Improved drug loading and antibacterial activity of minocycline-loaded PLGA nanoparticles prepared by solid/oil/water ion pairing method

Abstract

Background: Low drug entrapment efficiency of hydrophilic drugs into poly(lactic-co-glycolic acid) (PLGA) nanoparticles is a major drawback. The objective of this work was to investigate different methods of producing PLGA nanoparticles containing minocycline, a drug suitable for periodontal infections.

Methods: Different methods, such as single and double solvent evaporation emulsion, ion pairing, and nanoprecipitation were used to prepare both PLGA and PEGylated PLGA nanoparticles. The resulting nanoparticles were analyzed for their morphology, particle size and size distribution, drug loading and entrapment efficiency, thermal properties, and antibacterial activity.

Results: The nanoparticles prepared in this study were spherical, with an average particle size of 85-424 nm. The entrapment efficiency of the nanoparticles prepared using different methods was as follows: solid/oil/water ion pairing (29.9%) > oil/oil (5.5%) > water/oil/water (4.7%) > modified oil/water (4.1%) > nano precipitation (0.8%). Addition of dextran sulfate as an ion pairing agent, acting as an ionic spacer between PEGylated PLGA and minocycline, decreased the water solubility of minocycline, hence increasing the drug entrapment efficiency. Entrapment efficiency was also increased when low molecular weight PLGA and high molecular weight dextran sulfate was used. Drug release studies performed in phosphate buffer at pH 7.4 indicated slow release of minocycline from 3 days to several weeks. On antibacterial analysis, the minimum inhibitory concentration and minimum bactericidal concentration of nanoparticles was at least two times lower than that of the free drug.

Conclusion: Novel minocycline-PEGylated PLGA nanoparticles prepared by the ion pairing method had the best drug loading and entrapment efficiency compared with other prepared nanoparticles. They also showed higher in vitro antibacterial activity than the free drug.

Keywords: PEGylation; PLGA; antibacterial; ion pairing; minocycline; nanoparticle.

Figure 1

Synthesis of PEGylated-PLGA copolymer. Abbreviations: PEG, poly(ethylene) glycol; PLGA, poly(lactic-co-glycolic acid).

Figure 2

H-Nuclear magnetic resonance spectrum of synthesized PEGylated PLGA in CDCL₃. Abbreviations: PEG, poly(ethylene) glycol; PLGA, poly(lactic-co-glycolic acid).

Figure 3

A typical scanning electron microphotograph of nanoparticles prepared by S/O/W ion pairing method, SOW10 (upper and lower image is presented at 30,000 and 60,000× magnification, respectively).

Figure 4

Particle size distributions of nanoparticles prepared by (A) S/O/W ion pairing method (SOW10) and (B) nanoprecipitation method (NP11).

Figure 5

DSC thermograms of minocycline, PLGA-PEG, and minocycline-PLGA-PEG nanoparticles. Abbreviations: DSC, differential scanning calorimetry; PEG, poly(ethylene) glycol; PLGA, poly(lactic-co-glycolic acid).

Figure 6

In vitro cumulative release of minocycline from nanoparticles (A) OW1, OO5, and WOW6; (B) modified O/W (OW2, OW3, and OW4), and (C) S/O/W ion pairing method (SOW7–10), in phosphate buffer solution (pH 7.4, 37°C).

Figure 7

Scheme of combination of S/O/W emulsion and ion pairing techniques.