| Strong fluorescence of water-soluble Quantum dots (Quantum dots, QDs), a novel biologicalimaging fluorescence material, is becoming a hot spot for the research of biological probes and drugtargeting tools. QDs are undoubtedly presenting attractive application prospects in biological andmedical fields, however, still the efficiency of Quantum dots targeting delivery into the tissues of thebody (lesions) needs to be greatly improved and biological safety is another debatable issue to be solved.This paper investigated the delivery processes of cadmium telluride quantum dots (CdTe QDs) andsilicon quantum dots (SiQDs), followed by the assessment of their subsequent biological toxicity inBombyx mori, which is an invertebrate insect model.1Synthesis and assessment of targeting delivery efficiency of CdTeQDs to silk glandIt is evidenced that QDs are capable of transporting in tissues, and even in vivo cells, however, dueto clearance of chemical groups on QDs’ surface by animal blood and non-specific phagocytosis by thereticuloendothelial system（RES）, QDs are not yet the viable options for drug delivery, targetingdelivery of drugs/probes to tumors in vivo via the blood circulation system because of the commonproblems associated with nonspecific uptake by liver, spleen and other organs, making it difficult toeffectively target and penetrate into the inner tissues of tumors. Therefore, how to extend the retentionof the QDs in the circulatory system and how to reduce the nonspecific uptake are the two most urgentissues remained unresolved before QDs can be reliably used in the targeted drug delivery.We systematically investigated the delivery, the distribution and transfer efficiency of QDs720andQDs530CdTe QDs, which are two different particle sized dots, by the mouth injection method insilkworm for5th instar larvae48h after molting. Silk gland tissues of silkworms were used for thestudy due to their ability of rapid synthesis and strong metabolism of proteins, which are very similar totumor cells. In this study, single amino acids Gly or Ala, which were required in large amounts duringprotein synthesis in silk glands, were linked to the QDs, followed by a systematical evaluation on the invivo targeting efficiency in specific tissues and biological toxicity reducing after oral exposure to QDs.The characteristic green fluorescence intensity of QDs530and Cd2+content, tested by atomabsorption spectrum apparatus, indicated that the transfer efficiency of QDs530-Ala and QDs530-Gly incirculatory system increased by2.6±0.31and1.5±0.29times, and further increased by7.8±0.89and 2.88±0.22times in target tissue silk glands respectively, after24h of QDs exposure, compared withbare QDs530. While the amount of QDs530-Ala and QDs530-Gly that entered the untargeted lipid body,which was functionally similar to liver in human, were reduced by68.4%and46.7%respectively. Thebare exposure of QDs to hemolymph by dorsal vessel injection also demonstrated a significant longerduration of QDs530-Ala and QDs530-Gly in hemolymph, with a significantly reduced rate in enteringthe untargeted hemolymphs. The transfer efficiency to the target tissues of silkgland was improved, andthe structural integrity of QDs was better maintained in tissues, which eventually reduce the death ratesof the individual mortality and circulating blood cells.These results suggest that it is possible and promising to establish a more efficient and saferorganization transfer method of QDs by advantageously applying different rates of amino acidabsorption to varying tissues, or using single organic molecules for fast-growing tumor cells distinctivefrom normal cells.2Mechanism of biological toxicity reduction by surface-amino-acid-modified CdTeQDsThe detection of ROS showed that QDs530-Ala reduced the amount of reactive oxygen species(ROS) in hematopoietic organs, silkgland and fat body. The result of real time quantitative PCR and PIstaining indicated that QDs530-Ala and QDs530-Gly down regulated the expression of Atg6and Dronc,which regulated the pathways of autophagy and apoptosis, thus reducing the apoptosis and autophagy inthe organizations. The result of lysosome dyeing and transmission electron microscope confirmed thatQDs530-Ala and QDs530-Gly effectively reduced the production of lysosomes, indicating that QDs530conjugated Ala and Gly prevents the occurrence of apoptosis by reducing the production of ROS andtherefore significantly reduces the toxicity of CdTeQDs to organization and organism.Ala and Gly are also largely required for the conjugation of QDs530to target tissues in silkgland,significant difference was observed in the target transfer efficiency and toxicity of tissues. Since thenano particle structure could not be well maintained in the cycling and excretory systems, the transferefficiency of QDs530-Gly to target silkgland was reduced, while with an even higher tissue andorganism toxicity than QDs530-Ala. And this toxicity variance was conformed in the QDs reduced ROSproduction, lysosome level and the transcriptional levels of regulation genes in autophagy andapoptosis, indicating that more research work should be done on the variability of amino acids aswell as other single molecules to improve the transfer efficiency, and QDs stability in differentanimals and biological safety assessment are two pre conditions for these work.3The potential toxicity and independent repair of SiQDs on blood cells and hematopoieticfunctionSiQDs is supposed to be a type of novel and non-toxic or low toxicity quantum dots cell andorganism tissue in vitro, while few studies were conducted systematically on the inner functions ofSiQDs in tissues. Blood cells represent a cell model, which is used to study innate immune response andthe DNA damage in the body. At present, there are few reports on the effects of SiQDs on hematopoietic function. Our experiment investigated the delivery of SiQDs in the different types of blood cells insilkworm larva, and then constructed the animal evaluation models, which are used to investigate SiQDsimpact on the hematopoietic function. SiQDs were able to quickly enter the Granulocyte, Spherulocytesand Oenocytoids through the dorsal vessel injection with no blue fluorescence of SiQDs in thePlasmacytes and Prohaemocytes detected. The distribution of SiQDs was significantly different invarious types of blood cells, and the distribution of fluorescence in three kinds of cells was alsodifferent.SiQDs exposure could induce cells death, and the number of dead cell was increased in thehaemolymph with a dose response effect. Further investigation indicated that SiQDs exposure couldinduce the expression levels of Atg6, Atg8and Dronc as well as the levels of mitochondrion andlysosomes in blood cells, and an increased death rate of PI stained cells. And these changes could beobserved only in high dose of SiQDs, while the structures of lysosome and mitochondria of the bloodcells were not completely destroyed, and the number of circulating blood cells and the proportion of allkinds of blood cells also returned to normal, after a certain period of time exposure. Hanging drop cellculture of hematopoietic organs showed that SiQDs can lead to slow and poor growth of Hematopoieticorgan and a reduced ability of blood secretion, but within the scope of self-repair of silkworm. Thedetermination of ROS content indicated that high dose of SiQDs exposure did not induce high levels ofROS production as other common types of quantum dots. All of the results indicated that water-solubleSiQDs are able to cause significant symptoms of damage to the silkworm cells and hematopoietic organ,while the damage can be repaired by the worm itself. |
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