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Molecular characterization of a B-ring unsaturated estrogen: implications for conjugated equine estrogen components of premarin.

ABSTRACT: Conjugated equine estrogens (CEEs) are routinely used for hormone replacement therapy (HRT), making it important to understand the activities of individual estrogenic components. Although 17beta-estradiol (17beta-E2), the most potent estrogen in CEE, has been extensively characterized, the actions of nine additional less potent estrogens are not well understood. Structural differences between CEEs and 17beta-E2 result in altered interactions with the two estrogen receptors (ERalpha and ERbeta) and different biological activities. To better understand these interactions, we have determined the crystal structure of the CEE analog, 17beta-methyl-17alpha-dihydroequilenin (NCI 122), in complex with the ERalpha ligand-binding domain and a peptide from the glucocorticoid receptor-interacting protein 1 (GRIP1) coactivator. NCI 122 has chemical properties, including an unsaturated B-ring and 17alpha-hydroxyl group, which are shared with some of the estrogens found in CEEs. Structural analysis of the NCI 122-ERalpha LBD-GRIP1 complex, combined with biochemical and cell-based comparisons of CEE components, suggests that factors such as decreased ligand flexibility, decreased ligand hydrophobicity and loss of a hydrogen bond between the 17-hydroxyl group and His524, contribute significantly to the reduced potency of CEEs on ERalpha.

SUBMITTER: Hsieh RW

PROVIDER: S-EPMC2225582 | biostudies-literature | 2008 Jan

REPOSITORIES: biostudies-literature

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Molecular characterization of a B-ring unsaturated estrogen: implications for conjugated equine estrogen components of premarin.

Hsieh Robert W RW Rajan Shyamala S SS Sharma Sanjay K SK Sharma Sanjay K SK Greene Geoffrey L GL

Steroids 20070911 1

Conjugated equine estrogens (CEEs) are routinely used for hormone replacement therapy (HRT), making it important to understand the activities of individual estrogenic components. Although 17beta-estradiol (17beta-E2), the most potent estrogen in CEE, has been extensively characterized, the actions of nine additional less potent estrogens are not well understood. Structural differences between CEEs and 17beta-E2 result in altered interactions with the two estrogen receptors (ERalpha and ERbeta) a ...[more]

PMID: 17949766

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Project description:BackgroundResults of the Women's Health Initiative Memory Study (WHIMS) raised concerns regarding the timing and formulation of hormone interventions. Conjugated equine estrogens (CEE), used as the estrogen therapy in the WHIMS trial, is a complex formulation containing multiple estrogens, including several not secreted by human ovaries, as well as other biologically active steroids. Although the full spectrum of estrogenic components present in CEE has not yet been resolved, 10 estrogens have been identified. In the present study, we sought to determine which estrogenic components, at concentrations commensurate with their plasma levels achieved following a single oral dose of 0.625 mg CEE (the dose used in the WHIMS trial) in women, are neuroprotective and whether combinations of those neuroprotective estrogens provide added benefit. Further, we sought, through computer-aided modeling analyses, to investigate the potential correlation of the molecular mechanisms that conferred estrogen neuroprotection with estrogen interactions with the estrogen receptor (ER).ResultsCultured basal forebrain neurons were exposed to either beta-amyloid(25-35) or excitotoxic glutamate with or without pretreatment with estrogens followed by neuroprotection analyses. Three indicators of neuroprotection that rely on different aspects of neuronal damage and viability, LDH release, intracellular ATP level and MTT formazan formation, were used to assess neuroprotective efficacy. Results of these analyses indicate that the estrogens, 17alpha-estradiol, 17beta-estradiol, equilin, 17alpha-dihydroequilin, equilinen, 17alpha-dihydroequilenin, 17beta-dihydroequilenin, and Delta8,9-dehydroestrone were each significantly neuroprotective in reducing neuronal plasma membrane damage induced by glutamate excitotoxicity. Of these estrogens, 17beta-estradiol and Delta8,9-dehydroestrone were effective in protecting neurons against beta-amyloid25-35-induced intracellular ATP decline. Coadministration of two out of three neuroprotective estrogens, 17beta-estradiol, equilin and Delta8,9-dehydroestrone, exerted greater neuroprotective efficacy than individual estrogens. Computer-aided analyses to determine structure/function relationships between the estrogenic structures and their neuroprotective activity revealed that the predicted intermolecular interactions of estrogen analogues with ER correlate to their overall neuroprotective efficacy.ConclusionThe present study provides the first documentation of the neuroprotective profile of individual estrogens contained within the complex formulation of CEE at concentrations commensurate with their plasma levels achieved after an oral administration of 0.625 mg CEE in women. Our analyses demonstrate that select estrogens within the complex formulation of CEE contribute to its neuroprotective efficacy. Moreover, our data predict that the magnitude of neuroprotection induced by individual estrogens at relatively low concentrations may be clinically undetectable and ineffective, whereas, a combination of select neuroprotective estrogens could provide an increased and clinically meaningful efficacy. More importantly, these data suggest a strategy for determining neurological efficacy and rational design and development of a composition of estrogen therapy to alleviate climacteric symptoms, promote neurological health, and prevent age-related neurodegeneration, such as AD, in postmenopausal women.

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Molecular characterization of a B-ring unsaturated estrogen: implications for conjugated equine estrogen components of premarin.

Publications

Molecular characterization of a B-ring unsaturated estrogen: implications for conjugated equine estrogen components of premarin.

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