A systematic review and meta-analysis of tau phosphorylation in mouse models of familial Alzheimer's disease.

Transgenic models of familial Alzheimer's disease (AD) serve as valuable tools for probing the molecular mechanisms associated with amyloid-beta (Aß)-induced pathology. In this meta-analysis, we sought to evaluate levels of phosphorylated tau (p-tau) and explore potential age-related variations in tau hyperphosphorylation, within mouse models of AD. The PubMed and Scopus databases were searched for studies measuring soluble p-tau in 5xFAD, APPswe/PSEN1de9, J20 and APP23 mice. Data were extracted and analyzed using standardized procedures. For the 5xFAD model, the search yielded 36 studies eligible for meta-analysis. Levels of p-tau were higher in 5xFAD mice relative to control, a difference that was evident in both the carboxy-terminal (CT) and proline-rich (PR) domains of tau. Age negatively moderated the relationship between genotype and CT phosphorylated tau in studies using hybrid mice, female mice, and preparations from the neocortex. For the APPswe/PSEN1de9 model, the search yielded 27 studies. Analysis showed tau hyperphosphorylation in transgenic vs. control animals, evident in both the CT and PR regions of tau. Age positively moderated the relationship between genotype and PR domain phosphorylated tau in the neocortex of APPswe/PSEN1de9 mice. A meta-analysis was not performed for the J20 and APP23 models, due to the limited number of studies measuring p-tau levels in these mice (<10 studies). Although tau is hyperphosphorylated in both 5xFAD and APPswe/PSEN1de9 mice, the effects of ageing on p-tau are contingent upon the model being examined. These observations emphasize the importance of tailoring model selection to the appropriate disease stage when considering the relationship between Aß and tau, and suggest that there are optimal intervention points for the administration of both anti-amyloid and anti-tau therapies.

Protective effect of ibuprofen in a rat model of chronic oxaliplatin-induced peripheral neuropathy.

Despite extensive preclinical and clinical investigations, a clinically relevant neuroprotective agent against oxaliplatin-induced peripheral neuropathy, which affects the quality of life following chemotherapy, has not been identified. Epidemiological data suggest that ibuprofen may reduce the risk of neuropathy. Male rats were treated with oxaliplatin (n = 6), oxaliplatin and ibuprofen (n = 5) or vehicle (n = 5) every second day for 15 days. Neuropathy was evaluated using mechanical detection thresholds (MDT) at the hind paw and sensory nerve conduction velocity (SNCV) in the tail nerve at baseline, right after and 3 weeks after the end of treatment. Intraepidermal nerve fibre density (IENFD) was evaluated in the hind paw and inflammation in the dorsal root ganglia 3 weeks after treatment. Inflammation in the dorsal root ganglia was assessed using quantitative real-time RT-PCR (qPCR) of the mRNA levels for the pro-inflammatory cytokines, TNF-α and IL-1ß, and by immunohistochemical staining for Iba1+ macrophages. SNCV was reduced in rats treated with oxaliplatin and with oxaliplatin and ibuprofen compared to control rats 3 weeks after treatment. No differences were found for MDT 3 weeks after treatment. IENFD was reduced in rats treated with oxaliplatin. There was a trend towards up-regulation of TNF-α mRNA levels in rats treated with oxaliplatin and with oxaliplatin and ibuprofen. Morphological changes of Iba1+ macrophages suggested activation, but no differences were found in area fraction or size of macrophage cell bodies. The results did not support a neuroprotective effect of ibuprofen but indicated that inflammation may play a role in oxaliplatin-induced peripheral neuropathy.

Bis-pyridylethenyl benzene as novel backbone for amyloid-ß binding compounds.

Detection of cerebral ß-amyloid (Aß) by targeted contrast agents is of great interest for in vivo diagnosis of Alzheimer's disease (AD). Partly because of their planar structure several bis-styrylbenzenes have been previously reported as potential Aß imaging agents. However, these compounds are relatively hydrophobic, which likely limits their in vivo potential. Based on their structures, we hypothesized that less hydrophobic bis-pyridylethenylbenzenes may also label amyloid. We synthesized several bis-pyridylethenylbenzenes and tested whether these compounds indeed display improved solubility and lower LogP values, and studied their fluorescent properties and Aß binding characteristics. Bis-pyridylethenylbenzenes showed a clear affinity for Aß plaques on both human and murine AD brain sections. Competitive binding experiments suggested a different binding site than Chrysamine G, a well-known stain for amyloid. With a LogP value between 3 and 5, most bis-pyridylethenylbenzenes were able to enter the brain and label murine amyloid in vivo with the bis(4-pyridylethenyl)benzenes showing the most favorable characteristics. In conclusion, the presented results suggest that bis-pyridylethenylbenzene may serve as a novel backbone for amyloid imaging agents.

Synthesis, structure activity relationship, radiolabeling and preclinical evaluation of high affinity ligands for the ion channel of the N-methyl-d-aspartate receptor as potential imaging probes for positron emission tomography.

The N-methyl-d-aspartate receptor (NMDAr) is involved in many neurological and psychiatric disorders including Alzheimer's disease and schizophrenia. Currently, it is not possible to assess NMDAr availability in vivo. The purpose of this study was to develop a positron emission tomography (PET) ligand for the NMDAr ion channel. A series of di- and tri-N-substituted diarylguanidines was synthesized. In addition, in vitro binding affinity for the NMDAr ion channel in rat forebrain membrane fractions was assessed. Compounds 10, 11 and 32 were radiolabeled with either carbon-11 or fluorine-18. Ligands [(11)C]10 and [(18)F]32 were evaluated ex vivo in B6C3 mice. Biodistribution studies showed higher uptake of [(11)C]10 and [(18)F]32 in forebrain regions compared with cerebellum. In addition, for [(11)C]10 54% and for [(18)F]32 70% of activity in the brain at 60min was due to intact tracer. Pre-treatment with MK-801 (0.6mg·kg(-1), ip) slightly decreased uptake in NMDAr-specific regions for [(18)F]32, but not for [(11)C]10. As such [(18)F]32 has the best characteristics as a PET tracer for the ion channel of the NMDAr.

Structure-activity relationships of N-substituted 4-(trifluoromethoxy)benzamidines with affinity for GluN2B-containing NMDA receptors.

GluN2B subtype-selective NMDA antagonists represent promising therapeutic targets for the symptomatic treatment of multiple CNS pathologies. A series of N-benzyl substituted benzamidines were synthesised and the benzyl ring was further replaced with various polycyclic moieties. Compounds were evaluated for activity at GluN2B containing NMDA receptors where analogues 9, 12, 16 and 18 were the most potent of the series, replacement of the benzyl ring with polycycles resulted in a complete loss of activity.

Polyfluorinated bis-styrylbenzenes as amyloid-ß plaque binding ligands.

Detection of cerebral ß-amyloid (Aß) by targeted contrast agents remains of great interest to aid the in vivo diagnosis of Alzheimer's disease (AD). Bis-styrylbenzenes have been previously reported as potential Aß imaging agents. To further explore their potency as (19)F MRI contrast agents we synthetized several novel fluorinated bis-styrylbenzenes and studied their fluorescent properties and amyloid-ß binding characteristics. The compounds showed a high affinity for Aß plaques on murine and human brain sections. Interestingly, competitive binding experiments demonstrated that they bound to a different binding site than chrysamine G. Despite their high logP values, many bis-styrylbenzenes were able to enter the brain and label murine amyloid in vivo. Unfortunately initial post-mortem (19)F NMR studies showed that these compounds as yet do not warrant further MRI studies due to the reduction of the (19)F signal in the environment of the brain.

Natural antioxidants that act against Alzheimer's disease through modulation of the NRF2 pathway: a focus on their molecular mechanisms of action.

Characterized by a complex pathophysiology that includes the intraneuronal formation of neurofibrillary tangles and the extracellular deposition of ß-amyloid plaques, Alzheimer's disease (AD) is a terminal neurodegenerative disease that causes dementia in older adults. Oxidative stress in the brain is considered as one of the contributing factors to the pathogenesis of AD, and thus, antioxidants have attracted much interest as potential therapeutic agents against the disorder. Natural antioxidants are typically characterized by low acute and chronic toxicity, which facilitates their potential therapeutic application. One important molecular target for the beneficial effects of natural antioxidants is the nuclear factor erythroid-derived 2-related factor 2 (NFE2L2/NRF2). NRF2 is a key transcription factor that orchestrates the cellular antioxidant response through regulating the expression of oxidative stress-related genes harboring the antioxidant response element (ARE) in their promoters. Indeed, in the case of excessive oxidative damage, NRF2 migrates to the nucleus and binds to ARE, activating the transcription of antioxidant protector genes. There is increasing evidence that NRF2 is implicated in AD pathology through dysfunction and altered localization, which renders it as a potential therapeutic target for AD. Thus, this review summarizes the most recent (2018-2023) advances on the NRF2-modulating activity of natural antioxidants observed in vitro and in AD animal models. This information will help elucidate the molecular mechanisms governing the antioxidant activity of such phytochemicals to highlight their therapeutic potential against common neurodegenerative diseases, such as AD.

Efficacy of Chronic Paroxetine Treatment in Mitigating Amyloid Pathology and Microgliosis in APPSWE/PS1ΔE9 Transgenic Mice.

BACKGROUND: Modulation of serotonergic signaling by treatment with selective serotonin reuptake inhibitors (SSRIs) has been suggested to mitigate amyloid-ß (Aß) pathology in Alzheimer's disease, in addition to exerting an anti-depressant action. OBJECTIVE: To investigate the efficacy of chronic treatment with the SSRI paroxetine, in mitigating Aß pathology and Aß plaque-induced microgliosis in the hippocampus of 18-month-old APPswe/PS1ΔE9 mice. METHODS: Plaque-bearing APPswe/PS1ΔE9 and wildtype mice were treated with paroxetine per os at a dose of 5 mg/kg/day, from 9 to 18 months of age. The per os treatment was monitored by recording of the body weights and serum paroxetine concentrations, and by assessment of the serotonin transporter occupancy by [3H]DASB-binding in wildtype mice. Additionally, 5,7-dihydroxytryptamine was administered to 9-month-old APPswe/PS1ΔE9 mice, to examine the effect of serotonin depletion on Aß pathology. Aß pathology was evaluated by Aß plaque load estimation and the Aß42/Aß40 ratio by ELISA. RESULTS: Paroxetine treatment led to > 80% serotonin transporter occupancy. The treatment increased the body weight of wildtype mice, but not of APPswe/PS1ΔE9 mice. The treatment had no effect on the Aß plaque load (p = 0.39), the number and size of plaques, or the Aß plaque-induced increases in microglial numbers in the dentate gyrus. Three months of serotonin depletion did not significantly impact the Aß plaque load or Aß42/Aß40 ratio in APPswe/PS1ΔE9 mice at 12 months. CONCLUSION: Our results show that chronic treatment with the SSRI paroxetine does not mitigate Aß pathology and Aß plaque-induced microgliosis in the hippocampus of APPswe/PS1ΔE9 mice.

Tumor Necrosis Factor (TNF) Is Required for Spatial Learning and Memory in Male Mice under Physiological, but Not Immune-Challenged Conditions.

Increasing evidence demonstrates that inflammatory cytokines-such as tumor necrosis factor (TNF)-are produced at low levels in the brain under physiological conditions and may be crucial for synaptic plasticity, neurogenesis, learning and memory. Here, we examined the effects of developmental TNF deletion on spatial learning and memory using 11-13-month-old TNF knockout (KO) and C57BL6/J wild-type (WT) mice. The animals were tested in the Barnes maze (BM) arena under baseline conditions and 48 h following an injection of the endotoxin lipopolysaccharide (LPS), which was administered at a dose of 0.5 mg/kg. Vehicle-treated KO mice were impaired compared to WT mice during the acquisition and memory-probing phases of the BM test. No behavioral differences were observed between WT and TNF-KO mice after LPS treatment. Moreover, there were no differences in the hippocampal content of glutamate and noradrenaline between groups. The effects of TNF deletion on spatial learning and memory were observed in male, but not female mice, which were not different compared to WT mice under baseline conditions. These results indicate that TNF is required for spatial learning and memory in male mice under physiological, non-inflammatory conditions, however not following the administration of LPS. Inflammatory signalling can thereby modulate spatial cognition in male subjects, highlighting the importance of sex- and probably age-stratified analysis when examining the role of TNF in the brain.

Mild Microglial Responses in the Cortex and Perivascular Macrophage Infiltration in Subcortical White Matter in Dogs with Age-Related Dementia Modelling Prodromal Alzheimer's Disease.

BACKGROUND: Microglia contribute to Alzheimer's disease (AD) pathogenesis by clearing amyloid-ß (Aß) and driving neuroinflammation. Domestic dogs with age-related dementia (canine cognitive dysfunction (CCD)) develop cerebral amyloidosis like humans developing AD, and studying such dogs can provide novel information about microglial response in prodromal AD. OBJECTIVE: The aim was to investigate the microglial response in the cortical grey and the subcortical white matter in dogs with CCD versus age-matched cognitively normal dogs. METHODS: Brains from aged dogs with CCD and age-matched controls without dementia were studied. Cases were defined by dementia rating score. Brain sections were stained for Aß, thioflavin S, hyperphosphorylated tau, and the microglial-macrophage ionized calcium binding adaptor molecule 1 (Iba1). Results were correlated to dementia rating score and tissue levels of Aß. RESULTS: Microglial numbers were higher in the Aß plaque-loaded deep cortical layers in CCD versus control dogs, while the coverage by microglial processes were comparable. Aß plaques were of the diffuse type and without microglial aggregation. However, a correlation was found between the %Iba1 area and insoluble Aß 42 and N-terminal pyroglutamate modified Aß(N3pE)-42. The %Iba1 area was higher in white matter, showing phosphorylation of S396 tau, versus grey matter. Perivascular macrophage infiltrates were abundant in the white matter particularly in CDD dogs. CONCLUSION: The results from this study of the microglial-macrophage response in dogs with CCD are suggestive of relatively mild microglial responses in the Aß plaque-loaded deep cortical layers and perivascular macrophage infiltrates in the subcortical white matter, in prodromal AD.

Mouse strain differences in locomotor, sensitisation and rewarding effect of heroin; association with alterations in MOP-r activation and dopamine transporter binding.

There is growing agreement that genetic factors play an important role in the risk to develop heroin addiction, and comparisons of heroin addiction vulnerability in inbred strains of mice could provide useful information on the question of individual vulnerability to heroin addiction. This study examined the rewarding and locomotor-stimulating effects of heroin in male C57BL/6J and DBA/2J mice. Heroin induced locomotion and sensitisation in C57BL/6J but not in DBA/2J mice. C57BL/6J mice developed conditioned place preference (CPP) to the highest doses of heroin, while DBA/2J showed CPP to only the lowest heroin doses, indicating a higher sensitivity of DBA/2J mice to the rewarding properties of heroin vs C57BL/6J mice. In order to investigate the neurobiological substrate underlying some of these differences, the effect of chronic 'intermittent' escalating dose heroin administration on the opioid, dopaminergic and stress systems was explored. Twofold higher mu-opioid receptor (MOP-r)-stimulated [35S]GTPgammaS binding was observed in the nucleus accumbens and caudate of saline-treated C57BL/6J mice compared with DBA/2J. Heroin decreased MOP-r density in brain regions of C57BL/6J mice, but not in DBA/2J. A higher density of dopamine transporters (DAT) was observed in nucleus accumbens shell and caudate of heroin-treated DBA/2J mice compared with heroin-treated C57BL/6J. There were no effects on D1 and D2 binding. Chronic heroin administration decreased corticosterone levels in both strains with no effect of strain. These results suggest that genetic differences in MOP-r activation and DAT expression may be responsible for individual differences in vulnerability to heroin addiction.

Differential region-specific regulation of α4ß2* nAChRs by self-administered and non-contingent nicotine in C57BL/6J mice.

Neuronal nAChR upregulation is the hallmark of chronic nicotine exposure. Neuroplasticity to abused drugs, however, depends on whether their administration is forced by the experimenter or is under the control of the experimental animal. Neuroadaptation to chronic nicotine self-administration was examined with a yoked-control paradigm, using nose-poking as the operating procedure. Freely moving C57BL/6J mice that responded for 0.03 mg/kg/infusion of intravenous nicotine under a continuous schedule of reinforcement (FR-1), had control over the rate and amount of drug intake that a yoked littermate passively received (n = 11). The impact of response dependency on neurobiological changes in nicotinic and dopaminergic systems was subsequently assessed using quantitative autoradiography. Cytisine-sensitive [(125)I]epibatidine binding, [³H]SCH23390, [³H]raclopride and [³H]mazindol were used to label nAChRs with α4ß2* subtype properties, D1 and D2 dopaminergic receptors, and dopamine transporters, respectively. During a period of 12 days, self-administration was reliably initiated and maintained in animals receiving response-contingent nicotine. Region specific changes in the density of α4ß2* nAChRs were found to be dependent on the contingency of nicotine treatment. Higher levels of α4ß2* receptor binding were observed in the dorsal lateral geniculate nucleus and the ventral tegmental area of self-administering mice, compared to non-contingent animals. Moreover, response-independent increases in D2 binding were observed following chronic nicotine administration. No change in D1 and DAT binding was observed among groups. These findings indicate regional specific alterations in the regulation of the nicotinic cholinergic system following contingent and non-contingent nicotine exposure, and underline the importance of response dependency on the development of nicotine addiction.

Neuroinflammation and amyloid-beta 40 are associated with reduced serotonin transporter (SERT) activity in a transgenic model of familial Alzheimer's disease.

BACKGROUND: Discrepant and often contradictory results have accumulated regarding the antidepressant and pro-cognitive effects of serotonin transporter (SERT) antagonists in Alzheimer's disease. METHODS: To address the discrepancy, we measured the activity and density of SERT in the neocortex of 3-24-month-old APPswe/PS1dE9 and wild-type littermate mice, by using [3H]DASB autoradiography and the [3H]5-HT uptake assay. Levels of soluble amyloid-ß (Aß), and pro-inflammatory cytokines that can regulate SERT function, such as interleukin-1ß (IL-1ß), interleukin-6 (IL-6), and tumor necrosis factor (TNF), were measured in parallel. Neuroinflammation in aging APPswe/PS1dE9 mice was further evaluated by [3H]PK11195 autoradiography. RESULTS: Decreased SERT density was observed in the parietal and frontal cortex of 18-24-month-old APPswe/PS1dE9 mice, compared to age-matched, wild-type animals. The maximal velocity uptake rate (Vmax) of [3H]5-HT was reduced in neocortical preparations from 20-month-old transgenic vs. wild-type mice. The reduction was observed when the proportion of soluble Aß40 in the Aß40/42 ratio increased in the aged transgenic brain. At concentrations compatible with those measured in 20-month-old APPswe/PS1dE9 mice, synthetic human Aß40, but not Aß42, reduced the baseline Vmax of [3H]5-HT by ~ 20%. Neuroinflammation in APPswe/PS1dE9 vs. wild-type mice was evidenced by elevated [3H]PK11195 binding levels and increased concentration of IL-1ß protein, which preceded the reductions in neocortical SERT density and activity. Age-induced increases in the levels of IL-1ß, IL-6, and TNF were observed in both transgenic and wild-type animals. CONCLUSIONS: The progression of cerebral amyloidosis is associated with neuroinflammation and decreased presynaptic markers of serotonergic integrity and activity. The Aß40-induced reduction in the uptake kinetics of [3H]5-HT suggests that the activity of SERT, and potentially the effects of SERT antagonism, depend on the levels of interstitial Aß40.

Increased Inflammation and Unchanged Density of Synaptic Vesicle Glycoprotein 2A (SV2A) in the Postmortem Frontal Cortex of Alzheimer's Disease Patients.

Sections from the middle frontal gyrus (Brodmann area 46) of autopsy-confirmed Alzheimer's disease (AD) patients and non-demented subjects were examined for the prevalence of hallmark AD pathology, including amyloid-ß (Aß) plaques, phosphorylated tau (pTau) tangles, neuroinflammation and synaptic loss (n = 7 subjects/group). Dense-core deposits of Aß were present in all AD patients (7/7) and some non-demented subjects (3/7), as evidenced by 6E10 immunohistochemistry. Levels of Aß immunoreactivity were higher in AD vs. non-AD cases. For pTau, AT8-positive neurofibrillary tangles and threads were exclusively observed in AD patient tissue. Levels of [3H]PK11195 binding to the translocator protein (TSPO), a marker of inflammatory processes, were elevated in the gray matter of AD patients compared to non-demented subjects. Levels of [3H]UCB-J binding to synaptic vesicle glycoprotein 2A (SV2A), a marker of synaptic density, were not different between groups. In AD patients, pTau immunoreactivity was positively correlated with [3H]PK11195, and negatively correlated with [3H]UCB-J binding levels. No correlation was observed between Aß immunoreactivity and markers of neuroinflammation or synaptic density. These data demonstrate a close interplay between tau pathology, inflammation and SV2A density in AD, and provide useful information on the ability of neuroimaging biomarkers to diagnose AD dementia.

Ageing and amyloidosis underlie the molecular and pathological alterations of tau in a mouse model of familial Alzheimer's disease.

Despite compelling evidence that the accumulation of amyloid-beta (Aß) promotes neocortical MAPT (tau) aggregation in familial and idiopathic Alzheimer's disease (AD), murine models of cerebral amyloidosis are not considered to develop tau-associated pathology. In the present study, we show that tau can accumulate spontaneously in aged transgenic APPswe/PS1ΔE9 mice. Tau pathology is abundant around Aß deposits, and further characterized by accumulation of Gallyas and thioflavin-S-positive inclusions, which were detected in the APPswe/PS1ΔE9 brain at 18 months of age. Age-dependent increases in argyrophilia correlated positively with binding levels of the paired helical filament (PHF) tracer [18F]Flortaucipir, in all brain areas examined. Sarkosyl-insoluble PHFs were visualized by electron microscopy. Quantitative proteomics identified sequences of hyperphosphorylated and three-repeat tau in transgenic mice, along with signs of RNA missplicing, ribosomal dysregulation and disturbed energy metabolism. Tissue from the frontal gyrus of human subjects was used to validate these findings, revealing primarily quantitative differences between the tau pathology observed in AD patient vs. transgenic mouse tissue. As physiological levels of endogenous, 'wild-type' tau aggregate secondarily to Aß in APPswe/PS1ΔE9 mice, this study suggests that amyloidosis is both necessary and sufficient to drive tauopathy in experimental models of familial AD.

Binding characterization of N-(2-chloro-5-thiomethylphenyl)-N'-(3-[3 H]3 methoxy phenyl)-N'-methylguanidine ([3 H]GMOM), a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist.

Labeled with carbon-11, N-(2-chloro-5-thiomethylphenyl)-N'-(3-methoxyphenyl)-N'-methylguanidine ([11 C]GMOM) is currently the only positron emission tomography (PET) tracer that has shown selectivity for the ion-channel site of N-methyl-D-aspartate (NMDA) receptors in human imaging studies. The present study reports on the selectivity profile and in vitro binding properties of GMOM. The compound was screened on a panel of 80 targets, and labeled with tritium ([3 H]GMOM). The binding properties of [3 H]GMOM were compared to those of the reference ion-channel ligand [3 H](+)-dizocilpine maleate ([3 H]MK-801), in a set of concentration-response, homologous and heterologous inhibition, and association kinetics assays, performed with repeatedly washed rat forebrain preparations. GMOM was at least 70-fold more selective for NMDA receptors compared to all other targets examined. In homologous inhibition and concentration-response assays, the binding of [3 H]GMOM was regulated by NMDA receptor agonists, albeit in a less prominent manner compared to [3 H]MK-801. Scatchard transformation of homologous inhibition data produced concave upward curves for [3 H]GMOM and [3 H]MK-801. The radioligands showed bi-exponential association kinetics in the presence of 100 µmol L-1 l-glutamate/30 µmol L-1 glycine. [3 H]GMOM (3 nmol L-1 and 10 nmol L-1 ) was inhibited with dual affinity by (+)-MK-801, (R,S)-ketamine and memantine, in both presence and absence of agonists. [3 H]MK-801 (2 nmol L-1 ) was inhibited in a monophasic manner by GMOM under baseline and combined agonist conditions, with an IC50 value of ~19 nmol L-1 . The non-linear Scatchard plots, biphasic inhibition by open channel blockers, and bi-exponential kinetics of [3 H]GMOM indicate a complex mechanism of interaction with the NMDA receptor ionophore. The implications for quantifying the PET signal of [11 C]GMOM are discussed.

Age-Dependent Changes in the Sarkosyl-Insoluble Proteome of APPSWE/PS1ΔE9 Transgenic Mice Implicate Dysfunctional Mitochondria in the Pathogenesis of Alzheimer's Disease.

BACKGROUND: Alzheimer's disease (AD), the most common cause of dementia, is characterized by the intra- and extracellular aggregation and accumulation of proteins. The major molecular hallmark is the aggregation of amyloid-ß (Aß) and hyperphosphorylated tau proteins into plaques and tangles, respectively. Evidence points to the pre-fibrillary states of protein aggregates harboring the greatest neurotoxicity. OBJECTIVE: This study was designed to identify and quantify pre-fibrillary protein species enriched by their insolubility in the detergent sarkosyl in the APPSWE/PS1ΔE9 (APP/PS1) transgenic mouse model of AD. Sarkosyl insoluble fractions were isolated from the brains of APP/PS1 and littermate wild type (Wt) mice to identify pre-fibrillary protein species associated with AD. METHODS: Pre-fibrillary protein species were isolated from the brains of 3- and 24-month-old APP/PS1 and littermate Wt mice using sarkosyl extraction and subjected to quantitative proteomics analysis by the use of isobaric tags for relative and absolute quantitation (iTRAQ). RESULTS: The sarkosyl-insoluble pre-fibrillary proteome showed differential age- and genotype-induced effects. In addition to Aß and tau, old APP/PS1 mice showed significant enrichment in proteins in the sarkosyl fraction involved in oxidative phosphorylation and mitochondrial function. CONCLUSION: The results of this study implicate dysfunctional mitochondria as playing a key role of Aß- and potentially tau-induced pathological events in the APP/PS1 transgenic mouse model of AD.

Reduced Serotonin Transporter Levels and Inflammation in the Midbrain Raphe of 12 Month Old APPswe/PSEN1dE9 Mice.

BACKGROUND: Although mood and sleep disturbances are nearly universal among patients with Alzheimer's disease (AD), brain structures involved in non-cognitive processing remain under characterized in terms of AD pathology. OBJECTIVES: This study was designed to evaluate hallmarks of AD pathology in the brainstem of the APPswe/PS1dE9 mouse model of familial AD. METHODS: Fresh-frozen sections from female, 12 month old, transgenic and control B6C3 mice (n=6/genotype) were examined for amyloid burden and neurofibrillary alterations, by using 6E10 immunohistochemistry and the Gallyas silver stain, respectively. Serotonin transporter (SERT) densities in the dorsal and the median raphe were quantified by [3H]DASB autoradiography. SERT mRNA expression was measured by RT-PCR and visualized by in situ hybridization. Neuroinflammation was evaluated by immunohistochemical staining for microglia and astrocytes, and by measuring mRNA levels of the proinflammatory cytokines TNF-α, IL-1ß and IL-6. RESULTS: No amyloid- and tau-associated lesions were observed in the midbrain raphe of 12 month old APPswe/PS1dE9 mice. SERT binding levels were reduced in transgenic animals compared to age-matched controls, and SERT mRNA levels were decreased by at least 50% from control values. Intense microglial, but not astrocytic immunoreactivity was observed in APPswe/PS1dE9 vs. wild-type mice. Levels of TNF-α mRNA were two-fold higher than control and correlated positively with SERT mRNA expression levels in transgenic animals. CONCLUSIONS: There was no amyloid accumulation and tau-associated pathology in the midbrain raphe of 12 month old APPswe/PS1dE9 mice. However, there was a local neuroinflammatory response with loss of serotonergic markers, which may partially account for some of the behavioral symptoms of AD.

Established amyloid-ß pathology is unaffected by chronic treatment with the selective serotonin reuptake inhibitor paroxetine.

INTRODUCTION: Treatment with selective serotonin reuptake inhibitors has been suggested to mitigate amyloid-ß (Aß) pathology in Alzheimer's disease, in addition to an antidepressant mechanism of action. METHODS: We investigated whether chronic treatment with paroxetine, a selective serotonin reuptake inhibitor, mitigates Aß pathology in plaque-bearing double-transgenic amyloid precursor protein (APP)swe/presenilin 1 (PS1)ΔE9 mutants. In addition, we addressed whether serotonin depletion affects Aß pathology. Treatments were assessed by measurement of serotonin transporter occupancy and high-performance liquid chromatography. The effect of paroxetine on Aß pathology was evaluated by stereological plaque load estimation and Aß42/Aß40 ratio by enzyme-linked immunosorbent assay. RESULTS: Contrary to our hypothesis, paroxetine therapy did not mitigate Aß pathology, and depletion of brain serotonin did not exacerbate Aß pathology. However, chronic paroxetine therapy increased mortality in APPswe/PS1ΔE9 transgenic mice. DISCUSSION: Our results question the ability of selective serotonin reuptake inhibitor therapy to ameliorate established Aß pathology. The severe adverse effect of paroxetine may discourage its use for disease-modifying purposes in Alzheimer's disease.

First in human evaluation of [18F]PK-209, a PET ligand for the ion channel binding site of NMDA receptors.

BACKGROUND: Efforts to develop suitable positron emission tomography (PET) tracers for the ion channel site of human N-methyl-D-aspartate (NMDA) receptors have had limited success. [18F]PK-209 is a GMOM derivative that binds to the intrachannel phencyclidine site with high affinity and selectivity. Primate PET studies have shown that the volume of distribution in the brain was reduced by administration of the NMDA receptor antagonist MK-801, consistent with substantial specific binding. The purpose of the present study was to evaluate [18F]PK-209 in 10 healthy humans by assessing test-retest reproducibility and binding specificity following intravenous S-ketamine administration (0.5 mg âˆ™ kg-1). Five healthy subjects underwent a test-retest protocol, and five others a baseline-ketamine protocol. In all cases dynamic, 120-min PET scans were acquired together with metabolite-corrected arterial plasma input functions. Additional input functions were tested based on within-subject and population-average parent fractions. RESULTS: Best fits of the brain time-activity curves were obtained using an irreversible two-tissue compartment model with additional blood volume parameter. Mean test-retest variability of the net rate of influx Ki varied between 7 and 24% depending on the input function. There were no consistent changes in [18F]PK-209 PET parameters following ketamine administration, which may be a consequence of the complex endogenous ligand processes that affect channel gating. CONCLUSIONS: The molecular interaction between [18F]PK-209 and the binding site within the NMDA receptor ion channel is insufficiently reproducible and specific to be a reliable imaging agent for its quantification. TRIAL REGISTRATION: EudraCT 2014-001735-36. Registered 28 April 2014.