Therapeutic effect of stealth-type polymeric nanoparticles with encapsulated betamethasone phosphate on experimental autoimmune uveoretinitis.

The therapeutic effects of betamethasone phosphate (BP) encapsulated in biocompatible and biodegradable blended nanoparticles of poly(lactic acid) (PLA) homopolymers and PEG-block-PLA copolymers (stealth nanosteroids) were examined in an experimental autoimmune uveoretinitis (EAU) model in Lewis rats. EAU was induced by S-antigen peptide in Lewis rats. Accumulation of systemically administered Cy7-labeled stealth nanoparticles in inflamed eyes of rats with EAU was assessed using in vivo fluorescence imaging, and the therapeutic effect of stealth nanosteroids, nonstealth nanosteroids, or saline on EAU was examined. The eyes were obtained 7 days after the treatment, and the histologic score was determined using pathologic findings. The expression of inflammatory cytokines including IL-6, IL-17, and VEGF was determined immunohistochemically. Cy7-stealth nanoparticles accumulated in inflamed eyes of rats with EAU and remained in situ for a 3-day period. Systemically administered stealth nanosteroids (100 μg of BP) reduced the clinical scores of rats with EAU within 1 day and maintained the effect for 2 weeks. This treatment also decreased the histologic scores and the expression of inflammatory cytokines in the retina of EAU. The strong therapeutic benefit on EAU obtained with the stealth nanosteroids may have been due to prolonged blood circulation and targeting to the inflamed uvea and retina, in addition to sustained release in situ.