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

Rhein Induces Oxidative Stress and Apoptosis in Mouse Blastocysts and Has Immunotoxic Effects during Embryonic Development

Rhein, a glucoside chemical compound found in a traditional Chinese medicine derived from the roots of rhubarb, induces cell apoptosis and is considered to have high potential as an antitumor drug. Several previous studies showed that rhein can inhibit cell proliferation and trigger mitochondria-related or endoplasmic reticulum (ER) stress-dependent apoptotic processes. However, the side effects of rhein on pre- and post-implantation embryonic development remain unclear. Here, we show that rhein has cytotoxic effects on blastocyst-stage mouse embryos and induces oxidative stress and immunotoxicity in mouse fetuses. Blastocysts incubated with 5-20 μM rhein showed significant cell apoptosis, as well as decreases in their inner cell mass cell numbers and total cell numbers. An in vitro development assay showed that rhein affected the developmental potentials of both pre- and post-implantation embryos. Incubation of blastocysts with 5-20 μM rhein was associated with increased resorption of post-implantation embryos and decreased fetal weight in an embryo transfer assay. Importantly, in an in vivo model, intravenous injection of dams with rhein (1, 3, and 5 mg/kg body weight/day) for four days resulted in apoptosis of blastocyst-stage embryos, early embryonic developmental injury, and decreased fetal weight. Intravenous injection of dams with 5 mg/kg body weight/day rhein significantly increased the total reactive oxygen species (ROS) content of fetuses and the transcription levels of antioxidant proteins in fetal livers. Additional work showed that rhein induced apoptosis through ROS generation, and that prevention of apoptotic processes effectively rescued the rhein-induced injury effects on embryonic development. Finally, the transcription levels of the innate-immunity related genes, CXCL1, IL-1β and IL-8, were down-regulated in the fetuses of dams that received intravenous injections of rhein. These results collectively show that rhein has the potential to induce embryonic cytotoxicity and induce oxidative stress and immunotoxicity during the development of mouse embryos.

Rhein triggers apoptosis via induction of endoplasmic reticulum stress, caspase-4 and intracellular calcium in primary human hepatic HL-7702 cells

Rhein is an active component of rhubarb; a traditional Chinese medicine reported to induce apoptosis and cause liver toxicity. However, rhein's apoptotic-inducing effects, as well as its molecular mechanisms of action on hepatic cells need to be further explored. In the present study, rhein was found to trigger apoptosis in primary human hepatic HL-7702 cells as showed by annexin V/PI double staining assay and nuclear morphological changes demonstrated by Hoechst 33258 staining. Moreover, it was observed that the mechanism implicated in rhein-induced apoptosis was caspase-dependent, presumably via ER-stress associated pathways, as illustrated by up-regulation of glucose-regulated protein 78 (GRP 78), PKR-like ER kinase (PERK), C-Jun N-terminal kinase (JNK) and CCAAT/enhancer-binding protein homologous protein (CHOP). Meanwhile, caspase-4 as a hallmark of ER-stress, was also showed to be activated following by caspase-3 activation. Furthermore, rhein also promoted intracellular elevation of calcium that contributed in apoptosis induction. Interestingly, pre-treatment with calpain inhibitor I reduced the effects of rhein on apoptosis induction and JNK activation. These data suggested that rhein-induced apoptosis through ER-stress and elevated intracellular calcium level in HL-7702 cells.

Design, synthesis and biological evaluation of rhein derivatives as anticancer agents

A series of novel derivatives of rhein were synthesized and evaluated for their in vitro antiproliferative activity against six kinds of tumor cell lines. All derivatives displayed more potent anti-tumor activity than rhein, and most of them were even stronger than 5-FU. Compound 4v was the most promising candidate among the investigated compounds.

Rhein: A Review of Pharmacological Activities

Rhein (4, 5-dihydroxyanthraquinone-2-carboxylic acid) is a lipophilic anthraquinone extensively found in medicinal herbs, such as Rheum palmatum L., Cassia tora L., Polygonum multiflorum Thunb., and Aloe barbadensis Miller, which have been used medicinally in China for more than 1,000 years. Its biological activities related to human health are being explored actively. Emerging evidence suggests that rhein has many pharmacological effects, including hepatoprotective, nephroprotective, anti-inflammatory, antioxidant, anticancer, and antimicrobial activities. The present review provides a comprehensive summary and analysis of the pharmacological properties of rhein, supporting the potential uses of rhein as a medicinal agent.

Rhein Elicits In Vitro Cytotoxicity in Primary Human Liver HL-7702 Cells by Inducing Apoptosis through Mitochondria-Mediated Pathway

Objective. To study rhein-induced apoptosis signaling pathway and to investigate its molecular mechanisms in primary human hepatic cells. Results. Cell viability of HL-7702 cells treated with rhein showed significant decrease in dose-dependent manner. Following rhein treatment (25 μM, 50 μM, and 100 μM) for 12 h, the detection of apoptotic cells was significantly analyzed by flow cytometry and nuclear morphological changes by Hoechst 33258, respectively. Fatty degeneration studies showed upregulation level of the relevant hepatic markers (P < 0.01). Caspase activities expressed significant upregulation of caspase-3, caspase-9, and caspase-8. Moreover, apoptotic cells by rhein were significantly inhibited by Z-LEHD-FMK and Z-DEVD-FMK, caspase-9 inhibitor, and caspase-3 inhibitor, respectively. Overproduction of reactive oxygen species, lipid peroxidation, and loss of mitochondrial membrane potential were detected by fluorometry. Additionally, NAC, a ROS scavenger, significantly attenuated rhein-induced oxidative damage in HL-7702 cells. Furthermore, real-time qPCR results showed significant upregulation of p53, PUMA, Apaf-1, and Casp-9 and Casp-3 mRNA, with no significant changes of Fas and Cytochrome-c. Immunoblotting revealed significant Cytochrome-c release from mitochondria into cytosol and no change in Fas expression. Conclusion. Taken together, these observations suggested that rhein could induce apoptosis in HL-7702 cells via mitochondria-mediated signal pathway with involvement of oxidative stress mechanism.

Preparation, characterization, and in vivo study of rhein-loaded poly(lactic-co-glycolic acid) nanoparticles for oral delivery

A novel rhein formulation based on poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) suitable for oral administration was developed in this study. The designed nanosystems were obtained by a modified spontaneous emulsification solvent diffusion method. The morphology of rhein-loaded PLGA NPs showed a spherical shape with a smooth surface, without any particle aggregation. Mean size of the NPs was 140.5±4.3 nm, and the zeta potential was −16.9±3.1 mV. The average drug loading was 3.9%±0.7%, and encapsulation efficiency was 84.5%±6.2%. Meanwhile, NPs are characterized by the slower release (only about 70% of rhein is released within 5 hours), and the model that fitted best for rhein released from the NPs was Higuchi kinetic model with correlation coefficient r=0.9993, revealing that rhein could be controlled released from the NPs. In vivo, NPs altered the distribution of rhein, and the half-life after oral administration was prolonged remarkably more than those of suspensions (22.6 hours vs 4.3 hours). The pharmacokinetic results indicated that the NPs had sustained-release efficacy. The area under the curve_0–∞ of the NPs formulation was 3.07-fold higher than that of suspensions, suggesting that the encapsulated rhein had almost been absorbed in rats over the period of 12 hours. Although rhein-loaded PLGA NP formulations are hopefully used as a chemotherapeutic or adjuvant agent for human gastric cancer (SGC-7901), their in vivo antitumor effect and mechanisms at the molecular level still need further study.

Rhein induces apoptosis of human gastric cancer SGC-7901 cells via an intrinsic mitochondrial pathway

Rhein is a primary anthraquinone found in the roots of a traditional Chinese herb, rhubarb, and has been shown to have some anticancer effects. The aim of the present study was to investigate the effect of rhein on the apoptosis of the human gastric cancer line SGC-7901 and to identify the mechanism involved. SGC-7901 cells were cultured and treated with rhein (0, 50, 100, 150, and 200 µM) for 24, 48, or 72 h. Relative cell viability assessed by the MTT assay after treatment was 100, 99, 85, 79, 63% for 24 h; 100, 98, 80, 51, 37% for 48 h, and 100, 97, 60, 36, 15% for 72 h, respectively. Cell apoptosis was detected with TUNEL staining and quantified with flow cytometry using annexin FITC-PI staining at 48 h after 100, 200 and 300 µm rhein. The percentage of apoptotic cells was 7.3, 21.9, 43.5%, respectively. We also measured the mRNA levels of caspase-3 and -9 using real-time PCR. Treatment with 100 µM rhein for 48 h significantly increased mRNA expression of caspase-3 and -9. The levels of apoptosis-related proteins including Bcl-2, Bax, Bcl-xL, and pro-caspase-3 were evaluated in rhein-treated cells. Rhein increased the Bax:Bcl-2 ratio but decreased the protein levels of Bcl-xL and pro-caspase-3. Moreover, rhein significantly increased the expression of cytochrome c and apoptotic protease activating factor 1, two critical components involved in mitochondrial pathway-mediated apoptosis. We conclude that rhein inhibits SGC-7901 proliferation by inducing apoptosis and this antitumor effect of rhein is mediated in part by an intrinsic mitochondrial pathway.

The hydroalcoholic extract of Cassia alata (Linn.) leaves and its major compound rhein exhibits antiallergic activity via mast cell stabilization and lipoxygenase inhibition

ETHNOPHARMACOLOGICAL RELEVANCE

Leaves of Cassia alata (family: Caesalpiniaceae) are ethnomedically claimed as anti-asthmatic. In the current study we aimed to investigate the anti-allergic activities of hydro-methanolic extract of Cassia alata (Linn.) and its constituents rhein and kaempferol on triple antigen/sheep serum-induced mast-cell degranulation in rats.

MATERIALS AND METHODS

Antiallergic activity of hydroalcoholic extract of Cassia alata along with its two components rhein and kaempferol was evaluated using in vivo mast cell stabilization assay. Inhibitory effect on lipoxygenase (LOX) enzyme was also evaluated in vitro. Further chemical standardization of Cassia alata extract was done using rhein and kaempferol by HPTLC-densitometric method.

RESULTS

The hydroalcoholic extract of Cassia alata significantly inhibited mast cell degranulation at 200mg/kg dose. Both chemical constituents rhein and kaempferol also showed potent (>76%) inhibition of mast-cell degranulation at 5mg/kg. Extract and rhein inhibited LOX enzyme with IC(50) values of 90.2 and 3.9μg/mL, respectively, whereas kaempferol was inactive.

CONCLUSION

Our results suggest that Cassia alata exhibit anti-allergic activity through mast cell stabilization and LOX inhibition. Thus, Cassia alata or its active constituents could be potential alternative treatment for allergic diseases.

Rhein induces apoptosis in human breast cancer cells

Human breast cancers cells overexpressing HER2/neu are more aggressive tumors with poor prognosis, and resistance to chemotherapy. This study investigates antiproliferation effects of anthraquinone derivatives of rhubarb root on human breast cancer cells. Of 7 anthraquinone derivatives, only rhein showed antiproliferative and apoptotic effects on both HER2-overexpressing MCF-7 (MCF-7/HER2) and control vector MCF-7 (MCF-7/VEC) cells. Rhein induced dose- and time-dependent manners increase in caspase-9-mediated apoptosis correlating with activation of ROS-mediated activation of NF-κB- and p53-signaling pathways in both cell types. Therefore, this study highlighted rhein as processing anti-proliferative activity against HER2 overexpression or HER2-basal expression in breast cancer cells and playing important roles in apoptotic induction of human breast cancer cells.

Novel rhein analogues as potential anticancer agents

Two series of rhein analogues were synthesized with modification at the 3-position. Their cytotoxicities were evaluated using an MTT assay. Among all the compounds synthesized, one compound showed the best potency, with an IC(50) value of 2.7 μM against the HeLa cell line and 0.6 μM against the MOLT4 cell line.

Liver targeting effect of vinegar-baked Radix Bupleuri on rhein in rats

Vinegar-baked Radix Bupleuri (VBRB) is usually used to focus other drugs effect on liver in traditional Chinese medicine (TCM). However, no sufficient scientific data are available to support this concept. In this paper, the liver targeting enhancing effect of VBRB on rhein was investigated. 432 of rats were divided into two large groups according to the dose of rhein, low dose group of rhein (LDGR) and high dose group of rhein (HDGR). In each group, the rats were further divided into four subgroups, rhein control and rhein co-administered with three different doses of VBRB peroral. Concentrations of rhein and its metabolite in different tissues were determined by HPLC. Compared to the control group, VBRB significantly increased the distribution of both rhein and its metabolite in liver and meanwhile decreased their distribution in other tissues, indicating a strong liver targeting enhancing effect. This liver targeting effect of VBRB depended on the dose of VBRB and rhein. Low and high dose of VBRB had a more strong effect than medium dose in HDGR; high dose of rhein was more sensitive than low dose of rhein (P<0.05). Rhein existed in two forms after peroral administration in vivo. It was found that the liver targeting effect of VBRB was more remarkable with the native form of rhein compared to its derivative form. The results of this paper demonstrated that co-administration with VBRB is a simple and efficiencient method for liver targeting therapy, and the meridine guide theory of TCM was credible.

Emodin and rhein inhibit LIGHT-induced monocytes migration by blocking of ROS production

LIGHT is known to act as a novel mediator for atherogenesis. Furthermore, it has been reported that emodin, an active component extracted from rhubarb, can stop the growth of cancer cells. However, it is not known if emodin exerts anti-atherogenic effects in the human monocyte, THP-1, following treatment with LIGHT. In this study, we evaluated the inhibitory effect of emodin and rhein on LIGHT-induced migration in THP-1. Emodin and rhein decreased the level of LIGHT-induced generation of ROS, as well as the expression of CCR1, CCR2 and ICAM-1 and the production of IL-8, MCP-1, TNF-alpha, and IL-6. Emodin and rhein also decreased the phosphorylation of the p38 MAPK and IkB-alpha. Furthermore, the NADPH oxidase assembly inhibitor, AEBSF, and the blocker of NADPH oxidase, p47(phox) small interference RNA (siRNA), also efficiently blocked LIGHT-induced migration, CCR1, CCR2, ICAM-1, and HVEM expression, and p38 MAPK and NF-kB activation. These findings indicate that the inhibitory effects of emodin and rhein on LIGHT-induced migration occur via decreasing ROS production and NADPH oxidase p47(phox) activation. Taken together, these results indicate that emodin and rhein have the potential for use as an anti-atherosclerosis agent.

Rhein, the metabolite of diacerhein, reduces the proliferation of osteoarthritic chondrocytes and synoviocytes without inducing apoptosis

OBJECTIVE

The aim of this study was to determine the effects of pharmacologically relevant concentrations of rhein (1,8-dihydroxy-3-carboxyanthraquinone) on the cell proliferation rate of human chondrocytes and synoviocytes.

METHODS

Cultures of human osteoarthritic synoviocytes and chondrocytes were incubated with 10(-6), 10(-5), and 10(-4) M rhein. [3H]thymidine incorporation was used to determine rhein proliferative effects after incubation periods of 24 h, 48 h, and 1 week. The cytotoxicity of the drug was assayed with a nonradioactive assay kit. Nuclear extracts were used to detect variations in cell-cycle proteins (p21, p27, and cyclin D1) by Western blotting. The effect of rhein on apoptosis was investigated by measurement of caspase-3/7 activity and DNA fragmentation.

RESULTS

Rhein was found to downregulate the proliferation rate of both chondrocytes and synoviocytes, two-fold for 10(-5) M rhein and five- to six-fold for 10(-4) M rhein. No cytotoxicity of the drug was observed. Rhein (10(-4) M) decreased caspase-3/7 activity and did not induce DNA fragmentation. Western blots showed that 10(-4) M rhein increased the expression of p21 and/or p27, but not that of cyclin D1.

CONCLUSIONS

Rhein has previously been shown to reduce the interleukin (IL)-1beta deleterious effects on osteoarthritis (OA) cartilage through inhibition of the expression of degrading enzymes. Here, rhein was also found to inhibit proliferation of both synoviocytes and chondrocytes, suggesting that the drug may decrease the development of the inflammatory synovial tissue that accompanies joint pathologies. Both its anti-catabolic and anti-proliferative effects may explain its beneficial effect in the treatment of joint diseases.

Antitumor effects of arsenic trioxide in transformed human thyroid cells

BACKGROUND

To improve radioiodine treatment of metastasized differentiated thyroid carcinomas, substances that increase iodide uptake are needed. Many tumors are not responsive to retinoic acid as a differentiating agent. Therefore, identification of other differentiating substances is needed. Arsenic trioxide (ATO) was investigated for its potential to increase iodide uptake.

METHODS

The action of ATO on proliferation, differentiation, and apoptosis was evaluated in follicular and papillary thyroid carcinoma cell lines. To get insight into the mode of action of ATO, coincubations with inhibitors of the phosphoinositide 3 (PI3) kinase pathway (V-Akt Murine Thymoma Viral Oncogene Homolog 1, Akt inhibitors) were performed; glutathione (GSH) levels were determined, as well as synergistic effects of ATO with inhibitors of GSH metabolism, inductors of oxidative stress. As a potential additional target of the pleiotropic action of ATO, its effect on glucose uptake was investigated. The expression of sodium iodide symporter, pendrin, phospho-Akt, and glucose transporter 1 was studied to reveal a potential effect of ATO on the transcription of specific genes.

RESULTS

ATO reduced proliferation, increased iodide uptake and apoptosis, and, as an additional new mechanism, decreased glucose uptake in transformed thyrocytes. The pharmacological reduction of the amount of reduced GSH was effective in enhancing the differentiating action of ATO, whereas the combination of ATO with Akt-1 inhibitors reduced cell number but did not increase differentiation.

CONCLUSIONS

Our study suggests a new therapeutic option for postoperative treatment of radioiodine nonresponsive differentiated thyroid carcinomas.

Rhein induces apoptosis and cell cycle arrest in human hepatocellular carcinoma BEL-7402 cells

Rhein, an anthraquinone derivative of rhubarb, inhibits the proliferation of various human cancer cells. In this paper, we focused on studying the effects of rhein on human hepatocelluar carcinoma BEL-7402 cells and further understanding the underlying molecular mechanism in an effort to make the potential development of rhein in the treatment of cancers. Using MTT assay and flow cytometry, we demonstrate a critical role of rhein in the suppression of BEL-7402 cell proliferation in a concentration- and time-dependent manner. The increase of apoptosis rate was observed after incubation of BEL-7402 cells with rhein at 50-200 muM for 48 hours, and the cells exhibit typical apoptotic features including cellular morphological change and chromatin condensation. Moreover, rhein-induced cell cycle S-phase arrest. Additionally, after rhein treatment, expression levels of c-Myc gene were decreased, while those of caspase-3 gene were increased in a dose-dependent manner by using real-time PCR assay. The results demonstrate for the first time that cell cycle S-phase arrest is one of the mechanisms of rhein in inhibition of BEL-7402 cells. Rhein plays its role by inducing cell cycle arrest via downregulation of oncogene c-Myc and apoptosis through the caspase-dependent pathway. It is expected that rhein will be effective and useful as a new agent in hepatocelluar carcinoma treatment in the future.

Participation of cathepsin B in emodin-induced apoptosis in HK-2 Cells

Emodin (1,3,8-trihydroxy-6-methyl-anthraquinone) and rhein (4,5-dihydroxyanthraquinone-2-carboxyl acid) are two main active compounds in total rhubarb anthraquinones (TRAs), which showed nephrotoxicity in Sprague Dawley (S.D.) rats in our previous study. However, it is unknown yet whether emodin and rhein have cytotoxic effects on kidney. To address this issue, HK-2 cells, a human proximal tubular epithelial cell line, were treated with different concentrations of emodin or rhein, and cell viability and morphological changes were investigated. The ratio of hypodiploid cells and the activity of caspase 3 protease were also detected. Results showed that addition of emodin but not rhein at concentrations above 40microM for 24h reduced cell viability and induced apoptosis in HK-2 cells. Additionally, emodin at apoptosis-inducing concentrations caused expression of cathepsin B (CB) protein and activation of CB protease. Addition of CB inhibitor, CA-074, significantly attenuated the ratio of hypodiploid and apoptotic cells, partially blocked caspase 3 activation and inhibited reduction of cell viability induced by emodin. These data indicate that emodin possesses cytotoxic effects on HK-2 cells partially through induction of CB protein and activation of CB protease.

Diacerein inhibits the synthesis of resorptive enzymes and reduces osteoclastic differentiation/survival in osteoarthritic subchondral bone: a possible mechanism for a protective effect against subchondral bone remodelling

INTRODUCTION

Subchondral bone alterations represent an essential component of osteoarthritis (OA). Modifying the abnormal subchondral bone metabolism may be indicated to treat OA. We investigated the effect of diacerein and rhein on the changes occurring in subchondral bone during OA. To this end, we determined the drugs' effects on metalloprotease-13 (MMP-13) synthesis on subchondral bone and on the osteoblast signalling pathways. In osteoclasts, we studied MMP-13 and cathepsin K production as well as cell differentiation, proliferation, and survival.

METHODS

The effect of diacerein/rhein on the production of subchondral bone MMP-13 was determined by enzyme-linked immunosorbent assay. Signalling pathways were evaluated on osteoblasts by Western blot. Osteoclast experiments were performed using cells from the pre-osteoclastic murine cell line Raw 264.7. Osteoclast MMP-13 and cathepsin K activities were determined by specific bioassays and differentiation of these cells quantified by tartrate-resistant acid phosphatase staining.

RESULTS

Diacerein and rhein reduced, in a dose-dependent manner, the interleukin-1-beta (IL-1beta)-induced MMP-13 production in OA subchondral bone. This effect occurred through the inhibition of ERK1/2 (extracellular signal-regulated kinase-1/2) and p38. In osteoclasts, they significantly reduced the activity of MMP-13 and cathepsin K. Moreover, these drugs effectively blocked the IL-1beta effect on the osteoclast differentiation process and the survival of mature osteoclasts.

CONCLUSION

Altogether, these data suggest that diacerein/rhein could impact the abnormal subchondral bone metabolism in OA by reducing the synthesis of resorptive factors and osteoclast formation.

Rhein reverses the diabetic phenotype of mesangial cells over-expressing the glucose transporter (GLUT1) by inhibiting the hexosamine pathway

BACKGROUND AND PURPOSE

Rhein, an anthraquinone compound isolated from rhubarb, has been proved effective in treatment of experimental diabetic nephropathy (DN). To explore the mechanism of its therapeutic effect on DN, rhein was tested for its effect on the hexosamine pathway.

EXPERIMENTAL APPROACH

The influence of rhein on cellular hypertrophy, fibronectin synthesis, glucose uptake, glutamine: fructose 6-phosphate aminotransferase (GFAT) activity, UDP-N-acetylglucosamine (UDP-GlcNAc) level and TGF-beta1 and p21 expression was evaluated in MCGT1 cells, a GLUT1 transgenic rat mesangial cell line. GFAT activity in normal rat mesangial cells in high glucose concentrations and in vitro was also measured.

KEY RESULTS

Significantly increased fibronectin synthesis, cellular hypertrophy, much higher GFAT activity and UDP-GlcNAc level and increased TGF-beta1 and p21 expression were found in MCGT1 cells cultured in normal glucose concentration. Rhein treatment decreased all these features of MCGT1 cells but did not exert a direct effect on GFAT enzymatic activity.

CONCLUSIONS AND IMPLICATIONS

There was over-activity of the hexosamine pathway in MCGT1 cells, which may explain the higher expression of TGF-beta1 and p21, the cellular hypertrophy and the increased expression of extracellular matrix (ECM) components in the cells. By inhibiting the increased activity the hexosamine pathway, rhein decreased TGF-beta1 and p21 expression and thus contributed to the decreased cellular hypertrophy and ECM synthesis. Inhibition of the hexosamine pathway may be one of the mechanism through which rhein exerts its therapeutic role in diabetic nephropathy.

Anti-cancer properties of anthraquinones from rhubarb

Rhubarb has been used as a traditional Chinese medicine since ancient times and today it is still present in various herbal preparations. In this review the toxicological and anti-neoplastic potentials of the main anthraquinones from Rhubarb, Rheum palmatum, will be highlighted. It is interesting to note that although the chemical structures of various anthraquinones in this plant are similar, their bioactivities are rather different. The most abundant anthraquinone of rhubarb, emodin, was capable of inhibiting cellular proliferation, induction of apoptosis, and prevention of metastasis. These capabilities are reported to act through tyrosine kinases, phosphoinositol 3-kinase (PI3K), protein kinase C (PKC), NF-kappa B (NF-kappaB), and mitogen-activated protein kinase (MAPK) signaling cascades. Aloe-emodin is another major component in rhubarb found to have anti-tumor properties. Its anti-proliferative property has been demonstrated to be through the p53 and its downstream p21 pathway. Our recent proteomic study also suggests that the molecular targets of these two anthraquinones are different. However, both components were found to be able to potentiate the anti-proliferation of various chemotherapeutic agents. Rhein is the other major rhubarb anthraquinone, although less well studied. This compound could effectively inhibit the uptake of glucose in tumor cells, caused changes in membrane-associated functions and led to cell death. Interestingly, all three major rhubarb anthraquinones were reported to have in vitro phototoxic. This re-evaluation of an old remedy suggests that several bioactive anthraquinones of rhubarb possess promising anti-cancer properties and could have a broad therapeutic potential.

Rhein induces apoptosis in HL-60 cells via reactive oxygen species-independent mitochondrial death pathway

Rhein is an anthraquinone compound enriched in the rhizome of rhubarb, a traditional Chinese medicine herb showing anti-tumor promotion function. In this study, we first reported that rhein could induce apoptosis in human promyelocytic leukemia cells (HL-60), characterized by caspase activation, poly(ADP)ribose polymerase (PARP) cleavage, and DNA fragmentation. The efficacious induction of apoptosis was observed at 100 microM for 6h. Mechanistic analysis demonstrated that rhein induced the loss of mitochondrial membrane potential (DeltaPsi(m)), cytochrome c release from mitochondrion to cytosol, and cleavage of Bid protein. Rhein also induced generation of reactive oxygen species (ROS) and the phosphorylation of c-Jun N-terminal kinase (JNK) and p38 kinase. However, these actions seem not to be associated with the apoptosis induction because antioxidants including N-acetyl cysteine (NAC), Tiron, and catalase did not block rhein-induced apoptosis, although they could block the generation of ROS and the phosphorylation of JNK and p38 kinase. Our data demonstrate that rhein induces apoptosis in HL-60 cells via a ROS-independent mitochondrial death pathway.

The role of phosphometabolites in cell proliferation, energy metabolism, and tumor therapy

A common characteristic of tumor cells is the constant overexpression of glycolytic and glutaminolytic enzymes. In tumor cells the hyperactive hexokinase and the partly inactive pyruvate kinase lead to an expansion of all phosphometabolites from glucose 6-phosphate to phosphoenolpyruvate. In addition to the glycolytic phosphometabolites, synthesis of their metabolic derivatives such as P-ribose-PP, NADH, NADPH, UTP, CTP, and UDP-N-acetyl glucosamine is also enhanced during cell proliferation. Another phosphometabolite derived from P-ribose-PP, AMP, inhibits cell proliferation. The accumulation of AMP inhibits both P-ribose-PP-synthetase and the increase in concentration of phosphometabolites derived from P-ribose-PP. In cells with low glycerol 3-phosphate and malate-aspartate shuttle capacities the inhibition of the lactate dehydrogenase by low NADH levels leads to an inhibition of glycolytic ATP production. Several tumor-therapeutic drugs reduce NAD and NADH levels, thereby inhibiting glycolytic energy production. The role of AMP, NADH, and NADPH levels in the success of chemotherapeutic treatment is discussed.

The role of phosphometabolites in cell proliferation, energy metabolism, and tumor therapy

A common characteristic of tumor cells is the constant overexpression of glycolytic and glutaminolytic enzymes. In tumor cells the hyperactive hexokinase and the partly inactive pyruvate kinase lead to an expansion of all phosphometabolites from glucose 6-phosphate to phosphoenolpyruvate. In addition to the glycolytic phosphometabolites, synthesis of their metabolic derivatives such as P-ribose-PP, NADH, NADPH, UTP, CTP, and UDP-N-acetyl glucosamine is also enhanced during cell proliferation. Another phosphometabolite derived from P-ribose-PP, AMP, inhibits cell proliferation. The accumulation of AMP inhibits both P-ribose-PP-synthetase and the increase in concentration of phosphometabolites derived from P-ribose-PP. In cells with low glycerol 3-phosphate and malate-aspartate shuttle capacities the inhibition of the lactate dehydrogenase by low NADH levels leads to an inhibition of glycolytic ATP production. Several tumor-therapeutic drugs reduce NAD and NADH levels, thereby inhibiting glycolytic energy production. The role of AMP, NADH, and NADPH levels in the success of chemotherapeutic treatment is discussed.

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.