Biological Sciences Division, Pacific Northwest National Laboratory, Richland WA 99352, USA.
Part Fibre Toxicol. 2010 Nov 30;7(1):36. doi: 10.1186/1743-8977-7-36.
The difficulty of directly measuring cellular dose is a significant obstacle to application of target tissue dosimetry for nanoparticle and microparticle toxicity assessment, particularly for in vitro systems. As a consequence, the target tissue paradigm for dosimetry and hazard assessment of nanoparticles has largely been ignored in favor of using metrics of exposure (e.g. μg particle/mL culture medium, particle surface area/mL, particle number/mL). We have developed a computational model of solution particokinetics (sedimentation, diffusion) and dosimetry for non-interacting spherical particles and their agglomerates in monolayer cell culture systems. Particle transport to cells is calculated by simultaneous solution of Stokes Law (sedimentation) and the Stokes-Einstein equation (diffusion).
The In vitro Sedimentation, Diffusion and Dosimetry model (ISDD) was tested against measured transport rates or cellular doses for multiple sizes of polystyrene spheres (20-1100 nm), 35 nm amorphous silica, and large agglomerates of 30 nm iron oxide particles. Overall, without adjusting any parameters, model predicted cellular doses were in close agreement with the experimental data, differing from as little as 5% to as much as three-fold, but in most cases approximately two-fold, within the limits of the accuracy of the measurement systems. Applying the model, we generalize the effects of particle size, particle density, agglomeration state and agglomerate characteristics on target cell dosimetry in vitro.
Our results confirm our hypothesis that for liquid-based in vitro systems, the dose-rates and target cell doses for all particles are not equal; they can vary significantly, in direct contrast to the assumption of dose-equivalency implicit in the use of mass-based media concentrations as metrics of exposure for dose-response assessment. The difference between equivalent nominal media concentration exposures on a μg/mL basis and target cell doses on a particle surface area or number basis can be as high as three to six orders of magnitude. As a consequence, in vitro hazard assessments utilizing mass-based exposure metrics have inherently high errors where particle number or surface areas target cells doses are believed to drive response. The gold standard for particle dosimetry for in vitro nanotoxicology studies should be direct experimental measurement of the cellular content of the studied particle. However, where such measurements are impractical, unfeasible, and before such measurements become common, particle dosimetry models such as ISDD provide a valuable, immediately useful alternative, and eventually, an adjunct to such measurements.
直接测量细胞剂量的难度是应用目标组织剂量学评估纳米颗粒和微颗粒毒性的一个重大障碍，尤其是对于体外系统。因此，纳米颗粒剂量学和危害评估的目标组织范式在很大程度上被忽视，转而使用暴露度量（例如，培养介质中的μg 颗粒/mL、颗粒表面积/mL、颗粒数量/mL）。我们已经开发了一种用于非相互作用球形颗粒及其在单层细胞培养系统中的团聚体的溶液颗粒动力学（沉降、扩散）和剂量学的计算模型。通过同时求解斯托克斯定律（沉降）和斯托克斯-爱因斯坦方程（扩散）来计算颗粒向细胞的迁移。
体外沉降、扩散和剂量模型（ISDD）经过多次聚苯乙烯球（20-1100nm）、35nm 无定形二氧化硅和 30nm 氧化铁颗粒的大团聚体的测量迁移率或细胞剂量进行了测试。总体而言，在不调整任何参数的情况下，模型预测的细胞剂量与实验数据非常吻合，差异最小为 5%，最大为三倍，但在大多数情况下约为两倍，在测量系统的精度范围内。应用该模型，我们概括了粒径、颗粒密度、团聚状态和团聚体特征对体外靶细胞剂量的影响。
我们的结果证实了我们的假设，即在基于液体的体外系统中，所有颗粒的剂量率和靶细胞剂量并不相等；它们可以有很大的差异，这与使用基于质量的介质浓度作为剂量反应评估的暴露度量所隐含的等效剂量假设直接相反。基于 μg/mL 的等效名义介质浓度暴露与基于颗粒表面积或数量的靶细胞剂量之间的差异高达三个到六个数量级。因此，在基于质量的暴露度量被认为会驱动反应的情况下，利用体外暴露度量进行的危害评估固有地存在很大误差。体外纳米毒理学研究中颗粒剂量的金标准应该是对所研究颗粒的细胞内容物进行直接实验测量。然而，在这种测量不切实际、不可行的情况下，并且在这种测量变得普遍之前，像 ISDD 这样的颗粒剂量模型提供了一种有价值的、立即有用的替代方法，并最终成为这种测量的辅助手段。
