Accurate Determination of Amino Acids in Serum Samples by Liquid Chromatography-Tandem Mass Spectrometry Using a Stable Isotope Labeling Strategy

Spatial distribution of metabolites in processing Ziziphi Spinosae Semen as revealed by matrix-assisted laser desorption/ionization mass spectrometry imaging

Ziziphi Spinosae Semen (ZSS) is the first choice for the treatment of insomnia. This research aimed to reveal the spatial distribution of identifying quality markers of ZSS and to illustrate the metabolite quality characteristics of this herbal medicine. Here, we performed a matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) in situ to detect and image 33 metabolites in ZSS, including three saponins, six flavonoids, four alkaloids, eight fatty acids, and 12 amino acids. The MALDI images of the metabolites clearly showed the heterogeneous spatial distribution in different regions of ZSS tissues, such as the cotyledon, endosperm, and radicle. The distribution area of two saponins, six flavonoids, and three alkaloids increased significantly after the fried processing of ZSS. Based on the ion images, samples with different processing technologies were distinguished unambiguously by the pattern recognition method of orthogonal partial least squares discrimination analysis (OPLS-DA). Simultaneously, 23 major influencing components exerting higher ion intensities were identified as the potential quality markers of ZSS. Results obtained in the current research demonstrate that the processing of ZSS changes its content and distribution of the medicinal components. The analysis of MALDI-MSI provides a novel MS-based molecular imaging approach to investigate and monitor traditional medicinal plants.

Challenges and recent advances in quantitative mass spectrometry-based metabolomics

The field of metabolomics has gained tremendous interest in recent years. Whether the goal is to discover biomarkers related to certain pathologies or to better understand the impact of a drug or contaminant, numerous studies have demonstrated how crucial it is to understand variations in metabolism. Detailed knowledge of metabolic variabilities can lead to more effective treatments, as well as faster or less invasive diagnostics. Exploratory approaches are often employed in metabolomics, using relative quantitation to look at perturbations between groups of samples. Most metabolomics studies have been based on metabolite profiling using relative quantitation, with very few studies using an approach for absolute quantitation. Using accurate quantitation facilitates the comparison between different studies, as well as enabling longitudinal studies. In this review, we discuss the most widely used techniques for quantitative metabolomics using mass spectrometry (MS). Various aspects will be addressed, such as the use of external and/or internal standards, derivatization techniques, in vivo isotopic labelling, or quantitative MS imaging. The principles, as well as the associated limitations and challenges, will be described for each approach.

Chromatomass-Spectrometric Method for the Quantitative Determination of Amino- and Carboxylic Acids in Biological Samples

A highly sensitive method for the qualitative and quantitative determination of amino- and carboxylic acids, as well as a number of urea and methionine cycle metabolites in the studied solutions, is presented. Derivatives (esterification) were obtained for amino acids by their reaction in a solution of 3 N of hydrochloric acid in n-butanol for 15 min at 65 °C and for carboxylic acids by their reaction with phenol in ethyl acetate with 3 N of hydrochloric acid for 20 min at 65 °C. Experimental work on the determination of individual metabolites was carried out using the HPLC-MS/MS method and included the creation of a library of spectra of the analyzed compounds and their quantitative determination. Multiplex methods have been developed for the quantitative analysis of the desired metabolites in a wide range of concentrations of 3-4 orders of magnitude. The approach to the analysis of metabolites was developed based on the method of the dynamic monitoring of multiple reactions of the formation of fragments for a mass analyzer with a triple quadrupole (QQQ). The effective chromatographic separation of endogenous metabolites was carried out within 13 min. The calibration curves of the analyzed compounds were stable throughout the concentration range and had the potential to fit below empirical levels. The developed methods and obtained experimental data are of interest for a wide range of biomedical studies, as well as for monitoring the content of endogenous metabolites in biological samples under various pathological conditions. The sensitivity limit of the methods for amino acids was about 4.8 nM and about 0.5 μM for carboxylic acids. Up to 19 amino- and up to 12 carboxy acids and about 10 related metabolites can be tested in a single sample.

Options of the Main Derivatization Approaches for Analytical ESI and MALDI Mass Spectrometry

The inclusion of preliminary chemical labeling (derivatization) in the analysis process by such powerful and widespread methods as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is a popular and widely used methodological approach. This is due to the need to remove some fundamental limitations inherent in these powerful analytic methods. Although a number of special reviews has been published discussing the utilization of derivatization approaches, the purpose of the present critical review is to comprehensively summarize, characterize and evaluate most of the previously developed and practically applied, as well as recently proposed representative derivatization reagents for ESI-MS and MALDI-MS platforms in their mostly sensitive positive ion mode and frequently hyphenated with separation techniques. The review is focused on the use of preliminary chemical labeling to facilitate the detection, identification, structure elucidation, quantification, profiling or MS imaging of compounds within complex matrices. Two main derivatization approaches, namely the introduction of permanent charge-fixed or highly proton affinitive residues into analytes are critically evaluated. In situ charge-generation, charge-switch and charge-transfer derivatizations are considered separately. The potential of using reactive matrices in MALDI-MS and chemical labeling in MS-based omics sciences is given.

Chemical Isotope Labeling LC-MS for Metabolomics

Due to the great diversity of chemical and physical properties of metabolites as well as a wide range of concentrations of metabolites present in metabolomic samples, performing comprehensive and quantitative metabolome analysis is a major analytical challenge. Conventional approach of combining various techniques and methods with each detecting a fraction of the metabolome can lead to the increase in overall metabolomic coverage. However, this approach requires extensive investment in equipment and analytical expertise with still relatively low coverage and low sample throughput. Chemical isotope labeling (CIL) liquid chromatography mass spectrometry (LC-MS) offers an alternative means of increasing metabolomic coverage while maintaining high quantification precision and accuracy. This chapter describes the CIL LC-MS method and its key features for metabolomic analysis.

The Emerging role of Branch Chain Amino Acids in the Prediction of Diabetes: A Brief Review

Diabetes is a chronic condition; those with diabetes are at high risk of developing diabetes complications. One important approach to tackle the diabetes burden is to screen for undiagnosed diabetes and to identify factors that lead to the risk of developing diabetes in the future. The earlier identification of individuals at risk of developing diabetes is crucial for delaying or preventing the onset of type 2 diabetes. Numerous studies have demonstrated that circulating concentrations of branch chain amino acids (BCAAs) predict the risk for developing diabetes; thus, contributing to the recent resurgence of interest in these common analytes. The present review aimed to address the recent findings regarding BCAAs and their role in insulin resistance and diabetes. Recent studies demonstrate that BCAAs are strongly associated with a number of pathological mechanisms causing insulin resistance and type 2 diabetes. The research findings related to BCAA signaling pathways and metabolism broaden our understanding of this topic. However, it remains unclear how increased levels of BCAAs will assist in the prediction of future insulin resistance or type 2 diabetes. Future research needs to determine whether BCAAs are a causative factor for insulin resistance and type 2 diabetes, or just a biomarker of impaired insulin action.

Quantitative amino acid analysis by liquid chromatography-tandem mass spectrometry using low cost derivatization and an automated liquid handler

Amino acid analysis is central to newborn screening and the investigation of inborn errors of metabolism. Ion‐exchange chromatography with ninhydrin derivatization remains the reference method for quantitative amino acid analysis but offers slow chromatography and is susceptible to interference from other co‐eluting compounds. Liquid‐chromatography tandem mass spectrometry (LC‐MS/MS) provides a rapid and highly specific alternative, but sample preparation is frequently laborious and sometimes cost prohibitive. To address these limitations, we validated an LC‐MS/MS method using the aTRAQ Reagents Application Kit with a modified protocol consuming only half reagents. Adequate performance for clinical specimen measurement of 26 amino acids with high clinical relevance was achieved. An automated liquid handler and modified calibration and normalization approaches were used to ensure reproducible assay performance. Linear measurement between 5 and 2000 μM was achieved for most analytes despite use of a small, 10 μl sample size. Overall the method achieved near substantially improved throughput and enabled use of smaller samples volumes for batched analyses of clinical samples.

Amino and organic acid analysis: Essential tools in the diagnosis of inborn errors of metabolism

Inborn errors of metabolism (IEMs) are a large class of genetic disorders that result from defects in enzymes involved in energy production and metabolism of nutrients. For every metabolic pathway, there are defects that can occur and potentially result in an IEM. While some defects can go undetected in one's lifetime, some have moderate to severe clinical consequences. In the latter case, the biochemical defect leads to accumulation of metabolites and byproducts that are toxic or interfere with normal biological function. Disorders of amino acid metabolism, organic acid metabolism and the urea cycle comprise a large portion of IEMs. Two essential tools required for the diagnosis of these categories of disorders are amino acid and organic acid profiling. Most all clinical laboratories offering metabolic testing perform amino acid analysis, while organic acid profiling is restricted to more specialized pediatric hospitals and reference laboratories. In this chapter, we will provide an overview of various methodologies employed for amino acid and organic acid profiling as well as specific examples to demonstrate how these techniques are applied in clinical laboratories for the diagnosis of IEMs.

Rapid Determination of Amino Acids of Nitraria tangutorum Bobr. from the Qinghai-Tibet Plateau Using HPLC-FLD-MS/MS and a Highly Selective and Sensitive Pre-Column Derivatization Method

Amino acids are indispensable components of living organisms. The high amino acid content in Nitraria tangutorum Bobr. fruit distinguishes it from other berry plants and is of great significance to its nutritional value. Herein, using 10-ethyl-acridine-3-sulfonyl chloride as a fluorescent pre-column labeling reagent, a method for the efficient and rapid determination of amino acid content in N. tangutorum by pre-column fluorescence derivatization and on-line mass spectrometry was established and further validated. The limits of detection (signal-to-noise ratio = 3) were between 0.13 and 1.13 nmol/L, with a linear coefficient greater than 0.997 and a relative standard deviation between 1.37% and 2.64%. In addition, the method required a short analysis time, separating 19 amino acids within 20 min. Subsequently, the method was used to analyze the amino acid content of Nitraria tangutorum Bobr. from tissues retrieved from seven regions of the Qinghai-Tibet Plateau. Nitraria tangutorum Bobr. was shown to contain a large amount of amino acids, with the total content and main amino acid varying between the different tissues. This research supports the nutritional evaluation, quality control, and development and utilization of Nitraria tangutorum Bobr.

Simultaneous determination of amino acids, purines and derivatives in serum by ultrahigh-performance liquid chromatography/tandem mass spectrometry

RATIONALE

Amino acids, purines and derivatives play a key role in physiological and pathological processes, such as the development of gestational diabetes mellitus. However, little literature has reported the simultaneous quantification of amino acids and purines. Therefore, a reliable and robust method for the determination of amino acids and purines is necessary.

METHODS

A rapid and simple method based on ultrahigh-performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) was developed to determine the concentrations of twenty amino acids or derivatives and three purines or derivatives in serum.

RESULTS

The method was validated for linearity of calibration curve, limit of detection, limit of quantification, inter-day and intra-day precision, recovery, stability and matrix effect. The correlation coefficients of calibration curves were higher than 0.993 except for isoleucine. The recoveries ranged from 78.4% to 128.0% for three different concentrations of the spiked analytes. The matrix effect value ranged from -7.3% to 9.2%.

CONCLUSIONS

A rapid and simple UHPLC/MS/MS method for the simultaneous measurement of amino acids, purines and derivatives in serum samples was developed. The method was successfully applied to determine and compare the concentrations of analytes between gestational diabetes mellitus samples and controls.

Advances in Clinical Mass Spectrometry

Although mass spectrometry has been used clinically for decades, the advent of immunoassay technology moved the clinical laboratory to more labor saving automated platforms requiring little if any sample preparation. It became clear, however, that immunoassays lacked sufficient sensitivity and specificity necessary for measurement of certain analytes or for measurement of analytes in specific patient populations. This limitation prompted clinical laboratories to revisit mass spectrometry which could additionally be used to develop assays for which there was no commercial source. In this chapter, the clinical applications of mass spectrometry in therapeutic drug monitoring, toxicology, and steroid hormone analysis will be reviewed. Technologic advances and new clinical applications will also be discussed.

Quantification of Five Clinically Important Amino Acids by HPLC-Triple TOF™ 5600 Based on Pre-column Double Derivatization Method

Phenylalanine, tyrosine, glycine, cystine, and phosphoethanolamine are commonly measured amino acids in various physiological fluids to diagnose or follow-up various inborn errors of metabolism. The gold standard method for the amino acids quantitation has been ion exchange chromatography with ninhydrin post-column derivatization. However, this method is very laborious and time consuming. In recent years, liquid-chromatography mass spectrometry is being increasingly used for the assay of amino acids. Pre-column butyl derivatization with reverse phase chromatography has been widely used for mass spectrometry analysis of amino acids. Phosphoethanolamine is not butylated and cannot be measured by this method. Nevertheless, phosphoethanolamine can be dansyl-derivatized using dansyl chloride. We developed a double derivatization method by using butanol and dansyl chloride to derivatize carboxylic and amino groups separately, and then combining the derivatives to simultaneously measure these five amino acids using TOF-MS scan. Stable isotope-labeled internal standards were used.

Inborn Errors of Metabolism

Inborn errors of metabolism are single gene disorders resulting from the defects in the biochemical pathways of the body. Although these disorders are individually rare, collectively they account for a significant portion of childhood disability and deaths. Most of the disorders are inherited as autosomal recessive whereas autosomal dominant and X-linked disorders are also present. The clinical signs and symptoms arise from the accumulation of the toxic substrate, deficiency of the product, or both. Depending on the residual activity of the deficient enzyme, the initiation of the clinical picture may vary starting from the newborn period up until adulthood. Hundreds of disorders have been described until now and there has been a considerable clinical overlap between certain inborn errors. Resulting from this fact, the definite diagnosis of inborn errors depends on enzyme assays or genetic tests. Especially during the recent years, significant achievements have been gained for the biochemical and genetic diagnosis of inborn errors. Techniques such as tandem mass spectrometry and gas chromatography for biochemical diagnosis and microarrays and next-generation sequencing for the genetic diagnosis have enabled rapid and accurate diagnosis. The achievements for the diagnosis also enabled newborn screening and prenatal diagnosis. Parallel to the development the diagnostic methods; significant progress has also been obtained for the treatment. Treatment approaches such as special diets, enzyme replacement therapy, substrate inhibition, and organ transplantation have been widely used. It is obvious that by the help of the preclinical and clinical research carried out for inborn errors, better diagnostic methods and better treatment approaches will high likely be available.