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.

No abstract

D-Gluco- and D-xylopyranosylidene-spiro-hydantoins and -thiohydantoins were prepared from the parent sugars in a six-step, highly chemo-, regio-, and stereoselective procedure. In the key step of the syntheses C-(1-bromo-1-deoxy-beta-D-glycopyranosyl)formamides were reacted with cyanate ion to give spiro-hydantoins with a retained configuration at the anomeric center as the major products. On the other hand, thiocyanate ions gave spiro-thiohydantoins with an inverted anomeric carbon as the only products. On the basis of radical inhibition studies, a mechanistic rationale was proposed to explain this unique stereoselectivity and the formation of C-(1-hydroxy-beta-D-glycopyranosyl)formamides as byproducts. Enzyme assays with a and b forms of muscle and liver glycogen phosphorylases showed spiro-hydantoin 12 and spiro-thiohydantoin 14 to be the best and equipotent inhibitors with K(i) values in the low micromolar range. The study of epimeric pairs of D-gluco and D-xylo configurated spiro-hydantoins and N-(D-glucopyranosyl)amides corroborated the role of specific hydrogen bridges in binding the inhibitors to the enzyme.

Ischemia-reperfusion induces reactive oxygen species (ROS) formation, and ROS lead to cardiac dysfunction, in part, via the activation of the nuclear poly(ADP-ribose) polymerase (PARP, called also PARS and ADP-RT). ROS and peroxynitrite induce single-strand DNA break formation and PARP activation, resulting in NAD(+) and ATP depletion, which can lead to cell death. Although protection of cardiac muscle by PARP inhibitors can be explained by their attenuating effect on NAD(+) and ATP depletion, there are data indicating that PARP inhibitors also protect mitochondria from oxidant-induced injury. Studying cardiac energy metabolism in Langendorff heart perfusion system by (31)P NMR, we found that PARP inhibitors (3-aminobenzamide, nicotinamide, BGP-15, and 4-hydroxyquinazoline) improved the recovery of high-energy phosphates (ATP, creatine phosphate) and accelerated the reutilization of inorganic phosphate formed during the ischemic period, showing that PARP inhibitors facilitate the faster and more complete recovery of the energy production. Furthermore, PARP inhibitors significantly decrease the ischemia-reperfusion-induced increase of lipid peroxidation, protein oxidation, single-strand DNA breaks, and the inactivation of respiratory complexes, which indicate a decreased mitochondrial ROS production in the reperfusion period. Surprisingly, PARP inhibitors, but not the chemically similar 3-aminobenzoic acid, prevented the H(2)O(2)-induced inactivation of cytochrome oxidase in isolated heart mitochondria, suggesting the presence of an additional mitochondrial target for PARP inhibitors. Therefore, PARP inhibitors, in addition to their important primary effect of decreasing the activity of nuclear PARP and decreasing NAD(+) and ATP consumption, reduce ischemia-reperfusion-induced endogenous ROS production and protect the respiratory complexes from ROS induced inactivation, providing an additional mechanism by which they can protect heart from oxidative damages.