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Cerebral ischemia remains a leading cause of mortality worldwide. Although the incidence of death has decreased over the years, surviving patients may suffer from long-term cognitive impairments and have an increased risk for dementia. Unfortunately, research aimed toward developing therapies that can improve cognitive outcomes following cerebral ischemia has proved difficult given the fact that little is known about the underlying processes involved. Nevertheless, mechanisms that disrupt neural network activity may provide valuable insight, since disturbances in both local and global networks in the brain have been associated with deficits in cognition. In this review, we suggest that abnormal neural dynamics within different brain networks may arise from disruptions in synaptic plasticity processes and circuitry after ischemia. This discussion primarily concerns disruptions in local network activity within the hippocampus and other extra-hippocampal components of the Papez circuit, given their role in memory processing. However, impaired synaptic plasticity processes and disruptions in structural and functional connections within the Papez circuit have important implications for alterations within the global network, as well. Although much work is required to establish this relationship, evidence thus far suggests there is a link. If pursued further, findings may lead toward a better understanding of how deficits in cognition arise, not only in cerebral ischemia, but in other neurological diseases as well. [ABSTRACT FROM AUTHOR]

Despite a bulk of evidence supporting the idea that increased neurotoxic insults lead to Alzheimer's disease (AD), the possibility still remains that insufficiency of an endogenous defense system contributes to the disease progression. Humanin is a bioactive peptide that is likely to inhibit both neuronal death and dysfunction only related to AD by binding to a Humanin receptor on the cell-surface and by activating a STAT3-mediated signal, preventing the onset of dementia. A couple of recent studies presented evidence suggesting that the Humanin signal is decreased in neurons of AD patients. If this is the case, the restoration or activation of the Humanin signal in neurons may change the course of AD. [ABSTRACT FROM AUTHOR]

Levels of tau in cerebrospinal fluid (CSF) are elevated in Alzheimer's disease (AD) patients. It is believed this elevation is related to the tau pathology and neurodegeneration observed in AD, but not all tauopathies have increased CSF tau. There has been little pre-clinical work to investigate mechanisms of increased CSF tau due to the difficulty in collecting CSF samples from mice, the most commonly used pre-clinical models. We developed methods to collect CSF from mice without contamination from tau in brain tissue, which is approximately 50,000 fold more abundant in brain than CSF. Using these methods, we measured CSF tau from 3xTg, Tg4510, and Tau Alone transgenic mice. All three lines of mice showed age-dependent increases in CSF tau. They varied in phenotype from undetectable to severe tau pathology and neurodegeneration, suggesting that degenerating neurons are unlikely to be the only source of pathologic CSF tau. Overall, CSF tau levels mirrored expression levels and changes of tau in the brain, but they did not always correlate exactly. CSF tau was often more sensitive to changes in brain transgene expression and pathology. In addition, we also developed ELISA assays specific to different regions of the tau protein. We used these assays to provide evidence that CSF tau exists as fragments, with little intact C-terminus and partial loss of the N-terminus. Taken together, these assays and mouse models may be used to facilitate a deeper understanding of CSF tau in neurodegenerative disease. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is by far the main cause of dementia in the aged population. Because the amyloid-β peptide (Aβ) is the main component of senile plaques that develop in the brain of affected patients, numerous studies aimed at preventing its production or aggregation were conducted during the past 25 years. The inhibition of Aβ production via pharmacological inhibition of β- and γ-secretases is, with vaccination, one of the two main current challenges aimed at curing AD. However, the fact that there exist numerous substrates of these two activities renders this approach problematic since treatments with β- or γ-secretase inhibitors can cause deleterious effects. An alternative to the inhibition of the amyloidogenic enzymes would be to activate the α-secretase processing of AβPP. This cleavage is performed by two members of the disintegrin family of metalloproteases (ADAM10 and ADAM17). It is noteworthy that this cleavage can be seen as doubly beneficial regarding AD since it both occurs in the middle of the Aβ sequence and triggers the release of the neuroprotective sAβPPα product. However, similarly to β- and γ-secretases, ADAM10 and ADAM17 are responsible for the cleavage of a large number of proteins, the processing of some of them being tightly associated with important physiological functions but also with severe pathologies. This review focuses on our current knowledge of the various natural or synthetic compounds able to trigger α-secretase activities and on the possible ways to circumvent the deleterious side effects that would result from their broad activation. [ABSTRACT FROM AUTHOR]

The diagnosis of Alzheimer's disease (AD) relies principally on clinical criteria for probable and possible AD as defined by the NINCDS-ADRDRA. The field is desperately lacking of biological markers to assist with AD diagnosis and verification of treatment efficacy. According to the Consensus Report of the Working Group on Molecular and Biochemical Markers of Alzheimer's Disease, in order to qualify as a biomarker the sample in question must adhere to certain basic requirements, including the ability to: reflect AD pathology and differentiate it from other dementia with an 80% sensitivity; be reliable and reproducible; be easy to perform and analyze; remain relatively inexpensive. Beta secretases are crucial enzymes in the pathogenesis of AD. Given its primary role in brain amyloidogenesis and its ubiquitous expression, one may consider measuring peripheral BACE1 levels and activity as biomarkers of AD, like performed in the brain and cerebrospinal fluid. However, very little is known about the periphery and whether peripheral BACE1 is involved in AD pathogenesis or mirrors AD progression. Moreover, no investigation has focused on the possibility of monitoring peripheral BACE1 to assess the efficiency of BACE1 inhibitors during the course of clinical trials. Part of the problem may be attributed to the lack of sensitive molecular tools which are absolutely necessary to use BACE1 as a biomarker. In this review we evaluate the progress and feasibility of developing BACE1 as a biomarker for AD in different tissues. [ABSTRACT FROM AUTHOR]

An imbalance between production and clearance of the amyloid-β peptide (Aβ) is a key momentum of the complex pathological cascade of Alzheimer's disease (AD). It is caused by overproduction of Aβ or, more frequently, by impaired clearance from brain. Clearance can be reduced by increased aggregation, defective degradation, disturbed balance of transport across the blood-brain barrier, or inefficient peripheral removal of the peptide. In recent years these mechanisms have become targets of pharmacological interventions. Although several compounds have been discarded on the grounds of limited clinical efficacy, all major clearance-related approaches still hold promise. Some drug candidates have advanced to Phase III trials including anti-Aβ antibodies, metal complexing agents, ginseng extracts, and intravenous immunoglobulins. Data are currently not available from these studies that might allow an evaluation of efficacy and safety. Phase II trials on active and passive immunization have demonstrated a striking discrepancy between significant neurobiological effects regarding the removal of Aβ deposits and minor clinical outcomes. This does not preclude the possibility that clearance-related strategies have the potential of saving neurons and synapses via reducing the levels of soluble and particularly toxic Aβ species in brain. It may take longer than projected in ongoing trials for such neurobiological effects to translate into measurable changes of clinical progression. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is a chronic neurodegenerative disorder associated with dementia as a main feature. Despite decades of thorough research in the field of AD, the pathomechanism is still not fully understood. The development of novel experimental models can help us in the discovery of both genetic and non-genetic components of disease pathogenesis. As currently available therapies in AD can provide merely moderate or only temporary symptomatic relief, there is a great demand for the development of new drugs with higher therapeutic potential. Some of the candidates would be those targeting the kynurenine pathway, the neuroactive metabolites of which are surely involved in both neurodegeneration and neuroprotection, mainly in relation with glutamate excitotoxicity and oxidative stress. Both analogs of the neuroprotective kynurenic acid and small molecule enzyme inhibitors preventing the formation of neurotoxic compounds may have potential therapeutic significance. However, there is a great need for new strategies to improve efficacy, transport across the blood-brain barrier and bioavailability, naturally with simultaneous minimization of the adverse side-effects. [ABSTRACT FROM AUTHOR]

For hundreds of years, hydrogen sulfide (H2S) has been known solely as a toxic gas with the smell of rotten eggs. Nevertheless, the notoriety of H2S as a toxic gas is experiencing a transformation, with an increasing amount of research showing that it regulates a range of physiological and pathological processes in mammals. Hence H2S is a physiologically important molecule and has been referred to as the third gaseous mediator alongside nitric oxide and carbon monoxide. This past decade has seen an exponential growth of scientific interest in the physiological and pathological significance of H2S. In particular, in the central nervous system, H2S facilitates long-term potentiation and regulates intracellular calcium concentration and pH level in brain cells. Interestingly, H2S may exert antioxidant, anti-apoptotic, and anti-inflammatory effects which are related to neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and vascular dementia. Meanwhile, abnormal generation and metabolism of H2S are involved in most of these neurodegenerative disorders. This review presents current knowledge of H2S and its neuroprotective effects in neurodegenerative disorders, with a special emphasis on AD and PD. It is concluded that a H2S-modulated agent will be a new hope for neurodegenerative disorders including AD and PD. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is a progressive neurodegenerative disease associated with senile amyloid-β (Aβ) plaques, neuronal death, and cognitive decline. Neurogenesis in the adult hippocampus, which is notably affected by progressive neurodegeneration and Aβ pathology, is implicated in learning and memory regulation. Human postmortem brains of AD patients and AβPP/PS1 double transgenic mice show increased neurodegeneration. Leptin, an adipose-derived hormone, promotes neurogenesis in the adult hippocampus, but the way in which this process occurs in the AD brain is still unknown. Thus, we sought to determine if leptin stimulated the proliferation of neuronal precursors in AβPP/PS1 mice. We estimated the number proliferating hippocampal cells after intracerebroventricular administration of a lentiviral vector encoding leptin. After 3 months of treatment with leptin we observed an increase in the number of BrdU-positive cells in the subgranular zone of the dentate gyrus, as shown by morphometric analysis. This increase resulted mainly from an increased proliferation of neuronal precursors. Additionally, leptin led to an attenuation of Aβ-induced neurodegeneration, as revealed by Fluoro-Jade staining. Our results suggest that in AβPP/PS1 mice, leptin exerts changes resembling acute neurotrophic and neuroprotective effects. These effects could serve as the basis for the design of future treatment strategies in AD. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) continues to be one of most difficult human diseases to treat. The past 18 months have been a cruel reminder of the challenges of finding new and effective treatments. In 2010, several large Phase III clinical trials were terminated for lack of therapeutic efficacy. Concurrently, an NIH expert review panel was resigned to conclude that there was insufficient scientific evidence to recommend any treatment choices for slowing the progression of AD. Why has this disease proved so daunting? The answer is complex. To begin, it is still not clear whether AD is one disease with a single cause or multiple syndromes with common symptoms and/or a common pathology. Resolving this question is a prerequisite for forecasting whether to expect a 'magic bullet' therapy or only incremental progress in select patient populations. This review will explore some of the details of recent clinical trials and consider some of the lessons learned. As therapies approach clinical trials, it is essential to understand the expectations of regulatory agencies such as the FDA and EMA to obtain approval. Lastly, we will cover some of the essential gaps in our scientific understanding about the disease process and the impact this has on target validation. The hope of finding of a quick cure for AD without a complete understanding of the disease may have been too optimistic. However, a prudent review of the scientific evidence, a clear understanding of the expectations of regulators, and careful attention to patient needs may still lead to good therapies in the foreseeable future. [ABSTRACT FROM AUTHOR]

Oxidative stress is a metabolic condition arising from imbalance between the production of potentially reactive oxygen species and the scavenging activities. Mitochondria are the main providers but also the main scavengers of cell oxidative stress. The role of mitochondrial dysfunction and oxidative stress in the pathogenesis of neurodegenerative diseases is well documented. Therefore, therapeutic approaches targeting mitochondrial dysfunction and oxidative damage hold great promise in neurodegenerative diseases. Despite this evidence, human experience with antioxidant neuroprotectants has generally been negative with regards to the clinical progress of disease, with unclear results in biochemical assays. Here we review the antioxidant approaches performed so far in neurodegenerative diseases and the future challenges in modern medicine. [ABSTRACT FROM AUTHOR]

The neurons in the central nervous system (CNS) with high O2 consumption and prolonged life span are chronically exposed to high levels of reactive oxygen species (ROS). Accumulation of ROS-induced genome damage in the form of oxidized bases and single-strand breaks (SSBs) as well as their defective or reduced repair in the brain has been implicated in the etiology of various neurological disorders including Alzheimer's/Parkinson's diseases (AD/PD). Although inactivating mutations in some DNA repair genes have been linked to hereditary neurodegenerative diseases, the underlying mechanisms of repair deficiencies for the sporadic diseases is not understood. The ROS-induced DNA damage is predominantly repaired via the highly conserved and regulated base excision/SSB repair (BER/SSBR) pathway. We recently made an interesting discovery that the transition metals iron and copper, which accumulate excessively in the brains of AD, PD, and other neurodegenerative diseases, act as a 'double-edged sword' by inducing genotoxic ROS and inhibiting DNA damage repair at the same time. These metals inhibit the base excision activity of NEIL family DNA glycosylases by oxidizing them, changing their structure, and inhibiting their binding to downstream repair proteins. Metal chelators and reducing agents partially reverse the inhibition, while curcumin with both chelating and reducing activities reverses the inhibition nearly completely. In this review, we have discussed the possible etiological linkage of BER/SSBR defects to neurodegenerative diseases and the therapeutic potential of metal chelators in restoring DNA repair capacity. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is a progressive, yet irreversible, neurodegenerative disease for which there are limited means for its ante-mortem diagnosis. We previously identified a brain- and cell-specific oxidative stress-mediated mechanism for dehydroepiandrosterone (DHEA) biosynthesis present in rat, bovine, and human brain, independent of the cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17) enzyme activity found in the periphery. This alternative pathway is induced by pro-oxidant agents, such as Fe2+ and amyloid-β peptide. Using brain tissue specimens from control and AD patients we subsequently provided evidence that DHEA is formed in the AD brain by the oxidative stress-mediated metabolism of an unidentified precursor, thus depleting the levels of the precursor present in the blood stream. Here, we tested for the presence of this DHEA precursor in human serum using a simple Fe2+-based reaction and determined the amounts of DHEA formed. A total of 86 subjects were included in this study: 19 male and 20 female AD patients; 18 male and 22 female age-matched controls; and 4 men and 3 women with mild cognitive impairment. Serum oxidation resulted in a dramatic increase of DHEA level in control patients, whereas only a moderate or no increase was observed in the AD patients. The DHEA variation after oxidation correlated with the patients' cognitive and mental status. These results suggest that the comparison of DHEA levels in patient serum before and after oxidation could provide a useful tool to diagnose AD. [ABSTRACT FROM AUTHOR]

Both of the two most common neurodegenerative disorders, namely Alzheimer's disease (AD) and Parkinson's disease (PD), have multiple lines of evidence from molecular and cellular to epidemiological, that nicotinic transmission is implicated in their pathogenesis. This review article presents evidence of nicotinic acetylcholine receptor (nAChR)-mediated protection against neurotoxicity induced by amyloid-β (Aβ), glutamate, rotenone, and 6-hydroxydopamine (6-OHDA) and the signal transduction involved in this mechanism. Our studies clarified that survival signal transduction, α7 nAChR-Src family-PI3 K-AKT pathway, and subsequent upregulation of Bcl-2 and Bcl-x, would lead to neuroprotection. In addition to the PI3 K-AKT pathway, two other survival pathways, JAK2/STAT3 and MEK/ERK, are proposed by other groups. These three survival pathways are related to each other through intracellular signal transductions in neurons. The JAK2/STAT3 pathway is cholinergic anti-inflammation pathway mediated by α7 nAChR on macrophage and microglia as well as neuron. Recently analyzing the properties of galantamine, we clarify the 4th independent neuroprotective pathway, which is mediated by enhancement of microglial α7 nAChR resulting in upregulation of Aβ phagocytosis. Galantamine sensitizes microglial α7 nAChRs to choline and induce Ca2+ influx into microglia. The Ca2+-induced intracellular signaling cascades may then stimulate Aβ phagocytosis through actin reorganization. The discovery of the 4th pathway would facilitate further investigation of possible nAChRs enhancing drugs targeting not only neuronal but also microglial nAChRs. [ABSTRACT FROM AUTHOR]

Aging is the best-known risk factor for many disorders, including neurodegenerative diseases such as Alzheimer's disease (AD). The effect of epigenetic modulation of gene expression on normal aging and in pathological conditions is still unclear, but it is likely it may explain some of the complexity that is characteristic of these processes. Caffeine is a widely consumed psychoactive drug, which is emerging as a protective agent against AD progression and in aging associated deficits. This occurs mainly through the blockade of adenosine A2A receptors, whose expression and function become aberrant throughout aging and in age-related pathologies. Here, we discuss the data supporting the effects of caffeine in AD, focusing on adenosine A2A receptors and epigenetic modulation of gene expression. In addition, we speculate on the potential of caffeine as an epigenetic modulator and the consequences it might have for preventive and therapeutic applications of caffeine in AD. [ABSTRACT FROM AUTHOR]

β-secretase, a key enzyme involved in amyloid-β generation, is an attractive candidate for Alzheimer's disease therapy. Transition-state inhibitors of β-secretase are designed to achieve specificity. However, these inhibitors bind only to the active conformation of the enzyme and as the active β-secretase is sequestered in subcellular compartments, new strategies have to be implemented. We propose that membrane-anchoring of β-secretase inhibitors would render them endocytosis-competent thereby enabling the inhibitors to reach these compartments that harbor active β-secretase. By choosing cholesterol as a membrane anchor, we also enrich the inhibitor in lipid rafts where much of the β-secretase is present. In addition, membrane-anchoring of soluble inhibitors reduces the dimensionality of the inhibitor and consequently increases the inhibitor concentration at the target membrane plane. Such inhibitors have great potential in terms of substrate selectivity and reduced side effects. Not only for β-secretase, this strategy could be applied for many membrane targets that are localized either at the plasma membrane or in the endocytic compartments. [ABSTRACT FROM AUTHOR]

Despite the profound burden of Alzheimer's disease (AD) on public health, research to understand its underlying pathology has not yet produced new therapeutic approaches to improve symptoms or halt disease progression. AD is characterized by early cognitive deficits, particularly in short-term memory, followed by a gradual decline in other cognitive functions. Functional imaging studies indicate that hippocampal and medial temporal lobe cortices are the sites of early pathology underlying the initial memory impairments. Behaviors that rely on hippocampal integrity have been the focus of extensive research using animal models and represent useful functional endpoints in pre-clinical AD research. In this review, we argue that relevant information can be derived from studying normal, aging animals performing hippocampal-sensitive tasks. Because age is the greatest risk factor for developing clinical AD, the aspects of cognitive decline occurring in normal, aging animals that resemble those seen in aging humans are reliable endpoints that can be applied to improving human therapies. Ultimately, pre-clinical studies that employ tasks sensitive to hippocampal function can be applied toward novel hypotheses in AD intervention and could provide important insights for developing early detection devices for AD patients. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is a neurodegenerative disease with multiple etiologies. Advanced glycation end products (AGEs) accumulate in the aging brain and could be one of the reasons for age-related diseases like PD. Oxidative stress also leads to the formation of AGEs and may be involved in neurodegeneration by altering the properties of proteins. α-Synuclein is involved in pathogenesis of PD and there are limited studies on the role of AGE-α-synuclein in neurodegeneration. We studied the aggregation and DNA binding ability of AGE-α-synuclein in vitro. α-Synuclein is glycated using methylglyoxal and formation of AGE-α-synuclein is characterized using fluorescence studies, intrinsic tyrosine fluorescence, and fructosamine estimation. The results indicated that AGE-α-synuclein aggregates into smaller globular-like aggregates compared to fibrils formed with native α-synuclein. Further, it is found that AGE-α-synuclein induced conformational changes in scDNA from B-form to B-C-A mixed conformation. Additionally, AGE-α-synuclein altered DNA integrity as evidenced by the melting temperature, ethidium bromide, and DNAse I sensitivity studies. AGE-α-synuclein converted biphasic Tm to higher monophasic Tm. The Tm of AGE-α-synuclein-scDNA complex is more than that of native α-synuclein-scDNA complex, indicating that AGE-α-synuclein stabilized the uncoiled scDNA. AGE-α-synuclein could stabilize the uncoiled scDNA, as shown by the decrease in the number of ethidium bromide binding molecules per base pair of DNA. DNAse I sensitive studies indicated that both AGE-α-synuclein-scDNA and α-synuclein-scDNA are resistant to DNAse I digestion. The relevance of these findings to neuronal cell death is discussed. [ABSTRACT FROM AUTHOR]

Neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, Prion disease, Huntington's disease, and amyotrophic lateral sclerosis are o increasingly being realized to have common cellular and molecular mechanisms including protein aggregation and inclusion body formation in selected brain regions. The aggregates usually consist of insoluble fibrillar aggregates containing misfolded protein with β-sheet conformation. The most probable explanation is that inclusions and the aggregates symbolize an end stage of a molecular cascade of several events, and that earlier event in the cascade may be more directly tied up to pathogenesis than the inclusions themselves. Small intermediates termed as 'soluble oligomers' in the aggregation process might influence synaptic dysfunction, whereas large, insoluble deposits might function as reservoir of the bioactive oligomers. Compelling evidence suggests the role of misfolded proteins in the form of oligomers might lead to synaptic dysfunction, neuronal apoptosis and brain damage. However, the mechanism by which oligomers trigger neurodegeneration still remains mysterious. The aim of this article is to review the literature around the molecular mechanism and role of oligomers in neurodegeneration and leading approaches toward rational therapeutics. [ABSTRACT FROM AUTHOR]

Studies of Alzheimer's disease (AD) strongly support the hypothesis that amyloid-β (Aβ) deposition in the brain is the initiating event in the progression of AD. Aβ peptides easily form long insoluble amyloid fibrils, which accumulate in deposits known as senile plaques. On the other hand, recent work indicated that soluble Aβ oligomers, rather than monomers or insoluble Aβ fibrils, might be responsible for neuronal and synaptic dysfunction in AD. Curcumin, a low molecular weight yellow-orange pigment derived from the turmeric plant, has shown therapeutic effects in transgenic mouse models of AD. However, it remains unclear whether curcumin interacts directly with the Aβ oligomers. This study investigated any interaction between curcumin and Aβ oligomers such as globulomer and Aβ-derived diffusible ligand (ADDL). Globulomer was observed as a cluster of spherical structures by electron microscopic analysis, and ADDL was also detected as small spherical structures. Fluorescence analysis revealed a significant increase in the fluorescence of curcumin when reacted with both oligomers. Furthermore quartz crystal microbalance analysis showed significant frequency decreases in oligomer-immobilized electrodes following the addition of curcumin. These results strongly suggested that curcumin binds to Aβ oligomers and to Aβ fibrils. The association of curcumin with Aβ oligomers may contribute to the therapeutic effect on AD. Based on these findings, curcumin could provide the basis of a novel concept in AD therapies targeting Aβ oligomers. [ABSTRACT FROM AUTHOR]

Aluminum (Al) transport across yeast cells was studied using Dy(NO3)3 as a shift reagent by 27Al-NMR spectroscopy. The results showed that (a) Al enters the yeast cells at 15 min and over a period of time, within 4 h, an equilibrium sets in between outside and inside Al; (b) citrate does not favor Al going into the yeast cells at pH 5.0; and (c) EDTA brings out all the Al that has entered the yeast cells. (Mol Cell Biochem 175: 59–63, 1997) [ABSTRACT FROM AUTHOR]

The author offers perspectives and developments in the field of Alzheimer's and neurodegenerative diseases and where Panama might offer solutions. He cites the shift of research on new drug discoveries to the critical need to develop biomarkers that can distinguish the normal aging processes from neurodegeneration and other dementias. He also tackles the objective of Panama to become an international hub for science and technology and one of the leaders in bioscience and biomedicine.