1. Physiology and Pharmacology of Cannabis
CLAE Meeting, October 15, 2016
Mac Burnham
University of Toronto

2. Introductory Cannabis contains a number over 100 active compounds.
Two of the most abundant and best studied are tetrahydrocannabinol (THC) and cannabidiol (CBD).
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

3. Introductory
In combination, THC and CBD probably account for most of cannabis’ known effects.
They have very different physiological and pharmacological properties.
Both suppress seizures, perhaps by different mechanisms. They will be the focus of today’s talk.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

4. Delta 9 Tetrahydrocannabinol
THC
Delta 9 Tetrahydrocannabinol
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

5. THC - Structure Converted from THCa by drying, heating.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

6. THC – Actions
THC has a wide number of pharmacological actions, some of which have been known since antiquity.
Anxiolytic / Sedative (CB1)
Analgesic (CB1)
Anticonvulsant (CB1)
Appetite Stimulant (CB1)
Anti-emetic (CB1)
Anti-inflammatory / Immune Suppressant (CB2)
ETC.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

7. THC Receptors
Most of THC’s actions are mediated through two main receptors.
CB1 – mostly found on neurons (CNS and PNS) – g linked
(small amounts: kidney, liver, lungs)
CB2 – found in the immune system and microglia – g linked
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

8. THC Receptors
These g-linked receptors are part of the endogenous endocannabinoid system.
To explain how THC works, it will be useful to discuss the endocannabinoid system.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

9. Background for THC: The Physiology of the Endocannabinoid System
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

10. The Endocannabinoid System
The endocannabinoid systems consists of endogenous cannabinoids and their receptors.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

11. Endocannabinoid System – Edogenous Messengers
The are two major endogenous messengers that bind to the cannabinoid receptors:
2 AG (2-arachidonoylglycerol)
anadamide (arachidonoylethanolamine or AEA)
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

12. Endocannabinoid System – Edogenous Messengers
Anandamide and 2 AG are eicosanoids.
They are formed by the action of phospholipases on plasma membrane phospholipids.
They are broken down by FAAH and other enzymes. Blockade of FAAH extends their half-lives.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

13. Endocannabinoid System – Edogenous Messengers
Both bind to CB1 and CB2 receptors.
CB1 – 2 AG is a full agonist - anandamide is a partial agonist
CB2 – 2 AG binds with a higher affinity than anadamide
Anandamide was discovered first, but 2 AG is perhaps the more powerful ligand.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

14. Endocannabinoid System - Function
2 AG and anandamide are “retrograde inhibitors”.
They are released post-synaptically following receptor activation.
They then diffuse backwards to the presynaptic cell where they inhibit transmitter (CB1) or cytokine (CB2) release.
They act by closing Ca++ channels and opening K+ channels via Gi/o.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

15. Endocannabinoid System
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

16. Endocannabinoid System
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

17. Endocannabinoid System
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

18. Endocannabinoid System
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

19. Endocannabinoid System - Function
In the brain, endocannabinoid feedback reduces transmitter release in many different systems.
These include: GABA, glutamate, DA, NE, 5HT, glycine, etc.
In the above diagrams, post-synaptic Ca++ results from mGLUR activation. In other systems, other mechanisms would provide the Ca++.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

20. Endocannabinoid System - Function
In the brain, CB1 receptors are located in many different area and affect many different transmitters.
They are perhaps not a “system”, but rather a series of local feedback mechanisms.
THC and congeners, however, activate these receptors all at once.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

21. THC Pharmacology THC Stimulates CB1 and CB2 Receptors
Actions in the brain involve CB1
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

22. THC/CB1 Drugs Agonists for the CB1/THC Receptor (selected)
Plant derived – THC - partial agonist
Synthetic – dronabinol (Marinol), nabilone (Cesamet) (partial agonists?), WIN 55, full agonist
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

23. THC/CB1 Dugs Antagonists for the CB1 Receptor
Cannabindiol (CBD) – described as a specific or non-specific antagonist
Inverse Agonists for the CB1 Receptor
Rimonabant
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

24. THC/CB1 Drugs – Current Use
Current Medical Uses:
Agonists (cannabis, dronabinol, nabilone)
Anti-emetic (chemotherapy)
Appetite Stimulant (AIDs)
Analgesic (neuropathic pain, multiple sclerosis)
Inverse Agonist (rimonabant)
Weight loss , Smoking Reduction, Addiction
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

25. THC/CB1 Drugs – Possible Use
Possible Medical Use:
As AEDS
Animal studies have shown anti-seizure effects.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

26. THC - Anti-Seizure Effects - Animal Studies
THC has anti-seizure effects in most animal models – and also pro-convulsant effects in some models. These are produced via the CB1 receptor.
THC also has sedative/ataxic (psychotoxic) effects – also via the CB1.
THC’s psychotoxic effects limit its usefulness as an AED. CBD looks much more promising as an AED.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

27. CBD
Cannabidiol
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

28. CBD Structure Converted from CBDa by heating.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

29. CBD – Pharmacological Actions
Well Documented:
Anti-seizure effects
Suggested:
Analgesic (acute and chronic pain)
Antipsychotic
Anxiolytic
Anti-cancer
Anti-inflammatory
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

30. CBD Physiology
CBD does act via the endocannabinoid system as usually defined.
It does not activate CB1 or CB2 receptors - or mimic 2AG, anandamide or any known endocannabinoid.
It may interact with the endocannabinoid system indirectly, e.g. antagonizes CBD1 receptors and inhibits FAAH (?).
What receptors does it bind to?
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

31. CBD – Receptors?
A very confused field. It has been reported to act on:
5 HT 1A – partial agonist (anxiolytic? antidepressant?)
Adenosine receptors – agonist (anxiolytic?)
TRPV1 - weak agonist, desensitizes (analgesia?)
Mu and delta opiate receptors – allosteric modulator (analgesic?)
PPAR – agonist (anticancer?)
GPR55 – antagonist (effect?)
ETC, ETC
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

32. CBD Endogenous Ligand?
Effects of CBD are said to be “pleotropic”. It acts on many different receptors.
Unclear whether there is an endogenous ligand.
Except for the chemical messengers related to its various receptors (5 HT, opioids, etc.)
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

33. CBD – Drugs? Not much pharmacology.
CBD appears to be the only clear agonist in its class.
Although other cannabinoid extracts may have similar properties: e.g., cannabidivarin.
There don’t seem to be any antagonists.
But it does have anti-seizure effects in animals.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

34. CBD’s Anti-Seizure Effects – Animal Studies
NIH has recently tested CBD in the standard mouse seizure models.
It is active in the MES, MET and 6Hz ECS models.
It is active at doses that don’t cause sedation/ataxia.
Although sedation/ataxia does occur at higher doses.
We are in the process of testing it in the amygdala kindling model.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

35. CBD as an Anti-epileptic – Animal Studies
ED50’s from the NIH Study – Broad Spectrum
MES – 83.5 mg/kg
6 Hz ECS – 164 mg/kg
s.c. MET – 159 mg/kg
TD50 from the NIH Study (Rotarod) – Non-toxic
> 400 mg/kg
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

36. CBD as an Anti-epileptic – Animal Studies
The receptor(s) that mediates CBD’s anti-seizure effects is currently unknown.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

37. Acknowledgements I would like to acknowledge the help of:
Dr. Ruth Ross
Department of Pharmacology, University of Toronto.
Thanks to Dr. Ross in particular for providing her slides.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

38. Endocannabinoid Synthesis
Anandamide (arachidonoyletholamine; AEA)
Synthesis
Arachidonic acid (from phospholipids) + phosphatidyletholamine > N anachidonyl phosphatyletholomine (NAPE)>anandamide
Enzymes: (first step) N acetyltransferase; (last step): PLA2, PLC, NAPE-PLD
Degradation (very rapid – levels kept low)
Anandamide > arachidonic acid + ethanolamine
Enzyme: FAAH (fatty acid amide hydrolase)
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

39. Endocannabinoid Synthesis
2 AG (2 arachidonoylglycerol)
Synthesis (one pathway)(calcium dependent)
Phospholipids > diacylglycerol > 2 AG
Enzyme: (first step) PLC; (last step) DAG lipase
Degradation (levels not kept low)
2 AG > arachidonic acid and glycerol
Enzymes: MAGL (monoacylglycerol lipase), FAAH (fatty acid amide hydrolase) and others
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

40. Anandamide Synthesis and Degradation
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

41. Actions at the Nerve Terminal
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

42. Other Cannabinoids Canabinol – weakly anti-seizure but ataxia
Cannabidivarin - anticonvulsant
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

43. THC – Suggested Sites of Action
THC partially activates the CB1 Receptors all over the brain.
It would increase excitation/inhibition in many areas.
Some Possible Sites of Action
Hippocampus – memory impairment
Nucleus Accumbens – reward (increased DA release)
Hypothalamus – stimulation of appetite
Pain System - analgesia
EpLink | The Epilepsy Research Program of the Ontario Brain Institute

44. THC – Mechanism of Action – Immune Suppression
THC also activates CB2 receptors.
CB2 receptors also provide negative feedback in the immunological system.
They inhibit the release of cytokines.
This is the basis of THC’s anti-inflammatory/ immune suppressive effects.
EpLink | The Epilepsy Research Program of the Ontario Brain Institute