title: Increased osteoclast activity in the presence of increased homocysteine concentrations.
abstract: BACKGROUND
  Increased plasma homocysteine (HCY) may be an independent risk factor for osteoporotic fractures and therefore may also adversely affect bone metabolism. We analyzed the effect of HCY on human osteoclast (OC) activity.
  
  
  METHODS
  We cultured peripheral blood mononuclear cells from 17 healthy male donors [median (SD) age, 30 (5) years] for 20 days with 25 microg/L macrophage-colony-stimulating factor (days 0-11), 20 microg/L receptor-activator of nuclear factor-kappaB ligand (days 6-20), and 4 different concentrations of HCY (0, 10, 50, and 100 micromol/L; days 0-20). For control purposes, cysteine and glutathione were tested in equimolar concentrations. OCs were identified as large, multinucleated cells with tartrate-resistant acid phosphatase (TRAP) activity and surface vitronectin receptors. We quantified OC activity by measuring TRAP activity. We analyzed cathepsin K (CP-K) activity in 9 donor samples and estimated the dentine-resorbing activity on standard dentine slices in 3 samples.
  
  
  RESULTS
  After 20 days of culture, most cells were fully differentiated OCs. TRAP activity increased with increasing HCY concentrations (P < 0.001). HCY concentrations of 10, 50, and 100 micromol/L stimulated TRAP activity by 20%, 15%, and 42%. Additionally, HCY stimulated CP-K activity (P = 0.005): in the presence of 100 micromol/L HCY, CP-K activity was approximately 38% higher than in controls (P = 0.002). Bone-resorbing activity was significantly increased in cultures with 50 and 100 micromol/L HCY. Cysteine and glutathione significantly decreased TRAP and CP-K activity.
  
  
  CONCLUSIONS
  Increased HCY concentrations specifically stimulate OC activity in vitro, suggesting a mechanistic role of HCY for bone resorption. Future studies clarifying the mechanistic role of increased HCY concentrations in osteoporosis could have interesting therapeutic implications.
authors.affiliation: Abteilung für Klinische Chemie und Laboratoriumsmedizin/Zentrallabor and Klinik für Innere Medizin I, Universitätsklinikum des Saarlandes, Homburg/Saar, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Herrmann
authors.forename: Thomas
authors.initials: T
authors.lastname: Widmann
authors.forename: Graziana
authors.initials: G
authors.lastname: Colaianni
authors.forename: Silvia
authors.initials: S
authors.lastname: Colucci
authors.forename: Alberta
authors.initials: A
authors.lastname: Zallone
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Herrmann
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D000328:Adult; D056657:Cathepsin K; D002403:Cathepsins / Q000378:metabolism; D002478:Cells, Cultured; D003804:Dentin / Q000378:metabolism; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D010010:Osteoclasts / Q000166:cytology / Q000502:physiology*; D000071681:Tartrate-Resistant Acid Phosphatase
chemical_list: D007527:Isoenzymes; D006710:Homocysteine; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase; D002403:Cathepsins; C534130:CTSK protein, human; D056657:Cathepsin K