Ischaemia/reperfusion, inflammatory responses and acute lung injury

The relation of oxidative stress and apoptosis to histopathologic alterations in the lungs as a result of global cerebral ischemia

Heart attack and oxygen deficiency may cause necrosis in the brain and other tissues. We investigated the histopathological effects of nitric oxide (NO) on ischemia/reperfusion in lung and hippocampus using a rat brain bilateral occlusion ischemia model. Male rats were assigned to sham (SH), ischemic preconditioning (PC), global ischemia (GI) and ischemic reperfusion (IR) groups. Before ischemia was induced, blood was drawn to induce hypovolemic hypotension and for blood gas testing. After sacrifice, samples of hippocampus were harvested. Sections were examined using hematoxylin and eosin (H & E) staining and immunostaining using primary antibodies for GFAP, S100β, iNOS, eNOS and the TUNEL method. Following ischemia, we found evidence of gliosis induced oxidative stress and apoptosis in the hippocampus. No significant differences were detected between the SH and PC groups. In the GI and IR groups, apoptosis and necrosis were observed in the hippocampus. Lung sections were stained with H & E and Masson's trichrome (MT) and immunostained for iNOS and eNOS. The TUNEL method was used to detect apoptosis. Interstitial edema, vascular congestion, intra-alveolar hemorrhage, perivascular edema, neutrophil infiltration and disruption of alveoli were observed after global ischemia and ischemic reperfusion. Inflammatory cells were detected in the connective tissue. The IR and GI groups exhibited significantly more apoptotic cells than the SH or PC groups. Free radicals, such as nitric oxide (NO), that appear following ischemia and reperfusion in the brain may also injure the lungs. Increased NO in both lung and brain tissue suggests that apoptosis in these organs can be induced by reactive nitrogen species.

Deficiency in cold-inducible RNA-binding protein attenuates acute respiratory distress syndrome induced by intestinal ischemia-reperfusion

BACKGROUND

Intestinal ischemia-reperfusion can occur in shock and mesenteric occlusive diseases, causing significant morbidity and mortality. Aside from local injury, intestinal ischemia-reperfusion can result in remote organ damage, particularly in the lungs. Cold-inducible RNA-binding protein (CIRP) was identified as a novel inflammatory mediator. We hypothesized that a deficiency in CIRP would protect the lungs during intestinal ischemia-reperfusion injury.

METHODS

Intestinal ischemia was induced in adult male C57BL/6 wild-type and CIRP knock-out (CIRP^-/-) mice via clamping of the superior mesenteric artery for 60 minutes. Reperfusion was allowed for 4 hours or 20 hours, and blood, gut, and lung tissues were harvested for various analyses.

RESULTS

After intestinal ischemia-reperfusion, the elevated levels of serum lactate dehydrogenase and inflammatory cytokine interleukin-6 were reduced by 68% and 98%, respectively, at 20 hours after ischemia-reperfusion in CIRP^-/- mice compared with the wild-type mice. In the gut, mRNA levels of inflammatory cytokine interleukin-6 were reduced by 67% at 4 hours after ischemia-reperfusion in CIRP^-/- mice. In the lungs, inflammatory cytokine interleukin-6 protein and myeloperoxidase activity were reduced by 78% and 26% at 20 hours and 4 hours after ischemia-reperfusion, respectively, in CIRP^-/- mice. Finally, the elevated lung caspase-3 was significantly decreased by 55%, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells decreased by 91%, and lung injury score decreased by 37% in CIRP^-/- mice at 20 hours after ischemia-reperfusion.

CONCLUSION

Increased levels of proinflammatory cytokines, myeloperoxidase, and apoptosis are the hallmarks of acute respiratory distress syndrome. We noticed after intestinal ischemia-reperfusion the proinflammatory milieu in lungs was elevated significantly, while the CIRP^-/- mice had significantly decreased levels of proinflammatory cytokine, myeloperoxidase, and apoptotic cells leading to decreased lung injury. These findings strongly established a causal link between CIRP and acute respiratory distress syndrome during intestinal ischemia-reperfusion injuries. Targeting CIRP may therefore be beneficial for treatment of intestinal ischemia-reperfusion-associated acute respiratory distress syndrome acute respiratory distress syndrome.

Inhibition of ERK1/2 worsens intestinal ischemia/reperfusion injury

Background

The role of extracellular signal-regulated protein kinase (ERK) in intestinal ischemia/reperfusion (I/R) injury has not been well investigated. The aim of the current study was to examine the effect of inhibition of the ERK pathway in an in vitro and in vivo model of intestinal I/R injury.

Methods

ERK1/2 activity was inhibited using the specific inhibitor, U0126, in intestinal epithelial cells under hypoxia/reoxygenation conditions and in mice subjected to 1 hour of intestinal ischemia followed by 6 hours reperfusion. In vitro, cell proliferation was assessed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay, apoptosis by DNA fragmentation, and migration using an in vitro model of intestinal wound healing. Cells were also transfected with a p70S6K plasmid and the effects of overexpression similarly analyzed. In vivo, the effects of U0126 on intestinal cell proliferation and apoptosis, intestinal permeability, lung and intestinal neutrophil infiltration and injury, and plasma cytokine levels were measured. Survival was also assessed after U0126. Activity of p70S6 kinase (p70S6K) was measured by Western blot.

Results

In vitro, inhibition of ERK1/2 by U0126 significantly decreased cell proliferation and migration but enhanced cell apoptosis. Overexpression of p70S6K promoted cell proliferation and decreased cell apoptosis. In vivo, U0126 significantly increased cell apoptosis and decreased cell proliferation in the intestine, increased intestinal permeability, intestinal and lung neutrophil infiltration, and injury, as well as systemic pro-inflammatory cytokines, TNF-α, IL-6 and IL-1β. Mortality was also significantly increased by U0126. Inhibition of ERK1/2 by U0126 also abolished activity of p70S6K both in vitro and in vivo models.

Conclusion

Pharmacologic inhibition of ERK1/2 by U0126 worsens intestinal IR injury. The detrimental effects are mediated, at least in part, by inhibition of p70S6K, the major effector of mammalian target of rapamycin pathway.

Cyclic arginine-glycine-aspartate attenuates acute lung injury in mice after intestinal ischemia/reperfusion

Introduction

Intestinal ischemia is a critical problem resulting in multiple organ failure and high mortality of 60 to 80%. Acute lung injury (ALI) is a common complication after intestinal ischemia/reperfusion (I/R) injuries and contributes to the high mortality rate. Moreover, activated neutrophil infiltration into the lungs is known to play a significant role in the progression of ALI. Integrin-mediated interaction is involved in neutrophil transmigration. Synthetic peptides containing an arginine-glycine-aspartate sequence compete with adhesive proteins and inhibit integrin-mediated interaction and signaling. Thus, we hypothesized that the administration of a cyclic arginine-glycine-aspartate peptide (cRGD) inhibited neutrophil infiltration and provided protection against ALI induced by intestinal I/R.

Methods

Ischemia in adult male C57BL/6 mice was induced by fastening the superior mesenteric artery with 4-0 suture. Forty-five minutes later, the vascular suture was released to allow reperfusion. cRGD (5 mg/kg body weight) or normal saline (vehicle) was administered by intraperitoneal injection 1 hour prior to ischemia. Blood, gut, and lung tissues were collected 4 hours after reperfusion for various measurements.

Results

Intestinal I/R caused severe widespread injury to the gut and lungs. Treatment with cRGD improved the integrity of microscopic structures in the gut and lungs, as judged by histological examination. Intestinal I/R induced the expression of β₁, β₂ and β₃ integrins, intercellular adhesion molecule-1, and fibronectin. cRGD significantly inhibited myeloperoxidase activity in the gut and lungs, as well as neutrophils and macrophages infiltrating the lungs. cRGD reduced the levels of TNF-α and IL-6 in serum, in addition to IL-6 and macrophage inflammatory protein-2 in the gut and lungs. Furthermore, the number of TUNEL-staining cells and levels of cleaved caspase-3 in the lungs were significantly lowered in the cRGD-treated mice in comparison with the vehicle mice.

Conclusions

Treatment with cRGD effectively protected ALI and gut injury, lowered neutrophil infiltration, suppressed inflammation, and inhibited lung apoptosis after intestinal I/R. Thus, there is potential for developing cRGD as a treatment for patients suffering from ALI caused by intestinal I/R.

The effect of melatonin against FK506-induced renal oxidative stress in rats

BACKGROUND

Nephrotoxicity is an important side effect of FK506 and oxidative stress has been considered as one of the possible mechanisms. The present investigation examines the ability of melatonin to protect against FK506-induced renal oxidative stress.

METHODS

Thirty rats were divided into 3 groups (n = 10 each group). Group A was the sham group. Group B received 14 days FK506 (5 mg/kg/d, intraperitoneally [i.p.]) and group C received FK506 (5 mg/kg/d, i.p.) together with melatonin (4 mg/kg, i.p.) for 14 days. Kidney tissues were harvested to determine the tissue levels of malondialdehyde (MDA), total nitrite and nitric oxide (NO), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6).

RESULTS

In group C, the levels of TNF-α, IL-6, and NO were lower than in the group B (P < .01, P < .03, and P < .04, respectively) and although MDA levels were lower than in group B, the differences were not statistically significant (P > .05).

CONCLUSION

These results suggest that melatonin has protective effect against FK506-induced renal oxidative stress.

Pulmonary injury follows systemic inflammatory reaction in infrarenal aortic surgery

OBJECTIVE

To investigate whether an inflammatory response occurs in patients undergoing infrarenal aortic abdominal aneurysm repair, the localization and timing (ischemia and/or reperfusion) of this activation, and finally whether it affects postoperative pulmonary function.

DESIGN

Prospective, observational study.

SETTING

Academic referral center in Italy.

PATIENTS

We included 12 patients undergoing infrarenal aortic abdominal aneurysm repair and 12 patients undergoing major abdominal surgery.

INTERVENTIONS

Timed measurement of gene activation (angiotensinogen, angiotensin type 1 receptor, angiotensin-converting enzyme, and interleukin-6 genes) in muscle biopsies by reverse transcriptase-polymerase chain reaction (RT-PCR), and prospective assessment of interleukin-6 plasma concentration and pulmonary function (Pao2/FIO2 and Pao2/PAO2 ratios).

MEASUREMENTS AND MAIN RESULTS

After 30 mins of aortic clamping, angiotensinogen, angiotensin type 1 receptor, angiotensin-converting enzyme, and interleukin-6 genes were all overexpressed at RT-PCR studies in quadriceps muscle of patients undergoing aortic abdominal aneurysm repair, and the overexpression persisted after reperfusion. In situ hybridization and immunohistochemistry revealed that the inflammatory response was localized in endothelial cells. A significant increase in plasma interleukin-6 concentrations was then detectable at 6 and 12 hrs after reperfusion in aortic abdominal aneurysm surgery compared with patients undergoing abdominal surgery (p < .05). The increase in interleukin-6 plasma concentration was then followed (12 and 24 hrs after surgery) by a significant reduction of Pao2/ FIO2 and Pao2/PAO2 ratios (p < .05 vs. abdominal surgery).

CONCLUSIONS

The present study shows that a) during aortic surgery, the genes for interleukin-6 and for the components of the local renin-angiotensin system (angiotensinogen, angiotensin-converting enzyme, and angiotensin type 1 receptor subtype) are activated early in the ischemic muscle, and activation persists during reperfusion; b) interleukin-6 plasma concentration increases only in patients with tissue ischemia (aortic abdominal aneurysm), whereas no changes are detectable in patients with abdominal surgery; and finally c) the occurrence of systemic inflammatory reaction with increased interleukin-6 plasma concentrations is followed by impaired pulmonary function.