Metabolism of 2-hydroxy-4-methoxybenzophenone in isolated rat hepatocytes and xenoestrogenic effects of its metabolites on MCF-7 human breast cancer cells.
The metabolism and cytotoxicity of 2-hydroxy-4-methoxybenzophenone (HMB) in isolated rat hepatocytes and the xenoestrogenic activity of HMB and its metabolites in MCF-7 human breast cancer cells and an estrogen receptor competitive binding assay have been studied, respectively. The incubation of hepatocytes with HMB caused a concentration- and time-dependent decrease in cell viability, accompanied by loss of intracellular ATP and adenine nucleotide pools. HMB at a low-toxic level (0.25 mM) in the hepatocyte suspensions was converted enzymatically to 2,4-dihydroxybenzophenone (DHB) and a hydroxylated intermediate, which was tentatively identified as an isomer of 2,2prime prime or minute-dihydroxy-4-methoxybenzophenone (DHMB) as determined by mass spectroscopy coupled with HPLC. Furthermore, the parent compound and both intermediates were rapidly conjugated to glucuronides, whereas free unconjugated DHMB and 2,3,4-trihydroxybenzophenone (THB) were identified as trace intermediates. In another experiment, DHB and THB displaced competitively 17beta-estradiol bound to the recombinant human estrogen receptor alpha in a concentration-dependent manner: IC(50) of diethylstilbestrol and bisphenol A, which are known xenoestorogenic compounds, and DHB and THB was approximately 1 x 10(-8), 1 x 10(-5), 5 x 10(-5) and 5 x 10(-4) M, respectively. Further, DHB at concentrations from 10(-8) to 10(-6) M caused a concentration-dependent proliferation of MCF-7 cells. DHMB and THB at 10(-7) and 10(-6) M also elicited a slight increase in cell numbers, whereas HMB at concentrations from 10(-9) to 10(-4) M did not affect the cell proliferation. Based on the relative IC50 for the competitive binding and the proliferative effect on MCF-7 cells, it follows that in estrogenic potency, DHB>THB>DHMB. These results indicate that some hydroxylated intermediates such as DHB rather than the parent compound act as a xenoestrogen via biotransformation.
Nakagawa
Yoshio
Y
Department of Toxicology, Tokyo Metropolitan Research Laboratory of Public Health, 3-24-1, Hyakunin-cho, Shinjuku-ku, Tokyo 169-0073, Japan. yoshio@tokyo-eiken.go.jp
Suzuki
Toshinari
T
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001577:Benzophenones / Q000378:metabolism* / Q000633:toxicity; D001667:Binding, Competitive; D001711:Biotransformation; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000378:metabolism; D047628:Estrogen Receptor alpha; D004968:Estrogens, Non-Steroidal / Q000633:toxicity*; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D011960:Receptors, Estrogen / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013473:Sunscreening Agents / Q000378:metabolism* / Q000633:toxicity; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects
D001577:Benzophenones; D047628:Estrogen Receptor alpha; D004968:Estrogens, Non-Steroidal; D011960:Receptors, Estrogen; D011994:Recombinant Proteins; D013473:Sunscreening Agents; D004958:Estradiol; D000255:Adenosine Triphosphate; C005290:oxybenzone