Abstract
Purpose :
To test whether topical glycyrrhizin (GLY) alters the cytoarchitecture, physiological and/or immunological parameters of the normal mouse cornea and conjunctiva.
Methods :
Both normal corneas of C57BL/6 mice were treated topically with GLY (100μg/5μl) or PBS twice daily for 5 days and tested at 0, and/or 3 and 5 days. Slit lamp photography was used to assess bulbar conjunctival hyperemia and fluorescein staining was used to detect epithelial defects. Scanning electron microscopy (SEM) interrogated cell surface morphology, microvillar integrity and cell exfoliation. Phenol treated cotton threads were used to measure tear levels and a Cochet and Bonnet Esthesiometer was used before and after treatment to measure corneal sensitivity. Immunohistochemistry was used to examine corneal nerves (beta tubulin staining) and a phycoerythrin (PE) conjugated anti-langerin monoclonal antibody was used to stain and enumerate langerin positive cells. Intraocular pressure was measured with a tonometer before and after treatment. RT-PCR was used to compare mRNA levels of various TLRs and inflammatory molecules and ELISA assays were employed to compare protein levels of selected toll-like receptors (TLRs), cytokines, and neuropeptides [Substance P (SP) and Vasoactive Intestinal peptide (VIP)].
Results :
GLY vs PBS controls showed no evidence of bulbar hyperemia, epithelial defects nor changes in surface cell morphology after 5 days of treatment. However, GLY vs PBS treatment transiently reduced the density of corneal nerves significantly (7%) only at 3 days, yet neither tear production nor corneal sensitivity were changed. No differences in the number of langerin positive cells nor mRNA levels of TLR2, 4, 5 and 9 were affected by GLY vs PBS. In contrast, levels of IL-1β, HMGB1, and TNF-α mRNA were significantly reduced, but protein levels of these molecules, other cytokine and neuropeptides did not differ between groups.
Conclusions :
GLY transiently reduced corneal nerve density, but had no other measurable deleterious effect on the ocular surface that would preclude its therapeutic use.
This is a 2021 ARVO Annual Meeting abstract.