Cardiac and vascular fibrosis and hypertrophy in aldosterone-infused rats: role of endothelin-1

Increased plasma aldosterone-to-renin ratio is associated with impaired left ventricular longitudinal functional reserve in patients with uncomplicated hypertension

Relative aldosterone excess is associated with endothelial dysfunction and higher incidence of end organ damage. We sought to investigate whether plasma aldosterone-to-renin ratio (ARR) is associated with left ventricular (LV) longitudinal function reserve to exercise in patients with controlled hypertension. In the patients with controlled and uncomplicated hypertension without overt LV hypertrophy, plasma aldosterone concentrations (ng/dL) and renin activities (ng/mL/h) were measured. Then 28 consecutive patients with higher ARR (group II, ARR > or = 30, 55 +/- 10 years) and 56 age- and sex-matched patients with lower ARR (group I, ARR < 30) underwent supine bicycle exercise echocardiography. Despite similar 24-hour blood pressure, LV mass index was significantly higher in group II (91.1 +/- 16.4 vs 101.7 +/- 18.2 g/m(2), P = .008). Early diastolic and systolic mitral annular velocity (E' and S', cm/s) at 50-W exercise was significantly lower in group II compared with group I (9.91 +/- 1.66 vs 8.67 +/- 1.65 cm/s, P = .002; 9.52 +/- 1.71 vs 8.46 +/- 1.79, P = .010, respectively) despite similar resting values. Longitudinal diastolic functional reserve at 25-W and 50-W exercise, defined as DeltaE' (change from resting E', cm/s) of group II was significantly lower than that of group I (2.60 +/- 1.42 vs 1.85 +/- 1.44 cm/s, P = .016; 3.40 +/- 1.48 vs 2.36 +/- 1.43 cm/s, P = .003, respectively). In conclusion, in patients with hypertension without overt LV hypertrophy, increased ARR is associated with increased LV mass, and impaired LV longitudinal functional reserve during exercise.

Plasma aldosterone in hypertensive patients on chronic hemodialysis: distribution, determinants and impact on survival

A high plasma aldosterone concentration (PAC) is known to be associated with poor outcome in patients with cardiac disease. However, the prognostic value of PAC in chronic hemodialysis (HD) patients is unknown. In 1996 we examined 128 hypertensive patients treated with antihypertensive drugs, excluding angiotensin-converting enzyme inhibitors, who were undergoing chronic HD (ages 61.8+/-13.8 years, 62% male), and for whom PAC (ng/dl) data were obtained. We followed up these patients until November 2003. During the follow-up period, 30 patients died. About half of all patients (48%) had PAC values above the normal range. We assigned the 128 patients to a lower (<22.9) or higher (> or = 22.9) PAC group according to the median baseline PAC. The survival rate as calculated by the Kaplan-Meier method was 90.6% in the higher PAC group and 62.5% in the lower PAC group (p=0.003). In multivariate analysis, serum potassium and plasma renin activity were independent determinants of PAC. Cox proportional hazards analysis, with adjustment for other variables including diabetes, showed that lower PAC was independently predictive of death. The adjusted hazard ratio (95% confidence interval) of the lower PAC group was 2.905 (1.187-7.112, p=0.020). The significance of PAC became marginal by adjustment with albumin or potassium. These results indicate that higher PAC is common, but not associated with an increase in total and cardiovascular deaths among hypertensive patients undergoing chronic HD. The association between lower PAC and poor survival may be driven by volume retention and/or lower potassium.

Long-term mineralocorticoid receptor blockade reduces fibrosis and improves cardiac performance and coronary hemodynamics in elderly SHR

Aldosterone has been implicated as one of the mediators of cardiovascular injury in various diseases. This study examines whether mineralocorticoid antagonism ameliorates or prevents the adverse cardiac effects of hypertension and aging. Male 22-wk-old spontaneously hypertensive rats (SHR) were divided into two groups, 15 rats in each. One group received no treatment; the other was given eplerenone (∼100 mg·kg−1·day−1). At the age of 54 wk, indexes of cardiovascular mass, systemic and regional hemodynamics, including coronary, left ventricular function, and myocardial collagen content, were determined in all rats. Hemodynamic studies were done in conscious rats. Arterial pressure was lowered only slightly in eplerenone-treated rats, and cardiac output and total peripheral resistance did not differ from control rats. Left and right ventricular and aortic mass indexes were unaffected by eplerenone; however, concentration of hydroxyproline in the right and left ventricle was decreased significantly ( P < 0.05) by eplerenone. This was accompanied by an improvement in left ventricular diastolic function and coronary hemodynamics. In conclusion, long-term therapy with the mineralocorticoid receptor antagonist eplerenone ameliorated adverse cardiac effects of both hypertension and aging in SHR. Thus reduction in myocardial fibrosis, paralleled by improvements in left ventricular function and coronary hemodynamics, was observed in eplerenone-treated SHR.

Elevated endothelin-1 levels are associated with decreased arterial elasticity in hypertensive patients

Endothelin-1 stimulates collagen synthesis and is increased in hypertension, but its effect on collagen degradation remains unknown. The current study tested the hypothesis that elevated endothelin-1 levels are associated with decreased collagenase activity, markers of collagen degradation, and arterial compliance in hypertensive patients. Normotensive (n = 10) and hypertensive (n = 13) patients who were not on any antihypertensive medication were recruited, and small and large artery elasticity index, systemic vascular resistance, pulse pressure, and blood pressure were determined using blood pressure waveform analysis. Large artery elasticity index and collagen degradation products were decreased whereas endothelin-1, systemic vascular resistance, and pulse pressure were elevated in hypertensive patients. Plasma endothelin-1 was negatively correlated with a cross-linked C-terminal telopeptide of collagen type I, a collagen degradation marker (r = -0.43; p = 0.04), collagenase matrix metalloproteinase-1 (r = -0.48; p = 0.02), and large artery elasticity (r = -0.45; p = 0.03) and positively correlated with pulse pressure (r = 0.68; p = 0.0005). These results suggest that endothelin-1 contributes to decreased arterial compliance in hypertension via inhibition of collagen degradation.

The role of free radicals in the pathophysiology of muscular dystrophy

Null mutation of any one of several members of the dystrophin protein complex can cause progressive, and possibly fatal, muscle wasting. Although these muscular dystrophies arise from mutation of a single gene that is expressed primarily in muscle, the resulting pathology is complex and multisystemic, which shows a broader disruption of homeostasis than would be predicted by deletion of a single-gene product. Before the identification of the deficient proteins that underlie muscular dystrophies, such as Duchenne muscular dystrophy (DMD), oxidative stress was proposed as a major cause of the disease. Now, current knowledge supports the likelihood that interactions between the primary genetic defect and disruptions in the normal production of free radicals contribute to the pathophysiology of muscular dystrophies. In this review, we focus on the pathophysiology that results from dystrophin deficiency in humans with DMD and the mdx mouse model of DMD. Current evidence indicates three general routes through which free radical production can be disrupted in dystrophin deficiency to contribute to the ensuing pathology. First, constitutive differences in free radical production can disrupt signaling processes in muscle and other tissues and thereby exacerbate pathology. Second, tissue responses to the presence of pathology can cause a shift in free radical production that can promote cellular injury and dysfunction. Finally, behavioral differences in the affected individual can cause further changes in the production and stoichiometry of free radicals and thereby contribute to disease. Unfortunately, the complexity of the free radical-mediated processes that are perturbed in complex pathologies such as DMD will make it difficult to develop therapeutic approaches founded on systemic administration of antioxidants. More mechanistic knowledge of the specific disruptions of free radicals that underlie major features of muscular dystrophy is needed to develop more targeted and successful therapeutic approaches.

Changes in extracellular matrix in subcutaneous small resistance arteries of patients with primary aldosteronism

CONTEXT AND OBJECTIVE

It has been previously demonstrated that aldosterone may possess a strong profibrotic action in vitro and in animal models of genetic or experimental hypertension. Our aim was to evaluate whether such a profibrotic action is present also in the human microcirculation.

DESIGN AND PATIENTS

We investigated 13 patients with primary aldosteronism, seven patients with essential hypertension, and 10 normotensive controls. All subjects were submitted to a biopsy of gluteal sc fat tissue. Small resistance arteries were dissected and mounted on an isometric myograph, and the tunica media to internal lumen ratio was measured.

MAIN OUTCOME MEASURES

The total collagen content within the tunica media was detected (Sirius red staining and image analysis), and collagen subtypes were evaluated using polarized light microscopy; under this condition thicker type I collagen fibers appear orange or red, whereas thinner type III collagen fibers are yellow or green.

RESULTS

Tunica media to internal lumen ratio was significantly increased in primary aldosteronism and in essential hypertension compared with normotensive controls. Clinic blood pressure values were similar in primary aldosteronism and in essential hypertension, and greater than in normotensive controls. Normotensive controls had less total and type III collagen (3.23 +/- 0.58 and 1.60 +/- 0.22%, respectively) in respect to the two hypertensive groups (P < 0.001). Total collagen and type III vascular collagen were significantly greater in primary aldosteronism (total collagen, 8.17 +/- 1.38%; type III collagen, 6.06 +/- 0.74%; P < 0.05) than in essential hypertension (total collagen, 6.84 +/- 1.15%; type III collagen, 5.25 +/- 0.80%).

CONCLUSIONS

Our results indicate that, in small resistance arteries of patients with primary aldosteronism, a pronounced fibrosis may be detected, even more evident than in blood-pressure-matched patients with essential hypertension.

Aortic stiffness correlates with an increased extracellular matrix turnover in patients with dilated cardiomyopathy

BACKGROUND

An increased extracellular matrix (ECM) turnover has been associated with poor survival in patients with chronic heart failure (CHF) due to dilated cardiomyopathy (DCM). However, the influence of the accelerated collagen turnover on the progressive large artery stiffening process characterizing CHF has not been clarified. This is relevant because aortic stiffening imposes an additional systolic load and impairs exercise tolerance in CHF patients. Therefore, we investigated whether the serum aminoterminal propeptide of type III collagen (PIIINP), an established marker of ECM turnover and tissue fibrosis in DCM, was associated with aortic stiffness in DCM patients.

METHODS AND RESULTS

A total of 89 patients with clinical diagnosis of DCM (age 62 +/- 9 years, 80% men, mean ejection fraction 34% +/- 8%) were selected. Aortic pulse-wave velocity (PWV), a well-established marker of aortic stiffness, was measured by Doppler ultrasonography. Serum concentration of PIIINP was determined by radioimmunoassay. Mean aortic PWV was 5.7 +/- 2.3 m/s, and PIIINP was 5.0 +/- 1.3 microg/L. The variables correlated with aortic PWV were age (r = 0.33, P = .002), PIIINP (r = 0.30, P = .005), heart rate (r = 0.27, P = .02), stroke volume (r = -0.24, P = .03) and New York Heart Association class (r = 0.25, P = .02). In a multivariate analysis, age (P = .02) and PIIINP (P = .01) were independently related with aortic PWV, accounting for 27% of its variance.

CONCLUSIONS

Higher serum PIIINP levels are independently associated with a stiffer aorta in DCM patients. This suggests that abnormalities in the ECM turnover might involve the proximal elastic vasculature and could partially explain the progressive large artery stiffening process characterizing CHF.

Neurohormones and heart failure: the importance of aldosterone

Heart failure is a major cause of cardiovascular morbidity and mortality and its incidence is on the increase. The pathophysiology of heart failure is multi-factorial but recent studies suggest that aldosterone plays an important and independent role in its progression. Emerging evidence now suggests that aldosterone exerts renal-independent effects. It binds to its mineralocorticoid receptor to produce direct effects on the myocardium and vasculature, leading to damaging processes such as hypertrophy, necrosis, fibrosis and endothelial dysfunction, factors known to contribute to the pathophysiology of heart failure. Mineralocorticoid receptor antagonists have thus emerged as a new paradigm for the treatment of heart failure. The benefits of these agents on both morbidity and mortality when used in patients with chronic symptomatic heart failure have been demonstrated by recent trials.

NADPH oxidase-derived reactive oxygen species in cardiac pathophysiology

Chronic heart failure, secondary to left ventricular hypertrophy or myocardial infarction, is a condition with increasing morbidity and mortality. Although the mechanisms underlying the development and progression of this condition remain a subject of intense interest, there is now growing evidence that redox-sensitive pathways play an important role. This article focuses on the involvement of reactive oxygen species derived from a family of superoxide-generating enzymes, termed NADPH oxidases (NOXs), in the pathophysiology of ventricular hypertrophy, the accompanying interstitial fibrosis and subsequent heart failure. In particular, the apparent ability of the different NADPH oxidase isoforms to define the response of a cell to a range of physiological and pathophysiological stimuli is reviewed. If confirmed, these data would suggest that independently targeting different members of the NOX family may hold the potential for therapeutic intervention in the treatment of cardiac disease.

Aldosterone breakthrough during ras blockade: A role for endothelins and their antagonists?

Activation of the renin-angiotensin system (RAS), with ensuing aldosterone excess, detrimentally affects outcome in patients with hypertension and heart failure (HF). RAS blockade with angiotensin (Ang) 1-converting enzyme inhibitors (ACEIs) or Ang II type 1 receptor blockers (ARBs) is beneficial in such conditions. However, aldosterone secretion can persist despite these treatments. Hence, mechanisms besides Ang II acquire the role of aldosterone secretagogue. The RALES and EPHESUS studies have shown that this aldosterone "escape" or "breakthrough" is an important factor, because it is a determinant of outcome in HF patients. Endothelin (ET)-1, which stimulates aldosterone secretion via both A (ETA) and B (ETB) receptor subtypes, and which is increased in HF, is a candidate for the "aldosterone breakthrough." Moreover, the novel ET peptide ET-1(1-31) is involved in adrenocortical growth. Therefore, findings suggesting a role for the ET-1 system as an aldosterone secretagogue, along with the potential usefulness of endothelin antagonists for the prevention of "aldosterone breakthrough," are discussed.

AAV delivery of mineralocorticoid receptor shRNA prevents progression of cold-induced hypertension and attenuates renal damage

The aim of this study was to determine the effect of RNA interference inhibition of mineralocorticoid receptor (MR) on cold-induced hypertension (CIH) and renal damage. Recombinant adeno-associated virus (AAV) carrying short hairpin small interference (si)RNA for MR (AAV.MR-shRNA) was constructed and tested for the ability to inhibit renal MR and to control CIH. Three groups of rats with CIH received AAV.MR-shRNA (1.25 x 10(9) particles/rat, intravenous), AAV carrying scrambled shRNA (AAV.Control-shRNA) (1.25 x 10(9) particles/rat, intravenous) and phosphate buffer solution (PBS), respectively. All rats were kept in a cold chamber (6.7 degrees C) throughout the experiment. Adeno-associated virus delivery of MR-shRNA prevented progression of CIH. Blood pressure (BP) of the AAV.MR-shRNA-treated group did not increase and remained at 145+/-3 mm Hg, whereas BP of the AAV.Control-shRNA-treated and PBS-treated group increased to 167+/-4 and 161+/-3 mm Hg, respectively, at 3 weeks after gene delivery. Thus, the antihypertensive effect of a single injection of AAV.MR-shRNA lasted for at least 3 weeks (length of the study). Adeno-associated virus carrying short hairpin siRNA for MR significantly increased urinary sodium excretion and decreased proteinuria. It also decreased serum creatinine and blood urea nitrogen, suggesting enhanced renal function. Both Western blot and immunohistochemical analysis showed that MR expression was decreased significantly in the kidney in the AAV.MR-shRNA-treated rats, confirming that renal MR is effectively inhibited by AAV.MR-shRNA. Adeno-associated virus carrying short hairpin siRNA for MR also significantly attenuated renal hypertrophy. In addition, AAV delivery of MR-shRNA prevented atrophy and dilation of renal tubules and abolished tubular deposition of proteinaceous material seen in CIH rats.

CONCLUSIONS

(1) AAV delivery of MR-shRNA effectively silenced MR in vivo. (2) RNA interference inhibition of MR may open a new avenue for the long-term control of hypertension and renal damage.

Mineralocorticoid Receptor Activation Causes Cerebral Vessel Remodeling and Exacerbates the Damage Caused by Cerebral Ischemia

Mineralocorticoid receptor antagonists protect against ischemic cerebrovascular disease; this appears to be caused by changes in cerebral vessel structure that would promote blood flow. Therefore, we hypothesized that mineralocorticoid receptor activation with deoxycorticosterone acetate would cause deleterious remodeling of the cerebral vasculature and exacerbate the damage caused by cerebral ischemia. Six-week-old male Wistar rats were treated with deoxycorticosterone acetate (200 mg/kg) for 6 weeks. At 12 weeks of age, the deoxycorticosterone acetate-treated rats had elevated systolic blood pressure compared with age-matched controls (157+/-5.9 versus 124+/-3.1 mm Hg deoxycorticosterone acetate versus control; P<0.05). The area of ischemic damage resulting from middle cerebral artery occlusion was greater in the deoxycorticosterone acetate-treated rats than control (63.5+/-3.72 versus 46.6+/-5.52% of the hemisphere infarcted, deoxycorticosterone acetate versus control; P<0.05). Middle cerebral artery structure was assessed using a pressurized arteriograph under calcium-free conditions. Over a range of intralumenal pressures, the lumen and ODs of the middle cerebral arteries were smaller in the deoxycorticosterone acetate-treated rats than the control rats (P<0.05). There was also an increase in the wall thickness and wall:lumen ratio in the vessels from deoxycorticosterone acetate-treated rats (P<0.05). The vessels from the deoxycorticosterone acetate-treated rats were stiffer than those from control rats as evidenced by a leftward shift in the stress/strain curve. These novel data suggest that mineralocorticoid receptor activation without salt loading and nephrectomy is sufficient to elicit deleterious effects on the cerebral vasculature that lead to inward hypertrophic remodeling and an increase in the ischemic damage in the event of a stroke.

Stimulation of serum- and glucocorticoid-regulated kinase-1 gene expression by endothelin-1

The serum- and glucocorticoid-regulated kinase-1 (SGK1) participates in the regulation of sodium homeostasis and blood pressure by mineralocorticoids. Aldosterone rapidly induces SGK1 transcription, which contributes to the activation of renal epithelial sodium channels. Another important regulator of blood pressure is the vasoactive hormone endothelin-1 (ET-1) that is systemically upregulated in chronic renal failure. In the present study, we investigated whether ET-1 modulates SGK1 expression, and thereby might explain some of its hypertensive effects. As assessed by real-time PCR analysis, ET-1 triggered the rapid increase of SGK1 mRNA levels in A-10 smooth muscle cells and also in intact aortas of adult rats. In A-10 cells transcriptional activation was associated with a more than 6-fold upregulation of SGK1 protein expression and in similar range as found after treatment with aldosterone. A stimulatory effect of ET-1 was not only observed in isolated cells, but also in an animal model. Upon subtotal nephrectomy (SNX) of rats, myocardial ET-1 levels strongly increased, which was followed by a more than 2-fold induction of SGK1 expression in the left ventricle. The myocardial upregulation of SGK1 was completely abrogated by a specific ET(A) receptor antagonist, thereby substantiating the in vivo role of ET-1 in SGK1 expression. Thus, these data demonstrate that ET-1 increases expression of SGK1 in vivo and in vitro, and therefore indicate that SGK1 upregulation might be involved in ET-1-dependent regulation of blood pressure and cardiac modelling during mild renal failure.

Endothelin-1 expression in vascular adventitial fibroblasts

Endothelial cells are a major source of endothelin (ET)-1, but the possibility that vascular adventitial fibroblasts generate ET-1 has not been explored. We hypothesized that aortic adventitial fibroblasts have the ability to produce ET-1, which may contribute to extracellular matrix synthesis. Vascular adventitial fibroblasts were isolated from mouse aorta and incubated with various concentrations of angiotensin II (ANG II). mRNA levels of preproET-1 and type I procollagen were detected with relative RT-PCR. ET-1 levels in culture medium were measured with ELISA. Protein levels of procollagen were detected with Western blotting. ANG II (10 and 100 nM, 1 microM) induced a time- and concentration-dependent increase in preproET-1 mRNA levels (P < 0.05). Induction of preproET-1 mRNA was accompanied by release of immunoreactive peptide ET-1 (P < 0.05). ANG II-evoked increases in preproET-1 mRNA expression and ET-1 release were blocked by losartan (100 microM), an AT1 receptor antagonist, but not PD-123319 (100 microM), an AT2 receptor antagonist. To further confirm our findings, we cloned and then sequenced vascular fibroblast preproET-1 bidirectionally with T7 and M13 reverse sequencing primers. Their nucleotide sequences were identical to preproET-1 cDNA from mouse vascular endothelial cells (accession no. AB081657). Moreover, ANG II-induced type I procollagen mRNA and protein expression were inhibited by BQ-123 (10 microM), an ET(A) receptor inhibitor, but not BQ-788 (10 microM), an ET(B) receptor inhibitor, suggesting a significant role of adventitial ET-1 in regulation of extracellular matrix synthesis. The results demonstrate that vascular adventitial fibroblasts are able to synthesize and release ET-1 in response to ANG II.

Calcium paradox of aldosteronism and the role of the parathyroid glands

The hypercalciuria and hypermagnesuria that accompany aldosteronism contribute to a fall in plasma ionized extracellular Ca2+ and Mg2+ concentrations ([Ca2+]o and [Mg2+]o). Despite these losses and the decline in extracellular levels of these cations, total intracellular and cytosolic free Ca2+ concentration ([Ca2+]i) is increased and oxidative stress is induced. This involves diverse tissues, including peripheral blood mononuclear cells (PBMC) and plasma. The accompanying elevation in plasma parathyroid hormone (PTH) and reduction in bone mineral density caused by aldosterone (Aldo)-1% NaCl treatment (AldoST) led us to hypothesize that Ca2+ loading and altered redox state are due to secondary hyperparathyroidism (SHPT). Therefore, we studied the effects of total parathyroidectomy (PTx). In rats receiving AldoST, without or with a Ca2+-supplemented diet and/or PTx, we monitored urinary Ca2+ and Mg2+ excretion; plasma [Ca2+]o, [Mg2+]o, and PTH; PBMC [Ca2+]i and H2O2 production; plasma α1-antiproteinase activity; total Ca2+ and Mg2+ in bone, myocardium, and rectus femoris; and gp91phox labeling in the heart. We found that 1) the hypercalciuria and hypermagnesuria and decline ( P < 0.05) in plasma [Ca2+]o and [Mg2+]o that occur with AldoST were not altered by the Ca2+-supplemented diet alone or with PTx; 2) the rise ( P < 0.05) in plasma PTH with AldoST, with or without the Ca2+-supplemented diet, was prevented by PTx; 3) increased ( P < 0.05) PBMC [Ca2+]i and H2O2 production, increased total Ca2+ in heart and skeletal muscle, and fall in bone Ca2+ and Mg2+ and plasma α1-antiproteinase activity with AldoST were abrogated ( P < 0.05) by PTx; and 4) gp91phox activation in right and left ventricles at 4 wk of AldoST was attenuated by PTx. AldoST is accompanied by SHPT, with parathyroid gland-derived calcitropic hormones being responsible for Ca2+ overload in diverse tissues and induction of oxidative stress. SHPT plays a permissive role in the proinflammatory vascular phenotype.

Role of aldosterone in angiotensin II-induced cardiac and aortic inflammation, fibrosis, and hypertrophy

Activation of the renin-angiotensin-aldosterone system is associated with increased extracellular matrix and inflammatory markers in the cardiovascular system. We evaluated the effects of aldosterone antagonism on cardiovascular structure, collagen deposition, and expression of inflammatory markers in 2-week angiotensin (Ang) II-infused rats (120 ng.kg-1.min-1, s.c.)+/-spironolactone or hydralazine (25 mg.kg-1.d-1). Aortic and cardiac collagen density was evaluated with Sirius red staining. NFkappaB and AP-1 were measured by a electrophoretic mobility shift assay, and ED-1 (macrophage marker) and vascular cell adhesion molecule-1 (VCAM-1) were measured by immunohistochemistry. Ang II increased blood pressure (176+/-2 mmHg vs. 115+/-1 mmHg in controls, p<0.01), which was attenuated by spironolactone (147+/-4 mmHg, p<0.01) and prevented by hydralazine (124+/-2 mmHg, p<0.01). Ang II enhanced left ventricular interstitial collagen type I/III deposition (4.1%+/-0.1% vs. 3.1%+/-0.2%, p<0.05), and this was attenuated by spironolactone but not hydralazine. Ang II-induced cardiac perivascular fibrosis was prevented by spironolactone and hydralazine. Ang II significantly increased cardiac AP-1 activity and ED-1 expression, which was prevented by spironolactone only. Ang II-enhanced NFkappaB activity, and VCAM-1 expression was reduced by spironolactone and hydralazine, whereas aortic hypertrophy was prevented by spironolactone and slightly reduced by hydralazine. In conclusion, blockade of mineralocorticoid receptors with spironolactone inhibited Ang II-induced aortic hypertrophy, cardiac transcription factor activation, upregulation of downstream inflammatory markers, and collagen deposition, thus preventing Ang II-induced cardiovascular damage.

c-Src–Dependent Nongenomic Signaling Responses to Aldosterone Are Increased in Vascular Myocytes From Spontaneously Hypertensive Rats

Aldosterone plays an important role in the pathogenesis of hypertension. We previously demonstrated that nongenomic signaling by aldosterone in vascular smooth muscle cells occurs through c-Src–dependent pathways. Here we tested the hypothesis that upregulation of c-Src by aldosterone plays a role in increased mitogen-activated protein (MAP) kinase activation, [ 3 H]-proline incorporation, and NADPH-driven generation of reactive oxygen species, thereby inducing cell growth, collagen production, and inflammation, respectively, in vascular smooth muscle cells from spontaneously hypertensive rats. The time course of c-Src phosphorylation by aldosterone was shifted to the left in vascular myocytes from hypertensive animals. Aldosterone rapidly increased phosphorylation of p38 MAP kinase and extracellular signal–regulated kinase with significantly greater effects in cells from spontaneously hypertensive rats versus control cells ( P <0.05). Aldosterone increased NADPH oxidase activity with significantly greater responses in vascular smooth muscle cells from hypertensive animals ( P <0.05). These events were associated with enhanced [ 3 H]proline incorporation (index of collagen synthesis) in cells from spontaneously hypertensive rats ( P <0.05). The NADPH oxidase activity increase, collagen synthesis, c-Src, and MAP kinase phosphorylation induced by aldosterone were significantly reduced by eplerenone (selective mineralocorticoid receptor blocker) and PP2 (selective c-Src inhibitor). In conclusion, nongenomic signaling by exogenous aldosterone, mediated through c-Src, is increased in vascular smooth muscle cells from spontaneously hypertensive rats. Upregulation of c-Src signaling may be important in the profibrotic and proinflammatory actions of aldosterone in this genetic model of hypertension.

Bone loss in rats with aldosteronism

OBJECTIVE

We hypothesized that aldosteronism is accompanied by hypercalciuria and hypermagnesuria that lead to bone loss, which could be rescued by hydrochlorothiazide and spironolactone.

METHODS

We monitored 24-hour urinary Ca and Mg excretion; plasma ionized [Ca]o and [Mg]o and plasma K; and bone mineral density of the femur. The following groups (n=5 in each group) were studied: age- and gender-matched, untreated controls; controls + 4 weeks hydrochlorothiazide; 4 weeks aldosterone/salt treatment (ALDOST, 0.75 mug/h and dietary 1% NaCl/0.4% KCl); 4 weeks ALDOST+hydrochlorothiazide (50 mg/kg in prepared food); and 4 weeks ALDOST+hydrochlorothiazide+spironolactone (200 mg/kg day in divided doses by twice-daily gavage).

RESULTS

ALDOST increased (P<0.05) urinary Ca and Mg excretion four- and twofold, respectively; hydrochlorothiazide co-treatment attenuated (P<0.05) Ca excretion in controls and during ALDOST without affecting augmented Mg excretion whereas hydrochlorothiazide+spironolactone normalized Ca and reduced Mg excretion (P<0.05). Compared with controls, plasma [Ca]o at 4 weeks of ALDOST was reduced (0.89+/-0.02 versus 0.83+/-0.03 mmol/L; P<0.05) but remained no different from levels in controls with hydrochlorothiazide and hydrochlorothiazide+spironolactone (0.88+/-0.04 and 0.97+/-0.03 mmol/L, respectively). Plasma [Mg]o fell (P<0.05) with ALDOST+hydrochlorothiazide (0.23+/-0.01 versus 0.34+/-0.01 mmol/L) and was prevented with spironolactone co-treatment (0.33+/-0.01 mmol/ dL). Hypokalemia (2.9+/-0.2 mmol/L) occurred in rats with ALDOST+hydrochlorothiazide but not with spironolactone co-treatment. At 4 weeks of ALDOST, plasma parathyroid hormone was increased (30+/-4 versus 11+/-3 pg/mL; P<0.05) and bone mineral density was reduced (0.153+/-0.006 versus 0.170+/-0.002 g/cm; P<0.05). Co-treatments with either hydrochlorothiazide or hydrochlorothiazide+spironolactone each prevented bone loss.

CONCLUSIONS

Hypercalciuria and hypermagnesuria accompany aldosteronism and account for a decline in their plasma ionized concentrations and secondary hyperparathyroidism with bone resorption. Attenuation of bone loss in aldosteronism can be achieved with hydrochlorothiazide; however, mono- and divalent cation homeostasis, together with bone integrity, are each preserved with the combination hydrochlorothiazide+spironolactone.

Soluble cellular adhesion molecules, selectins, VEGF and endothelin-1 in patients with Wuchereria bancrofti infection and association with clinical status

Lymphatic filariasis, a mosquito-transmitted disease commonly known as Bancroftian filariasis, is characterized by debilitating pathology linked to the progression of lymphoedema to a chronic state of elephantiasis. We performed longitudinal measurements of endothelial adhesion and angiogenic molecules in 63 Polynesian patients living in an hyperendemic focus of Wuchereria bancrofti. Decreased serum concentrations of soluble (s-) L selectin (CD62L) were noticed in sera of of patients with chronic conditions (hydrocele and elephantiasis). Chyluria was associated with increased vascular endothelial growth factor (VEGF) levels, whereas elephantiasis presented a high endothelin-1 (ET-1) profile. By contrast, increased serum concentrations of soluble intercellular (sICAM-1, CD54), but not of vascular cell (sVCAM-1, CD106), adhesion molecules were observed in sera of patients with bacterial lymphangitis used as controls. These trends are consistent with the increased permeability of vascular structures, a major clinical feature observed in acute lymphatic pathology (of bacterial or filarial origin), and of fundamental differences in the pathogenesis of hydrocele and elephantiasis. Using markers correlated with the clinical status (high ET-1 and VEGF levels for elephantiasis and chyluria, respectively; low CD62L levels for hydrocoele and elephantiasis) it should be possible to monitor disease progression in lymphatic filariasis.

Vascular endothelin in hypertension

Endothelins are powerful vasoconstrictor peptides that also play numerous other functions in many different organs. Endothelin-1 (ET-1) is the most abundant and important of this family of peptides in blood vessels. Production of ET-1 is increased in the endothelium and the kidney in salt-dependent models of hypertension (e.g.: DOCA-salt rats and Dahl salt-sensitive rats, in salt-loaded SHR-SP, in angiotensin II-infused and in diabetic rats). ET-1 elicits an inflammatory response by increasing oxidant stress in the vascular wall, which induces vascular remodeling and endothelial dysfunction found in the hypertensive models that exhibit an endothelin-mediated component. Endothelin receptor antagonism reduces blood pressure and vascular hypertrophic remodeling present in these hypertensive models. Patients with stage 2 hypertension have enhanced vascular expression of ET-1. Endothelin receptor antagonists lower blood pressure in hypertensive patients. They could become therapeutic agents for prevention of target organ damage in hypertension and in type 2 diabetes, chronic renal failure and congestive heart failure. Side effects of endothelin receptor blockers have prevented up to the present their development for these indications. New endothelin antagonists devoid of these side effects, or alternatively inhibitors of the endothelin converting enzymes that generate ET-1 may in the future become available to block the endothelin system. However, to date endothelin antagonists have been approved only for the treatment of primary pulmonary hypertension, a rapidly fatal condition in which the endothelin system plays an important role and endothelin antagonists exert favorable effects.

Angiotensin II-Dependent Chronic Hypertension and Cardiac Hypertrophy Are Unaffected by gp91phox-Containing NADPH Oxidase

The gp91phox-containing NADPH oxidase is the major source of reactive oxygen species (ROS) in the cardiovascular system and inactivation of gp91phox has been reported to blunt hypertension and cardiac hypertrophy seen in angiotensin (Ang) II-infused animals. In the current study, we sought to determine the role of gp91phox-derived ROS on cardiovascular outcomes of chronic exposure to Ang II. The gp91phox-deficient mice were crossed with transgenic mice expressing active human renin in the liver (TTRhRen). TTRhRen mice exhibit chronic Ang II–dependent hypertension and frank cardiac hypertrophy by age 10 to 12 weeks. Four genotypes of mice were generated: control, TTRhRen trangenics (TTRhRen), gp91phox-deficient (gp91 − ), and TTRhRen transgenic gp91phox-deficient (TTRhRen/gp91 − ). Eight to 10 mice/group were studied. ROS levels were significantly reduced ( P <0.05) in the heart and aorta of TTRhRen/gp91 − and gp91 − mice compared with control counterparts, and this was associated with reduced cardiac, aortic, and renal NADPH oxidase activity ( P <0.05). Systolic blood pressure (SBP), cardiac mass, and cardiac fibrosis were increased in TTRhRen versus controls. In contrast to its action on ROS generation, gp91phox inactivation had no effect on development of hypertension or cardiac hypertrophy in TTRhRen mice, although interstitial fibrosis was reduced. Cardiac and renal expression of gp91phox homologues, Nox1 and Nox4, was not different between groups. Thus, although eliminating gp91phox-associated ROS production may be important in cardiovascular consequences in acute insult models, it does not prevent the development of hypertension and cardiac hypertrophy in a model in which the endogenous renin-angiotensin system is chronically upregulated.

Reduced left ventricular functional reserve in hypertensive patients with preserved function at rest

In many hypertensive patients, left ventricular pump function is normal at rest but abnormal during exercise. Myocardial dysfunction or altered left ventricular loading may be responsible for this finding. To verify the hypothesis of impaired myocardial functional reserve in the hypertensive heart, we assessed the response of stress-adjusted midwall shortening to graded, low-dose dobutamine infusion in hypertensive subjects with normal midwall shortening at rest. Sixty-five subjects (45 never treated hypertensive subjects and 20 normotensive volunteers comparable for age) received dobutamine at 1, 2, 3, 4, and 5 microg x kg(-1) x min(-1) for 5-minute steps; within this range of infusion rates, heart rate and systemic blood pressure were stable. Two-dimensional, M-mode, and Doppler echocardiography were performed at baseline and at the end of each step. In normotensive controls, midwall shortening increased from baseline during 2 microg x kg(-1) x min(-1) dobutamine by an average of 16+/-4.5% (P<0.01); a value of 2 standard deviations below this mean response was taken as the lower limit of normal. In the hypertensive subjects, 24 had a normal midwall shortening response to dobutamine at this dose (group I) and 21 had a subnormal response (group II). Whereas blood pressure and left ventricular mass were similar in group II and group I, the former had greater relative wall thickness (P<0.01) than the latter. beta-adrenergic stimulation by very-low-dose dobutamine unmasks subtle impairment of myocardial functional reserve in hypertensive subjects with normal myocardial performance at rest. This alteration seems to be related mainly to increase in left ventricular relative wall thickness.

Excess Aldosterone under Normal Salt Diet Induces Cardiac Hypertrophy and Infiltration via Oxidative Stress

Aldosterone is known to play a role in the pathophysiology of some cardiovascular diseases. However, previous studies on aldosterone infusion have been mostly performed in animals receiving sodium loading and uninephrectomy, and thus the cardiac action of aldosterone alone remains to be fully clarified. The present study was undertaken to investigate the direct cardiac action of aldosterone infusion alone in rats not subjected to salt loading and uninephrectomy. Aldosterone (0.75 microg/h) was subcutaneously infused into rats via an osmotic minipump for 14 days. Aldosterone infusion, under a normal salt diet, induced only a slight increase in the blood pressure of normal rats throughout the infusion. However, aldosterone significantly induced cardiac hypertrophy, as shown by echocardiography and measurement of cardiomyocyte cross-sectional area. Furthermore, aldosterone caused not only cardiac interstitial macrophage infiltration but also cardiac focal inflammatory lesions, which were associated with an increase in cardiac monocyte chemoattractant protein-1 (MCP-1) and osteopontin mRNA. The slight elevation of blood pressure by aldosterone infusion was completely prevented by tempol, the superoxide dismutase mimetic. However, tempol failed to suppress cardiac hypertrophy, the formation of inflammatory lesions, and upregulation of cardiac MCP-1 and osteopontin by aldosterone, while N-acetylcysteine could inhibit all of them. Our data provide evidence that aldosterone alone can induce cardiac hypertrophy and severe inflammatory response in the heart, independently of blood pressure, even in the absence of salt loading or nephrectomy. Aldosterone seems to induce cardiac inflammation and gene expression via oxidative stress that is inhibited by N-acetylcysteine but not by tempol.

Spironolactone prevents early renal injury in streptozotocin-induced diabetic rats

BACKGROUND

Glomerular and tubulointerstitial injury leads to chronic impairment of renal function, and thus, reversal of the injury may improve renal function and survival. The present study investigated whether and how mineralocorticoid receptor antagonist spironolactone ameliorates early renal injury in streptozotocin-induced diabetic rats.

METHODS

Streptozotocin (65 mg/kg, single intraperitoneal injection)- or vehicle-administered rats were used as diabetic or control rats, respectively. The streptozotocin-administered rats were treated with spironolactone (50 mg/kg/day sc) for 3 weeks. Among the 3 groups of rats, we compared renal fibrosis and renal hypertrophy, using picro-sirius red staining and immunohistochemistry of ED-1 macrophage marker, plasminogen activator inhibitor-1 (PAI-1), and transforming growth factor (TGF)-beta1.

RESULTS

Three weeks after administration of streptozotocin, rats exhibited increased collagen deposition in glomerular, tubulointerstitial, and perivascular areas in the kidney, which was completely attenuated by spironolactone treatment. In rats given streptozotocin alone, there were increases in ED-1-positive cell, PAI-1 expression, and TGF-beta1 expression in glomeruli and tubulointerstitiums, which were also suppressed by spironolactone treatment. Maximal glomerular and proximal tubular areas were not significantly different among the 3 groups. Rats given streptozotocin alone revealed an increase in proximal tubule wall-to-lumen ratio that was not influenced by treatment with spironolactone.

CONCLUSION

Streptozotocin-induced renal fibrosis, PAI-1 expression, TGF-beta1 expression, and macrophage infiltration occur via mineralocorticoid receptor, and spironolactone ameliorates renal fibrosis presumably via the inhibition of macrophage infiltration, PAI-1 expression, and TGF-beta1 expression in streptozotocin-induced early diabetic injury.

Independent and additional prognostic value of aminoterminal propeptide of type III procollagen circulating levels in patients with chronic heart failure

BACKGROUND

In chronic heart failure (CHF), changes in the extracellular space contribute to cardiac dysfunction. We aimed to determine whether aminoterminal-propeptide of type III procollagen (PIIINP), a marker of extracellular matrix turnover, might provide prognostic information in CHF patients.

METHODS AND RESULTS

A total of 101 consecutive CHF patients (mean age 61.7 +/- 8.7 years, 88% males) were followed up between 1999 and 2001. The combined endpoint of the study was death and hospitalization for heart failure. During follow-up there were 15 deaths and 11 hospitalizations for worsening heart failure. At the survival analysis, age (P = .02), New York Heart Association class (P = .014), s-creatinine (P = .014), plasma-PIIINP (p-PIIINP) levels (P = .005), left ventricular ejection fraction (LVEF) (P = .0002), and a restrictive mitral filling pattern (P = .0003) predicted event-free survival. At the multivariate analysis, p-PIIINP levels predicted outcome independently of other clinical variables, hormones, and echocardiographic and exercise testing variables (P < .05 in all models). In patients with LVEF <31%, the presence of p-PIIINP >4.7 microg/L levels was significantly associated with a higher risk of death and hospitalization as compared with the other patients (event-free survival rate at 12 months: 45% versus 95%; at 24 months: 27% versus 88%; at 36 months: 18% versus 85%, P < .0001).

CONCLUSIONS

In patients with CHF, PIIINP levels predict outcome independently of clinical status, hemodynamics and hormonal activation. PIIINP levels provide additional prognostic information to that of left ventricular function alone, suggesting that it may reflect more than cardiac extracellular matrix turnover.

Blockade of Endothelin Receptors Attenuates End-Organ Damage in Homozygous Hypertensive Ren-2 Transgenic Rats

BACKGROUND/AIMS

A growing body of evidence suggests that the interplay between the endothelin (ET) and the renin-angiotensin systems (RAS) plays an important role in the development of the malignant phase of hypertension. The present study was performed to evaluate the role of an interaction between ET and RAS in the development of hypertension and hypertension-associated end-organ damage in homozygous male transgenic rats harboring the mouse Ren-2 renin gene (TGRs) under conditions of normal-salt (NS, 0.45% NaCl) and high-salt (HS, 2% NaCl) intake.

METHODS

Twenty-eight-day-old homozygous male TGRs and age-matched transgene-negative male normotensive Hannover Sprague-Dawley (HanSD) rats were randomly assigned to groups with NS or HS intake. Nonselective ET(A/B) receptor blockade was achieved with bosentan (100 mg/kg/day). Systolic blood pressure (BP) was measured in conscious animals by tail plethysmography. Rats were placed into metabolic cages to determine proteinuria and clearance of endogenous creatinine. At the end of the experiment the final arterial BP was measured directly in anesthetized rats. Kidneys were taken for morphological examination.

RESULTS

All male HanSD fed either the NS or HS diet exhibited a 100% survival rate until 180 days of age (end of experiment). The survival rate in untreated homozygous male TGRs fed the NS diet was 41%, which was markedly improved by treatment with bosentan to 88%. The HS diet reduced the survival rate in homozygous male TGRs to 10%. The survival rate in homozygous male TGRs on the HS diet was significantly improved by bosentan to 69%. Treatment with bosentan did not influence either the course of hypertension or the final levels of BP in any of the experimental groups of HanSD rats or TGRs. Although the ET-1 content in the renal cortex did not differ between HanSD rats and TGRs, ET-1 in the left heart ventricle of TGRs fed the HS diet was significantly higher compared with all other groups. Administration of bosentan to homozygous male TGRs fed either the NS or HS diet markedly reduced proteinuria, glomerulosclerosis and attenuated the development of cardiac hypertrophy compared with untreated TGR.

CONCLUSIONS

Our data show that nonselective ET(A/B) receptor blockade markedly improves the survival rate and ameliorates end-organ damage in homozygous male TGRs without significantly lowering BP.

Eplerenone Prevents Salt-Induced Vascular Remodeling and Cardiac Fibrosis in Stroke-Prone Spontaneously Hypertensive Rats

We examined the effect of different levels of salt intake on the role of aldosterone on cardiac and vascular changes in salt-loaded stroke-prone spontaneously hypertensive rats (SHRSP). Eleven-week-old SHRSP were fed high-salt (4.2% NaCl), normal-salt (0.28%), or low-salt (0.03%) diets with or without eplerenone (100 mg/kg per day, in food) for 5 weeks. A group of high-salt SHRSP was also treated with hydralazine (25 mg/kg per day). Blood pressure increased more in high-salt rats than in other groups ( P <0.001). Eplerenone prevented further blood pressure rise in salt-loaded rats, with little effect on control and low-salt SHRSP. Increased media-to-lumen ratio of mesenteric resistance arteries induced by salt ( P <0.01) was prevented by eplerenone ( P <0.01). Maximal acetylcholine-induced vasodilation was impaired under salt loading ( P <0.01), but improved under eplerenone ( P <0.01). Eplerenone prevented ( P <0.01) increased heart weight and left and right ventricular collagen deposition induced by high salt. Blood pressure lowering by hydralazine in high-salt SHRSP did not influence endothelial function or left ventricular collagen. Our study demonstrates salt-dependency of aldosterone effects on severity of hypertension, endothelial dysfunction, and cardiac and vascular remodeling in SHRSP. These effects were attenuated by eplerenone, particularly in the salt-loaded state, underlining the pathophysiological role of aldosterone in salt-sensitive hypertension.

Aldosterone-synthase overexpression in heart: a tool to explore aldosterone's effects

Clinical observations indicate that elevated aldosterone impairs cardiovascular function. The mechanisms, however, are not totally understood although total and cardiovascular mortality are decreased by aldosterone antagonists. Experimentally, increased plasma aldosterone induces pericoronary inflammation and cardiac fibrosis. Our laboratory has discovered that aldosterone is synthesized in the rat heart, and has demonstrated that this cardiac aldosterone is involved in post-infarction cardiac remodeling. In man, activated cardiac aldosterone production has been described in patients with heart failure. In transgenic mice that overexpress aldosterone-synthase in the heart, we observe a normal cardiac function but a major coronary dysfunction, more pronounced in males. These observations converge to a potential physiological and pathological relevance of this system. Beneficial effects of anti-aldosterone treatment in heart failure may thus be secondary in part to blockade of cardiac aldosterone action.

ETA receptor mediates altered leukocyte-endothelial cell interaction and adhesion molecules expression in DOCA-salt rats

Leukocyte adhesion to endothelial cells plays a key role in inflammatory processes associated with end-organ injury. Endothelin-1 (ET-1), which stimulates inflammatory processes, contributes to cardiovascular damage in deoxycorticosterone (DOCA)-salt hypertension. We investigated whether ETA receptor blockade modulates in vivo leukocyte-endothelial cell interactions and expression of cell adhesion molecules (CAM) involved in these processes. DOCA-salt and control uninephrectomized rats were treated with the ETA antagonist BMS182874 (40 mg/kg per day) or vehicle. Analysis of CAMs expression by reverse transcription-polymerase chain reaction and immunohistochemistry showed increased cardiac platelet selectin (P-selectin), detected mainly in endothelial cells, and vascular cell adhesion molecule-1 (VCAM-1), but not intercellular adhesion molecule-1 (ICAM-1), in DOCA-salt rats. Cardiac expression of endothelial selectin (E-selectin) was decreased, whereas immunoreactivity to ED-1 and myeloperoxidase (MPO) activity, markers of macrophage and leukocyte infiltration, respectively, were increased in DOCA-salt. Leukocyte-endothelial cell interaction, functionally assessed in venules of internal spermatic fascia by intravital microscopy, was significantly altered in DOCA-salt rats as evidenced by increased leukocyte adhesion and decreased rolling. BMS182874 treatment normalized leukocyte-endothelium interactions, decreased cardiac VCAM-1 expression in DOCA and control groups, and had no effects on ICAM-1 expression. BMS182874 also increased E-selectin and abolished P-selectin expression in DOCA-salt, but not in control rats. The ETA antagonist reduced cardiac ED-1 content and MPO activity and prevented cardiac damage in DOCA-salt rats. These data indicate that ET-1 participates, via activation of ETA receptors, in altered leukocyte-endothelial cell interactions in DOCA-salt rats, possibly by modulating expression of CAMs, and that the inflammatory status is associated with cardiac damage in mineralocorticoid hypertension.

Endothelin???aldosterone interaction and proteinuria in low-renin hypertension

OBJECTIVE

To investigate whether endothelin and aldosterone participate in the increased prevalence and severity of nephrosclerosis in human low-renin hypertension, analogous to observations in experimental hypertension.

DESIGN

Comparison of endothelin, aldosterone and their relationships with proteinuria, in hypertensive patients with high aldosterone : renin ratios (HARR group, n = 14) or normal aldosterone : renin ratios (NARR group, n = 15).

METHODS

Urine protein and radioimmunoassay measurements of plasma renin activity, endothelin and aldosterone were carried out in individuals taking their usual diet, and after salt loading and salt depletion.

RESULTS

Compared with the NARR group, patients in the HARR group had higher blood pressure, greater salt sensitivity of their blood pressure, significantly greater urine protein and lower serum potassium concentrations, lower renin activities [0.14 +/- 0.03 ng AngiotensinI (AI)/l per s compared with 0.76 +/- 0.16 ng AI/l per s; P < 0.005], blunted renin-aldosterone responses to salt loading and salt depletion, enhanced catecholamine responses to salt depletion, and increased plasma endothelin (5.1 +/- 0.5 fmol/ml compared with 3.7 +/- 0.3 fmol/ml; P < 0.03). In the HARR group, endothelin and aldosterone concentrations were highly correlated, and both correlated with blood pressure and urine protein. In contrast, in the NARR group, endothelin and aldosterone did not correlate between them or with blood pressure, and only endothelin, not aldosterone, correlated with urine protein. Multivariate regression confirmed that the interaction between aldosterone and endothelin was the major predictor of urine protein in the HARR group (r = 0.442), whereas endothelin, renin and their interaction were predictors in the NARR group (r = 0.467).

CONCLUSIONS

Our results concur with experimental evidence for participation of endothelin in renal damage of angiotensin-dependent hypertension and for that of an endothelin-aldosterone interaction in low-renin hypertension. We propose that combined pharmacological antagonism of endothelin and aldosterone may confer renal protection beyond blood pressure reduction in patients with low-renin hypertension, a population at high risk for hypertensive nephrosclerosis.

NAD(P)H oxidase inhibitor prevents blood pressure elevation and cardiovascular hypertrophy in aldosterone-infused rats

Increased bioavailability of reactive oxygen species (ROS) has been implicated in the pathogenesis of mineralocorticoid hypertension. To find out the source of ROS, we evaluated the role of NAD(P)H oxidase in blood pressure (BP) elevation, cardiovascular hypertrophy, and fibrosis in aldosterone-salt rats. Aldosterone infusion (0.75 microg/h) significantly increased BP, which is attenuated by apocynin (1.5 mmol/L). Cardiac hypertrophy developed by aldosterone infusion was also normalized with apocynin. Greater mRNA for p22phox and NAD(P)H oxidase activity (more than twofold) in aorta of aldosterone-infused rats was reduced in apocynin-treated rats. Aldosterone infusion increased marginally procollagen I and III expression in LV compared to controls and apocynin decreased procollagen. Masson's Trichrome stain showed increased cardiac perivascular fibrosis, which was reduced by apocynin. These results suggest that NAD(P)H oxidase plays an important role in cardiovascular damage associated with mineralocorticoid hypertension.

Significance of recently identified peptides in hypertension: endothelin, natriuretic peptides, adrenomedullin, leptin

Arterial hypertension is one of the major risk factors in cardiovascular and renal disease. Advances in the study of pathophysiologic mechanisms and the relationship between several regulatory systems provide the basis for development of more selective therapeutic strategies. The increasing understanding of the role played by ETs, natriuretic peptides, AM, and leptin opens new frontiers in the care of hypertension and its complications, coronary artery disease and heart failure and other forms of cardiovascular disease.

Combined ETA/ETB receptor blockade of human peritoneal mesothelial cells inhibits collagen I RNA synthesis

BACKGROUND

Peritoneal fibrosis is a serious complication of peritoneal dialysis; however, the mechanisms are poorly understood. We studied osmolarity and physical stress-induced effects on collagen I RNA synthesis in human peritoneal mesothelial cells (HPMCs) and focused on endothelin as a possible mediator.

METHODS

HPMCs were grown in a medium containing either d-glucose or glycerol to analyze the impact of osmolarity on mesothelial endothelin-1 (ET-1) release and on collagen I RNA synthesis [reverse transcription-polymerase chain reaction (RT-PCR)]. A cellular model of nonlaminar fluid shear stress and cellular stretch was used to analyze the effects of physical forces. To neutralize the endothelin effects, a combined ETA/ETB receptor antagonist (LU 302 872) was chosen.

RESULTS

Glucose, but not glycerol, increased mesothelial ET-1 release in a concentration and time-dependent manner (P < 0.05 vs. controls). Collagen I RNA synthesis was significantly higher in glucose-challenged cell cultures (P < 0.05 vs. controls). The glucose-mediated collagen I RNA synthesis was completely inhibited by adding the combined ETA/ETB receptor antagonist to the medium. Fluid shear stress, but not cellular stretch, led to a significant increase in the mesothelial ET-1 release (P < 0.005 vs. controls) and collagen I RNA synthesis (P < 0.05 vs. controls). LU 302 872 completely inhibited these effects.

CONCLUSION

We found that glucose and fluid shear stress are potent stimuli for ET-1 release and collagen I RNA synthesis in a model cellular system. Although our system is highly artificial, our findings raise the hypothesis that similar effects may occur in the peritoneal membranes of peritoneal dialysis patients and suggest that endothelin might be involved.

Stress upregulates arterial matrix metalloproteinase expression and activity via endothelin A receptor activation

Degradation of the extracellular matrix proteins by matrix metalloproteinases (MMP) is an important regulatory step in the vascular remodeling process. Recent studies demonstrated that ETA receptors regulate cardiac MMP activity and fibrosis in DOCA-salt hypertension. However, little is known about endothelin (ET)-1 regulation of vascular MMP activity in hypertension. Thus early changes in ET-1-mediated regulation of MMP activity were measured in borderline hypertensive rats that develop impaired vasorelaxation and hypertension with chronic exposure to stress. Experiments were performed after 10 days of exposure to the behavioral stressor, air-jet stress, but before the onset of stress-induced hypertension. Study groups were 1) control (n = 8); 2) air-jet stress for 10 days (n = 8); 3) control plus ETA antagonist ABT-627 (n = 4), and 4) air-jet stress plus ETA antagonist (n = 4). MMP activity in the thoracic aorta was assessed by gelatin zymography. MMP protein and tissue ET-1 levels were evaluated by immunohistochemistry, and ET receptor density was determined by immunoblotting. Exposure to stress caused a twofold increase in plasma ET-1 levels (P < 0.05), and there was increased ET-1 staining at the tissue level. Total MMP activity and expression of MMP-2 and MMP-9 were increased in the stress group. ETA receptor antagonism prevented the increase in MMP expression and activation in the stress group. These results provide evidence that the MMP system is activated before the development of hypertension and ET-1 mediates these early events in vascular remodeling.

Regression of left ventricular hypertrophy is a key goal of hypertension management

Left ventricular hypertrophy (LVH) in patients with hypertension is associated with an increased risk for many cardiovascular events and predicts a higher mortality rate. The pathogenesis of LVH is complicated. In addition to the hemodynamic burden (pressure or volume overload) and demographic factors, several trophic humoral factors, such as angiotensin II, aldosterone, endothelin, leptin, and catecholamines, may also contribute to the development and progression of LVH. Effective antihypertensive therapy can reverse LVH as well as prevent its development. Regression of LVH decreases subsequent cardiovascular morbidity and mortality. The commonly used drugs have various effects on LVH. Angiotensin receptor blockers and angiotensin-converting enzyme inhibitors seem most effective. Several new agents, including direct antifibrotic drugs, aldosterone blockade, vasopeptidase inhibitors, and endothelin receptor antagonists that more specifically target the underlying pathogenesis of LVH may provide us with innovative approaches to treat LVH.

Endothelin antagonism on aldosterone-induced oxidative stress and vascular remodeling

Endothelin A (ETA) receptor blockade has prevented vascular remodeling in aldosterone and salt-induced hypertension. To evaluate effects of the ETA receptor antagonist, BMS 182874, compared with the aldosterone antagonist, spironolactone, on vascular remodeling in aldosterone-infused rats not exposed to a high salt diet, Sprague-Dawley rats were infused subcutaneously with aldosterone (0.75 microg/h) and treated with BMS 182874 (40 mg. kg-1. d-1), spironolactone, or hydralazine (both 25 mg. kg-1. d-1) while receiving a normal salt diet for 6 weeks. Aldosterone increased systolic BP (P<0.01), plasma endothelin (3.33+/-0.32 versus 1.85+/-0.40 pmol/L in control, P<0.05), systemic oxidative stress as shown by plasma thiobarbituric acid-reacting substances and vascular nicotinamide adenine dinucleotide phosphate (NADPH) activity. Aldosterone increased small artery media thickness (17.7+/-0.9 versus 13.6+/-0.8 microm in control, P<0.05) and media/lumen ratio (7.6+/-0.4 versus 5.5+/-0.4% in control, P<0.05), with growth index of 21% indicating hypertrophic remodeling. Laser confocal microscopy showed increased collagen and fibronectin deposition and intercellular adhesion molecule-1 (ICAM-1) content in the vessel wall of aldosterone-infused rats. The 3 treatments lowered BP, although hydralazine was slightly less effective. BMS 182874 and spironolactone decreased oxidative stress, normalized the hypertrophic remodeling, decreased collagen and fibronectin deposition, and reduced ICAM-1 abundance in the vascular wall of aldosterone-infused rats, whereas hydralazine only reduced NADPH activity in aorta but did not affect the remaining parameters. Vascular remodeling of small arteries occurs in aldosterone-infused rats exposed to a normal salt diet and may be mediated in part by ET-1 via stimulation of ETA receptors. Endothelin blockade may exert beneficial effects on vascular remodeling, fibrosis, oxidative stress, and adhesion molecule expression in aldosterone-induced hypertension.

Role of endothelins in animal models of hypertension: focus on cardiovascular protection

Investigation of the regulation of vascular function by endothelium-derived factors has been a prominent topic of research in the field of hypertension during the last decade. Of the different endothelial factors, endothelins, which play an important role in vasodilatation-vasoconstriction balance, have been the subject of great interest and an impressive number of publications. This peptide, a very potent vasoconstrictor, triggers as well events involved in growth, proliferation, matrix production and local inflammation. In parallel, its role in hypertension has evolved from a simple vasoconstrictor to a central local regulator of vascular homeostasis contributing not only to the elevation of blood pressure, but also to the complications of hypertension. This review summarizes research on endothelins and its receptor antagonists in experimental hypertension, with special emphasis on vascular remodeling and target-organ protection.

Role of endothelin-1 in hypertension

Endothelin-1 (ET-1) was first characterized as a potent vasoconstrictor and is overexpressed in the vasculature in different models of hypertension, such as deoxycorticosterone acetate-salt rats, Dahl salt-sensitive rats, and stroke-prone spontaneously hypertensive rats. Moreover, patients with moderate to severe hypertension present increased vascular levels of prepro-ET-1 mRNA. In addition to their blood pressure-lowering effects, ET receptor antagonists are able to reduce vascular growth. Recent data suggest the involvement of an inflammatory response in the effects of ET-1, which contributes to vascular remodeling and endothelial dysfunction. Increasing evidence underscores the potential therapeutic benefit of ET receptor antagonists in different hypertension-related complications, not only in essential hypertension, but also in patients with type 2 diabetes.

Heterogeneity in the acute control of vascular protein synthesis in vivo

In response to both hemodynamic and neurohumoral changes, the cardiovascular system remodels and this process could contribute to end organ damage. The aim of this study was to determine the early in vivo interactions between 3 systems known to contribute to vascular hypertrophic remodeling, in conduit and resistance arteries. Exogenous angiotensin II, norepinephrine and endothelin 1 administration elevated protein synthesis in the aorta and in small mesenteric arteries. In small arteries, the effect of angiotensin II was blocked by angiotensin II type 1, alpha-adrenergic and endothelin receptor antagonists, while only the alpha-adrenergic and endothelin receptor antagonists inhibited the effect of norepinephrine. Moreover, only the endothelin receptor antagonist significantly blunted the effect of exogenous endothelin on protein synthesis. In the aorta, the stimulation of angiotensin II on protein synthesis was also inhibited by the 3 antagonists. However, only the alpha-adrenoceptor antagonist blunted the response to norepinephrine, and the 3 antagonists prevented the endothelin-induced elevation of protein synthesis. The blood pressure effects of the drugs did not correlate with their capacity to stimulate or inhibit vascular protein synthesis. In conclusion, interactions in the control of protein synthesis are heterogeneous along the vascular tree. In small arteries, the interaction is linear with endothelin as the downstream effector. In the aorta, the local sympathetic nervous system appears to control protein synthesis. The heterogeneity in downstream effectors should be considered in studies investigating signaling events related to protein synthesis, which is used as an early marker of hypertrophy.

Aldosterone: a risk factor for vascular disease

Blockade of the renin-angiotensin-aldosterone system with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor antagonists has resulted in beneficial effects in essential hypertensive patients. However, occurrence of cardiovascular events has not been appropriately controlled beyond a certain percentage. One reason could be the effects of aldosterone, the final component of the system. The aldosterone escape phenomenon could explain undesirable outcomes observed in hypertensive patients even under treatment with ACE inhibitors or angiotensin antagonists. Aldosterone has direct effects on the vasculature and has been associated with vascular smooth muscle cell hypertrophy, endothelial dysfunction, cardiac fibrosis, proteinuria, and renal vascular injury. Animal models and clinical trials have proven the benefit of aldosterone receptor antagonism. With increased recognition of the prevalence of hyperaldosteronism in patients thought to have "essential" hypertension, the use of drugs that block aldosterone action may become more widespread and protect the vasculature from the deleterious effects of aldosterone.

Myocardial ultrasonic backscatter in hypertension: relation to aldosterone and endothelin

A disproportionate accumulation of fibrillar collagen is a characteristic feature of hypertensive heart disease, but the extent of myocardial fibrosis may differ in different models of hypertension. In experimental studies, aldosterone and endothelins emerge as important determinants of myocardial fibrosis. Changes in myocardial extracellular matrix and collagen deposition can be estimated noninvasively by analysis of the ultrasonic backscatter signal, which arises from tissue heterogeneity within the myocardium and describes myocardial texture. This study was designed to investigate the relations between myocardial integrated backscatter and circulating aldosterone and immunoreactive endothelin in human hypertension. The study population consisted of 56 subjects: 14 healthy normotensive volunteers and 42 hypertensive patients (14 with primary aldosteronism, 7 with renovascular hypertension, and 21 with essential hypertension). The patients with essential and secondary hypertension were matched for age, gender, body mass index, and blood pressure. Myocardial integrated backscatter at diastole was 19.8+/-2.0 and 20.8+/-2.9 decibels in normotensive control subjects and patients with essential hypertension and significantly higher in patients with primary aldosteronism (27.4+/-3.8 decibels, P<0.01) and renovascular hypertension (26.8+/-4.8 decibels, P<0.01). In the population as a whole, as well as in the hypertensive subpopulation, myocardial integrated backscatter was directly related to plasma aldosterone (r=0.73 and 0.71, P<0.01 for both) and immunoreactive endothelin (r=0.60 and 0.56, P<0.01 for both). The data of this study suggest that in human hypertension, circulating aldosterone and immunoreactive endothelin may induce alterations in left ventricular myocardial texture, possibly related to increased myocardial collagen content.

Resistance artery mechanics and composition in angiotensin II-infused rats: effects of aldosterone antagonism

BACKGROUND

Angiotensin (Ang) II stimulates aldosterone production, which may mediate some of the effects of Ang II.

OBJECTIVE

To test whether Ang II-induced structural and mechanical changes in resistance arteries may be prevented by the non-selective aldosterone receptor blocker, spironolactone, independently of reduction in blood pressure.

METHODS

Male Sprague-Dawley rats received Ang II [120 ng/kg per min subcutaneously (s.c.)] with or without spironolactone or hydralazine (25 mg/kg per day). Two additional groups received aldosterone (750 ng/h s.c.) with or without spironolactone. After 2 weeks, third-order mesenteric arteries were dissected and studied by pressurized myograph. Deposition of collagen type I/III in the vascular wall was evaluated by confocal immunofluorescence microscopy.

RESULTS

Ang II increased blood pressure significantly (P <0.01); this was partially prevented by spironolactone (P <0.01) and nearly normalized by hydralazine (P <0.01). Media thickness, media:lumen ratio and media cross-sectional area of mesenteric resistance arteries increased under Ang II or aldosterone (P <0.01) and this was partially prevented by spironolactone (P <0.01), but not by hydralazine. Compared with the control or Ang II + spironolactone groups, rats treated with Ang II with or without hydralazine presented stiffer vessels, with leftward shift of the stress-strain relationship and a raised slope of the incremental elastic modulus-stress relationship (P <0.05). Confocal microscopy demonstrated enhanced deposition of collagen type I/III in the media of arteries from rats infused with Ang II or aldosterone, an effect that was prevented partially by spironolactone but unaffected by hydralazine.

CONCLUSION

Ang II-induced vascular alterations in structure, mechanics and composition were partially prevented by spironolactone, independently of blood pressure reduction, providing further evidence that some actions of Ang II on resistance arteries are mediated by aldosterone.

Aldosterone augments endothelin-1-induced cardiac myocyte hypertrophy with the reinforcement of the JNK pathway

Aldosterone is thought to regulate cardiac work independently of sodium retention, though the mechanisms remain to be known. In the present study, we have demonstrated that aldosterone reinforces endothelin-mediated cardiac hypertrophy with the increase in cell surface area and upregulation of the transcripts characteristic of hypertrophy. We have also shown that aldosterone augments c-Jun N-terminal kinase activation induced by endothelin-1. Taken together, it is suggested that aldosterone modulates cardiac hypertrophy, at least partially, synergistically with extracellular signals that have been shown to be involved in cardiac remodeling.

Fibrosis, matrix metalloproteinases, and inflammation in the heart of DOCA-salt hypertensive rats: role of ET(A) receptors

In deoxycorticosterone acetate (DOCA)-salt hypertension, the endothelin-1 system is activated and plays a role in cardiac fibrosis. Remodeling of extracellular matrix (ECM) may lead to interstitial fibrosis, which may contribute to heart failure. Imbalance in synthesis and degradation of the ECM by matrix metalloproteinases (MMPs) as well as inflammation may play a role in matrix protein deposition and cardiac remodeling in hypertension. We measured expression of the extracellular matrix protein fibronectin, the activity of the gelatinases MMP-2 and MMP-9, the proinflammatory transcription factor NFkappaB, and the adhesion molecules, vascular cell adhesion molecule (VCAM)-1 and platelet-endothelial cell adhesion molecule (PECAM)-1 in hearts of DOCA-salt hypertensive (DS) rats treated or not with the endothelin ET(A) antagonist BMS 182874 (BMS). Unilaterally nephrectomized rats (UniNx) were compared with DS rats treated or not with BMS 40 mg/kg/d. Fibronectin deposition was detectable at the first week, and remained elevated thereafter. This increase was abrogated by administration of the ET(A) antagonist. Enzymatic activity of gelatinases was increased (P<0.01) in DS compared with control during the first and second week. BMS blocked the increase of MMP-2 and MMP-9 activity at week 1 (P<0.05); MMP activity remained lower than in DS at week 2. NF-kappaB binding activity in DS was higher (P<0.05) than it was in controls during the second week, and was reduced by BMS. The adhesion molecules VCAM-1 and PECAM-1, and the antiapoptotic molecule xIAP were upregulated in the left ventricle of the heart of DS rats and downregulated in the rats treated with the ET(A) antagonist. In conclusion, cardiac extracellular remodeling in rats with endothelin-dependent hypertension was associated with increased fibronectin, MMP activity, and upregulation of inflammatory mediators, all of which were reduced by ET(A) antagonism.