Ischemia/reperfusion-induced feline intestinal dysfunction: importance of granulocyte recruitment

Mechanisms responsible for enhanced inflammatory response to ischemia-reperfusion in diabetes

The objective of the present study was to assess the role of lipid mediators and adhesion molecule expression in exacerbation of ischemia-reperfusion-induced inflammatory response in diabetes. Leukocyte-endothelial cell interactions were studied in mesenteric venules by intravital microscopy. Endothelial expression of intercellular adhesion molecule (ICAM)-1 was measured by the double-radiolabeled monoclonal antibody technique, and beta2-integrin expression was measured by flow cytometry. Ischemia-reperfusion elicited significantly larger increases in leukocyte adhesion and emigration in diabetic rats that were prevented by a platelet-activating factor (PAF)-receptor antagonist or a leukotriene synthesis inhibitor. Leukotriene B4 (LTB4) superfusion induced similar leukocyte recruitment in diabetic and control rats, whereas PAF elicited larger increases in diabetic rats. CD11a, but not CD11b, expression was higher in leukocytes from diabetic animals. Endothelial ICAM-1 in mesentery and in intestine did not differ between diabetic and control rats. These results indicate that diabetes is associated with an enhanced response to ischemia-reperfusion that depends on both PAF and leukotrienes. An increased sensitivity to PAF, along with an increased CD11a expression, may account for the exaggerated inflammatory response to ischemia-reperfusion in diabetes.

Ischaemia-reperfusion injury to the intestine

Ischaemia-reperfusion injury (IRI) is of obvious relevance in situations where there is an interruption of blood supply to the gut, as in vascular surgery, or in the construction of free intestinal grafts. It is now appreciated that IRI also underlies the guy dysfunction that occurs in early shock, sepsis, and trauma. The events that occur during IRI are complex. However, recent advances in cellular biology have started to unravel these underlying processes. The aim of this review is to provide an outline of current knowledge on the mechanisms and consequences of IRI. Initially, IRI appears to be mediated by reactive oxygen metabolites and, at a later stage, by the priming and activation of polymorphonuclear neutrophils (PMN). Ischaemia-reperfusion injury can diminish the barrier function of the gut, and can promote an increase in the leakage of molecules (intestinal permeability) or the passage of microbes across the wall of the bowel (bacterial translocation). Ischaemia-reperfusion injury to the gut can result in the generation of molecules that may also harm distant tissues.

Influence of ischaemia-reperfusion injury on CD44 expression in rat small intestine

BACKGROUND

CD44 is an adhesion molecule expressed by neutrophils and lymphocytes which is involved in cell-cell and cell-matrix binding. In this study, the effect of ischaemia-reperfusion injury on CD44 messenger RNA (mRNA) and cell surface immunohistochemical expression of CD44 in the rat small intestine was evaluated.

METHODS

Wistar rats (n=16) were randomized to either serve as controls (sham surgery) or to be subjected to a standardized ischaemia-reperfusion injury (suprarenal aorta occluded for 1 h followed by 1 h of reperfusion). Standardized segments of jejunum were harvested after ischaemia-reperfusion injury (ischaemic and reperfused samples) to measure the mucosal protein and DNA content, mRNA expression of CD44 and the immunohistochemical expression of CD44.

RESULTS

Reperfusion significantly damaged the jejunal mucosa, e.g. mucosal protein content was lower after reperfusion compared with that in the control group (z=-2.31, P=0.02) and the ischaemic samples (z=-2.52, P=001). The expression of cell surface CD44 protein was also significantly decreased after ischaemic injury (z=-1.99, P=0.04); this coincided with a decrease in the amount of cytoplasmic CD44 mRNA within isolated enterocytes (z=-2.31, P=0.02).

CONCLUSION

Ischaemia-reperfusion injury decreases the expression of CD44 within the jejunal mucosa. This may contribute to the failure of the gut barrier after such injury.

Disruption of intestinal barrier function associated with experimental colitis: possible role of mast cells

The objective was to characterize changes in barrier and transport function in an experimental model of colitis, and to determine whether mast cells contribute to these changes. Colitis was induced in rats with intracolonic 2,4,6-trinitrobenzenesulfonic acid (TNBS, 30 mg) in 50% ethanol. Controls received 0.9% saline or the ethanol vehicle alone. In vivo loop perfusion was used to assess colonic water flux (in microliter.cm-1.h-1) and lumen-to-blood 51Cr-labeled EDTA clearance (% administered dose) after TNBS. Myeloperoxidase (MPO) was used as an index of granulocyte influx. TNBS or its vehicle caused a marked decrease in water absorption and an increase in permeability at 4 h after administration compared with saline. Neither dexamethasone (anti-inflammatory control) nor doxantrazole (mast cell stabilizer) was able to attenuate these early changes likely caused by the vehicle. In contrast, at later times, TNBS (but not its vehicle) also increased 51Cr-EDTA permeability and decreased water absorption; both effects were significantly attenuated by dexamethasone or doxantrazole. These drugs also significantly reduced TNBS-induced MPO accumulation and release of rat mast cell protease II. We conclude that experimental colitis is associated with severe defects in intestinal transport and barrier functions and that mast cells may contribute to the pathogenesis of these changes.

Endothelin 1 induces leukocyte adhesion in submucosal venules of the rat small intestine

BACKGROUND & AIMS

The release of endothelin 1 (ET-1) and the activation of leukocytes are involved in the pathophysiology of gastrointestinal ischemia/reperfusion injuries. The aim of this study was to define the in vivo relation between ET-1 and endothelial cell-leukocyte interactions.

METHODS

Anesthetized rats were studied to characterize the microvascular effects of increasing doses of local and systemic infusions of ET-1 in all layers of an ileal segment. Leukocyte-endothelial interactions were monitored with intravital fluorescence videomicroscopy. The ETA receptor-selective antagonist BQ 610, the novel ETA-receptor antagonist ETR-PI/fl peptide, and the ETB-receptor antagonist IRL 1038 were used to investigate the roles of receptor subtypes.

RESULTS

The functional capillary density of the mucosa was significantly decreased by 3 nmol/kg intravenous ET-1. After 30 minutes the rolling fraction of leukocytes reached 90% in the postcapillary venules, and the number of adherent leukocytes was significantly increased after 90 minutes. ETR-PI/fl peptide inhibited leukocyte rolling by 88%, BQ 610 by 73%, and IRL 1038 by 30%. Both ETA-receptor antagonists prevented ET-1-induced firm adhesion. The ETA-receptor antagonists but not IRL 1038 inhibited the ET-1-induced lymphatic muscle and mucosal capillary perfusion failure.

CONCLUSIONS

ET-1 induces leukocyte rolling and adherence through a predominantly ETA receptor-mediated mechanism in the submucosal venules of the intestinal microcirculation.

The protective effect of L-arginine on ischemia-reperfusion injury in rat skin flaps

The objective of this study was to examine whether the administration of L-arginine, a precursor of nitric oxide and substrate of nitric oxide synthase, prior to reperfusion could lead to decrease in neutrophil-mediated tissue injury and improved flap survival. Epigastric island skin flaps were elevated in 70 rats and rendered ischemic. Thirty minutes prior to reperfusion, the rats were treated with intraperitoneal saline (n = 15), L-arginine (n = 15), D-arginine (n = 15), or N omega-nitro-L-arginine methylester plus L-arginine in equimolar amounts (n = 15). Flap survival at 7 days and neutrophil counts at 24 hours were evaluated. Flap necrosis as expected in the sham group of animals (n = 10) was 0.0 percent, while the control (saline-treated) animals had 59.6 percent necrosis. Animals treated with L-arginine demonstrated a significant decrease in flap necrosis to 12.7 percent. This protective effect was almost completely negated by N omega-nitrol-L-arginine methylester, which significantly increased flap necrosis to 49.3 percent and was much less pronounced with D-arginine (28.6 percent). Neutrophil counts were significantly decreased in flaps from L-arginine-treated and sham animals versus both saline and N omega-nitro-L-arginine methylester-treated groups. We conclude that administration of L-arginine prior to reperfusion can significantly reduce the extent of flap necrosis and flap neutrophil counts due to ischemia-reperfusion injury. This protective effect is completely negated by nitric oxide synthase inhibition. Since L-arginine reduces the number of neutrophils within the flap and the extent of flap necrosis only in the presence of active nitric oxide synthase, we hypothesize that this protective effect of L-arginine on ischemia-reperfusion injury is secondary to a nitric oxide-mediated suppression of neutrophil-mediated injury.

Post-ischaemic organ dysfunction: a review

OBJECTIVES

The aim of this review is to consider the pathophysiology of ischaemia-reperfusion in organs that may be affected by either its local or remote consequences. Potential therapeutic strategies are also considered.

DESIGN

A general discussion of the biochemical (including oxygen free radicals, complement, cytokines) and cellular events (endothelial cells, neutrophils) responsible for the mediation of reperfusion injury is presented, with special consideration of the organ-specific differences affecting the myocardium, central nervous system, gut, liver, kidney and skeletal muscle. Similarly, events which promote remote organ injury are described.

CONCLUSIONS

Although it is recognised that prolonged ischaemia results in tissue and organ damage, the concept of reperfusion-induced tissue injury, defined as tissue damage occurring as a direct consequence of revascularisation, is relatively recent. Such events may increase the morbidity and mortality of patients undergoing vascular reconstruction, trauma surgery and transplantation. A clear understanding of the factors responsible for its development is therefore vital if protocols that reduce its impact are to be developed.

Is reperfusion injury an important cause of mucosal damage after porcine intestinal ischemia?

BACKGROUND

Intestinal ischemic injury is exacerbated by reperfusion in rodent and feline models because of xanthine oxidase-initiated reactive oxygen metabolite formation and neutrophil infiltration. Studies were conducted to determine the relevance of reperfusion injury in the juvenile pig, whose low levels of xanthine oxidase are similar to those of the human being.

METHODS

Ischemia was induced by means of complete mesenteric arterial occlusion, volvulus, or hemorrhagic shock. Injury was assessed by means of histologic examination and measurement of lipid peroxidation. In addition, myeloperoxidase, as a marker of neutrophil infiltration, and xanthine oxidase-xanthine dehydrogenase were measured.

RESULTS

Significant ischemic injury was evident after 0.5 to 3 hours of complete mesenteric occlusion or 2 hours of shock or volvulus. In none of these models was the ischemic injury worsened by reperfusion. To maximize superoxide production, pigs were ventilated on 100% O2, but only limited reperfusion injury (1.2-fold increase in histologic grade) was noted. Xanthine oxidase-xanthine dehydrogenase levels were negligible (0.4 +/- 0.4 mU/gm).

CONCLUSIONS

Reperfusion injury may not play an important role in intestinal injury under conditions of complete mesenteric ischemia and low-flow states in the pig. This may result from low xanthine oxidase-xanthine dehydrogenase levels, which are similar to those found in the human being.

Role of xanthine oxidase-derived oxidants and leukocytes in ethanol-induced jejunal mucosal injury

Previous reports indicate that intestinal intraluminal ethanol increases mucosal permeability (an index of mucosal injury) and histamine release by mast cells, and that the released histamine plays a role in mediating the increased permeability. In the present study, we investigated whether reactive oxygen metabolites and their major sources (xanthine oxidase and leukocytes) were involved in these ethanol effects. In rabbits, segments of the jejunum were perfused with a control solution or with 6% ethanol. In these segments, mucosal permeability was assessed by determining jejunal clearance of i.v. administered 51Cr-ethylenediaminetetraacetate (51Cr-EDTA) and 125I-bovine serum albumin (125I-BSA), and mast cell histamine release was estimated from the histamine concentration of the gut effluent. Ethanol increased 51Cr-EDTA clearance, 125I-BSA clearance, and histamine release. These ethanol effects decreased when the animals were given superoxide dismutase plus catalase (scavenger of O2- and H2O2, respectively), allopurinol, or oxypurinol (xanthine oxidase inhibitors). Administration of a monoclonal antibody (R15.7) against leukocyte adhesion molecule, CD18, inhibited completely the ethanol-induced increased 51Cr-EDTA and 125I-BSA clearances and histamine release. These and supplementary data suggest that (a) ethanol-induced mucosal injury and mast cell histamine release are mediated primarily by leukocytes, and (b) oxy radicals, especially those generated by xanthine oxidase, mediate these ethanol effects mainly by promoting leukocyte infiltration.

Cold restraint stress-induced gastric mucosal dysfunction. Role of nitric oxide

The objectives of this study were to determine the cold restraint stress-induced changes in gastric mucosal permeability and to assess whether nitric oxide synthesis inhibition affects gastric mucosal integrity after cold-restraint administration. Cold-restraint stress caused multiple gastric lesions in 90% of animals. The lesion index was found to be 3.87 +/- 0.97 mm. Gastric mucosal permeability to the [51CR]EDTA molecule was significantly elevated in the cold-restraint group compared to control. In order to evaluate the role of nitric oxide in cold restraint stress-induced gastropathy, L-arginine analog NG-nitro-L-arginine methyl ester (L-NAME) was given as a bolus (10 mg/kg, intravenously) and infused at a rate of 2 mg/ml/hr for 2 hr after cold-restraint administration. L-NAME greatly exacerbated gastric mucosal dysfunction associated with cold-restraint stress. D-NAME, the biologically inactive enantiomer, did not enhance mucosal dysfunction, whereas L-arginine, the substrate for nitric oxide, reversed the effect of L-NAME. In an additional group of experiments, effects of cold-restraint stress and L-NAME on net transmucosal fluid flux as well as tissue myeloperoxidase activity (MPO) were assessed. Cold-restraint stress administration significantly reduced the absorptive capacity of stomach, whereas L-NAME treatment did not affect the stress-induced alterations on net fluid absorption. Furthermore, L-NAME treatment did not affect the cold restraint stress-induced changes in tissue MPO activity. Our results suggest that gastric barrier function is altered after cold-restraint stress and nitric oxide production is important in minimizing mucosal barrier dysfunction associated with cold-restraint stress administration. Our results also indicate that L-NAME-induced alterations on mucosal permeability are not related to net transmucosal fluid flux and tissue neutrophils.

Anti-neutrophil serum attenuates dextran sulfate sodium-induced colonic damage in the rat

BACKGROUND

The role of neutrophils in experimental colonic damage induced by dextran sulfate sodium is uncertain. We test the hypothesis that neutrophils are of pathogenic significance and anti-neutrophil serum will attenuate the colonic damage induced by oral dextran sulfate sodium in rats.

METHODS

Rabbit anti-rat neutrophil serum (anti-neutrophil serum) or control rabbit serum was administered to, and circulating neutrophil count was monitored in, rats before and during feeding of dextran sulfate sodium or regular rat diet for 2 weeks. Histologic features of mucosal damage were evaluated in hematoxylin and eosin-stained proximal and distal colonic sections by a blinded observer.

RESULTS

Oral dextran sulfate sodium induces weight loss, diarrhea, peripheral neutrophilia, and colonic damage. Anti-neutrophil serum induced neutropenia and significantly attenuated the weight loss, the neutrophil infiltration in the colon, and the mucosal necrosis and pathologic index in the distal colon.

CONCLUSION

The data showing that anti-neutrophil serum attenuates distal colonic mucosal injury induced by dextran sulfate sodium support the hypothesis that neutrophils play a pathogenic role in this model of colonic mucosal damage.

Significance of reperfusion injury after venous strangulation obstruction of equine jejunum

Fifteen horses under halothane anesthesia were assigned randomly to three groups of 5 horses each as follows. In group 1, the distal 50% of the small intestine was measured through a ventral midline celiotomy and replaced in the abdomen so that these horses could serve as sham-operated controls. In group 2, the same segment of small intestine was subjected to venous strangulation obstruction (VSO) for 180 min. In group 3, the same segment of small intestine was subjected to VSO for 90 minutes, followed by 90 minutes of reperfusion. Biopsies of small intestine were taken from all horses to assess mucosal morphologic injury by light microscopy, to measure tissue levels of malondialdehyde as an indicator of lipid peroxidation, and to measure tissue myeloperoxidase activity as a measure of neutrophil accumulation. VSO for 90 min in horse jejunum increased lipid peroxidation and neutrophil influx to levels that remained constant over the following 90 min, regardless of whether VSO was maintained or was interrupted to allow reperfusion of the tissue. Reperfusion induced a similar mucosal lesion as continued VSO for the same time. From these results, it would appear that VSO causes more severe mucosal damage and inflammation than the subsequent reperfusion period, in contrast to the classical paradigm of reperfusion injury in small intestine.

Ischaemia-reperfusion injury--a small animal perspective

Disease processes that produce ischaemia are a common cause of morbidity and mortality in companion animals. The majority of damage to transiently ischaemia tissues occurs following reperfusion and not during ischaemia per se. This discovery raises the encouraging prospect that therapeutic intervention prior to reperfusion may reduce the severity of ischaemic damage. Recently, the central role of oxygen-derived free radicals (oxyradicals) in reperfusion injury has been demonstrated. It appears that the adverse consequences of ischaemic diseases can be reduced by optimizing the anti-oxidant capability of tissues with anti-oxidant nutrients or drugs. The importance of oxyradicals in individual ischaemic diseases of the dog and cat, however, remains largely uninvestigated. Similarly, the best pharmaceutical and nutritional approaches to the therapy of oxyradical-mediated damage have yet to be devised.

Mechanisms of gastrointestinal ischemia-reperfusion injury and potential therapeutic interventions: a review and its implications in the horse

Restoration of blood flow after a period of intestinal ischemia is necessary to maintain cell function and viability; however, the reintroduction of oxygen can initiate a cascade of events that exacerbates tissue injury. Intestinal I-R injury is manifested as increased microvascular and mucosal permeability, and mucosal necrosis. Reperfusion injury begins with the accumulation of hypoxanthine from ATP metabolism and the conversion of XDH to XO during ischemia. Upon reperfusion, the XO catalyzes the conversion of hypoxanthine to superoxide radicals in the presence of oxygen. Superoxide radicals are further reduced to highly reactive hydroxyl radicals, which initiate lipid peroxidation. Lipoperoxidation causes functional and structural alterations in cell membrane lipids and can release numerous inflammatory mediators, which exacerbate tissue damage. Neutrophils are recruited into tissues during ischemia and on reperfusion; then they undergo degranulation and release destructive products (proteases and OFRs), which mediate further tissue injury. A limited number of experimental studies in the gastrointestinal tract of horses have shown I-R injury. Additional studies are necessary to further elucidate and sequence the precise pathophysiologic mechanisms occurring in the equine intestine during I-R. Therapy should be focused on prevention of I-R injury by pharmacologic or chemical inhibition or modification of these pathophysiologic pathways. Selected pharmacologic agents or drug combinations may offer novel, scientifically relevant and yet practical approaches to alleviating intestinal I-R injury in horses. This may improve survival of horses with naturally acquired intestinal strangulation obstruction.

Free radicals and pathogenesis during ischemia and reperfusion of the cat small intestine

BACKGROUND/AIM

In spite of the interest in free radicals as mediators of ischemic damage, most information on these species in biological systems is derived from indirect measurements. Our aim was to obtain more direct information concerning sources of free radical production during ischemia and reperfusion.

METHODS

We have performed simultaneous measurement of radical generation, purine metabolites, reduced glutathione, neutrophil infiltration and morphological appearance in the cat small intestine in vivo during 60 minutes of ischemia followed by 60 minutes of reperfusion.

RESULTS

Radical formation increased abruptly on reperfusion and remained elevated in untreated animals. Inhibition by a monoclonal antibody (IB4) against the neutrophil and by allopurinol treatment was paralleled by improvement of biochemical and morphological parameters. The radicals detected during reperfusion could be divided into one component arising directly from the neutrophils, one due to the xanthine oxidase reaction, and one unknown source.

CONCLUSIONS

Neutrophils are a major source of radical production during reperfusion after ischemia. Radicals formed in the xanthine oxidase reaction seem to function as a primer for the neutrophils. The nonsignificant linear correlation between radical formation and morphological appearance suggests that factors other than free radicals are important for the development of intestinal damage after a period of ischemia.

Early mucosal and microvascular changes in feline intestinal transplants

BACKGROUND

Bowel transplantation in humans is being performed with increasing success, but little is known about the early physiological alterations occurring in the graft. The objectives of this study were to characterize the mucosal and microvascular alterations that occur in the early stages of reperfusion of small intestinal allografts after varying intervals of hypothermic preservation and to assess the role of reactive oxygen metabolites and leukocyte adhesion glycoproteins in mediating these alterations.

METHODS

A feline model of small intestinal transplantation was developed in which ileal grafts underwent 0-24 hours of cold ischemia before reperfusion. Some allografts, which underwent 6 hours of cold ischemia, were treated with monoclonal antibodies directed against either leukocyte (CD11/CD18) or endothelial cell (ICAM-1 or P-selectin) adhesion molecules or with a combination of superoxide dismutase and catalase.

RESULTS

Cold preservation for 6 hours resulted in significant increases in intestinal microvascular fluid and protein exchange, and mucosal function was compromised. These alterations were not affected by treatment with either superoxide dismutase and catalase or monoclonal antibodies against ICAM-1 or P-selectin; however, the microvascular dysfunction was largely prevented by immunoneutralization of CD11/CD18 on leukocytes.

CONCLUSIONS

CD11/CD18 antibodies may be useful in preserving microvascular function in allografts after prolonged hypothermic ischemia.