Metabolic Processes Of Arsenobetaine In The Marine Medaka And Mouse

Arsenic(As)is a toxic metalloid that is widely distributed in the world.Arsenic toxicity is related to its species,and inorganic As is more toxic than organic As.Inorganic As,such as arsenate(As(V))and arsenite(As(III))are highly toxic.Organic As,such as monomethylarsonic acid(MMA)and dimethylarsinic acid(DMA)are less toxic,and arsenobetaine(As B)and arsenocholine(As C)are considered weak or even non-toxic.Arsenic pollution has become increasingly serious in the water environment,and the total As content accumulated also increases in marine fish,which is a safety hazard for people who eat seafood.Arsenobetaine is the main As compound found in marine fish,accounting for more than 90%.Marine fishes overcome As stress mainly through the formation of non-toxic As B,but the biological transformation mechanism remains unclear.Humans ingest large amounts of As B through marine fish,and people will be posed with potential health risks by a long-term diet of marine fish with high As levels.The objectives of this study were to:(1)To reveal the synthesis mechanism of As B in the marine medaka,and screen and verify the key genes involved in the synthesis.(2)To simulate the long-term ingestion process of As B by humans,and illustrate the potential health risks of As B to mice by using the grouper-mouse food chain.Aiming at the above research objectives,this paper researches as follows:1.To explore the key genes involved in As B synthesis in Oryzias melastigma,we fed the As(V)-containing diet to Oryzias melastigma,and selected candidate genes related to As B synthesis by transcriptomic analysis.In the liver,40 genes were up-regulated and 23 genes were down-regulated.In the muscle,83 genes were up-regulated and 331 were down-regulated.We found that bhmt(betaine-homocysteine methyltransferase),mat2aa(methionine adenosyltransferase II,alpha a),and gstt1a(glutathione S-transferase theta 1a)played important roles in the glutathione and methionine metabolic pathways.And through the gene transformation experiment of E.coli BL21(DE3)in vitro,these three genes can affect the transformation of As C to As B.BL21-bhmt led to the oxidation of As C to As B.In addition,E.coli BL21 overexpressed mat2 aa and gstt1 a reduced the content of As B,and the expression of these two genes was down-regulated in the marine medaka.Therefore,bhmt,mat2 aa,and gstt1 a were involved in the synthesis of As B.In this study,transcriptomic screening and identification of key genes for As B synthesis in marine fishes were conducted,revealing the mechanism of As B synthesis in marine fishes and providing important insights into the process of As B synthesis.2.This study mimicked the biotransformation process of As B in mice,especially the biodegradation process,through the food chain [As B feed-grouper(Epinephelus fuscoguttatus)-mouse(Mus musicus)] to assess the potential health hazards of As B.The results showed that As B could be converted into As(V)and As(V)accumulated in the mouse tissue.The gut microbiome of mice also changed after exposure,with the abundance of Staphylococcus and Blautia increased,the expression of aqp7(aquaporin)and as3mt(As methyltransferase)was up-regulated.Conversely,sam(S-adenosine methionine)expression was down-regulated.These results suggested that demethylation and methylation occurred simultaneously in the intestine and the As demethylation capacity was greater than As methylation.In addition,Firmicutes,such as Staphylococcus and Blautia,were significantly negatively correlated with arachidonic acid,choline,and sphingosine.Microbiome and metabolomic analysis showed that Staphylococcus and Blautia,as well as arachidonic acid,choline,and sphingosine,were involved in the degradation of As B to As(V)in the mice intestine.Thus,ingestion of As B through long-term consumption of marine fish may be potentially harmful to human health.This study is helpful to assess the toxicological effects of As B on humans,and reveals the safety risks of As B acquired by humans through ingestion of marine fish,which is conducive to the early warning of the safety of aquatic products and food,and provides a theoretical basis for the health risk prediction of residents in coastal areas.In conclusion,the bhmt,mat2 aa,and gstt1 a genes were involved in the biotransformation process of As C into As B in the liver and muscle tissue of the marine medaka and affected the process of As detoxification in marine fish.Staphylococcus and Blautia,arachidonic acid,choline,and sphingosine affect the degradation process of As B to As(V)in mice.This paper revealed the regulatory mechanism of high As B enrichment in marine fish and simulated the transfer rule of As B from marine fish to mammals,which can provide theoretical support and an experimental basis for solving As pollution in marine products,reducing As toxicity,and evaluating the health hazards of As to human health,and have important practical significance for the As exposure prevention and control of human.