ToxSci Advance Access originally published online on September 21, 2009
Toxicological Sciences 2009 112(2):303-310; doi:10.1093/toxsci/kfp206
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Modulation of Aflatoxin B1–Mediated Genotoxicity in Primary Cultures of Human Hepatocytes by Diindolylmethane, Curcumin, and Xanthohumols
* Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington 98105
Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, Oregon 97331
1 To whom correspondence should be addressed at Department of Environmental and Occupational Health Sciences, University of Washington, 4225 Roosevelt Way NE, Suite 100, Seattle, WA 98105. Fax: 206-685-4696. E-mail: deaton{at}u.washington.edu.
Received June 18, 2009; accepted August 20, 2009
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Abstract |
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This study employed cultured human primary hepatocytes to investigate the ability of the putative chemopreventive phytochemicals curcumin (CUR), 3,3'-diindolylmethane (DIM), isoxanthohumol (IXN), or 8-prenylnaringenin (8PN) to reduce DNA adduct formation of the hepatocarcinogen aflatoxin B1 (AFB). Following 48 h of pretreatment, DIM and 8PN significantly increased AFB-DNA adduct levels, whereas CUR and IXN had no effect. DIM greatly enhanced the transcriptional expression of cytochrome P450 (CYP) 1A1 and CYP1A2 mRNA. Glutathione S-transferase mRNAs were not increased by any of the treatments. In vitro enzyme activity assays demonstrated that 8PN and DIM, but not CUR or IXN, inhibited human CYP1A1, CYP1A2, and CYP3A4 activities. To distinguish between treatment effects on transcription versus direct effects on enzyme activity for DIM, we evaluated the effects of pretreatment alone (transcriptional activation) versus cotreatment alone (enzyme inhibition). The results demonstrated that effects on gene expression, but not catalytic activity, are responsible for the observed effects of DIM on AFB-DNA adduct formation. The increase in AFB-DNA damage following DIM treatment may be explained through its substantial induction of CYP1A2 and/or its downregulation of GSTM1, both of which were significant. The increase in DNA damage by DIM raises potential safety risks for dietary supplements of DIM and its precursor indole-3-carbinol.
Key Words: phytochemicals; biotransformation; hepatocytes; human; CYP.