title: CYP2E1-mediated mechanism of anti-genotoxicity of the broccoli constituent sulforaphane.
abstract: The broccoli constituent sulforaphane (1-isothiocyanate-4-methylsulfinylbutane) has previously been shown to protect rats against 9,10-dimethyl-1,2-benz[a]anthracene tumorigenesis, thought to be due, at least in part, to induction of phase II detoxification. We investigated the ability of sulforaphane to also inhibit the phase I enzyme cytochrome P450 isoenzyme 2E1 (CYP2E1), which is responsible for activation of several carcinogens, including dialkylnitrosamines. Using the p-nitrophenol hydroxylation assay in microsomes from livers of acetone-treated Sprague-Dawley rats, sulforaphane was shown to be a potent competitive inhibitor of CYP2E1 with a Ki of 37.0 +/- 4.5 microM. In view of this result, we studied the capacity of sulforaphane to inhibit the genotoxicity of N-nitrosodimethylamine (NDMA). Sulforaphane at concentrations of > 0.8 microM inhibited the mutagenicity of NDMA (4.4 mg/plate) in Salmonella typhimurium strain TA100 after pre-incubation for 45 min with cytosol extract from livers of Balb/c mice pre-treated with acetone. Unscheduled DNA synthesis induced by NDMA (33.5 microM) in mouse hepatocytes was inhibited in a dose-dependent manner by sulforaphane at 0.064-20 microM. Sulforaphane was unable to inhibit mutagenicity of sodium azide (5 micrograms/plate), a direct acting mutagen, in the Salmonella assay. It was not itself genotoxic in hepatocytes, as measured by unscheduled DNA synthesis, or mutagenic in the strain of Salmonella employed and cytotoxic only at high concentrations (> or = 0.5 mM). These findings suggest that inhibition of CYP2E1 by sulforaphane may offer chemoprotection against carcinogenic substrates of this enzyme.
authors.affiliation: Department of Pharmaceutical Sciences, Aston University, Birmingham, UK.
authors.forename: S
authors.initials: S
authors.lastname: Barcelo
authors.forename: J M
authors.initials: JM
authors.lastname: Gardiner
authors.forename: A
authors.initials: A
authors.lastname: Gescher
authors.forename: J K
authors.initials: JK
authors.lastname: Chipman
mesh_terms: D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D001386:Azides / Q000633:toxicity; D001711:Biotransformation; D019392:Cytochrome P-450 CYP2E1; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D004260:DNA Repair; D017879:Isothiocyanates; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D006899:Mixed Function Oxygenases / Q000378:metabolism; D009152:Mutagenicity Tests; D009603:Nitroso Compounds / Q000037:antagonists & inhibitors; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012486:Salmonella typhimurium / Q000187:drug effects; D019810:Sodium Azide; D013454:Sulfoxides; D013861:Thiocyanates / Q000494:pharmacology* / Q000633:toxicity
chemical_list: D016588:Anticarcinogenic Agents; D001386:Azides; D065607:Cytochrome P-450 Enzyme Inhibitors; D017879:Isothiocyanates; D009603:Nitroso Compounds; D013454:Sulfoxides; D013861:Thiocyanates; C008651:4-nitrosodimethylaniline; C058305:phenethyl isothiocyanate; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D019810:Sodium Azide; D006899:Mixed Function Oxygenases; D019392:Cytochrome P-450 CYP2E1; D010089:Oxidoreductases, N-Demethylating; C016766:sulforaphane