Effects of nanoparticle size and surface charge on uptake into rat alveolar epithelial cells

Abstract

Physicochemical properties of nanoparticles, including size, composition and surface charge, are likely to affect nanoparticle interactions with biological cells/tissues. We reported previously that uptake of polystyrene nanoparticles (PNP) from apical fluid into primary cultured rat alveolar epithelial cell monolayers (RAECM) takes place in a manner dependent on exposure time and dose. Classical endocytosis pathways do not appear to play a role in the uptake of PNP, consistent with a ‘diffusional’ process. We also reported that autophagy is involved in cellular processing of PNP, in that accumulation of PNP in lysosomes occurs via autophagic flux. Lysosomal exocytosis of PNP (modulated by intracellular [Ca2+]), takes place in parallel with a slower ‘diffusional’ egress process. In this study, we investigated the effects of nanoparticle size and surface charge on uptake into RAECM grown on Anopore filters. RAECM were exposed apically to 80 μg/mL carboxylated or amidinated 20, 100 or 200 nm PNP (with near‐infrared fluorescent label) and intracellular [PNP] was monitored over 24 hr using live cell imaging. Results showed that intracellular [PNP] reached a plateau of ~0.6 mg/mL after ≥12 hr of apical exposure to both 20 nm carboxylated or amidinated [PNP] at 80 μg/mL. As PNP size increased from 20 to 100 to 200 nm, steady state intracellular [PNP] decreased from ~0.6 to ~0.3 to ~0.1 μg/mL, respectively, after ≥12 hr. These data indicate that, for RAECM, PNP uptake is strongly dependent on PNP size, while the role of surface charge appears to be less important. Additional factors (e.g., nanoparticle‐associated protein corona) might alter the charge effect. In general, understanding the role of physicochemical properties of nanoparticles in cellular interactions will lead to improved nanoparticle design for protection from cellular injury and approaches to therapeutic utilization in drug/gene delivery.Support or Funding InformationFunding: NIH; Hastings and Whittier Foundations.