Metabolic Charateristics And Toxic Effects Of BUVSs On Danio Rerio

Benzotriazole ultraviolet stabilizers(BUVSs)are emerging pollutants,which have environmental persistence,bioaccumulation,and endocrine disrupting effects.BUVSs are widely detected in waters and in aquatic organisms.Studies have shown that the toxic effects of BUVSs are structure-dependent,but the relationship of their biotransformation and toxic effect remains unclear.In this study,adult zebrafish(Danio rerio)was exposed to four typical BUVSs(UV-234,UV-326,UV-329 and UV-P)at10?g/L for 28 days.Intestinal histopathology was observed,and the expression levels of immune-related proteins in different tissues(kidney,intestine and blood)were evaluated to assess the immunotoxicity of BUVSs congeners.Then,two BUVSs(UV-234 and UV-326)with significant differences in structure and toxic effects were selected for futher study on metabolic process.Zebrafish embryos were exposed to 100?g/L UV-234 or UV-326 for 6 days.Toxicokinetics was studied to reveal the potency of bioaccumulation of 2 compounds.Then,the metabolomic analysis was performed to show the biological processes were changed after UV-234 or UV-326 exposure.In addition,the biotransfomation products were identified as well as activities of phase I and II metabolic enzymes were examined.Our results indicate the biotransfomation of2 BUVSs with different structures and elucidate the relationship between their metabolic process and toxicity.The main conclusions are as follows:(1)After a 28-d exposure to 10?g/L BUVSs,except for UV-326,the other BUVSs induced histological changes in intestine of adult zebrafish that included decreased goblet cells,increased mucus,and a decrease of the height of intestinal villi.Moreover,there were differences in the expression of immune-related proteins(i.e.IL-17A,IL-22,Ah R,CYP1A1,Ig G,and Ig-M)after exposure to different BUVSs.UV-234 and UV-326 exposure increased changes in Ah R and IL17/22,UV-326,UV-329,and UV-P all inhibit CYP1A1 expression,potentially causing metabolic abnormalities,leading to immunotoxicity and intestinal damage.(2)Toxicokinetic analysis showed that both the bioconcentration and depuration stages of BUVSs on zebrafish embryos/larvae conformed to the first-order kinetic model.The bioconcentration factor BCF_K of UV-234 and UV-326 was 29.72 and 39.96L/kg,respectively,indicating that the bioaccumulation capacity of UV-326 was stronger than that of UV-234.(3)The metabolomic data showed that there were 252 and 198 differential metabolites detected in 100?g/L UV-234 and UV-326 treatment groups,respectively.Amongst,145(47.5%)differential metabolites were commonly detected in both BUVSs,which were mainly associated with the energy metabolism,amino acid metabolism,and fatty acid metabolism.Pathway analysis showed that both UV-234and UV-326 affected the c GMP/PKG pathway in zebrafish larvae.UV-234 caused the increase of reactive oxygen species by affecting the metabolism of arachidonic acid and lipid metabolism,while UV-326 interfered with the metabolism of reactive oxygen species by affecting the energy cycle,resulting in oxidative stress.(4)Following exposure to 1 and 100?g/L UV-234,the fluorescence intensity of EROD and the activity of CYP1A1 enzyme were significantly increased,while the activity of GST enzyme was significantly decreased.In respnse to 100?g/L UV-326,the activity of CYP3A4 was significantly up-regulated,and the activities of GST and UGT were significantly decreased.These results indicate that phase I metabolism of UV-234 is mediated by CYP1A1 and phase I metabolism of UV-326 is mediated by CYP3A4.Moreover,both UV-234 and UV-326 could inhibit the activity of phase II metabolic enzymes in the process of biotransformation,but the types of enzymes and the degree of inhibition were different.In conclusion,BUVSs with different structures may exert their immunotoxicity through different mechanisms and have different toxicity.Due to the differences in metabolic sites as well as enzyme activities,UV-234 and UV-326 have different metabolic pathways.However,both compounds can significantly increase the activity of CYP enzymes and inhibit the activity of phase II metabolic enzymes,and commonly affected c GMP/PKG pathway.The present study will provide important toxicological proof for the environmental fate and ecological risk assessment of BUVSs.