粒線體與神經細胞死亡的研究(2/2)

Abstract

粒線體功能異常會引起許多不同年齡層 的神經病變。過去的研究顯示，3-nitropropionic acid 與許多神經毒物包括安非他命和甲基安非 他命一樣會導致神經細胞死亡。而這些神經細 胞的死亡與caspases 的活化有關。另外產生過 多的自由基也是一個可能的機轉。過去的研究 顯示，caspase 的活化通常因為粒線體功能的異 常所引起。因此，在本實驗中我們利用鼠腦初 級皮質神經細胞培養來探討導致這些神經毒 物神經毒性的原因。並比較這些神經細胞的死 亡導致caspases 活化的差異。我們第一年的研 究發現安非他命和甲基安非他命所導致神經 細胞死亡可使細胞自由基的產量增加，尤其甲 基安非他命所導致的增加更大，並造成細胞壞 死與細胞凋零。然而安非他命和甲基安非他命 僅引起輕微caspase-3 的活化。我們進一步發 現，施與少量3-nitropropionic acid 可使經安非 他命和甲基安非他命處理的細胞ATP 大量下 降，證明安非他命和甲基安非他命會影響粒線 體功能。我們接著比較發現安非他命和甲基安 非他命處理的細胞其caspase-3 的活化發生於 粒線體膜電位去極化後，而3-nitropropionic acid 處理的細胞其caspase-3 的活化發生於粒 線體膜電位去極化前即已進行。證明 3-nitropropionic acid 與安非他命和甲基安非他 命在caspase-3 的活化上是不一樣的。由於 3-nitropropionic acid 本身為粒線體毒物且會影 響Kreb cycle，是否因而誘發其他與粒線體無 關的caspase-3 活化值得進一步研究。相反的， 安非他命和甲基安非他命所導致神經細胞死 亡主要與自由基的產量增加有關，並進而影響 粒線體膜電位去極化。是否其他間接影響粒線 體膜電位去極化的神經毒物其caspase-3 活化 都與安非他命和甲基安非他命一樣發生於粒 線體膜電位去極化後值得進一步研究。

3-Nitropropionic acid (3-NP) is an irreversible inhibitor of succinate dehydrogenase. Previous studies had shown that 3-NP can lead to neuronal death following the activation of caspases. In the present study, we first investigate the neurotoxicity of methamphetamine and amphetamine in primary rat cortical neuronal cultures, and will compare the pathogenic mechanisms of neuronal death in methamphetamine and amphetamine with those in 3-NP. We found that there was a dose- and time-dependent increase of neuronal death following the application of methamphetamine and amphetamine. Significant elevation of reactive oxygen species was also found after the application of the drugs, especially in methamphetamine. Addition of low concentration of 3-NP significantly decreased the cellular ATP in amphetamine-treated neurons, indicating the effect of the drug on mitochondrial function. However, compared with that in 3-NP neurotoxicity, only mild activation of caspase-3 was found following the treatment of amphetamine. We further found that the caspase-3 activation in amphetamine and methamphetamine developed following mitochondrial depolarization. On the contrary, the caspase-3 activation in 3-NP developed before mitochondrial depolarization, indicating both a mitochondrial-dependent and independent pathways in 3-NP neurotoxicity. Because 3-NP is a direct mitochondrial toxins while amphetamine and methamphetamine are both indirect mitochondrial toxins, whether that’s one of the reasons leading to different caspase-3 activation needs further investigation.