(R)-Ketamine exerts antidepressant actions partly via conversion to (2R,6R)-hydroxynorketamine, while causing adverse effects at sub-anaesthetic doses.
Panos Zanos, Jaclyn N. Highland, Xin Liu, Timothy A. Troppoli, Polymnia Georgiou, Jacqueline Lovett, Patrick J. Morris, Brent W. Stewart, Craig J. Thomas, Scott M. Thompson, Ruin Moaddel, Todd D Gould
British Journal of Pharmacology July 1, 2019 DOI: 10.1111/bph.14683 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Preclinical study Peer reviewed |
|---|---|
| Population | Mice |
| Interventions | (R)-ketamine (2R 6R)-HNK |
| Topics | Esketamine Ketamine |
| Key points | Metabolism of (R)-ketamine to (2R,6R)-HNK increases its potency for antidepressant-relevant actions in mice, but adverse effects occur at sub-anaesthetic doses. |
Abstract
(R)-Ketamine (arketamine) may have utility as a rapidly acting antidepressant. While (R)-ketamine has lower potency than (R,S)-ketamine to inhibit NMDA receptors in vitro, the extent to which (R)-ketamine shares the NMDA receptor-mediated adverse effects of (R,S)-ketamine in vivo has not been fully characterised. Furthermore, (R)-ketamine is metabolised to (2R,6R)-hydroxynorketamine (HNK), which may contribute to its antidepressant-relevant actions. Using mice, we compared (R)-ketamine with a deuterated form of the drug (6,6-dideutero-(R)-ketamine, (R)-d2 -ketamine), which hinders its metabolism to (2R,6R)-HNK, in behavioural tests predicting antidepressant responses. We also examined the actions of intracerebroventricularly infused (2R,6R)-HNK. Further, we quantified putative NMDA receptor inhibition-mediated adverse effects of (R)-ketamine. (R)-d2 -Ketamine was identical to (R)-ketamine in binding to and functionally inhibiting NMDA receptors but hindered (R)-ketamine's metabolism to (2R,6R)-HNK. (R)-Ketamine exerted greater potency than (R)-d2 -ketamine in several antidepressant-sensitive behavioural measures, consistent with a role of (2R,6R)-HNK in the actions of (R)-ketamine. There were dose-dependent sustained antidepressant-relevant actions of (2R,6R)-HNK following intracerebroventricular administration. (R)-Ketamine exerted NMDA receptor inhibition-mediated behaviours similar to (R,S)-ketamine, including locomotor stimulation, conditioned-place preference, prepulse inhibition deficits, and motor incoordination, with approximately half the potency of the racemic drug. Metabolism of (R)-ketamine to (2R,6R)-HNK increases the potency of (R)-ketamine to exert antidepressant-relevant actions in mice. Adverse effects of (R)-ketamine require higher doses than those necessary for antidepressant-sensitive behavioural changes in mice. However, our data revealing that (R)-ketamine's adverse effects are elicited at sub-anaesthetic doses indicate a potential risk for sensory dissociation and abuse liability.
Comparable studies
Other preclinical and animal studies on ketamine, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| mTOR-Dependent Synapse Formation Underlies the Rapid Antidepressant Effects of NMDA Antagonists Rats | 2010 | Observational study | |
| Activation of Glutamatergic Neurotransmission by Ketamine: A Novel Step in the Pathway from NMDA Receptor Blockade to Dopaminergic and Cognitive Disruptions Associated with the Prefrontal Cortex Conscious rats | 1997 | Dose-response study with microdialysis and behavioral testing | |
| NMDAR inhibition-independent antidepressant actions of ketamine metabolites Mice | 2016 | Preclinical study | |
| The dissociative anaesthetics, ketamine and phencyclidine, selectively reduce excitation of central mammalian neurones by N‐methyl‐aspartate Spinal neurons in decerebrate or pentobarbitone-anaesthetized cats and rats | 1983 | Experimental study | |
| R-ketamine: a rapid-onset and sustained antidepressant without psychotomimetic side effects Mice | 2015 | Experimental study |
Citations in the library
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- Rapid‐acting antidepressant ketamine, its metabolites and other candidates: A historical overview and future perspective Psychiatry and Clinical Neurosciences June 19, 2019
- Pharmacological and behavioral divergence of ketamine enantiomers: implications for abuse liability Molecular Psychiatry April 15, 2021
- Ketamine as an antidepressant: overview of its mechanisms of action and potential predictive biomarkers Therapeutic Advances in Psychopharmacology 2020
- Molecular and cellular mechanisms underlying the antidepressant effects of ketamine enantiomers and its metabolites Translational Psychiatry November 7, 2019
- Mechanisms of Ketamine and its Metabolites as Antidepressants Biochemical Pharmacology December 1, 2021
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Cites 31
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- Subanesthetic Effects of the Noncompetitive NMDA Antagonist, Ketamine, in Humans Archives of General Psychiatry March 1, 1994
- mTOR-Dependent Synapse Formation Underlies the Rapid Antidepressant Effects of NMDA Antagonists Science August 19, 2010
- NMDAR inhibition-independent antidepressant actions of ketamine metabolites Nature April 24, 2016
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and 26 more in the library