ABSTRACT
The development of accurate in vitro screening assays to assess lung hazard potential of nanomaterials is a highly desirable goal. However, some studies have noted little correlation between in vitro and in vivo results. Moreover, a recent National Academy of Sciences report predicts that future hazard testing will be conducted primarily using cell culture assays. The three major objectives of this study were to compare lung toxicity impacts of nanoscale (NZnO) vs fine zinc oxide (FZnO) particulates, assess predictability of in vitro cell culture systems, and compare effects of instillation vs inhalation exposures in rats. Physicochemical aspects of ZnO particle types were rigorously characterized and did not agree with specifications provided by the supplier; i.e., the ZnO particle types were closer in size than advertised. Rats were exposed in vivo either by intratracheal instillation to 1 or 5 mg/kg of nanoscale or fine size zinc oxide particle types or by inhalation to aerosols of 25 or 50 mg/m3 for 1 or 3 h. Lung inflammation, cytotoxicity, and histopathological endpoints were assessed at several time points postexposure. Three different in vitro culture conditions were utilized. Cultures of (1) rat lung epithelial cells, (2) primary alveolar macrophages, and (3) alveolar macrophages-L2 lung epithelial cell cocultures were incubated with fine or nano ZnO particles and evaluated for cytotoxicity biomarkers (LDH) and proinflammatory cytokines (MIP-2 and TNF-alpha). In vivo exposures to instilled or inhaled fine or nanoscale ZnO produced "metal fume fever" responses, characterized by transient short-term lung inflammatory or cytotoxic responses. Alternatively, in vitro exposures to fine or nanoscale ZnO particles produced minor cytotoxic responses at 4 and 24 h, only in cocultures and at the highest (particle overload) dose with little detectable proinflammatory cytokine generation (MIP-2, and TNF-alpha). To summarize, the comparisons of in vivo and in vitro toxicity measurements following nano or fine ZnO particle exposures demonstrated little convergence and few differences in potency.
Subject(s)
Inhalation Exposure , Lung/drug effects , Nanoparticles/toxicity , Toxicity Tests/methods , Zinc Oxide/toxicity , Animals , Bronchoalveolar Lavage Fluid/chemistry , Bronchoalveolar Lavage Fluid/immunology , Cell Line , Lung/pathology , Male , Nanoparticles/administration & dosage , Rats , Zinc Oxide/administration & dosageABSTRACT
Upon contact with water, under a variety of conditions, C60 spontaneously forms a stable aggregate with nanoscale dimensions (d = 25-500 nm), termed here "nano-C60". The color, hydrophobicity, and reactivity of individual C60 are substantially altered in this aggregate form. Herein, we provide conclusive lines of evidence demonstrating that in solution these aggregates are crystalline in order and remain as underivatized C60 throughout the formation/stabilization process that can later be chemically reversed. Particle size can be affected by formation parameters such as rates and the pH of the water addition. Once formed, nano-C60 remains stable in solution at or below ionic strengths of 0.05 I for months. In addition to demonstrating aggregate formation and stability over a wide range of conditions, results suggest that prokaryotic exposure to nano-C60 at relatively low concentrations is inhibitory, indicated by lack of growth (> or = 0.4 ppm) and decreased aerobic respiration rates (4 ppm). This work demonstrates the fact that the environmental fate, distribution, and biological risk associated with this important class of engineered nanomaterials will require a model that addresses not only the properties of bulk C60 but also that of the aggregate form generated in aqueous media.
