The Toxic Effects And Mechanism Of CdSe/Zns Quantum Dots To Nile Tilapia (Oreochromis Niloticus)

As a class of semiconductor nanocrystals with unique optical properties, quantum dots (QDs) were widely used in biomarkers, biomedical applications as well as optical imaging. However, with the increasing usage of QDsthey could enter into the water through different ways and thus produce toxicity to aquatic organisms, resulting in a potential harmful factor to the aquatic ecosystem environment. As the primary-productivity of the water body, fish play a vital role in control of the structure of food web and the stability of aquatic ecosystems. In order to reveal the mechanism of biotoxicity of CdSe/ZnS QDs and to provide important information for aquatic toxicology studies and biological safety assessments, here the toxic effects of QDs on the fetal development, genotoxicity and damage on liver and kidney of Oreochromis niloticus were investigated. This research sets four QDs concentrations treatments,100, 200,400 and 800 nmol·L-1QDs. NaCl (0.65%) and Cd2+(an concentration equal to 800 nmol·L-1 QDs cadmium content)were used for negative and positive controls, respectively. In experiment Ⅰ, the morphological characteristics, oxidative damage and gene expression toxicity were examined for the effects of waterborne CdSe/ZnS QDs exposure on embryonic development. In experiment Ⅱ, the genetic toxicity (DNA damage of peripheral blood cells) for the CdSe/ZnS QDs (with different concentration) at 12 h,24 h and 48 h post intraperitoneal injected were tested using single-cell gel electrophoresis technique (SCEG). In experiment Ⅲ, blood biochemical parameters and liver, MT and Hsp 70 mRNA expression levels in kidney and the damage degree of liver and kidney caused by different concentration of CdSe/ZnS QDs intraperitoneal injected for 12 h.24 h and 48 h were tested.The main results of present study were as follows:(1) A significant impact on the early development of Oreochromis niloticus embryos after CdSe/ZnS QDs exposure was observed. Heart rates of 72 hpf embryos were decreased after CdSe/ZnS QDs exposure and theywere significantly decreased in the 800 nmol·L-1 QDs group (P< 0.05); However, embryo hatching inhibition rate were significant increased with the increase of the CdSe/ZnS QDs concentration (P < 0.05). CdSe/ZnS QDs exposure resulted in condensation of embryonic eggs, developmental stagnation and even curvature of the spine and so on; all the embryos in Cd+ control group died when incubated for 72 hpf.(2) CdSe/ZnS QDs exposure significantly altered activities of superoxide dismutase (SOD), during the early development of Oreochromis niloticus embryos, and the malondialdehyde (MDA) contents increased obviously with the increasing concentration of QDs; In addition, the mRNA expression level of MT and Hsp70 were significantly up-regulated after QDs (800 nmol·L-1) treatment (P< 0.05).(3) CdSe/ZnS QDs exposure significantly induced DNA damage of peripheral blood cells. The percentage of DNA in the tail, tail length, tail moment and Olive tail moment examined by SCEG were increased with the increase of the exposure time and dosage of QDs (P< 0.05). On the other hand, all comet assay parameters of Cd+ group were more significant than QDs treatment group and NaCl group (P< 0.05).(4) Several biochemical parameters were detected in Oreochromis niloticus after QDs exposure for assessing the toxicity effects on liver and kidney. The serum total protein (TP), albumin (ALB), creatinine (CREA), aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase catalase (LDH) were significantly changed, especially in high concentration group.(5) The mRNA expression of MT and Hsp70 in liver and kidney were significantly impacted after treatment of QDs. A significant up-regulation of MT and Hsp70 expression was found in Oreochromis niloticus liver and kidney exposed to 400 and 800 nmol·L-1 QDs for 12 h,24 h and 48 h (P< 0.05), with a dose-dependent manner. Besides, the mRNA expression level of MT and Hsp70 in liver and kidney were significantly higher in Cd+ group than other groups.The main conclusion as follow:(1) CdSe/ZnS QDs exposure lead to a variety of toxic effects including reduced survival rate, increased malformation, changed heart rate and hatching inhibition rate, resulting in antioxidant system imbalance, eg up-regulated expression of MT and Hsp70.(2) The QDs-induced cytotoxicity might be related to the intrinsic properties such as their size, surface chemistry and the release of free cadmium or more importantly the combined co-effects, which resulted in potentially oxidative stress, lipid peroxidation, excess of reactive oxygen radicals and the related gene up-regulation.(3) CdSe/ZnS QDs exposure caused significant increase in DNA damage of peripheral blood cells in Oreochromis niloticus. The percentage of DNA in the tail, tail length, tail moment and Olive tail moment were significant increased when compared to controls, indicating that QDs can induce obvious genetoxicity in Oreochromis niloticus.(4) CdSe/ZnS QDs exposure can cause toxic effects on Oreochromis niloticus liver and kidney, which was revealed by significant changes of the serum biochemical indicators that are related to the function of liver and kidney, and up-regulation of MT gene.