Evaluating cell specific cytotoxicity of differentially charged silver nanoparticles.

Silver nanoparticles (AgNPs) are one of the most commercially viable nanotechnological products, nevertheless; safety issues are raised regarding the use of such nanoparticles due to unintentional health and environmental impacts. In the present study, AgNPs were synthesized by chemically reducing silver nitrate alternatively with sodium borohydride, tannic acid, ascorbic acid and sodium citrate. AgNPs synthesized by reduction with tannic acid (TSNPs) and sodium borohydride (BSNPs) exhibited highest and lowest surface potential respectively. Therefore these two types of AgNPs were selected for their toxicity assessment in cellular environment. We treated skin epithelial A431, lung epithelial A549 and murine macrophages RAW264.7 cells with AgNPs over a range of doses (5-100μg/ml). Toxicity was evaluated by measuring changes in cellular morphology, ROS generation, metabolic activity and expression of various stress markers. Interestingly, TSNPs exhibited a higher negative zeta-potential and also higher toxicity. Higher toxicity of TSNPs was attested by dose-dependent increase in cellular disruption and ROS generation. BSNPs showed cytotoxic effect up to the concentration of 50μg/ml and thereafter the cytotoxic effect attenuated. TSNPs induced a dose dependent increase in the expression of stress markers pp38, TNF-α and HSP-70. Our report proposes that cytotoxicity of AgNPs changes with surface potential of nanoparticles and cells type.