Hydroxylated estrogen metabolites influence the proliferation of cultured human monocytes: possible role in synovial tissue hyperplasia.

INTRODUCTION: 17Beta-estradiol, estrone, and several of their hydroxylated metabolites, have been found to be significantly increased in synovial fluid of rheumatoid arthritis (RA) patients. In this study, we investigated whether the estrogen metabolites are able to exert direct effects on monocyte cell proliferation, which is important in RA synovial tissue activation and growth. METHODS: Human monocytes (THP-1) were treated with the following estrogen metabolites at different concentrations (from 10-8M, 10-9M, 10-10M to 10-11M) for 24, 48 and 72 hours: 16-hydroxyestrone (16OH-E1), 16-hydroxyestradiol (16OH-E2), 4-hydroxyestrone (4OH-E1), 4-hydroxyestradiol (4OH-E2), 2-hydroxyestrone (2OH-E1) and 2-hydroxyestradiol (2OH-E2). Monocytes were activated with interferon-gamma (INF-gamma). Cell cultures were also performed in presence of tamoxifen (10-7M) to evaluate whether the estrogen metabolites act through the estrogen receptors (ER). Cell growth was detected by MTT test and cell viability through the LDH release assay. RESULTS: 4OH-E1 and 2OH-E1 significantly increased cell growth at low concentration (10-10M), whereas they significantly reduced cell proliferation at high concentrations (10-9M). 16OH-E2 and 4OH-E2 induced opposite effects: cell proliferation at high concentration and antiproliferative action at low doses. On the contrary, 16OH-E1 and 2OH-E2 were found to be estrogen metabolites that induced cell proliferative effects for most of the tested doses. Tamoxifen caused the loss of effects on cell proliferation for almost all the metabolites. CONCLUSION: This study first demonstrates that different downstream estrogen metabolites interfere with monocyte proliferation and generally might modulate the immune response. Therefore, since estrogen metabolite/ratios are altered in the synovial fluid of RA patients, they might play important roles at least in RA synovial tissue hyperplasia.

Inhibition of the preovulatory LH surge after a catecholestrogen (2-hydroxyestrone) antiserum injection in the third ventricle of cycling female rats.

Administration of a catecholestrogen (2-hydroxyestrone, 2-OHE1) antiserum (2-OHE1-AS) in the third ventricle of cycling female rats, on the morning of proestrus, leads to a significant reduction in the afternoon LH surge. These responses are dose-dependent and can be observed even when the 2-OHE1-AS is injected on the diestrus morning. Almost similar results were obtained with an antiserum against 17 beta-estradiol (17 beta-E2). Nevertheless, the fact that the central immunoneutralization of 2-OHE1 impedes the preovulatory surge of LH at a time of high peripheral levels of 17 beta-E2 strengthens the idea of a specific role for 2-OHE1 in the control of cycling LH release.

Effect of catechol estrogens on the preovulatory content of luteinizing hormone-releasing hormone in the median eminence of the rat.

Cycling rats injected with 2-hydroxyestrone or 2-hydroxyestradiol at 09.00 or 10.00 h in the morning of proestrus do not express the normal preovulatory LH surge in the afternoon of the day. The LHRH content of the median eminence in control animals decreases sharply in the afternoon from elevated noon and morning levels. The catechol estrogen-treated rats fail to show the decrease. Thus the catechol estrogens block the LH surge at its usual time by influencing the changes in the concentration of LHRH in the median eminence on proestrus. Since the catechol estrogens have short biological half-lives, their effect on the LHRH content in the afternoon must originate in the morning at the time of the endogenous estradiol (E2) peak. These results have implications in the physiological processes responsible for the positive feedback of estradiol on the preovulatory LH surge in the rat.

Metabolic clearance rate and uterotropic activity of 2-hydroxyestrone in rats.

2-Hydroxyestrone (2-OHE1) has much lower uterotropic potency than might be predicted from its uterine estrogen receptor affinity. 2-OHE1 displaces saturably bound [3H]estradiol from rat uterine cytosol with a competitive inhibition constant of 8.6 nM, while the dissociation constant for 17 beta-estradiol (E2) is 0.42 nM. From this ratio of binding affinities, one would expect some agonist or antagonist activity of 2-OHE1 to be apparent at doses roughly 20-50 times the minimum effective dose of E2. Instead, at doses of 2-OHE1 1000 times an effective dose of E2, no uterotropic effect was observed. When 2-OHE1 was injected together with E2 at dose ratios of 500:1, there was no antagonism of the effect of E2. To examine this discrepancy, the plasma MCRs (MCRpS) of E2 and 2-OHE1 were determined by continuous infusion techniques. Plasma concentrations of 2-OHE1 and E2 during control and infusion periods were measured by RIAs. The MCRp of 2-OHE1 averaged 50,000 ml/h, more than 100 times that of E2 (approximately 400 ml/h). The extraordinarily high MCRp of 2-OHE1 may explain the failure to observe any biological effects of this catechol estrogen, even at high doses. This rapid metabolism, presumably occurring in the blood compartment, should be considered in handling blood samples for RIA and in devising studies of the actions of catechol estrogens.