Dopamine-derived endogenous N-methyl-(R)-salsolinol: its role in Parkinson's disease

Neuroprotective Activity of Enantiomers of Salsolinol and N-Methyl-(R)-salsolinol: In Vitro and In Silico Studies

Salsolinol (1-methyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol) is a close structural analogue of dopamine with an asymmetric center at the C1 position, and its presence in vivo, both in humans and rodents, has already been proven. Yet, given the fact that salsolinol colocalizes with dopamine-rich regions and was first detected in the urine of Parkinson's disease patients, its direct role in the process of neurodegeneration has been proposed. Here, we report that R and S enantiomers of salsolinol, which we purified from commercially available racemic mixture by means of high-performance liquid chromatography, exhibited neuroprotective properties (at the concentration of 50 μM) toward the human dopaminergic SH-SY5Y neuroblastoma cell line. Furthermore, within the study, we observed no toxic effect of N-methyl-(R)-salsolinol on SH-SY5Y neuroblastoma cells up to the concentration of 750 μM, either. Additionally, our molecular docking analysis showed that enantiomers of salsolinol should exhibit a distinct ability to interact with dopamine D2 receptors. Thus, we postulate that our results highlight the need to acknowledge salsolinol as an active dopamine metabolite and to further explore the neuroregulatory role of enantiomers of salsolinol.

Purpurascenines A-C, Azepino-Indole Alkaloids from Cortinarius purpurascens: Isolation, Biosynthesis, and Activity Studies on the 5-HT2A Receptor

Three previously undescribed azepino-indole alkaloids, named purpurascenines A-C (1-3), together with the new-to-nature 7-hydroxytryptophan (4) as well as two known compounds, adenosine (5) and riboflavin (6), were isolated from fruiting bodies of Cortinarius purpurascens Fr. (Cortinariaceae). The structures of 1-3 were elucidated based on spectroscopic analyses and ECD calculations. Furthermore, the biosynthesis of purpurascenine A (1) was investigated by in vivo experiments using 13C-labeled sodium pyruvate, alanine, and sodium acetate incubated with fruiting bodies of C. purpurascens. The incorporation of 13C into 1 was analyzed using 1D NMR and HRESIMS methods. With [3-13C]-pyruvate, a dramatic enrichment of 13C was observed, and hence a biosynthetic route via a direct Pictet-Spengler reaction between α-keto acids and 7-hydroxytryptophan (4) is suggested for the biosynthesis of purpurascenines A-C (1-3). Compound 1 exhibits no antiproliferative or cytotoxic effects against human prostate (PC-3), colorectal (HCT-116), and breast (MCF-7) cancer cells. An in silico docking study confirmed the hypothesis that purpurascenine A (1) could bind to the 5-HT2A serotonin receptor's active site. A new functional 5-HT2A receptor activation assay showed no functional agonistic but some antagonistic effects of 1 against the 5-HT-dependent 5-HT2A activation and likely antagonistic effects on putative constitutive activity of the 5-HT2A receptor.

Salsolinol Protects SH-SY5Y Cells Against MPP+ Damage and Increases Enteric S100-Immunoreactivity in Wistar Rats

A dopamine derivative, 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, known as salsolinol (SAL), has increasingly gained attention since its first detection in the urine of Parkinson's disease patients treated with levodopa, and has been proposed as a possible neurotoxic contributor to the disease. Yet, so far, the neurobiological role of SAL remains unclear. Thus, the main aims of our study were to compare the neurotoxic potential of SAL with MPP⁺ (1-methyl-4-phenylpyridinium ion) in vitro, and to examine intestinal and metabolic alterations following intraperitoneal SAL administration in vivo. In vitro, SH-SY5Y neuroblastoma cell line was monitored following MPP⁺ and SAL treatment. In vivo, Wistar rats were subjected to SAL administration by either osmotic intraperitoneal mini-pumps or a single intraperitoneal injection, and after two weeks, biochemical and morphological parameters were assessed. SH-SY5Y cells treated with MPP⁺ (1000 μM) and SAL (50 µM) showed increase in cell viability and fluorescence intensity in comparison with the cells treated with MPP⁺ alone. In vivo, we predominantly observed decreased collagen content in the submucosal layer, decreased neuronal density with comparable ganglionic area in the jejunal myenteric plexus, and increased glial S100 expression in both enteric plexuses, yet with no obvious signs of inflammation. Besides, glucose and triglycerides levels were lower after single SAL-treatment (200 mg/kg), and low- to high-density lipoprotein (LDL/HDL) ratio and aspartate to alanine aminotransferases (AST/ALT) ratio levels were higher after continuous SAL-treatment (200 mg/kg in total over 2 weeks). Low doses of SAL were non-toxic and exhibited pronounced neuroprotective properties against MPP⁺ in SH-SY5Y cell line, which supports the use of SAL as a reference compound for in vitro studies. In vivo results give insight into our understanding of gastrointestinal remodeling following intraperitoneal SAL administration, and might represent morphological correlates of a microglial-related enteric neurodegeneration and dopaminergic dysregulation.

"Reframing" dopamine signaling at the intersection of glial networks in the aged Parkinsonian brain as innate Nrf2/Wnt driver: Therapeutical implications

Dopamine (DA) signaling via G protein‐coupled receptors is a multifunctional neurotransmitter and neuroendocrine–immune modulator. The DA nigrostriatal pathway, which controls the motor coordination, progressively degenerates in Parkinson's disease (PD), a most common neurodegenerative disorder (ND) characterized by a selective, age‐dependent loss of substantia nigra pars compacta (SNpc) neurons, where DA itself is a primary source of oxidative stress and mitochondrial impairment, intersecting astrocyte and microglial inflammatory networks. Importantly, glia acts as a preferential neuroendocrine–immune DA target, in turn, counter‐modulating inflammatory processes. With a major focus on DA intersection within the astrocyte–microglial inflammatory network in PD vulnerability, we herein first summarize the characteristics of DA signaling systems, the propensity of DA neurons to oxidative stress, and glial inflammatory triggers dictating the vulnerability to PD. Reciprocally, DA modulation of astrocytes and microglial reactivity, coupled to the synergic impact of gene–environment interactions, then constitute a further level of control regulating midbrain DA neuron (mDAn) survival/death. Not surprisingly, within this circuitry, DA converges to modulate nuclear factor erythroid 2‐like 2 (Nrf2), the master regulator of cellular defense against oxidative stress and inflammation, and Wingless (Wnt)/β‐catenin signaling, a key pathway for mDAn neurogenesis, neuroprotection, and immunomodulation, adding to the already complex “signaling puzzle,” a novel actor in mDAn–glial regulatory machinery. Here, we propose an autoregulatory feedback system allowing DA to act as an endogenous Nrf2/Wnt innate modulator and trace the importance of DA receptor agonists applied to the clinic as immune modifiers.

Linking Ethanol-Addictive Behaviors With Brain Catecholamines: Release Pattern Matters

Using a variety of animal models that simulate key features of the alcohol use disorder (AUD), remarkable progress has been made in identifying neurochemical targets that may contribute to the development of alcohol addiction. In this search, the dopamine (DA) and norepinephrine (NE) systems have been long thought to play a leading role in comparison with other brain systems. However, just recent development and application of optogenetic approaches into the alcohol research field provided opportunity to identify neuronal circuits and specific patterns of neurotransmission that govern the key components of ethanol-addictive behaviors. This critical review summarizes earlier findings, which initially disclosed catecholamine substrates of ethanol actions in the brain and shows how the latest methodologies help us to reveal the significance of DA and NE release changes. Specifically, we focused on recent optogenetic investigations aimed to reveal cause-effect relationships between ethanol-drinking (seeking and taking) behaviors and catecholamine dynamics in distinct brain pathways. These studies gain the knowledge that is needed for the better understanding addiction mechanisms and, therefore, for development of more effective AUD treatments. Based on the reviewed findings, new messages for researches were indicated, which may have broad applications beyond the field of alcohol addiction.

Behavioral consequences of the downstream products of ethanol metabolism involved in alcohol use disorder

Research concerning Alcohol Use Disorder (AUD) has previously focused primarily on either the behavioral or chemical consequences experienced following ethanol intake, but these areas of research have rarely been considered in tandem. Compared with other drugs of abuse, ethanol has been shown to have a unique metabolic pathway once it enters the body, which leads to the formation of downstream metabolites which can go on to form biologically active products. These metabolites can mediate a variety of behavioral responses that are commonly observed with AUD, such as ethanol intake, reinforcement, and vulnerability to relapse. The following review considers the preclinical and chemical research implicating these downstream products in AUD and proposes a chemobehavioral model of AUD.

Environmental Enrichment Attenuates Oxidative Stress and Alters Detoxifying Enzymes in an A53T α-Synuclein Transgenic Mouse Model of Parkinson's Disease

Although environmental enrichment (EE) is known to reduce oxidative stress in Parkinson’s disease (PD), the metabolic alternations for detoxifying endogenous and xenobiotic compounds according to various brain regions are not fully elucidated yet. This study aimed to further understand the role of EE on detoxifying enzymes, especially those participating in phase I of metabolism, by investigating the levels of enzymes in various brain regions such as the olfactory bulb, brain stem, frontal cortex, and striatum. Eight-month-old transgenic PD mice with the overexpression of human A53T α-synuclein and wild-type mice were randomly allocated to either standard cage condition or EE for 2 months. At 10 months of age, the expression of detoxifying enzymes was evaluated and compared with wild-type of the same age raised in standard cages. EE improved neurobehavioral outcomes such as olfactory and motor function in PD mice. EE-treated mice showed that oxidative stress was attenuated in the olfactory bulb, brain stem, and frontal cortex. EE also reduced apoptosis and induced cell proliferation in the subventricular zone of PD mice. The overexpression of detoxifying enzymes was observed in the olfactory bulb and brain stem of PD mice, which was ameliorated by EE. These findings were not apparent in the other experimental regions. These results suggest the stage of PD pathogenesis may differ according to brain region, and that EE has a protective effect on the PD pathogenesis by decreasing oxidative stress.

Organic Cation Transporters in Health and Disease

The organic cation transporters (OCTs) OCT1, OCT2, OCT3, novel OCT (OCTN)1, OCTN2, multidrug and toxin exclusion (MATE)1, and MATE kidney-specific 2 are polyspecific transporters exhibiting broadly overlapping substrate selectivities. They transport organic cations, zwitterions, and some uncharged compounds and operate as facilitated diffusion systems and/or antiporters. OCTs are critically involved in intestinal absorption, hepatic uptake, and renal excretion of hydrophilic drugs. They modulate the distribution of endogenous compounds such as thiamine, L-carnitine, and neurotransmitters. Sites of expression and functions of OCTs have important impact on energy metabolism, pharmacokinetics, and toxicity of drugs, and on drug-drug interactions. In this work, an overview about the human OCTs is presented. Functional properties of human OCTs, including identified substrates and inhibitors of the individual transporters, are described. Sites of expression are compiled, and data on regulation of OCTs are presented. In addition, genetic variations of OCTs are listed, and data on their impact on transport, drug treatment, and diseases are reported. Moreover, recent data are summarized that indicate complex drug-drug interaction at OCTs, such as allosteric high-affinity inhibition of transport and substrate dependence of inhibitor efficacies. A hypothesis about the molecular mechanism of polyspecific substrate recognition by OCTs is presented that is based on functional studies and mutagenesis experiments in OCT1 and OCT2. This hypothesis provides a framework to imagine how observed complex drug-drug interactions at OCTs arise. Finally, preclinical in vitro tests that are performed by pharmaceutical companies to identify interaction of novel drugs with OCTs are discussed. Optimized experimental procedures are proposed that allow a gapless detection of inhibitory and transported drugs.

Evidence of a Role for the TRPC Subfamily in Mediating Oxidative Stress in Parkinson's Disease

Parkinson's disease (PD) represents one of the most common multifactorial neurodegenerative disorders affecting the elderly population. It is associated with the aggregation of α-synuclein protein and the loss of dopaminergic neurons in the substantia nigra pars compacta of the brain. The disease is mainly represented by motor symptoms, such as resting tremors, postural instability, rigidity, and bradykinesia, that develop slowly over time. Parkinson's disease can also manifest as disturbances in non-motor functions. Although the pathology of PD has not yet been fully understood, it has been suggested that the disruption of the cellular redox status may contribute to cellular oxidative stress and, thus, to cell death. The generation of reactive oxygen species and reactive nitrogen intermediates, as well as the dysfunction of dopamine metabolism, play important roles in the degeneration of dopaminergic neurons. In this context, the transient receptor potential channel canonical (TRPC) sub-family plays an important role in neuronal degeneration. Additionally, PD gene products, including DJ-1, SNCA, UCH-L1, PINK-1, and Parkin, also interfere with mitochondrial function leading to reactive oxygen species production and dopaminergic neuronal vulnerability to oxidative stress. Herein, we discuss the interplay between these various biochemical and molecular events that ultimately lead to dopaminergic signaling disruption, highlighting the recently identified roles of TRPC in PD.

Salsolinol-neurotoxic or Neuroprotective?

Salsolinol (6,7-dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline), widely available in many edibles, is considered to alter the function of dopaminergic neurons in the central nervous system and thus, multiple hypotheses on its either physiological and/or pathophysiological role have emerged. The aim of our work was to revisit its potentially neurotoxic and/or neuroprotective role through a series of both in vitro and in vivo experiments. Salsolinol in the concentration range 10-250 μM did not show any significant release of lactate dehydrogenase from necrotic SH-SY5Y cells and was able in the concentration of 50 and 100 μM to rescue SH-SY5Y cells from death induced by H₂O₂. Its neuroprotective effect against neurotoxin 6-hydroxydopamine was also determined. Salsolinol was found to decrease significantly the reactive oxygen species level in SH-SY5Y cells treated by 500 μM H₂O₂ and the caspase activity induced by 300 μM of H₂O₂ or 100 μM of 6-hydroxydopamine. Serum levels of TNFα and CRP of salsolinol-treated rats were not significantly different from control animals. Both TNFα and CRP served as indirect markers of neurotoxicity and/or neuroprotection. Although the neurotoxic properties of salsolinol have numerously been emphasized, its neuroprotective properties should not be neglected and need greater consideration.

A secret that underlies Parkinson's disease: The damaging cycle

Parkinson's disease (PD) is a movement disorder, and its common characteristics include the loss of dopaminergic neurons and the accumulation of a special type of cytoplasmic inclusions called Lewy bodies in the substantia nigra pars compacta, which are more prevalent in the elderly. However, the pathophysiology of PD is still elusive. In this review, we summarized five common factors involved in PD, namely, (i) oxidative stress, (ii) mitochondrial dysfunction, (iii) inflammation, (iv) abnormal α-synuclein, and (v) endogenous neurotoxins, and proposed a hypothesis involving a damaging cycle. Oxidative stress-triggered aldehydes react with biogenic amines to produce endogenous neurotoxins. They cause mitochondrial dysfunction and the formation of inflammasomes, which induce the activation of neuroglial cells and the infiltration of T lymphocytes. The synergistic effect of these processes fosters chronic inflammation and α-synuclein aggregation and further exacerbates the impact of oxidative stress to establish a damaging cycle that eventually results in the degeneration of dopaminergic neurons. This damaging cycle provides an explanation of progressive neuronal death during the pathogenesis of PD and provides new potential targets beneficial for developing new drugs and approaches for clinical neuroprotection.

Metabolomic Responses to Manganese Dose in SH-SY5Y Human Neuroblastoma Cells

Manganese (Mn)-associated neurotoxicity has been well recognized. However, Mn is also an essential nutrient to maintain physiological function. Our previous study of human neuroblastoma SH-SY5Y cells showed that Mn treatment comparable to physiological and toxicological concentrations in human brain resulted in different mitochondrial responses, yet cellular metabolic responses associated with such different outcomes remain uncharacterized. Herein, SH-SY5Y cells were examined for metabolic responses discriminated by physiological and toxicological levels of Mn using high-resolution metabolomics (HRM). Before performing HRM, we examined Mn dose (from 0 to100 μM) and time effects on cell death. Although we did not observe any immediate cell death after 5 h exposure to any of the Mn concentrations assessed (0-100 μM), cell loss was present after a 24-h recovery period in cultures treated with Mn ≥ 50 μM. Exposure to Mn for 5 h resulted in a wide range of changes in cellular metabolism including amino acids (AA), neurotransmitters, energy, and fatty acids metabolism. Adaptive responses at 10 μM showed increases in neuroprotective AA metabolites (creatine, phosphocreatine, phosphoserine). A 5-h exposure to 100 µM Mn, a time before any cell death occurred, resulted in decreases in energy and fatty acid metabolites (hexose-1,6 bisphosphate, acyl carnitines). The results show that adjustments in AA metabolism occur in response to Mn that does not cause cell death while disruption in energy and fatty acid metabolism occur in response to Mn that results in subsequent cell death. The present study establishes utility for metabolomics analyses to discriminate adaptive and toxic molecular responses in a human in vitro cellular model that could be exploited in evaluation of Mn toxicity.

90 years of monoamine oxidase: some progress and some confusion

It would not be practical to attempt to deal with all the advances that have informed our understanding of the behavior and functions of this enzyme over the past 90 years. This account concentrates key advances that explain why the monoamine oxidases remain of pharmacological and biochemical interest and on some areas of continuing uncertainty. Some issues that remain to be understood or are in need of further clarification are highlighted.

Adaptive Modifications of Maternal Hypothalamic-Pituitary-Adrenal Axis Activity during Lactation and Salsolinol as a New Player in this Phenomenon

Both basal and stress-induced secretory activities of the hypothalamic-pituitary-adrenal (HPA) axis are distinctly modified in lactating females. On the one hand, it aims to meet the physiological demands of the mother, and on the other hand, the appropriate and stable plasma cortisol level is one of the essential factors for the proper offspring development. Specific adaptations of HPA axis activity to lactation have been extensively studied in several animal species and humans, providing interesting data on the HPA axis plasticity mechanism. However, most of the data related to this phenomenon are derived from studies in rats. The purpose of this review is to highlight these adaptations, with a particular emphasis on stress reaction and differences that occur between species. Existing data on breastfeeding women are also included in several aspects. Finally, data from the experiments in sheep are presented, indicating a new regulatory factor of the HPA axis-salsolinol-which typical role was revealed in lactation. It is suggested that this dopamine derivative is involved in both maintaining basal and suppressing stress-induced HPA axis activities in lactating dams.

Salsolinol: an Unintelligible and Double-Faced Molecule-Lessons Learned from In Vivo and In Vitro Experiments

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline) is a tetrahydroisoquinoline derivative whose presence in humans was first detected in the urine of Parkinsonian patients on l-DOPA (l-dihydroxyphenylalanine) medication. Thus far, multiple hypotheses regarding its physiological/pathophysiological roles have been proposed, especially related to Parkinson’s disease or alcohol addiction. The aim of this review was to outline studies related to salsolinol, with special focus on in vivo and in vitro experimental models. To begin with, the chemical structure of salsolinol together with its biochemical implications and the role in neurotransmission are discussed. Numerous experimental studies are summarized in tables and the most relevant ones are stressed. Finally, the ability of salsolinol to cross the blood–brain barrier and its possible double-faced neurobiological potential are reviewed.

Analysis of drug-endogenous human metabolite similarities in terms of their maximum common substructures

In previous work, we have assessed the structural similarities between marketed drugs (‘drugs’) and endogenous natural human metabolites (‘metabolites’ or ‘endogenites’), using ‘fingerprint’ methods in common use, and the Tanimoto and Tversky similarity metrics, finding that the fingerprint encoding used had a dramatic effect on the apparent similarities observed. By contrast, the maximal common substructure (MCS), when the means of determining it is fixed, is a means of determining similarities that is largely independent of the fingerprints, and also has a clear chemical meaning. We here explored the utility of the MCS and metrics derived therefrom. In many cases, a shared scaffold helps cluster drugs and endogenites, and gives insight into enzymes (in particular transporters) that they both share. Tanimoto and Tversky similarities based on the MCS tend to be smaller than those based on the MACCS fingerprint-type encoding, though the converse is also true for a significant fraction of the comparisons. While no single molecular descriptor can account for these differences, a machine learning-based analysis of the nature of the differences (MACCS_Tanimoto vs MCS_Tversky) shows that they are indeed deterministic, although the features that are used in the model to account for this vary greatly with each individual drug. The extent of its utility and interpretability vary with the drug of interest, implying that while MCS is neither ‘better’ nor ‘worse’ for every drug–endogenite comparison, it is sufficiently different to be of value. The overall conclusion is thus that the use of the MCS provides an additional and valuable strategy for understanding the structural basis for similarities between synthetic, marketed drugs and natural intermediary metabolites.

Salsolinol-a potential inhibitor of the gonadotropic axis in sheep during lactation

This study tested the hypothesis that salsolinol, a derivative of dopamine, affects GnRH and LH secretion in lactating sheep. In the in vivo experiment, the structural analogue of salsolinol, 1-methyl-3,4-dihydroisoquinoline (1-MeDIQ), was infused into the infundibular nucleus-median eminence of sheep at the fifth wk of lactation to antagonize salsolinol's action. Simultaneously, cerebrospinal fluid from the third brain ventricle, to determine GnRH concentration, and plasma samples, to measure LH concentration, were collected. In the in vitro experiment, the anterior pituitary (AP) explants from weaned sheep were incubated in culture medium containing 2 doses of salsolinol, 20 and 100 μg/mL (S20 and S100, respectively). The concentration of LH in the collected media and relative expression of LHβ subunit messenger RNA in the AP explants were determined. No significant difference was found in mean GnRH concentration in response to 1-MeDIQ infusion, but both mean plasma LH concentration and LH pulse frequency increased significantly (P < 0.001 and P < 0.05, respectively) compared with those in controls. Significantly higher LH concentrations occurred during the first (P < 0.001), second (P < 0.001), and fourth (P < 0.05) h of 1-MeDIQ infusion. In the in vitro study, both the S20 and S100 doses of salsolinol caused a significant decrease in the mean medium LH concentration compared with that in the control (P < 0.01 and P < 0.001, respectively). Salsolinol had no effect on the relative LHβ subunit messenger RNA expression in the incubated tissue. In conclusion, salsolinol is a potential inhibitor of the secretory activity of the gonadotropic axis in lactating sheep, at least at the AP level. Although no significant changes in GnRH release were directly confirmed, an increase in the frequency of LH pulses does not allow to exclude the central action of salsolinol.

Tyrosine hydroxylase (TH), its cofactor tetrahydrobiopterin (BH4), other catecholamine-related enzymes, and their human genes in relation to the drug and gene therapies of Parkinson's disease (PD): historical overview and future prospects

Tyrosine hydroxylase (TH), which was discovered at the National Institutes of Health (NIH) in 1964, is a tetrahydrobiopterin (BH4)-requiring monooxygenase that catalyzes the first and rate-limiting step in the biosynthesis of catecholamines (CAs), such as dopamine, noradrenaline, and adrenaline. Since deficiencies of dopamine and noradrenaline in the brain stem, caused by neurodegeneration of dopamine and noradrenaline neurons, are mainly related to non-motor and motor symptoms of Parkinson's disease (PD), we have studied human CA-synthesizing enzymes [TH; BH4-related enzymes, especially GTP-cyclohydrolase I (GCH1); aromatic L-amino acid decarboxylase (AADC); dopamine β-hydroxylase (DBH); and phenylethanolamine N-methyltransferase (PNMT)] and their genes in relation to PD in postmortem brains from PD patients, patients with CA-related genetic diseases, mice with genetically engineered CA neurons, and animal models of PD. We purified all human CA-synthesizing enzymes, produced their antibodies for immunohistochemistry and immunoassay, and cloned all human genes, especially the human TH gene and the human gene for GCH1, which synthesizes BH4 as a cofactor of TH. This review discusses the historical overview of TH, BH4-, and other CA-related enzymes and their genes in relation to the pathophysiology of PD, the development of drugs, such as L-DOPA, and future prospects for drug and gene therapy for PD, especially the potential of induced pluripotent stem (iPS) cells.

Oxidative modification of human ceruloplasmin induced by a catechol neurotoxin, salsolinol

Salsolinol (SAL), a compound derived from dopamine metabolism, is the most probable neurotoxin involved in the pathogenesis of Parkinson's disease (PD). In this study, we investigated the modification and inactivation of human ceruloplasmin (hCP) induced by SAL. Incubation of hCP with SAL increased the protein aggregation and enzyme inactivation in a dose-dependent manner. Reactive oxygen species scavengers and copper chelators inhibited the SAL-mediated hCP modification and inactivation. The formation of dityrosine was detected in SAL-mediated hCP aggregates. Amino acid analysis post the exposure of hCP to SAL revealed that aspartate, histidine, lysine, threonine and tyrosine residues were particularly sensitive. Since hCP is a major copper transport protein, oxidative damage of hCP by SAL may induce perturbation of the copper transport system, which subsequently leads to deleterious conditions in cells. This study of the mechanism by which ceruloplasmin is modified by salsolinol may provide an explanation for the deterioration of organs under neurodegenerative disorders such as PD.

Salsolinol Damaged Neuroblastoma SH-SY5Y Cells Induce Proliferation of Human Monocyte THP-1 Cells Through the mTOR Pathway in a Co-culture System

Despite extensive efforts to study the inflammatory process in the central nervous system of Parkinson's disease (PD) patients, little is known about the role of peripheral blood mononuclear cells (PBMCs) in PD. In the present study, we used an in vitro co-culture system to study the role of the human monocyte cell line THP-1 in medium conditioned by the neuroblastoma cell line SH-SY5Y damaged with the endogenous neurotoxin 1-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinoline (Salsolinol, Sal) in co-culture with the human glioma cell line U87. For this purpose, SH-SY5Y and U87 co-cultures were treated with Sal, and this conditioned medium containing mediators, including the potential effector CCL2, was isolated and applied to THP-1 cells. This treatment resulted in approximately 19 % cell proliferation as well as activation of mTOR and induction of phosphorylated 4E-BP1, S6K1, PI3K, and AKT proteins. Treatment with rapamycin, an mTOR inhibitor, attenuated the proliferation of THP-1 cells. U87 glial cells were essential for this as medium conditioned without them had no effect on THP-1 cells. These results suggest a positive effect of THP-1 cells on Sal-induced neurotoxicity in a cellular model of PD and this is likely mediated by the enhancement of cell proliferation through activation of the mTOR signaling pathway. Hence, PBMCs and their mTOR signaling pathway could be of therapeutic benefit in treating the endogenous neurotoxin-induced neuroinflammation in PD.

Chronic salsolinol administration prevents the behavioral and neurochemical effects of L-DOPA in rats

1-Methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol) is a well-known endogenous compound that has been proposed as a factor involved in the pathogenesis of Parkinson’s disease. In the present study, we investigated the impact of acute and chronic salsolinol (100 mg.kg i.p.) administration on l-DOPA-induced locomotor hyperactivity and neurochemical changes (the dopamine level and its metabolism in rat brain structures). Moreover, using the in vivo microdialysis technique, we measured the effect of acute and chronic salsolinol injection on l-DOPA-induced dopamine release in the rat striatum. The behavioral data demonstrated that both acute and chronic salsolinol administration antagonized l-DOPA-mediated hyperactivity. An ex vivo neurochemical experiment indicated that chronic but not acute salsolinol administration partially inhibited the l-DOPA-induced increases in the concentration of dopamine and all of its metabolites in dopaminergic structures. Additionally, the in vivo dopamine release data obtained from the microdialysis experiments clearly indicated that the differences in the effect of salsolinol on the activities of l-DOPA depended on the mode of salsolinol treatment. Acute injection of salsolinol enhanced the l-DOPA-induced elevation of dopamine release (by ~1200 %; P < 0.01), whereas chronic administration of salsolinol completely blocked the l-DOPA-induced elevation of dopamine release in the rat striatum. These data demonstrated that chronic administration of salsolinol significantly impaired the response of dopaminergic neurons to l-DOPA administration. In conclusion, we propose that an elevated salsolinol level in parkinsonian patients may represent a serious risk factor of the clinical efficacy of l-DOPA therapy.

Parkinson's disease: dopaminergic nerve cell model is consistent with experimental finding of increased extracellular transport of α-synuclein

Background

Parkinson’s disease is an age-related disease whose pathogenesis is not completely known. Animal models exist for investigating the disease but not all results can be easily transferred to humans. Therefore, mathematical or probabilistic models for the human disease are to be constructed in silico in order to predict specific processes within a cell, such as the dopamine metabolism and transport processes in a neuron.

Results

We present a Systems Biology Markup Language (SBML) model of a whole dopaminergic nerve cell consisting of 139 reactions and 111 metabolites which includes, among others, the dopamine metabolism and transport, oxidative stress, aggregation of α-synuclein (αSYN), lysosomal and proteasomal degradation, and mitophagy. The predictive power of the model was investigated using flux balance analysis for the identification of steady model states. To this end, we performed six experiments: (i) investigation of the normal cell behavior, (ii) increase of O₂, (iii) increase of ATP, (iv) influence of neurotoxins, (v) increase of αSYN in the cell, and (vi) increase of dopamine synthesis. The SBML model is available in the BioModels database with identifier MODEL1302200000.

Conclusion

It is possible to simulate the normal behavior of an in vivo nerve cell with the developed model. We show that the model is sensitive for neurotoxins and oxidative stress. Further, an increased level of αSYN induces apoptosis and an increased flux of αSYN to the extracellular space was observed.

Alpha-synuclein overexpression induced mitochondrial damage by the generation of endogenous neurotoxins in PC12 cells

Alpha-synuclein is one of the important components of Lewy body which involved in neuropathology of Parkinson's disease (PD). The relationship between α-synuclein and cell death is still unclear. In the study, PC12 cell, stably over expressing α-synuclein model was used, and we investigated the level of intracellular oxidative stress, dopamine and endogenous neurotoxin. The results showed that the level of oxidative stress and intracytoplasmic dopamine (DA) was increased in cells over expressing α-synuclein compared with normal PC12 cells. Simultaneously, additional generation of endogenous neurotoxins 1-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinoline (salsolinol) and 1(R),2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolin (NM-salsolinol) was detected and this phenomenon was exacerbated after exposed to H₂O₂ for 24 h, but mitigated when treated with dopamine synthesis inhibitors. The presence of endogenous neurotoxins exacerbated α-synuclein induced mitochondrial damage. These results suggest that the endogenous neurotoxins may become a bridge between α-synuclein and cell death.

Salsolinol induced apoptotic changes in neural stem cells: amelioration by neurotrophin support

Salsolinol (SAL), a catechol isoquinoline has invited considerable attention due to its structural similarity with dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Its high endogenous presence in Parkinsonian brain implicated its possible association with the disease process. SAL is also present in alcohol beverages and certain food materials and can get access to brain especially in conditions of immature or impaired BBB. Besides this, the effect of SAL on neural stem cells (NSCs) which are potential candidates for adult neurogenesis and transplantation mediated rejuvenating attempts for Parkinson's disease (PD) brain has not been known so far. NSCs in both the cases have to overcome suppressive cues of diseased brain for their survival and function. In this study we explored the toxicity of SAL toward NSCs focusing on apoptosis and status of PI3K survival signaling. NSCs cultured from embryonic day 11 rat fetal brain including those differentiated to TH(+ve) colonies, when challenged with SAL (1-100μM), elicited a concentration and time dependent cell death/loss of mitochondrial viability. 10μM SAL on which significant mitochondrial impairment initiated was further used to study mechanism of toxicity. Morphological impairment, enhanced TUNEL positivity, cleaved caspase-3 and decreased Bcl-2:Bax suggested apoptosis. Sal toxicity coincided with reduced pAkt level and its downstream effectors: pCREB, pGSK-3β, Bcl-2 and neurotrophins GDNF, BDNF suggesting repressed PI3K/Akt signaling. Multiple neurotrophic factor support in the form of Olfactory Ensheathing Cell's Conditioned Media (OEC CM) potentially protected NSCs against SAL through activating PI3K/Akt pathway. This was confirmed on adding LY294002 the PI3K inhibitor which abolished the protection. We inferred that SAL exerts substantial toxicity toward NSCs. These findings will lead to better understanding of endogenous threats that might affect the fate of transplanted NSCs and their probable antidotes.

Increased vulnerability of parkin knock down PC12 cells to hydrogen peroxide toxicity: the role of salsolinol and NM-salsolinol

Dopamine-derived neurotoxins, 1-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinoline (salsolinol) and 1(R),2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (NM-salsolinol) are the two most possible 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-like endogenous neurotoxin candidates that involved in the pathogenesis of Parkinson's disease (PD). The levels of endogenously synthesized salsolinol and NM-salsolinol are increased in the cerebrospinal fluid (CSF) of PD patients. Both of them lead to neurotoxicity in dopaminergic cells by inhibiting mitochondrial electron transport chain. To study the role of salsolinol and NM-salsolinol in Parkin deficiency-induced dopaminergic cell damage, we determined the cellular level of oxidative stress, the formation of salsolinol and NM-salsolinol, the level of mitochondrial damage and cell viability with/without the presence of exogenous H₂O₂ using differentiated dopaminergic PC12 cells. Our data show that parkin knock down elevates cellular oxidative stress, salsolinol and NM-salsolinol levels, which are responsible for the higher cell mortality in Parkin-deficient cells upon exposure to exogenous H₂O₂. The level of mitochondrial membrane potential loss, cristae disruption and the release of cytochrome c increased significantly along with the increased level of salsolinol and NM-salsolinol, whereas compared to parkin knock down cells in the presence of H₂O₂, the mitochondrial damage and higher cell mortality were both diminished when the levels of salsolinol and NM-salsolinol was reduced. The results not only indicate the elevated level of salsolinol and NM-salsolinol, but also reveal the potential role of salsolinol and NM-salsolinol in parkin knock down-induced cell vulnerability. We assume that parkin deficiency is the trigger of excessive oxidative stress, elevated endogenous neurotoxin levels and mitochondrial damage, which eventually results in cell death of dopaminergic cells.

A guide to neurotoxic animal models of Parkinson's disease

Parkinson's disease (PD) is a neurological movement disorder primarily resulting from damage to the nigrostriatal dopaminergic pathway. To elucidate the pathogenesis, mechanisms of cell death, and to evaluate therapeutic strategies for PD, numerous animal models have been developed. Understanding the strengths and limitations of these models can significantly impact the choice of model, experimental design, and data interpretation. The primary objectives of this article are twofold: First, to assist new investigators who are contemplating embarking on PD research to navigate through the available animal models. Emphasis will be placed on common neurotoxic murine models in which toxic molecules are used to lesion the nigrostriatal dopaminergic system. And second, to provide an overview of basic technical requirements for assessing the pathology, structure, and function of the nigrostriatal pathway.

The possible involvement of salsolinol and hypothalamic prolactin in the central regulatory processes in ewes during lactation

Salsolinol, a dopamine-related compound and prolactin-producing cells were found in the ovine hypothalamus. This study was designed to test the hypothesis that salsolinol, acting from the CNS level, is able to stimulate pituitary prolactin release as well as prolactin mRNA expression in the anterior pituitary cells (AP) and in the mediobasal hypothalamus (MBH) in lactating ewes. The intracerebroventricular infusions of salsolinol in two doses, total of 50 ng or 5 μg, were performed in a series of five 10-min infusions at 20-min intervals. All infusions were made from 12:30 to 15:00 and the pre-infusion period was from 10:00 to 12.30 h. The prolactin concentration in plasma samples, collected every 10 min, was determined by radioimmunoassay; prolactin mRNA expression in AP and MBH tissues was determined by real-time PCR. The obtained results showed that salsolinol infused at the higher dose significantly (p < 0.001) increased plasma prolactin concentration in lactating ewes, when compared with the concentration noted before the infusion and with that in lactating controls. In lactating ewes, the relative levels of prolactin mRNA expression in the AP and MBH were up to twofold and fivefold higher respectively than in non-lactating ewes (p < 0.05). In our experimental design, salsolinol did not significantly affect the ongoing process of prolactin gene expression in these tissues. We conclude that in ewes, salsolinol may be involved, at least, in the process of stimulation of prolactin release during lactation and that hypothalamic prolactin plays an important role in the central mechanisms of adaptation to lactation.

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.

L-DOPA: a scapegoat for accelerated neurodegeneration in Parkinson's disease?

There is consensus that amelioration of the motor symptoms of Parkinson's disease is most effective with L-DOPA (levodopa). However, this necessary therapeutic step is biased by an enduring belief that L-DOPA is toxic to the remaining substantia nigra dopaminergic neurons by itself, or by specific metabolites such as dopamine. The concept of L-DOPA toxicity originated from pre-clinical studies conducted mainly in cell culture, demonstrating that L-DOPA or its derivatives damage dopaminergic neurons due to oxidative stress and other mechanisms. However, the in vitro data remain controversial as some studies showed neuroprotective, rather than toxic action of the drug. The relevance of this debate needs to be considered in the context of the studies conducted on animals and in clinical trials that do not provide convincing evidence for L-DOPA toxicity in vivo. This review presents the current views on the pathophysiology of Parkinson's disease, focusing on mitochondrial dysfunction and oxidative/proteolytic stress, the factors that can be affected by L-DOPA or its metabolites. We then critically discuss the evidence supporting the two opposing views on the effects of L-DOPA in vitro, as well as the animal and human data. We also address the problem of inadequate experimental models used in these studies. L-DOPA remains the symptomatic 'hero' of Parkinson's disease. Whether it contributes to degeneration of nigral dopaminergic neurons, or is a 'scapegoat' for explaining undesirable or unexpected effects of the treatment, remains a hotly debated topic.

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.

Assessment of salsolinol N-methyltransferase activity in rat peripheral lymphocytes by liquid chromatography-electrospray time-of-flight mass spectrometry

Salsolinol N-methyltranseferase (SNMT), which may play a crucial role in the pathogenesis of Parkinson's diseases (PD), is a key enzyme to metabolize salsolinol into N-methylsalsolinol that is a neurotoxin specific to dopaminergic neurons. A sensitive method for the quantitative determination of SNMT activity in rat peripheral lymphocytes was developed and validated using liquid chromatography-electrospray with time-of-flight mass spectrometry (LC-ESI-TOF). The calibration curve was linear over the range of 7.40-368.80 nM, with 7.40 nM of the lower limit of quantification. The inter-day and intra-day precisions and accuracy for all samples were acceptable. The validated method was successfully applied for the determination of SNMT activity in both the substantia nigra (SN) and peripheral lymphocytes of a unilateral 6-hydroxydopamine-lesion model of Parkinson's disease in rats. The SNMT activity in the peripheral lymphocytes treated with the 6-hydroxydopamine was significantly increased compared with the control and sham-operated groups, which was coincident with the alteration of SNMT activity in the SN. Our results might indicate that SNMT activity may become a potential clinical marker for PD.

Determination of salsolinol, norsalsolinol, and twenty-one biogenic amines using micellar electrokinetic capillary chromatography-electrochemical detection

Micellar electrokinetic chromatography coupled to amperometric electrochemical detection was used to resolve and then quantify biogenic amines and metabolites within the fruit fly Drosophila melanogaster. A new separation scheme was devised to allow resolution of 24 compounds of interest. This was accomplished by precisely controlling the amount of base added to the background buffer, optimizing the resolution of the separation, and then calculating the pH. Here we focused on measurements of six of the analytes that are thought to be involved in the response to alcohol, dopamine, salsolinol, norsalsolinol, N-acetyloctopamine, octopamine, and N-acetyldopamine. These were identified and quantified within the fly head. We believe that the identification of salsolinol and norsalsolinol in the fly brain is novel.

Fast liquid chromatography separation and multiple-reaction monitoring mass spectrometric detection of neurotransmitters

We describe here the fast LC-MS/MS separation of a mixture of neurotransmitters consisting of dopamine, epinephrine, norepinephrine, 3,4-dihydroxybenzylamine (DHBA), salsolinol, serotonin, and gamma-aminobutyric acid (GABA). The new UltiMate 3000 Rapid Separation system (RSLC) was successfully coupled to the 4000 QTRAP mass spectrometer operating in multiple-reaction monitoring (MRM) mode. The separation was attained using a 100 mm length, 2.2 microm particle size Acclaim column at a flow rate of 0.5 mL/min. The column back pressure was 350 bar, while the total run time including column re-equilibration was 5.2 min. The peak resolution was minimally affected by the fast separation. The RSLC-MRM separation was found to have a precision range based on peak area for 50 replicate runs of 2-5% CV for all analytes, and the reproducibility of the retention time for all analytes was found to range from 0-2% CV. The described method represents an almost seven times shorter analysis time of neurotransmitters using LC/MRM which is very useful in screening large quantities of biological samples for various neurotransmitters.

Different mechanisms of NMDA-mediated protection against neuronal apoptosis: a stimuli-dependent effect

The mechanisms of protective effect of N-methyl-D-aspartate (NMDA) receptor stimulation on apoptosis of neurons at their early stage of development are poorly understood. In the present study, we investigated the effects of NMDA on staurosporine (St)- and low-potassium (LP)-evoked apoptotic cell death in primary cerebellar granule cell (CGC) cultures at 7 days in vitro (DIV). We found that NMDA (200 microM) attenuated the St (0.5 microM)- and LP (5 mM KCl)-induced neuronal cell death in 7 but not 12 DIV CGC as confirmed by LDH release and MTT reduction assays. Moreover, NMDA attenuated St-and LP-evoked DNA fragmentation and cytosolic apoptosis inducing factor (AIF) protein level but not caspase-3 activation induced by both pro-apoptotic factors. Neuroprotective effects of NMDA on St-induced apoptosis in CGC were attenuated by inhibitors of ERK/MAPK-signaling, PD 98059 and U0126 but not by NMDA receptor antagonists, AP-5 (100 microM) and MK-801 (1 microM) or by inhibitors of PI3-K/Akt pathway (LY 294002 and wortmannin). In contrast to staurosporine model of apoptosis, AP-5 and MK-801 but not inhibitors of PI3-K/Akt and MAPK/ERK1/2 prevented the NMDA-mediated neuroprotection in LP-induced apoptosis of CGC. In separate experiments, we observed also the anti-apoptotic action of NMDA on St (0.5 microM)- and salsolinol (250 microM)-evoked cell death in human neuroblastoma SH-SY5Y cells without its influence on caspase-3 activity, induced by these pro-apoptotic factors. These data indicate that neuroprotection evoked by NMDA in CGC strongly depends on used pro-apoptotic agent and could engage NMDA channel function or be connected with the activation of pro-survival MAPK/ERK1/2 pathway. It is also suggested that anti-apoptotic effects of NMDA is connected with inhibition of fragmentation of DNA via caspase-3-independent mechanism.

Computational Modeling of Inclusion Complexes of β-Cyclodextrin with enantiomers of Salsolinol, N-Methyl-Salsolinol, and 1-Benzyl-Tetrahydroisoquinoline

Capillary electrophoresis with β-CD as a chiral selector has successfully separated the two enantiomers of salsolinol, N-methyl-salsolinol, and 1-benzyl-tetrahydroisoquinoline. The migration times of each enantiomer in capillary electrophoresis reflect the stability of their β-CD inclusion complexes. This paper reports a computational modeling study of the inclusion complexes of β-cyclodextrin (β-CD) with salsolinol, N-methyl-salsolinol, and 1-benzyl-tetrahydroisoquinoline by using PM3 (Parametric Method 3) semi-empirical molecular orbital calculations and the ONIOM hybrid method. Two types of the inclusion complexes, cis- and trans-orientations, are considered for each enantiomer of the guest molecules, salsolinol, N-methyl-salsolinol, and 1-benzyl-tetrahydroisoquinoline. In the cis-orientation, the nitrogen in the salsolinol, N-methyl-salsolinol, and 1-benzyl-tetrahydroisoquinoline points toward the secondary hydroxyls of the β-CD, while in the trans-orientation, the nitrogen in salsolinol, N-methyl-salsolinol, and 1-benzyl-tetrahydroisoquinoline points toward the primary hydroxyls of the β-CD. We found that the stabilization energies of these inclusion complexes from these PM3 and ONIOM different methods correlate very well with the migration order deduced from the study of capillary electrophoretic separation.

Regional distribution of tetrahydroisoquinoline derivatives in rodent, human, and Parkinson's disease brain

Several members of the tetrahydroisoquinoline (TIQ) family of monoamine alkaloids can be formed from dopamine or its oxidized metabolites and may be involved in the pathogenesis of monoaminergic cell death in Parkinson's disease (PD). Using enantiomeric-selective high-performance liquid chromatography with electrochemical detection and liquid chromatography with tandem mass spectroscopy, the regional concentrations of several TIQ derivatives, including salsolinols, were determined in mouse, rat, normal human, and PD brain. TIQ derivatives were detected in all regions subjected to analysis. In general, salsolinols were present at higher concentrations than TIQ and its benzyl and methyl derivatives, especially in human brain. Moreover, salsolinols were concentrated in areas with increased dopamine synthesis and turnover such as the ventral midbrain and striatum, respectively. A possible consequence of nigrostriatal dopaminergic cell death, significantly lower levels of (R)salsolinol, (S)salsolinol, N-methyl-(R)salsolinol and N-methyl-(S)salsolinol were found in the caudate nuclei of PD in comparison with normal human brain. Our data support the hypothesis of endogenous synthesis of salsolinols and provide evidence for their accumulation in catecholaminergic neurons.

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

Salsolinol, 1-methyl-6,7-dihydroxy-2,3,4,5-tetrahydroisoquinoline (SAL), is a precursor of a Parkinsonian neurotoxin, N-methysalsolinol (N-methyl-SAL). Previous studies have shown that individual enantiomers of N-methyl-SAL possess distinct neurotoxicological properties. In this work, a chiral high-performance liquid chromatography (HPLC) method with electrospray ionization tandem mass spectrometric (ESI-MS/MS) detection was developed for the quantification of (R/S)-SAL enantiomers. Enantioseparation was achieved on a beta-cyclodextrin-bonded silica gel column, and the resolved enantiomers were detected by ESI-MS/MS operated in positive ion mode. The ESI collision-induced dissociation (CID) mass spectrum of SAL was studied together with that of its deuterium-labeled analog (i.e. salsolinol-alpha,alpha,alpha,1-d(4), SAL-d(4)) so that the fragmentation pathways could be elucidated. Further, using SAL-d(4) as internal standard in HPLC/MS/MS analysis of SAL improved significantly assay accuracy and reliability. Determination of (R/S)-SAL enantiomers present in food samples such as dried banana chips was demonstrated.

Iron contributes to the formation of catechol isoquinolines and oxidative toxicity induced by overdose dopamine in dopaminergic SH-SY5Y cells

OBJECTIVE

The selective loss of dopaminergic neurons in Parkinson's disease is suspected to correlate with the increase of cellular iron, which may be involved in the pathogenesis of PD by promotion of oxidative stress. This research investigated dopamine-induced oxidative stress toxicity contributed by iron and the production of dopamine-derived neurotoxins in dopaminergic SH-SY5Y cells.

METHODS

After the SH-SY5Y cells were pre-incubated with dopamine and Fe2+ for 24 h, the cell viability, hydroxyl radical, melondialdehyde, cell apoptosis, and catechol isoquinolines were measured by lactate dehydrogenase assay, salicylic acid trapping method, thiobarbuteric acid assay, Hoechst 33258 staining and HPLC-electrochemical detection (HPLC-ECD), respectively.

RESULTS

(1) Optimal dopamine (150 micromol/L) and Fe2+ (40 or 80 micromol/L) significantly increased the concentrations of hydroxy radicals and melondialdehyde in SH-SY5Y cells. (2) Induction with dopamine alone or dopamine and Fe2+ (dopamine/Fe2+) caused cell apoptosis. (3) Compared with untreated cells, the catechol isoquinolines, salsolinol and N-methyl-salsolinol in dopamine/Fe2+-induced cells were detected in increasing amounts.

CONCLUSION

Due to dopamine/Fe2+-induced oxidative stress similar to the state in the parkinsonian substantia nigra neurons, dopamine and Fe2+ impaired SH-SY5Y cells could be used as the cell oxidative stress model of Parkinson's disease. The catechol isoquinolines detected in cells may be involved in the pathogenesis of Parkinson's disease as potential neurotoxins.