Catecholoestrogens: possible role in systemic lupus erythematosus.

It is well established that risk of developing SLE is higher among women compared with men but only very little is understood about the underlying mechanisms. Oestrogen and their catechol metabolites seem to play an important role in SLE but the exact patho-aetiology remains elusive. The evidences concerning the possibility of catecholoestrogens (CEs) in the development of SLE are very limited and preliminary. The possible mechanism involves quinone-semiquinone redox cycling of CEs to generate the free radical that can cause DNA damage. This would probably alter its immunogenicity leading to the induction and elevated levels of SLE autoantibodies cross-reacting with native DNA. The data demonstrate the possible role of CE in presenting unique neo-epitopes that might form one of the factors in induction of SLE autoantibodies. However, the role of oestrogen in immune modulation cannot be rule out as a mediator of various immune-related diseases.

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.

Are catechol oestrogens obligatory mediators of oestrogen action in the central nervous system? I. Characterization of pharmacological probes with different receptor binding affinities and catechol oestrogen formation rates.

In an attempt to define pharmacological probes with which to test the role of catechol oestrogen formation in the central nervous system, five oestrogens (oestradiol-17 beta, oestradiol-17 alpha, 4-fluoro-oestradiol, 2-fluoro-oestradiol and moxestrol (11 beta-methoxy-17 alpha-ethynyloestradiol) were studied for binding to oestrogen receptors and conversion to catechol metabolites. Binding to cytosol oestrogen receptors was measured in the hypothalamus-preoptic area-amygdala (HPA), pituitary gland and uterus of ovariectomized rats. Conversion to catechol oestrogens was tested in microsomes from the HPA, pituitary gland and liver, using a catechol-O-methyltransferase-coupled radioenzymatic assay. Oestradiol-17 alpha was the only weak oestrogen receptor ligand. Binding affinities of the other compounds tested were much higher and comparable to those of oestradiol-17 beta. In contrast, oestradiol-17 alpha was rapidly converted to catechol metabolites, while moxestrol was a relatively poor substrate for catechol oestrogen formation. 4-Fluoro-oestradiol could be 2-hydroxylated but not 4-hydroxylated. 2-Fluoro-oestradiol exhibited impaired 2-hydroxylation but normal 4-hydroxylation.

Are catechol oestrogens obligatory mediators of oestrogen action in the central nervous system? II. Potencies of natural and synthetic oestrogens for induction of gonadotrophin release and female sexual behaviour in the rat.

The role of catechol oestrogen formation in the mechanism by which circulating oestrogens facilitate gonadotrophin release and female sexual behaviour was explored in adult female rats. The effects of oestradiol-17 beta were compared with those of a group of oestrogens with either a reduced affinity for oestrogen receptors (oestradiol-17 alpha) or a reduced ability to act as substrates for catechol oestrogen formation (2-fluoro-oestradiol, 4-fluoro-oestradiol and moxestrol (11 beta-methoxy-17 alpha-ethynyloestradiol]. Rats were ovariectomized on the evening of dioestrus day 1 of the 4-day oestrous cycle and implanted s.c. 12 h later with infusion pumps containing either one of the test oestrogens or vehicle alone. Infusion rates for oestradiol-17 beta, moxestrol, 2-fluoro-oestradiol and 4-fluoro-oestradiol were adjusted to give concentrations of nuclear oestrogen receptors in the brain and pituitary gland within the range of those found in intact female rats during pro-oestrus. Oestradiol-17 alpha was infused at the same and at a tenfold higher rate than that of oestradiol-17 beta; neither of these treatments with oestradiol-17 alpha significantly increased brain or pituitary gland nuclear oestrogen receptor levels. On the day after the pump was implanted, samples of tail vein blood were withdrawn at 12.00, 14.00, 16.00 and 18.00 h for LH assay. All animals were then injected s.c. with 1 mg progesterone in propylene glycol, and tested for feminine sexual behaviour 5 h later. Oestradiol-17 beta, moxestrol, 2-fluoro-oestradiol and 4-fluoro-oestradiol all elicited pronounced LH surges and facilitated progesterone-triggered proceptive and lordosis behaviours.(ABSTRACT TRUNCATED AT 250 WORDS)

Human type 1 estrogen sulfotransferase: catecholestrogen metabolism and potential involvement in cancer promotion.

Using purified human type 1 estrogen sulfotransferase (hEST1), we show that the best substrate for this enzyme is 2-hydroxy-catecholestrogen. The enzyme also catalyzes the transformation of 4-hydroxy-estrogens and 16-hydroxy-estrogens, but with a lower affinity. We also present evidence to indicate that estrogen sulfotransferase may play a role in processes other than the detoxification and elimination of steroids. Indeed, hEST1 may also be involved in the production of stable precursors for local steroid biosynthesis or in the activation of promutagenic estrogen metabolites into carcinogens.

Are the catecholestrogens involved in estrogen-induced striatal dopamine receptor supersensitivity?

The ability of tamoxifen, an antiestrogen agent, to antagonise the striatal dopamine receptor hyperactivity induced in rats by chronic treatment with 17 beta-estradiol and 2-hydroxyestradiol or with two receptor blockers (haloperidol and sulpiride) was compared. It was found that tamoxifen antagonised both the increase in [3H]spiperone binding sites and the stereotyped behaviour induced by apomorphine in animals treated with the two steroids but had no effect in animals receiving the two dopamine blockers. These results run counter to the view that introduction of a catechol group in a steroid molecule is of decisive importance in the induction of striatal dopamine receptor hypersensitivity.

The role of beta-endorphins and catechol estrogens on the hypothalamic-pituitary axis in female athletes.

Competitive swimmers were followed over a 2-year period when they trained at different levels of exercise which coincided with distinct changes in their menstrual history. Oligomenorrhea was identified in 5 of 13 of these athletes when they swam approximately 100,000 yards per week. Weight and percentage of body fat were not significantly different between the period of oligomenorrhea and regular menstrual function (P = 0.24). Mean and median levels of luteinizing hormone, follicle-stimulating hormone, prolactin, and 17beta-estradiol were decreased and catechol estrogens and beta-endorphins were increased in serum during the strenuous, when compared with the moderate, training period. The serum levels of the steroid and protein hormones were similar to those of normal cycling, nonexercising control subjects during moderate exercise (60,000 yards per week). The significant differences between beta-endorphins and catechol estrogens during periods of strenuous exercise suggest an explanation for oligomenorrhea in female athletes. These hormonal changes result in hypothalamic anovulation, which appears to be reversible, because the hormone levels and menstrual cycles return to normal when the exercise is reduced.

Catechol estrogens mediated activation of Nrf2 through covalent modification of its quinone metabolite to Keap1.

The catechol metabolites (2-OHE and 4-OHE) of estrogen enter a redox cycle, thereby generating not only reactive oxygen species (ROS) but also electrophilic quinones. It is well recognized that chemicals causing oxidative stress or electrophiles activate a transcription factor Nrf2 that is negatively regulated by Keap1, leading to up-regulation of downstream proteins responsible for detoxification of electrophiles in cells. The purpose of the present study is to explore the roles of oxidative and electrophilic stress in Nrf2 activation caused by redox-active catechol estrogens. Exposure of RAW264.7 cells to 2- and 4-OHE activated Nrf2, resulting in induction of heme oxygenase-1 (HO-1) and glutamate cysteine ligase catalytic subunit (GCLC). Under these conditions, intracellular oxidants were generated; however, subsequent examinations revealed that quinoid metabolites derived from 2- and 4-OHE mainly participate in the Nrf2 activation. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis revealed Keap1 undergoes modification by such quinoid species through multiple reactive thiol groups. These results suggest that Nrf2 activation during redox cycling of catechol estrogens is dominantly attributable to formation of their ortho-quinones that covalently bind to Keap1.

Do catechol estrogens participate in the initiation of labor?

To assess the role of catechol estrogens in the initiation of labor, we compared the levels in amniotic fluid during the second and third trimesters and from women undergoing cesarean section at term not in labor and those with spontaneous labor at term. Catechol estrogen concentrations in amniotic fluid increased significantly with the progress of pregnancy. Further, concentrations (mean +/- SE) were significantly higher in spontaneous labor at term (468.6 +/- 29.5 pg/ml) compared with those obtained during cesarean section (242.6 +/- 22.3 pg/ml) at term not in labor. We suggest that catechol estrogens, through their stimulating effects on prostaglandin synthesis, participate in the initiation of labor.

Synthesis of prostaglandins by pig blastocysts cultured in medium containing estradiol or catechol estrogen.

Two experiments were conducted to determine the effects of 2-hydroxy-estradiol-17 beta (2-OH-E2; 0, 50 and 100 microM) and estradiol-17 beta (E2; 0, 25 and 50 microM) on prostaglandin (PG) E and PGF2 alpha synthesis by day-10 pig blastocysts (day 0 is first day of estrus). Blastocysts were incubated in a modified Krebs-Ringer bicarbonate medium, supplemented with bovine serum albumin (4 mg/ml) and the vitamins and amino acids (essential and nonessential) in Minimum Essential Medium (without phenol red or antibiotics). The incubations were conducted at 39 degrees C for three 2-h periods; the second and third periods included an E2 or catechol estrogen treatment. Release of PGF2 alpha into the culture medium decreased (p less than 0.001) linearly with increasing concentrations of 2-OH-E2 in both periods. Release of PGE was not affected by 2-OH-E2, therefore 2-OH-E2 increased (p less than 0.06) the PGE:PGF2 alpha. When E2 was added to the medium, release of PGE was decreased (p less than 0.01) during the second and third periods. Release of PGF2 alpha also was decreased (p less than 0.05) by E2 during period 2, but E2 did not alter the PGE:PGF2 alpha. Content of PGs in blastocysts at recovery was less than 10% of the PGs released in vitro. Therefore, these studies demonstrate effects of both the primary and catechol forms of E2 on the synthesis of PGE and PGF2 alpha. Catechol estrogens and E2 may inhibit PG synthesis and modify the PGE:PGF2 alpha during the establishment of pregnancy in pigs.

Effects of the ovary and conceptus on uterine blood flow in the pig.

Changes in uterine blood flow throughout pregnancy appear to be due to steroid-induced alterations in uterine arterial tone and contractility. Arterial contractility is a transient reduction in luminal diameter in response to nerve stimulation or to an alpha-1 adrenergic agonist, leading to short-term reduction in uterine blood flow. Tone is the pressure exerted by an arterial segment against an intraluminal flow (distensibility) and is considered to set the baseline rate of flow. These phenomena appear to be regulated individually, with tone changes predominating during pregnancy. In pregnancy, tone is markedly depressed as oestrogen concentrations rise, and the vessel is distended and flaccid. Arterial tone is a function of the amount of calcium available to the contractile proteins of the arterial smooth muscle, which is derived from extracellular sources. Calcium availability is regulated by the opening and closing of calcium channels in the surface membrane in response to changes in the membrane potential. The loss of uterine arterial tone associated with oestrogen results from a markedly depressed uptake of calcium by the vessels. A significant negative correlation (P less than 0.001; r = - 0.93) is observed between uterine arterial uptake of calcium and the concentrations of oestrogens in systemic blood of pigs throughout gestation. Several lines of evidence suggest that the blockade of potential-sensitive calcium channels associated with uterine hyperaemia is produced by catechol oestrogens, short-lived metabolites of oestrogens that are found in the circulation when oestrogen levels are high. Synthesis of catechol oestrogens from the parent oestrogens has been shown to occur in the placenta, endometrium and uterine arteries of pigs.(ABSTRACT TRUNCATED AT 250 WORDS)

Current concepts of the endocrine characteristics of normal menstrual function: the key to diagnosis and management of menstrual disorders.

Obviously, the endocrine mechanisms involved in producing the normal, cyclic pattern of menstrual bleeding are exceedingly complex. A review of even our current, far from complete, knowledge of the regulation of follicular growth, cyclic selection of a single dominant follicle, ovulation, and the neuroendocrine control of all three mechanisms only serves to emphasize the myriad of endogenous and exogenous factors that may adversely affect such a delicate balance and be manifest in menstrual disturbance. Indeed, one may wonder that the menstrual cycle is cyclic and predictable at all. Nevertheless, the efficiency with which the system normally operates is striking. Its very complexity often makes disorders of menstrual function a not infrequent symptom of disease outside the reproductive tract, a fact that should stress the need for prompt and thorough evaluation.