Developmental Toxicity Of Typical Chiral Insecticide Synthetic Pyrethroids And Their Metabolites On Zebrafish

The synthetic pyrethroids (SPs) are a class of potent and effective insecticides that have been designed and optimized based on the structures of the natural insecticide pyrethrum and widely used for agricultural and indoor pest control. Although SPs are characterized as low mammalian and avian toxic, they have been highly toxic to aquatic organisms such as fish. Furthermore, all known SPs contain two to three asymmetric positions, making them a family of pesticides with two to four pairs of enantiomers, which usually interact with biological systems selectively and may result in enantioselective aquatic toxicity. As a result, enantioselectivity in aquatic toxicity of SPs has been an issue of great concern and attracted worldwide attention.The occurrence of enantioselectivity in aquatic toxicity has been addressed for SPs mostly on acute toxicity, and several reports have also been issued on the developmental and endocrine disruption effects of fish. However, no information has been available with respect to the enantioselective toxicities on vascular development and behavior in fish so far. Besides, the aquatic toxicological assessment of SPs has been done based on the parent compounds without taking risks of the metaboites into consideration. Therefore, two pyrethroids permethrin (PM),cypermethrin (CP) and their metabolites 3-phenoxybenzoic alcohol (PBCOH),3-phenoxybenzaldehyde (PBCHO),3-phenoxybenzoic acid (PBCOOH)as well as two enantiomers of bifenthrin (BF) including 1R-BF and 1S-BF were chosen as the test compounds, and the details of our study were as follows:(1)Wild-type (AB strain) zebrafish and Fli-1:EGFP transgenic zebrafish were used to study the effects on locomotor behavior and early developmental toxicity of PM, CP and their metabolites PBCOH, PBCHO, PBCOOH. Results indicated that all the test compounds were toxic to the development of zebrafish, inducing the occurrence of sublethal malformations such as curved body axis,yolk sac edema and pericardial edema as well as mortality of zebrafish. Besides, locomotor activities of zebrafish larvae under alternating light conditions have been affected greatly by the pyrethroids and their metabolites.We also further investigated the effects on vascular development using Fli-1:EGFP transgenic zebrafish as models. The results indicated that all the test compounds were toxic to the early development and locomotor activity of zebrafish, with CP being the more toxic parent compound, and PBCHO the most toxic metabolite.(2) Previous studies have indicated that several pyrethroids including lambda-cyhalothrin, bifenthrin, fenvalerate and sumithrin possess estrogenic activities. Due to the high similarity of homologous gene between zebrafish and human as well as the significance of estrogen regulation in embryo development, the MCF-7 human breast carcinoma cell line was further chosen to evaluate the estrogenic effects of PM, CP and their metabolites PBCOH, PBCHO,PBCOOH. Results demonstrated, with exception to PBCHO, all test compounds exhibited estrogenic activities, with PBCOH being even more effective than its parent compounds by the MCF-7 cell proliferation assay (i.e.,the E-SCREEN assay) and the real-time quantitative polymerase chain reaction (qRT-PCR).The results coincided with what we have achieved in chapter 2, indicating that endocrine disruption may be one of the possible mechanisms by which SPs exert effects on early development and locomotor behavior in zebrafish.(3)Information on enantioselectivity in behavior toxicity of SPs has been restricted to the locomotor dysfunction of rodent models so far. Although previous studies have suggested that SPs possessed toxicities on behavior of aquatic organisms such as fish, no reports have been issued on the enantioselectivite effects. Therefore, we chose bifenthrin (BF) to investigate the enantioselectivity on the acute locomotor activity and the developmental toxicities of embryo-larval zebrafish, and significant differences were observed between the two enantiomers.The results indicated that 1R-BF was more toxic than 1S-BF in causing mortality and morphological impairments as well as the locomotor behavior disruption. Meanwhile, 1R-BF also had adverse effects on vascular development, causing intersegmental blood vessels to be crossed or even absent. 1R-BF-induced abnormal vascular development may be one of the reasons for the morphological impairment and locomotor behavior disruption.To sum up, we achieved conclusions as follows:first, SPs have enantioselective toxicities on early development and locomotor behavior in zebrafish, and the effects may be exerted by disruption of endocrine system and circulatory system. Behavior represents the unique interface between intrinsic and extrinsic forces, and the locomotor behavior assay using larval zebrafish may be a useful and sensitive approach for assessing the enantioselective aquatic toxicity of chiral chemicals. Secondly, our results also demonstrated that metabolites of SPs are effective both in causing developmental toxicity and endocrine disruption, indicating the metabolism may not always be a detoxification process.Therefore, the metabolites as well as the parent compound should be taken into consideration in the environmental safety assessment of SPs.