The use of a high-volume screening procedure to assess the effects of dietary flavonoids on human CYP1A1 expression

We examined the effects of several agents, including dietary flavonoids, on CYP1A1 expression utilizing a recently developed high-throughput screening system for assessing human cytochrome P450 (CYP) induction. HepG2 cells, s tably integrated with regulatory legions of human CYP1A1, were treated with resveratrol, apigenin, curcumin, kaempferol, green tea extract (GTE), (-)- epigallocatechin gallate (EGCG), quercetin, and naringenin. Of these flavon oids, resveratrol produced the greatest increase in CYP1A1-mediated lucifer ase activity (10-fold), whereas GTE, apigenin, curcumin, and kaempferol pro duced 2- to 3-fold increases in activity. Compared with 2,3,7,8-tetrachloro dibenzo-p-dioxin (TCDD), omeprazole, or benzanthracene, where increases in luciferase activity ranged from 12- to 35-fold, these flavonoids exhibited weak agonist activity. The remaining compounds, EGCG, quercetin, and naring enin, produced negligible effects. Cotreatment of cells with TCDD and GTE, naringenin, and apigenin resulted in 58, 77, and 74% reductions, respective ly, in TCDD-mediated CYP1A1 induction, indicating that these flavonoids exh ibit potential antagonist activity toward the aryl hydrocarbon (Ah) recepto r. Furthermore, results also suggest that GTE and apigenin possess Ah recep tor antagonist and weak agonist activities. Thus, we have shown that a 96-w ell plate assay allowing high-throughput screening for P450 induction in le ss than 24 h was efficient in determining the effects of flavonoids on huma n CYP1A expression. Signal-to-noise ratios were low, and well-to-well and r eplicate variability was below 10%, allowing induction to be easily detecte d in this system. These features illustrate the reliability and feasibility of this high-volume screening system for identifying CYP inducers. Further more, results produced with the stable cell line were corroborated in HepG2 cells and primary cultures of human hepatocytes, suggesting that stably in tegrated cell lines harboring enhancer elements of P450 genes may be highly conducive to high-throughput screening.