- Effect of metal ions on the stable adduct formation of 16α- hydroxyestrone with a primary amine via the Heyns rearrangement
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16α-Hydroxyestrone (16α-OHE1), one of the major estrogen metabolites in humans that may plays a role in cell transformation, has been found to form stable adducts with nuclear proteins. The mechanism for the formation of a stable covalent adduct of 16α- OHE1 with protein has been postulated via the Heyns rearrangement after Schiff base formation. The Heyns rearrangement on the steroidal D-ring α-hydroxyimine was investigated using 17-(2- methoxyethylimino)estra-1,3,5(10)-triene-3,16α-diol as a model intermediate. Rates of the Heyns rearrangement and hydrolysis of the steroidal α- hydroxyimine were determined by a high-performance liquid chromatography (HPLC) simultaneously. The Heyns rearrangement was demonstrated to be optimum at pH 6.2 and the reaction rate at physiological pH, 7.3-7.5, was more than 90% of that at the optimum pH. On the other hand, modulator(s) to the reactions were also examined. According to our previous finding of the proton-mediated mechanism of the Heyns rearrangement, the effects of cationic metal ions on the reactions were examined with 29 metal chlorides. Five metal ions, Pt4+, Cu2+, Ni2+, Co2+, and Mn2+, suppressed the formation of Heyns product significantly while Fe2+, Y3+, Gd3+, and Er3+ slightly increased it. The suppression rate was synergistically enhanced by the combination of Pt4+ with Co2+, Cu2+, or Ni2+. These results suggest the five metal ions, Pt4+, Cu2+, Ni2+, Co2+, and Mn2+, reduce the formation of the Heyns product in vivo and, therefore, would be useful tools to clarify the implication of the stable adduct formation of 16α-OHE1 with protein.
- Miyairi, Shinichi,Maeda, Kaoru,Oe, Tomoyuki,Kato, Toyoaki,Naganuma, Akira
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p. 252 - 258
(2007/10/03)
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- Roles of cytochromes P450 1A2 and 3A4 in the oxidation of estradiol and estrone in human liver microsomes
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Of seven cDNA-expressed human cytochrome P450 (P450) enzymes (P450s 1A2, 2B6, 2C9, 2C19, 2D6, 2E1, and 3A4) examined, P450 1A2 was the most active in catalyzing 2- and 4-hydroxylations of estradiol and estrone. P450 3A4 and P450 2C9 also catalyzed these reactions although to lesser extents than P450 1A2. P450 1A2 also efficiently oxidized estradiol at the 16α-position but was less active in estrone 16α-hydroxylation; the latter reaction and also estradiol 16α-hydroxylation were catalyzed by P450 3A4 at significant levels. Anti-P450 1A2 antibodies inhibited 2- and 4-hydroxylations of these two estrogens catalyzed by liver microsomes of some of the human samples examined. Estradiol 16α-hydroxylation was inhibited by both anti-P450 1A2 and anti-P450 3A4, while estrone 16α-hydroxylation was significantly suppressed by anti-P450 3A4 in human liver microsomes. Fluvoxamine efficiently inhibited the estrogen hydroxylations in human liver samples that contained high levels of P450 1A2, while ketoconazole affected these activities in human samples in which P450 3A4 levels were high. α- Naphthoflavone either stimulated or had no effect on estradiol hydroxylation catalyzed by liver microsomes; the intensity of this effect depended on the human samples and their P450s. Interestingly, in the presence of anti-P450 3A4 antibodies, α-naphthoflavone was found to be able to inhibit estradiol and estrone 2-hydroxylations catalyzed by human liver microsomes. The results suggest that both P450s 1A2 and 3A4 have major roles in oxidations of estradiol and estrone in human liver and that the contents of these two P450 forms in liver microsomes determine which P450 enzymes are most important in hepatic estrogen hydroxylation by individual humans. P450 3A4 may be expected to play a more important role for some of the estrogen hydroxylation reactions than P450 1A2. Knowledge of roles of individual P450s in these estrogen hydroxylations has relevance to current controversies in hormonal carcinogenesis.
- Yamazaki, Hiroshi,Shaw, Peter M.,Guengerich, F. Peter,Shimada, Tsutomu
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p. 659 - 665
(2007/10/03)
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- PREPARATION OF 16-SUBSTITUTED 3-HYDROXYESTRA-1,3,5(10)-TRIENE-17-ONE STARTING WITH THE BROMINATION OF ESTRONE ACETATE
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The bromination of estrone acetate (Ia) leads to a mixture of acetates of 16α-bromo-16β-bromo-, and 16,16-dibromoestrone (IIa, IIIa, and IVa) in a ratio of 63:28:9.On treatment with an aqueous methanolic solution of potash, depending on the conditions, a mixture of (IIa) and (IIIa) gives 3,16α-dihydroxyestra-1,3,5(10)-trien-17-one (V) or 3,17β-dihydroxyestra-1,3,5(10)-trien-16-one (VI).When 5 g of (Ia) was brominated with 2.8 g of Br2 in chloroform and the products were chromatographed on silica gel, 0.36 g of (IVa), C20H22Br2O3, mp 165-166 deg C (from ether) 0.37 g of (IIIa), mp 169-170.5 deg C, 4.6 g of a mixture of (IIa) and (IIIa), 30 mg of (Ia) and 0.2 g of a mixture of 16α- and 16β-bromoestrones was obtained.The action of potash on a mixture of (IIa) and (IIIa) in aqueous MeOH at 20 deg C led to the epimerization of the (IIa) into (IIIa) and then the conversion of the latter into (V) with mp 203.5-206 deg C; diacetate with mp 172-173 deg C (acetone-ethanol).Similarly, but with heating (98 deg C, 3 h), a mixture of (IIa) and (IIIa) was converted into (VI), with mp 234-236 deg C.Characteristics of the IR and PMR spectra of the compounds obtained are given.
- Fedorova, O. I.,Morozova, L. S.,Alekseeva, L. M.,Grinenko, G. S.
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p. 437 - 440
(2007/10/02)
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