Studies On Toxicity And Mechanism Of Selenium Nanoparticles On Medaka

Selenium is an essential trace element for animals and human,which possesses many physiological functions with anti-inflammatory,anti-cancer,anti-oxidation,regulation of the immune system and other effects,it was ingested mainly through food by human.The optimal range of selenium intake per day is 50-200?g;when the intake of selenium is less than 50?g/d,it will not only damage the microstructure of bone,but also lead to growth retardation.However,the range between the nutritional dose and the toxic dose of selenium is particularly narrow,and it is difficult to control the dose accurately,when the dose exceeds the critical concentration,the selenium and genetic material poisoning can be easily caused.In recent years,nano-selenium with protein as a stabilizer obtained by nanotechnology,which possesses special physical and chemical properties and low toxicity,has attracted widespread attention.Domestic and foreign scholars found that nano-Se showed considerable bioavailability,but showed lower toxicity compared with selenite,and selenomethionine in rats and mice;however,the study on the bioavailability,toxicity and biological activity of nano-selenium was carried only on nano-selenium by using bovine serum albumin as stabilizer,and related toxicity studies in aquatic animal are still rare,and no other studies have been reported on the use of other stabilizers,such as polysaccharide stabilizer.In view of this,this study used the medaka fish as the experimental object to explore the toxicity of polysaccharide-SeNP on the medaka fish and its toxicity mechanism,guiding the toxicity and application security for the further study of nano-selenium and laying the theoretical foundation for the application of nano-selenium in aquatic animal nutrition.The results are as follows,1.The preparation and the toxicity screening of polysaccharide-SeNPsFirstly,10 ml of pleurotus tuber-regium polysaccharide,chitosan,beta glucan,polyporus rhinoceros Cooke polysaccharide,Ganoderma lucidum polysaccharide,coriolus versicolor polysaccharide were added into a mixture of 7.5 ml of 0.23mol/l ascorbic acid and 5 ml2.4mol/l of acetic acid,followed by 0.25 ml of 0.51 mol/l Na₂SeO₃ slowly added to the previous mixture to obtain the corresponding nano-selenium;and then the polysaccharide-SeNPs were configured as 5?mol/L,10?mol/L,20?mol/L and 50?mol/L solution.Finally,the toxicity of several polysaccharide-SeNPs were studied by 7-day acute toxicity on juvenile medaka.The results showed that the polysaccharide-SeNPs were all toxic,of which chitosan-SeNPs was the most toxic,and at the concentration 50?mol/L,10 fishes died in 4hours,whereas the toxicity of?-glucan was the lowest.The chitosan-SeNP screened in this chapter lays the foundation for the further study of the toxicological experiments and the molecular mechanism of antioxidant enzymes.2.Study on the offspring developmental toxicity of Chitosan-SeNP,selenite and selenomethionineFertilization and malformation rate of offspring at pre-and post-exposure of 10,20?g se/g chitosan-SeNP,selenite and selenomethionine diet were analyzed to illustrate maternal inheritance on the offspring.The results showed that the difference of chitosan selenium,sodium selenite and selenomethionine fertilization rate at the concentration of 10?g/g were10.45%,21.75%,25.17%,and at 20?g/g were15.01%,25.11%,26.25%respectively;the number of abnormal embryos is cumulative abnormal rate,selenomethionine was greater than selenite;and selenite was greater than chitosan-Se NP in deformity;In addition,the deformity rate of 20?g/g selenomethionine and selenite on embryos were almost 2 times than those of10?g/g,the eye deformity is the main phenotype of medaka embryos,but the chitosan-SeNP had no significant difference,which may result from the character of nano-selenium.Altogether,these results indicate that chitosan-SeNP was less toxic compared with selenite and selenomethionine,and the toxicity of chitosan-SeNP can't vary significantly depend on selenium concentration.3.To explore the relationship between the toxicity of nano selenium and oxidative stressThe selenium content of liver,ovary and muscle of females exposed to 10?g/g,20?g/g chitosan-SeNP,selenite,selenomethionine and control group were detected by inductively coupled plasma mass spectrometry?ICP-MS?.The linear equation of selenium standard curve was Y=309.9X+257.16,R²=0.9999;the contents of selenium in the tissues were calculated by measuring the CPS.And the qpcr analysis was performed on the liver and ovary.The?-actin was used as the reference gene,we measured the expression level of catalase,glutathione-S-transferase,superoxide dismutase,glutathione reduction mRNA of liver and ovary exposed to 10?g/g,20?g/g chitosan-SeNP,selenite,selenomethionine relative to the control group using relative quantitative method???Ct method?.The results showed that the content of selenium in selenite,selenomethionine treatment were significantly higher than that in control group,and the selenium content of selenomethionine was significantly higher than that in selenite treatment,especially in liver,followed by ovaries and skeletal muscle.In contrast,the selenium content of chitosan-SeNP was less than selenite and selenomethionine treatment.The qgcr analysis showed that there was a close relationship between the toxicity induced by nano-selenium and the oxidative stress,and the induction of the mRNA of nano-selenium was similar to that of the control group indicating that the nano-selenium toxicity is the lowest among the common forms of selenium.