This grant proposes to address whether manufactured nanoparticles can gain access to the epidermis after topical exposure, the first step in a toxicological reaction. Exposure to metallic nanoparticles, whose physical properties would allow them to catalyze a number of biomolecular interactions, potentially could produce adverse toxicological effects. The difference between nanoparticles and ?traditional? hazardous chemical exposure is that decontamination of nanoparticles would be significantly more difficult than chemicals since solubilization or dilution, the two hallmarks of post-exposure decontamination, might be less efficacious for these solid structures.
The focus of this research is to assess the nature of interaction between manufactured nanoparticles and the skin; including dermal absorption, cutaneous toxicity as well as the ability to distribute to the skin after systemic exposure. The skin is a primary route of potential exposure to toxicants including novel nanoparticles. However, there is no information on whether particles are absorbed across the stratum corneum barrier or whether systemically administered particles can accumulate in dermal tissue. Our laboratory has developed a well validated humane alternative animal model that is predictive of in vivo human dermal absorption that is ideally suited to assess both the dermal absorption of nanoparticles as well as there potential accumulation in skin after systemic exposure. These studies will utilize iron oxide nanocrystals, cadmium selenide nanocrystals and carbon fullerene nanoparticles which are representative of the broad spectrum of nanoparticles presently being used by industry. Eight particle types selected from these commercially relevant manufactured nanoparticles will be studied to allow assessment of size, shape and composition on absorption, distribution or toxicity to the skin. These data would provide a preliminary but relevant assessment of both systemic exposure after topical administration as well as cutaneous hazard after both topical or systemic exposure, the two essential components of any risk assessment. We postulate that should carbon nanoparticles be accidentally modified or if exposure occurs before cleansing, they could have untoward consequences if they gain entry to tissues.
All studies will be conducted in three well characterized in vitro skin models: human skin keratinocyte cell cultures, porcine skin flow-through diffusion cells, and the isolated perfused porcine skin flap (IPPSF). Nanoparticles will be applied topically in three exposure scenarios (neat, water, mineral oil) at two doses to assess potential dermal absorption in the diffusion cell studies and to assess cellular toxicity (light and electron microscopy, viability) and irritation (IL-8 release) in cell culture. Those particles which penetrate skin or cause direct irritation will then be completely characterized in IPPSF studies which have previously been shown to be predictive of in vivo absorption in humans. Similarly, to model nanoparticle uptake into skin after systemic exposure, nanoparticles will be infused into the arterial blood supply of the IPPSF to assess ability to distribute out of the vasculature into the skin. Deposition of particles in epidermal tissue after both infusion and topical exposure will be evaluated using high-resolution electron microscopy.
Presently, there are minimal data available on the interaction between manufactured nanoparticles and biological tissues. The basic requirement for any risk assessment includes information on hazard (e.g. toxicity) and exposure (e.g. absorption). This proposal focuses on the health effects of nanoparticle interactions with the skin. This integrated research program will generate data on the ability of nanoparticles to be toxic to keratinocytes as well as assess the ability of nanoparticles to either be absorbed into skin after topical exposure, or distribute into skin as would occur after systemic exposure by an alternate route of administration. At the conclusion of the research, the boundaries of a dermal risk assessment for manufactured nanoparticle exposure will be available.
