The Mechanism of Volatile Oil of Rhodiola tangutica against Hypoxia-Induced Pulmonary Hypertension in Rats Based on RAS Pathway

Ethnopharmacological Relevance. Volatile oil is an important bioactive ingredient of Rhodiola tangutica (Maxim.) S.H. Fu, namely, R. tangutica in short. Previous studies have focused on its chemical composition. In our previous research, we found that the bioactive fraction of Rhodiola tangutica could significantly alleviate hypoxia-induced pulmonary hypertension (HPH) in rats. However, it remains unknown whether the volatile oil of Rhodiola tangutica (VORA) could alleviate HPH in rats. Aim of the Study. The main purpose of this study is to explore the effect as well as the corresponding mechanism of VORA among HPH rats, so as to provide evidences for the further exploration of aromatic substances of VORA. Materials and Methods. Seventy-five male Sprague-Dawley (SD) rats were separated into control (Ctr), hypoxia (Hyp), and Hyp+VORA treatment (100 mg/kg/d, 80 mg/kg/d, and 40 mg/kg/d) groups in random. To achieve the chronic hypoxia condition, rats were kept inside the hypobaric chamber with automatically adjusted inner pressure as well as oxygen content equal to those of 4500 m in altitude for 4 continuous weeks. After 4 weeks, the rats’ physiological parameters were determined (mean pulmonary artery pressure (mPAP); right ventricular hypertrophy index (RVHI)). Based on hematoxylin and eosin (HE) staining and transmission electron microscope (TEM), morphological features of their lung tissues were also analyzed. Proliferation of pulmonary arterial smooth muscle cells (PASMCs) was detected by MTS Cell Proliferation Colorimetric assay. The levels of glutathione (GSH), malondialdehyde (MDA), and superoxide dismutase (SOD) in PASMCs were detected through corresponding kits, respectively. The protein levels in PASMCs and HPH rats were evaluated by Western blot (WB). Chemical components of VORA were detected through gas chromatography-mass spectrometer (GC-MS). Results. After induced by hypoxia for 4 weeks, the mPAP and RVHI levels were increased significantly in hypoxia group in contrast to the Ctr group, indicating the establishment of HPH rat model. The subsequent administration of VORA decreased the mPAP and RVHI level. The vascular wall thickness and lumen size were also decreased after treated by VORA compared with Hyp group. Meanwhile, VORA suppressed the proliferation and oxidant stress in PASMCs. Therefore, the effect of VORA on decreasing vascular wall thickening and lumen size could be related to its antiproliferation effect on PASMCs. In addition, compared to the Hyp group, VORA downregulated the ACE, AngII, and AT1R protein expressions but increased ACE2 and MAS protein expressions ( $P<0.05$ ). A total of 48 constituents in VORA were identified by GC-MS in comparison with reference standards as well as the reference pieces of literatures. Conclusions. HPH rat model as established based on the significant increased mPAP and RVHI. VORA presented a significant antihypoxia function plus an inhibiting effect on PASMC proliferation induced by hypoxia. Moreover, VORA treatment inhibited oxidative stress among PASMCs. With regard to the mechanism, VORA reduced ACE, AngII, and AT1R protein expressions but increased ACE2 and MAS protein expressions. There were 48 constituents in VORA identified by GC-MS.