Effect of the neuroprotective compound SR57746A on nerve growth factor synthesis in cultured astrocytes from neonatal rat cortex

Strategies for Treatment of Disease-Associated Dementia Beyond Alzheimer's Disease: An Update

Memory, cognition, dementia, and neurodegeneration are complexly interlinked processes with various mechanistic pathways, leading to a range of clinical outcomes. They are strongly associated with pathological conditions like Alzheimer's disease, Parkinson's disease, schizophrenia, and stroke and are a growing concern for their timely diagnosis and management. Several cognitionenhancing interventions for management include non-pharmacological interventions like diet, exercise, and physical activity, while pharmacological interventions include medicinal agents, herbal agents, and nutritional supplements. This review critically analyzed and discussed the currently available agents under different drug development phases designed to target the molecular targets, including cholinergic receptor, glutamatergic system, GABAergic targets, glycine site, serotonergic targets, histamine receptors, etc. Understanding memory formation and pathways involved therein aids in opening the new gateways to treating cognitive disorders. However, clinical studies suggest that there is still a dearth of knowledge about the pathological mechanism involved in neurological conditions, making the dropouts of agents from the initial phases of the clinical trial. Hence, a better understanding of the disease biology, mode of drug action, and interlinked mechanistic pathways at a molecular level is required.

Xaliproden (SR57746A) Induces 5-Ht1A Receptors-Mediated Map Kinase Activation in Pc12 Cells

Neurotrophic growth factors are involved in cell survival. However, natural growth factors have a very limited therapeutic use because of their short half-life. In the present study, we investigated the mechanism of action of a non peptidic neurotrophic drug, Xaliproden, a potential molecule for the treatment of motoneuron diseases, since the transduction pathways of this synthetic 5-HT1A agonist are very poorly understood. Xaliproden does not activate the Trk receptor but causes a rapid increase in the activities of the ERK1 and ERK2 isoforms of MAP kinase, which then rapidly decrease to the basal level. We demonstrate that isoforms of the she adapter protein are phosphorylated independently of each other and are probably not the source of the Xaliproden-induced MAP kinases activation. The inhibitor of Ras farnesylation, FPT-1, and the protein kinase C inhibitors, GF 109203X and chelerythrine, inhibited the Xaliproden-induced MAP kinase activation, suggesting p21Ras and PKC involvement. Moreover, the observations that the 5-HT1A antagonist, pindobind, and pertussis toxin abolished the Xaliproden-induced ERK stimulation suggested that Xaliproden activates the MAP kinase pathways by stimulating the G-protein-coupled receptor, 5-HT1A. These results demonstrated clearly that the non peptidic compound, Xaliproden, exerts its neurotrophic effects through a mechanism of action differing from that of neurotrophins. These findings suggest that this compound does not involve MAPK activation by TrkA receptor stimulation but acts by MAP Kinase pathway by a pertussis toxin-sensitive mechanism involving 5-HT1A receptors, p21 Ras and MEK-1 and by PKC and Akt pathways.

Astrocytes and microglia: responses to neuropathological conditions

Activated astrocytes and microglia, hallmark of neurodegenerative diseases release different factors like array of pro and anti-inflammatory cytokines, free radicals, anti-oxidants, and neurotrophic factors during neurodegeneration which further contribute to neuronal death as well as in survival mechanisms. Astrocytes act as double-edged sword exerting both detrimental and neuroprotective effects while microglial cells are attributed more in neurodegenerative mechanisms. The dual and insufficient knowledge about the precise role of glia in neurodegeneration showed the need for further investigations and thorough review of the function of glia in neurodegeneration. In this review, we consolidate and categorize the glia-released factors which contribute in degenerative and protective mechanisms during neuropathological conditions.

Time-dependent activation of c-fos in limbic brain areas by ocular administration of nerve growth factor in adult rats

PURPOSE

The ocular administration of the neurotrophin nerve growth factor (NGF) has been successfully used in humans to recover damaged ocular tissues. Studies on animal models have demonstrated the ability of ocular applied NGF to reach the retina and the optic nerve and affect brain visual areas. The aim of this study was to examine whether the ocular application of NGF as eye drops might affect brain areas other than the primary visual centers.

METHODS

Two drops (10 μL) of NGF solution (200 μg/mL) or saline were applied as collyrium to both eyes of adult male Sprague-Dawley rats. The animals were sacrificed at 4, 8, or 24 h after treatment and the brains were fixed through intracardiac perfusion. Coronal brain sections were cut with a cryostat and used for immunohistochemical time series and double immunofluorescence studies using c-fos and NeuN as markers for neuronal activation.

RESULTS

The immunohistochemical studies show a time-dependent effect of NGF eye drop treatment. At 4 h after NGF ocular administration, the increase in c-fos immunoreactivity is mainly observed in areas belonging to the central visual system, such as the lateral geniculate nucleus and visual cortex. At 8 h posttreatment, c-fos expression is enhanced in several limbic structures, including the frontal cortex, hippocampus, amygdala, and hypothalamus. The effects of NGF on c-fos distribution persist at 24 h postadministration. Specificity of NGF-induced c-fos in brain was confirmed using inactivated NGF. The neuronal nature of the NGF-activated cells was demonstrated by confocal microscopy observation of c-fos and NeuN colocalization.

CONCLUSION

This study demonstrates that NGF, when applied on ocular surface, is able to activate c-fos in several areas of the limbic system in a time-dependent manner. These findings suggest that the effects of NGF eye drops are not restricted to the primary visual areas, but are extended to all the retinal central targets, including the forebrain structure. Based on these data, the use of NGF eye drops as a strategy to produce NGF-mediated protective and reparative actions in brain is hypothesizable.

Progress in the development of new drugs in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease with a global prevalence estimated at 26.55 million in 2006. During the past decades, several agents have been approved that enhance cognition of AD patients. However, the effectiveness of these treatments are limited or controversial and they do not modify disease progression. Recent advances in understanding AD pathogenesis have led to the development of numerous compounds that might modify the disease process. AD is mainly characterized neuropathologically by the presence of two kinds of protein aggregates: extracellular plaques of Abeta-peptide and intracellular neurofibrillary tangles. Abeta and tau could interfere in an original way contributing to a cascade of events leading to neuronal death and transmitter deficits. Investigation for novel therapeutic approaches targeting the presumed underlying pathogenic mechanisms is major focus of research. Antiamyloid agents targeting production, accumulation, clearance, or toxicity associated with Abeta peptide, are some approaches under investigation to limit extracellular plaques of Abeta-peptide accumulation. We can state as an example: Abeta passive and active immunization, secretases modulation, Abeta degradation enhancement, or antiaggregation and antifibrillization agents. Tau-related therapies are also under clinical investigation but few compounds are available. Another alternative approach under development is neuroprotective agents such as antioxidants, anti-inflammatory drugs, compounds acting against glutamate mediated neurotoxicity. Neurorestorative approaches through neurotrophin or cell therapy also represent a minor avenue in AD research. Finally, statins, receptor for advanced glycation end products inhibitors, thiazolidinediones, insulin, and hormonal therapies are some other ways of research for a therapeutic approach of Alzheimer's disease. Taking into account AD complexity, it becomes clear that polypharmacology with drugs targeting different sites could be the future treatment approach and a majority of the recent drugs under evaluation seems to act on multiple targets. This article exposes general classes of disease-modifying therapies under investigation.

SR 57746A/xaliproden, a non-peptide neurotrophic compound: prospects and constraints for the treatment of nervous system diseases

Neurodegenerative disorders such as Alzheimer's disease or amyotrophic lateral sclerosis as well as peripheral neuropathies are difficult to treat due to a limited range of effective drugs. Neurotrophic growth factors promote neuronal survival and differentiation and could hence be interesting tools to treat these diseases. Their therapeutic use is limited due their short half-life, their inability to cross the BBB and potential side effects including tumor promotion. SR 57746A is a non-peptide, orally active compound that exhibits neuroprotective effects in various model systems in vitro and in vivo. SR 57746A shows--amongst other activities--agonistic activity on 5-HT(1A) receptors. Several clinical trials examined SR 57746A in patients with Alzheimer's disease, amyotrophic lateral sclerosis or chemotherapy-induced peripheral sensory neuropathy. This article reviews the preclinical and clinical data on SR 57746A and points out potential future applications of this compound. However, due to disapointing results in phase III trials, Sanofi-Aventis recently decided to discontinue the development of this drug.

Targeting neuroprotection as an alternative approach to preventing and treating neuropathic pain

Neuropathic pain syndromes arise from dysfunction of the nerve itself, through traumatic or nontraumatic injury. Unlike acute pain syndromes, the pain is long-lasting and does not respond to common analgesic therapies. Drugs that disrupt nerve conduction and transmission or central sensitization, currently the only effective treatments, are only modestly effective for a portion of the patients suffering from neuropathic pain and come with the cost of serious adverse effects. Neurodegeneration, as a reaction to nerve trauma or chronic metabolic or chemical intoxication, appears to be an underlying cause of neuropathic pain. Identifying mechanisms of neurodegeneration and designing neuroprotective therapies is an ambitious goal toward treating or even preventing the development of these disabling disorders.

Taking the next steps in the treatment of Alzheimer's disease: disease-modifying agents

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder in the United States and the number of AD patients is increasing at an alarming rate. There is no cure for AD and the currently available treatments are symptomatic, providing only limited effects on disease pathophysiology and progression. An overwhelming need exists for therapies that can slow or halt this debilitating disease process. Disease modification in AD has been defined from patient-focused, regulatory, and neurobiological perspectives. The latter two of these perspectives rely largely on an interruption of the disease process and a clear demonstration of this interruption. As defined by Cummings, a disease-modifying treatment is a “pharmacologic treatment that retards the underlying process of AD by intervening in the neurobiological processes that constitute the pathology and pathophysiology of the disease and lead to cell death or dysfunction.” By this definition, the burden of confirmatory study is placed on any new treatment for which the claim of “disease modification” is to be made (Slide 1).

Disease-modifying therapies in Alzheimer's disease

Alzheimer's disease (AD) is a chronic, progressive, neurodegenerative disorder that places a substantial burden on patients, their families, and society. The disease affects approximately 5 million individuals in the United States, with an annual cost of care greater than $100 billion. During the past dozen years, several agents have been approved that enhance cognition and global function of AD patients, and recent advances in understanding AD pathogenesis has led to the development of numerous compounds that might modify the disease process. A wide array of antiamyloid and neuroprotective therapeutic approaches are under investigation on the basis of the hypothesis that amyloid beta (A beta) protein plays a pivotal role in disease onset and progression and that secondary consequences of A beta generation and deposition, including tau hyperphosphorylation and neurofibrillary tangle formation, oxidation, inflammation, and excitotoxicity, contribute to the disease process. Interventions in these processes with agents that reduce amyloid production, limit aggregation, or increase removal might block the cascade of events comprising AD pathogenesis. Reducing tau hyperphosphorylation, limiting oxidation and excitotoxicity, and controlling inflammation might be beneficial disease-modifying strategies. Potentially neuroprotective and restorative treatments such as neurotrophins, neurotrophic factor enhancers, and stem cell-related approaches are also under investigation.

Looking for novel ways to treat the hallmarks of Alzheimer's disease

Alzheimer's disease (AD) represents an increasing public health issue as demographic changes and generally improved medical care result in a larger aged population. Although significant advances have been made in the diagnosis and treatment of AD, the unmet medical need remains and few treatment options are available. This review focuses on emerging therapies that aim to treat the underlying causes of the disease rather than the symptoms. Such disease-modifying treatments, focused on the two main hallmarks of the disease (plaques and tangles), include new and old targets which have significant potential in the field and are on the cusp of providing new treatment paradigms within the coming years.

A study of the purine derivative AIT-082 in G93A SOD1 transgenic mice

AIT-082 is a purine derivative with neuroprotective and neurotrophic activity that is desirable in a candidate therapy for Amyotrophic Lateral Sclerosis. Consequently, we investigated the effect of AIT-082 in a transgenic mouse model of ALS. AIT-082 (0, 1, 3, 10, 30, 60, 100 mg/kg) was given to TgN(SOD1-G93A)1Gur transgenic mice from age 30 days until death. The age at onset of clinical signs of disease and the age at death were recorded for each animal. Disease progression was measured by the weekly average distance run in a running wheel. Analysis was made by the Kaplan Meier method with log rank statistics, log rank for trend and Cox regression. Neuropathological study of the brain, spinal cord, muscles and other organs was undertaken at death. In a second experiment we studied the effect of AIT-082 (30 mg/kg) at the onset of disease and during survival of transgenic G93A SOD1 mice, beginning dosing at different ages (20, 30, 40, 60, 80 days). Disease onset was mildly earlier (i.e. worse) at 1 and 10 mg/kg AIT-082 and mildly delayed at 30 mg/kg. This improvement did not reach the usual statistical significance. There was no difference in the age at death for any treatment dose. There was no difference in the neuropathology of treated and untreated G93A mice. However, there was an early improvement in the running wheel function at all tested doses. Using Cox regression, after adjustment for sex, the mice in the running wheels had slightly delayed onset of disease without change in survival and, after adjustment for exercise, the female mice had slightly improved survival. Consequently, AIT-082 would not be an attractive candidate for ALS clinical trials as monotherapy and justification for its use in combination therapy would require additional laboratory support. There was dissociation between the endpoints of disease progression (as judged by running wheel performance) and disease onset and survival. AIT-082 improved early running wheel performance yet led to accelerated late decline and had no impact on survival. It is possible that the drug facilitates early sprouting that leads to accelerated late decline.

Up-regulation of BDNF in astrocytes by TNF-alpha: a case for the neuroprotective role of cytokine

Tumor necrosis factor-alpha (TNF-alpha) is widely known to be involved in physiological and pathophysiological processes of the brain where this proinflammatory cytokine is implicated with regulation of inflammatory and survival components. We report that TNF-alpha up-regulates exon-IV-bdnf mRNA and brain-derived neurotrophic factor (BDNF) protein in primary astrocytes. The BDNF protein was detectable both in cellular lysate and in the extracellular medium. Activation of NF-kappaB by TNF-alpha and inhibition of TNF-alpha-induced BDNF expression by Deltap65 (a dominant-negative mutant) and NEMO-binding domain peptide (an inhibitor of NF-kappaB) suggests that TNF-alpha induces BDNF expression through the activation of NF-kappaB. Similarly, TNF-alpha induced the activation of C/EBPbeta and the expression of BDNF was sensitive to overexpression of DeltaC/EBPbeta (a dominant-negative mutant) and ETO (an inhibitor of C/EBPbeta). Among three MAP kinases, TNF-alpha-induced BDNF up-regulation was sensitive only to inhibitors of ERK MAP kinase. However, the ERK MAP kinase pathway was coupled to activation of C/EBPbeta but not NF-kappaB. Taken together, this study identifies a novel property of TNF-alpha in inducing the expression of BDNF via NF-kappaB and C/EBPbeta in astrocytes that may be responsible for neurotrophic activity of the cytokine.

Endothelin increases expression of exon III- and exon IV-containing brain-derived neurotrophic factor transcripts in cultured astrocytes and rat brain

The effects of endothelins (ETs) on brain-derived neurotrophic factor (BDNF) production in astrocytes were investigated. ET-1 (100 nM) increased the mRNA level and extracellular release of BDNF in cultured astrocytes. RT-PCR analyses using primer pairs that amplified exon-specific BDNF transcripts revealed that exon III- and exon IV-containing BDNF transcripts existed in cultured astrocytes, whereas exon I- and exon II-containing BDNF transcripts did not. ET-1 and Ala(1,3,11,15)-ET-1, an ET(B) receptor agonist, increased the expressions of the exon III and exon IV transcripts in cultured astrocytes. Intracerebroventricular administration of 500 pmol/day of Ala(1,3,11,15)-ET-1 increased exon III and exon IV BDNF transcripts in the rat striatum. In cultured astrocytes, Ca(2+)-chelation, W-7 (a calmodulin inhibitor), and KN93 (a Ca(2+)/calmodulin kinase inhibitor) inhibited the increases in exon IV BDNF mRNA and CCAAT enhancer-binding protein beta (C/EBPbeta) levels induced by ET-1. The ET-induced increases in exon III BDNF mRNA expression and phosphorylation of cAMP response element binding protein (CREB) were reduced by Ca(2+) chelation, W-7, KN93, PD98059 (a MEK inhibitor), and wortmannin (a phosphatidylinositol 3-kinase inhibitor). These results suggest that ETs stimulate the expressions of exon III and exon IV BDNF transcripts in astrocytes through CREB and C/EBPbeta-mediated mechanisms, respectively.

Astrocyte apoptosis: implications for neuroprotection

Astrocytes, the most abundant glial cell types in the brain, provide metabolic and trophic support to neurons and modulate synaptic activity. Accordingly, impairment in these astrocyte functions can critically influence neuronal survival. Recent studies show that astrocyte apoptosis may contribute to pathogenesis of many acute and chronic neurodegenerative disorders, such as cerebral ischemia, Alzheimer's disease and Parkinson's disease. We found that incubation of cultured rat astrocytes in a Ca(2+)-containing medium after exposure to a Ca(2+)-free medium causes an increase in intracellular Ca(2+) concentration followed by apoptosis, and that NF-kappa B, reactive oxygen species, and enzymes such as calpain, xanthine oxidase, calcineurin and caspase-3 are involved in reperfusion-induced apoptosis. Furthermore, we demonstrated that heat shock protein, mitogen-activated protein/extracellular signal-regulated kinase, phosphatidylinositol-3 kinase and cyclic GMP phosphodiesterase are target molecules for anti-apoptotic drugs. This review summarizes (1) astrocytic functions in neuroprotection, (2) current evidence of astrocyte apoptosis in both in vitro and in vivo studies including its molecular pathways such as Ca(2+) overload, oxidative stress, NF-kappa B activation, mitochondrial dysfunction, endoplasmic reticulum stress, and protease activation, and (3) several drugs preventing astrocyte apoptosis. As a whole, this article provides new insights into the potential role of astrocytes as targets for neuroprotection. In addition, the advance in the knowledge of molecular mechanisms of astrocyte apoptosis may lead to the development of novel therapeutic strategies for neurodegenerative disorders.

Neurotrophic activity of 2,4,4-trimethyl-3-(15-hydroxypentadecyl)-2-cyclohexen-1-one in cultured central nervous system neurons

Endogenous neurotrophic factors are essential for the development and maintenance of the nervous system. This suggests their potential utilization as therapeutic agents for neurodegenerative diseases. However, the clinical use of these proteic factors is still restricted, and brings about undesirable consequences, including adverse side effects, and bioavailability and stability difficulties. Therefore, the development of low-molecular weight, non-proteic synthetic compounds with neurotrophic properties appears as a promising approach. The aim of this study was to explore the biological activity of 2,4,4-trimethyl-3-(15-hydroxypentadecyl)-2-cyclohexen-1-one (tCFA15), a trimethyl cyclohexenonic long-chain fatty alcohol. To this end, neurons from fetal rat cerebral hemispheres were cultured in the presence of increasing doses of tCFA15 ranging from 0.1 to 1000 nM. Quantification of cell numbers after 48-h culture showed that 100 nM tCFA15 induced a significant increase in the number of surviving cells. Measurement of total neurite length in microtubule-associated protein 2-positive cells also revealed a stimulatory effect in a wider range of concentrations. The extent of this neuritogenic action was similar to that induced by dibutyryl-cyclic AMP, a well-known neurite outgrowth stimulator, but used at much higher concentration (1 mM). Analysis of structure-activity relationships with different tCFA15 analogs and derivatives corroborated the neurotrophic activity. Taken together, these findings provide strong evidence that tCFA15 exhibits neurotrophic properties in vitro.

Brain-derived neurotrophic factor superinduction parallels anti-epileptic--neuroprotective treatment in the pilocarpine epilepsy model

Antiepileptic drugs provide neuroprotection in several animal models of brain damage, including those induced by status epilepticus (SE). The mechanisms involved in this action are unknown, but neurotrophic factors such as brain-derived neurotrophic factor (BDNF) may play a role. In this study we investigated the changes in BDNF levels in rats in which SE had been induced by pilocarpine injection (400 mg/kg i.p.) and continued for several hours (unprotected group). In other animals (protected groups), SE was suppressed after 30 min by intraperitoneal injection of either diazepam (10 mg/kg) + pentobarbital (30 mg/kg) or paraldehyde (0.3 mg/kg). In diazepam + pentobarbital-treated rats the hippocampal damage caused by SE was significantly lower (p < 0.05) than in unprotected animals. In addition, 2 and 24 h after pilocarpine injection, the levels of BDNF mRNA were moderately increased in the unprotected group, but 'superinduced' in protected animals, especially in the neocortex and hippocampus. A time-dependent increase in BDNF immunoreactivity was also found by western blot analysis in rats treated with diazepam + pentobarbital. In contrast, a decrease of BDNF immunoreactivity occurred in the unprotected group. In conclusion, these results show that neuroprotection induced by anti-epileptic drugs in pilocarpine-treated rats is accompanied by strong potentiation of BDNF synthesis in brain regions involved in SE.