Characterization of l -Theanine Excitatory Actions on Hippocampal Neurons: Toward the Generation of Novel N-Methyl- d -aspartate Receptor Modulators Based on Its Backbone

Article abstract of DOI:10.1021/acschemneuro.7b00036

l-Theanine (or l-γ-N-ethyl-glutamine) is the major amino acid found in Camellia sinensis. It has received much attention because of its pleiotropic physiological and pharmacological activities leading to health benefits in humans, especially. We describe here a new, easy, efficient, and environmentally friendly chemical synthesis of l-theanine and l-γ-N-propyl-Gln and their corresponding d-isomers. l-Theanine, and its derivatives obtained so far, exhibited partial coagonistic action at N-methyl-d-aspartate (NMDA) receptors, with no detectable agonist effect at other glutamate receptors, on cultured hippocampal neurons. This activity was retained on NMDA receptors expressed in Xenopus oocytes. In addition, both GluN2A and GluN2B containing NMDA receptors were equally modulated by l-theanine. The stereochemical change from l-theanine to d-theanine along with the substitution of the ethyl for a propyl moiety in the γ-N position of l- and d-theanine significantly enhanced the biological efficacy, as measured on cultured hippocampal neurons. l-Theanine structure thus represents an interesting backbone to develop novel NMDA receptor modulators.

Full text of DOI:10.1021/acschemneuro.7b00036

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Article
Characterization of L-Theanine excitatory actions on
hippocampal neurons: towards the generation of novel N-
methyl-D-aspartate receptor modulators based on its backbone
Fatiha Sebih, Matthieu Rousset, Salima Bellahouel, Marc Rolland, Marie Celeste de Jesus Ferreira,
Janique Guiramand, Catherine Cohen-Solal, Gérard Barbanel, Thierry Cens, Mohammed Abouazza,
Adrien Tassou, Maud Gratuze, Céline Meunier, Pierre Charnet, Michel Vignes, and Valérie Rolland
ACS Chem. Neurosci., Just Accepted Manuscript • Publication Date (Web): 16 May 2017
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Characterization of L-Theanine excitatory actions on hippocampal neurons: towards
the generation of novel N-methyl-D-aspartate receptor modulators based on its
backbone
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Fatiha Sebiha,b, Matthieu Rousseta, Salima Bellahouelb, Marc Rollandc, Marie Celeste de Jesus
Ferreiraa, Janique Guiramanda, Catherine Cohen-Solala, Gérard Barbanela, Thierry Censa,
Mohammed Abouazzaa, Adrien Tassoua, Maud Gratuzea, Céline Meuniera, Pierre Charneta,
Michel Vignes#a and Valérie Rolland#a*
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a* IBMM-UMR5247, CNRS, UM, Place E. Bataillon, 34095 Montpellier Cedex5, France.
Fax: (+0033) 04 67 14 48 66
E-mail: valerie.rolland@umontpellier.fr
b
Laboratoire de Synthèse Organique Appliquée LSOA, Université d’Oran, Département de
Chimie, BP 1524 El M’Naouer, Oran 31000, Algeria
c
IEM-UMR5635,CNRS-UM-ENSCM, Place E. Bataillon, 34095 Montpellier Cedex 5,
France.
# shared seniority
Key words: L-Theanine, L-γ-N-propyl-glutamine, Microwave-assisted organic synthesis
(MAOS), NMDA receptors, intracellular Ca2+ homeostasis, hippocampal neurons, Xenopus
oocytes, expression, GluN2A, GluN2B
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Abstract
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L-Theanine (or L-γ-N-ethyl-glutamine) is the major amino acid found in Camellia sinensis. It
has received much attention because of its pleiotropic physiological and pharmacological
activities leading to health benefits in humans, especially. We describe here a new, easy,
efficient and environmentally-friendly chemical synthesis of L-Theanine and L-γ-N-propyl-
Gln and their corresponding D isomers. L-Theanine, and its derivatives obtained so far,
exhibited partial co-agonistic action at N-methyl-D-aspartate (NMDA) receptors, with no
detectable agonist effect at other glutamate receptors, on cultured hippocampal neurons. This
activity was retained on NMDA receptors expressed in Xenopus oocytes. In addition, both
GluN2A and GluN2B containing NMDA receptors were equally modulated by L-Theanine.
The stereochemical change from L-Theanine to D-Theanine along to the substitution of the
ethyl for a propyl moiety in the γ-N position of L- and D-Theanine significantly enhanced the
biological efficacy, as measured on cultured hippocampal neurons. L-Theanine structure thus
represents an interesting backbone to develop novel NMDA receptor modulators.
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Introduction
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L-Theanine (L-γ-N-ethyl-glutamine) is the major amino acid found in green tea (Camellia
sinensis). It represents, on average, 2% of the weight of dried green tea leaves. The multiple
health benefits of this amino acid are widely studied. This is particularly relevant in the
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central nervous system, as L-Theanine easily crosses the blood-brain barrier 1. In humans, L-
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Theanine has been shown to induce anti-stress/relaxing actions
and to improve sleep
induction 4. Further characterizations of its actions on animal models of Alzheimer’s disease 5
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and stroke indicate that L-Theanine also displays neuroprotective action which seems to
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rely on an antioxidant action and/or on modulation of neurotransmission, especially the
excitatory and inhibitory ones. Indeed, L-Theanine shares a lot of structural similarities with
glutamate and ligand-binding studies have established affinities for ionotropic, i.e. kainate, α-
amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartic acid
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(NMDA) receptors . Its neuroprotective actions may rely on interference with ionotropic or
metabotropic glutamate receptor-mediated neuronal processes 10,11. The prevention of
ischemic damage in the gerbil hippocampus could be attributed to the blockade of AMPA
receptors which actively contribute to ischemic injury 7,12. In addition, L-Theanine may also
modulate GABAergic transmission to produce neuroprotection under ischemia as evidenced
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in mice . Other studies uncovered an excitatory action of L-Theanine. Indeed, in striatal
neurons, L-Theanine treatment increases the exocytosis of various neurotransmitters,
including γ-amino-butyric acid (GABA), glycine and dopamine 13. This could be due to a
pleiotropic action on glutamatergic receptors. In this line, it has been shown that the
excitatory action of L-Theanine on cortical neurons can be blocked by NMDA receptor
antagonists 14. This could explain the beneficial action of L-Theanine on a rodent model of
schizophrenia induced by NMDA receptors hypo function. Indeed, NMDA receptors are
widely expressed on inhibitory interneurons. Their activation stimulates GABA release and
thus regulates the excitability of excitatory cells. This is particularly relevant in the prefrontal
cortex where a subset of GABAergic interneurons activated by cortical neurons regulate the
excitability of thalamic neurons, themselves exciting cortical neurons (so called ‘thalamo-
cortical loop’). Preventing the activity of these interneurons, by blocking NMDA receptors,
for instance, leads to dysregulation of the thalamo-cortical loop and to the occurrence of
pathological conditions as psychosis 15. Interestingly, L-Theanine treatment reverses
sensorimotor gating deficits which are associated with this pathological state 14. In addition,
partial agonists of the glycine site on NMDA receptors, as D-cycloserine, have proved to
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exhibited beneficial effects to alleviate the symptoms of various psychiatric diseases
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Therefore, targeting the glycine binding site with partial agonists represents an interesting
route to normalize NMDA receptor activity.
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NMDA receptors have long been associated with the synaptic plasticity that produces the
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long-term potentiation and the long-term depression in the hippocampus. However, the
molecular mechanisms responsible for the differential role of NMDA receptors of distinct
subunit composition are still poorly understood. L-Theanine could thus be an interesting
backbone for the synthesis of new modulators of the NMDA receptor with applications in
both fundamental research and therapeutic usage for NMDA receptors-associated pathologies
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(schizophrenia and neurodevelopmental disorders 20). We provide here a new, simple and
efficient synthesis of D and L-Theanine and N-alkylated derivatives. The effects of these
compounds are evaluated on cultured hippocampal neurons and on Xenopus oocytes
expressing NMDA receptors.
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Results
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Synthesis of theanine and alkylated derivatives
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The starting (commercially available) products were N-protected γ-glutamyl esters: Z-L-
Glu(O-CH2-Ph)-OH or Z-L-Glu(OCH3)-OH and 2M ethylamine solution (Z:
benzyloxycabonyl group). Synthetic L-Theanine was obtained by a new protocol for specific
amidification as described in Scheme 1.
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Scheme 1: Chemical route to L-Theanine (L-BS-68) synthesis
The reaction has been performed using microwave oven (Biotage initiator 60 EXP) in 2M
ethylamine solution in THF (6 equiv). The vessel was heated at different temperatures (for
example for 60°C: power: 600W). The reactions were followed by high-performance liquid
chromatography (HPLC). Absolutely no hydrolysis of newly synthesized Z-Theanine in Z-
Glu-OH was observed and this procedure provided approximately 20-fold acceleration (4
hours versus 1 day using conventional methods which led to about 40% of hydrolysis of Z-
Theanine in Z-glutamic acid, data not shown).
The enantiomeric purity of synthetic Z-L-Theanine was controlled by measuring αD and
further chiral HPLC analyses. To confirm that no racemization took place, the amidification
with 2M ethylamine solution in THF has been carried out with the commercially available Z-
D-Glu(OCH3)-OH. Under these conditions, optically pure Z-D-Theanine was obtained in the
same yield. Both syntheses have been followed by chiral HPLC separately and both
compounds appeared at different retention times.
In a second and final step, synthetic L-Theanine (L-BS-68) was obtained by removing the
benzyloxycarbonyl protecting group Z by catalytic hydrogenation in quantitative yield.
The synthesis of L-Theanine congeners by modifying the γ-N-alkyl group was then performed
by substituting the γ-N-ethyl group in L-Theanine for other alkyl moieties, in order to enhance
the hydrophobicity of the derivatives. We describe here the synthesis of the L-γ-N-
propylglutamine (or L-BS-77).
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With Z-L-Glu(OCH3)-OH as starting product, in solvent free system, thanks to pure liquid n-
propylamine (Bp = 47-51°C), and under microwave irradiations, Z-L-γ-N-propylglutamine
was quantitatively obtained in only one hour at 60°C (Scheme 2).
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Scheme 2: Chemical route to L-γ-N-propyl-Gln (L-BS-77) synthesis
As L-Theanine is closely related to glutamate and GABA, we have also analyzed the purity of
L-Theanine by HPLC. Under the elution conditions used, glutamate, L-Theanine and GABA
were well separated as single peaks appearing at 2.99, 5.78 and 8.42 min, respectively. L-
Theanine on its own contained neither glutamate nor GABA (Figure 1).
L-Theanine is a co-agonist of NMDA receptors
L-Theanine was previously shown to elicit [Ca2+]i increases when applied in the micromolar
range on cultured cortical neurons 14. We have thus checked whether L-Theanine was active
in this concentration range (1-100µM) on cultured hippocampal neurons. In the absence of
Mg2+ ions, L-Theanine elicited [Ca2+]i increases which were consistently detected at 1µM in
mature (16 days in vitro, DIV) cultured hippocampal neurons (Figure 2A). Under
physiological extracellular Mg2+ (1mM; Figure 2B) or in the presence of NMDA receptor
antagonist dizolcipine (MK-801, 10µM; Figure 2C) or without extracellular Ca2+ ions (Figure
6D) perfusion of L-Theanine had no effect on [Ca2+]i. These data demonstrate that L-
Theanine produced an influx of Ca2+ on mature cultured hippocampal neurons which mainly
relied on NMDA receptors. Non-NMDA ionotropic receptors and metabotropic mGlu1/5
receptors did not seem to be activated here by L-Theanine, as its effect was fully blocked by
MK-801.
Surprisingly, on immature hippocampal neurons (6-8 DIV), L-Theanine (range: 10µM up to
1mM) had absolutely no effect on [Ca2+]i, while NMDA could elicit responses sensitive to
glycine (Figure 3A). Therefore, we hypothesized that L-Theanine might be exerting positive
allosteric modulation or co-agonist action on NMDA receptors stimulated by the endogenous
glutamate release which occurs only in mature cultures of hippocampal neurons as observed
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previously . L-Theanine was thus tested in combination with NMDA on immature neurons,
where synaptic activation of NMDA receptors did not yet occur, and compared its effects with
those elicited by conventional NMDA receptor glycine site agonists, i.e. glycine and D-serine.
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L-Theanine (1µM-1mM) effectively potentiated Ca2+ influxes elicited by NMDA (10µM) in a
concentration dependent manner with a maximal effect at a concentration of 100µM (Figure
3B and E). Theanine was significantly less efficient than glycine or D-serine (Figure 3C, D
and E). Nevertheless, the action of L-Theanine was rather selective for NMDA receptors.
Indeed, we verified whether L-Theanine had any effect on non-NMDA ionotropic receptors.
For this, L-Theanine (1mM) was applied in combination with kainate (40µM). We observe
that kainate-mediated Ca2+ responses were totally insensitive to L-Theanine (Figure 3F).
Then, to test whether the presence of endogenous glutamate was a necessary prerequisite to
observe per se effects of L-Theanine on mature cultured neurons, experiments were
performed in the presence of tetrodotoxin (TTX; 500nM) a Na+ channel blocker which
prevents glutamate release and excitatory transmission in these neurons 21. TTX completely
inhibited the changes in [Ca2+]i produced by L-Theanine (10µM), glycine (10µM) or D-serine
(100µM) (Figure 4A) in mature cultured neurons. It is noticeable that NMDA response was
also partially inhibited. This could be associated with a decreased co-agonist tone obtained by
blocking synaptic transmission. However TTX did not prevent the potentiating effect of L-
Theanine, glycine or D-serine on NMDA responses, on mature neurons (Figure 4B). Finally,
the NMDA glycine binding site antagonist, 7-chlorokynurenic acid (0.1µM), completely
blocked L-Theanine-mediated [Ca2+]i increases in a reversible manner (Figure 4C). It is
noteworthy that at the concentration tested, 7-chlorokynurenic acid had a very modest
inhibitory effect on NMDA-mediated [Ca2+]i rises (less than 4%). Taken together, these
results confirm that L-Theanine behaves as a partial NMDA receptor co-agonist acting on the
glycine site and therefore strictly requires endogenous release of glutamate to produce per se
effects.
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In cultured hippocampal neurons, our experimental procedure used to measure intracellular
calcium allowed us to principally observe GluN2B-containing NMDA receptor responses as
ifenprodil (10µM), a selective antagonist of GluN2B subunit-containing NMDA receptor,
completely blocked the NMDA responses (Figure 2B). The selectivity towards either GluN2A
or GluN2B-containing NMDA receptors was further evaluated on Xenopus oocytes where the
subunit composition of the NMDA receptors can be easily controlled. The study was
restricted to GluN2A and GluN2B-containing NMDA receptors as these subunits were found
to exhibit the highest expression among GluN2 subunit family and we did not evidence the
presence GluN3 in our hippocampal cultures. L-Theanine (500µM) was without effect per se
on Xenopus oocytes expressing GluN1/GluN2A or GluN1/GluN2B NMDA receptors (Figure
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5). However, L-Theanine potentiated glutamate-elicited currents by co-application and to a
similar extent on both GluN1/GluN2A and GluN1/GluN2B expressing oocytes (Figure 5C).
By itself, glycine (10µM) elicited a small response which was not sensitive to L-Theanine.
Moreover, its co-agonist action was evidenced by recording large currents when co-applied
with glutamate. Nevertheless, the currents obtained by co-applying L-Theanine and glutamate
represented 19 8% (n = 12) and 23 9% (n = 11) of those elicited by glycine and glutamate
co-application on GluN1/GluN2A and GluN1/GluN2B expressing oocytes, respectively. The
difference between these fractions was not significant.
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Characterization of the effects L-Theanine derivatives: D-Theanine, L and D-γ-N-propyl-Gln
L-Theanine derivatives were further synthesized by substituting the γ-N-ethyl moiety and by
changing the chirality, i.e. from L to D, of the asymmetric carbon. Indeed, as observed for D-
serine, a D-chirality of the asymmetric carbon is also accepted for co-agonist binding on the
GluN1 subunit. Activity of derivatives was tested using them at the single concentration of
10µM on mature cultured hippocampal neurons. Among all the compounds synthesized, it
appears that the γ-N-propyl derivative exerted excitatory properties on [Ca2+]i in cultured
hippocampal neurons as well as L-Theanine did. Therefore, three compounds were further
synthesized and tested: D-Theanine, L- and D-γ-N-propyl-Gln. They all retained the
properties of NMDA receptor co-agonist as observed for L-Theanine, i.e. the blockade by
NMDA receptor antagonist MK-801 (Figure 6A, B, C), the dependency on extracellular Ca2+
(Figure 6D). In addition the [Ca2+]i rises elicited by these L-Theanine derivatives were not
observed in the presence of TTX (not shown). The direct comparison of the responses induced
by these compounds at a single concentration of 10µM indicated that both the change of
chirality and the γ-N-propyl substitution significantly enhanced the responses elicited by L-
Theanine (Figure 6E and F).
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We demonstrate here that L-Theanine exerts an excitatory action on hippocampal neurons
mainly by potentiating NMDA responses. L-Theanine had no detectable agonist effect on
other glutamate receptors, i.e. non-NMDA ionotropic and phospholipase C-associated mGlu
receptors. Per se, L-Theanine induced [Ca2+]i only in mature hippocampal neurons. This
effect of L-Theanine was completely blocked by a NMDA receptor antagonist, or by
extracellular Mg2+ ions, and was dependent on the presence of extracellular Ca2+ ions. This
strongly suggests that the increase in [Ca2+]i elicited by L-Theanine solely involves the direct
or the indirect activation of NMDA receptors. The fact that these effects were only seen on
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mature cultures of hippocampal neurons with functional excitatory synaptic transmission
suggests an indirect action where L-Theanine behaves as co-agonist of NMDA receptors
activated by endogenously released glutamate. Accordingly, blocking synaptic transmission
by TTX fully prevented the L-Theanine response in mature hippocampal neurons. The fact
that TTX partially reduced the NMDA response, suggests that glycine and/or D-serine may
also be synaptically released from mature hippocampal neurons. However, the existence of
residual intracellular calcium responses induced by NMDA in the presence of TTX in mature
hippocampal cultures, or by NMDA alone in immature cultures also suggests the presence of
extracellular endogenous co-agonist during recording, released from the cells by mechanisms
independent from the synaptic activity. The co-agonist action of L-Theanine was directly
confirmed by the enhancement of the NMDA induced [Ca2+]i response when L-Theanine and
NMDA were co-applied in the presence of TTX and by the inhibitory effect of the glycine
NMDA receptor site antagonist, 7-chlorokynurenic acid, on L-Theanine-elicited [Ca2+]i
changes.
A similar result was obtained on the NMDA responses recorded on Xenopus oocytes
expressing GluN1/GluN2A or GluN1/GluN2B NMDA receptors, suggesting that the effects
of L-Theanine were not restricted to one subtype of the GluN2 subunits. L-Theanine thus
behaves as ‘conventional’ NMDA receptor co-agonist, such as glycine or D-serine, which
exert their positive action by acting on the GluN1 subunit. This is in agreement with a
previous report showing that L-Theanine may bind the glycine binding site of NMDA
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receptors . Nevertheless, L-Theanine was found to be a lot less potent than glycine or D-
serine to exert its co-agonist effect at NMDA receptors.
In our hands, L-Theanine behaves as a partial agonist at the glycine binding site on NMDA
receptors in hippocampal neurons. This action is, to some extent, contrasting with previous
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finding demonstrating the interactions of L-Theanine with NMDA receptor-dependent
neurophysiological phenomena in the CA1 area of the hippocampus to improve cognition.
Indeed, long-lasting treatments with L-Theanine appear to decrease NMDA receptor-
dependent LTP, while it increases NMDA receptor-independent LTP 22,23. The opposite
would reasonably be expected from a positive modulation of NMDA receptor. Acute and
chronic administrations of L-Theanine may thus result in the occurrence of different
neuroplastic phenomena.
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The L-Theanine used for this study was synthesized in a new efficient two-step synthesis with
important improvements as compared to previous methods, including extraction from tea
leaves 24,25 and enzymatic biosynthesis 26, which are both expensive and low yield methods.
Indeed, under our optimized conditions, the amidification reaction proceeded smoothly.
Good-to-excellent conversion rates, higher yields and shorter reaction times were observed
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using microwaves irradiations as a source of heating and activation . The reaction occurred
in solvent-free system when the corresponding amines were liquid in an environmentally-
friendly protocol without any chromatographic purification. This procedure also enabled us to
obtain the D-enantiomer of Theanine and L- and D-γ-N-propyl-Gln with high yields and
without any racemization. Moreover, this process can be easily translated for the production
of gram scale of these derivatives using for example the microwave activation by MiniFlow
200SS model (Sairem). In addition, this reaction enabled the synthesis of derivatives by
changing the alkyl moiety on the nitrogen in γ position, leading to L-γ-N-alkyl and D-γ-N-
alkyl derivatives. Among these compounds, the D-γ-propyl-Gln appeared to be more potent
than L-Theanine itself to elicit [Ca2+]i changes on hippocampal neurons. These structural
modifications of the L-Theanine backbone may be helpful for characterizing its binding site
on NMDA receptors and testing whether or not it overlaps the glycine site on GluN1, as
suggested here. Studies of the crystal structure of NMDA receptors suggest however the
potential presence of many possible allosteric binding sites within the receptor 28.
Furthermore, we show that novel modulators of NMDA receptors with potential therapeutic
activity may be derived from L-Theanine. Indeed, glycine site NMDA receptors partial
agonists as D-cycloserine and GLYX13, which binds GluN1 glycine site, have proved to be
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beneficial in improving learning during ageing and in the course of pathological states as
30
depression
or conditions associated with hypo function of NMDA receptors, such as
psychosis 16. Many psychiatric diseases resulting from a reduced activity of NMDA receptors,
including psychosis 19, can be mimicked in rodents by a reduction in NMDA receptor function
31. In this line, L-Theanine has proved to alleviate psychotic-like symptoms in a rodent
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schizophrenia model as observed by the rescue of sensorimotor gating defects assessed by
measuring pre-pulse inhibition (PPI) 14. Moreover, L-Theanine seems to enhance PPI in
humans 32, thereby confirming its potential psychotropic effect for curative perspective of
neurological diseases. Further behavioural experiments will hopefully confirm the beneficial
actions of these L-Theanine derivatives in vivo, and present this novel class of NMDA
modulators as therapeutic strategy to alleviate the symptoms of various
neurological/psychiatric diseases.
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Chemistry
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Melting points were obtained using a Büchi 510 capillary apparatus and were uncorrected. H
NMR spectra were recorded at 300 MHz and 75 MHz using a Brüker AC300 instrument, at
600 MHz using a Brüker AC600 instrument. Chemical shifts are quoted in parts per million
and were referenced to the residual solvent peak. The following abbreviations used: s, singlet;
d, doublet; t, triplet; q, quartet; m, multiplet. Coupling constants were reported in Hertz (Hz).
High resolution mass spectra (HRMS) were recorded on micromass electrospray instrument
with only molecular ion and other major peaks being reported. LC-MS identification was by
electrospray on HPLC Waters Alliance 2690. Flash chromatography was carried out using E-
Merck Silica Gel (Kieselgel 60, 230-400mesh) as stationary phase. Thin layer
chromatography was carried out on aluminium plates pre-coated with Merck Silicagel 60F254
and were visualized by quenching of Ultra-Violet fluorescence, or by staining with a 10%
methanol phosphomolybdic acid solution followed by heating. Analytic HPLC were
performed on a Waters apparatus 717 plus autosampler with Millenium 32 program on
SymmetryShieldTM RP18 3.5µm 2.1x20mm column and using linear gradient of ACN in H2O
with 0.1% TFA in 5min with 3mL/min flow. Analytical chiral HPLC experiments were
performed on a unit composed of a Merck D-7000 system manager, Merck-Lachrom L-7100
pump, Merck-Lachrom L-7360 oven, Merck-Lachrom L-7400 UV-detector and Jasco OR-
1590 polarimeter using Beckman Coulter System Gold 126 Solvent Module HPLC machine
with column Chiralcel OD-RH (250x4.6mm) and water/acetonitrile solvent system or with
Chiralpk AD-H (250x4.6mm) and hexane/isopropanol solvent system. Both columns are from
Chiral Technologies Europe (Illkirch, France). Optical rotations were determined on a Perkin-
Elmer 341 polarimeter in appropriate solvent (20°C, sodium ray). THF was distilled from
sodium/benzophenone ketyl. Reagents were supplied from commercial sources (Sigma
Aldrich, Fluka).
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Z-L-Theanine synthesis
Two mmoles of substrate (Z-L-Glu(OCH3)-OH or Z-L-Glu(OBzl)-OH) was weighed in 0.5–
2.0mL microwave reactor. Ethylamine (12mmol, 2M in THF) was then added. The reactor
was sealed and heated under microwaves irradiation at 80°C (800W) for 4h. Then, the
suspension was dissolved in ethyl acetate and washed two times with concentrated NH4Cl.
The organic phase was dried over MgSO4, and concentrated under reduced pressure. Z-L-
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Theanine precipitated as white powder in Et2O (20mL), was filtered and lyophilized. 1H NMR
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(300 MHz, DMSO): δ = 1.02 (t, J=7.3 Hz, 3 H), 2.08 (m, 2 H), 2.17(m, 2 H), 3.24 (q,
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3J=7.29 Hz, 2 H), 4.43 (m, 1 H), 5.02 (s, 2 H), 5.71 (d, J=6.86 Hz, 1H), 7.28 (m, 5 H).
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13C NMR (75 MHz, DMSO): δ = 14.27, 25.73, 33.36, 37.22, 53.51, 67.6, 128.1, 128.31,
128.42, 135.09, 156.2, 171.59, 171.84. [α]D20: -11.0 (c=1, MeOH). MS (ESI): m/z 309.2
[M+H]+, 331.1[M+Na]+. Analytic Chiral HPLC: Chiralcel-OD column; H2O/ACN (87/13),
0.6mL/min, 45min, 214 nm, tR= 30.15min.
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Z-D-Theanine: [α]D20: 11.2 (c=1, MeOH). Analytic Chiral HPLC: Chiralcel-OD column;
H2O/ACN (87/13), 0.6mL/min, 45min, 214nm, tR= 34.17min.
Z-L-γ-N-propylglutamine characterization
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1H NMR (300 MHz, DMSO): δ = 0.82 (t, J=7.47 Hz, 3 H), 1.54(m, 2H), 1.90 (m, 2 H),
2.07(m, 2 H), 2.97 (t, 3J=7.09 Hz, 2 H), 3.71 (m, 1 H), 5.01 (s, 2 H), 6.61 (d, 3J=6.92 Hz, 1H),
7.28 (m, 5 H). 13C NMR (75 MHz, DMSO): δ = 11.32, 22.31, 28.75, 32.10, 40.27, 55.19,
65.04, 127.54, 127.63, 128.27, 137.21, 155.42, 172.05, 174.18. [α]D20: +2.5 (c=1, DMSO).
MS (ESI): m/z 323.2 [M+H]+, 345.1[M+Na]+.
L-Theanine characterization
Z-L-Theanine (0.36mmol, 100mg) was dissolved in freshly distilled THF (3ml) and 20%
Pd(OH)2/C (20mg) added. The mixture was hydrogenated (H2) at r.t. for 8h. Pd(OH)2/C was
filtered off on celite and THF was removed under reduced pressure. L-Theanine was obtained
in quantitative yield as a white powder. 1H NMR (300 MHz, D2O): δ = 1.08 (t, 3J=7.32 Hz, 3
3
3
H), 2.11 (dd, J=7.77 Hz, 3J=6.16 Hz, 2 H), 2.39(m, 2 H), 3.17 (q, J=7.32 Hz, 2 H), 3.74 (t,
3J=6.16 Hz, 1 H). 13C NMR (75 MHz, D2O): δ = 13.41, 26.53, 31.73, 34.57, 53.56, 173.95,
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174.29. [α]D20: + 8.4 (c=1, H2O) [α]D litt: + 8.1 (c=5, H2O). Mp = 215-219°C. MS (ESI):
+
m/z 175.1 [M+H] , 197.1 [M+Na]+. HRMS calcd for C7H14N2O3 m/z [M+H]+ 175.1004
found 175.1039. D Theanine: [α]D20: -8.3 (c=1, H2O).
Commercially available L-Theanine from Sigma Aldrich: 1H NMR (300 MHz, D2O): δ = 1.10
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(t, 3J=7.75 Hz, 3 H), 2.13 (dd, J=8.0 Hz, 3J=6.5 Hz, 2 H), 2.4(td, 3J=8.0 Hz, 3J=4.2 Hz 2 H),
3.2 (q, 3J=7.75 Hz, 2 H), 3.76 (t, 3J=8.0 Hz, 1 H).
L-γ
-N-propylglutamine characterization
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1H NMR (300 MHz, D2O): δ = 0.82 (t, 3J=7.43 Hz, 3 H), 1.45 (td, J=7.24 Hz, 3J=6.96 Hz, 2
3
3
13
H), 2.05 (m, 2H), 2.31(m, 2 H), 3.08 (t, J=6.96 Hz, 2 H), 3.64 (t, J=6.1 Hz, 1 H). C NMR
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(75 MHz, D2O): δ = 10.63, 21.79, 27.21, 31.83, 41.33, 54.43, 174.75, 175.04. [α]D : +13.9
(c=1, H2O). Mp = 207-209°C. MS (ESI): m/z 189.2 (M+H) + , 211.2 [M+Na]+. HRMS calcd
for C7H14N2O3 m/z [M+H]+ 189.1239 found 189.1239. D-γ-N-propylglutamine: [α]D20: -14.0
(c=1, H2O).
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HPLC measurement of Glutamate, GABA and L-Theanine
Determination of Glutamate, GABA and L-Theanine involved the HPLC separation of
precolumn derivatized amino-acids, detected and quantified via fluorescence detection. The
chromatographic system consisted in a Dionex ASI-100 cooled autosampler, a Dionex P-680
pump, a Dionex TCC-100 oven and a Dionex RF-2000 fluorescence detector. Chromeleon
software 6.80 SP4 was used to drive the HPLC system and to integrate the signals obtained.
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Derivatization protocol was based on the method previously reported
with slight
modifications. Briefly summarized, 100µL of sample or standards in borate buffer (0.1M;
pH 9.3) were added to 20µL of potassium cyanide (KCN; 10mM in borate buffer) and 20µL
of Naphtalene-2,3-dicarboxaldehyde (NDA; 6mM in HPLC-grade methanol), either freshly
prepared or stored at 4°C in the dark (for less than a week). Reagents were thorougly mixed in
the autosampler and the reaction was allowed to proceed, protected from light, at a
temperature of 6°C. After 20min, 20µL of the derivative was loaded into the HPLC system.
Separation was obtained using a Strategy C18 (150mm length x 3mm diameter, 3µm
granulometry) column (octadecyl 100Å porosity, 425m2/g, C18 end-capped silica with 19%
C) eluted and separated using an isocratic mobile phase contining Na2HPO4 (100mM), EDTA
(50µM) and HPLC grade MeOH (50:50), that was thoroughly filtered (Millipore 0.45µm
durapore) and continuously degased. Elution was performed at a rate of 0.8mL.min-1 at a
constant 20°C in less than 12min. Emission of derivatives was measured at 480nm after
excitation at 420nm.
Materials for biological characterizations
All experiments were carried out in accordance with the European Community Council
Directive of 24th November 1986 (86/609/ECC). Sprague–Dawley rats were from Janvier
Labs (France). Culture media (DMEM/Ham F12 with Hepes and 4.5 g/L glucose), Dulbecco’s
phosphate-buffered saline (Dulbecco’s PBS), Versene, antibiotics, and fetal calf serum (FCS)
were purchased from Invitrogen. Culture dishes were from Nunc. All chemicals were from
Sigma.
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Primary neuronal cultures were established from 18-day-old embryonic rat hippocampi, as
previously described 34,35, with minor modifications. After pre-incubation with Versene,
hippocampal cells were mechanically dissociated and plated at a density of 2.106 cells/dish, on
8-well plates containing square (10X10mm2) glass coverslips, previously coated with poly-D-
lysine (50µg/mL) and then with DMEM/HAM F12 containing 10% FCS. Cells were grown in
a defined medium containing DMEM/HAM F12, supplemented with 33mM glucose, 2mM
glutamine, 100U/mL penicillin, 100µg/mL streptomycin, 13mM sodium bicarbonate,
5.5µg/mL transferrin, 10µg/mL insulin, 1pM β-estradiol, 3nM triiodothyronine, 20nM
progesterone, 5ng/mL sodium selenite, and 100µM putrescine. Experiments were performed
on cell cultures grown from 6 to 16 DIV.
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Measurements of cytosolic-free Ca2+ concentration
Intracellular calcium concentration ([Ca2+]i) was measured with the fluorescent indicator fura-
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36. For this purpose, hippocampal cells grown on glass coverslips were loaded with fura-2
by a 30-min incubation at 37 C with 5 µM fura-2-AM and 0.02% Pluronic in the extracellular
solution comprising: 124 mM NaCl, 3.5 mM KCl, 25 mM NaHCO3, 1.25 mM NaH2-PO4, 1
mM CaCl2, 2 mM MgSO4, 10 mM D-Glucose and 10 mM HEPES (bubbled with O2/CO2:
95/5) pH 7.4. [Ca2+]i was monitored by videomicroscopy. After rinsing, the glass coverslip
was transferred to the recording chamber mounted on an inverted microscope (Leica,
DMIRB). Fura-2 emission was obtained by exciting alternatively at 340 and 380 nm with a
rotating filter wheel (Sutter Instruments) and by monitoring emissions (F340 and F380) at 510
nm. The ratio of emissions at 510 nm (F340/F380) was recorded in cells every second.
Fluorescent signals were collected with a CCD camera (Hamamatsu), digitized, and analyzed
with image analysis software (Acquacosmos, Hamamatsu). The coverslips were continually
superfused with the extracellular solution thermostated at 37°C. Unless otherwise stated,
experiments were carried in the absence of Mg2+ ions in the extracellular medium. Drug
application was performed with a gravity-fed system and lasted 1min for each compound
tested. Data are expressed as averages ( S.E.M) of the ratio between the fura-2 fluorescence
values of 340/380 nm excitation wavelengths ratios (F340/F380) normalized to the
corresponding basal F340/F380 measured prior to any drug application. Graphs presenting
time-courses of F340/F380 ratio changes have been obtained by averaging data from a
population of cells recorded individually during one single experiment. For a given
determination, three individual experiments were at least performed on three independent cell
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cultures. Therefore, the ‘‘n’’ values represent the entire population of cells recorded from at
least three independent cultures. One-way ANOVA followed by Dunn’s t-test was used for
multiple comparisons to determine significant differences between the experimental
determinations. Statistical analysis was performed with SigmaPlot 12.0 software. Values of
p < 0.05 were considered significant.
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Xenopus oocytes injection and oocyte currents recording
Xenopus oocytes were prepared and injected with in vitro transcribed RNA at 1ꢀg/ꢀL (20-
40nL) of rat GluN1-1a (named GluN1 herein) and rat GluN2A or mouse ε2 (named GluN2B
herein) with a stoichiometry of 1:1, as already been described 32. All constructions of NMDA
receptors subunits have been kindly provided by Pierre Paoletti (IBENS, ENS, Paris).
Macroscopic currents were recorded under two electrode voltage-clamp using a GeneClamp
500 amplifier (Axon Instruments) and analyzed in the ND96 HERG recording solution (in
mM: 96 NaCl, 3 KCl, 0.5 CaCl2, 5 Hepes, pH=7.2). Current and voltage electrodes (less than
1Mꢁ) were filled with 3M KCl. Currents were filtered (20Hz) and digitized (66Hz) using a
Digidata-1200 interface (Axon Instruments). Data acquisition was done using version 7 of the
pClamp software (Axon Instruments).
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Figure 1: HPLC chromatograms of L-Theanine alone (dotted line) and of a mixture of L-
Theanine, glutamate and GABA. The fluorescence of the derivatives was measured at 480nm
after excitation at 420nm and is expressed in arbitrary units.
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Figure 2: Characterization of the direct effects of L-Theanine on [Ca2+]i in mature (about 2
weeks in vitro) cultured hippocampal neurons. A: Concentration-dependency of L-Theanine
effect. L-Theanine was tested from 1 up to 100µM. On the left, an illustrative experiment in
which 21 cells were recorded is shown. The concentration-dependent curve shown on the
right have been obtained by measuring peak intensities of L-Theanine responses from n = 45
cells. B: Inhibitory effect of Mg2+ ions on L-Theanine-mediated responses. L-Theanine was
tested from 10µM up to 1mM in the presence of Mg2+ ions (1mM) in the extracellular
medium. As control, NMDA was tested in Mg2+-free and Mg2+-rich medium, as well as in the
presence of the NMDA receptor GluN2B subunit antagonist ifenprodil (10µM) which
completely inhibited NMDA-mediated responses. The graph represents an average of the
[Ca2+]i changes measured in 31 cells. This experiment has been performed on 60 cells in all.
C: Dependency on NMDA receptor activity of L-Theanine responses. L-Theanine or NMDA
were applied in the presence of the NMDA receptor non-competitive antagonist MK-801
(10µM). This antagonist exerted a reversible inhibition of the responses elicited by L-
Theanine or NMDA. The graph was obtained by averaging F340/F380 ratios from 31 cells.
This experiment has been performed on 70 cells in all.
Figure 3: NMDA receptor co-agonist action of L-Theanine on immature cultured
hippocampal neurons. A: Lack of L-Theanine (10µM-1mM) effect on [Ca2+]i in immature (6
DIV) cultured hippocampal neurons. NMDA (10µM) in combination with glycine (10µM)
was tested as control. The graph has been obtained by averaging data from 29 cells. The
experiment has been performed on 51 cells in all. B: Concentration-dependent potentiating
action of L-Theanine (from 10µM up to 1mM) on the NMDA-mediated [Ca2+]i increases in
immature (6 DIV) hippocampal neurons. Glycine (10µM) was also tested as control. The
graph was obtained by averaging data from 22 individual cells. C and D: Concentration-
dependent potentiating action of glycine (C) and D-serine (D) on NMDA-mediated [Ca2+]i
increases in immature hippocampal neurons. Co-agonists were tested in the concentration
range of 10nM up to 10µM. Data are from 24 and 26 cells, for glycine and D-serine,
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respectively. E: Recapitulative graph of the potentiating actions of glycine, D-serine and L-
Theanine on NMDA-mediated responses, as a function of the concentration of co-agonist
applied. Data have been obtained from 82, 80 and 71 cells for glycine, D-serine and L-
Theanine, respectively. Data are expressed as percentages of increase of NMDA-mediated
responses. They were obtained by normalizing the difference of the peak amplitudes of
NMDA responses measured either in the presence or in the absence of the co-agonist to the
amplitude of the NMDA response in each respective cell recorded. F: Effect of L-Theanine
(1mM) on [Ca2+]i increases elicited by kainate (40µM) in 6 DIV cultured neurons. The graph
was generated by averaging data obtained from 40 individual cells (n = 85 in all).
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Figure 4: Dependency of the L-Theanine-mediated [Ca2+]i increases on synaptic activity in
mature hippocampal cultured neurons. A: [Ca2+]i changes elicited by L-Theanine and by the
NMDA receptor co-agonists, glycine and D-serine, in mature hippocampal cultures (15 DIV)
measured either in the absence (open circles, ‘control’, 12 cells) or in the presence of
tetrodotoxin (filled circles, 26 cells). TTX (500nM) was applied throughout the recording.
Data obtained with each protocol were superimposed. The experiments with or without TTX
were performed on n = 50 and 47 cells in all, respectively. B: Co-agonist action of glycine, D-
serine and L-Theanine on NMDA receptors measured in the presence of TTX in mature
neurons. The co-agonists were applied at 10µM in combination to 10µM NMDA, in the
presence of 500nM TTX in the extracellular medium. The graph plots averaged data from 23
individual cells (n = 48 in all). C: Effect of 7-chlorokynurenic acid on the L-Theanine-
mediated [Ca2+]i changes. 7-chlorokynurenic (0,1µM) was applied 1min prior to the L-
Theanine (10µM) application. The graph plots averaged data from 20 individual cells (n = 50
in all).
Figure 5: Co-agonist action of L-Theanine at GluN1/GluN2A and GluN1/GluN2B NMDA
receptors. A and B: Currents evoked by successive applications or co-applications of 500µM
L-Theanine, 10µM glycine and 100µM glutamate, were measured on Xenopus oocyte
expressing NMDA receptors. Representative current traces of GluN1/GluN2A (A) and
GluN1/GluN2B (B) reveal the co-agonist action of L-Theanine as well as that of glycine. C:
Average potentiating effects of L-Theanine on GluN1/GluN2A and GluN1/GluN2B (left) and
graphs showing the large dispersion of both L-Theanine and glycine responses for
GluN1/Glu2A (middle) and GluN1/GluN2B (right).
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Figure 6: Activity of L-Theanine derivatives. A-C: Dependency on NMDA receptor activity
of D-Theanine-, L-γN-propyl-Gln- and D-γN-propyl-Gln-mediated [Ca2+]i increases in mature
(16 DIV) neurons. The [Ca2+]i increases mediated by 10µM D-Theanine (A), L-γN-propyl-
Gln (B) or D-γN-propyl-Gln (C) were challenged with MK-801 (10µM). NMDA (10µM) was
used as a control. D: Dependency on the presence of extracellular Ca2+ ions of the responses
elicited by L-Theanine and derivatives. E: Inhibitory effect of extracellular Mg2+ ions on the
[Ca2+]i responses induced by L-Theanine and derivatives. F: Cumulative graph plotting peak
responses elicited by 10µM L-Theanine or derivatives on [Ca2+]i. Data were obtained from
n = 199, 68, 222, and 114 cells for L-Theanine, D-Theanine, L-γN-propyl-Gln and D-γN-
propyl-Gln, respectively. Bars indicate that the differences between peak amplitudes were
statistically significant (p<0.001, one way ANOVA followed by Dunn's test).
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Acknowledgements:
We thank Dr Pierre Paoletti (ENS, IBENS, Paris) for the generous gift of the RNA constructs
encoding NMDA receptor subunits.
Author contributions
M.R., S.B., M.R., J.G., P.C., M.V. and V.R designed experiments
F.S., M.R., M.R., M.-C. de J.F., J. G., C. C.-S., G.B., T.C., M.A., A.T., M.G., C.M., P.C.,
M.V. and V.R. performed experiments.
M.R., M.R., J.G., P.C., M.V. and V.R wrote the paper
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References
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(1) Zhang, L., Zhang, Z.-Z., Lu, Y.-N., Zhang, J.-S., and Preedy, V. R. (2013) Chapter 35 - L-
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Glu + GABA + Theanine
Theanine
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2.5
5.0
7.5
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Time (min)
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B
A
Thea
Thea
Gly
Thea
Glu
Thea
Thea
Gly
Thea
Glu
Glu
Glu
Gly
Glu
Glu
Gly
Gly
Gly
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30s
30s
50nA
500nA
C
n.s
12
10
8
0
-1000
-2000
-3000
-4000
0
-200
-400
-600
-800
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4
GluN1 / GluN2A
GluN1 / GluN2B
2
-1000
0
Glu 100
Thea 500
Glu 100
Gly 10
Glu 100
Gly 10
Glu 100
Glu 100
Glu 100
GluN1
GluN2A
GluN1
GluN2B
Thea 500
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