Estrogen receptor alpha, but not beta, plays a major role in 17beta-estradiol-induced murine cholesterol gallstones.
OBJECTIVE
Cholesterol gallstones are more common in women than men, and exposure to oral contraceptive steroids and conjugated estrogens increases the risk for gallstones. It is hypothesized that estrogen enhances cholesterol cholelithogenesis by augmenting functions of hepatic estrogen receptors (ERs).


METHODS
To investigate molecular mechanisms of how estrogen influences cholesterol gallstones, we studied gonadectomized AKR/J mice of both genders that were implanted subcutaneously with pellets releasing 17beta-estradiol at 0, 3, or 6 microg/day and that were fed a lithogenic diet for 12 weeks. To test the hypothesis that ERs play a pivotal role in mediating lithogenic actions of estrogen and to dissect the potential pathophysiologic roles of each receptor subtype, ERalpha and ERbeta, in the formation of gallstones, we investigated gonadectomized mice treated with synthetic ER subtype-selective agonists or antagonists.


RESULTS
17beta-estradiol promoted gallstone formation by up-regulating hepatic expression of ERalpha but not ERbeta, and the lithogenic actions of estrogen can be blocked completely by the antiestrogenic ICI 182,780. The ERalpha-selective agonist propylpyrazole, but not the ERbeta-selective agonist diarylpropionitrile, augmented hepatic cholesterol output that resulted in cholesterol supersaturated bile and gallstones. Similar to the 17beta-estradiol treatment, tamoxifen significantly increased biliary cholesterol secretion and gallstone prevalence in both gonadectomized females and males.


CONCLUSIONS
The hepatic ERalpha, but not ERbeta, plays a critical role in 17beta-estradiol-induced cholesterol gallstones. Our findings may offer a new approach to treat gallstones by inhibiting hepatic ER activity with a liver-specific, ERalpha-selective antagonist.
Wang
Helen H
HH
Department of Medicine, Liver Center and Gastroenterology Division, Beth Israel Deaconess Medical Center, Harvard Medical School and Harvard Digestive Diseases Center, Boston, Massachusetts 02215, USA.
Afdhal
Nezam H
NH
Wang
David Q-H
DQ
D000818:Animals; D001646:Bile / Q000502:physiology; D002369:Castration; D002784:Cholesterol; D004343:Drug Implants / Q000008:administration & dosage / Q000009:adverse effects*; D004958:Estradiol / Q000008:administration & dosage / Q000009:adverse effects* / Q000819:agonists; D004965:Estrogen Antagonists / Q000494:pharmacology; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D005260:Female; D042882:Gallstones / Q000139:chemically induced / Q000737:chemistry / Q000209:etiology*; D015870:Gene Expression / Q000502:physiology; D050356:Lipid Metabolism; D008099:Liver / Q000502:physiology; D008297:Male; D051379:Mice; D023421:Models, Animal; D011960:Receptors, Estrogen / Q000235:genetics / Q000502:physiology*
D004343:Drug Implants; D004965:Estrogen Antagonists; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D011960:Receptors, Estrogen; D004958:Estradiol; D002784:Cholesterol