title: A Novel Modality for Functional Imaging in Acute Intervertebral Disk Herniation via Tracking Leukocyte Infiltration.
abstract: OBJECTIVE
  Inflammation plays a key role in the progression of intervertebral disk (IVD) herniation and associated low back pain. However, real-time spatial diagnosis of inflammation associated with acute disk herniation has not been investigated. We sought to detect local neutrophil and macrophage infiltration near disk herniation via the formyl peptide receptor 1 (FPR1)-mediated molecular imaging in a disk puncture mouse model to elucidate pathophysiological process of disk herniation.
  
  
  METHODS
  Disk herniation was induced in mouse with an established needle puncture procedure. Degenerative change of disk and infiltration of neutrophils and macrophages were detected with Safranin-O, hematoxylin and eosin (H&E), and immunohistochemical staining after injury. FPR1-specific imaging probes cFLFLF-PEG-Cy7 and [99mTc]HYNIC-PEG-cFLFLF were administered systemically to sham and disk injury mice. Leukocyte infiltration was tracked by in vivo near-infrared fluorescence (NIRF) and single-photon emission tomography (SPECT) imaging. The peptide-receptor binding specificity was further investigated with FPR1-/-mice via ex vivo NIRF scan and in vitro binding assays.
  
  
  RESULTS
  Safranin-O staining exhibited disorganized disk structure and loss of proteoglycan after puncture. Massive inflammatory cells were observed in the anterior region of punctured annulus in the injury group. The majority of neutrophils were detected at 1 through 3 days, while infiltration of macrophages appeared the most at 7 days after injury. NIRF and SPECT images revealed preferential accumulation of cFLFLF probes in herniation site in wild-type mice but not in FPR1-/-mice. Binding of the cFLFLF peptide to FPR1 was also observed in RAW 267.4 cells and macrophages isolated from wild-type mice, whereas much less signal was observed in macrophages from FPR1-/-mice. The presence of macrophage infiltration was also detected in human-herniated disk samples by immunohistochemistry.
  
  
  CONCLUSIONS
  For the first time, leukocyte infiltration around acute disk herniation site was detected directly and non-invasively in a timely fashion using FPR1-targeted molecular imaging modalities. Such functional imaging of disk herniation via infiltrated leukocytes would advance the understanding of etiology and facilitate drug delivery and treatment monitoring of disk herniation.
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Rm B051, Cobb Hall, 135 Hospital Dr., Charlottesville, VA, 22908, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Xiao
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Rm B051, Cobb Hall, 135 Hospital Dr., Charlottesville, VA, 22908, USA.
authors.forename: Mengmeng
authors.initials: M
authors.lastname: Ding
authors.affiliation: Department of Radiology and Biomedical Imaging, University of Virginia, Charlottesville, VA, 22908, USA.|Biomedical Imaging Research Institute, Cedars-Sinai Medical Center, 8700 Beverly Blvd. Davis Building, Rm G140, Los Angeles, CA, 90048, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Radiology and Biomedical Imaging, University of Virginia, Charlottesville, VA, 22908, USA.
authors.forename: Mahendra
authors.initials: M
authors.lastname: Chordia
authors.affiliation: Department of Radiology and Biomedical Imaging, University of Virginia, Charlottesville, VA, 22908, USA.
authors.forename: Dongfeng
authors.initials: D
authors.lastname: Pan
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Rm B051, Cobb Hall, 135 Hospital Dr., Charlottesville, VA, 22908, USA.
authors.forename: Adam
authors.initials: A
authors.lastname: Shimer
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Rm B051, Cobb Hall, 135 Hospital Dr., Charlottesville, VA, 22908, USA.
authors.forename: Francis
authors.initials: F
authors.lastname: Shen
authors.affiliation: Department of Cardiovascular Medicine, University of Virginia, Charlottesville, 22908, USA.
authors.forename: David
authors.initials: D
authors.lastname: Glover
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Rm B051, Cobb Hall, 135 Hospital Dr., Charlottesville, VA, 22908, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Jin
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, Rm B051, Cobb Hall, 135 Hospital Dr., Charlottesville, VA, 22908, USA. lispine@icloud.com.
authors.forename: Xudong
authors.initials: X
authors.lastname: Li
mesh_terms: D000818:Animals; D005260:Female; D005453:Fluorescence; D007249:Inflammation / Q000473:pathology; D055959:Intervertebral Disc Degeneration / Q000473:pathology*; D007405:Intervertebral Disc Displacement / Q000473:pathology*; D007962:Leukocytes / Q000473:pathology*; D008159:Lumbar Vertebrae / Q000473:pathology; D008264:Macrophages / Q000378:metabolism / Q000473:pathology; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D015335:Molecular Probes / Q000737:chemistry; D020556:Neutrophil Infiltration; D009504:Neutrophils / Q000378:metabolism / Q000473:pathology; D009842:Oligopeptides / Q000737:chemistry; D011677:Punctures; D000067996:RAW 264.7 Cells; D044042:Receptors, Formyl Peptide / Q000378:metabolism; D019265:Spectroscopy, Near-Infrared; D013194:Staining and Labeling; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: C469988:Fpr1 protein, mouse; D015335:Molecular Probes; D009842:Oligopeptides; D044042:Receptors, Formyl Peptide; C000605614:cinnamoyl-phenylalanyl-leucyl-phenylalanyl-leucyl-phenylalanine
keywords: Acute disk herniation; Formyl peptide receptor (FPR) 1; Leukocyte infiltration; Low back pain; Macrophage; Near-infrared fluorescence imaging (NIRF); Neutrophil; Single-photon emission computed tomography (SPECT)