Basic fibroblast growth factor increases regional cerebral blood flow and reduces infarct size after experimental ischemia in a rat model

Modified CFBP-bFGF targeting to ischemic brain promoted the functional recovery of cerebral ischemia

The cerebral ischemia was one of the most common causes of disability and death worldwide. Basic fibroblast growth factor (bFGF) was reported to have neuroprotective function as well as promoting angiogenesis in the ischemic brain, but the targeting delivery of bFGF to ischemic brain was still difficult. In present study, a specific peptide was used to modify bFGF to construct recombinant CFBP-bFGF, and CFBP-bFGF could specifically deliver to ischemic brain through binding with the upregulated protein-connective tissue growth factor (CTGF). When CFBP-bFGF was used in rats with cerebral ischemia by intravenous injection, local concentration of the bFGF in ischemic brain was significantly increased. In addition, enhanced neurons survival, increased angiogenesis, decreased neuroinflammation were observed, that improved the motor functional recovery of cerebral ischemic injury. These results demonstrated that the targeting delivery of CFBP-bFGF would be a potential therapeutic approach for cerebral ischemia.

Bone marrow mesenchymal stem cells repair the hippocampal neurons and increase the expression of IGF-1 after cardiac arrest in rats

The present study aimed to investigate the beneficial effects and underlying mechanisms of bone marrow mesenchymal stem cells (BMSCs) on global ischemic hypoxic brain injury. Cells collected from the femurs and tibias of male Sprague Dawley rats were used to generate BMSCs following three culture passages. A rate model of cardiac arrest (CA) was induced by asphyxia. One hour following return of spontaneous circulation (ROSC), BMSCs were transplanted through injection into the tail vein. Neurological status was assessed using modified neurological severity score (mNSS) tests 1, 3 and 7 days following ROSC. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and immunohistochemical staining were used to detect insulin-like growth factor 1 (IGF-1) expression in the hippocampus. Furthermore, double-fluorescent labeling of green fluorescent protein (GFP) and IGF-1 was used to detect the IGF-1 expression in transplanted BMSCs. Serum levels of protein S100-B were examined using ELISA. GFP-labeled BMSCs were observed in the hippocampus at 1, 3 and 7 days post transplantation through fluorescent microscopy. BMSC transplantation resulted in reduced protein S100-B levels. The mNSS of the BMSC-treatment group was significantly reduced compared with that of the CA group. The RT-qPCR analysis and immunohistochemistry results demonstrated that BMSC treatment significantly increased IGF-1 expression in the hippocampus. In addition, the double-fluorescent labeling results demonstrated that transplanted BMSCs expressed IGF-1 in the hippocampus. The results of the present study suggest that BMSC treatment promotes the recovery of cerebral function following CA in rats possibly through the secretion of IGF-1.

■ REVIEW : Basic Fibroblast Growth Factor: A Treatment for stroke?

Basic fibroblast growth factor (bFGF) is a polypeptide with potent trophic effects on brain cells. In particular, bFGF promotes the survival and outgrowth of brain neurons, and protects neurons against toxic processes that are important contributors to cell death after cerebral ischemia (stroke). Recent studies in animal models have suggested two potential uses of exogenously administered bFGF for the treatment of stroke: 1) intra venous bFGF to reduce infarct size in acute stroke, and 2) intracisternal bFGF to enhance neurological recovery in chronic stroke. Human clinical trials of the first of these applications are currently in progress. NEUROSCIENTIST 3:247-250,1997

Role of vascular endothelial growth factor and other growth factors in post-stroke recovery

Stroke is a major health problem world-wide and its burden has been rising in last few decades. Until now tissue plasminogen activator is only approved treatment for stroke. Angiogenesis plays a vital role for striatal neurogenesis after stroke. Administration of various growth factors in an early post ischemic phase, stimulate both angiogenesis and neurogenesis and lead to improved functional recovery after stroke. However vascular endothelial growth factors (VEGF) is the most potent angiogenic factor for neurovascularization and neurogenesis in ischemic injury can be modulated in different ways and thus can be used as therapy in stroke. In response to the ischemic injury VEGF is released by endothelial cells through natural mechanism and leads to angiogenesis and vascularization. This release can also be up regulated by exogenous administration of Mesenchymal stem cells, by various physical therapy regimes and electroacupuncture, which further potentiate the efficacy of VEGF as therapy in post stroke recovery. Recent published literature was searched using PubMed and Google for the article reporting on methods of up regulation of VEGF and therapeutic potential of growth factors in stroke.

Propofol increases expression of basic fibroblast growth factor after transient cerebral ischemia in rats

Anesthetics such as propofol can provide neuroprotective effects against cerebral ischemia. However, the underlying mechanism of this beneficial effect is not clear. Therefore, we subjected male Sprague-Dawley rats to 2 h of middle cerebral artery occlusion and investigated how post-ischemic administration of propofol affected neurologic outcome and the expression of basic fibroblast growth factor (bFGF). After 2 h of ischemia, just before reperfusion, the animals were randomly assigned to receive either propofol (20 mg kg(-1) h(-1)) or vehicle (10 % intralipid, 2 ml kg(-1) h(-1)) intravenously for 4 h. Neurologic scores, infarct volume, and brain water content were measured at different time points after reperfusion. mRNA level of bFGF was measured by real-time PCR, and the protein expression level of bFGF was analyzed by immunohistochemistry and Western blot. At 6, 24, 72 h, and 7 days of reperfusion, infarct volume was significantly reduced in the propofol-treated group compared to that in the vehicle-treated group (all P < 0.05). Propofol post-treatment also attenuated brain water content at 24 and 72 h and reduced neurologic deficit score at 72 h and 7 days of reperfusion (all P < 0.05). Additionally, in the peri-infarct area, bFGF mRNA and protein expression were elevated at 6, 24, and 72 h of reperfusion compared to that in the vehicle-treated group (all P < 0.05). These results show that post-ischemic administration of propofol provides neural protection from cerebral ischemia-reperfusion injury. This protection may be related to an early increase in the expression of bFGF.

Therapeutic effect of human umbilical cord multipotent mesenchymal stromal cells in a rat model of stroke

BACKGROUND

Human umbilical cord multipotent mesenchymal stromal cells (UC-MSC) have recently been identified as ideal candidate stem cells for cell-based therapy. The present study was designed to evaluate therapeutic potentials of intracerebral administration of UC-MSC in a rat model of stroke.

METHODS

Rats were subjected to 2-hr middle cerebral artery occlusion and received 2 10 UC-MSC or phosphate-buffered saline as a control. Neurologic function evaluation was conducted weekly after transplantation. Brain injury volume and in vivo differentiation of transplanted UC-MSC were detected 2 or 5 weeks after the UC-MSC treatment. In addition, vascular density, vascular endothelial growth factor, and basic fibroblast growth factor expression in ipsilateral hemisphere after treatment and in vitro angiogenic potential of UC-MSC were assessed.

RESULTS

The transplanted UC-MSC survived for at least 5 weeks in rat brain. Compared with the phosphate-buffered saline control, the UC-MSC treatment significantly reduced injury volume and neurologic functional deficits of rats after stroke. In ischemic brain, UC-MSC widely incorporated into cerebral vasculature and a subset of them was capable of differentiating into endothelial cells. Furthermore, the UC-MSC treatment substantially increased vascular density and vascular endothelial growth factor and basic fibroblast growth factor expression in ipsilateral hemisphere of stroke. In vitro induction and tube formation assay further confirmed their angiogenic properties.

CONCLUSIONS

UC-MSC transplantation could accelerate neurologic functional recovery of rats after stroke, which may be mediated by their ability to promote angiogenesis.

Dynamic changes in vascular permeability, cerebral blood volume, vascular density, and size after transient focal cerebral ischemia in rats: evaluation with contrast-enhanced magnetic resonance imaging

Postischemic cerebral blood flow and blood volume changes have been associated with angiogenesis; nevertheless, the spatiotemporal changes in vascular permeability, vascular density, and vessel size have not been investigated. Here we report a prolonged increase in vascular permeability from day 3 to day 21 after ischemia, in particular in the reperfused outer cortical layers and leptomeninges. Increased cerebral blood volume (CBV) was observed from day 3 to day 14, whereas increased blood volume in small vessels, primarily capillaries, was noticed from day 7 to day 14 in the reperfused cortex. An initial decrease in vascular density and a reciprocal increase in vessel size were observed within the reperfused cortex at days 1 and 3 after ischemia. Immunohistological analysis confirmed a similar decrease in microvessel density and an increase in vessel size in vessels with a diameter greater than 30 microm. These large-sized vessels exhibited intense basic fibroblast growth factor and endothelial nitric oxide synthase immunoreactivity, suggesting the growth of collateral vessels. By contrast, a late increase in vascular density was noticed in the reperfused outer cortex at days 14 and 21 after ischemia. Together, these findings suggest that the early phase of CBV increase is likely because of the improvement in collateral circulation, whereas the late phase of CBV increase is attributed to the surge of angiogenesis.

Transplanted bone marrow stromal cells migrate, differentiate and improve motor function in rats with experimentally induced cerebral stroke

Bone marrow stromal cells are multipotential cells that can be induced to differentiate into osteoblasts, chondrocytes, myocytes and adipocytes in different microenvironments. Recent studies revealed that bone marrow stromal cells could improve neurological deficits of various damages or diseases of the central nervous system such as Parkinson's disease, brain trauma, spinal cord injury and multiple sclerosis, and promote glia-axonal remodeling in animal brain subjected to an experimentally induced stroke. In the present study, bone marrow stromal cells were intracerebrally transplanted into the cerebrum following a transient middle cerebral artery occlusion. Our aim was to find out whether the bone marrow stromal cells could survive and express neural phenotypic proteins and, in addition, whether they could restore the behavioral and functional deficits of the cerebral ischemic rats. Our results demonstrated that transplanted bone marrow stromal cells survived and migrated to areas around the lesion site. Some of them exhibited marker proteins of astrocytes and oligodendrocytes. Bone marrow stromal cell implantation significantly reduced the transient middle cerebral artery occlusion-induced cortical loss and thinning of the white matter and enhanced cortical beta-III-tubulin immunoreactivity. Rats implanted with bone marrow stromal cells showed significant improvement in their performance of elevated body swing test and forelimb footprint analysis and only transient recovery of the adhesive-removal test. Our data support bone marrow stromal cells as a valuable source of autologous or allogenic donor cells for transplantation to improve the outcome following cerebral ischemia.

Therapeutic efficacy of basic fibroblast growth factor on experimental focal ischemia studied by magnetic resonance imaging

The purpose of this study was to evaluate the effect of intravenous infusion of basic fibroblast growth factor (bFGF) in a permanent ischemia model at the subacute phase (2 weeks) as well as at 24 hours and 1 week using T2-weighted magnetic resonance imaging (MRI). The middle cerebral artery (MCA) in Sprague-Dawley rats was occluded using an intraluminal suture method. The rats were randomly divided into 2 groups to receive either bFGF (45 mircrog/kg/hr) or saline solution. The infusion was started 30 minutes after MCA occlusion (MCAO) and continued for 3 hours. Regional cerebral blood flow (rCBF) was measured using laser Doppler flowmetry throughout the infusion. T2-weighted MRI was carried out before MCAO, 24 hours after MCAO, and days 7 and 14 after MCAO. Although an elevation in rCBF was seen after the infusion, no significant change between the groups was observed. A significant difference between the bFGF and saline groups in T2-derived lesion volume was observed at 24 hours (P < .05), on day 7 (P < .05), and on day 14 (P < .01). The percentage of lesion area calculated from the ipsilateral hemisphere using hematoxylin and eosin staining on day 14 showed a significant difference between the bFGF and saline groups (P < .05). No significant change in the number of bromodeoxyuridine (BrdU)-labeled cells between the groups was observed. This study demonstrates that bFGF, infused intravenously starting 30 minutes after the induction of permanent MCAO, significantly reduces region volume even at day 14, as well as at days 1 and 7, compared with the corresponding saline group.

Activin A In Brain Injury

Activin A is a growth factor composed of two betaA subunits belonging to the transforming growth factor beta (TGF-beta) superfamily of dimeric proteins. The biological activity of activin A is mediated by two different types of receptors, the type I (ARI and ARIB) and the type II receptors (ARII and ARIIB), and by two activin-binding proteins, follistatin and follistatin-related gene. These factors bind to activin A and thereby inhibit its biological effects. Activin A, its receptors, and binding proteins are widely distributed throughout the brain. Studies employing models of acute brain injury strongly implicate enhanced activin A expression as a common response to acute neuronal damage of various origins. Hypoxic/ischemic injury, mechanical irritation, and chemical damage of brain evoke a strong upregulation of activin A. Subsequent experimental studies have shown that activin A has a beneficial role to neuronal recovery and that, by activating different pathways, activin A has robust neuroprotective activities. Because activin A induction occurs early after brain injury, its measurement may provide a potential biochemical index of the presence, location, and extent of brain injury. This approach may also facilitate the diagnosis of subclinical lesions at stages when monitoring procedures are unable to detect brain lesion and furthermore establish a prognosis.

Permeability of injured blood brain barrier for exogenous bFGF and protection mechanism of bFGF in rat brain ischemia

The study aims to explore the protection mechanism of exogenous basic fibroblast growth factor (exo-bFGF) in brain ischemia. The first part of experiment was to determine the optimal time window for the permeation of exo-bFGF through damaged blood-brain barrier in rats with permanently occluded middle cerebral arteries. 125I labeled bFGF was administered to the rats through the caudal vein. The level of gamma-rays of 125I-bFGF in the ischemic brain were found to increase at 2 h and a high level was maintained for 14 days. The morphology of the basement membrane of capillaries was observed using anti-blood-brain barrier basement membrane glycoprotein immunohistochemistry. The normal continuous linear or ribbon-like immunostain of the basement membrane became granular at 0.5 h, gradually faint and finally negative. The newly formed capillaries at the edge of the infarct still showed a negative stain after 14 days. The result suggested the optimal time window of exo-bFGF began 2 h after insult. The second part of experiment was to observe the dynamic expression of early growth response protein (Egr-1), endogenous basic fibroblast growth factor (endo-bFGF) and bFGF receptor (bFGFR) using immunohistochemistry after exo-bFGF is administered to brain. Egr-1 was more significantly enhanced in the exo-bFGF-used group than in the control group. Endo-bFGF increased gradually, reaching its peak at 7 days in the control group, while in experiment group, the endo-bFGF expression showed its first peak at 6 h, indicating that exo-bFGF could induce earlier and stronger expression of endo-bFGF. The bFGFR-group presented an early expression, reaching its maximal level at 3 h, and declining at 6 h. There were no difference in expression of bFGFR between the two groups. The infarct areas reduced from 17% to 24% in the different time intervals. The results suggested that in exo-bFGF enhanced Egr-1 protein. Egr-1 in turn might play an important role in up-regulating the expression of endo-bFGF which overlapped with the expression of bFGFR to ensure the combination of ligand and receptor to protect against brain ischemia.

Serial measurement of serum basic fibroblast growth factor in patients with acute cerebral infarction

Basic fibroblast growth factor (bFGF) has been reported to be involved in the pathophysiological changes following cerebral infarction. Basic fibroblast growth factor is upregulated in the brain and conduces to neuroprotection and angiogenesis in experimental brain ischemia, but the change of serum bFGF in cerebral infarction patients has not been reported. In the present study, we investigated the dynamic changes of serum bFGF in 30 patients with acute cerebral infarction and found that serum bFGF increased significantly after cerebral infarction compared with the control group (p<0.05). Serum bFGF peaked on day 3 (15.46 +/- 5.58 pg/ml; p<0.01) and remained significantly elevated on day 14 following cerebral infarction. In this study, it was also found that the levels of bFGF with large infarction were higher at each time point than those with moderate or small infarction (p<0.05). There was a positive correlation between the peak level of bFGF and improvement of clinical neurological deficits scored by Scandinavian Stroke Scale (SSS) (r=0.596; p<0.05). These results suggest that the serum bFGF level increased significantly after cerebral infarction and the level of serum bFGF could be of value to estimate the infarction size and clinical prognosis.

Expression of basic fibroblast growth factor mRNA and protein in the human brain following ischaemic stroke

Our previous work has demonstrated that angiogenesis occurs in the damaged brain tissue of patients surviving acute ischaemic stroke and increased microvessel density in the penumbra is associated with longer patient survival. The brain is one of the richest sources of FGF-2 and several studies have noted its angiogenic and neuroprotective effects in the nervous system. These findings led us to investigate the expression and localisation of both FGF-2 mRNA and protein in brain tissue collected within 12 h of death from 10 patients who survived for between 24 h and 43 days after acute stroke caused by thrombosis or embolus. Western blot analysis demonstrated increased FGF-2 protein expression in both grey and white matter in the infarcted core and the penumbra region compared to the normal contralateral hemisphere of all 10 patients studied. Using indirect immunoperoxidase staining of paraffin embedded sections, we observed the presence of FGF-2 in neurones, astrocytes, macrophages and endothelial cells. In situ hybridisation was used to localise and quantify mRNA expression in ischaemic brain tissue of the same 10 patients. The expression of FGF-2 in the penumbra of all patients was significantly raised compared with infarcted tissue and normal-looking contralateral hemisphere. In addition, serum FGF-2 was significantly increased between 1 and 14 days (P<0.001) in many patients with both ischaemic stroke (n=28) and intra-cerebral haemorrhage (n=16) compared with age-matched control subjects undergoing routine medical examinations (n=20). We suggest that up-regulation of FGF-2 is one of the mechanisms that leads to angiogenesis and neuro-protection in the penumbra region after acute stroke in man.

Angiogenesis and stem cell transplantation as potential treatments of cerebral ischemic stroke

Ischemic stroke is a leading cause of human death and disability. Although stroke survivors may gain spontaneous partial functional recovery, they often suffer from sensory-motor dysfunctions, behavioral/neurological alterations, and various degrees of paralysis. Currently, limited clinical intervention is available to prevent ischemic damage and restore lost function in stroke victims. In addition to the extensive research on protective maneuvers against ischemia-induced cell death, increasing attention has been focused on potential strategies of promoting tissue repair and functional recovery in the damaged post-ischemic brain. Angiogenesis, or the growth of new blood vessels, may contribute to cell survival and functional recovery of the area of insult. The study of angiogenesis will increase the understanding of the mechanism underlying post-ischemia neurovascular plasticity and regeneration. Additionally, stem cell transplantation has emerged in the last few years as a potential therapy for ischemic stroke, because of their capability to differentiate into multiple cell types and the possibility that they may provide trophic support for cell survival, tissue repair, and functional recovery.

Reduction of infarct volume and apoptosis by grafting of encapsulated basic fibroblast growth factor—secreting cells in a model of middle cerebral artery occlusion in rats

Object. This study was conducted to evaluate the effects of grafting encapsulated basic fibroblast growth factor (bFGF)—secreting cells in rat brains subjected to ischemic injury.

Methods. Two cell lines were used for encapsulated grafting in this experiment, namely, a bFGF-secreting cell line established by genetic manipulation of baby hamster kidney (BHK) cells, and a naive BHK cell line. Forty-seven Sprague—Dawley rats were used in this experiment. The animals were divided into the following three groups: those receiving grafts of encapsulated bFGF-secreting cells (BHK-bFGF group); those with grafts of encapsulated naive BHK cells (naive BHK group); and those with no grafts (control group). The authors implanted encapsulated cells into the right striatum of host rats in the BHK-bFGF and naive BHK groups. Six days after grafting, the host and control animals underwent permanent right middle cerebral artery occlusion (MCAO) with an intraluminal suture procedure. The infarct volume was evaluated using 2,3,5-triphenyltetrazolium chloride staining and computerized image analysis 24 hours after MCAO. Fragmentations of DNA in the host brains were analyzed using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling 12 hours after MCAO.

The authors found that the infarct volume in the BHK-bFGF group was reduced by approximately 30% compared with that in the naive BHK and control groups. In the ischemic penumbral area, the number of apoptotic cells in the BHK-bFGF group was significantly decreased compared with that in the other groups.

Conclusions. The grafting of encapsulated BHK bFGF-secreting cells protected the brain from ischemic injury. Encapsulation and grafting of genetically engineered cells such as bFGF-secreting cells is thus thought to be a useful method for protection against cerebral ischemia.

Angiogenic factors in the central nervous system

The past decade has seen considerable advances in the understanding of angiogenesis. Blood vessel development and growth in the central nervous system are tightly controlled processes that are regulated by angiogenic factors. Angiogenic factors have been implicated in the pathogenesis of a wide variety of disorders, including primary and metastatic brain tumors, aneurysms, arteriovenous malformations, and cavernous malformations. The potential clinical applications of angiogenesis research include inhibition of angiogenesis to control brain tumors and therapeutic angiogenesis to promote collateral blood vessel formation among patients at risk of ischemia. This article summarizes the processes of blood vessel formation in the brain, examines the angiogenic factors that are prominent in the central nervous system, reviews the clinical use of angiogenesis inhibitors, and identifies areas for future investigation.

Fibroblast growth factors and neuroprotection

Several members of the FGF family, in particular FGF2, are intimately involved in neuronal protection and repair after ischemic, metabolic or traumatic brain injury. Expression of Fgf2 mRNA and protein is strongly upregulated after neuronal damage, with glial cells as the predominant source. Given its survival-promoting effects on cultured neurons, exogenous FGF2 was tested in several animal models of stroke and excitotoxic damage, in which it consistently proved protective against neuronal loss. FGF2 affords neuroprotection by interfering with a number of signaling pathways, including expression and gating of NMDA receptors, maintenance of Ca2+ homeostasis and regulation of ROS detoxifying enzymes. FGF2 prevents apoptosis by strengthening anti-apoptotic pathways and promotes neurogenesis in adult hippocampus after injury. The protective action of FGF2 has been linked to its augmenting effect on the lesion-induced upregulation of activin A, a member of the TGF-beta superfamily. Despite the well-documented benefits of FGF2 in animal models of stroke, there is currently no clinical development in stroke, after a phase II/III trial with FGF2 in acute stroke patients was discontinued because of an unfavorable risk-to-benefit ratio. As the molecular targets of FGF2 are going to be unraveled over the next years, new therapeutic strategies will hopefully emerge that enable us to influence the various protective mechanisms of FGF2 in a more specific fashion.

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.

Temporal profile of angiogenesis and expression of related genes in the brain after ischemia

Angiogenesis is an intricately regulated phenomenon. Its mechanisms in the ischemic brain have not been clearly elucidated. The authors investigated expression of angiogenesis-related genes using a complementary DNA (cDNA) array method as well as Western blotting and immunohistochemistry, and compared these studies with a temporal profile of angiogenesis in mouse brains after ischemia. The number of vessels significantly increased 3 days after injury, and proliferating endothelial cells increased as early as 1 day. This means that angiogenesis occurs immediately after the injury. Ninety-six genes implicated in angiogenesis were investigated with a cDNA array study. It was found that 42, 29, and 13 genes were increased at 1 hour, 1 day, and 21 days, respectively. Most of the well-known angiogenic factors increased as early as 1 hour. Vessel-stabilizing factors such as thrombospondins also increased. At 1 day, however, thrombospondins decreased to lower levels than in the control, indicating a shift from vascular protection to angiogenesis. At 21 days, many genes were decreased, but some involved in tissue repair were newly increased. Western blotting and immunohistochemistry showed findings compatible with the cDNA array study. Many molecules act in an orchestrated fashion in the brain after ischemia and should be taken into account for therapeutic angiogenesis for stroke.

Survival and death-promoting events after transient spinal cord ischemia in rabbits: induction of Akt and caspase3 in motor neurons

OBJECTIVE

The mechanism of spinal cord injury has been thought to be related to the vulnerability of spinal motor neuron cells to ischemia. However, the mechanisms of such vulnerability are not fully understood. We previously reported that spinal motor neurons might be lost as a result of programmed cell death and investigated a possible mechanism of neuronal death by means of immunohistochemical analysis for CPP32 (caspase3) and serine-threonine kinase (Akt).

METHODS

We used a rabbit spinal cord ischemia model with use of a balloon catheter. The spinal cord was removed at 8 hours or 1, 2, or 7 days after 15 minutes of transient ischemia, and histologic changes were studied with hematoxylin and eosin staining. Western blot analysis for Akt and caspase3, temporal profiles of Akt and caspase3 immunoreactivity, and double-label fluorescence immunocytochemical studies were performed.

RESULTS

The majority of motor neurons were preserved until 2 days but were selectively lost at 7 days of reperfusion. Western blot analysis revealed no immunoreactivity for Akt and caspase3 in the sham-operated spinal cords. However, such immunoreactivity became apparent at 8 hours after transient ischemia, decreased at 1 day, and returned to the baseline level at 2 days. A double-label fluorescence immunocytochemical study revealed that both Akt and caspase3 were positive at 8 hours of reperfusion in the same motor neurons, which eventually die.

CONCLUSION

These results suggests that transient spinal cord ischemia activates both cell death and survival pathways after ischemia. The activation of Akt protein at the early stage of reperfusion might be one of the factors responsible for the delay in neuronal death after spinal cord ischemia.

The roles of activins in repair processes of the skin and the brain

A recent study from our laboratory demonstrated a strong upregulation of activin expression during cutaneous wound healing. To further analyze the role of activin A in skin morphogenesis and wound repair, we generated transgenic mice that overexpress activin A under the control of the keratin 14 promoter. The latter targets expression of transgenes to the basal, proliferating layer of the epidermis. Hetero- as well as homozygous transgenic animals were viable and fertile. However, they were smaller than non-transgenic littermates and they had smaller ears and shorter tails. Histological analysis of their skin revealed dermal hyperthickening, mainly due to the replacement of fatty tissue by connective tissue, and an increase in suprabasal, partially differentiated epidermal layers. After cutaneous injury, a strong enhancement of granulation tissue formation was observed. Furthermore, the extent of re-epithelialization was increased in some of the wounds. These data demonstrate that activin A is a potent stimulator of the wound healing process. Using an in vivo model of local brain injury, we found that activin A also plays a significant role in the early cellular response to neuronal damage. Expression of activin mRNA and protein is markedly upregulated within a few hours of injury. If applied exogenously, recombinant activin A is capable of rescuing neurons from acute cell death. Studying the interaction between bFGF, a well-established neuroprotective agent, which is currently being tested in stroke patients, and activin A, we arrived at the unexpected conclusion that it is the strong induction of activin A by bFGF which endows the latter with its beneficial actions in patients. These findings suggest that the development of substances directly targeting activin expression or receptor binding should offer new possibilities in the acute treatment of stroke and brain trauma.

Induction of phosphatidylinositol 3-kinase and serine-threonine kinase-like immunoreactivity in rabbit spinal cord after transient ischemia

The mechanism of spinal cord injury has been thought to be related with tissue ischemia, and spinal motor neuron cells are suggested to be vulnerable to ischemia. To evaluate the mechanism of such vulnerability of motor neurons, we attempted to make a reproducible model of rabbit spinal cord ischemia. Using this model, the inductions of phosphatidylinositol 3-kinase (PI3-k) and serine-threonine kinase (Akt) were investigated with immunohistochemical analyses for up to 7 days of the reperfusion following 15 min of ischemia in rabbit spinal cord. It has been demonstrated that both PI3-k and its downstream effector, Akt mediate growth factor-induced neuronal survival. Spinal cord sections from animals sacrificed at 8 h, 1, 2, and 7 days following the 15 min of ischemia were immunohistochemically evaluated using monoclonal antibodies for PI3-k and Akt. Following the 15 min of ischemia, the majority of the motor neurons showed selective cell death at 7 days of reperfusion. Immunoreactivity of PI3-k and Akt were induced at 8 h of reperfusion selectively in motor neuron cells. No glial cells and inter neurons were stained in the spinal cord sections. The activation of PI3-k and Akt protein at the early stage of reperfusion may be one of the factors responsible for the delay in neuronal death after spinal cord ischemia.

Vasodilatory effect of basic fibroblast growth factor in isolated rat cerebral arterioles: mechanisms involving nitric oxide and membrane hyperpolarization

Basic fibroblast growth factor (bFGF), a potent mitogen, acutely dilates cerebral blood vessels and may be effective in reducing cerebral infarction. However, the vasodilatory mechanism, which may involve nitric oxide (NO), is not completely understood. This study investigated whether membrane hyperpolarization is also involved in this mechanism. Membrane potential (MP) of smooth muscle cells and vessel diameter of isolated intracerebral arterioles were simultaneously measured following extraluminal application of bFGF in rats. The involvement of NO and adenosine triphosphate-sensitive potassium (KATP) channels in bFGF-induced vasodilation and membrane hyperpolarization was evaluated using specific inhibitors, NG-monomethyl-L-arginine (L-NMMA, 10(-4) M) and glibenclamide (GB, 10(-5) M), respectively. The resting MP was recorded at a mean value of -31.9 +/- 4.5 mV. bFGF (1 to 1000 ng/ml) produced significant vasodilation and hyperpolarization. Treatment with L-NMMA caused vasoconstriction and significantly attenuated bFGF-induced vasodilation without affecting membrane hyperpolarization. In the presence of GB, the membrane potential was significantly depolarized but the vessel diameter was only marginally reduced, so bFGF-induced membrane hyperpolarization was inhibited while arteriolar dilation was attenuated. These results suggest that bFGF-induced vasodilation is mediated by a mechanism involving both NO and membrane hyperpolarization, and that membrane hyperpolarization is caused by the activation of KATP channels.

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.

Impaired cerebromicrovascular perfusion. Summary of evidence in support of its causality in Alzheimer's disease

After nearly a century of inquiry, the cause of Alzheimer's disease (AD) remains to be found. In this review, basic and clinical evidence is presented that assembles and hypothetically explains most of the key pathologic events associated with the development of AD. These pathologic events are triggered in AD by impaired cerebral perfusion originating in the microvasculature that affects the optimal delivery of glucose and oxygen and results in an energy metabolic breakdown of brain cell biosynthetic and synaptic pathways. We propose that two factors must be present before cognitive dysfunction and neurodegeneration is expressed in the AD brain: (1) advanced aging, (2) presence of a condition that lowers cerebral perfusion, such as a vascular risk factor. The first factor introduces a normal but potentially menacing process that lowers cerebral blood flow in proportion to increased aging, while the second factor adds a crucial burden that further lowers brain perfusion and places vulnerable neurons in a state of metabolic compromise leading to a death pathway. These two factors will lead to a critically attained threshold of cerebral hypoperfusion (CATCH). CATCH is a self-sustaining and progressive circulatory insufficiency that will destabilize neurons, synapses, neurotransmission, and cognitive function, creating in its wake a neurodegenerative process characterized by the formation of senile plaques, neurofibrillary tangles, amyloid angiopathy, and, in some cases, Lewy bodies. Since any of a considerable number of vessel-related conditions must be present in the aging individual for cognition to be affected, CATCH supports the heterogeneic disease profile assumed to be characteristic of the AD syndrome. A brief discussion of target therapy based on the proposed pathogenesis of AD is also reviewed.

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.

Immunoreactive Akt, PI3-K and ERK protein kinase expression in ischemic rat brain

In order to clarify the role of protein kinases in ischemic brain injury, the spatiotemporal expression of immunoreactive serine-threonine kinase Akt, phosphatidylinositol 3-kinase (PI3-K) and extracellular signal-regulated kinase (ERK) were examined at 3, 8, or 24 h after permanent middle cerebral artery occlusion (MCAO) in rats. Weak staining for these protein kinases was found in both cortical and caudate neurons in sham controls. The staining for Akt-1 and PI3-K was increased at 3-8 h in the ischemic penumbral region and declined at 24 h. A slight induction of these kinases was observed in the ischemic core region. Robust expression of ERK was noted at 3-8 h in most neurons in the area of ischemia. At 24 h, ERK continued to be expressed in the ischemic penumbra, but decreased in the ischemic core. These findings suggest that the signaling for Akt and PI3-K are different from the ERK dependent signal transduction during ischemic brain injury.

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.

Cortical spreading depression increases protein synthesis and upregulates basic fibroblast growth factor

Protective effects of cortical spreading depression (CSD) against ischemic damage have been demonstrated in cortex when elicited at either 24 h or 3 days prior to ischemia. The present study was carried out to investigate possible mechanisms of neuroprotection following CSD. In Sprague-Dawley rats, 5 M KCl, 5 M NaCl, or physiological saline was applied to the cortex for 1 h. Repetitive CSD waves were elicited only in the KCl group. Measurements of cerebral glucose utilization demonstrated a marked reduction in affected cortex and subcortical regions in both the NaCl and the KCl groups, whereas cortical and hippocampal protein synthesis was discretely increased only in the KCl group. Immunohistochemistry of GFAP demonstrated a rapid activation in reactive astrocytes at 3 days in the KCl group whereas only a discrete activation was observed in the NaCl group. Similar changes were observed for basic fibroblast growth factor. Our results suggest that CSD-induced ischemic tolerance is not due to a reduction in energy metabolism but rather is associated with an upregulation of trophic factors and glial cell activation which might provide a mechanism for a long-lasting neuroprotection.

Expression of angiogenic factors in rabbit spinal cord after transient ischaemia

It is known that angiogenic factors are induced in brain by ischaemia, and new vessel formation is correlated with better prognosis in patients of stroke. However, the role of angiogenesis and expression of angiogenic factors in spinal cord ischaemia is uncertain. We here investigated expression of three highly potent angiogenic peptides, i.e. basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and hepatocyte growth factor (HGF) in the rabbit spinal cord after transient ischaemia, by Western blot and immunohistochemical analysis. Western blot analysis revealed that bFGF was induced at 8 h after transient ischaemia and decreased thereafter. Immunoreactive VEGF was also induced at 8 h, and it disappeared thereafter. HGF was not detected in the spinal cord with sham-operation or ischaemic injury. By immunohistochemical analysis, bFGF was weakly expressed in only a few small interneurons in sham-operated spinal cords. However, it was induced to a marked degree in motor neurons and interneurons of the anterior horn at 8 h after reperfusion. It was also induced in small neurons of the posterior horn. The expression in the anterior horn decayed thereafter though it lasted until 7 d in the posterior horn. VEGF was not expressed in sham-operated spinal cords, but the expression was induced in large motor neurons and interneurons at 8 h with marked reduction at 1 d. In contrast, HGF was not expressed in the spinal cord with sham-operation or ischaemic injury. These factors are known to play pivotal roles in angiogenesis, regulation of blood flow, and protection of endothelial cells. Through induction of these angiogenic peptides, protection of vascular endothelial cells and improvement of regional blood flow might be occurring in the spinal cord after ischaemia.

Induction of basic fibroblast growth factor (bFGF) expression following focal cerebral ischemia

Basic fibroblast growth factor (bFGF) is a biologically active polypeptide with mitogenic, angiogenic, and neurotrophic properties. In the present study, we examined the temporal and spatial expression profiles of bFGF mRNA and protein concentration in a focal cerebral ischemia model induced by transient occlusion of the right middle cerebral artery (MCA) and both common carotid arteries (CCAs). Results of Northern blot analysis shows a transient 2.5-fold increase in the 6.0 kb transcript of bFGF mRNA within the ischemic cortex of rats subjected to 60 min ischemic insult followed by 12 h of reperfusion. Although enhanced expression of bFGF mRNA was also noted in the ipsilateral hippocampus, the temporal induction profile appeared to be different from that of the ischemic cortex. A significant increase in bFGF mRNA was observed as early as 60 min following ischemia and remained elevated for up to 2 weeks after the onset of reperfusion. In situ hybridization studies revealed constitutive expression of bFGF mRNA in discrete brain regions of sham-operated animals. Following 60 min ischemia and 12 h reperfusion, increased expression of bFGF mRNA was observed in the ischemic cortex (both peri-infarct and infarct area). Increased expression of bFGF mRNA within the infarcted area is largely confined rostrally to the outer cortical layers of the infarct, an area with increased density of blood vessels. bFGF-like immunoreactivity was also detected in areas expressing bFGF mRNA. Furthermore, a striking increase in bFGF-like immunoreactivity was observed in the ipsilateral hippocampus. Double-staining with anti-GFAP antibody indicated that the majority of the bFGF-like immunoreactivity was localized in the astrocytes, however, not all astrocytes showed bFGF-like immunoreactivity. Some GFAP negative cell also showed bFGF-like immunoreactivity. In summary, increased expression of both bFGF mRNA and immunoreactivity following ischemia were located in the same brain regions. An increase in bFGF-like immunoreactivity after ischemic insult is likely due to an increase in the expression of its 6.0 kb bFGF mRNA transcripts. Although increased bFGF mRNA was observed in both ischemic cortex and ipsilateral hippocampus after ischemic insult, the temporal expression profiles differed. Results from the present study raise the possibility that increased expression of bFGF in the peri-infarcted area may limit the spread of ischemic injury.

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

Basic fibroblast growth factor (bFGF) is a heparin-binding polypeptide with potent trophic and protective effects on brain neurons, glia and endothelia. In previous studies, we showed that intravenously administered bFGF reduced the volume of cerebral infarcts following permanent occlusion of the middle cerebral artery in rats. In the current study, we examined the time dependence of bFGF infusion on infarct reduction, and the effect of co-infusion of bFGF with heparin. We found a significant reduction in infarct volume when the bFGF infusion (50 microg/kg per h for 3 h) was begun up to 3 h, but not 4 h after the onset of ischemia. The infarct reducing effects of bFGF were not altered by co-infusion of heparin. These results are potentially important in light of the ongoing clinical trials of intravenous bFGF in acute stroke.

Intraventricular brain-derived neurotrophic factor reduces infarct size after focal cerebral ischemia in rats

Brain-derived neurotrophic factor (BDNF), acting through the high-affinity receptor tyrosine kinase (TrkB), is widely distributed throughout the central nervous system and displays in vitro trophic effects on a wide range of neuronal cells, including hippocampal, cerebellar, and cortical neurons. In vivo, BDNF rescues motorneurons, hippocampal, and substantia nigral dopaminergic cells from traumatic and toxic brain injury. After transient middle cerebral artery occlusion (MCAO), upregulation of BDNF-mRNA in cortical neurons suggests that BDNF potentially plays a neuroprotective role in focal cerebral ischemia. In the current study, BDNF (2.1 micrograms/d) in vehicle or vehicle alone (controls) was delivered intraventricularly for 8 days, beginning 24 hours before permanent middle cerebral artery occlusion by intraluminal suture in Wistar rats (n = 13 per group). There were no differences in physiological variables recorded during surgery for the two groups. Neurological deficit (0 to 4 scale), which was assessed on a daily basis, improved in BDNF-treated animals compared with controls (P < 0.05; analysis of variance and Scheffe's test). There were no significant differences in weight in BDNF-treated animals and controls during the experiment. After elective killing on day 7 after MCAO, brains underwent 2,3,5-triphenyltetrazolium chloride staining for calculation of the infarct volume and for histology (hematoxylin and eosin and glial fibrillary acid protein). The mean total infarct volume was 83.1 +/- 27.1 mm3 in BDNF-treated animals and 139.2 +/- 56.4 mm3 in controls (mean +/- SD; P < 0.01, unpaired, two-tailed t-test). The cortical infarct volume was 10.8 +/- 7.1 mm3 in BDNF-treated animals and 37.9 +/- 19.8 mm3 in controls (mean +/- SD; P < 0.05; unpaired, two-tailed t-test), whereas ischemic lesion volume in caudoputaminal infarction was not significantly different. These results show that pretreatment with intraventricular BDNF reduces infarct size after focal cerebral ischemia in rats and support the hypothesis of a neuroprotective role for BDNF in stoke.

Expression of basic fibroblast growth factor mRNA after transient focal ischemia: comparison with expression of c-fos, c-jun, and hsp 70 mRNA

We have reported that basic fibroblast growth factor (bFGF) prevents retrograde degeneration of thalamic neurons after middle cerebral artery (MCA) occlusion. To identify the protective mechanism of bFGF, we examined bFGF mRNA expression in a model of transient focal ischemia with in situ hybridization. Compared to c-fos, c-jun, and hsp 70 mRNA expression, upregulation of the bFGF mRNA expression was delayed until 6 h after reperfusion. By 12 h, bFGF mRNA was markedly induced in the peri-infarcted cortex, cingulate cortex, and peri-infarcted white matter. At 24 h and 2 days the induction of bFGF mRNA in these regions persisted, and disappeared by 5 day. The quantitative assessment of bFGF mRNA expression revealed that optical density ratios of the cingulate gyrus and the caudoputamen were significantly higher at 12 h, 24 h, and 2 d after reperfusion than those in sham controls. Microscopic observation indicated bFGF mRNA signals were present in several types of cortical cells, including neurons and nonneuronal cells. Since intrinsic bFGF, released from the damaged tissue, can influence the healing response through receptors upregulated by injury, it is reasonable that this pattern of bFGF mRNA expression parallels the bFGFR mRNA expression previously reported.

Selective induction of fibroblast growth factor receptor-1 mRNA after transient focal ischemia in the cerebral cortex of rats

The expression of the mRNA of four members of the fibroblast growth factor (FGF) receptor family, was examined in rats subjected to temporal middle cerebral artery occlusion using an in situ hybridization technique. Fibroblast growth factor receptor-1 (FGFR-1) mRNA was strongly expressed in neurons of the cerebral cortex, whereas mRNAs of the other 3 subtypes of FGFRs (FGFR-2, -3, and -4) were not expressed. After temporal occlusion of the middle cerebral artery, expression of FGFR-1 mRNA in cerebral cortical neurons markedly increased in association with the progressive neuronal death; this increase was evident for at least 5 days after the focal ischemia. In view of the neuroprotective activity of basic FGF reported so far, the present results suggest that FGFR-1 induction may subserve to self-protect neurons in the ischemic penumbral field of the cerebral cortex.