Effect of rhein on the glucose metabolism of Ehrlich ascites tumor cells

UPLC-ESI-MS/MS-Based Widely Targeted Metabolomics Analysis of Wood Metabolites in Teak (Tectona grandis)

The properties of teak wood, such as natural durability and beautiful color, are closely associated with wood extractives. In order to further understand the performance differences between teak heartwood and sapwood, we analyzed the chemical components of extractives from 12 wood samples using an ultrahigh-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS)-based metabolomics approach. In total, 691 metabolites were identified, and these were classified into 17 different categories. Clustering analysis and principal component analysis of metabolites showed that heartwood samples could be clearly separated from sapwood samples. Differential metabolite analysis revealed that the levels of primary metabolites, including carbohydrates, amino acids, lipids, and nucleotides, were significantly lower in the heartwood than in the sapwood. Conversely, many secondary metabolites, including flavonoids, phenylpropanoids, and quinones, had higher levels in the heartwood than in the sapwood. In addition, we detected 16 specifically expressed secondary metabolites in the heartwood, the presence of which may correlate with the durability and color of teak heartwood. Our study improves the understanding of differential metabolites between sapwood and heartwood of teak, and provides a reference for the study of heartwood formation.

Rhein inhibits angiogenesis and the viability of hormone-dependent and -independent cancer cells under normoxic or hypoxic conditions in vitro

Hypoxia is a hallmark of solid tumors, including breast cancer, and the extent of tumor hypoxia is associated with treatment resistance and poor prognosis. Considering the limited treatment of hypoxic tumor cells and hence a poor prognosis of breast cancer, the investigation of natural products as potential chemopreventive anti-angiogenic agents is of paramount interest. Rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid), the primary anthraquinone in the roots of Cassia alata L., is a naturally occurring quinone which exhibits a variety of biologic activities including anti-cancer activity. However, the effect of rhein on endothelial or cancer cells under hypoxic conditions has never been delineated. Therefore, the aim of this study was to investigate whether rhein inhibits angiogenesis and the viability of hormone-dependent (MCF-7) or -independent (MDA-MB-435s) breast cancer cells in vitro under normoxic or hypoxic conditions. Rhein inhibited vascular endothelial growth factor (VEGF(165))-stimulated human umbilical vein endothelial cell (HUVEC) tube formation, proliferation and migration under normoxic and hypoxic conditions. In addition, rhein inhibited in vitro angiogenesis by suppressing the activation of phosphatidylinositol 3-kinase (PI3K), phosphorylated-AKT (p-AKT) and phosphorylated extracellular signal-regulated kinase (p-ERK) but showed no inhibitory effects on total AKT or ERK. Rhein dose-dependently inhibited the viability of MCF-7 and MDA-MB-435s breast cancer cells under normoxic or hypoxic conditions, and inhibited cell cycle in both cell lines. Furthermore, Western blotting demonstrated that rhein inhibited heat shock protein 90alpha (Hsp90α) activity to induce degradation of Hsp90 client proteins including nuclear factor-kappa B (NF-κB), COX-2, and HER-2. Rhein also inhibited the expression of hypoxia-inducible factor-1 alpha (HIF-1α), vascular endothelial growth factor (VEGF(165)), epidermal growth factor (EGF), and the phosphorylation of inhibitor of NF-κB (I-κB) under normoxic or hypoxic conditions. Taken together, these data indicate that rhein is a promising anti-angiogenic compound for breast cancer cell viability and growth. Therefore, further studies including in vivo and pre-clinical need to be performed.

Anthraquinone cytotoxicity and apoptosis in primary cultures of rat hepatocytes

We compared three different anthraquinones, rhein (4,5-dihydroxy-anthraquinone-2-carboxylic acid), danthron (1,8-dihydroxy-anthraquinone) and chrysophanol (1,8-dihydroxy-3-methylanthraquinone), with respect to their toxicity and ability to induce apoptosis in primary cultures of rat hepatocytes. Rhein was the most effective in producing free radicals, and was the only one of the tested anthraquinones that could induce apoptosis. Addition of 50 microM rhein to hepatocyte cultures led to depletion of intracellular reduced glutathione (GSH) and ATP and accumulation of lipid peroxidation products. The substances N,N'-diphenyl-p-phenylenediamine (DPPD), dithiothreitol (DTT), nifedipine and desferal all protected the hepatocytes, i.e. prevented viability loss and ATP depletion, and decreased the GSH depletion. Cultures exposed to rhein for 15 min and subsequently rinsed and incubated for 16 h under normal culture conditions (complete medium) exhibited apoptosis, as shown by DNA fragmentation, nuclear condensation and positive TUNEL reaction. Pretreatment with the antioxidant DPPD and the iron-chelator desferal gave complete protection against apoptosis. No signs of oxidative cell damage were detected when the cultures were exposed to danthron or chrysophanol. All three anthraquinones did, however, cause an immediate increase in the intracellular Ca2+ concentration. We conclude that rhein, which contains one carboxyl group, is a suitable substrate for one-electron-reducing enzymes and an effective redox cycler, which leads to the production of oxygen-derived free radicals that eventually induce apoptotic cell death.

The hepatotoxicity of rhein involves impairment of mitochondrial functions

Metabolism of rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid) in primary cultures of rat hepatocytes caused production of oxygen-derived free radicals by redox cycling; this was shown as an increased rate of superoxide-dismutasesensitive NAD(P)H oxidation and NAD(P)H-cytochrome c reduction. Furthermore, rhein caused a depletion of intracellular reduced glutathione and an immediate, almost 10-fold increase in intracellular free Ca2+. Exposure to rhein also induced the following: a decrease in the mitochondrial membrane potential, as analyzed by uptake of rhodamine 123 (Rh 123); initiation of lipid peroxidation, measured as accumulation of malondialdehyde and 4-hydroxyalkenals; and cell death (LD50 = 20 microM). Pretreatment of cell cultures with dithiothreitol (DTT), nifedipin or N',N'-diphenyl-p-phenylenediamine (DPPD) increased the intracellular free Ca2+ concentration 5-fold but inhibited rhein-induced cytotoxicity. Moreover, addition of these protecting substances maintained the level of ATP and glutathione (GSH) and prevented accumulation of lipid peroxidation products. Depletion of intracellular glutathione by pretreatment with buthionine sulfoximine (BSO), or inhibition of glutathione reductase with 1,3-bis-2-chloroethyl-1-nitrosourea (BCNU) decreased cell viability (LD50 = 2.5 microM). On the other hand, increasing GSH by pretreatment with L-2-oxothiazolidine-4-carboxylic acid (OTC) did not provide complete protection. In summary, rhein undergoes redox cycling that gives rise to oxygen metabolites that affect the mitochondrial membranes (recorded as a decreased membrane potential) and after the plasma membrane (i.e. induced the formation of surface blebs). Mitochondrial malfunction also causes changes in Ca2+ homeostasis and depletion of ATP, which eventually lead to cell death.

Effect of diacetyl rhein on the development of experimental osteoarthritis. A biochemical investigation

OBJECTIVE

To investigate the effect of diacetyl rhein (DAR) on the synthesis, turnover and composition of cartilage in an experimental model of osteoarthritis in beagle bitches.

DESIGN

Osteoarthritis was induced in mature beagle bitches by the transection of the cranial cruciate ligament. Six animals received DAR 20 mg/kg daily for 11 weeks. A matched group received empty capsules daily for the same period. At 11 weeks, articular cartilage was examined for the ratio of the 6:4-sulfated disaccharides of chondroitin and the tissue concentration of hydroxyproline and glycosaminoglycan. In addition, labeling studies were performed to estimate the effect of DAR on proteoglycan synthesis and turnover.

RESULTS

DAR had no effect on body weight or food consumption but induced a mild diarrhea and slightly increased the incidence of vomiting. DAR tended to reduce proteoglycan synthesis, however, DAR did reduce proteoglycan turnover in the femoral cartilage. DAR produced changes in the composition of the osteoarthritic cartilage that could only partly be accounted for by changes in hydration and/or swelling. In addition, it was noted that induction of osteoarthritis increased the ratio of chondroitin 6-sulfated to chondroitin 4-sulfated disaccharides; DAR reduced the ratio in tibial plateau cartilage from osteoarthritic joints compared with untreated tissue from osteoarthritic joints. DAR showed moderate reduction on the biosynthesis of proteoglycans. DAR also produced a reduction in proteoglycan turnover from all anatomical areas compared with non-treated controls in both the lateral and medial femoral condyles.

CONCLUSIONS

DAR was well tolerated by the experimental animals, but did not produce significant changes in the synthesis or turnover of proteoglycans. The slight reduction in proteoglycan synthesis may prove to be biologically significant after chronic dosing. DAR's effects on the hydroxyproline and glycosaminoglycan content suggest, however, that it must influence the swelling of cartilage and loss of glycosaminoglycan. This indicates that small changes can translate, to significant differences in cartilage composition over an 11-week time period.

An in vivo investigation of the effect of anthraquinones on the turnover of aggrecans in spontaneous osteoarthritis in the guinea pig

We present details of a method which allows for the determination of chondroitin sulphate turnover in vivo using the guinea pig. Such methods have been utilised to examine the effects of diacetyl rhein, a compound with purported anti-osteoarthritic activity, and several related anthraquinone analogues on the turnover of chondroitin. Since the guinea pig develops spontaneous osteoarthritis, this may give useful information on the potential for such compounds to inhibit the progression of osteoarthritis. The results show that several of the anthraquinones are capable of reducing the turnover of chondroitin 4- but not 6-sulphate. This may indicate potential mechanisms for the breakdown of guinea pig cartilage aggrecans. We propose that these techniques could be useful for the screening of chemical agents with useful activity against osteoarthritis.

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.

Differential sensitivity of AS-30D rat hepatoma cells and normal hepatocytes to anoxic cell damage

A substantial fraction of cells present within hard tumors experience extremely hypoxic and hypoglycemic conditions that can lead to phenotypic alterations such as increased metastatic potential and chemotherapeutic drug resistance. Little is known regarding the influence of anoxic aglycemia on tumor cell energy metabolism and viability, and no direct comparisons have been made between the effects of this form of metabolic stress on tumor cells and their tissue of origin. In this study, the effects of in vitro aglycemic incubation under N2 (with or without iodoacetate) on trypan blue exclusion, lactate dehydrogenase release, cell surface blebbing, ATP levels, and mitochondrial respiratory capacity of rat AS-30D ascites hepatoma cells and normal hepatocytes were measured. Under anoxic-aglycemic conditions, the period of incubation during which 50% viability was lost was 2 h for hepatocytes and 6-8 h for AS-30D cells. In contrast, the rate of anoxia-induced loss of ATP was comparable for the two cell types, and mitochondrial damage was actually accelerated in the tumor cells. These findings suggest that tumor cells are more resistant to anoxic cell death because of their greater ability to withstand deenergization and subcellular injury.

Inhibition of protein synthesis in neoplastic cells by rhein

The action of rhein, 4,5-dihydroxyanthraquinone-2-carboxylic acid, on protein synthesis of neoplastic cells has been investigated. Rhein decreases amino acid incorporation in all cells tested. The inhibition of incorporation of labeled precursors into acid-insoluble material cannot be ascribed to an impairment of amino acid uptake, which is unaffected by the drug. Tests on cell-free system showed that rhein does not inhibit the TMV-mRNA directed in vitro protein synthesis, thus indicating that the protein machinery per se is not affected. The inhibition of protein brought about by the drug must be ascribed to an effect on the energy-yielding processes with a remarkable decrease in ATP content. The mechanism is similar to that of other metabolic inhibitors, but rhein, for its capability to inhibit both respiration and glycolysis, is effective at much lower concentrations.