title: Synthesis of insulin-like growth factor binding protein 3 in vitro in human articular cartilage cultures.
abstract: OBJECTIVE
  To quantify the rate of synthesis of insulin-like growth factor binding protein 3 (IGFBP-3) and insulin-like growth factor 1 (IGF-1) by in vitro cultures of normal and osteoarthritic (OA) human articular cartilage.
  
  
  METHODS
  Levels of IGF-1 and IGFBP-3 in media from in vitro cultures of human cartilage were determined by radioimmunoassay (RIA). IGFBPs were characterized by immunoblots and ligand blots. Ultrafiltration and RIA analysis of synovial fluid (SF) samples and washings of cartilage samples ex vivo were used to calculate partition coefficients and to estimate the amount of IGF-1 and IGFBP-3 in cartilage in vivo.
  
  
  RESULTS
  OA cartilage synthesized 150 ng of IGFBP-3 per gm of cartilage per day, compared with 50 ng synthesized by normal cartilage. The surface zone of normal cartilage produced more IGFBP-3 than did the deep zone. Immunoblots and ligand blots confirmed the presence of IGFBP-3. IGFBP-3 synthesis was stimulated by exogenous IGF-1. No freshly synthesized IGF-1 was detected. The quantities of IGF-1 and IGFBP-3 present ex vivo were 11.3 and 78.7 ng/gm of cartilage in normal cartilage and 21.6 and 225.4 ng/gm in OA cartilage.
  
  
  CONCLUSIONS
  The results show that while IGFBP-3 is synthesized in explant cultures, IGF-1 is not. The rate of IGFBP-3 synthesis is 3 times higher in OA than in normal cartilage. Both IGFBP-3 and IGF-1 penetrate into cartilage from SF in vivo. We estimate that the quantities of IGFBP-3 produced in culture by human cartilage are small compared with the amount supplied in the form of "small complexes" from the circulation. The high value of the partition coefficient of IGFBP-3 implies binding to the matrix.
authors.affiliation: Technion-Israel Institute of Technology, Haifa, Israel.
authors.forename: Tamar
authors.initials: T
authors.lastname: Eviatar
authors.forename: Hannah
authors.initials: H
authors.lastname: Kauffman
authors.forename: Alice
authors.initials: A
authors.lastname: Maroudas
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002358:Cartilage, Articular / Q000166:cytology* / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D066298:In Vitro Techniques; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000096:biosynthesis* / Q000737:chemistry; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis / Q000494:pharmacology; D008875:Middle Aged; D008970:Molecular Weight; D010003:Osteoarthritis / Q000378:metabolism / Q000473:pathology
chemical_list: D018972:Insulin-Like Growth Factor Binding Protein 3; D007334:Insulin-Like Growth Factor I