Toxicity and tumorigenicity of purpurin, a natural hydroxanthraquinone in rats: induction of bladder neoplasms

Copper-mediated DNA damage caused by purpurin, a natural anthraquinone

Background

Purpurin (1,2,4-trihydroxy-9,10-anthraquinone), a natural red anthraquinone pigment, has historically been used as a textile dye. However, purpurin induced urinary bladder tumors in rats, and displayed a mutagenic activity in assay using bacteria and mammalian cells. Many carcinogenic dyes are known to induce bladder cancers via DNA adduct formation, but carcinogenic mechanisms of purpurin remain unknown. In this study, to clarify the mechanism underlying carcinogenicity of purpurin, copper-mediated DNA damage induced by purpurin was examined using ³²P-labeled DNA fragments of human genes relevant to cancer. Furthermore, we also measured 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG), an indicator of oxidative DNA damage, in calf thymus DNA.

Results

Purpurin plus Cu(II) cleaved ³²P-labeled DNA fragments only under piperidine treatment, indicating that purpurin caused base modification, but not breakage of the DNA backbone. In the absence of Cu(II), purpurin did not induce DNA cleavage even with piperidine treatment. Purpurin plus Cu(II) caused piperidine-labile sites predominantly at G and some T residues. Bathocuproine, a Cu(I) chelator, completely prevented the occurrence of piperidine-labile sites, indicating a critical role of Cu(I) in piperidine-labile sites induced by purpurin plus Cu(II). On the other hand, methional, a scavenger of a variety of reactive oxygen species (ROS) and catalase showed limited inhibitory effects on the induction of piperidine-labile sites, suggesting that ROS could not be major mediators of the purpurin-induced DNA damage. Considering reported DNA adduct formation by quinone metabolites of several carcinogenic agents, quinone form of purpurin, which is possibly generated via purpurin autoxidation accompanied by Cu(I)/Cu(II) redox cycle, might lead to DNA adducts and piperidine-labile sites. In addition, we measured contents of 8-oxodG. Purpurin moderately but significantly increased 8-oxodG in calf thymus DNA in the presence of Cu(II). The 8-oxodG formation was inhibited by catalase, methional and bathocuproine, suggesting that Cu(I)-hydroperoxide, which was generated via Cu(I) and H₂O₂, caused oxidative DNA base damage.

Conclusions

We demonstrated that purpurin induces DNA base damage possibly mediated by Cu(I)/Cu(II) redox cycle both with and without ROS generation, which are likely to play an important role in its carcinogenicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41021-022-00245-2.

The natural anthraquinone dye purpurin exerts antibacterial activity by perturbing the FtsZ assembly

There is an increasing demand to discover novel antibacterial drugs to counter the ever-evolving genetic machinery of bacteria. The cell division protein FtsZ plays a vital role in bacterial cytokinesis and has been recognized as an effective antibacterial drug target. In this study, we have shown that the madder dye purpurin inhibited bacterial cytokinesis through perturbation of FtsZ assembly. Purpurin inhibited the growth of bacterial cells in a concentration-dependent manner and induced bacterial cell filamentation. Microscopy studies showed that it inhibited the localization of the Z ring at the midcell, and FtsZ was dispersed throughout the cells. Further, purpurin bound firmly to FtsZ with a dissociation constant of 11 µM and inhibited its assembly in vitro. It reduced the GTP hydrolysis by binding closer to the nucleotide-binding site of FtsZ. Purpurin inhibited the proliferation of mammalian cancer cells at higher concentrations without disturbing the polymerization of tubulin. The results collectively suggest that the natural anthraquinone purpurin can potently inhibit the growth of bacteria and serve as a lead molecule for the development of antibacterial agents.

Purpurin: A natural anthraquinone with multifaceted pharmacological activities

Purpurin is a naturally occurring anthraquinone isolated from the roots of Rubia cordifolia. Historically, it has been used as a red dye. However, its photosensitizing property and biological effects have deciphered its novel application. Purpurin shows antigenotoxic, anticancer, neuromodulatory, and antimicrobial potential associated with antioxidant action in in vivo and in vitro experiments. A robust antioxidant nature of purpurin is responsible for the majority of its pharmacological effects. It produces anti-inflammatory activity by reducing oxidative stress, which is a fundamental property to target diseases involving endoplasmic reticulum and mitochondrial stress. It can cross the blood-brain barrier and produce neuroprotective effects, including antidepressant and anti-Alzheimer action. It shows antimutagenic property via inhibiting essential CYP-450 enzymes. Interestingly, it gets photosensitized by UV-light and produces target-specific ROS-dependent apoptosis in cancer cells. Therefore, it owns cell killing and cell survival potential subject to the influence of external conditions. Hitherto, limited research studies are performed with purpurin to understand its therapeutic potential. Hence, this review describes and discusses different in vivo, in vitro, and in silico studies performed using purpurin. It also covers physicochemical, pharmacokinetics, and toxicology aspects of purpurin. Moreover, in the end, the prospect of purpurin in the management of cancer has also been proposed.

Purpurin exerted antidepressant-like effects on behavior and stress axis reactivity: evidence of serotonergic engagement

RATIONALE AND OBJECTIVES

Major depression represents a significant public health problem worldwide, and effective regimen is lacking. The present study investigated the antidepressant-like effects of purpurin, a natural anthraquinone compound from Rubia tinctorum L., and explored the underlying mechanism(s).

METHODS

Forced swim test (FST) and tail suspension test (TST) were used to assess antidepressant-like effects of purpurin in mice. Effects of purpurin on neuroendocrine responsivity were evaluated at the level of corticosterone and ACTH following acute restraint stress and intracerebroventricular injection of corticotrophin-releasing-factor (CRF). Serotonergic mechanisms underlying purpurin antidepressant effect were explored using biochemical, neurochemical, and pharmacological paradigms.

RESULTS

Chronic purpurin treatment exerted in mice dose-dependently antidepressant-like effects on behavior and stress axis reactivity (n = 9-11 per group). The purpurin-triggered antidepressant-like effects are serotonergically dependent, since purpurin-treated mice showed escalated levels of brain serotonin and suppressed monoamine oxidase (MAO) activity (n = 8-11 per group). Consistently, chemical depletion of brain serotonin by p-chlorophenylalanine (PCPA) abolished the antidepressant-like effects of purpurin on behavior and stress axis responsivity (n = 9-10 per group). Moreover, the antidepressant effect by purpurin was preferentially counteracted by 1A-selective 5-HT receptor antagonist WAY-100635, but potentiated by 1A-selective agonist 8-OH-DPAT and sub-effective dose of serotonergic antidepressant fluoxetine (n = 9-11 per group), suggesting a crucial role for 5-HT1A related serotonergic system in mediating such purpurin antidepressant effect.

CONCLUSION

We have revealed the antidepressant-like effects of purpurin on both behavior and stress axis reactivity in mice, with serotonergic system that preferentially couples with 5-HT1A receptors being critically engaged.

Anti-hyperglycemic and genotoxic studies of 1-O-methyl chrysophanol, a new anthraquinone isolated from Amycolatopsis thermoflava strain SFMA-103

The compound 1-O-methyl chrysophanol (OMC) which belongs to a class of hydroxyanthraquinones was isolated from Amycolatopsis thermoflava strain SFMA-103 and studied for their anti-diabetic properties. OMC was evaluated as an anti-diabetic agent based on in silico studies which initially predicted the binding energy with α-amylase (-188.81 KJ mol^-1) and with α-glucosidase (70.53 KJ mol^-1). Further, these results were validated based on enzyme inhibition assays where OMC demonstrated enzyme inhibitory activity towards α-amylase (IC₅₀ 3.4 mg mL^-1) and α-glucosidase (IC₅₀ 38.49 μg mL^-1). To confirm the anti-diabetic activity, in vivo studies (oral dose in Wistar rats) revealed that OMC inhibited significantly the increase in glucose concentration at 100 mg/kg as compared to starch control (p < 0.05). Further, to understand the safety of OMC as a therapeutic agent, the genotoxic analysis was performed in both in vitro Chinese Hamster Ovary cells (250, 500, and 1000 µM/mL) and in vivo Swiss albino mice (250, 500, and 1000 mg/kg). In vitro results showed that OMC concentration of up to 250 µM/mL did not elicit significant changes in CAs, MI, and MN counts in CHO cells. Similarly, in mice experiments (i.p. injection), no significant changes in CAs, MI, and MN induction were observed till 500 mg/kg of OMC when compared with chrysophanic acid (Cy) (200 mg/kg). In addition, mice that received the lowest dose of OMC (250 mg/kg) did not show any histological changes in liver, kidney, and heart. The study concluded that five times higher therapeutic dose (100 mg/kg) of OMC can be utilized against hyperglycemia with no genotoxic effects.

Identification of Hydroxyanthraquinones as Novel Inhibitors of Hepatitis C Virus NS3 Helicase

Hepatitis C virus (HCV) is an important etiological agent of severe liver diseases, including cirrhosis and hepatocellular carcinoma. The HCV genome encodes nonstructural protein 3 (NS3) helicase, which is a potential anti-HCV drug target because its enzymatic activity is essential for viral replication. Some anthracyclines are known to be NS3 helicase inhibitors and have a hydroxyanthraquinone moiety in their structures; mitoxantrone, a hydroxyanthraquinone analogue, is also known to inhibit NS3 helicase. Therefore, we hypothesized that the hydroxyanthraquinone moiety alone could also inhibit NS3 helicase. Here, we performed a structure-activity relationship study on a series of hydroxyanthraquinones by using a fluorescence-based helicase assay. Hydroxyanthraquinones inhibited NS3 helicase with IC50 values in the micromolar range. The inhibitory activity varied depending on the number and position of the phenolic hydroxyl groups, and among different hydroxyanthraquinones examined, 1,4,5,8-tetrahydroxyanthraquinone strongly inhibited NS3 helicase with an IC50 value of 6 µM. Furthermore, hypericin and sennidin A, which both have two hydroxyanthraquinone-like moieties, were found to exert even stronger inhibition with IC50 values of 3 and 0.8 µM, respectively. These results indicate that the hydroxyanthraquinone moiety can inhibit NS3 helicase and suggest that several key chemical structures are important for the inhibition.

Blockade of LTB4-induced chemotaxis by bioactive molecules interfering with the BLT2-Galphai interaction

BLT2, a low-affinity leukotriene B4 (LTB4) receptor, is a member of the G-protein coupled receptor (GPCR) family and is involved in the pathogenesis of inflammatory diseases such as asthma. Despite its clinical implications, however, no pharmacological inhibitors are available. In the present study, we screened for small molecules that interfere with the interaction between the third intracellular loop region of BLT2 (BLT2iL3) and the Galphai3 protein subunit (Galphai3), using a high-throughput screening (HTS) assay with a library of 1040 FDA-approved drugs and bioactive compounds. We identified two small molecules-purpurin [1,2,4-trihydroxy-9,10-anthraquinone; IC50 = 1.6 microM for BLT2] and chloranil [tetrachloro-1,4-benzoquinone; IC50 = 0.42 microM for BLT2]-as specific BLT2-blocking agents. We found that blockade of the BLT2iL3-Galphai3 interaction by these small molecules inhibited the BLT2-downstream signaling cascade. For example, BLT2-signaling to phosphoinositide-3 kinase (PI3K)/Akt phosphorylation was completely abolished by these molecules. Furthermore, we observed that these small molecules blocked LTB4-induced chemotaxis by inhibiting the BLT2-PI3K/Akt-downstream, Rac1-reactive oxygen species-dependent pathway. Taken together, our results show that purpurin and chloranil interfere with the interaction between BLT2iL3 and Galphai3 and thus block the biological functions of BLT2 (e.g., chemotaxis). The present findings suggest a potential application of purpurin and chloranil as pharmacological therapeutic agents against BLT2-associated inflammatory human diseases.

Induction of kidney and liver cancers by the natural food additive madder color in a two-year rat carcinogenicity study

Madder color (MC) extracted from the roots of Rubia tinctorum (madder root) has been used as a food coloring in Japan. Our previous studies revealed MC to have obvious subchronic and chronic toxicity and potent carcinogenicity targeting rat liver and kidney. In the present two-year carcinogenicity study, conducted to further elucidate the long-term effects of MC and its target organs, male and female F344 rats were fed diet containing 0%, 2.5%, and 5.0% MC for 104 weeks. Body weights were significantly decreased in treated groups of both sexes throughout the feeding period. However, survival rates at week 104 were higher in treated groups of both sexes than in controls. Relative weights of the kidneys and liver were significantly increased in treated groups of both sexes. Histopathologically, karyomegaly and atypical tubules/hyperplasias, as well as renal cell adenomas and carcinomas were significantly increased in treated groups of both sexes with dose-dependence. Moreover, the incidence of hepatocellular adenomas and/or carcinomas was increased significantly with a dose-relation in treated groups of both sexes. These data provide clear evidence that MC exerts unequivocal carcinogenicity against renal tubule cells and hepatocytes in rats.

Enhancement of phase II enzyme activity by purpurin resulting in the suppression of MeIQx-DNA-adduct formation in mice

We previously demonstrated using a bacterial system that the antigenotoxic activity of the anthraquinone compounds purpurin and alizarin was due to the suppression of microsomal enzyme activity involved in the activation of mutagens. In the present study we determined the effect of purpurin and alizarin on (i) MeIQx-DNA-adduct formation in mouse tissues and (ii) the activity of phases I and II enzymes in liver fractions, the liver being the target tissue of MeIQx. The amount of MeIQx-DNA adduct formed was determined using 32P-postlabeling methods. Methoxyresorufin-O-demethylase (MROD) and ethoxyresorufin-O-deethylase (EROD) enzyme activities, which reflect CYP 1A activity, were measured as markers for phase I enzymes, and UDP-glucuronyltransferase (UGT) and glutathione S-transferase (GST) activities were determined as markers for phase II enzymes. Mice fed with a diet containing 0.5% purpurin for 3 days prior to MeIQx administration had 70% fewer MeIQx-DNA adducts in the lung and kidney, and fewer DNA adducts (insignificant, statistically) in the liver compared with mice fed a diet lacking purpurin. MROD and EROD activities in the liver of these mice increased six- and eight-fold, respectively, and were higher than those determined for the control mice within 1 day following commencement of purpurin treatment. These elevated activities were maintained during treatment and declined immediately following removal of purpurin from the diet. GST and UGT activities gradually increased 2.5- and 3-fold, respectively, following purpurin treatment, and were maintained at significantly high levels even after purpurin administration ceased. Alizarin did not significantly affect DNA-adduct formation and enzyme activity, except in the case of UGT. Taken together, our results show that purpurin reduced MeIQx-DNA-adduct formation by maintaining elevated phase II enzyme activities, thereby facilitating accelerated excretion of MeIQx.

Evaluation of photo-mutagenicity and photo-cytotoxicity of food coloring agents

Pigments extracted from natural products are widely used for food coloration in Japan. An investigation concerning the photo-mutagenicity and photo-carcinogenicity of frequently used colorants in Japan was performed. Colorants examined were from Laccifer lacca (lac-color), Coccus cacti (cochineal-color), Carthamus tinctorius (carthamus yellow), Gardenia augusta (gardenia yellow and gardenia blue), Monascus anka and Monascus purpureus (monascus red), the skin of Vitis vinifera and Vitis labrusca (grape-skin color), Tamarindus indica (tamarind brown) and Beta vulgaris (beet red). No significant increase in bacterial mutation was found when Salmonella typhimurium TA98, TA100 and TA102 were simultaneously treated with colorants and subjected to UVA irradiation for 30 min. When colorant solutions were subjected to UVA irradiation for 4 h, irradiated solutions containing lac-color became slightly mutagenic toward S.typhimurium TA98 without metabolic activation. A decrease in cell survival resulted when WTK-1 cells were subjected to UVA irradiation for 60 min in the presence of purpurin at 1 mg/ml. Delayed cytotoxicity was also observed following 24 h incubation in fresh medium of samples that were subjected to UVA irradiation for 60 min in the presence of colorant (carthamus yellow, grape-skin color, gardenia blue, cochineal-color, monascus red or purpurin).

Influence of functional group substitutions on the carcinogenicity of anthraquinone in rats and mice: analysis of long-term bioassays by the National Cancer Institute and the National Toxicology Program

The carcinogenic activities of anthraquinone and six derivatives were compared and contrasted. Studies included representatives of amino, alkyl, nitro, hydroxy, or halogen-containing anthraquinones, with the purpose of uncovering general structure-activity relationships. Anthraquinone, 2-aminoanthraquinone, 1-amino-2-methylanthraquinone, 2-methyl-1-nitroanthraquinone,1-amino-2,4-dibromoanthraquinone, 1,4,5,8-tetraaminoanthraquinone, and 1,3,8-trihydroxy-6-methylanthraquinone (of varying purities) were administered via feed to Fischer 344/N rats and B6C3F, mice. In rats, anthraquinone induced tumors in the liver, kidney, and urinary bladder. A 2-amino substitution narrowed the carcinogenicity to the liver, while multiple amino substitutions led to a carcinogenic response in the urinary bladder alone. A methyl substitution ortho to a 1-aminogroup preserved the hepatic and renal neoplasms seen with the parent anthraquinone, but did not induce urinary bladder tumors; amino or bromo substitutions para to a 1-amino group were related to urinary bladder neoplasms. The intestine may have been a target organ for bromine-substituted anthraquinones. The presence of a nitro group altered the targets of carcinogenicity, and skin tumors may have been associated with this particular functional group in both rats and mice. Over-all for mice, the findings were somewhat different and limited by the small number of common target organs. The parent anthraquinone was clearly carcinogenic only to the liver. There were no other effects of single amino substitutions, in the presence or absence of an additional methyl group, on the carcinogenicity or the site of carcinogenesis of anthraquinone in mice. Multiple amino substitutions diminished, while bromine substitutions enhanced the carcinogenicity induced by anthraquinone and extended the target organs to include forestomach and lung.

Protection against Trp-P-2 DNA adduct formation in C57bl6 mice by purpurin is accompanied by induction of cytochrome P450

Purpurin, an anthraquinone constituent from madder root, has previously been reported as antimutagenic in the Ames Salmonella bacterial mutagenicity assay and as antigenotoxic in Drosophila melanogaster, against a range of environmental carcinogens. Short-term dietary supplementation with purpurin inhibits the formation of hepatic DNA adducts in male C57bl6 mice after a single dose of the heterocyclic amine dietary carcinogen Trp-P-2 (30 mg/kg). Inhibition of adduct formation was dose-dependent. No DNA adducts were observed in animals treated only with purpurin. The decrease in adduct formation was accompanied by significant, dose-dependent inductions of hepatic cytochrome P450-dependent dealkylations of methoxy- (CYP1A2), ethoxy- (CYP1A1), and pentoxy- (CYP2B) resorufins, total cytochrome P450, and NADPH cytochrome P450 reductase. It is hypothesized that purpurin exhibits chemopreventive potential by inhibiting the cytochrome P450-dependent metabolism of heterocyclic amines to their genotoxic N-hydroxylamines.

Inhibition of human cytochrome P450 1B1, 1A1 and 1A2 by antigenotoxic compounds, purpurin and alizarin

Recently we have shown that anthraquinone food pigments such as purpurin and alizarin suppress the genotoxic activities of several mutagens including heterocyclic amines and polycyclic aromatic hydrocarbons in the Drosophila DNA repair test and in the Ames test. To investigate the mechanism of this inhibition, we have now examined the effects of these anthraquinone pigments on enzymes that metabolize xenobiotics. The activities of eight human recombinant cytochrome P450 (CYP) isozymes were measured in the presence of purpurin, alizarin or carminic acid. Purpurin and alizarin strongly inhibited the activities of CYP1A1, CYP1A2 and CYP1B1, and weakly suppressed those of CYP2A6 and CYP2E1 in a dose-dependent manner, but did not inhibit those of CYP2C19, CYP3A4 and CYP3A5. Carminic acid did not affect the activities of any CYPs tested. CYP1B1 was the most strongly affected CYP molecule by purpurin and alizarin among CYPs examined in this study. From kinetic analysis, it was shown that the inhibition by purpurin on CYP1B1 was both competitive and non-competitive, and that by alizarin was competitive. The values of slopes obtained from Lineweaver-Burk plots are proportional to the square of purpurin concentration. This observation suggests that two molecules of purpurin are interacting with one molecule of CYP1B1. The K(m) value of CYP1B1 was 11 microM, and the K(i) value of purpurin and alizarin against CYP1B1 was 0.7 microM(2) and 0.5 microM, respectively. We also examined the effects of these pigments on the mutagenicities of MeIQx and B[a]P in the Ames test, using Salmonella typhimurium TA1538 co-expressing each form of human CYP and NADPH-cytochrome P450 reductase (OR). The mutagenicity of MeIQx in TA1538 1A2/OR or 1B1/OR was suppressed by purpurin and alizarin but not by carminic acid. Purpurin also reduced the mutagenicity of B[a]P in TA1538 1A1/OR or 1B1/OR. These results suggest that the antigenotoxic activities of purpurin and alizarin can be explained by inhibition of CYP activities responsible for activating the 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.