Comparison on Metabolism of Estradiol and Its 17-Sulfate by Recombinant Human CYP Isoforms.

To identify the CYP isoforms involved in the production of 2-hydroxyestradiol 17-sulfate (2-OH-ES), which we assume to be an antioxidant in vivo, the 2-hydroxylation reaction of estradiol 17-sulfate (ES) by human liver microsome was investigated. As a result, it was estimated that CYP2C8 and 2C9 were largely involved in the production of 2-OH-ES. Therefore, the 2-hydroxylation kinetic analysis of ES was performed for both CYPs, and the metabolic clearance Vmax/Km (µL/nmol CYP/min) was determined. On comparing the results of ES with those of estradiol (E2), it was found that CYP2C8 was about 2.5 times higher and CYP2C9 was about 3 times higher, and ES was more likely to be a substrate for the 2-hydroxylation reaction by both CYPs. The CYP isoforms involved in A-ring hydroxylation of E2 and ES differed. From this, it was speculated that 2-OH-ES plays a different role to 2-hydroxyestradiol (2-OH-E2), which is recognized as an antioxidant in the body.

Synthesis of oligodeoxynucleotides containing a single 6alpha- or 6beta-diastereoisomer of N2-(estradiol-6-yl)-2'-deoxyguanosine.

DNA damage induced by estrogens is associated with developing breast, ovary, and endometrial cancers. The quinone of 2-hydroxyestrogen (2-OHE), a major estrogen metabolite, produces 2-OHE-derived dG and dA adducts in DNA. N(2)-[Estradiol-6(alpha or beta)-yl]-2'-deoxyguanosine [dG-N(2)-6(alpha or beta)-E(2)] lacking a 2-OH moiety may also be formed through sulfonation of 6-hydroxyestrogen. To explore the biological properties of such estrogen-DNA adducts, oligodeoxynucleotides modified by estrogen-derived DNA adduct were prepared by chemical synthesis. Initially, 6alpha- and 6beta-aminoestradiol 17-acetate (6alpha- and 6beta-NH(2)-E(2) 17Ac) were prepared by reductive amination of 6-oxo-estradiol 3,17-diacetate. The DMT-phosphoramidite derivative of N(2)-(3,17-diacetoxyestradiol-6alpha-yl)-2'-deoxyguanosine and its 6beta-isomer were prepared by coupling 5'-O-(4,4'-dimethoxytrityl)-2-fluoro-O(6)-[2-(4-nitrophenyl)ethyl]-2'-deoxyinosine separately with 6alpha- and 6beta-forms of NH(2)-E(2) 17Ac, respectively, followed by selective acetylation of the steroidal 3-hydroxyl group. The desired oligodeoxynucleotide containing a single dG-N(2)-6alpha-E(2) or dG-N(2)-6beta-E(2) was prepared efficiently by an automated DNA synthesizer. Synthesis of these site-specifically modified oligodeoxynucleotides will benefit further research into the biological properties and three-dimensional structure of 6alpha- and 6beta-diastereoisomers of estrogen-DNA adducts.

Studies on the interactions between drugs and estrogen. III. Inhibitory effects of 29 drugs reported to induce gynecomastia on the glucuronidation of estradiol.

To determine the inhibition effects of drugs on the glucuronidation of estradiol (E2), 29 drugs that have been reported to induce gynecomastia were examined in the presence of UDP-glucuronic acid using human hepatic microsomes (pooled) as the enzyme source. The percentage inhibition of the E2 glucuronidation was determined at drug concentrations of 1 microM (approximate therapeutic concentration) and 100 microM (non-clinical overdose concentration) based on the rate constants for the 3- and 17-glucuronidation of E2 (11.2 and 2.52 pmol/min/mg protein, respectively). The only drug that exhibited 50% or higher inhibition of the 3-glucuronidation at a concentration of 1 microM was manidipine (54.4%). When the concentration was 100 microM, manidipine exhibited 100% inhibition of the 3-glucuronidation, and other drugs that exhibited 50% or higher inhibition of the 3-glucuronidation were nicardipine (92%), nisoldipine (90%), nifedipine (84%), domperidone (81%), tacrolimus (80%), nitrendipine (77%) and ketoconazole (69%). Conversely, ipriflavone accelerated the formation of estradiol 3-glucuronide in the activity of 165% at the concentration of 100 microM. On the 17-glucuronidation, all of the drugs showed less than 50% inhibition at the concentration of 1 microM, but at the concentration of 100 microM, drugs that exhibited 50% or higher inhibition consisted of manidipine (79%), chlormadinone acetate (74%), nisoldipine (66%), nitrendipine (60%) and ketoconazole (55%). Although IC(50) values of these drugs were all lower than the K(m) value (285 microM) for the 3-glucuronidation of E2, they were higher than the K(m) value for the 17-glucuronidation (18.8 microM). Thus, the effect of the drugs on the E2 glucuronidation should be greater for hydroxy group at the C-3 than that at the C-17 of E2 molecule. On the other hand, metabolic clearances (V(max)/K(m)) of the 3- and 17-glucuronidation were about 1/14th and 1/18th of that of the 2-hydroxylation of E2, respectively. The result implies that, when the contribution of the glucuronidation to enterohepatic circulation is taken into consideration, the effect of this metabolic inhibition in the estrogen pool cannot be ignored.

Comparison of ex vivo inhibitory effect between 2-hydroxyestradiol and its 17-sulfate on rat hepatic microsomal lipid peroxidation.

Two endogenous antioxidants that are speculated to be defense substances against preeclampsia, 2-hydroxyestradiol (2-OH-E2) and its 17-sulfate, 2-hydroxyestradiol 17-sulfate (2-OH-E2-17-S), were administered to rats to compare their inhibitory effects on hepatic microsomal lipid peroxidation, and the lipid peroxides were determined in NADPH- and ascorbic acid-dependent systems. The two catechols showed a strong inhibitory effect on lipid peroxidation in both systems, and the effect was dose dependent. However, a large difference was observed in their inhibition patterns. After administration of 2-OH-E2, the effect appeared immediately and decreased gradually with time. In contrast, the effect of 2-OH-E2-17-S appeared some time after administration and persisted for a longer time. Both catechols also showed a striking difference in their dynamics. After administration, 2-OH-E2 was detected in the blood together with its metabolites, 2-methoxyestradiol and 2-methoxyestrone, and they disappeared immediately. In contrast, 2-OH-E2-17-S was present in the blood for a longer time together with its O-methylated product, 2-methoxyestradiol 17-sulfate, but disappeared from liver microsomes within 2 h after administration. The results imply no occurrence of a direct inhibition effect of 2-OH-E2-17-S.

[Studies on 2-hydroxyestradiol 17-sulfate derived from fetoplacental unit: the antioxidant as a potential defense substance against preeclampsia].

The antioxidant 2-hydroxyestradiol 17-sulfate (2-OH-E2-17-S) was found to be present in the placenta and to prevent the onset of preeclampsia. From experiments using rats, 2-OH-E2-17-S was confirmed to be a highly functional compound with stronger antioxidant activity than alpha-tocopherol and to sustain its antioxidant activity. 2-OH-E2-17-S was confirmed to be produced in the placenta from its precursor, estradiol 17-sulfate (E2-17-S), which is derived from fetal testosterone sulfate (TS). Since the fetal adrenal gland has been shown to convert testosterone (T) into TS, the following metabolic pathway may exist during pregnancy: T-->TS-->E2-17-S-->2-OH-E2-17-S. This fetoplacental pathway may contribute to the maintenance of healthy pregnancy. Details and the experimental outline of these discoveries are reported in this review.

Metabolism of [6,7-3H, 35S] estradiol 17-sulfate in rats.

To confirm whether or not the sulfo group of estradiol 17-sulfate (ES) is removed during in vivo metabolism in rats, the doubly labeled conjugate [6,7-3H, 35S] ES was injected into rats, and its biliary and urinary metabolites were determined by reverse isotope dilution method (RIDM). In male rats, the major radioactivity was detected in biliary disulfate fraction, which was composed of mainly ES and its two minor metabolites, 2-hydroxyestradiol 17-sulfate (2-OH-ES) and 2-methoxyestradiol 17-sulfate (2-MeO-ES). In female rats, in contrast, the radioactivity was dispersed into three fractions:biliary monosulfate, biliary disulfate, and urinary monosulfate fractions (Frs.) In both monosulfate Frs., 7beta-hydroxyestradiol 17-sulfate was detected as the major metabolite followed by 6alpha-, 6beta-, and 15beta-hydroxyestradiol 17-sulfates. Like male rats, 2-OH-ES and 2-Meo-ES as the minor products were detected in biliary disulfate fraction. The isotope ratios of ES and its metabolites in both sexes were essentially the same as that of the dose except that of 6alpha-hydroxylated metabolite, which may be derived from the loss of the tritium labeled at C6. These results confirm the occurrence of the direct metabolism of ES in rats.

On the structures of hydroxylated metabolites of estradiol 17-sulfate by rat liver microsomes.

The metabolism of estradiol 17-sulfate (ES) by hepatic microsomes of female rats produced four new metabolites in addition to 2- and 4-hydroxyestradiol 17-sulfates (2- and 4-OH-ES), which were detected on an HPLC chromatogram. By comparison with synthetic specimens, three of these compounds were identified as 6alpha-, 6beta-, and 7beta-hydroxyestradiol 17-sulfates. To elucidate the structure of the remaining metabolite, a large-scale incubation of ES was carried out, followed by isolation using preparative HPLC to give the single material, which was assigned as 15beta-hydroxyestradiol 17-sulfate by instrumental analyses. On the other hand, when ES was incubated with the microsomes of male rats, 2-OH-ES was produced accompanied by two minor products: 4-OH-ES and a metabolite of unknown structure. The results show clearly that the metabolism of ES by rat hepatic microsomes is remarkably different between the sexes.