Leucocytes represent a very important host defence against a number of invading pathogens and neoplasia. However, the activity of phagocytic leucocytes has been heavily implicated in the development of ischaemia-reperfusion injury, and as an aetiological factor in the pathology of other clinically important inflammatory conditions. Ischaemia-reperfusion injury occurs in diseases such as stroke and ischaemic heart disease (IHD), and during surgical procedures such as orthopaedic surgery. Investigations presented here employed a model of tourniquet-induced forearm ischaemia-reperfusion injury to investigate the effect on leucocyte adhesion and trapping (n=20). Neutrophil and monocyte leucocyte subpopulations were isolated by density gradient centrifugation techniques. Neutrophil and monocyte cell surface expression of the adhesion molecule CD11b was measured by labelling with fluorescent anti-CD11b monoclonal antibody via flow cytometry. Plasma concentrations of the soluble intercellular adhesion molecule-1 (sICAM-1) and soluble L-selectin (sL-selectin) adhesion molecules were measured using commercially available ELISA kits. Leucocyte trapping was investigated by measuring the concentration of leukocytes in venous blood leaving the arm. During ischaemia-reperfusion there was an increase in CD11b expression on neutrophils (p=0.040) and monocytes (p=0.049), a decrease in sL-selectin (p=0.387) and sICAM-1 (p=0.089) concentrations, and a decrease in peripheral blood leucocyte concentration (p=0.019). Evidence of increased leucocyte adhesion and trapping during ischaemia-reperfusion injury was supported by an increase in CD11b cell surface expression of neutrophils and monocytes. CD11b is expressed on phagocytic leucocytes and binds to ICAM-1 expressed on the surface of vascular endothelium. This increased expression of CD11b on leucocytes may therefore play a central role as the mechanism by which leucocyte trapping in the microcirculation occurs. The measured decrease in plasma concentration of sICAM-1 and sL-selectin suggests that these adhesion molecules retain their functional activity, and may bind to their corresponding cell surface ligands. It is therefore reasonable to believe that ICAM-1 expressed on the endothelium and L-selectin expressed on leucocytes is also binding to their corresponding cell surface ligands. A decrease in the number of leucocytes in the peripheral circulation may be due to increased trapping of leucocytes in the microcirculation. When leucocytes become trapped their concentration in blood leaving the microcirculation decreases, resulting in the measured decrease in leucocyte concentration. In conclusion, this study confirms the important role of leucocytes during ischaemia-reperfusion injury, which could allow for the possibility of future research that may provide therapeutic intervention for inflammatory conditions

Introduction: The paradoxical further damage done to ischaemic tissue when blood flow and oxygenation are restored is termed ischaemia-reperfusion injury. The underlying mechanisms are complex but centre on oxidative damage to the cell membrane, which suggest a therapeutic role for antioxidants such as endogenous amino acid taurine. Methods: In this study, 23 rats in 5 groups were subjected to right hind limb ischaemia-reperfusion injury. The right femoral vascular bundle was exposed and the femoral vein cannulated, and a tourniquet applied to the right hind limb. The left hind limb acted as a control in each animal. In group 1 there was no treatment administered, group 2 had normal saline injected into the femoral vein distal to the tourniquet, group 3 had turbine 200mg/Kg injected distal to the tourniquet, group 4 had taurine 200mg/Kg injected proximal to the tourniquet, and group 5 had taurine 100mg/Kg distally and 100mg/Kg proximally. After 4 hours of ischaemia and 30 minutes reperfusion, gastrocnemius biopsies were taken from right and left hind limbs and their contraction strength in response to a standardised electrical impulse was measured. Results: There was a statistically significant difference in contraction strength between right and left hind limb samples in all groups. The difference in-group 4 was an order of magnitude less than that in groups 1, 2, and 3, with an intermediate value in-group 5. Histological examination confirmed inflammatory changes consistent with ischaemia-reperfusion injury and not simple necrosis. Conclusion: These data suggest that taurine in the reperfusing blood, rather than in the ischaemic tissues, confers some protection against ischaemia-reperfusion injury mediated functional impairment in rat skeletal muscle

Summary Statement. Ischaemic preconditioning protected skeletal myotubes against the effects of ischaemia-reperfusion in vitro. This protection was associated with increased Nrf2 signalling. Introduction. Ischaemic preconditioning (IPC) is a well recognised and powerful phenomenon where a tissue becomes more tolerant to a period of prolonged ischaemia when it is first subjected to short bursts of ischaemia/reperfusion. While much is known about the ability of ischaemic preconditioning to protect myocardial tissue against ischaemia-reperfusion injury, its potential to confer benefit in an orthopaedic setting by protecting skeletal muscle remains relatively unexplored to date. One mechanism by which ischaemic preconditioning may induce protection is through a reduction in oxidative stress. Reactive oxygen species (ROS) are generated both during prolonged ischaemia and also upon reperfusion by infiltrating neutrophils, thereby leading to an increase in oxidative stress. The transcription factor, NF-E2-related factor 2 (Nrf2), is a key regulator of the cells response to oxidative stress as it regulates the expression of a network of anti-oxidant/detoxifying enzymes. Nrf2 signalling has recently been shown to protect against ischaemia-reperfusion injury in both a kidney cell line and in liver biopsies, indicating that this transcription factor may play a key role in the protection provided by ischaemic preconditioning. To date, the involvement of Nrf2 in the response of skeletal muscle to ischaemia-reperfusion has not been investigated. Thus, the aims of this study were to investigate the ability of ischaemic preconditioning to protect skeletal myotubes against ischaemia-reperfusion and to determine the role of Nrf2 signalling in this protection. Materials & Methods. C2C12 mouse myoblasts were maintained at 37. o. C in a humidified atmosphere of 95% air and 5% CO. 2. in DMEM containing 20% FBS. When cultures were approximately 90% confluent, myoblasts were differentiated to myotubes by changing to DMEM supplemented with 2% horse serum and culturing for 7–10 days. Differentiated myotubes were then exposed to simulated ischaemia for 4h (1% O. 2. ) followed by 2h reoxygenation (21% O. 2. ). To precondition myotubes, cells were subjected to 30 min of simulated ischaemia followed by 1 hour reoxygenation prior to the prolonged ischaemic event. Cell survival was assessed by lactate dehydrogenase release. Changes in Nrf2 expression were assessed using real-time PCR, Western blotting and immunofluorescence. Changes in sequestosome-1 (SQSTM1), catalase (CAT), glutathione S-transferase theta-1 (GSTT1), heme oxygenase-1 (HO-1) expression were assessed using a combination of real-time PCR and Western blotting. Results. Preconditioned myotubes showed greater viability both after 4h of ischaemia, and after 4h ischaemia followed by 2h of reoxygenation. This increase in cell viability was associated with increased Nrf2 expression. In addition, increased expression of SQSTM1, and the antioxidant enzymes, CAT, GSTT1 and HO-1 was observed in preconditioned myotubes. Discussion. Our findings indicate that ischaemic preconditioning can protect skeletal myotubes against the effects of ischaemia-reperfusion in vitro. This protection is associated with increased Nrf2 signalling indicating that this transcription factor may play a role in mediating the protection induced by ischaemic preconditioning. By modulating the response of skeletal muscle to ischaemia, ischaemic preconditioning has the potential to limit reperfusion injury, which in turn, may lead to improvements in outcome following orthopaedic surgery

Introduction and Aims: To determine whether taurine influences skeletal muscle ischaemia-reperfusion injury in a rat hindlimb model. Method: Twenty-three rats in five groups were subjected to right hindlimb ischaemia-reperfusion injury. The right femoral vein was exposed and cannulated, and a tourniquet applied to the right hindlimb. The left hindlimb acted as a control in each animal. In group 1 there was no treatment, group 2 had normal saline injected into the femoral vein distal to the tourniquet, group 3 had taurine 200mg/Kg injected distal to the tourniquet, group 4 had taurine 200mg/Kg injected proximal to the tourniquet, and group 5 had taurine 100mg/Kg distally and 100mg/Kg proximally. After ischaemia (four hours) and reperfusion (30 minutes), right and left gastrocnemius biopsies were taken and their contraction strength in response to a standardised electrical impulse was measured. Results: Histology of all right-sided biopsies confirmed inflammatory changes consistent with ischaemia-reperfusion injury. In groups 1, 2, 4, and 5, the mean contraction strength of the right (ischaemia-reperfusion injury) biopsies was significantly less than that of the left (control) biopsies. In group 3 (taurine distal to the tourniquet) the difference in strength between right and left was an order of magnitude less than in the other groups, and was not statistically significant. Conclusion: These data suggest that taurine during ischaemia confers some protection against ischaemia-reperfusion injury mediated functional impairment in rat skeletal muscle

Introduction: Limb reperfusion in patients following pneumatic tourniquet-controlled surgery is associated with nitric oxide (NO) generation. Meanwhile, NO mediates vascular endothelial growth factor (VEGF)-cytoprotection in myocardial ischaemia-reperfusion injury. In addition, VEGF is contributory in attenuating skeletal muscle ischaemia-reperfusion injury (SMRI). Whether this effect of VEGF is NO-mediated in SMRI is unknown. We investigate whether systemic nitric oxide production in tourniquet-induced SMRI is dependent on VEGF release. Methods: Anaesthetised male C57BL/6 mice were randomised (n=10 per group) into two groups: time controls (no tourniquet) and test animals with bilateral hindlimb tourniquets (SMRI; 2 hours of ischaemia, 2 hours of reperfusion). Blood samples were collected in test animals prior to ischaemia and after 2 hours of reperfusion. In controls, blood samples were collected at the same corresponding time points. Serum VEGF, nitric oxide metabolites (nitrite and nitrate) and the proinflammatory cytokine tumour necrosis fractor (TNF)-α (an indicator of systemic inflammation) were determined. At the end of reperfusion, the lungs and muscle (right gastrocnemius) were harvested and tissue injury determined by measuring myeloperoxidase (MPO) activity, a marker of neutrophil infiltration. Data are presented as mean ± SEM and statistical comparison was performed using one-way analysis of variance (ANOVA) with significance attributed to P,0.05. Results: In comparison to control animals, both the muscle (4.9±0.3 versus 4±0.03 units/g of wet tissue; P=0.02) and lung (16.7±1.9 versus 10.4±0.5; P=0.005) MPO activity at the end of reperfusion was significantly greater in test animals. Conclusions: Our data demonstrates that SMRI results in local and systemic proinflammatory responses. In contrast to myocardial ischaemia-reperfusion injury, nitric oxide production in tourniquet-induced SMRI is VEGF-independent. Alternative mechanisms for nitric oxide production in tourniquet-controlled limb surgery requires further evaluation

To determine whether systemic nitric oxide production in tourniquet-induced skeletal muscle ischaemia-reper-fusion injury (SMRI) is dependent on release of vascular endothelial growth factor (VEGF), a modulator of nitric oxide cytoprotection in myocardial ischaemia-reperfusion injury. Mice were randomised (n=10 per group) into: time controls (no tourniquet) and test animals (bilateral hindlimb tourniquet ischaemia). Blood samples were collected in test animals prior to ischaemia and after reper-fusion. In controls, blood samples were collected at the same corresponding time points. Serum VEGF, nitric oxide metabolites (nitrite and nitrate) and the proinflammatory cytokine tumour necrosis factor (TNF)-α (an indicator of systemic inflammation) were determined. At the end of reperfusion, the lungs and muscle (right gastrocnemius) were harvested and tissue injury determined by measuring myeloperoxidase (MPO) activity, a marker of neutrophil infiltration. Data are presented as mean ± SEM and statistical comparison was performed using one-way analysis of variance (ANOVA) with significance attributed to P < 0.05. In comparison to control animals, muscle (4.9±0.3 versus 4±0.03 units/g of wet tissue; P=0.02) and lung (16.7±1.9 versus 10.4±0.5; P=0.005) MPO activity at the end of repercussion was significantly greater in test animals. The table shows the results with respect to serum cytokine levels and nitricxide metabolites. These data demonstrate that SMRI results in local and systemic proinflammatory responses. In contrast to myocardial ischaemia-reperfusion injury, nitric oxide production in tourniquet-induced SMRI is VEGF-independent. Alternative mechanisms for nitric oxide production in tourniquet-controlled extremity surgery requires further evaluation

Introduction. Ischaemic preconditioning (IPC) is a phenomenon whereby a tissue is more tolerant to an insult if it is first subjected to short bursts of sublethal ischaemia and reperfusion. The potential of this powerful mechanism has been realised in many branches of medicine where there is an abundance of ongoing research. However, there has been a notable lack of development of the concept in Orthopaedic surgery. The routine use of tourniquet-controlled limb surgery and traumatic soft tissue damage are just two examples of where IPC could be utilised to beneficial effect in Orthopaedic surgery. Methods. We conducted a randomized controlled clinical trial looking at the role of a delayed remote IPC stimulus on a cohort of patients undergoing a total knee arthroplasty (TKA). We measured the effect of IPC by analysing gene expression in skeletal muscle samples from these patients. Specifically we looked at the expression of Heat shock protein-90 (HSP-90), Catalase and Cyclo-oxygenase-2 (COX-2) at the start of surgery and at one hour into surgery. Gene analysis was performed using real time polymerase chain reaction amplification. As a second arm to the project we developed an in-vitro model of IPC using a human skeletal muscle cell line. A model was developed, tested and subsequently used to produce a simulated IPC stimulus prior to a simulated ischaemia-reperfusion (IR) injury. The effect of this on cell viability was investigated using crystal violet staining. Results. In the clinical arm of the study 4 patients were randomized to a control group and 4 randomized to IPC. Operative and post-operative periods were without any adverse incident. For each gene in question there was a different pattern in expression. COX-2 showed an initial up-regulation of 1.43 (p=0.83) at the start of surgery and a subsequent down-regulation of 0.07 (p=0.01) at one hour into surgery. Catalase expression was lower than control at the start of surgery (0.62, p= 0.46) and at one hour into surgery (0.5, p=0.1). HSP-90 expression was initially lower than control at the start of surgery (0.59, p= 0.07) then up-regulated at one hour into surgery (1.13, p=0.62). In the in-vitro section of the study we found that 15 hours of simulated ischaemia was required for a cell death of approximately 50 % (p=0.00001). The introduction of a simulated IPC stimulus increased cell death at a 1 hour reperfusion time-point (IPC group had 18% more cell death than IR group, p=0.003) and at a 24 hour reperfusion time-point (IPC group had 19% more cell death than IR group, p= 0.00001). At a 72 hours reperfusion time-point the IPC group had a 30% greater survival than the IR group (p=0.000006). Conclusion. Our clinical study was subject to small sample size. Despite this it suggests a particular importance of COX-2 in the IPC mechanism. The in-vitro model we developed is an essential resource for further studies into IPC in Orthopaedic Surgery. Preliminary results from this model point towards the ‘second window of protection’ of IPC as a stronger phenomenon than immediate preconditioning