Neurotrophic factor therapy for nervous system degenerative diseases

An Electrophysiologic Model for Functional Assessment of Effects of Neurotrophic Factors on Facial Nerve Reinnervation

OBJECTIVES

To establish a sound objective model for assessing the effects of neurotrophic factors on facial nerve function after injury and to compare the effects of brain-derived neurotrophic factor (BDNF) with its neutralizing antibody on facial nerve function after injury.

DESIGN

Prospective electrophysiologic analysis of recovery of function 4 weeks after axotomy involving facial nerve transection and primary end-to-end reanastomosis in adult rats and blind comparison with randomized intramuscular injection of either BDNF, monoclonal antibody to BDNF in neutralizing concentration, or control solution.

RESULTS

There were no statistically significant differences between groups in latencies, duration, amplitude, area, or conduction velocity before axotomy, and recorded conduction velocities were consistent with previously reported values, which suggests that the recordings were reliable and reproducible. After transection, there was a mean increase in latency 1 and decreases in latency 2, integrated average area, muscle action potential duration, amplitude, and conduction velocity for all 3 groups. When the groups were compared after transection, the anti-BDNF group showed a significant decrease in conduction velocity and muscle action potential duration (Kruskal-Wallis P = .01 and P = .008, respectively) compared with the other groups. There were no statistically significant differences in latencies, amplitude, or area among the groups.

CONCLUSIONS

We have established an electrophysiologic model for objective assessment of facial nerve function in the rat. Future studies should combine functional electrophysiologic assessment and histologic examination to provide a more robust model for studying the effects of neurotrophic factors on facial nerve reinnervation and synkinesis.

Efficient synthesis and structure-activity relationship of honokiol, a neurotrophic biphenyl-type neolignan

Honokiol, a biphenyl-type neolignan, which shows the remarkable neurotrophic effect in primary cultured rat cortical neurons, has been effectively synthesized in 21% yield over 14 steps starting from 5-bromosalicylic acid and p-hydroxybenzoic acid by utilizing Pd-catalyzed Suzuki-Miyaura coupling reaction as a key step. Additionally, the structure-activity relationship between neurite outgrowth-promoting activity and its O-methylated and/or its hydrogenated analogues was examined in the primary cultures of fetal rat cortical neurons, suggesting that 5-allyl and 4'-hydroxyl groups are essential for affecting the neurotrophic activity of honokiol.

Gene expression profiles of reactive astrocytes in dopamine-depleted striatum

We have used cDNA array analysis to examine the expression of genes in reactive astrocytes of dopamine-depleted striatum of rats in vivo, an animal model for Parkinson disease, compared to those from control striatum. The striatum of both normal adult rats and rats whose substantia nigra had been lesioned with 6-hydroxydopamine was removed one week following lesion. After fixing the tissue in RNAlater, individual astrocytes, isolated directly from dissociated striatum and confirmed to be astocytes by expression of glial fibrillary acidic protein (GFAP) mRNA using single cell RT-PCR, were used as the source of mRNA. Co-localization of GFAP with either of 2 antibodies known to label only reactive astrocytes in vivo confirmed that virtually all astrocytes in the lesioned striatum were reactive. The analysis has identified 29 genes whose expression is turned on or enhanced in dopamine-depleted striatal astrocytes and 2 whose expression is decreased. In situ hybridization was used to confirm the localization of 8 of these genes to astrocytes: these included GDNF, NGF, bFGF, TNF-alpha, MIP-1alpha, c-jun, Fra-1 and Fra-2. Understanding these gene differences that occur in astrocytes in response to dopamine depletion should enhance our ability to promote recovery from the injury.

Long-lasting rescue of age-associated deficits in cognition and the CNS cholinergic phenotype by a partial agonist peptidomimetic ligand of TrkA

Previously, we developed a proteolytically stable small molecule peptidomimetic termed D3 as a selective ligand of the extracellular domain of the TrkA receptor for the NGF. Ex vivo D3 was defined as a selective, partial TrkA agonist. Here, the in vivo efficacy of D3 as a potential therapeutic for cholinergic neurons was tested in cognitively impaired aged rats, and we compared the consequence of partial TrkA activation (D3) versus full TrkA/p75 activation (NGF). We show that in vivo D3 binds to TrkA receptors and affords a significant and long-lived phenotypic rescue of the cholinergic phenotype both in the cortex and in the nucleus basalis. The cholinergic rescue was selective and correlates with a significant improvement of memory/learning in cognitively impaired aged rats. The effects of the synthetic ligand D3 and the natural ligand NGF were comparable. Small, proteolytically stable ligands with selective agonistic activity at a growth factor receptor may have therapeutic potential for neurodegenerative disorders.

Search for constituents with neurotrophic factor-potentiating activity from the medicinal plants of paraguay and Thailand

20 medicinal plants of Paraguay and 3 medicinal plants of Thailand were examined on nerve growth factor (NGF)-potentiating activities in PC12D cells. The trail results demonstrated that the methanol extracts of four plants, Verbena littoralis, Scoparia dulcis, Artemisia absinthium and Garcinia xanthochymus, markedly enhanced the neurite outgrowth induced by NGF from PC12D cells. Furthermore, utilizing the bioactivity-guided separation we successfully isolated 32, 4 and 5 constituents from V. littoralis, S. dulcis and G. xanthochymus, respectively, including nine iridoid and iridoid glucosides (1-9), two dihydrochalcone dimers (10 and 11), two flavonoids and three flavonoid glycosides (12-16), two sterols (17 and 18), ten triterpenoids (19-28), five xanthones (29-33), one naphthoquinone (34), one benzenepropanamide (35), four phenylethanoid glycosides (36-39) and two other compounds (40 and 41). Among which, 15 compounds (1-4, 10-11, 14-18, 29-31 and 34) were new natural products. The results of pharmacological trails verified that littoralisone (1), gelsemiol (5), 7a-hydroxysemperoside aglucone (6), verbenachalcone (10), littorachalcone (11), stigmast-5-ene 3beta,7alpha,22alpha-triol (18), ursolic acid (19), 3beta-hydroxyurs-11-en-28,13beta-olide (24), oleanolic acid (25), 2alpha,3beta-dihydroxyolean-12-en-28-oic acid (26), 1,4,5,6-tetrahydroxy-7,8-di(3-methylbut-2-enyl)xanthone (29), 1,2,6-trihydroxy-5-methoxy-7-(3-methylbut-2-enyl)xanthone (30), 1,3,5,6-tetrahydroxy-4,7,8-tri(3-methyl-2-butenyl)xanthone (31), 12b-hydroxy-des-D-garcigerrin A (32), garciniaxanthone E (33) and (4R)-4,9-dihydroxy-8-methoxy-alpha-lapachone (34) elicited marked enhancement of NGF-mediated neurite outgrowth in PC12D cells. These substances may contribute to the basic study and the medicinal development for the neurodegenerative disorder.

Microspheres containing insulin-like growth factor I for treatment of chronic neurodegeneration

The therapeutic potential of peptide growth factors as insulin-like growth factor I (IGF-I) is currently under intense scrutiny in a wide variety of diseases, including neurodegenerative illnesses. A new poly(lactic-co-glycolide)-based microsphere IGF-I controlled release formulation for subcutaneous (SC) delivery has been developed by a triple emulsion method. The resulting microspheres displayed a mean diameter of 1.5microm, with an encapsulation efficiency of 74.3%. The protein retained integrity after the microencapsulation process as evaluated by circular dichroism and SDS-PAGE. The administration of IGF-I in microspheres caused at least a 30-fold increase in IGF-I mean residence time in rats and mice when compared with the conventional SC solution. Therefore, dosing can be changed from the conventional twice a day to once every 2 weeks. Therapeutic efficacy of this new formulation has been studied in mutant mice with inherited Purkinje cell degeneration (PCD). These mice show a chronic limb discoordination that is resolved after continuous systemic delivery of IGF-I. Normal motor coordination was maintained as long as IGF-I microsphere therapy is continued. Moreover, severely affected PCD mice, with marked ataxia, muscle wasting and shortened life-span showed a significant improvement after continuous IGF-I microsphere therapy as determined by enhanced motor coordination, marked weight gain and extended survival. This new formulation can be considered of great therapeutic promise for some chronic brain diseases.

Traumatic injury-induced midkine expression in the adult rat spinal cord during the early stage

Spinal cord injury is a debilitating condition. Midkine (MK) is involved in the generation of the central nervous system during development; however, the role of MK in the mature spinal cord has not been clarified. We examined the expression of MK, which has neurotrophic activity, before and after traumatic injury to the adult rat spinal cord. Following laminectomy, the rat spinal cord was injured at the T-9 level by applying extradural static weight-compression, in which a cylindrical compressor was used to induce complete and irreversible transverse spinal cord injury with paralysis of the lower extremities. The expression of MK was examined up to 14 days after the injury by immunohistochemical and Western blot analyses. Intense MK immunoreactivity was observed in the gray matter around the injury site but not in the necrotic lesion 1-7 days postinjury, although it was slightly positive 14 days after the injury. MK immunoreactivity was not detected in the normal spinal cord. The expression of MK was an early event, and its expression was compared to the increased production of glial fibrillary acidic protein (GFAP), a marker of reactive astrocytes, that was elevated at 2 days postinjury and continued over a 14 day period following the injury. Double immunostaining with anti-MK and anti-GFAP showed the existence of MK in the astrocytic cytoplasm. These findings suggest that MK was produced in astrocytes approximating the damaged region and may represent a reparative neurotrophic factor during the early phase of traumatic injury of the spinal cord.

Quinolinic acid lesions of the caudate putamen in the rat lead to a local increase of ciliary neurotrophic factor

When applied prior to excitotoxic lesions, ciliary neurotrophic factor (CNTF) has been shown to be neuroprotective. However, data concerning the endogenous CNTF content of the intact rat striatum are rare and have not until now been available for the quinolinic acid (QA)-lesioned striatum. Therefore, we investigated the CNTF content in the QA-lesioned rat striatum for at least 1 month using immunohistochemistry and Western blot analysis. In lesioned striata a neuronal loss was observed by Nissl staining and by a reduction of NeuN-immunoreactive cells, whereas increased glial fibrillary acidic protein immunoreactivity showed a gliotic reaction. With CNTF immunohistochemistry we found that in the QA-lesioned striatum CNTF was increased over time, whereas it was not detectable in intact and sham-lesioned striata. CNTF-immunoreactive cells had the morphology of protoplasmatic astrocytes. Furthermore, quantitative Western blotting demonstrated that the content of CNTF protein from striatal lysates containing 1 mg of whole protein 1 month after QA lesioning (2.76 +/- 1.71 ng) was significantly increased (P < 0.05, U-test) compared with sham-lesioned hemispheres (0.68 +/- 0.25 ng) and intact controls (0.55 +/- 0.25 ng). We conclude that CNTF content is correlated with glial scar formation and suggest that our results may be of relevance to cell grafting strategies for the treatment of Huntington's disease.

Rescue of NGF-deficient mice II: basal forebrain cholinergic projections require NGF for target innervation but not guidance

Basal forebrain cholinergic (BFC) neurons are an important substrate of cognitive function and are hypothesized to require the presence of nerve growth factor (NGF) for survival and target innervation. NGF-deficient mice develop BFC neurons that extend projections into telencephalic targets, but the mice perish before innervation is fully established. Rescue of NGF-deficient mice by transgenic expression of NGF under the keratin promoter yields viable mice with disrupted CNS expression of NGF. In the current study, rescued NGF-deficient mice contain normal numbers of septal cholinergic neurons yet reveal severe compromise of cholinergic innervation of both cortex and hippocampus. Surprisingly, intracerebroventricular infusion of NGF into juvenile mice can induce an essentially normal pattern of cholinergic innervation of the hippocampus. These results indicate that NGF is required for induction of proper innervation by BFC neurons, but that the cellular pattern of expression of this factor is not critical for specifying the distribution of axon terminals.

A non‐peptidyl neurotrophic small molecule for midbrain dopaminergic neurons

Abstract A small organic molecule (CUR-162590) that selectively enhances survival of midbrain dopaminergic neurons was identified by screening small molecule compound libraries. In embryonic midbrain cultures, CUR-162590 increased dopamine uptake and the number of dopaminergic neurons without altering the number of total neurons or astroglia or the uptake of GABA or serotonin. CUR-162590 reduced apoptosis of cultured dopaminergic neurons and protected against death induced by toxins such as MPP(+). Several synthetic analogs of CUR-162590 also had similar bioactivities. CUR-162590 thus represents a new class of neurotrophic small molecules that may have utility in the treatment of Parkinson's disease, which is marked by degeneration of midbrain dopaminergic neurons.

Prenylated xanthones with NGF-potentiating activity from Garcinia xanthochymus

Two prenylated xanthones, 1,4,5,6-tetrahydroxy-7,8-di(3-methylbut-2-enyl)xanthone (1) and 1,2,6-trihydroxy-5-methoxy-7-(3-methylbut-2-enyl)xanthone (2), were isolated from the wood of Garcinia xanthochymus along with a known xanthone, 12b-hydroxy-des-D-garcigerrin A (3). Their structures were elucidated by spectroscopic analysis. Compound 1 (10 muM), 2 (10-30 muM) and 3 (10 muM) showed a markedly enchancing activity of nerve growth factor (NGF)-mediated neurite outgrowth on PC12D cells.

Tumour necrosis factor-alpha- vs. growth factor deprivation-promoted cell death: distinct converging pathways

Perturbations of neuronal physiological homeostasis are likely to underscore neuronal demise/impairments that are reportedly associated with aging of the central nervous system and age-related neurodegenerative diseases such as Alzheimer's disease (AD). A number of age- and/or disease-associated neurotoxic events has been described. These include abnormally modified proteins such as beta amyloid and hyper-phosphorylated Tau, cytokines such as tumour necrosis factor-alpha (TNFalpha), high levels of free radicals conducive to oxidative stress, and impaired/decreased neuronal trophic support by neurotrophic factors. Overall, it could be argued that toxic events in the aged brain are either active, such as those due to a direct action of cytokines, or passive, such as those due to lack of growth factor support. It is therefore conceivable that cellular responses to such diverse toxic stimuli are different, suggesting that interventions should be targeted accordingly. In order to begin answering this question, we determined in PC12 cells the time course of activity, in response to TNFalpha (active) or growth factor withdrawal (passive), of protein kinase c-zeta (PKCzeta), nuclear factor kappa B (NFkappaB), caspases 3 and 8, and poly (ADP-ribose) polymerase (PARP), key signal transduction elements associated with modulation of cell death/survival in PC12 cells. We found that the overall activity of PKCzeta, NFkappaB and caspase 8 was significantly different depending on the apoptotic initiator. The pattern of caspase 3 and PARP activity, however, was not statistically different between serum-free- and TNFalpha-induced cell death conditions. This suggests that two distinct cell responses are elicited that converge at caspase 3, which then induces downstream events involved in the execution of a common apoptotic programme. These results contribute to the aim of differentially targeting neuronal death in the aged brain (characterized by neurotrophic factor impairments) or in the diseased brain (e.g. AD, characterized by elevated levels of pro-inflammatory cytokines).

Littorachalcone, a new enhancer of NGF-mediated neurite outgrowth, from Verbena littoralis

A new dihydrochalcone dimer, 2',4',3",2"',4"'-pentahydroxy-4-O-4"-tetrahydrobichalcone, given the name littorachalcone, was isolated from the aerial parts of Verbena littoralis H. B. K. along with two known flavonoids 4'-hydroxywogonin and 8,3'-dimethoxy-5,7,4'-trihydroxyflavone. Littorachalcone caused a significant enhancement of nerve growth factor-mediated neurite outgrowth from PC12D cells.

Exercise increases the vulnerability of rat hippocampal neurons to kainate lesion

Available evidence suggests that regular, moderate-intensity exercise has beneficial effects on neural health, perhaps including neuroprotection. To evaluate this idea further, we compared the severity of kainate-induced neuronal loss in exercised versus sedentary female rats. Stereological estimations of neuron number revealed that rats in the exercise condition exhibited significantly greater neuron loss in hippocampal region CA2/3, suggesting that high levels of physical activity may increase neuronal vulnerability to excitotoxicity.

Tumour necrosis factor-alpha- vs. growth factor deprivation-promoted cell death: different receptor requirements for mediating nerve growth factor-promoted rescue

Physiological and pathological aging of the central nervous system (CNS) is characterized by functional neuronal impairments which may lead to perturbed cell homeostasis and eventually to neuronal death. Many toxic events may underlie age-related neurodegeneration. These include the effects of beta amyloid, Tau and mutated presenilin proteins, free radicals and oxidative stress, pro-inflammatory cytokines and lack of growth factor support, which can be individually or collectively involved. Taken individually, these toxicants can induce very diverse cell responses, thus requiring individually targeted corrective interventions upstream of common cell death (apoptotic) pathways. Recent preliminary evidence suggests that the pro-inflammatory cytokine tumour necrosis factor alpha (TNFalpha) and growth factor withdrawal can both activate a common apoptotic pathway in nerve growth factor (NGF)-responsive PC12 cells involving caspase 3, albeit through very distinct upstream pathways: the former through active signalling and the latter through passive or lack of survival signalling. Here, we show that NGF can rescue PC12 cells from both growth factor withdrawal- and TNFalpha-promoted cell death. However, NGF rescue from growth factor withdrawal requires NGF signalling through the high-affinity tyrosine kinase receptor (TrkA), while NGF rescue from TNFalpha-promoted cell death requires NGF signalling through the low-affinity p75NTR receptor. These results strengthen the idea that prevention of age- or pathology-associated neurodegeneration may require varied molecular approaches reflecting the diversity of the toxicants involved, possibly acting simultaneously.

Exogenous NGF restores endogenous NGF distribution in the brain of the cognitively impaired aged rat

Alzheimer's disease and normal aging may impair retrograde transport of nerve growth factor (NGF) from cortical areas to basal forebrain cholinergic neurons. We demonstrate a relationship between performance in a spatial reference memory task and NGF distribution in the aged rat brain. In addition, exogenous NGF restored endogenous NGF distribution in cognitively impaired aged rats. These data suggest that NGF administration restores utilization of endogenous growth factor in the brain of cognitively impaired aged rats.

BDNF heightens the sensitivity of motor neurons to excitotoxic insults through activation of TrkB

The survival promoting and neuroprotective actions of brain-derived neurotrophic factor (BDNF) are well known but under certain circumstances this growth factor can also exacerbate excitotoxic insults to neurons. Prior exploration of the receptor through which BDNF exerts this action on motor neurons deflects attention away from p75. Here we investigated the possibility that BDNF acts through the receptor tyrosine kinase, TrkB, to confer on motor neurons sensitivity to excitotoxic challenge. We blocked BDNF activation of TrkB using a dominant negative TrkB mutant or a TrkB function blocking antibody, and found that this protected motor neurons against excitotoxic insult in cultures of mixed spinal cord neurons. Addition of a function blocking antibody to BDNF to mixed spinal cord neuron cultures is also neuroprotective indicating that endogenously produced BDNF participates in vulnerability to excitotoxicity. We next examined the intracellular signaling cascades that are engaged upon TrkB activation. Previously we found that inhibition of the phosphatidylinositide-3'-kinase (PI3'K) pathway blocks BDNF-induced excitotoxic sensitivity. Here we show that expression of a constitutively active catalytic subunit of PI3'K, p110, confers excitotoxic sensitivity (ES) upon motor neurons not incubated with BDNF. Parallel studies with purified motor neurons confirm that these events are likely to be occuring specifically within motor neurons. The abrogation of BDNF's capacity to accentuate excitotoxic insults may make it a more attractive neuroprotective agent.

Neurotrophic factors attenuate microvascular permeability disturbances and axonal injury following trauma to the rat spinal cord

Alterations of the blood-spinal cord barrier (BSCB) following spinal cord injury (SCI) and leakage of serum proteins induce vasogenic edema and cell damage. The possibility that two members of the neurotrophin family, BDNF or IGF-1 induce neuroprotection by attenuating the BSCB permeability following trauma was examined in a rat model. Repeated topical application of BDNF or IGF-1 (0.1 1microg, 0.5 microg or 1 microg in 10 microl) onto the spinal cord 30 min before SCI or 2, 5, 10 or 30 min thereafter significantly attenuated BSCB permeability to Evans blue and iodine. In the neurotrophin treated rats. edema formation, degradation of MBP, and myelin vesiculation were much less frequent compared to the untreated traumatised rats. The protective effect of BDNF and IGF-1 was most pronounced at the high dose (1 microg in 10 microl) given either 30 min before or within 10 min after SCI. The observations suggest that early intervention with neurotrophins in high doses following trauma (within 10 min) attenuates disturbances of the fluid microenvironment of the spinal cord. This indicates that BSCB opening plays an important role in SCI induced myelin vesiculation and cord pathology.

The role of cell therapy for stroke

Cellular therapy has been evaluated in small animals, subhuman primates, and now humans for the potential repair of brain injury due to stroke. Experimental striate stroke models have proven useful for the purpose of evaluating different treatment paradigms. Early clinical trials involving neuronal transplantation in patients suffering motor-related stroke in the basal ganglia region have begun.

This research will be described in this report.

Expression profiling to understand actions of NMDA/glutamate receptor antagonists in rat brain

Agents acting as noncompetitive N-methyl-D-aspartate (NMDA)/glutamate receptor antagonists induce the expression of several genes in limbic cortical regions, such as the cingulate, retrosplenial, and entorhinal cortices. These include important regulatory genes such as the neurotrophin brain-derived neurotrophic factor (BDNF), its receptor trkB, and c-fos. We applied expression profiling methods to find genes coregulated with BDNF following treatment with the prototypical NMDA/glutamate receptor antagonist MK-801. Expression profiling provides a useful technique for describing the molecular and transcriptional level events that follow various processes. We illustrate the utility of microarrays to find novel ESTs regulated by MK-801. We also used expression profiling with microarrays to characterize the levels of transcription factor cAMP response element modulator (CREM) and inducible cAMP early repressor (ICER) isoforms that are induced by MK-801. These factors may act as the eventual repressors for BDNF expression via competition and heterodimerization with phosphorylated CREB, a transcription factor important for BDNF expression. Finally, we find and confirm the regulation of Erp29, RTNI, and an ABC transporter by antagonism of NMDA/glutamate receptors as potential stress related molecules in brain. The emerging picture generated by using these expression profiling approaches, identifies several of what likely will be many molecules that take part in the complex events that occur during BDNF signaling mediated by blockade of NMDA/ glutamate receptors.

A preliminary approach to nonenolizable beta,beta-tricarbonyls: assembly of a hyperevolutin prototype

A synthetic approach to the hyperevolutin A acylated phloroglucinol ring system is described. Thus, intramolecular allene-nitrile oxide cycloaddition of 10 was used to construct the bicyclic framework and vicinal quaternary centers in cycloadduct 20 in the key bond-forming step. Treatment of 20 with Raney nickel and hydrogen gas produced primary enamine 21 which contains a nonenolizable beta,beta-tricarbonyl group in latent form.

Neural transplantation for stroke

Tremendous achievements in neuroscience over the past three decades have provided a solid foundation for basic and clinical research in neurotransplantation. Restorative neurosurgical procedures will develop from different directions, and it is likely that a combination of approaches will be necessary to maximise patient outcomes. We believe that cerebral infarction and selected neurodegenerative disorders are appropriate initial candidates for this research.

Failure of brain-derived neurotrophic factor-dependent neuron survival in mouse trisomy 16

The neurotrophin, brain derived neurotrophic factor (BDNF), exerts multiple effects on the development and maintenance of the nervous system, including regulating synaptic plasticity and promoting neuron survival. Here we report the selective failure of BDNF-dependent survival in cultured hippocampal neurons from the trisomy 16 (Ts16) mouse, an animal model of Down syndrome. This failure is accompanied by overexpression of a truncated, kinase-deficient isoform (T1) of the BDNF receptor tyrosine receptor kinase B (trkB). Adenovirus-mediated introduction of exogenous full-length trkB into Ts16 neurons fully restored BDNF-dependent survival, whereas exogenous truncated trkB expression in normal, euploid neurons reproduced the Ts16 BDNF signaling failure. Thus, the failure of Ts16 neurons to respond to BDNF is caused by dysregulation of trkB isoform expression. Such a neurotrophin signaling defect could contribute to developmental and degenerative disorders of the nervous system.

Effect of dexamethasone on the expression of brain-derived neurotrophic factor and neurotrophin-3 messenger ribonucleic acids after forebrain ischemia in the rat

OBJECTIVE

To determine whether a large dose of dexamethasone affected brain damage induced by concurrent cerebral ischemia, we used in situ hybridization to examine the expression of brain-derived neurotrophic factor and neurotrophin-3 messenger ribonucleic acids (mRNAs) in rats with and without dexamethasone administration after transient forebrain ischemia.

DESIGN

Prospective experimental study in rats.

SETTING

Experimental laboratory in a teaching hospital and university.

SUBJECTS

Eighty adult rats.

INTERVENTIONS

Twenty minutes of transient forebrain ischemia was induced by occlusion of four vessels in lightly anesthetized rats. Thirty-six animals received dexamethasone (15 mg/kg, intraperitoneally) after initial reperfusion. Thirty-six dexamethasone-control rats were injected with saline, and the remaining animals underwent sham surgery but no ischemia or dexamethasone.

MEASUREMENTS AND MAIN RESULTS

Using in situ hybridization, we determined hippocampal brain-derived neurotrophic factor and neurotrophin-3 mRNA expression 2, 4, 6, 12, and 24 hrs and 2, 3, 4, and 7 days after brain ischemia. Additionally, hippocampal CA1 region cell death was measured with Nissl stains. Both brain-derived neurotrophic factor and neurotrophin-3 mRNA exhibited a biphasic response after ischemia. Brain-derived neurotrophic factor mRNA showed two peaks of 4.07-fold and 2.84-fold increases relative to sham operation at 6 hrs and 2 days, respectively. Neurotrophin-3 mRNA initially decreased to 59% of sham levels at 4 hrs and then increased to 146% at 3 days before it returned to basal levels. When the ischemic rats were treated with dexamethasone, the elevation of brain-derived neurotrophic factor mRNA and the reduction of neurotrophin-3 mRNA level were prevented within the first 24 hrs, and hippocampal CA1 neurons were protected from ischemia-induced cell loss 7 days after brain ischemia. The protein levels of both brain-derived neurotrophic factor and neurotrophin-3 in general correspond to the mRNA levels in the hippocampal region.

CONCLUSIONS

Dexamethasone modulates the intriguing temporal and spatial expression of brain-derived neurotrophic factor and neurotrophin-3 that predominantly supports neuronal innervation at different times after brain ischemia and also may provide specific trophic support for various neurons in the central nervous system.

Restoration of mitochondrial function reverses developmental neuronal death in vitro

In a previous study characterizing morphological and functional features of cell death in trophically deprived chick ciliary ganglion neurons (Pena and Pilar [2000] J. Comp. Neurol. 424:377-396), we hypothesized that early cell death events might be targets for reversal, allowing for rescue of dying neurons. To test this hypothesis, ciliary ganglion (CG) neurons were cultured with or without trophic support (choroid, iris, and pigment epithelium soluble extract [CIPE]), or without trophic support for 11 or 18 hours and then exposed to trophic support. Prior to and at the onset of cell death commitment (11 hours) CIPE-deprived neurons exhibited increased membrane permeability, blebbing, cytoplasmic vacuolization, swollen mitochondria, low adenosine triphosphate levels, and release of cytochrome c from mitochondria. CIPE readdition at 11 hours reversed these changes. Between 11 and 18 hours, irreversible DNA fragmentation increased in CIPE-deprived neurons. Cyclosporin A and bongkrekic acid (inhibitors of mitochondrial transition permeability pores) prevented membrane permeability increases and delayed the progression to death in trophically deprived neurons by 12 hours; however, by 48 hours all neurons had died. BOC-Asp-CH2F (BAF), a pan-caspase inhibitor, did not prevent early events of cell death including increased membrane permeability and Cyto c release, but it inhibited DNA fragmentation and prolonged neuronal survival to 48 hours. We conclude that mitochondria changes occur early, prior to commitment and that the suppression of these changes can prevent all the downstream events of death, whereas caspase inhibitors have no effect on the early mitochondria/plasma membrane changes. Mitochondria thus play a critical role in the transition from reversible to irreversible commitment to developmental neuronal death. Furthermore, neuronal death is brought about by activation of one of two distinct pathways, one localized in mitochondria and the other dependent on activation of caspases.

GDNF and NGF family members and receptors in human fetal and adult spinal cord and dorsal root ganglia

We describe the expression of mRNA encoding ligands and receptors of members of the GDNF family and members of the neurotrophin family in the adult human spinal cord and dorsal root ganglia (DRG). Fetal human spinal cord and ganglia were investigated for the presence of ligands and receptors of the neurotrophin family. Tissues were collected from human organ donors and after routine elective abortions. Messenger RNA was found encoding RET, GFR alpha-1, BDNF, trkB, and trkC in the adult human spinal cord and BDNF, NT-3, p75, trkB, and trkC in the fetal human spinal cord. The percentage of adult human DRG cells expressing p75, trkA, trkB, or trkC was 57, 46, 29, and 24%, respectively, and that of DRG cells expressing RET, GFR alpha-1, GFR alpha-2, or GFR alpha-3 was 79, 20, 51, and 32%, respectively. GFR alpha-2 was expressed selectively in small, GFR alpha-3 principally in small and GFR alpha-1 and RET in both large and small adult human DRG neurons. p75 and trkB were expressed by a wide range of DRG neurons while trkA was expressed in most small diameter and trkC primarily in large DRG neurons. Fetal DRG cells were positive for the same probes as adult DRG cells except for NT-3, which was only found in fetal DRG cells. Messenger RNA species only expressed at detectable levels in fetal but not adult spinal cord tissues included GDNF, GFR alpha-2, NT-3, and p75. Notably, GFR alpha-2, which is expressed in the adult rat spinal cord, was not found in the adult human spinal cord.

The neuroprotective agent memantine induces brain-derived neurotrophic factor and trkB receptor expression in rat brain

Memantine is a medium-affinity uncompetitive N-methyl-d-aspartate receptor antagonist and has been clinically used as a neuroprotective agent to treat Alzheimer's and Parkinson's diseases. We have examined the effect of memantine (ip 5-50 mg/kg; 4 h) on the expression of brain-derived neurotrophic factor (BDNF) and trkB receptor mRNAs in rat brain by in situ hybridization. Memantine at a clinically relevant dose markedly increased BDNF mRNA levels in the limbic cortex, and this effect was more widespread and pronounced at higher doses. Effects of memantine on BDNF mRNA were also reflected in changes in BDNF protein levels. Moreover, memantine induced isoforms of the BDNF receptor trkB. Taken together, these data suggest that the neuroprotective properties of memantine could be mediated by the increased endogenous production of BDNF in the brain. These findings may open up new possibilities of pharmacologically regulating the expression of neurotrophic factors in the brain.

Identification and molecular cloning of a novel brain-specific receptor protein that binds to brain injury-derived neurotrophic peptide. Possible role for neuronal survival

Brain injury-derived neurotrophic peptide (BINP) is a synthetic 13-mer peptide that supports neuronal survival and protects hippocampal neurons in primary cultures from cell death caused by glutamate. We have developed a monoclonal antibody named mAb 6A22 against the 40-kDa BINP-binding protein, p40BBP. mAb 6A22 inhibits binding between BINP and rat brain synaptosomes and abolishes the protective effect of BINP. The antigen of mAb 6A22 should be the BINP-binding protein that mediates the neuroprotective action of BINP. Using an expression cloning approach with mAb 6A22, we isolated a cDNA encoding a novel receptor protein that shows binding activity of BINP. COS7 cells transfected with the cloned cDNA show binding of BINP and cell surfaces that are stained by 6A22. The mRNA for p40BBP is specific for the rat brain and is increased after birth. From immunohistochemical studies using mAb 6A22, p40BBP increased after kainic acid treatment in rat hippocampal neurons.

Survival promotion of mesencephalic dopaminergic neurons by depolarizing concentrations of K+ requires concurrent inactivation of NMDA or AMPA/kainate receptors

The death of dopaminergic neurons that occurs spontaneously in mesencephalic cultures was prevented by depolarizing concentrations of K+ (20-50 mM). However, unlike that observed previously in other neuronal populations of the PNS or CNS, promotion of survival required concurrent blockade of either NMDA or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptors by the specific antagonists, MK-801 and GYKI-52466, respectively. Rescued neurons appeared to be healthy and functional because the same treatment also dramatically enhanced their capacity to accumulate dopamine. The effects on survival and uptake were rather specific to dopaminergic neurons, rapidly reversible and still observed when treatment was delayed after plating. Glutamate release increased substantially in the presence of elevated concentrations of K+, and chronic treatment with glutamate induced a loss of dopaminergic neurons that was prevented by MK-801 or GYKI-52466 suggesting that an excitotoxic process interfered with survival when only the depolarizing treatment was applied. The effects of the depolarizing stimulus in the presence of MK-801 were mimicked by BAY K-8644 and abolished by nifedipine, suggesting that neuroprotection resulted from Ca(2+) influx through L-type calcium channels. Measurement of intracellular calcium revealed that MK-801 or GYKI-52466 were required to maintain Ca(2+) levels within a trophic range, thus preventing K+-induced excitotoxic stress and Ca(2+) overload. Altogether, our results suggest that dopaminergic neurons may require a finely tuned interplay between glutamatergic receptors and calcium channels for their development and maturation.

The pro-sequence facilitates folding of human nerve growth factor from Escherichia coli inclusion bodies

Nerve growth factor (beta-NGF), a neurotrophin required for the development and survival of specific neuronal populations, is translated as a prepro-protein in vivo. While the presequence mediates translocation into the endoplasmic reticulum, the function of the pro-peptide is so far unknown. As the pro-sequences of several proteins are known to promote folding of the mature part, the renaturation behaviour of recombinant human beta-NGF pro-protein was compared to that of the mature form. Expression of rh-pro-NGF in Escherichia coli led to the formation of inclusion bodies (IBs). The presence of the covalently attached pro-sequence significantly increased the yield and rate of refolding with concomitant disulfide bond formation when compared to the in vitro refolding of mature NGF (rh-NGF). Physicochemical characterization revealed that rh-pro-NGF is a dimer. The pro-peptide could be removed by limited proteolysis with trypsin yielding biologically active, mature rh-NGF. Furthermore, rh-pro-NGF exhibited biological activity in the same concentration range as rh-NGF.

Analysis of effects and pharmacokinetics of subcutaneously administered BDNF

Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family and has been shown to be a potent and effective trophic factor for motor neurons and other neurons of the peripheral and central nervous. Little is known, however, about the relationship between the efficacy and pharmacokinetics of s.c. administered BDNF. In this study, the efficacy of BDNF on motor neuron protection in sciatic or facial nerve axotomy models was examined and compared with the concommitant concentrations of BDNF in plasma. Delayed treatment (started at 1 week after surgery) of BDNF was also shown to retard choline acetyltransferase reduction in sciatic nerve axotomy models.

Purification and characterization of murine beta-nerve growth factor

Beta-nerve growth factor (beta-NGF) is a trophic factor in the nervous system. We aimed to isolate and characterize this protein in view of its potential therapeutic use in neurodegenerative diseases. For purification a two-step ion-exchange procedure was followed. The characterization was performed using separation and immunological techniques, as well as a biological assay. These studies showed that the obtained protein consisted of a mixture of beta-NGF molecules, intact at their NH2-terminal extreme, and molecules which have lost the NH2-terminal octapeptide and exhibit modifications increasing its hydrophobicity. All these molecular species were recognized immunologically and showed biological activity.

Activation of Trk neurotrophin receptors in the absence of neurotrophins

Neurotrophins regulate neuronal cell survival and synaptic plasticity through activation of Trk receptor tyrosine kinases. Binding of neurotrophins to Trk receptors results in receptor autophosphorylation and downstream phosphorylation cascades. Here, we describe an approach to use small molecule agonists to transactivate Trk neurotrophin receptors. Activation of TrkA receptors in PC12 cells and TrkB in hippocampal neurons was observed after treatment with adenosine, a neuromodulator that acts through G protein-coupled receptors. These effects were reproduced by using the adenosine agonist CGS 21680 and were counteracted with the antagonist ZM 241385, indicating that this transactivation event by adenosine involves adenosine 2A receptors. The increase in Trk activity could be inhibited by the use of the Src family-specific inhibitor, PP1, or K252a, an inhibitor of Trk receptors. In contrast to other G protein-coupled receptor transactivation events, adenosine used Trk receptor signaling with a longer time course. Moreover, adenosine activated phosphatidylinositol 3-kinase/Akt through a Trk-dependent mechanism that resulted in increased cell survival after nerve growth factor or brain-derived neurotrophic factor withdrawal. Therefore, adenosine acting through the A(2A) receptors exerts a trophic effect through the engagement of Trk receptors. These results provide an explanation for neuroprotective actions of adenosine through a unique signaling mechanism and raise the possibility that small molecules may be used to elicit neurotrophic effects for the treatment of neurodegenerative diseases.

Nerve growth factor prevents 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced cell death via the Akt pathway by suppressing caspase-3-like activity using PC12 cells: relevance to therapeutical application for Parkinson's disease

Nerve growth factor (NGF) mediates a variety of nerve cell actions through receptor tyrosine kinase TrkA. It has been revealed that the Akt pathway contributes to the prevention of apoptosis. It is thought that Parkinson's disease involves apoptosis, and NGF prevents apoptosis in an in vivo model system. However, there is no evidence that the Akt pathway helps to prevent parkinsonism. Here, we report that NGF prevents apoptosis induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in PC12 cells as an in vitro model system of parkinsonism and that this survival effect diminishes on addition of LY294002, a specific inhibitor of phosphatidylinositol 3-kinase. Immunocytochemical analysis revealed that 1 mM MPTP-treated cells or dominant negative Akt-expressing cells, to which were added NGF and MPTP, undergo apoptosis. Moreover, the caspase-3-like activity is increased by addition of MPTP or MPTP with NGF and LY294002. The importance of another signal pathway is shown by PD98059, a specific inhibitor of MAP kinase (MAPK) kinase, but PD98059 does not alter the survival effect in this model system. These results indicate that the Akt pathway helps to prevent parkinsonism by suppressing caspase-3-like activity, but the MAPK pathway is not involved in the NGF-dependent survival enhancing effect in this model system.

Stimulatory role of dopamine on fibroblast growth factor-2 expression in rat striatum

We have previously shown that systemic injection of (-)nicotine produces a selective up-regulation of fibroblast growth factor (FGF)-2 mRNA levels in rat striatum. Because (-)nicotine can increase striatal release of dopamine and glutamate, in the present study we have investigated the contribution of these neurotransmitters in the modulation of FGF-2 expression. We found that coinjection of dopaminergic D1 (SCH23390) or D2 (haloperidol) receptor antagonists prevents nicotine-induced elevation of FGF-2 expression. However, injection of the NMDA receptor antagonist MK-801 produced a significant increment of FGF-2 mRNA and protein levels in rat striatum similar to the effect produced by (-)nicotine alone. Interestingly this effect of MK-801 could also be prevented by D1 or D2 receptor antagonists, suggesting that an elevation of dopamine levels may be required for the regulation of the trophic molecule. Accordingly we found that the non-selective dopaminergic agonist apomorphine can similarly increase striatal FGF-2 mRNA levels. Despite the observation that both D1 and D2 receptors appear to contribute to the modulation of FGF-2 expression, only a direct activation of D2 receptors, through quinpirole administration, was able to mimic the effect of apomorphine. On the basis of FGF-2 neurotrophic activity, these results suggest that direct or indirect activation of dopaminergic system can be neuroprotective and might reduce cell vulnerability in degenerative disorders.

Insulin-like growth factor-I and its receptor in the frontal cortex, hippocampus, and cerebellum of normal human and alzheimer disease brains

Assimilated evidence indicates that the neurotoxic potential of amyloid beta (Abeta) peptide and an alteration in the level of growth factor(s) may possibly be involved in the loss of neurons observed in the brain of patients suffering from Alzheimer disease (AD), the prevalent cause of dementia in the elderly. In the present study, using receptor binding assays and immunocytochemistry, we evaluated the pharmacological profile of insulin-like growth factor-I (IGF-I) receptors and the distribution of IGF-I immunoreactivity in the frontal cortex, hippocampus, and cerebellum of AD and age-matched control brains. In control brains, [(125)I]IGF-I binding was inhibited more potently by IGF-I than by Des(1-3)IGF-I, IGF-II or insulin. The IC(50) values for IGF-I in the frontal cortex, hippocampus, and cerebellum of the normal brain did not differ significantly from the corresponding regions of the AD brain. Additionally, neither K(D) nor B(max) values were found to differ in the hippocampus of AD brains from the controls. At the regional levels, [(125)I]IGF-I binding sites in the AD brain also remained unaltered compared to the controls. As for the peptide itself, IGF-I immunoreactivity, in normal control brains, was evident primarily in a subpopulation of astrocytes in the frontal cortex and hippocampus, and in certain Purkinje cells of the cerebellum. In AD brains, a subset of Abeta-containing neuritic plaques, apart from astrocytes, exhibit IGF-I immunoreactivity. These results, taken together, suggest a role for IGF-I in compensatory plasticity and/or survival of the susceptible neurons in AD brains.

Fibroblast growth factor-2-producing fibroblasts protect the nigrostriatal dopaminergic system from 6-hydroxydopamine

We tested the hypothesis that fibroblasts, which had been genetically engineered to produce fibroblast growth factor-2 (FGF-2), can protect nigrostriatal dopaminergic neurons. Three groups of rats received either a burr hole only (n=5) or implantation of fibroblasts, which had been genetically engineered to produce beta-galactosidase (beta-gal) (n=8) or FGF-2 (n=8), at two sites in the right striatum. Two weeks later, the animals received an injection of 25 microg of 6-hydroxydopamine hydrobromide (6-OHDA) midway between the two implant sites. The group that received FGF-2-fibroblasts had significantly fewer apomorphine-induced rotations than the groups that received a burr hole only or beta-gal-fibroblasts at weeks 2 and 3 following lesioning with 6-OHDA. Testing for amphetamine-induced rotation revealed a mild reduction in rotation in the beta-gal-fibroblast group compared to the burr hole only group, but a striking attenuation of amphetamine-induced rotation in the FGF-2-fibroblast group. There was also preservation of TH-IR neurons on the lesioned side relative to both control groups. The size of the grafts and the gliosis surrounding the injection sites did not differ between the FGF-2-fibroblast and beta-gal-fibroblast groups. To further characterize the production of FGF-2 by the FGF-2-fibroblasts, we implanted FGF-2-fibroblasts and beta-gal-fibroblast into the striatum of rats but did not lesion the animals with 6-OHDA. The animals were then sacrificed at 1, 2 and 5 weeks following implantation. Prior to implantation the FGF-2 fibroblasts contained 148 ng/mg of FGF-2-immunoreactive (FGF-2-IR) material per mg of protein of cell lysate. After implantation FGF-2-IR material was noted in the grafts of FGF-2-fibroblasts, most conspicuously at 1 and 2 weeks following implantation. We also noted FGF-2-IR material in the nuclei of reactive astrocytes adjacent to the implants, and OX-42-immunoreactive (OX-42-IR) cells adjacent and occasionally within the implants. Our work indicates that fibroblasts genetically engineered to produce FGF-2 and implanted in the striatum can protect the nigrostriatal dopaminergic system and may be useful in the treatment of Parkinson's disease.

Brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4/5 prevent the death of striatal projection neurons in a rodent model of Huntington's disease

Intrastriatal injection of quinolinate has been proven to be a very useful animal model to study the pathogenesis and treatment of Huntington's disease. To determine whether growth factors of the neurotrophin family are able to prevent the degeneration of striatal projection neurons, cell lines expressing brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or neurotrophin-4/5 (NT-4/5) were grafted in the adult rat striatum before quinolinate injection. Three days after lesioning, ongoing cell death was assessed by in situ detection of DNA fragmentation. In animals grafted with the control cell line, quinolinate injection induced a gradual cell loss that was differentially prevented by intrastriatal grafting of BDNF-, NT-3-, or NT-415-secreting cells. Seven days after lesioning, we characterized striatal projection neurons that were protected by neurotrophins. Quinolinate injection, alone or in combination with the control cell line, induced a selective loss of striatal projection neurons. Grafting of a BDNF-secreting cell line pre-vented the loss of all types of striatal projection neurons analyzed. Glutamic acid decarboxylase 67-, preproenkephalin-, and preprotachykinin A- but not prodynorphin-expressing neurons were protected by grafting of NT-3- or NT-4/5-secreting cells but with less efficiency than the BDNF-secreting cells. Our findings show that neurotrophins are able to promote the survival of striatal projection neurons in vivo and suggest that BDNF might be beneficial for the treatment of striatonigral degenerative disorders, including Huntington's disease.

Design and solution structure of functional peptide mimetics of nerve growth factor

The C-D loop in nerve growth factor (NGF) is involved in binding to the NGF receptor, TrkA. It is flexible and adopts several different types conformations in different NGF crystal forms. We have previously shown that a small cyclic peptide derived from the C-D loop of NGF binds to the TrkA receptor by mimicking the structure of this loop. To understand structure-function relationships in NGF C-D loop mimetics, we have produced a series of peptides predicted to form different types of beta-turns. The peptides were tested for their ability to promote cell survival in serum-free medium and to induce TrkA tyrosine phosphorylation. NMR structural studies were used to determined the backbone conformation and the spatial orientation of side chains involved in binding to the TrkA receptor. Peptides that form type I or type gammaL-alphaR beta-turns were the most active. The variety of active loop conformations suggests that the mimetics (and NGF) accommodate the binding site on TrkA by an 'induced fit' mechanism. In agreement with this hypothesis, NMR relaxation measurements detected both fast and slow motion in the peptides. We also characterized a retro-inverso peptide derived from the NGF C-D loop. This D-amino acid cyclic peptide did not adopt a conformation homologous to the NGF C-D loop and was inactive. This may be representative of difficulties in producing structural and functional mimetics by retro-inverso schemes.

Statistical comparison of axon-scaled neurochemical production

Treatments designed to increase neurochemical levels may also result in increases in the numbers of axons that produce the neurochemicals of interest. A natural research question is how does one compare the average neurochemical production per axon between two (or more) experimental groups. Two statistical methods are proposed for this problem. The first method utilizes a delta-method approximation to the variance of a function of random variables while the second method is based on the bootstrap. These methods are illustrated with data obtained from perivascular norepinephrine following intracerebroventricular infusion of neurotrophin nerve growth factor in adult rats and are studied in a small simulation experiment. The delta-method confidence intervals exhibited better coverage properties than the bootstrap alternative.

rhGGF2 protects against cisplatin-induced neuropathy in the rat

In many patients treated with cisplatin a peripheral sensory neuropathy develops. This side-effect is considered dose-limiting, and therefore restricts the total dose of cisplatin that can be administered. Recent in vitro and in vivo studies suggest that recombinant human Glial Growth Factor 2 (rhGGF2) has neuroprotective effects. This prompted us to investigate in a rat model whether rhGGF2 ameliorates cisplatin neuropathy. A total of 48 rats were randomly divided into four groups of 12 rats each. Three groups received cisplatin and were treated with either 0.1 mg/kg rhGGF2, 0.3 mg/kg rhGGF2 or placebo. The fourth group (saline/placebo) served as age-matched controls. In the cisplatin/placebo treated rats a neuropathy developed, as determined by measurements of the nerve conduction velocity (NCV). Treatment with rhGGF2 dose-dependently protected against the neuropathy. Histological examination and morphometric analysis revealed that rhGGF2 also protects against cisplatin-induced changes in the morphology and size of DRG satellite cell nuclei. In a control study rhGGF2 did not affect normal NCV development. We conclude that rhGGF2 treatment is of benefit in the treatment of cisplatin neuropathy in the rat.