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NANOSIZE TITANIA STIMULATES REACTIVE OXYGEN SPECIES IN BRAIN MICROGLIA AND DAMAGES NEURONS.
Citation:
LONG, T., P. SAMA, N. SALEH, J. PARKER, C. SWARTZ, G. V. LOWRY, AND B. VERONESI. NANOSIZE TITANIA STIMULATES REACTIVE OXYGEN SPECIES IN BRAIN MICROGLIA AND DAMAGES NEURONS. Presented at 11th International Conference on Ti02 Photocatalysis, Pittsburgh, PA, September 26 - 29, 2006.
Description:
Research that addresses the environmental impact and biological consequences of widely distributed, commonly used nanoparticles is needed. Nanosize titanium dioxide (i.e., titania, TiO2) is used in air and water remediation and in numerous products designed for direct human use and consumption. Its effectiveness in deactivating pollutants and killing microorganisms relates to photo-activation and the resulting free radical activity. This property and its multiple potential exposure routes, suggest that nanosize titania could pose a risk to biological targets that are sensitive to oxidative stress damage (e.g., brain). In this study, immortalized rodent brain microglia (BV2), dopaminergic neurons (N27) and co-cultures of BV2+N27 were exposed to physicochemically characterized (i.e., dispersion stability, particle size distribution, zeta potential) Degussa P25. Universal microarrays and various fluorescent probes were used to measure reactive oxygen species (ROS) in the microglia and membrane leakage, intracellular ATP levels, and apoptosis in the neurons. Light and electron microscopy documented the engulfment of the titania by the microglia. P25 aggregation was rapid and concentration-dependent, with the hydrodynamic diameter of stable aggregates ranging from 826 to 2368 nm in size. BV2 microglia responded to non-cytotoxic (2.5-120 ppm) concentrations of P25 with a rapid (<5 min) and sustained (120 min) release of ROS. Microarray analysis of RNA taken from 2-hr exposed microglia indicated that numerous apoptotic and oxidative stress pathways were affected. Light microscopy and transmission electron microscopy indicated that small groups of nanosized particles and micron-sized aggregates were engulfed by the microglia and sequestered as intra-cytoplasmic aggregates after 1 and 6 hr exposure to P25 (2.5 ppm). Isolated mesencephalic neurons and those co-cultured with microglia both showed loss of intra-cellular ATP within 24 hr exposure to concentrations >20 ppm. Leakage of their cellular membrane occurred in both isolated neurons and co-cultures after 24 hr in concentrations >20 ppm. The data confirm and extend our earlier in vitro findings that mouse microglia respond to Degussa P25 with cellular and morphological expressions of ROS formation. These data also indicate that P25 reduces intracellular ATP levels and damages the cell membrane of Dopaminergic neurons. These latter findings will be re-examined in more integrated culture systems and ultimately animals before P25 can be considered neurotoxic. DISCLAIMER: This abstract has been reviewed by the NHEERL of the EPA and approved for publication. Approval does not signify that the contents reflect the views of the Agency, nor does mention of trade names or commercial products constitute the endorsement of recommendation for use.