Effects of macitentan and tadalafil monotherapy or their combination on the right ventricle and plasma metabolites in pulmonary hypertensive rats.

Pulmonary arterial hypertension is a severe respiratory disease characterized by pulmonary artery remodeling. RV dysfunction and dysregulated circulating metabolomics are associated with adverse outcomes in pulmonary arterial hypertension. We investigated effects of tadalafil and macitentan alone or in combination on the RV and plasma metabolomics in SuHx and PAB models. For SuHx model, rats were injected with SU5416 and exposed to hypoxia for three weeks and then were returned to normoxia and treated with either tadalafil (10 mg/kg in chow) or macitentan (10 mg/kg in chow) or their combination (both 10 mg/kg in chow) for two weeks. For PAB model, rats were subjected to either sham or PAB surgery for three weeks and treated with above-mentioned drugs from week 1 to week 3. Following terminal echocardiographic and hemodynamic measurements, tissue samples were collected for metabolomic, histological and gene expression analysis. Both SuHx and PAB rats developed RV remodeling/dysfunction with severe and mild plasma metabolomic alterations, respectively. In SuHx rats, tadalafil and macitentan alone or in combination improved RV remodeling/function with the effects of macitentan and combination therapy being superior to tadalafil. All therapies similarly attenuated SuHx-induced changes in plasma metabolomics. In PAB rats, only macitentan improved RV remodeling/function, while only tadalafil attenuated PAB-induced changes in plasma metabolomics.

Influence of gender in monocrotaline and chronic hypoxia induced pulmonary hypertension in obese rats and mice.

BACKGROUND: Obesity and pulmonary hypertension (PH) share common characteristics, such as augmented inflammation and oxidative stress. However, the exact role of obesity in the pathology of PH is largely uninvestigated. Therefore, we have hypothesized that in the context of obesity the gender difference may have influence on development of PH in animal models of this disease. METHODS: Animal experiments were conducted in monocrotaline (MCT) and chronic hypoxia (HOX) models of PH. Lean and obese Zucker rats or B6 mice of both genders were used for MCT or HOX models, respectively. Echocardiography, hemodynamic measurements, histology and immuno-histochemistry were performed to analyze various parameters, such as right ventricular function and hypertrophy, hemodynamics, pulmonary vascular remodeling and lung inflammation. RESULTS: Both lean and obese male and female Zucker rats developed PH after a single MCT injection. However, negligible differences were seen between lean and obese male rats in terms of PH severity at the end stage of disease. Conversely, a more prominent and severe PH was observed in obese female rats compared to their lean counterparts. In contrast, HOX induced PH in lean and obese, male and female mice did not show any apparent differences. CONCLUSION: Gender influences PH severity in obese MCT-injected rats. It is also an important factor associated with altered inflammation. However, further research is necessary to investigate and reveal the underlying mechanisms.

Altered proteasome function in right ventricular hypertrophy.

AIMS: In patients with pulmonary hypertension, right ventricular hypertrophy (RVH) is a detrimental condition that ultimately results in right heart failure and death. The ubiquitin proteasome system has been identified as a major protein degradation system to regulate cardiac remodelling in the left heart. Its role in right heart hypertrophy, however, is still ambiguous. METHODS AND RESULTS: RVH was induced in mice by pulmonary artery banding (PAB). Both, expression and activity of the proteasome was found to be up-regulated in the hypertrophied right ventricle (RV) compared to healthy controls. Catalytic inhibition of the proteasome by the two proteasome inhibitors Bortezomib (BTZ) and ONX-0912 partially improved RVH both in preventive and therapeutic applications. Native gel analysis revealed that specifically the 26S proteasome complexes were activated in experimental RVH. Increased assembly of 26S proteasomes was accompanied by elevated expression of Rpn6, a rate-limiting subunit of 26S proteasome assembly, in hypertrophied cardiomyocytes of the right heart. Intriguingly, patients with RVH also showed increased expression of Rpn6 in hypertrophied cardiomyocytes of the RV as identified by immunohistochemical staining. CONCLUSION: Our data demonstrate that alterations in expression and activity of proteasomal subunits play a critical role in the development of RVH. Moreover, this study provides an improved understanding on the selective activation of the 26S proteasome in RVH that might be driven by the rate-limiting subunit Rpn6. In RVH, Rpn6 therefore represents a more specific target to interfere with proteasome function than the commonly used catalytic proteasome inhibitors.

Pulmonary Vascular Pressure Response to Acute Cold Exposure in Kyrgyz Highlanders.

Background/Aims: Long-term high altitude residence leads to a sustained increase in pulmonary vascular resistance and elevation of pulmonary artery pressure due to chronic alveolar hypoxia. However, living at high altitude is also associated with other environmental factors such as cold. There is still little experimental evidence suggesting detrimental effects of low temperatures on the pulmonary vasculature. Therefore, our objective was to investigate acute effects of cold exposure on the pulmonary circulation in Kyrgyz high altitude natives. Methods: Responses of the pulmonary circulation during acute exposure to controlled cold conditions (4°C-6°C) for 60 minutes were measured in highlanders using Doppler echocardiography. Based on the Doppler echocardiography-derived tricuspid regurgitant systolic pressure gradient (TRG), subjects with TRG ≥40 mmHg were allocated into the pulmonary hypertension (PH) group. Participants from the PH group were compared with volunteer control subjects with TRG <40 mmHg. All baseline measurements were evaluated in a warm room during 60 minutes (22°C-28°C). Following baseline echocardiography, the subjects were assigned to either warm or cold exposure for an additional 60 minutes. Results: Acute cold exposure significantly increased TRG both in the control (ΔTRG, 4.93 mmHg) and in the PH (ΔTRG, 8.15 mmHg) group, compared to the respective warm exposure conditions (ΔTRG, -0.14 and -0.05 mmHg). No changes in cardiac output were observed upon cold exposure. Conclusion: Thus, acute exposure to cold leads to elevation of pulmonary artery pressure in high altitude residents.

Circulating Apoptotic Signals During Acute and Chronic Exposure to High Altitude in Kyrgyz Population.

Background: Circulating apoptotic signals (CASs) have been described in the pathologies associated with dysregulated apoptosis, such as cancer, heart diseases, and pulmonary hypertension (PH). However, nothing is known about the expression profiles of these markers in the circulation of humans exposed to acute and chronic effects of high altitude (HA). Methods: Gene expression levels of different apoptotic signals (ASs) were analyzed in human pulmonary artery smooth muscle cells (PASMCs) upon hypoxia incubation. In addition, we measured the plasma values of relevant CAS in Kyrgyz volunteers during acute and chronic exposure to HA. Finally, we analyzed the effects of pro-apoptotic mediator Fas ligand (FasL) on apoptosis and proliferation of human PASMCs. Results: Several cellular AS were increased in PASMCs exposed to hypoxia, in comparison to normoxia condition. Among analyzed CAS, there was a prominent reduction of FasL in lowlanders exposed to HA environment. Furthermore, decreased circulatory levels of FasL were found in highlanders with HA-induced PH (HAPH), as compared to the lowland controls. Furthermore, FasL concentration in plasma negatively correlated with tricuspid regurgitant gradient values. Finally, FasL exerted pro-apoptotic and anti-proliferative effects on PASMCs. Conclusion: Our data demonstrated that circulating levels of FasL are reduced during acute and chronic exposure to HA environment. In addition, dysregulated FasL may play a role in the context of HAPH due to its relevant functions on apoptosis and proliferation of PASMCs.

Phosphodiesterase 10A upregulation contributes to pulmonary vascular remodeling.

Phosphodiesterases (PDEs) modulate the cellular proliferation involved in the pathophysiology of pulmonary hypertension (PH) by hydrolyzing cAMP and cGMP. The present study was designed to determine whether any of the recently identified PDEs (PDE7-PDE11) contribute to progressive pulmonary vascular remodeling in PH. All in vitro experiments were performed with lung tissue or pulmonary arterial smooth muscle cells (PASMCs) obtained from control rats or monocrotaline (MCT)-induced pulmonary hypertensive (MCT-PH) rats, and we examined the effects of the PDE10 inhibitor papaverine (Pap) and specific small interfering RNA (siRNA). In addition, papaverine was administrated to MCT-induced PH rats from day 21 to day 35 by continuous intravenous infusion to examine the in vivo effects of PDE10A inhibition. We found that PDE10A was predominantly present in the lung vasculature, and the mRNA, protein, and activity levels of PDE10A were all significantly increased in MCT PASMCs compared with control PASMCs. Papaverine and PDE10A siRNA induced an accumulation of intracellular cAMP, activated cAMP response element binding protein and attenuated PASMC proliferation. Intravenous infusion of papaverine in MCT-PH rats resulted in a 40%-50% attenuation of the effects on pulmonary hypertensive hemodynamic parameters and pulmonary vascular remodeling. The present study is the first to demonstrate a central role of PDE10A in progressive pulmonary vascular remodeling, and the results suggest a novel therapeutic approach for the treatment of PH.