADPH-induced superoxide generation was reduced by gp91ds-tat and apocynin, inhibitors of p47phox-gp91phox interactions. Our results suggest that HVSMCs possess a functionally active gp91phox-containing neutrophil-like NAD(P)H oxidase. Ang II regulates the enzyme by inducing phosphorylation of p47phox, translocation of cytosolic subunits, and de novo protein synthesis. These novel findings provide insight into the molecular regulation of NAD(P)H oxidase by Ang II in HVSMCs. Furthermore, we identify differences in gp91phox homologue expression in VSMCs from rats and human small and large arteries.

The 2009 Canadian Hypertension Education Program recommendations for the management of hypertension: Part 2 – therapy

OBJECTIVE To update the evidence-based recommendations for the prevention and management of hypertension in adults for 2009. OPTIONS AND OUTCOMES For lifestyle and pharmacological interventions, evidence from randomized controlled trials and systematic reviews of trials was preferentially reviewed. Changes in cardiovascular morbidity and mortality were the primary outcomes of interest. However, for lifestyle interventions, blood pressure lowering was accepted as a primary outcome given the lack of long-term morbidity and mortality data in this field. Progression of kidney dysfunction was also accepted as a clinically relevant primary outcome among patients with chronic kidney disease. EVIDENCE A Cochrane collaboration librarian conducted an independent MEDLINE search from 2007 to August 2008 to update the 2008 recommendations. To identify additional published studies, reference lists were reviewed and experts were contacted. All relevant articles were reviewed and appraised independently by both content and methodological experts using prespecified levels of evidence. RECOMMENDATIONS For lifestyle modifications to prevent and treat hypertension, restrict dietary sodium to less than 2300 mg (100 mmol)/day (and 1500 mg to 2300 mg [65 mmol to 100 mmol]/day in hypertensive patients); perform 30 min to 60 min of aerobic exercise four to seven days per week; maintain a healthy body weight (body mass index 18.5 kg/m(2) to 24.9 kg/m(2)) and waist circumference (smaller than 102 cm for men and smaller than 88 cm for women); limit alcohol consumption to no more than 14 units per week in men or nine units per week in women; follow a diet that is reduced in saturated fat and cholesterol, and that emphasizes fruits, vegetables and low-fat dairy products, dietary and soluble fibre, whole grains and protein from plant sources; and consider stress management in selected individuals with hypertension. For the pharmacological management of hypertension, treatment thresholds and targets should be predicated on by the patients global atherosclerotic risk, target organ damage and comorbid conditions. Blood pressure should be decreased to lower than 140/90 mmHg in all patients, and to lower than 130/80 mmHg in those with diabetes mellitus or chronic kidney disease. Most patients will require more than one agent to achieve these target blood pressures. Antihypertensive therapy should be considered in all adult patients regardless of age (caution should be exercised in elderly patients who are frail). For adults without compelling indications for other agents, initial therapy should include thiazide diuretics. Other agents appropriate for first-line therapy for diastolic and/or systolic hypertension include angiotensin- converting enzyme (ACE) inhibitors (in patients who are not black), long-acting calcium channel blockers (CCBs), angiotensin receptor antagonists (ARBs) or beta-blockers (in those younger than 60 years of age). A combination of two first-line agents may also be considered as the initial treatment of hypertension if the systolic blood pressure is 20 mmHg above the target or if the diastolic blood pressure is 10 mmHg above the target. The combination of ACE inhibitors and ARBs should not be used. Other agents appropriate for first-line therapy for isolated systolic hypertension include long- acting dihydropyridine CCBs or ARBs. In patients with angina, recent myocardial infarction or heart failure, beta-blockers and ACE inhibitors are recommended as first-line therapy; in patients with cerebrovascular disease, an ACE inhibitor/diuretic combination is preferred; in patients with proteinuric nondiabetic chronic kidney disease, ACE inhibitors or ARBs (if intolerant to ACE inhibitors) are recommended; and in patients with diabetes mellitus, ACE inhibitors or ARBs (or, in patients without albuminuria, thiazides or dihydropyridine CCBs) are appropriate first-line therapies. All hypertensive patients with dyslipidemia should be treated using the thresholds, targets and agents outlined in the Canadian Cardiovascular Society position statement (recommendations for the diagnosis and treatment of dyslipidemia and prevention of cardiovascular disease). Selected high-risk patients with hypertension who do not achieve thresholds for statin therapy according to the position paper should nonetheless receive statin therapy. Once blood pressure is controlled, acetylsalicylic acid therapy should be considered. VALIDATION All recommendations were graded according to strength of the evidence and voted on by the 57 members of the Canadian Hypertension Education Program Evidence-Based Recommendations Task Force. All recommendations reported here achieved at least 95% consensus. These guidelines will continue to be updated annually.

Clinical practice guidelines for the management of hypertension in the community a statement by the American Society of Hypertension and the International Society of Hypertension.

Clinical Practice Guidelines for the Management of Hypertension in the Community A Statement by the American Society of Hypertension and the International Society of Hypertension

NADPH Oxidases, Reactive Oxygen Species, and Hypertension Clinical implications and therapeutic possibilities

Reactive oxygen species (ROS) influence many physiological processes including host defense, hormone biosynthesis, fertilization, and cellular signaling. Increased ROS production (termed “oxidative stress”) has been implicated in various pathologies, including hypertension, atherosclerosis, diabetes, and chronic kidney disease. A major source for vascular and renal ROS is a family of nonphagocytic NAD(P)H oxidases, including the prototypic Nox2 homolog-based NAD(P)H oxidase, as well as other NAD(P)H oxidases, such as Nox1 and Nox4. Other possible sources include mitochondrial electron transport enzymes, xanthine oxidase, cyclooxygenase, lipoxygenase, and uncoupled nitric oxide synthase. NAD(P)H oxidase-derived ROS plays a physiological role in the regulation of endothelial function and vascular tone and a pathophysiological role in endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, fibrosis, angiogenesis, and rarefaction, important processes underlying cardiovascular and renal remodeling in hypertension and diabetes. These findings have evoked considerable interest because of the possibilities that therapies against nonphagocytic NAD(P)H oxidase to decrease ROS generation and/or strategies to increase nitric oxide (NO) availability and antioxidants may be useful in minimizing vascular injury and renal dysfunction and thereby prevent or regress target organ damage associated with hypertension and diabetes. Here we highlight current developments in the field of reactive oxygen species and cardiovascular disease, focusing specifically on the recently identified novel Nox family of NAD(P)H oxidases in hypertension. We also discuss the potential role of targeting ROS as a therapeutic possibility in the management of hypertension and cardiovascular disease.

Reactive oxygen species in vascular biology: implications in hypertension

Reactive oxygen species (ROS), including superoxide (·O2−), hydrogen peroxide (H2O2), and hydroxyl anion (OH-), and reactive nitrogen species, such as nitric oxide (NO) and peroxynitrite (ONOO−), are biologically important O2 derivatives that are increasingly recognized to be important in vascular biology through their oxidation/reduction (redox) potential. All vascular cell types (endothelial cells, vascular smooth muscle cells, and adventitial fibroblasts) produce ROS, primarily via cell membrane-associated NAD(P)H oxidase. Reactive oxygen species regulate vascular function by modulating cell growth, apoptosis/anoikis, migration, inflammation, secretion, and extracellular matrix protein production. An imbalance in redox state where pro-oxidants overwhelm anti-oxidant capacity results in oxidative stress. Oxidative stress and associated oxidative damage are mediators of vascular injury and inflammation in many cardiovascular diseases, including hypertension, hyperlipidemia, and diabetes. Increased generation of ROS has been demonstrated in experimental and human hypertension. Anti-oxidants and agents that interrupt NAD(P)H oxidase-driven ·O2− production regress vascular remodeling, improve endothelial function, reduce inflammation, and decrease blood pressure in hypertensive models. This experimental evidence has evoked considerable interest because of the possibilities that therapies targeted against reactive oxygen intermediates, by decreasing generation of ROS and/or by increasing availability of antioxidants, may be useful in minimizing vascular injury and hypertensive end organ damage. The present chapter focuses on the importance of ROS in vascular biology and discusses the role of oxidative stress in vascular damage in hypertension.

Spironolactone Improves Angiotensin-Induced Vascular Changes and Oxidative Stress

Abstract—Angiotensin II plays an important role in vascular remodeling. We investigated the role of aldosterone, which is stimulated by angiotensin II, as a mediator of angiotensin II–induced vascular structural and functional alterations. Sprague-Dawley rats (n=8 to 12/group) received angiotensin II (120 ng/kg per minute, subcutaneously) for 14 days ± spironolactone or hydralazine (25 mg/kg per day). An additional group received aldosterone (750 ng/h, subcutaneously) ± spironolactone. Systolic blood pressure was increased by angiotensin II (P <0.001) and reduced by spironolactone and hydralazine (P <0.001). Aldosterone-induced increase of blood pressure was reduced by spironolactone (P <0.05). In mesenteric small arteries studied on a pressurized myograph, media/lumen ratio was increased (P <0.001) and acetylcholine-mediated relaxation was impaired in angiotensin II–infused rats (P <0.001); both were partially improved by spironolactone (P <0.05) but not by hydralazine. Aldosterone-induced increase of media/lumen ratio (P <0.001) and impaired response to acetylcholine (P <0.001) were normalized by spironolactone. Response to sodium nitroprusside was similar in all groups. Aortic NADPH oxidase activity was increased (P <0.01) by angiotensin II and reduced by spironolactone and hydralazine. Aldosterone also increased (P <0.05) activation of NADPH oxidase, an effect abolished by spironolactone. Plasma thiobarbituric acid–reactive substances (a marker of oxidative stress), higher in angiotensin II and aldosterone rats (P <0.001), were normalized by spironolactone. In conclusion, spironolactone, which inhibited aldosterone actions, partially corrected structural and functional angiotensin II–induced abnormalities. These effects were associated with reduced vascular NADPH oxidase activity and decreased plasma markers of oxidative stress. Our findings suggest that aldosterone may mediate some of angiotensin II–induced vascular effects in hypertension, in part via increased oxidative stress.

Clinical practice guidelines for the management of hypertension in the community: a statement by the American Society of Hypertension and the International Society of Hypertension.

Michael A. Weber, MD; Ernesto L. Schiffrin, MD; William B. White, MD; Samuel Mann, MD; Lars H. Lindholm, MD; John G. Kenerson, MD; John M. Flack, MD; Barry L. Carter, Pharm D; Barry J. Materson, MD; C. Venkata S. Ram, MD; Debbie L. Cohen, MD; Jean-Claude Cadet, MD; Roger R. Jean-Charles, MD; Sandra Taler, MD; David Kountz, MD; Raymond R. Townsend, MD; John Chalmers, MD; Agustin J. Ramirez, MD; George L. Bakris, MD; Jiguang Wang, MD; Aletta E. Schutte, MD; John D. Bisognano, MD; Rhian M. Touyz, MD; Dominic Sica, MD; Stephen B. Harrap, MD

The 2008 Canadian Hypertension Education Program recommendations for the management of hypertension: Part 1 - blood pressure measurement, diagnosis and assessment of risk.

OBJECTIVE To provide updated, evidence-based recommendations for the diagnosis and assessment of adults with hypertension. OPTIONS AND OUTCOMES The diagnosis of hypertension is dependent on appropriate blood pressure measurement, the timely assessment of serially elevated readings, degree of blood pressure elevation, method of measurement (office, ambulatory, home) and associated comorbidities. The presence of cardiovascular risk factors and target organ damage should be ascertained to assess global cardiovascular risk and determine the urgency, intensity and type of treatment required. EVIDENCE MEDLINE searches were conducted from November 2006 to October 2007 with the aid of a medical librarian. Reference lists were scanned, experts were contacted, and the personal files of authors and subgroup members were used to identify additional studies. Content and methodological experts assessed studies using prespecified, standardized evidence-based algorithms. Recommendations were based on evidence from peer-reviewed, full-text articles only. RECOMMENDATIONS Recommendations for blood pressure measurement, criteria for hypertension diagnosis and follow-up, assessment of global cardiovascular risk, diagnostic testing, diagnosis of renovascular and endocrine causes of hypertension, home and ambulatory monitoring, and the use of echocardiography in hypertensive individuals are outlined. Key messages in 2008 include continued emphasis on the expedited, accurate diagnosis of hypertension, the importance of global risk assessment and the need for ongoing monitoring of hypertensive patients to identify incident type 2 diabetes. VALIDATION All recommendations were graded according to strength of the evidence and voted on by the 57 members of the Canadian Hypertension Education Program Evidence-Based Recommendations Task Force. All recommendations reported here received at least 70% consensus. These guidelines will continue to be updated annually.

Angiotensin-(1-7) Through Receptor Mas Mediates Endothelial Nitric Oxide Synthase Activation via Akt-Dependent Pathways

Angiotensin-(1-7) [Ang-(1-7)] causes endothelial-dependent vasodilation mediated, in part, by NO release. However, the molecular mechanisms involved in endothelial NO synthase (eNOS) activation by Ang-(1-7) remain unknown. Using Chinese hamster ovary cells stably transfected with Mas cDNA (Chinese hamster ovary-Mas), we evaluated the underlying mechanisms related to receptor Mas–mediated posttranslational eNOS activation and NO release. We further examined the Ang-(1-7) profile of eNOS activation in human aortic endothelial cells, which constitutively express the Mas receptor. Chinese hamster ovary-Mas cells and human aortic endothelial cell were stimulated with Ang-(1-7; 10−7 mol/L; 1 to 30 minutes) in the absence or presence of A-779 (10−6 mol/L). Additional experiments were performed in the presence of the phosphatidylinositol 3-kinase inhibitor wortmannin (10−6 mol/L). Changes in eNOS (at Ser1177/Thr495 residues) and Akt phosphorylation were evaluated by Western blotting. NO release was measured using both the fluorochrome 2,3-diaminonaphthalene and an NO analyzer. Ang-(1-7) significantly stimulated eNOS activation (reciprocal phosphorylation/dephosphorylation at Ser1177/Thr495) and induced a sustained Akt phosphorylation (P<0.05). Concomitantly, a significant increase in NO release was observed (2-fold increase in relation to control). These effects were blocked by A-779. Wortmannin suppressed eNOS activation in both Chinese hamster ovary-Mas and human aortic endothelial cells. Our findings demonstrate that Ang-(1-7), through Mas, stimulates eNOS activation and NO production via Akt-dependent pathways. These novel data highlight the importance of the Ang-(1-7)/Mas axis as a putative regulator of endothelial function.