Molecular pathogenesis of Alzheimer's disease: reductionist versus expansionist approaches

Simple ammonium salt and sigma-1 receptor ligand dipentylammonium provides neuroprotective effects in cell culture and Caenorhabditis elegans models of Alzheimer's disease

The sigma-1 receptor (σ-1R), a chaperone protein located at the mitochondria-associated membrane (MAM) of the endoplasmic reticulum, can interact with and modify the signaling pathways of various proteins, thereby modulating many disease pathologies, including Alzheimer's disease (AD). The σ-1R ligand dipentylammonium (DPA) was analyzed for its anti-AD properties using PC12 cells (in vitro) and Caenorhabditis elegans (in vivo) models along with molecular docking (in silico) analysis. DPA at 1 and 10 µM concentrations was able to significantly potentiate NGF-induced neurite growth length by 137.7 ± 12.0 and 187.8 ± 16.4, respectively, when compared to the control 76.9 ± 7.4. DPA also regulated neurite damage caused by Aβ(25-35) treatment in differentiated PC12 cells by improving cell viability and neurite length. In C. elegans, DPA could significantly extend the median and maximum lifespan of Aβ transgenic strain CL2006 without impacting wild-type nematodes. Additionally, it could significantly reduce the paralysis phenotype of another Aβ transgenic strain, CL4176, thereby improving the overall health in AD pathogenesis. This effect depended on σ-1R, as DPA could not modulate the lifespan of σ-1R mutant TM3443. This was further confirmed using agonist PRE084 and antagonist BD1047, wherein the agonist alone could extend the lifespan of CL2006, while the antagonist suppressed the effect of DPA in CL2006. Interestingly, neither had an TM3443. Further, molecular docking analysis showed that DPA had a similar binding affinity as that of PRE084, BD1047 and pentazocine against the σ-1R receptor in humans and C. elegans, which collectively suggests the anti-AD properties of DPA.

Marine-derived Compounds: A Powerful Platform for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a debilitating form of dementia that primarily affects cholinergic neurons in the brain, significantly reducing an individual's capacity for learning and creative skills and ultimately resulting in an inability to carry out even basic daily tasks. As the elderly population is exponentially increasing, the disease has become a significant concern for society. Therefore, neuroprotective substances have garnered considerable interest in addressing this universal issue. Studies have shown that oxidative damage to neurons contributes to the pathophysiological processes underlying AD progression. In AD, tau phosphorylation and glutamate excitotoxicity may play essential roles, but no permanent cure for AD is available. The existing therapies only manage the early symptoms of AD and often come with numerous side effects and toxicities. To address these challenges, researchers have turned to nature and explored various sources such as plants, animals, and marine organisms. Many historic holy books from different cultures emphasize that adding marine compounds to the regular diet enhances brain function and mitigates its decline. Consequently, researchers have devoted significant time to identifying potentially active neuroprotective substances from marine sources. Marine-derived compounds are gaining recognition due to their abundant supply of diverse chemical compounds with biological and pharmacological potential and unique mechanisms of action. Several studies have reported that plants exhibit multitarget potential in treating AD. In light of this, the current study focuses on marine-derived components with excellent potential for treating this neurodegenerative disease.

Biomarkers of diagnosis, prognosis, pathogenesis, response to therapy: Convergence or divergence? Lessons from Alzheimer's disease and synucleinopathies

Alzheimer's disease (AD) is the most common disorder associated with cognitive impairment. Recent observations emphasize the pathogenic role of multiple factors inside and outside the central nervous system, supporting the notion that AD is a syndrome of many etiologies rather than a "heterogeneous" but ultimately unifying disease entity. Moreover, the defining pathology of amyloid and tau coexists with many others, such as α-synuclein, TDP-43, and others, as a rule, not an exception. Thus, an effort to shift our AD paradigm as an amyloidopathy must be reconsidered. Along with amyloid accumulation in its insoluble state, β-amyloid is becoming depleted in its soluble, normal states, as a result of biological, toxic, and infectious triggers, requiring a shift from convergence to divergence in our approach to neurodegeneration. These aspects are reflected-in vivo-by biomarkers, which have become increasingly strategic in dementia. Similarly, synucleinopathies are primarily characterized by abnormal deposition of misfolded α-synuclein in neurons and glial cells and, in the process, depleting the levels of the normal, soluble α-synuclein that the brain needs for many physiological functions. The soluble to insoluble conversion also affects other normal brain proteins, such as TDP-43 and tau, accumulating in their insoluble states in both AD and dementia with Lewy bodies (DLB). The two diseases have been distinguished by the differential burden and distribution of insoluble proteins, with neocortical phosphorylated tau deposition more typical of AD and neocortical α-synuclein deposition peculiar to DLB. We propose a reappraisal of the diagnostic approach to cognitive impairment from convergence (based on clinicopathologic criteria) to divergence (based on what differs across individuals affected) as a necessary step for the launch of precision medicine.

Aluminium Induced Neurodegeneration in Rat Cerebellum in the Presence of Ethanol Coexposure

Introduction:

Both aluminium and ethanol are pro-oxidants and neurotoxic. Moderately intake of alcohol may favor the body in coronary heart disease and diabetes mellitus etc. Being cheaper aluminium and increasing consumption of alcohol in India mixed with each other and may induce neurotoxicity. The present study was planned to identify the level of aluminium induced neurodegeneration in presence of ethanol coexposure in the cerebellum.

Materials and Methods:

An experimental study was carried out at Dr. RP Government Medical College, Kangra, and Government Medical College, Amritsar, India after due approval from the Institute Animal Ethics Committee. Thirty-two Wistar rats were divided into one vehicle control and three experimental groups. Group I received the normal saline water as the vehicle control group. Group II received aluminium chloride 4.2 mg/kg body weight as the experimental group. Group III received ethanol 1 g/kg body weight as the experimental group. Group IV received both aluminium chloride 4.2 mg/kg body weight and ethanol 1 g/kg body weight as the experimental group. After 3 months of treatment, cerebellum was processed for histopathological observation under the microscope.

Results:

Experimental group treated with aluminium and ethanol separately showed reduction in the number of Purkinje cells, without a prominent nucleolus and well-defined nuclear membrane. Eosinophilic swelling adjacent to Purkinje cell bodies observed. The effects of combined administration of aluminium ethanol treated groups showed with acute neurodegeneration of Purkinje cell layer and granular layer. Pyknosis and neurofibrillary tangle seen in Purkinje cells.

Conclusions:

It has been suggested that the ethanol-induced the effects of aluminium on the cerebellum and plays a significant role in neurotoxicity.

Dementia screening of geriatric patients by implementing an informant-based Alzheimer's disease eight-item tool in KSA

Objectives

The screening of dementia among geriatrics is necessary to identify probable cases, confirm diagnosis, institute treatment, and plan for future family caregiving strategies. This study aimed to screen the incidence of dementia among geriatric patients using the informant-based Alzheimer's disease eight-item tool for dementia (AD8) in a KSA region.

Methods

A cross-sectional study was conducted among geriatric patients in the KSA region at selected hospitals from December 2019 to March 2020. The caregivers of 100 geriatric patients were interviewed using the AD8.

Results

Among the 100 patients, 43% were 65–75 years old, 52% were men, and 48% were women, mean age was (78) for both genders. Diabetes mellitus was the most reported chronic illness, found in 68% of the patients, followed by a history of cerebrovascular disease (52%). Loss of more than four but less than half of the teeth was reported in 41% of the patients, while 10% were reported to be undergoing polypharmacy. Dementia was diagnosed in 74% of patients and had a statistically significant association with a history of stroke (p < 0.001), number of teeth lost (p = 0.02), and number of drugs administered (p = 0.006). A binary logistic regression model fitted to predict dementia based on the effect of a stroke history, number of missing teeth, and number of drugs administered showed that patients with stroke were 1.43 (95% CI 1.4–4.2) times likely to develop dementia than those with no history of stroke.

Conclusion

Cases of dementia are frequent among geriatric patients in the Qassim region of KSA. A dementia positive screening is correlated with a history of stroke, number of lost teeth, polypharmacy, and age. Stroke prevention and early treatment can potentially reduce the likelihood of dementia occurrence.

Tocotrienol Rich Fraction Supplementation Modulate Brain Hippocampal Gene Expression in APPswe/PS1dE9 Alzheimer's Disease Mouse Model

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by loss of memory and other cognitive abilities. AD is associated with aggregation of amyloid-β (Aβ) deposited in the hippocampal brain region. Our previous work has shown that tocotrienol rich fraction (TRF) supplementation was able to attenuate the blood oxidative status, improve behavior, and reduce fibrillary-type Aβ deposition in the hippocampus of an AD mouse model. In the present study, we investigate the effect of 6 months of TRF supplementation on transcriptome profile in the hippocampus of APPswe/PS1dE9 double transgenic mice. TRF supplementation can alleviate AD conditions by modulating several important genes in AD. Moreover, TRF supplementation attenuated the affected biological process and pathways that were upregulated in the AD mouse model. Our findings indicate that TRF supplementation can modulate hippocampal gene expression as well as biological processes that can potentially delay the progression of AD.

Understanding the Amyloid Hypothesis in Alzheimer's Disease

The amyloid hypothesis (AH) is still the most accepted model to explain the pathogenesis of inherited Alzheimer's disease (IAD). However, despite the neuropathological overlapping with the non-inherited form (NIAD), AH waver in explaining NIAD. Thus, 30 years after its first statement several questions are still open, mainly regarding the role of amyloid plaques (AP) and apolipoprotein E (APOE). Accordingly, a pathogenetic model including the role of AP and APOE unifying IAD and NIAD pathogenesis is still missing. In the present understanding of the AH, we suggested that amyloid-β (Aβ) peptides production and AP formation is a physiological aging process resulting from a systemic age-related decrease in the efficiency of the proteins catabolism/clearance machinery. In this pathogenetic model Aβ peptides act as neurotoxic molecules, but only above a critical concentration [Aβ]c. A threshold mechanism triggers IAD/NIAD onset only when [Aβ]≥[Aβ]c. In this process, APOE modifies [Aβ]c threshold in an isoform-specific way. Consequently, all factors influencing Aβ anabolism, such as amyloid beta precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2) gene mutations, and/or Aβ catabolism/clearance could contribute to exceed the threshold [Aβ]c, being characteristic of each individual. In this model, AP formation does not depend on [Aβ]c. The present interpretation of the AH, unifying the pathogenetic theories for IAD and NIAD, will explain why AP and APOE4 may be observed in healthy aging and why they are not the cause of AD. It is clear that further studies are needed to confirm our pathogenetic model. Nevertheless, our suggestion may be useful to better understand the pathogenesis of AD.

Role of aromatic amino acids in amyloid self-assembly

Amyloids are proteins of a cross-β structure found as deposits in several diseases and also in normal tissues (nails, spider net, silk). Aromatic amino acids are frequently found in amyloid deposits. Although they are not indispensable, aromatic amino acids, phenylalanine, tyrosine and tryptophan, enhance significantly the kinetics of formation and thermodynamic stability, while tape or ribbon-like morphology is represented in systems with experimentally detected π-π interactions between aromatic rings. Analysis of geometries and energies of the amyloid PDB structures indicate the prevalence of aromatic-nonaromatic interactions and confirm that aromatic-aromatic interactions are not crucial for the amyloid formation.

Exploring the potential of marine microbes in clinical management of Alzheimer's disease: A road map for bioprospecting and identifying promising isolates

Pervasiveness of Alzheimer's disease (AD) across the globe is on rise, devitalizing the essential brain functions of the afflicted individual. Multiple neurological pathways viz., cholinergic, amyloidogenic and tau protein pathways underlying the disease and interdependence make it more complex to develop effective treatment strategies. Existing drug treatments for Alzheimer's disease majorly belong to the class of cholinergic inhibitors which improve the behavioral symptoms. But there are no drugs that could arrest the disease progression. Inhibition of beta secretase enzyme could prevent the deposition of amyloid plaques in the neurons, thereby arresting the disease progression. Search for novel drugs to treat the underlying pathogenesis of the disease is pivotal in this day and age. The source of most active lead molecules discovered recently is from the nature. Marine ecosystem provides a plethora of pharmacologically lead molecules from various living organisms inhabiting the sea. Among all, marine microbes are the most under-explored and indispensable source of many bioactive metabolites. Studies have been reported on potent metabolites from marine microbes which could inhibit the key enzymes involved in the AD pathogenesis. The advancement in microbial bioprospecting and molecular biology techniques have eased the process of cultivation and identification of microbes, isolation of novel bioactive metabolites of clinical use. Exploring such marine natural resources for pharmacological lead molecules could give a breakthrough in the drug discovery domain for treating AD such debilitating diseases. In this review, a comprehensive account of bioprospecting methods and reports of marine microbial isolates are discussed.

Excess cerebral TNF causing glutamate excitotoxicity rationalizes treatment of neurodegenerative diseases and neurogenic pain by anti-TNF agents

The basic mechanism of the major neurodegenerative diseases, including neurogenic pain, needs to be agreed upon before rational treatments can be determined, but this knowledge is still in a state of flux. Most have agreed for decades that these disease states, both infectious and non-infectious, share arguments incriminating excitotoxicity induced by excessive extracellular cerebral glutamate. Excess cerebral levels of tumor necrosis factor (TNF) are also documented in the same group of disease states. However, no agreement exists on overarching mechanism for the harmful effects of excess TNF, nor, indeed how extracellular cerebral glutamate reaches toxic levels in these conditions. Here, we link the two, collecting and arguing the evidence that, across the range of neurodegenerative diseases, excessive TNF harms the central nervous system largely through causing extracellular glutamate to accumulate to levels high enough to inhibit synaptic activity or kill neurons and therefore their associated synapses as well. TNF can be predicted from the broader literature to cause this glutamate accumulation not only by increasing glutamate production by enhancing glutaminase, but in addition simultaneously reducing glutamate clearance by inhibiting re-uptake proteins. We also discuss the effects of a TNF receptor biological fusion protein (etanercept) and the indirect anti-TNF agents dithio-thalidomides, nilotinab, and cannabinoids on these neurological conditions. The therapeutic effects of 6-diazo-5-oxo-norleucine, ceptriaxone, and riluzole, agents unrelated to TNF but which either inhibit glutaminase or enhance re-uptake proteins, but do not do both, as would anti-TNF agents, are also discussed in this context. By pointing to excess extracellular glutamate as the target, these arguments greatly strengthen the case, put now for many years, to test appropriately delivered ant-TNF agents to treat neurodegenerative diseases in randomly controlled trials.

APOε2 and education in cognitively normal older subjects with high levels of AD pathology at autopsy: findings from the Nun Study

Asymptomatic Alzheimer's disease (ASYMAD) subjects are individuals characterized by preserved cognition before death despite substantial AD pathology at autopsy. ASYMAD subjects show comparable levels of AD pathology, i.e. β-amyloid neuritic plaques (Aβ-NP) and tau-neurofibrillary tangles (NFT), to those observed in mild cognitive impairment (MCI) and some definite AD cases. Previous clinicopathologic studies on ASYMAD subjects have shown specific phenomena of hypertrophy in the cell bodies, nuclei, and nucleoli of hippocampal pyramidal neurons and other cerebral areas. Since it is well established that the allele APOε4 is a major genetic risk factor for AD, we examined whether specific alleles of APOE could be associated with the different clinical outcomes between ASYMAD and MCI subjects despite equivalent AD pathology. A total of 523 brains from the Nun Study were screened for this investigation. The results showed higher APOε2 frequency (p < 0.001) in ASYMAD (19.2%) vs. MCI (0%) and vs. AD (4.7%). Furthermore, higher education in ASYMAD vs. MCI and AD (p < 0.05) was found. These novel autopsy-verified findings support the hypothesis of the beneficial effect of APOε2 and education, both which seem to act as contributing factors in delaying or forestalling the clinical manifestations of AD despite consistent levels of AD pathology.

Molecular Targets in Alzheimer's Disease: From Pathogenesis to Therapeutics

Alzheimer's disease (AD) is characterized by progressive cognitive decline usually beginning with impairment in the ability to form recent memories. Nonavailability of definitive therapeutic strategy urges developing pharmacological targets based on cell signaling pathways. A great revival of interest in nutraceuticals and adjuvant therapy has been put forward. Tea polyphenols for their multiple health benefits have also attracted the attention of researchers. Tea catechins showed enough potentiality to be used in future as therapeutic targets to provide neuroprotection against AD. This review attempts to present a concise map of different receptor signaling pathways associated with AD with an insight into drug designing based on the proposed signaling pathways, molecular mechanistic details of AD pathogenesis, and a scientific rationale for using tea polyphenols as proposed therapeutic agents in AD.

The arsenic exposure hypothesis for Alzheimer disease

Prior research has shown that arsenic exposure induces changes that coincide with most of the developmental, biochemical, pathologic, and clinical features of Alzheimer disease (AD) and associated disorders. On the basis of this literature, we propose the Arsenic Exposure Hypothesis for AD that is inclusive of and cooperative with the existing hypotheses. Arsenic toxicity induces hyperphosphorylation of protein tau and overtranscription of the amyloid precursor protein, which are involved in the formation of neurofibrillary tangles and brain amyloid plaques, consistent with the amyloid hypothesis of AD. Arsenic exposure has been associated with cardiovascular diseases and associated risk factors, which is in agreement with the vascular hypothesis of AD. Arsenic exposure invokes brain inflammatory responses, which resonates with the inflammatory hypotheses of AD. Arsenic exposure has been linked to reduced memory and intellectual abilities in children and adolescents, which provides a biologic basis for the developmental origin of health and disease hypothesis for AD. Arsenic and its metabolites generate free radicals causing oxidative stress and neuronal death, which fits the existing oxidative stress hypothesis. Taken together, the arsenic exposure hypothesis for AD provides a parsimonious testable hypothesis for the development and progression of this devastating disease at least for some subsets of individuals.

Yizhijiannao Granule and a combination of its effective monomers, icariin and Panax notoginseng saponins, inhibit early PC12 cell apoptosis induced by beta-amyloid (25-35)

One of our previous studies showed that Yizhijiannao Granule, a compound Chinese medicine, effectively improved the clinical symptoms of Alzheimer's disease. In the present study, we established a model of Alzheimer's disease using beta-amyloid (25–35) in PC12 cells, and treated the cells with Yizhijiannao Granule and its four monomers, i.e., icariin, catechin, Panax notoginseng saponins, and eleutheroside E. Flow cytometry showed that Yizhijiannao Granule-containing serum, icariin, Panax notoginseng saponins, and icariin + Panax notoginseng saponins were protective against beta-amyloid (25–35)-induced injury in PC12 cells. Icariin in combination with Panax notoginseng saponins significantly inhibited early apoptosis of PC12 cells with beta-amyloid (25–35)-induced injury compared to icariin or Panax notoginseng saponins alone. The effects of icariin + Panax notoginseng saponins were similar to the effects of Yizhijiannao Granule. The findings indicate that two of the effective monomers of Yizhijiannao Granule, icariin and Panax notoginseng saponins, can synergistically inhibit early apoptosis of PC12 cells induced by beta-amyloid (25–35).

Our "energy-Ca(2+) signaling deficits" hypothesis and its explanatory potential for key features of Alzheimer's disease

Sporadic Alzheimer's disease (sAD) has not been explained by any current theories, so new hypotheses are urgently needed. We proposed that "energy and Ca(2+) signaling deficits" are perhaps the earliest modifiable defects in brain aging underlying memory decline and tau deposits (by means of inactivating Ca(2+)-dependent protease calpain). Consistent with this hypothesis, we now notice that at least eight other known calpain substrates have also been reported to accumulate in aging and AD. Thus, protein accumulation or aggregation is not a "pathogenic" event, but occurs naturally and selectively to a peculiar family of proteins, and is best explained by calpain inactivation. Why are only calpain substrates accumulated and how can they stay for decades in the brain without being attacked by many other non-specific proteases there? We believe that these long-lasting puzzles can be explained by calpain's unique properties, especially its unusual specificity and exclusivity in substrate recognition, which can protect the substrates from other proteases' attacks after calpain inactivation. Interestingly, our model, in essence, may also explain tau phosphorylation and the formation of amyloid plaques. Our studies suggest that α-secretase is an energy-/Ca(2+)-dual dependent protease and is also the primary determinant for Aβ levels. Therefore, β- and γ-secretases can only play secondary roles and, by biological laws, they are unlikely to be "positively identified". This study thus raises serious questions for policymakers and researchers and these questions may help explain why sAD can remain an enigma today.

Neuropathological approaches to cerebral aging and neuroplasticity

Cerebral aging is a complex and heterogenous process related to a large variety of molecular changes involving multiple neuronal networks, due to alterations of neurons (synapses, axons, dendrites, etc), particularly affecting strategically important regions, such as hippocampus and prefrontal areas. A substantial proportion of nondemented, cognitively unimpaired elderly subjects show at least mild to moderate, and rarely even severe, Alzheimer-related lesions, probably representing asymptomatic preclinical Alzheimer's disease, and/or mixed pathologies. While the substrate of resilience to cognitive decline in the presence of abundant pathologies has been unclear, recent research has strengthened the concept of cognitive or brain reserve, based on neuroplasticity or the ability of the brain to manage or counteract age-related changes or pathologies by reorganizing its structure, connections, and functions via complex molecular pathways and mechanisms that are becoming increasingly better understood. Part of neuroplasticity is adult neurogenesis in specific areas of the brain, in particular the hippocampal formation important for memory function, the decline of which is common even in “healthy” aging. To obtain further insights into the mechanisms of brain plasticity and adult neurogenesis, as the basis for prevention and potential therapeutic options, is a major challenge of modern neurosciences.

Neuropathological approaches to cerebral aging and neuroplasticity

Cerebral aging is a complex and heterogenous process related to a large variety of molecular changes involving multiple neuronal networks, due to alterations of neurons (synapses, axons, dendrites, etc), particularly affecting strategically important regions, such as hippocampus and prefrontal areas. A substantial proportion of nondemented, cognitively unimpaired elderly subjects show at least mild to moderate, and rarely even severe, Alzheimer-related lesions, probably representing asymptomatic preclinical Alzheimer's disease, and/or mixed pathologies. While the substrate of resilience to cognitive decline in the presence of abundant pathologies has been unclear, recent research has strengthened the concept of cognitive or brain reserve, based on neuroplasticity or the ability of the brain to manage or counteract age-related changes or pathologies by reorganizing its structure, connections, and functions via complex molecular pathways and mechanisms that are becoming increasingly better understood. Part of neuroplasticity is adult neurogenesis in specific areas of the brain, in particular the hippocampal formation important for memory function, the decline of which is common even in "healthy" aging. To obtain further insights into the mechanisms of brain plasticity and adult neurogenesis, as the basis for prevention and potential therapeutic options, is a major challenge of modern neurosciences.

Screening of treatment targets for Alzheimer's disease from the molecular mechanisms of impairment by β-amyloid aggregation and tau hyperphosphorylation

β-Amyloid (Aβ) over-expression and tau hyperphosphorylation are considered to be the central events in the pathogenesis of Alzheimer's disease (AD). Studies on them may help elucidate the precise molecular pathogenesis of AD. Until now, although tau protein and Aβ remain the foci of AD research, the etiopathogenesis of AD and effective drugs for AD treatment are still largely unsolved. The present review was mainly focused on the molecular mechanism of Aβ aggregation-related impairment and the pathways leading to tau hyperphosphorylation, based on which some promising therapeutic targets for AD were also proposed.

Changes in the expression of genes associated with intraneuronal amyloid-beta and tau in Alzheimer's disease

The clinical hallmark of Alzheimer's disease (AD) is impairment of cognition associated with loss of synapses, accumulation of amyloid-beta (Abeta) both within neurons and as extracellular deposits, and neurofibrillary degeneration composed of phospho-tau. Neurons in the hippocampus are among those that are most vulnerable. The purpose of this study was to investigate the expression of genes associated with cognition, synapse, and mitochondrial function in hippocampal neurons of AD compared to normal individuals. Neurons from the hippocampus with intraneuronal Abeta immunoreactivity were captured with laser microdissection; RNA was extracted; and levels of brain-derived neurotrophic factor (BDNF), TrkB (BDNF receptor), dynamin-1 (DYN), and cytochrome C oxidase subunit II (COX2) were assessed with quantitative real-time polymerase chain reaction. We found no significant differences in the expression of these genes in AD between neurons associated with Abeta compared to those lacking Abeta immunoreactivity. Double immunofluorescence microscopy showed the number of hippocampal neurons coexpressing Abeta or phospho-tau and either BDNF, TrkB, or DYN was similar in AD and controls. Our results suggest that neither intraneuronal Abeta nor phospho-tau has obligatory effects on reducing the expression of genes important for memory and cognition in hippocampus of AD.

Basic mechanisms of neurodegeneration: a critical update

Neurodegenerative diseases are characterized by progressive dysfunction of specific populations of neurons, determining clinical presentation. Neuronal loss is associated with extra and intracellular accumulation of misfolded proteins, the hallmarks of many neurodegenerative proteinopathies. Major basic processes include abnormal protein dynamics due to deficiency of the ubiquitin-proteosome-autophagy system, oxidative stress and free radical formation, mitochondrial dysfunction, impaired bioenergetics, dysfunction of neurotrophins, 'neuroinflammatory' processes and (secondary) disruptions of neuronal Golgi apparatus and axonal transport. These interrelated mechanisms lead to programmed cell death is a long run over many years. Neurodegenerative disorders are classified according to known genetic mechanisms or to major components of protein deposits, but recent studies showed both overlap and intraindividual diversities between different phenotypes. Synergistic mechanisms between pathological proteins suggest common pathogenic mechanisms. Animal models and other studies have provided insight into the basic neurodegeneration and cell death programs, offering new ways for future prevention/treatment strategies.

G protein-coupled receptors, cholinergic dysfunction, and Abeta toxicity in Alzheimer's disease

The beta-amyloid (Abeta) peptide is associated with the pathogenesis of Alzheimer's disease (AD). Evidence gathered over the last two decades suggests that the gradual accumulation of soluble and insoluble Abeta peptide species triggers a cascade of events that leads to the clinical manifestation of AD. Abeta accumulation has also been associated with the cholinergic dysfunction observed in AD, which is characterized by diminished acetylcholine release and impaired coupling of the muscarinic acetylcholine receptors (mAChRs) to heterotrimeric GTP-binding proteins (G proteins). Although the mechanism of Abeta-mediated toxicity is not clearly understood, evidence shows that Abeta accumulation has an effect on the oligomerization of the angiotensin II (AngII) AT(2) (angiotensin type 2) receptor and sequestration of the Galpha(q/11) family of G proteins. Sequestration of Galpha(q/11) results in dysfunctional coupling and signaling between M(1) mAChR and Galpha(q/11) and accompanies neurodegeneration, tau phosphorylation, and neuronal loss in an AD transgenic mouse model. Collectively, these results provide a putative link among Abeta toxicity, AT(2) receptor oligomerization, and disruption of the signaling pathway through M(1) mAChR and Galpha(q/11) and potentially contribute to our understanding of the cholinergic deficit observed in AD.

Neurodegenerative disorders and nanoformulated drug development

Degenerative and inflammatory diseases of the CNS include, but are not limited to, Alzheimer's and Parkinson's disease, amyotrophic lateral sclerosis, stroke, multiple sclerosis and HIV-1-associated neurocognitive disorders. These are common, debilitating and, unfortunately, hold few therapeutic options. In recent years, the application of nanotechnologies as commonly used or developing medicines has served to improve pharmacokinetics and drug delivery specifically to CNS-diseased areas. In addition, nanomedical advances are leading to therapies that target CNS pathobiology and as such, can interrupt disordered protein aggregation, deliver functional neuroprotective proteins and alter the oxidant state of affected neural tissues. This article focuses on the pathobiology of common neurodegenerative disorders with a view towards how nanomedicine may be used to improve the clinical course of neurodegenerative disorders.

Does Alzheimer's disease begin in the brainstem?

Although substantial evidence indicates that the progression of pathological changes of the neuronal cytoskeleton is crucial in determining the severity of dementia in Alzheimer's disease (AD), the exact causes and evolution of these changes, the initial site at which they begin, and the neuronal susceptibility levels for their development are poorly understood. The current clinical criteria for diagnosis of AD are focused mostly on cognitive deficits produced by dysfunction of hippocampal and high-order neocortical areas, whereas noncognitive, behavioural and psychological symptoms of dementia such as disturbances in mood, emotion, appetite, and wake-sleep cycle, confusion, agitation and depression have been less considered. The early occurrence of these symptoms suggests brainstem involvement, and more specifically of the serotonergic nuclei. In spite of the fact that the Braak and Braak staging system and National Institutes of Aging - Reagan Institute (NIA-RI) criteria do not include their evaluation, several recent reports drew attention to the possibility of selective and early involvement of raphe nuclei, particularly the dorsal raphe nucleus (DRN), in the pathogenesis of AD. Based on these findings of differential susceptibility and anatomical connectivity, a novel pathogenetic scheme of AD progression was proposed. Although the precise mechanisms of neurofibrillary degeneration still await elucidation, we speculated that cumulative oxidative damage may be the main cause of DRN alterations, as the age is the main risk factor for sporadic AD. Within such a framework, beta-amyloid production is considered only as one of the factors (although a significant one in familial cases) that promotes molecular series of events underlying AD-related neuropathological changes.