Meet the Experts

Interview:

Q: What does the preclinical respiratory research area currently look like for cannabis?

A: There are several preclinical cannabis groups in the USA and Canada  (e.g. Virginia Commonwealth University in Richmond, Wilfrid Laurier University in Waterloo, ON, and the University of Florida in Gainesville). Presently, preclinical cannabis research is mainly focused on neurophysiology, behavioral effects, and aerosol characterization. Many studies focus on the acute effects of cannabis smoke, and future studies are required to deepen our understanding of the chronic effects of cannabis inhalation.

Q: What are the next steps for research in this area?

A: Surprisingly, one area that needs further exploration includes the respiratory and cardio effects in preclinical cannabis exposure models, along with the overall long-term effects of cannabis use.

More research is absolutely needed for developing mouse models of inhaled cannabis exposure to better understand the underlying mechanisms of the endocannabinoid system.

Q: Given that further research is necessary to understand the relationship between cannabis and respiratory illnesses, what regulatory issues do you think are limiting this type of research in the United States?

A: The licensing process is extremely difficult, getting plant materials requires as much work as a mini-grant proposal. Once licensed, the cannabis must be kept under high security and requires multiple people to maintain and control the inventory.

Currently Novartis is the primary group supplying cannabis in the US.

Q: Tobacco research is highly standardized, what do you think are the next steps to similarly standardize cannabis research?

A: We standardized our protocol by using the inExpose to generate a reproducible puff shape and size. We decided to deliver three 3-second puffs of cannabis smoke from the tabletop Volcano® vaporizer, followed by 20 s of fresh air.  The vaporized was packed with an equal density of leaf each time. The three 3-second puffs were chosen to balance desired delivered aerosol concentration while providing the mice with breaks of fresh air.

Another important factor for standardization includes correlating the input weighed mass with the aerosolized mass.

Correlation of the input mass to the THC in the blood is also essential. The THC concentration is measured immediately after exposure by cardiac puncture of the right ventricle, as the THC half-life in mice is extremely short, much shorter than cotinine, which is the biomarker from cigarette smoke. Cardiac puncture is preferred over the trunk blood method, as it is more easily reproducible in mice.

Establishing a target delivery dose concentration range is another key factor for standardization. This is very difficult to achieve, even with the cotinine target for cigarettes. In clinical studies with humans, a 750mg dose is required to yield a “high”. We set our pre-clinical target for mice at 300-450mg.

It is also crucial to report the supplier and the concentration of cannabis, including the THC content and strain.

Q: There are a wide variety of methods that cannabis can be smoked, which can change the characteristics of the smoke inhaled. What factors do you look for when conducting your research?

A: Some factors we look to include

• Particle characterization (particulate matter concentration, size of particles, etc.)
• Packing density of cannabis inside the vaporizer/joint.
• Moisture or humidity of the plant and the room (measured, but not controlled)

Q: How does intraperitoneal injection compare to inhalation?

A: How cannabis is delivered will heavily change the dosing and effects.

• Intraperitoneal injection is less translatable, and less relevant.
• Systemic injection of THC or CBD is not a route of administration in humans.
• Intraperitoneal injection may be better for studying CB receptor mechanisms and downstream pathways.
• Inhalation exposure is the most translational method.
  
  

Q: The most common route of administration in humans is smoking, however, things such as vaping cannabis extracts and synthetic cannabinoids with e-cigarettes is becoming more popular. What is the importance of using the most common route of administration in humans on mice?

A: This area of research is becoming increasingly important. According to the literature, smoking joints is still the most common route of cannabis inhalation, however most of these statistics and literature were published prior to this year’s spike in THC pods. Following the spike, NHLBI encouraged people who are studying tobacco to shift their focus to vaping.

Additionally, there is a misconception among the public that if something is food safe, like the propylene glycol and vegetable glycerin in vape e-liquids, it’s safe to inhale. However, it’s evident that this isn’t the case.

Q: How is cannabis use quantified in respiratory research?

A: Cannabis use in a clinical setting is quantified by joints per day, however the size and constituents of the joint are not taken into consideration at all. Variabilities in joint constituents includes black market or regulated cannabis, smoked with or without a filter, or the addition of tobacco. It’s very difficult to take these variabilities into consideration in a preclinical or clinical context.

Q: When developing a model to research the effects of cannabinoids on respiratory physiology, what do you think are the benefits of whole-body exposure versus a nose-only exposure?

A: The nose-only method allows for control of the exposure route, as it limits the ingestion opportunities that are present with whole body exposure. This results in a more translatable model, including better dosimetry calculations.

Q: Once there is an accurate and reproducible model, the next step would be to investigate the in-vivo effects of cannabinoids on respiratory physiology and lung mechanics. What are some key points of interest?

A: For our chronic cannabis studies, we plan on using the flexiVent to obtain lung function measurements including detailed and overall respiratory mechanics and lung volumes.

Thank you, Dr. Jessica Oakes and Dr. Chiara Bellini, for this interview!

Dr. Jessica Oakes is an Assistant Professor in the Department of Bioengineering at Northeastern University. Her research area is quite diverse and includes pulmonary physiology, e-cigarettes, marijuana, computational biomechanics, MRI, and multi-scale airflow and aerosol modeling.

Dr. Chiara Bellini is also an Assistant Professor in the Department of Bioengineering at Northeastern University. Her primary research focus is on diseases of the cardiovascular system, effects of cell mediated growth and remodeling process on tissue and organ mechanics, and impact of inhaled aerosols (e.g. e-cigarettes, marijuana, fore smoke) on the vascular system.

Check out their recently published paper on the effects of nose-only exposure to vaporized cannabis in mice here:

Farra, Y. M., Eden, M. J., Coleman, J. R., Kulkarni, P., Ferris, C. F., Oakes, J. M., & Bellini, C. (2020). Acute neuroradiological, behavioral, and physiological effects of nose-only exposure to vaporized cannabis in C57BL/6 mice. Inhalation Toxicology, 1-18.

To learn more on the state of cannabis research, check out our blog post

If you have any questions about the flexiVent or inExpose for cannabis research, please contact us!