Long-term neuroprotection with 2-iminobiotin, an inhibitor of neuronal and inducible nitric oxide synthase, after cerebral hypoxia-ischemia in neonatal rats

2-iminobiotin, a selective inhibitor of nitric oxide synthase, improves memory and learning in a rat model after four vessel occlusion, mimicking cardiac arrest

Survivors of out-of-hospital cardiac arrest (OHCA) experience between 30% and 50% cognitive deficits several years post-discharge. Especially spatial memory is affected due to ischemia-induced neuronal damage in the hippocampus. Aim of this study was to investigate the potential neuroprotective effect of 2-iminobiotin (2-IB), a biotin analogue, on memory and learning in a four-vessel occlusion model of global ischemia using the Water Maze test. Sprague-Dawley rats were randomly assigned to either sham operation (n = 6), vehicle treatment (n = 20), 1.1 (n = 15), 3.3 (n = 14), 10 (n = 14), or 30 mg/kg/dose 2-IB treatment (n = 15). Treatment was subcutaneously (s.c.) administered immediately upon reperfusion, at 12h, and at 24h after reperfusion. Memory function on day 32 was significantly preserved in all doses of 2-IB rats compared to vehicle, as was the learning curve in the 1.1, 3.3 and 30 mg/kg dose group. Adult rats treated s.c. with 3 gifts of 2-IB every 12 h in a dose range of 1.1-30 mg/kg/dose directly upon reperfusion showed significant improved memory and learning after four vessel occlusion compared to vehicle-treated rats. Since 2-IB has already shown to be safe in a phase 1 clinical trial in adult human volunteers, it is a suitable candidate for translation to a human phase 2 study after OHCA.

Arsenic alters nitric oxide signaling similar to autism spectrum disorder and Alzheimer's disease-associated mutations

Epidemiological studies have proven that exposure to Arsenic (AS) leads to the development of many neurological disorders. However, few studies have investigated its molecular mechanisms in the brain. Our previous work has revealed nitric oxide (NO)-mediated apoptosis and SNO reprogramming in the cortex following arsenic treatment, yet the role of NO and S-nitrosylation (SNO) in AS-mediated neurotoxicity has not been investigated. Therefore, we have conducted a multidisciplinary in-vivo study in mice with two different doses of Sodium Arsenite (SA) (0.1 ppm and 1 ppm) in drinking water. We used the novel SNOTRAP-based mass spectrometry method followed by the bioinformatics analysis, Western blot validation, and five different behavioral tests. Bioinformatics analysis of SA-treated mice showed significant SNO-enrichment of processes involved in mitochondrial respiratory function, endogenous antioxidant systems, transcriptional regulation, cytoskeleton maintenance, and regulation of apoptosis. Western blotting showed increased levels of cleaved PARP-1 and cleaved caspase-3 in SA-treated mice consistent with SA-induced apoptosis. Behavioral studies showed significant cognitive dysfunctions similar to those of Autism spectrum disorder (ASD) and Alzheimer's disease (AD). A comparative analysis of the SNO-proteome of SA-treated mice with two transgenic mouse strains, models of ASD and AD, showed molecular convergence of SA environmental neurotoxicity and the genetic mutations causing ASD and AD. This is the first study to show the effects of AS on SNO-signaling in the striatum and hippocampus and its effects on behavioral characteristics. Finally, further investigation of the NO-dependent mechanisms of AS-mediated neurotoxicity may reveal new drug targets for its prevention.

Free radicals and neonatal encephalopathy: mechanisms of injury, biomarkers, and antioxidant treatment perspectives

Neonatal encephalopathy (NE), most commonly a result of the disruption of cerebral oxygen delivery, is the leading cause of neurologic disability in term neonates. Given the key role of free radicals in brain injury development following hypoxia-ischemia-reperfusion, several oxidative biomarkers have been explored in preclinical and clinical models of NE. Among these, antioxidant enzyme activity, uric acid excretion, nitric oxide, malondialdehyde, and non-protein-bound iron have shown promising results as possible predictors of NE severity and outcome. Owing to high costs and technical complexity, however, their routine use in clinical practice is still limited. Several strategies aimed at reducing free radical production or upregulating physiological scavengers have been proposed for NE. Room-air resuscitation has proved to reduce oxidative stress following perinatal asphyxia and is now universally adopted. A number of medications endowed with antioxidant properties, such as melatonin, erythropoietin, allopurinol, or N-acetylcysteine, have also shown potential neuroprotective effects in perinatal asphyxia; nevertheless, further evidence is needed before these antioxidant approaches could be implemented as standard care.

Pharmacokinetics and short-term safety of the selective NOS inhibitor 2-iminobiotin in asphyxiated neonates treated with therapeutic hypothermia

BACKGROUND

Neonatal encephalopathy following perinatal asphyxia is a leading cause for neonatal death and disability, despite treatment with therapeutic hypothermia. 2-Iminobiotin is a promising neuroprotective agent additional to therapeutic hypothermia to improve the outcome of these neonates.

METHODS

In an open-label study, pharmacokinetics and short-term safety of 2-iminobiotin were investigated in neonates treated with therapeutic hypothermia. Group A (n = 6) received four doses of 0.16 mg/kg intravenously q6h. Blood sampling for pharmacokinetic analysis and monitoring of vital signs for short-term safety analysis were performed. Data from group A was used to determine the dose for group B, aiming at an AUC_0-48 h of 4800 ng*h/mL.

RESULTS

Exposure in group A was higher than targeted (median AUC_0-48 h 9522 ng*h/mL); subsequently, group B (n = 6) received eight doses of 0.08 mg/kg q6h (median AUC_0-48 h 4465 ng*h/mL). No changes in vital signs were observed and no adverse events related to 2-iminobiotin occurred.

CONCLUSION

This study indicates that 2-iminobiotin is well tolerated and not associated with any adverse events in neonates treated with therapeutic hypothermia after perinatal asphyxia. Target exposure was achieved with eight doses of 0.08 mg/kg q6h. Optimal duration of therapy for clinical efficacy needs to be determined in future clinical trials.

A Phase IIa Clinical Trial of 2-Iminobiotin for the Treatment of Birth Asphyxia in DR Congo, a Low-Income Country

AIM

The main burden of hypoxic-ischemic encephalopathy falls in low-income countries. 2-Iminobiotin, a selective inhibitor of neuronal and inducible nitric oxide synthase, has been shown to be safe and effective in preclinical studies of birth asphyxia. Recently, safety and pharmacokinetics of 2-iminobiotin treatment on top of hypothermia has been described. Since logistics and the standard of medical care are very different in low-resource settings, the aim of this study was to investigate safety and pharmacokinetics of Two-IminoBiotin in the Democratic Republic of Congo (TIBC).

METHODS

Near-term neonates, born in Kinshasa, Democratic Republic of Congo, with a Thompson score ≥ 7 were eligible for inclusion. Excluded were patients with (1) inability to insert an umbilical venous catheter for administration of the study drug; (2) major congenital or chromosomal abnormalities; (3) birth weight < 1800 g; (4) clear signs of infection; and (5) moribund patients. Neonates received six infusions of 2-iminobiotin 0.16 mg/kg started within 6 h after birth, with 4-h intervals, targeting an AUC_0-4h of 365 ng*h/mL. Safety, defined as vital signs, the need for clinical intervention after administration of study drug, occurrence of (serious) adverse events, and pharmacokinetics were assessed.

RESULTS

After parental consent, seven patients were included with a median Thompson score of 10 (range 8-16). No relevant changes in vital signs were observed over time. There was no need for clinical intervention due to administration of study drug. Three patients died, two after completing the study protocol, one was moribund at inclusion and should not have been included. Pharmacokinetic data of 2-iminobiotin were best described using a two-compartment model. Median AUC_0-4h was 664 ng*h/mL (range 414-917). No safety issues attributed to the administration of 2-iminobiotin were found.

CONCLUSION

The present dosing regimen resulted in higher AUCs than targeted, necessitating a change in the dose regimen in future efficacy trials. No adverse effects that could be attributed to the use of 2-iminobiotin were observed. EudraCT number 2015-003063-12.

Novel interventions to reduce oxidative-stress related brain injury in neonatal asphyxia

Perinatal asphyxia-induced brain injury may present as hypoxic-ischemic encephalopathy in the neonatal period, and disability including cerebral palsy in the long term. The brain injury is secondary to both the hypoxic-ischemic event and the reoxygenation-reperfusion following resuscitation. Early events in the cascade of brain injury can be classified as either inflammation or oxidative stress through the generation of free radicals. The objective of this paper is to present efforts that have been made to limit the oxidative stress associated with hypoxic-ischemic encephalopathy. In the acute phase of ischemia/hypoxia and reperfusion/reoxygenation, the outcomes of asphyxiated infants can be improved by optimizing the initial delivery room stabilization. Interventions include limiting oxygen exposure, and shortening the time to return of spontaneous circulation through improved methods for supporting hemodynamics and ventilation. Allopurinol, melatonin, noble gases such as xenon and argon, and magnesium administration also target the acute injury phase. Therapeutic hypothermia, N-acetylcysteine2-iminobiotin, remote ischemic postconditioning, cannabinoids and doxycycline target the subacute phase. Erythropoietin, mesenchymal stem cells, topiramate and memantine could potentially limit injury in the repair phase after asphyxia. To limit the injurious biochemical processes during the different stages of brain injury, determination of the stage of injury in any particular infant remains essential. Currently, therapeutic hypothermia is the only established treatment in the subacute phase of asphyxia-induced brain injury. The effects and side effects of oxidative stress reducing/limiting medications may however be difficult to predict in infants during therapeutic hypothermia. Future neuroprotection in asphyxiated infants may indeed include a combination of therapies. Challenges include timing, dosing and administration route for each neuroprotectant.

Neuroprotective strategies following perinatal hypoxia-ischemia: Taking aim at NOS

Perinatal asphyxia is characterized by oxygen deprivation and lack of perfusion in the perinatal period, leading to hypoxic-ischemic encephalopathy and sequelae such as cerebral palsy, mental retardation, cerebral visual impairment, epilepsy and learning disabilities. On cellular level PA is associated with a decrease in oxygen and glucose leading to ATP depletion and a compromised mitochondrial function. Upon reoxygenation and reperfusion, the renewed availability of oxygen gives rise to not only restoration of cell function, but also to the activation of multiple detrimental biochemical pathways, leading to secondary energy failure and ultimately, cell death. The formation of reactive oxygen species, nitric oxide and peroxynitrite plays a central role in the development of subsequent neurological damage. In this review we give insight into the pathophysiology of perinatal asphyxia, discuss its clinical relevance and summarize current neuroprotective strategies related to therapeutic hypothermia, ischemic postconditioning and pharmacological interventions. The review will also focus on the possible neuroprotective actions and molecular mechanisms of the selective neuronal and inducible nitric oxide synthase inhibitor 2-iminobiotin that may represent a novel therapeutic agent for the treatment of hypoxic-ischemic encephalopathy, both in combination with therapeutic hypothermia in middle- and high-income countries, as well as stand-alone treatment in low-income countries.

Nitric Oxide Synthase Inhibition as a Neuroprotective Strategy Following Hypoxic-Ischemic Encephalopathy: Evidence From Animal Studies

BACKGROUND

Hypoxic-ischemic encephalopathy following perinatal asphyxia is a leading cause of neonatal death and disability worldwide. Treatment with therapeutic hypothermia reduced adverse outcomes from 60 to 45%. Additional strategies are urgently needed to further improve the outcome for these neonates. Inhibition of nitric oxide synthase (NOS) is a potential neuroprotective target. This article reviews the evidence of neuroprotection by nitric oxide (NO) synthesis inhibition in animal models.

METHODS

Literature search using the EMBASE, Medline, Cochrane, and PubMed databases. Studies comparing NOS inhibition to placebo, with neuroprotective outcome measures, in relevant animal models were included. Methodologic quality of the included studies was assessed.

RESULTS

26 studies were included using non-selective or selective NOS inhibition in rat, piglet, sheep, or rabbit animal models. A large variety in outcome measures was reported. Outcome measures were grouped as histological, biological, or neurobehavioral. Both non-selective and selective inhibitors show neuroprotective properties in one or more outcome measures. Methodologic quality was either low or moderate for all studies.

CONCLUSION

Inhibition of NO synthesis is a promising strategy for additional neuroprotection. In humans, intervention can only take place after the onset of the hypoxic-ischemic event. Therefore, combined inhibition of neuronal and inducible NOS seems the most likely candidate for human clinical trials. Future studies should determine its safety and effectiveness in neonates, as well as a potential sex-specific neuroprotective effect. Researchers should strive to improve methodologic quality of animal intervention studies by using a systematic approach in conducting and reporting of these studies.

2-Iminobiotin Superimposed on Hypothermia Protects Human Neuronal Cells from Hypoxia-Induced Cell Damage: An in Vitro Study

Perinatal asphyxia represents one of the major causes of neonatal morbidity and mortality. Hypothermia is currently the only established treatment for hypoxic-ischemic encephalopathy (HIE), but additional pharmacological strategies are being explored to further reduce the damage after perinatal asphyxia. The aim of this study was to evaluate whether 2-iminobiotin (2-IB) superimposed on hypothermia has the potential to attenuate hypoxia-induced injury of neuronal cells. In vitro hypoxia was induced for 7 h in neuronal IMR-32 cell cultures. Afterwards, all cultures were subjected to 25 h of hypothermia (33.5°C), and incubated with vehicle or 2-IB (10, 30, 50, 100, and 300 ng/ml). Cell morphology was evaluated by brightfield microscopy. Cell damage was analyzed by LDH assays. Production of reactive oxygen species (ROS) was measured using fluorometric assays. Western blotting for PARP, Caspase-3, and the phosphorylated forms of akt and erk1/2 was conducted. To evaluate early apoptotic events and signaling, cell protein was isolated 4 h post-hypoxia and human apoptosis proteome profiler arrays were performed. Twenty-five hour after the hypoxic insult, clear morphological signs of cell damage were visible and significant LDH release as well as ROS production were observed even under hypothermic conditions. Post-hypoxic application of 2-IB (10 and 30 ng/ml) reduced the hypoxia-induced LDH release but not ROS production. Phosphorylation of erk1/2 was significantly increased after hypoxia, while phosphorylation of akt, protein expression of Caspase-3 and cleavage of PARP were only slightly increased. Addition of 2-IB did not affect any of the investigated proteins. Apoptosis proteome profiler arrays performed with cellular protein obtained 4 h after hypoxia revealed that post-hypoxic application of 2-IB resulted in a ≥ 25% down regulation of 10/35 apoptosis-related proteins: Bad, Bax, Bcl-2, cleaved Caspase-3, TRAILR1, TRAILR2, PON2, p21, p27, and phospho Rad17. In summary, addition of 2-IB during hypothermia is able to attenuate hypoxia-induced neuronal cell damage in vitro. Combination treatment of hypothermia with 2-IB could be a promising strategy to reduce hypoxia-induced neuronal cell damage and should be considered in further animal and clinical studies.

Insights into the neuroprotective mechanisms of 2-iminobiotin employing an in-vitro model of hypoxic-ischemic cell injury

Several animal models have been used to simulate cerebral hypoxia-ischemia and suggested neuroprotective effects of the biotin analogue 2-iminobiotin (2-IB). The aims of this study were to employ a human in-vitro hypoxia model to confirm protective effects of 2-IB on neuronal cells, determine the optimal neuroprotective concentrations of 2-IB and scrutinize underlying cellular effects of 2-IB. Neuronal IMR-32 cells were exposed to hypoxia employing an enzymatic hypoxia system and were thereafter incubated with various concentrations of 2-IB (10 to 300ng/ml). Cell damage, metabolic activity and generation of reactive oxygen species were quantified using colorimetric/fluorometric lactate dehydrogenase (LDH), tetrazolium-based (MTS) and reactive oxygen species assays. Proteome profiling arrays were performed to evaluate the regulation of cell stress protein expression by hypoxia and 2-IB. Seven hours of hypoxia led to morphological changes in IMR-32 cultures, increased neuronal cell damage (P<0.001), reduction of metabolic activity (P<0.01) and enhanced reactive oxygen species production (P<0.05). Post-hypoxic application of 2-IB (30ng/ml) attenuated hypoxia-induced LDH release (P<0.05) and increased metabolic activity of IMR-32 cells (P<0.05), while reactive oxygen species production was only by trend decreased. Array-based protein expression profiling revealed that 2-IB attenuated the expression of several hypoxia-induced cell stress-associated proteins by more than 25% (pp38α, HIF2α, ADAMTS1, pHSP27, PON2, PON3 and p27). Hypoxia-induced neuronal cell damage can be simulated using the described in-vitro model. 2-IB inhibits hypoxia-mediated neurotoxicity most efficiently at 30ng/ml and the underlying mechanisms involve a downregulation of stress-associated protein expression. Our results suggest 2-IB as a potential drug for the treatment of perinatal hypoxia-ischemia.

Neonatal Encephalopathy: Update on Therapeutic Hypothermia and Other Novel Therapeutics

Neonatal encephalopathy (NE) is a major cause of neonatal mortality and morbidity. Therapeutic hypothermia (TH) is standard treatment for newborns at 36 weeks of gestation or greater with intrapartum hypoxia-related NE. Term and late preterm infants with moderate to severe encephalopathy show improved survival and neurodevelopmental outcomes at 18 months of age after TH. TH can increase survival without increasing major disability, rates of an IQ less than 70, or cerebral palsy. Neonates with severe NE remain at risk of death or severe neurodevelopmental impairment. This review discusses the evidence supporting TH for term or near term neonates with NE.

Neuroprotective agents for neonatal hypoxic-ischemic brain injury

Hypoxic-ischemic (H-I) brain injury in newborns is a major cause of morbidity and mortality that claims thousands of lives each year. In this review, we summarize the promising neuroprotective agents tested on animal models and pilot clinical studies of neonatal H-I brain injury according to the different phases of the disease. These agents target various phases of injury including the early phase of excitotoxicity, oxidative stress and apoptosis as well as late-phase inflammatory reaction and neural repair. We analyze the cell survival and cell death pathways modified by these agents in neonatal H-I brain injury. We aim to 'build a bridge' between animal trials of neuroprotective agents and potential candidate treatments for future clinical applications against H-I encephalopathy.

Taming glutamate excitotoxicity: strategic pathway modulation for neuroprotection

Much work has been carried out in recent years showing that elevated glutamate levels in the extracellular environment of the central nervous system play a pivotal role in neurodegeneration in acute CNS injuries. With the elucidation of the mechanism governing glutamate excitotoxicity, researchers are devising therapeutic strategies to target different parts of the pathway which begins with glutamate accumulation and ultimately results in neuronal cell death. In this article, we review some of the major classes of agents that are currently being investigated and highlight some of the key studies for each. Glutamate scavenging is a relatively new approach that directly decreases glutamate levels in the brain, thus preventing excitotoxicity. Nitric oxide inhibitors and free radical scavengers are more well-studied strategies that continue to yield promising results.

New antioxidant drugs for neonatal brain injury

The brain injury concept covers a lot of heterogeneity in terms of aetiology involving multiple factors, genetic, hemodynamic, metabolic, nutritional, endocrinological, toxic, and infectious mechanisms, acting in antenatal or postnatal period. Increased vulnerability of the immature brain to oxidative stress is documented because of the limited capacity of antioxidant enzymes and the high free radicals (FRs) generation in rapidly growing tissue. FRs impair transmembrane enzyme Na⁺/K⁺-ATPase activity resulting in persistent membrane depolarization and excessive release of FR and excitatory aminoacid glutamate. Besides being neurotoxic, glutamate is also toxic to oligodendroglia, via FR effects. Neuronal cells die of oxidative stress. Excess of free iron and deficient iron/binding metabolising capacity are additional features favouring oxidative stress in newborn. Each step in the oxidative injury cascade has become a potential target for neuroprotective intervention. The administration of antioxidants for suspected or proven brain injury is still not accepted for clinical use due to uncertain beneficial effects when treatments are started after resuscitation of an asphyxiated newborn. The challenge for the future is the early identification of high-risk babies to target a safe and not toxic antioxidant therapy in combination with standard therapies to prevent brain injury and long-term neurodevelopmental impairment.

The protective effects of Cyperus rotundus on behavior and cognitive function in a rat model of hypoxia injury

CONTEXT

Hypoxia injury (HI) with its long-term neurological complications is one of the leading causes of morbidity and mortality in the world. Currently, the treatment regimens for hypoxia are aimed only at ameliorating the damage without complete cure. The need, therefore, for novel therapeutic drugs to treat HI continues.

OBJECTIVE

This study investigates the protective effects of the ethanol extract of Cyperus rotundus L. (Cyperaceae) (EECR), a medicinal plant used in Ayurvedic traditional medicine against sodium nitrite-induced hypoxia in rats.

MATERIALS AND METHODS

We have evaluated the protective effect of 200 and 400 mg/kg of EECR against sodium nitrite-induced hypoxia injury in rats by assessing the cognitive functions, motor, and behavioral effects of EECR treatment along with the histological changes in the brain. By comparing the protective effects of standard drugs galantamine, a reversible cholinesterase inhibitor and pyritinol, an antioxidant nootropic drug against sodium nitrite-induced hypoxia in rats, we have tested the protective ability of EECR.

RESULTS

EECR at doses of 200 and 400 mg/kg was able to protect against the cognitive impairments, and the locomotor activity and muscular coordination defects, which are affected by sodium nitrite-induced hypoxia injury in rats.

CONCLUSION

Based on our results, we suggest that the medicinal herb C. rotundus possesses a protective effect against sodium nitrite-induced hypoxia in rats. Further studies on these protective effects of EECR may help in designing better therapeutic regimes for hypoxia injury.

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.

Pharmacological neuroprotection after perinatal hypoxic-ischemic brain injury

Perinatal hypoxia-ischemia (HI) is an important cause of neonatal brain injury. Recent progress in the search for neuroprotective compounds has provided us with several promising drugs to reduce perinatal HI-induced brain injury. In the early stage (first 6 hours after birth) therapies are concentrated on prevention of the production of reactive oxygen species or free radicals (xanthine-oxidase-, nitric oxide synthase-, and prostaglandin inhibition), anti-inflammatory effects (erythropoietin, melatonin, Xenon) and anti-apoptotic interventions (nuclear factor kappa B- and c-jun N-terminal kinase inhibition); in a later stage stimulation of neurotrophic properties in the neonatal brain (erythropoietin, growth factors) can be targeted to promote neuronal and oligodendrocyte regeneration. Combination of pharmacological means of treatment with moderate hypothermia, which is accepted now as a meaningful therapy, is probably the next step in clinical treatment to fight post-asphyxial brain damage. Further studies should be directed at a more rational use of therapies by determining the optimal time and dose to inhibit the different potentially destructive molecular pathways or to enhance endogenous repair while at the same time avoiding adverse effects of the drugs used.

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.

Neuroprotection in the newborn infant

Neonatal brain injury is an important cause of death and disability, with pathways of oxidant stress, inflammation, and excitotoxicity that lead to damage that progresses over a long period of time. Therapies have classically targeted individual pathways during early phases of injury, but more recent therapies such as growth factors may also enhance cell proliferation, differentiation, and migration over time. More recent evidence suggests combined therapy may optimize repair, decreasing cell injury while increasing newly born cells.

Does inflammation after stroke affect the developing brain differently than adult brain?

The immature brain is prone to hypoxic-ischemic encephalopathy and stroke. The incidence of arterial stroke in newborns is similar to that in the elderly. However, the pathogenesis of ischemic brain injury is profoundly affected by age at the time of the insult. Necrosis is a dominant type of neuronal cell death in adult brain, whereas widespread neuronal apoptosis is unique for the early postnatal synaptogenesis period. The inflammatory response, in conjunction with excitotoxic and oxidative responses, is the major contributor to ischemic injury in both the immature and adult brain, but there are several areas where these responses diverge. We discuss the contribution of various inflammatory mechanisms to injury and repair after cerebral ischemia in the context of CNS immaturity. In particular, we discuss the role of lower expression of selectins, a more limited leukocyte transmigration, undeveloped complement pathways, a more rapid microglial activation, differences in cytokine and chemokine interplay, and a different threshold to oxidative stress in the immature brain. We also discuss differences in activation of intracellular pathways, especially nuclear factor kappaB and mitogen-activated protein kinases. Finally, we discuss emerging data on both the supportive and adverse roles of inflammation in plasticity and repair after stroke.

Maternal allopurinol during fetal hypoxia lowers cord blood levels of the brain injury marker S-100B

BACKGROUND

Fetal hypoxia is an important determinant of neonatal encephalopathy caused by birth asphyxia, in which hypoxia-induced free radical formation plays an important role.

HYPOTHESIS

Maternal treatment with allopurinol, will cross the placenta during fetal hypoxia (primary outcome) and reduce S-100B and free radical formation (secondary outcome).

METHODS

In a randomized, double-blind feasibility study, 53 pregnant women in labor (54 fetuses) with a gestational age of >36 weeks and fetal hypoxia, as indicated by abnormal/nonreassuring fetal heart rate tracing or fetal scalp pH of <7.20, received 500 mg of allopurinol or placebo intravenously. Severity of fetal hypoxia, brain damage and free radical formation were assessed by arterial cord blood lactate, S-100B and non-protein-bound-iron concentrations, respectively. At birth, maternal and cord blood concentrations of allopurinol and its active metabolite oxypurinol were determined.

RESULTS

Allopurinol and oxypurinol concentrations were within the therapeutic range in the mother (allopurinol > 2 mg/L and/or oxypurinol > 4 mg/L) but not always in arterial cord blood. We therefore created 3 groups: a placebo (n = 27), therapeutic allopurinol (n = 15), and subtherapeutic allopurinol group (n = 12). Cord lactate concentration did not differ, but S-100B was significantly lower in the therapeutic allopurinol group compared with the placebo and subtherapeutic allopurinol groups (P < .01). Fewer therapeutic allopurinol cord samples had measurable non-protein-bound iron concentrations compared with placebo (P < .01).

CONCLUSIONS

Maternal allopurinol/oxypurinol crosses the placenta during fetal hypoxia. In fetuses/newborns with therapeutic allopurinol/oxypurinol concentrations in cord blood, lower plasma levels of the brain injury marker protein S-100B were detected. A larger allopurinol trial in compromised fetuses at term seems warranted. The allopurinol dosage must be adjusted to achieve therapeutic fetal allopurinol/oxypurinol concentrations.

Nitric oxide system alteration at spinal cord as a result of perinatal asphyxia is involved in behavioral disabilities: hypothermia as preventive treatment

Perinatal asphyxia (PA) is able to induce sequelae such as spinal spasticity. Previously, we demonstrated hypothermia as a neuroprotective treatment against cell degeneration triggered by increased nitric oxide (NO) release. Because spinal motoneurons are implicated in spasticity, our aim was to analyze the involvement of NO system at cervical and lumbar motoneurons after PA as well as the application of hypothermia as treatment. PA was performed by immersion of both uterine horns containing full-term fetuses in a water bath at 37 degrees C for 19 or 20 min (PA19 or PA20) or at 15 degrees C for 20 min (hypothermia during PA-HYP). Some randomly chosen PA20 rats were immediately exposed for 5 min over grain ice (hypothermia after PA-HPA). Full-term vaginally delivered rats were used as control (CTL). We analyzed NO synthase (NOS) activity, expression and localization by nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) reactivity, inducible and neuronal NOS (iNOS and nNOS) by immunohistochemistry, and protein nitrotyrosilation state. We observed an increased NOS activity at cervical spinal cord of 60-day-old PA20 rats, with increased NADPH-d, iNOS, and nitrotyrosine expression in cervical motoneurons and increased NADPH-d in neurons of layer X. Lumbar neurons were not altered. Hypothermia was able to maintain CTL values. Also, we observed decreased forelimb motor potency in the PA20 group, which could be attributed to changes at cervical motoneurons. This study shows that PA can induce spasticity produced by alterations in the NO system of the cervical spinal cord. Moreover, this situation can be prevented by perinatal hypothermia.

Therapeutics for neonatal brain injury

Neonatal brain injury is an important cause of death and neurodevelopmental delay. Multiple pathways of oxidant stress, inflammation, and excitotoxicity lead to both early and late phases of cell damage and death. Therapies targeting these different pathways have shown potential in protecting the brain from ongoing injury. More recent therapies, such as growth factors, have demonstrated an ability to increase cell proliferation and repair over longer periods of time. Even though hypothermia, which decreases cerebral metabolism and possibly affects other mechanisms, may show some benefit in particular cases, no widely effective therapeutic interventions for human neonates exist. In this review, we summarize recent findings in neuroprotection and neurogenesis for the immature brain, including combination therapy to optimize repair.

Pathways to ischemic neuronal cell death: are sex differences relevant?

We have known for some time that the epidemiology of human stroke is sexually dimorphic until late in life, well beyond the years of reproductive senescence and menopause. Now, a new concept is emerging: the mechanisms and outcome of cerebral ischemic injury are influenced strongly by biological sex as well as the availability of sex steroids to the brain. The principal mammalian estrogen (17 β estradiol or E2) is neuroprotective in many types of brain injury and has been the major focus of investigation over the past several decades. However, it is becoming increasingly clear that although hormones are a major contributor to sex-specific outcomes, they do not fully account for sex-specific responses to cerebral ischemia. The purpose of this review is to highlight recent studies in cell culture and animal models that suggest that genetic sex determines experimental stroke outcome and that divergent cell death pathways are activated after an ischemic insult. These sex differences need to be identified if we are to develop efficacious neuroprotective agents for use in stroke patients.

Low endogenous G-protein-coupled receptor kinase 2 sensitizes the immature brain to hypoxia-ischemia-induced gray and white matter damage

Hypoxic-ischemic brain injury is regulated in part by neurotransmitter and chemokine signaling via G-protein-coupled receptors (GPCRs). GPCR-kinase 2 (GRK2) protects these receptors against overstimulation by inducing desensitization. Neonatal hypoxic-ischemic brain damage is preceded by a reduction in cerebral GRK2 expression. We determined the functional importance of GRK2 in hypoxic-ischemic brain damage. Nine-day-old wild-type and GRK2(+/-) mice with a approximately 50% reduction in GRK2 protein were exposed to unilateral carotid artery occlusion and hypoxia. In GRK2(+/-) animals, gray and white matter damage was aggravated at 3 weeks after hypoxia-ischemia. In addition, cerebral neutrophil infiltration was increased in GRK2(+/-) animals. Neutrophil depletion reduced brain damage, but neuronal loss was still more pronounced in GRK2(+/-) animals. Onset of neuronal loss was advanced in GRK2(+/-) animals regardless of neutrophil depletion. White matter injury was advanced in GRK2(+/-) animals and was not affected by neutrophil depletion. Activation/infiltration of microglia/macrophages was stronger in GRK2(+/-) brains but only occurred 24 h after hypoxia-ischemia and is therefore not the primary cause of increased damage. During hypoxia, cerebral blood flow was reduced to the same extent in both genotypes. In vitro, GRK2(+/-) hippocampal slices and cerebellar granular neurons were more sensitive to glutamate-induced death. We propose the novel concept that the kinase GRK2 regulates onset and magnitude of hypoxic-ischemic brain damage. Increased gray and white matter damage in GRK2(+/-) animals was not dependent on infiltrating neutrophils and occurred before microglia/macrophage activation was detected. Collectively, our data suggest that cerebral GRK2 has an important endogenous neuroprotective role in ischemic cerebral damage.

Gender-specific neuroprotection by 2-iminobiotin after hypoxia-ischemia in the neonatal rat via a nitric oxide independent pathway

We have shown earlier that 2-iminobiotin (2-IB) reduces hypoxia-ischemia (HI)-induced brain damage in neonatal rats, and presumed that inhibition of nitric oxide synthases (NOS) was the underlying mechanism. We now investigated the effect of 2-IB treatment in P7 rat pups to determine the role of gender and the neuroprotective mechanism. Pups were subjected to HI (occlusion of right carotid artery and 120 mins FiO(2) 0.08) and received subcutaneous (s.c.) 10 mg/kg 2-IB at 0, 12 and 24 h after hypoxia. After 6 weeks, neuronal damage was assessed histologically. We determined cerebral nitrite and nitrate (NO(x)) and nitrotyrosine, heat-shock protein 70, cytosolic cytochrome c, cleaved caspase 3, nuclear translocation of apoptosis-inducing factor (AIF) and the effect of 2-IB on NOS activity in cultured cells. 2-Iminobiotin treatment reduced long-term brain damage in female but not male rats. Unexpectedly, 2-IB treatment did not reduce cerebral NO(x) or nitrotyrosine levels, and did not inhibit NOS activity in vitro. The gender-dependent neuroprotective effect of 2-IB was reflected in inhibition of the HI-induced increase in cytosolic cytochrome c and cleaved caspase 3 in females only. Hypoxia-ischemia-induced activation of AIF was observed in males only and was not affected by 2-IB. Post-HI treatment with 2-IB provides gender-specific long- and short-term neuroprotection in female P7 rats via inhibition of the cytochrome c-caspase 3 neuronal death pathway. 2-Iminobiotin did not alter cerebral NO(x) nor inhibited NOS in intact cells. Therefore, we conclude that it is highly unlikely that the neuroprotective effect of 2-IB involves NOS inhibition.

Gender-Dependent Pathways of Hypoxia-Ischemia-Induced Cell Death and Neuroprotection in the Immature P3 Rat

Previously, we demonstrated neuroprotection with 2-iminobiotin (2-IB) after cerebral hypoxia-ischemia (HI) in female, but not in male P7 rats. Given the different patterns of brain injury in more immature rats, we examined whether these gender differences could also be observed in P3 rats. HI was induced by unilateral carotid ligation and FiO2 reduction, followed by 2-IB administration. HSP70 protein expression and cytochrome c release from the mitochondria, markers of short-term outcome, were induced by HI to the same extent in male and female animals. However, reduction in HSP70 production and cytochrome c release by 2-IB was seen in female rats only. Long-term cerebral injury after HI, assessed with histology, was similar in male and female P3 rats, but long-term neuroprotection by 2-IB was observed in female rats only. In conclusion, 2-IB provides neuroprotection after cerebral HI in female, but not in male immature P3 rats.

Nitrotyrosine in brain tissue of neonates after perinatal asphyxia

HYPOTHESIS

Nitrotyrosine, a reaction product of peroxynitrite and proteins, could be demonstrated in the postmortem examination of brain tissue of full-term neonates who had severe perinatal asphyxia.

METHODS

The brain tissue of 22 full-term neonates who died after severe perinatal asphyxia was examined, including cerebral cortex, basal ganglia, thalamus, hippocampus, brain stem, olives and cerebellum. Median age at death was 52 h. Routine histopathological examination and additional immunohistological staining were carried out with anti-cysteine protease protein 32 antibodies to detect activated caspase 3, anti-nitrotyrosine antibodies to detect nitrotyrosine and anti-CD68 antibodies to detect activated microglia and macrophages, which might be associated with the production of nitric oxide. Staining was scored as none, weak (1-25% positive cells), moderate (26-75% positive cells) or severe (>75% positive cells).

RESULTS

14 patients showed global injury, 4 showed injury of the basal ganglia and thalamus, and 4 showed predominantly parasagittal brain injury. One neonate without perinatal asphyxia served as a control. Nitrotyrosine staining of neurones was shown in all neonates with asphyxia, mostly in the thalamus (70%) and inferior olives (68%). Total nitrotyrosine staining tended to be less in the base of the pons and inferior olives of neonates with parasagittal brain injury. Activated caspase 3 was found mostly in the thalamus (60%) and hippocampus (53%). Positive CD68 staining was mainly present in the thalamus (70% positive).

CONCLUSION

Nitrotyrosine was found in brain tissue of full-term neonates, suggesting that nitric oxide toxicity might have a role in hypoxic-ischaemic brain injury at term. This may be relevant for neuroprotective strategies in full-term neonates with perinatal asphyxia.

Aminoguanidine inhibits caspase-3 and calpain activation without affecting microglial activation following neonatal transient cerebral ischemia

Microglial cells, the resident macrophages of the CNS, can be both beneficial and detrimental to the brain. These cells play a central role as mediators of neuroinflammation associated with many neurodegenerative states, including cerebral ischemia. Because microglial cells are both a major source of inducible nitric oxide synthase (iNOS)/nitric oxide (NO) production locally in the injured brain and are activated by NO-mediated injury, we tested whether iNOS inhibition reduces microglial activation and ischemic injury in a neonatal focal ischemia-reperfusion model. Post-natal day 7 rats were subjected to a 2 h transient middle cerebral artery (MCA) occlusion. Pups with confirmed injury on diffusion-weighted magnetic resonance imaging (MRI) during occlusion were administered 300 mg/kg/dose aminoguanidine (AG) or vehicle at 0, 4 and 18 h after reperfusion, and animals were killed at 24 or 72 h post-reperfusion. The effect of AG on microglial activation as judged by the acquisition of ED1 immunoreactivity and proliferation of ED1-positive cells, on activation of cell death pathways and on injury volume, was determined. The study shows that while AG attenuates caspase 3 and calpain activation in the injured tissue, treatment does not affect the rapidly occurring activation and proliferation of microglia following transient MCA occlusion in the immature rat, or reduce injury size.

Cerebral cortical tissue damage after hemorrhagic hypotension in near-term born lambs

Hypotension reduces cerebral O(2) supply, which may result in brain cell damage and loss of brain cell function in the near-term neonate. The aim is to elucidate 1) to what extent the functional disturbance of the cerebral cortex, as measured with electrocortical brain activity (ECBA), is related to cerebral cortical tissue damage, as estimated by MAP2; and 2) whether there is a relationship between the glutamate, nitric oxide (NO), cGMP pathway and the development of cerebral cortical tissue damage after hemorrhagic hypotension. Seven lambs were delivered at 131 d of gestation. Hypotension was induced by withdrawal of blood until mean arterial blood pressure was reduced to 30% of normotension. Cerebral O(2) supply, consumption, and ECBA were calculated in normotensive conditions and after 2.5 h of hypotension. Concentrations of glutamate and aspartate in cerebrospinal fluid (CSF), NO(2) and NO(3) (NOx) in plasma, and cGMP in cortical brain tissue were determined in both conditions. CSF and brain tissue from siblings were used to determine normotensive values. Cortical neuronal damage was detected after 2.5 h of hypotension. ECBA was negatively related to the severity of the cortical damage. ECBA was related to respectively glutamate, NOx, and cGMP concentrations. In conclusion, cortical neuronal damage is detected after 2.5 h of hemorrhagic hypotension in the near-term born lamb. The damage is reflected by a reduction of ECBA. The glutamate, NOx, cGMP pathway is likely to be involved in the pathogenesis of cerebral cortical damage.

Selective inhibition of nuclear factor-kappaB activation after hypoxia/ischemia in neonatal rats is not neuroprotective

Activated nuclear factor-kappaB (NFkappaB) has been shown to increase transcription of several genes that could potentially contribute to neuronal damage, such as proinflammatory cytokines, chemokines, and inducible nitric oxide synthase. The aim of our study was to investigate whether inhibition of NFkappaB activation could prevent hypoxia/ischemia (HI)-induced cerebral damage in neonatal rats. We used a cell permeable peptide (NEMO binding domain [NBD] peptide) that is known to prevent the association of the regulatory protein NEMO with IKK, the kinase that activates NFkappaB. Via this mechanism, the NBD peptide can specifically block the activation of NFkappaB, without inhibiting basal NFkappaB activity. Cerebral HI was induced in neonatal rats by occlusion of the right carotid artery followed by 90 min of hypoxia (Fio(2) = 0.08). Immediately upon reoxygenation, as well as 6 and 12 h later, rats were treated with vehicle or NBD peptide (20 mg/kg i.p.). Histologic analysis of brain damage was performed at 6 wk after HI. To assess NFkappaB activation, electromobility shift assays (EMSAs) were performed on brain nuclear extracts obtained 6 h after reoxygenation. Increased NFkappaB activity could be shown at 6 h after HI in both hemispheres. Peripheral administration of NBD peptide prevented this HI-induced increase in NFkappaB activity in both hemispheres. Histologic analysis of long-term cerebral damage revealed that inhibition of NFkappaB activation by administration of NBD peptide at 0, 6, and 12 h after HI resulted in an increment of neuronal damage. In conclusion, our data suggest that inhibition of NFkappaB activation using NBD peptide early after HI increases brain damage in neonatal rats.

Different apoptotic mechanisms are activated in male and female brains after neonatal hypoxia-ischaemia

Sex-related brain injury was evaluated after unilateral hypoxia-ischaemia (HI) in C57/BL6 mice on postnatal day (P) 5, 9, 21 or 60, corresponding developmentally to premature, term, juvenile and adult human brains. There was no sex difference in brain injury when the insult was severe, as evaluated by pathological scoring or tissue loss, but when the insult was moderate, adult (P60) females displayed less injury. In the immature (P9) male brains, neurones displayed a more pronounced translocation of apoptosis-inducing factor (AIF) (loss of AIF from the mitochondrial fraction and increase in nuclear AIF) after HI, whereas the female brain neurones displayed a stronger activation of caspase 3 (more pronounced loss of pro-caspase 3, increase in cleaved caspase 3 and increase in caspase 3 enzymatic activity). Two other mechanisms of injury, peroxynitrite-induced formation of nitrotyrosine and autophagy, were no different between males and females at P9. These data show that the CNS is more resistant to HI in adult females compared with males, whereas no sex differences were found in the extent of injury in neonatal mice. However, critical sex-dependent differences were demonstrated in vivo with regard to cellular, apoptosis-related mechanisms.

Expression of nitric oxide synthase isoforms and nitrotyrosine formation after hypoxia-ischemia in the neonatal rat brain

BACKGROUND AND PURPOSE

Production of nitric oxide is thought to play an important role in neuroinflammation. Previously, we have shown that combined inhibition of neuronal nitric oxide synthase (nNOS) and inducible NOS (iNOS) can reduce hypoxia-ischemia-induced brain injury in 12-day-old rats. The aim of this study was to analyze changes in expression of nNOS, iNOS and endothelial NOS (eNOS), and nitrotyrosine (NT) formation in proteins in neonatal rats up to 48 h after cerebral hypoxia-ischemia.

METHODS

Twelve-day-old rats were subjected to unilateral carotid artery occlusion and hypoxia, resulting in unilateral cerebral damage. NOS and nitrotyrosine expression were determined by immunohistochemistry and Western blot analysis at 30 min-48 h after hypoxia-ischemia.

RESULTS

nNOS was increased in both hemispheres from 30 min to 3 h after hypoxia-ischemia. In the contralateral hemisphere, eNOS was decreased 1-3 h after hypoxia-ischemia. In the ipsilateral hemisphere, eNOS was decreased at 0.5 h after hypoxia-ischemia, normalized at 1-3 h and was increased 6-12 h after hypoxia-ischemia. At 24 and 48 h after hypoxia-ischemia, eNOS levels normalized. Surprisingly, iNOS expression did not change from 30 min up to 48 h after hypoxia-ischemia in the ipsi- or contralateral hemisphere. In addition, the regional expression of iNOS in the brain as determined by immunohistochemistry did not change after hypoxia-ischemia. Expression of nitrotyrosine was slightly increased in both hemispheres only at 30 min after hypoxia-ischemia.

CONCLUSION

In 12-day-old rat pups, cerebral hypoxia-ischemia induced a transient increase in nNOS, eNOS, and nitrotyrosine in proteins, but no change in iNOS expression up to 48 h after the insult.