Research On The Combined Toxicity Of Zinc Nano-oxide And Other Food Additives

With the rapid development of nanotechnology, metal oxide nanoparticles have been used widely in food additives and raised attention in science. The present standards of food additives are only based on their single toxicity. So far,research on the combined toxicity between the metal oxide nanoparticles and other food additives has just started. Zinc oxide nanoparticles(Zn O NPs) have been used in many food as a nutrition enhancer. After we investigate the market, we found that the commonly added food additives with Zn O NPs in food are Vitamin c(Vc) and Casein Phosphopeptides(CPP).We have systematic researched the combined toxicity of Zn O NPs, Vc and CPP. The results showed that the nontoxicity concentration of Zn O NPs in human gastric epithelial cell line(GES-1) and neural stem cells(C17.2) is 15 mg/L, the IC50 in GES-1 is 20 mg/L. the nontoxicity concentration of Vc is 300 mg/L. CPP is nontoxicity in GES-1. However, after co-incubation of 15 mg/L Zn O NPs and 300 mg/L Vc in GES-1 and C17.2, the cell viability reduced to 37.6 % and 35.7 % respectively. This toxicity is mainly caused by zinc ion solubilized by Zn O NPs. Furthermore, we found that the most of zinc ion were in lysosome of the cells based on the confocal study. After then, we studied its mechanism of apoptosis, the results showed that the level of reactive oxygen(ROS) has increased to about 420 %, mitochondrial membrane potential(MMP) has reduced to 40 % around, the activity of capase-3 in GES-1 and C17.2 increased to 150 % and 160 % around respectively. Furthermore, we have studied the combined toxicity in vivo with Kun Ming mice as the animal models. We chosed 14 mg/kg Zn O NPs and 50 mg/kg Vc according to the state food and nutrition enhancer standards-GB14880-2012 to administer mice every day orally for 30 days and 90 days. The results indicated that the mice administered for 30 days almost did not show any lesion. However, many indexshad changed in the Zn O NPs & Vc group mice administered for 90 days. Firstly, in serum biochemicals, blood urea nitrogen(BUN) and T-bilirubin(TBIL) showed the statistical significance compared with the control. Secondly, the related factor of Liver and kidney gene expression-apolipoprotein(APO), fatty acid binding protein(L-FABP) and Neutrophil gelatinase-associated lipocalin(NGAL) showed significant changes. Theses changes indicated some damage in liver and kidney of Zn O NPs & Vc group mice administered by 90 days. At last, we investigated the histological section of liver, spleen, lung and kidney, the results indicated that only the volume of liver cells of Zn O NPs & Vc group became larger, the color of liver cytoplasm became faint, had some imflammatory cells. The other groups did not show obvious changes.On the other hand, we found that any concentration of CPP can protect GES-1 against the toxicity induced by Zn O NPs, and increased cell viability from 50 % to 100 % around. Therefore, we detected the index correlated to redox in GES-1, they are ROS, Malondialdehyde(MDA), Glutathione(GSH) and Superoxide dismutase(SOD), the results showed that the index of Zn O NPs & CPP group to Zn O NPs is 350 % to 120 %, 6 to 3 nmol/mg prot, 8 to 16 nmol mg prot and 30 to 50 U/mg prot respectively. These changes showed that CPP can protect GES-1 against Zn O NPs induced injury through the down regulation of oxidative stress.Different complicated system has great difference in affecting the toxicity of Zn O NPs. Therefore, there must be more basic data about the combined toxicity in complex system to provide more reference for the evaluation of bio-safety.