Interactions of safrole and isosafrole and their metabolites with cytochromes P-450

Betel quid containing safrole enhances metabolic activation of tobacco specific 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)

Cigarette smoking (CS) and betel quid (BQ) chewing are two known risk factors that have synergistic potential for the enhancing the development of oral squamous cell carcinoma (OSCC) in Taiwan. Most mutagens and carcinogens are metabolically activated by cytochrome P450 (CYP450) to exert their mutagenicity or carcinogenicity. Previous studies have shown that metabolic activation of the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), by CYP2A6 activity determines NNK-induced carcinogenesis. In addition, safrole affects cytochrome P450 activity in rodents. However, the effect of BQ safrole on the metabolism of tobacco-specific NNK and its carcinogenicity remains elusive. This study demonstrates that safrole (1 mg/kg/d) induced CYP2A6 activity, reduced urinary 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) levels, and increased NNK-induced DNA damage, including N7-methylguanine, 8-OH-deoxyguanosine and DNA strand breaks in a Syrian golden hamster model. Furthermore, altered NNK metabolism and increased NNK-induced DNA damage were also observed in healthy subjects with CS and BQ chewing histories compared to healthy subjects with CS histories. In conclusion, BQ containing safrole induced tobacco-specific NNK metabolic activation, resulting in higher NNK-induced genotoxicity. This study provides valuable insight into the synergistic mechanisms of CS- and BQ-induced OSCC.

Stimulatory effect of sesamin on hepatic cytochrome P450 activities in Atlantic salmon (Salmo salar L.) is not directly associated with expression of genes related to xenobiotic metabolism

1. This study examined hepatic cytochrome P450 (CYP450) response to dietary sesamin in combination with different n-6/n-3 fatty acid ratios in fish diet. Over a period of 4 months, fish were fed seven different experimental diets an n-6/n-3 FA ratio of either 0.5 or 1.0 in combination with two sesamin levels: low sesamin = 1.16 g/kg feed and high sesamin = 5.8 g/kg feed. Control diets did not contain sesamin. 2. The CYP450-associated activities of ethoxyresorufin O-deethylase (EROD), 7-benzyloxy-4-trifluoromethylcoumarin O-debenzylation (BFCOD), pentoxyresorufin O-depentylase (PROD), coumarin hydroxylase (COH), methoxyresorufin O-deethylase (MROD) and p-nitrophenol hydroxylase (PNPH) were significantly induced by dietary sesamin in a dose-related manner. 3. Expressions of the genes CYP1A1, CYP1A3, CYP3A, AhR1α, AhR2β, AhR2δ and PXR involved in the regulation of CYP450 activities, was not the primary source of this induction.

DNA adducts from alkoxyallylbenzene herb and spice constituents in cultured human (HepG2) cells

Alkoxy derivatives of allylbenzene, including safrole, estragole, methyleugenol, myristicin, dill apiol, and parsley apiol, are important herb and spice constituents. Human exposure occurs mainly through consumption of food and drinks. Safrole, estragole, and methyleugenol are weak animal carcinogens. Experimental data reveal the genotoxicity and/or carcinogenicity of some allylbenzenes; however, except for safrole, the potential capacity of allylbenzenes for forming adducts in human cellular DNA has not been investigated. In the present study, we have exposed metabolically competent human hepatoma (HepG2) cells to three concentrations (50, 150, and 450 muM) of each of the six aforementioned allylbenzenes and shown by the monophosphate (32)P-postlabeling assay that each compound formed DNA adducts. With the exception of methyleugenol, DNA adduction was dose dependent, decreasing in the order, estragole > methyleugenol > safrole approximately myristicin > dill apiol > parsley apiol. These results demonstrate that safrole, estragole, methyleugenol, myristicin, dill apiol, and parsley apiol are capable of altering the DNA in these cells and thus may contribute to human carcinogenesis.

Inhibition of human cytochrome P450 enzymes by the natural hepatotoxin safrole

The hepatotoxin, safrole is a methylenedioxy phenyl compound, found in sassafras oil and certain other essential oils. Recombinant cytochrome P450 (CYP, P450) and human liver microsomes were studied to investigate the selective inhibitory effects of safrole on human P450 enzymes and the mechanisms of action. Using Escherichia coli-expressed human P450, our results demonstrated that safrole was a non-selective inhibitor of CYP1A2, CYP2A6, CYP2D6, CYP2E1, and CYP3A4 in the IC(50) order CYP2E1 < CYP1A2 < CYP2A6 < CYP3A4 < CYP2D6. Safrole strongly inhibited CYP1A2, CYP2A6, and CYP2E1 activities with IC(50) values less than 20 microM. Safrole caused competitive, non-competitive, and non-competitive inhibition of CYP1A2, CYP2A6 and CYP2E1 activities, respectively. The inhibitor constants were in the order CYP1A2 < CYP2E1 < CYP2A6. In human liver microsomes, 50 microM safrole strongly inhibited 7-ethoxyresorufin O-deethylation, coumarin hydroxylation, and chlorzoxazone hydroxylation activities. These results revealed that safrole was a potent inhibitor of human CYP1A2, CYP2A6, and CYP2E1. With relatively less potency, CYP2D6 and CYP3A4 were also inhibited.

Induction of rat hepatic cytochrome P4501A and P4502B by the methoxsalen

The effect of methoxsalen, the inhibitor of the hepatic mixed function oxidase, on the expression of liver cytochrome P450s was examined in rats. Administration of methoxsalen to rats significantly increased the hepatic content of P450 and activities of microsomal ethoxyresorufin O-deethylase (EROD), methoxyresorufin O-demethylase (MROD), pentoxyresorufin O-dealkylase (PROD), a representative activity of P4501A1, P4501A2 and P4502B1/2, respectively, in a dose-dependent manner. In contrast, there was no effect on the P4502E1 catalyzed aniline hydroxylase. In the time-course experiment, methoxsalen exhibited a biphasic effect on EROD, MROD, and PROD activities, an initial inhibitory phase was followed by a phase of induction following a single treatment. Immunoblot analysis using anti-rat liver P4501A and P4502B revealed that increase in the apoprotein levels of P4501A1/2 and P4502B1/2 by methoxsalen was consistent with those in enzyme activity levels. Levels of mRNA of P4501A1/2 and P4502B1/2 were also increased by methoxsalen in Northern blot analysis. These results demonstrated that methoxsalen acts as an inducer of the hepatic microsomal mixed function oxidase; selective induction of P4501A and P4502B families involved increases in mRNA levels.

Computer graphics analysis of the interaction of alkoxy methylenedioxybenzenes with cytochromes P4501

A quantitative structure-activity relationship (QSAR) in a homologous series of alkoxy methylenedioxybenzenes (MDBs) is reported. Measurements of molecular dimensions from computer-generated space-filling structures have provided values for the shape parameter area/depth2. These have been shown to correlate with the extent of inhibition of ethoxyresorufin O-deethylase activity by a series of MDBs. The implication of this is that the MDB nucleus fits the cytochrome P4501 substrate binding site and that this ability decreases with increase in the alkyl chain length of the alkoxy substituent. These findings are in agreement with previous results relating to the spatial dimensions of the cytochrome P4501 binding site, showing that substrate specificity can be rationalized in terms of overall molecular shape.

Induction of rat hepatic cytochrome P-450 I proteins by the antimutagen anthraflavic acid

Administration of the antimutagen anthraflavic acid to rats gave rise to significant increases in the hepatic microsomal O-deethylations of ethoxyresorufin and ethoxycoumarin, but not in the O-dealkylation of pentoxyresorufin nor in cytosolic glutathione S-transferase activity. Immunoblot studies of solubilized microsomes from anthraflavic acid-treated rats revealed that anthraflavic acid induced the apoproteins P-450 I A1 and A2 but not P-450 B1 and B2. Pretreatment with anthraflavic acid resulted in a marked increase in the in vitro bioactivation of 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole and 2-amino-3,2-amino-3-methylimidazomethylimidazo[4,5-f]-quinoline (IQ) to mutagenic intermediate(s); IQ is a carcinogen against which anthraflavic acid has displayed strong antimutagenic effect in the Ames test when incorporated into the metabolic activation system. The increase in mutagenicity of IQ was the result of enhancement of both the microsomal and cytosolic activation steps. It is concluded that anthraflavic acid is a specific inducer of P-450 I proteins in the rat and this compound is not only unlikely to exhibit any anticarcinogenic effect in vivo but may act as a co-carcinogen.

Induction of cytochrome P-448 activity as exemplified by the O-deethylation of ethoxyresorufin. Effects of dose, sex, tissue and animal species

The effects of tissue, sex, animal species and dose on the induction of cytochrome P-448 activity by various inducing agents were investigated using O-ethoxyresorufin as a model substrate. The liver was by far more effective in catalysing the O-deethylation of ethoxyresorufin (EROD) than the lung and kidney. The extent of induction was also highest in the liver, with the exception of benzo(a)pyrene and 3-methylcholanthrene where inducibility was more pronounced in the kidney. The benzo(a)pyrene-induced hepatic EROD activity in the rat decayed to reach control levels four days after a single administration. Rat hepatic EROD activity was induced in both sexes but tended to be higher in the male. Marked species differences in the inducibility of hepatic EROD activity by various chemicals was observed, the rat being always more responsive when compared to the hamster or mouse. The induction of rat hepatic EROD activity by benzo(a)pyrene, 2-acetylaminofluorene and safrole was dose-dependent, maximum induction being achieved with single doses of 5, 2 and 5 mg/kg, respectively.