Insulin for treatment of neurotrophic ulcers: Clinical evidence and potential mechanism

Abstract

Purpose : Neurotrophic keratopathy causing non-healing epithelial defects represents a significant clinical challenge. Besides nerve growth factor, insulin has been shown to be a promising therapeutic agent promoting epithelial wound healing, but proper dosing and cellular mechanisms have not been clarified. In this study we substantiated clinical use of insulin for treatment of refractory neurotrophic corneal ulcers in vivo and investigated potential cellular mechanisms underlying re-epithelialization of corneal epithelial wounds in vitro.

Methods : In a retrospective, single-center case series, the outcomes of 20 eyes of 20 patients treated with topical insulin eye drops for neurotrophic corneal ulcers, refractory for conservative treatment, were analyzed. Corneal epithelial wound closure was monitored daily. Human primary limbal epithelial cells were incubated in serum-free medium without or with different concentrations (0.05 to 150 µg/ml) of insulin for 24 hours. Gene expression profiles were analyzed using the Human Wound Healing PCR array and verified using specific real-time PCR assays and immunocytochemistry. The influence of insulin on cell migration and proliferation was assessed using appropriate assays.

Results : Complete corneal re-epithelialization was observed in all 20 eyes following insulin standard treatment regimens (25 U/ml = 0.5 U/drop). Higher doses did not enhance outcome but appeared to induce corneal angiogenesis. Experimental analyses provided evidence for a significant dose-dependent effect of insulin on epithelial migration with lower doses (0.5-1.0 µg/ml) being most effective. Expression profiling studies revealed significant upregulation of genes involved in cell migration (e.g. FSCN2, TSPAN1) and downregulation of cell adhesion molecules, including integrin subunits, upon exposure to 1.0-5.0 µg/ml insulin. However, higher doses (50-150 µg/ml) induced a 2.5-fold upregulation of vascular endothelial growth factor A.

Conclusions : The findings confirm previous studies on a beneficial effect of topical insulin on corneal epithelial wound healing following standard treatment regimens. At lower doses, insulin stimulates corneal epithelial cell migration by coordinated effects on cell detachment and increased motility, whereas higher doses appear to induce angiogenesis. These findings may have important implications in treating neurotrophic keratopathy and epithelial wound healing defects.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.