Risks Associated with Misuse of Ketamine as a Rapid-Acting Antidepressant

Comparison of antidepressant and side effects in mice after intranasal administration of (R,S)-ketamine, (R)-ketamine, and (S)-ketamine

The N-methyl-d-aspartate receptor (NMDAR) antagonist (R,S)-ketamine produces rapid and sustained antidepressant effects in treatment-resistant patients with depression although intranasal use of (R,S)-ketamine in ketamine abusers is popular. In March 5, 2019, nasal spray of (S)-ketamine for treatment-resistant depression was approved as a new antidepressant by the US Food Drug Administration. Clinical study of (R)-ketamine is underway. In a chronic social defeat stress (CSDS) model, we compared the antidepressant effects of (R,S)-ketamine, (R)-ketamine, and (S)-ketamine after a single intranasal administration. Furthermore, we also compared the side effects (i.e., locomotion, prepulse inhibition (PPI), abuse liability) of these three compounds in mice. The order of potency of antidepressant effects after a single intranasal administration was (R)-ketamine > (R,S)-ketamine > (S)-ketamine. In contrast, the order of locomotor activity and prepulse inhibition (PPI) deficits after a single intranasal administration was (S)-ketamine > (R,S)-ketamine > (R)-ketamine. In the conditioned place preference (CPP) test, both (S)-ketamine and (R,S)-ketamine increased CPP scores in mice after repeated intranasal administration, in a dose dependent manner. In contrast, (R)-ketamine did not increase CPP scores in mice. These findings suggest that intranasal administration of (R)-ketamine would be a safer antidepressant than (R,S)-ketamine and (S)-ketamine.

Drug addiction: a curable mental disorder?

Drug addiction is a chronic, relapsing brain disorder. Multiple neural networks in the brain including the reward system (e.g., the mesocorticolimbic system), the anti-reward/stress system (e.g., the extended amygdala), and the central immune system, are involved in the development of drug addiction and relapse after withdrawal from drugs of abuse. Preclinical and clinical studies have demonstrated that it is promising to control drug addiction by pharmacologically targeting the addiction-related systems in the brain. Here we review the pharmacological targets within the dopamine system, glutamate system, trace amine system, anti-reward system, and central immune system, which are of clinical interests. Furthermore, we discuss other potential therapies, e.g., brain stimulation, behavioral treatments, and therapeutic gene modulation, which could be effective to treat drug addiction. We conclude that, although drug addiction is a complex disorder that involves complicated neural mechanisms and psychological processes, this mental disorder is treatable and may be curable by therapies such as gene modulation in the future.

AMPA Receptor Activation-Independent Antidepressant Actions of Ketamine Metabolite (S)-Norketamine

BACKGROUND

Ketamine, an N-methyl-D-aspartate receptor antagonist, exerts robust antidepressant effects in patients with treatment-resistant depression. The precise mechanisms underlying ketamine's antidepressant actions remain unclear, although previous research suggests that alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) activation plays a role. We investigated whether (S)-norketamine and (R)-norketamine, the two main metabolites of (R,S)-ketamine, also play a significant role in ketamine's antidepressant effects and whether the effects are mediated by AMPAR.

METHODS

Cellular mechanisms of antidepressant action of norketamine enantiomers were examined in mice.

RESULTS

(S)-Norketamine had more potent antidepressant effects than (R)-norketamine in inflammation and chronic social defeat stress models. Furthermore, (S)-norketamine induced more beneficial effects on decreased dendritic spine density and synaptogenesis in the prefrontal cortex and hippocampus compared with (R)-norketamine. Unexpectedly, AMPAR antagonists did not block the antidepressant effects of (S)-norketamine. The electrophysiological data showed that, although (S)-norketamine inhibited N-methyl-D-aspartate receptor-mediated synaptic currents, (S)-norketamine did not enhance AMPAR-mediated neurotransmission in hippocampal neurons. Furthermore, (S)-norketamine improved reductions in brain-derived neurotrophic factor-tropomyosin receptor kinase B signaling in the prefrontal cortex of mice susceptible to chronic social defeat stress, whereas the tropomyosin receptor kinase B antagonist and a mechanistic target of rapamycin inhibitor blocked the antidepressant effects of (S)-norketamine. In contrast to (S)-ketamine, (S)-norketamine did not cause behavioral abnormalities, such as prepulse inhibition deficits, reward effects, loss of parvalbumin immunoreactivity in the medial prefrontal cortex, or baseline gamma-band oscillation increase.

CONCLUSIONS

Our data identified a novel AMPAR activation-independent mechanism underlying the antidepressant effects of (S)-norketamine. (S)-Norketamine and its prodrugs could be novel antidepressants without the detrimental side effects of (S)-ketamine.

Ketamine for pain management

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Intravenous Ketamine for Adolescents with Treatment-Resistant Depression: An Open-Label Study

BACKGROUND

Novel interventions for treatment-resistant depression (TRD) in adolescents are urgently needed. Ketamine has been studied in adults with TRD, but little information is available for adolescents. This study investigated efficacy and tolerability of intravenous ketamine in adolescents with TRD, and explored clinical response predictors.

METHODS

Adolescents, 12-18 years of age, with TRD (failure to respond to two previous antidepressant trials) were administered six ketamine (0.5 mg/kg) infusions over 2 weeks. Clinical response was defined as a 50% decrease in Children's Depression Rating Scale-Revised (CDRS-R); remission was CDRS-R score ≤28. Tolerability assessment included monitoring vital signs and dissociative symptoms using the Clinician-Administered Dissociative States Scale (CADSS).

RESULTS

Thirteen participants (mean age 16.9 years, range 14.5-18.8 years, eight biologically male) completed the protocol. Average decrease in CDRS-R was 42.5% (p = 0.0004). Five (38%) adolescents met criteria for clinical response. Three responders showed sustained remission at 6-week follow-up; relapse occurred within 2 weeks for the other two responders. Ketamine infusions were generally well tolerated; dissociative symptoms and hemodynamic symptoms were transient. Higher dose was a significant predictor of treatment response.

CONCLUSIONS

These results demonstrate the potential role for ketamine in treating adolescents with TRD. Limitations include the open-label design and small sample; future research addressing these issues are needed to confirm these results. Additionally, evidence suggested a dose-response relationship; future studies are needed to optimize dose. Finally, questions remain regarding the long-term safety of ketamine as a depression treatment; more information is needed before broader clinical use.

Metabolomics of Major Depressive Disorder and Bipolar Disorder: Overview and Future Perspective

Major depressive disorder (MDD) and bipolar disorder (BD) are the most common mood disorders. They are etiologically related, but clinically distinct psychiatric illnesses. Their shared clinical features result in high rates of misdiagnosis due to a lack of biomarkers that allow their differentiation. BD is more frequently misdiagnosed as MDD because of overlapping symptomology, often later onset of mania, and frequent occurrence of depressive episodes in patients with BD. Misdiagnosis is also increased when patients with BD present symptoms indicative of a clinically significant depressive episode, but are premorbid for manic symptoms, or previous manic states not recognized. Therefore, the development of specific biomarkers for these disorders would be invaluable for establishing the correct diagnosis and treatment of MDD and BD. This chapter presents an overview and future perspective of the identification of biomarkers for mood disorders using metabolomics.

Mechanistic Target of Rapamycin-Independent Antidepressant Effects of (R)-Ketamine in a Social Defeat Stress Model

BACKGROUND

The role of the mechanistic target of rapamycin (mTOR) signaling in the antidepressant effects of ketamine is controversial. In addition to mTOR, extracellular signal-regulated kinase (ERK) is a key signaling molecule in prominent pathways that regulate protein synthesis. (R)-Ketamine has a greater potency and longer-lasting antidepressant effects than (S)-ketamine. Here we investigated whether mTOR signaling and ERK signaling play a role in the antidepressant effects of two enantiomers.

METHODS

The effects of mTOR inhibitors (rapamycin and AZD8055) and an ERK inhibitor (SL327) on the antidepressant effects of ketamine enantiomers in the chronic social defeat stress (CSDS) model (n = 7 or 8) and on those of ketamine enantiomers in these signaling pathways in mouse brain regions were examined.

RESULTS

The intracerebroventricular infusion of rapamycin or AZD8055 blocked the antidepressant effects of (S)-ketamine, but not (R)-ketamine, in the CSDS model. Furthermore, (S)-ketamine, but not (R)-ketamine, significantly attenuated the decreased phosphorylation of mTOR and its downstream effector, ribosomal protein S6 kinase, in the prefrontal cortex of susceptible mice after CSDS. Pretreatment with SL327 blocked the antidepressant effects of (R)-ketamine but not (S)-ketamine. Moreover, (R)-ketamine, but not (S)-ketamine, significantly attenuated the decreased phosphorylation of ERK and its upstream effector, mitogen-activated protein kinase/ERK kinase, in the prefrontal cortex and hippocampal dentate gyrus of susceptible mice after CSDS.

CONCLUSIONS

This study suggests that mTOR plays a role in the antidepressant effects of (S)-ketamine, but not (R)-ketamine, and that ERK plays a role in (R)-ketamine's antidepressant effects. Thus, it is unlikely that the activation of mTOR signaling is necessary for antidepressant actions of (R)-ketamine.

Possible role of the gut microbiota-brain axis in the antidepressant effects of (R)-ketamine in a social defeat stress model

Accumulating evidence suggests that the gut microbiota-brain axis plays a role in the pathogenesis of depression, thereby contributing to the antidepressant actions of certain compounds. (R)-ketamine has a greater potency and longer-lasting antidepressant effects than (S)-ketamine. Here, we investigated whether the gut microbiota plays a role in the antidepressant effects of these two ketamine enantiomers. The role of the gut microbiota in the antidepressant effects of ketamine enantiomers in a chronic social defeat stress (CSDS) model of depression was examined using 16S ribosomal RNA gene sequencing of fecal samples. At the phylum level, CSDS-susceptible mice showed alterations in the levels of Tenericutes and Actinobacteria; however, neither ketamine enantiomers influenced these alterations. At the class level, both ketamine enantiomers significantly attenuated the increase in the levels of Deltaproteobacteria in the susceptible mice after CSDS. Furthermore, (R)-ketamine, but not (S)-ketamine, significantly attenuated the reduction in the levels of Mollicutes in the susceptible mice. At the genus level, both ketamine enantiomers significantly attenuated the decrease in the levels of Butyricimonas in the susceptible mice. Notably, (R)-ketamine was more potent than (S)-ketamine at reducing the levels of Butyricimonas in the susceptible mice. In conclusion, this study suggests that the antidepressant effects of two enantiomers of ketamine in CSDS model may be partly mediated by the restoration of the gut microbiota. Furthermore, the specific effect of (R)-ketamine on the levels of Mollicutes and Butyricimonas may explain its robust antidepressant action.

Fisetin provides antidepressant effects by activating the tropomyosin receptor kinase B signal pathway in mice

Depression has been associated with a low-grade chronic inflammatory state, suggesting a potential therapeutic role for anti-inflammatory agents. Fisetin is a naturally occurring flavonoid in strawberries that has anti-inflammatory activities, but whether fisetin has antidepressant effects is unknown. In this study, we exposed mice to spatial restraint for 2 weeks with or without treatment with fisetin. Immobility time in the forced swimming and tail suspension test after this restraint increased in the untreated group, but this increase did not occur in the fisetin group. We administered fisetin to Abelson helper integration site-1 (Ahi1) knockout mice, which have depressive phenotypes. We found that fisetin attenuated the depressive phenotype of these Ahi1 knockout mice. We further investigated the potential mechanism of fisetin's antidepressant effects. Because TrkB is a critical signaling pathway in the mechanisms of depression, we examined whether phosphorylated TrkB was involved in the antidepressant effects of fisetin. We found that fisetin increased phosphorylated TrkB level without altering total TrkB; this increase was attenuated by K252a, a specific TrkB inhibitor. Taken together, our results demonstrated that fisetin may have therapeutic potential for treating depression and that this antidepressant effect may be mediated by the activation of the TrkB signaling pathway.

Analysis of print news media framing of ketamine treatment in the United States and Canada from 2000 to 2015

OBJECTIVES

There are multifaceted views on the use of ketamine, a potentially addictive substance, to treat mental health problems. The past 15 years have seen growing media coverage of ketamine for medical and other purposes. This study examined the print news media coverage of medical and other uses of ketamine in North America to determine orientations and trends over time.

METHODS

Print newspaper coverage of ketamine from 2000 to 2015 was reviewed, resulting in 43 print news articles from 28 North American newspapers. A 55-item structured coding instrument was applied to assess news reports of ketamine. Items captured negative and positive aspects, therapeutic use of ketamine, and adverse side effects. Chi-squares tested for changes in trends over time.

RESULTS

In the 15-year reviewed period, the three most frequent themes related to ketamine were: abuse (68.2%), legal status (34.1%), and clinical use in anesthesia (31.8%). There was significant change in trends during two periods (2000-2007 and 2008-2015). In 2008-2015, print news media articles were significantly more likely to encourage clinical use of ketamine to treat depression (p = 0.002), to treat treatment resistant depression (p = 0.043), and to claim that ketamine is more effective than conventional antidepressants (p = 0.043).

CONCLUSIONS

Our review found consistent positive changes in the portrayals of ketamine by the print news media as a therapeutic antidepressant that mirror the recent scientific publications. These changes in news media reporting might influence the popularity of ketamine use to treat clinical depression. Guidance is required for journalists on objective reporting of medical research findings, including limitations of current research evidence and potential risks of ketamine.