Estradiol protects against ethanol-induced bone loss by inhibiting up-regulation of receptor activator of nuclear factor-kB ligand in osteoblasts

Authors: CHEN, JIN-RAN - ACNC/UAMS; HALEY, RANI - ACNC; HIDESTRAND, MATS - ACNC/UAMS; SHANKAR, KARTIK - ACNC/UAMS; LIU, XIAOLI - ACNC/UAMS; LUMPLIN, CHARLES - ACH/UAMS; SIMPSON, PIPPA - ACH/UAMS; BADGER, THOMAS - ACNC/UAMS; RONIS, MARTIN - ACNC/UAMS

Submitted to: Journal of Pharmacology and Experimental Therapeutics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2006
Publication Date: 12/15/2006
Citation: Chen, J., Haley, R.L., Hidestrand, M., Shankar, K., Liu, X., Lumplin, C.K., Simpson, P.M., Badger, T.M., Ronis, M.J. 2006. Estradiol protects against ethanol-induced bone loss by inhibiting up-regulation of receptor activator of nuclear factor-kB ligand in osteoblasts. Journal of Pharmacology and Experimental Therapeutics. 319(3):1182-1190.

Interpretive Summary: Chronic alcohol intake is well known to cause harmful bone effect and increase fracture risk in men and women. The reason why alcohol consumption results in bone loss and an interaction between alcohol and female hormones are currently not well understood. To investigate the effects of female hormones such as estradiol and progesterone on alcohol-induced bone loss, we fed rats alcohol diets i.g. for 3 weeks. Using bone density measurement machine peripheral quantitative computerized tomography and gene detection technology, significant bone loss was observed. The bone loss that was caused by alcohol could be prevented by treatment with female hormone estradiol in those experimental rats. Addition of one of other birth control pill component progesterone did not enhance the beneficial effect of estradiol alone. The main reason for why alcohol and female hormone interacted on bone loss was also addressed. We found that alcohol digest enzyme Class I alcohol dehydrogenase was present in bone cells. By different regulation of alcohol dehydrogenase and other cellular enzyme call extracellular signal-regulated kinase by alcohol and estradiol, the genes esponsible for bone formation and bone resorbtion were changed in opposite directions. These observations suggest that female hormone estradiol prevents alcohol-induced bone loss by opposing the up-regulation of bone resorbtion genes, and thereby, provides a new strategy for treatment of alcohol-induced osteoporosis.

Technical Abstract: To investigate the effects of sex hormones on ethanol (EtOH)-induced bone loss, female Sprague-Dawley rats were fed control or EtOH-containing diets (12 g/kg/day) by intragastric infusion. After 3 weeks, rats receiving EtOH had significant decreases in tibial trabecular and total bone mineral density, induction of receptor activator of nuclear factor-B ligand (RANKL) mRNA expression, and enhanced bone resorption, all of which were prevented by treatment with 17-estradiol (E2). The addition of progesterone did not enhance the beneficial effect of E2 alone. Consistent with our in vivo findings, EtOH stimulated RANKL mRNA expression in cultured primary osteoblasts, and this expression was blocked by 4-methylpyrazole. Acetaldehyde also induced RANKL expression. Class 1 alcohol dehydrogenase was found to be expressed and EtOH-inducible in cultured osteoblasts, whereas CYP2E1 was undetectable. We found that EtOH induced phosphorylation of extracellular signal-regulated kinase (ERK) and signal transducers and activators of transcription 3 (STAT3). E2 and the mitogenactivated protein kinase kinase inhibitor 2'-amino-3'-methoxyflavone (PD98059) blocked ERK and STAT3 phosphorylation and blocked RANKL induction. Moreover, E2 completely blocked EtOH-induced osteoclastogenesis in a primary osteoblast and osteoclast precursor coculture system. The E2 effects were estrogen receptor-mediated. Therefore, E2 prevents EtOH-induced bone loss by opposing the induction of RANKL mRNA in osteoblasts and ethanol-induced osteoclastogenesis, through opposing effects on sustained ERK signaling.