| 摘要: | 鎘是一種有毒的重金屬並且已經被廣泛地在工業中使用。已有文獻指出鎘容易經由食物鏈(food-chain)進入哺乳動物體內進而累積在很多器官裡並且引起嚴重的毒性。尤其許多研究已經發現在暴露在鎘污染環境之工人的尿液中鎘含量越高，會使胰臟的胰島beta-細胞功能減弱並且引發糖尿病有關之病症出現。然而，鎘引起的胰臟的胰島beta-細胞損害的明確作用機制依然不清楚。本研究目的是要探討鎘引起胰臟胰島beta-細胞功能損傷與細胞凋亡之確切作用機轉；實驗結果發現：給予大鼠胰臟胰島beta-細胞暴露氯化鎘(CdCl2)24小時後，隨著濃度的增加(1~10μM)，細胞存活率亦顯著的減少。同時，胰島素(Insulin)之分泌也受到抑制。藉由給予螢光探針-2`，7`- dichlorofluorescin diacetate(DCFH-DA)，利用流
式細胞儀(Flow cytometry)分析發現：胰島beta-細胞在暴露鎘後會顯著的誘發活性氧物種(Reactive oxygen species, ROS)的產生，並且使細胞膜脂質過氧化(Lipid peroxidation, LPO)堆積。暴露鎘引起胰島beta-細胞凋亡主要是藉由粒線體調控機制和半胱氨酸蛋白酶依賴路徑，鎘包括引起與細胞凋亡有關之mRNA(Bcl-2、Bax、P53、Mdm-2)表現，粒線體膜電位去極化、釋放細胞色素 c 從粒線體到細胞質、PARP( poly（ADP-ribose）Polymerase)分裂活化和半胱氨酸蛋白酶(caspase)-3、-7表現。此外給予胰島beta-細胞暴露氯化鎘(CdCl2)亦會引起JNK、ERK、P38-mitogen activated protein kinase(MAPK)磷酸化表現。而給予JNK專一性抑制劑：SP600125，能明顯的回復鎘所引起的細胞凋亡作用。在動物實驗之結果中，我們也發現給予ICR鼷鼠餵食10 mg/kg/day的氯化鎘(CdCl2)2週後，即能顯著的抑制鼷鼠血清中胰島素之含量。而在餵食氯化鎘(CdCl2)6週後，亦能造成鼷鼠對葡萄糖的不耐受性增加。總和以上之研究結果指出氯化鎘(CdCl2)能造成胰島beta-細胞功能損傷與細胞凋亡之產生，其主要之作用機制是透過：ROS調控JNK-MAPK-粒線體依賴性之細胞凋亡路徑。同時，本研究結果提供鎘可能是引發糖尿病相當重要的環境危險因子之科學証據！
Cadmium is a toxic heavy metal and has been widely used in industry. It has been demonstrated that cadmium was easily accumulated by food-chain in many organs of mammal, and caused severe cytotoxicity. Especially, some studies have been found that cadmium levels of urinary in industrial workers are dose-dependently associated with both impaired pancreatic islet beta-cell function and induced diabetic-related syndromes. However, the precise action mechanisms of cadmium-induced pancreatic beta-cells damage remain unclear. The aims of this study were attempted to elucidate
whether cadmium induced dysfunction and apoptosis, and to investigate the precise mechanisms by which cadmium caused cytotoxicity in pancreatic?n beta-cell. The number of viable cells was reduced after CdCl2 treatment with pancreatic beta-cell line: RIN-m5F cells for 24h in a dose-dependent manner with a range from 1~10 μM. Lipid peroxidation production and 2`,7`-chlorofluorescein fluorescence intensity, as an indicator of reactive oxygen species formation after exposure of RIN-m5F cells to CdCl2 were significantly increased. Cadmium-induced apoptosis involved a mitochondria-mediated mechanism and caspase-dependent pathway, in that the critical apoptotic events induced by cadmium including: activation of JNK, ERK, and p38 phosphorylation, apoptotic-related mRNA expression, the abilities in disruption of mitochondrial membrane potential and release of cytochrome c from the mitochondria to the cytosol, and activation of PARP cleavage and caspase cascades. In contrast, blockage of JNK, not ERK and p38, by pharmacological inhibitor (SP600125) could be reversed the cadmium-induced apoptosis. Moreover, it was significant decrease the plasma insulin levels of ICR mice after oral administration with 10 mg/kg/day CdCl2 for consecutive weeks and cause dysfunction of glucose regulation(glucose intolence). Taken together, these results indicated that CdCl2 is capable of inducing cellular responses to cause pancreastic beta-cell dysfunctional apoptosis through ROS-mediated JNK-mitochondria-dependant apoptosis pathway. Cadmium may be an important environmental risk factor for diabetes progressing. |
