Caspase-1-processed interleukins in hyperoxia-induced cell death in the developing brain

Lame from birth: early concepts of cerebral palsy

Deformations have been attributed to supernatural causes since antiquity. Cerebral palsy was associated with God's wrath, witchcraft, the evil eye, or maternal imagination. Greek scholars recommended prevention by tight swaddling, a custom that persisted into modern times. In the Middle Ages, the midwife's negligence was held responsible as was difficult teething. Morgagni described in 1769 that the neonatal brain can liquefy, and Bednar described leukomalacia in 1850 as a distinct disorder of the newborn. In 1861, Little associated cerebral palsies with difficult or protracted labor and neonatal asphyxia, but he was challenged by Freud, who in 1897 declared that most cases are prenatal in origin. In 1868, Virchow demonstrated inflammatory changes, a view recently confirmed by Leviton and Nelson. Although a causal relationship of cerebral palsy to the birth never has been established, the habit to put the blame for cerebral palsy on someone remained a frequent attitude.

Bacterial pore-forming cytolysins induce neuronal damage in a rat model of neonatal meningitis

BACKGROUND

Group B Streptococcus (GBS) and Streptococcus pneumoniae (SP) are leading causes of bacterial meningitis in neonates and children. Each pathogen produces a pore-forming cytolytic toxin, β-hemolysin/cytolysin (β-h/c) by GBS and pneumolysin by SP. The aim of this study was to understand the role of these pore-forming cytotoxins, in particular of the GBS β-h/c, as potential neurotoxins in experimental neonatal meningitis.

METHODS

Meningitis was induced in 7- and 11-day-old rats by intracisternal injection of wild type (WT) GBS or SP and compared with isogenic β-h/c- or pneumolysin-deficient mutants, or a double mutant of SP deficient in pneumolysin and hydrogen peroxide production.

RESULTS

GBS β-h/c and SP pneumolysin contributed to neuronal damage, worsened clinical outcome and weight loss, but had no influence on the early kinetics of leukocyte influx and bacterial growth in the cerebrospinal fluid. In vitro, β-h/c-induced neuronal apoptosis occurred independently of caspase-activation and was not preventable by the broad spectrum caspase-inhibitor z-VAD-fmk.

CONCLUSIONS

These data suggest that both cytolytic toxins, the GBS β-h/c and SP pneumolysin, contribute to neuronal damage in meningitis and extend the concept of a key role for bacterial pore-forming cytolysins in the pathogenesis and sequelae of neonatal meningitis.

Early protective effect of hypothermia in newborn pigs after hyperoxic, but not after normoxic, reoxygenation

Abstract Mild hypothermia can attenuate the development of brain damage after asphyxia. Supplemental oxygen during resuscitation increases generation of reactive oxygen species, compared to room air. It is unknown if supplemental oxygen affects hypothermic neuroprotection. We studied the early effects of hyperoxic reoxygenation and subsequent hypothermia on tissue oxygenation, microcirculation, inflammation and brain damage after global hypoxia. Anesthetized newborn pigs were randomized to control (n=6), or severe global hypoxia (n=46). Three pigs died during hypoxia or reoxygenation. After 20-min reoxygenation with room air (n=22) or 100% oxygen (n=21), pigs were randomized to normothermia (deep rectal temperature 39 degrees C, n=22) or total body cooling (35 degrees C, n=21) for 6.5 h before the experiment was terminated. We demonstrated a differential effect of post-hypoxic hypothermia between animals reoxygenated with 100% oxygen and with room air, with reduced damage only in hypothermic animals reoxygenated with 100% oxygen (P=0.001). Hyperoxic reoxygenation resulted in a significant overshoot in striatal oxygen tension, without affecting microcirculation. Inflammatory response after the insult did not differ between groups. The results indicate an early protective effect of hypothermia which may vary with oxygen level used during reoxygenation.

Erythropoietin attenuates hyperoxia-induced oxidative stress in the developing rat brain

Oxygen toxicity contributes to the pathogenesis of adverse neurological outcome in survivors of preterm birth in clinical studies. In infant rodent brains, hyperoxia triggers widespread apoptotic neurodegeneration, induces pro-inflammatory cytokines and inhibits growth factor signaling cascades. Since a tissue-protective effect has been observed for recombinant erythropoietin (rEpo), we hypothesized that rEpo would influence hyperoxia-induced oxidative stress in the developing rat brain. The aim of this study was to investigate the level of glutathione (reduced and oxidized), lipid peroxidation and the expression of heme oxygenase-1 (HO-1) and acetylcholinesterase (AChE) after hyperoxia and rEpo treatment. Six-day-old Wistar rats were exposed to 80% oxygen for 2-48 h and received 20,000 IU/kg rEpo intraperitoneally (i.p.). Sex-matched littermates kept under room air and injected with normal saline or rEpo served as controls. Treatment with rEpo significantly reduced hyperoxia-induced upregulation of oxidized glutathione (GSSG) and malondialdehyde, a product of lipid breakdown, whereas reduced glutathione (GSH) was upregulated by rEpo. In parallel, hyperoxia-treated immature rat brains revealed rEpo-suppressible upregulation of synaptic AChE-S as well as of the stress-inducible AChE-R variant, together predicting rEpo-protected cholinergic signaling and restrained inflammatory reactions. Furthermore, treatment with rEpo induced upregulation of HO-1 on mRNA, protein and activity level in the developing rat brain. Our results suggest that rEpo generates its protective effect against oxygen toxicity by a reduction of diverse oxidative stress parameters and by limiting the stressor-inducible changes in both HO-1 and cholinergic functions.

Effect of hyperoxic resuscitation on propensity of germinal matrix haemorrhage and cerebral injury

AIMS

Intraventricular haemorrhage (IVH) and cerebral injury are major neurological disorders of premature infants. The effect of hyperoxic resuscitation on the occurrence of IVH and cerebral injury is elusive. Therefore, we asked whether hyperoxia during neonatal resuscitation increased the incidence and severity of IVH and cerebral injury in premature newborns.

METHODS

Premature rabbit pups, delivered by C-section, were sequentially assigned to receive 100%, 40% or 21% oxygen for 15 or 60 min at birth. The pups were treated with intraperitoneal glycerol at 24-h postnatal age to determine the incidence and severity of glycerol-induced IVH. Vascular endothelial growth factor and angiopoietin-2 genes and protein expression, endothelial proliferation as well as free radical levels and antioxidants were assessed in the germinal matrix, white matter and cortex of pups exposed to 100% oxygen and to 21% oxygen.

RESULTS

Exposure with 100% oxygen for 1 h did not adversely exacerbate the incidence of glycerol-induced IVH in premature rabbit pups. Compared with room air, 100% oxygen enhanced mRNA expression of both vascular endothelial growth factor and angiopoietin-2 as well as reactive oxygen species levels in the germinal matrix. Hyperoxia did not affect endothelial proliferation, apoptosis or neuronal degeneration in the forebrain.

CONCLUSION

Our data suggest that 100% oxygen exposure for 1 h does not increase the risk of IVH or cerebral injury in premature rabbit pups. Although extrapolating rabbit neural developmental data into humans has obvious limitations, we speculate that hyperoxia of short duration at birth in premature infants may not result in major neurological adverse effects.

Changes of caspase-1 after the application of orthodontic forces in the periodontal tissues of rats

OBJECTIVE

To investigate the changes of caspase-1 in orthodontic tooth movement and to determine whether the changes are phase-specific.

MATERIALS AND METHODS

Eighty Wistar rats were included in this study. Sentalloy closed-coil springs were placed to induce a mesial traction force on the lower right first molar. The animals were killed after 1, 3, 7, and 14 days (n = 20 at each time point). The mandibles of 10 rats were sampled for histomorphometric analysis and immunohistochemical assay, and the periodontal tissues of 10 other rats were sampled for detecting caspase-1 mRNA and protein by real-time RT-PCR and by Western blotting, respectively.

RESULTS

The inflammatory reaction was evident in paraffin sections with hematoxylin-eosin staining. The immunohistochemical assay showed that orthodontic forces significantly increased the number of caspase-1-positive cells in the periodontal ligament (PDL). Mechanical force triggered an increase of caspase-1 mRNA in periodontal tissues. The expression of caspase-1 mRNA increased from day 1, reached the peak on day 3, and then decreased. The results of Western blotting indicated that the levels of both procaspase-1 and P20 subunit significantly increased after the application of orthodontic forces, compared with those in controls (P < .05).

CONCLUSION

Caspase-1 level increases during orthodontic tooth movement and changes with different phases, which might play a significant role in orthodontic tooth movement.

Region-specific effects on brain metabolites of hypoxia and hyperoxia overlaid on cerebral ischemia in young and old rats: a quantitative proton magnetic resonance spectroscopy study

Background

Both hypoxia and hyperoxia, deregulating the oxidative balance, may play a role in the pathology of neurodegenerative disorders underlain by cerebral ischemia. In the present study, quantitative proton magnetic resonance spectroscopy was used to evaluate regional metabolic alterations, following a 24-hour hypoxic or hyperoxic exposure on the background of ischemic brain insult, in two contrasting age-groups of rats: young - 3 months old and aged - 24 months old.

Methods

Cerebral ischemia was induced by ligation of the right common carotid artery. Concentrations of eight metabolites (alanine, choline-containing compounds, total creatine, γ-aminobutyric acid, glutamate, lactate, myo-inositol and N-acetylaspartate) were quantified from extracts in three different brain regions (fronto-parietal and occipital cortices and the hippocampus) from both hemispheres.

Results

In the control normoxic condition, there were significant increases in lactate and myo-inositol concentrations in the hippocampus of the aged rats, compared with the respective values in the young ones. In the ischemia-hypoxia condition, the most prevalent changes in the brain metabolites were found in the hippocampal regions of both young and aged rats; but the effects were more evident in the aged animals. The ischemia-hyperoxia procedure caused less dedicated changes in the brain metabolites, which may reflect more limited tissue damage.

Conclusions

We conclude that the hippocampus turns out to be particularly susceptible to hypoxia overlaid on cerebral ischemia and that old age further increases this susceptibility.

Triggers of apoptosis in the immature brain

Apoptosis occurs physiologically in the mammalian brain during the period of the growth spurt, which in human starts in the 3rd trimester of gestation and ends by the third year of life. Environmental factors can interact with programmed cell death mechanisms to increase the number of neurons undergoing apoptosis and thus produce neuropathological sequelae in the brain. In a series of studies it could be shown that classes of drugs which block N-methyl-D-aspartate (NMDA) glutamate receptors, promote gamma-aminobutyric-acid (GABA(A)) receptor activation or block voltage gated sodium channels, when administered to immature rodents during the period of the brain growth spurt, trigger widespread apoptotic neurodegeneration throughout the developing brain. Studies have also shown that short exposures to non-physiologic oxygen levels can trigger apoptotic neurodegeneration in the brains of infant rodents. Pathomechanisms involved in the proapoptotic action of sedative and anticonvulsant drugs and oxygen include decreased expression of neurotrophins, inactivation of survival signaling proteins, activation of inflammatory cytokines as well as oxidative stress. These findings raise concerns pertaining to the treatment of infants and young children with sedative and anticonvulsant drugs and premature infants with oxygen. The experimental findings imply that new approaches should be developed for patients within these vulnerable age groups.

A critical role for Fas/CD-95 dependent signaling pathways in the pathogenesis of hyperoxia-induced brain injury

OBJECTIVE

Prematurely born infants are at risk for development of neurocognitive impairment in later life. Oxygen treatment has been recently identified as a trigger of neuronal and oligodendrocyte apoptosis in the developing rodent brain. We investigated the role of the Fas death receptor pathway in oxygen-triggered developmental brain injury.

METHODS

Six-day-old Wistar rats were exposed to 80% oxygen for various periods (2, 6, 12, 24, 48, and 72 hours), and mice deficient in either Fas (B6.MRL-Tnfrsf6(lpr)) or Fas ligand (B6Smn.C3-Fasl(gld)) and control mice (C57BL/6J) were exposed to 80% oxygen for 24 hours. Polymerase chain reaction, Western blotting, and caspase activity assays of thalamus and cortex tissue were performed.

RESULTS

Fas and Fas ligand messenger RNA and protein were upregulated. Furthermore, hyperoxia resulted in induction of downstream signaling events of Fas, such as Fas-associated death domain (FADD), the long and short form of FADD-like interleukin-1beta-converting enzyme (FLICE) inhibitory protein (FLIP-L, FLIP-S), and cleavage of caspase-8 and caspase-3. Injection of a selective caspase-8 inhibitor (TRP801, 1mg/kg) at the beginning of hyperoxia blocked subsequent caspase-3 cleavage in this model. B6.MRL-Tnfrsf6(lpr) mice were protected against oxygen-mediated injury, confirming Fas involvement in hyperoxia-induced cell death. Mice deficient in Fas ligand did not differ from control animals in the amount of cell death.

INTERPRETATION

We conclude that neonatal hyperoxia triggers Fas receptor and its downstream signaling events in a Fas ligand-independent fashion. Lack of functional Fas receptors and selective pharmacological inhibition of caspase-8 prevents activation of caspase-3 and provides significant neuroprotection.

Erythropoietin protects the developing brain from hyperoxia-induced cell death and proteome changes

OBJECTIVE

Oxygen toxicity has been identified as a risk factor for adverse neurological outcome in survivors of preterm birth. In infant rodent brains, hyperoxia induces disseminated apoptotic neurodegeneration. Because a tissue-protective effect has been observed for recombinant erythropoietin (rEpo), widely used in neonatal medicine for its hematopoietic effect, we examined the effect of rEpo on hyperoxia-induced brain damage.

METHODS

Six-day-old C57Bl/6 mice or Wistar rats were exposed to hyperoxia (80% O(2)) or normoxia for 24 hours and received rEpo or normal saline injections intraperitoneally. The amount of degenerating cells in their brains was determined by DeOlmos cupric silver staining. Changes of their brain proteome were determined through two-dimensional electrophoresis and mass spectrometry. Western blot, enzyme activity assays and real-time polymerase chain reaction were performed for further analysis of candidate proteins.

RESULTS

Systemic treatment with 20,000 IE/kg rEpo significantly reduced hyperoxia-induced apoptosis and caspase-2, -3, and -8 activity in the brains of infant rodents. In parallel, rEpo inhibited most brain proteome changes observed in infant mice when hyperoxia was applied exclusively. Furthermore, brain proteome changes after a single systemic rEpo treatment point toward a number of mechanisms through which rEpo may generate its protective effect against oxygen toxicity. These include reduction of oxidative stress and restoration of hyperoxia-induced increased levels of proapoptotic factors, as well as decreased levels of neurotrophins.

INTERPRETATION

These findings are highly relevant from a clinical perspective because oxygen administration to neonates is often inevitable, and rEpo may serve as an adjunctive neuroprotective therapy.

Ritonavir and disulfiram have potential to inhibit caspase-1 mediated inflammation and reduce neurological sequelae after minor blast exposure

Caspase-1 triggers cytokine release following acceleration-induced concussive head injury. Minor blast injury in which no physical tissue injury occurs, results in the release of cytokines in a similar fashion. Ritonavir, a generically available protease inhibitor with a benign short-term side-effect profile, has been shown to inhibit expression of caspase-1. We review the relevant literature and propose that ritonavir may be of benefit in reducing adverse neuropsychiatric outcomes and hastening recovery following mild blast injury. Further research in animal models of blast injury followed by clinical studies would determine whether this therapy is effective.

Suramin induces and enhances apoptosis in a model of hyperoxia-induced oligodendrocyte injury

Recent evidence suggests oxygen as a powerful trigger for cell death in the immature white matter, leading to periventricular leukomalacia (PVL) as a cause of adverse neurological outcome in survivors of preterm birth. This oligodendrocyte (OL) death is associated with oxidative stress, upregulation of apoptotic signaling factors (i.e., Fas, caspase-3) and decreased amounts of neurotrophins. In search of neuroprotective strategies we investigated whether the polysulfonated urea derivative suramin, recently identified as a potent inhibitor of Fas signaling, affords neuroprotection in an in vitro model of hyperoxia-induced injury to immature oligodendrocytes. Immature OLs (OLN-93) were subjected to 80% hyperoxia (48 h) in the presence or absence of suramin (0, 30, 60, 120 microM). Cell death was assessed by flow cytometry (Annexin V, caspase-3 activity assay) and immunohistochemistry for activated caspase-3. Immunoblotting for the death receptor Fas, cleaved caspase-8 and the phosphorylated isoform of the serine-threonin kinase Akt (pAkt) was performed. Suramin lead to OL apoptosis and potentiated hyperoxia-induced injury in a dose-dependent manner. Immunoblotting revealed increased Fas and caspase-8 expression by suramin treatment. This effect was significantly enhanced when suramin was combined with hyperoxia. Furthermore, pAkt levels decreased following suramin exposure, indicating interference with neurotrophin-dependent growth factor signaling. These data indicate that suramin causes apoptotic cell death and aggravates hyperoxia-induced cell death in immature OLs. Its mechanism of action includes an increase of previously described hyperoxia-induced expression of pro-apoptotic factors and deprivation of growth factor dependent signaling components.

Cytokines and myelination in the central nervous system

Myelin abnormalities that reflect damage to developing and mature brains are often found in neurological diseases with evidence of inflammatory infiltration and microglial activation. Many cytokines are virtually undetectable in the uninflamed central nervous system (CNS), so that their rapid induction and sustained elevation in immune and glial cells contributes to dysregulation of the inflammatory response and neural cell homeostasis. This results in aberrant neural cell development, cytotoxicity, and loss of the primary myelin-producing cells of the CNS, the oligodendrocytes. This article provides an overview of cytokine and chemokine activity in the CNS with relevance to clinical conditions of neonatal and adult demyelinating disease, brain trauma, and mental disorders with observed white matter defects. Experimental models that mimic human disease have been developed in order to study pathogenic and therapeutic mechanisms, but have shown mixed success in clinical application. However, genetically altered animals, and models of CNS inflammation and demyelination, have offered great insight into the complexities of neuroimmune interactions that impact oligodendrocyte function. The intracellular signaling pathways of selected cytokines have also been highlighted to illustrate current knowledge of receptor-mediated events. By learning to interpret the actions of cytokines and by improving methods to target appropriate predictors of disease risk selectively, a more comprehensive understanding of altered immunoregulation will aid in the development of advanced treatment options for patients with inflammatory white matter disorders.

Effect of erythropoietin on oxygen-induced brain injury in the newborn rat

The developing nervous system is sensitive to supraphysiological oxygen concentrations. Recent studies showed that exposure to hyperoxia in infant rats leads to extensive apoptotic degeneration in the cortex and white matter of the developing brain. A wide variety of experimental studies have shown that erythropoietin exerts a remarkable neuroprotection in both cell cultures and in animal models of nervous system disorders. In the present study, we investigated the effect of erythropoietin against hyperoxia-induced neurodegeneration in the developing brain. Eighteen Wistar rat pups were divided into three groups: control group, hyperoxia+saline-treated group and hyperoxia+erythropoietin-treated group. Hyperoxia groups were exposed to 80% oxygen (n=12) in a plexiglas chamber in which the oxygen concentration was monitored twice daily from birth until postnatal day 5. Hyperoxia exposure was 24h/day for 5 days. The hyperoxia+erythropoietin group received an intraperitoneal injection of recombinant human erythropoietin at a dose of 1000U/(kgday). At postnatal day 5, all animals were sacrificed. Neuronal cell death and apoptosis were evaluated. Histopathological examination showed that erythropoietin significantly diminished apoptosis in the CA1 region and dentate gyrus of hippocampus and parietal cortex in hyperoxia+erythropoietin-treated group. Regarding the safety profile of erythropoietin in premature and mature infants, this agent may be potentially beneficial in preventing hyperoxic brain injury.

Comprehensive evaluation of positional candidates in the IL-18 pathway reveals suggestive associations with schizophrenia and herpes virus seropositivity

Interactions between genetic variation and environmental factors have been invoked in schizophrenia genesis, but pathways linking them are uncertain. We used a pathway-oriented approach to evaluate six genes mediating IL18 function (IL-18, IL18BP, IL18R1, IL18RAP, IL12B, and IL12A). The first five are also localized to regions previously linked with schizophrenia. Fifty-four representative tag SNPs were selected from comprehensive sequence data and genotyped in 478 patients with schizophrenia/schizoaffective disorder (DSM IV criteria) and 501 unscreened control individuals. Exposure to three herpes viruses previously suggested as risk factors for schizophrenia was estimated simultaneously among the cases. Five SNPs in four genes were associated with schizophrenia, most prominently rs2272127 at IL18RAP (P = 0.0007, odds ratio for C allele 1.49, 95% CI: 1.18-1.87; P = 0.03 following correction for multiple comparisons). Exploratory analysis revealed that rs2272127 was also associated with herpes simplex virus 1 (HSV1) seropositivity in cases (P = 0.04, OR for G allele 1.58, 95% CI: 1.04-2.39). Similar patterns were observed at another correlated SNP (rs11465702, P = 0.005 and 0.006, respectively for associations with schizophrenia and HSV1 seropositivity). We suggest plausible, testable hypotheses linking IL-18 signaling and HSV1 in schizophrenia pathogenesis.

Hyperoxia causes maturation-dependent cell death in the developing white matter

Periventricular leukomalacia is the predominant injury in the preterm infant leading to cerebral palsy. Oxygen exposure may be an additional cause of brain injury in these infants. In this study, we investigated pathways of maturation-dependent oligodendrocyte (OL) death induced by hyperoxia in vitro and in vivo. Developing and mature OLs were subjected to 80% oxygen (0-24 h). Lactate dehydrogenase (LDH) assay was used to assess cell viability. Furthermore, 3-, 6-, and 10-d-old rat pups were subjected to 80% oxygen (24 h), and their brains were processed for myelin basic protein staining. Significant cell death was detected after 6-24 h incubation in 80% oxygen in pre-OLs (O4+,O1-), but not in mature OLs (MBP+). Cell death was executed by a caspase-dependent apoptotic pathway and could be blocked by the pan-caspase inhibitor zVAD-fmk. Overexpression of BCL2 (Homo sapiens B-cell chronic lymphocytic leukemia/lymphoma 2) significantly reduced apoptosis. Accumulation of superoxide and generation of reactive oxygen species (ROS) were detected after 2 h of oxygen exposure. Lipoxygenase inhibitors 2,3,5-trimethyl-6-(12-hydroxy-5-10-dodecadiynyl-1,4-benzoquinone and N-benzyl-N-hydroxy-5-phenylpentamide fully protected the cells from oxidative injury. Overexpression of superoxide dismutase (SOD1) dramatically increased injury to pre-OLs but not to mature OLs. We extended these studies by testing the effects of hyperoxia on neonatal white matter. Postnatal day 3 (P3) and P6 rats, but not P10 pups, showed bilateral reduction in MBP (myelin basic protein) expression with 24 h exposure to 80% oxygen. Hyperoxia causes oxidative stress and triggers maturation-dependent apoptosis in pre-OLs, which involves the generation of ROS and caspase activation, and leads to white matter injury in the neonatal rat brain. These observations may be relevant to white matter injury observed in premature infants.

Myelin expression is altered in the brains of neonatal rats reared in a fluctuating oxygen atmosphere

BACKGROUND

Preterm infants receiving supplemental oxygen therapy experience frequent fluctuations in their blood oxygen levels, the magnitude of which has been associated with the incidence and severity of retinopathy of prematurity in such infants.

OBJECTIVE

Our objective was to investigate in a relevant animal model whether the immature brain with its poorly vascularised white matter might also be susceptible to injury when exposed to such fluctuations in blood oxygen.

METHODS

Newborn rats were reared in an atmosphere in which a computer reproduced the oxygen fluctuations derived from the transcutaneous oxygen levels of a 24-week preterm infant who had developed severe retinopathy. Following 14 days of exposure, we measured the expression of active caspase-3, myelin basic protein (MBP) and glial fibrillary acidic protein (GFAP) in the brains comparing with rat pups raised in room air.

RESULTS

Compared to room air controls, at day 14, the expression of active caspase-3 was increased by up to 162% (significant increase in 7 of 9 regions), MBP decreased by up to 70% (significant in the hypothalamus only) and GFAP increased by up to 103% (significant in 6 of 7 regions. On day 21, following 7 days of reparative recovery, GFAP levels in most areas of oxygen-exposed brains had returned to near control levels. There were no longer significant differences in caspase-3 levels apart from the cerebral cortex, cerebellum and striatum. In contrast, MBP expression was now much higher in most regions of the treated brains compared to controls.

CONCLUSION

We conclude that fluctuations in blood oxygen, observed in preterm survivors, may constitute a source of injury to the white matter and corpus striatum of the developing brain and contribute to the neurological sequelae in extremely premature infants.

Early growth in brain volume is preserved in the majority of preterm infants

OBJECTIVE

Preterm infants have reduced cerebral tissue volumes in adolescence. This study addresses the question: Is reduced global brain growth in the neonatal period inevitable after premature birth, or is it associated with specific medical risk factors?

METHODS

Eighty-nine preterm infants at term equivalent age without focal parenchymal brain lesions were studied with 20 full-term control infants. Using a deformation-based morphometric approach, we transformed images to a reference anatomic space, and we used the transformations to calculate whole-brain volume and ventricular volume for each subject. Patterns of volume difference were correlated with clinical data.

RESULTS

Cerebral volume is not reduced compared with term born control infants (p = 0.765). Supplemental oxygen requirement at 28 postnatal days is associated with lower cerebral tissue volume at term (p < 0.001), but there were no significant differences in cerebral volumes attributable to perinatal sepsis (p = 0.515) and quantitatively defined diffuse white matter injury (p = 0.183). As expected, the ventricular system is significantly larger in preterm infants at term equivalent age compared with term control infants (p < 0.001).

INTERPRETATION

Cerebral volume is not reduced during intensive care for the majority of preterm infants, but prolonged supplemental oxygen dependence is a risk factor for early attenuation of global brain growth. The reduced cerebral tissue volume seen in adolescents born preterm does not appear to be an inevitable association of prematurity, but rather caused by either specific disease during intensive care or factors operating beyond the neonatal period.

Long-term histological outcome after post-hypoxic treatment with 100% or 40% oxygen in a model of perinatal hypoxic-ischemic brain injury

Hypoxic newborns have traditionally been given supplemental oxygen, and until recently, guidelines for neonatal resuscitation recommended that 100% oxygen be used. Exposure to 100% oxygen after hypoxic injury, however, may exacerbate oxidative stress. The current study evaluated the effect of exposure to 100, 40 or 21% oxygen after neonatal hypoxic-ischemic injury on the severity of brain injury after long-term survival. The severity of histological brain injury was not different in animals exposed to 100% oxygen versus room air. Male animals treated with 40% oxygen post-hypoxia had the lowest mean total histology scores, but this was not statistically significant due to the large variation in injury within each treatment group. These results support the growing number of studies in human infants and experimental animals that show no benefit of 100% oxygen over room air for neonatal resuscitation. Our results suggest that post-hypoxia treatment with 40% oxygen may be beneficial, particularly in males. Further studies of the effects of different concentrations of oxygen on brain injury are warranted and should have sufficient power to examine sex differences.

TLR8: an innate immune receptor in brain, neurons and axons

Toll-like receptors (TLRs) play essential roles in generating innate immune responses, and are evolutionarily conserved across species. In mammals, TLRs specifically recognize the conserved microbial structural motifs referred to as pathogen-associated molecular patterns (PAMPs). Ligand recognition by TLRs activates signaling cascades that culminate in proinflammatory cytokine production and eventual elimination of invading pathogens. Although TLRs in mammals are expressed predominantly in the immune system, certain TLRs with poorly characterized function are also found in neurons. We recently profiled TLR8 expression during mouse brain development and established its localization in neurons and axons. We uncovered a novel role for TLR8 as a suppressor of neurite outgrowth as well as an inducer of neuronal apoptosis, and found that TLR8 functions in neurons through an NF-kappaB-independent mechanism. These findings add a new layer of complexity for TLR signaling, and expand the realm of mammalian TLR function to the CNS beyond the originally discovered immune context. Herein, we complement our earlier report with additional data, discuss their biological and mechanistic implications in central nervous system (CNS) developmental and pathological processes, and thus further our perspective on TLR signaling and potential physiological roles in mammals.

Estradiol attenuates hyperoxia-induced cell death in the developing white matter

OBJECTIVE

Periventricular leukomalacia is the predominant type of brain injury in preterm infants underlying the development of cerebral palsy. Periventricular leukomalacia has its peak incidence at 23 to 32 weeks postconceptional age characterized by extensive oligodendrocyte migration and maturation. Oxygen toxicity has been identified as a possible contributing factor to the pathogenesis of cerebral palsy in survivors of preterm birth. 17beta-estradiol (E2) is important for the development and function of the central nervous system. Furthermore, neuroprotective properties have been attributed to estrogens. We examined the effect of E2 on hyperoxia-induced cell death in the developing white matter in the rat brain.

METHODS

Six-day-old (P6) rat pups, the immature oligodendroglial cell line (OLN-93), and primary oligodendrocyte cultures were subjected to 80% O(2) in the presence or absence of E2 (600 microg/kg intraperitoneally in vivo, 10(-6)-10(-10)M in vitro). Cell counts and lactate dehydrogenase assay were used to assess cell survival. Immunoblot analysis was used for detection of estrogen receptor expression and investigation of apoptotic signaling pathways. White matter injury was assessed by myelin basic protein immunocytochemistry at P11.

RESULTS

E2 produced significant dose-dependent protection against oxygen-induced apoptotic cell death in primary oligodendrocytes. Treatment with E2 prevented hyperoxia-induced proapoptotic Fas-upregulation and caspase-3 activation. Finally, E2 antagonized hyperoxia-induced inactivation of extracellular signal-regulated kinase 1 and 2 and Akt, key kinases of the mitogen-activated protein kinase and phosphatidylinositol 3-kinase cell survival promoting pathways, respectively. Loss of myelin basic protein labeling was seen in P11 pups after oxygen exposure, and E2 attenuated this injury.

INTERPRETATION

These results suggest a possible role for estrogens in the prevention of neonatal oxygen-induced white matter injury.

Cerebral inflammatory response after fetal asphyxia and hyperoxic resuscitation in newborn sheep

Resuscitation with pure oxygen at birth after fetal asphyxia may aggravate brain damage by inducing pro-inflammation. The toll-like receptors (TLRs) may serve a pro-inflammatory role in hyperoxemia during ischemia-reperfusion. Sixteen near-term fetal sheep (132-136 d) were subjected to 10 min of cord occlusion, delivery and mechanical ventilation with 100% O2 (n = 8), or 21% O2 (n = 8) for 30 min followed by normoxemia for 90 min. Eight sheep fetuses were delivered immediately with inspired O2 targeted at normoxemia for 120 min (controls). Levels and distributions of mRNAs for IL-1beta, TNF-alpha, IL-12p40, IL-18, IL-6, IL-10, IFN-gamma, TLR-2, -3 and -4 in cerebral tissue at 2 h after birth were evaluated with real-time polymerase chain reaction (PCR) and in situ hybridization. Expressions of IL-1beta, IL-12p40, TLR-2, and TLR-4 were increased in cortex/subcortex after resuscitation with 100% O2 compared with 21% O2 (all p < 0.05) and to controls (all p < 0.05). Increased cellular expression of IL-1beta was localized to sub-meningeal cortical layers and to sub-cortical white matter. Hyperoxic resuscitation at birth following fetal asphyxia induces a cerebral pro-inflammatory response with an up-regulation of TLR-2 and -4. These may be early events leading to increased tissue damage after exposure to hyperoxemia at birth.

Oxygen as a neonatal health hazard: call for détente in clinical practice

Education in oxygenation and in how oxygen is given to newborns needs to increase. Treatment with oxygen should no longer be considered proverbial and customary, regardless of our 'past experience' or consensus recommendations in clinical guidelines, since oxygen may lead to acute or chronic health effects.

CONCLUSION

Inappropriate oxygen use is a neonatal health hazard associated with aging, DNA damage and cancer, retinopathy of prematurity, injury to the developing brain, infection and others. Neonatal exposure to pure O2, even if brief, or to pulse oximetry >95% when breathing supplemental O2 must be avoided as much as possible.

Interleukin-1beta, interleukin-18, and interferon-gamma expression in the cerebrospinal fluid of premature infants with posthemorrhagic hydrocephalus--markers of white matter damage?

Posthemorrhagic hydrocephalus (PHHC) represents a major complication of preterm birth. The aim of this study was to determine whether cerebrospinal fluid (CSF) levels of the pro-inflammatory cytokines IL-1beta, IL-18, and interferon (IFN)-gamma are altered in the CSF of preterm infants with PHHC and may serve as a marker of white matter damage (WMD). Twenty-seven preterm infants with PHHC were included in the study; 13 of them had signs of cystic WMD (cWMD) on ultrasound examinations. CSF sample 1 was obtained at first ventriculostomy, sample 2 at shunt implantation. Results were compared with a control group of 20 age-matched patients without neurologic diseases. IL-1beta concentrations were elevated in CSF sample 1 of PHHC patients without WMD and in sample 1 of patients with cWMD. Concentrations of IL-18 were increased in both samples of patients without WMD and in sample 2 of patients with cWMD. CSF levels of IFN-gamma were elevated in sample 1 of PHHC patients with cWMD. The pro-inflammatory cytokine IL-1beta and IL-18 levels in the CSF are elevated in patients with PHHC. Higher IFN-gamma levels are detected in a subgroup of patients developing cWMD, indicating its involvement in the pathogenesis of cWMD in the context of PHHC.

Activation of caspase-1 dependent interleukins in developmental brain trauma

Focal mechanical cortical trauma triggers diffuse apoptotic neurodegeneration in the developing rat brain which is associated with invasion of brain tissue with inflammatory mediators. We hypothesized that caspase-1 and the two caspase-1-processed cytokines, interleukin (IL)-1beta and IL-18, are involved in trauma-induced neuronal cell death in the developing brain. 7-day-old Wistar rats or C57/BL6 mice were subjected to head trauma using a weight drop device. Animals were sacrificed at defined time points following trauma and brains were processed for histology and molecular analyses. Neuronal cell death in the immature brain peaked at 12-24 h and was accompanied by a marked increase of mRNA and protein levels for caspase-1, IL-1beta and IL-18 within 2 to 12 h following the injury. Caspase-1 levels were elevated for 72 h, whereas IL-1beta decreased earlier at 48 h. IL-18 remained high over a period of 3 days and decreased to normal levels by day 7 after the injury. Intraperitoneal injection of recombinant human IL-18-binding protein (IL-18BP), a specific inhibitor of IL-18, attenuated traumatic brain injury. Mice deficient in IL-18 (IL-18-/-) were protected against trauma-induced brain damage. These findings indicate that IL-18 is involved in trauma-induced neuronal cell death in the immature rodent brain and might serve as a potential therapeutic target.

Maturation-dependent oligodendrocyte apoptosis caused by hyperoxia

In the immature human brain, periventricular leukomalacia (PVL) is the predominant white matter injury underlying the development of cerebral palsy. PVL has its peak incidence during a well-defined period in human brain development (23-32 weeks postconceptional age) characterized by extensive oligodendrocyte migration and maturation. We hypothesized that the dramatic rise of oxygen tissue tension associated with mammalian birth and additional oxygen exposure of the preterm infant during intensive care may be harmful to immature oligodendrocytes (OLs). We therefore investigated the effects of hyperoxia on rat oligodendroglia cells in vitro and in vivo. Immature OLs (OLN-93), their progenitors [preoligodendrocytes (pre-OL)], and mature OLs were subjected to 80% hyperoxia (24-96 hr). Flow cytometry was used to assess cell death. Cell viability was measured by metabolism of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium (MTT). In addition, 6-day-old rat pups were subjected to 80% oxygen (24 hr) and then sacrificed, and their brains were processed for immunfluorescence staining. Apoptosis was detected at various stages (annexin-V, activated caspase-3) after 24-48 hr of incubation in 80% oxygen in pre- and immature OLs. Mature OLs were resistant to oxygen exposure. These results were confirmed by MTT assay. This cell death was blocked by administration of the pan-caspase inhibitor zVAD-fmk. Degeneration of OLs was confirmed in 7-day-old rat brains by positive staining for activated caspase-3. Hyperoxia triggers maturation-dependent apoptosis in immature and pre-OLs and involves caspase activation. This mechanism may be relevant to the white matter injury observed in infants born preterm.

The role of caspases in photoreceptor cell death of the retinoschisin-deficient mouse

Early schisis cavities in the retinal bipolar cell layer accompanied by progressive loss of cone and rod photoreceptor cells are the hallmark of the retinoschisin-deficient (Rs1h(-/Y)) murine retina. With this study we aimed at elucidating the molecular events underlying the photoreceptor cell death in this established murine model of X-linked juvenile retinoschisis. We show that photoreceptor degeneration in the Rs1h(-/Y) mouse is due to apoptotic events peaking around postnatal day 18. Cell death is accompanied by increased expression of initiator and inflammatory caspases but not by downstream effector caspases. The strong induction of caspase-1 (Casp1) prompted us to explore its involvement in the apoptotic process. We therefore generated double knock-out mice deficient for both retinoschisin and Casp1. No direct influence of the Casp1 genotype on apoptosis could be identified although striking differences in the overall number of resident microglia were observed independent of the Rs1h genotype.

Acute and long-term proteome changes induced by oxidative stress in the developing brain

The developing mammalian brain experiences a period of rapid growth during which various otherwise innocuous environmental factors cause widespread apoptotic neuronal death. To gain insight into developmental events influenced by a premature exposure to high oxygen levels and identify proteins engaged in neurodegenerative and reparative processes, we analyzed mouse brain proteome changes at P7, P14 and P35 caused by an exposure to hyperoxia at P6. Changes detected in the brain proteome suggested that hyperoxia leads to oxidative stress and apoptotic neuronal death. These changes were consistent with results of histological and biochemical evaluation of the brains, which revealed widespread apoptotic neuronal death and increased levels of protein carbonyls. Furthermore, we detected changes in proteins involved in synaptic function, cell proliferation and formation of neuronal connections, suggesting interference of oxidative stress with these developmental events. These effects are age-dependent, as they did not occur in mice subjected to hyperoxia in adolescence.

IL-18: a key player in neuroinflammation and neurodegeneration?

Interleukin (IL)-18 is a potent inflammatory cytokine of the IL-1 family. It is synthesized as an inactive precursor (pro-IL-18), which is cleaved into its functionally active form by caspase-1. Resident cells of the CNS express IL-18 and caspase-1 constitutively, thus providing a local IL-18-dependent immune response. Recent studies have highlighted a crucial role for IL-18 in mediating neuroinflammation and neurodegeneration in the CNS under pathological conditions, such as bacterial and viral infection, autoimmune demyelinating disease, and hypoxic-ischemic, hyperoxic and traumatic brain injuries. This review provides a synopsis of the current knowledge of IL-18-dependent mechanisms of action during acute neurodegeneration in immature and adult brains.