Altın Nanopartiküllerde Polimer Kaplamanın Oksidatif Stres Ve DNA Hasarı Üzerine Etkileri

Abstract

Gold nanoparticles (Au NPs) are preferred in many biological and medical applications due to their easy surface functioning property and their ability to absorb light in near infrared (NIR) region. Au NPs are specifically used in many applications like monitoring and visualization, biosensoring, gene and cancer therapy, photothermal therapy and drug delivery. The results of some studies in literature pointed out that Au NPs could increase intracellular oxidative stress and cause DNA damage; however results of studies in this field are contradictory. In order to reduce their toxic effects, it is suggested that the surface properties of Au NPs should be changed. For this reason, polyethyleneglycol (PEG) and polyethyleneimine (PEI) coatings can be used. PEG is neutral and highly hydrophilic; therefore it prevents the uptake of Au NPs by reticuloendothelial system, inhibits specific protein adsorption and increases their circulation period in the body. In addition, it adds several properties to nanoparticles, including stability, biocompatibility and multi- functioning. On the other hand, as PEI is also biocompatible, it was indicated that it can also increase the stability and biocompatibility of Au NPs. However, there is not any comprehensive study in literature that compares the effects of the variations of Au NPs on oxidative stress. The aim of this thesis is to examine the effects of Au NPs on cytotoxicity, oxidant/antioxidant parameters and DNA damage in human hepatoma cells iii (HepG2) in detail and to search for the protective roles of PEG and PEI coatings. For this, Au NPs (45 nm) were coated with PEG or PEI (molecular weights of 2000 and 25000) and the study groups were determined as control, Au, Au-PEG, Au-PEI 2000 and Au-PEI 25000. After incubating HepG2 cells with different concentrations of Au NPs for 24 hours, the half maximal inhibitory concentration (IC50) values using (3-(4,5- dimethylthiazol-2-yl)-2,5-dphenyltetrazolium bromide (MTT) assay for Au, Au-PEG and Au-PEI 2000 were found to be 167 μg/ml, 257 μg/ml, and 198 μg/ml, respectively. The IC50 value for the Au-PEI 25000 group was not determined. In the study groups, intracellular reactive oxygen species, antioxidant enzyme activities [glutathione peroxidase 1 (GPx1), catalase (CAT), superoxide dismutase (SOD)]; total glutathione (GSH), lipid peroxidation and protein oxidation levels as well as DNA damage were determined. After HepG2 cells were exposed to IC30 concentrations of Au NPs, intracellular ROS levels were increased; however no other changes were determined in any of the measured parameters in the Au group vs. control. In all of the coated Au groups, the intracellular ROS levels were significantly higher vs control; however other than intracellular ROS levels, no significant alterations (except an increase in protein oxidation) were observed in Au-PEG group vs. Au group. In Au-PEI 2000 group, there were significant changes in some of the antioxidant enzyme activities (SOD, GPx1) vs. control; however, in Au-PEI 25000 group, all of the oxidant/antioxidant parameters were markedly altered vs. both control and Au group. 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels were measured as a marker of DNA base damage and 8-OHdG levels were not different in any of the study groups when compared to control. The results of this study suggest that at IC30 doses, Au NPs does not affect oxidative stress and DNA damage significantly; PEG coating does not have an impact on toxicity; however coating Au NPs with PEI (particularly by PEI 25000) can induce oxidative stress.