Differential effects of phospholipase inhibitors on free fatty acid efflux in rat cerebral cortex during ischemia-reperfusion injury

Free fatty acid (FFA) elevation in the brain has been shown to correlate with the severity of damage in ischemic injury. The etiology of this increase in FFA remains unclear and has been hypothesized to result from phospholipase activation. This study examines the effects of specific phospholipase inhibitors on FFA efflux during ischemia-reperfusion injury. A four-vessel occlusion model of cerebral ischemia was utilized to assess the effects of PLA(2) and PLC inhibitors on FFA efflux from rat cerebral cortex. In addition, FFA efflux from non-ischemic cortices exposed to PLA(2) and PLC was measured. Concentrations of arachidonic, docosahexaenoic, linoleic, myristic, oleic, and palmitic acids in cortical superfusates were determined using high performance liquid chromatography (HPLC). Exposure to the non-selective PLA(2) inhibitor 4-bromophenylacyl bromide (BPB) significantly inhibited FFA efflux during ischemia-reperfusion injury (P<0.01 arachidonic, oleic and palmitic; P<0.05 all others); exposure to the PLC inhibitor U73122 had no observed effect. The effects of the Ca(2+)-dependent PLA(2) inhibitor arachidonyl trifluoromethyl ketone (AACOCF(3)) mirrored the effects of BPB and led to reductions in all FFA levels (P<0.01 arachidonic, oleic and palmitic; P<0.05 all others). Exposure to the secretory PLA(2) inhibitor 3-(3-acetamide-1-benzyl-2-ethyl-indolyl-5-oxy) propane sulfonic acid (LY311727) and to the Ca(2+)-independent PLA(2) inhibitor bromoenol lactone (BEL) had only minimal effects on FFA efflux. Application of both PLA(2) and PLC to non-ischemic cortices resulted in significant increases in efflux of all FFA (P<0.05). The study suggests that FFA efflux during ischemia-reperfusion injury is coupled to activation of Ca(2+)-dependent PLA(2) and provides further evidence of the potential neuroprotective benefit of Ca(2+)-dependent PLA(2) inhibitors in ischemia.

Concurrent formation of peroxynitrite with the expression of inducible nitric oxide synthase in the brain during middle cerebral artery occlusion and reperfusion in rats

Peroxynitrite is assumed to play a crucial role in brain damage associated with the overproduction of nitric oxide (NO). The purpose of this study is to examine time-dependent changes of nitrite and nitrate (NOx) concentration in the circulation, and peroxynitrite formation as well as the expression of inducible nitric oxide synthase (iNOS) in the penumbra of rat brains during transient middle cerebral artery occlusion (MCAO) of Wistar rat for 2 h and reperfusion for 4-70 h. NOx concentration in the circulation was continuously monitored at the right jugular vein by microdialysis. The expression of iNOS was detected at 22-70 h after reperfusion in vascular walls and the cortex. Nitrotyrosine, a marker of peroxynitrite, appeared 4 h after reperfusion in the cortex, increasing substantially at 22-46 h in vascular walls. NOx level in dialysate increased immediately after MCAO. After a gradual decrease, the level increased again 4 h after reperfusion, reaching a maximum at 46 h. Brain myeloperoxidase activity, a marker of neutrophil infiltration, was not detected 4 h after reperfusion, but greatly increased at 22 h and then decreased. These results suggest that a marked increase of NOx level in the circulation might reflect the expression of iNOS, while neuronal NOS may contribute to peroxynitrite formation in the cortex observed at an earlier phase of reperfusion. This study indicates that monitoring NOx level in the circulation serves to assess the progress of stroke, and to determine appropriate therapeutic measures.

Platelet adhesion mediated by fibrinogen-intercelllular adhesion molecule-1 binding induces tissue injury in the postischemic liver in vivo

BACKGROUND

Platelets are thought to be involved in the induction of hepatic ischemia-reperfusion (I/R) injury. The mechanisms of platelet adhesion in the hepatic microvasculature and the role of platelets in the pathogenesis of I/R-induced liver damage in vivo remain unclear.

METHODS

In C57BL/6 mice, platelet- and leukocyte-endothelial cell interactions were quantitatively analyzed using intravital fluorescence microscopy in sham-operated animals, after warm lobar hepatic I/R (90/20 min) in wild-type and intercellular adhesion molecule (ICAM)-1-deficient mice, and after I/R in wild-type mice treated with an antifibrinogen antibody. Fibrinogen deposition on the endothelium was detected by intravital microscopy and by immunostaining. Reperfusion injury was assessed by measurement of liver enzyme and caspase-3 activities and of lipid peroxidation.

RESULTS

Hepatic I/R induced fibrinogen deposition on hepatic endothelium, followed by a dramatic increase in the number of firmly adherent platelets in the liver microvasculature. Simultaneously, the number of adherent leukocytes in postsinusoidal venules and the aspartate aminotransferase/alanine aminotransferase and caspase-3 activities were elevated. Although ICAM-1 deficiency attenuated postischemic adherence of both platelets and leukocytes, the application of an antifibrinogen antibody selectively reduced the number of adherent platelets but did not influence leukocyte adhesion. The selective blockade of platelet adherence significantly prevented the postischemic increase in liver enzyme and caspase-3 activities. Furthermore, sinusoidal perfusion failure and lipid peroxidation were attenuated in the treated group.

CONCLUSIONS

These in vivo data show that platelet adhesion mediated through fibrinogen deposition on ICAM-1 expressed on the endothelium of postischemic hepatic microvessels induces microvascular injury and hepatocellular apoptosis after I/R of the liver during early reperfusion.

In vivo measurement of oxygen-derived free radicals during reperfusion injury

By use of an optimized cytochrome c-based biosensor, superoxide radical production was measured continuously in vivo. The aim of this study was the online detection of superoxide concentration during reperfusion after a variable time of ischemia. Measurements were performed by placing the detecting sensor into gastrocnemius muscle tissue. Ischemia was induced by clamping the vena and arteria femoralis. Current response of the sensor was recorded continuously as an equivalent for superoxide concentration. Ischemia times varied from 5 to 120 minutes. The minimum ischemia time to record superoxide production was 10 minutes. By inducing longer periods of ischemia, an increase in superoxide concentration reached its highest levels at 2 hours. Furthermore, the total time of superoxide production after reperfusion depended on the total time of ischemia.

Improved energetic recovery of skeletal muscle in response to ischemia and reperfusion injury followed by in vivo 31P-magnetic resonance spectroscopy

It is of great clinical interest to improve postischemic tissue recovery during microsurgical transfers. The effect of singlet oxygen energy (SOE) as photon illumination at 634 nm on rat skeletal muscle during ischemia and postischemic reperfusion was investigated noninvasively and continuously by in vivo (31)P-magnetic resonance spectroscopy ((31)P-MRS). A model of pedicled rat rectus femoris muscle was used, where phosphorous metabolites were followed before onset of ischemia (control), after 4 h of ischemia, and after 1 h of reperfusion. Two groups were studied: one control group (n = 10), and one SOE-treated group (n = 10). Blood perfusion was measured by laser Doppler flowmetry (LDF) during the study. After 4 h of ischemia, ATP levels were 72% and 51% of normal control values in the illuminated group and the control group, respectively (P < 0.05). After 1 h of postischemic reperfusion, phosphocreatine (PCr) recovered to 79% and adenosine triphosphate (ATP) to 71% in the illuminated group, whereas in the control group, the recovery was 57% and 51%, respectively (P < 0.05). It is concluded that singlet oxygen energy has a beneficial effect on the energy state of skeletal muscle during ischemia and postischemic reperfusion.

Alterations of intestinal motor responsiveness in a model of mild mesenteric ischemia/reperfusion in rats

In this study we investigate the changes in intestinal motor responsiveness after mild mesenteric ischemia/reperfusion in anaesthetized rats. Motor responsiveness to pharmacological/electrical stimulation was studied in isolated ileum excised from sham-operated rats or animals which underwent occlusion of superior mesenteric artery (1 h) plus interruption of collateral blood flow and reperfusion for 0, 24, 72 h. Only 24 h reperfusion resulted in a significant suppression in acetylcholine induced contractile response and in indomethacin induced relaxation. In the presence of adrenergic and cholinergic blockade a greater relaxant response to field stimulation (trains 10 s every min, 120 mA, 1 ms and 10 Hz) was unmasked in all groups except 24 h reperfused rats. Such effect was sensitive to N(G)-Nitro-L-arginine methyl ester (NOS unselective inhibitor) and the proteolytic enzyme alpha-chymotrypsin but resistant to aminoguanidine (iNOS selective inhibitor). In conclusion, in this rat model, intestinal mild ischemia/24 h reperfusion induces reversible changes in enteric motility attributable to a decrease in eicosanoids, nitric oxide and neuropeptides availability.

In vivo microscopic assessment of microcirculatory changes in a concordant xenogeneic primate experimental set up

Organ transplantation is always connected with ischemia and thus reperfusion injury of the graft. One of the characteristics in this process is the temporary and permanent adherence of leukocytes to the endothelium of the graft. This cell-to-cell interaction allows the immunocompetent cells to interact in the sense of antigen recognition with mainly defect endothelial cells. It was the aim to study whether induction therapy with poly-clonal ATG's would reduce or even prohibit these early interactions.

MATERIAL AND METHODS

The distal extremities of cynomolgus monkeys were flushed via the femoral vessels and reperfused with ABO-compatible human heparinised blood of a hct of 30%. Microcirculation was observed applying intra-vital microscopy. The images taken by a CCD-camera are recorded on video tapes for later off line evaluation. pATG 1 is directed against jurkat cells, pATG 2 against human thymocytes. In controls the blood vessels were perfused with untreated blood. In groups 2 and 3 the blood was treated with the amount of the ATG's used in clinical therapy 15 min. prior to perfusion. The total ischemia time was 1 hour.

RESULTS

Five minutes after perfusion rolling was seen in the untreated animal, this increased to change into sticking after 30 min. The blood flow (RBC) in larger venoles remained almost normal. Both polyclonal ATG's inhibited the adhesion to a large extend.

CONCLUSION

Ischemia reperfusion results in increasing adherence of leukocytes in the described model. pATG's suppress this phenomenon completely. This suggests that pATG's contain a number of antibodies directed against various types of cell surface molecules which are involved in reperfusion injury and that pATG's have a favourable influence on the early I/R-mechanisms after organ transplantation and a protective action when used as pre-operative induction therapy.

The physiological role of dehydroascorbic acid

Dehydroascorbic acid (DHA) is abundant in the human diet and also is generated from vitamin C (ascorbic acid, AA) in the lumen of the gastrointestinal tract. DHA is absorbed from the lumen of the small intestine and reduced to AA, which subsequently circulates in the blood. Utilization of AA as an antioxidant and enzyme cofactor causes its oxidation to DHA in extracellular fluid and cells. DHA has an important role in many cell types because it can be used to regenerate AA. Both physiological (e.g. insulin, insulin-like growth factor I, cyclic AMP) and pathological (e.g. oxidative stress, diabetes, sepsis) factors alter the transport and metabolic mechanisms responsible for this DHA recycling.

The protective role of caffeic acid phenethyl ester (CAPE) on testicular tissue after testicular torsion and detorsion

Testicular artery occlusion causes an enhanced formation of reactive oxygen species, which contributes to the pathophysiology of tissue damage. Here, we have investigated the effects of caffeic acid phenethyl ester (CAPE), a new antioxidant and antiinflammatory agent, in rats subjected to testicular torsion/detorsion (T/D). Thirty-five male rats were divided into four groups: sham operation group ( n=8), torsion group ( n=9), T/D+saline group ( n=9) and T/D+CAPE group ( n=9). Rats, except the sham operation group, were subjected to left unilateral torsion (720 degrees rotation in the clockwise direction) without including the epididymis. After torsion (2 h) and detorsion (4 h) periods, rats were sacrificed and bilateral orchidectomy was performed. Testis tissues were washed with cold saline solution, cut into small pieces with scissors, placed into glass bottles and homogenised in four volumes of ice-cold Tris-HCl buffer. Clear supernatant fluid was used for biochemical analyses. Treating rats with CAPE (applied at 10 micro mol/kg, 30 min prior to T/D) attenuated the testicular injury, as well as the increase in the tissue levels of myeloperoxidase and thiobarbituric acid-reactant substances (TBARS) caused by T/D in the testis. Testis tissues showed a significant increase in glutathione peroxidase (GSH-Px) activity compared to the torsion group when CAPE was applied. Taken together, our results clearly demonstrate that CAPE treatment exerts a protective effect on testicular T/D, and part of this effect may be due to inhibiting the neutrophil-mediated cellular injury.

Platelet glycoprotein IIb/IIIa receptor antagonist (abciximab) inhibited platelet activation and promoted skin flap survival after ischemia/reperfusion injury

BACKGROUND

Evidence has shown that platelets play an important role in the pathogenesis of flap failure. Employing a rat inferior epigastric artery skin flap as a flap reperfusion injury model, we investigated whether platelet activation was involved in the skin flap failure and whether administration of abciximab (ReoPro, chimeric 7E3 Fab) could decrease platelet activation/aggregation and promote flap survival.

METHODS

Normal saline and abciximab (0.06 mg/kg; 0.2 mg/kg; 1 mg/kg) were injected intravenously into skin flaps 30 min before reperfusion and 1 h after reperfusion (each subgroup n = 6). Platelet activation as demonstrated by P-selectin (CD62P) was analyzed by flow cytometry. P-selectin expression on flap vessels was detected by immunohistochemical staining. Platelet aggregation was induced with adenosine diphosphate (ADP). Laser Doppler flowmetry monitored tissue perfusion. The surviving area was evaluated 7 days postoperatively.

RESULTS

CD62P progressively increased after reperfusion. The peak CD62P occurred after reperfusion for 12 h. Immunohistochemical staining showed CD62P significantly deposited on the endothelium after reperfusion. Administration of abciximab (1 mg/kg) effectively improved flap survival rate (P = 0.003), significantly decreased ADP-induced platelet aggregation (P < 0.001), and suppressed CD62P expression on blood platelets (P = 0.002) and its deposition on the flap vessels.

CONCLUSION

Abciximab promotion of skin flap survival is due to blocked platelet activation/aggregation and decreased activated-platelet deposition on the vascular endothelium. Thus, administration of a platelet glycoprotein IIb/IIIa receptor antagonist such as abciximab may save the skin flap from reperfusion injury after a long period of ischemia.

Pathophysiological contributions of fucosyltransferases in renal ischemia reperfusion injury

Ischemia reperfusion injury (IRI) is a major cause of delayed graft function. Recent studies have shown that selectins play an important role in IRI. Selectins bind to sialylated and fucosylated sLe(x) receptors, and two enzymes, fucosyltransferase IV (FucT-IV) and VII (FucT-VII), are important in the function of these receptors. We hypothesized that fucosyltransferase (FucT) enzymes were important pathophysiologic mediators of renal IRI. We therefore evaluated renal IRI in mice deficient in FucT-IV, FucT-VII, and both FucT-IV and FucT-VII and compared their renal function, tubular injury, selectin ligand expression, and neutrophil infiltration to those in wild-type control mice. Bilateral 30-min renal IRI was performed, and the results demonstrated that mice deficient in both FucT-IV/FucT-VII were significantly protected from renal IRI at 24 and 48 h compared with wild-type control mice. FucT-IV-deficient mice showed only modest protection from renal injury at 24 h. However, FucT-VII-deficient mice had similar injury as wild-type mice. Histological analysis of kidney tissue postischemia revealed that mice deficient in both FucT-IV and FucT-VII had significantly reduced tubular injury compared with wild-type mice. Selectin ligand expression increased postischemia in wild-type, but not FucT-IV/FucT-VII-deficient, mice. Neutrophil infiltration in postischemic kidneys of FucT-IV/FucT-VII-deficient mice was also attenuated. These data demonstrate that fucosyltransferases are important in the pathogenesis of renal IRI and are potential therapeutic targets.

[An experimental study of therapeutic effect of basic fibroblast growth factor on experimental retinal ischemia/reperfusion injury]

OBJECTIVE

To evaluate the therapeutic effect of basic fibroblast growth factor (bFGF) injected into the vitreous cavity on experimental retinal ischemia/reperfusion injury.

METHOD

The Wistar rat model of experimental retinal ischemia/reperfusion injury was made by increasing the intraocular pressure. The rats were divided into normal, ischemia and treatment groups randomly. At the beginning of reperfusion, normal saline was injected into the vitreous cavity in ischemia group and 2 micro g of bFGF was injected into the treatment group. The histological and ultrastructural changes in retina of different time after reperfusion were observed. The retinal ganglion cell number was counted by using microscope. The thickness of inner layer of retina was measured by using Image Diagnosis System.

RESULT

In the early period of retinal ischemia/reperfusion injury, the edematous status of retina of treatment group was lighter than that of the ischemia group. The retinal inner layer thickness and the RGC number of treatment group were greater than that of the ischemia group during all the post-reperfusion stages. At 168 hours after reperfusion, the thickness of the retinal nerve fiber layer and the RGC numbers of ischemia groups were obviously lower than that of the normal groups. But the differences of thickness of the nerve fiber layer and RGC number between the treatment and normal group were of no statistical importance. The nuclear membranes of RGCs were edematous and the mitochondrial cristae were unclear at 24th hour after reperfusion, the apoptotic body can be found, and the microtubules in nerve fibers became unclear and even disappeared in the ischemic group. While in the treatment group, the nucleus was clear, only part of the nuclear membrane was edematous, the cell organs were abundant and the structures of mitochondria and microtubules were clear.

CONCLUSION

Injection of bFGF into the vitreous cavity has the therapeutic effect on experimental retinal ischemia/reperfusion injury.

Testing of cerebral endothelium function with L-arginine after stroke

BACKGROUND

Endothelium-dependent vasodilatation could be impaired during hypoperfusion. L-arginine (L-A), a precursor of nitric oxide, is able to elicit endothelium-dependent vasodilatation. To determine cerebral vascular endothelial function in the early stages after ischemic stroke, we studied cerebrovascular reactivity to L-A with transcranial Doppler (TCD).

METHODS

The study group consisted of 15 patients with the middle cerebral artery syndrome, aged 57.6+/-9.8 years. They were investigated on days 7 to 10 after ischemic stroke. The control group consisted of 15 healthy volunteers, aged 58+/-10.7 years. All subjects received an intravenous infusion of L-A over 20 min at a rate of 1.5 g/min. The mean arterial velocity (vm) was measured in both middle cerebral arteries by using a bitemporal monitoring system (Multi-Dop X4, DWL). At the same time, the mean arterial pressure (MAP) and heart rate (HR) were measured by Finapres and ECG. The end-tidal CO2 (Et-Co2) was monitored by capnograph. The Vm over 5-min intervals at rest and during the infusion of L-A was determined by using the DWL TCD8 software.

RESULTS

The Vm significantly increased in both hemispheres of both groups (p=0.00). Vm differences between rest and L-A stimulation were lower in the ischemic hemispheres compared to the healthy ones (p=0.00), but did not differ between the ischemic hemispheres and hemispheres of the healthy group (p>0.05). MAP, HR and Et-Co2 did not change during the infusion (p>0.05).

CONCLUSIONS

Cerebrovascular reactivity to L-A is impaired in patients with recent stroke. The amino acid could thus be useful in testing endothelium function both in healthy persons and in stroke patients since endothelium dysfunction seems to be an important factor in reperfusion injury.

The role of endothelin-1 in ischemia-reperfusion induced acute inflammation of the bladder in rats

PURPOSE

Endothelin (ET)-1 is causatively involved in ischemia-reperfusion induced acute inflammatory reactions and microcirculatory disturbances in many organs. We investigated the role of endothelin-1 in the microcirculatory consequences of ischemia-reperfusion of the bladder using intravital fluorescence videomicroscopy.

MATERIALS AND METHODS

Male Sprague-Dawley rats were used in the experiments. The animals were randomly assigned to a sham operated group or to 1 of 2 ischemia-reperfusion groups that underwent 60 minutes of ischemia followed by 30 minutes of bladder reperfusion. In 1 ischemia-reperfusion group the animals were pretreated with BQ 610, a specific ET-A receptor blocker. The bladder was placed on an especially designed stage for intravital fluorescence videomicroscopy measurements. Venular red blood cell velocity, functional capillary density, venular and arteriolar diameter, venular and arteriolar macromolecular leakage, and leukocyte-endothelial cell interactions in postcapillary venules were determined using a computer assisted analyzing system.

RESULTS

Functional capillary density, red blood cell velocity, venular and arteriolar diameter were significantly decreased and macromolecular leakage was significantly enhanced after bladder ischemia-reperfusion. The number of rolling and adherent leukocytes was significantly increased in postcapillary venules. Pretreatment with BQ 610 was effective for attenuating the effects of ischemia-reperfusion induced inflammation but could not completely prevent microcirculatory failure.

CONCLUSIONS

Ischemia-reperfusion induced cystitis leads to significant impairment of the microcirculation and ET-1 is suggested to have an important role in this process. Pretreatment with an ET-A receptor antagonist reduces ischemia-reperfusion related microvascular disturbances in the bladder.

Quantitative real-time RT-PCR analysis of inflammatory gene expression associated with ischemia-reperfusion brain injury

Ischemia-reperfusion brain injury initiates an inflammatory response involving the expression of adhesion molecules and cytokines, some of which are regulated by the nuclear transcription factor NF-kappaB. In this study the authors examined mRNA expression levels for several important genes associated with inflammation at five time points (3, 6, 12, 24, and 72 hours) after transient middle cerebral artery occlusion (MCAO) in Sprague-Dawley rats. A sensitive and quantitative technique (TaqMan real-time QRT-PCR) was used to simultaneously measure mRNA levels for key cell adhesion molecules and inflammatory cytokines. Gene expression increased significantly in the injured hemisphere for interleukin (IL)-1beta (12-fold increase at 24 hours), IL-6 (25-fold increase at 6 hours) and ICAM-1 (4-fold increase at 24 hours), and the interhemispheric differences for these genes were significant for every time point examined (P < 0.05 for all values). Tumor necrosis factor-alpha mRNA was upregulated in the injured versus uninjured hemisphere from 3 to 24 hours (5-fold increase at 6 hours), while E-selectin showed a significant increase in mRNA levels from 6 to 24 hours after MCAO (10-fold increase at 6 hours) (P < 0.05 for all values). VCAM-1 mRNA levels did not respond differentially to injury at any time point between the two brain hemispheres. At all time points examined, activated NF-kappaB immunoreactivity was observed in cells throughout the infarct-damaged tissue. These results are consistent with the proinflammatory properties of the induced molecules, which are involved in the initiation of the inflammatory cascade, and may thus contribute to secondary cellular responses that lead to further brain damage.

Poly(ADP-ribose) polymerase triggers the microvascular mechanisms of hepatic ischemia-reperfusion injury

Activation of poly(ADP-ribose) polymerase (PARP) mediates oxidative stress-induced cell injury. We tested the hypothesis that PARP contributes to ischemia-reperfusion (I/R) damage of the liver by triggering the mechanisms of microcirculatory failure. Leukocyte- and platelet-endothelial cell interactions as well as sinusoidal perfusion were analyzed by intravital fluorescence microscopy after lobar hepatic I/R (90 min/30 min) in C57BL/6 x 129/Sv wild-type (PARP+/+) and PARP-deficient (PARP-/-) mice. Hepatic I/R induced leukocyte/platelet-endothelial cell interactions and tissue injury in PARP+/+ mice, as indicated by impaired sinusoidal perfusion and increased alanine aminotransferase (ALT)/aspartate aminotransferase (AST) serum activities. In PARP-/- mice, however, the postischemic increase in the numbers of rolling/adherent leukocytes and platelets was significantly lower. In addition, I/R-induced translocation of CD62P as well as mRNA expression of CD62E, CD54, and CD106 were attenuated. The degree of perfusion failure was reduced and the increase in the ALT/AST activities was lower in PARP-/- mice compared with PARP+/+ mice. We conclude that PARP contributes to hepatic microvascular injury by triggering the expression/translocation of adhesion molecules and modulating leukocyte/platelet-endothelial cell interactions.

The effect of endothelin antagonists on renal ischaemia-reperfusion injury and the development of acute renal failure in the rat

BACKGROUND

It is recognized that endothelins are released in response to hypoperfusion and anoxia of the kidney and may be responsible for the consequent deterioration in renal function. This study examined the ability of a non-selective (SB209670) and ET(A)-selective (UK-350,926) endothelin antagonist to attenuate ischaemia-induced renal failure in unilaterally nephrectomized rats.

METHODS

The animals were anaesthetized, drug infusion commenced, and the renal artery occluded for 30 min. The endothelin antagonists were given for 30 min before, during, and 60 min after the ischaemic period, at 10, 30 and 100 micro g/kg/min or for 60 min after the start of reperfusion.

RESULTS

On day 1, following 30 min renal artery occlusion, there was a 95% reduction in glomerular filtration rate, an 8-10-fold increase in plasma creatinine, and 10-15-fold increases in fractional excretions of sodium and potassium, which were partially resolved on day 3 and normalized on day 8. The lowest dose of SB209670 was without effect on the renal functional responses but they were blunted (all P<0.05) by the highest dose. At 30 and 100 micro g/kg/min UK-350,926, the decreases in renal function subsequent to the ischaemic challenge were attenuated. Administration of UK-350,926 at 100 micro g/kg/min for 1 h starting 60 min after the start of reperfusion, had no effect on the magnitude of the renal disturbances over the first 3 days.

CONCLUSIONS

The data show that both the ET(A)/ET(B) and selective ET(A)-receptor antagonist ameliorated the ischaemia-reperfusion injury when given in the peri-ischaemic period but not when the ET(A)-receptor antagonist was given for 60 min at 100 micro g/kg/min after the ischaemic period.

Bench to bedside: brain edema and cerebral resuscitation: the present and future

Sudden cardiac arrest (CA) claims approximately 1,200 lives daily in the United States. Cardiopulmonary resuscitation attempts have so far achieved suboptimal results, and even when restoration of spontaneous circulation (ROSC) is achieved, about 30% of survivors suffer permanent brain damage. This illustrates the need for an improved basic scientific understanding of the pathophysiology of global cerebral injury caused by whole-body ischemia/reperfusion (I/R) injury following CA. Brain edema has been recently documented in experimental CA followed by one hour of ROSC. Brain edema has also been documented in CA and stroke patients by computed tomography or magnetic resonance imaging scanning, and has been shown to predict a poor neurologic outcome. The mechanisms underlying brain edema formation elicited by CA are unclear. New scientific findings of the roles of blood-brain barrier (BBB) permeability, matrix metalloproteinases (MMPs) of a family of proteases, aquaporin 4 (AQP4) of a family of membrane water-channel proteins, and the N-methyl-D-aspartate (NMDA) receptors in the mechanisms underlying CA-elicited brain edema were reviewed. By defining the roles of BBB permeability, MMPs, AQP4, and NMDA receptors in CA-induced brain edema formation, effective new therapeutic strategies to extend cellular and tissue survival, and preserve neurologic function following CA may be feasible.

Do vitamins C and E attenuate the effects of reactive oxygen species during pulmonary reperfusion and thereby prevent injury?

BACKGROUND

We established an in vivo pig model of standardized lung ischemia to analyze pulmonary reperfusion injury. Enhanced chemiluminescence measurement (CM) allowed immediate quantification of reactive oxygen species (ROS) and subsequent lipid peroxidation. In such model we analyzed efficacy of vitamins C and E to prevent reperfusion injury.

METHODS

After left lateral thoracotomy in group I (n = 6), normothermic lung ischemia was maintained for 90 minutes followed by a 5-hour reperfusion period. In group II, animals (n = 6) underwent ischemia as in group I, but received vitamins (preoperative IV bolus C = 1 g, E = 0.75 g, then continuous infusion (125 mg/h) each throughout the study). In Group III, animals (n = 6) underwent sham surgery and served as controls. Hemodynamic variables and gas exchange were assessed. The CM was performed for injury quantification in blood samples and to determine activation of isolated PMNs. The Wilcox rank test was used for statistical analysis.

RESULTS

During reperfusion, all animals in group I developed significant pulmonary edema with significant loss of pulmonary function. The addition of vitamins (group II) improved oxygenation and almost abolished pulmonary inflammatory cell infiltration; however, as in group I, pulmonary compliance still tended to decline and the number of circulating leucocytes increased. The CM showed that, compared with group I, vitamins reduced O2- basic release by PMNs significantly (460% to 170%, p < 0.05; control 165%), but could not prevent an increase of free ROS in whole blood similar to group I (443% to 270%, p = ns, control 207%). With regard to lipid peroxidation only a trend of reduction was observed (117% to 105%, p = ns, control 100%).

CONCLUSIONS

Differentiated analysis by CM demonstrated that vitamins C and E inhibited PMN activation but were not able to prevent radical production by other sources. This offers a potential explanation why radical scavengers like vitamins only attenuate but ultimately do not prevent reperfusion injury.

Role of ICAM-1 in chronic ethanol consumption-enhanced liver injury after gut ischemia-reperfusion in rats

Intercellular adhesion molecule-1 (ICAM-1) has been implicated in the hepatic microvascular dysfunction elicited by gut ischemia-reperfusion (I/R). Although the effects of chronic ethanol (EtOH) consumption on the liver are well known, it remains unclear whether this condition renders the hepatic microcirculation more vulnerable to the deleterious effects of gut and/or hepatic I/R. The objectives of this study were to determine whether chronic EtOH consumption alters the severity of gut I/R-induced hepatic microvascular dysfunction and hepatocellular injury and to determine whether ICAM-1 contributes to this response. Male Wistar rats, pair fed for 6 wk a liquid diet containing EtOH or an isocaloric control diet, were exposed to gut I/R. Intravital video microscopy was used to monitor leukocyte recruitment in the hepatic microcirculation, the number of nonperfused sinusoids (NPS), and plasma concentrations of endotoxin and tumor necrosis factor-alpha. Plasma alanine aminotransferase (ALT) levels were measured 6 h after the onset of reperfusion. In control rats, gut I/R elicited increases in the number of stationary leukocytes, NPS, and plasma endotoxin, tumor necrosis factor-alpha, and ALT. In EtOH-fed rats, the gut I/R-induced increases in NPS and leukostasis were blunted in the midzonal region, while exaggerated leukostasis was noted in the pericentral region and terminal hepatic venules. Chronic EtOH consumption also enhanced the gut I/R-induced increase in plasma endotoxin and ALT. The exaggerated responses to gut I/R normally seen in EtOH-fed rats were largely prevented by pretreatment with a blocking anti-ICAM-1 monoclonal antibody. In conclusion, these results suggest that chronic EtOH consumption enhances gut I/R-induced hepatic microvascular dysfunction and hepatocellular injury in the pericentral region and terminal hepatic venules via an enhanced hepatic expression of ICAM-1.

Neuroregulative mechanism of hypothalamic paraventricular nucleus on gastric ischemia-reperfusion injury in rats

A rat model of gastric ischemia-reperfusion injury (GI-RI) was established by clamping the celiac artery for 30 min and allowing reperfusion for 1 h, on which the regulatory effect of the paraventricular nucleus (PVN) and its neural mechanisms were investigated. The results were: 1. Electrical stimulation of the PVN obviously attenuated the GI-RI. Microinjection of L-glutamic acid into PVN produced an effect similar to that of PVN stimulation. 2. Electrolytic ablation of the PVN aggravated the GI-RI. 3. Nucleus tractus solitarius (NTS) ablation could eliminate the protective effect of electrical stimulation of PVN on GI-RI. 4. Hypophysectomy did not alter the effect of electrical stimulation of PVN. 5. Vagotomy or sympathectomy both could increase the effect of PVN stimulation on GI-RI. These results indicate that the PVN participates in the development of GI-RI as a specific area in the CNS, exerting protective effects on the GI-RI. The NTS and vagus and sympathetic nerve may be involved in the regulative mechanism of PVN on GI-RI, but the PVN mechanism here is independent of the PVN-hypophyseal pathway.

Cerebral postischemic reperfusion-induced demethylation of the protein phosphatase 2A catalytic subunit

Brain reperfusion after a period of global ischemia induces changes in the phosphorylation state of a great number of proteins. Neuronal responses to ischemia and reperfusion are quite different depending on the brain region, and phosphorylation changes may be implicated in this tissue-specific response. For this reason, we have used both biochemical and immunohistochemical methods to investigate the potential role of PP2A, the most abundant Ser/Thr phosphatase in the brain, in ischemic injury. PP2A activity as measured with phosphorylase a as substrate was slightly inhibited after 30 min ischemia followed by 30 min reperfusion, and this inhibition correlated with an increased S6K1 and ERK1/2 phosphorylation. Using a monoclonal antibody unable to recognize the methylated form of PP2Ac, we demonstrated that the catalytic subunit of PP2A (PP2Ac) was highly methylated in the brain. In addition, the postischemic reperfusion-induced changes in PP2Ac methylation were studied in sections from cerebral cortex, hippocampus and striatum. Regional differences in PP2Ac methylation were observed within control brains, and the postischemic reperfusion caused a generalized demethylation of PP2Ac. Those regions in the control brains containing highest levels of methylated PP2Ac were the most intensively demethylated after reperfusion and corresponded to the regions most vulnerable to ischemic damage.

Time course of lung ischemia-reperfusion-induced ICAM-1 expression and its role in ischemia-reperfusion lung injury

Upregulation of intercellular adhesion molecule-1 (ICAM-1) expression is an important mechanism underlying ischemia-reperfusion (I/R) induced neutrophil activation and tissue injury in other organs. However, I/R of the lungs has not been shown to upregulate ICAM-1 expression. We determined the time course profile of lung I/R-induced ICAM-1 expression and assessed the role of ICAM-1 in mediating neutrophil sequestration, transmigration, and I/R injury in the isolated blood-perfused rat lungs. I/R had a biphasic effect on ICAM-1 expression, an early downregulation and a late-phase upregulation. Superoxide dismutase and neutrophil depletion prevented the early ICAM-1 downregulation. The late-phase ICAM-1 upregulation coincided with the I/R-induced increase in pulmonary microvascular leakage index. ICAM-1 monoclonal antibody (MAb) reversed the I/R-induced increase in pulmonary microvascular leakage index, with control antibody being ineffective. Neither I/R nor ICAM-1 MAb affected lung MPO activity and circulating neutrophil count. Lung I/R significantly increased bronchoalveolar lavage fluid neutrophil count and the GSSG-to-(GSSG+GSH) ratio. ICAM-1 MAb blocked the I/R-induced increase in GSSG-to-(GSSG+GSH) ratio but had no effect on bronchoalveolar lavage fluid neutrophil count. Our results demonstrated that lung I/R up- and downregulates ICAM-1 expression depending on the duration of reperfusion. ICAM-1 upregulation is an important mechanism of I/R-induced pulmonary endothelial injury.

Gut barrier permeability, reticuloendothelial system function and protease inhibitor levels following intestinal ischaemia and reperfusion--effects of pretreatment with N-acetyl-L-cysteine and indomethacin

BACKGROUND

Pathophysiological mechanisms and ways to intervene on intestinal barrier dysfunction following small intestinal ischaemia and prolonged reperfusion are still not fully clarified.

AIMS

To evaluate the effect of oxygen free radical and prostaglandin inhibition on intestinal barrier injury following intestinal ischaemia/reperfusion.

METHODS

Endothelial and epithelial barrier permeability was evaluated by clearance of radiolabelled albumin. Parameters included 125I-Escherichia coli uptake rate index, host reticuloendothelial system function and organ distribution, as well as protease inhibitor and proenzyme activities in rats subjected to small intestinal ischaemia for 40 minutes followed by 12 hours reperfusion (ischaemia/reperfusion), pretreated with N-acetyl-L-cysteine or indomethacin.

RESULTS

Following ischaemia/reperfusion, endothelial and epithelial permeability increased, reticuloendothelial system activation occurred and plasma protease inhibitors were consumed. N-acetyl-L-cysteine pretreatment resulted in improved endothelial and epithelial barrier integrity, a decrease in protease inhibitor consumption and less pronounced reticuloendothelial system activation. Pretreatment with indomethacin was not effective.

CONCLUSION

Oxygen free radicals seem to play an important role in the development of intestinal barrier impairment following ischaemia/reperfusion. N-acetyl-L-cystine may be a potential agent for preventing ischaemia/reperfusion damage.