title: Targeted folate receptor β fluorescence imaging as a measure of inflammation to estimate vulnerability within human atherosclerotic carotid plaque.
abstract: The probability of atherosclerotic plaque rupture and its thrombotic sequelae are thought to be increased at sites of macrophage accumulation. Folate receptor β (FR-β) is present on activated macrophages but not on quiescent macrophages or other immune cells. By conjugating the ligand folate with a fluorescent contrast agent, fluorescein isothiocyanate (FITC), we aimed to explore the potential role of FR-β fluorescence imaging in the distinction of vulnerable sites from more stable regions.
  
  
  METHODS
  Carotid specimens were taken from 20 patients and incubated with folate-FITC for 30 min. Ex vivo fluorescence imaging was performed to determine the exact location of folate-FITC uptake. Sections displaying regions of high uptake (determined as hot spots) were compared with sections showing low uptake (cold spots) through immunohistochemistry and real-time quantitative reverse-transcription polymerase chain reaction for FR-β.
  
  
  RESULTS
  Hot spots showed significantly higher folate-FITC uptake than cold spots (P < 0.001). Hot spots tended to contain more macrophages and areas of hypoxia than cold spots. A positive correlation between messenger RNA levels of CD68 (marker for macrophages), FR-β (r = 0.53, P = 0.045), and hypoxia-inducible factor-1α expression (marker for intraplaque hypoxia; r = 0.55, P = 0.034) was found.
  
  
  CONCLUSIONS
  Compared with areas with low folate-FITC uptake, areas of high folate-FITC uptake within human atherosclerotic plaques had an increased number of activated macrophages and higher areas of hypoxia. These characteristics of vulnerability imply that molecular imaging of FR-β through folate conjugates might be a good indicator for plaque vulnerability in future noninvasive imaging studies.
authors.affiliation: Department of Surgery, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
authors.forename: Nynke A
authors.initials: NA
authors.lastname: Jager
authors.forename: Johanna
authors.initials: J
authors.lastname: Westra
authors.forename: Gooitzen M
authors.initials: GM
authors.lastname: van Dam
authors.forename: Nato
authors.initials: N
authors.lastname: Teteloshvili
authors.forename: René A
authors.initials: RA
authors.lastname: Tio
authors.forename: Jan-Cees
authors.initials: JC
authors.lastname: Breek
authors.forename: Riemer H J A
authors.initials: RH
authors.lastname: Slart
authors.forename: Hendrikus
authors.initials: H
authors.lastname: Boersma
authors.forename: Phillip S
authors.initials: PS
authors.lastname: Low
authors.forename: Marc
authors.initials: M
authors.lastname: Bijl
authors.forename: Clark J
authors.initials: CJ
authors.lastname: Zeebregts
mesh_terms: D000368:Aged; D001692:Biological Transport; D002340:Carotid Artery Diseases / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D015687:Cell Hypoxia; D005260:Female; D016650:Fluorescein-5-isothiocyanate / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D058976:Folate Receptor 2 / Q000235:genetics / Q000378:metabolism*; D005492:Folic Acid / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics; D007249:Inflammation / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008264:Macrophages / Q000378:metabolism / Q000473:pathology; D008297:Male; D057054:Molecular Imaging; D010865:Pilot Projects; D058226:Plaque, Atherosclerotic / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015203:Reproducibility of Results; D013050:Spectrometry, Fluorescence
chemical_list: D005456:Fluorescent Dyes; D058976:Folate Receptor 2; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger; D005492:Folic Acid; D016650:Fluorescein-5-isothiocyanate