Chiral Polychlorinated Biphenyls Are Biotransformed Enantioselectively by Mammalian Cytochrome P-450 Isozymes to Form Hydroxylated Metabolites
Bibliographic record
Abstract
In vitro incubations of purified rat cytochrome P-450 (CYP) 2B1 and human CYP 2B6 were performed to determine if CYP isozymes biotransform polychlorinated biphenyls (PCBs) enantioselectively. Enantioselective metabolism of chiral PCBs 45, 84, 91, 95, 132, and 136 and production of hydroxylated PCB metabolites (OH-PCBs) were observed, while no changes in PCB 183 atropisomer composition were observed for either isozyme. Enantiomer fractions (EFs) of parent PCBs, individually incubated as racemates at 25 ng/mL initial concentration, with rat CYP 2B1 ranged from 0.353 to 0.822. Enantioselectivity was also observed for PCBs 45 (EF = 0.437) and 132 (EF = 0.537) incubated at that concentration with human CYP 2B6. Both atropisomers of chiral PCBs appeared to be biotransformed simultaneously by rat CYP 2B1, except for (+)-PCB 132, but at different rates. Hydroxylated PCBs were identified using gas chromatography-high resolution mass spectrometry for all chiral PCBs enantioselectively transformed by CYPs. These metabolites did not correspond to any commercially available authentic standards, supporting the hypothesis that many unidentified OH-PCBs detected in wildlife may have arisen from in vivo biotransformation of chiral PCBs. A rough estimate suggested that more than half of the total congener metabolized by rat CYP 2B1 was converted to OH-PCBs. Similar concentration decreases were observed for congeners incubated with human CYP 2B6, but less OH-PCBs were formed. Formation of OH-PCBs via an enantioselective OH insertion mechanism was suggested, and may be a source of the unidentified OH-PCBs currently found in the environment.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".