Ethyl acetate-n-butanol gradient solvent system for high-speed countercurrent chromatography to screen bioactive substances in okra

Chemical characterization and microencapsulation of extracellular fungal pigments

In this work, extracellular colored metabolites obtained from the filamentous fungi Talaromyces australis and Penicillium murcianum, isolated in the Andean-Patagonian native forests of Chile, were studied as prospect compounds to increase the sustainability of cosmetic products. The chemical and antioxidant properties of these natural pigments were characterized and strategies for their microencapsulation were also studied. UHPLC/MS-MS analyses indicated that the predominant metabolites detected in the cultures of P. murcianum were monascin (m/z = 411.15) and monashexenone (m/z = 319.10), while athrorosin H (m/z = 458.20) and damnacanthal (m/z = 281.05) were detected in cultures of T. australis. ORAC tests revealed that P. murcianum's metabolites had the greatest antioxidant properties with values higher than 2000 μmol of trolox equivalents/g. The fungal metabolites were successfully microencapsulated by ionic gelation into structures made of 1.3% sodium alginate, 0.2% chitosan, and 0.07% hyaluronic acid. The microencapsulation process generated structures of 543.57 ± 0.13 µm of mean diameter (d₅₀) with an efficiency of 30% for P. murcianum, and 329.59 ± 0.15 µm of mean diameter (d₅₀) and 40% efficiency, for T. australis. The chemical and biological characterization show the biotechnological potential of these fungal species to obtain pigments with antioxidant activity that could be useful in the cosmetic industry. The encapsulation process enables the production of easy-to-handle dry powder from the fungal metabolites, which could be potentially marketed as a functional cosmetic ingredient. KEY POINTS: • The predominant fungal pigments were of azaphilone and anthraquinoid classes. • The fungal pigments showed high antioxidant activity by ORAC assay. • Fungal pigment microcapsules obtained by ionic gelation were characterized.

Effect of the Ethanol Extract of Red Okra Pods (Abelmoschus esculentus (L.) Moench) to Inhibit Cervical Cancer Cells Growth through Cell Cycle-Associated Oncogenes

This study aims to evaluate the potency of ethanol extract of red okra pods (EEROP) in inhibiting growth of cervical cancer cells through repression of the cell cycle-associated oncogenes. The EEROP treatment was given to HeLa cells cultured with RPMI medium and incubated at 37°C with 5% CO₂. The MTT method was used to measure HeLa cell growth and IC₅₀ values. The mRNA levels of the three cell cycle-associated oncogenes (MYC, TYMS, and MDM2) were evaluated by qRT-PCR to determine the effect of EEROP treatment on the cell cycle. The lowest percentage of viable cells at 24, 48, and 72 hours after EEROP treatment was in the dose of 1000 μg/mL with a growth percentage of 71.60% at 24 hours, 55.61% at 48 hours, and 46.97% at 72 hours. The IC₅₀ values were 2845, 1153, and 776.8 μg/mL for 24, 48, and 72 hours, respectively. The three oncogenes at a dose of 1000 μg/mL significantly decreased the lowest mRNA levels compared to other doses with MYC oncogene that experienced the greatest decrease. The mRNA level of dose 1000 μg/mL EEROP at the MYC oncogene was 0.014-fold changes, at the TYMS oncogene was 0.097-fold changes, and at the MDM2 oncogene was 0.028-fold changes. The EEROP has been shown to decrease the expression of three cell cycle-associated oncogenes. This is also supported by the growth of HeLa cells that did not increase throughout 24, 48, and 72 hours. However, further research is needed on the main active components in red okra that function as anticancer, so that in the future, okra can not only stop cancer cell growth but also induce cancer cell death.

Application of Linear Gradient Solvent System in Centrifugal Partition Chromatography Facilitating Bioassay-Guided Fractionation of Yongdamsagan-Tang, Traditional Oriental Decoction

As important pharmaceutical resources, traditional herbal medicines retain continuous attention. To do that, isolation and identification of bioactive molecules from traditional herbal decoction are important. However, conventional fractionation through octadecyl silica column faces irreversible sample adsorption that causes a bias in bioactivity assessment. However, liquid-liquid chromatographic system suffers tedious K value calculation as well as insufficient capacity in separation power when crude extract composed of widely ranging polarities. Here, we developed a comprehensive linear gradient solvent system for centrifugal partition chromatography (CPC) to aid bioassay-guided isolation. The lower aqueous phase of the n-hexane-acetonitrile-water (10:2:8, v/v) was used as the stationary, whereas its upper organic phase followed by the upper phase of ethyl acetate-acetonitrile-water and water-saturated n-butanol-acetonitrile-water in the same ratio were eluted in a linear gradient mode, thereby increasing polarity in the mobile phase. The HPLC profiling of CPC fraction showed that proposed gradient CPC was suitable to separate metabolites from Yongdamsagan-Tang, a traditional medicinal decoction made of ten herbal plants. Exhibiting a high recovery yield of 98.3%, antioxidant response element (ARE) luciferase-inducing assay in HepG2 cells indicated that the fractions composed of baicalein and wogonin, the marker natural products of Scutellaria baicalensis, were to be the most effective molecules from Yongdamsagan-Tang. The presented results demonstrated that bioassay-guided separation that assisted with a linear gradient CPC is an incomparable alternative to HPLC and biphasic CPC in terms of higher yield rate and redundant K value calculation, respectively, which led to an unbiased/time-saving separation and identification of bioactive molecules from the complex crude extract of natural products.

Okra fruit: LC-ESI/LTQOrbitrap/MS/MSn based deep insight on polar lipids and specialized metabolites with evaluation of anti-oxidant and anti-hyperglycemic activity

Okra is a vegetable crop very popular in tropical, subtropical, and warm temperate regions of the world for its edible fruit. Nowadays, this species can be easily found in European local markets, as a basic ingredient in many local and traditional dishes. Considering the extensive and spread use of okra fruits, to achieve deep insight on its chemical composition the analysis of the polar extract by high-performance liquid chromatography coupled to multiple-stage linear ion-trap and orbitrap high-resolution mass spectrometry in negative electrospray ionization mode was carried out. By this approach, 39 metabolites belonging to different polar lipid classes, such as oxylipins, phospholipids, glycolipids, and sphingolipids, were putatively identified for the first time in A. esculentus. Moreover, LC-HRMS/MS analyses guided the isolation and characterization by NMR experiments of 19 specialized metabolites belonging to phenolic acid and flavonoid classes, 8 of them never reported before in A. esculentus. Finally, antioxidant activity and inhibition of α-glucosidase activity were assayed, suggesting a good anti-oxidant anti-hyperglycemic activity for okra fruit.

Advances in Separation and Purification of Bioactive Polysaccharides through High-speed Counter-Current Chromatography

Polysaccharides, with an extensive distribution in natural products, represent a group of natural bioactive substances having widespread applications in health-care food products and as biomaterials. Devising an efficient system for the separation and purification of polysaccharides from natural sources, hence, is of utmost importance in the widespread applicability and feasibility of research for the development of polysaccharide-based products. High-speed counter-current chromatography (HSCCC) is a continuous liquid-liquid partitioning chromatography with the ability to support a high loading amount and crude material treatment. Due to its flexible two-phase solvent system, HSCCC has been successfully used in the separation of many natural products. Based on HSCCC unique advantages over general column chromatography and its enhanced superiority in this regard when coupled to aqueous two-phase system (ATPS), this review summarizes the separation and purification of various bioactive polysaccharides through HSCCC and its coupling to ATPS as an aid in future research in this direction.

A strategy based on isocratic and linear-gradient high-speed counter-current chromatography for the comprehensive separation of platycosides from Platycodi radix

Platycosides, the generally recognized main active constituents of Platycodi radix, have been studied extensively for their wide pharmacological activities. Herein, we have successfully developed an efficient method for the enrichment and comprehensive isolation of platycosides from Platycodi radix by MCI resin column chromatography (CC) and two different modes of high-speed counter-current chromatography (HSCCC). MCI resin CC was the preferable enrichment operation for platycosides from the 70%-ethanol extract of Platycodi radix and rendered target platycosides when eluted by 60% aqueous methanol solution. As for the separation, two different modes, including isocratic HSCCC and linear-gradient HSCCC, were applied together to separate the platycosides using a mixture of ethyl acetate, n-butanol and water coupled with evaporative light scattering detection, for the first time. Isocratic HSCCC was applied to separate crude platycosides from Platycodi radix using ethyl acetate-n-butanol-water (1 : 1 : 2, v/v), yielding seven pure platycosides (compounds 1-6, 8) and two fractions of enriched mixtures of compounds 7, 9, 10, and 11. Linear-gradient HSCCC was employed to rapidly separate compounds 7, 9, 10, and 11 by constantly changing the proportions of ethyl acetate and n-butanol in the ethyl acetate-n-butanol-water solvent system. Finally, platycoside E (1), deapio-platycodin D₃ (2), platycodin D₃ (3), deapio-platycodin D₂ (4), platycodin D₂ (5), platycodin D (6), polygalacin D₂ (7), polygalacin D (8), and three tautomers, namely 2''-O-acetylplatycodin D (9) and 3''-O-acetylplatycodin D (9'), 2''-O-acetylpolygalacin D₂ (10) and 3''-O-acetylpolygalacin D₂ (10'), and 2''-O-acetylpolygalacin D (11) and 3''-O-acetylpolygalacin D (11'), were obtained from 300 mg of crude platycosides from Platycodi radix.

Efficient Separation of Phytochemicals from Muehlenbeckia volcanica (Benth.) Endl. by Polarity-Stepwise Elution Counter-Current Chromatography and Their Antioxidant, Antiglycation, and Aldose Reductase Inhibition Potentials

Muehlenbeckia volcanica (Benth.) Endl. (M. volcanica), native to South America, is a traditional Peruvian medicinal plant that has multi-therapeutic properties; however, no phytochemicals have been identified from it yet. In this study, a five-step polarity-stepwise elution counter-current chromatography (CCC) was developed using methanol/water (1:5, v/v) as the stationary phase and different ratios of n-hexane, ethyl acetate, and n-butanol as mobile phases to separate the compounds from the 70% methanol extract of M. volcanica, by which six compounds with a wide range of polarities were separated in a single run of CCC and were identified as gallic acid, protocatechuic acid, 4,4'-dihydroxy-3,3'-imino-di-benzoic acid, rutin, quercitrin, and quercetin. Then, two compounds from the fractions of stepwise elution CCC were separated using conventional high-speed CCC, pH-zone-refining CCC, and preparative high-performance liquid chromatography, and identified as shikimic acid and miquelianin. These compounds are reported from M. volcanica for the first time. Notably, except for shikimic acid, all other compounds showed anti-diabetic potentials via antioxidant, antiglycation, and aldose reductase inhibition. The results suggest that the polarity-stepwise elution CCC can be used to efficiently separate or fractionate compounds with a wide range of polarities from natural products. Moreover, M. volcanica and its bioactive compounds are potent anti-diabetic agents.

Bioassay-Guided Separation of Centipeda minima Using Comprehensive Linear Gradient Centrifugal Partition Chromatography

A comprehensive linear gradient solvent system for centrifugal partition chromatography (CPC) was developed for the bioassay-guided isolation of natural compounds. The gradient solvent system consisted of three different ternary biphasic solvents types: n-hexane–acetonitrile–water (10:2:8, v/v), ethyl acetate–acetonitrile–water (10:2:8, v/v), and water-saturated n-butanol–acetonitrile–water (10:2:8, v/v). The lower phase of the n-hexane–acetonitrile–water (10:2:8, v/v) was used as the stationary phase, while its upper phase, as well as ethyl acetate–acetonitrile–water (10:2:8), and water-saturated n-butanol–acetonitrile–water (10:2:8, v/v) were pumped to generate a linear gradient elution, increasing the mobile phase polarity. We used the gradient CPC to identify antioxidant response elements (AREs), inducing compounds from Centipeda minima, using an ARE-luciferase assay in HepG2 cells, which led to the purification of the active molecules 3-methoxyquercetin and brevilin A. The developed CPC solvent systems allow the separation and isolation of compounds with a wide polarity range, allowing active molecule identification in the complex crude extract of natural products.

Methanol linear gradient counter-current chromatography for the separation of natural products: Sinopodophyllum hexandrum as samples

Counter-current chromatography (CCC) is a unique, liquid-liquid partition chromatography process. Both the mobile and stationary phases are liquids, so no solid support matrix is used. CCC has gained wide acceptance as a preparative technique in a variety of fields. Because the mobile and stationary phases are both liquids, gradient elution is difficult to perform with CCC. Phase equilibrium must be maintained, so any change in the composition of one phase may induce a compositional change in the other. In this work, a new linear gradient elution method was developed for CCC. Biphasic solvent systems containing heptane, ethyl acetate, methanol, and water (HepEMWat) in various ratios were prepared and used to optimize both isocratic and linear gradient CCC separation with methanol. We first separated a test mixture of four standard compounds with partition coefficients ranging from 0.8 to 7.8. The separation resembled a reversed-phase process, and elution was performed while progressively decreasing the polarity of the mobile phase. Target molecules with small partition coefficients eluted first in the lower phase of the optimized HepEMWat solvent system. Elution of constituents with large partition coefficients was quite slow under isocratic conditions. Separation time was significantly reduced when elution was performed with a linear gradient using methanol and the optimal HepEMWat system. Elution with a 3:7:4:6 (v/v/v/v) HepEMWat system took approximately 200 min. This included an 80-min isocratic step, followed by gradient elution with methanol from 0% to 30%. The optimized methanol linear gradient CCC method was then used to separate a complex mixture of natural products isolated from Sinopodophyllum hexandrum (Royle) Ying roots. Twelve compounds with a wide range of polarities were well-resolved in a single separation. We have developed a convenient and cost-effective strategy for the separation of complex mixtures. No tedious mobile phase preparation step is required. The volume of unused mobile phase is minimal, so little solvent is wasted. The method is an important advance for the separation of mixtures that contain many compounds with a large range of polarities and partition coefficients, which are common features of natural products.

Abelmoschus esculentus (L.): Bioactive Components' Beneficial Properties-Focused on Antidiabetic Role-For Sustainable Health Applications

The main features of the okra, Abelmoschus esculentus (L.), are highlighted. The evaluation of interactions between biologically active compounds and other components of the food matrix can be considered as the first action in the investigation of potential benefits of this annual herb. Moreover, updated examples of current and innovative directions in an integrated and multidisciplinary approach are discussed, with particular attention to chemometrics. Among the main effects attributed to okra, its antidiabetic property is the focus. Finally, the use of okra in different fields will be discussed.

Optimization of ultrasound-assisted extraction of okra (Abelmoschus esculentus (L.) Moench) polysaccharides based on response surface methodology and antioxidant activity

This study determined the optimal conditions for ultrasound-assisted extraction of a water-soluble polysaccharide, Raw Okra Polysaccharide, from the fruit of okra using response surface methodology. The optimal extraction temperature, extraction time and ultrasonic power were 59°C, 30min and 522W, respectively, giving a yield of 10.35±0.11%. ROP was further isolated, lyophilized and purified using a DEAE-Sepharose Fast Flow column and Sepharose CL-6B column, revealing three elution peaks subsequently designated ROP -1, -2, and -3, respectively. Of these, ROP-2 showed the highest yield, and was therefore selected for physicochemical analysis and evaluation of antioxidant activity. Gas chromatography, fourier transform infrared spectroscopy, and high-performance liquid chromatography were used to characterize the primary structural features and molecular weight, revealing that ROP-2 is composed of glucose, mannose, galactose, arabinose, xylose, fructose, and rhamnose (molar percentages: 28.8, 12.5, 13.1, 15.9, 9.2, 13.7, and 6.8%, respectively) and has an average molecular weight of 1.92×105Da. A superoxide radical scavenging assay and DPPH radical scavenging assay further revealed the significant in vitro antioxidant activity of ROP-2. These findings present an effective technique for extraction of the natural antioxidant ROP-2, warranting further analysis of its potential application in the food industry.

Separation of caffeoylquinic acids and flavonoids from Asteris souliei by high-performance counter-current chromatography and their anti-inflammatory activity in vitro

Eleven compounds were successfully separated from Asteris souliei by using a two-step high-performance counter-current chromatography method. The first step involved a reversed phase isocratic counter-current chromatography separation using hexane/ethyl acetate/methanol/water (1:0.8:1:1 v/v/v/v), which produced three fractions, the first two of which were mixtures. The second step used step-gradient reversed-phase counter-current chromatography with hexane/butanol/ethyl acetate/methanol/water (1:0.5:3.5:1:4 v/v/v/v/v) initially followed by hexane/ethyl acetate/methanol/water (1:2:1:2 v/v/v/v) to separate Fraction 1 into seven compounds; and hexane/ethyl acetate/methanol/water (1:1:1:1.2 v/v/v/v) to separate Fraction 2 into three further compounds. The chemical structures of the separated compounds were identified by ESI-MS and NMR spectroscopy (¹ H and ¹³ C). Baicalin (5), eriodictyol (7), apigenin-7-glycoside (8), quercetin (9), luteolin (10), and apigenin (11) showed obvious inhibitory effects on lipopolysaccharide-induced nitric oxide production in RAW264.7 cells at a concentration of 10 μg/mL.

Alternating isocratic and step gradient elution high-speed counter-current chromatography for the isolation of minor phenolics from Ormocarpum kirkii bark

A total of 14 compounds were isolated from the ethanol bark extract of O. kirkii S. Moore (Fabaceae) by alternating isocratic and step gradient elution high-speed counter-current chromatography (HSCCC) methods, using several solvent systems with reference to the polarity of compounds being purified. The extract was successively fractionated with generic solvent systems including n-hexane-ethanol-water (4:2:2) and ethyl acetate-water (1:1). Resulting fractions were further purified using the following preparative gradient elution consisting of ethyl acetate-n-butanol-water (X:Y:10), (X:Y=9:1 (I); 8:2 (II); 7:3 (III); 6:4 (IV); 5:5 (V); 4:6 (VI) 3:7 (VII) and n-hexane- ethyl acetate-methanol-water (1:X:1:1), X=1, 2, 2.5, 3 solvent systems. Two flavone glycosides, apigenin-6-C-β-d-glucopyranosyl-4'-O-[β-d-glucopyranosyl-(1→5)]-β-d-apiofuranoside (1) and apigenin-6-C-β-d-glucopyranosyl-4'-O-β-d-apiofuranoside (2), and one biflavanone diglycoside 7,7″-di-O-β-d-glucosylliquiritigeninyl-(I-3,II-3)-naringenin (4) were isolated as new compounds along with other 11 known ones. The structures of the isolated compounds were identified by HPLC-UV, ESI-MS, 1D and 2D NMR and comparison with literature data. Thus, over common traditional chromatographic methods, the present study shows that HSCCC is a useful and fast method for natural product research with no losses and lower solvent use.

High-speed counter-current chromatography coupled online to high performance liquid chromatography-diode array detector-mass spectrometry for purification, analysis and identification of target compounds from natural products

A challenge in coupling high-speed counter-current chromatography (HSCCC) online with high performance liquid chromatography (HPLC) for purity analysis was their time incompatibility. Consequently, HSCCC-HPLC was conducted by either controlling HPLC analysis time and HSCCC flow rate or using stop-and-go scheme. For natural products containing compounds with a wide range of polarities, the former would optimize experimental conditions, while the latter required more time. Here, a novel HSCCC-HPLC-diode array detector-mass spectrometry (HSCCC-HPLC-DAD-MS) was developed for undisrupted purification, analysis and identification of multi-compounds from natural products. Two six-port injection valves and a six-port switching valve were used as interface for collecting key HSCCC effluents alternatively for HPLC-DAD-MS analysis and identification. The ethyl acetate extract of Malus doumeri was performed on the hyphenated system to verify its efficacy. Five main flavonoids, 3-hydroxyphloridzin (1), phloridzin (2), 4',6'-dihydroxyhydrochalcone-2'-O-β-D-glucopyranoside (3, first found in M. doumeri), phloretin (4), and chrysin (5), were purified with purities over 99% by extrusion elution and/or stepwise elution mode in two-step HSCCC, and 25mM ammonium acetate solution was selected instead of water to depress emulsification in the first HSCCC. The online system shortened manipulation time largely compared with off-line analysis procedure and stop-and-go scheme. The results indicated that the present method could serve as a simple, rapid and effective way to achieve target compounds with high purity from natural products.