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 tirne-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 2,2'-dihydroxy-4-methoxybenzophenone (DHMB) as determined by mass spectroscopy coupled with HPLC. Furthermore, the parent compound and both intermediates were rapidly conjugated to glucuromides, 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: IC50 of diethylstilbestrol and bisphenol A. which are known xenoestorogenic compounds. and DHB and THB was approximate to 1 x 10(-8). 1 x 10(-5), 5x 10(-5) and 5x 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. (C) 2002 Elsevier Science Ireland Ltd. All rights, reserved.