N-desmethylclozapine, an allosteric agonist at muscarinic 1 receptor, potentiates N-methyl-D-aspartate receptor activity.
The molecular and neuronal substrates conferring on clozapine its unique and superior efficacy in the treatment of schizophrenia remain elusive. The interaction of clozapine with many G protein-coupled receptors is well documented but less is known about its biologically active metabolite, N-desmethylclozapine. Recent clinical and preclinical evidences of the antipsychotic activity of the muscarinic agonist xanomeline prompted us to investigate the effects of N-desmethylclozapine on cloned human M1-M5 muscarinic receptors. N-desmethylclozapine preferentially bound to M1 muscarinic receptors with an IC50 of 55 nM and was a more potent partial agonist (EC50, 115 nM and 50% of acetylcholine response) at this receptor than clozapine. Furthermore, pharmacological and site-directed mutagenesis studies suggested that N-desmethylclozapine preferentially activated M1 receptors by interacting with a site that does not fully overlap with the acetylcholine orthosteric site. As hypofunction of N-methyl-d-aspartate (NMDA) receptor-driven neuronal ensembles has been implicated in psychotic disorders, the neuronal activity of N-desmethylclozapine was electrophysiologically investigated in hippocampal rat brain slices. N-desmethylclozapine was shown to dose-dependently potentiate NMDA receptor currents in CA1 pyramidal cells by 53% at 100 nM, an effect largely mediated by activation of muscarinic receptors. Altogether, our observations provide direct evidence that the brain penetrant metabolite N-desmethylclozapine is a potent, allosteric agonist at human M1 receptors and is able to potentiate hippocampal NMDA receptor currents through M1 receptor activation. These observations raise the possibility that N-desmethylclozapine contributes to clozapine's clinical activity in schizophrenics through modulation of both muscarinic and glutamatergic neurotransmission.
Sur
Cyrille
C
Department of Neuroscience, Merck & Co. Inc., West Point, PA 19486, USA. cyrille_sur@merck.com
Mallorga
Pierre J
PJ
Wittmann
Marion
M
Jacobson
Marlene A
MA
Pascarella
Danette
D
Williams
Jacinta B
JB
Brandish
Philip E
PE
Pettibone
Douglas J
DJ
Scolnick
Edward M
EM
Conn
P Jeffrey
PJ
D000495:Allosteric Site; D000818:Animals; D001921:Brain / Q000378:metabolism; D002460:Cell Line; D003024:Clozapine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D006224:Cricetinae; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism; D006801:Humans; D020128:Inhibitory Concentration 50; D016297:Mutagenesis, Site-Directed; D009474:Neurons / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D043643:Receptor, Muscarinic M1 / Q000819:agonists* / Q000737:chemistry*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D013997:Time Factors
D018076:DNA, Complementary; D043643:Receptor, Muscarinic M1; D016194:Receptors, N-Methyl-D-Aspartate; C058272:norclozapine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D003024:Clozapine