THC and CBD Analysis Insufficient for Characterizing Cannabis Strains
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Archaeological finds and historical text analysis - from China and surrounding Northeast Asia - indicate that humans have been using and cultivating cannabis and hemp plants since Neolithic times, around 6000 years ago. Early hemp and cannabis plants were grown for their use in the textile industry and as a medicinal drug, though there is also evidence supporting that the recreational use of cannabis as an intoxicant was also common practice.
In modern times, laboratory-made pharmaceuticals and industrial cotton farming have taken over the industries where hemp and cannabis were most commonly used. Cannabis does continue to be cultivated as a medicinal and recreational drug in many countries, with growers selectively breeding the plants for consumer-favored levels of the intoxicating tetrahydrocannabinol (THC) and therapeutic cannabidiol (CBD). There are now over 2500 strains of cannabis listed in some databases, with the potential for many more undocumented strains.
The individuality of strains
When these strains are being sold in a retail marketplace, they are normally characterized by their unique street name, as well as the levels of CBD and THC present. Given the huge number of strains in existence, many cannabis scientists are now of the mind that differentiating strains based purely on these characteristics may be giving an inaccurate picture of how closely genetically related many strains are.
"People have had informal breeding programs for a long time," explains Professor Susan Murch, of the University of British Columbia Okanagan. "In a structured program we would keep track of the lineage, such as where the parent plants came from and their characteristics. With unstructured breeding, which is the current norm, particular plants were picked for some characteristic and then given a new name."
“We wanted to know how different they truly are, given the variety of unique and exotic names.”
Elizabeth Mudge, a doctoral student working with Professor Murch and Dr Paula Brown, of the British Columbia Institute of Technology, has set out to do just that. Using chemotaxonomy techniques, Mudge’s research looked at the cannabinoid profiles of 33 strains of cannabis from five licensed producers in an attempt to elucidate the true phytochemical diversity of cannabis.
After preparing the samples and passing them through a chromatographic separation process, targeted metabolomics was used to analyze 11 known cannabinoids, including CBD, THC, and their acidic derivatives CBDA and THCA; an untargeted metabolomics approach was then used to characterize a further 21 unknown cannabinoids.
Strains inhabit distinct groups
Going into the study, it was hypothesized that individual plant breeders were able to selectively influence cannabis strains by up-regulating or down-regulating certain enzymes within the biosynthetic pathways in the plant, causing a redirection of metabolites between THCA and CBDA pathways.
Following principal component analysis (PCA) and multiple linear regression (MLR) analysis, five clusters of chemotaxonomically indistinguishable strains were identified within the 33 commercial cannabis strains. These five clusters each fell within a narrow range of total CBD/THC values, which were characteristic to each cluster.
Three of the clusters contained strains that produced CBDA in significant quantities while the remaining two were shown to direct more metabolic resources towards the THCA production pathways, resulting in strains with inflated levels of THCA and THC.
Strains from all of the five clusters contained amounts of THC, THCA, cannabigerol (CBG), and its acidic form CBGA. Two of the clusters contained strains that have no detectable levels of CBD or CBDA. One cluster made up of only a single strain was found to have significant levels of CBD, CBG, and cannabichromene (CBC), but only low levels of THC and THCA.
In addition to these known cannabinoids, ten of the unknown cannabinoids were found in multiple strains across the cluster groups. Some of these were found to correlate with the expression of other known cannabinoids, specifically CBDA, CBD, and THC.
The effects of domestication
In the past, cannabis strains were described as either being of “sativa” or “indica” lineage, with sativa strains having originated from European hemp plants, and indica strains coming from more potent Indian cannabis plants. Nowadays, strains are often referred to as “dominant” in one lineage or the other, based on physical attributes; these labels aren’t considered a proper chemotaxonomical classification due to generations of cultivation and strain hybridization.
Instead of relying on sativa or indica ancestry to describe the predicted effects of a cannabis strain, it has become a habit to distinguish strains and associated properties by the levels of CBD and THC present. The five clusters and the corresponding variation in minor cannabinoid content observed in this study indicate that this CBD/THC description is also an insufficient way to classify cannabis strains.
Further research by cannabis scientists into the nuances of these five clusters, and how the variation of minor cannabinoids affects the human body, may be particularly helpful to medicinal cannabis users, who currently have very little scientific information on which to base their product choice and treatment programmes.