Protective effects of N-acetyl-L-cysteine in human oligodendrocyte progenitor cells and restoration of motor function in neonatal rats with hypoxic-ischemic encephalopathy

Hypoxic-Ischemic Encephalopathy: Pathogenesis and Promising Therapies

Hypoxic-ischemic encephalopathy (HIE) is a brain lesion caused by inadequate blood supply and oxygen deprivation, often occurring in neonates. It has emerged as a grave complication of neonatal asphyxia, leading to chronic neurological damage. Nevertheless, the precise pathophysiological mechanisms underlying HIE are not entirely understood. This paper aims to comprehensively elucidate the contributions of hypoxia-ischemia, reperfusion injury, inflammation, oxidative stress, mitochondrial dysfunction, excitotoxicity, ferroptosis, endoplasmic reticulum stress, and apoptosis to the onset and progression of HIE. Currently, hypothermia therapy stands as the sole standard treatment for neonatal HIE, albeit providing only partial neuroprotection. Drug therapy and stem cell therapy have been explored in the treatment of HIE, exhibiting certain neuroprotective effects. Employing drug therapy or stem cell therapy as adjunctive treatments to hypothermia therapy holds great significance. This article presents a systematic review of the pathogenesis and treatment strategies of HIE, with the goal of enhancing the effect of treatment and improving the quality of life for HIE patients.

Emerging ferroptosis inhibitors as a novel therapeutic strategy for the treatment of neonatal hypoxic-ischemic encephalopathy

Neonatal hypoxia-ischemia encephalopathy (NHIE), an oxygen deprivation-mediated brain injury due to birth asphyxia or reduced cerebral blood perfusion, often leads to lifelong sequelae, including seizures, cerebral palsy, and mental retardation. NHIE poses a significant health challenge, as one of the leading causes of neonatal morbidity and mortality globally. Despite this, available therapies are limited. Numerous studies have recently demonstrated that ferroptosis, an iron-dependent non-apoptotic regulated form of cell death characterized by lipid peroxidation (LPO) and iron dyshomeostasis, plays a role in the genesis of NHIE. Moreover, recently discovered compounds have been shown to exert potential therapeutic effects on NHIE by inhibiting ferroptosis. This comprehensive review summarizes the fundamental mechanisms of ferroptosis contributing to NHIE. We focus on various emerging therapeutic compounds exhibiting characteristics of ferroptosis inhibition and delineate their pharmacological benefits for the treatment of NHIE. This review suggests that pharmacological inhibition of ferroptosis may be a potential therapeutic strategy for NHIE.

N-Acetylcysteine Administration Attenuates Sensorimotor Impairments Following Neonatal Hypoxic-Ischemic Brain Injury in Rats

Hypoxic ischemic (HI) brain injury that occurs during neonatal period has been correlated with severe neuronal damage, behavioral deficits and infant mortality. Previous evidence indicates that N-acetylcysteine (NAC), a compound with antioxidant action, exerts a potential neuroprotective effect in various neurological disorders including injury induced by brain ischemia. The aim of the present study was to investigate the role of NAC as a potential therapeutic agent in a rat model of neonatal HI brain injury and explore its long-term behavioral effects. To this end, NAC (50 mg/kg/dose, i.p.) was administered prior to and instantly after HI, in order to evaluate hippocampal and cerebral cortex damage as well as long-term functional outcome. Immunohistochemistry was used to detect inducible nitric oxide synthase (iNOS) expression. The results revealed that NAC significantly alleviated sensorimotor deficits and this effect was maintained up to adulthood. These improvements in functional outcome were associated with a significant decrease in the severity of brain damage. Moreover, NAC decreased the short-term expression of iNOS, a finding implying that iNOS activity may be suppressed and that through this action NAC may exert its therapeutic action against neonatal HI brain injury.

Methylglyoxal impairs ATP- and UTP-induced relaxation in the rat carotid arteries

Although methylglyoxal (MGO), a highly reactive dicarbonyl compound, influences the functioning of the vasculature, modulating its effects on vascular reactivity to various substances remains unclear, especially purinoceptor ligands. Therefore, we sought to investigate the direct effects of MGO on relaxation induced by adenosine 5'-triphosphate (ATP) and uridine 5'-triphosphate (UTP) in isolated rat carotid arteries. When carotid arteries were exposed to MGO (420 μM for 1 h), relaxation induced by acetylcholine or sodium nitroprusside was not affected by MGO. However, ATP- and UTP-induced relaxation was impaired by MGO compared with the control. In both ATP- and UTP-induced relaxation, endothelial denudation, incubation with the nitric oxide (NO) synthase inhibitor N^G-nitro-L-arginine or the selective P2Y purinoceptor 2 (P2Y₂) receptor antagonist AR-C118925XX reduced relaxation in both the control and MGO groups, while the differences between the control and MGO groups were eliminated. The cyclooxygenase (COX) inhibitor indomethacin inhibited the differences in ATP/UTP-mediated relaxations between the control and MGO groups. Moreover, N-acetyl-L-cysteine (NAC), an antioxidant, could augment carotid arterial relaxation induced by ATP/UTP in the presence of MGO. MGO increased arachidonic acid-induced contraction, which was suppressed by NAC. Following both ATP/UTP stimulation, MGO increased the release of prostanoids. These results suggest that MGO impaired ATP- and UTP-induced relaxation in carotid arteries, which was caused by suppressed P2Y₂ receptor-mediated signaling and reductions in endothelial NO. Moreover, MGO partially contributed to COX-derived vasoconstrictor prostanoids through increased oxidative stress.

Ferroptosis: A Promising Therapeutic Target for Neonatal Hypoxic-Ischemic Brain Injury

Ferroptosis is a type of programmed cell death caused by phospholipid peroxidation that has been implicated as a mechanism in several diseases resulting from ischemic-reperfusion injury. Most recently, ferroptosis has been identified as a possible key injury mechanism in neonatal hypoxic-ischemic brain injury (HIBI). This review summarizes the current literature regarding the different ferroptotic pathways, how they may be activated after neonatal HIBI, and which current or investigative interventions may attenuate ferroptotic cell death associated with neonatal HIBI.

High replication stress and limited Rad51-mediated DNA repair capacity, but not oxidative stress, underlie oligodendrocyte precursor cell radiosensitivity

Cranial irradiation is part of the standard of care for treating pediatric brain tumors. However, ionizing radiation can trigger serious long-term neurologic sequelae, including oligodendrocyte and brain white matter loss enabling neurocognitive decline in children surviving brain cancer. Oxidative stress-mediated oligodendrocyte precursor cell (OPC) radiosensitivity has been proposed as a possible explanation for this. Here, however, we demonstrate that antioxidants fail to improve OPC viability after irradiation, despite suppressing oxidative stress, suggesting an alternative etiology for OPC radiosensitivity. Using systematic approaches, we find that OPCs have higher irradiation-induced and endogenous γH2AX foci compared to neural stem cells, neurons, astrocytes and mature oligodendrocytes, and these correlate with replication-associated DNA double strand breakage. Furthermore, OPCs are reliant upon ATR kinase and Mre11 nuclease-dependent processes for viability, are more sensitive to drugs increasing replication fork collapse, and display synthetic lethality with PARP inhibitors after irradiation. This suggests an insufficiency for homology-mediated DNA repair in OPCs—a model that is supported by evidence of normal RPA but reduced RAD51 filament formation at resected lesions in irradiated OPCs. We therefore propose a DNA repair-centric mechanism of OPC radiosensitivity, involving chronically-elevated replication stress combined with ‘bottlenecks’ in RAD51-dependent DNA repair that together reduce radiation resilience.

NAC and Vitamin D Improve CNS and Plasma Oxidative Stress in Neonatal HIE and Are Associated with Favorable Long-Term Outcomes

N-acetylcysteine (NAC) and vitamin D provide effective neuroprotection in animal models of severe or inflammation-sensitized hypoxic ischemic encephalopathy (HIE). To translate these FDA-approved drugs to HIE neonates, we conducted an early phase, open-label trial of 10 days of NAC (25, 40 mg/kg q12h) + 1,25(OH)₂D (calcitriol 0.05 mg/kg q12h, 0.03 mg/kg q24h), (NVD), for pharmacokinetic (PK) estimates during therapeutic hypothermia and normothermia. We paired PK samples with pharmacodynamic (PD) targets of plasma isoprostanoids, CNS glutathione (GSH) and total creatine (tCr) by serial MRS in basal ganglia (BG) before and after NVD infusion at five days. Infants had moderate (n = 14) or severe HIE (n = 16), funisitis (32%), and vitamin D deficiency (75%). NVD resulted in rapid, dose-responsive increases in CNS GSH and tCr that correlated positively with plasma [NAC], inversely with plasma isofurans, and was greater in infants with lower baseline [GSH] and [tCr], suggesting increases in these PD markers were titrated by neural demand. Hypothermia and normothermia altered NAC PK estimates. NVD was well tolerated. Excluding genetic syndromes (2), prolonged ECMO (2), lost-to-follow-up (1) and SIDS death (1), 24 NVD treated HIE infants have no evidence of cerebral palsy, autism or cognitive delay at 24–48 months. These data confirm that low, safe doses of NVD in HIE neonates decreased oxidative stress in plasma and CNS, improved CNS energetics, and are associated with favorable developmental outcomes at two to four years.

Myelin Defects in Niemann-Pick Type C Disease: Mechanisms and Possible Therapeutic Perspectives

Niemann–Pick type C (NPC) disease is a wide-spectrum clinical condition classified as a neurovisceral disorder affecting mainly the liver and the brain. It is caused by mutations in one of two genes, NPC1 and NPC2, coding for proteins located in the lysosomes. NPC proteins are deputed to transport cholesterol within lysosomes or between late endosome/lysosome systems and other cellular compartments, such as the endoplasmic reticulum and plasma membrane. The first trait of NPC is the accumulation of unesterified cholesterol and other lipids, like sphingosine and glycosphingolipids, in the late endosomal and lysosomal compartments, which causes the blockade of autophagic flux and the impairment of mitochondrial functions. In the brain, the main consequences of NPC are cerebellar neurodegeneration, neuroinflammation, and myelin defects. This review will focus on myelin defects and the pivotal importance of cholesterol for myelination and will offer an overview of the molecular targets and the pharmacological strategies so far proposed, or an object of clinical trials for NPC. Finally, it will summarize recent data on a new and promising pharmacological perspective involving A_2A adenosine receptor stimulation in genetic and pharmacological NPC dysmyelination models.

Mechanism and Treatment Related to Oxidative Stress in Neonatal Hypoxic-Ischemic Encephalopathy

Hypoxic ischemic encephalopathy (HIE) is a type of neonatal brain injury, which occurs due to lack of supply and oxygen deprivation to the brain. It is associated with a high morbidity and mortality rate. There are several therapeutic strategies that can be used to improve outcomes in patients with HIE. These include cell therapies such as marrow mesenchymal stem cells (MSCs) and umbilical cord blood stem cells (UCBCs), which are being incorporated into the new protocols for the prevention of ischemic brain damage. The focus of this review is to discuss the mechanism of oxidative stress in HIE and summarize the current available treatments for HIE. We hope that a better understanding of the relationship between oxidative stress and HIE will provide new insights on the potential therapy of this devastating condition.

Variants of the OLIG2 Gene are Associated with Cerebral Palsy in Chinese Han Infants with Hypoxic-Ischemic Encephalopathy

Cerebral palsy (CP) is a leading cause of neurological disability among young children. Congenial and adverse perinatal clinical conditions, such as genetic factors, perinatal infection, and asphyxia, are risk factors for CP. Oligodendrocyte transcription factor (OLIG2) is a protein that is expressed in brain oligodendrocyte cells and is involved in neuron repair after brain injury. In this study, we employed a Chinese Han cohort of 763 CP infants and 738 healthy controls to study the association of OLIG2 gene polymorphisms with CP. We found marginal association of the SNP rs6517135 with CP (p = 0.044) at the genotype level, and the association was greatly strengthened when we focused on the subgroup of CP infants who suffered from hypoxic-ischemic encephalopathy (HIE) after birth, with p = 0.003 (OR = 0.558) at the allele level and p = 0.007 at the genotype level, indicating a risk-associated role of the T allele of the SNP rs6517135 under HIE conditions. The haplotype CTTG for rs6517135-rs1005573-rs6517137-rs9653711 in OLIG2 was also significantly associated with the occurrence of CP in infants with HIE (p = 0.01, OR = 0.521). Our results indicate that in the Han Chinese population, the polymorphisms of OLIG2 were associated with CP, especially in patients who had suffered HIE injury. This finding could be used to develop personalized care for infants with high susceptibility to CP.

Improvement by Human Oligodendrocyte Progenitor Cells of Neurobehavioral Disorders in an Experimental Model of Neonatal Periventricular Leukomalacia

The effects of human oligodendrocyte progenitor (F3.olig2) cells on improving neurobehavioral deficits were investigated in an experimental model of periventricular leukomalacia (PVL). Seven-day-old male rats were subjected to hypoxia-ischemia-lipopolysaccharide injection (HIL), and intracerebroventricularly transplanted with F3.olig2 (4 × 10⁵ cells/rat) once at post-natal day (PND) 10 or repeatedly at PND10, 17, 27, and 37. Neurobehavioral disorders were evaluated at PND14, 20, 30, and 40 via cylinder test, locomotor activity, and rotarod performance, and cognitive function was evaluated at PND41-45 through passive avoidance and Morris water-maze performances. F3.olig2 cells recovered the rate of use of the forelimb contralateral to the injured brain, improved locomotor activity, and restored rotarod performance of PVL animals; in addition, marked improvement of learning and memory function was seen. It was confirmed that transplanted F3·olig2 cells migrated to injured areas, matured to oligodendrocytes expressing myelin basic protein (MBP), and markedly attenuated the loss of host MBP in the corpus callosum. The results indicate that the transplanted F3.olig2 cells restored neurobehavioral functions by preventing axonal demyelination, and that human oligodendrocyte progenitor cells could be a candidate for cell therapy of perinatal hypoxic-ischemic and infectious brain injuries including PVL and cerebral palsy.

Fabricating PLGA microparticles with high loads of the small molecule antioxidant N-acetylcysteine that rescue oligodendrocyte progenitor cells from oxidative stress

Reactive oxygen species (ROS), encompassing all oxygen radical or non-radical oxidizing agents, play key roles in disease progression. Controlled delivery of antioxidants is therapeutically relevant in such oxidant-stressed environments. Encapsulating small hydrophilic molecules into hydrophobic polymer microparticles via traditional emulsion methods has long been a challenge due to rapid mass transport of small molecules out of particle pores. We have developed a simple alteration to the existing water-in-oil-in-water (W/O/W) drug encapsulation method that dramatically improves loading efficiency: doping external water phases with drug to mitigate drug diffusion out of the particle during fabrication. PLGA microparticles with diameters ranging from 0.6 to 0.9 micrometers were fabricated, encapsulating high loads of 0.6-0.9 µm diameter PLGA microparticles were fabricated, encapsulating high loads of the antioxidant N-acetylcysteine (NAC), and released active, ROS-scavenging NAC for up to 5 weeks. Encapsulation efficiencies, normalized to the theoretical load of traditional encapsulation without doping, ranged from 96% to 400%, indicating that NAC-loaded external water phases not only prevented drug loss due to diffusion, but also doped the particles with additional drug. Antioxidant-doped particles positively affected the metabolism of oligodendrocyte progenitor cells (OPCs) under H₂ O₂ -mediated oxidative stress when administered both before (protection) or after (rescue) injury. Antioxidant doped particles improved outcomes of OPCs experiencing multiple doses of H₂ O₂ by increasing the intracellular glutathione content and preserving cellular viability relative to the injury control. Furthermore, antioxidant-doped particles preserve cell number, number of process extensions, cytoskeletal morphology, and nuclear size of H₂ O₂ -stressed OPCs relative to the injury control. These NAC-doped particles have the potential to provide temporally-controlled antioxidant therapy in neurodegenerative disorders such as multiple sclerosis (MS) that are characterized by continuous oxidative stress.

Vitamin D improves functional outcomes in neonatal hypoxic ischemic male rats treated with N-acetylcysteine and hypothermia

Hypothermia treatment neuroprotects approximately 50% of neonates who present with moderate to severe hypoxic ischemic encephalopathy (HIE). N-acetylcysteine (NAC), a potent antioxidant, is neuroprotective in combination with hypothermia in neonatal hypoxia-ischemia (HI) female rats, but less protective in males. Vitamin D is a neurosteroid, which may provide immunomodulation and improve outcomes for both sexes. We investigated the efficacy of this combination of drugs with hypothermia after severe HI, as well as potential mechanisms of vitamin D effects in the transition to chronic inflammation. DOL 7 rats were randomized to sham, or HI and hypothermia treated with either saline (HYPO), NAC (50 mg/kg/d, HNAC), or HNAC plus 1,25-dihydroxy-vitamin D₃ (0.1 μg/kg/d, HNAC + VitD) daily for 2 weeks. A second set of animals were randomized and treated for 11 days to investigate vitamin D metabolism and inflammatory mediators. Rats treated with HNAC + VitD performed significantly better on tests of strength and use of affected limb, adaptive sensorimotor skills, motor sequence learning, and working memory than either HYPO or HNAC, particularly benefiting male rats. Significantly fewer rats in the HNAC + VitD group had severe hemispheric volume loss. HI injury decreased serum vitamin D at 11 days and induced the enzyme that deactivates vitamin D in the hippocampus, particularly in males. Persistent vitamin D dysregulation was seen in both hippocampi in males, which was not reversed by hypothermia. Vitamin D in combination with hypothermia and NAC supports functional recovery in both sexes of neonatal rats significantly better than hypothermia alone or hypothermia and NAC in this severe HI model.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate's secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury.

Role of Antioxidants in Neonatal Hypoxic-Ischemic Brain Injury: New Therapeutic Approaches

Hypoxic-ischemic brain damage is an alarming health and economic problem in spite of the advances in neonatal care. It can cause mortality or detrimental neurological disorders such as cerebral palsy, motor impairment and cognitive deficits in neonates. When hypoxia-ischemia occurs, a multi-faceted cascade of events starts out, which can eventually cause cell death. Lower levels of oxygen due to reduced blood supply increase the production of reactive oxygen species, which leads to oxidative stress, a higher concentration of free cytosolic calcium and impaired mitochondrial function, triggering the activation of apoptotic pathways, DNA fragmentation and cell death. The high incidence of this type of lesion in newborns can be partly attributed to the fact that the developing brain is particularly vulnerable to oxidative stress. Since antioxidants can safely interact with free radicals and terminate that chain reaction before vital molecules are damaged, exogenous antioxidant therapy may have the potential to diminish cellular damage caused by hypoxia-ischemia. In this review, we focus on the neuroprotective effects of antioxidant treatments against perinatal hypoxic-ischemic brain injury, in the light of the most recent advances.

Cereboost™, an American ginseng extract, improves cognitive function via up-regulation of choline acetyltransferase expression and neuroprotection

In Alzheimer disease (AD), amyloid-beta (Aβ) peptides induce the degeneration of presynaptic cholinergic system, in which decreased activity of enzyme choline acetyltransferase (ChAT) responsible for acetylcholine synthesis is observed. Cereboost™, an extract of American ginseng extract, contains a high concentration of Rb1 ginsenoside which is a well-known ingredient improving human cognitive function. We investigated the effects of Cereboost™ on learning and memory function of mice challenged with an Aβ1-42 peptide and the underlying mechanisms in vitro. Cereboost™ protected against Aβ1-42-induced cytotoxicity in F3.ChAT stem cells, and enhanced the ChAT gene expression. Aβ1-42 injection into the mouse brain impaired the cognitive function, which was recovered by oral administration of Cereboost™. In addition, Cereboost™ restored brain microtubule-associated protein 2 and synaptophysin as well as acetylcholine concentration. The results demonstrate that Cereboost™ administration recovered the cognitive function of AD model animals by enhancing acetylcholine level via ChAT gene expression and neuroprotection.

Protective effects of carnosine on white matter damage induced by chronic cerebral hypoperfusion

Carnosine is a dipeptide that scavenges free radicals, inhibits inflammation in the central nervous system, and protects against ischemic and hypoxic brain damage through its anti-oxidative and anti-apoptotic actions. Therefore, we hypothesized that carnosine would also protect against white matter damage caused by subcortical ischemic injury. White matter damage was induced by right unilateral common carotid artery occlusion in mice. The animals were treated with 200, 500 or 750 mg/kg carnosine by intraperitoneal injection 30 minutes before injury and every other day after injury. Then, 37 days later, Klüver-Barrera staining, toluidine blue staining and immunofluorescence staining were performed. Carnosine (200, 500 mg/kg) substantially reduced damage to the white matter in the corpus callosum, internal capsule and optic tract, and it rescued expression of myelin basic protein, and alleviated the loss of oligodendrocytes. However, carnosine at the higher dose of 750 mg/kg did not have the same effects as the 200 and 500 mg/kg doses. These findings show that carnosine, at a particular dose range, protects against white matter damage caused by chronic cerebral ischemia in mice, likely by reducing oligodendroglial cell loss.