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

Figures & data

Figure 1 Stepwise synthesis of PLA-PEG copolymer showing (A) PEG, (B) PEGDA, (C) PEGDA amine, (D) activated PLA, and (E) PLA-PEG copolymer.

Abbreviations: PEG, poly(ethylene glycol); PLA, polylactic acid; PEGDA, PEG diacrylate.

Table 1 Particle size and encapsulation efficiency of synthesized PLA-PEG nanoparticles with different PEG chain lengths

Particle composition	Particle size (nm)	Total insulin (IU/g)	Loading of particles (IU/g)	Insulin encapsulation efficiency (%)
PLA	150.2	500	165.1	33.4
PLA-PEG(575)	168.5	500	190.8	38.4
PLA-PEG(2000)	175.2	500	230.5	46.7
PLA-PEG(4000)	181.9	500	313.4	58.5

Abbreviations: PEG, poly(ethylene glycol); PLA, polylactic acid.

Figure 2 Molecular mass distribution of PLA-PEG copolymer determined by gel permeation chromatography.

Abbreviations: PEG, poly(ethylene glycol); PLA, polylactic acid.

Figure 3 Nuclear magnetic resonance spectra of (A) PEGDA, (B) PEGDA aminated, (C) PLA, and (D) PLA-PEG.

Abbreviations: PEG, poly(ethylene glycol); PLA, polylactic acid; PEGDA, PEG diacrylate.

Table 2 Computational parameters used to construct aqueous-phase model building and simulations

S no	Parameter	Description
1	Periodic box dimensions	15 × 15 × 20Å
2	Cut-offs	Switched
3	Dielectric (epsilon)	Constant
4	1–4 scale factors	Electrostatic: 0.5 van der Waals: 0.5
5	Outer radius	7.5Å
6	Inner radius	3.5Å
7	Water molecules	149
8	Solvent/polymer distance	2.3Å

Figure 4 Transmission electron micrograph of PLA-PEG nanoparticles.

Abbreviations: PEG, poly(ethylene glycol); PLA, polylactic acid.

Figure 5 In vitro release of insulin from PLA-PEG₄₀₀₀ nanoparticles (n = 3) at pH 7.4.

Abbreviations: PEG, poly(ethylene glycol); PLA, polylactic acid.

Figure 6 Hypoglycemic effect of PLA-PEG₄₀₀₀ nanoparticles parenteral depot administered to diabetic rabbits (n = 4) at a dose of 25 and 50 IU/kg body weight of insulin.

Abbreviations: PEG, poly(ethylene glycol); PLA, polylactic acid.

Figure 7 Low intensity photomicrograph of a skin section from (A) a control animal and (B) an animal subcutaneously administered PLA-PEG nanoparticles.

Abbreviations: PEG, poly(ethylene glycol); PLA, polylactic acid.

Figure 8 High intensity photomicrograph of a skin section from (A) a control animal and (B) an animal subcutaneously administered PLA-PEG nanoparticles.

Abbreviations: PEG, poly(ethylene glycol); PLA, polylactic acid.

Figure 9 Visualization of geometrical preferences of (A) PLA-PEG1, (B) PLA-PEG2, and (C) PLA-PEG4 after molecular simulation in vacuum.

Notes: Elements are color coded: cyan = C; red = O; blue = N; yellow = P; white = H; brown = Zn.

Abbreviations: PEG, poly(ethylene glycol); PLA, polylactic acid.

Figure 10 Visualization of geometrical preferences of (A) PLA-PEG1, (B) PLA-PEG2, and (C) PLA-PEG4 after molecular simulation in a solvated system consisting of 149 water molecules (blue molecules).

Note: The PLA (yellow) and PEG (red) are rendered in tube display.

Abbreviations: PEG, poly(ethylene glycol); PLA, polylactic acid.

Figure 11 Visualization of geometrical preferences of the insulin molecule in complexation with (A) PLA-PEG1₄, (B) PLA-PEG2₂, and (C) PLA-PEG4₁ after molecular simulations in vacuum.

Notes: The peptide molecules are rendered in tube (elements color coded) and thin-ribbon secondary structures (violet). Color codes for insulin tube rendering: C (cyan), O (red), H (white), and P (yellow). The respective Connolly molecular electrostatic potential surfaces for the nanoparticulate matrix in transparent display mode are also shown.