Protective effects of caffeine on chronic hypoxia-induced perinatal white matter injury

Chronic perinatal hypoxia reduces glutamate-aspartate transporter function in astrocytes through the Janus kinase/signal transducer and activator of transcription pathway

The cellular and molecular mechanisms that govern the response of the perinatal brain to injury remain largely unexplored. We investigated the role of white matter astrocytes in a rodent model of diffuse white matter injury produced by exposing neonatal mice to chronic hypoxia-a paradigm that mimics brain injury in premature infants. We demonstrate the absence of reactive gliosis in the immature white matter following chronic hypoxia, as determined by astrocyte proliferation index and glial fibrillary acidic protein levels. Instead, Nestin expression in astrocytes is transiently increased, and the glial-specific glutamate transporters glutamate-aspartate transporter (GLAST) and glutamate transporter 1 (GLT-1) are reduced. Finally, we demonstrate that Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling-which is important in both astrocyte development and response to injury-is reduced in the white matter following hypoxia, as well as in primary astrocytes exposed to hypoxia in vitro. Hypoxia and JAK/STAT inhibition reduce glutamate transporter expression in astrocytes, but unlike hypoxia JAK/STAT inhibition downregulates GLAST expression without affecting GLT-1, as demonstrated in vitro by treatment with JAK inhibitor I and in vivo by treatment with the JAK/STAT inhibitor AG490 [(E)-2-cyano-3-(3,4-dihydrophenyl)-N-(phenylmethyl)-2-propenamide]. Our findings (1) demonstrate specific changes in astrocyte function after perinatal hypoxia, which might contribute to the particular pathogenesis of perinatal white matter injury, (2) provide evidence that at least part of these changes result from a disturbance of the JAK/STAT pathway by hypoxia, and (3) identify JAK/STAT signaling as a potential therapeutic target to restore normal GLAST expression and uptake of glutamate after perinatal brain injury.

Mouse intermittent hypoxia mimicking apnoea of prematurity: effects on myelinogenesis and axonal maturation

Premature babies are at high risk for both infantile apnoea and long-term neurobehavioural deficits. Recent studies suggest that diffuse structural changes in brain white matter are a positive predictor of poor cognitive outcomes. Since oligodendrocyte maturation, myelination, axon development, and synapse formation mainly occur in the third trimester of gestation and first postnatal year, infantile apnoea could lead to and/or exaggerate white matter impairments in preterm neonates. Therefore, we investigated oligodendroglia and axon development in a neonatal mouse model of intermittent hypoxia between postnatal days 2 and 10. During critical phases of central nervous system development, intermittent hypoxia induced hypomyelination in the corpus callosum, striatum, fornix, and cerebellum, but not in the pons or spinal cord. Intermittent hypoxia-elicited alterations in myelin-forming processes were reflected by decreased expression of myelin proteins, including MBP, PLP, MAG, and CNPase, possibly due to arrested maturation of oligodendrocytes. Ultrastructural abnormalities were apparent in the myelin sheath and axon. Immature oligodendrocytes were more vulnerable to neonatal intermittent hypoxia exposures than developing axons, suggesting that hypomyelination may contribute, at least partially, to axonal deficits. Insufficient neurofilament synthesis with anomalous components of neurofilament subunits, β-tubulin, and MAP2 isoforms indicated immaturity of axons in intermittent hypoxia-exposed mouse brains. In addition, down-regulation of synapsin I, synaptophysin, and Gap-43 phosphorylation suggested a potential stunt in axonogenesis and synaptogenesis. The region-selective and complex impairment in brain white matter induced by intermittent hypoxia was further associated with electrophysiological changes that may underlie long-term neurobehavioural sequelae.

Desensitization of adenosine A(1) receptors in rat immature cortical neurons

Adenosine plays an important neuroprotective role in brain, usually mediated by the activation of adenosine A₁ receptors. Prolonged activation of a G-protein-coupled receptor generally leads to the partial loss of the responsiveness of receptor-mediated transduction pathways (desensitization). Rat immature cortical neurons were treated with 100 nM⁻N⁶-phenylisopropyladenosine (R-PIA), a selective A₁ receptor agonist, and the effect on adenosine A₁ receptor/adenylyl cyclase pathway was studied. Incubation with R-PIA for 6, 12, 24 and 48 h elicited a time-dependent decrease in adenosine A₁ receptors in plasma membranes (92, 58, 43 and 26% of control, respectively), which was associated with variations in microsomal fraction (21, 56, 124 and 233% of control, respectively), suggesting the internalization and down-regulation of adenosine A₁ receptors. Moreover, real-time PCR assays showed a significant increase in mRNA levels coding adenosine A₁ receptor after the longest treatment period (48 h). In addition, αGi₁₋₂ protein levels detected in microsomes and mRNA levels coding αGi₁ protein were increased after 48 h of treatment with R-PIA, suggesting the synthesis of new αGi₁ proteins. Finally, adenylyl cyclase inhibition elicited by 2-Chloro-N6-cyclopentyladenosine (CPA), a selective adenosine A₁ receptor agonist, was significantly reduced after 12, 24 and 48h of treatment (37, 24 and 23%, respectively) as compared to controls (54%), suggesting the desensitization of adenosine A₁ receptor/adenylyl cyclase pathway. These results suggest that adenosine A₁ receptors desensitize slowly after prolonged receptor activation in immature cortical neurons, showing mechanisms of desensitization similar to those described not only in fetal but also in adult rat brain.

Histopathological correlates of magnetic resonance imaging-defined chronic perinatal white matter injury

OBJECTIVE

Although magnetic resonance imaging (MRI) is the optimal imaging modality to define cerebral white-matter injury (WMI) in preterm survivors, the histopathological features of MRI-defined chronic lesions are poorly defined. We hypothesized that chronic WMI is related to a combination of delayed oligodendrocyte (OL) lineage cell death and arrested maturation of preoligodendrocytes (preOLs). We determined whether ex vivo MRI can distinguish distinct microglial and astroglial responses related to WMI progression and arrested preOL differentiation.

METHODS

We employed a preterm fetal sheep model of global cerebral ischemia in which acute WMI results in selective preOL degeneration. We developed novel algorithms to register histopathologically-defined lesions with contrast-weighted and diffusion-weighted high-field ex vivo MRI data.

RESULTS

Despite mild delayed preOL degeneration, preOL density recovered to control levels by 7 days after ischemia and was ~2 fold greater at 14 days. However, premyelinating OLs were significantly diminished at 7 and 14 days. WMI evolved to mostly gliotic lesions where arrested preOL differentiation was directly proportional to the magnitude of astrogliosis. A reduction in cerebral WM volume was accompanied by four classes of MRI-defined lesions. Each lesion type displayed unique astroglial and microglial responses that corresponded to distinct forms of necrotic or non-necrotic injury. High-field MRI defined 2 novel hypointense signal abnormalities on T(2) -weighted images that coincided with microscopic necrosis or identified astrogliosis with high sensitivity and specificity.

INTERPRETATION

These studies support the potential of high-field MRI for early identification of microscopic necrosis and gliosis with preOL maturation arrest, a common form of WMI in preterm survivors.

Intrauterine growth restriction affects the maturation of myelin

Intrauterine growth-restriction (IUGR) can lead to adverse neurodevelopmental sequelae in postnatal life. Our objective was to determine whether IUGR, induced by chronic placental insufficiency (CPI) in the guinea pig results in long-term deficits in brain myelination and could therefore contribute to altered neural function. CPI was induced by unilateral ligation of the uterine artery at mid-gestation (term~67 days of gestation; dg), producing growth-restricted (GR) foetuses (60 dg), neonates (1 week) and young adults (8 week); controls were from the unligated horn or sham-operated animals. In GR foetuses (n=8) and neonates (n=7), white matter (WM) volume was reduced (p<0.05); this reduction did not persist in young adults (n=11) however the corpus callosum width was reduced (p<0.05). Immunoreactivity (IR) for myelin basic protein (MBP), myelin-associated glycoprotein (MAG) and myelin proteolipid protein (PLP), all markers of myelinating oligodendrocytes (OL), was reduced in GR foetuses compared to controls. MBP was the most markedly affected with an abnormal retention of protein in the OL soma and a reduction of its incorporation into the myelin sheath. MAG-IR OL density was reduced (p<0.05), while the density of OLs immunoreactive for Olig-2, a transcription factor expressed throughout the entire OL lineage, was increased (p<0.05). MBP-, MAG- and PLP-IR recovered to control levels postnatally. These results suggest that IUGR transiently delays OL maturation and myelination in utero but that myelination and WM volume are restored to control levels postnatally. Long-term deficits in myelination are therefore unlikely to be the major factor underlying the altered neurological function which can be associated with IUGR.

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

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

A neonatal mouse model of intermittent hypoxia associated with features of apnea in premature infants

A neonatal mouse model of intermittent hypoxia (IH) simulating the recurring hypoxia/reoxygenation episodes of apnea of prematurity (AOP) was developed. C57BL/6 P2 pups were culled for exposure to either intermittent hypoxia or intermittent air as control. The IH paradigms consisted of alternation cycles of 20.9% O2 and either 8.0% or 5.7% O2 every 120 or 140s for 6h a day during daylight hours from day 2 to day 10 postnatally, i.e., roughly equivalent to human brain development in the perinatal period. IH exposures elicited modest to severe decrease in oxygen saturation along with bradycardia in neonatal mice, which were severity-dependent. Hypomyelination in both central and peripheral nervous systems was observed despite the absence of visible growth retardation. The neonatal mouse model of IH in this study partially fulfills the current diagnostic criteria with features of AOP, and provides opportunities to reproduce in rodents some of the pathophysiological changes associated with this disorder, such as alterations in myelination.

The protective effects of inosine against chemical hypoxia on cultured rat oligodendrocytes

Inosine is a purine nucleoside and is considered protective to neural cells including neurons and astrocytes against hypoxic injury. However, whether oligodendrocytes (OLs) could also be protected from hypoxia by inosine is not known. Here we investigated the effects of inosine on primarily cultured rat OLs injured by rotenone-mediated chemical hypoxia, and the mechanisms of the effects using ATP assay, MTT assay, PI-Hoechst staining, TUNEL, and immunocytochemistry. Results showed that rotenone exposure for 24 h caused cell death and impaired viability in both immature and mature OLs, while pretreatment of 10 mM inosine 30 min before rotenone administration significantly reduced cell death and improved the viability of OLs. The same concentration of inosine given 120 min after rotenone exposure also improved viability of injured mature OLs. Immunocytochemistry for nitrotyrosine and cellular ATP content examination indicated that inosine may protect OLs by providing ATP and scavenging peroxynitrite for cells. In addition, immature OLs were more susceptible to hypoxia than mature OLs; and at the similar degree of injury, inosine protected immature and mature OLs differently. Quantitative real-time PCR revealed that expression of adenosine receptors was different between these two stages of OLs. These data suggest that inosine protect OLs from hypoxic injury as an antioxidant and ATP provider, and the protective effects of inosine on OLs vary with cell differentiation, possibly due to the adenosine receptors expression profile. As OLs form myelin in the central nervous system, inosine could be used as a promising drug to treat demyelination-involved disorders.

Apnea of prematurity: pathogenesis and management strategies

Apnea of prematurity (AOP) is a significant clinical problem manifested by an unstable respiratory rhythm reflecting the immaturity of respiratory control systems. This review will address the pathogenesis of and treatment strategies for AOP. Although the neuronal mechanisms leading to apnea are still not well understood, recent decades have provided better insight into the generation of the respiratory rhythm and its modulation in the neonate. Ventilatory responses to hypoxia and hypercarbia are impaired and inhibitory reflexes are exaggerated in the neonate. These unique vulnerabilities predispose the neonate to the development of apnea. Treatment strategies attempt to stabilize the respiratory rhythm. Caffeine remains the primary pharmacological treatment modality and is presumed to work through blockade of adenosine receptors A(1) and A(2). Recent evidences suggest that A(2A) receptors may have a greater role than previously thought. AOP typically resolves with maturation suggesting increased myelination of the brainstem.

Adverse and protective influences of adenosine on the newborn and embryo: implications for preterm white matter injury and embryo protection

Few signaling molecules have the potential to influence the developing mammal as the nucleoside adenosine. Adenosine levels increase rapidly with tissue hypoxia and inflammation. Adenosine antagonists include the methylxanthines caffeine and theophylline. The receptors that transduce adenosine action are the A1, A2a, A2b, and A3 adenosine receptors (ARs). In the postnatal period, A1AR activation may contribute to white matter injury in the preterm infant by altering oligodendrocyte (OL) development. In models of perinatal brain injury, caffeine is neuroprotective against periventricular white matter injury (PWMI) and hypoxic-ischemic encephalopathy (HIE). Supporting the notion that blockade of adenosine action is of benefit in the premature infant, caffeine reduces the incidence of bronchopulmonary dysplasia and CP in clinical studies. In comparison with the adverse effects on the postnatal brain, adenosine acts via A1ARs to play an essential role in protecting the embryo from hypoxia. Embryo protective effects are blocked by caffeine, and caffeine intake during early pregnancy increases the risk of miscarriage and fetal growth retardation. Adenosine and adenosine antagonists play important modulatory roles during mammalian development. The protective and deleterious effects of adenosine depend on the time of exposure and target sites of action.

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

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

Towards improved animal models of neonatal white matter injury associated with cerebral palsy

Newborn neurological injuries are the leading cause of intellectual and motor disabilities that are associated with cerebral palsy. Cerebral white matter injury is a common feature in hypoxic-ischemic encephalopathy (HIE), which affects full-term infants, and in periventricular leukomalacia (PVL), which affects preterm infants. This article discusses recent efforts to model neonatal white matter injury using mammalian systems. We emphasize that a comprehensive understanding of oligodendrocyte development and physiology is crucial for obtaining new insights into the pathobiology of HIE and PVL as well as for the generation of more sophisticated and faithful animal models.

Methylxanthines during pregnancy and early postnatal life

World-wide, many fetuses and infants are exposed to methylxanthines via maternal consumption of coffee and other beverages containing these substances. Methylxanthines (caffeine, theophylline and aminophylline) are also commonly used as a medication for apnea of prematurity.The metabolism of methylxanthines is impaired in pregnant women, fetuses and neonates, leading to accumulating levels thereof. Methylxanthines readily passes the placenta barrier and enters all tissues and thus may affect the fetus/newborn at any time during pregnancy or postnatal life, given that the effector systems are mature.At clinically relevant doses, the major effector system for methylxanthines is adenosine receptors. Animal studies suggest that adenosine receptors in the cardiovascular, respiratory and immune system are developed at birth, but that cerebral adenosine receptors are not fully functional. Furthermore animal studies have shown protective positive effects of methylxanthines in situations of hypoxia/ischemia in neonates. Similarly, a positive long-term effect on lung function and CNS development was found in human preterm infants treated with high doses of caffeine for apneas. There is now evidence that the overall benefits from methylxanthine therapy for apnea of prematurity outweigh potential short-term risks.On the other hand it is important to note that experimental studies have indicated that long-term effects of caffeine during pregnancy and postnatally may include altered behavior and altered respiratory control in the offspring, although there is currently no human data to support this.Some epidemiology studies have reported negative effects on pregnancy and perinatal outcomes related to maternal ingestion of high doses of caffeine, but the results are inconclusive. The evidence base for adverse effects of caffeine in first third of pregnancy are stronger than for later parts of pregnancy and there is currently insufficient evidence to advise women to restrict caffeine intake after the first trimester.

Caffeine and brain development in very preterm infants

OBJECTIVE

Caffeine improves neurological outcome in very preterm infants, but the mechanisms responsible for this neurological benefit are unknown. The objective of this study was to assess whether caffeine influenced brain macro- or microstructural development in preterm infants.

METHODS

Seventy preterm infants <1,251 g birthweight randomly allocated to either caffeine (n = 33) or placebo (n = 37) underwent brain magnetic resonance imaging (MRI) at term-equivalent age; white and gray matter abnormalities were qualitatively scored, global and regional brain volumes were measured, and white matter microstructure was evaluated using diffusion-weighted imaging.

RESULTS

There were no significant differences between the groups in the extent of white matter or gray matter abnormality, or in global or regional brain volumes. In contrast, although only available in 28 children, caffeine exposure was associated with reductions in the apparent diffusion coefficient, and radial and axial diffusivity with the greatest impact in the superior brain regions. The alterations in diffusion measures were not mediated by lowering the rate of lung injury, known as bronchopulmonary dysplasia.

INTERPRETATION

These diffusion changes are consistent with improved white matter microstructural development in preterm infants who received caffeine.

Apotransferrin-induced recovery after hypoxic/ischaemic injury on myelination

We have previously demonstrated that aTf (apotransferrin) accelerates maturation of OLs (oligodendrocytes) in vitro as well as in vivo. The purpose of this study is to determine whether aTf plays a functional role in a model of H/I (hypoxia/ischaemia) in the neonatal brain. Twenty-four hours after H/I insult, neonatal rats were intracranially injected with aTf and the effects of this treatment were evaluated in the CC (corpus callosum) as well as the SVZ (subventricular zone) at different time points. Similar to previous studies, the H/I event produced severe demyelination in the CC. Demyelination was accompanied by microglial activation, astrogliosis and iron deposition. Ferritin levels increased together with lipid peroxidation and apoptotic cell death. Histological examination after the H/I event in brain tissue of aTf-treated animals (H/I aTF) revealed a great number of mature OLs repopulating the CC compared with saline-treated animals (H/I S). ApoTf treatment induced a gradual increase in MBP (myelin basic protein) and myelin lipid staining in the CC reaching normal levels after 15 days. Furthermore, significant increase in the number of OPCs (oligodendroglial progenitor cells) was found in the SVZ of aTf-treated brains compared with H/I S. Specifically, there was a rise in cells positive for OPC markers, i.e. PDGFRα and SHH⁺ cells, with a decrease in cleaved-caspase-3⁺ cells compared with H/I S. Additionally, neurospheres from aTf-treated rats were bigger in size and produced more O4/MBP⁺ cells. Our findings indicate a role for aTf as a potential inducer of OLs in neonatal rat brain in acute demyelination caused by H/I and a contribution to the differentiation/maturation of OLs and survival/migration of SVZ progenitors after demyelination in vivo.

Effects of congenital heart disease on brain development

Brain and heart development occurs simultaneously in the fetus with congenital heart disease. Early morphogenetic programs in each organ share common genetic pathways. Brain development occurs across a more protracted time-course with striking brain growth and activity-dependent formation and refinement of connections in the third trimester. This development is associated with increased metabolic activity and the brain is dependent upon the heart for oxygen and nutrient delivery. Congenital heart disease leads to derangements of fetal blood flow that result in impaired brain growth and development that can be measured with advanced magnetic resonance imaging. Delayed development results in a unique vulnerability to cerebral white matter injury in newborns with congenital heart disease. Delayed brain development and acquired white matter injury may underlay mild but pervasive neurodevelopmental impairment commonly observed in children following neonatal congenital heart surgery.

Diazoxide promotes oligodendrocyte precursor cell proliferation and myelination

Background

Several clinical conditions are associated with white matter injury, including periventricular white matter injury (PWMI), which is a form of brain injury sustained by preterm infants. It has been suggested that white matter injury in this condition is due to altered oligodendrocyte (OL) development or death, resulting in OL loss and hypomyelination. At present drugs are not available that stimulate OL proliferation and promote myelination. Evidence suggests that depolarizing stimuli reduces OL proliferation and differentiation, whereas agents that hyperpolarize OLs stimulate OL proliferation and differentiation. Considering that the drug diazoxide activates K_ATP channels to hyperpolarize cells, we tested if this compound could influence OL proliferation and myelination.

Methodology/Findings

Studies were performed using rat oligodendrocyte precursor cell (OPC) cultures, cerebellar slice cultures, and an in vivo model of PWMI in which newborn mice were exposed to chronic sublethal hypoxia (10% O₂). We found that K_ATP channel components Kir 6.1 and 6.2 and SUR2 were expressed in oligodendrocytes. Additionally, diazoxide potently stimulated OPC proliferation, as did other K_ATP activators. Diazoxide also stimulated myelination in cerebellar slice cultures. We also found that diazoxide prevented hypomyelination and ventriculomegaly following chronic sublethal hypoxia.

Conclusions

These results identify KATP channel components in OLs and show that diazoxide can stimulate OL proliferation in vitro. Importantly we find that diazoxide can promote myelination in vivo and prevent hypoxia-induced PWMI.

Timing of appearance of late oligodendrocyte progenitors coincides with enhanced susceptibility of preterm rabbit cerebral white matter to hypoxia-ischemia

Emerging evidence supports that premature infants are susceptible to both cerebral white and gray matter injury. In a fetal rabbit model of placental insufficiency, preterm rabbits at embryonic day 22 (E22) exhibited histologic evidence of gray matter injury but minimal white matter injury after global hypoxia-ischemia (H-I). We hypothesized that the dissociation between susceptibility to gray and white matter injury at E22 was related to the timing of appearance of late oligodendrocyte progenitors (preOLs) that are particularly vulnerable in preterm human white matter lesions. During normal rabbit oligodendrocyte (OL) lineage progression, early OL progenitors predominated at E22. PreOL density increased between E24 and E25 in major forebrain white matter tracts. After H-I at E22 and E25, we observed a similar magnitude of cerebral H-I, assessed by cortical microvascular blood flow, and gray matter injury, assessed by caspase activation. However, the increased preOL density at E25 was accompanied by a significant increase in acute white matter injury after H-I that coincided with enhanced preOL degeneration. At E29, significant white matter atrophy developed after H-I at E25 but not E22. Thus, the timing of appearance of preOLs coincided with onset of a developmental window of enhanced white but not gray matter susceptibility to H-I.

Simvastatin attenuates hypomyelination induced by hypoxia-ischemia in neonatal rats

OBJECTIVES

Simvastatin, the most widely used cholesterol-lowering drug, has been reported to protect the adult brain from ischemia. Nevertheless, little is known about its action on developing brain after stroke. Although a few reports have found recently that simvastatin displays anti-inflammation and anti-apoptosis properties and improves the cognitive and morphological consequences in the neonatal rats after hypoxia-ischemia (HI) damage, to our best knowledge, there has been no study of the effect of it on myelin formation after neonatal brain damage. Therefore, we investigated whether simvastatin could promote the myelination of oligodendrocytes in the neonatal rats after HI and explored the possible role of microglial responses in this process.

METHODS

Postnatal day 7 Sprague-Dawley rats were subjected to HI. White matter integrity and myelination were evaluated by the densitometry of myelin basic protein (MBP) immunostaining. OX-42 immunoreactivity and nissl staining were used for identifying microglial responses and the structure changes of white matter and adjacent gray matter after HI. Simvastatin was administrated prophylactically to rats.

RESULTS

HI induced serious hypomyelination especially in external and internal capsules 3 and 7 days after HI, accompanying with microglial activation remarkably. Simvastatin treatment greatly increased the densities of MBP immunostaining, inhibited microglial activation and reduced the numbers of pyknotic cells and neuronal loss.

DISCUSSION

The present study shows that simvastatin treatment in neonatal rats attenuates HI-induced developing oligodendrocytes injury and hypomyelination. Its anti-inflammatory properties via suppression of microglial activation are likely to contribute to this action. It provides experimental evidence to support the neuroprotective effects of statins in neonatal ischemic stroke.

Caffeine protects against alcoholic liver injury by attenuating inflammatory response and oxidative stress

OBJECTIVE AND DESIGN

The present investigation was designed to determine the effects of caffeine on alcohol-induced hepatic injury in mice.

MATERIAL

Five groups of mice (8 each) were used.

TREATMENT

The mice treated with different doses of caffeine (5, 10, and 20 mg/kg, respectively).

METHODS

The degree of alcoholic liver injury was evaluated biochemically by measuring serum markers and pathological examination. Real time PCR and ELISA methods were used to check the expression of cytokines and CYP 450.

RESULTS

Treatment with caffeine significantly attenuated the elevated serum aminotransferase enzymes and reduced the severe extent of hepatic cell damage, steatosis and the immigration of inflammatory cells. Interestingly, caffeine decreased hepatic mRNA expression of lipogenic genes, while it had no effect on protein expression of hepatic CYP2E1. Furthermore, caffeine decreased serum and tissue inflammatory cytokines levels, tissue lipid peroxidation and inhibited the necrosis of hepatocytes. Kupffer cells isolated from ethanol-fed mice produced high amounts of reactive oxygen species (ROS) and tumor necrosis factor alpha (TNF-alpha), whereas Kupffer cells from caffeine treatment mice produced less ROS and TNF-alpha.

CONCLUSIONS

These findings suggest that caffeine may represent a novel, protective strategy against alcoholic liver injury by attenuating oxidative stress and inflammatory response.

Regulation of cerebrospinal fluid production by caffeine consumption

Background

Caffeine is the most commonly consumed psycho-stimulant in the world. The effects of caffeine on the body have been extensively studied; however, its effect on the structure of the brain has not been investigated to date.

Results

In the present study we found that the long-term consumption of caffeine can induce ventriculomegaly; this was observed in 40% of the study rats. In the caffeine-treated rats with ventriculomegaly, there was increased production of CSF, associated with the increased expression of Na⁺, K⁺-ATPase and increased cerebral blood flow (CBF). In contrast to the chronic effects, acute treatment with caffeine decreased the production of CSF, suggesting 'effect inversion' associated with caffeine, which was mediated by increased expression of the A₁ adenosine receptor, in the choroid plexus of rats chronically treated with caffeine. The involvement of the A₁ adenosine receptor in the effect inversion of caffeine was further supported by the induction of ventriculomegaly and Na⁺, K⁺-ATPase, in A₁ agonist-treated rats.

Conclusion

The results of this study show that long-term consumption of caffeine can induce ventriculomegaly, which is mediated in part by increased production of CSF. Moreover, we also showed that adenosine receptor signaling can regulate the production of CSF by controlling the expression of Na⁺, K⁺-ATPase and CBF.

Hypoxic injury during neonatal development in murine brain: correlation between in vivo DTI findings and behavioral assessment

Preterm birth results in significant neurodevelopmental disability. A neonatal rodent model of chronic sublethal hypoxia (CSH), which mimics effects of preterm birth, was used to characterize neurodevelopmental consequences of prolonged exposure to hypoxia using tissue anisotropy measurements from diffusion tensor imaging. Corpus callosum, cingulum, and fimbria of the hippocampus revealed subtle, yet significant, hypoxia-induced modifications during maturation (P15-P51). Anisotropy differences between control and CSH mice were greatest at older ages (>P40) in these regions. Neither somatosensory cortex nor caudate putamen revealed significant differences between control and CSH mice at any age. We assessed control and CSH mice using tests of general activity and cognition for behavioral correlates of morphological changes. Open-field task revealed greater locomotor activity in CSH mice early in maturation (P16-P18), whereas by adolescence (P40-P45) differences between control and CSH mice were insignificant. These results may be associated with lack of cortical and subcortical anisotropy differences between control and CSH mice. Spatial-delayed alternation and free-swim tasks in adulthood revealed lasting impairments for CSH mice in spatial memory and behavioral laterality. These differences may correlate with anisotropy decreases in hippocampal and callosal connectivities of CSH mice. Thus, CSH mice revealed developmental and behavioral deficits that are similar to those observed in low birth weight preterm infants.

Effects of restricted caffeine intake by mother on fetal, neonatal and pregnancy outcome

BACKGROUND

Maternal caffeine consumption during pregnancy may have adverse effects on fetal, neonatal and maternal outcomes.

OBJECTIVES

This review investigates the effects of restricting caffeine intake by mothers on fetal, neonatal and pregnancy outcomes.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (December 2008), scanned bibliographies of published studies and corresponded with investigators.

SELECTION CRITERIA

Randomised controlled trials including quasi-randomised controlled trials (RCTs) investigating the effect of caffeine and/or supplementary caffeine versus restricted caffeine intake or placebo on pregnancy outcome.

DATA COLLECTION AND ANALYSIS

The two review authors independently assessed trial quality and extracted data.

MAIN RESULTS

One study met the inclusion criteria. Caffeinated instant coffee (568 women) was compared with decaffeinated instant coffee (629 women) and it was found that reducing the caffeine intake of regular coffee drinkers (3+ cups/day) during the second and third trimester by an average of 182 mg/day did not affect birthweight or length of gestation.

AUTHORS' CONCLUSIONS

There is insufficient evidence to confirm or refute the effectiveness of caffeine avoidance on birthweight or other pregnancy outcomes. There is a need to conduct high-quality, double-blinded RCTs to determine whether caffeine has any effect on pregnancy outcome.

Brain maturation is delayed in infants with complex congenital heart defects

OBJECTIVE

Small head circumferences and white matter injury in the form of periventricular leukomalacia have been observed in populations of infants with severe forms of congenital heart defects. This study tests the hypothesis that congenital heart defects delay in utero structural brain development.

METHODS

Full-term infants with hypoplastic left heart syndrome or transposition of the great arteries were prospectively evaluated with preoperative brain magnetic resonance imaging. Patients with independent risk factors for abnormal brain development (shock, end-organ injury, or intrauterine growth retardation) were excluded. Outcome measures included head circumferences and the total maturation score on magnetic resonance imaging. Total maturation score is a previously validated semiquantitative anatomic scoring system used to assess whole brain maturity. The total maturation score evaluates 4 parameters of maturity: (1) myelination, (2) cortical infolding, (3) involution of glial cell migration bands, and (4) presence of germinal matrix tissue.

RESULTS

The study cohort included 29 neonates with hypoplastic left heart syndrome and 13 neonates with transposition of the great arteries at a mean gestational age of 38.9 +/- 1.1 weeks. Mean head circumference was 1 standard deviation below normal. The mean total maturation score for the cohort was 10.15 +/- 0.94, significantly lower than reported normative data in infants without congenital heart defects, corresponding to a delay of 1 month in structural brain development.

CONCLUSION

Before surgery, term infants with hypoplastic left heart syndrome and transposition of the great arteries have brains that are smaller and structurally less mature than expected. This delay in brain development may foster susceptibility to periventricular leukomalacia in the preoperative, intraoperative, and postoperative periods.

Preoperative brain injury in transposition of the great arteries is associated with oxygenation and time to surgery, not balloon atrial septostomy

BACKGROUND

Preoperative brain injury is an increasingly recognized phenomenon in neonates with complex congenital heart disease. Recently, reports have been published that associate preoperative brain injury in neonates with transposition of the great arteries with the performance of balloon atrial septostomy (BAS), a procedure that improves systemic oxygenation preoperatively. It is unclear whether BAS is the cause of brain injury or is a confounder, because neonates who require BAS are typically more hypoxemic. We sought to determine the relationship between preoperative brain injury in neonates with transposition of the great arteries and the performance of BAS. We hypothesized that brain injury results from hypoxic injury, not from the BAS itself.

METHODS AND RESULTS

Infants with transposition of the great arteries (n=26) were retrospectively included from a larger cohort of infants with congenital heart disease who underwent preoperative brain MRI as part of 2 separate prospective studies. Data collected included all preoperative pulse oximetry recordings, all values from preoperative arterial blood gas measurements, and BAS procedure data. MRI scans were performed on the day of surgery, before the surgical repair. Of the 26 neonates, 14 underwent BAS. No stroke was seen in the entire cohort, whereas 10 (38%) of 26 patients were found to have hypoxic brain injury in the form of periventricular leukomalacia. Periventricular leukomalacia was not associated with BAS; however, neonates with periventricular leukomalacia had lower preoperative oxygenation (P=0.026) and a longer time to surgery (P=0.028) than those without periventricular leukomalacia.

CONCLUSIONS

Preoperative brain injury in neonates with transposition of the great arteries is associated with hypoxemia and longer time to surgery. We found no association between BAS and brain injury.

[Is it possible to protect the preterm infant brain and to decrease later neurodevelopmental disabilities?]

With improving neonatal survival for very premature babies, the challenge for neonatalogists is to ameliorate outcome of surviving babies. Several pharmacological molecules have been shown to have protective effects in different types of in vitro or in vivo animal models of acquired cerebral brain damages. However translational research and conduction of therapeutic trials in human remain difficult due to failure to recognize start of deleterious cascade leading to cerebral damage and additional toxic effect of potential protective molecules. This review concentrates on best evidence emerging in recent years on prevention on brain damage by early drug administration. It has been shown in two randomised trials that prenatal low-dose of magnesium sulphate does not increase paediatric mortality in very-preterm infants and has non significant neuroprotective effects on occurrence of motor dysfunction (with a 0.62 odds ratio in the French trial Premag and 0.71 relative risk in the Australian trial ACTOMgSO4), justifying that magnesium sulphate should be discussed as a stand-alone treatment or as part of a combination treatment, at least in the context of clinical trials. Antenatal corticosteroid therapy increases the survival of very-preterm infants, including the most immature. Moreover in an observational recent study of the Epipage cohort, it has been observed a significant decrease in white matter injury in the 28-32 weeks' gestation group but no effect on long term outcome and behaviour. Conversely in the most immature of the 24-27 weeks' gestation group, no effect has been detected either in white matter injury incidence or in long term outcome rates. Caffeine has a protective effect since a decrease in cerebral palsy has been noted in the caffeine group in a randomised trial studying caffeine versus placebo. For what concern other widely used potential protective molecules during the perinatal period, there is no evidence of cerebral protection with indometacine, nitric oxide, eythropoietin, phenobarbital, and etamsylate. Due to their specific properties, a careful evaluation of aspirin, anaesthetic drugs and tocolytics should be done in the next months.

Neuroprotection in infant heart surgery

Neonatal hypoxic-ischemic encephalopathy, prematurity, sepsis-meningitis, and serious forms of complex congenital heart disease requiring infant heart surgery are just a few examples of disorders that share high mortality and morbidity rates. Newborn heart surgery represents a period of planned and deliberate ischemia-reperfusion injury, which is obliged to occur to cure or palliate complex forms of congenital heart disease. Advances in cardiothoracic surgical and anesthetic techniques, including cardiopulmonary bypass and deep hypothermic circulatory arrest, have substantially decreased mortality, expanding the horizon to address functional neurologic and cardiac outcomes in long-term survivors. Interest in the functional status of survivors now stretches beyond the newborn period to childhood, adolescence, and adulthood.

Neonatal apnea: what's new?

Apnea of prematurity (AOP) remains a major clinical problem in present day neonatology that warrants frequent evaluations and imposes challenges in therapeutic strategies. Although the pathogenesis of AOP is poorly understood, it is probably a manifestation of physiologic immaturity of breathing control rather than a pathologic disorder. Immature breathing responses to hypoxia, hypercapnia and exaggerated inhibitory pulmonary reflexes in preterm infants might also contribute to the occurrence or severity of AOP. Recent data suggest a role for genetic predisposition. Although typically resolve with maturation, the role of bradycardia and desaturation episodes associated with AOP in the development of sleep disorder breathing and neurodevelopmental delay needs further clarification. Pharmacological treatment with methylxanthines and CPAP remain the mainstay for treatment of AOP. However, recent studies have implicated central inhibitory neuromodulators including prostaglandins, GABA and adenosine in its pathogenesis, the fact that might provide future specific targets for treatment. This review will summarize new insights involving these issues as well as others involving the pathogenesis, treatment strategies and consequences of apnea in premature infants.

Rolipram, a phosphodiesterase type IV inhibitor, exacerbates periventricular white matter lesions in rat pups

Periventricular white matter injury is the leading cause of cerebral palsy in premature infants for which no effective treatments are available. Our previous studies have demonstrated that pharmacological activation of the cAMP response element-binding protein (CREB) signaling pathway, before hypoxic-ischemia protected against neuronal injury in neonatal rats. We examined whether rolipram, a phosphodiesterase type IV inhibitor, treatment after hypoxic-ischemia is protective against white matter injury in neonatal rats. Rats were exposed to hypoxia-ischemia (HI) on P7 and then treated with daily injections of various doses of rolipram (P7-P11). Immunohistochemical staining for myelin basic protein, ED1, glial fibrillary acidic protein, CREB and O1 were examined on P11. We found that the periventricular white matter and deep cortical lesions were exacerbated by rolipram administration after HI injury. The lesions in the rolipram-treated group also showed increased astrogliosis and increased CREB phosphorylation in the activated microglia and astrocytes. Furthermore, the rolipram-posttreated HI group had markedly depleted preoligodendrocytes in the ipsilateral hemisphere, which may be related to decreased preoligodendrocytes proliferation after rolipram treatment per se. These data suggest that rolipram treatment after hypoxic-ischemia is not protective; in contrast, rolipram may exacerbate hypoxic-ischemic white matter injury in neonatal rat brains.

Magnetic resonance imaging and developmental outcome following preterm birth: review of current evidence

Preterm birth is associated with an increased risk of developmental difficulties. Magnetic resonance imaging (MRI) is increasingly being used to identify damage to the brain following preterm birth. It is hoped this information will aid prognostication and identify neonates who would benefit from early therapeutic intervention. Cystic periventricular white matter damage has traditionally been associated with abnormal motor developmental and cerebral palsy, but its presence on MRI does not preclude normal cognitive development. This has led to increasing interest in the identification of diffuse periventricular white matter damage with conventional and sophisticated MRI. However, the correlation between these appearances and developmental outcome remains unclear. Measurements of the size, volumes, and growth rates of many regions of the brain, such as the corpus callosum, ventricular system, cortex, deep grey matter, and cerebellum, are all also altered following preterm birth, but there is insufficient evidence to use this data in the clinical setting. This article is a review of the current evidence on MRI and developmental outcome, suggesting possible indications for the use of MRI following preterm birth.

Potential therapeutic interest of adenosine A2A receptors in psychiatric disorders

The interest on targeting adenosine A(2A) receptors in the realm of psychiatric diseases first arose based on their tight physical and functional interaction with dopamine D(2) receptors. However, the role of central A(2A) receptors is now viewed as much broader than just controlling D(2) receptor function. Thus, there is currently a major interest in the ability of A(2A) receptors to control synaptic plasticity at glutamatergic synapses. This is due to a combined ability of A(2A) receptors to facilitate the release of glutamate and the activation of NMDA receptors. Therefore, A(2A) receptors are now conceived as a normalizing device promoting adequate adaptive responses in neuronal circuits, a role similar to that fulfilled, in essence, by dopamine. This makes A(2A) receptors particularly attractive targets to manage psychiatric disorders since adenosine may act as go-between glutamate and dopamine, two of the key players in mood processing. Furthermore, A(2A) receptors also control glia function and brain metabolic adaptation, two other emerging mechanisms to understand abnormal processing of mood, and A(2A) receptors are important players in controlling the demise of neurodegeneration, considered an amplificatory loop in psychiatric disorders. Current data only provide an indirect confirmation of this putative role of A(2A) receptors, based on the effects of caffeine (an antagonist of both A(1) and A(2A) receptors) in psychiatric disorders. However, the introduction of A(2A) receptors antagonists in clinics as anti-parkinsonian agents is hoped to bolster our knowledge on the role of A(2A) receptors in mood disorders in the near future.

Arrested oligodendrocyte lineage maturation in chronic perinatal white matter injury

OBJECTIVE

Abnormal myelination is a major pathological sequela of chronic periventricular white matter injury in survivors of premature birth. We tested the hypothesis that myelination failure in chronic hypoxia-ischemia-induced periventricular white matter injury is related to persistent depletion of the oligodendrocyte (OL) precursor pool required to generate mature myelinating OLs.

METHODS

A neonatal rat model of hypoxia-ischemia was used where acute degeneration of late OL progenitors (preOLs) occurs via a mostly caspase-independent mechanism. The fate of OL lineage cells in chronic cerebral lesions was defined with OL lineage-specific markers.

RESULTS

Acute caspase-3-independent preOL degeneration from hypoxia-ischemia was significantly augmented by delayed preOL death that was caspase-3-dependent. Degeneration of preOLs was offset by a robust regenerative response that resulted in a several-fold expansion in the pool of surviving preOLs in chronic lesions. However, these preOLs displayed persistent maturation arrest with failure to differentiate and generate myelin. When preOL-rich chronic lesions sustained recurrent hypoxia-ischemia at a time in development when white matter is normally resistant to injury, an approximately 10-fold increase in caspase-dependent preOL degeneration occurred relative to lesions caused by a single episode of hypoxia-ischemia.

INTERPRETATION

The mechanism of myelination failure in chronic white matter lesions is related to a combination of delayed preOL degeneration and preOL maturation arrest. The persistence of a susceptible population of preOLs renders chronic white matter lesions markedly more vulnerable to recurrent hypoxia-ischemia. These data suggest that preOL maturation arrest may predispose to more severe white matter injury in preterm survivors that sustain recurrent hypoxia-ischemia.

Cerebral blood flow heterogeneity in preterm sheep: lack of physiologic support for vascular boundary zones in fetal cerebral white matter

Periventricular white matter (PVWM) injury is the leading cause of neurologic disability in survivors of prematurity. To address the role of ischemia in PVWM and cerebral cortical injury, we hypothesized that immaturity of spatially distal vascular 'end zones' or 'border zones' predisposes PVWM to greater decreases in cerebral blood flow (CBF) than more proximal structures. We quantified regional CBF with fluorescently labeled microspheres in 0.65 gestation fetal sheep in histopathologically defined three-dimensional regions by post hoc digital dissection and coregistration algorithms. Basal flow in PVWM was significantly lower than in gyral white matter and cortex, but was equivalent in superficial, middle, and deep PVWM. Absolute and relative CBF (expressed as percentage of basal) did not differ significantly during ischemia or reperfusion between PVWM, gyral white matter, or cortex. Moreover, CBF during ischemia-reperfusion was equivalent in three adjacent PVWM levels and was not consistent with the magnitude of severity of PVWM injury, defined by TUNEL (terminal deoxynucleotidyltransferase-mediated dUPT nick end labeling) staining. However, the magnitude of ischemia was predicted by the severity of discrete cortical lesions. Hence, unlike cerebral cortex, unique CBF disturbances did not account for the distribution of PVWM injury. Previously defined cellular maturational factors, thus, appear to have a greater influence on PVWM vulnerability to ischemic injury than the presence of immature vascular boundary zones.

Sustained hypoxia modulates mitochondrial DNA content in the neonatal rat brain

The effects of placental insufficiency and preterm birth on neurodevelopment can be modeled in experimental settings of neonatal hypoxia in rodents. Here, rat pups were reared in reduced oxygen (9.5%) for 11 days, starting on postnatal day 3 (P3). This led to a significant reduction in brain and body weight gain in hypoxic pups compared to age-matched normoxia-reared controls, plausibly reflecting an inability to fulfill the energetic needs of normal growth and development. Adaptive processes designed to augment energetic capacity in eukaryotes include stimulation of mitochondrial biogenesis. We show that after 11 days of sustained hypoxia, the levels of nuclear respiratory factor-1 and mitochondrial transcription factor A are elevated and the content of mitochondrial DNA (mtDNA) is greater in the hypoxic P14 pup brain compared to normoxic conditions. Corresponding immunohistochemical analyses reveal increased density of mtDNA in large cortical neurons. In contrast, no changes in mtDNA content are observed in the brain of pups reared for 24 h (P3-P4) under hypoxic conditions. Together, these data suggest that prolonged inadequate oxygenation may trigger a compensatory increase in neuronal mitochondrial DNA content to partially mitigate compromised energy homeostasis and reduced energetic capacity in the developing hypoxic brain.

Perinatal hypoxia induces anterior chamber changes in the eyes of offspring fish

Hypoxia is a consistent challenge for aquatic animals. It is a pressing environmental problem; hypoxia can cause cranial edema and ovarium dysfunction in fish. Although several studies have reported the effect of hypoxic insult to the visual system, the hypoxic effect on perinatal animals and in particular their offspring has yet to be elucidated. In this study, activated caspase-3 activity was investigated using immunohistochemistry in order to examine the perinatal hypoxic damage in offspring fish. Offspring were divided into groups based on different time points of sacrifice. This allowed assessment of ocular development for different age groups. The results indicated that perinatal hypoxia induced ocular developmental defects in the offspring. The defects took the form of trabecular cell death and fibre degeneration, corneal thinning and lens fibre derangement. A concomitant change in intraocular pressure was recorded by tonometer in the experimental animals compared with the controls. Further investigation should be initiated to develop strategies to prevent developmental disability due to perinatal hypoxia and to increase survivability of the offspring.

A1 adenosine receptors play an essential role in protecting the embryo against hypoxia

Embryos can be exposed to environmental factors that induce hypoxia. Currently, our understanding of the effects of hypoxia on early mammalian development is modest. Potential mediators of hypoxia action include the nucleoside adenosine, which acts through A(1) adenosine receptors (A(1)ARs) and mediates adverse effects of hypoxia on the neonatal brain. We hypothesized that A(1)ARs may also play a role in mediating effects of hypoxia on the embryo. When pregnant dams were exposed to hypoxia (10% O(2)) beginning at embryonic day (E) 7.5 or 8.5 and continued for 24-96 h, A(1)AR+/+ embryos manifested growth inhibition and a disproportionate reduction in heart size, including thinner ventricular walls. Yet, when dams were exposed to hypoxia, embryos lacking A(1)ARs (A(1)AR-/-) had much more severe growth retardation than A(1)AR+/+ or +/- embryos. When levels of hypoxia-inducible factor 1alpha (HIF1alpha) were examined, A(1)AR-/- embryos had less stabilized HIF1alpha protein than A(1)AR+/- littermates. Normal patterns of cardiac gene expression were also disturbed in A(1)AR-/- embryos exposed to hypoxia. These results show that short periods of hypoxia during early embryogenesis can result in intrauterine growth retardation. We identify adenosine and A(1)ARs as playing an essential role in protecting the embryo from hypoxia.