Radioiodination of nicotine with specific activity high enough for mapping nicotinic acetylcholine receptors

Autor: Dietlind Sorger, Reinhard Schliebs, Klaus Schulze, Klaus Günther, Wiebke Kärger, Ingrid Kämpfer, W. H. Knapp
Rok vydání: 1996
Předmět:
Zdroj: European Journal of Nuclear Medicine. 23:157-162
ISSN: 1619-7089
0340-6997
DOI: 10.1007/bf01731839
Popis: A novel radiochemical method is presented to synthesize 5-[123I/125I/131I]-dL-nicotine by radioiodination of 5-bromonicotine. Radioiodination of the precursor 5-dL-bromonicotine was achieved using a copper (I)-assisted nucleophilic exchange reaction in the presence of reducing agent. The reaction conditions were optimized by varying pH, concentration of Sn(II) salt, ascorbic acid, Cu(I)chloride and reaction temperature. After purification by high-performance liquid chromatography the radiochemical purity of the product exceeded 98%, with a radiochemical yield of 55% and a specific activityor =5 GBq/micromol. Specific binding of the iodinated nicotine was demonstrated in rat brain by autoradiography. The radioactivity from the specific structures was displaced by an excess of non-radioactive nicotine (10(-3)M) with KD and Bmax of 13.1+/-7.8 nM and 22+/-2.7 fmol/mg protein and unspecific binding of about 40%. The in vivo distribution of 5-[131I]iodonicotine was determined in 20 female Wistar rats at various time intervals of 15s to 90 min post injection (p.i.) by well counting and autoradiography. Brain activity peaked within 0.5 min p.i., and then showed a biexponential washout. Initially, activity within the cerebral cortex exceeded that of the cerebellum by a factor of 1.5-2.0. It was also increased in the striatum and thalamus. However, as soon as 15 min p.i. activity was almost homogeneously distributed. In conclusion, synthesis of 5-iodo-dL-nicotine (labelled with 131I, 125I or 123I, respectively) with appropriately high specific activity for receptor studies was achieved and specific binding to nicotine receptors in rat brain was demonstrated; following intravenous injection, however, there is considerable unspecific binding, obviously due to highly flow-dependent tissue retention.
Databáze: OpenAIRE
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