Pharmacological and genetic inhibition of NADPH oxidase does not reduce brain damage in different models of perinatal brain injury in newborn mice.

BACKGROUND: Inflammation and reactive oxygen species (ROS) are important in the development of perinatal brain injury. The ROS-generating enzyme NADPH oxidase (Nox2) is present in inflammatory cells and contributes to brain injury in adult animal models. HYPOTHESIS: NADPH oxidase contributes to ROS formation and development of injury in the immature brain and inhibition of NADPH oxidase attenuates perinatal brain injury. METHODS: We used animal models of term hypoxia-ischemia (HI) (P9 mice) as well as ibotenate-induced excitotoxic injury (P5 mice) mimicking features of periventricular leukomalacia in preterm infants. In vitro microglia cell cultures were used to investigate NADPH oxidase-dependent ROS formation. In vivo we determined the impact 1) of HI on NADPH oxidase gene expression 2) of genetic (gp91-phox/Nox2 knock-out) and 3) of pharmacological NADPH oxidase inhibition on HI-induced injury and NMDA receptor-mediated excitotoxic injury, respectively. Endpoints were ROS formation, oxidative stress, apoptosis, inflammation and extent of injury. RESULTS: Hypoxia-ischemia increased NADPH oxidase subunits mRNA expression in total brain tissue in vivo. In vitro ibotenate increased NADPH oxidase-dependent formation of reactive oxygen species in microglia. In vivo the inhibition of NADPH oxidase did not reduce the extent of brain injury in any of the animal models. In contrast, the injury was increased by inhibition of NADPH oxidase and genetic inhibition was associated with an increased level of galectin-3 and IL-1beta. CONCLUSION: NADPH oxidase is upregulated after hypoxia-ischemia and activated microglia cells are a possible source of Nox2-derived ROS. In contrast to findings in adult brain, NADPH oxidase does not significantly contribute to the pathogenesis of perinatal brain injury. Results obtained in adult animals cannot be transferred to newborns and inhibition of NADPH oxidase should not be used in attempts to attenuate injury.

Dextromethorphan is protective against sensitized N-methyl-D-aspartate receptor-mediated excitotoxic brain damage in the developing mouse brain.

Enhanced glutamate release and inflammation play an important role in the pathogenesis of developmental brain injury. Although N-methyl-d-aspartate receptor (NMDAR) antagonists potently attenuate neonatal brain damage in several animal models, they can also impact trophic functions in the developing brain. As a consequence, high-affinity NMDAR antagonists have been shown to trigger widespread apoptotic neurodegeneration in the newborn brain. Dextromethorphan (DM), a low-affinity NMDAR antagonist with anti-inflammatory properties, may be neuroprotective against excitotoxic and inflammation-enhanced excitotoxic brain injury, without the associated stimulation of apoptotic degeneration. Using an established newborn mouse model of excitotoxic brain damage, we determined whether systemic injection of DM significantly attenuates excitotoxic lesion size. We investigated several doses and time regimens; a dose of 5 microg/g DM given in a combination of both pre-injury and repetitive post-injury treatment proved most effective. DM treatment significantly reduced lesion size in gray and white matter by reducing cell death as shown by a decreased Fluoro-Jade B staining and caspase-3 activation. Pre-treatment with interleukin-1beta and lipopolysaccharide enhanced NMDAR-mediated excitotoxic brain injury and microglial cell activation. This sensitizing effect was abolished by DM treatment, as the effectiveness of DM in reducing lesion size and microglial cell activation was similar to phosphate-buffered saline-pre-treated controls. In all cases, no gender-specific differences were detected. DM treatment did not trigger any apoptotic neurodegeneration (caspase-3 cleavage, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, Fluoro-Jade B staining). Although functional parameters were not measured, our data corroborate reports that DM is neuroprotective and that it may therefore improve functional outcome following perinatal brain injury.

Agomelatine, a melatonin receptor agonist with 5-HT(2C) receptor antagonist properties, protects the developing murine white matter against excitotoxicity.

Periventricular leukomalacia is a major cause of cerebral palsy. Perinatal white matter lesions associated with cerebral palsy appears to involve glutamate excitotoxicity. When injected intracerebrally into newborn mice, the glutamatergic analog, ibotenate, induces white matter cysts mimicking human periventricular leukomalacia. Intraperitoneal injection of melatonin was previously shown to be neuroprotective in this mouse model. The goal of the present study was to compare in this model the protective effects of agomelatine (S 20098), a melatonin derivative, with melatonin. Mice that received intraperitoneal S 20098 or melatonin had significant reductions in size of ibotenate-induced white matter cysts when compared with controls. Although agomelatine and melatonin did not prevent the initial appearance of white matter lesions, they did promote secondary lesion repair. Interestingly, while melatonin effects were only observed when given within the first two hours following the excitotoxic insult, agomelatine was still significantly neuroprotective when administered eight hours after the insult. The protective effects of agomelatine and melatonin were counter-acted by co-administration of luzindole or S 20928, two melatonin receptor antagonists. Agomelatine, acting through melatonin receptors, could represent a promising new drug for treating human periventricular leukomalacia and have beneficial effects on neuroplasticity.

T3 replacement does not prevent excitotoxic cell death but reduces developmental neuronal apoptosis in newborn mice.

BACKGROUND: Periventricular leukomalacia (PVL) is a major cause of neurological handicap in pre-term infants. At present, there are no effective or causal therapies available. Thyroid hormones play an essential role in brain development and are reported to be decreased in pre-terms and following brain injury in adults. HYPOTHESIS: Excitotoxic brain damage of newborn mice decreases thyroid hormone concentrations. Exogenous T3 administration restores thyroid hormone levels and reduces perinatal brain damage in an animal model of PVL. DESIGN AND METHOD: To create white and gray matter (WM/GM) lesion mimicking several key aspects of PVL, we injected ibotenic acid (Ibo), a glutamate analog, into the right hemisphere (intracranially (i.c.)) of 5-day-old mice. T3 (10 microg/kg body weight (bw)) was injected intraperitoneally (i.p.) 1 h or repeatedly 1/24/48/72/96 h post-insult. We determined lesion size, number of apoptotic cells in WM/GM and serum T3/T4 concentration at 24 and 120 h after injury. Serum T3/T4 concentration was also determined before and 1 and 2h after T3 administration. RESULTS: Excitotoxic brain damage did not alter serum T3/T4 concentrations within 120 h of injury. Serum T3 levels were distinctly elevated within 1 h of T3 injection; however, this elevation was relatively short-lived (half-life estimated to be less than 12 h). Neither single nor repetitive T3 treatment regimen reduced excitotoxic lesion size, but it did reduce apoptosis. CONCLUSIONS: T3 replacement does not prevent excitotoxic cell death, but it does reduce developmental neuronal apoptosis, which could participate to the beneficial neuropsychological effects of hormone therapy. Further study is therefore warranted.

Converging evidences on language impairment in Landau-Kleffner Syndrome revealed by behavioral and brain activity measures: a case study.

OBJECTIVE: To assess the linguistic abilities of a boy having Landau-Kleffner Syndrome, and relate the focal disturbance of brain activity due to epilepsy to the cognitive and linguistic deficits. METHODS: Several kinds of assessments were carried out, including epileptic source analysis using electronic source localization methods and PET, neuropsychological assessment of cognitive functions, and assessment of speech perception skills (discrimination of phonetic and stress cues) using ERPs. RESULTS: The source of epileptic activity was localized in the left superior temporal lobe. The neuropsychological assessment showed dissociation between verbal and nonverbal functions, and the performance in former was bellow the normal range. ERPs obtained to the processing of phonetic and stress speech cues indicated that the two cues were processed asymmetrically: the mismatch negativity component (MMN) was obtained for the phoneme difference, but not for the stress pattern difference. CONCLUSIONS: Our data converged as it showed that the patient presented a selective impairment of the language system, and the verbal working memory system appeared to be especially defective. It is suggested that the language deficit is at least partly due to the focal disturbance of those neural networks that underlie the functioning of the working memory system. SIGNIFICANCE: LKS is a childhood language disorder that might serve as a model in studying what happens to the language system if, in the course of development, the essential neural circuits are severely disturbed.

Erythropoietin is neuroprotective against NMDA-receptor-mediated excitotoxic brain injury in newborn mice.

Using an established mouse model of human periventricular leukomalacia, we investigated whether EPO could reduce excitotoxic damage. When administered 1 h following intracerebral injection of 10 microg ibotenic acid at day 5 of life, both a single injection of EPO (5000 IU/kg bw) and repetitive administrations of EPO reduced white and gray matter lesion size. The therapeutic window for protection was small as the protective effect of EPO was lost when EPO administration was delayed to 4 h post-insult. EPO-mediated upregulation of EPO-R, but not EPO, mRNA was observed within 4 h of the excitotoxic insult. The EPO effect was gender independent. Minor hematopoetic effects were observed following EPO treatment. We conclude that a single dose of EPO is sufficient to reduce excitotoxic brain injury and may therefore possess therapeutic relevance in the clinical setting.

Systemic application of granulocyte-colony stimulating factor and stem cell factor exacerbates excitotoxic brain injury in newborn mice.

Granulocyte-colony stimulating factor (G-CSF) has been shown to reduce brain lesion size and mortality in adult mice after hypoxic-ischemic injury. Another hematopoietic growth factor, stem cell factor (SCF), has been shown to be up-regulated in the brains of adult rodents following brain damage, where it stimulates postlesional neurogenesis. Injection of the excitotoxic agent ibotenate into the brain of newborn mice produces a brain lesion characterized by neuronal death and white matter cysts, which is similar to periventricular leucomalacia. The aim of the present study was to investigate whether administration of SCF and G-CSF is neuroprotective against ibotenate lesions in neonatal mice. Contrary to our expectations, cortical and white matter brain lesions induced by ibotenate were enhanced following the administration of 50 microg/kg SCF or 200 microg/kg G-CSF. Dose-response studies indicated that G-CSF could increase grey matter lesions even at lower dosages (22 and 66 microg/kg). Administration of SCF and G-CSF in combination also increased cortical and white matter lesions, to 133 +/- 8% and 187 +/- 12%. In the undamaged brain, G-CSF or G-CSF+SCF treatment had no effect on apoptosis in the grey or white matter; however, these treatments significantly increased apoptosis in the damaged brain. Our data clearly demonstrate that G-CSF and SCF are not neuroprotective and result in deleterious enhancement of excitotoxic brain damage in newborn mice. We conclude that G-CSF and SCF should be used cautiously in newborn infants with brain lesions; if they are used, long term neurologic and neurodevelopmental follow-up is warranted.