By Dr Michael Flower February 24, 2017 Edited by Dr Ed Wild
Weeding out the truth: can cannabis improve Huntington’s?
What can individual experiences with cannabis tell us about Huntington's disease?
Whether in synthetic or natural form, there is no proper scientific evidence that cannabis helps Huntington’s disease patients
By Dr Michael Flower February 24, 2017 Edited by Dr Ed Wild
Cannabis, or medical marijuana, has been touted as a treatment for lots of conditions, and Huntington’s disease is no exception. Whenever it hits the news there’s a lot of interest, and recently cannabis found the spotlight again with videos claiming it can reverse the nerve cell damage in Huntington’s disease. These are extraordinary assertions that deserve to be explored.
What is cannabis?
It’s a plant, originally from Asia and India, that’s been known for thousands of years to have effects on the human brain. Many cultures have used it medically and recreationally. It’s psychoactive, which means that when taken – for example, by smoking its leaves – it alters the way our mind perceives things, characteristically inducing relaxation and euphoria, but it can also cause anxiety and paranoia.
It wasn’t until the 1940s that we discovered the active ingredients, which are oily chemicals called cannabinoids. Other plants make cannabinoids too, including some herbal teas, truffles and even cocoa.
How it works
In the late 1980s, we discovered that humans have tiny sensors, called receptors, for these cannabinoids on the surface of our cells. There are two main types of
receptor – CB1 and CB2. Most
CB1 receptors are in the brain and spinal cord. It’s these ones that are thought to produce the psychoactive effects. The receptors affect how active our nerve cells are, for example controlling the amount of pain a person feels. In contrast,
CB2 receptors are found on immune cells that circulate in our blood, and activating them can have an anti-inflammatory effect. Normally there are very few CB2 receptors in the brain, and those that are there, are found on immune cells.
Having found sensors for cannabinoids in the human body, the logical conclusion was that we might also naturally make cannabinoids. And indeed, the first of these was found in the early 1990s, followed shortly after by several more. Nerve cells use them as a way of regulating their own activity level. Normally one nerve cell passes information to another by sending a neurotransmitterchemical. Cannabinoids are a way for the second nerve cell to pass a message back to first, telling it to calm down.
‘Cannabinoid’ is the name we call any chemical that activates cannabinoid receptors. The ones that plants make are called phytocannabinoids. Phyto- comes from the Greek for plant. The ones our own bodies make are called endocannabinoids, derived from the Greek for ‘within’. It’s also possible to manufacture chemicals that activate these receptors, and we call these synthetic cannabinoids.
Different cannabinoids have stronger or weaker effects at each
receptor, so they can have varied effects on our bodies. Once in the body, they are eventually broken down by the liver. Some are also stored in fatty tissues, along with their breakdown products from the liver, and these can be detected for several weeks afterwards in blood ‘drug tests’.
“Through proper clinical trials, researchers can prove whether a potential treatment is both effective and safe. This is the standard that all other medicines are held to, and it shouldn’t be any different for cannabinoids. ”
The cannabis plant contains over 100 different cannabinoids, but the most psychoactive is tetrahydrocannabinol, otherwise known as THC, which potently activates CB1 receptors. The other main cannabinoid, cannabidiol (CBD), isn’t psychoactive. In fact, it reduces the activation of both CB1 and 2 receptors.
Cannabinoids can be extracted from plants and purified. Different strains of the plant are bred for different purposes, and each contains a different proportion of the cannabinoids. Hemp, for example, is a sturdy fibre that’s been used in paper and clothes and is low in the psychoactive chemical THC. Cannabis plants used recreationally tend to have high THC. Cannabis is illegal in some places, while elsewhere it is legal for medicinal or recreational use. Scientific research is going on to see if it could benefit people with Huntington’s disease.
Do cannabinoids improve Huntington’s disease?
Scientists around the world have been studying their effects in Huntington’s disease. Most work has been done in cells grown in the lab, or in animals bred to have the disease-causing gene. Some research suggests that CB1-targeting chemicals may protect cells against toxins. In the brains of Huntington’s mice, CB1
receptor levels have been found to be reduced and CB2 levels are increased. Loss of CB1 receptors may be involved in some symptoms of the disease, because Huntington’s mice that lack the CB1
receptor tend to have worse movement control. The increase in CB2 receptors may be one of the body’s ways of dealing with HD. This theory is strengthened by research showing that mice treated with CB2-targeting chemicals have less nerve cell death – possibly because this calms down the immune system in the brain.
These results in cells and animals are encouraging, but humans are a lot more complex. Bitter experience has taught us that very often results can be inconsistent, or even completely different, when therapies are scaled up for use in humans. Unfortunately, no cannabinoids have translated into effective treatments in people with Huntington’s disease yet. Several clinical trials with cannabis extracts or synthetic cannabinoids
didn’t reduce the abnormal movements, like
chorea, or affect the course of the disease.
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