Nanomaterial-Induced Extra-Pulmonary Health Effects - the Importance of Next Generation Physiologically Relevant In Vitro Test Systems for the Future of Nanotoxicology.

Manufactured nanomaterials (NMs) offer incredible scientific and societal benefits but their potential hazard to human health is not yet fully comprehended. In the last decade, a significant body of evidence indicates that certain NMs are capable of translocating from the primary exposure site (skin, lungs and gastrointestinal tract) to a number of secondary organs which includes the liver. Moreover, recent advances in the field of nanomedicine has resulted in increasing direct intravenous injection of NMs with the liver being a particularly important organ with regards to potential toxic effects and accumulation of said materials. It is generally acknowledged that it is not always possible to make direct or meaningful comparisons between in vitro and in vivo xenobiotic-induced toxicological responses. One of the main reasons for the lack of comparability between the testing strategies is that biological responses are not often alike which can in part be attributed to the numerous limitations of traditional mono-cellular in vitro test systems which are acting as a surrogate for a whole organ. In an attempt to address and highlight this important issue, this chapter will discuss the progress made in the production and validation oof next generation more physiologically relevant multi-cellular in vitro models of skin, GIT and the liver utilised for the assessment of the NM-induced toxicological effects.

Density-dependent location and interactions of truncated APC and beta-catenin.

Adenomatous polyposis coli (APC) is a multifunctional tumour suppressor protein, central to development and the mature organism. It is mutated in most cases of colorectal cancer, rendering it ineffective in mediating beta-catenin degradation. We show that localization of full-length APC in colon carcinoma and noncancer cell lines is independent of cell density. However, the location of truncated APC is a function of cell density and in high-density cells truncated APC is predominantly not nuclear. Although the distribution of truncated APC and beta-catenin is closely linked in subconfluent SW480 cells, at high cell density they are not colocalized. We postulated that in this cell line this could be due to an increase in beta-catenin bound to E-cadherin with formation of adherens junctions at high cell density. However, while in coimmunoprecipitation assays we observe an increase in binding between beta-catenin and E-cadherin and a corresponding decrease in binding between beta-catenin and APC at high cell density, we did not observe a strict colocalization of beta-catenin and E-cadherin at the membrane of all cells.