title: Induction of apoptosis in human leukemia cells through the production of reactive oxygen species and activation of HMOX1 and Noxa by benzene, toluene, and o-xylene.
abstract: Whereas benzene (BZ) is a well-known human carcinogen, toluene (TOL) and o-xylene (o-XY) are not; however, all three compounds are important environmental pollutants. Although BZ, TOL, and o-XY have been shown to induce apoptosis in vitro, their mechanism of toxicity remains unclear. In this study, we sought to identify the apoptotic pathway(s) activated by BZ, TOL, and o-XY in human HL-60 promyelocytic leukemia cells. Cell cycle analysis by propidium iodide (PI) staining and flow cytometric analyses of Annexin V/PI double-stained cells revealed similar patterns of apoptosis following BZ, TOL, and o-XY exposure. Though reactive oxygen species (ROS) production contributes significantly to BZ metabolite-induced apoptotic cell death, we hypothesized that BZ, TOL, and o-XY can themselves trigger ROS production, leading to the activation of apoptotic signaling. Dose-dependent increases in ROS production and significant tail moments were observed in HL-60 cells exposed to all three compounds. Real-time RT-PCR revealed increased HMOX1 and Noxa expression in BZ-, TOL-, and o-XY-treated HL-60 cells, confirming the results of previous microarray analyses. Similar expression profiles were found in human K562 erythromyeloblastoid leukemia cells and human U937 leukemic monocyte lymphoma cells. Pretreatment with the ROS scavenger N-acetyl cysteine decreased the effects of exposure to BZ, TOL, and o-XY. In summary, this study provides useful insights into the mechanism of BZ-, TOL-, and o-XY-induced apoptosis in leukemia cells.
authors.affiliation: Cellular and Molecular Toxicology Laboratory, Korea Institute of Science & Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Republic of Korea. sarma@kist.re.kr
authors.forename: Sailendra Nath
authors.initials: SN
authors.lastname: Sarma
authors.forename: Youn-Jung
authors.initials: YJ
authors.lastname: Kim
authors.forename: Mee
authors.initials: M
authors.lastname: Song
authors.forename: Jae-Chun
authors.initials: JC
authors.lastname: Ryu
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology*; D001554:Benzene / Q000633:toxicity*; D018922:HL-60 Cells; D051547:Heme Oxygenase-1 / Q000378:metabolism* / Q000633:toxicity; D006801:Humans; D020014:K562 Cells; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism* / Q000633:toxicity; D017382:Reactive Oxygen Species / Q000378:metabolism* / Q000633:toxicity; D014050:Toluene / Q000633:toxicity*; D020298:U937 Cells; D014992:Xylenes / Q000633:toxicity*
chemical_list: C498702:PMAIP1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D014992:Xylenes; D014050:Toluene; C496541:HMOX1 protein, human; D051547:Heme Oxygenase-1; D001554:Benzene; C026114:2-xylene