Evaluation of neurotoxic and neuroprotective pathways affected by antiepileptic drugs in cultured hippocampal neurons

In this study we evaluated the neurotoxicity of eslicarbazepine acetate (ESL), and of its in vivo metabolites eslicarbazepine (S-Lic) and R-licarbazepine (R-Lic), as compared to the structurally-related compounds carbamazepine (CBZ) and oxcarbazepine (OXC), in an in vitro model of cultured rat hippocampal neurons. The non-related antiepileptic drugs (AEDs) lamotrigine (LTG) and sodium valproate (VPA) were also studied. We assessed whether AEDs modulate pro-survival/pro-apoptotic pathways, such as extracellular-regulated kinase (ERK1/2), Akt and stress activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK).We found that neither ESL nor its metabolites, CBZ or LTG, up to 0.3 mM, for 24 h of exposure, decreased cell viability. OXC was the most toxic drug decreasing cell viability in a concentration-dependent manner, leading to activation of caspase-3 and PARP cleavage. VPA caused the appearance of the apoptotic markers, but did not alter cell viability. ESL, S-Lic and OXC decreased the levels of phospho-ERK1/2 and of phospho-Akt, when compared to basal levels, whereas CBZ decreased phospho-SAPK/JNK and phospho-Akt levels. LTG and VPA increased the phosphorylation levels of SAPK/JNK.These results suggest that ESL and its main metabolite S-Lic, as well as CBZ, LTG and VPA, are less toxic to hippocampal neurons than OXC, which was the most toxic agent.     

Methylene blue and the neurotoxic mechanisms of ifosfamide encephalopathy

In cancer chemotherapy with ifosfamide the occurrence of a drug-related encephalopathy represents a severe adverse-effect of unknown origin. We found that the underlying mechanism resides in the mitochondrial toxicity of ifosfamide metabolites. The electron accepting drug methylene blue can substitute for the demonstrated flavoprotein deficiency and its administration leads to resolution of the encephalopathy in patients. The prophylactic administration of methylene blue is equally effective via another principal mechanism, namely oxidation of the excessive quantity of NADH formed during ifosfamide metabolism. The inhibition by methylene blue of multiple amine oxidase activities also prevents formation of the neurotoxic chloroacetaldehyde from ifosfamide-derived chloroethyl amine. Thus, methylene blue exhibits several synergistic modes of actions which enable the dose-limiting neurotoxicity of alkylating chemotherapy with ifosfamide in cancer patients to be overcome Received: 9 October 1995/Accepted in revised form: 30 January 1996     

Resveratrol, a neuroprotective supplement for Alzheimer's disease

The polyphenolic compound resveratrol (3,4',5-trihydroxystilbene) is a naturally occurring phytochemical which has been found in more than 70 plant species, including herbs and human food products such as grapes, berries, and peanuts. Resveratrol was first isolated in 1940; however, little attention was paid to it until its benefits in coronary heart disease were studied in 1992. Since then, increasing evidence has indicated that resveratrol may be useful in treating cardiovascular diseases, cancers, pain, inflammation, tissue injury, and in reducing the risk of neurodegenerative disorders, especially Alzheimer's disease (AD). AD is characterized by a progressive dementia, and is one of the most common neurodegenerative disorders in the elderly. It has been reported that resveratrol exhibits neuroprotective benefits in animal models of AD. Resveratrol promotes the non-amyloidogenic cleavage of the amyloid precursor protein, enhances clearance of amyloid beta-peptides, and reduces neuronal damage. Despite the effort spent trying to understand the mechanisms by which resveratrol functions, the research work in this field is still incomplete. Many concerns such as bioavailability, biotransformation, synergism with other dietary factors, and risks inherent to its possible pro-oxidant activities still need to be addressed. This review summarizes and discusses the neuroprotective effects of resveratrol on AD, and their potential mechanisms.     

Approaches to neuroprotective strategies in multiple sclerosis

Importance of the field: Multiple sclerosis (MS) is a neurologic disease that is the most common nontraumatic cause of serious disability in young adults.

Areas covered in this review: We discuss the natural history of the disease, methods of measuring disease activity and burden, and cellular and molecular mechanisms of damage, in particular recent advances. These imply new therapeutic targets, which are beginning to be tested in animal models of MS as well as in patients.

What the reader will gain: The reader will learn about some recent advances in understanding MS, especially the evolution from an inflammatory phase to a neurodegenerative phase, which have different therapeutic approaches.

Take home message: MS has a long-term course of accumulating deficit in which neuroinflammation evolves into neurodegeneration, which require different treatment strategies – immune modulation and neuroprotection. Neuroprotective strategies are still under development.     

Mood stabilizers in Alzheimer's disease: symptomatic and neuroprotective rationales

OBJECTIVE: This paper provides a case study of 'reverse translational research', in which empirical clinical trials focused on relieving psychopathological symptoms of Alzheimer's disease (AD) ultimately led to mechanism-based trials addressing aspects of the underlying pathophysiology of Alzheimer's disease. AD is multi-dimensional in nature, characterized not only by cognitive and functional decline but by neuropsychiatric symptoms that develop commonly and are associated with considerable morbidity. There have been a large number of empirical trials of various pharmacological agents to reduce these symptoms, such as agitation. Although antipsychotics are used most frequently for agitation, the usual effect size is modest, and there is a range of tolerability and/or safety issues, leading to the hope that alternatives can be found. Furthermore, most clinical trials addressing psychopathology have not been mechanism-based and none have attempted an alternative approach, namely, to delay or prevent the emergence of psychopathology. FINDINGS: The evidence of clinical trials is reviewed regarding the safety, tolerability, and apparent efficacy of the mood stabilizers carbamazepine and valproate for agitation associated with AD. Possible mechanisms of action of valproate are reviewed, leading to the surprising conclusion that neuroprotective properties may account for some of its clinical effects. These mechanisms (including activation of wnt-dependent signaling and upregulation of bcl-2, among others) may be particularly relevant for long-term treatment of AD. CONCLUSIONS: These clinical and mechanistic findings were combined in the development of a novel clinical trial examining whether chronic valproate therapy can attenuate the clinical progression of AD, which will be implemented by the Alzheimer's Disease Cooperative Study. The design addresses valproate's potential to delay or prevent the onset of agitation in patients lacking agitation to begin with, as well as to slow progressive decline in cognition and daily functioning.     

Minocycline: neuroprotective mechanisms in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by cardinal features of tremor, bradykinesia, rigidity and postural instability. In addition to the motor symptoms patients experience cognitive decline eventually resulting in severe disability. Pathologically PD is characterized by neurodegeneration in the substantia nigra pars compacta (SNc) with intracytoplasmic inclusions known as Lewy bodies. In addition to the SNc there is neurodegeneration in other areas including cerebral cortex, raphe nuclei, locus ceruleus, nucleus basalis of meynert, cranial nerves and autonomic nervous system. Recent evidence supports the role of inflammation in Parkinson's disease. Apoptosis has been shown to be one of the pathways of cell death in PD. Minocycline, a tetracycline derivative is a caspase inhibitor, and also inhibits the inducible nitric oxide synthase which are important for apoptotic cell death. Furthermore, Minocycline has been shown to block microglial activation of 6-hydroxydopamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned parkinsonism animal models and protect against nigrostriatal dopaminergic neurodegeneration. In this review, we present the current experimental evidence for the potential use of tetracycline derivative, minocycline, as a neuroprotective agent in PD.     

Lipoic acid as an anti-inflammatory and neuroprotective treatment for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that destroys patient memory and cognition, communication ability with the social environment and the ability to carry out daily activities. Despite extensive research into the pathogenesis of AD, a neuroprotective treatment - particularly for the early stages of disease - remains unavailable for clinical use. In this review, we advance the suggestion that lipoic acid (LA) may fulfil this therapeutic need. A naturally occurring cofactor for the mitochondrial enzymes pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase, LA has been shown to have a variety of properties which can interfere with the pathogenesis or progression of AD. For example, LA increases acetylcholine (ACh) production by activation of choline acetyltransferase and increases glucose uptake, thus supplying more acetyl-CoA for the production of ACh. LA chelates redox-active transition metals, thus inhibiting the formation of hydroxyl radicals and also scavenges reactive oxygen species (ROS), thereby increasing the levels of reduced glutathione. In addition, LA down-regulates the expression of redox-sensitive pro-inflammatory proteins including TNF and inducible nitric oxide synthase. Furthermore, LA can scavenge lipid peroxidation products such as hydroxynonenal and acrolein. In human plasma, LA exists in an equilibrium of free and plasma protein bound form. Up to 150 muM, it is bound completely, most likely binding to high affinity fatty acid sites on human serum albumin, suggesting that one large dose rather than continuous low doses (as provided by "slow release" LA) will be beneficial for delivery of LA to the brain. Evidence for a clinical benefit for LA in dementia is yet limited. There are only two published studies, in which 600 mg LA was given daily to 43 patients with AD (receiving a standard treatment with choline-esterase inhibitors) in an open-label study over an observation period of up to 48 months. Whereas the improvement in patients with moderate dementia was not significant, the disease progressed extremely slowly (change in ADAScog: 1.2 points=year, MMSE: -0.6 points=year) in patients with mild dementia (ADAScog<15). Data from cell culture and animal models suggest that LA could be combined with nutraceuticals such as curcumin, (-)-epigallocatechin gallate (from green tea) and docosahexaenoic acid (from fish oil) to synergistically decrease oxidative stress, inflammation, Abeta levels and Abeta plaque load and thus provide a combined benefit in the treatment of AD.     

Therapeutic strategies for Alzheimer's disease

Alzheimer's disease is a progressive and ultimately fatal neurological disorder for which there is no effective treatment at present. The disease is characterized pathologically by cerebral plaques that contain the amyloid-beta peptide and thread-like neuronal structures composed of the microtubule-associated protein TAU. Both amyloid-beta and TAU are thought to be crucial to pathogenesis, but compelling evidence supports amyloid-beta as the 'prime mover'. The main efforts for developing therapeutics are therefore focused on preventing amyloid-beta production, aggregation or downstream neurotoxic events. The progress of these and other approaches raises the hope that effective agents for the prevention and treatment of Alzheimer's disease will be available in the near future.     

Neuronal cell death in Alzheimer's disease and a neuroprotective factor, humanin

Brain atrophy caused by neuronal loss is a prominent pathological feature of Alzheimer's disease (AD). Amyloid beta (Abeta), the major component of senile plaques, is considered to play a central role in neuronal cell death. In addition to removal of the toxic Abeta, direct suppression of neuronal loss is an essential part of AD treatment; however, no such neuroprotective therapies have been developed. Excess amount of Abeta evokes multiple cytotoxic mechanisms, involving increase of the intracellular Ca(2+) level, oxidative stress, and receptor-mediated activation of cell-death cascades. Such diversity in cytotoxic mechanisms induced by Abeta clearly indicates a complex nature of the AD-related neuronal cell death. We have identified a 24-residue peptide, Humanin (HN), which suppresses in vitro neuronal cell death caused by all AD-related insults, including Abeta, so far tested. The anti-AD effect of HN has been further confirmed in vivo using mice with Abeta-induced amnesia. Altogether, such potent neuroprotective activity of HN against AD-relevant cytotoxicity both in vitro and in vivo suggests the potential clinical applications of HN in novel AD therapies aimed at controlling neuronal death.     

牡荆素的神经保护作用及机制研究进展

牡荆素是一种天然黄酮类化合物,具有广泛的药理活性。近年来研究发现其对中枢系统和周围神经系统具有明显的保护作用,包括抗记忆损伤、抗癫痫、抗缺血缺氧性脑损伤、抗抑郁、镇痛等作用。这些神经保护作用可能是通过降低自由基水平、对抗神经凋亡、调节炎症因子及其通路、调节神经递质及相关受体等多途径,多靶点的机制实现的。该文就近年来牡荆素的神经保护作用及相关作用机制的研究进展作简要概述。     

Inflammatory mechanisms in Alzheimer's disease

Alzheimer's disease is aetiologically heterogeneous, but the pathogenesis is often considered to be initiated by the deposition of amyloid fibrils, followed by neuritic tau pathology and neuronal death. A variety of inflammatory proteins has been identified in the brains of patients with Alzheimer's disease postmortem. In this article, Piet Eikelenboom and colleagues review evidence to suggest that the inflammatory processes are intimately involved in several crucial events in the pathological cascade. This suggests possibilities for the treatment of Alzheimer's disease with anti-inflammatory drugs.     

Pathogenic mechanisms in Alzheimer's disease

Alzheimer's disease is a progressive neurodegenerative disorder associated with aging and characterized by neurofibrillary tangles and amyloid plaques that deposit in the brain, triggering the neurodegenerative phenomena and leading to neuronal death. Amyloid plaques are primarily composed of beta-amyloid peptides, which derive from the Amyloid Precursor Protein (APP) upon the consequential action of beta- and gamma-secretase. This review discusses recent literature on beta- and gamma-secretase, and on those cellular factors, like cholesterol and phosphorylation of APP, that are involved in aging and may affect the function of both beta- and gamma-secretase.     

Tau-targeted treatment strategies in Alzheimer's disease

With populations ageing worldwide, the need for treating and preventing diseases associated with high age is pertinent. Alzheimer's disease (AD) is reaching epidemic proportions, yet the currently available therapies are limited to a symptomatic relief, without halting the degenerative process that characterizes the AD brain. As in AD cholinergic neurons are lost at high numbers, the initial strategies were limited to the development of acetylcholinesterase inhibitors, and more recently the NMDA receptor antagonist memantine, in counteracting excitotoxicity. With the identification of the protein tau in intracellular neurofibrillary tangles and of the peptide amyloid-β (Aβ) in extracellular amyloid plaques in the AD brain, and a better understanding of their role in disease, newer strategies are emerging, which aim at either preventing their formation and deposition or at accelerating their clearance. Interestingly, what is well established to combat viral diseases in peripheral organs - vaccination - seems to work for the brain as well. Accordingly, immunization strategies targeting Aβ show efficacy in mice and to some degree also in humans. Even more surprising is the finding in mice that immunization strategies targeting tau, a protein that forms aggregates in nerve cells, ameliorates the tau-associated pathology. We are reviewing the literature and discuss what can be expected regarding the translation into clinical practice and how the findings can be extended to other neurodegenerative diseases with protein aggregation in brain.     

Humanin: a potential peptide for neuroprotective therapy against Alzheimer's disease

Neuronal cell death is a pathologic hallmark of Alzheimer's disease (AD), a devastating neurodegenerative disorder. To understand the cytotoxic mechanism underlying AD pathogenesis, a functional screen termed the ‘disease-based death trap’ has been used. This method was developed to identify antagonistic genes against neuronal cell death caused by an AD-associated insult. Among several antagonistic genes obtained, a cDNA was found that encodes a novel 24-residue peptide, which was later designated humanin (HN). The synthetic HN peptide suppresses neuronal cell death induced by all AD-related insults so far examined, including amyloid β in vitro. A highly potent HN derivative ameliorates amnesia in an AD mouse model, suggesting that therapy involving HN effectively targets neuronal death in AD.     

Pharmaceutical research strategies in Alzheimer's disease

The hypothesis that the symptomatology of Alzheimer's disease is attributable to loss of cortical cholinergic innervation is supported by post-mortem studies demonstrating both reduced choline acetyltransferase (CAT) activity and reduced high-affinity choline uptake (HAChT) in the cortex, and neuron cell loss in the basal forebrain nucleus basalis of Meynert. Cholinergic denervation occurs early in the course of the disease and correlates with the severity of cognitive impairment. Pharmaceutical research strategies based on the cholinergic hypothesis and focusing on the development of acetylcholine esterase inhibitors and muscarinic agonist will be discussed. An alternative hypothesis to explain the dementia of Alzheimer's disease is the glutamatergic hypothesis. This is based on postmortem evidence indicating loss of glutamate, reduced binding and uptake of the neuro-transmitter and loss of pyramidal cells in the cortex. The possibility of developing glutamatergic drugs for treating the symptomatology of Alzheimer's disease will be considered. Studies have also indicated that the cellular processes involved in Alzheimer's disease occur in non-neuronal cells as well as in the brain. The possibility that Alzheimer's disease is a systemic disease and that drugs can be developed to treat the disease process will be considered.