Co-exposure To ZnO Nanoparticles And Pb²⁺ Enhances Liver Injury In Non-alcoholic Fatty Liver Disease （NAFLD） Mice Model

In recent years, obesity has become a global problem as the change in diet and lifestyle. A survey by the world health organization, in obese people can be as high as 75%～100% patients with nonalcoholic fatty liverdisease (NAFLD). NAFLD is a common metabolic syndrome of the liver, which can cause chronic liver disease. In NAFLD patients about 25% can develop into non-alcoholic steatohepatitis (NASH) with liver fibrosis, liver cirrhosis and liver cancer. NAFLD as associated with obesity is one of the most common chronic metabolic diseases, and the incidence showed a increasing trend year by year.With the rapid development of industry, environment pollution is more and more serious. Lead is a very common environment pollutant in environmental and biological systems. There are large amounts of lead in large number of industrial waste gas, car exhaust emissions and industrial wastewater. The study found that lead can cause a wide range of physiological disorders in humans and laboratory animals. Lead poisoning can cause serious damage of liver, kidney, the nervous system and hematopoietic system.ZnO nanoparticles show excellent physical, chemical and biological properties, so ZnO nanoparticles have been widelyused in daiy necessities, biological medicine and biological sensing and many other fields. In addition, ZnO nanoparticles properties desirable for water and wastewater application include high activity for photo catalysis, antimicrobial properties. In the process of water treatment nanomaterial can adsorb water pollutants such as heavy metal ions. So this can lead to co-exposure to biological of nonmaterial and heavy metal ions. Research of co-exposure to nanomaterial and heavy metal ions is limited to some healthy single-celled aquatic organisms. TiO2nanoparticles increased the accumulation of cadmium ions and zinc ions in Ceriodaphnia. TiO2 nanoparticles and arsenic ionsco-exposure can cause synergetic toxicity in daphnia. Without in mammalian, especially the biological effect and toxic mechanism ofco-exposure of nanomaterial and heavy metal ions to the vulnerable groups such as NAFLD, is not caused people’s enough attention.This research built mice model of NAFLD through feeding high fat food for long-term. Feeding high fat food after 8 weeks, body weight and liver of mice, the serum total cholesterol (CHOL), triglyceride (TG), high-density lipoprotein (HDL) and low density lipoprotein (LDL) levels have significantly increased. In addition, the liver pathological observation shows that there are a lot of fat vacuole in the liver. So the NAFLD model established successfully.Then we start to exposure of nanoparticles for 2 weeks. We evaluated the toxic effect and the mechanism on normal mice and NAFLD mice of co-exposure to ZnO nanoparticles and lead ions.We use ICP-MS to analyze the distribution of major organs in mice after exposure to ZnO nanoparticles and Pb. Results show that, whether in healthy adult mice, or NAFLD model mice, co-exposure to ZnO nanomparticles and lead ion increases the Zn and Pb accumulation in the major organs and it also indicates that co-exposure to ZnO nanoparticles and lead ion may be a greater security risks.According to the results of the toxicity of healthy adult mice, no matter single exposure to ZnO nanoparticles or lead ions, or co-exposure to ZnO nanoparticles and lead ion, caused no significant toxicity effect; exposure to nanoparticles did not cause a change of the mice serum biochemical index [alanine aminotransferase (ALT), aspertate aminotransferase (AST) and alkaline phosphatase (ALP)]; not cause significant changes of liver pathology. Results of molecular biology analysis show that under the condition of this experiment exposure dose, exposure of nanoparticles did not cause any oxidative stress or inflammation response of liver in healthy adult mice.In NAFLD model mice, single exposure to ZnO nanoparticles or lead ions have no differences in the level of serum biochemical indexes. The liver pathological observation shows that there are only mild inflammatory cell infiltration and ballooming degeneration of liver cell. Co-exposure to ZnO nanoparticles and lead ions in NAFLD model mice caused significant rise of ALT, AST and ALP, and caused the significant balloon sample of liver, watery, inflammatory cell infiltration and necrosis of liver cells. In order to further study the possible mechanism of aggravating liver injury in mice, we examinedlevels of oxidative stress and inflammatory cytokines release under the condition ofexposure of nanoparticles in NAFLD mice. The oxidative stress index SOD and MDA, and inflammatory cytokines levels of IL-6 and IL-1 β showed co-exposure to ZnO nanoparticles and lead ions lead to higher levels of oxidative stress and inflammation in NAFLD mice.In summary, co-exposure to ZnO nanoparticles and lead ion increased the distribution of Zn and Pb in major organs in mice, there is possible a greater security risks. Because of the decrease of antioxidant ability and immune function, mice are not well balanced the oxidative stress and immune response in the liver, which caused by co-exposure of to ZnO nanoparticles and lead ions. So co-exposure aggravated the damage of liver tissue. Therefore, co-exposure to environmental pollutants and nanoparticles for NAFLD can lead to a greater health threat. This topic will provide important experimental basis for the study the toxicity and mechanism of co-exposure to ZnO nanoparticles and lead ions to NAFLD.