Adrenal steroids and cardiac fibrosis

Activation of Liver X Receptors by GW3965 Attenuated Deoxycorticosterone Acetate-Salt Hypertension-Induced Cardiac Functional and Structural Changes

In this study, the effect of liver X receptor (LXR) activation on hypertension-induced cardiac structural and functional alterations was investigated. Hypertension was induced by deoxycorticosterone acetate (DOCA)-salt administration in uninephrectomized rats for 6 weeks. LXR agonist GW3965 (3-{3-[(2-chloro-3-trifluoromethyl-benzyl)-(2,2-diphenyl-ethyl)-amino]-propoxy}-phenyl)-acetic acid was given for the past week. Rhythmic activity and contractions of the isolated heart tissues were recorded. Biochemical parameters were assessed in ventricular tissue and plasma samples. Cardiac expressions of various proteins were examined, and histopathological evaluation was performed in the left ventricle and liver. GW3965 reduced systolic blood pressure and enhanced noradrenaline-stimulated papillary muscle contraction induced by DOCA-salt + uninephrectomy. Plasma and tissue total antioxidant capacity (TAC) increased and tissue 4-hydroxynonenal (4-HNE) levels decreased in the DOCA-salt group. GW3965 elevated plasma and tissue TAC levels in both of groups. Glucose-regulated protein-78 (GRP78), phospho-dsRNA-activated-protein kinase-like ER kinase (p-PERK), matrix metalloproteinase-2 (MMP-2), and nuclear factor-κB p65 (NF-κB p65) expression was augmented, and inhibitor-κB-α (IκB-α) expression was reduced in hypertensive hearts. The altered levels of all these markers were reversed by GW3965. Also, GW3965 ameliorated DOCA-salt + uninephrectomy-induced cardiac and hepatic inflammation and fibrosis. However, GW3965 unchanged the plasma lipid levels and hepatic balloon degeneration score. These results demonstrated that LXR activation may improve hypertension-induced cardiac changes without undesired effects.

Deficiency of T-type Ca2+ channels Cav3.1 and Cav3.2 has no effect on angiotensin II-induced hypertension but differential effect on plasma aldosterone in mice

T-type Ca²⁺ channel Ca_v3.1 promotes microvessel contraction ex vivo. It was hypothesized that in vivo, functional deletion of Ca_v3.1, but not Ca_v3.2, protects mice against angiotensin II (ANG II)-induced hypertension. Mean arterial blood pressure (MAP) and heart rate were measured continuously with chronically indwelling catheters during infusion of ANG II (30 ng·kg^-1·min^-1, 7 days) in wild-type (WT), Ca_v3.1^-/-, and Ca_v3.2^-/- mice. Plasma aldosterone and renin concentrations were measured by radioimmunoassays. In a separate series, WT mice were infused with ANG II (100 ng·kg^-1·min^-1) with and without the mineralocorticoid receptor blocker canrenoate. Ca_v3.1^-/- and Ca_v3.2^-/- mice exhibited no baseline difference in MAP compared with WT mice, but day-night variation was blunted in both Ca_v3.1 and Ca_v3.2^-/- mice. ANG II increased significantly MAP in WT, Ca_v3.1^-/-, and Ca_v3.2^-/- mice with no differences between genotypes. Heart rate was significantly lower in Ca_v3.1^-/- and Ca_v3.2^-/- mice compared with control mice. After ANG II infusion, plasma aldosterone concentration was significantly lower in Ca_v3.1^-/- compared with Ca_v3.2^-/- mice. In response to ANG II, fibrosis was observed in heart sections from both WT and Ca_v3.1^-/- mice and while cardiac atrial natriuretic peptide mRNA was similar, the brain natriuretic peptide mRNA increase was mitigated in Ca_v3.1^-/- mice ANG II at 100 ng/kg yielded elevated pressure and an increased heart weight-to-body weight ratio in WT mice. Cardiac hypertrophy, but not hypertension, was prevented by the mineralocorticoid receptor blocker canrenoate. In conclusion, T-type channels Ca_v3.1and Ca_v3.2 do not contribute to baseline blood pressure levels and ANG II-induced hypertension. Ca_v3.1, but not Ca_v3.2, contributes to aldosterone secretion. Aldosterone promotes cardiac hypertrophy during hypertension.

Mineralocorticoid Receptor Signaling as a Therapeutic Target for Renal and Cardiac Fibrosis

Activation of the mineralocorticoid receptor (MR) plays important roles in both physiological and pathological events. Blockade of MR signaling with MR antagonists (MRAs) has been used clinically to treat kidney and cardiac disease associated with hypertension and other chronic diseases, resulting in suppression of fibrosis in these organs. However, the current use of steroidal MRAs has been limited by off target effects on other hormone receptors or adverse effects on kidney tubular function. In this review, we summarize recent insights into the profibrotic roles of MR signaling in kidney and cardiovascular disease. We review experimental in vitro data identifying the pathological mechanisms associated with MR signaling in cell types found in the kidney (mesangial cells, podocytes, tubular cells, macrophages, interstitial fibroblasts) and heart (cardiomyocytes, endothelial cells, vascular smooth muscle cells, macrophages). In addition, we demonstrate the in vivo importance of MR signaling in specific kidney and cardiac cell types by reporting the outcomes of cell type selective MR gene deletion in animal models of kidney and cardiac disease and comparing these findings to those obtained with MRAs treatment. This review also includes a discussion of the potential benefits of novel non-steroidal MRAs for targeting kidney and cardiac fibrosis compared to existing steroidal MRAs, as well as the possibility of novel combination therapies and cell selective delivery of MRAs.

Effects of Reduced Kidney Function Because of Living Kidney Donation on Left Ventricular Mass

Living kidney donation is associated with a small but significant increase in cardiovascular mortality. In addition, mildly decreased kidney function is associated with an increase of left ventricular mass and with cardiovascular disease in patients with chronic kidney disease. To investigate this association, we evaluated the impact of mildly decreased kidney function after living kidney donation on subclinical cardiac structural and functional changes. In this prospective cohort study, cardiac and renal magnetic resonance imaging and laboratory analyses were performed in 23 living kidney donors (mean age 54±10 years, 52% male) before donation and at 4 and 12 months after nephrectomy. Mean estimated glomerular filtration rate was 102±15 mL min −1 1.73 m −2 before donation and 70±13 mL min −1 1.73 m −2 at 12 months ( P <0.001). Left ventricular mass increased from 112±22 to 115±23 g ( P <0.001). In addition, heart rate was significantly increased (65±7 to 74±14; P =0.04). Concurrently, kidney and adrenal gland volume increased from 163±33 to 195±34 mL ( P <0.001) and from 7.6±2.2 to 8.4±2.4 mL ( P =0.032), respectively, as did procollagen type III (Δ0.11 ng/mL, P <0.001) and not N-terminal probrain natriuretic peptide (Δ14 pg/mL, P =0.25). The mild decrease in kidney function after living kidney donation leads to a significant but clinically negligible increase in left ventricular mass 12 months after living kidney donation. This study of a longitudinal analysis of living kidney donors provides direct evidence of a kidney–heart link.

Suppression of aldosterone mediates regression of left ventricular hypertrophy in patients with hypertension

Background: High circulating aldosterone levels stimulate myocardial fibrosis and left ventricular hypertrophy (LVH). However, it is not clear whether suppression of aldosterone directly contributes to LVH regression in hypertensive patients.

Methods: The Aliskiren in Left Ventricular Hypertrophy (ALLAY) trial randomised 465 hypertensive overweight subjects with LVH to the direct renin inhibitor aliskiren 300 mg, losartan 100 mg or the combination and followed patients for 9 months. All patients were treated to standard blood pressure targets. Left ventricular (LV) mass index (LVMI) and LV wall thickness (LVWT) were assessed by cardiac magnetic resonance. A subset of 136 patients who had plasma aldosterone concentration (ALDO) measured at baseline and study end was analysed.

Results: At baseline, plasma ALDO was modestly related to systolic blood pressure, LVMI, and wall thickness (all, p < 0.05). Aliskiren, either alone or in combination, was associated with a significantly greater reduction from baseline to 9 months in plasma aldosterone than losartan alone ( p < 0.02). Reduction in ALDO was related to reduction in LVMI even after adjustment for baseline ALDO, BP reduction and treatment group ( p for trend = 0.042).

Conclusion: In hypertensive patients with increased LVWT, aliskiren alone or in combination with the angiotensin receptor blocker losartan provides greater reduction in aldosterone compared to losartan alone. Moreover, suppression of aldosterone was associated with reduction of LVH, independently of the change in SBP, suggesting that suppression of aldosterone, a known mediator of LVH, may be particularly important for LVH regression and as a target for therapy.

Ligand-selective potentiation of rat mineralocorticoid receptor activation function 1 by a CBP-containing histone acetyltransferase complex

The rat mineralocorticoid receptor (MR) has two activation functions in distinct regions of the A/B domain, designated activation function 1a (AF-1a; amino acids 1 to 169) and AF-1b (amino acids 451 to 600). Since the p160 family protein TIF2, a known component of the AF-2 coactivator complex, potentiates the transactivation function of AF-1b but not that of AF-1a, it is likely that some other, novel protein complex interacts with the AF-1a region. Therefore, we attempted to identify such coactivator complexes from HeLa nuclear extracts by biochemical purification using a glutathione S-transferase-MR AF-1a fusion protein. Purified AF-1a region-interacting proteins were found to contain RNA helicase A (RHA) and CBP. Further analysis showed that RHA interacted with the AF-1a region directly and then recruited a complex with histone acetyltransferase (HAT) activity that contained CBP. For full-length MR, aldosterone, but not hydrocortisone, was found to induce the binding of RHA/CBP complexes to the AF-1a region, as well as to allow the cooperative potentiation of MR transcriptional activity by RHA and CBP. In addition, a chromatin immunoprecipitation assay showed that aldosterone-bound MR, but not hydrocortisone-bound MR, recruited RHA/CBP complexes to native MR target gene promoters. Our results suggested that an altered conformation of the A/B region induced by aldosterone, but not hydrocortisone, might determine the accessibility of MR AF-1a to RHA/CBP complexes.

Treatment of familial hyperaldosteronism type I: only partial suppression of adrenocorticotropin required to correct hypertension

In familial hyperaldosteronism type I, inheritance of a hybrid 11beta-hydroxylase/aldosterone synthase gene leads to ACTH-regulated overproduction of aldosterone (causing hypertension) and of "hybrid" steroids, 18-hydroxy- and 18-oxo-cortisol. To determine whether complete suppression of the hybrid gene is necessary to normalize blood pressure, we sought evidence of persisting expression in eight patients who were rendered normotensive for 1.3-4.5 yr by glucocorticoid treatment. At the time of the study, six patients were receiving dexamethasone (0.125-0.25 mg/day) and two patients were taking prednisolone (2.5 or 5 mg/day). Urinary 18-oxo-cortisol levels during treatment demonstrated close correlation with mean "day curve" (blood collected every 2 h for 24 h) cortisol (r = 0.74), consistent with regulation by ACTH. Although urinary 18-oxo-cortisol levels were lower during than before treatment (mean 12.6 +/- 2.4 SEM vs. 35.0 +/- 5.6 nmol/mmol creatinine; P < 0.01), they remained above normal (0.8-5.2 nmol/mmol creatinine) in all eight patients. Although mean upright plasma potassium levels during treatment were higher, aldosterone levels lower, PRA levels higher, and aldosterone to PRA ratios lower than before treatment, PRA levels were uncorrected (< 13 pmol/L x min) and aldosterone to PRA ratios were uncorrected (>65) during treatment in four patients. For each of the eight patients, day curve aldosterone levels during treatment correlated more tightly with cortisol (mean r for the eight patients, 0.87 +/- 0.05 SEM) than with PRA (mean r = 0.36 +/- 0.10 SEM). Hence, control of hypertension by glucocorticoid treatment was associated, in all patients, with only partial suppression of ACTH-regulated hybrid steroid and aldosterone production. Normalization of urinary hybrid steroid levels and abolition of ACTH-regulated aldosterone production is not a requisite for hypertension control and, if used as a treatment goal, may unnecessarily increase the risk of Cushingoid side effects.

Inhibition of tissue repair by spironolactone: role of mineralocorticoids in fibrous tissue formation

Mineralocorticoids have been implicated in promoting fibrous tissue formation in various organs. In the present study, we sought to address the potential contribution of mineralocorticoids to fibrous tissue formation using a skin pouch model which has proved valuable for the analysis of inflammatory and wound healing responses. Skin pouches were induced in rats by administration of a phorbol ester, croton oil (0.5 ml of a 1% solution). After 2 weeks, rats were killed and intact pouch tissue collected. Pouch weights of control and aldosterone-treated (0.75 microg/h via osmotic minipump) rats were similar (3.33 +/- 0.44 g vs. 3.70 +/- 0.28 g respectively). However, pouch weights were reduced by more than 50% in spironolactone-treated (25 mg/day powdered in food) animals (1.62 +/- 0.22 g and 1.27 +/- 0.23 g respectively in aldosterone and spironolactone alone groups). To ascertain the effects of different treatments on collagen accumulation, hydroxyproline concentration was measured. Compared with controls, hydroxyproline concentration was significantly reduced following spironolactone treatment (17.1 +/- 0.08 vs. 7.5 +/- 2.0 microg/mg dry wt, respectively, p < 0.01). This response to spironolactone was negated by coadministration of aldosterone (hydroxyproline concentration was 18.6 +/- 2.1 microg/mg dry wt). Following bilateral adrenalectomy, spironolactone reduced pouch weight and hydroxyproline concentration, which was not the case for adrenalectomy alone. Two week aldosterone administration in uninephrectomized rats on high salt diet was deemed ineffective in modulating pouch development (pouch wet wts were 3.48 +/- 0.4 g vs. 3.00 +/- 0.19 g in controls and aldosterone-treated rats, respectively). Mineralocorticoid receptor expression in pouch tissue was demonstrated by RT/PCR. Furthermore, NADP+-dependent 11beta-hydroxysteroid dehydrogenase 1 (11beta-HSD1) activity was detected in pouch tissue, together with lower levels of NAD+-dependent 11beta-HSD2. Spironolactone (p < 0.05) significantly reduced 11beta-HSD1 activity compared with controls. Thus, fibrous tissue possesses requisite components of MC action, and antagonism of mineralocorticoid receptors by spironolactone attenuates its formation. Pouch formation is under the influence of circulating MC and, we would like to propose, is also mediated through corticosteroids generated de novo at the site of tissue repair.

Contractile systolic and diastolic dysfunction in renin-induced hypertensive cardiomyopathy

The present study investigated whether functional, molecular, and biochemical alterations occurring in chronic heart failure can already be detected in compensated hypertensive cardiac hypertrophy. Force of contraction (isolated papillary muscle strip preparations), sarcoplasmic reticulum (SR) protein and myosin heavy chain isoform expression (Northern and Western blot analysis), myocardial fibrosis (collagen stains, hydroxyproline quantification), myocardial renin mRNA (RT-PCR), and angiotensin II levels and plasma aldosterone concentrations (radioimmunoassay) were studied in hypertrophied myocardium from transgenic rats harboring the mouse Ren-2d gene. Contraction and relaxation velocities of isolated papillary muscle strips were significantly reduced in cardiac hypertrophy. The beta-/alpha-myosin heavy chain ratio was significantly increased in the hypertrophied left ventricles, whereas SR Ca2+-ATPase (SERCA 2a) and phospholamban mRNA and protein levels were significantly decreased. The decrease in SERCA 2a was more pronounced than the decrease in phospholamban levels. There was no increased myocardial fibrosis. Left ventricular myocardial renin mRNA and angiotensin II concentrations, as well as plasma aldosterone levels, were higher in transgenic than in control rats. In hypertensive cardiac hypertrophy, myosin heavy chain isoform shift and reduction of SR protein levels are related to systolic and diastolic dysfunction, respectively. These alterations precede the development of myocardial fibrosis. Increased myocardial renin mRNA and angiotensin II concentrations suggest that an activated tissue renin-angiotensin system might contribute to these alterations. Since the alterations in compensated cardiac hypertrophy apparently precede those in chronic heart failure, they might accelerate the transition from hypertrophy to failure and could therefore be targets for pharmacological interventions.

The antiglucocorticoid action of mifepristone

Glucocorticoid hormones influence the physiological activity of almost all cell types in the mammal. This is accomplished via a soluble receptor that, in the presence of an appropriate steroid, modifies the activity of RNA polymerase by binding to the site where different factors assemble for the initiation of cell transcription. The development of antiglucocorticoids has permitted the molecular elucidation of a number of underlying events. Contrary to the classical view, it is now clear that the affinity, stability and activability of the glucocorticoid receptor in the presence of a steroid are cell- and/or tissue-dependent events. The antiglucocorticoid RU 38486 can even activate transcription by binding to sites distinct from those that process transactivation by the agonist. Furthermore, glucocorticoids can sometimes activate the mineralocorticoid receptor, whereas mineralocorticoids can bind the glucocorticoid receptor. Since mifepristone is devoid of adverse toxicity, it has been used for the paraclinical diagnosis of the hypothalamus-pituitary-adrenal axis in normal volunteers, subjects with disorders of the behaviour, and the treatment of Cushing's disease. However, the whole spectrum of cell-specific processes that are antagonized by RU 38486 suggests wide ranging possibilities in the eventual application of antigluco-corticoids.