An 18-kDa translocator protein (TSPO) polymorphism explains differences in binding affinity of the PET radioligand PBR28

David R Owen, Astrid J Yeo, Roger N Gunn, Kijoung Song, Graham Wadsworth, Andrew Lewis, Chris Rhodes, David J Pulford, Idriss Bennacef, Christine A Parker, Pamela L StJean, Lon R Cardon, Vincent E Mooser, Paul M Matthews, Eugenii A Rabiner, Justin P Rubio, David R Owen, Astrid J Yeo, Roger N Gunn, Kijoung Song, Graham Wadsworth, Andrew Lewis, Chris Rhodes, David J Pulford, Idriss Bennacef, Christine A Parker, Pamela L StJean, Lon R Cardon, Vincent E Mooser, Paul M Matthews, Eugenii A Rabiner, Justin P Rubio

Abstract

[(11)C]PBR28 binds the 18-kDa Translocator Protein (TSPO) and is used in positron emission tomography (PET) to detect microglial activation. However, quantitative interpretations of signal are confounded by large interindividual variability in binding affinity, which displays a trimodal distribution compatible with a codominant genetic trait. Here, we tested directly for an underlying genetic mechanism to explain this. Binding affinity of PBR28 was measured in platelets isolated from 41 human subjects and tested for association with polymorphisms in TSPO and genes encoding other proteins in the TSPO complex. Complete agreement was observed between the TSPO Ala147Thr genotype and PBR28 binding affinity phenotype (P value=3.1 × 10(-13)). The TSPO Ala147Thr polymorphism predicts PBR28 binding affinity in human platelets. As all second-generation TSPO PET radioligands tested hitherto display a trimodal distribution in binding affinity analogous to PBR28, testing for this polymorphism may allow quantitative interpretation of TSPO PET studies with these radioligands.

Figures

Figure 1
Figure 1
(A) Competition binding assay using unlabelled PBR28 to displace [3H]PK11195 in human platelets isolated from whole blood (n=41). The dashed vertical line indicates the concentration of PBR28 used to generate panel B. The fractional binding is described by the following equations, One site model Two site model where B, binding signal; NS, nonspecific binding; Ki, binding affinity; and fH, the fraction of high-affinity binding sites. (B) Box-whisker plot of the residual [3H]PK11195 binding in the presence of 100 nmol/L unlabelled PBR28 (expressed as a percentage of the total [3H]PK11195 binding in the absence of PBR28) stratified on rs6971 genotype. Percentage residual of total binding is plotted as blue diamonds for each individual. HAB, high affinity binder; LAB, low affinity binder; MAB, mixed affinity binder.

References

    1. Banati RB, Newcombe J, Gunn RN, Cagnin A, Turkheimer F, Heppner F, Price G, Wegner F, Giovannoni G, Miller DH, Perkin GD, Smith T, Hewson AK, Bydder G, Kreutzberg GW, Jones T, Cuzner ML, Myers R. The peripheral benzodiazepine binding site in the brain in multiple sclerosis: quantitative in vivo imaging of microglia as a measure of disease activity. Brain. 2000;123 (Pt 11:2321–2337.
    1. Chauveau F, Boutin H, Van CN, Dolle F, Tavitian B. Nuclear imaging of neuroinflammation: a comprehensive review of [11C]PK11195 challengers. Eur J Nucl Med Mol Imaging. 2008;35:2304–2319.
    1. Costa B, Pini S, Gabelloni P, Da PE, Abelli M, Lari L, Preve M, Lucacchini A, Cassano GB, Martini C. The spontaneous Ala147Thr amino acid substitution within the translocator protein influences pregnenolone production in lymphomonocytes of healthy individuals. Endocrinology. 2009a;150:5438–5445.
    1. Costa B, Pini S, Martini C, Abelli M, Gabelloni P, Landi S, Muti M, Gesi C, Lari L, Cardini A, Galderisi S, Mucci A, Lucacchini A, Cassano GB. Ala147Thr substitution in translocator protein is associated with adult separation anxiety in patients with depression. Psychiatr Genet. 2009b;19:110–111.
    1. Korkhov VM, Sachse C, Short JM, Tate CG. Three-dimensional structure of TspO by electron cryomicroscopy of helical crystals. Structure. 2010;18:677–687.
    1. Kreisl WC, Fujita M, Fujimura Y, Kimura N, Jenko KJ, Kannan P, Hong J, Morse CL, Zoghbi SS, Gladding RL, Jacobson S, Oh U, Pike VW, Innis RB. Comparison of [(11)C]-(R)-PK 11195 and [(11)C]PBR28, two radioligands for translocator protein (18 kDa) in human and monkey: Implications for positron emission tomographic imaging of this inflammation biomarker. Neuroimage. 2010;49:2924–2932.
    1. Murail S, Robert JC, Coic YM, Neumann JM, Ostuni MA, Yao ZX, Papadopoulos V, Jamin N, Lacapere JJ. Secondary and tertiary structures of the transmembrane domains of the translocator protein TSPO determined by NMR. Stabilization of the TSPO tertiary fold upon ligand binding. Biochim Biophys Acta. 2008;1778:1375–1381.
    1. Owen DR, Gunn RN, Rabiner EA, Bennacef I, Fujita M, Kreisl WC, Innis RB, Pike VW, Reynolds R, Matthews PM, Parker CA. Mixed-affinity binding in humans with 18-kDa translocator protein ligands. J Nucl Med. 2011a;52:24–32.
    1. Owen DR, Howell OW, Tang SP, Wells LA, Bennacef I, Bergstrom M, Gunn RN, Rabiner EA, Wilkins MR, Reynolds R, Matthews PM, Parker CA. Two binding sites for [(3)H]PBR28 in human brain: implications for TSPO PET imaging of neuroinflammation. J Cereb Blood Flow Metab. 2010;30:1608–1618.
    1. Owen DR, Lewis AJ, Reynolds R, Rupprecht R, Eser D, Wilkins MR, Bennacef I, Nutt DJ, Parker CA. Variation in binding affinity of the novel anxiolytic XBD173 for the 18 kDa translocator protein in human brain. Synapse. 2011b;65:257–259.
    1. Ramensky V, Bork P, Sunyaev S. Human non-synonymous SNPs: server and survey. Nucleic Acids Res. 2002;30:3894–3900.
    1. Taylor JD, Briley D, Nguyen Q, Long K, Iannone MA, Li MS, Ye F, Afshari A, Lai E, Wagner M, Chen J, Weiner MP. Flow cytometric platform for high-throughput single nucleotide polymorphism analysis. Biotechniques. 2001;30:661–669.
    1. VanLiere JM, Rosenberg NA. Mathematical properties of the r2 measure of linkage disequilibrium. Theor Popul Biol. 2008;74:130–137.
    1. Venneti S, Lopresti BJ, Wiley CA. The peripheral benzodiazepine receptor (Translocator protein 18 kDa) in microglia: from pathology to imaging. Prog Neurobiol. 2006;80:308–322.
    1. Wigginton JE, Cutler DJ, Abecasis GR. A note on exact tests of Hardy-Weinberg equilibrium. Am J Hum Genet. 2005;76:887–893.

Source: PubMed

Sponsorer og samarbejdspartnere

Medicinske tilstande

Narkotikainterventioner

3
Abonner