Postischemic treatment with ethyl pyruvate prevents adenosine triphosphate depletion, ameliorates inflammation, and decreases thrombosis in a murine model of hind-limb ischemia and reperfusion

Renal and Vascular Functional Decline in Aged Low Birth Weight Murine Adults

INTRODUCTION

Maternal undernutrition (MUN)-induced low birth weight (LBW) neonates are susceptible to the development of high blood pressure and kidney disease later in life, although the underlying pathological causes remain unclear. The study here investigated the role of renal oxidative stress, impairment of vascular function, and altered sensitivity to angiotensin II (Ang II) as factors that contribute to these pathologies in aged LBW mice.

METHODS

LBW offspring were generated using a combined protein and caloric restricted MUN mouse model. The resulting LBW offspring were examined 1 year after birth for mean arterial blood pressure (MABP) (carotid artery catheterization), renal blood flow (RBF) (laser Doppler flowmetry), glomerular filtration rate (GFR) (sinistrin clearance), vasoreactivity (myograph), renal vascular density (CD31 staining), and reactive oxygen species (ROS) (ROS probes). Immunoblotting examined Ang II type 1 receptor (AT1R), soluble guanylate cyclase (sGC), and antioxidant systems. Pharmacological agents delivered to animals included the sGC stimulator δ-aminolevulinic acid (ALA), the AT1R inhibitor losartan, the antioxidant ethyl pyruvate (EP), and the toll-like receptor 4 inhibitor TAK242.

RESULTS

After 1 year, MABP was increased, while RBF, GFR, vascular reactivity, renal vascular density, and sGC were all reduced in the LBW aged adult. All four pharmacological agents improved MABP, RBF, GFR, vascular density, and vascular reactivity. Renal ROS was increased in the LBW adult but was reduced by ALA, EP, and TAK242 treatment. AT1R was upregulated in the LBW adult, while sGC was decreased, an effect reversed by ALA treatment. Endogenous antioxidant systems, including SOD1, catalase, and glutathione were downregulated in the LBW adult.

CONCLUSION

MUN-induced LBW mice experience increased Ang II sensitivity and oxidative stress. The increased Ang II sensitivity and ROS generation influences vascular density and reactivity, which drive an increase in MABP, and a concomitantly decrease in RBF and glomerular filtration. Pharmacological intervention that inhibits AT1R, enhances levels of sGC, reduces ROS, or inhibits toll-like receptor 4 improves vascular and renal function in the LBW adult.

Ethyl pyruvate, a versatile protector in inflammation and autoimmunity

Ethyl pyruvate (EP) has potent influence on redox processes, cellular metabolism, and inflammation. It has been intensively studied in numerous animal models of systemic and organ-specific disorders whose pathogenesis involves a strong immune component. Here, basic chemical and biological properties of EP are discussed, with an emphasis on its redox and metabolic activity. Further, its influence on myeloid and T cells is considered, as well as on intracellular signaling beyond its effect on immune cells. Also, the effects of EP on animal models of chronic inflammatory and autoimmune disorders are presented. Finally, a possibility to apply EP as a treatment for such diseases in humans is discussed. Scientific papers cited in this review were identified using the PubMed search engine that relies on the MEDLINE database. The reference list covers the most important findings in the field in the past twenty years.

The anticoagulant effects of ethyl pyruvate in whole blood samples

BACKGROUND

Ethyl pyruvate (EP), the ethyl ester of pyruvate, has proven antiinflammatory and antioxidative properties. Additionally, anticoagulant properties have been suggested recently. EP, therefore, is a potentially antiatherosclerotic drug. We aimed to investigate whether EP possesses antiplatelet and anticoagulant properties particularly in the physiological environment of whole blood.

METHODS

We investigated the effects of increasing concentrations of EP on platelet function, on the course of clot development, and on standard coagulation times. Additionally, clot ultrastructure using scanning electron microscopy was analysed.

RESULTS

EP exerted significant antiplatelet actions: i) Impedance aggregometry amplitudes (11.7 ± 3.0 ohm, 0 μg/mL EP) dose dependently decreased (7.8 ± 3.1 ohm, 1000 μg/mL EP; -33.3%). ATP exocytosis (0.87 ± 0.24 nM, 0 μg/mL EP) measured by the luminiscent method dose-dependently decreased (0.56 ± 0.14 nM, 1000 μg/mL; -35.6%). ii) Closure times (104.4 ± 23.8 s, 0 μg/mL EP) using the Platelet function analyzer were dose-dependently prolonged (180.5 ± 82.5 s, 1000 μg/mL EP; +72.9%) using membranes coated with collagen/ADP. iii) Surface coverage (15.9 ± 5.1%, 0 μg/mL EP) dose-dependently decreased (9.0 ± 3.7%, 1000 μg/mL EP; -43.4%) using the Cone and Platelet analyzer. EP also exerted significant anticoagulant actions: Coagulation times (177.9 ± 37.8, 0 μg/mL EP) evaluated by means of thrombelastometry were dose-dependently prolonged (212.8 ± 57.7 s, 1000 μg/mL EP; +19.6%). Activated partial thromboplastin times (31.5 ± 1.8 s, 0 μg/mL EP) were dose-dependently prolonged (35.6 ± 2.3 s, 1000 μg/mL EP; +13.0%). Prothrombin times (0.94 ± 0.02 INR, 0 μg/mL EP) were dose-dependently prolonged (1.09 ± 0.04 INR, 1000 μg/mL EP; +16.0%).

CONCLUSION

We found that EP possesses antiplatelet and anticoagulant properties in whole blood. Together with its proven anti-inflammatory and antioxidative properties, EP is a potentially antiatherogenic drug.

Enhancement of ATP production ameliorates motor and cognitive impairments in a mouse model of MPTP-induced Parkinson's disease

Approximately 30-40% of patients with Parkinson's disease (PD) exhibit cognitive impairments. However, there are currently no clinically effective drugs for the treatment of cognitive impairment in patients with PD. Previous studies have suggested that mitochondrial dysfunction such as decreased adenosine triphosphate (ATP) production triggers dopaminergic neurodegeneration in patients with PD and that mitochondria represent a potential target for the development of novel treatments for preventing PD. Therefore, in the present study, we investigated the cognition-enhancing effects of ethyl pyruvate (EP) and 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl) piperazine dihydrochloride (SA4503) in mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinsonism. PD model mice were generated via treatment with MPTP (25 mg/kg, i.p.) once a day for 5 consecutive days. Twenty-four hours after the final injection of MPTP, mice were intraperitoneally injected with EP (25, 50, 100 mg/kg) or SA4503 (1 mg/kg) once a day for 4 weeks. Chronic administration of EP (100 mg/kg i.p.) or SA4503 (1 mg/kg, i.p.) improved both motor deficits and cognitive impairments in MPTP-treated mice. Furthermore, treatment with EP or SA4503 attenuated decreases in the levels of ATP and tyrosine hydroxylase (TH) in the substantia nigra pars compacta (SNpc)/ventral tegmental area (VTA), striatum, and hippocampal CA1 region. Administration of EP or SA4503 protected the dopaminergic neurons from MPTP-induce toxicity and restored the dopamine levels in the striatum. Elevated 4-hydroxy-2-nonenal- (4-HNE-) and nitrotyrosine-reactive protein levels induced by MPTP-treatment were suppressed by EP or SA4503 treatment in the SNpc-VTA, striatum, and hippocampal CA1 region. These observations suggest that EP and SA4503 attenuate cognitive impairments and motor dysfunction in mice with MPTP-induced PD.

Ethyl pyruvate treatment ameliorates pancreatic damage: evidence from a rat model of acute necrotizing pancreatitis

INTRODUCTION

Ethyl pyruvate (EP), a natural flavoring and fragrance agent, has been shown to exert anti-inflammatory and antioxidant actions. We tested the potential beneficial effects of EP in a rat model of acute necrotizing pancreatitis (ANP), a serious condition with a significant inflammatory explosion and oxidative stress.

MATERIAL AND METHODS

Fifty-two adult male Sprague-Dawley rats were divided into four groups: sham + saline, sham + EP, ANP + saline, and ANP + EP. The ANP was induced by glycodeoxycholic acid and cerulein. Animals were sacrificed at 48 h and biochemical, hematological, and histological markers of ANP and inflammation were assessed. The extent of mortality, systemic cardiorespiratory variables, pancreatic microcirculation, renal/hepatic functions, acinar cell injury and enzyme markers for pancreas and lung tissues were investigated.

RESULTS

The EP-treated ANP group presented significantly lower mortality than the untreated ANP group (44% (7/16) vs. 19% (3/16), respectively, p < 0.05). Administration of EP resulted in significantly lower levels of IL-6 (ANP + saline: 5470 ±280 vs. ANP + EP: 2250 ±180 pg/ml, p < 0.05). Compared with the ANP group, the ANP + EP group had a lower pancreatic necrosis score (1.45 ±0.2 vs. 0.96 ±0.2, p < 0.05). Moreover, intraperitoneal EP administration had a positive effect on most indices of pancreatitis (amylase and alanine transaminase levels) and lung damage (except lung malondialdehyde levels) as they decreased towards baseline values.

CONCLUSIONS

The results from this experimental study indicate that EP, a nontoxic chemical approved by the Food and Drug Administration as a food additive, provides positive effects on the course of pancreatitis, suggesting potential usefulness in management of ANP.

Ethyl pyruvate improves skin flap survival after ischaemia reperfusion injury

BACKGROUND & OBJECTIVES

Reperfusion after ischaemia is detrimental to the tissues. The oxidative stress created and cytokines released are mostly responsible in this process. In this study, ethyl pyruvate, a known agent for its anti-inflammatory and antioxidant properties, was used to investigate the effects on ischaemia/reperfusion injury on skin island flaps in rats.

METHODS

Sixty rats were randomly distributed in three groups (non-ischaemic, ischaemic and medication groups). Ethyl pyruvate was administered in the medication group with a dose of 50 mg/kg. After 24 h and one week, the animals were sacrificed, and the flaps were analyzed macroscopically, histopathologically, biochemically (total nitrite, malondialdehyde and myeloperoxidase).

RESULTS

Biochemical markers indicating oxidative stress, were found elevated in ischaemic group, whereas medication with ethyl pyruvate significantly reduced these values. There was a significant reduction (P<0.05) in the levels of these markers between ischaemic and medication groups. Ethyl pyruvate improved all the parameters significantly.

INTERPRETATION & CONCLUSION

Ethyl pyruvate showed strong scavenger activity against reactive oxygen species. It could be a potential candidate to improve the flap viability in reconstructive microsurgery, especially in free tissue transfers. However, more studies are warranted in experimental models to confirm these findings.

Perfusion of isolated rat kidney with Mesenchymal Stromal Cells/Extracellular Vesicles prevents ischaemic injury

Kidney donation after circulatory death (DCD) is a less than ideal option to meet organ shortages. Hypothermic machine perfusion (HMP) with Belzer solution (BS) improves the viability of DCD kidneys, although the graft clinical course remains critical. Mesenchymal stromal cells (MSC) promote tissue repair by releasing extracellular vesicles (EV). We evaluated whether delivering MSC-/MSC-derived EV during HMP protects rat DCD kidneys from ischaemic injury and investigated the underlying pathogenic mechanisms. Warm ischaemic isolated kidneys were cold-perfused (4 hrs) with BS, BS supplemented with MSC or EV. Renal damage was evaluated by histology and renal gene expression by microarray analysis, RT-PCR. Malondialdehyde, lactate, LDH, glucose and pyruvate were measured in the effluent fluid. MSC-/EV-treated kidneys showed significantly less global ischaemic damage. In the MSC/EV groups, there was up-regulation of three genes encoding enzymes known to improve cell energy metabolism and three genes encoding proteins involved in ion membrane transport. In the effluent fluid, lactate, LDH, MDA and glucose were significantly lower and pyruvate higher in MSC/EV kidneys as compared with BS, suggesting the larger use of energy substrates by MSC/EV kidneys. The addition of MSC/EV to BS during HMP protects the kidney from ischaemic injury by preserving the enzymatic machinery essential for cell viability and protects the kidney from reperfusion damage.

Inhibitory effects of ethyl pyruvate on platelet aggregation and phosphatidylserine exposure

Ethyl pyruvate (EP) is a stable lipophilic pyruvate derivative. Studies demonstrated that EP shows potent anti-oxidation, anti-inflammatory and anti-coagulant effects. Inflammation and coagulation are closely interacted with platelet activation. However, it is unclear whether EP has anti-platelet effects. Therefore, we investigated the anti-platelet effect of EP in this study in vitro. We found that EP inhibited agonists induced platelets aggregation, ATP release and adhesion to collagen. Flow cytometric analysis revealed that EP inhibited agonist induced platelets PAC-1 binding, as well as P-selectin and CD40L expression. The underlying mechanism of action may involve the inhibition of platelet PI3K/Akt and Protein Kinase C (PKC) signaling pathways. Additionally, EP dose dependently inhibited platelet PS exposure induced by high concentration thrombin. Lactate dehydrogenase (LDH) activity assay and mice platelet count implied that EP may have no toxic effect on platelets. Therefore, we are the first to report that EP has potent anti-platelet activity and attenuates platelet PS exposure in vitro, suggesting that the inhibitory effects of EP on platelets may also play important roles in improvement of inflammation and coagulation disorder in related animal models.

Effects of hPTPβ inhibitor on microcirculation of rat cremaster muscle flap following ischemia-reperfusion injury

INTRODUCTION

Inhibition of protein tyrosine phosphatases (PTP) enhances endothelial receptor tyrosine kinases activation and may have beneficial effects on vessel growth and improve blood flow to ischemic tissue. The purpose of this study is to determine influence of hPTPß inhibitors on ischemia-reperfusion injury in muscle flap.

MATERIALS AND METHODS

Following cremaster muscle dissection, 60 rats divided into 10 experimental groups (placebo and treatment groups following 0, 1, 2, 3, and 4 h of ischemia). Following group-specific treatment (placebo/hPTPß inhibitor, 15 mg/kg), 2 h of reperfusion is initiated. Observations are performed at 4 h after completion of reperfusion and microcirculatory hemodynamics and leukocyte-endothelial activation were recorded.

RESULTS

Administration of hPTPß inhibitor showed preservation of capillary perfusion in group subjected to 2 h of ischemia when compared with placebo (P < .05). The effect of hPTPβ inhibitor on mean venule diameter was found to be altered by duration of ischemia and this effect was statistically significant (P < .05). Treated ischemic groups (1 h, 2 h, and 3 h) showed decreased activation of rolling, sticking, and transmigrating leukocytes compared to respective placebo groups at all time points. The differences were significant for transmigrating leukocytes after 2 h and 3 h of ischemia (P < .05). Endothelial edema index was also significantly reduced in 2 h ischemia group (P < .05).

CONCLUSION

Administration of hPTP inhibitors after submission of tissue to subcritical ischemia (1-2 h) improved functional capillary perfusion and decreased leukocyte-endothelial activation after 4 h after reperfusion. These results indicate that hPTP inhibitor has a potential postischemic therapeutic effect applied after tissue ischemia just before the reperfusion injury.

Ethyl pyruvate protects against sepsis by regulating energy metabolism

Background

Ethyl pyruvate (EP) is a derivative of pyruvic acid that has been demonstrated to be a potential scavenger of reactive oxygen species as well as an anti-inflammatory agent. In this study, we investigated the protective effects of EP and its role in regulating the energy metabolism in the livers of cecal-ligation-and-puncture-induced septic mice.

Methods

The animals were treated intraperitoneally with 0.2 mL of Ringer’s lactate solution or an equivalent volume of Ringer’s lactate solution containing EP immediately after cecal ligation and puncture. Each mouse in the Sham group was only subjected to a laparotomy. At 30-, 60-, 180-, and 360-minute time points, we measured the histopathological alterations of the intestines, and the plasma levels of interleukin (IL)-1β, IL-6, IL-10, and tumor necrosis factor-α, and the total antioxidative capacity, malondialdehyde content, and lactate and lactate/pyruvate levels in livers. Furthermore, we detected the levels of adenosine triphosphate, total adenylate, and energy charge in the livers.

Results

Our results demonstrated that the administration of EP significantly improved the survival rate and reduced intestinal histological alterations. EP inhibited the plasma levels of IL-1β, IL-6, and tumor necrosis factor-α and increased the IL-10 level. EP significantly inhibited the elevation of the malondialdehyde, lactate, and lactate/pyruvate levels and enhanced the total antioxidative capacity levels in the liver tissues. The downregulation of the adenosine triphosphate, total adenylate, and energy charge levels in the liver tissues was reversed in the septic mice treated with EP.

Conclusion

The results suggest that EP administration effectively modulates the energy metabolism, which may be an important component in treatment of sepsis.

Possible local stem cells activation by microcurrent application in experimentally injured soleus muscle

BACKGROUND

Severe injuries in skeletal muscle result in muscle weakness that delays recovery and contribute to progressive decline in muscle function. Microcurrent therapy (MCT) is a novel treatment method used in soft tissue injury and tissue regeneration therapy. The regenerative capacity of skeletal muscle tissue resides in satellite cells, the quiescent adult stem cells.

AIM

The present work aimed at investigating the relation between microcurrent therapy and local stem cells in regeneration of induced skeletal muscle injury in albino rat.

MATERIALS AND METHODS

Twenty six adult male albino rats were divided into Sham group, Injury group (I): subjected to soleus muscle injury and subdivided into subgroups I1 & I2 sacrificed 2 and 4 weeks after injury respectively. Microcurrent group (M): subjected to muscle injury and micro-current was applied. The animals were subdivided into subgroups M1 and M2 sacrificed 2 and 4 weeks after injury. Histological, immunohistochemical and morphometric studies were performed.

RESULTS

Atypical fibers widely separated by infiltrating cells and strong acidophilic sarcoplasm with focal vacuolations were found in injury group. In M1 subgroup few atypical fibers were found. In M2 subgroup multiple typical fibers were detected. A significant decrease in the mean area of atypical fibers, a significant increase in the mean area% of alpha SMA+ve cells and that of CD34+ve cells were found in microcurrent group compared to injury group.

CONCLUSION

A definite therapeutic effect of the microcurrent was found on induced skeletal muscle injury. This effect was proved to be related to satellite cell activation.

Fatal early peripheral post-reperfusion syndrome and the role of cutaneous signs

The purpose of this report is to present the case of a 75-year-old male affected by right common femoral artery and abdominal aortic aneurysms. His clinical history was also characterised by post-ischaemic cardiomyopathy, arterial hypertension, chronic respiratory disease and peripheral arterial disease. We performed two surgical procedures: right femoral aneurysmectomy and femoro-femoral bypass and subsequently a femoro-femoral crossover bypass plus right femoro-popliteal bypass below the knee. The second operation became necessary in order to treat acute occlusion of the right iliac-femoral arterial axis. The patient developed a progressive and aggressive lower limb post-perfusion syndrome associated to frank peripheral oedema, myocardial stunning, reperfusion arrhythmias, renal failure and respiratory distress. Cutaneous alterations (oedema of the leg, mottled skin and cyanosis of the foot) were more specific compared with Doppler ultrasound that showed the presence of adequate blood flow in the early phase. On the basis of this experience and of pertinent literature, this study represents a challenge for the understanding of the exact mechanism of origin and progression of post-reperfusion syndrome.

Role of ethyl pyruvate in systemic inflammatory response and lung injury in an experimental model of ruptured abdominal aortic aneurysm

Objectıve. The purpose of this study is to evaluate the effect of ethyl pyruvate (EP) on systemic inflammatory response and lung injury in an experimental rat model of ruptured abdominal aortic anurysm (RAAA). Methods. Anaesthetized 30 Sprague-Dawley male rats were randomized to sham (Sh n : 6) (Sh + EP n : 6) or shock and clamp (S/C) groups (S/C n : 9) (S/C + EP n : 9). In the S/C and S/C + EP groups, hemorrhagic shock, lower torso ischemia, and reperfusion were created, S/C group was given 1 mL saline and S/C + EP group was given 40 mg/kg EP. At the end of reperfusion process some biochemical and histological parameters were studied in serum and lung tissues. Results. An increase was observed in all parameters except interleukin-6 (IL-6) in the S/C group in comparison to the sham groups. In the S/C + EP group, serum myeloperoxydase (MPO), malondialdehyde (MDA), and tumor necrosis factor alpha (TNF-α) as well as lung MPO and MDA values decreased significantly (P < 0.016). In the lung tissues, histological injury scores and lung tissue wet/dry ratio were significantly decreased in the S/C + EP group as compared to the S/C group (P < 0.016). Conclusions. Ethyl pyruvate may reduce systemic inflammatory response and lung injury which resulted from shock and ischemia/reperfusion in an experimental model of RAAA.

Poly-ADP-ribose-polymerase inhibition ameliorates hind limb ischemia reperfusion injury in a murine model of type 2 diabetes

INTRODUCTION

Diabetes is known to increase poly-ADP-ribose-polymerase (PARP) activity and posttranslational poly-ADP-ribosylation of several regulatory proteins involved in inflammation and energy metabolism. These experiments test the hypothesis that PARP inhibition will modulate hind limb ischemia reperfusion (IR) in a mouse model of type-II diabetes and ameliorate the ribosylation and the activity/transnuclear localization of the key glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH).

METHODS

db/db mice underwent 1.5 hours of hind limb ischemia followed by 1, 7, or 24 hours of reperfusion. The treatment group received the PARP inhibitor PJ34 (PJ34) over a 24-hour period; the untreated group received Lactated Ringer (LR) at the same time points. IR muscles were analyzed for indices of PARP activity, fiber injury, metabolic activity, inflammation, GAPDH activity/intracellular localization, and poly-ADP-ribosylation of GAPDH.

RESULTS

PARP activity was significantly lower in the PJ34-treated groups than in the Lactated Ringer group at 7 and 24 hours of reperfusion. There was significantly less muscle fiber injury in the PJ34-treated group than in the Lactated Ringer-treated mice at 24 hours of reperfusion. PJ34 lowered levels of select proinflammatory molecules at 7 hours and 24 hours of IR. There were significant increases in metabolic activity only at 24 hours of IR in the PJ34 group, which temporally correlated with increase in GAPDH activity, decreased GAPDH poly-ADP-ribosylation, and nuclear translocation of GAPDH.

CONCLUSIONS

PJ34 reduced PARP activity, GAPDH ribosylation, and GAPDH translocation; ameliorated muscle fiber injury; and increased metabolic activity after hind limb IR injury in a murine model of type-II diabetes. PARP inhibition might be a therapeutic strategy after IR in diabetic humans.

Pyruvate-enriched resuscitation: metabolic support of post-ischemic hindlimb muscle in hypovolemic goats

Tourniquet-imposed ischemia-reperfusion of extremities generates reactive oxygen and nitrogen species (RONS), which can disrupt intermediary metabolism and ATP production. This study tested the hypothesis that fluid resuscitation with pyruvate, a natural antioxidant and metabolic fuel, ameliorates the deleterious effects of ischemia-reperfusion on intermediary metabolism in skeletal muscle. Anesthetized male goats (∼25 kg) were bled to a mean arterial pressure of 48 ± 1 mmHg and then subjected to 90 min hindlimb ischemia with a tourniquet and femoral crossclamp, followed by 4-h reperfusion. Lactated Ringers (LR) or pyruvate Ringers (PR) was infused intravenous for 90 min, from 30 min ischemia to 30 min reperfusion, to deliver 0.05 mmol kg(-1) min(-1) lactate or pyruvate. Time controls (TC) underwent neither hemorrhage nor hindlimb ischemia. Lipid peroxidation product 8-isoprostane, RONS-sensitive aconitase and creatine kinase activities, antioxidant superoxide dismutase activity, and phosphocreatine phosphorylation potential ([PCr]/[{Cr}{P(i)}]), an index of tissue energy state, were measured in reperfused gastrocnemius at 90 min resuscitation (n = 6 all groups) and 3.5 h post-resuscitation (n = 8 TC, 9 LR, 10 PR). PR more effectively than LR suppressed 8-isoprostane formation, prevented inactivation of aconitase and creatine kinase, doubled superoxide dismutase activity, and augmented [PCr]/([Cr][P(i)]). Pyruvate-enriched Ringer's is metabolically superior to Ringer's lactate for fluid resuscitation of tourniqueted muscle.

Reduced hind limb ischemia-reperfusion injury in Toll-like receptor-4 mutant mice is associated with decreased neutrophil extracellular traps

OBJECTIVE

Ischemia-reperfusion (IR) injury is a significant problem in the management of patients with acute limb ischemia. Despite rapid restoration of blood flow after technically successful open and endovascular revascularization, complications secondary to IR injury continue to occur and limit clinical success. Our aim was to create a murine model of hind limb IR injury to examine the role of Toll-like receptor-4 (TLR4) and to determine whether inactive TLR4 led to a decrease in the detection of neutrophil extracellular traps (NETs), which are known to be highly thrombogenic and may mediate microvascular injury.

METHODS

A calibrated tension tourniquet was applied to unilateral hind limb of wild-type (WT) and TLR4 receptor mutant (TLR4m) mice for 1.5 hours to induce ischemia and then removed to initiate reperfusion. At the end of 48 hours of reperfusion, mice were euthanized and hind limb tissue and serum specimens were collected for analysis. Hematoxylin and eosin-stained sections of hind limb skeletal muscle tissue were examined for fiber injury. For immunohistochemistry, mouse monoclonal antihistone H2A/H2B/DNA complex antibody to detect NETs and rabbit polyclonal antimyeloperoxidase antibody were used to identify infiltrating cells containing myeloperoxidase. Muscle adenosine triphosphate levels, nuclear factor (NF)-κB activity, the α-subunit of inhibitor of NF-κB light polypeptide gene enhancer, poly (adenosine diphosphate-ribose) polymerase activity, and inducible nitric oxide synthase expression were measured. Systemic levels of keratinocyte-derived chemokine, monocyte chemotactic protein-1, and vascular endothelial growth factor in the serum samples were also examined.

RESULTS

IR injury in the hind limb of WT mice demonstrated significant levels of muscle fiber injury, decreased energy substrates, increased NF-κB activation, decreased levels of α-subunit of inhibitor of NF-κB light polypeptide gene enhancer, increased inducible nitric oxide synthase expression, and increased poly (adenosine diphosphate-ribose) polymerase activity levels compared with the TLR4m samples. Additionally, there was marked decrease in the level of neutrophil and monocyte infiltration in the TLR4m mice, which corresponded to similar levels of decreased NET detection in the interstitial space and in microvascular thrombi. In situ nuclease treatment of WT tissue sections significantly diminished the level of NET immunostaining, demonstrating the specificity of the antibody to detect NETs and suggesting a potential role for nuclease treatment in IR injury.

CONCLUSIONS

These results suggest a pivotal role for TLR4 in mediating hind limb IR injury and suggest that NETs may contribute to muscle fiber injury.