Reduction of post injury neointima formation due to 17beta-estradiol and phytoestrogen treatment is not influenced by the pure synthetic estrogen receptor antagonist ICI 182,780 in vitro

Potential vascular actions of 2-methoxyestradiol

2-Methoxyestradiol (2-ME) is a biologically active metabolite of 17beta-estradiol that appears to inhibit key processes associated with cell replication in vitro. The molecule has been suggested to have potent growth-inhibitory effects on proliferating cells, including smooth muscle cells and endothelial cells, and may be antiangiogenic. Because of these potential roles for 2-ME, its lack of cytotoxicity and low estrogenic activity, we hypothesize that 2-ME could be a valuable therapeutic molecule for prevention and treatment of cardiovascular diseases. Whether 2-ME is as effective in vivo as it is in vitro at modulating vascular processes remains controversial. Here we discuss recent developments regarding mechanisms by which 2-ME might regulate vascular activity and angiogenesis and speculate on the therapeutic implications of these developments.

Isoflavones--safe food additives or dangerous drugs?

The sales volume of products containing isoflavone has increased since the publication of the Women's Health Initiative. The many apparently contradictory results published on the effects of isoflavones on a variety of estrogen-regulated organs point to both beneficial as well as adverse effects on human health. It is of particular importance that psychovegetative climacteric complaints such as hot flushes are, if at all, only slightly influenced by isoflavones. The substances appear to have weak anti-osteoporotic effect. Their anti-atherosclerotic action is debatable, as not all authors find any beneficial effect on lipids. Most importantly, there is dispute as to whether isoflavones derived from soy or red clover have negative, positive or any effect at all on the mammary gland or endometrium. It is beyond any doubt that soy products may have cancer preventing properties in a variety of organs including the mammary gland. However, these properties may only be exerted if the developing organ was under the influence of isoflavones during childhood and puberty. This may also explain the often quoted "Japanese Phenomenon", the fact that breast cancer occurs to a lesser extent in Japanese women. When administered to isoflavone "inexperienced" women at the time of menopause, the phytoestrogens appear to share the same effects as estrogen used in classical preparations for hormone replacement therapy, i.e. they may stimulate the proliferation of endometrial and mammary gland tissue with at present unknown and unpredictable risk to these organs. Therefore, the following question arises for the clinician: Why should soy or red clover products containing isoflavone be recommended, if the positive effects are only negligible but the adverse effects serious?

Consumption of soy isoflavones does not affect plasma total homocysteine or asymmetric dimethylarginine concentrations in healthy postmenopausal women

Postmenopausal women are at increased risk for cardiovascular disease because many risk factors are aggravated by menopause. Phytoestrogens may modulate risk factors favorably, involving mechanisms similar to estrogen. The effect of phytoestrogens on the atherogenic amino acids homocysteine and asymmetric dimethylarginine (ADMA) was investigated in a controlled intervention study in healthy postmenopausal women. A multicenter, double-blind, crossover intervention trial in 89 postmenopausal women from Denmark, Germany, and the UK was performed. Subjects consumed fruit cereal bars with or without soy isoflavones (50 mg/d) for 8 wk each with an 8-wk washout period in between. Urinary phytoestrogens increased significantly after isoflavone intervention (P < 0.001). Isoflavone supplementation did not affect plasma total homocysteine or ADMA. For homocysteine, changes from baseline were 0.32 micromol/L (range: -0.31-0.92; 95% CI 0.13-0.72), and 0.29 micromol/L (range: -0.45-1.09; 95% CI 0.01-0.63, P = 0.286) for isoflavone treatment and placebo, respectively. For ADMA concentrations, changes from baseline were -0.02 micromol/L (range: -0.08-0.03; 95% CI -0.04-0.01, and 0.00 micromol/L (range: -0.05-0.03; 95% CI -0.03-0.01, P = 0.397) for isoflavone treatment and placebo, respectively. There was no association between plasma total homocysteine and ADMA. Changes from baseline in plasma ADMA and folate were negatively correlated (r = -0.18, P = 0.017). These results challenge the overall health effect of isoflavone supplementation in healthy postmenopausal women.

Catecholamines block the antimitogenic effect of estradiol on human coronary artery smooth muscle cells

Sequential conversion of estradiol to catecholestradiols and methoxyestradiols by cytochrome-P(450) (CYP450) and catechol-O-methyltransferase (COMT), respectively, contributes to the antimitogenic effects of estradiol on vascular smooth muscle cell (SMC) growth via estrogen receptor-independent mechanisms. Because catecholamines are also substrates for COMT, we hypothesize that catecholamines may abrogate the vasoprotective effects of estradiol by competing for COMT and inhibiting methoxyestradiol formation. To test this hypothesis, we investigated the antimitogenic/inhibitory effects of estradiol on human coronary artery SMC growth (cell number, DNA synthesis, collagen synthesis, and SMC migration) and ERK1/2 phosphorylation in the presence and absence of catecholamines. Norepinephrine, epinephrine, isoproterenol, and OR486 (COMT inhibitor) abrogated the inhibitory effects of estradiol on SMC growth and ERK1/2 phosphorylation. The interaction of catecholamines with estradiol was not affected by phentolamine or propanolol, alpha- and beta-adrenoceptor antagonists, respectively. The antimitogenic effects of 2-hydroxy-estradiol, but not 2-methoxyestradiol, were abrogated by epinephrine, isoproterenol, and OR486. Catecholamines inhibited the conversion of both estradiol and 2-hydroxy-estradiol to 2-methoxyestradiol, and SMCs expressed CYP1A1 and CYP1B1. Our findings suggest that catecholamines within the coronary arteries may abrogate the antivasoocclusive effects of estradiol by blocking the conversion of catecholestradiols to methoxyestradiols. The interaction between catecholamines and estradiol metabolism may importantly define the cardiovascular effects of estradiol therapy in postmenopausal women.

Genistein Inhibits Expressions of NADPH Oxidase p22phox and Angiotensin II Type 1 Receptor in Aortic Endothelial Cells from Stroke-Prone Spontaneously Hypertensive Rats

Phytoestrogens are considered to be natural selective estrogen receptor modulators exerting antioxidant activity and improving vascular function. However, the mechanisms responsible for their antioxidative effects remain largely unknown. This study tested the hypothesis that genistein may provide significant endothelial protection by antioxidative effects through attenuating NADPH oxidase expression and activity. The results showed that genistein suppressed the expressions of the p22phox NADPH oxidase subunit and angiotensin II (Ang II) type 1 (AT1) receptor in a concentration- and time-dependent manner in aortic endothelial cells from stroke-prone spontaneously hypertensive rats examined by Western blot analysis. Treatment with genistein also remarkably reduced the Ang II-induced superoxide by the reduction of nitroblue tetrazolium, inhibited nitrotyrosine formation, and attenuated endothelin-1 production by ELISA via the stimulation of Ang II. However, when cells were pretreated with ICI-182780, an estrogen-receptor antagonist, at a concentration of 50 micromol/l for 30 min and then co-incubated with ICI-182780 and genistein for 24 h, the inhibitory effect of genistein was not blocked. In contrast, the inhibitory effect of genistein treatment was partially reversed by 30-min pretreatment of endothelial cells with GW9662, a peroxisome proliferator-activated receptor gamma (PPARgamma) antagonist. Genistein thus appears to act as an antioxidant at the transcription level by the downregulation of p22phox and AT1 receptor expression. Our data also showed that the PPARgamma pathway was involved, at least in part, in the inhibitory effect of genistein on the expression of p22phox and AT1 receptors. The endothelial-protective effects of phytoestrogen may contribute to improvement of cardiovascular functions.

Methoxyestradiols mediate the antimitogenic effects of 17beta-estradiol: direct evidence from catechol-O-methyltransferase-knockout mice

BACKGROUND

Studies using pharmacological agents suggest but do not prove that the antimitogenic effects of estradiol are caused by conversion of estradiol to hydroxyestradiols (mediated by CYP450s) followed by methylation of hydroxyestradiols to methoxyestradiols (mediated by catechol-O-methyltransferase, COMT).

METHODS AND RESULTS

To test this hypothesis more rigorously, we used aortic smooth muscle cells (SMCs) from mice lacking COMT (COMT-KO). Wild-type (WT) but not COMT-KO SMCs efficiently converted 2-hydroxyestradiol to 2-methoxyestradiol. Both WT and COMT-KO SMCs expressed estrogen receptors. Estradiol and 2-hydroxyestradiol concentration-dependently inhibited serum-induced DNA synthesis, cell numbers, and collagen synthesis in WT but not COMT-KO SMCs. 2-Methoxyestradiol inhibited DNA synthesis, cell numbers, and collagen synthesis in both WT and COMT-KO SMCs.

CONCLUSIONS

These data provide strong evidence that the vascular antimitogenic effects of estradiol are estrogen receptor-independent and involve the sequential conversion of estradiol to hydroxyestradiols and then to methoxyestradiols.

Cardiovascular Pharmacology of Estradiol Metabolites

A discussion of the role of endogenous estradiol metabolites in mediating important biological actions of estradiol is essentially nonexistent in standard textbooks of pharmacology and endocrinology. Indeed, the prevailing view is that all biological effects of estradiol are initiated by binding of estradiol per se to estrogen receptors and that estradiol metabolites are more or less irrelevant. This orthodox view, which is most likely incorrect, is the fundamental premise (an estrogen is an estrogen is an estrogen) underlying the design of important clinical trials such as the Heart and Estrogen/Progestin Replacement Study and the Women's Health Initiative Study. Accumulating data provide convincing evidence that some metabolites of estradiol, the major estrogen secreted by human ovaries, are biologically active and mediate multiple effects on the cardiovascular and renal systems that are largely independent of estrogen receptors. More specifically, metabolites of estradiol, particularly catecholestradiols and methoxyestradiols, induce multiple estrogen receptor-independent actions that protect the heart, blood vessels, and kidneys from disease. These protective effects are mediated in part by the inhibition of the ability of vascular smooth muscle cells, cardiac fibroblasts, and glomerular mesangial cells to migrate, proliferate, and secrete extracellular matrix proteins, as well as by an improvement in vascular endothelial cell function. The purpose of this review is to highlight the cardiovascular and renal pharmacology of catecholestradiols and methoxyestradiols. The take home message is simple: that when it comes to cardiovascular and renal protection, the concept that all estrogenic compounds are created equal may not be true.