title: Evaluation of Rho-kinase activity in mice brain using N-[11C]methyl-hydroxyfasudil with positron emission tomography.
abstract: OBJECTIVE
  Rho is a small molecular weight GTP-binding protein and works as a molecular shuttling switch between an active (GTP-bound) and inactive (GDP-bound) state. Rho is known to be involved in cell motility, cell adhesion, and cytokinesis through actin cytoskeleton reorganization. The GTP-bound form of Rho interacts with its specific downstream target, triggering intracellular signaling cascades. Rho effectors such as Rho-kinases have been isolated on the basis of their selective binding to the GTP-bound form of Rho. Rho-kinase is thought to have an important role in the pathogenesis of a variety of neurological diseases because activation of the Rho/Rho-kinase pathway has been observed in various central nervous system disorders. Previous histochemical studies have shown multiple molecular mechanisms for the regulation of Rho-kinase. Neuroimaging of Rho/Rho-kinase has rarely been studied because of a lack of appropriate radiotracers. Recently, N-[(11)C]methyl-hydroxyfasudil, a new radiotracer for positron emission tomography (PET), has been introduced to measure Rho-kinase activity. In this study, the regional distribution and kinetics of N-[(11)C]methyl-hydroxyfasudil were investigated in the brains of mice.
  
  
  METHODS
  A 90-min dynamic scan was performed following intravenous infusion of N-[(11)C]methyl-hydroxyfasudil.
  
  
  RESULTS
  The uptake of N-[(11)C]methyl-hydroxyfasudil reached a maximum within 5 min and gradually decreased in all organs. The standard uptake values (SUVs) in the brain, liver, and kidney on average between 30 to 60 min were 0.17 ± 0.03, 0.76 ± 0.18, and 0.62 ± 0.18 and from 60 to 90 min were 0.15 ± 0.01, 0.69 ± 0.33, and 0.64 ± 0.17, respectively. N-[(11)C]Methyl-hydroxyfasudil showed a widespread distribution throughout the brain, with low levels of radioactivity. Radioactivity concentration in plasma at 90 min after injection of N-[(11)C]methyl-hydroxyfasudil resulted in SUVs in the control and fasudil pretreatment of 0.0013 and 0.0023 ± 0.0008, respectively. Compared to normal control mice, about twofold higher radioactivity concentration was observed in fasudil-pretreated mice. In a cold brain injury mouse model, accumulation of N-[(11)C]methyl-hydroxyfasudil was slightly higher at the injury site than that at the control site, and the difference was statistically significant in the "24 h after injury" group (P < 0.05).
  
  
  CONCLUSIONS
  These results suggest that following brain injury, N-[(11)C]methyl-hydroxyfasudil binds to the active form of Rho-kinase. PET imaging using N-[(11)C]methyl-hydroxyfasudil could provide new insights into the pathophysiology of a variety of neurological disorders including stroke, inflammatory diseases, demyelinating diseases, Alzheimer's disease, and neuropathic pain.
authors.affiliation: Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Taniguchi
authors.forename: Chie
authors.initials: C
authors.lastname: Seki
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Takuwa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kawaguchi
authors.forename: Yoko
authors.initials: Y
authors.lastname: Ikoma
authors.forename: Masayuki
authors.initials: M
authors.lastname: Fujinaga
authors.forename: Iwao
authors.initials: I
authors.lastname: Kanno
authors.forename: Ming-Rong
authors.initials: MR
authors.lastname: Zhang
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kuwabara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ito
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging / Q000201:enzymology*; D002250:Carbon Radioisotopes / Q000493:pharmacokinetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D049268:Positron-Emission Tomography / Q000379:methods*; D054460:rho-Associated Kinases / Q000378:metabolism*
chemical_list: D002250:Carbon Radioisotopes; C547762:N-methyl-hydroxyfasudil; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D054460:rho-Associated Kinases