POLY(ADENOSINE DIPHOSPHATE RIBOSE) POLYMERASE INHIBITION PREVENTS NECROSIS INDUCED BY H2O2 BUT NOT APOPTOSIS

Background and Aims: H2O2 causes DNA damage, which activates poly(aden osine diphosphate ribose) polymerase (PARP), a nuclear enzyme that use s nicotinamide adenine dinucleotide (NAD) as a substrate. When DNA str and breaks are extensive, consumption of NAD by PARP can cause adenosi ne triphosphate depletion. The aim was to study the effect of PARP inh ibition on H2O2 induced cell injury in the intestinal epithelial cell line HT-29-18-C1. Methods: Cell injury was assessed by the 3-(4,5-dime thylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide test and flow cytom etric analysis. Results: The PARP inhibitors 3-aminobenzamide and nico tinamide both prevented cell death immediately after exposure to 1 mmo l/L H2O2 and loss of cellular NAD and adenosine triphosphate. The inac tive structural analogues 3-aminobenzoic acid and nicotinic acid had n o such protective effect. H2O2 also caused HT-29 cells to detach from the monolayer up to 24 hours after exposure and die by apoptosis in th e incubating medium. Flow cytometric analysis showed that 3-aminobenza mide had no effect on this delayed detachment process. Conclusions: H2 O2 induces two distinct death pathways in HT-29 cells: one that is imm ediate and may represent necrosis and another that is delayed, causing cell detachment leading to apoptosis. PARP inhibition prevents necros is but has no effect on delayed cell detachment leading to apoptosis.