Effects of L-theanine on Motor Cortex Excitability in Healthy Subjects: A Paired-Pulse TMS Study

August 30, 2021 updated by: Butler Hospital

Effects of Single-dose L-theanine on Motor Cortex Excitability in Healthy Subjects: A Double-blinded, Randomized Order, Cross-over Paired-Pulse Transcranial Magnetic Stimulation Study

Major depressive disorder (MDD) is a serious mental illness and the leading cause of disability worldwide. New pharmacotherapeutic agents with complementary neurobiological mechanism and better side effect profile are of great needs. In addition to the monoamine system, the glutamatergic system plays a crucial role in MDD.

L-theanine (N5-ethyl-L-glutamine) is the primary psychoactive component uniquely in green tea. Preclinical studies have demonstrated anti-depressant effect of L-theanine in rodents and provided evidences for its pharmacological properties of N-methyl-D-aspartate (NMDA) and gamma-aminobutyric acid (GABA) agonism. Yet these effects have not been proven in humans. Only one open-label clinical trial has studied and supported antidepressant effects of L-theanine in MDD patients. We propose using pair-pulse transcranial magnetic stimulation (ppTMS) to probe how L-theanine may manipulate the glutamatergic and GABA systems in the frontal region by changing cortical excitability first in healthy subjects. We plan to investigate the neurobiological effects of L-theanine in healthy subjects first.

Granted that the first phase pilot trial provides neurophysiological evidence of L-theanine on motor cortex excitability in human subjects, next phases of studies on L-theanine in MDD patients cortical excitability could be justified.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Detailed Description

Background and Significance:

Major depressive disorder (MDD) is a serious mental illness and the leading cause of disability worldwide. Although many antidepressants acting on synaptic monoamine levels have been used as the first-line drug treatment for MDD, around one third of MDD are pharmacologically resistant. Side effects of these medications impose additional hardship on adherence and further affect treatment outcome. New pharmacotherapeutic agents with complementary neurobiological mechanism and better side effect profile are of great needs. In addition to the monoamine system, the glutamatergic system plays a crucial role in MDD.

L-theanine (N5-ethyl-L-glutamine) is the primary psychoactive component uniquely in green tea. Epidemiological studies support that green tea consumption is an independent factor associated with lower prevalence of depression. Preclinical studies have demonstrated anti- depressant effect of L-theanine in rodents and provided evidences for its pharmacological properties of N-methyl-D-aspartate (NMDA) and gamma-aminobutyric acid (GABA) agonism. Yet these effects have not been proven in humans. Only one open-label clinical trial has studied and supported antidepressant effects of L-theanine in MDD patients. We propose using pair-pulse transcranial magnetic stimulation (ppTMS) to probe how L-theanine may manipulate the glutamatergic and GABA systems in the frontal region by changing cortical excitability first in healthy subjects. ppTMS is a well-established technique to investigate frontal motor cortical excitability mediated by the inter-neuron NMDA and GABA receptors. Specific changes of ppTMS measures, including impaired short-term and long-term intracortical inhibition (SICI, mediated by GABA-A receptor; LICI, mediated by GABA-B receptor) and intracortical facilitation (ICF, mediated by NMDA receptor), have been demonstrated in MDD. Using this technique, we plan to investigate the neurobiological effects of L-theanine in healthy subjects first.

Granted that the first phase pilot trial provides neurophysiological evidence of L-theanine on motor cortex excitability in human subjects, next phases of studies on L-theanine in MDD patients cortical excitability could be justified. This will lay foundation for further exploration of L-theanine's potential as an augmenting agent for MDD in a placebo- controlled design.

Aims and Hypothesis:

Given the potential NMDA and GABA agonistic effects of L-theanine, we hypothesize that it increases intracortical inhibition and facilitation through enhancement of NMDA- and GABA-receptor mediated neurotransmission, in healthy subjects (N=10 to complete study).

Study Procedures:

Double-blinded, Randomized-order, Cross-over placebo-controlled to evaluate acute effect of single-dose L-theanine on motor cortex excitability by ppTMS in 10 healthy subjects.

Dose of L-theanine or placebo is 400mg. At baseline, subjects will be randomized to L- theanine or placebo group, then receive ppTMS protocol before drug administration. The ppTMS protocol is repeated after 30min of administration. Then subjects will return to clinic after 1 week free of any medications and repeat the above protocol with the second drug condition. Visual analog scale will be used to evaluate psychosomatic symptoms and wellbeing of the subjects pre- and post-each drug administration.

Data Analytic Plan:

Wilcoxon test will be used to compare the baseline-to-post-drug means of SICI, LICI and ICF measures. Prespecified covariates include age, sex, handedness, level of fatigue will be analyzed in linear regression model. The time-condition relationship with continuous dependent variables of ICI and ICF values will be evaluated by Mixed Effect Model. Two- sided P value < 0.05 is considered statistically significant.

Study Type

Interventional

Enrollment (Actual)

11

Phase

  • Early Phase 1

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • United States
    • Rhode Island
      • Providence, Rhode Island, United States, 02906
        • Butler Hospital

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

16 years to 63 years (Adult, Older Adult)

Accepts Healthy Volunteers

No

Genders Eligible for Study

All

Description

Inclusion Criteria:

  1. Adult, aged between 18 and 65 years old;
  2. Able to read/speak English and give informed consent
  3. No current or history of Axis I psychiatric disorders by DSM-5.
  4. Free of psychotropic medication use

Exclusion Criteria:

  1. History of significant acute or chronic neurological or medical disorder or condition that increases risk for seizure with TMS;
  2. History of alcohol use disorder, nicotine dependence, adjustment disorder;
  3. History of allergic reactions to L-theanine or green tea;
  4. Pregnancy;
  5. Unable/unwilling to abstain from nutraceutical supplements and psychotropic agents during participation in the study
  6. Unable/ unwillingness to refrain from recreational substance use (e.g. alcohol or marijuana) during participation in the study;
  7. Meet criteria for exclusion from TMS or MRI procedures, including intracranial metal implants or nonremovable ferromagnetic items in the head/neck.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Other
  • Allocation: Randomized
  • Interventional Model: Crossover Assignment
  • Masking: Double

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Active Comparator: L-Theanine
Subject will receive 400mg single dose of L-theanine, by oral ingestion with water. The capsules are prepared and dispensed by hospital pharmacy, with the investigator and participant both blinded.
Drug: L-theanine
The subject will receive paired-pulse TMS (ppTMS) procedure before and 30min after taking the drug orally, to assess motor cortex excitability, measured by surface electromyogram (EMG). The ppTMS procedure is administered by a TMS stimulator controlled a program software named Signal. The coil of the stimulator is placed above the scalp where the stimulation would activate the left primary motor cortex region that controls the right thumb. When a pulse stimulation is delivered by the coil, the EMG over a thumb muscle (abductor pollicis brevis) will record a motor-evoked potential on the tracing. Cross-over with placebo in two separate sessions at least 72 hours apart.
Drug: Placebo
The subject will receive paired-pulse TMS (ppTMS) procedure before and 30min after taking the drug orally, to assess motor cortex excitability, measured by surface electromyogram (EMG). The ppTMS procedure is administered by a TMS stimulator controlled a program software named Signal. The coil of the stimulator is placed above the scalp where the stimulation would activate the left primary motor cortex region that controls the right thumb. When a pulse stimulation is delivered by the coil, the EMG over a thumb muscle (abductor pollicis brevis) will record a motor-evoked potential on the tracing. Cross-over with L-theanine in two separate sessions at least 72 hours apart.
Placebo Comparator: Placebo
Subject will receive 400mg single dose of matching Placebo, by oral ingestion with water. The capsules are prepared and dispensed by hospital pharmacy, with the investigator and participant both blinded.
Drug: L-theanine
The subject will receive paired-pulse TMS (ppTMS) procedure before and 30min after taking the drug orally, to assess motor cortex excitability, measured by surface electromyogram (EMG). The ppTMS procedure is administered by a TMS stimulator controlled a program software named Signal. The coil of the stimulator is placed above the scalp where the stimulation would activate the left primary motor cortex region that controls the right thumb. When a pulse stimulation is delivered by the coil, the EMG over a thumb muscle (abductor pollicis brevis) will record a motor-evoked potential on the tracing. Cross-over with placebo in two separate sessions at least 72 hours apart.
Drug: Placebo
The subject will receive paired-pulse TMS (ppTMS) procedure before and 30min after taking the drug orally, to assess motor cortex excitability, measured by surface electromyogram (EMG). The ppTMS procedure is administered by a TMS stimulator controlled a program software named Signal. The coil of the stimulator is placed above the scalp where the stimulation would activate the left primary motor cortex region that controls the right thumb. When a pulse stimulation is delivered by the coil, the EMG over a thumb muscle (abductor pollicis brevis) will record a motor-evoked potential on the tracing. Cross-over with L-theanine in two separate sessions at least 72 hours apart.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
The Change of Motor Cortex Excitability Measures by ppTMS
Time Frame: Before and 30 minutes after each drug administration (no long-term follow up as this is a study on acute effect of a single-dose agent).

The changes of Short-interval Intracortical Inhibition (SICI), Intracortical Facilitation (ICF), and Long-interval Intracortical Inhibition (LICI) before and 30 minutes after each drug administration.

SICI, ICF and LICI are paired-pulse TMS (ppTMS)-EMG outcome measures that assess the activity of motor cortex GABA-A, NMDA and GABA-B interneurons, respectively. They are measured by the ratio between the peak-to-peak amplitude of motor-evoked potential (MEP) elicited by a testing TMS pulse (120% of the intensity of the resting motor threshold, following a conditioning pulse at different inter-stimuli interval, 2-5 milliseconds for SICI, 10-20 milliseconds for ICF, 100-200 milliseconds for LICI) and the peak-to-peak MEP amplitude elicited by a single pulse (120% of the intensity of the resting motor threshold).

The baseline-to-post-drug change of SICI, ICF and LICI elicited by L-theanine will be compared to that elicited by placebo within each subject.
Before and 30 minutes after each drug administration (no long-term follow up as this is a study on acute effect of a single-dose agent).

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
The Change of Visual Analog Scale (VAS)
Time Frame: Throughout each session; each session lasts up to 3 hours; 2 sessions for each subject. The 2 sessions are 3-7 days apart.
VAS is a quick scale to assess and track how the participant subjectively feels through out each study session, e.g. anxiety, depression, excitement, etc. The score for each word ranges from "0" being the least in your life and "100" being the most in your life. It takes 3-4 minutes to complete each VAS, and there are 4 takes of VAS during each session. The outcome measure is the change of VAS throughout the 4 time points: 1) before the baseline ppTMS procedure; 2) before drug administration; 3) 30 minutes after drug administration; 4) before discharge from the session, during the session.
Throughout each session; each session lasts up to 3 hours; 2 sessions for each subject. The 2 sessions are 3-7 days apart.

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Butler Hospital

Investigators

  • Principal Investigator: Linda Carpenter, MD, Brown University-Butler Hospital

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

June 9, 2020

Primary Completion (Actual)

May 31, 2021

Study Completion (Actual)

May 31, 2021

Study Registration Dates

First Submitted

January 27, 2021

First Submitted That Met QC Criteria

February 8, 2021

First Posted (Actual)

February 11, 2021

Study Record Updates

Last Update Posted (Actual)

September 23, 2021

Last Update Submitted That Met QC Criteria

August 30, 2021

Last Verified

August 1, 2021

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 202006-003

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

No

IPD Plan Description

To protect subject confidential information.

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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