The cellular and genomic response of rat dopaminergic neurons (N27) to coated nanosilver.

This study examined if nanosilver (nanoAg) of different sizes and coatings were differentially toxic to oxidative stress-sensitive neurons. N27 rat dopaminergic neurons were exposed (0.5-5 ppm) to a set of nanoAg of different sizes (10nm, 75 nm) and coatings (PVP, citrate) and their physicochemical, cellular and genomic response measured. Both coatings retained their manufactured sizes in culture media, however, the zeta potentials of both sizes of PVP-coated nanoAg were significantly less electronegative than those of their citrate-coated counterparts. Markers of oxidative stress, measured at 0.5-5 ppm exposure concentrations, indicated that caspase 3/7 activity and glutathione levels were significantly increased by both sizes of PVP-coated nanoAg and by the 75 nm citrate-coated nanoAg. Both sizes of PVP-coated nanoAg also increased intra-neuronal nitrite levels and activated ARE/NRF2, a reporter gene for the oxidative stress-protection pathway. Global gene expression on N27 neurons, exposed to 0.5 ppm for 8h, indicated a dominant effect by PVP-coated nanoAg over citrate. The 75 nm PVP-coated material altered 196 genes that were loosely associated with mitochondrial dysfunction. In contrast, the 10nm PVP-coated nanoAg altered 82 genes that were strongly associated with NRF2 oxidative stress pathways. Less that 20% of the affected genes were shared by both sizes of PVP-coated nanoAg. These cellular and genomic findings suggest that PVP-coated nanoAg is more bioactive than citrate-coated nanoAg. Although both sizes of PVP-coated nanoAg altered the genomic expression of N27 neurons along oxidative stress pathways, exposure to the 75 nm nanoAg favored pathways associated with mitochondrial dysfunction, whereas the 10nm PVP-coated nanoAg affected NRF2 neuronal protective pathways.