抑制醣化終產物對慢性腎衰竭大鼠動脈硬化之影響

Abstract

慢性腎臟病的病程持續進展，最後終究會演變為慢性腎衰竭或末期腎臟疾病，並會造成比正常人多出十到二十倍的心血管併發症發生率。在慢性腎衰竭的患者中，造成心血管疾病的主要危險因子是動脈硬化，它同時也是高血壓患者或是一般人罹患心血管疾病的發病率與致死率之強力指標。動脈的硬化多半是由於血管收縮素II的刺激，或是活性氧族群，或是醣化蛋白終產物使動脈基質中的膠原蛋白產生交互連結，而造成動脈壁的延展性降低所導致的。醣化蛋白終產物同時也在正常老化或是疾病的情況，扮演促使併發症發生的角色，而其中的病理生理機制，也是近年來透過體外研究、動物以及人體試驗，才更進一步被了解。醣化蛋白終產物已被證實與腎臟疾病發病有關，同時也成為治療腎臟疾病的新治療目標。 在本論文的第一部份研究中，我們針對血管收縮素第一型接受器阻斷劑─Olmesartan (OLM) 進行試驗，以部分腎切除術引發慢性腎衰竭的大鼠為動物模型， 評估該藥物對於動脈硬化的保護作用。慢性腎衰竭大鼠在經過OLM治療八週後，所有血液動力學上的異常，包括心輸出量降低、主動脈壓上升、周邊總阻力升高和左心室重量與體重的比值上升，都獲得改善。OLM的治療對於左心室後負荷的影響包括可以減少主動脈特徵阻抗與波反射係數，並增加主動脈順應性與波傳輸時間，結果顯示OLM可以改善慢性腎衰竭大鼠的左心室收縮負荷與心臟肥大的情況。此外，OLM的功能還包括可以減少慢性腎衰竭大鼠主動脈組織與血漿內的脂質過氧化物─丙二醛，與主動脈組織內醣化蛋白終產物的含量。因此，我們得到的結論是，OLM在慢性腎衰竭大鼠的動物模式中具有抑制主動脈壁的丙二醛與醣化蛋白終產物，同時改善動脈硬化的治療效果。 另外，論文的第二部份研究我們著重在維生素B6之一的吡哆胺─Pyridoxamin (PM)，評估其對於部分腎切除術引發之慢性腎衰竭大鼠的疾病預防與治療潛力。研究結果顯示，在接受PM給藥八週後，慢性腎衰竭大鼠的體重與心血管參數，包含左心室肥大與血壓升高的現象，都獲得明顯的改善。同時，肌酸酐及血中尿素氮的清除率，在給予PM治療後也獲得改善。利用主動脈組織的西方墨點法、免疫組織染色及丙二醛分析，進行PM對於慢性腎衰竭大鼠體內醣化蛋白終產物形成的改善程度之評估。結論是對於慢性腎衰竭患者補充PM也許可以緩解醣化蛋白終產物造成的病理過程，及早預防腎臟的損壞，對於慢性腎衰竭的治療提供一個新的藥理策略。至於將來的研究，則應著重在闡明PM的輔助治療對於慢性腎衰竭引發的心血管與腎臟損壞的預防或治療所扮演的潛在角色。

Chronic kidney diseases always develop to chronic renal failure (CRF) or end-stage renal diseases eventually, and associated with 10 to 20-fold increased incidence in cardiovascular complications than normal individuals. The major risk factor for cardiovascular disease in CRF is associated with arterial stiffness, which is a strong predictor of morbidity and mortality among those with hypertension and in the general population. Arterial stiffness results from altered distensibility of aortic walls and is associated with stimulation of angiotensin II, reactive oxygen species (ROS), and advanced glycation end products (AGEs) crosslink of collagen in arteries matrix. AGEs also play important roles in promoting complications of normal aging and diseases. Their pathophysiological implications were disclosed in studies of in vitro, animals and humans and only recently becoming understood in more detail. AGEs contribute to the pathogenesis of renal diseases and have become a new therapeutic target for treatment. In this study, we investigated whether an angiotensin II type 1 receptor blocker, olmesartan (OLM), could prevent arterial stiffness in rats with CRF induced by 5/6 subtotal nephrectomy. After 8 weeks of OLM treatment, all hemodynamic abnormalities were abrogated in CRF rats, including decreased cardiac output, increased aortic pressure, total peripheral resistance, and the ratio of left ventricular weight to body weight (LVW/BW). Regarding the oscillatory components of the ventricular afterload, OLM decreased the aortic characteristic impedance and wave reflection factor as well as increased the arterial compliance and wave transit time, all of which suggested that OLM attenuated the increased systolic load of the left ventricle and prevented cardiac hypertrophy in CRF rats. In addition to these functional improvements, OLM reduced the levels of malondialdehyde (MDA) equivalents in aortic tissues and serum and the amounts of MDA equivalents and AGEs in the aortic walls of CRF rats. Thus, we concluded that OLM treatment could ameliorate arterial stiffness in CRF rats with concomitant inhibition of MDA and AGEs levels in the aortic wall. Moreover, we also evaluated the therapeutic or preventive potential of pyridoxamine (PM) against CRF in a 5/6 subtotal nephrectomy rat model. Significant and beneficial contributions to body weight and cardiovascular parameters, including left ventricular hypertrophy (LVH) and blood pressure were observed in CRF rats receiving PM for 8 weeks. Clearances of both creatinine and BUN were also significantly improved in the CRF rats following PM administration. The involvement of AGEs in CRF and the profound effects on reducing AGEs of PM treatment were demonstrated by western blotting, immunostaining and MDA assessment for the aortic samples of CRF rats. PM supplementation might be considered as one of pharmacological strategies for preventing AGE-related pathologies and early stages of renal damage. Prospective trials are needed to elucidate a potential role for PM in adjunctive therapy and to confirm the adequate amount on cardiovascular and renal outcomes in CRF.