Enhancement of trans-corneal permeation of riboflavin-5'-phosphate from new ophthalmic solutions. A promising, non-invasive approach for corneal trans-ephithelial cross linking treatment

Corneal accumulation of riboflavin-5’-phosphate (Riboflavin) is an essential step in the so called collagen cross-linking (CXL), the elective therapeutic approach for the treatment of keratoconus, also adopted in the treatment of corneal ectasia and irregular astigmatism. Since corneal epithelium impedes the passage of riboflavin, which, therefore, is unable to penetrate deep into the corneal stroma in a relatively short time, CXLis usually performed aftersurgicaldebridement of corneal epithelium. D-alpha-tocopheryl poly(ethylene glycol) 1000 succinate (VE-TPGS) is a really effective permeation enhancer used to increase adsorption of drugs trough different biological barriers. Moreover, belonging to the group of tocopherols pro-drugs, VE-TPGS exerts a protective effect on biological membrane against free-radical damage. The aim of this work is the evaluation of VE-TPGS effects on intact cornea permeability ofriboflavin, and the potential protective effect against free-radicals generated in CXL procedures. Different solutions containing riboflavin (0.125% w/w), dextran(20.0% w/w) and increasing concentration of VE-TPGS were prepared. Corneal permeation was evaluated in vitroby the use of modified Franz-cell type diffusion cells and freshly excised porcine corneas as barrier. The effect of VE-TPGS on Riboflavin corneal penetration was compared with standard commercial solution of riboflavinin dextran at different times. Accumulation experiments were conducted both on normal and disepithelized corneas.Moreover, intact porcine corneas,treated with the new proposed solutions, were subjected toan in vitro CXL procedure and compared with disephitelized corneas, treated withcommercial solution of riboflavin. Differences were measured by meansoffirmnessof treated corneas using Young’s modulus. The photo-protective effect of proposed solutions on corneal epithelium was, finally, evaluated. CXL protocol was applied, in vitro, on human explanted corneas and resulting morphology of corneal epithelium was investigated by scanning electron microscopy.