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Updated: Jun 25, 2026
A Rapid and Specific Microplate Assay for the Determination of Intra- and Extracellular Ascorbate in Cultured Cells
Published on: April 11, 2014
Ascorbic acid suppresses the 2,3,7,8-tetrachloridibenxo-p-dioxin (TCDD)-induced CYP1A1 expression in human HepG2
Hee J Chang1, Jung S Park, Eun K Lee
1The Brain Korea 21 Project, Center for Biomedical Human Resources at Chonnam National University, Department of Biochemistry, Chonnam National University Medical School, 5 Hakdong, Gwangju 501-190, Republic of Korea.
Abstract:
The mechanisms involving the inhibitory effects of ascorbic acid (AA) on carcinogenesis have not fully defined, except for its free-radical scavenging activity against oxidative DNA damage. In this study, we examined the effects of AA on the expression of the aryl hydrocarbon receptor (AhR)-regulated gene cytochrome P4501A1 (CYP1A1), which catalyzes the activation of genotoxic metabolites that can lead to mutagenesis. Cultured human HepG2 cells were incubated with AA with or without the potent AhR agonist/CYP1A1 inducer 2,3,7,8-tetrachloridibenxo-p-dioxin (TCDD). AA was highly effective at suppressing CYP1A1 induction following coincubation of the cells with 1nM TCDD. The preventive effects of AA were seen at the level of mRNA and protein expression as well as CYP1A1-specific 7-ethoxyresorufin O-deethylase (EROD) activity. A transient transfection assay using a dioxin response element (DRE)-linked luciferase reporter and an electrophoretic mobility shift assay revealed that AA reduced the amount of AhR that could form a complex with the DRE sequence in the promoter region of the CYP1A1 gene. In addition, AA inhibited the TCDD-induced Ecto-ATPase activity, which is known to be requiring for AhR translocation to the nucleus. These results suggest that AA may exert at least part of its anticarcinogenesis effect by controlling the expression of CYP1A1 at the transcription level.
Insights
Ascorbic acid (AA) inhibits carcinogenesis by suppressing the aryl hydrocarbon receptor (AhR) and its target gene, cytochrome P4501A1 (CYP1A1). This mechanism, distinct from free-radical scavenging, offers new insights into cancer prevention strategies.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Research
Background:
- The exact mechanisms of ascorbic acid (AA) in preventing cancer are not fully understood, beyond its known antioxidant properties.
- Ascorbic acid's role in modulating the aryl hydrocarbon receptor (AhR) pathway, which influences the expression of genes involved in carcinogenesis, requires further investigation.
Purpose of the Study:
- To investigate the inhibitory effects of ascorbic acid (AA) on the expression of the AhR-regulated gene cytochrome P4501A1 (CYP1A1).
- To elucidate the molecular mechanisms by which AA influences CYP1A1 gene expression and its potential role in anticarcinogenesis.
Main Methods:
- Human HepG2 cells were treated with ascorbic acid (AA) and/or 2,3,7,8-tetrachloridibenzo-p-dioxin (TCDD), a potent AhR agonist.
- Quantitative analysis of CYP1A1 mRNA and protein levels, 7-ethoxyresorufin O-deethylase (EROD) activity, and Ecto-ATPase activity.
- Transient transfection assays with a dioxin response element (DRE)-linked luciferase reporter and electrophoretic mobility shift assays (EMSA) were performed.
Main Results:
- Ascorbic acid (AA) significantly suppressed TCDD-induced CYP1A1 gene and protein expression, as well as CYP1A1-specific EROD activity.
- AA reduced the binding of the aryl hydrocarbon receptor (AhR) to the DRE sequence in the CYP1A1 promoter region.
- AA inhibited TCDD-induced Ecto-ATPase activity, a process crucial for AhR nuclear translocation.
Conclusions:
- Ascorbic acid (AA) exerts anticarcinogenic effects, at least partly, by inhibiting CYP1A1 expression at the transcriptional level.
- AA interferes with the aryl hydrocarbon receptor (AhR) pathway, specifically hindering AhR binding to the CYP1A1 gene promoter.
- These findings reveal a novel mechanism for AA's chemopreventive potential, independent of its free-radical scavenging activity.
