Performance comparison of electrospray ionization and atmospheric pressure chemical ionization in untargeted and targeted liquid chromatography/mass spectrometry based metabolomics analysis of grapeberry metabolites

Plasma-Excited Nebulizer Gas-Assisted Electrospray Ionization: Enhancing the Sensitivity of Pesticide in Mass Spectrometry

Liquid chromatography-mass spectrometry (LC-MS) is widely used in the detection of pesticide residues. However, the detection sensitivity of low-polarity pesticides by commonly used electrospray ionization may be severely suppressed, which greatly affects the limit of detection and repeatability. Herein, a plasma-excited nebulizer gas-assisted electrospray ionization (PENG-ESI) device has been developed. By introducing the discharge plasma formed by Tesla coil into the electrospray nebulizer gas channel, the sensitivity of low-polarity pesticides was significantly increased while maintaining sensitivity to polar pesticides. Under the optimized conditions, the limit of detection for S-bioallethrin was achieved at the level of 100 pg/g with good linearity (R2 > 0.99) and precision (RSD ≤ 4.61%). The matrix effect of a series of spiked matrix samples is less than 13.1%. Finally, different pyrethroid pesticide residues were successfully analyzed without separation, highlighting that the technology has potential application prospects in food quality control, environmental monitoring, and other fields.

Decoding Metabolic Reprogramming in Plants under Pathogen Attacks, a Comprehensive Review of Emerging Metabolomics Technologies to Maximize Their Applications

In their environment, plants interact with a multitude of living organisms and have to cope with a large variety of aggressions of biotic or abiotic origin. What has been known for several decades is that the extraordinary variety of chemical compounds the plants are capable of synthesizing may be estimated in the range of hundreds of thousands, but only a fraction has been fully characterized to be implicated in defense responses. Despite the vast importance of these metabolites for plants and also for human health, our knowledge about their biosynthetic pathways and functions is still fragmentary. Recent progress has been made particularly for the phenylpropanoids and oxylipids metabolism, which is more emphasized in this review. With an increasing interest in monitoring plant metabolic reprogramming, the development of advanced analysis methods should now follow. This review capitalizes on the advanced technologies used in metabolome mapping in planta, including different metabolomics approaches, imaging, flux analysis, and interpretation using bioinformatics tools. Advantages and limitations with regards to the application of each technique towards monitoring which metabolite class or type are highlighted, with special emphasis on the necessary future developments to better mirror such intricate metabolic interactions in planta.

Effect of Position 1 Substituent and Configuration on APCI-MS Fragmentation of Norditerpenoid Alkaloids Including 1-epi-Condelphine

Norditerpenoid alkaloids (NDA) are hexacyclic highly oxygenated compounds, and the analysis of their 3D configuration is important as it helps to interpret their bioactive conformations. High-performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/MS-APCI) is a promising technique to investigate NDA stereochemistry. The effect of the alpha (α)-substituent at carbon 1 and its configuration on the stability of NDA in the mass spectrometer was studied. It was observed that 1-OH NDA are more stable compared to 1-OMe NDA due to the intramolecular H-bonding that exists in 1-OH NDA. In addition, 1-epi-condelphine 9 was found to be less stable in the mass spectrometer compared to condelphine 7 as the nitrogen is no longer hydrogen-bonded to the β-hydroxyl at position 1, which highlights the importance of the substituent configuration at carbon 1.

Elucidating a Complicated Enantioselective Metabolic Profile: A Study From Rats to Humans Using Optically Pure Doxazosin

Doxazosin (DOX) is prescribed as a racemic drug for the clinical treatment of benign prostatic hyperplasia and hypertension. Recent studies found that the two enantiomers of DOX exhibit differences in blood concentration and pharmacological effects. However, the stereoselective metabolic characteristics and mechanisms for DOX are not yet clear. Herein, we identified 34 metabolites of DOX in rats based on our comprehensive and effective strategy. The relationship among the metabolites and the most discriminative metabolites between (−)-DOX and (+)-DOX administration was analyzed according to the kinetic parameters using state-of-the-art multivariate statistical methods. To elucidate the enantioselective metabolic profile in vivo and in vitro, we carefully investigated the metabolic characteristics of metabolites after optically pure isomers administration in rat plasma, rat liver microsomes (RLMs) or human liver microsomes (HLMs), and recombinant human cytochrome P450 (CYP) enzymes. As a result, the differences of these metabolites were found based on their exposure and elimination rate, and the metabolic profile of (±)-DOX was more similar to that of (+)-DOX. Though the metabolites identified in RLMs and HLMs were the same, the metabolic profiles of the metabolites from (−)-DOX and (+)-DOX were greatly different. Furthermore, four human CYP enzymes could catalyze DOX to produce metabolites, but their preferences seemed different. For example, CYP3A4 highly specifically and selectively catalyzed the formation of the specific metabolite (M22) from (−)-DOX. In conclusion, we established a comprehensive metabolic system using pure optical isomers from in vivo to in vitro, and the complicated enantioselectivity of the metabolites of DOX was clearly shown. More importantly, the comprehensive metabolic system is also suitable to investigate other chiral drugs.

Improved coverage of plant metabolites using powder laser desorption/ionization coupled with Fourier-transform ion cyclotron mass spectrometry

In this study, the effectiveness of powder laser desorption/ionization (LDI) coupled with Fourier-transform ion cyclotron mass spectrometry (FT-ICR MS) was evaluated for the improved coverage of plant metabolites. Ground plant (powder) was fixed on a metal plate using double-sided tape. Compared with the conventional approach involving liquid extraction, which is followed by electrospray ionization MS analysis, a smaller amount of sample (∼200 µg) was required in the proposed method. Additionally, the laborious steps of liquid extraction, concentration, and solid-phase extraction were avoided. Employing the proposed method in Centella asiatica leaves analysis, higher number of reproducible molecular formulas (>5000) and metabolites (>650) were obtained than the conventional methods. Flavonoids, phenolic acids, xanthones, lipids, carbohydrates, terpenoids, and alkaloids compounds were detected from leaves, stems, and roots of C. asiatica. This study indicates that LDI FT-ICR MS is a quick and effective tool for enhanced plant metabolite profiling in the solid phase.

Pharmacokinetic study of Ninjin'yoeito: Absorption and brain distribution of Ninjin'yoeito ingredients in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Ninjin'yoeito (NYT), a Japanese traditional Kampo medicine, has been reported to exert various clinical benefits such as relief from fatigue, malaise, anorexia, frailty, sarcopenia, and cognitive dysfunction. Recently, some review articles described the pharmacological effects of NYT and additionally indicated the possibility that multiple ingredients in NYT contribute to these effects. However, pharmacokinetic data on the ingredients are essential in addition to data on their pharmacological activities to accurately determine the active ingredients in NYT.

AIM OF THE STUDY

This study assessed the in vivo pharmacokinetics of NYT using mice.

MATERIALS AND METHODS

Target liquid chromatography-mass spectrometry (LC-MS) and wide target LC-MS or LC-tandem MS of NYT ingredients in plasma and the brain after oral administration of NYT were performed. Imaging MS was performed to investigate the detailed brain distributions of NYT ingredients.

RESULTS

The concentrations of 13 ingredients in plasma and schizandrin in the brain were quantified via target LC-MS, and the wide target analysis illustrated that several ingredients are absorbed into blood and transported into the brain. Imaging MS revealed that schizandrin was homogenously dispersed in the NYT-treated mouse brain.

CONCLUSION

These results should be useful for clarifying the active ingredients of NYT and their mechanisms of actions.

Metabolomic Profiling and Antioxidant Activity of Fruits Representing Diverse Apple and Pear Cultivars

The false fruits of apple (Malus domestica) and pear (Pyrus communis) are consumed all over the world, contributing to the dietary intake of health-promoting antioxidant phytochemicals. For example, polyphenols confer many beneficial effects (according to their chemical structure, bioavailability, and absorption efficiency in the gut) and the consumption of polyphenol-rich apple and pear fruits may therefore reduce the risk of some diseases. However, the content of such molecules is highly dependent on the specific fruit cultivar. To examine this metabolic diversity in detail, we used metabolomic analysis (NMR and HPLC-DAD/MS) to profile the metabolome of six apple and five pear cultivars. We also determined the antioxidant capacity of the extracts (FRAP assay) and correlated this with the metabolomic composition and abundance of specific metabolites. We observed the cultivar-specific accumulation of sugars, amino acids, malic acid, and various polyphenols, which was also related to the growing season for some cultivars. We found that the ancient Italian apple Pom Prussian was enriched for chlorogenic acid as well as more characteristic polyphenols (phloretin derivatives), the pear cultivar Abate Fetel was low in sucrose, and both cultivars displayed high in vitro antioxidant activity. These cultivars may, therefore, be particularly attractive to health-conscious consumers.

Metabolite Profiling of Manilkara zapota L. Leaves by High-Resolution Mass Spectrometry Coupled with ESI and APCI and In Vitro Antioxidant Activity, α-Glucosidase, and Elastase Inhibition Assays

High-resolution mass spectrometry equipped with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources was used to enhance the characterization of phytochemicals of ethanol extracts of Manilkara zapota L. leaves (ZLE). Sugar compounds, dicarboxylic acids, compounds of phenolic acids and flavonoids groups, and other phytochemicals were detected from the leaves. Antioxidant activity and inhibition potentiality of ZLE against α-glucosidase enzyme, and elastase enzyme activities were evaluated in in vitro analysis. ZLE significantly inhibited activities of α-glucosidase enzyme at a lower concentration (IC50 2.51 ± 0.15 µg/mL). Glucose uptake in C2C12 cells was significantly enhanced by 42.13 ± 0.15% following the treatment with ZLE at 30 µg/mL. It also exhibited potential antioxidant activities and elastase enzyme inhibition activity (IC50 27.51 ± 1.70 µg/mL). Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) detected more m/z peaks than electrospray ionization mass spectrometry (ESI-MS), and both ionization techniques illustrated the biological activities of the detected compounds more thoroughly compared to single-mode analysis. Our findings suggest that APCI along with ESI is a potential ionization technique for metabolite profiling, and ZLE has the potential in managing diabetes by inhibiting α-glucosidase activity and enhancing glucose uptake.

MS2 and LC libraries for untargeted metabolomics: Enhancing method development and identification confidence

As part of the "omics" technologies in the life sciences, metabolomics is becoming increasingly important. In untargeted metabolomics, unambiguous metabolite identification and the inevitable coverage bias that comes with the selection of analytical conditions present major challenges. Reliable compound annotation is essential for translating metabolomics data into meaningful biological information. Here, we developed a fast and transferable method for generating in-house MS² libraries to improve metabolite identification. Using the new method we established an in-house MS² library that includes over 4,000 fragmentation spectra of 506 standard compounds for 6 different normalized collision energies (NCEs). Additionally, we generated a comprehensive liquid chromatography (LC) library by testing 57 different LC-MS conditions for 294 compounds. We used the library information to develop an untargeted metabolomics screen with maximum coverage of the metabolome that was successfully tested in a study of 360 human serum samples. The current work demonstrates a workflow for LC-MS/MS-based metabolomics, with enhanced metabolite identification confidence and the possibility to select suitable analysis conditions according to the specific research interest.

ESI outcompetes other ion sources in LC/MS trace analysis

Choosing an appropriate ion source is a crucial step in liquid chromatography mass spectrometry (LC/MS) method development. In this paper, we compare four ion sources for LC/MS analysis of 40 pesticides in tomato and garlic matrices. We compare electrospray ionisation (ESI) source, thermally focused/heated electrospray (HESI), atmospheric pressure photoionisation (APPI) source with and without dopant, and multimode source in ESI mode, atmospheric pressure chemical ionisation (APCI) mode, and combined mode using both ESI and APCI, i.e. altogether seven different ionisation modes. The lowest limits of detection (LoDs) were obtained by ESI and HESI. Widest linear ranges were observed with the conventional ESI source without heated nebuliser gas. In comparison to HESI, ESI source was significantly less affected by matrix effect. APPI ranked second (after ESI) by not being influenced by matrix effect; therefore, it would be a good alternative to ESI if low LoDs are not required. Graphical abstract.

Response in Ambient Low Temperature Plasma Ionization Compared to Electrospray and Atmospheric Pressure Chemical Ionization for Mass Spectrometry

Modern technical evolution made mass spectrometry (MS) an absolute must for analytical chemistry in terms of application range, detection limits and speed. When it comes to mass spectrometric detection, one of the critical steps is to ionize the analyte and bring it into the gas phase. Several ionization techniques were developed for this purpose among which electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are two of the most frequently applied atmospheric pressure methods to ionize target compounds from liquid matrices or solutions. Moreover, recent efforts in the emerging field of "ambient" MS enable the applicability of newly developed atmospheric pressure techniques to solid matrices, greatly simplifying the analysis of samples with MS and anticipating, to ease the required or even leave out any sample preparation and enable analysis at ambient conditions, outside the instrument itself. These developments greatly extend the range of applications of modern mass spectrometry (MS). Ambient methods comprise many techniques; a particular prominent group is, however, the plasma-based methods. Although ambient MS is a rather new field of research, the interest in further developing the corresponding techniques and enhancing their performance is very strong due to their simplicity and often low cost of manufacturing. A precondition for improving the performance of such ion sources is a profound understanding how ionization works and which parameters determine signal response. Therefore, we review relevant compound characteristics for ionization with the two traditional methods ESI and APCI and compare those with one of the most frequently employed representatives of the plasma-based methods, i.e., low temperature plasma ionization. We present a detailed analysis in which compound characteristics are most beneficial for the response of aromatic nitrogen-containing compounds with these three methods and provide evidence that desorption characteristics appear to have the main common, general impact on signal response. In conclusion, our report provides a very useful resource to the optimization of instrumental conditions with respect to most important requirements of the three ionization techniques and, at the same time, for future developments in the field of ambient ionization.

Rapid characterization of nonpolar or low-polarity solvent extracts from herbal medicines by solvent-assisted electrospray ionization mass spectrometry

RATIONALE

The direct detection of nonpolar and low-polarity solvent extracts of herbal medicine is difficult by conventional electrospray ionization mass spectrometry (ESI-MS). This problem can be solved by solvent-assisted electrospray ionization mass spectrometry (SAESI-MS). With the help of assisted solvents (ESI-friendly solvents) at the tip of the spray needle, compounds (especially the low-polarity compounds) in nonpolar and low-polarity solvent extracts can be ionized directly.

METHODS

Herbal medicines were ultrasonically extracted with nonpolar or low-polarity solvents, such as petroleum ether. Thereafter, the extracts were analyzed by conventional ESI-MS, atmospheric pressure chemical ionization mass spectrometry (APCI-MS) and SAESI-MS. The mass spectra obtained from these three methods were compared and analyzed.

RESULTS

Unstable ion signals, and even no ion signals, were observed when the nonpolar and low-polarity solvent extracts were detected directly by conventional ESI-MS. Better specificity, higher sensitivity or cleaner spectra were acquired from SAESI-MS by comparing with the performance of conventional ESI-MS. The ion signals generated by SAESI-MS and APCI-MS were observed in clearly different m/z ranges. A variety of potential compounds were detected in the petroleum ether extracts of Pogostemon cablin and Ligusticum chuanxiong. The relative abundances and signal intensities of the same ion signals from the stems, leaves and decoction pieces of Pogostemon cablin were significantly different by SAESI-MS.

CONCLUSIONS

As a convenient and efficient method, SAESI-MS can be used to directly detect compounds (especially the low-polarity compounds) in nonpolar or low-polarity solvent extracts of herbal medicines, providing abundant chemical information for pharmacological studies. SAESI-MS allows the simultaneous qualitative analysis of multiple compounds in the same complex samples and is thus particularly suitable for the preliminary screening of compounds in complex samples. SAESI-MS can be used to differentiate the different parts of herbal medicines.

Metabolite Profiling Reveals Developmental Inequalities in Pinot Noir Berry Tissues Late in Ripening

Uneven ripening in Vitis vinifera is increasingly recognized as a phenomenon of interest, with substantial implications for fruit and wine composition and quality. This study sought to determine whether variation late in ripening (∼Modified Eichhorn-Lorenz stage 39) was associated with developmental differences that were observable as fruits within a cluster initiated ripening (véraison). Four developmentally distinct ripening classes of berries were tagged at cluster véraison, sampled at three times late in ripening, and subjected to untargeted HPLC-MS to measure variation in amino acids, sugars, organic acids, and phenolic metabolites in skin, pulp, and seed tissues separately. Variability was described using predominantly two strategies. In the first, multivariate analysis (Orthogonal Projections to Latent Structures-Discriminant Analysis, OPLS-DA) was used to determine whether fruits were still distinguishable per their developmental position at véraison and to identify which metabolites accounted for these distinctions. The same technique was used to assess changes in each tissue over time. In a second strategy and for each annotated metabolite, the variance across the ripening classes at each time point was measured to show whether intra-cluster variance (ICV) was growing, shrinking, or constant over the period observed. Indeed, berries could be segregated by OPLS-DA late in ripening based on their developmental position at véraison, though the four ripening classes were aggregated into two larger ripening groups. Further, not all tissues were dynamic over the period examined. Although pulp tissues could be segregated by time sampled, this was not true for seed and only moderately so for skin. Ripening group differences in seed and skin, rather than the time fruit was sampled, were better able to define berries. Metabolites also experienced significant reductions in ICV between single pairs of time points, but never across the entire experiment. Metabolites often exhibited a combination of ICV expansion, contraction and persistence. Finally, we observed significant differences in the abundance of some metabolites between ripening classes that suggest the berries that initiated ripening first remained developmentally ahead of the lagging fruit even late in the ripening phase. This presents a challenge to producers who would seek to harvest at uniformity or at a predefined level of variation.