Comparative metabolomic analysis in plasma and cerebrospinal fluid of humans and in plasma and brain of mice following antidepressant-dose ketamine administration

Abstract

Subanesthetic-dose racemic (R,S)-ketamine (ketamine) produces rapid, robust, and sustained antidepressant effects in major depressive disorder (MDD) and bipolar disorder (BD) and has also been shown to effectively treat neuropathic pain, complex regional pain syndrome, and post-traumatic stress disorder (PTSD). However, to date, its mechanism of action remains unclear. Preclinical studies found that (2 R,6 R;2 S,6 S)-hydroxynorketamine (HNK), a major circulating metabolite of ketamine, elicits antidepressant effects similar to those of ketamine. To help determine how (2 R,6 R)-HNK contributes to ketamine's mechanism of action, an exploratory, targeted, metabolomic analysis was carried out on plasma and CSF of nine healthy volunteers receiving a 40-minute ketamine infusion (0.5 mg/kg). A parallel targeted metabolomic analysis in plasma, hippocampus, and hypothalamus was carried out in mice receiving either 10 mg/kg of ketamine, 10 mg/kg of (2 R,6 R)-HNK, or saline. Ketamine and (2 R,6 R)-HNK both affected multiple pathways associated with inflammatory conditions. In addition, several changes were unique to either the healthy human volunteers and/or the mouse arm of the study, indicating that different pathways may be differentially involved in ketamine's effects in mice and humans. Mechanisms of action found to consistently underlie the effects of ketamine and/or (2 R,6 R)-HNK across both the human metabolome in plasma and CSF and the mouse arm of the study included LAT1, IDO1, NAD+, the nitric oxide (NO) signaling pathway, and sphingolipid rheostat.

Trial registration: ClinicalTrials.gov NCT03065335.

Conflict of interest statement

Dr. Zarate is listed as a co-inventor on a patent for the use of ketamine in major depression and suicidal ideation. Drs. Zarate and Moaddel are co-inventors on a patent for the use of (2 R,6 R)-hydroxynorketamine, (S)-dehydronorketamine, and other stereoisomeric dehydroxylated and hydroxylated metabolites of (R,S)-ketamine metabolites in the treatment of depression and neuropathic pain. Drs. Zarate, Moaddel, Gould, Zanos, Morris, and Thomas are co-inventors on a patent application for the use of (2 R,6 R)-hydroxynorketamine and (2 S,6 S)-hydroxynorketamine in the treatment of depression, anxiety, anhedonia, suicidal ideation, and post-traumatic stress disorders, and crystal forms and methods of synthesis of (2 R,6 R)-hydroxynorketamine and (2 S,6 S)-hydroxynorketamine. Drs. Morris and Thomas are co-inventors on a patent application for the salts of (2 R,6 R)-hydroxynorketamine, their crystal forms, and methods of making the same and the process for synthesis and purification of (2 R,6 R)-hydroxynorketamine. Drs. Zarate, Moaddel, Morris, and Thomas have assigned their patent rights to the U.S. government but will share a percentage of any royalties that may be received by the government. Drs. Gould and Zanos have assigned their patent rights to the University of Maryland, Baltimore but will share a percentage of any royalties that may be received by the University of Maryland, Baltimore. All other authors have no conflict of interest to disclose, financial or otherwise.

© 2022. This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.

Figures

Fig. 1. Selected results of principal components analysis (PCA) on human metabolome.

A, C Features with the 20 strongest loadings on PC2 in plasma (A) and cerebrospinal fluid (CSF) (C). B, D Result of mixed model estimating mean (95% CI) baseline-normalized PC2 values at each timepoint in plasma (B) and CSF (D). Y-axis is a PC score and has no units.

Fig. 2. Mouse AUC comparisons.

The area under the curve (AUC) of each metabolite was compared using Z-transformation between groups receiving 10 mg/kg ketamine (KET), 10 mg/kg (2 R,6 R)-hydroxynorketamine (HNK), or saline (SAL). Volcano plots show the p-value for the between-group comparison against fold change in feature. Heatmaps show the test statistics (Z) for features with at least one -log(p) > 2. All heatmaps share the legend at far right. A Volcano plot for plasma MxP500. B Heatmap for plasma MxP500. C Volcano plot for hypothalamus features. D Heatmap for hypothalamus features. E Volcano plot for hippocampus features. E Heatmap for hippocampus features.

Fig. 3. Potential mechanism identified for ketamine and/or (2 R, 6 R)-hydroxynorketamine (HNK).

Overview of the exploratory metabolomic results on the potential mechanism of ketamine and/or (2 R,6 R)-HNK, including inflammation, the nitric oxide (NO) signaling pathway, cholesterol metabolism, mammalian target of rapamycin (mTOR) and/or mitochondrial oxidative capacity. Directional changes of the metabolites and/or ratios are indicated as well as the source (red: human plasma; light blue: cerebrospinal fluid (CSF); yellow: mouse plasma and/or whole blood; dark blue: mouse brain). Light grey lines indicate additional interactions.