Differential uptake of O-(2-18F-fluoroethyl)-L-tyrosine, L-3H-methionine, and 3H-deoxyglucose in brain abscesses.
The amino acid O-(2-(18)F-fluoroethyl)-L-tyrosine ((18)F-FET) has been shown to be a useful tracer for brain tumor imaging. Experimental studies demonstrated no uptake of (18)F-FET in inflammatory cells but increased uptake has been reported in single cases of human brain abscesses. To explore this inconsistency, we investigated the uptake of (18)F-FET in comparison with that of L-[methyl-(3)H]methionine ((3)H-MET) and D-(3)H-deoxyglucose ((3)H-DG) in brain and calf abscesses in rats.


METHODS
Abscesses were induced in the brain (n = 9) and calf (n = 5) of Fisher CDF rats after inoculation of Staphylococcus aureus. Five days later, (18)F-FET and (3)H-MET (n = 10) or (18)F-FET and (3)H-DG (n = 4) were injected intravenously. One hour after injection the rats were sacrificed, and the brain or calf muscle was investigated using dual-tracer autoradiography. Lesion-to-background ratios (L/B) and standardized uptake values (SUVs) were calculated. The autoradiograms were compared with histology and immunostaining for glial fibrillary acidic protein (GFAP), CD68 for macrophages, and CD11b for microglia.


RESULTS
(18)F-FET uptake in the area of macrophage infiltration and activated microglia at the rim of the brain abscesses was low (L/B, 1.5 +/- 0.4). In contrast, high uptake was observed for (3)H-MET as well as for (3)H-DG (L/B, 4.1 +/- 1.1 for (3)H-MET vs. 3.1 +/- 1.5 for (3)H-DG; P < 0.01 vs. (18)F-FET). Results for calf abscesses were similar. In the vicinity of the brain abscesses, slightly increased uptake was noted for (18)F-FET (L/B, 1.8 +/- 0.3) and (3)H-MET (L/B, 1.8 +/- 0.4), whereas (3)H-DG distribution was normal (L/B, 1.2 +/- 0.2). Anti-GFAP immunofluorescence showed a diffuse astrocytosis in those areas.


CONCLUSIONS
Our results demonstrate that there is no accumulation of (18)F-FET in macrophages and activated microglia in experimental brain abscesses, whereas (3)H-MET and (3)H-DG exhibit high uptake in these cells. Thus, the specificity of (18)F-FET for gliomas may be superior to that (3)H-MET and (3)H-DG. Increased (18)F-FET uptake in human brain abscesses appears to be related to reactive astrocytosis.
Salber
Dagmar
D
C. & O. Vogt Institute of Brain Research, Heinrich-Heine-University, Düsseldorf, Germany.
Stoffels
Gabriele
G
Pauleit
Dirk
D
Oros-Peusquens
Anna-Maria
AM
Shah
Nadim Jon
NJ
Klauth
Peter
P
Hamacher
Kurt
K
Coenen
Heinz Hubert
HH
Langen
Karl-Josef
KJ
D000818:Animals; D001812:Blood-Brain Barrier; D001922:Brain Abscess / Q000378:metabolism*; D003847:Deoxyglucose / Q000493:pharmacokinetics*; D005462:Fluorine Radioisotopes; D008297:Male; D008715:Methionine / Q000493:pharmacokinetics*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D051381:Rats; D011916:Rats, Inbred F344; D014316:Tritium; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics
D005462:Fluorine Radioisotopes; C117289:O-(2-fluoroethyl)tyrosine; D019275:Radiopharmaceuticals; D014316:Tritium; D014443:Tyrosine; D003847:Deoxyglucose; D008715:Methionine