Bleomycin-induced unscheduled DNA synthesis in non-permeabilized human and rat hepatocytes is not paralleled by 8-oxo-7,8-dihydrodeoxyguanosine formation.
The genetic toxicity of the antitumour antibiotic bleomycin (BLM) is thought to involve the formation of a reactive oxygen intermediate. 8-Oxo-7,8-dihydrodeoxyguanosine (oxo8dG), an oxidation product of deoxyguanosine, is one of the major products formed when isolated DNA is exposed to oxygen radical generating systems. Gamma-irradiation (10-500 Gy 60Co; 10 Gy/min) or BLM and Fe2+ (37.5-150 U/L and 0.5 mM, respectively) treatment of isolated DNA (0.25 mg/mL) increased oxo8dG above background. In the latter case, the effect was greater than that with Fe2+ (0.5 mM) alone and was dependent on the dose of BLM. When DNA was irradiated with 500 Gy60Co, deoxyguanosine oxidation was inhibited by antioxidants (ethanol: 37.5 and 98% inhibition at 2 and 20 mM, respectively; mannitol: 20.5, 60 and 92% inhibition at 0.1, 1.0 and 10 mM, respectively). Similarly the BLM-induced production of oxo8dG was inhibited (64%) by mannitol (10 mM). BLM also caused production of base propenals on interaction with isolated DNA. In contrast, oxo8dG was not induced above background concentration (27 mol oxo8dG/10(6) mol dG) in permeabilized (37 degrees) and non-permeabilized (4 degrees and 37 degrees) rat hepatocytes treated with BLM (260 U/L). Despite this, there was extensive BLM-induced unscheduled DNA synthesis (10 and 100 U/L) in non-permeabilized rat and human hepatocytes in the absence of hydroxyurea. These findings, in accord with other observations, draw into question the role of .OH in BLM-induced DNA damage and the mimicry of ionizing radiation in cellular systems.
Winyard
P G
PG
Inflammation Research Group, London Hospital Medical College, U.K.
Faux
S P
SP
Smith
A J
AJ
Davies
J E
JE
Chipman
J K
JK
D000080242:8-Hydroxy-2'-Deoxyguanosine; D000818:Animals; D001761:Bleomycin / Q000494:pharmacology*; D004247:DNA / Q000096:biosynthesis* / Q000302:isolation & purification / Q000528:radiation effects; D004249:DNA Damage; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000032:analysis / Q000096:biosynthesis; D006801:Humans; D006878:Hydroxides / Q000032:analysis; D017665:Hydroxyl Radical; D008099:Liver / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008315:Malondialdehyde / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar
D006878:Hydroxides; D001761:Bleomycin; D017665:Hydroxyl Radical; D008315:Malondialdehyde; D000080242:8-Hydroxy-2'-Deoxyguanosine; D004247:DNA; D003849:Deoxyguanosine