Effect of Poly(Lactide-Co-Glycolide) Nanoparticles on Local Retention of Fluorescent Material: An Experimental Study in Mice

Objective: Poly(lactide-co-glycolide) (PLGA) nanoparticles are promising materials for the development of new drugreleasing systems. The purpose of this study was to evaluate the in vivo retention time of materials loaded in nanoparticles as compared with that of the material alone by in vivo imaging in nude mice. Materials and Methods: Mice (n = 20) were injected with 0.1 mL fluorescent material 1,1'-dioctadecyl-3,3,3',3' tetramethylindotricarbocyanine iodide (DiR)-loaded PLGA nanoparticles (200 nm) into the right paraspinal muscle, and the same volume of pure DiR solution was injected into the left paraspinal muscle. Fluorescence images were obtained using an in vivo optical imaging system. Fluorescent images were taken 1 day after the injection, and seven more images were taken at 1-week intervals. Image analysis was done with ImagedJ program, and one region of interest was chosen manually, which corresponded to the highest signal-intensity area of fluorescence signal intensity. Results: After 7 weeks, 12 mice showed a right-sided dominant signal, representing the DiR loaded PLGA nanoparticles; 5 mice showed a left-side dominant signal, representing the free DiR solution; and 3 mice showed no signal at all beginning 1 day after the injection. During the 7-week period, the mean signal intensities of the free DiR solution and DiR-loaded PLGA nanoparticles diverged gradually. On day 1, the mean signal intensity of free DiR solution was significantly higher than that of DiR-loaded PLGA (p < 0.001). Finally, by week 7, DiR-loaded PLGA express significantly high signal intensity compared with free DiR solution (p = 0.031). Conclusion: The results of the current study suggested that therapeutic agents bound to PLGA nanoparticles may exhibit prolonged retention times.