2,2',4'-trihydroxychalcone from Glycyrrhiza glabra as a new specific BACE1 inhibitor efficiently ameliorates memory impairment in mice.

Alzheimer's disease (AD) characterizes a progressive neurodegenerative disorder of the brain, while AD patients are afflicted with irreversible loss of neurons and further the intellectual abilities including memory and reasoning. One of the typical hallmarks of AD is the deposition of senile plaque that is contributed mainly by amyloid-beta (Abeta), whose production is initiated by beta-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1). Inhibition of BACE1 is thereby regarded as an attractive strategy for anti-AD drug discovery. Here, we reported that the natural product 2,2',4'-trihydroxychalcone (TDC) from Glycyrrhiza glabra functioned as a specific non-competitive inhibitor against BACE1 enzyme, and potently repressed beta-cleavage of APP and production of Abeta in human embryo kidney cells-APPswe cells. Moreover, the amelioration ability of this compound against the in vivo memory impairment was further evaluated by APP-PS1 double transgenic mice model. It is discovered that treatment of 9 mg/kg/day of TDC could obviously decrease Abeta production and Abeta plaque formation, while efficiently improve the memory impairment based on Morris water maze test. Our findings thus demonstrated that the natural product TDC as a new BACE1 inhibitor could ameliorate memory impairment in mice, and is expected to be potentially used as a lead compound for further anti-AD reagent development.

Oral apolipoprotein A-I mimetic peptide improves cognitive function and reduces amyloid burden in a mouse model of Alzheimer's disease.

Recent evidence indicates that inflammation may significantly contribute to the pathogenesis of Alzheimer's disease (AD). Since the apo A-I mimetic peptide D-4F has been shown to inhibit atherosclerotic lesion formation and regress already existing lesions (in the presence of pravastatin) and the peptide also decreases brain arteriole inflammation, we undertook a study to evaluate the efficacy of oral D-4F co-administered with pravastatin on cognitive function and amyloid beta (A beta) burden in the hippocampus of APPSwe-PS1 Delta E9 mice. Three groups of male mice were administered D-4F and pravastatin, Scrambled D-4F (ScD-4F, a control peptide) and pravastatin in drinking water, while drinking water alone served as control. The escape latency in the Morris Water Maze test was significantly shorter for the D-4F+statin administered animals compared to the other two groups. While the hippocampal region of the brain was covered with 4.2+/-0.5 and 3.8+/-0.6% of A beta load in the control and ScD-4F+statin administered groups, in the D-4F+statin administered group A beta load was only 1.6+/-0.1%. Furthermore, there was a significant decrease in the number of activated microglia (p<0.05 vs the other two groups) and activated astrocytes (p<0.05 vs control) upon oral D-4F+statin treatment. Inflammatory markers TNFalpha and IL-1 beta levels were decreased significantly in the D-4F+statin group compared to the other two groups (for IL-1 beta p<0.01 vs the other two groups and for TNF-alpha p<0.001 vs control) and the expression of MCP-1 were also less in D-4F+statin administered group compared to the other two groups. These results suggest that the apo A-I mimetic peptide inhibits amyloid beta deposition and improves cognitive function via exerting anti-inflammatory properties in the brain.

Age effects on the regulation of adult hippocampal neurogenesis by physical activity and environmental enrichment in the APP23 mouse model of Alzheimer disease.

An active lifestyle is to some degree protective against Alzheimer's disease (AD), but the biological basis for this benefit is still far from clear. We hypothesize that physical and cognitive activity increase a reserve for plasticity by increasing adult neurogenesis in the hippocampal dentate gyrus (DG). We thus assessed how age affects the response to activity in the murine APP23 model of AD compared with wild type (WT) controls and studied the effects of physical exercise (RUN) and environmental enrichment (ENR) in comparison with standard housing (CTR) at two different ages (6 months and 18 months) and in both genotypes. At 18 months, both activity paradigms reduced the hippocampal human Abeta1-42/Abeta1-40 ratio when compared with CTR, despite a stable plaque load in the hippocampus. At this age, both RUN and ENR increased the number of newborn granule cells in the DG of APP23 mice when compared with CTR, whereas the levels of regulation were equivalent to those in WT mice under the same housing conditions. At 6 months, however, neurogenesis in ENR but not RUN mice responded like the WT. Quantifying the number of cells at the doublecortin-positive stage in relation to the number of cells on postmitotic stages we found that ENR overproportionally increased the number of the DCX-positive "late" progenitor cells, indicative of an increased potential to recruit even more new neurons. In summary, the biological substrates for activity-dependent regulation of adult hippocampal neurogenesis were preserved in the APP23 mice. We thus propose that in this model, ENR even more than RUN might contribute to a "neurogenic reserve" despite a stable plaque load and that age affects the outcome of an interaction based on "activity."

Thiamine deficiency induces oxidative stress and exacerbates the plaque pathology in Alzheimer's mouse model.

Mitochondrial dysfunction, oxidative stress and reductions in thiamine-dependent enzymes have been implicated in multiple neurological disorders including Alzheimer's disease (AD). Experimental thiamine deficiency (TD) is an established model for reducing the activities of thiamine-dependent enzymes in brain. TD diminishes thiamine-dependent enzymes throughout the brain, but produces a time-dependent selective neuronal loss, glial activation, inflammation, abnormalities in oxidative metabolism and clusters of degenerating neurites in only specific thalamic regions. The present studies tested how TD alters brain pathology in Tg19959 transgenic mice over expressing a double mutant form of the amyloid precursor protein (APP). TD exacerbated amyloid plaque pathology in transgenic mice and enlarged the area occupied by plaques in cortex, hippocampus and thalamus by 50%, 200% and 200%, respectively. TD increased Abeta(1-42) levels by about three fold, beta-CTF (C99) levels by 33% and beta-secretase (BACE1) protein levels by 43%. TD-induced inflammation in areas of plaque formation. Thus, the induction of mild impairment of oxidative metabolism, oxidative stress and inflammation induced by TD alters metabolism of APP and/or Abeta and promotes accumulation of plaques independent of neuron loss or neuritic clusters.

Beta-secretase-1 elevation in transgenic mouse models of Alzheimer's disease is associated with synaptic/axonal pathology and amyloidogenesis: implications for neuritic plaque development.

The presence of neuritic plaques is a pathological hallmark of Alzheimer's disease (AD). However, the origin of extracellular beta-amyloid peptide (Abeta) deposits and the process of plaque development remain poorly understood. The present study attempted to explore plaque pathogenesis by localizing beta-secretase-1 (BACE1) elevation relative to Abeta accumulation and synaptic/neuritic alterations in the forebrain, using transgenic mice harboring familial AD (FAD) mutations (5XFAD and 2XFAD) as models. In animals with fully developed plaque pathology, locally elevated BACE1 immunoreactivity (IR) coexisted with compact-like Abeta deposition, with BACE1 IR occurring selectively in dystrophic axons of various neuronal phenotypes or origins (GABAergic, glutamatergic, cholinergic or catecholaminergic). Prior to plaque onset, localized BACE1/Abeta IR occurred at swollen presynaptic terminals and fine axonal processes. These BACE1/Abeta-containing axonal elements appeared to undergo a continuing process of sprouting/swelling and dystrophy, during which extracellular Abeta IR emerged and accumulated in surrounding extracellular space. These data suggest that BACE1 elevation and associated Abeta overproduction inside the sprouting/dystrophic axonal terminals coincide with the onset and accumulation of extracellular amyloid deposition during the development of neuritic plaques in transgenic models of AD. Our findings appear to be in harmony with an early hypothesis that axonal pathogenesis plays a key or leading role in plaque formation.

Decreased acetylcholine release is correlated to memory impairment in the Tg2576 transgenic mouse model of Alzheimer's disease.

Acetylcholine (ACh) release is one of the key factors in memory mechanisms. To clarify whether beta-amyloid (Abeta) induces a disturbance of the cholinergic system leading to memory impairment, we examined memory impairment and measured hippocampal ACh release in Tg2576 (Tg) mice that over-express the Swedish mutant amyloid precursor protein (APPsw). Furthermore, we examined Abeta burden with aging. Tg mice aged 9-11 months, but not aged 4-6 months, showed memory impairment in the 8-arm radial maze behavior test. Spontaneous ACh release was not altered in Tg mice compared with age-matched control mice at 4-6 or 9-11 months of age. On the other hand, high-K(+)-evoked ACh release was decreased in Tg mice aged 9-11 months, but not in Tg mice aged 4-6 months. Hippocampal Abeta increased in an age-dependent manner, but evident amyloid plaques were not found in the hippocampus of Tg mice aged 11 months. These results suggest that memory impairment in Tg mice could be attributed to cholinergic synapse dysfunction that could not be caused predominantly by amyloid plaques. Measuring ACh release in this model might be a useful index for the screening of new drugs to treat the early-phase of Alzheimer's disease.

Selective induction of calcineurin activity and signaling by oligomeric amyloid beta.

Alzheimer's disease (AD) is a terminal age-associated dementia characterized by early synaptic dysfunction and late neurodegeneration. Although the presence of plaques of fibrillar aggregates of the amyloid beta peptide (Abeta) is a signature of AD, evidence suggests that the preplaque small oligomeric Abeta promotes both synaptic dysfunction and neuronal death. We found that young Tg2576 transgenic mice, which accumulate Abeta and develop cognitive impairments prior to plaque deposition, have high central nervous system (CNS) activity of calcineurin (CaN), a phosphatase involved in negative regulation of memory function via inactivation of the transcription factor cAMP responsive element binding proteins (CREB), and display CaN-dependent memory deficits. These results thus suggested the involvement of prefibrillary forms of Abeta. To investigate this issue, we compared the effect of monomeric, oligomeric, and fibrillar Abeta on CaN activity, CaN-dependent pCREB and phosphorylated Bcl-2 Associated death Protein (pBAD) levels, and cell death in SY5Y cells and in rat brain slices, and determined the role of CaN on CREB phosphorylation in the CNS of Tg2576 mice. Our results show that oligomeric Abeta specifically induces CaN activity and promotes CaN-dependent CREB and Bcl-2 Asociated death Protein (BAD) dephosphorylation and cell death. Furthermore, Tg2576 mice display Abeta oligomers and reduced pCREB in the CNS, which is normalized by CaN inhibition. These findings suggest a role for CaN in mediating effects of oligomeric Abeta on neural cells. Because elevated CaN levels have been reported in the CNS of cognitively impaired aged rodents, our results further suggest that abnormal CaN hyperactivity may be a common event exacerbating the cognitive and neurodegenerative impact of oligomeric Abeta in the aging CNS.

Abeta plaques lead to aberrant regulation of calcium homeostasis in vivo resulting in structural and functional disruption of neuronal networks.

Alzheimer's disease is characterized by the deposition of senile plaques and progressive dementia. The molecular mechanisms that couple plaque deposition to neural system failure, however, are unknown. Using transgenic mouse models of AD together with multiphoton imaging, we measured neuronal calcium in individual neurites and spines in vivo using the genetically encoded calcium indicator Yellow Cameleon 3.6. Quantitative imaging revealed elevated [Ca(2+)]i (calcium overload) in approximately 20% of neurites in APP mice with cortical plaques, compared to less than 5% in wild-type mice, PS1 mutant mice, or young APP mice (animals without cortical plaques). Calcium overload depended on the existence and proximity to plaques. The downstream consequences included the loss of spinodendritic calcium compartmentalization (critical for synaptic integration) and a distortion of neuritic morphologies mediated, in part, by the phosphatase calcineurin. Together, these data demonstrate that senile plaques impair neuritic calcium homeostasis in vivo and result in the structural and functional disruption of neuronal networks.

What initiates the formation of senile plaques? The origin of Alzheimer-like dementias in capillary haemorrhages.

Although the key pathologies of the demented brain have been known for over a century, and the senile plaque is the focus of intense research, the mechanisms that cause plaques to form are not established. This paper proposes that the formation of each plaque is initiated by bleeding from a cerebral capillary, which creates the conditions for formation of an amyloid-rich plaque. Specifically, it is argued that ischaemia caused by the haemorrhage upregulates the expression of beta-amyloid by local neural cells, and that haemoglobin released into the neuropil binds to the beta-amyloid and promotes its oligomerisation. The premise that the event that initiates plaque formation is vascular explains why the risk factors for ALDs and cardiovascular diseases overlap; why drugs and lifestyle changes with vaso-protective effects protect against dementia; and why oxidative stress is prominent early in the genesis of Alzheimer-like dementias. The vascular premise also suggests that the anatomical substrate for the spread of plaque formation is the capillary bed of the cerebral cortex, and provides an explanation of why plaque formation is age-related, occurring as the capillary bed becomes fragile with age. The more specific premise, that haemorrhage creates the conditions for plaque formation, explains many of the features of plaques: their small and relatively uniform size, each being the site of a capillary bleed; why plaques form around capillaries; why haem is found in every plaque; why an inflammatory response is prominent where plaques form; why plaque formation and haemorrhagic stroke commonly co-occur in both sporadic and familial dementias; why plaques form around vessels in mouse models of plaque formation induced by transgenes that mimic the mutations that cause familial disease; why the acute petechial bleeding caused by brain trauma can lead to the formation of plaques. The hypothesis also suggests an explanation of how ALD's can occur without plaque formation, as when the cerebral capillaries become blocked or constricted in flow, without haemorrhage. Advances in the prevention of dementia will be gained, it is argued, from understanding of why the cerebral capillary bed becomes unstable with age, and how that instability can be prevented, delayed or slowed. Advances in the treatment of dementia will be gained from techniques that minimise the neural damage caused by a multitude of tiny strokes.

Neurogenic responses to amyloid-beta plaques in the brain of Alzheimer's disease-like transgenic (pPDGF-APPSw,Ind) mice.

Formation and accumulation of amyloid-beta (A beta) plaques are associated with declined memory and other neurocognitive function in Alzheimer's disease (AD) patients. However, the effects of A beta plaques on neural progenitor cells (NPCs) and neurogenesis from NPCs remain largely unknown. The existing data on neurogenesis in AD patients and AD-like animal models remain controversial. For this reason, we utilized the nestin second-intron enhancer controlled LacZ (pNes-LacZ) reporter transgenic mice (pNes-Tg) and Bi-transgenic mice (Bi-Tg) containing both pPDGF-APPSw,Ind and pNes-LacZ transgenes to investigate the effects of A beta plaques on neurogenesis in the hippocampus and other brain regions of the AD-like mice. We chose transgenic mice at 2, 8 and 12 months of age, corresponding to the stages of A beta plaque free, plaque onset and plaque progression to analyze the effects of A beta plaques on the distribution and de novo neurogenesis of (from) NPCs. We demonstrated a slight increase in the number of NPCs in the hippocampal regions at the A beta plaque free stage, while a significant decrease in the number of NPCs at A beta plaque onset and progression stages. On the other hand, we showed that A beta plaques increase neurogenesis, but not gliogenesis from post-mitotic NPCs in the hippocampus of Bi-Tg mice compared with age-matched control pNes-Tg mice. The neurogenic responses of NPCs to A beta plaques suggest that experimental approaches to promote de novo neurogenesis may potentially improve neurocognitive function and provide an effective therapy for AD.

Disease modifying approaches for Alzheimer's pathology.

Alzheimer's disease (AD) is the most common age-associated neurodegenerative disease in the world. The major neuropathological features of AD are synaptic loss, neuronal loss, neurofibrillary tangles and the deposition of amyloid-beta (Abeta) as plaques and in cerebral blood vessels. Numerous Abeta targeting therapeutic approaches have been shown to prevent amyloid deposition and resulting in cognitive improvement in transgenic mouse models of AD. Some of these approaches are currently in early clinical trials. It remains to be seen if these approaches will be proven effective in patients. Future anti-AD therapies will likely be multi-modal and individually tailored depending on the patient's immune status, genetic background and their amyloid burden, as determined by imaging studies using Abeta specific labeling ligands. Pre-clinical data suggests that it will be much more feasible to prevent AD related pathology, then to clear existing pathology, making early diagnosis critically important.

Physiological and biophysical factors that influence Alzheimer's disease amyloid plaque targeting of native and putrescine modified human amyloid beta40.

Amyloid beta40 (Abeta40) and its derivatives are being developed as probes for the ante-mortem diagnosis of Alzheimer's disease. Putrescine-Abeta40 (PUT-Abeta40) showed better plaque targeting than the native Abeta40, which was not solely explained by the differences in their blood-brain-barrier (BBB) permeabilities. The objective of this study was to elucidate the physiological and biophysical factors influencing the differential targeting of Abeta40 and PUT-Abeta40. Despite better plaque-targeting ability 125I-PUT-Abeta40 was more rapidly cleared from the systemic circulation than amyloid beta40 labeled with 125I (125I-Abeta40) after i.v. administration in mice. The BBB permeability of both compounds was inhibited by circulating peripheral Abeta40 levels. 125I-Abeta40 but not 125I-PUT-Abeta40 was actively taken up by the mouse brain slices in vitro. Only fluorescein-Abeta40, not fluorescein-PUT-Abeta40, was localized in the brain parenchymal cells in vitro. The metabolism of 125I-Abeta40 in the brain slices was twice as great as 125I-PUT-Abeta40. 125I-Abeta40 efflux from the brain slices was saturable and found to be 5 times greater than that of 125I-PUT-Abeta40. Thioflavin-T fibrillogenesis assay demonstrated that PUT-Abeta40 has a greater propensity to form insoluble fibrils compared with Abeta40, most likely due to the ability of PUT-Abeta40 to form beta sheet structure more readily than Abeta40. These results demonstrate that the inadequate plaque targeting of Abeta40 is due to cellular uptake, metabolism, and efflux from the brain parenchyma. Despite better plaque targeting of PUTAbeta40, its propensity to form fibrils may render it less suitable for human use and thus allow increased focus on the development of novel derivatives of Abeta with improved characteristics.

Metales de transición y enfermedad de Alzheimer / Transition metals and Alzheimer´s disease

El hipocampo y la corteza del cerebro de pacientes con enfermedad de Alzheimer (EA), presentan: a) una extensa lesión neuronal; b) un incremento de los productos de daño oxidativo, y c) una acumulación de agregados/oligómeros proteicos, que en conjunto podrían ser responsables de la pérdida progresiva de las capacidades cognitivas observadas en la EA. El principal componente de los agregados/oligómeros proteicos, llamados placas seniles (PS), es el péptido β-amiloide (βA), generado por el corte proteolítico de la proteína precursora del amiloide (PPA). Las evidencias genéticas, bioquímicas y de biología celular obtenidas hasta el momento sugieren que los oligómeros del péptido βA serían los responsables del daño neuronal observado en la EA. Además, se ha propuesto que moléculas accesorias modularían la toxicidad del péptido βA. En este contexto, se ha demostrado que algunos metales de transición como el cobre, el hierro y el cinc, que se acumulan en las placas seniles, se asocian al péptido βA, induciendo su agregación y la producción de especies reactivas de oxígeno. Por lo tanto, la interacción entre estos metales de transición y el péptido βA podría explicar en parte la lesión neuronal y la presencia de daño oxidativo detectado en el cerebro de pacientes que presentan EA

The hippocampus and cortex of the brains of patients with Alzheimer´s disease (AD) show 1) extensive neuronal death; 2) an increase in oxidative damage products; and 3) an accumulation of proteinaceous oligomers/aggregates, which all together may be responsible for the progressive loss of cognitive capacities observed in AD. The principal component of these proteinaceous oligomers/aggregates, called senile plaques (SP), is the amyloid-β peptide (Aβ), which is generated by proteolytic processing of the amyloid precursor protein. The genetic, cellular and biochemical evidence obtained so far suggests that the oligomeric species of the Aβ peptide may be responsible for the neuronal damage in AD. Moreover, it has been proposed that some accessory molecules could modulate Aβ peptide toxicity. In this context, it has been shown that transition metals such as copper, iron and zinc, which accumulate in SP, can interact with the Aβ peptide, promoting amyloid aggregation and the formation of reactive oxygen species. Therefore, the interaction between transition metals and the Aβ peptide may partially explain the neuronal and oxidative damage detected in the brains of patients with AD

Developmental origins of aging in brain and blood vessels: an overview.

Emerging evidence suggests a remarkable convergence of inflammatory mechanisms in the etiology of cardiovascular disease and Alzheimer disease. A broad set of NSAIDs and statins used to reduce the risk of vascular occlusion and to slow atherogensis may also be protective for Alzheimer disease. Elevated blood levels of C-reactive protein are risk factors for cardiovascular disease and possibly for Alzheimer disease. Monocyte-lineage cells are also fundamental to both conditions: in blood vessels, macrophages are important to atherogenesis for the accumulation of lipids (foam cells), whereas brain microglia show activation during aging and direct involvement in amyloid metabolism in the senile plaque. Genetic influences are recognized through the apoE4 allele, which is associated with hypercholesterolemia and is a risk factor in vascular events and Alzheimer disease, and is recognized for its proinflammatory profile. ApoE4 also accelerates Alzheimer disease pathogenesis in Down's syndrome and many other chronic neurodegenerative conditions, as is well-supported by animal models. Inflammatory changes are present at the earliest stages of vascular disease and Down's syndrome in human fetuses, and are also prominent early in Alzheimer disease. These findings give a basis for considering inflammatory processes early in life which can lead to fully fired pathogenesis of cardiovascular disease and possibly for Alzheimer disease.

Neuronal structure is altered by amyloid plaques.

During the course of Alzheimer's disease (AD), neurons undergo extensive remodeling, contributing to the loss of function observed in the disease. Many brain regions in patients with AD show changes in axonal and dendritic fields, dystrophic neurites, synapse loss, and neuron loss. Accumulation of amyloid-beta protein, a pathological hallmark of the disease, contributes to many of these alterations of neuronal structure. Areas of the brain displaying a high degree of plasticity are particularly vulnerable to degeneration in Alzheimer's disease. This article describes neuronal changes that occur in AD, reviews evidence that amyloid-beta contributes to these changes, and finally discusses the recovery of amyloid-induced changes in the brains of transgenic mice, lending hope to the idea that therapeutic strategies which reduce amyloid-beta production will lead to functional recovery in patients with AD.

Cortical synaptic integration in vivo is disrupted by amyloid-beta plaques.

The accumulation of amyloid-beta protein into plaques is a characteristic feature of Alzheimer's disease. However, the contribution of amyloid-beta plaques to neuronal dysfunction is unknown. We compared intracellular recordings from neocortical pyramidal neurons in vivo in APP-Sw (Tg2576 transgenic mice overexpressing amyloid precursor protein with the Swedish mutation) transgenic mice to age-matched nontransgenic cohorts at ages either before or after deposition of cortical plaques. We show that the evoked synaptic response of neurons to transcallosal stimuli is severely impaired in cortex containing substantial plaque accumulation, with an average 2.5-fold greater rate of response failure and twofold reduction in response precision compared with age-matched nontransgenic controls. This effect correlated with the presence of amyloid-beta plaques and alterations in neuronal process geometry. Responses of neurons in younger APP-Sw animals, before plaque accumulation, were similar to those in nontransgenic controls. In all cases, spontaneous membrane potential dynamics were similar, suggesting that overall levels of synaptic innervation were not affected by plaques. Our results show that plaques disrupt the synchrony of convergent inputs, reducing the ability of neurons to successfully integrate and propagate information.