Group II Metabotropic Glutamate Receptors Reduce Apoptosis and Regulate BDNF and GDNF Levels in Hypoxic-Ischemic Injury in Neonatal Rats.

Birth asphyxia causes brain injury in neonates, but a fully successful treatment has yet to be developed. This study aimed to investigate the effect of group II mGlu receptors activation after experimental birth asphyxia (hypoxia-ischemia) on the expression of factors involved in apoptosis and neuroprotective neurotrophins. Hypoxia-ischemia (HI) on 7-day-old rats was used as an experimental model. The effects of intraperitoneal application of mGluR2 agonist LY379268 (5 mg/kg) and the specific mGluR3 agonist NAAG (5 mg/kg) (1 h or 6 h after HI) on apoptotic processes and initiation of the neuroprotective mechanism were investigated. LY379268 and NAAG applied shortly after HI prevented brain damage and significantly decreased pro-apoptotic Bax and HtrA2/Omi expression, increasing expression of anti-apoptotic Bcl-2. NAAG or LY379268 applied at both times also decreased HIF-1α formation. HI caused a significant decrease in BDNF concentration, which was restored after LY379268 or NAAG administration. HI-induced increase in GDNF concentration was decreased after administration of LY379268 or NAAG. Our results show that activation of mGluR2/3 receptors shortly after HI prevents brain damage by the inhibition of excessive glutamate release and apoptotic damage decrease. mGluR2 and mGluR3 agonists produced comparable results, indicating that both receptors may be a potential target for early treatment in neonatal HI.

The Mechanism of the Neuroprotective Effect of Kynurenic Acid in the Experimental Model of Neonatal Hypoxia-Ischemia: The Link to Oxidative Stress.

The over-activation of NMDA receptors and oxidative stress are important components of neonatal hypoxia-ischemia (HI). Kynurenic acid (KYNA) acts as an NMDA receptor antagonist and is known as a reactive oxygen species (ROS) scavenger, which makes it a potential therapeutic compound. This study aimed to establish the neuroprotective and antioxidant potential of KYNA in an experimental model of HI. HI on seven-day-old rats was used as an experimental model. The animals were injected i.p. with different doses of KYNA 1 h or 6 h after HI. The neuroprotective effect of KYNA was determined by the measurement of brain damage and elements of oxidative stress (ROS and glutathione (GSH) level, SOD, GPx, and catalase activity). KYNA applied 1 h after HI significantly reduced weight loss of the ischemic hemisphere, and prevented neuronal loss in the hippocampus and cortex. KYNA significantly reduced HI-increased ROS, GSH level, and antioxidant enzyme activity. Only the highest used concentration of KYNA showed neuroprotection when applied 6 h after HI. The presented results indicate induction of neuroprotection at the ROS formation stage. However, based on the presented data, it is not possible to pinpoint whether NMDA receptor inhibition or the scavenging abilities are the dominant KYNA-mediated neuroprotective mechanisms.

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

Hypoxia-ischemia (HI) in an immature brain results in energy depletion and excessive glutamate release resulting in excitotoxicity and oxidative stress. An increase in reactive oxygen species (ROS) production induces apoptotic processes resulting in neuronal death. Activation of group II mGluR was shown to prevent neuronal damage after HI. The application of agonists of mGluR3 (N-acetylaspartylglutamate; NAAG) or mGluR2 (LY379268) inhibits the release of glutamate and reduces neurodegeneration in a neonatal rat model of HI, although the exact mechanism is not fully recognized. In the present study, the effects of NAAG (5 mg/kg) and LY379268 (5 mg/kg) application (24 h or 1 h before experimental birth asphyxia) on apoptotic processes as the potential mechanism of neuroprotection in 7-day-old rats were investigated. Intraperitoneal application of NAAG or LY379268 at either time point before HI significantly reduced the number of TUNEL-positive cells in the CA1 region of the ischemic brain hemisphere. Both agonists reduced expression of the proapoptotic Bax protein and increased expression of Bcl-2. Decreases in HI-induced caspase-9 and caspase-3 activity were also observed. Application of NAAG or LY379268 24 h or 1 h before HI reduced HIF-1α formation likely by reducing ROS levels. It was shown that LY379268 concentration remains at a level that is required for activation of mGluR2 for up to 24 h; however, NAAG is quickly metabolized by glutamate carboxypeptidase II (GCPII) into glutamate and N-acetyl-aspartate. The observed effect of LY379268 application 24 h or 1 h before HI is connected with direct activation of mGluR2 and inhibition of glutamate release. Based on the data presented in this study and on our previous findings, we conclude that the neuroprotective effect of NAAG applied 1 h before HI is most likely the result of a combination of mGluR3 and NMDA receptor activation, whereas the beneficial effects of NAAG pretreatment 24 h before HI can be explained by the activation of NMDA receptors and induction of the antioxidative/antiapoptotic defense system triggered by mild excitotoxicity in neurons. This response to NAAG pretreatment is consistent with the commonly accepted mechanism of preconditioning.

Synthesis of Dolichols in Candida albicans Is Co-Regulated with Elongation of Fatty Acids.

Protein glycosylation requires dolichyl phosphate as a carbohydrate carrier. Dolichols are α-saturated polyprenols, and their saturation in S. cerevisiae is catalyzed by polyprenyl reductase Dfg10 together with some other unknown enzymes. The aim of this study was to identify such enzymes in Candida. The Dfg10 polyprenyl reductase from S. cerevisiae comprises a C-terminal 3-oxo-5-alpha-steroid 4-dehydrogenase domain. Alignment analysis revealed such a domain in two ORFs (orf19.209 and orf19.3293) from C. albicans, which were similar, respectively, to Dfg10 polyprenyl reductase and Tsc13 enoyl-transferase from S. cerevisiae. Deletion of orf19.209 in Candida impaired saturation of polyprenols. The Tsc13 homologue turned out not to be capable of saturating polyprenols, but limiting its expression reduce the cellular level of dolichols and polyprenols. This reduction was not due to a decreased expression of genes encoding cis-prenyltransferases from the dolichol branch but to a lower expression of genes encoding enzymes of the early stages of the mevalonate pathway. Despite the resulting lower consumption of acetyl-CoA, the sole precursor of the mevalonate pathway, it was not redirected towards fatty acid synthesis or elongation. Lowering the expression of TSC13 decreased the expression of the ACC1 gene encoding acetyl-CoA carboxylase, the key regulatory enzyme of fatty acid synthesis and elongation.