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Pulmonary hypertension (PH) is a fatal disease characterized by endothelial dysfunction, hypercontraction and proliferation of vascular smooth muscle cells, and migration of inflammatory cells for which no satisfactory treatment has yet been developed. It has been recently demonstrated that Rho-kinase, an effector of the small GTPase Rho, is involved in the pathogenesis of arteriosclerosis and that long-term inhibition of Rho-kinase markedly ameliorates monocrotaline-induced PH in rats. However, it remains to be examined whether direct inhibition of Rho-kinase also ameliorates PH with a different etiology and whether endothelial nitric oxide synthase (eNOS) is involved in the beneficial effects of Rho-kinase inhibition. This study was designed to address those 2 important issues in a hypoxia-induced PH model using wild-type (WT) and eNOS-deficient (eNOS) mice. Long-term blockade of Rho-kinase with fasudil (100 mg/kg/d) for 3 weeks markedly improved PH and right ventricular hypertrophy in WT mice with a lesser but significant inhibition noted in eNOS mice. Fasudil upregulated eNOS with increased Akt phosphorylation in WT but not in eNOS mice. These results suggest that long-term inhibition of Rho-kinase also ameliorates hypoxia-induced PH in mice, for which eNOS activation may partially be involved.

Pulmonary arterial hypertension is a progressive and fatal disease for which Rho-kinase may be substantially involved. In this study, we examined the acute vasodilator effects of fasudil, a Rho-kinase inhibitor, in monocrotaline (MCT)-induced pulmonary hypertension (PH) in rats. Three weeks after a single subcutaneous injection of MCT (60 mg/kg), hemodynamic variables were measured under conscious and free-moving conditions before and after oral administration of fasudil. MCT caused a significant elevation of mean pulmonary arterial pressure (mPAP). Although a low dose of fasudil (3 mg/kg) had no effect on mPAP, a middle dose (10 mg/kg) caused a significant reduction in mPAP without change in mean systemic arterial pressure (mSAP), and a high dose (30 mg/kg) significantly reduced both mPAP and mSAP. Rho-kinase activity was significantly increased by MCT injection in pulmonary arteries but not in the aorta. Fasudil (10 mg/kg) inhibited only the Rho-kinase activity in pulmonary arteries without any effect in the aorta. Plasma concentration of hydroxyfasudil, a metabolite of fasudil, was within its clinical range in humans. These results demonstrate that fasudil exerts effective and selective vasodilatation of pulmonary arteries in rats with MCT-induced PH at a given dose, suggesting its usefulness for the treatment of the fatal disorder.

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Pulmonary arterial hypertension (PAH) is a disease with poor prognosis characterized by progressive elevation of pulmonary arterial pressure and vascular resistance due to pulmonary artery hyperconstriction and remodeling. However, the precise mechanism of PAH still remains to be elucidated. Although anticoagulant agents, vasodilators (e.g., prostaglandins, sildenafil, and bosentan), and lung transplantation are currently used for the treatment of PAH, more effective treatment needs to be developed. Rho-kinase causes vascular smooth muscle hyperconstriction and vascular remodeling through inhibition of myosin phosphatase and activation of its downstream effectors. In a series of experimental and clinical studies, we have demonstrated that Rhokinase-mediated pathway plays an important role in various cellular functions, not only in vascular smooth muscle hyperconstriction but also in actin cytoskeleton organization, cell adhesion and motility, cytokinesis, and gene expression, all of which may be involved in the pathogenesis of arteriosclerosis. We also have recently demonstrated that Rho-kinase is activated in animal models of PAH with different etiologies (monocrotaline and chronic hypoxia) associated with enhanced pulmonary vasoconstricting and proliferating responses, impaired endothelial vasodilator functions, and pulmonary remodeling. Indeed, we were able to demonstrate that intravenous fasudil, a selective Rho-kinase inhibitor, exerts acute pulmonary vasodilator effects in patients with severe PAH who were refractory to conventional therapies. Taken together, our findings indicate that Rho-kinase is a novel and important therapeutic target of PAH in humans and that Rho-kinase inhibitors are a promising new class of drugs for the fatal disorder.pulmonary arterial hypertension; pulmonary arteriosclerosis; pulmonary arterial hyperconstriction; Rho-kinase © 2007 Tohoku University Medical Press Pulmonary hypertension (PH) is defined as a mean pulmonary arterial pressure greater than 25 mmHg at rest or greater than 30 mmHg during exercise (Barst et al. 2004). Pulmonary arterial hypertension (PAH) is characterized by progressive elevation of pulmonary artery pressure and vascular resistance with poor prognosis (Barst et al.

Diastolic heart failure (DHF) is a major cardiovascular disorder with poor prognosis; however, its molecular mechanism still remains to be fully elucidated. We have previously demonstrated the important roles of Rho-kinase pathway in the molecular mechanisms of cardiovascular fibrosis/hypertrophy and oxidative stress, but not examined in the development of heart failure. Therefore, we examined in this study whether Rho-kinase pathway is also involved in the pathogenesis of DHF in Dahl salt-sensitive rats, an established animal model of DHF. They were maintained with or without fasudil, a Rho-kinase inhibitor (30 or 100 mg/kg/day, PO) for 10 weeks. Untreated DHF group exhibited overt heart failure associated with diastolic dysfunction but with preserved systolic function, characterized by increased myocardial stiffness, cardiomyocyte hypertrophy, and enhanced cardiac fibrosis and superoxide production. Fasudil treatment significantly ameliorated those DHF-related myocardial changes. Western blot analysis showed that cardiac Rho-kinase activity was significantly increased in the untreated DHF group and was dose-dependently inhibited by fasudil. Importantly, there was a significant correlation between the extent of myocardial stiffness and that of cardiac Rho-kinase activity. These results indicate that Rho-kinase pathway plays an important role in the pathogenesis of DHF and thus could be an important therapeutic target for the disorder.

Pulmonary hypertension (PH) is a fatal disease characterized by endothelial dysfunction, hypercontraction and proliferation of vascular smooth muscle cells, and migration of inflammatory cells, for which no satisfactory treatment has yet been developed. We have previously demonstrated that long-term inhibition of Rho-kinase, an effector of the small GTPase Rho, ameliorates monocrotaline-induced PH in rats and hypoxia-induced PH in mice. We also have reported that prostacyclin and its oral analogue, beraprost sodium (BPS), may lack direct inhibitory effect on Rho-kinase in vitro, suggesting that combination therapy with a Rho-kinase inhibitor and BPS is effective for the treatment of PH. In this study, we addressed this point in monocrotaline-induced PH model in rats. Male Sprague-Dawley rats were given a subcutaneous injection of monocrotaline (60 mg/kg). They were maintained with or without the treatment with a Rho-kinase inhibitor, fasudil (30 mg/kg/day), BPS (200 microg/kg/day), or a combination of both drugs for 3 weeks. The combination therapy, when compared with each monotherapy, showed significantly more improvement in PH, right ventricular hypertrophy, and pulmonary medial thickness without any adverse effects. Plasma concentrations of fasudil were not affected by BPS. These results suggest that combination therapy with a Rho-kinase inhibitor and prostacyclin exerts further beneficial effects on PH.