In vitro evaluation of the carcinogenic potential of perfluorinated chemicals.

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are the major components of long-chain per- and polyfluorinated alkyl substances (PFAS), known for their chemical stability and environmental persistence. Even if PFOA and PFOS have been phased out or are limited in use, they still represent a concern for human and environmental health. Several studies have been per­formed to highlight the toxicological behavior of these chemicals and their mode of action (MoA). Data have suggested a causal association between PFOA or PFOS exposure and carcinogenicity in humans, but the outcomes of epidemiological studies showed some inconsistency. Moreover, the hypothesized MoA based on animal studies is considered not relevant for human cancer. To improve the knowledge on PFAS toxicology and contribute to the weight of evidence for the regu­latory classification of PFAS, we used the BALB/c 3T3 cell transformation assay (CTA), an in vitro model under consideration to be included in an integrated approach to testing and assessment for non-genotoxic carcinogens (NGTxCs). PFOS and PFOA were tested at several concentrations using a validated experimental protocol. Our results demonstrate that PFOA does not induce cell transformation, whereas PFOS exposure induced a concentration-related increase of type III foci. Malignant foci formation was triggered at PFOS concentrations equal to or higher than 50 ppm and was not directly associated with cytotoxicity or proliferation induction. The divergent CTA outcomes suggest that different molecular events could be responsible for the toxicological profiles of PFOS and PFOA, which were not fully captured in our study.

PFAS chemicals are known for their durability and resistance to heat, water, and oil. They are per­sistent in the environment and may pose health risks despite decreased use. This study explored PFOS and PFOA, two common PFAS chemicals, to understand their potential harm and cancer risk. To better understand how they might be harmful, we conducted a cell-based test that can resemble the carcinogenesis process in experimental animals. The test revealed PFOS, but not PFOA, can cause cancer-like changes, at levels of 50 parts per million or higher. This result suggests different PFAS chemicals affect cells differently, but we need more research to understand exactly how they work and how they might cause cancer. Understanding this could help regulate and reduce PFAS harmful effects. This research aligns with 3R principles by using cell-based tests as an alternative to animal testing, thereby promoting ethical research practices.

Mechanistic Interrogation of Cell Transformation In Vitro: The Transformics Assay as an Exemplar of Oncotransformation.

The Transformics Assay is an in vitro test which combines the BALB/c 3T3 Cell Transformation Assay (CTA) with microarray transcriptomics. It has been shown to improve upon the mechanistic understanding of the CTA, helping to identify mechanisms of action leading to chemical-induced transformation thanks to RNA extractions in specific time points along the process of in vitro transformation. In this study, the lowest transforming concentration of the carcinogenic benzo(a)pyrene (B(a)P) has been tested in order to find molecular signatures of initial events relevant for oncotransformation. Application of Enrichment Analysis (Metacore) to the analyses of the results facilitated key biological interpretations. After 72 h of exposure, as a consequence of the molecular initiating event of aryl hydrocarbon receptor (AhR) activation, there is a cascade of cellular events and microenvironment modification, and the immune and inflammatory responses are the main processes involved in cell response. Furthermore, pathways and processes related to cell cycle regulation, cytoskeletal adhesion and remodeling processes, cell differentiation and transformation were observed.

Co-carcinogenic effects of vitamin E in prostate.

A large number of basic researches and observational studies suggested the cancer preventive activity of vitamin E, but large-scale human intervention trials have yielded disappointing results and actually showed a higher incidence of prostate cancer although the mechanisms underlying the increased risk remain largely unknown. Here we show through in vitro and in vivo studies that vitamin E produces a marked inductive effect on carcinogen-bioactivating enzymes and a pro-oxidant status promoting both DNA damage and cell transformation frequency. First, we found that vitamin E in the human prostate epithelial RWPE-1 cell line has the remarkable ability to upregulate the expression of various phase-I activating cytochrome P450 (CYP) enzymes, including activators of polycyclic aromatic hydrocarbons (PAHs), giving rise to supraphysiological levels of reactive oxygen species. Furthermore, our rat model confirmed that vitamin E in the prostate has a powerful booster effect on CYP enzymes associated with the generation of oxidative stress, thereby favoring lipid-derived electrophile spread that covalently modifies proteins. We show that vitamin E not only causes DNA damage but also promotes cell transformation frequency induced by the PAH-prototype benzo[a]pyrene. Our findings might explain why dietary supplementation with vitamin E increases the prostate cancer risk among healthy men.

Hazard assessment of air pollutants: The transforming ability of complex pollutant mixtures in the Bhas 42 cell model.

The use of in vitro alternative methods is a promising approach to characterize the hazardous properties of environmental chemical mixtures, including urban airborne particulate matter (PM). The aim of this study was to examine seasonal differences in the toxic and transforming potential of PM samples, by using the in vitro cell transformation assay in Bhas 42 cells for the prediction of potential carcinogenic effects. Bhas 42 cells are already initiated, and the v-Ha-ras transfection, together with genetic modification following the immortalization process, makes them a valuable model to study the late steps of cellular transformation leading to the acquisition of the malignant phenotype. Exposure to organic extracts of PM1 and PM2.5 induced dose-related effects. The transforming and cytotoxic properties are related to the amount of PM collected during the sampling campaign and associated with the concentrations of polycyclic aromatic hydrocarbons (PAHs) in the samples. All the samples induced cell transformation following prolonged exposure of 2 weeks. Our results support the utility of the in vitro top-down approach to characterise the toxicity of real mixtures, thereby supporting regulators in the decision-making process. The results also identify the need for appropriate assay selection within the in vitro testing strategy to address the complexity of the final adverse outcomes.

The transformics assay: first steps for the development of an integrated approach to investigate the malignant cell transformation in vitro.

The development of alternative methods to animal testing is a priority in the context of regulatory toxicology. Carcinogenesis is a field where the demand for alternative methods is particularly high. The standard rodent carcinogenicity bioassay requires a large use of animals, high costs, prolonged duration and shows several limitations, which can affect the comprehension of the human relevance of animal carcinogenesis. The cell transformation assay (CTA) has long been debated as a possible in vitro test to study carcinogenesis. This assay provides an easily detectable endpoint of oncotransformation, which can be used to anchor the exposure to the acquisition of the malignant phenotype. However, the current protocols do not provide information on either molecular key events supporting the carcinogenesis process, nor the mechanism of action of the test chemicals. In order to improve the use of this assay in the integrated testing strategy for carcinogenesis, we developed the transformics method, which combines the CTA and transcriptomics, to highlight the molecular steps leading to in vitro malignant transformation. We studied 3-methylcholanthrene (3-MCA), a genotoxic chemical able to induce in vitro cell transformation, at both transforming and subtransforming concentrations in BALB/c 3T3 cells and evaluated the gene modulation at critical steps of the experimental protocol. The results gave evidence for the potential key role of the immune system and the possible involvement of the aryl hydrocarbon receptor (AhR) pathway as the initial steps of the in vitro transformation process induced by 3-MCA, suggesting that the initiating events are related to non-genotoxic mechanisms.

Identification of pathway-based toxicity in the BALB/c 3T3 cell model.

The particulate matter represents one of the most complex environmental mixtures, whose effects on human health and environment vary according to particles characteristics and source of emissions. The present study describes an integrated approach, including in vitro tests and toxicogenomics, to highlight the effects of air particulate matter on toxicological relevant endpoints. Air samples (PM2.5) were collected in summer and winter at different sites, representative of different levels of air pollution. Samples organic extracts were tested in the BALB/c 3T3 CTA at a dose range 1-12m(3). The effect of the exposure to the samples at a dose of 8m(3) on the whole-genome transcriptomic profile was also assessed. All the collected samples induced dose-related toxic effects in the exposed cells. The modulated gene pathways confirmed that toxicity was related to sampling season and sampling site. The analysis of the KEGG's pathways showed modulation of several gene networks related to oxidative stress and inflammation. Even if the samples did not induce cell transformation in the treated cells, gene pathways related to the onset of cancer were modulated as a consequence of the exposure. This integrated approach could provide valuable information for predicting toxic risks in humans exposed to air pollution.

Morpho-physiological and biochemical responses in the floating lamina of Trapa natans exposed to molybdenum.

The response to molybdenum (Mo) was studied in the metal-tolerant hydrophyte Trapa natans L. Previously, it was shown that the plant accumulates Mn in the floating lamina by means of phenolic compounds and responded with acclimation responses of the chloroplast. Since the involvement of phenolics has been proposed also in Mo resistance, we tested the response of T. natans to increasing doses (5, 50, 150, 600 microM) of Mo using the photosynthetic apparatus as an indicator of cellular stress. Only 5 microM Mo did not cause evident modifications with respect to controls. Conversely, 50 to 600 microM Mo induced progressively marked alterations of the lamina morphology. The chloroplast ultrastructure showed disorganisation of the thylakoid system, and correspondingly, the photosynthetic pigment pattern was altered with a fall-down in photosynthesis. Microspectrofluorimetry indicated alterations of photosystem II, with differences among the three cell layers (first and second palisade and spongy tissues). While the highest dose caused plant death, 50 and 150 microM Mo-treated plants underwent partial recovery, and the plant survived up to the end of the vegetative season. However, reproduction was unsuccessful. Mo treatment did not induce increase in total phenolics, but only in anthocyanin. In contrast to Mn, detoxification of Mo by chelation inside vacuoles, possibly by anthocyanins, is suggested to be an insufficient mechanism to reduce Mo toxicity, which probably includes an impairment of nitrogen metabolism. However, the metal was accumulated in the lamina. On the whole, T. natans showed limited capabilities to survive Mo excess as compared with Mn.