Time window of infarct reduction by intravenous basic fibroblast growth factor in focal cerebral ischemia

SUN11602, a novel aniline compound, mimics the neuroprotective mechanisms of basic fibroblast growth factor

Basic fibroblast growth factor (bFGF) offers some measure of protection against excitotoxic neuronal injuries by upregulating the expression of the calcium-binding protein calbindin-D28k (Calb). The newly synthesized small molecule 4-({4-[[(4-amino-2,3,5,6-tetramethylanilino)acetyl](methyl)amino]-1-piperidinyl}methyl)benzamide (SUN11602) mimics the neuroprotective effects of bFGF, and thus, we examined how SUN11602 exerts its actions on neurons in toxic conditions of glutamate. In primary cultures of rat cerebrocortical neurons, SUN11602 and bFGF prevented glutamate-induced neuronal death. This neuroprotection, which occurred in association with the augmented phosphorylation of the bFGF receptor-1 (FGFR-1) and the extracellular signal-regulated kinase-1/2 (ERK-1/2), was abolished by pretreatment with PD166866 (a FGFR-1 tyrosine kinase-specific inhibitor) and PD98059 (a mitogen-activated protein kinase [MAPK]/[ERK-1/2] kinase [MEK] inhibitor). In addition, SUN11602 and bFGF increased the levels of CALB1 gene expression in cerebrocortical neurons. Whether this neuroprotection was linked to Calb was investigated with primary cultures of cerebrocortical neurons from homozygous knockout (Calb(-/-)) and wild-type (WT) mice. In WT mice, SUN11602 and bFGF increased the levels of newly synthesized Calb in cerebrocortical neurons and suppressed the glutamate-induced rise in intracellular Ca(2+). This Ca(2+)-capturing ability of Calb allowed the neurons to survive severe toxic conditions of glutamate. In contrast, Calb levels remained unchanged in Calb(-/-) mice after exposure to SUN11602 or bFGF, and due to a loss of function of the gene, these neurons were no longer resistant to toxic conditions of glutamate. These findings indicated that SUN11602 activated a number of cellular molecules (FGFR-1, MEK/ERK intermediates, and Calb) and consequently contributed to intracellular Ca(2+) homeostasis as observed in the case of bFGF.

Interactive effect of excitotoxic injury and dietary restriction on neurogenesis and neurotrophic factors in adult male rat brain

Dietary restriction (DR) is known to have potential health benefits including enhanced resistance of neurons to excitotoxic, oxidative and metabolic insults, cancer, stress, diabetes, reduced morbidity, and increased life span. In the present study, we examined the effect of DR (alternate day feeding regimen) on neurogenesis, expression of immature neuronal marker polysialic acid neural cell adhesion molecule (PSA-NCAM) and neurotrophic factors from different brain regions such as subventricular zone (SVZ), subgranular zone (SGZ) of hippocampus, median eminence arcuate (ME-ARC) region of hypothalamus, and piriform cortex (PIR) of adult male rats and further challenged ad libitum fed (AL) and DR rats with pilocarpine to induce excitotoxic injury. The quantitative analysis of bromodeoxyuridine (BrdU) labeling revealed a significant increase in the proliferation rate of neuronal progenitor cells from discrete brain regions in DR rats with and without pilocarpine induced seizures as compared to AL rats. DR significantly enhanced the expression of PSA-NCAM and neurotrophic factors, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3). There was a marked reduction in neuronal cell death in SVZ and PIR cortex after pilocarpine administration in DR rats. These results add to the accumulating evidence that DR may be an effective intervention to enhance the resistance of brain to excitotoxic injury.

Growth factors and stroke

Current options for the treatment of stroke are extremely limited, partly because of the rapidity with which brain cells die when deprived of their blood supply. Several recent studies suggest that growth factors can produce improvement in animal models of stroke, even when administered at postischemic intervals of many hours to days, when conventional neuroprotective approaches are typically futile. Several growth factors can access the brain after systemic administration, making them more attractive as therapeutic agents. Finally, growth factors are key mediators of neurogenesis in the adult brain, which could have a role in brain repair and functional recovery following stroke.

Influence of age on the response to fibroblast growth factor-2 treatment in a rat model of stroke

Basic fibroblast growth factor (FGF-2) has been reported to protect against ischemic injury in the brains of young adult rodents. However, little is known about whether FGF-2 retains this capability in the aged ischemic brain. Since stroke in human is much more common in older people than among younger adults, to address this question is clinically important. In this study, aged (24-month-old) rats were treated with intracerebroventricular infusion of FGF-2 or vehicle for 3 days, beginning 48 h before (pre-ischemia), 24 h after (early post-ischemia), or 96 h after (late post-ischemia) 60 min of middle cerebral artery occlusion, and were killed 10 days after ischemia. Aged rats given FGF-2 pre-ischemia showed better symmetry of movement and forepaw outstretching, and reduced infarct volumes, compared to rats treated with vehicle, but no significant improvement was found in aged rats given FGF-2 after focal ischemia. In contrast, young adult (3-month-old) rats treated with FGF-2 for 3 days beginning 24 h post-ischemia showed significant neurobehavioral improvement and better histological outcome. In addition, we also found that newborn neurons in the rostral subventricular zone (SVZ) were increased in aged rats treated with FGF-2 prior to ischemia. However, unlike in young adult ischemic rats, only a few of newly generated cells migrated into the damaged region in aged brain after focal ischemia. These findings point to differences in the response of aged versus young adult rats to FGF-2 in cerebral ischemia, and suggest that such differences need to be considered in the development of neuroprotective agents for stroke.

Exercise preconditioning ameliorates inflammatory injury in ischemic rats during reperfusion

There is evidence that physical activity is associated with decreased brain injury resulting from transient middle cerebral artery (MCA) occlusion. We investigated whether exercise could reduce stroke-induced brain inflammatory injury and its associated mediators. Sprague Dawley rats (3 months old) were subjected to 30 min exercise on a treadmill each day for 1-3 weeks. Stroke, in exercised and non-exercised animals, was then induced by a 2-h MCA occlusion followed by 48 h of reperfusion using an intraluminal filament. Endothelial expression of the intercellular adhesion molecule 1 (ICAM-1) and leukocyte infiltration were determined by immunocytochemistry. Expressions of tumor necrosis factor-alpha (TNF-alpha) and ICAM-1 mRNA were detected using a real-time reverse transcriptase-polymerase chain reaction in ischemic rats with or without exercise, and in non-ischemic control rats following exercise. Expression of TNF-alpha increased after exercise for 2 and 3 weeks. The overexpression of TNF-alpha was not further elevated in 3-week exercised rats subjected to a transient MCA occlusion and 6 or 12 h of reperfusion, as compared to that in non-exercised rats. Furthermore, ICAM-1 mRNA expression remained at significantly (P<0.01) low levels in exercised animals during ischemia/reperfusion. Pre-ischemic exercise significantly (P<0.01) reduced numbers of ICAM-1-positive vessels and infiltrating leukocytes in the frontoparietal cortex and dorsolateral striatum in ischemic rats after 48 h of reperfusion. Exercised ischemic rats demonstrated an 11+/-7% infarct volume of contralateral hemisphere as compared to a 52+/-3% volume in non-exercised ischemic rats. The data suggests that exercise inhibits inflammatory injury (i.e., decreased expression of inflammatory mediators and reduced accumulation of leukocytes) during reperfusion, leading to reduced brain damage. Chronically increased expression of TNF-alpha during exercise prevent the same downstream inflammatory events as does acutely elevated TNF-alpha after ischemia/reperfusion.

Exercise pre-conditioning reduces brain damage in ischemic rats that may be associated with regional angiogenesis and cellular overexpression of neurotrophin

There is increasing evidence that physical activity is associated with a decreased stroke risk. The purpose of this study was to determine if exercise could also reduce brain damage in rats subjected to transient middle cerebral artery (MCA) occlusion, and if the reduced brain injury is associated with angiogenesis as well as cellular expression of the nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) in regions supplied by the MCA. Adult male Sprague Dawley rats (n=36) exercised 30 min each day for 3 weeks on a treadmill on which repetitive locomotor movement was required. Then, stroke was induced by a 2-h MCA occlusion using an intraluminal filament, followed by 48 h of reperfusion. In addition to the two exercised groups of animals with or without MCA occlusion, there were two other groups of animals, with or without MCA occlusion, housed for the same duration and used as non-exercised controls. Brain damage in ischemic rats was evaluated by neurologic deficits and infarct volume. Exercise preconditioned and non-exercised brains were processed for immunocytochemistry to quantify the number of microvessels or NGF- and BDNF-labeled cells. Pre-ischemic motor activity significantly (P<0.01) reduced neurologic deficits and infarct volume in the frontoparietal cortex and dorsolateral striatum. Cellular expressions of NGF and BDNF were significantly (P<0.01) increased in cortex (neuron) and striatum (glia) of rats under the exercise condition. Significant (P<0.01) increases in microvessel density were found in striatum. Physical activity reduced stroke damage. The reduced brain damage may be attributable to angiogenesis and neurotrophin overexpression in brain regions supplied by the MCA following exercise.

Effect of Basic Fibroblast Growth Factor Treatment on Brain Progenitor Cells After Permanent Focal Ischemia in Rats

Background and Purpose— Intracisternal basic fibroblast growth factor (bFGF) enhances sensorimotor recovery after focal cerebral infarction in rats. One possible mechanism is stimulation of endogenous progenitor cells in brain. We investigated the effects of intracisternal bFGF on brain progenitor cells after stroke.

Methods— Proliferating brain cells were labeled with bromodeoxyuridine (BrdU) before middle cerebral artery (MCA) occlusion or sham surgery in rats. bFGF (0.5 μg) or vehicle was administered intracisternally at 24 and 48 hours after MCA occlusion, and rats were killed at 7, 14, or 21 days after stroke. Immunohistochemistry for BrdU and neuron- or astrocyte-specific markers was used to characterize progenitor cells and their progeny in the subventricular zone and dentate gyrus of the hippocampus.

Results— Infarct size did not differ among rats with or without bFGF treatment. MCA occlusion alone increased the number of BrdU-labeled cells in the ipsilateral subventricular zone at days 7 to 21, and there was a trend toward increased cell proliferation with bFGF treatment. In the dentate gyrus, the number of BrdU-labeled cells was increased bilaterally after MCA occlusion (peak at day 7). This increase was greater after bFGF treatment. In the subventricular zone, 30% of BrdU-labeled cells were immunopositive for the immature neuron-specific marker doublecortin at day 7, and their number declined to 2% at day 21. In the dentate gyrus, the majority of BrdU-labeled cells colabeled with doublecortin at day 7, becoming NeuN positive at day 21.

Conclusions— Stroke produces significant changes in progenitor cells in brain that are augmented by bFGF treatment.

Akt is a molecular target for signal transduction therapy in brain ischemic insult

Growth factors including insulin-like growth factor-1 (IGF-1) promote cell survival in ischemic brain injury. Stimulation of IGF-1 receptor coupled with tyrosine kinase activates phosphatidylinositol 3-kinase and subsequently, protein kinase B (Akt) in hippocampal neurons. Here we introduce a new approach of signal transduction therapy for brain damage occurring in ischemic insult. As has been shown for IGF-1, intracerebroventricular injection of sodium orthovanadate, a protein tyrosine phosphatase inhibitor, prior to ischemic insult blocked delayed neuronal death in the CA1 region. The neuroprotective effects of orthovanadate and IGF-1 were associated with an increased Akt activity in the CA1 region. We discuss here potential targets for Akt relevant to such neuroprotective activity. Our findings lead to the conclusion that Akt activity is a potential target for neuroprotective drugs in brain ischemic insult and other episodes of excitotoxic neuronal apoptosis such as seizure and Huntington's and Parkinson's diseases.

Effect of topically applied basic fibroblast growth factor on injured cochlear nerve

OBJECTIVE

Trauma-induced hearing loss after cerebellopontine angle manipulation has been regarded as having a hopeless natural course once it occurs. To challenge such a pessimistic view, we investigated whether pharmacological interventions with basic fibroblast growth factor (bFGF) could ameliorate trauma-induced cochlear nerve degeneration.

METHODS

The cerebellopontine angle portion of the cochlear nerve of rats was quantitatively compressed, and bFGF was topically administered for 2 weeks with a bFGF-soaked absorbable sponge and an osmotic minipump. The animals were killed 2 weeks after the compression procedure. The effect of bFGF in ameliorating cochlear neuronal death was evaluated from the residual number of spiral ganglion cells.

RESULTS

Cerebellopontine angle cisternal application of bFGF ameliorated cochlear nerve degeneration after the compression. Immunocytochemical studies of FGF receptors indicated that topically administered bFGF was internalized by a receptor-mediated mechanism through FGF receptor-1 and/or FGF receptor-2.

CONCLUSION

This report demonstrated that therapeutic application of bFGF was feasible to ameliorate trauma-induced cochlear nerve degeneration. Recent technological advances for deafened ears, such as cochlear implants and auditory brainstem implants, in combination with neurotrophic and/or growth factor therapeutic intervention, would be of great potential benefit for patients with hearing loss.

Postischemic administration of basic fibroblast growth factor improves sensorimotor function and reduces infarct size following permanent focal cerebral ischemia in the rat

Basic fibroblast growth factor (bFGF) is a polypeptide with potent trophic and protective effects on the brain. bFGF has been reported to exert neuroprotection against a wide variety of insults, including ischemic neuronal injury. To date, animal models of focal ischemia have not been translated to efficacy in stroke clinically with respect to testing of neuroprotective agents. Because functional outcome is the measurement of efficacy for putative neuroprotective agents in the clinic, we sought to evaluate the functional consequences of bFGF administration in rats subjected to focal ischemia. In this study, we assessed the effects of bFGF on functional outcome as well as infarct size in rats subjected to severe cerebral ischemia by permanent occlusion of the middle cerebral artery (MCAO). Male Sprague-Dawley rats were subjected to permanent MCAO by the intraluminal filament technique. Two hours following occlusion, rats were infused intravenously with either bFGF, at a dose of 150 microg/kg, or vehicle alone. Functional sensorimotor impairment, which was assessed by the accelerating rotarod test, was recorded at baseline and compared to performance assessed at 24 h after MCAO. Permanent occlusion of the MCA caused marked impairment in rotarod performance in both groups. Treatment of rats with bFGF showed a significant 46% improvement in rotarod fall latency when compared with that from the animals treated with vehicle alone. The volume of cortical infarction was significantly reduced by 32% as a function of bFGF treatment. These results suggest that the delayed intravenous administration of bFGF improves sensorimotor function as well as reduces infarct size following permanent focal ischemia in rat.

Acute administration of Ginkgo biloba extract (EGb 761) affords neuroprotection against permanent and transient focal cerebral ischemia in Sprague-Dawley rats

We examined the neuroprotective action of a standardized extract of Ginkgo biloba leaves (EGb 761) in permanent and transient middle cerebral artery (MCA) occlusion models in Sprague-Dawley rats. Forty-four animals were given either EGb 761 (50-200 mg/kg) or vehicle intraperitoneally, 1 hr before permanent MCA occlusion, to evaluate the dose-response effects. An additional 58 animals received EGb 761 (200 mg/kg) or vehicle, 0.5- 4 hr after permanent MCA occlusion, for establishing the therapeutic window. Delayed treatment was also employed in 110 animals treated with either EGb 761 (100-200 mg/kg) or vehicle at 2-3 hr following transient focal cerebral ischemia induced by MCA occlusion for 2 hr. Neurobehavioral scores were determined 22-24 hr after permanent MCA occlusion and either 3 or 7 days after transient MCA occlusion, and brain infarction volumes were measured upon sacrifice. Local cortical blood flow (LCBF) was serially measured in a subset of animals receiving EGb 761 (100-200 mg/kg) or vehicle, 0.5 hr and 2 hr after permanent and transient MCA occlusion, respectively. Relative to vehicle-treated controls, rats pretreated with EGb761 (100 and 200 mg/kg) had significantly reduced infarct volumes, by 36% and 49%, respectively, and improved sensory behavior (P < 0.05). Delayed treatment with EGb 761 also significantly reduced brain infarction, by 20-29% and 31%, when given up to 2 and 3 hr following transient and permanent MCA occlusion, respectively, whereas improved neurobehavioral scores were noted up to 2 hr after the onset of MCA occlusion (P < 0.05). LCBF was significantly improved in the ipsilateral cortex following the EGb 761 treatment, whereas a higher dose showed a more sustained effect. In conclusion, EGb 761 protected against transient and permanent focal cerebral ischemia and was effective after a prolonged reperfusion period even when therapy is delayed up to 2 hr. This neuroprotection may be at least partially attributed to the beneficial effects of selectively improved LCBF in the area at risk of infarction.

White matter injury after cerebral ischemia in ovine fetuses

The effects of cerebral ischemia on white matter changes in ovine fetuses were examined after exposure to bilateral carotid artery occlusion. Fetal sheep were exposed to 30 min of ischemia followed by 48 (I/R-48, n = 8) or 72 (I/R-72, n = 10) h of reperfusion or control sham treatment (control, n = 4). Serial coronal sections stained with Luxol fast blue/hematoxylin and eosin were scored for white matter, cerebral cortical, and hippocampal lesions. All areas received graded pathologic scores of 0 to 5, reflecting the degree of injury where 0 = 0%, 1 = 1% to 25%, 2 = 26% to 50%, 3 = 51% to 75%, 4 = 76% to 95%, and 5 = 96% to 100% of the area damaged. Dual-label immunofluorescence using antibodies against glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP) were used to characterize white matter lesions. Basic fibroblast growth factor (FGF-2) was measured in the frontal cortex by ELISA. Results of the pathologic scores showed that the white matter of the I/R-72 (2.74 +/- 0.53, mean +/- SEM) was more (p < 0.05) damaged when compared with the control (0.80 +/- 0.33) group. Cortical lesions were greater (p < 0.05) in the I/R-48 (2.12 +/- 0.35) than the control (0.93 +/- 0.09) group. White matter lesions were characterized by reactive GFAP-positive astrocytes and a loss of MBP in oligodendrocytes. The ratio of MBP to GFAP decreased (p < 0.05) as a function of ischemia, indicative of a proportionally greater loss of MBP than GFAP. FGF-2 concentrations were higher (p < 0.05) in the I/R-72 than the control group and there was a direct correlation between the pathologic scores (PS) and FGF-2 concentrations (FGF-2 = e((1.6 PS-0.90)) + 743, n = 17, r = 0.73, p < 0.001). We conclude that carotid artery occlusion results in quantifiable white matter lesions that are associated with a loss of MBP from myelin, and that FGF-2, a purported mediator of recovery from brain injury in adult subjects, increases in concentration in proportion to the severity of brain damage in the fetus.

Cerebral ischemia and trauma-different etiologies yet similar mechanisms: neuroprotective opportunities

Cerebral ischemia leads to brain damage caused by pathogenetic mechanisms that are also activated by neurotrauma. These mechanisms include among others excitotoxicity, over production of free radicals, inflammation and apoptosis. Furthermore, cerebral ischemia and trauma both trigger similar auto-protective mechanisms including the production of heat shock proteins, anti-inflammatory cytokines and endogenous antioxidants. Neuroprotective therapy aims at minimizing the activation of toxic pathways and at enhancing the activity of endogenous neuroprotective mechanisms. The similarities in the damage-producing and endogenous auto-protective mechanisms may imply that neuroprotective compounds found to be active against one of these conditions may indeed be also protective in the other. This review summarizes the pathogenetic events of ischemic and traumatic brain injury and reviews the neuroprotective strategies employed thus far in each of these conditions with a special emphasize on their clinical relevance and on future directions in the field of neuronal protection.

Enhanced neuroprotective effects of basic fibroblast growth factor in regional brain ischemia after conjugation to a blood-brain barrier delivery vector

Basic fibroblast growth factor (bFGF) has minimal pharmacological effects in the central nervous system in the absence of blood-brain barrier (BBB) disruption. BBB transport of bFGF occurs via an absorptive-mediated transcytosis mechanism, which is relatively inefficient. To enhance the BBB transport of bFGF, this neurotrophin was reformulated to enable receptor-mediated transport across the BBB via the transferrin receptor. bFGF was monobiotinylated and coupled to a BBB drug-delivery vector comprised of streptavidin (SA) and the OX26 monoclonal antibody to the rat transferrin receptor. The entire conjugate of biotinylated bFGF bound to the OX26-SA is designated bio-bFGF/OX26-SA. The bFGF retains receptor-binding affinity and has increased brain uptake following conjugation to OX26-SA. The bio-bFGF/OX26-SA conjugate protects cortical cell cultures against hypoxia/reoxygenation insult in a dose-dependent manner in vitro. A single intravenous injection of bio-bFGF/OX26-SA, equivalent to a dose of 25 microg/kg bFGF, produces an 80% reduction in infarct volume in the brain of rats subjected to permanent occlusion of the middle cerebral artery in parallel with a significant improvement of neurologic deficit. The neuroprotection is time-dependent, and there is a 67% reduction in stroke volume if the conjugate is administered at 60 min after arterial occlusion, whereas no significant reduction in stroke volume is observed if treatment is delayed 2 h. In conclusion, neuroprotection in regional brain ischemia is possible following the delayed intravenous injection of low doses of bFGF providing the neurotrophin is conjugated to a BBB drug-targeting system.

Environmental enrichment enhances recovery of function but exacerbates ischemic cell death

Prior exposure to brief 'conditioning' episodes of ischemia protects hippocampal CA1 neurons against a subsequent more severe ischemic insult. However, protected cells exhibit abnormal function and as survival times are extended this ischemic tolerance dissipates and cells begin to die. In this study, we sought to determine whether environmental enrichment could alter the above pattern of delayed cell death and functional impairment in a gerbil model of ischemic tolerance. Gerbils received either ischemic preconditioning, 5 min of ischemia without preconditioning or sham surgery. Three days after ischemia, gerbils were placed in either an enriched environment or standard laboratory housing. Open field habituation was assessed 3, 7, 10, 30 and 60 days after ischemia. Subsequently, animals were trained in two versions (win-shift and win-stay) of a T-maze task. Following behavioral testing, extracellular CA1 field potential amplitudes and CA1 cell counts were determined. Initial open field activity was significantly higher in all experimental groups compared to sham animals (P<0.001). By 60 days, enriched ischemic preconditioned and enriched ischemic gerbils were not different than shams whereas non-enriched, ischemic preconditioned and ischemic gerbils continued to have higher activity scores (P<0.05). Preconditioned and enriched ischemic animals learned the win-shift T-maze problem as quickly as shams while non-enriched ischemic gerbils were severely impaired compared with all other groups (P<0.001). Only the sham and enriched preconditioned groups readily acquired the win-stay paradigm. CA1 field potential amplitudes were lower (P<0.05) in ischemic than sham gerbils irrespective of treatment. Surprisingly, CA1 cell counts were significantly lower (P<0.01) in enriched versus non-enriched ischemic preconditioned animals. These data demonstrate that early, intensive intervention after ischemia can improve functional outcome but that this is accompanied by increased brain damage. Careful consideration needs to be given to the timing of rehabilitation after stroke and related types of brain injury.

Fibroblast growth factor-2 induces astroglial and microglial reactivity in vivo

A role for fibroblast growth factor-2 (FGF-2) has been proposed in mediating the glial response to injury in the central nervous system (CNS). We have tested this possibility in vivo, by injecting FGF-2 into the cerebrospinal fluid (CSF) of the brain ventricles of young rats and analysing glial cells in the anterior medullary velum (AMV), which partly roofs the IVth ventricle. FGF-2 was administered at two different doses, low FGF-2 (500 ng mL(-1) CSF) and high FGF-2 (10 microg mL(-1) CSF), and saline vehicle was injected in controls. Injections were performed twice daily for three days, commencing at postnatal day (P) 6, and AMV were analysed at P9, using immunohistochemistry and Western blotting. Glial cells were unaffected by treatment with saline or low FGF-2, whereas high FGF-2 induced reactive changes in glial cell types: (1) there was increased GFAP expression in astrocytes, demonstrated by Western blot and immunohistochemistry, and astrocytes appeared hypertrophic, with increased process thickness and number; (2) the number of ED1 labelled microglia/macrophages was doubled, from 47 +/- 6 to 114 +/- 17 cells per field (0.75 mm2; values are mean +/- SEM), and microglia appeared activated, with a multipolar and granular appearance; (3) NG2 positive glial cells appeared more fibrous and there was increased density of processes, although there was no significant increase in their number; (4) oligodendrocyte somata were enlarged and there was a loss of myelin sheaths. The results show that at high CSF titres of FGF-2 induce glial reactivity in vivo and support a role for FGF-2 in the pathology of CNS injury and EAE.

Delayed multidose treatment with nicotinamide extends the degree and duration of neuroprotection by reducing infarction and improving behavioral scores up to two weeks following transient focal cerebral ischemia in Wistar rats

A single, delayed dose of nicotinamide (NAm) was shown to be protective against focal cerebral ischemia in rats, but the protection was limited to three to seven days following stroke. The investigation reported here was conducted to examine if the use of multiple doses of NAm, administered after the onset of focal cerebral ischemia, would extend the duration of neuroprotection compared with a single dose treatment regimen. Male Wistar rats were subjected to transient focal cerebral ischemia by occluding the right middle cerebral artery (MCAo) for two hours. Following MCAo, motor and sensory behavioral tests were performed daily and the cerebral infarct volumes were measured at two weeks after sacrifice. Each animal was placed into one of four groups that received either normal saline alone (Group S), one (Group A), two (Group B), or three (Group C) doses of NAm (500 mg/kg). Each animal, therefore, received three treatments over two weeks, with the first dose administered intravenously two hours after the onset of MCAo. Single and multiple doses of NAm reduced the infarction (p < 0.01) and improved (p < 0.05) the neurologic sensory and motor behavior when compared with the saline-treated animals up to two weeks after stroke. Moreover, animals that received multiple doses of NAm recuperated full motor function not different from normal, preoperative motor behavior. Delayed treatment with NAm given as multiple doses, therefore, further enhances the extent and duration of neuroprotection by significantly reducing cerebral infarct volumes, improving neurologic behavioral scores, and confers a complete motor recovery up to two weeks from the onset of focal cerebral ischemia in Wistar rats.

The temporal patterns of c-Fos and basic fibroblast growth factor expression following a unilateral anteromedial cortex lesion

Following a unilateral anteromedial cortex lesion, a critical period of 12 h to 6 days exists during which the recovery process is exquisitely vulnerable to manipulation. Certain anti-convulsant drugs, as well as convulsive seizures impede recovery when administered during, but not after, the critical period. The mechanisms underlying these behavioral phenomena have not been delineated. Thus, the present study was designed to determine potential mechanisms underlying and responsible for the critical period. To this end, we measured the immunoreactivity of two important markers of the post-injury response cascade, c-Fos and bFGF, at designated times after a unilateral anteromedial cortex lesion. These temporal patterns of expression in the perilesional cortex and ipsilateral dorsal striatum were mapped onto functional recovery patterns. Within the critical period, c-Fos was dramatically elevated through 48 h after the lesion, while bFGF peaked later, on day 6. Upregulation of these markers preceded recovery from somatosensory deficits, which was most dramatic after post-operative day 9 and complete by day 23. Early post-lesion expression of c-Fos may contribute to lesion-induced bFGF expression, which through its neurotrophic properties could be responsible for subsequent functional recovery. Gaining a similar understanding of the critical period following human traumatic brain injury could be an important first step toward improved treatment strategies and neurobehavioral outcome.

Intravenous basic fibroblast growth factor produces a persistent reduction in infarct volume following permanent focal ischemia in rats

Basic fibroblast growth factor (bFGF) is a polypeptide with potent survival-promoting and protective effects on brain cells. In previous studies, we showed that intravenous administration of bFGF reduced infarct volume in models of focal cerebral ischemia in rats, mice, and cats. In these previous studies, infarct volume was measured within 1-7days of the onset of ischemia. The current study was undertaken to determine whether the reduction in infarct volume by bFGF was persistent beyond the first week after stroke. Mature male Sprague-Dawley rats received an intravenous infusion of bFGF (50 microg/kg per h) or vehicle during 0.5-3.5h after permanent proximal middle cerebral artery occlusion. We found a 27% reduction in infarct volume in bFGF- compared to vehicle-treated animals at three months after infarction (P<0.05). The data show that intravenous bFGF treatment produces a persistent reduction in infarct volume, at least up to three months following focal stroke.

Intravenous basic fibroblast growth factor (bFGF) decreases DNA fragmentation and prevents downregulation of Bcl-2 expression in the ischemic brain following middle cerebral artery occlusion in rats

In previous studies, we showed that basic fibroblast growth factor (bFGF) reduced infarct volume when infused intravenously in animal models of focal cerebral ischemia. In the current study, we examined the potential mechanism of infarct reduction by bFGF, especially effects on apoptosis within the ischemic brain. We found that bFGF decreased DNA fragmentation in the ischemic hemisphere, as assessed by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) histochemical methods combined with morphological criteria. bFGF also prevented reduction of immunoreactivity of the anti-apoptotic protein Bcl-2 in the ischemic hemisphere, but did not alter immunoreactivity of the pro-apoptotic proteins Bax, Caspase-1, or Caspase-3. These changes in TUNEL histochemistry and Bcl-2 immunoreactivity were especially prominent in cortex at the borders ('penumbra') of infarcts, spared by bFGF treatment. We conclude that the infarct-reducing effects of bFGF may be due, in part, to prevention of downregulation of Bcl-2 expression and decreased apoptosis in the ischemic brain.

Brain-derived neurotrophic factor mediates an excitoprotective effect of dietary restriction in mice

Dietary restriction (DR; reduced calorie intake) increases the lifespan of rodents and increases their resistance to cancer, diabetes and other age-related diseases. DR also exerts beneficial effects on the brain including enhanced learning and memory and increased resistance of neurons to excitotoxic, oxidative and metabolic insults. The mechanisms underlying the effects of DR on neuronal plasticity and survival are unknown. In the present study we show that levels of brain-derived neurotrophic factor (BDNF) are significantly increased in the hippocampus, cerebral cortex and striatum of mice maintained on an alternate day feeding DR regimen compared to animals fed ad libitum. Damage to hippocampal neurons induced by the excitotoxin kainic acid was significantly reduced in mice maintained on DR, and this neuroprotective effect was attenuated by intraventricular administration of a BDNF-blocking antibody. Our findings show that simply reducing food intake results in increased levels of BDNF in brain cells, and suggest that the resulting activation of BDNF signaling pathways plays a key role in the neuroprotective effect of DR. These results bolster accumulating evidence that DR may be an effective approach for increasing the resistance of the brain to damage and enhancing brain neuronal plasticity.

Neovascularization with blood-brain barrier breakdown in delayed neuronal death

Various kinds of acute pathological events in the central nervous system, such as ischemia, hemorrhage, and trauma, often cause brain edema. The edema may advance for days or weeks while inducing extensive damage in neural function, regardless of the extent of the original damage, and often results in death. Delayed edema is thought to be vasogenic; however, the mechanism underlying edema induction remains unknown. We found delayed vascular cell proliferation with a blood-brain barrier breakdown in and around the gerbil CA1 hippocampus, a region known to be involved in delayed apoptotic neuronal death 2-6 days after transient ischemia. Vascular cell proliferation, assessed by (3)H-thymidine incorporation, was most prominent 4-6 days after ischemia, and extravasation of exogenously applied dye or endogenous serum albumin from blood vessels was observed concomitantly. We propose neovascularization in delayed neuronal death as a cause of brain edema advancing days after neurological events.

Time window of intracisternal osteogenic protein-1 in enhancing functional recovery after stroke

Osteogenic protein-1 (OP-1, BMP-7) is a member of the bone morphogenetic protein subfamily of the TGF-ss superfamily that selectively stimulates dendritic neuronal outgrowth. In previous studies, we found that the intracisternal injection of OP-1, starting at one day after stroke, enhanced sensorimotor recovery of the contralateral limbs following unilateral cerebral infarction in rats. In the current study, we further explored the time window during which intracisternal OP-1 enhances sensorimotor recovery, as assessed by limb placing tests. We found that intracisternal OP-1 (10 microg) given 1 and 3 days, or 3 and 5 days, but not 7 and 9 days after stroke, significantly enhanced recovery of forelimb and hindlimb placing. There was no difference in infarct volume between vehicle- and OP-1-treated animals. The mechanism of OP-1 action might be stimulation of new dendritic sprouting in the remaining uninjured brain.

Delayed treatment with AM-36, a novel neuroprotective agent, reduces neuronal damage after endothelin-1-induced middle cerebral artery occlusion in conscious rats

BACKGROUND AND PURPOSE

AM-36 is a novel arylalkylpiperazine with combined antioxidant and Na(+) channel blocking actions. Individually, these properties have been shown to confer neuroprotection in a variety of in vitro and in vivo animal models of stroke. Preliminary studies have shown that AM-36 is neuroprotective in vivo. The purpose of the present study was to assess the neuroprotective and behavioral outcome after delayed administration of AM-36 in an endothelin-1-induced, middle cerebral artery model of cerebral ischemia in conscious rats.

METHODS

Conscious male hooded Wistar rats were subjected to middle cerebral artery occlusion by perivascular microinjection of endothelin-1 via a previously implanted cannula. AM-36 (6 mg/kg IP) or vehicle was administered intraperitoneally 30, 60, or 180 minutes after middle cerebral artery occlusion. Functional outcome was determined 24, 48, and 72 hours after stroke by neurological deficit score, motor performance, and sensory hemineglect tests. Rats were killed at 72 hours, and infarct area and volume were determined by histology and computerized image analysis.

RESULTS

Endothelin-1-induced middle cerebral artery occlusion resulted in marked functional deficits and neuronal damage. AM-36 significantly reduced cortical damage when administration was delayed until 30, 60, or 180 minutes after stroke. Interestingly, neuronal damage was time-dependently reduced, with the greatest protection found when AM-36 was administered 180 minutes after stroke. Striatal damage was significantly reduced after treatment with AM-36 at 180 minutes after stroke. Functional outcome paralleled histopathology. Rota-rod performance, sensory hemineglect, and neurological deficit scores returned to preischemia levels in AM-36-treated rats by 72 hours after stroke when administration was delayed by 180 minutes after stroke.

CONCLUSIONS

AM-36 potently protects against both neuronal damage and functional deficits even when administered up to 180 minutes after induction of stroke. In fact, the greatest protection was found when administration was delayed by 180 minutes after stroke. The possible mechanisms of action of AM-36 are discussed. The present findings suggest that AM-36 may have great promise in the acute treatment of human stroke.

Roles of p53, c-Myc, Bcl-2, Bax and caspases in serum deprivation-induced neuronal apoptosis: a possible neuroprotective mechanism of basic fibroblast growth factor

Using flow cytometric analysis, we examined the temporal changes of p53, c-Myc, Bcl-2, Bax expression in rat primary cortex neurons after serum deprivation. Activities of caspase-1 and caspase-3 were also measured. Serum deprivation induced apoptosis accompanied by a rapid down-regulation of p53, Bcl-2 and an up-regulation of c-Myc, Bax and caspase-3 activity. Pretreatment with basic fibroblast growth factor prevented the apoptosis with an attenuation of the changes of p53, Bcl-2, Bax levels and caspase-3 activity but had no effect on the change of c-Myc level. These results suggest that serum deprivation induces apoptosis through a signaling pathway involving p53, Bcl-2, Bax, c-Myc and caspase-3. The effect of the basic fibroblast growth factor against apoptosis may result from its capability of blocking the apoptosis cascade.

Increased expression and nuclear accumulation of basic fibroblast growth factor in primary cultured astrocytes following ischemic-like insults

Basic fibroblast growth factor (bFGF) is a biological active polypeptide with potent trophic effects on neurons, glia and endothelial cells. In the present study, we examined the temporal expression profile of bFGF protein in cultured cortical astrocytes under ischemic-like conditions such as serum-free, glucose-free or glutamate application. A peak increase of bFGF level was observed at 24 h after the initiation of insults. A striking increase in the bFGF immunoreactivity and a moderate increase in the fibroblast growth factor receptor-1 (FGFR-1) immunoreactivity were also found in the astrocytes treated with serum- or glucose-deprivation or glutamate. The increased bFGF immunoreactivity and FGFR-1 immunoreactivity were mainly accumulated in the nuclei of astrocytes. The results suggest that the expression of bFGF and FGFR-1 in the astrocytes, especially in the nuclear interior, can be up-regulated under ischemic-like conditions and that the up-regulation of bFGF and FGFR-1 may play an important role in the maintenance and repair of the central nervous system (CNS) after ischemia.

Roles of p53, c-Myc, Bcl-2, Bax and caspases in glutamate-induced neuronal apoptosis and the possible neuroprotective mechanism of basic fibroblast growth factor

By using flow-cytometric analysis, we examined the involvement of p53, c-Myc, Bcl-2 and Bax in the glutamate-induced cell death in cultured cortical neurons. The activities of caspase-1-like and caspase-3-like proteases were also measured after the glutamate treatment. The apoptosis rate of the cells increased after 12 h and 24 h treatment with glutamate. The temporal profile of p53, c-Myc, Bcl-2, Bax expression and caspases activation after glutamate treatment suggest that Bcl-2, c-Myc and caspase-3 play important roles in the excitotoxic neuronal cell death. The down-regulation of Bcl-2 may be an important early stage event, which may cause the activation of caspase-3. c-Myc is also involved in the process of apoptosis though its precise role remains elusive. bFGF exhibited the capability to antagonize the neuronal apoptosis caused by glutamate. The antiapoptotic potential of bFGF may result from its attenuating effect on the down-regulation of Bcl-2 induced by glutamate and, subsequently, blockade of apoptosis cascade. This may provide a possible explanation for its neuroprotective effect against ischemic cell death.

Intracisternal antisense oligonucleotide to growth associated protein-43 blocks the recovery-promoting effects of basic fibroblast growth factor after focal stroke

Focal infarction (stroke) of the lateral cerebral cortex of rats (including the sensorimotor cortex) produces deficits in sensorimotor function of the contralateral limbs that recover partially over time. In previous studies, we found that the intracisternal injection of basic fibroblast growth factor (bFGF), a potent neurotrophic growth factor, starting at 1 day after stroke, significantly enhanced recovery of sensorimotor function of the contralateral forelimb and hindlimb. Moreover, immunoreactivity (IR) for growth-associated protein-43 (GAP-43), a molecular marker of new axonal growth, was increased in the intact contralateral sensorimotor cortex following bFGF treatment. In the current study, we found that the intracisternal administration of antisense, but not missense, oligonucleotide to GAP-43 blocked the recovery-enhancing effects of bFGF and blocked the increase in GAP-43 IR in the contralateral cortex. These results suggest that upregulation of GAP-43 expression and consequent enhanced axonal sprouting in intact uninjured parts of the brain are likely mechanisms for the recovery-promoting effects of bFGF.

Protective effect of acidic fibroblast growth factor against ischemia-induced learning and memory deficits in two tasks in gerbils

The influence of transient forebrain ischemia on behavioral performance, and the effect of intracerebroventricular (i.c.v.) injection of acidic fibroblast growth factor (aFGF) on such ischemia-induced deficits were examined in Mongolian gerbils by assessing learning and memory in two tasks: passive avoidance and Morris water maze. A 5-min period of forebrain ischemia led to learning and memory deficits in both tasks, and also to neuronal death in the hippocampal CA1 region. Continuous i.c.v. infusion of aFGF bilaterally into the lateral ventricules by osmotic minipumps over 2 days before, and 5 days after the ischemia (a total of 3.6 microg/gerbil) largely prevented both the ischemia-induced behavioral deficits and the neuronal death in the hippocampus. These observations suggest that the hippocampus is a critical site for the performance of the two tasks, and that aFGF has a protective effect against such ischemia-induced learning and memory deficits in gerbils.

Synergistic effects of a combination of low-dose basic fibroblast growth factor and citicoline after temporary experimental focal ischemia

BACKGROUND AND PURPOSE

Basic fibroblast growth factor (bFGF) and citicoline (cytidine 5'-diphosphate choline, an endogenous compound that stabilizes membrane function) have demonstrated neuroprotective effects after focal cerebral ischemia. Both agents are candidates for future stroke therapy in humans. For evaluation of synergistic effects of bFGF and citicoline, a low-dose combination of both compounds was tested against each compound alone and placebo.

METHODS

Four groups of Sprague-Dawley rats (n=12 per group) underwent 90 minutes of focal cerebral ischemia with the use of the suture model of middle cerebral artery occlusion. Animals were randomly and blindly assigned to one of the following treatment groups: placebo, low-dose citicoline (250 mg/kg IP daily for 4 days), low-dose bFGF (10 microg/kg per hour IV for 3 hours), and the combination of both (250 mg/kg citicoline and 10 microg/kg per hour bFGF). Triphenyltetrazolium chloride staining was used after 4 days to determine postmortem infarction. Neurological scores were assessed on a daily basis.

RESULTS

The premature mortality rate was 41.7% in the placebo and citicoline groups, 33.3% in the bFGF group, and 25% (P=NS) in the combination group. The mean neurological score on day 4 was 3.1+/-1.6 (placebo), 3.1+/-1.6 (citicoline), 2.9+/-1.5 (bFGF), and 2.4+/-1.4 (combination) (P=NS). The mean volume of infarction was significantly reduced in the combination group (136. 5+/-25.4 mm3) versus placebo (172.6+/-48.9 mm3; P=0.036, Fisher test), versus citicoline alone (186.0+/-35.7 mm3; P=0.005, Fisher test), and versus bFGF alone (176.0+/-49.2 mm3; P=0.023, Fisher test).

CONCLUSIONS

These results demonstrate synergistic effects of a low-dose combination of the growth factor bFGF and citicoline after temporary experimental focal cerebral ischemia and furthermore support the effectiveness of a combination treatment regimen for the management of acute stroke.

Nicotinamide reduces infarction up to two hours after the onset of permanent focal cerebral ischemia in Wistar rats

Ischemia depletes ATP and initiates cascades leading to irreversible tissue injury. Nicotinamide is a precursor of nicotinamide adenine dinucleotide (NAD+) which increases neuronal ATP concentration and protects against malonate-induced neurotoxicity, trauma and nitric oxide toxicity. We therefore examined whether nicotinamide could protect against stroke, using a model of permanent middle cerebral artery occlusion (MCA) occlusion in Wistar rats. Nicotinamide reduced neuronal infarction in a dose-specific manner. Furthermore, nicotinamide (500 mg/kg) reduced infarcts when administered up to 2 h after the onset of permanent MCA occlusion. The mechanism of action underlying the neuroprotection observed with nicotinamide remains to be clarified. These results are potentially important since nicotinamide is already used clinically, though not in the treatment of stroke.

Six-hour window of opportunity for calpain inhibition in focal cerebral ischemia in rats

BACKGROUND AND PURPOSE

Stroke patients often experience a significant temporal delay between the onset of ischemia and the time to initiation of therapy. Thus, there is a need for neuroprotectants with a long therapeutic window of opportunity. The efficacy of a potent, central nervous system-penetrating calpain inhibitor (MDL 28,170) was evaluated in a temporary model of focal cerebral ischemia to determine the window of opportunity for intracellular protease inhibition.

METHODS

An ex vivo brain protease inhibition assay established pharmacodynamic dosing parameters for MDL 28,170. Middle cerebral artery (MCA) occlusion was accomplished by advancing a monofilament through the internal carotid artery to the origin of the MCA. Postmortem infarct volumes were determined by quantitative image analysis of triphenyltetrazolium-stained brain sections.

RESULTS

Maximal inhibition of brain protease activity was observed 30 minutes after injection of MDL 28,170 with an estimated pharmacodynamic half-life of 2 hours. MDL 28,170 caused a dose-dependent reduction in infarct volume when administered 30 minutes after MCA occlusion. A window of opportunity study was conducted to determine the maximal delay between the onset of ischemia and the initiation of efficacious therapy. MDL 28,170 reduced infarct volume when therapy was delayed for 0.5, 3, 4, and 6 hours after the initiation of ischemia. The protective effect of MDL 28,170 was lost after an 8-hour delay.

CONCLUSIONS

These data indicate that the therapeutic window of opportunity for calpain inhibition is at least 6 hours in a reversible focal cerebral ischemia model. This protection is observed despite the lethal hypoxic and excitotoxic challenge, suggesting that calpain activation may be an obligatory, downstream event in the ischemic cell death cascade.