Olive leaf extract-based eye drop formulations for corneal wound healing

Abstract

Wound healing is a multifaceted process that can be enhanced through effective therapeutic strategies. This study explores the application of quaternary ammonium chitosan-methyl-β-cyclodextrin (QA-Ch-MCD) as a mucoadhesive polymer to enhance the delivery and efficacy of olive leaf extract (OLE-GS) derived from drought-stressed Italian olive cultivars (Giarraffa, Leccino, and Maurino) in corneal wound healing. QA-Ch-MCD contributes to these enhancements through its strong complexing ability, which protects the polyphenolic compounds in OLE-GS from degradation after prolonged exposure, thereby increasing their stability. Its mucoadhesive properties may reduce drug elimination from the ocular surface, thus improving bioavailability, while its intrinsic antioxidant activity complements the bioactives in OLE-GS, amplifying the overall therapeutic effect. In vitro scratch assays revealed that while OLE-GS promoted cell migration, its combination with QA-Ch-MCD significantly accelerated scratch closure rates compared to controls. Indeed, Notably, QA-Ch-MCD/OLE-GS demonstrated significantly greater effectiveness in promoting scratch closure compared to all other formulations tested (p < 0.05 vs all formulations). The QA-Ch-MCD polymer improved both the stability of polyphenols, indeed polyphenols complexed with the formulation were more stable than the free ones for up to 4 h and enhanced the antioxidant activity of OLE-GS, by protecting the viability of cells exposed to oxidative damage. Furthermore, an eyedrop formulation based on QA-Ch-MCD and OLE-GS exhibited excellent cytocompatibility and in vivo tolerability; as demonstrated by in vitro cytotoxicity studies in which the formulation showed no toxicity at the concentrations of 5–10 μg/mL, and by in vivo studies in which no signs of ocular irritation were detected. Taken together, the results indicate that QA-Ch-MCD is an efficient functional excipient for OLE-GS in eye drop formulations. This single excipient not only provides robust protection against oxidation, preserving the stability and efficacy of the extract, but also significantly enhances its delivery. Thus, these findings highlight QA-Ch-MCD as a functional excipient that enhances the therapeutic efficacy of OLE-GS, representing a promising approach in ocular drug delivery systems for corneal wound healing.