The in vitro methods used to test nanomaterials very much depend on the context they are being tested in, for example for regulatory purposes or as part of research, but also the tissue and endpoint of interest. Testing for regulatory purposes such as within chemical regulation (i.e. REACH regulation within the EU) or cosmetics regulation is very much prescribed and requires the following of set guidelines such as those developed by the OECD. Taking REACH as an example, there are a limited number of in vitro based OECD test guidelines including those addressing dermal effects such as irritation (OECD TG 439), corrosion (OECD TG 430/431) or phototoxicity (TG 432) as well as more generic tests such as the micronucleus test for genotoxicity (TG 487). A key challenge with in vitro test methods, especially within the regulatory context, which requires a high degree of reproducibility and rigour, is that the complexity of multicellular biological interactions can be difficult to reproduce in simplified cellular models. This is why despite the advancement in in vitro technology; animal testing in many regulatory settings has not been fully replaced.
In relation to the research setting, the range of testing approaches within in vitro toxicology is very wide but again, focused on tissue (e.g. lung or skin) of concern as well as the endpoint(s), such as inflammation, genotoxicity etc. Common in vitro test systems for the lung involve the use of single cell models such as lung epithelial cells representative of the gas exchange region or macrophages, which are mobile cells that clear deposited particles and debris from the deep lung. Within these cells typical endpoints to be addressed would be cell death (cytotoxicity), secretion of cytokines and chemokines that indicate an inflammatory reaction, oxidative stress and damage as well as genetic damage that could indicate the potential for cancer. When looking at dermal toxicity, skin cell such as keratinocytes may be used yet whilst looking at liver toxicity, liver cells (hepatocytes) would be the most relevant models and each target such as the brain, gut kidney etc. have relevant cell models.
Organs consist not just of one cell type, but many cell types which interact and communicate locally as well with other cells and systems elsewhere in the body as part of normal function and when reacting to a damaging substance. For this reason, multi-cell models are also used which may include growing two or more relevant cell types in the same environment (co-culture) or may involve the use of complex reconstructed tissues such as EpiDerm which is a 3D model of human skin tissue.
As part of our range of services, SAFENANO can perform benchmarked in vitro toxicology studies for inhalation, dermal, and ingestion exposure . For further information, please visit our service page or contact us.