An immunosuppressant, FK506, protects against neuronal dysfunction and death but has no effect on electrographic and behavioral activities induced by systemic kainate

Immunosuppressant Tacrolimus Treatment Delays Acute Seizure Occurrence, Reduces Elevated Oxidative Stress, and Reverses PGF2α Burst in the Brain of PTZ-Treated Rats

It is still an urgent need to find alternative and effective therapies to combat epileptic seizures. Tacrolimus as a potent immunosuppressant and calcineurin inhibitor is emerging as promising drug to suppress seizures. However, there are few reports applying tacrolimus to epilepsy and providing data for its antiseizure properties. In this study, we investigated the antiseizure effects of 5 and 10 mg/kg doses of tacrolimus treatment priorly to pentylenetetrazol (PTZ) induction of seizures in rats. As an experimental design, we establish two independent rat groups where we observe convulsive seizures following 70 mg/kg PTZ and sub-convulsive seizures detected by electroencephalography (EEG) following 35 mg/kg PTZ. Thereafter, we proceed with biochemical analyses of the brain including assessment of malondialdehyde level as an indicator of lipid peroxidation and detection of superoxide dismutase (SOD) enzyme activity and PGF2α. Tacrolimus pre-treatment dose-dependently resulted in lesser seizure severity according to Racine's scale, delayed start-up latency of the first myoclonic jerk and attenuated the spike percentages detected by EEG in seizure-induced rats. However, only the higher dose of tacrolimus was effective to restore lipid peroxidation. An increase in SOD activity was observed in the PTZ group, mediated by seizure activity per se, however, it was greater in the groups that received treatment with 5 and 10 mg/kg of Tacrolimus. PGF2α bursts following PTZ induction of seizures were reversed by tacrolimus pre-treatment in a dose-dependent manner as well. We report that the well-known immunosuppressant tacrolimus is a promising agent to suppress seizures. Comparative studies are necessary to determine the possible utilization of tacrolimus in clinical cases.

The effects of calcineurin inhibitor FK506 on actin cytoskeleton, neuronal survival and glial reactions after pilocarpine-induced status epilepticus in mice

After status epilepticus (SE), actin cytoskeleton (F-actin) becomes progressively deconstructed in the hippocampus, which is consistent with the delayed pyramidal cell death in both time course and spatial distribution. A variety of experiments show that calcineurin inhibitors such as FK506 are able to inhibit the SE-induced actin depolymerization. However, it is still unclear what changes happen to the F-actin in the epileptic brain after FK506 treatment. A pilocarpine model of SE in mice was used to examine the effects of FK506 on the F-actin in the hippocampal neurons. The post SE (PSE) mice with or without FK506 treatment were monitored consecutively for 14 days to examine the frequency and duration of spontaneous seizures. The effects of FK506 on the activity of cofilin and actin dynamics were assessed at 7 and 14 d PSE by western blots. The organization of F-actin, neuronal cell death, and glial reactions were investigated by phalloidin staining, histological and immunocytochemical staining, respectively. As compared to the PSE + vehicle mice, FK506 treatment significantly decreased the frequency and duration of spontaneous seizures. Relative to the PSE + vehicle mice, western blots detected a partial restoration of phosphorylated cofilin and a significant increase of F/G ratio in the hippocampus after FK506 treatment. In the PSE + vehicle mice, almost no F-actin puncta were left in the CA1 and CA3 subfields at 7 and 14 d PSE. FK506-treated PSE mice showed a similar decrease of F-actin, but the extent of damage was significantly ameliorated. Consistently, the surviving neurons became significantly increased in number after FK506 treatment, relative to the PSE + vehicle groups. After FK506 treatment, microglial reaction was partially inhibited, but the expression of GFAP was not significantly changed, compared to the PSE + vehicle mice. The results suggest that post-epileptic treatment with FK506 ameliorated, but could not stop the deconstruction of F-actin or the delayed neuronal loss in the PSE mice.

Status Epilepticus Triggers Time-Dependent Alterations in Microglia Abundance and Morphological Phenotypes in the Hippocampus

Status epilepticus (SE) is defined by the occurrence of prolonged “non-stop” seizures that last for at least 5 min. SE provokes inflammatory responses including the activation of microglial cells, the brain’s resident immune cells, which are thought to contribute to the neuropathology and pathophysiology of epilepsy. Microglia are professional phagocytes that resemble peripheral macrophages. Upon sensing immune disturbances, including SE, microglia become reactive, produce inflammatory cytokines, and alter their actin cytoskeleton to transform from ramified to amoeboid shapes. It is widely known that SE triggers time-dependent microglial expression of pro-inflammatory cytokines that include TNFα and IL-1β. However, less is known in regards to the spatiotemporal progression of the morphological changes, which may help define the extent of microglia reactivity after SE and potential function (surveillance, inflammatory, phagocytic). Therefore, in this study, we used the microglia/macrophage IBA1 marker to identify and count these cells in hippocampi from control rats and at 4 h, 3 days, and 2 weeks after a single episode of pilocarpine-induced SE. We identified, categorized, and counted the IBA1-positive cells with the different morphologies observed after SE in the hippocampal areas CA1, CA3, and dentate gyrus. These included ramified, hypertrophic, bushy, amoeboid, and rod. We found that the ramified phenotype was the most abundant in control hippocampi. In contrast, SE provoked time-dependent changes in the microglial morphology that was characterized by significant increases in the abundance of bushy-shaped cells at 4 h and amoeboid-shaped cells at 3 days and 2 weeks. Interestingly, a significant increase in the number of rod-shaped cells was only evident in the CA1 region at 2 weeks after SE. Taken together, these data suggest that SE triggers time-dependent alterations in the morphology of microglial cells. This detailed description of the spatiotemporal profile of SE-induced microglial morphological changes may help provide insight into their contribution to epileptogenesis.

Effect of the calcineurin inhibitor FK506 on K+-Cl- cotransporter 2 expression in the mouse hippocampus after kainic acid-induced status epilepticus

Calcineurin (CaN)-mediated excitotoxicity impairs γ-aminobutyric acid (GABA) transmission and induces neuronal apoptosis. Ca(2+)-dependent K(+)-Cl(-) cotransporter 2 (KCC2) participates in GABAergic inhibitory transmission. However, the mechanism by which CaN mediates GABA receptor-mediated KCC2 in seizures is not fully understood. In the present study, we investigated the altered expression of KCC2 and the effects of the CaN inhibitor FK506 on KCC2 expression in the mouse hippocampus following kainic acid (KA) treatment. FK506 was injected twice 24 h and 30 min before KA treatment and then mice were treated with KA and killed 2 days later. FK506 had anticonvulsant effect on KA-induced seizure activities. CaN cleavage was evident in the hippocampus 24 h after KA treatment. FK506 pretreatment blocked the truncation of CaN in the KA-treated hippocampus. Cresyl violet and TUNEL staining showed that FK506 prevented KA-induced hippocampal cell death. In particular, Western blot analysis showed that KCC2 expression was time dependent, with a peak at 6 h and a return to decreased levels at 48 h, whereas FK506 pretreatment inhibited the KA-induced decrease in KCC2 expression in the hippocampus. Immunofluorescence showed that FK506 pretreatment protected the loss of inhibitory GABAergic KCC2-expressing neurons following KA treatment. Taken together, these results provide evidence that altered KCC2 expression may be associated with Ca(2+)-mediated seizure activity and indicate that neuron-specific KCC2 may be involved in neuroprotection after seizures.

Hypoxia enhances high-voltage-activated calcium currents in rat primary cortical neurons via calcineurin

Hypoxia regulates neuronal ion channels, sometimes resulting in seizures. We evaluated the effects of brief sustained hypoxia (1% O(2), 4h) on voltage-gated calcium channels (VGCCs) in cultured rat primary cortical neurons. High-voltage activated (HVA) Ca(2+) currents were acquired immediately after hypoxic exposure or after 48h recovery in 95% air/5% CO(2). Maximal Ca(2+) current density increased 1.5-fold immediately after hypoxia, but reverted to baseline after 48h normoxia. This enhancement was primarily due to an increase in L-type VGCC activity, since nimodipine-insensitive residual Ca(2+) currents were unchanged. The half-maximal potentials of activation and steady-state inactivation were unchanged. The calcineurin inhibitors FK-506 (in the recording pipette) or cyclosporine A (during hypoxia) prevented the post-hypoxic increase in HVA Ca(2+) currents, while rapamycin and okadaic acid did not. L-type VGCCs were the source of Ca(2+) for calcineurin activation, as nimodipine during hypoxia prevented post-hypoxic enhancement. Hypoxia transiently potentiated L-type VGCC currents via calcineurin, suggesting a positive feedback loop to amplify neuronal calcium signaling that may contribute to seizure generation.

The spine loss paradox: clues to mechanisms and meaning

A Cellular Mechanism for Dendritic Spine Loss in the Pilocarpine Model of Status Epilepticus. Kurz JE, Moore BJ, Henderson SC, Campbell JN, Churn SB. Epilepsia 2008 May 8. [Epub ahead of print] PURPOSE: Previous studies have documented a synaptic translocation of calcineurin (CaN) and increased CaN activity following status epilepticus (SE); however, the cellular effect of these changes in CaN in the pathology of SE remains to be elucidated. This study examined a CaN-dependent modification of the dendritic cytoskeleton. CaN has been shown to induce dephosphorylation of cofilin, an actin depolymerization factor. The ensuing actin depolymerization can lead to a number of physiological changes that are of interest in SE. METHODS: SE was induced by pilocarpine injection, and seizure activity was monitored by video-EEG. Subcellular fractions were isolated by differential centrifugation. CaN activity was assayed using a paranitrophenol phosphate (pNPP) assay protocol. Cofilin phosphorylation was assessed using phosphocofilin-specific antibodies. Cofilin–actin binding was determined by coimmunoprecipitation, and actin polymerization was measured using a triton-solubilization protocol. Spines were visualized using a single-section rapid Golgi impregnation procedure. RESULTS: The immunoreactivity of phosphocofilin decreased significantly in hippocampal and cortical synaptosomal samples after SE. SE-induced cofilin dephosphorylation could be partially blocked by the preinjection of CaN inhibitors. Cofilin activation could be further demonstrated by increased actin–cofilin binding and a significant depolymerization of neuronal actin, both of which were also blocked by CaN inhibitors. Finally, we demonstrated a CaN-dependent loss of dendritic spines histologically. DISCUSSION: The data demonstrate a CaN-dependent, cellular mechanism through which prolonged seizure activity results in loss of dendritic spines via cofilin activation. Further research into this area may provide useful insights into the pathology of SE and epileptogenic mechanisms.

A cellular mechanism for dendritic spine loss in the pilocarpine model of status epilepticus

PURPOSE

Previous studies have documented a synaptic translocation of calcineurin (CaN) and increased CaN activity following status epilepticus (SE); however, the cellular effect of these changes in CaN in the pathology of SE remains to be elucidated. This study examined a CaN-dependent modification of the dendritic cytoskeleton. CaN has been shown to induce dephosphorylation of cofilin, an actin depolymerization factor. The ensuing actin depolymerization can lead to a number of physiological changes that are of interest in SE.

METHODS

SE was induced by pilocarpine injection, and seizure activity was monitored by video-EEG. Subcellular fractions were isolated by differential centrifugation. CaN activity was assayed using a paranitrophenol phosphate (pNPP) assay protocol. Cofilin phosphorylation was assessed using phosphocofilin-specific antibodies. Cofilin-actin binding was determined by coimmunoprecipitation, and actin polymerization was measured using a triton-solubilization protocol. Spines were visualized using a single-section rapid Golgi impregnation procedure.

RESULTS

The immunoreactivity of phosphocofilin decreased significantly in hippocampal and cortical synaptosomal samples after SE. SE-induced cofilin dephosphorylation could be partially blocked by the preinjection of CaN inhibitors. Cofilin activation could be further demonstrated by increased actin-cofilin binding and a significant depolymerization of neuronal actin, both of which were also blocked by CaN inhibitors. Finally, we demonstrated a CaN-dependent loss of dendritic spines histologically.

DISCUSSION

The data demonstrate a CaN-dependent, cellular mechanism through which prolonged seizure activity results in loss of dendritic spines via cofilin activation. Further research into this area may provide useful insights into the pathology of SE and epileptogenic mechanisms.

Kainate seizures cause acute dendritic injury and actin depolymerization in vivo

Seizures may cause brain injury via a variety of mechanisms, potentially contributing to cognitive deficits in epilepsy patients. Although seizures induce neuronal death in some situations, they may also have "nonlethal" pathophysiological effects on neuronal structure and function, such as modifying dendritic morphology. Previous studies involving conventional fixed tissue analysis have demonstrated a chronic loss of dendritic spines after seizures in animal models and human tissue. More recently, in vivo time-lapse imaging methods have been used to monitor acute changes in spines directly during seizures, but documented spine loss only under severe conditions. Here, we examined effects of secondary generalized seizures induced by kainate, on dendritic structure of neocortical neurons using multiphoton imaging in live mice in vivo and investigated molecular mechanisms mediating these structural changes. Higher-stage kainate-induced seizures caused dramatic dendritic beading and loss of spines within minutes, in the absence of neuronal death or changes in systemic oxygenation. Although the dendritic beading improved rapidly after the seizures, the spine loss recovered only partially over a 24 h period. Kainate seizures also resulted in activation of the actin-depolymerizing factor, cofilin, and a corresponding decrease in filamentous actin, indicating that depolymerization of actin may mediate the morphological dendritic changes. Finally, an inhibitor of the calcium-dependent phosphatase, calcineurin, antagonized the effects of seizures on cofilin activation and spine morphology. These dramatic in vivo findings demonstrate that seizures produce acute dendritic injury in neocortical neurons via calcineurin-dependent regulation of the actin cytoskeleton, suggesting novel therapeutic targets for preventing seizure-induced brain injury.

Status epilepticus-induced somatostatinergic hilar interneuron degeneration is regulated by striatal enriched protein tyrosine phosphatase

Excitotoxic cell death is one of the precipitating events in the development of temporal lobe epilepsy. Of particular prominence is the loss of GABAergic hilar neurons. Although the molecular mechanisms responsible for the selective vulnerability of these cells are not well understood, activation of the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathway has been implicated in neuroprotective responses to excitotoxicity in other neuronal populations. Here, we report that high levels of the striatal-enriched protein tyrosine phosphatase (STEP), a key regulator of ERK/MAPK signaling, are found in vulnerable somatostatin-immunoreactive hilar interneurons. Under both control conditions and after pilocarpine-induced status epilepticus (SE), ERK/MAPK activation was repressed in STEP-immunoreactive hilar neurons. This contrasts with robust SE-induced ERK/MAPK activation in the granule cell layer of the dentate gyrus, a cell region that does not express STEP. During pilocarpine-induced SE, in vivo disruption of STEP activity allowed activation of the MAPK pathway, leading to immediate-early gene expression and significant rescue from cell death. Thus, STEP increases the sensitivity of neurons to SE-induced excitotoxicity by specifically blocking a latent neuroprotective response initiated by the MAPK pathway. These findings identify a key set of signaling events that render somatostatinergic hilar interneurons vulnerable to SE-induced cell death.

Beneficial effects of FK506 for experimental temporal lobe epilepsy

FK506, originally classified as an immunosuppressant, may also be implicated in some events in the central nervous system. FK506 elicits both neuroprotective and neurotrophic effects in vitro. FK506 is neuroprotective for focal cerebral ischemia, but it is not clear whether FK506 has neuroprotective effects for other brain diseases. In this study, we investigated possible neuroprotective effects of FK506 in experimental temporal lobe epilepsy (TLE) induced by kainic acid (KA) or trimethyltin (TMT). In rat models, we observed marked protection against seizures, abnormal behaviors, and accompanying delayed neuronal damage in the hippocampus by the systemic injection of FK506.

Epilepsy and apoptosis pathways

Epilepsy is a common, chronic neurologic disorder characterized by recurrent unprovoked seizures. Experimental modeling and clinical neuroimaging of patients has shown that certain seizures are capable of causing neuronal death. Such brain injury may contribute to epileptogenesis, impairments in cognitive function or the epilepsy phenotype. Research into cell death after seizures has identified the induction of the molecular machinery of apoptosis. Here, the authors review the clinical and experimental evidence for apoptotic cell death pathway function in the wake of seizure activity. We summarize work showing intrinsic (mitochondrial) and extrinsic (death receptor) apoptotic pathway function after seizures, activation of the caspase and Bcl-2 families of cell death modulators and the acute and chronic neuropathologic impact of intervening in these molecular cascades. Finally, we describe evolving data on nonlethal roles for these proteins in neuronal restructuring and cell excitability that have implications for shaping the epilepsy phenotype. This review highlights the work to date on apoptosis pathway signaling during seizure-induced neuronal death and epileptogenesis, and speculates on how emerging roles in brain remodeling and excitability have enriched the number of therapeutic strategies for protection against seizure-damage and epileptogenesis.

Bim regulation may determine hippocampal vulnerability after injurious seizures and in temporal lobe epilepsy

Programmed cell death pathways have been implicated in the mechanism by which neurons die following brief and prolonged seizures, but the significance of proapoptotic Bcl-2 family proteins in the process remains poorly defined. Expression of the death agonist Bcl-2-interacting mediator of cell death (Bim) is under the control of the forkhead in rhabdomyosarcoma (FKHR) transcription factors. This prompted us to examine the response of this pathway to experimental seizures and in hippocampi from patients with intractable temporal lobe epilepsy. A short period of status epilepticus in rats that damaged the hippocampus activated FKHR/FKHRL-1 and induced a significant increase in expression of Bim. Blocking of FKHR/FKHRL-1 dephosphorylation after seizures improved hippocampal neuronal survival in vivo, and Bim antisense oligonucleotides were neuroprotective against seizures in vitro. Inhibition of Akt increased the FKHR/Bim response and DNA fragmentation within the normally resistant cortex. Analysis of hippocampi from patients with intractable epilepsy revealed that Bim levels were significantly lower than in controls and FKHR was inhibited; we were able to reproduce these results experimentally in rats by evoking multiple brief, noninjurious electroshock seizures. We conclude that Bim expression may be a critical determinant of whether seizures damage the brain, and that its control may be neuroprotective in status epilepticus and epilepsy.

Critical Role of Calpain-mediated Cleavage of Calcineurin in Excitotoxic Neurodegeneration

Calcineurin and calpain, a Ca2+/calmodulin-dependent protein phosphatase and a Ca2+-dependent cysteine protease, respectively, mediate neuronal cell death through independent cascades. Here, we report that during neuroexcitotoxicity, calcineurin A (CnA) is directly cleaved by calpain in vitro and in vivo, resulting in the enzyme being converted to an active form. Mass spectrometry identified three cleavage sites in CnA, two of which were constitutively active forms. Overexpression of the cleaved CnA induced caspase activity and neuronal cell death. Calpain inhibitors and membrane-permeable calpastatin peptides not only blocked the cleavage of CnA, but also protected against excitotoxic neuronal cell death in vitro and in vivo. These results indicate that CnA is a crucial target for calpain, and the calpain-mediated activation of CnA triggers excitotoxic neurodegeneration. This study established a molecular link between calpain and calcineurin, thereby demonstrating a new mechanism for proteolytical regulation of calcineurin by calpain in response to certain pathological states.

Excitotoxic and excitoprotective mechanisms: abundant targets for the prevention and treatment of neurodegenerative disorders

Activation of glutamate receptors can trigger the death of neurons and some types of glial cells, particularly when the cells are coincidentally subjected to adverse conditions such as reduced levels of oxygen or glucose, increased levels of oxidative stress, exposure to toxins or other pathogenic agents, or a disease-causing genetic mutation. Such excitotoxic cell death involves excessive calcium influx and release from internal organelles, oxyradical production, and engagement of programmed cell death (apoptosis) cascades. Apoptotic proteins such as p53, Bax, and Par-4 induce mitochondrial membrane permeability changes resulting in the release of cytochrome c and the activation of proteases, such as caspase-3. Events occurring at several subcellular sites, including the plasma membrane, endoplasmic reticulum, mitochondria and nucleus play important roles in excitotoxicity. Excitotoxic cascades are initiated in postsynaptic dendrites and may either cause local degeneration or plasticity of those synapses, or may propagate the signals to the cell body resulting in cell death. Cells possess an array of antiexcitotoxic mechanisms including neurotrophic signaling pathways, intrinsic stress-response pathways, and survival proteins such as protein chaperones, calcium-binding proteins, and inhibitor of apoptosis proteins. Considerable evidence supports roles for excitotoxicity in acute disorders such as epileptic seizures, stroke and traumatic brain and spinal cord injury, as well as in chronic age-related disorders such as Alzheimer's, Parkinson's, and Huntington's disease and amyotrophic lateral sclerosis. A better understanding of the excitotoxic process is not only leading to the development of novel therapeutic approaches for neurodegenerative disorders, but also to unexpected insight into mechanisms of synaptic plasticity.

Protection provided by cyclosporin A against excitotoxic neuronal death is genotype dependent

PURPOSE

Previous studies have shown that the immunosuppressant cyclosporin A (CsA), a specific blocker of the mitochondrial permeability transition (MPT) pore, can dramatically ameliorate the selective neuronal necrosis resulting from ischemia-reperfusion, traumatic brain injury, and N-methyl-d-aspartate (NMDA)-evoked neurotoxicity. The purpose of this study was to determine whether two different immunosuppressants, CsA and FK-506, could ameliorate the neuronal damage observed after kainate-induced seizures in strains that are differentially susceptible to excitotoxin-induced cell death.

METHODS

Excitotoxin-resistant (C57BL/6) or -susceptible (FVB/N) mice were administered kainate alone (30 mg/kg), CsA alone (5, 10, or 20 mg/kg), or one of the immunosuppressants (CsA, 5 mg/kg or 10 mg/kg; FK-506, 0.5 mg/kg) followed by kainate. After drug administration, mice were monitored continuously for the onset and extent of seizure activity. After a survival of 7 days, animals were assessed for hippocampal damage.

RESULTS

Whereas CsA alone induced no epileptogenic effects and both immunosuppressants were without effect on the induction of kainate-induced seizures, administration of CsA to excitotoxin-susceptible mice (FVB/N) virtually eliminated neuronal cell death. In contrast, induction of neuronal cell death was evident when CsA was administered to excitotoxin-resistant mice (C57BL/6). Administration of FK-506, another commonly used immunosuppressant, which lacks an effect on the MPT, had no effect on modification of susceptibility to kainate-induced cell death in either strain.

CONCLUSIONS

As our data show differential protection of hippocampal neurons against excitotoxic cell death by pretreatment with CsA, these results suggest that strain-dependent differences in mitochondrial integrity and function may exist.

The immunophilin-ligands FK506 and V-10,367 mediate neuroprotection by the heat shock response

(1) The macrolid FK506 is widely used in transplantation to suppress allograft rejection. FK506 and its derivatives are powerful neuroprotective molecules, but the underlying mechanisms remain to be resolved. We have previously shown that the FK506 mediated neuroprotection against oxygen radicals is independent of the inhibition of calcineurin but depends on de novo protein synthesis. (2) Here, we have shown that FK506 mediates protection against H(2)O(2), UV-light or thapsigargin in neuronal cell lines, but not in non-neuronal cells such as R3T3 fibroblasts. We compared in detail the effect of FK506 on apoptotic features in PC12 cells after H(2)O(2) with V-10,367 which binds to FKBPs but does not inhibit calcineurin. Both molecules exert the same neuroprotective effect after H(2)O(2) stimulation. FK506, but not V-10,367, inhibited the cytochrome c release out of the mitochondria and the caspase 3 activation, while both molecules inhibited the cleavage of Poly-(ADP-ribose)-polymerase (Parp) and prevented the expression of p53. (3) FK506 and V-10,367 rapidly induced the expression of Hsp70 and Hsp27, but not Hsp90. Their neuroprotective actions could be completely blocked by quercetin, a functional inhibitor of the heat shock proteins. (4) We conclude that immunophilin-ligands such as FK506 and V-10,367 exert their neuroprotection independent of calcineurin through the induction of the heat shock response. The identification of the underlying signal transduction from application of immunophilin ligands to the expression of heat shock proteins represents a novel target cascade for neuroprotection.

To die or not to die for neurons in ischemia, traumatic brain injury and epilepsy: a review on the stress-activated signaling pathways and apoptotic pathways

After a severe episode of ischemia, traumatic brain injury (TBI) or epilepsy, it is typical to find necrotic cell death within the injury core. In addition, a substantial number of neurons in regions surrounding the injury core have been observed to die via the programmed cell death (PCD) pathways due to secondary effects derived from the various types of insults. Apart from the cell loss in the injury core, cell death in regions surrounding the injury core may also contribute to significant losses in neurological functions. In fact, it is the injured neurons in these regions around the injury core that treatments are targeting to preserve. In this review, we present our cumulated understanding of stress-activated signaling pathways and apoptotic pathways in the research areas of ischemic injury, TBI and epilepsy and that gathered from concerted research efforts in oncology and other diseases. However, it is obvious that our understanding of these pathways in the context of acute brain injury is at its infancy stage and merits further investigation. Hopefully, this added research effort will provide a more detailed knowledge from which better therapeutic strategies can be developed to treat these acute brain injuries.

Activation of Bcl-2-associated death protein and counter-response of Akt within cell populations during seizure-induced neuronal death

Bcl-2 family gene products are critical to the integration of cell death stimuli that target the mitochondrion. Proapoptotic BAD (Bcl-2-associated death protein) has been shown to dissociate from its sequestered site with the molecular chaperone protein 14-3-3 and displace proapoptotic BAX (Bcl-2-associated X protein) from antiapoptotic BCL-Xl. BAX subsequently translocates to the mitochondrion and induces cytochrome c release and caspase activation. Herein we report the response of the key members of this proposed pathway after seizures. Seizures evoked by microinjection of kainic acid into the amygdala of the rat induced unilateral CA3 pyramidal neuron death with features of apoptosis. In control hippocampus and cortex, BAD was found constitutively bound to 14-3-3, whereas BCL-Xl bound BAX. Within damaged hippocampus, seizures induced the dissociation of BAD from 14-3-3 and the subsequent dimerization of BAD with BCL-Xl as determined by immunoprecipitation and immunohistochemical colocalization. 14-3-3 was found to translocate to the nucleus of degenerating neurons, whereas BAX accumulated at mitochondrial membranes. In contrast, the primarily uninjured cortex exhibited increased phosphorylation of Akt (protein kinase B), which may phosphorylate and inhibit BAD, and no altered binding of BAD to BCL-Xl. Finally, administration of an inhibitor of phosphatidylinositol 3-kinase (LY294002), thought to be an upstream activator of Akt, exacerbated cortical apoptosis after seizures. These data suggest that seizures elicit divergent cell death and survival responses within neuronal populations and that the BAD cell death pathway may perform an instigator or reinforcement role in seizure-induced neuronal death.

The Ca2+/calmodulin system in neuronal hyperexcitability

Calmodulin (CaM) is a major Ca2+-binding protein in the brain, where it plays an important role in the neuronal response to changes in the intracellular Ca2+ concentration. Calmodulin modulates numerous Ca2+-dependent enzymes and participates in relevant cellular functions. Among the different CaM-binding proteins, the Ca2+/CaM dependent protein kinase II and the phosphatase calcineurin are especially important in the brain because of their abundance and their participation in numerous neuronal functions. Therefore, the role of the Ca2+/CaM signalling system in different neurotoxicological or neuropathological conditions associated to alterations in the intracellular Ca2+ concentration is a subject of interest. We here report different evidences showing the involvement of CaM and the CaM-binding proteins above mentioned in situations of neuronal hyperexcitability induced by convulsant agents. Signal transduction pathways mediated by specific CaM binding proteins warrant future study as potential targets in the development of new drugs to inhibit convulsant responses or to prevent or attenuate the alterations in neuronal function associated to the deleterious increases in the intracellular Ca2+ levels described in different pathological situations.

Chemotherapeutic neuropathy

Peripheral neurotoxicity is a dose-limiting side-effect for a number of effective chemotherapeutic agents, including platinum compounds, taxanes, and vinca alkaloids. New experimental chemotherapy drugs that cause neuropathy include suramin and Dolostatin-10. A better understanding of cellular mechanisms will lead to novel treatment strategies that will protect neurons without decreasing therapeutic efficacy.

Synthesis and cytotoxic evaluation of cycloheximide derivatives as potential inhibitors of FKBP12 with neuroregenerative properties

On the basis of the new finding that the protein synthesis inhibitor cycloheximide (1, 4-[2-(3, 5-dimethyl-2-oxocyclohexyl)-2-hydroxyethyl]-2,6-piperidinedione) is able to competitively inhibit hFKBP12 (K(i) = 3.4 microM) and homologous enzymes, a series of derivatives has been synthesized. The effect of the compounds on the activity of hFKBP12 and their cytotoxicity against eukaryotic cell lines (mouse L-929 fibroblasts, K-562 leukemic cells) were determined. As a result, several less toxic or nontoxic cycloheximide derivatives were identified by N-substitution of the glutarimide moiety and exhibit IC(50) values in the range of 22.0-4.4 microM for inhibition of hFKBP12. Among these compounds cycloheximide-N-(ethyl ethanoate) (10, K(i) = 4.1 microM), which exerted FKBP12 inhibition to an extent comparable to that of cycloheximide (1), was found to cause an approximately 1000-fold weaker inhibitory effect on eukaryotic protein synthesis (IC(50) = 115 microM). Cycloheximide-N-(ethyl ethanoate) (10) was able to significantly speed nerve regeneration in a rat sciatic nerve neurotomy model at dosages of 30 mg/kg.

A calcineurin inhibitor, FK506, blocks voltage-gated calcium channel-dependent LTP in the hippocampus

The effects of FK506, an immunosuppressant and protein phosphatase 2B (calcineurin) inhibitor, on the voltage-gated calcium channel (VGCC)-dependent long-term potentiation (LTP) were investigated in the CA1 region of mice hippocampal slices. VGCC-dependent LTP was induced either by a brief application of a potassium channel blocker tetraethyleneanmonium (TEA), or by a strong tetanic stimulation under the blockade of NMDA-receptors. FK506 (1-50 microM) produced dose-dependent inhibition on TEA-induced LTP. Cyclosporin A (CysA 50 microM), another calcineurin inhibitor, showed a similar inhibitory effect on TEA-induced LTP. FK506 (10 microM) also blocked the strong tetanus-induced LTP, but had no effect on the post-tetanic potentiation. By using a subthreshold weak tetanic stimulation protocol, we also found that low concentration of FK506 (1 microM) produced neither inhibition nor potentiation on VGCC-dependent LTP. These results showed FK506 and CysA exerted inhibitory effects on VGCC-dependent LTP, and suggest that calcineurin is involved in the processes of this kind of synaptic plasticity.