An immunosuppressant, FK506, protects hippocampal neurons from forebrain ischemia in the mongolian gerbil

Combination of therapeutic hypothermia and other neuroprotective strategies after an ischemic cerebral insult

Abrupt deprivation of substrates to neuronal tissue triggers a number of pathological events (the “ischemic cascade”) that lead to cell death. As this is a process of delayed neuronal cell death and not an instantaneous event, several pharmacological and non-pharmacological strategies have been developed to attenuate or block this cascade. The most promising neuroprotectant so far is therapeutic hypothermia and its beneficial effects have inspired researchers to further improve its protective benefit by combining it with other neuroprotective agents. This review provides an overview of all neuroprotective strategies that have been combined with therapeutic hypothermia in rodent models of focal cerebral ischemia. A distinction is made between drugs interrupting only one event of the ischemic cascade from those mitigating different pathways and having multimodal effects. Also the combination of therapeutic hypothermia with hemicraniectomy, gene therapy and protein therapy is briefly discussed. Furthermore, those combinations that have been studied in a clinical setting are also reviewed.

Effect of neural stem cell transplantation on cognitive functions of mice after cerebral ischemia-reperfusion

This study is aimed to determine the effect of transplantation of neural progenitor cells (NPCs) isolated from fetal hippocampus on cognitive functions of experimental animals after short-term global cerebral ischemia. NPCs were isolated from hippocampus of FVB-Cg-Tg(GFPU)5Nagy/J mice, transgenic by the GFP. Ischemic brain injury in FVB “wild” type mice was modeled by bilateral occlusion of the common carotid arteries for 20 min. GFP-positive NPCs were stereotaxically transplanted into the hippocampus of experimental animals in 24 hours after ischemia-reperfusion. Cognitive functions were evaluated using Morris water maze. Results of this study showed that global short-term cerebral ischemia resulted into cognitive impairments in mice. Stereotaxic transplantation of NPCs promoted the cognitive function recovery in experimental animals after ischemic brain injury. Thus, the data indicates that transplantation of NPCs may have a therapeutic effect in treating of ischemic stroke.

Effects of FK506 on Hippocampal CA1 Cells Following Transient Global Ischemia/Reperfusion in Wistar Rat

Transient global cerebral ischemia causes loss of pyramidal cells in CA1 region of hippocampus. In this study, we investigated the neurotrophic effect of the immunosuppressant agent FK506 in rat after global cerebral ischemia. Both common carotid arteries were occluded for 20 minutes followed by reperfusion. In experimental group 1, FK506 (6 mg/kg) was given as a single dose exactly at the time of reperfusion. In the second group, FK506 was administered at the beginning of reperfusion, followed by its administration intraperitoneally (IP) 6, 24, 48, and 72 hours after reperfusion. FK506 failed to show neurotrophic effects on CA1 region when applied as a single dose of 6 mg/kg. The cell number and size of the CA1 pyramidal cells were increased, also the number of cell death decreased in this region when FK506 was administrated 48 h after reperfusion. This work supports the possible use of FK506 in treatment of ischemic brain damage.

Degradation of PEP-19, a calmodulin-binding protein, by calpain is implicated in neuronal cell death induced by intracellular Ca2+ overload

Excessive elevation of intracellular Ca2+ levels and, subsequently, hyperactivation of Ca2+/calmodulin-dependent processes might play an important role in the pathologic events following cerebral ischemia. PEP-19 is a neuronally expressed polypeptide that acts as an endogenous negative regulator of calmodulin by inhibiting the association of calmodulin with enzymes and other proteins. The aims of the present study were to investigate the effect of PEP-19 overexpression on cell death triggered by Ca2+ overload and how the polypeptide levels are affected by glutamate-induced excitotoxicity and cerebral ischemia. Expression of PEP-19 in HEK293T cells suppressed calmodulin-dependent signaling and protected against cell death elicited by Ca2+ ionophore. Likewise, primary cortical neurons overexpressing PEP-19 became resistant to glutamate-induced cell death. In immunoprecipitation assay, wild type PEP-19 associated with calmodulin, whereas mutated PEP-19, which contains mutations within the calmodulin binding site of PEP-19, failed to associate with calmodulin. We found that the mutation abrogates both the ability to suppress calmodulin-dependent signaling and to protect cells from death. Additionally, the endogenous PEP-19 levels in neurons were significantly reduced following glutamate exposure, this reduction precedes neuronal cell death and can be blocked by treatment with calpain inhibitors. These data suggest that PEP-19 is a substrate for calpain, and that the decreased PEP-19 levels result from its degradation by calpain. A similar reduction of PEP-19 also occurred in the hippocampus of gerbils subjected to transient global ischemia. In contrast to the reduction in PEP-19, no changes in calmodulin occurred following excitotoxicity, suggesting the loss of negative regulation of calmodulin by PEP-19. Taken together, these results provide evidence that PEP-19 overexpression enhances resistance to Ca2+-mediated cytotoxicity, which might be mediated through calmodulin inhibition, and also raises the possibility that PEP-19 degradation by calpain might produce an aberrant activation of calmodulin functions, which in turn causes neuronal cell death.

Novel neuroprotective compound SCH-20148 rescues thymocytes and SH-SY5Y cells from thapsigargin-induced mitochondrial membrane potential reduction and cell death

Mitochondrial membrane potential plays an important role in cell survival. Transitions in mitochondrial permeability, which indicate the imminent destruction of the organelles, have been observed in damaged neuronal cells both in vitro and in vivo. In this study, C57/BL6n mouse thymocytes were put under stress using thapsigargin, a Ca2+ ATP-ase inhibitor, after which the change in mitochondrial membrane potential was monitored with a JC-1 dual-emission probe. This was done in an attempt to identify a novel compound that can suppress mitochondrial membrane potential reduction and cell death. In this assay system, the novel compound SCH-20148 [2,3-dihydroxypropyl-5-bromo-N-(2-methyl-3-trifluoromethylphenyl)anthranilate] was found to protect mouse thymocytes against thapsigargin (3 nM)-induced mitochondrial membrane potential reduction (IC50=42 nM). SCH-20148 also prevented A23187- or ionomycin-induced shifts in mitochondrial membrane potential but it did not have any effect on the changes induced by tunicamycin, staurosporine, or dexamethasone. The potent immunosuppressants tacrolimus and cyclosporine A prevented the effect of thapsigargin, but did not prevent the A23187- or ionomycin-induced changes. Calcium-modulating agents, an anti-oxidant, a protein kinase C inhibitor, and anti-inflammatory agents were not effective against thapsigargin-induced mitochondrial permeability transition which implies that SCH-20148 exerts a protective effect via its specific mechanism. In addition, SH-20148 demonstrated a neuroprotective effect against thapsigargin-induced neuronal cell death in neuroblastoma SH-SY5Y cells. Taken together, these results suggest the potential of SCH-20148 as novel neuroprotective drug.

Tacrolimus (FK506) attenuates biphasic cytochrome c release and Bad phosphorylation following transient cerebral ischemia in mice

Tacrolimus (FK506) has a neuroprotective action on cerebral infarction produced by cerebral ischemia, however, detailed mechanisms underlying this action have not been fully elucidated. We examined temporal profiles of survival-and death-related signals, Bad phosphorylation, release of cytochrome c (cyt.c), activation of caspase 3 and DNA fragmentation in the brain during and after middle cerebral artery occlusion (MCAo) in mice, and then examined the effect of tacrolimus on these signals. C57BL/6J mice were subjected to transient MCAo by intraluminal suture insertion for 60 min. Tacrolimus (1 mg/kg, i.p.) was administered immediately after MCAo. There were biphasic increases in the release of cyt.c in the ischemic core and penumbra; with the first increase toward the end of the occlusion period and the second increase 3-12 h after reperfusion. Tacrolimus significantly inhibited the increase of cytosolic cyt.c during ischemia and reperfusion. Phosphorylated Bad, Ser-136 (P-Bad(136)) and Ser-155 (P-Bad(155)) were detected 30 min after MCAo and after reperfusion in the ischemic cortex, respectively. Tacrolimus increased P-Bad(136) during ischemia and prolonged P-Bad(155) expression after reperfusion. Tacrolimus also decreased caspase-3 and terminal deoxynucleotidyl transferase-mediated DNA nick-end labeling-positive cells, and reduced the size of infarct 24 h after reperfusion. Our study provided the first evidence that the neuroprotective action of tacrolimus involved inhibition of biphasic cyt.c release from mitochondria, possibly via up-regulation of Bad phosphorylation at different sites after focal cerebral ischemia and reperfusion.

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.

Neuroregenerative Effects of Preinjury FK-506 Administration

BACKGROUND

FK-506 is used in organ transplantation because it promotes neurite outgrowth in vitro and enhances neuroregeneration in peripheral nerve injury transection models. Immunosuppressive mechanisms of FK-506 are well defined, with demonstration of decreased neuroregenerative effects with delayed administration. The purpose of this study was to describe the effects of preinjury administration of FK-506 in rats with tibial nerve transection injury.

METHODS

Eight inbred male Lewis rats per group in three separate groups underwent tibial nerve transection with primary repair. Group I received placebo, group II received FK-506 treatment at 1 day before surgery, and group III received FK-506 preloading 3 days before surgery.

RESULTS

Histologic and histomorphometric results demonstrated the preload FK-506 group had superior results compared with the immediate FK-506 group. Both FK-506 groups were superior to the placebo group. The preload FK-506 demonstrated superior regeneration in mean total nerve fiber counts (p < 0.05), greater percentage neural tissue (p < 0.05), greater mean nerve fiber density (p < 0.05), and lower percentage of debris (p > 0.05). Mean nerve fiber widths were similar in the preload and immediate FK-506 groups but superior to the placebo group.

CONCLUSION

These data suggest that enhancement of FK-506's neuroregenerative effect is enhanced when administered before nerve injury such as when performing elective surgery.

Generation of constitutively active calcineurin by calpain contributes to delayed neuronal death following mouse brain ischemia

Calpain, a Ca(2+)-dependent cysteine protease, in vitro converts calcineurin (CaN) to constitutively active forms of 45 kDa and 48 kDa by cleaving the autoinhibitory domain of the 60 kDa subunit. In a mouse middle cerebral artery occlusion (MCAO) model, calpain converted the CaN A subunit to the constitutively active form with 48 kDa in vivo. We also confirmed increased Ca(2+)/CaM-independent CaN activity in brain extracts. The generation of constitutively active and Ca(2+)/CaM-independent activity of CaN peaked 2 h after reperfusion in brain extracts. Increased constitutively active CaN activity was associated with dephosphorylation of dopamine-regulated phosphoprotein-32 in the brain. Generation of constitutively active CaN was accompanied by translocation of nuclear factor of activated T-cells (NFAT) into nuclei of hippocampal CA1 pyramidal neurons. In addition, a novel calmodulin antagonist, DY-9760e, blocked the generation of constitutively active CaN by calpain, thereby inhibiting NFAT nuclear translocation. Together with previous studies indicating that NFAT plays a critical role in apoptosis, we propose that calpain-induced CaN activation in part mediates delayed neuronal death in brain ischemia.

Neuroprotective effects of tacrolimus (FK506) in a model of ischemic cortical cell cultures: role of glutamate uptake and FK506 binding protein 12 kDa

BACKGROUND

The mechanisms underlying the neuroprotective effects of the immunosuppressant tacrolimus, observed in vivo, remain unclear. Here we quantify these effects in vitro, and evaluate the potential involvement of the glutamate and/or immunophilin FK506 binding protein 12 kDa in tacrolimus-induced neuroprotection.

METHODS

Primary cultures of neurons and astrocytes from rat cerebral cortex were subjected to transient oxygen-glucose deprivation. Neuronal injury was evaluated by cell counting after immunostaining experiments, lactate dehydrogenase release and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction. The involvement of the immunophilin FK506 binding protein 12 kDa was explored using an anti-FK506 binding protein 12 kDa antibody, (3-3-pyridyl)-1-propyl(2 s)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidine carboxylate and rapamycin. Extracellular glutamate and glutamate uptake were respectively measured by high performance liquid chromatography and l-[3H]glutamate incorporation.

RESULTS

When added during either oxygen-glucose deprivation or reoxygenation, FK506 (50-500 pM) offered significant neuroprotection. During oxygen-glucose deprivation, it was able to reverse the oxygen-glucose deprivation-induced increase in extracellular glutamate and decrease in glutamate uptake and this effect was reversed in the presence of threo-3-methyl glutamate, a specific inhibitor of glutamate transporter-1. Blocking FK506 binding protein 12 kDa inhibited the neuroprotection induced by tacrolimus added during either oxygen-glucose deprivation or reoxygenation. Tacrolimus-induced neuroprotection was also reversed in the presence of rapamycin, an immunosuppressant FK506 binding protein 12 kDa ligand devoid of neuroprotective properties and (3-3-pyridyl)-1-propyl(2 s)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidine carboxylate, a non-immunosuppressant ligand of FK506 binding protein 12 kDa, exerteing neuroprotective effects.

CONCLUSION

The beneficial effects of tacrolimus during in vitro ischemia/reperfusion seem to indicate the restoration of a glutamate transporter-1-mediated activity and could be mediated by a FK506 binding protein 12 kDa pathway.

Protective effect of FK506 against apoptosis of SH-SY5Y cells correlates with regulation of the serum inducible kinase gene

Recently, we established an in vitro model of apoptosis induced by exposure of neuroblastoma SH-SY5Y cells to thapsigargin, an endoplasmic reticular calcium-ATPase inhibitor, and demonstrated that FK506 (tacrolimus) protected against apoptosis. The purpose of this paper was to investigate a possible correlation between the protective effect of FK506 against apoptosis and the regulation of the serum inducible kinase (SNK) and fibroblast growth factor inducible kinase (FNK) genes-which are polo-like kinases expressed abundantly in the brain by FK506. Thapsigargin increased the mRNA level of SNK and FNK in SH-SY5Y cells. FK506 inhibited the increase in SNK mRNA but not FNK mRNA. Deletion analysis of the SNK promoter showed that the promoter site, which was regulated by thapsigargin and FK506 in a calcineurin-dependent manner, is a cAMP response element (CRE)/activating transcription factor (ATF)-like element located 84 base pairs (bp) proximal to the transcriptional initiation site. Although transcription of the SNK gene was also regulated by tunicamycin, etoposide, or staurosporine, FK506 did not show any effects on these regulations. We recently reported that FK506 did not protect against apoptosis induced by these agents. These results indicate that the induction of SNK mRNA by thapsigargin in SH-SY5Y cells is regulated by FK506 via an inhibition of calcineurin at the transcriptional stage, and the transcriptional regulation of the SNK gene by FK506 was well correlated with the protective effect of the compound against apoptosis. Thus, transcriptional regulation of the SNK gene may be a biological marker for analysis of apoptosis of SH-SY5Y cells.

Ginkgo biloba extract (EGb761) and FK506 preserve energy metabolites in the striatum during focal cerebral ischemia and reperfusion in gerbils monitored by microdialysis

Cell death after cerebral ischemia is mediated by the accumulation of excitatory amino acids, calcium influx into cells and the generation of free radicals. The aim of this study was to evaluate changes in energy-related metabolites in the striatum of gerbils subjected to focal cerebral ischemia after pretreatment with Ginkgo biloba extract (EGb761), a well-known antioxidant, and FK506, a calcium-dependent phosphatase calcineurin inhibitor. Ischemia was induced by occlusion of the right common carotid artery and the right middle cerebral artery for 60 min. A microdialysis probe was inserted into the right striatum to monitor extracellular glucose, lactate and pyruvate levels. This study showed decreases in glucose (10% of the baseline), pyruvate (20% of the baseline) and lactate (60% of the baseline), and a 5-fold increase in the lactate to pyruvate ratio during ischemia in the control group. Both EGb761 treatment and the combination (EGb761 and FK506) therapy significantly preserved glucose (50% of the baseline) and pyruvate (60% of the baseline) levels during ischemia. The marked increase in the lactate to pyruvate ratio was not observed in the combination group. These results suggest that preservation of cellular energy metabolism during cerebral ischemia and after restoration with reperfusion may contribute to the neuroprotective effects of EGb761 and FK506.

FK506 abrogates delayed neuronal death via suppression of nitric oxide production in rats

BACKGROUND AND PURPOSE

The mechanism of the neuroprotective effect of FK506 in relation to nitric oxide (NO) production has not been clarified in vivo. We have investigated the effect of FK506 on ischemia-induced NO production in association with the pathogenesis of delayed neuronal death (DND) in rats.

METHODS

In vivo microdialysis was performed in the hippocampus of male Sprague-Dawley rats (250-350 g). Dialysate samples were collected every 3 min. In the ischemia group (n=16), global ischemia was induced for 21 min and reperfusion was achieved. In the FK506 treatment group (n=25), FK506 (1 mg/kg, i.v.) was administered 21 min prior to the onset of global ischemia. Sham operations were done (n=15). The levels of NO(2)(-) in the dialysate samples were determined by the Griess reaction. The animals were decapitated 7 days after ischemia. Coronal brain sections were stained with hematoxylin and eosin.

RESULTS

In the ischemia group, the NO(2)(-) level significantly increased during ischemia. In the FK506 treatment group, there was no significant change in the NO(2)(-) level during ischemia. In histological examinations, FK506 treatment showed a neuroprotective effect against DND.

CONCLUSIONS

The effect of FK506 inhibiting NO production contributes to the neuro-protective effect of FK506 on DND in the hippocampus.

Mild hypothermia enhances the neuroprotective effects of FK506 and expands its therapeutic window following transient focal ischemia in rats

FK506 (tacrolimus), an immunosuppressant, reportedly reduces ischemic brain injury following transient middle cerebral artery occlusion (MCAO) in rats. The authors previously reported that the therapeutic window of FK506 in this model is more than 1 h, but less than 2 h. The aim of the present study is to determine whether mild hypothermia (35 degrees C) enhances the neuroprotective effects of FK506 and expands its therapeutic window. Sprague-Dawley rats were subjected to 2 h MCAO followed by 24 h reperfusion. Animals were randomly divided into four groups: (I) vehicle-treated normothermic group; (II) FK506-treated normothermic group; (III) vehicle-treated hypothermic group; (IV) FK506-treated hypothermic group. Animals received a single injection of FK506 (0.3 mg/kg) or vehicle intravenously at 2 h after ischemic induction. During ischemia, temporal muscle and rectal temperatures were maintained at 37 degrees C in the normothermic animals and at 35 degrees C in the hypothermic animals. Infarct volumes and neurological performance were evaluated at 24 h after reperfusion. The combination of FK506 and mild hypothermia significantly reduced infarct volume (cortex, -61%; striatum, -31%) and edema volume (cortex, -57%; striatum, -41%), while mild hypothermia or FK506 alone failed to improve ischemic brain damage. Furthermore, this combination also provided for the best functional outcome. These results demonstrate that the combination of FK506 and mild hypothermia significantly reduces ischemic brain damage following transient MCAO in rats, and expands the therapeutic window for FK506. This therapy may be a new approach for treatment of acute stroke.

FK506 attenuates the post-ischemic perturbation of protein kinases and tyrosine phosphorylation in the gerbil hippocampal CA1 sectors

To explore effects of Immunosuppressant FK506 on signal transduction pathway. we studied changes in subcellular distribution of protein kinase Cgamma (PKCgamma), CaM kinase II (CaMKII), as well as changes of tyrosine phosphorylation levels after ischemia. Male Mongolian gerbils were divided into 3 groups; FK506 (1 mg/kg, 3 mg/kg) and vehicle. FK506 was administered intravenously after 5 min ischemia. At the designated time points (0 time, 5 min ischemia, 1 hour, or 24 hour recovery), heads were frozen and samples were taken from CAI subfield of hippocampus. Western blot analysis was carried out with specific antibodies for PKCgamma, CaMKII, and phosphotyrosine. FK506 administration significantly decreased translocation of PKCgamma and CaMKII at 24 h of recovery (p < 0.05, ANOVA followed by Student-Newman Keuls' test) in P2 fraction. The levels of tyrosine phosphorylated p160, p140, p100, p90, and p80 in P2 fraction were also significantly decreased with FK506 treatment at 24 h of recovery. The persistently elevated PKCgamma and CaMKII level in P2 fraction which may be related to cell death, are attenuated with FK506 treatment. FK506 may contribute to recover calcium homeostasis in the post ischemic phase and promote cell survival.

Effect of tacrolimus (FK506) on ischemia-induced brain damage and memory dysfunction in rats

The behavioral and neurohistological protective effects of tacrolimus (FK506) were examined in rats subjected to 15-min global forebrain ischemia. Learning and memory performance were evaluated in an aversive, non-food-motivated, eight-arm radial maze. In one experiment, naive rats were rendered ischemic, and 15 days later they were tested for acquisition of a spatial task (postoperative training). In a complementary experiment, rats were trained for 8 days and then subjected to ischemia (preoperative training); 15 days later (on Day 24 of testing) they were retested for retention of cognition. FK506 (1.0 mg/kg) was given intravenously at the beginning of reperfusion, followed by doses applied intraperitoneally 6, 24, 48 and 72 h postischemia. Behavioral performance was expressed by latency to find the goal box, and number of errors. Ischemia did not affect acquisition performance. In contrast, retention of cognition was markedly impaired by ischemia, particularly working memory (P<.05-.001). This ischemia-induced, retrograde amnesia was significantly reduced by FK506 compared to vehicle alone on Day 24, as measured by latency and working memory errors (P<.025). A neuroprotective effect of FK506 was also seen on working memory, when postischemic performance was compared to that prior to ischemia (P>.05, Day 24 vs. Day 8, paired samples), in contrast to the significant, retrograde amnesia found in the ischemic, vehicle-treated group (P<.01). FK506 also significantly reduced the extent of hippocampal CA1 cell loss; however, this effect did not correlate with behavior. The present results suggest that the histological, neuroprotective effect of FK506 may be accompanied by a reduction in cognitive impairment, as assessed in a novel, non-food-motivated, eight-arm radial maze after transient, global, cerebral ischemia in rats.

Protective Effect of DY-9760e, a Calmodulin Antagonist, against Neuronal Cell Death

An excessive elevation of intracellular Ca(2+) levels is known to play a key role in the pathological events following cerebral ischemia. DY-9760e, 3-[2-[4-(3-chloro-2-methylphenylmethyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate, is a potent calmodulin antagonist that attenuates brain damage in focal ischemia models. In the present study, we investigated the effect of DY-9760e on neuronal cell death induced by a variety of cell-toxic stimuli that increase intracellular Ca(2+). Cell death was induced by the exposure of primary cultured neurons to excitotoxic agents such as glutamate and N-methyl-D-aspartate, membrane-depolarizing agents such as veratridine and high KCl, or thapsigargin an endoplasmic reticulum Ca(2+)-ATPase inhibitor. Treatment with DY-9760e resulted in a dose-dependent prevention of neuronal cell death elicited by excitotoxicity, voltage-gated channel opening, and inhibition of endoplasmic reticulum Ca(2+)-ATPase. These results indicate that DY-9760e can rescue neurons from various types of cell-toxic stimuli, which may contribute to attenuation of brain injury after cerebral ischemia.

Neuroprotective effects of FK-506, l-carnitine and azathioprine on spinal cord ischemia-reperfusion injury

OBJECTIVE

In our experimental study, we aimed to test the effect of FK506, azathioprine and L-carnitine on protection of spinal cord injury due to ischemia-reperfusion.

METHODS

Twenty-seven Sprague-Dawley male rats were randomly divided into five groups. They were subjected to spinal cord ischemia by clamping the abdominal aorta for 45 min. Thirty minutes before the aortic clamping, group I received 0.5 mg/kg FK506, group II received 100 mg/kg L-carnitine, group III received 4 mg/kg azathioprine, the fourth group was the control group and received only normal saline injection intravenously and the last group was the sham group. Neurological status was scored by using the Tarlov scoring system. Sections of the lumbar cord were harvested for histopathological grades (1-4), having regard to percentage of the apoptotic cells.

RESULTS

Hind-limb motor function had recovered normally 48 h after the operation in all rats which received FK506, azathioprine and L-carnitine prophylactically. In contrast, all rats in the control group had deteriorated to paraplegia by 48 h after the operation (P<0.05). Histopathologic sections in the involved spinal cord segment showed that a greater number of motor neuron cells were preserved and there were less apoptotic cells in the rats that received FK506, azathioprine and L-carnitine than those in control group.

CONCLUSIONS

These results suggest that prophylactic use of FK506, azathioprine and L-carnitine protects motor neuron cells from ischemic spinal cord injury.

Changes in peptidyl-prolyl cis/trans isomerase activity and FK506 binding protein expression following neuroprotection by FK506 in the ischemic rat brain

FK506 is an immunosuppressant also showing neuroprotection following cerebral ischemia. FK506 binds to intracellular proteins (FKBP) which have a wide range of functions but have in common the peptidyl-prolyl cis/trans isomerase activity. Following transient focal ischemia, we have analyzed the expression of FKBP12, 52 and 65 and the total FKBP enzyme activity. Furthermore, we have investigated the effect of FK506 on signal transduction in neurons and perfusion changes in the infarct area. After 90 min of transient middle cerebral artery occlusion in male rats the expression of FKBP12, 52 and 65 was analyzed by Western blot in FK506-treated and control animals and the peptidyl-prolyl cis/trans isomerase activity was determined. Magnetic resonance imaging was used to measure tissue perfusion, development of vasogenic edema and infarct size. To investigate the neuronal stress signal cascade, activating transcription factor 2 (ATF-2), Fas-ligand (Fas-L) and c-Jun expression and phosphorylation were analyzed by immunohistochemistry. FK506 decreased the cerebral infarct volume by 53% and reduced the cytotoxic edema. The total FKBP enzymatic activity in the infarct area was increased and blocked dose dependently by FK506. FKBP expression was selectively up-regulated by cerebral ischemia. FK506 treatment does not influence the expression patterns. c-Jun phosphorylation in neurons of the peri-infarct area and Fas-L expression was reduced by FK506 treatment whereas ATF-2 expression was preserved. Cerebral ischemic damage to the brain was reduced by FK506. It was shown for the first time that neuroprotection by FK506 also included the suppression of the cerebral peptidyl-prolyl cis/trans isomerase activity of FKBP in vivo whereas the expression levels of FKBP12, 52 and 65 following ischemia changed slightly and FK506 treatment does not suppress the expression patterns. However, changes of FKBP enzymatic activity result in suppression of the stress cell body response in the peri-infarct area as observed by suppression of c-Jun phosphorylation and Fas-L expression.

Detailed in vitro pharmacological analysis of FK506-induced neuroprotection

FK506, a calcineurin inhibitor, shows potent neuroprotective effects in animal models such as those of stroke and neurodegenerative diseases. However, the mechanism underlying these neuroprotective effects is unclear. In this study, an in vitro model, in which FK506 protected the cells against cell death, was established and analyzed in detail by pharmacological experiments. Thapsigargin (TG), an inhibitor of endoplasmic reticulum calcium-ATPase, induced SH-SY5Y cell death. FK506 concentration-dependently protected the cells from this type of death. In contrast, FK506 did not suppress SH-SY5Y cell death caused by the following molecules: tunicamycin (TM), an inhibitor of N-linked glycosylation; etoposide (Eto), a topoisomerase II inhibitor; and staurosporine (STS), a phospholipid/calcium-dependent protein kinase inhibitor. Additionally, FK506 did not inhibit TG-induced cell death in either SK-N-MC or HeLa cell lines. FK506 completely inhibited caspase-3 activation and apoptosis caused by TG in a concentration-dependent manner, but not that caused by TM, Eto, and STS. TG did not activate caspase-3 in SK-N-MC cells, although it slightly activated caspase-3 in HeLa cells. FK506 did not change caspase-3 activity in either SK-N-MC or HeLa cell lines. Cyclosporin A, another calcineurin inhibitor, showed the same results as FK506 in this study, whereas rapamycin, an immunosuppressant not associated with calcineurin activity, did not have any effect in this context. Thus, the suppressive effects of FK506 on cell death are specific to SH-SY5Y cells treated with TG and are caused by the inhibition of calcineurin and subsequent suppression of caspase-3 activation. Therefore, an in vitro system using SH-SY5Y cells treated with TG could provide a model reflective of certain aspects of the neuroprotective activity of FK506.

Effects of FK506 on the translocation of protein kinase C and CaM kinase II in the gerbil hippocampal CA1 neurons

To explore biochemical basis for cerebroprotective effect of immunosuppressant FK506, we studied changes in subcellular distribution of protein kinase C gamma (PKC gamma) as well as calcium/calmodulin-dependent protein kinase II (CaMKII) after ischemia. Male Mongolian gerbils were subjected to 5 min forebrain ischemia. FK506 (1 or 3 mg kg-1) was administered at 1 min after recirculation, which was confirmed to be cerebroprotective by histological examination at seven days after ischemia. At the designated time points (before ischemia, 5 min ischemia, 1 and 24 h recovery), heads were frozen and samples were taken from CA1 subfield of hippocampus. Western blot analysis was carried out. Persistent translocations of PKC gamma and CaMKII to synaptosomal P2 fraction were observed in vehicle-treated group. FK506 significantly decreased levels of PKC gamma and CaMKII in P2 fraction at 24 h of recovery. The present results suggest FK506 downregulates translocated PKC gamma and CaMKII, which may contribute to its survival promoting effect after cerebral ischemia.

Pharmacological evidence for a correlation between hippocampal CA1 cell damage and hyperlocomotion following global cerebral ischemia in gerbils

Global ischemia, induced in Mongolian gerbils by bilateral occlusion of the carotid arteries for 5 min, produced a significant increase in locomotor activity at 1 day post-occlusion and a severe loss of hippocampal CA1 neurons at 4 days post-occlusion. To explore the pharmacological relationship between ischemia-induced hypermotility and CA1 cell death in the hippocampus, we evaluated the efficacy of diverse classes of putative neuroprotective agents for preventing hypermotility and delayed neuronal death. Administration of any drug 30 min before global ischemia dose-dependently, and with similar potency, ameliorated both hippocampal delayed neuronal death and locomotor hyperactivity, with a rank order: tacrolimus (FK506)>nizofenone>clonindine>dizocilpine (MK-801)>6-(1H-imidazol-1-yl)-7-nitro-2,3(1H,4H)-quinoxalinedione hydrochloride (YM90K)>phencyclidine>pentobarbital>2-(4-(p-fluorobenzoyl)-piperidin-1-yl)-2'-acetonaphthone hydrochloride (E-2001)>cis-(+/-)-4-phosphonomethyl-2-piperidine carboxylic acid (CGS19755)>3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide (U-50,488H)>piroxicam>eliprodil>vinpocetine. Furthermore, potencies of the protective effect on delayed neuronal death and inhibitory effects on hypermotility were closely correlated (r=0.98). These results suggest that post-ischemic CA1 injury and hypermotility share common mechanisms, and further imply that it is possible to predict the neuroprotective efficacy of drugs more easily by examining the inhibitory effects on post-ischemic hypermotility in global ischemia model in gerbils.

Tacrolimus (FK506) reduces ischemia-induced hippocampal damage in rats: a 7- and 30-day study

The neuroprotective effect of the immunosuppressant agent FK506 was evaluated in rats after brain ischemia induced for 15 min in the 4-vessel occlusion model. In the first experimental series, single doses of 1.0, 3.0 or 6.0 mg FK506/kg were given intravenously (iv) immediately after ischemia. In the second series, FK506 (1.0 mg/kg) was given iv at the beginning of reperfusion, followed by doses applied intraperitoneally (ip) 6, 24, 48, and 72 h post-ischemia. The same protocol was used in the third series except that all 5 doses were given iv. Damage to the hippocampal field CA1 was assessed 7 or 30 days post-ischemia on three different stereotaxic planes along the septotemporal axis of the hippocampus. Ischemia caused marked neurodegeneration on all planes (P<0.001). FK506 failed to provide neuroprotection to CA1 both when applied iv as a single dose of 1.0, 3.0 or 6.0 mg/kg (experiment 1), and after five iv injections of 1.0 mg/kg (experiment 3). In contrast, the repeated administration of FK506 combining iv plus ip administration reduced CA1 cell death on all stereotaxic planes both 7 and 30 days post-ischemia (experiment 2; P<=0.01). Compared to vehicle alone, FK506 reduced rectal temperature in a dose-dependent manner (P<=0.05); however, this effect did not alter normothermia (37 C). FK506 reduced ischemic brain damage, an effect sustained over time and apparently dependent on repeated doses and on delivery route. The present data extend previous findings on the rat 4-vessel occlusion model, further supporting the possible use of FK506 in the treatment of ischemic brain damage.

Hippocampal CA1 neuron survival and cytosolic FKBP12, the 12 kDa FK506-binding protein, after ischemia and tacrolimus treatment in gerbils

To assess the neuroprotective effect of tacrolimus (FK506) in transient forebrain ischemia models in gerbils, 10.0 mg/kg of FK506 was injected intraperitoneally immediately following reperfusion and at intervals of 1, 3, 6, 9, and 12 h after reperfusion. FK506 produced a significant neuroprotective effect for up to 6 h after 5 min of ischemia. Immunoblot and immunohistochemistry revealed that the amount of FKBP12, the 12-kDa FK506-binding protein, in the cytosol remained unchanged until 12 h after reperfusion. Translocation of FKBP12 from the nucleus to the cytosol was not observed until 24 h after reperfusion. Administration of FK506 did not appear to induce the cytosolic increase in FKBP12. In this study, no correlation was apparent between the post-ischemic therapeutic efficacy of FK506 and the post-ischemic changes in the cytosolic FKBP12.

Neuroprotective action of tacrolimus (FK506) in focal and global cerebral ischemia in rodents: dose dependency, therapeutic time window and long-term efficacy

Tacrolimus (FK506), a potent immunosuppressive drug, is effective in attenuating brain infarction after cerebral ischemia. However, there has been no report characterizing the neuroprotective action and therapeutic time window of tacrolimus systematically using different types of stroke models and extended observation periods. Therefore, we evaluated the neuroprotective effect of tacrolimus in three different animal models of cerebral ischemia: transient and permanent focal ischemia in rats and transient global ischemia in gerbils. Tacrolimus at doses higher than 0.1 mg/kg (i.v.) produced a statistically significant reduction in ischemic brain damage following permanent and transient focal ischemia in rats when administered immediately after the onset of ischemia. Tacrolimus (1 mg/kg, i.v.) demonstrated similar neuroprotective activity even after delayed administration (2 h after permanent or 1 h after transient focal ischemia). The neuroprotective effect of tacrolimus was still present 2 weeks after transient focal ischemia and 1 week after permanent focal ischemia. After transient global ischemia in gerbils, tacrolimus (1 mg/kg, i.v.) given immediately after reperfusion also produced long-lasting neuroprotective effects with a protective time-window of 1-2 h. Taken together, the results clearly indicate that tacrolimus exerts potent, long-term neuroprotective effects with a favorable therapeutic time-window, regardless of the model of cerebral ischemia. These results strengthen the notion that tacrolimus might be of clinical value for the treatment of acute stroke.

Calmodulin and calmodulin-dependent kinase II mediate neuronal cell death induced by depolarization

Depolarization has been known to play an important role in the neuronal damage that occurs following cerebral ischemia. In the present study, we investigated the roles of calmodulin (CaM) and CaM-dependent enzymes in depolarization-induced neuronal cell death. Treatment of primary cortical neurons with 10 microM veratridine, a voltage sensitive Na(+) channel activator, induced cell death as indicated by lactate dehydrogenase leakage from neurons. CaM antagonists (calmidazolium, trifluoperazine, W-7, and W-5) inhibited cell death induced by veratridine in a concentration-dependent manner. CaM kinase II (CaMKII) inhibitors (KN-62, KN-93, and myristoylated autocamtide-2 related inhibitory peptide), but not inhibitors of nitric oxide synthase or calcineurin, prevented veratridine-induced neuronal cell death. Veratridine rapidly activated CaMKII in neurons, and CaM antagonists and a CaMKII inhibitor suppressed the CaMKII activation. These results suggest that the CaM-CaMKII pathway contributes to depolarization-evoked cell death in neurons.

Effects of immunosuppressants, calcineurin inhibition, and blockade of endoplasmic reticulum calcium channels on free fatty acid efflux from the ischemic/reperfused rat cerebral cortex

Elevated levels of free fatty acids (FFA) have been implicated in the pathogenesis of neuronal injury and death induced by cerebral ischemia. This study evaluated the effects of immunosuppressants agents, calcineurin inhibitors and blockade of endoplasmic reticulum (ER) calcium channels on free fatty acid formation and efflux in the ischemic/reperfused (I/R) rat brain. Changes in the extracellular levels of arachidonic, docosahexaenoic, linoleic, myristic, oleic and palmitic acids in cerebral cortical superfusates during four-vessel occlusion-elicited global cerebral ischemia were examined using a cortical cup technique. A 20-min period of ischemia elicited large increases in the efflux of all six FFAs, which were sustained during the 40 min of reperfusion. Cyclosporin A (CsA) and trifluoperazine, which reportedly inhibit the I/R elicited opening of a mitochondrial permeability transition (MPT) pore, were very effective in suppressing ischemia/reperfusion evoked release of all six FFAs. FK506, an immunosuppressant which does not directly affect the MPT, but is a calcineurin inhibitor, also suppressed the I/R-evoked efflux of FFAs, but less effectively than CsA. Rapamycin, a derivative of FK506 which does not inhibit calcineurin, did not suppress I/R-evoked FFA efflux. Gossypol, a structurally unrelated inhibitor of calcineurin, was also effective, significantly reducing the efflux of docosahexaenoic, arachidonic and oleic acids. As previous experiments had implicated elevated Ca(2+) levels in the activation of phospholipases with FFA formation, agents affecting endoplasmic reticulum stores were also evaluated. Dantrolene, which blocks the ryanodine receptor (RyR) channel of the ER, significantly inhibited I/R-evoked release of docosahexaenoic, arachidonic, linoleic and oleic acids. Ryanodine, which can either accentuate or block Ca(2+) release, significantly enhanced ischemia/reperfusion-elicited efflux of linoleic acid, with non-significant increases in the efflux of myristic, arachidonic, palmitic and oleic acids. Xestospongin C, an inhibitor of the inositol triphosphate (IP(3)R) channel, failed to affect I/R-evoked FFA efflux. Thapsigargin, an inhibitor of the Ca(2+)-ATPase ER uptake pump, elicited significant elevations in the efflux of myristic, arachidonic and linoleic acids, in the absence of ischemia. Collectively, the data suggest an involvement of both ER and mitochondrial Ca(2+) stores in the chain of events which lead to PLA(2) activation and FFA formation.

FK506 binding protein 12 is expressed in rat penile innervation and upregulated after cavernous nerve injury

To evaluate whether FK506 and other immunophilin ligands may have potential therapeutic efficacy for erectile function preservation after penile nerve injury, we demonstrated localizations of the immunophilin FK506 binding protein 12 (FKBP 12) in intact and injured rat penile nerves and correlated these findings with localizations of neuronal nitric oxide synthase (nNOS), which neuronally forms nitric oxide for mediation of penile erection, in response to systemically administered FK506. Adult male Sprague-Dawley rats were subjected to unilateral right cavernous nerve forceps crush injury and administered FK506 (1 mg/kg i.p.) or saline at the same time and daily up to 7 days. At 1, 3 and 7 days after injury, bilateral cavernous nerves and major pelvic ganglia were collected for nNOS immunohistochemistry, FKBP 12 immunohistochemistry, and FKBP 12 in situ hybridisation. Protein expressions of nNOS and FKBP 12 were observed in major pelvic ganglion, cavernous nerve and nerve terminals within the rat penis as well as mRNA expression of FKBP 12 observed in the rat major pelvic ganglion neuronal cell bodies to a minimal extent at baseline conditions. After cavernous nerve injury, nNOS immunoreactivity was observed to be slightly diminished in ipsilateral penile nerve structures at only one day following injury while both FKBP 12 protein and mRNA expressions were observed to be increased at each interval of study. FK506 treatment did not affect staining of intact or injured nerves. Our demonstration that FKBP 12 is localized to penile innervation in the rat and becomes upregulated following cavernous nerve crush injury, independent of FK506 treatment, suggests that this immunophilin mediates a neurotrophic mechanism. Whether FK506 affords neuroprotection that preserves penile erection through FKBP 12 upregulation is unclear.

A small dose of the immunosuppressive agent FK506 (tacrolimus) protects peripheral nerve from ischemic fiber degeneration

The immunosuppressant agent FK506 (tacrolimus) has proven to be neuroprotective against brain ischemia, but there are no data on potential neuroprotective effects of FK506 in peripheral nerve ischemia. We examined the potential effects of two doses of FK506 in protecting peripheral nerve from ischemic fiber degeneration. Ischemia in the left sciatic nerve of the rat was produced by injecting 2 x 10(6) microspheres (14 microm) into the left femoral, hypogastric, and superior gluteal arteries in proportions of 47%, 37%, and 17%, respectively. After embolization, FK506 was injected into the left femoral, hypogastric, and superior gluteal arteries in doses of 9.4, 7.4, and 3.4 microg, respectively, for the high-dose group and 4.7, 3.7, and 1.7 microg, respectively, for the low-dose group. The control rats were injected with saline. FK506 treatment resulted in dramatic behavioral improvement in nerve function, in the number of functioning nerve fibers, and in the salvage of a majority of nerve fibers from ischemic fiber degeneration in a dose-dependent fashion. These results suggest that a small dose of FK506 protects peripheral nerve from ischemic fiber degeneration and that it may have potential in the treatment of ischemic neuropathy.

Neuroprotective effect of immunosuppressant FK506 in transient focal ischemia in rat: therapeutic time window for FK506 in transient focal ischemia

Tacrolimus (FK506), an immunosuppressant currently used in clinic, is known to have neuroprotective properties. However, effects in focal ischemia are shown only in a endothelin induced middle cerebral artery (MCA) occlusion model or with filament technique at a relatively high dose. We have previously shown that FK506 had significant protective effects at a low dose of 0.3 mg kg(-1) when administered immediately after ischemia. In this study, we explored the therapeutic time window of FK506 at this low dose, in a transient focal ischemia model using filament technique. Male Sprague-Dawley rats were subjected to 2 h MCA occlusion and subsequent reperfusion. They received FK506 or vehicle (0.3 mg kg(-1)) i.v. at 30, 60 or 120 min after induction of ischemia, and were decapitated 24 h after ischemia. FK506 injected at 30 and 60 min significantly reduced cortical infarction volume (FK506 vs. vehicle; 30 min: 95 +/- 33 mm3 vs. 170 +/- 62 mm3, p < 0.05; 60 min: 93 +/- 45 mm3, vs. 168 +/- 35 mm3, p < 0.05, respectively). FK506 was ineffective when given at 120 min after ischemia. FK506 had no effect on edema formation, nor on the infarct volume in striatum. The therapeutic time window for this low dose of FK506 given i.v. is between 60 and 120 min in this model.

Intravenously injected FK506 failed to inhibit hippocampal calcineurin

FK506 (tacrolimus) is known as an inhibitor for calcineurin and is used in numerous research fields. It is not clear whether intravenously injected FK506 inhibits neuronal calcineurin. We measured the calcineurin activities of normal and postischemic rat hippocampi after intravenous injection of FK506 (3 mg/kg). Intravenously injected FK506 had no inhibitory effect on calcineurin activity in the hippocampi of normal and postischemic rats, whereas FK506 inhibited the calcineurin in vitro (purified enzyme, hippocampal homogenate, and hippocampal slice culture homogenate). Thus, it is considered that intravenously injected FK506 does not act on intraneuronal calcineurin and that several effects of FK506 are not due to the inhibition of neuronal calcineurin.

The effects of FK506 on neurologic and histopathologic outcome after transient spinal cord ischemia induced by aortic cross-clamping in rats

Spinal cord injury is a devastating complication of thoracoabdominal aortic surgery. We investigated the effect of the immunosuppressant FK506, a macrolide antibiotic demonstrated to have neuroprotective effects in cerebral ischemia models, in a rat model of transient spinal cord ischemia. Spinal cord ischemia was induced in anesthetized rats by using direct aortic arch plus left subclavian artery cross-clamping through a limited thoracotomy. Experimental groups were as follows: sham-operation; control, receiving only vehicle; FK506 A, receiving FK506 (1 mg/kg IV) before clamping; and FK506 B, receiving FK506 (1 mg/kg IV) at the onset of reperfusion. Neurologic status was assessed at 24 h and then daily up to 96 h with a 0 to 6 scale (0, normal function; 6, severe paraplegia). Rats were randomly killed at 24, 48, or 96 h, and spinal cords were harvested for histopathology. Physiologic variables did not differ significantly among experimental groups. All control rats suffered severe and definitive paraplegia. FK506-treated rats had significantly better neurologic outcome compared with control. Histopathologic analysis disclosed severe injury in the lumbar gray matter of all control rats, whereas most FK506-treated rats had less injury. These data suggest that FK506 can improve neurologic recovery and attenuate spinal cord injury induced by transient thoracic aortic cross-clamping.

IMPLICATIONS

A single dose-injection of the immunosuppressant FK506 significantly improved neurologic outcome and attenuated spinal cord injury induced by transient thoracic aortic cross-clamping in the rat.

Effects of tacrolimus on hemispheric water content and cerebrospinal fluid levels of glutamate, hypoxanthine, interleukin-6, and tumor necrosis factor-α following controlled cortical impact injury in rats

Object. Disturbance of calcium homeostasis contributes to evolving tissue damage and energetic impairment following traumatic brain injury (TBI). Calcium-mediated activation of calcineurin results in production of tissue-damaging nitric oxide and free oxygen radicals. Inhibition of calcineurin induced by the immunosuppressant tacrolimus (FK506) has been shown to reduce structural and functional damage after ischemia. The aims of the present study were to investigate time- and dose-dependent short-term antiedematous effects of tacrolimus following TBI.

Methods. A left temporoparietal contusion (controlled cortical impact injury [CCII]) was induced in 51 male Sprague—Dawley rats. Tacrolimus (1 or 3 mg/kg body weight) was administered by a single intraperitoneal injection at 5 minutes, 30 minutes, or 4 hours after CCII occurred. Control rats received physiological saline. Water contents of traumatized and nontraumatized hemispheres, as well as cerebrospinal fluid (CSF) levels of mediators reflecting tissue damage (the proinflammatory cytokines interleukin [IL]-6 and tumor necrosis factor [TNF]—α, the excitotoxin glutamate, and the adenosine triphosphate—degradation product hypoxanthine), were determined 24 hours after trauma.

Although CSF levels of IL-6 and TNFα were completely suppressed by tacrolimus at all time points and at both concentrations, CSF levels of glutamate and hypoxanthine, as well as edema formation, were only marginally influenced. Significant reduction of cerebral water content was confined to nontraumatized hemispheres. In addition, the higher dose of tacrolimus failed to exert significant antiedematous effects on traumatized hemispheres.

Conclusions. Under the present study design, the potency of tacrolimus in reducing edema formation following CCII seems limited. However, its immunosuppressive effects could be of value in influencing the posttraumatic inflammatory response known to aggravate tissue damage.

Neuroimmunophilin ligand enhances neurite outgrowth and effect of fetal dopamine transplants

Neuroimmunophilin ligands have been shown to enhance neurite outgrowth in several neuronal systems in culture, including primary dopaminergic neurons from fetal ventral mesencephalon. We investigated the ability of neuroimmunophilin ligands to enhance outgrowth of transplanted fetal dopamine neurons in vivo. Rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal dopamine system were transplanted with rat embryonic day 14 ventral mesencephalon into the striatum, then treated orally with a neuroimmunophilin ligand (15mg/kg) or vehicle once per day for 14 days. All transplanted animals regained dopamine function over a 10 week behavioral test period, as indicated by decrease and reversal of amphetamine-induced rotation. In addition, neuroimmunophilin ligand-treated animals showed a more pronounced motor response during the first 10min after amphetamine injection, possibly reflecting increased striatal reinnervation or increased functional capacity. At post-mortem analyses, neuroimmunophilin ligand-treated rats showed a significantly higher density of tyrosine hydroxylase-positive fibers reinnervating the lesioned striatum, both immediately surrounding the transplant (92% of unlesioned density in neuroimmunophilin-treated rats vs 67% of unlesioned levels in vehicle-treated rats) and at some distance from the transplant/host interface. The number of tyrosine hydroxylase-positive cells within the transplants was not different between groups. This study demonstrates that short-term oral administration of a neuroimmunophilin ligand can enhance neurite outgrowth from fetal dopamine neuronal transplants.

Calcineurin-mediated BAD dephosphorylation activates the caspase-3 apoptotic cascade in traumatic spinal cord injury

We report here that activation of the caspase-3 apoptotic cascade in spinal cord injury is regulated, in part, by calcineurin-mediated BAD dephosphorylation. BAD, a proapoptotic member of the bcl-2 gene family, is rapidly dephosphorylated after injury, dissociates from 14-3-3 in the cytosol, and translocates to the mitochondria of neurons where it binds to Bcl-x(L). Pretreatment of animals with FK506, a potent inhibitor of calcineurin activity, or MK801, an NMDA glutamate receptor antagonist, blocked BAD dephosphorylation and abolished activation of the caspase-3 apoptotic cascade. These findings extend previous in vitro observations and are the first to implicate the involvement of glutamate-mediated calcineurin activation and BAD dephosphorylation as upstream, premitochondrial signaling events leading to caspase-3 activation in traumatic spinal cord injury.

Postischemic changes in the immunophilin FKBP12 in the rat brain

An immunosuppressant tacrolimus (FK506) protects against neuronal damage following cerebral ischemia. On the other hand, the major physiological role of the immunophilin FK506-binding protein-12 (FKBP12) is a modulation of intracellular calcium flux. Since an increase in intracellular calcium concentration is a major mediator of ischemic neuronal death, we investigated the changes in FKBP12 following cerebral ischemia in the rat. We induced focal cerebral ischemia by intraluminal occlusion of the middle cerebral artery for 1 h, and global cerebral ischemia for 10 min by bilateral carotid artery occlusion combined with hypotension. The animals were killed at 4 h to 7 days after reperfusion. Immunohistochemistry was performed on paraffin sections using a monoclonal antibody raised against recombinant FKBP12. Immunoreactivity to FKBP12 in control brains was most pronounced in the CA1 subfield of the hippocampus and the striatum, the localization being primarily neuronal. Following focal ischemia, FKBP12 immunoreactivity decreased rapidly in the ischemic core by 4 h, but increased in surviving neurons in penumbra areas (4 h-7 days). Within an area of infarction, invading leukocytes and macrophages exhibited immunoreactivity to FKBP12 (3-7 days). Following global ischemia, FKBP12 immunoreactivity in CA1 neurons decreased after 1 day, and then it was lost between 2 and 7 days, although many CA1 neurons showed a transient increase in FKBP12 at 2 days. No FKBP12 immunoreactivity was observed in reactive glial cells. Thus, FKBP12 declined in dying neurons, whereas FKBP12 was upregulated in less severely injured neurons. The findings suggest that (1) FKBP12 plays an important role in the process of neuronal survival and death following cerebral ischemia, and (2) FKBP12 is involved in inflammatory reactions that occur within an area of infarction.

Inhibition of neuronal nitric oxide synthase activity by 3-[2-[4-(3-chloro-2-methylphenyl)- 1-piperazinyl]ethyl]-5, 6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate (DY-9760e), a novel neuroprotective agent, in vitro and in cultured neuroblastoma cells in situ

DY-9760e, 3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5, 6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate, a novel calmodulin (CaM) antagonist, possesses neuroprotective activity. In the current study, we examined the effects of DY-9760e on nitric oxide synthase (NOS) activities in vitro and on calcium ionophore-induced NO production in situ. DY-9760e inhibited both neuronal NOS and endothelial NOS activities without affecting inducible NOS activity. It also inhibited purified neuronal NOS activity with a potency similar to that seen for purified CaM kinase II activity in vitro. Furthermore, DY-9760e significantly inhibited Ca(2+) ionophore (A23187)-induced NO production in mouse N1E-115 neuroblastoma cells, at a concentration of less than 1 microM. In contrast, no apparent inhibitory effect on Ca(2+)/CaM-dependent protein kinase II activity was observed in cultured hippocampal neurons up to 5 microM. These results suggest that the inhibitory effect of DY-9760e on CaM-dependent NOS activities underlies neuroprotective effects of the agent.

Mitochondria and neuronal survival

Mitochondria play a central role in the survival and death of neurons. The detailed bioenergetic mechanisms by which isolated mitochondria generate ATP, sequester Ca(2+), generate reactive oxygen species, and undergo Ca(2+)-dependent permeabilization of their inner membrane are currently being applied to the function of mitochondria in situ within neurons under physiological and pathophysiological conditions. Here we review the functional bioenergetics of isolated mitochondria, with emphasis on the chemiosmotic proton circuit and the application (and occasional misapplication) of these principles to intact neurons. Mitochondria play an integral role in both necrotic and apoptotic neuronal cell death, and the bioenergetic principles underlying current studies are reviewed.

Control of brain temperature during experimental global ischemia in rats

Temperature control during experimental ischemia continues to be of major interest. However, if exposure of brain tissue is necessary during the experiment, regional heat loss may occur even when the core temperature is maintained. Furthermore, valid non-invasive brain temperature monitoring is difficult in small rodents. This paper describes a method for both monitoring and maintenance of brain temperature during small animal preparations in a stereotaxic frame. The device used includes an ear-bar thermocouple probe and a small near-infrared radiator. The new equipment permitted to maintain peri-ischemic brain temperature at a desired level while carrying out non-invasive continuous recordings of cerebral blood flow (laser Doppler-flowmetry) and of electrical brain function (EEG). In contrast, without extracranial heat application, superficial and basal brain temperatures decreased during global cerebral ischemia by 4.1 +/- 0.1 and 4.6 +/- 0.4 degrees C (mean +/- SEM), respectively, returning to baseline values at 15-30 min of reperfusion while rectal (core) temperature remained stable at baseline values. The ear-bar thermocouple probe (tympanic membrane) reliably reflected basal brain temperature, and temperature in superficial brain areas correlated well with that in the temporal muscle. Our data show that the new system allows to exclude unwanted hypothermic neuroprotection, and does not interfere with optical and electrical measurement techniques.

FK506 and the role of the immunophilin FKBP-52 in nerve regeneration

In summary, FKBP-12 does not mediate the neurite outgrowth-promoting properties of neuroimmunophilin ligands (e.g., FK506). Instead, the neurotrophic properties of neuroimmunophilin ligands (FK506) and steroid hormones are mediated by disruption of steroid-receptor complexes. It remains unclear which component mediates neurite outgrowth, although the most likely candidates are FKBP-52, hsp-90, and p23 [42]. Regardless of the underlying mechanism involved, the FKBP-52 antibody data reveal that it should be possible to design, based on the structure of FK506, non-FKBP-12-binding (nonimmunosuppressant) compounds selective for FKBP-52 and test these new libraries for their ability to augment nerve regeneration. It may also be possible to exploit the structure of geldanamycin to develop a new class of hsp-90-binding compounds for use in nerve regeneration.

The effects of FK506 on dorsal column axons following spinal cord injury in adult rats: neuroprotection and local regeneration

There is considerable evidence that immunophilin ligands can promote the regeneration of axons in peripheral nerves and act as neuroprotective agents in the CNS. We have examined the effects of FK506 and GPI 1046 on the responses to partial transection of ascending spinal dorsal column axons at T9, in some cases combined with crush of one sciatic nerve. FK506 (0.5 or 2.0 mg/kg) and GPI 1046 (10 or 40 mg/kg) was administered subcutaneously immediately after surgery and five times a week thereafter. Some animals received methylprednisolone (MP) (two subcutaneous doses of 30 mg/kg) in addition to, or instead of, FK506. After survival times of 1-12 weeks, dorsal column axons were labeled transganglionically with cholera toxin B-HRP. There was massive axonal sprouting at the lesion sites in animals with sciatic nerve injury and immunophilin ligand treatment. In FK506-treated animals a few severed sensory axons regenerated for up to 10 mm rostral to the lesion. Of greater significance, 30% of 71 FK506-treated animals had spared axons in the dorsal column, extending to the nucleus gracilis, versus 8% of 50 control animals (P < 0.05), showing that FK506 reduces the likelihood of axonal destruction due to secondary injury. A combination of FK506 and MP afforded greater protection than MP alone (P < 0.05), but axonal survival was not affected by sciatic nerve crush, dose of FK506, or survival time after injury. GPI 1046 (n = 11) did not promote axonal survival. Thus FK506 protects axons from secondary injury following spinal cord trauma, and in this experimental model, its neuroprotective effect is greater than that of MP.

Activities of calcineurin and phosphatase 2A in the hippocampus after transient forebrain ischemia

We investigated the changes in the enzyme activity and immunoreactivity of calcineurin in the rat hippocampus after transient forebrain ischemia. Immediately after 20-min transient forebrain ischemia, calcineurin activity decreased to about 40% of the control in the CA1 region and to about 55% in other regions. Protein phosphatase 2A activity showed no remarkable changes. By 12 h after ischemia, calcineurin activity recovered, more in the CA1 region than in other regions. At 24 h it decreased again, but only in the CA1 region. Immunohistochemical- and immunoblot analyses showed no remarkable change in calcineurin in any region of the hippocampus within 12 h after ischemia. Thus, the activity of calcineurin is dissociated from its immunoreactivity and quantity. Several studies have suggested that unknown inhibitory factor(s) and/or reversible changes in calcineurin act to modify enzyme activity after ischemia. In contrast, phosphatase 2A activity underwent no obvious changes during the post-ischemia period we examined. This unique time course of calcineurin activity may contribute to the mechanism of ischemic neuronal injury.

Potential role of calcineurin for brain ischemia and traumatic injury

Calcineurin belongs to the family of Ca2+/calmodulin-dependent protein phosphatase, protein phosphatase 2B. Calcineurin is the only protein phosphatase which is regulated by a second messenger, Ca2+. Furthermore, calcineurin is highly localized in the central nervous system, especially in those neurons vulnerable to ischemic and traumatic insults. For these reasons, calcineurin is considered to play important roles in neuron-specific functions. Recently, on the basis of the finding that FK506 and cyclosporin A serve as calcineurin-specific inhibitors, this enzyme has become the subject of much study. It is clear that calcineurin is involved in many neuronal (or non-neuronal) functions such as neurotransmitter release, regulation of receptor functions, signal transduction systems, neurite outgrowth, gene expression and neuronal cell death. In this review, we describe the calcineurin functions, functions of the substrates, and the pathogenesis of traumatic and ischemic insults, and we discuss the potential role of calcineurin. There are many similarities in traumatic and ischemic pathogenesis of the brain in which the release of excessive glutamate is followed by an intracellular Ca2+ increase. However, the intracellular cascade which leads to neuronal cell death after the release of excess Ca2+ is unclear. Although calcineurin is thought to be a key toxic enzyme on the basis of studies using immunosuppressants (FK506 or cyclosporin A), many of the functions of the substrates for calcineurin protect against neuronal cell death. We concluded that calcineurin is a bi-directional enzyme for neuronal cell death, having protective and toxic actions, and the balance of the bi-directional effects may be important in ischemic and traumatic pathogenesis.

DY-9760e, a novel calmodulin antagonist, reduces brain damage induced by transient focal cerebral ischemia

Perturbations in Ca2+ homeostasis have been proposed to lead to neuronal damage after cerebral ischemia. DY-9760e (3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1- (4-imidazolylethyl)-1H-indazole dihydrochloride 3.5 hydrate) is a novel calmodulin antagonist. In this study, we examined the effects of DY-9760e on brain damage in rats subjected to transient (1 h) focal cerebral ischemia. DY-9760e (0.25-1.00 mg kg(-1) h(-1)) was intravenously infused for 6 h, starting 1 h after middle cerebral artery occlusion. Treatment with DY-9760e 0.25, 0.50 and 1.00 mg kg(-1) h(-1) reduced infarct volume by 30, 42 (P < 0.05), and 60% (P < 0.05), respectively. Furthermore, the effect of DY-9760e on ischemia-induced fodrin breakdown was examined in the same model. Pronounced fodrin breakdown was observed in the cerebral cortex and striatum at 24 h after ischemia. DY-9760e caused potent suppression of fodrin breakdown in the cerebral cortex at the same doses as those that had a protective action against cerebral infarction. From these results DY-9760e may have a therapeutic effect against cerebral ischemic damage in the acute stage.

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

Kainate is a potent agonist of an excitatory amino acid receptor subtype in the central nervous system, and causes neuronal death in several regions of the brain. Neurons are preferentially killed in the hippocampus, especially in the CA1 region, by systemic administration of kainate. It is speculated that functional alterations occur in the neurons preceding death. We examined the effect of FK506 on kainate-induced neuronal death and functional alterations in the rat hippocampal CA1 region. FK506 had no effect on electrographic and behavioral seizure activities induced by kainate; however, it prevented neuronal death measured seven days after administration. Although neither death nor morphological alterations of neurons were observed in the CA1 region 24 h after administration, the neurons exhibited decreased excitatory postsynaptic potentials and enhanced long-term potentiation. This functional alteration was not detected in the rats administered FK506 prior to kainate. Taken together, these observations indicate that functional alteration precedes neuronal death in rats systemically administered kainate and that FK506 prevents both. It is suggested that FK506 exerts its neuroprotective effect not by attenuating electrographic and behavioral seizure activities, but by protecting neurons from kainate-induced functional disorders.