CB2 cannabinoid receptor compounds boosted the effectiveness of common antidepressants in mice | Research

The takeaway

In mice, both activation and blockade of CB2 receptors enhanced antidepressant effects of imipramine, escitalopram, and reboxetine without affecting brain drug levels, pointing to a pharmacodynamic interaction.

Psychopharmacologists, endocannabinoid researchers, and drug development scientists targeting CB2 receptors.

CB2 agonist AND antagonist both enhanced 3 classes of antidepressants

What the researchers found

Sub-effective doses of JWH133 (CB2 agonist, 0.25 mg/kg) and AM630 (CB2 inverse agonist, 0.25 mg/kg) each significantly enhanced the antidepressant effects of imipramine (15 mg/kg), escitalopram (2 mg/kg), and reboxetine (2.5 mg/kg) in both forced swim and tail suspension tests. Brain levels of antidepressants were unchanged, and locomotor activity was unaffected.

Why it matters

These findings suggest CB2 receptors modulate mood independently of CB1, the more studied cannabinoid receptor. The enhancement of three different antidepressant classes (tricyclic, SSRI, NRI) suggests a broad-spectrum augmentation effect.

The numbers in context

JWH133 0.25 mg/kg + each antidepressant: significant immobility reduction in FST and TST; AM630 0.25 mg/kg + each: same effect; no brain level changes; no locomotor effects.

How the study worked

Mouse forced swim test (FST) and tail suspension test (TST) assessing combinations of CB2 receptor ligands with conventional monoaminergic antidepressants (imipramine, escitalopram, reboxetine). HPLC measured brain drug concentrations; locomotor activity monitored to rule out non-specific motor effects.

What this study cannot tell us

Animal model only; mouse behavioral tests have debated translational validity; acute dosing (no chronic studies); both agonist and antagonist showing same effect is mechanistically puzzling; only tested at single sub-effective doses.

How to read the evidence

Preliminary: animal behavioral study; mechanistically intriguing but far from clinical application.

When this study was published

Published 2020.

The bigger picture

CB2 receptors were long thought to be peripheral (immune system). Their role in antidepressant augmentation adds to growing evidence that CB2 plays a central role in mood regulation, opening new targets for antidepressant drug development.

Questions still open

How can both CB2 activation and blockade enhance antidepressant effects? Are CB2 receptors a viable drug target for depression in humans?

Common questions

What is the CB2 receptor?

One of two main cannabinoid receptors. CB2 was originally thought to function mainly in the immune system, but growing evidence shows it also plays a role in the brain, particularly in mood regulation.

Could CB2 drugs become antidepressant boosters?

Possibly. This study found CB2 compounds enhanced three different classes of antidepressants in mice. However, the finding that both activating and blocking CB2 had the same effect is puzzling and needs mechanistic clarification before clinical development.

Read the original research

Ligands of the CB2 cannabinoid receptors augment activity of the conventional antidepressant drugs in the behavioural tests in mice.

Behavioural brain research, 378, 112297

View on PubMed ↗Publisher’s paper ↗

Citation

Poleszak, Ewa; Wośko, Sylwia; Sławińska, Karolina; Wyska, Elżbieta; Szopa, Aleksandra; Sobczyński, Jan; Wróbel, Andrzej; Doboszewska, Urszula; Wlaź, Piotr; Wlaź, Aleksandra; Szponar, Jarosław; Skałecki, Piotr; Serefko, Anna. (2020). Ligands of the CB2 cannabinoid receptors augment activity of the conventional antidepressant drugs in the behavioural tests in mice.. Behavioural brain research, 378, 112297. https://doi.org/10.1016/j.bbr.2019.112297