The utility of metabolic activation mixtures containing human hepatic post-mitochondrial supernatant (S9) for<i>in vitro</i>genetic toxicity assessment
Bibliographic record
Abstract
In vitro genotoxicity assessment routinely employs an exogenous metabolic activation mixture to simulate mammalian metabolism. Activation mixtures commonly contain post-mitochondrial liver supernatant (i.e. S9) from chemically induced Sprague Dawley rats. Although Organization for Economic Cooperation and Development (OECD) test guidelines permit the use of other S9 preparations, assessments rarely employ human-derived S9. The objective of this study is to review and evaluate the use of human-derived S9 for in vitro genetic toxicity assessment. All available published genotoxicity assessments employing human S9 were compiled for analysis. To facilitate comparative analyses, additional matched Ames data using induced rat liver S9 were obtained for certain highly cited chemicals. Historical human and induced rat S9 quality control reports from Moltox were obtained and mined for enzyme activity and mutagenic potency data. Additional in vitro micronucleus data were experimentally generated using human and induced rat S9. The metabolic activity of induced rat S9 was found to be higher than human S9, and linked to high mutagenic potency results. This study revealed that human S9 often yields significantly lower Salmonella mutagenic potency values, especially for polycyclic aromatic hydrocarbons, aflatoxin B1 and heterocyclic amines (~3- to 350-fold). Conversely, assessment with human S9 activation yields higher potency for aromatic amines (~2- to 50-fold). Outliers with extremely high mutagenic potency results were observed in the human S9 data. Similar trends were observed in experimentally generated mammalian micronucleus cell assays, however human S9 elicited potent cytotoxicity L5178Y, CHO and TK6 cell lines. Due to the potential for reduced sensitivity and the absence of a link between enzyme activity levels and mutagenic potency, human liver S9 is not recommended for use alone in in vitro genotoxicity screening assays; however, human S9 may be extremely useful in follow-up tests, especially in the case of chemicals with species-specific metabolic differences, such as aromatic amines.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".