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Proc. Natl. Acad. Sci. USA
Vol. 95, pp. 8268–8273, July 1998
Medical Sciences
Cannabidiol and (2)D
9
-tetrahydrocannabinol are
neuroprotective antioxidants
A. J. HAMPSON*
†
,M.GRIMALDI
‡
,J.AXELROD*, AND D. WINK
§
*Laboratory of Cellular and Molecular Regulation, National Institutes of Mental Health, Bethesda, MD 20892;
‡
Laboratory of Adaptive Systems, National
Institute of Neurological Disorders and Stroke, Bethesda, MD 20892; and
§
Radiology and Biology Branch, National Cancer Institute, Bethesda,
MD 20892
Contributed by Julius Axelrod, April 27, 1998
ABSTRACT The neuroprotective actions of cannabidiol
and other cannabinoids were examined in rat cortical neuron
cultures exposed to toxic levels of the excitatory neurotrans-
mitter glutamate. Glutamate toxicity was reduced by both
cannabidiol, a nonpsychoactive constituent of marijuana, and
the psychotropic cannabinoid (2)D
9
-tetrahydrocannabinol
(THC). Cannabinoids protected equally well against neuro-
toxicity mediated by N-methyl-D-aspartate receptors, 2-ami-
no-3-(4-butyl-3-hydroxyisoxazol-5-yl)propionic acid recep-
tors, or kainate receptors. N-methyl-D-aspartate receptor-
induced toxicity has been shown to be calcium dependent; this
study demonstrates that 2-amino-3-(4-butyl-3-hydroxyisox-
azol-5-yl)propionic acidykainate receptor-type neurotoxicity
is also calcium-dependent, partly mediated by voltage sensi-
tive calcium channels. The neuroprotection observed with
cannabidiol and THC was unaffected by cannabinoid receptor
antagonist, indicating it to be cannabinoid receptor indepen-
dent. Previous studies have shown that glutamate toxicity may
be prevented by antioxidants. Cannabidiol, THC and several
synthetic cannabinoids all were demonstrated to be antioxi-
dants by cyclic voltametry. Cannabidiol and THC also were
shown to prevent hydroperoxide-induced oxidative damage as
well as or better than other antioxidants in a chemical (Fenton
reaction) system and neuronal cultures. Cannabidiol was
more protective against glutamate neurotoxicity than either
ascorbate or
a
-tocopherol, indicating it to be a potent anti-
oxidant. These data also suggest that the naturally occurring,
nonpsychotropic cannabinoid, cannabidiol, may be a poten-
tially useful therapeutic agent for the treatment of oxidative
neurological disorders such as cerebral ischemia.
Cannabinoid components of marijuana are known to exert
behavioral and psychotropic effects but also to possess ther-
apeutic properties including analgesia (1), ocular hypotension
(2), and antiemesis (3). This report examines another potential
therapeutic role for cannabinoids as neuroprotectants and
describes their mechanism of action in rat cortical neuronal
cultures.
During an ischemic episode, large quantities of the excita-
tory neurotransmitter glutamate are released. This event
causes neuronal death by over-stimulating N-methyl-
D-
aspartate receptors (NMDAr) and 2-amino-3-(4-butyl-3-
hydroxyisoxazol-5-yl)propionic acid (AMPA) and kainate-
type receptors and results in metabolic stress and accumulation
of toxic levels of intracellular calcium (4). In vitro and in vivo
studies (4, 5, 6) have demonstrated that such neurotoxicity can
be reduced by antioxidants or antagonists to NMDAr and
AMPAykainate receptors. Antioxidants such as
a
-tocopherol
(5, 6) are effective neuroprotectants because of their ability to
reduce the toxic reactive oxygen species (ROS) formed during
ischemic metabolism. Cannabinoids like (2)D
9
-tetrahydrocan-
nabinol (THC) and its psychoactive analogues also have been
reported to be neuroprotective against glutamate toxicity in
vitro (7). Cannabinoids have been suggested to prevent gluta-
mate neurotoxicity by activating cannabinoid receptors (7, 8),
which can reduce calcium influx through voltage sensitive
calcium channels (8, 9). A synthetic cannabinoid (HU-211)
also has been demonstrated to be neuroprotective even though
it does not activate cannabinoid receptors. This compound is
an atypical cannabinoid, however, in that it, unlike other
cannabinoids, directly antagonizes NMDAr (10) and possesses
some antioxidant properties (11). The present study examines
classical cannabinoids as neuroprotectants in vitro but focuses
on the nonpsychoactive cannabinoid cannabidiol. Like THC,
cannabidiol is a natural component of the marijuana plant,
Cannabis sativa, although unlike THC, cannabidiol does not
activate cannabinoid receptors and so is devoid of psychoactive
effects (12). This study reports that cannabidiol and other
cannabinoids such as THC are potent antioxidants that protect
neurons from glutamate-induced death without cannabinoid
receptor activation.
MATERIALS AND METHODS
Materials. Cannabidiol, THC, and reagents other than
those specifically listed below were purchased from Sigma.
Cyclothiazide, glutamatergic ligands, and MK-801 were ob-
tained from Tocris Cookson (Bristol, U.K.). Dihydrorhodam-
ine was supplied by Molecular Probes. Tert-butyl hydroperox-
ide, tetraethylammonium chloride, ferric citrate, and sodium
dithionite were all purchased from Aldrich. Agatoxin and
conotoxin were obtained through Biomol (Plymouth Meeting,
PA). All culture media were GIBCOyBRL products.
Solution Preparation. Solutions of cannabinoids, cyclothia-
zide, and other lipophiles were prepared by evaporating a 10
mM ethanolic solution (under a stream of nitrogen) in a
siliconized microcentrifuge tube. Dimethyl sulfoxide (,0.05%
of final volume) was added to ethanol to prevent the lipophile
from completely drying onto the tube wall. After evaporation,
1 ml of culture media was added, and the drug was dispersed
by using a high power sonic probe. Special attention was used
to ensure the solution did not overheat or generate foam. After
dispersal, all solutions were made to their final volume in
siliconized glass tubes by mixing with an appropriate quantity
of culture media.
Neuronal Cultures. Primary cortical neuron cultures were
prepared according to the method of Ventra et al (13). In brief,
fetuses were extracted by C-section from a 17-day pregnant
The publication costs of this article were defrayed in part by page charge
payment. This article must therefore be hereby marked ‘‘advertisement’’ in
accordance with 18 U.S.C. §1734 solely to indicate this fact.
0027-8424y98y958268-6$0.00y0
PNAS is available online at http:yywww.pnas.org.
Abbreviations: AMPA, 2-amino-3-(4-butyl-3-hydroxyisoxazol-5-
yl)propionic acid; BHT, butylhydroxytoluene; NMDAr, N-methyl-D-
aspartate receptors; ROS, reactive oxygen species; THC, (2)D
9
-
tetrahydrocannabinol.
†
To whom reprint requests should be addressed. e-mail: aidan@
codon.nih.gov.
8268
Wistar rat, and the fetal brains were placed into phosphate
buffered saline. The cortices then were dissected out, cut into
small pieces, and incubated with papain for 9 min at 37°. After
this time, the tissue was dissociated by passage through a
fire-polished Pasteur pipette, and the resultant cell suspension
was separated by centrifugation over a gradient consisting of
10 mgyml BSA and 10 mgyml ovomucoid (a trypsin inhibitor)
in Earle’s balanced salt solution. The pellet then was resus-
pended in high glucose, phenol red-free DMEM containing
10% fetal bovine serum, 2 mM glutamine, 100 units of
penicillin, and 100
m
gyml streptomycin (DMEM). Cells were
counted, were tested for vitality by using the trypan blue
exclusion test, and were seeded onto poly-
D-lysine coated 24
multiwell plates. After 96 hr, 10
m
M fluorodeoxyuridine and 10
m
M uridine were added to block glial cell growth. This protocol
results in a highly neuron-enriched culture (13).
Preparation of (Type I) Astrocytes and Conditioned Media.
Astrocyte-conditioned DMEM (phenol red-free) was used
throughout the AMPAykainate toxicity procedure and after
glutamate exposure in the NMDAr-mediated toxicity proto-
col. Media were conditioned by 24 hr of treatment over a
confluent layer of type I astrocytes prepared from 2-day-old
Wistar rat pups (14). In brief, cortices were dissected, were cut
into small pieces, were digested enzymatically with 0.25%
trypsin, and then were dissociated mechanically by passage
through a plastic pipette. The cell suspension then was plated
into untreated 75-cm
2
T-flasks, and, after 24 hr, the media
were replaced and unattached cells were removed. Once
astrocytes achieved confluency, cells were divided into four
flasks. Media for experiments were conditioned by a 24-hr
exposure to these astrocytes, after which time they were frozen
at 220°C until use. Astrocyte cultures were used to condition
DMEM for no longer than 2 months.
NMDAr-Mediated Toxicity Procedure. NMDAr-mediated
glutamate toxicity was examined by exposing neurons (cul-
tured for 14–18 days) to 250
m
M glutamate for 10 min in a
phenol red-free and magnesium-free saline. The saline was
composed of 125 mM NaCl, 25 mM Glucose, 10 mM Hepes
(pH 7.4), 5 mM KCl, 1.8 mM calcium chloride, and 5% BSA.
After exposure, cells were washed twice with saline and were
incubated for 18 hr in conditioned DMEM. Toxicity was
prevented completely by addition of the NMDAr antagonist
MK-801 (500 nM) (data not shown).
AMPA and Kainate Receptor-Mediated Toxicity Proce-
dures. Unlike NMDAr, which are regulated by magnesium
ions, AMPAykainate receptors rapidly desensitize after ligand
binding. To examine AMPA and kainate receptor-mediated
toxicity, neurons were cultured for 7–13 days and then were
exposed to 100
m
M glutamate and 50
m
M cyclothiazide (used
to prevent AMPA receptor desensitization). Cells were incu-
bated with glutamate in the presence of 500 nM MK-801 for
18–20 hr before analysis. Specific AMPA and kainate receptor
ligands also were used to separately examine the effects of
cannabinoids on AMPA and kainate receptor-mediated
events. Fluorowillardiine (1.5
m
M) and 4-methyl glutamate (10
m
M) were used to investigate AMPA and kainate (15) recep-
tor-mediated toxicity, respectively. When specifically examin-
ing kainate receptor activity, cyclothiazide was replaced with
0.15 mgyml Concanavalin-A.
Although the neuron preparation technique described
above results in a largely neuronal culture, a minority of
astrocytic cells remain. Astrocytes are highly resistant to
glutamate toxicity (16) because of their lack of functional
NMDAr (17, 18), although glutamate toxicity in astrocytes has
been observed to prevent AMPA receptor desensitization if
cyclothiazide is present (19). To examine whether AMPAy
kainate-type toxicity affects astrocytes in our cultures, astro-
cytes (as prepared above) were exposed to glutamate under the
same conditions used on neuron-enriched cultures. Under
these conditions, astrocytes were resistant to glutamate tox-
icity, with 20 hr of exposure resulting in a lactate dehydroge-
nase release of only 5% above background, compared with
100–200% of the background observed in neuron-enriched
cultures (data not shown). It was concluded, therefore, that
astrocyte contamination does not contribute substantially to
the effects of glutamate in our neuronal cultures.
ROS Toxicity Assay. To examine the effects of cannabinoids
on ROS toxicity, 7- to 13-day-old cultured neurons were
incubated with 300
m
M tert-butyl hydroperoxide (an oxidant)
in conditioned DMEM. Tert-butyl hydroperoxide was used
because its miscibility with both water and lipids allows
oxidation to occur in both cytosolic and membrane-delimited
cellular compartments.
Toxicity Assay. Cell toxicity was assessed 18–20 hrs after
insult by measuring lactate dehydrogenase release into the
(phenol red-free) culture media. Experiments were conducted
with triple or quadruple values at each point, and all plates
contained positive (glutamate alone) and baseline controls.
The assay was validated by comparison with a tetrazolium-
based viability assay (XTT) (20). Results were similar with
either system, although lactate dehydrogenase release was
used in this study because it provided a greater signal to noise
ratio than the XTT assay.
Cyclic Voltametry. Cyclic voltametry was performed with an
EG & G Princeton Applied Research potentiostatygalvanostat
(
MODEL 273yPAR 270 software). The working electrode was a
glassy carbon disk with a platinum counter electrode and
silverysilver chloride reference. Tetraethylammonium chlo-
ride in acetonitrile (0.1 M) was used as an electrolyte. Cyclic
voltametry scans were done from 0 to 11.8 V at scan rate of
100 mV per second.
Iron-Catalysed Dihydrorhodamine Oxidation (Fenton Re-
action). The antioxidant activities of each of the compounds
were evaluated by their ability to prevent oxidation of dihy-
drorhodamine to the fluorescent compound rhodamine. Ox-
idant was generated by ferrous catalysis (diothionite-reduced
ferric citrate) of tert-butyl hydroperoxide in a 50:50 water-to-
acetonitrile (volyvol) solution. Dihydrorhodamine (50
m
M)
was incubated with 300
m
M tert-butyl hydroperoxide and 0.5
m
M iron for 5 min. After this time, oxidation was assessed by
spectrofluorimetry (Excitation 5 500 nm, Emission 5 570
nm). Various concentrations of cannabinoids and butylhy-
droxytoluene (BHT) were included to examine their ability to
prevent dihydrorhodamine oxidation.
Data Analysis. Data are reported as mean values plus and
minus standard error. Significance was examined by using a
Student’s t test, (P # 0.05). Kinetic data was analyzed by using
GraphPad’s
PRISM software package (GraphPad, San Diego)
for PC.
RESULTS
Cannabidiol Blocks NMDAr and AMPA and Kainate Re-
ceptor-Mediated Neurotoxicity. Glutamate neurotoxicity can
be mediated by NMDAr, AMPA receptors, or kainate recep-
tors. To examine NMDAr-mediated toxicity, rat cortical neu-
rons were exposed to glutamate for 10 min in a magnesium-
free medium, and the level of lactate dehydrogenase released
was used as an index of cell injury. To examine AMPAykainate
receptor-mediated toxicity, neurons were incubated for 20 hr
with glutamate or a specific AMPA or kainate receptor ligand
(fluorowillardiine or 4-methyl-glutamate, respectively). An
NMDAr antagonist (MK-801) and an agent to prevent recep-
tor desensitization also were included. Cannabidiol prevented
cell death equally well (EC
50
of 2–4
m
M) in both NMDAr and
AMPAykainate toxicity models (Fig. 1 A and B). Similar data
also was observed when glutamate was replaced with either
AMPA-specific or kainate receptor-specific ligands (data not
shown). These results suggest that cannabidiol protects simi-
Medical Sciences: Hampson et al. Proc. Natl. Acad. Sci. USA 95 (1998) 8269
larly, regardless of whether toxicity is mediated by NMDA,
AMPA, or kainate receptors.
AMPAyKainate Toxicity Is Calcium Dependent. Increased
calcium influx is known to be a key factor in NMDAr-induced
cell death (4), but its role in AMPA and kainate toxicity is less
clear. It has been suggested that AMPAykainate receptors may
not directly allow entry of sufficient calcium to kill cells.
However, AMPAykainate receptors flux large amounts of
sodium, which can depolarize cell membranes. Such depolar-
ization may activate both voltage-sensitive calcium channels
(21) and facilitate NMDAr activation (22, 23). In this way,
AMPAykainate receptor stimulation may lead indirectly to
accumulation of toxic intracellular calcium levels. Addition of
the calcium chelator EDTA reduced toxicity in a concentra-
tion-dependent manner, demonstrating the involvement of
calcium in AMPAykainate-type toxicity (data not shown).
EDTA (2 mM) eliminated '70% of glutamate toxicity (Fig. 2)
even though the presence of MK-801 prevented NMDAr
activation. Toxicity also was reduced by inhibitors to L-, N-,
and PyQ- type calcium channels (nifedipine, agatoxin IVa, and
conotoxin GVIa, respectively; Fig. 2), indicating that voltage-
sensitive calcium channels also are involved in AMPAy
kainate-type toxicity. However, a combination of these calcium
channel inhibitors did not completely block EDTA-
preventable (calcium-dependant) cell death.
Neuroprotection by Tetrahydrocannabinol. Unlike canna-
bidiol, THC is a ligand for the brain cannabinoid receptor (24),
and this action has been proposed to explain the ability of THC
to protect neurons from NMDAr toxicity in vitro (7). However,
in AMPAykainate receptor toxicity assays, THC and canna-
bidiol were similarly protective, suggesting that cannabinoid
neuroprotection may be independent of cannabinoid receptor
activation. This was confirmed by inclusion of a cannabinoid
receptor antagonist, SR-141716A (Fig. 3). Neither THC or
cannabidiol neuroprotection was affected by cannabinoid re-
ceptor antagonist.
Cannabinoids as Antioxidants. Cells use easily oxidizable
compounds such as glutathione, ascorbate, and
a
-tocopherol
as antioxidants that protect important cellular structures (e.g.,
DNA, proteins, and membranes) from ROS damage. Studies
have suggested that ROS damage may be involved in glutamate
neurotoxicity (5, 6). To investigate whether cannabinoids
could protect neurons against glutamate by reacting with ROS,
the antioxidant properties of cannabidiol and other cannabi-
noids were assessed. Cyclic voltametry, a procedure that
measures the ability of a compound to accept or donate
electrons under a variable voltage potential, was used to
measure the oxidation potentials of several natural and syn-
thetic cannabinoids. Cannabidiol, THC, and the synthetic
FIG. 2. The involvement of calcium and calcium channels in
AMPAykainate-mediated toxicity. The effects of 2 mM EDTA and
various combinations of the voltage-sensitive calcium channel inhib-
itors
v
-Agatoxin IVa (Ag) (250 nM),
v
-Conotoxin GVIa (CTx) (500
nM), and Nifedipine (Nif) (1
m
M) were used to probe the role and
source of calcium in AMPAykainate receptor-mediated toxicity. Data
represents mean values 6 SEM from four experiments, each with four
replicates. Cannabinoids were present throughout the glutamate ex-
posure period. See Materials and Methods for further experimental
details. Significant difference between EDTA and other treatments is
indicated with an asterisk.
FIG. 1. Effect of cannabidiol on NMDAr- (A) and AMPAykainate receptor- (B) mediated neurotoxicity. Data shown represents mean values 6
SEM from a single experiment with four replicates. Each experiment was repeated on at least four occasions with essentially the same results.
Cannabinoids were present during (and, in the case of NMDAr mediated toxicity, after) the glutamate exposure periods. See Materials and Methods
for further experimental details.
8270 Medical Sciences: Hampson et al. Proc. Natl. Acad. Sci. USA 95 (1998)
cannabinoid HU-211 all donated electrons at a similar poten-
tial as the antioxidant BHT. Anandamide (arachidonyl-
ethanolamide), which is not a cannabinoid in structure but is
an endogenous ligand for the cannabinoid receptor, did not
undergo oxidation in this assay (Fig. 4A). Three other canna-
binoids, cannabinol, nabilone, and levanantrodol, also were
tested, and they, too, exhibited oxidation profiles similar to
cannabidiol and THC (data not shown).
The ability of cannabinoids to be oxidized readily suggests
that they may possess antioxidant properties comparable to
BHT. These properties were examined further in a Fenton
reaction (iron-catalyzed ROS generation). Tert-butyl hy-
droperoxide was used to generate ROS and oxidize dihydror-
hodamine into the fluorescent compound rhodamine. Canna-
bidiol, THC, and BHT all prevented dihydrorhodamine oxi-
dation in a similar, concentration-dependent manner (Fig. 4B),
indicating cannabinoids to be comparable to BHT in antiox-
idant potency. To confirm that cannabinoids act as antioxi-
dants in the intact cell, neurons were incubated with tert-butyl
hydroperoxide and varying concentrations of cannabidiol (Fig.
5A). The oxidant was chosen for its solubility in both aqueous
and organic solvents, thereby facilitating oxidation in both
cytosolic and membrane cell compartments. As observed in
studies with glutamate, cannabidiol protected neurons against
ROS toxicity in a concentration-related manner. Cannabidiol
also was compared with antioxidants in an AMPAykainate
toxicity protocol. Neurons were exposed to glutamate and
equimolar cannabidiol,
a
-tocopherol, BHT, or ascorbate (Fig.
5B). Although all of the antioxidants attenuated glutamate
toxicity, cannabidiol was significantly more protective than
either
a
-tocopherol or ascorbate.
DISCUSSION
The nonpsychoactive marijuana constituent cannabidiol was
found to prevent both glutamate neurotoxicity and ROS-
induced cell death. The psychoactive principle of Cannabis,
THC, also blocked glutamate neurotoxicity with a similar
potency to cannabidiol. In both cases, neuroprotection was
unaffected by cannabinoid receptor antagonist. This suggests
that cannabinoids may have potentially useful therapeutic
effects that are independent of psychoactivity-inducing can-
nabinoid receptors (12) and so are not necessarily accompa-
nied by psychotropic side effects.
Cannabidiol blocked glutamate toxicity in cortical neurons
with equal potency regardless of whether the insult was
mediated by NMDAr, AMPA receptors, or kainate receptors.
This suggests that either cannabinoids antagonize all three
glutamate receptors with the same affinity, or, more likely,
their site of action is downstream of initial receptor activation
FIG. 3. Effect of THC, cannabidiol, and cannabinoid receptor
antagonist on glutamate induced neurotoxicity. Neurons exposed to
glutamate in an AMPAykainate receptor toxicity model were incu-
bated with 10
m
M cannabidiol or THC in the presence or absence of
SR141716A (500nM). See Materials and Methods for experimental
details. Data represents mean values 6 SEM from four experiments,
each with three replicates.
FIG.4. (A) A comparison of the oxidation potentials of cannabinoids and the antioxidant BHT. The oxidation profiles of (750
m
M) BHT,
cannabinoids, and anandamide were compared by cyclic voltametry. Anandamide, a cannabinoid receptor ligand with a noncannabinoid structure,
was used as a nonresponsive control. Experiments were repeated three times with essentially the same results. See Materials and Methods for
experimental details. (B) Effect of cannabidiol and THC on dihydrorhodamine oxidation. Cannabinoids were compared with BHT for their ability
to prevent tert-butyl hydroperoxide-induced oxidation of dihydrorhodamine. See Materials and Methods for experimental details. Data represent
mean values 6 SEM from a single experiment with three replicates. This experiment was repeated four times with essentially the same results.
Medical Sciences: Hampson et al. Proc. Natl. Acad. Sci. USA 95 (1998) 8271
events. Neurotoxic concentrations of glutamate induce mas-
sive calcium influx through NMDAr (4) that ultimately kills
the cell. This study has demonstrated that the toxic effects of
glutamate are also calcium-dependent when mediated by
AMPAykainate receptors. Both EDTA (a calcium chelator)
and voltage-sensitive calcium channel inhibitors reduced
AMPA-ykainate-type neurotoxicity, indicating that a portion
of calcium influx-associated AMPA-ykainate-receptor activa-
tion is mediated by secondary activation of calcium channels.
However, the mixture of calcium channel inhibitors and
NMDAr antagonist did not eliminate completely glutamate
toxicity or reduce cell death as efficiently as EDTA. This
suggests that although toxicity resulting from AMPAykainate
receptor stimulation may be caused by calcium entering the
cell by several routes, it is not caused exclusively by calcium
channel activity. These studies also demonstrate that NMDAr
activation is not required for AMPA-ykainate-type toxicity [as
suggested (22)].
Accumulation of ROS has been shown to be involved in
NMDAr-mediated cell death (4). The current study has sim-
ilarly demonstrated that AMPAykainate receptor-induced
toxicity also involves ROS formation and may be prevented
with antioxidant treatment. Cannabidiol and THC were found
to be comparable with BHT (antioxidant) in both their ability
to prevent dihydrorhodamine oxidation (Fenton reaction) and
their cyclic voltametric profiles. Synthetic cannabinoids such as
HU-211, nabilone, and levanantradol also exhibited similar
profiles. Anandamide, which is a natural cannabinoid receptor
ligand but is not structurally related to cannabinoids, did not
give an antioxidant-like profile by cyclic voltametry, which
indicates that cannabinoids can act as reducing agents (in a
chemical system). To confirm that cannabinoids also can
function as antioxidants in living cells, a lipid hydroperoxide
was used to generate ROS toxicity in neuronal cultures. As
observed in the Fenton reaction system, cannabidiol attenu-
ated this ROS-induced neurotoxicity. These observations in-
dicate that many cannabinoids exert a considerable protective
antioxidant effect in neuronal cultures. The similarity of the
voltamagrams observed with cannabidiol, HU-211, and several
other cannabinoids also suggests that the reported antioxidant
effect of HU-211 is not a feature unique to this atypical
cannabinoid, (as previously implied; e.g., ref. 11) but, rather,
a common property of classical cannabinoid structures. The
potency of cannabidiol as an antioxidant was examined by
comparing it on an equimolar basis with other commonly used
antioxidants. Cannabidiol protected neurons to a greater
degree than either of the dietary antioxidants,
a
-tocopherol or
ascorbate. As in the Fenton reaction system, cannabidiol
protected neurons with comparable efficacy to the potent
antioxidant BHT. The similar antioxidant abilities of canna-
bidiol and BHT in this chemical system and their comparable
protection in neuronal cultures implies that cannabidiol neu-
roprotection is caused by an antioxidant effect.
The antioxidative properties of cannabinoids suggest a
therapeutic use as neuroprotective agents, and the particular
properties of cannabidiol make it a good candidate for such
development. Although cannabidiol was similar in neuropro-
tective capacity to BHT, cannabidiol has no known tumor-
promoting effects [unlike BHT (25, 26)]. The lack of psycho-
activity associated with cannabidiol allows it to be adminis-
tered in higher doses than would be possible with psychotropic
cannabinoids such as THC. Furthermore, the ability of can-
nabidiol to protect against neuronal injury without inhibiting
NMDAr may reduce the occurrence of toxicity or side effects
associated with NMDAr antagonists (27). Previous studies
have indicated that cannabidiol is not toxic, even when chron-
ically administered to humans (28) or given in large acute doses
[700 mgyday (29)]. In vivo studies to examine the efficacy of
cannabidiol as a treatment for experimentally induced isch-
emic stroke are currently in progress.
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