Dalcin Karina B, Rosa Rafael B, Schmidt Anna L, Winter Juliana S, Leipnitz Guilhian, Dutra-Filho Carlos S, Wannmacher Clóvis M D, Porciúncula Lisiane O, Souza Diogo O, Wajner Moacir
Departamento de Bioquímica, ICBS, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos, 2600-Anexo, CEP 90035-003, Porto Alegre, RS, Brazil.
Cell Mol Neurobiol. 2007 Sep;27(6):805-18. doi: 10.1007/s10571-007-9197-2. Epub 2007 Sep 5.
(1) In the present study we determined the effects of glutaric (GA, 0.01-1 mM) and 3-hydroxyglutaric (3-OHGA, 1.0-100 microM) acids, the major metabolites accumulating in glutaric acidemia type I (GA I), on Na(+)-independent and Na(+)-dependent [(3)H]glutamate binding to synaptic plasma membranes from cerebral cortex and striatum of rats aged 7, 15 and 60 days. (2) GA selectively inhibited Na(+)-independent [(3)H]glutamate binding (binding to receptors) in cerebral cortex and striatum of rats aged 7 and 15 days, but not aged 60 days. In contrast, GA did not alter Na(+)-dependent glutamate binding (binding to transporters) to synaptic membranes from brain structures of rats at all studied ages. Furthermore, experiments using the glutamatergic antagonist CNQX indicated that GA probably binds to non-NMDA receptors. In addition, GA markedly inhibited [(3)H]kainate binding to synaptic plasma membranes in cerebral cortex of 15-day-old rats, indicating that this effect was probably directed towards kainate receptors. On the other hand, experiments performed with 3-OHGA revealed that this organic acid did not change Na(+)-independent [(3)H]glutamate binding to synaptic membranes from cerebral cortex and striatum of rats from all ages, but inhibited Na(+)-dependent [(3)H]glutamate binding to membranes in striatum of 7-day-old rats, but not in striatum of 15- and 60-day-old rats and in cerebral cortex of rats from all studied ages. We also provided some evidence that 3-OHGA competes with the glutamate transporter inhibitor L-trans-pyrrolidine-2,4-dicarboxylate, suggesting a possible interaction of 3-OHGA with glutamate transporters on synaptic membranes. (3) These results indicate that glutamate binding to receptors and transporters can be inhibited by GA and 3-OHGA in cerebral cortex and striatum in a developmentally regulated manner. It is postulated that a disturbance of glutamatergic neurotransmission caused by the major metabolites accumulating in GA I at early development may possibly explain, at least in part, the window of vulnerability of striatum and cerebral cortex to injury in patients affected by this disorder.
(1) 在本研究中,我们测定了戊二酸(GA,0.01 - 1 mM)和3 - 羟基戊二酸(3 - OHGA,1.0 - 100 microM)这两种在I型戊二酸血症(GA I)中积累的主要代谢产物,对7日龄、15日龄和60日龄大鼠大脑皮层和纹状体突触质膜上不依赖Na⁺和依赖Na⁺的[³H]谷氨酸结合的影响。(2) GA选择性抑制7日龄和15日龄大鼠大脑皮层和纹状体中不依赖Na⁺的[³H]谷氨酸结合(与受体的结合),但对60日龄大鼠无此作用。相比之下,GA在所有研究年龄的大鼠脑结构中均未改变依赖Na⁺的谷氨酸结合(与转运体的结合)至突触膜的情况。此外,使用谷氨酸能拮抗剂CNQX的实验表明,GA可能与非NMDA受体结合。另外,GA显著抑制15日龄大鼠大脑皮层中[³H]海人藻酸与突触质膜的结合,表明这种作用可能针对海人藻酸受体。另一方面,用3 - OHGA进行的实验表明,这种有机酸并未改变所有年龄大鼠大脑皮层和纹状体中不依赖Na⁺的[³H]谷氨酸与突触膜的结合,但抑制了7日龄大鼠纹状体中依赖Na⁺的[³H]谷氨酸与膜的结合,而对15日龄和60日龄大鼠纹状体以及所有研究年龄大鼠大脑皮层中的结合无此作用。我们还提供了一些证据表明3 - OHGA与谷氨酸转运体抑制剂L - 反式 - 脯氨酸 - 2,4 - 二羧酸竞争,提示3 - OHGA可能与突触膜上的谷氨酸转运体相互作用。(3) 这些结果表明,GA和3 - OHGA可在大脑皮层和纹状体中以发育调控的方式抑制谷氨酸与受体及转运体的结合。据推测,GA I早期发育过程中积累的主要代谢产物所导致的谷氨酸能神经传递紊乱,可能至少部分解释了该疾病患者纹状体和大脑皮层对损伤的易损窗口期。