Role of the swelling activated chloride current on geno and cytotoxity of silver nanoparticles on human glioblastoma multiforme

The evaluation of therapeutic use of silver nanoparticles (AgNPs) in brain cancer represents a relevant new area of research. Several studies have shown that AgNPs induce inhibition of glioblastoma multiforme (GBM) cell growth in vitro, and this inhibition is correlated to NAD depletion, ROS production and DNA damage. AgNPs are synthetized from silver nitrate reduction with NaBH4 utilizing as stabilizing agent dodecanthiol (Kang e Kim, 1998). Dodecanethiolate-stabilized silver nanoparticles (AgNPsdode) display homogenous distribution size with mean diameter of about 5 nm, as estimated with TEM analysis in accordance with AgNPs plasmonic resonance properties. Our data show that AgNPsdode at the subnanomolar range decrease mitochondrial activity of U251 glioblastoma cell line, estimated with MTT assay and proliferation rate upon 24 and 48 hours treatment. Under the same conditions, the induction of apoptotic and necrotic processes were observed by Comet test assay and citoflurimetric analysis. Since apoptosis/necrosis process involves ion channels activity, an electro-physiological study was performed during AgNPs application in U251 glioblastoma. Acutely AgNPdode application activates a chloride current with biophysical and pharmacological profile similar to that previously found for the swelling activated chloride current (IClSW) in glioblastoma cells (Fioretti et al., 2004). Similar IClSW activa-tion was observed with AgNPs obtained with another synthesis strategy that used citrate as reduc-tive and stabilizing agent, indicating that the biological effect observed is independent from the AgNPs synthesis approach. The chloride current was blocked by DIDS, NPPB and the selective IClSW blocker DCPIB, and displayed significant inactivation at positive membrane voltages. Since the activation of IClSW by AgNPs was preserved upon catalase pretreatment and mimed by hydrogen peroxide application, the involvement of oxygen radical specie (ROS) in the electrophysiological effects of AgNPs is suggested. The involvment of IClSW activity in exerting the effects of AgNPsdode on cell metabolism and proliferation was further investigated. Our results indicate that the activation of IClSW may represent a new signal to rationalize the effects and thus the use of AgNPs in nanomedicine, namely in GBM therapy.