Tandem Mass Spectrum Similarity-Based Network Analysis Using 13C-Labeled and Non-labeled Metabolome Data to Identify the Biosynthetic Pathway of the Blood Pressure-Lowering Asparagus Metabolite Asparaptine A

Interaction of Asparagusic Acid, Asparaptines and Related Dithiolane Derivatives With Angiotensin-Converting Enzyme-2 (ACE-2): A Molecular Docking Study

A variety of sulfur-containing small molecules can be found in the spears of asparagus (Asparagus Officinalis L.) including compounds derived from asparagusic acid such as the amino acid derivatives asparaptines A, B, and C. The previous characterization of asparaptine A as an inhibitor of angiotensin-converting enzyme (ACE) prompted us to compare the binding of the three asparaptines to ACE2 using molecular modeling. The lysine conjugate asparaptine B was found to bind better to the enzyme than the arginine (asparaptine A) and histidine (asparaptine C) conjugates. The stability of ACE2-asparaptine B complexes was only a little inferior to that observed with the reference ACE2 inhibitor MLN-4760. On this basis, 20 additional compounds bearing a thiol group or a dithiolane motif were evaluated as potential binders to ACE2 using the same docking methodology. Three compounds emerged as robust ACE2 binders: the natural products isovalthine and N-acetyl-felinine, and the drug candidate CMX-2043. The empirical energy of interaction (ΔE) of N-acetyl-felinine with ACE2 was comparable to that measured with asparaptine B, and a little higher with the thiol metabolite isovalthine. Remarkably, CMX-2043 revealed a high capacity to form stable complexes with ACE2, superior to that of the reference MLN-4760. Both the l-Glu-l-Ala dipeptide motif and the α-lipoic acid moiety of CMX-2043 are implicated in the protein interaction. Our observations pave the way to the design of novel ligands of ACE2 equipped with a dithiolane motif.

The ability of callus tissues induced from three Allium plants to accumulate health-beneficial natural products, S-alk(en)ylcysteine sulfoxides

S-Alk(en)ylcysteine sulfoxides (CSOs), such as methiin, alliin, and isoalliin, are health-beneficial natural products biosynthesized in the genus Allium. Here, we report the induction of multiple callus tissue lines from three Allium vegetables, onion (A. cepa), Welsh onion (A. fistulosum), and Chinese chive (A. tuberosum), and their ability to accumulate CSOs. Callus tissues were initiated and maintained in the presence of picloram and 2-isopentenyladenine as auxin and cytokinin, respectively. For all plant species tested, the callus tissues almost exclusively accumulated methiin as CSO, while the intact plants contained a substantial amount of isoalliin together with methiin. These results suggest that the cellular developmental conditions and the regulatory mechanisms required for the biosynthesis of methiin are different from those of alliin and isoalliin. The methiin content in the callus tissues of onion and Welsh onion was much higher compared to that in the intact plants, and its cellular concentration could be estimated as 1.9-21.7 mM. The activity of alliinase that degrades CSOs in the callus tissues was much lower than that of the intact plants for onion and Welsh onion, but at similar levels as in the intact plants for Chinese chive. Our findings that the callus tissues of onion and Welsh onion showed high methiin content and low alliinase activity highlighted their potential as a plant-based system for methiin production.

Assessment of Contents and Health Impacts of Four Metals in Chongming Asparagus-Geographical and Seasonal Aspects

In this paper, the contents of four typical metals (Pb, Cd, Hg, and As) in asparagus, water, and soil from Chongming Island were quantitatively determined by inductively coupled plasma mass spectrometry (ICP-MS). The contents of these metals in asparagus showed a common rule of Pb > As > Cd > Hg in different harvest seasons and regions. Significant seasonal differences were found in the contents by difference analysis, but no obvious regional differences were observed. Furthermore, the asparagus did not accumulate these four metals from the soil in Chongming Island by the assessment of bio-concentration factor. The asparagus was proved safe by the analysis of single-factor pollution index and Nemerow pollution index. Through combining the analysis of the above indexes and the geological accumulation index, we found that 51.62% of soil samples were mildly polluted by cadmium. The results of health risk analysis showed that the risk value of children was higher than that of adults under oral exposure, but the four metals in asparagus possessed no obvious risk to health. The above assessments illustrate that the daily consumption of asparagus in Chongming Island will not cause potential health impacts. It is of benefit to ensure the quality and economic interests of asparagus planting in Chongming Island through the investigation of this study.

Spatial metabolomics using imaging mass spectrometry to identify the localization of asparaptine A in Asparagus officinalis

Spatial metabolomics uses imaging mass spectrometry (IMS) to localize metabolites within tissue section. Here, we performed matrix-assisted laser desorption/ionization-Fourier transform ion cyclotron resonance-IMS (MALDI-FTICR-IMS) to identify the localization of asparaptine A, a naturally occurring inhibitor of angiotensin-converting enzyme, in green spears of asparagus (Asparagus officinalis). Spatial metabolome data were acquired in an untargeted manner. Segmentation analysis using the data characterized tissue-type-dependent and independent distribution patterns in cross-sections of asparagus spears. Moreover, asparaptine A accumulated at high levels in developing lateral shoot tissues. Quantification of asparaptine A in lateral shoots using liquid chromatography-tandem mass spectrometry (LC-MS/MS) validated the IMS analysis. These results provide valuable information for understanding the function of asparaptine A in asparagus, and identify the lateral shoot as a potential region of interest for multiomics studies to examine gene-to-metabolite associations in the asparaptine A biosynthesis.