De Novo Adipose Tissue Generation through Long-Term, Local Delivery of Insulin and Insulin-Like Growth Factor-1 by PLGA/PEG Microspheres in an in Vivo Rat Model: A Novel Concept and Capability

Abstract

This study was undertaken to characterize the duration of long-term growth factor delivery by poly(lactic-co-glycolic-acid)-polyethylene glycol (PLGA/PEG) microspheres and to evaluate the potential of long-term delivery of insulin and insulin-like growth factor-1 (IGF-1) for the de novo generation of adipose tissue in vivo. PLGA/PEG microspheres containing insulin and IGF-1, separately, were produced by a double-emulsion solvent-extraction technique. In the first phase of the experiment, the in vitro release kinetics of the microspheres were evaluated for the optical density and polyacrylamide gel electrophoresis of solutions incubated with insulin-containing microspheres for four different periods of time (n = 1). The finding of increased concentrations of soluble insulin with increased incubation time confirmed continual protein release. In the second stage of the experiment, 16 rats were divided equally into four study groups (insulin, IGF-1, insulin + IGF-1, and blank microspheres) (n = 4). Insulin and IGF-1 containing microspheres were administered directly to the deep muscular fascia of the rat abdominal wall to evaluate the potential for de novo adipose tissue generation via adipogenic differentiation from native nonadipocyte cell pools in vivo. Animals treated with blank microspheres served as an external control group. At the 4-week harvest period, multiple ectopic islands of adipose tissue were observed on the abdominal wall of the animals treated with insulin, IGF-1, and insulin + IGF-1 microspheres. Such islands were not seen in the blank microsphere group. Hematoxylin and eosin-stained sections of the growth factor groups demonstrated mature adipocytes interspersed with fibrous tissue superficial to the abdominal wall musculature and continuous with the fascia. Oil-Red-O stained sections demonstrated that these cells contained lipid. Computer-aided image analysis of histologic sections confirmed that there were statistically significant increases in the amount of "ectopic" adipose neotissue developed on the abdominal wall of animals treated with growth factor microspheres. In conclusion, this study confirms the long-term release of proteins from PLGA/PEG microspheres up to 4 weeks and demonstrates the potential of long-term local insulin and IGF-1 to induce adipogenic differentiation to mature lipid-containing adipocytes from nonadipocyte cell pools in vivo at 4 weeks.

Liver tissue engineering at extrahepatic sites in mice as a potential new therapy for genetic liver diseases

“…Bioerodible polyethylene glycol-polylactide-co-glycolide (Polysciences, Warrington, PA) MS were prepared as a modification of previously described techniques. 16,17 An 8:1 ratio of polylactide-co-glycolide (PLGA; 75:25; Polysciences, Warrington, PA) to PEG-8000 (polyethylene glycol, MW 8000, Sigma, St. Louis, MO) was employed with the double emulsion technique to generate MS of final mean diameter 8 to 10 m. Additionally, a pH buffer of 7.4 was incorporated in all MS preparations as a modification of other techniques to limit local pH changes. MS were prepared to give a continuous mean daily release of 0 ng (saline), 0.0167 ng, 0.167 ng, and 1.67 ng for 14 days in aFGF-MS-G1, aFGF-MS-G2, aFGF-MS-G3, and aFGF-MS-G4, respectively.…”

Adipogenic Factor-Loaded Microspheres Increase Retention of Transplanted Adipose Tissue

“…21,22 The release of insulin to induce adipogenesis has been demonstrated, using in vitro and in vivo studies, resulting in fat tissue increased weight in a couple of weeks. 23,24 Biodegradable drug delivery systems, such as PLGApolyethylene glycol (PLGA-PEG) MS, have been studied as delivery vehicles for insulin, insulin-like growth factor-1 (IGF-1), and basic fibroblast growth factor. In a subcutaneous rat model, incorporating these growth factors improved autologous free fat graft weight and volume, with the best results observed for either insulin or IGF-1 alone or in combination.…”

Local Stent-Based Release of Transforming Growth Factor–β1 Limits Arterial In-Stent Restenosis

“…[33][34][35][36] A mixture of 75:25 PLGA (Polysciences, Warrington, PA) and PEG-8000 (Fisher Scientific, Fair Lawn, NJ) was employed with the double emulsion technique to generate a final microsphere diameter of 10 µm and a degradation and drug release time of approximately 4 wk, as characterized previously. [33][34][35][36] In addition, a pH buffer of 7.4 was incorporated to limit local pH changes, stabilize incorporated TGF-β1, and render the microspheres more biocompatible. 37 During the microsphere manufacturing process, recombinant TGF−β1 (Calbiochem, San Diego, CA; 0.0083 µg per week per stent) was added as an aqueous solution to the polymer solution.…”