臺灣博碩士論文加值系統

腹主動脈瘤(Abdominal aortic aneurysm)是一種退化性的血管疾病，在破裂時會造成極高的死亡率。直到目前為止，腹主動脈瘤尚無有效的治療藥物，這顯示出我們對腹動脈瘤的致病機制需要更完善的了解。我們實驗室之前的研究指出，長時間窄化迷你豬腎動脈離心端的腹主動脈十二週後會在窄化區域的遠心端誘發腹主動脈瘤的形成。為了加速實驗的進展，我們嘗試在大鼠以窄化誘導腹主動脈瘤。然而，單純窄化腹主動脈無法誘導大鼠主動脈顯著的擴張。因此，我們進行了三組實驗，希望藉此進一步促進大鼠形成腹主動脈瘤。在第一組實驗中，我們在原來的主動脈窄化之外加上單側的總髂動脈結紮(CI組)以及原來的主動脈窄化加上單側的總髂動脈和單側腎動脈結紮(CIR組)，藉此來促進腹主動脈瘤的形成。在第二組實驗中，我們測試低濃度的氯化鈣(CaCl2)是否會造成血管壁的硬化以及壓力。在第三組實驗中，我們在大鼠進行主動脈窄化/單側髂動脈結紮以及低濃度氯化鈣的共同處理。我們假設主動脈窄化/單側髂動脈結紮所誘導的機械性壓力以及低濃度的氯化鈣所導致的節段性動脈硬化(segmental aortic stiffening)會造成主動脈壁產生氧化壓力並促進腹主動脈瘤形成。為了瞭解主動脈壁的變化，我們偵測了窄化的遠心端(亦即末段)和腎動脈近心端腹主動脈彈性纖維板(elastic lamellae)的排列、主動脈硬度、細胞內與粒線體的氧化壓力及氧化造成的DNA和蛋白質損傷。在第一組實驗中，在主動脈窄化/髂動脈結紮處理十二週後，主動脈並無擴張的狀況。在CI和CIR組的主動脈管壁中，有局部性、中度的彈性纖維板斷裂及管壁重塑的現象，但遠心端腹主動脈的細胞內以及粒線體的活性氧物質(Reactive oxygen species)的量並未增加。此外，環狀應力(circumferential strain)值，一個血管硬度的負指標，亦與對照組類似。在第二組實驗中，我們偵測以0.15 M和0.25 M氯化鈣溶液短暫包覆主動脈，處理四週後對血管壁產生的壓力。正如預期，經過氯化鈣處理後主動脈硬度增加且維持。在兩種氯化鈣濃度處理的腎動脈遠心端的腹主動脈段都偵測到區域性的彈性纖維板斷裂與降解，其中0.25 M氯化鈣的處理引起更顯著的降解。細胞內活性氧物質、氧化造成的蛋白質損傷以及巨噬細胞的浸潤都有增加的趨勢，但氧化造成的DNA損傷則沒有增加。在了解低濃度氯化鈣對主動脈壁的影響後，我們著手進行第三組實驗，包括主動脈窄化/髂動脈結紮、0.15 M氯化鈣處理以及共同處理主動脈窄化/髂動脈結紮和0.15 M氯化鈣。在處理十週後，我們仍未偵測到腹主動脈瘤。在三個實驗組的窄化遠心端腹主動脈管壁中，都偵測到明顯的彈性纖維板斷裂與降解，並且在共同處理組發現有增強的現象，這個結果與共同處理十週後主動脈硬度的急劇增加的結果一致。在兩個腹主動脈區段，細胞內與粒線體的氧化壓力都沒有增加；氧化造成的蛋白質損傷在三個實驗組的遠心端腹主動脈區段以及CI組的腎動脈近心端腹主動脈區段都有明顯的增加。相對的，氧化造成的DNA損傷則未增加。綜合上述結果，我們推測主動脈窄化/髂動脈結紮和低濃度氯化鈣會誘發氧化壓力，造成累積的氧化蛋白質損傷。此外，主動脈窄化/髂動脈結紮誘發的機械性壓力和低濃度氯化鈣導致的節段性動脈硬化會對主動脈壁產生協同壓力，可能因而促進腹主動脈瘤的形成。

Abdominal aortic aneurysm (AAA) is a degenerative vascular disease that causes high mortality when ruptured. Currently, no drug therapy is available to treat AAA, pointing to the need for better understanding on AAA pathogenesis. Previous studies from our laboratory showed that prolonged coarctation of an infrarenal segment of the abdominal aorta (AA) for 12 weeks induced AAA formation in the distal AA segment of mini pigs. To facilitate experimental progress, coarctation-induced AAA was explored in rats. However, AA coarctation alone did not cause significant aortic dilatation in rats. Therefore, we performed three sets of experiments to facilitate AAA formation in rats. In the first experiment, we performed coarctation of infrarenal AA with ligation of one iliac artery (CI) or ligation of one iliac artery plus one renal artery (CIR) to facilitate AAA formation. In the second experiment, we examined low-concentration CaCl2-caused stiffness and stress in the aortic wall. In the third experiment, we examined co-treatment of AA coarctation/iliac ligation with low-concentration CaCl2. We hypothesized that AA coarctation/iliac ligation-induced mechanical stress and low-concentration CaCl2-caused segmental aortic stiffening cause oxidative stress in the aortic wall to promote AAA formation. To characterize changes in the aortic wall, we examined elastic lamellae assembly, aortic stiffness, cellular and mitochondrial oxidative stress, and oxidative damages of DNA and proteins in the distal and suprarenal AA segments. In the first experiment, following AA coarctation/iliac ligation for 12 weeks, AA dilatation was not detected. While moderate fragmentation of elastic lamellae and aortic wall remodeling were detected focally, cellular and mitochondrial ROS levels did not increase in the distal AA segment of CI or CIR group. Furthermore, circumferential strain values, a negative indicator of vascular stiffness, did not change compared to sham group. We next examined peri-aortic treatment of 0.15 M and 0.25 M CaCl2 on aortic stress at 4 weeks post-treatment. As expected, sustained increase in aortic stiffness was detected following CaCl2 treatment. In CaCl2-treated infrarenal AA segment, focal fragmentation and degradation of elastic lamellae were detected with 0.25 M CaCl2 treatment causing more pronounced degeneration. Cellular ROS levels, oxidative protein damage, and macrophage infiltration tended to increase whereas oxidative DNA damage did not increase. After characterizing effects of low-concentration CaCl2 on the aortic wall, we performed AA coarctation/iliac ligation, 0.15 M CaCl2, and co-treatment of 0.15 M CaCl2 and AA coarctation/iliac ligation. At 10 weeks post-treatment, AAA formation was not detected in rats. Marked fragmentation and degradation of elastic lamellae were detected in all three experimental groups with enhanced effect observed in the co-treatment group. This result was in agreement with a drastic increase in aortic stiffness at 10 weeks after co-treatment. No increase in cellular or mitochondrial oxidative stress was detected in both AA segments. Oxidative protein damage increased significantly in the distal AA segment of all three experimental groups and in the suprarenal AA segment of CI group. In contrast, no increase in oxidative DNA damage was detected. These results suggest that AA coarctation/iliac ligation and low-concentration CaCl2 induce oxidative stress to cause cumulative oxidative protein damage. Furthermore, mechanical stress induced by AA coarctation/iliac ligation and segmental aortic stiffening caused by low-concentration CaCl2 may exert synergistic stress to the aortic wall and thereby facilitate AAA formation.

Chinese abstract...................I
English abstract...................III
Acknowledgement...................V
Introduction...................1
Abdominal aortic aneurysm...................1
Risk factors of AAA...................1
Pathogenesis of AAA...................2
Oxidative stress in AAA formation...................2
Stiffness of vessel wall...................4
Animal models of AAA...................4
Objective of this study...................6
Materials and Methods...................7
Materials...................7
Methods...................12
Results...................20
Discussion...................25
References...................29
Figures...................34
Appendix...................49

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