Cardiovascular effects in rats following exposure to a receptor tyrosine kinase inhibitor.

The receptor tyrosine kinase receptor (RTK) signaling pathway, mesenchymal-epithelial transition factor (c-Met)/hepatocyte growth factor receptor (HGFR), has been implicated in oncogenesis and is a target of interest in cancer therapy. PF-04254644 is a potent and selective inhibitor of c-Met/HGFR. Wide ligand binding profiling of PF-04254644 revealed a potentially significant interaction with phosphodiesterase (PDE) 3, and follow-up PDE enzyme activity assays confirmed PF-04254644 as a potent inhibitor of PDE3 as well as other PDEs (1, 2, 5, 10, and 11). Clinical observations, laboratory, and echocardiography parameters were recorded in Sprague-Dawley (SD) rats that received PF-04254644 oral dosing for up to seven consecutive days. Toxicological evaluations revealed myocardial degeneration as an adverse event at all tested doses. Echocardiographic evaluations revealed an increase in heart rate (HR) and contractility after the first dose with PF-04254644 and myocardial fibrosis correlated with decreased cardiac function after repeat dosing. A study in telemetry-instrumented rats substantiated that PF-04254644 induced a sustained increased HR and decreased contractility after six days of treatment. Data suggest that the decreased cardiac function and cardiotoxicity are likely due to inhibition of multiple PDEs by PF-04254644.

Effects of chronic PPAR-agonist treatment on cardiac structure and function, blood pressure, and kidney in healthy sprague-dawley rats.

PPAR-γ agonists have been associated with heart failure (HF) in diabetic patients. These incidences have been reported mostly in patient populations who were at high risk for HF or had pre-existing impaired cardiovascular function. However, whether there are similar effects of these agents in subjects with no or reduced cardiovascular pathophysiology is not clear. In this study, the effects of chronic treatment with PD168, a potent peroxisome proliferator activated receptor (PPAR) subtype-γ agonist with weak activity at PPAR-α, and rosiglitazone (RGZ), a less potent PPAR-γ agonist with no PPAR-α activity, were evaluated on the cardiovascular-renal system in healthy male Sprague-Dawley (SD) rats by serial echocardiography and radiotelemetry. Rats were treated with vehicle (VEH), PD168, @ 10 or 50 mg/kg.bw/day (PD-10 or PD-50, resp.) or RGZ @ 180 mg/kg.bw/day for 28 days (n = 10/group). Relative to VEH, RGZ, and both doses of PD168 resulted in a significant fall in blood pressure. Furthermore, RGZ and PD168 increased plasma volume (% increase from baseline) 18%, 22%, and 48% for RGZ, PD-10, and PD-50, respectively. PD168 and RGZ significantly increased urinary aldosterone excretion and heart-to-body weight ratio relative to VEH. In addition, PD168 significantly decreased (10-16%) cardiac ejection fraction (EF) and increased left ventricular area (LVA) in systole (s) and diastole (d) in PD-10 and -50 rats. RGZ significantly increased LVAd; however, it did not affect EF relative to VEH. In conclusion, chronic PPAR-γ therapy may predispose the cardiorenal system to a potential sequela of structural and/or functional changes that may be deleterious with regard to morbidity and mortality.

Time course of AQP-2 and ENaC regulation in the kidney in response to PPAR agonists associated with marked edema in rats.

Peroxisome-proliferator-activated receptor (PPAR-gamma) agonists improve insulin sensitivity, but are associated with edema. Increased distal tubule sodium and water reabsorption through the epithelial sodium channel (ENaC) and aquaporin-2 (AQP-2) have been suggested to play mechanistic roles. To determine the molecular regulation of these proteins, we treated male, Sprague-Dawley rats daily by gavage with either vehicle, rosiglitazone (RGZ, 50mg/kg bw), or PD168 (a test compound causing marked edema, 10mg/kg bw), for 1, 3, or 5 days (n=6/treatment/time). On day 1, urine sodium excretion was significantly reduced by RGZ with a strong trend for PD168 (p-values 0.047 and 0.053, respectively) indicating early sodium retention. Blood pressure was lowered by RGZ- or PD168 treatment by 12h. Immunoblotting of whole kidney homogenates (WKHs) and a membrane-enriched fraction (MF) revealed increased band densities for AQP-2 in WKH (29 kDa and glycosylated bands) by both drugs at 1 day. However, at 5 days, the 29-kDa band was significantly decreased ( approximately 30% of vehicle). alpha-ENaC was increased by RGZ at 3 days; however both agents decreased alpha-ENaC by 5 days. In contrast, beta- and gamma-ENaC (85 kDa) were unchanged or decreased at all times by both agents. However, the 70-kDa band of gamma-ENaC (active band) in MF was increased in density (120-600%) by both agents on days 3-5. Overall, both agents resulted in early alterations in banding patterns for AQP-2 and ENaC subunits, many of which are described as activating changes. However, later reduction in AQP-2 and alpha-ENaC may represent an attempt to re-establish sodium and water balance.

Aldosterone/salt induces renal inflammation and fibrosis in hypertensive rats.

BACKGROUND: We evaluated the role of aldosterone as a mediator of renal inflammation and fibrosis in a rat model of aldosterone/salt hypertension using the selective aldosterone blocker, eplerenone. METHODS: Unnephrectomized, Sprague-Dawley rats were given 1% NaCl (salt) to drink and randomized to receive treatment for 28 days: vehicle infusion (control); 0.75 microg/hour aldosterone subcutaneous infusion; or aldosterone infusion + 100 mg/kg/day oral dose of eplerenone. Blood pressure and urinary albumin were measured and kidneys were evaluated histologically. Renal injury, inflammation, and fibrosis were assessed by immunohistochemistry, in situ hybridization, and reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: Aldosterone/salt induced severe hypertension compared to controls (220 +/- 4 mm Hg vs. 131 +/- 4 mm Hg, P < 0.05), which was partially attenuated by eplerenone (179 +/- 4 mm Hg, P < 0.05). In aldosterone/salt treated rats, renal histopathologic evaluation revealed severe vascular and glomerular sclerosis, fibrinoid necrosis and thrombosis, interstitial leukocyte infiltration, and tubular damage and regeneration. Aldosterone/salt increased circulating osteopontin (925.0 +/- 80.2 ng/mL vs. 53.6 +/- 6.3 ng/mL) and albuminuria (75.8 +/- 10.9 mg/24 hours vs. 13.2 +/- 3.0 mg/24 hours) compared to controls and increased expression of proinflammatory molecules. Treatment with eplerenone reduced systemic osteopontin (58.3 +/- 4.2 ng/mL), albuminuria (41.5 +/- 7.2 mg/24 hours), and proinflammatory gene expression: osteopontin (OPN), monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), and interleukin-1beta (IL-1beta). CONCLUSION: These findings indicate that aldosterone/salt-induced renal injury and fibrosis has inflammatory components involving macrophage infiltration and cytokine up-regulation. Attenuation of renal damage and inflammation by eplerenone supports the protective effects of aldosterone blockade in hypertensive renal disease.

Structural, functional, and molecular characterization of the SHHF model of heart failure.

Heart failure is a complex multifactorial disease resulting in a myriad of progressive changes at the molecular, cellular, and physiological level. To better understand the mechanisms associated with the development of congestive heart failure, a comprehensive examination of the aging lean male spontaneously hypertensive, heart failure-prone rat (SHHF) was conducted. Myocardial function and structural integrity progressively diminished as evidenced by decreased ejection fraction and increased left ventricular volume measured using echocardiography. Functional and structural changes were accompanied by elevations in circulating inflammatory markers, including tumor necrosis factor-alpha (TNF-alpha), IL-6, and TNF receptors type 1 and 2. Increased systemic inflammatory marker levels were consistent with age-dependent changes in the expression pattern of genes that contribute to stress, inflammation, and the extracellular matrix in SHHF animals analyzed from age 4 to 18 mo. In summary, the SHHF rat shares many hallmark features of the human disease state and represents a key experimental model for the dissection of complex human heart failure pathophysiology.