Influence of aldosterone on collagen synthesis and proliferation of rat cardiac fibroblasts

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.

Spironolactone (an adjuvant therapy) in rheumatoid arthritis: a case control study

OBJECTIVES

Disease-modifying anti-rheumatic drugs (DMARDs) are conventionally used in rheumatoid arthritis (RA). The role of spironolactone as add on therapy to DMARDs in RA patients was evaluated.

MATERIAL AND METHODS

A total of 100 patients with rheumatoid arthritis diagnosed as per 1987 criteria having evidence of active disease despite ongoing DMARD therapy were enrolled in this study. Patients were assigned randomly to two groups. Group I (n = 50) patients were treated with 50 mg/day of spironolactone along with their maintenance DMARD and NSAID therapy. Group II (n = 50) patients continued their maintenance DMARD therapy without spironolactone. Disease activity was assessed using the Disease Activity Score-28 (DAS28) and the Clinical Disease Activity Index (CDAI) in each patient of each group was evaluated monthly for the next three months.

RESULTS

All patients completed the study. Mean age of group I was 46.44 ±11.67 and of group II 44.52 ±11.82. DAS28 assessed in time according to the schedule was for group I 6.78 ±0.74, 5.34 ±0.74, 3.98 ±0.7, 3.00 ±0.75, while in group II it was 6.61 ±0.82, 5.49 ±0.90, 4.58 ±0.81, 3.55 ±0.93 at baseline, 4, 8, and 12 weeks respectively. CDAI in group I was 41.68 ±11.14, 24.36 ±8.13, 12.34 ±5.73, 6.42 ±4.4 and in group II 37.84 ±11.12, 24.54 ±9.4, 16.38 ±6.81, 9.62 ±6.1 at baseline, 4, 8, and 12 weeks respectively. Group I showed significant improvement in disease activity in the form of tender joint count (p = 0.001), swollen joint count (p = 0.023), patient global assessment (p = 0.001), physician global health (p = 0.001), DAS28 (p < 0.001) and CDAI (p = 0.001) but other parameters showed non-significant improvement compared to group II. No serious adverse events were observed in either group during the course of the study.

CONCLUSIONS

Spironolactone as an adjuvant therapy can improve the effect of conventional DMARD treatment of patients with RA.

Pathophysiology of Myocardial Infarction

Myocardial infarction is defined as sudden ischemic death of myocardial tissue. In the clinical context, myocardial infarction is usually due to thrombotic occlusion of a coronary vessel caused by rupture of a vulnerable plaque. Ischemia induces profound metabolic and ionic perturbations in the affected myocardium and causes rapid depression of systolic function. Prolonged myocardial ischemia activates a "wavefront" of cardiomyocyte death that extends from the subendocardium to the subepicardium. Mitochondrial alterations are prominently involved in apoptosis and necrosis of cardiomyocytes in the infarcted heart. The adult mammalian heart has negligible regenerative capacity, thus the infarcted myocardium heals through formation of a scar. Infarct healing is dependent on an inflammatory cascade, triggered by alarmins released by dying cells. Clearance of dead cells and matrix debris by infiltrating phagocytes activates anti-inflammatory pathways leading to suppression of cytokine and chemokine signaling. Activation of the renin-angiotensin-aldosterone system and release of transforming growth factor-β induce conversion of fibroblasts into myofibroblasts, promoting deposition of extracellular matrix proteins. Infarct healing is intertwined with geometric remodeling of the chamber, characterized by dilation, hypertrophy of viable segments, and progressive dysfunction. This review manuscript describes the molecular signals and cellular effectors implicated in injury, repair, and remodeling of the infarcted heart, the mechanistic basis of the most common complications associated with myocardial infarction, and the pathophysiologic effects of established treatment strategies. Moreover, we discuss the implications of pathophysiological insights in design and implementation of new promising therapeutic approaches for patients with myocardial infarction.

Twenty-four-hour urinary aldosterone predicts inappropriate left ventricular mass index in patients with primary aldosteronism

Objective. Primary aldosteronism (PA) is associated with inappropriate left ventricular hypertrophy (LVH) in relation to a given gender and body size. There is no ideal parameter to predict the presence of LVH or inappropriate LVH in patients with PA. We investigate the performance of 24-hour urinary aldosterone level, plasma renin activity and aldosterone-to-renin ratio on this task. Methods. We performed echocardiography in 106 patients with PA and 31 subjects with essential hypertension (EH) in a tertiary teaching hospital. Plasma renin activity, aldosterone concentration, and 24-hour urinary aldosterone level were measured. Results. Only 24-hour urinary aldosterone was correlated with left ventricular mass index (LVMI) and excess LVMI among these parameters. The multivariate analysis revealed the urinary aldosterone level as an independent predictor for LVMI and excess LVMI. Analyzing the ability of urinary aldosterone, plasma aldosterone concentration, and plasma aldosterone-to-renin ratio to identify the presence of LVH (ROC AUC = 0.701, 0.568, 0.656, resp.) and the presence of inappropriate LV mass index (defined as measured LVMI in predicting LVMI ratio >135%) (ROC area under curve = 0.61, 0.43, 0.493, resp.) revealed the better performance of 24-hour urinary aldosterone. Conclusions. In conclusion, 24-hour urinary aldosterone level performed better to predict the presence of LVH and inappropriate LVMI in patients with PA.

Impact of salt on cardiac differential gene expression and coronary lesion in normotensive mineralocorticoid-treated mice

We previously reported that excess of deoxycorticosterone-acetate (DOCA)/salt-induced cardiac hypertrophy in the absence of hypertension in one-renin gene mice. This model allows us to study molecular mechanisms of high-salt intake in the development of cardiovascular remodeling, independently of blood pressure in a high mineralocorticoid state. In this study, we compared the effect of 5-wk low- and high-salt intake on cardiovascular remodeling and cardiac differential gene expression in mice receiving the same amount of DOCA. Differential gene and protein expression was measured by high-density cDNA microarray assays, real-time PCR and Western blot analysis in DOCA-high salt (HS) vs. DOCA-low salt (LS) mice. DOCA-HS mice developed cardiac hypertrophy, coronary perivascular fibrosis, and left ventricular dysfunction. Differential gene and protein expression demonstrated that high-salt intake upregulated a subset of genes encoding for proteins involved in inflammation and extracellular matrix remodeling (e.g., Col3a1, Col1a2, Hmox1, and Lcn2). A major subset of downregulated genes encoded for transcription factors, including myeloid differentiation primary response (MyD) genes. Our data provide some evidence that vascular remodeling, fibrosis, and inflammation are important consequences of a high-salt intake in DOCA mice. Our study suggests that among the different pathogenic factors of cardiac and vascular remodeling, such as hypertension and mineralocorticoid excess and sodium intake, the latter is critical for the development of the profibrotic and proinflammatory phenotype observed in the heart of normotensive DOCA-treated mice.

Proteins mediating collagen biosynthesis and accumulation in arterial repair: novel targets for anti-restenosis therapy

Events contributing to restenosis after coronary interventions include platelet aggregation, inflammatory cell infiltration, growth factor release, and accumulation of smooth muscle cells (SMCs) and extracellular matrix (ECM). The ECM is composed of various collagen subtypes and proteoglycans and over time constitutes the major component of the mature restenotic plaque. The pathophysiology of collagen accumulation in the ECM during arterial restenosis is reviewed. Factors regulating collagen synthesis and degradation, including various cytokines and growth factors involved in the process, may be targets for therapies aimed at prevention of in-stent restenosis.

Regulation of placental growth by aldosterone and cortisol

During pregnancy, trophoblasts grow to adapt the feto-maternal unit to fetal requirements. Aldosterone and cortisol levels increase, the latter being inactivated by a healthy placenta. By contrast, preeclamptic placental growth is reduced while aldosterone levels are low and placental cortisol tissue levels are high due to improper deactivation. Aldosterone acts as a growth factor in many tissues, whereas cortisol inhibits growth. We hypothesized that in preeclampsia low aldosterone and enhanced cortisol availability might mutually affect placental growth and function. Proliferation of cultured human trophoblasts was time- and dose-dependently increased with aldosterone (P < 0.04 to P < 0.0001) and inhibited by spironolactone and glucocorticoids (P < 0.01). Mineralo- and glucocorticoid receptor expression and activation upon agonist stimulation was verified by visualization of nuclear translocation of the receptors. Functional aldosterone deficiency simulated in pregnant mice by spironolactone treatment (15 μg/g body weight/day) led to a reduced fetal umbilical blood flow (P < 0.05). In rat (P < 0.05; R(2) = 0.2055) and human (X(2) = 3.85; P = 0.0249) pregnancy, placental size was positively related to plasma aldosterone. Autocrine production of these steroid hormones was excluded functionally and via the absence of specific enzymatic transcripts for CYP11B2 and CYP11B1. In conclusion, activation of mineralocorticoid receptors by maternal aldosterone appears to be required for trophoblast growth and a normal feto-placental function. Thus, low aldosterone levels and enhanced cortisol availability may be one explanation for the reduced placental size in preeclampsia and related disorders.

Chronic intermittent hypoxia induces 11beta-hydroxysteroid dehydrogenase in rat heart

Corticosteroids are known to not only regulate electrolyte homeostasis but also play a role in the cardiovascular system, including myocardial remodeling. Because transgenic mice that overexpress 11beta-hydroxysteroid dehydrogenase (11HSD) type 2 in cardiomyocytes have been shown to spontaneously develop cardiac hypertrophy and fibrosis, we investigated whether changes in the cardiac metabolism of glucocorticoids accompany remodeling of the heart under physiological conditions. In the present study, glucocorticoid metabolism and 11HSD2 were explored in the hearts of rats exposed to chronic intermittent hypobaric hypoxia (CIH), which induces hypertrophy and fibrosis of the right and less of the left ventricle. We first demonstrated that adaptation to CIH led to a significant increase in 11HSD2 transcript levels and activity in the myocardium. In contrast, neither 11HSD1 activity and mRNA level nor the abundance of mineralocorticoid and glucocorticoid receptor mRNA were up-regulated. The adaptation to CIH also led to an increase of 11HSD2 mRNA in isolated cardiomyocytes, whereas 11HSD1, glucocorticoid receptor, and mineralocorticoid receptor mRNA levels were not changed in comparison with the cardiomyocytes of control normoxic rats. The changes in cardiac metabolism of glucocorticoids were accompanied by inflammatory responses. The expression levels of the proinflammatory markers cyclooxygenase-2 and osteopontin were significantly increased in both the myocardium and the cardiomyocytes isolated from rats exposed to CIH. These findings suggest that myocardial remodeling induced by CIH is associated with the up-regulation of cardiac 11HSD2. Consequently, local metabolism of glucocorticoids could indeed play a role in cardiac hypertrophy and fibrosis.

Salt-sensitive blood pressure in mice with increased expression of aldosterone synthase

To study the effects of modestly increased expression of aldosterone synthase (AS), we generated mice (AS(hi/hi)) by replacing the 3' untranslated region of AS mRNA with that from a stable mRNA. AS(hi/hi) mice on a normal-salt diet had 1.5 times the wild-type AS mRNA in adrenals, although their blood pressure and plasma aldosterone did not differ from wild-type mice. Changes in dietary salt did not affect the blood pressure of wild-type mice, but AS(hi/hi) mice had approximately 10-mm Hg higher blood pressure on a high-salt diet than on a low-salt diet and than wild-type mice on either diet. The AS(hi/hi) mice on a high-salt diet also had higher plasma aldosterone, lower plasma potassium, and greater renal expression of the alpha subunit of epithelial sodium channel compared with wild-type mice. The AS(hi/hi) mice on a high-salt diet also had more water intake and urine volume and less urine osmolality than wild-type mice. On a low-salt diet, AS(hi/hi) mice maintained normal blood pressure with less activation of the renin-angiotensin-aldosterone system than wild-type mice. The AS(hi/hi) mice also had less water intake and urine volume and higher urine osmolality than wild-type mice. On a medium high-salt diet, AS(hi/hi) mice were more susceptible than wild-type mice to infusion of angiotensin II, having a higher blood pressure, greater cardiac hypertrophy, and increased oxidative stress. Thus, a modest increase in AS expression makes blood pressure more sensitive to salt, suggesting that genetically increased AS expression in humans may contribute to hypertension and cardiovascular complications in societies with high-salt diets.

A look between the cardiomyocytes: the extracellular matrix in heart failure

The extracellular matrix (ECM) of the heart dynamically interacts with various cellular components of the myocardium, including the myocytes and connective tissue cells. With the development and progression of heart failure, left ventricular (LV) myocardial remodeling occurs. The progression of LV remodeling is accompanied by alterations in the structure and function of the ECM that occur after injury resulting from neurohormonal activation, changes in LV loading conditions, and alterations in myocardial perfusion and metabolism and is secondary to a host of nonmyocyte signaling pathways that affect repair and remodeling of the myocardium as a whole. This article attempts to review some of these processes and their interactions and to provide a focus to the often overlooked contribution of the ECM to the development and progression of heart failure and thereby its potential role as a target for therapy for heart failure.

Somatostatin at nanomolar concentration reduces collagen I and III synthesis by, but not proliferation of activated rat hepatic stellate cells

Previous studies have shown antifibrotic effects of somatostatin. Since hepatic stellate cells (HSC) express somatostatin receptors and play a key role in hepatic fibrogenesis, we investigated the in vitro antifibrotic effect of somatostatin on rat HSC. At day 12 after isolation, cells were exposed to different concentrations of somatostatin (10(-6)-10(-9) mol l(-1)). mRNA expression of collagen types I and III, and of smooth muscle alpha-actin (alpha-SMA) was analysed by Northern blotting. At 10(-9) mol l(-1), somatostatin significantly reduced mRNA expression of collagen I (72.3 +/- 10.7%; 95% confidence interval (95% CI): 45.5-99.0), collagen III (79.0 +/- 4.5%; 95% CI: 67.6-90.4) and alpha-SMA (65.7 +/- 5.9%; 95% CI: 51.1-80.2), as compared to control normalized at 100%. These results were confirmed by quantitative RT-PCR. Cycloheximide experiments indicated that somatostatin has no direct transcriptional effect.Using immunoprecipitation, we demonstrated that somatostatin also decreased de novo synthesis of collagen I (73 +/-10%; 95% CI: 48-98%), collagen III (65 +/- 13%; 95% CI: 33-97%) and alpha-SMA (47 +/- 9%; 95% CI: 25-69%). Remarkably, at higher concentrations, somatostatin did not suppress collagen mRNA expression nor de novo protein synthesis. We ascribe this observation to desensitization of the cells for somatostatin. Cell proliferation, as measured by 5-bromo-2'-deoxyuridine labelling, was not altered by somatostatin. No significant effect on the intermediate and actin cytoskeleton were detected by immunohistochemistry and Western blotting. Our findings imply that in vivo antifibrotic effects of somatostatin could result partially from a direct action of somatostatin on HSC, but other, in vivo effects are probably also involved.

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.

Chemopreventive effect of five drugs on renal interstitial fibrosis induced by an aristolochic acid-containing Chinese herb in rats

BACKGROUND/AIMS

This study focuses on the chemopreventive effect of five drugs on renal interstitial fibrosis induced by an aristolochic acid-containing Chinese herb Mu-Tong.

METHODS

Renal interstitial fibrosis was induced in rats by administration of the Mu-Tong solution intragastrically for 6 weeks, and 36 rats were randomly divided into six groups: (1) Mu-Tong, (2) Mu-Tong + captopril, (3) Mu-Tong + losartan, (4) Mu-Tong + simvastatin, (5) Mu-Tong + spironolactone, and (6) Mu-Tong + diammonium glycyrrhizinate. Blood biochemistry and extracellular matrix were detected at weeks 0, 2, 4, and 6. At the end of week 6, kidney tissue of all groups was evaluated with special Masson staining for the degree of renal fibrosis as well as regular histopathology.

RESULTS

Mu-Tong caused progressive elevation of blood urea nitrogen, creatinine, hyaluronic acid, procollagen type III, and laminin. All five drugs suppressed elevation of blood biochemistry and extracellular matrix to some degree, but only the simvastatin group showed a significantly reduced percentage of positive Masson staining area in renal section compared to the Mu-Tong group (p < 0.05).

CONCLUSIONS

Our study indicates that Mu-Tong induces a similar kidney injury with general characteristics in patients with renal interstitial fibrosis. All five different drugs have suppressive effects on Mu-Tong-induced renal function damage, and in particular, simvastatin shows a protective effect on development of Mu-Tong-induced renal interstitial fibrosis to a certain degree.

Effects of adrenomedullin on aldosterone-induced cell proliferation in rat cardiac fibroblasts

Aldosterone induces cardiac remodeling in cardiovascular diseases by stimulating the proliferation, production and secretion of collagen in fibroblasts. It also stimulates vascular smooth muscle cells to produce and secrete adrenomedullin (ADM), which has a cytoprotective effect against cardiovascular damage. We examined the effect of aldosterone on ADM production and secretion in rat cardiac fibroblasts, and the effect of ADM on aldosterone-stimulated fibroblast proliferation to observe the interaction between endogenous ADM and aldosterone. We detected ADM produced and secreted from cultured cardiac fibroblasts and the intracellular cAMP level by radioimmunoassay; evaluated cell proliferation by the level of [3H]-thymine incorporation; measured preproADM gene expression by reverse transcriptase polymerase chain reaction (RT-PCR); and monitored extracellular signal related kinase (ERK) activity by the phosphorylation of myelin basic protein in the presence of [gamma-32P] ATP. Our results showed that aldosterone-stimulated secretion of ADM and its mRNA expression were concentration-dependent, which could be inhibited by the specific antagonist of mineralocorticoid receptor, spironolactone. In contrast, ADM inhibited aldosterone-induced fibroblast proliferation and ERK activity. Treatment with ADM24-50 (a new antagonist of specific ADM receptors) and calcitonin gene-related peptide (CGRP)8-37 (the antagonist of CGRP receptor type 1), to attenuate the action of endogenous ADM, reinforced the aldosterone-induced proliferation and inhibited the intracellular cAMP production stimulated by aldosterone. Thiorphan, an inhibitor of ADM degradation, inhibited the [3H]-thymine incorporation and reinforced the intracellular cAMP level induced by aldosterone. We reach the conclusion that aldosterone stimulates rat cardiac fibroblasts to produce and secrete ADM, which in turn regulates the proliferation-induced effects of aldosterone in these cells.

Expression of somatostatin receptors in normal and cirrhotic human liver and in hepatocellular carcinoma

BACKGROUND

Somatostatin analogues have been used with conflicting results to treat advanced hepatocellular carcinoma (HCC). The aim of this study was to investigate expression of somatostatin receptor (SSTR) subtypes in human liver, and to examine the effect of selective SSTR agonists on proliferation, apoptosis, and migration of hepatoma cells (HepG2, HuH7) and hepatic stellate cells (HSCs).

METHODS

Expression of SSTRs in cell lines, normal and cirrhotic liver, and HCC was examined by immunohistochemistry and reverse transcription-polymerase chain reaction. Effects of SSTR agonists on proliferation and apoptosis of tumour cells and HSCs were assessed by the 5-bromo-2' deoxyuridine and TUNEL methods, respectively. The influence of SSTR agonists on migration was investigated using Boyden chambers.

RESULTS

In normal liver, both hepatocytes and HSCs were negative for all five SSTRs. Cirrhotic liver and HCC as well as cultured hepatoma cells and HSCs expressed all five SSTRs, both at the protein and mRNA levels, except for HuH7 cells which did not immunoreact with SSTR3. None of the agonists influenced proliferation or apoptosis. However, compared with untreated cells, L-797,591, an SSTR1 agonist, reduced migration of HepG2, HuH7, and HSCs significantly to 88 (7)% (p<0.05), 83 (11)% (p<0.05), and 67 (13)% (p<0.01), respectively.

CONCLUSIONS

Cirrhotic liver and HCC express SSTRs. Although the somatostatin analogues used in this study did not affect proliferation and apoptosis, stimulation of SSTR1 may decrease invasiveness of HCC by reducing migration of hepatoma cells and/or HSCs. Clinical trials evaluating somatostatin analogues for the treatment of HCC should take these findings into account.

Aldosterone antagonist facilitates the cardioprotective effects of angiotensin receptor blockers in hypertensive rats

BACKGROUND

There is increasing evidence to support the importance of blocking aldosterone to prevent target-organ damage in hypertension. We recently demonstrated an aldosterone breakthrough phenomenon during administration of an angiotensin type 1 receptor blocker (ARB).

OBJECTIVE

To elucidate the pathophysiological significance of residual aldosterone by investigating the influence of the aldosterone antagonist on the cardioprotective effects of the ARB in hypertensive rats.

METHODS

Injection vehicle alone, ARB (1.0 mg/kg per day candesartan by mouth), aldosterone antagonist (10 mg/kg per day spironolactone, subcutaneously), or combined treatment were administered to male stroke-prone spontaneously hypertensive rats for 24 weeks from the age of 4 weeks. Blood pressure, plasma angiotensin II and aldosterone concentrations, left ventricular weight, expression of type I and type III collagen mRNA, and histological findings were determined.

RESULTS

In the ARB-treated group, aldosterone concentrations remained unchanged (1.10 +/- 0.20 nmol/l, compared with 1.17 +/- 0.46 nmol/l in the control group), whereas systolic blood pressure (178 +/- 9 mmHg), left ventricular weight (0.372 +/- 0.035 g/100 g body weight), expression of collagen mRNA, and cardiac interstitial and perivascular fibrosis all decreased significantly compared with the control group (systolic blood pressure: 222 +/- 10 mmHg, P < 0.05; left ventricular weight: 0.483 +/- 0.021 g/100 g body weight, P < 0.05). Although blood pressure (217 +/- 9 mmHg) and left ventricular weight (0.467 +/- 0.027 g/100 g body weight) remained unchanged in the group receiving spironolactone, the expression of both types of collagen mRNA and cardiac interstitial and perivascular fibrosis showed a significant decrease compared with the vehicle-treated group. In the rats receiving combined treatment with the ARB and spironolactone, left ventricular weight (0.352 +/- 0.005 g/100 g body weight, P < 0.05), expression of collagen mRNA, and cardiac interstitial and perivascular fibrosis all showed a further improvement compared with both the ARB and spironolactone groups.

CONCLUSIONS

These results demonstrate that residual aldosterone has a significant impact on target-organ damage in hypertension, even during chronic administration of an ARB. The addition of an aldosterone antagonist has an advantage in facilitating the cardioprotective effects of ARBs.

Effect of HMG-CoA reductase inhibitors on proliferation and protein synthesis by rat hepatic stellate cells

BACKGROUND/AIMS

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors called statins, have besides their cholesterol-lowering function, therapeutic value in conditions such as neo-angiogenesis and atherosclerosis. We investigated the effect of two statins on the proliferation rate and protein steady state levels of hepatic stellate cells (HSC).

METHODS

Cellular DNA synthesis under the influence of statins and/or platelet derived growth factor (PDGF) and mevalonate was evaluated by measuring BrdU incorporation. Synthesis of collagens type I, III, IV and fibronectin was quantified by ELISA. Additionally, we examined the influence of simvastatin on isoprenylation of Ras and RhoA proteins.

RESULTS

Lovastatin and simvastatin induced a dose-dependent inhibition of the proliferation rate of HSC. Subsequent addition of PDGF and/or mevalonate, after long-term exposure of simvastatin to HSC, did not reverse simvastatins' antiproliferative effect. Lovastatin and simvastatin reduced the protein steady state level of collagens type I (-40%), III (-45%) and IV (-27%). Membrane bound Ras steady state levels decreased under the influence of simvastatin. Membrane bound RhoA remained unaltered, whereas, cytosolic RhoA protein level was strongly reduced.

CONCLUSIONS

Our data showed that lovastatin and simvastatin inhibited HSC proliferation and collagen steady state levels by mechanisms independent of their lipid reducing activities.

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.

Actin filament formation, reorganization and migration are impaired in hepatic stellate cells under influence of trichostatin A, a histone deacetylase inhibitor

BACKGROUND/AIMS

Previously, trichostatin A (TSA), a histone deacetylase inhibitor, has been shown to exhibit strong antifibrotic characteristics in hepatic stellate cells (HSC), which are known to play a central role in chronic liver diseases. TSA retained a more quiescent phenotype in spite of culture conditions that favor transdifferentiation into activated HSC.

METHODS

To identify TSA-sensitive genes, differential mRNA display, Northern and Western blot analysis were used and genes were functionally validated by using contraction and motility assays.

RESULTS

TSA prevented new actin filament formation by down-regulation of two nucleating proteins, actin related protein 2 (Arp2) and Arp3, and by up-regulation of adducin like protein 70 (ADDL70) and gelsolin, two capping proteins. RhoA, a key mediator in the development of the actin cytoskeleton, decreased following TSA exposure. Expression of proteins of Class III intermediate filaments was affected by TSA. Furthermore, F-actin and G-actin were expressed heterogeneously under influence of TSA. Functionally, TSA treatment abrogated migration of quiescent HSC, while migration was reduced in transitional HSC. The endothelin-1-induced contractility properties of HSC was not affected by TSA.

CONCLUSIONS

These data indicate that TSA affects the development of the actin cytoskeleton in quiescent HSC and thereby abrogates the process of HSC transdifferentiation.

Upregulation of arterial serotonin 1B and 2B receptors in deoxycorticosterone acetate-salt hypertension

Previous studies have established a role for 5-hydroxytryptamine (5-HT)(2B) and 5-HT(1B) receptors in mediating enhanced contraction to serotonin (5-HT) in arteries from hypertensive deoxycorticosterone acetate (DOCA)-salt rats. To determine whether the observed increase in responsiveness was due to upregulation of 5-HT receptors, we used Western analysis to measure 5-HT(1B) and 5-HT(2B) receptor protein density. In endothelium-denuded aortas from hypertensive DOCA-salt rats (mean systolic blood pressure 192 +/- 6 mm Hg), 5-HT(1B) and 5-HT(2B) receptor proteins were upregulated approximately 2-fold compared with the response in the aortas of sham-operated control rats (mean systolic blood pressure 119 +/- 2 mm Hg). Contraction to 5-HT(2B) receptor agonists was also enhanced in arteries from Wistar-Furth rats given DOCA and salt. This strain is relatively resistant to the hypertensive effects of DOCA and salt treatment. A common factor between the model of DOCA-salt hypertension and the DOCA-salt--treated Wistar-Furth rats is the presence of mineralocorticoids. Therefore, we tested the hypothesis that mineralocorticoids can upregulate 5-HT(1B) and 5-HT(2B) receptors. Aortas from normal Sprague-Dawley rats were incubated with aldosterone (100 nmol/L) for 8, 12, 24, and 48 hours. The expression of 5-HT(2B) and 5-HT(1B) receptor proteins was significantly increased (approximately 2- fold over vehicle treatment) by 8 hours. 5-HT(2B) and 5-HT(1B) receptors were upregulated by aldosterone in a concentration-dependent manner, and incubation with spironolactone (10 micromol/L) blocked this upregulation. These data support the conclusion that the increased expression of 5-HT(1B) and 5-HT(2B) receptors observed in arteries from DOCA-salt rats may be partially due to mineralocorticoids acting via the mineralocorticoid receptor to modulate gene expression.