Sul Donggun, Kim Hyo-Shin, Cho Eun-Kyung, Lee Min, Kim Hyun Sook, Jung Woon-Won, Hwang Kwang Woo, Park So-Young
Graduate School of Medicine, Korea University, Anamdong 5, Seoul 136-705, Republic of Korea.
Toxicology. 2009 Jan 8;255(1-2):65-71. doi: 10.1016/j.tox.2008.10.006. Epub 2008 Oct 19.
One of the most notorious environmental toxicants, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), easily accumulates in the environment and most organisms, including humans, because of its high lipophilicity and resistance to degradation. TCDD exposure causes a variety of adverse health effects in humans including immunotoxicity, hepatotoxicity, neurotoxicity, and carcinogenesis. For the most part, studies regarding the adverse effects of TCDD on the central nervous system (CNS) have been limited to neurodevelopmental processes. In this study, we investigated the neurotoxicity of TCDD in neuronal cells using a neuroblastoma cell line (clone N2a) and explored the possible mechanisms of action. MTT and Comet assays were conducted to determine if TCDD is cytotoxic and if it causes DNA damage, respectively. The results of these assays revealed that treatment with 100, 300, 500 and 1000 nM TCDD decreased the viability of N2a cells and increased DNA damage in a dose-dependent manner compared to controls. Additionally, a malondialdehyde (MDA) assay was performed to determine if TCDD induces lipid peroxidation. The results of this assay revealed that 100, 300 and 500 nM TCDD induced lipid peroxidation in a dose-dependent manner. Finally, TCDD neurotoxicity (300 nM or higher) in N2a cells was accompanied by elevated intracellular calcium levels. These increased calcium levels increased the phosphorylation of tau via up-regulation of phospho-glycogen synthase kinase-3beta (GSK-3beta). Taken together, these results indicate that TCDD exposure induces neurotoxicity in N2a cells by increasing DNA damage, oxidative stress and intracellular calcium levels. The TCDD-mediated increase of tau phosphorylation in particular indicates an important role for tau hyperphosphorylation in TCDD-induced neurotoxicity.
2,3,7,8-四氯二苯并对二恶英（TCDD）是最臭名昭著的环境毒物之一，由于其高亲脂性和抗降解性，它很容易在环境以及包括人类在内的大多数生物体中蓄积。TCDD暴露会对人类造成多种不良健康影响，包括免疫毒性、肝毒性、神经毒性和致癌作用。在很大程度上，关于TCDD对中枢神经系统（CNS）不良影响的研究一直局限于神经发育过程。在本研究中，我们使用神经母细胞瘤细胞系（克隆N2a）研究了TCDD在神经元细胞中的神经毒性，并探讨了可能的作用机制。分别进行MTT和彗星试验以确定TCDD是否具有细胞毒性以及是否会导致DNA损伤。这些试验结果显示，与对照组相比，用100、300、500和1000 nM TCDD处理会使N2a细胞的活力降低，并以剂量依赖的方式增加DNA损伤。此外，进行了丙二醛（MDA）试验以确定TCDD是否诱导脂质过氧化。该试验结果显示，100、300和500 nM TCDD以剂量依赖的方式诱导脂质过氧化。最后，N2a细胞中TCDD神经毒性（300 nM或更高）伴随着细胞内钙水平升高。这些升高的钙水平通过上调磷酸化糖原合酶激酶-3β（GSK-3β）增加了tau的磷酸化。综上所述，这些结果表明，TCDD暴露通过增加DNA损伤、氧化应激和细胞内钙水平在N2a细胞中诱导神经毒性。特别是TCDD介导的tau磷酸化增加表明tau过度磷酸化在TCDD诱导的神经毒性中起重要作用。
