Journal
FREE RADICAL RESEARCH
Volume 35, Issue 3, Pages 281-299Publisher
HARWOOD ACAD PUBL GMBH
DOI: 10.1080/10715760100300821
Keywords
apoptosis; 2,2 '-azobis (2-amidinopropane) dihydrochloride; hyperthermia; lipid peroxidation; mitochondrial membrane potential; inositol 1,4,5-trisphosphate receptor; intracellular Ca2+
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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 degreesC 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 (IP(3)R1). 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 Psim) 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 vitamine 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 IP(3)R1 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.
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