Sulforaphane and quercetin modulate PhIP-DNA adduct formation in human HepG2 cells and hepatocytes.
Level 5 - mechanism / opinion, no new human data
In vitro laboratory study using human cell lines and primary hepatocytes (bench research).
PubMed 12949046 · doi:10.1093/carcin/bgg157
What was done
Human HepG2 cells and primary human hepatocytes were exposed to 14C-labelled 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP, 100 pM to 20 µM) with or without co-treatment with sulforaphane (SFN, 1–10 µM) or quercetin (5–20 µM). DNA adduct formation was measured using accelerator mass spectrometry. Investigators evaluated phase I (CYP1A2), phase II (UGT1A1, GSTA1), and DNA repair enzyme mRNA expression (apurinic endonuclease, DNA polymerase beta) and activities using real-time RT-PCR and enzyme assays, and tested post-exposure treatment to assess effects on DNA repair.
What was found
PhIP generated DNA adducts linearly between 100 pM and 20 µM. Co-treatment with SFN or quercetin dose-dependently reduced adduct levels. At 100 pM PhIP, adduct levels fell below the detection limit (0.15 amol PhIP/µg DNA); protection was 60% at 10 nM PhIP and 10% at 1 µM PhIP. In primary human hepatocytes exposed to 10 nM PhIP, protection reached up to 60% but showed large inter-individual variation, with some individuals showing no protection. Mechanistically, quercetin inhibited CYP1A2, whereas SFN induced UGT1A1 and GSTA1 mRNA. Neither compound altered DNA repair enzyme expression or post-exposure adduct clearance.
Why it matters
This study provides cellular evidence that dietary phytochemicals can mitigate dietary carcinogen-induced DNA damage by inhibiting metabolic activation and inducing detoxification pathways rather than enhancing DNA repair.
Limits
The study is restricted to in vitro human cell models and cannot account for human physiological bioavailability or tissue distribution. The abstract does not specify the number of hepatocyte donors, and protection dropped sharply at higher carcinogen concentrations while displaying high inter-individual variation in primary cells.
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