https://scholars.lib.ntu.edu.tw/handle/123456789/144436
標題: | 腎素血管張力素系統和心臟血管疾病
-著重在心房纖維顫動結構及電生理病變機制的研究及新治療藥物的尋求 Renin-angiotensin System and Cardiovascular Diseases- Focusing on Mechanisms of Structural and Electrical Remodelings in Atrial Fibrillation and Pharmacological Approach |
作者: | 蔡佳醍 Tsai, Chia-Ti |
關鍵字: | 腎素血管張力素系統;心房纖維顫動;Renin-angiotensin system;atrial fibrillation | 公開日期: | 2006 | 摘要: | 本研究的目的,主要在於血管張力素(angiotensin II)和心房纖維顫動(atrial fibrillation)發生機轉的關係。最近的研究發現,在心房壓力上升時,會活化心房局部腎素-血管張力素系統(renin-angiotensin system),使心房局部血管張力素濃度上升。血管張力素會活化分裂原蛋白激酶訊息傳導系統(mitogen-activated protein kinase pathway; MAPK),造成心房結構上的病變(remodeling),使心房纖維化及擴大。另外,血管張力素也可造成心房電生理病變,使得心房有效不反應期(atrial refractory period)縮短,且靜注血管張力素阻斷劑(如candesartan)或血管張力素轉化酶抑制劑(如captopril),可避免心房有效不反應期在右心房快速激搏(rapid right atrial pacing)時縮短。因此,心房纖維顫動的發生和腎素-血管張力素系統有很大的關係,血管張力素可使得心房纖維顫動更容易發生及維持。 我們首先利用遺傳相關之研究,證實腎素-血管張力素系統基因群的變異,和臨床上病人會不會罹患心房纖維顫動有密切相關。本研究延續碩士班的研究,首先把心房纖維顫動和腎素-血管張力素系統基因相關研究之病人數增加至超過兩倍以上,結果和之前碩士班研究的結果一樣,且由於病人數增加的原因,P值最加顯著,另外我們也使用特殊的多基因分析,證實腎素-血管張力素系統基因變異不只和心房纖維顫動的發生有關,也和高血壓和冠狀動脈心臟病的發生有關,由於腎素-血管張力素系統和高血壓、冠狀動脈心臟病制病機轉之研究文獻已有許多報告,因此我們下一步的研究著重在腎素-血管張力素系統或血管張力素加重或促進心房纖維顫動之可能機制。我們從電生理變化和結構變化兩方面切入。 在結構性病變方面,首先在我們的右心房快速激搏引發心房纖維顫動豬模式中,發現心房纖維顫動豬的心房有顯著纖維化及發炎反應,且心房組織中血管張力素濃度會上升,且Rac1,訊息傳遞子及轉錄活化子1 (Signal transducers and activators of transcription 1; STAT1)及訊息傳遞子及轉錄活化子3 (STAT3)會被活化,反而分裂原蛋白激酶訊息傳導系統(mitogen-activated protein kinase pathway; MAPK)並沒有被活化。在細胞模式中,我們發現血管張力素在培養心房心肌細胞及纖維母細胞可以活化STAT3,且是經由Rac1來達成。血管張力素在心房心肌細胞及纖維母細胞可以促進蛋白質製造,間接表示血管張力素可以促成心房心肌細胞肥大及心房纖維母細胞纖維化,而上述的這些現象可以被Rac1活化抑制劑,也是降血脂藥物的simvastatin及血管張力素第一型受體阻斷劑losartan所抑制,因此血管張力素及訊息傳遞子及轉錄活化子3 (STAT3)在快速右心房激博之心房纖維顫動模式之結構病變可能扮演重要的角色。 在電生理機轉方面,經由L型鈣離子通道使細胞內鈣離子濃度上升是心房纖維顫動的重要電生理致病機轉。我們發現血管張力素可以增加L型鈣離子通道的mRNA表現及蛋白的量,增加L型鈣離子電流及細胞內鈣離子濃度,,而機制主要是經由過氧化物及cAMP結合轉譯蛋白(cAMP response element binding protein; CREB)相關之訊息傳導路徑,且同樣地可被血管張力素第一型受體阻斷劑Losartan及且有抗氧化作用之降血脂藥物simvastatin所抑制。 至於為何心房纖維顫動會造成心房組織中血管張力素濃度上升的機制並不清楚。有可能是伴隨於心房纖維顫動之其它心臟病如:心臟衰竭或僧帽瓣疾病造成左心房被擴張,而增加血管張力素的製造。我們假設快速去極化本身也可增加心房組織中血管張力素的製造。我們使用豬和細胞模式來探討這個問題。我們發現快速去極化會增加培養心房心肌細胞血管張力素轉化酶、血管張力素原和糜蛋白肽的表現,進而增加血管張力素的製造,在豬模式中,我們也發現到一致的結果。另外,血管張力素會刺激心房心肌細胞及心房纖維母細胞蛋白製造增加。快速去極化本身就可引起心房的結構病變,並不需要心房因心臟衰竭或僧帽瓣疾病而受到機械力擴張,因此血管張力素可能扮演旁泌素的角色引起心房結構病變。。 在臨床研究方面,我們首先利用心臟超音波的方法來評估左心房的體積和功能,因為我們研究的基本假說為血管張力素在心房結構病變扮演重要的角色,血管張力素轉化酶抑制劑或血管張力素阻斷劑可能可以改善心房結構病變,因此我們必須利用非侵入性的方法,如心臟超音波的方法來評估心房的體積和功能在藥物治療後有無改善,我們首先研究高血壓病人之左心房體積和功能的變化,來作為一超音波評估心房體積和功能的工具平台。我们發現從血壓正常的控制組到重度高血壓病人,左心室舒張功能逐漸惡化,伴隨著左心房擴張功能也相對地逐漸惡化,左心室舒張功能及左心房擴張功能在接受高血壓治療後有明顯的改善。左心室舒張機能失調嚴重度的增加和左心房擴張功能的惡化是相關的, 且左心房擴張功能能代表左心房舒張的功能。因此,心臟超音波可以作為評估心房體積和功能的非侵入性工具。 最後,由以上研究得知statin類藥物可以阻斷血管張力素之訊息傳導,因此我們假設simvastatin可以預防心房結構及電生理病變,而具有治療心房纖維顫動的效果。我們設計一前瞻性、隨機分派的臨床試驗來證實它。心房纖維顫動雖是一個很亂的心律不整,但有時發作的時候,病人會不自覺,因此要評估藥物的有效性有時較難。在年紀大的病人,因患有心搏過慢而裝置心律調節器,這些病人因年紀大,心房有結構病變,因此常有陣發性心房纖維顫動,我們利用他們有植入心律調節器,可以詳細紀錄心律不整的功能,來評估atorvastatin減少陣發性心房纖維顫動效果之評估,這是一個前瞻性隨機分派非雙盲的臨床試驗,且我們發現atorvastatin可以減少心搏過慢病人心房纖維顫動的發作頻率,且伴隨著左心房體積變小。 總結而言,本研究由遺傳相關研究切入,發現心房纖維顫動和腎素血管張力素系統基因變異的關係,再利用動物、細胞模式及基礎分生研究來證實血管張力素和心房纖維顫動發生的可能分子機轉,進而發現losartan和simvastatin可以阻斷血管張力素訊息傳遞,有治療心房纖維顫動的效果,因此我們以前瞻性隨機分派臨床試驗來證實另一statin藥物atorvastatin治療心房纖維顫動的效果。因此,本研究結合了基礎研究及臨床研究來證實血管張力素和心房纖維顫動的密切關係。 The aim of the present doctoral thesis is to investigate the detailed molecular mechanism by which angiotensin II (AngII) is involved in the pathegenesis of atrial fibrillation (AF). Recently, it has been shown that local atrial rennin-angiotensin system (RAS) is activated with increased tissue AngII level during AF. AngII activates the downstream mitogen-activated protein kinase pathway (MAPK) signaling pathways, resulting in atrial structural remodeling. AngII is also involved in atrial electrical remodeling, and it has also been shown that blockage of endogenous AngII prevents rapid-pacing induced shortening of atrial effective refractory period (AERP). In our previous study, we first demonstrated the genetic association between RAS genetic variations and the development of AF. In the present study, we further increased the sample size of our genetic association study to more than 2 fold, and have found more significant results. We also showed that RAS genetic variations and gene-gene interactions among RAS genes were also associated with the development of various cardiovascular diseases, including hypertension and coronary artery disease, in addition to AF. Because the molecular mechanisms by which AngII is involved in the pathogenesis of hypertension or coronary artery disease are well known, the following study subjects were focusing on the molecular mechanisms by which AngII is involved in the pathogenesis of AF, with emphases on the structural and electrical remodelings. Regarding AngII and structural remodeling, we used a rapid-pacing porcine AF model. AF was induced by atrial pacing at 600/min in adult pigs. Significant structural and inflammatory changes were noted in the AF pigs. Although atrial tissue angiotensin II level was elevated in the AF pigs, the MAPK pathways were not activated. However, signal transducers and activators of transcription-1 (STAT1) and STAT3 were activated with increased STAT3 nuclear translocation in the AF pigs. Membrane translocation and activation of Rac1 was also noted. Furthermore, in cultured atrial myocytes and fibroblasts, angiotensin II activated STAT3 through a Rac1-dependent mechanism, which was inhibited by dominant negative Rac1, losartan and simvastatin. We found that the STATs pathways, but not the MAPKs, were activated by angiotensin II and might contribute to structural and inflammatory changes in AF. The activation of STAT3 was dependent on Rac1 and was blocked by losartan and simvastatin. Regarding AngII and electrical remodeling, we investigated whether AngII modulates L-type calcium channel (LCC) current through transcriptional regulation, using a murine atrial HL-1 cells model. AngII increased LCC α1C subunit mRNA and protein levels and LCC current density, which resulted in an augmented calcium transient. AngII significantly increased promoter activity of LCC α1C subunit gene in a concentration- and time-dependent manner. Truncation and mutational analysis of the LCC α1C subunit gene promoter showed that cAMP response element (CRE)(-1853 to –1845) was an important cis-element in Ang II-induced LCC α1C subunit gene expression. AngII induced serine 133 phosphorylation of CRE binding protein (CREB), binding of CREB to CRE, and increase of LCC α1C subunit gene promoter activity through a protein kinase C (PKC)/NADPH oxidase/reactive oxygen species (ROS) dependent pathway, which was blocked by the AngII type 1 receptor blocker losartan and the antioxidant simvastatin. In summary, Ang II increases LCC α1C subunit expression, LCC current density, and amplitude of the calcium transient in atrial myocytes. AngII-induced LCC α1C subunit expression was PKC-, ROS-, and CREB-dependent, and was blocked by losartan and simvastatin. Why local atrial tissue angiotensin II (AngII) production is up-regulated during atrial fibrillation (AF)? It is possible that atrial myocytes express all the components of renin-angiotensin system (RAS), and AF or rapid depolarization per se could increase AngII production by up-regulating the expressions of components of RAS. Again, we used porcine and cellular models to prove this hypothesis. In the cell model, AF was simulated in the cultured murine atrial HL-1 cells by rapid field pacing (RES)(1.0 V/cm, 10 Hz). AngII concentration was measured by ELISA, and expressions of angiotensin converting enzyme (ACE), chymase, angiotensinogen (AGT), renin, AngII type 1 receptor (AT1R) and type 2 receptor (AT2R) were measured by immnunoblotting. In the porcine model, atrial tissue AngII, ACE, chymase and AGT were up-regulated in the AF pigs, but renin was down-regulated. AT1R was up-regulated in the left atria, but down-regulated in the right atria. AT2R was up-regulated in both left atria and right atria. In the cellular model, RES induced a similar pattern of expressions of RAS components, and increased AngII concentrations in the mediums and cellular extracts. RES induced AngII production was attenuated by ACEI Enalapril and chymase inhibitor chymostatin. These results suggest that combination of ACEI and chymase inhibitor prevents rapid-depolarization induced AngII production and atrial structural remodeling. Regarding clinical studies, to evaluate whether echocardiography could be used to evaluate atrial volume and function that may be related to atrial structural remodeling, we first designed a study to evaluate the left atrial (LA) volume, and LA systolic (contractile) and diastolic (expansion) functions in different stages of hypertension with or without atrial fibrillation, as well as the effects of good blood pressure control. This was a prospective observational study. Individuals including 22 normotensive controls, 23 patients with mild hypertension (MH), 20 with severe hypertension (SH), and 17 with both hypertension and paroxysmal atrial fibrillation (AH) were recruited for paired echocardiography studies at baseline and 6 months after medical control of hypertension. We found that with increasing severity of hypertension, LV diastolic function deteriorated progressively from controls, MH, SH, to AH patients. LA expansion index was reduced in parallel. LA expansion index was correlated positively with LV E’/A’ ratio and inversely with LV E/E’ ratio. Significant improvement of LV diastolic function and LA expansion index preceded the reduction of LA volume after 6 months of effective blood pressure control. In summary, with progressive LV diastolic dysfunction in different stages of hypertension, there was a corresponding deterioration in LA expansion or diastolic function, which preceded changes in LA volume and LA contractile function. Recently there is increasing evidence that AF is an inflammatory disease. It has also been shown that statin is a potent anti-inflammatory agent. Furthermore, in the above studies, we have showed that statin blocked AngII signaling pathways, which play important roles in atrial structural and electrical remodeling. Therefore, we hypothesized that statin therapy may provide an effective treatment strategy for AF. We conducted a prospective randomzed clinical study to test the efficacy of atorvastatin in the treatment of paroxysmal AF (PAF). We chose patients who have received implantation of a pacemaker. By pacemaker interrogation, we could accurately detect the first attack of AF to see the effect of atorvastatin to prevent AF attack. Fifty-two patients (23 males, 70±13 years old) were randomized to the statin group and 54 (25 males, 72±13 years old) to the control group. Around 70 % of the patients had SSS and the remaining AVB. Around 75 % of the patients had underwent implantation of a dual chamber pacemaker (DDD[R]), and the remaining single chamber PM (AAI[R]). Three patients did not complete the follow-up and the other patients completed the followed-up for one year. Significant atrial high rate episode (AHE)(rate>180/min and duration≧10 min) occurred in 3 of 50 patients (6.0%) in the statin group, and 10 of 53 patients (18.9%)(OR=0.27; 95% confidence interval [CI] 0.05-0.96, p=0.03) in the control group. Patients in the non-statin group were more likely to develop significant AHE that those in the statin group (log-rank p=0.028). The present study clearly and accurately demonstrated the efficacy of atorvastatin to prevent the occurrence of AF in patients with bradycardia. The possible molecular mechanisms warrant further studies. In conclusions, the present doctoral thesis combined genetic association studies, molecular studies and clinical studies to demonstrate how AngII is involved in the pathogeneses of atrial structural and electrical remodeling, which are important substrates of AF. We first showed the association between RAS genetic variants and the development of AF. Second, we further investigated the possible molecular mechanisms by which AngII is involved in the pathogeneses of atrial structural and electrical remodelings. Third, we found that echocardiography was a useful tool to non-invasively evaluate atrial volume and function, which could serve as a clinical surrogate to represent atrial structural remodeling. Finally, we performed a prospective and randomized clinical trial showing a decrease of AF by statin, which has been shown to block AngII signaling pathways in the former basic molecular studies. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/55481 | 其他識別: | zh-TW |
顯示於: | 臨床醫學研究所 |
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