title: The influence of calcitonin gene-related peptide on markers of bone metabolism in MG-63 osteoblast-like cells co-cultured with THP-1 macrophage-like cells under virtually osteolytic conditions.
abstract: BACKGROUND
  The neuropeptide calcitonin gene-related peptide (CGRP) has been described to have an inhibitory effect on endotoxin- and wear particle-induced inflammation in the early stages of periprosthetic osteolysis. In the present study, the crosstalk between immune cells and osteoblasts in osteolytic conditions treated with CGRP has been analyzed to evaluate whether the anti-inflammatory properties of the peptide also have a beneficial, i.e. an anti-resorptive and osteo-anabolic impact on bone metabolism.
  
  
  METHODS
  MG-63 osteoblast-like cells were co-cultured with THP-1 macrophage-like cells stimulated with either ultra-high molecular weight polyethylene (UHMWPE) particles or different concentrations of bacterial lipopolysaccharides (LPS) and simultaneously treated with CGRP. Inflammation was monitored in terms of measuring the levels of tumor necrosis factor (TNF)-α secretion. Furthermore, the production of the osteoblast markers osteoprotegerin (OPG), receptor activator of nuclear factor κB ligand (RANKL), alkaline phosphatase (ALP) and osteopontin (OPN) was quantified. Also, ALP enzymatic activity was measured.
  
  
  RESULTS
  Stimulation of co-cultured THP-1 macrophages with either high levels of LPS or UHMWPE induced the secretion of TNF-α which could be inhibited by CGRP to a great extent. However, no remarkable changes in the OPG/RANKL ratio or bone ALP activity were observed. Interestingly, OPN was exclusively produced by THP-1 cells, thus acting as a marker of inflammation. In addition, TNF-α production in THP-1 single cell cultures was found to be considerably higher than in co-cultured cells.
  
  
  CONCLUSIONS
  In the co-culture system used in the present study, no obvious relation between inflammation, its mitigation by CGRP, and the modulation of bone metabolism became evident. Nonetheless, the results suggest that during the onset of periprosthetic osteolysis the focus might lie on the modulation of inflammatory reactions. Possibly, implant-related inflammation might merely have an impact on osteoclast differentiation rather than on the regulation of osteoblast activity.
authors.affiliation: University Hospital Essen, Department of Orthopedic and Trauma Surgery, University of Duisburg-Essen, Hufelandstrasse 55, Essen, 45147, Germany. heidrun.jablonski@uk-essen.de.
authors.forename: Heidrun
authors.initials: H
authors.lastname: Jablonski
authors.affiliation: University Hospital Essen, Department of Orthopedic and Trauma Surgery, University of Duisburg-Essen, Hufelandstrasse 55, Essen, 45147, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Rekasi
authors.affiliation: University Hospital Essen, Department of Orthopedic and Trauma Surgery, University of Duisburg-Essen, Hufelandstrasse 55, Essen, 45147, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Jäger
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D015519:Bone Density / Q000187:drug effects / Q000502:physiology; D016723:Bone Remodeling / Q000187:drug effects / Q000502:physiology*; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D018920:Coculture Techniques; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D010014:Osteolysis / Q000378:metabolism*; D016211:Transforming Growth Factor alpha / Q000378:metabolism
chemical_list: D015415:Biomarkers; D018836:Inflammation Mediators; D016211:Transforming Growth Factor alpha; D015740:Calcitonin Gene-Related Peptide
keywords: Bone metabolism; CGRP; Co-culture; Inflammation; LPS; MG-63 osteoblasts; Osteolysis; Particles; THP-1 macrophages