Dose-Dependent Telomerase Activation By Topical Cycloastragenol In The Anterior Segment

This study assessed the long-term ocular impact of cycloastragenol (CAG) eye drops at increasing concentrations, with particular emphasis on corneal endothelial cell (CEC) preservation and telomerase reverse transcriptase (TERT) activation within anterior segment tissues.

 Kirikkale University, Faculty of Veterinary Medicine, Department of Preclinical Sciences, Kirikkale, Turkiye

Sixteen-month-old male New Zealand rabbits (n=24) were assigned to receive CAG at 4, 8, or 12 µg/50 µL twice daily in the left eye for six months, while the right eye served as an untreated control. Corneal endothelial cell density (CD) was measured by specular microscopy at baseline and months 2, 5, and 6. Baseline-normalized CD values were analyzed using repeated-measures two-way ANOVA or mixed-effects modeling. After completion, eyes were enucleated for histopathology and immunohistochemical evaluation of TERT expression using the Allred scoring method.

CAG treatment reduced age-related loss of CD, with increasing benefit at higher concentrations. The 4 µg group showed near-significant preservation, while the 8 µg and 12 µg groups had significant improvements by month 6 (p<0.05). Histopathology and immunohistochemical analyses revealed a dose-responsive increase in TERT activity. Mild immunoreactivity appeared in the 4 µg group, whereas the 8 µg group showed robust epithelial and endothelial staining together with heightened activity in the ciliary processes. The 12 µg group displayed diffuse cytoplasmic and nuclear TERT localization across the corneal epithelium and CEC, alongside intense staining in iris and ciliary body tissues. Controls consistently showed minimal TERT expression.

In conclusion, prolonged topical administration of CAG significantly enhanced TERT activity and preserved corneal endothelial cell density in an aging rabbit model, in a clear dose-dependent manner. Histological and immunohistochemical analyses confirmed marked TERT expression in anterior segment tissues, with the greatest effects observed at the highest concentration. These results indicate that CAG eye drops may offer a promising therapeutic approach for mitigating age-related corneal endothelial cell loss through telomerase activation mechanisms.