Methoxyestradiols Mediate Estradiol-Induced Antimitogenesis in Human Aortic SMCs

Abstract

Abstract-Estrogen receptors (ERs) are considered to mediate the ability of 17␤-estradiol (estradiol) to reduce injury-induced proliferation of vascular smooth muscle cells (VSMCs), leading to vascular lesions. However, the finding that estradiol attenuates formation of vascular lesions in response to vascular injury in knockout mice that lack either ER-␣ or ER-␤ challenges this concept. Our hypothesis is that the local metabolism of estradiol to methoxyestradiols, metabolites of estradiol with little affinity for ERs, mediates the ER-independent antimitogenic effects of estradiol on VSMCs. In human VSMCs, 2-methoxyestradiol and 2-hydroxyestradiol were more potent than was estradiol in inhibiting DNA synthesis ( 3 [H]-thymidine incorporation), collagen synthesis ( 3 [H]-proline incorporation), cell proliferation (cell number), and cell migration (movement of cells across a polycarbonate membrane). The inhibitory effects of estradiol on VSMCs were enhanced by cytochrome-P450 (CYP450) inducers 3-methylcholanthrene and phenobarbital. Moreover, the inhibitory effects of estradiol were blocked in the presence of the CYP450 inhibitor 1-aminobenzotriazole and the catechol-O-methyltransferase inhibitors quercetin and OR486. Both OR486 and quercetin blocked the conversion of 2-hydroxyestradiol to 2-methoxyestradiol; moreover, they blocked the antimitogenic effects of 2-hydroxyestradiol but not of 2-methoxyestradiol. The ER antagonist ICI182780 blocked the inhibitor effects of estradiol on VSMCs, but only at concentrations (Ͼ50 mol/L) that also inhibit the metabolism of estradiol to hydroxyestradiols (precursors of methoxyestradiols). In conclusion, the inhibitory effects of locally applied estradiol on human VSMCs are mediated via a novel ER-independent mechanism involving estradiol metabolism. These findings imply that vascular estradiol metabolism may be an important determinant of the cardiovascular protective effects of estradiol and that nonfeminizing estradiol metabolites may confer cardiovascular protection regardless of gender.

Methoxyestradiols Mediate the Antimitogenic Effects of 17β-Estradiol

“…8 ER␣ and ER␤ expression were analyzed by Western blots. 9 Experiments were conducted in triplicate (repeated 3 or 4 times). Results are expressed as meanϮSEM.…”

Menopause, Estrogens, and Endothelial Dysfunction: Current Concepts

“…27 In addition to these actions on the vascular tonus, estrogen exerts an antiproliferative action on the vascular smooth layer. 48 Also, it appears to have a major role in vascular remodeling, inhibiting the proliferation of the inner layer after injury 49 and increasing the expression of contractile proteins in the myocardium. 50 In other tissues, such as the liver, estrogen can mediate both beneficial (expression of genes of apoproteins that improve the lipid profile) and adverse effects (increase in the expression of procoagulant factors and decrease of fibrinolytic factors).…”

Sex Steroids, Cardiovascular Disease, and Hypertension

“…Mori et al reported that the estradiol was protective against neointimal proliferation in female rats subjected to balloon dilatation of the carotids. 26 In addition, Dubey et al have reported that estradiol and some of its metabolites are antimitogenic in human aortic smooth muscle cells, 27 mesangial cells, 28 and cardiac fibroblasts. 29 Estradioleluting stents are now available and are being used in clinical trials in humans 30 to determine whether the estradiol-eluting stents are successful in protecting against neointimal proliferation.…”