In vitro evaluation of enhancing effect of borneol on transcorneal permeation of compounds with different hydrophilicities and molecular sizes

To investigate the enhancing effect of borneol on transcorneal permeation of compounds with different hydrophilicities and molecular sizes. Six compounds, namely rhodamine B, sodium-fluorescein, fluorescein isothiocyanate (FITC) dextrans of 4, 10, 20 and 40 kDa were selected as model drugs. Permeation studies were performed using excised cornea of rabbits by a Franz-type diffusion apparatus. The safety of borneol was assessed on the basis of corneal hydration level and Draize eye test. The application of 0.2% borneol to the cornea increased the apparent permeability coefficient by 1.82—(P<0.05), 2.49—(P<0.05), 4.18—(P<0.05) and 1.11-fold (not significant) for rhodamine B, sodium-fluorescein, FITC-dextrans of 4 and 10 kDa, respectively. No significant permeability enhancement of FITC dextrans of 10, 20 and 40 kDa with borneol was found compared to control. The permeability coefficient enhanced by 0.2% borneol was linear correlated to the molecular weight of model drugs (R2=0.9976). With the 0.05%, 0.1% and 0.2% borneol application, the corneal hydration values were <83% and Draize scores were <4. Borneol may improve the transcorneal penetration of both hydrophilic and lipophilic compounds without causing toxic reactions, especially hydrophilic ones. Furthermore, 0.2% borneol can enhance the permeation of hydrophilic compounds with molecular weight ≤4 kDa. Hence, borneol can be considered as a safe and effective penetration enhancer for ocular drug administration.