LC-ESI-MS-MS Method for Monitoring Dopamine, Serotonin and Their Metabolites in Brain Tissue

Novel mimetic tissue standards for precise quantitative mass spectrometry imaging of drug and neurotransmitter concentrations in rat brain tissues

Understanding the relationship between the concentration of a drug and its therapeutic efficacy or side effects is crucial in drug development, especially to understand therapeutic efficacy in central nervous system drug, quantifying drug-induced site-specific changes in the levels of endogenous metabolites, such as neurotransmitters. In recent times, evaluation of quantitative distribution of drugs and endogenous metabolites using matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry imaging (MSI) has attracted much attention in drug discovery research. However, MALDI-MSI quantification (quantitative mass spectrometry imaging, QMSI) is an emerging technique, and needs to be further developed for practicable and convenient use in drug discovery research. In this study, we developed a reliable QMSI method for quantification of clozapine (antipsychotic drug) and dopamine and its metabolites in the rat brain using MALDI-MSI. An improved mimetic tissue model using powdered frozen tissue for QMSI was established as an alternative method, enabling the accurate quantification of clozapine levels in the rat brain. Furthermore, we used the improved method to evaluate drug-induced fluctuations in the concentrations of dopamine and its metabolites. This method can quantitatively evaluate drug localization in the brain and drug-induced changes in the concentration of endogenous metabolites, demonstrating the usefulness of QMSI.

The humanised CYP2C19 transgenic mouse exhibits cerebellar atrophy and movement impairment reminiscent of ataxia

AIMS

CYP2C19 transgenic mouse expresses the human CYP2C19 gene in the liver and developing brain, and it exhibits altered neurodevelopment associated with impairments in emotionality and locomotion. Because the validation of new animal models is essential for the understanding of the aetiology and pathophysiology of movement disorders, the objective was to characterise motoric phenotype in CYP2C19 transgenic mice and to investigate its validity as a new animal model of ataxia.

METHODS

The rotarod, paw-print and beam-walking tests were utilised to characterise the motoric phenotype. The volumes of 20 brain regions in CYP2C19 transgenic and wild-type mice were quantified by 9.4T gadolinium-enhanced post-mortem structural neuroimaging. Antioxidative enzymatic activity was quantified biochemically. Dopaminergic alterations were characterised by chromatographic quantification of concentrations of dopamine and its metabolites and by subsequent immunohistochemical analyses. The beam-walking test was repeated after the treatment with dopamine receptor antagonists ecopipam and raclopride.

RESULTS

CYP2C19 transgenic mice exhibit abnormal, unilateral ataxia-like gait, clasping reflex and 5.6-fold more paw-slips in the beam-walking test; the motoric phenotype was more pronounced in youth. Transgenic mice exhibited a profound reduction of 12% in cerebellar volume and a moderate reduction of 4% in hippocampal volume; both regions exhibited an increased antioxidative enzyme activity. CYP2C19 mice were hyperdopaminergic; however, the motoric impairment was not ameliorated by dopamine receptor antagonists, and there was no alteration in the number of midbrain dopaminergic neurons in CYP2C19 mice.

CONCLUSIONS

Humanised CYP2C19 transgenic mice exhibit altered gait and functional motoric impairments; this phenotype is likely caused by an aberrant cerebellar development.

Pomegranate Juice Ameliorates Dopamine Release and Behavioral Deficits in a Rat Model of Parkinson's Disease

Pomegranate juice (PJ) is a rich source of ellagitannins (ETs), precursors of colonic metabolite urolithin A, which are believed to contribute to pomegranate's neuroprotective effect. While many experimental studies involving PJ's role in Alzheimer's disease and hypoxic-ischemic brain injury have been conducted, our knowledge of pomegranate's effects against Parkinson's disease (PD) is very limited. Previously, we have reported that PJ treatment improved postural stability, which correlated well with enhancement of neuronal survival, protection against oxidative damage, and α-synuclein aggregation. Since olfactory and motor deficits are typical symptoms of PD, in this study, we aimed to investigate the capability of PJ to protect against olfactory, motoric, and neurochemical alterations. To evaluate its efficiency, Wistar rats were given a combined treatment with ROT (1.3 mg/kg b.w./day, s.c.) and PJ (500 mg/kg/day, p.o.) for 35 days. After this, we assessed the olfactory discrimination index (DI) and vertical and horizontal activities as well as levels of dopamine and its main metabolite 3,4-Dihydroxyphenylacetic acid (DOPAC) in the dissected midbrain of animals. Our findings provide the first evidence that PJ treatment protects against ROT-induced DA depletion in the midbrain, which correlates well with improved olfactory function and vertical activity as well as with the presence of urolithin A in the brain.

Effects of an environmentally relevant PFAS mixture on dopamine and steroid hormone levels in exposed mice

In the present study, we investigated the dopaminergic and steroid hormone systems of A/J mice fed environmentally relevant concentrations of a perfluoroalkyl substance (PFAS) mixture over a period of 10 weeks. The PFAS mixture was chosen based on measured PFAS concentrations in earthworms at a Norwegian skiing area (Trondheim) and consisted of eight different PFAS. Dietary exposure to PFAS led to lower total brain dopamine (DA) concentrations in male mice, as compared to control. On the transcript level, brain tyrosine hydroxylase (th) of PFAS exposed males was reduced, compared to the control group. No significant differences were observed on the transcript levels of enzymes responsible for DA metabolism, namely - monoamine oxidase (maoa and maob) and catechol-O methyltransferase (comt). We detected increased transcript level for DA receptor 2 (dr2) in PFAS exposed females, while expression of DA receptor 1 (dr1), DA transporter (dat) and vesicular monoamine transporter (vmat) were not affected by PFAS exposure. Regarding the steroid hormones, plasma and muscle testosterone (T), 11-ketotestosterone (11-KT) and 17β-estradiol (E2) levels, as well as transcripts for estrogen receptors (esr1 and esr2), gonadotropin releasing hormone (gnrh) and aromatase (cyp19) were unaltered by the PFAS treatment. These results indicate that exposure to PFAS doses, comparable to previous observation in earthworms at a Norwegian skiing area, may alter the dopaminergic system of mice with overt consequences for health, general physiology, cognitive behavior, reproduction and metabolism.

Screening of Potential Stress Biomarkers in Sweat Associated with Sports Training

BACKGROUND

Intense and continuous physical training in sports is related with psychological and physiological stress, affecting the health and well-being of athletes. The development of non-invasive sampling methodologies is essential to consider sweat as a potential biological fluid for stress biomarker assessment. In the current work, the identification in sweat samples of potential molecules that may be used as stress biomarkers was pursued.

METHODS

A sweat pool sample from football players after a 90-min intense training game was studied.

RESULTS

An analysis method using liquid chromatography with detection by tandem mass spectrometry (LC-MSMS) to attain a screening profile of sweat composition is presented. The major focus was on neurotransmitters (e.g. monoamines and metabolites) and other biological molecules related with physical training, such as precursors of biogenic amines (phenylaniline, tyrosine, etc.).

CONCLUSIONS

This study allowed the identification of small biomolecules, neurotransmitters and other related molecules in sweat that are potentially associated with stress conditions. The developed methodology intends to contribute to the assessment and study of physical and psychological stress biomarkers related with intense sports using non-invasive methods.

Pneumatically Sprayed Gold Nanoparticles for Mass Spectrometry Imaging of Neurotransmitters

Using citrate-capped gold nanoparticles (AuNPs) for laser desorption ionization mass spectrometry (LDI-MS) is an approach that has demonstrated broad applicability to ionization of different classes of molecules. Here, we show a simple AuNP-based approach for the ionization of neurotransmitters. Specifically, the detection of acetylcholine, dopamine, epinephrine, glutamine, 4-aminobutyric acid, norepinephrine, octopamine, and serotonin was achieved at physiologically relevant concentrations in serum and homogenized tissue. Additionally, pneumatic spraying of AuNPs onto tissue sections facilitated mass spectrometry imaging (MSI) of rabbit brain tissue sections, zebrafish embryos, and neuroblastoma cells for several neurotransmitters simultaneously using this quick and simple sample preparation. AuNP LDI-MS achieved mapping of neurotransmitters in fine structures of zebrafish embryos and neuroblastoma cells at a lateral spatial resolution of 5 μm. The use of AuNPs to ionize small aminergic neurotransmitters in situ provides a fast, high-spatial resolution method for simultaneous detection of a class of molecules that typically evade comprehensive detection with traditional matrixes.

Dual-retention mechanism of dopamine-related compounds on monolithic stationary phase with zwitterion functionality

Seven retention models have been selected to describe a dual-retention behavior of ten dopamine-related compounds on polymer-based monolithic stationary phase with zwitterion sulfobetaine functionality. Regression quality, as well as a statistical significance of individual regression parameters, have been evaluated. Better regression performance showed two four-parameter models when compared to three-parameter models. On the other hand, limited number of experimental points disqualified statistical robustness of four-parameter models. Among three-parameter models, retention description introduced by Horváth and Liang provided comparable quality of regression at significantly improved robustness. Multivariate analysis of the best three-parameter models provided the description of physicochemical properties of dopamine precursors and metabolites. Principal component analysis and logistic regression allowed structural characterization of dopamine-related compounds based solely on regression parameters extracted from an isocratic elution data. Both polarity and type of functional groups has been correctly assigned for 3-methoxytyramine that has not been part of an evaluation study. Among applied dual-retention models, Horváth´s model, initially developed to describe a retention of ionic compounds on nonpolar stationary phases, provided robust regression of experimental data and allowed an extraction of structural characteristics of dopamine-related compounds.

Monitoring of kynurenine pathway metabolites, neurotransmitters and their metabolites in blood plasma and brain tissue of individuals with latent toxoplasmosis

The aim of the presented work was to develop a highly sensitive, accurate and rapid analytical method for the determination of concentration levels of tryptophan and its metabolites of kynurenine catabolic pathway, as well as neurotransmitters and their metabolites in complex biological matrices (brain tissue and blood plasma). The developed analytical method consists of analytes separation from the biological matrices by protein precipitation (blood plasma) or solvent extraction (brain tissue), derivatization of the analytes and their detection by high-performance liquid chromatography combined with mass spectrometry. Individual steps of the whole process were optimized and the method was validated in the terms of selectivity, linearity (R²≥0.980), precision (RSD ≤ 13.3%), recovery (≥82.0%), limit of detection (1.8 ng/mL of blood plasma, 2.2 pg/mg of brain tissue) and limit of quantification (2.5 ng/mL of blood plasma, 2.8 pg/mg of brain tissue). The method was subsequently verified by an animal study, where the concentration levels of the analytes in biological matrices (blood plasma and brain tissue) of T. gondii - infected rats and control animals were compared. All the data obtained from the animal study were statistically evaluated. Increased concentration levels of kynurenine catabolic pathway metabolites (e.g. kynurenine, 3-hydroxykynurenine, quinolinic acid) were observed in the case of T. gondii - infected rats in contrast to the control group. The opposite effect was determined in the case of serotonin and its metabolite 5-hydroxyindoleacetic acid, where higher concentration levels were found in blood plasma of healthy subjects. Finally, Principal Component Analysis (PCA) was utilized for a score plot formation. PCA score plots have demonstrated the similarities of individuals within each group and the differences among the groups.

Sensitive determination of monoamine neurotransmitters, their main metabolites and precursor amino acids in different mouse brain components by liquid chromatography-electrospray tandem mass spectrometry after selective sample clean-up

For the assessment of diets and supplements formulated for the treatment of phenylketonuria, a highly sensitive and selective method was developed and validated for the quantification of dopamine (DA), serotonin (5-HT), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindoleacetic acid (5-HIAA), phenylalanine, tyrosine and tryptophan in mouse cerebellum, brain stem, hypothalamus, parietal cortex, anterior piriform cortex and bulbus olfactorius. Samples were extracted by deproteinization with acetonitrile, and the extracts were cleaned up by strong anion exchange and weak cation exchange applied sequentially. The substances were detected by rapid liquid chromatography tandem mass spectrometry. Matrix components were largely removed by the clean-up, resulting in low matrix effects. The lower limits of quantification for an extracted tissue mass of 100 mg were 0.3, 0.3, 0.2 and 2 ng/g for DA, 5-HT, 5-HIAA and DOPAC, respectively. The mean true extraction recoveries were 80-102%. The relative intra-laboratory reproducibility standard deviations were generally <11% at concentrations of 20-1000 ng/g for DA, 5-HT, 5-HIAA and DOPAC and 7% at concentrations of 5-50 μg/g for the amino acids. This method was successfully used in a phenylketonuria mice study including nearly 300 brain tissue samples and for small sample masses (for example, 2 mg of bulbus olfactorius).

Controlling selectivity of polymer-based monolithic stationary phases

In this work, we aimed to prepare a monolithic capillary column that allowed an isocratic separation of ten dopamine precursors and metabolites in a single run. Segments of five zwitterion sulfobetaine polymer monoliths have been modified by zwitterion phoshorylcholine by using an ultraviolet-initiated two-step photografting. Columns with 0, 33, 50, 66, and 100% of modified length were prepared. Effect of length of the modified segment and mobile phase composition has been tested. All columns provided dual-retention mechanism with reversed-phase retention in highly aqueous mobile phase and hydrophilic interaction mechanism in highly organic mobile phase. The retention mechanism was controlled by the composition of the mobile phase and has been described by a three-parameter model. We have used regression parameters to characterize the retention of analyzed compounds and to study individual pathways of dopamine metabolism. Comprehensive optimization of mobile phase composition allowed to find an optimal composition of the mobile phase and stationary phase surface chemistry arrangement to achieve desired separation. Optimized columns provided an isocratic separation of all tested compounds in less than nine min.

Neuroimmunological Implications of Subclinical Lipopolysaccharide from Salmonella Enteritidis

Mounting evidence has indicated that lipopolysaccharide (LPS) is implicated in neuroimmunological responses, but the body’s response to subclinical doses of bacterial endotoxin remains poorly understood. The influence of a low single dose of LPS from Salmonella Enteritidis, which does not result in any clinical symptoms of intoxication (subclinical lipopolysaccharide), on selected cells and signal molecules of the neuroimmune system was tested. Five juvenile crossbred female pigs were intravenously injected with LPS from S. Enteritidis (5 μg/kg body weight (b.w.)), while five pigs from the control group received sodium chloride in the same way. Our data demonstrated that subclinical LPS from S. Enteritidis increased levels of dopamine in the brain and neuropeptides such as substance P (SP), galanin (GAL), neuropeptide Y (NPY), and active intestinal peptide (VIP) in the cervical lymph nodes with serum hyperhaptoglobinaemia and reduction of plasma CD4 and CD8 T-lymphocytes seven days after lipopolysaccharide administration. CD4 and CD8 T-lymphocytes from the cervical lymph node and serum interleukin-6 and tumour necrosis factor α showed no significant differences between the control and lipopolysaccharide groups. Subclinical lipopolysaccharide from S. Enteritidis can affect cells and signal molecules of the neuroimmune system. The presence of subclinical lipopolysaccharide from S. Enteritidis is associated with unknown prolonged consequences and may require eradication and a deeper search into the asymptomatic carrier state of Salmonella spp.

Simultaneous determination of 10 kinds of biogenic amines in rat plasma using high-performance liquid chromatography coupled with fluorescence detection

We describe a simple, rapid, selective and sensitive HPLC method coupled with fluorescence detection for simultaneous determination of 10 kinds of biogenic amines (BAs: tryptamine, 2-phenethylamine, putrescine, cadaverine, histamine, 5-hydroxytryptamine, tyramine, spermidine, dopamine and spermine). BAs and IS were derivated with dansyl chloride. Fluorescence detection (λ_ex /λ_em = 340/510 nm) was used. A satisfactory result for method validation was obtained. The assay was shown to be linear over the ranges 0.005-1.0 μg/mL for tryptamine, 2-phenethylamine and spermidine, 0.025-1.0 μg/mL for putrescine, 0.001-1.0 μg/mL for cadaverine, 0.25-20 μg/mL for histamine, 0.25-10 μg/mL for 5-hydroxytryptamine and dopamine, and 0.01-1.0 μg/mL for tyramine and spermine. The limits of detection and the limits of quantification were 0.3-75.0 ng/mL and 1.0-250.0 ng/mL, respectively. Relative standard deviations were ≤5.14% for intra-day and ≤6.58% for inter-day precision. The recoveries of BAs ranged from 79.11 to 114.26% after spiking standard solutions of BAs into a sample at three levels. Seven kinds of BAs were found in rat plasma, and the mean values of tryptamine, 2-phenethylamine, putrescine, cadaverine, histamine, spermidine and spermine determined were 52.72 ± 7.34, 11.45 ± 1.56, 162.56 ± 6.26, 312.75 ± 18.11, 1306.50 ± 116.16, 273.89 ± 26.41 and 41.51 ± 2.07 ng/mL, respectively.

Elevated CYP2C19 expression is associated with depressive symptoms and hippocampal homeostasis impairment

The polymorphic CYP2C19 enzyme metabolizes psychoactive compounds and is expressed in the adult liver and fetal brain. Previously, we demonstrated that the absence of CYP2C19 is associated with lower levels of depressive symptoms in 1472 Swedes. Conversely, transgenic mice carrying the human CYP2C19 gene (2C19TG) have shown an anxious phenotype and decrease in hippocampal volume and adult neurogenesis. The aims of this study were to: (1) examine whether the 2C19TG findings could be translated to humans, (2) evaluate the usefulness of the 2C19TG strain as a tool for preclinical screening of new antidepressants and (3) provide an insight into the molecular underpinnings of the 2C19TG phenotype. In humans, we found that the absence of CYP2C19 was associated with a bilateral hippocampal volume increase in two independent healthy cohorts (N=386 and 1032) and a lower prevalence of major depressive disorder and depression severity in African-Americans (N=3848). Moreover, genetically determined high CYP2C19 enzymatic capacity was associated with higher suicidality in depressed suicide attempters (N=209). 2C19TG mice showed high stress sensitivity, impaired hippocampal Bdnf homeostasis in stress, and more despair-like behavior in the forced swim test (FST). After the treatment with citalopram and 5-HT_1A receptor agonist 8OH-DPAT, the reduction in immobility time in the FST was more pronounced in 2C19TG mice compared with WTs. Conversely, in the 2C19TG hippocampus, metabolic turnover of serotonin was reduced, whereas ERK1/2 and GSK3β phosphorylation was increased. Altogether, this study indicates that elevated CYP2C19 expression is associated with depressive symptoms, reduced hippocampal volume and impairment of hippocampal serotonin and BDNF homeostasis.

Highly sensitive isotope-dilution liquid-chromatography-electrospray ionization-tandem-mass spectrometry approach to study the drug-mediated modulation of dopamine and serotonin levels in Caenorhabditis elegans

Dopamine (DA) and serotonin (SRT) are monoamine neurotransmitters that play a key role in regulating the central and peripheral nervous system. Their impaired metabolism has been implicated in several neurological disorders, such as Parkinson's disease and depression. Consequently, it is imperative to monitor changes in levels of these low-abundant neurotransmitters and their role in mediating disease. For the first time, a rapid, specific and sensitive isotope-dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of DA and SRT in the nematode Caenorhabditis elegans (C. elegans). This model organism offers a unique approach for studying the effect of various drugs and environmental conditions on neurotransmitter levels, given by the conserved DA and SRT biology, including synaptic release, trafficking and formation. We introduce a novel sample preparation protocol incorporating the usage of sodium thiosulfate in perchloric acid as extraction medium that assures high recovery of the relatively unstable neurotransmitters monitored. Moreover, the use of both deuterated internal standards and the multiple reaction monitoring (MRM) technique allows for unequivocal quantification. Thereby, to the best of our knowledge, we achieve a detection sensitivity that clearly exceeds those of published DA and SRT quantification methods in various matrices. We are the first to show that exposure of C. elegans to the monoamine oxidase B (MAO-B) inhibitor selegiline or the catechol-O-methyltransferase (COMT) inhibitor tolcapone, in order to block DA and SRT degradation, resulted in accumulation of the respective neurotransmitter. Assessment of a behavioral output of the dopaminergic system (basal slowing response) corroborated the analytical LC-MS/MS data. Thus, utilization of the C. elegans model system in conjunction with our analytical method is well-suited to investigate drug-mediated modulation of the DA and SRT system in order to identify compounds with neuroprotective or regenerative properties.

Biochemical, histopathological and morphological profiling of a rat model of early immune stimulation: relation to psychopathology

Perinatal immune challenge leads to neurodevelopmental dysfunction, permanent immune dysregulation and abnormal behaviour, which have been shown to have translational validity to findings in human neuropsychiatric disorders (e.g. schizophrenia, mood and anxiety disorders, autism, Parkinson’s disease and Alzheimer’s disease). The aim of this animal study was to elucidate the influence of early immune stimulation triggered by systemic postnatal lipopolysaccharide administration on biochemical, histopathological and morphological measures, which may be relevant to the neurobiology of human psychopathology. In the present study of adult male Wistar rats we examined the brain and plasma levels of monoamines (dopamine, serotonin), their metabolites, the levels of the main excitatory and inhibitory neurotransmitters glutamate and γ-aminobutyric acid and the levels of tryptophan and its metabolites from the kynurenine catabolic pathway. Further, we focused on histopathological and morphological markers related to pathogenesis of brain diseases - glial cell activation, neurodegeneration, hippocampal volume reduction and dopaminergic synthesis in the substantia nigra. Our results show that early immune stimulation in adult animals alters the levels of neurotransmitters and their metabolites, activates the kynurenine pathway of tryptophan metabolism and leads to astrogliosis, hippocampal volume reduction and a decrease of tyrosine hydroxylase immunoreactivity in the substantia nigra. These findings support the crucial pathophysiological role of early immune stimulation in the above mentioned neuropsychiatric disorders.

Tissue sample preparation in bioanalytical assays

Analytical quantitation of compounds in tissue has become a more prevalent addition to biological sample analysis in recent times. This increase will most certainly continue to bring the question of proper analytical method validation to the forefront of discussion. Thoughtful design of sample homogenization, analyte fortification and extraction can ensure a successful analysis. This review presents current trends in tissue sample preparation by harvesting, homogenization techniques, as well as concerns for calibrator and QC preparation. Strategies for consideration and resolution of common pitfalls in method development, for example stability issues and control biomatrices in endogenous analysis, are also presented.