N-Acetylaspartylglutamate (NAAG) Pretreatment Reduces Hypoxic-Ischemic Brain Damage and Oxidative Stress in Neonatal Rats

Abstract

N-acetylaspartylglutamate (NAAG), the most abundant peptide transmitter in the mammalian nervous system, activates mGluR3 at presynaptic sites, inhibiting the release of glutamate, and acts on mGluR3 on astrocytes, stimulating the release of neuroprotective growth factors (TGF-β). NAAG can also affect N-methyl-d-aspartate (NMDA) receptors in both synaptic and extrasynaptic regions. NAAG reduces neurodegeneration in a neonatal rat model of hypoxia-ischemia (HI), although the exact mechanism is not fully recognized. In the present study, the effect of NAAG application 24 or 1 h before experimental birth asphyxia on oxidative stress markers and the potential mechanisms of neuroprotection on 7-day old rats was investigated. The intraperitoneal application of NAAG at either time point before HI significantly reduced the weight deficit of the ischemic brain hemisphere, radical oxygen species (ROS) content and activity of antioxidant enzymes, and increased the concentration of reduced glutathione (GSH). No additional increase in the TGF-β concentration was observed after NAAG application. The fast metabolism of NAAG and the decrease in TGF-β concentration that resulted from NAAG pretreatment, performed up to 24 h before HI, excluded the involvement mGluR3 in neuroprotection. The observed effect may be explained by the activation of NMDA receptors induced by NAAG pretreatment 24 h before HI. Inhibition of the NAAG effect by memantine supports this conclusion. NAAG preconditioning 1 h before HI results in a mixture of mGluR3 and NMDA receptor activation. Preconditioning with NAAG induces the antioxidative defense system triggered by mild excitotoxicity in neurons. Moreover, this response to NAAG pretreatment is consistent with the commonly accepted mechanism of preconditioning. However, this theory requires further investigation.

Pretreatment with mGluR2 or mGluR3 Agonists Reduces Apoptosis Induced by Hypoxia‐Ischemia in Neonatal Rat Brains

“…Our previous experiments confirmed these observations, showing that application of LY379268 or NAAG not only shortly after HI but also up to 24 h before HI attenuated neurodegeneration [13,28,29]. Our results concerning the prolonged effects of pretreatment with LY379268 are in agreement with those presented by Bond et al [23].…”

“…Our results concerning the prolonged effects of pretreatment with LY379268 are in agreement with those presented by Bond et al [23]. The neuroprotective effect of NAAG applied 1 h before hypoxic exposure but after unilateral common carotid occlusion in a neonatal rat model of hypoxia-ischemia was described by Cai et al [27]; however, the neuroprotective effect of NAAG applied 24 h before HI was presented for the first time in our laboratory [29]. Moreover, we showed that the neuroprotective effect of NAAG applied 1 h before HI results from a Figure 3: The effect of LY379268 or NAAG application 24 h or 1 h before HI on caspase-9 (a) and caspase-3 (b) activity.…”

“…Results are presented as the mean ± SEM, n = 5; statistically significant differences: * p < 0:01 and * * p < 0:001 compared to HI; # p < 0:001 compared to the sham-operated group. 6 Oxidative Medicine and Cellular Longevity combination of activation of mGluR3 and NMDA receptors, whereas the neuroprotective effect of NAAG applied 24 h before HI is primarily due to NMDA receptors [29]. We also demonstrated that application of both LY379268 and NAAG 24 h or 1 h before HI resulted in a significant reduction in oxidative stress, suggesting that processes leading to apoptotic cell death could also be attenuated [28,29].…”

“…In our previous study, we showed that application of NAAG or LY379268 a short time after HI reduced oxidative stress [13]. We also demonstrated that pretreatment of animals with each agonist up to 24 h before HI resulted in neuroprotection and reduced ROS production, although the molecular mechanisms of their activity seemed to be distinct [13,28,29].…”

“…Their important role in the development of the phenomenon of "ischemic tolerance" was also strongly implicated [35]. In our recent paper, we suggested that the neuroprotective effect of NAAG pretreatment may be part of the induction of ischemic tolerance by activation of NMDA receptors ( [29] in press).…”