This open-label, between-subjects study (n=59) examined the peripheral immune profiles in patients with depression (n=33) before and after ketamine treatment (35mg/70kg) compared to healthy participants (n=26). Pro-inflammatory cytokines were consistently elevated among patients with depression, and although ketamine infusion transiently lowers these markers of inflammation, these changes appear not to be directly linked to clinical antidepressant effects on the long-term.

Abstract

“Introduction: A subset of patients with depression have elevated levels of inflammatory cytokines, and some studies demonstrate interaction between inflammatory factors and treatment outcome. However, most studies focus on only a narrow subset of factors in a patient sample.

Methods: In the current study, we analyzed broad immune profiles in blood from patients with treatment-resistant depression (TRD) at baseline and following treatment with the glutamate modulator ketamine. Serum was analyzed from 26 healthy control and 33 actively depressed TRD patients free of antidepressant medication, and matched for age, sex and body mass index. All subjects provided baseline blood samples, and TRD subjects had additional blood draw at 4 and 24 h following intravenous infusion of ketamine (0.5 mg kg⁻¹). Samples underwent multiplex analysis of 41 cytokines, chemokines and growth factors using quantitative immunoassay technology. Our a priori hypothesis was that TRD patients would show elevations in canonical pro-inflammatory cytokines;

Results: analyses demonstrated significant elevation of the pro-inflammatory cytokine interleukin-6. Further exploratory analyses revealed significant regulation of four additional soluble factors in patients with TRD. Several cytokines showed transient changes in level after ketamine, but none correlated with treatment response. Low pretreatment levels of fibroblast growth factor 2 were associated with ketamine treatment response.

Discussion: In sum, we found that patients with TRD demonstrate a unique pattern of increased inflammatory mediators, chemokines and colony-stimulating factors, providing support for the immune hypothesis of TRD. These patterns suggest novel treatment targets for the subset of patients with TRD who evidence dysregulated immune functioning.”

Authors: D. D. Kiraly, S R Horn, N T Van Dam, S Costi, J Schwartz, S Kim-Schulze, M Patel, G E Hodes, S J Russo, M Merad, D V Iosifescu, D S Charney & J W Murrough

Summary

INTRODUCTION

Major depressive disorder (MDD) is a debilitating condition that can have profound effects on both the mind and body of individuals who suffer from the disorder. Some studies have shown that increased inflammation may be a contributing factor to depression, making the understanding of pathophysiology and alternative treatment strategies critical research aim.

Recent evidence has shown that patients with MDD have altered signaling and metabolism of glutamate, and that ketamine, an N-methyl-D-aspartate receptor antagonist, has anti-inflammatory properties. Ketamine may also modulate inflammatory signaling in ways that contribute to its antidepressant efficacy.

The current study examined a broad panel of inflammatory mediators in patients with TRD compared with healthy controls. The data can be used to develop further hypotheses about the role of inflammation in depression.

Male and female adults with TRD and HC volunteers were recruited through an outpatient psychiatric research program at Icahn School of Medicine at Mount Sinai. They were free of all antidepressant medications for at least 2 weeks prior to starting the study protocol. Patients with TRD were excluded if they had a history of psychotic disorder, substance abuse, unstable medical illness or active nicotine use. Healthy volunteers were free of active infections or systemic illness.

Individuals with TRD meeting the above criteria were eligible if they were also enrolled in a concurrent clinical trial of ketamine at Mount Sinai. The study sample size was determined using G*power software.

Sample collection and ketamine infusion procedures

All blood samples were obtained via antecubetal venous collection using standard techniques. The primary clinical outcome was change in depressive severity from baseline to +24 h following a single intravenous infusion of ketamine.

Multiplex analysis

Measurement of cytokines, chemokines and growth factors was performed on serum samples isolated as above. A Luminex 200 multiplex immunoassay system was used for analysis, and IL-6 levels were correlated with enzyme-linked immunosorbent assay analysis of the same samples.

Data analysis

Data were analyzed and graphed using SPSS and GraphPad Prism, and baseline group differences were examined using linear regression. Changes in cytokine levels at 4 and 24 h were performed via paired t-tests, and inflammatory cytokines were found to be elevated in TRD patients.

Patient characteristics

Thirty-three patients with TRD and 26 healthy volunteers completed all study procedures and were included in the analyses.

At baseline, inflammatory cytokines were significantly elevated in TRD patients compared to medication-free subjects. After ketamine treatment, inflammatory cytokines decreased modestly, but significantly, from baseline levels.

Exploration of altered cytokines, chemokines and growth factors in TRD patients

Four different analytes were significantly different between HC and TRD subjects, including MCP-1, G-CSF, GM-CSF and PDGF-BB. Brain-derived neurotrophic factor did not change with ketamine treatment.

We also examined a panel of exploratory markers to determine whether any of them were influenced by the treatment with ketamine. Three showed modest changes after ketamine treatment, but none were significantly different from baseline level at the 24-h time point.

Table 1 shows the demographic characteristics of the healthy control, antidepressant, electroconvulsive therapy, major depressive episode, substance use disorder, and treatment-resistant depression populations.

Table 2 shows the levels of cytokines, chemokines and growth factors in the cerebrospinal fluid of healthy controls and treatment-resistant depression subjects.

We analyzed baseline levels of factors in patients who did and did not show adequate response to ketamine. We found that patients with lower levels of FGF-2 had a higher likelihood of responding to ketamine (pg ml 1/hr), which was correlated with a lower depression rating scale score.

DISCUSSION

In this study, we examined peripheral immune profiles in medication-free patients with TRD before and after treatment with ketamine. We found that a subset of TRD patients had increased inflammatory markers, and low levels of serum FGF-2 were a specific predictor of treatment response.

Inflammation and treatment response

We found that IL-6 and IL-1 levels were elevated in the depressed population, and that ketamine decreased levels of IL-6 and IL-1 4 h after the infusion, but that these decreases did not correlate with clinical response to ketamine treatment.

Exploratory cytokines

We found that several factors were significantly upregulated in our TRD population, including two colony-stimulating factors and the chemotactic cytokine MCP-1. This suggests that a subset of patients may have increased mobilization of monocytes from the bone marrow, and increased chemotactic factors drawing them to target organs, including the brain.

FGF-2 was found to be a good predictor of ketamine treatment response, although baseline delta sleep ratio, CNS glutamate levels or cognitive function were also found to be useful. FGF-2 has received considerable attention for its role in depression. Patients with low levels of FGF-2 may represent a specific subset of patients who may be more likely to respond to ketamine treatment.

Comparisons to recent literature and limitations

The results of our study suggest that ketamine treatment response is not directly related to a reduction of inflammatory cytokines such as IL-6. This runs counter to a recent study that suggested that decreases in IL-6 after ketamine treatment were predictive of antidepressant treatment response.

A study by Park et al. found that ketamine increased IL-6 levels in patients with active MDD or bipolar depression, but this effect was minimal, transient, and did not correlate with treatment response.

Although our data showed altered cytokine levels in patients with TRD compared to HC, we cannot say that these changes are specific to TRD and would not be seen in treatment-responsive MDD. Further study is needed to fully establish how cytokines may be altered specifically in treatment resistance.

Our study adds to the growing literature implicating dysregulation of immune signaling in depression, however, ketamine does not appear to be directly linked to clinical antidepressant effects.

CONFLICT OF INTEREST

Dr Iosifescu has consulted for several companies, and Dr Murrough has received grant/research support from several companies. Dr Charney and the Icahn School of Medicine at Mount Sinai could potentially benefit if ketamine were to gain approval for the treatment of depression.

ACKNOWLEDGMENTS

Dr Murrough was funded by the National Institute of Mental Health and Dr Kiraly by the Leon Levy Foundation.

The molecular neurobiology of depression is described by Krishnan V, Nestler EJ, Rush AJ, Trivedi MH, Wisniewski SR, Nierenberg AA, Stewart JW, Warden D et al., and Hodes GE, Kana V, Menard C, Merad M, Russo SJ. Khandaker GM, Pearson RM, Zammit S, Lewis G, Jones PB, Maes M, De Jongh R, Kenis G, Vandoolaeghe G, Neels H. Association of serum interleukin 6 and C-reactive protein in childhood with depression and psychosis in young adult life. A systematic review and meta-analysis of randomized clinical trials found that anti-inflammatory treatment improved depression, depressive symptoms, and adverse effects, and that a glutamate hypothesis of depression is an emerging frontier of neuropsychopharmacology for mood disorders. Ketamine may be an effective treatment for major depressive disorder and for treatment-resistant major depression. It may also be used to reduce inflammation following surgery. Ketamine exerts antidepressant effects and reduces IL-1 and IL-6 levels in the prefrontal cortex and hippocampus of rats and mice, and is a predictive biomarker for ketamine’s antidepressant effect in treatment-resistant patients with major depression.

The role of inflammation in depression is discussed, and the kynurenine pathway is proposed as a common target for ketamine. IFN-alpha-induced cortical and subcortical glutamate changes assessed by magnetic resonance spectroscopy are associated with increased basal ganglia glutamate in patients with major depression. Inflammation is associated with decreased functional connectivity within corticostriatal reward circuitry in depression, and plasma cytokine profiles are higher in patients who fail to respond to selective serotonin reuptake inhibitor therapy. Individual differences in the peripheral immune system promote resilience versus susceptibility to social stress, and increased microglial priming and macrophage recruitment in the dorsal anterior cingulate white matter are associated with depression and suicide. Stress-induced recruitment of bone marrow-derived monocytes to the brain promotes anxiety-like behavior, and knock-down of interleukin-1 receptor type-1 on endothelial cells attenuates stress-induced neuroinflammation and prevents anxiety-like behavior. Ketamine and other nmda antagonists have been shown to improve depression. Ketamine treatment for major depression is associated with clinical predictors, anxious depression is associated with adverse effects, and Shank3 may be a biomarker of treatment response.

Adipokines and fibroblast growth factor play an important role in the rapid antidepressant effects of ketamine and in the dysregulation of the fibroblast growth factor system in patients with major depressive disorder.

This work is licensed under a Creative Commons Attribution 4.0 International License. To reproduce any of the images in this article, please obtain permission from the author.