In vitro methods Clause Samples

In vitro methods. When performing risk assessment mostly based on in vitro test results, in vitro to in vivo extrapolation (IVIVE) shall be performed. One of the essential aspects of IVIVE is kinetic information. In vitro tests generally do not consider the kinetics of a body as animal tests do: the absorption in the gut, for example, is not considered in an in vitro test with liver cells. Thus, in vitro test results must be supplemented with kinetic data using kinetic models to enable IVIVE. This approach is valid for non-nano (molecular) substances and there is no reason why this general approach should not be valid for NMs as well. Some NMs can dissolve into the molecular or ionic form. As a result, such NMs essentially lose their nanoparticle properties and can be dealt with using the same approach applied to the non- nano (molecular) substances. For the NMs that do not dissolve (and are thus durable), there is a high potential for accumulation as no other elimination pathways are currently known besides dissolution. In case of accumulation of molecular substances and NMs, the accurate determination of the kinetics becomes of greater importance for the correct estimation of human health risk as an extrapolation over time needs to be made. Even though kinetic information in general is just as important for molecular substances as for NMs, the type of kinetic information that is necessary differs (Table 3.8). Available kinetic studies generally demonstrate a distribution pattern for nanoparticles that differs from molecular substances. Particles tend to disappear from the blood very rapidly and distribute to liver, spleen, and to a lesser extent to lung and testis (▇.▇. ▇▇▇▇▇▇▇ et al. 2014, van ▇▇▇▇▇▇▇▇ et al. 2014). It is remarked that comparisons between molecular substances and nanoforms are not always possible as some of the most widely used nanoparticles are not available in molecular form. A few PBPK- models23 for nanoparticles have been published based on the paradigm that the distribution is not a diffusion-driven process (as for most organic molecular substances) but a process governed by the active uptake of the nanoparticles by macrophages (▇.▇. ▇▇▇▇▇▇▇ et al. 2015, ▇▇▇▇▇▇▇▇▇ et al. 2016, ▇▇▇ et al. 2016). This implies that sampling plasma is not suitable to monitor nanoparticle exposure and kinetics. Kinetic parameters important for IVIVE with NMs are: • Dissolution rate in the various surroundings (including in macrophages); • Protein corona composition and s...