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Under several pathological conditions, reactive oxygen species-induced damages play important roles in pathogenesis (1-3). High levels of reactive oxygen species are generated from a variety of sources such as the xanthine oxidase system (1), the leakage of electrons from the mitochondrial respiratory chain (2, 4), the cyclooxygenase pathway of arachidonic acid metabolism (3,5), and the respiratory burst of phagocyte cells (6, 7), and they can cause DNA damage-generating singlestranded DNA breaks (8). Poly(ADP-ribose)polymerase (PARP-1, 2 EC 2.4.2.30) is a multifunctional nuclear enzyme (9) that is activated by DNA strand breaks and catalyzes the covalent coupling of branched chains of ADP-ribose units to various nuclear proteins such as histone proteins and PARP-1 itself. PARP-1 is involved in chromatin remodeling, DNA repair, replication, transcription, and the maintenance of genomic stability by, in part, poly(ADP-ribosyl)ation (9). With moderate amounts of DNA damage, PARP-1 is thought to participate in the DNA repair process (10, 11). However, oxidative stress, which induces a large amount of DNA damage, can cause excessive activation of PARP-1, leading to depletion of its substrate NAD ϩ ; and in an effort to resynthesize NAD ϩ , ATP is also depleted, resulting in cell death as a consequence of energy loss (12-15). PARP inhibitors show pronounced protection against myocardial ischemia (16), neuronal ischemia (17, 18), acute lung inflammation (19), acute septic shock (20), zymogen-induced multiple organ failure (21), and diabetic pancreatic damage (22-24), providing evidence for the role of excessive PARP-1 activation in cell death. It is believed that by preventing excessive NAD ϩ and ATP utilization, PARP inhibitors protect cells against oxidative damage, but some recent data suggest a more complex mechanism for the cytoprotection (25, 26). There is evidence that PARP activation can contribute to exaggeration of mitochondrial damage (27) and mitochondrial reactive oxygen species production (28), indicating that PARP activation can modulate processes outside of the nucleus. Recent works reported the existence of mitochondrial PARP that can be blocked with PARP-1 inhibitors (29); therefore, it would be important to clarify whether the mitochondrial protection by PARP inhibitors is a direct consequence of the inhibition of mitochondrial ADP-ribosylation or the inhibition of nuclear PARP modulation by yet unidentified processes that are responsible for the mitochondrial protection. Our previous works demonstrated that PARP inhibitors induced the phosphorylation and activation of Akt in the liver, lung, and spleen of lipopolysaccharide-treated mice, raising the possibility that the protective effect of PARP inhibition can be mediated through the PI3-kinase/Akt pathway (30). These observations indicate that the protective effect of PARP inhibitors should be far more In the present study, we analyzed the effect of PARP inhibition by pharmacologic agents, by the transdominant expression of the PARP N-terminal DNA...

Activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) is involved in numerous pathophysiological conditions. Because PARP-1 knockout mice are resistant to endotoxininduced shock and inhibitors of the enzyme were reported to have similar beneficial properties, we investigated the effect of 4-hydroxyquinazoline (4-HQN), a potent PARP-1 inhibitor, on the modulation of kinase cascades and the regulation of transcription factors in a rodent septic shock model. T2-weighted magnetic resonance imaging showed the pattern of anatomical localization of the inflammatory response in bacterial lipopolysaccharide (LPS)-treated mice and the anti-inflammatory effect of the PARP-1 inhibitor. We have found that 4-HQN activated the phosphatidylinositol 3 (PI3)-kinase/Akt pathway in lung, liver, and spleen, and down-regulated two elements of the MAP kinase system. Namely, it dramatically attenuated the activation of the LPS-induced extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein (MAP) kinase in a tissue-specific manner. Furthermore, phosphorylation of p90RSK, a downstream target of ERK1/2, showed a similar pattern of down-regulation as did the phosphorylation of ERK1/2 and p38 after LPS and 4-HQN treatment. As a consequence of the aforementioned effects on the kinase pathways, 4-HQN decreased the activation of transcription factor nuclear factor-B (NF-B) and activator protein 1 (AP-1) in LPS-induced endotoxic shock. Our results provide evidence for the first time that the beneficial effects of PARP inhibition in endotoxic shock, such as attenuation of NF-B-and AP-1 transcription factor activation, are mediated, at least partially, through the regulation of the PI3-kinase/Akt pathway and MAP kinase cascades.

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