Poly (ADP-ribose) synthetase mediates intestinal mucosal barrier dysfunction after mesenteric ischemia

Peroxynitrite-mediated DNA strand breaks trigger poly (ADP-ribose) syntheta se (PARS) activation, resulting in intracellular energetic failure and orga n dysfunction, We investigated the role of PARS activation on the inflammat ory and functional response of the intestine to mesenteric ischemia-reperfu sion injury. Anesthetized rats exposed to 15 min occlusion of the superior mesenteric artery showed an increased mucosal PARS activity (ex vivo incorp oration of radiolabelled NAD(+) in gut mucosal scrapings) as soon as 10 min after reperfusion. During the first 30 min of reperfusion, significant muc osal damage developed, as well as mucosal hyperpermeability to a 4000 MW fl uorescent dextran (FD4). These alterations were significantly reduced by tr eatment with the NO synthase inhibitor L-NMA, which blocks the production o f peroxynitrite, as well as with the PARS inhibitors 3-aminobenzamide and n icotinamide, whereas they were markedly enhanced by the glutathione depleto r L-buthionine-(S,R)-sulfoximine. Also, PARS inhibition significantly reduc ed ileal neutrophil infiltration (myeloperoxidase activity) at 3 h reperfus ion. In a second set of experiments, the effects of 15 or 30 min ischemia f ollowed by 3 h reperfusion were evaluated in PARS knockout and wild-type mi ce. Significant protection against histological damage, neutrophil infiltra tion, and mucosal barrier failure (evaluated by the mucosal-to-serosal FD4 clearance of everted ileal sacs incubated ex vivo) was noted in PARS knocko ut mice, who also showed reduced alterations in remote organs, as shown by lesser lipid peroxidation (malondialdehyde formation) and neutrophil infilt ration in the lung and liver. In conclusion, PARS plays a crucial role in m ediating intestinal injury and dysfunction in the early and late phases of mesenteric reperfusion. Pharmacological inhibition of PARS may be a novel a pproach to protect tissues from reperfusion-related damage.