辛伐他汀干预对慢性心力衰竭兔模型心室重构的影响

目的观察辛伐他汀对慢性心力衰竭兔心室重构的影响.方法将24只新西兰白兔分为4组,每组6只,第1、第2、第3组通过破坏主动脉瓣和缩窄腹主动脉,增加左心室前、后负荷,建立慢性心力衰竭模型.第1组:心力衰竭对照组;第2组:心力衰竭早干预组,术后每天给予辛伐他汀5 mg/kg灌胃,观察6周;第3组:心力衰竭晚干预组,手术4周后每天给予辛伐他汀5 mg/kg灌胃,观察4周;第4组为假手术组.各组术后及观察结束时行超声心动图检查;观察心肌细胞肥大情况;计算各组凋亡指数.结果早干预组室间隔厚度(LVSd)、左心室舒张期内径(LVIDd)、左心室后壁厚度(LVPwd)、左心室收缩期内径(LVIDs)、心脏重量、左心室重量、心脏/体重、左心室/体重、心肌细胞凋亡指数(AI)显著低于心力衰竭对照组;左心室射血分数(EF)、左心室长轴缩短率(FS)显著高于心力衰竭对照组.晚干预组LVSd、LVIDs、心脏重量、左心室重量、心脏/体重、心肌细胞凋亡指数(AI)显著低于心力衰竭对照组;EF、FS显著高于心力衰竭对照组.结论辛伐他汀干预可抑制慢性心力衰竭兔心脏扩张、室壁增厚、心肌细胞调亡,改善心肌重构.     

Rho激酶在心室重构中的作用

心室重构是多种心脏疾病的病理生理基础,干预心室重构进程是治疗相关疾病的重要手段.Rho激酶（ROCK）是小G蛋白Rho的下游因子.近年研究发现,Rho激酶在心肌细胞肥大、心肌纤维细胞分化增殖及细胞凋亡等病理进程中发挥重要作用,可能是心室重构的潜在干预靶点.本文将对Rho激酶在心室重构的作用进行综述.     

辛伐他汀对慢性心力衰竭兔心肌细胞糖原合成激酶3β活性、蛋白表达及β-连环蛋白表达的影响

目的:观察辛伐他汀对慢性心力衰竭(心衰)兔心肌重构及心功能的影响,对心肌细胞中糖原合成激酶3β(GSK3β)活性、蛋白表达及β-连环蛋白(β-catenin)表达的影响.方法:24只新西兰白兔分为4组,每组6只.假手术组:为健康对照.其余兔行主动脉瓣反流及腹主动脉缩窄术,建立慢性心衰模型后,分为心衰对照组:术后不给药;早干预组:术后第2天给予辛伐他汀5 mg/(d·kg),连续8周;晚干预组:术后第4周给予辛伐他汀5 mg/(d·kg),连续4周.术后8周观察结束时行左心导管检查,记录左心室舒张末压,处死后称体重、心脏重量、左心室重量,计算心脏质量指数(心脏重量/体重)、左心室质量指数(左心室重量/体重).West-ern-blotting分析心肌细胞浆GSK3β、细胞核β-catenin表达.免疫沉淀分析GSK3β活性.结果:术后8周时,心衰对照组左心室舒张末压、心脏重量、左心室重量、心脏质量指数及左心室质量指数均显著高于假手术组(P均<0.01);术后8周,早干预组心脏重量、左心室重量、心脏质量指数及左心室质量指数均显著低于心衰对照组(P<0.05-0.01);晚干预组心脏重量、左心室重量、心脏质量指数均显著低于心衰对照组(P<0.05-0.01).术后8周,早干预组及晚干预组左心室舒张末压均显著低于心衰对照组(P均<0.05).心衰对照组心肌胞浆中GSK3β活性较假手术组显著降低(P<0.01),而心肌细胞核B-catenin表达显著增加(P<0.01),差异均有统计学意义.早干预组及晚干预组GSK3β活性与心衰对照组比较均显著增加(P均<0.01),而心肌细胞核β-catenin表达均显著降低(P均<0.01).结论:辛伐他汀治疗有效抑制心力衰竭兔心肌重构、改善心功能;其作用与增加GSK3β活性、抑制心肌细胞核β-catenin表达有关.     

辛伐他汀早期干预能更有效抑制压力负荷高血压大鼠心肌肥厚

目的:比较辛伐他汀早期干预与晚期干预对高血压心肌肥厚的防治效果,并初步探讨其机制.方法:采用腹主动脉缩窄法建立压力负荷高血压大鼠模型,在心肌肥厚形成的不同阶段分别给予辛伐他汀[10 mg/(kg·d),ig]干预.采用天狼猩红染色、血流动力学测定等方法,观察和比较辛伐他汀对高血压心肌肥厚和心功能的影响.应用ELISA法...     

辛伐他汀对心肌梗死后心力衰竭大鼠心肌氧化负荷和心室重构的影响

目的了解辛伐他汀对急性心肌梗死（AMI）后心衰大鼠心室重构和心功能的影响,并研究NADPH氧化酶亚基p47phox的变化以研究辛伐他汀在CHF中可能的作用机制。方法随机选取雄性Sprague Dawly,通过结扎大鼠左冠状动脉前降支制作大鼠AMI模型致CHF,并随机选取大鼠做假手术对照。AMI术后大鼠被随机分为大剂量辛伐他汀组[hSIM,4mg/（kg·d）],小剂量辛伐他汀组[lSIM,0.4mg/（c）]与单纯模型组。干预12周后测体质量（BM）,左室质量（LVM）等,并行血流动力学测定。选取左室非梗死区心肌检测p47phox mRNA相对表达率及蛋白含量。结果单纯模型组、hSIM和lSIM组LVM均较假手术组增加;hSIM和lSIM组平均最大左室压力变化（m±dp/dtmax）均较单纯模型组升高,p47phox mRNA表达、p47phox含量均降低;p47phox含量hSIM和lSIM组组有显著性差异。结论在AMI后CHF大鼠,大体检查和血流动力学检测可证实辛伐他汀减轻CHF的发展。其机制与NADPH氧化酶亚单位p47phox介导产生的反应性氧簇有关。     

辛伐他汀逆转左室肥厚的作用与抑癌基因PTEN表达的关系

目的观察辛伐他汀逆转自发性高血压大鼠(SHR)左心室肥厚(LVH)的作用及其与抑癌基因-第10号染色体缺失的张力蛋白同源区(PTEN)表达的关系.方法16只雄性8周龄SHR测量体重和收缩压后,随机分为SHR治疗组和SHR对照组,分别给予辛伐他汀和安慰剂灌胃治疗,性别、年龄、数量匹配的Wistar大鼠给予安慰剂治疗作为正常对照组,疗程10周,观察辛伐他汀对大鼠收缩压和左心室重量/体重比值(LVW/BW)的影响,采用逆转录聚合酶链式反应(RT-PCR)和蛋白免疫印迹法(Westernblot)检测辛伐他汀对心肌组织PTEN表达的影响.结果(1)治疗前两组SHR收缩压无显著差异(P＞0.05),均高于Wistar正常对照组大鼠(P＜0.01);给予辛伐他汀后,SHR治疗组收缩压(217.3±8.5)mmHg较SHR对照组(220.8±9.9)mm Hg略有降低,但无统计学意义(P＞0.05),且两组SHR收缩压仍高于Wistar正常对照组大鼠(126.0±5.8)mm Hg,差异非常显著(P＜0.01).(2)SHR对照组大鼠的LVM/BW(4.10±0.13)mg/g明显高于Wistar正常对照组(3.04±0.12)mg/g,并有统计学意义(P＜0.01),而SHR辛伐他汀治疗组的LVM/BW(3.73±0.08)mg/g较SHR对照组明显下降(P＜0.01).(3)SHR对照组大鼠心肌组织PTEN的mRNA表达水平(0.36±0.04)低于Wistar正常对照组(0.87±0.05),差异非常显著(P＜0.01),SHR治疗组大鼠的PTEN mRNA表达水平(0.60±0.05)较SHR对照组显著升高,并有统计学意义(P＜0.01).(4)Wistar正常对照组、SHR对照组和SHR治疗组大鼠心肌组织PTEN蛋白表达水平分别为50.53±2.92、24.65±3.89和40.32±4.04,其中SHR对照组明显低于Wistar正常对照组(P＜0.01),SHR治疗组则较SHR对照组显著升高(P＜0.01).结论辛伐他汀能够逆转SHR的LVH,其机制可能与PTEN表达水平增加有关.     

RhoA/Rho激酶在氟伐他汀对组织因子表达影响中的调控作用

目的研究RhoA/Rho激酶在氟伐他汀(fluvastatin,Flu)影响组织因子蛋白表达过程中的调控作用,探讨氟伐他汀在抗动脉粥样硬化血栓形成作用的新靶点。方法将同一簇人脐静脉内皮细胞(HUVEC)株进行培养、传代后,分设对照组、肿瘤坏死因子α(TNF-α)组、Flu组及干预组(TNF-α+Flu组),采用RT-PCR方法测定组织因子(tissue factor,TF)mRNA表达水平,用Western blot方法测定TF蛋白表达和RhoA的活化水平;随后,以血管紧张素Ⅱ(AngⅡ)、Y27632为干预因素,再分设空白对照组、TNF-α+AngⅡ组、AngⅡ组、TNF-α组、TNF-α+Y27632组,采用Western blot方法测定TF蛋白表达水平。结果 TNF-α在诱导HUVEC TF表达的同时,可使RhoA活化,氟伐他汀可抑制TF表达与RhoA活化;AngⅡ可促进TNF-α诱导的HUVEC TF蛋白表达水平,而Y27632可抑制TNF-α诱导的HUVEC TF蛋白表达水平。结论 RhoA/Rho激酶通路在G蛋白水平上参与了氟伐他汀抑制组织因子表达的调控机制。     

缬沙坦对自发性高血压大鼠心肌凋亡及bcl-2、bax蛋白的表达的影响

目的　探讨自发性高血压大鼠 (SHR) ,左心室肥厚过程中 ,心肌组织凋亡情况及凋亡调节蛋白bcl 2、bax表达的变化 ,AT1受体拮抗剂缬沙坦对心肌细胞凋亡的影响。方法　实验动物为 8周龄分为缬沙坦治疗组和非治疗组(SHR无药组 ) ,以Wistar鼠作为正常血压对照组 ,观察期限为 8周。采用TdT介导的dUTP缺口末端标记技术(TUNEL)判定心肌细胞凋亡 ,并行免疫组化、Western印迹等方法检测实验动物心肌组织凋亡调节蛋白bcl- 2、bax的表达情况。结果　SHR心肌组织中存在细胞凋亡现象 ,并有bax高表达。缬沙坦治疗 8周后 ,SHR心肌组织bax蛋白表达显著降低至接近Wistar组。Bcl 2蛋白在SHR治疗组及Wistar组表达较SHR非治疗组有增高趋势 (P >0 0 5 )。前两组bax/bcl 2比值较后者显著降低 (P <0 0 5 )。结论　心肌细胞凋亡是代偿性心肌肥厚可能机制之一。高血压病早期缬沙坦在降压同时可有效抑制心肌细胞凋亡 ,具有积极的抗心室重建作用。     

RhoA/Rho激酶1在慢性阻塞性肺疾病患者肺小静脉、肺小动脉及小气道平滑肌的表达研究

目的探讨RhoA/Rho激酶1(ROCK1)参与细胞外基质(ECM)沉积对慢性阻塞性肺疾病(COPD)患者肺小静脉、肺小动脉及小气道平滑肌重塑的病理生理意义。方法本研究为病例对照研究。采用非随机抽样法, 分析2019年10月至2020年12月宁夏医科大学总医院收治的因原发性肺肿瘤而接受肺切除术患者的肺组织, 结合患者肺功能及临床病史分为COPD组(n=13), 对照组(n=12)。使用α-平滑肌肌动蛋白(α-SMA)抗体鉴定平滑肌细胞, 选取高倍视野下结构完整的肺小静脉及肺小动脉(血管横断面外径<500 μm)、小气道(气道横断面外径<2 000 μm), 使用Image-Pro Plus测量肺小静脉、肺小动脉血管外径, 小气道基底膜周长, 计算肺小静脉、肺小动脉及小气道平滑肌层面积占管腔横断面面积百分比(WA%)作为评估平滑肌重塑的指标。采用免疫组织化学及蛋白免疫印迹法检测目的蛋白的表达。分析形态学和临床资料之间的相关性。结果 COPD组肺小静脉、肺小动脉、小气道WA%均较对照组增高(P值均<0.05)。免疫组织化学检测显示COPD组肺小静脉、肺小动脉、小气道平滑肌...     

辛伐他汀逆转左室肥厚的作用与抑癌基因PTEN表达的关系

目的观察辛伐他汀逆转自发性高血压大鼠(SHR)左心室肥厚(LVH)的作用及其与抑癌基因第10号染色体缺失的张力蛋白同源区(PTEN)表达的关系。方法16只雄性8周龄SHR测量体重和收缩压后,随机分为SHR治疗组和SHR对照组,分别给予辛伐他汀和安慰剂灌胃治疗,性别、年龄、数量匹配的Wistar大鼠给予安慰剂治疗作为正常对照组,疗程10周,观察辛伐他汀对大鼠收缩压和左心室重量/体重比值(LVW/BW)的影响,采用逆转录聚合酶链式反应(RTPCR)和蛋白免疫印迹法(Westernblot)检测辛伐他汀对心肌组织PTEN表达的影响。结果(1)治疗前两组SHR收缩压无显著差异(P>0.05),均高于Wistar正常对照组大鼠(P<0.01);给予辛伐他汀后,SHR治疗组收缩压(217.3±8.5)mmHg较SHR对照组(220.8±9.9)mmHg略有降低,但无统计学意义(P>0.05),且两组SHR收缩压仍高于Wistar正常对照组大鼠(126.0±5.8)mmHg,差异非常显著(P<0.01)。(2)SHR对照组大鼠的LVM/BW(4.10±0.13)mg/g明显高于Wistar正常对照组(3.04±0.12)mg/g,并有统计学意义(P<0.01),而SHR辛伐他汀治疗组的LVM/BW(3.73±0.08)mg/g较SHR对照组明显下降(P<0.01)。(3)SHR对照组大鼠心肌组织PTEN的mRNA表达水平(0.36±0.04)低于Wistar正常对照组(0.87±0.05),差异非常显著(P<0.01),SHR治疗组大鼠的PTENmRNA表达水平(0.60±0.05)较SHR对照组显著升高,并有统计学意义(P<0.01)。(4)Wistar正常对照组、SHR对照组和SHR治疗组大鼠心肌组织PTEN蛋白表达水平分别为50.53±2.92、24.65±3.89和40.32±4.04,其中SHR对照组明显低于Wistar正常对照组(P<0.01),SHR治疗组则较SHR对照组显著升高(P<0.01)。结论辛伐他汀能够逆转SHR的LVH,其机制可能与PTEN表达水平增加有关。     

Alterations in mitochondrial function in cardiac hypertrophy and heart failure

Normal cardiac function requires high and continuous supply with ATP. As mitochondria are the major source of ATP production, it is apparent that mitochondrial function and cardiac function need to be closely related to each other. When subjected to overload, the heart hypertrophies. Initially, the development of hypertrophy is a compensatory mechanism, and contractile function is maintained. However, when the heart is excessively and/or persistently stressed, cardiac function may deteriorate, leading to the onset of heart failure. There is considerable evidence that alterations in mitochondrial function are involved in the decompensation of cardiac hypertrophy. Here, we review metabolic changes occurring at the mitochondrial level during the development of cardiac hypertrophy and the transition to heart failure. We will focus on changes in mitochondrial substrate metabolism, the electron transport chain and the role of oxidative stress. We will demonstrate that, with respect to mitochondrial adaptations, a clear distinction between hypertrophy and heart failure cannot be made because most of the findings present in overt heart failure can already be found in the various stages of hypertrophy.     

辛伐他汀对心力衰竭家兔左室收缩功能及交感活性的影响

目的:观察辛伐他汀对心力衰竭(心衰)家兔左室收缩功能和交感活性的影响,以阐明辛伐他汀改善非缺血性心衰心功能的可能机制。方法:30只家兔随机分为3组:假手术组(10只)、心衰组(10只)、辛伐他汀干预组(10mg.kg-1.d-1,10只);心衰组和辛伐他汀干预组家兔应用超容量负荷联合压力负荷建立非缺血性心衰模型,共观察7周。利用左心导管术和心脏多谱勒观察家兔血流动力学和心脏功能的变化,采用酶联免疫吸附法测定血浆脑钠肽(BNP)、去甲肾上腺素(NE)水平,以及蛋白免疫印迹法检测心肌组织蛋白激酶A(PKA)、受磷蛋白(PLB)及第16位丝氨酸磷酸化受磷蛋白(Pser16-PLB)的蛋白表达水平。结果:①与心衰组比较,辛伐他汀干预组家兔左室舒张末压、心率、血浆BNP和NE水平明显降低(P<0.05),而左室射血分数(EF)明显增加(P<0.05);②辛伐他汀干预组家兔心肌组织PKA和Pser16-PLB表达水平较心衰组家兔明显降低(P<0.05),2组间总PLB表达无明显差别。结论:辛伐他汀具有抗交感作用,是其延缓非缺血性心衰左室收缩功能减退的可能机制之一。     

Chronic inhibition of Na+/H+-exchanger attenuates cardiac hypertrophy and prevents cellular remodeling in heart failure

OBJECTIVE: In patients with heart disease, the transition from compensatory hypertrophy to heart failure (HF) is associated with altered calcium handling. Up-regulated Na(+)/H(+)-exchanger (NHE-1) activity underlies increased [Na(+)](i) and disturbance of cellular calcium handling in HF. We hypothesize that chronic inhibition of NHE-1 activity prevents the hypertrophic response, cellular remodeling, and development of HF. METHODS: Rabbits received a control or cariporide (inhibitor of NHE-1) diet for 3 months, starting after induction of combined volume and pressure overload. Age-matched animals served as control. Development of HF was examined echocardiographically and electrocardiographically after 3 months. [Na(+)](i), [Ca(2+)](i), pH(i), and action potentials were measured in left ventricular midmural myocytes with SBFI, indo-1, SNARF, and di-4-anepps. Sarcoplasmic reticulum calcium content was calculated from the response of [Ca(2+)](i) to rapid cooling. Calcium after-transients were elicited by cessation of rapid stimulation (3 Hz) in the presence of 100 nmol/l noradrenalin. RESULTS: Chronic treatment of rabbits with the specific Na(+)/H(+)-exchanger activity inhibitor cariporide greatly attenuated development of hypertrophy and entirely abolished development of HF; the heart/body weight ratio increased only little, no change in lung weight occurred, left ventricular dimensions and fractional shortening changed mildly, ascites was not present, QT duration did not increase, and sudden death did not occur. Chronic cariporide treatment also prevented cellular electrical and ionic remodeling. Myocyte dimensions were unaltered, action potentials were not prolonged, cytoplasmic sodium and NHE-1 activity did not increase, cytoplasmic and SR calcium handling remained undisturbed, and no increase of the incidence of calcium after-transient dependent delayed after depolarizations (DADs) occurred. CONCLUSION: We conclude that enhanced activity of NHE-1 underlies cardiac cellular electrical and ionic remodeling in experimental heart failure, and that chronic dietary treatment with cariporide attenuates hypertrophy, development of HF, and cellular remodeling.     

Myofibrillar remodeling in cardiac hypertrophy, heart failure and cardiomyopathies

BACKGROUND: A wide variety of pathological conditions have been shown to result in cardiac remodelling and myocardial dysfunction. However, the mechanisms of transition from adaptive to maladaptive alterations, as well as those for changes in cardiac performance leading to heart failure, are poorly understood. OBSERVATIONS: Extensive studies have revealed a broad spectrum of progressive changes in subcellular structures and function, as well as in signal transduction and metabolism in the heart, among different cardiovascular disorders. The present review is focused on identifying the alterations in molecular and biochemical structure of myofibrils (myofibrillar remodelling) in hypertrophied and failing myocardium in different types of heart diseases. Numerous changes at the level of gene expression for both contractile and regulatory proteins have already been reported in failing hearts and heart diseases; these changes are potential precursors for heart failure such as cardiac hypertrophy and cardiomyopathies. Myofibrillar remodelling, as a consequence of proteolysis, oxidation, and phosphorylation of some functional groups in both contractile and regulatory proteins in hearts failing due to different etiologies, has also been described. CONCLUSIONS: Although myofibrillar remodelling appears to be associated with cardiac dysfunction, alterations in both contractile and regulatory proteins are dependent on the type and stage of heart disease.     

Transgenic model of aldosterone-driven cardiac hypertrophy and heart failure

Aldosterone classically promotes unidirectional transepithelial sodium transport, thereby regulating blood volume and blood pressure. Recently, both clinical and experimental studies have suggested additional, direct roles for aldosterone in the cardiovascular system. To evaluate aldosterone activation of cardiomyocyte mineralocorticoid receptors, transgenic mice overexpressing 11beta-hydroxysteroid dehydrogenase type 2 in cardiomyocytes were generated using the mouse alpha-myosin heavy chain promoter. This enzyme converts glucocorticoids to receptor-inactive metabolites, allowing aldosterone occupancy of cardiomyocyte mineralocorticoid receptors. Transgenic mice were normotensive but spontaneously developed cardiac hypertrophy, fibrosis, and heart failure and died prematurely on a normal salt diet. Eplerenone, a selective aldosterone blocker, ameliorated this phenotype. These studies confirm the deleterious consequences of inappropriate activation of cardiomyocyte mineralocorticoid receptors by aldosterone and reveal a tonic inhibitory role of glucocorticoids in preventing such outcomes under physiological conditions. In addition, these data support the hypothesis that aldosterone blockade may provide additional therapeutic benefit in the treatment of heart failure.     

Activation of adenosine A1 receptor attenuates cardiac hypertrophy and prevents heart failure in murine left ventricular pressure-overload model

Sympathomimetic stimulation, angiotensin II, or endothelin-1 is considered to be an essential stimulus mediating ventricular hypertrophy. Adenosine is known to protect the heart from excessive catecholamine exposure, reduce production of endothelin-1, and attenuate the activation of the renin-angiotensin system. These findings suggest that adenosine may also attenuate myocardial hypertrophy. To verify this hypothesis, we examined whether activation of adenosine receptors can attenuate cardiac hypertrophy and reduce the risk of heart failure. Our in vitro study of neonatal rat cardiomyocytes showed that 2-chloroadenosine (CADO), a stable adenosine analogue, inhibits protein synthesis of cardiomyocytes induced by phenylephrine, endothelin-1, angiotensin II, or isoproterenol, which were mimicked by the stimulation of adenosine A1 receptors. For our in vivo study, cardiac hypertrophy was induced by transverse aortic constriction (TAC) in C57BL/6 male mice. Four weeks after TAC, both heart to body weight ratio (6.80+/-0.18 versus 8.34+/-0.33 mg/g, P<0.0001) as well as lung to body weight ratio (6.23+/-0.27 versus 10.03+/-0.85 mg/g, P<0.0001) became significantly lower in CADO-treated mice than in the TAC group. Left ventricular fractional shortening and left ventricular dP/dtmax were improved significantly by CADO treatment. Similar results were obtained using the selective adenosine A1 agonist N6-cyclopentyladenosine (CPA). A nonselective adenosine antagonist, 8-(p-sulfophenyl)-theophylline, and a selective adenosine A1 antagonist, 8-cyclopentyl-1,3-dipropylxanthine, eliminated the antihypertrophic effect of CADO and CPA, respectively. The plasma norepinephrine level was decreased and myocardial expression of regulator of G protein signaling 4 was upregulated in CADO-treated mice. These results indicate that the stimulation of adenosine receptors attenuates both the cardiac hypertrophy and myocardial dysfunction via adenosine A1 receptor-mediated mechanisms.     

Oxidative stress and redox signalling in cardiac hypertrophy and heart failure

Substantial evidence suggests the involvement of oxidative stress in the pathophysiology of congestive heart failure and its antecedent conditions such as cardiac hypertrophy and adverse remodelling after MI. Oxidative stress describes an imbalance between antioxidant defences and the production of reactive oxygen species (ROS), which at high levels cause cell damage but at lower levels induce subtle changes in intracellular signalling pathways (termed redox signalling). ROS are derived from many sources including mitochondria, xanthine oxidase, uncoupled nitric oxide synthases and NADPH oxidases. The latter enzymes are especially important in redox signalling, being implicated in the pathophysiology of hypertension and atherosclerosis, and activated by diverse pathologically relevant stimuli. We review the contribution of ROS to heart failure pathophysiology and discuss potential therapies that may specifically target detrimental redox signalling. Indeed, drugs such as ACE inhibitors and statins may act in part through such mechanisms. A better understanding of redox signalling mechanisms may enable the development of new targeted therapeutic strategies rather than the non-specific antioxidant approaches that have to date been disappointing in clinical trials.