Rhein Research Articles

Rhein, an inhibitor of adipocyte differentiation and adipogenesis

Rhein (RH), a compound purified from Radix et Rhizoma Rhei, has been used to alleviate liver and kidney damage. It is found that RH inhibited the differentiation of 3T3-L1 preadipocytes induced by differentiation medium in a time- and dose-dependent manner. It was revealed that RH downregulated the expression of adipogenesis-specific transcription factors PPARγ and C/EBPα, as well as their upstream regulator, C/EBPβ. Furthermore, the PPARγ target genes that are involved in adipocyte differentiation, such as CD36, aP2, acyl CoA oxidase, uncoupled protein 2, acetyl-CoA carboxylase, and fatty acid synthase, were reduced after to RH. In addition, high-fat diet-induced weight gain and adiposity were reversed by RH in C57BL/6 mice. Consistent with the cells' results, RH downregulated the mRNA levels of PPARγ and C/EBPα, and their downstream target genes in C57BL/6 mice. Taken together, adipocyte differentiation and adipogenesis were inhibited by RH in cultured cells and in rodent models of obesity. The evidence implied that RH was a potential candidate for preventing metabolic disorders.

Pharmacokinetic Study of Rhein and its Carboxyl-esterification Derivatives in Rats

Aim To explore the effects of carboxyl-esterification on pharmacokinetics of rhein in rat. Methods Rhein methylate (REM) and Rhein ethylate (REE) were used as model drugs while rhein (RE) as a positive control. The simultaneous detection of three analytes in rat plasma samples was carried out by an HPLC-fluorescence method. Single dose of RE, REM or REE was administered to rats by both ig route at 70 mg·kg −1 and iv route at 0.7 mg·kg −1. Results REM and REE were entirely metabolized to rhein after ig and iv administration of either REE or REM to rats and only rhein was detected in plasma. Therefore, the pharmacokinetic comparisons among RE, REE and REM in rat were carried out based on the profiles of rhein in rat plasma after the administration of each compound. The main pharmacokinetic parameters of REM, REE and RE after ig administration were as follows: c max (0.058 ± 0.035), (0.95 ± 0.090), (42.66 ± 14.41) mg·L −1; T max (6.7 ± 2.3), (10.7 ± 2.3), (0.9 ± 0.1) h; t 1/2β (6.0 ± 1.7), (6.4 ± 1.0), (3.2 ± 0.6) h; AUC 0-∞ (1.03 ± 0.76), (12.79 ± 0.96), (80.28 ± 13.59) h·mg·L −1. Conclusion The reconstruction of carboxyl-esterification can significantly reduce the net exposure amount of rhein in vivo, leading to its inaptitude in the development of drug precursors of rhein.

Intestinal Transport of Free Anthraquinones in Caco-2 Cell Model

AIM: To investigate the transepithelial transport of the six free anthraquinones 1,8-dihydroxyanthraquinone (DQ),chrysophanol (CP),emodin (EN),rhein (RN),aloe-emodin (AE) and citreorosein (CN) in the human intestinal Caco-2 cell monolayer model. METHODS: The monolayers of the human intestinal epithelial cancer cell line Caco-2 were incubated with DQ,CP,EN,RN,AE and CN to model its intestinal absorption and transport,respectively. The determination of the compounds was performed by high-performance liquid chromatography. RESULTS: The apparent permeability coefficients (Papp) in the Caco-2 cell monolayers for DQ,CP,EN,RN,AE and CN were (2.16±0.38)×10-6,(3.00±0.09)×10-7,(1.99±0.94)×10-6,(4.58±0.20)×10-6,(6.24±0.19)×10-6 and (7.34±0.61)×10-6 cm ·s-1 from the apical-to-basolateral direction,respectively,and (3.20±0.10)×10-6,(4.50 ± 0.02)×10-7,(2.22 ± 0.62)×10-6,(4.94 ± 0.39)×10-6,(2.87 ± 0.18)×10-6 and (6.80 ± 0.37)×10-6 cm ·s-1 from the basolateral-to-apical direction,respectively. The Papp values of DQ,EN,RN,AE and CN were about 10 times less than those (6.30 ± 0.26)×10-5 cm ·s-1 of propranolol as a reference standard compound of high permeability and the main mechanism of intestinal absorption by passive diffusion,and about 10 times higher than those ( 1×10-7 cm ·s-1) of atenolol as a reference standard compound of poor permeability and the main mechanism of intestinal absorption by passive diffusion. Whereas,the Papp value of CP was at nearly the same magnitude with those of atenolol. In the presence of iodoacetamide,the Papp of AE were not affected in both apical-to-basolateral and basolateral-to-apical directions. CONCLUSION: The intestinal absorption of all test compounds was passive diffusion as the dominating process in Caco-2 cell monolayer model. DQ,EN,RN,AE and CN will be moderately absorbed compounds and CP was estimated to be a poorly absorbed compound.

Global transcriptional response of Staphylococcus aureus to Rhein, a Natural Plant Product

Staphylococcus aureus ( S. aureus) is one of the most important pathogens in humans and animals , multiply resistant strains are increasingly widespread, new agents are needed for the treatment of S. aureus. Rhein (RH), a natural plant product , has been reported to have potential antimicrobial activity against S. aureus, but the response mechanisms of S. aureus to RH are still poorly understood. RH showed good in vitro antibacterial activity against all 21 tested S. aureus strains in this experiment. We performed commercial Affymetrix GeneChips™ to determine the overall transcriptional response of S. aureus ATCC25923 triggered by the treatment of subinhibitory concentrations of RH at one time point 45 min. A total of 88 genes were identified to be differentially regulated by RH. Of these, 28 transporter genes were differentially regulated by RH; RH stress elevated the transcription of genes ( srtB and isdABCDEFGI) encoding iron-regulated surface determinants system and genes ( nrdIEF and nrdDG) involved in ribonucleotide reductase systems; but RH repressed genes ( pflAB, nirBDR, narGH, ldh1, COL-SA0660, COL-SA2363 and COL-SA2386) responsible for anaerobic respiration and fermentation. To our knowledge, this genome-wide transcriptomics approach revealed first insights into the response of S. aureus to RH challenge.

Simultaneous determination of baicalin, rhein and berberine in rat plasma by column-switching high-performance liquid chromatography

A simple HPLC method using column-switching and ultraviolet detection was developed for the simultaneous determination of baicalin (BA), rhein (RH) and berberine (BE) in rat plasma. Plasma samples were injected directly onto a Capcell Pak MF C(8) column (150 mm x 4.6 mm i.d.) to remove protein and to be pre-separated by an isocratic elution using 50 mmol/L phosphate sodium (pH 6.85)-acetonitrile (10:1, v/v). After the drug-containing fractions were transferred to a Kromasil C(18) column (150 mm x 4.6 mm i.d.) by a valve switching step, the valve position was switched back and the main separation was performed by an isocratic elution using triethylamine adjusted 20 mmol/L phosphoric acid (pH 6.78)-acetonitrile (4:1, v/v). The flow rate was always 1.0 mL/min. The calibration curve showed excellent linear relationship (r>or=0.9997) over the concentration range of 0.4-7.9 microg/mL for baicalin, 0.2-7.8 microg/mL for rhein and 0.4-7.7 microg/mL for berberine in rat plasma. The intra- and inter-day assay precisions (R.S.D.) of three analytes were in the range of 0.34-4.3% and the accuracies were between 98.0% and 102.4%. Their recoveries were all greater than 95%. The method was successfully applied to the multi-constituents plasma concentration-time curve study after oral administration of a traditional Chinese medicine prescription Xiexin-Tang in rats.

Pharmacokinetics of (-)Epicatechin 3-O-Gallate, Glycyrrhetic Acid and Rhein in Healthy Male Volunteers after a Single Dose Administration of TJ-8117 (Unpito), a Japanese Traditional Medicine for Renal Failure

Aims: Unpito, an herbal medicine extracted from a mixture of five crude medicines (Rhei Rhizoma, Glycyrrhizae Radix, Ginseng Radix, Zingiberis Rhizoma and Aconiti Tuber), has been developed as a drug for chronic renal failure. In general, it is difficult to estimate the absorption and excretion of herbal medicines due to the presence of a wide variety of components. The purpose of the current study was to examine the systemic pharmacokinetics and elimination of Unpito in healthy volunteers as part of the clinical study of the medicine.Methods: Three compounds, (-) epicatechin 3-O-gallate (ECG), glycyrrhetic acid (GA) and rhein (RH) were selected as markers, to examine the clinical pharmacokinetics of Unpito based on their levels in this medicine. The disposition of each compound was evaluated in 32 healthy volunteers receiving single oral doses (2, 4, 8, and 12 capsules).Results: After a single oral administration, ECG and RH exhibited linear pharmacokinetics in AUC and Cmax, while GA did not exhibit linear pharmacokinetics. A cross-over study was conducted to evaluate the effect of food at a single dose of 4 capsules. The effect of food was observed for the plasma concentrations of ECG and RH, while not for GA. The potential accumulations of δ-(3, 4-dihydroxyphenyl) γ-valerolactone (VL-2), a metabolite of ECG and RH were not observed. GA was not detected in urine.Conclusions: This is the first study presenting pharmacokinetics of ECG, GA and RH derived from Unpito, an herbal medicine, in healthy volunteers after single dose administration.

Simultaneous determination of Aloe-emodin and Rhein by synchronous fluorescence spectroscopy

A simple sensitive and quick assay to simultaneously determine Aloe-emodin (AE) and Rhein (RH) has been described based on their natural fluorescence. Due to their similar molecule structures, it is difficult to analysis and determine their contents by conventional fluorometry. Overlapping of fluorescence spectra was resolved by using synchronous fluorometry. The synchronous spectrum, maintaining a constant difference of Δ λ=25 nm between the emission and excitation wavelengths, has been selected as optimum to perform the determination. This method was applied to the simultaneous determination of AE and RH in simulated mixtures. Analytical recoveries range from 94.5 to 105.5% for AE and from 98.7 to 107.5% for RH. At the same time, the content of AE abstracted from Cassitora L. was successfully analyzed. The results were satisfactory.

Electrophoretic behavior study and determination of some active components in Chinese medicinal preparations by capillary electrophoresis.

The determination of icariin (IC), rhein (RH), chrysophanol (CH), physcion (PHY), glycyrrhetic acid (GE), and glycyrrhizic acid (GI), in traditional Chinese preparations, Anshen Bunao oral liquid and Maren pill, has been investigated by micellar electrokinetic capillary electrophoresis. With borate buffer (10 mM), SDS (20 mM) and acetonitrile (10%) as background electrolyte (pH 9.55), 20 kV applied voltage and 254 nm UV detection, the six active compounds were completely separated within 10 min. The effects of buffer pH, concentration of borate, SDS and modifier on electrophoretic behavior and separation are discussed. Regression equations revealed linear relationships (correlation coefficients: 0.9960-0.9999) between the peak-area of each component and the content. In addition, the levels of the six active compounds in two kinds of traditional Chinese medicinal preparations were easily determined with recoveries of from 94.7% to 106.4%.

Rhein enhances the effect of adriamycin on mitochondrial respiration by increasing antibiotic-membrane interaction

The effect of the combination of Adriamycin (ADM) with rhein (RH), an anti-inflammatory drug, on the electron flow through site III and IV of the respiratory chain of rat liver mitochondria was investigated. RH, even at high concentrations, does not inhibit either duroquinol (DHQ) oxidation or cytochrome oxidase activity both of which are decreased by ADM in a dose-dependent manner. The analysis of interaction, performed with the isobolar method, shows a strong synergistic effect that cannot be ascribed to increased permeability of the mitochondrial membranes brought about by RH. The mechanism by which RH potentiates the effect of ADM on DHQ oxidation and cytochrome oxidase activity is most likely to be changes induced in the physical status of the inner mitochondrial membrane such as to permit low ADM concentrations to bind and segregate enough cardiolipin to inhibit electron transport through complex III and IV.

Rhein inhibits glucose uptake in Ehrlich ascites tumor cells by alteration of membrane-associated functions.

Rhein (RH), 4,5 dihydroxyanthraquinone-2-carboxylic acid, is known to inhibit the glycolysis of neoplastic cells by impairing glucose uptake. In order to establish whether this might be due to a selective interaction of the carrier with the drug or to functional modifications of the cell membrane, the effect of RH on glucose uptake in Ehrlich ascites tumor cells has been investigated. RH strongly inhibits the uptake of both 2-deoxyglucose and 3-O-methylglucose, so the reduced influx therefore cannot be ascribed to an effect on glucose phosphorylation. The inhibition of glucose transport does not depend on a reduction of the number of the carriers as indicated by the inability of the drug to interfere with the synthesis of the transporter. Moreover, the extent of total binding of cytochalasin B, as well as the fact that glucose specificity is not altered, indicate that the intrinsic activity of the glucose carrier is not affected. We therefore conclude that the inhibition of glucose uptake must be ascribed to an interaction of the drug with cell membranes that results in an alteration of membrane-associated functions.

Inhibition of membrane redox activity by rhein and adriamycin in human glioma cells.

The effect of the combination of adriamycin (ADM) with the anti-inflammatory drug rhein (RH) on the membrane redox activity in human glioma cells was investigated. RH, although less effective than ADM, inhibits ferricyanide reduction by human glioma cells in a dose-dependent manner as well as ferricyanide-induced proton release. The inhibition of the plasma membrane redox system might represent a further mechanism by which RH, other than ATP depletion, affects cell survival. The analysis of the interaction between ADM and RH, performed with the isobolar method, demonstrates a strong synergic response, probably due to an effect on different sites of action. The synergism of the ADM-RH association allows us to achieve a pre-established extent of inhibition with ADM concentrations much lower than with ADM alone. RH might, therefore, represent a very useful tool to improve the therapeutic index of ADM and to lower its general toxicity.

Survival response of a human glioma cell line to hyperthermia associated with rhein

The effect of association of hyperthermia with the anti-inflammatory drug rhein (RH), 4,5-dihydroxyanthraquinone-2-carboxylic acid, on the clonogenic activity of human glioma cells has been examined. RH inhibits neoplastic growth mainly through an ATP depletion, but thermal cell killing is not mediated by the drug-induced changes in the energy status of the cell. The analysis of the interaction between RH and hyperthermia, performed with the isobolar method, demonstrates an additivity of the response so that the effectiveness of the combined treatment is the result of two independent effects. Although the effect of this combination is purely additive, RH allows us to achieve a pre-established cell killing with exposure times at 42 degrees C, which is generally accepted to be clinically achievable. RH might, therefore, be employed to reduce the side effects of hyperthermia without impairing its therapeutic effectiveness.