Application of Normal-Phase Silica Column in Hydrophilic Interaction Liquid Chromatography Mode for Simultaneous Determination of Underivatized Amino Acids from Human Serum Samples via Liquid Chromatography-Tandem Mass Spectrometry

In neonatal screening, amino acids have a significant diagnostic role. Determination of their values may identify abnormal conditions. Early diagnosis and continuous monitoring of amino acid disorders results in a better disease outcome. An easy and simple LC-MS/MS method was developed for the quantitation of underivatized amino acids. Amino acids were separated using a normal-phase HPLC column having a totally porous silica stationary phase and using classical reversed-phase eluents. Mass spectrometry in multiple reaction monitoring mode was used for the analysis, providing high selectivity and sensitivity. A standard addition calibration model was applied for quantitation using only one isotope-labeled internal standard for all amino acids. Five calibration points were used for quantitation, and the method was successfully validated. The slopes of the calibration curves of the individual amino acids in parallel measurements were found to be similar. Since the measured slopes were reproducible, one serum sample could represent every series of serum samples of a given day. The method was tested on human serum samples and adequate results were obtained. This new method can be easily applied in clinical laboratories.

L-Cysteine as a reducing/capping/gel-forming agent for the preparation of silver nanoparticle composites with anticancer properties

The present article reports the in situ preparation of silver nanoparticles (AgNPs) homogeneously distributed in the gel matrix formed using only L-cysteine (CYS) as a bio-reducing agent. The physicochemical methods of analysis confirmed the formation of a gel-network from aggregates consisting of spherical/elliptical cystine-stabilized AgNPs (core) and cysteine/Ag⁺ complexes (shell) regardless of the used silver salt - AgNO₃, AgNO₂ or AgOOCCH₃. CYS/AgNO₃ and CYS/AgOOCCH₃ aqueous solution systems needed the addition of electrolytes (Cl^- and SO₄^2-) for the gelation process, but the gel-formation in CYS/AgNO₂ occurred in one stage without any additional components. The AgNP sizes were about 1-5 nm in diameter for CYS/AgNO₃, 5-10 nm for CYS/AgOOCCH₃ and 20-40 nm for CYS/AgNO₂ systems. The zeta-potential values varied from +60 mV for CYS/AgNO₃ to +25 mV for the CYS/AgNO₂ system. The MTT-test showed that the obtained composites suppressed the MCF-7 breast cancer cells and the CYS/AgNO₃ system possessed the highest activity. Flow cytofluorimetry confirmed that the cell death occurred by apoptosis and this effect was the strongest for the CYS/AgNO₃ system. All systems were non-toxic to fibroblast cells. The novel simplest "green chemistry" approach, combining the knowledge of organic, inorganic, physical and supramolecular chemistry could open possibilities for the creation of the newest soft gel materials used in various fields of our life.

L-Cysteine/AgNO2 low molecular weight gelators: self-assembly and suppression of MCF-7 breast cancer cells

We report a new supramolecular hydrogel based on simple amino acids and silver salt compounds with low molecular weights. The in situ formation of silver nanoparticles during the self-assembly process endows the hydrogel with high cytotoxicity towards adenocarcinoma breast cells but no toxic effects towards embryonic fibroblasts.

Redox-Mediated Post-Translational Modifications of Proteolytic Enzymes and Their Role in Protease Functioning

Proteolytic enzymes play a crucial role in metabolic processes, providing the cell with amino acids through the hydrolysis of multiple endogenous and exogenous proteins. In addition to this function, proteases are involved in numerous protein cascades to maintain cellular and extracellular homeostasis. The redox regulation of proteolysis provides a flexible dose-dependent mechanism for proteolytic activity control. The excessive reactive oxygen species (ROS) and reactive nitrogen species (RNS) in living organisms indicate pathological conditions, so redox-sensitive proteases can swiftly induce pro-survival responses or regulated cell death (RCD). At the same time, severe protein oxidation can lead to the dysregulation of proteolysis, which induces either protein aggregation or superfluous protein hydrolysis. Therefore, oxidative stress contributes to the onset of age-related dysfunction. In the present review, we consider the post-translational modifications (PTMs) of proteolytic enzymes and their impact on homeostasis.

A reliable LC-MS/MS method for the quantification of natural amino acids in mouse plasma: Method validation and application to a study on amino acid dynamics during hepatocellular carcinoma progression

A simple and fast LC-MS/MS method was developed and validated for simultaneous quantification of 20 proteinogenic l-amino acids (AAs) in a small volume (5 μL) of mouse plasma. Chromatographic separation was achieved on an Intrada Amino Acid column within 13 min via gradient elution with an aqueous solution containing 100 mM ammonium formate and an organic mobile phase containing acetonitrile, water and formic acid (v:v:v = 95:5:0.3), at the flow rate of 0.6 mL/min. Individual AAs and corresponding stable-isotope-labeled AAs internal standards were analyzed by multiple reaction monitoring (MRM) in positive ion mode under optimized conditions. Method validation consisted of linearity, sensitivity, accuracy and precision, recovery, matrix effect, and stability, and the results demonstrated this LC-MS/MS method as a specific, accurate, and reliable assay. This LC-MS/MS method was thus utilized to compare the dynamics of individual plasma AAs between healthy and orthotopic hepatocellular carcinoma (HCC) xenograft mice housed under identical conditions. Our results revealed that, 5 weeks after HCC tumor progression, plasma l-arginine concentrations were significantly decreased in HCC mice while l-alanine and l-threonine levels were sharply increased. These findings support the utilities of this LC-MS/MS method and the promise of specific AAs as possible biomarkers for HCC.

Recent trends in analytical methods for the determination of amino acids in biological samples

Amino acids are widely distributed in biological fluids and involved in many biological processes, such as the synthesis of proteins, fatty acids, and ketone bodies. The altered levels of amino acids in biological fluids have been found to be closely related to several diseases, such as type 2 diabetes, kidney disease, liver disease, and cancer. Therefore, the development of analytical methods to measure amino acid concentrations in biological samples can contribute to research on the physiological actions of amino acids and the prediction, diagnosis and understanding of diseases. This review describes the analytical methods reported in 2012-2016 that utilized liquid chromatography and capillary electrophoresis coupled with ultraviolet, fluorescence, mass spectrometry, and electrochemical detection. Additionally, the relationship between amino acid concentrations and several diseases is also summarized.