Randolph Seidler

Regression of Isoproterenol-Induced Cardiac Hypertrophy by Na+/H+ Exchanger Inhibition

Abstract— Cardiac hypertrophy is often associated with an increased sympathetic drive, and both in vitro and in vivo studies have demonstrated the development of cardiomyocyte hypertrophy in response to either [alpha]‐ or [beta]‐adrenergic stimulation. Because an association between the Na+/H+ exchanger and cellular growth has been proposed, this study aimed to analyze the possible role of the antiporter in isoproterenol‐induced cardiac hypertrophy. Isoproterenol alone (5 mg/kg IP once daily) or combined with a selective inhibitor of the Na+/H+ exchanger activity (3 mg · kg‐1 · d‐1 BIIB723) was given to male Wistar rats for 30 days. Sex‐ and age‐matched rats that received 0.9% saline IP daily served as controls. Echocardiographic follow‐up showed a 33% increase in left ventricular mass in the isoproterenol‐treated group, whereas it did not increase in the isoproterenol+BIIB723‐treated group. Heart weight–to–body weight ratio at necropsy was 2.44±0.11 in controls and increased to 3.35±0.10 (P <0.05) with isoproterenol, an effect that was markedly attenuated by BIIB723 (2.82±0.07). Intense cardiomyocyte enlargement and severe subendocardial fibrosis were found in isoproterenol‐treated rats, and both effects were attenuated by BIIB723. Myocardial Na+/H+ exchanger activity and protein expression significantly increased in isoproterenol‐treated rats compared with the control group (1.45±0.11 vs 0.91±0.05 arbitrary units, P <0.05). This effect was significantly reduced by BIIB723 (1.17±0.02, P <0.05). In conclusion, our results show that Na+/H+ exchanger inhibition prevented the development of isoproterenol‐induced hypertrophy and fibrosis, providing strong evidence in favor of a key role played by the antiporter in this model of cardiac hypertrophy.

Characterization of sabiporide, a new specific NHE-1 inhibitor exhibiting slow dissociation kinetics and cardioprotective effects.

Sabiporide, a new benzoguanidine, was characterized on fibroblasts stably expressing the Na(+)/H(+) exchanger isoforms NHE-1, NHE-2 and NHE-3. 22Na(+) uptake experiments show that this compound possesses a K(i) of 5+/-1.2 x 10(-8) M for NHE-1, and discriminates efficiently between the NHE-1, -2 and -3 isoforms (K(i) for NHE-2: 3+/-0.9 x 10(-6) M, and K(i)>1 mM for NHE-3). Similar K(i) values are obtained on rat cardiomyocytes and human platelets expressing NHE-1 (K(i)s of 7+/-1 x 10(-9) and 2.7+/-0.4 x 10(-8) M respectively). Interestingly, when compared with amiloride and cariporide, sabiporide inhibition persists even after this molecule had been rinsed out (half time of 7 h for sabiporide, and of 1 and 2.5 min for amiloride and cariporide, respectively), the decay of all these molecules exhibiting a complex multiexponential behavior. Thus, sabiporide, which possesses remarkable cardioprotective properties, is a specific NHE-1 inhibitor possessing unique binding kinetics.

Renoprotective effects of telmisartan in the 5/6 nephrectomised rats

The purpose of this study was to investigate the renoprotective effect of telmisartan on the advanced stages of nephropathy in rats with 5/6 nephrectomy (5/6 Nx).Telmisartan was orally administered for 12 weeks to rats that previously underwent 5/6 Nx or sham operations. After completion of the administration period, the degree of renal injury was examined histopathologically using indices of glomerulosclerosis and lesions of the renal tubule and interstitium.An immunohistochemical staining for transforming growth factor—beta (TGF-β1) was also performed. The suppression of urinary protein was statistically significant in surviving animals dosed with telmisartan.The enalapril groups urinary protein was also significantly suppressed for these same parameters in surviving animals. Histopathologically, telmisartan significantly decreased the progression of glomerulosclerosis and the interstitial cell infiltration at all doses tested. As assessed by immunohistochemical staining the TGF-β1 reactivity in the glomerular tissue tended to decrease in the telmisartan group when compared to the vehicle group. Thus, the progressive Thus, telmisartan ameliorates the progressive nephropathy in the remaining kidney after 5/6 Nx by non-haemodynamic as well as antihypertensive actions of the drug. pharmacological properties of telmisartan, clinical studies have been conducted to evaluate the clinical effectiveness and safety of telmisartan on diabetic nephropathy in patients with type 2 diabetes. It has been reported that telmisartan arrested progressive renal dysfunction in hypertensive patients with early-stage diabetic nephropathy. Makino et al.8 reported the effectiveness of this drug therapy in suppressing the progression of nephropathy in type 2 diabetic patients with or without hypertension, without serious safety concerns. Remuzzi and Remuzzi9 reviewed the potential protective effects of telmisartan on renal function deterioration and suggested that telmisartan may effectively ameliorate renal dysfunction in patients affected by the metabolic syndrome. In addition, telmisartan also showed renoprotective effects in some animal models: spontaneously hypertensive rats (SHR), 10 as well as the hypertensive diabetic model that combines SHR with streptozotocininduced diabetes.11 Ohmura et al.12 investigated the mechanism of the renoprotective effect of telmisartan using obese Zucker diabetic rats. Ciclosporin A-induced nephropathy in pigs was attenuated by telmisartan without any reduction of blood pressure (BP).13 This animal data suggested that the suppressive effect on the progression of nephropathy might be due to both haemodynamic and non-haemodynamic action(s) of the drug.

Nonviral monocyte chemoattractant protein-1 gene transfer improves arteriogenesis after femoral artery occlusion

Local infusion of recombinant monocyte chemoattractant protein-1 (MCP-1) has been shown to enhance collateral artery formation in rabbit and pig hindlimb models. Owing to clinical disadvantages of protein infusion, a nonviral, liposome-based MCP-1 gene transfer was developed. Collateralization in a porcine hindlimb model served to provide a proof-of-principle for the functional benefit of MCP-1 overexpression. Development of arterial conductance as a measure of functionally relevant collateralization was evaluated in occluded as well as untreated hindlimbs in each animal. At the time of occlusion, MCP-1 and control DNA/DC-30 lipoplexes were transferred to femoral arteries of Goettingen minipigs (two therapeutic MCP-1 groups: 2 and 4 μg and one control group), using the Infiltrator® local drug-delivery device. At 2 weeks following occlusion, collateralization was determined as changes in peripheral haemodynamic conductance, peripheral over aortic blood pressure ratio and angiographically visible morphology of the peripheral vessel tree. Nonviral MCP-1 gene transfer significantly improved peripheral conductance (control 11.69±2.78%, 2 μg 23.81±2.81%, P<0.05 and 4 μg 23.36±3.1%, P<0.05; n=12 per group) as well as the ratio of peripheral over aortic blood pressure (control 0.64±0.03%, 2 μg 0.75±0.02%, P<0.05 and 4 μg 0.75±0.02%, P<0.05; n=12 per group) when compared to the untreated controls 2 weeks after occlusion. Thus, it could be demonstrated for the first time that in situ overexpression of MCP-1 following local nonviral gene transfer is a potential approach to improve peripheral collateralization.

Effects of BIIB513 on ischemia-induced arrhythmias and myocardial infarction in anesthetized rats

Abstract Na+/H+ exchange (NHE) plays an important role in the regulation of the intracellular pH (pHi) and in cardiac cell injury induced by ischemia and reperfusion. In the present study, we investigated the effects of BIIB513, a selective NHE-1 inhibitor on myocardial ischemia induced arrhythmias and myocardial infarction, provoked by 30 minutes of left main coronary artery occlusion followed by 2 hours of reperfusion in an anesthetized rat model. Intravenous administration of BIIB513 (0.01–3.0 mg/kg) did not induce changes in blood pressure or heart rate. BIIB513 (0.01, 0.1, 0.3, 1.0, 3.0 mg/kg) given prior to the coronary artery occlusion dose-dependently reduced ventricular premature beats, ventricular tachycardia, and a complete suppression of ventricular fibrillation down to the dose of 0.1 mg/kg. BIIB513 (0.01, 0.1, 0.3, 1.0, 3.0 mg/kg) given prior to the coronary artery occlusion dose-dependently reduced the infarct size with an ED50 value of 0.16 mg/kg. BIIB513 (1.0 mg/kg) given prior to reperfusion also reduced infarct size by 47.3 ± 13.1%. The reduction in infarct size was accompanied by a decrease in circulating levels of creatine phosphokinase (CPK). In conclusion, the present study demonstrates the cardioprotective ability of NHE-1 inhibition during myocardial ischemia and reperfusion by reducing serious ventricular arrhythmias and myocardial infarct size in anesthetized rats.

Short-term intra-arterial infusion of monocyte chemoattractant protein-1 results in sustained collateral artery growth

Monocyte chemoattractant protein-1 (MCP-1) is a stimulator of collateral artery growth and has been shown to increase collateral artery conductance in rabbits and pigs. The minimal infusion duration and the minimally effective dose of MCP-1 are currently unknown, as is the sustainability of the therapeutic effect over a longer observation period than tested before. MCP-1 was infused intra-arterially in pigs after unilateral femoral artery occlusion in different doses and infusion durations between 2 hours and 2 weeks. Two weeks after ligation, arterial conductance under maximal vasodilatation was measured. The long-term efficacy was investigated in 2 additional groups of animals after 6 weeks. Infusion with 2 µg/min of MCP-1 for 6 hours was sufficient to double arterial conductance, and arterial conductance after 6 weeks was still significantly increased.