Quantification of the neurotransmitters melatonin and N-acetyl-serotonin in human serum by supercritical fluid chromatography coupled with tandem mass spectrometry

Matrix effect in bioanalytical assay development using supercritical fluid chromatography-mass spectrometry

Matrix effect (ME) is commonly caused by coelution of compounds with target analytes, resulting in either suppression or enhancement of analyte ionization. Thus, to achieve the desired accuracy, precision, and sensitivity, ME needs to be evaluated and controlled during bioanalytical method development. As the application of supercritical fluid chromatography-mass spectrometry (SFC-MS) for analysis of biological samples has increased, ME using SFC-MS has also been investigated with a focus on the difference in ME in SFC-MS compared to other chromatographic techniques used for achiral separation in biological samples. Here, we provide a summary of the status of ME evaluation and mitigation in SFC-MS methods. This review presents an overview of the phenomenon of ME and methods for evaluating ME in bioanalysis. Next, the factors that can impact ME in SFC-MS-based bioanalytical methods are discussed in detail with an emphasis on SFC. A literature review of the evaluation of ME in targeted bioanalytical methods using SFC-MS is included at the end. Robust instrumentation, effective sample preparation, and superb separation selectivity are the foundations of reliable analytical methods as well as the ability to mitigate detrimental ME in SFC-MS methods.

Melatonin in different food samples: Recent update on distribution, bioactivities, pretreatment and analysis techniques

Melatonin (MLT) plays a significant role on maintaining the basic physiological functions and regulating various metabolic processes in plentiful organisms. Recent years have witnessed an increase in MLT's share in global market with its affluent functions. However, the worrisome quality issues and inappropriate or excessive application of MLT take place inevitably. In addition, its photosensitive properties, oxidation, complex substrate concentration and trace levels leave exact detection of MLT doubly difficult. Therefore, it is essential to exploit precise, sensitive and stable extraction and detection methods to resolve above questions. In this study, we reviewed the distribution and bioactivities of MLT and conducted a comprehensive overview of the developments of pretreatment and analysis methods for MLT in food samples since 2010. Commonly used pretreatment methods for MLT include not only traditional techniques, but also novel ones, such as solid-phase extraction, QuEChERS, microextraction by packed sorbent, solid phase microextraction, liquid phase microextraction, and so on. Analysis methods include liquid chromatography coupled with different detectors, GC methods, capillary electrophoresis, sensors, and so on. The advantages and disadvantages of different techniques have been compared and the development tendency was prospected.

Design and Fabrication of α-MnO2-Nanorods-Modified Glassy-Carbon-Electrode-Based Serotonin Sensor

Serotonin is a very important monoamine neurotransmitter, which takes part in biological and psychological processes. In the present scenario, design and fabrication of a serotonin electrochemical sensor is of great significance. In this study, we have synthesized α-MnO₂ via a hydrothermal synthesis method using potassium permanganate as a precursor. The physiochemical properties, such as structural and phase-purity of the prepared α-MnO₂, were investigated by various characterization techniques and methods (powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy). Furthermore, the serotonin sensor was fabricated using α-MnO₂ as an electrode modifier or electro-catalyst. The bare glassy carbon electrode (GCE) was adopted as a working substrate, and its active carbon surface was modified with the synthesized α-MnO₂. This modified GCE (α-MnO₂/GCE = MGCE) was explored as a serotonin sensor. The electrochemical investigations showed that the MGCE has excellent electro-catalytic properties towards determination of serotonin. The MGCE exhibits an excellent detection limit (DL) of 0.14 µM, along with good sensitivity of 2.41 µAµM^-1 cm^-2. The MGCE also demonstrated excellent selectivity for determination of serotonin in the presence of various electro-active/interfering molecules. The MGCE also exhibits good cyclic repeatability, stability, and storage stability.

Real-time monitoring of 5-HT release from cells based on MXene hybrid single-walled carbon nanotubes modified electrode

Serotonin (5-HT) is an essential inhibitory neurotransmitter in vivo that is critical for interneuronal communication of the nervous system. Herein, we constructed an electrochemical cell-sensing platform for 5-HT detection based on MXene/single-walled carbon nanotubes (SWCNTs) nanocomposite. The one-dimensional SWCNTs with good electrical conductivity are uniformly dispersed on the surface and intermediate layers of the two-dimensional MXene to form a tightly heterogeneous heterostructure. The synthesized MXene-SWCNTs could improve the stacking problem of MXene nanosheets and expose more active sites, effectively promoting the conductive properties and electrochemical activity of the composite. The fabricated MXene-SWCNTs/GCE possessed outstanding detection capability for 5-HT with a wide linear range of 4 nM-103.2 μM and a low detection limit of 1.5 nM. Moreover, the sensor was further applied for the real-time monitoring trace amount of 5-HT releasing from different cell lines, which confirmed its promising applications in 5-HT related physiological and pathological fields. MXene-SWCNTs/GCE was developed and applied for the real-time monitoring of trace amounts of 5-HT secreted from living cells.

Downregulation of AANAT by c-Fos in tubular epithelial cells with membranous nephropathy

Melatonin is a hormone majorly secreted by the pineal gland and contributes to a various type of physiological functions in mammals. The melatonin production is tightly limited to the AANAT level, yet the most known molecular mechanisms underlying AANAT gene transcription is limited in the pinealocyte. Here, we find that c-Fos and cAMP-response element-binding protein (CREB) decreases and increases the AANAT transcriptional activity in renal tubular epithelial cell, respectively. Notably, c-Fos knockdown significantly upregulates melatonin levels in renal tubular cells. Functional results indicate that AANAT expression is decreased by c-Fos and resulted in enhancement of cell damage in albumin-injury cell model. We further find an inverse correlation between c-Fos and AANAT levels in renal tubular cells from experimental membranous nephropathy (MN) samples and clinical MN specimens. Our finding provides the molecular basis of c-Fos in transcriptionally downregulating expression of AANAT and melatonin, and elucidate the protective role of AANAT in preventing renal tubular cells death in albumin-injury cell model and MN progression.

A technical overview of supercritical fluid chromatography-mass spectrometry (SFC-MS) and its recent applications in pharmaceutical research and development

In this paper, we review the growing development and applications of supercritical fluid chromatography-mass spectrometry (SFC-MS) for the analysis of small molecular analytes and biomarkers in drug discovery. As an alternative chromatographic technique, SFC instrumentation and methodology have dramatically advanced over the last decade. Mass spectrometry (MS) provides the powerful detection capability as it couples with SFC. A growing number of SFC-MS/MS applications were reported over the last decade and the application areas of SFC-MS/MS is rapidly expanding. The first part of this review is devoted to the different aspects of SFC-MS development and recent technological advancements. In the second part of this review, we highlight the recent application areas in pharmaceutical research and development.

Up-to-date studies regarding the determination of melatonin by chromatographic methods

Melatonin is an indolic compound that has been reported in the literature to exist in human-based samples, vertebrates, vegetables, fruits, and pharmaceutical products. Melatonin is considered a dietary supplement and can regulate circadian rhythms, although it has not been classified as a drug by the US Food and Drug Administration. Several analytical methods have been used for its detection. This study aimed to summarize the recent outcomes of the chromatographic methods such as electrophoretic methods, gas chromatography, and liquid chromatography, which have been used for the determination of melatonin in the last three decades, with the focus on gas chromatography and high-performance liquid chromatography methods.

Finger sweat analysis enables short interval metabolic biomonitoring in humans

Metabolic biomonitoring in humans is typically based on the sampling of blood, plasma or urine. Although established in the clinical routine, these sampling procedures are often associated with a variety of compliance issues, which are impeding time-course studies. Here, we show that the metabolic profiling of the minute amounts of sweat sampled from fingertips addresses this challenge. Sweat sampling from fingertips is non-invasive, robust and can be accomplished repeatedly by untrained personnel. The sweat matrix represents a rich source for metabolic phenotyping. We confirm the feasibility of short interval sampling of sweat from the fingertips in time-course studies involving the consumption of coffee or the ingestion of a caffeine capsule after a fasting interval, in which we successfully monitor all known caffeine metabolites as well as endogenous metabolic responses. Fluctuations in the rate of sweat production are accounted for by mathematical modelling to reveal individual rates of caffeine uptake, metabolism and clearance. To conclude, metabotyping using sweat from fingertips combined with mathematical network modelling shows promise for broad applications in precision medicine by enabling the assessment of dynamic metabolic patterns, which may overcome the limitations of purely compositional biomarkers.

Microbial production of beneficial indoleamines (serotonin and melatonin) with potential application to biotechnological products for human health

Micro-organisms have showed the ability to produce biologically active compounds associated with neurotransmission in higher organisms. In particular, serotonin- and melatonin-producing microbes are valuable sources for the development of eco-friendly bioproducts. Serotonin and melatonin are indoleamines that have received special attention due to their positive effects on human health. These biomolecules exert a critical role in several physiological or pathological processes, including some mental and neurological disorders. This article includes a review of the microbial production of serotonin and melatonin, their functions in micro-organisms and their potential uses as therapeutic and/or preventive agents to improve human health. A description of the quantification methods employed to detect indoleamines and the evidence found concerning their microbial production at laboratory and industrial scale-for application in biotechnological products-is also provided. The microbial ability to synthesize beneficial indoleamines should be further studied and harnessed, to allow the development of sustainable bioprocesses to produce foods and pharmaceuticals for human health.

Serotonin pathway in carcinoid syndrome: Clinical, diagnostic, prognostic and therapeutic implications

Carcinoid syndrome represents the most common functional syndrome that affects patients with neuroendocrine neoplasms. Its clinical presentation is really heterogeneous, ranging from mild and often misdiagnosed symptoms to severe manifestations, that significantly worsen the patient's quality of life, such as difficult-to-control diarrhoea and fibrotic complications. Serotonin pathway alteration plays a central role in the pathophysiology of carcinoid syndrome, accounting for most clinical manifestations and providing diagnostic tools. Serotonin pathway is complex, resulting in production of biologically active molecules such as serotonin and melatonin, as well as of different intermediate molecules and final metabolites. These activities require site- and tissue-specific catalytic enzymes. Variable expression and activities of these enzymes result in different clinical pictures, according to primary site of origin of the tumour. At the same time, the biochemical diagnosis of carcinoid syndrome could be difficult even in case of typical symptoms. Therefore, the accuracy of the diagnostic methods of assessment should be improved, also attenuating the impact of confounding factors and maybe considering new serotonin precursors or metabolites as diagnostic markers. Finally, the prognostic role of serotonin markers has been only evaluated for its metabolite 5-hydroxyindole acetic acid but, due to heterogeneous and biased study designs, no definitive conclusions have been achieved. The most recent progress is represented by the new therapeutic agent telotristat, an inhibitor of the enzyme tryptophan hydroxylase, which blocks the conversion of tryptophan in 5-hydroxy-tryptophan. The present review investigates the clinical significance of serotonin pathway in carcinoid syndrome, considering its role in the pathogenesis, diagnosis, prognosis and therapy.

Determination of melatonin by a whole cell bioassay in fermented beverages

Melatonin is a bioactive compound that is present in fermented beverages, such as wine and beer, at concentrations ranging from picograms to nanograms per mL of product. The purpose of this study was to optimize a novel fluorescent bioassay for detecting melatonin based on a cell line that contains the human melatonin receptor 1B gene and to compare these results with LC-MS/MS as a reference method. Conditions that could affect cell growth and detection (cell number per well, stimulation time, presence or absence of fetal bovine serum and adhesion of cells) were tested in the TANGO^® cell line. Food matrices (wine and grape must) could not be directly used for the cell line due to low response. Therefore, for the determination of melatonin in food samples, an extraction procedure was required before conducting the assay. We demonstrated an improvement in melatonin determination by the cell-based bioassay due to increased sensitivity and specificity and improved quantification in complex matrices. Therefore, this method is a good alternative to determine melatonin content in some food samples, especially for those containing very low melatonin levels.

Current state of bioanalytical chromatography in clinical analysis

Chromatographic methods have become popular in clinical analysis in both routine and research laboratories.

Supercritical fluid chromatography: a promising alternative to current bioanalytical techniques

During the last years, chemistry was involved in the worldwide effort toward environmental problems leading to the birth of green chemistry. In this context, green analytical tools were developed as modern Supercritical Fluid Chromatography in the field of separative techniques. This chromatographic technique knew resurgence a few years ago, thanks to its high efficiency, fastness and robustness of new generation equipment. These advantages and its easy hyphenation to MS fulfill the requirements of bioanalysis regarding separation capacity and high throughput. In the present paper, the technical aspects focused on bioanalysis specifications will be detailed followed by a critical review of bioanalytical supercritical fluid chromatography methods published in the literature.