Cognitive enhancing effects of an AMPA receptor positive modulator on place learning in mice

AMPA receptor potentiators: from drug design to cognitive enhancement

Positive allosteric modulators of ionotropic glutamate receptors have emerged as a target for treating cognitive impairment and neurodegeneration, but also mental illnesses such as major depressive disorder. The possibility of creating a new class of pharmaceutical agent to treat refractive mental health issues has compelled researchers to redouble their efforts to develop a safe, effective treatment for memory and cognition impairments. Coupled with the more robust research methodologies that have emerged, including more sophisticated high-throughput-screens, higher resolution structural biology techniques, and more focused assessment on pharmacokinetics, the development of positive modulators of AMPA receptors holds great promise. We describe recent approaches that improve our understanding of the basic physiology underlying memory and cognition, and their application toward promoting human health.

M1 and m2 muscarinic receptor subtypes regulate antidepressant-like effects of the rapidly acting antidepressant scopolamine

Scopolamine produces rapid and significant symptom improvement in patients with depression, and most notably in patients who do not respond to current antidepressant treatments. Scopolamine is a nonselective muscarinic acetylcholine receptor antagonist, and it is not known which one or more of the five receptor subtypes in the muscarinic family are mediating these therapeutic effects. We used the mouse forced-swim test, an antidepressant detecting assay, in wild-type and transgenic mice in which each muscarinic receptor subtype had been genetically deleted to define the relevant receptor subtypes. Only the M1 and M2 knockout (KO) mice had a blunted response to scopolamine in the forced-swim assay. In contrast, the effects of the tricyclic antidepressant imipramine were not significantly altered by gene deletion of any of the five muscarinic receptors. The muscarinic antagonists biperiden, pirenzepine, and VU0255035 (N-[3-oxo-3-[4-(4-pyridinyl)-1-piper azinyl]propyl]-2,1,3-benzothiadiazole-4-sulfonamide) with selectivity for M1 over M2 receptors also demonstrated activity in the forced-swim test, which was attenuated in M1 but not M2 receptor KO mice. An antagonist with selectivity of M2 over M1 receptors (SCH226206 [(2-amino-3-methyl-phenyl)-[4-[4-[[4-(3 chlorophenyl)sulfonylphenyl]methyl]-1-piperidyl]-1-piperidyl]methanone]) was also active in the forced-swim assay, and the effects were deleted in M2 (-/-) mice. Brain exposure and locomotor activity in the KO mice demonstrated that these behavioral effects of scopolamine are pharmacodynamic in nature. These data establish muscarinic M1 and M2 receptors as sufficient to generate behavioral effects consistent with an antidepressant phenotype and therefore as potential targets in the antidepressant effects of scopolamine.

AMPA receptor inhibitors for the treatment of epilepsy: the role of perampanel

α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in the postsynaptic membrane are involved in fast excitatory signaling in the brain and their activation may lead to the firing of action potentials. Talampanel and perampanel were the first noncompetitive AMPA receptor antagonists to be tested as add-on drugs in patients with refractory partial seizures, and were found to be effective in improving seizure control. Due to an unfavorable kinetic and tolerability profile, talampanel clinical development in the field of epilepsy was discontinued early while perampanel has been recently approved in Europe and the USA as adjunctive therapy for adults with partial seizures with or without secondary generalization. The recommended perampanel starting dose is 2 mg/day once daily, which can be increased up to the recommended maintenance dose of 4-8 mg/day. Increments should be of 2 mg/day and based on clinical response and tolerability. Titration should be performed at 1-week intervals or at lower speed and a 12-mg daily dose should be considered after careful evaluation. To date, no serious and/or idiosyncratic adverse effects have been associated with this agent. Most frequently reported adverse effects are dizziness, ataxia, aggression, irritability, vertigo, somnolence, fatigue, headache and gait disturbance. Weight increase is the only non-neurological adverse effects associated with perampanel.

Does increasing the ratio of AMPA-to-NMDA receptor mediated neurotransmission engender antidepressant action? Studies in the mouse forced swim and tail suspension tests

Monoamine-based antidepressant drugs increase α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) function and decrease N-methyl-d-aspartate receptor (NMDAR) function. The NMDAR antagonist ketamine shows potent antidepressant action in humans and the antidepressant-like effects of ketamine and monoamine-based antidepressants in rodents depend on increased AMPAR throughput. Further, the antidepressant-like effects of monoamine-based antidepressants are enhanced by AMPAR potentiation and by NMDAR antagonism. This has led to a hypothesis that antidepressant efficacy involves an increases ratio of AMPAR-to-NMDAR-mediated neurotransmission. To further elucidate the interaction of AMPAR, NMDAR and monoamine transmission we tested combinations of the AMPAR positive allosteric modulator (AMPA potentiator), (R,R)-N,N-(2,20-[biphenyl-4-40-diyl]bis[propane-2,1-diyl])dimethanesulfonamide (PIMSD), with: the uncompetitive NMDAR antagonist MK-801; nicotine, which has potent glutamate-releasing properties; and the selective serotonin reuptake inhibitor escitalopram using the mouse forced swim (mFST) and tail suspension tests (mTST). MK-801, nicotine or escitalopram did not induce antidepressant-like effects in either of the two tests. PIMSD enhanced the effect of MK-801 in the mFST, supporting the hypothesis that increasing AMPAR-to-NMDAR-mediated neurotransmission conveys antidepressant action. Nicotine-induced glutamate release simultaneously activates NMDARs and AMPARs and showed no net effect in the mFST when given alone. However, increasing the ratio of AMPAR-to-NMDA-R transmission by favouring AMPAR throughput with PIMSD revealed an antidepressant-like action of nicotine in the mFST. PIMSD also enhanced the effect of escitalopram treatment in the mFST and mTST, supporting existing evidence and suggesting a synergistic effect of simultaneously facilitating monoamine transmission and increasing the ratio of AMPAR-to-NMDAR throughput. No synergistic effects of the PIMSD+MK-801 or PIMSD+nicotine were found in the mTST, indicating a differential sensitivity of mFST and mTST when investigating glutamate-based antidepressant mechanisms. This study corroborates existing evidence that there may be an unexploited therapeutic potential in treating depression by directly increasing the ratio of AMPAR-to-NMDAR neurotransmission, possibly in combination with monoamine-based mechanisms.

The adverse event profile of perampanel: meta-analysis of randomized controlled trials

BACKGROUND AND PURPOSE

To identify adverse events (AEs) significantly associated with perampanel treatment in double-blind clinical studies (RCTs). Serious AEs, study withdrawals due to AEs and dose-effect responses of individual AEs were also investigated.

METHODS

All placebo controlled, double-blind RCTs investigating therapeutic effects of oral perampanel were searched. AEs were assessed for their association with perampanel after exclusion of synonyms, rare AEs and non-assessable AEs. Risk difference (RD) was used to evaluate the association of any AE (99% confidence intervals) and withdrawals or serious AEs (95% confidence intervals) with perampanel.

RESULTS

Nine RCTs (five in pharmacoresistant epilepsy and four in Parkinson's disease) were included in our study. Almost 4000 patients had been recruited, 2627 of whom were randomized to perampanel and treated with drug doses of 0.5 mg/day (n = 68), 1 mg/day (n = 65), 2 mg/day (n = 753), 4 mg/day (n = 1017), 8 mg/day (n = 431) or 12 mg/day (n = 293). Serious AEs were not significantly associated with perampanel treatment. The experimental drug was significantly associated with an increased risk of AE-related study withdrawals at 4 mg/day [RD (95% confidence interval) 0.03 (0.00, 0.06)] and 12 mg/day [RD (95% confidence interval) 0.13 (0.07, 0.18)]. Of 15 identified AEs, five (dizziness, ataxia, somnolence, irritability and weight increase) were found to be significantly associated with perampanel and one (seizure worsening) was significantly associated with placebo.

CONCLUSIONS

Vestibulocerebellar AEs (dizziness, ataxia), sedative effects (somnolence), irritability and weight increase were significantly associated with perampanel treatment.