PET measurement of the in vivo affinity of 11C-(R)-rolipram and the density of its target, phosphodiesterase-4, in the brains of conscious and anesthetized rats

Tetsuji Itoh, Koji Abe, Sami S. Zoghbi, Osamu Inoue, Jinsoo Hong, Masao Imaizumi, Victor W. Pike, Robert B. Innis, Masahiro Fujita

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

A variety of phosphodiesterases hydrolyze and terminate the effects of the intracellular second messenger 3′,5′-cyclic adenosine monophosphate (cAMP). Phosphodiesterase subtype 4 (PDE4) is particularly abundant in the brain and has been imaged with 11C-(R)-rolipram, a selective inhibitor of PDE4. We sought to measure in vivo both the binding site density (B max) and the radioligand affinity (1/KD) of 11C-(R)-rolipram in the rat brain. We also studied 2 critical factors in small-animal PET scans: the influence of anesthesia and the difference in binding under in vivo and in vitro conditions. Methods: In vivo, Bmax and KD were measured in PET saturation experiments by the administration of 11C-(R)-rolipram and various doses of carrier (R)-rolipram in conscious and isoflurane-anesthetized rats. The metabolite-corrected arterial input function was measured in each scan. To image conscious rats, the head of the rat was fixed in a holder and the animals were trained to comply with this apparatus. Bound and free (R)-rolipram levels were calculated under transient equilibrium conditions (i.e., at the time of peak specific binding). Results: The Bmax and KD of conscious rats were significantly greater than those of anesthetized rats, by 29% and 59%, respectively. In addition, the in vitro KD was 3-7 times greater than was the in vivo KD, although the Bmax was similar in both conditions. Conclusion: The in vivo Bmax and KD of (R)-rolipram were successfully measured in both conscious and anesthetized rats. KD was affected to a greater extent than was Bmax by the 2 conditions. That is, KD was increased in the conscious rat, compared with in the anesthetized rat, and KD was increased in vitro, compared with in vivo. The current study shows that the rat, a readily available species for research, can be used to measure in vivo both affinity and density of radioligand targets, which can later be directly assessed with standard in vitro techniques.

Original languageEnglish
Pages (from-to)749-756
Number of pages8
JournalJournal of Nuclear Medicine
Volume50
Issue number5
DOIs
Publication statusPublished - May 1 2009
Externally publishedYes

Fingerprint

Type 4 Cyclic Nucleotide Phosphodiesterase
Rolipram
Brain
Phosphodiesterase 4 Inhibitors
Isoflurane
Phosphoric Diester Hydrolases
Second Messenger Systems
Positron-Emission Tomography
Cyclic AMP
Anesthesia
Binding Sites
Head

Keywords

  • cAMP
  • Compartmental analysis
  • Isoflurane
  • Small-animal PET
  • Transient equilibrium

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

Cite this

PET measurement of the in vivo affinity of 11C-(R)-rolipram and the density of its target, phosphodiesterase-4, in the brains of conscious and anesthetized rats. / Itoh, Tetsuji; Abe, Koji; Zoghbi, Sami S.; Inoue, Osamu; Hong, Jinsoo; Imaizumi, Masao; Pike, Victor W.; Innis, Robert B.; Fujita, Masahiro.

In: Journal of Nuclear Medicine, Vol. 50, No. 5, 01.05.2009, p. 749-756.

Research output: Contribution to journalArticle

Itoh, Tetsuji ; Abe, Koji ; Zoghbi, Sami S. ; Inoue, Osamu ; Hong, Jinsoo ; Imaizumi, Masao ; Pike, Victor W. ; Innis, Robert B. ; Fujita, Masahiro. / PET measurement of the in vivo affinity of 11C-(R)-rolipram and the density of its target, phosphodiesterase-4, in the brains of conscious and anesthetized rats. In: Journal of Nuclear Medicine. 2009 ; Vol. 50, No. 5. pp. 749-756.
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abstract = "A variety of phosphodiesterases hydrolyze and terminate the effects of the intracellular second messenger 3′,5′-cyclic adenosine monophosphate (cAMP). Phosphodiesterase subtype 4 (PDE4) is particularly abundant in the brain and has been imaged with 11C-(R)-rolipram, a selective inhibitor of PDE4. We sought to measure in vivo both the binding site density (B max) and the radioligand affinity (1/KD) of 11C-(R)-rolipram in the rat brain. We also studied 2 critical factors in small-animal PET scans: the influence of anesthesia and the difference in binding under in vivo and in vitro conditions. Methods: In vivo, Bmax and KD were measured in PET saturation experiments by the administration of 11C-(R)-rolipram and various doses of carrier (R)-rolipram in conscious and isoflurane-anesthetized rats. The metabolite-corrected arterial input function was measured in each scan. To image conscious rats, the head of the rat was fixed in a holder and the animals were trained to comply with this apparatus. Bound and free (R)-rolipram levels were calculated under transient equilibrium conditions (i.e., at the time of peak specific binding). Results: The Bmax and KD of conscious rats were significantly greater than those of anesthetized rats, by 29{\%} and 59{\%}, respectively. In addition, the in vitro KD was 3-7 times greater than was the in vivo KD, although the Bmax was similar in both conditions. Conclusion: The in vivo Bmax and KD of (R)-rolipram were successfully measured in both conscious and anesthetized rats. KD was affected to a greater extent than was Bmax by the 2 conditions. That is, KD was increased in the conscious rat, compared with in the anesthetized rat, and KD was increased in vitro, compared with in vivo. The current study shows that the rat, a readily available species for research, can be used to measure in vivo both affinity and density of radioligand targets, which can later be directly assessed with standard in vitro techniques.",
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AU - Abe, Koji

AU - Zoghbi, Sami S.

AU - Inoue, Osamu

AU - Hong, Jinsoo

AU - Imaizumi, Masao

AU - Pike, Victor W.

AU - Innis, Robert B.

AU - Fujita, Masahiro

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KW - Isoflurane

KW - Small-animal PET

KW - Transient equilibrium

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