Towards an alternative testing strategy for nanomaterials used in nanomedicine: lessons from NanoTEST.

In spite of recent advances in describing the health outcomes of exposure to nanoparticles (NPs), it still remains unclear how exactly NPs interact with their cellular targets. Size, surface, mass, geometry, and composition may all play a beneficial role as well as causing toxicity. Concerns of scientists, politicians and the public about potential health hazards associated with NPs need to be answered. With the variety of exposure routes available, there is potential for NPs to reach every organ in the body but we know little about the impact this might have. The main objective of the FP7 NanoTEST project ( www.nanotest-fp7.eu ) was a better understanding of mechanisms of interactions of NPs employed in nanomedicine with cells, tissues and organs and to address critical issues relating to toxicity testing especially with respect to alternatives to tests on animals. Here we describe an approach towards alternative testing strategies for hazard and risk assessment of nanomaterials, highlighting the adaptation of standard methods demanded by the special physicochemical features of nanomaterials and bioavailability studies. The work has assessed a broad range of toxicity tests, cell models and NP types and concentrations taking into account the inherent impact of NP properties and the effects of changes in experimental conditions using well-characterized NPs. The results of the studies have been used to generate recommendations for a suitable and robust testing strategy which can be applied to new medical NPs as they are developed.

Dichloro-dihydro-fluorescein diacetate (DCFH-DA) assay: a quantitative method for oxidative stress assessment of nanoparticle-treated cells.

No consensus exists on how to address possible toxicity of nanomaterials as they interfere with most in vitro screening tests based on colorimetric and fluorimetric probes such as the dichloro-dihydro-fluorescein diacetate (DCFH-DA) assay for detection of oxidative species. In the present research, nanomaterial interaction with DCFH-DA was studied in relation to its nature and/or assay conditions (cell-based and time exposure) by incubating Rhodamine (Rhd)-labeled 25nm and 50nm silica (SiO2), naked and oleic acid coated magnetite, (Fe3O4) and maghemite (Fe2O3) iron oxide, titanium dioxide (TiO2) and poly(ethylene oxide)-poly(lactide/glycolide) acid (PLGA-PEO) nanoparticles (NPs) with metabolically active rat hepatocytes for 4 and 24-h periods. Data indicated that nanoparticle uptake correlated with quenching of dye fluorescence emission. In spite of their masking effect, the oxidative potential of NPs could be detected at a limited threshold concentration when exposed for periods of time longer than those frequently used for this test. However, changes in the experimental conditions did not systematically result in free radical formation for all nanomaterials tested. Overall data indicate that despite the quenching effect of nanoparticles on DCFH-DA assay, it can be considered as a useful tool for quantitative measurement of NPs-induced oxidative stress by minor modifications of standardized protocols.