| Objects: To develop intravitreally injectable sustained-release submicrospheres for suppression of proliferative vitreoretinopathy (PVR). PVR is an intractable ophthalmopathy, which can cause blindness. The regime applied is operation repair which leaves much too desired because about 30% of the patients have the experienced resurgence of PVR. It was reported that intravitreal injection with the matrine solution could effectively suppress the inflammatory reaction and proliferation of fibroblasts. But the half-life of the drug is so short that frequent injection was needed to provide therapeutical concentration at the target site. A reasonable drug delivery formulation could be used to solve the problem. For one thing, they can offer longer time period of drug concentration within therapeutic range than conventional formulations; for another, they cause less side effects than the free drug solution. In this study, intravitreally injectable sustained-release submicrospheres were prepared, incorporating matrine as model drug and biodegradable poly-L-lactide (PLLA) as carrier, to improve bioavailability and decrease side effect, which could lay a foundation for its clinic use in the future.Methods: On the basis of scientific literatures and pretesting, the Matrine poly-L-lactide submicrospheres were prepared by organic-phase dispersing and solvent diffusion technique, and the fundamental preparation condition such as formula factors and process factors were evaluated in the preliminary experiments. The formulation was optimized by a central composite design-response surface methodology, using drug loading, encapsulation efficiency, mean diameter and polydispersity as evaluation indexes. Prediction was carried out through comparing the observed and predicted values.The physicochemical properties of optimized submicrospheres were investigated. The surface morphology of submicrospheres was observed by scanning electron micrograph, and the diameter and size distribution was determined by particle sizer. The crystalline nature of matrine in submicrospheres was showed by differential scanning calorimetry. In vitro release of matrine from submicrospheres was performed by oscillating in constant temperature method. The release data were analyzed with traditional models to study the release mechanism, incorporating degradation test in vitro. The chemical and physical stability of optimal formula was investigated under following circumstances: high humidity, high tempreture, strong light, long natural store condition (25±2℃/RH60% for 6 months) and 60Co irradiation.The pharmacokinetics and tissue distribution of matrine in ophthalmic tissues of rabbits were studied after a single intravitreal injection of Matrine-loaded submicrospheres and free Matrine solution. Ophthalmic tissues such as vitreous body, iris, sclera, retina and choroids were dissected at different times, using High-performance Liquid Chromatograph to detemine concentration of matrine in ophthalmic tissues. CBmax B and TBmaxwere select from the true values. AUC0-∞, MRT and relative bioavailability were calculated using the trapezoid method.Rsults: The optimal formulation and process were defined through preliminary experiments and the central composite design. It was found that PLLA concentration, theoretical drug loading and gelatin concentration had much more influence on indexes of submicrosphere. Submicrospheres prepared under the optimal formula were smooth and spherical, and have good dispersibility and narrow size distribution. The evaluation indexes showed that the optimal formula and process had fine reproducity and stability. Drug loading, encapsulation efficiency, mean diameter and polydispersity were 6.526%, 50.2%, 699.2nm and 0.005, respectively. The biases to values predicted were small, and it indicated that the optimum mathematic model was highly predictive.Diferential scanning calorimetry showed that Matrine dispersed uniformly in poly-L-lactide matrix as amorphous. The aucumulative release from submicrospheres in vitro reached about 80.66% in 30 days. The accumulative release profile could be distributed by Higuichi equation. The release mechanism showed that drug was released by small and complex holes in submicrospheres.Stability experiment: Under the condition of 40℃and strong light (4500±500lx) for 10 days, the appearance and flow ability, dispersibility, content and release characteristics of submicrospheres changed little. Under the condition of RH90%±5% and RH75%±5% for 10 days, the weight increasing ratios of submicrospheres were more than 5%. After storaged at 25±2℃/RH60% for 6 months, submicrospheres had no significant difference in appearance, flow ability, dispersibility, content and release characteristics. And 60Co irradiation had no effect on these characteristics either.Tissue distribution and pharmacokinetics study: The submicrospheres showed lower concentrations but longer-term existence of the drug in all the tissues, and showed a remarkable bioavailability increase compared to free Matrine. In Matrine solution group, vitreous body got the peak concentration of Matrine 1 hour after injection, and could not determine at 12h. Other tissues were similar. In submicrospheres group, vitreous body got the peak concentration of Matrine at 1d, and could still determine at 25d. Other tissues were similar.Conclusions: The results showed that Matrine poly-L-lactide submicrospheres could prolong the residence time of drug in vitreous body and increase the bioavailability of Matrine. And this dosage form can be easily prepared, and its quality can be control. Therefore it showes great potential in the ocular application.
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