Immunohistochemical expression of tumor necrosis factor alpha in neonatal leukomalacia

Maternal N-Acetyl-Cysteine Prevents Neonatal Hypoxia-Induced Brain Injury in a Rat Model

Perinatal hypoxia is a major cause of infant brain damage, lifelong neurological disability, and infant mortality. N-Acetyl-Cysteine (NAC) is a powerful antioxidant that acts directly as a scavenger of free radicals. We hypothesized that maternal-antenatal and offspring-postnatal NAC can protect offspring brains from hypoxic brain damage.Sixty six newborn rats were randomized into four study groups. Group 1: Control (CON) received no hypoxic intervention. Group 2: Hypoxia (HYP)-received hypoxia protocol. Group 3: Hypoxia-NAC (HYP-NAC). received hypoxia protocol and treated with NAC following each hypoxia episode. Group 4: NAC Hypoxia (NAC-HYP) treated with NAC during pregnancy, pups subject to hypoxia protocol. Each group was evaluated for: neurological function (Righting reflex), serum proinflammatory IL-6 protein levels (ELISA), brain protein levels: NF-κB p65, neuronal nitric oxide synthase (nNOS), TNF-α, and IL-6 (Western blot) and neuronal apoptosis (histology evaluation with TUNEL stain). Hypoxia significantly increased pups brain protein levels compared to controls. NAC administration to dams or offspring demonstrated lower brain NF-κB p65, nNOS, TNF-α and IL-6 protein levels compared to hypoxia alone. Hypoxia significantly increased brain apoptosis as evidenced by higher grade of brain TUNEL reaction. NAC administration to dams or offspring significantly reduce this effect. Hypoxia induced acute sensorimotor dysfunction. NAC treatment to dams significantly attenuated hypoxia-induced acute sensorimotor dysfunction. Prophylactic NAC treatment of dams during pregnancy confers long-term protection to offspring with hypoxia associated brain injury, measured by several pathways of injury and correlated markers with pathology and behavior. This implies we may consider prophylactic NAC treatment for patients at risk for hypoxia during labor.

Fetal neuroprotective mechanism of maternal magnesium sulfate for late gestation inflammation: in a rodent model

Background: Maternal administration of magnesium sulfate (Mg) is used in humans to protect the fetal brain during preterm delivery. We sought to determine the neuroprotective mechanism of Mg in a rat model of late gestation maternal inflammation.Methods: Pregnant rats at 20 d of gestation (20 total, four groups, N = 5 in each group) received i.p. LPS or saline. Dams were randomized for s.c. saline or Mg supplementation 2 h prior and following the LPS/saline injections. Dams were sacrificed 4 h following the last treatment. Fetal brains were collected from the four treatment groups. Fetal brain caspase 3 active form, NF-kB p65, neuronal nitric oxide synthase (phospho-nNos), and proinflammatory cytokines levels were determined by western blot.Results: Maternal LPS at e20 significantly (p < .01) increased fetal brain caspase 3 active form (af) (0.27 ± 0.02 versus 0.15 ± 0.06u), NFkB (0.23 ± 0.01 versus 0.13 ± 0.01u), and phospho-nNOS (0.22 ± 0.01 versus 0.12 ± 0.01u) and fetal brain proinflammatory cytokines (IL-6 0.21 ± 0.01 versus 0.11 ± 0.01 u; TNFα 0.29 ± 0.01 versus 0.15 ± 0.01u), compared with control fetuses. Mg treatment significantly (p < .05) reduced fetal brain caspase 3 af (0.16 ± 0.01u), NFkB p65 (0.11 ± 0.01u), phospho-nNOS (0.1 ± 0.01u), as well as brain proinflammatory cytokines (IL-6 0.07 ± 0.01u; TNFα 0.15 ± 0.01u) to levels similar to controls.Conclusion: Maternal inflammation-induced fetal brain injury at late gestation may be mediated by the activation of inflammatory response, oxidative stress, and apoptosis. Maternal Mg may attenuate the injury by inhibition of these putative pathways.

mTOR pathway inhibition prevents neuroinflammation and neuronal death in a mouse model of cerebral palsy

BACKGROUND AND PURPOSE

Mammalian target of rapamycin (mTOR) pathway signaling governs cellular responses to hypoxia and inflammation including induction of autophagy and cell survival. Cerebral palsy (CP) is a neurodevelopmental disorder linked to hypoxic and inflammatory brain injury however, a role for mTOR modulation in CP has not been investigated. We hypothesized that mTOR pathway inhibition would diminish inflammation and prevent neuronal death in a mouse model of CP.

METHODS

Mouse pups (P6) were subjected to hypoxia-ischemia and lipopolysaccharide-induced inflammation (HIL), a model of CP causing neuronal injury within the hippocampus, periventricular white matter, and neocortex. mTOR pathway inhibition was achieved with rapamycin (an mTOR inhibitor; 5mg/kg) or PF-4708671 (an inhibitor of the downstream p70S6kinase, S6K, 75 mg/kg) immediately following HIL, and then for 3 subsequent days. Phospho-activation of the mTOR effectors p70S6kinase and ribosomal S6 protein and expression of hypoxia inducible factor 1 (HIF-1α) were assayed. Neuronal cell death was defined with Fluoro-Jade C (FJC) and autophagy was measured using Beclin-1 and LC3II expression. Iba-1 labeled, activated microglia were quantified.

RESULTS

Neuronal death, enhanced HIF-1α expression, and numerous Iba-1 labeled, activated microglia were evident at 24 and 48 h following HIL. Basal mTOR signaling, as evidenced by phosphorylated-S6 and -S6K levels, was unchanged by HIL. Rapamycin or PF-4,708,671 treatment significantly reduced mTOR signaling, neuronal death, HIF-1α expression, and microglial activation, coincident with enhanced expression of Beclin-1 and LC3II, markers of autophagy induction.

CONCLUSIONS

mTOR pathway inhibition prevented neuronal death and diminished neuroinflammation in this model of CP. Persistent mTOR signaling following HIL suggests a failure of autophagy induction, which may contribute to neuronal death in CP. These results suggest that mTOR signaling may be a novel therapeutic target to reduce neuronal cell death in CP.

Effect of dexamethasone administered with magnesium sulfate on inflammation-mediated degradation of the blood-brain barrier using an in vitro model

Patients at risk for preterm delivery are frequently administered both antenatal steroids for fetal maturation and magnesium sulfate for neuroprotection. In this study, we investigate whether steroids coadministered with magnesium sulfate preserve blood-brain barrier integrity in neuroinflammation. Human umbilical vein endothelial cells were grown in astroglial conditioned media in a 2-chamber cell culture apparatus. Treatment with tumor necrosis factor-α (TNF-α) or catalytically active recombinant matrix metalloproteinase 9 (MMP-9) simulated neuroinflammation. Membrane integrity was assessed by zona occludens 1 (ZO-1) immunoreactivity, permeability to fluorescently conjugated dextran, and transendothelial electrical resistance (TEER). The TNF-α and MMP-9 treatment increased the rate of dextran transit, decreased TEER, and decreased ZO-1 immunoreactivity at junctional interfaces. Dexamethasone pretreatment alone or in combination with 0.5 mmol/L magnesium sulfate preserved monolayer integrity after inflammatory insult. Magnesium sulfate alone was not protective. This study supports a possible interaction between steroids and magnesium in neuroprotection.

Models of fetal brain injury, intrauterine inflammation, and preterm birth

Intrauterine infection and inflammation are known risk factors for brain damage in the neonate irrespective of the gestational age. Infection-induced maternal immune activation leads to a fetal inflammatory response mediated by cytokines that has been implicated in the development of not only periventricular leukomalacia and cerebral palsy but also a spectrum of neurodevelopmental disorders such as autism and schizophrenia (Behav Brain Res 2009; 204:313, Ann Neurol 2005; 57:67, Am J Obstet Gynecol 2000; 182:675). A common link among the neurobehavioral disorders associated with intrauterine inflammation appears to be the evidence for immune dysregulation in the developing brain (Behav Brain Res 2009; 204:313). The timing of the immune challenge with respect to the gestational age and neurologic development of the fetus may be crucial in the elicited response (J Neurosci 2006; 26:4752). Studies involving animal models of maternal inflammation serve a key role in elucidation of mechanisms involved in fetal brain injury associated with exposure to the maternal milieu. These animal models have been shown to result in fetal microglial activation, neurotoxicity as well motor deficits and behavioral abnormalities in the offspring (J Neurosci 2006; 26:4752, J Neurosci Res 2010; 88:172, Am J Obstet Gynecol 2009; 201:279, Am J Obstet Gynecol 2008; 199:651). A better understanding of the mechanisms of perinatal brain injury will allow discoveries of novel neuroprotective agents, better outcomes following preterm birth and stratification of fetuses and neonates for therapies in cases of preterm birth, preterm premature rupture of membranes, and chorioamnionitis.

Genetic variations in fetal and maternal tumor necrosis factor-α and interleukin 10: is there an association with preterm birth or periventricular leucomalacia?

OBJECTIVE

The aim of the study was to identify whether tumor necrosis factor-α (TNF-α) (-308) and interleukin (IL)-10 (-1082; -819) genotypes were associated with preterm delivery and cystic periventricular leucomalacia (PVL).

STUDY DESIGN

Venous blood, buccal swabs or cord blood were collected from mother/child pairs with infants born at term (200) or preterm (106) in the presence and absence of neonatal PVL and of premature infants with PVL (7). Extracted genomic DNA served as template for determination of IL-10 (-1082), IL-10 (-819) and TNF-α (-308) genotypes by allele-specific PCR.

RESULT

No significant difference was observed in the frequencies of IL-10 (-1082), IL-10 (-819) and TNF-α (-308) genotypes in mothers or in children of term versus preterm deliveries with or without PVL.

CONCLUSION

Maternal and infant IL-10 (-1082, -819) and TNF-α (-308) genotypes are not indicative for an increased risk of preterm birth or the development of PVL in premature newborns.

The biological basis of injury and neuroprotection in the fetal and neonatal brain

A compromised intrauterine environment that delivers low levels of oxygen and/or nutrients, or is infected or inflammatory, can result in fetal brain injury, abnormal brain development and in cases of chronic compromise, intrauterine growth restriction. Preterm birth can also be associated with injury to the developing brain and affect the normal trajectory of brain growth. This review will focus on the effects that episodes of perinatal hypoxia (acute, chronic, associated with inflammation or as an antecedent of preterm birth) can have on the developing brain. In animal models of these conditions we have found that relatively brief (acute) periods of fetal hypoxemia can have significant effects on the fetal brain, for example death of susceptible neuronal populations (cerebellum, hippocampus, cortex) and cerebral white matter damage. Chronic placental insufficiency which includes fetal hypoxemia, nutrient restriction and altered endocrine status can result in fetal growth restriction and long-term deficits in neural connectivity in addition to altered postnatal function, for example in the auditory and visual systems. Maternal/fetal inflammation can result in fetal brain damage, particularly but not exclusively in the white matter; injury is more pronounced when associated with fetal hypoxemia. In the baboon, in which the normal trajectory of growth is affected by preterm birth, there is a direct correlation between a higher flux in oxygen saturation and a greater extent of neuropathological damage. Currently, the only established therapy for neonatal encephalopathy in full term neonates is moderate hypothermia although this only offers some protection to moderately but not severely affected brains. There is no accepted therapy for injured preterm brains. Consequently the search for more efficacious treatments continues; we discuss neuroprotective agents (erythropoietin, N-acetyl cysteine, melatonin, creatine, neurosteroids) which we have trialed in appropriate animal models. The possibility of combining hypothermia with such agents or growth factors is now being considered. A deeper understanding of causal pathways in brain injury is essential for the development of efficacious strategies for neuroprotection.

Astrocytes promote TNF-mediated toxicity to oligodendrocyte precursors

Neuroinflammation and increased production of tumor necrosis factor (TNF) in the CNS have been implicated in many neurological diseases including white matter disorders periventricular leukomalacia and multiple sclerosis. However, the exact role of TNF in these diseases and how it mediates oligodendrocyte injury remain unclear. Previously, we demonstrated that lipopolysaccharide (LPS) selectively kills oligodendrocyte precursors (preOLs) in a non-cell autonomous fashion through the induction of TNF in mixed glial cultures. Here, we report that activation of oligodendroglial, but not astroglial and microglial, TNFR1 is required for LPS toxicity, and that astrocytes promote TNF-mediated preOL death through a cell contact-dependent mechanism. Microglia were the sole source for TNF production in LPS-treated mixed glial cultures. Ablation of TNFR1 in mixed glia completely prevented LPS-induced death of preOLs. TNFR1-expressing preOLs were similarly susceptible to LPS treatment when seeded into wildtype and TNFR1(-/-) mixed glial cultures, demonstrating a requirement for oligodendroglial TNFR1 in the cell death. Although exogenous TNF failed to cause significant cell death in enriched preOL cultures, it became cytotoxic when preOLs were in contact with astrocytes. Collectively, our results demonstrate oligodendroglial TNFR1 in mediating inflammatory destruction of preOLs and suggest a previously unrecognized role for astrocytes in promoting TNF toxicity to preOLs.

In vivo MRI analysis of an inflammatory injury in the developing brain

Cerebral periventricular white matter injury stands as a leading cause of cognitive, behavioral and motor impairment in preterm infants. There is epidemiological and histopathological evidence demonstrating the role of prenatal or neonatal inflammation in brain injury in preterm infants. In order to define the effect of an inflammatory insult in the developing brain on magnetic resonance (MR) imaging, we obtained high resolution conventional and diffusion MR images of the brain of rat pups after an inflammatory injury. Rat pups were subjected on postnatal day 5 (P5) to a stereotaxic injection of lipopolysaccharide in the corpus callosum and then imaged at 11.7 T on days 0, 2 and 4 following the injury. They were subsequently sacrificed for immunohistochemistry. Diffusion tensor imaging (DTI) acquired at high spatial resolution showed an initial reduction of the apparent diffusion coefficient (ADC) in the white matter. This was followed by an increase in ADC value and in T2 relaxation time constant in the white matter, with an associated increase of radial diffusivity of the corpus callosum, and a 10-fold increase in ventricular size. On histology, these MR changes corresponded to widespread astrogliosis, and decreased proportion of the section areas containing cresyl violet positive stain. The increase in radial diffusivity, typically attributed to myelin loss, occurred in this case despite the absence of myelin at this developmental stage.

Systemic inflammation sensitizes the neonatal brain to excitotoxicity through a pro-/anti-inflammatory imbalance: key role of TNFalpha pathway and protection by etanercept

Systemic inflammation sensitizes the perinatal brain to an ischemic/excitotoxic insult but the mechanisms are poorly understood. We hypothesized that the mechanisms involve an imbalance between pro- and anti-inflammatory factors. A well characterized mouse model where a systemic injection of IL-1beta during the first five postnatal days (inflammatory insult) is combined with an intracerebral injection of the glutamatergic analogue ibotenate (excitotoxic insult) at postnatal day 5 was used. Following the inflammatory insult alone, there was a transient induction of IL-1beta and TNFalpha, compared with controls measured by quantitative PCR, ELISA, and Western blot. Following the combined inflammatory and excitotoxic insult, there was an induction of IL-1beta, TNFalpha, and IL-6 but not of IL-10 and TNFR1, indicating an altered pro-/anti-inflammatory balance after IL-1beta sensitized lesion. We then tested the hypothesis that the TNFalpha pathway plays a key role in the sensitization and insult using TNFalpha blockade (etanercept) and TNFalpha(-/-) mice. Etanercept given before the insult did not affect brain damage, but genetic deletion of TNFalpha or TNFalpha blockade by etanercept given after the combined inflammatory and excitotoxic insult reduced brain damage by 50%. We suggest this protective effect was centrally mediated, since systemic TNFalpha administration in the presence of an intact blood-brain barrier did not aggravate the damage and etanercept almost abolished cerebral TNFalpha production. In summary, sensitization was, at least partly, mediated by an imbalance between pro- and anti-inflammatory cytokines. Cerebral TNFalpha played a key role in mediating brain damage after the combined inflammatory and excitatory insult.

Erythropoietin is neuroprotective in a preterm ovine model of endotoxin-induced brain injury

Intrauterine infection and inflammation have been linked to preterm birth and brain damage. We hypothesized that recombinant human erythropoietin (rhEPO) would ameliorate brain damage in anovine model of fetal inflammation. At 107 +/- 1 day of gestational age (DGA), chronically catheterized fetal sheep received on 3 consecutive days 1) an intravenous bolus dose of lipopolysaccharide ([LPS] approximately 0.9 microg/kg; n = 8); 2) an intravenous bolus dose of LPS, followed at 1 hour by 5,000 IU/kg of rhEPO (LPS + rhEPO, n = 8); or 3) rhEPO (n = 5). Untreated fetuses (n = 8) served as controls. Fetal physiological parameters were monitored, and fetal brains and optic nerves were histologically examined at 116 +/- 1 DGA. Exposure to LPS, but not to rhEPO alone or saline, resulted in fetal hypoxemia, hypotension (p < 0.05), brain damage, including white matter injury, and reductions in numbers of myelinating oligodendrocytes in the corticospinal tract and myelinated axons in the optic nerve (p < 0.05 for both). Treatment of LPS-exposed fetuses with rhEPO did not alter the physiological effects of LPS but reduced brain injury and was beneficial to myelination in the corticospinal tract and the optic nerve. This is the first study in a long-gestation species to demonstrate the neuroprotective potential of rhEPO in reducing fetal brain and optic nerve injury after LPS exposure.

Notch signaling: key role in intrauterine infection/inflammation, embryonic development, and white matter damage?

The mechanisms or pathophysiologies that lead to cerebral white matter damage during development are complex and not fully understood. It is postulated that exposure of the preterm brain to inflammatory cytokines during intrauterine infection/inflammation contributes to brain white matter damage, and this damage may affect the function and differentiation of progenitor oligodendrocyte cells under physiological conditions. The Notch pathway, an important signaling pathway controlling various cells' differentiation, functions in the timing of oligodendrocyte differentiation, and Notch signaling may contribute to white matter damage and may mediate neurogenesis in a pathophysiological phase. Recent studies have led to recognition of the role of the Notch pathway in neurogenesis in cerebral ischemic damage and in myelination and axonal damage of neurodegenerative diseases. Moreover, Notch plays a critical role in steering an immune response toward inflammation by regulating expression of various cytokines and proinflammatory cytokines resulting in the activation of Notch signaling. Thus, the Notch signaling pathway likely plays a key role in intrauterine infection/inflammation, brain development, and white matter damage, and future research directed toward understanding its role will be important. Insofar as Notch signaling could have an important effect on neurogenesis, mobilization of progenitor cells is one strategy for compensating for the neuronal losses seen in white matter damage after intrauterine infection/inflammation.

A history of our understanding of cerebral vascular development and pathogenesis of perinatal brain damage over the past 30 years

This article reviews our studies focusing on cerebral vascular development, the pathogenesis of subependymal/intraventricular hemorrhage (SEH/IVH), periventricular leukomalacia (PVL), and pontosubicular neuron necrosis (PSN). Their pathogenesis consists of predisposing developmental and causal factors. SEH/IVH may be caused by reperfusion or overperfusion following ischemia in the subependymal germinal matrix with characteristic vasculature. The cause of PVL is multifactorial (ie, ischemia and inflammation), predisposed by the maturational status of the vasculature and oligodendroglia in the white matter. Focal PVL is ischemic necrosis, and diffuse PVL or white matter injury may include cytotoxic damage. PSN has an apoptotic character, and may be induced by ischemic and oxidative stress on specific immature neurons. Further studies on preventive and therapeutic measures are necessary in clinical, pathologic, and experimental fields. The monitoring and control methods of brain hemodynamics and cellular stability should be more developed to prevent brain damages.

TNF-alpha system response in a rat model of very preterm brain injuries induced by lipopolysaccharide and/or hypoxia-ischemia

OBJECTIVE

The aim of this study was to determine, with the use of a rat model, the expression of tumor necrosis factor (TNF)-alpha, its receptors, and TNF-alpha-converting enzyme in perinatal brain lesions of early premature neonates.

STUDY DESIGN

Lipopolysaccharide (LPS) was injected intraperitoneally in pregnant rats at the end of gestation. At postnatal day 1, the right carotid artery was ligated and followed by exposure to hypoxia. Forebrains (n = 220) were collected to study the TNF-alpha system.

RESULTS

LPS alone or combined with hypoxia-ischemia (HI) led to a slight decrease of intracerebral TNF-alpha, whereas sole HI induced no variation. TNF-alpha-converting enzyme followed the same pattern of expression as TNF-alpha. TNF receptor 1 was up-regulated in forebrains that were submitted to LPS alone or combined with HI. No variation was observed in TNF receptor 2 expression.

CONCLUSION

The minimal expression of the TNF-alpha system that we observed may indicate that this pathway is not central in the pathogenesis of brain lesions in early premature neonates.

Interleukin-1beta-induced brain injury in the neonatal rat can be ameliorated by alpha-phenyl-n-tert-butyl-nitrone

To examine the possible role of inflammatory cytokines in mediating perinatal brain injury, we investigated effects of intracerebral injection of interleukin-1beta (IL-1beta) on brain injury in the neonatal rat and the mechanisms involved. Intracerebral administration of IL-1beta (1 microg/kg) resulted in acute brain injury, as indicated by enlargement of ventricles bilaterally, apoptotic death of oligodendrocytes (OLs) and loss of OL immunoreactivity in the neonatal rat brain. IL-1beta also induced axonal and neuronal injury in the cerebral cortex as indicated by elevated expression of beta-amyloid precursor protein, short beaded axons and dendrites, and loss of tyrosine hydroxylase-positive neurons in the substantia nigra and the ventral tegmental areas. Administration of alpha-phenyl-n-tert-butyl-nitrone (PBN, 100 mg/kg i.p.) immediately after the IL-1beta injection protected the brain from IL-1beta-induced injury. Protection of PBN was linked with the attenuated oxidative stress induced by IL-1beta, as indicated by decreased elevation of 8-isoprostane content and by the reduced number of 4-hydroxynonenal or malondialdehyde or nitrotyrosine-positive cells following IL-1beta exposure. PBN also attenuated IL-1beta-stimulated inflammatory responses as indicated by the reduced activation of microglia. The finding that IL-1beta induced perinatal brain injury was very similar to that induced by lipopolysaccharide (LPS), as we previously reported and that PBN was capable to attenuate the injury induced by either LPS or IL-1beta suggests that IL-1beta may play a critical role in mediating brain injury associated with perinatal infection/inflammation.

Early-life programming of later-life brain and behavior: a critical role for the immune system

The immune system is well characterized for its critical role in host defense. Far beyond this limited role however, there is mounting evidence for the vital role the immune system plays within the brain, in both normal, “homeostatic” processes (e.g., sleep, metabolism, memory), as well as in pathology, when the dysregulation of immune molecules may occur. This recognition is especially critical in the area of brain development. Microglia and astrocytes, the primary immunocompetent cells of the CNS, are involved in every major aspect of brain development and function, including synaptogenesis, apoptosis, and angiogenesis. Cytokines such as tumor necrosis factor (TNF)α, interleukin [IL]-1β, and IL-6 are produced by glia within the CNS, and are implicated in synaptic formation and scaling, long-term potentiation, and neurogenesis. Importantly, cytokines are involved in both injury and repair, and the conditions underlying these distinct outcomes are under intense investigation and debate. Evidence from both animal and human studies implicates the immune system in a number of disorders with known or suspected developmental origins, including schizophrenia, anxiety/depression, and cognitive dysfunction. We review the evidence that infection during the perinatal period of life acts as a vulnerability factor for later-life alterations in cytokine production, and marked changes in cognitive and affective behaviors throughout the remainder of the lifespan. We also discuss the hypothesis that long-term changes in brain glial cell function underlie this vulnerability.

Tumor necrosis factor alpha mediates lipopolysaccharide-induced microglial toxicity to developing oligodendrocytes when astrocytes are present

Reactive microglia and astrocytes are present in lesions of white matter disorders, such as periventricular leukomalacia and multiple sclerosis. However, it is not clear whether they are actively involved in the pathogenesis of these disorders. Previous studies demonstrated that microglia, but not astrocytes, are required for lipopolysaccharide (LPS)-induced selective killing of developing oligodendrocytes (preOLs) and that the toxicity is mediated by microglia-derived peroxynitrite. Here we report that, when astrocytes are present, the LPS-induced, microglia-dependent toxicity to preOLs is no longer mediated by peroxynitrite but instead by a mechanism dependent on tumor necrosis factor-alpha (TNFalpha) signaling. Blocking peroxynitrite formation with nitric oxide synthase (NOS) inhibitors or a decomposition catalyst did not prevent LPS-induced loss of preOLs in mixed glial cultures. PreOLs were highly vulnerable to peroxynitrite; however, the presence of astrocytes prevented the toxicity. Whereas LPS failed to kill preOLs in cocultures of microglia and preOLs deficient in inducible NOS (iNOS) or gp91(phox), the catalytic subunit of the superoxide-generating NADPH oxidase, LPS caused a similar degree of preOL death in mixed glial cultures of wild-type, iNOS-/-, and gp91(phox-/-) mice. TNFalpha neutralizing antibody inhibited LPS toxicity, and addition of TNFalpha induced selective preOL injury in mixed glial cultures. Furthermore, disrupting the genes encoding TNFalpha or its receptors TNFR1/2 completely abolished the deleterious effect of LPS. Our results reveal that TNFalpha signaling, rather than peroxynitrite, is essential in LPS-triggered preOL death in an environment containing all major glial cell types and underscore the importance of intercellular communication in determining the mechanism underlying inflammatory preOL death.

Amoeboid microglia in the periventricular white matter induce oligodendrocyte damage through expression of proinflammatory cytokines via MAP kinase signaling pathway in hypoxic neonatal rats

Hypoxic injury in the perinatal period results in periventricular white matter (PWM) lesions with axonal damage and oligodendroglial loss. It also alters macrophage function by perpetuating expression of inflammatory mediators. Relevant to this is the preponderance of amoeboid microglial cells (AMC) characterized as active macrophages in the developing PWM. This study aimed to determine if AMC produce proinflammatory cytokines that may be linked to the oligodendroglial loss observed in hypoxic PWM damage (PWMD). Wistar rats (1 day old) were subjected to hypoxia, following which upregulated expression of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), TNF receptor 1 (TNF-R(1)) and IL-1 receptor 1 (IL-1R(1)) was observed. This was coupled with apoptosis and expression of TNF-R(1) and IL-1R(1) in oligodendrocytes. Primary cultured microglial cells subjected to hypoxia (3% oxygen, 5% CO(2) and 92% nitrogen) showed enhanced expression of TNF-alpha and IL-1beta. Furthermore, mitogen-activated protein (MAP) kinase signaling pathway was involved in the expression of TNF-alpha and IL-1beta in microglia subjected to hypoxia. Our results suggest that following a hypoxic insult, microglial cells in the neonatal rats produce inflammatory cytokines such as TNF-alpha and IL-1beta via MAP kinase signaling pathway. These cytokines are detrimental to oligodendrocytes resulting in PWM lesion.

The fetal inflammatory response syndrome

The fetal inflammatory response syndrome (FIRS) is a condition characterized by systemic inflammation and an elevation of fetal plasma interleukin-6. This syndrome has been observed in fetuses with preterm labor with intact membranes, preterm prelabor rupture of the membranes, and also fetal viral infections such as cytomegalovirus. FIRS is a risk factor for short-term perinatal morbidity and mortality after adjustment for gestational age at delivery and also for the development of long-term sequelae such as bronchopulmonary dysplasia and brain injury. Multiorgan involvement in FIRS has been demonstrated in the hematopoietic system, thymus, adrenal glands, skin, kidneys, heart, lung, and brain. This article reviews the fetal systemic inflammatory response as a mechanism of disease. Potential interventions to control an exaggerated inflammatory response in utero are also described.

An adverse intrauterine environment: implications for injury and altered development of the brain

Abnormal development of the brain during fetal life is now thought to contribute to the aetiology of many functional and behavioural disorders that manifest throughout life. Many factors are likely to underlie such abnormal development including genetic makeup and an adverse intrauterine environment. This review will focus on prenatal hypoxic-ischemic injury and inflammatory/infective insults. A range of experimental models have been used to characterise lesions formed in response to these insults and to determine mechanisms of damage resulting from such events. Relatively brief periods of fetal hypoxia result in neuronal death (cerebellum, hippocampus, and cerebral cortex), white matter damage and reduced growth of neural processes. These effects are more profound at mid than late gestation. Chronic mild placental insufficiency can result in fetal growth restriction and deficits in neural connectivity and myelination. Exposure of the preterm fetus to inflammatory agents causes brain damage particularly in the white matter and this is exacerbated by hypoxia. These studies show that the timing, severity and nature of specific insults are critical in determining the pattern of injury and thus the extent to which neurological function will be affected postnatally. Defining the causes, patterns and mechanisms of brain injury is crucial if we are to develop rational neuroprotective strategies to reduce the burden of altered brain growth and poor functional and behavioural outcomes.

Altered nestin expression in the cerebrum with periventricular leukomalacia

Nestin is a cytoskeletal protein expressed by neural stem cells, and by immature neurons and glial cells. In an effort to explore the potential of the infant brain for repair and plasticity, we immunohistochemically studied nestin expression in the human cerebral cortex of control subjects and of patients with periventricular leukomalacia. During normal development, nestin immunoreactivity of the cortical gray and white matter was detectable throughout the fetal period, and disappeared around birth. In brain with periventricular leukomalacia, nestin expression was altered in a time- and space-dependent manner. In the cortical gray matter, neuronal immunoreactivity was often reduced in the subacute stage, but was increased in chronic and remote stages. In the white matter near a lesion of periventricular leukomalacia, glial immunoreactivity was increased in all stages. In many cases, neurons and axons far from a lesion also showed an altered expression of nestin. These findings indicate that in brain with periventricular leukomalacia, neurons and glial cells may recapitulate nestin expression in response to ischemic brain injury, suggesting functional relevance in repair and plasticity.

IGF-1 protects oligodendrocyte progenitors against TNFα-induced damage by activation of PI3K/Akt and interruption of the mitochondrial apoptotic pathway

Proinflammatory cytokine-mediated injury to oligodendrocyte progenitor cells (OPCs) has been proposed as a cause of periventricular leukomalacia (PVL), the most common brain injury found in preterm infants. Preventing death of OPCs is a potential strategy to prevent or treat PVL. In the current study, we utilized an in vitro cell culture system to investigate the effect of insulin-like growth factor-1 (IGF-1) on tumor necrosis factor-alpha (TNFalpha)-induced OPC injury and the possible mechanisms involved. OPCs were isolated from neonatal rat optic nerves and cultured in chemically defined medium (CDM) supplemented with platelet-derived growth factor and basic fibroblast growth factor. Exposure to TNFalpha resulted in death of OPCs. IGF-1 protected OPCs from TNFalpha cytotoxicity in a dose-dependent manner as measured by the XTT and TUNEL assays. IGF-1 activates both the PI3K/Akt and the extracellular signal-regulated kinase (ERK) pathway. However, IGF-1-enhanced cell survival signals were mediated by the PI3K/Akt, but not by the ERK pathway, as evidenced by the observation that IGF-1-enhanced cell survival was partially abrogated by Akti, the Akt inhibitor, or wortmannin, the PI3K inhibitor, but not by PD98,059, the MAPK kinase/ERK kinase inhibitor. The downstream events of IGF-1-triggered survival signals included phosphorylation of BAD, blockade of TNFalpha-induced translocation of Bax from the cytosol to the mitochondrial membrane, and suppression of caspase-9 and caspase-3 activation. These observations indicate that the protection of OPCs by IGF-1 is mediated, at least partially, by interruption of the mitochondrial apoptotic pathway via activation of PI3K/Akt.

Microglia and inflammation: impact on developmental brain injuries

Inflammation during the perinatal period has become a recognized risk factor for developmental brain injuries over the past decade or more. To fully understand the relationship between inflammation and brain development, a comprehensive knowledge about the immune system within the brain is essential. Microglia are resident immune cells within the central nervous system and play a critical role in the development of an inflammatory response within the brain. Microglia are critically involved with both the innate and adaptive immune system, regulating inflammation and cell damage within the brain via activation of Toll-like receptors, production of cytokines, and a myriad of other intracellular and intercellular processes. In this article, microglial physiology is reviewed along with the role of microglia in developmental brain injuries in humans and animal models. Last, microglial functions within the innate and adaptive immune system will be summarized. Understanding the processes of inflammation and microglial activation is critical for formulating effective preventative and therapeutic strategies for developmental brain injuries.

Inflammation, brain damage and visual dysfunction in preterm infants

Antenatal intrauterine infection and the fetal inflammatory response appear to be important pathogenetic factors in preterm birth and subsequent neonatal disorders of the lung and brain. In this paper, we expand this concept to include visual dysfunction. Although present data tend to support our notion, we suggest that more experimental and epidemiological research is needed to elucidate mechanisms of infection/inflammation-induced damage to the eye and visual brain pathways of preterm infants.

Chronic endotoxin exposure causes brain injury in the ovine fetus in the absence of hypoxemia

OBJECTIVE

Intrauterine infection has been linked to brain injury in human infants, although the mechanisms are not fully understood. We recently showed that repeated acute exposure of preterm fetal sheep to bacterial endotoxin (lipopolysaccharide [LPS]) results in fetal hypoxemia, hypotension, increased systemic proinflammatory cytokines, and brain damage, including white matter injury. However, it is not clear whether this injury is caused by reduced cerebral oxygen delivery or inflammatory pathways independent of hypoxia. The aim of the present study was to determine the effects on the fetal brain and placenta of a chronic intrauterine inflammatory state, induced by LPS infusion into the fetal circulation, a model that did not cause hypoxia.

METHODS

At 0.65 of term, eight catheterized fetal sheep received intravenous infusions of LPS (5 to 15 mug) over 5 days; control fetuses received saline. Fetal physiologic responses were monitored throughout the infusion. Fetal brain and placental tissues were examined histologically 6 days after the conclusion of the infusion.

RESULTS

LPS infusions did not result in physiologically significant alterations to fetal blood gases or mean arterial pressure; however, plasma proinflammatory cytokine levels were elevated. Following LPS exposure there was no difference in fetal body or brain weights (P >.05); placental weight was reduced (P <.05), consistent with reduced placentome cross-sectional area (P <.05). In the cerebral hemispheres subcortical white matter injury was present in six LPS-exposed fetuses and included axonal damage, microgliosis, oligodendrocyte injury, and increased beta amyloid precursor protein (beta-APP) expression.

CONCLUSIONS

Chronic, systemic exposure of the fetus to LPS resulted in fetal brain damage in the absence of hypoxemia or hypotension, although the resulting injury was less severe than following repeated acute exposure.

Perinatal infections, prematurity and brain injury

PURPOSE OF REVIEW

The association between perinatal infection and brain injury is widely accepted but a cause-and-effect relationship has not yet been proven. This article summarizes available evidence and current primary publications for debate.

RECENT FINDINGS

Work completed during the review period has reinforced current understanding of perinatal infection, prematurity and brain injury. In animal experiments: lipopolysaccharides have been further implicated in brain injury, not only as a cause of brain injury but also as mediators of preconditioning and protection. Recent studies suggest that cerebral injury following low-dose lipopolysaccharide administration may become compensated in adulthood. Other studies have emphasized the complexity of the response by showing that plasma cytokine levels may not reflect those in the central nervous system or inflammatory events in the brain.

SUMMARY

Perinatal infection and maternofetal inflammation is strongly associated with preterm birth. Inflammation probably represents an important mechanism for cerebral damage, and both overt lesions and maldevelopment can result. Epidemiological data and multiple animal models to link infection, inflammation and brain damage exist, but proof of causation is elusive.

Effects of maternal Campylobacter rectus infection on murine placenta, fetal and neonatal survival, and brain development

BACKGROUND

Maternal periodontal infection has been associated with increased risk of prematurity and low birthweight. Infection and inflammatory pathways that mediate prematurity have also been implicated in neonatal developmental impairments. The objective of this study was to determine whether maternal Campylobacter rectus infection that induces fetal growth restriction in a mouse model also compromises neonatal pup survival, growth, and neurodevelopment.

METHODS

Timed pregnant mice were challenged with C. rectus on gestation day 7.5. One group of animals was sacrificed on embryonic day 16.5 for placental histology and measurement of fetal brain mRNA expression of tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma. Another group of animals was allowed to deliver to follow pup survival, growth, and brain structure at day 9.

RESULTS

C. rectus challenge resulted in abnormal placental architecture with inflammation and a 2.8-fold increase in fetal brain expression of IFN-gamma (P = 0.04). Pup birthweight was unaffected by C. rectus exposure, but lethality was 3.9-fold higher after 1 week. Ultrastructurally, the 9-day neonatal brain tissue displayed cellular and myelin alterations consistent with white matter damage.

CONCLUSIONS

Maternal C. rectus infection induces placental inflammation and decidual hyperplasia as well as concomitant increase in fetal brain IFN-gamma. Maternal infection increased pup mortality, and preliminary findings demonstrate ultrastructural changes in the hippocampal region of the neonatal brain, in a manner analogous to the effects of maternal infection on white matter damage seen in humans. Thus, the threat of maternal oral infectious exposure during pregnancy may not be limited to the duration of gestation, but may also potentially affect perinatal neurological growth and development.

Activation of NF-κB transcription factor in the preterm ovine brain and placenta after acute LPS exposure

Intrauterine infection may be causally related to inflammation and injury of the fetal brain, however the mechanisms by which this occurs are unclear. We have investigated whether nuclear factor (NF)-kappaB, a transcription factor for proinflammatory cytokines, is activated in the fetal brain after acute LPS-exposure. At 95 days of gestation (term = approximately 147 days), 5 fetuses received a single intravenous bolus dose of LPS (1 microg/kg); 6 fetuses served as controls. Fetal blood samples were taken hourly for 6 hr post LPS-exposure to assess physiological status. Ewes and fetuses were then euthanased, placental and brain tissue examined histologically, and NF-kappaB activation assessed in several regions of the fetal brain using an electromobility shift assay (EMSA). Oxidative stress was measured using lipid peroxidation and 8-isoprostane biochemical assays and brain cytokine concentrations analysed by enzyme linked immunosorbent assay (ELISA). LPS-exposed fetuses (relative to controls) were hypoxemic and the haematocrit and lactate levels had increased. In the brains of LPS-exposed fetuses compared to controls, NF-kappaB binding activity was elevated in the hippocampus and the thalamus/basal ganglia; 8-isoprostane levels were elevated overall (P < 0.05) in the parietal/occipital/temporal lobes and thalamus/basal ganglia. TNF-alpha and IL-6 concentrations were not elevated, however, there was a tendency for an elevation of IFN-gamma concentrations in the thalamus/basal ganglia. IFN-gamma concentration was elevated (P < 0.05) in the plasma 4 hr after LPS-exposure. In the placenta, NF-kappaB binding activity was increased (P < 0.05). We conclude that acute systemic administration of LPS leads to increased binding activity of NF-kappaB subunits in specific regions of the fetal brain and in the placenta, but that there is no clear-cut relationship between this elevation and vulnerability to endotoxic damage.

Periventricular leukomalacia: overview and recent findings

Periventricular leukomalacia (PVL), the main substrate for cerebral palsy, is characterized by diffuse injury of deep cerebral white matter, accompanied in its most severe form by focal necrosis. The classic neuropathology of PVL has given rise to several hypotheses about the pathogenesis, largely relating to hypoxia-ischemia and reperfusion in the sick premature infant. These include free radical injury, cytokine toxicity (especially given the epidemiologic association of PVL with maternofetal infection), and excitotoxicity. Among the recent findings directly in human postmortem tissue is that immunocytochemical markers of lipid peroxidation (hydroxy-nonenal and malondialdehyde) and protein nitration (nitrotyrosine) are significantly increased in PVL. Premyelinating oligodendrocytes, which predominate in periventricular regions during the window of vulnerability to PVL (24 to 34 postconceptional weeks), are the targets of this free radical injury, and suffer cell death. Susceptibility can be attributed, at least in part, to a relative deficiency of superoxide dismutases in the preterm white matter, including premyelinating oligodendrocytes. Several cytokines, including interferon-gamma (known to be directly toxic to immature oligodendroglia in vitro), as well as tumor necrosis factor-alpha and interleukins 2 and 6, have been demonstrated in PVL. Microglia, which express toll-like receptors to bacterial products such as lipopolysaccharide, are increased in PVL white matter and may contribute to the injury. Preliminary work suggests a role for glutamate receptors and glutamate transporters in PVL, as has been seen in experimental animals. These findings pave the way for eventual therapeutic or preventive strategies for PVL.

Neuropathologic substrate of cerebral palsy

Animal models have assisted in understanding the mechanisms of brain injury underlying cerebral palsy. Nevertheless, no such models replicate every aspect of the human disease. This review summarizes the classic and more recent studies of the neuropathology of human perinatal brain injury most commonly associated with cerebral palsy, for use by researchers and clinicians alike who need to analyze published animal models with respect to their fidelity to the human disorder. The neuropathology underlying cerebral palsy includes white-matter injury, known as periventricular leukomalacia, as well as germinal matrix hemorrhage with intraventricular extension, and injury to the cortex, basal ganglia, and thalamus. Each has distinctive features while sharing some risk factors, such as prematurity and/or hypoxia-ischemia in the perinatal period. Periventricular leukomalacia consists of diffuse injury of deep cerebral white matter, with or without focal necrosis. Recent work directly in human postmortem tissue has focused on the role of free radical injury, cytokine toxicity (especially in light of the epidemiologic association of periventricular leukomalacia with maternofetal infection), and excitotoxicity in the development of periventricular leukomalacia. Premyelinating oligodendrocytes, which predominate in periventricular regions during the window of vulnerability to periventricular leukomalacia (24-34 postconceptional weeks), are the targets of free radical injury, as determined by immunocytochemical markers of lipid peroxidation and protein nitration. This maturational susceptibility can be attributed in part to a relative deficiency of superoxide dismutases in developing white matter. Microglia, which respond to cytokines and to bacterial products such as lipopolysaccharide via Toll-like receptors, are increased in periventricular leukomalacia white matter and can contribute to cellular damage. Indeed, several cytokines, including tumor necrosis factor-a and interleukins 2 and 6, as well as interferon-g, have been demonstrated in periventricular leukomalacia. Preliminary work suggests a role for glutamate receptors and glutamate transporters in periventricular leukomalacia based on expression in human developing oligodendrocytes. Germinal matrix hemorrhage, with or without intraventricular hemorrhage, occurs in premature infants and can coexist with periventricular leukomalacia. Studies in human germinal matrix tissue have focused on maturation-based vascular factors, such as morphometry and expression of molecules related to the structure of the blood-brain barrier. Gray-matter injury, seen more commonly in term infants, includes cortical infarcts and status marmoratus. Subtle cortical injury overlying periventricular leukomalacia is the subject of current interest as a possible substrate for the cognitive difficulties seen in patients with cerebral palsy. In summary, it is hoped that work in human tissue, in conjunction with experimental animal models, will lead to eventual therapeutic or preventive strategies for the perinatal brain injury underlying cerebral palsy.

Oxidative and nitrative injury in periventricular leukomalacia: a review

Periventricular leukomalacia (PVL) is the major substrate of cerebral palsy in survivors of prematurity. Its pathogenesis is complex and likely involves ischemia/reperfusion in the critically ill premature infant, with impaired regulation of cerebral blood flow, as well as inflammatory mechanisms associated with maternal and/or fetal infection. During the peak period of vulnerability for PVL, developing oligodendrocytes (OLs) predominate in the white matter. We hypothesize that free radical injury to the developing OLs underlies, in part, the pathogenesis of PVL and the hypomyelination seen in long-term survivors. In human PVL, free radical injury is supported by evidence of oxidative and nitrative stress with markers to lipid peroxidation and nitrotyrosine, respectively. Evidence in normal human cerebral white matter suggests an underlying vulnerability of the premature infant to free radical injury resulting from a developmental mismatch of antioxidant enzymes (AOE) and subsequent imbalance in oxidant metabolism. In vitro studies using rodent OLs suggest that maturational susceptibility to reactive oxygen species is dependent, not only on levels of individual AOE, but also on specific interactions between these enzymes. Rodent in vitro data further suggest 2 mechanisms of nitric oxide damage: one involving the direct effect of nitric oxide on OL mitochondrial integrity and function, and the other involving an activation of microglia and subsequent release of reactive nitrogen species. The latter mechanism, while important in rodent studies, remains to be determined in the pathogenesis of human PVL. These observations together expand our knowledge of the role that free radical injury plays in the pathogenesis of PVL, and may contribute to the eventual development of therapeutic strategies to alleviate the burden of oxidative and nitrative injury in the premature infant at risk for PVL.

Interleukin-6 and interleukin-8 are elevated in the cerebrospinal fluid of infants exposed to chorioamnionitis

BACKGROUND

The clinical or histologic diagnosis of chorioamnionitis has been associated with an increased risk of neuropathology and adverse neurologic outcomes in premature and term infants. Inflammatory cytokines have been implicated in the pathogenesis of these processes. The objective of this study was to determine whether exposure to chorioamnionitis and fetal inflammatory syndrome is associated with elevated concentrations of inflammatory cytokines (TNF-alpha, IL-6, and IL-8) in the CSF of term and preterm infants.

METHODS

Eighty-four mother/infant pairs were studied, 54 infants were premature. Twenty-eight showed signs of maternal (n = 14), or fetal (n = 14) inflammation based on placental pathology; mothers of 24 infants showed signs of clinical chorioamnionitis not confirmed by placental pathology and 32 infants were considered as 'controls' since they had only transient difficulty adjusting to extra-uterine life warranting evaluation for sepsis. The cytokine concentrations in the CSF were measured within 24 h of birth.

RESULTS

When compared to the control group (IL-8 = 341 +/- 170 pg/ml and IL-6 = 7.4 +/- 1.8 pg/ml) significantly higher concentrations of IL-8 were detected in the CSF of infants exposed to clinical chorioamnionitis (1,854 +/- 878 pg/ml; p = 0.001) and maternal/fetal inflammation (1,754 +/- 787 pg/ml; p = 0.001) and of IL-6 in infants with maternal/fetal inflammation (47.6 +/- 45.1 pg/ml; p = 0.01).

CONCLUSIONS

These results indicate that infants exposed to clinical chorioamnionitis, or inflammation in utero, experience at least a transient elevation in inflammatory cytokines in CSF.

Effect of tumor necrosis factor-alpha on developing optic nerve oligodendrocytes in culture

There is increasing evidence that proinflammatory cytokines are involved in the development of periventricular leukomalacia (PVL), a condition in which developing oliodendrocytes (OLs) are preferentially injured. In the present study, we utilized an in vitro assay to demonstrate that the A2B5+ OL progenitors as well as the O4+ prooligodendrocytes (pro-OLs) were more susceptible to tumor necrosis factor-alpha (TNF-alpha) cytotoxicity than the O4+/O1+ immature OLs. OL progenitors were isolated from optic nerves of 7-day-old rat pups and cultured in chemically defined medium supplemented with platelet-derived growth factor and basic fibroblast growth factor. OL progenitors were allowed to differentiate into pro-OLs and immature OLs under special cultural conditions. Cells at three different developmental stages were subjected to TNF-alpha treatment. Cell death, presumably by apoptosis as evidenced by TUNEL staining and caspase-3 activation, was observed following TNF-alpha treatment. Corresponding to TNF-alpha-induced apoptosis, cell survival rate decreased in a time- and dose-dependent manner. The sensitivity of different OL developmental stages to TNF-alpha decreased with the progression of cell maturation. However, this differential response was not related to differentially expressed TNF-alpha receptors. Consistent with reports that progenitor cells are preferentially injured in PVL, our results may further support the role of TNF-alpha as a potential mediator of PVL.

The relationship of CSF and plasma cytokine levels to cerebral white matter injury in the premature newborn

Ischemia and systemic infection are implicated in the etiology of periventricular white matter injury, a major cause of adverse motor and cognitive outcome in preterm infants. Cytokines are signaling proteins that can be produced as part of the inflammatory response to both ischemia and infection. The aim of this study was to relate cerebrospinal fluid (CSF) concentrations of IL-6, IL-8, IL-10, tumor necrosis factor alpha (TNF-alpha), and interferon gamma (IFN-gamma) to magnetic resonance-defined white matter injury in preterm infants. Relationships between CSF and plasma cytokine concentrations were also examined. Preterm infants (<or=32 wk) and more mature infants from The Royal Women's Hospital, Melbourne, Australia, and Christchurch Women's Hospital, Christchurch, New Zealand, were eligible for study if they required a clinically indicated lumbar puncture. Plasma samples were obtained in a subgroup of Christchurch infants. Preterm infants underwent advanced quantitative volumetric magnetic resonance imaging using a 1.5-Tesla scanner at term equivalent. One hundred forty-six infants were enrolled and 190 CSF and 42 plasma samples obtained. There was no significant correlation between paired CSF and plasma concentrations for any cytokine. In comparing plasma and CSF concentrations, levels of IL-8 were significantly higher in CSF than plasma. Preterm infants with MRI-defined cerebral white matter injury had higher levels of IL-6, IL-10, and TNF-alpha in the CSF than infants without such injury. Plasma cytokine concentrations may not reflect CSF cytokine levels or inflammatory events within the brain. Elevated CSF levels of cytokines in infants with white matter injury suggest an altered inflammatory balance.

Characterisation of the cytokine inflammatory response in LPS stimulated full-term cord blood

OBJECTIVE

Abnormal inflammatory responses are implicated in the pathogenesis of neonatal disease. This study aimed to describe the neonatal cytokine response using an in vitro model of stimulated cord blood.

METHODS

Cord blood samples (n = 12) were incubated in RPMI 1640 medium with and without lipopolysaccharide. Concentrations of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-8, interferon (IFN)-gamma and IL-10 were determined by multiplex immunoassay at 0, 1, 3, 6 and 24 hours of incubation. The difference between stimulated and control response was defined as the potential secretory capacity (mean +/- S.E.M.; pg/million white cells). Analysis included a Kruskal-Wallis test and post-hoc Mann-Whitney U test.

RESULTS

All cytokine capacities increased rapidly by 1 hour (p<0.001), except IL-10 (p=0.04). TNF-alpha peaked between 3-6 hours (1581 +/- 377 pg/million WC), declining by 24 hours. Similarly, IFN-gamma peaked at 3 hours. Capacity ascended throughout the incubation period for IL-6, IL-8 (631 +/- 75 pg/million WC) and IL-10 (311 +/- 37 pg/million WC). Overall, IFN-gamma capacity was lowest (72 +/- 10 pg/million WC) and IL-6 capacity was greatest (61489 +/- 7059 pg/million WC).

CONCLUSION

The neonatal inflammatory response is chronologically similar to that determined in adults. Immature neonatal T-cell function may account for the lower IFN-gamma production. These results may expand our knowledge of neonatal disease, etiology and management.

Fetal and neonatal inflammatory response and adverse outcome

This article will define the concept of fetal/neonatal inflammatory response, and examine the complex interaction between inflammation and neurotoxicity. There appear to be important interactions between infection/inflammation and hypoxia-ischaemia leading to cytokine release and subsequent brain injury. This article will also define adverse outcome and summarize the complexities inherent to neurodevelopmental assessment. Finally, this article will investigate the currently available evidence suggesting a link between inflammatory response and adverse neurodevelopmental outcome, and focus on those variables that need further study: timing and nature of the infectious/inflammatory process; established and new anti-insult strategies; morbidity in organs other than the brain; genetic influences; and environmental factors.

Maternal poly I:C exposure during pregnancy regulates TNF alpha, BDNF, and NGF expression in neonatal brain and the maternal-fetal unit of the rat

Maternal infection during pregnancy is associated with increased risk for neurodevelopmental disorders. Polyriboinosinic-polyribocytidilic acid (poly I:C) or saline was administered to rats to model maternal infection; levels of TNFalpha, brain-derived neurotrophic factor (BDNF), and nerve growth factor (NGF) were determined by ELISA. TNFalpha was significantly increased in maternal plasma, placenta, and amniotic fluid, while it was significantly decreased in fetal liver/spleen and neonatal brain. NGF and BDNF were significantly decreased in the placenta and fetal liver/spleen. There was no change in BDNF or NGF in the fetal or neonatal brain. Changes in TNFalpha, BDNF, and NGF after maternal exposure to poly I:C represent a potential mechanism through which maternal infection increases risk for neurodevelopmental disorders.

Brain injury induced by intracerebral injection of interleukin-1beta and tumor necrosis factor-alpha in the neonatal rat

To examine the possible role of inflammatory cytokines in mediating neonatal brain injury, we investigated effects of intracerebral injection of IL-1beta (IL-1beta) or tumor necrosis factor-alpha (TNFalpha) on brain injury in the neonatal rat. A stereotaxic intracerebral injection of IL-1beta or TNFalpha (10 ng per pup) was performed in postnatal day 5 (P5) SD rats. Although no necrosis of neurons was found, increased astrogliosis, as indicated by GFAP positive staining was observed 24 and 72 h following the injection of IL-1beta or TNFalpha. IL-1beta induced apoptotic cell death in the rat brain 24 h after the injection, as indicated by increases in positive TUNEL staining and caspase-3 activity, and apoptotic cell death was partially blocked by systemic administration of NBQX, an antagonist of the AMPA glutamate receptor. IL-1beta also significantly reduced the number of developing oligodendrocytes (OLs) 24 h after the injection and this impairment was not prevented by NBQX. On the contrary, TNFalpha induced a much smaller increase in the number of TUNEL positive cells and did not reduce the number of developing OLs. By P8, myelin basic protein (MBP) was clearly detected in the control rat brain, while MBP positive staining was very weak, if any, in the IL-1beta treated rat brain. MBP expression in the TNFalpha treated rat brain was less affected. The overall results indicate that IL-1beta may directly cause injuries to developing OLs and impair myelination in the neonatal rat brain and TNFalpha may have different roles in mediating brain injury.

Inflammatory brain damage in preterm newborns--dry numbers, wet lab, and causal inferences

Epidemiologic observations support the contention that infection, inflammation, and neonatal white matter damage (WMD) are associated. We also have documentation from multiple experimental models that infection/inflammation can damage developing white matter. Based on these observations in humans and animals, we offer causal inferences using widely accepted causal criteria and the multivariable model of causation. As much as we want to, however, we are reluctant to state unequivocally that inflammation causes WMD in humans born much before term. The main reason is that we lack convincing evidence that inflammation precedes WMD (temporal evidence). We also need more (and more detailed) observational studies clarifying the presumed infection --> inflammation --> WMD sequence before we can initiate intervention trials to reduce the risk of WMD.

Prenatal infection and risk for schizophrenia: IL-1beta, IL-6, and TNFalpha inhibit cortical neuron dendrite development

Prenatal exposure to infection increases risk for schizophrenia, and we have hypothesized that inflammatory cytokines, generated in response to maternal infection, alter neuron development and increase risk for schizophrenia. We sought to study the effect of cytokines generated in response to infection-interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNFalpha), and interleukin-6 (IL-6)-on the dendritic development of cortical neurons. Primary mixed neuronal cultures were obtained from E18 rats and exposed to 0, 100, or 1000 units (U)/ml of IL-1beta, TNFalpha, IL-6, or IL-1beta+TNFalpha for 44 h. MAP-2-positive neurons were randomly identified for each condition and the number of primary dendrites, nodes, and total dendrite length was determined. We found that 100 U of TNFalpha significantly reduced the number of nodes (27%, p=0.02) and total dendritic length (14%, p=0.04), but did not affect overall neuron survival. A measure of 100 U IL-1beta+TNFalpha significantly reduced the number of primary dendrites (17%, p=0.006), nodes (32%, p=0.001), and total dendritic length (30%, p<0.0001), although it did not affect overall neuron survival. At 1000 U, each cytokine significantly reduced the number of primary dendrites (14-24%), nodes (28-37%), as well as total dendritic length (25-30%); neuron survival was reduced by 14-21%. These results indicate that inflammatory cytokines can significantly reduce dendrite development and complexity of developing cortical neurons, consistent with the neuropathology of schizophrenia. These findings also support the hypothesis that cytokines play a key mechanistic role in the link between prenatal exposure to infection and risk for schizophrenia.

Interferon-gamma expression in periventricular leukomalacia in the human brain

Periventricular leukomalacia (PVL), the major lesion underlying cerebral palsy in survivors of prematurity, is characterized by focal periventricular necrosis and diffuse gliosis of immature cerebral white matter. Causal roles have been ascribed to hypoxiaischemia and maternal-fetal infection, leading to cytokine responses, inflammation, and oligodendrocyte cell death. Because interferon-gamma (IFN-gamma) is directly toxic to immature oligodendrocytes, we tested the hypothesis that it is expressed in PVL (N = 13) compared to age-adjusted controls (N = 31) using immunocytochemistry. In PVL, IFN-gamma immunopositive macrophages were clustered in necrotic foci, and IFN-gamma immunopositive reactive astrocytes were present throughout the surrounding white matter (WM). The difference in the number of IFN-gamma immunopositive glial cells/high power field (IFN-gamma score, Grades 0-3) between PVL cases (age-adjusted mean 2.59+/-0.25) and controls (age-adjusted mean 1.39+/-0.16) was significant (p<0.001). In the gliotic WM, the IFN-gamma score correlated with markers for lipid peroxidation, but not nitrative stress. A subset of premyelinating (04+) oligodendrocytes expressed IFN-gamma receptors in PVL and control cases, indicating that these cells are vulnerable to IFN-gamma toxicity via receptor-mediated interactions. In PVL, IFN-gamma produced by macrophages and reactive astrocytes may play a role in cytokine-induced toxicity to premyelinating oligodendrocytes as part of a cytokine response stimulated by ischemia and/or infection.