Quantitative analyses of [¹¹C]Ro15-4513 binding to subunits of GABAA/benzodiazepine receptor in the living human brain.

Yoshiyuki Asai, Yoko Ikoma, Akihiro Takano, Jun Maeda, Hinako Toyama, Fumihiko Yasuno, Tetsuya Ichimiya, Hiroshi Ito, Tetsuya Suhara

Index: Nucl. Med. Commun. 30(11) , 872-80, (2009)

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Abstract

Gamma-aminobutyric acid (GABA)A/benzodiazepine (BZ) receptor chloride channel consists of several subunits. The diversity of the α subunits results in the various ligand selectivity and functionally different properties of the GABAA/BZ receptor. Although [¹¹C] Ro15-4513 is reported to be a radioligand that has relatively high affinity for α5 subunit-containing GABAA/BZ receptor, it remained to be evaluated fully.The aim of this study was to evaluate the quantitative analyses of [¹¹C]Ro15-4513 in the living human brain.Positron emission tomography examinations were performed in eight healthy male volunteers after intravenous injection of [¹¹C]Ro15-4513. Kinetic analysis of data was performed with the two-compartment and three-compartment models using arterial input function. Linear graphical analysis and the simplified reference tissue model analysis (SRTM) were also performed using pons as a reference region. In a simulation study, the effects of noise to the estimation of binding potentials were evaluated.The accumulation of [¹¹C]Ro15-4513 in the limbic system was relatively higher than in other cortex. The bindings were well described by the three-compartment model in the regions with specific binding. Binding potentials obtained from the graphical method and SRTM correlated well with those obtained from the three-compartment model. In the simulation study, estimated parameters from SRTM were less affected by noise compared with those from the graphical method.The reference tissue methods using pons as a reference region can be used for quantitative analysis of [¹¹C]Ro15-4513 binding. SRTM seemed less susceptible to noise than does graphical analysis.