| Quantum dots (QDs) are composed of metalloid core, which often encapsulated by a shell. QDs are nano-matertials which accept the light’s excitation and produce fluorescence. The modified shell of the QDs can conjunct various substances such as the biological groups, antibody and protein. QDs are coated with organic groups that can increase its dispersibility in water and bio-compatibility, and also increase the fluorescence imaging observation in specific target tissues. Currently, the most applied prospects of the QDs are used as the fluorescent markers in the biological systems. Based on the high photostability of the QDs, long-term observation can be made from the marked organisms.As the continuous and increasing application of the QDs, it raised many attentions on their security, the healthy and environmental aspects in the ODs. The core of QDs is composed of toxic heavy metal atoms. QDs can be oxidized and degraded in organism or external environment, and then heavy metals such as cadmium released from the core. Currently, most studies are focus on the cell-culture toxicity of QDs in vivo. However, those studies that focused on the in vitro toxicity and safe using dose of the QDs are few. Therefore, researches on the QDs’ biological toxicity and safe using dose in vivo are very necessary to resolve these problems.The present study selected the same batch juvenile Nile tilapia(Oreochromis niloticus) as experimental fishes that are the artificial propagation and breeding fishes in key laboratory of aquatic organism reproduction and development(southwest university) ministry of education from July2010. Our recent in vivo studies were concentrated on the tissues’ distribution and toxicokenetics of QDs. The experimental fishes were injected intraperitoneally by a single dose. According to the different fishes’ body weight, experimental fishes were injected with a2ml20n mol/L QDs per kilogram dissolved in sterilized normal saline. The blank control group was seted. The sampling tissues of the Nile tilapia were made at the assigned times (1h、4h、8h、12h、1d、2d、4d and7d). The concentrations of cadmium ion and metallothionein (MT) in the sampling tissues were measured and the tissue sections of these tissues were also conducted. The main conclusions of the present study were as follows:(1) The previous studies had found that cadmium ion had a great correlation wih the QDs. The concentrations of cadmium ion were determined by an inductively coupled plasma optical emission spectrometer (ICP-OES). Our results showed that:QDs had been found mainly in the intestines, liver, kidney, heart and spleen whereas QDs were rarely distributed in the gonads, gills and muscle. The content curve of cadmium ion in liver at1d was highest, after1d the content decreased, then gradually increased after2d. The two contents of cadmium ion concentration at1d and7d after injection were high. However, these two peak values were not significant different from each other. The concentrations of cadmium ion in gonads among eight sampling time points were also not significant different from each other. It worthy noted that the peak concentrations of cadmium ion in spleen were found at1h after injection. Over the1h, the concentrations of cadmium ion in spleen showed a first decreased, then increased and decreased finally course. The concentrations of cadmium ion in spleen among eight sampling time points were also not significant different from each other. The cadmium ion concentrations in kidney at1h and1d were high respectively. However, there was no significant difference between1h and1d. The peak concentrations of cadmium ion in heart occurred at1h after injection, and the concentrations of cadmium ion decreased gradually as experimental time increased. The concentrations of cadmium ion in intestines reached to peak in1h after injection. Like the heart, the concentrations of cadmium ion in intestines decreased also during periods of experiment. The cadmium ion concentrations of both the gills and muscle were much lower that were less than50ng/g when compared to above tissues.(2)The metallothione concentrations of four specific tissues of Nile tilapia which exposed to QDs were measured. The results showed that:the gradient order of metallothione concentrations in four kinds of tissues were in the spleen, the intestines, the kidney and the liver. The concentrations of metallothione in spleen reached the peak1h after injection when compared to the control group and the peak was much higher than in the control group. At the same time, QDs in spleen had induced the synthesis of metallothione. After1h, the metallothione concentrations in spleen decreased gradually and showed no significant difference when compared to the control group. This change trait in spleen corresponded to that in the cadmium ion. The metallothione concentrations in intestines were much higher than in the control group at1h. Metallothione in intestines were induced by the QDs, and the metallothione concentrations maintained a relatively stable state after1h. The metallothione concentrations in kidney were higher than in the control group at1h,8h and1d after injection and at the same time QDs have promoted the synthesis of metallothione in the kidney. The metallothione concentrations in kidney maintained stably in the other five sampling time points. When compared to the other three tissues, the metallothione concentrations in liver were lower. However, there were significant differences in1h,4h and1d, when compared to control group. At this point, metallothione in liver was induced by QDs.(3)Using the methods of paraffin section of tissues, we observed the QDs’fluorescence under the fluorescent microscope. Our results showed that:large quantity of QDs with red fluorescence was found in the spleen and kidney, and most QDs with red-illumination had distributed in the spleen’ macrophages. In kidney, QDs mainly located in the surrounding lymphoid tissues between renal tubules and renal capsule, few QDs particles were found in the proximal tubes and distal convoluted tubes. The QDs were scattered in the myocardial fibrosis of heart. As to the intestine, QDs were mainly distributed in the mucosal layer, tunica propria and goblet cells of intestines. The red fluorescence in the mucosa layer was much stronger than in the tunica propria. The QDs have not been observed in the gills and muscle. The results of HE staining showed that QDs had a slight damage to the liver, kidney, spleen, heart and intestines and all of these issue decreased the size of cells, thinned the myocardial fibrosis and increased the marcrophages in the spleen. However, some parts of these tissues can restore to the control levels at7d after injection of the QDs.These results suggested that:after injected with the QDs, the QDs were mainly gathered in the intestines, liver, kidney, heart and spleen, few QDs particles were found in the gonads, gills and muscle. When fishes were injected after1h, the concentrations of metallothione in the spleen, intestines, kidney and liver were higher than in the control group. At this time, QDs in four tissues induced the synthesis and expressions of metallothione. QDs can be observed in most of the tissues under fluorescence microscope, only gills and muscle did not. |
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