title: Triamcinolone acetonide activates an anti-inflammatory and folate receptor-positive macrophage that prevents osteophytosis in vivo.
abstract: BACKGROUND
  Triamcinolone acetonide (TA) is used for osteoarthritis management to reduce pain, and pre-clinical studies have shown that TA limits osteophyte formation. Osteophyte formation is known to be facilitated by synovial macrophage activation. TA injections might influence macrophage activation and subsequently reduce osteophytosis. Although widely applied in clinical care, the mechanism through which TA exerts this effect remains unknown. In this animal study, we investigated the in vivo effects of TA injections on macrophage activation, osteophyte development and joint degeneration. Furthermore, in vitro macrophage differentiation experiments were conducted to further explain working mechanisms of TA effects found in vivo.
  
  
  METHODS
  Osteoarthritis was induced in rat knees using papain injections and a running protocol. Untreated and TA-treated animals were longitudinally monitored for 12 weeks with in vivo micro-computed tomography (μCT) to measure subchondral bone changes. Synovial macrophage activation was measured in vivo using folate receptor β (FRβ)-targeted single-photon emission computed tomography/computed tomography. Articular cartilage was analyzed at 6 and 12 weeks with ex vivo contrast-enhanced μCT and histology. To further explain the outcomes of our in vivo study, TA on macrophages was also studied in vitro. These cultured macrophages were either M1- or M2-activated, and they were analyzed using fluorescence-activated cell sorting for CD163 and FRβ expression as well as for messenger RNA (mRNA) expression of interleukin (IL)-10.
  
  
  RESULTS
  Our in vivo study showed that intra-articular injections with TA strongly enhanced FRβ(+) macrophage activation. Despite stimulated macrophage activation, osteophyte formation was fully prevented. There was no beneficial effect of TA against cartilage degradation or subchondral bone sclerosis. In vitro macrophage cultures showed that TA strongly induced monocyte differentiation towards CD163(+) and FRβ(+) macrophages. Furthermore, TA-stimulated M2 macrophages showed enhanced IL-10 expression at the mRNA level.
  
  
  CONCLUSIONS
  TA injections potently induce a CD163(+)- and FRβ(+)-activated macrophage with anti-inflammatory characteristics such as reduced IL-10 production in vitro and lack of osteophytosis in vivo.
authors.affiliation: Department of Orthopaedics, Erasmus Medical Centre, P.O. Box 2040, 3000, CA, Rotterdam, The Netherlands. m.siebelt@erasmusmc.nl.|Department of Otorhinolaryngology, Erasmus Medical Centre, Rotterdam, The Netherlands. m.siebelt@erasmusmc.nl.
authors.forename: Michiel
authors.initials: M
authors.lastname: Siebelt
authors.affiliation: Department Orthopaedics, UMC Utrecht, Utrecht, The Netherlands. n.m.korthagen@uu.nl.|Department Rheumatology, UMC Utrecht, Utrecht, The Netherlands. n.m.korthagen@uu.nl.
authors.forename: Nicoline
authors.initials: N
authors.lastname: Korthagen
authors.affiliation: Department of Orthopaedics, Erasmus Medical Centre, P.O. Box 2040, 3000, CA, Rotterdam, The Netherlands. w.wei@erasmusmc.nl.
authors.forename: Wu
authors.initials: W
authors.lastname: Wei
authors.affiliation: Department of Nuclear Medicine, Erasmus Medical Centre, Rotterdam, The Netherlands. harald@groen.org.
authors.forename: Harald
authors.initials: H
authors.lastname: Groen
authors.affiliation: Department of Orthopaedics, Erasmus Medical Centre, P.O. Box 2040, 3000, CA, Rotterdam, The Netherlands. y.bastiaansen@erasmusmc.nl.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Bastiaansen-Jenniskens
authors.affiliation: Centre for Radiopharmaceutical Sciences, Swiss Federal Institute of Technology (ETH) Zurich, Paul Scherrer Institute, University Hospital Zurich, Villigen, Switzerland. cristina.mueller@psi.ch.
authors.forename: Christina
authors.initials: C
authors.lastname: Müller
authors.affiliation: Department of Orthopaedics, Erasmus Medical Centre, P.O. Box 2040, 3000, CA, Rotterdam, The Netherlands. e.waarsing@erasmusmc.nl.
authors.forename: Jan Hendrik
authors.initials: JH
authors.lastname: Waarsing
authors.affiliation: Department Rheumatology, UMC Utrecht, Utrecht, The Netherlands. m.hendriks-dejong@erasmusmc.nl.|Department of Radiology, Erasmus Medical Centre, Rotterdam, The Netherlands. m.hendriks-dejong@erasmusmc.nl.
authors.forename: Marion
authors.initials: M
authors.lastname: de Jong
authors.affiliation: Department Orthopaedics, UMC Utrecht, Utrecht, The Netherlands. h.h.weinans@umcutrecht.nl.|Department Rheumatology, UMC Utrecht, Utrecht, The Netherlands. h.h.weinans@umcutrecht.nl.|Department of Biomechanical Engineering, Delft University of Technology, Delft, The Netherlands. h.h.weinans@umcutrecht.nl.
authors.forename: Harrie
authors.initials: H
authors.lastname: Weinans
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D004195:Disease Models, Animal; D008262:Macrophage Activation / Q000187:drug effects* / Q000276:immunology; D008264:Macrophages / Q000187:drug effects / Q000276:immunology; D008297:Male; D010003:Osteoarthritis / Q000473:pathology*; D054850:Osteophyte / Q000473:pathology*; D051381:Rats; D017208:Rats, Wistar; D014222:Triamcinolone Acetonide / Q000494:pharmacology*
chemical_list: D000893:Anti-Inflammatory Agents; D014222:Triamcinolone Acetonide