Determination of S-Allylmercaptocysteine in Rat Plasma by LC-MS/MS and its Application to a Pharmacokinetics Study

A novel screening method for free non-standard amino acids in human plasma samples using AccQ·Tag reagents and LC-MS/MS

There are at least 500 naturally occurring amino acids, of which only 20 standard proteinogenic amino acids are used universally across all organisms in the synthesis of peptides and proteins. Non-standard amino acids can be incorporated into proteins or are intermediates and products of metabolic pathways. While the analysis of standard amino acids is well-defined, the analysis of non-standard amino acids can be challenging due to the wide range of physicochemical properties, and the lack of both reference standards and information in curated databases to aid compound identification. It has been shown that the use of an AccQ·Tag™ derivatization kit along with LC-MS/MS is an attractive option for the analysis of free standard amino acids in complex samples because it is fast, sensitive, reproducible, and selective. It has been demonstrated that the most abundant quantitative transition for MS/MS analysis of 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) derivatized amino acids corresponds to the fragmentation of the molecule at the 6-aminoquinoline carbonyl group producing a common m/z 171 fragment ion and occurs at similar mass spectrometry collision energy and cone voltages. In this study, the unique properties of AQC derivatized amino acids producing high intensity common fragment ions, along with chromatographic separation of amino acids under generic chromatography conditions, were used to develop a novel screening method for the detection of trace levels of non-standard amino acids in complex matrices. Structural elucidation was carried out by comparing the MS/MS fragment ion mass spectra generated with in silico predicted fragmentation spectra to enable a putative identification, which was confirmed using an appropriate analytical standard. This workflow was applied to screen human plasma samples for bioactive thiol-group modified cysteine amino acids and S-allylmercaptocysteine (SAMC), S-allylcysteine sulfoxide (SACS or alliin) and S-propenylcysteine (S1PC) are reported for the first time to be present in human plasma samples after the administration of garlic supplements.

Establishment of LC-MS/MS method for determination of aloperine in rat plasma and its application in preclinical pharmacokinetics

Aloperine, a novel natural active alkaloid derived from Sophora alopecuroides L., has attracted much attention for its anti-inflammatory, antiviral, anti-tumor, anti-allergy and other pharmacological activities. In this study, we first established and validated an efficient and sensitive high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of aloperine in rat plasma. Cytisine was used as the internal standard (IS). The separation of aloperine and IS was conducted on a Phenomenex Luna Omega Polar C18 column (2.1 × 50 mm, 1.6 μm) with 0.3% (v/v) formic acid aqueous (containing 5 mM ammonium acetate) and 0.3% (v/v) formic acid acetonitrile using isocratic elution condition at a flow rate of 0.20 mL/min. Aloperine and IS were determined under the transitions of m/z 233.2 → 98.1 and m/z 191.2 → 148.2 (positive ionization mode), respectively. The calibration curve of aloperine was established in the range of 5 (LLOQ) to 2000 ng/mL (r2 = 0.994). The well validated method was full compliance with the bioanalytical method validation of FDA, and was applied to the pharmacokinetic study of aloperine in Sprague-Dawley rats after 50 mg/kg oral administration and 5 mg/kg intravenous injection. This study provides valuable references for the further study of Sophora alopecuroides L., especially for the drug development and clinical application of aloperine.

S-Allylmercaptocysteine improves alcoholic liver disease partly through a direct modulation of insulin receptor signaling

Alcoholic liver disease (ALD) causes insulin resistance, lipid metabolism dysfunction, and inflammation. We investigated the protective effects and direct regulating target of S-allylmercaptocysteine (SAMC) from aged garlic on liver cell injury. A chronic ethanol-fed ALD in vivo model (the NIAAA model) was used to test the protective functions of SAMC. It was observed that SAMC (300 mg/kg, by gavage method) effectively ameliorated ALD-induced body weight reduction, steatosis, insulin resistance, and inflammation without affecting the health status of the control mice, as demonstrated by histological, biochemical, and molecular biology assays. By using biophysical assays and molecular docking, we demonstrated that SAMC directly targeted insulin receptor (INSR) protein on the cell membrane and then restored downstream IRS-1/AKT/GSK3β signaling. Liver-specific knock-down in mice and siRNA-mediated knock-down in AML-12 cells of Insr significantly impaired SAMC (250 μmol/L in cells)-mediated protection. Restoration of the IRS-1/AKT signaling partly recovered hepatic injury and further contributed to SAMC's beneficial effects. Continuous administration of AKT agonist and recombinant IGF-1 in combination with SAMC showed hepato-protection in the mice model. Long-term (90-day) administration of SAMC had no obvious adverse effect on healthy mice. We conclude that SAMC is an effective and safe hepato-protective complimentary agent against ALD partly through the direct binding of INSR and partial regulation of the IRS-1/AKT/GSK3β pathway.

Chemistry of aged garlic: Diversity of constituents in aged garlic extract and their production mechanisms via the combination of chemical and enzymatic reactions

Raw garlic contains characteristic compounds, such as S-alk(en)ylcysteine sulfoxides, γ-glutamyl-S-alk(en)-ylcysteines and polysaccharides. These compounds undergo various transformation processes during the aging process. Among these compounds, the change of sulfur-containing molecules is diverse and time-dependent. Previously, by means of the liquid chromatography (LC)/LC-mass spectrometry (MS) method, a number of unidentified peaks corresponding to candidates of sulfur-containing molecules were detected in the chromatogram of aged garlic extract (AGE), and identified using MS and nuclear magnetic resonance (NMR). The production mechanisms of these compounds were then examined by model reactions and laboratory experiments mimicking the aging process. Three γ-glutamyl tripeptides [γ-glutamyl-γ-glutamyl-S-methylcysteine, γ-glutamyl-γ-gluta-myl-S-allylcysteine (GGSAC), γ-glutamyl-γ-glutamyl-S-1-propenylcysteine], γ-glutamyl-S-allylmercaptocysteine (GSAMC) and cis-S-1-propenylcysteine (cis-S1PC) were isolated and identified. GGSAC was produced from GSAC through the enzymatic reaction catalyzed by γ-glutamyltranspeptidase (GGT), and two other tripeptides could be produced in similar reactions. GSAMC was produced by the reaction between γ-glutamyl dipeptides and allicin. Furthermore, GSAMC was a precursor compound of S-allyl-mercaptocysteine (SAMC), and thus it was produced from GSAMC by GGT. cis-S1PC was produced from trans-S1PC by the isomerization reaction. A number of other compounds were also identified, including Maillard reaction products; however, their production mechanisms have not been elucidated. In this review, we present the changes in characteristic constituents in raw garlic and garlic extract during the aging process and discuss their production mechanisms involving the various chemical and enzymatic reactions.