Differential Age-Dependent Mitochondrial Dysfunction, Oxidative Stress, and Apoptosis Induced by Neonatal Hypoxia-Ischemia in the Immature Rat Brain

Neonatal hypoxia-ischemia (HI) is among the main causes of mortality and morbidity in newborns. Experimental studies show that the immature rat brain is less susceptible to HI injury, suggesting that changes that occur during the first days of life drastically alter its susceptibility. Among the main developmental changes observed is the mitochondrial function, namely, the tricarboxylic acid (TCA) cycle and respiratory complex (RC) activities. Therefore, in the present study, we investigated the influence of neonatal HI on mitochondrial functions, redox homeostasis, and cell damage at different postnatal ages in the hippocampus of neonate rats. For this purpose, animals were divided into four groups: sham postnatal day 3 (ShP3), HIP3, ShP11, and HIP11. We initially observed increased apoptosis in the HIP11 group only, indicating a higher susceptibility of these animals to brain injury. Mitochondrial damage, as determined by flow cytometry showing mitochondrial swelling and loss of mitochondrial membrane potential, was also demonstrated only in the HIP11 group. This was consistent with the decreased mitochondrial oxygen consumption, reduced TCA cycle enzymes, and RC activities and induction of oxidative stress in this group of animals. Considering that HIP3 and the sham animals showed no alteration of mitochondrial functions, redox homeostasis, and showed no apoptosis, our data suggest an age-dependent vulnerability of the hippocampus to hypoxia-ischemia. The present results highlight age-dependent metabolic differences in the brain of neonate rats submitted to HI indicating that different treatments might be needed for HI newborns with different gestational ages.

Neural Stem Cells Expressing bFGF Reduce Brain Damage and Restore Sensorimotor Function after Neonatal Hypoxia-Ischemia

BACKGROUND/AIMS

Neonatal hypoxia-ischemia (HI) causes severe brain damage and significantly increases neonatal morbidity and mortality. Increasing evidences have verified that stem cell-based therapy has the potential to rescue the ischemic tissue and restore function via secreting growth factors after HI. Here, we had investigated whether intranasal neural stem cells (NSCs) treatment improves the recovery of neonatal HI, and NSCs overexpressing basic fibroblast growth factor (bFGF) has a better therapeutic effect for recovery than NSCs treatment only.

METHODS

We performed permanent occlusion of the right common carotid artery in 9-day old ICR mice as animal model of neonatal hypoxia-ischemia. At 3 days post-HI, NSC, NSC-GFP, NSC-bFGF and vehicle were delivered intranasally. To determine the effect of intranasal NSC, NSC-GFP and NSC-bFGF treatment on recovery after HI, we analyzed brain damage, sensor-motor function and cell differentiation.

RESULTS

It was observed that intranasal NSC, NSC-GFP and NSC-bFGF treatment decreased gray and white matter loss area in comparison with vehicle-treated mouse. NSC, NSC-GFP and NSC-bFGF treatment also significantly improved sensor motor function in cylinder rearing test and adhesive removal test, however, NSC-bFGF-treatment was more effective than NSC-treatment in the improvement of somatosensory function. Furthermore, compared with NSC and NSC-GFP, NSC-bFGF treatment group appeared to differentiate into more neurons.

CONCLUSION

Taken together, intranasal administration of NSCs is a promising therapy for treatment of neonatal HI, but NSCs overexpressing bFGF promotes the survival and differentiation of NSCs, and consequently achieves a better therapeutic effect in improving recovery after neonatal HI.