Determination of (R)- and (S)-salsolinol sulfate and dopamine sulfate levels in plasma of nonalcoholics and alcoholics

Quantitative Determination of Endogenous Tetrahydroisoquinolines, Potential Parkinson's Disease Biomarkers, in Mammals

Current diagnostic options for Parkinson's disease are very limited and primarily based on characteristic clinical symptoms. Thus, there are urgent needs for reliable biomarkers that enable us to diagnose the disease in the early stages, differentiate it from other atypical Parkinsonian syndromes, monitor its progression, increase knowledge of its pathogenesis, and improve the development of potent therapies. A promising group of potential biomarkers are endogenous tetrahydroisoquinoline metabolites, which are thought to contribute to the multifactorial etiology of Parkinson's disease. The aim of this critical review is to highlight trends and limitations of available traditional and modern analytical techniques for sample pretreatment (extraction and derivatization procedures) and quantitative determination of tetrahydroisoquinoline derivatives in various types of mammalian fluids and tissues (urine, plasma, cerebrospinal fluid, brain tissue, liver tissue). Particular attention is paid to the most sensitive and specific analytical techniques, involving immunochemistry and gas or liquid chromatography coupled with mass spectrometric, fluorescence, or electrochemical detection. The review also includes a discussion of other relevant agents proposed and tested in Parkinson's disease.

Biomarkers of intake for tropical fruits

Consumption of fruit and vegetable is a key component of a healthy and sustainable diet. However, their accurate dietary assessment remains a challenge. Due to errors in self-reporting methods, the available dietary information is usually biased. Biomarkers of intake constitute objective tools to better reflect the usual or recent consumption of different foods, including fruits and vegetables. Partners of The Food Biomarker Alliance (FoodBall) Project have undertaken the task of reviewing the available literature on putative biomarkers of tropical fruit intake. The identified candidate biomarkers were subject to validation evaluation using eight biological and chemical criteria. This publication presents the current knowledge on intake biomarkers for 17 tropical fruits including banana, mango, and avocado as the most widely consumed ones. Candidate biomarkers were found only for banana, avocado, and watermelon. An array of banana-derived metabolites has been reported in human biofluids, among which 5-hydroxyindole-acetic acid, dopamine sulfate, methoxyeugenol glucuronide, salsolinol sulfate, 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-β-carboline-sulfate, and other catecholamine metabolites. Their validation is still at an early stage, with insufficient data on dose-response relationship. Perseitol and mannoheptulose have recently been reported as candidate biomarkers for avocado intake, while the amino acid citrulline has been associated with watermelon intake. Additionally, the examination of food composition data revealed some highly specific phytochemicals, which metabolites after absorption may be further studied as putative BFI for one or several tropical fruits. To make the field move forward, untargeted metabolomics, as a data-driven explorative approach, will have to be applied in both intervention and observational studies to discover putative BFIs, while their full validation and the establishment of dose-response calibration curves will require quantification methods at a later stage.

High-performance liquid chromatographic and subcritical fluid chromatographic separation of α-arylated ß-carboline, N-alkylated tetrahydroisoquinolines and their bioisosteres on polysaccharide-based chiral stationary phases

New, pharmacologically interesting chiral amino compounds, namely, stereoisomers of α-hydroxynaphthyl-ß-carboline, benz[d]azepine and benz[c]azepine analogs as well as N-α-hydroxynaphthylbenzyl-substituted isoquinolines were enantioseparated by high-performance liquid chromatographic and subcritical fluid chromatographic methods on polysaccharide-based chiral stationary phases. Separation of the stereoisomers was optimized in both subcritical fluid chromatography and normal phase liquid chromatographic modes by investigating the effects of the composition of the bulk solvent, temperature, and the structures of the analytes and selectors. Both normal phase liquid chromatography and subcritical fluid chromatography exhibited satisfactory performance, albeit with somewhat different effectiveness in the separation of the stereoisomers studied. The optimized methods offer the possibility to apply preparative-scale separations thereby enabling further pharmacological investigations of the enantiomers.

Acquisition, Maintenance and Relapse-Like Alcohol Drinking: Lessons from the UChB Rat Line

This review article addresses the biological factors that influence: (i) the acquisition of alcohol intake; (ii) the maintenance of chronic alcohol intake; and (iii) alcohol relapse-like drinking behavior in animals bred for their high-ethanol intake. Data from several rat strains/lines strongly suggest that catalase-mediated brain oxidation of ethanol into acetaldehyde is an absolute requirement (up 80%–95%) for rats to display ethanol’s reinforcing effects and to initiate chronic ethanol intake. Acetaldehyde binds non-enzymatically to dopamine forming salsolinol, a compound that is self-administered. In UChB rats, salsolinol: (a) generates marked sensitization to the motivational effects of ethanol; and (b) strongly promotes binge-like drinking. The specificity of salsolinol actions is shown by the finding that only the R-salsolinol enantiomer but not S-salsolinol accounted for the latter effects. Inhibition of brain acetaldehyde synthesis does not influence the maintenance of chronic ethanol intake. However, a prolonged ethanol withdrawal partly returns the requirement for acetaldehyde synthesis/levels both on chronic ethanol intake and on alcohol relapse-like drinking. Chronic ethanol intake, involving the action of lipopolysaccharide diffusing from the gut, and likely oxygen radical generated upon catechol/salsolinol oxidation, leads to oxidative stress and neuro-inflammation, known to potentiate each other. Data show that the administration of N-acetyl cysteine (NAC) a strong antioxidant inhibits chronic ethanol maintenance by 60%–70%, without inhibiting its initial intake. Intra-cerebroventricular administration of mesenchymal stem cells (MSCs), known to release anti-inflammatory cytokines, to elevate superoxide dismutase levels and to reverse ethanol-induced hippocampal injury and cognitive deficits, also inhibited chronic ethanol maintenance; further, relapse-like ethanol drinking was inhibited up to 85% for 40 days following intracerebral stem cell administration. Thus: (i) ethanol must be metabolized intracerebrally into acetaldehyde, and further into salsolinol, which appear responsible for promoting the acquisition of the early reinforcing effects of ethanol; (ii) acetaldehyde is not responsible for the maintenance of chronic ethanol intake, while other mechanisms are indicated; (iii) the systemic administration of NAC, a strong antioxidant markedly inhibits the maintenance of chronic ethanol intake; and (iv) the intra-cerebroventricular administration of anti-inflammatory and antioxidant MSCs inhibit both the maintenance of chronic ethanol intake and relapse-like drinking.

Racemic Salsolinol and its Enantiomers Act as Agonists of the μ-Opioid Receptor by Activating the Gi Protein-Adenylate Cyclase Pathway

Background: Several studies have shown that the ethanol-derived metabolite salsolinol (SAL) can activate the mesolimbic system, suggesting that SAL is the active molecule mediating the rewarding effects of ethanol. In vitro and in vivo studies suggest that SAL exerts its action on neuron excitability through a mechanism involving opioid neurotransmission. However, there is no direct pharmacologic evidence showing that SAL activates opioid receptors.

Methods: The ability of racemic (R/S)-SAL, and its stereoisomers (R)-SAL and (S)-SAL, to activate the μ-opioid receptor was tested in cell-based (light-emitting) receptor assays. To further characterizing the interaction of SAL stereoisomers with the μ-opioid receptor, a molecular docking study was performed using the crystal structure of the μ-opioid receptor.

Results: This study shows that SAL activates the μ-opioid receptor by the classical G protein-adenylate cyclase pathway with an half-maximal effective concentration (EC₅₀) of 2 × 10⁻⁵ M. The agonist action of SAL was fully blocked by the μ-opioid antagonist naltrexone. The EC₅₀ for the purified stereoisomers (R)-SAL and (S)-SAL were 6 × 10⁻⁴ M and 9 × 10⁻⁶ M respectively. It was found that the action of racemic SAL on the μ-opioid receptor did not promote the recruitment of β-arrestin. Molecular docking studies showed that the interaction of (R)- and (S)-SAL with the μ-opioid receptor is similar to that predicted for the agonist morphine.

Conclusions: It is shown that (R)-SAL and (S)-SAL are agonists of the μ-opioid receptor. (S)-SAL is a more potent agonist than the (R)-SAL stereoisomer. In silico analysis predicts a morphine-like interaction between (R)- and (S)-SAL with the μ-opioid receptor. These results suggest that an opioid action of SAL or its enantiomers is involved in the rewarding effects of ethanol.

Dual motor responses elicited by ethanol in the posterior VTA: Consequences of the blockade of μ-opioid receptors

A recent hypothesis, based on electrophysiological and behavioural findings, suggests that ethanol simultaneously exerts opposed effects on the activity of dopamine (DA) neurons in the ventral tegmental area (VTA) through two parallel mechanisms, one promoting and the other reducing the GABA release onto VTA DA neurons. In this sense, the activating effects are mediated by salsolinol, a metabolite of ethanol, acting on the μ-opioid receptors (MORs) located in VTA GABA neurons. The inhibitory effects are, however, triggered by the non-metabolized fraction of ethanol which would cause the GABAA receptors-mediated inhibition of VTA DA neurons. Since both trends tend to offset each other, only the use of appropriate pharmacological tools allows analysis of this phenomenon in depth. Herein, we present new behavioural findings supporting this hypothesis. Motor activity was evaluated in rats after intra-VTA administration of ethanol 35 nmol, an apparently ineffective dose, 24 h after the irreversible blockade of MORs in the VTA with β-FNA. Our results showed that this pre-treatment turned the initially ineffective ethanol dose into a depressant one, confirming that the activating effect of ethanol can be selectively suppressed without affecting the depressant effects mediated by the non-biotransformed fraction of ethanol.

Salsolinol modulation of dopamine neurons

Salsolinol, a tetrahydroisoquinoline present in the human and rat brains, is the condensation product of dopamine and acetaldehyde, the first metabolite of ethanol. Previous evidence obtained in vivo links salsolinol with the mesolimbic dopaminergic (DA) system: salsolinol is self-administered into the posterior of the ventral tegmental area (pVTA) of rats; intra-VTA administration of salsolinol induces a strong conditional place preference and increases dopamine release in the nucleus accumbens (NAc). However, the underlying neuronal mechanisms are unclear. Here we present an overview of some of the recent research on this topic. Electrophysiological studies reveal that DA neurons in the pVTA are a target of salsolinol. In acute brain slices from rats, salsolinol increases the excitability and accelerates the ongoing firing of dopamine neurons in the pVTA. Intriguingly, this action of salsolinol involves multiple pre- and post-synaptic mechanisms, including: (1) depolarizing dopamine neurons; (2) by activating μ opioid receptors on the GABAergic inputs to dopamine neurons – which decreases GABAergic activity – dopamine neurons are disinhibited; and (3) enhancing presynaptic glutamatergic transmission onto dopamine neurons via activation of dopamine type 1 receptors, probably situated on the glutamatergic terminals. These novel mechanisms may contribute to the rewarding/reinforcing properties of salsolinol observed in vivo.

Salsolinol facilitates glutamatergic transmission to dopamine neurons in the posterior ventral tegmental area of rats

Although in vivo evidence indicates that salsolinol, the condensation product of acetaldehyde and dopamine, has properties that may contribute to alcohol abuse, the underlying mechanisms have not been fully elucidated. We have reported previously that salsolinol stimulates dopamine neurons in the posterior ventral tegmental area (p-VTA) partly by reducing inhibitory GABAergic transmission, and that ethanol increases glutamatergic transmission to VTA-dopamine neurons via the activation of dopamine D(1) receptors (D(1)Rs). In this study, we tested the hypothesis that salsolinol stimulates dopamine neurons involving activation of D(1)Rs. By using whole-cell recordings on p-VTA-dopamine neurons in acute brain slices of rats, we found that salsolinol-induced increase in spike frequency of dopamine neurons was substantially attenuated by DL-2-amino-5-phosphono-valeric acid and 6, 7-dinitroquinoxaline-2, 3-dione, the antagonists of glutamatergic N-Methyl-D-aspartic acid and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors. Moreover, salsolinol increased the amplitude of evoked excitatory postsynaptic currents (EPSCs) and the frequency but not the amplitude of spontaneous EPSCs. Additionally, SKF83566, a D(1)R antagonist attenuated the salsolinol-induced facilitation of EPSCs and of spontaneous firing of dopamine neurons. Our data reveal that salsolinol enhances glutamatergic transmission onto dopamine neurons via activation of D(1)Rs at the glutamatergic afferents in dopamine neurons, which contributes to salsolinol's stimulating effect on p-VTA dopamine neurons. This appears to be a novel mechanism which contributes toward rewarding properties of salsolinol.

Salsolinol stimulates dopamine neurons in slices of posterior ventral tegmental area indirectly by activating μ-opioid receptors

Previous studies in vivo have shown that salsolinol, the condensation product of acetaldehyde and dopamine, has properties that may contribute to alcohol abuse. Although opioid receptors, especially the μ-opioid receptors (MORs), may be involved, the cellular mechanisms mediating the effects of salsolinol have not been fully explored. In the current study, we used whole-cell patch-clamp recordings to examine the effects of salsolinol on dopamine neurons of the ventral tegmental area (VTA) in acute brain slices from Sprague-Dawley rats. Salsolinol (0.01-1 μM) dose-dependently and reversibly increased the ongoing firing of dopamine neurons; this effect was blocked by naltrexone, an antagonist of MORs, and gabazine, an antagonist of GABA(A) receptors. We further showed that salsolinol reduced the frequency without altering the amplitude of spontaneous GABA(A) receptor-mediated inhibitory postsynaptic currents in dopamine neurons. The salsolinol-induced reduction was blocked by both naltrexone and [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin, an agonist of MORs. Thus, salsolinol excites VTA-dopamine neurons indirectly by activating MORs, which inhibit GABA neurons in the VTA. This form of disinhibition seems to be a novel mechanism underlying the effects of salsolinol.

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.

Locomotor stimulant effects of acute and repeated intrategmental injections of salsolinol in rats: role of mu-opioid receptors

RATIONALE

Microinjections of ethanol and acetaldehyde into ventral tegmental area (VTA) produce locomotor activation in rats through mechanisms dependent on the mu-opioid receptors. However, it is not clear how these drugs can interact with these receptors. It has been hypothesized that salsolinol could be the responsible for this interaction.

OBJECTIVES

The aim of the study was to investigate the ability of salsolinol to induce both motor activation and motor sensitization in rats after repeated intra-VTA administration.

MATERIALS

Rats received one microinjection into the posterior VTA of artificial cerebrospinal fluid (aCSF; 200 nL), salsolinol (0.3-3,000.0 pmol/200 nL), or salsolinol (30.0 pmol/200 nL) with either naltrexone (13.2 nmol/200 nL) or with the antagonist of the mu-opioid receptors, beta-funaltrexamine (beta-FNA; 2.5 nmol/300 nL). In the sensitization experiments, four microinjections of salsolinol (30.0 pmol/200 nL) or aCSF (200 nL) were performed over a 2-week period. This period was followed by a single challenge session, in which 0.3 pmol of salsolinol was microinjected to rats. Spontaneous activity was always monitored postinjection.

RESULTS

Intra-VTA salsolinol administration induces an increase of the spontaneous motor activity of the rats with the maximal effect at the dose of 30.0 pmol/200 nL. Salsolinol effects were blocked by the treatment with naltrexone or beta-FNA. Moreover, repeated injections of salsolinol produced locomotor sensitization.

CONCLUSIONS

Salsolinol induces locomotor activity and motor sensitization after intra-VTA administration. Moreover, the implication of the mu-opioid receptors was shown since the treatment with naltrexone or beta-FNA was able to suppress the salsolinol effects.

A critical evaluation of influence of ethanol and diet on salsolinol enantiomers in humans and rats

BACKGROUND

(R/S)-Salsolinol (SAL), a condensation product of dopamine (DA) with acetaldehyde, has been speculated to have a role in the etiology of alcoholism. Earlier studies have shown the presence of SAL in biological fluids and postmortem brains from both alcoholics and nonalcoholics. However, the involvement of SAL in alcoholism has been controversial over several decades, since the reported SAL levels and their changes after ethanol exposure were not consistent, possibly due to inadequate analytical procedures and confounding factors such as diet and genetic predisposition. Using a newly developed mass spectrometric method to analyze SAL stereoisomers, we evaluated the contribution of ethanol, diet, and genetic background to SAL levels as well as its enantiomeric distribution.

METHODS

Simultaneous measurement of SAL enantiomers and DA were achieved by high performance liquid chromatography-tandem mass spectrometry (HPLC/MS/MS). Plasma samples were collected from human subjects before and after banana (a food rich in SAL) intake, and during ethanol infusion. Rat plasma and brain samples were collected at various time points after the administration of SAL or banana by gavage. The brain parts including nucleus accumbens (NAC) and striatum (STR) were obtained from alcohol-non-preferring (NP) or alcohol-preferring (P) rats as well as P-rats which had a free access to ethanol (P-EtOH).

RESULTS

Plasma SAL levels were increased significantly after banana intake in humans. Consistently, administration of banana to rats also resulted in a drastic increase of plasma SAL levels, whereas brain SAL levels remained unaltered. Acute ethanol infusion did not change SAL levels or R/S ratio in plasma from healthy humans. The levels of both SAL isomers and DA were significantly lower in the NAC of P rats in comparison to NP rats. The SAL levels in NAC of P rats remained unchanged after chronic free-choice ethanol drinking. There were decreasing trends of SAL in STR and DA in both brain regions. No changes in enantiomeric ratio were observed after acute or chronic ethanol exposure.

CONCLUSIONS

SAL from dietary sources is the major contributor to plasma SAL levels. No significant changes of SAL plasma levels or enantiomeric distribution after acute or chronic ethanol exposure suggest that SAL may not be a biomarker for ethanol drinking. Significantly lower SAL and DA levels observed in NAC of P rats may be associated with innate alcohol preference.

Local salsolinol modulates dopamine extracellular levels from rat nucleus accumbens: shell/core differences

Salsolinol (SAL), a condensation product of dopamine and acetaldehyde that appears in the rat and human brain after ethanol ingestion, has been largely implicated in the aetiology of alcoholism. Although the behavioural consequences of systemic or intracerebral SAL administrations have been described, the neurochemical effects of pharmacologically relevant doses of SAL and other tetrahydroisoquinolines (THIQs) in the brain areas involved in alcohol addiction are practically unknown. To gain an insight into this topic, male Wistar rats were stereotaxically implanted with one concentric microdialysis probe in either the shell or the core of the nucleus accumbens (NAc). Treatments involved local administration of 0.1, 5 and 25 microM SAL for 20 min through the dialysis probe. Dopamine (DA) concentrations in the shell or core of the NAc were on-line analyzed every 20 min by HPLC with electrochemical detection. Implantation of the probe was histologically evaluated at the end of the experiments. Our results indicate that dialysis application of 5 and 25 microM SAL into the core increased the dialysate levels of DA. Conversely, the administration of the same doses of this drug into the shell significantly reduced the DA levels in this subregion. In conclusion, these data reveal that local application of SAL affects the DA levels in the NAc subterritories in a region-specific manner. These findings may prove useful in probing CNS sites and mechanisms involved in alcohol consumption.

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.

Quantitative chiral analysis of salsolinol in different brain regions of rats genetically predisposed to alcoholism

A method to determine the catecholamine content in putamen (CPU) and midbrain (MB) regions of the brain of alcohol-preferring rats (P) is presented with a focus on the low-level detection of S,R-salsolinol, a metabolite of dopamine and a putative alcoholism marker. The developed strategy allows both quantitative profiling of related catecholamines and the enantiomeric separation and quantification of the S- and R-salsolinol isomers and their ratios. The described LC/MS strategy simplifies the current methodology that typically employs GC-MS by eliminating the need for derivatization. The data also suggest an increase in the non-enzymatic formation of salsolinol as a consequence of ethanol exposure.

The reinforcing properties of salsolinol in the ventral tegmental area: evidence for regional heterogeneity and the involvement of serotonin and dopamine

BACKGROUND

Salsolinol (SAL), the condensation product of acetaldehyde and dopamine, may be a factor contributing to alcohol abuse. Previous research indicated that both ethanol and acetaldehyde are self-administered into the posterior ventral tegmental area (VTA). The current study examined SAL self-infusions into the VTA, and determined the involvement of dopamine neurons and 5-HT3 receptors in this process.

METHODS

The intracranial self-administration technique was used to determine the self-infusion of SAL into the VTA of adult, male Wistar rats. The rats were placed in 2-lever (active and inactive) experimental chambers, and allowed to respond for the self-infusion of 0, 0.03, 0.1, 0.3, 1.0 or 3.0 microM SAL into the posterior or anterior VTA. In a second experiment, rats self-administered 0.3 microM SAL for the initial 4 sessions, co-administered SAL with ICS-205,930 (a 5-HT3 receptor antagonist) or quinpirole (a D(2,3) receptor agonist) for sessions 5 and 6, and then only 0.3 microM SAL for session 7.

RESULTS

Wistar rats, given 0.03 to 0.3 microM SAL, received more infusions per session than did the group given artificial cerebrospinal fluid (aCSF) alone (e.g., 41 infusions for 0.1 microM SAL versus 9 infusions for the aCSF group), and responded more on the active than inactive lever. These effects were observed in the posterior but not in anterior VTA. Co-infusion of 100 microM ICS-205,930, or quinpirole significantly reduced self-infusions and active lever responding.

CONCLUSIONS

SAL produces reinforcing effects in the posterior VTA of Wistar rats, and these effects are mediated by activation of DA neurons and local 5-HT3 receptors.

Simultaneous determination of salsolinol enantiomers and dopamine in human plasma and cerebrospinal fluid by chemical derivatization coupled to chiral liquid chromatography/electrospray ionization-tandem mass spectrometry

A sensitive, specific, and robust method to simultaneously determine enantiomeric salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, SAL), a potential biomarker implicated in alcohol-related neurotoxicity in a stereoselective manner, and its precursor dopamine (DA) has been developed using simple chemical derivatization and chiral separation coupled with electrospray ionization-tandem mass spectrometry (ESI-MS/MS). SAL enantiomers and DA were converted to stable pentafluorobenzyl (PFB) derivatives directly from aqueous media. Bulky PFB groups introduced into the SAL structure enabled baseline separation of SAL stereoisomers on a chiral column without cumbersome chiral derivatization to unstable SAL diastereomers. Subsequent analysis by ESI-MS/MS with multiple reaction monitoring (MRM) in the presence of deuterium-labeled internal standards allowed specific detection of both derivatives with a wide dynamic range (SAL, 0.5-5000 pg; DA, 0.02-20 ng). The limit of quantitation assayed in the plasma matrix was below 10 pg for each SAL enantiomer and 100 pg for DA. Both coefficient of variance and error for inter- and intraday measurements in the blank plasma were less than 10% for SAL and DA in the concentration range of 10-4000 pg/mL and 0.1-8 ng/mL, respectively. This strategy enabled routine and specific determination of both SAL enantiomers and DA from 0.5 mL of human plasma and cerebrospinal fluid, which has not been possible using existing methodologies.

The role of acetaldehyde in the neurobehavioral effects of ethanol: A comprehensive review of animal studies

Acetaldehyde has long been suggested to be involved in a number of ethanol's pharmacological and behavioral effects, such as its reinforcing, aversive, sedative, amnesic and stimulant properties. However, the role of acetaldehyde in ethanol's effects has been an extremely controversial topic during the past two decades. Opinions ranged from those virtually denying any role for acetaldehyde in ethanol's effects to those who claimed that alcoholism is in fact "acetaldehydism". Considering the possible key role of acetaldehyde in alcohol addiction, it is critical to clarify the respective functions of acetaldehyde and ethanol molecules in the pharmacological and behavioral effects of alcohol consumption. In the present paper, we review the animal studies reporting evidence that acetaldehyde is involved in the pharmacological and behavioral effects of ethanol. A number of studies demonstrated that acetaldehyde administration induces a range of behavioral effects. Other pharmacological studies indicated that acetaldehyde might be critically involved in several effects of ethanol consumption, including its reinforcing consequences. However, conflicting evidence has also been published. Furthermore, it remains to be shown whether pharmacologically relevant concentrations of acetaldehyde are achieved in the brain after alcohol consumption in order to induce significant effects. Finally, we review current evidence about the central mechanisms of action of acetaldehyde.

Systematic Regional Study of Dopamine, Norsalsolinol, and (R/S)-Salsolinol Levels in Human Brain Areas of Alcoholics

BACKGROUND

Dopamine (DA)-derived tetrahydroisoquinolines (TIQs) are discussed as neurochemical factors of addiction processes in alcoholism. In a prospective study, the regional distribution of DA, (R)-salsolinol (SAL), and (S)-SAL, as well as norsalsolinol (NorSAL) was examined systematically in a large collective of human brain samples obtained by autopsy.

METHODS

The material comprises 44 brains of alcoholics and 47 controls with 6 standardized specimens in each case. The analytes were determined after solid-phase extraction and enantioselective derivatization using gas chromatography-mass spectrometry.

RESULTS

Levels of DA, (R/S)-SAL, and NorSAL in alcoholics did not differ significantly from those of the control group. A relationship between alcohol consumption and SAL formation could not be proved. Topical differences and no ubiquitous occurrence were encountered. Significant amounts of (R)-SAL and (S)-SAL as well as NorSAL only were found in DA-rich areas of the basal ganglia, whereas in other regions of the brain, no TIQs were detected. Especially in the nucleus caudatus, the concentrations of DA, SAL, and NorSAL decreased significantly with rising age.

CONCLUSION

These findings do not support the hypothesis that one of the SAL enantiomers or NorSAL is involved in the genesis of alcoholism. However, they suggest that the concentration of the substrate DA may determine the alkaloid level during in vivo formation. The revealed data can serve as reference for other studies in humans concerning the cause of alcoholism or other neurodegenerative diseases with the involvement of TIQs.

Comparison of column performances in direct high-performance liquid chromatographic enantioseparation of 1- or 3-methyl-substituted tetrahydroisoquinoline analogs. Application of direct and indirect methods

The enantioseparability of 1- or 3-methyl-substituted tetrahydroisoquinolines was investigated by direct and indirect high-performance liquid chromatography. Alpha- and beta-cyclodextrin-, macrocyclic glycopeptide- and cellulose-based chiral columns and isothiocyanate- and Sanger-type chiral derivatizing agents (CDAs) were applied to attain satisfactory enantioseparation. Of the chiral columns, beta-cyclodextrin-, vancomycin- and teicoplanin-containing macrocyclic glycopeptide-based columns appeared to be most suitable; of the CDAs, (1S,2R)-1-acetoxy-1-phenyl-2-propyl isothiocyanate was most favorable. The differences between the selectivities of the columns and CDAs were compared and optimized to yield the best resolution.

Salsolinol produces reinforcing effects in the nucleus accumbens shell of alcohol-preferring (P) rats

BACKGROUND

The formation of salsolinol (SAL) has been hypothesized to be a factor contributing to alcoholism and alcohol abuse. If SAL is formed under chronic alcohol-drinking conditions, then it may contribute to alcohol addiction by being rewarding itself. Because SAL can be formed by the nonenzymatic condensation of acetaldehyde with dopamine, the reinforcing effects of SAL were tested in the nucleus accumbens shell, a dopamine-rich site considered to be involved in regulating alcohol-drinking behavior.

METHODS

The intracranial self-administration technique was used to test the reinforcing properties of SAL. Adult, female alcohol-preferring (P) rats were stereotaxically implanted with guide cannulae aimed at the nucleus accumbens shell. After 7 to 10 days to allow recovery from surgery, P rats were attached to the electrolytic microinfusion transducer system, placed in two-lever experimental chambers, and allowed to respond for the self-infusion of 100 nl of modified artificial cerebrospinal fluid (aCSF) or 0.03, 0.3, 3.0, or 12.5 microM SAL (3-1250 fmol/100 nl). Sessions were 4 hr in duration and were conducted in the dark cycle every 48 hr. The effects of coinfusing 10 to 400 microM sulpiride (given in sessions 5 and 6 after four acquisition sessions) on the intracranial self-administration of 3.0 microM SAL were tested in a separate experiment.

RESULTS

P rats given 0.3 to 12.5 microM SAL received significantly more infusions per session than did the group given aCSF alone (e.g., 50 infusions for 3.0 microM SAL versus 10 or fewer infusions for the aCSF group) and responded significantly more on the active than inactive lever. Coinfusion of 100 or 400 microM sulpiride reduced the responding on the active lever (80-100 responses/session without sulpiride) to levels observed for the inactive lever (fewer than 10 responses/session with sulpiride). This effect was reversible because giving SAL alone in session 7 reinstated responding on the active lever.

CONCLUSIONS

SAL is reinforcing in the nucleus accumbens shell of P rats at concentrations that are pharmacologically possible, and these reinforcing actions are mediated in part by D2/D3-like receptors.

Chromatographic methods for the determination of markers of chronic and acute alcohol consumption

The development in chromatographic methods for the determination of markers of alcohol consumption is summarized in this review. The markers included in this article are ethanol in body fluids, ethanol congeners, fatty acid ethyl esters (FAEEs), ethyl glucuronide (EtG), cocaethylene (CE), carbohydrate-deficient transferrin (CDT), phosphatidylethanol (PEth), 5-hydroxytryptophol (5-HTOL), dolichol, ketone bodies, acetaldehyde-protein adducts, and salsolinol (SAL). Some of these markers for alcohol consumption do not only indicate previous ethanol ingestion, but also approximate the amount of intake and the time when ethanol ingestion last occurred. Basic information about the procedures, work-up, and chromatographic conditions are summarized in tables. Also the main metabolic pathways and reaction schemes are demonstrated in figures. Some examples of typical applications are presented. The author points out that in many of the reviewed papers validation data of the procedures as well as specificities and sensitivities were not clearly presented and consequently were not comparable.

Assay of salsolinol in peripheral blood mononuclear cells of alcoholics and healthy subjects by gas chromatography-mass spectrometry

Endogenous 6,7-dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline (salsolinol) could be a potential marker involved in the aetiology of alcoholism. Whereas the amount of salsolinol in plasma and urine depends on several dietary conditions, the salsolinol from peripheral mononuclear cells should be formed endogenously. Salsolinol was quantified in lymphocytes of 10 controls and 11 alcoholics (after 1 and 13 weeks of abstinence) using solid phase extraction and gas chromatography/mass spectrometry. Alcoholics showed significantly lower salsolinol concentration than the controls. After 13 weeks of abstinence a further significant decrease of SAL levels could be seen in the lymphocytes of alcoholics. The findings of this study support the theory that salsolinol might be a trait marker in alcoholism.

Iron enhancement of oxidative DNA damage and neuronal cell death induced by salsolinol

A group of naturally occurring isoquinoline alkaloids have been detected in certain regions of mammalian brain. One such compound is salsolinol (SAL; 1-methyl-6, 7-dihydroxy-1,2,3,4-tetrahydroisoquinoline). This endogenous isoquinoline derivative has been considered to be implicated in the pathophysiology of chronic alcoholism and Parkinsonism. The present study deals with the DNA strand scission induced by SAL in the presence of iron. Incubation of phiX174 DNA with SAL and ferric ion led to conversion of the supercoiled DNA to open circular and linear forms, which was inhibited by the iron chelator deferoxamine, catalase, and scavengers of reactive oxygen species. SAL in combination with Fe(III) also produced 8-hydroxydeoxyguanosine in calf thymus DNA. Exposure of PC12 cells to SAL produced concentration-dependent reduction in viability, which was exacerbated by iron and ameliorated by deferoxamine.

Enantio-selective occurrence of (S)-tetrahydropapaveroline in human brain

Tetrahydropapaveroline is an endogenous complex alkaloid derived from dopamine through the oxidation by monoamine oxidase. This alkaloid is considered to be involved in the pathogenesis of alcoholism and to act as a false neurotransmitter. Recently the (S) enantiomer was proposed to be a precursor of morphine biosynthesis in the opium poppy. In this paper stereo-chemical characteristic of tetrahydropapaveroline in human brains was examined. In all four control human brains examined, only the (S)-tetrahydropapaveroline was detected. The concentrations were 0.12-0.22 pmol/g wet weight of brain tissue, and the presence of alcohol in blood did not affect the concentration. The results suggest that (S)-tetrahydropapaveroline may be enantio-selectively synthesized in human brain and it may be an intermediate of the de novo synthesis of morphine analogues.

Quantitative determination of endogenous tetrahydroisoquinoline salsolinol in peripheral blood mononuclear cells by gas chromatography-mass spectrometry

Endogenous 1-methyl-1, 2, 3, 4-tetrahydro-6,7-dihydroxyisoquinoline (salsolinol) could be a potential marker involved in the etiology of alcoholism. The amount of salsolinol analyzed previously from plasma and urine by different methods depends on several dietary conditions because nutrition has an important influence on salsolinol excretion. Whereas plasma salsolinol is influenced by the diet the salsolinol from peripheral mononuclear cells should be endogenously formed. Therefore, a method for the quantification of S-and R-salsolinol from lymphocytes by using gas chromatography-mass spectrometry was developed. The average amount of salsolinol in 10(6) cells was 1.25 ng corresponding to 2.41 x 10(-5) M and was shown to be much higher than the plasma salsolinol concentration (2.6 x 10(-9) M).

A systematic regional study of dopamine and dopamine-derived salsolinol and norsalsolinol levels in human brain areas

Dopamine and the dopamine-derived tetrahydroisoquinoline alkaloids salsolinol and norsalsolinol were measured by high-performance liquid chromatography with electrochemical detection in 15 regions of the human brain. The regional distribution of dopamine in 32 brains was similar to previous reports with highest concentrations in the basal ganglia, especially in the striatum, followed by the substantia nigra and the hypothalamus. Significant amounts of salsolinol and norsalsolinol were only found in these dopamine-rich areas, whereas in the other regions no alkaloids were detected. These findings suggest that the concentration of the substrate dopamine may determine the alkaloid level during in vivo formation.

The quantitative determination of R- and S-salsolinol in the striatum and adrenal gland of rats selectively bred for disparate alcohol drinking

To explore the hypothesis that endogenous 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol) might be involved in the etiology of alcoholism, its concentration was determined in the striatum and adrenal gland of rats bred selectively for disparate alcohol drinking. The alcohol-naive alcohol-preferring (P) and the high-alcohol-drinking (HAD) lines of rats demonstrated significantly lower striatal and adrenal salsolinol content when compared with the alcohol-non-preferring (NP) and the low-alcohol-drinking (LAD) lines. In the P-line of rats, 4 weeks of free-choice alcohol drinking had no significant effect on striatal salsolinol levels, although adrenal levels of salsolinol were significantly higher. The salsolinol assayed in the striatum of all lines of rats occurred as a racemic mixture of enantiomers that was unchanged following 4 weeks of alcohol exposure. Unlike striatal tissue, the adrenals of alcohol naive P-rats contained significantly more S- than R-salsolinol (ratio S/R = 83/17) and alcohol consumption resulted in the formation of a nearly racemic mixture of enantiomers. These results suggest a role for genetic factors in the formation of endogenous salsolinol and its potential regulation by short-term alcohol intake.

R- and S-salsolinol are not increased in cerebrospinal fluid of Parkinsonian patients

Various investigators address an augmented synthesis of tetrahydroisoquinolines, such as salsolinol (SAL), or an increased N-methylation of these compounds as putative pathophysiologic mechanisms in Parkinson's disease (PD). Objectives of this study were (1) the evaluation of a putative elevation of enantiomers (R-, S-) of SAL and (2) the investigation of relations between these metabolic precursors of neurotoxic N-methylated-SAL (NMSAL) and dopamine in cerebrospinal fluid of untreated de-novo Parkinsonian patients and age- and sex-matched healthy controls. Levels of R- and S-SAL and dopamine did not significantly (R-SAL: P = 0.75, S-SAL: P = 0.69, dopamine: P = 0.46) differ and dopamine did not correlate to R-SAL and S-SAL in both groups. We conclude, that central accumulation of R-NMSAL, which is neurotoxic to dopaminergic nigrostriatal neurons, is not due to elevated synthesis of R-SAL and/or S-SAL in PD.

Discriminative stimulus effects of ethanol: neuropharmacological characterization

Generally, compounds discriminated by animals possess psychotropic effects in animals and humans. As with many other drugs of abuse, strength of the ethanol discriminative stimulus is dose related. The majority of studies show that doses close to 1.0 g/kg are close to the minimum at which the discrimination can be learned easily. Substitution studies suggest that anxiolytic, sedative, atactic, and myorelaxant effects of ethanol all play an important role in the formation of its intercoeptive stimulus. Low doses of ethanol produce more excitatory cues, similar to amphetamine-like subjective stimuli, whereas higher doses produce rather sedative/hypnotic stimuli similar to those elicited by barbiturates. Substitution studies have shown that the complete substitution for ethanol may be exerted by certain GABA-mimetic drugs acting through different sites within the GABA(A)-benzodiazepine receptor complex (e.g., diazepam, pentobarbital, certain neurosteroids), gamma-hydroxybutyrate, and antagonists of the glutamate NMDA receptor. Among the NMDA receptor antagonists both noncompetitive (e.g., dizocilpine) and competitive antagonists (e.g., CGP 40116) are capable of substituting for ethanol. Further, some antagonists of strychnine-insensitive glycine modulatory sites among the NMDA receptor complex (e.g., L-701,324) dose-dependently substitute for the ethanol discriminative stimulus. On the other hand, neither GABA-benzodiazepine antagonists nor NMDA receptor agonists produce contradictory effects (i.e., reduce the ethanol discriminative stimulus). There is influence of a particular training dose of ethanol on the substitution pattern of different compounds. For example, 5-HT(1B/2C) agonists substitute for intermediate (1.0 g/kg) but not higher (2.0 g/kg) ethanol training doses. Discrimination studies with ethanol and drugs acting on NMDA and GABA receptors consistently indicate asymmetrical generalization. For example, ethanol is able to generalize to barbiturates and benzodiazepines, but neither the benzodiazepine nor barbiturate response generalizes to ethanol. Only a few drugs are able to antagonize, at least to some extent, the discriminative stimulus of ethanol (e.g., partial inverse GABA-benzodiazepine receptor antagonist Ro 15-4513 and the opioid antagonist naloxone). The ethanol stimulus effect may be increased (i.e., stronger recognition) by N-cholinergic drugs (nicotine), dopaminergic drugs (apomorphine), and 5-HT3 receptor agonists (m-chlorophenylbiguanide). Thus, the ethanol stimulus is composed of the several components, with the NMDA receptor and GABA(A) receptor complex being of particular importance. This suggests that a drug mixture may be more capable of substituting for ethanol (or block its stimulus) than a single compound. The ability of drugs to substitute for the ethanol discriminative stimulus is frequently, although not preclusively, associated with the reduction of voluntary ethanol consumption. The examples of positive correlation are gamma-hydroxybutyrate, possibly memantine and certain serotonergic drugs such as fluoxetine. However, it remains uncertain to what extent the discriminative stimulus of ethanol can be seen as relevant in the understanding of the complex mechanisms of dependence.

Determination of biological markers for alcohol abuse

Alcoholism is one of the most frequent addictions and an important subject in forensic medicine and clinical toxicology. Several laboratory abnormalities are associated with excessive alcohol consumption. They are useful in the diagnosis of alcoholism especially during the follow-up of various treatment programs. The biological markers mostly used for diagnosis of alcoholism are presented. Especially, methods for the determination of the following diagnostic tools are reviewed: congener alcohols, gamma-glutamyltransferase, aspartate and alanine aminotransferase, beta-hexosaminidase, erythrocyte aldehyde dehydrogenase, alpha-amino-n-butyric acid to leucine ratio, macrocytosis, carbohydrate-deficient transferrin, (apo)lipoproteins, fatty acid ethyl esters, blood acetate, acetaldehyde adducts, 5-hydroxytryptophol, dolichol and condensation products. No laboratory test exists that is reliable enough for the exact diagnosis of alcoholism. The combination of physician interview, questionnaire and laboratory markers is necessary for the diagnosis of alcoholism.

Antisocial tendencies in alcohol-dependent men and their relation to harman, salsolinol and dopamine

Plasma dopamine, β-carbolines (norharman, harman) and isoquinolines ((R)- and (S)-salsolinol) were examined for their relationship to antisocial tendencies in 138 drinking men with an alcohol dependence syndrome according to ICD-10 criteria. Antisociality was assessed according to the following criteria: delinquency, involvement in fist-fights and homelessness. The personality structure was documented by the Tridimensional Personality Questionnaire of Cloninger. An early age of onset of alcohol dependence and a high degree of 'novelty seeking' were associated with antisocial tendencies. Of the β-carbolines and isoquinolines, harman and (S)-salsolinol were significantly decreased among antisocial alcoholics. Norharman, (R)-salsolinol and dopamine were not associated with antisocial personality. The contribution of endogenous alkaloids to the biological characterization of antisocial tendencies in alcoholics is described.

Long-term changes of markers of alcoholism after orthotopic liver transplantation (OLT)

Both physical rehabilitation and the course of the alcoholism improve after orthotopic liver transplantation (OLT) in patients with end-stage alcoholic liver cirrhosis. In the present study including 17 alcoholics and 14 nonalcoholics, after OLT, three of the alcoholic patients resumed their pre-OLT alcohol drinking habits, 4 consumed alcohol occasionally, 10 remained abstinent over the observation period of 13 to 36 months. The laboratory parameters before OLT did not discriminate alcoholics from nonalcoholic patients. Furthermore, the blood levels of two so-called alcogens (harman and norharman) were determined to investigate whether they discriminate between the two groups. Alcogens are natural compounds that are presumed to induce alcohol abuse in predisposed individuals. Both alcogens measured were elevated in plasma from nonalcoholics and alcoholics before OLT, suggesting a disturbance in inactivation in end-stage liver disease. Following OLT, the alcogens normalized but in the alcoholics this process was slower with respect to harman. The present exploratory study suggests that the normalized metabolic capacity of the liver after OLT causes a normalization of the levels of alcogens, for which harman and norharman are representative. These changes could contribute to the observed benefit to the outcome in alcoholics with respect to the alcohol dependence.

Tetrahydroisoquinolines and alcoholism: where are we today?

The present status of research on the tetrahydroisoquinoline (THIQ) family of compounds and other aldehyde metabolites in the field of alcoholism is described. A brief history of the background of experimental studies on the actions of the THIQ's and beta-carbolines on alcohol drinking is presented. A computer data base search of articles published in this field reveals that both the historical and current research trends have waxed and waned since the 1960s. The clinical utility of naltrexone in terms of the cerebral function of opioid compounds in drinking behavior and alcoholism is likewise considered. Finally, the residual controversy concerning the significance of multiple intermediary metabolites in alcohol dependence and craving should ultimately be resolved in the future by broad-based investigations which employ state-of-the-art experimental approaches.