Quantitative Assessment of Nanoparticle Biodistribution by Fluorescence Imaging, Revisited

Abstract

Fluorescence-based whole body imaging is widely used in the evaluation of nanoparticles (NPs) in small animals, often combined with quantitative analysis to indicate their spatiotemporal distribution following systemic administration. An underlying assumption is that the fluorescence label represents NPs and the intensity increases with the amount of NPs and/or the labeling dyes accumulated in the region of interest. We prepare DiR-loaded poly(lactic-co-glycolic acid) (PLGA) NPs with different surface layers (polyethylene glycol with and without folate terminus) and compare the distribution of fluorescence signals in a mouse model of folate-receptor expressing tumor by near infrared fluorescence whole body imaging. Unexpectedly, we observe that fluorescence distribution patterns differ far more dramatically with DiR loading than with the surface ligand, reaching opposite conclusions with the same type of NPs (tumor-specific delivery vs. predominant liver accumulation). Analysis of DiR-loaded PLGA NPs reveal that fluorescence quenching, dequenching and signal saturation, which occur with the increasing dye content and local NP concentration, are responsible for the conflicting interpretations. This study highlights the critical need for validating fluorescence labeling of NPs in the quantitative analysis of whole body imaging. In light of our observation, we make suggestions for future whole body fluorescence imaging in the in vivo evaluation of NP behaviors.

Mesenchymal Stem Cell-Derived Exosomes: A Promising Therapeutic Ace Card to Address Autoimmune Diseases

“…In this investigation, exosomes were mostly found in kidney, spleen, liver, and lung as filtering organs of the body (54). Apart from utilization of fluorescent molecules to chase organ localization of EVs, lower sensitivity of fluorophores negatively affect pharmacokinetic analysis of their applications (especially for quantification of exosome accumulated in a target tissue) (55). Radiolabeling with iodine-125 and bioluminescence emitted from luciferase provide a more practical solution for whole-body imaging of exosome-treated animals with significantly higher sensitivity of detection (56,57).…”

Tumor-Targeting, MicroRNA-Silencing Porous Silicon Nanoparticles for Ovarian Cancer Therapy

“…However, the reason for the greater accumulation of the CRA particles seen in the heart is not clear at this time. Although it can be difficult to use fluorescence imaging data to infer biodistribution in different organs due to differences in light absorbance and fluorophore quenching effects in the different tissues, 67 the greater accumulation in heart seen for the CRA control particles is statistically significant, and both the peptide label and the anti-miR-21 label showed higher accumulation in this organ relative to the CGKRK particles. We note that the biodistribution analysis was based on the fluorescent signal of the nanoparticle nucleic acid payload and of the attached FAM-labeled peptide; therefore, additional portions of silicon material ending up in the liver during the course of the experiments may not have been detected.…”

Complex Size and Surface Charge Determine Nucleic Acid Transfer by Fusogenic Liposomes

“…However, fusion events per time calculated here are subject to a large uncertainty. This is because we cannot exclude fluorescent quenching effects [62,63] due to strongly differing fluorophore concentrations in FLs and plasma membranes after fusion. Additionally, putative differences in FL size distribution or complexation status that preferably bind to planar surfaces or are able to fuse with cellular membranes have been neglected.…”