Preparation and characterization of insulin-loaded bioadhesive PLGA nanoparticles for oral administration

Poly(D,L-lactide-co-glycolide) nanoparticles (PLGA-NP) have been extensively used as a drug delivery system for proteins and peptides. However, their negative surface charge decreases bioavailability under oral administration. Recently, cationically modified PLGA-NP has been introduced as novel carriers for oral delivery. The characteristics of the nanoparticles, such as particle size, surface charge, and bioadhesion are considered the most significant determinants of the effect of these nanoparticles both in vitro and in vivo. Our aim was to introduce and evaluate the physiochemical characteristics, bioadhesion, and biological activity of positively charged chitosan-coated PLGA-NP (CS-PLGA-NP), using insulin as a model drug. Results were compared to those of common negatively charged PLGA-NP and the in vitro cytotoxicity of the two types of nanoparticles was examined. These results indicate that both CS-PLGA-NP and PLGA-NP had a narrow size distribution, averaging less than 150 nm. CS-PLGA-NP was positively charged (+43.1 ± 0.3 mV), exhibiting the cationic nature of chitosan, whereas PLGA-NP showed a negative surface charge (-1.72 ± 0.2 mV). CS-PLGA-NP exhibited stronger bioadhesive potency than PLGA-NP and much greater relative pharmacological availability with regard to orally delivered insulin. In addition, an evaluation of cytotoxicity by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed no increase in toxicity in either kind of nanoparticle during the formulation process. The study proves that CS-PLGA-NP can be used as a vector in oral drug delivery systems for proteins and peptides due to its positive surface charge and bioadhesive properties.