title: Suppressive effects of irbesartan on inflammation and apoptosis in atherosclerotic plaques of apoE-/- mice: molecular imaging with 14C-FDG and 99mTc-annexin A5.
abstract: OBJECTIVE
  To investigate the effects of irbesartan on inflammation and apoptosis in atherosclerotic plaques by histochemical examination and molecular imaging using (14)C-FDG and (99m)Tc-annexin A5.
  
  
  BACKGROUND
  Irbesartan has a peroxisome proliferator-activated receptor gamma (PPARγ) activation property in addition to its ability to block the AT1 receptor. Accordingly, irbesartan may exert further anti-inflammatory and anti-apoptotic effects in atherosclerotic plaques. However, such effects of irbesartan have not been fully investigated. Molecular imaging using (18)F-FDG and (99m)Tc-annexin A5 is useful for evaluating inflammation and apoptosis in atherosclerotic plaques.
  
  
  METHODS
  Female apoE(-/-) mice were treated with irbesartan-mixed (50 mg/kg/day) or irbesartan-free (control) diet for 12 weeks (n = 11/group). One week after the treatment, the mice were co-injected with (14)C-FDG and (99m)Tc-annexin A5, and cryostat sections of the aortic root were prepared. Histochemical examination with Movat's pentachrome (plaque size), Oil Red O (lipid deposition), Mac-2 (macrophage infiltration), and TUNEL (apoptosis) stainings were performed. Dual-tracer autoradiography was carried out to evaluate the levels of (14)C-FDG and (99m)Tc-annexin A5 in plaques (%ID×kg). In vitro experiments were performed to investigate the mechanism underlying the effects.
  
  
  RESULTS
  Histological examination indicated that irbesartan treatment significantly reduced plaque size (to 56.4%±11.1% of control), intra-plaque lipid deposition (53.6%±20.2%) and macrophage infiltration (61.9%±20.8%) levels, and the number of apoptotic cells (14.5%±16.6%). (14)C-FDG (43.0%±18.6%) and (99m)Tc-annexin A5 levels (45.9%±16.8%) were also significantly reduced by irbesartan treatment. Irbesartan significantly suppressed MCP-1 mRNA expression in TNF-α stimulated THP-1 monocytes (64.8%±8.4% of un-treated cells). PPARγ activation was observed in cells treated with irbesartan (134%±36% at 3 µM to 3329%±218% at 81 µM) by a PPARγ reporter assay system.
  
  
  CONCLUSIONS
  Remissions of inflammation and apoptosis as potential therapeutic effects of irbesartan on atherosclerosis were observed. The usefulness of molecular imaging using (18)F-FDG and (99m)Tc-annexin A5 for evaluating the therapeutic effects of irbesartan on atherosclerosis was also suggested.
authors.affiliation: Department of Nuclear Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Integrated Molecular Imaging, Graduate School of Medicine, Hokkaido University, Sapporo, Japan ; Shionogi Innovation Center for Drug Discovery, Shionogi & Co., Ltd., Sapporo, Japan.
authors.forename: Ayahisa
authors.initials: A
authors.lastname: Watanabe
authors.affiliation: Department of Tracer Kinetics & Bioanalysis, Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
authors.forename: Songji
authors.initials: S
authors.lastname: Zhao
authors.affiliation: Shionogi Innovation Center for Drug Discovery, Shionogi & Co., Ltd., Sapporo, Japan.
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: Shionogi Innovation Center for Drug Discovery, Shionogi & Co., Ltd., Sapporo, Japan.
authors.forename: Keita
authors.initials: K
authors.lastname: Fukao
authors.affiliation: Shionogi Innovation Center for Drug Discovery, Shionogi & Co., Ltd., Sapporo, Japan.
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Tanaka
authors.affiliation: Shionogi Innovation Center for Drug Discovery, Shionogi & Co., Ltd., Sapporo, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Nakano
authors.affiliation: Shionogi Innovation Center for Drug Discovery, Shionogi & Co., Ltd., Sapporo, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yoshida
authors.affiliation: Shionogi Innovation Center for Drug Discovery, Shionogi & Co., Ltd., Sapporo, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takemoto
authors.affiliation: Department of Nuclear Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
authors.forename: Nagara
authors.initials: N
authors.lastname: Tamaki
authors.affiliation: Department of Tracer Kinetics & Bioanalysis, Graduate School of Medicine, Hokkaido University, Sapporo, Japan ; Central Institute of Isotope Science, Hokkaido University, Sapporo, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kuge
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D017304:Annexin A5; D001057:Apolipoproteins E / Q000235:genetics; D017209:Apoptosis / Q000187:drug effects*; D001345:Autoradiography; D001391:Azo Compounds; D001713:Biphenyl Compounds / Q000494:pharmacology*; D005260:Female; D006651:Histocytochemistry / Q000379:methods; D007091:Image Processing, Computer-Assisted; D020287:In Situ Nick-End Labeling; D007249:Inflammation / Q000188:drug therapy*; D000077405:Irbesartan; D051379:Mice; D018345:Mice, Knockout; D057054:Molecular Imaging / Q000379:methods*; D058226:Plaque, Atherosclerotic / Q000188:drug therapy*; D013667:Technetium; D013777:Tetrazoles / Q000494:pharmacology*
chemical_list: D017304:Annexin A5; D001057:Apolipoproteins E; D001391:Azo Compounds; D001713:Biphenyl Compounds; D013777:Tetrazoles; D013667:Technetium; C011049:oil red O; D000077405:Irbesartan