Development of microparticles for controlled release of resveratrol to adipose tissue and the impact of drug loading on particle morphology and drug release.

Resveratrol is a small molecule produced by various plants with a remarkable range of beneficial functions in animals. One of these is stimulating signaling pathways in adipose tissue that protect against obesity. Unfortunately, resveratrol suffers from poor bioavailability that inhibits its accumulation in target tissues, including fat, thus hindering the realization of its therapeutic potential. To address this, we are developing biodegradable microparticles as drug depots for controlled release of resveratrol within fat. In this study, resveratrol was encapsulated into poly(lactide-co-glycolide) microparticles using an oil-in-water emulsion/solvent evaporation technique. The oil phase consisted of resveratrol and poly(lactide-co-glycolide) dissolved in a mixture of dichloromethane and ethanol; meanwhile, the aqueous phase contained poly(vinyl alcohol) as the emulsifier. Increasing ethanol's volume ratio increased resveratrol's solubility in the oil phase and particle drug loading. The maximal loading achieved was 65 µg/mg (6.5%) and occurred when the ethanol to dichloromethane ratio was 1:3. Under these conditions, particles exhibited ruffled surfaces, which resulted in variable drug release over the first three days of a six-week release assay. By decreasing resveratrol and ethanol in the oil phase and increasing poly(vinyl alcohol) in the aqueous phase, smooth particles were achieved, but they suffered a 15-25-fold decrease in drug loading depending on size. Small particles exhibited higher drug loading and burst drug release compared to larger particles because of their higher specific surface area. Utilizing mild chemistry, we functionalized poly(vinyl alcohol) with fluorescein isothiocyanate and demonstrated that encapsulation of resveratrol in the particle decreases the amount of fluorescent polymer on the particle surface, suggesting resveratrol displaces the emulsifier during particle formation. Taken together, resveratrol can be encapsulated into poly(lactide-co-glycolide) microparticles, but it accumulates at the particle surface impacting drug loading, surface roughness, and drug release.