Oxygen glucose deprivation in rat hippocampal slice cultures results in alterations in carnitine homeostasis and mitochondrial dysfunction

Neurosteroid pathway derangement in asphyctic infants treated with hypothermia: an untargeted metabolomic approach

BACKGROUND

The pathobiological mechanisms associated with perinatal asphyxia and hypoxic-ischemic encephalopathy are complex and poorly understood. The metabolic effects of therapeutic hypothermia have been partially explored.

METHODS

We conducted a single-center longitudinal study to investigate the metabolic effects of perinatal asphyxia and hypoxic-ischemic encephalopathy on the urinary metabolome of a group of 12 asphyctic infants over time compared to 22 matched healthy newborns, using untargeted metabolomics based on mass spectrometry.

FINDINGS

Over-representation pathway analysis identified the steroidogenesis pathway as being significantly disrupted, with reduced steroid levels in the first three days of life despite treatment with hypothermia. Comparison with matched healthy newborns showed that the urinary steroid content was lower in asphyctic infants before hypothermia. The lysine degradation and carnitine synthesis pathways were also significantly affected.

INTERPRETATION

Steroidogenesis is significantly disrupted in asphyctic infants compared to healthy newborns. Given how neurosteroids are involved in neuromodulation and neuroprotection, translational research is warranted on the potential role of neurosteroid-based intervention in asphyctic infants.

FUNDING

None.

Naked mole-rat brain mitochondria tolerate in vitro ischaemia

Naked mole-rats (NMRs; Heterocephalus glaber) are among the most hypoxia-tolerant mammals. There is evidence that the NMR brain tolerates in vitro hypoxia and NMR brain mitochondria exhibit functional plasticity following in vivo hypoxia; however, if and how these organelles tolerate ischaemia and how ischaemic stress impacts mitochondrial energetics and redox regulation is entirely unknown. We hypothesized that mitochondria fundamentally contribute to in vitro ischaemia resistance in the NMR brain. To test this, we treated NMR and CD-1 mouse cortical brain sheets with an in vitro ischaemic mimic and evaluated mitochondrial respiration capacity and redox regulation following 15 or 30 min of ischaemia or ischaemia/reperfusion (I/R). We found that, relative to mice, the NMR brain largely retains mitochondrial function and redox balance post-ischaemia and I/R. Specifically: (i) ischaemia reduced complex I and II-linked respiration ∼50-70% in mice, vs. ∼20-40% in NMR brain, (ii) NMR but not mouse brain maintained relatively steady respiration control ratios and robust mitochondrial membrane integrity, (iii) electron leakage post-ischaemia was lesser in NMR than mouse brain and NMR brain retained higher coupling efficiency, and (iv) free radical generation during and following ischaemia and I/R was lower from NMR brains than mice. Taken together, our results indicate that NMR brain mitochondria are more tolerant of ischaemia and I/R than mice and retain respiratory capacity while avoiding redox derangements. Overall, these findings support the hypothesis that hypoxia-tolerant NMR brain is also ischaemia-tolerant and suggest that NMRs may be a natural model of ischaemia tolerance in which to investigate evolutionarily derived solutions to ischaemic pathology. KEY POINTS: Ischaemia is highly deleterious to the mammalian brain and this damage is largely mediated by mitochondrial dysfunction. Naked mole-rats are among the most hypoxia-tolerant mammals and their brain tolerates ischaemia ex vivo, but the impact of ischaemia on mitochondrial function is unknown. Naked mole-rat but not mouse brain mitochondria retain respiratory capacity and membrane integrity following ischaemia or ischaemia/reperfusion. Differences in free radical management and respiratory pathway control between species may mediate this tolerance. These results help us understand how natural models of hypoxia tolerance also tolerate ischaemia in the brain.

Vitamin C Deficiency in the Young Brain-Findings from Experimental Animal Models

Severe and long-term vitamin C deficiency can lead to fatal scurvy, which is fortunately considered rare today. However, a moderate state of vitamin C (vitC) deficiency (hypovitaminosis C)-defined as a plasma concentration below 23 μM-is estimated to affect up to 10% of the population in the Western world, albeit clinical hallmarks in addition to scurvy have not been linked to vitC deficiency. The brain maintains a high vitC content and uniquely high levels during deficiency, supporting vitC's importance in the brain. Actions include both antioxidant and co-factor functions, rendering vitamin C deficiency likely to affect several targets in the brain, and it could be particularly significant during development where a high cellular metabolism and an immature antioxidant system might increase sensitivity. However, investigations of a non-scorbutic state of vitC deficiency and effects on the developing young brain are scarce. This narrative review provides a comprehensive overview of the complex mechanisms that regulate vitC homeostasis in vivo and in the brain in particular. Functions of vitC in the brain and the potential consequences of deficiency during brain development are highlighted, based primarily on findings from experimental animal models. Perspectives for future investigations of vitC are outlined.

Acylcarnitine profile in neonatal hypoxic-ischemic encephalopathy: The value of butyrylcarnitine as a prognostic marker

Optimal prognostic markers evaluating early neuroprotective interventions in neonatal hypoxic-ischemic encephalopathy (HIE) are lacking. This study was designed to assess the prognostic value of acylcarnitines in neonatal HIE.An observational cohort study was conducted over 10 years in 67 HIE. Variables analyzed included sex, blood cord pH, Apgar score, hypothermia treatment (yes/no), neuron-specific enolase (NSE) levels, and clinical outcome (neurological examination, brain magnetic resonance imaging [MRI], and electroencephalogram) before discharge and at 6 months. Acylcarnitine profiles were analyzed by tandem-mass spectrometry on dried-blood spots collected on day 3 for newborn screening. A cohort of healthy newborns was used as control group.HIE patients had significantly increased C4, C5, C5:1, C6, C6-OH, C8 levels (all P < .01) and decreased long-chain acylcarnitine levels (P < .03). Hypothermia treatment was associated with a decrease in C4 levels (p = 0.005) and an increase in most long-chain acylcarnitine levels (P < .01). A significant association was found between C4 levels and NSE on day 1 of hypothermia treatment (P = .002) and abnormal brain magnetic resonance imaging (MRI) at discharge (P = .037). In the hypothermia group, C4 levels decreased in patients with favorable outcomes but remained high in those who progressed unfavorably.C4 appears to be a good prognostic marker in HIE, as blood levels correlated with NSE levels and abnormal MRI findings. Furthermore, hypothermia did not lead to decreased levels in patients with adverse outcomes.

Docosanoids and elovanoids from omega-3 fatty acids are pro-homeostatic modulators of inflammatory responses, cell damage and neuroprotection

The functional significance of the selective enrichment of the omega-3 essential fatty acid docosahexaenoic acid (DHA; 22C and 6 double bonds) in cellular membrane phospholipids of the nervous system is being clarified by defining its specific roles on membrane protein function and by the uncovering of the bioactive mediators, docosanoids and elovanoids (ELVs). Here, we describe the preferential uptake and DHA metabolism in photoreceptors and brain as well as the significance of the Adiponectin receptor 1 in DHA retention and photoreceptor cell (PRC) survival. We now know that this integral membrane protein is engaged in DHA retention as a necessary event for the function of PRCs and retinal pigment epithelial (RPE) cells. We present an overview of how a) NPD1 selectively mediates preconditioning rescue of RPE and PR cells; b) NPD1 restores aberrant neuronal networks in experimental epileptogenesis; c) the decreased ability to biosynthesize NPD1 in memory hippocampal areas of early stages of Alzheimer's disease takes place; d) NPD1 protection of dopaminergic circuits in an in vitro model using neurotoxins; and e) bioactivity elicited by DHA and NPD1 activate a neuroprotective gene-expression program that includes the expression of Bcl-2 family members affected by Aβ42, DHA, or NPD1. In addition, we highlight ELOVL4 (ELOngation of Very Long chain fatty acids-4), specifically the neurological and ophthalmological consequences of its mutations, and their role in providing precursors for the biosynthesis of ELVs. Then we outline evidence of ELVs ability to protect RPE cells, which sustain PRC integrity. In the last section, we present a summary of the protective bioactivity of docosanoids and ELVs in experimental ischemic stroke. The identification of early mechanisms of neural cell survival mediated by DHA-synthesized ELVs and docosanoids contributes to the understanding of cell function, pro-homeostatic cellular modulation, inflammatory responses, and innate immunity, opening avenues for prevention and therapeutic applications in neurotrauma, stroke and neurodegenerative diseases.

Ambient but not local lactate underlies neuronal tolerance to prolonged glucose deprivation

Neurons require a nearly constant supply of ATP. Glucose is the predominant source of brain ATP, but the direct effects of prolonged glucose deprivation on neuronal viability and function remain unclear. In sparse rat hippocampal microcultures, neurons were surprisingly resilient to 16 h glucose removal in the absence of secondary excitotoxicity. Neuronal survival and synaptic transmission were unaffected by prolonged removal of exogenous glucose. Inhibition of lactate transport decreased microculture neuronal survival during concurrent glucose deprivation, suggesting that endogenously released lactate is important for tolerance to glucose deprivation. Tandem depolarization and glucose deprivation also reduced neuronal survival, and trace glucose concentrations afforded neuroprotection. Mass cultures, in contrast to microcultures, were insensitive to depolarizing glucose deprivation, a difference attributable to increased extracellular lactate levels. Removal of local astrocyte support did not reduce survival in response to glucose deprivation or alter evoked excitatory transmission, suggesting that on-demand, local lactate shuttling is not necessary for neuronal tolerance to prolonged glucose removal. Taken together, these data suggest that endogenously produced lactate available globally in the extracellular milieu sustains neurons in the absence of glucose. A better understanding of resilience mechanisms in reduced preparations could lead to therapeutic strategies aimed to bolster these mechanisms in vulnerable neuronal populations.

L-Carnitine and Acetyl-L-carnitine Roles and Neuroprotection in Developing Brain

L-Carnitine functions to transport long chain fatty acyl-CoAs into the mitochondria for degradation by β-oxidation. Treatment with L-carnitine can ameliorate metabolic imbalances in many inborn errors of metabolism. In recent years there has been considerable interest in the therapeutic potential of L-carnitine and its acetylated derivative acetyl-L-carnitine (ALCAR) for neuroprotection in a number of disorders including hypoxia-ischemia, traumatic brain injury, Alzheimer's disease and in conditions leading to central or peripheral nervous system injury. There is compelling evidence from preclinical studies that L-carnitine and ALCAR can improve energy status, decrease oxidative stress and prevent subsequent cell death in models of adult, neonatal and pediatric brain injury. ALCAR can provide an acetyl moiety that can be oxidized for energy, used as a precursor for acetylcholine, or incorporated into glutamate, glutamine and GABA, or into lipids for myelination and cell growth. Administration of ALCAR after brain injury in rat pups improved long-term functional outcomes, including memory. Additional studies are needed to better explore the potential of L-carnitine and ALCAR for protection of developing brain as there is an urgent need for therapies that can improve outcome after neonatal and pediatric brain injury.

Cytoprotective effects of myristicin against hypoxia‑induced apoptosis and endoplasmic reticulum stress in rat dorsal root ganglion neurons

The aim of the present study was to investigate the role of myristicin (Myr; 1‑allyl‑5‑methoxy‑3,4‑methylenedioxybenzene), an active aromatic compound isolated from nutmeg, carrot, basil, cinnamon and parsley, in hypoxia‑induced apoptosis in rat dorsal root ganglion (DRG) neurons. It was observed that Myr significantly enhanced cell viability in hypoxia‑induced DRG neurons in a dose‑dependent manner; the optimal concentration of Myr was 50 µM. Furthermore, Myr reduced the percentage of deoxynucleotidyl transferase‑mediated dUTP nick end‑labeling‑positive neuronal cells and influenced the expression of the pro‑apoptotic gene B‑cell lymphoma 2 (Bcl‑2) associated X protein, the apoptosis protease cleaved caspase‑3 and the anti‑apoptotic gene Bcl‑2, in the hypoxia‑induced group. In addition, Myr protected against hypoxic injury in DRG neurons by inhibiting malondialdehyde and lactate dehydrogenase, however upregulating superoxide dismutase and glutathione peroxidase. Myr reduced the expression of endoplasmic reticulum stress (ERS) markers, including CCAAT/enhancer‑binding protein‑homologous protein, glucose‑related protein 78 and cleaved caspase‑12 in the hypoxia‑induced group. To the best of our knowledge, this is the first demonstration of the activity of Myr against hypoxia‑induced apoptosis in rat DRG neurons via inhibition of the ERS pathway.

Sevoflurane Post-conditioning Enhanced Hippocampal Neuron Resistance to Global Cerebral Ischemia Induced by Cardiac Arrest in Rats through PI3K/Akt Survival Pathway

The purpose of this current study was to evaluate whether improvement of mitochondrial dysfunction was involved in the therapeutic effect of sevoflurane post-conditioning in global cerebral ischemia after cardiac arrest (CA) via the PI3K/Akt pathway. In the first experiment, animals were randomly divided into three groups: a sham group, a CA group, a CA+sevoflurane post-conditioning group (CA+SE). Sevoflurane post-conditioning was achieved by administration of 2.5% sevoflurane for 30 min after resuscitation. Sevoflurane post-conditioning has a significant neuroprotective effect by increasing survival rates and reducing neuronal apoptosis. Additionally, the gene and protein expression of PGC-1α, NRF-1, and TFAM, the master regulators of mitochondrial biogenesis, were up-regulated in the CA+SE group, when compared to the CA group. Similarly, in contrast to the CA group, mitochondria-specific antioxidant enzymes, including heat-shock protein 60 (HSP60), peroxiredoxin 3 (Prx3), and thioredoxin 2 (Trx2) were also increased in the CA+SE group. Finally, administration of sevoflurane ameliorated mitochondrial reactive oxygen species (ROS) formation and maintained mitochondrial integrity. In the second experiment, we investigated the relationship between the PI3K/Akt pathway and mitochondrial biogenesis and mitochondria-specific antioxidant enzymes in sevoflurane-induced neuroprotection. The selective PI3K inhibitor wortmannin not only eliminated the beneficial biochemical processes of sevoflurane by reducing the level of mitochondrial biogenesis-related proteins and aggravating mitochondrial integrity, but also reversed the elevation of mitochondria-specific antioxidant enzymes induced by sevoflurane. Therefore, our data suggested that sevoflurane post-conditioning provides neuroprotection via improving mitochondrial biogenesis and integrity, as well as increasing mitochondria-specific antioxidant enzymes by a mechanism involving the PI3K/Akt pathway.

In vitro detection of oxygen and glucose deprivation-induced neurodegeneration and pharmacological neuroprotection based on hippocampal stratum pyramidale width

Ischemia is one of the most prominent risk factors of neurodegenerative diseases such as Alzheimer's disease. The effects of oxygen and glucose depletion in hippocampal tissue due to ischemia can be mimicked in vitro using the oxygen and glucose deprivation (OGD) model. In this study, we applied OGD on acute rat hippocampal slices in order to design an elementary yet quantitative histological technique that compares the neuroprotective effects of (l)-carnitine to known neuroprotectors, such as the N-methyl-d-aspartate (NMDA) receptor antagonist memantine and the gamma-aminobutyric acid (GABA)-B receptor agonist baclofen. The level of neurodegeneration and the efficiency of pharmacological applications were estimated via stratum pyramidale width measurements in CA1 and CA3 regions of Nissl-stained 200-μm thick hippocampal slices. We demonstrated that (l)-carnitine is an effective pharmacological target against the neurodegeneration induced by in vitro ischemia in a narrow range of concentrations. Even though the effect of chemical neuroprotection was significant, full recovery was not achieved in the dose interval of 5-100μM. In addition to chemical applications, hypothermia was used as a physical neuroprotection against ischemia-related neurodegeneration. Our results showed that incubation of slices for 60min at 4°C provided the same level of neuroprotection as the most effective doses of memantine, baclofen, and (l)-carnitine.

Let-7f Regulates the Hypoxic Response in Cerebral Ischemia by Targeting NDRG3

microRNAs are a class of non-coding RNAs including approximately 22 nucleotides in length and play a pivotal role in post-transcriptional gene regulation. Currently, the role of miRNAs in the pathophysiology of ischemic stroke has been the subject of recent investigations. In particular, antagomirs to microRNA (miRNA) let-7f have been found to be neuroprotective in vivo, although the detailed function of let-7f during cerebral ischemia has not been fully illustrated. NDRG3 is an N-myc downstream-regulated gene (NDRG) family member that has been observed in the nuclei in most brain cells. Recently, a NDRG3-mediated lactate signaling, in which stabilized NDRG3 protein can promote angiogenesis and cell growth by activating the Raf-ERK pathway in hypoxia was discovered. In this study, we preliminarily explored the change in the expression of the NDRG3 protein which indicated that NDRG3 protein is an oxygen-regulated protein in neurons in rat cerebral ischemia in vivo and in vitro. We further identified let-7f as an upstream regulator of NDRG3 by the lentiviral transfection of rat cortical neurons and the dual luciferase analysis of human genes. In addition, a dual-color fluorescence in situ hybridization assay showed that when the expression of let-7f was elevated, the expression of NDRG3 mRNA was accordingly reduced in rat cerebral ischemia. Taken together, our results identify a new regulatory mechanism of let-7f on NDRG3 expression in the hypoxic response of cerebral ischemia and raise the possibility that the let-7f/NDRG3 pathway may serve as a potential target for the treatment of ischemic stroke.

Docosahexaenoic Acid Reduces Cerebral Damage and Ameliorates Long-Term Cognitive Impairments Caused by Neonatal Hypoxia-Ischemia in Rats

As the interest in the neuroprotective possibilities of docosahexaenoic acid (DHA) for brain injury has grown in the recent years, we aimed to investigate the long-term effects of this fatty acid in an experimental model of perinatal hypoxia-ischemia in rats. To this end, motor activity, aspects of learning, and memory function and anxiety, as well as corticofugal connections visualized by using tracer injections, were evaluated at adulthood. We found that in the hours immediately following the insult, DHA maintained mitochondrial inner membrane integrity and transmembrane potential, as well as the integrity of synaptic processes. Seven days later, morphological damage at the level of the middle hippocampus was reduced, since neurons and myelin were preserved and the astroglial reactive response and microglial activation were seen to be diminished. At adulthood, the behavioral tests revealed that treated animals presented better long-term working memory and less anxiety than non-treated hypoxic-ischemic animals, while no difference was found in the spontaneous locomotor activity. Interestingly, hypoxic-ischemic injury caused alterations in the anterograde corticofugal neuronal connections which were not so evident in rats treated with DHA. Thus, our results indicate that DHA treatment can lead to long-lasting neuroprotective effects in this experimental model of neonatal hypoxia-ischemic brain injury, not only by mitigating axonal changes but also by enhancing cognitive performance at adulthood.

Bone Marrow Mesenchymal Stem Cells Attenuate Mitochondria Damage Induced by Hypoxia in Mouse Trophoblasts

Objective

We aimed to observe the change of mitochondrial function and structure as well as the cell function induced by hypoxia in mouse trophoblasts, and moreover, to validate the restoration of these changes after co-culture with bone marrow mesenchymal stem cells (hereinafter referred to as “MSCs”). Further, we explored the mechanism of MSCs attenuating the functional damage of trophoblasts caused by hypoxia.

Methods

Cells were divided into two groups, trophoblasts and MSCs+trophoblasts respectively, and the two groups of cells were incubated with normoxia or hypoxia. Chemiluminescence was used to assay the β-HCG and progesterone in cell culture supernatants quantitatively. Western blotting and PCR were applied to detect the expression of Mfn2, MMP-2, MMP-9 and integrin β1 in the two groups. The mitochondrial membrane potential of each group of cells was detected with JC-1 dye and the ATP content was measured by the phosphomolybdic acid colorimetric method. We utilized transmission electron microscopy for observing the ultrastructure of mitochondria in trophoblasts. Finally, we assessed the cell apoptosis with flow cytometry (FCM) and analyzed the expression of the apoptosis related genes—Bcl-2, Bax, Caspase3 and Caspase9 by western blotting.

Results

The results showed that the Mfn2 expression was reduced after 4 h in hypoxia compared with that in normoxia, but increased in the co-culture group when compared with that in the separated-culture group (p<0.05). In addition, compared with the separated-culture group, theβ-HCG and progesterone levels in the co-culture group were significantly enhanced (p<0.05), and so were the expressions of MMP-2, MMP-9 and integrin β1 (p<0.05). Moreover, it exhibited significantly higher in ATP levels and intensified about the mitochondrial membrane potential in the co-culture group. TEM revealed disorders of the mitochondrial cristae and presented short rod-like structure and spheroids in hypoxia, however, in the co-culture group, the mitochondrial cristae had a relatively regular arrangement and the mitochondrial ultrastructure showed hyperfusion. The expression of Bax, Caspase3 and Caspase9 was decreased in the co-culture group when compared with that in trophoblast cells cultured alone (p<0.05), while the Bcl-2 levels and the Apoptosis Index (AI) were markedly increased in the co-culture group (p<0.05).

Conclusion

Bone marrow mesenchymal stem cells can attenuate mitochondria damage and cell apoptosis induced by hypoxia; the mechanism could be upregulating the expression of Mfn2 in mouse trophoblasts and changing mitochondrial structure.

Hyperbaric oxygen preconditioning ameliorates hypoxia-ischemia brain damage by activating Nrf2 expression in vivo and in vitro

The present study aimed to investigate whether hyperbaric oxygen preconditioning (HBO-PC) could ameliorate hypoxia-ischemia brain damage (HIBD) by an increase of Nrf2 expression. P7 Sprague-Dawley rats (aged 7 d, n = 195) were used in two in vivo experiments, including BO-PC exposure experiments in non-HIBD models and treatment experiments in HIBD models. 2,3,5-triphenyltetrazolium chloride (TTC) staining, Nissl Staining, and TUNEL staining were performed. And expressions of Nrf2, HO-1, and GSTs were measured. For in vitro studies, oxygen-glucose deprivation cells were established. Morphological and apoptotic staining and gene silencing of Nrf2 by siRNA transfection were investigated. For exposure experiments, HBO-PC for longer time increased the expression of Nrf2 significantly. And for treatment experiments, HBO-PC treatment significantly decreased infarction area, lessened neuronal injury, reduced apoptosis, and increased both the expression of Nrf2 and activities of its downstream proteins. Cytology tests confirmed effects of HBO-PC treatments. Besides, Nrf2 siRNA significantly reduced protective effects of HBO-PC. These observations demonstrated that an up-regulation of Nrf2 by HBO-PC might play an important role in the generation of tolerance against HIBD.

Alternative mitochondrial electron transfer for the treatment of neurodegenerative diseases and cancers: Methylene blue connects the dots

Brain has exceptional high requirement for energy metabolism with glucose as the exclusive energy source. Decrease of brain energy metabolism and glucose uptake has been found in patients of Alzheimer's, Parkinson's and other neurodegenerative diseases, providing a clear link between neurodegenerative disorders and energy metabolism. On the other hand, cancers, including glioblastoma, have increased glucose uptake and rely on aerobic glycolysis for energy metabolism. The switch of high efficient oxidative phosphorylation to low efficient aerobic glycolysis pathway (Warburg effect) provides macromolecule for biosynthesis and proliferation. Current research indicates that methylene blue, a century old drug, can receive electron from NADH in the presence of complex I and donates it to cytochrome c, providing an alternative electron transfer pathway. Methylene blue increases oxygen consumption, decrease glycolysis, and increases glucose uptake in vitro. Methylene blue enhances glucose uptake and regional cerebral blood flow in rats upon acute treatment. In addition, methylene blue provides protective effect in neuron and astrocyte against various insults in vitro and in rodent models of Alzheimer's, Parkinson's, and Huntington's disease. In glioblastoma cells, methylene blue reverses Warburg effect by enhancing mitochondrial oxidative phosphorylation, arrests glioma cell cycle at s-phase, and inhibits glioma cell proliferation. Accordingly, methylene blue activates AMP-activated protein kinase, inhibits downstream acetyl-coA carboxylase and cyclin-dependent kinases. In summary, there is accumulating evidence providing a proof of concept that enhancement of mitochondrial oxidative phosphorylation via alternative mitochondrial electron transfer may offer protective action against neurodegenerative diseases and inhibit cancers proliferation.

Organotypic Hippocampal Slices as Models for Stroke and Traumatic Brain Injury

Organotypic hippocampal slice cultures (OHSCs) have been used as a powerful ex vivo model for decades. They have been used successfully in studies of neuronal death, microglial activation, mossy fiber regeneration, neurogenesis, and drug screening. As a pre-animal experimental phase for physiologic and pathologic brain research, OHSCs offer outcomes that are relatively closer to those of whole-animal studies than outcomes obtained from cell culture in vitro. At the same time, mechanisms can be studied more precisely in OHSCs than they can be in vivo. Here, we summarize stroke and traumatic brain injury research that has been carried out in OHSCs and review classic experimental applications of OHSCs and its limitations.

Potential protective effects of l-carnitine against neuromuscular ischemia-reperfusion injury: From experimental data to potential clinical applications

BACKGROUND & AIM

Ischemia-reperfusion (I/R) injury plays important role in morbidity and mortality in several pathologies, including myocardial infarction, ischemic stroke, acute kidney injury, trauma, and circulatory arrest. An imbalance in metabolic supply and tissue's demand during ischemia results in profound tissue hypoxia and microvascular dysfunction. Subsequently, reperfusion further results in activation of immune responses and cell death programs. l-carnitine and its derivatives have been administered to improve tolerance against I/R injury in various tissues. Anti-ischemic properties of l-carnitine and its derivative in neuromuscular organs will be reviewed here at the light of pertinent results from basic and clinical researches.

METHOD

All available in vitro and in vivo studies, patents, clinical trials, and meeting abstracts in English language that examined the protective effects of l-carnitine against I/R induced injury in neuromuscular organs were reviewed. Materials were obtained by searching ELSEVIER, web of knowledge, PubMed, Scopus, clinical trials, and Cochrane database of systematic reviews.

CONCLUSION

Although animal studies on central nervous system and some human studies on muscular system were in favors of effects of l-carnitine against I/R injury, however, more clinical trials are needed to clarify the clinical importance of l-carnitine as a treatment option to manage I/R-induced injury of neuromuscular system.

L-carnitine enhances axonal plasticity and improves white-matter lesions after chronic hypoperfusion in rat brain

Chronic cerebral hypoperfusion causes white-matter lesions (WMLs) with oxidative stress and cognitive impairment. However, the biologic mechanisms that regulate axonal plasticity under chronic cerebral hypoperfusion have not been fully investigated. Here, we investigated whether L-carnitine, an antioxidant agent, enhances axonal plasticity and oligodendrocyte expression, and explored the signaling pathways that mediate axonal plasticity in a rat chronic hypoperfusion model. Adult male Wistar rats subjected to ligation of the bilateral common carotid arteries (LBCCA) were treated with or without L-carnitine. L-carnitine-treated rats exhibited significantly reduced escape latency in the Morris water maze task at 28 days after chronic hypoperfusion. Western blot analysis indicated that L-carnitine increased levels of phosphorylated high-molecular weight neurofilament (pNFH), concurrent with a reduction in phosphorylated phosphatase tensin homolog deleted on chromosome 10 (PTEN), and increased phosphorylated Akt and mammalian target of rapamycin (mTOR) at 28 days after chronic hypoperfusion. L-carnitine reduced lipid peroxidation and oxidative DNA damage, and enhanced oligodendrocyte marker expression and myelin sheath thickness after chronic hypoperfusion. L-carnitine regulates the PTEN/Akt/mTOR signaling pathway, and enhances axonal plasticity while concurrently ameliorating oxidative stress and increasing oligodendrocyte myelination of axons, thereby improving WMLs and cognitive impairment in a rat chronic hypoperfusion model.

Examination of physiological function and biochemical disorders in a rat model of prolonged asphyxia-induced cardiac arrest followed by cardio pulmonary bypass resuscitation

Background

Cardiac arrest induces whole body ischemia, which causes damage to multiple organs particularly the heart and the brain. There is clinical and preclinical evidence that neurological injury is responsible for high mortality and morbidity of patients even after successful cardiopulmonary resuscitation. A better understanding of the metabolic alterations in the brain during ischemia will enable the development of better targeted resuscitation protocols that repair the ischemic damage and minimize the additional damage caused by reperfusion.

Method

A validated whole body model of rodent arrest followed by resuscitation was utilized; animals were randomized into three groups: control, 30 minute asphyxial arrest, or 30 minutes asphyxial arrest followed by 60 min cardiopulmonary bypass (CPB) resuscitation. Blood gases and hemodynamics were monitored during the procedures. An untargeted metabolic survey of heart and brain tissues following cardiac arrest and after CPB resuscitation was conducted to better define the alterations associated with each condition.

Results

After 30 min cardiac arrest and 60 min CPB, the rats exhibited no observable brain function and weakened heart function in a physiological assessment. Heart and brain tissues harvested following 30 min ischemia had significant changes in the concentration of metabolites in lipid and carbohydrate metabolism. In addition, the brain had increased lysophospholipid content. CPB resuscitation significantly normalized metabolite concentrations in the heart tissue, but not in the brain tissue.

Conclusion

The observation that metabolic alterations are seen primarily during cardiac arrest suggests that the events of ischemia are the major cause of neurological damage in our rat model of asphyxia-CPB resuscitation. Impaired glycolysis and increased lysophospholipids observed only in the brain suggest that altered energy metabolism and phospholipid degradation may be a central mechanism in unresuscitatable brain damage.

Ginsenoside Rb1 attenuates oxygen-glucose deprivation-induced apoptosis in SH-SY5Y cells via protection of mitochondria and inhibition of AIF and cytochrome c release

To investigate the role of mitochondria in the protective effects of ginsenoside Rb1 on cellular apoptosis caused by oxygen-glucose deprivation, in this study, MTT assay, TUNEL staining, flow cytometry, immunocytochemistry and western blotting were used to examine the cellular viability, apoptosis, ROS level, mitochondrial membrane potential, and the distribution of apoptosis inducing factor, cytochrome c, Bax and Bcl-2 in nucleus, mitochondria and cytoplasm. We found that pretreatment with GRb1 improved the cellular viability damaged by OGD. Moreover, GRb1 inhibited apoptosis in SH-SY5Y cells induced by OGD. Further studies showed that the elevation of cellular reactive oxygen species levels and the reduction of mitochondrial membrane potential caused by OGD were both counteracted by GRb1. Additionally, GRb1 not only suppressed the translocation of apoptosis inducing factor into nucleus and cytochrome c into cytoplasm, but also inhibited the increase of Bax within mitochondria and alleviated the decrease of mitochondrial Bcl-2. Our study indicates that the protection of GRb1 on OGD-induced apoptosis in SH-SY5Y cells is associated with its protection on mitochondrial function and inhibition of release of AIF and cytochrome c.

Localization of mitochondrial carnitine/acylcarnitine translocase in sensory neurons from rat dorsal root ganglia

The carnitine/acylcarnitine transporter is a transport system whose function is essential for the mitochondrial β-oxidation of fatty acids. Here, the presence of carnitine/acylcarnitine carrier (CACT) in nervous tissue and its sub-cellular localization in dorsal root ganglia (DRG) neurons have been investigated. Western blot analysis using a polyclonal anti-CACT antibody produced in our laboratory revealed the presence of CACT in all the nervous tissue extracts analyzed. Confocal microscopy experiments performed on fixed and permeabilized DRG neurons co-stained with the anti-CACT antibody and the mitochondrial marker MitoTracker Red clearly showed a mitochondrial localization for the carnitine/acylcarnitine transporter. The transport activity of CACT from DRG extracts reconstituted into liposomes was about 50 % in respect to liver extracts. The experimental data here reported represent the first direct evidence of the expression of the carnitine/acylcarnitine transporter in sensory neurons, thus supporting the existence of the β-oxidation pathway in these cells.

Isoquercetin protects cortical neurons from oxygen-glucose deprivation-reperfusion induced injury via suppression of TLR4-NF-кB signal pathway

In the present study, oxygen-glucose deprivation followed by reperfusion (OGD/R), an in vitro model of ischemia, was used to evaluate the neuroprotective effect of isoquercetin in primary culture of rat cortical neuronal cells. It was found that isoquercetin administered prior to the insult could prevent OGD/R-induced intracellular calcium concentrations ([Ca(2+)]i) increase, lactate dehydrogenase (LDH) release and cell viability decrease. For the first time, isoquercetin is described as a neuroprotective agent that potentially explains the alleviation and prevention from OGD/R-induced injury in neurons. Mechanistic studies showed that the neuroprotective effect of isoquercetin was carried out by anti-inflammatory signaling pathway of inhibiting protein expression of toll-like receptor 4 (TLR4) and nuclear factor-kappa B (NF-κB), and mRNA expression of TNF-α and IL-6, accompanied by the anti-apoptotic signaling pathway of deactivation of extracellular-regulated kinase (ERK), Jun kinase (JNK) and p38, and inhibition of activity of caspase-3. Therefore, these studies highlighted the confirmation of isoquercetin, a flavonoid compound, as an anti-inflammation and anti-apoptosis factor which might be used as a therapeutic strategy for the ischemia/reperfusion (I/R) brain injury and related diseases.

Ca²⁺/calmodulin-dependent protein kinase II contributes to hypoxic ischemic cell death in neonatal hippocampal slice cultures

We have recently shown that p38MAP kinase (p38MAPK) stimulates ROS generation via the activation of NADPH oxidase during neonatal hypoxia-ischemia (HI) brain injury. However, how p38MAPK is activated during HI remains unresolved and was the focus of this study. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) plays a key role in brain synapse development, neural transduction and synaptic plasticity. Here we show that CaMKII activity is stimulated in rat hippocampal slice culture exposed to oxygen glucose deprivation (OGD) to mimic the condition of HI. Further, the elevation of CaMKII activity, correlated with enhanced p38MAPK activity, increased superoxide generation from NADPH oxidase as well as necrotic and apoptotic cell death. All of these events were prevented when CaMKII activity was inhibited with KN93. In a neonatal rat model of HI, KN93 also reduced brain injury. Our results suggest that CaMKII activation contributes to the oxidative stress associated with neural cell death after HI.

Role of mitochondrial function in the protective effects of ischaemic postconditioning on ischaemia/reperfusion cerebral damage

Objective

To investigate the effects of ischaemic postconditioning on brain injury and mitochondria in focal ischaemia and reperfusion, in rats.

Methods

Adult male Wistar rats ( n = 15 per group) underwent sham surgery, ischaemia (2-h middle cerebral artery occlusion), or ischaemia followed by ischaemic postconditioning (three cycles of 30 s reperfusion/30 s reocclusion). Brain infarction size, neurological function, mitochondrial reactive oxygen species (ROS) production, mitochondrial membrane potential and mitochondrial swelling were evaluated 24 h postsurgery.

Results

Infarct size was significantly smaller, and neurological function was significantly better, in the ischaemic postconditioning group than in the ischaemia group. Ischaemia resulted in significant increases in mitochondrial ROS production and swelling, and a reduction in mitochondrial membrane potential, all of which were significantly reversed by postconditioning.

Conclusions

The protective role of ischaemic postconditioning in focal ischaemia/reperfusion may be due to decreased mitochondrial ROS production, reduced mitochondrial membrane potential and suppressed mitochondria swelling. Mitochondria are potential targets for new therapies to prevent brain damage caused by ischaemia and reperfusion.

Impact of perinatal systemic hypoxic-ischemic injury on the brain of male offspring rats: an improved model of neonatal hypoxic-ischemic encephalopathy in early preterm newborns

In this study, we attempted to design a model using Sprague-Dawley rats to better reproduce perinatal systemic hypoxic-ischemic encephalopathy (HIE) in early preterm newborns. On day 21 of gestation, the uterus of pregnant rats were exposed and the blood supply to the fetuses of neonatal HIE groups were thoroughly abscised by hemostatic clamp for 5, 10 or 15 min. Thereafter, fetuses were moved from the uterus and manually stimulated to initiate breathing in an incubator at 37 °C for 1 hr in air. We showed that survival rates of offspring rats were decreased with longer hypoxic time. TUNEL staining showed that apoptotic cells were significant increased in the brains of offspring rats from the 10 min and 15 min HIE groups as compared to the offspring rats in the control group at postnatal day (PND) 1, but there was no statistical difference between the offspring rats in the 5 min HIE and control groups. The perinatal hypoxic treatment resulted in decreased neurons and increased cleaved caspase-3 protein levels in the offspring rats from all HIE groups at PND 1. Platform crossing times and the percentage of the time spent in the target quadrant of Morris Water Maze test were significantly reduced in the offspring rats of all HIE groups at PND 30, which were associated with decreased brain-derived neurotrophic factor levels and neuronal cells in the hippocampus of offspring rats at PND 35. These data demonstrated that perinatal ischemic injury led to the death of neuronal cells and long-lasting impairment of memory. This model reproduced hypoxic ischemic encephalopathy in early preterm newborns and may be appropriate for investigating therapeutic interventions.