Metabolic Engineering: Cannabinoids
Historically, the dialogue surrounding the production and sale of cannabis has been heated and divisive. Supporters of legalization often tout its perceived health benefits while opponents claim that it hurts people and society. Regardless, states move forward by continuing to lift restrictions on the sale of cannabis and the federal government begins to discuss regulating and taxing it. In 2020 alone, legal sales of cannabis increased by 46%, highlighting the increasing demand for this emerging industry.
The breadth of scientific literature studying the physiological and psychological health effects of cannabis is largely focused on compounds called cannabinoids. These compounds bind to cannabinoid receptors (referred to as CB1 and CB2) in the brain and throughout the body. The most common cannabinoids are Cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC). Although the FDA has only approved one cannabis-derived drug product, Epidiolex (CBD), for the treatment of seizures associated with tuberous sclerosis complex, there are a variety of other therapeutic applications of cannabinoids in clinical trials such as: acting as antiemetics for adults with chemotherapy-induced nausea and vomiting, reducing pain for adults with chronic pain, and improving spasticity symptoms in adults with multiple sclerosis.
The mechanisms by which cannabinoids interact with the body is still being studied, highlighting the necessity for efficient means of production. However, we can get a better understanding of these processes by taking a look at the central nervous system. As mentioned before, humans have cannabinoid receptors, CB1 and CB2. CB1 receptors are primarily localized in neurons and CB2 receptors are expressed in the immune system. These receptors are present in humans because we naturally produce cannabinoids within our own bodies, known as endocannabinoids (whereas “phytocannabinoids” are found in the cannabis plant). The activation of CB1 receptors, for example, results in the inhibition of synaptic transmission which alters the signaling pathways within the brain. Endo-cannabinoid signaling pathways have been shown to be involved in the pathophysiology of epilepsy, and drugs such as Epidiolex can target these pathways for therapeutic purposes
Despite the potential for therapeutic uses of cannabinoids, traditional means of farming cannabis has significant environmental impacts. Commercially produced cannabis has been shown to contribute to forest fragmentation, soil erosion, and landslides. Additionally, cannabis emits volatile organic compounds (VOCs) called terpenes that are extremely reactive in the atmosphere and produce ozone-degrading aerosols. Lastly, cannabis cultivation has a huge electricity demand, prompting more state regulations on this emerging industry. An alternative and perhaps more environmentally friendly means of producing CBD and THC is through metabolic engineering.
Picture an organic chemist synthesizing compounds for pharmaceutical use in a laboratory setting. A variety of reagents, glassware, expensive analytical instruments, and years of expertise are required. At the industrial level, this process can be sped up in manufacturing facilities to produce compounds in large-scale quantities.
Now picture this process automated at the cellular level. The cells that make up single-cell organisms, plants, and animals (yes, even you) are constantly producing new compounds through a variety of reactions, almost acting as miniature factories. If we follow the familiar reaction of yeast fermentation, used to produce your favorite beer at a local brewery, we can see how cellular metabolism can be a useful tool for the production of chemical compounds. In large vats, breweries typically mix sugary media that allows yeast to undergo fermentation, the process by which yeast extract energy from carbohydrates. The particular strain of yeast used in breweries produces ethanol (alcohol) and carbon dioxide (bubbles) during fermentation.
The process of fermentation, used in making alcohol and cannabinoids
Metabolic engineering can take advantage of processes such as yeast fermentation by modifying the metabolism processes of yeast to produce cannabinoids (instead of, or in addition to alcohol) during fermentation. In a recent groundbreaking study (2019) done by researchers at Berkeley, the metabolic pathway of yeast to produce cannabinoid precursors was laid out, presenting a clearer platform for the cannabinoid production.
The chemical process of cannabinoid metabolic engineering
There are over 100 cannabinoids that are found in cannabis, but scientists usually only study CBD and THC. These cannabinoids are abundant in cannabis, which makes them easy to study. However, the other 100 are not as robustly studied because they are more difficult to isolate and require more plant biomass to extract them. These rare cannabinoids have potential applications that we are currently unable to probe. With metabolic engineering, it is possible to engineer cells to produce these rare cannabinoids efficiently and scale-up using different fermentation processes.
A handful of companies have already started to implement metabolic engineering to produce cannabinoids. Demetrix and Hyacynth are two new companies that have begun engineering yeast strains to produce cannabinoids using the fermentation process discussed earlier. These companies modify the metabolic pathway of yeast to convert sugar into compounds that can then be converted using enzymes to make THC and CBD.
In addition to using yeast as production platforms for cannabinoids, other microbes have also been suggested. Farmako, a German biotech company, uses bacteria instead of yeast to produce rare cannabinoids. Bacteria are useful because the cannabinoids are naturally separated from the bacteria whereas in a yeast-system, the cannabinoids have to be separated from the yeast in a second step. In 900 hours, Farmako has reported that 4.5 kg of THC are produced per 1 g of bacterial mass. Renew Biopharma, a company that develops therapeutics for neuroinflammatory diseases, has started using microalgae as a production host for cannabinoids.
The field of metabolic engineering continues to grow, and numerous companies have taken interest in using this technology as a tool to efficiently produce compounds such as cannabinoids. Using the fermentation processes discussed here, producing cannabinoids can be more sustainable and affordable than traditional cannabis cultivation. In the future, you might even imagine recreational CBD and THC breweries as social hubs. Greater yields of cannabinoids, without the need for large volumes of plant biomass, will allow scientists to take a deeper dive into their biological mechanisms and better understand what is appearing to be a useful tool.
Written by Katie Kloska, Associate & PhD Candidate
