| Quantum dots are group IIB-VIA (eg, CdSe, CdTe) or group IIIA-VA (eg, InP, GaAs) semiconductor nanocrystals in the size range of2-100nm. Due to their symmetric and narrow emission spectrum, tunable fluorescence emission, broad excitation spectra and high resistance to photobleaching, quantum dots have superior optical properties over other organic fluorescent dyes, and present a broad potential for biomedical applications. With the development of quantum dots applications, chance of people exposed to such substances is growing. Numerous studies have shown that liver and kidney are the main target organs for cadmium-based quantum dots, which are also found for cadmium. Hepatocytes are widely used for evaluation of cytotoxicity of cadmium, and tubular epithelial cells constitute an established model in renal toxicology. Therefore, primary hepatocytes and renal tubular epithelial cells were used in this research as an evaluation model for cytotoxicity of CdTe QDs. In addition, nanomaterials may be covered with a ’corona’ of biological molecules like proteins immediately upon contact with the physiological environment. This combination gives these nanoparticles new "biological identity" and subsequently determine the response of cells or organs, hence we also investigated the interactions of CdTe QDs and proteins, which related to the cytotoxicity of quantum dots. In this research, we explored the toxicity of CdTe QDs from the cellular and molecular perspectives. The major works and results are as follows:Firstly, glutathione-capped CdTe QDs were synthesized via a one pot method, and the characterization of the CdTe QDs was presented.The cytotoxicity of CdTe QDs were preliminary analysed by assessment of cell viability was performed using the Cell Counting Kit-8(CCK-8) assay. To investigate cytotoxicity mechanisms of CdTe QDs, the cells containing CdTe QDs and cadmium ion, ROS content, cell oxidative damage (MDA content, the activity of catalase and SOD), cell apoptosis were determined. Moreover, single cell gel electrophoresis assay was employed to study the genotoxicity of CdTe QDs. The experimental results showed that:(1) CdTe QDs causes cytotoxicity to these two types of cells. CdTe QDs induced more serious cytotoxicity injury on renal tubular epithelial cells than hepatocytes.(2) CdTe QDs can enter these two cells. Only a small number of cells were found to contain Cd2+. The number of cells containing CdTe QDs increased with the exposure concentration. The observation from inverted fluorescence microscope confirmed the presence of the QDs in the cells.(3) Cd2+was released from the CdTe QDs after internalization in cells. The number of cells containing Cd2+increased with the exposure concentration. Trojan horse-type mechanism explained the release of cadmium ions in the renal tubular epithelial cells and hepatocytes.(4) CdTe QDs induced oxidative damage to these two types of cells. Cellular ROS content increased with the exposure dose; MDA content and the activity of SOD increased synchronous with QDs concentrations, while the activity of catalase declined.(5) The CdTe QDs induced apoptosis in renal tubular epithelial cells and hepatocytes.(6) CdTe QDs induced DNA damage. Olive tail moment and tail DNA content increased with exposure concentrations of CdTe QDs.Then, interactions between CdTe QDs and proteins (serum albumin, catalase, Cu/Zn superoxide dismutases) were investigated using spectroscopy, isothermal titration calorimetry. The results show that the interactions between CdTe QDs and these three proteins are weak, and no profound conformational change of these proteins occurs. In addition, the analysis of catalase and Cu/Zn-SOD activity showed that CdTe QDs did not affect the function of these two antioxidant enzyme.In this research, we explored the toxicity of CdTe QDs from the cellular and molecular perspectives, which provides valuable information to understand the toxicity of quantum dots in vitro and can be used to assist in the design of biocompatible and stable quantum dots. |
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