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Diosmin and diosmetin are agonists of the aryl hydrocarbon receptor that differentially affect cytochrome P450 1A1
H P Ciolino1, T T Wang, G C Yeh
1Cellular Defense and Carcinogenesis Section, Division of Basic Sciences, National Cancer Institute-Frederick Cancer Research and Development Center, NIH, Maryland 21702-1201, USA. hciolino@mail.ncifcrf.gov
Abstract:
We investigated the effect of the chemopreventive compound diosmin and its aglycone form, diosmetin, on the carcinogen activation pathway mediated by the aryl hydrocarbon receptor (AhR) in MCF-7 human breast epithelial cancer cells. Treatment of the cells with diosmin caused a dose-dependent increase in the metabolism of the mammary carcinogen 7,12-dimethylbenz(a)anthracene (DMBA), as assessed by increased formation of DMBA-DNA adducts and by DMBA-induced cytotoxicity. In contrast, treatment of the cells with diosmetin decreased both parameters. Diosmetin, but not diosmin, directly inhibited cytochrome P450 1A1 (CYP1A1) activity in a noncompetitive manner in microsomes isolated from DMBA-treated cells, as assayed by ethyoxyresorufin-O-deethylase activity. Treatment of the cells with diosmin or diosmetin, on the other hand, caused a dose- and time-dependent increase in CYP1A1 activity in intact cells that was comparable to that induced by DMBA or by the aryl hydrocarbon benzo(a)pyrene. Both diosmin and diosmetin caused an increase in the transcription of the CYP1A1 gene, as measured by increased levels of CYP1A1 mRNA. Both compounds caused the activation of the DNA-binding capacity of the AhR for the xenobiotic-responsive element of CYP1A1. These results indicate that diosmin and diosmetin are natural dietary agonists of the AhR, causing a potent increase in CYP1A1 transcription and CYP1A1 activity; however, only diosmetin is capable of inhibiting CYP1A1 enzyme activity, thus inhibiting carcinogen activation.
Insights
Diosmin and diosmetin activate the aryl hydrocarbon receptor (AhR), increasing CYP1A1 activity. However, only diosmetin inhibits carcinogen activation by blocking cytochrome P450 1A1 (CYP1A1) enzyme activity.
Area of Science:
- Biochemistry
- Pharmacology
- Cancer Research
Background:
- The aryl hydrocarbon receptor (AhR) pathway is crucial in regulating genes involved in xenobiotic metabolism, including cytochrome P450 1A1 (CYP1A1).
- Dysregulation of AhR signaling and CYP1A1 activity is implicated in the metabolic activation of carcinogens, contributing to cancer development.
- Dietary compounds like diosmin and diosmetin are being investigated for their potential chemopreventive properties.
Purpose of the Study:
- To investigate the effects of diosmin and its aglycone, diosmetin, on the AhR-mediated carcinogen activation pathway in human breast cancer cells.
- To determine the impact of these compounds on CYP1A1 activity, gene transcription, and carcinogen metabolism.
Main Methods:
- MCF-7 human breast epithelial cancer cells were treated with varying doses of diosmin and diosmetin.
- Carcinogen metabolism was assessed by measuring 7,12-dimethylbenz(a)anthracene (DMBA)-DNA adducts and DMBA-induced cytotoxicity.
- Cytochrome P450 1A1 (CYP1A1) activity was measured using ethoxyresorufin-O-deethylase assays in intact cells and isolated microsomes.
- Gene expression analysis included measuring CYP1A1 mRNA levels and assessing AhR DNA-binding capacity.
Main Results:
- Diosmin treatment increased DMBA metabolism and cytotoxicity, indicating enhanced carcinogen activation.
- Diosmetin treatment decreased DMBA metabolism and cytotoxicity, suggesting inhibition of carcinogen activation.
- Both diosmin and diosmetin acted as AhR agonists, increasing CYP1A1 transcription and activity in a dose- and time-dependent manner.
- Diosmetin directly inhibited CYP1A1 enzyme activity, whereas diosmin did not.
Conclusions:
- Diosmin and diosmetin are dietary agonists of the AhR, potently increasing CYP1A1 transcription and activity.
- Diosmetin exhibits chemopreventive potential by directly inhibiting CYP1A1 activity and thus reducing carcinogen activation.
- These findings highlight the differential effects of diosmin and diosmetin on carcinogen metabolism and suggest diosmetin as a promising agent for cancer prevention.