Inhibition of neutrophil adhesion does not prevent ischemic spinal cord injury

Depletion of Ly6G/Gr-1 leukocytes after spinal cord injury in mice alters wound healing and worsens neurological outcome

Spinal cord injury (SCI) induces a robust inflammatory response and the extravasation of leukocytes into the injured tissue. To further knowledge of the functions of neuroinflammation in SCI in mice, we depleted the early arriving neutrophils using an anti-Ly6G/Gr-1 antibody. Complete blood counts revealed that neutrophils increased approximately 3-fold over uninjured controls and peaked at 6-12 h after injury, and that anti-Ly6G/Gr-1 treatment reduced circulating neutrophils by >90% at these time points. Intravital and spinning disk confocal microscopy of the exposed posterior vein and postcapillary venules showed a significant reduction in rolling and adhering neutrophils in vivo after anti-Ly6G/Gr-1 treatment; this was accompanied by a parallel reduction in neutrophil numbers within the injured spinal cord at 24 and 48 h as determined by flow cytometry. The evolution of astrocyte reactivity, a wound healing response, was reduced in anti-Ly6G/Gr-1-treated mice, which also had less spared white matter and axonal preservation compared with isotype controls. These histological outcomes may be caused by alterations of growth factors and chemokines important in promoting wound healing. Importantly, anti-Ly6G/Gr-1 treatment worsened behavioral outcome as determined using the Basso Mouse Scale and subscores. Although the spectrum of cells affected by anti-Ly6G/Gr-1 antibody treatment cannot be fully ascertained at this point, the correspondence of neutrophil depletion and worsened recovery suggests that neutrophils promote recovery after SCI through wound healing and protective events that limit lesion propagation.

Dynamics of the inflammatory response after murine spinal cord injury revealed by flow cytometry

Spinal cord injury (SCI) triggers a robust inflammatory response that contributes in part to the secondary degeneration of spared tissue. Here, we use flow cytometry to quantify the inflammatory response after SCI. Besides its objective evaluation, flow cytometry allows for levels of particular markers to be documented that further aid in the identification of cellular subsets. Analyses of blood from SCI mice for CD45 (common leukocyte antigen), CD11b (complement receptor-3), Gr-1 (neutrophil/monocyte marker), and CD3 (T-cell marker) revealed a marked increase in circulating neutrophils (CD45(high):Gr-1(high)) at 12 hr compared with controls. Monocyte density in blood increased at 24 hr, and in contrast, lymphocyte numbers were significantly decreased. Mirroring the early increase in neutrophils within the blood, flow analysis of the spinal cord lesion site revealed a significant (P < 0.01) and maintained increase in blood-derived leukocytes (CD45(high):CD11b(high)) from 12 to 96 hr compared with sham-injured and naive controls. Importantly, this technique clearly distinguishes blood-derived neutrophils (CD45:Gr-1(high):F4/80(negative)) and monocyte/macrophages (CD45(high)) from resident microglia (CD45(low)) and revealed that the majority of the blood-derived infiltrate were neutrophils. Our results highlight an assumed, but previously uncharacterized, marked and transient increase in leukocyte populations in blood early after SCI followed by the orchestrated invasion of neutrophils and monocytes into the injured cord. In contrast to mobilization of neutrophils, SCI induces lymphopenia that may contribute negatively to the overall outcome after spinal cord trauma.

Tonicity of resuscitative fluids influences outcome after spinal cord injury

OBJECTIVE

This investigation was designed to test the hypothesis that the tonicity of resuscitative fluids administered after spinal cord injury influences the magnitude of secondary injury and, therefore, outcome.

METHODS

Rat spinal cords were compressed with 50 g of weight for 5 minutes to produce injury. After spinal cord injury, the animals were randomized into three experimental groups. Group 1 (n = 10) received no fluid resuscitation after spinal cord injury. Group 2 (n = 6) received 5 ml/kg of intravenously administered Ringer's lactate 1 minute after the removal of compression. Group 3 (n = 7) was treated with 5 ml/kg of intravenously administered 7.5% hypertonic saline 1 minute after the removal of compression. Neurological outcome was assessed daily for 10 days using the Basso, Beattie, and Bresnahan locomotor rating scale. Histological evaluations of the spinal cord were obtained on Day 10.

RESULTS

The average number of recovery days before the rats were able to spontaneously void their bladders was significantly less (P < 0.05) in the hypertonic saline-treated group. Spontaneous hindlimb movement also occurred sooner in the hypertonic saline-treated animals. The average neurological score was significantly higher (P < 0.05) in the hypertonic saline-treated group during each of the 10 days of recovery. Histological evaluation supported the finding of attenuation of injury in the hypertonic saline-treated animals.

CONCLUSION

The results of this investigation with a chronic model of spinal cord injury support the contention that hypertonic saline treatment may provide protection to the spinal cord after mechanical injury.

Pharmacologic neuroprotection in experimental spinal cord ischemia: a systematic review

Various surgical procedures may cause temporary interruption of spinal cord blood supply and may result in irreversible ischemic injury and neurological deficits. The cascade of events that leads to neuronal death following ischemia may be amenable to pharmacological manipulations that aim to increase the tolerable duration of ischemia. Many agents have been evaluated in experimental spinal cord ischemia (SCI). In order to investigate whether an agent is available that justifies clinical evaluation, the literature on pharmacological neuroprotection in experimental SCI was systematically reviewed to assess the neuroprotective efficacy of the various agents. In addition, the strength of the evidence for neuroprotection was investigated by analyzing the methodology. The authors used a systematic review to conduct this evaluation. The included studies were analyzed for neuroprotection and methodology. In order to be able to compare the various agents for neuroprotective efficacy, relative risks and confidence intervals were calculated from the data in the results sections. A total of 103 studies were included. Seventy-nine different agents were tested. Only 14 of the agents tested did not afford protection at all. A large variation was observed in the experimental models to produce SCI. This variation limited comparison of the individual agents. In 48 studies involving 31 single agents, the relative risks and confidence intervals could be calculated. An analysis of the methodology revealed poor temperature management and lack of statistical power in the majority of the 103 studies. The results suggest that numerous agents may protect the spinal cord from transient ischemia. However, poor temperature management and lack of statistical power severely weakened the evidence. Consequently, clinical evaluation of pharmacological neuroprotection in surgical procedures that carry a risk of ischemic spinal cord damage is not justified on the basis of this study.

Retrograde perfusion with a sodium channel antagonist provides ischemic spinal cord protection

BACKGROUND

Neuronal voltage-dependent sodium channel antagonists have been shown to provide neuroprotection in focal and global cerebral ischemic models. We hypothesized that retrograde spinal cord venous perfusion with phenytoin, a neuronal voltage-dependent sodium channel antagonist, would provide protection during prolonged spinal cord ischemia.

METHODS

In a rabbit model, spinal cord ischemia was induced for 45 minutes. Six groups of animals were studied. Controls (group I, n = 8) received no intervention during aortic cross-clamping. Group II (n = 8) received systemic phenytoin (100 mg). Group III (n = 4) received systemic phenytoin (200 mg). Group IV (n = 8) received retrograde infusion of room temperature saline (22 degrees C) only. Group V (n = 8) and group VI (n = 9) received retrograde infusion of 50 mg and 100 mg of phenytoin, respectively, (infusion rate: 0.8 mL x kg(-1) x min(-1) during the ischemic period). Mean arterial blood pressure was monitored continuously. Animals were allowed to recover for 24 hours before assessment of neurologic function using the Tarlov scale.

RESULTS

Tarlov scores (0 = complete paraplegia, 1 = slight lower limb movement, 2 = sits with assistance, 3 = sits alone, 4 = weak hop, 5 = normal hop) were as follows (mean +/- SEM): group I, 0.50 +/- 0.50; group II, 0.25 +/- 0.46; group IV, 1.63 +/- 0.56; group V, 4.13 +/- 0.23; and group VI, 4.22 +/- 0.22 (p < 0.0001 V, VI versus I, II, IV by analysis of variance). No differences in mean arterial blood pressure were observed. All animals in group III became profoundly hypotensive and died before the conclusion of the 45-minute ischemic time.

CONCLUSIONS

Retrograde venous perfusion of the spinal cord with phenytoin, a voltage-sensitive sodium channel blocker, is safe and provides significant protection during prolonged spinal cord ischemia.

Induction of glial cell line-derived neurotrophic factor and c-ret porto-oncogene-like immunoreactivity in rabbit spinal cord after transient ischemia

The mechanism of spinal cord injury has been thought to be related with tissue ischemia, and spinal motor neuron cells are suggested to be vulnerable to ischemia. To evaluate the mechanism of such vulnerability of motor neurons, we attempted to make a reproducible model of spinal cord ischemia. Using this model, the inductions of glial cell line-derived neurotrophic factor (GDNF) and the c-ret porto-oncogene (RET) receptor tyrosine kinase were investigated with immunohistochemical analyses for up to 7 days of the reperfusion following 15 min of ischemia in rabbit spinal cord. Spinal cord sections from animals sacrificed at 8 h, 1, 2, and 7 days following the 15 min of ischemia were immunohistochemically evaluated using monoclonal antibodies for GDNF and RET. Following the 15 min of ischemia, the majority of the motor neurons showed selective cell death at 7 days of reperfusion. Immunoreactivity of GDNF and RET were induced at 8 h of reperfusion selectively in motor neuron cells. No glial cells were stained in the spinal cord sections. The induction of GDNF and RET proteins at the early stage of reperfusion may be related to the transient functional recovery of neurons after ischemia.

Spinal cord protection during aortic cross-clamping using retrograde venous perfusion

BACKGROUND

Paraplegia remains a devastating complication following thoracic aortic operation. We hypothesized that retrograde perfusion of the spinal cord with a hypothermic, adenosine-enhanced solution would provide protection during periods of ischemia due to temporary aortic occlusion.

METHODS

In a rabbit model, a 45-minute period of spinal cord ischemia was produced by clamping the abdominal aorta and vena cava just below the left renal vessels and at their bifurcations. Four groups (n = 8/group) were studied: control, warm saline, cold saline, and cold saline with adenosine infusion. In the experimental groups, saline or saline plus adenosine was infused into the isolated cavae throughout the ischemic period. Clamps were removed and the animals to recovered for 24 hours before blinded neurological evaluation.

RESULTS

Tarlov scores (0 = paraplegia, 1 = slight movement, 2 = sits with assistance, 3 = sits alone, 4 = weak hop, 5 = normal hop) were (mean +/- standard error of the mean): control, 0.50 +/- 0.50; warm saline, 1.63 +/- 0.56; cold saline, 3.38 +/- 0.26; and cold saline plus adenosine, 4.25 +/- 0.16 (analysis of variance for all four groups, p < 0.00001). Post-hoc contrast analysis showed that cold saline plus adenosine was superior to the other three groups (p < 0.0001).

CONCLUSION

Retrograde venous perfusion of the spinal cord with hypothermic saline and adenosine provides functional protection against surgical ischemia and reperfusion.

Prevention of spinal cord ischaemic complications after thoracoabdominal aortic surgery

Since the publication of prior reviews on this topic, substantial clinical experience with a variety of operative strategies to prevent ischaemic cord complications has been reported. The available data on angiographic localisation of critical intercostal vessels, and, in particular, the evoked potential response to cross-clamping in patients indicates that risk of paraplegia varies considerably even among patients with equivalent TAA extent. Factors such as individual development of the ASA, patent critical intercostals, and the particulars of collateral circulation when intercostal aortic ostia are already occluded likely account for this variability. Information available from SSEP monitoring relative to the dynamic course of cord ischaemia with cross-clamping, and the parallel, if not, frustrating experience with angiographic localisation and intercostal vessel reconstruction indicates that a narrow temporal threshold of cord ischaemia with clamping is present in many patients. This reinforces the importance of both expeditious clamp intervals, critical intercostal re-anastomoses, and the desirability of neuroprotective manoeuvres during cross-clamp induced cord ischemia. As suggested in compelling experimental work our contemporary clinical experience, and predicted by prior reviewers, regional cord hypothermia provides significant promise for limiting or eliminating, in particular, immediate perioperative deficits. Avoidance of postoperative hypotension, spinal cord oedema, and preservation of critical intercostal vessels are additional strategies necessary to impact the development of delayed deficits favourably.

Inductions of Cu/Zn superoxide dismutase- and nitric oxide synthase-like immunoreactivities in rabbit spinal cord after transient ischemia

The distributions and inductions of Cu/Zn superoxide dismutase (SOD), neuronal and endothelial nitric oxide (NO) synthase (nNOS and eNOS), and nitrotyrosine (NT) were immunohistochemically examined in rabbit spinal cords after 5 and 15 min of transient ischemia. The neurons in the anterior horns (AH) were selectively lost 7 days after 15-min ischemia as compared with those of sham-operated controls. In the normal spinal cords, a number of neurons in the AHs were positive for the nNOS, and only slightly positive for the Cu/Zn SOD and the eNOS. Immunoreactivities for the proteins were induced at 8-24 h both after 5- and 15-min ischemia. In contrast, NT-like immunoreactivity was negative both in the normal and postischemic spinal cords. These results suggest that Cu/Zn SOD- and nNOS-, and eNOS-like immunoreactivities are induced, but that, even though an interaction of Cu/Zn SOD with NO could be present, NT was not detected in the motor neurons in the rabbit spinal cords after transient ischemia. Other factors could be required for NT formation found in degenerative motor neuron death in humans.