Our body’s cannabinoid receptor system may play a part in
protecting our nervous system following trauma, Israeli researchers
believe.
A team at the Hebrew University of Jerusalem has found that rats
and mice subjected to traumatic brain injury (TBI) showed significantly
better recovery when treated with cannabinoid compounds, possibly
opening the way for clinical trials in the near future.
Cannabinoids are chemical compounds, either derived from cannabis or
manufactured, that act on specific cannabinoid receptors in our body’s
cells. The most well-known is tetrahydrocannabinol, or THC, marijuana’s
main psychoactive compound. The endocannabinoid system, our body’s
natural cannabinoid receptors, is found in the brain and most organs of
the body, and is believed to be a part of the neuroprotective mechanism
in mammals, said Prof. Esther Shohami of the Hebrew University of
Jerusalem.
When an external event like stroke or trauma occurs, the body
responds by producing these molecules that should protect the brain,
Shohami said.
In previous studies,
the researchers looked at the endocannabinoid 2-AG in mice following a
traumatic brain injury. 2-AG is produced by the body naturally, but in
relatively low amounts that are not enough to effectively protect the
brain.
The researchers noticed that 2-AG levels were significantly higher following trauma, although they weren’t sure why.
“A high level doesn’t mean anything, what matters is what it’s there for,” Shohami said.
They administered additional plant-derived 2-AG to mice following a
brain injury, and found that the compound helped the mice recover.
“It is administered by the brain but it’s not enough to protect the
brain, so we had to augment,” Shohami said. “The brain creates
protection; we wanted to mimic what the brain does, and we wanted to do
it better.”
The mice only received a single dose, but showed positive effects up
to three months after the injury. 2-AG’s main effect is as an
anti-inflammatory compound, Shohami said.
“The outcome of trauma was better, the motor function, the cognitive
function,” Shohami said. “All the parameters we looked at as part of the
damage were affected by the 2-AG, and were better than the untreated
mice.”
The problem was that both cannabinoid receptors type 1 and 2, or CB1
and CB2, were involved in the response. CB1 is responsible for the
psychoactive effects of cannabinoids, and is less stable, so it could
not be used as a drug. CB2 is not involved in the psychoactive effects
of cannabinoids.
“If
you can distinguish between the two receptors you can make this drug
more attractive for pharma, for doctors to prescribe, because the
concern about side effects would be significantly reduced,” Shohami
said.
Shohami and her team developed synthetic molecules, modeled on 2-AG,
that selectively activate the CB2 receptors and do not bind to the
psychoactive, CB1 receptors. The researchers looked at the effect of
these molecules, called HU-910 and HU-914, on rats following a closed
head injury. They studied the effects of the compounds on both the rats’
brains and on the corticospinal tracts, a neural pathway originating in
the brain which extends down the spinal cord and is responsible for the
body’s motor control.
No one had looked at the effects of cannabis on the corticospinal tract before, Shohami said.
The researchers found improved
recovery after TBI in the brain and in this tract, and improved motor
skills, which is one important parameter of recovery.
There are no drugs approved for treating traumatic brain injury,
Shohami said, partly due to failures in developing treatment by the
industry in the 1990s and 2000s, which has made drug companies reluctant
to endorse new treatments.
“It’s a very complex condition. Treatment has to be very carefully
designed both in terms of mechanism and timing. Timing of treatment is
very critical and this was the basis of failure for many of the trials,”
Shohami said.
The drug would need to be administered as a single dose in a specific therapeutic window within a few hours of the injury.
Not all of the team’s data has been published, but the researchers
hope the treatment will advance to clinical trials, and eventually
become a prescribed treatment for TBI.
Prof. Raphael Mechoulam, who collaborated on the research, first
discovered the structure of THC. Mechoulam also uncovered the
endocannabinoid system in the 1990s.
Shohami
will present her research, titled “The role of CB2 receptors in the
recovery of mice after traumatic brain injury,” at the
Cann10 International Medical Cannabis Conference, which will be held in Tel Aviv on June 4-6.
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