Lack of synergistic effect of molsidomine and sildenafil on development of pulmonary hypertension in chronic hypoxic rats

Nitric Oxide-cGMP Pathway Modulation in an Experimental Model of Hypoxic Pulmonary Hypertension

Manipulation of nitric oxide (NO) may enable control of progression and treatment of pulmonary hypertension (PH). Several approaches may modulate the NO-cGMP pathway in vivo. Here, we investigate the effectiveness of 3 modulatory sites: (i) the amount of l-arginine; (ii) the size of plasma NO stores that stimulate soluble guanylate cyclase; (iii) the conversion of cGMP into inactive 5′-GMP, with respect to hypoxia, to test the effectiveness of the treatments with respect to hypoxia-induced PH. Male rats (n = 80; 10/group) maintained in normoxic (21% O₂) or hypoxic chambers (10% O₂) for 14 days were subdivided in 4 sub-groups: placebo, l-arginine (20 mg/ml), the NO donor molsidomine (15 mg/kg in drinking water), and phoshodiesterase-5 inhibitor sildenafil (1.4 mg/kg in 0.3 ml saline, i.p.). Hypoxia depressed homeostasis and increased erythropoiesis, heart and right ventricle hypertrophy, myocardial fibrosis and apoptosis inducing pulmonary remodeling. Stimulating anyone of the 3 mechanisms that enhance the NO-cGMP pathway helped rescuing the functional and morphological changes in the cardiopulmonary system leading to improvement, sometimes normalization, of the pressures. None of the treatments affected the observed parameters in normoxia. Thus, the 3 modulatory sites are essentially similar in enhancing the NO-cGMP pathway, thereby attenuating the hypoxia-related effects that lead to pulmonary hypertension.

Cystamine Treatment Fails to Prevent the Development of Pulmonary Hypertension in Chronic Hypoxic Rats

INTRODUCTION

Pulmonary hypertension is characterized by vasoconstriction and remodeling of pulmonary arteries, leading to right ventricular hypertrophy and failure. We have previously found upregulation of transglutaminase 2 (TG2) in the right ventricle of chronic hypoxic rats. The hypothesis of the present study was that treatment with the transglutaminase inhibitor, cystamine, would inhibit the development of pulmonary arterial remodeling, pulmonary hypertension, and right ventricular hypertrophy.

METHODS

Effect of cystamine on transamidase activity was investigated in tissue homogenates. Wistar rats were exposed to chronic hypoxia and treated with vehicle, cystamine (40 mg/kg/day in mini-osmotic pumps), sildenafil (25 mg/kg/day), or the combination for 2 weeks.

RESULTS

Cystamine concentration-dependently inhibited TG2 transamidase activity in liver and lung homogenates. In contrast to cystamine, sildenafil reduced right ventricular systolic pressure and hypertrophy and decreased pulmonary vascular resistance and muscularization in chronic hypoxic rats. Fibrosis in the lung tissue decreased in chronic hypoxic rats treated with cystamine. TG2 expression was similar in the right ventricle and lung tissue of drug and vehicle-treated hypoxic rats.

DISCUSSION/CONCLUSIONS

Cystamine inhibited TG2 transamidase activity, but cystamine failed to prevent pulmonary hypertension, right ventricular hypertrophy, and pulmonary arterial muscularization in the chronic hypoxic rat.

Novel selective PDE type 1 inhibitors cause vasodilatation and lower blood pressure in rats

BACKGROUND AND PURPOSE

The PDE enzymes (PDE1-11) hydrolyse and thus inactivate cyclic nucleotides and are important in the regulation of the cardiovascular system. Here,we have investigated the effects on the cardiovascular system, of two novel selective PDE1 inhibitors, Lu AF41228 and Lu AF58027.

EXPERIMENTAL APPROACH

We used rat mesenteric small arteries (internal diameters of 200-300 μm), RT-PCR and measured isometric wall tension. Effects of Lu AF41228 and Lu AF58027 on heart rate and BP were assessed in both anaesthetized and conscious male rats.

KEY RESULTS

Nanomolar concentrations of Lu AF41228 and Lu AF58027 inhibited PDE1A, PDE1B and PDE1C enzyme activity, while micromolar concentrations were required to observe inhibitory effects at other PDEs. RT-PCR revealed expression of PDE1A, PDE1B and PDE1C in rat brain, heart and aorta, but only PDE1A and PDE1B in mesenteric arteries. In rat isolated mesenteric arteries contracted with phenylephrine or U46619, Lu AF41228 and Lu AF58027 induced concentration-dependent relaxations which were markedly reduced by inhibitors of guanylate cyclase, ODQ, and adenylate cyclase, SQ22536, and in preparations without endothelium. In anaesthetized rats, Lu AF41228 and Lu AF58027 dose-dependently lowered mean BP and increased heart rate. In conscious rats with telemetric pressure transducers, repeated dosing with Lu AF41228 lowered mean arterial BP 10-15 mmHg and increased heart rate.

CONCLUSIONS AND IMPLICATIONS

These novel PDE1 inhibitors induce vasodilation and lower BP, suggesting a potential use of these vasodilators in the treatment of hypertension and vasospasm.

The principal pathways involved in the in vivo modulation of hypoxic pulmonary vasoconstriction, pulmonary arterial remodelling and pulmonary hypertension

Hypoxic pulmonary vasoconstriction (HPV) serves to optimize ventilation-perfusion matching in focal hypoxia and thereby enhances pulmonary gas exchange. During global hypoxia, however, HPV induces general pulmonary vasoconstriction, which may lead to pulmonary hypertension (PH), impaired exercise capacity, right-heart failure and pulmonary oedema at high altitude. In chronic hypoxia, generalized HPV together with hypoxic pulmonary arterial remodelling, contribute to the development of PH. The present article reviews the principal pathways in the in vivo modulation of HPV, hypoxic pulmonary arterial remodelling and PH with primary focus on the endothelin-1, nitric oxide, cyclooxygenase and adenine nucleotide pathways. In summary, endothelin-1 and thromboxane A₂ may enhance, whereas nitric oxide and prostacyclin may moderate, HPV as well as hypoxic pulmonary arterial remodelling and PH. The production of prostacyclin seems to be coupled primarily to cyclooxygenase-1 in acute hypoxia, but to cyclooxygenase-2 in chronic hypoxia. The potential role of adenine nucleotides in modulating HPV is unclear, but warrants further study. Additional modulators of the pulmonary vascular responses to hypoxia may include angiotensin II, histamine, serotonin/5-hydroxytryptamine, leukotrienes and epoxyeicosatrienoic acids. Drugs targeting these pathways may reduce acute and/or chronic hypoxic PH. Endothelin receptor antagonists and phosphodiesterase-5 inhibitors may additionally improve exercise capacity in hypoxia. Importantly, the modulation of the pulmonary vascular responses to hypoxia varies between species and individuals, with hypoxic duration and age. The review also define how drugs targeting the endothelin-1, nitric oxide, cyclooxygenase and adenine nucleotide pathways may improve pulmonary haemodynamics, but also impair pulmonary gas exchange by interference with HPV in chronic lung diseases.

Pulmonary hypertension in chronic obstructive and interstitial lung diseases

The purpose of the present review is to summarize the current knowledge on PH in relation to COPD and ILD from a clinical perspective with emphasis on diagnosis, biomarkers, prevalence, impact, treatment, and practical implications. PH in COPD and ILD is associated with a poor prognosis, and is considered one of the most frequent types of PH. However, the prevalence of PH among patients with COPD and ILD is not clear. The diagnosis of PH in chronic lung disease is often established by echocardiographic screening, but definitive diagnosis requires right heart catheterization, which is not systematically performed in clinical practice. Given the large number of patients with chronic lung disease, biomarkers to preclude or increase suspicion of PH are needed. NT-proBNP may be used as a rule-out test, but biomarkers with a high specificity for PH are still required. It is not known whether specific treatment with existent drugs effective in pulmonary arterial hypertension (PAH) is beneficial in lung disease related PH. Studies investigating existing PAH drugs in animal models of lung disease related PH have indicated a positive effect, and so have case reports and open label studies. However, treatment with systemically administered pulmonary vasodilators implies the risk of worsening the ventilation-perfusion mismatch in patients with lung disease. Inhaled vasodilators may be better suited for PH in lung disease, but new treatment modalities are also required.

BAY 41-2272 inhibits the development of chronic hypoxic pulmonary hypertension in rats

The present study investigated whether BAY 41-2272(5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine), a novel pyrazolopyridine that activates guanylyl cyclase and sensitizes the enzyme towards nitric oxide (NO), inhibits the development of pulmonary hypertension. BAY 41-2272 (1 or 10 mg/kg/day) was administered intraperitoneally, and sildenafil (25 mg/kg/day), an inhibitor phosphodiesterase type 5, was given in the drinking water to rats kept under chronic hypobaric hypoxia for two weeks. Right ventricular systolic pressure and hypertrophy, degree of muscularization and relaxation of pulmonary arteries were measured, and immunoblotting was performed. Chronic hypoxia increased right ventricular systolic pressure and expression of soluble guanylyl cyclase and phosphorylated vasodilator-stimulated phosphoprotein (VASP-P(ser239)). BAY 41-2272 prevented hypoxia-induced increase in right ventricular systolic pressure and right ventricular hypertrophy to the same extent as sildenafil. Only sildenafil significantly decreased hypoxia-induced muscularization of pulmonary arteries. Expressed relative to soluble guanylyl cyclase expression, VASP-P(ser239) was increased in lungs from rats treated with BAY 41-2272. Acutely BAY 41-2272 caused pulmonary as well as systemic vasodilatation. In the chronic setting systemic blood pressure was not different to baseline at trough after intraperitoneally administered BAY 41-2272. BAY 41-2272 vasorelaxation in isolated pulmonary resistance arteries was inhibited by an inhibitor of guanylyl cyclase, ODQ (1H-[1,2,4] oxadiazolo[4,3-a]quinoxaline-1-one), and of Na(+)-K(+)-ATPase, ouabain. In conclusion, in an adult rat model of chronic hypoxic pulmonary hypertension, BAY 41-2272 to a similar degree as sildenafil prevents pulmonary hypertension. Thus, BAY 41-2272 may provide a novel therapeutic compound for treating chronic hypoxic pulmonary hypertension.

Sildenafil inhibits chronically hypoxic upregulation of canonical transient receptor potential expression in rat pulmonary arterial smooth muscle

In pulmonary arterial smooth muscle cells (PASMCs), Ca2+ influx through store-operated Ca2+ channels thought to be composed of canonical transient receptor potential (TRPC) proteins is an important determinant of intracellular free calcium concentration ([Ca2+](i)) and pulmonary vascular tone. Sildenafil, a type V phosphodiesterase inhibitor that increases cellular cGMP, is recently identified as a promising agent for treatment of pulmonary hypertension. We previously demonstrated that chronic hypoxia elevated basal [Ca2+](i) in PASMCs due in large part to enhanced store-operated Ca2+ entry (SOCE); moreover, ex vivo exposure to prolonged hypoxia (4% O2 for 60 h) upregulated TRPC1 and TRPC6 expression in PASMCs. We examined the effect of sildenafil on basal [Ca2+](i), SOCE, and the expression of TRPC in PASMCs under prolonged hypoxia exposure. We also examined the effect of sildenafil on TRPC1 and TRPC6 expression in pulmonary arterial smooth muscle (PA) from rats that developed chronically hypoxic pulmonary hypertension (CHPH). Compared with vehicle control, treatment with sildenafil (300 nM) inhibited prolonged hypoxia induced increases of 1) basal [Ca2+](i), 2) SOCE, and 3) mRNA and protein expression of TRPC in PASMCs. Moreover, sildenafil (50 mg . kg(-1) . day(-1)) inhibited mRNA and protein expression of TRPC1 and TRPC6 in PA from chronically hypoxic (10% O2 for 21 days) rats, which was associated with decreased right ventricular pressure and right ventricular hypertrophy. Furthermore, we found, in PASMCs exposed to prolonged hypoxia, that knockdown of TRPC1 or TRPC6 by their specific small interference RNA attenuated the hypoxic increases of SOCE and basal [Ca2+]i, suggesting a cause and effect link between increases of TRPC1 and TRPC6 expression and the hypoxic increases of SOCE and basal [Ca2+]i. These results suggest that sildenafil may alter basal [Ca2+](i) in PASMCs by decreasing SOCE through downregulation of TRPC1 and TRPC6 expression, thereby contributing to decreased vascular tone of pulmonary arteries during the development of CHPH.

Vardenafil increases coronary flow response to hypercapnic acidosis in isolated guinea pig heart

The hypothesis was tested that vardenafil, a PDE5 inhibitor, specifically enhances coronary vasodilation during acidosis. In isolated constant pressure perfused guinea pig hearts, infusion of vardenafil (<or= 1 microM) increased coronary flow concentration-dependently 34 % above baseline. In parallel, cGMP release increased (0.44 +/- 0.094 vs. 0.14 +/- 0.017 pmol/min x g at 0.5 microM vardenafil vs. baseline). Flow increases occurred in the absence of changes in heart function (LVP, heart rate, dP/dt(max), heart rate - pressure product). Infusion of the NO synthase blocker L-NMMA (100 microM) caused a rightward shift of the dose-response curve of vardenafil. To test whether vardenafil treatment may enhance metabolic coronary vasodilation, arterial pCO(2) was raised from 38 to 61 mmHg, which resulted in a steady state flow increase of 18.8 +/- 4.5%. Infusion of vardenafil, given at a threshold flow enhancing concentration, doubled the coronary flow response during hypercapnic acidosis to 38.4 +/- 4.2 % (p=0.004). This flow amplification during acidosis was not shared by the K(ATP) channel opener cromakalim, indicating a specific effect of vardenafil on flow control during myocardial acidosis. We conclude that vardenafil specifically relaxes coronary resistance vessels through NO/cGMP-dependent pathways and increases the coronary flow response toward hypercapnic acidosis. This finding further supports the importance of the NO-cGMP axis in mediation of this flow response.

Combined NMR-crystallographic and modelling investigation of the inclusion of molsidomine into α-, β- and γ-cyclodextrins

A NMR spectroscopic and crystallographic investigation supported by molecular modelling methods has been employed to describe the inclusion properties of molsidomine into the three underivatized alpha-, beta- and gamma-cyclodextrins, aimed to point out the factors affecting the complexation selectivity and stabilization. The NMR results were compared and validated by the analysis of crystallographic data as retrieved from the Cambridge Structural Database and molecular modelling studies.

Differential effects of the phosphodiesterase type 5 inhibitors sildenafil, vardenafil, and tadalafil in rat aorta

Presumably, the vasorelaxant properties of phosphodiesterase type 5 (PDE5) inhibitors are similar in isolated blood vessels. We aimed to explore the mechanisms underlying the vasorelaxation induced by the selective PDE5 inhibitors sildenafil, vardenafil, and tadalafil in the rat aorta. Aortic rings were mounted in 5-ml organ baths, and concentration-response curves for PDE5 inhibitors (0.0001-10 microM) were constructed in phenylephrine (PE)-precontracted endothelium-intact and -denuded rings. Cyclic nucleotides were measured using enzyme immunoassay kits. Sildenafil, vardenafil, and tadalafil concentration dependently relaxed aortic rings and increased cGMP, but not cAMP, concentrations. Endothelium denudation caused marked rightward shifts in the curves to sildenafil (45-fold), tadalafil (21-fold), and vardenafil (251-fold). Maximal responses to sildenafil and tadalafil were substantially reduced (38 +/- 1% and 53 +/- 2%, respectively), whereas that evoked by vardenafil was not affected. Likewise, inhibition of NO synthase (N(omega)-nitro-L-arginine methyl ester, 100 microM), guanylyl cyclase (1H-[1,2,4]oxadiazolo [4,3,-a]quinoxalin-1-one, 10 microM), or scavenging of NO ([carboxy-PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), 100 microM]) caused similar attenuation of the vasorelaxations evoked by PDE5 inhibitors. Sildenafil, tadalafil, and vardenafil significantly potentiated relaxations mediated by glyceryl trinitrate (0.0001-3 microM; 8-13-fold) and atrial natriuretic peptide (0.1-100 nM; 2-3-fold). Contractions evoked by CaCl(2) (0.01-5 mM) in PE-treated rings were significantly reduced (26 +/- 4%) by vardenafil, but not sildenafil or tadalafil, whereas phorbol 12,13-dibutyrate-induced contractions were not affected. Ouabain, cyclopiazonic acid, and calyculin A failed to affect vasorelaxations induced by the PDE5 inhibitors. These results suggest that vardenafil, but not sildenafil or tadalafil, affects Ca(2+) handling in the rat aorta in addition to increasing cGMP levels through inhibition of PDE5 to cause relaxation.