title: Enhancement of hyperthermia-induced apoptosis by a free radical initiator, 2,2'-azobis (2-amidinopropane) dihydrochloride, in human histiocytic lymphoma U937 cells.
abstract: To elucidate the mechanism how a free radical initiator, 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH), induces cell death at hyperthermic temperatures, apoptosis in a human histiocytic lymphoma cell line, U937, was investigated. Free radical formation deriving from the thermal decomposition of AAPH was examined by spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). An assay for DNA fragmentation, observation of nuclear morphological changes, and flow cytometry for phosphatidylserine (PS) externalization were used to detect apoptosis and revealed enhancement of 44.0 degrees C hyperthermia-induced apoptosis by free radicals due to AAPH. However, free radicals alone derived from AAPH did not induce apoptosis. Hyperthermia induced the production of lipid peroxidation (LPO), an increase in intracellular Ca2+ concentration ([Ca2+]i) and enhanced expression of the type 1 inositol 1,4,5-trisphosphate receptor (IP3R1). The effects of hyperthermia on LPO and [Ca2+]i were enhanced markedly by the combination with AAPH. A significant decrease in Bcl-2 expression, increase in Bax expression, a loss of mitochondrial membrane potential (delta psi m) and a marked increase in cytochrome c expression were found only in cells treated with hyperthermia and AAPH. Although an intracellular Ca2+ ion chelator, BAPTA-AM, completely inhibited DNA fragmentation, water-soluble vitamin E, Trolox, only partially suppressed DNA fragmentation and the increase in [Ca2+]i. In contrast, LPO was inhibited completely by Trolox, but no inhibition by BAPTA-AM was found. These results suggest that apoptosis induced by hyperthermia alone is due to the increase in [Ca2+]i arising from increased expression of IP3R1 and LPO. Additional increase in [Ca2+]i due to increased LPO and the activation of mitochondria-caspase dependent pathway play a major role in the enhancement of apoptosis by the combination with hyperthermia and AAPH.
authors.affiliation: Department of Radiological Sciences, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Toyama, 930-0194, Japan.
authors.forename: F J
authors.initials: FJ
authors.lastname: Li
authors.forename: T
authors.initials: T
authors.lastname: Kondo
authors.forename: Q L
authors.initials: QL
authors.lastname: Zhao
authors.forename: K
authors.initials: K
authors.lastname: Tanabe
authors.forename: R
authors.initials: R
authors.lastname: Ogawa
authors.forename: M
authors.initials: M
authors.lastname: Li
authors.forename: Y
authors.initials: Y
authors.lastname: Arai
mesh_terms: D000578:Amidines / Q000494:pharmacology*; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D053148:Caspase 3; D061945:Caspase Inhibitors; D002455:Cell Division / Q000187:drug effects; D002614:Chelating Agents / Q000494:pharmacology; D002839:Chromans / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D005609:Free Radicals / Q000378:metabolism; D006358:Hot Temperature; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors; D015227:Lipid Peroxidation / Q000528:radiation effects*; D008564:Membrane Potentials; D009842:Oligopeptides / Q000494:pharmacology; D016877:Oxidants / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D020298:U937 Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D051028:bcl-2-Associated X Protein
chemical_list: D000578:Amidines; D000975:Antioxidants; C494826:BAX protein, human; D015220:Calcium Channels; D061945:Caspase Inhibitors; D002614:Chelating Agents; D002839:Chromans; D015853:Cysteine Proteinase Inhibitors; D003574:Cytochrome c Group; D005609:Free Radicals; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D009842:Oligopeptides; D016877:Oxidants; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D018160:Receptors, Cytoplasmic and Nuclear; D051028:bcl-2-Associated X Protein; C110772:benzoylcarbonyl-aspartyl-glutamyl-valyl-aspartyl-fluoromethyl ketone; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; C046728:2,2'-azobis(2-amidinopropane); C505407:CASP3 protein, human; D053148:Caspase 3; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid; D002118:Calcium