Effects of Chronic Rosiglitazone Treatment on Renal Handling of Salt and Water in Rats With Volume-Overload Congestive Heart Failure

Abnormal expression of PRKAG2-AS results in dysfunction of cardiomyocytes through regulating PRKAG2 transcription by interacting with PPARG

The role of PRKAG2 in the maintenance of heart function is well established, but little is known about how PRKAG2 is regulated in cardiomyocytes. In this study, we investigated the role of the lncRNA PRKAG2-AS, which is present at the PRKAG2 promoter, in the regulation of PRKAG2 expression. PRKAG2-AS expression was predominantly nuclear, as determined by RNA nucleoplasmic separation and fluorescence in situ hybridization. Knockdown of PRKAG2-AS in the nucleus, but not the cytoplasm, significantly decreased the expression of PRKAG2b and PRKAG2d. Interestingly, we found that PRKAG2-AS and its target genes, PRKAG2b and PRKAG2d, were reduced in the hearts of patients with ischemic cardiomyopathy, suggesting a potential role for PRKAG2-AS in myocardial ischemia. Indeed, knockdown of PRKAG2-AS in the nucleus resulted in apoptosis of cardiomyocytes. We further elucidated the mechanism by which PRKAG2-AS regulates PRKAG2 transcription by identifying 58 PRKAG2-AS interacting proteins. Among them, PPARG was selected for further investigation based on its correlation and potential interaction with PRKAG2-AS in regulating transcription. Overexpression of PPARG, or its activation with rosiglitazone, led to a significant increase in the expression of PRKAG2b and PRKAG2d in cardiomyocytes, which could be attenuated by PRKAG2-AS knockdown. This finding suggests that PRKAG2-AS mediates, at least partially, the protective effects of rosiglitazone on hypoxia-induced apoptosis. However, given the risk of rosiglitazone in heart failure, we also examined the involvement of PRKAG2-AS in this condition and found that PRKAG2-AS, as well as PRKAG2b and PRKAG2d, was elevated in hearts with dilated cardiomyopathy (DCM) and that overexpression of PRKAG2-AS led to a significant increase in PRKAG2b and PRKAG2d expression, indicating that up-regulation of PRKAG2-AS may contribute to the mechanism of heart failure by promoting transcription of PRKAG2. Consequently, proper expression of PRKAG2-AS is essential for maintaining cardiomyocyte function, and aberrant PRKAG2-AS expression induced by hypoxia or other stimuli may cause cardiac dysfunction.

Effects of Angiotensin 1-7 and Mas Receptor Agonist on Renal System in a Rat Model of Heart Failure

Congestive heart failure (CHF) is often associated with impaired kidney function. Over- activation of the renin-angiotensin-aldosterone system (RAAS) contributes to avid salt/water retention and cardiac hypertrophy in CHF. While the deleterious effects of angiotensin II (Ang II) in CHF are well established, the biological actions of angiotensin 1-7 (Ang 1-7) are not fully characterized. In this study, we assessed the acute effects of Ang 1-7 (0.3, 3, 30 and 300 ng/kg/min, IV) on urinary flow (UF), urinary Na⁺ excretion (UNaV), glomerular filtration rate (GFR) and renal plasma flow )RPF) in rats with CHF induced by the placement of aortocaval fistula. Additionally, the chronic effects of Ang 1-7 (24 µg/kg/h, via intra-peritoneally implanted osmotic minipumps) on kidney function, cardiac hypertrophy and neurohormonal status were studied. Acute infusion of either Ang 1-7 or its agonist, AVE 0991, into sham controls, but not CHF rats, increased UF, UNaV, GFR, RPF and urinary cGMP. In the chronic protocols, untreated CHF rats displayed lower cumulative UF and UNaV than their sham controls. Chronic administration of Ang 1-7 and AVE 0991 exerted significant diuretic, natriuretic and kaliuretic effects in CHF rats, but not in sham controls. Serum creatinine and aldosterone levels were significantly higher in vehicle-treated CHF rats as compared with controls. Treatment with Ang 1-7 and AVE 0991 reduced these parameters to comparable levels observed in sham controls. Notably, chronic administration of Ang 1-7 to CHF rats reduced cardiac hypertrophy. In conclusion, Ang 1-7 exerts beneficial renal and cardiac effects in rats with CHF. Thus, we postulate that ACE2/Ang 1-7 axis represents a compensatory response to over-activity of ACE/AngII/AT1R system characterizing CHF and suggest that Ang 1-7 may be a potential therapeutic agent in this disease state.

Rosiglitazone treatment restores renal responsiveness to atrial natriuretic peptide in rats with congestive heart failure

The thiazolidinedione (TZD) class of Peroxisome proliferator‐activated receptor gamma agonists has restricted clinical use for diabetes mellitus due to fluid retention and potential cardiovascular risks. These side effects are attributed in part to direct salt‐retaining effect of TZDs at the renal collecting duct. A recent study from our group revealed that prolonged rosiglitazone (RGZ) treatment caused no Na+/H₂O retention or up‐regulation of Na⁺ transport‐linked channels/transporters in experimental congestive heart failure (CHF) induced by surgical aorto‐caval fistula (ACF). The present study examines the effects of RGZ on renal and cardiac responses to atrial natriuretic peptide (ANP), Acetylcholine (Ach) and S‐Nitroso‐N‐acetylpenicillamine (SNAP‐NO donor). Furthermore, we assessed the impact of RGZ on gene expression related to the ANP signalling pathway in animals with ACF. Rats subjected to ACF (or sham) were treated with either RGZ (30 mg/kg/day) or vehicle for 4 weeks. Cardiac chambers pressures and volumes were assessed invasively via Miller catheter. Kidney excretory and renal hemodynamic in response to ANP, Ach and SNAP were examined. Renal clearance along with cyclic guanosine monophosphate (cGMP), gene expression of renal CHF‐related genes and ANP signalling in the kidney were determined. RGZ‐treated CHF rats exhibited significant improvement in the natriuretic responses to ANP infusion. This ‘sensitization’ to ANP was not associated with increases in neither urinary cGMP nor in vitro cGMP production. However, RGZ caused down‐regulation of several genes in the renal cortex (Ace, Nos3 and Npr1) and up‐regulation of ACE2, Agtrla, Mme and Cftr along down‐regulation of Avpr2, Npr1,2, Nos3 and Pde3 in the medulla. In conclusion, CHF+RGZ rats exhibited significant enhancement in the natriuretic responses to ANP infusion, which are known to be blunted in CHF. This ‘sensitization’ to ANP is independent of cGMP signalling, yet may involve post‐cGMP signalling target genes such as ACE2, CFTR and V2 receptor. The possibility that TZD treatment in uncomplicated CHF may be less detrimental than thought before deserves additional investigations.

Does Thiazolidinedione therapy exacerbate fluid retention in congestive heart failure?

The ever-growing global burden of congestive heart failure (CHF) and type 2 diabetes mellitus (T2DM) as well as their co-existence necessitate that anti-diabetic pharmacotherapy will modulate the cardiovascular risk inherent to T2DM while complying with the accompanying restrictions imposed by CHF. The thiazolidinedione (TZD) family of peroxisome proliferator-activated receptor γ (PPARγ) agonists initially provided a promising therapeutic option in T2DM owing to anti-diabetic efficacy combined with pleiotropic beneficial cardiovascular effects. However, the utility of TZDs in T2DM has declined in the past decade, largely due to concomitant adverse effects of fluid retention and edema formation attributed to salt-retaining effects of PPARγ activation on the nephron. Presumably, the latter effects are potentially deleterious in the context of pre-existing fluid retention in CHF. However, despite a considerable body of evidence on mechanisms responsible for TZD-induced fluid retention suggesting that this class of drugs is rightfully prohibited from use in CHF patients, there is a paucity of experimental and clinical studies that investigate the effects of TZDs on salt and water homeostasis in the CHF setting. In an attempt to elucidate whether TZDs actually exacerbate the pre-existing fluid retention in CHF, our review summarizes the pathophysiology of fluid retention in CHF. Moreover, we thoroughly review the available data on TZD-induced fluid retention and proposed mechanisms in animals and patients. Finally, we will present recent studies challenging the common notion that TZDs worsen renal salt and water retention in CHF.

A modified approach to induce predictable congestive heart failure by volume overload in rats

The model of infrarenal aortocaval fistula (ACF) has recently gained new interest in its use to investigate cardiac pathophysiology. Since in previous investigations the development of congestive heart failure (CHF) was inconsistent and started to develop earliest 8–10 weeks after fistula induction using a 18G needle, this project aimed to induce a predictable degree of CHF within a definite time period using a modified approach. An aortocaval fistula was induced in male Wistar rats using a 16G needle as a modification of the former 18G needle-technique described by Garcia and Diebold. Results revealed within 28±2 days of ACF significantly increased heart and lung weight indices in the ACF group accompanied by elevated filling pressure. All hemodynamic parameters derived from a pressure-volume conductance-catheter in vivo were significantly altered in the ACF consistent with severe systolic and diastolic left ventricular dysfunction. This was accompanied by systemic neurohumoral activation as demonstrated by elevated rBNP-45 plasma concentrations in every rat of the ACF group. Furthermore, the restriction in overall cardiac function was associated with a β1- and β2-adrenoreceptor mRNA downregulation in the left ventricle. In contrast, β3-adrenoreceptor mRNA was upregulated. Finally, electron microscopy of the left ventricle of rats in the ACF group showed signs of progressive subcellular myocardial fragmentation. In conclusion, the morphometric, hemodynamic and neurohumoral characterization of the modified approach revealed predictable and consistent signs of congestive heart failure within 28±2 days. Therefore, this modified approach might facilitate the examination of various questions specific to CHF and allow for pharmacological interventions to determine pathophysiological pathways.

Diuretics prevent thiazolidinedione-induced cardiac hypertrophy without compromising insulin-sensitizing effects in mice

Much concern has arisen regarding critical adverse effects of thiazolidinediones (TZDs), including rosiglitazone and pioglitazone, on cardiac tissue. Although TZD-induced cardiac hypertrophy (CH) has been attributed to an increase in plasma volume or a change in cardiac nutrient preference, causative roles have not been established. To test the hypothesis that volume expansion directly mediates rosiglitazone-induced CH, mice were fed a high-fat diet with rosiglitazone, and cardiac and metabolic consequences were examined. Rosiglitazone treatment induced volume expansion and CH in wild-type and PPARγ heterozygous knockout (Pparg(+/-)) mice, but not in mice defective for ligand binding (Pparg(P465L/+)). Cotreatment with the diuretic furosemide in wild-type mice attenuated rosiglitazone-induced CH, hypertrophic gene reprogramming, cardiomyocyte apoptosis, hypertrophy-related signal activation, and left ventricular dysfunction. Similar changes were observed in mice treated with pioglitazone. The diuretics spironolactone and trichlormethiazide, but not amiloride, attenuated rosiglitazone effects on volume expansion and CH. Interestingly, expression of glucose and lipid metabolism genes in the heart was altered by rosiglitazone, but these changes were not attenuated by furosemide cotreatment. Importantly, rosiglitazone-mediated whole-body metabolic improvements were not affected by furosemide cotreatment. We conclude that releasing plasma volume reduces adverse effects of TZD-induced volume expansion and cardiac events without compromising TZD actions in metabolic switch in the heart and whole-body insulin sensitivity.

Thiazolidinedione-induced fluid retention: recent insights into the molecular mechanisms

Peroxisome proliferator-activated receptor- γ (PPAR γ ) agonists such as rosiglitazone and pioglitazone are used to improve insulin sensitivity in patients with diabetes mellitus. However, thiazolidinediones induce fluid retention, edema, and sometimes precipitate or exacerbate heart failure in a subset of patients. The mechanism through which thiazolidinediones induce fluid retention is controversial. Most studies suggest that this effect results from the increase in tubular sodium and water reabsorption in the kidney, but the role of specific nephron segments and sodium carriers involved is less clear. Some studies suggested that PPAR γ agonist stimulates Na(+) reabsorption in the collecting duct by activating epithelial Na(+) channel (ENaC), either directly or through serum and glucocorticoid-regulated kinase-1 (SGK-1). However, other studies did not confirm this mechanism and even report the suppression of ENaC. Alternative mechanisms in the collecting duct include stimulation of non-ENaC sodium channel or inhibition of chloride secretion to the tubular lumen. In addition, thiazolidinediones may augment sodium reabsorption in the proximal tubule by stimulating the expression and activity of apical Na(+)/H(+) exchanger-3 and basolateral Na(+)-HCO3 (-) cotransporter as well as of Na(+),K(+)-ATPase. These effects are mediated by PPAR γ -induced nongenomic transactivation of the epidermal growth factor receptor and downstream extracellular signal-regulated kinases (ERK).

Metformin prevents the development of chronic heart failure in the SHHF rat model

Insulin resistance is a recently identified mechanism involved in the pathophysiology of chronic heart failure (CHF). We investigated the effects of two insulin-sensitizing drugs (metformin and rosiglitazone) in a genetic model of spontaneously hypertensive, insulin-resistant rats (SHHF). Thirty SHHF rats were randomized into three treatment groups as follows: 1) metformin (100 mg/kg per day), 2) rosiglitazone (2 mg/kg per day), and 3) no drug. Ten Sprague-Dawley rats served as normal controls. At the end of the treatment period (12 months), the cardiac phenotype was characterized by histology, echocardiography, and isolated perfused heart studies. Metformin attenuated left ventricular (LV) remodeling, as shown by reduced LV volumes, wall stress, perivascular fibrosis, and cardiac lipid accumulation. Metformin improved both systolic and diastolic indices as well as myocardial mechanical efficiency, as shown by improved ability to convert metabolic energy into mechanical work. Metformin induced a marked activation of AMP-activated protein kinase, endothelial nitric oxide synthase, and vascular endothelial growth factor and reduced tumor necrosis factor-α expression and myocyte apoptosis. Rosiglitazone did not affect LV remodeling, increased perivascular fibrosis, and promoted further cardiac lipid accumulation. In conclusion, long-term treatment with metformin, but not with rosiglitazone, prevents the development of severe CHF in the SHHF model by a wide-spectrum interaction that involves molecular, structural, functional, and metabolic-energetic mechanisms.