REPOSITORY > RESULTS

Abstract

Exposure to environmental pollutants in everyday life is inevitable. Humans and other organisms are constantly exposed to a mixture of chemicals consisting of naturally present and anthropogenic substances. Lack of data on toxicological properties and biochemical interactions between different chemicals is the main limitation for efficient risk assessment.
In this thesis, two groups of pollutants originating from distinct sources were selected and their cytotoxic and genotoxic potential was assessed – cyanotoxins as naturally produced and bisphenols as anthropogenic pollutants. Cyanotoxins are cyanobacterial metabolites present in waters, especially where the growth of cyanobacteria is expanded due to eutrophication and global warming. Adverse effects of certain known cyanotoxins are proven; however, numerous newly discovered cyanotoxins that are increasingly occurring in blooming water have been detected recently while their toxicological profiles have not been investigated yet. Contrary to cyanotoxins, bisphenol A and its analogues are produced by humans as important components in the production of plastic and epoxy materials. They are present in various food packagings and other products in everyday use, but due to the leakage from the production industry as well as plastic waste, they are nowadays ubiquitously present in the environment. Both groups of these pollutants include several substances known to be genotoxic. This thesis aims to assess genotoxic potential of cyanobacterial toxins and BPA congeners for which this information is missing and their genotoxic potential in combined exposure scenarios relevant for the environmental exposure.
We provided the first data on the genotoxicity of cyanotoxins L-BMAA and microginins. Results showed that L-BMAA is not causing mutations and DNA damage in the bacterial test system, while microginins have the potential to induce DNA strand breaks and genomic instability in the human-derived cell line HepG2.
Exposure of HepG2 cells to cyanobacterial extract containing different microginins and to the mixture of microcystin LR (MCLR) and cylindrospermopsin (CYN) revealed that combined genotoxic effects of these cyanotoxins are not equal to the sum of individual effects. The results indicate antagonistic interactions or prevalence of the effect of one substance. In the MCLR/CYN mixtures, the genotoxic effect CYN was shown to be predominant. MCLR is a well-studied cyanotoxin characterised as a possible human carcinogen; however, it was observed that CYN evinces even stronger genotoxic activity.
The comparison of genotoxic activity of bisphenol A and its most common analogues, bisphenols (BPs) S, F, and AF, revealed that BPAF has the highest genotoxic potential, despite the presumption that the analogues are safer than BPA itself. The transcriptomic analyses demonstrated that BPA and BPAF, as well as their combinations with other bisphenols, induced changes in gene expression also at low, for human exposure relevant concentrations. Combined exposure to bisphenols and cyanotoxin CYN confirmed the predominant DNA damaging effect of CYN, while transcriptomic analyses indicated additive or synergistic interactive effects in the CYN/BPs mixtures on the expression of several tested genes.
The need for reliable in vitro toxicological data for the risk assessment is rising with increasing production of new chemicals and the ethical issue of animal testing. The 3D experimental models that better represent in vivo conditions than conventional monolayer cell cultures are being developed to bridge the gap between in vitro and animal studies. In this study, we applied a novel 3D in vitro HepG2 model, which we developed for assessing the cytotoxicity and genotoxicity of CYN. CYN affected the growth of spheroids and induced cell cycle arrest. Gene transcription analyses revealed deregulation of genes involved in phase I and phase II metabolism, DNA damage response, cell proliferation and apoptosis.
The results of the thesis provided the missing toxicological data of emerging pollutants - cyanotoxins and bisphenols, and contributed to better understanding of chemical interactions in the co-exposure. It was again confirmed that the concentration addition concept in mixture risk assessment is unjustified, since the experimental data indicate more complex interactions. Moreover, we emphasise the importance of considering the co-exposure to chemicals of distinct sources and functions, which is often neglected in risk assessment.