The Biological Significance Of Redox Homeostasis In The Study Of Toxicity Of Dioxins

Dioxins are a type of environmentally persistent organic pollutants that are highly toxic and can easily be harm to humans through food chain enrichment.Such substances not only produce hepatotoxicity and immunotoxicity,but also have reproductive toxicity and irreversible "triple" toxicity,ie teratogenic,carcinogenic and mutagenic.The mechanism of action of dioxins is still not very clear,but most of the toxic effects are mediated through AhR.AhR can specifically induce the expression of cyplal gene,the effects of dioxin-induced cyp1a1 gene expression induced by AhR is understood through three levels of experiments from animal experiments to cell experiments and gene expression,mainly the effect of redox,can provide some clues and information for the study of the toxic mechanism of dioxins.Part I Effect of Dioxins(PCB77)on Redox Homeostasis of Tissues and Organs in AnimalsObjective To study the effect of acute exposure of 3,3',4,4'-tetrachlorobiphenyl(PCB77)on the redox status of liver and spleen tissues in mouse,which can be used to obtain the empirical index of follow-up study.Methods 60 male Kunmin mice were randomly grouped into control(C)and treatment ?(0.036 mg/kg bw),?(0.18 mg/kg bw),?(0.9 mg/kg bw),and IV(4.5 mg/kg bw)to determine the activities of GSH-Px and SOD,and the amounts of MDA when they were respectively exposed at Id,3d,and 7d.Results ?Compared with control group,MDA in liver and spleen were elevated in every treatment group significantly,however the MDA started to decrease from day 3 for all treatment groups.?Compared with control group,the activities of SOD and GSH-Px in liver and spleen were lower in all treatment groups,however,significant differences were found in II-IV(p<0.01)but not in treatment I(p>0.05).The activity of the two enzymes increased first and then decreased with the extended exposure time.Conclusions Statistically significant differences in the activities of GSH-Px,SOD and the contents of MDA in mouse liver showed time-and dose-dependent patterns.The relevant molecules and pathway which play an important role in redox status may be the goal in further research of these toxic substances.Part ? Cytotoxicity of Dioxins(PCB77)and Its Effect on Cell Redox HomeostasisObjective To investigate the cytotoxicity of PCB77 on HepG2 and A549 and its effect on cell redox homeostasis,which may pave the way for gene expression experiments.Methods The HepG2 cells and A549 cells were exposed under 4?M(?)?8pM(?)?16pM(?)?32?M(?)?64pM(?)and 128?M(?)PCB77 treatment groups and one DMSO control group(C).MTT assay and CB assay were used to observe the Cytotoxicity of different concentrations of PCB77,the ROS levels in each group of infected cells were also detected.Results ?As the concentration of PCB77 increased,the absorbance values measured by MTT and CB decreased significantly,and the difference was statistically significant.?The ROS level in the cells increased with the increasing of PCB77,and there was a statistically significant difference between the dose groups.Conclusions PCB77 has an effect on the intracellular redox homeostasis and a certain cytotoxicity.With the increase of PCB77 concentration,the intracellular ROS level is significantly increased,and the cytotoxicity is also significantly enhanced.Part ? Uniform Design Experiment to Examine the Time-Dose-Effect Relationship of Cyclal Expression Induced by Dioxins(PCB77)Objective Uniform design experiments were performed to analyze the time-dose-effect relationship of PCB77-induced cyp1a1 expression,which can be helpful to explain the results of animal and cell experiments.Methods According to the uniform design,10 test points with different exposed time and PCB77 dose were selected.Each test point had 6 parallel samples.The expression level of cyplal gene in each sample was measured by RT-PCR and real-time qPCR.Do three times and average the values to perform multiple linear regression analysis to examine the relationship between time-dose and cyp1a1 expression.Results Through the multiple linear regression analysis of the uniform design experiment results,the expression of cyp1a1 has a certain correlation with the exposed time and dose of PCB77,also the regression equation of the expression of cyp1a1 and the time-dose is obtained.Conclusions There is a clear linear correlation between the expression of cyp1a1 and the concentration of PCB77;in the early stage of PCB77 action or short-term exposure of PCB(exposure time is less than 50h),the expression of cyp1a1 will decrease,but then it will gradually increase.