Photoacoustic Imaging of Human Mesenchymal Stem Cells Labeled with Prussian Blue–Poly(l-lysine) Nanocomplexes

Abstract

Acoustic imaging is affordable and accessible without ionizing radiation. Photoacoustic imaging increases the contrast of traditional ultrasound and can offer good spatial resolution when used at high frequencies with excellent temporal resolution. Prussian blue nanoparticles (PBNPs) are an emerging photoacoustic contrast agent with strong optical absorption in the near-infrared region. In this study, we developed a simple and efficient method to label human mesenchymal stem cells (hMSCs) with PBNPs and imaged them with photoacoustic imaging. First, PBNPs were synthesized by the reaction of FeCl3 with K4[Fe(CN)6] in the presence of citric acid and complexed with the cationic transfection agent poly-l-lysine (PLL). The PLL-coated PBNPs (PB-PLL nanocomplexes) have a maximum absorption peak at 715 nm and could efficiently label hMSCs. Cellular uptake of these nanocomplexes was studied using bright field, fluorescence, and transmission electron microscopy. The labeled stem cells were successfully differentiated into two downstream lineages of adipocytes and osteocytes, and they showed positive expression for surface markers of CD73, CD90, and CD105. No changes in viability or proliferation of the labeled cells were observed, and the secretome cytokine analysis indicated that the expression levels of 12 different proteins were not dysregulated by PBNP labeling. The optical properties of PBNPs were preserved postlabeling, suitable for the sensitive and quantitative detection of implanted cells. Labeled hMSCs exhibited strong photoacoustic contrast in vitro and in vivo when imaged at 730 nm, and the detection limit was 200 cells/µL in vivo. The photoacoustic signal increased as a function of cell concentration, indicating that the number of labeled cells can be quantified during and after cell transplantations. In hybrid ultrasound/photoacoustic imaging, this approach offers real-time and image-guided cellular injection even through an intact skull for brain intraparenchymal injections. Our labeling and imaging technique allowed the detection and monitoring of 5 × 104 mesenchymal stem cells in living mice over a period of 14 days.

Photoacoustic Imaging: Contrast Agents and Their Biomedical Applications

“…The C‐HSA‐BOPx‐IR825 NP was employed to test the pH in the tumor region by both ratiometric PA and fluorescence imaging. Other NIR dyes, including naphthalocyanines, phthalocyanine, croconine, squaraine, and Prussian blue, can also serve as PA contrast agents.…”

Nanomaterials in Neural‐Stem‐Cell‐Mediated Regenerative Medicine: Imaging and Treatment of Neurological Diseases

“…PAI combines the advantages of pure optical imaging and pure ultrasound imaging, providing high‐resolution and high‐contrast tissue imaging. Kim et al recently reported the long‐term (up to 14 d) and highly sensitive (200 cells mL −1 in vivo) PAI of human MSCs labeled with Prussian‐blue–poly( l ‐lysine) nanocomplexes.…”

An erythrocyte membrane coated mimetic nano-platform for chemo-phototherapy and multimodal imaging

“…19 In addition, PB-poly-L-lysine (PLL) nanocomplex has been used as a highly efficient photoacoustic contrast agent for stem cells labelling and tracking. 20 However, these nano-drug delivery systems based on bare PB NPs showed the short systemic circulation time, which extremely limited the drug accumulation at tumor sites. 21 Meanwhile, the weak evading ability from macrophage uptake and strong blood clearance preference also reduced the therapy efficiency.…”