| Selenium(Se)is an essential trace element of fundamental importance to human health,such as the regulation of redox balance and the prevention of cancer,HIV infection and cardiovascular disease.However,the narrow margin between the nutrient and toxicity dosage of Se tremendously inhibits its application.Traditional Se compounds as inorganic and organic selenium forms are inefficient due to their low activity and inadequate toxicity.In the recent years,selenium nanoparticles(SeNPs),the red zero valent selenium,have garnered a great deal of attention as potential chemopreventive agent due to their high biological activity and low toxicity.However,the molecular mechanism by which SeNPs exert the biological function is unclear.In particular,Se atom as the active site of the selenoenzymes,there lacks the view of mimic enzyme on their high biological activity and low toxicity.Atherosclerotic cardiovascular disease seriously threatens human health due to their high morbidity and mortality.A large number of works have shown that atherosclerosis(AS)is induced by risk factors such as oxidative stress,hyperlipemia and hyperglycaemia,etc.Previous studies have shown that SeNPs has multiple biological effects,such as antioxidation,anti-hyperglycemic activity,reducing blood lipid,suggesting that SeNPs may has anti-atherosclerotic activity,but there were no reports at present.In this work,we first studied whether biocompatibility SeNPs possessed intrinsic oxidase-like activity.Then,we used Se as the doping atom to form Pt-Se hybrid nanostructures,and evaluated the synergistic effect of Se and Pt on oxidase-like activity as well as the application of the oxidase mimic enzymatic activity of Pt-Se nanostructures in detection of Hg2+.Finally,we investigated the effect and possible mechanism of SeNPs on AS formation and liver injury in ApoE-/-mice.The main results were as follows:Using selenite as a precursor and glutathione as a reductant,biocompatibility SeNPs were synthesized by the wet chemical reduction method in the presence of bovine serum albumin.The results of structure characterization revealed that synthesized SeNPs were amorphous red elementary selenium with spherical morphology,and ranged in size from 25 to 70 rm size with a mean size 38.7 nm.The oxidase-like activity of the as-synthesized SeNPs was tested with 3,3 ',5,5'-tetramethylbenzidine(TMB)as a substrate.The results indicated that SeNPs could catalyze the oxidization of TMB by dissolved oxygen.These SeNPs showed an optimum catalytic activity at pH 4 and 30 ?,and the oxidase-like activity was higher as the concentration of SeNPs increased and the size of SeNPs decreased.The michaelis constant(Km)values and maximal reaction velocity(Vmax)of the SeNPs for TMB oxidation was 0.0083 mol/L and 3.042 ?M-min-1.Dissolved oxygen plays an important role as electron acceptor in the process of oxidase mimic.The oxidase-like activity of SeNPs may be due to the adsorption capacity of Se on the oxidation state and the size effect of nanomaterials,which accelerates the electron transfer between the electron donor TMB and the electron acceptor oxygen.Platinum(Pt)-based binary hybrid nanomaterials exhibit unique stability and enhanced catalytic property in comparison with the monometallic Pt nanoparticles.In this paper,Pt-Se nanostructure and Pt nanoparticles were synthesized by a facile one-step chemical reduction route in aqueous solution,and their catalytic performance was evaluated as oxidase-mimic.The results of structure characterization revealed that Pt-Se nanostructure was consists of Pt and Se atoms(the Pt/Se atomic molar ratio is approximately 7:3 with a mean diameter of about 13.5 nm,while Pt nanoparticles was consist of pure element Pt with a mean diameter of about 5.4 nm.The oxidase-like activity of Pt-Se nanostructure and Pt nanoparticles was evaluated with TMB as substrate.The results indicated that Pt-Se nanostructure showed an optimum catalytic activity at pH 4.4 and 40 ?,while Pt nanoparticles was at pH 3.8 and 30 0C.The steady-state kinetic assay showed that Pt-Se nanostructure had a lower Michaelis constant(Km)values and higher catalytic constant(Kcat)for TMB oxidation than that of Pt nanoparticles.The lower Km values and higher Kcat mean that the binary Pt-Se hybrid nanostructure has stronger binding affinity with the substrate TMB and higher catalytic activity in comparison with monometallic Pt nanoparticles.The reason for the enhanced oxidase-like activity of Pt-Se nanostructure may be that element Se doped in binary Pt-Se hybrid nanostructure can provide more active sites for the substrate adsorption.On the other hand,the anchoring effect of heteroatom Se enhances the tolerance of Pt for oxidation products.It was found that mercury(?)ions(Hg2+)could inhibit the oxidase mimetic activity of Pt-Se nanostructure and resulted in a color change of the reaction system.Based on this mechanism,a facile colorimetric assay for Hgig was developed with a detection limit as low as 70 nM and a linear range of 0-2.5 ?M.The effect and possible mechanism of SeNPs for the prevention against AS were investigated with apolipoprotein E gene knockout(ApoE-/-)mice as an animal model of AS.Thirty two ApoE-/-mice aged 8 weeks were randomly divided into 4 groups:AS model group,statin group,SeNPs group and statin + SeNPs group.Mice in all groups were fed with high-fat diet.The drug was given by intragastric administration:statin group(atorvastatin 10 mg/kg/d)?SeNPs group(SeNPs 50 ?g/kg/d),statin + SeNPs group(atorvastatin 10 mg/kg/d + SeNPs 50 ?g/kg/d).AS model group was received gavage of normal saline with same volume.Drug intervention was terminated after 8 weeks.Serum samples were collected to test their serum lipid levels,glutathione peroxidase(GPx),superoxide dismutase(SOD),malondialdehyde(MDA)and nitric oxide(NO)level.The pathological changes of aorta,heart and kidney were observed with HE stain.The mRNA expression level of liver antioxidant selenoenzyme/selenoprotein and total selenium content in liver and kidney were also studied.As compared with AS model group,SeNPs significantly reduced the serum total cholesterol(TC),total triglyceride(TG)and low density lipoprotein cholesterol(LDL-C)level,and attenuated pathological changes in the aorta,heart and kidney tissue.SeNPs significantly increased serum GPx and SOD activity,reduced MDA levels and elevated NO levels.Furthermore,SeNPs also upregulated the antioxidant selenoenzyme/selenoprotein mRNA expression level and increase Se content in liver and kidney.These results suggested that SeNPs could significantly reduce blood lipid levels and inhibit atherosclerotic lesion in ApoE-/-mice.The underly mechanism may be involved in the inhibitory effect of SeNPs on oxidative stress,through up-regulating the expression of the antioxidant selenoenzyme/selenoprotein and enhanced the activity of antioxidant enzyme.The combination of SeNPs and atorvastatin did not exhibit the synergistic inhibitory effect on AS.The inhibitory effect and possible mechanism of SeNPs on liver injury in ApoE-/-mice were studied finally.The liver TC and TG levels and the pathological changes of liver tissue were detected.The liver antioxidant factors as glutathione(GSH),GPx and catalase(CAT)were tested.In addition,the mRNA expression levels of key molecules or enzymes invovled in liver cholesterol metabolism were determined.In comparison with the AS model group,SeNPs decreased the liver TC and TG level,significantly enhanced the level or activity of liver antioxidant factors GPx,CAT and GSH.SeNPs regulated the mRNA expression level related to cholesterol synthesis and metabolism in the liver,thus maintaining cholesterol feedback regulation mechanism and ensuring the balance of cholesterol level in the liver and the body.These results revealed that SeNPs not only could inhibit the initial liver injury caused by excessive lipid accumulation,but also could inhibit the deep liver damage induced by excessive oxidative stress and inflammation.The combination of statins and SeNPs resulted in the increase of liver TG level,and the damage of cholesterol feedback regulation mechanism,which aggravated the liver injury in ApoE-/-mice.However,the mechanism of liver injury was needed further studied. |
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