Role of leukocyte accumulation and oxygen radicals in ischemia-reperfusion-induced injury in skeletal muscle

Recurrent atraumatic compartment syndrome as a manifestation of genetic neuromuscular disease

Compartment syndrome (CS) is a medical emergency that occurs secondary to excessively high pressures within a confined fibro-osseous space, resulting in reduced perfusion and subsequent tissue injury. CS can be divided into acute forms, most commonly due to trauma and considered an orthopaedic emergency, and chronic forms, most commonly presenting in athletes with recurrent exercise-induced pain. Downstream pathophysiological mechanisms are complex but do share commonalities with mechanisms implicated in genetic neuromuscular disorders. Here we present 3 patients with recurrent CS in the context of a RYR1-related disorder (n = 1) and PYGM-related McArdle disease (n = 2), two of whom presented many years before the diagnosis of an underlying neuromuscular disorder was suspected. We also summarize the literature on previously published cases with CS in the context of a genetically confirmed neuromuscular disorder and outline how the calcium signalling alterations in RYR1-related disorders and the metabolic abnormalities in McArdle disease may feed into CS-causative mechanisms. These findings expand the phenotypical spectrum of RYR1-related disorders and McArdle disease; whilst most forms of recurrent CS will be sporadic, above and other genetic backgrounds ought to be considered in particular in patients where other suggestive clinical features are present.

Ginsenoside Rg1 protects against hind-limb ischemia reperfusion induced lung injury via NF-κB/COX-2 signaling pathway

BACKGROUND/AIMS

Ginsenoside Rg1 is regarded as the primary bioactive ingredient in Panax notoginseng that has been well recognized for its protective effects against ischemia/reperfusion (IR) injury. However, the mechanisms still remain elusive. Our study aims to investigate the effects of Rg1 against lung injury induced by hind-limb IR in rats.

METHODS

Twenty-four Sprague Dawley rats were randomly submitted to sham operation (SM group), hind-limb IR (IR group), hind-limb IR + Rg1 (Rg1 group), and hind-limb IR + Pro-DTC group (PD group). All the rats except those in SM group were subjected to 3 h of ischemia followed by 6 h of reperfusion, and extra intravenous Rg1 and pyrrolidine dithiocarbamate (Pro-DTC), a selective inhibitor of nuclear factor kappa B (NF-κB), was administered intravenously before ischemia in the Rg1 and PD group, respectively. The activities of myeloperoxidase (MPO), superoxide dismutase (SOD) and catalase (CAT), as well as protein expressions of NF-κB p65 and cyclooxygenases-2 (COX-2) in lung tissue, and thromboxane B2 (TXB2) and 6-keto-ProstaglandinF_1α (6-keto-PGF_1α) levels in bronchoalveolar lavage (BAL) fluid were detected. Morphological changes, index of quantitative assessment of histologic lung injury (IQA), apoptosis index (AI) and lung Wet/Dry ratio were also evaluated.

RESULTS

The levels of Wet/Dry ratio, IQA, AI, activities of MPO and 6-keto-PGF_1α/TXB₂ ratio were increased, and NF-κB p65 and COX-2 protein expression were upregulated, while SOD and CAT levels were decreased in lung tissue in IR group as compared with SM group (p < 0.05), all the alterations could be significantly reversed by Rg1 or Pro-DTC pretreatment (p < 0.05). And Rg1 and Pro-DTC also significantly attenuated the pulmonary histological abnormalities induced by IR.

CONCLUSION

Ginsenoside Rg1 potentially attenuated lung injury induced by hind-limb IR by regulating NF-κB/COX-2 signaling pathway.

Chronology of mitochondrial and cellular events during skeletal muscle ischemia-reperfusion

Peripheral artery disease (PAD) is a common circulatory disorder of the lower limb arteries that reduces functional capacity and quality of life of patients. Despite relatively effective available treatments, PAD is a serious public health issue associated with significant morbidity and mortality. Ischemia-reperfusion (I/R) cycles during PAD are responsible for insufficient oxygen supply, mitochondriopathy, free radical production, and inflammation and lead to events that contribute to myocyte death and remote organ failure. However, the chronology of mitochondrial and cellular events during the ischemic period and at the moment of reperfusion in skeletal muscle fibers has been poorly reviewed. Thus, after a review of the basal myocyte state and normal mitochondrial biology, we discuss the physiopathology of ischemia and reperfusion at the mitochondrial and cellular levels. First we describe the chronology of the deleterious biochemical and mitochondrial mechanisms activated by I/R. Then we discuss skeletal muscle I/R injury in the muscle environment, mitochondrial dynamics, and inflammation. A better understanding of the chronology of the events underlying I/R will allow us to identify key factors in the development of this pathology and point to suitable new therapies. Emerging data on mitochondrial dynamics should help identify new molecular and therapeutic targets and develop protective strategies against PAD.

Hydrogen peroxide-activatable antioxidant prodrug as a targeted therapeutic agent for ischemia-reperfusion injury

Overproduction of hydrogen peroxide (H₂O₂) causes oxidative stress and is the main culprit in the pathogenesis of ischemia/reperfusion (I/R) injury. Suppression of oxidative stress is therefore critical in the treatment of I/R injury. Here, we report H₂O₂-activatable antioxidant prodrug (BRAP) that is capable of specifically targeting the site of oxidative stress and exerting anti-inflammatory and anti-apoptotic activities. BRAP with a self-immolative boronic ester protecting group was designed to scavenge H₂O₂ and release HBA (p-hydroxybenzyl alcohol) with antioxidant and anti-inflammatory activities. BRAP exerted potent antioxidant and anti-inflammatory activity in lipopolysaccharide (LPS)- and H₂O₂-stimulated cells by suppressing the generation of ROS and pro-inflammatory cytokines. In mouse models of hepatic I/R and cardiac I/R, BRAP exerted potent antioxidant, anti-inflammatory and anti-apoptotic activities due to the synergistic effects of H₂O₂-scavenging boronic esters and therapeutic HBA. In addition, administration of high doses of BRAP daily for 7 days showed no renal or hepatic function abnormalities. Therefore BRAP has tremendous therapeutic potential as H₂O₂-activatable antioxidant prodrug for the treatment of I/R injuries.

H2O2-responsive molecularly engineered polymer nanoparticles as ischemia/reperfusion-targeted nanotherapeutic agents

The main culprit in the pathogenesis of ischemia/reperfusion (I/R) injury is the overproduction of reactive oxygen species (ROS). Hydrogen peroxide (H₂O₂), the most abundant form of ROS produced during I/R, causes inflammation, apoptosis and subsequent tissue damages. Here, we report H₂O₂-responsive antioxidant nanoparticles formulated from copolyoxalate containing vanillyl alcohol (VA) (PVAX) as a novel I/R-targeted nanotherapeutic agent. PVAX was designed to incorporate VA and H₂O₂-responsive peroxalate ester linkages covalently in its backbone. PVAX nanoparticles therefore degrade and release VA, which is able to reduce the generation of ROS, and exert anti-inflammatory and anti-apoptotic activity. In hind-limb I/R and liver I/R models in mice, PVAX nanoparticles specifically reacted with overproduced H₂O₂ and exerted highly potent anti-inflammatory and anti-apoptotic activities that reduced cellular damages. Therefore, PVAX nanoparticles have tremendous potential as nanotherapeutic agents for I/R injury and H₂O₂-associated diseases.

Hydrogen peroxide-responsive copolyoxalate nanoparticles for detection and therapy of ischemia-reperfusion injury

The main culprit in the pathogenesis of ischemia/reperfusion (I/R) injury is the generation of high level of hydrogen peroxide (H2O2). In this study, we report a novel diagnostic and therapeutic strategy for I/R injury based on H2O2-activatable copolyoxalate nanoparticles using a murine model of hind limb I/R injury. The nanoparticles are composed of hydroxybenzyl alcohol (HBA)-incorporating copolyoxalate (HPOX) that, in the presence of H2O2, degrades completely into three known and safe compounds, cyclohexanedimethanol, HBA and CO2. HPOX effectively scavenges H2O2 in a dose-dependent manner and hydrolyzes to release HBA which exerts intrinsic antioxidant and anti-inflammatory activities both in vitro and in vivo models of hind limb I/R. HPOX nanoparticles loaded with fluorophore effectively and robustly image H2O2 generated in hind limb I/R injury, demonstrating their potential for bioimaging of H2O2-associated diseases. Furthermore, HPOX nanoparticles loaded with anti-apoptotic drug effectively release the drug payload after I/R injury, exhibiting their effectiveness for a targeted drug delivery system for I/R injury. We anticipate that multifunctional HPOX nanoparticles have great potential as H2O2 imaging agents, therapeutics and drug delivery systems for H2O2-associated diseases.

Small incision fasciotomy in a patient with compartment syndrome and peripheral arterial occlusive disease

An 82-year-old-man with a previous history of atrial fibrillation was admitted with acute limb ischemia. Emergent embolectomy was performed, but after the operation, the patient suffered from recurrent ischemic pain. Peripheral angiography revealed thrombosis of the distal popliteal artery due to pre-existing peripheral arterial occlusive disease. Bypass surgery of the popliteal artery and posterior tibial artery was then performed. Although peripheral blood flow was restored after the operation, he suffered from compartment syndrome the next day. The patient was treated with an emergent bed-side fasciotomy using a small incision, achieving full recovery of blood flow to the distal artery. The wound closed secondarily without surgical closure. In a patient with peripheral arterial occlusive disease, fasciotomy should be performed at a lower compartment pressure due to a lack of peripheral perfusion pressure. Emergent small incision fasciotomy was effective in this patient with an acute compartment syndrome and an ischemic limb.

Effect of ischemia post-conditioning on skeletal muscle oxidative injury, mTOR, Bax, Bcl-2 proteins expression, and HIF-1α/β-actin mRNA, IL-6/β-actin mRNA and caveolin-3/β-actin mRNA expression in ischemia-reperfusion rabbits

This study is designed to investigate the effect of ischemia post-conditioning on IR-induced skeletal muscle injury in limbs of experimental rabbits. Rabbits are randomized to one of the following three groups: sham control, ischemic reperfusion, ischemic postconditioning. The lipid peroxidation level, antioxidant enzymes activities, skeletal muscle mammalian target of rapamycin (mTOR), Bax, Bcl-2 proteins expression and Bcl-2/Bax, and HIF-1α/β-actin mRNA, interleukin-6 (IL-6)/β-actin mRNA and caveolin-3/β-actin mRNA expression were tested in the current study. The results suggested that ischemic postconditioning might decrease lipid peroxidation level, lactic dehydrogenase (LDH), creatine kinase (CK) activities, Bcl-2 proteins expression and Bcl-2/Bax, HIF-1α/β-actin mRNA expression and increase skeletal muscle antioxidant enzymes activities, Bax protein expression and IL-6/β-actin mRNA and caveolin-3/β-actin mRNA expression. These indicated that protective effect of ischemic postconditioning against IR-induced skeletal muscle injury involve into a complex molecular mechanism. Our research results may offer a theoretical guidance for therapy of related clinical diseases.

Hemodynamic and oxidative mechanisms of tourniquet-induced muscle injury: near-infrared spectroscopy for the orthopedics setting

During orthopedic procedures, the tourniquets used to maintain bloodless surgical fields cause ischemia and then reperfusion (I/R), leading to oxidative muscle injury. Established methods exist neither for monitoring orthopedic I/R nor for predicting the extent of tourniquet-associated oxidative injury. To develop a predictive model for tourniquet-associated oxidative muscle injury, this study combined real-time near-infrared spectroscopy (NIRS) monitoring of I/R with Western blotting (WB) for oxidized proteins. We hypothesized strong correlations between NIRS-derived I/R indices and muscle protein oxidation. In 17 patients undergoing ankle fracture repair, a thigh tourniquet was inflated on the injured limb (300 mmHg). Using a continuous-wave (CW) NIRS setup, oxygenated (O2Hb), deoxygenated (HHb), and total (tHb) hemoglobin were monitored bilaterally (tourniquet versus control) in leg muscles. Leg muscle biopsies were collected unilaterally (tourniquet side) immediately after tourniquet inflation (pre) and before deflation (post). Average ischemia duration was 43.2 ± 14.6 min. In post-compared to pre-biopsies, muscle protein oxidation (quantified using WB) increased 172.3%± 145.7% (P<0.0005). Changes in O2Hb and tHb were negatively correlated with protein oxidation (respectively: P=0.040, R2=0.25 and P=0.003, R2=0.58). Reoxygenation rate was positively correlated with protein oxidation (P=0.041, R2=0.25). These data indicate that using CW NIRS, it is possible to predict orthopedic tourniquet-associated muscle oxidative injury noninvasively.

Influence of ShuJinHuoXue tablets on ischemia reperfusion injury of animals' skeletal muscle

Ischemia-reperfusion (IR) can lead to serious tissue oxidative injury in animals. ShuJinHuoXue tablet (SJHXT) is a Chinese Traditional Medicine which can relax the muscles and stimulate the blood circulation and has been used as a clinical medicine. In the present study, we investigated the effects of SJHXT pretreatment on oxidative injury using an animal model of acute limb IR. Results showed that SJHXT pre-treatment (200, 300 and 400 mg/kg/day) markedly reduced serum endothelin-1 (ET-1), thromboxane B2 (TXB₂) levels and thromboxane B2/6-keto- prostaglandin F1α (TXB₂/6-Keto-PGF(1α)), wet weight/dried weight (W/D) ratio, myeloperoxidase (MPO), creatine kinase (CK), lactate dehydrogenase (LDH) activities, and increased serum nitric oxide (NO), 6-Keto-PGF(1α) levels and NO/ET-1 ratio in the IR+SJHXT groups. In addition, the SJHXT pre-treatment (200, 300 and 400 mg/kg/day) markedly reduced skeletal muscle Ca²⁺, malondialdehyde (MDA) levels, increased Na⁺-K⁺-ATPase, Ca²⁺-Mg²⁺-ATPase, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities. Our results suggest that SJHXT pre-treatment may improve skeletal muscle blood vessel microcirculation, decrease skeletal muscle oxidative injury and enhance antioxidant enzymes activities in IR animals.

Compartment syndrome-induced microvascular dysfunction: an experimental rodent model

BACKGROUND

Acute compartment syndrome (CS) is a limb-threatening disease that results from increased intracompartmental pressure. The pathophysiologic mechanisms by which this occurs are poorly understood. This study was designed to measure the effects of increased intracompartmental pressure on skeletal muscle microcirculation, inflammation and cellular injury using intravital videomicroscopy (IVVM) in a clinically relevant small animal model.

METHODS

We induced CS in 10 male Wistar rats (175-250 g), using a saline infusion technique. Intracompartmental pressure was controlled between 30 and 40 mm Hg and maintained for 45 minutes. After fasciotomy, the extensor digitorum longus muscle was visualized using IVVM, and perfusion was quantified. We quantified leukocyte recruitment to measure the inflammatory response. We measured muscle cellular injury using a differential fluorescent staining technique.

RESULTS

The number of nonperfused capillaries increased from 12.7 (standard error of the mean [SEM] 1.4 ) per mm in the control group to 30.0 (SEM 6.7) per mm following 45 minutes of elevated intracompartmental pressure (CS group; p = 0.031). The mean number of continuously perfused capillaries (and SEM) decreased from 78.4 (3.2) per mm in the control group to 41.4 (6.9) per mm in the CS group (p = 0.001). The proportion of injured cells increased from 5.0% (SEM 2.1%) in the control group to 16.3% (SEM 6.8%) in the CS group (p = 0.006). The mean number of activated leukocytes increased from 3.6 (SEM 0.7) per 100 μm(2) in the control group to 8.6 (SEM 1.8) per 100 μm(2) in the CS group (p = 0.033).

CONCLUSION

Early CS-induced microvascular dysfunction resulted in a decrease in nutritive capillary perfusion and an increase in cellular injury and was associated with a severe acute inflammatory component.

Neutrophil Infiltration in Exercise-Injured Skeletal Muscle

Neutrophils have not consistently been detected in exercise-injured skeletal muscle and, therefore, neutrophil infiltration in this muscle has become a controversial issue. Thirty-eight animal and human studies that assessed injured muscle for neutrophils and employed acute exercise (e.g. level, uphill or downhill running, eccentric contractions, or swimming) were analysed to help clarify the relationship between neutrophil infiltration and exercise-induced muscle injury. Findings from nearly three-quarters of the reviewed studies suggest that neutrophil accumulation follows exercise-induced muscle injury. Intramuscular neutrophil infiltration was present in 85% and 55% of the animal and human studies, respectively. However, no consistent relationship between the potential damaging effect of the exercise type and neutrophil infiltration can be conclusively established from these studies. Specific animal-related factors that could influence these results include age, animal strain, catecholamines, corticosterone, acute stressors and muscle type, whereas a specific human-related influencing factor is physical activity status. Factors affecting both animal and human studies could include sex hormones, muscle sampling techniques and neutrophil detection approaches. General categories of methods that have been used to detect neutrophil infiltration are microscopy, myeloperoxidase (MPO) biochemical assay, antibody staining and white blood cell radionuclide imaging. Only studies employing white blood cell radionuclide imaging have consistently detected neutrophil infiltration. However, antibody staining with a quantitative analysis is currently the most feasible, valid and sensitive method. Research recommendations, therefore, are warranted to resolve the neutrophil infiltration controversy. We propose two approaches for animal studies. The first approach encompasses (i) studying or measuring factors that could influence neutrophil infiltration; (ii) using quantitative antibody staining analysis (in all studies and employing a panel of anti-neutrophil antibodies); (iii) examining the relationship between fibre morphological changes and neutrophil antigen expression; and (iv) developing a neutrophil antibody-radionuclide imaging technique. The second approach will yield animal findings complementing or addressing the gaps from the human exercise studies. For human studies, we suggest that (i) physical activity status is investigated; (ii) quantitative antibody staining analysis is performed (including staining injured muscle with a panel of antibodies such as anti-elastase, anti-MPO, anti-CD11b and anti-CD15 or assessing injured muscle using both immunohistochemistry and the MPO biochemical assay); and (iii) the relationship between fibre morphological changes and neutrophil antigen expression is examined. Studies that incorporate these recommendations could lead to an increased understanding of whether neutrophils are essential for the recovery from an exercise-induced muscle injury.

Influence of groin incision, duration of ischemia, and prostaglandin E1 on ischemia-reperfusion injury of the lower limb

OBJECTIVE

The influences of groin incision, duration of ischemia, and the effects of prostaglandin E1 (PGE1) on ischemia-reperfusion (I/R) injury of the hind limb in rabbits were evaluated.

DESIGN

A prospective study.

SETTING

Laboratory.

PARTICIPANTS

In 64 rabbits, bilateral hind limb ischemia was induced by occlusion of the abdominal aorta. Volume changes, neuromuscular function of the hind limb, and creatine kinase (CK) release were measured as variables of tissue injury.

INTERVENTIONS

Eight rabbits served as untreated controls (CON). In 2 groups (each n = 14), 3 hours of ischemia were followed by 3 hours of reperfusion (I/R). In 2 different groups (each n = 14), 45 minutes of ischemia were followed by 2 hours of reperfusion. To determine effects of PGE1, 1 I/R group of each ischemia duration was treated intravenously with 80 ng/kg/min of PGE1 starting 30 minutes after the onset of ischemia (I/R-PGE1). To determine effects of groin incision on edema formation, volume changes were determined in the "operated" right (CON-R, 3h-R, 3h-PGE1-R and 45 min-R, 45 min-PGE1-R) or in the "nonoperated" left hind limb (CON-L, 3h-L, 3h-PGE1-L and 45 min-L, 45 min-PGE1-L), representing a subgroup analysis.

MEASUREMENTS AND MAIN RESULTS

Volume changes after I/R occurred only in operated legs after ischemia (3h-R: 2.3 +/- 0.3 mL, p < 0.0001 v CON-R and 3h-L; 45 min-R: 0.8 +/- 0.2 mL, p < 0.01 v 45 min-L). PGE1 reduced edema formation in the operated legs (3h-PGE1-R: 1.0 +/- 0.4 mL, p < 0.0001 v 3h-R; 45 min-PGE1-R: 0.5 +/- 0.3 mL, p = 1.0 v 45 min-R). Groin incision without I/R had no effect on edema formation (CON-R: -0.13 +/- 0.17 mL of baseline). The increase of CK release from 616 +/- 584 U/L in controls to 5,921 +/- 2,156 U/L after 3 hours of ischemia (p < 0.001) was attenuated by treatment with PGE1 (3,732 +/- 2,653, p < 0.05 v I/R). Forty-five minutes of ischemia did not lead to cellular damage as measured by CK release (I/R: 606 +/- 364 U/L). Recovery of neuromuscular function was not affected by PGE1.

CONCLUSION

Development of edema during I/R depends on groin incision of the hind limb and on the duration of ischemia. The I/R injury is attenuated by PGE1 treatment, in terms of reduced edema formation and CK release, but not in terms of neuromuscular function.

Oestrogen influence on myogenic satellite cells following downhill running in male rats: a preliminary study

AIM

This study examined the effect of oestrogen supplementation in rats on myogenic satellite cell quantities in type I and II muscles following eccentric exercise.

METHODS

Gonad intact adult male rats divided into four groups, oestrogen supplemented (25 mg oestrogen pellet) control (EC), oestrogen supplemented, exercised (EE), sham (no oestrogen) control (SC) and sham, exercised (SE). After 1 week of oestrogen exposure the EE and SE animals performed 90 min of intermittent downhill running (5 min running/2 min rest @-13.5 degrees incline and 17 m min(-1) speed). Seventy-two hours later exercised (EE and SE) and control (EC and SC) animals were killed and blood samples taken and soleus and white (superficial) vastus muscles surgically removed. Histochemical sections of soleus and white vastus muscles were examined for myogenic satellite cell content by use of Pax7 antibody and for neutrophil content by use of haematoxylin and eosin (H and E) staining procedures.

RESULTS

Downhill running resulted in significant elevations in satellite cells and neutrophils detected in both soleus and white vastus muscle samples (P < 0.01). Interestingly, oestrogen supplementation resulted in significantly greater (P < 0.01) post-exercise elevations in satellite cells detected in both soleus and white vastus muscle samples compared with sham (no oestrogen) rats. Increases in neutrophils were significantly (P < 0.05) attenuated in oestrogen supplemented rats relative to sham in soleus but not in white vastus muscles.

CONCLUSIONS

Oestrogen supplementation in male rats may have accentuated the 72 h post-downhill running increase in Pax7 detected myogenic satellite cell number in both soleus and white vastus muscles relative to unsupplemented rats. The mechanisms and physiological consequences of this effect are yet to be determined.

Protective effects of a potent c5a receptor antagonist on experimental acute limb ischemia-reperfusion in rats

OBJECTIVES

The capacity of a potent C5a receptor antagonist to inhibit various parameters of local and remote organ injury following lower limb ischemia-reperfusion (I/R) in rats was investigated.

METHODS

Rats were subjected to 2 h bilateral hindlimb ischemia and 4 h reperfusion. Drug-treated rats received AcF-[OPdChaWR] (1 mg/kg) iv either 10 min before ischemia or 10 min prior to reperfusion, or orally (10 mg/kg) 30 min prior to ischemia. Levels of circulating creatine kinase (CK), lactate dehydrogenase (LDH), alanine and aspartate aminotransferase (ALT/AST), creatinine, blood urea nitrogen (BUN), polymorphonuclear leukocytes (PMNs), and calcium (Ca(++)) and potassium (K(+)) ions were determined. Other parameters measured included urinary protein levels, muscle edema, and myeloperoxidase (MPO) concentrations in the lung, liver, and muscle along with liver homogenate tumor necrosis factor-alpha (TNF-alpha) concentrations.L RESULTS: imb I/R injury was characterized by significant elevations of CK, LDH, ALT, AST, creatinine, BUN, proteinuria, PMNs, serum K(+), muscle edema, organ MPO, and liver homogenate TNF-alpha concentrations, but a significant reduction in serum Ca(2+) concentrations. When rats were treated with AcF-[OPdChaWR], there were significant improvements in all these parameters.

CONCLUSIONS

These results indicate a pivotal role for C5a in inducing local and remote organ injury and suggest a possible new drug therapeutic category for preventing anticipated tissue injury associated with I/R.

Aprotinin and preservation of myocardial function after ischemia-reperfusion injury

Ischemia-reperfusion injury, a complex process involving the generation and release of inflammatory cytokines, accumulation and infiltration of neutrophils and macrophages, release of oxygen free radicals, activation of proteases, and generation of nitric oxide (NO), may result in myocardial dysfunction and possible injury to other major organs. Aprotinin, a nonspecific serine protease inhibitor used to reduce the blood loss and transfusion requirements accompanying cardiac surgery, has dose-dependent effects on coagulation, fibrinolytic, and inflammatory variables. Data indicate that aprotinin may provide protection from ischemia-reperfusion injury. In myocardial tissue models of ischemia and reperfusion, aprotinin has been shown to reduce uptake of tumor necrosis factor-alpha (TNF-alpha), generation of NO, and accumulation of leukocytes. Improved myocardial function has been observed with aprotinin treatment in animal models of ischemia-reperfusion injury. In humans, data indicate that integrin expression associated with leukocyte transmigration as well as markers of myocardial damage are reduced in patients receiving aprotinin. Further, data suggest that patients who receive aprotinin may have a reduced need for inotropic support and a decreased incidence of postoperative atrial fibrillation. In all, review of this topic indicates that aprotinin may reduce aspects of ischemia-reperfusion injury and prospective clinical studies are needed to evaluate the impact of aprotinin on associated patient outcomes.

Up-regulation of MMP-2 and MMP-9 leads to degradation of type IV collagen during skeletal muscle reperfusion injury; protection by the MMP inhibitor, doxycycline

OBJECTIVES

to determine the role of matrix metalloproteinases, MMP-2 and MMP-9, in reperfusion injury following skeletal muscle ischaemia and whether inhibition of MMPs by doxycycline protects against tissue damage.

METHODS

rats were anaesthetised and a tourniquet applied to the proximal thigh to occlude blood flow. Four hours of ischaemia was followed by reperfusion for 0, 4, 24 or 72 h. Two further groups received doxycycline for 7 days prior to bilateral ischaemia and 24 h reperfusion. Skeletal muscle from both limbs, kidneys and lungs were harvested for zymography and immunohistochemical staining for type IV collagen.

RESULTS

upregulation of MMP-2 and MMP-9 was detected by zymography in the ischaemic leg and lung but not in the kidney. Quantitative immunohistochemical analysis showed marked degradation of type IV collagen in reperfused muscle, lung and kidney. Doxycycline-treated rats showed significant preservation of type IV collagen in skeletal muscle and a trend towards preservation in kidney and lung.

CONCLUSIONS

MMP-2 and MMP-9 are strongly upregulated in skeletal muscle ischaemia/reperfusion injury and are also upregulated in remote organs, leading to degradation of basement membranes. Inhibition of MMP activity may therefore be potentially therapeutically useful in reducing the severity of reperfusion injury.

Effects of ovariectomy and estrogen on ischemia-reperfusion injury in hindlimbs of female rats

The effects of estrogen and ovariectomy on indexes of muscle damage after 2 h of complete hindlimb ischemia and 2 h of reperfusion were investigated in female Sprague-Dawley rats. The rats were assigned to one of three experimental groups: ovariectomized with a 17beta-estradiol pellet implant (OE), ovariectomized with a placebo pellet implant (OP), or control with intact ovaries (R). It was hypothesized that following ischemia-reperfusion (I/R), muscle damage indexes [serum creatine kinase (CK) activity, calpain-like activity, inflammatory cell infiltration, and markers of lipid peroxidation (thiobarbituric-reactive substances)] would be lower in the OE and R rats compared with the OP rats due to the protective effects of estrogen. Serum CK activity following I/R was greater (P < 0.01) in the R rats vs. OP rats and similar in the OP and OE rats. Calpain-like activity was greatest in the R rats (P < 0.01) and similar in the OP and OE rats. Neutrophil infiltration was assessed using the myeloperoxidase (MPO) assay and immunohistochemical staining for CD43-positive (CD43+) cells. MPO activity was lower (P < 0.05) in the OE rats compared with any other group and similar in the OP and R rats. The number of CD43+ cells was greater (P < 0.01) in the OP rats compared with the OE and R rats and similar in the OE and R rats. The OE rats had lower (P < 0.05) thiobarbituric-reactive substance content following I/R compared with the R and OP rats. Indexes of muscle damage were consistently attenuated in the OE rats but not in the R rats. A 10-fold difference in serum estrogen content may mediate this. Surprisingly, serum CK activity and muscle calpain-like activity were lower (P < 0.05) in the OP rats compared with the R rats. Increases in serum insulin-like growth factor-1 content (P < 0.05) due to ovariectomy were hypothesized to account for this finding. Thus both ovariectomy and estrogen supplementation have differential effects on indexes of I/R muscle damage.