The γ-secretase inhibitor 2-[(1R)-1-[(4-chlorophenyl)sulfonyl](2,5-difluorophenyl) amino]ethyl-5-fluorobenzenebutanoic acid (BMS-299897) alleviates Aβ1–42 seeding and short-term memory deficits in the Aβ25–35 mouse model of Alzheimer's disease

The selective butyrylcholinesterase inhibitor UW-MD-95 shows symptomatic and neuroprotective effects in a pharmacological mouse model of Alzheimer's disease

AIMS

Alzheimer's disease (AD) is a devastating dementia characterized by extracellular amyloid-β (Aβ) protein aggregates and intracellular tau protein deposition. Clinically available drugs mainly target acetylcholinesterase (AChE) and indirectly sustain cholinergic neuronal tonus. Butyrylcholinesterase (BChE) also controls acetylcholine (ACh) turnover and is involved in the formation of Aß aggregates and senile plaques. UW-MD-95 is a novel carbamate-based compound acting as a potent pseudo-irreversible BChE inhibitor, with high selectivity versus AChE, and showing promising protective potentials in AD.

METHODS

We characterized the neuroprotective activity of UW-MD-95 in mice treated intracerebroventricularly with oligomerized Aβ25-35 peptide using behavioral, biochemical, and immunohistochemical approaches.

RESULTS

When injected acutely 30 min before the behavioral tests (spontaneous alternation in the Y-maze, object recognition, or passive avoidance), UW-MD-95 (0.3-3 mg/kg) showed anti-amnesic effects in Aβ25-35-treated mice. When injected once a day over 7 days, it prevented Aβ25-35-induced memory deficits. This effect was lost in BChE knockout mice. Moreover, the compound prevented Aβ25-35-induced oxidative stress (assessed by lipid peroxidation or cytochrome c release), neuroinflammation (IL-6 and TNFα levels or GFAP and IBA1 immunoreactivity) in the hippocampus and cortex, and apoptosis (Bax level). Moreover, UW-MD-95 significantly reduced the increase in soluble Aβ1-42 level in the hippocampus induced by Aβ25-35.

CONCLUSION

UW-MD-95 appeared as a potent neuroprotective compound in the Aβ25-35 model of AD, with potentially an impact on Aβ1-42 accumulation that could suggest a novel mechanism of neuroprotection.

Side effects based network construction and drug repositioning of ropinirole as a potential molecule for Alzheimer's disease: an in-silico, in-vitro, and in-vivo study

Alzheimer's disease (AD) is the leading cause of dementia in older adults. Drug repositioning is a process of finding new therapeutic applications for existing drugs. One of the methods in drug repositioning is to use the side-effect profile of a drug to identify a new therapeutic indication. The drugs with similar side-effects may act on similar biological targets and could affect the same biochemical process. In this study, we explored the Food and Drug Administration-approved drugs using PROMISCUOUS database to find those that have adverse effects profile comparable with the ligands being studied or used to treat AD. Here, we found that the ropinirole, a dopamine receptor agonist, shared a maximum number of side-effects with the drugs proven beneficial for treating AD. Furthermore, molecular modelling demonstrated that ropinirole exhibited strong binding affinity (-9.313 kcal/mol) and best ligand efficiency (0.49) with sigma-1 receptor. Here, we observed that the quaternary amino group of ropinirole is essential for binding with sigma-1 receptor. Molecular dynamic simulation indicated that the movement of the carboxy-terminal helices (α4/α5) could play a major role in the receptor's physiological functions. The neurotoxicity induced by Aβ25-35 in SH-SY5Y cells was reduced by ropinirole at concentrations 10, 30, and 50 µM. The effect on spatial learning and memory was examined in mice with Aβ25-35 induced memory deficit using the radial arm maze. Ropinirole (10 and 20 mg/kg) significantly improved the short and long-term memories in the radial arm maze test. Our results suggest that ropinirole has the potential to be repositioned for AD treatment.Communicated by Ramaswamy H. Sarma.

The pathomimetic oAβ25–35 model of Alzheimer's disease: Potential for screening of new therapeutic agents

Alzheimer's disease (AD) is the most common form of dementia in the elderly, currently affecting more than 40 million people worldwide. The two main histopathological hallmarks of AD were identified in the 1980s: senile plaques (composed of aggregated amyloid-β (Aβ) peptides) and neurofibrillary tangles (composed of hyperphosphorylated tau protein). In the human brain, both Aβ and tau show aggregation into soluble and insoluble oligomers. Soluble oligomers of Aβ include their most predominant forms - Aβ_1-40 and Aβ_1-42 - as well as shorter peptides such as Aβ_25-35 or Aβ_25-35/40. Most animal models of AD have been developed using transgenesis, based on identified human mutations. However, these familial forms of AD represent less than 1% of AD cases. In this context, the idea emerged in the 1990s to directly inject the Aβ_25-35 fragment into the rodent brain to develop an acute model of AD that could mimic the disease's sporadic forms (99% of all cases). This review aims to: (1) summarize the biological activity of Aβ_25-35, focusing on its impact on the main structural and functional alterations observed in AD (cognitive deficits, APP misprocessing, tau system dysfunction, neuroinflammation, oxidative stress, cholinergic and glutamatergic alterations, HPA axis dysregulation, synaptic deficits and cell death); and (2) confirm the interest of this pathomimetic model in AD research, as it has helped identify and characterize many molecules (marketed, in clinical development, and in preclinical testing), and to the development of alternative approaches for AD prevention and therapy. Today, the Aβ_25-35 model appears as a first-intent choice model to rapidly screen the symptomatic or neuroprotective potencies of new compounds, chemical series, or innovative therapeutic strategies.

Cholinergic regulation of object recognition memory

Object recognition memory refers to a basic memory mechanism to identify and recall various features of objects. This memory has been investigated by numerous studies in human, primates and rodents to elucidate the neuropsychological underpinnings in mammalian memory, as well as provide the diagnosis of dementia in some neurological diseases, such as Alzheimer's disease and Parkinson's disease. Since Alzheimer's disease at the early stage is reported to be accompanied with cholinergic cell loss and impairment in recognition memory, the central cholinergic system has been studied to investigate the neural mechanism underlying recognition memory. Previous studies have suggested an important role of cholinergic neurons in the acquisition of some variants of object recognition memory in rodents. Cholinergic neurons in the medial septum and ventral diagonal band of Broca that project mainly to the hippocampus and parahippocampal area are related to recognition memory for object location. Cholinergic projections from the nucleus basalis magnocellularis innervating the entire cortex are associated with recognition memory for object identification. Especially, the brain regions that receive cholinergic projections, such as the perirhinal cortex and prefrontal cortex, are involved in recognition memory for object-in-place memory and object recency. In addition, experimental studies using rodent models for Alzheimer's disease have reported that neurodegeneration within the central cholinergic system causes a deficit in object recognition memory. Elucidating how various types of object recognition memory are regulated by distinct cholinergic cell groups is necessary to clarify the neuronal mechanism for recognition memory and the development of therapeutic treatments for dementia.

Heptafluoroisobutyronitrile (C4F7N), a gas used for insulating and arc quenching in electrical switchgear, is neurotoxic in the mouse brain

Fluoronitrile gas (C₄F₇N, CAS number 42532-60-5) is one of the most promising candidates as insulating and/or breaking medium in high and medium voltage electrical equipment. Besides its promising properties, C₄F₇N gas is however not devoid of acute toxicity when used pure or in gas mixtures. The toxicity was not extensively analyzed and reported. The aim of the present study was to analyze in mice the consequences of a single exposure to C₄F₇N gas, at different concentrations and different timepoints after exposure. Male and female Swiss mice were exposed to breathable air or C₄F₇N gas, at 800 ppmv or 1500 ppmv, for 4 h on day 0. Behavioral tests (spontaneous alternation in the Y-maze and object recognition) were performed on days 1, 7 and 14 to assess memory alterations. The animals were then sacrificed and their brains dissected for biochemical analyses or fixed with paraformaldehyde for histology and immunohistochemistry. Results showed behavioral impairments and memory deficits, with impairments of alternation at days 1 and 7 and object recognition at day 14. Histological alterations of pyramidal neuronal layer in the hippocampus, neuroinflammatory astroglial reaction, and microglial alterations were observed, more marked in female than male mice. Moreover, the biochemical analyses done in the brain of 1500 ppmv exposed female mice showed a reductive stress with decreased lipid peroxidation and release of cytochrome c, leading to apoptosis with increases in caspase-9 cleavage and γ-H2AX/H2AX ratio. Finally, electrophysiological analyses using a multi-electrode array allowed the measure of the extracellular activity of pyramidal neurons in the CA2 area and revealed that exposure to the gas not only prevented the induction of long-term potentiation but even provoked an epileptoid-like activity in some neurons suggesting major alterations of synaptic plasticity. This study therefore showed that an acute exposure of mice to C₄F₇N gas provoked, particularly in female animals, memory alterations and brain toxicity characterized by a reductive stress, microglial toxicity, loss of synaptic plasticity and apoptosis. Its use in industrial installations must be done with extreme caution.

Development of novel phenoxyalkylpiperidines as high-affinity Sigma-1 (σ1) receptor ligands with potent anti-amnesic effect

The sigma-1 (σ1) receptor plays a significant role in many normal physiological functions and pathological disease states, and as such represents an attractive therapeutic target for both agonists and antagonists. Here, we describe a novel series of phenoxyalkylpiperidines based on the lead compound 1-[ω-(4-chlorophenoxy)ethyl]-4-methylpiperidine (1a) in which the degree of methylation at the carbon atoms alpha to the piperidine nitrogen was systematically varied. The affinity at σ1 and σ2 receptors and at Δ8-Δ7 sterol isomerase (SI) ranged from subnanomolar to micromolar Ki values. While the highest-affinity was displayed at the σ1, the increase of the degree of methylation in the piperidine ring progressively decreased the affinity. The subnanomolar affinity 1a and 1-[ω-(4-methoxyphenoxy)ethyl]-4-methylpiperidine (1b) displayed potent anti-amnesic effects associated with σ1 receptor agonism, in two memory tests. Automated receptor-small-molecule ligand docking provided a molecular structure-based rationale for the agonistic effects of 1a and 1b. Overall, the class of the phenoxyalkylpiperidines holds potential for the development of high affinity σ1 receptor agonists, and compound 1a, that appears as the best in class (exceeding by far the activity of the reference compound PRE-084) deserves further investigation.

AZP2006, a new promising treatment for Alzheimer's and related diseases

Progranulin (PGRN) is a protein with multiple functions including the regulation of neuroinflammation, neuronal survival, neurite and synapsis growth. Although the mechanisms of action of PGRN are currently unknown, its potential therapeutic application in treating neurodegenerative diseases is huge. Thus, strategies to increase PGRN levels in patients could provide an effective treatment. In the present study, we investigated the effects of AZP2006, a lysotropic molecule now in phase 2a clinical trial in Progressive Supranuclear Palsy patients, for its ability to increase PGRN level and promote neuroprotection. We showed for the first time the in vitro and in vivo neuroprotective effects of AZP2006 in neurons injured with Aβ1-42 and in two different pathological animal models of Alzheimer's disease (AD) and aging. Thus, the chronic treatment with AZP2006 was shown to reduce the loss of central synapses and neurons but also to dramatically decrease the massive neuroinflammation associated with the animal pathology. A deeper investigation showed that the beneficial effects of AZP2006 were associated with PGRN production. Also, AZP2006 binds to PSAP (the cofactor of PGRN) and inhibits TLR9 receptors normally responsible for proinflammation when activated. Altogether, these results showed the high potential of AZP2006 as a new putative treatment for AD and related diseases.

Selective Pseudo-irreversible Butyrylcholinesterase Inhibitors Transferring Antioxidant Moieties to the Enzyme Show Pronounced Neuroprotective Efficacy In Vitro and In Vivo in an Alzheimer's Disease Mouse Model

A series of multitarget-directed ligands (MTDLs) was designed by functionalizing a pseudo-irreversible butyrylcholinesterase (BChE) inhibitor. The obtained hybrids were investigated in vitro regarding their hBChE and hAChE inhibition, their enzyme kinetics, and their antioxidant physicochemical properties (DPPH, ORAC, metal chelating). In addition, in vitro assays were applied to investigate antioxidant effects using murine hippocampal HT22 cells and immunomodulatory effects on the murine microglial N9 cell line. The MTDLs retained their antioxidative properties compared to the parent antioxidant-moieties in vitro and the inhibition of hBChE was maintained in the submicromolar range. Representative compounds were tested in a pharmacological Alzheimer's disease (AD) mouse model and demonstrated very high efficacy at doses as low as 0.1 mg/kg. The most promising compound was also tested in BChE^-/- mice and showed reduced efficacy. In vivo neuroprotection by BChE inhibition can be effectively enhanced by incorporation of structurally diverse antioxidant moieties.

γ-Secretase inhibitors for breast cancer and hepatocellular carcinoma: From mechanism to treatment

The γ-secretase complex is a key hydrolase for many type 1 transmembrane proteins. It is very important for activation of the Notch receptor and regulation of target-gene transcription. Abnormal activation and expression of the Notch pathway are closely related to the occurrence and development of many tumor types, including breast cancer and liver cancer. In this review, we elaborated on the basic situation of γ-secretase complex and the biological function and role of γ-secretase in APP and Notch signal pathway are described in detail. Subsequently, all currently known γ-secretase inhibitors and γ-secretase modulators are listed and their mechanism of action, value of IC₅₀, chemical structure and current research stage are summarized. Next, the selection presented the treatment progress of γ-secretase inhibitors in breast cancer and hepatocellular carcinoma in the past five years. Finally, the mechanism of action of γ-secretase-mediated breast cancer and hepatocellular carcinoma and the advantages and disadvantages of γ-secretase inhibitors are discussed, and the concept of further research is proposed.

Anti-Amnesic and Neuroprotective Effects of Fluoroethylnormemantine in a Pharmacological Mouse Model of Alzheimer's Disease

BACKGROUND

Current therapies in Alzheimer's disease (AD), including Memantine, have proven to be only symptomatic but not curative or disease modifying. Fluoroethylnormemantine (FENM) is a structural analogue of Memantine, functionalized with a fluorine group that allowed its use as a positron emission tomography tracer. We here analyzed FENM neuroprotective potential in a pharmacological model of AD compared with Memantine.

METHODS

Swiss mice were treated intracerebroventricularly with aggregated Aβ 25-35 peptide and examined after 1 week in a battery of memory tests (spontaneous alternation, passive avoidance, object recognition, place learning in the water-maze, topographic memory in the Hamlet). Toxicity induced in the mouse hippocampus or cortex was analyzed biochemically or morphologically.

RESULTS

Both Memantine and FENM showed symptomatic anti-amnesic effects in Aβ 25-35-treated mice. Interestingly, FENM was not amnesic when tested alone at 10 mg/kg, contrarily to Memantine. Drugs injected once per day prevented Aβ 25-35-induced memory deficits, oxidative stress (lipid peroxidation, cytochrome c release), inflammation (interleukin-6, tumor necrosis factor-α increases; glial fibrillary acidic protein and Iba1 immunoreactivity in the hippocampus and cortex), and apoptosis and cell loss (Bcl-2-associated X/B-cell lymphoma 2 ratio; cell loss in the hippocampus CA1 area). However, FENM effects were more robust than observed with Memantine, with significant attenuations vs the Aβ 25-35-treated group.

CONCLUSIONS

FENM therefore appeared as a potent neuroprotective drug in an AD model, with a superior efficacy compared with Memantine and an absence of direct amnesic effect at higher doses. These results open the possibility to use the compound at more relevant dosages than those actually proposed in Memantine treatment for AD.

In Vitro and In Vivo Neuroprotective Effects of Etifoxine in β-Amyloidinduced Toxicity Models

Aim:

The aim of this study is to examine the effect of etifoxine on β-amyloid-induced toxicity models.

Background:

Etifoxine is an anxiolytic compound with a dual mechanism of action; it is a positive allosteric modulator of GABAergic receptors as well as a ligand for the 18 kDa mitochondrial Translocator Protein (TSPO). TSPO has recently raised interest in Alzheimer’s Disease (AD), and experimental studies have shown that some TSPO ligands could induce neuroprotective effects in animal models.

Objective:

In this study, we examined the potential protective effect of etifoxine in an in vitro and an in vivo model of amyloid beta (Aβ)-induced toxicity in its oligomeric form, which is a crucial factor in AD pathologic mechanisms.

Method:

Neuronal cultures were intoxicated with Aβ1-42, and the effects of etifoxine on oxidative stress, Tau-hyperphosphorylation and synaptic loss were quantified. In a mice model, behavioral deficits induced by intracerebroventricular administration of Aβ25-35 were measured in a spatial memory test, the spontaneous alternation and in a contextual memory test, the passive avoidance test.

Results:

In neuronal cultures intoxicated with Aβ1-42, etifoxine dose-dependently decreased oxidative stress (methionine sulfoxide positive neurons), tau-hyperphosphorylation and synaptic loss (ratio PSD95/synaptophysin). In a mice model, memory impairments were fully alleviated by etifoxine administered at anxiolytic doses (12.5-50mg/kg). In addition, markers of oxidative stress and apoptosis were decreased in the hippocampus of these animals.

Conclusion:

Our results have shown that in these two models, etifoxine could fully prevent neurotoxicity and pathological changes induced by Aβ. These results confirm that TSPO ligands could offer an interesting therapeutic approach to Alzheimer’s disease.

Glucocorticoid receptors signaling impairment potentiates amyloid-β oligomers-induced pathology in an acute model of Alzheimer's disease

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis occurs early in Alzheimer's disease (AD), associated with elevated circulating glucocorticoids (GC) and glucocorticoid receptors (GR) signaling impairment. However, the precise role of GR in the pathophysiology of AD remains unclear. Using an acute model of AD induced by the intracerebroventricular injection of amyloid-β oligomers (oAβ), we analyzed cellular and behavioral hallmarks of AD, GR signaling pathways, processing of amyloid precursor protein, and enzymes involved in Tau phosphorylation. We focused on the prefrontal cortex (PFC), particularly rich in GR, early altered in AD and involved in HPA axis control and cognitive functions. We found that oAβ impaired cognitive and emotional behaviors, increased plasma GC levels, synaptic deficits, apoptosis and neuroinflammatory processes. Moreover, oAβ potentiated the amyloidogenic pathway and enzymes involved both in Tau hyperphosphorylation and GR activation. Treatment with a selective GR modulator (sGRm) normalized plasma GC levels and all behavioral and biochemical parameters analyzed. GR seems to occupy a central position in the pathophysiology of AD. Deregulation of the HPA axis and a feed-forward effect on PFC GR sensitivity could participate in the etiology of AD, in perturbing Aβ and Tau homeostasis. These results also reinforce the therapeutic potential of sGRm in AD.

7-O-Esters of taxifolin with pronounced and overadditive effects in neuroprotection, anti-neuroinflammation, and amelioration of short-term memory impairment in vivo

Alzheimer's disease (AD) is a multifactorial disease and the most common form of dementia. There are no treatments to cure, prevent or slow down the progression of the disease. Natural products hold considerable interest for the development of preventive neuroprotectants to treat neurodegenerative disorders like AD, due to their low toxicity and general beneficial effects on human health with their anti-inflammatory and antioxidant features. In this work we describe regioselective synthesis of 7-O-ester hybrids of the flavonoid taxifolin with the phenolic acids cinnamic and ferulic acid, namely 7-O-cinnamoyltaxifolin and 7-O-feruloyltaxifolin. The compounds show pronounced overadditive neuroprotective effects against oxytosis, ferroptosis and ATP depletion in the murine hippocampal neuron HT22 cell model. Furthermore, 7-O-cinnamoyltaxifolin and 7-O-feruloyltaxifolin reduced LPS-induced neuroinflammation in BV-2 microglia cells as assessed by effects on the levels of NO, IL6 and TNFα. In all in vitro assays the 7-O-esters of taxifolin and ferulic or cinnamic acid showed strong overadditive activity, significantly exceeding the effects of the individual components and the equimolar mixtures thereof, which were almost inactive in all of the assays at the tested concentrations. In vivo studies confirmed this overadditive effect. Treatment of an AD mouse model based on the injection of oligomerized Aβ_25-35 peptide into the brain to cause neurotoxicity and subsequently memory deficits with 7-O-cinnamoyltaxifolin or 7-O-feruloyltaxifolin resulted in improved performance in an assay for short-term memory as compared to vehicle and mice treated with the respective equimolar mixtures. These results highlight the benefits of natural product hybrids as a novel compound class with potential use for drug discovery in neurodegenerative diseases due to their pharmacological profile that is distinct from the individual natural components.

Dual-Acting Cholinesterase-Human Cannabinoid Receptor 2 Ligands Show Pronounced Neuroprotection in Vitro and Overadditive and Disease-Modifying Neuroprotective Effects in Vivo

We have designed and synthesized a series of 14 hybrid molecules out of the cholinesterase (ChE) inhibitor tacrine and a benzimidazole-based human cannabinoid receptor subtype 2 (hCB2R) agonist and investigated them in vitro and in vivo. The compounds are potent ChE inhibitors, and for the most promising hybrids, the mechanism of human acetylcholinesterase (hAChE) inhibition as well as their ability to interfere with AChE-induced aggregation of β-amyloid (Aβ), and Aβ self-aggregation was assessed. All hybrids were evaluated for affinity and selectivity for hCB1R and hCB2R. To ensure that the hybrids retained their agonist character, the expression of cAMP-regulated genes was quantified, and potency and efficacy were determined. Additionally, the effects of the hybrids on microglia activation and neuroprotection on HT-22 cells were investigated. The most promising in vitro hybrids showed pronounced neuroprotection in an Alzheimer's mouse model at low dosage (0.1 mg/kg, i.p.), lacking hepatotoxicity even at high dose (3 mg/kg, i.p.).

Intraventricular murine Aβ infusion elicits hippocampal inflammation and disrupts the consolidation, but not retrieval, of conditioned fear in C57BL6/J mice

Although one of the defining characteristics of Alzheimer's disease is the presence of amyloid-beta (Aβ) plaques, the early accumulation of soluble Aβ oligomers (AβOs) may disrupt synaptic function and trigger cognitive impairments long before the appearance of plaques. Furthermore, murine models aimed at understanding how AβOs alter formation and retrieval of associative memories are conducted using human Aβ species, which are more neurotoxic in the mouse brain than the native murine species. Unfortunately, there is currently a lack of attention in the literature as to what the murine version of the peptide (mAβ) does to synaptic function and how it impacts the consolidation and retrieval of associative memories. In the current study, adult mice were infused with mAβ 0, 2, 6, or 46 h after contextual-fear conditioning, and were tested 2-48 h later. Interestingly, only mAβ infusions within 2 h of training reduced freezing behavior at test, indicating that mAβ disrupted the consolidation, but not retrieval of fear memory. This consolidation deficit coincided with increased IL-1β and reduced synaptophysin mRNA levels, without disrupting other synaptic signaling-related genes here examined. Despite differences between murine and human Aβ, the deleterious functional outcomes of early-stage synaptic oligomer presence are similar. Thus, models utilizing or inducing the production of mAβ in non-transgenic animals are useful in exploring the role of dysregulated synaptic plasticity and resultant learning deficits induced by Aβ oligomers.

N-acetylcysteine Treatment Reduces Age-related Hearing Loss and Memory Impairment in the Senescence-Accelerated Prone 8 (SAMP8) Mouse Model

Age-related hearing loss (ARHL) is the most common sensory disorder in the elderly population. SAMP8 mouse model presents accelerated senescence and has been identified as a model of gerontological research. SAMP8 displays a progressive age-related decline in brain function associated with a progressive hearing loss mimicking human aging memory deficits and ARHL. The molecular mechanisms associated with SAMP8 senescence process involve oxidative stress leading to chronic inflammation and apoptosis. Here, we studied the effect of N-acetylcysteine (NAC), an antioxidant, on SAMP8 hearing loss and memory to determine the potential interest of this model in the study of new antioxidant therapies. We observed a strong decrease of auditory brainstem response thresholds from 45 to 75 days of age and an increase of distortion product amplitudes from 60 to 75 days in NAC treated group compared to vehicle. Moreover, NAC treated group presented also an increase of memory performance at 60 and 105 days of age. These results confirm that NAC delays the senescence process by slowing the age-related hearing loss, protecting the cochlear hair cells and improving memory, suggesting that antioxidants could be a pharmacological target for age-related hearing and memory loss.

In vivo and ex vivo analyses of amyloid toxicity in the Tc1 mouse model of Down syndrome

RATIONALE

The prevalence of Alzheimer's disease is increased in people with Down syndrome. The pathology appears much earlier than in the general population, suggesting a predisposition to develop Alzheimer's disease. Down syndrome results from trisomy of human chromosome 21, leading to overexpression of possible Alzheimer's disease candidate genes, such as amyloid precursor protein gene. To better understand how the Down syndrome context results in increased vulnerability to Alzheimer's disease, we analysed amyloid-β [25-35] peptide toxicity in the Tc1 mouse model of Down syndrome, in which ~75% of protein coding genes are functionally trisomic but, importantly, not amyloid precursor protein.

RESULTS

Intracerebroventricular injection of oligomeric amyloid-β [25-35] peptide in three-month-old wildtype mice induced learning deficits, oxidative stress, synaptic marker alterations, activation of glycogen synthase kinase-3β, inhibition of protein kinase B (AKT), and apoptotic pathways as compared to scrambled peptide-treated wildtype mice. Scrambled peptide-treated Tc1 mice presented high levels of toxicity markers as compared to wildtype mice. Amyloid-β [25-35] peptide injection in Tc1 mice induced significant learning deficits and enhanced glycogen synthase kinase-3β activity in the cortex and expression of apoptotic markers in the hippocampus and cortex. Interestingly, several markers, including oxidative stress, synaptic markers, glycogen synthase kinase-3β activity in the hippocampus and AKT activity in the hippocampus and cortex, were unaffected by amyloid-β [25-35] peptide injection in Tc1 mice.

CONCLUSIONS

Tc1 mice present several toxicity markers similar to those observed in amyloid-β [25-35] peptide-treated wildtype mice, suggesting that developmental modifications in these mice modify their response to amyloid peptide. However, amyloid toxicity led to severe memory deficits in this Down syndrome mouse model.

In Vivo Characterization of ARN14140, a Memantine/Galantamine-Based Multi-Target Compound for Alzheimer's Disease

Alzheimer's disease (AD) is a chronic pathological condition that leads to neurodegeneration, loss of intellectual abilities, including cognition and memory, and ultimately to death. It is widely recognized that AD is a multifactorial disease, where different pathological cascades (mainly amyloid and tau) contribute to neural death and to the clinical outcome related to the disease. The currently available drugs for AD were developed according to the one-target, one-drug paradigm. In recent times, multi-target strategies have begun to play an increasingly central role in the discovery of more efficacious candidates for complex neurological conditions, including AD. In this study, we report on the in vivo pharmacological characterization of ARN14140, a new chemical entity, which was obtained through a multi-target structure-activity relationship campaign, and which showed a balanced inhibiting profile against the acetylcholinesterase enzyme and the NMDA receptor. Based on the initial promising biochemical data, ARN14140 is here studied in mice treated with the amyloidogenic fragment 25-35 of the amyloid-β peptide, a consolidated non-transgenic AD model. Sub-chronically treating animals with ARN14140 leads to a prevention of the cognitive impairment and of biomarker levels connected to neurodegeneration, demonstrating its neuroprotective potential as new AD agent.

Hippocampal Aβ expression, but not phosphorylated tau, predicts cognitive deficits following repeated peripheral poly I:C administration

Alzheimer's disease is marked by the accumulation of the amyloid-beta (Aβ) peptide, and increases in phosphorylation of the microtubule associated protein, tau. Changes in these proteins are considered responsible, in part, for the progressive neuronal degeneration and cognitive deficits seen in AD. We examined the effect of repeated consecutive peripheral poly I:C injections on cognitive deficits, central Aβ, and phosphorylated tau accumulation, following three treatment durations: 7, 14, and 21 days. Forty-eight hours after the final injection, animals were trained in a contextual fear-conditioning paradigm, and tested 24h later. Immediately after testing, the hippocampus was collected to quantify Aβ and phosphorylated tau accumulation. Results showed that, although poly I:C-induced Aβ was significantly elevated at all time points examined, poly I:C only disrupted cognition after 14 and 21 days of administration. Moreover, elevations in phosphorylated tau were not seen until the 14-day time point. Interestingly, phosphorylated tau expression then declined at the 21-day time point. Finally, we demonstrated that Aβ levels are a stronger predictor of cognitive dysfunction, explaining 37% of the variance, whereas phosphorylated tau levels only accounted for 0.2%. Taken together, these results support the hypothesis that inflammation-induced elevation in Aβ disrupts cognition, independently of phosphorylated tau, and suggest that long-term administration of poly I:C may provide a model to investigate the contribution of long-term inflammation toward the development of Alzheimer's-like pathology.

A Novel, Multi-Target Natural Drug Candidate, Matrine, Improves Cognitive Deficits in Alzheimer's Disease Transgenic Mice by Inhibiting Aβ Aggregation and Blocking the RAGE/Aβ Axis

The treatment of AD is a topic that has puzzled researchers for many years. Current mainstream theories still consider Aβ to be the most important target for the cure of AD. In this study, we attempted to explore multiple targets for AD treatments with the aim of identifying a qualified compound that could both inhibit the aggregation of Aβ and block the RAGE/Aβ axis. We believed that a compound that targets both Aβ and RAGE may be a feasible strategy for AD treatment. A novel and small natural compound, Matrine (Mat), was identified by high-throughput screening of the main components of traditional Chinese herbs used to treat dementia. Various experimental techniques were used to evaluate the effect of Mat on these two targets both in vitro and in AD mouse model. Mat could inhibit Aβ42-induced cytotoxicity and suppress the Aβ/RAGE signaling pathway in vitro. Additionally, the results of in vivo evaluations of the effects of Mat on the two targets were consistent with the results of our in vitro studies. Furthermore, Mat reduced proinflammatory cytokines and Aβ deposition and attenuated the memory deficits of AD transgenic mice. We believe that this novel, multi-target strategy to inhibit both Aβ and RAGE, is worthy of further exploration. Therefore, our future studies will focus on identifying even more effective multi-target compounds for the treatment of AD based on the molecular structure of Mat.

Protection by sigma-1 receptor agonists is synergic with donepezil, but not with memantine, in a mouse model of amyloid-induced memory impairments

Drugs activating the sigma-1 (σ1) chaperone protein are anti-amnesic and neuroprotective in neurodegenerative pathologies like Alzheimer's disease (AD). Since these so-called σ1 receptor (σ1R) agonists modulate cholinergic and glutamatergic systems in a variety of physiological responses, we addressed their putative additive/synergistic action in combination with cholinergic or glutamatergic drugs. The selective σ1 agonist PRE-084, or the non-selective σ1 drug ANAVEX2-73 was combined with the acetylcholinesterase inhibitor donepezil or the NMDA receptor antagonist memantine in the nontransgenic mouse model of AD-like memory impairments induced by intracerebroventricular injection of oligomeric Aβ25-35 peptide. Two behavioral tests, spontaneous alternation and passive avoidance response, were used in parallel and both protective and symptomatic effects were examined. After determination of the minimally active doses for each compound, the combinations were tested and the combination index (CI) calculated. Combinations between the σ1 agonists and donepezil showed a synergic protective effect, with CI<1, whereas the combinations with memantine showed an antagonist effect, with CI>1. Symptomatic effects appeared only additive for all combinations, with CI=1. A pharmacological analysis of the PRE-084+donepezil combination revealed that the synergy could be due to an inter-related mechanism involving α7 nicotinic ACh receptors and σ1R. These results demonstrated that σ1 drugs do not only offer a protective potential alone but also in combination with other therapeutic agents. The nature of neuromodulatory molecular chaperone of the σ1R could eventually lead to synergistic combinations.

Learning performances and vulnerability to amyloid toxicity in the butyrylcholinesterase knockout mouse

Butyrylcholinesterase (BChE) is an important enzyme for detoxication and metabolism of ester compounds. It also hydrolyzes the neurotransmitter acetylcholine (ACh) in pathological conditions and may play a role in Alzheimer's disease (AD). We here compared the learning ability and vulnerability to Aβ toxicity in male and female BChE knockout (KO) mice and their 129Sv wild-type (Wt) controls. Animals tested for place learning in the water-maze showed increased acquisition slopes and presence in the training quadrant during the probe test. An increased passive avoidance response was also observed for males. BChE KO mice therefore showed enhanced learning ability in spatial and non-spatial memory tests. Intracerebroventricular (ICV) injection of increasing doses of amyloid-β[25-35] (Aβ25-35) peptide oligomers resulted, in Wt mice, in learning and memory deficits, oxidative stress and decrease in ACh hippocampal content. In BChE KO mice, the Aβ25-35-induced deficit in place learning was attenuated in males and blocked in females. No change in lipid peroxidation or ACh levels was observed after Aβ25-35 treatment in male or female BChE KO mice. These data showed that the genetic invalidation of BChE in mice augmented learning capacities and lowered the vulnerability to Aβ toxicity.

Intranasal H102 Peptide-Loaded Liposomes for Brain Delivery to Treat Alzheimer's Disease

PURPOSE

H102, a novel β-sheet breaker peptide, was encapsulated into liposomes to reduce its degradation and increase its brain penetration through intranasal administration for the treatment of Alzheimer's disease (AD).

METHODS

The H102 liposomes were prepared using a modified thin film hydration method, and their transport characteristics were tested on Calu-3 cell monolayers. The pharmacokinetics in rats' blood and brains were also investigated. Behavioral experiments were performed to evaluate the improvements on AD rats' spatial memory impairment. The neuroprotective effects were tested by detecting acetylcholinesterase (AchE), choline acetyltransferase (ChAT) and insulin degrading enzyme (IDE) activity and conducting histological assays. The safety was evaluated on rats' nasal mucosa and cilia.

RESULTS

The liposomes prepared could penetrate Calu-3 cell monolayers consistently. After intranasal administration, H102 could be effectively delivered to the brain, and the AUC of H102 liposomes in the hippocampus was 2.92-fold larger than that of solution group. H102 liposomes could excellently ameliorate spatial memory impairment of AD model rats, increase the activities of ChAT and IDE and inhibit plaque deposition, even in a lower dosage compared with H102 intranasal solution. H102 nasal formulations showed no toxicity on nasal mucosa.

CONCLUSIONS

The H102-loaded liposome prepared in this study for nasal administration is stable, effective and safe, which has great potential for AD treatment.

Combining two repurposed drugs as a promising approach for Alzheimer's disease therapy

Alzheimer disease (AD) represents a major medical problem where mono-therapeutic interventions demonstrated only a limited efficacy so far. We explored the possibility of developing a combinational therapy that might prevent the degradation of neuronal and endothelial structures in this disease. We argued that the distorted balance between excitatory (glutamate) and inhibitory (GABA/glycine) systems constitutes a therapeutic target for such intervention. We found that a combination of two approved drugs – acamprosate and baclofen – synergistically protected neurons and endothelial structures in vitro against amyloid-beta (Aβ) oligomers. The neuroprotective effects of these drugs were mediated by modulation of targets in GABA/glycinergic and glutamatergic pathways. In vivo, the combination alleviated cognitive deficits in the acute Aβ_25–35 peptide injection model and in the mouse mutant APP transgenic model. Several patterns altered in AD were also synergistically normalised. Our results open up the possibility for a promising therapeutic approach for AD by combining repurposed drugs.

Osteopontin expression in acute immune response mediates hippocampal synaptogenesis and adaptive outcome following cortical brain injury

Traumatic brain injury (TBI) produces axotomy, deafferentation and reactive synaptogenesis. Inflammation influences synaptic repair, and the novel brain cytokine osteopontin (OPN) has potential to support axon regeneration through exposure of its integrin receptor binding sites. This study explored whether OPN secretion and proteolysis by matrix metalloproteinases (MMPs) mediate the initial degenerative phase of synaptogenesis, targeting reactive neuroglia to affect successful repair. Adult rats received unilateral entorhinal cortex lesion (UEC) modeling adaptive synaptic plasticity. Over the first week postinjury, hippocampal OPN protein and mRNA were assayed and histology was performed. At 1-2d, OPN protein increased up to 51 fold, and was localized within activated, mobilized glia. OPN transcript also increased over 50 fold, predominantly within reactive microglia. OPN fragments known to be derived from MMP proteolysis were elevated at 1d, consistent with prior reports of UEC glial activation and enzyme production. Postinjury minocycline immunosuppression attenuated MMP-9 gelatinase activity, which was correlated with the reduction of neutrophil gelatinase-associated lipocalin (LCN2) expression, and reduced OPN fragment generation. The antibiotic also attenuated removal of synapsin-1 positive axons from the deafferented zone. OPN KO mice subjected to UEC had similar reduction of hippocampal MMP-9 activity, as well as lower synapsin-1 breakdown over the deafferented zone. MAP1B and N-cadherin, surrogates of cytoarchitecture and synaptic adhesion, were not affected. OPN KO mice with UEC exhibited time dependent cognitive deficits during the synaptogenic phase of recovery. This study demonstrates that OPN can mediate immune response during TBI synaptic repair, positively influencing synapse reorganization and functional recovery.

Jujuboside A, a neuroprotective agent from semen Ziziphi Spinosae ameliorates behavioral disorders of the dementia mouse model induced by Aβ 1-42

Semen Ziziphi Spinosae (SZS) has been used as a hypnotic-sedative medicine for thousands of years. Recently, SZS has also shown notable neuroprotective activities via anti-oxidative and anti-inflammatory effects in dementia animals. Jujuboside A (JuA), isolated from SZS, has been proved to be a major hypnotic-sedative component of SZS. In the present study, we firstly evaluated the effects of intracerebroventricular (ICV) injection of JuA (0.02 and 0.2mg/kg) for five consecutive days on cognitive impairment induced by ICV injection of Aβ 1-42. The results showed that ICV treatment with JuA significantly mitigated learning and memory impairment in mice induced by Aβ 1-42 as measured by the Y-maze, active avoidance and Morris water maze. Furthermore, ICV treatment with JuA reduced the level of Aβ 1-42 in hippocampus, significantly inhibited the activities of acetylcholinesterase (AChE) and NO, and decreased the amount of the increased malondialdehyde (MDA) in the hippocampus and cerebral cortex of mice treated with ICV injection of Aβ 1-42. Shrinkage of nuclei, swollen and eccentrically dispersed neuronal bodies were observed in hippocampus of AD mice induced by Aβ 1-42, however, JuA noticeably improved the histopathological damage. Cumulatively, the present study indicates that JuA may serve as a potential therapeutic agent for the treatment of Alzheimer' disease.

Blockade of Tau hyperphosphorylation and Aβ₁₋₄₂ generation by the aminotetrahydrofuran derivative ANAVEX2-73, a mixed muscarinic and σ₁ receptor agonist, in a nontransgenic mouse model of Alzheimer's disease

The main objective of the present study was to establish whether the mixed σ₁/muscarinic ligand ANAVEX2-73, shown to be neuroprotective in Alzheimer's disease (AD) models in vivo and currently in clinical phase I/IIa, could have the ability to reduce the appearance of hyperphosphorylated Tau and amyloid-β₁₋₄₂ (Aβ₁₋₄₂ in the Aβ₂₅₋₃₅ mouse model of AD. We therefore first confirmed that Aβ₂₅₋₃₅ injection induced hyperphosphorylation of Tau protein, by showing that it rapidly decreased Akt activity and activated glycogen synthase kinase-3β (GSK-3β) in the mouse hippocampus. Second, we showed that the kinase activation, and resulting Tau alteration, directly contributed to the amyloid toxicity, as co-administration of the selective GSK-3β inhibitor 2-thio(3-iodobenzyl)-5-(1-pyridyl)-[1,3,4]-oxidiazole blocked both Tau phosphorylation and Aβ₂₅₋₃₅-induced memory impairments. Third, we analyzed the ANAVEX2-73 effect on Tau phosphorylation and activation of the related kinase pathways (Akt and GSK-3β). And fourth, we also addressed the impact of the drug on Aβ₂₅₋₃₅-induced Aβ₁₋₄₂ seeding and observed that the compound significantly blocked the increase in Aβ₁₋₄₂ and C99 levels in the hippocampus, suggesting that it may alleviate amyloid load in AD models. The comparison with PRE-084, a selective and reference σ₁ receptor agonist, and xanomeline, a muscarinic ligand presenting similar profile as ANAVEX2-73 on M1 and M2 subtypes, confirmed that both muscarinic and σ₁ targets are involved in the ANAVEX2-73 effects. The drug, acting synergistically on both targets, but with moderate affinity, presents a promising pharmacological profile.

Pharmacological characterization of memoquin, a multi-target compound for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is characterized by progressive loss of cognitive function, dementia and altered behavior. Over 30 million people worldwide suffer from AD and available therapies are still palliative rather than curative. Recently, Memoquin (MQ), a quinone-bearing polyamine compound, has emerged as a promising anti-AD lead candidate, mainly thanks to its multi-target profile. MQ acts as an acetylcholinesterase and β-secretase-1 inhibitor, and also possesses anti-amyloid and anti-oxidant properties. Despite this potential interest, in vivo behavioral studies with MQ have been limited. Here, we report on in vivo studies with MQ (acute and sub-chronic treatments; 7-15 mg/kg per os) carried out using two different mouse models: i) scopolamine- and ii) beta-amyloid peptide- (Aβ-) induced amnesia. Several aspects related to memory were examined using the T-maze, the Morris water maze, the novel object recognition, and the passive avoidance tasks. At the dose of 15 mg/kg, MQ was able to rescue all tested aspects of cognitive impairment including spatial, episodic, aversive, short and long-term memory in both scopolamine- and Aβ-induced amnesia models. Furthermore, when tested in primary cortical neurons, MQ was able to fully prevent the Aβ-induced neurotoxicity mediated by oxidative stress. The results support the effectiveness of MQ as a cognitive enhancer, and highlight the value of a multi-target strategy to address the complex nature of cognitive dysfunction in AD.