Related Experiment Video
Updated: Jun 26, 2026
Mass Spectrometry and Luminogenic-based Approaches to Characterize Phase I Metabolic Competency of In Vitro Cell Cultures
Published on: March 28, 2017
Comparison of citrus coumarins on carcinogen-detoxifying enzymes in Nrf2 knockout mice
Misty Prince1, Yan Li, Asper Childers
1Department of Pharmacology, Toxicology and Neuroscience, Louisiana State University Health Sciences Center, Feist-Weiller Cancer Center, Shreveport, LA 71130, United States.
Abstract:
Naturally occurring coumarins possess anti-carcinogenic activities in part by inducing carcinogen-detoxifying enzymes glutathione S-transferase (GST) and/or NAD(P)H quinone oxidoreductase (NQO1). Our goal was to determine whether citrus coumarins induce hepatic GST and/or NQO1 via activation of Nrf2 and the antioxidant response element (ARE). First, HepG2 cells stably transfected with the ARE and a green fluorescent protein (GFP) reporter were treated with increasing concentrations of coumarins and compared to positive controls. tert-Butylhydroquinone (TBHQ) and oltipraz increased GFP fluorescence, as did coumarin, limettin, auraptene, imperatorin, and 7,8-benzoflavone, suggesting that they activate the ARE, whereas isopimpinellin did not increase GFP fluorescence. Next, the effects of orally administered coumarins and oltipraz on hepatic GST and NQO1 activities were compared in Nrf2 knockout mice or Nrf2 heterozygous mice exhibiting the wild-type phenotype. Oltipraz, auraptene, imperatorin, isopimpinellin, and auraptene all significantly increased liver cytosolic GST activities in Nrf2 heterozygous mice. This effect was abrogated in Nrf2(-/-) mice dosed with oltipraz, attenuated in mice Nrf2(-/-) mice treated with auraptene and imperatorin, and still significant in Nrf2(-/-) mice treated with isopimpinellin. Of these compounds, only isopimpinellin significantly increased liver cytosolic NQO1 activities, and this effect was not attenuated in Nrf2(-/-) mice. These results strongly suggest that imperatorin and auraptene induce murine liver cytosolic GST activities via the Nrf2/ARE mechanism. Although structurally similar, isopimpinellin did not appear to activate HepG2-ARE-GFP and the Nrf2 knockout mouse study suggests that isopimpinellin may induce GST and NQO1 via additional mechanisms.
Insights
Citrus coumarins auraptene and imperatorin activate cancer-detoxifying enzymes via the Nrf2 pathway. Some coumarins like isopimpinellin may use additional mechanisms to boost these protective enzymes.
Area of Science:
- Biochemistry
- Pharmacology
- Toxicology
Background:
- Naturally occurring coumarins exhibit anti-carcinogenic properties.
- These effects are partly mediated by the induction of carcinogen-detoxifying enzymes: glutathione S-transferase (GST) and NAD(P)H quinone oxidoreductase (NQO1).
- The Nrf2-antioxidant response element (ARE) pathway is a key regulator of these detoxification enzymes.
Purpose of the Study:
- To investigate whether citrus coumarins can induce hepatic GST and NQO1.
- To determine if this induction occurs through the activation of the Nrf2/ARE pathway.
Main Methods:
- HepG2 cells transfected with an ARE-GFP reporter were treated with various coumarins.
- In vivo studies involved oral administration of coumarins to Nrf2 knockout and heterozygous mice.
- Hepatic GST and NQO1 activities were measured in treated animals.
Main Results:
- Coumarin, limettin, auraptene, imperatorin, and 7,8-benzoflavone activated the ARE reporter in HepG2 cells.
- Auraptene and imperatorin significantly increased hepatic GST activity in Nrf2 heterozygous mice, an effect attenuated in Nrf2 knockout mice.
- Isopimpinellin increased hepatic GST and NQO1 activities, but its induction of GST was less dependent on Nrf2, and it did not activate the ARE reporter.
Conclusions:
- Auraptene and imperatorin induce murine liver GST via the Nrf2/ARE pathway.
- Isopimpinellin may induce GST and NQO1 through Nrf2-dependent and Nrf2-independent mechanisms.
- Citrus coumarins demonstrate potential as chemopreventive agents by modulating key detoxification enzymes.
