Inhibition of 17beta-hydroxysteroid oxidoreductase by flavonoids in breast and prostate cancer cells.

Several flavonoids and isoflavonoids were found to inhibit 17beta-oxidoreduction of estrogens by the purified 17beta-HSOR type 1, or in cell lines expressing 17beta-HSOR type 1 enzyme (T-47D breast cancer cells) or type 2 (PC-3 prostate cancer cells). The structural demands for the inhibition of estrone (E1) reduction and estradiol (E2) oxidation catalyzed by 17beta-HSOR types 1 and 2, respectively, were not identical. Flavones, flavanones, and isoflavones hydroxylated at both the double ring (positions 5 and 7) and ring B (position 4') were the most potent inhibitors of E1 reduction in T-47D cells, and by the purified type 1 enzyme whereas flavones hydroxylated at positions 3, 5, and 7 of rings A and C, with or without a hydroxyl group in ring B, were capable of inhibiting E2 oxidation in PC-3 cells. Change to flavanone structure, or hydroxylation at position 3 of ring C of flavones, or methylation of the hydroxyl group at position 4' of ring B of flavones and isoflavones reduced or abolished their inhibitory activity on E1 reduction in T-47D cells. On the contrary, hydroxyl group at position 3 of flavones (flavonol structure) markedly increased the inhibition of E2 oxidation in PC-3 cells. Thus, changes in the number and location of hydroxyl groups may discriminate inhibition of E1 reduction and E2 oxidation. Some of the differences may be due to differences in pharmacokinetics of these compounds in T-47D and PC-3 cells. Inhibition of 17beta-HSORs could lead to an alteration in the availability of the highly active endogenous estrogen, but the effects of these compounds in vivo cannot be predicted on the basis of these results alone. Some of these compounds (isoflavones) are estrogenic per se, and they may replace endogenous estrogens, whereas flavones are only very weakly estrogenic or nonestrogenic. Regarding prevention or treatment of estrogen-related diseases, apigenin, coumestrol, and genistein raise special interest.

Phytoestrogens: potential endocrine disruptors in males.

Exposure to diethylstilbestrol (DES) induces persistent structural and functional alterations in the developing reproductive tract of males. It is possible that xenoestrogens other than DES alter sexual differentiation in males and account for the increasing incidence of developmental disorders of the reproductive tract in men and wild animals. Phytoestrogens (coumestans, isoflavonoids, flavonoids, and lignans) present in numerous edible plants are quantitatively the most important environmental estrogens when their hormonal potency is assessed in vitro. They exert their estrogenic activity by interacting with estrogen receptors (ERs) in vitro. They may also act as antiestrogens by competing for the binding sites of estrogen receptors or the active site of the estrogen biosynthesizing and metabolizing enzymes, such as aromatase and estrogen-specific 17 beta-hydroxysteroid oxidoreductase (type 1). In theory, phytoestrogens and structurally related compounds could harm the reproductive health of males also by acting as antiestrogens. There are very little data on effects of phytoestrogens in males. Estrogenic effects in wildlife have been described but the evidence for the role of phytoestrogens is indirect and seen under conditions of excessive exposure. In doses comparable to the daily intake from soybased feed, isoflavonoids such as genistein were estrogen agonists in the prostate of adult laboratory rodents. When given neonatally, no persistent effects were observed. In contrast, the central nervous system (CNS)-gonadal axis and the male sexual behavior of the rat appear to be sensitive to phytoestrogens during development. The changes were similar but not identical to those seen after neonatal treatment with DES, but higher doses of phytoestrogens were needed.

Estrogen-specific 17 beta-hydroxysteroid oxidoreductase type 1 (E.C. 1.1.1.62) as a possible target for the action of phytoestrogens.

Several plant estrogens, especially coumestrol and genistein, were found to reduce the conversion of [3H]estrone to [3H] 17 beta-estradiol catalyzed by estrogen-specific 17 beta-hydroxysteroid oxidoreductase Type 1 (E.C. 1.1.1.62) in vitro. Coumestrol, the most potent inhibitor in our experiments, is the best inhibitor of the enzyme known to date. All compounds with inhibitory effects were also estrogenic. However, structural demands for 17 beta-HSOR Type 1 inhibition and estrogenicity of tested compounds in breast cancer cells (judged by increased cell proliferation) were not identical. Zearalenone and diethylstilbestrol, both potent estrogens, did not inhibit 17 beta-HSOR Type 1. Thus, changes in the estrogen molecule may discriminate between active sites of 17 beta-HSOR Type 1 and estrogen binding sites of the ER. The effects of these compounds in vivo cannot be predicted on the basis of these results. Inhibition of 17 beta-HSOR Type 1 enzyme could lead to a decrease in the availability of the highly active endogenous estrogen. However, these compounds are estrogenic per se, and they may thus replace endogenous estrogens. Additional studies are needed to further understand the role of these plant estrogens in the etiology of hormone-dependent cancers. It is not easily conceivable how the chemopreventive action of Asian diets, possibly mediated by phytoestrogens in soya products, can be based on the inhibition of estrone reduction at the target cells by phytoestrogens or related compounds, unless they are "incomplete estrogens" (i.e., unable to induce all effects typical of endogenous estrogens).

Effect of glucose on the major testosterone-maintained protein in the cultured rat ventral prostate.

The effect of glucose on the androgen-maintained protein synthesis was studied in the cultured rat ventral prostate. The explants were cultivated for 5 days in the glucose-free medium containing 10% fetal calf serum with or without 10 mM glucose and 10(-7) M testosterone. In some experiments tunicamycin, a specific inhibitor of protein glycosylation was added to the glucose-containing medium. The morphological integrity of the tissue was maintained in all the mediums used. At the end of the culture, the explants were incubated with [35S]methionine. Soluble radioactive proteins were separated by the SDS-polyacrylamide gel electrophoresis and analyzed further by the fluorography. Glucose was necessary for the testosterone-maintained accumulation of three components (Mr less than 14,000) of the major prostatic secretory protein. The electrophoretic migration, glycosylation pattern and immunological data (not shown) indicated that it was the well-known prostatic binding protein. On the other hand, two prominent polypeptides (Mr 70,000 and 100,000) appeared in the absence of glucose. Glucose starvation and the inhibition of glycosylation with tunicamycin caused similar effects on the labelling of the newly-synthesized soluble proteins. The mechanisms of glucose maintenance of the major prostatic protein and suppression of two high molecular weight proteins seemed to be different, although glycosylation was probably involved in both glucose effects.

Indirect androgenic control of citrate accumulation in rat ventral prostate.

Androgenic control of citrate metabolism was studied by measuring the conversion of (2-14C)acetate or (6-14C)glucose to (14C)citrate and 14CO2 in the ventral prostate of the rat. The decarboxylation of (2-14C)acetate showed that androgen preferentially increased (14C)citrate oxidation, probably to meet the increased energy demands of cellular synthetic reactions. This led to the decreased accumulation of (14C)citrate from (2-14C)acetate. On the other hand, both the production of (14C)citrate and the formation of 14CO2 from (6-14C)glucose were decreased by castration and increased by testosterone, this being mainly due to the androgenic control of pyruvate dehydrogenase. These changes were more marked and rapid than those in oxygen consumption, in (2-14C)acetate oxidation, or in the total content of prostatic citrate that was maintained by testosterone. Glucose as the main source of citrate in testosterone-treated rats can thus be replaced by alternative substrates in castrated rats. The rate of citrate accumulation could be more dependent on the number of secretory cells than their hormonal activation.