Molecular Mechanisms of Cannabidiol

Hemp is a complex natural product with hundreds of constituents including over 100 different phytocannabinoids, most of which still await pharmacological interrogation. The most abundant and well-researched non-psychotropic phytocannabinoid is known as cannabidiol, or CBD. Regarding its pharmacodynamics and molecular targets, many questions persist.

Unlike THC, CBD fails to activate CB receptors directly. This is partly due to the differential recognition of bent vs. planar conformation of CBD and THC, respectively, at the receptor ligand binding sites. However, CBD may potentiate anandamide-mediated activation of CB receptors by attenuating anandamide hydrolysis. This is achieved by weak inhibition of fatty acid amide hydrolase (FAAH), the enzyme that degrades anandamide.

Interaction of CBD with classical endocannabinoid signaling — CBD inhibits FAAH, which hydrolyzes the endocannabinoid anandamide. As a result, more anandamide is available to support canonical endocannabinoid signaling. This signaling, in this example, starts with excitatory neurotransmitter discharge (1), which activates anandamide biosynthesis from membrane lipids (2). Retrograde transport culminates in CB1 receptor activation and homeostatic attenuation of further excitatory neurotransmission. Since the affinity of CBD for FAAH is weak, this mode of action is unlikely to account for the clinical effects of CBD.

So, how does CBD work?

Until further research explores how CBD works in humans receiving the low doses (<30 mg) widely available as supplements, we don’t really know how it works. With confidence, I can say there is very little, if any, involvement of direct interaction with canonical CB receptors. Instead, evolving research underscores disparate effectors such as serotonin receptors, ion channels and reuptake systems.

The following mechanisms are well-supported by in vitro and animal data [1-13]:

Activation of serotonin 5HT_1A receptors plays a part in the anxiolytic effects of CBD in the limbic system, a brain region involved in emotional processing, mood and behavior.
Inhibition of transient receptor potential cation channel subfamily V member 1 (TRPV1) ion channels. In the peripheral nervous system, CBD modulates neurosensory responses by activating and subsequently desensitizing them.
Adenosine receptor activation and reuptake inhibition. Adenosine is an inhibitory neurotransmitter and immune modulator.
Activation of peroxisome proliferator activated receptor gamma (PPARγ), which is involved in metabolic regulation and immune function.
Blockade of GPR55, a novel interaction implicated in osteoclast function.

Primary molecular effectors of CBD comprising the focus of current preclinical research. Arrows indicate activation; diamond arrows reflect inhibition. IC₅₀ and EC₅₀values reflect inhibitory or effective concentrations required to achieve 50% inhibition or activation in the experimental model, respectively. Low values reflect higher affinity, a prerequisite for physiological significance.

References

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