Ischemia activates neutrophils but inhibits their local and remote diapedesis

Lipid Peroxides in the Mechanism of Ischemia/Reperfusion Injury in Skeletal Muscle—Experimental Studies

Two sets of experiments were conducted to investigate whether oxygen-de rived free radicals are involved in the mechanism of ischemia/reperfusion (I/R) injury of skeletal muscle and vitamin E is effective in alleviating the injury.

In the first set of experiments, twenty adult mongrel dogs were divided into three groups: group 1 (n=7) control, group 2 (n = 6) I/R, and group 3 (n=7) I/R with 500 mg of vitamin E. Serum creatine phosphokinase (CPK) and lipid per oxides (LPO) were measured as markers of rhabdomyolysis and biomembrane injury due to oxygen-derived free radicals, respectively. CPK increased signifi cantly after reperfusion with a peak value of 38,000 ± 9,800 mU/mL in group 2, when compared with a peak value of 1,060 ± 290 mU/mL in group 3 (p < 0.02). LPO also significantly increased with a peak value of 20.4 ±3.7 nmol/mL in group 2, when compared with a peak value of 9.2 ± 2.2 nmol/mL in group 3 (p < 0.04).

In the second sets of experiments, 13 dogs were divided into two groups: group A (n=5) control and group B (n=8) I/R. Tissue LPO was measured eighteen hours after reperfusion in the gracilis muscle and gastrocnemius mus cle. The mean value of LPO in the gracilis muscle was 0.94 ± 0.46 nmol/mg protein in group A, compared with 1.13 ± 0.67 nmol/mg protein in group B. It was higher in group B, but there was no significant difference. Mean LPO in the gastrocnemius muscle was 0.85 ± 0.34 nmol/mg protein in group A, and 1.83 ± 0.71 nmol/mg protein in group B. There was a significant difference (p < 0.02).

Serum CPK and LPO were significantly higher in group 2 than in groups 1 and 3, and tissue LPO was also high in skeletal muscle after reperfusion. Serum CPK and LPO were effectively suppressed by administration of vitamin E be fore reperfusion.

These results show that oxygen-derived free radicals are involved in the mechanism of I/R injury in skeletal muscle and suggest that vitamin E is effec tive in alleviating the injury.

Transgenic expression of human complement regulators reduces skeletal muscle ischaemia/reperfusion injury in mice

This study aimed to explore the hypothesis that activated complement components contribute significantly to I/R (ischaemia/reperfusion) injury in skeletal muscle. After 50, 70 and 90 min of tourniquet ischaemia and 24 h of reperfusion, viability of the medial gastrocnemius muscle in CBA-C57BL/6 wild-type mice, assessed histochemically by reduction of NBT (Nitro Blue Tetrazolium) dye, was 60, 21 and 8% respectively. Skeletal muscle viability after 70 min of ischaemia and 24 h of reperfusion in transgenic mice expressing a combination of human CD46, CD55 and CD59, all inhibitors of complement activation, was 45% compared with 24% in ischaemic reperfused wild-type mice (P=0.008; n=6 per group). Muscle from sham-treated transgenic mice and wild-type littermates had no significant loss of viability relative to normal contralateral gastrocnemius muscle. A significant reduction in myeloperoxidase activity (a measure of neutrophil infiltration), xanthine oxidase activity (a source of free radicals) and water content (a measure of oedema) was observed in ischaemic reperfused muscle from transgenic mice compared with ischaemic reperfused wild-type muscle (P<0.05). Haematoxylin and eosin-stained histological sections also showed less damage and less apparent leucocyte infiltration in muscles from ischaemic reperfused transgenic mice than those from wild-type animals given the same degree of injury. Muscles from sham-treated transgenic and wild-type controls were almost identical with normal muscle. It is concluded that complement activation contributes to the pathogenesis of I/R injury in murine skeletal muscle, resulting in increased neutrophil infiltration into the injured muscle, increased free radical production and vascular permeability during reperfusion, and a net detrimental effect on muscle viability.

Temporal expression and activation of matrix metalloproteinases-2, -9, and membrane type 1-matrix metalloproteinase following acute hindlimb ischemia

OBJECTIVE

Matrix metalloproteinase (MMP) activity is essential for remodeling of ischemic tissue. The murine hindlimb ischemia model exhibits tissue remodeling including revascularization in part due to angiogenesis. MMP-2 and -9 are type IV collagenases necessary for basement membrane degradation as a part of extracellular matrix remodeling and angiogenesis. Polymorphonuclear leukocytes (PMNs) contain MMP-9, and in the presence of membrane type 1 (MT1)-MMP, are able to activate proMMP-2 in vitro. Activation of MMP-2 and -9 may be essential in ischemic limbs both for tissue remodeling and revascularization via angiogenesis. We hypothesized that MMP-2 and -9 would be activated following acute hindlimb ischemia (HI), and this activation would be temporally related to PMN infiltration.

DESIGN OF STUDY

HI was achieved by unilateral femoral artery ligation in 20 FVB/N mice. Five mice underwent sham operation without hindlimb ischemia. Gastrocnemius muscle was harvested from both hindlimbs at 1, 3, 14, and 30 days following ligation and assayed for MMP-2, -9 (gelatin zymography), and MT1-MMP (Western blotting). MMP-2 and -9 expression and activation were analyzed by gelatin zymography and quantified by densitometry with NIH Image Analysis software. Neutrophils per high power field were counted. The results were expressed as a ratio of ischemic to nonischemic limbs and compared at each time point using ANOVA.

RESULTS

Zymographic analysis revealed a 212% increase in active MMP-2 3 days postligation (P <.05). Active MMP-9 reached its maximum level (800% over baseline) on postoperative day 3 and continued to be elevated on day 14 (737% over baseline) (P <.05). The increase in active MMP-2 and -9 levels paralleled PMN infiltration that also peaked 3 days postligation (1184% over baseline) (P <.05). PMN count, MMP-2, and -9 all returned to baseline levels by postoperative Day 30. MT1-MMP was present in tissue samples from all time points as confirmed by Western blot.

CONCLUSIONS

Limb ischemia causes an early activation of MMP-2 and -9 in temporal relation to PMN infiltration. HI may prime PMNs, leading to their sequestration in ischemic tissue. Primed PMNs, along with constitutively expressed MT1-MMP, may activate MMPs-2 and -9 and enable tissue remodeling essential for limb revascularization and angiogenesis.

Intramuscular gene transfer of interleukin-10 reduces neutrophil recruitment and ameliorates lung graft ischemia-reperfusion injury

Interleukin-10 (IL-10) has potent anti-inflammatory properties but its direct effects on neutrophil trafficking in lung transplant ischemia-reperfusion (I/R) injury are unknown. This study was performed to determine if recipient intramuscular IL-10 gene transfer reduces neutrophil infiltration in lung isografts and ameliorates I/R injury. Twenty-four hours before transplantation, recipient rodents received intramuscular injection with 1 x 10(10) plaque-forming units (pfu) adenovirus encoding human IL-10 (hIL-10), 1 x 10(10) pfu adenovirus control encoding p-galactosidase, or saline. Gene expression in muscle and plasma was confirmed. Lung grafts were harvested, stored at 4 degrees C for 18h, and assessed 24 h after transplantation. Peak muscle and plasma expression of hIL-10 was achieved 24h after gene transfer and returned to baseline by 7 days (p < 0.05 vs. controls). Gene transfer of hIL-10 reduced neutrophil sequestration and emigration in lung grafts as measured by morphometry and myeloperoxidase activity (p < 0.03 vs. controls). Furthermore, hIL-10 improved graft oxygenation and reduced lung edema (p <0.01 vs. controls). Intramuscular gene transfer of hIL-10 releases hIL-10 protein into plasma and reduces neutrophil sequestration and emigration in lung isografts. This is associated with a reduction in I/R injury with improved isograft oxygenation and reduced tissue edema. Intramuscular gene transfer may be a useful strategy to reduce clinical l/R injury.

Role of 5-Lipoxygenase Products in the Local Accumulation of Neutrophils in Dermal Inflammation in the Rabbit

Studies were undertaken to define the role of 5-lipoxygenase (5-LO) products and, in particular, of leukotriene (LT) B4 in the polymorphonuclear leukocyte (PMN) emigration process using a rabbit model of dermal inflammation. Our results show that i.v. administration to rabbits of MK-0591, a compound that inhibits LT biosynthesis in blood and tissues when administered in vivo, significantly reduced 51Cr-labeled PMN accumulation in response to intradermally injected chemotactic agonists, including IL-8, FMLP, C5a, and LTB4 itself. In addition, pretreatment of the labeled PMN with MK-0591 ex vivo before their injection in recipient animals was equally effective in reducing 51Cr-labeled PMN emigration to dermal inflammatory sites. These results support a role for de novo synthesis of 5-LO metabolites by PMN for their chemotactic response to inflammatory mediators. Other studies demonstrated that elevated intravascular concentration of LTB4 interferes with PMN extravasation inasmuch as a continuous i.v. infusion of LTB4, in the range of 5–300 ng/min/kg, dose-dependently inhibited extravascular PMN accumulation to acute inflammatory skin sites elicited by the chemoattractants LTB4, FMLP, C5a, and IL-8 and by TNF-α, IL-1β, and LPS; such phenomena may constitute a natural protective mechanism from massive tissue invasion by activated PMN in specific pathologic conditions such as ischemia (and reperfusion). These studies demonstrate additional functions of 5-LO products in the regulation of PMN trafficking, distinct from the well-characterized chemotactic activity of LTB4 present in the extravascular compartment.

Pentafraction for superior resuscitation of the ovine thermal burn

OBJECTIVE

To determine if a new hydroxyethyl starch, pentafraction, will cause better capillary retention of fluid in thermally burned and nonburned tissues when compared with some currently used volume expanders.

DESIGN

Randomized, controlled, experimental study.

SETTING

University research laboratory.

SUBJECTS

Twenty-one healthy adult range ewes.

INTERVENTIONS

Sheep, surgically prepared for chronic study, were randomly assigned to one of three colloid groups for the resuscitation of thermal injuries: a) ovine fresh-frozen plasma group; b) pentastarch group; and c) pentafraction group. Twenty-one sheep were subjected to a 40% total body surface, third-degree flame burn under anesthesia (1.5% to 2% halothane). When awakened, the sheep received 15 mL/kg of one of the above colloids, and then lactated Ringer's solution (2 mL/hr/kg). All animals survived and were killed at 48 hrs after burn injury.

MEASUREMENTS AND MAIN RESULTS

We found that cardiac index decreased and systemic vascular resistance increased in the pentastarch and plasma groups. However, cardiac index increased in the pentafraction group, while systemic vascular resistance increased by only half as much as in the other two groups. Cardiac index in the plasma group decreased significantly for the first 8 hrs, and did not return to the baseline value for 48 hrs. Systemic vascular resistance increased significantly for the first 8 hrs in both the plasma and pentastarch groups. Prefemoral lymph flow was significantly more increased in the pentastarch group, while the lung lymph/plasma oncotic gradient was maintained only by the pentafraction group.

CONCLUSIONS

Pentafraction is as good, or even superior, for volume resuscitation in the burn patients, when compared with pentastarch and plasma. This conclusion is made most evident by the attenuated changes in systemic vascular resistance and cardiac index. Pentafraction decreases the fluid flux and potential subsequent edema significantly in burned tissues and effectively maintains the pulmonary microvascular integrity.

Pharmacological reduction of the systemically damaging effects of local ischaemia

Many patients with intermittent claudication are encouraged to exercise. However, transient exercise-induced muscle ischaemia results in systemic vascular endothelial injury associated with increased vascular permeability manifest as an increase in urinary albumin excretion. Repetitive systemic vascular endothelial injury leads to accelerated atherogenesis and may explain the high cardiovascular mortality rate of claudicants. Oxpentifylline, a haemorheological agent, has recently been shown to prevent vascular endothelial injury in animal models. A double-blind, placebo-controlled, cross-over trial was undertaken to determine the effect of oxpentifylline on exercise-induced systemic vascular endothelial injury in 20 claudicants. Urinary albumin, expressed as a creatinine ratio (ACR), was measured before and 1 and 2 hours after standardised exercise following 1 week treatment with either active drug or placebo. Oxpentifylline reduced the median (range) 1 hour post exercise increase in ACR from 0.35 (-0.46-12.72) to 0.02 (-6.00-14.10) mg/mmol. (p = 0.030, z = 2.2 Wilcoxon rank sign test). These results confirm that local ischaemia is associated with a potentially deleterious systemic effect and that it may be possible to attenuate this pharmacologically. The clinical significance of this is yet to be determined.

In vivo microscopy of microcirculatory injury in skeletal muscle following ischemia/reperfusion

While the sequence of biochemical and cellular events in the pathogenesis of ischemia/reperfusion injury is increasingly well understood, the way that these processes interact at the level of microcirculation to promote a distinctive reperfusion injury is less well defined. It is becoming clear, however, that these processes are initiated at the level of microcirculation, and that microcirculatory damage may precede actual tissue injury. Such damage causes microvascular no-reflow, which in turn effectively prolongs the time of tissue ischemia and extends tissue injury. Recently, microcirculatory models have been adapted for study of the microvascular effects of ischemia/reperfusion. We have used a new in vivo mouse cremaster muscle model to study, by direct and quantitative measurement, the acute microvascular changes involved in ischemia/reperfusion. Previously described changes in capillary perfusion and venular leukocyte adhesion were observed in this model following reperfusion after prolonged ischemia (4-6 hours). We have further characterized an intense reactive vasoconstriction or vasospasm that occurs after prolonged ischemia; this vessel reaction may represent an important overlooked cause of no-reflow following ischemia/reperfusion. This article summarizes our work in the context of other available methods that have been used to define the microvascular changes of ischemia/reperfusion.

Microproteinuria predicts the severity of systemic effects of reperfusion injury following infrarenal aortic aneurysm surgery

Noncardiogenic pulmonary dysfunction can be demonstrated in all patients following elective aortic aneurysm repair and is a cause of postoperative morbidity. Aortic clamping and reperfusion initiate a systemic inflammatory response producing endothelial damage and increases in vascular permeability. In the lung this is manifest as pulmonary edema and in the kidney as detectable increases in urinary protein excretion (microproteinuria). Immunoassay of low-level protein excretion appears to provide an index of the systemic effects of local reperfusion injury and may allow early prediction of complications such as pulmonary edema. Hourly urinary albumin and IgG excretion was measured in 40 patients undergoing infrarenal aortic aneurysm repair and expressed as ratios to urinary creatinine (albumin/creatinine ratio [ACR] and IgG/creatinine ratio [IgGCR]). These were compared to clinical outcome. Pulmonary dysfunction was assessed according to PaO2:FiO2 ratios and chest radiography. Within 180 minutes of beginning surgery all patients had significant increases in ACR and IgGCR. Ten patients who manifested respiratory dysfunction had significantly higher ACRs at 4 hours (median 84.8, 95% confidence intervals, range 47.7 to 136) than patients who made uneventful recoveries (median 16.6, 95% confidence intervals, range 7.9 to 31.7). IgGCR increases paralleled that of ACRs. Differences persisted for 24 hours. Urinary protein excretion rises rapidly during aortic surgery. The degree of increase appears to predict development of pulmonary dysfunction. This simple test may provide a rational basis for evaluation of therapeutic modalities to limit reperfusion injury in these patients.

Reperfusion plasma contains a neutrophil activator

Aortic aneurysm repair produces inflammatory mediators, neutrophil activation, and remote organ injury. Reperfusion plasma from these patients produces microvascular injury in an ex vivo chemotactic model. This study investigates the mechanism of this injury. Vena caval blood was obtained before and 15 minutes after aortic clamp removal (n = 16) or at laparotomy (n = 10). Plasma or saline solution was introduced into unit dose chambers fixed atop dermabrasions on the back of depilated anesthetized rabbits. Animals were treated with intravenous saline solution (n = 4); made neutropenic with nitrogen mustard (n = 4); pretreated with the xanthine oxidase inhibitor allopurinol (n = 4); or cotreated intravenously with the free radical scavengers superoxide dismutase (SOD) and catalase (n = 4). Three hours later neutrophil counts (polymorphonuclear cells [PMN]/mm3) and activity (free radical production by flow cytometry), protein leakage, and inflammatory mediators (thromboxane [TX] and leukotriene B4 [LTB4]) were measured. In contrast to control plasma in untreated rabbits, reperfusion plasma produced TX and LTB4 generation (1090 +/- 105 and 794 +/- 91 pg/ml, respectively, p < 0.01), PMN accumulation (1636 +/- 210/mm3, p < 0.01) and activation (276 +/- 31 mean fluorescent units), and microvascular permeability (554 +/- 90 micrograms/ml, p < 0.01). Neutropenia (3 +/- 1 PMN/mm3) and cotreatment with SOD and catalase abolished these responses, whereas pretreatment with allopurinol did not. Human reperfusion plasma contains a soluble factor that stimulates free radical generation by rabbit neutrophils to produce a microvascular injury characterized by de novo TX production, neutrophil accumulation and activation, and increased microvascular permeability to protein.

Interleukin-2 induces early multisystem organ edema mediated by neutrophils

Interleukin-2 (IL-2), an agent known to activate neutrophils (PMN) with thromboxane (Tx)B2 release, produces pulmonary edema within 6 hours of intravenous infusion. This study tests the role of PMN in mediating the edema. Anesthetized rats received 10(6)U recombinant human IL-2 (n = 15) or vehicle (n = 14) as a constant intravenous infusion during a period of 1 hour. At this time there was leukopenia 3.63 +/- 0.43 (x10(3)/mm3) relative to vehicle-infused control rats 6.12 +/- 0.86 and a decline in PMN, 2.19 +/- 0.14 relative to control value of 3.33 +/- 0.05 (both p less than 0.05). After 6 hours edema, as measured by increase in the wet to dry weight (W/d) ratio, was present in the lungs (4.93 +/- 0.20 relative to control 4.06 +/- 0.10), heart (4.09 +/- 0.11 versus 3.76 +/- 0.08), liver (3.50 +/- 0.10 versus 3.18 +/- 0.10), and kidney (4.25 +/- 0.07 versus 4.00 +/- 0.07) (all p less than 0.05). There was increased lung permeability demonstrated by bronchoalveolar lavage fluid protein concentration of 1970 +/- 210 micrograms/mL relative to control 460 +/- 90 micrograms/mL (p less than 0.05). Interleukin-2 resulted in lung PMN sequestration of 53 +/- 7 PMN/10 high-power fields (HPF) relative to 23 +/- 2 PMN/10 HPF in controls (p less than 0.05) and increased plasma TxB2 levels to 1290 +/- 245 pg/mL relative to control 481 +/- 93 pg/mL (p less than 0.05). Pretreatment of other rats (n = 8) with selective anti-rat neutrophil antiserum 18 hours before the experiment led to a peripheral PMN count 10% of baseline and prevented edema in the lungs (W/d ratio 4.20 +/- 0.16) and heart (3.67 +/- 0.07) (both p less than 0.05) but not liver or kidney. Protein in lung lavage was reduced to 760 +/- 220 micrograms/mL (p less than 0.05). The protection afforded by leukopenia was associated with lack of PMN sequestration and prevention of the increase in plasma Tx levels (484 +/- 120 pg/mL, p less than 0.05). These data indicate that the rapid induction of lung and heart edema with a 1-hour infusion of IL-2 in the rat is mediated, in large part, by activated PMNs.

Ischemia/reperfusion injury in skeletal muscle

Ischemia/reperfusion injury to skeletal muscle may be explained by a cascade of cellular and systemic events initiated by an ischemic period followed by reperfusion. During the period of ischemia there is a gradual reduction of intracellular energy stores. Adenosine triphosphate is gradually depleted despite the buffering effect of creatine phosphate which is present in large stores in muscles. As well, glycogen stores are depleted with resultant production of small amounts of energy and large accumulations of lactate. Upon reperfusion there is a reactive hyperemia, resulting in an overall increase in muscle blood flow, despite the fact that areas may continue to be underperfused. Results of this blood flow are mixed with the beneficial effects of removing metabolic by-products and supplying exogenous substrates and oxygen. However, this blood flow also causes harmful effects by washing out necessary precursors for adenine nucleotide resynthesis. Production of oxygen free radicals occurs with resultant membrane lipid peroxidation, and calcium influx occurs upon reoxygenation with resultant disruption of oxidative rephosphorylation in the mitochondria. The sequestration of white blood cells in the muscle due to up regulation of both neutrophil receptors and endothelial leukocyte adhesion molecules results in a prolongation of the reperfusion injury. This subsequently results in damage to remote organs, including lung, heart, and kidneys. The future for therapeutic interventions aimed at reducing this injury lie mostly in the ability to modulate the reperfusion effect.

Thromboxane mediates diapedesis after ischemia by activation of neutrophil adhesion receptors interacting with basally expressed intercellular adhesion molecule-1

Ischemic injury is characterized by neutrophil (PMN)--endothelial cell adhesion and diapedesis associated with thromboxane (TX) generation. Neutrophil-endothelial cell interaction is regulated in part by the leukocyte adhesion receptor CD 18 glycoprotein complex and the endothelial intercellular adhesion molecule-1 (ICAM-1). This study tests the role of TX in ischemia-induced diapedesis and evaluates whether the diapedesis is regulated by neutrophil or endothelial adhesion receptors. Plasma derived from rabbit hind limbs made ischemic for 3 hours (n = 6) and reperfused for 10 minutes had increased levels of TXB2 3,450 pg/ml, which was higher than sham rabbit (n = 6) values of 653 pg/ml (p less than 0.05). When introduced into abraded skin chambers placed on the dorsum of other normal rabbits (n = 6), this ischemic plasma induced 1,000 pg/ml of new TX synthesis and diapedesis of 1,235 PMN/mm3. The total TX concentration and PMN accumulations in blister fluid were correlated (r = 0.88, p less than 0.05). In contrast, sham rabbit plasma induced no TX synthesis and diapedesis of only 77 PMN/mm3 (p less than 0.05). Administration of 50 ng/ml of authentic TXB2 into blisters induced an accumulation of 453 PMN/mm3, which was higher than that in saline controls (18 PMN/mm3) (p less than 0.05). Pretreatment of normal rabbits used for the diapedesis assay (n = 4) with the TX synthetase inhibitor OKY 046 (2 mg/kg/hr) limited ischemic plasma and authentic TXB2 induced diapedesis to 142 and 76 PMN/mm3, respectively (both p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)