Metabolism of exogenous 4- and 2-hydroxyestradiol in the human male

The metabolic fate of the isomeric catecholestrogens 4-hydroxyestradiol (4-OHE2) and 2-hydroxyestradiol (2-OHE2) was studied to elucidate possible differences in their metabolism as an explanation for their different bioactivities. Healthy young men (n = 3 each) were infused (90 min) with 4-OHE2 (60 micrograms/h) or 2-OHE2 (100 micrograms/h). The main metabolites were determined in plasma and urine before, during and after infusion. Unconjugated and conjugated steroids, the latter after hot acid hydrolysis, were subjected to chromatography on LH-20 columns and measured by specific RIAs. During the infusion 4-OHE2 reached significant plasma concentrations whereas 2-OHE2 was so rapidly metabolised that its plasma levels remained virtually undetectable in spite of a higher infusion rate. The metabolism of 4-OHE2 was dominated by direct conjugation, that of 2-OHE2 by methyl ether formation. These findings were corroborated by the urinary excretion rates: during the infusion and the first hours afterwards, 4-OHE2 was mainly excreted as 4-OHE2 and 4-hydroxyestrone, while 2-OHE2 was predominantly excreted as 2-hydroxyestradiol 2-methyl ether and 2-hydroxyestrone 2-methyl ether.     

Catecholestrogens excretion in smoking and non-smoking postmenopausal women receiving estrogen replacement therapy

Estrogens are involved in the etiology of breast cancer. Their blastomogenic influence may be partly realized through their conversion into catecholestrogens, rate of which may be modified by smoking. The risk of having breast cancer diagnosed can increase in women using estrogen replacement therapy (ERT). The principal aim of this investigation was to compare the excretion of classical estrogens and catecholestrogens in smoking and non-smoking postmenopausal women receiving Progynova (estradiol valerate, 2 mg/day, 1 month). Total 16 women were studied before and after treatment. Urinary estrogen profile method based on isotope dilution capillary gas chromatography-mass spectrometry was used. Before ERT, significantly lower excretion of 16-epiestriol and 4-hydroxyestrone (4-OHE1) and lower ratio of 4-OHE1/E1 were revealed in smokers. After ERT, much higher excretion of 2-OHE1, and 4-hydroxyestradiol (4-OHE2), higher ratios of 2-OHE1/E1 and 4-OHE1/E1 and lower ratio of 2-methoxyestrone/2-OHE1 were discovered in smokers as compared to non-smoking women. In conclusion only combination of ERT + smoking and not smoking itself leads to the specific prevalence of catecholestrogens (2-OH- and carcinogenic and DNA-damaging 4-OH-metabolites) that may increase risk of genotoxic variant of hormone-induced breast carcinogenesis without influence on the total morbidity.     

Nitric oxide enhances catechol estrogen-induced oxidative stress in LNCaP cells

Catechol estrogens (CEs), such as 4-hydroxyestradiol (4-OHE2), undergo redox cycling during which reactive oxygen species (ROS) such as superoxide (O2*-) and the chemically reactive estrogen semiquinone (CE-SQ) and quinone (CE-Q) intermediates are produced. The quinone's putative mutagenicity may be enhanced by ROS and/or reactive nitrogen species. High concentrations of nitric oxide (NO) present during inflammatory conditions may react with (O2*-) to form peroxynitrite (ONOO-), a potent oxidant implicated in many pathological conditions. In this study, the possible generation of peroxynitrite from the interaction of CEs and NO and its effect on plasmid DNA and intact cells were investigated. A combination of 4-OHE2 and NO increased the level of single strand breaks (SSB) in plasmid DNA by more than 60% compared to vehicle controls in a metal-free buffer system. 4-OHE2 alone or NO alone had no effect. Results obtained from use of different antioxidants and ROS scavengers suggested a role of peroxynitrite in oxidative stress. In cells, 4-OHE2 or NO alone induced dose-dependent DNA damage as assessed by single cell gel electrophoresis. Co-treatment with 4-OHE2 and NO had an additive effect at lower doses. Generation of intracellular ROS was measured by the oxidation of carboxy-2',7'-dichlorofluorescein diacetate to the fluorescent compound carboxy-2',7'-dichlorofluorescein. NO alone, in oxygenated media, generated little ROS whereas 4-OHE2 produced approximately 70% increase in fluorescence. When added together 4-OHE2 and NO, produced a 2-fold increase in ROS. The generation and involvement ofperoxynitrite to this increase was implied since uric acid inhibited it. Generation ofperoxynitrite was also observed by use of dihydrorhodamine 123. Therefore, we conclude that combined treatments with 4-OHE2 and NO generated peroxynitrite seen from increased fluorescence and its inhibition by uric acid or combined SOD and catalase treatments. Results reported here suggest a role of peroxynitrite in causing damage to biomolecules when CEs and NO are present simultaneously. This may have biological relevance as high concentrations of NO formed during inflammatory conditions may exacerbate cancers due to estrogens.     

The characteristic binding of catechol estrogens to estrogen receptors in 7,12-dimethylbenz(a)anthracene-induced rat mammary tumors

The binding of catechol estrogens (2-hydroxyestrone, 4-hydroxyestrone, 2-hydroxyestradiol, and 4-hydroxyestradiol) to estrogen receptors in 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumor cytosols was investigated. Cytosol estrogen receptors exhibited high affinities (Ka = 1.12-1.88 X 10(8) M-1) for all catechol estrogens as well as estradiol. The receptor level of catechol estrogens (46.1-97.5 fmol/mg protein) was 1.6-3.0 times higher than that of estradiol; especially the binding of 4-hydroxyestrone to estrogen receptors was the highest of all catechol estrogens and estradiol. In judging the receptor level of more than 20 fmol/mg protein to be positive, the binding of catechol estrogens to estrogen receptors was approximately correlated with that of estradiol. The positive receptor level of catechol estrogens was found in a half of tumor cytosols which showed the negative receptor level of estradiol. These results suggested that characteristic estrogen receptors indicating high affinities for catechol estrogens might be present in rat mammary tumor cytosols.     

Detoxication of Benzo[a]pyrene-7,8-dione by Sulfotransferases (SULTs) in Human Lung Cells

Polycyclic aromatic hydrocarbons (PAH) are environmental and tobacco carcinogens. Human aldo-keto reductases catalyze the metabolic activation of proximate carcinogenic PAH trans-dihydrodiols to yield electrophilic and redox-active o-quinones. Benzo[a]pyrene-7,8-dione a representative PAH o-quinone is reduced back to the corresponding catechol to generate a futile redox-cycle. We investigated whether sulfonation of PAH catechols by human sulfotransferases (SULT) could intercept the catechol in human lung cells. RT-PCR identified SULT1A1, -1A3, and -1E1 as the isozymes expressed in four human lung cell lines. The corresponding recombinant SULTs were examined for their substrate specificity. Benzo[a]pyrene-7,8-dione was reduced to benzo[a]pyrene-7,8-catechol by dithiothreitol under anaerobic conditions and then further sulfonated by the SULTs in the presence of 3'-[(35)S]phosphoadenosine 5'-phosphosulfate as the sulfonate group donor. The human SULTs catalyzed the sulfonation of benzo[a]pyrene-7,8-catechol and generated two isomeric benzo[a]pyrene-7,8-catechol O-monosulfate products that were identified by reversed phase HPLC and by LC-MS/MS. The various SULT isoforms produced the two isomers in different proportions. Two-dimensional (1)H and (13)C NMR assigned the two regioisomers of benzo[a]pyrene-7,8-catechol monosulfate as 8-hydroxy-benzo[a]pyrene-7-O-sulfate (M1) and 7-hydroxy-benzo[a]pyrene-8-O-sulfate (M2), respectively. The kinetic profiles of three SULTs were different. SULT1A1 gave the highest catalytic efficiency (k(cat)/K(m)) and yielded a single isomeric product corresponding to M1. By contrast, SULT1E1 showed distinct substrate inhibition and formed both M1 and M2. Based on expression levels, catalytic efficiency, and the fact that the lung cells only produce M1, it is concluded that the major isoform that can intercept benzo[a]pyrene-7,8-catechol is SULT1A1.     

Prevention of estrogen-DNA adduct formation in MCF-10F cells by resveratrol

Resveratrol (Resv), a natural occurring phytolexin present in grapes and other foods, possesses chemopreventive effects revealed by its striking modulation of diverse cellular events associated with tumor initiation, promotion, and progression. Catechol estrogens generated in the metabolism of estrogens are oxidized to catechol quinones that react with DNA to form predominantly depurinating estrogen-DNA adducts. This event can generate the mutations responsible for cancer initiation. In this regard, Resv acts as both an antioxidant and an inducer of the phase II enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1). In this report, we present the effects of Resv on the metabolism of estrogens in normal breast epithelial cells (MCF-10F) treated with 4-hydroxyestradiol (4-OHE(2)) or estradiol-3,4-quinone (E(2)-3,4-Q). Resv induced NQO1 in a dose- and time-dependent manner, but did not affect the expression of catechol-O-methyltransferase. Ultraperformance liquid chromatography/tandem mass spectrometry was used to determine the effects of Resv on estrogen metabolism. Preincubation of the cells with Resv for 48 h decreased the formation of depurinating estrogen-DNA adducts from 4-OHE(2) or E(2)-3,4-Q and increased formation of methoxycatechol estrogens. When Resv was also present with the 4-OHE(2) or E(2)-3,4-Q, even greater increases in methoxycatechol estrogens were observed, and the DNA adducts were undetectable. We conclude that Resv can protect breast cells from carcinogenic estrogen metabolites, suggesting that it could be used in breast cancer prevention.     

Interactions of the human cytosolic sulfotransferases and steroid sulfatase in the metabolism of tibolone and raloxifene

Sulfation is important in the metabolism and inactivation of steroidal compounds and hormone replacement therapeutic (HRT) agents in human tissues. Although generally inactive, many steroid sulfates are hydrolyzed to their active forms by sulfatase activity. Therefore, the specific sulfotransferase (SULT) isoforms and the levels of steroid sulfatase (STS) activity in tissues are important in regulating the activity of steroidal and HRT compounds. Tibolone (Tib) is metabolized to three active metabolites and all four compounds are readily sulfated. Tib and the Δ4-isomer are sulfated at the 17β-OH group by SULT2A1 and the 17-sulfates are resistant to hydrolysis by human placental STS. 3-OH and 3β-OH Tib can form both 3- and 17-monosulfates as well as disulfates. Only the 3β-sulfates are susceptible to STS hydrolysis. Raloxifene monosulfation was catalyzed by at least seven SULT isoforms and SULT1E1 also synthesizes raloxifene disulfate. SULT1E1 forms both monosulfates in a ratio of approximately 8:1 with the more abundant monosulfate migrating on HPLC identical to the SULT2A1 synthesized monosulfate. The raloxifene monosulfate formed by both SULT isoforms is sensitive to STS hydrolysis whereas the low abundance monosulfate formed by SULT1E1 is resistant. The benzothiophene sulfates of raloxifene and arzoxifene were hydrolyzed by STS whereas the raloxifene 4′-phenolic sulfate was resistant. These results indicate that tissue specific expression of SULT isoforms and STS could be important in the inactivation and regeneration of the active forms of HRT agents.     

Kinetics of catechol estrogen-estrogen receptor dissociation: a possible factor underlying differences in catechol estrogen biological activity

The mechanisms underlying the differences in uterotrophic potency between 2- and 4-hydroxyestrogens were explored. Doses of estradiol (E2)(10 micrograms/kg), 2-OHE2 (500 micrograms/kg) and 4-OHE2 (100 micrograms/kg) sufficient to induce near maximal cell nuclear estrogen receptor (ERn) binding were injected subcutaneously into 26 day old female rats. Uterine ERn concentrations declined more rapidly after 2-OHE2 than after E2 or 4-OHE2. E2 and 4-OHE2 both elicited a significant increase in uterine wet weight, measured at 24-36 hrs after injection. 2-OHE2 had no significant effect and neither synergized with nor antagonized the effects of simultaneously administered E2 or 4-OHE2. Under in vitro conditions at 25 degrees C, 2-hydroxyestrone (2-OHE1) and 2-OHE2 both dissociated from the receptors more rapidly than either their parent monophenolic estrogens or the corresponding 4-hydroxyestrogens. These results suggest that differences in estrogenic potency between 2- and 4-hydroxyestrogens may partly be a function of the dissociation kinetics of their estrogen receptor complexes.     

Resveratrol and N-acetylcysteine block the cancer-initiating step in MCF-10F cells

Substantial evidence suggests that catechol estrogen-3,4-quinones react with DNA to form predominantly the depurinating adducts 4-hydroxyestrone (estradiol)-1-N3Ade [4-OHE(1)(E(2))-1-N3Ade] and 4-OHE(1)(E(2))-1-N7Gua. Apurinic sites resulting from these adducts generate critical mutations that can initiate cancer. The paradigm of cancer initiation is based on an imbalance in estrogen metabolism between activating pathways that lead to estrogen-DNA adducts and deactivating pathways that lead to estrogen metabolites and conjugates. This imbalance can be improved to minimize formation of adducts by using antioxidants, such as resveratrol (Resv) and N-acetylcysteine (NAcCys). To compare the ability of Resv and NAcCys to block formation of estrogen-DNA adducts, we used the human breast epithelial cell line MCF-10F treated with 4-OHE(2). Resv and NAcCys directed the metabolism of 4-OHE(2) toward protective pathways. NAcCys reacted with the quinones and reduced the semiquinones to catechols. This pathway was also carried out by Resv. In addition, Resv induced the protective enzyme quinone reductase, which reduces E(1)(E(2))-3,4-quinones to 4-OHE(1)(E(2)). Resv was more effective at increasing the amount of 4-OCH(3)E(1)(E(2)) than NAcCys. Inhibition of estrogen-DNA adduct formation was similar at lower doses, but at higher doses Resv was about 50% more effective than NAcCys. Their combined effects were additive. Therefore, these two antioxidants provide an excellent combination to protect catechol estrogens from oxidation to catechol quinones.     

Estrogenic and antiestrogenic activities of 16alpha- and 2-hydroxy metabolites of 17beta-estradiol in MCF-7 and T47D human breast cancer cells

The comparative mitogenic activities of 17beta-estradiol (E2) and four metabolites, 2-hydroxyestradiol (2-OHE2), 2-hydroxyestrone (2-OHE1), 16alpha-hydroxyestradiol (16alpha-OHE2) and 16alpha-hydroxyestrone (16alpha-OHE1) were determined in estrogen receptor (ER)-positive MCF-7 and T47D human breast cancer cells. E2 (1 nM) induced a 7- to 13-fold increase in cell number in both cell lines compared to untreated cells and the mitogenic potencies of 16alpha-OHE1 or 16alpha-OHE2 were comparable to or greater than E2. In contrast, 2-OHE1 and 2-OHE2 were weak mitogens in both cell lines and in cells cotreated with 1 nM E2 and 100 or 1000 nM 2-OHE1 or 2-OHE2, there was a significant inhibition of hormone-induced cell proliferation. The comparative ER agonist/antagonist activities of E2 and the metabolites on transactivation were determined in T47D cells transiently transfected with constructs containing promoter inserts from the cathepsin D (pCD) and creatine kinase B (pCKB) genes. E2, 16alpha-OHE2 and 16alpha-OHE1 induced reporter gene activity in both MCF-7 or T47D cells transfected with pCKB or pCD. In contrast, 2-OHE1 and 2-OHE2 did not exhibit ER agonist activity for these transactivation assays, but in cells cotreated with E2 plus 2-OHE1 or 2-OHE2, there was a significant decrease in the hormone-induced response. These results demonstrate that 16alpha-OHE1/16alpha-OHE2 exhibit estrogenic activities similar to that observed for E2, whereas the 2-catecholestrogens are weak ER agonists (cell proliferation) or antagonists (cell proliferation and transactivation).     

CYP1B1 prevents proteasome-mediated XIAP degradation by inducing PKCε activation and phosphorylation of XIAP

Cytochrome P450 1B1 (CYP1B1) is a key enzyme that catalyzes the metabolism of 17β-estradiol (E2) into catechol estrogens, such as 2-hydroxyestradiol (2-OHE2) and 4-hydroxyestradiol (4-OHE2). CYP1B1 is related to tumor formation and is over-expressed in a variety of cancer cells. In particular, CYP1B1 is highly expressed in hormone-related cancers such as breast cancer, ovarian cancer, or prostate cancer compared to other cancers. However, the detailed mechanisms involving this protein remain unclear. In this study, we demonstrate that CYP1B1 affects X-linked inhibitor of apoptosis protein (XIAP) expression. When CYP1B1 was over-expressed in cells, there was significant increase in the XIAP protein level, whereas the XIAP mRNA level was not affected by CYP1B1 expression. Treatment with 4-OHE2, mainly formed by CYP1B1 activity, also increased XIAP protein levels, whereas treatment with 2-OHE2 did not have a significant effect. Treatment with 4-OHE2 significantly prevented proteasome-mediated XIAP degradation. In addition, phosphorylation of XIAP on serine 87, which is known to stabilize XIAP, was up-regulated by 4-OHE2, indicating that 4-OHE2 affects XIAP stability through XIAP phosphorylation. We also found that phosphorylation of protein kinase C (PKC)ε, which is required for XIAP phosphorylation, increased when cells were treated with 4-OHE2. In summary, our data show that CYP1B1 may play an important role in preventing ubiquitin-proteasome-mediated XIAP degradation through the activation of PKCε signaling in cancer cells.     

Phytoestrogens and xenoestrogens: the contribution of diet and environment to endocrine disruption

Some endocrine disrupting compounds such as phthalates and phenols act non-genomically by inhibiting the sulfotransferase (SULT 1E1 and SULT 1A1) isoforms which inactivate estrogens by sulfonation. A range of environmental phenolic contaminants and dietary flavonoids was tested for inhibition of the human SULT 1A1, 1E1 and 2A1 isoforms. In particular, the plasticisers 4-n-octyl- and 4-n-nonyl-phenol inhibit SULT 1E1 with IC₅₀ values of 0.16 μM vs. 10 nM estradiol while the 2-substituted chlorophenols show similar values. Flavonoids are also SULT inhibitors; tricin is a competitive inhibitor of SULT 1E1 with a K_i of 1.5 ± 0.8 nM. In a small pilot study to determine whether ingestion of soy flavonoids would affect SULT1A1 activity in vivo as well as in vitro, sulfonation of daidzein was reduced in a group of women ‘at risk’ of breast cancer, as compared with controls, although the SULT 1A1*1/SULT 1A1*2 allele ratio was not different. Endocrine disrupting effects in man may be multifactorial when components from both the diet and the environment act at the same point in steroid metabolism.     

A comparative study of the sulfation of bile acids and a bile alcohol by the Zebra danio (Danio rerio) and human cytosolic sulfotransferases (SULTs)

The current study was designed to examine the sulfation of bile acids and bile alcohols by the Zebra danio (Danio rerio) SULTs in comparison with human SULTs. A systematic analysis using the fifteen Zebra danio SULTs revealed that SULT3 ST2 and SULT3 ST3 were the major bile acid/alcohol-sulfating SULTs. Among the eleven human SULTs, only SULT2A1 was found to be capable of sulfating bile acids and bile alcohols. To further investigate the sulfation of bile acids and bile alcohols by the two Zebra danio SULT3 STs and the human SULT2A1, pH-dependence and kinetics of the sulfation of bile acids/alcohols were analyzed. pH-dependence experiments showed that the mechanisms underlying substrate recognition for the sulfation of lithocholic acid (a bile acid) and 5α-petromyzonol (a bile alcohol) differed between the human SULT2A1 and the Zebra danio SULT3 ST2 and ST3. Kinetic analysis indicated that both the two Zebra danio SULT3 STs preferred petromyzonol as substrate compared to bile acids. In contrast, the human SULT2A1 was more catalytically efficient toward lithocholic acid than petromyzonol. Collectively, the results imply that the Zebra danio and human SULTs have evolved to serve for the sulfation of, respectively, bile alcohols and bile acids, matching the cholanoid profile in these two vertebrate species.     

Mutagenic properties of estrogen quinone-derived DNA adducts in simian kidney cells

DNA damage caused by catechol estrogens has been shown to play an etiologic role in tumor formation. Catechol estrogens are reactive to DNA and form several DNA adducts via their quinone forms. To explore the mutagenic properties of 2-hydroxyestrogen-derived DNA adducts in mammalian cells, N(2)-(2-hydroxyestrogen-6-yl)-2'-deoxyguanosine and N(6)-(2-hydroxyestrogen-6-yl)-2'-deoxyadenosine adducts induced by quinones of 2-hydroxyestrone, 2-hydroxyestradiol, or 2-hydroxyestriol were incorporated site-specifically into the oligodeoxynucleotides ((5)(')TCCTCCTCXCCTCTC, where X is dG, dA, 2-OHE-N(2)-dG, or 2-OHE-N(6)-dA). The modified oligodeoxynucleotides were inserted into single-stranded phagemid vectors followed by transfection into simian kidney (COS-7) cells. Preferential incorporation of dCMP, the correct base, was observed opposite all 2-OHE-N(2)-dG adducts. Only targeted G --> T transversions were detected; the highest mutation frequency (18.2%) was observed opposite the 2-OHE(2)-N(2)-dG adduct, followed by 2-OHE(1)-N(2)-dG (4.4%) and 2-OHE(3)-N(2)-dG (1.3%). When 2-OHE-N(6)-dA adducts were used, preferential incorporation of dTMP, the correct base, was observed. Targeted mutations representing A --> T transversions were detected, accompanied by small numbers of A --> G transitions. The highest mutation frequencies were observed with 2-OHE(1)-N(6)-dA and 2-OHE(3)-N(6)-dA (14.5 and 14.1%, respectively), while 2-OHE(2)-N(6)-dA exhibited a mutation frequency of only 6.0%. No mutations were detected with vectors containing unmodified oligodeoxynucleotides. Thus, 2-OHE quinone-derived DNA adducts are mutagenic, generating primarily G --> T and A --> T mutations in mammalian cells. The mutational frequency varied depending on the nature of the 2-OHE moiety.     

Oral contraceptives as substrates and inhibitors for human cytosolic SULTs

Cytosolic sulfotransferases (SULTs) in mammals are involved in the biotransformation and homeostasis of various endogenous and xenobiotic compounds. The current study aimed to examine the sulfation of contraceptive compounds by various human cytosolic SULTs and to investigate the inhibitory effects and mode of action of these compounds on the sulfation of 17beta-estradiol, a major endogenous estrogen. A systematic study using all eleven known human cytosolic SULTs revealed the differential substrate specificity of these enzymes for the eight representative contraceptive compounds and two endogenous estrogens (estrone and 17beta-estradiol) tested as substrates. Activity data showed that SULT1A1 displayed the strongest activity toward 17alpha-ethynylestradiol. Kinetic studies revealed that the V (max) value of the sulfation of 17alpha-ethynylestradiol by SULT1A1 was 1.64 times that of the sulfation of 17beta-estradiol, while the K (m) values were almost equal for the two compounds. The inhibitory effects of three contraceptive compounds on the sulfation of 17beta-estradiol by SULT1A1 were examined. IC(50) values determined were 0.193, 1.84, and 2.98 mM, respectively, for 19-norethindrone acetate, ethynodiol diacetate and mifepristone. Kinetic analyses indicated that the mechanism underlying the inhibition by these contraceptives is of a mixed noncompetitive type. Metabolic labeling experiments confirmed the sulfation of contraceptive compounds and the release of their sulfated derivatives by HepG2 human hepatoma cells. Collectively, the results obtained suggest a role of sulfation in the metabolism of contraceptive compounds in vivo. Moreover, in view of their inhibitory effects on the sulfation of 17beta-estradiol, these compounds may potentially act to disrupt the homeostasis of endogenous estrogens.     

Sulfotransferase 2A1 forms estradiol-17-sulfate and celecoxib switches the dominant product from estradiol-3-sulfate to estradiol-17-sulfate

Using recombinant sulfotransferases (SULTs) expressed in E. coli, β-estradiol (E2) sulfonation was examined to determine which SULT enzyme is responsible for producing E2-17-sulfate (E2-17-S). SULTs 1A1*1, 1A1*2, 1A3, 1E1 and 2A1 all sulfated E2 to varying extents. No activity was observed with SULT1B1. Among the SULTs studied, SULT2A1 produced primarily E2-3-sulfate (E2-3-S), but also some E2-17-S and trace amounts of E2 disulfate. SULT2A1 had a K_m value of 1.52 μM for formation of E2-3-S and 2.95 μM for formation of E2-17-S. SULT2A1 had the highest V_max of 493 pmol/min/mg protein for formation of E2-3-S, which was 8.8- and 47-fold higher than the maximal rates of formation of E2-17-S and E2 disulfate, respectively. SULT2A1 formed E2-3-S more efficiently. However, when celecoxib (0–160 μM) was included in the incubation with either SULT2A1 or human liver cytosol, sulfonation switched from E2-3-S to E2-17-S in a concentration-dependent manner. The ratio of E2-17-S/E2-3-S went up to 15 with SULT2A1, and was saturated at 1 with human liver cytosol. In both cases, more E2-17-S was formed, with the unreacted E2 remained unchanged, suggesting celecoxib probably bound to a separate effector site to cause a conformational change in SULT2A1, which favored production of E2-17-S. The ability of celecoxib to alter the position of sulfonation of E2 may in part explain its success in the experimental prevention and treatment of breast cancer.     

Catechol estrogen quinones as initiators of breast and other human cancers: implications for biomarkers of susceptibility and cancer prevention

Exposure to estrogens is associated with increased risk of breast and other types of human cancer. Estrogens are converted to metabolites, particularly the catechol estrogen-3,4-quinones (CE-3,4-Q), that can react with DNA to form depurinating adducts. These adducts are released from DNA to generate apurinic sites. Error-prone base excision repair of this damage may lead to the mutations that can initiate breast, prostate and other types of cancer. The reaction of CE-3,4-Q with DNA forms the depurinating adducts 4-hydroxyestrone(estradiol) [4-OHE1(E2)-1-N3Ade and 4-OHE1(E2)-1-N7Gua. These two adducts constitute more than 99% of the total DNA adducts formed. Increased levels of these quinones and their reaction with DNA occur when estrogen metabolism is unbalanced. Such an imbalance is the result of overexpression of estrogen activating enzymes and/or deficient expression of the deactivating (protective) enzymes. This unbalanced metabolism has been observed in breast biopsy tissue from women with breast cancer, compared to control women. Recently, the depurinating adduct 4-OHE1(E2)-1-N3Ade has been detected in the urine of prostate cancer patients, but not in urine from healthy men. Mutagenesis by CE-3,4-Q has been approached from two different perspectives: one is mutagenic activity in the lacI reporter gene in Fisher 344 rats and the other is study of the reporter Harvey-ras gene in mouse skin and rat mammary gland. A-->G and G-->A mutations have been observed in the mammary tissue of rats implanted with the CE-3,4-Q precursor, 4-OHE2. Mutations have also been observed in the Harvey-ras gene in mouse skin and rat mammary gland within 6-12 h after treatment with E2-3,4-Q, suggesting that these mutations arise by error-prone base excision repair of the apurinic sites generated by the depurinating adducts. Treatment of MCF-10F cells, which are estrogen receptor-alpha-negative immortalized human breast epithelial cells, with E2, 4-OHE2 or 2-OHE2 induces their neoplastic transformation in vitro, even in the presence of the antiestrogen ICI-182,780. This suggests that transformation is independent of the estrogen receptor. The transformed cells exhibit specific mutations in several genes. Poorly differentiated adenocarcinomas develop when aggressively transformed MCF-10F cells are selected and injected into severe combined immune depressed (SCID) mice. These results represent the first in vitro/in vivo model of estrogen-induced carcinogenesis in human breast epithelial cells. In other studies, the development of mammary tumors in estrogen receptor-alpha knockout mice expressing the Wnt-1 oncogene (ERKO/Wnt-1) provides direct evidence that estrogens may cause breast cancer through a genotoxic, non-estrogen receptor-alpha-mediated mechanism. In summary, this evidence strongly indicates that estrogens can become endogenous tumor initiators when CE-3,4-Q react with DNA to form specific depurinating adducts. Initiated cells may be promoted by a number of processes, including hormone receptor stimulated proliferation. These results lay the groundwork for assessing risk and preventing disease.     

Genetic Polymorphisms of Sulfotransferases (SULT1A1 and SULT1A2) in a Turkish Population

Sulfotransferases (SULTs) play a significant role in the biotransformation of a variety of xenobiotics and endogenous compounds. SULTs are genetically polymorphic enzymes; to date, 12 human cytosolic SULT isoforms have been identified. This study investigated SULT1A1 and SULT1A2 gene polymorphism using a PCR-RFLP method (n = 303). The frequency of the SULT1A1*1 allele was 76.2% and SULT1A1*2 was 23.8%. The SULT1A1*3 allele could not be identified. The SULT1A2 frequencies were 69.2% (SULT1A2*1), 18.3% (SULT1A2*2), and 12.5% (SULT1A2*3). The SULT1A1 and SULT1A2 loci were in Hardy-Weinberg equilibrium (SULT1A1 χ2 = 0.58, P = 0.44; SULT1A2 χ2 = 7.28, P = 0.06). Linkage analysis indicated a close linkage between these two genes (χ2 = 5.31, P < 0.01); therefore, the statistical hypothesis that SULT1A1 and SULT1A2 alleles are independently distributed was rejected. Additionally, a strongly positive linkage was detected between SULT1A1*2 and SULT1A2*2 alleles in this population (D' = 0.79, χ2 = 33.33).     

Is bisphenol A a weak carcinogen like the natural estrogens and diethylstilbestrol?

Bisphenol A (BPA) displays weak estrogenic properties and could be a weak carcinogen by a mechanism similar to that of estrone (E(1)), estradiol (E(2)) and the synthetic estrogen diethylstilbestrol, a human carcinogen. A wide variety of scientific evidence supports the hypothesis that certain estrogen metabolites, predominantly catechol estrogen-3,4-quinones, react with DNA to cause mutations that can lead to the initiation of cancer. One of the major pathways of estrogen metabolism leads to the 4-catechol estrogens, 4-OHE(1)(E(2)), which are oxidized to their quinones, E(1)(E(2))-3,4-Q. The quinones react with DNA to form predominantly the depurinating adducts 4-OHE(1)(E(2))-1-N3Ade and 4-OHE(1)(E(2))-1-N7Gua. This process constitutes the predominant pathway in the initiation of cancer by estrogens. One pathway of BPA metabolism is hydroxylation of one of its symmetric benzene rings to form its catechol, 3-OHBPA. Subsequent oxidation to BPA-3,4-quinone would lead to reaction with DNA to form predominantly the depurinating adducts 3-OHBPA-6-N3Ade and 3-OHBPA-6-N7Gua. The resulting apurinic sites in the DNA could generate mutations in critical genes that can initiate human cancers. The catechol of BPA may also alter expression of estrogen-activating and deactivating enzymes, and/or compete with methoxylation of 4-OHE(1)(E(2)) by catechol-O-methyltransferase, thereby unbalancing the metabolism of estrogens to increase formation of E(1)(E(2))-3,4-Q and the depurinating estrogen-DNA adducts leading to cancer initiation. Thus, exposure to BPA could increase the risk of developing cancer by direct and/or indirect mechanisms. Knowledge of these mechanisms would allow us to begin to understand how BPA may act as a weak carcinogen and would be useful for regulating its use.     

Studies on the stoichiometry of estrogen oxidation catalyzed by purified prostaglandin-H-synthase holoenzyme

Prostaglandin-H-synthase (PHS) is a key enzyme in the biosynthesis of prostaglandins (PGs) from arachidonic acid and can oxidatively metabolize synthetic and steroidal estrogens. To investigate the relationship between estrogen cooxidation and PG synthesis, purified PHS-holoenzyme was incubated with radiolabeled arachidonic acid and various estrogens, namely diethylstilbestrol (DES), estradiol (E2), 2-hydroxyestradiol (2-OHE2), and 2-methoxyestradiol (2-MeOE2). The amount and pattern of PGs synthesized were analyzed by TLC and HPLC, estrogen metabolism was studied by HPLC. All tested compounds increased conversion of arachidonic acid to PG H2-derived prostanoids. A stoichiometric ratio between net estrogen oxidation and net PG H2 formation of approximately 2:1 for monophenolic compounds (2-MeOE2, E2) and of 1:1 for diphenolic estrogens (DES, 2-OHE2) was found, indicating that estrogens are apparently acting as electron donors for the PHS-peroxidase. In contrast, glutathione was not found to provide electrons for the reduction of PGG2 to PGH2, and rather decreased the conversion of arachidonic acid. The results of this in vitro study are discussed with respect to its implications for the in vivo situation.