Ketamine metabolism via hepatic CYP450 isoforms contributes to its sustained antidepressant actions.
(R,S)-ketamine (ketamine) has rapid and sustained antidepressant (AD) efficacy at sub-anesthetic doses in depressed patients. A metabolite of ketamine, including (2R,6R)-hydroxynorketamine ((6)-HNKs) has been reported to exert antidepressant actions in rodent model of anxiety/depression. To further understand the specific role of ketamines metabolism in the AD actions of the drug, we evaluated the effects of inhibiting hepatic cytochrome P450 enzymes on AD responses. We assessed whether pre-treatment with fluconazole (10 and 20 mg/kg, i.p.) 1 hour prior to ketamine or HNKs (10 mg/kg, i.p.) administration would alter behavioral and neurochemical actions of the drugs in male BALB/cJ mice with a highly anxious phenotype. Extracellular microdialysate levels of glutamate and GABA (Gluext, GABAext) were also measured in the medial prefrontal cortex (mPFC). Pre-treatment with fluconazole altered the pharmacokinetic profile of ketamine, by increasing both plasma and brain levels of ketamine and (R,S)-norketamine, while robustly reducing those of (6)-HNKs. At 24 hours post-injection (t24h), fluconazole prevented the sustained AD-like response of ketamine responses in the forced swim test and splash test, as well as the enhanced cortical GABA levels produced by ketamine. A single (2R,6R)-HNK administration selectively rescued the antidepressant-like activity of ketamine in mice pretreated with fluconazole within 24 hours of treatment. Overall, these findings are consistent with an essential role of (6)-HNK in mediating the sustained antidepressant-like effects of ketamine and suggest potential interactions between pharmacological CYPIs and ketamine during antidepressant treatment in patients.