Liver is the central detoxification organ and main regulator of systemic iron homeostasis and storage. Iron is an essential micronutrient for almost all organisms. Iron plays a vital role in numerous biological processes, such as oxygen metabolism, mitochondrial energy metabolism, hematopoiesis, muscle function, production of enzymes responsible for cell growth and differentiation, DNA replication and repair. On the other hand, iron is a bioactive element, which promotes the formation of reactive oxygen species. Increased iron stores may lead to DNA strand breaks, protein fragmentation, DNA adducts formation, oxidation of proteins and lipids, factors that promote cell necrosis and apoptosis development. Primary liver cancer is one of the most common causes of cancer-related death worldwide. The main risk factors that account for most hepatocellular carcinoma (HCC) cases are chronic viral hepatitis B and C infection, cirrhosis, liver fibrosis, chemical exposure, alcohol consumption, obesity, and non-alcoholic fatty liver disease (NAFLD). In recent years, it has become increasingly evident that alterations in systemic and intracellular iron homeostasis play an important role in HCC development and progression. However, there is a lack of conclusive information regarding the hepatotoxins and hepatocarcinogens influence on the status of hepatic iron metabolism and mechanisms of their action. Based on these considerations, in current study, we investigated 2-acetylaminofluorene (2-AAF) effect on the iron metabolism status in the livers of Sprague-Dawley rats. The aromatic amine 2-AAF is a potent mutagen and carcinogen causing tumors in various species and tissues, including liver. 2-AAF shows genotoxic (genetic) and non-genotoxic (epigenetic) effects. Conversion of 2-AAF to N-sulfonoxy-2-acetylaminofluorene (acetylaminofluorene-N-sulfate), which appears to be the main carcinogenic metabolite in rat liver, leads to formation of non-enzymatic reaction with nucleophilic sites on proteins and nucleic acids. Non-genotoxic ability of 2-AAF to induce chronic liver toxicity and cellular homeostasis disturbance, may also play important role in tumors development and progression. In our study, using quantitative reverse transcription-PCR techniques and Western blot analysis, we showed that treatment of male Sprague-Dawley rats with 0.02% of 2-AAF for 24 weeks increased the expression of iron metabolism-related genes, transferrin receptor 1 (Tfrc) and ferritin light chain (Ftl), while the level of ferroportin (Fpn1) mRNA was decreased. In the mammalian cells, especially in hepatocytes, TFRC and FTL play the major role in iron uptake and storage, when FPN1 is an important iron exporter. Additionally, exposure of rats to 2-AAF resulted in an increase of TFRC and FTL protein level. In contrast, the level of FPN1 did not change in the liver of 2-AAF-treated rats. This resulted in an elevation of TFRC/FPN1 ratio, a condition that favors an accumulation of iron in the preneoplastic livers. Thus, the findings of the presented study demonstrate extensive alterations of hepatic iron metabolism, and these dysregulation may be involved in the pathogenesis and mechanism of chemical-induced liver carcinogenicity. These results may provide a basis for the developing of mechanism-based preventive strategies for chemical-mediated liver cancer and pathologies.
Keywords: iron metabolism, cancer, liver
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