title: Binding of 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]pyridinium ion (HPP+), a metabolite of haloperidol, to synthetic melanin: implications for the dopaminergic neurotoxicity of HPP+.
abstract: The toxicity of 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]pyridinium ion (HPP+), a metabolite of haloperidol, toward dopaminergic neurons was investigated. When HPP+ (approximately 100 microM) was added to primary cultures prepared from rat embryonic mesencephalon for 1 h, the survivability of dopaminergic neurons decreased significantly, and this effect was not inhibited by the dopamine transporter (DAT) inhibitor GBR 12909. In addition, HPP+ bound to neuromelanin, which is abundant in dopaminergic neurons. A binding analysis using the Scatchard method showed that there are two classes of binding sites: high affinity sites with a dissociation constant K(d1) of 20.2 nM, and low affinity sites with a K(d2) of 4.0 microM. HPP+ was released easily from synthetic melanin using phosphate buffer (pH 7.0), suggesting that this binding is reversible. The results suggest that the toxicity of HPP+ in dopaminergic neurons is due not to DAT-mediated uptake, but to the binding to neuromelanin.
authors.affiliation: Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto 606-8501.
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Kawashima
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Iida
authors.forename: Youji
authors.initials: Y
authors.lastname: Kitamura
authors.forename: Hideo
authors.initials: H
authors.lastname: Saji
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D050483:Dopamine Plasma Membrane Transport Proteins; D004305:Dose-Response Relationship, Drug; D005260:Female; D006220:Haloperidol / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000633:toxicity*; D008543:Melanins / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008636:Mesencephalon / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D011247:Pregnancy; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D011726:Pyridinium Compounds / Q000378:metabolism / Q000633:toxicity*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D050483:Dopamine Plasma Membrane Transport Proteins; D008543:Melanins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D011726:Pyridinium Compounds; C493216:Slc6a3 protein, rat; C085216:N-(4'-fluorobutyrophenone)-4-(4-chlorophenyl)pyridinium; D006220:Haloperidol