The rapid proliferation of many different engineered nanomaterials (defined as materials designed and produced to have structural features with at least one dimension of 100 nanometers or less) presents a dilemma to regulators regarding hazard identification. The International Life Sciences Institute Research Foundation/Risk Science Institute convened an expert working group to develop a screening strategy for the hazard identification of engineered nanomaterials. The working group report presents theelementsof a screening strategy rather than a detailed testing protocol. Based on an evaluation of the limited data currently available, the report presents a broad data gathering strategy applicable to this early stage in the development of a risk assessment process for nanomaterials. Oral, dermal, inhalation, and injection routes of exposure are included recognizing that, depending on use patterns, exposure to nanomaterials may occur by any of these routes. The three key elements of the toxicity screening strategy are: Physicochemical Characteristics,In VitroAssays (cellular and non-cellular), andIn VivoAssays.There is a strong likelihood that biological activity of nanoparticles will depend on physicochemical parameters not routinely considered in toxicity screening studies. Physicochemical properties that may be important in understanding the toxic effects of test materials include particle size and size distribution, agglomeration state, shape, crystal structure, chemical composition, surface area, surface chemistry, surface charge, and porosity.In vitrotechniques allow specific biological and mechanistic pathways to be isolated and tested under controlled conditions, in ways that are not feasible inin vivotests. Tests are suggested for portal-of-entry toxicity for lungs, skin, and the mucosal membranes, and target organ toxicity for endothelium, blood, spleen, liver, nervous system, heart, and kidney. Non-cellular assessment of nanoparticle durability, protein interactions, complement activation, and pro-oxidant activity is also considered.Tier 1in vivoassays are proposed for pulmonary, oral, skin and injection exposures, and Tier 2 evaluations for pulmonary exposures are also proposed. Tier 1 evaluations include markers of inflammation, oxidant stress, and cell proliferation in portal-of-entry and selected remote organs and tissues. Tier 2 evaluations for pulmonary exposures could include deposition, translocation, and toxicokinetics and biopersistence studies; effects of multiple exposures; potential effects on the reproductive system, placenta, and fetus; alternative animal models; and mechanistic studies.

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Due to the superior photoemission and photostability characteristics, quantum dots (QD) are novel tools in biological and medical applications. However, the toxicity and mechanism of QD uptake are poorly understood. QD nanoparticles with an emission wavelength of 655 nm are ellipsoid in shape and consist of a cadmium/selenide core with a zinc sulfide shell. We have shown that QD with a carboxylic acid surface coating were recognized by lipid rafts but not by clathrin or caveolae in human epidermal keratinocytes (HEKs). QD were internalized into early endosomes and then transferred to late endosomes or lysosomes. In addition, 24 endocytic interfering agents were used to investigate the mechanism by which QD enter cells. Our results showed that QD endocytic pathways are primarily regulated by the G-protein–coupled receptor associated pathway and low density lipoprotein receptor/scavenger receptor, whereas other endocytic interfering agents may play a role but with less of an inhibitory effect. Lastly, low toxicity of QD was shown with the 20nM dose in HEK at 48 h but not at 24 h by the live/dead cell assay. QD induced more actin filaments formation in the cytoplasm, which is different from the actin depolymerization by cadmium. These findings provide insight into the specific mechanism of QD nanoparticle uptake in cells. The surface coating, size, and charge of QD nanoparticles are important parameters in determining how nanoparticle uptake occurs in mammalian cells for cancer diagnosis and treatment, and drug delivery.

Skin is the largest organ of the body and is a potential route of exposure to engineered nanomaterials, but the permeability of the skin to these nanomaterials is unknown. We selected commercially available quantum dots (QD) of two core/shell sizes and shapes and three different surface coatings to determine if QD could penetrate intact skin in a size- or coating-dependent manner. Spherical 4.6 nm core/shell diameter QD 565 and ellipsoid 12 nm (major axis) by 6 nm (minor axis) core/shell diameter QD 655 with neutral (polyethylene glycol), anionic (carboxylic acids) or cationic (polyethylene glycol-amine) coatings were topically applied to porcine skin in flow-through diffusion cells at an occupationally relevant dose for 8 h and 24 h. Confocal microscopy revealed that spherical QD 565 of each surface coating penetrated the stratum corneum and localized within the epidermal and dermal layers by 8 h. Similarly, polyethylene glycol– and polyethylene glycol-amine–coated ellipsoid QD 655 localized within the epidermal layers by 8 h. No penetration of carboxylic acid–coated QD 655 was evident until 24 h, at which time localization in the epidermal layers was observed. This study showed that quantum dots of different sizes, shapes, and surface coatings can penetrate intact skin at an occupationally relevant dose within the span of an average-length work day. These results suggest that skin is surprisingly permeable to nanomaterials with diverse physicochemical properties and may serve as a portal of entry for localized, and possibly systemic, exposure of humans to QD and other engineered nanoscale materials.