Regulatory Mechanisms Of Carbon Nanomaterials On Cytotoxicity Of Dioxins And Polycyclic Aromatic Hydrocarbons

Eco-environmental sustainability and human health are now severely threatened by environmental pollution.Such adverse impacts from environmental pollution are ubiquitously caused by joint toxicities from multiple pollutants.The practical issue of how to solve the fact that people are almost always exposed to the mixed pollutants becomes one of the most challenging tasks in environmental pollution research.The rapid development of nanotechnology and wide application of nanomaterials allow nanomaterials to be massively released into the environment.As emissions increase,the probability of interaction between nanomaterials and co-existing contaminants in the environment increases gradually.However,the potential environmental health risks triggered by co-exposure of nanomaterials and pollutants are still not clear,and the combined effects and potential mechanisms are still not well understood.Therefore,it becomes important to explore the combined biological effects of nanomaterials with pollutants and reveal the underlying molecular mechanisms.Previous studies have often focused on the combined toxic effects of single nanomaterials and pollutants,and lacked systematic research on the effects of nanomaterials with different components and surface modification on the toxic effects of environmental pollutants.In this work,widely distributed nanomaterials in the environment and carbon nanomaterials with different surface modifications were selected,the persistent organic pollutants dioxin(2,3,7,8-TCDD)and benzo[a]pyrene(BaP)were used as contaminant models to study the regulatory effects of nanomaterials on the toxic effects of pollutants and their potential molecular mechanisms.The main results of this work are summarized as follows:(1)Explored the effects and molecular mechanisms of nanomaterials with wide application and high environmental exposure risks on the metabolism of very low-dose pollutants.Six commercial nanomaterials,including multi-walled carbon nanotubes(MWCNTs),graphene oxide(GO),zinc oxide nanoparticles(nZnO),silica nanoparticles(nSiO2),titanium dioxide nanoparticles(nTiO2)and silver nanoparticles(AgNPs),were selected,and 2,3,7,8-TCDD was used as contaminant model to explore the potential effects of nanomaterials on cytochrome P450 1A1 enzyme(CYP1A1),a molecular marker of metabolic functions.By examining the effects of six nanomaterials at non-lethal concentrations on the CYP1A1 promoter activity,CYP1A1 protein expression level and CYP1A1 enzyme activity induced by very low doses of 2,3,7,8-TCDD,we found that the composition of nanomaterials at non-lethal concentrations significantly affected CYP1A1 regulatory pathways and the cellular metabolic function to 2,3,7,8-TCDD.MWCNTs and go inhibited 2,3,7,8-TCDD induced upregulation of CYP1A1 expression and enzyme activity in a concentration dependent manner.nZnO and nSiO2 only showed inhibitory effects on CYP1A1 gene expression at high concentrations.The inhibition of CYP1A1 enzymatic activity by AgNPs may promote the transcription of CYP1A1 through negative feedback loop.Subsequently,the inhibition mechanisms of MWCNTs was found that MWCNTs inhibited CYP1A1 expression by blocking the nuclear translocation of AhR.In this study,the interference effect of nanomaterials on cell detoxification function was evaluated from the levels of gene expression and enzyme activity,and a completely new mechanism of AhR-CYP1A1 pathway inhibition by MWCNTs was discovered.(2)A panel of carbon nanomaterials were prepared including pristine(p-),aninated(-NH2)and carboxylated(-COOH)MWCNTs and GOs.We found that the surface modification of carbon nanomaterials affected its combined cytotoxicity with BaP.Among the six carbon nanomaterials.p-MWCNTs.MWCNTs-COOH and GO-NH2 had no significant effect on the cytotoxicity of BaP,while M WCNTs-NH2,p-GO and GO-COOH could significantly inhibit the BaP-induced cytotoxicity,and GO-COOH had the strongest antagonistic effect on the cytotoxicity caused by BaP.We further evaluated the toxic pathways of carbon nanomaterials and BaP,and found that surface modification is a key factor determining the toxic effects of carbon nanomaterials and BaP.Although MWCNTs-NH2,p-GO and GO-COOH could inhibit the toxic effects of BaP,the mechanisms may be significantly different.MWCNTs-NH2 and pGO inhibited the metabolic activation of BaP,While GO-COOH promoted BaP metabolic activation while activating antioxidant defense system,inhibiting BaP induced DNA damage and cytotoxicity.(3)The molecular mechanism of GO-COOH inhibiting BaP-induced cytotoxicity was further studied.It was found that GO-COOH reduced the cytotoxicity of BaP by inhibiting the apoptosis of HepG2 cells.Further mechanisms shown that GO-COOH inhibited BaP-induced mitochondrial dysfunction such as decreased mitochondrial membrane potential,decreased mitochondrial ROS production and ATP synthesis by down-regulating the level of pro-apoptotic Bcl-2 family proteins,and maintained intracellular homeostasis,thereby reducing BaP-induced apoptosis.GO-COOH could not only inhibited the DNA damage response induced by BaP,downregulated the expression of pro-apoptotic proteins mediated by p53.but also scavenged excessive ROS,reduced lipid peroxidation and depletion of GSH.then alleviated oxidative stress.