Unveiling spatial metabolome of Paeonia suffruticosa and Paeonia lactiflora roots using MALDI MS imaging

LC-MS and MALDI-MSI-based metabolomic approaches provide insights into the spatial-temporal metabolite profiles of Tartary buckwheat achene development

Tartary buckwheat, celebrated as the "king of grains" for its flavonoid and phenolic acid richness, has health-promoting properties. Despite significant morphological and metabolic variations in mature achenes, research on their developmental process is limited. Utilizing Liquid chromatography-mass spectrometry and atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry imaging, we conducted spatial-temporal metabolomics on two cultivars during achene development. Metabolic profiles including 17 phenolic acids and 83 flavonoids are influenced by both varietal distinctions and developmental intricacies. Notably, flavonols, as major flavonoids, accumulated with achene ripening and showed a tissue-specific distribution. Specifically, flavonol glycosides and aglycones concentrated in the embryo, while methylated flavonols and procyanidins in the hull. Black achenes at the green achene stage have higher bioactive compounds and enhanced antioxidant capacity. These findings provide insights into spatial and temporal characteristics of metabolites in Tartary buckwheat achenes and serve as a theoretical guide for selecting optimal resources for food production.

In situ mass spectrometry imaging reveals pesticide residues and key metabolic pathways throughout the entire cowpea growth process

Cowpea plants, renowned for their high edibility, pose a significant risk of pesticide residue contamination. Elucidating the behavior of pesticide residues and their key metabolic pathways is critical for ensuring cowpea safety and human health. This study investigated the migration of pesticide residues and their key metabolic pathways in pods throughout the growth process of cowpea plants via in situ mass spectrometry. To this end, four pesticides--including systemic (thiram), and nonsystemic (fluopyram, pyriproxyfen, and cyromazine) pesticides--were selected. The results indicate the direct upward and downward transmission of pesticides in cowpea stems and pods. Systemic pesticides gradually migrate to the core of cowpea plants, whereas nonsystemic pesticides remain on the surface of cowpea peels. The migration rate is influenced by the cowpea maturity, logarithmic octanol-water partition coefficient (log Kow) value, and molecular weight of the pesticide. Further, 20 types of key metabolites related to glycolysis, tricarboxylic acid cycle, and flavonoid synthesis were found in cowpea pods after pesticide treatment. These findings afford insights into improving cowpea quality and ensuring the safe use of pesticides.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2021-2022

The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates is a well-established technique and this review is the 12th update of the original article published in 1999 and brings coverage of the literature to the end of 2022. As with previous review, this review also includes a few papers that describe methods appropriate to analysis by MALDI, such as sample preparation, even though the ionization method is not MALDI. The review follows the same format as previous reviews. It is divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of computer software for structural identification. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other general areas such as medicine, industrial processes, natural products and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. MALDI is still an ideal technique for carbohydrate analysis, particularly in its ability to produce single ions from each analyte and advancements in the technique and range of applications show little sign of diminishing.

Active metabolites combination therapies: towards the next paradigm for more efficient and more scientific Chinese medicine

Traditional Chinese medicine (TCM) formulae have been studied extensively in various human diseases and have proven to be effective due to their multi-component, multi-target advantage. However, its active metabolites are not clear and the specific mechanisms are not well established, which limits its scientific application. Recently, combination therapies are attracting increasing attention from the scientific community in the past few years and are considered as the next paradigm in drug discovery. Here, we tried to define a new concept of "active metabolites combination therapies (AMCT)" rules to elucidate how the bioactive metabolites from TCMs to produce their synergistic effects in this review. The AMCT rules integrate multidisciplinary technologies like molecular biology, biochemistry, pharmacology, analytical chemistry and pharmacodynamics, etc. Meanwhile, emerging technologies such as multi-omics combined analysis, network analysis, artificial intelligence conduce to better elucidate the mechanisms of these combination therapies in disease treatment, which provides new insights for the development of novel active metabolites combination drugs. AMCT rules will hopefully further guide the development of novel combination drugs that will promote the modernization and international needs of TCM.

Phytochemical Analysis, Biological Activities, and Molecular Docking Studies of Root Extracts from Paeonia Species in Serbia

Without being aware of their chemical composition, many cultures have used herbaceous peony roots for medicinal purposes. Modern phytopreparations intended for use in human therapy require specific knowledge about the chemistry of peony roots and their biological activities. In this study, ethanol-water extracts were prepared by maceration and microwave- and ultrasound-assisted extractions (MAE and UAE, respectively) in order to obtain bioactive molecules from the roots of Paeonia tenuifolia L., Paeonia peregrina Mill., and Paeonia officinalis L. wild growing in Serbia. Chemical characterization; polyphenol and flavonoid content; antioxidant, multianti-enzymatic, and antibacterial activities of extracts; and in vitro gastrointestinal digestion (GID) of hot water extracts were performed. The strongest anti-cholinesterase activity was observed in PT extracts. The highest anti-ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical potential was observed in PP extracts, whereas against DPPH (2,2-diphenyl-1-picrylhydrazyl radicals), the best results were achieved with PO extracts. Regarding antibacterial activity, extracts were strongly potent against Bacillus cereus. A molecular docking simulation was conducted to gather insights into the binding affinity and interactions of polyphenols and other Paeonia-specific molecules in the active sites of tested enzymes. In vitro GID of Paeonia teas showed a different recovery and behavior of the individual bioactives, with an increased recovery of methyl gallate and digallate and a decreased recovery of paeoniflorin and its derivatives. PT (Gulenovci) and PP (Pirot) extracts obtained by UAE and M were more efficient in the majority of the bioactivity assays. This study represents an initial step toward the possible application of Paeonia root extracts in pharmacy, medicine, and food technologies.

Novel Small Molecule Matrix Screening for Simultaneous MALDI Mass Spectrometry Imaging of Multiple Lipids and Phytohormones

Most of the traditional matrices cannot simultaneously image multiple lipids and phytohormones, so screening and discovery of novel matrices stand as essential approaches for broadening the application scope of matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). In this work, 12 organic small molecule compounds were comprehensively screened and investigated as potential MALDI matrices for simultaneous imaging analysis of various lipids and phytohormones. In the positive ionization mode, p-nitroaniline, m-nitroaniline, and 2-aminoterephthalic acid displayed good performance for the highly sensitive detection of lysophosphatidylcholines (LPCs), phosphatidylcholines (PCs), and triacylglycerols (TGs). Furthermore, p-nitroaniline possessed excellent characteristics of strong ultraviolet absorption and homogeneous cocrystallization, making it a desirable matrix for MALDI-MSI analysis of eight plant hormones. Compared with conventional matrices (2,5-dihydroxybenzoic acid (DHB), α-cyano-4-hydroxycinnamic acid (CHCA), and 9-aminoacridine (9-AA), the use of p-nitroaniline resulted in higher ionization efficiency, superior sensitivity, and clearer imaging images in dual polarity mode. Our research offers valuable guidance and new ideas for future endeavors in matrix screening.

Imaging plant metabolism in situ

Mass spectrometry imaging (MSI) has emerged as an invaluable analytical technique for investigating the spatial distribution of molecules within biological systems. In the realm of plant science, MSI is increasingly employed to explore metabolic processes across a wide array of plant tissues, including those in leaves, fruits, stems, roots, and seeds, spanning various plant systems such as model species, staple and energy crops, and medicinal plants. By generating spatial maps of metabolites, MSI has elucidated the distribution patterns of diverse metabolites and phytochemicals, encompassing lipids, carbohydrates, amino acids, organic acids, phenolics, terpenes, alkaloids, vitamins, pigments, and others, thereby providing insights into their metabolic pathways and functional roles. In this review, we present recent MSI studies that demonstrate the advances made in visualizing the plant spatial metabolome. Moreover, we emphasize the technical progress that enhances the identification and interpretation of spatial metabolite maps. Within a mere decade since the inception of plant MSI studies, this robust technology is poised to continue as a vital tool for tackling complex challenges in plant metabolism.

Integrated Metabolomics Approach Reveals the Dynamic Variations of Metabolites and Bioactivities in Paeonia ostii 'Feng Dan' Leaves during Development

Paeonia ostii 'Feng Dan' is widely cultivated in China for its ornamental, medicinal, and edible properties. The whole plant of tree peony is rich in bioactive substances, while the comprehensive understanding of metabolites in the leaves is limited. In this study, an untargeted metabolomics strategy based on UPLC-ESI-TOF-MS was conducted to analyze the dynamic variations of bioactive metabolites in P. ostii 'Feng Dan' leaves during development. A total of 321 metabolites were rapidly annotated based on the GNPS platform, in-house database, and publications. To accurately quantify the selected metabolites, a targeted method of HPLC-ESI-QQQ-MS was used. Albiflorin, paeoniflorin, pentagalloylglucose, luteolin 7-glucoside, and benzoylpaeoniflorin were recognized as the dominant bioactive compounds with significant content variations during leaf development. Metabolite variations during the development of P. ostii 'Feng Dan' leaves are greatly attributed to the variations in antioxidant activities. Among all tested bacteria, the leaf extract exhibited exceptional inhibitory effects against Streptococcus hemolytis-β. This research firstly provides new insights into tree peony leaves during development. The stages of S1-S2 may be the most promising harvesting time for potential use in food or pharmaceutical purposes.

Combined Widely Targeted Metabolomic, Transcriptomic, and Spatial Metabolomic Analysis Reveals the Potential Mechanism of Coloration and Fruit Quality Formation in Actinidia chinensis cv. Hongyang

Postharvest kiwifruit (Actinidia chinensis cv. Hongyang) pulp is mainly composed of outer yellow-flesh (LR) and inner red-flesh (HR). However, information about the differences in coloration and fruit quality between these two parts are limited. In this study, widely targeted metabolomic, transcriptomic, and spatial metabolomic analyses were used to reveal the potential mechanism of coloration and fruit quality formation. The results show that a total of 1001 metabolites were identified in Hongyang kiwifruit, and the accumulation of 211 metabolites were significantly higher in the HR than LR, including 69 flavonoids, 53 phenolic acids, and 38 terpenoids. There were no significant differences in the content of citric acid, quinic acid, glucose, fructose, or sucrose between the LR and HR. These results were consistent with the results from the RNA-seq profile and spatial metabolomic analysis. In addition, a total of 23 key candidate genes related to flesh color and fruit quality formation were identified and validated by qRT-PCR analysis. This study provides a theoretical basis for elucidating the underlying mechanism of the formation of kiwifruit flesh color and fruit quality.

Unveiling targeted spatial metabolome of rice seed at the dough stage using Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry imaging

Rice (Oryza sativa) seeds contain a variety of metabolites, which not only provide energy for their own growth and development, but also are an important source of nutrition for humans. It is crucial to study the distribution of metabolites in rice seeds, but the spatial metabolome of rice seeds is rarely investigated. In this study, Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS) imaging was used to reveal the spatial distribution of free soluble sugars (glucose, fructose, sucrose, and maltose), amino acids (9 essential amino acids and 2 amino acids affecting rice eating quality: L-aspartic acid and L-glutamic acid), and 4 metabolites in the flavonoids synthesis pathway (cinnamic acid, naringenin chalcone, naringenin, and dihydrokaempferol) in rice seed at the dough stage. It was found that the 4 free soluble sugars present similar spatial distribution, mainly distributed in the seed cortex and embryo with high abundance. The majority of amino acids are also concentrated in the rice cortex and embryo, while the others are abundant in the whole seed. Besides cinnamic acid distributed in the seed cortex and embryo, the naringenin chalcone, naringenin, and dihydrokaempferol were also found in the endosperm and had lower content. Furthermore, a colocalization phylogenetic tree according to the spatial distribution imaging of each metabolite was constructed. This study revealed the distribution diversity of metabolites in different segmentations of rice seed at the dough stage, providing clues for the nutritional differences between brown rice and white rice, and serving as a reference for people to target a healthy diet.

Unveiling the spatial distribution and molecular mechanisms of terpenoid biosynthesis in Salvia miltiorrhiza and S. grandifolia using multi-omics and DESI-MSI

Salvia miltiorrhiza and S. grandifolia are rich in diterpenoids and have therapeutic effects on cardiovascular diseases. In this study, the spatial distribution of diterpenoids in both species was analyzed by a combination of metabolomics and mass spectrometry imaging techniques. The results indicated that diterpenoids in S. miltiorrhiza were mainly abietane-type norditerpenoid quinones with a furan or dihydrofuran D-ring and were mainly distributed in the periderm of the roots, e.g. cryptotanshinone and tanshinone IIA. The compounds in S. grandifolia were mainly phenolic abietane-type tricyclic diterpenoids with six- or seven-membered C-rings, and were widely distributed in the periderm, phloem, and xylem of the roots, e.g. 11-hydroxy-sugiol, 11,20-dihydroxy-sugiol, and 11,20-dihydroxy-ferruginol. In addition, the leaves of S. grandifolia were rich in tanshinone biosynthesis precursors, such as 11-hydroxy-sugiol, while those of S. miltiorrhiza were rich in phenolic acids. Genes in the upstream pathway of tanshinone biosynthesis were highly expressed in the root of S. grandifolia, and genes in the downstream pathway were highly expressed in the root of S. miltiorrhiza. Here, we describe the specific tissue distributions and mechanisms of diterpenoids in two Salvia species, which will facilitate further investigations of the biosynthesis of diterpenoids in plant synthetic biology.

A novel visualization method for the composition analysis of processed garlic by MALDI-TOF imaging mass spectrometry (MSI) and Q-TOF LC-MS/MS

Laba garlic is a kind of vinegar processed garlic (Allium sativum L.) product with multiple health effects. This study applied matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-TOF MSI) and Q-TOF LC-MS/MS for the first time to investigate the garlic tissue spatial distribution changes of low molecular weight compounds during the Laba garlic processing. The distribution characteristics of the compounds were observed in processed and unprocessed garlic including amino acids and derivatives, organosulfur compounds, pigment precursors, polysaccharides and saponins. During Laba garlic processing, some bioactive compounds such as alliin and saponins were lost because they were transformed into other compounds or leached into the acetic acid solution, and some new compounds including pigments-related compounds occurred. This study provided a basis for the spatial distributions and changes of compounds in garlic tissue during Laba garlic processing, which suggested that the bioactivities of garlic might be changed after processing owing to the transformation and change of the constituents.

MALDI Imaging Assisted Discovery of a Di-O-glycosyltransferase from Platycodon grandiflorum Root

A matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) assisted genome mining strategy was developed for the discovery of glycosyltransferase (GT) from the root of Platycodon grandiflorum. A di-O-glycosyltransferase PgGT1 was discovered and characterized that is capable of catalyzing platycoside E (PE) synthesis through the attachment of two β-1,6-linked glucosyl residues sequentially to the glucosyl residue at the C3 position of platycodin D (PD). Although UDP-glucose is the preferred sugar donor for PgGT1, it could also utilize UDP-xylose and UDP-N-acetylglucosamine as weak donors. Residues S273, E274, and H350 played important roles in stabilizing the glucose donor and positioning the glucose in the optimal orientation for the glycosylation reaction. This study clarified two key steps involved in the biosynthetic pathway of PE and could greatly contribute to improving its industrial biotransformation.

Kampo herbal ointments for skin wound healing

The management of skin wound healing problems is a public health issue in which traditional herbal medicines could play a determining role. Kampo medicine, with three traditionally used ointments, provides interesting solutions for these dermatological issues. These ointments named Shiunkō, Chuōkō, and Shinsen taitsukō all have in common a lipophilic base of sesame oil and beeswax from which herbal crude drugs are extracted according to several possible manufacturing protocols. This review article brings together existing data on metabolites involved in the complex wound healing process. Among them are representatives of the botanical genera Angelica, Lithospermum, Curcuma, Phellodendron, Paeonia, Rheum, Rehmannia, Scrophularia, or Cinnamomum. Kampo provides numerous metabolites of interest, whose content in crude drugs is very sensitive to different biotic and abiotic factors and to the different extraction protocols used for these ointments. If Kampo medicine is known for its singular standardization, ointments are not well known, and research on these lipophilic formulas has not been developed due to the analytical difficulties encountered in biological and metabolomic analysis. Further research considering the complexities of these unique herbal ointments could contribute to a rationalization of Kampo's therapeutic uses for wound healing.

Spatial segmentation of mass spectrometry imaging data featuring selected principal components

Spatial segmentation aims to find homogeneous/heterogeneous subgroups of spectra or ion images in mass spectrometry imaging (MSI) data. The maps it generated inform researchers of vital characteristics of the data and thus provide the basis for strategizing further biological analysis. Dimensional reduction and clustering are two basic steps of segmentation. Due to the variations in the quality, resolution, density of spectral information, and sizes, not all datasets could be segmented ideally with combinations of different dimensional reduction and clustering algorithms. Here, we proposed a segmentation pipeline that utilized pattern compression by principal component analysis (PCA) and represented by principal components. Instead of preprocessed or raw MSI data, normalized principal components were used for the segmentation process. Multiple datasets of rat brains and mouse kidneys were tested, and the proposed segmentation pipeline presented the obvious advantage of easy-to-use and can be readily intergraded with other existing innovative pipelines.

Metabolomics-centered mining of plant metabolic diversity and function: Past decade and future perspectives

Plants are natural experts in organic synthesis, being able to generate large numbers of specific metabolites with widely varying structures that help them adapt to variable survival challenges. Metabolomics is a research discipline that integrates the capabilities of several types of research including analytical chemistry, statistics, and biochemistry. Its ongoing development provides strategies for gaining a systematic understanding of quantitative changes in the levels of metabolites. Metabolomics is usually performed by targeting either a specific cell, a specific tissue, or the entire organism. Considerable advances in science and technology over the last three decades have propelled us into the era of multi-omics, in which metabolomics, despite at an earlier developmental stage than genomics, transcriptomics, and proteomics, offers the distinct advantage of studying the cellular entities that have the greatest influence on end phenotype. Here, we summarize the state of the art of metabolite detection and identification, and illustrate these techniques with four case study applications: (i) comparing metabolite composition within and between species, (ii) assessing spatio-temporal metabolic changes during plant development, (iii) mining characteristic metabolites of plants in different ecological environments and upon exposure to various stresses, and (iv) assessing the performance of metabolomics as a means of functional gene identification , metabolic pathway elucidation, and metabolomics-assisted breeding through analyzing plant populations with diverse genetic variations. In addition, we highlight the prominent contributions of joint analyses of plant metabolomics and other omics datasets, including those from genomics, transcriptomics, proteomics, epigenomics, phenomics, microbiomes, and ion-omics studies. Finally, we discuss future directions and challenges exploiting metabolomics-centered approaches in understanding plant metabolic diversity.

In situ detection and mass spectrometry imaging of protein-related metabolites in Bombyx batryticatus before and after frying with wheat bran

Bombyx batryticatus is derived from the dried larva of Bombyx mori Linnaeus infected by Beauveria bassiana (Bals.) Vuillant. Raw Bombyx batryticatus should be stir-fried before oral administration due to its irritation to the gastrointestinal tract. Nevertheless, it is still an arduous task to uncover the intrinsic mechanism of Bombyx batryticatus processing. In this study, we collected two types of Bombyx batryticatus, one being stir-fried and the other serving as a control. Then, an informative approach, which integrated matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) with chemometrics analysis, was established to screen processing-associated markers and reveal in situ spatial distribution patterns of protein-related metabolites. After optimization of experimental conditions, 21 ions were initially detected from Bombyx batryticatus, including amino acids and peptides. In addition, 15 differential markers were screened by orthogonal projection to potential structure discriminant analysis (OPLS-DA), which were localized and visualized in the transverse section of Bombyx batryticatus by MSI. Eventually, it can be demonstrated that the stir-frying process reduces toxicity while potentially boosting specific biological activities of Bombyx batryticatus. In summary, the established strategy could not only clarify the chemical transformation of protein-related metabolites from Bombyx batryticatus before and after frying with wheat bran, but also reveal the significance of Chinese medicine processing technology.

A mass spectrometry imaging approach on spatiotemporal distribution of multiple alkaloids in Gelsemium elegans

Gelsemium elegans contains multiple alkaloids with pharmacological effects, thus researchers focus on the identification and application of alkaloids extracted from G. elegans. Regretfully, the spatiotemporal distribution of alkaloids in G. elegans is still unclear. In this study, the desorption electrospray ionization mass spectrometry imaging (DESI-MSI) was applied to simultaneously analyze the distribution of pharmacologically important alkaloids in different organ/tissue sections of G. elegans at different growth stages. Finally, 23 alkaloids were visualized in roots, stems and leaves at seedling stage and 19 alkaloids were observed at mature stage. In mature G. elegans, 16 alkaloids were distributed in vascular bundle region of mature roots, 15 alkaloids were mainly located in the pith region of mature stems and 2 alkaloids were enriched in epidermis region of mature stems. A total of 16 alkaloids were detected in leaf veins of mature leaves and 17 alkaloids were detected in shoots. Interestingly, diffusion and transfer of multiple alkaloids in tissues have been observed along with the development and maturation. This study comprehensively characterized the spatial metabolomics of G. elegans alkaloids, and the spatiotemporal distribution of alkaloid synthesis. In addition, the results also have reference value for the development and application of Gelsemium elegans and other medicinal plants.

Spatially resolved metabolomics reveals variety-specific metabolic changes in banana pulp during postharvest senescence

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Both post-ripening stages and banana varieties contribute to metabolite variation.

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AuNP-assisted LDI-MSI was firstly used in mapping functional metabolites in pulps.

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AAs and monoamines exclusively accumulated in the middle region near the seed zone.

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Monosaccharides locate in whole pulps but enrich in the intermediate microregion.

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Di/trisaccharides exhibit different accumulation patterns as monosaccharides.

Banana is one of most popular fruits globally due to health-promoting and disease-preventing effects, yet little is known about in situ metabolic changes across banana varieties. Here, we integrated gold nanoparticle (AuNP)-assisted laser desorption/ionization mass spectrometry imaging (LDI-MSI) and metabolomics to investigate the spatiotemporal distribution and levels of metabolites within Brazil and Dongguan banana pulps during postharvest senescence. Metabolomics results indicated that both postripening stages and banana varieties contribute to metabolite levels. Benefiting from improved ionization efficiency of small-molecule metabolites and less peak interference, we visualized the spatiotemporal distribution of sugars, amino acids (AAs) and monoamines within pulps using AuNP-assisted LDI-MSI for the first time, revealing that AAs and monoamines exclusively accumulated in the middle region near the seed zone. Monosaccharides and di/trisaccharides were generally distributed across entire pulps but exhibited different accumulation patterns. These findings provide a guide for breeding new varieties and improving extraction efficiency of bioactive compounds.

Advances in mass spectrometry imaging for toxicological analysis and safety evaluation of pharmaceuticals

Safety issues caused by pharmaceuticals have frequently occurred worldwide, posing a tremendous threat to human health. As an essential part of drug development, the toxicological analysis and safety evaluation is of great significance. In addition, the risk of pharmaceuticals accumulation in the environment and the monitoring of the toxicity from natural medicines have also received ongoing concerns. Due to a lack of spatial distribution information provided by common analytical methods, analyses that provide spatial dimensions could serve as complementary safety evaluation methods for better prediction and evaluation of drug toxicity. With advances in technical solutions and software algorithms, mass spectrometry imaging (MSI) has received increasing attention as a popular analytical tool that enables the simultaneous implementation of qualitative, quantitative, and localization without complex sample pretreatment and labeling steps. In recent years, MSI has become more attractive, powerful, and sensitive and has been applied in several scientific fields that can meet the safety assessment requirements. This review aims to cover a detailed summary of the various MSI technologies utilized in the biomedical and pharmaceutical area, including technical principles, advantages, current status, and future trends. Representative applications and developments in the safety-related issues of different pharmaceuticals and natural medicines are also described to provide a reference for pharmaceutical research, improve rational clinical medicine use, and ensure public safety.

Recent advances in proteomics and metabolomics in plants

Over the past decade, systems biology and plant-omics have increasingly become the main stream in plant biology research. New developments in mass spectrometry and bioinformatics tools, and methodological schema to integrate multi-omics data have leveraged recent advances in proteomics and metabolomics. These progresses are driving a rapid evolution in the field of plant research, greatly facilitating our understanding of the mechanistic aspects of plant metabolisms and the interactions of plants with their external environment. Here, we review the recent progresses in MS-based proteomics and metabolomics tools and workflows with a special focus on their applications to plant biology research using several case studies related to mechanistic understanding of stress response, gene/protein function characterization, metabolic and signaling pathways exploration, and natural product discovery. We also present a projection concerning future perspectives in MS-based proteomics and metabolomics development including their applications to and challenges for system biology. This review is intended to provide readers with an overview of how advanced MS technology, and integrated application of proteomics and metabolomics can be used to advance plant system biology research.

Image to insight: exploring natural products through mass spectrometry imaging

Covering: 2017 to 2022Mass spectrometry imaging (MSI) has become a mature molecular imaging technique that is well-matched for natural product (NP) discovery. Here we present a brief overview of MSI, followed by a thorough discussion of different MSI applications in NP research. This review will mainly focus on the recent progress of MSI in plants and microorganisms as they are the main producers of NPs. Specifically, the opportunity and potential of combining MSI with other imaging modalities and stable isotope labeling are discussed. Throughout, we focus on both the strengths and weaknesses of MSI, with an eye on future improvements that are necessary for the progression of MSI toward routine NP studies. Finally, we discuss new areas of research, future perspectives, and the overall direction that the field may take in the years to come.

Recognition of Gallotannins and the Physiological Activities: From Chemical View

Gallotannins, characterized with the glycosidic core and galloyl unit, are seemed as vital components of hydrolyzable tannins. Benefit from the more and more discoveries of their bioactivities and edibility, application of gallotannins in food industry, pharmacy industry, and other fields is increasing. Inheriting previous study achievements, chemical structure of gallotannins was illustrated and degradation as well as synthetic routes to gallotannins were summarized. On this basis, distribution in the nature also including the distinction of gallotannins was discussed. More than that, activities involving in antioxidant, anti-inflammatory, enzyme inhibitions, protein binding, and so on, as well as applications in the field of food industry, biopharmaceutical science, agricultural production, etc., were combed. Finally, improvement of bioavailability, chemical modification of the structure, and accurate determination of new gallotannins were pointed out to be the orientation in the future.

Integrated metabolite profiling and transcriptome analysis reveals tissue-specific regulation of terpenoid biosynthesis in Artemisia argyi

Artemisia argyi L. is a widely distributed medicinal plant in China. The major bioactive substances of essential oils extracted from leaves are terpenoids. Although many researches have studied the pharmacological effects of the essential oils, the tissue-specific accumulation of terpenoid biosynthesis and the regulatory networks in A. argyi are poorly understood. This study conducted an integrated metabolomic and transcriptomic analysis of roots, stems, and leaves to investigate the tissue-specific regulatory network of terpenoid biosynthesis in A. argyi. We identified 77 unigenes putatively involved in terpenoid backbone biosynthesis. Three rate-determining enzyme genes (DXS, DXR, and HDR) of the methylerythritol phosphate pathway were predominantly expressed in leaves, and strongly co-expressed with eight transcription factors (2 MYBs, 4 WRKYs, and 2 AP2s). An metabolite-transcript correlation analysis revealed 26 putative cytochrome P450s related to terpenoid metabolism in leaves. These results provide a foundation for the future metabolic engineering of useful terpenoids in A. argyi.

Mass Spectrometry Imaging for Spatial Chemical Profiling of Vegetative Parts of Plants

The detection of chemical species and understanding their respective localisations in tissues have important implications in plant science. The conventional methods for imaging spatial localisation of chemical species are often restricted by the number of species that can be identified and is mostly done in a targeted manner. Mass spectrometry imaging combines the ability of traditional mass spectrometry to detect numerous chemical species in a sample with their spatial localisation information by analysing the specimen in a 2D manner. This article details the popular mass spectrometry imaging methodologies which are widely pursued along with their respective sample preparation and the data analysis methods that are commonly used. We also review the advancements through the years in the usage of the technique for the spatial profiling of endogenous metabolites, detection of xenobiotic agrochemicals and disease detection in plants. As an actively pursued area of research, we also address the hurdles in the analysis of plant tissues, the future scopes and an integrated approach to analyse samples combining different mass spectrometry imaging methods to obtain the most information from a sample of interest.

Unraveling the drug distribution in brain enabled by MALDI MS imaging with laser-assisted chemical transfer

Accurate localization of central nervous system (CNS) drug distribution in the brain is quite challenging to matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI), owing to the ionization competition/suppression of highly abundant endogenous biomolecules and MALDI matrix. Herein, we developed a highly efficient sample preparation technique, laser-assisted chemical transfer (LACT), to enhance the detection sensitivity of CNS drugs in brain tissues. A focused diode laser source transilluminated the tissue slide coated with α-cyano-4-hydroxycinnamic acid, an optimal matrix to highly absorb the laser radiation at 405 nm, and a very thin-layer chemical film mainly containing drug molecule was transferred to the acceptor glass slide. Subsequently, MALDI MSI was performed on the chemical film without additional sample treatment. One major advantage of LACT is to minimize ionization competition/suppression from the tissue itself by removing abundant endogenous lipid and protein components. The superior performance of LACT led to the successful visualization of regional distribution patterns of 16 CNS drugs in the mouse brain. Furthermore, the dynamic spatial changes of risperidone and its metabolite were visualized over a 24-h period. Also, the brain-to-plasma (B/P) ratio could be obtained according to MALDI MSI results, providing an alternative means to assess brain penetration in drug discovery.

Advanced applications of mass spectrometry imaging technology in quality control and safety assessments of traditional Chinese medicines

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicines (TCMs) have made great contributions to the prevention and treatment of human diseases in China, and especially in cases of COVID-19. However, due to quality problems, the lack of standards, and the diversity of dosage forms, adverse reactions to TCMs often occur. Moreover, the composition of TCMs makes them extremely challenging to extract and isolate, complicating studies of toxicity mechanisms.

AIM OF THE REVIEW

The aim of this paper is therefore to summarize the advanced applications of mass spectrometry imaging (MSI) technology in the quality control, safety evaluations, and determination of toxicity mechanisms of TCMs.

MATERIALS AND METHODS

Relevant studies from the literature have been collected from scientific databases, such as "PubMed", "Scifinder", "Elsevier", "Google Scholar" using the keywords "MSI", "traditional Chinese medicines", "quality control", "metabolomics", and "mechanism".

RESULTS

MSI is a new analytical imaging technology that can detect and image the metabolic changes of multiple components of TCMs in plants and animals in a high throughput manner. Compared to other chemical analysis methods, such as liquid chromatography-mass spectrometry (LC-MS), this method does not require the complex extraction and separation of TCMs, and is fast, has high sensitivity, is label-free, and can be performed in high-throughput. Combined with chemometrics methods, MSI can be quickly and easily used for quality screening of TCMs. In addition, this technology can be used to further focus on potential biomarkers and explore the therapeutic/toxic mechanisms of TCMs.

CONCLUSIONS

As a new type of analysis method, MSI has unique advantages to metabolic analysis, quality control, and mechanisms of action explorations of TCMs, and contributes to the establishment of quality standards to explore the safety and toxicology of TCMs.

Comparative Elucidation of Age, Diameter, and "Pockmarks" in Roots of Paeonia lactiflora Pall. (Shaoyao) by Qualitative and Quantitative Methods

Paeonia lactiflora Pall. is a world-famous ornamental plant, whose roots have been used as an important traditional Chinese medicine, Shaoyao, to treat diseases for more than 1,000 years. Because of the excellent curative effect of Shaoyao, its quality has attracted wide attention, however, there is a lack of comprehensive research on the different influencing factors of quality of Shaoyao. In this study, ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q/TOF-MS) and high-performance liquid chromatography with diode-array detection (HPLC-DAD) were utilized to systematically analyze the Shaoyao of different ages, diameters and roots with "pockmarks." 60 metabolites were detected and identified from Shaoyao using the UPLC-Q/TOF-MS, of which 20 potential quality markers of dissected roots with and without "pockmarks" were selected for the first time using the orthogonal partial least squares discriminant analysis (OPLS-DA) and the variable importance for projection (VIP) plot. Then, a selective and accurate HPLC-DAD quantitative assay has been developed for the simultaneous determination of 11 bioactive components in Shaoyao. The results showed that the total content of five monoterpene glycosides including oxypaeoniflorin, albiflorin, paeoniflorin, lactiflorin, and benzoylpaeoniflorin and six phenols including gallic acid, catechin, methyl gallate, ethyl gallate, apiopaeonoside and benzoic acid in the 3-year-old Shaoyao was higher than that of 4-year-old and 5-year-old Shaoyao. In Shaoyao of the same age, the total content of five monoterpene glycosides and six phenols decreased with an increase in diameter. In addition, regardless of whether it is a whole or a divided root, the contents of five monoterpene glycosides and six phenols in Shaoyao with "pockmarks" were higher than those of Shaoyao without "pockmarks." In summary, this work has explored several factors that might affect the quality of Shaoyao, and provide a guide for more comprehensive quality evaluation in its further production, processing, and rational utilization.

Tracing the migration and transformation of metabolites in xylem during wood growth by mass spectrometry imaging

MALDI MSI was used to explore the rule of metabolite migration and transformation for the first time. The rules of heartwood formation and resin secretion were visualized and fully explored.

Paeoniflorin in Paeoniaceae: Distribution, influencing factors, and biosynthesis

Paeoniflorin, a monoterpene glucoside, is increasingly used in the clinical treatment of many diseases because it has a variety of pharmacological activities. Besides, paeoniflorin has been considered the characteristic chemical constituent of Paeoniaceae plants since it was first reported in 1963. Therefore, how to better develop and utilize paeoniflorin in Paeoniaceae has always been a research hotspot. We reviewed the current knowledge on paeoniflorin in Paeoniaceae, with particular emphasis on its distribution and influencing factors. Moreover, the limited understanding of the biosynthesis pathway has restricted the production of paeoniflorin by synthetic biology. This review provides insights into the post-modification pathway of paeoniflorin biosynthesis and proposes directions for further analysis in the future.

Characterizing the spatial distribution of dipeptides in rodent tissue using MALDI MS imaging with on-tissue derivatization

A highly efficient on-tissue derivatization method for the matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) of dipeptides in tissues has been developed via a combination of a home-built laser-assisted chemical transfer (LACT) technique and hexafluoroisopropanol (HFIP).