Characterization of Rabbit Corneas Subjected to Stromal Stiffening by the Açaí Extract (<i>Euterpe oleracea</i>)

<p><i>Purpose</i>: In this study, we characterized rabbit corneas subjected to corneal cross-linking (CXL) with açaí extract compared with a riboflavin photo-stimulated procedure.</p> <p><i>Materials and Methods</i>: The corneas of the slaughterhouse rabbits were divided into three groups: control, consisting of untreated corneal samples; riboflavin/UVA, where corneas were treated with 0.1% riboflavin photo-stimulated at 365 nm as the standard protocol; and açaí, where the samples were subjected to 4% açaí extract for 0.5–2 h. After the CXL procedure, corneas of the three groups were characterized by analyzing their elastic modulus and thermal denaturation profile.</p> <p><i>Results</i>: The elastic modulus at 3% strain showed an approximately threefold increase in the riboflavin/UVA group and 10.5 times in the corneas treated with 4% açaí extract for 2 h, compared with the control group (<i>p</i> < 0.01). The denaturation temperature values of the two groups of crosslinked corneas increased significantly (<i>p</i> < 0.05) and were more pronounced in the açaí group.</p> <p><i>Conclusions</i>: The açaí extract was effective in promoting CXL in rabbit corneas as characterized by the different techniques.</p

Photograph of corneal buttons of rabbit eyes soaked with riboflavin-5-phosphate nanoemulsion or standard 0.1% riboflavin.

<p>Cornea with intact epithelium after exposure to 0.5% riboflavin-5-phosphate nanoemulsion for 240 minutes (A). Cornea with intact epithelium after exposure to the standard 0.1% riboflavin solution for 240 minutes (B). De-epithelialized cornea exposed to 0.1% riboflavin solution for 30 minutes - standard technique (C).</p

Change of transmittance and absorption coefficient of rabbit corneas in the course of time.

<p>Transmittance change (A) and absorption coefficient change (B) of corneas soaked with riboflavin formulations. Dashed lines show group I values (standard treatment).</p

Absorption spectra of riboflavin-5-phosphate nanoemulsion and riboflavin-base nanoemulsion.

<p>Absorption spectra of riboflavin-5-phosphate nanoemulsion and riboflavin-base nanoemulsion.</p

Photograph of the corneal buttons of rabbit eyes of after exposure to different riboflavins.

<p>Corneas with intact epithelium (A, B, and C) after exposure to 0.1% riboflavin-dextran solution for 30 minutes (A) and for 240 minutes (B), as well as after exposure to concentrated 1% riboflavin-dextran for 240 minutes (C). De-epithelialized cornea soaked with 0.1% riboflavin-dextran for 30 minutes - standard technique (D). The yellow staining shows that riboflavin diffused into the stroma only when the epithelium was removed.</p

Stability evaluation of the nanoemulsions over time.

<p>Key: (□) Unloaded nanoemulsion (R = 0.9965); (○) Riboflavin-5-loaded nanoemulsion (R = 0.9927). Mean of 10 analytical determinations ± standart deviation.</p