Cannabis : From Cultivar to Chemovar II—A Metabolomics. Approach to Cannabis Classification
Arno Hazekamp, Katerina Tejkalova, and Stelios Papadimitriou
Cannabis and Cannabinoid Research, 2016, Volume 1, (1)
Doi : 10.1089/can.2016.0017
Introduction : There is a large disparity between the ‘‘cultural’’ language used by patients using cannabis for selfmedication and the ‘‘chemical’’ language applied by scientists to get a deeper understanding of cannabis effects in laboratory and clinical studies. The distinction between Sativa and Indica types of cannabis, and the different biological effects associated with them, is a major example of this. Despite the widespread use of cannabis by selfmedicating patients, scientific studies are yet to identify the biochemical markers that can sufficiently explain differences between cannabis varieties.
Methods : A metabolomics approach, combining detailed chemical composition data with cultural information available for a wide range of cannabis samples, can help to bridge the existing gap between scientists and patients. Such an approach could be helpful for decision-making, for example, when identifying which varieties of cannabis should be made legally available under national medicinal cannabis programs. In our study, we analyzed 460 cannabis accessions obtained from multiple sources in The Netherlands, including hemp- and drug-type cannabis.
Results : Based on gas chromatography analysis of 44 major terpenes and cannabinoids present in these samples, followed by Multivariate Data Analysis of the resulting chromatographic data, we were able to identify the cannabis constituents that may act as markers for distinction between Indica and Sativa. This information was subsequently used to map the current chemical diversity of cannabis products available within the Dutch medicinal cannabis program, and to introduce a new variety missing from the existing product range.
Conclusion : This study represents the analysis of the widest range of cannabis constituents published to date. Our results indicate the usefulness of a metabolomics approach for chemotaxonomic mapping of cannabis varieties for medical use.
Keywords : cannabinoids; cannabis; gas chromatography; multivariate data analysis; terpenes; varieties
Research into herbal cannabis poses serious challenges to modern medicine, which operates mainly according to the ‘‘single compound–single target’’ paradigm of pharmacology. Although it was once believed that THC (see Table 1 for abbreviations) was the unique active principle found in cannabis, it is becoming clear that a much wider range of cannabis constituents may be involved in its various therapeutic effects. Currently, many different subtypes of cannabis are known to exist, and the high number of (potential) active components significantly complicates a conventional reductionist approach using analytical chemistry, animal studies, and clinical trials, where typically a single active ingredient is identified before development of a final medicine is possible. With the recent growth in medicinal use of cannabis, the need to clearly distinguish between various cannabis plants and their expected (therapeutic) effects has become more important than ever.
Medicinal cannabis may have therapeutic effects on various illnesses ranging from chronic pain and multiple sclerosis (MS), to epilepsy and anxiety.1,2 An obvious question is how the chemical composition of cannabis reflects these various medicinal effects, and what types of cannabis should consequently be made available to provide patients with a full spectrum of therapeutic benefits. Already more than 700 different cultivated varieties (cultivars) of cannabis have been cataloged3 and many more are thought to exist, each one with a potentially different effect on body and mind. Although pharmacopoeia
monographs for the chemical analysis of cannabis have been developed in several countries,4–6 these are intended for potency, quality, and adulteration issues only. They are not designed to map out the complex chemical variations found among different cannabis products. A better classification of cannabis varieties, and the chemical differences between them, would certainly promote further
implementation of cannabis-based products into (pre)clinical research and modern medicine.
Science-based classification systems
The scientific debate about classification of the cannabis species has been going on for centuries. According to current scientific consensus, Cannabis is monotypic and consists only of a single species Cannabis sativa L., as originally described by Leonard Fuchs in the 16th century. 3 Within this species, two important subdivisions are commonly made. One of them recognizes drugtype versus fiber-type cannabis based on the intended use of the plant, and ismostly relevant for legal purposes. The other subdivision is based on botanical principles and identifies Sativa versus Indica types of cannabis, both regarded as a subspecies of Cannabis sativa L.7
According to the botanical description of cannabis, Sativa types of cannabis were originally grown in the Western world on an industrial scale for fiber, oil, and animal feedstuff. They are characterized by tall growth with few, widely spaced, branches and long, thin leaves. In contrast, plants of the Indica type originated in South Asia and were known historically as Indian hemp. They are characterized by shorter bushy plants and broader leaves, typically maturing relatively fast. The two groups tend to have a different smell, whichmay reflect a different profile of fragrant terpenes. Most cannabis plants that are currently commercially available are in fact a hybrid (cross-breed) of Sativa and Indica ancestors. Cannabis-type ruderalis is sometimes also recognized as a separate subspecies. It is a smaller and ‘‘weedy’’ plant originally from Central Russia.7
Various scientific attempts have been made to classify cannabis plants based on their cannabinoid composition, as outlined in more detail in our previous article.8 For forensic and legal purposes, the most important classification is that of the drug type (marijuana) versus the fiber type (hemp), with an emphasis on the total THC content in the flowers of the plant. Until recently, cannabis products used for medicinal purposes in official programs all belonged to the drug type, because of their high content of the biologically active THC. However, it is becoming increasingly clear that multiple constituents may be involved in the overall effect of the drug.9 This includes the cannabinoids CBD,10,11 CBG,12,13 and THCV,14,15 as well as a variety of terpenes.16
Terpenes are volatile compounds responsible for the typical smell and taste of cannabis. More than 120 different types have been identified in cannabis and their relative composition can vary widely between varieties. 17,18 Terpenes present in cannabis have a wide range of known biological effects, and some may be involved in regulating and/or modifying the effects of THC and other cannabinoids.16 Expanding our scientific understanding of the therapeutic benefits of terpenes is a budding new frontier of medical cannabis research. Nevertheless, no currently used cannabis classification system takes the terpenes into account. Since the publication of the draft genome of cannabis, 19 various studies have looked into the genetic analysis of cannabis as a means of identifying distinct (sub)groups.20,21 Such studies have been able to clearly differentiate hemp from marijuana-type cannabis,21 but they find only a moderate correlation between the ancestry of cannabis strains, as reported by breeders, and the ancestry inferred from their DNA. As a result, the genetic identity of cannabis products could not be reliably inferred by its vernacular name or by its reported ancestry as supplied by cannabis growers.