Thesis title: Genotoxic effects of plastic leachates and plastic-related chemicals, Bisphenol A (BPA) and perfluorooctanoic acid (PFOA), in Drosophila melanogaster
The object of this thesis was to test the genotoxic effect of emerging contaminants on an exceptional model organism such as Drosophila melanogaster. Its easy manipulation under experimental conditions, the genomic resources it has to monitor changes at the DNA level and its extreme sensitivity to environmental stress factors, have made it a perfect organism to understand the potential harmful effect of contaminants with which all organisms, including humans , come into contact every day.
The choice of this organism in toxicology studies has given rise to a new area of research: Drosophototoxicology.
In our study, the toxicological effects of contaminants deriving from the leaching of plastic materials of polyethylene (PE) and polypropylene (PP), both oxo-degradable and non-oxo-degradable, additives of plastic materials such as bisphenol BPA and a persistent organic compound, perfluorooctanoic acid PFOA, were evaluated.
The toxicological effects of these contaminants were assessed, integrating genetic, molecular and behavioural approaches.
A multitude of toxicities have been found; exposure to leachates induced chromosomal abnormalities and activation of transposable elements, mobile genetic elements that constitute an important fraction of eukaryotic genomes and enable them to adapt and respond environmental challenges.
Their de-silencing emerged following the decondensation of heterochromatin, an extremely compact region of the genome, which , due to the presence of the leachates loses its structural characteristics, by expressing sequences that are generally kept silenced. In support of the derepression of these sequences, the genetic test of variegation by position effect (concerning the epigenetic silencing of a euchromatic gene that is relocated to the constitutive heterochromatin) confirmed the decondensation of heterochromatin.
The latter was further evidenced through cytological analysis of larval brains, which showed not only decondensations but also multiple chromosomal abnormalities, indicative of genomic instability. For this reason, it was useful and essential to study the ability of these substances to interfere with the locomotor function of flies through the behavioural assay known as climbing assay, which confirmed the neurotoxicity induced by these substances.
The combined effects of DNA damage and transposition events, in addition to contributing to genomic instability promote heterozygosity loss events and enhance tumour growth and metastatic behaviour of RASV12 clones.
These last two events were also observed following treatment with emerging contaminants such as BPA and PFOA, which also caused chromosomal abnormalities in larval brains, evidenced by cytological analysis.
The ability of these toxicants to synergize with the oncogenic potential RASV12, promoting neoplastic growth with metastasis events and uncontrolled tumour expansion, highlights the carcinogenic role of these substances.
Among the toxicities tested, melanisation events observed through visual analysis of larval cuticles were a clear response of immune system hyperactivation, delineating a framework of immunotoxicity. This required a molecular investigation of the expression levels of effector genes downstream of immune system pathways. Although these data are preliminary and require further investigation in the future, the visibly increased expression levels confirmed the hyperactivation of the immune system. This thesis focuses on understanding the biological damage induced by emerging contaminants, which are extremely resistant and ubiquitous in all ecosystems.