The Pharmacological Characteristics Of The Combined Antihypertensive Effect And The Improvement To Congestive Heart Failure Of Novel ATP-sensitive Potassium Channel Openers

ATP-sensitive potassium channel (KATP) channels are membrane sensors ofenergy metabolism that, by virtue of specialized nucleotide responsiveness, supplies afeedback mechanism capable of adjusting cell excitability to match demand. KATPchannels are distributed in many vital tissues and organs, such as heart, smoothmuscle cells, endothelial cells, brain, kidney, pancreas, and so on. Under physiologicalconditions, the KATPchannel is closed. However, when cells are ischemia or hypoxia,the KATPchannels are open to regulate cell functions by affecting cell excitability.Therefore, KATPplays an important role in pathophysiological processes of numerouscardiovascular diseases such as hypertension, myocardial ischemia and heart failure.And it becomes an new target to treat patients with high risk for cardiovasculardiseases.The KATPconsists of inward rectifier potassium channel subunits (Kir6s) andregulative sulfonylurea receptors (SURs), the former to form ion channels and thelater to determine the KATPfunction. It has been reported that SUR1/Kir6.2,SUR2A/Kir6.2, and SUR2B/Kir6.1KATPchannel subtypes are mainly expressed inβ-islet pancreatic cells, cardiac cells, and blood vessels, respectively. KATPchannels invascular smooth muscle cells consist of SUR1, SUR2A, SUR2B, Kir6.1, and Kir6.2subunits; however, the SUR2B/Kir6.1subtype is mainly distributed in vascularendothelial cells. Endothelial dysfunction is a reliable prognostic indicator of cardiovascularevents in hypertension and CHF, including reduced release of endothelium-derivednitric oxide (NO) and prostacyclin (PGI2), and increased generation of endothelin-1(ET-1). Improving endothelial dysfunction may be an important strategy for treatpatients at high risk of cardiovascular diseases. However, no pharmaceutical agentsthat specifically target the endothelium are available for clinical use. Based on a seriesof researches, Wang et al. proposed the hypothesis that activation of endothelialSUR2B/Kir6.1KATPchannels of endothelium could improve endothelial dysfunctionin2007.Iptakalim and it’s derivative natakalim are novel KATPchannel openers, whichselectively opens the SUR2B/Kir6.1channel subtype. Phase III clinical trials haveshown that iptakalim, a new antihypertensive agent, had explicit, stable andlong-lasting antihypertensive effect; besides, it had good safety withouttreatment-related serious adverse events. As an anti-congestive heart failure agentnatakalim have been carried out systematic pre-clinical studies, and our laboratoryhas demonstrated that natakalim can inhibit the progression of cardiac hypertrophyto failure induced by pressure overload. This project is to study the pharmacologicalcharacteristic of novel ATP-sensitive potassium channel openers from the followingtwo parts.Part Ⅰ Characteristics of cardiovascular effects between iptakalim andclinical first-line antihypertensive agentsThe incidence of hypertension is linear upward trend worldwide, and becomingthe first risk factor of death. There are200million people suffered from hypertensionin China, however, treatment and control rates of hypertension is very low, only24.7%and6.1%respectively. Therefore China is one of the most serious hazardscountries. Hypertension is the most common chronic disease and major risk factors ofcardiovascular disease. Stroke, myocardial infarction, heart failure and chronic kidneydisease is a major complication of hypertension.At present, blood pressure targets are achieved in only a small number ofhypertensive patients using monotherapy, while the majority requires two or morekinds of antihypertensive agents. Data shows that only29%of hypertensive patientscan be controlled with a single drug, up to44%of patients can be controlled with twokinds of drugs, and there are27%patients who need three or more kinds of drugs tocontrol hypertension. Iptakalim is a new ATP-sensitive potassium channel opener which has a uniquechemical structure that differs from other KATPopeners. Animal studies and Phase IIIclinical trials have shown that iptakalim had explicit, stable and long-lastingantihypertensive effect; besides, it had good safety without treatment-related seriousadverse events. Amlodipine besylate (Aml)---dihydropyridine calcium antagonists,lisinopril (Lis)---angiotensin Ⅰconverting enzyme inhibitors, hydrochlorothiazide(Hyd)---thiazide diuretics or propranolol (Pro)---β blockers are the most commonlyused antihypertensive drugs in clinical currently. As a new antihypertensive agent, theinteractions between Ipt and clinical first-line antihypertensive agents have not beendocumented. In this research, effects of combined treatment of Ipt with Aml, Lis, Hydor Pro on cardiovascular in normal anesthetized rats were observed. Therefore wecould provide a theoretical basis for the clinical development of new combinedantihypertensive therapy program.The primary object of this fundamental research was to survey the synergisticcardiovascular effects of combination of Ipt and clinical first-line antihypertensivedrugs, such as calcium antagonists, angiotensin-converting enzyme inhibitors, thiazidediuretics and β receptor blockers by a2×2factorial-design experiment in normalanesthetized rats.Results:According to the biggest drop of HR (P＜0.05) of combination Ipt with Aml,there was strong positive interaction between them. There was addition between Iptand Aml on the biggest changes of SBP, DBP, and MABP. According to the biggestchanges of SBP, DBP, MABP, LVSP and LVEDP (P <0.05) of combination Ipt withLis, there was strong positive interaction between them, but there was no interactionbetween Ipt and Aml on the biggest changes of HR. According to the biggest changesof DBP, MABP, LVSP and LVEDP (P <0.05) of combination Ipt with Hyd, therewas strong positive interaction between them. But there was no interaction betweenIpt and Hyd on the biggest drop of SBP and HR (P>0.05). According to the biggestdrops of DBP, MABP of combination Ipt with Pro, there was strong positiveinteraction between them (P <0.05). But there was no interaction between Ipt andPro on the biggest changes of SBP, LVSP and LVEDP and HR (P>0.05).Part Ⅱ Natakalim prevents progression of myocardial hypertrophy tofailure induced by myocardial infarction through Improving endothelialdysfunction Congestive heart failure (CHF) is a common critical clinical syndrome and it isthe final pathway for many diseases that affect the heart with high incidence andmortality. The survival rate of CHF is very low and5-year survival rate of CHF issimilar with malignant tumors’. Epidemiological statistics show that at present thereare more than400million patients with heart failure in China. Approximately0.9%ofthe adult population in China has CHF, with the prevalence rising to≥1.3%amongthe older. Moreover, the mortality rate of heart failure has increased by6times in thepast40years in China. Despite novel treatment options for patients suffering fromCHF, morbidity and mortality rates of CHF are still high. Existing drugs to treat CHFmainly target the heart and smooth muscle, but these drugs have many adversereactions. Thus, it is important to find new therapeutic targets and pharmaceuticalagents for CHF so as to prevent cardiovascular remodeling, to protect target organs,and to improve the quality of life in patients.Previous experiments showed that novel KATPopener---iptakalim couldsignificantly improve the cardiovascular remodeling of spontaneously hypertensiverats, protect the damage of vital organs induced by hypertension, attenuate rightventricular remodeling induced by pulmonary hypertension and inhibit theprogression of cardiac hypertrophy to failure induced by pressure overload. All theprotections of iptakalim were related to correct endothelial dysfunction by selectivelyopening the SUR2B channel subtypes. Natakalim is a derivative of iptakalim thatselectively opens the SUR2B/Kir6.1channel subtype, and it can improve the injury ofthe aortic endothelial cells induced by homocysteine and hypoxic. A growing body ofevidence suggests that endothelial dysfunction is more important in the pathogenesisand progressiveness of coronary heart disease and myocardial infarction (MI), and italso may be an important initial factor contributing to the progression of post-MI CHF.Our laboratory has demonstrated that natakalim can prevent progression of cardiachypertrophy to failure induced by pressure overload by protecting against endothelialdysfunction, and we hypothesized that natakalim can prevent the progression ofpost-MI CHF by protecting endothelial function.To evaluate the pharmacological characteristics and experimental therapeuticeffects of natakalim on left ventricular remodeling and heart failure in a rat model ofmyocardial infarction caused by left anterior descending coronary artery (LAD)ligation and explore the mechanisms involved. Result:1. The effects of anterior descending coronary artery ligation for8weeks on ratsLVSP,+dp/dtmax, Vpm, Vmax, LVEDP and–dp/dtmaxwere recorded asventricular function parameters; the first four relate to left ventricular systolic function,the last two relate to left ventricular diastolic function. Compared with sham-operatedrats, MABP, LVSP,+dp/dtmax, Vpm, Vmax and-dp/dtmax were all significantlydecreased in rats after LAD occlusion for8weeks. In contrast, LVEDP wassignificantly increased. It suggested that MI rats were suffered from cardiac systolicand diastolic dysfunction.Left ventricular hypertrophy (LVH) was characterized by the augmentation ofHW/BW and LVW/BW ratios and myocyte cross-sectional area, whereas the BWshowed no significant difference between groups. Histological examinationdemonstrated that compensatory myocyte hypertrophy and fibrosis of the heartoccurred in the left ventricular myocardium. Histology of the hearts from MI ratsshowed that myocyte cross-sectional area and levels of myocardial fibrosis allincreased significantly compared with the control groups. The hydroxyproline contentreflecting the collagen level in cardiac tissue and the extent of myocardial fibrosisincreased36.4%in MI rats when compared with sham groups. Ultrastructuralexamination revealed myofbril disarray with grouped mitochondria was found in MIrats. All these evidences showed that ventricular remodeling was observed due toLAD ligation for8weeks.The intiation and transition from LVH to heart failure is characterized bypulmonary chronic, right ventricular hypertrophy, and overexpression of ANP andBNP: two molecular markers of heart failure. The LW/BW and RVW/BW ratios wereincreased and the ANP and BNP mRNAs were overexpressed in MI rats whencompared with sham-operated rats.These results implied that LVH and heart failure occurred in LAD model rats.Therefore it was successful establishment of heart failure model induced by acute MIafter anterior descending coronary artery ligation for8weeks.2. The experimental therapeutic effects of natakalim on heart failure induced byMI and its characteristicsCompared with Sham-operated rats, MABP, LVSP,+dp/dtmax, Vpm, Vmax and-dp/dtmaxwere all significantly decreased in rats after LAD occlusion for8weeks. Incontrast, LVEDP was significantly increased. These changes could be prevented bytreatment with natakalim in dose-dependent manners. Long term treatment with natakalim (1,3, and9mg/kg/d) did not affect the heart rate in MI rats.HW/BW and LVW/BW ratios were reduced in natakalim group rats. Improvedhistological changes and smaller myocyte cross-sectional area were found in innatakalim group rats. Treatment with Nat could reduce hydroxyproline content andthe collagen level in cardiac tissue to mitigate myocardial fibrosis. Ultrastructuralexamination of heart revealed well-organized myofbrils with mitochondria groupedalong the periphery of longitudinally oriented fbers in natakalim group rats.Consequently natakalim at all doses reverse ventricular remodeling.The initiation and transition from LVH to heart failure in model groups ischaracterized by pulmonary congestion, right ventricular hypertrophy, andover-expression of ANP and BNP: two molecular markers of heart failure. Natakalimcould extenuate the pulmonary congestion and reduce LW/BW ratio indose-dependent manners. RVW/BW ratio was decreased and the ANP and BNPmRNAs were down-regulation in natakalim group rats. Natakalim prevents theprogression of hypertrophy to cardiac failure.3. The pharmacological mechanism of natakalim on heart failure in MI rats3.1Effects of natakalim on endothelial systemThe serum concentration of ET-1was significantly increased in rats after ligatingLAD for8weeks and the cardiac tissue protein levels of ETAand ETBmeasured byimmunohisto-chemistry were also significantly increased too. Treatment withnatakalim for8weeks significantly decreased the elevated serum level of ET-1andthe increased production of ETAand ETBproteins in cardiac tissue to nearly normallevels.3.2Effects of Natakalim on nitric oxide/nitric oxide synthasesThe cardiac tissue protein levels of eNOS and iNOS were measured by westernblot. The eNOS protein expression was significantly decreased in MI-induced chronicheart failure rats, but the concentration of serum NO and iNOS protein expression wassignificantly increased. Treatment with natakalim for8weeks, the concentration ofserum NO and the cardiac tissue protein levels of eNOS and iNOS expression werenearly back to the normal levels.3.3Effects of Natakalim on PGI2and TXA2The half-life of PGI2and TXA2are very short and they are decomposed rapidlyto prostaglandin F1a (6-keto-PGF1a) and thromboxane B2(TXB2), respectively. Therefore the levels of6-keto-PGF1aand TXB2in plasma are used to reflect the levelof plasma PGI2and TXA2, respectively. The concentration of plasma6-keto-PGF1asignificantly decreased in MI-induced chronic heart failure rats, but the concentrationof plasma TXB2was significantly increased. Treatment with natakalim for8weeks,the concentrations of plasma6-keto-PGF1aand TXB2were nearly back to the normallevels.Conclusion:1. It is the first time to study the effects of amlodipine, lisinopril,hydrochlorothiazide or propranolol, which had different mechanisms of action fromIpt, on cardiovascular effects of Ipt in anesthetized normal rats. This research provedthat the combination of Ipt with Lis, Hyd or Pro respectively had significantsynergism on lowering blood pressure, while the combination of Ipt/Aml had additiveaction on lowering blood pressure. Meanwhile the antihypertensive effect was explicit,stable and long-lasting. Iptakalim thus appears suitable for the clinical treatment ofhypertensive people who need two or more kinds of antihypertensive agents.2. The present study has reported that natakalim counteracted cardiachypertrophy and prevented the progression of cardiac hypertrophy to failure inducedby MI.Nat could ameliorate endothelium-derived NO, suppress endothelium-derived NO, inhibit the endothelin system, and redress the imbalance between PGI2and TXA2of heart failure rats induced by MI. It is the first time to find that theprotection of Nat for post-MI heart failure was related to correct endothelialdysfunction.It seems to be a novel therapy strategy to correct endothelial dysfunction;meanwhile natakalim appears suitable for the clinical treatment of coronary heartdisease and post-MI heart failure, but a series of well-designed trials is needed toaffirm this point.