Comparative investigation of phytochemicals among ten citrus herbs by ultra high performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry and evaluation of their antioxidant properties

Integrated metabolomics and network pharmacology to reveal antioxidant mechanisms and potential pharmacological ingredients of citrus herbs

The benefits of citrus herbs are strongly associated with their secondary metabolites. In the study, we conducted widely-targeted metabolomics and ultra-high performance liquid chromatography (UPLC) to compare the variability of ingredients in four citrus herbs. In total, we discovered 1126 secondary metabolites, primarily comprising flavonoids, phenolic acids, lignans and coumarins, and alkaloids. Differential metabolites of citrus herbs were searched by multivariate statistical analysis. Notably, Citri Reticulatae Pericarpium contained higher levels of flavonoids, while Zhique and Huajuhong demonstrated a greater abundance of coumarins. Among the flavonoids determined by UPLC, Guangchenpi demonstrated significantly elevated levels of polymethoxyflavones (tangeretin and nobiletin) compared to other citrus herbs. Additionally, we determined their antioxidant capacity (Chenpi > Guangchenpi > Huajuhong > Zhique) using in vitro assays. Finally, we utilized network pharmacology to explore the antioxidant mechanisms and potential pharmacological ingredients, providing a basis for future preventive and therapeutic applications of these metabolites.

Narirutin. A flavonoid found in citrus fruits modulates cell cycle phases and inhibits the proliferation of hormone-refractory prostate cancer cells by targeting hyaluronidase

Narirutin is a dietary flavanone found in lemons, oranges, passion fruit, bergamot and grapefruit. It possesses anti-allergic, cardioprotective, neuroprotective, hepatoprotective potential, and its enriched fraction suppresses the growth of prostate cancer cells; however, there is currently no information on the chemopreventive potential of narirutin alone against hormone-refractory prostate cancer cells (PC-3) and its mode of action. Thus, the chemopreventive possibility of narirutin was investigated in PC-3 cells by utilising cytotoxicity assays. Further, a mechanism was deduced targeting hyaluronidase, an early-stage diagnosis marker, by cell-free, cell-based and in silico studies. The results indicate that narirutin reduced the viability of PC-3 cells with the inhibitory concentration range of 66.87-59.80 μM. It induced G0/G1 phase arrest with a fold change of 1.12. Besides, it increased the generation of reactive oxygen species (ROS) with a fold change of 1.34 at 100 μM. Narirutin inhibited hyaluronidase's activity in cell-free (11.17 μM) and cell-based assays (67.23 μM) and showed a strong binding interaction with hyaluronidase. Finally, the MD simulation analysis supported the idea that narirutin binding enhanced compactness and stability and created a stable complex with hyaluronidase. In addition, ADMET prediction indicates that it is a non-toxic, non-CYPs inhibitor and thus didn't alter the metabolism. The results reveal that narirutin may be a potential chemopreventive agent for hormone-resistant prostate cancer cells in addition to offering data for supporting diet-based nutraceutical agents to prevent prostate cancer.

Evaluation and Optimization of Quality Based on the Physicochemical Characteristics and Metabolites Changes of Qingpi during Storage

Qingpi, the dried immature pericarp of Citrus reticulata Blanco, is a commonly used medicinal food with some health-promoting benefits. In general, it is essential that Qingpi be stored for a period of time, but there are no reports about the number of storage years needed to obtain the best quality of Qingpi. Our aim was to determine the best storage time of Qingpi by studying the physicochemical properties and metabolite changes in product stored from 1 to 5 years. As a result, the color of Qingpi became darker during storage. Both the levels of three flavonoids (hesperidin, nobiletin, and tangeretin) and total flavonoids (TFs) and the antioxidant activity decreased during storage and the total phenolics (TPs) content fluctuated during storage. Cluster analysis was performed on the color parameters measured using a color difference meter, revealing that the color of Qingpi differed before and after 3 years of storage. A total of 9 special differential metabolites were identified that could be used to distinguish the storage years of Qingpi. This is the first study to report the quality changes of Qingpi during storage. The optimized results of the quality evaluation indicated that Qingpi should be stored for no more than 3 years.

Development and validation of ultra-high performance supercritical fluid chromatography method for quantitative determination of four target flavonoids components in citrus samples

A new method for the analysis of four target flavonoids in two kinds of citrus samples by ultra-high performance supercritical fluid chromatography (UHPSFC) method was developed. Main variables affecting the UHPSFC separation were optimized, and under the optimized conditions the four target compounds (tangeretin, nobiletin, hesperetin and naringenin) can be separated within 10 min. The UHPSFC method allowed the determination of the four target compounds in the diluted stock solutions with limit of detection (LOD) ranging from 1.08 to 2.28 μg mL−1, and limit of quantification (LOQ) ranging from 1.45 to 4.52 μg mL−1, respectively. The coefficients of determination (R 2) of the calibration curves were higher than 0.9950. The recoveries of the four target compounds at three different concentrations were in the range of 82.4–117.6%. The validation results demonstrated that the proposed method is simple, accurate, time-saving and environment friendly, and it is applicable to a variety of complex samples such as medicine-food dual purpose herbs and functional foods.

Systematic Identification of Bioactive Compositions in Leaves of Morus Cultivars Using UHPLC-ESI-QTOF-MS/MS and Comprehensive Screening of High-Quality Resources

Morus spp. leaves (MSLs) show various beneficial effects in the treatment of metabolic-related diseases, which have created a growing interest in MSL development as dietary supplements and functional foods. The illustration of chemical compositions and screening of high-quality MSL resources are therefore necessary for further application. This study developed a new UHPLC-ESI-QTOF-MS/MS strategy of in-source collision-induced dissociation (IS-CID) and target collision-cell CID (TCC-CID) to quickly capture analogues with consistent skeleton, and combined global natural product social molecular networking (GNPS) to efficiently annotate bioactive phytochemicals in MSLs. For the results, 49 bioactive ingredients, including quercetin-type flavonoids, kaempferol-type flavonoids, chlorogenic acid isomers, 1-deoxynojirimycin, γ-aminobutyric acid, amino acids, and unsaturated fatty acids, were systematically identified in MSLs for the first time. Quantification for the typical components was simultaneously carried out in MSLs of 90 Morus resources collected from different locations. Partial least squares discriminant analysis (PLS-DA) indicated that quercetin-3-O-(6″-O-malonyl)-glucoside, rutin, kaempferol-3-O-(6″-O-malonyl)-glucoside, kaempferol-3-O-rutinoside, and chlorogenic acid showed high variable importance in the project (VIP > 1) that were significant constituents for the differences between MSL species. Then, high-quality MSLs were comprehensively screened in multiple Morus cultivars based on the criteria importance through intercriteria correlation (CRITIC) method. This study presented an efficient strategy to annotate bioactive compounds, revealed the difference of bioactive components in MSLs, and provided important information for the high-value production of Morus cultivars in food and supplement fields.

Improving the antioxidant activity of natural antioxidant honokiol by introducing the amino group

Exploring and synthesizing the compounds with stronger antioxidant activity have always been the goal of researchers. Herein, the substitution effects of the amino (NH₂-) group with the excellent electron-donating ability in different positions on the antioxidant activity of Honokiol (Hon) were systematically explored by using the quantum chemistry calculation based on the density functional theory method. The three possible antioxidant mechanisms of Hon and its four NH₂-substituted derivatives (Hon1-Hon4), containing the hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET), were explored in depth considering the gas and solvent phases. In addition, the frontier molecular orbital energies, natural bond orbital (NBO) charge population, and global descriptive parameters were used to study their antioxidant activity. The results indicate that compared with the original molecule Hon, the NH₂ substituents would have the stronger antioxidant activity. Moreover, the radical scavenging process of Hon and its derivatives has a disposition to the HAT and SPLET mechanisms in the gas and solvent phases, respectively. Meaningfully, owing to the lowest bond dissociation enthalpy and proton affinity values, Hon4 would show the most prominent antioxidant activity by comparison with the other compounds. In conclusion, this work will provide the purposeful reference for designing and synthesizing the antioxidants with more outstanding performance.

Development of a LC-HRMS based approach to boost structural annotation of isomeric citrus flavanones

INTRODUCTION

The structural annotation of target relies on high-resolution mass spectrometry (HRMS) information resulting in dubious identities in most cases. The accurate annotation of isomeric structures is still challenging to be confirmed with significant bottleneck.

OBJECTIVE

This study focused on the improvement of structural annotation of candidate structures via four pairs of isomeric flavanone-7-O-diglucosides and their basic flavanone aglycones commonly detected in citrus products.

METHOD

An integrated liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS) approach merging retention time, accurate mass, tandem mass spectrometry (MS/MS) information (diagnostic ions), ion ratio at selected collision energy was established successfully.

RESULTS

Feasibility of this approach was validated confidently in biological samples with relative standard deviation (RSD) of ion ratio range from 3.91 to 12.28%. Differences of fragmentation patterns of citrus flavanones were illustrated reasonably. MS/MS fragments of (S)-hesperetin and (S)-isosakuranetin were complicated and showed typical radical ion [^1,2 A - H]^•- (m/z 164) in negative ESI mode due to the methoxyl group on B-ring, which showed huge difference with (R)-hesperetin and (R)-isosakuranetin.

CONCLUSION

This study integrated multiple levels to boost the confidence of structural annotation relied on LC-HRMS, and provided important values in practice for precise identification of citrus flavanones in biological matrices.

Preparative isolation of antioxidative gallic acid derivatives from Saxifraga tangutica using a class separation method based on medium-pressure liquid chromatography and reversed-phase liquid chromatography

Saxifraga tangutica is widely used as a medicinal herb to treat hepatic diseases. Here, we developed a class separation method to separate gallic acid derivatives 1,1-diphenyl-2-picrylhydrazyl inhibitors from the methanol extract of Saxifraga tangutica. Firstly, an MCI GEL CHP20P medium-pressure liquid chromatography was used to pretreat the crude extract from Saxifraga tangutica (500 g) and the target sample (fraction Fr1, 1.7 g) was obtained. Then, an online reversed-phase liquid chromatography-1,1-diphenyl-2-picrylhydrazyl assay was employed for recognizing potential 1,1-diphenyl-2-picrylhydrazyl inhibitors and six 1,1-diphenyl-2-picrylhydrazyl inhibitors fractions were recognized from fraction Fr1. Subsequently, the six 1,1-diphenyl-2-picrylhydrazyl inhibitors fractions were isolated via a ReproSil-Pur C18 AQ preparative column. During the separation process, the hydrophilic liquid chromatography was used to enrich the target compounds (Fr1-3-1-1 and Fr1-3-1-2) from the fraction Fr1-3, which were hardly isolated only by one step reversed-phase liquid chromatography. Finally, six gallic acid derivatives were obtained and identified as gallic acid (Fr1-1-1), gallic acid 3-O-β-D-glucoside (Fr1-1-2), protocatechuic acid (Fr1-2), 4-O-galloyl-(-)-shikimic acid (Fr1-3-1-1), 5-O-galloyl-(-)-shikimic acid (Fr1-3-1-2), and 3-O-galloyl-shikimic acid (Fr1-4), respectively. Thus, the present study indicated that this method was highly efficient for the preparative separation of gallic acid derivatives 1,1-diphenyl-2-picrylhydrazyl inhibitors from natural products.

Bioactivity Ingredients of Chaenomeles speciosa against Microbes: Characterization by LC-MS and Activity Evaluation

Chaenomeles speciosa (Sweet) Nakai is a dual-purpose Chinese herbal medicine and functional food favored by minorities in Southwest China, and its fruits are used for the treatment of dyspepsia, dysentery, enteritis, and rheumatism inflammation. Some diseases may be related to microbial infection; however, it is not known how the fruits possess antimicrobial activity. We evaluated the antimicrobial bioctivity of different evaluation extracts of C. speciosa fruits by in vitro and in vivo with colony-forming unit assays, and the strongest bioactive-guided fraction was selected for column chromatography (CC), UHPLC-QTOF-MS/MS, and NMR spectroscopy to confirm the chemical constituents. The most possible antimicrobial mechanism of C. speciosa fruits was explored by metabolomics approach, fluorescence microscopy imaging, and scanning electron microscopy (SEM). Thirty compounds, which were major characteristic ions of the bioactive fraction, were determined precisely. The bioactive fraction could inhibit 18 pathogenic microorganisms, significantly reduced, especially drug-resistant bacteria, compared to ampicillin sodium salt, fluconazole, and berberine chloride form; and the minimum inhibitory concentration (MIC) or minimum fungicidal concentration (MFC) values were in the range of 0.1-1 mg/mL. The compounds 2'-methoxyaucuparin (1) and oleanolic acid (20) not only have antibacterial activity but also may have synergistic effects. Further, the bioactive fraction might inhibit the biofilm formation, enhance immunity, and restore bacterial infection damage in vitro and in vivo to kill microorganisms. The data indicated that C. speciosa fruits' major bioactive fraction enriched with triterpenes, flavonoids, and phenolics could be developed as a functional supplement for individuals to prevent and treat microbial infection.

The levels of bioactive ingredients in Citrus aurantium L. at different harvest periods and antioxidant effects on H2 O2 -induced RIN-m5F cells

BACKGROUND

Citrus aurantium L. (Aurantii fructus) is a multi-purpose citrus fruit with high medicinal and nutritional value, but currently there are no data that can be used to investigate the appropriate harvest time to obtain high-quality citrus bioactive ingredients from it.

RESULTS

Phytochemicals and the levels of the main bioactive ingredients were investigated by ultra high performance liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (UHPLC-ESI-Q-TOF/MS). The flavanone, polymethoxyflavone, coumarin, synephrine, and limonin content in the citrus fruit was analyzed at different harvest periods, and significant differences, ranging from 0.03 ± 0.01 to 116.26 ± 40.20 g kg^-1 (DW), were shown. These compounds were present in higher amounts in June and then decreased gradually, while the biomass accumulation of most of them showed an increasing tendency around harvest time. The H₂ O₂ -induced RIN-m5F cells model was employed to evaluate their antioxidant capacity. Citrus fruit harvested from June 11 to July 7 possessed an excellent antioxidant capacity by inhibiting the intensity of intracellular reactive oxygen species (ROS) (P < 0.01) and improving superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH) activity (P < 0.01). The chemical composition and antioxidant capacity of citrus leaves, stems, and roots were also evaluated, and these showed great variation compared with other citrus fruits. Multivariate statistical analysis indicated that harvesting time was related closely to the phytochemical contents and antioxidant capacity.

CONCLUSION

Citrus fruit can be appropriately harvested from June to early July when the levels of bioactive ingredients and antioxidant activity reach higher values. This research provides practical information for producing high-quality citrus products. © 2020 Society of Chemical Industry.

Rapid qualitative profiling and quantitative analysis of phenolics in Ribes meyeri leaves and their antioxidant and antidiabetic activities by HPLC-QTOF-MS/MS and UHPLC-MS/MS

Ribes meyeri leaves are used as traditional Kazakh medicine in China. However, no study on the characterization of the phenolic compounds in R. meyeri leaves has been reported, resulting in the lack of quality control measures and poor standardization. This study was conducted to identify the phenolic compounds in R. meyeri leaves and evaluate their antioxidant and antidiabetic activities. A total of 77 phenolics were tentatively identified by liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry. Ultra-high performance liquid chromatography coupled with triple quadrupole mass spectrometry was applied to simultaneously quantify 12 phenolics in R. meyeri leaves. Rutin, epigallocatechin, isoquercitrin, epicatechin, protocatechuic acid, and kaempferol-3-O-rutinoside were abundant in the R. meyeri leaves. The methanol extract and four different extracts enhanced the glucose uptake in 3T3-L1 adipocytes. The ethyl acetate extracts showed a total phenolic content of 966.89 ± 3.59 mg gallic acid equivalents/g, a total flavonoid content of 263.58 ± 17.09 mg catechin equivalents/g, and good protein-tyrosine phosphatase-1B inhibitory activities (IC₅₀ : 0.60 ± 0.03 μg/mL). To our knowledge, this work is the first to identify and quantify the major phenolics in R. meyeri leaves.

In situ antioxidation-assisted matrix solid-phase dispersion microextraction and discrimination of chiral flavonoids from citrus fruit via ion mobility quadrupole time-of-flight high-resolution mass spectrometry

A simple and sensitive in situ antioxidation process assisted with a matrix solid-phase dispersion method for extracting chiral flavonoids in citrus fruit was established, and samples were further analyzed using ion mobility quadrupole time-of-flight high-resolution mass spectrometry. The collision cross-sections of the target compounds were studied using single-field and stepped-field methods. The optimal conditions were obtained using 30 mg of C₁₈ as a dispersant, methanol as an elution solvent and 0.6 mM 1,1-diphenyl-2-picrylhydrazyl (DPPH) as a radical solution. Additionally, the method showed satisfactory limits of detection (3.70-6.52 ng/mL) and good recoveries (96.78-104.67%) for four flavonoids in citrus fruit. The IC₅₀ values of DPPH radical-scavenging activities ranged from 817.8 to 981.55 μg/mL for tested samples. The method was a good alternative for the microextraction and determination of antioxidant capacity and chiral differentiation of narirutin, naringin, hesperidin and neohesperidin in citrus fruit.

Flavonoids from Aurantii Fructus Immaturus and Aurantii Fructus: promising phytomedicines for the treatment of liver diseases

Background

Liver diseases and related complications are major sources of morbidity and mortality, which places a huge financial burden on patients and lead to nonnegligible social problems. Therefore, the discovery of novel therapeutic drugs for the treatment of liver diseases is urgently required. Aurantii Fructus Immaturus (AFI) and Aurantii Fructus (AF) are frequently used herbal medicines in traditional Chinese medicine (TCM) formulas for the treatment of diverse ailments. A variety of bioactive ingredients have been isolated and identified from AFI and AF, including alkaloids, flavonoids, coumarins and volatile oils.

Main body

Emerging evidence suggests that flavonoids, especially hesperidin (HD), naringenin (NIN), nobiletin (NOB), naringin (NRG), tangeretin (TN), hesperetin (HT) and eriodictyol (ED) are major representative bioactive ingredients that alleviate diseases through multi-targeting mechanisms, including anti-oxidative stress, anti-cytotoxicity, anti-inflammation, anti-fibrosis and anti-tumor mechanisms. In the current review, we summarize the recent progress in the research of hepatoprotective effects of HD, NIN, NOB, NRG, TN, HT and ED and highlight the potential underlying molecular mechanisms. We also point out the limitations of the current studies and shed light on further in-depth pharmacological and pharmacokinetic studies of these bioactive flavonoids.

Conclusion

This review outlines the recent advances in the literature and highlights the potential of these flavonoids isolated from AFI and AF as therapeutic agents for the treatment of liver diseases. Further pharmacological studies will accelerate the development of natural products in AFI and AF and their derivatives as medicines with tantalizing prospects in the clinical application.