Lack of relapse with tryptophan depletion following successful treatment with ECT

Changes in Tryptophan-Kynurenine Metabolism in Patients with Depression Undergoing ECT-A Systematic Review

The kynurenine pathway of tryptophan (Trp) metabolism generates multiple biologically active metabolites (kynurenines) that have been implicated in neuropsychiatric disorders. It has been suggested that modulation of kynurenine metabolism could be involved in the therapeutic effect of electroconvulsive therapy (ECT). We performed a systematic review with aims of summarizing changes in Trp and/or kynurenines after ECT and assessing methodological issues. The inclusion criterium was measures of Trp and/or kynurenines before and after ECT. Animal studies and studies using Trp administration or Trp depletion were excluded. Embase, MEDLINE, PsycInfo and PubMed were searched, most recently in July 2022. Outcomes were levels of Trp, kynurenines and ratios before and after ECT. Data on factors affecting Trp metabolism and ECT were collected for interpretation and discussion of the reported changes. We included 17 studies with repeated measures for a total of 386 patients and 27 controls. Synthesis using vote counting based on the direction of effect found no evidence of effect of ECT on any outcome variable. There were considerable variations in design, patient characteristics and reported items. We suggest that future studies should include larger samples, assess important covariates and determine between- and within-subject variability. PROSPERO (CRD42020187003).

Non-Invasive Brain Stimulation Effects on Biomarkers of Tryptophan Metabolism: A Scoping Review and Meta-Analysis

Abnormal activation of the kynurenine and serotonin pathways of tryptophan metabolism is linked to a host of neuropsychiatric disorders. Concurrently, noninvasive brain stimulation (NIBS) techniques demonstrate high therapeutic efficacy across neuropsychiatric disorders, with indications for modulated neuroplasticity underlying such effects. We therefore conducted a scoping review with meta-analysis of eligible studies, conforming with the PRISMA statement, by searching the PubMed and Web of Science databases for clinical and preclinical studies that report the effects of NIBS on biomarkers of tryptophan metabolism. NIBS techniques reviewed were electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS), and transcranial direct current stimulation (tDCS). Of the 564 search results, 65 studies were included with publications dating back to 1971 until 2022. The Robust Bayesian Meta-Analysis on clinical studies and qualitative analysis identified general null effects by NIBS on biomarkers of tryptophan metabolism, but moderate evidence for TMS effects on elevating serum serotonin levels. We cannot interpret this as evidence for or against the effects of NIBS on these biomarkers, as there exists several confounding methodological differences in this literature. Future controlled studies are needed to elucidate the effects of NIBS on biomarkers of tryptophan metabolism, an under-investigated question with substantial implications to clinical research and practice.

Interaction between two HTR2A polymorphisms and gender is associated with treatment response in MDD

The 5HT2A receptor gene (HTR2A) polymorphisms rs7997012 and rs6311 have in some earlier studies been associated with serotonin selective reuptake inhibitor (SSRI) treatment response in major depressive disorder (MDD), but the findings are inconsistent. The aim of the present study was to test for an association between two HTR2A polymorphisms (rs7997012 and rs6311), their interaction and the Montgomery and Åsberg Depression Rating Scale (MADRS) score change after ECT or SSRI treatment. The total number of patients was 218. All were treated in outpatient care. Of these, 119 subjects had treatment-resistant MDD and were treated with ECT and 99 were depressive patients treated with SSRI. Treatment response was assessed by MADRS. Patients scoring <8 on post-treatment MADRS were considered remitters. Neither rs7997012 nor rs6311 HTR2A polymorphism was significantly associated with MADRS score change alone, but the interaction between them and gender explained 14% of the variance in MADRS score change. The finding suggests an association between MADRS score change and interaction of HTR2A polymorphisms, rs7997012 and rs6311 and gender.

Antidepressant response to electroconvulsive therapy is sustained after catecholamine depletion

Although the antidepressant mechanism of ECT is unknown, there are data to support noradrenergic involvement. Patients who had been recently successfully treated with ECT for major depression were studied in a randomized double-blind cross-over design comparing catecholamine depletion using alpha-methyl-para-tyrosine to a placebo procedure. Mean MADRS scores at baseline (4.2 SD 2.7) and following depletion (4.6 SD 1.1) were similar, despite a 57.7% decrease in serum homovanillic acid (HVA) and a 61.5% decrease in 3-methoxy-4-hydroxyenylethyleneglycol (MHPG). These data suggest that catecholamine availability may not be necessary for acutely maintaining an antidepressant response to ECT.

Diminished central nervous 5-HT neurotransmission and mood self-ratings in children and adolescents with ADHD: no clear effect of rapid tryptophan depletion

INTRODUCTION

Research on 5-HT-functioning in adult patients and healthy subjects using rapid tryptophan depletion (RTD) has indicated weak but stable effects on mood ratings. Altered mood in children and adolescents with attention-deficit/hyperactivity disorder (ADHD) can confound the differential diagnosis between severe ADHD and mood disorders such as pediatric bipolar disorder. The present study investigated the effects of RTD induced lowered central nervous 5-HT-levels on mood self-ratings in children with ADHD.

METHODS

Seventeen boys with ADHD participated in the study in a double-blind within-subject crossover-design. They were administered RTD within an amino acid drink lacking tryptophan, thus lowering central nervous 5-HT-synthesis. On another day they received a placebo. Self-rated mood was assessed on both days at baseline conditions and at three different post-drink time-points.

RESULTS

RTD had no clear effect on mood within the whole sample. Low scorers on venturesomeness were more strongly affected by RTD in terms of feelings of inactivity and negative feelings compared to high venture patients.

CONCLUSIONS

Our data did not show a significant effect of RTD on mood self-ratings. However, the findings must be considered as preliminary and require further replication, in particular as they could be due to sampling bias.

Patients with a major depressive episode responding to treatment with repetitive transcranial magnetic stimulation (rTMS) are resistant to the effects of rapid tryptophan depletion

Repetitive transcranial magnetic stimulation (rTMS) appears to be efficacious in the treatment of major depression based on the results of controlled studies, but little is known about its antidepressant mechanism of action. Mood sensitivity following rapid tryptophan depletion (RTD) has been demonstrated in depressed patients responding to SSRI antidepressants and phototherapy, but not in responders to electroconvulsive therapy (ECT). We sought to study the effects of RTD in patients with major depression responding to a course of treatment with rTMS. Twelve subjects treated successfully with rTMS monotherapy underwent both RTD and sham depletion in a double-blind crossover design. Depressive symptoms were assessed using both a modified Hamilton Depression Rating Scale (HDRS) and Beck Depression Inventory (BDI). The differential change in depression scores across the procedures was compared. No significant difference in mood symptoms was noted between RTD and the sham-depletion procedure on either continuous measures of depression, or in the proportions of subjects that met predefined criteria for a significant degree of mood worsening. Responders to rTMS are resistant to the mood perturbing effects of RTD. This suggests that rTMS does not depend on the central availability of serotonin to exert antidepressant effects in major depression.

Mood is indirectly related to serotonin, norepinephrine and dopamine levels in humans: a meta-analysis of monoamine depletion studies

Dysfunction in the monoamine systems of serotonin (5-HT), norepinephrine (NE) and dopamine (DA) may causally be related to major depressive disorder (MDD). Monoamine depletion studies investigate the direct effects of monoamines on mood. Acute tryptophan depletion (ATD) or para-chlorophenylalanine (PCPA) deplete 5-HT, acute phenylalanine/tyrosine depletion (APTD) or alpha-methyl-para-tyrosine (AMPT) deplete NE/DA. Available depletion studies found conflicting results in heterogeneous populations: healthy controls, patients with previous MDD in remission and patients suffering from MDD. The decrease in mood after 5-HT and NE/DA depletion in humans is reviewed and quantified. Systematic search of MEDLINE and EMBASE (1966-October 2006) and cross-references was carried out. Randomized studies applying ATD, PCPA, APTD or AMPT vs control depletion were included. Pooling of results by meta-analyses was stratified for studied population and design of the study (within or between subjects). Seventy-three ATD, 2 PCPA, 10 APTD and 8 AMPT studies were identified of which 45 ATD and 8 APTD studies could be meta-analyzed. 5-HT or NE/DA depletion did not decrease mood in healthy controls. 5-HT or NE/DA depletion slightly lowered mood in healthy controls with a family history of MDD. In drug-free patients with MDD in remission, a moderate mood decrease was found for ATD, without an effect of APTD. ATD induced relapse in patients with MDD in remission who used serotonergic antidepressants. In conclusion, monoamine depletion studies demonstrate decreased mood in subjects with a family history of MDD and in drug-free patients with MDD in remission, but do not decrease mood in healthy humans. Although depletion studies usefully investigate the etiological link of 5-HT and NE with MDD, they fail to demonstrate a causal relation. They presumably clarify a vulnerability trait to become depressed. Directions for further investigation of this vulnerability trait are proposed.

Acute tryptophan depletion. Part II: clinical effects and implications

OBJECTIVE

This is the second of two articles reviewing the modern dietary technique of acute tryptophan depletion (ATD), a method of transiently reducing central serotonin levels in both healthy volunteers and clinical populations. This article details the clinical studies to date and discusses the implications of this research methodology.

METHOD

The authors present a review of clinical ATD studies collated from a MEDLINE search, unpublished communications and the authors' considerable experience with this paradigm.

RESULTS

Following from the initial use of ATD in subjects with depressive illness, studies of anxiety disorders and other psychiatric illnesses have been reported. Sleep, aggressive and cognitive effects are also active areas of research and are reviewed here.

CONCLUSIONS

Acute tryptophan depletion remains a useful psychiatric research tool. The findings from the clinical studies reviewed here are summarized and implications for future research detailed.

Response to tryptophan depletion in major depression treated with either cognitive therapy or selective serotonin reuptake inhibitor antidepressants

BACKGROUND

Mood sensitivity to rapid tryptophan depletion (RTD) has been demonstrated in patients treated with antidepressants that act preferentially on the serotonergic system. Depressed patients treated with bright-light therapy also show sensitivity to RTD, but those treated with electroconvulsive therapy or total sleep deprivation do not. Patients treated with an empirically supported psychotherapy have not been investigated for sensitivity to tryptophan depletion. This study compares the effects of RTD in patients treated with either selective serotonin re-uptake inhibitors (SSRIs) or cognitive therapy (CT).

METHODS

Twenty patients treated with either SSRIs or CT underwent both rapid tryptophan depletion and sham-depletion using a blinded crossover design. Depressive symptoms were assessed using a modified Hamilton Depression Rating Scale (HDRS) and the Beck Depression Inventory (BDI). The differential change in depression scores across procedures between the groups was compared, and effect sizes were calculated.

RESULTS

The differential worsening of mood for the SSRI group compared with the CT group was significant on the BDI. The effect size of the differential change was 1.6 for the BDI and.8 for the HDRS. Furthermore, the SSRI group experienced significant mood worsening during depletion compared with sham on both the HDRS and the BDI, whereas the CT group did not.

CONCLUSIONS

The CT group was resistant to the effects of tryptophan depletion, but the SSRI group was not.

The role of serotonin in human mood and social interaction. Insight from altered tryptophan levels

Alterations in brain tryptophan levels cause changes in brain serotonin synthesis, and this has been used to study the implication of altered serotonin levels in humans. In the acute tryptophan depletion (ATD) technique, subjects ingest a mixture of amino acids devoid of tryptophan. This results in a transient decline in tissue tryptophan and in brain serotonin. ATD can result in lower mood and increase in irritability or aggressive responding. The magnitude of the effect varies greatly depending on the susceptibility of the subject to lowered mood or aggressivity. Unlike ATD, tryptophan can be given chronically. Tryptophan is an antidepressant in mild to moderate depression and a small body of data suggests that it can also decrease aggression. Preliminary data indicate that tryptophan also increases dominant behavior during social interactions. Overall, studies manipulating tryptophan levels support the idea that low serotonin can predispose subjects to mood and impulse control disorders. Higher levels of serotonin may help to promote more constructive social interactions by decreasing aggression and increasing dominance.

The effects of tryptophan depletion on mood and psychiatric symptoms

BACKGROUND

The number of studies using tryptophan depletion (TD) challenge has increased markedly in the past few years. Recently, a number of negative results have been published, implicating that the effect of TD on mood may be less consistent than previously thought.

METHODS

The literature on the mood effects of TD in psychiatric patients and healthy volunteers was reviewed.

RESULTS

TD has a mood-lowering effect in subgroups of recovered depressed patients, patients with seasonal affective disorder and vulnerable healthy subjects. The mood effect in former patients is of a different quality, however, than the effect in healthy subjects. Some recent negative studies in depression might be explained by insufficient lowering of plasma tryptophan levels. Preliminary evidence exists for an effect of TD on bulimia nervosa, autism, aggression and substance dependence.

CONCLUSIONS

The effects of TD on mood may be more consistent than suggested by a number of recent negative studies. Response to TD in recovered depressed patients is associated with prior treatment. However, even in SSRI-treated patients the relapse rates are not higher than 50-60%, which needs to be explained. The clinical usefulness of the response to TD in recovered patients (prediction of relapse after treatment discontinuation) and in symptomatic patients (prediction of treatment refractoriness) deserves more research attention. Further suggestions for future research include the cognitive effects of TD in recovered depressed patients and the effect of dietary habits on response to TD.