Monoamine oxidase binding not expected to significantly affect [18F]flortaucipir PET interpretation.

PURPOSE: [18F]-labeled positron emission tomography (PET) radioligands permit in vivo assessment of Alzheimer's disease biomarkers, including aggregated neurofibrillary tau (NFT) with [18F]flortaucipir. Due to structural similarities of flortaucipir with some monoamine oxidase A (MAO-A) inhibitors, this study aimed to evaluate flortaucipir binding to MAO-A and MAO-B and any potential impact on PET interpretation. METHODS: [18F]Flortaucipir autoradiography was performed on frozen human brain tissue slices, and PET imaging was conducted in rats. Dissociation constants were determined by saturation binding, association and dissociation rates were measured by kinetic binding experiments, and IC50 values were determined by competition binding. RESULTS: Under stringent wash conditions, specific [18F]flortaucipir binding was observed on tau NFT-rich Alzheimer's disease tissue and not control tissue. In vivo PET experiments in rats revealed no evidence of [18F]flortaucipir binding to MAO-A; pre-treatment with MAO inhibitor pargyline did not impact uptake or wash-out of [18F]flortaucipir. [18F]Flortaucipir bound with low nanomolar affinity to human MAO-A in a microsomal preparation in vitro but with a fast dissociation rate relative to MAO-A ligand fluoroethyl-harmol, consistent with no observed in vivo binding in rats of [18F]flortaucipir to MAO-A. Direct binding of flortaucipir to human MAO-B was not detected in a microsomal preparation. A high concentration of flortaucipir (IC50 of 1.3 µM) was found to block binding of the MAO-B ligand safinamide to MAO-B on microsomes suggesting that, at micromolar concentrations, flortaucipir weakly binds to MAO-B in vitro. CONCLUSION: These data suggest neither MAO-A nor MAO-B binding will contribute significantly to the PET signal in cortical target areas relevant to the interpretation of [18F]flortaucipir.

Use of the PET ligand florbetapir for in vivo imaging of pancreatic islet amyloid deposits in hIAPP transgenic mice.

AIMS/HYPOTHESIS: Islet amyloid deposits contribute to beta cell dysfunction and death in most individuals with type 2 diabetes but non-invasive methods to determine the presence of these pathological protein aggregates are currently not available. Therefore, we examined whether florbetapir, a radiopharmaceutical agent used for detection of amyloid-ß deposits in the brain, also allows identification of islet amyloid in the pancreas. METHODS: Saturation binding assays were used to determine the affinity of florbetapir for human islet amyloid polypeptide (hIAPP) aggregates in vitro. Islet amyloid-prone transgenic mice that express hIAPP in their beta cells and amyloid-free non-transgenic control mice were used to examine the ability of florbetapir to detect islet amyloid deposits in vitro, in vivo and ex vivo. Mice or mouse pancreases were subjected to autoradiographic, histochemical and/or positron emission tomography (PET) analyses to assess the utility of florbetapir in identifying islet amyloid. RESULTS: In vitro, florbetapir bound synthetic hIAPP fibrils with a dissociation constant of 7.9 nmol/l. Additionally, florbetapir bound preferentially to amyloid-containing hIAPP transgenic vs amyloid-free non-transgenic mouse pancreas sections in vitro, as determined by autoradiography (16,475 ± 5581 vs 5762 ± 575 density/unit area, p < 0.05). In hIAPP transgenic and non-transgenic mice fed a high-fat diet for 1 year, intravenous administration of florbetapir followed by PET scanning showed that the florbetapir signal was significantly higher in amyloid-laden hIAPP transgenic vs amyloid-free non-transgenic pancreases in vivo during the first 5 min of the scan (36.83 ± 2.22 vs 29.34 ± 2.03 standardised uptake value × min, p < 0.05). Following PET, pancreases were excised and florbetapir uptake was determined ex vivo by γ counting. Pancreatic uptake of florbetapir was significantly correlated with the degree of islet amyloid deposition, the latter assessed by histochemistry (r = 0.74, p < 0.001). CONCLUSIONS/INTERPRETATION: Florbetapir binds to islet amyloid deposits in a specific and quantitative manner. In the future, florbetapir may be useful as a non-invasive tool to identify islet amyloid deposits in humans.

A rapid gene delivery-based mouse model for early-stage Alzheimer disease-type tauopathy.

The perforant pathway projection from the entorhinal cortex (EC) to the hippocampal dentate gyrus is critically important for long-term memory and develops tau and amyloid pathologies and progressive degeneration starting in the early stages of Alzheimer disease (AD). However, perforant pathway function has not been assessed in experimental models of AD, and a therapeutic agent that protects its structure and function has not yet been identified. Therefore, we developed a new adeno-associated virus-based mouse model for perforant pathway tauopathy. Microinjection into the lateral EC of vectors designed to express either human tau bearing a pathogenic P301L mutation or enhanced green fluorescent protein as a control selectively drove transgene expression in lateral EC layer II perikarya and along the entire rostrocaudal extent of the lateral perforant pathway afferents and dentate terminal field. After human tau expression, hyperphosphorylated tau accumulated only within EC layer II perikarya, thereby modeling Braak stage I of transentorhinal AD tauopathy. Expression of pathologic human tau but not enhanced green fluorescent protein led to specific dose-dependent apoptotic death of perforant pathway neurons and loss of synapses in as little as 2 weeks. This novel adeno-associated virus-based method elicits rapid tauopathy and tau-mediated neurodegeneration localized to the mouse perforant pathway and represents a new experimental approach for studying tau-driven pathogenic processes and tau-based treatment strategies in a highly vulnerable neural circuit.

Wake-promoting agents: search for next generation modafinil: part IV.

In search of a next generation molecule to the novel wake promoting agent modafinil, a series of diphenyl ether derived wakefulness enhancing agents (in rat) was developed. From this work, racemic compound 16 was separated into its chiral enantiomers to profile them individually.

Amyloid deposition and advanced age fails to induce Alzheimer's type progression in a double knock-in mouse model.

It has been challenging to develop transgenic and gene-targeted mouse models that recapitulate all of the neuropathological features of Alzheimer's disease (AD). For example, in the APP/PS-1 double knock-in mutant mouse (DKI), frank neurodegeneration is not observed at middle age and synapse loss is pronounced only within amyloid plaques. Here, we investigated whether continued amyloid deposition and advanced age of 24-27 months lead to loss of neurons and synapses, tau hyperphosphorylation, and other pathological features of AD. We focused on the perforant pathway projection from entorhinal cortex to hippocampal dentate gyrus, since it is preferentially impacted by plaques, tangles, and neuronal loss early in the course of AD. Compared with wild type controls matched for age and gender, expression of neither reelin nor NeuN was altered in the entorhinal layer 2 neurons of origin. Retrograde labeling of the perforant pathway with Fluorogold indicated no cell loss, axonal atrophy, or nerve terminal degeneration. The lack of neuronal loss or atrophy was confirmed by volumetric analysis of the ventral dentate gyrus and immunostaining for a synaptic marker. We also searched for other hallmarks of AD neuropathology by labeling for hyperphosphorylated pre-tangle tau, accumulation of cathepsin D-containing autolysosomes, and cyclin A-positive neurons aberrantly re-entering the cell cycle. None of these AD pathologies were observed in the entorhinal cortex, dentate gyrus, or any other forebrain region. Our results indicate that the DKI mouse does not show appreciable Alzheimer-type disease progression, even at advanced age and in the phase of over 18 months of robust cerebral amyloid deposition. The insufficiency of amyloid deposition to induce other AD-type neuropathologies and neurodegeneration in the aging mouse brain suggests an important role for tauopathy or other factors for triggering the pathogenesis of AD.

Wake promoting agents: search for next generation modafinil, lessons learned: part III.

In searching for a next generation molecule to the novel wake promoting agent modafinil (compound 1), a series of fluorene-derived wakefulness enhancing agents were developed and evaluated in rat. Extensive pharmacokinetic studies of a potent member of the series (compound 15) revealed that the wake promotion activity of the analog was likely due to an active metabolite (compound 3).

Wake-promoting agents: search for next generation modafinil: part II.

In search of a next generation molecule to modafinil, a novel wake promoting agent, we previously disclosed bi-phenyl derived racemate compound (±)-2 as a new generation of wake-promoting agent. Here we describe the profiles of the individual enantiomers (-)-2 and (+)-2, respectively.

Wake-promoting agents: search for next generation modafinil: part I.

In search of a next generation molecule to the novel wake promoting agent modafinil, a series of bi-phenyl derived wakefulness enhancing agents (in rat) was developed. From this work, compound 17 has been selected for additional studies.

Identification of pyridazin-3-one derivatives as potent, selective histamine H3 receptor inverse agonists with robust wake activity.

H(3)R structure-activity relationships on a novel class of pyridazin-3-one H(3)R antagonists/inverse agonists are disclosed. Modifications of the pyridazinone core, central phenyl ring and linker led to the identification of molecules with excellent target potency, selectivity and pharmacokinetic properties. Compounds 13 and 21 displayed potent functional H(3)R antagonism in vivo in the rat dipsogenia model and demonstrated robust wake activity in the rat EEG/EMG model.

The roles of dopamine transport inhibition and dopamine release facilitation in wake enhancement and rebound hypersomnolence induced by dopaminergic agents.

STUDY OBJECTIVE: Rebound hypersomnolence (RHS: increased sleep following increased wake) is a limiting side-effect of many wake-promoting agents. In particular, RHS in the first few hours following wake appears to be associated with dopamine (DA)-releasing agents, e.g., amphetamine, but whether it can also be produced by DA transporter (DAT) inhibition alone is unknown. In these studies, DA-releasing and DAT-inhibiting agents and their interaction were systematically examined for their ability to increase wake and induce RHS. DESIGN: Chronically implanted rats were evaluated in a blinded, pseudo-randomized design. PARTICIPANTS: 237 rats were used in these studies with 1 week between repeat tests. INTERVENTIONS: Animals were habituated overnight and dosed the next day, 5 h after lights on, with test agents. MEASUREMENTS AND RESULTS: Sleep/wake activityand RHS were evaluated using EEG/EMG recording up to 22 h post dosing. In vitro dopamine release was evaluated in rat synaptosomes. At doses that produced equal increases in wake, DA-releasing (amphetamine, methamphetamine, phentermine) and several DAT-inhibiting agents (cocaine, bupropion, and methylphenidate) produced RHS during the first few hours after the onset of sleep recovery. However, other DAT-inhibiting agents (mazindol, nomifensine, GBR-12909, and GBR-12935) did not produce RHS. Combination treatment with amphetamine and nomifensine produced waking activity greater than the sum of their individual activities alone while ameliorating the amphetamine-like RHS. In rat synaptosomes, nomifensine reduced the potency of amphetamine to induce DA release approximately 270-fold, potentially explaining its action in ameliorating amphetamine-induced RHS. CONCLUSIONS: All DA releasing agents tested, and some DAT-inhibiting agents, produced RHS at equal wake-promoting doses. Thus amphetamine-like DA release appears sufficient for inducing RHS, but additional properties (pharmacologic and/or pharmacokinetic) evidently underlie RHS of other DAT inhibitors. Enhancing wake while mitigating RHS can be achieved by combining DAT-inhibiting and DA-releasing agents.

Armodafinil promotes wakefulness and activates Fos in rat brain.

Modafinil increases waking and labeling of Fos, a marker of neuronal activation. In the present study, armodafinil, the R-enantiomer of racemic modafinil, was administered to rats at 30 or 100 mg/kg i.p. about 5 h after lights on (circadian time 5 and near the midpoint of the sleep phase of the sleep:wake cycle) to assess its effects on sleep/wake activity and Fos activation. Armodafinil at 100 mg/kg increased wakefulness for 2 h, while 30 mg/kg armodafinil only briefly increased wakefulness. Armodafinil (30 and 100 mg/kg) also increased latencies to the onset of sleep and motor activity. Armodafinil had differential effects in increasing neuronal Fos immunolabeling 2 h after administration. Armodafinil at 100 mg/kg increased numbers of Fos-labeled neurons in striatum and anterior cingulate cortex, without affecting nucleus accumbens. Armodafinil at 30 mg/kg only increased numbers of light Fos-labeled neurons in the anterior cingulate cortex. In brainstem arousal centers, 100 mg/kg armodafinil increased numbers of Fos-labeled neurons in the tuberomammillary nucleus, pedunculopontine tegmentum, laterodorsal tegmentum, locus coeruleus, and dorsal raphe nucleus. Fos activation of these brainstem arousal centers, as well as of the cortex and striatum, is consistent with the observed arousal effects of armodafinil.

A transgenic rat model of Alzheimer's disease with extracellular Abeta deposition.

Many transgenic mouse models of Alzheimer's disease (AD) that deposit amyloid (Abeta) have been produced, but development of an Abeta-depositing rat model has not been successful. Here, we describe a rat model with extracellular fibrillar Abeta deposition. Two lines of Sprague Dawley rats with transgenes expressing human amyloid precursor protein (APP) with the familial AD (FAD) mutations K670N/M671L and K670N/M671L/V717I were crossed. Abeta production in the double homozygous rats was sufficient for deposition by 17-18 months of age. The age of onset of Abeta deposition was reduced by crossing in a third rat line carrying a human presenilin-1 (PS-1) transgene with the FAD M146V mutation. The triple homozygous line had an onset of Abeta deposition by 7 months of age. Deposits appeared similar to those observed in the mouse models and displayed surrounding glial and phosphorylated tau reactivity. Abeta levels measured by ELISA were comparable to those reported in mouse models, suggesting that substantially greater amounts of soluble Abeta are not required in the rat to generate Abeta deposition.

FAD mutant PS-1 gene-targeted mice: increased A beta 42 and A beta deposition without APP overproduction.

To investigate the consequences of mutant presenilin-1 (PS-1) expression under the control of the normal PS-1 gene, a gene-targeted mouse bearing the FAD mutation P264L was made. Gene-targeted models are distinct from transgenic models because the mutant gene is expressed at normal levels, in the absence of the wild-type protein. PS-1(P264L/P264L) mice had normal expression of PS-1 mRNA, but levels of the N- and C-terminal protein fragments of PS-1 were reduced while levels of the holoprotein were increased. When crossed into Tg(HuAPP695.K670N/M671L)2576 mice, the PS-1(P264L) mutation accelerated the onset of amyloid (Abeta) deposition in a gene-dosage dependent manner. Tg2576/PS-1(P264L/P264L) mice also had Abeta deposition that was widely distributed throughout the brain and spinal cord. APP(NLh/NLh)/PS-1(P264L/P264L) double gene-targeted mice had elevated levels of Abeta42, sufficient to cause Abeta deposition beginning at 6 months of age. Abeta deposition increased linearly over time in APP(NLh/NLh)/PS-1(P264L/P264L) mice, whereas the increase in Tg2576 mice was exponential. The APP(NLh/NLh)/PS-1(P264L/P264L) double gene-targeted mouse represents an animal model that exhibits Abeta deposition without overexpression of APP.

Activation of c-Jun N-terminal kinase and p38 in an Alzheimer's disease model is associated with amyloid deposition.

The mechanisms by which neurons and synapses are lost in Alzheimer's disease (AD) are not completely understood. To characterize potential signaling events linked to AD pathogenesis, activation-specific antibodies were used to examine mitogen-activated protein kinase (MAPK) kinase pathways at various ages in mice transgenic for human amyloid precursor protein-695 with the Swedish familial AD mutations (Tg2576) and homozygous for a P264L familial AD mutation introduced by targeting of the presenilin-1 gene (PS1(P264L)). Although the c-Jun N-terminal kinase (JNK) and p38 pathways were significantly activated in the cortex at both 7 and 12 months of age, there was no significant activation of the extracellular signal-regulated kinase pathway. MAPK kinase-4, an upstream activator of JNK, was also significantly activated at 7 and 12 months, whereas c-Jun, a downstream effector of JNK-associated apoptotic signaling, was not induced. The lack of c-Jun activation is consistent with the absence of neuronal loss in both cortex and hippocampal CA1 at 12 months. The JNK activation was localized to amyloid deposits, within neurites containing phosphorylated tau. Synaptophysin was quantified biochemically as a measure of synaptic integrity and was significantly reduced in an age-dependent manner in the Tg2576/PS1(P264L) cortex but not in either PS1(P264L) or Tg2576 cortex. Stress-responsive MAP kinase pathways were activated in the brain of the Tg2576/PS1(P264L) AD model, and this activation was coincident with the age-dependent increase in amyloid deposition, tau phosphorylation, and loss of synaptophysin.