RNA therapeutics directed to the non coding regions of APP mRNA, in vivo anti-amyloid efficacy of paroxetine, erythromycin, and N-acetyl cysteine

Lead compounds directed to the 5' leader of the Amyloid Precursor Protein transcript (i.e., paroxetine (SSRI), N-acetyl cysteine (antioxidant), and erythromycin (macrolide antibiotic)) were employed in a pilot study to evaluate their anti-amyloid efficacy in the TgCRND8 transgenic mouse model for Alzheimer's Disease (AD). The relative levels of Abeta peptide were reduced after exposure of mice to paroxetine (N=5), NAC (N=7), and erythromycin (N=7) relative to matched placebo counterparts. Paroxetine limited the levels of APP holoprotein and total Abeta peptide levels (measurements of Abeta were performed at two separate sites by quantitative western blotting and ELISA assay). The paroxetine data provided proof-of-concept for our strategy for further screening the APP 5'UTR target to identify novel drugs that exhibit anti-amyloid efficacy in vivo. Erythromycin and azithromycin were macrolide antibiotics that markedly changed the cleavage of the APP C-Terminal Fragment (CTF) in SH-SY5Y cells. Erythromycin provided orally to TgCRND8 mice consistently (100%) reduced brain Abeta(1-42) levels. These data demonstrated a highly statistically significant anti-amyloid trend for paroxetine, NAC and erythromycin. The potential for conducting further studies with these compounds using larger cohorts of TgCRND8 mice is discussed, particularly since erythromycin has recently been exposed to mice for a further 6 months (N=6). It will be possible to employ the chemical structures of paroxetine and erythromycin as starting points for drug design and development for AD therapeutics.

Palmitic acid-treated astrocytes induce BACE1 upregulation and accumulation of C-terminal fragment of APP in primary cortical neurons

High-fat diet is a significant risk factor for the development of Alzheimer's disease (AD). In addition, the AD brain is characterized by elevated levels of fatty acids as compared to that of healthy controls. Despite this, it is unclear how elevated levels of fatty acids are related to the pathogenesis of AD. The present study examines the role of saturated fatty acid, palmitic acid (PA), in causing BACE1 upregulation and consequent amyloidogenic processing of beta-amyloid precursor protein (APP), one of the main characteristic signatures of AD pathology. Here, primary rat cortical neurons and astrocytes were treated with pathological concentration of PA. There was no change in the BACE1 levels in the rat cortical neurons treated directly with PA as compared to controls. The conditioned medium from PA-treated astrocytes, however, caused BACE1 upregulation in the cortical neurons. Moreover, there was a consequent increase in the cleavage of APP leading to the accumulation of the C-terminal fragment of APP (C99) in the cortical neurons. Co-treatment of neurons with 1,3-dimethyl urea (DMU), an antioxidant, decreased PA-induced upregulation in the levels of BACE1 and C99. The present results establish an important role of saturated fatty acids in AD-associated amyloidogenesis through astroglia-mediated oxidative stress.

The effect of S-adenosylmethionine on CNS gene expression studied by cDNA microarray analysis

High homocysteine (Hcy) together with low S-adenosylmethionine (SAM) levels are often observed in Alzheimer disease (AD), and this could be a sign of alteration of SAM/Hcy metabolism. It has already been shown that DNA methylation is involved in amyloid-beta-protein precursor (AbetaPP) processing and amyloid-beta(Abeta) production through the regulation of Presenilin 1 (PS1) expression and that exogenous SAM can silence the gene reducing Abeta. To investigate whether SAM administration globally influenced gene expression in the brain, we analysed 588 genes of the central nervous system in SK-N-BE neuroblastoma cells, with cDNA probes derived from untreated (DM; Differentiation Medium) or SAM treated (DM+SAM) cultures. In these conditions only seven genes were modulated by SAM treatment (and therefore by DNA methylation); three were up-regulated and four down-regulated, showing low levels of modulation.

Postinjury administration of pituitary adenylate cyclase activating polypeptide (PACAP) attenuates traumatically induced axonal injury in rats

Pituitary adenylate cyclase activating polypeptide (PACAP) has several different actions in the nervous system. Numerous studies have shown its neuroprotective effects both in vitro and in vivo. Previously, it has been demonstrated that PACAP reduces brain damage in rat models of global and focal cerebral ischemia. Based on the protective effects of PACAP in cerebral ischemia and the presence of common pathogenic mechanisms in cerebral ischemia and traumatic brain injury (TBI), the aim of the present study was to investigate the possible protective effect of PACAP administered 30 min or 1 h postinjury in a rat model of diffuse axonal injury. Adult Wistar male rats were subjected to impact acceleration, and PACAP was administered intracerebroventricularly 30 min (n = 4), and 1 h after the injury (n = 5). Control animals received the same volume of vehicle at both time-points (n = 5). Two hours after the injury, brains were processed for immunohistochemical localization of damaged axonal profiles displaying either beta-amyloid precursor protein (beta-APP) or RMO-14 immunoreactivity, both considered markers of specific features of traumatic axonal injury. Our results show that treatment with PACAP (100 microg) 30 min or 1 h after the induction of TBI resulted in a significant reduction of the density of beta-APP-immunopositive axon profiles in the corticospinal tract (CSpT). There was no significant difference between the density of beta-APP-immunopositive axons in the medial longitudinal fascicle (MLF). PACAP treatment did not result in significantly different number of RMO-14-immunopositive axonal profiles in either brain areas 2 hours post-injury compared to normal animals. While the results of this study highlighted the complexity of the pathogenesis and manifestation of diffuse axonal injury, they also indicate that PACAP should be considered a potential therapeutic agent in TBI.

Cerebrolysin decreases amyloid-beta production by regulating amyloid protein precursor maturation in a transgenic model of Alzheimer's disease

Cerebrolysin is a peptide mixture with neurotrophic effects that might reduce the neurodegenerative pathology in Alzheimer's disease (AD). We have previously shown in an amyloid protein precursor (APP) transgenic (tg) mouse model of AD-like neuropathology that Cerebrolysin ameliorates behavioral deficits, is neuroprotective, and decreases amyloid burden; however, the mechanisms involved are not completely clear. Cerebrolysin might reduce amyloid deposition by regulating amyloid-beta (Abeta) degradation or by modulating APP expression, maturation, or processing. To investigate these possibilities, APP tg mice were treated for 6 months with Cerebrolysin and analyzed in the water maze, followed by RNA, immunoblot, and confocal microscopy analysis of full-length (FL) APP and its fragments, beta-secretase (BACE1), and Abeta-degrading enzymes [neprilysin (Nep) and insulin-degrading enzyme (IDE)]. Consistent with previous studies, Cerebrolysin ameliorated the performance deficits in the spatial learning portion of the water maze and reduced the synaptic pathology and amyloid burden in the brains of APP tg mice. These effects were associated with reduced levels of FL APP and APP C-terminal fragments, but levels of BACE1, Notch1, Nep, and IDE were unchanged. In contrast, levels of active cyclin-dependent kinase-5 (CDK5) and glycogen synthase kinase-3beta [GSK-3beta; but not stress-activated protein kinase-1 (SAPK1)], kinases that phosphorylate APP, were reduced. Furthermore, Cerebrolysin reduced the levels of phosphorylated APP and the accumulation of APP in the neuritic processes. Taken together, these results suggest that Cerebrolysin might reduce AD-like pathology in the APP tg mice by regulating APP maturation and transport to sites where Abeta protein is generated. This study clarifies the mechanisms through which Cerebrolysin might reduce Abeta production and deposition in AD and further supports the importance of this compound in the potential treatment of early AD.

Retinoic acid normalizes nuclear receptor mediated hypo-expression of proteins involved in β-amyloid deposits in the cerebral cortex of vitamin A deprived rats

Recent data have revealed that disruption of vitamin A signaling observed in Alzheimer's disease (AD) leads to a deposition of beta-amyloid (Abeta). The aim of this study was to precise the role of vitamin A and its nuclear receptors (RAR) in the processes leading to the Abeta deposits. Thus, the effect of vitamin A depletion and subsequent administration of retinoic acid (RA, the active metabolite of vitamin A) on the expression of RARbeta, and of proteins involved in amyloidogenic pathway, e.g., amyloid precursor protein (APP), beta-secretase enzyme (BACE), and APP carboxy-terminal fragment (APP-CTF) was examined in the whole brain, hippocampus, striatum, and cerebral cortex of rats. Rats fed a vitamin A-deprived diet for 13 weeks exhibited decreased amount of RARbeta, APP695, BACE, and of APP-CTF in the whole brain and in the cerebral cortex. Administration of RA is able to restore all expression. The results suggest that fine regulation of vitamin A mediated gene expression seems fundamental for the regulation of APP processing.

Cyclohexanehexol inhibitors of Abeta aggregation prevent and reverse Alzheimer phenotype in a mouse model

When given orally to a transgenic mouse model of Alzheimer disease, cyclohexanehexol stereoisomers inhibit aggregation of amyloid beta peptide (Abeta) into high-molecular-weight oligomers in the brain and ameliorate several Alzheimer disease-like phenotypes in these mice, including impaired cognition, altered synaptic physiology, cerebral Abeta pathology and accelerated mortality. These therapeutic effects, which occur regardless of whether the compounds are given before or well after the onset of the Alzheimer disease-like phenotype, support the idea that the accumulation of Abeta oligomers has a central role in the pathogenesis of Alzheimer disease.

Nicotine modulates expression of amyloid precursor protein and amyloid precursor-like protein 2 in mouse brain and in SH-SY5Y neuroblastoma cells

Epidemiological studies indicate that tobacco smoking can be protective against neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). The objective of the present study was to examine the changes in gene expression induced by chronic oral nicotine administration (100 mug/ml in 2% saccharin for 14 days), with special emphasis on amyloid precursor protein (APP) and its homologue, amyloid precursor-like protein 2 (APLP2), in different brain regions of C57BL/6 mice using a pathway-focused microarray. Our results revealed that nicotine stimulated mRNA expression of APP in the amygdala (64%; P = 0.003) and hippocampus (32%; P = 0.034) and of APLP2 in the amygdala (39%; P = 0.002). These results were verified by quantitative real-time RT-PCR except that expression of APLP2 was also significantly upregulated by nicotine in the hippocampus. In addition, in vitro nicotine treatment of SH-SY5Y neuroblastoma cells resulted in a significant increase in expression of APP protein, soluble APP, and APLP2, whereas co-treatment with mecamylamine (an antagonist of nicotinic acetylcholine receptors) attenuated the stimulating effect of nicotine on APP and APLP2 expression. These findings suggest that nicotine treatment facilitates the increase in the expression of mRNA and protein of the APP and APLP2 genes in rat brain and SH-SY5Y neuroblastoma cells.

Coated-platelets retain amyloid precursor protein on their surface

Coated-Platelets are a subset of platelets produced by dual-agonist activation with collagen plus thrombin and are characterized by strong retention of several procoagulant, alpha-granule proteins on the cell surface. In this report we demonstrate that coated-platelets also retain full-length amyloid precursor protein (APP) on their surface in contrast to the cleavage of APP in platelets activated with a single agonist. In addition, western blot analysis indicated that APP is derivatized during coated-platelet synthesis. We subsequently measured coated-platelet production in patients with Alzheimer's disease (AD). Twenty-two AD patients showed a wide distribution of coated-platelet values; however the least impaired AD patients produced coated-platelets at a level significantly above that of aged controls (41.0 +/- 9.9 vs. 28.7 +/- 11.4%; mean +/- 1SD; p = 0.017). These findings suggest that coated-platelets may be a model of aberrant APP processing in early AD patients.

BACE inhibitor reduces APP-beta-C-terminal fragment accumulation in axonal swellings of okadaic acid-induced neurodegeneration

Emerging evidence suggests that not only beta-amyloid but also other amyloid precursor protein (APP) fragments, such as the beta-C-terminal fragment (betaCTF), might be involved in Alzheimer's disease (AD). Treatment of neurons with okadaic acid (OA), a protein phosphatase-2A inhibitor, has been used to induce tau phosphorylation and neuronal death to create a research model of AD. In this study, we analyzed axonopathy and APP regulation in cultured rat neurons treated with OA. After OA treatment, the neurons presented with axonal swellings filled with vesicles, microtubule fragments, and transport molecules such as kinesin and synapsin-I. Western blotting showed that intracellular APP levels were increased and immunocytochemistry using antibodies against the APP C-terminus showed that APP accumulated in the axonal swellings. This APP C-terminus immunoreactivity disappeared when neurons were cotreated with a beta-secretase inhibitor, but not with alpha- or gamma-secretase inhibitors, indicating that the accumulation was primarily composed of APP-betaCTF. These findings provide the first evidence that APP-betaCTF can accumulate in the axons of OA-treated neurons, and may suggest that APP-betaCTF is involved in the pathogenesis of AD.

The anti-inflammatory and cholinesterase inhibitor bifunctional compound IBU-PO protects from β-amyloid neurotoxicity by acting on Wnt signaling components

Changes in signal transduction are implicated in neuronal responses to the Alzheimer's amyloid-beta-peptide (Abeta), which include neurotransmitter systems and pathways involved in the maintenance of the nervous system. We report here that a new bifunctional compound IBU-PO, which combines a non-steroidal anti-inflammatory drug (NSAID) (Ibuprofen) and a cholinesterase (ChE) inhibitor (Octyl-Pyridostigmine), is neuroprotective against Abeta-neurotoxicity, and its activity is associated to Wnt signaling components in rat hippocampal and mouse cortical neurons. IBU-PO (0.01-1 microM) inhibits glycogen-synthase-kinase-3beta (GSK-3beta) and stabilizes cytoplasmic beta-catenin reverting the silencing of the Wnt pathway caused by Abeta-toxicity and GSK-3beta overexpression. In addition, IBU-PO enhances, dose-dependently, the non-amyloidogenic amyloid precursor protein (APP) cleavage by increasing secreted APP and decreasing endogenous Abeta1-40 in rat hippocampal neurons.

Drug discovery: estrogen-related compounds in mouse models of Alzheimer's disease

Despite promising epidemiological studies that showed a decreased incidence of Alzheimer disease (AD) in women who used hormone replacement therapy (HRT), the results of the recently released Women's Health Initiative Memory Study has dampened any enthusiasm for the use of HRT in women to prevent or delay the onset of AD. In this position paper, we review these data, along with our own--using estrogens in a transgenic mouse model of AD--and introduce our current working hypothesis and research.

Cholesterol, statins and dementia

PURPOSE OF REVIEW

Advances in cholesterol biology suggest that cholesterol metabolism modulates beta-amyloid production, and that pharmaceuticals that inhibit cholesterol metabolism might be valuable in therapy of Alzheimer's disease. Although the genetics and cell biology continue to support the link between cholesterol and Alzheimer's disease, recent clinical studies suggest that the animal studies might not directly translate to clinical studies in humans.

RECENT FINDINGS

This review will highlight advances in genetics, cell biology and clinical sciences investigating the relationship between cholesterol and Alzheimer's disease.

SUMMARY

Cholesterol, its catabolites and proteins that regulate cholesterol levels all modulate processing of amyloid precursor protein. Statins hold promise in therapy of Alzheimer's disease, but the current data are more consistent with a model of statins that act as neuroprotective agents rather than inhibitors of beta-amyloid production.

Cerebral Perfusion Pressure Elevation with Oxygen-Carrying Pressor after Traumatic Brain Injury and Hypotension in Swine

BACKGROUND

Previously, we had shown that elevation of cerebral perfusion pressure, using pressors, improved short-term outcomes after traumatic brain injury and hemorrhagic shock in swine. The current study evaluates outcomes after resuscitation with diaspirin cross-linked hemoglobin (DCLHb)--a hemoglobin-based oxygen carrier with pressor activity--in the same swine model of traumatic brain injury and hemorrhagic shock.

METHODS

Anesthetized and ventilated swine received traumatic brain injury via cortical fluid percussion (6-8 atm) followed by 45% blood volume hemorrhage. One hour later, animals were randomized to either a control group (SAL) resuscitated with normal saline equal to three times shed blood volume or to one of two experimental groups resuscitated with DCLHb. The two experimental groups consisted of a low-dose group, resuscitated with 250 mL of DCLHb (Hb1), and a high-dose group, resuscitated with 500 mL of DCLHb (Hb2). Animals were observed for 210 minutes postresuscitation. Outcomes evaluated were cerebral oxygenation by measuring partial pressure and saturation of oxygen in cerebrovenous blood; cerebral function by evaluating the preservation and magnitude of cerebrovascular carbon dioxide reactivity; and brain structural damage by semiquantitatively assessing beta amyloid precursor protein positive axons.

RESULTS

Postresuscitation, cerebral perfusion pressure was higher in the DCLHb groups (p < 0.05, Hb1 and Hb2 vs. SAL), and intracranial pressure was lower in the Hb2 group (p < 0.05 vs. SAL). Cerebrovenous oxygen level was similar in all groups (p > 0.05). At baseline, 5% carbon dioxide evoked a 16 +/- 1% increase in cerebrovenous oxygen saturation, indicating vasodilatation. At 210 minutes, this response was nearly absent in SAL (4 +/- 4%) (p < 0.05 vs. baseline) and Hb1 (1 +/- 5%), but was partially preserved in Hb2 (9 +/- 5%). There was no intergroup difference in beta amyloid precursor protein positive axons. Five of 20 SAL and 0 of 13 DCLHb animals developed brain death (flat electroencephalogram) (p = 0.05, SAL vs. DCLHb). Postresuscitation, DCLHb animals maintained higher mean pulmonary arterial pressure (28 +/- 1 mm Hg, SAL; 42 +/- 1 mm Hg, Hb1; 45 +/- 1 mm Hg, Hb2) (p < 0.05, Hb1 and Hb2 vs. SAL) and lower cardiac output (3.9 +/- 1.6 L/min, SAL; 2.6 +/- 0.1 L/min, Hb1; 2.7 +/- 0.1 L/min, Hb2) (p < 0.05, Hb1 and Hb2 vs. SAL). Three Hb2 animals died as a result of cardiac failure, and one SAL animal died as a result of irreversible shock.

CONCLUSION

In this swine model of traumatic brain injury and hemorrhagic shock, resuscitation with DCLHb maintained a higher cerebral perfusion pressure. Low-dose DCLHb (minimal increase in oxygen carriage) failed to significantly improve short-term outcome. With high-dose DCLHb (significant improvement in oxygen carriage), intracranial pressure was lower and cerebrovascular carbon dioxide reactivity was partially preserved; however, this was at the cost of poorer cardiac performance secondary to high afterload.

Intracellular accumulation of amyloidogenic fragments of amyloid-beta precursor protein in neurons with Niemann-Pick type C defects is associated with endosomal abnormalities

Niemann-Pick type C disease (NPC) is characterized by neurodegeneration secondary to impaired cholesterol trafficking and excessive glycosphingolipid storage. Abnormal cholesterol and ganglioside metabolism may influence the generation and aggregation of amyloidogenic fragments (ie, C99 and Abeta) from amyloid-beta precursor protein (APP), crucial factors causing neurodegeneration in Alzheimer's disease. To reveal whether abnormal accumulation and aggregation of APP fragments also occurs in NPC, we studied their expression in cultured cortical neurons treated with U18666A, a compound widely used to induce NPC defects, and also in brain tissues from NPC patients. U18666A treatment resulted in increased intraneuronal levels of C99 and insoluble Abeta42, which were distributed among early and late endosomes, in compartments distinct from where endogenous cholesterol accumulates. Analyses of NPC brains revealed that C99 or other APP C-terminal fragments (APP-CTF), but not Abeta42, accumulated in Purkinje cells, mainly in early endosomes. In contrast, in hippocampal pyramidal neurons, the major accumulated species was Abeta42, in late endosomes. Similar to what has been shown in Alzheimer's disease, cathepsin D, a lysosomal hydrolase, was redistributed to early endosomes in NPC Purkinje cells, where it co-localized with C99/APP-CTF. Our results suggest that endosomal abnormalities related to abnormal lipid trafficking in NPC may contribute to abnormal APP processing and Abeta42/C99/APP-CTF deposition.

Estrogen alters amyloid precursor protein as well as dendritic and cholinergic markers in a mouse model of Down syndrome

Individuals with Down syndrome (DS) develop the pathological hallmarks of Alzheimer's disease at an early age, later followed by memory decline and dementia. Women with DS are twice as likely to undergo early menopause, and levels of estradiol correlate with onset of cognitive decline in these women. We have demonstrated that a mouse model of DS, mice with segmental trisomy of chromosome 16 (Ts65Dn), develop a significant deficit in both reference and working memory as young adults (6-10 months of age), coupled with phenotypic loss of cholinergic neurons in the basal forebrain and altered growth factor levels. In the present study we examined cholinergic and dendritic markers in the hippocampal formation and levels of the amyloid precursor protein (APP) in different brain regions of Ts65Dn mice treated with estradiol for 60 days. The density of the dendritic marker Map2 was significantly decreased in the hippocampal formation of middle-aged trisomic mice (9-15 months old), and the density of cholinergic neurites (acetylcholinesterase [AChE] histochemistry) was also decreased in specific layers of the hippocampus. Treatment with 17beta-estradiol alleviated the decreases in Map2 and AChE staining, but had no effect on full-length APP levels in the hippocampus. In contrast, a main effect of treatment on APP levels in the striatum was noted, with significant elevations observed in controls and trisomics. These findings demonstrate that estrogen can alleviate deficits in cholinergic and dendritic elements in the hippocampal formation and further strengthens the rationale to explore estrogen replacement therapy in women with DS.

New therapeutic approaches in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects a large proportion of the elderly population. It causes a progressive decline in memory and other cognitive functions. There is no effective treatment of AD despite the great effort in trying to find one. Herein new therapeutic approaches including those closely targeting the pathogenesis of the disease have been discussed. Potential disease modifying treatments that are being considered as future treatment of AD include avaccination, secretase inhibitors, cholesterol lowering drugs, metal chelators and anti- inflammatory agents. According to Evidence Based Dementia Practice, only inhibitors of acetylcholinesterase (AChE) are approved in mild and moderate stages of AD treatment. From the end of 2003, FDA also approved memantine for much severer phases of AD. When all the presented possibilities are taken into account, the most important target for scientists and physicians is not only to find ways for causative cure of AD, but also to be ready for that moment. There is a great need for finding routine biomarkers and sensitive enough clinical tests for diagnosis of AD in which the lasting pathological process does not destroy too many neurones.

β-Synuclein-Derived Peptides With Neuroprotective Activity: An Alternative Treatment of Neurodegenerative Disorders?

The 140-amino-acid protein alpha-synuclein (alpha-syn) is the major constituent of Lewy bodies. The protein interacts with several intracellular signal transduction pathways. Reasons for onset of abnormal aggregation of alpha-syn are unclear. Metal ions, oxidative stress, and beta-amyloid 1-42 (Abeta1-42) are important induction factors for alpha-syn aggregation. beta-Synuclein (beta-syn) can counteract alpha-syn aggregation. Cross-breeding of beta-syn transgenic mice with animals overexpressing alpha-syn significantly decreased alpha-syn-positive neuronal inclusion bodies and improved motor function. This was an important proof of concept for the role of beta-syn in regulating alpha-syn aggregation. A drug discovery program based on peptide derivatives (N-terminal amino acids 1-15) of beta-syn was initiated. For screening, tissue culture models simulating disease-specific conditions were utilized. They protected against growth factor withdrawal, Abeta toxicity, and oxidative stress. Three peptides were selected (KEGV, SMAKEGV, MDFMKGLSMAKE) for in vivo studies because they also decreased expression of Abeta1-40 and Abeta1-42. First, in vivo experiments were made in human amyloid precursor protein (APP [Swedish and London mutation]) transgenic mice, as well as alpha-syn transgenic mice. Treatment was performed with the peptides as an intraperitoneal injection or as intranasal droplets for 2 mo. Behavioral studies in APP transgenic mice were performed after 1 and 2 mo of treatment and showed clear effects of these peptides.

Amyloid Precursor Protein Compartmentalization Restricts β-Amyloid Production: Therapeutic Targets Based on BACE Compartmentalization

Alzheimer's disease (AD) is defined by deposits of the 42-residue amyloid-beta peptide (Abeta42) in the brain. Abeta42 is a minor metabolite of the amyloid precursor protein (APP), but its relative levels are increased by mutations on APP and presenilins 1 and 2 linked to familial AD. beta-secretase (BACE-1), an aspartyl protease, cleaves approx 10% of the APP in neuronal cells on the N-terminal side of Abeta to produce the C-terminal fragment (CTFbeta), which is cleaved by gamma-secretase to produce mostly Abeta of 40 residues (90%) and approx10% Abeta42. A third enzyme, alpha-secretase, cleaves APP after Abeta16 to secrete sAPPalpha and CTFalpha, the major metabolites of APP. Moreover, previous studies have demonstrated that phorbol esters stimulate processing of APP by alpha-secretase. Because alpha-secretase and BACE-1 cleave APP within the secretory pathway, it is likely that the two enzymes compete for the APP substrate. This type of competition can explain the failure to saturate the minor BACE-1 pathway by overexpressing APP in the cell. In this study, we demonstrate that inhibition of constitutive alpha-secretase processing in a human neuroblastoma cell line does not increase the yield of Abeta, suggesting that the APP substrate targeted for alpha-secretase processing is not diverted to the BACE-1 pathway. However, when phorbol ester-induced alpha-secretase was similarly inhibited, we detected an increase in BACE-1 processing and AB yield. We explain these results compartmentalization of BACE-1 and alpha-secretase with processing depending on sorting of APP to the two compartments. The simplest explanation for the detection of competition between the two pathways upon phorbol ester stimulation is the partial failure of this compartmentalization by phorbol ester-induced release of secretory vesicles.

Effect of haloperidol and risperidone on amyloid precursor protein levels in vivo

The neurotoxic beta-amyloid peptide of Alzheimer's disease is formed from the amyloid precursor protein (APP), which is a member of an evolutionarily highly conserved gene family with significant functional importance. Because behavioral and psychiatric symptoms treated with antipsychotics may influence the course of the disease, we have investigated traditional and atypical antipsychotic drugs, administered through the intraperitoneal route, for their effects on rat cortical APP. Western-immunoblotting was utilized for semi-quantitative evaluation of APP levels. Treatment with haloperidol resulted in an acute elevation of cortical APP both in therapeutic and toxic doses, however, it had no significant chronic impact on APP. Atypical antipsychotic risperidone did not change cortical APP concentration. These results indicate that both haloperidol and risperidone are considered to be relatively safe with respect to APP metabolism. Possible mechanisms, including involvement of calcium and APP itself as a receptor, are discussed.

Chronic glial activation, neurodegeneration, and APP immunoreactive deposits following acute administration of double-stranded RNA

Several neurodegenerative disorders, including Alzheimer's and Parkinson's diseases, are associated with immunocompetent microglia, leading to the suggestion that chronic glial-mediated inflammation contributes to the neurodegeneration seen in these diseases. Little direct evidence supports this hypothesis, and no suitable rodent models exist that do not involve the use of blunt trauma or ischaemia, events that are infrequently encountered in the human disease state. In the present study, we report that administration of double-stranded RNA, a classical inducer of interferon-gamma (IFN-gamma), causes rapid and persistent activation of microglia and astrocytes, as well as induction of interleukin-1beta (IL-beta) and nitric oxide synthase. In close temporal succession to glial activation, there is neurodegeneration, with neuron loss involving apoptosis in selected brain regions including the septal nucleus, hippocampus, cortex and thalamus, along with hippocampal atrophy. This neuronal loss is accompanied by punctate deposits of material that are immunoreactive for amyloid precursor protein, beta-amyloid peptide (Abeta), and apolipoprotein E. The findings may have clinical relevance, since the administration of the nonsteroidal antiinflammatory agent (NSAID) ibuprofen markedly reduces the neurodegeneration observed in the absence of significant glial inhibition. These findings may be relevant to the pathogenesis of Alzheimer's disease in particular, and to other neurodegenerative diseases involving inflammation.

Characterization of the effect of ganstigmine (CHF2819) on amyloid precursor protein metabolism in SH-SY5Y neuroblastoma cells

We have investigated the effect of ganstigmine (CHF2819), a novel geneserine derived acetylcholinesterase (AChE) inhibitor, on the expression and metabolism of the amyloid precursor protein (APP) in neuroblastoma cell line SH-SY5Y. The rationale was based on the suggestion that cholinergic activity may also be involved in the regulation of APP metabolism. We studied the acute effect on APP metabolism following the secretion of sAPPalpha in the conditioned medium of cells. Following short term treatment (2h), ganstigmine promoted a slight increase in the release of sAPPalpha, the maximal effect approaching on average 1.5 fold baseline value. The data obtained in the long term experiments demonstrate that continuous inhibition of AchE obtained with 100 nM ganstigmine following an exposure of 24 hours did not influence APP isoforms expression. However, the compound appeared to increase the constitutive release of sAPPalpha, with a mechanism that is derived from an indirect cholinergic stimulation.

Insulin dose-response effects on memory and plasma amyloid precursor protein in Alzheimer's disease: interactions with apolipoprotein E genotype

In previous studies, adults with Alzheimer's disease (AD) showed memory enhancement when plasma insulin levels were raised to 85 microU/ml, whereas normal adults' memory was unchanged. Degree of memory enhancement was also related to apolipoprotein E (apoE) genotype status for AD patients. Response differences between normal and AD groups could reflect dose-response differences for insulin. To examine this question, 22 adults with AD and 15 normal adults received five doses of insulin on separate days in counterbalanced order, resulting in five plasma insulin levels (10, 25, 35, 85 and 135 microU/ml), while plasma glucose levels of ~100 mg/dl were maintained. Cognitive performance and plasma APP levels were measured after 120 min of infusion. Relative to baseline, AD patients who were not apoE- epsilon 4 homozygotes had improved memory at higher insulin levels of 35 and 85 microuU/ml, whereas normal adults and AD patients who were epsilon 4 homozygotes showed improved memory at insulin levels of 25 microU/ml. Normal adults' memory was also improved at insulin levels of 85 microU/ml. Plasma APP was lowered for adults with AD without the epsilon 4 allele at higher levels (85 microU/ml) than for normal adults and epsilon 4 homozygotes, who showed decreased APP at the 35 microU/ml level. AD patients with a single epsilon 4 allele showed a different pattern of insulin effects on APP than did other subjects. In general, few effects of insulin were seen at the highest dose for any subject group. These results support a role for insulin in normal memory and APP modulation that follows a curvilinear response pattern, and suggest that AD patients who are not epsilon 4 homozygotes have reduced sensitivity to insulin that may interfere with such modulation.

Role of acetylcholinesterase inhibitors in the metabolism of amyloid precursor protein

Potentiation of central cholinergic activity has been proposed as a therapeutic approach for improving the cognitive function in patients with Alzheimer's disease (AD). Increasing the acetylcholine concentration in the brain by modulating acetylcholine-sterase (AChE) activity is among the most promising therapeutic strategies. Efforts to treat the underlying pathology based on the modulation of amyloid precursor protein (APP) processing in order to decrease the accumulation of beta-amyloid are also very important. Alterations in APP metabolism have recently been proposed to play a key role in the long-lasting effects of AChE inhibitors. This review surveys recent data from in vivo and in vitro studies that have contributed to our understanding of the role of AChE inhibitors in APP processing. The regulatory mechanisms relating to the muscarinic agonist effect, protein kinase C activation and mitogen-activated protein kinase phosphorylation, involving the alpha-secretase or the 5 -UTR region of the APP gene, are also discussed. Further work is warranted to elucidate the exact roles in APP metabolism of the AChE inhibitors used in AD therapy at present.

Glucagon-like peptide-1 decreases endogenous amyloid-beta peptide (Abeta) levels and protects hippocampal neurons from death induced by Abeta and iron

Glucagon-like peptide-1(7-36)-amide (GLP-1) is an endogenous insulinotropic peptide that is secreted from the gastrointestinal tract in response to food. It enhances pancreatic islet beta-cell proliferation and glucose-dependent insulin secretion and lowers blood glucose and food intake in patients with type 2 diabetes mellitus. GLP-1 receptors, which are coupled to the cyclic AMP second messenger pathway, are expressed throughout the brains of rodents and humans. It was recently reported that GLP-1 and exendin-4, a naturally occurring, more stable analogue of GLP-1 that binds at the GLP-1 receptor, possess neurotrophic properties and can protect neurons against glutamate-induced apoptosis. We report here that GLP-1 can reduce the levels of amyloid-beta peptide (Abeta) in the brain in vivo and can reduce levels of amyloid precursor protein (APP) in cultured neuronal cells. Moreover, GLP-1 and exendin-4 protect cultured hippocampal neurons against death induced by Abeta and iron, an oxidative insult. Collectively, these data suggest that GLP-1 can modify APP processing and protect against oxidative injury, two actions that suggest a novel therapeutic target for intervention in Alzheimer's disease.