Characterisation of metabolites of the putative cancer chemopreventive agent quercetin and their effect on cyclo-oxygenase activity

Can Compounds of Natural Origin Be Important in Chemoprevention? Anticancer Properties of Quercetin, Resveratrol, and Curcumin-A Comprehensive Review

Malignant tumors are the second most common cause of death worldwide. More attention is being paid to the link between the body's impaired oxidoreductive balance and cancer incidence. Much attention is being paid to polyphenols derived from plants, as one of their properties is an antioxidant character: the ability to eliminate reactive oxygen and nitrogen species, chelate specific metal ions, modulate signaling pathways affecting inflammation, and raise the level and activity of antioxidant enzymes while lowering those with oxidative effects. The following three compounds, resveratrol, quercetin, and curcumin, are polyphenols modulating multiple molecular targets, or increasing pro-apoptotic protein expression levels and decreasing anti-apoptotic protein expression levels. Experiments conducted in vitro and in vivo on animals and humans suggest using them as chemopreventive agents based on antioxidant properties. The advantage of these natural polyphenols is low toxicity and weak adverse effects at higher doses. However, the compounds discussed are characterized by low bioavailability and solubility, which may make achieving the blood concentrations needed for the desired effect challenging. The solution may lie in derivatives of naturally occurring polyphenols subjected to structural modifications that enhance their beneficial effects or work on implementing new ways of delivering antioxidants that improve their solubility and bioavailability.

Transcriptomic and targeted metabolomic analyses provide insights into the flavonoids biosynthesis in the flowers of Lonicera macranthoides

BACKGROUND

Flavonoids are one of the bioactive ingredients of Lonicera macranthoides (L. macranthoides), however, their biosynthesis in the flower is still unclear. In this study, combined transcriptomic and targeted metabolomic analyses were performed to clarify the flavonoids biosynthesis during flowering of L. macranthoides.

RESULTS

In the three sample groups, GB_vs_WB, GB_vs_WF and GB_vs_GF, there were 25, 22 and 18 differentially expressed genes (DEGs) in flavonoids biosynthetic pathway respectively. A total of 339 flavonoids were detected and quantified at four developmental stages of flower in L. macranthoides. In the three sample groups, 113, 155 and 163 differentially accumulated flavonoids (DAFs) were detected respectively. Among the DAFs, most apigenin derivatives in flavones and most kaempferol derivatives in flavonols were up-regulated. Correlation analysis between DEGs and DAFs showed that the down-regulated expressions of the CHS, DFR, C4H, F3'H, CCoAOMT_32 and the up-regulated expressions of the two HCTs resulted in down-regulated levels of dihydroquercetin, epigallocatechin and up-regulated level of kaempferol-3-O-(6''-O-acetyl)-glucoside, cosmosiin and apigenin-4'-O-glucoside. The down-regulated expressions of F3H and FLS decreased the contents of 7 metabolites, including naringenin chalcone, proanthocyanidin B2, B3, B4, C1, limocitrin-3,7-di-O-glucoside and limocitrin-3-O-sophoroside.

CONCLUSION

The findings are helpful for genetic improvement of varieties in L.macranthoides.

Nuclear factor-κB plays an important role in Tamarixetin-mediated inhibition of matrix metalloproteinase-9 expression

Flavonoids possess a broad spectrum of pharmacological properties, including anti-cancer, anti-oxidant and immunomodulatory activities. The current study explored the potential of some less-studied flavonoids in inhibiting Matrix Metalloproteinase-9 (MMP-9), a prominent biomarker, upregulated in a variety of cancers and known to promote migration and invasion of cancer cells. Amongst these, Tamarixetin, a naturally occurring flavonoid derivative of Quercetin, demonstrated significant dose-dependent inhibition of MMP-9 expression. Furthermore, a substantial inhibition of migration, invasion and clonogenic potential of HT1080 cells was also observed in the presence of Tamarixetin, which further suggests its role as a potential anti-cancer agent. It is noteworthy that Tamarixetin inhibits nuclear translocation as well the activity of nuclear factor kappa B (NFκB), both of which are functions essential for the activation of MMP-9 in promoting tumorigenesis. Additionally, the endogenous regulators of MMP-9 that tightly control its activity were also modulated by Tamarixetin, as evident from the 1.9 fold increase in the expression of Tissue Inhibitor of Metalloproteinase-1 (TIMP-1), with a concomitant 2.2 fold decrease in Matrix Metalloproteinase-14 (MMP-14) expression. The results obtained were further corroborated in three dimensional (3D) tumor models, which showed significant inhibition of MMP-9 activity as well as reduced invasive potential in the presence of Tamarixetin. Taken together, our observations demonstrate for the first time, the anti-invasive potential of Tamarixetin in cancer cells, indicating its possible use as a template for novel therapeutic applications.

Glucuronidation of Methylated Quercetin Derivatives: Chemical and Biochemical Approaches

Botanical supplements derived from grapes are functional in animal model systems for the amelioration of neurological conditions, including cognitive impairment. Rats fed with grape extracts accumulate 3'-O-methyl-quercetin-3-O-β-d-glucuronide (3) in their brains, suggesting 3 as a potential therapeutic agent. To develop methods for the synthesis of 3 and the related 4'-O-methyl-quercetin-7-O-β-d-glucuronide (4), 3-O-methyl-quercetin-3'-O-β-d-glucuronide (5), and 4'-O-methyl-quercetin-3'-O-β-d-glucuronide (6), which are not found in the brain, we have evaluated both enzymatic semisynthesis and full chemical synthetic approaches. Biocatalysis by mammalian UDP-glucuronosyltransferases generated multiple glucuronidated products from 4'-O-methylquercetin, and is not cost-effective. Chemical synthetic methods, on the other hand, provided good results; 3, 5, and 6 were obtained in six steps at 12, 18, and 30% overall yield, respectively, while 4 was synthesized in five steps at 34% overall yield. A mechanistic study on the unexpected regioselectivity observed in the quercetin glucuronide synthetic steps is also presented.

Quercetin Triggers Induction of Apoptotic and Lysosomal Death of Sensitive and Multidrug Resistant Leukaemia HL60 Cells

Multidrug resistance (MDR) constitutes the major cause of the failure in anticancer therapy. One of the most important mechanisms leading to the occurrence of MDR is related to the modulation of cellular death pathways. The aim of this study was to determine the effect of quercetin (Q) on triggering the programed death of human promyelocytic leukemia sensitive cells HL60 as well as multidrug resistant HL60/VINC cells overexpressing P-glycoprotein and HL60/MX2 cells characterized by the presence of mutated α isoform of topoisomerase II and the absence of β isoform of this enzyme. Q exerted comparable cytotoxic activities toward sensitive HL60 cells and their MDR counterparts. It was also found that this compound modulated the cellular level of reactive oxygen species (ROS) and led to the marked decrease in cellular GSH level. Furthermore, it was demonstrated that Q used at IC₅₀ and IC₉₀ significantly increased the percentage of sub-G1 subpopulation of all studied leukemia cells causing oligonucleosomal DNA fragmentation. The present study also indicated that Q used at IC₉₀ triggers predominantly programed cell death of sensitive HL60 cells and their MDR counterparts by induction of apoptosis occurring with the involvement of caspase-3 and caspase-8 as well as by lysosome membrane permeabilization-dependent mechanisms.

Total flavonoids from the Carya cathayensis Sarg. leaves inhibit HUVEC senescence through the miR-34a/SIRT1 pathway

Aging shows a significant relationship with changed vascular structure and function, and advancing age is a major nonmodifiable risk factor in the occurrence of cardiovascular diseases. The senescence of endothelial cells is one of the hallmarks of vascular aging and can induce vascular dysfunction. This study aimed to investigate the effect of total flavonoids (TFs) on human umbilical vein endothelial cells (HUVEC) senescence and identify the potential mechanisms involved. A HUVEC senescence model was induced by angiotensin II. The senescence markers, including senescence-associated β-galactosidase (SA-β-gal), p53, p21, and stagnate G0/G1, were measured. The effects of TFs on miR-34/ SIRT1 were examined by quantitative polymerase chain reaction analysis and Western blot analysis. TFs decreased the percentage of SA-β-gal-positive cells and resulted in G0/G1 cell cycle arrest, while the percentage of cells in the S phase increased. Furthermore, TFs reduced miR-34a expression and increased the expression of SIRT1. After treatment with TFs and a miR-34a inhibitor, the percentage of SA-β-gal-positive cells and the expression of miR-34a decreased, and the expression of SIRT1 increased. The TFs inhibited HUVEC senescence, and the mechanism was related to the miR-34a/Sirtuin1 pathway.

Total Flavonoids from Carya cathayensis Sarg. Leaves Alleviate H9c2 Cells Hypoxia/Reoxygenation Injury via Effects on miR-21 Expression, PTEN/Akt, and the Bcl-2/Bax Pathway

This study aimed to investigate whether the total flavonoids (TFs) from Carya cathayensis Sarg. leaves alleviate hypoxia/reoxygenation (H/R) injury in H9c2 cardiomyocytes and to explore potential mechanisms. H9c2 cells pretreated with TFs for 24h were exposed to H/R treatment. The results indicated that TFs significantly alleviate H/R injury, which include inhibiting apoptosis and enhancing antioxidant capacity. The protective effects of TFs resulted in higher expression of miR-21 in H/R-induced H9c2 cells than that of controls, which in turn upregulated Akt signaling activity via suppressing the expression of PTEN together with decreasing the ratio of Bax/Bcl-2, caspase3, and cleaved-caspase3 expression in H/R-induced H9c2 cells. Conversely, blocking miR-21 expression with miR-21 inhibitor effectively suppressed the protective effects of TFs against H/R-induced injury. Our study suggests that TFs can decrease cell apoptosis, which may be mediated by altering the expression of miR-21, PTEN/Akt, and Bcl/Bax.

Mechanisms of Phytonutrient Modulation of Cyclooxygenase-2 (COX-2) and Inflammation Related to Cancer

The link between chronic inflammation and cancer involves cytokines and mediators of inflammatory pathways. Cyclooxygenase-2 (COX-2), a key enzyme in fatty acid metabolism, is upregulated during both inflammation and cancer. COX-2 is induced by pro-inflammatory cytokines at the site of inflammation and enhanced COX-2-induced synthesis of prostaglandins stimulates cancer cell proliferation, promotes angiogenesis, inhibits apoptosis, and increases metastatic potential. As a result, COX-2 inhibitors are a subject of intense research interest toward potential clinical applications. Epidemiological studies highlight the potential benefits of diets rich in phytonutrients for cancer prevention. Plants contain numerous phytonutrient secondary metabolites shown to modulate COX-2. Studies have shown that these metabolites, some of which are used in traditional medicine, can reduce inflammation and carcinogenesis. This review describes the molecular mechanisms by which phytonutrients modulate inflammation, including studies of carotenoids, phenolic compounds, and fatty acids targeting various inflammation-related molecules and pathways associated with cancer. Examples of pathways include those of COX-2, mitogen-activated protein kinase kinase kinase, mitogen-activated protein kinase, pro-inflammatory cytokines, and transcription factors like nuclear factor kappa B. Such phytonutrient modulation of COX-2 and inflammation continue to be explored for applications in the prevention and treatment of cancer.

Dehydrocostus lactone, a natural sesquiterpene lactone, suppresses the biological characteristics of glioma, through inhibition of the NF-κB/COX-2 signaling pathway by targeting IKKβ

Dehydrocostus lactone (DHE), a natural sesquiterpene lactone, has been used for treatment of various diseases with its anti-inflammatory activity. Recently, it has caused extensive interest in researchers due to it has anti-cancer abilities in some types of carcinomas. However, the anti-cancer effect and mechanism of DHE in glioma remains unclear. The present study conducted to determine the biological effects of DHE on the glioblastoma cells, as well as the mechanisms underlying these effects. After treatment with DHE, the glioblastoma (U118, U251 or U87) cells were significantly inhibited in their viability, proliferation and migration. At the meantime, DHE also induced mitochondria-mediated apoptosis by promoting the release of cytochrome c into cytosol, which activating caspase signaling pathway. Furthermore, our results fully demonstrate that DHE significantly suppressed COX-2 expression by inhibiting the phosphorylation of IKKβ via targeting the ATP-binding site, thereby abrogating NF-κB binding and p300 recruitment to COX-2 promoter. Moreover, the current study firstly demonstrated that DHE can cross blood-brain barrier (BBB). In addition, treatment with DHE markedly inhibited neoplastic weight and volume without the notable adverse effects in the xenograft nude mice model, and these effects may be mediated through inhibition of the IKKβ/NF-κB/COX-2 signaling pathway. These findings provide the pharmacological evidence for development of DHE as a potential agent against glioma.

The Role of the MAPK Signaling, Topoisomerase and Dietary Bioactives in Controlling Cancer Incidence

Reactive oxygen species (ROS) are common products of mitochondrial oxidative phosphorylation, xenobiotics metabolism and are generated in response to several environmental stress conditions. Some of them play important biochemical roles in cellular signal transduction and gene transcription. On the other hand, ROS are known to be involved in a wide range of human diseases, including cancer. The excessive production of such ROS together with disruption of homeostasis detoxifying mechanisms can mediate a series of cellular oxidative stresses. The oxidative stress of redundant free radicals production can lead to oxidative denaturation of cellular macromolecules including proteins, lipids and DNA. Moreover, oxidative damage is one of the major causes of DNA mutations, replication errors and genomic abnormalities which result in either inhibition or induction of transcription, and end with the disturbance of signal transduction pathways. Among affected signaling pathways are redox-sensitive kinases. The stimulation of these kinases induces several transcription factors through the phosphorylation of their module proteins. The activation of such pathways induces proliferation and cellular transformation. A diet rich in antioxidant compounds has potential health benefits, and there is a growing interest in the role of natural antioxidants in nutrition for prevention and cure of cancer diseases. A controversy has risen regarding the relation between antioxidants and the significant decrease in the risk of cancer incidence. In this review, we will focus on redox-sensitive kinases signaling pathways, highlighting the effects of dietary antioxidant on the prevention, incidence, prognosis or even treatment of human cancers. In addition, we will place emphasis on the chemical classes of pterocarpans as natural anti-oxidants/cancers as well as their underlying mechanisms of action, including their effects on MAPKs and topoisomerase activities.

Natural Compounds as Occult Ototoxins? Ginkgo biloba Flavonoids Moderately Damage Lateral Line Hair Cells

Several drugs, including aminoglycosides and platinum-based chemotherapy agents, are well known for their ototoxic properties. However, FDA-approved drugs are not routinely tested for ototoxicity, so their potential to affect hearing often goes unrecognized. This issue is further compounded for natural products, where there is a lack of FDA oversight and the manufacturer is solely responsible for ensuring the safety of their products. Natural products such as herbal supplements are easily accessible and commonly used in the practice of traditional eastern and alternative medicine. Using the zebrafish lateral line, we screened a natural products library to identify potential ototoxins. We found that the flavonoids quercetin and kaempferol, both from the Gingko biloba plant, demonstrated significant ototoxicity, killing up to 30 % of lateral line hair cells. We then examined a third Ginkgo flavonoid, isorhamnetin, and found similar levels of ototoxicity. After flavonoid treatment, surviving hair cells demonstrated reduced uptake of the vital dye FM 1-43FX, suggesting that the health of the remaining hair cells was compromised. We then asked if these flavonoids enter hair cells through the mechanotransduction channel, which is the site of entry for many known ototoxins. High extracellular calcium or the quinoline derivative E6 berbamine significantly protected hair cells from flavonoid damage, implicating the transduction channel as a site of flavonoid uptake. Since known ototoxins activate cellular stress responses, we asked if reactive oxygen species were necessary for flavonoid ototoxicity. Co-treatment with the antioxidant D-methionine significantly protected hair cells from each flavonoid, suggesting that antioxidant therapy could prevent hair cell loss. How these products affect mammalian hair cells is still an open question and will be the target of future experiments. However, this research demonstrates the potential for ototoxic damage caused by unregulated herbal supplements and suggests that further supplement characterization is warranted.

Enhancing the anti-colon cancer activity of quercetin by self-assembled micelles

Colorectal cancer, a type of malignant neoplasm originating from the epithelial cells lining the colon and/or rectum, has been the third most frequent malignancy and one of the leading causes of cancer-related deaths in the US. As a bioflavonoid with high anticancer potential, quercetin (Qu) has been proved to have a prospective applicability in chemotherapy for a series of cancers. However, quercetin is a hydrophobic drug, the poor hydrophilicity of which hinders its clinical usage in cancer therapy. Therefore, a strategy to improve the solubility of quercetin in water and/or enhance the bioavailability is desired. Encapsulating the poorly water-soluble, hydrophobic agents into polymer micelles could facilitate the dissolution of drugs in water. In our study, nanotechnology was employed, and quercetin was encapsulated into the biodegradable nanosized amphiphilic block copolymers of monomethoxy poly(ethylene glycol)-poly(ε-caprolactone) (MPEG-PCL), attempting to present positive evidences that this drug delivery system of polymeric micelles is effective. The quercetin-loaded MPEG-PCL nanomicelles (Qu-M), with a high drug loading of 6.85% and a minor particle size of 34.8 nm, completely dispersed in the water and released quercetin in a prolonged period in vitro and in vivo. At the same time, compared with free quercetin, Qu-M exhibited improved apoptosis induction and cell growth inhibition effects in CT26 cells in vitro. Moreover, the mice subcutaneous CT26 colon cancer model was established to evaluate the therapy efficiency of Qu-M in detail, in which enhanced anti-colon cancer effect was proved in vivo: Qu-M were more efficacious in repressing the growth of colon tumor than free quercetin. In addition, better effects of Qu-M on inducing cell apoptosis, inhibiting tumor angiogenesis, and restraining cell proliferation were observed by immunofluorescence analysis. Our study indicated that Qu-M were a novel nanoagent of quercetin with an enhanced antitumor activity, which could serve as a promising potential candidate for colon cancer chemotherapy.

Identification of phenolic compounds in red wine extract samples and zebrafish embryos by HPLC-ESI-LTQ-Orbitrap-MS

The zebrafish embryo is a highly interesting biological model with applications in different scientific fields, such as biomedicine, pharmacology and toxicology. In this study, we used liquid chromatography/electrospray ionisation-linear ion trap quadrupole-Orbitrap-mass spectrometry (HPLC/ESI-LTQ-Orbitrap-MS) to identify the polyphenol compounds in a red wine extract and zebrafish embryos. Phenolic compounds and anthocyanin metabolites were determined in zebrafish embryos previously exposed to the red wine extract. Compounds were identified by injection in a high-resolution system (LTQ-Orbitrap) using accurate mass measurements in MS, MS(2) and MS(3) modes. To our knowledge, this research constitutes the first comprehensive identification of phenolic compounds in zebrafish by HPLC coupled to high-resolution mass spectrometry.

Gamabufotalin, a bufadienolide compound from toad venom, suppresses COX-2 expression through targeting IKKβ/NF-κB signaling pathway in lung cancer cells

BACKGROUND

Gamabufotalin (CS-6), a major bufadienolide of Chansu, has been used for cancer therapy due to its desirable metabolic stability and less adverse effect. However, the underlying mechanism of CS-6 involved in anti-tumor activity remains poorly understood.

METHODS

The biological functions of gamabufotalin (CS-6) were investigated by migration, colony formation and apoptosis assays in NSCLC cells. The nuclear localization and interaction between transcriptional co-activator p300 and NF-κB p50/p65 and their binding to COX-2 promoter were analyzed after treatment with CS-6. Molecular docking study was used to simulate the interaction of CS-6 with IKKβ. The in vivo anti-tumor efficacy of CS-6 was also analyzed in xenografts nude mice. Western blot was used to detect the protein expression level.

RESULTS

Gamabufotalin (CS-6) strongly suppressed COX-2 expression by inhibiting the phosphorylation of IKKβ via targeting the ATP-binding site, thereby abrogating NF-κB binding and p300 recruitment to COX-2 promoter. In addition, CS-6 induced apoptosis by activating the cytochrome c and caspase-dependent apoptotic pathway. Moreover, CS-6 markedly down-regulated the protein levels of COX-2 and phosphorylated p65 NF-κB in tumor tissues of the xenograft mice, and inhibited tumor weight and size.

CONCLUSIONS

Our study provides pharmacological evidence that CS-6 exhibits potential use in the treatment of COX-2-mediated diseases such as lung cancer.

Cyclooxygenase-2 and inflammation mediators have a crucial role in reflux-related esophageal histological changes and Barrett's esophagus

BACKGROUND

Gastroesophageal reflux (GER) causes injury of the esophageal squamous epithelium, a condition called reflux esophagitis. The sequence reflux-esophagitis-intestinal metaplasia-dysplasia-invasive cancer is widely accepted as the main adenocarcinogenetic pathway in the esophagus; however, the mechanisms of this progression need to be better defined.

AIMS

We evaluated COX-2 expression and activity in biopsies from patients affected with GER, and these parameters have been correlated with the stage of the disease, ceramide expression, apoptotic process, and angiogenesis. The effects of celecoxib on bile acid- and EGF-induced mucosal proliferation, apoptosis and angiogenesis have been also investigated.

METHODS

Four groups of patients were distinguished: non esophagitis, non erosive esophagitis, erosive esophagitis, and Barrett's esophagus. COX-2 expression, basal PGE2 levels, proliferative activity, VEGF expression and apoptosis were evaluated in esophageal biopsies.

RESULTS

COX-2 expression, basal PGE2 levels, proliferative activity, VEGF expression and apoptosis progressively increase from non esophagitis patients to patients with non erosive and erosive esophagitis, to those with BE. Incubation of the cells with DCA/EGF increases PGE2 production, proliferative activity and VEGF production, effects prevented by celecoxib pretreatment. Ceramide expression increased from non esophagitis patients to patients with non erosive and erosive esophagitis, and decreased in BE; caspase-3 activity progressively decreased from non esophagitis to BE patients, suggesting an impairment of the apoptotic process with disease progression.

CONCLUSION

These results stand for a close relationship between progression of initial steps of gastroesophageal reflux disease (GERD) and COX-2, proliferative activity and EGF/VEGF expression and could have implications in GERD treatment in order to prevent its neoplastic evolution.

Regiospecific methylation of a dietary flavonoid scaffold selectively enhances IL-1β production following Toll-like receptor 2 stimulation in THP-1 monocytes

It is now recognized that innate immunity to intestinal microflora plays a significant role in mediating immune health, and modulation of microbial sensing may underpin the impact of plant natural products in the diet or when used as nutraceuticals. In this context, we have examined five classes of plant-derived flavonoids (flavonols, flavones, flavanones, catechins, and cyanidin) for their ability to regulate cytokine release induced by the Toll-like receptor 2 (TLR2) agonist Pam3CSK4. We found that the flavonols selectively co-stimulated IL-1β secretion but had no impact on the secretion of IL-6. Importantly, this costimulation of TLR2-induced cytokine secretion was dependent on regiospecific methylation of the flavonol scaffold with a rank order of quercetin-3,4'-dimethylether > quercetin-3-methylether > casticin. The mechanism underpinning this costimulation did not involve enhanced inflammasome activation. In contrast, the methylated flavonols enhanced IL-1β gene expression through transcriptional regulation, involving mechanisms that operate downstream of the initial NF-κB and STAT1 activation events. These studies demonstrate an exquisite level of control of scaffold bioactivity by regiospecific methylation, with important implications for understanding how natural products affect innate immunity and for their development as novel immunomodulators for clinical use.

Induction of G2/M phase arrest and apoptosis by the flavonoid tamarixetin on human leukemia cells

Flavonoids are naturally occurring polyphenolic compounds which display a vast array of biological activities. In this study, we investigated the effects of tamarixetin on viability of human tumor cell lines and found that it was cytotoxic against leukemia cells and in particular P-glycoprotein-overexpressing K562/ADR cells. This compound inhibited proliferation in a concentration- and time-dependent manner, induced apoptosis and blocked cell cycle progression at G2 -M phase. This was associated with the accumulation of cyclin B1, Bub1 and p21(Cip1/Waf-1), changes in the phosphorylation status of cyclin B1, Cdk1, Cdc25C and MPM-2, and inhibition of tubulin polymerization. Moreover, cell death was found to be associated with cytochrome c release and cleavage of caspases and of poly(ADP-ribose) polymerase, and completely abrogated by the free-radical scavenger N-acetyl-L-cysteine. The sensitivity of leukemic cells to tamarixetin suggests that it should be considered for further preclinical and in vivo testing.

Pluchea lanceolata protects against Benzo(a) pyrene induced renal toxicity and loss of DNA integrity

Evidence from epidemiological, experimental and clinical trial data indicates that a plant based diet can reduce the risk of chronic diseases and reduces toxic effects. In the present study, we report the antioxidant and anticlastogenic activity of Pluchea lanceolata (PL), an important medicinal plant, in both in vitro and in vivo model. Benzo(a)pyrene (B(a)P) administration leads to depletion of renal glutathione and its metabolizing enzymes. Pretreatment with PL (100 and 200 mg /kg b.wt) restored renal glutathione content and its dependent enzymes significantly (p<0.001) with simultaneous increase in catalase(CAT), quinone reductase(QR) in mouse kidney. Prophylactic administration of PL prior to B (a) P administration significantly decreased the malondialdehyde(MDA), H2O2 and xanthineoxidase (XO) levels at a significance of p<0.001, at both the doses. PL extract pretreated groups showed marked inhibition in B(a)P induced micronuclei formation in mouse bone marrow cells with simultaneous restoration of DNA integrity, viz. alkaline unwinding assay and DNA damage shown by gel-electrophoresis. HPTLC confirms the presence of quercetin in plant extract which could be responsible for PL protecting efficacy. In conclusion, the present findings strongly support the antioxidant efficacy of PL, possibly by modulation of antioxidant armory.

Differential hepatoprotective mechanisms of rutin and quercetin in CCl(4)-intoxicated BALB/cN mice

AIM

To investigate the mechanisms underlying the protective effects of quercetin-rutinoside (rutin) and its aglycone quercetin against CCl(4)-induced liver damage in mice.

METHODS

BALB/cN mice were intraperitoneally administered rutin (10, 50, and 150 mg/kg) or quercetin (50 mg/kg) once daily for 5 consecutive days, followed by the intraperitoneal injection of CCl(4) in olive oil (2 mL/kg, 10% v/v). The animals were sacrificed 24 h later. Blood was collected for measuring the activities of ALT and AST, and the liver was excised for assessing Cu/Zn superoxide dismutase (SOD) activity, GSH and protein concentrations and also for immunoblotting. Portions of the livers were used for histology and immunohistochemistry.

RESULTS

Pretreatment with rutin and, to a lesser extent, with quercetin significantly reduced the activity of plasma transaminases and improved the histological signs of acute liver damage in CCl(4)-intoxicated mice. Quercetin prevented the decrease in Cu/Zn SOD activity in CCl(4)-intoxicated mice more potently than rutin. However, it was less effective in the suppression of nitrotyrosine formation. Quercetin and, to a lesser extent, rutin attenuated the inflammation in the liver by down-regulating the CCl(4)-induced activation of nuclear factor-kappa B (NF-κB), tumor necrosis factor-α (TNF-α) and cyclooxygenase (COX-2). The expression of inducible nitric oxide synthase (iNOS) was more potently suppressed by rutin than by quercetin. Treatment with both flavonoids significantly increased NF-E2-related factor 2 (Nrf2) and heme oxygenase (HO-1) expression in injured livers, although quercetin was less effective than rutin at an equivalent dose. Quercetin more potently suppressed the expression of transforming growth factor-β1 (TGF-β1) than rutin.

CONCLUSION

Rutin exerts stronger protection against nitrosative stress and hepatocellular damage but has weaker antioxidant and anti-inflammatory activities and antifibrotic potential than quercetin, which may be attributed to the presence of a rutinoside moiety in position 3 of the C ring.

The increased cellular uptake and biliary excretion of curcumin by quercetin: a possible role of albumin binding interaction

Curcumin and quercetin are natural compounds with a wide spectrum of activities, including antioxidant and anticancer activities. In this study, the combined effect of the two compounds was investigated, with special emphasis on the pharmacokinetics of curcumin by the quercetin-induced changes in the albumin binding of curcumin. We evaluated the effect of quercetin on the binding of curcumin to albumin and on the uptake of curcumin into the cells of the human colon carcinoma cell line WiDr. In addition, we also investigated changes in the in vivo pharmacokinetics of curcumin and curcumin sulfate (the major metabolite of curcumin) coadministered with quercetin. We found that quercetin inhibited the binding of curcumin to albumin and increased the uptake of curcumin into WiDr cells, the human colon carcinoma cell. The quercetin-induced increased uptake (1.6-fold) of curcumin into WiDr cells was also confirmed by an ex vivo study. The in vivo pharmacokinetics of curcumin showed obvious changes when it was coadministered with quercetin, with the significantly lower plasma concentration and greater biliary excretion of curcumin and curcumin sulfate. The present study suggests that quercetin could enhance the cellular uptake of curcumin and modulate in vivo pharmacokinetics of curcumin, and it could be related to albumin-binding interaction.

Tissue distribution and metabolism of the putative cancer chemopreventive agent 3',4',5'-trimethoxyflavonol (TMFol) in mice

3',4',5'-Trimethoxyflavonol (TMFol) is a synthetic flavonol with preclinical cancer chemopreventive properties. The hypothesis was tested that, in mice, p.o. administration of TMFol results in measureable levels of the parent in target tissues. A single oral dose (240 mg/kg) was administered to mice (n = 4 per time point) with time points ranging from 5 to 1440 min. TMFol and its metabolites were identified and quantitated in all tissues by high-performance liquid chromatography (HPLC). Plasma levels of TMFol were at the limit of quantification or below, although metabolites were identified. Peak levels of TMFol in the gastrointestinal tract and the prostate averaged 1671 ± 265 µg/g (5.3 µmol/g) and 6.0 ± 1.6 µg/g (18.4 nmol/g), and occurred 20 and 360 min post-dose, respectively. The area under the tissue concentration-time curve (AUC) for TMFol was greater than those of the metabolites, indicating that TMFol is relatively metabolically stable. Micromolar TMFol levels are easily achieved in the prostate and gastrointestinal tract, suggesting that TMFol might exert chemopreventive efficacy at these tissue sites. Further investigations are warranted to elucidate the potential chemopreventive potency of TMFol.

Fisetin disposition and metabolism in mice: Identification of geraldol as an active metabolite

Although the natural flavonoid fisetin (3,3',4',7-tetrahydroxyflavone) has been recently identified as an anticancer agent with antiangiogenic properties in mice, its in vivo pharmacokinetics and metabolism are presently not characterized. Our purpose was to determine the pharmacokinetics and metabolism of fisetin in mice and determine the biological activity of a detected fisetin metabolite. After fisetin administration of an efficacious dose of 223 mg/kg i.p. in mice, the maximum fisetin concentration reached 2.5 μg/ml at 15 min and the plasma concentration declined biphasically with a rapid half-life of 0.09 h and a terminal half-life of 3.1h. Three metabolites were detected, one of which was a glucuronide of fisetin (M1), whereas another glucuronide (M2) was a glucuronide of a previously unknown fisetin metabolite (M3). HPLC-MS/MS analysis indicated that M3 was a methoxylated metabolite of fisetin (MW=300 Da). The UV spectrum of M3 was identical to that of fisetin and standard 3,4',7-trihydroxy-3'-methoxyflavone (geraldol). In addition, because M3 co-eluted with standard geraldol in 4 different chromatographic ternary gradient conditions, M3 was therefore assigned to geraldol. Of interest, this metabolite was shown to achieve higher concentrations than fisetin in Lewis lung tumors. We also compared the cytotoxic and antiangiogenic activities of fisetin and geraldol in vitro and it was found that the latter was more cytotoxic than the parent compound toward tumor cells, and that it could also inhibit endothelial cells migration and proliferation. In conclusion, these results suggest that fisetin metabolism plays an important role in its in vivo anticancer activities.

Characterization of the glutathione conjugate of the semisynthetic flavonoid monoHER

Flavonoids protect against oxidative stress by scavenging free radicals. During this protection flavonoids are oxidized. The oxidized flavonoids formed are often reactive. Consequently, protection by flavonoids can result in the formation of toxic products. In this study the oxidation of 7-mono-O-(beta-hydroxyethyl)rutoside (monoHER), which is a constituent of the registered drug Venoruton, was studied in the absence and presence of glutathione (GSH). MonoHER was oxidized by horseradish peroxidase/H(2)O(2). Spectrophotometric and HPLC analysis showed that in the presence of GSH, a monoHER-GSH conjugate was formed, which was identified as 2'-glutathionyl monohydroxyethylrutoside by mass spectrometric analysis and (1)H NMR. Preferential formation of this glutathione adduct in the B ring at C2' was confirmed by molecular quantum chemical calculations. This conjugate was also detected in the bile fluid of a healthy volunteer after iv administration of monoHER, demonstrating its formation in vivo. These results indicate that in the process of offering protection against free radicals, monoHER is converted into an oxidation product that is reactive toward thiols. The formation of this thiol-reactive oxidation product is potentially harmful. Thus, the supposed beneficial effect of monoHER as an antioxidant may be accompanied by the formation of products with an electrophilic, toxic potential.

Anti-Inflammatory and antiproliferative activities of trifolirhizin, a flavonoid from Sophora flavescens roots

Trifolirhizin, a pterocarpan flavonoid, was isolated from the roots of Sophora flavescens, and its chemical structure was confirmed by (1)H and (13)C NMR and MS spectra. Its anti-inflammatory activity was examined in lipopolysaccharide (LPS)-stimulated mouse J774A.1 macrophages. Trifolirhizin not only dose-dependently inhibited LPS-induced expression of pro-inflammatory cytokines including tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) but also inhibited lipopolysaccharide (LPS)-induced expression of cyclooxygenase-2 (COX-2). In addition, trifolirhizin showed in vitro inhibitory effects on the growth of human A2780 ovarian and H23 lung cancer cells. These results suggest that trifolirhizin possesses potential anti-inflammatory and anticancer activities.

Inhibition of heat shock induction of heat shock protein 70 and enhancement of heat shock protein 27 phosphorylation by quercetin derivatives

Inhibitors of heat-induced heat shock protein 70 (HSP70) expression have the potential to enhance the therapeutic effectiveness of heat-induced radiosensitization of tumors. Among known small molecule inhibitors, quercetin has the advantage of being easily modified for structure-activity studies. Herein, we report the ability of five monomethyl and five carbomethoxymethyl derivatives of quercetin to inhibit heat-induced HSP70 expression and enhance HSP27 phosphorylation in human cells. While quercetin and several derivatives inhibit HSP70 induction and enhance HSP27 phosphorylation at Ser78, other analogues selectively inhibit HSP70 induction without enhancing HSP27 phosphorylation that would otherwise aid in cell survival. We also show that good inhibitors of HSP70 induction are also good inhibitors of both CK2 and CamKII, kinases that are known to activate HSP70 expression by phosphorylation of heat shock transcription factor 1. Derivatives that show poor inhibition of either or both kinases are not good inhibitors of HSP70 induction, suggesting that quercetin's effectiveness is due to its ability to inhibit both kinases.

FAF-Drugs2: free ADME/tox filtering tool to assist drug discovery and chemical biology projects

BACKGROUND

Drug discovery and chemical biology are exceedingly complex and demanding enterprises. In recent years there are been increasing awareness about the importance of predicting/optimizing the absorption, distribution, metabolism, excretion and toxicity (ADMET) properties of small chemical compounds along the search process rather than at the final stages. Fast methods for evaluating ADMET properties of small molecules often involve applying a set of simple empirical rules (educated guesses) and as such, compound collections' property profiling can be performed in silico. Clearly, these rules cannot assess the full complexity of the human body but can provide valuable information and assist decision-making.

RESULTS

This paper presents FAF-Drugs2, a free adaptable tool for ADMET filtering of electronic compound collections. FAF-Drugs2 is a command line utility program (e.g., written in Python) based on the open source chemistry toolkit OpenBabel, which performs various physicochemical calculations, identifies key functional groups, some toxic and unstable molecules/functional groups. In addition to filtered collections, FAF-Drugs2 can provide, via Gnuplot, several distribution diagrams of major physicochemical properties of the screened compound libraries.

CONCLUSION

We have developed FAF-Drugs2 to facilitate compound collection preparation, prior to (or after) experimental screening or virtual screening computations. Users can select to apply various filtering thresholds and add rules as needed for a given project. As it stands, FAF-Drugs2 implements numerous filtering rules (23 physicochemical rules and 204 substructure searching rules) that can be easily tuned.

TRAIL apoptosis is enhanced by quercetin through Akt dephosphorylation

TNF-related apoptosis-inducing ligand (TRAIL) is a promising cancer therapy that preferentially induces apoptosis in cancer cells. However, many neoplasms are resistant to TRAIL by mechanisms that are poorly understood. Here we demonstrated that human prostate cancer cells, but not normal prostate cells, are dramatically sensitized to TRAIL-induced apoptosis and caspase activation by quercetin. Quercetin, a ubiquitous bioactive plant flavonoid, has been shown to inhibit the proliferation of cancer cells. We have shown that quercetin can potentiate TRAIL-induced apoptotic death. Human prostate adenocarcinoma DU-145 and LNCaP cells were treated with various concentrations of TRAIL (10-200 ng/ml) and/or quercetin (10-200 microM) for 4 h. Quercetin, which caused no cytotoxicity by itself, promoted TRAIL-induced apoptosis. The TRAIL-mediated activation of caspase, and PARP (poly(ADP-ribose) polymerase) cleavage were both enhanced by quercetin. Western blot analysis showed that combined treatment with TRAIL and quercetin did not change the levels of TRAIL receptors (death receptors DR4 and DR5, and DcR2 (decoy receptor 2)) or anti-apoptotic proteins (FLICE-inhibitory protein (FLIP), inhibitor of apoptosis (IAP), and Bcl-2). However, quercetin promoted the dephosphorylation of Akt. Quercetin-induced potent inhibition of Akt phosphorylation. Taken together, the present studies suggest that quercetin enhances TRAIL-induced cytotoxicity by activating caspases and inhibiting phosphorylation of Akt.

Red wine alcohol promotes quercetin absorption and directs its metabolism towards isorhamnetin and tamarixetin in rat intestine in vitro

Moderate consumption of red wine has been associated with beneficial effects on human health, and this has been attributed to the flavonoid content. Factors that influence the bioavailability of this group of polyphenolic compounds are therefore important. Using the rat cannulated everted jejunal sac technique, we have investigated the effect of alcohol on the intestinal absorption of quercetin and its 3-O-glucoside from red wine. Tissue preparations were incubated in whole or dealcoholised red wine, diluted 1 : 1 with Krebs buffer for 20 min at 37 degrees C, after which the mucosa was removed and processed for HPLC analysis. Tissues exposed to red wine had significantly higher amounts of both quercetin (x 3; P < 0.001) and quercetin-3-O-glucoside (x 1.5; P < 0.01) associated with them, compared with sacs incubated in the dealcoholised equivalent. In addition, both tamarixetin (T) and isorhamnetin (I), in the mucosal tissue from sacs exposed to the whole wine, were significantly elevated approximately two fold (P < 0.05; P < 0.01, respectively). Similar results were obtained when sacs were incubated in Krebs buffer containing a mixture of pure quercetin and quercetin-3-O-glucoside with or without alcohol, and, although effects on the apparent absorption of Q and Q-3-G were not so marked, concentrations of the metabolites quercetin-3-O-glucuronide and I were significantly increased by the presence of alcohol (P < 0.01 and P < 0.001, respectively). It is therefore plausible that the moderate alcohol content of red wine contributes to its beneficial health effects in humans by both increasing the absorption of quercetin and quercetin-3-O-glucoside and by channelling their metabolism towards O-methylation to yield compounds (T and I), which have potential protective effects against cancer and cardiovascular diseases.

Rat gastrointestinal tissues metabolize quercetin

Quercetin and quercetin glycosides from food or dietary supplements appear in body tissues almost exclusively as glucuronated, sulfated, and methylated quercetin conjugates, suggesting that the in vivo bioactivity of quercetin may be due to its metabolites. In this study, pre- and postabsorptive metabolism of orally ingested quercetin was examined by comparing the metabolite pattern in gastrointestinal (GI) tissues, contents, and internal tissues. F344 rats (n = 6) were fed for 6 wk a diet containing 0.45% quercetin and the metabolite patterns were determined in the tissues and contents of stomach, small intestine, cecum, and colon and in liver, kidney, and plasma using LC-MS/MS. GI contents contained predominantly unmetabolized quercetin at 94-100%, whereas quercetin in GI tissues was present as 11 different sulfated, glucuronated, and methylated metabolites at 32% in stomach, 88% in small intestine, 27% in cecum, and 46% in colon. Quercetin was further metabolized postabsorption and found in liver, kidney, and plasma almost exclusively as sulfated methyl-quercetin glucuronide. The unique pattern of quercetin metabolites in each GI tissue indicates extensive biotransformation before absorption and distribution in rats.

Modulatory effects of quercetin on proliferation and differentiation of the human colorectal cell line Caco-2

The effect of the dietary flavonoid quercetin was investigated on proliferation and differentiation of the human colon cancer cell line Caco-2. Confluent Caco-2 monolayers exposed to quercetin showed a biphasic effect on cell proliferation and a decrease in cell differentiation (0.001<P<0.05). During differentiation Caco-2 cells formed 5 phase II metabolites, of which the amount of 4'-O-methyl-quercetin-3'-O-glucuronide correlated with the differentiation grade (r=0.99, P<0.003). The increment of cell proliferation at low quercetin concentrations and the decrease in cell differentiation are effects opposite to what would be expected for a functional food ingredient with anti-carcinogenic potential.