Studies On Braintide-PLGA Microspheres

In this paper, Braintide (MEP 421), a synthesized small peptide (Asn-Leu-Pro-Arg acetate) for the treatment of Alzheimer's disease, was selected as the model drug and various type of polylactic-co-glycolic acid (PLGA) were used as the carrier materials to prepare injectable biodegrable microspheres by the W1/O/W2 double emulsion-solvent evaporation method.Reversed phase high performance liquid chromatography (RP-HPLC) equipped with ultraviolet (UV) detector was applied for determination of braintide in solution, drug loading and drug entrapment efficiency (EE). Such analytical method was proved to be specification, stable, precise and accuracy.Various proprieties of braintide, such as the apparent solubility, partition coefficient and stability in solutions were investigated. The results showed that the solubility of braintide in certain organic solvent, such as dichloromethane (DCM) and ethyl acetate (EA), was small and the partition coefficients were less than 3.0×10^-2. Braintide was more stable in acid solution. Addition of certain stabilizers, such as EDTA, can increase the stability of braintide.Braintide-PLGA microspheres were prepared by W₁/O/W₂ double emulsion-solvent evaporation method. The typical procedures were described as follow: Braintide was dissolved in bovine serum albumin (BSA) solution (adjusting pH 5 with acetic acid) (W₁). PLGA, dissolved in a solvent-mixture of DCM and EA (3 : 2, v/v)(O), was mixed with braintide solution by ultrasonic vibration. The W₁/O primary emulsion was poured into polyvinyl alcohol (PVA) solution, and then dispersed vigorously to form W₁/O/W₂ emulsion. The resulting W₁/O/W₂ emulsion was stirred gently for about 6 h to remove the organic solvent. The microspheres were collected by filtration after washing several times with distilled water and dried under vacuum at room temperature. The influence of formulation and manufacture parameters on particle size, size distribution, and drug entrapment efficiency was studied. The braintide-PLGA micropsheres with mean particle size between 20～30μm, and EE greater than 90% was successfully prepared. Such microspheres are suitable for 1M or SC administrated, long active depot formulation.The influence of preparation conditions, type of PLGA, etc. on in vitro drug release was also investigated. The drug release profile exhibited a significant burst release followed by nearly constant drug release. The burst release phase was fitted to the Higuchi equation, and the constant release phase was well fitted to zero-release function. The burst release could be well controlled within 20% in the first 24 h, by adjusted the composition of inner-water phase and the concentration of PLGA in oil phase, or use the mixture of different type of PLGA as matrix material.In vivo drug release experiment showed that the drug release profiles of braintide-PLGA microspheres in vivo were similar to that in vitro. The results of biocompatibility study indicated good biocompatibility of braintide-PLGA microspheres.Braintide-PLGA microspheres were prepared, with suitable particle size, high entrapment efficiency and lower "burst release". The microspheres can be suspended in proper medium for IM or SC to sustained release drug in a relatively long period of time. The experimental results showed good in vitro/in vivo correlation of drug release and biocompatibility.