Interactions between marine nutrients and 2, 3, 7, 8 – Tetrachlorodibenzo-p-dioxin toxicity on reproduction of male wistar han rats
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Dioxins and dioxin-like polychlorinated biphenyls (dl-PCBs) are chemical congeners formed as by-products from incomplete thermic reactions, found in the environment because of improper disposal from industrial processes and combustions. Dioxins and dl-PCBs are of human concern, as they are persistent to degradation and bioaccumulates in marine food-webs. Salmon (Salmo salar) is recommended to be a part of the human diet because of healthy marine nutrients including omega-3 fatty acids, but is also one of the main routes of dioxin and dl-PCBs exposure. Dioxins and dl-PCBs which binds to the aryl hydrocarbon receptor (AHR) and elicits toxic responses, are incorporated in the toxic equivalency factor (TEF)-system. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is indicated to be the most potent congener, because of its high binding affinity to the AHR. Earlier research has found that the toxicity of TCDD alters the male reproductive system by disrupting spermatogenesis, thereby reducing sperm quantity and sperm motility, decreasing reproductive organs weights, and causing a delay in puberty. In 2018, the European food safety authority (EFSA) estimated a new tolerable weekly intake (TWI) of dioxins and dl-PCBs in food, reducing it from 14 to 2 pg toxic equivalency quotient (TEQ)/kg body weight/week. Male reproduction was one of the pivotal effects when estimating the new TWI, where the daily exposure in adults should be kept below 0.25 pg TEQ/kg bw/day. The aim of the study was to investigate if continuous doses of TCDD impacts the reproductive system, the spermatogenesis, and sperm quantity in male Wistar HAN rats. In addition, we measured whether inclusion of salmon in the diet could possibly reduce the toxicity of TCDD. Observations made throughout the animal experiment, including body mass development, feed efficiency, haematology tests, and the TCDD-levels in the liver upon sacrifice was analysed to get a wider view of possible effects between the experimental groups. An investigation on male reproduction was performed, assessing the concentration of gonadotropins participating in spermatogenesis, sperm quantity and motility, and the morphology of testis. Lastly, proteomics was performed on testis to obtain a closer look if TCDD or salmon impacts protein abundance and regulation, possibly related to spermatogenesis. In addition, a cell study using gonadotropin releasing hormone-TAG 1-7 cells were performed, assessing the toxicity of various dioxins, furans and PCB126 at doses ranging from 48pM – 1.55nM at equivalent TEQ. The results from the animal experiment analyses indicate that the toxicity of the utilised TCDD dose did not affect the reproductivity in male Wistar HAN rats, and the inclusion of salmon did not affect the toxicity. However, the results from the testis proteomics revealed that proteins related to spermatogenesis are regulated differently, but still present, when exposed to TCDD compared to the control. The conclusion is that the toxicity from the applied dose of TCDD do not disrupt male Wistar HAN reproduction in a crucial state, as no significant differences related to spermatogenesis or sperm quantity was found. The results from the in vitro cell study confirms that the applied congeners induced cells death in a dose-dependent manner, with varying toxicity even when the doses had an equivalent TEQ.
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