Improved Methods for Nanoparticle Toxicity Research
Work will lead to more accurate, more interpretable tests of potential health hazards
Results: Researchers at Pacific Northwest National Laboratory (PNNL) are working to improve the basis for in vitro laboratory assessment of nanoparticle toxicity. To understand nanotoxicity, an accurate understanding of the dose to cells is first required. The PNNL team introduced the concept of cellular dose in vitro as an important metric. Their results, which appeared as the cover story in the February 2007 issue of Toxicological Sciences, included a review of experimental methods for measuring cellular dose in vitro and an outline for a computational approach to in vitro nanomaterial dosimetry.
Why it matters: Nanoparticles are particles of matter that measure less than 100 nanometers (a nanometer is one-billionth of a meter). They exhibit unique properties that have novel applications in a wide range of industries. However, nanomaterial researchers and manufacturers face an increasing concern from the governmental, environmental and industrial groups regarding the potential health hazards of nanoparticles. This will be addressed, in part, by providing rapid assessments using high-throughput, in vitro cell-based systems.
The factors and processes controlling cellular doses of nanoparticles are different than for chemicals. In solution, nanoparticles diffuse and settle according to their size and density, unlike chemicals. Varied total amounts of particles with different sizes and densities will therefore reach cells in the bottom of cell culture dishes used in these test systems. Thus, defining dose for nanoparticles in an in vitro system is more dynamic and complicated and less comparable across particle types than it is for chemicals. The researchers developed the principles that can be used to understand these processes and their affect on toxicity assessments.
Panel A shows that the dose for nanoparticles in vitro increases in specificity and relevancy as dose measures move from administered amount to amount delivered to cells or internalized by cells (SA, surface area; #, particle number). Panel B contains images that demonstrate the principles shown in A. An alveolar epithelial cell was grown in culture and exposed to fluorescence-tagged 500-nm amorphous silica particles. The cell membrane is marked (red) by a membrane-specific fluorescent marker that was also internalized over time as an integral part of endocytotic vesicles. The first image illustrates delivered dose: a silica particle (green) on the apical surface of the cell. In the second image, the particle is no longer visible as the focal plane moves into the interior of the cell. In the third image, silica particles taken up into the cell are observed as the focal plane moves farther into the interior of the cell. Enlarged View
Improving the basis for comparative dose-response analysis in vitro for nanoparticles by considering kinetics and applying the principle of target tissue dose (cellular dose in vitro) will impact research areas such as discovery of fundamental particle characteristics influencing toxicity and uptake, comparative nanoparticle toxicity, and the dynamics of cellular response to nanoparticles.
Methods: The researchers integrated aspects of material science, solution physics and kinetics to identify the factors and processes affecting the cellular dose for particles. The work improves the basis for in vitro assessment of nanoparticle toxicity by advancing the understanding of particle solution dynamics in cell culture media as they relate to dosimetry and dose-response assessment.
Next steps: The researchers are developing a computational model of particle kinetics and dosimetry that can be used to guide experimental design and interpret in vitro toxicity studies.
Source: Teeguarden JG, PM Hinderliter, G Orr, BD Thrall, and JG Pounds. 2007. "Particokinetics In Vitro: Dosimetry Considerations for In Vitro Nanoparticle Toxicity Assessments." Toxicological Sciences 95(2):300-312.
Funding and Research team: The research was conducted under PNNL's Environmental Biomarkers Initiative. The research team included Justin Teeguarden, Joel Pounds, Galya Orr, Paul Hinderliter and Brian Thrall.