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.

Neurotoxic Pyridinium Metabolites of Haloperidol Are Substrates of Human Organic Cation Transporters

“…Furthermore, HPP ϩ shows a moderate brain uptake index, which indicates that it may permeate the blood-brain barrier. These results support the hypothesis that HPP ϩ is formed mainly in the liver, circulates in the bloodstream, and enters the brain, where it induces damage to brain dopaminergic neurons (Kawashima et al, 2002(Kawashima et al, , 2004.…”

Interaction of Neuromelanin with Xenobiotics and Consequences for Neurodegeneration; Promising Experimental Models

“…After short (30 min) [ 3 H]haloperidol incubation with either human brain SN or superior cerebellar peduncle homogenates in vitro, centrifugation revealed that about twice as much haloperidol bound to pigmented bands (containing NM) from SN than non-pigmented bands from superior cerebellar peduncle (similar results were obtained for [ 3 H]imipramine and [ 3 H]chlorpromazine) [ 106 ]. Haloperidol can undergo biotransformation into 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]pyridinium ion (HPP + , resembling MPP + ) which bound to synthetic melanin in a reversible manner [ 111 ]. HPP + damaged rat embryonic primary cultured dopaminergic neurons [ 111 ], but which does not demonstrate NM involvement of toxicity (young cultured cells are considered not to have NM)).…”

“…Haloperidol can undergo biotransformation into 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]pyridinium ion (HPP + , resembling MPP + ) which bound to synthetic melanin in a reversible manner [ 111 ]. HPP + damaged rat embryonic primary cultured dopaminergic neurons [ 111 ], but which does not demonstrate NM involvement of toxicity (young cultured cells are considered not to have NM)). HPP + was moderately taken up into brains of rats [ 112 ].…”

Neurotoxins and neurotoxic species implicated in neurodegeneration

“…Thiols also release iron from monoferrictransferrin (Baldwin et al, 1990). Recently, it was found that binding of the haloperidol metabolite 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]pyridinium ion (HPP + ), which chemically resembles MPP + , to melanin had a major influence of HPP + -induced neurotoxicity to primary cultures of rat embryonic mesencephalon (Kawashima et al, 2004). A new mechanism for iron neurotoxicity has been reported, since iron toxicity is dependent on (i) Fedopamine complex formation, (ii) uptake through the monoaminergic transporter, and (iii) inhibition of DTdiaphorase by dicoumarol.…”