Potential Toxicological Mechanism Of Zinc Oxide Nanoparticles On Keratinocytes In Psoriasis-like Skin Lesions

BaclkgroundZinc oxide nanoparticles(ZnO NPs)are widely used in the field of biomedicine.It is one of the commonly used materials in stomatology and often exposed to the skin and mucous membrane of the oral and maxillofacial region.With the widespread application of ZnO NPs in the population,its biosafety has attracted increasing attention from producers,users and researchers.Previous studies have shown that ZnO NPs can only enter the epidermal stratum corneum when applied to normal skin and will not cause pathological damage.However,it should not be ignored that people with inflammatory damage to the skin barrier also have a high chance of frequent exposure to ZnO NPs.Keratinocytes are the basic unit of the epidermal barrier,and the effects of ZnO NPs exposure on inflammatory skin lesions and keratinocytes in the skin lesions have not been systematically studied.This research used psoriasis-like inflammatory skin lesions with classic in vivo and in vitro models to explore this problem.ObjectiveTo determine whether ZnO NPs can enter the deep epidermis or dermis through psoriasis-like inflammatory skin lesions;to verify whether ZnO NPs affects the outcome of local inflammatory skin lesions;to explore the mechanism of ZnO NPs affecting keratinocytes in the skin lesions.Materials and methodsThe physical and chemical characteristics of ZnO NPs and its suspension were characterized by XRD,TEM and DLS.C57 mice were treated with imiquimod(IMQ)to construct the animal models of psoriasis-like inflammatory skin lesions.Human immortalized keratinocytes(HaCaT cells)were treated with human recombinant tumor necrosis factor-?(rh-TNF-?)to construct an in vitro model of the keratinocytes in inflammatory skin lesions.In vivo and in vitro models were treated with ZnO NPs suspensions or the complete medium containing ZnO NPs,separately.The changes induced by ZnO NPs in psoriasis-like inflammatory skin lesions were determined by immunohistochemistry,immunofluorescence and western blotting,the mechanism of which were clarified through applying inhibitors of ERK,p38,JNK and NF-?B and NAC.Results1.The ZnO NPs used in this research is prism-shaped with an average particle size of 41.34 nm,which agglomerated to varying degrees in pure water,normal saline,and complete medium.2.After treated with IMQ,the back skin of the mice were covered with scales,the epidermis thickened,the connection between epidermal cells lost,and the inflammatory cells infiltrated in dermis.3.ZnO NPs in the suspensions entered the deep epidermis and dermis in IMQ-induced inflammatory lesions,and were discovered in the intercellular space,basal cells and nucleus of epidermis.After ZnO NPs exposure,the level of zinc in the dermis was elevated.4.In vivo,ZnO NPs exposure delayed the recovery of IMQ-induced psoriasis-like inflammatory skin lesions,which is manifested by increased expression levels of inflammatory factors and cyclooxygenase-2 in epidermis;increased counts of inflammatory cell in dermis;increased levels of inflammatory response and apoptosis,the significant oxidative stress response and disordered glutathione antioxidant system in full-thickness skin.5.In vitro,ZnO NPs induced the increased inflammatory response and oxidative stress response and apoptosis.ZnO NPs induced alterations including the increased phosphorylation level of MAPK and NF-?B,significant nuclear translocation of NF-?B p65 as well as the upregulation of cleaved-caspase 3 and the ratio of BAX/Bcl-2.MAPK inhibitors can reduce the ZnO NP-induced inflammatory response.The inhibition of NF-?B p65 nuclear translocation and the supplement of NAC are effective to ameliorate ZnO NP-induced cell viability decline,activation of apoptosis-related pathways as well as cysteine deficiency.6.In vivo and in vitro,ZnO NPs exposure also leads to the abnormality of desmosome structure and the aggregation and collapse of keratins.ConclusionZnO NPs can enter the deep epidermis and dermis and delay the recovery of psoriasis-like inflammatory skin lesions through promoting inflammation and keratinocyte apoptosis-via the nuclear translocation of NF-?B p65 and cysteine deficiency as well as through decreasing the structural stability of epidermal barrier in subcellular level.This work reminds the public that ZnO NPs are not safe for pathological skin,especially in inflammatory skin diseases such as psoriasis,and has revealed a partial mechanism by which ZnO NPs delay the recovery of pathological skin,promoting the appropriate use of ZnO NPs.