Chiral CE Separation of Dopamine-Derived Neurotoxins

Abstract

An enantiomeric separation of dopamine-derived neurotoxins by capillary electrophoresis has been developed. Tetrahydroisoquinoline (TIQ), dopamine (DA), (R/S)-1-benzyl-TIQ (BTIQ), (R/S)-6,7-dihydroxy-1-methyl-TIQ (salsolinol, Sal), and (R/S)-6,7-dihydroxy-1, 2-dimethyl-TIQ (N-methyl-salsolinol, NMSal) were studied as model compounds. The CE running buffer (50 mM phosphate buffer at pH 3.0) contained 1.5 M urea and 12 mM β-CD as a chiral selector. During separation, the (R)-enantiomers formed more stable inclusion complexes with β-CD, and thus had a longer migration time than their optical antipodes. It was noticed that the recovery rates of these TIQ derivatives were very poor (< 15%) during protein precipitation, a procedure widely used for cleaning up biological samples. The recovery was significantly improved by pre-mixing the sample with a surfactant (e.g., sodium hexanesulfonate or Triton X-100) to reduce the co-precipitation. The present method in combination with electrospray ionization tandem mass spectrometry (ESI-MS/MS) was applied to study samples obtained from in vitro incubation of two catecholamines, dopamine and epinine, with aldehydes forming neurotoxins including (S)-and (R)-NMSal enantiomers. The later is known to induce Parkinsonism in rats.

(R)-Salsolinol, a product of ethanol metabolism, stereospecifically induces behavioral sensitization and leads to excessive alcohol intake

“…The elution time of the enantiomers was approximately 6.2 minutes for (S)-SAL and 7.4 minutes for (R)-SAL (Fig. 1a), which is in line with the elution patterns described by other authors using a similar HPLC system (Baum & Rommelspacher 1994;Deng et al 1995;Naoi et al 1996;Liu et al 2000;Tóth et al 2001;Quan et al 2005;Cai & Liu 2008;Rojkovicova et al 2008;Lee et al 2010). This elution pattern is also supported by compu- tational modeling, evaluating the total energy for stabilization, demonstrating that the complex formed by (R)-SAL and β-cyclodextrin is stronger than the complex of (S)-SAL and β-cyclodextrin.…”

“…packed with silica gel modified with β-cyclodextrin (MachereyNagel, Düren, Germany) kept at 30°C; (2) an isocratic pump adjusted to 0.80 ml/minute (Shimadzu LC-10AD, Kyoto, Japan); and (3) an LC-4C BAS amperometric detector (ED) set at a potential of 0.7 V. The mobile phase was 100 mM ammonium acetate containing 10 mM triethylamine (pH 4.0). Under these conditions and using a similar chiral HPLC system, it was reported that (S)-SAL was the first to elute (Baum & Rommelspacher 1994;Deng et al 1995;Naoi et al 1996;Liu et al 2000;Tóth et al 2001;Quan et al 2005;Cai & Liu 2008;Rojkovicova et al 2008;Huang et al 2009;Lee et al 2010).…”

“…Complete separation of (R)-SAL and (S)-SAL was achieved by high-performance liquid chromatography (HPLC) on a β-cyclodextrin-modified column, which has the ability to separate these enantiomers (Baum & Rommelspacher 1994;Quan et al 2005;Huang, Quan & Liu 2009). Studies were conducted to determine the differential effects of intra-VTA administration of (R)-or (S)-SAL on the generation of (1) conditioned place preference (CPP); (2) locomotor sensitization; and (3) voluntary ethanol consumption.…”

Enzymatic condensation of dopamine and acetaldehyde: a salsolinol synthase from rat brain

“…Three endogenous alkaloids were proposed as potential candidates of dopaminergic neurotoxins named salsolinol 2,3,Sal), tetrahydropapaveroline (THP) derivative (1BnTIQ) and β-carbolines. Sal, in particular, is toxic to dopaminergic neurons and has recently gained much attention due to its structural similarity with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, a potent neurotoxin that specifically degenerates the nigrostriatal dopaminergic neurons, resulting in dopamine deficiency in the striatum, and hence the symptoms of Parkinsonism (Quan et al 2005). Therefore, Sal may have an influential role directly or indirectly in causing PD.…”

Chiral separations by capillary electrophoresis: Recent developments and applications

“…Enantiomeric separation of dopamine-derived neurotoxins was performed with b-CD as chiral selector [163]. This group showed that the addition of a surfactant improved the recovery rates of these compounds from the deproteinization procedure.…”