Corneal Absorption of a New Riboflavin-Nanostructured System for Transepithelial Collagen Cross-Linking

Abstract

Corneal collagen cross-linking (CXL) has been described as a promising therapy for keratoconus. According to standard CXL protocol, epithelium should be debrided before treatment to allow penetration of riboflavin into the corneal stroma. However, removal of the epithelium can increase procedure risks. In this study we aim to evaluate stromal penetration of a biocompatible riboflavin-based nanoemulsion system (riboflavin-5-phosphate and riboflavin-base) in rabbit corneas with intact epithelium. Two riboflavin nanoemulsions were developed. Transmittance and absorption coefficient were measured on corneas with intact epithelia after 30, 60, 120, 180, and 240 minutes following exposure to either the nanoemulsions or standard 0.1% or 1% riboflavin-dextran solutions. For the nanoemulsions, the epithelium was removed after measurements to assure that the riboflavin had passed through the hydrophobic epithelium and retained within the stroma. Results were compared to de-epithelialized corneas exposed to 0.1% riboflavin solution and to the same riboflavin nanoemulsions for 30 minutes (standard protocol). Mean transmittance and absorption measured in epithelialized corneas receiving the standard 0.1% riboflavin solution did not reach the levels found on the debrided corneas using the standard technique. Neither increasing the time of exposure nor the concentration of the riboflavin solution from 0.1% to 1% improved riboflavin penetration through the epithelium. When using riboflavin-5-phosphate nanoemulsion for 240 minutes, we found no difference between the mean absorption coefficients to the standard cross-linking protocol (p = 0.54). Riboflavin nanoemulsion was able to penetrate the corneal epithelium, achieving, after 240 minutes, greater stromal concentration when compared to debrided corneas with the standard protocol (p = 0.002). The riboflavin-5-phosphate nanoemulsion diffused better into the stroma than the riboflavin-base nanoemulsion.

Corneal Collagen Crosslinking: A Systematic Review

“…Other methods, investigated in rabbit corneas, include: phonophoresis (ultrasound-assisted drug penetration) and a biocompatible riboflavin-based nanoemulsion system. Both have shown potential in increasing transepithelial penetration of riboflavin [80,81]. Lastly, the use of a hypoosmolar riboflavin solution (with 0.44% NaCl) was also investigated and appears to contribute to the transepithelial absorption of riboflavin [74].…”

Fundamental Aspects in the Development of Microemulsion Systems Containing Amphotericin B for Ophthalmic Use

“…Moreover, as mentioned earlier, the eye is not an easily accessible organ mainly due to the constant presence of nasolacrimal drainage and corneal barrier 16 . In this context, the MEs are presented as an interesting therapeutic alternative for the ophthalmic route.…”

Biomechanical Strengthening of the Human Cornea Induced by Nanoplatform-Based Transepithelial Riboflavin/UV-A Corneal Cross-Linking

“…Bottos et al 33 have previously demonstrated that 0.5% riboflavin-5-phosphate nanoemulsion could penetrate efficiently in the stroma of rabbit eyes through the intact epithelium, however, after 2 hours of soaking time. Although the results were comparable to standard stromal soaking, the long soaking time makes the methodology unsuitable for clinical use; in addition, the authors did not provide any information on the stromal stiffening induced by UV-A irradiation of the rabbit cornea.…”