Blodd-brain transport of large neutral amino acids (LNAAS) studied with O-methyl-[18F]fluoro-L-DOPA ([18F]OMFD).


Blodd-brain transport of large neutral amino acids (LNAAS) studied with O-methyl-[18F]fluoro-L-DOPA ([18F]OMFD).

Kuwabara, H.; Brust, P.; Steinbach, J.; Johannsen, B.

OBJECTIVES: Blood-brain transport of LNAAs may be altered in certain neurological conditions, including brain tumors. We tested an alternative method to characterize the transport, independent of plasma LNAA levels.
METHODS: Five young pigs were studied with PET for two hours following an intravenous injection of 18F]OMFD. One-fourth of the total [18F]OMFD (~40 MBq) was continuously infused throughout the scan after 20 minutes. The radioactivity and concentrations of LNAAs in plasma were determined at ten minute intervals after 35 minutes. The distribution volume of [18F]OMFD (Vd: the ratio of the unidirectional blood-to-brain and brain-to-blood clearances, K1/k2) was obtained as the brain-plasmaradioactivity ratio. A Michaelis-Menten model was used to describe the changes in Vd in amino acid infusion experiments (n=3; infusion between 40 and 120 minutes). The model equation is given by: Vd= (1+Sigma Ce[LNAAi](T)/Ki)/(1+Beta . Sigma Cp[LNAAi](T)/Ki) where Ce[LNAAi](T) and Cp[LNAAi, assuming changes in brain LNAA levels are negligible relative to those changes in plasma.
RESULTS: The present tracer infusion scheme stabilized Vd over time without amino acid infusion (n=2). We found the M-M model was appropriate to describe plots of Vd (ranges: 0.45-0.87 ml/g) versus CpLNAAi. Estimates of Alpha ranged from 1.02 to 1.07, and Beta from 0.009 to 0.012 for the whole cortex of the three pigs.
CONCLUSION: We indicated that the proposed method enabled characterization of LNAA transport in brain regions using two constants and may be of clinical use

  • Poster
    46th Annual Meeting of the Society of Nuclear Medicine, Los Angeles, 06.-10.06.1999
  • Abstract in refereed journal
    J. Nucl. Med. 40 (5) (1999) 145P

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Publ.-Id: 3071