For longer than marijuana has been prohibited, cannabis has been used to treat many diseases and conditions. Since prohibition in the 1930s and the racist propaganda of the Reefer Madness film, cannabis has been mostly thought of as an illicit recreational drug. But the discovery of the endocannabinoid system (ECS) in the 1990s has driven researchers to understand the effects of cannabinoids on a range of diseases and disorders.
According to the American Glaucoma Society, one of the main goals in treating glaucoma is to lower the IOP—intraocular pressure. Promising evidence has already shown that cannabinoids have the effect of lowering IOP as well as providing neuroprotection to the retinal ganglion cells. Researchers are currently developing modes of treatments that would use these cannabinoid properties to treat glaucoma patients.
The Neuroprotective Properties of Cannabinoids
The full mechanism of action of cannabinoids in the human eye is not fully understood. A lot of research has demonstrated that cannabinoids enhance survival of neurons in neurodegenerative diseases. In glaucoma, for instance, the final pathway that results in vision loss is the death of ganglion cells (which occurs selectively) via apoptosis (cellular death). This death is initiated by injury of the axons at the optic disc by ischemia or compression. In ischemia, glutamate is released, and this activates the receptor for N-methyl-D-aspartate. This activation is one of the numerous pathways that results in apoptosis. It causes the inflow of calcium into the cells, resulting in the generation of free radicals. Tetrahydrocannabinol (THC) can stall the release of glutamic acid by decreasing the permeability of potassium while increasing that of calcium. It can also inhibit the activation of N-methyl-D-aspartate and glutamate.
Studies have shown that cannabinoids have vaso-relaxant and antioxidant properties, and may include blood flow to the eyes. Patients suffering from open-angle glaucoma may experience an increase in plasma endothelin-1 in response to vasospastic stimuli. A study by Marscicano et al showed that cannabinoids caused a reduction in calcium mobilization induced by endothelin, thus inhibiting constriction of blood vessels. Cannabinoids could also be of benefit to the eyes with optic damage induced by ischemia.
Cannabinoids have neuroprotective properties that may be applicable to ganglion cells in the retina and other neurons in the visual pathway, thus lowering IOP. It is important that we advocate for the research and education regarding all the ways in which cannabinoids could potentially treat, prevent or even cure the huge number of diseases it addresses through the ECS.
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