3-4-dihydro-5-(4-(1-piperidinyl)butoxy)-1(2h)-isoquinolinone and Necrosis

Overactivation of the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) plays a key role in the mechanisms responsible for neuronal death. In the present study, we examined the effects of the PARP-1 inhibitor 3,4-dihydro-5-[4-1(1-piperidinyl)buthoxy]-1(2H)-isoquinolinone (DPQ) in two models of N-methyl-d-aspartate (NMDA)-induced neurotoxicity. The exposure of mixed cultured cortical cells to 300 microM NMDA for 10 min induced a caspase-dependent type of apoptotic neuronal death. Conversely, exposure to 2 mM NMDA for 10 min led to the appearance of morphological features of necrosis, with no increase in caspase-3 activity and depletion in adenosine triphosphate (ATP) levels. DPQ (10 microM) reduced the NMDA-induced PARP activation, restored ATP to near control levels and significantly attenuated neuronal injury only in the severe NMDA exposure model. Similar results were obtained when pure neuronal cortical cultures were used. PARP-1 activation thus appears to play a preferential role in necrotic than in caspase-dependent apoptotic neuronal death.

Topics: Adenosine Triphosphate; Animals; Apoptosis; Caspase 3; Caspases; Cells, Cultured; Cerebral Cortex; Coculture Techniques; Dose-Response Relationship, Drug; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Isoquinolines; Mice; Models, Biological; N-Methylaspartate; Necrosis; Neurons; Neurotoxins; Piperidines; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases

An excessive activation of poly(ADP-ribose) polymerase (PARP) has been proposed to play a key role in post-ischemic neuronal death. We examined the neuroprotective effects of the PARP inhibitors benzamide, 6(5H)-phenanthridinone, and 3,4-dihydro-5-[4-1(1-piperidinyl)buthoxy]-1(2H)-isoquinolinone in three rodent models of cerebral ischemia. Increasing concentrations of the three PARP inhibitors attenuated neuronal injury induced by 60 min oxygen-glucose deprivation (OGD) in mixed cortical cell cultures, but were unable to reduce CA1 pyramidal cell loss in organotypic hippocampal slices exposed to 30 min OGD or in gerbils following 5 min bilateral carotid occlusion. We then examined the necrotic and apoptotic features of OGD-induced neurodegeneration in cortical cells and hippocampal slices using biochemical and morphological approaches. Cortical cells exposed to OGD released lactate dehydrogenase into the medium and displayed ultrastructural features of necrotic cell death, whereas no caspase-3 activation nor morphological characteristics of apoptosis were observed at any time point after OGD. In contrast, a marked increase in caspase-3 activity was observed in organotypic hippocampal slices after OGD, together with fluorescence and electron microscope evidence of apoptotic neuronal death in the CA1 subregion. Moreover, the caspase inhibitor Z-VAD-FMK reduced OGD-induced CA1 pyramidal cell loss. These findings suggest that PARP overactivation may be an important mechanism leading to post-ischemic neurodegeneration of the necrotic but not of the apoptotic type.

Topics: Animals; Apoptosis; Benzamides; Brain Ischemia; Caspase 3; Caspases; Cell Death; Cell Line; Cerebral Cortex; Enzyme Inhibitors; Gerbillinae; In Vitro Techniques; Isoquinolines; Microscopy, Electron; Microscopy, Fluorescence; Necrosis; Neurons; Neuroprotective Agents; Phenanthrenes; Piperidines; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases; Pyramidal Cells; Rats; Rats, Wistar