Aldosterone blockade by Spironolactone improves the hypertensive vascular hypertrophy and remodeling in angiotensin II overproducing transgenic mice

Pharmacological Inhibition of Mammalian Target of Rapamycin Attenuates Deoxycorticosterone Acetate Salt-Induced Hypertension and Related Pathophysiology: Regulation of Oxidative Stress, Inflammation, and Cardiovascular Hypertrophy in Male Rats

ABSTRACT

The present study aimed to explore the contribution of mammalian target of rapamycin (mTOR) in deoxycorticosterone acetate (DOCA) salt-induced hypertension and related pathophysiological changes in cardiovascular and renal tissues. DOCA salt loading resulted in an increase in systolic blood pressure, diastolic blood pressure, and mean blood pressure along with the activity of ribosomal protein S6, the effector protein of mTOR. Treatment with rapamycin, the selective inhibitor of mTOR, initiated at the fourth week of DOCA- salt administration normalized the systolic blood pressure and attenuated ribosomal protein S6 activity in the heart, aorta, and kidney. Cardiac and vascular hypertrophy, oxidative stress, and infiltration of macrophages (CD68+), the marker of inflammation, were also reduced in rapamycin-treated, DOCA-salt, hypertensive rats. In addition, renal hypertrophy and dysfunction were also reduced with rapamycin-treated hypertensive rats. Moreover, these pathophysiological changes in DOCA-salt hypertensive rats were associated with increased NADPH oxidase (NOX) activity, gp91phox (formerly NOX2) expression, ERK1/2, and p38 MAPK activities in the heart, aorta, and kidney were minimized by rapamycin. These data indicate that mTOR plays an important role in regulating blood pressure and the development of cardiovascular and renal pathophysiological changes, most likely due to increased NOX expression/activity, ERK1/2, and p38 MAPK activity with macrophages infiltration in the heart, kidney, and aorta. Pharmacological inhibition of mTOR and related signaling pathways could serve as a novel target for the treatment of hypertension.

Mineralocorticoid receptor antagonist treatment of established pulmonary arterial hypertension improves interventricular dependence in the SU5416-hypoxia rat model

Treatment with mineralocorticoid receptor (MR) antagonists beginning at the outset of disease, or early thereafter, prevents pulmonary vascular remodeling in preclinical models of pulmonary arterial hypertension (PAH). However, the efficacy of MR blockade in established disease, a more clinically relevant condition, remains unknown. Therefore, we investigated the effectiveness of two MR antagonists, eplerenone (EPL) and spironolactone (SPL), after the development of severe right ventricular (RV) dysfunction in the rat SU5416-hypoxia (SuHx) PAH model. Cardiac magnetic resonance imaging (MRI) in SuHx rats at the end of week 5, before study treatment, confirmed features of established disease including reduced RV ejection fraction and RV hypertrophy, pronounced septal flattening with impaired left ventricular filling and reduced cardiac index. Five weeks of treatment with either EPL or SPL improved left ventricular filling and prevented the further decline in cardiac index compared with placebo. Interventricular septal displacement was reduced by EPL whereas SPL effects were similar, but not significant. Although MR antagonists did not significantly reduce pulmonary artery pressure or vessel remodeling in SuHx rats with established disease, animals with higher drug levels had lower pulmonary pressures. Consistent with effects on cardiac function, EPL treatment tended to suppress MR and proinflammatory gene induction in the RV. In conclusion, MR antagonist treatment led to modest, but consistent beneficial effects on interventricular dependence after the onset of significant RV dysfunction in the SuHx PAH model. These results suggest that measures of RV structure and/or function may be useful endpoints in clinical trials of MR antagonists in patients with PAH.

Mineralocorticoid receptor in cardiovascular diseases-Clinical trials and mechanistic insights

Aldosterone binds to the mineralocorticoid receptor (NR3C2), a transcription factor of the nuclear receptor family, present in the kidney and in various other non-epithelial cells including the heart and the vasculature. Indeed, extra-renal pathophysiological effects of this hormone have been characterized, extending its actions to the cardiovascular system. A growing body of clinical and pre-clinical evidence suggests that mineralocorticoid receptor overactivation plays an important pathophysiological role in cardiovascular remodelling by promoting cardiac hypertrophy, fibrosis, arterial stiffness and in inflammation and oxidative stress. The following review article outlines the role of mineralocorticoid receptor in cardiovascular disease with a focus on myocardial remodelling and heart failure (HF) including clinical trials as well as cellular and animal studies.

atg7-Based Autophagy Activation Reverses Doxorubicin-Induced Cardiotoxicity

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Vascular cell-specific roles of mineralocorticoid receptors in pulmonary hypertension

Abnormalities that characterize pulmonary arterial hypertension include impairment in the structure and function of pulmonary vascular endothelial and smooth muscle cells. Aldosterone levels are elevated in human pulmonary arterial hypertension and in experimental pulmonary hypertension, while inhibition of the aldosterone-binding mineralocorticoid receptor attenuates pulmonary hypertension in multiple animal models. We explored the role of mineralocorticoid receptor in endothelial and smooth muscle cells in using cell-specific mineralocorticoid receptor knockout mice exposed to sugen/hypoxia-induced pulmonary hypertension. Treatment with the mineralocorticoid receptor inhibitor spironolactone significantly reduced right ventricular systolic pressure. However, this is not reproduced by selective mineralocorticoid receptor deletion in smooth muscle cells or endothelial cells. Similarly, spironolactone attenuated the increase in right ventricular cardiomyocyte area independent of vascular mineralocorticoid receptor with no effect on right ventricular weight or interstitial fibrosis. Right ventricular perivascular fibrosis was significantly decreased by spironolactone and this was reproduced by specific deletion of mineralocorticoid receptor from endothelial cells. Endothelial cell-mineralocorticoid receptor deletion attenuated the sugen/hypoxia-induced increase in the leukocyte-adhesion molecule, E-selectin, and collagen IIIA1 in the right ventricle. Spironolactone also significantly reduced pulmonary arteriolar muscularization, independent of endothelial cell-mineralocorticoid receptor or smooth muscle cell-mineralocorticoid receptor. Finally, the degree of pulmonary perivascular inflammation was attenuated by mineralocorticoid receptor antagonism and was fully reproduced by smooth muscle cell-specific mineralocorticoid receptor deletion. These studies demonstrate that in the sugen/hypoxia pulmonary hypertension model, systemic-mineralocorticoid receptor blockade significantly attenuates the disease and that mineralocorticoid receptor has cell-specific effects, with endothelial cell-mineralocorticoid receptor contributing to right ventricular perivascular fibrosis and smooth muscle cell-mineralocorticoid receptor participating in pulmonary vascular inflammation. As mineralocorticoid receptor antagonists are being investigated to treat pulmonary arterial hypertension, these findings support novel mechanisms and potential mineralocorticoid receptor targets that mediate therapeutic benefits in patients.

The Role of Oxidative Stress in Cardiovascular Aging and Cardiovascular Diseases

Aging can be seen as process characterized by accumulation of oxidative stress induced damage. Oxidative stress derives from different endogenous and exogenous processes, all of which ultimately lead to progressive loss in tissue and organ structure and functions. The oxidative stress theory of aging expresses itself in age-related diseases. Aging is in fact a primary risk factor for many diseases and in particular for cardiovascular diseases and its derived morbidity and mortality. Here we highlight the role of oxidative stress in age-related cardiovascular aging and diseases. We take into consideration the molecular mechanisms, the structural and functional alterations, and the diseases accompanied to the cardiovascular aging process.

Impact of mineralocorticoid receptor blockade with direct renin inhibition in angiotensin II-dependent hypertensive mice

It has been suggested that aldosterone breakthrough during treatment with a type 1 angiotensin II receptor (AT1R) blocker (ARB) may be an important risk factor for the progression of renal and cardiovascular disease. We examined whether the direct renin inhibitor, aliskiren caused aldosterone breakthrough in angiotensin II (Ang II)-dependent hypertensive mice. The effect of combination therapy with aliskiren and eplerenone was compared with that of therapy using renin-angiotensin system (RAS) blockade. Tsukuba hypertensive mice were treated for 12 weeks with aliskiren (30 mg/kg/day, i.p), candesartan (5 mg/kg/day, p.o), eplerenone (100 mg/kg/day, p.o) aliskiren and candesartan, aliskiren and eplerenone or candesartan and eplerenone. Blood pressure, urinary aldosterone and angiotensinogen (AGTN) excretion; plasma endothelin-1 concentration; kidney weight; urinary albumin excretion (UAE); glomerular injury; and renal messenger RNA (mRNA) levels for transforming growth factor (TGF)-β1, plasminogen activator inhibitor (PAI)-1, angiotensin-converting enzyme (ACE) and AT1R were measured. Combination therapy with aliskiren and candesartan caused a further decrease in blood pressure (p < 0.05) compared with either agent alone. Urinary aldosterone excretion was decreased significantly by 4 weeks of treatment with aliskiren or candesartan (p < 0.05). However, it was increased again by treatment with candesartan or aliskiren for 12 weeks. Combination therapy with aliskiren and eplerenone significantly decreased UAE, the glomerulosclerosis index, and PAI-1 and TGF-β1 mRNA levels compared with all other therapies (p < 0.05). Treatment with aliskiren decreased urinary aldosterone excretion at 4 weeks and increased it at 12 weeks. Combination therapy with a direct renin inhibitor and a mineralocorticoid receptor blocker may be effective for the prevention of renal injury in Ang II-dependent hypertension.

Diuretics prevent Rho-kinase activation and expression of profibrotic/oxidative genes in the hypertensive aortic wall

BACKGROUND

Diuretics are current antihypertensive drugs since they reduce blood pressure and cardiovascular risk. Increased vascular tone is modulated in a relevant way by the RhoA/Rho-kinase (ROCK) pathway, by acting on vascular smooth muscle cell contraction. This pathway has also proremodeling vascular effects. There are few data on the role of diuretics on both vascular ROCK activation and on proremodeling effects. We assessed the effects of hydrochlorothiazide (HCTZ) and spironolactone (spiro) alone and in combination with the ROCK inhibitor fasudil (FAS) on ROCK activation, gene expression of proremodeling markers and on hypertrophy in the aortic wall of hypertensive rats.

METHODS

Deoxycorticosterone acetate (DOCA)-salt hypertensive rats (male, Sprague-Dawley) were randomized to the specific ROCK inhibitor FAS, HCTZ, spiro or the combinations of FAS/HCTZ or FAS/spiro for 3 weeks. At the end of the study, ROCK activation (by western blot), gene expression of proremodeling markers (by reverse transcription polymerase chain reaction, RT-PCR) and vascular hypertrophy (by morphometry) were determined in the aortic wall.

RESULTS

All treatments significantly reduced blood pressure. In the DOCA rats the p-myosin phosphatase target protein-1 (MYPT1)/t-MYPT1 ratio, index of ROCK activation was higher by 2.8 fold (p < 0.05) compared with control rats. All treatments reduced ROCK activation in the aortic wall to control levels (p < 0.05). Besides, significantly increased protein levels of transforming growth factor β1 (TGF-β₁), gene expression of TGF-β₁, connective tissue growth factor (CTGF), p22 phox and gp91 phox subunits of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, as well as increased media thickness and aortic media area/lumen area (AM/LA) in the untreated hypertensive rats were significantly reduced (p < 0.05) to control levels by all treatments. Similar effects were observed using both diuretics alone or in combination with FAS.

CONCLUSIONS

In the aortic wall, both HCTZ and spiro in antihypertensive doses reduce ROCK activation, subsequent expression of genes that promote vascular remodeling and hypertrophy in this experimental model of hypertension. These effects could explain some of their clinical benefits in hypertensive patients.

Up-regulation of the mammalian target of rapamycin complex 1 subunit Raptor by aldosterone induces abnormal pulmonary artery smooth muscle cell survival patterns to promote pulmonary arterial hypertension

Activation of the mammalian target of rapamycin complex 1 (mTORC1) subunit Raptor induces cell growth and is a downstream target of Akt. Elevated levels of aldosterone activate Akt, and, in pulmonary arterial hypertension (PAH), correlate with pulmonary arteriole thickening, which suggests that mTORC1 regulation by aldosterone may mediate adverse pulmonary vascular remodeling. We hypothesized that aldosterone-Raptor signaling induces abnormal pulmonary artery smooth muscle cell (PASMC) survival patterns to promote PAH. Remodeled pulmonary arterioles from SU-5416/hypoxia-PAH rats and monocrotaline-PAH rats with hyperaldosteronism expressed increased levels of the Raptor target, p70S6K, which provided a basis for investigating aldosterone-Raptor signaling in human PASMCs. Aldosterone (10(-9) to 10(-7) M) increased Akt/mTOR/Raptor to activate p70S6K and increase proliferation, viability, and apoptosis resistance in PASMCs. In PASMCs transfected with Raptor-small interfering RNA or treated with spironolactone/eplerenone, aldosterone or pulmonary arterial plasma from patients with PAH failed to increase p70S6K activation or to induce cell survival in vitro Optimal inhibition of pulmonary arteriole Raptor was achieved by treatment with Staramine-monomethoxy polyethylene glycol that was formulated with Raptor-small interfering RNA plus spironolactone in vivo, which decreased arteriole muscularization and pulmonary hypertension in 2 experimental animal models of PAH in vivo Up-regulation of mTORC1 by aldosterone is a critical pathobiologic mechanism that controls PASMC survival to promote hypertrophic vascular remodeling and PAH.-Aghamohammadzadeh, R., Zhang, Y.-Y., Stephens, T. E., Arons, E., Zaman, P., Polach, K. J., Matar, M., Yung, L.-M., Yu, P. B., Bowman, F. P., Opotowsky, A. R., Waxman, A. B., Loscalzo, J., Leopold, J. A., Maron, B. A. Up-regulation of the mammalian target of rapamycin complex 1 subunit Raptor by aldosterone induces abnormal pulmonary artery smooth muscle cell survival patterns to promote pulmonary arterial hypertension.

Vascular Fibrosis in Aging and Hypertension: Molecular Mechanisms and Clinical Implications

Aging is the primary risk factor underlying hypertension and incident cardiovascular disease. With aging, the vasculature undergoes structural and functional changes characterized by endothelial dysfunction, wall thickening, reduced distensibility, and arterial stiffening. Vascular stiffness results from fibrosis and extracellular matrix (ECM) remodelling, processes that are associated with aging and are amplified by hypertension. Some recently characterized molecular mechanisms underlying these processes include increased expression and activation of matrix metalloproteinases, activation of transforming growth factor-β1/SMAD signalling, upregulation of galectin-3, and activation of proinflammatory and profibrotic signalling pathways. These events can be induced by vasoactive agents, such as angiotensin II, endothelin-1, and aldosterone, which are increased in the vasculature during aging and hypertension. Complex interplay between the “aging process” and prohypertensive factors results in accelerated vascular remodelling and fibrosis and increased arterial stiffness, which is typically observed in hypertension. Because the vascular phenotype in a young hypertensive individual resembles that of an elderly otherwise healthy individual, the notion of “early” or “premature” vascular aging is now often used to describe hypertension-associated vascular disease. We review the vascular phenotype in aging and hypertension, focusing on arterial stiffness and vascular remodelling. We also highlight the clinical implications of these processes and discuss some novel molecular mechanisms of fibrosis and ECM reorganization.

Mineralocorticoid receptor: a critical player in vascular remodeling

Vascular remodeling is a pathological condition with structural changes of blood vessels. Both inside-out and outside-in hypothesis have been put forward to describe mechanisms of vascular remodeling. An integrated model of these two hypotheses emphasizes the importance of immune cells such as monocytes/macrophages, T cells, and dendritic cells. These immune cells are at the center stage to orchestrate cellular proliferation, migration, and interactions of themselves and other vascular cells including endothelial cells (ECs), vascular smooth muscle cells (VSMCs), and fibroblasts. These changes on vascular wall lead to inflammation and oxidative stress that are largely responsible for vascular remodeling. Mineralocorticoid receptor (MR) is a classic nuclear receptor. MR agonist promotes inflammation and oxidative stress and therefore exacerbates vascular remodeling. Conversely, MR antagonists have the opposite effects. MR has direct roles on vascular cells through non-genomic or genomic actions to modulate inflammation and oxidative stress. Recent studies using genetic mouse models have revealed that MR in myeloid cells, VSMCs and ECs all contribute to vascular remodeling. In conclusion, data in the past years have demonstrated that MR is a critical control point in modulating vascular remodeling. Studies will continue to provide evidence with more detailed mechanisms to support this notion.

Mineralocorticoid receptor antagonism attenuates experimental pulmonary hypertension

Mineralocorticoid receptor (MR) activation stimulates systemic vascular and left ventricular remodeling. We hypothesized that MR contributes to pulmonary vascular and right ventricular (RV) remodeling of pulmonary hypertension (PH). We evaluated the efficacy of MR antagonism by spironolactone in two experimental PH models; mouse chronic hypoxia-induced PH (prevention model) and rat monocrotaline-induced PH (prevention and treatment models). Last, the biological function of the MR was analyzed in cultured distal pulmonary artery smooth muscle cells (PASMCs). In hypoxic PH mice, spironolactone attenuated the increase in RV systolic pressure, pulmonary arterial muscularization, and RV fibrosis. In rat monocrotaline-induced PH (prevention arm), spironolactone attenuated pulmonary vascular resistance and pulmonary vascular remodeling. In the established disease (treatment arm), spironolactone decreased RV systolic pressure and pulmonary vascular resistance with no significant effect on histological measures of pulmonary vascular remodeling, or RV fibrosis. Spironolactone decreased RV cardiomyocyte size modestly with no significant effect on RV mass, systemic blood pressure, cardiac output, or body weight, suggesting a predominantly local pulmonary vascular effect. In distal PASMCs, MR was expressed and localized diffusely. Treatment with the MR agonist aldosterone, hypoxia, or platelet-derived growth factor promoted MR translocation to the nucleus, activated MR transcriptional function, and stimulated PASMC proliferation, while spironolactone blocked these effects. In summary, MR is active in distal PASMCs, and its antagonism prevents PASMC proliferation and attenuates experimental PH. These data suggest that MR is involved in the pathogenesis of PH via effects on PASMCs and that MR antagonism may represent a novel therapeutic target for this disease.

Aldosterone-induced osteopontin expression in vascular smooth muscle cells involves MR, ERK, and p38 MAPK

Osteopontin (OPN) is known to be one of the cytokines that is involved in the vascular inflammation caused by aldosterone (Ald). Previous reports have shown that Ald increases OPN expression, and the mechanisms for this remain to be clarified. In this study, we investigated how Ald increases OPN expression in the vascular smooth muscle cells (VSMCs) of rats. Ald increased OPN expression time dependently as well as dose dependently. This increase was diminished by spironolactone, a mineralocorticoid receptor (MR) antagonist. PD98059, an inhibitor of p42/44 MAPK pathway, and SB203580, an inhibitor of p38 MAPK pathway, suppressed Ald-induced OPN expression and secretion in VSMCs. VSMCs migration stimulated by aldosterone required OPN expression. In conclusion, these data suggest that Ald-induced OPN expression in VSMC is mediated by MR and signaling cascades involving ERK and p38 MAPK. These molecules may represent therapeutic targets for the prevention of pathological vascular remodeling.

Angiotensin II- and salt-induced kidney injury through Rac1-mediated mineralocorticoid receptor activation

Experiments with hyperaldosteronemic animals suggest that, despite lowering plasma aldosterone, salt worsens renal injury by paradoxical activation of the mineralocorticoid receptor (MR). Salt and aldosterone synergistically contribute to renal impairment through Rac1-mediated activation of the MR, but whether angiotensin II also promotes renal injury through this mechanism is unknown. Here, we placed angiotensin II-overproducing double transgenic Tsukuba hypertensive mice on a low- or high-salt intake for 6 weeks and treated some animals with adrenalectomy, the MR antagonist eplerenone, the Rac inhibitor EHT1864, or hydralazine. High-salt intake, but not low-salt intake, led to hypertension and prominent kidney injury. Adrenalectomy prevented angiotensin II/salt-induced nephropathy in mice receiving high-salt intake, which was recapitulated by aldosterone supplementation, suggesting the involvement of aldosterone/MR signaling. Plasma aldosterone levels, however, were lower in high- than low-salt conditions. Instead, angiotensin II/salt-evoked MR activation associated with Rac1 activation and was not dependent on plasma aldosterone level. Both EHT1864 and eplerenone repressed the augmented MR signaling and mitigated kidney injury with partial but significant reduction in BP with high-salt intake. Hydralazine similarly reduced BP, but it neither suppressed the Rac1-MR pathway nor ameliorated the nephropathy. Taken together, these results show that angiotensin II and salt accelerate kidney injury through Rac1-mediated MR activation. Rac inhibition may be a promising strategy for the treatment of CKD.

Angiotensin II type 2 receptor signaling attenuates aortic aneurysm in mice through ERK antagonism

Angiotensin II (AngII) mediates progression of aortic aneurysm, but the relative contribution of its type 1 (AT1) and type 2 (AT2) receptors remains unknown. We show that loss of AT2 expression accelerates the aberrant growth and rupture of the aorta in a mouse model of Marfan syndrome (MFS). The selective AT1 receptor blocker (ARB) losartan abrogated aneurysm progression in the mice; full protection required intact AT2 signaling. The angiotensin-converting enzyme inhibitor (ACEi) enalapril, which limits signaling through both receptors, was less effective. Both drugs attenuated canonical transforming growth factor-β (TGFβ) signaling in the aorta, but losartan uniquely inhibited TGFβ-mediated activation of extracellular signal-regulated kinase (ERK), by allowing continued signaling through AT2. These data highlight the protective nature of AT2 signaling and potentially inform the choice of therapies in MFS and related disorders.

Vascular endothelial function and hypertension: insights and directions

Hypertension contributes significantly to worldwide cardiovascular morbidity and mortality. Hypertension appears to have a complex association with endothelial dysfunction, a phenotypical alteration of the vascular endothelium that precedes the development of adverse cardiovascular events and portends future cardiovascular risk. This review concentrates on recent findings with respect to the mechanisms of hypertension-associated endothelial dysfunction, the interrelationship between these two entities, and the relationship of the efficacy of antihypertensive therapies to improvements in vascular homeostasis beyond blood pressure reduction. Current evidence suggests that hypertension and endothelial dysfunction are integrally related with respect to pathophysiologic mechanisms. Future studies will need to identify the key connections between hypertension and endothelial dysfunction to allow novel interventions to be designed and promulgated.

Tempol, a superoxide dismutase mimetic, prevents cerebral vessel remodeling in hypertensive rats

Increased reactive oxygen species (ROS) production is involved in the pathogenesis of hypertension and stroke. The effects of ROS on cerebral vessels from hypertensive rats have not been studied. We hypothesized that tempol, a superoxide dismutase mimetic, would prevent middle cerebral artery (MCA) remodeling in stroke-prone spontaneously hypertensive rats (SHRSP). Six-week-old male SHRSP were treated with tempol (1mM) for 6weeks. The MCA was then removed and mounted in a pressure myograph to study tone generation, vessel reactivity, and passive vessel structure. Data are shown as mean±SEM, tempol vs. control. Plasma thiobarbituric acid reactive substances (TBARS) were decreased by tempol treatment (14.15±1.46 vs. 20.55±1.25nM of malondialdehyde [MDA]/ml, p=0.008). Maximum serotonin-induced constriction was increased by tempol treatment, without changes in dilation to adenosine diphosphate or tone generation. At an intralumenal pressure of 80mmHg, tempol caused a dramatic increase in the MCA lumen diameter (246±5 vs. 207±3μm, p<0.001), outer diameter (281±5 vs. 241±3μm, p<0.001), lumen cross-sectional area, and vessel cross-sectional area. Collagen IV mRNA expressions were increased by 2.4-fold after tempol treatment. These results suggest that ROS are involved in the remodeling of the cerebral vasculature of SHRSP and that ROS scavenging can attenuate this process.

Aldosterone enhances IGF-I-mediated signaling and biological function in vascular smooth muscle cells

The IGF-I pathway and renin-angiotensin-aldosterone axis are both involved in the pathogenesis of hypertension and atherosclerosis, but no information is available about IGF-I and aldosterone interaction or their potential synergistic effects in vascular smooth muscle cells (VSMCs). The aims of this study were to investigate whether aldosterone influences IGF-I signaling and to determine the mechanism(s) by which aldosterone affects IGF-I function. Aldosterone resulted in significant increases in the Akt (1.87 ± 0.24, P < 0.001), MAPK (1.78 ± 0.13, P < 0.001), p70S6kinase (1.92 ± 0.15, P < 0.001), IGF-I receptor (1.69 ± 0.05, P < 0.01), and insulin receptor substrate-1 (1.7 ± 0.04, P < 0.01) (fold increase, mean ± SEM, n = 3) phosphorylation responses to IGF-I compared with IGF-I treatment alone. There were also significant increases in VSMC proliferation, migration, and protein synthesis (1.63 ± 0.03-, 1.56 ± 0.08-, and 1.51 ± 0.04-fold increases compared with IGF-I alone, respectively, n = 3, P < 0.001). Aldosterone induced osteopontin (OPN) mRNA expression and activation of αVβ3-integrin as well as an increase in the synthesis of IGF-I receptor. The enhancing effects of aldosterone were inhibited by eplerenone (10 μmol/liter), actinomycin-D (20 nmol/liter), and an anti-αVβ3-integrin antibody that blocks OPN binding. The antioxidant N-acetylcysteine (2 mmol/liter) completely inhibited the ability of aldosterone to induce any of these changes. In conclusion, our results show that aldosterone enhances IGF-I signaling and biological actions in VSMCs through induction of OPN followed by its subsequent activation of the αVβ3-integrin and by increasing IGF-I receptor. These changes are mediated in part through increased oxidative stress. The findings suggest a new mechanism by which aldosterone could accelerate the development of atherosclerosis.

Central interactions of aldosterone and angiotensin II in aldosterone- and angiotensin II-induced hypertension

Many studies have implicated both angiotensin II (ANG II) and aldosterone (Aldo) in the pathogenesis of hypertension, the progression of renal injury, and cardiac remodeling after myocardial infarction. In several cases, ANG II and Aldo have been shown to have synergistic interactions in the periphery. In the present studies, we tested the hypothesis that ANG II and Aldo interact centrally in Aldo- and ANG II-induced hypertension in male rats. In rats with blood pressure (BP) and heart rate (HR) measured by DSI telemetry, intracerebroventricular (icv) infusions of the mineralocorticoid receptor (MR) antagonists spironolactone and RU28318 or the angiotensin type 1 receptor (AT1R) antagonist irbesartan significantly inhibited Aldo-induced hypertension. In ANG II-induced hypertension, icv infusion of RU28318 significantly reduced the increase in BP. Moreover, icv infusions of the reactive oxygen species (ROS) scavenger tempol or the NADPH oxidase inhibitor apocynin attenuated Aldo-induced hypertension. To confirm these effects of pharmacological antagonists, icv injections of either recombinant adeno-associated virus carrying siRNA silencers of AT1aR (AT1aR-siRNA) or MR (MR-siRNA) significantly attenuated the development of Aldo-induced hypertension. The immunohistochemical and Western blot analyses of AT1aR-siRNA- or MR-siRNA-injected rats showed a marked reduction in the expression of AT1R or MR in the paraventricular nucleus compared with scrambled siRNA rats. When animals from all studies underwent ganglionic blockade with hexamethonium, there was a smaller reduction in the fall of BP in animals receiving icv AT1R or MR antagonists. These results suggest that ANG II and Aldo interact in the brain in a mutually cooperative manner such that the functional integrity of both brain AT1R and MR are necessary for hypertension to be induced by either systemic ANG II or Aldo. The pressor effects produced by systemic ANG II or Aldo involve increased central ROS and sympathetic outflow.

An angiotensin II- and NF-kappaB-dependent mechanism increases connexin 43 in murine arteries targeted by renin-dependent hypertension

AIMS

Connexins (Cxs) play a role in the contractility of the aorta wall. We investigated how connexins of the endothelial cells (ECs; Cx37, Cx40) and smooth muscle cells (SMCs; Cx43, Cx45) of the aorta change during renin-dependent and -independent hypertension.

METHODS AND RESULTS

We subjected both wild-type (WT) mice and mice lacking Cx40 (Cx40(-/-)), to either a two-kidney, one-clip procedure or to N-nitro-l-arginine-methyl-ester treatment, which induce renin-dependent and -independent hypertension, respectively. All hypertensive mice featured a thickened aortic wall, increased levels of Cx37 and Cx45 in SMC, and of Cx40 in EC (except in Cx40(-/-) mice). Cx43 was up-regulated, with no effect on its S368 phosphorylation, only in the SMCs of renin-dependent models of hypertension. Blockade of the renin-angiotensin system of Cx40(-/-) mice normalized blood pressure and prevented both aortic thickening and Cx alterations. Ex vivo exposure of WT aortas, carotids, and mesenteric arteries to physiologically relevant levels of angiotensin II (AngII) increased the levels of Cx43, but not of other Cx. In the aortic SMC line of A7r5 cells, AngII activated kinase-dependent pathways and induced binding of the nuclear factor-kappa B (NF-kappaB) to the Cx43 gene promoter, increasing Cx43 expression.

CONCLUSION

In both large and small arteries, hypertension differently regulates Cx expression in SMC and EC layers. Cx43 is selectively increased in renin-dependent hypertension via an AngII activation of the extracellular signal-regulated kinase and NF-kappaB pathways.

A randomized, double-blind, placebo-controlled trial of spironolactone on carotid intima-media thickness in nondiabetic hemodialysis patients

BACKGROUND AND OBJECTIVES

Hemodialysis patients (HD) display high rates of cardiac diseases and mortality. In chronic kidney disease, vascular injury leads to coronary artery disease, heart failure, and stroke. Carotid intima-media thickness (CIMT) measurements are currently widely used in randomized controlled trials (RCTs) to study the efficacy of interventions. An RCT was designed for the assessment of the safety and effectiveness of spironolactone to inhibit the progression of CIMT in HD patients as a primary outcome. Secondary outcomes included measurements of plasma potassium.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

HD patients were randomly assigned to receive 50 mg spironolactone or placebo thrice weekly after dialysis. In between dialysis sessions, plasma potassium concentrations were measured every month. Ultrasonographic measurements of CIMT were done at the beginning of the study and after 2 years.

RESULTS

Fifty-three age- and sex-adjusted patients (30 with drug and 23 with placebo) successfully completed the trial. There were no significant differences between the two groups in all profiles studied at baseline. Measurements of CIMT after 2 years showed a progression in the placebo group, whereas in the spironolactone group a significant decrease or even reversed CIMT was observed. Progression rates (mm/yr) were: common carotid, placebo: 0.06 +/- 0.07, spironolactone: 0.01 +/- 0.04; carotid bifurcation, placebo: 0.15 +/- 0.27, spironolactone: 0.0001 +/- 0.01; internal carotid, placebo: 0.10 +/- 0.12, spironolactone: -0.10 +/- 0.15. No episodes of hyperkalemia were observed, but a slight increase in plasma potassium was found in the spironolactone group.

CONCLUSIONS

Fifty milligrams of spironolactone thrice weekly significantly reduced the progression of CIMT in HD patients.

Mineralocorticoid receptor blockers and chronic kidney disease

The increasing prevalence of chronic kidney disease (CKD) and the public health initiatives for detection and slowing its progression have placed special emphasis on controlling proteinuria and the renin-angiotensin-aldosterone system (RAAS). In addition to the traditional blockers of angiotensin-converting enzyme and angiotensin receptors, mineralocorticoid receptor blockers (MRBs) have come into focus as anti-proteinuric agents with moderate anti-hypertensive effects. The beneficial effects of MRBs on mortality in patients with cardiac disease have been well described. We review the role of aldosterone in end-organ damage, the rationales for using MRBs as adjuncts to angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) in treating CKD, and the adverse effects that may occur when these agents are used in combination. Suggestions are included for avoiding serious adverse events in CKD patients treated with MRBs. There is a clearly defined need for prospective outcome studies focused on cardiovascular mortality as well as progression of CKD in patients treated with MRBS and other inhibitors of the RAAS.