Development of a triple hyphenated HPLC-radical scavenging detection-DAD-SPE-NMR system for the rapid identification of antioxidants in complex plant extracts

Targeted metabolite profiling of Salvia rosmarinus Italian local ecotypes and cultivars and inhibitory activity against Pectobacterium carotovorum subsp. carotovorum

Introduction

The development of agriculture in terms of sustainability and low environmental impact is, at present, a great challenge, mainly in underdeveloped and marginal geographical areas. The Salvia rosmarinus "Eretto Liguria" ecotype is widespread in Liguria (Northwest Italy), and farmers commonly use it by for cuttings and for marketing. In the present study, this ecotype was characterized in comparison with other cultivars from the same geographical region and Campania (Southern Italy), with a view to application and registration processes for the designation of protected geographical indications. Moreover, the possibility of using the resulting biomass after removing cuttings or fronds as a source of extracts and pure compounds to be used as phytosanitary products in organic farming was evaluated. Specifically, the potential of rosemary extracts and pure compounds to prevent soft rot damage was then tested.

Methods

A targeted NMR metabolomic approach was employed, followed by multivariate analysis, to characterize the rosemary accessions. Bacterial soft rot assay and disk diffusion test were carried out to evaluate the activity of extracts and isolated compounds against Pectobacterium carotovorum subsp. carotovorum. Enzymatic assay was performed to measure the in vitro inhibition of the pectinase activity produced by the selected pathogen. Molecular docking simulations were used to explore the possible interaction of the selected compounds with the pectinase enzymes.

Results and Discussion

The targeted metabolomic analysis highlighted those different geographical locations can influence the composition and abundance of bioactive metabolites in rosemary extracts. At the same time, genetic factors are important when a single geographical area is considered. Self-organizing maps (SOMs) showed that the accessions of "Eretto Liguria" appeared well characterized when compared to the others and had a good content in specialized metabolites, particularly carnosic acid. Soft rotting Enterobacteriaceae belonging to the Pectobacterium genus represent a serious problem in potato culture. Even though rosemary methanolic extracts showed a low antibacterial activity against a strain of Pectobacterium carotovorum subsp. carotovorum in the disk diffusion test, they showed ability in reducing the soft rot damage induced by the bacterium on potato tissue. 7-O-methylrosmanol, carnosol and isorosmanol appeared to be the most active components. In silico studies indicated that these abietane diterpenoids may interact with P. carotovorum subsp. carotovorum pectate lyase 1 and endo-polygalacturonase, thus highlighting these rosemary components as starting points for the development of agents able to prevent soft rot progression.

Recent Advances in Standardization of Herbal Drugs

Background:

Herbal drugs play a significant role to maintain the human healthiness and to treat the ailments since the dawn of civilization. Moreover, these plants have provided many lead compounds that culminated in modern medicine. A single herb is regarded as mini-combinatorial library of phytoconstituents hence the quality control of herbal drugs in an herbal formulation is not an easy task because a number of factors impact their pharmacological efficiency and consistent therapeutic effects. Hence, to provide consistent beneficial therapeutic effects, standardized herbal products of consistent quality and purity are required.

Methods:

This review is based on publications obtained by a selective search in PubMed using the keywords “Standardized herbal products”, “fingerprinting”, “authentication”, “chemometric, hyphenated techniques”, “quality control of herbal drugs”, “identification”.

Results:

In the era of modernization, chromatographic techniques coupled with sophisticated spectroscopic analytical methods are used in estimating the authenticity, identity and characteristic of herbal products. Further, with the advancement of computer technology, chemometrics methods have become a leading tool with an unsupervised pattern recognition technique for handling multivariate data without prior knowledge about the studied samples and mines more beneficial and valuable information about the chemical entities from the raw data.

Conclusion:

Standardization of HDs chromatographic fingerprint is not always a perfect way to present all compounds. To assess the quality of medicinal plants, new ways are regularly being explored such as combination chemical fingerprint with biological methods, biofingerprint and metabolic fingerprint quality metrology, pharmacodynamics and export system of medicinal plants have been researched in some groups but still a significant amount of work is required to achieve a perfect system for quality evaluation of herbal drugs. Further, novel chemometric techniques have been unfolded that mines more beneficial and valuable information about the chemical entities from the raw data. So this review emphasis mainly on hyphenated techniques associated with chemometric method used in herbal drugs for identifying more valuable information and various methods for providing data, among which most commonly used techniques are chemometric resolution method and Principal Component Analysis (PCA) method.

Abietane Diterpenoids with Antioxidative Damage Activity from Rosmarinus officinalis

Nine new and nineteen known compounds were isolated and identified from Rosmarinus officinalis under the guidance of bioassay and LCMS. They all belonged to abietane diterpenoids which enriched the types of compounds in R. officinalis, especially the discovery of a series of 20-norabietane diterpenoids (4, 6-9, and 26-27). The antioxidative damage activity of the compounds was tested on H₂O₂ damaged SH-SY5Y cells. Compounds 5, 6, and 7 presented moderate ability for promoting the growth of damaged cells. Compounds 10, 11, 13-20, 27, and 28 displayed a high antioxidative damage effect whose cell viability rates were more than 80%. The antioxidative damage effect of 11, 16, 18, and 20 were higher than that of EGCG (positive control) in which 11, 18, and 20 were the acetylated derivatives of carnosic acid (10), 7α-methoxy-isocarnosol (16), and carnosol (19), respectively. It suggested that 10-carboxyl/formyl of abietane diterpenoids was essential for maintaining the antioxidative damage activity and the adjacent hydroxyl groups on the benzene ring was less important for holding the bioactivity. These acetylated derivatives with high bioactivity and stability could be regarded as new sources of antioxidants or antioxidative damage agents being used in the food and medical industry.

Turn-on fluorescent assay for antioxidants based on their inhibiting polymerization of dopamine on graphene quantum dots

We describe a sensitive turn-on fluorescent assay for antioxidants by using fluorescence-tunable graphene quantum dots (GQDs). GQDs exhibited strong fluorescence without dopamine (DA). DA could self-polymerize to a thin polydopamine (PDA) film on the surface of GQDs under alkaline environment, resulting in the fluorescence quenching of GQDs via fluorescence resonance energy transfer (FRET). However, the self-polymerization of DA could be effectively inhibited in the presence of antioxidants including glutathione (GSH), ascorbic acid (AA), cysteine (Cys), and homocysteine (Hcys). Thus, the fluorescence of GQDs restored. The "turn-on" sensing of antioxidants could be achieved with high sensitivity. The detection limit for GSH, AA, Cys, and Hcys could be achieved as low as 2.4 nM, 1.5 nM, 4.2 nM, and 4.4 nM, respectively. Finally, the GQDs@PDA system was applied for monitoring cerebral antioxidants in rat brain microdialysates. This work promises new opportunities to evaluate antioxidant capacity in physiological and pathological fields.

Various Dereplication Strategies Using LC-MS for Rapid Natural Product Lead Identification and Drug Discovery

Natural products are the most consistently successful source of drug leads. The rapid identification of known compounds from natural product extracts, or ‘dereplication’, is an important step in an efficiently run drug discovery program. Modern spectroscopic methods have largely revolutionized compound identification and tremendously accelerated the pace at which isolated compounds can be identified. Dereplication strategies use analytical techniques and database searching to determine the identity of an active compound at the earliest possible stage in the discovery process. This prevents wasted effort on samples with no potential for development and allows resources to be focused on the most promising lead. In the past few years, advances in technology have allowed the development of tandem analytical techniques, such as HPLC-PDA, LC-MS, LC-MS-MS, LC-NMR, and LC-NMR-MS. This review describes the principles and performance of a number of hyphenated techniques involving LC-MS that can be used for dereplication of natural products for rapid lead identification.

Rosmarinic acid prevents fibrillization and diminishes vibrational modes associated to β sheet in tau protein linked to Alzheimer's disease

Alzheimer's disease is a common tauopathy where fibril formation and aggregates are the hallmark of the disease. Efforts targeting amyloid-β plaques have succeeded to remove plaques but failed in clinical trials to improve cognition; thus, the current therapeutic strategy is at preventing tau aggregation. Here, we demonstrated that four phenolic diterpenoids and rosmarinic acid inhibit fibrillization. Since, rosmarinic acid was the most active compound, we observe morphological changes in atomic force microscopy images after treatment. Hence, rosmarinic acid leads to a decrease in amide regions I and III, indicating that rosmarinic acid prevents β-sheet assembly. Molecular docking study inside the steric zipper model of the hexapeptide 306VQIVYK311 involved in fibrillization and β sheet formation, suggests that rosmarinic acid binds to the steric zipper with similar chemical interactions with respect to those observed for orange G, a known pharmacofore for amyloid.

Isolation and identification of human metabolites from a novel anti-tumor candidate drug 5-chlorogenic acid injection by HPLC-HRMS/MSn and HPLC-SPE-NMR

A novel anti-tumor candidate drug, 5-chlorogenic acid (5-CQA) injection, was used for the treatment of malignant glioma in clinical trial (phase I) in China. The isolation and identification of the metabolites of 5-CQA injection in humans were investigated in the present study. Urine and feces samples obtained after intramuscular administration of 5-CQA injection to healthy adults have been analyzed by high-performance liquid chromatography coupled with high-resolution mass and multiple-stage mass spectrometry (HPLC-HRMS/MSⁿ). No metabolite was detected in human feces; however, in human urine, a total of six metabolites were identified including isomerized 5-CQA (P1 and P2), hydrolyzed 5-CQA (M1and M2), and methylated 5-CQA (M3 and M4). Among them, M3 and M4 were the main metabolites and target analytes for human mass balance study. Additionally, the structure of M3 and M4 was characterized by high-performance liquid chromatography-solid phase extraction-nuclear magnetic resonance (HPLC-SPE-NMR), and the results demonstrated that the methoxy group of M3 and M4 was exclusively attributed to C-3' and C-4', respectively. Due to the unavailability of commercial reference, the pure products of M3 and M4 were synthesized by 5-CQA methylation and followed by isolation and purification. Moreover, the potential activity of M3 and M4 on malignant glioma was predicted using a reverse molecular docking analysis on eight malignant glioma-related pathways. The results showed that M3 and M4 had various interactions against malignant glioma-related targets. Our study provides an insight into the metabolism of 5-CQA injection in humans and supports the clinical human mass balance study. Graphical abstract ᅟ.

Antioxidant Activity/Capacity Measurement. 3. Reactive Oxygen and Nitrogen Species (ROS/RNS) Scavenging Assays, Oxidative Stress Biomarkers, and Chromatographic/Chemometric Assays

There are many studies in which the antioxidant potential of different foods have been analyzed. However, there are still conflicting results and lack of information as a result of unstandardized assay techniques and differences between the principles of the methods applied. The measurement of antioxidant activity, especially in the case of mixtures, multifunctional or complex multiphase systems, cannot be evaluated satisfactorily using a simple antioxidant test due to the many variables influencing the results. In the literature, there are many antioxidant assays that are used to measure the total antioxidant activity/capacity of food materials. In this review, reactive oxygen and nitrogen species (ROS/RNS) scavenging assays are evaluated with respect to their mechanism, advantages, disadvantages, and potential use in food systems. On the other hand, in vivo antioxidant activity (AOA) assays including oxidative stress biomarkers and cellular-based assays are covered within the scope of this review. Finally, chromatographic and chemometric assays are reviewed, focusing on their benefits especially with respect to their time saving, cost-effective, and sensitive nature.

Antioxidant activities of orange peel extract in ghee (butter oil) stored at different storage temperatures

Antioxidant activities of butylatedhydroxyanisole (BHA) and orange peel powder extract in ghee stored at different storage temperatures (T1:6 ± 2 °C; T2: 32 ± 2 °C; T3:60 ± 2 °C) were evaluated during storage period of 21 days. Peroxide value (PV), thiobarbituric acid (TBA), radical scavenging activity (RSA) and free fatty acids (FFA) of ghee samples were analyzed during the study. PV, TBA and FFA of ghee samples increased significantly while radical scavenging activity (RSA) of ghee samples decreased significantly at accelerated temperature (T3) as compared to the temperatures at T1 and T2. Effect of storage temperature on development of peroxides and TBA of ghee samples was significantly higher than the effect of treatment and storage period while treatment had more significant effect on the change in FFA and RSA as compared to storage temperature and storage period. Ghee incorporated with orange peel extract (OPE) showed stronger activity in quenching DPPH radicals and least development of PV, TBA and FFA than ghee incorporated with BHA and control. The study revealed that orange peel could be a good natural source of antioxidants which can be used in fat rich food products like ghee to retard oxidative deterioration.

HPLC-SPE-NMR characterization of major metabolites in Salvia fruticosa Mill. extract with antifungal potential: relevance of carnosic acid, carnosol, and hispidulin

Plant pathogenic fungi are considered of significant economic importance for adversely affecting both quantitatively and qualitatively fresh and processed produce. Extracts of Salvia fruticosa were initially screened for their antifungal activity, and the ethyl acetate fraction, being the most active, was further analyzed using HPLC-SPE-NMR hyphenation. The methoxylated flavones hispidulin, salvigenin, and cirsimaritin and the diterpenes carnosic acid, carnosol, and 12-methoxycarnosic acid were identified as the major components of the extract. In addition, the concentration levels of all identified components were determined using q-NMR. The antifungal activity of the crude extract and selected phytochemicals was estimated against the fungal species Aspergillus tubingensis, Botrytis cinerea, and Penicillium digitatum. The estimated MIC and MFC values of the ethyl acetate extract of S. fruticosa, as well as three of its major constituents, carnosic acid, carnosol, and hispidulin, support their antifungal activity, especially against B. cinerea and P. digitatum, suggesting their potential use in food and agricultural systems.

The breakthrough curve combination for xenon sampling dynamics in a carbon molecular sieve column

In the research of xenon sampling and xenon measurements, the xenon breakthrough curve plays a significant role in the xenon concentrating dynamics.

Bioactive compounds from culinary herbs inhibit a molecular target for type 2 diabetes management, dipeptidyl peptidase IV

Greek oregano (Origanum vulgare), marjoram (Origanum majorana), rosemary (Rosmarinus officinalis), and Mexican oregano (Lippia graveolens) are concentrated sources of bioactive compounds. The aims were to characterize and examine extracts from greenhouse-grown or commercially purchased herbs for their ability to inhibit dipeptidyl peptidase IV (DPP-IV) and protein tyrosine phosphatase 1B (PTP1B), enzymes that play a role in insulin secretion and insulin signaling, respectively. Greenhouse herbs contained more polyphenols (302.7-430.1 μg of gallic acid equivalents/mg of dry weight of extract (DWE)) and flavonoids (370.1-661.4 μg of rutin equivalents/mg of DWE) compared to the equivalent commercial herbs. Greenhouse rosemary, Mexican oregano, and marjoram extracts were the best inhibitors of DPP-IV (IC₅₀=16, 29, and 59 μM, respectively). Commercial rosemary, Mexican oregano, and marjoram were the best inhibitors of PTP1B (32.4-40.9% at 500 μM). The phytochemicals eriodictyol, naringenin, hispidulin, cirsimaritin, and carnosol were identified by LC-ESI-MS as being present in greenhouse-grown Mexican oregano and rosemary. Computational modeling indicated that hispidulin, carnosol, and eriodictyol would have the best binding affinities for DPP-IV. Biochemically, the best inhibitors of DPP-IV were cirsimaritin (IC₅₀=0.43±0.07 μM), hispidulin (IC₅₀=0.49±0.06 μM), and naringenin (IC₅₀=2.5±0.29 μM). Overall, herbs contain several flavonoids that inhibit DPP-IV and should be investigated further regarding their potential in diabetes management.

High-resolution screening combined with HPLC-HRMS-SPE-NMR for identification of fungal plasma membrane H(+)-ATPase inhibitors from plants

Crude extracts of 33 plant species were assessed for fungal plasma membrane (PM) H(+)-ATPase inhibition. This led to identification of 18 extracts showing more than 95% inhibition at a concentration of 7.5 mg/mL and/or a concentration-dependent activity profile. These extracts were selected for semi-high-resolution fungal PM H(+)-ATPase inhibition screening, and, on the basis of these results, Haplocoelum foliolosum (Hiern) Bullock and Sauvagesia erecta L. were selected for investigation by high-resolution fungal PM H(+)-ATPase inhibition screening. Structural analysis performed by high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy (HPLC-HRMS-SPE-NMR) led to identification of chebulagic acid (1) and tellimagrandin II (2) from H. foliolosum. Preparative-scale isolation of the two metabolites allowed determination of IC50 values for PM H(+)-ATPase, and growth inhibition of Saccharomyces cerevisiae and Candida albicans. Chebulagic acid and tellimagrandin II are both potent inhibitors of the PM H(+)-ATPase with inhibitory effect on the growth of S. cerevisiae.

Ultrathin g-C3N4/TiO2composites as photoelectrochemical elements for the real-time evaluation of global antioxidant capacity

Using utg-C₃N₄/TiO₂, a photoelectrochemical platform was designed for the sensing of global antioxidant capacity, which presented a rapid response, and anti-fouling and colour-interference-proof properties.

High-resolution screening combined with HPLC-HRMS-SPE-NMR for identification of potential health-promoting constituents in sea aster and searocket--new Nordic food ingredients

Sea aster (Aster tripolium L.) and searocket (Cakile maritima Scop.), potential ingredients in the New Nordic Diet, were analyzed by high-resolution radical scavenging and high-resolution α-glucosidase inhibition assays. Results from the two bioactivity profiles were used to guide subsequent structural analysis toward constituents with potential health-promoting effects. Structural analysis was performed by high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction and automated tube transfer nuclear magnetic resonance spectroscopy, that is, HPLC-HRMS-SPE-ttNMR. High-resolution mass spectrometry together with detailed analysis of one- and two-dimensional proton detected NMR experiments enabled unambiguous assignment of the targeted analytes. This revealed a series of caffeoyl esters (1, 2, 5), flavonoid glycosides (3, 4, 6, 11-15), flavonoids (7-9), sinapate esters (10, 16, 17), and sinapinic acid (18) associated with radical scavenging and/or α-glucosidase inhibition. In vitro assays implemented in this study showed that sea aster holds potential as a future functional food ingredient for lowering postprandial blood glucose level for diabetics, but further investigations are needed to prove the effect in vivo.

Targeting high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance analysis with high-resolution radical scavenging profiles-Bioactive secondary metabolites from the endophytic fungus Penicillium namyslowskii

The high-resolution radical scavenging profile of an extract of the endophytic fungus Penicillium namyslowskii was used to target analysis by high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy, i.e., HPLC-HRMS-SPE-NMR, for identification of anti-oxidative secondary metabolites. This revealed the two chromatographic peaks with the highest relative response in the radical scavenging profile to be griseophenone C and peniprequinolone. The HPLC-HRMS-SPE-NMR analysis was performed in the tube-transfer mode using a cryogenically cooled NMR probe designed for 1.7mm NMR tubes. To further explore the potential of the above HPLC-HRMS-SPE-NMR platform for analysis of endophytic extracts, six peaks displaying no radical scavenging activity were also analyzed. This allowed unambiguous identification of six metabolites, i.e., dechlorogriseofulvin, dechlorodehydrogriseofulvin, griseofulvin, dehydrogriseofulvin, mevastatin acid, and mevastatin. The high mass sensitivity of the 1.7mm cryogenically cooled NMR probe allowed for the first time acquisition of direct detected (13)C NMR spectra of fungal metabolites, i.e., dechlorogriseofulvin and griseofulvin, directly from crude extract via HPLC-HRMS-SPE-NMR. Dechlorodehydrogriseofulvin was reported for the first time from nature.

Applicability of a blood-brain barrier specific artificial membrane permeability assay at the early stage of natural product-based CNS drug discovery

While numerous natural products (NPs) possess activity on central nervous system (CNS) targets, there has been no analytical approach to effectively identify compounds with high brain penetration potential in complex mixtures at the early stage of drug discovery. To overcome this issue, the performance of an in vitro parallel artificial membrane permeability assay for the blood-brain barrier (PAMPA-BBB) for natural products and for plant extracts has been validated and characterized. It was found that the PAMPA-BBB assay preserves its predictive power in the case of natural products and provides high phytochemical selectivity, which enables its use as a unique filtering tool in terms of selecting brain-penetrable compounds from plant extracts. Moreover, the present study has demonstrated that simple modifications in the assay design allow the direct use of PAMPA-BBB filtered samples in a dereplication process, as performed by NMR and LC-MS. The applicability of this procedure was demonstrated using extracts prepared from Tanacetum parthenium, Vinca major, Salvia officinalis, and Corydalis cava, representing different types of chemical diversity and complexity. Thus, the proposed protocol represents a potentially valuable strategy in the NP-based CNS drug discovery environment with a high-throughput screening platform.

The importance of hyphenated techniques in the discovery of new lead compounds from nature

Nature represents an extraordinary reservoir of novel molecules and there is currently a resurgence of interest in natural products as a possible source of new lead compounds for introduction into therapeutical screening programmes. To discover new bioactive natural products, the dereplication of crude extracts performed prior to isolation work is of crucial importance for avoiding the tedious isolation of known constituents. In this respect, chemical screening strategies based on hyphenated techniques such as liquid chromatography-ultraviolet photodiode array detection, liquid chromatography-mass spectrometry, liquid chromatography tandom mass spectrometry and liquid chromatography-nuclear magnetic resonance (LC-NMR) are more and more extensively used. In the laboratory of Hostettmann's group, these analytical methods have been fully integrated into the isolation process and are used for the chemical screening of crude plant extracts, in complement with online or at-line bioassays, for rapid localisation and identification of new bioactive compounds. In this paper, possibilities and limitations of hyphenated techniques for de novo online natural product identification are discussed. As LC-NMR is playing a key role in this respect, the main part of the paper is dedicated to this technique. In particular, various ways of integrating NMR in the dereplication process are illustrated and strategies involving either direct or indirect hyphenation are presented.

Structure activity relationship of phenolic diterpenes from Salvia officinalis as activators of the nuclear factor E2-related factor 2 pathway

Nuclear factor E2-related factor 2 (Nrf2) is a transcription factor known to activate cytoprotective genes which may be useful in the treatment of neurodegenerative disease. In order to better understand the structure activity relationship of phenolic diterpenes from Salvia officinalis L., we isolated carnosic acid, carnosol, epirosmanol, rosmanol, 12-methoxy-carnosic acid, sageone, and carnosaldehyde using polyamide column, centrifugal partition chromatography, and semi-preparative high performance liquid chromatography. Isolated compounds were screened in vitro for their ability to active the Nrf2 and general cellular toxicity using mouse primary cortical cultures. All compounds except 12-methoxy-carnosic acid were able to activate the antioxidant response element. Furthermore both carnosol and carnoasldehyde were able to induce Nrf2-dependent gene expression as well as protect mouse primary cortical neuronal cultures from H(2)O(2) induced cell death.

Antidepressant-like effects of fractions, essential oil, carnosol and betulinic acid isolated from Rosmarinus officinalis L

The aim of this study was to investigate the antidepressant-like effect of fractions from Rosmarinus officinalis L.: ethyl acetate 1 and 2 (AcOEt1 and 2), hexane (HEX), ethanolic (ET), and essential oil-free (EOF) fractions, as well as essential oil, the isolated compounds carnosol and betulinic acid in the tail suspension test, a predictive test of antidepressant activity. Swiss mice were acutely administered by oral route (p.o.) with fractions, essential oil or isolated compounds, 60 min before the tail suspension test or open-field test. All of them produced a significant antidepressant-like effect: AcOEt1, ET, EOF fractions and essential oil (0.1-100mg/kg, p.o); HEX (0.1-10mg/kg, p.o) and AcOEt2 fraction (0.1-1mg/kg, p.o), carnosol (0.01-0.1mg/kg, p.o.) isolated from the HEX fraction and betulinic acid (10mg/kg, p.o.), isolated from the AcOEt1 and AcOEt2 fractions. No psychostimulant effect was shown in the open-field test, indicating that the effects in the tail suspension test are specific. This study suggests that carnosol and betulinic acid could be responsible for the anti-immobility effect of extracts from R. officinalis.

An evidence-based systematic review of rosemary (Rosmarinus officinalis) by the Natural Standard Research Collaboration

An evidence-based systematic review of rosemary (Rosmarinus officinalis), including written and statistical analysis of scientific literature, expert opinion, folkloric precedent, history, pharmacology, kinetics/dynamics, interactions, adverse effects, toxicology, and dosing.

Development of on-line high performance liquid chromatography (HPLC)-biochemical detection methods as tools in the identification of bioactives

Biochemical detection (BCD) methods are commonly used to screen plant extracts for specific biological activities in batch assays. Traditionally, bioactives in the most active extracts were identified through time-consuming bio-assay guided fractionation until single active compounds could be isolated. Not only are isolation procedures often tedious, but they could also lead to artifact formation. On-line coupling of BCD assays to high performance liquid chromatography (HPLC) is gaining ground as a high resolution screening technique to overcome problems associated with pre-isolation by measuring the effects of compounds post-column directly after separation. To date, several on-line HPLC-BCD assays, applied to whole plant extracts and mixtures, have been published. In this review the focus will fall on enzyme-based, receptor-based and antioxidant assays.

Genesis and development of DPPH method of antioxidant assay

α, α-diphenyl-β-picrylhydrazyl (DPPH) free radical scavenging method offers the first approach for evaluating the antioxidant potential of a compound, an extract or other biological sources. This is the simplest method, wherein the prospective compound or extract is mixed with DPPH solution and absorbance is recorded after a defined period. However, with the advancement and sophistication in instrumental techniques, the method has undergone various modifications to suit the requirements, even though the basic approach remains same in all of them. This article presents a critical review on various developments to the DPPH method.

On-line high-performance liquid chromatography-diode array detection-electrospray ionization-mass spectrometry-chemiluminescence assay of radical scavengers in Epimedium

An on-line analysis method for the simultaneous detection and identification of radical scavenging compounds in plant extracts was developed by combining HPLC with hydrogen dioxide radical scavenging and HPLC-DAD-MS-CL system. The structural identification and activity characteristics of various constituents could be rapidly achieved by the on-line assay of UV, MS and CL in one run. In 4 species of Epimedium studied 32 compounds, including phenolic acids, 8-isopentenyl-flavonoid glycosides and flavonoid glycosides containing a ortho-hydroxyl group, were identified by comparison with authentic standards and published mass data. Among these compounds, phenolic acids and flavonoid glycosides containing an ortho-hydroxyl group could obviously inhibit CL, which suggested their strong radical scavenging activity. These four species each exhibited different active properties, which might correlate to their respective quality. The results indicated that the on-line HPLC-DAD-MS-CL system would be a potential method to rapidly and sensitively screen radical scavengers in herbal medicines, and could display an integrated fingerprint based on different detectors.

Activation of the nuclear receptor PPARγ by metabolites isolated from sage (Salvia officinalis L.)

ETHNOPHARMACOLOGICAL RELEVANCE

Salvia officinalis has been used as a traditional remedy against diabetes in many countries and its glucose-lowering effects have been demonstrated in animal studies. The active compounds and their possible mode of action are still unknown although it has been suggested that diterpenes may be responsible for the anti-diabetic effect of Salvia officinalis.

AIM OF THE STUDY

To investigate whether the reported anti-diabetic effects of Salvia officinalis are related to activation of the nuclear receptor peroxisome proliferator-activated receptor (PPAR)γ and to identify the bioactive constituents.

MATERIALS AND METHODS

From a dichloromethane extract of Salvia officinalis able to activate PPARγ several major metabolites were isolated by chromatographic techniques. To assess bioactivity of the isolated metabolites a PPARγ transactivation assay was used.

RESULTS

Eight diterpenes were isolated and identified including a new abietane diterpene being the epirosmanol ester of 12-O-methyl carnosic acid and 20-hydroxyferruginol, which was isolated from Salvia officinalis for the first time, as well as viridiflorol, oleanolic acid, and α-linolenic acid. 12-O-methyl carnosic acid and α-linolenic acid were able to significantly activate PPARγ whereas the remaining metabolites were either unable to activate PPARγ or yielded insignificant activation.

CONCLUSIONS

Selected metabolites from Salvia officinalis were able to activate PPARγ and hence, the anti-diabetic activity of this plant could in part be mediated through this nuclear receptor.

Gastroprotective effect of carnosic acid gamma-lactone derivatives

Carnosic acid (1) has been shown to possess gastroprotective activity in vitro and in vivo. However, little is known of the gastroprotective effect or cytotoxicity of carnosic acid gamma-lactone (3). To determine structure-activity relationships, a series of 17 esters of 3 were prepared including aliphatic, aromatic, and heterocyclic derivatives. Also, two units of 3 were coupled with succinic and phthalic acid as linkers. The compounds were assessed for their gastroprotective effect in the HCl/EtOH-induced gastric lesions model in mice and for cytotoxicity in human lung fibroblasts, human adenocarcinoma AGS cells, and Hep G2 hepatocellular carcinoma cells. At a single oral dose of 40 mg/kg, the gastroprotective effect increased moderately with the length of the alkyl chain. The best effects were observed for the butyrate (9) and chloroacetate (6) derivatives. Activity of fatty acid esters increased with chain length but decreased with unsaturation. The best gastroprotective effect, with lowest cytotoxicity, was found for the palmitate (11) and oleate (12) derivatives.

Revealing the metabonomic variation of rosemary extracts using 1H NMR spectroscopy and multivariate data analysis

The molecular compositions of rosemary ( Rosmarinus officinalis L.) extracts and their dependence on extraction solvents, seasons, and drying processes were systematically characterized using NMR spectroscopy and multivariate data analysis. The results showed that the rosemary metabonome was dominated by 33 metabolites including sugars, amino acids, organic acids, polyphenolic acids, and diterpenes, among which quinate, cis-4-glucosyloxycinnamic acid, and 3,4,5-trimethoxyphenylmethanol were found in rosemary for the first time. Compared with water extracts, the 50% aqueous methanol extracts contained higher levels of sucrose, succinate, fumarate, malonate, shikimate, and phenolic acids, but lower levels of fructose, glucose, citrate, and quinate. Chloroform/methanol was an excellent solvent for selective extraction of diterpenes. From February to August, the levels of rosmarinate and quinate increased, whereas the sucrose level decreased. The sun-dried samples contained higher concentrations of rosmarinate, sucrose, and some amino acids but lower concentrations of glucose, fructose, malate, succinate, lactate, and quinate than freeze-dried ones. These findings will fill the gap in the understanding of rosemary composition and its variations.