Pulmonary hypertension (PH) is a multifactorial disease characterized by pulmonary arteries (PA) hyperreactivity and remodelling involving an imbalance of contractile and proliferative agents such as 5-hydroxytryptamine (5-HT). Mitochondria and associated reactive oxygen species (ROS) production were shown to contribute to these phenomena. OP2 Drugs recently demonstrated that Anethole Trithione (ATT), the active ingredient of its principal lead OP2113, specifically inhibits mitochondrial ROS (mtROS) production from complex I in its reverse mode. In this context, this study aims to assess the effects of ATT on PH hallmarks.

Male rats were either exposed to normoxia or chronic hypoxia (10% O2) during 3 weeks to induce PH (CH-PH). The effect of ATT on PA reactivity was determined ex vivo by isometric tension measurements of arterial rings. PA contraction was induced by 5-HT, prostaglandin F2α (PGF2α), phenylephrine (Phe) or endothelin-1 (ET-1) whereas relaxation was induced by carbachol (Cch) on preconstricted vessels with PGF2α. The effect of ATT on calcium responses induced by 5-HT was assessed in rat PA smooth muscle cells using confocal imaging. Proliferative responses induced by 5-HT were evaluated by ELISA BrdU on human PASMC in presence or absence of ATT.

In rats with CH-PH, ATT reduced contractile hyperreactivity induced by 5-HT and PGF2α. In control rats, ATT treatment also decreased contraction to 5-HT and Phe, but not contraction to ET-1 and PGF2α as well as relaxation to Cch. Interestingly, acute ATT exposure did not modify basal cytosolic calcium signal in control rat PASMC. However, the number of 5-HT responding cells was reduced in presence of ATT whereas neither maximal peak of cytosolic calcium responses nor the global calcium variations were affected. Finally, 5-HT-induced proliferation was reduced by ATT in control human PASMC.

In conclusion, ATT improves vascular hyperreactivity of PA from rats with CH-PH whereas in control condition ATT altered 5-HT-induced contraction in rat PA, calcium signalling to 5-HT in rat PASMC and 5-HT-induced human PASMC proliferation. Although mechanisms underlying ATT influence on PH hallmarks need to be further elucidated, these Results suggest that OP2113 may be used to develop new PH therapies.