Hazard Assessment and Risk Estimation of Inhaled Nanomaterials Exposure

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DESCRIPTION (provided by applicant): Engineered nanomaterials (ENM) have the potential to revolutionize every-day life due to unique properties that have led to advances in electronics, materials science, and drug delivery. Many types of ENM are produced by the metric ton per year and, thus, exposures in occupational and environmental settings are likely. The respiratory tract is a primary route of entry for ENM in such exposure settings. Recent in vitro and in vivo studies have demonstrated the ability of ENM to induce oxidative stress, inflammatory and profibrotic mediator release, and pathology. However, the long-term consequences of ENM exposures at realistic concentrations in humans are unclear because short-term testing is often done at unreasonably high doses and/or under unrealistic conditions. This project is aimed at characterizing risk from realistic human exposures to ENM. Research Plan: We hypothesize that inhaled ENM induce inflammation in the lungs through their oxidative stress-inducing potential that is related to their reactive surface properties and that the ensuing pulmonary inflammatory response enhances translocation to and effects in secondary target sites such as pleura and central nervous system. Furthermore, we hypothesize that rapid screening assays can be developed that are predictive of short- and long-term health outcomes if they are related to relevant mechanisms of toxicity at realistic doses. Our objectives are to assess the predictability of short-term acellular, cellular in vitro, and in vivo assays for long-term adverse health outcomes in the respiratory tract and to quantitate ENM translocation- related effects in secondary tissues following realistic inhalation exposure using a multidisciplinary tiered testing approach. The objectives to test the hypothesis will be met with four Specific Aims to: 1) evaluate workplace ENM exposures; 2) use acellular systems to assess the characteristics and oxidative reactivity of ENM; 3) compare pulmonary and secondary tissue responses to and biokinetics of ENM following single and repeated respiratory tract exposures in rats under realistic conditions using a novel aerosolization system; and 4) evaluate ENM dose-response relationships in cultured primary and secondary organ target cells using doses that are derived from in vivo biokinetics studies of inhaled ENM. Extensive correlation analyses will be done to test a new concept of a response metric that can be used to reliably compare outcome measures from different short-term tests. Expected Results: We expect that acellular and cellular assays of ENM activity will correlate with and be predictive of target cell inflammatory responses, lung inflammation, and secondary organ responses in vivo. These results, as well as information about exposure levels at workplaces and about the persistence of ENM in lung and secondary target tissues, can be used for preliminary risk estimations of the long-term adverse human health outcomes related to ENM exposure and as a basis for more extensive risk assessment. PUBLIC HEALTH RELEVANCE: The use of engineered nanomaterials (ENM) in consumer products has raised concerns about risks to human health following release into workplaces or the environment and some recent studies have described adverse outcomes following in vitro and in vivo exposures. We will conduct comprehensive studies - including workplace exposure characterizations, acellular ENM functional characterizations, in vitro tests of effects in cultured target cells, and in vivo effects and material distribution studies in rodents - to assess dose-related effects in the lung, pleura, and central nervous system following realistic inhalation exposures to ENM that are delivered in their native state without additional surface modifications. These results will be used to develop and validate short-term tests that can be used for estimating potential human risk following ENM exposure.