Protein binding modulates the cellular uptake of silver nanoparticles into human cells: implications for in vitro to in vivo extrapolations?

Nanoparticles (NP) absorbed in the body will come in contact with blood proteins and form NP/protein complexes termed protein coronas, which may modulate NP cellular uptake. This study quantitated human epidermal keratinocyte (HEK) uptake of silver (Ag) NP complexed to different human serum proteins. Prior to HEK dosing, AgNP (20nm and 110nm citrate BioPure™; 40nm and 120nm silica-coated) were preincubated for 2h at 37°C without (control) or with physiological levels of albumin (44mg/ml), IgG (14.5mg/ml) or transferrin (3mg/ml) to form protein-complexed NP. HEK were exposed to the protein incubated AgNP for 3h, rinsed and incubated for 24h, rinsed in buffer and lysed. Ag was assayed by inductively-coupled plasma optical emission spectrometry. Uptake of Ag in HEK was <4.1% of applied dose with proteins suppressing citrate, but not silica coated Ag uptake. IgG exposure dramatically reduced 110nm citrate AgNP uptake. In contrast, greatest uptake of 20nm silica AgNP was seen with IgG, while 110nm silica AgNP showed minimal protein effects. Electron microscopy confirmed cellular uptake of all NP but showed differences in the appearance and agglomeration state of the NP within HEK vacuoles. This work suggests that NP association with different serum proteins, purportedly forming different protein coronas, significantly modulates Ag uptake into HEK compared to native NP uptake, suggesting caution in extrapolating in vitro uptake data to predict behavior in vivo where the nature of the protein corona may determine patterns of cellular uptake, and thus biodistribution, biological activity and toxicity.