Eric Detrait

Lack of synaptic vesicle protein SV2B protects against amyloid-β25–35-induced oxidative stress, cholinergic deficit and cognitive impairment in mice

SV2B is a synaptic protein widely distributed throughout the brain, which is part of the complex vesicle protein machinery involved in the regulation of synaptic vesicle endocytosis and exocytosis, and therefore in neurotransmitters release. The aims of the present work were twofold: (1) phenotype SV2B knockout mice (SV2B KO) in a battery of cognitive tests; and (2) examine their vulnerability to amyloid-β25-35 (Aβ25-35) peptide-induced toxicity. SV2B KO mice showed normal learning and memory abilities in absence of Aβ25-35 injection. SV2B KO mice were protected against the learning deficits induced after icv injection of an oligomeric preparation of amyloid-β25-35 peptide, as compared to wild-type littermates (SV2B WT). These mice failed to show Aβ25-35-induced impairments in a number of cognitive domains: working memory measured by a spontaneous alternation procedure, recognition memory measured by a novel object recognition task, spatial reference memory assessed in a Morris water-maze, and long-term contextual memory assessed in a inhibitory avoidance task. In addition, SV2B KO mice were protected against Aβ25-35-induced oxidative stress and decrease in ChAT activity in the hippocampus. These data suggest that SV2B could be a key modulator of amyloid toxicity at the synaptic site.

Behavioural phenotyping reveals anxiety-like features of SV2A deficient mice.

Synaptic vesicle protein 2A (SV2A) is involved in neurotransmitter release and has been identified as the binding site for levetiracetam (Keppra), a novel antiepileptic drug. Homozygous SV2A (-/-) mice are not viable beyond a few weeks. In contrast, heterozygous SV2A (+/-) mice have a normal lifespan. We performed a behavioural phenotyping on SV2A (+/-) mice in a battery of tests: gross behavioural observation, spontaneous locomotor activity, sensori-motor coordination, acute pain sensitivity, exploration in an elevated plus-maze and an assessment of learning abilities in an inhibitory avoidance procedure. SV2A (+/-) mice were compared to age-matched, 2-month-old wild type controls. Overall, gross behaviour, spontaneous locomotor activity, sensori-motor coordination and acute pain sensitivity were comparable between wild type and SV2A (+/-) mice. When tested in a plus-maze, SV2A (+/-) mice displayed significant increased avoidance of open elevated arms whereas locomotor activity was not altered. Finally, both SV2A (+/-) and wild type mice showed comparable memory performance at the end of a multi-trial passive avoidance procedure. Interestingly, SV2A (+/-) mice exhibited increased avoidance of the lit area during the first sessions without foot shock. These results suggest an anxiety-like phenotype for SV2A (+/-) mice indicated by increased open-arm avoidance in the elevated plus-maze test as well as a shorter latency to escape from a lit area in the inhibitory avoidance procedure.

Discovery of novel selective Sigma-1 ligands as cognitive enhancers

We disclose the identification and SAR of phenylcyclopropylcarboxamide compounds as novel, selective Sigma-1 ligands presenting excellent drug-like properties, high solubility and metabolic stability. A selected representative, compound 14, demonstrated in vivo very good brain exposure and antiamnesic effect in a mouse model of recognition memory.

The inhibitory avoidance test optimized for discovery of cognitive enhancers

In the present article, we describe a new protocol for the inhibitory avoidance test, with a dual purpose: (1) to provide a leß variable and more reliable aßeßment of the efficacy of potential cognitive enhancers in antagonizing scopolamine-induced long-term-memory deficits, and (2) to secure a high throughput for pharmacological screening of cognitive enhancers. The new protocol consists of two acquisition trials that are followed 24 h later by a single retention trial. In the present study, this protocol clearly dißociated the frequency distributions of retention latencies between scopolamine- and vehicle-treated groups and allowed validation by means of two acetylcholinesterase inhibitors—tacrine and donepezil—that proved to be active in counteracting the scopolamine-induced memory deficit. This protocol also produced stability of the behavioral response to pharmacological agents over a 3-year period. A statistical power analysis indicated that, depending on the efficacy of the drug/dose, a sample size of 5–12 mice was required in order to show a reversal of the scopolamineinduced memory deficit. The double-trial acquisition protocol is suitable for testing cognitive enhancers, while also providing a clearly enhanced throughput.

Acetamide Scanning around Bicyclic Thiazoles: SAR at the H3 Receptor

The third histamine receptor (H3R) is expressed mainly in the central nervous system (CNS) and regulates the release of numerous other neurotransmitters. It is highly interesting as a target for the control of CNS disorders such as excessive daytime sleepiness and cognitive disorders such as Alzheimer’s disease. In our medicinal chemistry investigations around this receptor, we have identified nanomolar-affinity ligands based on a phenyloxazole scaffold (Figure 1). We noticed that affinity increased between isomers I and II. Starting from thiazole III, we embarked on a systematic comparison of rigid bicyclic thiazoles bearing the N-acetyl side chain in all orientations in an attempt to identify the isomer with the best properties. This isomer was then used to further explore the structure– activity relationships (SAR).

Brain catechol-O-methyltransferase (COMT) inhibition by tolcapone counteracts recognition memory deficits in normal and chronic phencyclidine-treated rats and in COMT-Val transgenic mice.

The critical involvement of dopamine in cognitive processes has been well established, suggesting that therapies targeting dopamine metabolism may alleviate cognitive dysfunction. Catechol-O-methyl transferase (COMT) is a catecholamine-degrading enzyme, the substrates of which include dopamine, epinephrine, and norepinephrine. The present work illustrates the potential therapeutic efficacy of COMT inhibition in alleviating cognitive impairment. A brain-penetrant COMT inhibitor, tolcapone, was tested in normal and phencyclidine-treated rats and COMT-Val transgenic mice. In a novel object recognition procedure, tolcapone counteracted a 24-h-dependent forgetting of a familiar object as well as phencyclidine-induced recognition deficits in the rats at doses ranging from 7.5 to 30 mg/kg. In contrast, entacapone, a COMT inhibitor that does not readily cross the blood–brain barrier, failed to show efficacy at doses up to 30 mg/kg. Tolcapone at a dose of 30 mg/kg also improved novel object recognition performance in transgenic mice, which showed clear recognition deficits. Complementing earlier studies, our results indicate that central inhibition of COMT positively impacts recognition memory processes and might constitute an appealing treatment for cognitive dysfunction related to neuropsychiatric disorders.

Inhibitory effects of sigma-1 ligands on handling-induced tachycardia in conscious tethered rats

We used conscious tethered Sprague‐Dawley rats to evaluate the cardiovascular effects of four sigma‐1 (σ1) agonists and five antagonists, given alone or in combination. All drugs were administered as a single intraperitoneal dose. The agonists were given at doses reported as efficacious in rodent cognition models, while the antagonists were administered at doses neutralizing agonist effects in vivo. Systolic blood pressure (SBP) and heart rate (HR) were continuously recorded for 20 min before and 60 min postadministration. Immediately after injection, a sudden, transitory increase in HR and SBP was noted in all animals, because of the stress induced by handling. For both parameters, a peak value (ΔHRmax and ΔSBPmax) and an area under the curve of changes from baseline over the period 5–20 min postinjection (ΔHR_AUC5–20 min and ΔSBP_AUC5–20 min) were calculated. Three of the four σ1 agonists (SKF‐10,047, dehydroepiandrosterone (DHEAS), Compound 14) significantly reduced ΔHR_AUC5–20 min value without changing ΔHRmax, while the fourth one, SA‐4503, had no significant effect. None of the antagonists (haloperidol, rimcazole, NE‐100, and BD1047) reduced, and even one (progesterone) enhanced the stress‐induced effects on HR. No changes in SBP were noted with any compound. When the antagonist NE‐100 was administered just before SKF‐10,047, it completely reversed the inhibitory effects of the σ1 agonist on HR increase. In conclusion, we demonstrated for the first time the involvement of σ1 receptors in the regulation of handling‐induced tachycardia in the conscious rat. Although additional investigations are needed to fully understand this role, it might offer new therapeutic perspectives to σ1 ligands in the cardiovascular sphere.