Yourick Debra L, Koenig Michael L, Durden Anna V, Long Joseph B
Division of Neurosciences, Walter Reed Army Institute of Research, 503 Robert Grant Ave, Silver Spring, MD 20910-7500, USA.
Brain Res. 2003 Nov 21;991(1-2):56-64. doi: 10.1016/s0006-8993(03)03533-9.
The acidic dipeptide N-acetylaspartylglutamate (NAAG) is the most prevalent peptide in the central nervous system. NAAG is a low potency agonist at the NMDA receptor, and hydrolysis of NAAG yields the more potent excitatory amino acid neurotransmitter glutamate. beta-NAAG is a competitive inhibitor of the NAAG hydrolyzing enzyme N-acetylated alpha-linked acidic dipeptidase (NAAG peptidase activity) or glutamate carboxypeptidase II, and may also act as a NAAG-mimetic at some of the sites of NAAG pharmacological activity. Since NAAG has been shown to have neuroprotective characteristics in a number of experimental preparations, it is the purpose of the present study to specifically evaluate the possible efficacy of NAAG and beta-NAAG against NMDA- and hypoxia-induced injury to spinal cord mixed neuronal and glial cell cultures. NAAG (500-1000 microM) protected against NMDA- or hypoxia-induced injuries to spinal cord cultures, and the nonhydrolyzable analog beta-NAAG (250-1000 microM) completely eliminated the loss of viability caused by either insult. Both peptides also attenuated NMDA-induced increases in intraneuronal Ca(2+). Nonspecific mGluR antagonists, pertussis toxin, a stable cAMP analog, and manipulation of NAAG peptidase activity did not by themselves alter cell damage and did not influence the neuroprotective effects of NAAG. NAAG was not protective against kainate- or AMPA-induced cellular injury, while beta-NAAG was partially neuroprotective against both insults. At 2 mM, NAAG and beta-NAAG reduced neuronal survival and increased intraneuronal Ca(2+); these effects were only marginally attenuated by dizocilpine and APV. The results indicate that NAAG and beta-NAAG protect against excitotoxic and hypoxic injury to spinal cord neurons, and do so predominantly by interactions with NMDA and not mGluR receptors.
酸性二肽N - 乙酰天冬氨酰谷氨酸（NAAG）是中枢神经系统中最普遍的肽。NAAG是N - 甲基 - D - 天冬氨酸（NMDA）受体的低效激动剂，NAAG水解产生更强效的兴奋性氨基酸神经递质谷氨酸。β - NAAG是NAAG水解酶N - 乙酰化α - 连接酸性二肽酶（NAAG肽酶活性）或谷氨酸羧肽酶II的竞争性抑制剂，并且在NAAG药理活性的某些位点也可能充当NAAG模拟物。由于已证明NAAG在许多实验制剂中具有神经保护特性，本研究的目的是具体评估NAAG和β - NAAG对NMDA和缺氧诱导的脊髓混合神经元和神经胶质细胞培养物损伤的可能疗效。NAAG（500 - 1000微摩尔）可保护脊髓培养物免受NMDA或缺氧诱导的损伤，不可水解的类似物β - NAAG（250 - 1000微摩尔）完全消除了由任何一种损伤引起的活力丧失。两种肽还减弱了NMDA诱导的神经元内Ca（2 +）增加。非特异性代谢型谷氨酸受体（mGluR）拮抗剂、百日咳毒素、一种稳定的环磷酸腺苷（cAMP）类似物以及对NAAG肽酶活性的操纵本身并未改变细胞损伤，也不影响NAAG的神经保护作用。NAAG对海人藻酸或α - 氨基 - 3 - 羟基 - 5 - 甲基 - 4 - 异恶唑丙酸（AMPA）诱导的细胞损伤无保护作用，而β - NAAG对这两种损伤均有部分神经保护作用。在2毫摩尔时，NAAG和β - NAAG降低神经元存活率并增加神经元内Ca（2 +）；地佐环平（MK - 801）和2 - 氨基 - 5 - 磷酰基戊酸（APV）仅略微减弱了这些作用。结果表明，NAAG和β - NAAG可保护脊髓神经元免受兴奋性毒性和缺氧损伤，并且主要通过与NMDA而非mGluR受体相互作用来实现。
