Preparation and evaluation of insulin-loaded polylactide microspheres using factorial design

In vivo evaluation of a conjugated poly(lactide-ethylene glycol) nanoparticle depot formulation for prolonged insulin delivery in the diabetic rabbit model

Poly(ethylene glycol) (PEG) and polylactic acid (PLA)-based copolymeric nanoparticles were synthesized and investigated as a carrier for prolonged delivery of insulin via the parenteral route. Insulin loading was simultaneously achieved with particle synthesis using a double emulsion solvent evaporation technique, and the effect of varied PEG chain lengths on particle size and insulin loading efficiency was determined. The synthesized copolymer and nanoparticles were analyzed by standard polymer characterization techniques of gel permeation chromatography, dynamic light scattering, nuclear magnetic resonance, and transmission electron microscopy. In vitro insulin release studies performed under simulated conditions provided a near zero-order release pattern up to 10 days. In vivo animal studies were undertaken with varied insulin loads of nanoparticles administered subcutaneously to fed diabetic rabbits and, of all doses administered, nanoparticles containing 50 IU of insulin load per kg body weight controlled the blood glucose level within the physiologically normal range of 90-140 mg/dL, and had a prolonged effect for more than 7 days. Histopathological evaluation of tissue samples from the site of injection showed no signs of inflammation or aggregation, and established the nontoxic nature of the prepared copolymeric nanoparticles. Further, the reaction profiles for PLA-COOH and NH(2)-PEGDA-NH(2) were elucidated using molecular mechanics energy relationships in vacuum and in a solvated system by exploring the spatial disposition of various concentrations of polymers with respect to each other. Incorporation of insulin within the polymeric matrix was modeled using Connolly molecular surfaces. The computational results corroborated the experimental and analytical data. The ability to control blood glucose levels effectively coupled with the nontoxic behavior of the nanoparticles indicates that these nanoparticles are a potential candidate for insulin delivery.

Preparation, characterization, and in vivo evaluation of insulin-loaded PLA-PEG microspheres for controlled parenteral drug delivery

AIM

The aim of this study was to prepare insulin-loaded poly(lactic acid)-polyethylene glycol microspheres that could control insulin release at least for 1 week and evaluate their in vivo performance in a streptozotocin-induced diabetic rat model.

METHODS

The microspheres were prepared using a water-in-oil-in-water double emulsion solvent evaporation technique. Different formulation variables influencing the yield, particle size, entrapment efficiency, and in vitro release profiles were investigated. The pharmacokinetic study of optimized formulation was performed with single dose in comparison with multiple dose of Humulin 30/70 as a reference product in streptozotocin-induced diabetic rats.

RESULTS

The optimized formulation of insulin microspheres was nonporous, smooth-surfaced, and spherical in structure under scanning electron microscope with a mean particle size of 3.07 microm and entrapment efficiency of 42.74% of the theoretical amount incorporated. The in vitro insulin release profiles was characterized by a bimodal behavior with an initial burst release because of the insulin adsorbed on the microsphere surface, followed by slower and continuous release corresponding to the insulin entrapped in polymer matrix.

CONCLUSIONS

The optimized formulation and reference were comparable in the extent of absorption. Consequently, these microspheres can be proposed as new controlled parenteral delivery system.

Development of novel 5-FU-loaded poly(methylidene malonate 2.1.2)-based microspheres for the treatment of brain cancers

In order to treat malignant brain tumors by local delivery of antineoplastic agents, the feasibility of 5-fluorouracil (5-FU)-sustained release biodegradable microspheres with a novel material, poly(methylidene malonate 2.1.2), was investigated using an emulsion/extraction method. This polymer was expected to present a slow degradation rate, thus leading to a long term local delivery system. Microparticles were successfully obtained and characterized in terms of drug loading, size, morphology and release profile. The size of the particles was between 40 and 50 microm, which was compatible with a stereotactic injection through a needle. Sufficient drug loadings were obtained (i.e. compatible with the preparation of therapeutic 5-FU doses in a minimal volume of injection), and perfectly spherical microspheres were observed. The respective influences of the polymer molecular weight, the polymer concentration, and the emulsion time on the release profiles were studied using a 2(3) factorial design. In the same objective, the solvent extraction time was extended while keeping all the previous parameters fixed at their optimal values. The in vitro study of these different parameters allowed a reduction of the initial burst release, with a percentage of 5-FU released after 24 h that was lowered from 90 to 65%, and the achievement of a long term drug delivery system, since the release was still ongoing after 43 days. Moreover, the microparticles could be gamma-sterilized (25 kGy) without modification of the release kinetics. Thus, the requested specifications to perform animal experiments were attained.

Potential applications of polymeric microsphere suspension as subcutaneous depot for insulin

The objective of this investigation was to develop an injectable, depot-forming drug delivery system for insulin based on microparticle technology to maintain constant plasma drug concentrations over prolonged period of time for the effective control blood sugar levels. Formulations were optimized with two well-characterized biodegradable polymers namely, poly(DL-lactide-co-glycolide) and poly-epsilon-caprolactone and evaluated in vitro for physicochemical characteristics, drug release in phosphate buffered saline (pH 7.4), and evaluated in vivo in streptozotocin-induced hypoglycemic rats. With a large volume of internal aqueous phase during w/o/w double emulsion solvent evaporation process and high molecular weight of the polymers used, we could not achieve high drug capture and precise control over subsequent release within the study period of 60 days. However, this investigation revealed that upon subcutaneous injection, the biodegradable depot-forming polymeric microspheres controlled the drug release and plasma sugar levels more efficiently than plain insulin injection. Preliminary pharmacokinetic evaluation exhibited steady plasma insulin concentration during the study period. These formulations, with their reduced frequency of administration and better control over drug disposition, may provide an economic benefit to the user compared with products currently available for diabetes control.