Location: Arkansas Children's Nutrition CenterTitle: NADPH oxidases are critical targets for prevention of ethanol-induced bone loss Author
Submitted to: Society of Toxicology
Publication Type: Abstract Only
Publication Acceptance Date: 12/9/2009
Publication Date: 3/1/2010
Citation: Chen, J., Lazarenko, O.P., Shankar, K., Blackburn, M.L., Badger, T.M., Ronis, M.J. 2010. NADPH oxidases are critical targets for prevention of ethanol-induced bone loss. The Toxicologist: 114(1):162. Abstract No. 762. Interpretive Summary:
Technical Abstract: The molecular mechanisms through which chronic alcohol consumption induce bone loss and osteoporosis are largely unknown. Ethanol increases expression and activates NADPH (nicotinamide adenine dinucleotide phosphate) oxidase enzymes (Nox) in osteoblasts leading to accumulation of reactive oxygen species. This might be the initiating step in inhibition of bone formation and stimulation of bone resorption. Using cycling female Sprague-Dawley rats treated with ethanol (12 g/kg/d) using total enteral nutrition, we found that EtOH treatment for 28 d reduced trabecular bone mineral density (BMD) (P<0.05). EtOH effects on BMD were blocked by exogenous 17-beta estradiol (25 "micro"g/kg/d, s.c.) (P<0.05). Moreover, co-administration of the antioxidant N-acetyl cysteine (NAC, 2 g/kg/d), or diphenylene iodonium (DPI, 1 mg/kg/d, s.c.) a pan-Nox inhibitor also abolished chronic EtOH-induced bone loss. EtOH treatment was associated with up-regulation of mRNA levels in bone of three Nox subtypes 1, 2, 4 and RANKL (receptor activator of NF-kB ligand), an essential factor for differentiation of bone marrow monocyte-macrophage lineage cells into osteoclasts (P<0.05). Protein expression of Nox 4, a constitutively active Nox isoform expressed in non-phagocytic cells, was also up-regulated by EtOH in bone (P<0.05). All three compounds, 17-beta estradiol, NAC and DPI were able to block EtOH-induced up-regulation of Nox and RANKL. In vitro studies using pre-osteoblastic ST2 stromal cells and osteoblastic UMR-106 cells demonstrated that 50 mM EtOH directly up-regulated Nox expression in osteoblasts (P<0.05). Furthermore, DPI dose-dependently blocked EtOH and hydrogen peroxide-induced RANKL gene expression and activated RANKL promoter activity in osteoblasts (P< 0.05). These data demonstrate a critical role for Nox in EtOH-induced osteoblast-dependent bone loss, and perhaps other oxidative stress associated processes mediating bone resorption.