Preparation and purification of raffinose family oligosaccharides from Rehmannia glutinosa Libosch. by fast protein liquid chromatography coupled with refractive index detection

Application of an α-galactosidase from Bacteroides fragilis on structural analysis of raffinose family oligosaccharides

Raffinose family oligosaccharides (RFOs) have diverse structures and exhibit various biological activities. When using RFOs as prebiotics, their structures need to be identified. If we first knew whether an RFO was classical or non-classical, structural identification would become much easier. Here, we cloned and expressed an α-galactosidase (BF0224) from Bacteroides fragilis which showed strict specificity for hydrolyzing α-Gal-(1 → 6)-Gal linkages in RFOs. BF0224 efficiently distinguished classical from non-classical RFOs by identifying the resulting hydrolyzed oligo- and mono-saccharides with HPAEC-PAD-MS. Using this strategy, we identified a non-classical RFO from Pseudostellaria heterophylla (Miquel) Pax with DP6 (termed PHO-6), as well as a classical RFO from Lycopus lucidus Turcz. with DP7 (termed LTO-7). To characterize these RFO structures, we employed four other commercial or reported α-galactosidases in combination with NMR and methylation analysis. Using this approach, we elucidated the accurate chemical structure of PHO-6 and LTO-7. Our study provides an efficient analytical approach to structurally analyze RFOs. This enzyme-based strategy also can be applied to structural analysis of other glycans.

A universal method for profiling and characterization of oligosaccharides in traditional Chinese medicines

Oligosaccharides constitute fundamental components in numerous traditional Chinese medicines (TCMs). Conventional chromatographic methods for natural product analysis are not suitable for oligosaccharides due to their large polarity and structural similarity. Herein, an ultra-high performance liquid chromatography with charged aerosol detector (UHPLC-CAD) method was developed for the profiling of oligosaccharides using 9 neutral (DP3-DP11) reference oligosaccharides. Various factors, including columns, mobile phase, elution conditions, flow rate, and column temperature were systematically examined. Optimal separation was achieved using an Amide column with gradient elution within 18 min, at 0.5 mL/min flow rate and 30°C column temperature. Moreover, an ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS) method was also optimized to provide structural information. The developed method was applied to detect oligosaccharides in several TCMs, including Morindae Officinalis Radix (MOR), Ziziphi Spinosae Semen (ZSS), Menthae Haplocalycis Herba (MHH) and Chrysanthemi Indici Flos (CIF), revealing 9 and 16 oligosaccharides being uncovered from MHH and CIF respectively for the first time. This study presents a versatile UHPLC-CAD and UHPLC-Q-TOF/MS method with the potential for advancing oligosaccharides discovery and contributing to the quality analysis of TCMs.

A Novel Bifunctional Alginate Lyase and Antioxidant Activity of the Enzymatic Hydrolysates

Alginate lyase Aly448, a potential new member of the polysaccharide lyase (PL) 7 family, which was cloned and identified from the macroalgae-associated bacterial metagenomic library, showed bifunctionality. The molecular docking results revealed that Aly448 has two completely different binding sites for alginate (polyMG), poly-α-l-guluronic acid (polyG), and poly-β-d-mannuronic acid (polyM) substrates, respectively, which might be the molecular basis for the enzyme's bifunctionality. Truncational results confirmed that predicted key residues affected the bifunctionality of Aly448, but did not wholly explain. Besides, Aly448 presented excellent biochemical characteristics, such as higher thermal stability and pH tolerance. Degradation of polyMG, polyM, and polyG substrates by Aly448 produced tetrasaccharide (DP4), disaccharide (DP2), and galactose (DP1), which exhibited excellent antioxidant activity. These findings provide novel insights into the substrate recognition mechanism of bifunctional alginate lyases and pave a new path for the exploitation of natural antioxidant agents.

A Surface Matrix of Au NPs Decorated Graphdiyne for Multifunctional Laser Desorption/Ionization Mass Spectrometry

The development of the valid strategy to enhance laser desorption/ionization efficiency gives rise to widespread concern in surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) technology. Herein, a hybrid of Au NP-decorated graphdiyne (Au/GDY) was fabricated and employed as the SALDI-MS matrix for the first time, and a mechanism based on photothermal and photochemical energy conversions was proposed to understand LDI processes. Given theoretical simulations and microstructure characterizations, it was revealed that the formation of a coupled thermal field and internal electric field endow the as-prepared Au/GDY matrix with superior desorption and ionization efficiency, respectively. Moreover, laser-induced matrix ablation introduced strain and defect level into the Au/GDY hybrid, suppressing the recombination of charge carriers and thereby facilitating analyte ionization. The optimized Au/GDY matrix allowed for reliable detection of trace sulfacetamide and visualization of exogenous/endogenous components in biological tissues. This work offers an integrated solution to promote LDI efficiency based on collaborative photothermal conversion and internal electric field, and may inspire the design of novel semiconductor-based surface matrices.

Combination of Internal Extractive Electrospray Ionization Mass Spectrometry and Statistical Analysis for High-Throughput Molecular Differentiation of Rehmannia glutinosa Samples

Rehmannia glutinosa (Gaert.) Libosch. ex Fisch. et Mey. is a perennial herb of the Scrophulariaceae family, which has long enjoyed a good reputation in China, and has a wide range of pharmacological effects and clinical applications. The place of origin is an important factor affecting the chemical composition of R. glutinosa, resulting in different pharmacological effects. Herein, internal extractive electrospray ionization mass spectrometry (iEESI-MS) combined with statistical techniques was established for high-throughput molecular differentiation of different R. glutinosa samples. Dried and processed R. glutinosa samples from four different places of origin were analyzed by iEESI-MS with high throughput (>200 peaks) and rapidness (<2 min/sample) without sample pretreatment. Clear separation models created by OPLS-DA were then established for distinguishing the places of origin of dried and processed R. glutinosa by using the obtained MS data. In addition, the molecular differences between the pharmacological effects of dried and processed R. glutinosa were also investigated by OPLS-DA, and 31 different components were screened out. This work provides a promising method for evaluating the quality of traditional Chinese medicines and studying the biochemical mechanism of processing.

Targeted isolation of cyclooxygenase-2 inhibitors from Saussurea obvallata using affinity ultrafiltration combined with preparative liquid chromatography

Saussurea obvallata (S. obvallata) is widely used in Qinghai-Tibet Plateau with high medicinal and edible values of reducing inflammation. But, the individual components and mechanisms of action still ill-defined. In this work, an integrated method using affinity ultrafiltration combined with preparative liquid chromatography was developed to identify and separate cyclooxygenase-2 (COX-2) inhibitors from S. obvallata. The sample was pretreated using on-line medium pressure liquid chromatography to yield the active fraction. Then, the potential COX-2 ligands were screened out using affinity ultrafiltration from the targeted fraction and the identified compounds were isolated via preparative liquid chromatography. As a result, four main compounds, coniferin (1), syringin (2), roseoside (3) and grasshopper ketone (4) were targeted isolated with IC₅₀ values of 12.34 ± 1.81, 4.04 ± 0.43, 13.91 ± 2.46 and 7.97 ± 1.21 µM, respectively. Results of this work demonstrated that the developed strategy was effective for the targeted separation of COX-2 inhibitors from natural product extracts.

Alginate Lyases from Marine Bacteria: An Enzyme Ocean for Sustainable Future

The cell wall of brown algae contains alginate as a major constituent. This anionic polymer is a composite of β-d-mannuronate (M) and α-l-guluronate (G). Alginate can be degraded into oligosaccharides; both the polymer and its products exhibit antioxidative, antimicrobial, and immunomodulatory activities and, hence, find many commercial applications. Alginate is attacked by various enzymes, collectively termed alginate lyases, that degrade glycosidic bonds through β-elimination. Considering the abundance of brown algae in marine ecosystems, alginate is an important source of nutrients for marine organisms, and therefore, alginate lyases play a significant role in marine carbon recycling. Various marine microorganisms, particularly those that thrive in association with brown algae, have been reported as producers of alginate lyases. Conceivably, the marine-derived alginate lyases demonstrate salt tolerance, and many are activated in the presence of salts and, therefore, find applications in the food industry. Therefore, this review summarizes the structural and biochemical features of marine bacterial alginate lyases along with their applications. This comprehensive information can aid in the expansion of future prospects of alginate lyases.

Evolving strategies for marine enzyme engineering: recent advances on the molecular modification of alginate lyase

Alginate, an acidic polysaccharide, is formed by β-d-mannuronate (M) and α-l-guluronate (G). As a type of polysaccharide lyase, alginate lyase can efficiently degrade alginate into alginate oligosaccharides, having potential applications in the food, medicine, and agriculture fields. However, the application of alginate lyase has been limited due to its low catalytic efficiency and poor temperature stability. In recent years, various structural features of alginate lyase have been determined, resulting in modification strategies that can increase the applicability of alginate lyase, making it important to summarize and discuss the current evidence. In this review, we summarized the structural features and catalytic mechanisms of alginate lyase. Molecular modification strategies, such as rational design, directed evolution, conserved domain recombination, and non-catalytic domain truncation, are also described in detail. Lastly, the application of alginate lyase is discussed. This comprehensive summary can inform future applications of alginate lyases.

Reverse tracing anti-thrombotic active ingredients from dried Rehmannia Radix based on multidimensional spectrum-effect relationship analysis of steaming and drying for nine cycles

ETHNOPHARMACOLOGICAL RELEVANCE

In traditional Chinese medicine (TCM) and modern pharmacodynamics, dried Rehmannia Radix (DRR) possesses prominent anti-thrombotic activity that decreases after processing by nine steaming and drying cycles to develop processed Rehmannia Radix (PRR). Due to the complexity of the DRR components, the chemical mechanism leading to efficacy changes of DRR caused by processing is still unclear.

AIM OF STUDY

This study aimed to trace the anti-thrombotic active compounds of DRR and different degrees of processed RR (PRR) and to evaluate the synergistic effects among different active components.

MATERIALS AND METHODS

The anti-thrombotic active chemical fraction of DRR extracts was evaluated. Targeted fractions of the processed products of RR were prepared at different processing stages. The changes in monosaccharides, oligosaccharides and secondary metabolites during processing were characterized by multidimensional high-performance liquid chromatography (HPLC). The anti-thrombotic effects of targeted fractions of different RR samples were evaluated by analyzing the length of tail thrombus (LT) and serum biochemical indicators in carrageenan-induced tail-thrombus mice. The spectrum-effect relationships were investigated by partial least squares regression (PLSR) analysis and gray correlation analysis (GRA). Finally, the active compounds were screened by spectrum-effect relationship analysis and validated in vivo, and their synergistic effects were determined by Webb's fraction multiplication method.

RESULTS

Six ingredients highly associated with anti-thrombotic activities were screened out by the spectrum-effect relationship analysis, of which oligosaccharides (stachyose, sucrose and raffinose) and iridoid glycosides (catalpol, leonuride and melitoside) possessed a synergistic effect on tumor necrosis factors (TNF-α), interleukin 1β (IL-1β) and plasminogen activator inhibitor 1 (PAI-1)/tissue-type plasminogen activator (t-PA) ratio in vivo with synergistic coefficient (SC) > 1.

CONCLUSION

The main material basis of the anti-thrombotic activities of DRR is oligosaccharide components of stachyose, raffinose and sucrose, iridoid glycosides components of catalpol, leonuride and melittoside. The two kinds of components exert synergistic anti-thrombotic effects by inhibiting the expression of inflammatory factors and regulating the balance of the fibrinolysis system.

Targeted isolation of 1,1-diphenyl-2-picrylhydrazyl inhibitors from Saxifraga atrata using medium- and high- pressure liquid chromatography combined with online high performance liquid chromatography-1,1-diphenyl-2- picrylhydrazyl detection

Traditional Tibetan medicine (TTM) is a valuable source of novel therapeutic lead molecules inspired by natural products (NPs). The health benefits of Saxifraga atrata are well documented in TTM, but reports on its chemical composition are limited, most likely due to the complicated purification process. Herein, target separation and identification of 4 main radical scavenging compounds from the methanolic extract of S. atrata was were performed using medium- and high-pressure liquid chromatography coupled with online HPLC-DPPH detection. The sample was pretreated using medium pressure liquid chromatography with MCI GELⓇ CHP20P styrene-divinylbenzene beads as a stationary phase, yielding 1.4 g of the target DPPH inhibitors (Fr4, 11.9% recovery). The compounds were further purified and isolated using HPLC on RP-C18 (ReproSil-Pur C18 AQ) followed by HILIC (Click XIon) column separation, resulting in 2.8 mg of fraction Fr4-1-1, 6.8 mg of fraction Fr4-2, 244.9 mg of the Fr4-3-1 sample, and 38.3 mg of Fr4-4-1. The structure and purity of the target compounds were determined, and four compounds (ethyl gallate, 11-O-galloylbergenin, rutin and isoquercitrin) were isolated with >95% purity. The developed methodology is efficient for targeted isolation of high-purity radical scavengers from NP extracts and could be used for rapid identification and isolation of DPPH inhibitors from various NPs.

Preparation and identification of oligosaccharides in lotus seeds and determination of their distribution in different parts of lotus

Three fractions (I-III) were separated from crude oligosaccharides of lotus seeds by fast protein liquid chromatography with final purity of 97.6, 96.3, and 96.8%, respectively. The fractions were identified as sucrose, raffinose, and stachyose by using TLC, HPLC with charged aerosol detector (CAD), LC-MS, and methylation analysis. Subsequently sucrose and raffinose family oligosaccharides (RFOs) with degree of polymerization (DP) 3-5 (raffinose, stachyose, and verbascose) have been quantified by HPLC-CAD for the first time. All calibration curves for investigated analytes showed good linear regression (R2  > 0.9952). Their limit of detection and limit of quantity were in the ranges 0.14-0.28 and 0.36-0.48 μg/mL, respectively. The recoveries ranged from 96.6 to 103.4%. The contents of sucrose and RFOs DP3-DP5 were different in lotus seeds and other parts of lotus samples, but similar in their own variety. Additionally, the distribution of RFOs in different parts of lotus were also compared and the results indicated that RFOs might be mainly synthesized in lotus seeds. This work is helpful for understanding the way of biosynthesis of RFOs in lotus as well as quality control of plants containing RFOs.

Separation of Oligosaccharides from Lotus Seeds via Medium-pressure Liquid Chromatography Coupled with ELSD and DAD

Lotus seeds were identified by the Ministry of Public Health of China as both food and medicine. One general function of lotus seeds is to improve intestinal health. However, to date, studies evaluating the relationship between bioactive compounds in lotus seeds and the physiological activity of the intestine are limited. In the present study, by using medium pressure liquid chromatography coupled with evaporative light-scattering detector and diode-array detector, five oligosaccharides were isolated and their structures were further characterized by electrospray ionization-mass spectrometry and gas chromatography-mass spectrometry. In vitro testing determined that LOS3-1 and LOS4 elicited relatively good proliferative effects on Lactobacillus delbrueckii subsp. bulgaricus. These results indicated a structure-function relationship between the physiological activity of oligosaccharides in lotus seeds and the number of probiotics applied, thus providing room for improvement of this particular feature. Intestinal probiotics may potentially become a new effective drug target for the regulation of immunity.

Alginate lyase: Review of major sources and classification, properties, structure-function analysis and applications

Alginate lyases catalyze the degradation of alginate, a complex copolymer of α-L-guluronate and its C5 epimer β-D-mannuronate. The enzymes have been isolated from various kinds of organisms with different substrate specificities, including algae, marine mollusks, marine and terrestrial bacteria, and some viruses and fungi. With the progress of structural biology, many kinds of alginate lyases of different polysaccharide lyases families have been characterized by obtaining crystal structures, and the catalytic mechanism has also been elucidated. Combined with various studies, we summarized the source, classification and properties of the alginate lyases from different polysaccharide lyases families. The relationship between substrate specificity and protein sequence was also investigated.