title: In vivo retention and bioactivity of IL-1ra microspheres in the rat intervertebral disc: a preliminary investigation.
abstract: BACKGROUND
  Inflammatory cytokines such as interleukin-1 beta (IL-1β) contribute to the progression of intervertebral disc degeneration. Previously we demonstrated, in vitro, that by delivering interleukin-1 receptor antagonist (IL-1ra) from poly(lactic co-glycolic acid) (PLGA) microspheres, we could attenuate the degradative effects of IL-1β on the nucleus pulposus (NP) for up to 20 days. The objective of this study was to undertake a preliminary investigation into whether microspheres could be successfully delivered to and retained in the disc in vivo, and whether IL-1ra released from those microspheres remained biologically active. For retention studies, fluorescently-labeled microspheres were delivered to the NPs of rat caudal discs. Rats were sacrificed at time points up to 56 days, and microspheres were localized using fluorescent microscopy. To investigate whether IL-1ra microspheres could effectively inhibit the effects of IL-1β in vivo, four disc levels were allocated to the following treatment groups: intact; saline; IL-1β; or IL-1β + IL-1ra microspheres. Rats were sacrificed after seven days and NP glycosaminoglycan content was measured.
  
  
  RESULTS
  Microspheres were visible in the disc at all time points up to 28 days, and localized to the NP, the annulus fibrosus (AF), or both. Glycosaminoglycan content for discs injected with IL-1β alone was significantly lower than for intact controls. For discs injected with IL-1β along with IL-1ra microspheres, glycosaminoglycan content was not significantly different from intact controls.
  
  
  CONCLUSIONS
  Microspheres can successfully be delivered to the disc in vivo and retained for a clinically relevant time frame. IL-1ra released from microspheres can effectively prevent IL-1β-induced NP glycosaminoglycan loss in vivo.
authors.affiliation: Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, 424 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, 19104, PA, USA. dgorth@gmail.com.|Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, 424 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, 19104, PA, USA. dgorth@gmail.com.|Translational Musculoskeletal Research Center, Veterans Affairs Medical Center, 3900 Woodland Avenue, Philadelphia, 19104, PA, USA. dgorth@gmail.com.
authors.forename: Deborah J
authors.initials: DJ
authors.lastname: Gorth
authors.affiliation: Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, 424 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, 19104, PA, USA. johnma@mail.med.upenn.edu.|Translational Musculoskeletal Research Center, Veterans Affairs Medical Center, 3900 Woodland Avenue, Philadelphia, 19104, PA, USA. johnma@mail.med.upenn.edu.
authors.forename: John T
authors.initials: JT
authors.lastname: Martin
authors.affiliation: Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, 424 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, 19104, PA, USA. gdodge@mail.med.upenn.edu.|Translational Musculoskeletal Research Center, Veterans Affairs Medical Center, 3900 Woodland Avenue, Philadelphia, 19104, PA, USA. gdodge@mail.med.upenn.edu.
authors.forename: George R
authors.initials: GR
authors.lastname: Dodge
authors.affiliation: Department of Biomedical Engineering, College of Engineering, University of Delaware, 125 E. Delaware Ave, Newark, 19716, DE, USA. delliott@udel.edu.
authors.forename: Dawn M
authors.initials: DM
authors.lastname: Elliott
authors.affiliation: Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, 424 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, 19104, PA, USA. nrm@uphs.upenn.edu.|Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, 424 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, 19104, PA, USA. nrm@uphs.upenn.edu.
authors.forename: Neil R
authors.initials: NR
authors.lastname: Malhotra
authors.affiliation: Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, 424 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, 19104, PA, USA. lemauck@mail.med.upenn.edu.|Translational Musculoskeletal Research Center, Veterans Affairs Medical Center, 3900 Woodland Avenue, Philadelphia, 19104, PA, USA. lemauck@mail.med.upenn.edu.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Mauck
authors.affiliation: Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, 424 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, 19104, PA, USA. lachlans@mail.med.upenn.edu.|Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, 424 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, 19104, PA, USA. lachlans@mail.med.upenn.edu.|Translational Musculoskeletal Research Center, Veterans Affairs Medical Center, 3900 Woodland Avenue, Philadelphia, 19104, PA, USA. lachlans@mail.med.upenn.edu.
authors.forename: Lachlan J
authors.initials: LJ
authors.lastname: Smith
keywords: In vivo; Inflammation; Interleukin-1 receptor antagonist; Intervertebral disc degeneration; PLGA microspheres; Rat