title: Homocysteine enhances bone resorption by stimulation of osteoclast formation and activity through increased intracellular ROS generation.
abstract: Hyperhomocystinemia is a modifiable risk factor for osteoporosis and fracture. Physiologic concentrations of Hcy directly activate osteoclast formation and activity through stimulation of p38 MAPK and integrin beta3. The effects of Hcy were mediated by generation of intracellular ROS.
  
  
  BACKGROUND
  Hyperhomocysteinemia is a modifiable risk factor for osteoporosis and its related bone fractures. It has been reported that bone resorption and turnover rate were increased in hyperhomocystinemia. Using mouse bone marrow cells, we examined the direct effects of homocysteine (Hcy) on osteoclast formation and activity.
  
  
  METHODS
  Osteoclast formation was determined by TRACP staining and TRACP activity. Intracellular reactive oxygen species (ROS) generation was measured using a fluorescent probe, dichlorodihydrofluorescein diacetate. Intracellular signaling cascades of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and NF-kappaB were measured by Western blotting. Integrin beta3 mRNA levels were measured by RT-PCR. Actin ring formation and bone resorption assays were also performed.
  
  
  RESULTS
  Physiologic concentrations of Hcy upregulated TRACP+ multinucleated cells and TRACP activity, stimulated actin ring formation, and increased the number of nuclei per cell and the level of expression of integrin beta3 mRNA. In addition, Hcy increased bone resorption and stimulated p38 MAPK activity and intracellular reactive oxygen species (ROS) generation. All of these Hcy-induced changes were blocked by pretreatment with the antioxidant, N-acetyl cysteine.
  
  
  CONCLUSIONS
  Hcy directly activates osteoclast formation and activity through increased generation of intracellular ROS. These findings suggest that, in individuals with mild to moderate hyperhomocystinemia, increased bone resorption by osteoclasts may contribute to osteoporosis and that an antioxidant may attenuate bone loss in these individuals.
authors.affiliation: Division of Endocrinology and Metabolism, Asan Medical Center, University of Ulsan College of Medicine, Songpa-Gu, Seoul, Korea.
authors.forename: Jung-Min
authors.initials: JM
authors.lastname: Koh
authors.forename: Young-Sun
authors.initials: YS
authors.lastname: Lee
authors.forename: Yang Soon
authors.initials: YS
authors.lastname: Kim
authors.forename: Duk Jae
authors.initials: DJ
authors.lastname: Kim
authors.forename: Hong-Hee
authors.initials: HH
authors.lastname: Kim
authors.forename: Joong-Yeol
authors.initials: JY
authors.lastname: Park
authors.forename: Ki-Up
authors.initials: KU
authors.lastname: Lee
authors.forename: Ghi Su
authors.initials: GS
authors.lastname: Kim
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D000818:Animals; D001854:Bone Marrow Cells / Q000378:metabolism*; D001862:Bone Resorption / Q000188:drug therapy*; D002454:Cell Differentiation / Q000187:drug effects*; D002478:Cells, Cultured; D050723:Fractures, Bone / Q000378:metabolism; D006710:Homocysteine / Q000378:metabolism / Q000494:pharmacology*; D020138:Hyperhomocysteinemia / Q000150:complications / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D008813:Mice, Inbred ICR; D010010:Osteoclasts / Q000378:metabolism*; D010024:Osteoporosis / Q000209:etiology / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012307:Risk Factors; D000071681:Tartrate-Resistant Acid Phosphatase
chemical_list: D007527:Isoenzymes; D017382:Reactive Oxygen Species; D006710:Homocysteine; D011494:Protein Kinases; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase