Ye Z C, Sontheimer H
Department of Neurobiology, The University of Alabama at Birmingham, 35294, USA.
Cancer Res. 1999 Sep 1;59(17):4383-91.
Elevated levels of extracellular glutamate ([Glu]o) cause uncontrolled Ca2+ increases in most neurons and are believed to mediate excitotoxic brain injury following stroke and other nervous system insults. In the normal brain, [Glu]o is tightly controlled by uptake into astrocytes. Because the vast majority of primary brain tumors (gliomas) are derived from astrocytes, we investigated glutamate uptake in glioma cells surgically isolated from glioma patients (glioblastoma multiforme) and in seven established human glioma cell lines, including STTG-1, D-54 MG, D-65 MG, U-373 MG, U-138 MG, U-251 MG, and CH-235 MG. All glioma cells studied showed impaired glutamate uptake, with a Vmax < 10% that of normal astrocytes. Moreover, rather than removing glutamate from the extracellular fluid, glioma cells release large amounts of glutamate, resulting in elevations of [Glu]o in excess of 100 microM within hours in a space that is 1000-fold larger than the cellular volume. Exposure of cultured hippocampal neurons to glioma-conditioned medium elicited sustained [Ca2+]i elevations that were followed by widespread neuronal death. Similarly, coculturing of hippocampal neurons and glioma cells, either with or without direct contact, resulted in neuronal death. Glioma-induced neuronal death could be completely prevented by treating neurons with the N-methyl-D-aspartate receptor antagonists MK-801/D(-)-2-amino-5-phosphonopentanoic acid or by depletion of glutamate from the medium. Interestingly, several phenylglycine derivatives including the metabotropic glutamate receptor agonist/antagonist (S)-4-carboxyphenylglycine (S-4CPG) potently and selectively inhibited glutamate release from glioma cells and prevented neurotoxicity. These data suggest that growing glioma tumors may actively kill surrounding neuronal cells through the release of glutamate. This glutamate release may also be responsible in part for tumor-associated seizures that occur frequently in conjunction with glioma. These data also suggest that neurotoxic release of glutamate by gliomas may be prevented by phenylglycine derivatives, which may thus be useful as an adjuvant treatment for brain tumors.
细胞外谷氨酸（[Glu]o）水平升高会导致大多数神经元内的Ca2+不受控制地增加，据信这在中风和其他神经系统损伤后介导了兴奋性毒性脑损伤。在正常大脑中，[Glu]o通过被星形胶质细胞摄取而受到严格控制。由于绝大多数原发性脑肿瘤（胶质瘤）起源于星形胶质细胞，我们研究了从胶质瘤患者（多形性胶质母细胞瘤）手术分离的胶质瘤细胞以及七种已建立的人胶质瘤细胞系（包括STTG-1、D-54 MG、D-65 MG、U-373 MG、U-138 MG、U-251 MG和CH-235 MG）中的谷氨酸摄取情况。所有研究的胶质瘤细胞均显示谷氨酸摄取受损，其最大反应速度（Vmax）小于正常星形胶质细胞的10%。此外，胶质瘤细胞非但不能从细胞外液中清除谷氨酸，反而会释放大量谷氨酸，导致在数小时内，在比细胞体积大1000倍的空间内，[Glu]o升高超过100微摩尔。将培养的海马神经元暴露于胶质瘤条件培养基中会引发持续的细胞内钙浓度（[Ca2+]i）升高，随后是广泛的神经元死亡。同样，海马神经元与胶质瘤细胞共培养，无论有无直接接触，都会导致神经元死亡。通过用N-甲基-D-天冬氨酸受体拮抗剂MK-801/D-(-)-2-氨基-5-膦酰基戊酸处理神经元或从培养基中耗尽谷氨酸，可完全防止胶质瘤诱导的神经元死亡。有趣的是，几种苯甘氨酸衍生物，包括代谢型谷氨酸受体激动剂/拮抗剂（S）-4-羧基苯甘氨酸（S-4CPG），能有效且选择性地抑制胶质瘤细胞释放谷氨酸并预防神经毒性。这些数据表明，不断生长的胶质瘤肿瘤可能通过释放谷氨酸来主动杀死周围的神经元细胞。这种谷氨酸释放也可能部分导致与胶质瘤经常同时发生的肿瘤相关癫痫发作。这些数据还表明，苯甘氨酸衍生物可能预防胶质瘤的谷氨酸神经毒性释放，因此可能作为脑肿瘤的辅助治疗手段。
