The role of marine nutrients in 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity in vitro and in vivo

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most potent dioxin congener and is associated with several adverse health effects. As a result of its high lipophilicity and slow degradation the compound easily accumulates in the environment and foods. A prominent source for human exposure to TCDD is through the consumption of fatty fish. However, fatty fish is also a prominent dietary source for the essential 3-n fatty acids DHA and EPA. Risk-benefit analyses consistently concludes that the health benefits obtained through fish consumption outweighs the risk of dioxin exposure. However, in 2018 EFSA reduced the tolerable weekly intake (TWI) by 7-fold for dioxin and dl-PCBs in foods. The reduction was based on a longitudinal study investigating the negative effects in semen parameters by dioxin and dl-PCBs in Russian boys. The aim of the present study was to investigate if TCDD can induce a similar toxic response in testis as in the liver, and if the toxicity is related to the induction of the aryl hydrocarbon receptor. Furthermore, potential interactions between TCDD and n-3 fatty acids was investigated, to examine whether n-3 fatty acids can affect TCDD toxicity. The aims were investigated using in vitro and in vivo models. Established cell lines, including hepatocytes, Sertoli, and Leydig cells, were pre-incubated with n-3 fatty acids prior to TCDD exposure. Additionally, a previously performed animal study based on salmon fed mice was included to examine the potential differences in established cell lines and in a complete biological system. The aims were primarily investigated using cell impedance assay, and protein- and gene expression analysis. The present study demonstrates lack of Cyp1a1 expression in testis at protein- and gene level and highlights possible alternative TCDD-mediated responses. Analyses of hepatocytes and Sertoli cells identified no significant interaction effects between TCDD and n-3 fatty acids. Nor a significant interaction between TCDD and marine nutrients was observed. A distinct difference in Cyp1a1 protein expression in liver was observed in vitro versus in vivo. Cyp1a1 was only observed in in vitro hepatocytes. The results of the present study indicate that alternative mechanisms are involved as TCDD-mediates its toxicity in testis. Interaction effects between TCDD and n-3 fatty acids was not observed in this study. However, n-3 fatty acids’ potential in protecting against the effect of TCDD toxicity is promising and should thus be further elucidated