Is a liver comparable to a liver? A comparison of different rat-derived S9-fractions with a biotechnological animal-free alternative in the Ames fluctuation assay

DNA adductomics aided rapid screening of genotoxic impurities using nucleosides and 3D bioprinted human liver organoids

Current genotoxicity assessment methods are mainly employed to verify the genotoxic safety of drugs, but do not allow for rapid screening of specific genotoxic impurities (GTIs). In this study, a new approach for the recognition of GTIs has been proposed. It is to expose the complex samples to an in vitro nucleoside incubation model, and then draw complete DNA adduct profiles to infer the structures of potential genotoxic impurities (PGIs). Subsequently, the genotoxicity is confirmed in human by 3D bioprinted human liver organoids. To verify the feasibility of the approach, lansoprazole chloride compound (Lanchlor), a PGI during the synthesis of lansoprazole, was selected as the model drug. After confirming genotoxicity by Comet assay, it was exposed to different models to map and compare the DNA adduct profiles by LC-MS/MS. The results showed Lanchlor could generate diverse DNA adducts, revealing firstly its genotoxicity at molecular mechanism of action. Furthermore, the largest variety and content of DNA adducts were observed in the nucleoside incubation model, while the human liver organoids exhibited similar results with rats. The results showed that the combination of DNA adductomics and 3D bioprinted organoids were useful for the rapid screening of GTIs.

Curcumol metabolized by rat liver S9 fraction and orally administered in mouse suppressed the proliferation of colon cancer in vitro and in vivo

Following 3R (reduction, refinement, and replacement) principles, we employed the rat liver S9 fraction to mimic liver metabolism of curcumol having high in vitro IC50 on cancer cells. In HCT116 and HT29 colon cancer cells, the metabolites of curcumol by S9 fraction exerted more enhanced activity in inducing cell cycle arrest and apoptosis via regulating the expression of cyclin D1, CDK1, p21, PARP and Bcl-2 than curcumol. In addition, oral administration of curcumol at 4 mg/kg BW significantly suppressed the development of colon tumor induced by azoxymethane/dextran sulfate sodium, and induced cell cycle arrest and apoptosis in tumor tissues. In mass analysis, curcumenol and curzerene were identified as the metabolites of curcumol by S9 fraction metabolism. Taken together, curcumol metabolites showed the enhanced suppressive effect on colon cancer, suggesting that S9 fraction can be considered as simple, fast, and bio-mimicking platform for the screening of chemical libraries on different chronic diseases.

Replacing animal-derived components in in vitro test guidelines OECD 455 and 487

The evaluation of single substances or environmental samples for their genotoxic or estrogenic potential is highly relevant for human- and environment-related risk assessment. To examine the effects on a mechanism-specific level, standardized cell-based in vitro methods are widely applied. However, these methods include animal-derived components like fetal bovine serum (FBS) or rat-derived liver homogenate fractions (S9-mixes), which are a source of variability, reduced assay reproducibility and ethical concerns. In our study, we evaluated the adaptation of the cell-based in vitro OECD test guidelines TG 487 (assessment of genotoxicity) and TG 455 (detection of estrogenic activity) to an animal-component-free methodology. Firstly, the human cell lines A549 (for OECD TG 487), ERα-CALUX® and GeneBLAzer™ ERα-UAS-bla GripTite™ (for OECD TG 455) were investigated for growth in a chemically defined medium without the addition of FBS. Secondly, the biotechnological S9-mix ewoS9R was implemented in comparison to the induced rat liver S9 to simulate in vivo metabolism capacities in both OECD test guidelines. As a model compound, Benzo[a]pyrene was used due to its increased genotoxicity and endocrine activity after metabolization. The metabolization of Benzo[a]Pyrene by S9-mixes was examined via chemical analysis. All cell lines (A549, ERα-CALUX® and GeneBLAzer™ Erα-UAS-bla GripTite™) were successfully cultivated in chemically defined media without FBS. The micronucleus assay could not be conducted in chemically defined medium due to formation of cell clusters. The methods for endocrine activity assessment could be conducted in chemically defined media or reduced FBS content, but with decreased assay sensitivity. The biotechnological ewoS9R showed potential to replace rat liver S9 in the micronucleus in FBS-medium with A549 cells and in the ERα-CALUX® assay in FBS- and chemically defined medium. Our study showed promising steps towards an animal-component free toxicity testing. After further improvements, the new methodology could lead to more reproducible and reliable results for risk assessment.

Quinoline is more genotoxic than 4-methylquinoline in hiHeps cells and rodent liver

Environmental pollutants, such as quinoline (QN) and 4-methylquinoline (4-MeQ), may be genotoxic and carcinogenic. Earlier studies, including in vitro genotoxicity tests, indicated that 4-MeQ is more mutagenic than QN. However, we hypothesized that the methyl group of 4-MeQ favors detoxication over bioactivation, and this factor may be overlooked in in vitro tests that do not incorporate supplementation with cofactors for enzymes that catalyze conjugation reactions. We used human induced hepatocyte cells (hiHeps), which express such enzymes, and compared the genotoxicity of 4-MeQ and QN. We also carried out an in vivo micronucleus (MN) test in rat liver, since 4-MeQ is not genotoxic in rodent bone marrow. In the Ames test and the Tk gene mutation assay, with rat S9 activation, 4-MeQ was more mutagenic than QN. However, QN induced significantly higher MN frequencies in hiHeps and rat liver than did 4-MeQ. Furthermore, QN upregulated genotoxicity marker genes much more than did 4-MeQ. We also investigated the roles of two important detoxication enzymes, UDP-glucuronosyltransferases (UGTs) and cytosolic sulfotransferases (SULTs). When hiHeps were preincubated with hesperetin (UGT inhibitor) and 2,6-dichloro-4-nitrophenol (SULT inhibitor), MN frequencies were elevated approximately 1.5-fold for 4-MeQ, whereas no significant effects were seen for QN. This study shows that QN is more genotoxic than 4-MeQ, when the roles of SULTs and UGTs in detoxication are considered and our results may improve understanding the structure-activity relationships of quinoline derivatives.

Genotoxicity of 12 Mycotoxins by the SOS/umu Test: Comparison of Liver and Kidney S9 Fraction

Liver S9 fraction is usually employed in mutagenicity/genotoxicity in vitro assays, but some genotoxic compounds may need another type of bioactivation. In the present work, an alternative S9 fraction from the kidneys was used for the genotoxicity assessment of 12 mycotoxins with the SOS/umu test. The results were compared with liver S9 fraction, and 2-4 independent experiments were performed with each mycotoxin. The expected results were obtained with positive controls (4-nitroquinoline-N-oxide and 2-aminoanthracene) without metabolic activation or with liver S9, but a potent dose-dependent effect with 4-nitroquinoline-N-oxide and no activity of 2-aminoanthracene with kidney S9 were noticed. Aflatoxin B1 was genotoxic with metabolic activation, the effect being greater with liver S9. Sterigmatocystin was clearly genotoxic with liver S9 but equivocal with kidney S9. Ochratoxin A, zearalenone and fumonisin B1 were negative in all conditions. Trichothecenes were negative, except for nivalenol, 3-acetyldeoxynivalenol, 15-acetyldeoxynivalenol, T-2 and HT-2 toxins, which showed equivocal results with kidney S9 because a clear dose-response effect was not observed. Most of the mycotoxins have been assessed with kidney S9 and the SOS/umu test for the first time here. The results with the positive controls and the mycotoxins confirm that the organ used for the S9 fraction preparation has an influence on the genotoxic activity of some compounds.

Direct Comparison of the Lowest Effect Concentrations of Mutagenic Reference Substances in Two Ames Test Formats

The Ames assay is the standard assay for identifying DNA-reactive genotoxic substances. Multiple formats are available and the correct choice of an assay protocol is essential for achieving optimal performance, including fit for purpose detection limits and required screening capacity. In the present study, a comparison of those parameters between two commonly used formats, the standard pre-incubation Ames test and the liquid-based Ames MPF™, was performed. For that purpose, twenty-one substances with various modes of action were chosen and tested for their lowest effect concentrations (LEC) with both tests. In addition, two sources of rat liver homogenate S9 fraction, Aroclor 1254-induced and phenobarbital/β-naphthoflavone induced, were compared in the Ames MPF™. Overall, the standard pre-incubation Ames and the Ames MPF™ assay showed high concordance (>90%) for mutagenic vs. non-mutagenic compound classification. The LEC values of the Ames MPF™ format were lower for 17 of the 21 of the selected test substances. The S9 source had no impact on the test results. This leads to the conclusion that the liquid-based Ames MPF™ assay format provides screening advantages when low concentrations are relevant, such as in the testing of complex mixtures.