An automatic on-line 2,2-diphenyl-1-picrylhydrazyl-high performance liquid chromatography method for high-throughput screening of antioxidants from natural products

Rapid screening and target-guided isolation of antioxidants from German chamomile by 2,2-diphenyl-1-picrylhydrazyl-ultra-high-performance liquid chromatography-mass spectrometry coupled with off-line two-dimensional high-speed countercurrent chromatography

German chamomile is one of the most effective herbal elements used in anti-allergic products and as an antioxidant. Herein, the antioxidant activity of different extract fractions of German chamomile was initially evaluated using an off-line 2,2-diphenyl-1-picrylhydrazyl spectrophotometric assay. The ethyl acetate extract demonstrated the highest efficacy in scavenging free radicals. Based on this, a rapid screening and separation method using ultra-high-performance liquid chromatography combined with the 2,2-diphenyl-1-picrylhydrazyl assay was implemented to identify antioxidants in the ethyl acetate fraction of German chamomile flowers. Ten potential radical scavengers were tentatively screened from German chamomile using a target-guided isolating approach with off-line two-dimensional high-speed countercurrent chromatography and the structures of the compounds were analyzed and identified. Ultimately, 10 radical scavengers were obtained from the ethyl acetate extract with a purity quotient exceeding 90%. The results demonstrated the effectiveness and reproducibility of this method for isolating potential antioxidants from complex mixtures in a targeted manner. This strategy can be applied to the target-guided isolation of complex mixtures of natural products with broad K-values and similar structures.

Spectrum-Effect Relationships as an Effective Approach for Quality Control of Natural Products: A Review

As natural products with biological activity, the quality of traditional Chinese medicines (TCM) is the key to their clinical application. Fingerprints based on the types and contents of chemical components in TCM are an internationally recognized quality evaluation method but ignore the correlation between chemical components and efficacy. Through chemometric methods, the fingerprints represented by the chemical components of TCM were correlated with its pharmacodynamic activity results to obtain the spectrum-effect relationships of TCM, which can reveal the pharmacodynamic components information related to the pharmacodynamic activity and solve the limitations of segmentation of chemical components and pharmacodynamic research in TCM. In the 20th anniversary of the proposed spectrum-effect relationships, this paper reviews its research progress in the field of TCM, including the establishment of fingerprints, pharmacodynamic evaluation methods, chemometric methods and their practical applications in the field of TCM. Furthermore, the new strategy of spectrum-effect relationships research in recent years was also discussed, and the application prospects of this technology were discussed.

Study on quality control of Zuojin pill by HPLC fingerprint with quantitative analysis of multi-components by single marker method and antioxidant activity analysis

Current quality control methods for Zuojin Pill (ZJP) lack comprehensiveness and practicability. This study aimed to develop a comprehensive strategy for the quality evaluation of ZJP and the prediction of potential bioactive components in ZJP. First, an HPLC method with excellent separation of main components was developed and was used to establish the chromatographic fingerprint of ZJP. Similarities were calculated by comparing 28 batches of ZJPs with the reference fingerprint and the resulting similarity values were all greater than 0.976. The 28 samples were classified into different groups according to their origins by Hierarchical Cluster Analysis, Principal component analysis, and orthogonal partial least squares discriminant analysis. Based on the classification, eight quality markers (Q-Markers) affecting the quality of ZJP were discovered. Then, using berberine as an internal standard substance, quantitative analysis of multi-components by single marker method (QAMS) for the determination of eight Q-markers was developed. The results showed that there was no significant difference between QAMS and external standard method (P＞0.05). Finally, using an off-line antioxidant system and partial least-squares model (PLS), the fingerprint-efficacy relationship of ZJP was constructed to explore and predict the bioactive components in ZJP. The present study strategy could be also applied to comprehensive quality study of other TCMs.

The Isolation and Preparation of Samwinol from Dracocephalum heterophyllum and Prevention on Aβ25-35-Induced Neuroinflammation in PC-12 Cells

Dracocephalum heterophyllum (D. heterophyllum) is a traditional Chinese Tibetan medicine that has been used for the treatment of lymphitis, hepatitis, and bronchitis. However, only a few selected chemical components are currently obtained from D. heterophyllum, which limits its further pharmacological applications. In this study, we have obtained samwinol from D. heterophyllum by medium- and high-pressure liquid chromatography separation for the first time. Thereafter, we investigated the protective actions of samwinol against amyloid beta protein fragment 25-35 (Aβ_25-35) induced neurotoxicity in cultured rat pheochromocytoma PC-12 cells and explored its underlying mechanisms of action. The results indicated that samwinol could increase cell viability and inhibit the production of reactive oxygen species (ROS) and mitochondria-derived ROS, as assessed by MTT assay, Giemsa staining, and flow cytometry assay. Through Western blot analysis, it was found that samwinol substantially inhibited the phosphorylation of ERK(1/2) and promoted the expression of HO-1 and Nrf2. The data obtained from molecular docking were also consistent with the above conclusions. All of these results showed that samwinol from D. heterophyllum can display significant anti-neuroinflammatory and antioxidant activities in vitro, which are associated with the suppression of ERK/AKT phosphorylation and the activation of the Nrf2/HO-1 signaling pathway. In the future, additional in-depth mechanism studies will be carried out to provide more evidence for the potential of samwinol in the treatment of Alzheimer's disease.

On-line screening of natural antioxidants and the antioxidant activity prediction for the extracts from flowers of Chrysanthemum morifolium ramat

ETHNOPHARMACOLOGY RELEVANCE

Chrysanthemum morifolium Ramat. (Flos Chrysanthemi, FC) the most economically significant "food and drug dual-use" plants, with positive effects on relieving eye fatigue, and reduce internal heat, shows significant activities, such as anti-inflammatory, antioxidant, and neuroprotective, as well as alleviating diabetes effects.

AIM OF THE STUDY

This study was undertaken to a screening of natural antioxidants in five kinds of medicinal FC and development of an integrated quality control method based on the antioxidant activity.

MATERIALS AND METHODS

A novel quality control method for FC was established by combining the on-line HPLC-DPPH, ESI-MS, and NIR spectra analysis. Firstly, the on-line HPLC-DPPH-MS system was employed to identify the antioxidants in FC extracts. Then, the relationship between the NIR spectra and antioxidant activities of FC samples was calibrated to evaluate the total antioxidant capacity of FC rapidly.

RESULTS

The established antioxidant activity-fingerprints contain both chemical information and antioxidant activity characteristics of FC. A total of 16 antioxidants were identified by on-line HPLC-ESI-MS analysis. The results of heat map analysis and cluster analysis showed that the classification method based on antioxidants in FC can be used to identify different cultivars of FC. The optimal pretreatment of the NIR spectra was determined to be row center (RC) 1st der + multiple-scatter correction (MSC) with an optimal LV value of 11. The developed spectral-antioxidant activity model had the excellent predictive ability and was successfully used to evaluate new batches of FC samples, where R_cal = 0.9445 and R_val = 0.8821.

CONCLUSIONS

This comprehensive strategy may prove to be a powerful technique for the rapid screening, identification, and activity prediction of antioxidants, which could be used for the quality control of FC, and can serve as reference for design of quality control of other herbs and foods samples.

A simple and effective method based on enzyme-ligand complex for affinity analysis of lipase inhibitor from Schisandra chinensis (Turcz.) Baill

Schisandra chinensis (Turcz.) Baill has various biological activities including anti-obesity. Rapid analysis and screening of active compounds from natural extracts is one of the challenges faced by natural drug research. In order to analyze and screen lipase inhibitor from Schisandra chinensis extract, a method inspired by the specific binding of enzyme to ligand was developed and established. Through optimization of incubation conditions, such as time, temperature, and pH, the potential active compound was locked by comparing the change of the chemical components of the S. chinensis extract before and after incubation with lipase. Subsequently, the target compound was isolated by high-speed counter-current chromatography and was identified as 5-hydroxymethyl-2-furaldehyde. Moreover, in vitro activity determination confirmed that 5-hydroxymethyl-2-furaldehyde with an IC₅₀ value of 284.78 ± 16.45 μg/mL interacted with the lipase through non-competitive inhibition. Furthermore, molecular docking further revealed that 5-hydroxymethyl-2-furaldehyde can be embedded into the active pocket of lipase via multiple hydrogen bonds and other interactions. This study not only screened a potential lipase inhibitor from S. chinensis through the newly developed method, but also can be used as a typical reference for the discovery of active components from functional foods and natural products.

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.

Integrated molecular network and HPLC-UV-FLD analysis to explore antioxidant ingredients in camellia nitidissima Chi

At present, screening of active ingredients from natural products for pharmacological and clinical research is mostly time-consuming and costly. In this study, a molecular network (MN) guided high performance liquid chromatography-ultraviolet-fluorescence detector (HPLC-UV-FLD) method was carried out to profile the global antioxidant activity compounds, including the trace amount ingredients in Camellia nitidissima Chi (CNC). Firstly, HPLC-UV-FLD postcolumn derivatization system was utilized to screen the antioxidants. Then the MN of CNC was established via mass spectrometry (MS) data for getting the connection between ingredient structures. As a result, HPLC-UV-FLD indicated three antioxidant ingredients: gallic acid (126.3 mg/g), catechin (564.8 mg/g), and salicylic acid (24.3 mg/g). Combined with the MN, the actives' precise location and connection relationship were clarified based on the structural similarities. A new antioxidant ingredient, okicamelliaside, was suggested and evaluated at free radical scavenging and enzymatic protection. The novel method of activity and structural correlation analysis based on MN could provide a useful guide for screening trace active ingredients in natural products. PRACTICAL APPLICATION: Three main ingredients were screened out from Camellia nitidissima Chi by HPLC-UV-FLD postcolumn derivatization system. Integrated molecular network and HPLC-UV-FLD analysis, a new type of antioxidant okicamelliaside was selected. The novel method of activity and structural correlation analysis based on molecular network could provide a useful guide for screening trace active ingredients in natural products.

Preparative separation of high-purity trans- and cis-ferulic acid from wheat bran by pH-zone-refining counter-current chromatography

Ferulic acid stereoisomers are the most abundant phenolic acids in cereal bran. However, it is challenging to separate them because of the similar structures and properties. In this study, a preparative separation method of ferulic acid stereoisomers from the crude extract of wheat bran was successfully developed. The method contained a two-step separation, the traditional counter-current chromatography (CCC, hexane: ethyl acetate: methanol: water = 2:5:2:4) was followed with a pH-zone-refining CCC (hexane: ethyl acetate: acetonitrile: water = 2:5:2:2, 10 mmol L^-1 trifluoroacetic acid in organic stationary phase and 10 mmol L^-1 ammonia in aqueous mobile phase). Trans-ferulic acid and cis-ferulic acid with HPLC high purity over than 99% and 98% can be yielded in large-scale separation. Moreover, it is found that different proton affinity, deprotonation ability and interaction site of hydrogen bond result in distinct partition behavior of stereoisomers, which is illustrated by quantitative analysis of molecular surface. This contributes to our in-depth understanding of the separation mechanism toward pH-zone refining CCC. The developed method can be applied in the exploitation of ferulic acids and related phenolic acids from other resources.

Uncovering the antioxidant characteristics of black tea by coupling in vitro free radical scavenging assay with UHPLC-HRMS analysis

Black tea (BT) is rich in dietary antioxidants, but its antioxidant composition has not been fully understood. To identify the true antioxidants occurring in BT, we established an approach based on 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay coupled with ultra-high performance liquid chromatography-high resolution mass spectrometry (DPPH-UHPLC-HRMS). The employment of HRMS enable us to detect trace antioxidants, resolve co-eluted antioxidants, and characterize chemical structures of unknown antioxidants. In total, 56 phenolic compounds were screened as potential antioxidants from 106 compounds identified in BT. Catechol and pyrogallol were revealed as the key substructures in enhancing the antioxidant abilities of phenolic compounds. During BT brewing, high temperature with extended time promote antioxidant leaching but may induce the degradation of esterified and glycosylated compounds such as theaflavin-3-gallate and rutin. In conclusion, this work identified the true antioxidant constituents of BT, their structural characteristics, and their dynamic changes under various brewing conditions.

Glucose consumption assay discovers coptisine with beneficial effect on diabetic mice

Many drugs with anti-diabetic effects regulate glucose consumption in peripheral tissues. Via cellular glucose consumption assays, we identified that coptisine, a main effective constituent from the plant Coptis chinensis, enhanced hepatic and skeletal muscle glucose consumption. We further explored its effects on glucose metabolism in diabetic animals to elucidate its mechanism of action. Our results showed that coptisine did not show cytotoxicity. Intragastric administration of coptisine for ten days in normal ICR mice markedly decreased fasting blood-glucose levels without significant effects on body weight. In alloxan-induced type 1 diabetic mice, intragastric administration of coptisine for 28 days decreased fasting and non-fasting blood-glucose levels as well. In type 2 diabetic KKAy mice, intragastric administration of coptisine for nine weeks improved glucose tolerance. It decreased fasting/non-fasting blood-glucose and fructosamine levels. Coptisine decreased low-density lipoprotein and total cholesterol levels, however, had no significant effect on triglyceride levels. Coptisine increased AMPK phosphorylation while decreasing Akt phosphorylation in HepG2 hepatic cells and C2C12 myotubes. Coptisine also reduced mitochondrial respiration in isolated and cellular mitochondria, suggesting that coptisine lowered cellular energy levels. In particularly, coptisine administration (10^-6 M) decreased the mitochondrial oxygen consumption rate (OCR) with a greater extracellular acidification rate (ECAR), resulting in an oxidative-to-glycolysis phosphorylation shifted for cellular energy generation. Our results demonstrate that coptisine acts as an enhancer of peripheral glucose consumption could improve glucose metabolism in diabetic animals. Coptisine may serve as a novel anti-diabetic agent and warrant further evaluation.

Target-Guided Isolation of Three Main Antioxidants from Mahonia bealei (Fort.) Carr. Leaves Using HSCCC

Mahonia bealei (Fort.) Carr. is an economically important plant that is widely cultivated in Southwest China. Its leaves are commonly used for tea and contain an abundance of antioxidant compounds. However, methods of the systematic purification of antioxidants from M. bealei are lacking. In this study, antioxidants from this plant were effectively and rapidly enriched. First, antioxidants were screened using online 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH)-high performance liquid chromatography (HPLC), followed by separation using high-speed countercurrent chromatography with an optical solvent system composed of n-hexane/ethyl acetate/methanol/water (1:5:1:5, v/v/v/v). Three phenolics-chlorogenic acid (1, 8.3 mg), quercetin-3-O-β-d-glucopyranoside (2, 20.5 mg), and isorhamnetin-3-O-β-d-glucopyranoside (3, 28.4 mg)-were obtained from the ethyl acetate-soluble fraction (240 mg) by one-step separation. The chemical structures of the phenolics were characterized by MS and NMR techniques, and the purity of each compound was >92.0% as determined by HPLC. The isolated compounds were assessed by scavenging activities on DPPH and superoxide radicals as well as cytoprotective assays, all of which showed similar trends regarding the antioxidant capacities of the compounds. Moreover, compounds 1-3 significantly attenuated the lipid peroxidation and antioxidant enzyme activities in H₂O₂-treated RAW264.7 cells. Our study demonstrated the efficiency of a newly developed integrative system for the comprehensive characterization of pure compounds from M. bealei, which will allow their use as reference substances.

Antioxidant Activity and Spectroscopic Characteristics of Extractable and Non-Extractable Phenolics from Terminalia sericea Burch. ex DC

The aim of this study was to determine the antioxidant activity of the extractable and non-extractable phenolics of Terminalia. Sericea Burch. Ex DC. Free, ester bound, ether or glycoside bound and insoluble phenolics were extracted from the fruit, leaves, stem, and root samples. Follin Ciocalteu was used to estimate the phenolic content while DPPH (2,2-diphenyl-1-picrylhydrazyl) assay was used to determine the antioxidant activity. The data obtained were subjected to multivariate analysis for relationships. The result indicated that the highest average total phenolic contents and antioxidant activities were found in the free (14.8 mgGAE/g; IC50 6.8 μg/mL) and ester bound (15.1 mgGAE/g; IC50 6.4 μg/mL) extractable phenolics. There was a strong negative correlation between TPC and DPPH (r = -0.828). Agglomerative hierarchical clustering revealed three clusters. Cluster one contained the insoluble and glycoside phenolics while cluster 2 contained only free phenolic acid of the root. The third cluster was predominantly free and ester bound phenolic extracts. The principal component analysis score plot indicated two major clusters with factor 1 (F1) explaining 61% of the variation. The nuclear magnetic resonance spectroscopy spectra indicated that gallic acid and resveratrol are the major phenolic compounds present in the root. This study has demonstrated that extractable phenolics contributed more to the antioxidant activities compared to the non-extractables.

Systematic Chemical Analysis Approach Reveals Superior Antioxidant Capacity via the Synergistic Effect of Flavonoid Compounds in Red Vegetative Tissues

The flavonoid system comprises an abundance of compounds with multiple functions; however, their potential synergism in antioxidant function remains unclear. We established an approach using ever-red (RL) and ever-green leaves (GL) of crabapple cultivars during their development to determine interrelationships among flavonoid compounds. RL scored significantly better than GL in terms of the type, composition, and diversity of flavonoids than GL. Principal component analysis predicted flavonoids in RL to have positive interaction effects, and the total antioxidant capacity was significantly higher than the sum of antioxidant capacities of the individual compounds. This synergy was verified by the high antioxidant capacity in rat serum after feeding on red leaves. Our findings suggest that the synergistic effect is a result of the high transcription levels regulated by McMYBs in RL. In summary, individual flavonoids cooperate in a flavonoid system, thus producing a synergistic antioxidant effect, and the approach used herein can provide insights into the roles of flavonoids and other compounds in future studies.