In Vitro And In Vivo Study On The Hepatotoxicity Of CdSe/ZnS Quantum Dots

Quantum dots(QDs) are new fluorescent materials that have wide range of applications including medicine. However, their toxicities are not well studied. Liver plays key roles in drug metabolism and detoxification, so it is important to study the toxicity of QDs in the liver. In this study, we investigated the toxicological effects of CdSe/ZnS QDs in the liver.We first used transmission electron microscope and particle size analyzer to demonstrate that CdSe/ZnS QDs have diameter of 5-10 nm, with zeta potential of-35.1 mV, and the particles are well dispersed. By fluorescence spectrophotometer measurements, we showed that CdSe/ZnS QDs have maximum absorption wavelength around 250 nm and maximum emission wavelength 655 nm.In order to study the hepatocytotoxicity of CdSe/ZnSQDs in vitro in the liver cells, SK-Hep1, Hep G2 cell lines and murine primary hepatocytes culture were used as the experimental models. After a 4-hour treatment with CdSe/ZnSQDs, we found that more than 98% of the liver cells had uptaken QDs. After 24 or 48 h incubation, QDs significantly decreased cell viability as determined by MTT assay. In HepG2 cells, CdSe/ZnS QDs treatment dose-dependently increased the expression of caspase-9 and cleaved Caspase-3 protein levels, suggesting that QDs induced apoptosis. When HepG2 cells were incubated with CdSe/ZnSQDs for 4 h, increased ROS production and oxidative stress level were detected.For in vivo hepatotoxicity study, 4-week-old male BALB/c mice were used as experimental animals. Briefly, each mouse was injected through tail vein with 40 pmol of either CdSe/Zn S QDs(experiment group), or saline(control group). Mice were sacrifices at one day and 42 day post-treatment, blood and liver were collected. Our results showed that liver absorbed large number of QDs as early as one day post-treatment. At 42 day post-treatment, the level of QDs, decreased as the fluorescence intensity was lower than that found in the one day post-treatment group. These results suggested that QDs have high fluorescence stability and resistance to degradation/ metabolism. In addition, no significant difference were found in the liver coefficient(liver/body ratio) between the experimental and control groups(P>0.05). Pathological analysis of the liver and blood biochemical determinations(on liver cell damage, protein synthesis, and inflammation) showed no significant difference between the control and experimental groups(P>0.05).In summary, CdSe/ZnS QDs are uptaken by hepatic cells. At a concentration higher than 0.5 nM, CdSe/ZnS QDs produced large amount of ROS and induced oxidative stress, which could trigger cell apoptosis and resulted in decreased cell viability. Results from in vivo experiments also indicated that QDs accumulated in the liver. Although under conditions used in this study, no detectable toxicity had been found, however, more studies are needed enlarged samples size, to determine median lethal dose(LD50), and the effects on liver function, especially metabolic activity, and the potential hepatotoxicity with higher dosage as well as in combination with other drugs.