Research On Cd²⁺ Release,Toxic Effects And Mechanisms Of Cd-QDs Within Cells

Cadmium containing Quantum dots(Cd-QDs),as one kinds of semiconductor nanomaterial,possess excellent optical properties such as wide absorption,narrow emission,adjustable luminescence wavelength,high fluorescence intensity and anti-light bleaching.Cd-QDs materials have shown good prospects in the fields of biomarkers,pharmaceutical chemistry and chemical catalysis etc.However,Cd2+ can be released by Cd-QDs within cells,inducing cytotoxicity.Biological safety of Cd-QDs limits the promotion and application of such materials and technologies.Cd-QDs could distribute to detoxification and immune organs once entering into organisms.Research on Cd2+ release,toxic effects and mechanism of Cd-QDs within cells are essential in the early prevention and treatment of health hazards caused by cadmium pollution and the development of new Cd-QDs materials with excellent safety and performance.The cytotoxicity of Cd-QDs is closely related to the release of Cd2+ Currently,due to the lack of detection for Cd2+ and Cd-QDs within cells in situ,the release mechanisms of Cd2+ from Cd-QDs have not been clarified yet.The commonly used method to determine the concentration of Cd-QDs is lamberbier's law.The sensitivity of this method is not high enough.Atomic absorption spectrometry(AAS)and inductively coupled plasma mass spectrometry(ICP-MS)have high sensitivity for the detection.The detection environment of AAS and ICP-MS was very different from that within cells,which affect the accuracy and reliability of Cd2+ and Cd-QDs concentration determination,however.Compared with traditional toxicology,nano-toxicology is more complicated.For same nanomaterial,different conclusions can be drawn due to different experimental conditions and research objects.Cd-QDs induced oxidative stress and immune damages related toxic effects and its underlying mechanisms have not been completely clarified yet.To solve above problems,this paper planned to build up a new strategy to quantify the contents of Cd-QDs and Cd2+ in situ respectively.The release rule of Cd2+ from Cd-QDs within single cell will be proved.Furthermore,this research intended to explore the toxicity and mechanism of oxidative stress,cell apoptosis induced by Cd-QDs and Cd2+.This paper is mainly consisted with the following three parts:1.As the mainly targeted organs of Cd-QDs,hepatocytes and kidney cells were chosen to study the release mechanisms of Cd2+ from CdTe QDs in situ.Results showed that Cd2+ is continuously released from the QDs until the solution was balanced.We found that CdTe QDs and Cd2+ were all existed in dead hepatocytes,none in the living cells.However,different phenomenen were exist in kidney cells.Besides,oxidative stress damages induced by CdTe QDs were also studied,including the level change of ROS and the cell apoptosis.Results showed that the effects of oxidative stress and the cell apoptosis induced by CdTe QDs and Cd2+ are in time-and dose-dependent manners.CdTe QDs exposure led to the decrease of CAT activity and ROS level in hepatocytes and kidney cells.2.The mouse spleen cells and CD4+,CD8+ T cells were chosen as the immune cells to study the damages induced by CdTe QDs at the cellular level.CdTe QDs and Cd2+ levels within cells were also measured in situ.Cell viability and apoptosis percentage were measured after CdTe QDs exposure.No free CdTe QDs exists in living spleen cells.Oxidative stress-mediated apoptosis reduced the cell viability of the spleen cells and CD4+,CD8+ T cells.This study demonstrated that Cd-QDs-induced the oxidative stress and immune related damages to the immune organs.3.Functional enzymes-glutathione peroxidase3(Gpx3)?lysozyme(LYZ)and candida rugosa lipase(CRL)were selected as study objects.Enzyme activity changes at differernt levels after CdTe QDs exposure were determined.Multi-spectrum methods were used to characterize the structural changes of enzymes.Molecular docking and calorimetric methods were ulized to explore the binding parameters and binding sites of CdTe QDs with enzymes.The structural and functional alterations of proteins were clarified:(1)The response of Gpx3 to CdTe QDs and the interaction mechanism of CdTe QDs with Gpx3 were firstly investigated from animal,cellular and molecular levels.The activities of Gpx3 were inhibited and microenvironment and conformation of Gpx were altered.CdTe QDs binds to Gpx3 through Van der Waals' force and hydrogen bonds.(2)CdTe QDs binds to LYZ mainly through van der Waals forces and hydrogen bonding.Secondary structure was changed and microenvironment of aromatic amino acid residues was altered by CdTe QDs.Enzyme activity was inhibited as CdTe QDs bind to the active site of LY Z preferentially.(3)The ability of CRL to bind CdTe QDs was studied.Instrinsic fluorescence was statically quenched by CdTe QDs and new complexes were formed during the binding process.Structural and conformational changes of CRL were observed.CdTe QDs interacts with Ser 209 around the active site of CRL through hydrophobic forces.This paper combined different exposure routes on different levels to evaluate the oxidative stress induced by CdTe QDs in different types of cells.The underlying release mechanism of Cd2+ from CdTe QDs and the detection of CdTe QDs in situ were carried out.Research strategies to explore the binding mode of CdTe QDs with important functional proteins and the underlying mechanisms of these systems were established.This research could help to provide references of CdTe QDs induced oxidative and immune damages under CdTe QDs and Cd.U exposure.This research may provide technical support for early diagnosis of disease and high risk population and references to judge the results obtained from different exposure approaches.