Simultaneous determination of seven anthraquinones in Cassiae semen by natural deep eutectic solvent extraction

INTRODUCTION

Anthraquinones are considered to be an important class of bioactive substances in Cassiae semen, and the content of anthraquinones is an essential indicator of the quality of Cassiae semen raw herbal materials.

OBJECTIVES

The present study aimed to propose a novel, efficient and effective ultra-high-performance liquid chromatography (UHPLC) method for the simultaneous determination of aurantio-obtusin, aloe-emodin, rhein, obtusin, emodin, chrysophanol and physcion, with the help of natural deep eutectic solvents (NADESs) as extraction solvents.

METHODOLOGY

NADESs were introduced to the simultaneous extraction of anthraquinones from Cassiae semen samples. Several NADESs were designed by menthol, choline chloride, d-glucose as hydrogen bond acceptors, with nine different acids and appropriate water as hydrogen bond donors. The parameters affecting the extraction efficiency of seven anthraquinones were demonstrated in detail.

RESULTS

Among the obtained NADESs, the highest extraction efficiency was demonstrated by a solution consisting of d-glucose, lactic acid and water with a molar ratio of 1:5:4. The seven anthraquinones were separated on an ACQUITY UPLC® BEH C₁₈ column (2.1 mm × 100 mm, 1.8 μm) and detected within 12 min by a photodiode array (PDA) detector at 254 and 284 nm. The limits of detection and quantitation were from 1.00 to 7.26 μg/l and 3.29 to 24.22 μg/l, respectively. And Cassiae semen sample-based recoveries ranged from 81.13% to 113.78% with the relative standard deviation (RSD) (n = 6) of 1.4% to 10.1%.

CONCLUSION

The developed method demonstrated that NADESs were applied successfully to analyse the anthraquinones in Cassiae semen samples collected from different regions in China.

Preparative isolation of apple flavan-3-ols monomers and oligomers using pH-zone-refining centrifugal partition chromatography combined with reversed-phase liquid chromatography

Flavan-3-ols (catechin monomers and procyanidins) are the main class of polyphenols in apples and are found in high concentrations in cider apple varieties. They are known to be involved in bitterness and astringency in apple-based beverages, and also contribute to polyphenol nutritional intake.Therefore, highly purified flavan-3-ol fractions isolated from raw materials are needed to study their various properties. For this purpose, a gentle strategy combining pH-zone-refining centrifugal partition chromatography (pH-ZRCPC) and preparative reversed-phase liquid chromatography (Prep-RPLC) was developed to recover one hundred milligrams of a high purity apple flavan-3-ol fraction. First, pH-ZRCPC fractionation in descending mode was optimized to remove hydroxycinnamic acid derivatives using a biphasic mixture composed of ethyl acetate/n-butanol/water (3/2/5, v/v). Trifluoroacetic acid and sodium hydroxide were used as retainer and eluter, in the upper and lower phases, respectively. Secondly, Prep-RPLC separation was carried out in isocratic mode at 20% ACN to remove dihydrochalcones. Finally, from one gram of a crude polyphenol extract, four hundred and nine milligrams of a highly purified fraction of flavan-3-ols with an average degree of polymerization close to 3.1 was obtained with 73% recovery.

Anthraquinones from Cassiae semen as thrombin inhibitors: in vitro and in silico studies

Thrombin inhibitor therapy is one of the most effective therapeutic strategies for the prevention and treatment of cardiovascular and thrombotic diseases. Although several marketed direct thrombin inhibitors (DTIs) have been widely used in clinic, the potentially serious complications of these DTIs prompted the researchers to find more DTIs with improved safety profiles. Herein, we report that natural anthraquinones in Cassiae semen (the seed of Cassia obtusifolia L. or C. tora L.), including obtusifolin, obtusin, aurantio-obtusin and chryso-obtusin, display strong to moderate inhibition on human thrombin, with the IC₅₀ values ranging from 9.08 μM to 27.88 μM. Further investigation on the inhibition kinetics demonstrates that these anthraquinones are mixed inhibitors against thrombin-mediated Z-GGRAMC acetate hydrolysis, while obtusifolin and aurantio-obtusin show strong thrombin inhibition capacity, with the K_i values of 9.63 μM and 10.30 μM, respectively. Docking simulations demonstrate that both obtusifolin and aurantio-obtusin can simultaneously bind on the catalytic cavity and the two anion binding exosites (ABE1 and ABE2), while the hydroxyl group at the C-7 site and the methoxyl group at the C-8 site can create key interactions with the amino acids surrounding the catalytic cavity via hydrogen bonding. All these findings suggest that obtusifolin and aurantio-obtusin are strong thrombin inhibitors possessing a unique anthraquinone skeleton, and could be used as lead compounds for the development of new thrombin inhibitors with improved properties.

Fushiming Capsule Attenuates Diabetic Rat Retina Damage via Antioxidation and Anti-Inflammation

Aims

Diabetic retinopathy (DR) remains one of the leading causes of acquired blindness. Fushiming capsule (FSM), a compound traditional Chinese medicine, is clinically used for DR treatment in China. The present study was to investigate the effect of FSM on retinal alterations, inflammatory response, and oxidative stress triggered by diabetes.

Main Methods

Diabetic rat model was induced by 6-week high-fat and high-sugar diet combined with 35 mg/kg streptozotocin (STZ). 30 days after successful establishment of diabetic rat model, full field electroretinography (ffERG) and optical coherence tomography (OCT) were performed to detect retinal pathological alterations. Then, FSM was administered to diabetic rats at different dosages for 42-day treatment and diabetic rats treated with Calcium dobesilate (CaD) capsule served as the positive group. Retinal function and structure were observed, and retinal vascular endothelial growth factor-α (VEGF-α), glial fibrillary acidic (GFAP), and vascular cell adhesion protein-1 (VCAM-1) expressions were measured both on mRNA and protein levels, and a series of blood metabolic indicators were also assessed.

Key Findings

In DR rats, FSM (1.0 g/kg and 0.5 g/kg) treatment significantly restored retinal function (a higher amplitude of b-wave in dark-adaptation 3.0 and OPs2 wave) and prevented the decrease of retinal thickness including inner nuclear layer (INL), outer nuclear layer (ONL), and entire retina. Additionally, FSM dramatically decreased VEGF-α, GFAP, and VCAM-1 expressions in retinal tissues. Moreover, FSM notably improved serum antioxidative enzymes glutathione peroxidase, superoxide dismutase, and catalase activities, whereas it reduced serum advanced glycation end products, methane dicarboxylic aldehyde, nitric oxide, and total cholesterol and triglycerides levels.

Significance

FSM could ameliorate diabetic rat retina damage possibly via inhibiting inflammation and improving antioxidation.

New Vortex-Synchronized Matrix Solid-Phase Dispersion Method for Simultaneous Determination of Four Anthraquinones in Cassiae Semen

In this study, a green ionic-liquid based vortex-synchronized matrix solid-phase dispersion (VS-MSPD) combined with high performance liquid chromatography (HPLC) method was developed as a quantitative determination method for four anthraquinones in Cassiae Semen. Two conventional adsorbents, C₁₈ and silica gel were investigated. The strategy included two steps: Extraction and determination. Wasted crab shells were used as an alternative adsorbent and ionic liquid was used as an alternative solvent in the first step. Factors affecting extraction efficiency were optimized: A sample/adsorbent ratio of 2:1, a grinding time of 3 min, a vortex time of 3 min, and ionic liquid ([Domim]HSO₄, 250 mM) was used as eluent in the VS-MSPD procedure. As a result, the established method provided satisfactory linearity (R > 0.999), good accuracy and high reproducibility (RSD < 4.60%), and it exhibited the advantages of smaller sample amounts, shorter extraction time, less volume of elution solvent, and was much more environmental-friendly when compared with other conventional methods.

Application of pH-zone-refining countercurrent chromatography in the chiral separation of two β-adrenergic blocking agents

Two β-adrenergic blocking agents, 1-[(1-methylethyl)amino]-3-phenoxy-2-propanol (1) and 1-[(1-methylethyl)amino]-3-(3-methylphenoxy)-2-propanol (2; Toliprolol), were enantioseparated by pH-zone-refining countercurrent chromatography. A two-phase solvent system composed of chloroform containing 0.10 mol/L of di-n-hexyl l-tartrate/0.10 mol/L of boric acid aqueous solution (1:1, v/v) was selected, in which 20 mmol/L triethylamine was added in the organic phase as a retainer and 2 mmol/L HCl was added in the aqueous phase as an eluter. Fifty milligrams of each racemate was completely enantioseparated by pH-zone-refining countercurrent chromatography to yield each enantiomer with a purity of more than 98%, and the recovery of each separated enantiomer reached around 76-82%.