Original Full Length Article Preoperative irradiation for the prevention of heterotopic ossification induces local inflammation in humans Paula Hoff a, b, ⁎, Anastasia Rakow d , Timo Gaber a, b, c , Martin Hahne a, b, e , Ufuk Sentürk d , Cindy Strehl a, b , Monique Fangradt a, b , Katharina Schmidt-Bleek f , Dörte Huscher a, b , Tobias Winkler d , Dörte Matziolis d , Georg Matziolis c, d , Harun Badakhshi g , Gerd-Rüdiger Burmester a , Georg N. Duda d, f , Carsten Perka c, d , Frank Buttgereit a, b, c a Department of Rheumatology and Clinical Immunology, Charité University Hospital, Berlin, Germany b German Rheumatism Research Center (DRFZ), Berlin, Germany c Berlin-Brandenburg Center for Regenerative Therapies, Berlin, Germany d Center for Musculoskeletal Surgery, Charité University Hospital, Berlin, Germany e Berlin-Brandenburg School for Regenerative Therapies, Berlin, Germany f Julius Wolff Institut, Berlin, Germany g Department of Radiotherapy, Charité University Hospital, Berlin, Germany abstract article info Article history: Received 9 January 2013 Revised 28 March 2013 Accepted 29 March 2013 Available online 6 April 2013 Edited by: Rene Rizzoli Keywords: Heterotopic ossification Immune cells Cytokines Total hip arthroplasty Inflammation Radiation of the hip is an established method to prevent heterotopic ossification (HO) following total hip arthroplasty (THA) but the precise mechanism is unclear. As inflammatory processes are suggested to be in- volved in the pathogenesis of HO, we hypothesized that the preoperative irradiation impacts local immune components. Therefore, we quantified immune cell populations and cytokines in hematomas resulting from the transection of the femur in two groups of patients receiving THA: patients irradiated preoperatively (THA-X-hematoma: THA-X-H group) in the hip region (7 Gy) in order to prevent HO and patients who were not irradiated (THA-H group) but were postoperatively treated with non-steroidal anti-inflammatory drugs (NSAIDs). Radiation resulted in significantly increased frequencies of T cells, cytotoxic T cells, NKT cells and CD25 + CD127 - T reg cells, whereas the number of naive CD45RA-expressing cytotoxic T cells was reduced. These results indicate differential immune cell activation, corroborated by our findings of significantly higher concentrations of pro-inflammatory cytokines (e.g. IL-6, IFNγ) and chemokines (e.g. MCP-1, RANTES) in the THA-X-H group as compared to THA-H group. In contrast, the concentration of the angiogenic VEGF was sig- nificantly suppressed in the THA-X-H group. We conclude that preoperative irradiation results in significant changes in immune cell composition and cytokine secretion in THA-hematomas, establishing a specific – rather proinflammatory – milieu. This increase of inflammatory activity together with the observed suppres- sion in VEGF secretion may contribute to the prevention of HO. © 2013 Elsevier Inc. All rights reserved. Introduction Total hip arthroplasty (THA) can lead to the development of het- erotopic ossification (HO), which is characterized by endochondral bone formation in soft-tissues [1]. However, the underlying mecha- nisms of action are unknown. Different factors such as prostaglandin E2, hypercalcemia, hypoxia, abnormal nerve activities, mast cell acti- vation or immobilization have been suggested to play a role in the de- velopment of HO [1–4]. Fibrodysplasia ossificans progressiva, a hereditary form of HO, is associated with a mutation in the BMP type I receptor ACVR1 [5,6]. Thus, disturbance of the normal homeo- stasis of BMP signaling has also been suggested to play a role in non-hereditary forms of HO [7,8]. Moreover, involvement of the immune system is implicated by the clinical observation that inflam- matory events are able to trigger HO progress [7,9]. Macrophage re- sponse to tissue injury was found to stimulate progenitor cells to bony differentiation [7]. Thus, inflammatory processes may play a role in the pathogenesis of HO. HO is not a trivial side effect of THA as it can lead to limitations in the range of motion [1]. Preoperative radiation of the hip region and postoperative treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) are established methods to prevent heterotopic ossification [10]. The mode of action of NSAIDs is based on cyclooxygenase (COX) inhibition [11,12], but direct effects on osteoblasts have also been reported [13,14]. COX-1 is expressed in healthy bone and during Bone 55 (2013) 93–101 ⁎ Corresponding author at: Department of Rheumatology and Clinical Immunology, Charité University Hospital, Charitéplatz 1, 10117 Berlin, Germany. Fax: +49 30 450 513917. E-mail address: paula.hoff@charite.de (P. Hoff). 8756-3282/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.bone.2013.03.020 Contents lists available at SciVerse ScienceDirect Bone journal homepage: www.elsevier.com/locate/bone