Specific binding of 3h-spiperone to peripheral blood cells: Relevance for the interpretation of binding studies in psychiatric disorders

Abstract

1. 1. There is an ongoing discussion regarding the elevated binding of 3H-spiperone to lymphocytes of schizophrenic patients. Several authors described an atypical binding pattern with a saturable high-affinity and a nonsaturable binding site both displaceable by (+)-butaclamol. Recent findings are still controversial (Fartacek et al., 1997; Wodarz et al., 1996), possibly due to methodological differences. The authors investigated 3H-spiperone binding to different peripheral blood cells including B- and T-lymphoblastoids. 2. 2.B-lymphocytes (K d = 0.081 nM; B max = 0.46 × 10 −15 mol/10 6 cells) and macrophages (K d = 0.11 nM, B max = 2.44 × 10 −15 mol/10 6 cells) are characterized by a minor but saturable binding of 3H-spiperone in a concentration range between 0.5 and 1 nM. Above 1 nM, only nonsaturable binding was measurable. Interestingly, Epstein-Barr virus (EBV) transformed lymphoblastoids (K d = 0.13 nM) have nearly the same affinity for 3H-spiperone as native B-cells, but an increased number of binding sites ( B max = 1.76 × 10 −15 mol/ 10 6 cells). 3. 3.Membranes from B-lymphoblastoids displayed a saturable binding in a concentration between 0 and 1.8 nM of 3H-spiperone (K d = 0.5 nM and B max = 1.72 × 10 −15 mol/mg protein>). Extraction with 1 % digitonin resulted in a similar binding characteristic (K d = 0.17 nM and B max = 1.97 × 10 −15 mol/mg protein). 4. 4.T-cells, granulocytes and MOLT-3-cells did not show a saturable binding even not at high concentrations of 3H-spiperone. 5. 5.The pharmacological profile of the high-affinity 3H-spiperone binding site is clearly different from the dopamine D 2 and D 4, serotonin 5-HT 2 histamine H 1 and noradrenergic alpha, and alpha 2 receptor, respectively. 6. 6.In summary, the results suggest that spiperone binding studies to enriched lymphocytes of psychiatric patients should be interpreted cautiously. Variable amounts of leucocytes might result in a higher proportion of nonsaturable, butaclamol displaceable spiperone binding with relevance for the calculation of K d and B max of the saturable high-affinity site. Interestingly, homogenous B-lymphoblastoid cell lines have the same binding characteristics as native B-225 lymphocytes and therefore should be recommended for characterization of 3H-spiperone binding sites.