Effects of O+ and a Non-O+ Blood Type, Number Concentration, and Membrane Phosphatidylserine Flipping on the Circulation Dynamics and Biodistribution of Microsized Erythrocyte-Derived Optical Particles in Mice.

Erythrocyte-derived microparticles containing near-infrared (NIR) dyes such as indocyanine green present a promising cell-based platform for optical imaging and phototherapeutics. Using real-time intravital NIR fluorescence imaging of mice vasculature, we investigated the effects of blood type, specifically O+ and B+, used in fabricating these particles, the number concentration (Nv) of the particles, and the relocalization of phosphatidylserine (PS) to the outer leaflet of the particles' membrane on the resulting circulation dynamics following a single retro-orbital injection. Additionally, we quantified the biodistribution of particles in various organs. We found that the fluorescence emission half-life for particles engineered from O+ blood type extended from 11.4 ± 3.0 to 43.1 ± 9.6 min with increased Nv from a low range of 0.4-0.6 to high range of 1.4-1.6 million particles/per μL, when only 30-55% of the particles demonstrated externalized PS. For these particles, the liver and gallbladder, lungs, and spleen showed similar levels of accumulation at 60 min post administration. When >90% of O+-particles showed PS externalization, or when the particles were fabricated from B+ blood type despite PS externalization in 30-55% of the particles, the emission half-life was reduced to 15.8 ± 5.9 and 18.1 ± 4.6 min, respectively. There was lower accumulation of these particles in the spleen as compared to the liver and gallbladder and the lungs. In vitro experiments demonstrated increased PS externalization correlated to a more efficient uptake of the particles by macrophages. These findings emphasize the importance of blood type, Nv, and PS in engineering erythrocyte-derived particles for future clinical applications.