Evaluation of Penetration Depth for Alternative Photosensitizers in Photodynamic Antimicrobial Therapy

Abstract

Purpose : Photodynamic antimicrobial therapy using rose bengal is an effective method to treat infectious keratitis. However, rose bengal penetration is insufficient to treat deeper infections, like fungal keratitis. We hypothesize that hydrophobic formulations of rose bengal or alternative photosensitizers may improve penetration for antimicrobial applications.

Methods : Human corneas less than 30 days postmortem were soaked for 30 minutes epithelial side down in 0.0075% concentration of disodium rose bengal (n=5), lactone rose bengal (n=5), disodium Erythrosin B (n=3), lactone Erythrosin B (n=3), or disodium Eosin Y (n=3). NaCl solution was the control (n=5). DAPI stain was applied to the endothelial layer. Samples were imaged with confocal microscopy to assess photosensitizer penetration depth and corneal thickness via the Z-stack. Statistical significance was quantified using one-way ANOVA.

Results : There was no significant difference between the mean corneal thickness in all 5 groups (p=0.353). All photosensitizers penetrated a significant depth within the cornea as compared to control (control: 0±0µm; lactone RB: 113±21 µm, disodium RB: 102±12 µm, lactone Erythrosin B: 217±24 µm, Erythrosin B: 280±34 µm, disodium Eosin Y: 258±8 µm). Between photosensitizer groups, all differences were significant (p<0.05) except between lactone RB and disodium RB (p=0.63) and between disodium Erythrosin B and disodium Eosin Y (p=0.771).

Conclusions : Our results demonstrate that alternative photosensitizers may provide a viable solution to poor penetration issues in photodynamic therapy. Additionally, since lactone and disodium formulations of rose bengal had comparable penetration, our results show that hydrophobicity alone cannot improve penetration depth.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Figure 1: Comparison of photosensitizer penetration measured on confocal Z stack between: Rose Bengal Disodium, Rose Bengal Lactone, Erythrosin Lactone, Erythrosin Disodium, and Eosin Y

 

Figure 2: Representative Z stack images of each of the different photosensitizers: Rose Bengal Disodium, Rose Bengal Lactone, Erythrosin Lactone, Erythrosin Disodium, and Eosin Y