The genotoxicity potential of luteolin is enhanced by CYP1A1 and CYP1A2 in human lymphoblastoid TK6 cells.

Luteolin (5,7,3',4'-tetrahydroxyflavone) belongs to the flavone subclass of flavonoids. Luteolin and its glycosides are present in many botanical families, including edible plants, fruits, and vegetables. While the beneficial properties of luteolin have been widely studied, fewer studies have investigated its toxicity. In the present study, using human lymphoblastoid TK6 cells and our newly developed TK6-derived cell lines that each stably express a single human cytochrome P450 (CYP1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C18, 2C9, 2C19, 2D6, 2E1, 3A4, 3A5, and 3A7), we systematically evaluated luteolin-induced cytotoxicity and genotoxicity, and the role of specific CYPs in the bioactivation of luteolin. Treatments with luteolin for 4-24 h induced cytotoxicity, apoptosis, DNA damage, and chromosome damage in a concentration-dependent manner. Subsequently, we observed that luteolin-induced cytotoxicity and genotoxicity, measured by the high-throughput micronucleus assay, were significantly increased in TK6 cells transduced with CYP1A1 and 1A2. In addition, key apoptosis and DNA damage biomarkers, including cleaved PARP-1, cleaved caspase-3, and phosphorylated histone 2AX (γH2A.X), were all significantly increased in the CYP1A1- and 1A2-expressing cells compared with the empty vector controls. Analysis by LC-MS/MS revealed that TK6 cells biotransformed the majority of luteolin into diosmetin, a less toxic O-methylated flavone, after 24 h; the presence of CYP1A1 and 1A2 partially reversed this process. Altogether, these results indicate that metabolism by CYP1A1 and 1A2 enhanced the toxicity of luteolin in vitro. Our results further support the utility of our TK6 cell system for identification of the specific CYPs responsible for chemical bioactivation and toxicity potential.

In vivo and in vitro toxicological evaluations of aqueous extract from Cecropia pachystachya leaves.

CECROPIA PACHYSTACHYA: leaves are popularly used to treat asthma and diabetes. Despite the widespread consumption of this plant, there are few scientific studies regarding its toxicological potential. In order to conduct a thorough study concerning the potential adverse effects, the aim of this study was to assess acute and subacute toxicity tests of crude aqueous extract from C. pachystachya leaves (CAE-Cp) using in vivomodel, as well as in vitro cytotoxicity, genotoxicity and antioxidant activity. In addition, genotoxicity, and cytotoxicity of chlorogenic acid (CGA) and cytotoxicity of isoorientin (ISOO) were also evaluated. The antioxidant activity was verified by DPPH, cytotoxicity using sulforhodamine B (SRB) assay and genotoxicity by comet assay on V79 cells. The phytochemical analysis of CAE-Cp detected flavonoids and tannins, CGA and ISOO as the major compounds utilizing HPLC. The total flavonoid content (6.52 mg/g EQ) and antioxidant activity (EC50 = 62.15 µg/ml) of CAE-Cp were determined. In vitro evaluations with CAE-Cp showed genotoxic effects at 0.31 to 2.5 mg/ml and an expressive cytotoxicity on HT-29 (IC50 = 4.43 µg/ml) cells. CGA was genotoxic against V79 cells at 0.07 mg/ml and cytotoxic against to HT-29 (IC50 = 71.70 µg/ml), OVCAR-3 (IC50 = 80.07 µg/ml), MCF-7 (IC50 = 45.58 µg/ml) and, NCI-H460 (IC50 = 71.89 µg/ml) cancer cell lines. Wistar rats treated with a single dose (2,000 mg/kg) CAE-Cp decreased hemoglobin levels after 14 days, although no significant toxicity was observed in animals after 28 days. In view of the in vitro cytotoxicity and genotoxicity detected, further studies are necessary to establish the safe use of CAE-Cp.

Nonhomologous end joining and homologous recombination involved in luteolin-induced DNA damage in DT40 cells.

Luteolin (3',4',5,7-tetrahydroxyflavone), a naturally occurring flavonoid, has been shown to have anticancer activity in many types of cancer cell lines. The anticancer capacity of luteolin may be related to its ability to induce DNA double-strand breaks (DSBs). Here, we used DT40 cells to determine whether nonhomologous end joining (NHEJ) and homologous recombination (HR) are involved in the repair mechanism of luteolin-induced DNA damage. Cells defective in Ku70 (an enzyme associated with NHEJ) or Rad54 (an enzyme essential for HR) were hypersensitive and presented more apoptosis in response to luteolin. Moreover, the sensitivity and apoptosis of Ku70-/- and Rad54-/- cells were associated with increased DNA damage when the numbers of γ-H2AX foci and chromosomal aberrations (CAs) were compared with those from WT cells. Additionally, after treatment with luteolin, Ku70-/- cells presented more Top2 covalent cleavage complexes (Top2cc). These results indicated that luteolin induced DSBs in DT40 cells and demonstrated that both NHEJ and HR participated in the repair of luteolin-induced DSBs, which might be related to the inhibition of topoisomerases. These results imply that simultaneous inhibition of NHEJ and HR with luteolin treatment would provide a powerful protocol in cancer chemotherapy.

Bioflavonoids cause DNA double-strand breaks and chromosomal translocations through topoisomerase II-dependent and -independent mechanisms.

Bioflavonoids have a similar chemical structure to etoposide, the well-characterized topoisomerase II (Top2) poison, and evidence shows that they also induce DNA double-strand breaks (DSBs) and promote genome rearrangements. The purpose of this study was to determine the kinetics of bioflavonoid-induced DSB appearance and repair, and their dependence on Top2. Cells were exposed to bioflavonoids individually or in combination in the presence or absence of the Top2 catalytic inhibitor dexrazoxane. The kinetics of appearance and repair of γH2AX foci were measured. In addition, the frequency of resultant MLL-AF9 breakpoint cluster region translocations was determined. Bioflavonoids readily induced the appearance of γH2AX foci, but bioflavonoid combinations did not act additively or synergistically to promote DSBs. Myricetin-induced DSBs were mostly reduced by dexrazoxane, while genistein and quercetin-induced DSBs were only partially, but significantly, reduced. By contrast, luteolin and kaempferol-induced DSBs increased with dexrazoxane pre-treatment. Sensitivity to Top2 inhibition correlated with a significant reduction of bioflavonoid-induced MLL-AF9 translocations. These data demonstrate that myricetin, genistein, and quercetin act most similar to etoposide although with varying Top2-dependence. By contrast, luteolin and kaempferol have distinct kinetics that are mostly Top2-independent. These findings have implications for understanding the mechanisms of bioflavonoid activity and the potential of individual bioflavonoids to promote chromosomal translocations. Further, they provide direct evidence that specific Top2 inhibitors or targeted drugs could be developed that possess less leukemic potential or suppress chromosomal translocations associated with therapy-related and infant leukemias.

Identification of new drug-like compounds from millets as Xanthine oxidoreductase inhibitors for treatment of Hyperuricemia: A molecular docking and simulation study.

Xanthine oxidoreductase plays an important role in formation of uric acid and its regulation during purine catabolism. Uncontrolled expression of this enzyme is responsible for overproduction and deposition of uric acid in blood that is potentially injurious because it can breakdown DNA and protein molecules, triggering many diseases. Human Xanthine oxidoreductase (HsXOR) is considered to be a pharmacological target for the treatment of hyperuricemia. Many of the HsXOR-inhibitor drugs such as Febuxostat and Allopurinol are known to have significant adverse effects. Therefore, there is an urgent need to develop new HsXOR-inhibitor drugs with less or no toxicity for the long-term treatment or prevention of hyperuricemia-related diseases. Many nutritious and medical functions have been reported in millets. Present work deals with identification of millet derived compounds in terms of their interaction with target, HsXOR through molecular docking and dynamic simulation studies. Of thirty two chosen compounds, Luteolin and Quercitin showed more binding affinity with HsXOR than reference drugs, Febuxostat and Allopurinol. Molecular dynamics simulations (20 ns long) revealed that Luteolin-protein complex was energetically more stable than Quercitin-protein complex. The millet derived compounds i.e. Luteolin and Quercitin showed binding energy -9.7 kcal/mol whereas the known drugs i.e. Febuxostat and Allopurinol showed binding energy -8.0 kcal/mol and -5.5 kcal/mol respectively. Based on the study, Luteolin possess high potential to be considered for trial as an inhibitor of HsXOR as it may regulate the pathway by inhibiting HsXOR. Further investigations are proposed to consider Luteolin for developing future drugs from millets and other natural sources.

Correlation of binding efficacies of DNA to flavonoids and their induced cellular damage.

Flavonoids are dietary intakes which are bestowed with several health benefits. The most studied property of flavonoids is their antioxidant efficacy. Among the chosen flavonoids Quercetin, Kaempferol and Myricetin is catagorized as flavonols whereas Apigenin and Luteolin belong to the flavone group. In the present study anti-cancer properties of flavonoids are investigated on the basis of their binding efficacy to ct-DNA and their ability to induce cytotoxicity in K562 leukaemic cells. The binding affinities of the flavonoids with calf thymus DNA (ct-DNA) are in the order Quercetin>Myricetin>Luteolin>Kaempferol>Apigenin. Quercetin with fewer OH than myricetin has higher affinity towards DNA suggesting that the number and position of OH influence the binding efficacies of flavonoids to ct-DNA. CD spectra and EtBr displacement studies evidence myricetin and apigenin to be stronger intercalators of DNA compared to quercetin. From comet assay results it is observed that quercetin and myricetin when used in combination induce higher DNA damage in K562 leukemic cells than when tested individually. Higher binding efficacy has been recorded for quercetin to DNA at lower pH, which is the micro environment of cancerous cells, and hence quercetin can act as a potential anti-cancer agent. Presence of Cu also increases cellular damage as recorded by comet assay.

Cytotoxicity of luteolin in primary rat hepatocytes: the role of CYP3A-mediated ortho-benzoquinone metabolite formation and glutathione depletion.

Luteolin (LUT), an active ingredient in traditional Chinese medicines and an integral part of the human diet, has shown promising pharmacological activities with a great potential for clinical use. The purpose of this study was to evaluate the role of cytochrome P450 (CYP450)-mediated reactive ortho-benzoquinone metabolites formation and glutathione (GSH) depletion in LUT-induced cytotoxicity in primary rat hepatocytes. A reactive ortho-benzoquinone metabolite was identified by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) in rat liver microsomes (RLMs) and rat hepatocytes. Using a specific chemical inhibitor method, the CYP3A subfamily was found to be responsible for the reactive metabolite formation in RLMs. Induction of CYP3A by dexamethasone enhanced LUT-induced cytotoxicity, whereas inhibition of CYP3A by ketoconazole (Keto) decreased the cytotoxicity. The cytotoxicity and cell apoptosis induced by LUT were related to the amount of reactive metabolite formation. Furthermore, Keto inhibited the LUT-induced GSH exhaustion. The cytotoxicity was significantly enhanced by pretreatment with L-buthionine sulfoximine to deplete the intracellular GSH. A time course experiment showed that GSH depletion by LUT was not via oxidation of GSH and occurred prior to the increase in 2', 7'-dichlorofluorescein in hepatocytes. Collectively, these data suggest that CYP3A-mediated reactive metabolite formation plays a critical role in LUT-induced hepatotoxicity, and the direct GSH depletion is an initiating event in LUT-mediated cytotoxicity in primary rat hepatocytes.

Rooibos flavonoids, orientin and luteolin, stimulate mineralization in human osteoblasts through the Wnt pathway.

SCOPE: Several epidemiological studies have shown that tea consumption is associated with higher bone mineral density in women. Flavonoids in tea are recognized as potential estrogen mimics and may positively influence bone metabolism in estrogen-deficient women. Luteolin and orientin, flavonoids from rooibos tea, are of particular interest as rooibos tea contains no caffeine that can be detrimental to bone health. This study analyzed changes in mineral content when luteolin or orientin was added to a human osteoblast cell line and the potential mechanisms involved. Measurements included alkaline phosphatase (ALP) activity, cell mitochondrial activity, toxicity, and changes in regulatory proteins involved in osteoblast metabolism. METHODS AND RESULTS: Mineral was significantly elevated in Saos2 cells treated with orientin (0.1-1.0 µM, 15-100 µM) or luteolin (5.0 µM) and was associated with increased ALP and mitochondrial activity, as determined by the production of p-nitrophenol and the reduction of 2-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, respectively. Greater mineral content was also associated with lower toxicity as determined by lactate dehydrogenase activity and lower expression of TNF-α, IL-6, sclerostin, osteopontin, and osteoprotegerin. CONCLUSION: Orientin and luteolin, flavonoids in rooibos tea, enhance mineral content in Saos2 cells. These findings provide guidance for doses to be studied in well-established animal models.

Simultaneous separation of apigenin, luteolin and rosmarinic acid from the aerial parts of the copper-tolerant plant Elsholtzia splendens.

Elsholtzia splendens is a copper-tolerant plant species which grows on copper deposits in China. The generation of a valuable E. splendens biomass on specific contaminated sites has become one of the promising phytotechnologies. The simultaneous separations of apigenin, luteolin, and rosmarinic acid yielded in the ethyl acetate extracts of the flowering aerial parts was achieved by the use of a macroporous resin, polyamide, and silicagel columns during chromatography. Chemical identification confirmed the structures based on the spectra of FTIR, NMR, and HPLC/ESI-MS. The isolated compounds of purity above 98.3% were evaluated for their in vitro cytotoxic activities against human cancer cell lines including A549 (non-small lung), A431 (skin), and Bcap37 (breast). Among these compounds, luteolin and apigenin presented the best cytotoxic activities against A549, A431, and Bcap37 cells and, therefore, both could be the valuable products for the post-harvest processing of E. splendens biomass.

Flavonoids as receptor tyrosine kinase FLT3 inhibitors.

The Fms-like tyrosine kinase 3 (FLT3), a receptor tyrosine kinase, is involved in the proliferation, differentiation and apoptosis of hematopoietic cells. FLT3 is highly overexpressed in acute myeloid leukemia (AML) of the majority of patients. Screening for flavonoids including flavones, flavanones, flavonols, and flavanonols disclosed that luteolin was potent FLT3 enzyme inhibitor. Furthermore, luteolin suppressed cell proliferation in MV4;11 cells with constitutively activated FLT3.

Isoorientin induces apoptosis through mitochondrial dysfunction and inhibition of PI3K/Akt signaling pathway in HepG2 cancer cells.

Isoorientin (ISO) is a flavonoid compound that can be extracted from several plant species, such as Phyllostachys pubescens, Patrinia, and Drosophyllum lusitanicum; however, its biological activity remains poorly understood. The present study investigated the effects and putative mechanism of apoptosis induced by ISO in human hepatoblastoma cancer (HepG2) cells. The results showed that ISO induced cell death in a dose-dependent manner in HepG2 cells, but no toxicity in human liver cells (HL-7702) and buffalo rat liver cells (BRL-3A) treated with ISO at the indicated concentrations. ISO-induced cell death included apoptosis which characterized by the appearance of nuclear shrinkage, the cleavage of poly (ADP-ribose) polymerase (PARP) and DNA fragmentation. ISO significantly (p<0.01) increased the Bax/Bcl-2 ratio, disrupted the mitochondrial membrane potential (MMP), increased the release of cytochrome c, activated caspase-3, and enhanced intracellular levels of reactive oxygen species (ROS) and nitric oxide (NO). In addition, ISO effectively inhibited the phosphorylation of Akt and increased FoxO4 expression. The PI3K/Akt inhibitor LY294002 enhanced the apoptosis-inducing effect of ISO. However, LY294002 markedly quenched ROS and NO generation and diminished the protein expression of heme peroxidase enzyme (HO-1) and inducible nitric oxide synthase (iNOS). Furthermore, the addition of a ROS inhibitor (N-acetyl cysteine, NAC) or iNOS inhibitor (N-[3-(aminomethyl) benzyl] acetamidine, dihydrochloride, 1400W) significantly diminished the apoptosis induced by ISO and also blocked the phosphorylation of Akt. These results demonstrated for the first time that ISO induces apoptosis in HepG2 cells and indicate that this apoptosis might be mediated through mitochondrial dysfunction and PI3K/Akt signaling pathway, and has no toxicity in normal liver cells, suggesting that ISO may have good potential as a therapeutic and chemopreventive agent for liver cancer.

A superoxide-mediated mitogen-activated protein kinase phosphatase-1 degradation and c-Jun NH(2)-terminal kinase activation pathway for luteolin-induced lung cancer cytotoxicity.

Although luteolin is identified as a potential cancer therapeutic and preventive agent because of its potent cancer cell-killing activity, the molecular mechanisms by which its cancer cell cytotoxicity is achieved have not been well elucidated. In this report, luteolin-induced cellular signaling was systematically investigated, and a novel pathway for luteolin's lung cancer killing was identified. The results show that induction of superoxide is an early and crucial step for luteolin-induced apoptotic and nonapoptotic death in lung cancer cells. The c-Jun N-terminal kinase (JNK) was potently activated after superoxide accumulation. Suppression of superoxide completely blocked luteolin-induced JNK activation, which was well correlated to alleviation of luteolin's cytotoxicity. Although luteolin slightly stimulated the JNK-activating kinase mitogen-activated protein kinase kinase 7, the latter was not dependent on superoxide. We further found that luteolin triggers a superoxide-dependent rapid degradation of the JNK-inactivating phosphatase mitogen-activated protein kinase phosphatase-1 (MKP-1). Introduction of a degradation-resistant MKP-1 mutant effectively attenuated luteolin-induced JNK activation and cytotoxicity, suggesting that inhibition of the JNK suppressor MKP-1 plays a major role in luteolin-induced lung cancer cell death. Taken together, our results unveil a novel pathway consisting of superoxide, MKP-1, and JNK for luteolin's cytotoxicity in lung cancer cells, and manipulation of this pathway could be a useful approach for applying luteolin for lung cancer prevention and therapy.

Protective effect of quercetin and luteolin in human melanoma HMB-2 cells.

Multifunctional effects of flavonoids are reported to be markedly connected with their structure and the functional groups in the molecule. The important role in the activity play C2-C3 double bond, hydroxyl group at C3 and the number of hydroxyl groups at phenyl ring (B). In this paper, the DNA protective free radical scavenging potential of quercetin (QU) and luteolin (LU) against H2O2 and their clastogenic effect alone and in combination with melphalan (MH) were investigated in human melanoma HMB-2 cells. Elevated frequency of chromosomal aberrations induced by MH, that at high doses have shown a variety of toxic side effects, was statistically decreased by studied flavonoids regarding to control (QU at the concentration of 50 microM and LU already at the concentration of 20 microM). The results concerning DNA protective potential against free radicals in HMB-2 cells demonstrated that QU and LU have significant effect in dose dependent manner. The percentage of QU protective effect is 40% at the concentration 20 microM, resp. 80% at the concentration 100 microM. Comparable values were obtained with LU. Results are correlated to their structural arrangement and organization of the hydroxyl groups.

Hypoglycaemic activity of Gentiana olivieri and isolation of the active constituent through bioassay-directed fractionation techniques.

Hypoglycemic effect of Gentiana olivieri Griseb. (Gentianaceae) flowering herbs on oral administration were studied using in vivo models in normal, glucose-hyperglycemic and streptozotocin-induced diabetic rats. Through in vivo bioassay-guided fractionation processes isoorientin, a known C-glycosylflavone, was isolated from the ethylacetate fraction by silica gel column chromatography as the main active ingredient from the plant. Isoorientin exhibited significant hypoglycemic and antihyperlipidemic effects at 15 mg/kg b.w.dose. Isoorientin concentration of the extracts and fractions were determined by HPLC in order to establish a correlation between the hypoglycaemic activity.

Pro-apoptotic effects of the flavonoid luteolin in rat H4IIE cells.

Polyphenols are ubiquitous substances in the diet. Their anti-oxidative, anti-inflammatory and anti-viral effects are of interest for human health, and polyphenols such as luteolin are used at high concentrations in food supplements. The aim of this project was to determine the intrinsic effects of luteolin in H4IIE rat hepatoma cells. Luteolin is relatively toxic, cell death was caused via induction of apoptosis as detected by DNA-ladder formation, by nuclear fragmentation and activation of apoptotic enzymes (caspase-2, -3/7, -9 and -8/10). Luteolin (250 microM, 24 h) increased the caspase-3/7 activity four-fold and the caspase-9 activity six-fold. In a time course experiment caspase-9 is activated after 6h, while caspase-2 and -3/7 are activated after 12 h. After 24 h, caspase-8/10 also displays activation. We found a concentration-dependent increase in malondialdehyde release suggesting a prooxidative effect of luteolin. Furthermore, we analysed DNA strand break formation by luteolin and found a distinct increase of DNA strand breaks after incubation for 3h with 100 microM luteolin, a concentration which induces oligonucleosomal DNA cleavage at 24h. In conclusion, the sequence of events is compatible with the assumption that luteolin triggers the mitochondrial pathway of apoptosis, probably by inducing DNA damage.