Evaluation of the clastogenic, DNA intercalative, and topoisomerase II-interactive properties of bioflavonoids in Chinese hamster V79 cells

Induction apoptosis of luteolin in human hepatoma HepG2 cells involving mitochondria translocation of Bax/Bak and activation of JNK

Since hepatocellular carcinoma remains a major challenging clinical problem in many parts of the world including Eastern Asia and Southern Africa, it is imperative to develop more effective chemopreventive and chemotherapy agents. Herein, we present an investigation regarding the anticancer potential of luteolin, a natural flavonoid, and the mechanism of its action in human hepatoma HepG2 cells. Using DNA fragmentation assay and nuclear staining assay, it showed that luteolin induced apoptosis of HepG2 cells. Luteolin induced the cytosolic release of cytochrome c and activated CPP32. We found that Bax and Bak translocated to mitochondria apparently, whereas Fas ligand (FasL) was unchanged after a treatment with luteolin for 3 h. In addition, it showed that c-Jun NH2-terminal kinase (JNK) was activated after the treatment of luteolin for 3-12 h. Further investigation showed that a specific JNK inhibitor, SP600125, reduced the activation of CPP 32, the mitochondrial translocation of Bax, as well as the cytosolic release of cytochrome c that induced by luteolin. Finally, the apoptosis induced by luteolin was suppressed by a pretreatment with SP600125 via evaluating annexin V-FITC binding assay. These data suggest that luteolin induced apoptosis via mechanisms involving mitochondria translocation of Bax/Bak and activation of JNK.

DNA damage-induced activation of ATM and ATM-dependent signaling pathways

Ataxia-telangiectasia mutated (ATM) plays a key role in regulating the cellular response to ionizing radiation. Activation of ATM results in phosphorylation of many downstream targets that modulate numerous damage response pathways, most notably cell cycle checkpoints. In this review, we describe recent developments in our understanding of the mechanism of activation of ATM and its downstream signaling pathways, and explore whether DNA double-strand breaks are the sole activators of ATM and ATM-dependent signaling pathways.

Risks and safety of polyphenol consumption

This article gives an overview of the potential hazards of polyphenol consumption, as reported during the round-table discussion at the 1st International Conference on Polyphenols and Health, held in Vichy, France, November 2003. Adverse effects of polyphenols have been evaluated primarily in experimental studies. It is known, for example, that certain polyphenols may have carcinogenic/genotoxic effects or may interfere with thyroid hormone biosynthesis. Isoflavones are of particular interest because of their estrogenic activity, for which beneficial as well as detrimental effects have been observed. Furthermore, consumption of polyphenols inhibits nonheme iron absorption and may lead to iron depletion in populations with marginal iron stores. Finally, polyphenols may interact with certain pharmaceutical agents and enhance their biologic effects. It is important to consider the doses at which these effects occur, in relation to the concentrations that naturally occur in the human body. Future studies evaluating either beneficial or adverse effects should therefore include relevant forms and doses of polyphenols and, before the development of fortified foods or supplements with pharmacologic doses, safety assessments of the applied doses should be performed.

Antigenotoxic and antioxidant effect of grapefruit juice in mice treated with daunorubicin

Grapefruit juice (GJ) is widely consumed in many countries. Several of its constituents possess nutritive value, as well as antigenotoxic and antioxidant effects. Therefore, the aim of this investigation was to evaluate the capacity of GJ to inhibit the micronucleated polychromatic erythrocytes (MNPE) produced by daunorubicin (Dau) in an acute assay in mice, as well as to determine its antioxidant potential in mouse hepatic microsomes, and its capacity to trap free radicals in vitro. In regard to the first point, GJ produced no toxic or genotoxic damage; on the contrary, it generated a significant reduction of the MNPE formed by Dau. The effect was found throughout the examined schedule (from 24 to 96 h). The two high doses produced inhibition of about 60% at 48 h, 86% at 72 h and 100% at 96 h after the treatment. With respect to the GJ antioxidant potential, a 50% decrease in liver microsomal lipid peroxidation produced by Dau was found by quantifying malondialdehyde formation. Finally, a strong GJ scavenging activity evaluated with the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) was observed, giving rise to a concentration-dependent curve with a correlation coefficient of 0.98. Overall, our results established an efficient anticlastogenic potential of GJ, probably related to its antioxidant capacity, or to alterations of Dau metabolism, suggesting the pertinence of extending research on the matter using other mutagens and biological models.

The Molecular Basis of Leukemia

Major strides have been made in our understanding of the molecular basis of adult and pediatric leukemias. More than one hundred disease alleles have been identified and characterized in cell culture and murine models of leukemia. In some instances, molecularly targeted therapies have been developed based on these insights that are currently in clinical trials, such as small molecule inhibitors of FLT3. In addition, it has recently been appreciated that, as with normal hematopoiesis, there is a hierarchical organization among leukemic cells that includes a rare population of leukemic stem cells that have properties of self-renewal. Understanding the characteristics of these leukemic stem cells may provide new insights into leukemia therapies that target self-renewal pathways.

In Section I, Dr. Craig Jordan reviews the data that supports the existence of a “leukemia stem cell.” He provides an overview of the functional properties of leukemic stem cells, their relationship to hematopoietic stem cells, and the relevance of leukemic stem cells in other human malignancies including solid tumors. He briefly discusses what is known of the pathways that regulate properties of self-renewal.

Dr. Gary Gilliland provides an overview of the genetics of adult leukemias in Section II and ongoing genome-wide strategies for discovery of new disease alleles. He describes the clinical and therapeutic implications of these findings and provides examples of bench-to-bedside translation of molecularly targeted therapies for AML, including the use of FLT3 inhibitors.

In Section III, Dr. Carolyn Felix reviews recent advances in our understanding of the genetics and therapy of pediatric leukemias. She provides an overview of leukemias that are common in pediatric malignancies but rarely observed in adults, including the TEL-AML1 (ETV6-RUNX1) fusion associated with pediatric B-cell ALL, the OTT-MAL fusion associated with infant megakaryoblastic leukemia, PTPN11 mutations in juvenile myelomonocytic leukemia, and MLL fusion genes in leukemogenesis, among others.

Evaluation of DNA intercalation potential of pharmaceuticals and other chemicals by cell-based and three-dimensional computational approaches

To what extent noncovalent chemical-DNA interactions, in particular weak nonbonded DNA intercalation, contribute to genotoxic responses in mammalian cells has not been fully elucidated. Moreover, with the exception of predominantly flat, multiple-fused-ring structures, our ability to predict intercalation ability of novel compounds is nearly completely lacking. Computational programs such as DEREK and MCASE recognize primarily those molecules that can form irreversible covalent adducts with DNA since their learning sets, for the most part, have not been populated by compounds for which a relationship between noncovalent interaction and genotoxicity exists. We describe here a novel three-dimensional (3D) computational DNA-docking model for prediction of DNA intercalative activity of molecules with both classical and nonclassical intercalating structures. The 3D docking results show a remarkable concordance with results obtained from testing these molecules directly in the Chinese hamster V79 cell-based bleomycin amplification system suggesting that either or both of these approaches may have utility in defining noncovalent chemical-DNA interactions. The ability to predict and/or demonstrate cellular DNA intercalation of novel molecules may well provide fresh insights into the nature and mechanistic basis of structurally unexpected genotoxicity observed during safety testing.

Reduction of genistein clastogenicity in Chinese hamster V79 cells by daidzein and other flavonoids

A broad spectrum of health benefits has been ascribed to soy products. These products contain soy protein and relatively high levels of polyphenolic compounds known as flavonoids. While they are the most likely candidates for biological activity, flavonoids as a class, and of specific interest, genistein, are well known to be genotoxic due to their ability to "poison" cellular DNA topoisomerase II (topo II) resulting in stable chromosome breakage and mutation and raising questions about the long term health effects associated with chronic flavonoid exposure. Interestingly, some flavonoids, such as biochanin, galangin and daidzein, are catalytic topo II inhibitors (not poisons) and actually antagonize the clastogenicity of topo II poisons. It is shown in the present paper that flavonoids possessing catalytic topo II inhibitory activity, strongly antagonize the clastogenicity of genistein in Chinese hamster V79 cells. Importantly, one of these, daidzein, is a major constituent of marketed soy products. It is conjectured that the potential human clastogenic risk of soy products containing genistein might be mitigated or abolished due to the presence of daidzein or other flavonoids in those products.