Macrophages are a significant cell group of the innate immune system that play a critical role in pathogen clearance, wound healing, and homeostasis in various coordinated pathways. These pathways are extensively studied and have been linked to contributing factors to major diseases such as vascular inflammation, autoimmunity, and several cancers. Studying these pathways requires identifying and discerning macrophages from other cells with macrophage-specific fluorophore-labeled contrast reagents. Fluorophores widely used in research are cyanine’s with a wavelength between 600 and 700 nanometers; however, the recent push for lower-wavelength fluorophores has led to the development of dyes in the 500-nanometer wavelengths, allowing for deeper tissue penetration. Current chemical methods of developing macrophage-sensing nanoparticles are complex, low yielding, and often result in unstable nanoparticles leading to decomposition. Our group developed a new technique consisting of ferumoxytol nanoparticle (FMX) and a unique lysine-fluorophore which was conjugated to the surface of the nanoparticle using EDCI chemistry. Our novel FMX nanoparticle formed microaggregates that were characterized by fluorescence and light scattering.  Fluorophores developed and used in our study include cyanine Cy-AL5 and Cy-AM7 and a newly developed Alexa Fluor 555 (AF555) fluorophore. We confirmed FMX-fluorophore labeling with UV-VIS spectroscopy designated by the respectable absorbances of several fluorophores. We also took nanoparticle diameter measurements to verify that this new nanoparticle is an acceptable candidate for in-vivo macrophage imaging.  Our preliminary results show that FMX nanoparticles illuminate macrophages on in vivo near-infrared fluorescence (NIRF) imaging and preferentially localize to macrophage-rich organs.

Fluorochrome-functionalized of feraheme for macrophage imaging in biological systems

ACS Spring 2022

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