(592c) Differential Distribution and Toxicity of Nanomaterials in Vivo

Industrial and scientific communities must work together to integrate toxicological and safety evaluations into nanomaterial research and development schemes so that actual risks of nanomaterials are defined and adverse environmental consequences are minimized. Nanotechnology is most likely to gain society acceptance if environmental and human health considerations are thoroughly investigated and those results are used to optimize safety and performance together to produce effective and non-toxic profitable technologies. It is expected that nano-scale materials will interact differently than their bulk counterpart within biological systems since their properties and attributes (i.e. magnetic, optical, tensile strength) appear to be unique to their size. It is unknown if any generalizations can be made about the toxicity of nano-scale materials on the basis of structural characteristics, physicochemical properties and/or features of the bulk materials. This enormous gap in nanoparticle toxicological data dictates the need for the characterization of nanoparticle uptake, distribution and effects in integrated biological systems.

The biological activity of nanomaterials will likely depend on inherent physicochemical properties not routinely considered in toxicity studies (e.g. particle size and size distribution, agglomeration status, interactions with environmental and biological moieties). It is therefore important that chemical engineers work together with toxicologists to provide critical information on the potential biological and environmental impacts of the newly emerging nanotechnology industry. A classical toxicokinetic approach would use well-defined, radio-labeled nanomaterials to define each of the above parameters prior to toxicity evaluations. Although this approach is solid, it is perhaps not the most efficient way to assess toxicity of the ever-growing number of novel nanomaterials. It is clear that there is a need to develop rapid, relevant and efficient testing strategies to assess these emerging materials of concern.

Here we present an alternative approach that utilizes a dynamic whole animal (in vivo) assay to reveal whether a nanomaterial is potentially toxic at multiple levels of biological organization (i.e. molecular, cellular, systems, organismal). Early developmental life stages are often uniquely sensitive to environmental insult, due in part to the enormous changes in cellular differentiation, proliferation and migration required to form the required cell types, tissues and organs. Molecular signaling underlies all of these processes. Most toxic responses result from disruption of proper molecular signaling, thus, early developmental life stages are perhaps the ideal life stage to determine if chemicals or nanomaterials are toxic. Therefore, the embryonic zebrafish model was chosen to investigate nanomaterial biological activity and toxic potential. Zebrafish embryos have been successfully used as an in vivo model organism for evaluating integrated system effects because: 1) zebrafish are vertebrates that share many cellular, anatomical and physiological characteristics with higher vertebrates, 2) numerous effects can be assessed visually (non-invasive) over the course of development due to the transparent nature of the embryos; 3) embryos develop rapidly with most body organs formed by 48 hours post-fertilization (hpf) so developmental endpoints can be evaluated promptly; 4) females produce hundreds of eggs weekly so large sample sizes are easily achieved for statistically powerful dose-response studies; and 5) many routes of exposure (i.e. ingestion, injection and dermal) can be assessed individually or in combination.

Our working hypothesis is that the inherent properties of some engineered nanomaterials make them potentially toxic. We used the embryonic zebrafish toxicity assay to define in vivo responses to nanomaterials in order to identify the physicochemical properties that lead to adverse biological consequences. Our results indicate that the embryonic zebrafish model is well-suited to rapidly evaluate for potential toxicity of engineered nanomaterials. We will present data on the differential toxicity of commercially available metal oxides (aluminum oxide, titanium (IV) oxide, zirconium (IV) oxide, cerium (IV) oxide, gadolinium (III) oxide, dysprosium (III) oxide, yttrium (III) oxide, homium (III) oxide, samarium (III) oxide, silicon dioxide, alumina doped, and erbium (III) oxide) and fullerenes (C₇₀, C₆₀, and hydroxylated C₆₀). The disposition of fluorescent nanomaterials (Qdots and FluoSphere®) determined using the embryonic zebrafish assay was dependent on surface functionalization (amino-polyethylene glycol, carboxyl, organic, sulfate, aldehyde-sulfate) and route of administration (oral, injection, dermal).