Thiolated nanostructured lipid carriers as a potential ocular drug delivery system for cyclosporine A: Improving in vivo ocular distribution.

Ophthalmic drug delivery with long pre-corneal retention time and high penetration into aqueous humor and intraocular tissues is the key-limiting factor for the treatment of ocular diseases and disorders. Within this study, the conjugate of cysteine-polyethylene glycol monostearate (Cys-PEG-SA) was synthesized and was used to compose the thiolated nanostructured lipid carrier (Cys-NLC) as a potential nanocarrier for the topical ocular administration of cyclosporine A (CyA). The rapid cross-linking process of Cys-PEG-SA in vitro was found in simulated physiological environment. The in vitro CyA release from Cys-NLC was slower than that of non-thiolated nanostructured lipid carriers (NLC) due to the cross-linking of thiomers on the surface of nanocarriers. After topical ocular administration in rabbits, the in vivo ocular distribution of CyA was investigated in comparison of Cys-NLC with non-thiolated NLCs and oil solution. The results showed that CyA concentration in systemic blood was very low and close to the detection limit. The area-under-the-curve (AUC(0-24h)) and mean retention time (MRT(0-24h)) of Cys-NLC group in aqueous humor, tear and eye tissues were significantly higher than that of oil solution, non-thiolated NLCs (p<0.05). These results demonstrated that the thiolated NLC could deliver high level of CyA into intraocular tissues due to its bioadhesive property and sustained release characteristics.