Erythropoietin Attenuates Post-Traumatic Injury in Organotypic Hippocampal Slices

Slice Culture Modeling of CNS Viral Infection

The complexity of the central nervous system (CNS) is not recapitulated in cell culture models. Thin slicing and subsequent culture of CNS tissue has become a valued means to study neuronal and glial biology within the context of the physiologically relevant tissue milieu. Modern membrane-interface slice culturing methodology allows for straightforward access to both CNS tissue and feeding medium, enabling experimental manipulations and analyses that would otherwise be impossible in vivo. CNS slices can be successfully maintained in culture for up to several weeks for investigation of evolving pathology and long-term intervention in models of chronic neurologic disease.Herein, membrane-interface slice culture models for studying viral encephalitis and myelitis are detailed, with emphasis on the use of these models for investigation of pathogenesis and evaluation of novel treatment strategies. We describe techniques to (1) generate brain and spinal cord slices from rodent donors, (2) virally infect slices, (3) monitor viral replication, (4) assess virally induced injury/apoptosis, (5) characterize "CNS-specific" cytokine production, and, (6) treat slices with cytokines/pharmaceuticals. Although our focus is on CNS viral infection, we anticipate that the described methods can be adapted to address a wide range of investigations within the fields of neuropathology, neuroimmunology, and neuropharmacology.

Erythropoietin, a putative neurotransmitter during hypoxia, is produced in RVLM neurons and activates them in neonatal Wistar rats

Recent studies indicate that erythropoietin (EPO) is present in many areas of the brain and is active in the restoration of impaired neurons. In this study, we examined the presence of EPO and its role in bulbospinal neurons in the rostral ventrolateral medulla (RVLM). Hypoxia is often accompanied by a high blood pressure (BP). We hypothesized that EPO is produced in response to hypoxia in RVLM neurons and then activates them. To investigate whether RVLM neurons are sensitive to EPO, we examined the changes in the membrane potentials (MPs) of bulbospinal RVLM neurons using the whole cell patch-clamp technique during superfusion with EPO. A brainstem-spinal cord preparation was used for the experiments. EPO depolarized the RVLM neurons, and soluble erythropoietin receptor (SEPOR), an antagonist of EPO, hyperpolarized them. Furthermore, hypoxia-depolarized RVLM neurons were significantly hyperpolarized by SEPOR. In histological examinations, the EPO-depolarized RVLM neurons showed the presence of EPO receptor (EPOR). The RVLM neurons that possessed EPORs showed the presence of EPO and hypoxia-inducible factor (HIF)-2α. We also examined the levels of HIF-2α and EPO messenger RNA (mRNA) in the ventral sites of the medullas (containing RVLM areas) in response to hypoxia. The levels of HIF-2α and EPO mRNA in the hypoxia group were significantly greater than those in the control group. These results suggest that EPO is produced in response to hypoxia in RVLM neurons and causes a high BP via the stimulation of those neurons. EPO may be one of the neurotransmitters produced by RVLM neurons during hypoxia.

Neuroprotection against Traumatic Brain Injury by Xenon, but Not Argon, Is Mediated by Inhibition at the N-Methyl-d-Aspartate Receptor Glycine Site

Background:

Xenon, the inert anesthetic gas, is neuroprotective in models of brain injury. The authors investigate the neuroprotective mechanisms of the inert gases such as xenon, argon, krypton, neon, and helium in an in vitro model of traumatic brain injury.

Methods:

The authors use an in vitro model using mouse organotypic hippocampal brain slices, subjected to a focal mechanical trauma, with injury quantified by propidium iodide fluorescence. Patch clamp electrophysiology is used to investigate the effect of the inert gases on N-methyl-d-aspartate receptors and TREK-1 channels, two molecular targets likely to play a role in neuroprotection.

Results:

Xenon (50%) and, to a lesser extent, argon (50%) are neuroprotective against traumatic injury when applied after injury (xenon 43 ± 1% protection at 72 h after injury [N = 104]; argon 30 ± 6% protection [N = 44]; mean ± SEM). Helium, neon, and krypton are devoid of neuroprotective effect. Xenon (50%) prevents development of secondary injury up to 48 h after trauma. Argon (50%) attenuates secondary injury, but is less effective than xenon (xenon 50 ± 5% reduction in secondary injury at 72 h after injury [N = 104]; argon 34 ± 8% reduction [N = 44]; mean ± SEM). Glycine reverses the neuroprotective effect of xenon, but not argon, consistent with competitive inhibition at the N-methyl-d-aspartate receptor glycine site mediating xenon neuroprotection against traumatic brain injury. Xenon inhibits N-methyl-d-aspartate receptors and activates TREK-1 channels, whereas argon, krypton, neon, and helium have no effect on these ion channels.

Conclusions:

Xenon neuroprotection against traumatic brain injury can be reversed by increasing the glycine concentration, consistent with inhibition at the N-methyl-d-aspartate receptor glycine site playing a significant role in xenon neuroprotection. Argon and xenon do not act via the same mechanism.

Slice culture modeling of central nervous system (CNS) viral infection

The complexity of the central nervous system (CNS) is not recapitulated in cell culture models. Thin slicing and subsequent culture of CNS tissue has become a valued means to study neuronal and glial biology within the context of the physiologically relevant tissue milieu. Modern membrane-interface slice culturing methodology allows straightforward access to both CNS tissue and feeding medium, enabling experimental manipulations and analyses that would otherwise be impossible in vivo. CNS slices can be successfully maintained in culture for up to several weeks for investigation of evolving pathology and long-term intervention in models of chronic neurologic disease.Herein, membrane-interface slice culture models for studying viral encephalitis and myelitis are detailed, with emphasis on the use of these models for investigation of pathogenesis and evaluation of novel treatment strategies. We describe techniques to (1) generate brain and spinal cord slices from rodent donors, (2) virally infect slices, (3) assess virally induced injury/apoptosis, (4) characterize "CNS-specific" cytokine production, and (5) treat slices with cytokines/pharmaceuticals. Although our focus is on CNS viral infection, we anticipate that the described methods can be adapted to address a wide range of investigations within the fields of neuropathology, neuroimmunology, and neuropharmacology.

In vitro models of traumatic brain injury

In vitro models of traumatic brain injury (TBI) are helping elucidate the pathobiological mechanisms responsible for dysfunction and delayed cell death after mechanical stimulation of the brain. Researchers have identified compounds that have the potential to break the chain of molecular events set in motion by traumatic injury. Ultimately, the utility of in vitro models in identifying novel therapeutics will be determined by how closely the in vitro cascades recapitulate the sequence of cellular events that play out in vivo after TBI. Herein, the major in vitro models are reviewed, and a discussion of the physical injury mechanisms and culture preparations is employed. A comparison between the efficacy of compounds tested in vitro and in vivo is presented as a critical evaluation of the fidelity of in vitro models to the complex pathobiology that is TBI. We conclude that in vitro models were greater than 88% predictive of in vivo results.

Erythropoietin neuroprotection with traumatic brain injury

Numerous experimental studies in recent years have suggested that erythropoietin (EPO) is an endogenous mediator of neuroprotection in various central nervous system disorders, including TBI. Many characteristics of EPO neuroprotection that have been defined in TBI experimental models suggest that it is an attractive candidate for a new treatment of TBI. EPO targets multiple mechanisms known to cause secondary injury after TBI, including anti-excitotoxic, antioxidant, anti-edematous, and anti-inflammatory mechanisms. EPO crosses the blood-brain barrier. EPO has a known dose response and time window for neuroprotection and neurorestoration that would be practical in the clinical setting. However, EPO also stimulates erythropoiesis, which can result in thromboembolic complications. Derivatives of EPO which do not bind to the classical EPO receptor (carbamylated EPO) or that have such a brief half-life in the circulation that they do not stimulate erythropoiesis (asialo EPO and neuro EPO) have the neuroprotective activities of EPO without these potential thromboembolic adverse effects associated with EPO administration. Likewise, a peptide based on the structure of the Helix B segment of the EPO molecule that does not bind to the EPO receptor (pyroglutamate Helix B surface peptide) has promise as another alternative to EPO that may provide neuroprotection without stimulating erythropoiesis.

Synergistic benefits of erythropoietin and simvastatin after traumatic brain injury

Simvastatin and recombinant human erythropoietin (rhEpo) are implicated as potential therapeutic candidates for traumatic brain injury (TBI). Prominent effects of simvastatin include its anti-inflammatory, neurotrophic and neuroregenerative actions studied in various models of neuronal injury. On the other hand, rhEpo has been shown to promote cell survival mechanisms by producing anti-apoptotic and cell proliferative actions. Beneficial effects of rhEpo and statin monotherapies have been well studied. However, there are no reports showing combined use of rhEpo and statins after TBI. This investigation examined if combined efficacy of cell proliferative ability of rhEpo along with the neuroregenerative ability of simvastatin will render maximum recovery in a controlled cortical impact (CCI) mouse model of TBI. Results showed that compared to baseline TBI, rhEpo was more effective than simvastatin in promoting cell proliferation while simvastatin was more effective than rhEpo in restoring axonal damage following TBI. Combined treatment with simvastatin and rhEpo maximally restored axonal integrity while simultaneously inducing greater proliferation of newly formed cells resulting in better functional recovery after TBI than either alone. This is the first study showing the efficacy of erythropoietin-simvastatin combinational therapeutic approach in achieving greater structural and cognitive recovery after TBI.

Nitric oxide synthase mediates the ability of darbepoetin alpha to improve the cognitive performance of STOP null mice

STOP (stable tubule only polypeptide) null mice display neurochemical and behavioral abnormalities that resemble several well-recognized features of schizophrenia. Recent evidence suggests that the hematopoietic growth factor erythropoietin improves the cognitive performance of schizophrenics. The mechanism, however, by which erythropoietin is able to improve the cognition of schizophrenics is unclear. To address this question, we first determined whether acute administration of the erythropoietin analog known as darbepoetin alpha (D. alpha) improved performance deficits of STOP null mice in the novel objective recognition task (NORT). NORT performance of STOP null mice, but not wild-type littermates, was enhanced 3 h after a single injection of D. alpha (25 microg/kg, i.p.). Improved NORT performance was accompanied by elevated NADPH diaphorase staining in the ventral hippocampus as well as medial and cortical aspects of the amygdala, indicative of increased nitric oxide synthase (NOS) activity in these structures. NOS generates the intracellular messenger nitric oxide (NO) implicated in learning and memory. In keeping with this hypothesis, D. alpha significantly increased NO metabolite levels (nitrate and nitrite, NOx) in the hippocampus of both wild-type and STOP null mice. The NOS inhibitor, N (G)-nitro-L- arginine methyl ester (L-NAME; 25 mg/kg, i.p.), completely reversed the increase in hippocampal NOx levels produced by D. alpha. Moreover, L-NAME also inhibited the ability of D. alpha to improve the NORT performance of STOP null mice. Taken together, these observations suggest D. alpha enhances the NORT performance of STOP null mice by increasing production of NO.

Argon: neuroprotection in in vitro models of cerebral ischemia and traumatic brain injury

INTRODUCTION

Recently, it has been shown in several experimental settings that the noble gases xenon and helium have neuroprotective properties. In this study we tested the hypothesis that the noble gas argon has a neuroprotective potential as well. Since traumatic brain injury and stroke are widespread and generate an enormous economic and social burden, we investigated the possible neuroprotective effect in in vitro models of traumatic brain injury and cerebral ischemia.

METHODS

Organotypic hippocampal slice cultures from mice pups were subjected to either oxygen-glucose deprivation or to a focal mechanical trauma and subsequently treated with three different concentrations (25, 50 and 74%) of argon immediately after trauma or with a two-or-three-hour delay. After 72 hours of incubation tissue injury assessment was performed using propidium iodide, a staining agent that becomes fluorescent when it diffuses into damaged cells via disintegrated cell membranes.

RESULTS

We could show argon's neuroprotective effects at different concentrations when applied directly after oxygen-glucose deprivation or trauma. Even three hours after application, argon was still neuroprotective.

CONCLUSIONS

Argon showed a neuroprotective effect in both in vitro models of oxygen-glucose deprivation and traumatic brain injury. Our promising results justify further in vivo animal research.

Propofol: neuroprotection in an in vitro model of traumatic brain injury

Introduction

The anaesthetic agent propofol (2,6-diisopropylphenol) has been shown to be an effective neuroprotective agent in different in vitro models of brain injury induced by oxygen and glucose deprivation. We examined its neuroprotective properties in an in vitro model of traumatic brain injury.

Methods

In this controlled laboratory study organotypic hippocampal brain-slice cultures were gained from six- to eight-day-old mice pups. After 14 days in culture, hippocampal brain slices were subjected to a focal mechanical trauma and subsequently treated with different molar concentrations of propofol under both normo- and hypothermic conditions. After 72 hours of incubation, tissue injury assessment was performed using propidium iodide (PI), a staining agent that becomes fluorescent only when it enters damaged cells via perforated cell membranes. Inside the cell, PI forms a fluorescent complex with nuclear DNA.

Results

A dose-dependent reduction of both total and secondary tissue injury could be observed in the presence of propofol under both normo- and hypothermic conditions. This effect was further amplified when the slices were incubated at 32°C after trauma.

Conclusions

When used in combination, the dose-dependent neuroprotective effect of propofol is additive to the neuroprotective effect of hypothermia in an in vitro model of traumatic brain injury.

Carbamylated erythropoietin is neuroprotective in an experimental model of traumatic brain injury

OBJECTIVE

The well-documented neuroprotective effects of recombinant human erythropoietin (rhEPO) are commonly associated with untoward erythrocyte-stimulating effects (polycythemia), with subsequent risk of thromboembolic complications. A carbamylated-rhEPO (CEPO) derivative, which is neuroprotective but lacks hematopoietic activity, has been recently developed. In this study, we evaluated the neuroprotective capability of CEPO in an in vitro model of cerebral trauma in which rhEPO was previously shown to reduce posttraumatic cell death.

DESIGN

Prospective, controlled experiment.

SETTING

Animal, basic science laboratory.

SUBJECTS

Wistar rats, 8 days old.

INTERVENTIONS

Organotypic hippocampal slices, obtained from rat brains, were subjected to a well-characterized model of mechanical injury followed by addition of 10 IU/mL rhEPO, 10-100 IU/mL CEPO, or vehicle (injured control) to the incubation medium at different times to assess the temporal window of therapeutic neuroprotection.

MEASUREMENTS AND MAIN RESULTS

Posttraumatic cell death was quantified at 12, 24, or 48 hrs after injury by measuring propidium iodide fluorescence in the selectively vulnerable CA1 hippocampal area. Posttraumatic injury, observed in injured, vehicle-treated hippocampal slices, was significantly attenuated by addition of either 10 IU/mL rhEPO or 10 IU/mL CEPO. The neuroprotective efficacy of 10 IU/mL rhEPO or CEPO remained intact even when administration was delayed 1 hr after trauma. Qualitative microscopy in semithin sections showed that both rhEPO and CEPO exerted a marked pyramidal neuron-sparing effect.

CONCLUSION

Our study shows that 10 IU/mL CEPO exerts neuroprotective effects comparable with those of rhEPO in an in vitro model of mechanical cerebral trauma. Because CEPO lacks hematopoietic effects and seems to possess a prolonged therapeutic time window, this erythropoietin derivative may represent an exciting new pharmacologic tool in treating patients with mechanical injury to the brain.

Stretch-induced injury in organotypic hippocampal slice cultures reproduces in vivo post-traumatic neurodegeneration: role of glutamate receptors and voltage-dependent calcium channels

The relationship between an initial mechanical event causing brain tissue deformation and delayed neurodegeneration in vivo is complex because of the multiplicity of factors involved. We have used a simplified brain surrogate based on rat hippocampal slices grown on deformable silicone membranes to study stretch-induced traumatic brain injury. Traumatic injury was induced by stretching the culture substrate, and the biological response characterized after 4 days. Morphological abnormalities consistent with traumatic injury in humans were widely observed in injured cultures. Synaptic function was significantly reduced after a severe injury. The N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 attenuated neuronal damage, prevented loss of microtubule-associated protein 2 immunoreactivity and attenuated reduction of synaptic function. In contrast, the NMDA receptor antagonists 3-[(R)-2-carboxypiperazin-4-yl]-propyl-1-phosphonic acid (CPP) and GYKI53655, were neuroprotective in a moderate but not a severe injury paradigm. Nifedipine, an L-type voltage-dependent calcium channel antagonist was protective only after a moderate injury, whereas omega-conotoxin attenuated damage following severe injury. These results indicate that the mechanism of damage following stretch injury is complex and varies depending on the severity of the insult. In conclusion, the pharmacological, morphological and electrophysiological responses of organotypic hippocampal slice cultures to stretch injury were similar to those observed in vivo. Our model provides an alternative to animal testing for understanding the mechanisms of post-traumatic delayed cell death and could be used as a high-content screen to discover neuroprotective compounds before advancing to in vivo models.

Cannabinoids and neuronal damage: differential effects of THC, AEA and 2-AG on activated microglial cells and degenerating neurons in excitotoxically lesioned rat organotypic hippocampal slice cultures

Cannabinoids (CBs) are attributed neuroprotective effects in vivo. Here, we determined the neuroprotective potential of CBs during neuronal damage in excitotoxically lesioned organotypic hippocampal slice cultures (OHSCs). OHSCs are the best characterized in vitro model to investigate the function of microglial cells in neuronal damage since blood-borne monocytes and T-lymphocytes are absent and microglial cells represent the only immunocompetent cell type. Excitotoxic neuronal damage was induced by NMDA (50 microM) application for 4 h. Neuroprotective properties of 9-carboxy-11-nor-delta-9-tetrahydrocannabinol (THC), N-arachidonoylethanolamide (AEA) or 2-arachidonoylglycerol (2-AG) in different concentrations were determined after co-application with NMDA by counting degenerating neurons identified by propidium iodide labeling (PI(+)) and microglial cells labeled by isolectin B(4) (IB(4)(+)). All three CBs used significantly decreased the number of IB(4)(+) microglial cells in the dentate gyrus but the number of PI(+) neurons was reduced only after 2-AG treatment. Application of AM630, antagonizing CB2 receptors highly expressed by activated microglial cells, did not counteract neuroprotective effects of 2-AG, but affected THC-mediated reduction of IB(4)(+) microglial cells. Our results indicate that (1) only 2-AG exerts neuroprotective effects in OHSCs; (2) reduction of IB(4)(+) microglial cells is not a neuroprotective event per se and involves other CB receptors than the CB2 receptor; (3) the discrepancy in the neuroprotective effects of CBs observed in vivo and in our in vitro model system may underline the functional relevance of invading monocytes and T-lymphocytes that are absent in OHSCs.

Erythropoietin is neuroprotective, improves functional recovery, and reduces neuronal apoptosis and inflammation in a rodent model of experimental closed head injury

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality in young people in industrialized countries. Although various anti-inflammatory and antiapoptotic modalities have shown neuroprotective effects in experimental models of TBI, to date, no specific pharmacological agent aimed at blocking the progression of secondary brain damage has been approved for clinical use. Erythropoietin (Epo) belongs to the cytokine superfamily and has traditionally been viewed as a hematopoiesis-regulating hormone. The newly discovered neuroprotective properties of Epo lead us to investigate its effect in TBI in a mouse model of closed head injury. Recombinant human erythropoietin (rhEpo) was injected at 1 and 24 h after TBI, and the effect on recovery of motor and cognitive functions, tissue inflammation, axonal degeneration, and apoptosis was evaluated up to 14 days. Motor deficits were lower, cognitive function was restored faster, and less apoptotic neurons and caspase-3 expression were found in rhEpo-treated as compared with vehicle-treated animals (P<0.05). Axons at the trauma area in rhEpo-treated mice were relatively well preserved compared with controls (shown by their density; P<0.01). Immunohistochemical analysis revealed a reduced activation of glial cells by staining for GFAP and complement receptor type 3 (CD11b/CD18) in the injured hemisphere of Epo- vs. vehicle-treated animals. We propose that further studies on Epo in TBI should be conducted in order to consider it as a novel therapy for TBI.

Emerging biological roles for erythropoietin in the nervous system

Erythropoietin mediates an evolutionarily conserved, ancient immune response that limits damage to the heart, the nervous system and other tissues following injury. New evidence indicates that erythropoietin specifically prevents the destruction of viable tissue surrounding the site of an injury by signalling through a non-haematopoietic receptor. Engineered derivatives of erythropoietin that have a high affinity for this receptor have been developed, and these show robust tissue-protective effects in diverse preclinical models without stimulating erythropoiesis. A recent successful proof-of-concept clinical trial that used erythropoietin to treat human patients who had suffered a stroke encourages the evaluation of both this cytokine and non-erythropoietic derivatives as therapeutic agents to limit tissue injury.

Insonation facilitates plasmid DNA transfection into the central nervous system and microbubbles enhance the effect

Many of the diseases which affect the central nervous system are intractable to conventional therapies and therefore require alternative treatments such as gene therapy. Therapy requires safety, since the central nervous system is a critical organ. Choice of nonviral vectors such as naked plasmid DNA may have merit. However, transfection efficiencies of these vectors are low. We have investigated the use of 210.4 kHz ultrasound and found that 5.0 W/cm(2) of insonation for 5 s most effectively transfected a plasmid DNA into culture slices of mouse brain (147.68-fold increase compared with 0 W/cm(2) of insonation for 5 s). The effect was reinforced by combination with echo contrast agent, Levovist. One hundred fifty mg/mL of Levovist significantly increased gene transfection by ultrasound (5.23-fold when insonated at 5.0 W/cm(2) for 5 s). When DNA was intracranially injected, Levovist also enhanced gene transfection in newborn mice (4.49-fold increase when insonated at 5.0 W/cm(2) for 5 s). Since ultrasound successfully transfected naked plasmid DNA into the neural tissue and Levovist enhanced the effect, this approach may have a significant role in gene transfer to the central nervous system.