Toxicological Mechanism Study Of TDCIPP And TPhP In Marine Medaka (Oryzias Melastigma)

Organophosphorus flame retardants(OPFRs)are an important type of phosphorus flame retardants,which are widely used in many fields such as home furnishings and building materials.As an important substitute for polybrominated diphenyl ethers(PBDEs)in the market,OPFRs are widely favored by the market due to their low environmental hazards,including tris(1,3-dichloro-2-propyl)phosphate(TDCIPP)and triphenyl phosphate(TPhP).However,with the extensive use of OPFRs,the environmental safety hazards brought about by them have gradually emerged.At present,OPFRs have been detected in a variety of environmental media such as the atmosphere,soil,water,sediments and other organisms such as mammals and freshwater organisms.Therefore,the environmental ecotoxicological effects of OPFRs have received widespread attention from the society.Previous studies have found that exposure of TDCIPP and TPhP affects the survival,development,reproduction and metabolism of aquatic organisms.The concentration levels of TDCIPP and TPhP in the marine environment are equivalent to those in the freshwater environment.However,the study of toxicity mechanism mostly focuses on freshwater organisms,and there is little research on marine organisms and lack of in-depth discussion.Therefore,this study used the marine model species-marine medaka(Oryzias melastigma)as the test organism.The marine medaka is small in size,has a short life cycle,transparent in embryos and adults,and has high spawning and easy reproduction which is easy to cultivate and carry out experiments in the laboratory.Through real-time quantitative polymerase chain reaction(q-PCR),our study explored the toxic mechanism of TDCIPP and TPhP,from the four aspects of cartilage and bone development,heart development,fatty acid synthesis and metabolism,and endocrine regulation.The main research contents and conclusions are as follows:1.TDCIPP and TPhP affect the expression of bmp2,bmp4 and runx2 genes related to the cartilage and bone development of the marine medaka,causing developmental abnormalities in the organism.Among them,TDCIPP led to the up-regulation of the expression of regulatory genes related to cartilage and bone development in the two generations of larvae,while TPhP exposure led to the down-regulation of the expression of these genes.Therefore,although these two substances can cause the pectoral fins of turn out and the spinal curvature of adult,they have different mechanisms for the regulation of cartilage and bone development.2.The development of the heart of the marine medaka is affected by exposure of TDCIPP and TPhP,resulting in the abnormality of embryonic heart rate slowing and pericardial cysts in larvae.Among them,TDCIPP exposure caused damage to the heart development of marine medaka which mainly due to the up-regulation of cypla and cox-2 expression and the up-regulation of gata4 induced by the AHR/ARNT receptor pathway.In contrast,the mechanism of TPhP is different.TPhP may affect cyp1a gene expression by activating AHR/ARNT receptor function,but has no significant effect on arnt gene expression.3.Exposure to TDCIPP and TPhP affects the expression of genes that control fatty acid synthesis and metabolism in the marine medaka,leading to the disorder of fatty acid metabolism.In the larval stage,TDCIPP exposure led to the up-regulation of fatty acid synthesis genes(ppary,accα,fas,srebp-1c and srebp2),which in turn induced an increase in fatty acid synthesis,resulting in an increase in fat content in the liver of adult fish.However,TPhP exposure resulted in the down-regulation of fatty acid synthesis and metabolism-related genes(pparγ,accα,fas,srebp-1c,srebp2,ppara and cpt-1),causing metabolic disorders in the medaka fish.4.TDCIPP and TPhP affect the sex hormones and the expression of HPG axis regulatory factors in the organism.They led to an increase in the E2/T ratio which causing developmental toxicity such as abnormal gonadal dysplasia,abnormal sex ratio,and reproductive toxicity such as decreased fertility.It had different toxic effects from exposure.TDCIPP exposure resulted in increased expression of genes related to steroid production(cyp17a1,cyp19a,star,cyplla,3β-hsd and 17β-hsd)and HPG axis related genes(gnrh2,gnrhr2,fshβ,Ihβ,fshr and lhr).Exposure caused an increase in the expression of T transformation-related genes(srd5al),while the expression of E2 transformation-related genes(cyp1a1 and cyp1b1)was basically stable.This increased the E2 content and decreased the T content.TPhP exposure increased the expression of genes related to the HPG axis(gnrh2,fshβ and lhβ)in male fish,and increased the expression of genes related to FSH production and in the HPG axis of female fish.In both males and females,the expression of T transformation-related genes increased,while the expression of E2 transformation-related genes was basically stable.This resulted in the increase of E2 and T content in male fish;the increase of E2 content in female fish,and the basically stable T content.TDCIPP and TPhP led to a significant increase in the expression of the estrogen-like interferor marker vtg in the liver,indicating that the two may play a role through the estrogen-like interferor.