Modulators of vascular sex hormone receptors and their effects in estrogen-deficiency states associated with menopause

Abstract

Cardiovascular disease (CVD) is more prevalent in postmenopausal than premenopausal women, suggesting vascular protective effects of estrogen. Also, experimental studies have demonstrated beneficial effects of estrogen in improving vascular function and reducing vascular injury. However, clinical trials including HERS I, HERS II, WHI and WISDOM have demonstrated minimal beneficial vascular effects of menopausal hormone therapy (MHT) in postmenopausal women with CVD. The discrepancies between the experimental findings and clinical data may be related to the vascular estrogen receptors (ER), the type, route of administration, or dosage of MHT, and subject's age. Vascular ERs mediate both genomic and non-genomic effects of estrogen on the endothelium, vascular smooth muscle (VSM), and extracellular matrix (ECM). Postmenopausal changes in vascular ER structure, polymorphisms, amount, subcellular location, affinity or signaling could modify their responsiveness to estrogen and thereby the outcome of MHT. Recent investigations and patents have been centered on developing new ER modulators and alternatives for the traditional natural and synthetic forms of MHT which carry the risk of invasive breast cancer and venous thromoboembolism. Phytoestrogens may have similar effects as traditional MHT and have not demonstrated harmful side effects. Specific estrogen receptor modulators (SERMs) such as raloxifene and tamoxifen have also been tested. ER agonists that selectively target ERalpha, ERbeta and perhaps GPR30 may modify specific vascular signaling pathways. Also, the dose, route of administration, and timing of MHT are integral to optimizing the beneficial effects and minimizing the side effects of MHT. Progesterone, testosterone and modulators of their specific receptors may also affect the overall vascular effects of MHT in estrogen-deficiency states associated with menopause.