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 (<i>N</i>_v) 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 <i>N</i>_v 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, <i>N</i>_v, and PS in engineering erythrocyte-derived particles for future clinical applications.