Ischemia-reperfusion: mechanisms of microvascular dysfunction and the influence of risk factors for cardiovascular disease

Leucocyte and platelet adhesion in different layers of the small bowel during experimental total warm ischaemia and reperfusion

Background

Ischaemia and reperfusion (IR) of the small bowel is involved in many clinical conditions. A key component in IR-induced tissue damage is microvascular dysfunction. The aim was to investigate the role of leucocytes and platelets in capillary flow impediment and tissue damage.

Methods

Anaesthetized rats were subjected to 30 min warm ischaemia of the small bowel, followed by 1 h reperfusion. To elucidate the influence of leucocytes on platelet adhesion, leucocyte–vessel wall interactions induced by IR were prevented by anti-platelet activating factor (PAF) or anti-intercellular adhesion molecule (ICAM)-1. Intravital videomicroscopy was performed and tissue injury was evaluated histologically.

Results

In submucosal venules, IR induced an increase in the median number of interacting leucocytes from 3 to 10 and 20 leucocytes per 100-µm venule segment after 10 and 60 min reperfusion respectively. Anti-PAF or anti-ICAM-1 completely attenuated this increase, resulting in an eightfold improvement in submucosal capillary flow and reduced tissue injury. Shedding of villi no longer occurred. Platelet–vessel wall interactions occurred particularly in submucosal venules, but were not affected by anti-PAF or anti-ICAM-1.

Conclusion

Small bowel IR initiated an inflammatory and thrombotic response in the submucosal layer only. Attenuation of leucocyte adhesion improved submucosal capillary perfusion, preventing shedding of mucosal villi.

Reactive oxygen species participate in acute renal vasoconstrictor responses induced by ETAand ETBreceptors

Reactive oxygen species (ROS) play important roles in renal vasoconstrictor responses to acute and chronic stimulation by angiotensin II and norepinephrine, as well as in long-term effects of endothelin-1 (ET-1). Little is known about participation of ROS in acute vasoconstriction produced by ET-1. We tested the influence of NAD(P)H oxidase inhibition by apocynin [4 mg·kg−1·min−1, infused into the renal artery (ira)] on ETAand ETBreceptor signaling in the renal microcirculation. Both receptors were stimulated by ET-1, ETAreceptors by ET-1 during ETBantagonist BQ-788, and ETBby ETBagonist sarafotoxin 6C. ET-1 (1.5 pmol injected ira) reduced renal blood flow (RBF) 17 ± 4%. Apocynin raised baseline RBF (+10 ± 1%, P < 0.001) and attenuated the ET-1 response to 10 ± 2%, i.e., 35 ± 9% inhibition ( P < 0.05). Apocynin reduced ETA-induced vasoconstriction by 42 ± 12% ( P < 0.05) and that of ETBstimulation by 50 ± 8% ( P < 0.001). During nitric oxide (NO) synthase inhibition ( Nω-nitro-l-arginine methyl ester), apocynin blunted ETA-mediated vasoconstriction by 60 ± 8% ( P < 0.01), whereas its effect on the ETBresponse (by 87 ± 8%, P < 0.001) was even larger without than with NO present ( P < 0.05). The cell-permeable superoxide dismutase mimetic tempol (5 mg·kg−1·min−1ira), which reduces O2−and may elevate H2O2, attenuated ET-1 responses similar to apocynin (by 38 ± 6%, P < 0.01). We conclude that ROS, O2−rather than H2O2, contribute substantially to acute renal vasoconstriction elicited by both ETAand ETBreceptors and to basal renal vasomotor tone in vivo. This physiological constrictor action of ROS does not depend on scavenging of NO. In contrast, scavenging of O2−by NO seems to be more important during ETBstimulation.

Increasing heel skin perfusion by elevation

OBJECTIVE

To determine the efficacy of elevation in the primary prevention and treatment of pressure ulcers by studying the blood flow in tissue at risk of ulceration.

DESIGN

A prospective study was used to compare different preventative devices with an elevating prosthesis.

SETTING

: Wollongong Hospital Wollongong, New South Wales, Australia.

PARTICIPANTS

Normal subjects and subjects with vasculopathy were tested with their heel resting on a hospital bed, medical-grade lamb's wool, or a viscoelastic gel overlay, with or without the test prosthesis. Skin perfusion was measured throughout using a laser Doppler monitor.

INTERVENTION

A device designed to elevate the heel off the bed and distribute the weight of the leg and foot on the calf.

MAIN OUTCOME MEASURE

Heel capillary blood perfusion.

MAIN RESULTS

Perfusion in the heel was significantly greater when elevated than when using the other devices tested. The differences in mean red blood cell flux were significant, with P < .0001 for bed-normals, ie, subjects with no peripheral vascular disease on an alpha Xcell mattress overlay as the control with flux increasing from 7.6 to 163.1 arbitrary units (AU); P < .005 bed-vasculopathy, ie, subjects with peripheral vascular disease on an alpha Xcell mattress overlay as the control with flux increasing from 31.6 to 224.7 AU; P < .0001 viscoelastic overlay subjects where the viscoelastic overlay was the control with flux increasing from 26.6 to 291.4 AU; and P < .01 lamb's wool subjects where the lamb's wool was the control with flux increasing from 27.7 AU to 169.2 AU.

CONCLUSION

In this study, when the heels were elevated, tissue perfusion to that area was substantially increased. When the heel was transferred to the elevating splint, the heel capillary bed underwent reactive hyperemia, indicating the alleviation of tissue hypoxia. Elevation is therefore an important technique in pressure ulcer prevention and treatment and should be incorporated into health care practice.

A Global Assessment of the Inflammatory Response Elicited Upon Open Abdominal Aortic Aneurysm Repair

The inflammatory response during elective open infrarenal abdominal aortic aneurysm repair and its impact on outcome is investigated. Twenty high-risk patients were enrolled, and blood samples were obtained at 8 perioperative time points. Endotoxin, cytokines (tumor necrosis factor-α and interleukin-1β, and interleukin-6), CD11b expression, and nitric oxide were measured. Peak endotoxin levels occurred within 30 minutes of reperfusion and were higher among patients developing complications. Interleukin-6 levels increased during reperfusion, reaching a peak on the first postoperative day. Interleukin-6 increase correlated with aortic clamp time and morbidity. CD11b expression increased 30 minutes after reperfusion, and this effect was greater among patients who developed complications. Endotoxin may be important in the pathogenesis of multiple organ dysfunction syndrome. Activated neutrophils may have a central role in tissue injury after reperfusion. Intraoperative CD11b upregulation may be an early marker for postoperative complications after infrarenal abdominal aortic aneurysm repair.

In vivo reactive oxygen species production induced by ischemia in muscle arterioles of mice: involvement of xanthine oxidase and mitochondria

Reactive oxygen species (ROS) participate in tissue injury after ischemia-reperfusion. Their implication in leukocyte adherence and increase in permeability at the venular side of the microcirculation have been reported, but very little is known about ROS production in arterioles. The objective of this work was to evaluate, in the arteriole wall in vivo, the temporal changes in superoxide anion production during ischemia and reperfusion and to identify the source of this production. Mouse cremaster muscle was exposed to 1 h of ischemia followed by 30 min of reperfusion, and superoxide anion production was assessed by a fluorescent probe, i.e., intracellular dihydroethidium oxidation. During ischemia, we found a significant increase in dihydroethidium oxidation; however, we observed no additional increase in fluorescence during the subsequent reperfusion. This phenomenon was significantly inhibited by pretreatment with superoxide dismutase. Allopurinol (xanthine oxidase inhibitor) or stigmatellin [Q(o)-site (oriented toward the intermembrane space) inhibitor of mitochondrial complex III] or simultaneous administration of these two inhibitors significantly reduced superoxide production during ischemia to 80%, 88%, and 72%, respectively, of that measured in the untreated ischemia-reperfusion group. By contrast, no significant inhibition was found when NADPH oxidase was inhibited by apocynin or when mitochondrial complex I or complex II was inhibited by rotenone or thenoyltrifluoroacetone. A significant increase in ROS was found with antimycin A [Q(i)-site (located in the inner membrane and facing the mitochondrial matrix) inhibitor of mitochondrial complex III]. We conclude that a significant increase in ROS production occurs during ischemia in the arteriolar wall. This increased production involves both a cytoplasmic source (i.e., xanthine oxidase) and the mitochondrial complex III at the Q(o) site.

Activation of the annexin 1 counter‐regulatory circuit affords protection in the mouse brain microcirculation

The purpose of this study was to investigate the role of the homeostatic antiinflammatory axis centered on annexin 1 (AnxA1) in cerebral microvascular dysfunction and tissue injury associated with middle cerebral artery (MCA) occlusion and reperfusion. Intravital fluorescence microscopy was used to visualize the mouse cerebral microcirculation: AnxA1 null mice exhibited more white blood cell adhesion in cerebral venules than their wild-type counterparts, and this was accompanied by a larger cerebral infarct vol and worse neurological score. All parameters were rescued by delivery of human recombinant AnxA1. To further explore these findings using pharmacological tools, the effect of a short AnxA1 peptidomimetic was tested. When given during the reperfusion phase, peptide Ac2-26 produced similar cerebroprotection, which was associated with a marked attenuation of cell adhesion and markers of inflammation as measured in tissue homogenates. The pharmacological effects of peptide Ac2-26 occurred via receptors of the formyl-peptide receptor (FPR) family, most likely FPR-rs2, as deduced by displacement assays with transfected cells and in vivo experiments with transgenic mice and receptor antagonists. Our findings indicate that the endogenous antiinflammatory circuit centered on AnxA1 produces significant cerebral protection, and that these properties might have therapeutic potential for stroke treatment.

The endothelial glycocalyx: composition, functions, and visualization

This review aims at presenting state-of-the-art knowledge on the composition and functions of the endothelial glycocalyx. The endothelial glycocalyx is a network of membrane-bound proteoglycans and glycoproteins, covering the endothelium luminally. Both endothelium- and plasma-derived soluble molecules integrate into this mesh. Over the past decade, insight has been gained into the role of the glycocalyx in vascular physiology and pathology, including mechanotransduction, hemostasis, signaling, and blood cell–vessel wall interactions. The contribution of the glycocalyx to diabetes, ischemia/reperfusion, and atherosclerosis is also reviewed. Experimental data from the micro- and macrocirculation alludes at a vasculoprotective role for the glycocalyx. Assessing this possible role of the endothelial glycocalyx requires reliable visualization of this delicate layer, which is a great challenge. An overview is given of the various ways in which the endothelial glycocalyx has been visualized up to now, including first data from two-photon microscopic imaging.

Haptoglobin Genotype Determines Myocardial Infarct Size in Diabetic Mice

OBJECTIVES

We sought to understand the importance of oxidative stress in explaining why the haptoglobin (Hp) genotype determines myocardial infarction (MI) size in diabetes mellitus (DM).

BACKGROUND

Two common alleles (1 and 2) exist at the Hp locus in humans. The Hp 2 allele is associated with increased MI size in individuals with DM. In vitro, the Hp 2 protein is associated with increased generation of oxidatively active iron, whereas the Hp 1 protein is associated with increased production of the antioxidant cytokine interleukin (IL)-10.

METHODS

Myocardial infarction was produced by myocardial ischemia-reperfusion (IR) in DM C57BL/6 mice carrying the Hp 1 or Hp 2 allele. Myocardial oxidative stress after IR was assessed using electrospray ionization mass spectrometry. Redox active iron and IL-10 were measured in the serum after IR.

RESULTS

Myocardial infarction size was significantly larger in Hp 2 mice as compared with Hp 1 mice (44.3 +/- 9.3% vs. 21.0 +/- 4.0%, p = 0.03), and these larger infarctions were associated with a significant increase in a panel of hydroxyl-eicosatetraenoic acids. Redox active iron was greater in Hp 2 mice (0.45 +/- 0.11 micromol/l vs. 0.14 +/- 0.05 micromol/l, p = 0.02), whereas IL-10 was greater in Hp 1 mice (85.8 +/- 12.9 pg/microl vs. 46.7 +/- 10.8 pg/microl, p = 0.04) after IR. Administration of an antioxidant (BXT-51072) to Hp 2 mice reduced myocardial injury after IR by more than 80% (p = 0.003), but no myocardial protection was provided by the antioxidant to Hp 1 mice.

CONCLUSIONS

The increased MI size in DM Hp 2 mice occurring after IR may be due to increased oxidative stress.

The effect of coronary angioplasty on plasma NT-proBNP level in patients with and without arterial hypertension

AIMS

The purpose of the study was to assess the effect of percutaneous transluminal coronary angioplasty (PTCA) on plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) level in hypertensive and normotensive subjects with and without systolic left ventricular dysfunction.

METHODS AND RESULTS

Forty patients affected by ischemic heart disease and submitted to PTCA were studied. The patients were divided into four groups: group I - 10 patients with essential arterial hypertension (HT) and normal left ventricular ejection fraction (EF); group II - 10 patients with HT and EF < 55%; group III - 10 patients without HT and with normal EF; group IV - 10 patients without HT and with EF < 55%. Blood samples were collected twice: 24 h before and after PTCA. The plasma NT-proBNP concentrations increased significantly in group I (368+/-103 pg/ml vs 488 +/- 182 pg/ml; p < 0.05), in group III (257 +/- 107 pg/ml vs 447 +/- 198 pg/ml; p < 0.05), and in group IV (419 +/- 99 pg/ml vs 826 +/- 432 pg/ml; p < 0.05) 24 h after PTCA. There were significant differences in the relative change in plasma NT-proBNP concentrations between groups I and II, and between groups III and IV.

CONCLUSIONS

Successful coronary angioplasty results in a rise in plasma NT-proBNP concentration. The increase is less expressive in patients with systolic left ventricular dysfunction. The presence of hypertension does not affect NT-proBNP concentration after PTCA.

Evaluating therapeutic targets for reperfusion-related brain hemorrhage

OBJECTIVE

Early reperfusion after an ischemic stroke can cause blood-brain barrier injury with subsequent cerebral edema and devastating brain hemorrhage. These complications of early reperfusion, which result from excess production of reactive oxygen species, significantly limit the benefits of stroke therapies. In this article, we use a novel animal model that facilitates identification of specific components of the reperfusion injury process, including vascular injury and secondary brain damage, and allows assessment of therapeutic interventions.

METHODS

Knock-out (KO) mice containing 50% manganese-superoxide dismutase activity (SOD2-KO) and transgenic mice overexpressing SOD2 undergo transient focal ischemia and reperfusion followed by assessment of infarct, edema, hemorrhage rates, metalloproteinase activation, and microvascular injury.

RESULTS

SOD2-KO mice demonstrate delayed (>24h) blood-brain barrier breakdown associated with activation of matrix metalloproteinases, inflammation, and high brain hemorrhage rates. These adverse consequences are absent in wild-type littermates and minocycline-treated SOD2-KO animals. Increased hemorrhage rates also are absent in SOD2 overexpressors, which have reduced vascular endothelial cell death. Finally, we show that the tight junction membrane protein, occludin, is an early and specific target in oxidative stress-induced microvascular injury.

INTERPRETATION

This model is ideal for studying ischemia/reperfusion-induced vascular injury and secondary brain hemorrhage and offers a unique opportunity to evaluate antioxidant-based neurovascular protective strategies as potential adjunct treatments to currently approved stroke therapies such as thrombolysis and endovascular clot retrieval.

Role of endothelin-1 and cyclic nucleotides in ischemia/reperfusion-mediated microvascular leak

BACKGROUND

A consequence of ischemia/reperfusion (IR) is endothelial barrier dysfunction and intravascular volume loss. The purposes of our study are to explore the impact of: 1) cyclic guanosine monophosphate (cGMP) synthesis inhibition, 2) cyclic adenosine monophosphate (cAMP) synthesis inhibition, 3) treatment with endothelin-1, and 4) endothelin-1 (ET-1)-mediated cAMP changes on IR-induced fluid leak. We hypothesize that IR-mediated microvascular fluid leak results from increased cGMP activity and ET-1 decreases IR-induced fluid leak via cAMP.

METHODS

A micro-cannulation technique was used to determine fluid leak or hydraulic permeability (Lp) in rat mesenteric venules. Lp was measured during IR and after treatment with 1) cGMP synthesis inhibitor (LY83583,10 micromol/L) 2) cAMP synthesis inhibitor (2',5'dideoxyadenosine,10 micromol/L), 3) ET-1 (80 pM), and 4) cAMP synthesis inhibitor plus ET-1 (n=6 in each group; Lp represented as mean+/-standard error of the mean; units 10-cm/sec/cmH2O).

RESULTS

IR resulted in an increase in Lp (Lp=7.07+/-0.20) sevenfold above baseline (1.05+/-0.31) (p<or=0.001). Compared with IR alone, 1) pretreatment with cGMP synthesis inhibitor completely blocked IR-induced fluid leak (Lp=1.08+/-0.18) (p<or=0.001), 2) pretreatment with cAMP synthesis inhibitor attenuated fluid leak (Lp=3.92+/-0.20) (p<or=0.005), 3) treatment with ET-1 decreased fluid leak (Lp=5.38+/-0.28) (p<or=0.005), and 4) pretreatment with a cAMP inhibitor plus treatment with ET-1 reduced fluid leak nearly 50% compared with ET-1 alone (Lp=2.95+/-0.12) (p<or=0.005).

CONCLUSION

cGMP inhibition completely blocks fluid leak, pointing toward a central role as a mediator of IR-induced postcapillary venular leak. ET-1 mildly decreased leak. Furthermore, ET-1 may not exert its effects on microvascular fluid leak during IR via cAMP.

Leukocyte adherence inhibits adenosine-dependent venular control of arteriolar diameter and nitric oxide

Venular control of arteriolar perfusion has been the focus of several investigations in recent years. This study investigated 1) whether endogenous adenosine helps control venule-dependent arteriolar dilation and 2) whether venular leukocyte adherence limits this response via an oxidant-dependent mechanism in which nitric oxide (NO) levels are decreased. Intravital microscopy was used to assess changes in arteriolar diameters and NO levels in rat mesentery. The average resting diameter of arterioles (27.5 +/- 1.0 microm) paired with venules with minimal leukocyte adherence (2.1 +/- 0.3 per 100-microm length) was significantly larger than that of unpaired arterioles (24.5 +/- 0.8 microm) and arterioles (23.3 +/- 1.3 microm) paired with venules with higher leukocyte adherence (9.0 +/- 0.5 per 100-microm length). Local superfusion of adenosine deaminase (ADA) induced significant decreases in diameter and perivascular NO concentration in arterioles closely paired to venules with minimal leukocyte adherence. However, ADA had little effect on arterioles closely paired to venules with high leukocyte adherence or on unpaired arterioles. To determine whether the attenuated response to ADA for the high-adherence group was oxidant dependent, the responses were also observed in arterioles treated with 10(-4) M Tempol. In the high-adherence group, Tempol fully restored NO levels to those of the low-adherence group; however, the ADA-induced constriction remained attenuated, suggesting a possible role for an oxidant-independent vasoconstrictor released from the inflamed venules. These findings suggest that adenosine- and venule-dependent dilation of paired arterioles may be mediated, in part, by NO and inhibited by venular leukocyte adherence.

Mechanisms of the anti-inflammatory effects of the natural secosteroids physalins in a model of intestinal ischaemia and reperfusion injury

Reperfusion of an ischaemic tissue is associated with an intense inflammatory response and inflammation-mediated tissue injury. Physalins, a group of substances with secosteroidal chemical structure, are found in Physalis angulata stems and leaves. Here, we assessed the effects of physalins on the local, remote and systemic injuries following intestinal ischaemia and reperfusion (I/R) in mice and compared with the effects of dexamethasone. Following I/R injury, dexamethasone (10 mg kg(-1)) or physalin B or F markedly prevented neutrophil influx, the increase in vascular permeability in the intestine and the lungs. Maximal inhibition occurred at 20 mg kg(-1). Moreover, there was prevention of haemorrhage in the intestine of reperfused animals. Dexamethasone or physalins effectively suppressed the increase in tissue (intestine and lungs) and serum concentrations of TNF-alpha. Interestingly, treatment with the compounds was associated with enhancement of IL-10. The anti-inflammatory effects of dexamethasone or physalins were reversed by pretreatment with the corticoid receptor antagonist RU486 (25 mg kg(-1)). The drug compounds suppressed steady-state concentrations of corticosterone, but did not alter the reperfusion-associated increase in levels of corticosterone. The IL-10-enhancing effects of the drugs were not altered by RU486. In conclusion, the in vivo anti-inflammatory actions of physalins, natural steroidal compounds, appear to be mostly due to the activation of glucocorticoid receptors. Compounds derived from these natural secosteroids may represent novel therapeutic options for the treatment of inflammatory diseases.

NF-kappaB plays a major role during the systemic and local acute inflammatory response following intestinal reperfusion injury

1 The nuclear translocation of transcription factors may be a critical factor in the intracellular pathway involved in ischaemia/reperfusion (I/R) injury. Here, we examined whether NF-kappaB and AP-1 participated in the cascade of events leading to TNF-alpha production, neutrophil recruitment, tissue injury and lethality following intestinal I/R. 2 The superior mesenteric artery (SMA) of mice was made ischaemic for 60 min followed by 30 min of reperfusion. The effects of NF-kappaB and AP-1 were studied by the administration of the thioredoxin inhibitor, MOL-294 (methyl 4-hydroxy-4-(8-methyl-1,3-dioxo-2-phenyl-2,3,5,8-tetrahydro-1H-[1,2,4]triazolo[1,2-a]pyridazin-5-yl)but-2-ynoate), and the AP-1 inhibitor, PNRI-299 (N-benzyl-2-(3-cyanophenyl)-1,3,7-trioxo-2,3,7,8-tetrahydro-1H-[1,2,4]triazolo[1,2-a]pyridazine-5-carboxamide). After I/R, there was increase of translocation of NF-kappaB, but not of AP-1, in the intestine and lungs, as assessed by a gel shift assay. 3 Treatment with MOL-294 inhibited the increase in vascular permeability, neutrophil accumulation, hemorrhage and proinflammatory cytokine levels, induced by intestinal I/R injury in the intestine. In the lungs, MOL-294 partially inhibited edema formation, TNF-alpha production, but did not alter neutrophil recruitment. 4 Treatment with MOL-294 inhibited reperfusion-associated lethality, an effect likely to be secondary to the inhibition of systemic TNF-alpha levels. PNRI-299 had no effects on the inflammatory changes or lethality induced by I/R injury. 5 Our results point to an important role for NF-kappaB in triggering endogenous proinflammatory networks during intestinal I/R injury. Inhibition of NF-kappaB prevents tissue injury and lethality, and this was associated with inhibition of TNF-alpha production and decrease in neutrophil recruitment.

The balance between the production of tumor necrosis factor-alpha and interleukin-10 determines tissue injury and lethality during intestinal ischemia and reperfusion

A major goal in the treatment of acute ischemia of a vascular territory is to restore blood flow to normal values, i.e. to "reperfuse" the ischemic vascular bed. However, reperfusion of ischemic tissues is associated with local and systemic leukocyte activation and trafficking, endothelial barrier dysfunction in postcapillary venules, enhanced production of inflammatory mediators and great lethality. This phenomenon has been referred to as "reperfusion injury" and several studies demonstrated that injury is dependent on neutrophil recruitment. Furthermore, ischemia and reperfusion injury is associated with the coordinated activation of a series of cytokines and adhesion molecules. Among the mediators of the inflammatory cascade released, TNF-alpha appears to play an essential role for the reperfusion-associated injury. On the other hand, the release of IL-10 modulates pro-inflammatory cytokine production and reperfusion-associated tissue injury. IL-1beta, PAF and bradykinin are mediators involved in ischemia and reperfusion injury by regulating the balance between TNF-alpha and IL-10 production. Strategies that enhance IL-10 and/or prevent TNF-alpha concentration may be useful as therapeutic adjuvants in the treatment of the tissue injury that follows ischemia and reperfusion.

Ischemia–Reperfusion Impairs Ascending Vasodilation in Feed Arteries of Hamster Skeletal Muscle

OBJECTIVE

Vasodilation originating within the microcirculation ascends into proximal feed arteries during muscle contraction to attain peak levels of muscle blood flow. Ascending vasodilation (AVD) requires an intact endothelium, as does conducted vasodilation in response to acetylcholine (ACh). Whereas ischemia-reperfusion (I-R) can affect endothelial cell function, the effect of I-R on AVD is unknown. The authors tested the hypothesis that I-R (1h-1h) would impair AVD.

METHODS

Using the retractor muscle of anesthetized hamsters, contractions were evoked using field stimulation (200 ms at 40 Hz every 2 s for 1 min) and ACh was delivered using microiontophoresis (1 microm tip, 500-4000 ms pulse at 800 nA). Feed artery responses were monitored 500-1500 microm upstream.

RESULTS

Neither resting (51 +/- 4 microm) nor maximal diameter (81 +/- 5 microm; 10 microm sodium nitroprusside) following I-R (n = 8) were different from time-matched controls (n = 10). With peak active tension of 23 +/- 4 mN x mm(-2), control AVD was 26 +/- 2 microm. Following I-R, active tension fell by 48% (p < .05) and AVD by 57% (p < .05). Stimulation at 70 Hz restored active tension but AVD remained depressed by nearly half (p < .05), as did local and conducted responses to ACh. Nevertheless, control responses to 500 ms ACh were restored by increasing stimulus duration to 4000 ms.

CONCLUSIONS

Ischemia-reperfusion impairs the initiation of feed artery dilation with muscle contraction and with ACh while conduction along the vessel wall is preserved. Respective components of endothelial cell signaling events may differ in their susceptibility to I-R.

The microcirculation: a motor for the systemic inflammatory response and large vessel disease induced by hypercholesterolaemia?

There is abundant evidence that links hypercholesterolaemia to both vascular inflammation and atherogenesis. While atherosclerosis is a large vessel disease that is characterized by leucocyte infiltration and lipid deposition in the wall of lesion-prone arteries, the inflammatory response does not appear to be confined to these locations. There is evidence supporting a systemic inflammatory response that is characterized by endothelial cell activation in multiple vascular beds and the appearance of activated immune cells and a wide range of inflammatory mediators in blood. The mechanism(s) responsible for initiating this systemic response remain poorly defined, although several inciting factors have been proposed, including infectious agents and oxidative stress resulting from one or more of the cardiovascular risk factors (e.g. hypercholesterolaemia, hypertension). While cells within lesion-prone arteries are often inferred as the source of circulating inflammatory mediators during atherogenesis, the fact that endothelial cells throughout the vasculature are activated raises the possibility that the microvasculature (which encompasses a vast endothelial surface area) may contribute to creating the systemic inflammatory milieu that is linked to atherogenesis. This review addresses evidence that links the microvasculature to the inflammatory responses induced by hypercholesterolaemia and offers the hypothesis that inflammatory events initiated within the microcirculation may contribute to initiation and/or progression of large vessel disease.

Chimeric SOD2/3 inhibits at the endothelial-neutrophil interface to limit vascular dysfunction in ischemia-reperfusion

After an ischemic episode, reperfusion causes profound oxidative stress in the vasculature of the afflicted tissue/organ. The dysregulated accumulation of reactive oxygen species (ROS), such as superoxide, has been closely linked to the production and release of proinflammatory mediators, a profound increase in adhesion molecule expression by the vascular endothelium, and infiltration of neutrophils during ischemia-reperfusion (I/R). Superoxide dismutase (SOD) has been shown to protect tissues and organs against I/R-induced injury; however, the drug had to be continuously perfused or kidneys had to be occluded to prevent clearance. We used intravital microscopy, a system that allowed us to visualize neutrophil-endothelial interactions within the mesenteric postcapillary venules of cats subjected to I/R and tested the hypothesis that I/R-induced neutrophil recruitment was inhibited by treatment with SOD2/3. SOD2/3 is a chimeric fusion gene product that contains the mature SOD2 as well as the COOH-terminal "tail" of SOD3 and, unlike the three naturally occurring SODs (SOD1, SOD2, and SOD3), which bear a net negative charge at pH 7.4, SOD2/3 is positively charged and physiologically stable. Our results suggest that not only does SOD2/3 have a much greater efficacy in vivo than the native human SOD2, but its administration prevents I/R-induced neutrophil-endothelial cell interactions and microvascular dysfunction. Moreover, our data support the hypothesis that reactive oxidants mediate I/R-induced injury and that the chimeric recombinant SOD2/3 has the potential to be a therapeutic agent against this debilitating illness.

Effects of Acute and Chronic Treatment with the Sodium Hydrogen Exchanger 1 (NHE-1) Inhibitor Cariporide on Myocardial Infarct Mass in Rabbits with Hypercholesterolaemia

We investigated the cardioprotective effect of acute and chronic sodium hydrogen exchanger 1 (NHE-1) inhibition with cariporide under pathological conditions in rabbits fed an atherogenic diet (0.25% cholesterol, 3% coconut oil), an experimental model of atherosclerosis. New Zealand White rabbits were fed over 4 weeks with normal diet or with atherogenic diet and randomized in 3 subgroups (n=7 in each group); placebo, acute cariporide (0.3 mg/kg, 10 min. before occlusion of left anterior descending coronary artery and chronic cariporide (4 weeks 0.1% in chow). In the final infarction experiments the animals were subjected to 30 min. of myocardial ischaemia by occlusion of a branch of the left anterior descending coronary artery followed by 2 hr of reperfusion. Infarct mass was evaluated by triphenyl-tetrazolium chloride staining and the infarct size expressed as a percentage of area at risk. Besides the assessment of aortic endothelium-dependent function aortic and cardiac vessels were inspected for atherosclerotic lesions. In cholesterol-fed rabbits, the infarct size was significantly increased when compared with normal diet animals (63+/-3% versus 41+/-3%). Acute cariporide treatment reduced the infarct size in normal diet rabbits to 14%+/-3% (66% decrease, P<0.05) as well as in atherogenic diet rabbits to 22+/-3% (65% decrease, P<0.05). Chronic treatment with cariporide also reduced the infarct size significantly: normal diet 19+/-2% (53% decrease, P<0.05), atherogenic diet 32+/-3% (49% decrease, P<0.05). Total cholesterol serum levels in rabbits with atherogenic diet were significantly higher (15.3+/-2.7 mmol/l) than those on a standard diet (0.65+/-0.08 mmol/l). Chronic cariporide treatment significantly attenuated the increase of serum cholesterol (7.9+/-1.9 mmol/l) and improved the lipoprotein pattern. Although the aortas and heart vessels of hypercholesterolaemic animals were without any histological evidence of atherosclerosis they developed endothelial dysfunction (reduced endothelium-dependent relaxation by ACh), which was prevented by chronic cariporide treatment. Acute and chronic treatment with the NHE-1 inhibitor cariporide significantly reduced infarct mass. This effect was associated with improved endothelial function.

Matrix Metalloproteinase-9 and Myeloperoxidase Expression

BACKGROUND AND PURPOSE

Expression of matrix metalloproteinases (MMPs), proteolytic enzymes that degrade extracellular proteins, is altered after ischemia/reperfusion injury and may contribute to blood-brain barrier (BBB) breakdown. Neutrophils, a source of reactive oxygen species and MMP-9, infiltrate damaged tissue 6 to 24 hours after ischemia and have also been implicated in delayed secondary tissue damage. Here we examined the spatial-temporal relation between MMP-9 expression and neutrophil infiltration after stroke.

METHODS

Knockout mice containing 50% manganese superoxide dismutase activity (SOD2-KOs), which are more susceptible to ischemic damage than wild-type (WT) littermates, underwent quantitative antigen (MMP-9, myeloperoxidase) immunohistochemistry (24 and 72 hours) analysis and protein expression by Western blotting (6, 12, 24, 48, and 72 hours) after transient focal cerebral ischemia. BBB breakdown was determined by Evans blue extravasation.

RESULTS

There was a clear spatial relation between MMP-9 expression and Evans blue extravasation. MMP-9-positive cell and vessel counts for SOD2-KOs (72 hours) were significantly different from SOD2-KO (24 hours, P=0.004), WT (24 hours, P=0.01), and WT (72 hours, P=0.007) mice. In contrast, MMP-9-positive neutrophil counts were comparatively low and did not differ by time or animal type. MMP-9 expression was biphasic in SOD2-KOs but not in WT littermates, with a significant increase observed 6 to 12 hours after ischemic insult and again at 48 to 72 hours. SOD2-KOs showed increased MMP-9 expression compared with WT littermates at all time points studied (P< or =0.05).

CONCLUSIONS

In this model, neutrophils are not the primary source of MMP-9 protein and thus are unlikely the key contributor to BBB breakdown observed in SOD2-KOs.

Intestinal ischemia and reperfusion injury in growing rats: hypothermia and N-acetylcysteine modulation

Our objective was to evaluate intestinal ischemia-reperfusion injury in growing rats, modulated by hypothermia (I/RH) and N-acetylcysteine (NAC). We used 30 EPM-1 Wistar male rats, aged around 35 days, weighing 90 g. Rats were randomized into 5 groups with 6 animals in each: I/RH group, intestinal ischemia under hypothermia for 40 min and reperfusion for 30 min; I/RH-NAC group, same procedure but adding NAC (150 mg x kg(-1)), previously with ischemia; S-H group, topic hypothermia for 40 min, and observation for 30 min; I/R H-Ve group; and S-NAC group, NAC administration and observation for 70 min. All animals were heparinized and anesthetized with ketamine (60 mg kg(-1)) and xylazine (10 mg kg(-1)) intramuscularly. Surgical procedures were done under microsurgical technique (augmentation, 10x). After laparotomy, the superior mesenteric artery was dissected and clamped to promote ischemia. Topic hypothermia was obtained by using plastic bags at 4 degrees C, changed every 10 min. Rats were sacrificed by exsanguination, and blood samples were utilized to measure D(-)lactate. Intestinal fragments were removed for morphological study. Statistical analysis was done with nonparametric tests (P <or= 0.05). Concerning to D(-)lactate, the data showed biochemical tissue injury, with hypothermia only (S-H = 27 mg/dl), and this became more important when intestinal ischemia and reperfusion were associated to hypothermia (I/RH = 36 mg/dl). NAC decreased ischemia-reperfusion injury (I/RH-NAC = 19 mg/dl). Morphologic tissue injuries, evaluated by hematoxylin-eosin staining, showed grades 4 and 5 for the I/RH and I/RH-Ve groups, respectively, in contrast with other groups (I/RH-NAC = 2, S-H = 1, and S-NAC = 1). Based on our data, we conclude that intestinal ischemia reperfusion injury occurred morphologically as well as functionally, even under hypothermia. However, NAC showed a protective effect on the small bowel from ischemia-reperfusion injury.

Anti-inflammatory therapy ameliorates leukocyte adhesion and microvascular flow abnormalities in transgenic sickle mice

In sickle cell disease, inflammatory activation of vascular endothelium and increased leukocyte-endothelium interaction may play an important role in the occurrence of vasoocclusion. In sickle mouse models, inflammatory stimuli (e.g., hypoxia-reoxygenation and cytokines) result in increased leukocyte recruitment and can initiate vasoocclusion, suggesting that anti-inflammatory therapy could be beneficial in management of this disease. We have tested the hypothesis that inhibition of endothelial activation in a transgenic mouse model by anti-inflammatory agents would lead to reduced leukocyte recruitment and improved microvascular blood flow in vivo. In transgenic sickle mice, hypoxia-reoxygenation resulted in greater endothelial oxidant production than in control mice. This exaggerated inflammatory response in transgenic mice, characterized by increased leukocyte recruitment and microvascular flow abnormalities, was significantly attenuated by antioxidants (allopurinol, SOD, and catalase). In contrast, control mice exhibited a muted response to antioxidant treatment. In addition, hypoxia-reoxygenation induced activation of NF-kappaB in transgenic sickle mice but not in control mice. In transgenic sickle mice, sulfasalazine, an inhibitor of NF-kappaB activation and endothelial activation, attenuated endothelial oxidant generation, as well as NF-kappaB activation, accompanied by a marked decrease in leukocyte adhesion and improved microvascular blood flow. Thus targeting oxidant generation and/or NF-kappaB activation may constitute promising therapeutic approaches in sickle cell disease.

Leukocyte dependence of platelet adhesion in postcapillary venules

Reperfusion of ischemic tissues results in development of a proinflammatory, prothrombogenic phenotype, culminating in the recruitment of leukocytes and platelets within postcapillary venules. Recent studies have indicated an interdependence of platelet and leukocyte adhesion, suggesting that heterotypic blood cell interactions may account for postischemic platelet recruitment. The objectives of this study were to 1) determine whether ischemia-reperfusion (I/R)-induced platelet recruitment is leukocyte dependent and 2) quantify the contributions of leukocytes and endothelial cells in this platelet recruitment. Intravital microscopy was used to monitor the recruitment of fluorescently labeled platelets in postcapillary venules of the small intestine after 45-min ischemia and 4-h reperfusion. To assess the leukocyte dependence of platelet adhesion, platelets from wild-type mice were infused into mice deficient in neutrophils and/or lymphocytes and mice deficient in key leukocyte adhesion molecules (CD18 and ICAM-1). These antileukocyte strategies resulted in significantly reduced platelet recruitment. Simultaneous visualization of platelets and leukocytes enabled quantification of leukocyte-dependent and endothelium-dependent platelet adhesion. It was observed that in wild-type animals 74% of I/R-induced platelet adhesion was a result of platelet-leukocyte interactions. Although the majority of adherent platelets were associated with leukocytes, <50% of adherent leukocytes were platelet bearing, suggesting that not all adherent leukocytes support platelet adhesion. These results are consistent with leukocytes playing a major role in supporting I/R-induced platelet adhesion.

Myeloperoxidase gene variation and coronary flow reserve in young healthy men

Chronic inflammation may lead to endothelial dysfunction, which manifests as an impaired coronary reactivity. Impairment in coronary flow reserve (CFR), preceding the clinical symptoms of coronary artery disease, can be measured noninvasively by positron emission tomography. Myeloperoxidase (MPO) is an oxidative enzyme present in phagocytes and atherosclerotic lesions. The MPO gene has a promoter polymorphism (-463G/A) which affects gene transcription. Whether these variants associate with coronary artery function is not known. Myocardial blood flow at rest and during adenosine-induced hyperemia was assessed in 49 healthy young men with normal or slightly elevated serum total cholesterol. These subjects were divided into high (G/G) and low (A/G, A/A) MPO expression groups and effect of MPO genotype on myocardial blood flow was evaluated. We found a significant difference between MPO genotypes in CFR after adjusting for age, body mass index, smoking and family history of cardiovascular disease (p = 0.019). Men with G/G genotype had 18.1% lower CFR than subjects with low-expression genotypes (A/G and A/A). This was due to an 11.5% lower adenosine-stimulated flow of the G/G genotype carriers (p = 0.049). These findings provide evidence that MPO polymorphism is associated with coronary artery reactivity. However, the number of individuals investigated was low and our observation should be confirmed by a larger number of subjects.

Cerebral microvascular responses to hypercholesterolemia: roles of NADPH oxidase and P-selectin

Although hypercholesterolemia is widely accepted as a major risk factor for coronary artery and peripheral vascular diseases, its role in the pathogenesis of stroke is controversial. The objectives of this study were to determine how hypercholesterolemia affects the cerebral microcirculation under resting conditions and after ischemia-reperfusion (I/R). Platelet- and leukocyte-endothelial cell interactions and oxidant production (using the oxidant-sensitive fluorochrome dihydrorhodamine-123) were monitored by intravital videomicroscopy in the cerebral microvasculature of mice placed on either a normal (ND) or cholesterol-enriched diet (HCD). Platelets labeled with carboxyfluorescein diacetate succinimidyl ester (CFDASE) and leukocytes labeled with rhodamine 6G were seen to roll and firmly adhere, with a corresponding increase in oxidant production, in venules of mice on HCD, but not ND. Immunoneutralization of P-selectin attenuated the platelet- and leukocyte-endothelial cell interactions and the enhanced oxidant production associated with HCD. A GPIIb/IIIa blocking antibody did not alter the blood cell-vessel wall interactions to HCD. Mice deficient in the NADPH oxidase subunit gp91(phox) exhibited significantly blunted platelet and leukocyte recruitment responses to HCD. Focal I/R also elicited inflammatory and prothrombogenic responses in cerebral venules and these were exaggerated in mice on HCD. These results implicate an oxidant-dependent, P-selectin-mediated mechanism in the blood cell-vessel wall interactions induced by hypercholesterolemia in the brain and demonstrate that the deleterious effects of I/R on the brain are exacerbated by this cardiovascular risk factor.

Orthogonal properties of the redox siblings nitroxyl and nitric oxide in the cardiovascular system: a novel redox paradigm

Endogenous formation of nitric oxide (NO) and related nitrogen oxides in the vascular system is critical to regulation of multiple physiological functions. An imbalance in the production or availability of these species can result in progression of disease. Nitrogen oxide research in the cardiovascular system has primarily focused on the effects of NO and higher oxidation products. However, nitroxyl (HNO), the one-electron-reduction product of NO, has recently been shown to have unique and potentially beneficial pharmacological properties. HNO and NO often induce discrete biological responses, providing an interesting redox system. This article discusses the emerging aspects of HNO chemistry and attempts to provide a framework for the distinct effects of NO and HNO in vivo.

Acute adenosinergic cardioprotection in ischemic-reperfused hearts

Cells of the cardiovascular system generate and release purine nucleoside adenosine in increasing quantities when constituent cells are "stressed" or subjected to injurious stimuli. This increased adenosine can interact with surface receptors in myocardial, vascular, fibroblast, and inflammatory cells to modulate cellular function and phenotype. Additionally, adenosine is rapidly reincorporated back into 5'-AMP to maintain the adenine nucleotide pool. Via these receptor-dependent and independent (metabolic) paths, adenosine can substantially modify the acute response to ischemic insult, in addition to generating a more sustained ischemia-tolerant phenotype (preconditioning). However, the molecular basis for acute adenosinergic cardioprotection remains incompletely understood and may well differ from more widely studied preconditioning. Here we review current knowledge and some controversies regarding acute cardioprotection via adenosine and adenosine receptor activation.

Oxidative stress promotes blood cell-endothelial cell interactions in the microcirculation

Oxidative stress occurs when the production of reactive oxygen species (ROS) exceeds the capacity of the cell to detoxify these potentially injurious oxidants using endogenous antioxidant defense systems. Conditions associated with oxidative stress include ischemia/reperfusion, hypercholesterolemia, diabetes, and hypertension. The adhesion of circulating blood cells (leukocytes, platelets) to vascular endothelium is a key element of the pro-inflammatory and prothrombogenic phenotype assumed by the vasculature in these and other disease states that are associated with an oxidative stress. There is a growing body of evidence that links the blood cell endothelial cell interactions in these conditions to the enhanced production of ROS. Potential enzymatic sources of ROS within the microcirculation include xanthine oxidase, NAD(P)H oxidase, and nitric oxide synthase. ROS can promote a pro-inflammatory/prothrombogenic phenotype within the microvasculature by a variety of mechanisms, including the inactivation of nitric oxide, the activation of redox-sensitive transcription factors (e.g., nuclear factor-kappaB) that govern the expression of endothelial cell adhesion molecules (e.g., P-selectin), and the activation of enzymes (e.g., phospholipase A(2)) that produce leukocyte-stimulating inflammatory mediators (e.g., platelet-activating factor). The extensively documented ability of different oxidant-ablating interventions to attenuate blood cell endothelial cell interactions underscores the importance of ROS in mediating the dysfunctional microvascular responses to oxidative stress.

Role of PAF receptors during intestinal ischemia and reperfusion injury. A comparative study between PAF receptor-deficient mice and PAF receptor antagonist treatment

1 The reperfusion of ischemic tissues may be associated with local and systemic inflammation that prevents the full benefit of blood flow restoration. The present study aimed to confirm a role for platelet-activating factor receptor(s) (PAFR) during ischemia and reperfusion injury by using genetically modified mice deficient in the PAFR (PAFR(-/-) mice) and to evaluate comparatively the effectiveness of pharmacological treatment using the PAFR antagonist UK-74,505 (modipafant). 2 The reperfusion of the ischemic superior mesenteric artery (SMA) induced marked local (intestine) and remote (lungs) tissue injury, as assessed by the increase in vascular permeability, neutrophil influx and intestinal hemorrhage and in the production of TNF-alpha. There was also a systemic inflammatory response, as shown by the increase in serum TNF-alpha concentrations and marked reperfusion-associated lethality. 3 After reperfusion of the ischemic SMA, PAFR(-/-) mice had little tissue or systemic inflammation and lethality was delayed, but not prevented, in these mice. Interestingly, the reperfusion-associated increases in tissue concentrations of IL-10 were significantly greater in PAFR(-/-) than wild-type mice. 4 Pretreatment with PAFR antagonist UK-74,505 (1 mg kg(-1)) markedly prevented tissue injury, as assessed by the increase in vascular permeability, neutrophil accumulation, hemorrhage and TNF-alpha concentrations in the intestine and lungs. In contrast, UK-74,505 failed to affect reperfusion-associated lethality and increases in serum TNF-alpha when used at 1 mg kg(-1). 5 Reperfusion-associated lethality and increase in serum TNF-alpha were only affected when a supra-maximal dose of the antagonist was used (10 mg kg(-1)). At this dose, UK-74,505 also induced a marked enhancement of reperfusion-associated increases in tissue concentrations of IL-10. However, at the same dose, UK-74,505 failed to prevent reperfusion-associated lethality in PAFR(-/-) mice any further. 6 The present studies using genetically modified animals and a receptor antagonist firmly establish a role of PAFR activation for the local, remote and systemic inflammatory injury and lethality which follows reperfusion of the ischemic SMA in mice. Moreover, it is suggested that high doses of PAFR antagonists need to be used if the real efficacy of these compounds is to be tested clinically.

Time-dependent platelet-vessel wall interactions induced by intestinal ischemia-reperfusion

Platelets roll and adhere in venules exposed to ischemia-reperfusion (I/R). This platelet-endothelial adhesion may influence leukocyte trafficking because platelet depletion decreases I/R-induced leukocyte emigration. The objectives of this study were 1) to assess the time course of platelet adhesion in the small bowel after I/R and 2) to determine the roles of endothelial and/or platelet P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1) in this adhesion. The adhesion of fluorescently labeled platelets was monitored by intravital microscopy in postcapillary venules exposed to 45 min of ischemia and up to 8 h of reperfusion. Peak platelet adhesion was observed at 4 h of reperfusion. To assess the contributions of platelet and endothelial cell P-selectin, platelets from P-selectin-deficient and wild-type mice were infused into wild-type and P-selectin-deficient mice, respectively. Platelets deficient in P-selectin exhibited low levels of adhesion comparable to that in sham-treated animals. In the absence of endothelial P-selectin, platelet adhesion was reduced by 65%. Treatment with a blocking antibody against PSGL-1 reduced adhesion by 57%. These results indicate that I/R induces a time-dependent platelet-endothelial adhesion response in postcapillary venules via a mechanism that involves PSGL-1 and both platelet and endothelial P-selectin, with platelet P-selectin playing a greater role.

Role of interferon-gamma in hypercholesterolemia-induced leukocyte-endothelial cell adhesion

BACKGROUND

A T-cell-mediated inflammatory response occurs in the microcirculation during acute hypercholesterolemia. The objective of this study was to define the contribution of T-lymphocyte-derived interferon-gamma (IFN-gamma) to the leukocyte-endothelial cell adhesion induced by hypercholesterolemia.

METHODS AND RESULTS

Intravital videomicroscopy was used to quantify the adhesion and emigration of leukocytes and oxidant stress (dihydrorhodamine [DHR] oxidation) in cremasteric venules. Wild-type (WT), IFN-gamma-/-, and severe combined immunodeficiency (SCID) mice were placed on either a normal (ND) or high-cholesterol (HC) diet for 2 weeks. WT-HC mice exhibited exaggerated adhesion and emigration of leukocytes and enhanced DHR oxidation compared with WT-ND. The exaggerated adhesion responses and increased DHR oxidation were not seen in IFN-gamma-/--HC mice. SCID-HC mice also exhibited attenuated inflammatory responses compared with WT-HC. Reconstitution of either SCID-HC or IFN-gamma-/--HC mice with WT-HC splenocytes restored the inflammatory responses, whereas reconstitution of SCID-HC with IFN-gamma-/--HC splenocytes did not. The HC-induced oxidant stress was restored in IFN-gamma-/--HC mice reconstituted with WT-HC splenocytes.

CONCLUSIONS

These findings implicate IFN-gamma as a cause of the inflammatory phenotype that is assumed by the microvasculature of hypercholesterolemic mice and suggest that T lymphocytes are a major source of this proinflammatory cytokine.

Hypercholesterolemia promotes P-selectin-dependent platelet-endothelial cell adhesion in postcapillary venules

OBJECTIVE

The objectives of this study were to determine whether hypercholesterolemia promotes platelet-endothelial cell (P/E) adhesion in murine postcapillary venules and define the contributions of endothelial or platelet associated P-selection to hypercholesterolemia-induced P/E interactions.

METHODS AND RESULTS

Wild-type (WT) or P-selectin deficient (P-sel-/-) platelets were isolated and labeled with the fluorochrome CFSE and administered to either WT or P-sel-/- mice placed on a normal diet (ND) or high cholesterol diet (HCD). Intravital videomicroscopy was used to quantify platelet saltation and firm adhesion. HCD-WT mice exhibited a time-dependent increase in P/E cell interactions (relative to ND-WT). Flow cytometry revealed an increased expression of P-selectin on circulating platelets of HCD-WT mice at 2 weeks compared with ND-WT mice. When WT platelets were monitored in HCD-P-sel-/- mice, P/E adhesion was dramatically reduced. However, when P-sel-/- platelets were monitored in HCD-WT recipients, P/E adhesive interactions were reduced even further, comparable to ND-WT mice.

CONCLUSIONS

These results indicate that elevated cholesterol levels promote P/E adhesion in postcapillary venules and that whereas both endothelial and platelet P-selectin contribute to hypercholesterolemia-induced recruitment of platelets, platelet-associated P-selectin seems to play a more important role in producing the prothrombogenic phenotype in venules.

Intracellular sodium hydrogen exchange inhibition and clinical myocardial protection

Although the mechanisms underlying ischemia/reperfusion injury remain elusive, evidence supports the etiologic role of intracellular calcium overload and oxidative stress induced by reactive oxygen species. Activation of the sodium hydrogen exchanger (NHE) is associated with intracellular calcium accumulation. Inhibition of the NHE-1 isoform may attenuate the consequences of this injury. Although there is strong preclinical and early clinical evidence that NHE inhibitors may be cardioprotective, definitive proof of this concept in humans awaits the results of ongoing clinical trials.

Low venular shear rates promote leukocyte-dependent recruitment of adherent platelets

The influence of reductions in venular shear rate on platelet-endothelial (P/E) cell adhesion has not been previously addressed. The objectives of this study were to define the effects of reductions in venular shear rate on P/E cell adhesion and to determine the interdependence of P/E cell adhesion and leukocyte-endothelial (L/E) cell adhesion at low shear rates. Intravital videomicroscopy was used to quantify P/E and L/E cell adhesion in rat mesenteric venules exposed to shear rates ranging between 118 +/- 9 and 835 +/- 44 s(-1). Shear rate was altered in postcapillary venules by rapid, graded blood withdrawal, without retransfusion of shed blood. Reducing shear rate from >600 s(-1) to <200 s(-1) resulted in an eightfold increase in L/E cell adhesion, whereas P/E cell adhesion increased 18-fold. A blocking antibody directed against P-selectin blunted both the P/E and L/E cell adhesion elicited by low shear rates. Immunoneutralization of CD11/CD18 on leukocytes or rendering animals neutropenic also blocked the shear rate-dependent recruitment of both platelets and leukocytes. These findings indicate that 1) low shear rates promote P/E and L/E cell adhesion in mesenteric venules, and 2) adherent neutrophils (mediated by CD11/CD18) create a platform onto which platelets can bind to the venular wall at low shear rates.

Structure and function of xanthine oxidoreductase: where are we now?

Xanthine oxidoreductase (XOR) is a complex molybdoflavoenzyme, present in milk and many other tissues, which has been studied for over 100 years. While it is generally recognized as a key enzyme in purine catabolism, its structural complexity and specialized tissue distribution suggest other functions that have never been fully identified. The publication, just over 20 years ago, of a hypothesis implicating XOR in ischemia-reperfusion injury focused research attention on the enzyme and its ability to generate reactive oxygen species (ROS). Since that time a great deal more information has been obtained concerning the tissue distribution, structure, and enzymology of XOR, particularly the human enzyme. XOR is subject to both pre- and post-translational control by a range of mechanisms in response to hormones, cytokines, and oxygen tension. Of special interest has been the finding that XOR can catalyze the reduction of nitrates and nitrites to nitric oxide (NO), acting as a source of both NO and peroxynitrite. The concept of a widely distributed and highly regulated enzyme capable of generating both ROS and NO is intriguing in both physiological and pathological contexts. The details of these recent findings, their pathophysiological implications, and the requirements for future research are addressed in this review.

Effects of hypothermia and rewarming on the mucosal villus microcirculation and survival after rat intestinal ischemia-reperfusion injury

OBJECTIVE

To determine the effects of hypothermia and rewarming on changes in the villus microcirculation induced by intestinal ischemia-reperfusion (I/R).

SUMMARY BACKGROUND DATA

The small intestine is extremely sensitive to I/R injury, and although hypothermia can reduce cellular injury, its capacity to influence the villous microcirculation after intestinal I/R is unclear, especially after the return to normothermic conditions.

METHODS

Core body temperature of PVG rats was maintained at either 36 degrees to 38 degrees C (n = 12) or 30 degrees to 32 degrees C (n = 24) and then subjected to 30 minutes of intestinal ischemia. A subgroup of hypothermic animals (n = 12) were returned to normothermic conditions 120 minutes after clamp removal. The mucosal surface was visualized in an exteriorized ileal segment and macromolecular leak (MML) and leukocyte adhesion were monitored using in vivo microscopy (n = 6 in each group). MML from individual villi and numbers of adherent leukocytes within villi were determined for 2 to 4 hours after clamp removal. Heart rate and mean blood pressure were monitored in all animals. Control animals underwent sham surgery (n = 12).

RESULTS

Ten of 12 normothermic animals failed to survive the reperfusion period, whereas all hypothermic animals and 11 of 12 of the hypothermic animals that were returned to normothermic conditions survived. MML was significantly increased in all animals subjected to I/R, although leakage was more marked in animals subjected to continuous normothermia. Enhanced leukocyte adhesion and decreased blood flow were observed only in normothermic animals.

CONCLUSIONS

Hypothermia might prove to be an effective strategy for preventing adverse side effects in clinical settings in which intestinal I/R can be predicted.

Venular-arteriolar communication in the regulation of blood flow

Muscle blood flow is regulated to meet the metabolic needs of the tissue. With the vasculature arranged as a successive branching of arterioles and the larger, >50 microm, arterioles providing the major site of resistance, an increasing metabolic demand requires the vasodilation of the small arterioles first then the vasodilation of the more proximal, larger arterioles. The mechanism(s) for the coordination of this ascending vasodilation are not clear and may involve a conducted vasodilation and/or a flow-dependent response. The close arteriolar-venular pairing provides an additional mechanism by which the arteriolar diameter can be increased due to the diffusion of vasoactive substances from the venous blood. Evidence is presented that the venular endothelium releases a relaxing factor, a metabolite of arachidonic acid, that will vasodilate the adjacent arteriole. The stimulus for this release is not known, but it is hypothesized that hypoxia-induced ATP release from red blood cells may be responsible for the stimulation of arachidonic release from the venular endothelial cells. Thus the venous circulation is in an optimal position to monitor the overall metabolic state of the tissue and thus provide a feedback regulation of arteriolar diameter.

Endothelial dysfunction is induced by proinflammatory oxidant hypochlorous acid

The myeloperoxidase (MPO)-derived oxidant hypochlorous acid (HOCl) plays a role in tissue injury under inflammatory conditions. The present study tests the hypothesis that HOCl decreases nitric oxide (NO) bioavailability in the vasculature of Sprague-Dawley rats. Aortic ring segments were pretreated with HOCl (1-50 microM) followed by extensive washing. Endothelium-dependent relaxation was then assessed by cumulative addition of acetylcholine (ACh) or the calcium ionophore A23187. HOCl treatment significantly impaired both ACh- and A23187-mediated relaxation. In contrast, endothelium-independent relaxation induced by sodium nitroprusside was unaffected. The inhibitory effect of HOCl on ACh-induced relaxation was reversed by exposure of ring segments to L-arginine but not D-arginine. In cellular studies, HOCl did not alter endothelial NO synthase (NOS III) protein or activity, but inhibited formation of the NO metabolites nitrate (NO3(-) and nitrite (NO2(-). The reduction in total NO metabolite production in bovine aortic endothelial cells was also reversed by addition of L-arginine. These data suggest that HOCl induces endothelial dysfunction via modification of L-arginine.

Microcirculatory effects of experimental acute limb ischaemia-reperfusion

BACKGROUND

The object of this study was to develop an animal model in which changes in microvascular haemodynamics and leucocyte-vessel wall interactions due to acute limb ischaemia-reperfusion (I/R) can be measured in the skin. Furthermore, it was investigated whether these changes are related to local muscle injury.

METHODS

Male Lewis rats were subjected to unilateral limb ischaemia for 1 h (n = 8) or 2 h (n = 8) by cuff inflation, or to a sham protocol (n = 6). Intravital video microscopic measurements of leucocyte-vessel wall interactions, venular diameter, red blood cell velocity and reduced velocity (which is proportional to wall shear rate) were performed in skin venules before ischaemia and at 0.5, 1, 2, 3 and 4 h after the start of reperfusion. Oedema and leucocyte infiltration of ischaemic/reperfused skeletal muscle were quantified histologically.

RESULTS

In skin venules, both 1 and 2 h of ischaemia induced a significant increase in leucocyte rolling (six and five times baseline, respectively; P < 0.05) and adherence during reperfusion (eight and four times baseline; P < 0.05). No significant increase in muscular leucocyte infiltration was detected. After an initial hyperaemic response of 180 per cent of baseline values (P < 0.05), blood flow decreased to about 60 per cent after 4 h of reperfusion in skin venules of both experimental groups. I/R induced tibial muscle oedema, the severity of which depended on the ischaemic interval (wet to dry ratio: control, 4.0; 1 h, 4.5 (P not significant); 2 h, 5.8 (P < 0.05)).

CONCLUSION

A non-invasive animal model was developed that enables investigation of the consequences of acute limb I/R.

L-arginine chlorination products inhibit endothelial nitric oxide production

The myeloperoxidase-derived oxidant hypochlorous acid (HOCl) is thought to contribute to endothelial dysfunction, but the mechanisms underlying this inhibitory effect are unknown. The present study tested the hypothesis that HOCl and L-arginine (L-Arg) react to form novel compounds that adversely affect endothelial function by inhibiting nitric oxide (NO) formation. Using spectrophotometric techniques, we found that HOCl and L-Arg react rapidly (k = 7.1 x 10(5) m(-1) s(-1)) to form two major products that were identified by mass spectrometry as monochlorinated and dichlorinated adducts of L-Arg. Pretreatment of bovine aortic endothelial cells with the chlorinated L-Arg metabolites (Cl-l-Arg) inhibited the -induced formation of the NO metabolites nitrate (NO(3)(-)) and nitrite (NO(2)(-)) in a concentration-dependent manner. Preincubation of rat aortic ring segments with Cl-L-Arg resulted in concentration-dependent inhibition of acetylcholine-induced relaxation. In contrast, blood vessels relaxed normally to the endothelium-independent vasodilator sodium nitroprusside. In vivo administration of Cl-L-Arg to anesthetized rats increased carotid artery vascular resistance. A greater than 10-fold excess of L-Arg was required to reverse the inhibitory effects of Cl-L-Arg in vivo and in vitro. Reaction of HOCl with D-arginine (D-Arg) did not result in the formation of inhibitory products. These results suggest that HOCl reacts with L-Arg to form chlorinated products that act as nitric-oxide synthase inhibitors.

Hepatic microvascular responses to ischemia-reperfusion in low-density lipoprotein receptor knockout mice

The overall objective of this study was to determine whether genetically induced hypercholesterolemia alters the inflammatory and microvascular responses of mouse liver to ischemia-reperfusion (I/R). The accumulation of rhodamine 6G-labeled leukocytes and the number of nonperfused sinusoids (NPS) were monitored (by intravital microscopy) in the liver of wild-type (WT) and low-density lipoprotein receptor-deficient (LDLr(-/-)) mice for 1 h after a 30-min period of normothermic ischemia. Plasma alanine transaminase (ALT) levels were used to monitor hepatocellular injury. Microvascular leukostasis as well as increases in NPS and plasma ALT were observed at 60 min after hepatic I/R in both WT and in LDLr(-/-) mice; however, these responses were greatly exaggerated in LDLr(-/-) mice. Pretreatment of LDLr(-/-) mice with gadolinium chloride, which reduces Kupffer cell function, attenuated the hepatic leukostasis, NPS, and hepatocellular injury elicited by I/R. Similar protection against I/R was observed in LDLr(-/-) mice pretreated with antibodies directed against tumor necrosis factor-alpha, intercellular adhesion molecule-1 (ICAM-1), or P-selectin. These findings indicate that chronic hypercholesterolemia predisposes the hepatic microvasculature to the deleterious effects of I/R. Kupffer cell activation and the leukocyte adhesion receptors ICAM-1 and P-selectin appear to contribute to the exaggerated inflammatory responses observed in the postischemic liver of LDLr(-/-) mice.

Lipocortin 1 reduces myocardial ischemia-reperfusion injury by affecting local leukocyte recruitment

We assessed here the effect of the glucocorticoid-regulated protein lipocortin 1 (LC1) in a model of rat myocardial ischemia reperfusion. Treatment of animals with human recombinant LC1 at the end of a 25-min ischemic period significantly reduced the extent of infarct size in the area at risk as measured 2 h later, with approximately 50% inhibition at the highest dose tested of 50 microg per rat (equivalent to 5.4 nmol/kg). The protective effect of LC1 was abolished by protein denaturation and not mimicked by the structurally related protein annexin V. A combination of electron and light microscopy techniques demonstrated the occurrence of the myocardial damage at the end of the reperfusion period, with loss of fiber organization. LC1 provided a partial and visible protection. The dose-dependent protection afforded by LC1 was paralleled by lower values of myeloperoxidase activity, tumor necrosis factor a, and macrophage inflammatory protein-1a. The functional link between migrated leukocytes and the myocardial damage was confirmed by electron and light microscopy, and a significantly lower number of extravasated leukocytes was counted in the group of rats treated with LC1 (50 microg). In conclusion, we demonstrate for the first time that LC1 reduces the leukocyte-dependent myocardial damage associated with an ischemia-reperfusion procedure.

Oxidative stress and cardiac disease

Reactive oxygen species (ROS) are formed at an accelerated rate in postischemic myocardium. Cardiac myocytes, endothelial cells, and infiltrating neutrophils contribute to this ROS production. Exposure of these cellular components of the myocardium to exogenous ROS can lead to cellular dysfunction and necrosis. While it remains uncertain whether ROS contribute to the pathogenesis of myocardial infarction, there is strong support for ROS as mediators of the reversible ventricular dysfunction (stunning) that often accompanies reperfusion of the ischemic myocardium. The therapeutic potential of free radical-directed drugs in cardiac disease has not been fully realized.

Hypoxia/reoxygenation causes inflammatory response in transgenic sickle mice but not in normal mice

In sickle cell anemia, the initiation, progression, and resolution of a vasoocclusive episode may present features of ischemia-reperfusion injury, with recurrent episodes of ischemia/hypoxia and reoxygenation promoting inflammation. Here, we have tested the hypothesis that hypoxia/reoxygenation triggers inflammation in the transgenic sickle mouse. In these mice, even at ambient air, peripheral leukocyte counts are elevated by 1.7-fold and neutrophil counts by almost 3-fold. Two hours of hypoxia, followed by reoxygenation, induced a greater than normal rolling flux and adhesion of leukocytes in these mice, but no leukocyte extravasation. When 3 hours of hypoxia was followed by reoxygenation, sickle mice, but not normal mice, showed a distinct inflammatory response characterized by an increased number of adherent and emigrated leukocytes. Because these events, which are exaggerated in sickle mice, are not seen in response to hypoxia alone, we conclude that they represent a form of reperfusion injury. Studies using an H(2)O(2)-sensitive probe revealed clear evidence of oxidant production in vascular endothelial cells after hypoxia/reoxygenation in sickle mice. Infusion of an anti-P-selectin antibody, but not an anti-E-selectin antibody, completely inhibited this inflammatory response and significantly increased wall shear rates. These findings suggest that leukocyte-endothelium interaction contribute to vasoocclusive events in the sickle mice and perhaps in human sickle disease.

Reperfusion injury pathophysiology in sickle transgenic mice

Reperfusion of tissues after interruption of their vascular supply causes free-radical generation that leads to tissue damage, a scenario referred to as “reperfusion injury.” Because sickle disease involves repeated transient ischemic episodes, we sought evidence for excessive free-radical generation in sickle transgenic mice. Compared with normal mice, sickle mice at ambient air had a higher ethane excretion (marker of lipid peroxidation) and greater conversion of salicylic acid to 2,3-dihydroxybenzoic acid (marker of hydroxyl radical generation). During hypoxia (11% O2), only sickle mice converted tissue xanthine dehydrogenase to oxidase. Only the sickle mice exhibited a further increase in ethane excretion during restitution of normal oxygen tension after 2 hours of hypoxia. Only the sickle mice showed abnormal activation of nuclear factor–κB after exposure to hypoxia-reoxygenation. Allopurinol, a potential therapeutic agent, decreased ethane excretion in the sickle mice. Thus, sickle transgenic mice exhibit biochemical footprints consistent with excessive free-radical generation even at ambient air and following a transient induction of enhanced sickling. We suggest that reperfusion injury physiology may contribute to the evolution of the chronic organ damage characteristic of sickle cell disease. If so, novel therapeutic approaches might be of value.

Reperfusion injury pathophysiology in sickle transgenic mice

Reperfusion of tissues after interruption of their vascular supply causes free-radical generation that leads to tissue damage, a scenario referred to as “reperfusion injury.” Because sickle disease involves repeated transient ischemic episodes, we sought evidence for excessive free-radical generation in sickle transgenic mice. Compared with normal mice, sickle mice at ambient air had a higher ethane excretion (marker of lipid peroxidation) and greater conversion of salicylic acid to 2,3-dihydroxybenzoic acid (marker of hydroxyl radical generation). During hypoxia (11% O2), only sickle mice converted tissue xanthine dehydrogenase to oxidase. Only the sickle mice exhibited a further increase in ethane excretion during restitution of normal oxygen tension after 2 hours of hypoxia. Only the sickle mice showed abnormal activation of nuclear factor–κB after exposure to hypoxia-reoxygenation. Allopurinol, a potential therapeutic agent, decreased ethane excretion in the sickle mice. Thus, sickle transgenic mice exhibit biochemical footprints consistent with excessive free-radical generation even at ambient air and following a transient induction of enhanced sickling. We suggest that reperfusion injury physiology may contribute to the evolution of the chronic organ damage characteristic of sickle cell disease. If so, novel therapeutic approaches might be of value.