Novel radioiodinated γ-hydroxybutyric acid analogues for radiolabeling and photolinking of high-affinity γ-hydroxybutyric acid binding sites

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gamma-Hydroxybutyric acid (GHB) is a therapeutic drug, a drug of abuse and an endogenous substance that binds to low and high-affinity sites in the mammalian brain. To target the specific GHB binding sites, we have developed a (125)I-labeled GHB analogue and characterized its binding in rat brain homogenate and slices. Our data show that [(125)I]BnOPh-GHB binds to one site in rat brain cortical membranes with low nanomolar affinity (K(d) 7 nM, B(max) 61 pmol/mg protein). The binding is inhibited by GHB and selected analogues, but not by GABA. Autoradiography using horizontal slices from rat brain demonstrates the highest density of binding in hippocampus and cortical regions and the lowest density in the cerebellum. Altogether the findings correlate with the labeling and brain regional distribution of high-affinity GHB sites or [(3)H](E,RS)-(6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylidene)acetic acid ([(3)H]NCS-382) binding sites. Using a (125)I-labeled photoaffinity derivative of the new GHB ligand, we have performed denaturing protein electrophoresis and detected one major protein band with an apparent weight of 50 kDa from cortical and hippocampal membranes. [(125)I]BnOPh-GHB is the first reported (125)I-labeled GHB radioligand and is a useful tool for in vitro studies of the specific high-affinity GHB binding sites. The related photoaffinity linker [(125)I]azido-BnOPh-GHB can be used as a probe for isolation of the elusive GHB binding protein.
Original languageEnglish
JournalJournal of Pharmacology and Experimental Therapeutics
Issue number2
Pages (from-to)458-464
Publication statusPublished - 2010

ID: 21772160