Investigations on DNA binding in rat liver and in Salmonella and on mutagenicity in the Ames test by emodin, a natural anthraquinone

The natural anthraquinone dye emodin: Eco/genotoxicological characterization for aquatic organisms

Emodin is an anthraquinone secondary metabolite produced by several species of plants and fungi. Emodin is known for its pharmacological versatility, and, in the textile industry, for its good dyeing properties. However, its use in the textile industry can result in the formation and disposal of large volumes of wastewater. Emodin mutagenicity has been shown in bacteria and in human cells, but little is known about its possible toxic, genotoxic, or mutagenic effects in aquatic organisms. We have evaluated the eco/genotoxicity of emodin to aquatic organisms. Emodin was toxic to Daphnia similis (EC50 = 130 μg L-1) and zebrafish embryos (LC50 = 25 μg L-1). No toxicity was observed for Raphidocelis subcapitata, Ceriodaphnia dubia, or Parhyale hawaiensis. Additional biochemistry/molecular studies are needed to elucidate the toxic/mutagenic pathways of emodin in aquatic organisms. The PNEC value for emodin was 0.025 μg L-1. In addition to mutagenicity in the Salmonella/microsome assay, emodin was mutagenic in the micronucleus assay in the amphipod P. hawaiensis. Among the anthraquinone dyes tested to date, natural or synthetic, emodin was the most toxic to aquatic species.

Naturally occurring anthraquinones: chemistry and therapeutic potential in autoimmune diabetes

Anthraquinones are a class of aromatic compounds with a 9,10-dioxoanthracene core. So far, 79 naturally occurring anthraquinones have been identified which include emodin, physcion, cascarin, catenarin, and rhein. A large body of literature has demonstrated that the naturally occurring anthraquinones possess a broad spectrum of bioactivities, such as cathartic, anticancer, anti-inflammatory, antimicrobial, diuretic, vasorelaxing, and phytoestrogen activities, suggesting their possible clinical application in many diseases. Despite the advances that have been made in understanding the chemistry and biology of the anthraquinones in recent years, research into their mechanisms of action and therapeutic potential in autoimmune disorders is still at an early stage. In this paper, we briefly introduce the etiology of autoimmune diabetes, an autoimmune disorder that affects as many as 10 million worldwide, and the role of chemotaxis in autoimmune diabetes. We then outline the chemical structure and biological properties of the naturally occurring anthraquinones and their derivatives with an emphasis on recent findings about their immune regulation. We discuss the structure and activity relationship, mode of action, and therapeutic potential of the anthraquinones in autoimmune diabetes, including a new strategy for the use of the anthraquinones in autoimmune diabetes.

Combined phytochemistry and chemotaxis assays for identification and mechanistic analysis of anti-inflammatory phytochemicals in Fallopia japonica

Plants provide a rich source of lead compounds for a variety of diseases. A novel approach combining phytochemistry and chemotaxis assays was developed and used to identify and study the mechanisms of action of the active compounds in F. japonica, a medicinal herb traditionally used to treat inflammation. Based on a bioactivity-guided purification strategy, two anthranoids, emodin and physcion, were identified from F. japonica. Spectroscopic techniques were used to characterize its crude extract, fractions and phytochemicals. The crude extract, chloroform fraction, and anthranoids of F. japonica significantly inhibited CXCR4-mediated chemotaxis. Mechanistic studies showed that emodin and physcion inhibited chemotaxis via inactivating the MEK/ERK pathway. Moreover, the crude extract and emodin could prevent or treat type 1 diabetes in non-obese diabetic (NOD) mice. This study illustrates the applicability of a combinational approach for the study of anti-inflammatory medicine and shows the potential of F. japonica and its anthranoids for anti-inflammatory therapy.

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Molecular mechanism of emodin action: transition from laxative ingredient to an antitumor agent

Anthraquinones represent a large family of compounds having diverse biological properties. Emodin (1,3,8-trihydroxy-6-methylanthraquinone) is a naturally occurring anthraquinone present in the roots and barks of numerous plants, molds, and lichens, and an active ingredient of various Chinese herbs. Earlier studies have documented mutagenic/genotoxic effects of emodin, mainly in bacterial system. Emodin, first assigned to be a specific inhibitor of the protein tyrosine kinase p65lck, has now a number of cellular targets interacting with it. Its inhibitory effect on mammalian cell cycle modulation in specific oncogene overexpressed cells formed the basis of using this compound as an anticancer agent. Identification of apoptosis as a mechanism of elimination of cells treated with cytotoxic agents initiated new studies deciphering the mechanism of apoptosis induced by emodin. At present, its role in combination chemotherapy with standard drugs to reduce toxicity and to enhance efficacy is pursued vigorously. Its additional inhibitory effects on angiogenic and metastasis regulatory processes make emodin a sensible candidate as a specific blocker of tumor-associated events. Additionally, because of its quinone structure, emodin may interfere with electron transport process and in altering cellular redox status, which may account for its cytotoxic properties in different systems. However, there is no documentation available which reviews the biological activities of emodin, in particular, its growth inhibitory effects. This review is an attempt to analyze the biological properties of emodin, a molecule offering a broad therapeutic window, which in future may become a member of anticancer armamentarium.

Synthesis and Human Telomerase Inhibition of a Series of Regioisomeric Disubstituted Amidoanthraquinones

Telomerase is the enzymatic activity that maintains the ends of eukaryotic chromosomes. Telomerase activity is detected in most tumor cells whereas it is low or undetectable in most normal somatic cells. Expression of the telomerase catalytic component, the human telomerase reverse transcriptase (hTERT), is believed to be controlled primarily at the level of transcription. Because of this selective expression property of telomerase, it has been touted as a specific target for antitumor chemotherapeutics. However, a concern for the applicability of telomerase inhibitors is that they require a long lag time for telomeres to be shortened to critical length before cancer cells stop proliferating. Here we investigate telomerase inhibitory, cytotoxicity and the hTERT repressing effects on a number of synthesized 2,6-diamidoanthraquinones and 1,5-diamidoanthraquinones as compared to their disubstituted homologues. We found that several of the 1,5-diamidoanthraquinones and 2,6-diamidoanthraquinones inhibited telomerase activity effectively with IC50 at the sub-micro to micro molar range and caused acute cytotoxicity to cancer cells with EC50 similar or better than that of mitoxantrone. Particularly, 2,6-diamidoanthraquinone with 2-ethylaminoacetamido side chains 33, even though not affecting cell proliferation, showed to be endowed with a strong telomerase effect, probably related to a marked stabilization of the G-quadruplex-binding structure. The results suggested that these compounds caused multiple effects to cancer cells. More significantly, they overcome the long lag period problem of classical telomerase inhibitors that they are also potent cytotoxic agents. These results greatly expand the potential of tricyclic anthraquinone pharmacophore in preventive and/or curative therapy.

SOS induction of selected naturally occurring substances in Escherichia coli (SOS chromotest)

Naturally occurring substances were tested for genotoxicity using a modified laboratory protocol of the Escherichia coli PQ37 genotoxicity assay (SOS chromotest) in the presence and in the absence of an exogenous metabolizing system from rat liver S9-mix. Aristolochic acid I, II, the plant extract aristolochic acid and psoralene were genotoxic; cycasine, emodine, monocrotaline and retrorsine were classified as marginal genotoxic in the SOS chromotest in the absence of S9-mix. In the presence of an exogenous metabolizing system from rat liver S9-mix aristolochic acid I, the plant extract, beta-asarone, cycasin, monocrotaline, psoralen and retrorsine showed genotoxic effects; aristolochic acid II marginal genotoxic effects. Arecoline, benzyl acetate, coumarin, isatidine dihydrate, reserpine, safrole, sanguinarine chloride, senecionine, senkirkine, tannin and thiourea revealed no genotoxicity in the SOS chromotest either in the presence or in the absence of an exogenous metabolizing system from rat liver S9-mix. For 17 of 20 compounds, the results obtained in the SOS chromotest could be compared to those obtained in the Ames test. It was found that 12 (70.6%) of these compounds give similar responses in both tests (6 positive and 6 negative responses). The present investigation and those reported earlier, the SOS chromotest, using E. coli PQ37, was able to detect correctly most of the Salmonella mutagens and non-mutagens.

Protection against the bacterial mutagenicity of heterocyclic amines by purpurin, a natural anthraquinone pigment

Purpurin (1,2,4-trihydroxy-9,10-anthraquinone) is a naturally occurring anthraquinone pigment found in species of madder root. We have found that the presence of purpurin in bacterial mutagenicity assays is responsible for a marked inhibition of mutagenicity induced by food-derived heterocyclic amines. Purpurin was found to be a better inhibitor of Trp-P-2-dependent mutagenicity than either epigallocatechin gallate or chlorophyllin both of which are well-established anti-mutagenic components of diet. Inhibition of Trp-P-2(NHOH) mutagenicity by purpurin was dependent upon pH. It was a better inhibitor in neutral than acidic conditions. Purpurin was protective against the direct mutagen Trp-P-2(NHOH) in both the presence and the absence of hepatic S9 but required pre-incubation. Finally, purpurin was responsible for the inhibition of human CYP1A2 and human NADPH-cytochrome P450 reductase and a decrease in the bioactivation of Trp-P-2 by these enzymes when they were expressed in Salmonella typhimurium TA1538ARO. However, inhibition of Trp-P-2(NHOH)-dependent mutations suggests purpurin also has a direct effect on this mutagen in addition to inhibiting its formation by CYP1A2.

Effect of anthraquinone-laxatives on the proliferation and urokinase secretion of normal, premalignant and malignant colonic epithelial cells

Even though 1,8-dihydroxyanthraquinone (DHA)-laxatives have been implicated in colon carcinogenesis, the available information is still inconclusive. The aim of this study was to demonstrate the effect of the DHA-laxatives, danthrone, rhein, aloe-emodin and sennidine, on colorectal tumour cells. In SW480 carcinoma cultures, dose-dependent induction of urokinase secretion into the medium was the predominant effect. Simultaneously, cell numbers were decreased by DHA-aglycones, but not by sennoside or the biphenylic laxative bisacodyl. DNA synthesis was not similarly reduced: 0.4-4 microM danthrone and sennidine even stimulated 5-bromo-2'-desoxyuridine (BrdU) uptake into DNA. When uptake was normalised to cell number, danthrone and sennidine doubled BrdU uptake/10(6) cells, 18 microM rhein and 0.7 microM aloe-emodin induced increases of 37 and 50%, respectively. This may at least partially be due to selective resistance of S-phase cells to DHA-caused cell loss. In VACO235 adenoma cells, sennidine and aloe-emodin did not affect urokinase secretion, but stimulated growth. Both cell numbers and DNA synthesis were increased. In contrast to SW480 carcinoma cells, VACO235 cells were also sensitive to sennoside and bisacodyl. No effects of DHA were observed in normal colorectal epithelial cells. The biological effects were preceeded by specific phosphorylation of cellular proteins with molecular weights of 110, 78, 63, 57 kDa, indicating the specific induction of a cellular signalling cascade by the laxatives.

Assessment of the genotoxic risk from laxative senna products

Laxative senna products and several of their specific components have been submitted to a large number of genetic tests. While most studies gave negative responses, results from some of the studies suggest that components of senna products, particularly emodin and aloe-emodin, have genotoxic activity. Assessment of the genotoxicity profile of these substances, in light of other data from animal and human metabolism or kinetic studies, human clinical trials and rodent carcinogenicity studies do not support concerns that senna laxatives pose a genotoxic risk to humans when consumed under prescribed use conditions.

Genotoxicity of the laxative drug components emodin, aloe-emodin and danthron in mammalian cells: topoisomerase II mediated?

1,8-Dihydroxyanthraquinones are under debate as plant-derived carcinogens that are found in laxatives, food colors, and possibly vegetables. Published genotoxicity data are controversial, and so three of them (emodin, danthron and aloe-emodin) were tested in a number of in vitro assay systems. All three compounds induced tk-mutations in mouse lymphoma L5178Y cells. Induction of micronuclei also occurred in the same cell line, and was dose-dependent, with the potency ranking being danthron > aloe-emodin > emodin. In a DNA decatenation assay with a network of mitochondrial DNA of C. fasciulata, all three test compounds inhibited the topoisomerase II-mediated decatenation. Danthron and aloe-emodin, but not emodin, increased the fraction of DNA moving into comet tails when tested at concentrations around 50 microM in single-cell gel-electrophoresis assays (SCGE; comet assay). Comet assays were also used in modified form to determine whether pretreatment of the cells with the test compounds would reduce the effects of etoposide, a potent topoisomerase II inhibitor. All three test chemicals were effective in this pretreatment protocol, with danthron again being the most potent. Given clearcut evidence of their genotoxic activity, further research on the human cancer risk of these compounds may be warranted.

OTC pharmaceuticals and genotoxicity testing: the paracetamol, anthraquinone, and griseofulvin cases

Genotoxic effects are hardly assessable in an exposed population but are generally considered to be serious due to their unpredictable effects on subsequent generations and to the link between genotoxicity and cancer. Lack of knowledge about a genotoxic/carcinogenic potential has to be stated for numerous compounds which are often in pharmaceutical use known for a long time. A thorough testing programme like it is done for new compounds is essential for such compounds that are not completely unsuspicious with respect to being reactive with macromolecules or that have the potential to generate reactive metabolites in the body. Paracetamol, anthraquinone-containing preparations, and griseofulvin are examples for pharmaceuticals that have been in use for a long time but for which genotoxicity testing revealed a possible deleterious potential only recently. The Federal Health Office/Federal Institute for Drugs and Medical Devices therefore imposed new studies upon companies marketing these compounds in the last years. These studies in part led to a more thorough description of possible adverse effects or even restrictions for use. Paracetamol exhibits a genotoxic potential in vitro and in vivo probably via indirect, cytotoxicity or enzyme inhibition-mediated effects. Further studies will have to clarify whether a threshold could be established and whether effects do not occur at therapeutic dose levels. Genotoxicity data on the mixed group of anthraquinones reveal positive and negative findings. Compounds such as lucidin, danthron, emodin supposedly have a genotoxic and carcinogenic potential. Further studies with anthraquinone-containing plant preparations will have to clarify the content and genotoxic activity of the preparations and the active ingredients. Lucidin- and danthron-containing preparations are currently no longer in use now whereas restrictions apply for other anthraquinone-containing laxatives. Griseofulvin is acknowledged in the meantime as an aneugen for somatic and germ cells. It is in vitro effective in concentrations that correspond to therapeutic plasma levels.

Mutagenicity of substituted anthraquinones in the Ames/Salmonella microsome system

Unsubstituted anthraquinone, 4 substituted anthraquinones (emodin, danthron, physcion, a new compound M-108-C) and 3 dimers (skyrin, rugulosin, rugulin) were tested using the Ames/Salmonella assay (strains TA98, TA100, TA1537 and TA102). Danthron and emodin were found to be mutagenic for TA1537 with or without metabolic activation, physcion only with metabolic activation. A significant difference was found between the mutagenic activities of emodin (16.2 His+/nmole) and danthron (6.5 His+/nmole) as well as a high specific mutagenic activity for physcion (11.6 His+/nmole). These results on structure-mutagenic activity relationships suggest that the 6-methyl group plays an important role in the mutagenic activity after metabolic activation. Furthermore, and contrary to emodin, physcion exhibited a weak mutagenic activity for TA102, probably due to the formation of a different metabolite. Such information is necessary to evaluate the potential carcinogenic hazard of these compounds.

Antimutagenicity profiles for some model compounds

The concept of activity profile listings and plots, already applied successfully to the display of mutagenicity data, has been modified for application to antimutagenicity data. The activity profiles are bar graphs that have been organized in two general ways: for antimutagens that have been tested in combination with a given mutagen and for mutagens that have been tested in combination with a given antimutagen. Doses from both the mutagen and the antimutagen are displayed and plotted together with results on enhancement or inhibition of mutagenic activity. The short-term tests that have been used extensively to identify mutagens and potential carcinogens are increasingly being used to identify antimutagens and potential anticarcinogens. Three model mutagens, N-methyl-N'-nitro-N-nitrosoguanidine, aflatoxin B1 and benzo[a]pyrene, and 4 model antimutagens, butylated hydroxyanisole, butylated hydroxytoluene, glutathione and disulfiram, were selected from the data surveyed in the published literature. It is not clear at the present time whether the inhibition of carcinogen-induced mutation is a good indicator of anticarcinogenic properties, and further research is needed. Nevertheless, the activity profiles are useful for the assessment of the available antimutagenesis data by providing rapid visualization of considerable dose information and experimental results.

The classification of chemical carcinogens

Various approaches to classification of chemical carcinogens developed by international and national agencies are described. Special features of each classification scheme with their strengths and weaknesses and their usefulness in regulation are discussed. Some recent examples of regulatory decisions on chemical hazards in Canada are presented, illustrating the many factors that need to be considered for risk assessment, in addition to merely categorizing carcinogens.

Trenbolone growth promotant: covalent DNA binding in rat liver and in Salmonella typhimurium, and mutagenicity in the Ames test

DNA binding in vivo: [6,7-3H]beta-trenbolone (beta-TBOH) was administered p.o. and i.p. to rats. After 8 or 16 h, DNA was isolated from the livers and purified to constant specific radioactivity. Enzymatic digestion to deoxyribonucleotides and separation by HPLC revealed about 90% of the DNA radioactivity eluting in the form of possible TBOH-nucleotide adducts. The extent of this genotoxicity, expressed in units of the Covalent Binding Index, CBI = (mumol TBOH bound per mol nucleotide)/(mmol TBOH administered per kg body weight) spanned from 8 to 17, i.e. was in the range found with weak genotoxic carcinogens. Ames test: low doses of beta-TBOH increased the number of revertants in Salmonella strain TA100 reproducibly and in a dose-dependent manner. The mutagenic potency was 0.2 revertants per nmol after preincubation of the bacteria (20 min at 37 degrees C) with doses between 30 and 60 micrograms per plate (47 and 94 micrograms/ml preincubation mixture). Above this dose, the number of revertants decreased to control values, accompanied by a reduction in survival. The addition of rat liver S9 inhibited the mutagenicity. DNA binding in vitro: calf thymus DNA was incubated with tritiated beta-TBOH with and without rat liver S9. Highest DNA radioactivities were determined in the absence of the "activation" system. Addition of inactive S9 (without cofactors) reduced the DNA binding by a factor of up to 20. Intermediate results were found with active S9. DNA binding in Salmonella: beta-TBOH was irreversibly bound to DNA isolated from S. typhimurium TA100 after incubation of bacteria with [3H]beta-TBOH.