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Ligand-complex formation between cytochromes P-450 and P-448 and methylenedioxyphenyl compounds.

The formation of ligand complexes between hepatic microsomal cytochrome P-450 and safrole, isosafrole and other methylenedioxyphenyl compounds was studied in vivo and in vitro in rats pretreated with either phenobarbital or 3-methylcholanthrene. Both the phenobarbital-induced cytochrome P-450 and the 3-methylcholanthrene-induced cytochrome P-448 metabolically convert safrole, isosafrole, and those metabolites possessing an intact methylenedioxy group, to reactive metabolites which then interact with the cytochromes to form ligand complexes. Formation of these ligand complexes was accompanied by loss of mixed-function oxidase activities, and dissociation of the complexes with the type I substrate biphenyl restored activities. Safrole and, to a lesser extent, 1'-hydroxysafrole formed complexes in vivo when administered to phenobarbital-pretreated rats; none was obtained with epoxysafrole. However, when administered to 3-methylcholanthrene-pretreated animals all three compounds formed complexes, safrole being the least effective. Epoxysafrole and 1'-hydroxysafrole administered to phenobarbital-pretreated rats resulted in slight inhibition of the type I binding of safrole to liver microsomal P-450 in vitro; in contrast, with 3-methylcholanthrene-pretreated animals marked competitive inhibition was observed. This study shows that oxidation of the allyl chain of safrole analogues enhances their affinity for cytochrome P-448, but not for cytochrome P-450, and further demonstrates that these cytochromes possess distinctly different binding sites.

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Induction of three histochemically distinct populations of hepatic foci in C57BL/6J mice.

Although expression of the enzyme gamma-glutamyl transpeptidase (GGT) is the most common phenotypic marker of preneoplastic foci in the livers of carcinogen-treated rats, it is not generally expressed in mouse liver tumors or hepatic foci. However, several carcinogens, including safrole and ortho-azoaminotoluene (OAT), have been reported to induce GGT-positive foci in mice. We asked whether safrole and OAT induce GGT expression in preneoplastic foci or if these compounds select for a distinct set of lesions that can be identified by their GGT-positive phenotype. We treated 12-day-old male and female C57BL/6J mice with N,N-diethylnitrosamine (DEN) (0.20 mumol/g body wt) to initiate hepatocarcinogenesis. From 6 to 24 weeks of age, during the promotion phase of hepatocarcinogenesis, groups of mice were treated with 3,4,5,3',4',5'-hexabromobiphenyl (HBB), safrole or OAT. Additional groups of female mice were ovariectomized at 6 weeks of age with or without subsequent chronic treatment with testosterone. All the animals were killed at 24 weeks of age and serial liver sections were stained for glucose-6-phosphatase (G6Pase) or GGT. Both testosterone and HBB were strong promoters of the development of G6Pase-deficient foci. No GGT-positive foci were observed in animals treated with these agents or with DEN alone. In mice fed safrole or OAT during the promotion period, female mice developed more G6Pase-deficient foci than male mice, and GGT-positive foci were observed. Analysis of serial sections revealed that the G6Pase-deficient foci and the GGT-positive foci were independent populations. The relative number of these two classes of foci varied according to the treatment regimen. In females fed safrole, 7% of the foci in the liver were GGT-positive while in female mice fed OAT, 45% were GGT-positive. In all groups of mice in which we observed GGT-positive foci and in ovariectomized female mice, we noted a third independent population of foci which demonstrated significantly increased expression of G6Pase relative to surrounding normal liver. These data indicate that different treatments during the promotion stage of hepatocarcinogenesis in the mouse may give rise to distinct populations of preneoplastic lesions. Further studies of the molecular events giving rise to these distinct lesions will provide insights into the multiple pathways that result in hepatocarcinogenesis.

Animals↗

The prevention of CCl4-induced liver necrosis in mice by naturally occurring methylenedioxybenzenes.

Methylenedioxybenzenes (MDBs) and structurally related alkenylbenzenes were compared for their effectiveness in preventing carbon tetrachloride (CCl4)-induced liver necrosis in mice. Pretreatment with isosafrole, safrole, dihydrosafrole, and benzodioxole at dosages as low as 10 mg/kg significantly prevented the increase in plasma transaminase levels and histochemical changes associated with CCl4-induced liver necrosis, whereas piperonyl butoxide (PBO), eugenol, isoeugenol, sesamol, and curcumin did not prevent CCl4 hepatotoxicity even at 200 mg/kg. However, isosafrole was only partly hepatoprotective if administered 10 min after the toxicant. Liver microsomes isolated 1 hr after isosafrole but not after PBO administration had a markedly decreased CYP2E1 activity. Isosafrole, safrole, dihydrosafrole, and benzodioxole in vitro also inhibited CYP2E1-dependent metabolism more effectively than eugenol and isoeugenol, whereas PBO did not inhibit CYP2E1 activity. The protective effects of isosafrole, safrole, and benzodioxole were therefore predominantly attributed to their ability to inactivate CYP2E1, the major isozyme involved in CCl4 bioactivation. The marked potentiation of CCl4 hepatotoxicity in CYP2E1-induced mice was also completely prevented by isosafrole but not PBO pretreatment, supporting the hypothesis that CYP2E1 inhibition by isosafrole contributes to its hepatoprotective effect against CCl4. Isosafrole and safrole also prevented bromotrichloromethane (BrCCl3)-induced hepatocyte cytotoxicity, whereas PBO was ineffective.

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Comparison of percutaneous absorption of fragrances by humans and monkeys.

The percutaneous absorption of two cosmetic fragrance materials, safrole and cinnamyl anthranilate, as well as of cinnamic alcohol and cinnamic acid, has been measured at occluded and non-occluded application sites. Absorption values were determined in the rhesus monkey in vivo. Absorption through human skin was measured by using excised skin in diffusion cells. Because of the insolubility in water of safrole and cinnamyl anthranilate, a nonionic surfactant solution (6% oleth 20) was used in the receptor chamber of the diffusion cell in order to facilitate the partitioning of the compounds from the skin into the receptor fluid. The relative volatility of the compounds was determined in order to aid in the interpretation of the absorption results. The greatest difference between in vivo and in vitro absorption values occurred with safrole, which was the least well absorbed and the most volatile compound. Cinnamic acid absorption through non-occluded human skin (17.8 +/- 4.9%, mean +/- SEM) was significantly lower than through monkey skin (38.6 +/- 8.3%). The values for absorption through human and monkey skin did not differ significantly for cinnamyl anthranilate (24.0 +/- 5.1% v. 26.1 +/- 2.3%) or cinnamic alcohol (33.9 +/- 7.3% v. 25.4 +/- 4.4%). Occlusion of the skin resulted in greater permeation of all of the compounds; a significant difference in permeability between the two types of skin occurred only with safrole. The fragrances were absorbed well, but their volatility must be considered in a toxicity evaluation. There was reasonable agreement between the values obtained from the studies of the human skin in vitro and the monkey skin in vivo.

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