Temporal progression of tau pathology and neuroinflammation in a rhesus monkey model of Alzheimer's disease.

INTRODUCTION: The understanding of the pathological events in Alzheimer's disease (AD) has advanced dramatically, but the successful translation from rodent models into efficient human therapies is still problematic. METHODS: To examine how tau pathology can develop in the primate brain, we injected 12 macaques with a dual tau mutation (P301L/S320F) into the entorhinal cortex (ERC). An investigation was performed using high-resolution microscopy, magnetic resonance imaging (MRI), positron emission tomography (PET), and fluid biomarkers to determine the temporal progression of the pathology 3 and 6 months after the injection. RESULTS: Using quantitative microscopy targeting markers for neurodegeneration and neuroinflammation, as well as fluid and imaging biomarkers, we detailed the progression of misfolded tau spreading and the consequential inflammatory response induced by glial cells. DISCUSSION: By combining the analysis of several in vivo biomarkers with extensive brain microscopy analysis, we described the initial steps of misfolded tau spreading and neuroinflammation in a monkey model highly translatable to AD patients. HIGHLIGHTS: Dual tau mutation delivery in the entorhinal cortex induces progressive tau pathology in rhesus macaques. Exogenous human 4R-tau coaptates monkey 3R-tau during transneuronal spread, in a prion-like manner. Neuroinflammatory response is coordinated by microglia and astrocytes in response to tau pathology, with microglia targeting early tau pathology, while astrocytes engaged later in the progression, coincident with neuronal death. Monthly collection of CSF and plasma revealed a profile of changes in several AD core biomarkers, reflective of neurodegeneration and neuroinflammation as early as 1 month after injection.

In vitro and in vivo pharmacological characterization of dasotraline, a dual dopamine and norepinephrine transporter inhibitor in vivo.

Inhibitors of dopamine transporters (DAT), norepinephrine transporters (NET) and serotonin transporters (SERT) are effective treatments for neuropsychiatric diseases. Dasotraline [(1R,4 S)- 4-(3,4-dichlorophenyl)- 1,2,3,4-tetrahydro-1-naphthalenamine, also known as SEP-225289) was evaluated for its inhibitory potency at DAT, NET and SERT using in vitro and in vivo assays. In vitro radiometric functional uptake studies showed preferential inhibition by dasotraline of hDAT (IC50 =3 nM) and hNET (IC50 =4 nM relative to hSERT(IC50 =15 nM). In mouse ex vivo occupancy studies, dasotraline demonstrated total plasma concentration-dependent occupancy at DAT, NET and SERT. Determination of the TO50 (50% transporter occupancy) were 32, 109 and 276 ng/ml, respectively. In SPECT imaging studies in baboons, dasotraline (0.2 mg/kg iv) displaced radiotracer binding to DAT by 87% but only 20% at NET and SERT. Rat microdialysis studies were performed in prefrontal cortex and striatum. Dasotraline produced sustained (>4 h) increases in dopamine and norepinephrine concentrations. Dasotraline was also more potent at increasing synaptic dopamine in the striatum, and norepinephrine in the prefrontal cortex than serotonin in these regions. In summary, dasotraline preferentially inhibits DAT and NET relative to SERT. Together, the occupancy and neurochemical profile of dasotraline provide a mechanistic basis for the treatment of diseases that have an underlying causality involving dopamine and norepinephrine dysfunction.

Safety, pharmacokinetics and pharmacodynamics of TAK-418, a novel inhibitor of the epigenetic modulator lysine-specific demethylase 1A.

AIMS: Dysregulation of histone methylation epigenetic marks may result in intellectual and developmental disability, as seen in Kabuki syndrome. Animal data suggest that increasing histone methylation by inhibiting lysine-specific demethylase 1A (LSD1) may improve cognitive outcomes in a model of Kabuki syndrome. TAK-418 is a novel LSD1 inhibitor, developed as a potential therapeutic agent for central nervous system disorders such as Kabuki syndrome. Here, we report safety, tolerability, pharmacokinetic and pharmacodynamic profiles of single and multiple doses of TAK-418 (ClinicalTrials.gov: NCT03228433, NCT03501069). METHODS: Two randomized, double-blind, placebo-controlled, phase 1 studies of oral TAK-418 were performed, a first-in-human single-rising-dose (SRD) study (5-60 mg) in healthy adult male and female volunteers (placebo, n = 10; TAK-418, n = 30), and an SRD (120-160 mg) and multiple-rising-dose (MRD) study (20-160 mg once daily for 10 days) in healthy female volunteers (placebo, n = 2 [SRD] and n = 6 [MRD]; TAK-418, n = 6 [SRD] and n = 18 [MRD]). RESULTS: TAK-418 was well tolerated. No clinically significant changes in laboratory test results or vital signs were observed and no serious adverse events were reported. TAK-418 had a nearly linear pharmacokinetic profile, with rapid absorption and short terminal half-life across the evaluated dose range. No obvious accumulation was observed after daily administration for 10 days. Administration with food delayed peak plasma concentrations but overall exposure was unaffected. TAK-418 rapidly crossed the blood-brain barrier and generally showed a dose-dependent response in the peripheral pharmacodynamic biomarker formyl-flavin adenine dinucleotide. CONCLUSION: The brain-penetrant LSD1 inhibitor TAK-418 was well tolerated, with pharmacokinetic and pharmacodynamic effects that support further investigation.

Assessment of brain cholesterol metabolism biomarker 24S-hydroxycholesterol in schizophrenia.

Plasma 24S-hydroxycholesterol mostly originates in brain tissue and likely reflects the turnover of cholesterol in the central nervous system. As cholesterol is disproportionally enriched in many key brain structures, 24S-hydroxycholesterol is a promising biomarker for psychiatric and neurologic disorders that impact brain structure. We hypothesized that, as schizophrenia patients have widely reported gray and white matter deficits, they would have abnormal levels of plasma 24S-hydroxycholesterol, and that plasma levels of 24S-hydroxycholesterol would be associated with brain structural and functional biomarkers for schizophrenia. Plasma levels of 24S-hydroxycholesterol were measured in 226 individuals with schizophrenia and 204 healthy controls. The results showed that levels of 24S-hydroxycholesterol were not significantly different between patients and controls. Age was significantly and negatively correlated with 24S-hydroxycholesterol in both groups, and in both groups, females had significantly higher levels of 24S-hydroxycholesterol compared to males. Levels of 24S-hydroxycholesterol were not related to average fractional anisotropy of white matter or cortical thickness, or to cognitive deficits in schizophrenia. Based on these results from a large sample and using multiple brain biomarkers, we conclude there is little to no value of plasma 24S-hydroxycholesterol as a brain metabolite biomarker for schizophrenia.

CoREST Complex-Selective Histone Deacetylase Inhibitors Show Prosynaptic Effects and an Improved Safety Profile To Enable Treatment of Synaptopathies.

Synaptic dysfunction is a pathological feature in many neurodegenerative disorders, including Alzheimer's disease, and synaptic loss correlates closely with cognitive decline. Histone deacetylases (HDACs) are involved in chromatin remodeling and gene expression and have been shown to regulate synaptogenesis and synaptic plasticity, thus providing an attractive drug discovery target for promoting synaptic growth and function. To date, HDAC inhibitor compounds with prosynaptic effects are plagued by known HDAC dose-limiting hematological toxicities, precluding their application to treating chronic neurologic conditions. We have identified a series of novel HDAC inhibitor compounds that selectively inhibit the HDAC-co-repressor of repressor element-1 silencing transcription factor (CoREST) complex while minimizing hematological side effects. HDAC1 and HDAC2 associate with multiple co-repressor complexes including CoREST, which regulates neuronal gene expression. We show that selectively targeting the CoREST co-repressor complex with the representative compound Rodin-A results in increased spine density and synaptic proteins, and improved long-term potentiation in a mouse model at doses that provide a substantial safety margin that would enable chronic treatment. The CoREST-selective HDAC inhibitor Rodin-A thus represents a promising therapeutic strategy in targeting synaptic pathology involved in neurologic disorders.

Fosmetpantotenate (RE-024), a phosphopantothenate replacement therapy for pantothenate kinase-associated neurodegeneration: Mechanism of action and efficacy in nonclinical models.

In cells, phosphorylation of pantothenic acid to generate phosphopantothenic acid by the pantothenate kinase enzymes is the first step in coenzyme A synthesis. Pantothenate kinase 2, the isoform localized in neuronal cell mitochondria, is dysfunctional in patients with pantothenate kinase-associated neurodegeneration. Fosmetpantotenate is a phosphopantothenic acid prodrug in clinical development for treatment of pantothenate kinase-associated neurodegeneration, which aims to replenish phosphopantothenic acid in patients. Fosmetpantotenate restored coenzyme A in short-hairpin RNA pantothenate kinase 2 gene-silenced neuroblastoma cells and was permeable in a blood-brain barrier model. The rate of fosmetpantotenate metabolism in blood is species-dependent. Following up to 700 mg/kg orally, blood exposure to fosmetpantotenate was negligible in rat and mouse, but measurable in monkey. Consistent with the difference in whole blood half-life, fosmetpantotenate dosed orally was found in the brains of the monkey (striatal dialysate) but was absent in mice. Following administration of isotopically labeled-fosmetpantotenate to mice, ~40% of liver coenzyme A (after 500 mg/kg orally) and ~50% of brain coenzyme A (after 125 µg intrastriatally) originated from isotopically labeled-fosmetpantotenate. Additionally, 10-day dosing of isotopically labeled-fosmetpantotenate, 12.5 µg, intracerebroventricularly in mice led to ~30% of brain coenzyme A containing the stable isotopic labels. This work supports the hypothesis that fosmetpantotenate acts to replace reduced phosphopantothenic acid in pantothenate kinase 2-deficient tissues.

Pharmacological evaluation of a novel phosphodiesterase 10A inhibitor in models of antipsychotic activity and cognition.

In this study, we report the pharmacological effects of a novel PDE10A inhibitor, SEP-39. SEP-39 is a potent (1.0nM) inhibitor of human PDE10A in vitro, with good selectivity (>16000-fold) against other PDEs. In an in vivo occupancy study, the RO50 value was determined to be 0.7mg/kg (p.o.), corresponding to plasma and brain exposures of 28ng/mL and 43ng/g, respectively. Using microdialysis, we show that 3mg/kg (p.o.) SEP-39 significantly increased rat striatal cGMP concentrations. Furthermore, SEP-39 inhibits PCP-induced hyperlocomotion at doses of 1 and 3mg/kg (p.o.) corresponding to 59-86% occupancy. At similar doses in a catalepsy study, the time on the bar was increased but the maximal effect was less than that seen with haloperidol. In an EEG study, 3 and 10mg/kg (p.o.) SEP-39 suppressed REM intensity and increased the latency to REM sleep. We also demonstrate the procognitive effects of SEP-39 in the rat novel object recognition assay. These effects appear to require less PDE10A inhibition than the reversal of PCP-induced hyperlocomotion or EEG effects, as improvements in recognition index were seen at doses of 0.3mg/kg and above. Our data demonstrate that SEP-39 is a potent, orally active PDE10A inhibitor with therapeutic potential in a number of psychiatric indications.

Differential BDNF responses of triple versus dual reuptake inhibition in neuronal and astrocytoma cells as well as in rat hippocampus and prefrontal cortex.

Monoamine reuptake inhibitors increase brain-derived neurotrophic factor (BDNF) activity, and this growth factor is regarded as an interesting target for developing new antidepressant drugs. The aims of this study were to evaluate whether monoaminergic reuptake inhibition increases BDNF in vivo and in vitro as predicted by the neurotrophic hypothesis of depression, and whether triple reuptake inhibition has a superior BDNF response compared to dual reuptake inhibition. Twenty-one days of oral treatment (30 mg/kg) with the dual serotonin/noradrenaline reuptake inhibitor duloxetine or the triple serotonin/noradrenaline/dopamine reuptake inhibitor DOV 216,303 restored BDNF protein levels in the rat hippocampus, which were initially decreased due to injection stress. The prefrontal cortex contained increased BDNF levels only after DOV 216,303 treatment. In vitro, neither duloxetine nor DOV 216,303 altered intracellular BDNF levels in murine HT22 neuronal cells. In contrast, BDNF release was more effectively decreased following treatment with DOV 216,303 in these cells. In rat C62B astrocytomas, both antidepressants increased intracellular BDNF levels at their highest nontoxic concentration. C62B astrocytomas did not release BDNF, even after antidepressant treatment. Increased BDNF levels support the neurotrophic hypothesis of depression, but our findings do not clearly evidence that the BDNF response after triple reuptake inhibitors is more effective than after dual reuptake inhibitors. Moreover, the data suggest that the role of BDNF in neurons and astrocytes is complex and likely depends on factors including specificity of cell types in different brain regions, cell-cell interactions, and different mechanisms of action of antidepressants used.

Design, synthesis, and structure-activity relationships of novel bicyclic azole-amines as negative allosteric modulators of metabotropic glutamate receptor 5.

A novel series of diaryl bicyclic azole-amines that are potent selective negative modulators of metabotropic glutamate receptor 5 (mGluR5) were identified through rational design. An initial hit compound 5a of modest potency (IC(50) = 1.2 µM) was synthesized. Evaluation of structure-activity relationships (SAR) on the left-hand side of the molecule revealed a preference for a 2-substituted pyridine group linked directly to the central heterocycle. Variation of the central azolo-amine portion of the molecule revealed a preference for the [4,5-c]-oxazoloazepine scaffold, while right-hand side variants showed a preference for ortho- and meta-substituted benzene rings linked directly to the tertiary amine of the saturated heterocycle. These iterations led to the synthesis of 29b, a potent (IC(50) = 16 nM) and selective negative modulator that showed good brain penetrance, high receptor occupancy, and a duration of action greater than 1 h in rat when administered intraperitoneally. Formal PK studies in rat and Rhesus monkey revealed a short half-life that was attributable to high first-pass clearance.

The putative antidepressant DOV 216,303, a triple reuptake inhibitor, increases monoamine release in the prefrontal cortex of olfactory bulbectomized rats.

The first line of antidepressant treatment nowadays are selective serotonin reuptake inhibitors. Although they are relatively safe to use, selective serotonin reuptake inhibitors (SSRIs) can induce severe side effects. New promising antidepressants may be the triple monoamine reuptake inhibitors, which not only enhance serotonin and norepinephrine neurotransmission, but also increase brain dopamine levels. Recently it has been shown that one of the triple reuptake inhibitors, DOV 216,303 has antidepressant-like effects in the olfactory bulbectomy (OBX) model of depression, but the alterations in monoaminergic neurotransmission in these animals are still unknown. In the present study we investigated not only the effect of acute, but also chronic treatment of DOV 216,303 in OBX rats on monoamine and metabolite levels. The main results are decreased baseline dopamine levels in the prefrontal cortex one day after OBX, while 38days after OBX no difference could be observed in monoamine levels after vehicle treatment. Treatment with DOV 216,303 leads to increased extracellular levels of serotonin and norepinephrine neurotransmission, but also increased dopamine levels in OBX animals as well as their controls. This increase could be observed after one single administration, but also after chronic treatment. However, a DOV 216,303 challenge in chronically treated animals resulted in lower monoamine concentrations than the same challenge in untreated animals. More research is needed to investigate this seemingly hyporesponsivity to chronic DOV 216,303 treatment.

Dynamic changes in vesicular glutamate transporter 1 function and expression related to methamphetamine-induced glutamate release.

The vesicular glutamate (GLU) transporter (VGLUT1) is a critical component of glutamatergic neurons that regulates GLU release. Despite the likely role of GLU release in drug abuse pathology, there is no information that links VGLUT1 with drugs of abuse. This study provides the first evidence that methamphetamine (METH) alters the dynamic regulation of striatal VGLUT1 function and expression through a polysynaptic pathway. METH increases cortical VGLUT1 mRNA, striatal VGLUT1 protein in subcellular fractions, and the Vmax of striatal vesicular GLU uptake. METH also increases glyceraldehyde-3-phosphate dehydrogenase (GAPDH) protein in the crude vesicle fraction. METH-induced increases in cortical VGLUT1 mRNA, as well as striatal VGLUT1 and GAPDH, are GABA(A) receptor-dependent because they are blocked by GABA(A) receptor antagonism in the substantia nigra. These results show that VGLUT1 can be dynamically regulated via a polysynaptic pathway to facilitate vesicular accumulation of GLU for subsequent release after METH.

Causes and consequences of methamphetamine and MDMA toxicity.

Methamphetamine (METH) and its derivative 3,4-methylenedioxymethamphetamine (MDMA; ecstasy) are 2 substituted amphetamines with very high abuse liability in the United States. These amphetamine-like stimulants have been associated with loss of multiple markers for dopaminergic and serotonergic terminals in the brain. Among other causes, oxidative stress, excitotoxicity and mitochondrial dysfunction appear to play a major role in the neurotoxicity produced by the substituted amphetamines. The present review will focus on these events and how they interact and converge to produce the monoaminergic depletions that are typically observed after METH or MDMA administration. In addition, more recently identified consequences of METH or MDMA-induced oxidative stress, excitotoxicity, and mitochondrial dysfunction are described in relation to the classical markers of METH-induced damage to dopamine terminals.

Methamphetamine-induced inhibition of mitochondrial complex II: roles of glutamate and peroxynitrite.

High-dose methamphetamine (METH) is associated with long-term deficits in dopaminergic systems. Although the mechanism(s) which contributes to these deficits is not known, glutamate and peroxynitrite are likely to play a role. These factors are hypothesized to inhibit mitochondrial function, increasing the free radical burden and decreasing neuronal energy supplies. Previous studies suggest a role for the mitochondrial electron transport chain (ETC) in mediating toxicity of METH. The purpose of the present studies was to determine whether METH administration selectively inhibits complex II of the ETC in rats. High-dose METH administration (10 mg/kg every 2 h x 4) rapidly (within 1 h) decreased complex II (succinate dehydrogenase) activity by approximately 20-30%. In addition, decreased activity of complex II-III, but not complex I-III, of the mitochondrial ETC was also observed 24 h after METH. This inhibition was not due to direct inhibition by METH or METH-induced hyperthermia and was specific to striatal brain regions. METH-induced decreases in complex II-III were prevented by MK-801 and the peroxynitrite scavenger 5,10,15,20-tetrakis (2,4,6-trimethyl-3,5-sulphonatophenyl) porphinato iron III. These findings provide the first evidence that METH administration, via glutamate receptor activation and peroxynitrite formation, selectively alters a specific site of the ETC.