Zeevalk G D, Bernard L P, Nicklas W J
UMDNJ-Robert Wood Johnson Medical School, Department of Neurology, Piscataway, New Jersey 08854, USA.
J Neurochem. 1998 Apr;70(4):1421-30. doi: 10.1046/j.1471-4159.1998.70041421.x.
Alterations in the glutathione system and impairment in energy metabolism have both been implicated in the loss of dopamine neurons in Parkinson's disease. This study examined the importance of cellular glutathione and the involvement of oxidative stress in the loss of mesencephalic dopamine and GABA neurons due to inhibition of energy metabolism with malonate, the reversible, competitive inhibitor of succinate dehydrogenase. Consistent with previous findings, exposure to malonate for 24 h followed by 48 h of recovery caused a dose-dependent loss of the dopamine population with little effect on the GABA population. Toxicity was assessed by simultaneous measurement of the high-affinity uptake of [3H]dopamine and [14C]GABA. Total glutathione content in rat mesencephalic cultures was decreased by 65% with a 24-h pretreatment with 10 microM buthionine sulfoxamine. This reduction in glutathione level greatly potentiated damage to both the dopamine and GABA populations and removed the differential susceptibility between the two populations in response to malonate. These findings point to a role for oxidative stress occurring during energy impairment by malonate. Consistent with this, several spin-trapping agents, alpha-phenyl-tert-butyl nitrone and two cyclic nitrones, MDL 101,002 and MDL 102,832, completely prevented malonate-induced damage to the dopamine neurons in the absence of buthionine sulfoxamine. The spin-trapping agents also completely prevented toxicity to both the dopamine and GABA populations when cultures were exposed to malonate after pretreatment with buthionine sulfoxamine to reduce glutathione levels. Counts of tyrosine hydroxylase-positive neurons verified enhancement of cell loss by buthionine sulfoxamine plus malonate and protection against cell loss by the spin-trapping agents. NMDA receptors have also been shown to play a role in malonate-induced dopamine cell loss and are associated with the generation of free radicals. Consistent with this, toxicity to the dopamine neurons due to a 1-h exposure to 50 microM glutamate was attenuated by the nitrone spin traps. These findings provide evidence for an oxidative challenge occurring during inhibition of energy metabolism by malonate and show that glutathione is an important neuroprotectant for midbrain neurons during situations when energy metabolism is impaired.
谷胱甘肽系统的改变和能量代谢受损都与帕金森病中多巴胺能神经元的丧失有关。本研究探讨了细胞内谷胱甘肽的重要性以及氧化应激在丙二酸抑制能量代谢导致中脑多巴胺能和GABA能神经元丧失过程中的作用。丙二酸是琥珀酸脱氢酶的可逆性竞争性抑制剂。与先前的研究结果一致，暴露于丙二酸24小时后再恢复48小时会导致多巴胺能神经元数量呈剂量依赖性减少，而对GABA能神经元数量影响较小。通过同时测量[3H]多巴胺和[14C]GABA的高亲和力摄取来评估毒性。用10微摩尔丁硫氨酸亚砜胺预处理24小时后，大鼠中脑培养物中的总谷胱甘肽含量降低了65%。谷胱甘肽水平的这种降低极大地增强了对多巴胺能和GABA能神经元群体的损伤，并消除了这两个群体对丙二酸反应的易感性差异。这些发现表明氧化应激在丙二酸导致能量损伤过程中发挥作用。与此一致的是，几种自旋捕捉剂，α-苯基叔丁基硝酮和两种环状硝酮，MDL 101,002和MDL 102,832，在没有丁硫氨酸亚砜胺的情况下完全防止了丙二酸诱导的多巴胺能神经元损伤。当用丁硫氨酸亚砜胺预处理培养物以降低谷胱甘肽水平后再暴露于丙二酸时，自旋捕捉剂也完全防止了对多巴胺能和GABA能神经元群体的毒性。酪氨酸羟化酶阳性神经元的计数证实了丁硫氨酸亚砜胺加丙二酸会增强细胞损失，而自旋捕捉剂可防止细胞损失。NMDA受体也已被证明在丙二酸诱导的多巴胺能细胞损失中起作用，并且与自由基的产生有关。与此一致的是，硝酮自旋捕捉剂减轻了50微摩尔谷氨酸暴露1小时对多巴胺能神经元的毒性。这些发现为丙二酸抑制能量代谢过程中发生的氧化应激挑战提供了证据，并表明在能量代谢受损的情况下，谷胱甘肽是中脑神经元的重要神经保护剂。
