Quantification of Thiazolidine-4-carboxylic Acid in Toxicant-Exposed Cells by Isotope-Dilution Liquid Chromatography–Mass Spectrometry Reveals an Intrinsic Antagonistic Response to Oxidative Stress-Induced Toxicity

Does Deteriorating Antioxidant Defense and Impaired γ-Glutamyl Cycle Induce Oxidative Stress and Hemolysis in Individuals with Sickle Cell Disease?

Sickle cell disease (SCD) affects two-thirds of African and Indian children. Understanding the molecular mechanisms contributing to oxidative stress may be useful for therapeutic development in SCD. We evaluated plasma elemental levels of Indian SCD patients, trait, and healthy controls (n = 10 per group) via inductively coupled plasma mass spectrometry. In addition, erythrocyte metabolomics of Indian SCD and healthy (n = 5 per group) was carried out using liquid chromatography-mass spectrometry. Followed by assessment of antioxidant defense enzymes namely glutathione reductase (GR), superoxide dismutase (SOD), and catalase (CAT) in erythrocytes and plasma of Indian SCD patients (n = 31) compared with trait (n = 10) and healthy (n = 10). In SCD plasma an elevated plasma 24 Mg, 44Ca, 66Zn, 208Pb, 39K and reduced 57Fe, 77Se, and 85Rb levels indicated higher hemolysis and anemia. Erythrocyte metabolome of SCD patients clustered separately from healthy revealed 135 significantly deregulated metabolic features, including trimethyllysine, pyroglutamate, glutathione, aminolevulinate, and d-glutamine, indicating oxidative stress and membrane fragility. Repressed GR, SOD, and CAT activities were observed in SCD patients of which GR and CAT activities did not change under hypoxia. These findings lead to the hypothesis that SCD-associated metabolic deregulations and a shift to ATP-consuming aberrant γ-glutamyl cycle leads to anemia, dehydration, oxidative stress, and hemolysis driving the biomechanical pathophysiology of erythrocyte of SCD patients.

Proline Analogues

Within the canonical repertoire of the amino acid involved in protein biogenesis, proline plays a unique role as an amino acid presenting a modified backbone rather than a side-chain. Chemical structures that mimic proline but introduce changes into its specific molecular features are defined as proline analogues. This review article summarizes the existing chemical, physicochemical, and biochemical knowledge about this peculiar family of structures. We group proline analogues from the following compounds: substituted prolines, unsaturated and fused structures, ring size homologues, heterocyclic, e.g., pseudoproline, and bridged proline-resembling structures. We overview (1) the occurrence of proline analogues in nature and their chemical synthesis, (2) physicochemical properties including ring conformation and cis/trans amide isomerization, (3) use in commercial drugs such as nirmatrelvir recently approved against COVID-19, (4) peptide and protein synthesis involving proline analogues, (5) specific opportunities created in peptide engineering, and (6) cases of protein engineering with the analogues. The review aims to provide a summary to anyone interested in using proline analogues in systems ranging from specific biochemical setups to complex biological systems.

Decoding the Structure of Non-Proteinogenic Amino Acids: The Rotational Spectrum of Jet-Cooled Laser-Ablated Thioproline

The broadband rotational spectrum of jet-cooled laser-ablated thioproline was recorded. Two conformers of this system were observed and identified with the help of DFT and ab initio computations by comparison of the observed and calculated rotational constants and ¹⁴N quadrupole coupling constants as well as the predicted energies compared to the observed relative populations. These conformers showed a mixed bent/twisted arrangement of the five-membered ring similar to that of the related compound thiazolidine with the N–H bond in axial configuration. The most stable form had the COOH group in an equatorial position on the same side of the ring as N-H. The arrangement of the C=O group close to the N-H bond led to a weak interaction between them (classified as type I) characterized by a noncovalent interaction analysis. The second form had a trans-COOH arrangement showing a type II O–H···N hydrogen bond. In thioproline, the stability of conformers of type I and type II was reversed with respect to proline. We show how the conformation of the ring depends on the function associated with the endocyclic N atom when comparing the structures of isolated thioproline with its zwitterion observed in condensed phases and with peptide forms.

Quantitation of γ-Glutamylcysteine-Formaldehyde Conjugate in Formaldehyde- and Oxidative Stress-Exposed Cells by Liquid Chromatography-Tandem Mass Spectrometry

Humans are constantly exposed to formaldehyde (FA) of both exogenous and endogenous sources, and FA exposure is associated with the development of many human diseases, including cancers. Marker molecules that can provide information on exposure history and amounts will assist disease risk assessment and early interventions. To develop marker signatures of FA exposure, we explored in this study the conjugation reaction of FA with γ-glutamylcysteine (GGC), one of the precursors to glutathione biosynthesis, under physiologically relevant conditions. The results showed that the reaction produced a stable metabolite of FA, (S)-1-((((R)-2-amino-2-carboxyethyl)thio)methyl)-5-oxopyrrolidine-2-carboxylic acid (COCA). Using liquid chromatography-tandem mass spectrometry coupled to a stable isotope-dilution method, we then quantitated for the first time the formation of this novel metabolite in FA- and Fe²⁺-EDTA-exposed human cells. The results revealed the exposure time- and concentration-dependent formation of COCA in FA- or Fe²⁺-EDTA-exposed cells, suggesting that COCA may serve as a biomarker of FA and oxidative stress exposure. Furthermore, the study sheds light on a previously unknown protective role of GGC against FA and oxidative stress.

Analysis of aristolochic acids in Houttuynia cordata by liquid chromatography-tandem mass spectrometry

Houttuynia cordata (H. cordata) is a popular vegetable in Asian countries and is also used extensively as herbal medicine in treating various diseases. H. cordata contains aristolactams, which have a similar Chinese name as aristolochic acids (AAs); hence, an emerging concern in the greater China region has arisen about the potential linkage between H. cordata and aristolochic acid nephropathy (AAN). However, only a single study has tested for the presence of AAs in H. cordata samples, and the analysis was limited by the analytical sensitivity of the method. Thus, further analysis of AAs in H. cordata using analytical method of higher sensitivity is needed to alleviate public anxiety over the use of this popular vegetable. In this study, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was used to analyze H. cordata samples for the natural existence of aristolochic acid I (AA-I) and aristolochic acid II (AA-II), which are the most carcinogenic and nephrotoxic compounds in the AA family. After evaluating the method performance by fortifying blank samples with three concentrations of AAs, the validated method was applied to identify AA-I and AA-II in both fresh and sun-dried H. cordata samples (n = 20) collected from different cities in China. The LC-MS/MS method achieved method detection limits (MDLs) as low as 2 ng/g of AAs in H. cordata. Analysis of the collected fresh and sun-dried H. cordata samples revealed that AA-I and AA-II either do not exist naturally in H. cordata or exist at concentrations below the MDLs. Therefore, it is not very likely that consumption of H. cordata will result in AAN because AA-I and AA-II, the nephrotoxic and carcinogenic culprits of AAN, are not produced naturally in the plant or are produced at levels that do not pose a risk of AAN.

Identification and Quantitation of Four New 2-Alkylthiazolidine-4-carboxylic Acids Formed in Orange Juice by a Reaction of Saturated Aldehydes with Cysteine

Despite several technological efforts to maximize the quality and shelf life of chilled stored not-from-concentrate orange juice, changes in the overall aroma profile might occur during storage. Besides the degradation of terpenoids, a loss of the aroma-active aldehydes, hexanal, octanal, nonanal, and decanal as well-as of 1-penten-3-one were recently confirmed as a major cause for the changes in the aroma profile of orange juice even during storage under aseptic conditions at 0 °C. To unravel the fate of the aroma-active aldehydes, model experiments were carried out considering the oxidation into the corresponding acids as well as a reaction with free amino acids present in orange juice. The oxidation into the acids could be confirmed by isotope labeling experiments; additionally, the reaction of the four aldehydes mentioned above with l-cysteine yielded four new compounds identified as 2-alkylsubstituted thiazolidine-4-carboxylic acids. Their quantitation in orange juice samples by newly developed stable isotope dilution assays revealed that these acids were already present in the fresh samples but were considerably increased after storage. Labeling experiments in orange juice administered with either labeled octanal or labeled cysteine confirmed that the reaction quickly occurs in the juice. The data contribute another puzzle piece to the loss of aroma-active aldehydes during orange juice storage, which may also be relevant in other foods.

Biotransformation and bioactivation reactions - 2016 literature highlights

We are pleased to present a second annual issue highlighting a previous year's literature on biotransformation and bioactivation. Each contributor to this issue worked independently to review the articles published in 2016 and proposed three to four articles, which he or she believed would be of interest to the broader research community. In each synopsis, the contributing author summarized the procedures, analyses and conclusions as described in the original manuscripts. In the commentary sections, our authors offer feedback and highlight aspects of the work that may not be apparent from an initial reading of the article. To be fair, one should still read the original article to gain a more complete understanding of the work conducted. Most of the articles included in this review were published in Drug Metabolism and Disposition or Chemical Research in Toxicology, but attempts were made to seek articles in 25 other journals. Importantly, these articles are not intended to represent a consensus of the best papers of the year, as we did not want to make any arbitrary standards for this purpose, but rather they were chosen by each author for their notable findings and descriptions of novel metabolic pathways or biotransformations. I am pleased that Drs. Rietjens and Dalvie have again contributed to this annual review. We would like to welcome Grover P Miller as an author for this year's issue, and we thank Tom Baillie for his contributions to last year's edition. We have intentionally maintained a balance of authors such that two come from an academic setting and two come from industry. Finally, please drop us a note if you find this review helpful. We would be pleased to hear your opinions of our commentary, and we extend an invitation to anyone who would like to contribute to a future edition of this review. This article is dedicated to Professor Thomas Baillie for his exceptional contributions to the field of drug metabolism.

Quantitation of Aristolochic Acids in Corn, Wheat Grain, and Soil Samples Collected in Serbia: Identifying a Novel Exposure Pathway in the Etiology of Balkan Endemic Nephropathy

While to date investigations provided convincing evidence on the role of aristolochic acids (AAs) in the etiology of Balkan endemic nephropathy (BEN) and upper urothelial cancer (UUC), the exposure pathways by which AAs enter human bodies to cause BEN and UUC remain obscure. The goal of this study is to test the hypothesis that environmental pollution by AAs and root uptake of AAs in the polluted soil may be one of the pathways by which AAs enter the human food chain. The hypothesis driving this study was that the decay of Aristolochia clematitis L., a AA-containing herbaceous plant that is found growing widespread in the endemic regions, could release free AAs to the soil, which could be taken up by food crops growing nearby, thereby transferring this potent human nephrotoxin and carcinogen into their edible parts. Using the highly sensitive and selective high-performance liquid chromatography coupled with fluorescence detection method, we identified and quantitated in this study for the first time AAs in corn, wheat grain, and soil samples collected from the endemic village Kutles in Serbia. Our results provide the first direct evidence that food crops and soil in the Balkans are contaminated with AAs. It is possible that the presence of AAs in edible parts of crops originating from the AA-contaminated soil could be one of the major pathways by which humans become exposed to AAs.

Quantitation of Thioprolines in Grape Wine by Isotope Dilution-Liquid Chromatography-Tandem Mass Spectrometry

Cysteine reacts with reactive carbonyls to form thioprolines, which have been demonstrated to possess various pharmaceutical properties. Therefore, thioproline formation is considered as a major detoxification pathway for carcinogenic reactive carbonyls. In this study, we report the initial identification of thiazolidine-4-carboxylic acid (1) and 2-methylthiazolidine-4-carboxylic acid (2), two very common thioprolines, formed by reacting formaldehyde and acetaldehyde with cysteine in grape wine samples. We have developed an isotope dilution-liquid chromatography-tandem mass spectrometry method featuring high sensitivity (limit of detection of ≤1.5 ng/mL) and selectivity to quantitate compounds 1 and 2. The method after validated to be highly accurate (recovery of ≥92%) and precise [intraday relative standard deviation (RSD) of ≤4.1% and interday RSD of ≤9.7%] was applied to determine the varying compound 1 and 2 contents in grape wine samples. Results revealed the grape type and storage duration-dependent formation of thioprolines in grape wines. Overall, the results are expected to facilitate compound-dependent investigations of the health benefits of grape wine, and our findings could be adopted to predict the age of grape wine.