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PET imaging shows no changes in TSPO brain density after IFN-α immune challenge in healthy human volunteers

Nettis, M. A., Veronese, M., Nikkheslat, N., Mariani, N., Lombardo, G., Sforzini, L., Enache, D., Harrison, N. A., Turkheimer, F. E., Mondelli, V. and Pariante, C. M. 2020. PET imaging shows no changes in TSPO brain density after IFN-α immune challenge in healthy human volunteers. Translational Psychiatry 10 (1) , 89. 10.1038/s41398-020-0768-z

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Depression is associated with peripheral inflammation, but its link with brain microglial activity remains unclear. In seven healthy males, we used repeated translocator protein-Positron Emission Tomography (TSPO-PET) dynamic scans with [11C]PBR28 to image brain microglial activation before and 24 h after the immune challenge interferon (IFN)-α. We also investigated the association between changes in peripheral inflammation, changes in microglial activity, and changes in mood. IFN-α administration decreased [11C]PBR28 PET tissue volume of distribution (Vt) across the brain (−20 ± 4%; t6 = 4.1, p = 0.01), but after correction for radioligand free-plasma fraction there were no longer any changes (+23 ± 31%; t = 0.1, p = 0.91). IFN-α increased serum IL-6 (1826 ± 513%, t6 = −7.5, p < 0.001), IL-7 (39 ± 12%, t6 = −3.6, p = 0.01), IL-10 (328 ± 48%, t6 = −12.8, p < 0.001), and IFN-γ (272 ± 64%, t6 = −7.0, p < 0.001) at 4–6 h, and increased serum TNF-α (49 ± 7.6%, t6 = −7.5, p < 0.001), IL-8 (39 ± 12%, t6 = −3.5, p = 0.013), and C-reactive protein (1320 ± 459%, t6 = −7.2, p < 0.001) at 24 h. IFN-α induced temporary mood changes and sickness symptoms after 4–6 h, measured as an increase in POMS-2 total mood score, confusion and fatigue, and a decrease in vigor and friendliness (all p ≤ 0.04). No association was found between changes in peripheral inflammation and changes in PET or mood measures. Our work suggests that brain TSPO-PET signal is highly dependent of inflammation-induced changes in ligand binding to plasma proteins. This limits its usefulness as a sensitive marker of neuroinflammation and consequently, data interpretation. Thus, our results can be interpreted as showing either that [11C]PBR28 is not sensitive enough under these conditions, or that there is simply no microglial activation in this model.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Medicine
MRC Centre for Neuropsychiatric Genetics and Genomics (CNGG)
Publisher: Springer Nature
ISSN: 2158-3188
Date of First Compliant Deposit: 4 June 2020
Date of Acceptance: 24 February 2020
Last Modified: 08 Jun 2020 09:15

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