Safety Evaluation For Nano-MnO₂

Safety of nano-materials has been evoking more and more attention in the entire world with rapid technical development and widespread application of nano-materials. Toxicity of nano-materials is shown mainly interference on immune system and respiratory system,especially toxicity effects on damage of animal lung.Nano-materials can affect function and structure of cell surface in micro,then result in cell metabolic disorder,influent cell cytoactive and induce cellular apoptosis and necrosis.Nano-MnO₂ has some very important application in electrochemistry due to its favorable electrochemical efficiency,excellent ion/electron conductimetry and higher electric potential.However,the research on its safety has been shown importance increasingly.In order to explore cytotoxicity induced by nano-MnO₂,this study took HeLa cells as experimental object and applied morphological observation,MTT assay to evaluate cytoactive influence by nano-MnO₂.Then the study assessed Hela cells DNA single-strand break(DSSB)degree and intracellular reactive oxygen species(ROS) levels so as to explore cell oxidative damage and possible mechanism induced by nano-MnO₂.Meanwhile,many researches indicated that some atoxic and low toxic granular material could strengthen their toxicity when their sizes became nanometer.So in order to explore relation between toxicity and size of MnO₂,the study still contrasted effects of Hela cells oxidative damage degree induced by normal MnO₂ and nano-MnO₂. The results show as follows:1 An influence of Hela cytoactive by normal MnO₂ and nano-MnO₂In order to explore whether normal MnO₂ and nano-MnO₂ had a effect of cytotoxicity,this study took Hela cells as materials and applied cell morphology observation and MTT assay to assess Hela cytoactive after exposure to different final concentrations of 50,100,200 and 400μg/mL normal MnO₂ and nano-MnO₂ for 12h. The results demonstrated that the cytoactive decreased obviously after exposure to these two kinds of MnO₂ and there was an obvious dose-dependent relation.There was no significant depressant effects of cell growth and alteration of cell morphology after Hela cells exposure to lower concentration normal MnO₂(50 and 100μg/mL)for 12h,but higher concentration normal MnO₂(200 and 400μg/mL)could inhibit significantly cell growth(p＜0.01)after Hela cells incubated with the particles for 12h,cell morphology became unclear gradually and some cells shrunk into round.However,just 50μg/mL nano-MnO₂ could induce cytotoxicity,compared with relative normal MnO₂ groups, there was significant difference(p＜0.01).2 DNA damage of Hela cell induced by normal MnO₂ and nano-MnO₂In order to contrast DNA damage of Hela cell induced by normal MnO₂ and nano-MnO₂,this study made Hela cells exposure to lanai concentration 50,100,200, 400μg/mL normal MnO₂ and nano-MnO₂ respectively,then applied SCGE to assess DSSB degree of Hela cells so as to evaluate DNA damage level induced by normal MnO₂ and nano-MnO₂.The results showed that tail moment and tail DNA%increased with exposure to normal MnO₂ and nano-MnO₂ concentration increasing,and there was a dose-dependent relation.Both normal MnO₂ and nano-MnO₂ could result in DNA damage at different concentration level,but damage degrees of these two materials were different.Increased tail moment and tail DNA%in all nano-MnO₂ concentration groups were stronger compared with the identical concentration normal MnO₂ groups(p＜0.01)3 Effects of intracellular ROS levels increasing induced by normal MnO₂ and nano-MnO₂Some studies showed that DNA was the main target of ROS and ROS generation was the most important mechanism of DNA damage induced by ultrafine particles (UFPs).In order to confirm whether intraeellular ROS levels increased with DNA damage degree increasing induced by normal MnO₂ and nano-MnO₂,this study applied eell-permeant 2,7'-dichloro dihydro fluoreseein(H₂DCF)to assess intraeellular ROS levels after exposure to different final concentration(50,100,200,400μg/mL)normal MnO₂ and nano-MnO₂ for 12h.The results indicated that the ROS levels increased in a concentration-dependent manner and was significant statistically increased(p＜0.01)in all concentration examined.Compared to the each normal MnO₂ concentration group, DCF fluorescence intensity approximately increased by 11%,7%,5%and 4.4%which after exposure to 50,100,200 and 400μg/mL of nano-MnO₂,respectively.However, only the fluorescence intensity increasing in 50μg/mL nano-MnO₂ group had statistical significance(p＜0.01).