三丁基錫影響胰島素分泌及血糖調控之細胞及動物模式探討

In vitro and in vivo effects of tributyltin on insulin secretion and blood glucose regulation

蔡景任(Jing-Ren Tsai)

指導教授 ： 劉興華

國立臺灣大學/醫學院/毒理學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.00401

摘要

三丁基錫 (tributyltin，TBT) 是廣泛的環境物染物。文獻指出TBT會造成哺乳類動物的神經毒性、肝毒性、皮膚、免疫毒性及內分泌失調，但對胰島細胞及糖尿病的研究目前尚不清楚，近年來已有報告指出另一有機錫化合物，三苯基錫 (triphenyltin，TPT) 會造成動物模式中高血糖及胰島素分泌減少的症狀，但機轉不明，因此本研究目的在探討TBT對胰島細胞的功能影響、細胞毒性及血糖調控作用並釐清其機制。
研究結果顯示RIN-m5F cells (Rat β-cell line) 在處理較低劑量TBT (0.1 and 0.2 μM) 會刺激胰島素分泌的現象，同時觀察到細胞內鈣離子增加和及PKC活化。N-acetylcystein (NAC，抗氧化劑)、BAPTA/AM (內鈣螯合劑)、Ro32-0432 (PKC抑制劑) 及ICI182780 (雌激素受體拮抗劑) 可以回復TBT造成的胰島素分泌作用。另一方面處理較高劑量的TBT (0.5 and 1 μM) 24 hr後，TBT會造成細胞自體凋亡 (apoptosis)、ROS生成、JNK磷酸化、caspase-3及cleaved PARP活性表現。給予NAC (抗氧化劑)、SP600125 (JNK抑制劑) 及BAPTA/AM (內鈣螯合劑) 可以降低TBT所誘導的細胞自體凋亡及JNK的磷酸化。此外，我們觀察口服餵食TBT (0.025、0.25 mg/kg/day) 實驗小鼠2-4週，發現會有降低血漿胰島素含量、高血糖現象、脂質過氧化物產生及葡萄糖耐受性不良。同時，曝露TBT的實驗小鼠所分離出的胰島細胞 (islets) 會出現胰島素分泌降低現象。NAC (抗氧化劑) 可以改善TBT所造成的反應。
綜合上述結果，較低劑量TBT所造成胰島素分泌作用是透過ROS、Ca2+/PKC訊號傳導或雌激素受體訊號傳導。另一方面，較高劑量的TBT造成β-cells功能喪失、細胞自體凋亡是經由ROS或Ca2+調控JNK的磷酸化、caspase-3活性增加及cleaved PARP表現的訊息傳導路徑。此外，動物實驗證實TBT所誘導的氧化壓力扮演一個很重要的角色。

關鍵字

三丁基錫 ； 氧化性壓力 ； 胰島素分泌 ； 細胞凋亡 ； 糖尿病

並列摘要

Tributyltin (TBT) is a widespread environmental pollutant. TBT causes neurotoxicity, hepatotoxicity, skin toxicity and immunotoxicity as well as impaired endocrine regulation. However, the pathophysiological effect of TBT on the function of pancreaticβ-cells remains unknown. It has been reported that triphenyltin (TPT), an other organotin compound, could induce hyperglycemia with decreased insulin secretion in vivo, but its mechanism is still unclear. The aim of this study is designed to investigate the effects and mechanisms of TBT on the function of pancreatic β-cells and cell viability and blood glucose regulation.
Submicromolar-concentration TBT (0.1 – 1 μM) contains bi-phasic effects on β-cells. 0.1 and 0.2 μM TBT increased insulin secretion, intracellular Ca2+ and stimulated PKC activation in β-cell derived RIN-m5f cells. Antioxidant N-acetylcysteine (NAC), intracellular Ca2+ chelator BAPTA/AM, PKC inhibitor Ro32-0432 and estrogen receptor antagonist ICI182780 significantly reversed TBT-induced increase of insulin secretion. On the other hand, the cell viability and insulin secretion were significantly reduced at 24 hr after 0.5 and 1 μM TBT treatment. We found that higher-dose TBT triggered cell apoptosis, ROS production, phosphorylation of JNK, increase caspase-3 activity and cleaved poly-ADP-ribose polymerase (PARP) expression. Antioxidant NAC, JNK inhibitor SP600125 and intracellular Ca2+ chelator BAPTA/AM prevented TBT-induced cell apoptosis and JNK phosphorylation. We next observed that 2- or 4-week oral exposure of TBT (0.025 and 0.25 mg/kg/day) to mice, significantly caused the decrease in plasma insulin and displayed the elevation of blood glucose and plasma lipid peroxidation and glucose intolerance. Insulin secretion was decrease in islets isolated from TBT-exposed mice. NAC effectively antagonized TBT-induced responses.
In conclusion, these results indicate that lower-dose TBT enhanced insulin secretion from pancreatic β-cells, via ROS regulation or Ca2+/PKC pathway or estrogen receptor. On the other hand, the higher-dose TBT triggered pancreatic β-cells dysfunction and apoptosis via ROS or Ca2+/JNK/caspase-3/cleaved PARP signaling pathway. Moreover, oxidative stress may play an important role in TBT-induced responses in vivo.

並列關鍵字

TBT ； ROS ； insulin secretion ； apoptosis ； diabetes

參考文獻

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