Biodistribution and Biotoxicity Assessment of Fluorescent Conjugated Polymer Dots.

Conjugated polymer dots (Pdots) have shown potential in the biomedical fields due to their optical properties and customizable design. However, the limited research on the biotoxicity of Pdots hinders their further application and translation. Lipophilic Pdots are prone to adsorbing specific proteins, leading to targeted tissue accumulation. Therefore, lipophilic fluorescent Pdots (Bare-Pdots) are synthesized using the conjugated polymer poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) to systematically evaluate their biodistribution and biotoxicity in stem cells, zebrafish embryos, and mice. It is observed that Bare-Pdots are readily internalized by cells and adhered to the embryonic chorion. Additionally, Bare-Pdots exhibit a distinct distribution in brown adipose tissue and heart, closely associated with phagocytosis of capillary endothelial cells involved in lipid metabolism. Notably, injection of Bare-Pdots at 5 mg kg-1 results in dysfunction of brown adipose tissue and an increased risk of obesity 90 days post-injection. Furthermore, hydrophilic COOH-Pdots and NH2-Pdots with reduced lipophilicity are synthesized using amphiphilic ligands. NH2-Pdots show similar distribution but lower biotoxicity compared to Bare-Pdots. Nevertheless, injection of COOH-Pdots at 5 mg kg-1 causes a decrease in white blood cells and renal tubular damage. These findings provide valuable insights for optimizing dosage to ensure the safe use of Pdots in preclinical applications.

Triglyceride-Rich Lipoprotein-Mediated Polymer Dots for Multimodal Imaging Interscapular Brown Adipose Tissue Capillaries.

Brown adipose tissues (BATs) have been identified as a promising target of metabolism disorders. [18F]FDG-PET (FDG = fluorodeoxyglucose; PET = positron emission tomography) has been predominantly employed for BAT imaging, but its limitations drive the urgent need for novel functional probes combined with multimodal imaging approaches. It has been reported that polymer dots (Pdots) display rapid BAT imaging without additional cold stimulation. However, the mechanism by which Pdots image BAT remains unclear. Here, we made an intensive study of the imaging mechanism and found that Pdots can bind to triglyceride-rich lipoproteins (TRLs). By virtue of their high affinity to TRLs, Pdots selectively accumulate in capillary endothelial cells (ECs) in interscapular brown adipose tissues (iBATs). Compared to poly(styrene-co-maleic anhydride)cumene terminated (PSMAC)-Pdots with a short half-life and polyethylene glycol (PEG)-Pdots with low lipophilicity, naked-Pdots have good lipophilicity, with a half-life of about 30 min and up to 94% uptake in capillary ECs within 5 min, increasing rapidly after acute cold stimulation. These results suggested that the accumulation changes of Pdots in iBAT can reflect iBAT activity sensitively. Based on this mechanism, we further developed a strategy to detect iBAT activity and quantify the TRL uptake in vivo using multimodal Pdots.

Imaging of fluorescent polymer dots in relation to channels and immune cells in the lymphatic system.

Polymer dots (Pdots) have been applied to imaging lymph nodes (LNs) and lymphatic vessels (LVs) in living mice and rats. However, the mechanism of absorption, distribution, metabolism, and excretion of Pdots in LNs and LVs is still unclear. Therefore, the relationship between Pdots and immune cells, LVs and collagen fibers in lymphatics was studied by multiple in vivo and ex vivo microscopic imaging methods and detection techniques. Flow cytometry showed that Pdots could be phagocytosed by macrophages and monocytes, and had no relationship with B cells, T cells and dendric cells in LNs. Silver staining, immunofluorescence and two-photon microscope showed that Pdots gathered in collagen fibers and LVs of LNs. Furthermore, immunofluorescence imaging results verified that Pdots were distributed in the extracellular space of collecting LVs endothelial cells. In addition, Pdots in the collecting LVs were basically cleared by leaking into the surrounding tissue or draining LNs after 21 days of injection. During the long-time observation, Pdots also helped monitor the contraction frequency and variation range of LV. Our study lays a foundation on the research of Pdots as the carrier to study lymphatic structure and function in the future.