# Formulation and Characterization of an Oleuropein-Enriched Oral Spray Gel: Microbiological Performance and In Ovo Histopathological Safety

## TL;DR

This study develops an oral spray gel with oleuropein, a compound from olive leaves, and tests its antimicrobial properties and safety in an egg-based model.

## Contribution

The paper introduces a novel sprayable oral gel formulation enriched with oleuropein and evaluates its antimicrobial efficacy and biological safety.

## Key findings

- The optimized oral spray gel delivered 32.6 µg of oleuropein per spray and showed antimicrobial activity against cariogenic bacteria.
- In ovo testing revealed antiangiogenic effects and dose-dependent tissue changes in heart and liver without fibrosis or steatosis.
- The formulation maintained stable physicochemical properties during storage with consistent dose delivery.

## Abstract

Background/Objectives: Oleuropein is a bioactive phenolic compound from olive leaves with antimicrobial and antioxidant activity. This study aimed to develop a sprayable oral gel containing an oleuropein-rich aqueous extract and to evaluate its pharmaceutical performance antimicrobial efficacy and in ovo biological response. Methods: Oleuropein content was quantified using a validated chromatographic method. Polymeric systems were screened to select an optimized sprayable formulation. Physicochemical stability, dose uniformity, and antimicrobial activity against major cariogenic bacteria were evaluated. In ovo biological evaluation was conducted using the chick chorioallantoic membrane angiogenesis model together with histopathological examination of embryonic heart and liver tissues. Results: Oleuropein content was determined as 288.6 µg/mL in the olive leaf extract and 255.1 µg/mL in the final formulation. The optimized oral spray showed stable physicochemical properties, with pH maintained at 6.90 ± 0.02 and no relevant changes in viscosity during storage. The mean delivered dose per actuation was 0.128 ± 0.015 g, corresponding to 32.6 µg oleuropein per spray. The formulation exhibited inhibitory activity against all tested cariogenic microorganisms, with MIC values ranging from 13.3 to 170.7 µg/mL and MBC values generally two-fold higher. In the CAM assay, significant concentration- and time-dependent antiangiogenic effects were observed after 24–48 h at moderate and higher concentrations. Histopathological evaluation revealed dose-dependent acute degenerative and congestive changes in heart and liver tissues without evidence of fibrosis or steatosis. Conclusions: The oleuropein-based sprayable oral gel is a promising localized delivery system with adequate stability dose uniformity and antimicrobial efficacy. In ovo findings provide a conservative assessment of systemic exposure and support further development for oral biofilm and caries-related applications.