Acute mesenteric venous hypertension and resuscitation-induced gut edema, in the absence of ischemia/reperfusion injury, is associated with delayed intestinal transit and altered gut barrier function.

HTS resuscitation protects against inflammation, injury, and impaired intestinal transit after gut I/R in part by inducing HO-1. This is a novel mechanism of HO-1 protection.

Mesenteric ischemia-reperfusion injury is a serious complication of shock. Because activation of nuclear factor-kappaB (NF-kappaB) has been implicated in this process, we treated rats with vehicle or the IkappaB-alpha inhibitor BAY 11-7085 (25 mg/kg ip) 1 h before mesenteric ischemia-reperfusion (45 min of ischemia followed by reperfusion at 30 min or 6 h) and examined the ileal injury response. Vehicle-treated rats subjected to ischemia-reperfusion exhibited severe mucosal injury, increased myeloperoxidase (MPO) activity, increased expression of interleukin-6 and intercellular adhesion molecule 1 protein, and a biphasic peak of NF-kappaB DNA-binding activity during the 30-min and 6-h reperfusion courses. In contrast, BAY 11-7085-pretreated rats subjected to ischemia-reperfusion exhibited less histological injury and less interleukin-6 and intercellular adhesion molecule 1 protein expression at 30 min of reperfusion but more histological injury at 6 h of reperfusion than vehicle-treated rats subjected to ischemia-reperfusion. Studies with phosphorylation site-specific antibodies demonstrated that IkappaB-alpha phosphorylation at Ser(32),Ser(36) was induced at 30 min of reperfusion, whereas tyrosine phosphorylation of IkappaB-alpha was induced at 6 h of reperfusion. BAY 11-7085 inhibited the former, but not the latter, phosphorylation pathway, whereas alpha-melanocyte-stimulating hormone, which is effective in limiting late ischemia-reperfusion injury to the intestine, inhibited tyrosine phosphorylation of IkappaB-alpha. Thus NF-kappaB appears to play an important role in the generation and resolution of intestinal ischemia-reperfusion injury through different activation pathways.

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Cyclooxygenase (COX)-2 has been identified as an important mediator elaborated during ischemia/reperfusion, with pro- and anti-inflammatory properties having been reported. As the role of COX-2 in the small intestine remains unclear, we hypothesized that COX-2 expression would mediate mesenteric ischemia/reperfusion-induced gut injury, inflammation, and impaired transit and that these deleterious effects could be reversed by the selective COX-2 inhibitor, N-[2-(cyclohexyloxy)-4-nitrophenyl] methanesulphanamide (NS-398). Additionally, we sought to determine the role of peroxisome proliferator-activated receptor gamma (PPARgamma) in mediating protection by NS-398 in this model. Rats underwent sham surgery or were pretreated with NS-398 (3, 10, or 30 mg/kg) intraperitoneally 1 h before 60 min of superior mesenteric artery occlusion and 30 min to 6 h of reperfusion. In some experiments, NS-398 (30 mg/kg) was administered postischemia. Ileum was harvested for COX-2 mRNA and protein, PGE2, myeloperoxidase (inflammation), histology (injury), intestinal transit and PPARgamma protein expression, and DNA-binding activity. COX-2 expression and PGE2 production increased after mesenteric ischemia/reperfusion and were associated with gut inflammation, injury, and impaired transit. Inhibition of COX-2 by NS-398 (30 mg/kg, but not 3 or 10 mg/kg) not only reversed the deleterious effects of COX-2, but additionally induced expression and nuclear translocation of PPARgamma. NS-398 given postischemia was equally protective. In conclusion, COX-2 may function as a proinflammatory mediator in a rodent model of mesenteric ischemia/reperfusion. Reversal of gut inflammation, injury, and impaired transit by high-dose NS-398 is associated with PPAR activation, suggesting a potential role for PPAR-gamma in shock-induced gut protection.

Gut ischemia-reperfusion (I/R) injury is a serious complication of shock. Previously we demonstrated that the administration of alpha-melanocyte-stimulating hormone (MSH) immediately before mesenteric I/R protected against postischemic gut injury. In this report, we tested the therapeutic efficacy of alpha-MSH on gut I/R (60 min ischemia, 6 h reperfusion) injury when given at different time points of reperfusion. Rats underwent sham surgery or were treated with saline or with alpha-MSH that was given 1, 2, or 4 h after superior mesenteric artery clamping. Vehicle-treated I/R rats exhibited severe mucosal injury and increased NF-kappaB DNA binding activity, myeloperoxidase (MPO) activity, and interleukin-6 and heme oxygenase-1 (HO-1) expression. In contrast, rats given alpha-MSH at 1 h of reperfusion, but not 2 h or 4 h, exhibited much less mucosal injury. Rats given alpha-MSH at 1 h or 2 h of reperfusion, but not 4 h, exhibited less MPO activity, NF-kappaB DNA binding activity, and interleukin-6 protein and even higher levels of heme oxygenase-1 than vehicle-treated rats. In addition, we found that combined use of alpha-MSH, a known inhibitor of IkappaBalpha tyrosine phosphorylation, with BAY 11-7085, an inhibitor of IkappaBalpha Ser 32,36 phosphorylation, abrogates gut MPO induction and tissue injury at early and late time points of reperfusion. Thus, alpha-MSH, an endogenous peptide with a favorable side-effect profile, is effective in treating experimental gut I/R injury when given early after the initial ischemia and may represent a candidate therapy for gut I/R in humans in whom recognition and treatment are often delayed.

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