Current Alzheimer Research (v.8, #7)
Voluntary Running and Environmental Enrichment Restores Impaired Hippocampal Neurogenesis in a Triple Transgenic Mouse Model of Alzheimer’s Disease by J.J. Rodriguez, H. N. Noristani, M. Olabarria, J. Fletcher, T.D.D. Somerville, C.Y. Yeh, A. Verkhratsky (707-717).
Alzheimer’s disease (AD) affects memory and neurogenesis. Adult neurogenesis plays an important role inmemory function and impaired neurogenesis contributes to cognitive deficits associated with AD. Increased physical/cognitive activity is associated with both reduced risk of dementia and increased neurogenesis. Previous attempts torestore hippocampal neurogenesis in transgenic mice by voluntary running (RUN) and environmental enrichment (ENR)provided controversial results due to lack of non-transgenic (non-Tg) control and inclusion of social isolation as standardhousing environment. Here, we determine the effect of RUN and ENR upon hippocampal neurogenesis in a tripletransgenic (3xTg-AD) mouse model of AD, which mimics AD pathology in humans. We used single and double immunohistochemistryto determine the area density of hippocampal proliferating cells, measured by the presence of phosphorylatedHistone H3 (HH3), and their potential neuronal and glial phenotype by co-localizing the proliferating cellswith the immature neuronal marker doublecortin (DCX), mature neuronal marker (NeuN) and specific astroglial marker(GFAP). Our results show that 3xTg-AD mice in control environment exhibit impaired hippocampal neurogenesis comparedto non-Tg animals at 9 months of age. Exposure to RUN and ENR housing restores hippocampal neurogenesis in3xTg-AD animals to non-Tg control levels. Differentiation into neurones and glial cells is affected neither by transgenicstatus nor by housing environment. These results suggest that hippocampus of 3xTg-AD animals maintains the potentialfor cellular plasticity. Increase in physical activity and/or cognitive experience enhances neurogenesis and provides a potentialfor stimulation of cognitive function in AD.
Chronic Psychosocial Stress Exacerbates Impairment of Synaptic Plasticity in β -Amyloid Rat Model of Alzheimer’s Disease: Prevention by Nicotine by Karim A. Alkadhi, Karem H. Alzoubi, Marisa Srivareerat, Trinh T. Tran (718-731).
Alzheimer’s disease (AD) is a degenerative disorder that leads to progressive, irreversible cognitive decline. Itdevelops as a result of over-production and aggregation of β-amyloid (Aβ) peptides in the brain. We have recently shownthat stress exacerbates, while nicotine prevents long-term memory impairment induced by β-Amyloid. In this study, weevaluated the effect of chronic psychosocial stress on synaptic plasticity (Late-phase long-term potentiation; L-LTP, andlong-term depression; LTD) in the β-Amyloid rat model of AD, and the positive impact of chronic nicotine treatment.Chronic psychosocial stress was induced by an intruder method. The Rat AD model was induced by 14-day i.c.v. osmoticpump infusion of a 1:1 mixture of 300 pmol/day Aβ1-40/Aβ1-42. The rats were treated with nicotine (2 mg/kg/day) for 6weeks. In vivo electrophysiological recordings of L-LTP, and LTD in hippocampal area CA1 showed that chronic stressby itself did not affect L-LTP. However, it markedly aggravated the impairment of this response as well as LTD in Aβ-treated rats. The effects of Aβ and the combination of stress and Aβ were totally prevented by chronic nicotine treatment.Immunoblot analysis revealed that stress and/or Aβ significantly increased the basal levels of calcineurin and preventedthe expected L-LTP-induced increase in CREB phosphorylation, and CaMKIV levels. These effects were not seen in Aβ-infused rats chronically treated with nicotine. The changes in synaptic plasticity-related molecules may explain the effectsof stress and/or chronic nicotine on L-LTP in Aβ animals.
Amyloid β Peptide Levels Increase in Brain of AβPP Swedish Mice after Exposure to Chlorpyrifos by Jose G. Salazar, Diana Ribes, Maria Cabre, Jose L. Domingo, Fernando Sanchez-Santed, Maria Teresa Colomina (732-740).
Chlorpyrifos (CPF) is an organophosphate pesticide widely used in intensive agriculture. Various studies havedemonstrated delayed neurotoxic effects in adult mammals after acute CPF exposure. This pesticide induces oxidativestress and neuronal damage, which suggests a possible relationship between CPF exposure and Alzheimer’s disease (AD).In the present study, we examined in a mice model of AD, long-term changes in the behavior and brain levels of amyloidβ after acute CPF exposure. Fifty mg/kg of CPF were subcutaneously injected to Tg2576 (Tg) mice carrying the Swedishamyloid-β protein precursor (AβPP) mutation for AD. General status, body weight, acetyl cholinesterase (AChE) inhibition,and behavioral changes were assessed. Amyloid β fragment (1-40 and 1-42) levels were also measured in the corticaland hippocampal brain regions. A significant and transient decrease in body weight was observed 72 hr after treatment,while no autonomic effects were noted. Motor activity was decreased in Tg mice seven months after CPF treatment. Acquisitionlearning in a water maze task was not affected, but retention was ameliorated in CPF-exposed Tg mice. Amyloidβ levels increased in the brains of treated Tg mice eight months after CPF exposure. The results of this study show thatsome behavioral changes persisted or emerged months after acute CPF exposure, while amyloid β levels increased. Thesefindings raise concern about the risk of developing neurodegenerative diseases following moderate exposure to CPF invulnerable subjects.
The Potential Dual Effects of Anesthetic Isoflurane on Aβ-Induced Apoptosis by Zhipeng Xu, Yuanlin Dong, Xu Wu, Jun Zhang, Sayre McAuliffe, Chuxiong Pan, Yiying Zhang, Fumito Ichinose, Yun Yue, Zhongcong Xie (741-752).
β-amyloid protein (Aβ)-induced neurotoxicity is the main component of Alzheimer's disease (AD) neuropathogenesis.Inhalation anesthetics have long been considered to protect against neurotoxicity. However, recent researchstudies have suggested that the inhalation anesthetic isoflurane may promote neurotoxicity by inducing apoptosis and increasingAβ levels. We therefore set out to determine whether isoflurane can induce dose- and time-dependent dual effectson Aβ-induced apoptosis: protection versus promotion. H4 human neuroglioma cells, primary neurons from naive mice,and naive mice were treated with Aβ and/or isoflurane, and levels of caspase-3 cleavage (activation), apoptosis, Bcl-2,Bax, and cytosolic calcium were determined. Here we show for the first time that the treatment with 2% isoflurane for sixhours or 30 minutes potentiated, whereas the treatment with 0.5% isoflurane for six hours or 30 minutes attenuated, theAβ-induced caspase-3 activation and apoptosis in vitro. Moreover, anesthesia with 1.4% isoflurane for two hours potentiated,whereas the anesthesia with 0.7% isoflurane for 30 minutes attenuated, the Aβ-induced caspase-3 activation in vivo.The high concentration isoflurane potentiated the Aβ-induced reduction in Bcl-2/Bax ratio and caused a robust elevationof cytosolic calcium levels. The low concentration isoflurane attenuated the Aβ-induced reduction in Bcl-2/Bax ratio andcaused only a mild elevation of cytosolic calcium levels. These results suggest that isoflurane may have dual effects (protectionor promotion) on Aβ-induced toxicity, which potentially act through the Bcl-2 family proteins and cytosolic calcium.These findings would lead to more systematic studies to determine the potential dual effects of anesthetics on ADassociatedneurotoxicity.
Effect of Cholinergic Stimulation in Early Alzheimer's Disease - Functional Imaging During a Recognition Memory Task by Pekka S. Miettinen, Maija Pihlajamaki, Anne M. Jauhiainen, Ina M. Tarkka, Heidi Grohn, Eini Niskanen, Tuomo Hanninen, Ritva Vanninen, Hilkka Soininen (753-764).
Treatment of Alzheimer’s disease (AD) with acetylcholinesterase inhibitors (AChEI) enhances cholinergic activityand alleviates clinical symptoms. In the present functional magnetic resonance imaging (fMRI) study, we investigatedthe effect of the AChEI rivastigmine on cognitive function and brain activation patterns during a face recognitionmemory task. Twenty patients with newly-diagnosed mild AD were administered a single oral dose of placebo, a singledose of rivastigmine (acute), and twice-daily treatment with rivastigmine for 4 weeks (chronic). After each treatment, thepatients underwent a facial recognition task during fMRI. The prefrontal areas known to be involved in face recognitionmemory processing demonstrated greater fMRI activity in both the acute and chronic rivastigmine conditions compared tothe placebo condition. In the same brain areas, differences in both fMRI activation at the map level and regional fMRIsignal intensity measures between the placebo and chronic treatment conditions correlated negatively with the Mini-Mental State Examination score. In the chronic rivastigmine condition, patients with better preserved cognitive abilitiesdemonstrated less enhanced prefrontal activity, whereas patients with poorer cognition showed greater prefrontal activity.These findings suggest that the prefrontal attention/working memory systems are already impaired in the early stages ofAD and that the effect of cholinergic medication in the brain areas involved in recognition memory, i.e., increased or decreasedfMRI activation patterns, depends on the severity of the disease. These findings also suggest the importance ofearly AChEI treatment in the course of AD, at the point when there is still some cognitive reserve available and the therapyhas the highest potential efficacy.
Genetic Polymorphisms in Sigma-1 Receptor and Apolipoprotein E Interact to Influence the Severity of Alzheimer’s Disease by Yue Huang, Lan Zheng, Glenda Halliday, Carol Dobson-Stone, Ying Wang, Hui-Dong Tang, Li Cao, Yu-Lei Deng, Gang Wang, Yu-Mei Zhang, Jian-Hua Wang, Marianne Hallupp, John Kwok, Sheng-Di Chen (765-770).
Apolipoprotein E (APOE) ε4 allele and sigma-1 receptor (SIGMAR1) c.5C (Q2P) polymorphisms have beenacknowledged as risk factors for developing Alzheimer’s disease (AD). However, whether these polymorphisms influencethe disease process is unclear. Therefore, two cohorts with a clinical diagnosis of AD were recruited, a postmortem confirmedAustralian cohort (82 cases) from the Australian Brain Bank Network, and a Chinese cohort with detailed clinicalassessments recruited through an epidemiology study in Shanghai and through the neurology department outpatients clinicof Shanghai Ruijin Hospital (330 cases). SIGMAR1 Q2P and APOE genotyping was performed on all cases. Dementiaseverity in the Chinese cohort was assessed using MMSE scores, and the stages of senile plaques and neurofibrillary tangles(NFT) assessed in the Australian cohort. Associations between SIGMAR1 Q2P and APOE genotypes and disease severitywere assessed using SPSS. Results confirmed that APOE ε4 allele associated with increased NFT stages and cognitivedecline, with carriers with one APOE ε2 or ε3 allele often having better clinical outcomes compared to carriers withnone or two ε2 or ε3 alleles respectively. SIGMAR1 c.5C polymorphism alone did not associate with MMSE score variabilityin Chinese or with pathological stages in Caucasians. However, the association studies revealed a significant geneticinteraction between the APOE ..4 allele and SIGMAR1 2P carriers in both populations, i.e., in APOE non ε4 allelecarriers, SIGMAR1 2P variant had increased cognitive dysfunction and more advanced stages of NFT. Our data demonstratethat SIGMAR1 and APOE interact to influence AD severity across ethnic populations.
Effects of Galantamine in Alzheimer’s Disease: Double-blind Withdrawal Studies Evaluating Sustained Versus Interrupted Treatment by M. Gaudig, U. Richarz, J. Han, B. Van Baelen, B. Schauble (771-780).
To evaluate the effects of galantamine withdrawal, and compare this with uninterrupted therapy, two 6-weekdouble-blind withdrawal studies (Studies 1 and 2) were performed. These enrolled individuals who had completed one oftwo 3- or 5-month randomized clinical trials (parent trials) involving patients with mild to moderate Alzheimer’s disease(AD). In Study 1 (GAL-USA-11; n=723), patients continuously treated with galantamine 16 mg/day exhibited a mean (±standard error [SE]) improvement in 11-item cognitive subscale of the Alzheimer’s Disease Assessment Scale score of 1.8(± 0.46) points at Week 6 compared with the parent trial baseline, (p<0.001 vs placebo; observed cases analysis). Over thesame period, patients switched from galantamine to placebo and those who had received continuous placebo, exhibitedmean (± SE) deteriorations of 0.7 (± 0.49) and 1.2 (± 0.49) points, respectively. Similar trends were apparent in Study 2(GAL-USA-5; n=118). In Study 1, subgroup analyses demonstrated cognitive benefits with continuing galantamine treatmentand deterioration associated with galantamine withdrawal in patients with advanced moderate AD (baseline Mini-Mental State Examination score ≤14) and in individuals deemed non-responsive in terms of Clinician’s Interview-BasedImpression of Change-plus Caregiver Input (CIBIC-plus) evaluation at the end of the parent trial (CIBIC-plus score >4).No safety issues were identified. In patients with mild to moderate AD who have exhibited cognitive benefits from up to 5months’ galantamine treatment, continuing therapy reinforces previously achieved benefit, whereas in patients in whomgalantamine is discontinued, although no safety concerns arise, the natural progression of AD is apparent.
Determination of Spatial and Temporal Distribution of Microglia by 230nm-High-Resolution, High-Throughput Automated Analysis Reveals Different Amyloid Plaque Populations in an APP/PS1 Mouse Model of Alzheimer’s Disease by Katja Scheffler, Jan Stenzel, Markus Krohn, Cathleen Lange, Jacqueline Hofrichter, Toni Schumacher, Thomas Bruning, Anne-Sophie Plath, Lary Walker, Jens Pahnke (781-788).
One early and prominent pathologic feature of Alzheimer’s disease (AD) is the appearance of activated microgliain the vicinity of developing β-amyloid deposits. However, the precise role of microglia during the course of AD isstill under discussion. Microglia have been reported to degrade and clear β-amyloid, but they also can exert deleterious effectsdue to overwhelming inflammatory reactions. Here, we demonstrate the occurrence of developing plaque populationswith distinct amounts of associated microglia using time-dependent analyses of plaque morphology and the spatialdistribution of microglia in an APP/PS1 mouse model. In addition to a population of larger plaques (>700μm2) that areoccupied by a moderate contingent of microglial cells across the course of aging, a second type of small β-amyloid depositsdevelops (≤400μm2) in which the plaque core is enveloped by a relatively large number of microglia. Our analyses indicatethat microglia are strongly activated early in the emergence of senile plaques, but that activation is diminished inthe later stages of plaque evolution (>150 days). These findings support the view that microglia serve to restrict thegrowth of senile plaques, and do so in a way that minimizes local inflammatory damage to other components of the brain.
Combining Neuropsychological and Structural Neuroimaging Indicators of Conversion to Alzheimer’s Disease in Amnestic Mild Cognitive Impairment by Annalena Venneri, Giovanni Gorgoglione, Cristian Toraci, Luca Nocetti, Patrizia Panzetti, Paolo Nichelli (789-797).
Morphometric and neuropsychological retrospective studies of amnestic mild cognitive impairment (MCI) havedemonstrated that regional atrophies and cognitive impairments may differentiate stable from progressing MCI. No measurehas proved helpful prospectively. In this study, twenty five amnestic MCI patients and 25 healthy controls underwentstructural MRI and comprehensive neuropsychological assessment. The groups’ grey matter volumes were compared withvoxel based morphometry and were also correlated with scores obtained on paired associates learning and category fluencytasks. MCI patients had significantly reduced grey matter volume in left mediotemporal and other neocortical regionscompared with controls. Atrophy in perirhinal and anterior inferior temporal cortex was associated with poor scoreson both category fluency and paired associates learning tasks. After 36 months, 44% of the MCI sample converted to dementia.Converter and non-converter MCI subgroups differed in paired associates learning and in category fluency scores,and showed limited differences in grey matter loss in the hippocampal complex. Variable atrophy in the hippocampus wasnot a relevant element in the converter/non converter distinction, but converters had significant volumetric reductions inthe perhirinal cortex and in other anterior temporal and frontal neocortical areas. A high proportion of converters (91%)could be identified from baseline data using a combination of measures of regional atrophy in left temporal associationcortex and poor scores on paired associates learning and category fluency tasks. This combined approach may offer a betteroption than using each measure alone to prospectively identify individuals at more immediate risk of conversion todementia in the MCI population. The clinical advantage of this combination of structural MRI and neuropsychologicalmeasures in predicting conversion to dementia will need additional prospective validation.
Mild Cognitive Impairment (MCI) - The Novel Trend of Targeting Alzheimer's Disease in Its Early Stages - Methodological Considerations by C. Pater (798-807).
While much uncertainty exists in the estimates of the global burden of Alzheimer's disease and about the potentialimpact of various interventions, there is a widespread acceptance of the fact that the steady increase in the incidenceand prevalence of the condition worldwide is becoming a massive public health problem as well as a huge economicburden for all healthcare systems and societies. These heavy demands are further compounded by the poor qualityof life of the affected individuals, of their families and of their caregivers. The epidemic proportion of Alzheimer's diseasehas triggered relentless attempts for development of treatment approaches during the past two decades by a multitude ofpharmaceuticals and biotech companies. Commercial development of the acetylcholinesterase inhibitors has, until recently,virtually dominated the field and, although efficacy has been demonstrated for five different products, the longtermclinical results suggested that alternate approaches were warranted. Disease modifying strategies targeting the β-amyloid plaques (e.g., decreasing β-amyloid formation through β- and β-secretase inhibition, diminishing β-amyloid aggregationthrough anti-aggregants or enhancement of β-amyloid clearance through active/passive immunization), targetingthe neurofibrillary tangles through inhibition of tau protein hyperphosphorilation or, more recently, by increasing mitochondrialpermeability, all these potential treatment modalities are facing major methodological challenges during theconduct of a myriad of clinical trials meant to bring the novel therapies to the market. Failure of more than 400 productstested in more than 800 clinical trials to date, with many of these failures occurring in late stage development (phase III)have triggered a paradigm shift toward targeting of the early stages of cognitive deficiencies (mild cognitive impairment-MCI) and a refinement of the investigative methodologies. The great heterogeneity of the disease entity itself (MCI) coupledwith inadequate sensitivity, specificity and positive/negative predictive values of the many common diagnostic outcomescales, outcome measures, and of many of the currently used biomarkers expose the drug development professionalsto the risk of methodological flaws rendering the products explored ineffective, while very expensive.