Differential Uptake of O-(2-¹⁸F-Fluoroethyl)-L-Tyrosine, L-³H-Methionine, and ³H-Deoxyglucose in Brain Abscesses

¹ C. & O. Vogt Institute of Brain Research, Heinrich-Heine-University, Düsseldorf, Germany; Brain Imaging Centre West, Research Centre Jülich, Jülich, Germany
² Brain Imaging Centre West, Research Centre Jülich, Jülich, Germany; Institute of Neuroscience and Biophysics–Medicine, Research Centre Jülich, Jülich, Germany
³ Institute of Chemistry and Dynamics of the Geosphere, Research Centre Jülich, Jülich, Germany
⁴ Brain Imaging Centre West, Research Centre Jülich, Jülich, Germany; Institute of Neuroscience and Biophysics–Nuclear Chemistry, Research Centre Jülich, Jülich, Germany

^* To whom correspondence should be addressed. E-mail: k.j.langen{at}fz-juelich.de.

	Abstract

The amino acid O-(2-¹⁸F-fluoroethyl)-L-tyrosine (¹⁸F-FET) has been shown to be a useful tracer for brain tumor imaging. Experimental studies demonstrated no uptake of ¹⁸F-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 ¹⁸F-FET in comparison with that of L-[methyl-³H]methionine (³H-MET) and D-³H-deoxyglucose (³H-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, ¹⁸F-FET and ³H-MET (n = 10) or ¹⁸F-FET and ³H-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: ¹⁸F-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 ³H-MET as well as for ³H-DG (L/B, 4.1 ± 1.1 for ³H-MET vs. 3.1 ± 1.5 for ³H-DG; P < 0.01 vs. ¹⁸F-FET). Results for calf abscesses were similar. In the vicinity of the brain abscesses, slightly increased uptake was noted for ¹⁸F-FET (L/B, 1.8 ± 0.3) and ³H-MET (L/B, 1.8 ± 0.4), whereas ³H-DG distribution was normal (L/B, 1.2 ± 0.2). Anti-GFAP immunofluorescence showed a diffuse astrocytosis in those areas. Conclusion: Our results demonstrate that there is no accumulation of ¹⁸F-FET in macrophages and activated microglia in experimental brain abscesses, whereas ³H-MET and ³H-DG exhibit high uptake in these cells. Thus, the specificity of ¹⁸F-FET for gliomas may be superior to that ³H-MET and ³H-DG. Increased ¹⁸F-FET uptake in human brain abscesses appears to be related to reactive astrocytosis.

Key Words: abscess, O-(2-¹⁸F-fluoroethyl)-L-tyrosine, L-[methyl-³H]methionine, autoradiography

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