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: 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.

Background: Low molecular weight heparins (LMWH) are of undoubted efficacy as thromboprophylaxis in orthopaedic surgical practice. However, prolonged dosage inhibits bone nodule formation in vitro and we have previously reported that daily dosing significantly delays fracture healing. To further investigate these phenomena we hypothesised that LMWH’s would reduce osteoblast survival and thus bone formation by inducing programmed cell death (apoptosis).

Methods: Primary human osteoblasts were isolated from femoral heads excised during hip arthoplasty and cultured to passage 3–5. These were examined for VEGF receptor expression using a biotinylated binding assay on flow cytometry. Osteoblasts were grown to confluence and then incubated for 24 hours in control medium or medium treated with enoxaparin (200 – 2X10(−4) IU/mL) or combination of enoxaparin (200 – 2X10 (−4) IU/mL) and VEGF (1ng/ml). Apoptosis was determined by measuring cytosolic histone-associated DNA fragmentation using an enzyme linked immunosorbant assay. Results were confirmed by DNA fragmentation analysis on agarose gel electrophoresis. Cell functional viability was measured by a tetrazolium bioreduction colorimetric assay.

Results: Data is expressed as percentage of control apoptosis or viability, illustrates mean ± s.e.m. and n=4 experiments in each case. ANOVA was employed for statistical analysis; *versus control, #versus enoxaparin treated; p< 0.05 was considered significant.

Conclusions: Therapeutic doses of LMWH attenuate osteo-blast survival by inducing significant apoptosis. This effect is partly abrogated by VEGF, which independently enhances osteoblast viability, thus delaying spontaneous and enoxaparin induced apoptosis. These findings may explain the bone resorptive effects of prolonged LMWH therapy and suggest a potential therapeutic role for VEGF in conditions of delayed bone formation.