title: Insulin is essential for in vitro chondrogenesis of mesenchymal progenitor cells and influences chondrogenesis in a dose-dependent manner.
abstract: OBJECTIVE
  Insulin is a commonly used additive in chondrogenic media for differentiating mesenchymal stem cells (MSCs). The indispensability of other bioactive factors like TGF-β or dexamethasone in these medium formulations has been shown, but the role of insulin is unclear. The purpose of this study was to investigate whether insulin is essential for MSC chondrogenesis and if there is a dose-dependent effect of insulin on MSC chondrogenesis.
  
  
  METHODS
  We cultivated human MSCs in pellet culture in serum-free chondrogenic medium with insulin concentrations between 0 and 50 μg/ml and assessed the grade of chondrogenic differentiation by histological evaluation and determination of glycosaminoglycan (GAG), total collagen and DNA content. We further tested whether insulin can be delivered in an amount sufficient for MSC chondrogenesis via a drug delivery system in insulin-free medium.
  
  
  RESULTS
  Chondrogenesis was not induced by standard chondrogenic medium without insulin and the expression of cartilage differentiation markers was dose-dependent at insulin concentrations between 0 and 10 μg/ml. An insulin concentration of 50 μg/ml had no additional effect compared with 10 μg/ml. Insulin was delivered by a release system into the cell culture under insulin-free conditions in an amount sufficient to induce chondrogenesis.
  
  
  CONCLUSIONS
  Insulin is essential for MSC chondrogenesis in this system and chondrogenic differentiation is influenced by insulin in a dose-dependent manner. Insulin can be provided in a sufficient amount by a drug delivery system. Therefore, insulin is a suitable and inexpensive indicator substance for testing drug release systems in vitro.
authors.affiliation: Department for Trauma Surgery, University of Regensburg Medical Center, Regensburg, Germany. michaelbmueller@web.de
authors.forename: Michael B
authors.initials: MB
authors.lastname: Mueller
authors.forename: Torsten
authors.initials: T
authors.lastname: Blunk
authors.forename: Bernhard
authors.initials: B
authors.lastname: Appel
authors.forename: Angelika
authors.initials: A
authors.lastname: Maschke
authors.forename: Achim
authors.initials: A
authors.lastname: Goepferich
authors.forename: Johannes
authors.initials: J
authors.lastname: Zellner
authors.forename: Carsten
authors.initials: C
authors.lastname: Englert
authors.forename: Lukas
authors.initials: L
authors.lastname: Prantl
authors.forename: Richard
authors.initials: R
authors.lastname: Kujat
authors.forename: Michael
authors.initials: M
authors.lastname: Nerlich
authors.forename: Peter
authors.initials: P
authors.lastname: Angele
mesh_terms: D000704:Analysis of Variance; D002454:Cell Differentiation; D002478:Cells, Cultured; D020219:Chondrogenesis / Q000187:drug effects*; D003094:Collagen / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D016503:Drug Delivery Systems; D004797:Enzyme-Linked Immunosorbent Assay; D006025:Glycosaminoglycans / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology*; D059630:Mesenchymal Stem Cells / Q000187:drug effects*; D013194:Staining and Labeling
chemical_list: D006025:Glycosaminoglycans; D007328:Insulin; D003094:Collagen; D004247:DNA