Advertisement

Evaluation of a radiolabelled peripheral benzodiazepine receptor ligand in the central nervous system inflammation of experimental autoimmune encephalomyelitis: a possible probe for imaging multiple sclerosis

  • F. Mattner
  • A. Katsifis
  • M. Staykova
  • P. Ballantyne
  • D. O. Willenborg
Original Article

Abstract

Purpose

Peripheral benzodiazepine receptors (PBRs) are upregulated on macrophages and activated microglia, and radioligands for the PBRs can be used to detect in vivo neuroinflammatory changes in a variety of neurological insults, including multiple sclerosis. Substituted 2-phenyl imidazopyridine-3-acetamides with high affinity and selectivity for PBRs have been prepared that are suitable for radiolabelling with a number of positron emission tomography and single-photon emission computed tomography (SPECT) isotopes. In this investigation, the newly developed high-affinity PBR ligand 6-chloro-2-(4′-iodophenyl)-3-(N,N-diethyl)imidazo[1,2-a]pyridine-3-acetamide, or CLINDE, was radiolabelled with 123I and its biodistribution in the central nervous system (CNS) of rats with experimental autoimmune encephalomyelitis (EAE) evaluated.

Methods

EAE was induced in male Lewis rats by injection of an emulsion of myelin basic protein and incomplete Freund’s adjuvant containing Mycobacterium butyricum. Biodistribution studies with 123I-CLINDE were undertaken on EAE rats exhibiting different clinical disease severity and compared with results in controls. Disease severity was confirmed by histopathology in the spinal cord of rats. The relationship between inflammatory lesions and PBR ligand binding was investigated using ex vivo autoradiography and immunohistochemistry on rats with various clinical scores.

Results

123I-CLINDE uptake was enhanced in the CNS of all rats exhibiting EAE when compared to controls. Binding reflected the ascending nature of EAE inflammation, with lumbar/sacral cord > thoracic cord > cervical cord > medulla. The amount of ligand binding also reflected the clinical severity of disease. Ex vivo autoradiography and immunohistochemistry revealed a good spatial correspondence between radioligand signal and foci of inflammation and in particular ED-1+ cells representing macrophages and microglia.

Conclusion

These results demonstrate the ability of 123I-CLINDE to measure in vivo inflammatory events represented by increased density of PBRs and suggest that 123I-CLINDE warrants further investigation as a potential SPECT marker for imaging of CNS inflammation.

Keywords

Peripheral benzodiazepine receptors SPECT Inflammation Multiple sclerosis Experimental autoimmune encephalomyelitis 

Notes

Acknowledgements

The authors thank Dr. Christian Loc’h for the helpful discussions during the preparation of this manuscript. This work was supported in part by the Australian Institute of Nuclear Science and Engineering (AINSE), the National Health and Medical Research Council (NH&MRC), Multiple Sclerosis Australia and The Canberra Hospital Private Practice Fund.

References

  1. 1.
    Papadopoulos V, Amri H, Li H, Yao Z, Brown RC, Vidic B, et al. Structure, function and regulation of the mitochondrial peripheral-type benzodiazepine receptor. Therapie 2001;56:549–56.PubMedGoogle Scholar
  2. 2.
    Benavides J, Quarteronet D, Imbault F, Malgouris C, Uzan A, Renault C, et al. Labelling of “peripheral-type” benzodiazepine binding sites in the rat brain by using [3H]PK 11195, an isoquinoline carboxamide derivative: kinetic studies and autoradiographic localization. J Neurochem 1983; 41:1744–50.Google Scholar
  3. 3.
    Bono F, Lamarche I, Prabonnaud V, Le Fur G, Herbert JM. Peripheral benzodiazepine receptor agonists exhibit potent antiapoptotic activities. Biochem Biophys Res Commun 1999;265:457–61.CrossRefPubMedGoogle Scholar
  4. 4.
    Brown RC, Papadopoulos V. Role of the peripheral-type benzodiazepine receptor in adrenal and brain steroidogenesis. Int Rev Neurobiol 2001;46:117–43.CrossRefPubMedGoogle Scholar
  5. 5.
    Li H, Yao Z, Degenhardt B, Teper G, Papadopoulos V. Cholesterol binding at the cholesterol recognition/interaction amino acid consensus (CRAC) of the peripheral-type benzodiazepine receptor and inhibition of steroidogenesis by an HIV TAT-CRAC peptide. Proc Natl Acad Sci U S A 2001;98:1267–72.CrossRefPubMedGoogle Scholar
  6. 6.
    Culty M, Luo L, Yao ZX, Chen H, Papadopoulos V, Zirkin BR. Cholesterol transport, peripheral benzodiazepine receptor, and steroidogenesis in aging Leydig cells. J Androl 2002;23:439–47.PubMedGoogle Scholar
  7. 7.
    Banati RB. Visualising microglial activation in vivo. Glia 2002;40:206–17.CrossRefPubMedGoogle Scholar
  8. 8.
    Banati RB. Neuropathological imaging: in vivo detection of glial activation as a measure of disease and adaptive change in the brain. Br Med Bull 2003;65:121–31.CrossRefPubMedGoogle Scholar
  9. 9.
    Kuhlmann AC, Guilarte TR. Cellular and subcellular localization of peripheral benzodiazepine receptors after trimethyltin neurotoxicity. J Neurochem 2000;74:1694–704.CrossRefPubMedGoogle Scholar
  10. 10.
    Mankowski JL, Queen SE, Tarwater PJ, Adams RJ, Guilarte TR. Elevated peripheral benzodiazepine receptor expression in simian immunodeficiency virus encephalitis. J Neurovirol 2003;9:94–100.PubMedGoogle Scholar
  11. 11.
    Messmer K, Reynolds GP. Increased peripheral benzodiazepine binding sites in the brain of patients with Huntington’s disease. Neurosci Lett 1998;241:53–6.CrossRefPubMedGoogle Scholar
  12. 12.
    Cagnin A, Myers R, Gunn RN, Lawrence AD, Stevens T, Kreutzberg GW, et al. In vivo visualization of activated glia by [11C] (R)-PK11195-PET following herpes encephalitis reveals projected neuronal damage beyond the primary focal lesion. Brain 2001;124:2014–27.CrossRefPubMedGoogle Scholar
  13. 13.
    Banati RB, Newcombe J, Gunn RN, Cagnin A, Turkheimer F, Heppner F, et al. 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;123:2321–37.CrossRefPubMedGoogle Scholar
  14. 14.
    Vowinckel E, Reutens D, Becher B, Verge G, Evans A, Owens T, et al. PK11195 binding to the peripheral benzodiazepine receptor as a marker of microglia activation in multiple sclerosis and experimental autoimmune encephalomyelitis. J Neurosci Res 1997;50:345–53.PubMedGoogle Scholar
  15. 15.
    Bruck W, Sommermeier N, Bergmann M, Zettl U, Goebel HH, Kretzschmar HA, et al. Macrophages in multiple sclerosis. Immunobiology 1996;195:588–600.PubMedGoogle Scholar
  16. 16.
    Lucchinetti C, Bruck W, Parisi J, Scheithauer B, Rodriguez M, Lassmann H. Heterogeneity of multiple sclerosis lesions: implications for the pathogenesis of demyelination. Ann Neurol 2000;47:707–17.CrossRefPubMedGoogle Scholar
  17. 17.
    Sobel RA. The pathology of multiple sclerosis. Neurol Clin 1995;13:1–21.PubMedGoogle Scholar
  18. 18.
    Banati RB, Myers R, Kreutzberg GW. PK (‘peripheral benzodiazepine’)—binding sites in the CNS indicate early and discrete brain lesions: microautoradiographic detection of [3H]PK11195 binding to activated microglia. J Neurocytol 1997;26:77–82.CrossRefPubMedGoogle Scholar
  19. 19.
    Dumont F, De Vos F, Versijpt J, Jansen HM, Korf J, Dierckx RA, et al. In vivo evaluation in mice and metabolism in blood of human volunteers of [123I]iodo-PK11195: a possible single-photon emission tomography tracer for visualization of inflammation. Eur J Nucl Med 1999;26:194–200.CrossRefPubMedGoogle Scholar
  20. 20.
    Katsifis A, Mattner F, Mardon K, Papazian V, Dikic B. Synthesis and evaluation of [123I]imidazo[1,2-a]pyridines as potential probes for the study of the peripheral benzodiazepine receptors using SPECT. J Nucl Med 1998;39(5):50.Google Scholar
  21. 21.
    Katsifis A, Mattner F, Dikic B, Papazian V. Synthesis of substituted [123I]imidazo[1,2-a]pyridines as potential probes for the study of the peripheral benzodiazepine receptors using SPECT. Radiochim Acta 2000;88(3–4):229–32.Google Scholar
  22. 22.
    Eylar EH. The structure and immunologic properties of basic proteins of myelin. Ann N Y Acad Sci 1972;195:481–91.PubMedGoogle Scholar
  23. 23.
    Mattner F, Papazian V, Chapman J, Katsifis A. Ex vivo pharmacological evaluation of the peripheral benzodiazepine receptor radioligand [123I]-ClINDE in animal tumour models. J Lab Comp Radiopharm 2003;46:S9.Google Scholar
  24. 24.
    Katsifis A, Mattner F, Chapman J, Izard B, Papazian V, Dikic B, et al. Synthesis and Evaluation of [123I]-labelled peripheral benzodiazepine receptor ligands in tumour bearing rodents. Eur J Nucl Med Mol Imaging 2002;29:S163.CrossRefGoogle Scholar
  25. 25.
    Debruyne JC, Versijpt J, Van Laere KJ, De Vos F, Keppens J, Strijckmans K, et al. PET visualization of microglia in multiple sclerosis patients using [11C]PK11195. Eur J Neurol 2003;10:257–64.PubMedGoogle Scholar

Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • F. Mattner
    • 1
  • A. Katsifis
    • 1
  • M. Staykova
    • 2
  • P. Ballantyne
    • 1
  • D. O. Willenborg
    • 2
  1. 1.Radiopharmaceuticals DivisionANSTOLucas HeightsAustralia
  2. 2.Neurosciences Research UnitAustralian National University Medical School, The Canberra HospitalWodenAustralia

Personalised recommendations