A Combination of Oral Sildenafil and Beraprost Ameliorates Pulmonary Hypertension in Rats

Vardenafil oral jellies as a potential approach for management of pediatric irritable bowel syndrome

Irritable bowel syndrome (IBS); a widespread disorder in gastrointestinal tract especially in children, burdens their healthcare systems and upsets families. Great attention was paid to understand the pathophysiological cause of disorder. However, developing a convenient treatment especially for children remains a challenge. Phosphodiesterase inhibitors were recently introduced for IBS management. Vardenafil (VDF), a phosphodiesterase-5 inhibitor, exhibiting limited bioavailability when taken orally due to extensive first-pass effect, was the choice for study. This study aimed to formulate VDF jellies as a buccal dosage form to improve pediatric compliance and achieve maximum drug efficacy. VDF oral jellies were prepared by heat and congeal method, and were evaluated for their pH, content uniformity, physical stability, general appearance, and in-vitro drug release. VDF jellies (F1), with satisfactory organoleptic properties and highest percent of drug released compared to other formulations was selected as a master formula for further study to ensure in-vivo efficacy. cyclic Guanosine Mono Phosphate (cGMP), used as indicator of VDF concentration in blood, was highly increased after administration of VDF jellies (F1), compared to oral VDF suspension. Increased defecation with improved fecal consistency strongly favored oral jellies as a potential alternative route for VDF for IBS management with high pediatric acceptance.

Metformin prevents the development of monocrotaline-induced pulmonary hypertension by decreasing serum levels of big endothelin-1

Pulmonary hypertension (PH) is a disease with poor prognosis, and it is characterized by the progressive elevation of pulmonary vascular resistance and pressure. Various factors are associated with the pathology of PH, including AMP-activated protein kinase (AMPK) deficiency. The present study aimed to evaluate the therapeutic effect of metformin, an AMPK activator, in a monocrotaline (MCT)-induced PH rat model. Rats were randomly divided into the following three groups: i) Saline-injected group (sham group); ii) monocrotaline (MCT)-injected group (PH group); iii) MCT-injected and metformin-treated group (MT group). Four weeks following MCT injection, cardiac ultrasonography, invasive hemodynamic measurements, measurement of serum levels of big endothelin-1 (big ET-1) and histological analysis were performed to evaluate the effect of metformin treatment in PH. Pulmonary arterial pressure and serum big ET-1 concentrations were reduced in the MT group compared with the PH group. Medial wall thickness and wall area of the pulmonary arterioles in the MT group were decreased compared with the PH group. Comparing the right heart functional parameters among groups revealed that the acceleration time/ejection time ratio improved in the MT group compared with the PH group. Thus, the present study demonstrated the efficacy of metformin in an MCT-induced PH rat model and suggested that metformin may be a valuable, potential novel therapeutic for the treatment of PH.

Eulophia macrobulbon extract relaxes rat isolated pulmonary artery and protects against monocrotaline-induced pulmonary arterial hypertension

BACKGROUND

Extract of the wild orchid, Eulophia macrobulbon (EM) inhibits phosphodiesterase5 (PDE5) suggesting it could preferentially dilate the pulmonary vasculature.

PURPOSE AND STUDY DESIGN

To pharmacologically characterize the vascular actions of EM ethanolic extract and its active compound, 1-(4'-hydroxybenzyl)-4,8-dimethoxyphenanthrene-2,7-diol using isolated pulmonary arteries (PA) from rats having pulmonary arterial hypertension (PAH) induced by monocrotaline (MCT). PA were fixed and prepared for histology.

RESULTS

EM extract relaxed PA (EC₅₀ = 0.17  mg/ml, E_max ∼ 94%) but less so for aorta (EC₅₀ = 0.51 mg/ml, E_max ∼ 62%), suggesting some selectivity towards the pulmonary circulation. PA vasorelaxation was reduced by endothelial removal or N^G-nitro-L-arginine methyl ester, but unaffected by indomethacin, apamin +charybdotoxin, 4-aminopyridine, glibenclamide, iberiotoxin, or 1H - [1,2,4]oxadiazolo[4,3-a]quinoxalin -1- one. Sodium nitroprusside-induced relaxation was enhanced by EM extract, probably via PDE5 inhibition. EM extract reduced contractions evoked by extracellular Ca²⁺application, and inhibited intracellular Ca²⁺release activated by phenylephrine. The phenanthrene relaxed PA independently of the endothelium. MCT thickened walls and decreased lumens of PA, and hypertrophied right ventricular myocytes, effects ameliorated by 3 weeks of oral sildenafil (20  mg/kg) or EM extract (15, 450 or 1000  mg/kg).

CONCLUSION

PAH is improved by EM extract acting through PA relaxation mediated through endothelial NO, reduced Ca²⁺-mobilization, and reduced PA wall thickness and right ventricular hypertrophy.

CB2-deficiency is associated with a stronger hypertrophy and remodeling of the right ventricle in a murine model of left pulmonary artery occlusion

AIMS

Pulmonary hypertension (PH) leads to right ventricular (RV) adaptation and remodeling and has deleterious long-term effects on RV function. The endocannabinoid receptor CB2 has been associated with protective effects in adaptation and remodeling of the left ventricle after ischemia. Therefore, we investigated the role of CB2 receptor in RV adaptation after occlusion of the left pulmonary artery (LPA) in a murine model.

MAIN METHODS

C57/Bl6 (WT)- and CB2 receptor-deficient (Cnr2^-/^-)-mice underwent paramedian sternotomy and LPA was occluded using a metal clip. Right heart hemodynamic study (Millar®) preceded organ harvesting for immunohistochemistry and mRNA analysis 7 and 21 days (d) post-occlusion.

KEY FINDINGS

LPA occlusion led to higher RV systolic pressure in Cnr2^-/^--hearts, while hemodynamics were comparable with WT-hearts after 21d. Cnr2^-/^--hearts showed higher macrophage infiltration and lower interleukin-10 expression after 7 d, but otherwise a comparable inflammatory mediator expression profile. Cardiomyocyte-hypertrophy was stronger in Cnr2^-/^--mice, presenting with higher tenascin-C expression than WT-hearts. Planimetry revealed higher collagen area in Cnr2^-/^--hearts and small areas of cardiomyocyte-loss. Surrounding cardiomyocytes were cleaved caspase-3- and TUNEL positive in Cnr2^-/^--hearts. This was associated by maladaptation of myosin heavy-chain isoforms and lower reactive oxygen scavenger enzymes induction in Cnr2^-/^--hearts. We found comparable morphological changes in both lungs between the two genotypes.

SIGNIFICANCE

LPA occlusion led to increased systolic pressure and adaptation of RV in CB2-deficient mice. CB2 receptor seems to modulate RV adaptation through expression of contractile elements, reactive oxygen scavenger enzymes, and inflammatory response in order to prevent cardiomyocyte apoptosis.

Oxygen therapy may worsen the survival rate in rats with monocrotaline-induced pulmonary arterial hypertension

Although oxygen therapy rapidly improves arterial oxygen saturation in idiopathic pulmonary arterial hypertension, the effects of chronic administration of oxygen are unknown. The purpose of the present study was to investigate the effects of chronic oxygen therapy on the histological changes and survival rate in rats with idiopathic pulmonary arterial hypertension. Idiopathic pulmonary arterial hypertension was induced by monocrotaline injection. The rats were then randomly assigned to receive or not receive oxygen therapy (O₂ group and non-O₂ group, respectively). The rats in the O₂ group were exposed to a high (90%) oxygen environment from day 17 following injection of monocrotaline, when hypoxemia was first observed. The pulmonary arteriole walls were significantly thicker in monocrotaline-injected rats than in saline-injected rats as vehicle on day 19 and were significantly thicker in the rats that received oxygen therapy than in the rats that did not. Right ventricular inflammations were significantly higher in monocrotaline-injected rats than in saline-injected rats on day 19 and were significantly higher in the rats that received oxygen therapy than in the rats that did not. By day 20 after injection of monocrotaline, the survival rate was significantly lower in the rats that received oxygen therapy than in those that did not. Superoxide dismutase activity in the lungs was higher in monocrotaline-injected rats than in saline-injected rats on day 19 after monocrotaline injection and was also higher in the saline-injected rats that received oxygen therapy than in the saline-injected rats that did not. No interaction was detected between monocrotaline injection and oxygen therapy. These results suggest that chronic oxygen therapy worsens the histological changes and survival rate in idiopathic pulmonary arterial hypertension. The fact that degradation of the histological changes and survival rate was accompanied by increase in superoxide dismutase activity suggests that antioxidant capacity may contribute to the degradation.

Liposomal-delivery of phosphodiesterase 5 inhibitors augments UT-15C-stimulated ATP release from human erythrocytes

The use of liposomes to affect targeted delivery of pharmaceutical agents to specific sites may result in the reduction of side effects and an increase in drug efficacy. Since liposomes are delivered intravascularly, erythrocytes, which constitute almost half of the volume of blood, are ideal targets for liposomal drug delivery.

In vivo, erythrocytes serve not only in the role of oxygen transport but also as participants in the regulation of vascular diameter through the regulated release of the potent vasodilator, adenosine triphosphate (ATP). Unfortunately, erythrocytes of humans with pulmonary arterial hypertension (PAH) do not release ATP in response to the physiological stimulus of exposure to increases in mechanical deformation as would occur when these cells traverse the pulmonary circulation. This defect in erythrocyte physiology has been suggested to contribute to pulmonary hypertension in these individuals.

In contrast to deformation, both healthy human and PAH erythrocytes do release ATP in response to incubation with prostacyclin analogs via a well-characterized signaling pathway. Importantly, inhibitors of phosphodiesterase 5 (PDE5) have been shown to significantly increase prostacyclin analog-induced ATP release from human erythrocytes.

Here we investigate the hypothesis that targeted delivery of PDE5 inhibitors to human erythrocytes, using a liposomal delivery system, potentiates prostacyclin analog- induced ATP release. The findings are consistent with the hypothesis that directed delivery of this class of drugs to erythrocytes could be a new and important method to augment prostacyclin analog-induced ATP release from these cells. Such an approach could significantly limit side effects of both classes of drugs without compromising their therapeutic effectiveness in diseases such as PAH.

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PDE5 inhibitors can be successfully delivered to human erythrocytes via liposomes.

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This results in augmented PGI₂ analog-mediated ATP release.

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Liposomal binding to erythrocytes is rapid without affecting erythrocyte rheology.

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This is a novel method to augment PGI₂ analog-induced ATP release from erythrocytes.

PK/PD studies on non-selective PDE inhibitors in rats using cAMP as a marker of pharmacological response

In recent years, phosphodiesterase (PDE) inhibitors have been frequently tested for the treatment of experimental inflammatory and immune disorders. It is suggested that anti-inflammatory properties of PDE inhibitors are related to their ability to increase cAMP levels. The aim of this study was to verify the hypothesis that cAMP may be a useful marker of pharmacological response following administration of non-selective PDE inhibitors (pentoxifylline and (±)-lisofylline) to endotoxemic rats. Male Wistar rats were administered LPS (1 mg kg⁻¹, i.v.) simultaneously with either compound given at two doses (40 and 80 mg kg⁻¹, i.v.). Levels of cAMP and both compounds in animal plasma were measured by the validated HPLC methods. Pharmacokinetic-pharmacodynamic analysis was performed using basic and modified indirect response (IDR) models II in Phoenix WinNonlin. The results of this study indicate that, in contrast to pentoxifylline, (±)-lisofylline demonstrates a non-linear pharmacokinetics in rats with endotoxemia. In vitro study using human recombinant PDE4B and PDE7A revealed the occurrence of additive interaction between studied compounds. Moreover, (±)-lisofylline is a more potent inhibitor of PDEs compared to pentoxifylline, as evidenced by lower IC₅₀ values. Following administration of both compounds, levels of cAMP in rat plasma increased in a dose-dependent manner. The modified IDR model II better described cAMP levels over time profiles. The validity of the proposed marker was confirmed by measuring plasma TNF-α levels in the studied animals. In conclusion, cAMP may be used in future preclinical and clinical studies of some PDE inhibitors to evaluate the drug concentration–effect relationship.

Tadalafil induces antiproliferation, apoptosis, and phosphodiesterase type 5 downregulation in idiopathic pulmonary arterial hypertension in vitro

Idiopathic pulmonary arterial hypertension (IPAH) is a fatal disease of the pulmonary artery resulting from a currently unidentified etiology. IPAH is pathologically characterized as sustained vasoconstriction and vascular remodeling of the pulmonary artery. Vascular remodeling is mediated by enhanced proliferation and reduced apoptosis in pulmonary arterial smooth muscle cells (PASMCs). Based on its pathological mechanism, specific phosphodiesterase type 5 (PDE5) inhibitors have been used in the treatment of IPAH. In addition to sildenafil, tadalafil has been approved for the treatment of IPAH. However, the effects of tadalafil on excessive proliferation of IPAH-PASMCs currently remain unknown. In the present study, the in vitro pharmacological profiles of tadalafil for cell proliferation and apoptosis were assessed in IPAH-PASMCs using MTT, BrdU incorporation, and caspase 3/7 assays. Expression analyses revealed that PDE5 mRNA and protein expression levels were markedly higher in IPAH-PASMCs than in normal-PASMCs. The treatment with tadalafil inhibited the excessive proliferation of IPAH-PASMCs in a concentration-dependent manner with an IC₅₀ value of 4.5μM. On the other hand, tadalafil (0.03-100μM) did not affect cell growth of PASMCs from normal subjects and patients with chronic thromboembolic pulmonary hypertension (CTEPH). In addition, tadalafil induced apoptosis in IPAH-PASMCs. The antiproliferative and apoptotic effects of tadalafil were markedly stronger than those of sildenafil and vardenafil. The upregulated expression of PDE5 in IPAH-PASMCs was significantly attenuated by a long-term treatment with tadalafil. Taken together, these results indicate that tadalafil attenuates vascular remodeling by inhibiting cell proliferation, promoting apoptosis, and downregulating PDE5 in IPAH-PASMCs, thereby ameliorating IPAH.

Beneficial effects of aqueous extract of stem bark of Terminalia arjuna (Roxb.), An ayurvedic drug in experimental pulmonary hypertension

ETHNOPHARMACOLOGICAL RELEVANCE

The stem bark of Terminalia arjuna (Roxb.) is widely used in Ayurveda in various cardiovascular diseases. Many animal and clinical studies have validated its anti-ischemic, antihypertensive, antihypertrophic and antioxidant effects. Pulmonary hypertension (PH) is a fatal disease which causes right ventricular hypertrophy and right heart failure. Pulmonary vascular smooth muscle hypertrophy and increased oxidative stress are major pathological features of PH. As available limited therapeutic options fail to reduce the mortality associated with PH, alternative areas of therapy are worth exploring for potential drugs, which might be beneficial in PH.

AIM OF THE STUDY

The effect of a standardised aqueous extract of the stem bark of Terminalia arjuna (Roxb.) in preventing monocrotaline (MCT)-induced PH in rat was investigated.

MATERIALS AND METHODS

The study was approved by Institutional Animal Ethics Committe. Male Wistar rats (150-200g) were randomly distributed into five groups; Control, MCT (50mg/kg subcutaneously once), sildenafil (175µg/kg/day three days after MCT for 25 days), and Arjuna extract (TA125 and TA250 mg/kg/day orally after MCT for 25 days). PH was confirmed by right ventricular weight to left ventricular plus septum weight (Fulton index), right ventricular systolic pressure (RVSP), echocardiography, percentage medial wall thickness of pulmonary arteries (%MWT). Oxidative stress in lung was assessed by super oxide dismutase (SOD), catalase, reduced glutathione (GSH) and thiobarbituric acid reactive substance (TBARS). The protein expressions of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX-1) in lung and gene expression of Bcl2 and Bax in heart were analyzed by Western blot and RT PCR respectively.

RESULTS

MCT caused right ventricular hypertrophy (0.58±0.05 vs 0.31±0.05; P<0.001 vs. control) and increase in RVSP (33.5±1.5 vs 22.3±4.7mm of Hg; P<0.001). Both sildenafil and Arjuna prevented hypertrophy and RVSP. Pulmonary artery acceleration time to ejection time ratio in echocardiography was decreased in PH rats (0.49±0.05 vs 0.32±0.06; P<0.001) which was prevented by sildenafil (0.44±0.06; P<0.01) and TA250 (0.45±0.06; P<0.01). % MWT of pulmonary arteries was increased in PH and was prevented by TA250. Increase in TBARS (132.7±18.4 vs 18.8±1.6nmol/mg protein; P<0.001) and decrease in SOD (58.4±14.1 vs 117.4±26.9U/mg protein; P<0.001) and catalase (0.30±0.05 vs 0.75±0.31U/mg protein; P<0.001) were observed in lung tissue of PH rats, which were prevented by sildenafil and both the doses of Arjuna extract. Protein expression of NOX1 was significantly increased in lung and gene expression of Bcl2/Bax ratio was significantly decreased in right ventricle in MCT-induced PH, both were significantly prevented by Arjuna and sildenafil.

CONCLUSIONS

Aqueous extract of Terminalia arjuna prevented MCT-induced pulmonary hypertension which may be attributed to its antioxidant as well as its effects on pulmonary arteriolar wall thickening.

Phosphodiesterase 5 inhibitors augment UT-15C-stimulated ATP release from erythrocytes of humans with pulmonary arterial hypertension

Both prostacyclin analogs and phosphodiesterase 5 (PDE5) inhibitors are effective treatments for pulmonary arterial hypertension (PAH). In addition to direct effects on vascular smooth muscle, prostacyclin analogs increase cAMP levels and ATP release from healthy human erythrocytes. We hypothesized that UT-15C, an orally available form of the prostacyclin analog, treprostinil, would stimulate ATP release from erythrocytes of humans with PAH and that this release would be augmented by PDE5 inhibitors. Erythrocytes were isolated and the effect of UT-15C on cAMP levels and ATP release were measured in the presence and absence of the PDE5 inhibitors, zaprinast or tadalafil. In addition, the ability of a soluble guanylyl cyclase inhibitor to prevent the effects of tadalafil was determined. Erythrocytes of healthy humans and humans with PAH respond to UT-15C with increases in cAMP levels and ATP release. In both groups, UT-15C-induced ATP release was potentiated by zaprinast and tadalafil. The effect of tadalafil was prevented by pre-treatment with an inhibitor of soluble guanylyl cyclase in healthy human erythrocytes. Importantly, UT-15C-induced ATP release was greater in PAH erythrocytes than in healthy human erythrocytes in both the presence and the absence of PDE5 inhibitors. The finding that prostacyclin analogs and PDE5 inhibitors work synergistically to enhance release of the potent vasodilator ATP from PAH erythrocytes provides a new rationale for the co-administration of these drugs in this disease. Moreover, these results suggest that the erythrocyte is a novel target for future drug development for the treatment of PAH.

Dysregulation of PTEN in cardiopulmonary vascular remodeling induced by pulmonary hypertension

Pulmonary hypertension (PH) is a disorder of lung vasculature characterized by arterial narrowing. Phosphatase-and-tensin homolog on chromosome 10 (PTEN), associated in the progression of multiple cancers, is implicated in arterial remodeling. However, the involvement of PTEN in PH remains unclear. The objective of the present study was to determine the role of PTEN in pulmonary vascular remodeling using established models of PH. The study used rat models of PH, induced by monocrotaline (MCT) administration (60 mg/kg) or continuous hypoxic exposure (10% oxygen) for 3 weeks. Pulmonary artery smooth muscle cells (SMCs) were used for in vitro confirmation. Development of PH was verified by hemodynamic, morphological and histopathology analyses. PTEN and key downstream proteins in pulmonary and cardiac tissues were analyzed by western blotting and RT-PCR. PTEN was significantly decreased (MCT, 53%; Hypoxia, 40%), pAkt was significantly increased (MCT, 42%; Hypoxia, 55%) in tissues of rats with PH. Similar results were observed in SMCs exposed to hypoxia (1% oxygen) for 48 h. Ubiquitination assay showed that PTEN degradation occurs via proteasomal degradation pathway. Western blotting demonstrated a significant downregulation of cell-cycle regulatory proteins p53 and p27, and upregulation of cyclin-D1 in the lungs of both models. The results showed that PTEN-mediated modulation of PI3K pathway was independent of the focal adhesion kinase and fatty acid synthase. The study, for the first time, established that PTEN plays a key role in the progression of pulmonary hypertension. The findings may have potential for the treatment of pulmonary hypertension using PTEN as a target.

Chronic overcirculation-induced pulmonary arterial hypertension in aorto-caval shunt

Pulmonary arterial hypertension is a common complication of congenital heart defects with left-to-right shunts. Current preclinical models do not reproduce clinical characteristics of shunt-related pulmonary hypertension. Aorto-caval shunt was firstly described as a model of right ventricle volume overload. The pathophysiology and the possible determination of pulmonary arterial hypertension of different periods of shunt exposure are still undefined. A method to create standardized, reproducible aorto-caval shunt was developed in growing rats (260±40 g). Three groups of animals were considered: shunt exposure for 10 weeks, shunt exposure for 20 weeks and control (sham laparotomy). Echocardiography and magnetic resonance revealed increased right ventricular end diastolic area in shunt at 10 weeks compared to control. Hemodynamic analysis demonstrated increased right ventricular afterload and increased effective pulmonary arterial elastance (Ea) in shunt at 20 weeks compared to control (1.29±0.20 vs. 0.14±0.06 mmHg/μl, p=0.004). At the same time point, the maximal slope of end-systolic pressure-volume relationship (Ees) decreased (0.5±0.2 mmHg/ml vs. 1.2±0.3, p<0.001). Consequently, right ventricular-arterial coupling was markedly deteriorated with a ≈50% decrease in the ratio of end-systolic to pulmonary artery elastance (Ees/Ea). Finally, left ventricular preload diminished (≈30% decrease in left ventricular end-diastolic volume). Histology demonstrated medial hypertrophy and small artery luminal narrowing. Chronic exposure to aorto-caval shunt is a reliable model to produce right ventricular volume overload and secondary pulmonary arterial hypertension. This model could be an alternative with low mortality and high reproducibility for investigators on the underlying mechanisms of shunt-related pulmonary hypertension.

Sildenafil, a PDE5 inhibitor, in the treatment of pulmonary hypertension

Pulmonary hypertension is a devastating disorder, characterized by vascular proliferation, intimal hypertrophy and vasoconstriction. In this disorder, alterations in the nitric oxide pathway have borne out to be important in not only vascular proliferation, but also in the maintenance of vascular tone. After synthesis by soluble guanylate cyclase, cGMP effects vasodilation via protein kinase G and other mediators, and is hydrolyzed by phosphodiesterases (PDEs). PDE5 is abundantly expressed in the mammalian lung and its inhibition by sildenafil has been demonstrated to improve pulmonary vascular physiology in vitro and in vivo animal models of pulmonary hypertension. Recent human data has confirmed the efficacy of sildenafil in therapy for humans with pulmonary arterial hypertension. The following review will discuss the underlying basic science supporting the use of sildenafil, as well as human evidence supporting the critical role of this drug in therapy of patients with pulmonary hypertension.

L-Arginine in Combination With Sildenafil Potentiates the Attenuation of Hypoxic Pulmonary Hypertension in Rats

Chronic hypoxia induces an increased production of nitric oxide (NO) in pulmonary prealveolar arterioles. Bioavailability of the NO in the pulmonary vessels correlates with concentration of L-arginine as well as activity of phosphodiesterase-5 enzyme (PDE-5). We tested a hypothesis whether a combination of L-arginine and PDE-5 inhibitor sildenafil has an additive effect in reduction of the hypoxic pulmonary hypertension (HPH) in rats. Animals were exposed to chronic normobaric hypoxia for 3 weeks. In the AH group, rats were administered L-arginine during chronic hypoxic exposure. In the SH group, rats were administered sildenafil during chronic hypoxic exposure. In the SAH group, rats were treated by the combination of L-arginine as well as sildenafil during exposure to chronic hypoxia. Mean PAP, structural remodeling of peripheral pulmonary arterioles (%DL) and RV/LV+S ratio was significantly decreased in the SAH group compared to hypoxic controls even decreased compared to the AH and the SH groups in first two measured parameters. Plasmatic concentration of cGMP and NOx were significantly lower in the SAH group compared to hypoxic controls. We demonstrate that NO synthase substrate L-arginine and phosphodiesterase-5 inhibitor sildenafil administered in combination are more potent in attenuation of the HPH compared to a treatment by substances given alone.

An inhibitory effect of tumor necrosis factor-alpha antagonist to gene expression in monocrotaline-induced pulmonary hypertensive rats model

Purpose

Tumor necrosis factor (TNF)-α is thought to contribute to pulmonary hypertension. We aimed to investigate the effect of infliximab (TNF-α antagonist) treatment on pathologic findings and gene expression in a monocrotaline-induced pulmonary hypertension rat model.

Methods

Six-week-old male Sprague-Dawley rats were allocated to 3 groups: control (C), single subcutaneous injection of normal saline (0.1 mL/kg); monocrotaline (M), single subcutaneous injection of monocrotaline (60 mg/kg); and monocrotaline + infliximab (M+I), single subcutaneous injection of monocrotaline plus single subcutaneous injection of infliximab (5 mg/kg). The rats were sacrificed after 1, 5, 7, 14, or 28 days. We examined changes in pathology and gene expression levels of TNF-α, endothelin-1 (ET-1), endothelin receptor A (ERA), endothelial nitric oxide synthase (eNOS), matrix metalloproteinase (MMP)2, and tissue inhibitor of matrix metalloproteinase (TIMP).

Results

The increase in medial wall thickness of the pulmonary arteriole in the M+I group was significantly lower than that in the M group on day 7 after infliximab treatment (P<0.05). The number of intra-acinar muscular arteries in the M+I group was lower than that in the M group on days 14 and 28 (P<0.05). Expression levels of TNF-α, ET-1, ERA, and MMP2 were significantly lower in the M+I group than in the M group on day 5, whereas eNOS and TIMP expressions were late in the M group (day 28).

Conclusion

Infliximab administration induced early changes in pathological findings and expression levels of TNF-α, and MMP2 in a monocrotaline-induced pulmonary hypertension rat model.

Sildenafil improves long-term effect of endothelial progenitor cell-based treatment for monocrotaline-induced rat pulmonary arterial hypertension

BACKGROUND AIMS

We hypothesized that the long-term therapeutic effect of combined sildenafil and bone marrow-derived endothelial progenitor cells (BMDEPCs) on monocrotaline (MCT)-induced rat pulmonary arterial hypertension (PAH) is superior to either treatment alone.

METHODS

Male Sprague-Dawley rats (n = 40) were equally divided into normal controls, MCT (65 mg/kg, subcutaneously) only, MCT + sildenafil (25 mg/kg/day, orally), MCT + BMDEPCs (2.0 × 10(6) autologous cells, intravenously) and MCT + sildenafil+ BMDEPCs. BMDEPCs and sildenafil were given on day 21 after MCT administration. Animals were sacrificed by day 90 after MCT administration.

RESULTS

The apoptotic (caspase 3, Bax) and inflammatory (tumor necrosis factor-α, matrix metalloproteinase-9) biomarkers in right ventricle and lung and pulmonary expressions of fibrotic biomarkers (transforming growth factor-β, p-Smad3) and connexin 43 protein were lower in monotherapy groups (i.e., MCT + sildenafil and MCT + BMDEPCs) and further decreased in normal controls and combined treatment groups (i.e., MCT + sildenafil + BMDEPCs) compared with untreated animals (i.e., MCT only) (all P < 0.01). Expressions of anti-fibrotic biomarkers (bone morphogenetic protein-2, p-Smad1/5) and numbers of alveolar sacs and arterioles in lung were higher in monotherapy groups and further increased in normal controls and combined treatment groups compared with untreated animals (all P < 0.005). In right ventricle, connexin 43 and α-myosin heavy chain (MHC) expressions were higher in the monotherapy groups and further elevated in normal controls and combined treatment groups compared with untreated animals, whereas β-MHC exhibited the opposite pattern (all P < 0.01). Right ventricular systolic pressure and weight were lower in the monotherapy animals and further reduced in normal controls and combined treatment groups compared with untreated animals (all P < 0.0001).

CONCLUSIONS

Combined therapy with BMDEPCs and sildenafil was superior to either treatment alone in attenuating rodent MCT-induced PAH.

Beraprost sodium attenuates cigarette smoke extract-induced apoptosis in vascular endothelial cells

Apoptosis is now widely recognized as an important part of chronic obstructive pulmonary disease (COPD) pathogenesis. Our previous study demonstrated that a prostacyclin (PGI(2)) analogue (beraprost sodium, BPS) prevented cigarette smoke extract (CSE) induced apoptosis of the pulmonary endothelium in rats. So we determined to clarify the apoptosis of vascular endothelial cells in COPD patient and the role of prostacyclin in the protection against apoptosis in vascular endothelial cells induced by CSE. Surgical specimens were obtained from 12 patients with COPD and 10 controls, and the level of apoptosis, prostacyclin synthase (PGI(2)S) expression and 6-keto-PGF1α (a stable metabolite of PGI(2)) were detected. The apoptotic index (AI), caspase-3 activity, expression of caspase-3 and 6-keto-PGF1α were examined in human umbilical vein endothelial cells (HUVECs) under exposure to varied concentrations of CSE for 24 h as well as under exposure to 2.5 % CSE for varied durations. Then, HUVECs under 2.5 % CSE were exposed to varied concentrations of BPS for 24 h and observed the alteration and the level of cAMP. Increased AI, decreased expression of PGI(2)S and 6-keto-PGF1α, were found in the lungs of patients with COPD compared with controls. Moreover, CSE induced apoptosis in means of both dose-dependent and time-dependent manners, and reduced the level of 6-keto-PGF1α in HUVECs. And with the treatment of BPS, an enhanced level of cAMP and decreased apoptosis were detected. The deficiency of PGI(2) critically contributes to the COPD-associated endothelial dysfunction and apoptosis. And BPS protects against the apoptosis in the vascular endothelial cells induced by CSE.

Changes of gene expression after bone marrow cell transfusion in rats with monocrotaline-induced pulmonary hypertension

Pulmonary artery hypertension (PAH) causes right ventricular failure and possibly even death by a progressive increase in pulmonary vascular resistance. Bone marrow-derived mesenchymal stem cell therapy has provided an alternative treatment for ailments of various organs by promoting cell regeneration at the site of pathology. The purpose of this study was to investigate changes of pulmonary haemodynamics, pathology and expressions of various genes, including ET (endothelin)-1, ET receptor A (ERA), endothelial nitric oxide synthase (NOS) 3, matrix metalloproteinase (MMP) 2, tissue inhibitor of matrix metalloproteinase (TIMP), interleukin (IL)-6 and tumor necrosis factor (TNF)-α in monocrotaline (MCT)-induced PAH rat models after bone marrow cell (BMC) transfusion. The rats were grouped as the control (C) group, monocrotaline (M) group, and BMC transfusion (B) group. M and B groups received subcutaneous (sc) injection of MCT (60 mg/kg). BMCs were transfused by intravenous injection at the tail 1 week after MCT injection in B group. Results showed that the average RV pressure significantly decreased in the B group compared with the M group. RV weight and the ratio of RH/LH+septum significantly decreased in the B group compared to the M group. Gene expressions of ET-1, ERA, NOS 3, MMP 2, TIMP, IL-6, and TNF-α significantly decreased in week 4 in the B group compared with the M group. In conclusion, BMC transfusion appears to improve survival rate, RVH, and mean RV pressure, and decreases gene expressions of ET-1, ERA, NOS 3, MMP 2, TIMP, IL-6, and TNF-α.

Changes of pulmonary pathology and gene expressions after simvastatin treatment in the monocrotaline-induced pulmonary hypertension rat model

BACKGROUND AND OBJECTIVES

Simvastatin's properties are suggestive of a potential pathophysiologic role in pulmonary hypertension. The objectives of this study were to investigate changes of pulmonary pathology and gene expressions, including endothelin (ET)-1, endothelin receptor A (ERA), inducible nitric oxide synthase (NOS2), endothelial nitric oxide synthase (NOS3), matrix metalloproteinase (MMP) 2, tissue inhibitor of matrix metalloproteinases (TIMP) and caspase 3, and to evaluate the effect of simvastatin on monocrotaline (M)-induced pulmonary hypertension.

MATERIALS AND METHODS

Six week old male Sprague-Dawley rats were treated, as follows: control group, subcutaneous (sc) injection of saline; M group, sc injection of M (60 mg/kg); and simvastatin group, sc injection of M (60 mg/kg) plus 10 mg/kg/day simvastatin orally.

RESULTS

On day 28, right ventricular hypertrophy (RVH) significantly decreased in the simvastatin group compared to the M group. Similarly, right ventricular pressure significantly decreased in the simvastatin group on day 28. From day 7, the ratio of medial thickening of the pulmonary artery was significantly increased in the M group, but there was no significant change in the simvastatin group. The number of muscular pulmonary arterioles was significantly reduced in the simvastatin group. On day 5, gene expressions of ET-1, ERA, NOS2, NOS3, MMP and TIMP significantly decreased in the simvastatin group.

CONCLUSION

Administration of simvastatin exerted weak inhibitory effects on RVH and on the number of muscular pulmonary arterioles, during the development of M-induced pulmonary hypertension in rats. Simvastatin decreased gene expressions on day 5.

Combination therapy for the treatment of pulmonary arterial hypertension

Multiple medical therapies have been developed for the treatment of pulmonary arterial hypertension (PAH) over the last decade and a half. Unfortunately, none of these medications is curative and the majority of patients develop disease progression despite treatment. Presently available medications target one of three known pathways that have been implicated in disease pathogenesis. The multiplicity of pulmonary vascular abnormalities identified in PAH provides the rationale for a therapeutic strategy that targets more than one mechanism at a time. Although a handful of studies have demonstrated clinical improvement in PAH patients who have a second medication added to stable background therapy in a randomized, placebo-controlled fashion, it is unclear whether the derived benefit is due to the combination of two therapies or merely the response to the new agent. This review discusses the rationale for combination therapy, critically reviews the findings of presently completed combination studies and outlines the need for new studies that are better designed to determine whether combination therapy is more efficacious than single agent therapies for the treatment of PAH.

Enhanced protection against pulmonary hypertension with sildenafil and endothelial progenitor cell in rats

BACKGROUND

Sildenafil and bone marrow-derived endothelial progenitor cells (BMDEPCs) have been shown to ameliorate monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH) in the rat. We test whether combined sildenafil and BMDEPC treatment exerts additional protection against MCT-induced PAH in rats.

METHODS

Male Sprague-Dawley rats were randomized to receive saline injection only (group 1), MCT (70 mg/kg) only (group 2), MCT plus autologous BMDEPC (2.0×10(6) cells) transplantation (group 3), MCT with sildenafil (30 mg/kg/day) (group 4), and MCT with combined BMDEPCs-sildenafil (30 mg/kg/day) (group 5). Intravenous BMDEPC and oral sildenafil were given on day 3 after MCT administration. Hemodynamics were analyzed using Labchart software, whereas cellular and molecular parameters were measured using flow cytometry, real-time PCR, TUNEL assay, Western blot, and immunohistochemical staining.

RESULTS

By day 35 following MCT treatment, lower expression of connexin43, protein kinase C-ε, Bcl-2, and endothelial nitric oxide synthase and higher expression of tumor necrosis factor-α and caspase 3 were found in right ventricle (RV) and lung in group 2 compared with other groups (all p<0.05). The number of alveolar sacs and lung arterioles were also lower in group 2 than in other groups (all p<0.05). Furthermore, RV systolic pressure (RVSP), RV weight, and RV-to-final body weight ratio were substantially increased in group 2 than in other groups, and notably higher in groups 3 and 4 than in groups 1 and 5 (all p<0.0001).

CONCLUSIONS

Combined therapy with autologous BMDEPC and sildenafil is superior to either BMDPEC or sildenafil alone for preventing MCT-induced PAH.

Differential regulation of PDE5 expression in left and right ventricles of feline hypertrophy models

Background

Though long known to affect smooth muscle biology, recent studies indicate that phosphodiesterase 5 (PDE5) is also expressed in myocardium. Recognizing that the regulation of PDE5 in hypertrophy is not well understood, we assessed the response of PDE5 expression and the level of cGMP-dependent kinase I (cGKI) in the left and right ventricles of feline hypertrophy models.

Methodology/Principal Findings

Using a cDNA library of feline aortic smooth muscle cells, we identified and cloned PDE5 cDNA for the first time in this species. The sequence shares 98% identity with its human orthologue at the amino acid level. E. coli expression of the cloned allele allowed selection of antibodies with appropriate specificity, facilitating the analysis of PDE5 expression in feline models created by selective proximal aortic (Ao) or pulmonary artery (PA) banding that resulted in hypertrophy of the left ventricle (LV) and right ventricle (RV), respectively. We demonstrated that PDE5 expression responded differentially with a decreased expression in the LV and an increased expression in the RV in the Ao-banded model. Similarly, in the PA-banded model, LV showed reduced expression while the RV expression was unaltered. In addition, the expression of cGKI was significantly decreased in the RV of Ao-banded group, correlating inversely with the increase in PDE5 expression.

Conclusions/Significance

The differential regulation of PDE5 and cGKI expression suggests that the mechanisms involved in hypertrophy could be different in RV vs. LV. Reciprocal PDE5 and cGKI expression in the RV of Ao-banded model suggests functional significance for PDE5 up-regulation.

Gene expressions of nitric oxide synthase and matrix metalloproteinase-2 in monocrotaline-induced pulmonary hypertension in rats after bosentan treatment

Background and Objectives

Nitric oxide (NO) is a major endothelium dependent vasomediator and growth inhibitor. NO synthesis is catalyzed by endothelial nitric oxide synthase (eNOS), and NO can also produce peroxynitrite, which activates matrix metalloproteinases (MMPs). The purpose of this study was to determine the gene expression of eNOS and MMP-2 in the lungs of a rat model of pulmonary hypertension after bosentan treatment.

Materials and Methods

Six-week-old male Sprague-Dawley rats were treated as follows: control group, subcutaneous (sc) injection of saline; monocrotaline (MCT) group, sc injection of MCT (60 mg/kg); and bosentan group, sc injection of MCT (60 mg/kg) plus 20 mg/day bosentan orally. The rats were sacrificed after 1, 5, 7, 14 and 28 days.

Results

The right ventricle/(left ventricle+septum) ratio significantly increased in the MCT group compared to the control group on day 14 and 28. The expression of eNOS messenger ribonucleic acid was significantly increased in the MCT group compared to the control group on day 28. MMP-2 gene expression was significantly increased in the MCT-treated rats compared to the control group on day 5 and 28. Following bosentan treatment to reduce pulmonary hypertension, the expression levels of MMP-2 gene were significantly decreased on day 7 and 28. eNOS and tissue inhibitor of MMPs genes were also significantly decreased on day 28 after bosentan treatment.

Conclusion

These results suggest that elevated eNOS expression may be responsible for MMP-2 activation. The causal relationship between eNOS and MMP-2 and their role in pulmonary hypertension require further investigations.

Sildenafil added to sitaxsentan in overcirculation-induced pulmonary arterial hypertension

Experimental left-to-right shunt-induced pulmonary arterial hypertension (PAH) can be partially prevented by the endothelin-A receptor blocker sitaxsentan or by the phosphodiesterase-5 inhibitor sildenafil. We hypothesized that the combined administration of these drugs would completely prevent shunt-induced PAH, arguing in favor of a major role of endothelial dysfunction in the initiation of the disease. Twenty-four 3-wk-old piglets were randomized to a sham operation or to placebo, sitaxsentan therapy, or sitaxsentan combined with sildenafil after the anastomosis of the left subclavian artery to the pulmonary arterial trunk. Three months later, the animals underwent a hemodynamic evaluation, followed by pulmonary tissue sampling for morphometry and quantitative real-time PCR for endothelin-1, angiopoietin-1, and bone morphogenetic protein receptor (BMPR) signaling molecules. Three months of left-to-right shunting induced an increase in pulmonary vascular resistance (PVR) and medial thickness, an overexpression of endothelin-1, and angiopoietin-1 and decreased expressions of BMPR-2 and BMPR-1A. Sitaxsentan partially prevented a shunt-induced increase in PVR, medial thickness, and associated biological disturbances. Sildenafil combined with sitaxsentan normalized PVR, medial thickness, and the expression of endothelin-1. However, the expression of angiopoietin-1 remained increased, and the expressions of BMPR-1A and BMPR-2 were incompletely returned to normal. The coupling of right ventricular end-systolic to arterial elastances was maintained in all circumstances. Sitaxsentan combined with sildenafil prevents shunt-induced PAH more effectively than sitaxsentan alone, suggesting a major role for the targeted signaling pathways in the initiation of the disease. Sitaxsentan alone or combined with sildenafil did not affect right ventricular function.

Gene expression of endothelin-1 and endothelin receptor a on monocrotaline-induced pulmonary hypertension in rats after bosentan treatment

BACKGROUND AND OBJECTIVES

Endothelin (ET)-1, a potent endothelium-derived vasoconstrictor peptide, has a potential pathophysiologic role in pulmonary hypertension. Bosentan, a dual ET receptor (ET(A)/ET(B)) antagonist, is efficacious in treatment of pulmonary hypertension. The objectives of this study were to investigate the expression of ET-1 and ET receptor A (ERA) genes and to evaluate the effect of bosentan in monocrotaline (MCT)-induced pulmonary hypertension.

MATERIALS AND METHODS

Four-week-old male Sprague-Dawley rats were treated as follows: control (n=36), subcutaneous (sc) injection of saline; MCT (n=36), sc injection of MCT (60 mg/kg); and bosentan (n=36), sc injection of MCT (60 mg/kg) plus 25 mg/kg/day bosentan orally.

RESULTS

Serum ET-1 concentrations in the MCT group were higher than the control group on day 28 and 42. Quantitative analysis of peripheral pulmonary arteries revealed that the increase in medial wall thickness after MCT injection was significantly attenuated in the bosentan group on day 28 and 42. In addition, the increase in the number of intra-acinar muscular arteries after MCT injection was reduced by bosentan on day 14, 28 and 42. The levels of ET-1 and ERA gene expression were significantly increased in the MCT group compared with control group on day 5, and bosentan decreased the expression of ET-1 on day 5.

CONCLUSION

ET-1 contributes to the progression of cardiopulmonary pathology in rats with MCT-induced pulmonary hypertension. Administration of bosentan reduced ET-1 gene expression in MCT-induced pulmonary hypertension in rats.

Sildenafil limits monocrotaline-induced pulmonary hypertension in rats through suppression of pulmonary vascular remodeling

We hypothesize that sildenafil attenuates pulmonary hypertension through suppressing pulmonary vascular remodeling. Thirty male adult Sprague-Dawley rats were randomized to receive saline injection (Group 1), subcutaneous monocrotaline (MCT) (60 mg/kg) (Group 2), and MCT plus oral sildenafil (30 g/kg per day) (Group 3) 5 days after MCT administration. By Day 35, Western blot showed lower connexin43 and membranous protein kinase C epsilon expressions but higher oxidative stress in right ventricle in Group 2 compared with the other groups. Additionally, pulmonary Smad1/5 was lowest, whereas connexin43 and Smad3 were highest in Group 2. Pulmonary mRNA expressions of tumor necrosis factor-alpha, caspase-3, plasminogen activator inhibitor-1, and transforming growth factor-beta were higher, whereas bone morphogenetic protein Type II receptor, Bcl-2, and endothelial nitric oxide synthase were lower in Group 2 than in the other groups. Similarly, mRNA expressions of tumor necrosis factor-alpha, caspase-3, and beta-myosin heavy chain were increased, whereas Bcl-2, endothelial nitric oxide synthase, and alpha-myosin heavy chain expressions in right ventricle were reduced in Group 2 compared with the other groups. Number of lung arterioles was lowest, whereas number of arterioles with muscularization of the medial layer was highest in Group 2. Right ventricle systolic pressure and weight were elevated in Group 2 compared with the other groups. In conclusion, sildenafil effectively alleviates MCT-induced pulmonary hypertension through suppressing pulmonary vascular remodeling.

Novel approaches to treat experimental pulmonary arterial hypertension: a review

Background. Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by an increase in pulmonary artery pressure leading to right ventricular (RV) hypertrophy, RV failure, and ultimately death. Current treatments can improve symptoms and reduce severity of the hemodynamic disorder but gradual deterioration in their condition often necessitates a lung transplant. Methods and Results. In experimental models of PAH, particularly the model of monocrotaline-induced pulmonary hypertension, efficacious treatment options tested so far include a spectrum of pharmacologic agents with actions such as anti-mitogenic, proendothelial function, proangiogenic, antiinflammatory and antioxidative. Emerging trends in PAH treatment are gene and cell therapy and their combination, like (progenitor) cells enriched with eNOS or VEGF gene. More animal data should be collected to investigate optimal cell type, in vitro cell transduction, route of administration, and number of cells to inject. Several recently discovered and experimentally tested interventions bear potential for therapeutic purposes in humans or have been shown already to be effective in PAH patients leading to improved life expectation and better quality of life. Conclusion. Since many patients remain symptomatic despite therapy, we should encourage research in animal models of PAH and implement promising treatments in homogeneous groups of PAH patients.

Pulmonary hemodynamic response to acute combination and monotherapy with sildenafil and brain natriuretic peptide in rats with monocrotaline-induced pulmonary hypertension

BACKGROUND

The lungs of patients with pulmonary arterial hypertension (PAH) exhibit decreased bioavailability of nitric oxide and downstream signaling through cyclic guanosine monophosphate (cGMP). Therapies that enhance cGMP-mediated vasodilation have shown efficacy in treating PAH. We tested the hypothesis that combination therapy with sildenafil, a cGMP phosphodiesterase type 5 inhibitor, and brain natriuretic peptide (BNP), a receptor-mediated guanosine cyclase stimulator, synergistically attenuates monocrotaline-induced PAH in rats compared with either monotherapy.

METHODS

Adult male Sprague-Dawley rats were subcutaneously injected with monocrotaline (n = 41, 50 mg/kg). After approximately 4 weeks, the rats were infused intravenously with vehicle solution, sildenafil (42 and 85 microg/kg/min), or BNP (50 and 100 ng/kg/min), alone and in varied combination. The primary endpoint was the relative change in right ventricular systolic pressure (RVSP) and mean arterial systemic pressure (MAP). Secondary endpoints included heart rate and dP/dt.

RESULTS

Vehicle infusions did not alter hemodynamic variables. Sildenafil85 (85 microg/kg/min) alone decreased RVSP (-16.6 +/- 5.6%) and decreased MAP (-4.0 +/- 4.7%). BNP50 (50 ng/kg/min) and BNP100 (100 ng/kg/min) decreased RVSP (-23.3 +/- 5.7% and -27.1 +/- 2.9%, respectively) and MAP (-6.4 +/- 5.8% and -14.3 +/- 4.1%, respectively). Combination therapy with sildenafil42 and BNP50 decreased RVSP (-20.7 +/- 5.6%) and showed a lessened systemic effect (MAP = -11.6 +/- 5.9%). Combination therapy with sildenafil85 and BNP100 decreased RVSP (-27.6 +/- 3.2%, P = NS) and showed increased systemic effect (MAP = -20.7 +/- 3.1%, P < 0.05) in comparison with sildenafil85.

CONCLUSIONS

This study suggests that intravenous administration of both sildenafil and BNP monotherapy produces significant improvement in RVSP, making them potentially viable options for the treatment of PAH, whereas combination therapy produces no additional improvement in pulmonary hemodynamics.

Animal models of pulmonary arterial hypertension: the hope for etiological discovery and pharmacological cure

At present, six groups of chronic pulmonary hypertension (PH) are described. Among these, group 1 (and 1′) comprises a group of diverse diseases termed pulmonary arterial hypertension (PAH) that have several pathophysiological, histological, and prognostic features in common. PAH is a particularly severe and progressive form of PH that frequently leads to right heart failure and premature death. The diagnosis of PAH must include a series of defined clinical parameters, which extend beyond mere elevations in pulmonary arterial pressures and include precapillary PH, pulmonary hypertensive arteriopathy (usually with plexiform lesions), slow clinical onset (months or years), and a chronic time course (years) characterized by progressive deterioration. What appears to distinguish PAH from other forms of PH is the severity of the arteriopathy observed, the defining characteristic of which is “plexogenic arteriopathy.” The pathogenesis of this arteriopathy remains unclear despite intense investigation in a variety of animal model systems. The most commonly used animal models (“classic” models) are rodents exposed to either hypoxia or monocrotaline. Newer models, which involve modification of classic approaches, have been developed that exhibit more severe PH and vascular lesions, which include neointimal proliferation and occlusion of small vessels. In addition, genetically manipulated mice have been generated that have provided insight into the role of specific molecules in the pulmonary hypertensive process. Unfortunately, at present, there is no perfect preclinical model that completely recapitulates human PAH. All models, however, have provided and will continue to provide invaluable insight into the numerous pathways that contribute to the development and maintenance of PH. Use of both classic and newly developed animal models will allow continued rigorous testing of new hypotheses regarding pathogenesis and treatment. This review highlights progress that has been made in animal modeling of this important human condition.

Tadalafil, a long-acting inhibitor of PDE5, improves pulmonary hemodynamics and survival rate of monocrotaline-induced pulmonary artery hypertension in rats

The aim of this study was to assess the effect of tadalafil (0.5, 2.5, and 10 mg/kg per day) on the progression of pulmonary arterial hypertension (PAH) in early treatment and on the survival rate in late treatment on the monocrotaline (MCT)-induced PAH rat model. Tadalafil was administered once daily to rats for 3 weeks from the day of MCT-injection or 21 days after the injection. With early treatment, tadalafil at 10 mg/kg per day prevented the development of PAH by maintaining mean pulmonary artery pressure within the normal range and attenuated right ventricular hypertrophy. With late treatment, tadalafil tended to increase the partial pressure of oxygen in arterial blood and dose-dependently improved the survival rate by 55%, 60%, and 70% at 0.5, 2.5, and 10 mg/kg per day, respectively, versus 40% in the MCT-control group. Both early and late treatments with tadalafil were associated with elevated lung cyclic guanosine monophosphate (cGMP). These results suggest that tadalafil relaxes pulmonary arteries by elevating cGMP in lungs and extend survival time by improving pulmonary hemodynamics even when treatment occurs in the late phase of PAH. Thus, it is expected that tadalafil may be an effective, once-daily treatment option in humans with PAH.

Prostanoids and phosphodiesterase inhibitors in experimental pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease with a poor prognosis, characterized by intimal lesions, medial hypertrophy, and adventitial thickening of precapillary pulmonary arteries. Several approved therapies are currently available for the treatment of PAH, of which intravenous epoprostenol is the best explored over the past decade. Newly available oral endothelin receptor antagonists, although clinically efficacious, bear the risk of liver toxicity in a significant portion of patients. Substances that stimulate the formation of the second messengers cyclic adenosine monophosphate (cAMP) or guanosine monophosphate (cGMP) have proved useful in the treatment of various forms of pre-capillary pulmonary hypertension. These second messengers of the endogenous vasodilator mediators that include prostacyclin and nitric oxide (NO) are hydrolyzed by cyclic nucleotide phosphodiesterases (PDEs), a class of enzymes from which 11 isoforms have been characterized. This chapter highlights developments in the treatment of experimental pulmonary hypertension with special attention to prostanoids and PDE inhibitors. We summarize findings for the acute vasodilatory as well as chronic effects of prostanoids, PDE inhibitors, or combinations of both, in animal models of pulmonary hypertension.

Sildenafil attenuates pulmonary inflammation and fibrin deposition, mortality and right ventricular hypertrophy in neonatal hyperoxic lung injury

Background

Phosphodiesterase-5 inhibition with sildenafil has been used to treat severe pulmonary hypertension and bronchopulmonary dysplasia (BPD), a chronic lung disease in very preterm infants who were mechanically ventilated for respiratory distress syndrome.

Methods

Sildenafil treatment was investigated in 2 models of experimental BPD: a lethal neonatal model, in which rat pups were continuously exposed to hyperoxia and treated daily with sildenafil (50–150 mg/kg body weight/day; injected subcutaneously) and a neonatal lung injury-recovery model in which rat pups were exposed to hyperoxia for 9 days, followed by 9 days of recovery in room air and started sildenafil treatment on day 6 of hyperoxia exposure. Parameters investigated include survival, histopathology, fibrin deposition, alveolar vascular leakage, right ventricular hypertrophy, and differential mRNA expression in lung and heart tissue.

Results

Prophylactic treatment with an optimal dose of sildenafil (2 × 50 mg/kg/day) significantly increased lung cGMP levels, prolonged median survival, reduced fibrin deposition, total protein content in bronchoalveolar lavage fluid, inflammation and septum thickness. Treatment with sildenafil partially corrected the differential mRNA expression of amphiregulin, plasminogen activator inhibitor-1, fibroblast growth factor receptor-4 and vascular endothelial growth factor receptor-2 in the lung and of brain and c-type natriuretic peptides and the natriuretic peptide receptors NPR-A, -B, and -C in the right ventricle. In the lethal and injury-recovery model we demonstrated improved alveolarization and angiogenesis by attenuating mean linear intercept and arteriolar wall thickness and increasing pulmonary blood vessel density, and right ventricular hypertrophy (RVH).

Conclusion

Sildenafil treatment, started simultaneously with exposure to hyperoxia after birth, prolongs survival, increases pulmonary cGMP levels, reduces the pulmonary inflammatory response, fibrin deposition and RVH, and stimulates alveolarization. Initiation of sildenafil treatment after hyperoxic lung injury and continued during room air recovery improves alveolarization and restores pulmonary angiogenesis and RVH in experimental BPD.

Protective effect of beraprost sodium, a stable prostacyclin analog, in the development of cigarette smoke extract-induced emphysema

Chronic inflammation, imbalance of proteolytic and anti-proteolytic activities, oxidative stress, and apoptosis of lung structural cells contribute to the pathogenesis of COPD. Prostacyclin protects cells against apoptosis, has anti-inflammatory properties, partially prevents cigarette smoke extract (CSE)-induced apoptosis of the pulmonary endothelium, and thus may be relevant in the pathogenesis of emphysema. We determined whether a synthetic stable prostacyclin analog, beraprost sodium (BPS), attenuates the development of CSE-induced emphysema and elucidated the molecular mechanisms involved in its effect. Sprague-Dawley rats were treated with BPS and injected with CSE once a week for 3 wk. We measured the DNA damage of cells, the expression of caspase-3, and the activity of matrix metalloproteinase (MMP)-2 and MMP-9. We also analyzed TNFalpha and IL-1beta concentrations and the serum antioxidant activity. BPS prevented the development of CSE-induced emphysema, resulting in significant attenuation in alveolar enlargement and pulmonary parenchymal destruction. BPS inhibited pulmonary apoptosis and induction of MMP-2 and MMP-9 activity. Moreover, the protective effect of BPS was associated with a reduction of the expression of proinflammatory cytokines including TNFalpha and IL-1beta and a normalized biological oxidant activity. BPS introduces all these events, probably by activating cAMP signaling through acting specific prostacyclin receptors. In conclusion, BPS protects against the development of CSE-induced emphysema by attenuating apoptosis, inhibiting proteolytic enzyme activity, reducing inflammatory cytokine levels, and augmenting antioxidant activity. BPS may potentially represent a new therapeutic option in the prevention of emphysema in humans in prospect.

Chronic inhibition of phosphodiesterase 5 does not prevent pressure-overload-induced right-ventricular remodelling

AIMS

Inhibition of phosphodiesterase 5 (PDE5) decreases pulmonary pressure and improves symptoms in patients with pulmonary arterial hypertension. It is unclear however, whether inhibition of PDE5 can prevent myocardial remodelling during right-ventricular pressure overload.

METHODS AND RESULTS

Right-ventricular pressure overload was produced in male rats in a pulmonary hypertension model (monocrotaline 60 mg/kg s.c.) or by surgical pulmonary artery banding. PDE5 inhibition using oral sildenafil (50 mg/kg/day in drinking water) or placebo was initiated 14 days after monocrotaline treatment and continued for 14 days until final examination. In the pulmonary artery banding groups, rats were treated with sildenafil (50 mg/kg/day) or placebo for 21 days following surgical pulmonary artery banding. At the final experiments, right-ventricular haemodynamics were measured and remodelling was analysed using histological, biochemical, and gene expression markers. Both monocrotaline and pulmonary artery banding increased right-ventricular systolic pressure to approximately 80 mmHg. In parallel, both interventions induced markers of hypertrophy (upregulation of natriuretic peptides, increase in myocyte diameter) and fibrosis (upregulation of collagen types 1A2 and 3A1) as well as mRNA expression of the tissue inhibitor of matrix metalloproteases 1 and osteopontin in the right ventricle. In monocrotaline model, sildenafil decreased pulmonary pressure, reduced right-ventricular hypertrophy, and prevented fibrosis marker gene upregulation. After pulmonary artery banding, in contrast, sildenafil increased markers of myocardial remodelling and right-ventricular myocyte diameter.

CONCLUSION

Sildenafil prevents myocardial remodelling in pulmonary hypertension through an indirect action via right-ventricular unloading.

Role of the prostanoid EP4 receptor in iloprost-mediated vasodilatation in pulmonary hypertension

RATIONALE

Iloprost is effective for the treatment of pulmonary hypertension. It acts through elevation of cAMP by binding to the prostacyclin receptor (IP receptor). However, there is evidence that patients with severe pulmonary hypertension have decreased expression of the IP receptor in the remodeled pulmonary arterial smooth muscle.

OBJECTIVES

We hypothesized that prostanoid receptors other than the IP receptor are involved in signal transduction by iloprost.

METHODS

Immunoblotting was used to detect the IP and prostanoid EP4 receptor in lung tissue from patients with idiopathic pulmonary arterial hypertension, and immunohistochemistry was used to detect these receptors in lung sections from rats treated with monocrotaline (MCT28d). Protein and mRNA were isolated from pulmonary arterial smooth muscle cells (PASMCs) from control and MCT28d rats treated with AH6809 (an EP2 receptor antagonist) and AH23848 (an EP4 receptor antagonist) in combination with iloprost. Intracellular cAMP was also assessed in these tissues.

MEASUREMENTS AND MAIN RESULTS

IP receptor expression was reduced in idiopathic pulmonary arterial hypertension patient lung samples and MCT28d rat lungs compared with the controls. Reverse transcriptase-polymerase chain reaction and immunoblotting of MCT28d rat PASMC extracts revealed scant expression of the IP receptor but stable expression of EP4 receptor, compared with controls. Iloprost-induced elevation in intracellular cAMP in PASMCs was dose-dependently reduced by AH23848, but not by AH6809.

CONCLUSIONS

Iloprost mediates vasodilatory functions via the EP4 receptor in the case of low IP receptor expression associated with pulmonary arterial hypertension. This is a previously unrecognized mechanism for iloprost, and illustrates that the EP4 receptor may be a novel therapeutic approach for the treatment of pulmonary arterial hypertension.