title: A novel method to detect articular chondrocyte death during early stages of osteoarthritis using a non-invasive ApoPep-1 probe.
abstract: BACKGROUND
  Current methods for early diagnosis of osteoarthritis (OA) are limited. We assessed whether in vivo detection of chondrocyte death by ApoPep-1 (CQRPPR), a peptide that binds to histone H1 of apoptotic and necrotic cells, could be used to detect the initiation of OA.
  
  
  METHODS
  Apoptosis-induced ATDC5 cells were labeled with Annexin V and ApoPep-1. Surgical destabilization of the medial meniscus (DMM) was performed on both knees of 12-week-old male mice and severity of OA was determined by histological analysis according to the Osteoarthritis Research Society International (OARSI) guidelines. At 1, 2, 4, and 8 weeks post-surgery, mice were intravenously injected with fluorescence-labeled ApoPep-1 or control peptide and in vivo imaging was performed within 30 minutes of injection by near-infrared fluorescence (NIRF). Binding of ApoPep-1 to OA joints was demonstrated by ex vivo imaging and immunofluorescent staining using TUNEL and histone H1 and type II collagen antibodies.
  
  
  RESULTS
  Strong signals of ApoPep-1 were observed on the apoptotic ATDC5 cells. Knees corresponded to grade II, III, and V OA at 2, 4, and 8 weeks after DMM, respectively. Between 2 and 8 weeks after surgery, the in vivo NIRF signal at OA-ApoPep1-injected joints was consistently stronger than sham-operated or OA-control peptide-injected joints. ApoPep-1, TUNEL, and histone H1 signals were stronger in grade II OA cartilage than sham-operated cartilage when detected by immunofluorescent staining. Type II collagen expression was similar between grade II OA and sham group.
  
  
  CONCLUSIONS
  ApoPep-1 can be used to detect OA in vivo by binding to apoptotic chondrocytes. This is a novel, sensitive, and rapid method which can detect apoptotic cells in OA rodent models soon after its onset.
authors.affiliation: Department of Biochemistry and Cell Biology, Kyungpook National University School of Medicine, Daegu, 700-422, Republic of Korea. xiangguo0622@gmail.com.
authors.forename: Xiangguo
authors.initials: X
authors.lastname: Che
authors.affiliation: Department of Biochemistry and Cell Biology, Kyungpook National University School of Medicine, Daegu, 700-422, Republic of Korea. lianhua621@hanmail.net.
authors.forename: Lianhua
authors.initials: L
authors.lastname: Chi
authors.affiliation: Department of Biochemistry and Cell Biology, Kyungpook National University School of Medicine, Daegu, 700-422, Republic of Korea. claraypark@gmail.com.
authors.forename: Clara Yongjoo
authors.initials: CY
authors.lastname: Park
authors.affiliation: Department of Biochemistry and Cell Biology, Kyungpook National University School of Medicine, Daegu, 700-422, Republic of Korea. wabjo@naver.com.
authors.forename: Gyoung-Ho
authors.initials: GH
authors.lastname: Cho
authors.affiliation: Department of Biochemistry and Cell Biology, Kyungpook National University School of Medicine, Daegu, 700-422, Republic of Korea. nrpark85@naver.com.
authors.forename: Narae
authors.initials: N
authors.lastname: Park
authors.affiliation: Department of Oral and Maxillofacial Surgery, College of Dentistry, Gangneung-Wonju National University, Gangneung, 210-702, Republic of Korea. kimsg@gwnu.ac.kr.
authors.forename: Seong-Gon
authors.initials: SG
authors.lastname: Kim
authors.affiliation: Department of Biochemistry and Cell Biology, Kyungpook National University School of Medicine, Daegu, 700-422, Republic of Korea. leebh823@gmail.com.
authors.forename: Byung-Heon
authors.initials: BH
authors.lastname: Lee
authors.affiliation: Department of Biochemistry and Cell Biology, Kyungpook National University School of Medicine, Daegu, 700-422, Republic of Korea. jechoi@knu.ac.kr.
authors.forename: Je-Yong
authors.initials: JY
authors.lastname: Choi
mesh_terms: D000818:Animals; D017209:Apoptosis; D019902:Chondrocytes / Q000473:pathology*; D003952:Diagnostic Imaging / Q000379:methods*; D004195:Disease Models, Animal; D042241:Early Diagnosis; D005455:Fluorescent Antibody Technique; D020287:In Situ Nick-End Labeling; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009842:Oligopeptides / Q000378:metabolism*; D010003:Osteoarthritis / Q000175:diagnosis*
chemical_list: D009842:Oligopeptides; C578342:cysteinyl-glutaminyl-arginyl-prolyl-prolyl-arginine