Evaluation of the effects of combined exposure to endocrine disruptor chemical substances in HEPG2 cell line

Endocrine disruptors are synthetic or natural substances that disrupt the normal functioning of the body by mimicking or blocking hormones. They are suggested to affect many basic periods and characteristics like growth, stress response, sexual development, reproduction ability, insulin production and utility. Bisphenol A (BPA) is a plasticizer used for the hardening plastics, epoxy resins and polycarbonates. Phthalates are softening plasticizers that give flexibility to polyvinyl chloride containing plastics. The most widely used phthalate derivative is di(2-ethylhexyl)phthalate (DEHP). Its main metabolite is mono(2-ethylhexyl)phthalate (MEHP) and it is more toxic than the parent compound. There are several studies in literature on their endocrine disrupting properties. On the other hand, it has been denoted that both BPA and phthalates are peroxisome proliferators and they cause hepatocarcinogenesis in rodents. Humans are exposed to these chemicals by different routes through their whole life starting from fetal period. In addition, exposure to these chemicals actualize not by one by one, by in a combination in everyday life. There are studies in literature on the endocrine disrupting effects; however there are very limited number of studies showing their combined effects. In light of this information, the toxic effects of BPA and/or MEHP are investigated in HepG2 cell line. In this thesis, cytotoxic properties as well as cytopathological and apoptotic changes were studied when cells were exposed to these plasticizers separately or in combination; oxidative stress, oxidant/antioxidant status alterations and endoplasmic reticulum (ER) stress were evaluated as possible underlying mechanisms for their unwanted effects after exposure. The results showed that particularly combined exposure to BPA and MEHP caused substantial increases in oxidative stress, ER stress marker protein expressions and also caused significant apoptosis. It can be suggested that combined exposure disrupts intracellular homeostasis by many different mechanisms. The results of ER stress studies indicate that one of the toxicity mechanisms underlying both single and combined exposures is the alterations of ER marker proteins in both cytoplasmic and nuclear cellular fractions. Moreover, combined exposure triggers apoptosis as well as necrotic and autophagic cell death. As a result, combined exposure to endocrine disrupting chemicals can cause serious toxicological outcomes and the data obtained herein can contribute significantly to the literature on endocrine disruptors.