Quantification of salsolinol enantiomers by stable isotope dilution liquid chromatography with tandem mass spectrometric detection

The Mechanism of Action of Salsolinol in Brain: Implications in Parkinson's Disease

1-Methyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol, commonly known as salsolinol, is a compound derived from dopamine. It was first discovered in 1973 and has gained attention for its role in Parkinson's disease. Salsolinol and its derivatives were claimed to play a role in the pathogenesis of Parkinson's disease as a neurotoxin that induces apoptosis of dopaminergic neurons due to its structural similarity to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its ability to induce Parkinsonism. In this article, we discussed the biosynthesis, distribution and blood-brain barrier permeability of salsolinol. The roles of salsolinol in a healthy brain, particularly the interactions with enzymes, hormone and catecholamine, were reviewed. Finally, we discussed the involvement of salsolinol and its derivatives in the pathogenesis of Parkinson's disease.

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

Ethanol is oxidized in the brain to acetaldehyde, which can condense with dopamine to generate (R/S)-salsolinol [(RS)-SAL]. Racemic salsolinol [(RS)-SAL] is self-infused by rats into the posterior ventral tegmental area (VTA) at significantly lower concentrations than those of acetaldehyde, suggesting that (RS)-SAL is a most active product of ethanol metabolism. Early studies showed that repeated intraperitoneal or intra-VTA administration of (RS)-SAL (10 mg/kg) induced conditioned place preference, led to locomotor sensitization and increased voluntary ethanol consumption. In the present study, we separated the (R)- and (S)-enantiomers from a commercial (RS)-SAL using a high-performance liquid chromatography with electrochemical detection system fitted with a β-cyclodextrin-modified column. We injected (R)-SAL or (S)-SAL (30 pmol/1.0 μl) into the VTA of naïve UChB rats bred as alcohol drinkers to study whether one or both SAL enantiomers are responsible for the motivated behavioral effects, sensitization and increase in voluntary ethanol intake. The present results show that repeated administration of (R)-SAL leads to (1) conditioned place preference; (2) locomotor sensitization; and (3) marked increases in binge-like ethanol intake. Conversely, (S)-SAL did not influence any of these parameters. Overall, data indicate that (R)-SAL stereospecifically induces motivational effects, behavioral sensitization and increases ethanol intake.

Salsolinol, an endogenous compound triggers a two-phase opposing action in the central nervous system

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline), an endogenous compound present in the brain, was suspected of participation in the etiopathogenesis of Parkinson’s disease, the most common serious movement disorder worldwide. In this study, we evaluated the effect of different (50, 100, and 500 µM) concentrations of salsolinol on markers of glutamate-induced apoptotic and neurotoxic cell damage, such as caspase-3 activity, lactate dehydrogenase (LDH) release, and the loss of mitochondrial membrane potential. Biochemical data were complemented with the cellular analysis, including Hoechst 33342 and calcein AM staining, to visualize apoptotic DNA-fragmentation and to assess cell survival, respectively. The assessment of all investigated parameters was performed in primary cultures of rat or mouse hippocampal and striatum cells. Our study showed that salsolinol had biphasic effects, namely, at lower concentrations (50 and 100 µM), it demonstrated a distinct neuroprotective activity, whereas in the highest one (500 µM) caused neurotoxic effect. Salsolinol in concentrations of 50 and 100 µM significantly antagonized the pro-apoptotic and neurotoxic effects caused by 1 mM glutamate. Salsolinol diminished the number of bright fragmented nuclei with condensed chromatin and increased cell survival in Hoechst 33342 and calcein AM staining in hippocampal cultures. Additionally, in the low 50 µM concentration, it produced a significant inhibition of glutamate-induced loss of membrane mitochondrial potential. Only the highest concentration of salsolinol (500 µM) enhanced the glutamate excitotoxicity. Ex vivo studies indicated that both acute and chronic administration of salsolinol did not affect the dopamine metabolism, its striatal concentration or α-synuclein and tyrosine hydroxylase protein level in the rat substantia nigra and striatum. Summarizing, the present studies exclude possibility that salsolinol under physiological conditions could be an endogenous factor involved in the neurogenerative processes; conversely, it can exert a protective action on nerve cells in the brain. These findings may have important implications for the development of the new strategies to treat or prevent neural degeneration.

Practical aspects and mechanism of asymmetric hydrogenation with chiral half-sandwich complexes

This review is oriented toward the asymmetric transfer hydrogenation (ATH) of imines regarding mostly fundamental, yet important topics from the practical point of view. Development of analytical methods for the monitoring of ATH (i.e., kinetics and stereoselectivity) belongs to those topics, as well as studies on the influence of reaction conditions and structural variations on the reaction performance. The second part is devoted to the reaction mechanism with the emphasis on imine ATH and catalyst behaviour under acidic conditions. The review also addresses the asymmetric hydrogenation (AH) of ketones and imines using molecular hydrogen and the application of ATH in pharmaceutical projects. The contributions of our group to each area are included.

Revisiting the controversial role of salsolinol in the neurobiological effects of ethanol: old and new vistas

The possible involvement of salsolinol (Sal), an endogenous condensation product of ACD (the first metabolite of ethanol) and dopamine, in the neurochemical basis underlying ethanol action has been repeatedly suggested although it has not been unequivocally established, still being a controversial matter of debate. The main goal of this review is to evaluate the presumed contribution of Sal to ethanol effects summarizing the reported data since the discovery in the 1970s of Sal formation in vitro during ethanol metabolism until the more recent studies characterizing its behavioral and neurochemical effects. Towards this end, we first analyze the production and detection of Sal, in different brain areas, in basal conditions and after alcohol consumption, highlighting its presence in regions especially relevant in regulating ethanol-drinking behaviour and the importance of the newly developed methods to differentiate both enantiomers of Sal which could help to explain some previous negative findings. Afterwards, we review the behavioral and neurochemical studies. Finally, we present and discuss the previous and current enunciated mechanisms of action of Sal in the CNS.

Chiral capillary electrophoresis-mass spectrometry of tetrahydroisoquinoline-derived neurotoxins: observation of complex stereoisomerism

Previous studies have shown that certain 1,2,3,4-tetrahydroisoquinoline derivatives (TIQs) are neurotoxins inducing Parkinsonism. Further, individual enantiomers of these toxins such as (R/S)-N-methylsalsolinol ((R/S)-NMSal) possess distinct neurotoxicological properties. In this work, a chiral capillary electrophoresis (CE) method with electrospray ionization-tandem mass spectrometric (ESI-MS/MS) detection was developed for the quantification of TIQ enantiomers. Enantioseparation was achieved with sulfated β-cyclodextrin (sulfated β-CD) as chiral selector. To avoid any potential contamination of MS ionization source by the non-volatile chiral selector, partial filling technique was deployed in the CE separation. TIQ derivatives, including (R/S)-6,7-dihydroxy-1-methy-TIQ (salsolinol, Sal), (R/S)-1-benzyl-TIQ (BTIQ), and (R/S)-NMSal, were base-line resolved with resolution values (R) ranging from 3 (for Sal) to 4.5 (for BTIQ), which were much better than those reported previously by HPLC methods. ESI-MS/MS detection of the resolved TIQ enantiomers was specific and sensitive (LOD=1.2 μM for Sal enantiomers). The proposed chiral CE-MS/MS method was used to study in vitro formation of (R/S)-NMSal. It was found that NMSal was formed from the incubation of epinine (a dopamine metabolite) with acetaldehyde (a metabolite of alcohol). More interestingly, four isomers of NMSal were separated and detected in the incubation solution. They were identified as (R)-e.e-NMSal, (R)-e.a-NMSal, (S)-e.e-NMSal, and (S)-e.a-NMSal. This was the first lab evidence that this Parkinsonian neurotoxin exists in multiple isomeric forms.