Increased apoptosis in the cingulate sulcus of newborn piglets following transient hypoxia-ischaemia is related to the degree of high energy phosphate depletion during the insult

Mitochondrial dysfunction in perinatal asphyxia: role in pathogenesis and potential therapeutic interventions

Perinatal asphyxia (PA)-induced brain injury may present as hypoxic-ischemic encephalopathy in the neonatal period, and long-term sequelae such as spastic motor deficits, intellectual disability, seizure disorders and learning disabilities. The brain injury is secondary to both the hypoxic-ischemic event and oxygenation-reperfusion following resuscitation. Following PA, a time-dependent progression of neuronal insult takes place in terms of transition of cell death from necrosis to apoptosis. This transition is the result of time-dependent progression of pathomechanisms which involve excitotoxicity, oxidative stress, and ultimately mitochondrial dysfunction in developing brain. More precisely mitochondrial respiration is suppressed and calcium signalling is dysregulated. Consequently, Bax-dependent mitochondrial permeabilization occurs leading to release of cytochrome c and activation of caspases leading to transition of cell death in developing brain. The therapeutic window lies within this transition process. At present, therapeutic hypothermia (TH) is the only clinical treatment available for treating moderate as well as severe asphyxia in new-born as it attenuates secondary loss of high-energy phosphates (ATP) (Solevåg et al. in Free Radic Biol Med 142:113-122, 2019; Gunn et al. in Pediatr Res 81:202-209, 2017), improving both short- and long-term outcomes. Mitoprotective therapies can offer a new avenue of intervention alone or in combination with therapeutic hypothermia for babies with birth asphyxia. This review will explore these mitochondrial pathways, and finally will summarize past and current efforts in targeting these pathways after PA, as a means of identifying new avenues of therapeutic intervention.

Epidermal Growth Factor Receptor Inhibition Reverses Cellular and Transcriptomic Alterations Induced by Hypoxia in the Neonatal Piglet Brain

Acute hypoxia (HX) causes extensive cellular damage in the developing human cerebral cortex. We found increased expression of activated-EGFR in affected cortical areas of neonates with HX and investigated its functional role in the piglet, which displays a highly evolved, gyrencephalic brain, with a human-like maturation pattern. In the piglet, HX-induced activation of EGFR and Ca²⁺/calmodulin kinase IV (CaMKIV) caused cell death and pathological alterations in neurons and glia. EGFR blockade inhibited CaMKIV activation, attenuated neuronal loss, increased oligodendrocyte proliferation, and reversed HX-induced astrogliosis. We performed for the first time high-throughput transcriptomic analysis of the piglet cortex to define molecular responses to HX and to uncover genes specifically involved in EGFR signaling in piglet and human brain injury. Our results indicate that specific molecular responses modulated by EGFR may be targeted as a therapeutic strategy for HX injury in the neonatal brain.

Fingolimod (FTY720) Preserves High Energy Phosphates and Improves Cardiac Function in Heterotopic Heart Transplantation Model

During heart transplantation, donor heart leads to reduced oxygen supply resulting in low level of high energy phosphate (HEP) reserves in cardiomyocyte. Lower HEP is one of the underlying reasons of cell death due to ischemia. In this study we investigated the role of Fingolimod (FTY720) in heart transplantation ischemia. Eight groups of Sprague-Dawley rats (n = 5 for each subgroup) were made, A1 and C1 were given FTY720 1 mg/kg while B1 and D1 were given normal saline. The hearts were implanted into another set of similar rats after preservation period of 1 h at 4–8 °C. Significantly higher Left ventricular systolic pressure (LVSP), dP/dT maximum (p < 0.05), dP/dT minimum (p < 0.05) were recorded in the FTY720 treated group after 24 h of reperfusion while after 1 h of reperfusion, there were no significant differences in LVSP, maximum and negative dP/dT, and Left ventricular end diastolic pressure (LVEDP) between the control and the FTY720-treated transplant groups. Coronary blood flow (CBF) was enhanced (p < 0.05) in the FTY720 treated group after 1 and 24 h. ATP p < 0.001, p < 0.05 at 1 and 24 h, ADP p < 0.001, p > 0.05 at 1 and 24 h, and phosphocreatine p < 0.05, p > 0.05 at 1 and 24 h were better preserved by FTY720 treatment as compared to control group. The study concluded that pretreatment of grafted hearts with FTY720 improved hemodynamics, CBF, high energy phosphate reserves, reduces the peroxynitrite level and poly (ADP ribose) polymerase (PARP) inhibition that prevents ischemia-reperfusion injury.

Oxygen dependency of mitochondrial metabolism indicates outcome of newborn brain injury

There is a need for a method of real-time assessment of brain metabolism during neonatal hypoxic-ischaemic encephalopathy (HIE). We have used broadband near-infrared spectroscopy (NIRS) to monitor cerebral oxygenation and metabolic changes in 50 neonates with HIE undergoing therapeutic hypothermia treatment. In 24 neonates, 54 episodes of spontaneous decreases in peripheral oxygen saturation (desaturations) were recorded between 6 and 81 h after birth. We observed differences in the cerebral metabolic responses to these episodes that were related to the predicted outcome of the injury, as determined by subsequent magnetic resonance spectroscopy derived lactate/N-acetyl-aspartate. We demonstrated that a strong relationship between cerebral metabolism (broadband NIRS-measured cytochrome-c-oxidase (CCO)) and cerebral oxygenation was associated with unfavourable outcome; this is likely to be due to a lower cerebral metabolic rate and mitochondrial dysfunction in severe encephalopathy. Specifically, a decrease in the brain tissue oxidation state of CCO greater than 0.06 µM per 1 µM brain haemoglobin oxygenation drop was able to predict the outcome with 64% sensitivity and 79% specificity (receiver operating characteristic area under the curve = 0.73). With further work on the implementation of this methodology, broadband NIRS has the potential to provide an early, cotside, non-invasive, clinically relevant metabolic marker of perinatal hypoxic-ischaemic injury.

A stabilized retro-inverso peptide ligand of transferrin receptor for enhanced liposome-based hepatocellular carcinoma-targeted drug delivery

The application of tumor targeting ligands to the treatment of cancer holds promise for improving efficacy and reducing toxicity. ^LT7 (_L(HAIYPRH)) peptide, a phage display-selected peptide, exhibited high binding affinity to transferrin receptor (TfR) overexpressed on tumor cells. However, its in vivo tumor targeting efficiency was impaired due to enzymatic degradation in blood circulation. To improve the stability and targeting ability, a retro-inverso analogue of ^LT7 peptide, named ^DT7 peptide (_D(HRPYIAH)), was designed for targeted therapy of hepatocellular carcinoma. The result of computer simulation predicted that ^DT7 bound to TfR protein more efficiently than ^LT7, and this prediction was confirmed experimentally by surface plasmon resonance (SPR). Ex vivo stability experiment demonstrated that ^DT7 possessed stronger ability against proteolysis than ^LT7 in fresh mouse serum. We further prepared ^DT7-, ^LT7-, and transferrin (Tf)-modified liposomes (^DT7-LIP, ^LT7-LIP, and Tf-LIP, respectively). ^DT7-LIP showed a significantly stronger in vitro targeting ability than ^LT7-LIP and Tf-LIP under normal condition and simulated biological condition. In addition, the in vitro antitumor effect of DTX-loaded ^DT7-LIP was markedly enhanced in comparison to DTX-loaded ^LT7-LIP and DTX-loaded Tf-LIP. In vivo imaging indicated that ^DT7-LIP had better tumor accumulation than ^LT7-LIP and Tf-LIP. For in vivo antitumor studies, the tumor growth rate of mice treated with DTX-loaded ^DT7-LIP was significantly inhibited compared to that in mice treated with DTX-loaded ^LT7-LIP and DTX-loaded Tf-LIP. Overall, this study verified the potential of the stable ^DT7 peptide in improving the efficacy of docetaxel in the treatment of hepatocellular carcinoma. STATEMENT OF SIGNIFICANCE: A phage display library-selected ^LT7 (_L(HAIYPRH)) peptide exhibited high affinity to transferrin receptor (TfR). However, its bioactivity was impaired in vivo as L-peptides are susceptible to degradation by proteolytic enzymes. Here, we designed a retro-inverso peptide ^DT7(_D(HRPYIAH)) and demonstrated its increased serum stability and higher binding affinity to TfR. A stabilized targeted drug delivery system was further constructed by modified ^DT7 peptide on the surface of liposomes. The data indicated that ^DT7 peptide-modified liposomes exhibited higher targeting ability in vitro and in vivo. More importantly, ^DT7-modified liposomes demonstrated positive preclinical significance in enhancing the therapeutic effects against hepatocellular carcinoma.

Effect of Src Kinase inhibition on Cytochrome c, Smac/DIABLO and Apoptosis Inducing Factor (AIF) Following Cerebral Hypoxia-Ischemia in Newborn Piglets

We have previously shown that cerebral Hypoxia-ischemia (HI) results in activation of Src kinase in the newborn piglet brain. We investigated the regulatory mechanism by which the pre-apoptotic proteins translocate from mitochondria to the cytosol during HI through the Src kinase. Newborn piglets were divided into 3 groups (n = 5/group): normoxic (Nx), HI and HI pre-treated with Src kinase inhibitor PP2 (PP2 + HI). Brain tissue HI was verified by neuropathological analysis and by Adenosine Triphosphate (ATP) and Phosphocreatine (PCr) levels. We used western blots, immunohistochemistry, H&E and biochemical enzyme assays to determine the role of Src kinase on mitochondrial membrane apoptotic protein trafficking. HI resulted in decreased ATP and PCr levels, neuropathological changes and increased levels of cytochrome c, Smac/DIABLO and AIF in the cytosol while their levels were decreased in mitochondria compared to Nx. PP2 decreased the cytosolic levels of pre-apoptotic proteins, attenuated the neuropathological changes and apoptosis and decreased the HI-induced increased activity of caspase-3. Our data suggest that Src kinase may represent a potential target that could interrupt the enzymatic activation of the caspase dependent cell death pathway.

Effect of Intranasally Delivered rh-VEGF165 on Angiogenesis Following Cerebral Hypoxia-Ischemia in the Cerebral Cortex of Newborn Piglets

Background: Vascular endothelial growth factor (VEGF) stimulates vascular genesis and angiogenesis. Cerebral Hypoxia-Ischemia (HI) leads to the reduction of vasculature in the cerebral cortex of newborn piglets. Objective: The present study tests the hypothesis that post-hypoxia intranasal administration of recombinant human VEGF₁₆₅ (rh-VEGF165) for 3 days increases the vascular density in the cerebral cortex of newborn piglets without promoting neovascularization. Design/Methods: Ventilated newborn piglets were divided into three groups (n = 5/group): normoxic (Nx), hypoxic-ischemic (HI), and HI treated with intranasal rh-VEGF165rh-VEGF165 (HI-VEGF). HI piglets were exposed to HI (0.05 FiO2) for 30 min. Recombinant h-VEGF165 (100 ng/kg) was administered 15 min after HI and then once daily for 3 days. The animals were perfused transcardially and coronal brains sections were processed for Isolectin, Hoechst, and ki-67 cell proliferation marker staining. To assess the vascular density, 30–35 fields per animal section were manually counted using image J software. Results: The vascular density (vessels/mm²) was 42.0 ± 8.0 in the Nx group, 26.4 ± 4.8 (p < 0.05 vs. Nx) in the HI group, and 46.0 ± 11.9 (p < 0.05 vs. HI) in the HI-VEGF group. When stained for newly formed vessels, via Ki-67 staining, the vascular density was 5.4 ± 3.6 in the Nx group (p < 0.05 vs. HI), 10.2 ± 2.1 in the HI group, and 10.9 ± 2.9 in the HI-VEGF group (p = 0.72 vs. HI). HI resulted in a decrease in vascular density. Intranasal rh-VEGF165rh-VEGF165 resulted in the attenuation of the HI-induced decrease in vascular density. However, rh-VEGF165 did not result in the formation of new vascularity, as evident by ki-67 staining. Conclusions: Intranasal rh-VEGF165 may prevent the HI-induced decrease in the vascular density of the brain and could serve as a promising adjuvant therapy for hypoxic-ischemic encephalopathy (HIE).

Selective inhibition of ASIC1a confers functional and morphological neuroprotection following traumatic spinal cord injury

Tissue loss after spinal trauma is biphasic, with initial mechanical/haemorrhagic damage at the time of impact being followed by gradual secondary expansion into adjacent, previously unaffected tissue. Limiting the extent of this secondary expansion of tissue damage has the potential to preserve greater residual spinal cord function in patients. The acute tissue hypoxia resulting from spinal cord injury (SCI) activates acid-sensing ion channel 1a (ASIC1a). We surmised that antagonism of this channel should provide neuroprotection and functional preservation after SCI. We show that systemic administration of the spider-venom peptide PcTx1, a selective inhibitor of ASIC1a, improves locomotor function in adult Sprague Dawley rats after thoracic SCI. The degree of functional improvement correlated with the degree of tissue preservation in descending white matter tracts involved in hind limb locomotor function. Transcriptomic analysis suggests that PcTx1-induced preservation of spinal cord tissue does not result from a reduction in apoptosis, with no evidence of down-regulation of key genes involved in either the intrinsic or extrinsic apoptotic pathways. We also demonstrate that trauma-induced disruption of blood-spinal cord barrier function persists for at least 4 days post-injury for compounds up to 10 kDa in size, whereas barrier function is restored for larger molecules within a few hours. This temporary loss of barrier function provides a “ treatment window” through which systemically administered drugs have unrestricted access to spinal tissue in and around the sites of trauma. Taken together, our data provide evidence to support the use of ASIC1a inhibitors as a therapeutic treatment for SCI. This study also emphasizes the importance of objectively grading the functional severity of initial injuries (even when using standardized impacts) and we describe a simple scoring system based on hind limb function that could be adopted in future studies.

Selective inhibition of ASIC1a confers functional and morphological neuroprotection following traumatic spinal cord injury

Tissue loss after spinal trauma is biphasic, with initial mechanical/haemorrhagic damage at the time of impact being followed by gradual secondary expansion into adjacent, previously unaffected tissue. Limiting the extent of this secondary expansion of tissue damage has the potential to preserve greater residual spinal cord function in patients. The acute tissue hypoxia resulting from spinal cord injury (SCI) activates acid-sensing ion channel 1a (ASIC1a). We surmised that antagonism of this channel should provide neuroprotection and functional preservation after SCI. We show that systemic administration of the spider-venom peptide PcTx1, a selective inhibitor of ASIC1a, improves locomotor function in adult Sprague Dawley rats after thoracic SCI. The degree of functional improvement correlated with the degree of tissue preservation in descending white matter tracts involved in hind limb locomotor function. Transcriptomic analysis suggests that PcTx1-induced preservation of spinal cord tissue does not result from a reduction in apoptosis, with no evidence of down-regulation of key genes involved in either the intrinsic or extrinsic apoptotic pathways. We also demonstrate that trauma-induced disruption of blood-spinal cord barrier function persists for at least 4 days post-injury for compounds up to 10 kDa in size, whereas barrier function is restored for larger molecules within a few hours. This temporary loss of barrier function provides a " treatment window" through which systemically administered drugs have unrestricted access to spinal tissue in and around the sites of trauma. Taken together, our data provide evidence to support the use of ASIC1a inhibitors as a therapeutic treatment for SCI. This study also emphasizes the importance of objectively grading the functional severity of initial injuries (even when using standardized impacts) and we describe a simple scoring system based on hind limb function that could be adopted in future studies.

Behavioral benefits of maternal swimming are counteracted by neonatal hypoxia-ischemia in the offspring

Hypoxia-ischemia (HI) represents one of the most common causes of neonatal encephalopathy. The central nervous system injury comprises several mechanisms, including inflammatory, excitotoxicity, and redox homeostasis unbalance leading to cell death and cognitive impairment. Exercise during pregnancy is a potential therapeutic tool due to benefits offered to mother and fetus. Swimming during pregnancy elicits a strong metabolic programming in the offspring's brain, evidenced by increased antioxidant enzymes, mitochondrial biogenesis, and neurogenesis. This article aims to evaluate whether the benefits of maternal exercise are able to prevent behavioral brain injury caused by neonatal HI. Female adult Wistar rats swam before and during pregnancy (30min/day, 5 days/week, 4 weeks). At 7(th) day after birth, the offspring was submitted to HI protocol and, in adulthood (60(th) day), it performed the behavioral tests. It was observed an increase in motor activity in the open field test in HI-rats, which was not prevented by maternal exercise. The rats subjected to maternal swimming presented an improved long-term memory in the object recognition task, which was totally reversed by neonatal HI encephalopathy. BDNF brain levels were not altered; suggesting that HI or maternal exercise effects were BDNF-independent. In summary, our data suggest a beneficial long-term effect of maternal swimming, despite not being robust enough to protect from HI injury.

Cortical structural abnormalities in very preterm children at 7 years of age

We analyzed long-lasting alterations in brain morphometry associated with preterm birth using volumetric and surface-based analyses applied to children at age 7 years. Comparison of 24 children born very preterm (VPT) to 24 healthy term-born children revealed reductions in total cortical gray matter volume, white matter volume, cortical surface area and gyrification index. Regional cortical shape abnormalities in VPT children included the following: shallower anterior superior temporal sulci, smaller relative surface area in the inferior sensori-motor cortex and posterior superior temporal cortex, larger relative surface area and a cingulate sulcus that was shorter or more interrupted in medial frontoparietal cortex. These findings indicate a complex pattern of regional vulnerabilities in brain development that may contribute to the diverse and long-lasting neurobehavioral consequences that can occur after very premature birth.

Hypothermia for hypoxic-ischemic encephalopathy

Moderate to severe hypoxic-ischemic injury in newborn infants, manifested as encephalopathy immediately or within hours after birth, is associated with a high risk of either death or a lifetime with disability. In recent multicenter clinical trials, hypothermia initiated within the first 6 postnatal hours has emerged as a therapy that reduces the risk of death or impairment among infants with hypoxic-ischemic encephalopathy. Prior to hypothermia, no therapies directly targeting neonatal encephalopathy secondary to hypoxic-ischemic injury had convincing evidence of efficacy. Hypothermia therapy is now becoming increasingly available at tertiary centers. Despite the deserved enthusiasm for hypothermia, obstetric and neonatology caregivers, as well as society at large, must be reminded that in the clinical trials more than 40% of cooled infants died or survived with impairment. Although hypothermia is an evidence-based therapy, additional discoveries are needed to further improve outcome after HIE. In this article, we briefly present the epidemiology of neonatal encephalopathy due to hypoxic-ischemic injury, describe the rationale for the use of hypothermia therapy for hypoxic-ischemic encephalopathy, and present results of the clinical trials that have demonstrated the efficacy of hypothermia. We also present findings noted during and after these trials that will guide care and direct research for this devastating problem.

Pathophysiology of an hypoxic–ischemic insult during the perinatal period

Hypoxia-ischemia is a leading cause of morbidity and mortality in the perinatal period with an incidence of 1/4000 live births. Biochemical events such as energy failure, membrane depolarization, brain edema, an increase of neurotransmitter release and inhibition of uptake, an increase of intracellular Ca(2+), production of oxygen-free radicals, lipid peroxidation, and a decrease of blood flow are triggered by hypoxia-ischemia and may lead to brain dysfunction and neuronal death. These abnormalities can result in mental impairments, seizures, and permanent motor deficits, such as cerebral palsy. The physical and emotional strain that is placed on the children affected and their families is enormous. The care that these individuals need is not only confined to childhood, but rather extends throughout their entire life span, so it is very important to understand the pathophysiology that follows a hypoxic-ischemic insult. This review will highlight many of the mechanisms that lead to neuronal death and include the emerging area of white matter injury as well as the role of inflammation and will provide a summary of therapeutic strategies. Hypothermia and oxygen will also be discussed as treatments that currently lack a specific target in the hypoxic/ischemic cascade.

Rescuing the neonatal brain from hypoxic injury with autologous cord blood

Brain injury resulting from perinatal hypoxic-ischemic encephalopathy (HIE) is a major cause of acute mortality in infants and chronic neurologic disability in surviving children. Recent multicenter clinical trials demonstrated the effectiveness of hypothermia initiated within the first 6 postnatal hours to reduce the risk of death or major neurological disabilities among neonates with HIE. However, in these trials, approximately 40% of cooled infants died or survived with significant impairments. Therefore, adjunct therapies are required to improve the outcome in neonates with HIE. Cord blood (CB) is a rich source of stem cells. Administration of human CB cells in animal models of HIE has generally resulted in improved outcomes and multiple mechanisms have been suggested including anti-inflammation, release of neurotrophic factors and stimulation of endogenous neurogenesis. Investigators at Duke are conducting studies of autologous CB infusion in neonates with HIE and in children with cerebral palsy. These pilot studies indicate no added risk from the regimens used, but results of ongoing placebo-controlled trials are needed to assess efficacy. Meanwhile, further investigations are warranted to determine the best strategies, that is, timing, dosing, route of delivery, choice of stem cells and ex vivo modulations, to attain long-term benefits of CB stem cell therapy.

Hypoxia-ischemia and retinal ganglion cell damage

Retinal hypoxia is the potentially blinding mechanism underlying a number of sight-threatening disorders including central retinal artery occlusion, ischemic central retinal vein thrombosis, complications of diabetic eye disease and some types of glaucoma. Hypoxia is implicated in loss of retinal ganglion cells (RGCs) occurring in such conditions. RGC death occurs by apoptosis or necrosis. Hypoxia-ischemia induces the expression of hypoxia inducible factor-1α and its target genes such as vascular endothelial growth factor (VEGF) and nitric oxide synthase (NOS). Increased production of VEGF results in disruption of the blood retinal barrier leading to retinal edema. Enhanced expression of NOS results in increased production of nitric oxide which may be toxic to the cells resulting in their death. Excess glutamate release in hypoxic-ischemic conditions causes excitotoxic damage to the RGCs through activation of ionotropic and metabotropic glutamate receptors. Activation of glutamate receptors is thought to initiate damage in the retina by a cascade of biochemical effects such as neuronal NOS activation and increase in intracellular Ca²⁺ which has been described as a major contributing factor to RGC loss. Excess production of proinflammatory cytokines also mediates cell damage. Besides the above, free-radicals generated in hypoxic-ischemic conditions result in RGC loss because of an imbalance between antioxidant- and oxidant-generating systems. Although many advances have been made in understanding the mediators and mechanisms of injury, strategies to improve the damage are lacking. Measures to prevent neuronal injury have to be developed.

Early regional response of apoptotic activity in newborn piglet brain following hypoxia and ischemia

Responses of selected neuroregulatory proteins that promote (Caspase 3 and Bax) or inhibit (Bcl-2, high Bcl-2/Bax ratio) apoptotic cell death were measured in the brain of piglets subjected to precisely controlled hypoxic and ischemic insults: 1 h hypoxia (decreasing FiO₂ from 21 to 6%) or ischemia (ligation of carotid arteries and hemorrhage), followed by 0, 2 and 4 h recovery with 21% FiO₂. Protein expression was measured in cortex, hippocampus and striatum by Western blot. There were no significant differences in expression of Caspase-3 between sham operated, hypoxic and ischemic groups. There were significant regional differences in expression of Bcl-2 and Bax in response to hypoxia and ischemia. The changes in Bcl-2/Bax ratio were similar for hypoxia and ischemia except for striatum at zero time recovery, with ischemia giving lower ratios than hypoxia. The Bcl-2/Bax ratio was also lower for the striatum than for the other regions of the brain, suggesting this region is the more susceptible to apoptotic injury.

The discovery of hypothermic neural rescue therapy for perinatal hypoxic-ischemic encephalopathy

The development of the concepts of delayed post-ischaemic neuronal death and neural rescue brought about a search for clinical treatments to reduce brain damage after birth asphyxia. Cooling had long been an unproven empyrical therapy, and a 20 year programme of careful laboratory and clinical research has proved that hypothermia reduces neurological damage in infants suffering perinatal asphyxial encephalopathy.

Use of therapeutic hypothermia for term infants with hypoxic-ischemic encephalopathy

Newborn encephalopathy represents a clinical syndrome with diverse causes, many of which may result in brain injury. Hypoxic-ischemic encephalopathy represents a subset of newborns with encephalopathy and, in contrast to other causes, may have a modifiable outcome. Laboratory research has demonstrated robust neuroprotection associated with reductions of brain temperature following hypoxia-ischemia in animals. The neuroprotective effects of hypothermia reflect antagonism of multiple cascades of events that contribute to brain injury. Clinical trials have translated laboratory observations into successful interventions. Hypoxicischemic encephalopathy is often unanticipated, unavoidable, and may occur in any obstetric setting. Pediatricians and other providers based in community hospitals play a critical role in the initial assessment, recognition, and stabilization of infants who may be candidates for therapeutic hypothermia.

Neonatal encephalopathy: treatment with hypothermia

In this article, the role of hypothermia and neuroprotection for neonatal encephalopathy will be discussed. The incidence of encephalopathy due to hypoxia ischemia as well as the pathophysiology will be presented. The diagnosis of encephalopathy in full-term neonates will be discussed. The current management of brain injury that occurs with hypoxia ischemia and the role of hypothermia in preventing brain injury in fetal and neonatal animal models will be reviewed. The current data from randomized control trials of hypothermia as neuroprotection for full-term infants will be presented along with the results of meta-analyses of these trials. Lastly, the status of ongoing neonatal hypothermia trials will be summarized.

Antioxidant therapy and neuroprotection in the newborn

Injury to the perinatal brain is a leading cause of childhood mortality and lifelong disability. Despite recent improvements in neonatal care, no effective treatment for perinatal brain lesions is available. The newborn, especially if preterm, is highly prone to oxidative stress (OS) and to the toxic effect of free radicals (FRs). At birth, the newborn is exposed to a relatively hyperoxic environment caused by an increased oxygen bioavailability with greatly enhanced generation of FRs. Additional sources (e.g., inflammation, hypoxia, ischemia, glutamate and free iron release) occur, magnifying OS. In the preterm baby, the perinatal transition is accompanied by the immaturity of the antioxidant systems and the reduced ability to induce efficient homeostatic mechanisms designed to control overproduction of cell-damaging FRs. Improved understanding of the pathophysiological mechanism involved in perinatal brain lesions helps to identify potential targets for neuroprotective interventions, and the knowledge of these mechanisms has enabled scientists to develop new therapeutic strategies that have confirmed their neuroprotective effects in animal studies. Considering the growing role of OS in preterm newborn morbidity in respect to the higher risk of FR damage in these babies, erythropoietin, allopurinol, melatonin and hypothermia demonstrate great promise as potential neuroprotectans. This article provides an overview of the pathogenesis of FR-mediated diseases of the newborn and the antioxidant strategies now tested in order to reduce OS and its damaging effects.

Stem cells: implications in experimental ischaemic stroke therapy

Ischaemic stroke is a syndrome characterized by rapid onset of neurological injury due to interruption of blood flow to the brain. Widespread neuronal damage throughout the CNS has been shown to cause marked and multifarious functional impairments in the ischaemic brain. Recent advances as enumerated above have propelled acute ischaemic stroke management into a therapeutic era. However, once the damage from a stroke event has maximized, little can be done to recover premorbid function. Experimental animal data suggests that stem cell therapy may be an effective alternate to the conventional disease management strategies of ischaemic stroke. Therefore, the present review focuses on detailing the scope of stem cell therapy in the treatment of ischaemic stroke.

Provisional hypotheses for the molecular genetics of cognitive development: imaging genetic pathways in the anterior cingulate cortex

Brain imaging genetic research involves a multitude of methods and spans many traditional levels of analysis. Given the vast permutations among several million common genetic variants with thousands of brain tissue voxels and a wide array of cognitive tasks that activate specific brain systems, we are prompted to develop specific hypotheses that synthesize converging evidence and state clear predictions about the anatomical sources, magnitude and direction (increases vs. decreases) of allele- and task-specific brain activity associations. To begin to develop a framework for shaping our imaging genetic hypotheses, we focus on previous results and the wider imaging genetic literature. Particular emphasis is placed on converging evidence that links system-level and biochemical studies with models of synaptic function. In shaping our own imaging genetic hypotheses on the development of Attention Networks, we review relevant literature on core models of synaptic physiology and development in the anterior cingulate cortex.

Hypothermia as a treatment for birth asphyxia

This chapter will report to the frequency of neonatal hypoxic-ischemic encephalopathy. The pathophysiology and the childhood outcome of encephalopathy due to hypoxia-ischemia will be examined. The limitations of current therapy for this condition and new therapies will be evaluated. Hypothermia seems to offer the most promise as a therapy for neuroprotection in hypoxic-ischemic encephalopathy. The evidence-based trials of hypothermia will be reviewed along with recommendations regarding clinical applications for this therapy and need for long-term follow-up of children receiving this therapy.

"Therapeutic time window" duration decreases with increasing severity of cerebral hypoxia-ischaemia under normothermia and delayed hypothermia in newborn piglets

OBJECTIVE

For optimal neuroprotection following transient perinatal hypoxia-ischaemia (HI), therapy should start before overt secondary energy failure and its irreversible neurotoxic cascade. Hypothermia is a promising neuroprotective intervention that also prolongs the therapeutic time window ("latent-phase"; the period between re-establishment of apparently normal cerebral metabolism after HI, and the start of secondary energy failure). The influences of HI severity on latent-phase duration and regional neuroprotection are unclear. Under normothermia and delayed whole-body cooling to 35 and 33 degrees C we aimed to assess relationships between HI severity and: (i) latent-phase duration; (ii) secondary-energy-failure severity; and (iii) neuronal injury 48 h following HI.

METHODS

Newborn piglets were randomized to: (i) HI-normothermia (n=12), (ii) HI-35 degrees C (n=7), and (iii) HI-33 degrees C (n=10). HI-35 degrees C and HI-33 degrees C piglets were cooled between 2 and 26 h after HI. Insult and secondary-energy-failure severity and latent-phase duration were evaluated using phosphorus magnetic resonance spectroscopy and compared with neuronal death in cortical-grey and deep-grey matter.

RESULTS

More severe HI was associated with shorter latent-phase (p=0.002), worse secondary energy failure (p=0.023) and more cortical-grey-matter neuronal death (p=0.016).

CONCLUSIONS

Latent-phase duration is inversely related to insult severity; latent-phase brevity may explain the apparently less effective neuroprotection following severe cerebral HI.

Effect of post-hypoxic reoxygenation on DNA fragmentation in cortical neuronal nuclei of newborn piglets

Previous studies have shown an increased fragmentation of genomic DNA following hypoxia in cortical neuronal nuclei of newborn piglets. The present study tests the hypothesis that DNA fragmentation following hypoxia persists during reoxygenation in cortical neuronal nuclei of newborn piglets. To test this hypothesis, DNA fragmentation was assessed in 36 newborn piglets divided into six groups: normoxic (Nx), hypoxic (Hx) and hypoxic/reoxygenated for 6, 12, 24h and 7 days. The Hx groups were exposed to 7% oxygen for 1h followed by reoxygenation to room air for 6, 12, 24h and 7 days. Cerebral tissue hypoxia was confirmed biochemically by ATP and phosphocreatine (PCr) levels. Nuclei were isolated and purified using discontinuous sucrose gradient. DNA was isolated by phenol/chloroform/isoamyl-alcohol extraction method. ATP/PCr (micromol/g brain) were 4.11+/-0.15/3.67+/-0.30 for Nx, 1.31+/-0.68/0.74+/-0.30 for Hx, 3.81+/-0.11/3.24+/-0.14 for 6h reoxygenation, 4.21+/-0.12/3.27+/-0.09 for 12h reoxygenation and 4.63+/-0.09/3.75+/-0.27 for 24h reoxygenation and 4.31+/-0.12/3.70+/-0.21 for 7 days reoxygenation. There was a significant difference in the ATP and PCr values between Nx and Hx groups (p<0.05) and between Hx and hypoxic reoxygenated groups (p<0.05). DNA fragments (OD/mm(2)) increased from 1776+/-267 in the Nx group to 3211+/-285 in the Hx group (p<0.05). In the reoxygenation groups, DNA fragments (OD/mm(2)) decreased to 2018+/-249 after 6h (p<0.05 versus Hx) but increased to 3408+/-206, 2782+/-406 and 3256+/-302 after 12, 24h and 7 days, respectively. The data show a decrease in DNA fragmentation in the early phase (6h) of reoxygenation but is comparable to acute hypoxia during the later phases (12, 24h and 7 days) of reoxygenation. We propose that the biphasic pattern of DNA fragmentation during reoxygenation occurs by an initial oxidative DNA injury followed by an enzymatic cleavage of DNA by endonucleases activation.

Consequential apoptosis in the cerebellum following injury to the developing rat forebrain

In focal brain lesions, alterations in blood flow and cerebral metabolism can be detected in brain areas remote from the primary injury. The cellular consequences of this phenomenon, originally termed diaschisis, are not fully understood. Here, we report that in two distinct models of forebrain injury, neuronal death in the cerebellum, a site distant to the primary injury, results as consequence of neuronal loss in the forebrain. Fourteen-day-old rats were subjected to unilateral forebrain injury, achieved by either hypoxia-ischemia (right carotid artery ligation and hypoxia) or direct needle injury to brain tissue. At defined times after injury, the presence of apoptosis was investigated by cell morphology, in situ end labeling, electron microscopy and poly-ADP-ribose polymerase (PARP) cleavage. Injury to the rat forebrain following hypoxia-ischemia increased apoptosis in the internal granular and Purkinje cell layers of the cerebellum, a site distant to that of the primary injury. The number of apoptotic cells in the cerebellum was significantly related to cell death in the hippocampus. Similarly, direct needle injury to the forebrain resulted in extensive apoptotic cell death in the cerebellum. These results emphasize the intimate relationship between defined neuronal populations in relatively distant brain areas and suggest a cellular basis for diaschisis.

Oxidative metabolism, apoptosis and perinatal brain injury

Perinatal hypoxic-ischaemic injury (HII) is a significant cause of neurodevelopmental impairment and disability. Studies employing 31P magnetic resonance spectroscopy to measure phosphorus metabolites in situ in the brains of newborn infants and animals have demonstrated that transient hypoxia-ischaemia leads to a delayed disruption in cerebral energy metabolism, the magnitude of which correlates with the subsequent neurodevelopmental impairment. Prominent among the biochemical features of HII is the loss of cellular ATP, resulting in increased intracellular Na+ and Ca2+, and decreased intracellular K+. These ionic imbalances, together with a breakdown in cellular defence systems following HII, can contribute to oxidative stress with a net increase in reactive oxygen species. Subsequent damage to lipids, proteins, and DNA and inactivation of key cellular enzymes leads ultimately to cell death. Although the precise mechanisms of neuronal loss are unclear, it is now clear both apoptosis and necrosis are the significant components of cell death following HII. A number of different factors influence whether a cell will undergo apoptosis or necrosis, including the stage of development, cell type, severity of mitochondrial injury and the availability of ATP for apoptotic execution. This review will focus on some pathological mechanisms of cell death in which there is a disruption to oxidative metabolism. The first sections will discuss the process of damage to oxidative metabolism, covering the data collected both from human infants and from animal models. Following sections will deal with the molecular mechanisms that may underlie cerebral energy failure and cell death in this form of brain injury, with a particular emphasis on the role of apoptosis and mitochondria.

Fas/CD95/APO-1 can function as a death receptor for neuronal cells in vitro and in vivo and is upregulated following cerebral hypoxic-ischemic injury to the developing rat brain

Fas/CD95/Apo-1 is a cell surface receptor that transduces apoptotic death signals following activation and has been implicated in triggering apoptosis in infected or damaged cells in disease states. Apoptosis is a major mechanism of neuronal loss following hypoxic-ischemic injury to the developing brain, although the role of Fas in this process has not been studied in detail. In the present study, we have investigated the expression and function of Fas in neuronal cells in vitro and in vivo. Fas was found to be expressed in the 14 day old rat brain, with strongest expression in the cortex, hippocampus and cerebellum. Cross-linking of Fas induced neuronal apoptosis both in neuronal PC12 cells in culture and following intracerebral injection in vivo, indicating that neuronal Fas was functional as a death receptor. This death was shown to be caspase dependent in primary neuronal cultures and was blocked by the selective caspase 8 inhibitor IETD. Finally, cerebral hypoxia-ischemia resulted in a strong lateralised upregulation of Fas in the hippocampus, that peaked six to twelve hours after the insult and was greater on the side of injury. These results suggest that Fas may be involved in neuronal apoptosis following hypoxic-ischemic injury to the developing brain.

Depth of delayed cooling alters neuroprotection pattern after hypoxia-ischemia

Hypothermia after perinatal hypoxia-ischemia (HI) is neuroprotective; the precise brain temperature that provides optimal protection is unknown. To assess the pattern of brain injury with 3 different rectal temperatures, we randomized 42 newborn piglets: (Group i) sham-normothermia (38.5-39 degrees C); (Group ii) sham-33 degrees C; (Group iii) HI-normothermia; (Group iv) HI-35 degrees C; and (Group v) HI-33 degrees C. Groups iii through v were subjected to transient HI insult. Groups ii, iv, and v were cooled to their target rectal temperatures between 2 and 26 hours after resuscitation. Experiments were terminated at 48 hours. Compared with normothermia, hypothermia at 35 degrees C led to 25 and 39% increases in neuronal viability in cortical gray matter (GM) and deep GM, respectively (both p < 0.05); hypothermia at 33 degrees C resulted in a 55% increase in neuronal viability in cortical GM (p < 0.01) but no significant increase in neuronal viability in deep GM. Comparing hypothermia at 35 and 33 degrees C, 35 degrees C resulted in more viable neurons in deep GM, whereas 33 degrees C resulted in more viable neurons in cortical GM (both p < 0.05). These results suggest that optimal neuroprotection by delayed hypothermia may occur at different temperatures in the cortical and deep GM. To obtain maximum benefit, you may need to design patient-specific hypothermia protocols by combining systemic and selective cooling.

Hypoxia modifies nuclear calcium uptake pathways in the cerebral cortex of the guinea-pig fetus

Nuclear Ca2+ signals are thought to play a critical role in the initiation and progression of programmed cell death. The present study tests the hypothesis that hypoxia alters nuclear Ca2+ transport pathways and leads to an increase in nuclear Ca(2+)-influx in cerebral cortical neuronal nuclei. To test this hypothesis the effect of tissue hypoxia on high affinity Ca(2+)-ATPase activity and the binding characteristics of inositol 1,4,5-triphosphate (IP3) and inositol 1,3,4,5-tetrakisphosphate (IP4) receptors were studied in neuronal nuclei from the cerebral cortex of guinea-pig fetuses. Results show increased high-affinity Ca(2+)-ATPase activity (nmol/mg protein/h) in the hypoxic group 969.7+/-79 as compared with 602.4+/-90.9 in the normoxic group, P<0.05. The number of IP3 receptors (Bmax, fmol/mg protein) increased from 61+/-21 in the normoxic group to 164+/-49 in the hypoxic group, P<0.05. K(d) values did not change following hypoxia. In contrast, IP4 receptor Bmax (fmol/mg protein) and K(d) (nM) values increased from 360+/-32 in the normoxic group to 626+/-136 in the hypoxic group (P<0.001) and, from 26+/-1 in the normoxic group to 61+/-9 in the hypoxic group (P<0.001), respectively. 45Ca(2+)-influx (pmol/mg protein) significantly increased from 6.3+/-1.9 in the normoxic group to 10.9+/-1.1 the hypoxic group (P<0.001). The data show that hypoxia modifies nuclear Ca2+ transport pathways and results in increased nuclear Ca(2+)-influx. We speculate that hypoxia increases nuclear Ca2+ uptake from the cytoplasm to the nucleoplasm, resulting in increased transcription of proapoptotic genes and subsequent activation of programmed cell death pathways.

Calpain inhibitor MDL 28170 protects hypoxic–ischemic brain injury in neonatal rats by inhibition of both apoptosis and necrosis

MDL 28170 is a CNS-penetrating calpain inhibitor, and we examined the effects of MDL 28170 on hypoxic-ischemic brain injury in immature brain using the Rice-Vannucci model. Immediately after hypoxic exposure, 24 mg/kg of MDL 28170 was injected intraperitoneally as an initial dose, followed by 12 mg/kg every 4 h for a total dose of 60 mg/kg over 12 h post-HI. A vehicle control group received peanut oil injection instead. Macroscopic evaluation of brain injury revealed the neuroprotective effect of MDL 28170 after 12 h post-HI. Neuropathological quantitative analysis of cell death showed that MDL 28170 significantly decreased the number of necrotic cells in all the examined regions except for cingular cortex, and the number of apoptotic cells in caudate putamen, parietal cortex, hippocampus CA1, and laterodorsal thalamus. Western blots showed that MDL 28170 suppressed 145/150 kDa subunits of alpha-spectrin breakdown products (SBDP) in cortex, hippocampus, thalamus, and striatum, and also 120-kDa subunit of SBDP in all regions except for striatum. This suggests that MDL 28170 inhibited activation of calpain and caspase-3, respectively. Our results indicate that post-hypoxic MDL 28170 injection is neuroprotective in HI newborn rat brain by decreasing both necrosis and apoptosis. SBDP expression also suggests that MDL 28170 injection inhibits both calpain and caspase-3 activation after HI insult.

Pathogenesis of hippocampal neuronal death after hypoxia-ischemia changes during brain development

Transient hypoxia-ischemia (HI) leads to delayed neuronal death in both mature and immature neurons but the underlying mechanisms are not fully understood. To understand whether the pathogenesis of HI-induced neuronal death is different between mature and immature neurons, we used a rat HI model at postnatal days 7 (P7), 15 (P15), 26 (P26) and 60 (P60) in order to investigate ultrastructural changes and active caspase-3 distribution in HI-injured neurons as a function of developmental age. In P7 pups, despite more than 95% of HI-injured neurons highly expressing active caspase-3, most of these active caspase-3-positive neurons revealed mixed features of apoptosis and necrosis (a chimera type) under electron microscopy (EM). Classical apoptosis was observed only in small populations of HI-injured P7 neurons. Furthermore, in rats older than P7, most HI-injured neurons displayed features of necrotic cell death under EM and, concomitantly, active caspase-3-positive neurons after HI declined dramatically. Classical apoptosis after HI was rarely found in neurons older than P15. In P60 rats, virtually all HI-injured neurons showed the shrinkage necrotic morphology under EM and were negative for active caspase-3. These results strongly suggest that pathogenesis of HI-induced neuronal death is shifting from apoptosis to necrosis during brain development.

Effect of neuronal nitric oxide synthase inhibition on CA2+/calmodulin kinase kinase and CA2+/calmodulin kinase IV activity during hypoxia in cortical nuclei of newborn piglets

The present study tests the hypothesis that cerebral tissue hypoxia results in increased Ca(2+)/calmodulin (CaM) kinase kinase activity and that the administration of nitric oxide synthase inhibitors (N-nitro-l-arginine [NNLA], or 7-nitroindazole sodium [7-NINA]) prior to the onset of hypoxia will prevent the hypoxia-induced increase in the enzyme activity. To test this hypothesis, CaM kinase kinase and CaM kinase IV activities were determined in normoxic, hypoxic, NNLA-treated hypoxic, and 7-NINA-treated hypoxic piglets. Hypoxia was induced (FiO(2)=0.05-0.08x1 h) and confirmed biochemically by tissue levels of ATP and phosphocreatine. CaM kinase kinase activity was determined in a medium containing protein kinase and phosphatase inhibitors, calmodulin, and a specifically designed CaM kinase kinase target peptide. CaM kinase IV activity was determined by (33)P-incorporation into syntide-2 in a buffer containing protein kinase and phosphatase inhibitors. Compared with normoxic animals, ATP and phosphocreatine levels were significantly lower in all hypoxic piglets whether or not pretreated with nitric oxide synthase inhibitors. There was a significant difference among CaM kinase kinase activity (pmol/mg protein/min) in normoxic (76.84+/-14.1), hypoxic (138.86+/-18.2, P<0.05 vs normoxia), NNLA-pretreated hypoxic (91.34+/-19.3; P=NS vs normoxia, P<0.05 vs hypoxia) and 7-NINA-pretreated hypoxic animals (100.12+/-23.3; P=NS vs normoxia, P<0.05 vs hypoxia). There was a significant difference among CaM kinase IV activity (pmol/mg protein/min) in normoxia (1270.80+/-126.1), hypoxia (2680.80+/-136.7; P<0.05 vs normoxia), NNLA-pretreated hypoxia (1666.00+/-154.8; P<0.05 vs normoxia, P<0.05 vs hypoxia), and 7-NINA-pretreated hypoxic (1712.9+/-231.5; P=NS vs normoxia, P<0.05 vs hypoxia). We conclude that the hypoxia-induced increase in CaM kinase kinase and CaM kinase IV activity is mediated by neuronal NOS-derived NO.

Adenine nucleotide metabolism and cell fate after oxidant exposure of rat cortical neurons: effects of inhibition of poly(ADP-ribose) polymerase

We exposed cultured neurons prelabeled with 14C-adenine to H2O2 with or without the poly(ADP-ribose) polymerase (PARP) inhibitor 3,4-Dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone (DPQ) to quantify its effects on acute ATP depletion, later ATP synthesis, cellular and nuclear morphology, extent of DNA fragmentation, and PARP cleavage. According to the extent of the acute ATP depletion, the exposures were classified as 'mild' (50 microM H2O2), 'moderate' (100-250 microM H2O2), or 'severe' (500 microM-1 mM H2O2) insults. Mild exposure had no significant effects on the parameters studied. In the 'moderately' exposed neurons, ATP depletion to 59+/-6% of control was associated with a decrease in the cell counts, apoptotic morphology, and cleavage of PARP. In this group, DPQ prevented the acute ATP (to 95+/-15% of control), preserved cell morphology, and improved cell survival. In the 'severe' group, ATP depletion to 18+/-4% was associated with necrosis and intact PARP. DPQ elevated ATP levels (to 44+/-12% of control) and post-insult ATP synthesis, improved cell counts, and altered cell morphology towards apoptosis rather than necrosis. Post-insult application of DPQ was less effective. Our results show that the extent of oxidant-induced ATP depletion and cell fate can be modified by PARP inhibition, to some extent also after the insult.

Nuclear mechanisms of hypoxic cerebral injury in the newborn

In early studies, we demonstrated that cerebral tissue hypoxia leads to N-methyl-D-aspartate receptor modification and results in increased intracellular Ca2+. Our subsequent studies have demonstrated an alteration in nuclear Ca2+ influx mechanisms and an increase in the nuclear Ca2+ influx after hypoxia. The hypoxia induced nuclear Ca2+ influx increase correlated in a curvilinear function with the increase in the degree of cerebral tissue hypoxia. The activity of nuclear membrane high-affinity Ca2+-ATPase also increased with the increase in cerebral hypoxia. The expression of the proapototic protein Bax increased as an inverse function with cerebral tissue ATP and phosphocreatine concentrations. However,the expression of the antiapoptotic protein Bcl-2 did not increase after hypoxia. Cerebral tissue hypoxia also led to the activation of caspases 3, 8, and 9. Furthermore, our studies demonstrated that the fragmentation of neuronal genomic DNA increased with increase in degree of cerebral tissue hypoxia. Studies presented in this article elucidate nuclear Ca2+ influx and nuclear Ca2+-mediated mechanisms, including signal transduction, apoptotic gene transcription,caspase activation, and nuclear DNA fragmentation, that result in hypoxic neuronal injury in the newborn brain.

Biomarkers of hypoxic brain injury in the neonate

The specific pathologic processes preceding the onset of irreversible cerebral injury seem to be a combination of several complex mechanisms due to the severity and duration of the insult to the biochemical modifications in the brain. An early diagnosis of the newborn at high risk for brain damage is relevant for preventive programs. Neuroprotective strategies will benefit from the detection of biochemical markers with high reliability and predictability for brain injury.

Hypoxia-induced modification of poly (ADP-ribose) polymerase and dna polymerase beta activity in cerebral cortical nuclei of newborn piglets: role of nitric oxide

Previous studies have shown that poly (ADP-ribose) polymerase (PARP) and DNA polymerase beta, nuclear enzymes, are associated with cell replication and DNA repair. The present study tests the hypothesis that hypoxia results in increased PARP and DNA polymerase activity in cerebral cortical neuronal nuclei to repair the hypoxia-induced damage to genomic DNA. Studies were conducted in 13 anesthetized and ventilated newborn piglets (age 3-5 days) divided into normoxic (n=5) and hypoxic (n=8) groups. Hypoxia was induced by decreasing inspired oxygen from 21% to 7% for 60 min. Cerebral tissue hypoxia was documented biochemically by determining the tissue levels of ATP and phosphocreatine (PCr). Following isolation of the cortical neuronal nuclei, the activity of PARP and DNA polymerase beta was determined. During hypoxia, the tissue ATP level decreased by 73% from 4.12+/-0.67 micromol/g brain to 1.12+/-0.34 micromol/g brain, and PCr decreased by 78% from 4.14+/-0.68-0.90+/-0.20 micromol/g brain. In hypoxic neuronal nuclei, PARP activity significantly increased from 5.88+/-0.51 pmol NAD/mg protein/h in normoxic nuclei to 10.04+/-2.02 (P=0.001). PARP activity inversely correlated with tissue ATP (r=0.78) and PCr levels (r=0.81). Administration of N-nitro-L-arginine prior to hypoxia decreased the hypoxia-induced increase in PARP activity by 67%. Endogenous DNA polymerase beta activity increased from 0.96+/-0.13 in normoxic nuclei to 1.39+/-0.18 nmol/mg protein/h in hypoxic nuclei (P<0.005). DNA polymerase beta activity in the presence of exogenous template increased from 1.54+/-0.14 in the normoxic to 2.42+/-0.26 nmol/mg protein/h in the hypoxic group (P<0.005). DNA polymerase beta activity in the presence or absence of template inversely correlated with the tissue ATP (r=0.95 and 0.84, respectively) and PCr levels (r=0.93 and 0.77, respectively). These results demonstrate that the activity of PARP and DNA polymerase beta enzymes increase with the increase in degree of cerebral tissue hypoxia. Furthermore, the results demonstrate a direct correlation between the PARP and the DNA polymerase beta activity. We conclude that tissue hypoxia results in increased PARP and DNA polymerase beta activities indicating activation of DNA repair mechanisms that may result in potential neuronal recovery following hypoxia and the hypoxia-induced increase in PARP activity is NO-mediated.

The effects of temperature on hypoxic-ischemic brain injury

Over the past 15 years it has been recognized that the temperature of the brain has an important influence on the extent of brain injury that follows intervals of hypoxia-ischemia. Available data in animals and humans show that brain injury is worsened when fever is superimposed on an ischemic event. Furthermore, data in neonates and adults strongly suggest a neuroprotective role for modest hypothermia (temperature reductions of 1 to 6 degrees C) applied during or following ischemia or hypoxia-ischemia. This article provides an overview of the effects of brain temperature, including its role in the development of brain injury, mechanisms of brain injury which may be temperature sensitive, the regulation of brain temperature, thermal characteristics during brain cooling, and current clinical investigations that use temperature as a therapeutic modality.

Biphasic ATP depletion caused by transient oxidative exposure is associated with apoptotic cell death in rat embryonal cortical neurons

Hypoxia-ischemia leads to an acute depletion of high-energy phosphates in neonatal brain. After reperfusion, energy status is restored, but may show progressive secondary failure, associated with neuronal loss, brain damage, or death. Oxidants are produced on reperfusion. We investigated whether a biphasic energy failure develops in cultured neurons after oxidant exposure, and whether the degree of primary disturbance correlates with later ATP synthesis and mode of cell death. Embryonic rat cortical neurons were exposed to varying doses of hydrogen peroxide for 60 min and incubated for 12, 24, or 48 h. Adenine nucleotides and the incorporation of [(14)C]adenine into adenine nucleotides were quantified. Apoptosis was evaluated by DNA electrophoresis and in situ end-labeling. A mild insult (10-50 microM) caused no ATP depletion or change in subsequent growth or energy metabolism, whereas an intermediate insult (100 microM) caused acute ATP depletion (49 +/- 12% of control). This recovered to 91 +/- 28% by 12 h, but then declined to 61 +/- 18% at 24 h. A severe insult (1 mM) depleted ATP to 15 +/- 3% of control, with no recovery. Moderate ATP depletion was associated with apoptotic cell death, whereas a severe insult caused acute necrosis. Transient oxidant exposure of embryonal cortical neurons causes a biphasic energy depletion followed by apoptosis in analogy with asphyxiated brains. This model may prove useful for the study of pathogenesis and treatment of hypoxic-ischemic encephalopathy.

Minocycline markedly protects the neonatal brain against hypoxic-ischemic injury

Hypoxic-ischemic brain injury in the perinatal period is a major cause of morbidity and mortality. Presently, there are no proven effective therapies with which to safeguard the human neonatal brain against this type of injury. Minocycline, a semisynthetic tetracycline, has been shown to be neuroprotective in certain adult ischemic injury/stroke and neurodegenerative disease models. However, minocycline's neuroprotective effects have not been assessed after insults to the neonatal brain. We now report that minocycline administered either immediately before or immediately after a hypoxic-ischemic insult substantially blocks tissue damage in a rodent model of neonatal hypoxic-ischemic brain injury. Minocycline treatment prevents the formation of activated caspase-3, a known effector of apoptosis, as well as the appearance of a calpain cleaved substrate, a marker of excitotoxic/necrotic cell death. To our knowledge, this is the first report of a systemic treatment that can be administered after a hypoxic-ischemic insult, which provides robust, nearly complete neuroprotection to the developing brain. Our data suggest that minocycline or a related neuroprotective tetracycline may be a candidate to consider in human clinical trials to protect the developing brain against hypoxic-ischemic-induced damage.

Effect of graded hypoxia on high-affinity Ca2+-ATPase activity in cortical neuronal nuclei of newborn piglets

Previous studies have shown that nuclear calcium signals control a variety of nuclear functions including gene transcription, DNA synthesis, DNA repair and nuclear envelope breakdown. The present study tested the hypothesis that the activity of the neuronal nuclear high affinity Ca2+-ATPase increases as a function of decreased energy metabolism in the cerebral cortex. Studies were performed in 11 ventilated newborn piglets, age 3-5 days, divided into normoxic (Nx, n = 4) and hypoxic (Hx, n = 7) groups. The animals were exposed to a single FiO2 in the range from 0.21 to 0.05 for one hr. Cerebral tissue hypoxia was confirmed biochemically by determining brain tissue ATP and phosphocreatine levels. Neuronal nuclei were isolated and the high-affinity Ca2+-ATPase activity determined. During graded hypoxia, cerebral tissue ATP decreased from 4.80 +/- 0.58 (normoxic) to 1.03 +/- 0.38 (ranging from 0.61-1.63) micromol/g brain (p < 0.05) and PCr decreased from 3.94 +/- 0.75 (normoxic) to 0.99 +/- 0.27 (ranging from 0.50 to 1.31) micromol/g brain (p < 0.05). The total high affinity Ca2+-ATPase activity in the hypoxic nuclei increased and ranged from 541 to 662 nmol/mg protein/hr, compared to activity in normoxic group of 327 to 446 nmol/mg protein/hr. During graded hypoxia, the level of nuclear high affinity Ca2+-ATPase activity correlated inversely with ATP (r = 0.91) and PCr levels (r = 0.82), with activity increasing as tissue high energy phosphates decreased. The results demonstrate that the decrease in cerebral energy metabolism during hypoxia is linearly correlated with an increase in activity of high affinity Ca2+-ATPase in cerebral cortical nuclei from immature brain. We propose that increased nuclear membrane high affinity Ca2+-ATPase activity, leading to increased nuclear Ca2+, will result in altered expression of apoptotic genes that could initiate programmed neuronal death.

Phosphorylation of Bcl-2 and Bax proteins during hypoxia in newborn piglets

Studies indicate that phosphorylated Bcl-2 cannot form a heterodimer with Bax and thus may lose its antiapoptotic potential. The present study tests the hypothesis that graded hypoxia in cerebral tissue induces the phosphorylation of Bcl-2, thus altering the heterodimerization of Bcl-2 with Bax and subsequently leading to apoptosis. Anesthetized, ventilated newborn piglets were assigned to a normoxic and a graded hypoxic group. Cerebral cortical neuronal nuclei were isolated and immunoprecipitated; immune complexes were separated and reacted with Bcl-2 and Bax specific antibodies. The results show an increased level of serine/tyrosine phosphorylated Bcl-2 in nuclear membranes of hypoxic animals. The level of phosphorylated Bcl-2 protein increased linearly with decrease in tissue PCr. The level of phosphorylated Bax in the neuronal nuclear membranes was independent of cerebral tissue PCr. The data shows that during hypoxia, there is increased phosphorylation of Bcl-2, which may prevent its heterodimerization with Bax and lead to increased proapoptotic activity due to excess Bax in the hypoxic brain. Further increased phosphorylation of Bcl-2 may alter the Bcl-2/Bax-dependent antioxidant, lipid peroxidation and pore forming activity, as well as the regulation of intranuclear Ca2+ and caspase activation pathways. We speculate that increased phosphorylation of Bcl-2 in neuronal nuclear membranes is a potential mechanism of programmed cell death activation in the hypoxic brain.

Expression of Bax and Bcl-2 proteins during hypoxia in cerebral cortical neuronal nuclei of newborn piglets: effect of administration of magnesium sulfate

This study tests the hypothesis that administration of magnesium sulfate, an antagonist of the NMDA receptor ion-channel, will prevent the hypoxia-induced alteration in the expression and the ratio of Bax and Bcl-2 proteins in cerebral cortical neuronal nuclear membranes. Anesthetized, ventilated and instrumented newborn piglets were divided into three groups: normoxic controls (Nx), untreated hypoxic (Hx), and magnesium sulfate-treated hypoxic (Mg-Hx) groups. Cerebral hypoxia was induced by lowering the FiO2 (0.05-0.07) for 1 h and the cerebral cortex was harvested immediately for isolation of neuronal nuclei and hypoxia was confirmed biochemically by a decrease in the tissue levels of ATP and phosphocreatine (PCr). Brain tissue PCr (micromol/g brain) was 2.74+/-0.77 (Nx), 0.38+/-0.09 (Hx, P<0.05 vs. Nx) and 0.69+/-0.60 (Mg-Hx, P<0.05 vs. Nx). The density of immunoblotted proteins was expressed as absorbance (Axmm(2)). The expression of Bax protein (Axmm(2)) was 222+/-31 (Nx), 279+/-32 (Hx), and 148+/-44 (Mg-Hx, P<0.05 vs. Hx). Bcl-2 protein expression was 77+/-1.0 (Nx), 37+/-5.0 (Hx) and 46+/-15 (Mg-Hx, P<0.05 vs. Nx). The ratio of Bax to Bcl-2 proteins increased more than twofold during hypoxia as compared to normoxia (7:1 Hx vs. 3:1 Nx). However, in the magnesium sulfate-treated group the Bax:Bcl-2 ratio was similar to normoxic controls. The data demonstrate that magnesium sulfate treatment prevents both the hypoxia-induced increase in Bax protein expression and the alteration of Bax:Bcl-2 protein ratios. We suggest that magnesium sulfate treatment before and during hypoxia may decrease hypoxia-induced programmed cell death by maintaining the normal ratio of Bax to Bcl-2 proteins.

Effect of graded hypoxia on cerebral cortical genomic DNA fragmentation in newborn piglets

Previous studies have shown that hypoxia is associated with modification of the cerebral cortical nuclear membrane, leading to increased intranuclear calcium. The increased intranuclear calcium activates calcium-dependent endonucleases, resulting in DNA fragmentation. The present study tests the hypothesis that the fragmentation of neuronal genomic DNA increases with an increase in the degree of cerebral tissue hypoxia. Sixteen newborn piglets were anesthetized, ventilated and divided into normoxic and hypoxic groups with varying degrees of hypoxia. Cerebral hypoxia was documented biochemically by measuring tissue levels of ATP and phosphocreatine. Isolation of cerebral cortical neuronal nuclei and DNA and their purity was confirmed by standard techniques. DNA samples were separated by electrophoresis on 1% agarose gel and stained with ethidium bromide. In the hypoxic samples, multiple low-molecular-weight DNA fragments were present as a smear pattern from 200 to 2,000 base pairs. Levels of high-energy phosphates were compared to the area of each smear for each animal to correlate the degree of hypoxia with the degree of DNA fragmentation. DNA fragmentation increased when high-energy phosphate levels decreased. We conclude that there is a critical threshold value of oxidative metabolism beyond which there are progressive changes in the cortical neuronal cells, leading to DNA fragmentation.

Perinatal asphyxia: timing and mechanisms of injury in neonatal encephalopathy

This article summarizes the recent medical literature regarding perinatal asphyxia with respect to timing and mechanisms of injury for neonates who were clinically diagnosed with an encephalopathy in the newborn period. Multiple mechanisms of injury are reviewed, including genetic vulnerability, acquired inflammatory responses, and clotting defects that can lead to ischemic-induced brain damage. Before effective treatments for fetal and neonatal brain disorders can be developed, accurate and timely diagnoses of fetal or neonatal brain injury must be achieved. Specific subsets of children can then benefit from neuroprotective strategies that can target the specific developmental aspects of brain adaptation or plasticity relative to the specific etiology and timing of injury after asphyxia.