The history of the cannabis dates back thousands of years, but the understanding of the action of its constituents on the human body is still in its infancy.
Cannabis, glaucoma and eye pressure
In case of primary open-angle glaucomareduction of intraocular pressure is the only way to prevent further damage to the optic nerve.
The main component of cannabis is the 9-tetrahydrocannabinol (delta-9-THC, THC), and as early as 1971, work by Hepler and Frank pointed out the beneficial effect on intraocular pressure (IOP). Since that study, much research has been done to understand the nature of this effect, but it is not yet known through which receptors the main components of cannabis regulate IOP.
It is assumed that THC acts through cannabinoid CB1 receptors, as agonists of these receptors reduce IOP, but this mechanism has not been demonstrated to date. CB1 receptors, the most characterised ones, are widely distributed in the brain and eye e regulate important physiological systems such as pain, mood, movement and memory. However, the cannabinoid signalling system consists of other receptors such as CB2, GPR18 and GPR119, as well as enzymes that produce and metabolise cannabinoid lipid messengers.
THC is not the only phytocannabinoid detected in cannabis, cannabidiol (CBD) may be, in fact, present in quantities comparable to THC, and despite being considered inactive for a long time, he showed beneficial action as an anti-epileptic in Dravet syndrome and was recently approved by the Food and Drug Administration (FDA) as an anti-epileptic. CBD has also exhibited other activities, including that of negative allosteric modulator of CB1 signalling pathways. This could suggest an action of CBD antagonistic to that of THC.
Researchers at Indiana University had, in previous studies, determined that at least three cannabinoid-related receptors (CB1, GPR18, GPR119) were implicated in the regulation of IOP in the vertebrate eye. The team of researchers recently published in Investigative Ophthalmology & Visual Sciencea study examining the effects of THC and CBD on IOP regulation. Specifically, the two active ingredients were applied locally in mice and their effects on IOP were assessed by tonometry and quantification of mRNA levels.
The possible effects of cannabis on glaucoma
The team demonstrated that a single topical application of THC reduced IOP within 8 hours (approx. of 28%) in male mice. This effect was due to to the combined activation of CB1 and GPR18 receptorseach of which lowered eye pressure when activated. The researchers also showed that theaction of THC was sex-dependent, was indeed stronger in male mice, in which CB1 and GPR18 mRNA levels were higher.
The study revealed, again, that the CBD is not inactive, indeed it showed two opposite effects on IOPone of which prevented THC from lowering eye pressure. CBD caused an increase in eye pressure in 18% mice for at least four hours after use.
The researchers conclude by emphasising the importance of further studies in order to understand the regulation of eye pressure by THC and CBD, as this is more complex than previously assumed.
Source
Dr. Carmelo Chines
Direttore responsabile
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