Imaging of inflammatory cellular protagonists in human atherosclerosis: a dual-isotope SPECT approach

Barrett, Hilary E.; Meester, Eric J.; van Gaalen, Kim; van der Heiden, Kim; Krenning, Boudewijn J.; Beekman, F.J.; Verhagen, H. J.; de Jong, M.; Gijsen, F.J.H.

doi:10.1007/s00259-020-04776-0

Imaging of inflammatory cellular protagonists in human atherosclerosis

Title

Imaging of inflammatory cellular protagonists in human atherosclerosis: a dual-isotope SPECT approach

Author

Barrett, Hilary E. (Erasmus MC)
Meester, Eric J. (Erasmus MC)
van Gaalen, Kim (Erasmus MC)
van der Heiden, Kim (Erasmus MC)
Krenning, Boudewijn J. (Erasmus MC)
Beekman, F.J. (TU Delft RST/Biomedical Imaging; MILabs B.V.; University Medical Center Utrecht)
Verhagen, H. J. (Erasmus MC)
de Jong, M. (Erasmus MC)
Gijsen, F.J.H. (Erasmus MC)

Date

2020

Abstract

Purpose: Atherosclerotic plaque development and progression signifies a complex inflammatory disease mediated by a multitude of proinflammatory leukocyte subsets. Using single photon emission computed tomography (SPECT) coupled with computed tomography (CT), this study tested a new dual-isotope acquisition protocol to assess each radiotracer’s capability to identify plaque phenotype and inflammation levels pertaining to leukocytes expressing leukocyte function-associated antigen-1 (LFA-1) and the leukocyte subset of proinflammatory macrophages expressing somatostatin receptor subtype-2 (SST₂). Individual radiotracer uptake was quantified and the presence of corresponding immunohistological cell markers was assessed. Methods: Human symptomatic carotid plaque segments were obtained from endarterectomy. Segments were incubated in dual-isotope radiotracers [¹¹¹In]In-DOTA-butylamino-NorBIRT ([¹¹¹In]In-Danbirt) and [^99mTc]Tc-[N^0–1 ₄,Asp⁰,Tyr³]-octreotate ([^99mTc]Tc-Demotate 2) before scanning with SPECT/CT. Plaque phenotype was classified as pathological intimal thickening, fibrous cap atheroma or fibrocalcific using histology sections based on distinct morphological characteristics. Plaque segments were subsequently immuno-stained with LFA-1 and SST₂ and quantified in terms of positive area fraction and compared against the corresponding SPECT images. Results: Focal uptake of co-localising dual-radiotracers identified the heterogeneous distribution of inflamed regions in the plaques which co-localised with positive immuno-stained regions of LFA-1 and SST₂. [¹¹¹In]In-Danbirt and [^99mTc]Tc-Demotate 2 uptake demonstrated a significant positive correlation (r = 0.651; p = 0.001). Fibrous cap atheroma plaque phenotype correlated with the highest [¹¹¹In]In-Danbirt and [^99mTc]Tc-Demotate 2 uptake compared with fibrocalcific plaques and pathological intimal thickening phenotypes, in line with the immunohistological analyses. Conclusion: A dual-isotope acquisition protocol permits the imaging of multiple leukocyte subsets and the pro-inflammatory macrophages simultaneously in atherosclerotic plaque tissue. [¹¹¹In]In-Danbirt may have added value for assessing the total inflammation levels in atherosclerotic plaques in addition to classifying plaque phenotype.