The Mechanisms of Genotoxicity Induced by ZnO and TiO2 Nanoparticles in Aquatic Environment during the Aging Process

Author:Wang Juan

Supervisor:xu an


Degree Year:2019





The large manufactured quantities and widespread use of nanomaterials confer substantial potential for environmental release.Unintentionally released nanomaterials would inevitably interact with environmental components,resulting in various transformation(chemical,physical and biological transformation)and consequently leading to unexpected health risk.Zinc oxide nanoparticles(ZnO NPs)and titanium dioxide nanoparticles(TiO2 NPs)as two typical metal oxide nanoparticles are being produced abundantly and applied increasingly in various fields.In aquatic environment,the unique properties of ZnO NPs and TiO2 NPs make them incline to undergo physicochemical transformation over time(aging),driving ZnO NPs and TiO2 NPs away from their pristine state,which in turn modify their bioavailability and toxicity.However,the subcellular targets and the underlying molecular mechanisms involved in the cyto-genotoxicity induced by ZnO NPs and TiO2 NPs during aging process are still unknown.With the help of human-hamster hybrid(AL)cells,the main objectives of this study were to clarify the adverse effects of ZnO NPs and Ti02 NPs during aging process,and then gain more insight into the subcellular targets and the underlying molecular mechanism.This study found that ZnO NPs undergo sophisticated physicochemical transformations with aging regardless of their size,and aged ZnO NPs less cytotoxic but higher genotoxicity compared with fresh NPs.While,regarding Ti02 NPs,there was no significant changes except for an aging-time dependent enhancement of average hydrodynamic size,and TiO2 NPs could induce the toxic-effects in an aging time-independent and size-dependent manner.To explore the underlying mechanisms,we found that the acute cytotoxic effects of fresh ZnO NPs were largely regulated by mitochondria-dependent apoptosis which increased the levels of cleaved Caspase-3 along with more mitochondrial damage than that of 60-day-aged ZnO NPs.In contrast,aged ZnO NPs induced more reactive oxygen species(ROS)production and endoplasmic reticulum(ER)stress marker protein(BIP/GRP78)expression and their genotoxicity could be dramatically suppressed by either ROS scavengers(dimethyl sulfoxide,catalase,and sodium azide)or ER stress inhibitor(4-phenylbutyrate).Using mitochondrial-DNA deficient(ρ0)AL cells,we further found that ER stress induced by aged ZnO NPs was triggered by ROS generated from mitochondria,which eventually mediated the genotoxicity of aged NPs.For TiO2 NPs,there was an aging-time dependent enhancement of average hydrodynamic size in TiO2 NPs stock suspensions.The cytotoxicity of fresh TiO2 NPs increased in a size-dependent manner;in contrast,their genotoxicity decreased with the increasing sizes of NPs.No significant toxicity difference was observed in cells exposed to either fresh or 60 day-aged TiO2 NPs.Both Fresh and aged TiO2 NPs efficiently induced mitochondrial dysfunction and activated Caspase-3/-7 in a size-dependent manner.Using mitochondrial-DNA deficient(p0)AL cells,we further discovered that mitochondrial dysfunction made significant contribution to the size-dependent toxicity induced by TiO2 NPs during the aging process.Taken together,our data indicated that TiO2 NPs could significantly induced the cytotoxicity and genotoxicity in an aging time-independent and size-dependent manner,which were triggered by mitochondrial dysfunction.Our data provided novel information on better understanding the contribution of subcellular targets to the genotoxic response of metal oxide nanoparticles during the aging process.This study will provide novel information in risk assessment of nanomaterials during their lifecycle.