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At least 199 records · Page 11Linked to original sources
PubMed1993

Activity of mushroom tyrosinase on catechol and on a catechol estrogen in an organic solvent.

A suspension of tyrosinase-coated glass beads in butanol effectively oxidizes catechol substrate. The enzyme is not soluble in the organic solvent and activity can be stopped by removal of the solid state enzyme after low-speed centrifugation or decantation. The product was assayed by HPLC and by its reactivity towards Besthorn's reagent, which gave a reaction typical for o-quinones. Addition of water to the extent of 0.5 to 4% raised the rate of substrate utilization but the accumulation of quinone first increased and then began to decrease. It is suggested that the product in dry butanol is prevented from reacting further by lack of water, which is necessary to promote secondary reactions causing free radical formation and leading ultimately to polymerization to melanin. Successive washes of the solid state enzyme with butanol increased enzyme activity, indicating presence of a butanol extractable inhibitor in the tyrosinase preparation. The enzyme on glass beads in butanol suspension was stabilized by the presence of substrate. 2-Hydroxyestradiol acted as an inhibitor of the tyrosinase-catalyzed oxidation of catechol. The data obtained can be interpreted to mean that the oxidation of the estrogen in the presence of tyrosinase, as previously reported, may be dependent upon the enzyme-catalyzed oxidation of catechol. The oxidation product of catechol, the o-quinone, is likely to function as oxidant towards 2-hydroxyestradiol.

Basidiomycota↗
PubMed2003

Nrf2, not the estrogen receptor, mediates catechol estrogen-induced activation of the antioxidant responsive element.

The antioxidant responsive element (ARE) plays an important role in the gene expression of phase II detoxification enzymes, such as NAD(P)H:quinone oxidoreductase 1 (NQO1), and NF-E2-related factor2 (Nrf2) is the transcription factor for the ARE-driven genes. Interestingly, estrogen receptor (ER) was reported to increase NQO1 gene expression through the ARE. In this study, we investigated the role of ER and Nrf2 in ARE activation using IMR-32 cells and mouse primary astrocytes. Among tested estrogen-related compounds, only catechol estrogens (i.e. 4-hydroxyestradiol) activated the ARE. Since 4-hydroxyestradiol-induced ARE activation was not inhibited by either 17beta-estradiol or tamoxifen, and overexpression of ER-alpha decreased 4-hydroxyestradiol-induced ARE activation, ARE activation by catechol estrogen was independent of ER. Nrf2, however, was very important in the 4-hydroxyestradiol-induced ARE activation. 4-Hydroxyestradiol did not activate the ARE in Nrf2 knockout (-/-) primary astrocytes, but did activate the ARE when Nrf2 was transfected into Nrf2-/- astrocytes. In addition, dominant negative Nrf2 completely blocked 4-hydroxyestradiol-induced ARE activation in Nrf2+/+ astrocytes, and only 4-hydroxyestradiol induced Nrf2 nuclear translocation in IMR-32 cells. A selective phosphatidylinositol 3-kinase (PI3-kinase) inhibitor (LY294002) blocked 4-hydroxyestradiol-induced Nrf2 nuclear translocation and NQO1 activity induction in IMR-32 cells. Taken together, these observations suggest that 4-hydroxyestradiol activates the ARE by a PI3-kinase-Nrf2 dependent mechanism, not involving ER.

Animals↗
PubMed1980

Rapid metabolic clearance of the catechol estrogen 2-hydroxyestrone.

The plasma metabolic clearance rate (MCRp) of 2-hydroxyestrone was measured in normal young adults by two methods: infusion of unlabeled 2-OHE1 to equilibrium with radioimmunoassay of plasma 2-OHE1 levels, and infusion of [3H]2-OHE1 to equilibrium with measurement of chromatographically purified plasma [3H]2-OHE1. MCR's were 40--70,000 L/day and 15--50,000 L/day, respectively. This is the highest known MCR for a naturally occurring steroid. The only measurable plasma metabolite of [3H]2-OHE1 co-migrated with 2-methoxyestrone. When [3H]2-OHE1 was incubated with blood samples in vitro, [3H] xi-methoxyestrone was rapidly formed. Since this MCR is higher than cardiac output, clearance must occur primarily in the blood compartment, probably largely by the action of erythrocyte catechol-0-methyltransferase.

Adult↗
PubMed1982

Catechol estrogens and thrombosis: lack of a direct effect of 2-hydroxyestradiol on platelets.

Women who use the oral contraceptive pill are at risk for a variety of thromboembolic complications, but the precise mechanism is unclear. Since 2-hydroxyestradiol is a major metabolite of estradiol and possesses some of the structural and functional properties of catecholamines, we examined whether this compound might influence thrombogenesis, in particular whether it would exert an epinephrine-like effect on the platelet. In vitro, 2-hydroxyestradiol does not cause or potentiate aggregation or thromboxane release, nor does it prevent the rise in cyclic AMP caused by anti-aggregatory prostaglandins. While 2-hydroxyestradiol does not exert a direct effect on the platelet in vitro, it may play a role in thrombosis in women who take oral contraceptives through another mechanism.

Blood Platelets↗
PubMed1991

Cimetidine inhibits catechol estrogen metabolism in women.

Chronic cimetidine use in men is associated with hyperestrogenic side effects such as gynecomastia, which may be linked to inhibition of estradiol 2-hydroxylation. As this property of the drug might be helpful in hypoestrogenic states such as osteoporosis, we investigated the effect of cimetidine on estradiol metabolism in premenopausal and postmenopausal women. Using an in vivo radiometric assay, we found that the extent of estradiol 2-hydroxylation in premenopausal women (n = 9) was decreased by a 1-month course of cimetidine, 800 mg twice daily (44.0% +/- 3.5% v 31.2% +/- 4.1%, P less than .001). Among premenopausal smokers (n = 3), the response to cimetidine was approximately the same as nonsmokers. Serum estradiol levels (follicular phase) in these women were unaltered by cimetidine after 1 month, while concentrations of sex hormone-binding globulin (SHBG) were decreased by 30% (P = .018). Postmenopausal women (n = 5) initially received a lower dose of cimetidine (600 mg twice daily) for 2 weeks, followed by a higher dose (1200 mg twice daily) for another 2 weeks. The extent of estradiol 2-hydroxylation was significantly reduced by the low dose (44.4% +/- 4.5% v 24.3% +/- 3.0%, P less than .005), with minimal further reduction after the high dose (21.7% +/- 1.6%). After 4 weeks of cimetidine treatment, serum estradiol levels increased significantly from 30.0 +/- 6.4 to 59.8 +/- 13.1 pg/mL (P = .033), while SHBG was unaffected. Cimetidine was found to have little effect on selected biochemical indices of bone and calcium metabolism in both groups of women.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗