Aromatase inhibition by 4 beta,5 beta-epoxides of 16 alpha-hydroxyandrostenedione and its 19-oxygenated analogs, potential precursors of estriol production in the feto-placental unit.
To gain insight into the nature of the substrate binding site and the catalytic function of aromatase, we studied the inhibition of androstenedione aromatization by 4beta,5beta-epoxy-16alpha-hydroxyandrostenedione (4) and its 19-hydroxy and 19-oxo derivatives, 5 and 6, as well as the biochemical aromatization of these steroids in human placental microsomes. The 19-methyl and 19-oxo compounds, 4 and 6, were weak competitive inhibitors of aromatase, with apparent K(i) values of 246 microM and 270 microM, respectively, whereas the 19-hydroxy compound 5 inhibited aromatase in a non-competitive manner with the K(i) of 135 microM. The 19-methyl compound 4 inactivated aromatase in a time-dependent manner with k(inact) of 0.213 min(-1) in the presence of NADPH in air, but the other two did not cause it. The conversion of the three epoxides into estrogen, as well as 19-oxygenation of 19-methyl steroid 4 with human placental microsomes in the presence of NADPH in air, were not detected by gas chromatography-mass spectrometry. The present results are consistent with the two binding sites theory in the active site of aromatase.
Numazawa
Mitsuteru
M
Tohoku Pharmaceutical University, Sendai, Japan. numazawa@tohoku-pharm.ac.jp
Yoshimura
Akiko
A
Watari
Yoko
Y
Matsuzaki
Hisao
H
D000735:Androstenedione / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology*; D001141:Aromatase / Q000378:metabolism; D047072:Aromatase Inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004852:Epoxy Compounds / Q000737:chemistry / Q000494:pharmacology*; D004964:Estriol / Q000096:biosynthesis*; D005333:Fetus / Q000187:drug effects / Q000201:enzymology; D006801:Humans; D010920:Placenta / Q000187:drug effects / Q000201:enzymology*
D047072:Aromatase Inhibitors; D004791:Enzyme Inhibitors; D004852:Epoxy Compounds; D000735:Androstenedione; C018202:16-hydroxyandrost-4-en-3,17-dione; D001141:Aromatase; D004964:Estriol