Treatment of experimental autoimmune uveoretinitis with poly(lactic acid) nanoparticles encapsulating betamethasone phosphate

Abstract

We have developed nanoparticles (NPs), which are capable of targeting a specific lesion and gradually releasing the agent at the site over a prolonged time period after a single intravenous administration. In this study, we evaluated the effects of intravenously administered poly(lactic acid) nanoparticles encapsulating betamethasone phosphate (BP-PLA NPs) on experimental autoimmune uveoretinitis (EAU) in Lewis rats. To determine the localization of NPs within the retina and choroid of rats with EAU, rhodamine (Rh)-encapsulated PLA NPs were injected intravenously and visualized by confocal microscopy. After the disease onset of EAU induced by S-antigen peptide in Lewis rats, either BP-PLA NPs, BP, or saline was injected intravenously, and the eyes were obtained 7 days following treatment and the histological score was determined. The clinical course of EAU was examined using pathological findings and the expression of the glial fibrillary acidic protein, rod opsin, and the surface markers of inflammatory cells (ED1 and pan T-cell) were immunohistochemically determined. Furthermore, T-cell proliferation and delayed-type hypersensitivity (DTH) to S-antigen were assessed. Intravenously injected Rh-PLA NPs accumulated in the retina and choroid of rats with EAU within 3 hr and remained over the succeeding 7-day-period. Furthermore, systemically administered BP-PLA NPs reduced the clinical scores of rats with EAU in 1 day, which were maintained for 2 weeks and decreased the histological scores. In addition, the ocular infiltration of activated T-cells and macrophages in addition to the hypertrophy of Müller cells were markedly reduced with this treatment. Meanwhile, T-cell proliferation and DTH of BP-PLA NPs-treated rats against S-antigen peptide were not significantly different from those of saline-treated rats. Systemically administered BP-PLA NPs inhibit the development of EAU due to the targeting and the sustained release of steroids in situ. The results of these studies suggest that the systemic administration of BP-PLA NPs may lead to a new therapeutic strategy in controlling intraocular inflammation.

Introduction

Systemic corticosteroid therapy is used to treat intraocular inflammation such as uveitis, retinitis and vitritis (Wakefield et al., 1986, Sasamoto et al., 1990). Although treatment targeting ocular inflammatory diseases has recently shifted from systemic to local therapies (Jaffe et al., 2000, Okabe et al., 2003, Kodama et al., 2003, de Kozak et al., 2004), systemic steroid therapy still plays an important role in controlling intraocular inflammation associated with systemic autoimmune diseases (Wakefield et al., 2000, Toker et al., 2002). Unfortunately, systemic steroid therapy is limited because of the high incidence of serious adverse effects (Dukes MNG, 1996). It is therefore necessary to develop a drug delivery system for steroids that shows enhanced localization at the target site and sustained drug release.

Recently, the use of various biodegradable polymeric particles has been investigated to increase the bioavailability and prolong the controlled release of drugs (Grizzi et al., 1995). Among these polymers, poly(d, l-lactic/glycolic acid) (PLGA) or poly(d, l-lactic acid) (PLA) whose degradation rate depends on the polymer's molecular weight and conformation are already being clinically employed (Niwa et al., 1993, Okada et al., 1994, Okada, 1997, Zhu et al., 2000, Schwendeman, 2002). Consequently, PLGA/PLA-nanoparticles (NPs) have the potential for the specific targeting and sustained delivery of drugs. We have recently developed betamethasone phosphate (BP)-encapsulated PLA NPs, which are prepared at a high efficiency in the presence of zinc (Ishihara et al., 2005). PLA NPs are less likely to burst at an early stage of administration so that they can gradually release the drug at a specific lesion site over a prolonged time period. They also had a diameter ranging from 100 to 200 nm, which is suitable for intravenous administration and accumulation at sites of inflammation. Moreover, BP in PLA NPs has gradually been released from incorporated murine macrophages in vitro (Ishihara et al., 2005).

This study investigates the anti-inflammatory effect of systemically administered BP-PLA NPs on experimental autoimmune uveoretinitis (EAU) in Lewis rats.