Andrea Parente1, David Vállez García1, Alexandre Shoji2, Isadora Lopes Alves1, Bram Maas1, Rolf Zijlma1, Rudi Ajo Dierckx1, Carlos A Buchpiguel3, Erik Fj de Vries1, Janine Doorduin4. 1. Department of Nuclear Medicine and Molecular Imaging, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands. 2. Department of Nuclear Medicine and Molecular Imaging, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands; Center of Nuclear Medicine, University of Sao Paulo, University of Sao Paulo Medical School, Sao Paulo, Brazil. 3. Center of Nuclear Medicine, University of Sao Paulo, University of Sao Paulo Medical School, Sao Paulo, Brazil. 4. Department of Nuclear Medicine and Molecular Imaging, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands. Electronic address: j.doorduin@umcg.nl.
Abstract
INTRODUCTION: [11C]Flumazenil is a well-known PET tracer for GABAA receptors and is mainly used as an imaging biomarker for neuronal loss. Recently, GABAA receptors on immune cells have been investigated as target for modulation of inflammation. Since neuronal loss is often accompanied by neuroinflammation, PET imaging with [11C]flumazenil is potentially affected by infiltrating immune cells. This may also compromise the validity of using the pons as reference tissue in quantitative pharmacokinetic analysis. This study aims to evaluate whether inflammatory processes in the brain can influence [11C]flumazenil uptake and affect the outcome of pharmacokinetic modeling when the pons is used as reference tissue. METHODS: The herpes simplex encephalitis (HSE) rat model is known to cause neuroinflammation in the brainstem. Dynamic [11C]flumazenil PET scans of 60-min, accompanied by arterial blood sampling and metabolite analysis, were acquired at day 6-7days post-infection of male Wistar rats (HSE, n=5 and control, n=6). Additionally, the GABAA receptor was saturated by injection of unlabeled flumazenil prior to the tracer injection in 4 rats per group. PET data were analyzed by pharmacokinetic modeling. RESULTS: No statistically significant differences were found in the volume of distribution (VT) or non-displaceable binding potential (BPND) between control and HSE rats in any of the brain regions. Pre-saturation with unlabeled flumazenil resulted in a statistically significant reduction in [11C]flumazenil VT in all brain regions. The BPND obtained from SRTM exhibited a good correlation to DVR - 1 values from the two-tissue compartment model, coupled with some level of underestimation. CONCLUSION: Reliable quantification of [11C]flumazenil binding in rats can be obtained by pharmacokinetic analysis using the pons as a pseudo-reference tissue even in the presence of strong acute neuroinflammation.
INTRODUCTION:[11C]Flumazenil is a well-known PET tracer for GABAA receptors and is mainly used as an imaging biomarker for neuronal loss. Recently, GABAA receptors on immune cells have been investigated as target for modulation of inflammation. Since neuronal loss is often accompanied by neuroinflammation, PET imaging with [11C]flumazenil is potentially affected by infiltrating immune cells. This may also compromise the validity of using the pons as reference tissue in quantitative pharmacokinetic analysis. This study aims to evaluate whether inflammatory processes in the brain can influence [11C]flumazenil uptake and affect the outcome of pharmacokinetic modeling when the pons is used as reference tissue. METHODS: The herpes simplex encephalitis (HSE) rat model is known to cause neuroinflammation in the brainstem. Dynamic [11C]flumazenil PET scans of 60-min, accompanied by arterial blood sampling and metabolite analysis, were acquired at day 6-7days post-infection of male Wistar rats (HSE, n=5 and control, n=6). Additionally, the GABAA receptor was saturated by injection of unlabeled flumazenil prior to the tracer injection in 4 rats per group. PET data were analyzed by pharmacokinetic modeling. RESULTS: No statistically significant differences were found in the volume of distribution (VT) or non-displaceable binding potential (BPND) between control and HSE rats in any of the brain regions. Pre-saturation with unlabeled flumazenil resulted in a statistically significant reduction in [11C]flumazenilVT in all brain regions. The BPND obtained from SRTM exhibited a good correlation to DVR - 1 values from the two-tissue compartment model, coupled with some level of underestimation. CONCLUSION: Reliable quantification of [11C]flumazenil binding in rats can be obtained by pharmacokinetic analysis using the pons as a pseudo-reference tissue even in the presence of strong acute neuroinflammation.
Authors: M Kessler; M Mamach; R Beutelmann; M Lukacevic; S Eilert; P Bascuñana; A Fasel; F M Bengel; J P Bankstahl; T L Ross; G M Klump; G Berding Journal: Mol Imaging Biol Date: 2020-04 Impact factor: 3.488
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