Sex-dependent metabolism of ketamine and (2R,6R)-hydroxynorketamine in mice and humans

Background: Ketamine is rapidly metabolized to norketamine and hydroxynorketamine (HNK) metabolites. In female mice, when compared to males, higher levels of ( 2R,6R;2S,6S)-HNK have been observed following ketamine treatment, and higher levels of ( 2R,6R)-HNK following the direct administration of ( 2R,6R)-HNK. Aim: The objective of this study was to evaluate the impact of sex in humans and mice, and gonadal hormones in mice on the metabolism of ketamine to form norketamine and HNKs and in the metabolism/elimination of ( 2R,6R)-HNK. Methods: In CD-1 mice, we utilized gonadectomy to evaluate the role of circulating gonadal hormones in mediating sex-dependent differences in ketamine and ( 2R,6R)-HNK metabolism. In humans (34 with treatment-resistant depression and 23 healthy controls) receiving an antidepressant dose of ketamine (0.5 mg/kg i.v. infusion over 40 min), we evaluated plasma levels of ketamine, norketamine, and HNKs. Results: In humans, plasma levels of ketamine and norketamine were higher in males than females, while ( 2R,6R;2S,6S)-HNK levels were not different. Following ketamine administration to mice (10 mg/kg i.p.), Cmax and total plasma concentrations of ketamine and norketamine were higher, and those of ( 2R,6R;2S,6S)-HNK were lower, in intact males compared to females. Direct ( 2R,6R)-HNK administration (10 mg/kg i.p.) resulted in higher levels of ( 2R,6R)-HNK in female mice. Ovariectomy did not alter ketamine metabolism in female mice, whereas orchidectomy recapitulated female pharmacokinetic differences in male mice, which was reversed with testosterone replacement. Conclusion: Sex is an important biological variable that influences the metabolism of ketamine and the HNKs, which may contribute to sex differences in therapeutic antidepressant efficacy or side effects.

Antidepressant efficacy of low-frequency repetitive transcranial magnetic stimulation in antidepressant-nonresponding bipolar depression: a single-blind randomized sham-controlled trial

Background To examine the antidepressant efficacy and response predictors of R-DLPFC-LF rTMS for antidepressant-nonresponding BD. Methods We conducted a single-blind randomized sham-controlled trial for 54 (28 sham, 26 active) patients with antidepressant-nonresponding BD (baseline MADRS ≥ 20). Patients received 15 daily sessions of active or sham neuronavigated rTMS (Figure-of-8 coil, five 1 Hz 60 s 110% RMT trains). Outcome measures included depressive response (≥ 50% MADRS reduction, CGI ≤ 2) and remission (MADRS < 7, CGI = 1) rates, treatment emergent hypo/mania (YMRS), depressive and anxiety symptoms (HAM-A). Results 48 patients (25 sham, 23 active) completed treatment, with 3 drop-outs each in active and sham groups. Active rTMS did not produce superior response or remission rates at endpoint or 6 or 12 weeks (ps > 0.05). There was no significant group * time interaction (ps > 0.05) in a multivariate ANOVA with MADRS, HAMA and YMRS as dependent variables. Exploratory analysis found MADRS improvement to be moderated by baseline anxiety (p = 0.02) and melancholia (p = 0.03) at week 3, and depressive onset at weeks 6 (p = 0.03) and 12 (p = 0.04). In subjects with below-mean anxiety (HAMA < 20.7, n = 24), MADRS improvement from active rTMS was superior to sham at week 3 (ITT, t = 2.49, p = 0.04, Cohen’s d = 1.05). No seizures were observed. Groups did not differ in treatment-emergent hypomania (p = 0.1). Limitations Larger sample size might be needed to power subgroup analyses. Moderation analyses were exploratory. Single-blind design. Unblinding before follow-up assessments due to ethical reasons. Conclusions 1-Hz 110% RMT (5 × 60 s trains) R-DLPFC-LF rTMS was not effective for antidepressant non-responding BD but may be further investigated at increased dosage and/or in BD patients with low anxiety. Trial registration CCRB Clinical Trials Registry, CUHK, CUHK_CCT00440. Registered 04 December 2014, https://www2.ccrb.cuhk.edu.hk/registry/public/279

Individualized Precision Targeting of Dorsal Attention and Default Mode Networks with Rtms in Traumatic Brain Injury-Associated Depression

Background At the group level, antidepressant efficacy of rTMS targets is inversely related to their normative connectivity with subgenual anterior cingulate cortex (sgACC). Individualized connectivity may yield better targets, particularly in patients with neuropsychiatric disorders who may have aberrant connectivity. However, sgACC connectivity shows poor test-retest reliability at the individual level. Individualized resting-state network mapping (RSNM) can reliably map inter-individual variability in brain network organization. Objective To identify individualized RSNM-based rTMS targets that reliably target the sgACC connectivity profile. Methods We used RSNM to identify network-based rTMS targets in 10 healthy controls and 13 individuals with traumatic brain injury-associated depression (TBI-D). These “RSNM targets” were compared with consensus structural targets and targets based on individualized anti-correlation with a group-mean-derived sgACC region (“anti-group-mean sgACC targets”). The TBI-D cohort was randomized to receive active (n=9) or sham (n=4) rTMS to RSNM targets. Results The group-mean sgACC connectivity profile was reliably estimated by individualized correlation with default mode network (DMN) and anti-correlation with dorsal attention network (DAN). Individualized RSNM targets were then identified based on DAN anti-correlation and DMN correlation. Counterintuitively, anti-correlation with the group-mean sgACC connectivity profile was stronger and more reliable for RSNM-derived targets than for “anti-group-mean sgACC targets”. Improvement in depression after RSNM-targeted rTMS was predicted by target anti-correlation with the portions of sgACC. Active treatment led to increased connectivity within and between several relevant regions. Conclusions RSNM may enable reliable individualized rTMS targeting, although further research is needed to determine whether this personalized approach can improve clinical outcomes.