the complex pharmacology of cannabis
TRANSCRIPT
© University of Reading 2009 www.reading.ac.uk/cinn 28 June 2013
The complex pharmacology of cannabis Ben J. Whalley
Outline
• Constituents of cannabis – Cannabinoids and non-cannabinoids – Historical changes in composition
• The endocannabinoid system – The physiological system affected by THC – Dispelling myths aka ‘Just because it has ‘cannab’ in the name…’ – Cannabinoids that do act via the endocannabinoid system
• Beyond the endocannabinoid system – Cannabinoids that don’t act via the endocannabinoid system
• Considerations for human medical development and use – Modulating the ubiquitous – Natural ≠ safe – Winning strategies: ‘Smaller & Quicker’ or ‘Slower & Larger’?
Constituents of cannabis • Cannabis: for the most part, we are talking about the plant
Cannabis sativa.
• You’ve probably gathered that it one of the most widely used recreational and medicinal drugs worldwide.
– ~150 million people smoking cannabis daily (WHO)
• May be the first non-food plant cultivated by humans (~8000 BC)[2].
• Best known for its psychoactive constituent, Δ9-tetrahydrocannabinol (‘THC’).
Much, much more than just D9-THC • In addition to D9-THC, cannabis also contains:
• >100 other ‘cannabinoids’ – Cannabinoids are chemical entities that are structurally similar to
THC[3].
– phenol ring, 5-carbon alkyl chain, central pyran ring and mono-unsaturated cyclohexyl ring.
– Not found in any other plant.
• >400 other non-cannabinoids[3]. – Cannot rule out specific effects of these non-cannabinoids.
– e.g. Eugenol: acts at similar receptors in the brain as other drugs (e.g. alcohol; GABAAR).
Constituents of cannabis II
From [4]
Hexanoyl CoA Acetyl CoA
Olivetolic acid
Cannabinerolic acid Cannabigerolic acid
THC acid
THC tetrahydrocannabinol
CBD acid
CBD cannabidiol
CBC acid
CBC cannabichromene
>30 more found since this paper was published in 2005…
…
Biosynthesis of phyto cannabinoids
Exist as the acid form in the plant and are decarboxylated by smoking and/or storage
A brief detour into history and human nature… • Historical/ancient use of psychoactive drugs relied upon the
raw plant material or very crude extracts. – E.g. Hashish from marijuana, shamanic drinking of reindeer urine
after feeding animals Amanita muscaria
• Human nature seems to aspire towards more purified and potent end products…often with unintended consequences.
Historical Contemporary
Marijuana/hashish Skunk (breeding)/hash oil
Psilocybe semilanceata (‘Magic mushrooms’), peyote
LSD
Coca leaves Cocaine/crack cocaine
Opium (crude extract) Heroin
Cannabis breeding/’genetics’ • ‘Genetics’ sounds modern and post-human genome project; for cannabis, it’s not.
• Cannabis genetics are based around classical Mendelian, inheritance-driven breeding of plants.
• Male/female plants and easy cloning (‘taking cuttings’) allow for straightforward experimental breeding to optimise for specific cannabinoid compositions
• Recreational use is ~2-3x alleged medicinal use; the majority of breeding has focussed upon optimising D9-THC levels for psychoactivity at the expense of other cannabinoids.
– Strong suggestions of over-emphasis of medicinal use and positive reporting bias.
• Some ‘medicinal’ growers starting to focus upon strains with higher CBD levels but still significant D9-THC present.
– Risks associated with D9-THC – Undesirable side effect profile – Particular risks in paediatrics (permanent ~10 point IQ drop)
7
http://www.genetics.org/content/163/1/335.full.pdf
The endocannabinoid system in a nutshell • The endocannabinoid systems was first
described in the late 1980s/early 1990s
• Comprises endogenous ligands, receptors, synthesic and degradation enzymes
• Cannabinoid receptors: – cell surface receptors – present on a wide variety of cell types. – two CBR types:
• CB1: principally in the CNS, affect neuronal excitability by modulating neurotransmitter release
• CB2: principally in non-brain areas and linked to immune response
• Endocannabinoids: – Two principal ECs thus far identified:
• anandamide • 2-arachidonoyl glycerol
8
Anandamide 2-arachidonoyl glycerol (2-AG)
But it’s got ‘cannab-’ in the name... • The endocannabinoid system was so named because the CB1 receptor is the target for
D9-THC. – This does not mean that all cannabinoids act via the endocannabinoid system!
• Numerous synthetic ligands for CB1Rs and CB2Rs have also been developed – e.g. WIN55-212,2, CP55-940, HU-210 (agonists) and AM251, SR141716A (antagonists)
• Most were developed as research compounds to probe the endocannabinoid system – Now notorious as constituents of ‘spice blends’ (‘legal highs’)
• Importantly, of the ~100 plant cannabinoids, 3 are known CB1R/CB2R ligands:
– D9-THC (tetrahydrocannabinol) • principal psychoactive component • Partial agonist at CB1R and CB2R
– CBN (cannabinol) • Agonist • ~50x times less potent than D9-THC
– THCV (tetrahydrocannabivarin) • Competitive antagonist at CB1R and CB2R
10
All CB1R ligands are not the same…
• D9-THC is a partial agonist at CB1 receptors[6]
• Partial agonists bind to, but do not fully activate the target
receptor.
• Not true for most synthetic cannabinoids
• Found in ‘spice blends’ and ‘incenses’
• Typically full agonists
11
WIN55-212,2
Beyond the endocannabinoid system • The pharmacology of the majority of cannabinoids remains
unknown or poorly defined.
• Goes well beyond effects mediated by the endocannabinoid system
• Cannabidiol (CBD) is typically the second most common plant cannabinoid and so serves as a good example
• No evidence of functional CBD interactions with CB1R/endocannabinoid system
– can act as a low affinity, high potency CB2R antagonist (i.e. at high micromolar concentrations) but concentrations required would be difficult to achieve in vivo.[5]
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Cannabidiol (CBD) pharmacology
• Non-endocannabinoid targets: – GPR55 antagonist (PMID 17876302)
– 5HT1A agonist (PMID 16258853)
– Adenosine reuptake inhibition
– TRPV1 agonism (PMID 16728591)
– Bidirectional modulation of intracellular Ca2+ (PMID 19228959)
– Allosteric modulator of mu and delta opioid receptors (PMID 16489449)
– VGSC blockade (only at high micromolar concs; unpublished)
• Caveats: – All are in vitro and have not been definitively linked to functional effects
in whole animals/humans.
– Some concentrations used are higher than can be reached in brain (functionally implausible).
13
Disentangling medicinal from recreational • Debates about recreational use of cannabis often invoke the
anecdotal (historical) and modern day evidence base associated with medicinal use.
• Significant risks associated with doing so since: – Assertions very often based on very early preclinical evidence. – Many making such assertions have no scientific, let alone medical,
training – A single personal experience is often used to substantiate
generalisations (‘the miracle of n=1’) – Ancient historical evidence is ascribed greater validity due to its age;
logical? – Personal/subjective/individual experience or perceived ‘persecution’
seem to limit broader thinking about populations and society
• Let’s have a look at some of the established evidence…
14
Historical medicinal use • Written evidence asserting medicinal use predates Christianity.
• Majority of claimed effects are likely to be via D9-THC or CBD as other constituents present in very limited quantities.
• Western knowledge of cannabis begins in the 19th century where medical claims are made for the following:
– Glaucoma – Cramps – Gout – Burns (topically) – Appetite stimulation – Bowel discomfort – Analgesia (pain relief) – Epilepsy – Colic – Insomnia – Diabetes – Complex mental health problems (most likely schizophrenia, depression etc.)
Compiled from: [6, 7 & 8]
Current medicinal use • There are more licensed cannabinoid-based drugs
currently available than one might think:
Name Content Indication
(use) Manufacturer Licence
granted
Sativex THC/CBD (50:50) Pain and spasticity
GW Pharma 2005
Marinol/dronabinol THC Nausea & vomiting, pain, appetite stimulation
Solvay 1988
Nabilone Synthetic THC Pain, nausea & vomiting
Valeant 1985
Rimonabant CB antagonist Anti-obesity/smoking cessation
Sanofi-Aventis 2006 (withdrawn 2008)
Medicinal use: historical vs present • Interesting comparisons between historical usage and
modern day disease targets for cannabinoid
therapeutics.
Historical Modern (L=licensed)
Glaucoma Currently being investigated
Appetite stimulation Marinol (L) and others being developed
Bowel discomfort, colic Colitis, IBS under investigation
Analgesia (pain relief) Sativex (L), Nabilone (L) and others being developed
Epilepsy URB597, CBD, CBDV, THC and THCV under investigation
Insomnia Under investigation
Diabetes THCV? CBD?
Complex mental health problems
CBD for schizophrenia
Natural ≠ safe or ‘the myth of herbals’ • >500 separate constituents of cannabis
• We don’t know what most of them do in the lab, let alone in people.
• We don’t know how many of them might interact with existing medicines or diseases.
• Sharks and deadly nightshade are ‘natural’ but you wouldn’t swim with one before eating the other!
• Whilst a large historical evidence base is useful, historical dogma should not rule the day
– Modern medicine demands modern medicines for hard to treat conditions.
– What’s best for patients?
– Small wins from decriminalising a crude and variable composition herb vs big wins from modern pharmaceuticals based on pure constituents, known mechanisms and randomised, controlled clinical trials.
18
So why no medicines?
• All drug development business models rely on being able
to protect IPR
• You can’t* patent a pure chemical constituent from a
plant.
• Difficult to find workable business models
• Decades of preclinical evidence is a hindrance.
– See next slide
19
*it’s certainly very tricky!
Epilepsy as an example...
• Huge evidence base asserting anticonvulsant effects.
• Few drugs have been successfully and repeatedly tested in as many preclinical models!
20
Compound
Sp
eci
es
Number of discrete conditions/models/designs
Dose Anticonvulsant No effect
Proconvulsant
THC 6 31 0.25-200 mg/kg
61% 29% 10%
CBD 2 21 1-400 mg/kg
81% 19% 0%
Other plant cannabinoids
2 7 N/A 100% 0% 0%
CB1 receptor agonists
2 55 N/A 73% 18% 2%
(7% mixed effect)
Species Strain Age Model type Disease model MethodSingle compound or co-
administration
Cannabinoid doses
testedDose timing Route Effect
Gross effect
(proconvulsant =
RED,
anticonvulsant =
GREEN, no effect
= BLACK)
Notes Reference
10 mg/kg 5-135 mins before test stimulus10 mg/kg 15-45 mins before test stimulus reduced number of
animals showing signs of seizures
1.25-10 mg/kg 15 mins before test stimulus2.5-10 mg/kg reduced number of animals showing signs of
seizures
10 mg/kg 15 -90 mins before priming stimulus10 mg/kg 15-45 mins before priming stimulus showed
reduced signs of seizures
10-50 mg/kg 15 -90 mins after priming stimulus No effect
Mouse QS Adult Acute Generalised seizure PTZ 1-80 mg/kg 30 mins before testing No effect PTZ threshold model
30 mins before testing >160 mg/kg protected against hindlimb extension
30 mins before testing 20-75 mg/kg significantly increased hindlimb extension
20 mg/kg 30 mins before testing i.v. Significantly decreased hindlimb extension
THC plus CBD plus CBN
50 mg/kg THC,
50mg/kg CBD, 50
mg/kg CBN
30 mins before testing p.o. Significantly decreased hindlimb extension
50mg/kg THC p.o. was proconvulsant alone
and 50 mg/kg CBD nor CBN p.o. are
anticonvulsant at these doses
THC plus PHN
50mg/kg THC (with a
range on phenytoin
doses)
30 mins before testing p.o. Significantly reduced phenytoin ED50
A proconvulsant THC dose (50 mg/kg p.o.)
reduces AED ED50. Supports earlier proposal
that cannabis and phenytoin interact
synergistically (Loewe et al., 1947)
THC plus PHN plus CBD
50 mg/kg THC, 50
mg/kg CBD (with a
range of phenytoin
doses)
30 mins before testing p.o. Significantly reduced phenytoin ED50
AED ED50 further reduced from that
achieved by coadministration of THC with
phenytoin
Mouse CF-1 Adult Acute Generalised seizure MES THC 1-100mg/kg 120 mins before testing i.p. Significant protection against seizures Blocked by SR141716A Wallace et al., 2001
THC plus PBL25-50 mg/kg THC plus
9.3-40 mg/kg PBL
THC: 120 mins; PBL: 60 mins before
testing
THC: p.o.,
PBL: i.p.Significant potentiation of PBL effect
Potentiation greater than that caused by CBD
reported in same study
THC plus CBD plus PBL
25 mg/kg THC, 25
mg/kg CBD, 9.3-40
mg/kg
phenobarbitone
THC & CBD: 120 mins; PBL: 60 mins
before testing
THC &
CBD: p.o.,
PBL: i.p.
Significant potentiation of PBL effectPotentiation comparable to that caused by
co-administration of THC 50 mg/kg alone
MES 15 mins to 24 hours before testing Significant increase in latency to hindlimb extensionDose timing variation revealed peak effects
at 30 mins
PTZ No effect
Nicotine No effect
Strychnine No effect
Single dose 50 mg/kg significantly dereased latency to seizure
o.d. for 6 days before testing No effect
0.25 mg/kg At onset of kindling Significant reduction of epileptiform after-discharges
At stage 3 (head nodding)
At stage 5 (clonic jumping)
At kindling endpoint
Rat Sprague-Dawley Adult ChronicTemporal lobe
epilepsyPilocarpine-induced SRS 0.5-30mg/kg
Single dose immediately before
EEG and behavioural monitoringi.p. Spontaneous seizures completely prevented Effect blocked by AM251 Wallace et al., 2003
Rat Not stated Adult Acute Generalised seizure PTZ 15-200 mg/kg 45 mins before testing i.p. Significant anticonvulsant effectAnticonvulsant effects described as
'unreliable'
Corcoran et al., 1973 &
Fried et al., 1973
Photogenic No effect
Amygdala kindling
(electrical)
Significant reduction in seizures and epileptiform after-
discharges
PhotogenicSignificant anticonvulsant effect after treatment at 0.5 but
not 2 hours
PTZ (35 mg/kg in epileptic
fowl)
PTZ (80 mg/kg in non-
epileptic fowl)
Mouse QS Adult Acute Generalised seizure MES CBD plus PBL
50 mg/kg CBD plus 9.3-
40 mg/kg
phenobarbitone
CBD: 2 hours, PBL: 1 hour before
testing
CBD: p.o.,
PBL: i.p.Significant potentiation of PBL effect None Chesher et al., 1975
Mouse CF-1 Adult Acute Generalised seizure MES CBD 1-100mg/kg 120 mins before testing i.p. Significant protection against seizures Not blocked by SR141716A Wallace et al., 2001
Rat Not stated Adult Acute Generalised seizure MES 1.5-12 mg/kg 1 hour before testing i.p. Significant anticonvulsant effect Notably low dose required Izquierdo et al., 1973
PTZ
MES
Mouse ICR Adult Acute Generalised seizure MES 120 mg/kg (ED50) 0.5-6 hours before testing i.p. Significant anticonvulsant effect None Karler et al., 1978
Rat Sprague-Dawley Adult Chronic Generalised seizure Limbic kindling (electrical) 0.3-3 mg/kg 15-300 minutes i.p. Significant increase in threshold to after-discharge None Turkanis et al., 1979
Rat Not stated Adult Chronic
Partial seizure with
secondary
generalisation
Cortical implantation of
cobalt60 mg/kg Twice daily after implantation i.p. No effect None Colasanti et al., 1982
MES Significant anticonvulsant effect
3-mercaptoproprionic acid No effect
Picrotoxin Significant anticonvulsant effect
Isonicotinic acid Significant anticonvulsant effect
Bicuculline Significant anticonvulsant effect
Hydrazine Significant anticonvulsant effect
PTZ Significant anticonvulsant effect
Strychnine No effect
Rat Wistar-Kyoto Adult Acute Generalised seizure PTZ Significant anticonvulsant effects at 1 & 100 mg/kg None Jones et al., 2010
Rat Wistar-Kyoto Adult AcuteTemporal lobe
seizurePilocarpine (acute) None Jones et al., 2012
Rat Wistar-Kyoto Adult Acute
Partial seizure with
secondary
generalisation
Penicillin None Jones et al., 2012
Mouse Adult Acute Generalised seizure MES CBN 230 mg/kg (ED50) 30 mins before testing i.p. Significant anticonvulsant effect None Karler et al., 1978
Rat Wistar-Kyoto Adult Acute Generalised seizure PTZ THCV 2.5 mg/kg 1 hour before testing i.p. Significant anticonvulsant effect Anticonvulsant effect lost Hill et al., 2010
Mouse DBA/2 Adult Acute Generalised seizure Audiogenic 1 hour before testing i.p. None
Mouse ICR Adult Acute Generalised seizure MES 1 hour before testing i.p. None
1 hour before testing i.p. None
3.5 hours before testing p.o. None
AcuteTemporal lobe
seizurePilocarpine 1 hour before testing i.p. None
WIN55,212 plus
clonazepam15 mins before testing No effect
15mg/kg WIN55,212 significantly affects
motor function when co-administered (no
effect noted without WIN55,212)
WIN55,212 plus
ethosuximide45 mins before testing
15mg/kg WIN55,212 enhanced anticonvulsant effect of
ethosuximide
15mg/kg WIN55,212 elevated ethosuximide
brain levels; 15mg/kg WIN55,212
significantly affects motor function when co-
administered (no effect noted without
WIN55,212)
WIN55,212 plus valproate 30 mins before testing15mg/kg WIN55,212 enhanced anticonvulsant effect of
valproate
15mg/kg WIN55,212 elevated valproate
levels in brain; 15mg/kg WIN55,212
significantly affects motor function when co-
administered (no effect noted without
WIN55,212)
WIN55,212 plus
phenobarbital60 mins before testing
15mg/kg WIN55,212 enhanced anticonvulsant effect of
phenobarbitone
15mg/kg WIN55,212 significantly affects
motor function when co-administered (no
effect noted without WIN55,212)
WIN55,212 plus valproate 30 mins before testing10mg/kg WIN55,212 enhanced anticonvulsant effect of
valproate
10mg/kg and higher impaired motor function
and memory.
WIN55,212 plus
carbamazepine30 mins before testing
10mg/kg WIN55,212 enhanced anticonvulsant effect of
carbamazepine
10mg/kg and higher impaired motor
function.
WIN55,212 plus
phenobarbitone60 mins before testing
10mg/kg WIN55,212 enhanced anticonvulsant effect of
phenobarbitone
10mg/kg and higher impaired motor function
and memory.
WIN55,212 plus
phenytoin120 mins before testing
10mg/kg WIN55,212 enhanced anticonvulsant effect of
phenytoin
10mg/kg and higher impaired motor function
and memory.
WIN55,212 2.5-15mg/kg 20 mins before testing 15mg/kg elevated threshold to seizure10mg/kg and higher impaired motor
function.
Rat Wistar Juvenile (P20) Acute Generalised seizure Kainic acid WIN55,212 0.5-5mg/kg 90 mins before testing i.p.All doses reduced severity vs vehicle controls but higher
WIN doses exerted a smaller effect on severity.
WIN effect on kainic acid induced seizures is
inversely related.Rudenko, 2012
ACEA 1.25-15mg/kg i.p. Increased threshold to seizure PMSF (FAAH inhibtor) used to prevent ACEA
metabolism
ACEA plus 30mg/kg
valproate1.25-2.5mg/kg i.p. ACEA enhanced the anticonvulsant effect of valproate
ACEA increase available valproate
concentration; ACEA had not effect on motor
function
Rat Long-Evans Adult Acute Generalised seizure PTZ 40mg/kg 2 hours prior to testingAnimals did not exhibit tonic seizures but progressed
directly to clonic seizures
PEA did not affect any other seizure
features.
Rat Long-Evans Adult Chronic Generalised seizure Amygdala kindling 1, 10 & 100mg/kg 2 hours prior to testing 1mg/kg PEA delayed onset of seizures
PEA only given prior to test session, not prior
to kindling stimuli. Effect on latency lost at
10 & 100mg/kg
PTZ Significantly reduced tonic convulsions
3-mercaptopropionic acid Significantly reduced tonic convulsions
Bicuculline Significantly reduced tonic convulsions
Strychnine Significantly reduced tonic convulsions
Picrotoxin Significantly reduced tonic convulsions
NMDA Significantly reduced tonic convulsions
MES 50 & 100mg/kg 50 & 100mg/kg significantly reduced seizures incidencePeak effect seen at 2 hours after
administration
MES Anandamide 50mg/kg 50mg/kg significantly reduced seizures incidence
WIN55,212 0.5-4mg/kg Significant protection against seizures
WIN55,212 plus diazepam0-4mg/kg of each in
mixed ratios
3:1 ratio (diazepam:WIN55,212) produced synergistic effect
upon protection from seizure
AM404 0.125-4mg/kg No significant effect
AM404 plus diazepam0-4mg/kg of each in
mixed ratiosNo significant effect
URB597 0.05-1mg/kg Significant protection against seizures
URB597 plus diazepam0-2mg/kg of each in
mixed ratiosURB597 antagonised effects of diazepam URB597 is a FAAH inhibitor
WIN55,212 1-100ug Significant increase in latency to seizure
WIN55,212 plus
isoguvacine
1-100ug and 5-50ug
respectively
No significant effect upon isoguvacine-induced increased
latency to seizureIsoguvacine is a GABAAR agonist
URB597 10-100ug No significant effect
URB597 plus isoguvacine10-100ug plus 5-50ug
respectively
No significant effect upon isoguvacine-induced increased
latency to seizureIsoguvacine is a GABAAR agonist
URB602 10-500ug Significant increase in latency to seizure at all doses URB602 is a MAGL inhibitor
ACEA plus carbamazepine No significant effect
ACEA plus lamotrigine No significant effect
ACEA plus oxcarbazepine No significant effect
ACEA phenobarbitone Action of phenobarbitone significantly increasedACEA did not affect phenobarbitone
availability
ACEA plus phenytoin No significant effect
ACEA plus topiramate No significant effect
Rat WAG/Rij Adult Chronic Absence Genetic WIN55,212 3-12mg/kg 2 hours prior to testing s.c.Significantly decreased spike wave discharge incidence but
concomitant increase in durationvanRijn, 2010
ACEA 0.25ug45 mins after establishment of
epileptiform activity.i.c.v.
Frequency and amplitude of epileptiform activity
significantly reduced
ACEA plus memantine0.25ug and 1-20mg/kg
respectively
Memantine 30 mins and ACEA 45
mins after establishment of
epileptiform activity.
i.c.v. Some potentiation of anticonvulsant effect of memantine Memantine is an NMDAR antagonist
Rat Wistar Adult Acute Partial seizureMaximal dentate gyrus
activationWIN55,212 1-21mg/kg
Monitored for up to 120 mins after
administrationi.p. Significant decrease in duration and increase in latency Blocked by co-administration of AM251 Rizzo, 2009
Rat Not stated Adult Acute Partial with Penicillin (i.c.v.) ACEA 2.5-15ug Monitored for up to 120 mins after i.c.v. Significant decrease in frequency only at highest dose Blocked by co-administration of AM251 Kozan, 2009
ACEA 0.1-8mg/kg Up to 60 mins before testing i.p. Significant increase in threshold to seizure
ACEA plus naltrexone0.1-8mg/kg and 1-
500pg/kg respectivelyUp to 60 mins before testing i.p. Significant potentiation of ACEA anticonvulsant effect
Mouse NMRI Adult Acute Generalised seizure PTZ ACEA 0.1-4mg/kg 60 mins before testing i.p. Significant increase in seizure threshold at 2 & 4 mg/kg ACEA Effect blocked by AM251 Bahremand et al., 2009
Mouse NMRI Adult Acute Generalised seizure PTZ ACEA 0.1-8mg/kg 15 mins before testing i.p. Significant increase in threshold to seizure at 2-8mg/kgEffect enhanced by ultra-low dose AM251
(100fg/kg-100ng/kg; fg = femtogram)Gholizadeh, 2007
Mouse NMRI Adult Acute Generalised seizure PTZ ACPA 0.5-2mg/kg 60 mins before testing i.p. Significant increase in threshold to seizure at 1.5-2mg/kg Blocked by AM251 Shafaroodi et al., 2004
Rat Sprague-Dawley Adult ChronicTemporal lobe
epilepsyPilocarpine-induced SRS WIN55,212 5mg/kg
Single dose immediately before
EEG and behavioural monitoringi.p. Spontaneous seizures completely prevented Effect blocked by AM251 Wallace et al., 2003
Mouse CF-1 Adult Acute Generalised seizure MES WIN55,212 1-100mg/kg 120 mins before testing i.p. Significant protection against seizures Blocked by SR141716A Wallace et al., 2001
30 or 60 mins before testing i.p. Seizure duration increased by 4mg/kg at 60 mins only Performed on fully kindled animals
30 mins before kindling stimulus i.p. Kindling significantly retarded Performed during kindling (epileptogenesis)
30 or 60 mins before testing i.p. 1 mg/kg at 30 mins increased afterdischarge threshold Performed on fully kindled animals
30 mins before kindling stimulus i.p. No significant effect Performed during kindling (epileptogenesis)
Rat Wistar Adult Acute Generalised seizure Audiogenic SR141716A 30mg/kg o.d. for 5 days p.o.Seizure severity and duration increased in rats susceptible to
seizure.
Rats not susceptible to audiogenic seizure
showed no seizure response to SR141716A.
High rimonabant dose.
vanRijn, 2011a
AM251 0.25-5mg/kg No significant effect
AM251 plus diazepam0-4mg/kg of each in
mixed ratiosNo significant effect
Rat WAG/Rij Adult Chronic Absence Genetic AM251 6-12mg/kg 2 hours prior to testing s.c. No significant effect vanRijn, 2010
AM251 7.5ug45 mins after establishment of
epileptiform activity.i.c.v.
Frequency and amplitude of epileptiform activity
significantly increasedCakil, 2011
AM251 plus memantine7.5ug and 1-20mg/kg
respectively
Memantine 30 mins and AM251 45
mins after establishment of
epileptiform activity.
i.c.v. No effect on anticonvulsant effect of memantine Memantine is an NMDAR antagonist
Rat Wistar Adult Acute Partial seizureMaximal dentate gyrus
activationAM251 1mg/kg
Monitored for up to 120 mins after
administrationi.p. No significant effect Rizzo, 2009
Rat Not stated Adult Acute
Partial with
secondary
generalisation
Penicillin (i.c.v.) AM251 0.125-1ugMonitored for up to 120 mins after
administrationi.c.v. Significant proconvulsant effect at 0.25 and 0.5ug only Kozan, 2009
Mouse NMRI Adult Acute Generalised seizure PTZ AM251 0.01-1mg/kg 15 mins before testing i.p. No significant effect Bahremand et al., 2009
Rat Sprague-Dawley Adult Chronic Epileptogenesis Kainic acid SR141716A 10mg/kgOnce at first sign of acute, kainic
acid-induced seizurei.p. No effect Dudek, 2010
Rat Wistar Adult/Immature Chronic
Juvenile head
trauma followed by
acute proconvulsant
challenge 6 weeks
later
Kainic acid SR141716A 1 & 10 mg/kg Immediately following head trama i.p.SR141716A treatment reduced seizure susceptibility to
control levelsEchegoyen, 2009
Mouse NMRI Adult Acute Generalised seizure PTZ AM251 1fg/kg-1mg/kg 45 mins before testing i.p. No significant effect fg = femtogram (ultra-low dose) Gholizadeh, 2007
Mouse NMRI Adult Acute Generalised seizure PTZ AM251 0.5-3mg/kg 60 mins before testing i.p.Significant proconvulsant effect at 0.75-3mg/kg (peak effect
at 1mg/kg)Shafaroodi et al., 2004
Rat Wistar Adult N/ANone (healthy
animals)EEG recording SR141716A 30mg/kg o.d. for at least 20 days p.o. 20% of animals (4/20) exhibited spontaneous seizures.
Note very high SR141716A dose; animals
were female and no note of stage of
oeastrous cycle in original report.
vanRijn, 2011a
THC 10mg/kg Increased incidence of seizures on handling
URB597 0.3mg/kg No effect on seizure incidence
HU210 0.01mg/kg Increased incidence of seizures on handling
1 & 3mg/kg
Acute
Rat Wistar-Kyoto
Hill et al., 2012
(submitted)
Published results of cannabinoid effects upon whole animal models of seizure and epilepsy
Generalised seizure i.p.
p.o.
Mouse C57BL/6 AcuteModel uses a priming stimulus at P+19
followed by a test stimulus at P+28
25 - 200 mg/kg
Audiogenic priming
Generalised seizure MES
AcuteMouse Generalised seizure MES
Spontaneously epileptic
Mouse Not stated Acute Generalised seizure 5-400 mg/kg 60 minutes before testing i.p.Apparently highly effective in models reliant
upon GABAergic systems.
CBD
Generalised seizure
MES
No effect
i.p.
i.p.Species exhibits photomyoclonus and is
susceptible to amygdala kindling
Subpopulation of chickens susceptible to
photic stimulation. Susceptible = 'epileptic'
No effect None
No indication of tolerance after 3-4 days
repeated administration
QS
Mouse Not stated Acute Generalised seizure
MES
No indication of tolerance after 3-4 days
repeated administration100 mg/kg
Threshold to seizure reduced60Hz electroshock
Not stated Chronic Generalised seizureAmygdala kindling
(electrical)None
Increased threshold to seizure
Significantly decreased hindlimb extension
Significant anticonvulsant effect
None
0.25 - 4 mg/kg
Generalised seizureChronicMeriones
unguiculatus
6Hz electroshockMouse Not stated Acute
Mouse QS Acute
Generalised seizureAcuteNot stated up to 80 mg/kg
i.p.o.d. for 3-4 days before testing
i.p.
Significantly decreased hindlimb extension
Significant anticonvulsant effect
Boggan et al., 1973
Chesher et al., 1974
Chesher et al., 1975
THC
No effect
~60 minutes before testing
i.p.
Loss of proconvulsant effect upon latency
with chronic treatment suggests
adaptation/tolerance
20 & 50 mg/kg
Standard MES model
Mouse Not stated Acute Generalised seizure 50-200 mg/kg 30 mins before testing p.o.
Acute Generalised seizure 0.25-1 mg/kg 0.5 or 2 hours before testing i.v.
100 mg/kg6Hz electroshock
60Hz electroshock
THC
Gallus
domesticus
Baboon Papio papio Chronic Generalised seizure 0.25-1 mg/kg
Cat
Gerbil
SwissMouse
5-15mg/kg Luszczki, 2011aAcute Generalised seizure PTZ
Karler et al., 1980
Chesher et al., 1974
Consroe et al., 1982
o.d. for 3-4 days before testing
1, 10 & 100 mg/kg 1 hour before testing i.p.
Significant anticonvulsant effects at ≥1 mg/kg
Significant anticonvulsant effect
CBDV 50-200 mg/kg Significant anticonvulsant effect
PTZGeneralised seizure
Luszczki, 2011b
Notable effects in non-seizure models
Adult
Adult
Adult
Adult
Adult
Adult
Adult
Adult
Adult
Adult
Adult
Adult
Adult
Adult
Synthetic CB1 antagonists (see also THCV)
Luszczki, 2006MES
10mg/kg and AED dose-
response
i.p.
MESGeneralised seizureAcute
10 mins prior to testingGeneralised seizureAcuteAdultSwissMouse
Sheerin, 2004
N-
palmitoylethanolamide
0.5 to 4 hours prior to testing
i.p.
i.p.
25mg/kg 2 hours prior to testing Ineffective against clonic convulsions
Lambert, 2001
Adult Acute Generalised seizure MES 30 mins before testing i.p. Naderi, 2008
Mouse OF1 Adult Acute Generalised seizure
Mouse NMRI Adult Acute Generalised seizure MES Naderi, 2008
Rat Wistar Adult Acute
Partial with
secondary
generalisation
Penicillin (i.c.v.) Cakil, 2011
Wendt et al., 2011Mouse NMRI Adult Chronic Generalised seizure Amygdala kindling
WIN55,212
URB597
2.5 & 4mg/kg
Acute
Partial with
secondary
generalisation
Penicillin (i.c.v.)
o.d. for 8 weeks i.p. Dowie, 2010Mouse R6/1 Adult Chronic Huntington's disease Behavioural observation
Rat Wistar Adult
Bahremand, 2008Mouse NMRI Adult Acute Generalised seizure PTZ
2.5mg/kg 10 mins prior to testing i.p. Luszczki, 2010Mouse Swiss Adult Acute Generalised seizure MES
Adult Acute Generalised seizure PTZ
Mouse NMRI
30 mins before testing
5 mins before testing i.c.v. Naderi, 2011Rat Wistar
Phytocannabinoids
D9-THC
Mouse
CBD
i.p.
Adult
Other phytocannabinoids
CB1 Agonists
Exogenous synthetic cannabinoids, endocannabinoids, derivatives and precursors
Johnson et al., 1975
Wada et al., 1975
Wada et al., 1975
Loskota et al., 1975
Sofia et al., 1974
Karler et al., 1980
Chicken
None30 mins before testing
Conclusions
• Natural doesn’t automatically mean safe
• Don’t get fooled by ‘cannab-’ in the name
• The endocannabinoid system and THC are only a small
facet to the overall story
• Small vs big wins?
21
Acknowledgements • Collaborators: Dr C. Williams, Dr G. Stephens, Dr G. Woodhall (Aston, UK),
Prof. L. Sander (NEC & UCL, UK), Prof. E. Williamson & Prof. R. Hampson
(Wake, USA).
• Researchers (past and present): Dr A. Hill, Mr N. Jones, Dr S. Weston, Dr J.
Farrimond, Dr I. Smith, Dr X. Wang, Dr Y. Yamasaki, Mr T. Hill, Mrs C. Hill, Mr
N. Amada, Miss I. Peres, Mrs R. Hadid, Mrs A. Al-Husaini, Mr S. Akiyama, Dr A.
Futamura, Miss M. Mercier, Mr S. Marshall.
22
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2. Childers SR, Breivogel CS. (1998) Cannabis and endogenous cannabinoid systems. Drug Alcohol
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3. Ashton (2001) Pharmacology and effects of cannabis: a brief review Br J Psychiatry. 178:101-6
4. Elsohly MA, Slade D (2005) Chemical constituents of marijuana: the complex mixture of natural
cannabinoids Life Sci. 78(5):539-48
5. Thomas et al. (2007) Br J Pharmacol 150(5): 613–623
6. Shen M, Thayer SA. (1999) Delta9-tetrahydrocannabinol acts as a partial agonist to modulate
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23