Lack of specific amyloid-beta(1-42) suppression by nonsteroidal anti-inflammatory drugs in young, plaque-free Tg2576 mice and in guinea pig neuronal cultures

Robust Translation of γ-Secretase Modulator Pharmacology across Preclinical Species and Human Subjects

The amyloid-β peptide (Aβ)—in particular, the 42–amino acid form, Aβ1-42—is thought to play a key role in the pathogenesis of Alzheimer’s disease (AD). Thus, several therapeutic modalities aiming to inhibit Aβ synthesis or increase the clearance of Aβ have entered clinical trials, including γ-secretase inhibitors, anti-Aβ antibodies, and amyloid-β precursor protein cleaving enzyme inhibitors. A unique class of small molecules, γ-secretase modulators (GSMs), selectively reduce Aβ1-42 production, and may also decrease Aβ1-40 while simultaneously increasing one or more shorter Aβ peptides, such as Aβ1-38 and Aβ1-37. GSMs are particularly attractive because they do not alter the total amount of Aβ peptides produced by γ-secretase activity; they spare the processing of other γ-secretase substrates, such as Notch; and they do not cause accumulation of the potentially toxic processing intermediate, β-C-terminal fragment. This report describes the translation of pharmacological activity across species for two novel GSMs, (S)-7-(4-fluorophenyl)-N2-(3-methoxy-4-(3-methyl-1H-1,2,4-triazol-1-yl)phenyl)-N4-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidine-2,4-diamine (BMS-932481) and (S,Z)-17-(4-chloro-2-fluorophenyl)-34-(3-methyl-1H-1,2,4-triazol-1-yl)-16,17-dihydro-15H-4-oxa-2,9-diaza-1(2,4)-cyclopenta[d]pyrimidina-3(1,3)-benzenacyclononaphan-6-ene (BMS-986133). These GSMs are highly potent in vitro, exhibit dose- and time-dependent activity in vivo, and have consistent levels of pharmacological effect across rats, dogs, monkeys, and human subjects. In rats, the two GSMs exhibit similar pharmacokinetics/pharmacodynamics between the brain and cerebrospinal fluid. In all species, GSM treatment decreased Aβ1-42 and Aβ1-40 levels while increasing Aβ1-38 and Aβ1-37 by a corresponding amount. Thus, the GSM mechanism and central activity translate across preclinical species and humans, thereby validating this therapeutic modality for potential utility in AD.

Untangling the Web: Toxic and Protective Effects of Neuroinflammation and PGE2 Signaling in Alzheimer's Disease

The neuroinflammatory response has received increasing attention as a key factor in the pathogenesis of Alzheimer's disease (AD). Microglia, the innate immune cells and resident phagocytes of the brain, respond to accumulating Aβ peptides by generating a nonresolving inflammatory response. While this response can clear Aβ peptides from the nervous system in some settings, its failure to do so in AD accelerates synaptic injury, neuronal loss, and cognitive decline. The complex molecular components of this response are beginning to be unraveled, with identification of both damaging and protective roles for individual components of the neuroinflammatory response. Even within one molecular pathway, contrasting effects are often present. As one example, recent studies of the inflammatory cyclooxygenase-prostaglandin pathway have revealed both beneficial and detrimental effects dependent on the disease context, cell type, and downstream signaling pathway. Nonsteroidal anti-inflammatory drugs (NSAIDs), which inhibit cyclooxygenases, are associated with reduced AD risk when taken by cognitively normal populations, but additional clinical and mouse model studies have added complexities and caveats to this finding. Downstream of cyclooxygenase activity, prostaglandin E2 signaling exerts both damaging pro-inflammatory and protective anti-inflammatory effects through actions of specific E-prostanoid G-protein coupled receptors on specific cell types. These complexities underscore the need for careful study of individual components of the neuroinflammatory response to better understand their contribution to AD pathogenesis and progression.

Alzheimer's Disease: Lessons Learned from Amyloidocentric Clinical Trials

Alzheimer's disease (AD) is one of the most debilitating neurodegenerative diseases and is predicted to affect 1 in 85 people by 2050. Despite much effort to discover a therapeutic strategy to prevent progression or to cure AD, to date no effective disease-modifying agent is available that can prevent, halt, or reverse the cognitive and functional decline of patients with AD. Several underlying etiologies to this failure are proposed. First, accumulating evidence from past trials suggests a preventive as opposed to therapeutic paradigm, and the precise temporal and mechanistic relationship of β-amyloid (Aβ) and tau protein should be elucidated to confirm this hypothesis. Second, we are in urgent need of revised diagnostic criteria to support future trials. Third, various technical and methodological improvements are required, based on the lessons learned from previous failed trials.

Interpreting Alzheimer's disease clinical trials in light of the effects on amyloid-β

The failure of several potential Alzheimer’s disease therapeutics in mid- to late-stage clinical development has provoked significant discussion regarding the validity of the amyloid hypothesis. In this review, we propose a minimum criterion of 25% for amyloid-β (Aβ) lowering to achieve clinically meaningful slowing of disease progression. This criterion is based on genetic, risk factor, clinical and preclinical studies. We then compare this minimum criterion with the degree of Aβ lowering produced by the potential therapies that have failed in clinical trials. If the proposed minimum Aβ lowering criterion is used, then the amyloid hypothesis has yet to be adequately tested in the clinic. Therefore, we believe that the amyloid hypothesis remains valid and remains to be confirmed or refuted in future clinical trials.

Pharmacological characterization of the novel γ-secretase modulator AS2715348, a potential therapy for Alzheimer's disease, in rodents and nonhuman primates

γ-Secretase is the enzyme responsible for the intramembranous proteolysis of various substrates, such as amyloid precursor protein (APP) and Notch. Amyloid-β peptide 42 (Aβ42) is produced through the sequential proteolytic cleavage of APP by β- and γ-secretase and causes the synaptic dysfunction associated with memory impairment in Alzheimer's disease. Here, we identified a novel cyclohexylamine-derived γ-secretase modulator, {(1R*,2S*,3R*)-3-[(cyclohexylmethyl)(3,3-dimethylbutyl)amino]-2-[4-(trifluoromethyl)phenyl]cyclohexyl}acetic acid (AS2715348), that may inhibit this pathological response. AS2715348 was seen to reduce both cell-free and cellular production of Aβ42 without increasing levels of APP β-carboxyl terminal fragment or inhibiting Notch signaling. Additionally, the compound increased Aβ38 production, suggesting a shift of the cleavage site in APP. The inhibitory potency of AS2715348 on endogenous Aβ42 production was similar across human, mouse, and rat cells. Oral administration with AS2715348 at 1 mg/kg and greater significantly reduced brain Aβ42 levels in rats, and no Notch-related toxicity was observed after 28-day treatment at 100 mg/kg. Further, AS2715348 significantly ameliorated cognitive deficits in APP-transgenic Tg2576 mice. Finally, AS2715348 significantly reduced brain Aβ42 levels in cynomolgus monkeys. These findings collectively show the promise for AS2715348 as a potential disease-modifying drug for Alzheimer's disease.

The Guinea Pig as a Model for Sporadic Alzheimer's Disease (AD): The Impact of Cholesterol Intake on Expression of AD-Related Genes

We investigated the guinea pig, Cavia porcellus, as a model for Alzheimer’s disease (AD), both in terms of the conservation of genes involved in AD and the regulatory responses of these to a known AD risk factor - high cholesterol intake. Unlike rats and mice, guinea pigs possess an Aβ peptide sequence identical to human Aβ. Consistent with the commonality between cardiovascular and AD risk factors in humans, we saw that a high cholesterol diet leads to up-regulation of BACE1 (β-secretase) transcription and down-regulation of ADAM10 (α-secretase) transcription which should increase release of Aβ from APP. Significantly, guinea pigs possess isoforms of AD-related genes found in humans but not present in mice or rats. For example, we discovered that the truncated PS2V isoform of human PSEN2, that is found at raised levels in AD brains and that increases γ-secretase activity and Aβ synthesis, is not uniquely human or aberrant as previously believed. We show that PS2V formation is up-regulated by hypoxia and a high-cholesterol diet while, consistent with observations in humans, Aβ concentrations are raised in some brain regions but not others. Also like humans, but unlike mice, the guinea pig gene encoding tau, MAPT, encodes isoforms with both three and four microtubule binding domains, and cholesterol alters the ratio of these isoforms. We conclude that AD-related genes are highly conserved and more similar to human than the rat or mouse. Guinea pigs represent a superior rodent model for analysis of the impact of dietary factors such as cholesterol on the regulation of AD-related genes.

Analysis of proteolytic processes and enzymatic activities in the generation of huntingtin n-terminal fragments in an HEK293 cell model

BACKGROUND

N-terminal fragments of mutant huntingtin (htt) that terminate between residues 90-115, termed cleavage product A or 1 (cp-A/1), form intracellular and intranuclear inclusion bodies in the brains of patients with Huntington's disease (HD). These fragments appear to be proteolytic products of the full-length protein. Here, we use an HEK293 cell culture model to investigate huntingtin proteolytic processing; previous studies of these cells have demonstrated cleavage of htt to cp-A/1 like htt fragments.

RESULTS

Recombinant N-terminal htt fragments, terminating at residue 171 (also referred to as cp-B/2 like), were efficiently cleaved to produce cp-A/1 whereas fragments representing endogenous caspase, calpain, and metalloproteinase cleavage products, terminating between residues 400-600, were inefficiently cleaved. Using cysteine-labeling techniques and antibody binding mapping, we localized the C-terminus of the cp-A/1 fragments produced by HEK293 cells to sequences minimally limited by cysteine 105 and an antibody epitope composed of residues 115-124. A combination of genetic and pharmacologic approaches to inhibit potential proteases, including γ-secretase and calpain, proved ineffective in preventing production of cp-A/1.

CONCLUSIONS

Our findings indicate that HEK293 cells express a protease that is capable of efficiently cleaving cp-B/2 like fragments of htt with normal or expanded glutamine repeats. For reasons that remain unclear, this protease cleaves longer htt fragments, with normal or expanded glutamine expansions, much less efficiently. The protease in HEK293 cells that is capable of generating a cp-A/1 like htt fragment may be a novel protease with a high preference for a cp-B/2-like htt fragment as substrate.

Impact and Therapeutic Potential of PPARs in Alzheimer's Disease

Peroxisome proliferator activated receptors (PPARs) are well studied for their role of peripheral metabolism, but they also may be involved in the pathogenesis of various disorders of the central nervous system (CNS) including multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer's and, Parkinson's disease. The observation that PPARs are able to suppress the inflammatory response in peripheral macrophages and in several models of human autoimmune diseases, lead to the idea that PPARs might be beneficial for CNS disorders possessing an inflammatory component. The neuroinflammatory response during the course of Alzheimer's disease (AD) is triggered by the deposition of the β-amyloid peptide in extracellular plaques and ongoing neurodegeneration. Non-steroidal anti-inflammatory drugs (NSAIDs) have been considered to delay the onset and reduce the risk to develop Alzheimer’s disease, while they also directly activate PPARγ. This led to the hypothesis that NSAID protection in AD may be partly mediated by PPARγ. Several lines of evidence have supported this hypothesis, using AD related transgenic cellular and animal models. Stimulation of PPARγ by synthetic agonist (thiazolidinediones) inducing anti-inflammatory, anti-amyloidogenic and insulin sensitizing effects may account for the observed effects. Several clinical trials already revealed promising results using PPARγ agonists, therefore PPARγ represents an attractive therapeutic target for the treatment of AD.

PPARs in Alzheimer's Disease

Peroxisome proliferator-activated receptors (PPARs) are well studied for their peripheral physiological and pathological impact, but they also play an important role for the pathogenesis of various disorders of the central nervous system (CNS) like multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer's, and Parkinson's disease. The observation that PPARs are able to suppress the inflammatory response in peripheral macrophages and in several models of human autoimmune diseases lead to the idea that PPARs might be beneficial for CNS disorders possessing an inflammatory component. The neuroinflammatory response during the course of Alzheimer's disease (AD) is triggered by the neurodegeneration and the deposition of the β-amyloid peptide in extracellular plaques. Nonsteroidal anti-inflammatory drugs (NSAIDs) have been considered to delay the onset and reduce the risk to develop Alzheimer's disease, while they also directly activate PPARγ. This led to the hypothesis that NSAID protection in AD may be partly mediated by PPARγ. Several lines of evidence have supported this hypothesis, using AD-related transgenic cellular and animal models. Stimulation of PPARγ receptors by synthetic agonist (thiazolidinediones) inducing anti-inflammatory, anti-amyloidogenic, and insulin sensitising effects may account for the observed effects. Several clinical trials already revealed promising results using PPAR agonists, therefore PPARs represent an attractive therapeutic target for the treatment of AD.

Lost in translation: neuropsychiatric drug development

Recent studies have identified troubling method and practice lapses in neuropsychiatric drug developments. These problems have resulted in errors that are of sufficient magnitude to invalidate clinical trial data and interpretations. We identify two potential sources for these difficulties: investigators selectively choosing scientific practices for demonstrations of efficacy in human-testing phases of drug development and investigators failing to anticipate the needs of practitioners who must optimize treatment for the individual patient. When clinical investigators neglect to use clinical trials as opportunities to test hypotheses of disease mechanisms in humans, the neuropsychiatric knowledge base loses both credibility and scope. When clinical investigators do not anticipate the need to translate discoveries into applications, the practitioner cannot provide optimal care for the patient. We conclude from this evidence that clinical trials, and other aspects of neuropsychiatric drug development, must adopt more practices from basic science and show greater responsiveness to conditions of clinical practice. We feel that these changes are necessary to overcome current threats to the validity and utility of studies of neurological and psychiatric drugs.

Mechanisms of action of non-steroidal anti-inflammatory drugs for the prevention of Alzheimer's disease

Alzheimer's disease (AD) is accompanied by an activation of the innate immune system, and many epidemiological studies have shown reduced risk for dementia or AD associated with chronic consumption of non-steroidal anti-inflammatory drugs (NSAIDs). These observations led to animal model studies to test the hypothesis that NSAIDs can be disease-modifying for some aspects of AD pathogenesis. NSAIDs cannot only suppress inflammatory targets, which could contribute to neuroprotection, they also slow amyloid deposition by mechanisms that remain unclear. Several large clinical trials with NSAID therapies with AD subjects have failed, and cyclooxygenase-2 does not appear to be a useful target for disease modifying therapy. However, there may be apolipoprotein E E4 pharmacogenomic effects and a real but delayed positive signal in a large primary prevention trial with naproxen. This encourages researchers to re-address possible mechanisms for a stage-dependent NSAID efficacy, the subject of this review.

NSAIDs: How they Work and their Prospects as Therapeutics in Alzheimer's Disease

There is significant epidemiological evidence to suggest that there are beneficial effects of treatment with non-steroidal anti-inflammatory drugs (NSAIDs) in Alzheimer's disease, although these effects have not been reproduced in clinical trials. The failure of the clinical trials may be attributed to several possible facts: (1) NSAIDS may have been delivered too late to patients, as they may only be effective in early stages of the disease and possibly counterproductive in the late stages; (2) the beneficial effect may depend on the drug, because different NSAIDs may have different molecular targets; (3) the NSAID concentration reaching the brain and the duration of the treatment could also be critical, so increasing drug penetration is important in order to improve the efficacy and avoid secondary gastro-intestinal effects of the NSAIDs. In this report we analyze these different factors, with special emphasis on the role of NSAIDs in microglia activation over time.

An update on the efficacy of non-steroidal anti-inflammatory drugs in Alzheimer's disease

Several epidemiological studies suggest that long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) may protect against Alzheimer's disease (AD), especially for patients carrying one or more epsilon4 allele of the apolipoprotein E. The biological mechanism of this protection is not completely understood and may involve inhibition of COX activity, inhibition of beta-amyloid(1-42) (Abeta42) production and aggregation, inhibition of beta-secretase activity, activation of PPAR-gamma or stimulation of neurotrophin synthesis. Unfortunately, long-term, placebo-controlled clinical trials with both non-selective and COX-2 selective NSAIDs in AD patients produced negative results. A secondary prevention study with rofecoxib in patients with mild cognitive impairment and a primary prevention study with naproxen and celecoxib in elderly subjects with a family history of AD were also negative. All these failures have diminished the hope that NSAIDs could be beneficial in the treatment of AD. It is hypothesized that the chronic use of NSAIDs may be beneficial only in the normal brain by inhibiting the production of Abeta42. Once the Abeta deposition process has started, NSAIDs are no longer effective and may even be detrimental because of their inhibiting activity on activated microglia of the AD brain, which mediates Abeta clearance and activates compensatory hippocampal neurogenesis.

Beyond the neurotransmitter-focused approach in treating Alzheimer's disease: drugs targeting beta-amyloid and tau protein

Drugs currently used to treat Alzheimer's Disease (AD) have limited therapeutic value and do not affect the main neuropathological hallmarks of the disease, i.e., senile plaques and neurofibrillar tangles. Senile plaques are mainly formed of beta-amyloid (Abeta), a 42-aminoacid peptide. Neurofibrillar tangles are composed of paired helical filaments of hyperphosphorylated tau protein. New, potentially disease-modifying, therapeutic approaches are targeting Abeta and tau protein. Drugs directed against Abeta include active and passive immunization, that have been found to accelerate Abeta clearance from the brain. The most developmentally advanced monoclonal antibody directly targeting Abeta is bapineuzumab, now being studied in a large Phase III clinical trial. Compounds that interfere with proteases regulating Abeta formation from amyloid precursor protein (APP) are also actively pursued. The discovery of inhibitors of beta-secretase, the enzyme that regulates the first step of the amyloidogenic metabolism of APP, has been revealed to be particularly difficult due to inherent medicinal chemistry problems, and only one compound (CTS-21166) has reached clinical testing. Conversely, several compounds that inhibit gamma-secretase, the pivotal enzyme that generates Abeta, have been identified, the most advanced being LY-450139 (semagacestat), now in Phase III clinical development. Compounds that stimulate alpha-secretase, the enzyme responsible for the non-amyloidogenic metabolism of APP, are also being developed, and one of them, EHT-0202, has recently entered Phase II testing. Potent inhibitors of Abeta aggregation have also been identified, and one of such compounds, PBT-2, has provided encouraging neuropsychological results in a recently completed Phase II study. Therapeutic approaches directed against tau protein include inhibitors of glycogen synthase kinase- 3 (GSK-3), the enzyme responsible for tau phosphorylation and tau protein aggregation inhibitors. NP-12, a promising GSK-3 inhibitor, is being tested in a Phase II study, and methylthioninium chloride, a tau protein aggregation inhibitor, has given initial encouraging results in a 50-week study. With all these approaches on their way, the hope for disease-modifying therapy in this devastating disease may become a reality in the next 5 years.

NSAIDs prevent, but do not reverse, neuronal cell cycle reentry in a mouse model of Alzheimer disease

Ectopic cell cycle events (CCEs) mark vulnerable neuronal populations in human Alzheimer disease (AD) and are observed early in disease progression. In transgenic mouse models of AD, CCEs are found before the onset of beta-amyloid peptide (Abeta) deposition to form senile plaques, a hallmark of AD. Here, we have demonstrated that alterations in brain microglia occur coincidently with the appearance of CCEs in the R1.40 transgenic mouse model of AD. Furthermore, promotion of inflammation with LPS at young ages in R1.40 mice induced the early appearance of neuronal CCEs, whereas treatment with 2 different nonsteroidal antiinflammatory drugs (NSAIDs) blocked neuronal CCEs and alterations in brain microglia without altering amyloid precursor protein (APP) processing and steady-state Abeta levels. In addition, NSAID treatment of older R1.40 animals prevented new neuronal CCEs, although it failed to reverse existing ones. Retrospective human epidemiological studies have identified long-term use of NSAIDs as protective against AD. Prospective clinical trials, however, have failed to demonstrate a similar benefit. Our use of CCEs as an outcome measure offers fresh insight into this discrepancy and provides important information for future clinical trials, as it suggests that NSAID use in human AD may need to be initiated as early as possible to prevent disease progression.

Inflammation in transgenic mouse models of neurodegenerative disorders

Much evidence is available that inflammation contributes to the development of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Our review investigates how well current mouse models reflect this aspect of the pathogenesis. Transgenic models of AD have been available for several years and are the most extensively studied. Modulation of cytokine levels, activation of microglia and, to a lesser extent, activation of the complement system have been reported. Mouse models of PD and HD so far show less evidence for the involvement of inflammation. An increasing number of transgenic mouse strains is being created to model human neurodegenerative diseases. A perfect model should reflect all aspects of a disease. It is important to evaluate continuously the models for their match with the human disease and reevaluate them in light of new findings in human patients. Although none of the transgenic mouse models recapitulates all aspects of the human disorder they represent, all models have provided valuable information on basic molecular pathways. In particular, the mouse models of Alzheimer disease have also led to the development of new therapeutic strategies such as vaccination and modulation of microglial activity.

Presenilins, Notch dose control the fate of pancreatic endocrine progenitors during a narrow developmental window

Canonical Notch signaling is thought to control the endocrine/exocrine decision in early pancreatic progenitors. Later, RBP-Jkappa interacts with Ptf1a and E12 to promote acinar differentiation. To examine the involvement of Notch signaling in selecting specific endocrine lineages, we deregulated this pathway by targeted deletion of presenilin1 and presenilin2, the catalytic core of gamma-secretase, in Ngn3- or Pax6-expressing endocrine progenitors. Surprisingly, whereas Pax6(+) progenitors were irreversibly committed to the endocrine fate, we discovered that Ngn3(+) progenitors were bipotential in vivo and in vitro. When presenilin amounts are limiting, Ngn3(+) progenitors default to an acinar fate; subsequently, they expand rapidly to form the bulk of the exocrine pancreas. gamma-Secretase inhibitors confirmed that enzymatic activity was required to block acinar fate selection by Ngn3 progenitors. Genetic interactions identified Notch2 as the substrate, and suggest that gamma-secretase and Notch2 act in a noncanonical titration mechanism to sequester RBP-Jkappa away from Ptf1a, thus securing selection of the endocrine fate by Ngn3 progenitors. These results revise the current view of pancreatic cell fate hierarchy, establish that Ngn3 is not in itself sufficient to commit cells to the endocrine fate in the presence of Ptf1a, reveal a noncanonical action for Notch2 protein in endocrine cell fate selection, and demonstrate that acquisition of an endocrine fate by Ngn3(+) progenitors is gamma-secretase-dependent until Pax6 expression begins.

Therapeutic targets in prostaglandin E2 signaling for neurologic disease

Prostaglandins (PGs) are potent autocrine and paracrine oxygenated lipid molecules that contribute appreciably to physiologic and pathophysiologic responses in almost all organs, including brain. Emerging data indicate that the PGs, and more specifically PGE2, play a central role in brain diseases including ischemic injury and several neurodegenerative diseases. Given concerns over the potential toxicity from protracted use of cyclooxygenase inhibitors in the elderly, attention is now focused on blocking PGE2 signaling that is mediated by interactions with four distinct G protein-coupled receptors, EP1-4, which are differentially expressed on neuronal and glial cells throughout the central nervous system. EP1 activation has been shown to mediate Ca2+-dependent neurotoxicity in ischemic injury. EP2 activation has been shown to mediate microglial-induced paracrine neurotoxicity as well as suppress microglia internalization of aggregated neurotoxic peptides. Animal models support the potential efficacy of targeting specific EP receptor subtypes in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and ischemic stroke. However promising these preclinical studies are, they have yet to be followed by clinical trials targeting any EP receptor in neurologic diseases.

Interactions between APP secretases and inflammatory mediators

There is now a large body of evidence linking inflammation to Alzheimer's disease (AD). This association manifests itself neuropathologically in the presence of activated microglia and astrocytes around neuritic plaques and increased levels of inflammatory mediators in the brains of AD patients. It is considered that amyloid-β peptide (Aβ), which is derived from the processing of the longer amyloid precursor protein (APP), could be the most important stimulator of this response, and therefore determining the role of the different secretases involved in its generation is essential for a better understanding of the regulation of inflammation in AD. The finding that certain non-steroidal anti-inflammatory drugs (NSAIDs) can affect the processing of APP by inhibiting β- and γ-secretases, together with recent revelations that these enzymes may be regulated by inflammation, suggest that they could be an interesting target for anti-inflammatory drugs. In this review we will discuss some of these issues and the role of the secretases in inflammation, independent of their effect on Aβ formation.

Cyclooxygenase-2 inhibition improves amyloid-beta-mediated suppression of memory and synaptic plasticity

Non-steroidal anti-inflammatory agents (NSAIDs) are associated with a marked reduction in the risk of developing Alzheimer's disease, a form of dementia characterized by the accumulation of amyloid plaques containing the amyloid-beta protein (Abeta). Studies of the effects of NSAIDs upon the inflammatory response surrounding amyloid plaques and upon the generation of Abeta from the amyloid precursor protein (APP) have led to two proposed mechanisms by which NSAIDs may protect against Alzheimer's disease: one, the selective lowering of Abeta42 by a subset of NSAIDs; and two, the reduction of inflammation. Although Alzheimer's disease is a disorder of brain and synaptic function, the effects of NSAIDs on Abeta-mediated suppression of synaptic plasticity and memory function have never been reported. We therefore investigated how three different NSAIDs, chosen for their distinct effects on Abeta42 production and the inhibition of the cyclooxygenase (COX) isoenzymes, COX-1 and COX-2, affect memory function and synaptic plasticity. By focusing upon brain and synapse function, we made novel observations about the effects of NSAIDs on Abeta-mediated neural processes. Here we report that the selective inhibition of COX-2, but not COX-1, acutely prevented the suppression of hippocampal long-term plasticity (LTP) by Abeta. The non-selective NSAIDs, ibuprofen and naproxen, and a selective COX-2 inhibitor, MF-tricyclic, each restored memory function in Tg2576 mice over-expressing APP, and also blocked Abeta-mediated inhibition of LTP. There was no advantage of ibuprofen, a selective Abeta42-lowering agent (SALA), over the non-SALAs, naproxen and MF-tricyclic. The beneficial effects on memory did not depend upon lowered levels of Abeta42 or the inflammatory cytokines, tumour necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta). Intriguingly, improved memory function was inversely related to prostaglandin E2 (PGE2) levels. Conversely, exogenous PGE2 prevented the restorative effects of COX-2 inhibitors on LTP. The data indicate that the inhibition of COX-2 blocks Abeta-mediated suppression of LTP and memory function, and that this block occurs independently of reductions in Abeta42 or decreases in inflammation. The results lead us to propose a third possible mechanism by which NSAIDs may protect against Alzheimer's disease, involving the blockade of a COX-2-mediated PGE2 response at synapses.

Possible mechanisms of action of NSAIDs and related compounds that modulate gamma-secretase cleavage

Genetic and biochemical evidence continues to implicate the production and accumulation of the Abeta42 peptide as the causative factor in Alzheimer's disease (AD). Thus, a variety of strategies have been developed to decrease the production and/or aggregation of this peptide, which may be clinically useful for the treatment of this devastating disorder. Recently, the discovery that some non-steroidal anti-inflammatory drugs (NSAIDs) appear to selectively decrease the production of Abeta42 has opened a novel therapeutic avenue for AD treatment that may circumvent potential toxicity associated with long-term global inhibition of gamma-secretase activity. One drug from this class of compounds, R-flurbiprofen, has advanced to phase 3 clinical trials and may soon provide insight into the viability of this strategy for the prevention or treatment of AD. Delineating the target and mechanism of these compounds is essential for developing new agents with increased potency and optimized pharmacologic properties. The evidence indicating that these chemicals modulate the production of Abeta peptides by directly interacting with the gamma-secretase complex is summarized.

The role of peroxisome proliferator-activated receptor-gamma (PPARgamma) in Alzheimer's disease: therapeutic implications

Alzheimer's disease is a complex neurodegenerative disorder, with aging, genetic and environmental factors contributing to its development and progression. The complexity of Alzheimer's disease presents substantial challenges for the development of new therapeutic agents. Alzheimer's disease is typified by pathological depositions of beta-amyloid peptides and neurofibrillary tangles within the diseased brain. It has also been demonstrated to be associated with a significant microglia-mediated inflammatory component, dysregulated lipid homeostasis and regional deficits in glucose metabolism within the brain. The peroxisome proliferator-activated receptor-gamma (PPARgamma) is a prototypical ligand-activated nuclear receptor that coordinates lipid, glucose and energy metabolism, and is found in elevated levels in the brains of individuals with Alzheimer's disease. A recently appreciated physiological function of this type of receptor is its ability to modulate inflammatory responses. In animal models of Alzheimer's disease, PPARgamma agonist treatment results in the reduction of amyloid plaque burden, reduced inflammation and reversal of disease-related behavioural impairment. In a recent phase II clinical trial, the use of the PPARgamma agonist rosiglitazone was associated with improved cognition and memory in patients with mild to moderate Alzheimer's disease. Thus, PPARgamma may act to modulate multiple pathophysiological mechanisms that contribute to Alzheimer's disease, and represents an attractive therapeutic target for the treatment of the disease.

NSAIDs: small molecules for prevention of Alzheimer's disease or precursors for future drug development?

Non-steroidal anti-inflammatory drugs (NSAIDs) have been considered for treatment and prevention of Alzheimer's disease (AD) for more than two decades. Biochemical markers in the brains of individuals with AD suggest that inflammation might be a driving cause of the disease that can be suppressed by drug treatment. In addition, a subgroup of widely used NSAIDs inhibits generation of the pathogenic amyloid-beta(1-42) peptide (Abeta42) independently of the inflammatory cyclooxygenase (COX) pathway. Here, we summarize evidence showing that the efficacy of NSAIDs in AD might be attributable to either anti-inflammatory or anti-amyloidogenic activities, and we acknowledge the possibility that current NSAIDs could be neuroprotective through synergistic mechanisms. Ongoing drug development efforts are concentrating on improvement of the COX-independent Abeta42-lowering activity to prevent amyloid pathology and secondary inflammatory reactions and to avoid the clinical side-effects associated with inhibition of COX.

1-(3′,4′-Dichloro-2-fluoro[1,1′-biphenyl]-4-yl)-cyclopropanecarboxylic Acid (CHF5074), a Novel γ-Secretase Modulator, Reduces Brain β-Amyloid Pathology in a Transgenic Mouse Model of Alzheimer's Disease without Causing Peripheral Toxicity

Some nonsteroidal anti-inflammatory drugs has been shown to allosterically modulate the activity of gamma-secretase, the enzymatic complex responsible for the formation of beta-amyloid (Abeta). 1-(3',4'-Dichloro-2-fluoro[1,1'-biphenyl]-4-yl)-cyclopropanecarboxylic acid (CHF5074) is a new gamma-secretase modulator, devoid of anticyclooxygenase (COX) and Notch-interfering activities in vitro. We evaluated the effects of chronic CHF5074 treatment on brain Abeta pathology in Tg2576 transgenic mice. Twenty-eight animals of 9.5 to 10.5 months of age received CHF5074-medicated diet (375 ppm) or standard diet for 17 weeks. Compared with controls, CHF5074 treatment significantly reduced the area occupied by plaques and the number of plaques in cortex (-52.2 +/- 5.6%, p = 0.0003 and -48.9 +/- 6.6%, p = 0.0004, respectively) and hippocampus (-76.7 +/- 6.4%, p = 0.004 and -66.2 +/- 10.3%, p = 0.037, respectively). Biochemical analysis confirmed the histopathological measures, with CHF5074-treated animals showing reduced total brain Abeta40 (-49.2 +/- 9.2%, p = 0.017) and Abeta42 (-43.5 +/- 9.7%, p = 0.027) levels. In a human neuroglioma cell line expressing Swedish mutated form of amyloid precursor protein (H4swe), CHF5074 reduced Abeta42 and Abeta40 secretion, with an IC50 of 3.6 and 18.4 microM, respectively, values consistent with those measured in the brain of the CHF5074-treated Tg2576 mice (6.4 +/- 0.4 microM). At 5 microM, no effects were observed on Notch intracellular cleavage in human embryonic kidney 293swe cells. CHF5074 was well tolerated by Tg2576 mice. No abnormal findings were observed upon histopathological examination of the gastrointestinal tract, indicating the absence of COX-related toxicity. Semiquantitative histochemical evaluation of goblet cells in the ileum of vehicle- and CHF5074-treated animals yielded similar results, suggesting no effects on Notch pathway. CHF5074 is therefore a promising therapeutic agent for Alzheimer's disease.

The role of amyloid beta peptide 42 in Alzheimer's disease

During the last 20 years, an expanding body of research has elucidated the central role of amyloid precursor protein (APP) processing and amyloid beta peptide (Abeta) production in the risk, onset, and progression of the neurodegenerative disorder Alzheimer's disease (AD), the most common form of dementia. Ongoing research is establishing a greater level of detail for our understanding of the normal functions of APP, its proteolysis products, and the mechanisms by which this processing occurs. The importance of this processing machinery in normal cellular function, such as Notch processing, has revealed specific concerns about targeting APP processing for therapeutic purposes. Aspects of AD that are now well studied include direct and indirect genetic and other risk factors for AD, APP processing, and Abeta production. Emerging from these studies is the particular importance of the long form of Abeta, Abeta42. Elevated Abeta42 levels, as well as particularly the elevation of the ratio of Abeta42 to the shorter major form Abeta40, has been identified as important in early events in the pathogenesis of AD. The specific pathological importance of Abeta42 has drawn attention to seeking drugs that will selectively lower the levels of this peptide through reduced production or increased clearance while allowing normal protein processing to remain substantially intact. An increasing variety of compounds that modulate APP processing to reduce Abeta levels are being identified, some with Abeta42 selectivity. Such compounds are now reaching clinical evaluation to determine how they may be of benefit in the treatment of AD.

In vitro and in vivo profiling of CHF5022 and CHF5074 Two beta-amyloid1-42 lowering agents

Long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) may delay or prevent the onset of Alzheimer's disease (AD). A subset of NSAIDs, including flurbiprofen, has been shown to selectively inhibit the production of beta-amyloid(1-42) (Abeta42), independently from their cyclooxygenase (COX) inhibiting activity. We evaluated the in vitro and in vivo profiles of CHF5022 and CHF5074, two flurbiprofen analogues. The in vitro Abeta inhibiting activity was evaluated in a human neuroglioma cell line (H4) carrying the double Swedish mutation (K595N/M596L) of the human amyloid precursor protein (APPsw). The in vitro anti-COX activity was evaluated using human recombinant enzymes isolated from transfected Sf-9 cells. The in vivo pharmacokinetic and pharmacodynamic profiles of the two compounds were evaluated in young APPsw transgenic mice (Tg2576) after oral gavage (100 or 300mgkg(-1) day(-1) for 4-5 days) and after medicated diet (375ppm for 4 weeks). R-Flurbiprofen was used as comparator. In vitro, CHF5022 and CHF5074 were found to be 3- and 7-fold more potent than R-flurbiprofen in inhibiting Abeta42 secretion (IC(50)s of 92, 40 and 268microM, respectively). Differently from R-flurbiprofen, CHF5022 and CHF5074 did not affect COX-1 (at 100microM) and COX-2 (at 300microM) activity. Similarly to R-flurbiprofen, no significant alteration in the expression profile of a subset of Notch intracellular domain-responsive genes was observed with either CHF5022 or CHF5074. In Tg2576 mice, CHF5022 was well tolerated when administered by oral gavage (100mgkg(-1) day(-1) for 5 days) or by medicated diet (56mg kg(-1) day(-1) for 4 weeks). R-Flurbiprofen was poorly tolerated in the diet (32mgkg(-1) day(-1)) with 55% of the animals dying during the first week of treatment. After 4-5 days of oral gavage, CHF5022 and CHF5074 plasma and brain levels at 3h were found to increase with the dose, leading to brain concentrations of about 10% and 5% of the corresponding plasma concentrations, respectively. In animals fed for 4 weeks with compound-supplemented diet, mean plasma (580microM) and brain (20microM) Cyrillic) concentrations of CHF5022 were 8 and 15 times higher than those of R-flurbiprofen. Plasma Abeta42 concentration was dose-dependently decreased by CHF5022 and CHF5074. Brain Abeta levels (formic acid-extractable) were not significantly affected by either compound, although Abeta42 levels tended to inversely correlate (P=0.105) with CHF5022 concentration in the brain. CHF5022 and CHF5074 thus appear to have a promising in vitro and in vivo profile. This warrants further evaluation of their long-term effects on Abeta brain pathology.

NSAIDs for the chemoprevention of Alzheimer's disease

Epidemiologic and laboratory studies suggest that non-steroidal anti-inflammatory drug (NSAID) use reduces the risk of Alzheimer's disease (AD). Initial reports in the early 1990's indicated that a history of arthritis, a presumed surrogate of NSAID use, was associated with a lower risk of AD. [1] These reports were followed by epidemiologic studies in which NSAID use was assessed directly and the majority of these reports confirmed the inverse association with risk for AD. [2, 3] Postmortem studies in humans [4], studies in animal models of AD [5, 6], and in vitro studies [7, 8] generally support the notion that NSAIDs can reduce the deleterious inflammation which surrounds amyloid beta (Abeta) plaques in the AD brain. In addition, some studies conducted in vitro and in rodents point to a subgroup of NSAIDs that may work by inhibiting amyloidogenic APP metabolism rather than through traditional anti-inflammatory mechanisms. [9-11] This novel property of NSAIDs is currently being explored in epidemiologic studies. Results from randomized clinical trials of NSAIDs and established AD and one trial on secondary prevention have not been promising and there have been no prevention trials completed. The feasibility of using NSAIDs as a chemopreventive agent in AD is discussed.

The novel gamma secretase inhibitor N-[cis-4-[(4-chlorophenyl)sulfonyl]-4-(2,5-difluorophenyl)cyclohexyl]-1,1,1-trifluoromethanesulfonamide (MRK-560) reduces amyloid plaque deposition without evidence of notch-related pathology in the Tg2576 mouse

There is a substantial body of evidence indicating that beta-amyloid peptides (Abeta) are critical factors in the onset and development of Alzheimer's disease (AD). One strategy for combating AD is to reduce or eliminate the production of Abeta through inhibition of the gamma-secretase enzyme, which cleaves Abeta from the amyloid precursor protein (APP). We demonstrate here that chronic treatment for 3 months with 3 mg/kg of the potent, orally bioavailable and brain-penetrant gamma-secretase inhibitor N-[cis-4-[(4-chlorophenyl)-sulfonyl]-4-(2,5-difluorophenyl)cyclohexyl]-1,1,1-trifluoromethanesulfonamide (MRK-560) attenuates the appearance of amyloid plaques in the Tg2576 mouse. These reductions in plaques were also accompanied by a decrease in the level of reactive gliosis. The morphometric and histological measures agreed with biochemical analysis of Abeta(40) and Abeta(42) in the cortex. Interestingly, the volume of the plaques across treatment groups did not change, indicating that reducing Abeta levels does not significantly alter deposit growth once initiated. Furthermore, we demonstrate that these beneficial effects can be achieved without causing histopathological changes in the ileum, spleen, or thymus as a consequence of blockade of the processing of alternative substrates, such as the Notch family of receptors. This indicates that in vivo a therapeutic window between these substrates seems possible--a key concern in the development of this approach to AD. An understanding of the mechanisms whereby MRK-560 shows differentiation between the APP and Notch proteolytic pathway of gamma-secretase should provide the basis for the next generation of gamma-secretase inhibitors.

Insights into the mechanisms of action of anti-Abeta antibodies in Alzheimer's disease mouse models

A number of hypotheses regarding how anti-Abeta antibodies alter amyloid deposition have been postulated, yet there is no consensus as to how Abeta immunotherapy works. We have examined the in vivo binding properties, pharmacokinetics, brain penetrance, and alterations in Abeta levels after a single peripheral dose of anti-Abeta antibodies to both wild-type (WT) and young non-Abeta depositing APP and BRI-Abeta42 mice. The rapid rise in plasma Abeta observed after antibody (Ab) administration is attributable to prolongation of the half-life of Abeta bound to the Ab. Only a miniscule fraction of Ab enters the brain, and despite dramatic increases in plasma Abeta, we find no evidence that total brain Abeta levels are significantly altered. Surprisingly, cerebral spinal fluid Abeta levels transiently rise, and when Ab:Abeta complex is directly injected into the lateral ventricles of mice, it is rapidly cleared from the brain into the plasma where it remains stable. When viewed in context of daily turnover of Abeta, these data provide a framework to evaluate proposed mechanisms of Abeta attenuation mediated by peripheral administration of an anti-Abeta monoclonal antibody (mAb) effective in passive immunization paradigm. Such quantitative data suggest that the mAbs are either indirectly enhancing clearance of Abeta or targeting a low abundance aggregation intermediate.

γ-Secretase Modulation with Aβ42-Lowering Nonsteroidal Anti-Inflammatory Drugs and Derived Compounds

The amyloid-beta (Abeta) peptides and specifically the highly amyloidogenic isoform Abeta42 appear to be key agents in the pathogenesis of familial and sporadic forms of Alzheimer's disease (AD). The final step in the generation of Abeta from the amyloid precursor protein is catalyzed by the multiprotein complex gamma-secretase, which constitutes a prime drug target for prevention and therapy of the disease. However, highly potent gamma-secretase inhibitors that block formation of all Abeta peptides have provoked troubling side effects in preclinical animal models of AD. This toxicity can be readily explained by the promiscuous substrate specificity of gamma-secretase and its essential role in the NOTCH signaling pathway. For that reason and because of the crucial role of Abeta42 in the pathogenesis of the disease, selective inhibition of Abeta42 production would seem to be a more promising alternative to complete inhibition of gamma-secretase activity. This theoretical concept has edged much closer to clinical reality with the surprising finding that certain nonsteroidal anti-inflammatory drugs (NSAIDs), including ibuprofen, and derived compounds display preferential Abeta42-lowering activity. In contrast to gamma-secretase inhibitors, these gamma-secretase modulators effectively suppress Abeta42 production while sparing processing of NOTCH and other gamma-secretase substrates. Although not fully resolved on the molecular level, the mechanism of action of Abeta42-lowering NSAIDs is independent of cyclooxygenase inhibition and most likely involves direct interaction with components of the gamma-secretase complex or its substrates. Current efforts to improve the pharmacological shortcomings of available gamma-secretase modulators will hopefully lead to the development of clinically useful Abeta42-lowering compounds in the near future.

Modulators and Inhibitors of γ- and β-Secretases

Most gene mutations associated with Alzheimer's disease point to the metabolism of amyloid precursor protein as a potential cause. The beta- and gamma-secretases are two executioners of amyloid precursor protein processing resulting in amyloid-beta. Significant progress has been made in the selective inhibition of both proteases, regardless of structural information for gamma-secretase. Several peptidic and nonpeptidic leads were identified for both targets.

Is there a future for cyclo-oxygenase inhibitors in Alzheimer's disease?

Several epidemiological studies have indicated that the long-term use of NSAIDs, most of which are cyclo-oxygenase (COX) inhibitors, may reduce the risk of Alzheimer's disease. For this reason, anti-inflammatory COX-inhibiting NSAIDs have received increased attention in experimental and therapeutic trials for Alzheimer's disease. However, several recent efforts attempting to demonstrate a therapeutic effect of NSAIDs in Alzheimer's disease have largely failed. Clinicians and scientists currently believe that this lack of success may be attributable to two key problems: (i) clinical trials of NSAIDs have been conducted in patients with late-stage Alzheimer's disease, wherein advanced neurodegeneration may be refractory to anti-inflammatory drug treatment; and (ii) it is not known which of the large family of NSAIDs (i.e. COX-1, COX-2 or mixed inhibitors) is most efficacious in preventing Alzheimer's disease. The wide list of putative functions for COX in the brain, and the significant functional heterogeneity of NSAIDs, which appear to influence the beta-amyloid (Abeta) neuropathology associated with Alzheimer's disease via both COX-dependent and COX-independent pathways, complicate the interpretation of the mechanisms through which COX-inhibiting NSAIDs may beneficially influence Alzheimer's disease. As discussed in this review, for patients at high risk of developing Alzheimer's disease (e.g. those with mild cognitive impairment), preventative treatment with COX-inhibiting NSAIDs may ultimately represent a viable strategy in the management of clinical Alzheimer's disease. However, the recent evidence showing an increased risk of major cardiovascular events among patients treated with certain COX-1 and COX-2 inhibitors leaves many questions unanswered. We suggest that further investigation into the physiological role(s) of COXs in normal health and in disease conditions, and the identification of safer and better tolerated COX inhibitors, will provide renewed impetus to the application of anti-inflammatory strategies for the prevention and treatment of Alzheimer's disease.

A Novel Phospholipid Derivative of Indomethacin, DP-155 [Mixture of 1-Steroyl and 1-Palmitoyl-2-{6-[1-(p-chlorobenzoyl)-5-methoxy-2-methyl-3-indolyl acetamido]hexanoyl}-sn-glycero-3-phosophatidyl Choline], Shows Superior Safety and Similar Efficacy in Reducing Brain Amyloid β in an Alzheimer's Disease Model

Indomethacin has been suggested for the treatment of Alzheimer's disease (AD), but its use is limited by gastrointestinal and renal toxicity. To overcome this limitation, D-Pharm Ltd. (Rehovot, Israel) developed DP-155 (mixture of 1-steroyl and 1-palmitoyl-2-{6-[1-(p-chlorobenzoyl)-5-methoxy-2-methyl-3-indolyl acetamido] hexanoyl}-Sn-glycero-3-phosophatidyl [corrected] choline), a lecithin derivative of indomethacin. Safety was tested by daily oral administration of DP-155 or indomethacin to rats in a dose range of 0.007 to 0.28 mmol/kg. The prevalence of gastrointestinal ulceration was significantly lower (10-fold) for DP-155 than for indomethacin, and the ulcerations were delayed. Signs of renal toxicity, namely reduced urine output and increased urine N-acetyl glycosaminidase to creatinine ratio, were 5-fold lower for DP-155. Indomethacin, but not an equimolar dose of DP-155, reduced urine bicyclo-prostaglandin E(2). An equimolar oral dose of DP-155 or indomethacin, administered every 4 h for 3 days, was equally efficacious in reducing the levels of Abeta42 in the brains of Tg2576 mice. Indomethacin was the principal metabolite of DP-155 in the serum. After DP-155 oral administration, indomethacin's half-life in the serum and the brain was 22 and 93 h, respectively, compared with 10 and 24 h following indomethacin oral administration. The brain to serum ratio was 3.5 times higher for DP-155 than indomethacin. This finding explains the efficacy of DP-155 in reducing Abeta42 brain levels, despite the low systemic blood concentrations of indomethacin derived from DP-155. In conclusion, compared with indomethacin, DP-155 has significantly lower toxicity in the gut and kidney while maintaining similar efficacy to indomethacin in lowering Abeta42 in the brains of Tg2576 mice. This superior safety profile highlights DP-155's potential as an improved indomethacin-based therapy for AD.

Reductions in levels of the Alzheimer's amyloid beta peptide after oral administration of ginsenosides

For millennia, ginseng and some of its components have been used to treat a wide variety of medical conditions, including age-related memory impairment. Because of its purported effects and apparently low rate of side effects, ginseng remains one of the top selling natural product remedies in the United States. Given its potential role for improving age-related memory impairments and its common use in China for the treatment of Alzheimer's disease-like symptoms, we analyzed the effects of commercially available preparations of ginseng on the accumulation of the Alzheimer's amyloid beta peptide (Abeta) in a cell-based model system. In this model system, ginseng treatment resulted in a significant reduction in the levels of Abeta in the conditioned medium. We next examined the effects of several compounds isolated from ginseng and found that certain ginsenosides lowered Abeta concentration in a dose-dependent manner with ginsenoside Rg3 having an approximate IC50 of under 25 microM against Abeta42. Furthermore, we found that three of these isolated components, ginsenoside Rg1, Rg3, and RE, resulted in significant reductions in the amount of Abeta detected in the brains of animals after single oral doses of these agents. The results indicate that ginseng itself, or purified ginsenosides, may have similarly useful effects in human disease.

The geminal dimethyl analogue of Flurbiprofen as a novel Aβ42 inhibitor and potential Alzheimer’s disease modifying agent

The subtle modification of a selection of Abeta42 inhibiting non-steroidal anti-inflammatory drugs (NSAIDs), through synthesis of the geminal dimethyl analogues, was anticipated to ablate their cyclooxygenase activity whilst maintaining Abeta42 inhibition. Methylflurbiprofen 6 exhibited similar in vitro Abeta42 inhibition to its parent NSAID Flurbiprofen and was further evaluated in the Tg2576 mouse model of Alzheimer's disease and an animal model of gastro-intestinal (GI) impairment, but proved unviable for further clinical development.

Deletion of the prostaglandin E2 EP2 receptor reduces oxidative damage and amyloid burden in a model of Alzheimer's disease

Epidemiological studies demonstrate that chronic use of nonsteroidal anti-inflammatory drugs (NSAIDs) in normal aging populations reduces the risk of developing Alzheimer's disease (AD). NSAIDs inhibit the enzymatic activity of cyclooxygenase-1 (COX-1) and inducible COX-2, which catalyze the first committed step in the synthesis of prostaglandins. These studies implicate COX-mediated inflammation as an early and potentially reversible preclinical event; however, the mechanism by which COX activity promotes development of AD has not been determined. Recent studies implicate the prostaglandin E2 (PGE2) E prostanoid subtype 2 (EP2) receptor in the development of the innate immune response in brain. Here, we report that deletion of the PGE2 EP2 receptor in the APPSwe-PS1DeltaE9 model of familial AD results in marked reductions in lipid peroxidation in aging mice. This reduction in oxidative stress is associated with significant decreases in levels of amyloid-beta (Abeta) 40 and 42 peptides and amyloid deposition. Aged APPSwe-PS1DeltaE9 mice lacking the EP2 receptor harbor lower levels of beta C-terminal fragments, the product of beta-site APP cleaving enzyme (BACE1) processing of amyloid precursor protein. Increases in BACE1 processing have been demonstrated in models of aging and AD and after oxidative stress. Our results indicate that PGE2 signaling via the EP2 receptor promotes age-dependent oxidative damage and increased Abeta peptide burden in this model of AD, possibly via effects on BACE1 activity. Our findings identify EP2 receptor signaling as a novel proinflammatory and proamyloidogenic pathway in this model of AD, and suggest a rationale for development of therapeutics targeting the EP2 receptor in neuroinflammatory diseases such as AD.

Novel therapeutic opportunities for Alzheimer's disease: focus on nonsteroidal anti-inflammatory drugs

Alzheimer's disease (AD) is the most common form of neurodegenerative disorder with dementia in the elderly. The AD brain pathology is characterized by deposits of amyloid-beta (Abeta) peptides and neurofibrillary tangles but also (among other aspects) by signs of a chronic inflammatory process. Epidemiological studies have shown that long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs) reduces the risk of developing AD and delays its onset. Classical targets of NSAIDs include cycloxygenase, nuclear factor kappaB, and peroxisome proliferator-activated receptors. Modulation of these pathways, all of which have been implicated in AD pathogenesis, could explain the NSAID effect on AD progression. However, recent studies indicate that a subset of NSAIDs such as ibuprofen, indomethacin, and flurbiprofen may have direct Abeta-lowering properties in cell cultures as well as transgenic models of AD-like amyloidosis. A renewed interest in the old and a discovery of new pharmacological properties of these drugs are providing vital insight for future clinical trials. In this review we will summarize how the combination of traditional (anti-inflammatory) and new (anti-amyloidogenic) properties of some NSAIDs is providing unprecedented opportunities for drug discovery and could potentially result in novel therapeutic approaches for the treatment of AD.

New pathways in drug discovery for alzheimer’s disease

Specific treatments for Alzheimer's disease (AD) were first introduced in the 1990s using the acetyl-cholinesterase inhibitors. More recently, the N-methyl-D-aspartate (NMDA) antagonist memantine has become available. Although these treatments do provide a modest improvement in the cognitive abnormalities present in AD, their pharmacology is based on manipulation of neurotransmitter systems, and there is no compelling evidence that they interfere with the underlying pathogenic process. Pathologic and genetic data have led to the hypothesis that a peptide called amyloid ss(Abeta) plays a primary role in the pathophysiology of AD. Several investigational therapies targeting Abeta are now undergoing clinical trials. This paper reviews the available data regarding Abeta-directed therapies that are in the clinic and summarizes the approach to biomarkers and clinical trial designs that can provide evidence of modification of the underlying disease process.

Fatty acid oxidation in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the most common dementing illness of the elderly and is a mounting public health problem. Pharmacoepidemiological data, analytical data from human tissue and body fluids, and mechanistic data mostly from murine models all have implicated oxidation products of two fatty acids, arachidonic acid (AA) and docosahexaenoic acid (DHA), in the pathogenesis of neurodegeneration. Here we review the biochemistry of AA and DHA oxidation, both enzyme-catalyzed and free radical mediated, and summarize those studies that have investigated these oxidation products as effectors of neurodegeneration and biomarkers of AD. Given the evolving appreciation for toxicity associated with current pharmaceuticals used to block AA and DHA oxidation, we close by speculating on likely areas of future research directed at suppressing this facet of neurodegeneration. If successful, these interventions are unlikely to cure AD, but may check its explosive growth and hopefully reduce its incidence and prevalence in the elderly.

Microglial EP2 as a new target to increase amyloid beta phagocytosis and decrease amyloid beta-induced damage to neurons

Epidemiologic and animal model data support a role for the prostaglandin pathway in AD pathogenesis. However, unexpected toxicity from protracted use of some nonsteroidal anti-inflammatory drugs (NSAIDs) compels investigation of therapeutic targets in this pathway other than COX inhibitors. Previously, we have shown that mice lacking one specific receptor for PGE2, EP2 (EP2-/-), are protected from the indirect neurotoxic effects of cerebral innate immune response mediated by CD14-dependent activation. Here we review data showing that EP2-/- microglia have a highly desirable combination of features: ablated indirect neurotoxicity following exposure to Abeta(1-42) coupled with enhanced phagocytosis of Abeta peptides, both synthetic and those deposited in human brain. These data point to microglial EP2 as a more focused target within the PG pathway for therapy in AD.

Activity of flurbiprofen and chemically related anti-inflammatory drugs in models of Alzheimer's disease

Currently, there is an intense debate on the potential use of nonsteroidal anti-inflammatory drugs (NSAIDs) in Alzheimer's disease (AD). NSAIDs are among the most widely prescribed drugs for the treatment of pain, fever, and inflammation. Their effects are largely attributed to the inhibition of the enzymatic activity of cyclooxygenase (COX)-1 and -2. The apparent activity of this class of drugs stems from one critical pathological process underlying AD and other neurodegenerative disorders, i.e., the presence of chronic neuroinflammation. In fact, prolonged use of NSAIDs is associated with reduced risk of AD. Besides COX inhibition, additional mechanisms could contribute to the potential activity of NSAIDs in AD. For example, several studies show that only a few selected NSAIDs also affect beta-amyloid (Abeta) deposition and metabolism. Among the Abeta-effective NSAIDs, flurbiprofen raised particular interest because of its multiple actions on key AD hallmarks. Studies in cell lines and animal models have shown that flurbiprofen racemate, its R-enantiomer and its nitric oxide (NO)-releasing derivatives, HCT 1026 and NCX 2216, are effective on AD amyloid pathology. Moreover, HCT 1026 and NCX 2216 differentially influence the cellular component of neuroinflammation (i.e., microglia activation) in some experimental settings, i.e., HCT 1026 inhibits the activation of microglia, while NCX 2216 can either enhance or inhibit microglial activation, depending upon the experimental conditions. It is still unclear which effects on microglia will prove most beneficial. Ultimately, clinical studies in AD patients will provide the best information as to whether selected NSAIDs will improve this devastating disease.