How microplate readers can support cannabinoid research

Medicinal cannabis

This paid-for advertorial by BMG Labtech appeared in DDW Volume 25 – Issue 2, Spring 2024.

Cannabinoid research has gained significant attention in recent years, as scientists have been exploring the potential therapeutic benefits of these compounds. From studying their role in treating neurological disorders to pain management, this field of study holds promise for medical advancements.

In addition to the ongoing decriminalisation of cannabis worldwide, interest in its medical use is growing steadily and with it the need for studies and background knowledge on the mode of action, safety of various cannabinoid substances or the development of new drugs with reduced side effects. Not only to save costs and time, but also to be able to meet the constantly growing demand for scientific analyses, the use of high-throughput methods is becoming more essential. Microplate readers can be a great support for a variety of analyses associated with cannabinoid research. In this article, we want to give a brief overview of the methods in which microplate readers can provide added value.

Cannabinoids are a diverse group of naturally occurring or synthetic chemical compounds. While endocannabinoids are produced in the human body and are responsible for the regulation and control of functions like learning and memory, phytocannabinoids are plant-derived but can partly bind to the same receptors. Further synthetic cannabinoid receptor agonists (SCRAs) have been made in the laboratory, mainly to study characteristics and signalling pathways of the naturally occurring compounds.

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Figure 1: TR-FRET assay to study binding affinity of phytocannabinoids to CB1 receptor. A) Assay principle of TR-FRET assay with terbium-labelled receptor and fluorescently labelled CB1 agonist competing with unlabelled agonists. B) TR-FRET ratio generated upon binding of fluorescently labelled agonist CELT-335. Different phytocannabinoids show different binding affinity to CB1 and decrease CELT-335 associated signal differentially.

Microplate readers have traditionally been used to detect phytocannabinoids or their metabolites in medical samples or in forensics. For this purpose, immunoassays such as ELISAs are typically used. ELISAs specifically bind the looked-for metabolites and consequently lead to a colour change or even a fluorescent or luminescent signal. Next to the quantification of phytocannabinoids in a sample, chemotyping of the plants can also be relevant in some scenarios. The chemotype refers to a subspecies of a plant with a different chemical composition. It may help to identify best botanical extracts for use or help to identify cannabis batches, that have been brought across geographic regions illegally1,2. 

Cannabinoids are potential tools to combat a variety of diseases including different neurological or metabolic conditions. The interest in potential drug discoveries is driving efforts to understand the pharmacology of naturally occurring and synthetic cannabinoids at the receptor level. Microplate-based methods using fluorescence polarisation, BRET or TR-FRET enable the sensitive and reliable detection of receptor binding as well as the identification of the activated downstream cascades. 

In the following approach, a TR-FRET-based method was used to study the differential binding of natural cannabinoids to the cannabinoid receptor 1 (CB1). Therefore, the fluorescent molecule CELT-335 was used, which acts as a ligand for CB1. To detect the interaction, CB1 was additionally labelled with terbium. When the fluorescent agonist binds to the receptor, energy is transferred from terbium to CELT-335 and light is emitted at 665 nm in addition to 620 nm (figure 1A). In a competitive setting with 100 nM CELT-335 the binding affinity of the phytocannabinoids ∆9-THC, ∆9-THCA and ∆9-THCV was monitored in the concentration range from 0-10 µM. The TR-FRET ratio was detected with BMG LABTECH’s PHERAstar® FSX and obtained data were normalsed to the TR-FRET ratio at the highest value (set to 100 %, figure 1B).

As shown in figure 1B, the competition was similar for ∆9-THC and ∆9-THCV with obtained pKi values of 7.2 ± 0.6 and 7.0 ± 0.3, respectively. Whereas the affinity for ∆9-THCA was considerably lower with a pKi of 5.8 ± 0.6. The Simultaneous Dual Emission (SDE) feature, available on the PHERAstar FSX, allows to measure both emission signals (from donor and acceptor) simultaneously. Next to its high sensitivity and reliability, which allows to detect even the smallest changes in receptor-ligand interactions, the SDE feature results in additional time savings and more robust data.

SCRAs have originally been developed as therapeutic agents or for legitimate scientific research. Unfortunately, they have emerged as drugs of abuse in recent years and are sadly associated with serious health risks including death3.  So far little is known about the detailed toxicology and pharmacology of SCRAs including their molecular mechanisms of action4. However, exactly this knowledge is urgently needed to pave the way for their use as therapeutic agents or to better assess and prevent the risks they pose.

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Figure 2: Monitoring cannabinoid signalling with a BRET assay. A) Assay principle of CAYMEL BRET biosensor detecting cAMP increase upon dissociation of Gαs subunit. B) cAMP generation upon stimulation with various cannabinoids in combination with forskolin.

Binding of a receptor agonist to CB1 (a GPCR) may lead to dissociation of the trimeric G-protein complex and the release of the subunits into the cytoplasm, initiating various signalling pathways and cellular responses. To study whether a selection of cannabinoids signal via the Gαi- or Gαs- subunit of the CB1 receptor, cAMP, a downstream second messenger of the Gαs -stimulated cascade, was analysed in the following study. cAMP levels were quantified with a BRET-based CAYMEL biosensor. The sensor is composed of an EPAC protein, a Renilla luciferase (Rluc) and a yellow fluorescent protein (YFP). Upon binding of cAMP by EPAC, Rluc and YFP are spatially separated due to a conformational change. This leads to a reduction of the BRET signal which is generated in absence of cAMP due to proximity of Rluc and YFP (fig. 2A). 

From the overall cAMP generation levels obtained by evaluating the area under the total signal curve, it can be concluded, that cannabinoid receptor agonists have significantly different efficacies in the activation of the Gαs pathway (fig. 2B). In this study, the PHERAstar once again impressed with high sensitivity and speed, which can be achieved with the SDE feature, making it ideal for high-throughput applications in all reading modes.

If you would like to know more about the application of microplate readers in cannabinoid research please contact us at applications@bmglabtech.com or visit us at www.bmglabtech.com.

References:

  1. DOI: 10.1093/jat/bkab107 
  2. DOI: 10.1007/s10681-015-1585-y
  3. DOI: 10.1056/NEJMp1505328 
  4. DOI: 10.3389/fpsyt.2020.00464 

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