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Genotoxicity and modulation of p53 protein expression in human lung A549 cells upon exposure to single and combined aflatoxin B1, sterigmatocystin and fumonisins B1 and B2

Background: Aflatoxin B1 (AFB1) and its structurally related precursor in biosynthesis sterigmatocystin (STC) are genotoxic liver cancerogens produced by different fungi, namely of the genus Aspergillus (1). Liver and kidneys are the target organs of fumonisins, mycotoxins also produced by various fungi. The toxic properties have been well established for FB1 isoforme that was generally considered a non- genotoxic cancerogen and a promotor of the cancerogenesis with an oxidative stress being a main cause of DNA damage. In more recent studies, it has been found that fumonisin B2 (FB2) is an isoforme produced by black Aspergilli (2). The p53 tumor suppressor protein regulates the transcription of numerous genes required for appropriate cellular response to DNA damage. DNA damage induces phosphorylation of p53 at Ser15 promoting both the accumulation and activation of p53 in response to DNA damage (3). Considering the simoultaneus presence of mycotoxins in various indoor environments (4) it is becoming interesting to investigate their effects on the cells originating from the respiratory system in order to estimate their effects upon the inhalation. Materials and methods: Alkaline comet assay was employed to investigate the genotoxic potencies of AFB1, STC, FB1 and FB2, applied single and in binary mixtures (AFB1 or STC + FB1 or FB2), on human lung adenocarcinoma cells (A549). Upon the same treatment in A549 cells' lysate p53 protein expression (total and phosphorylated at Ser15) was measured by ELISA commercial kit. Results and discussions: Significant levels of DNA damage were comfirmed for both AFB1 and STC applied in subcytotoxic concentrations indicating higher genotoxic potential of STC compared to AFB1. Those actions were supported by elevated levels of both total and phosporilated form of p53 that was not significantly affected upon addition of FB1 or FB2, single or in mixtures with AFB1. However, phospho-Ser15-p53 significantly increased upon simultaneous addition of STC and FB2. Conclusions: These results suggest specific and direct genotoxic effect of AFB1 and STC in A549 cells and antagonistic effect of their binary mixtures with FB1 or FB2 moderated by p53. References (1) Wang JS, Groopman JD. DNA damage by mycotoxins. Mutat Res 1999 ; 424(1–2):167–81. (2) Scott PM. Recent research on fumonisins: a review. Food Addit Contam Part A 2012 ; 29(2):242–8. (3) Milczarek GJ, Martinez J, Bowden GT. p53 Phosphorylation: biochemical and functional consequences. Life Sci 1997 ; 60(1):1–11. (4) Tӓubel M, Hyvӓrinen A. Occurence of mycotoxins in indoor environment. In: Viegas C, Pinheiro AC, Sabino R, Viegas S, Brandão J, Veríssimo C, editors. Environmental Mycology in Public Health- Fungi and mycotoxins risk assessment and management. 1st ed. Academic Press ; USA, 2016. p. 299–323.

A549 cells, aflatoxin B1, fumonisins, genotoxicity, p53, phospho-Ser15-p53, sterigmatocystin

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