Zeroing in on the Entourage Effect

The cannabis plant produces hundreds of biologically active compounds, including over 100 unique cannabinoids and more than 100 terpenes. With so many active components, it’s not surprising that there are several theories which serve to explain how these compounds might interact with each other.

Looking at these interactions, a new study from researchers at Macquarie University has concluded that the cannabis terpenes don’t significantly influence the functional effects of the cannabinoids on either the body’s human transient receptor potential ankyrin 1 (hTRPA1) channel, or the human transient receptor potential vanilloid 1 (hTRPV1) channel.

This finding casts further doubt on proposed theories for a terpene-cannabinoid entourage effect.

The entourage effect, in theory

The entourage effect is a title given to the idea that these cannabinoids and terpenes may interact to produce a much greater pharmacological effect than either compound might be able to produce individually.

While there is research detailing clear differences in effect seen when using full-spectrum extracts versus pure single cannabinoid extracts, relatively little is known about the exact mechanisms through which this effect might work.

Direct interaction between the cannabinoids present in the cannabis plant is one possible explanation of the entourage effect, and numerous studies have now examined interactions between tetrahydrocannabinol (THC) and cannabidiol (CBD). As it turns out, the interaction between these two compounds is incredibly complex; CBD is able to both inhibit and enhance some effects associated with THC consumption at varying dosages.

It has also been hypothesized that this entourage effect could be a result of major cannabinoids interacting with the terpenes produced by the cannabis plant, either through direct interaction with those cannabinoids or through influencing the actions of the cannabinoids at their receptor targets.

Terpenes aren’t unique to cannabis; these aromatic ‘essential oils’ are produced by many different varieties of plant and generally affect their flavor and aroma. These terpenes themselves have been linked to numerous therapeutic benefits individually. As they’re present in different amounts in different cannabis strains, they’re also thought to be responsible for some of the variation in the effects of consuming individual cannabis strains, whether through their individual effects or through some form of terpene-cannabinoid entourage effect synergy.

Ruling out potential mechanisms

In the new study out of Macquarie University, the researchers sought to advance the evidence base on these potential terpene-cannabinoid interactions.

A previous study from the same team of researchers found no evidence of significant terpene-cannabinoid interactions modulating the effects of the cannabinoids at the human CB1 or CB2 receptors, the two major cannabinoid receptors in the body’s endocannabinoid system. In this new study, the researchers focused on the body’s hTRPA1 and hTRPV1 channels, which respectively play an important role in the body’s response to pain and epilepsy. The TRPA1 channel is already known to be activated by THC, say the researchers, while CBD and some minor phytocannabinoids can activate the TRPV1 channel.

To further examine the potential synergistic effects of terpenes and the cannabinoids, the researchers selected seven of the most prominent cannabis terpenes – ⍺-pinene, 𝛽-pinene, 𝛽-caryophyllene, linalool, limonene, 𝛽-myrcene, and ⍺-humulene – and tested their activity on both channels, in addition to observing whether the compounds affected the activity of select cannabinoids and endocannabinoids on these channels. This activity was assessed using inducible HEK293 cell cultures transfected with hTRPA1 or hTRPV1 channels and observing real-time changes in intercellular calcium.

The researchers found no significant changes in intercellular calcium for either the hTRPA1 or the hTRPV1 expressing cell cultures. There was no evidence showing the terpenes affected the activation of either receptor caused by the presence of the phytocannabinoid THC, or the endocannabinoids anandamide (AEA) or 2-arachidonoylglycerol (2-AG).

What does this mean for the entourage effect?

The researchers do note several limits to their study. Firstly, their analysis was limited to assessing the effects of the terpenes and cannabinoids on an HEK cell tetracycline-regulated expression. It could be that other models, like a study using brain slices as the researchers suggest for further work, could produce different results. They also note the limited number of terpenes looked at in this study as a further restriction.

“The paper provides evidence that if there is entourage, it does not happen by the terpenes we tested interacting with THC/2-AG/AEA at TRPA1 or TRPV1… but there are other [terpenes] and ECS-related targets,” tweeted study author Mark Connor.

“Our studies (so far) are not providing evidence for a molecular basis of entourage, doesn't mean it doesn't happen. There are other possible explanations beyond direct terpene/cannabinoid interactions at receptor/channel… would love more clinical data to back the idea though,” he added, in an additional tweet.

In the paper, the authors list suggest the TRPV2, TRPV3, GPR18, GPR55, glycine, and PPARc receptors as further systems for examination in similar studies.

In light of the growing profile of medicinal cannabis and pharmaceutical grade cannabis-derived medicines, it’s important that research into the entourage effect continues to explore potential mechanisms for its action. Even if no solid evidence is found to support the entourage effect, advancing this research will with bring with it a greater general understanding of the complexities of human biochemistry and cannabis phytochemistry.