Isomeric Differences in Nanoparticle's Surface Chemistry Alter Macrophage Interactions In Vitro Due to Protein Corona

The interactions of nanoparticles (NPs) with macrophages after intravenous injection are critical in determining their biodistribution and pharmacokinetics. The formation of protein corona (PC) on the nanoparticles, often a result of NP-plasma protein interactions, influences macrophage response, thereby directly determining the NPs' fate in vivo. While the effect of NPs' surface chemistry on protein corona formation and macrophage interaction is extensively studied, the results are often confounded by the effects of surface charge and hydrophobicity. Therefore, to assess the impact of NPs' surface chemistry alone on protein corona and NP-macrophage interactions, we developed gold (Au) NPs surface-modified with the isomeric amino acids leucine (Leu) and isoleucine (Iso Leu), which have similar isoelectric points and hydropathy indices. The synthesized NPs had similar sizes, zeta potentials, hydrophobicities, and morphology. Incubation of the NPs in plasma under flow conditions resulted in a protein corona (PC) that differed in amount and composition. Pathway analysis showed that these variations in the PC corresponded to the activation of different phagocytic and inflammatory pathways. These in silico analyses were confirmed in macrophages, which showed higher uptake of the Leu-AuNP-PC complex compared to Iso Leu-AuNP-PC and a corresponding increase in inflammatory cytokines. These studies demonstrate the sensitivity of the PC to subtle changes in the surface chemistry of NPs, which could have significant in vivo implications for the clinical application of NPs.