Vincenzo Libri

Interaction of the amyloid imaging tracer FDDNP with hallmark Alzheimer’s disease pathologies

The distinctive cortical uptake of the tracer 18F‐FDDNP (2‐(1‐{6‐[(2‐fluoroethyl(methyl)amino]‐2‐naphthyl}ethylidene)malononitrile) in Alzheimer’s disease (AD) is believed to be because of its binding to both neurofibrillary tangles (NFTs) and highly fibrillar senile plaques. We therefore investigated the binding of a tracer concentration of 3H‐FDDNP to brain sections containing AD hallmark pathologies. Semi‐adjacent sections were labelled with 3H‐PIB (Pittsburgh compound‐B, 2‐[4′‐(methylamino)phenyl]‐6‐hydroxybenzothiazole) and 14C‐SB13 (4‐N‐methylamino‐4′‐hydroxystilbene) for comparison. Neocortical sections containing widespread senile plaques and cerebrovascular amyloid angiopathy, produced a sparse and weak labelling following incubation with 3H‐FDDNP. Furthermore, in sections containing NFTs, there was no overt labelling of the pathology by 3H‐FDDNP. In contrast, sections labelled with 3H‐PIB displayed extensive labelling of diffuse plaques, classical plaques, cerebrovascular amyloid angiopathy and NFTs. 14C‐SB13 produced a broadly similar binding pattern to PIB. Radioligand binding assays employing in vitro generated amyloid‐β peptide fibrils demonstrated a ∼10‐fold reduced affinity for 3H‐FDDNP (85.0 ± 2.0 nM) compared with 3H‐PIB (8.5 ± 1.3 nM). These data provide an alternative mechanistic explanation for the observed low cortical uptake of 18F‐FDDNP in AD; in that the ligand is only weakly retained by the hallmark neuropathology because of its low affinity for amyloid structures.

Pittsburgh Compound B (11C-PIB) and Fluorodeoxyglucose (18 F-FDG) PET in Patients With Alzheimer Disease, Mild Cognitive Impairment, and Healthy Controls

Amyloid load in the brain using Pittsburgh compound B (11C-PIB) positron emission tomography (PET) and cerebral glucose metabolism using fluorodeoxyglucose (18F-FDG) PET were evaluated in patients with mild Alzheimer disease (AD, n = 18), mild cognitive impairment (MCI, n = 24), and controls (CTR, n = 18). 11C-PIB binding potential (BPND) was higher in prefrontal cortex, cingulate, parietal cortex, and precuneus in AD compared to CTR or MCI and in prefrontal cortex for MCI compared to CTR. For 18F-FDG, regional cerebral metabolic rate for glucose (rCMRGlu) was decreased in precuneus and parietal cortex in AD compared to CTR and MCI, with no MCI—CTR differences. For the AD—CTR comparison, precuneus BPND area under the receiver operating characteristic (ROC) curve (AUC) was 0.938 and parietal cortex rCMRGlu AUC was 0.915; for the combination, AUC was 0.989. 11C-PIB PET BPND clearly distinguished diagnostic groups and combined with 18F-FDG PET rCMRGlu, this effect was stronger. These PET techniques provide complementary information in strongly distinguishing diagnostic groups in cross-sectional comparisons that need testing in longitudinal studies.

In vitro high affinity α-synuclein binding sites for the amyloid imaging agent PIB are not matched by binding to Lewy bodies in postmortem human brain

Amyloid containing deposits are a defining neuropathological feature of a wide range of dementias and movement disorders. The positron emission tomography tracer PIB (Pittsburgh Compound‐B, 2‐[4′‐(methylamino)phenyl]‐6‐hydroxybenzothiazole) was developed to target senile plaques, an amyloid containing pathological hallmark of Alzheimer’s disease, formed from the amyloid‐β peptide. Despite the fact that PIB was developed from the pan‐amyloid staining dye thioflavin T, no detailed characterisation of its interaction with other amyloid structures has been reported. In this study, we demonstrate the presence of a high affinity binding site (Kd∼4 nM) for benzothiazole derivatives, including [3H]‐PIB, on α‐synuclein (AS) filaments generated in vitro, and further characterise this binding site through the use of radioligand displacement assays employing 4‐N‐methylamino‐4′‐hydroxystilbene (SB13) (Ki = 87 nM) and 2‐(1‐{6‐[(2‐fluoroethyl(methyl)amino]‐2‐naphthyl}ethylidene)malononitrile (FDDNP) (Ki = 210 nM). Despite the presence of a high‐affinity binding site on AS filaments, no discernible interaction of [3H]‐PIB was detected with amygdala sections from Parkinson’s disease cases containing frequent AS‐immunoreactive Lewy bodies and related neurities. These findings suggest that the density and/or accessibility of AS binding sites in vivo are significantly less than those associated with amyloid‐β peptide lesions. Lewy bodies pathology is therefore unlikely to contribute significantly to the retention of PIB in positron emission tomography imaging studies.

A Pilot Randomized, Placebo Controlled, Double Blind Phase I Trial of the Novel SIRT1 Activator SRT2104 in Elderly Volunteers

Background SRT2104 has been developed as a selective small molecule activator of SIRT1, a NAD+-dependent deacetylase involved in the regulation of energy homeostasis and the modulation of various metabolic pathways, including glucose metabolism, oxidative stress and lipid metabolism. SIRT1 has been suggested as putative therapeutic target in multiple age-related diseases including type 2 diabetes and dyslipidemias. We report the first clinical trial of SRT2104 in elderly volunteers. Methods Oral doses of 0.5 or 2.0 g SRT2104 or matching placebo were administered once daily for 28 days. Pharmacokinetic samples were collected through 24 hours post-dose on days 1 and 28. Multiple pharmacodynamic endpoints were explored with oral glucose tolerance tests (OGTT), serum lipid profiles, magnetic resonance imaging (MRI) for assessment of whole body visceral and subcutaneous fat, maximal aerobic capacity test and muscle 31P magnetic resonance spectroscopy (MRS) for estimation of mitochondrial oxidative capacity. Results SRT2104 was generally safe and well tolerated. Pharmacokinetic exposure increased less than dose-proportionally. Mean Tmax was 2–4 hours with elimination half-life of 15–20 hours. Serum cholesterol, LDL levels and triglycerides decreased with treatment. No significant changes in OGTT responses were observed. 31P MRS showed trends for more rapid calculated adenosine diphosphate (ADP) and phosphocreatine (PCr) recoveries after exercise, consistent with increased mitochondrial oxidative phosphorylation. Conclusions SRT2104 can be safely administered in elderly individuals and has biological effects in humans that are consistent with SIRT1 activation. The results of this study support further development of SRT2104 and may be useful in dose selection for future clinical trials in patients. Trial Registration ClinicalTrials.gov NCT00964340

Determination of |[lsqb]|11C|[rsqb]|PBR28 binding potential in vivo: a first human TSPO blocking study

Positron emission tomography (PET) targeting the 18 kDa translocator protein (TSPO) is used to quantify neuroinflammation. Translocator protein is expressed throughout the brain, and therefore a classical reference region approach cannot be used to estimate binding potential (BP ND ). Here, we used blockade of the TSPO radioligand [11C]PBR28 with the TSPO ligand XBD173, to determine the non-displaceable volume of distribution (V ND ), and hence estimate the BP ND . A total of 26 healthy volunteers, 16 high-affinity binders (HABs) and 10 mixed affinity binders (MABs) underwent a [11C]PBR28 PET scan with arterial sampling. Six of the HABs received oral XBD173 (10 to 90 mg), 2 hours before a repeat scan. In XBD173-dosed subjects, V ND was estimated via the occupancy plot. Values of BP ND for all subjects were calculated using this V ND estimate. Total volume of distribution (V T ) of MABs (2.94 ± 0.31) was lower than V T of HABs (4.33 ± 0.29) (P<0.005). There was dose-dependent occupancy of TSPO by XBD173 (ED50 = 0.34 ± 0.13 mg/kg). The occupancy plot provided a V ND estimate of 1.98 (1.69, 2.26). Based on these V ND estimates, BP ND for HABs is approximately twice that of MABs, consistent with predictions from in vitro data. Our estimates of [11C]PBR28 V ND and hence BP ND in the healthy human brain are consistent with in vitro predictions. XBD173 blockade provides a practical means of estimating V ND for TSPO targeting radioligands.

Chronic (-)baclofen or CGP 36742 alters GABAB receptor sensitivity in rat brain and spinal cord.

Administration of the GABAB receptor agonist, (-)-baclofen 10 mg kg-1, i.p. daily for 21 days to rats prevented (-)-baclofen-induced hyperpolarizing responses and synaptically-evoked late inhibitory potentials (IPSPs) in olfactory cortical neurones recorded intracellularly from 450 microns brain slices. In contrast, pre-treatment with CGP 36742 induced a significant increase in (-)-baclofen-mediated post-synaptic responses and late IPSP amplitude. In the spinal cord, the potency of (-)-baclofen in inhibiting electrically-evoked substance P-like immunoreactivity or amino acid release was significantly reduced or increased in slices from rats pre-treated with the GABAB agonist or antagonist, respectively. These data suggest that functional responses to GABAB receptor activation in the mammalian central nervous system can be up- or down-regulated.

Voxel-Based Analysis of 11C-PIB Scans for Diagnosing Alzheimer's Disease

The positron emission tomography (PET) radioligand N-methyl-11C-2-(4-methylaminophenyl)-6-hydroxybenzothiazole (also known as 11C-6-OH-BTA-1 or 11C-PIB) binds to amyloid-β (Aβ), which accumulates pathologically in Alzheimers disease (AD). Although 11C-PIB accumulation is greater in patients with AD than in healthy controls at a group level, the optimal method for discriminating between these 2 groups has, to our knowledge, not been established. We assessed the use of data-determined standardized voxels of interest (VOIs) to improve the classification capability of 11C-PIB scans on patients with AD. Methods: A total of 16 controls and 14 AD age-matched patients were recruited. All subjects underwent a 11C-PIB scan and structural MRI. Binding potential (a measure of amyloid burden) was calculated for each voxel using the Logan graphical method with cerebellar gray matter as the reference region. Voxel maps were then partial-volume corrected and spatially normalized by MRI onto a standardized template. The subjects were divided into 2 cohorts. The first cohort (control, 12; AD, 9) was used for statistical parametric mapping analysis and delineation of data-based VOIs. These VOIs were tested in the second cohort (control, 4; AD, 5) of subjects. Results: Statistical parametric mapping analysis revealed significant differences between control and AD groups. The VOI map determined from the first cohort resulted in complete separation between the control and the AD subjects in the second cohort (P < 0.02). Binding potential values based on this VOI were in the same range as other reported individual and mean cortical VOI results. Conclusion: A standardized VOI template that is optimized for control or AD group discrimination provides excellent separation of control and AD subjects on the basis of 11C-PIB uptake. This VOI template can serve as a potential replacement for manual VOI delineation and can eventually be fully automated, facilitating potential use in a clinical setting. To facilitate independent analysis and validation with more and a broader variety of subjects, this VOI template and the software for processing will be made available through the Internet.

Metabotropic glutamate receptor subtypes mediating slow inward tail current (IADP) induction and inhibition of synaptic transmission in olfactory cortical neurones.

The pharmacological features of the pre‐ and postsynaptic metabotropic glutamate receptors (mGluRs) present in the guinea‐pig olfactory cortex, were examined in brain slices in vitro by use of a conventional intracellular current clamp/voltage clamp recording technique. Bath‐application of trans‐aminocyclopentane‐1,3‐dicarboxylic acid (trans‐ACPD) (50 μm) produced a sustained membrane depolarization, increase in cell excitability and induction of a post‐stimulus inward (afterdepolarizing) tail current (IADP) (measured under ‘hybrid’ voltage clamp) similar to those evoked by the muscarinic receptor agonist oxotremorine‐M (OXO‐M, 2 μm). l‐Glutamate (0.25–1 mm, in the presence of 20 μm 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and 100 μm dl‐amino‐5‐phosphono valeric acid (dl‐APV)) or the broad spectrum mGluR agonists 1S,3R‐aminocyclopentane‐1,3‐dicarboxylic acid (1S,3R‐ACPD, 10 μm), 1S,3S‐ACPD (50 μm), ibotenate (Ibo; 25 μm, in the presence of 100 μm dl‐APV), the selective mGluR I agonists (S)‐3,5‐dihydroxyphenylglycine ((S)‐3,5‐DHPG, 10 μm), (S)‐3‐hydroxyphenylglycine ((S)‐3HPG, 50 μm), or quisqualate (10 μm, in the presence of 20 μm CNQX), but not the mGluR II agonist 2S,1′S,2′S‐2‐(2′‐carboxycyclopropyl)‐glycine (l‐CCGI, 1 μm) or mGluR III agonist l(+)‐2‐amino‐4‐phosphonobutyric acid (l‐AP4, 1 mm), were all effective in producing membrane depolarization and inducing a post‐stimulus IADP. Unexpectedly, the proposed mGluR II‐selective agonist (2S,1′R,2′R,3′R)‐2‐(2′,3′‐dicarboxycyclopropyl)‐glycine (DCG‐IV, 10 μm, in the presence of 100 μm dl‐APV) was also active. The excitatory effects induced by 10 μm 1S,3R‐ACPD were reversibly antagonized by the mGluR I/II antagonist (+)‐α‐methyl‐4‐carboxyphenylglycine ((+)‐MCPG, 0.5–1 mm), as well as the selective mGluR I antagonists (S)‐4‐carboxyphenylglycine ((S)‐4CPG) and (S)‐4‐carboxy‐3‐hydroxyphenyl glycine ((S)‐4C3HPG) (both at 1 mm), but not the nonselective mGluR antagonist l(+)‐2‐amino‐3‐phosphonopropionic acid (l‐AP3, 1 mm) or the selective mGluR III antagonist (S)‐α‐methyl‐l‐AP4 (MAP4, 1 mm). The excitatory postsynaptic potentials (e.p.s.ps), induced by single focal stimulation of cortical excitatory fibre tracts, were markedly reduced by 1S,3R‐ACPD or l‐AP4 (both at 10 μm), and by the selective mGluR II agonists (mGluR I antagonists) (S)‐4CPG or (S)‐4C3HPG (both at 1 mm) but not (S)‐3,5‐DHPG or (S)‐3HPG (both at 100 μm). The inhibitory effects of 1S‐3R‐ACPD, but not l‐AP4, were reversibly blocked by (+)‐MCPG (1 mm), whereas those produced by l‐AP4, but not 1S,3R‐ACPD, were blocked by the selective mGluR III antagonist MAP4 (1 mm). It is concluded that a group I mGluR is most likely involved in mediating excitatory postsynaptic effects, whereas two distinct mGluRs (e.g. group II and III) might serve as presynaptic inhibitory autoreceptors in the guinea‐pig olfactory cortex.

Frontal and parietal activity after sleep deprivation is dependent on task difficulty and can be predicted by the fMRI response after normal sleep.

Sleep disturbance in neurological and psychiatric disorders is common and associated with diminished cognitive functioning. Whilst these deficits can be localised predominantly to frontal and parietal regions, there have been reported inconsistencies which may be due to differences in the difficulty and type of task. In the present study we examined the effects of sleep deprivation (SD) whilst parametrically varying working memory load using an n-back task. 20 right-handed males performed the n-back task after a night of normal sleep (RW: rested wakefulness) and after approximately 31 h of SD. Comparison of load responsive cerebral activation identified two clusters where the parametric response was altered after SD. In the right ventrolateral prefrontal cortex activity was reduced at the most difficult working memory load, whereas in the right inferior parietal lobe activity was increased at the simplest working memory load. The strength of activation in both of these regions during RW predicted the response of those same regions to SD. While the ability to predict signal change has previously been demonstrated using behavioural measures, to our knowledge this is the first study to show that the neuronal effects of SD can be predicted based upon activation during a normal rested condition.

AMPA receptor potentiation can prevent ethanol-induced intoxication

We present a substantial series of behavioral and imaging experiments, which demonstrate, for the first time, that increasing AMPA receptor-mediated neurotransmission via administration of potent and selective biarylsulfonamide AMPA potentiators LY404187 and LY451395 reverses the central effects of an acutely intoxicating dose of ethanol in the rat. Using pharmacological magnetic resonance imaging (phMRI), we observed that LY404187 attenuated ethanol-induced reductions in blood oxygenation level dependent (BOLD) in the anesthetized rat brain. A similar attenuation was apparent when measuring local cerebral glucose utilization (LCGU) via C14-2-deoxyglucose autoradiography in freely moving conscious rats. Both LY404187 and LY451395 significantly and dose-dependently reversed ethanol-induced deficits in both motor coordination and disruptions in an operant task where animals were trained to press a lever for food reward. Both prophylactic and acute intervention treatment with LY404187 reversed ethanol-induced deficits in motor coordination. Given that LY451395 and related AMPA receptor potentiators/ampakines are tolerated in both healthy volunteers and elderly patients, these data suggest that such compounds may form a potential management strategy for acute alcohol intoxication.