N-acetylcysteine and chitosan conjugate modified dexamethasone nanostructured lipid carriers: Enhanced permeability, precorneal retention and lower inflammation for the treatment of dry eye syndrome.

Dexamethasone (Dex) is a primary medication for treating dry eye syndrome, and tobramycin-dexamethasone eye drops are commercially available. However, the eye's complex physiological environment reduces its bioavailability, and repeated use can lead to significant systemic toxicity and side effects. This study introduces a novel conjugate of chitosan (CS) and N-acetylcysteine (NAC), a bioadhesive material, which was grafted onto the surface of a Dex-supported nanostructured lipid carrier (NLC) to develop an innovative nanoparticle lipid ocular drug delivery system (CS-NAC@Dex-NLC). The enhancements afforded by CS-NAC, such as adhesion, osmotic, and targeting properties, address the limitations of traditional eye drops. NMR characterization confirmed the successful synthesis of the copolymer (CS-NAC). Particle size (PS), zeta potential, and transmission electron microscopy (TEM) verified the proper formation of the CS-NAC@Dex-NLC system. Cytotoxicity tests confirmed its excellent biocompatibility and safety. Cellular uptake studies showed that CS-NAC@Dex-NLC achieved the highest efficiency. Pharmacokinetic assessments revealed a significant increase in Dex's bioavailability in tears and aqueous humor. In vitro corneal penetration and in vivo imaging experiments demonstrated effective corneal penetration and retention, enhancing the drug's duration on the ocular surface and overcoming the barrier effect. Pharmacodynamic studies in rabbits with dry eye syndrome indicated that CS-NAC@Dex-NLC effectively alleviates symptoms, repairs corneal damage, and stabilizes the tear film. ELISA results showed a reduction in inflammation caused by dry eye. These findings suggest that CS-NAC@Dex-NLC is a promising vector for dry eye treatment, offering significant clinical relevance.