Early cell death in the brain of fetal preterm lambs after hypoxic-ischemic injury

Cortical Gray Matter Injury in Encephalopathy of Prematurity: Link to Neurodevelopmental Disorders

Preterm-born infants frequently suffer from an array of neurological damage, collectively termed encephalopathy of prematurity (EoP). They also have an increased risk of presenting with a neurodevelopmental disorder (e.g., autism spectrum disorder; attention deficit hyperactivity disorder) later in life. It is hypothesized that it is the gray matter injury to the cortex, in addition to white matter injury, in EoP that is responsible for the altered behavior and cognition in these individuals. However, although it is established that gray matter injury occurs in infants following preterm birth, the exact nature of these changes is not fully elucidated. Here we will review the current state of knowledge in this field, amalgamating data from both clinical and preclinical studies. This will be placed in the context of normal processes of developmental biology and the known pathophysiology of neurodevelopmental disorders. Novel diagnostic and therapeutic tactics required integration of this information so that in the future we can combine mechanism-based approaches with patient stratification to ensure the most efficacious and cost-effective clinical practice.

Current Evidence on Cell Death in Preterm Brain Injury in Human and Preclinical Models

Despite tremendous advances in neonatal intensive care over the past 20 years, prematurity carries a high burden of neurological morbidity lasting lifelong. The term encephalopathy of prematurity (EoP) coined by Volpe in 2009 encompasses all aspects of the now known effects of prematurity on the immature brain, including altered and disturbed development as well as specific lesional hallmarks. Understanding the way cells are damaged is crucial to design brain protective strategies, and in this purpose, preclinical models largely contribute to improve the comprehension of the cell death mechanisms. While neuronal cell death has been deeply investigated and characterized in (hypoxic–ischemic) encephalopathy of the newborn at term, little is known about the types of cell death occurring in preterm brain injury. Three main different morphological cell death types are observed in the immature brain, specifically in models of hypoxic–ischemic encephalopathy, namely, necrotic, apoptotic, and autophagic cell death. Features of all three types may be present in the same dying neuron. In preterm brain injury, description of cell death types is sparse, and cell loss primarily concerns immature oligodendrocytes and, infrequently, neurons. In the present review, we first shortly discuss the different main severe preterm brain injury conditions that have been reported to involve cell death, including periventricular leucomalacia (PVL), diffuse white matter injury (dWMI), and intraventricular hemorrhages, as well as potentially harmful iatrogenic conditions linked to premature birth (anesthesia and caffeine therapy). Then, we present an overview of current evidence concerning cell death in both clinical human tissue data and preclinical models by focusing on studies investigating the presence of cell death allowing discriminating between the types of cell death involved. We conclude that, to improve brain protective strategies, not only apoptosis but also other cell death (such as regulated necrotic and autophagic) pathways now need to be investigated together in order to consider all cell death mechanisms involved in the pathogenesis of preterm brain damage.

Intranasally Administered Exosomes from Umbilical Cord Stem Cells Have Preventive Neuroprotective Effects and Contribute to Functional Recovery after Perinatal Brain Injury

Perinatal brain injury (PBI) in preterm birth is associated with substantial injury and dysmaturation of white and gray matter, and can lead to severe neurodevelopmental deficits. Mesenchymal stromal cells (MSC) have been suggested to have neuroprotective effects in perinatal brain injury, in part through the release of extracellular vesicles like exosomes. We aimed to evaluate the neuroprotective effects of intranasally administered MSC-derived exosomes and their potential to improve neurodevelopmental outcome after PBI. Exosomes were isolated from human Wharton's jelly MSC supernatant using ultracentrifugation. Two days old Wistar rat pups were subjected to PBI by a combination of inflammation and hypoxia-ischemia. Exosomes were intranasally administered after the induction of inflammation and prior to ischemia, which was followed by hypoxia. Infrared-labeled exosomes were intranasally administered to track their distribution with a LI-COR scanner. Acute oligodendrocyte- and neuron-specific cell death was analyzed 24 h after injury in animals with or without MSC exosome application using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and immunohistochemical counterstaining. Myelination, mature oligodendroglial and neuronal cell counts were assessed on postnatal day 11 using immunohistochemistry, Western blot or RT-PCR. Morris water maze assay was used to evaluate the effect of MSC exosomes on long-term neurodevelopmental outcome 4 weeks after injury. We found that intranasally administered exosomes reached the frontal part of the brain within 30 min after administration and distributed throughout the whole brain after 3 h. While PBI was not associated with oligodendrocyte-specific cell death, it induced significant neuron-specific cell death which was substantially reduced upon MSC exosome application prior to ischemia. MSC exosomes rescued normal myelination, mature oligodendroglial and neuronal cell counts which were impaired after PBI. Finally, the application of MSC exosomes significantly improved learning ability in animals with PBI. In conclusion, MSC exosomes represent a novel prevention strategy with substantial clinical potential as they can be administered intranasally, prevent gray and white matter alterations and improve long-term neurodevelopmental outcome after PBI.

Chronic intrauterine hypoxia alters neurodevelopment in fetal sheep

OBJECTIVE

We tested the hypothesis that chronic fetal hypoxia, at a severity present in many types of congenital heart disease, would lead to abnormal neurodevelopment.

METHODS

Eight mid-gestation fetal sheep were cannulated onto a pumpless extracorporeal oxygenator via the umbilical vessels and supported in a fluid-filled environment for 22 ± 2 days under normoxic or hypoxic conditions. Total parenteral nutrition was provided. Control fetuses (n = 7) were harvested at gestational age 133 ± 4 days. At necropsy, brains were fixed for histopathology. Neurons were quantified in white matter tracts, and the thickness of the external granular layer of the cerebellum was measured to assess neuronal migration. Capillary density and myelination were quantified in white matter. Data were analyzed with unpaired Student t tests or 1-way analysis of variance, as appropriate.

RESULTS

Oxygen delivery was reduced in hypoxic fetuses (15.6 ± 1.8 mL/kg/min vs 24.3 ± 2.3 mL/kg/min, P < .01), but umbilical blood flow and caloric delivery were not different between the 2 groups. Compared with normoxic and control animals, hypoxic fetuses had reduced neuronal density and increased external granular layer thickness. Compared with normoxic and control animals, hypoxic fetuses had increased capillary density in white matter. Cortical myelin integrity score was lower in the hypoxic group compared with normoxic and control animals. There was a significant negative correlation between myelin integrity and capillary density.

CONCLUSIONS

Chronic fetal hypoxia leads to white matter hyper-vascularity, decreased neuronal density, and impaired myelination, similar to the neuropathologic findings observed in children with congenital heart disease. These findings support the hypothesis that fetal hypoxia, even in the setting of normal caloric delivery, impairs neurodevelopment.

Neuroregenerative potential of intravenous G-CSF and autologous peripheral blood stem cells in children with cerebral palsy: a randomized, double-blind, cross-over study

OBJECTIVE

We performed a randomized, double-blind, cross-over study to assess the neuroregenerative potential of intravenous granulocyte colony-stimulating factor (G-CSF) followed by infusion of mobilized peripheral blood mononuclear cells (mPBMCs) in children with cerebral palsy (CP).

METHODS

Children with non-severe CP were enrolled in this study. G-CSF was administered for 5 days, then mPBMCs were collected by apheresis and cryopreserved. One month later (M1), recipients were randomized to receive either mPBMCs or a placebo infusion, and these treatment groups were switched at 7 months (M7) and observed for another 6 months (M13). We assessed the efficacy of treatment by evaluating neurodevelopmental tests, as well as by brain magnetic resonance imaging-diffusion tensor imaging (MRI-DTI) and ¹⁸F-fluorodeoxyglucose (FDG) brain positron emission tomography-computed tomography (PET-CT) scanning to evaluate the anatomical and functional changes in the brain.

RESULTS

Fifty-seven patients aged 4.3 ± 1.9 (range 2-10) years and weighing 16.6 ± 4.9 (range 11.6-56.0) kg were enrolled in this study. The administration of G-CSF as well as the collection and reinfusion of mPBMCs were safe and tolerable. The yield of mPBMCs was comparable to that reported in studies of pediatric donors without CP and patients with nonhematologic diseases. 42.6% of the patients responded to the treatment with higher neurodevelopmental scores than would normally be expected. In addition, larger changes in neurodevelopment test scores were observed in the 1 month after G-CSF administration (M0-M1) than during the 6 months after reinfusion with mPBMCs or placebo (M1-M7 or M7-M13). Patients who received G-CSF followed by mPBMC infusion at 7 months (T7 group) demonstrated significantly more neurodevelopmental improvement than patients who received G-CSF followed by mPBMC infusion at 1 month (T1 group). In contrast to the results of neurodevelopment tests, the results of MRI-DTI at the end of this study showed greater improvement in the T1 group. Although we observed metabolic changes to the cerebellum, thalamus and cerebral cortex in the ¹⁸F-FDG brain PET-CT scans, there were no significant differences in such changes between the mPBMC and placebo group or between the T1 and T7 group.

CONCLUSIONS

Neurodevelopmental improvement was seen in response to intravenous G-CSF followed by mPBMC reinfusion, particularly to the G-CSF alone even without mPBMC reinfusion. Further studies using a larger number of mPBMCs for the infusion which could be collected by repeated cycles of apheresis or using repeated cycles of G-CSF alone, are needed to clarify the effect of mPBMC reinfusion or G-CSF alone (Trial registration: ClinicalTrials.gov, NCT02983708. Registered 5 December, 2016, retrospectively registered).

Antioxidant Treatments Recover the Alteration of Auditory-Evoked Potentials and Reduce Morphological Damage in the Inferior Colliculus after Perinatal Asphyxia in Rat

Maturation of the auditory pathway is dependent on the central nervous system myelination and it can be affected by pathologies such as neonatal hypoxic ischemic (HI) encephalopathy. Our aim was to evaluate the functional integrity of the auditory pathway and to visualize, by histological and cellular methods, the damage to the brainstem using a neonatal rat model of HI brain injury. To carry out this morphofunctional evaluation, we studied the effects of the administration of the antioxidants nicotine, melatonin, resveratrol and docosahexaenoic acid after hypoxia-ischemia on the inferior colliculus and the auditory pathway. We found that the integrity of the auditory pathway in the brainstem was altered as a consequence of the HI insult. Thus, the auditory brainstem response (ABR) showed increased I-V and III-V wave latencies. At a histological level, HI altered the morphology of the inferior colliculus neurons, astrocytes and oligodendricytes, and at a molecular level, the mitochondria membrane potential and integrity was altered during the first hours after the HI and reactive oxygen species (ROS) activity is increased 12 h after the injury in the brainstem. Following antioxidant treatment, ABR interpeak latency intervals were restored and the body and brain weight was recovered as well as the morphology of the inferior colliculus that was similar to the control group. Our results support the hypothesis that antioxidant treatments have a protective effect on the functional changes of the auditory pathway and on the morphological damage which occurs after HI insult.

Effect of neonatal asphyxia on the impairment of the auditory pathway by recording auditory brainstem responses in newborn piglets: a new experimentation model to study the perinatal hypoxic-ischemic damage on the auditory system

INTRODUCTION

Hypoxia-ischemia (HI) is a major perinatal problem that results in severe damage to the brain impairing the normal development of the auditory system. The purpose of the present study is to study the effect of perinatal asphyxia on the auditory pathway by recording auditory brain responses in a novel animal experimentation model in newborn piglets.

METHOD

Hypoxia-ischemia was induced to 1.3 day-old piglets by clamping 30 minutes both carotid arteries by vascular occluders and lowering the fraction of inspired oxygen. We compared the Auditory Brain Responses (ABRs) of newborn piglets exposed to acute hypoxia/ischemia (n = 6) and a control group with no such exposure (n = 10). ABRs were recorded for both ears before the start of the experiment (baseline), after 30 minutes of HI injury, and every 30 minutes during 6 h after the HI injury.

RESULTS

Auditory brain responses were altered during the hypoxic-ischemic insult but recovered 30-60 minutes later. Hypoxia/ischemia seemed to induce auditory functional damage by increasing I-V latencies and decreasing wave I, III and V amplitudes, although differences were not significant.

CONCLUSION

The described experimental model of hypoxia-ischemia in newborn piglets may be useful for studying the effect of perinatal asphyxia on the impairment of the auditory pathway.

Short-term effects of erythropoietin on neurodevelopment in infants with cerebral palsy: a pilot study

OBJECTIVE

Cerebral palsy (CP) is a disabling condition characterized by the motor impairment, which is difficult to be ameliorated. In the brain of infants with CP, there are persistent pathomechanisms including accentuated neuroinflammation. Since erythropoietin was demonstrated to have neuroprotective effect via anti-inflammatory and anti-apoptotic properties, we hypothesized that the administration of recombinant human EPO (rhEPO) could help children with CP, especially young infants.

MATERIALS AND METHOD

We investigated the therapeutic efficacy of rhEPO for infants with CP, who had been undergoing active rehabilitation in hospitalized setting to eliminate treatment bias. Twenty infants with CP were randomly divided into EPO or control group equally. We compared the changes in the Gross Motor Function Measure (GMFM) and the Bayley Scales of Infant Development-II (BSID-II) scores during one month of hospitalization between two groups.

RESULTS

The improvements after 1 month on the GMFM A and GMFM total scores differed significantly between the groups (p = 0.003, p = 0.04, respectively). However, the changes after 6 months were not different between the two groups. The scores of BSID-II did not show any differences at 1-month and 6-months post-treatment.

CONCLUSION

These results indicated that rhEPO could have therapeutic efficacy for infants with CP during the active rehabilitation and anti-inflammation was suggested to be one of its therapeutic mechanisms.

Antenatal allopurinol reduces hippocampal brain damage after acute birth asphyxia in late gestation fetal sheep

Free radical-induced reperfusion injury is a recognized cause of brain damage in the newborn after birth asphyxia. The xanthine oxidase inhibitor allopurinol reduces free radical synthesis and crosses the placenta easily. Therefore, allopurinol is a promising therapeutic candidate. This study tested the hypothesis that maternal treatment with allopurinol during fetal asphyxia limits ischemia-reperfusion (I/R) damage to the fetal brain in ovine pregnancy. The I/R challenge was induced by 5 repeated measured compressions of the umbilical cord, each lasting 10 minutes, in chronically instrumented fetal sheep at 0.8 of gestation. Relative to control fetal brains, the I/R challenge induced significant neuronal damage in the fetal hippocampal cornu ammonis zones 3 and 4. Maternal treatment with allopurinol during the I/R challenge restored the fetal neuronal damage toward control scores. Maternal treatment with allopurinol offers potential neuroprotection to the fetal brain in the clinical management of perinatal asphyxia.

Using the endocannabinoid system as a neuroprotective strategy in perinatal hypoxic-ischemic brain injury

One of the most important causes of brain injury in the neonatal period is a perinatal hypoxic-ischemic event. This devastating condition can lead to long-term neurological deficits or even death. After hypoxic-ischemic brain injury, a variety of specific cellular mechanisms are set in motion, triggering cell damage and finally producing cell death. Effective therapeutic treatments against this phenomenon are still unavailable because of complex molecular mechanisms underlying hypoxic-ischemic brain injury. After a thorough understanding of the mechanism underlying neural plasticity following hypoxic-ischemic brain injury, various neuroprotective therapies have been developed for alleviating brain injury and improving long-term outcomes. Among them, the endocannabinoid system emerges as a natural system of neuroprotection. The endocannabinoid system modulates a wide range of physiological processes in mammals and has demonstrated neuroprotective effects in different paradigms of acute brain injury, acting as a natural neuroprotectant. The aim of this review is to study the use of different therapies to induce long-term therapeutic effects after hypoxic-ischemic brain injury, and analyze the important role of the endocannabinoid system as a new neuroprotective strategy against perinatal hypoxic-ischemic brain injury.

Neuroprotective therapies after perinatal hypoxic-ischemic brain injury

Hypoxic-ischemic (HI) brain injury is one of the main causes of disabilities in term-born infants. It is the result of a deprivation of oxygen and glucose in the neural tissue. As one of the most important causes of brain damage in the newborn period, the neonatal HI event is a devastating condition that can lead to long-term neurological deficits or even death. The pattern of this injury occurs in two phases, the first one is a primary energy failure related to the HI event and the second phase is an energy failure that takes place some hours later. Injuries that occur in response to these events are often manifested as severe cognitive and motor disturbances over time. Due to difficulties regarding the early diagnosis and treatment of HI injury, there is an increasing need to find effective therapies as new opportunities for the reduction of brain damage and its long term effects. Some of these therapies are focused on prevention of the production of reactive oxygen species, anti-inflammatory effects, anti-apoptotic interventions and in a later stage, the stimulation of neurotrophic properties in the neonatal brain which could be targeted to promote neuronal and oligodendrocyte regeneration.

Endocannabinoids reduce cerebral damage after hypoxic-ischemic injury in perinatal rats

Hypoxic-ischemic (HI) insult during the perinatal period remains as one of the most common causes of brain injury and produces long-term neurological deficits, and there is a growing need for effective therapies. The aim of the present work was to perform a prospective study designed to assess the possible protector effect of two endocannabinoids: 2-arachidonoylglycerol (2AG) and anandamide (AEA) in the brain after HI injury in perinatal rat model. We evaluate their effects on cell death and check several cellular parameters. 7-days-old Wistar rats were assigned to four different experimental groups (n=7-10): Sham, HI, and HI treated with 2AG or AEA. The injury was induced by the left carotid artery ligature and subsequent exposure to 8% O(2) for 120 min. Immediately after the injury, treated groups received a single dose of 2AG (1mg/kg) or AEA (5mg/kg) and then animals were sacrificed 24, 72 h or 7 days after the HI event. Brains fixed by perfusion were stained with Nissl for morphological studies, and non-fixed brains were dissociated and analyzed by flow cytometry to quantify apoptosis, mitochondrial state, intracellular calcium and reactive oxygen species. Our results show that both 2AG and AEA have beneficial effects after HI injury in this rat model, producing a remarkable amelioration of brain injury, reducing apoptotic cell death, contributing to the maintenance of mitochondrial functionality, and improving cellular parameters such as the influx of calcium and ROS production.

Apoptotic cell death correlates with ROS overproduction and early cytokine expression after hypoxia-ischemia in fetal lambs

Despite advances in neonatology, the hypoxic-ischemic injury in the perinatal period remains the single most important cause of brain injury in the newborn, leading to death or lifelong sequelae. Using a sheep model of intrauterine asphyxia, we evaluated the correlation between reactive oxygen species (ROS) overproduction, cytokine expression, and apoptotic cell death. Fetal lambs were assigned to sham group, nonasphyctic animals; and hypoxia-ischemia (HI) group, lambs subjected to 60 minutes of HI) by partial cord occlusion and sacrificed 3 hours later. Different brain regions were separated to quantify the number of apoptotic cells and the same territories were dissociated for flow cytometry studies. Our results suggest that the overproduction of ROS and the early increase in cytokine production after HI in fetal lambs correlate in a significant manner with the apoptotic index, as well as with each brain region evaluated.

Early Cerebral Hemodynamic, Metabolic, and Histological Changes in Hypoxic-Ischemic Fetal Lambs during Postnatal Life

The hemodynamic, metabolic, and biochemical changes produced during the transition from fetal to neonatal life may be aggravated if an episode of asphyxia occurs during fetal life. The aim of the study was to examine regional cerebral blood flow (RCBF), histological changes, and cerebral brain metabolism in preterm lambs, and to analyze the role of oxidative stress in the first hours of postnatal life following severe fetal asphyxia. Eighteen chronically instrumented newborn lambs were randomly assigned to either a control group or the hypoxic-ischemic (HI) group, in which case fetal asphyxia was induced just before delivery. All the animals were maintained on intermittent positive pressure ventilation for 3 h after delivery. During the HI insult, the injured group developed acidosis, hypoxia, hypercapnia, lactic acidosis, and tachycardia (relative to the control group), without hypotension. The intermittent positive pressure ventilation transiently improved gas exchange and cardiovascular parameters. After HI injury and during ventilatory support, there continued to be an increased RCBF in inner regions among the HI group, but no significant differences were detected in cortical flow compared to the control group. Also, the magnitude of the increase in TUNEL positive cells (apoptosis) and antioxidant enzymes, and decrease of ATP reserves was significantly greater in the brain regions where the RCBF was not higher. In conclusion, our findings identify early metabolic, histological, and hemodynamic changes involved in brain damage in premature asphyxiated lambs. Such changes have been described in human neonates, so our model could be useful to test the safety and the effectiveness of different neuroprotective or ventilation strategies applied in the first hours after fetal HI injury.

Protective effects of early hypoxic post-conditioning in cultured cortical neurons

PRIMARY OBJECTIVE

Recent evidence suggests that delayed hypoxic post-conditioning is neuroprotective. The aim of the present study was to test whether early post-conditioning applied immediately after hypoxia could protect cultured neurons from hypoxia/reoxygenation (H/R)-induced injuries.

METHODS

Primary cortical neuronal culture depleted of microglia was exposed to H/R. Post-conditioning started immediately after hypoxia and consisted of three cycles of 15-minutes of reoxygenation and 15-minutes of hypoxia. Cell viability assay was performed using Cell Counting Kit-8 (CCK-8). Apoptosis was evaluated by Hoechst 33258 staining, FITC-Annexin V/PI double staining and Western blot assay (testing the cleaved caspase-3 expression). Reactive oxygen species (ROS), intracellular Ca(2+) and mitochondrial membrane potential (MMP) were examined using confocal laser-scanning microscopy.

MAIN RESULTS

H/R significantly reduced cell viability and increased neuronal apoptosis and necrosis. Furthermore, the expression of cleaved caspase-3, ROS production and intracellular Ca(2+) were increased. MMP was attenuated. Injuries induced by H/R were substantially attenuated by early hypoxic post-conditioning. Changes in cleaved caspase-3 expression, ROS production, intracellular Ca(2+) level and MMP in response to H/R were significantly decreased by the post-conditioning.

CONCLUSIONS

The findings demonstrated that early hypoxic post-conditioning could protect neurons against H/R-induced injuries independent of microglial cells, possibly by inhibiting ROS over-production and intracellular Ca(2+) accumulation and maintaining MMP.

Non-viral systemic delivery of siRNA or antisense oligonucleotides targeted to Jun N-terminal kinase 1 prevents cellular hypoxic damage

Many pathological conditions and environmental impacts lead to the development of severe tissue hypoxia that aggravates the primary disorder, provokes cell death, and limits the patient’s recovery. We hypothesized that suppression of Jun N-terminal kinase 1 (JNK1) will limit tissue damage induced by severe hypoxia. To test the hypothesis, antisense oligonucleotides (ASO) or small interfering RNA (siRNA) targeted to JNK1 mRNA were incorporated or complexed with neutral or cationic liposomes, respectively, and administered systemically to mice prior to hypoxia exposure. The animals were placed in a special chamber ventilated with room air (normoxia) or a gas mixture containing 6% O₂ and 94% N₂ (hypoxia). Liposomes, ASO, and siRNA were found to accumulate in the lungs, kidney, spleen, and heart. Only trace amounts of liposomes and their payloads (ASO and siRNA) were found in the brain. The down regulation of JNK1 protein limited activation of cell death signal, apoptotic, and necrotic tissue damage under hypoxic conditions. Consequently, we were able to verify our hypothesis and provide proof of concept of a unique approach to the prevention of cellular hypoxic damage by the suppression of JNK1 signaling pathways after the efficient delivery of ASO or siRNA.

Fetal asphyxia leads to the loss of striatal presynaptic boutons in adult rats

Fetal asphyxic insults in the brain are known to be associated with developmental and neurological problems like neuromotor disorders and cognitive deficits. Little is known, however, about the long-term consequences of fetal asphyxia contributing to the development of different neurological diseases common in the adult or the aging brain. For that reason the present study aimed to investigate the long-term effects of fetal asphyxia on synaptic organization within the adult rat brain. Fetal asphyxia was induced at embryonic day 17 by 75-min clamping of the uterine and ovarian arteries. Presynaptic bouton densities and numbers were analyzed in the striatum and prefrontal cortex at the age of 19 months. A substantial decrease in presynaptic bouton density and number was observed in the striatum of fetal asphyxia rats compared to control rats, while an increase was found in the fifth layer of the prefrontal cortex. These results suggest that fetal asphyxia can have long-lasting effects on synaptic organization that might contribute to a developmental etiology of different neurological disorders and aging.