Particokinetics In Vitro: Dosimetry Considerations for In Vitro Nanoparticle Toxicity Assessments

Abstract

The rapid growth in the use of in vitro methods for nanoparticle toxicity assessment has proceeded with limited consideration of the unique kinetics of these materials in solution. Particles in general and nanoparticles specifically, diffuse, settle, and agglomerate in cell culture media as a function of systemic and particle properties: media density and viscosity and particle size, shape, charge and density, for example. Cellular dose then is also a function of these factors as they determine the rate of transport of nanoparticles to cells in culture. Here we develop and apply the principles of dosimetry in vitro and outline an approach for simulation of nanoparticle particokinetics in cell culture systems. We illustrate that where equal mass concentrations (mug/ml) imply equal doses for dissimilar materials, the corresponding particle number or surface area concentration doses differ by orders of magnitude. More importantly, when rates of diffusional and gravitational particle delivery are accounted for, trends and magnitude of the cellular dose as a function of particle size and density differ significantly from those implied by "concentration" doses. For example, 15-nm silver nanoparticles appear approximately 4000 times more potent than micron-sized cadmium oxide particles on a cm(2)/ml media basis, but are only approximately 50 times more potent when differences in delivery to adherent cells are considered. We conclude that simple surrogates of dose can cause significant misinterpretation of response and uptake data for nanoparticles in vitro. Incorporating particokinetics and principles of dosimetry would significantly improve the basis for nanoparticle toxicity assessment, increasing the predictive power and scalability of such assays.

Assessing nanoparticle toxicity in cell-based assays: influence of cell culture parameters and optimized models for bridging the in vitro–in vivo gap

“…This can affect the agglomeration or aggregation state of the NP, which determines its behaviour in dispersion and subsequently the uptake and toxicity induced by the NP either in a positive or negative way 116,117 . Therefore some groups have focussed on the development of methods to create a stable and uniform dispersion via surface modification, addition of surfactants etc.…”

“…In first instance it was assumed that this also applied to NP, as they were thought to be evenly dispersed by Brownian motion 35 . But this appeared not to be true since NP in dispersion are not only subject to diffusion but also to sedimentation and agglomeration 116 . Therefore the concept of dose is more complex and dynamic for NP as it is for chemicals.…”

“…Therefore the concept of dose is more complex and dynamic for NP as it is for chemicals. To address this issue Teeguarden et al developed the concept of particokinetics to model the NP behaviour in dispersion based on its likelihood to diffuse, sediment and agglomerate in dispersion 116,131 . Since both diffusion and sedimentation are influenced by agglomeration, the latter is expected to have a major impact on the NP uptake and toxicity 169 .…”

“…Brown et al for example found that nanorods and -fibres agglomerate more easily than spheres and Limbach et al saw a higher agglomeration rate for smaller NP in comparison to their larger counterparts at similar mass doses, which was explained by the higher number density 172,173 . This is of course also related to the concentration, which is another important factor as it is known that NP tend to agglomerate at higher concentrations 116 175,176 . Still, it can be concluded that NP agglomeration can either be promoted or mitigated depending on the medium composition 176 .…”

The dose makes the poison

“…However, unlike the soluble chemicals tested in traditional toxicology studies, nanoparticles have shapes and surface areas, and they can diffuse, aggregate/agglomerate and sediment according to their size, density and physical and chemical properties in solution. This means that traditional in vitro assays may misrepresent the response and cellular-uptake data for nanoparticles, making the test results less comparable across particle types than for soluble chemicals 4 …”