| Pulmonary arterial hypertension(PAH) is a chronic disease that has a serious threat to human health. PAH are characterized by pulmonary vasoconstriction,pulmonary vascular remodeling, pulmonary vascular smooth muscle cells proliferation, vascular wall thickening, lumens stenosis and occlusion, which raise pulmonary arterial pressure and eventually result in right heart failure. A survey had shown that the incidence of PAH was more than 8% among the people over 40 year old, and there were almost 25 million people suffered from PAH in china. PAH is very difficult to cure, the average survival age of PAH is just 2.8 years. Nearly 100 million people died from PAH each year. With an increasing incidence of PAH, the mortality will spot to the third in 2020. PAH was considered to irreversible, it will seriously affect the life quality of patients. However, there are no specific drugs to cure the disease. At present, relieving symptoms by adjusting the pulmonary artery diastolic dysfunction is the main treatment for PAH in clinic. Therefore, it is essential to find effective drugs targeted at newly therapeutical sites.The study found that KATP was one of an important target to regulating the tone of the resistance vasculature, the formation of PAH was related to functional damages in KATP channel. A new SUR2B/Kir6.1 subtype of KATP channel opener Iptakalim(Ipt)designed by our laboratory was able to reduce pulmonary arterial pressure selectively,while Ipt had no influence on systemic circulation. Our previous studies found that Ipt could significantly prevent pulmonary hypertension induced by long-term hypoxia and right heart failure in rats induced by monocrotaline. In addition, Ipt could reverse pulmonary hypertension and antagonized contractile response of isolated pulmonary arterial rings induced by ET-1. The results demonstrated that Ipt would be a very promising drug to treat pulmonary hypertension through dilating pulmonary arteries.However, the detailed molecular mechanism is still unclear. To clarify the pharmacological characteristics of Ipt for pulmonary hypertension, in the study, we investigated the effects of Ipt in dilating pulmonary arteries and the characteristics ofIpt combined with 5 pulmonary drugs by using DMT120 CP pressurized arterial myograph system, and further explored molecular mechanisms.Part one:The effects of Iptakalim against PAHObjective: Our previous studies showed that Ipt had an effective therapy in dilating mesenteric arterioles under the condition of different pressure or arteriolar diameter respectively. We found that the dosage of Ipt was 5mg/d in the clinical treatment of hypertension, this dose had no influence on pulmonary arterial hypertension. The aim of this work is to clarify the pharmacological characteristics of Ipt against PAH, and to provide the dosage basis for the clinical treatment.Methods: We compared the effects of Ipt between pulmonary arterioles and mesenteric arterioles in rats using DMT120 CP pressurized arterial myograph system,and observed the effects of Ipt(10-11~10-4mol/L) in the fouth pulmonary arterioles under different pressure, different diameter and in hypoxic condition.Results: The effects of Ipt in dilating pulmonary arterioles were weaker than the diastolic effects in circulation arterioles. Ipt could selectively dilate different pulmonary arterioles under the different pressure, the diastolic effects of Ipt were increased with the pressure increasing. Interestingly, Ipt had no effect on normal physiological pressure. In addition, we observed that the effects of Ipt had no significant difference between different diameters of pulmonary arterioles, which suggested that Ipt had no selectivity to pulmonary arterioles. However, under the normal pressure, the diastolic effects of Ipt in hypoxia were significantly enhanced,compared with normoxic pulmonary arterioles. Under high pressure conditions, the effects of Ipt had no significant difference between hypoxia and normoxic.Conclusion: Our result indicated that the clinical dosage of Ipt against PAH was7-10 times higher than that of Ipt against hypertension. Ipt could selectively dilate high-pressure pulmonary arterioles and have no influence on the normal pressure pulmonary arterioles, while Ipt could have no selectivity to vessel diameter of pulmonary arterioles.Part two: the molecular mechanisms of iptakalim against PAHObjective: A serial of studies had been reported that three important endothelium-derived relaxing factor, including NO, PGI2, EDHF, played an important role in regulating the tone of pulmonary vascular. Iptakalim, a new SUR2 B / Kir6.1subtypes KATP channel opener, could be able to selectively expand pulmonaryarterioles. We proposed that whether the endothelium-dependent diastolic function related to the three factors is unknown. This works further explored the molecular mechanisms of Ipt in expanding pulmonary arterioles.Methods: Gli(10-5mo/L), Indo(10-4mol/L), L-NAME(10-4mol/L),CTX(10-7mol/L), Apmin(10-7mol/L)were pre-incubated 30 min in 180-220μm pulmonary arterioles with prime 40 mm Hg perfusion pressure respectively or remove the vascular endothelial cells, we observed the influence of Ipt using DMT120 CP pressurized arterial myograph system.Results: The effects of Ipt were blocked by Gli, Indo, L-NAME and CTX+Apamin respectively. Ipt had no effects on endothelial injured pulmornay arterioles. the effects of Ipt combinated with Indo, L-NAME, CTX and Apamin together were completely blocked, which were consistent with these of endothelial injured pulmonary arterioles.Conclusion: The results confirmed the effects of Ipt against PAH through the SUR2B/Kir6.1 subtype of KATP channel, and these effects were mostly related to endothelial cells in blood vessels, suggesting endothelium-dependent vasodilator response mainly through NO, PGI2, EDHF pathways.Part three: The effects of Iptakalim combinated with five drugsObjective: PAH is a high mortality rate disease that has serious threats to human health. In the past 20 years, there have been many targeted therapy drugs to cure pulmonary hypertension endothelial injury, such as phosphodiesterase type 5(PDE-5)inhibitors, endothelin receptor antagonists, prostacyclin analogs. The study found that a single drug therapy of pulmonary hypertension could improve hemodynamics,increase exercise capacity of patients, decease mortality rate to 40% in short-term.However, long-term survival of a single drug therapy is still very low, the mortality rate of pulmonary hypertension is 15% annual. In order to improve the treatment of patients, combination therapy has become the focus of attention of scholars. It has been reported that combination therapy could significantly reduce the risk of clinical disease progression compared with monotherapy, meanwhile, the combination therapy can significantly improve motor function in patients. On account of different drugs have different therapeutic target, the combination therapy can enhance the effect of drugs, reduce the dosage and reduce adverse reactions, thus, combination therapy on pulmonary hypertension is an important direction of research.Methods: The main strategy of the clinical treatment of pulmonary hypertension is vasodilator drugs, there are five categories: endothelin receptor antagonist such as bosentan; 5 phosphodiesterase inhibitors(PDE-5) such as sildenafil; prostacyclin analogs such as remodulin; calcium channel blocker(CCB) such as diltiazem;αreceptor antagonists such as prazosin. This study researched the effects of bosentan,sildenafil, remodulin, diltiazem, prazosin on pulmonary arterioles by using DMT120 CP pressurized arterial myograph system, observed expansion characteristic of a new KATP channel opener Ipt combined with five drugs on pulmonary arterioles.Results: prazosin, sildenafil, treprostinil, bosentan, diltiazem showed concentration-dependent Diastolic effects in rat pulmonary arterioles. Iptakalim combined with prazosin had no significant improvement in dilating pulmonary arterioles compared to monotherapy. Iptakalim combinated with sildenafil had a synergistic effect, sildenafil can reduce EC50 values of Ipt on pulmonary arterioles.Iptakalim combinated with remodulin had a synergistic effect, remodulin can reduce EC50 values of Ipt on pulmonary arterioles. Iptakalim combinated with bosentan had a synergistic effect, Bosentan could increase the expansion rate of Ipt on pulmonary arterioles and reduce EC50 values of Ipt on pulmonary arterioles. Iptakalim combined with diltiazem had a synergistic effect.Conclusion: Iptakalim combinated with sildenafil, treprostinil, bosentan and diltiazem had a synergistic effect, combination therapy can reduce the dosage of drugs and enhanced efficacy. |
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