Efficacy of topical application of cannabinoid receptor ligands in experimental dry eye disease

Abstract

Purpose : Cannabinoid receptors (CBR) 1 and 2, as part of the endocannabinoid system, were previously reported to be present in the ocular surface. Using activating or inhibiting cannabinoid ligands may affect CBR-functions such as regulating neuro-sensation, inflammation and wound healing, which are also core mechanisms of dry eye disease (DED). This study investigates the effect of several CBR ligands as a topical therapy in an experimental DED mouse model.

Methods : C57/Bl6 female mice were exposed to desiccating stress (DS) for 14 days. CBR ligands tetrahydrocannabinol (THC, agonist), SR141716A and SR144528 (selective antagonists) were formulated in aqueous solution (DMSO and Cremophore EL). Drug formulations or carrier were topically applied 3 times/day from day 1 of DS. To investigate disease severity, tear production, corneal fluorescence staining, and corneal sensitivity tests were performed at day 3, 5, 7, 10. At the end of the experiment, corneal and conjunctival tissues were analyzed regarding the expression of CBR1 and CBR2 by qPCR in naïve, DED-induced, and treated mice. Also, corneal flat mounts were stained with β3-tubulin, then nerve density and length were semi-automatically quantified from obtained images.

Results : DS increased CBR expressions (p < 0.05). In treated mice, a reduced CBR expression was observed compared to DED mice (p < 0.05). After 10 days, all cannabinoid-ligands reduced fluorescence staining (p < 0.01) compared to untreated and carrier groups. Also, lower expression of IL-1β in the cornea (p < 0.05) was observed. Topical application of CBR1 antagonist and THC maintained corneal sensitivity (p < 0.05) compared to DED mice and carrier-treated mice. In contrast to antagonists, THC protected corneal nerve density during desiccating stress (p < 0.05).

Conclusions : CBR1 and 2 seem to be involved in DED pathogenesis. Topical application of cannabinoid ligands reduces the expression of CBR1 and 2, which is accompanied with improvements of corneal damage and inflammation. Applying THC protected nerve density, thus maintained corneal sensitivity. Particularly, the selective CBR1 antagonist maintained cornea sensitivity without changing nerve density, which indicated a role of CBR1 in corneal neurotransmission. Therefore, this study facilitates the development of DED therapies based on cannabinoid eye drops.

This is a 2021 ARVO Annual Meeting abstract.