Iron supplementation aggravates periventricular cystic white matter lesions in newborn mice

Targeting ferroptosis opens new avenues for the development of novel therapeutics

Ferroptosis is an iron-dependent form of regulated cell death with distinct characteristics, including altered iron homeostasis, reduced defense against oxidative stress, and abnormal lipid peroxidation. Recent studies have provided compelling evidence supporting the notion that ferroptosis plays a key pathogenic role in many diseases such as various cancer types, neurodegenerative disease, diseases involving tissue and/or organ injury, and inflammatory and infectious diseases. Although the precise regulatory networks that underlie ferroptosis are largely unknown, particularly with respect to the initiation and progression of various diseases, ferroptosis is recognized as a bona fide target for the further development of treatment and prevention strategies. Over the past decade, considerable progress has been made in developing pharmacological agonists and antagonists for the treatment of these ferroptosis-related conditions. Here, we provide a detailed overview of our current knowledge regarding ferroptosis, its pathological roles, and its regulation during disease progression. Focusing on the use of chemical tools that target ferroptosis in preclinical studies, we also summarize recent advances in targeting ferroptosis across the growing spectrum of ferroptosis-associated pathogenic conditions. Finally, we discuss new challenges and opportunities for targeting ferroptosis as a potential strategy for treating ferroptosis-related diseases.

Erythropoietin Improves Poor Outcomes in Preterm Infants with Intraventricular Hemorrhage

BACKGROUND

Intraventricular hemorrhage (IVH) is a common complication in preterm infants that has poor outcomes, especially in severe cases, and there are currently no widely accepted effective treatments. Erythropoietin has been shown to be neuroprotective in neonatal brain injury.

OBJECTIVE

The objective of this study was to evaluate the protective effect of repeated low-dose recombinant human erythropoietin (rhEPO) in preterm infants with IVH.

METHODS

This was a single-blinded prospective randomized controlled trial. Preterm infants ≤ 32 weeks gestational age who were diagnosed with IVH within 72 h after birth were randomized to receive rhEPO 500 IU/kg or placebo (equivalent volume of saline) every other day for 2 weeks. The primary outcome was death or neurological disability assessed at 18 months of corrected age.

RESULTS

A total of 316 eligible infants were included in the study, with 157 in the rhEPO group and 159 in the placebo group. Although no significant differences in mortality (p = 0.176) or incidence of neurological disability (p = 0.055) separately at 18 months of corrected age were seen between the rhEPO and placebo groups, significantly fewer infants had poor outcomes (death and neurological disability) in the rhEPO group: 14.9 vs. 26.4%; odds ratio (OR) 0.398; 95% confidence interval (CI) 0.199-0.796; p = 0.009. In addition, the incidence of Mental Development Index scores of < 70 was lower in the rhEPO group than in the placebo group: 7.2 vs. 15.3%; OR 0.326; 95% CI 0.122-0.875; p = 0.026.

CONCLUSIONS

Treatment with repeated low-dose rhEPO improved outcomes in preterm infants with IVH.

TRIAL REGISTRATION

The study was retrospectively registered on ClinicalTrials.gov on 16 April 2019 (NCT03914690).

Ferroptosis and Brain Injury

Ferroptosis is a nonapoptotic form of cell death characterized by the iron-dependent accumulation of toxic lipid reactive oxygen species. Small-molecule screening and subsequent optimization have yielded potent and specific activators and inhibitors of this process. These compounds have been employed to dissect the lethal mechanism and implicate this process in pathological cell death events observed in many tissues, including the brain. Indeed, ferroptosis is emerging as an important mechanism of cell death during stroke, intracerebral hemorrhage, and other acute brain injuries, and may also play a role in certain degenerative brain disorders. Outstanding issues include the practical need to identify molecular markers of ferroptosis that can be used to detect and study this process in vivo, and the more basic problem of understanding the relationship between ferroptosis and other forms of cell death that can be triggered in the brain during injury.

The Potential Role of Ferroptosis in Neonatal Brain Injury

Ferroptosis is an iron-dependent form of cell death that is characterized by early lipid peroxidation and different from other forms of regulated cell death in terms of its genetic components, specific morphological features, and biochemical mechanisms. Different initiation pathways of ferroptosis have been reported, including inhibition of system X_c ^-, inactivation of glutathione-dependent peroxidase 4, and reduced glutathione levels, all of which ultimately promote the production of reactive oxygen species, particularly through enhanced lipid peroxidation. Although ferroptosis was first described in cancer cells, emerging evidence now links mechanisms of ferroptosis to many different diseases, including cerebral ischemia and brain hemorrhage. For example, neonatal brain injury is an important cause of developmental impairment and of permanent neurological deficits, and several types of cell death, including iron-dependent pathways, have been detected in the process of neonatal brain damage. Iron chelators and erythropoietin have both shown neuroprotective effects against neonatal brain injury. Here, we have summarized the potential relation between ferroptosis and neonatal brain injury, and according therapeutic intervention strategies.

[Oxidative stress after preterm birth: origins, biomarkers, and possible therapeutic approaches]

The survival of preterm babies has increased over the last few decades. However, disorders associated with preterm birth, known as oxygen radical diseases of neonatology, such as retinopathy, bronchopulmonary dysplasia, periventricular leukomalacia, and necrotizing enterocolitis are severe complications related to oxidative stress, which can be defined by an imbalance between oxidative reactive species production and antioxidant defenses. Oxidative stress causes lipid, protein, and DNA damage. Preterm infants have decreased antioxidant defenses in response to oxidative challenges, because the physiologic increase of antioxidant capacity occurs at the end of gestation in preparation for the transition to extrauterine life. Therefore, preterm infants are more sensitive to neonatal oxidative stress, notably when supplemental oxygen is being delivered. Furthermore, despite recent advances in the management of neonatal respiratory distress syndrome, controversies persist concerning the oxygenation saturation targets that should be used in caring for preterm babies. Identification of adequate biomarkers of oxidative stress in preterm infants such as 8-iso-prostaglandin F2α, and adduction of malondialdehyde to hemoglobin is important to promote specific therapeutic approaches. At present, no therapeutic strategy has been validated as prevention or treatment against oxidative stress. Breastfeeding should be considered as the main measure to improve the antioxidant status of preterm infants. In the last few years, melatonin has emerged as a protective molecule against oxidative stress, with antioxidant and free-radical scavenger roles, in experimental and preliminary human studies, giving hope that it can be used in preterm infants in the near future.

Disparities and relative risk ratio of preterm birth in six Central and Eastern European centers

AIM

To identify characteristic risk factors of preterm birth in Central and Eastern Europe and explore the differences from other developed countries.

METHOD

Data on 33,794 term and 3867 preterm births (<37 wks.) were extracted in a retrospective study between January 1, 2007 and December 31, 2009. The study took place in 6 centers in 5 countries: Czech Republic, Hungary (two centers), Romania, Slovakia, and Ukraine. Data on historical risk factors, pregnancy complications, and special testing were gathered. Preterm birth frequencies and relevant risk factors were analyzed using Statistical Analysis System (SAS) software.

RESULTS

All the factors selected for study (history of smoking, diabetes, chronic hypertension, current diabetes, preeclampsia, progesterone use, current smoking, body mass index, iron use and anemia during pregnancy), except the history of diabetes were predictive of preterm birth across all participating European centers. Preterm birth was at least 2.4 times more likely with smoking (history or current), three times more likely with preeclampsia, 2.9 times more likely with hypertension after adjusting for other covariates. It had inverse relationship with the significant predictor body mass index, with adjusted risk ratio of 0.8 to 1.0 in three sites. Iron use and anemia, though significant predictors of preterm birth, indicated mixed patterns for relative risk ratio.

CONCLUSION

Smoking, preeclampsia, hypertension and body mass index seem to be the foremost risk factors of preterm birth. Implications of these factors could be beneficial for design and implementation of interventions and improve the birth outcome.

Could cord blood cell therapy reduce preterm brain injury?

Major advances in neonatal care have led to significant improvements in survival rates for preterm infants, but this occurs at a cost, with a strong causal link between preterm birth and neurological deficits, including cerebral palsy (CP). Indeed, in high-income countries, up to 50% of children with CP were born preterm. The pathways that link preterm birth and brain injury are complex and multifactorial, but it is clear that preterm birth is strongly associated with damage to the white matter of the developing brain. Nearly 90% of preterm infants who later develop spastic CP have evidence of periventricular white matter injury. There are currently no treatments targeted at protecting the immature preterm brain. Umbilical cord blood (UCB) contains a diverse mix of stem and progenitor cells, and is a particularly promising source of cells for clinical applications, due to ethical and practical advantages over other potential therapeutic cell types. Recent studies have documented the potential benefits of UCB cells in reducing brain injury, particularly in rodent models of term neonatal hypoxia–ischemia. These studies indicate that UCB cells act via anti-inflammatory and immuno-modulatory effects, and release neurotrophic growth factors to support the damaged and surrounding brain tissue. The etiology of brain injury in preterm-born infants is less well understood than in term infants, but likely results from episodes of hypoperfusion, hypoxia–ischemia, and/or inflammation over a developmental period of white matter vulnerability. This review will explore current knowledge about the neuroprotective actions of UCB cells and their potential to ameliorate preterm brain injury through neonatal cell administration. We will also discuss the characteristics of UCB-derived from preterm and term infants for use in clinical applications.

Reprint of "The developing oligodendrocyte: key cellular target in brain injury in the premature infant"

Brain injury in the premature infant, a problem of enormous importance, is associated with a high risk of neurodevelopmental disability. The major type of injury involves cerebral white matter and the principal cellular target is the developing oligodendrocyte. The specific phase of the oligodendroglial lineage affected has been defined from study of both human brain and experimental models. This premyelinating cell (pre-OL) is vulnerable because of a series of maturation-dependent events. The pathogenesis of pre-OL injury relates to operation of two upstream mechanisms, hypoxia-ischemia and systemic infection/inflammation, both of which are common occurrences in premature infants. The focus of this review and of our research over the past 15-20 years has been the cellular and molecular bases for the maturation-dependent vulnerability of the pre-OL to the action of the two upstream mechanisms. Three downstream mechanisms have been identified, i.e., microglial activation, excitotoxicity and free radical attack. The work in both experimental models and human brain has identified a remarkable confluence of maturation-dependent factors that render the pre-OL so exquisitely vulnerable to these downstream mechanisms. Most importantly, elucidation of these factors has led to delineation of a series of potential therapeutic interventions, which in experimental models show marked protective properties. The critical next step, i.e., clinical trials in the living infant, is now on the horizon.

The developing oligodendrocyte: key cellular target in brain injury in the premature infant

Brain injury in the premature infant, a problem of enormous importance, is associated with a high risk of neurodevelopmental disability. The major type of injury involves cerebral white matter and the principal cellular target is the developing oligodendrocyte. The specific phase of the oligodendroglial lineage affected has been defined from study of both human brain and experimental models. This premyelinating cell (pre-OL) is vulnerable because of a series of maturation-dependent events. The pathogenesis of pre-OL injury relates to operation of two upstream mechanisms, hypoxia-ischemia and systemic infection/inflammation, both of which are common occurrences in premature infants. The focus of this review and of our research over the past 15-20 years has been the cellular and molecular bases for the maturation-dependent vulnerability of the pre-OL to the action of the two upstream mechanisms. Three downstream mechanisms have been identified, i.e., microglial activation, excitotoxicity and free radical attack. The work in both experimental models and human brain has identified a remarkable confluence of maturation-dependent factors that render the pre-OL so exquisitely vulnerable to these downstream mechanisms. Most importantly, elucidation of these factors has led to delineation of a series of potential therapeutic interventions, which in experimental models show marked protective properties. The critical next step, i.e., clinical trials in the living infant, is now on the horizon.

In vivo assessment of experimental neonatal excitotoxic brain lesion with USPIO-enhanced MR imaging

PURPOSE

To assess the feasibility of magnetic resonance imaging (MRI) enhanced with ultrasmall superparamagnetic particles of iron oxide (USPIO) for assessing excitotoxic brain lesions in an experimental model of neonatal periventricular white matter (PWM) lesions.

MATERIALS AND METHODS

Brain lesions were induced by intracerebral injection of ibotenate in 14 newborn rats. Pre- and post-USPIO T2-weighted MRI was performed in seven of them (group A) and in five control newborns (group C). In seven newborns with induced cerebral lesions, USPIO-enhanced MRI was not performed (group B). We compared the signal intensity of the lesion to the contralateral unaffected brain (lesion-to-brain contrast, LBC) and the lesion signal-to-noise ratio (SNR) before and after USPIO injection. MR imaging was correlated with histology.

RESULTS

USPIO injection significantly (P<0.05) decreased LBC and SNR of brain lesion but induced no changes in normal controls. The densities of macrophages and iron-laden cells were higher on the lesion side than on the contralateral side (P<0.05). Neither lesion size nor the surrounding macrophage infiltrate was significantly different between groups A and B.

CONCLUSION

Post-USPIO T2-weighted MRI demonstrated negative enhancement of neonatal excitotoxic brain lesion. USPIO injection does not appear to exacerbate brain lesions.

Avoiding hyperoxia in infants < or = 1250 g is associated with improved short- and long-term outcomes

OBJECTIVE

To determine the rate and severity of short- and long-term morbidity in very low birth weight infants treated before and after the implementation of a change in clinical practice designed to avoid hyperoxia.

METHODS

Analysis of a prospectively collected database of all infants < or = 1250 g admitted to two Emory University NICU's from January 2000 to December 2004. A change in practice was instituted in January 2003 with the objective of avoiding hyperoxia in preterm infants with target O2 saturation (SpO2) at 93 to 85% (Period II). Before the change in practice, SpO2 high alarms were set at 100% and low alarms at 92% (Period I). Statistical analysis included bivariate analyses and multivariate logistic regression comparing outcomes between the two periods.

RESULTS

From January 2000 to December 2004, 502 infants met enrollment criteria and 202 (40%) were born in period II, after change in SpO2 targets. Birth weight, gestational age and survival were similar between both periods. The rates for any retinopathy of prematurity, supplemental oxygen at 36 weeks post-conceptional age and the use of steroids for chronic lung disease were significantly lower in the infants born in Period II. There was no difference in the rates of necrotizing enterocolitis, intraventricular hemorrhage and periventricular leukomalacia. At 18 months corrected age (CA), the infants treated during Period II had a higher Mental Developmental Index (MDI) scores (80.2 +/- 18.3 vs 89.2 +/- 18.5; P 0.02) and similar Psychomotor Developmental Index (PDI) scores (83.9 +/- 18.6 vs 89.4 +/- 17.2; P 0.08) than those treated during Period I. The proportion of infants with an MDI or a PDI less than 70 was similar between the periods.

CONCLUSIONS

The change in practice to avoid hyperoxia is associated with a significant decrease in neonatal morbidity and does not have a detrimental effect on developmental outcomes at 18 months CA.

Iron contributes to dopamine-induced toxicity in oligodendrocyte progenitors

Iron is potentially toxic to oligodendrocyte progenitors due to its high intracellular levels and its ability to catalyse oxidant-producing reactions. Oxidative stress resulting from a hypoxic-ischaemic insult has been implicated in death of oligodendrocyte progenitors that occurs in the hypomyelinating disorder periventricular leucomalacia. Ischaemic insults induce the release of various neurotransmitters, including dopamine (DA), and we previously showed that DA is toxic to cultured oligodendrocytes, by inducing oxidative stress and apoptosis. Therefore, we investigated the role of iron in DA-induced cell death in oligodendrocyte progenitors. Intracellular iron levels were altered using an iron chelator, deferoxamine (DFO), and supplementation with ferrous sulphate (FeSO(4)). Addition of FeSO(4) to cultures increased DA-induced toxicity as assessed by mitochondrial dehydrogenase activity and cellular release of lactate dehydrogenase. Furthermore, FeSO(4) increased expression of the stress protein heme oxygenase-1 (HO-1), nuclear condensation and caspase-3 activation. In contrast, preincubation with DFO reduced these events as well as cleavage of alpha-spectrin, a caspase-3 substrate. In addition, FeSO(4) reversed the protective effect of DFO on DA-induced cytotoxicity, HO-1 expression and caspase-3 activation. These results indicate that elevated levels of free iron contribute to DA-induced toxicity in oligodendrocyte progenitors.

Neurodevelopmental outcome of preterm infants with ventricular dilatation with and without associated haemorrhage

This study investigated whether in preterm children who had ventricular dilatation (VD) on neonatal cranial ultrasound outcome at age 8 years was influenced by the additional presence of germinal matrix haemorrhage--intraventricular haemorrhage (GMH-IVH). Six-hundred and ninety-nine preterm infants (<33 wks' gestation, mean 29.6 wks [SD 2.1]) with either normal cranial ultrasound (n=616; 286 females, 330 males), or with VD with (n=66; 32 females, 34 males) or without (n=17; 4 females, 13 males) GMH-IVH were enrolled in the study. At age 8 years outcome was assessed in 567 (81%) of the 699 children by neurological examination, the Test of Motor Impairment (TOMI), the test of Visuo-Motor Integration (VMI), and the Wechsler Intelligence Scales for Children. Results showed that the proportion of children with disabling impairments was higher in the group with VD and GMH-IVH. Performance on TOMI and VMI (even in those without disabling impairments) was poorer in those with VD and GMH-IVH than in children with normal scans or those with VD only. Children with VD and GMH-IVH had significantly lower performance IQ than children with normal ultrasound, whereas those with VD only were not different from those with normal scans. Results suggest the presence of subtle white matter injury that has not been identified by neonatal cranial ultrasound. Although this study did not investigate biochemical markers of haemorrhage, we hypothesize that non-protein-bound iron is likely to be a contributing factor to white matter damage in preterm infants.

Zinc protoporphyrin/heme as an indicator of iron status in NICU patients

OBJECTIVE

Zinc protoporphyrin/heme ratio (ZnPP/H) has been well established as an indicator of functional iron deficiency in subjects 6 months of age to adult. The primary objective of this study was to establish normative values for ZnPP/H in NICU patients and secondarily to explore the utility of this test as an indicator of iron deficiency in neonates. Study design ZnPP/H and complete blood counts were obtained weekly on consecutive NICU patients. Gestational age, growth variables, iron supplementation, erythropoietin treatment, and blood transfusions were documented. Results are reported as mean +/- SD. A value of P <.05 was considered significant.

RESULTS

ZnPP/H ratios (n = 639) were evaluated from 143 infants. During the first week of life, ZnPP/H was inversely correlated with gestational age (n = 78, P <.001, r = -0.72). Maternal diabetes, growth retardation, and exposure to chorioamnionitis were independent risk factors for high ZnPP/H. Both iron supplementation and blood transfusion decreased ZnPP/H (P <.001). Erythropoietin treatment was associated with an increase in reticulocyte count and ZnPP/H (P <.001).

CONCLUSIONS

ZnPP/H is inversely correlated with gestational age, and the range in all newborn infants is higher than in adults. ZnPP/H is elevated in certain infant subpopulations, which suggests that they may require additional iron supplementation.

Role of spin trapping and P2Y receptor antagonism in the neuroprotective effects of 2,2'-pyridylisatogen tosylate and related compounds

2,2'-Pyridylisatogen tosylate (PIT) is both an allosteric modulator of P2Y receptors, and an immine oxide, acting as a spin trap for free radicals. PIT (10 mg kg(-1), i.p.) was found to be a powerful neuroprotective agent in protecting against the lesions induced by 15 micro g S-bromo-willardiine injected into the cortex or white matter of 5-day-old mice pups. As the multiple effects of PIT may induce both beneficial and deleterious effects, a reanalysis of the structure-activity relationship was undertaken. PIT (50 micro M) and 2,3'-pyridylisatogen were potent antagonists of responses to ATP in the taenia preparation of the guinea-pig caecum, but 2,3'-nitrophenylisatogen was not. The reactive immine oxide group could be substituted by a keto moiety (N-(2'-pyridyl)phthalide) while maintaining antagonism of responses to ATP, equivalent to PIT. Thus, antagonism of P2Y receptors was not restricted to the isatogen nucleus. Other spin traps did not antagonise P2Y receptors, although dimethyl-pyrroline-N-oxide (DMPO) increased the sensitivity of responses to ATP. Both N-(2'-pyridyl)phthalide and 2,3'-nitrophenylisatogen was less neuroprotective than PIT (10 mg kg(-1), i.p.) in protecting against the S-bromo-willardiine-induced lesions in mice, implying that both antagonism of P2Y receptors and the immine oxide moiety may be important for the neuroprotective effects of PIT. However, the usefulness of the neuroprotection was limited because, in motoneurones obtained from rat embryos, PIT (10-100 micro M) exacerbated cell death.

Multiple pathways of neuroprotection against oxidative stress and excitotoxic injury in immature primary hippocampal neurons

In the immature brain hydrogen peroxide accumulates after excitotoxic hypoxia-ischemia and is neurotoxic. Immature hippocampal neurons were exposed to N-methyl-D-aspartate (NMDA), a glutamate agonist, and hydrogen peroxide (H(2)O(2)) and the effects of free radical scavenging and transition metal chelation on neurotoxicity were studied. alpha-Phenyl-N-tert.-butylnitrone (PBN), a known superoxide scavenger, attenuated both H(2)O(2) and NMDA mediated toxicity. Treatment with desferrioxamine (DFX), an iron chelator, at the time of exposure to H(2)O(2) was ineffective, but pretreatment was protective. DFX also protected against NMDA toxicity. TPEN, a metal chelator with higher affinities for a broad spectrum of transition metal ions, also protected against H(2)O(2) toxicity but was ineffective against NMDA induced toxicity. These data suggest that during exposure to free radical and glutamate agonists, the presence of iron and other free metal ions contribute to neuronal cell death. In the immature nervous system this neuronal injury can be attenuated by free radical scavengers and metal chelators.

The neuroprotective activity of 8-alkylamino-1,4-benzoxazine antioxidants

Antioxidant 8-alkylamino-1,4-benzoxazines, (R,S)-(3-tert-butyl-8-phenylethylamino-3,4-dihydro-2H-1,4-benzoxazin-5-yl) (phenyl) methanone (S 24429) and (R,S)-(3-cyclopentyl-8-benzylamino-3,4-dihydro-2H-1,4-benzoxazin-5-yl) (phenyl) methanone (S 24718), were prepared according to a two-step one-pot electrochemical procedure. These compounds had been selected from a previous study of structure/activity. Both compounds (1-100 microM) prevented the fall in ATP levels caused by 24 h of hypoxia in astrocytes. Both compounds (1 and 10 mg/kg i.p.) were powerful neuroprotective agents in protecting against the lesions induced by 15 microg S-bromo-willardiine injected into the cortex or white matter of 5-day old mice pups. In contrast, exifone, an antioxidant compound, was inactive at these doses. S 24429 and S 24718 appear to be novel neuroprotective agents, which are effective in a model of brain damage mimicking the lesions underlying cerebral palsy.

Update on oxygen radical disease in neonatology

An increasing number of articles related to free radicals in the newborn period is published. The hypothesis that there exists a socalled 'Oxygen radical disease of neonatology' has not been proven but an increasing body of evidence seems to indicate that free radicals are involved in several disease processes leading to conditions such as chronic lung disease, retinopathy of prematurity, necrotizing enterocolitis and periventricular leukomalacia. There are also accumulating data implying the involvement of reactive oxygen species and oxidative stress in signal transduction and they therefore perhaps affect growth and development. In the last year there have been no new breakthroughs in antioxidant therapy.

Cerebral white matter damage in the preterm infant: pathophysiology and risk factors

Based on clinical, epidemiologic, and experimental studies, the aetiology of white matter damage, specifically periventricular leukomalacia (PVL), is multifactorial and involves pre- and perinatal factors possibly including genetic factors, hypoxic-ischaemic insults, infection, excess cytokines, free radical production, increased excitatory amino acid release, and trophic factor deficiencies. The article summarizes research findings about the aetiology of white matter damage and cerebral palsy in preterm infants. The information is organized according to specific antecedents, for which we present epidemiological and neurobiological data. The most important prenatal factor appears to be intrauterine infection. We discuss the evidence supporting the hypothesis that the foetal inflammatory response contributes to neonatal brain injury and later developmental disability. We recently established an animal model of excitotoxic lesions in the developing mouse brain. Brain damage was induced by intra-cortical injections of ibotenate, a glutamatergic agonist. When administered on post-natal day 5 ibotenate induced the formation of white matter cysts. Our animal model could be used to further explore the mechanisms involved in the formation of PVL. Potentially preventive strategies will be discussed.

Nociceptin/orphanin FQ exacerbates excitotoxic white-matter lesions in the murine neonatal brain

Intracerebral administration of the excitotoxin ibotenate to newborn mice induces white-matter lesions, mimicking brain lesions that occur in human preterm infants. Nociceptin (NC), also called orphanin FQ, is the endogenous ligand of the opioid receptor-like 1 (ORL1) receptor and does not bind classical high-affinity opioid receptors. In the present study, administration of NC exacerbated ibotenate-induced white-matter lesions while coadministration of ibotenate with either of two NC antagonists reduced excitotoxic white-matter lesions by up to 64%. Neither ibotenate plus endomorphin I (a selective mu receptor agonist), nor ibotenate plus naloxone (a classical opioid receptor antagonist) modulated the excitotoxic lesion. Pretreatment with antisense oligonucleotides targeting the NC precursor peptide mRNA significantly reduced ibotenate-induced white-matter damage. Finally, high doses of fentanyl, which stimulates both classical mu-opioid receptors and ORL1, exacerbated excitotoxic white-matter lesion. This toxic effect was blocked by inhibiting ORL1 but not classical opioid receptors. Together, these findings show that endogenous or exogenous stimulation of the ORL1 receptor can be neurotoxic and that blocking NC signaling protects the white matter against excitotoxic challenge. These data point to potential new avenues for neuroprotection in human preterm infants at high risk of brain lesions.

Central role of microglia in neonatal excitotoxic lesions of the murine periventricular white matter

Periventricular leukomalacia (PVL) is the main cause of neurologic handicap in pre-term infants. The understanding of cellular and molecular mechanisms leading to white matter damage is critical for development of innovative therapeutic strategies for PVL. The pathogenesis of PVL remains unclear but possibly involves glutamate excitotoxicity as an important molecular pathway. We previously described a neonatal mouse model of excitotoxic white matter lesion mimicking human PVL. In the present study, we used this experimental tool to investigate the cellular populations and the glutamate receptor subtypes involved in excitotoxic white matter lesions. Combined immunohistochemical, electron microscopic, and cell death detection data revealed that microglial activation and astrocytic death were the primary responses of white matter to excitotoxic insult. In vitro experiments suggested that microglia activated by ibotenate released soluble factors that kill astrocytes. The use of selective agonists and antagonists of glutamate receptors revealed that N-methyl-D-aspartate (NMDA) receptor activation was essential and sufficient to produce cystic white matter lesions. NMDA receptor immunohistochemistry labeled microglial cells in the neonatal periventricular white matter. The developing white matter displayed a window of sensitivity to excitotoxic damage that was paralleled by the transient presence of NMDA receptor-expressing white matter cells. Assuming that similar pathophysiologic mechanisms are present in human pre- term infants, microglia and NMDA receptors could represent key targets for treatment of PVL.

VIP and PACAP 38 modulate ibotenate-induced neuronal heterotopias in the newborn hamster neocortex

Intracerebral administration of ibotenate produces, through activation of N-methyl-D-aspartate (NMDA) receptors, neuronal heterotopias in the newborn hamster neocortex: high doses of ibotenate induce periventricular and subcortical neuronal heterotopias, while low doses of ibotenate produce intracortical heterotopias and molecular layer ectopias. Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are closely related peptides with neurotrophic properties. They share common VPAC1 and VPAC2 receptors, which use cAMP as a second messenger. Previous studies have shown that VIP prevents excitotoxic neuronal death and exacerbates glutamate-induced c-fos neuronal expression. In order to gain new insight into the molecular control of neuronal migration, the present study examined the effects of VIP and PACAP on ibotenate-induced heterotopias in the newborn hamster. Co-treatment with VIP and a high dose of ibotenate produced a pattern of neuronal heterotopias similar to the one observed in animals treated with low doses of ibotenate alone. Pups co-injected with a low dose of ibotenate and a VIP antagonist displayed cortical dysgeneses similar to those observed in animals treated with high doses of ibotenate alone. The modulating effects of VIP on excitotoxin-induced heterotopias were mimicked by forskolin, PACAP, and by a specific VPAC2 receptor agonist but not by a VPAC1 agonist, and were blocked by a protein kinase A (PKA) inhibitor. Taken together, these data suggest that VIP and PACAP can attenuate ibotenate-induced heterotopias in newborn hamster and that this effect is mediated by the VPAC2 receptor utilizing the cAMP-PKA pathway.

VIP neuroprotection against excitotoxic lesions of the developing mouse brain

Intracerebral administration of the excitotoxin ibotenate to new-born mice induced white-matter lesions mimicking the periventricular leukomalacia occurring in human premature babies. In this model, co-injection of vasoactive intestinal peptide (VIP) prevented white-matter lesions. VIP did not prevent the initial appearance of white-matter lesion, but promoted a secondary repair with axonal regrowth. Co-administration of ibotenate, VIP, and transduction inhibitors showed that protein kinase C (PKC) and mitogen-associated protein kinase (MAPK) pathways were critical for neuroprotection. The combination of in vitro and in vivo studies suggested the following model: VIP activates PKC in astrocytes, which release soluble factors; these released factors activate neuronal MAPK and PKC, which will permit axonal regrowth. Previous studies had shown that VIP-treated cultured astrocytes release growth factors including activity-dependent neurotrophic factor (ADNF) and that a 14-amino-acid peptide derived from ADNF protected the developing white matter against ibotenate. However, co-treatment with ibotenate, VIP, and anti-ADNF antibodies did not abolish VIP-induced protection, suggesting that ADNF does not mediate VIP protective properties in the present model.