RIOCIGUAT-INDUCED DOWNREGULATION OF GENES RESPONSIBLE FOR SODIUM TRANSPORT THROUGH THE ALVEOLAR EPITHELIUM IN THE MONOCROTALINE MODEL OF PULMONARY HYPERTENSION

Objective: Pleural effusions (PLEF) in patients with pulmonary arterial hypertension (PAH) co-diagnosed with isolated right-sided heart failure (RHF) have been reported to be associated with increased mortality. We hypothesized that alterations of transporters responsible for alveolar fluid clearance contributes to fluid accumulation in lungs and secondary formation of PLEF. This was examined in a model of PAH including administration of riociguat (RIO) that as a stimulator of sGC may be responsible for cGMP-dependent inhibition of epithelial sodium channel (ENaC) and might affect alveolar epithelial sodium transport. Design and method: Wistar rats were injected with monocrotaline (MCT; 60 mg/kg, s.c.) or vehicle (CON). 2 weeks after MCT administration, RIO treatment (10 mg/kg/d, p.o.) was started (CON+RIO, MCT+RIO). MCT groups were subdivided: MCT4W - sacrificed 4 weeks after MCT application and prematurely terminated MCT (ptMCT) - sacrificed after PAH deterioration. Expressions of ENaC alpha, beta, gama subunits, Na-K-Cl cotransporter (NKCC1), sodium-glucose linked transporter (SGLT1), sodium-coupled neutral amino acid transporters (SNAT2, SNAT5), aquaporin 3 (AQP3) were determined by RT-qPCR in lungs. Lung samples were subjected to histological analysis. Results: Increased lung weight was observed in MCT4W (2.331g vs.CON, p<0.05) and ptMCT (2.778g, vs.MCT4W, p<0.05). Similar situation was observed in RIO treated groups, however, more profound compared to MCT4W (ptMCT+RIO = 3.086g, p<0.05). Expression of ENaC, SNAT5 was decreased in ptMCT and ptMCT+RIO. Expression of NKCC1 decreased in ptMCT+RIO (by 30%) and simultaneously expression of SNAT2 in MCT4W+RIO, ptMCT+RIO (by 58%), both p<0.05 vs.CON, without any changes in MCT4W and ptMCT. 15-fold increase in AQP3 expression was observed in ptMCT, ptMCT+RIO (p<0.05 vs.CON). The presence of fluid in alveoli was observed in MCT4W and ptMCT with incidence of PLEF 20% and 30% respectively (ns). Incidence of PLEF in MCT4W+RIO and ptMCT+RIO was 22% and 44% (p<0.05), however, with interstitial swelling present. Conclusions: Downregulation of ENaC in MCT-induced PAH may represent a predisposing factor for alveolar fluid clearance impairment contributing to accumulation of fluid in lungs manifested as lung weight increase. Incidence of PLEF is probably related to lung weight increase. Riociguat rather worsened the incidence of PLEF and downregulation of ENaC.