Hypothermic retrograde venous perfusion with adenosine cools the spinal cord and reduces the risk of paraplegia after thoracic aortic clamping

Role of induced hypothermia in thoracoabdominal aortic aneurysm surgery

For more than 50 years, hypothermia has been used in aortic surgery as a tool for neuroprotection. Hypothermia has been introduced into thoracoabdominal aortic aneurysm (TAAA) surgery by many cardiovascular centers to protect the body's organs, including the spinal cord. Numerous publications have shown that hypothermia can prevent immediate and delayed motor dysfunction after aortic cross-clamping. Here, we reviewed the historical application of hypothermia in aortic surgery, role of hypothermia in preclinical studies, cellular and molecular mechanisms by which hypothermia confers neuroprotection, and the role of systemic and regional hypothermia in clinical protocols to reduce and/or eliminate the devastating consequences of ischemic spinal cord injury after TAAA repair.

Maximizing neuroprotection: where do we stand?

Brain and spinal cord traumas include blunt and penetrating trauma, disease, and required surgery. Such traumas trigger events such as inflammation, infiltration of inflammatory and other cells, oxidative stress, acidification, excitotoxicity, ischemia, and the loss of calcium homeostasis, all of which cause neurotoxicity and neuron death. To prevent trauma-induced neurological deficits and death, each of the many neurotoxic events that occur in parallel or sequentially must be minimized or prevented. Although neuroprotective techniques have been developed that block single neurotoxic events, most provide only limited neuroprotection and are only applied singly. However, because many neurotoxicity triggers arise from common events, an approach for invoking more effective neuroprotection is to apply multiple neuroprotective methods simultaneously before the many neurotoxic triggers and cascades are initiated and become irreversible. This paper first discusses some triggers of neurotoxicity and neuroprotective mechanisms that block them, including hypothermia, alkalinization, and the administration of adenosine. It then examines how the simultaneous application of these techniques provides significantly greater neuroprotection than is provided by any technique alone. The paper also stresses the importance of determining whether the neuroprotection provided by these techniques can be further enhanced by combining them with additional techniques, such as the systemic administration of glucocorticoids. Finally, the paper stresses the absolute critical importance of applying these techniques within the "golden hour" following trauma, before the many neurotoxic events and cascades are manifest and before the neurotoxic cascades become irreversible.

Rapid ischemic preconditioning with a short reperfusion time prevents delayed paraplegia in a rabbit model

BACKGROUND

Surgery for thoracic and thoracoabdominal aortic aneurysms can be complicated by a significant incidence of neurogenic deficits due to spinal cord ischemia. In this study, we investigated whether ischemic preconditioning (IPC) improves neurologic outcome in a rabbit model.

METHODS

Forty rabbits underwent infrarenal aortic occlusion. The IPC group (n = 20) had 10 minutes of aortic occlusion to induce spinal cord ischemia, 40 minutes of reperfusion, and 30 minutes of ischemia, whereas the control group (n = 20) had only 30 minutes of ischemia. Tarlov scoring (0, paraplegia; 4, normal) was used to evaluate neurologic functions 7 days later, and spinal cord segments (L4-L6) were stained with hematoxylin and eosin for histologic evaluation.

RESULTS

Complete paraplegia (grade 0) occurred in 15 (75%) of the 20 control animals, whereas in the IPC group, 13 (65%) of 20 animals were completely normal (grade 4) (P < .05).

CONCLUSION

IPC is beneficial for protecting against neurologic damage after transient aortic occlusion in a rabbit model; however, the protective mechanisms are not clear.

Combinatorial techniques for enhancing neuroprotection: hypothermia and alkalinization

Brain and spinal cord (CNS) trauma typically kill a number of neurons, but even more neurons are killed by secondary causes triggered by the initial trauma. Thus, a minor insult may rapidly cause the death of a vastly larger number of neurons and complete paralysis. The best mechanism for reducing the extent of neurological deficits is to minimize the number of neurons killed by post-trauma sequelae. Neuroprotection techniques take many diverse forms with a breadth too great for a short review. Therefore, this review focuses on the neuroprotection provided by hypothermia and a number of other neuroprotective techniques, when administered singly or in combination, because it is generally found that combinations of applications lead to significantly better neuroprotection than is achieved by any one alone. The combinatorial approach to neuroprotection holds great promise for enhancing the degree of neuroprotection following trauma, leading to maximum maintenance of neurological function.

Neuroprotection by hypothermia plus alkalinization of dorsal root ganglia neurons through ischemia

Brain and spinal cord (CNS) trauma typically directly kill some neurons leading to permanent neurological deficits. However, they also lead to a number of triggers which in turn frequently kill a vastly larger number of neurons than were killed by the initial insult. The best mechanism for reducing the extent of neurological deficits is to minimize the number of neurons that die immediately due to the trauma, and post-trauma sequelae. Neuroprotection techniques have taken many diverse forms with a breadth too great for a short review. Therefore, this review is focused on the roles of only a small number of neuroprotective agents, with its primary focus being on neuroprotection provided by hypothermia, alone and when combined with the other methods. Included are also recent results involving a novel neuroprotective technique, tested on adult human dorsal root ganglion neurons, comparing the influences of hypothermia and alkalinization singly, providing fourfold and eightfold increases in neuroprotection, respectively, but when combined providing a 26-fold increase in neuroprotection. This combinatorial approach to neuroprotection holds great promise for enhancing the degree of neuroprotection clinically following CNS trauma, leading to the preservation of maximal neurological functions.

Spinal cord retrograde perfusion: review of the literature and experimental observations

BACKGROUND

Spinal cord damage represents a devastating complication of thoracic and thoracoabdominal aortic surgery. Retrograde perfusion as an alternative route to protect the spinal cord has recently been investigated with controversial results. We reviewed the literature and analyzed additional experimental observations.

METHODS

Ten juvenile pigs were divided into control and study groups (A and B, respectively). Through a lateral thoracotomy the distal aortic arch was cannulated and connected to a cardiotomy reservoir. All animals underwent 40-minute single cross-clamping of the proximal descending aorta while keeping proximal systolic arterial pressure above 100 mmHg. In group B, normothermic arterial blood was delivered retrogradely through the azygos vein, maintaining perfusion pressure within 25-30 mmHg. Animals were allowed to recover to perform a primary neurologic evaluation.

RESULTS

Flaccid paraplegia was uniformly observed in group A. In group B, all animals showed mild-to-moderate voluntary hind limb movements on awakening (p = 0.007). Controls also showed urine incontinence short after cross-clamping, and this was not observed in group B (p = 0.008). A different veno-arterial oxygen step-down was observed in blood collected from the excluded aorta in the two groups (p < 0.001).

CONCLUSIONS

Preliminary results indicate that controlled retrograde normothermic perfusion alone through the azygos system provides some degree of protection from spinal cord ischemia. Bladder dysfunction may represent a simple test to detect massive cord damage intraoperatively. Retrograde spinal cord perfusion warrants further investigation.

Functional and cytoarchitectural spinal cord protection by ATL-146e after ischemia/reperfusion is mediated by adenosine receptor agonism

BACKGROUND

ATL-146e protects the spinal cord from ischemia/reperfusion injury, presumably via adenosine A(2A) receptor activation, but this relationship remains unproven. We hypothesized that spinal cord functional and cytoarchitectural preservation from ATL-146e would be lost with simultaneous administration of the specific adenosine A(2A) antagonist ZM241385 (ZM), thus proving that adenosine A(2A) receptor activation is responsible for the protective effects of this compound.

METHODS

New Zealand White rabbits underwent 45 minutes of infrarenal aortic cross-clamping. Groups (n = 10) included sham, ischemia, ischemia plus ATL-146e (ATL-146E), ischemia plus ZM, or ischemia with both compounds (agonist-antagonist). Tarlov scores were recorded every 12 hours. After 48 hours, the spinal cord was fixed for histology and microtubule-associated protein 2 immunohistochemistry.

RESULTS

Tarlov scores at 48 hours were significantly better in the sham and ATL-146E groups (5.0 and 3.9, respectively) compared with the other three groups (all < or =1.3; P < .001). On hematoxylin and eosin, neuronal viability was higher in the sham, ATL-146E, and agonist-antagonist groups compared with the control and ZM groups (P < .05). Microtubule-associated protein 2 expression was preserved in the sham and ATL-146E groups but was lost in the ATL + ZM, ZM241385, and control groups.

CONCLUSIONS

ATL-146e preserves the spinal cord in terms of both cytoarchitecture and function after reperfusion of the ischemic spinal cord, but this preservation is not completely blocked by competitive adenosine A(2A) receptor antagonism. Although ATL-146e does seem to partially function through activation of the adenosine A(2A) receptor, the neuroprotective mechanism may not be limited to this particular receptor.

Comparison of systemic and retrograde delivery of adenosine A2A agonist for attenuation of spinal cord injury after thoracic aortic cross-clamping

BACKGROUND

Paraplegia remains a devastating complication of thoracic aortic surgery, which has been attenuated by retrograde adenosine and systemic adenosine A2A receptor activation. We hypothesized that despite retrograde spinal perfusion of an adenosine A2A agonist (ATL-146e), systemic therapy produces superior spinal cord protection with reduced inflammation.

METHODS

Forty pigs underwent 30-minute thoracic aortic cross-clamping. Pigs received: no therapy (control); retrograde saline (retrograde control); retrograde ATL-146e; systemic ATL-146e; systemic ATL-146e with retrograde saline; or systemic and retrograde ATL-146e. Retrograde therapies were given during ischemia. Systemic ATL-146e (0.06 microg.kg(-1).min(-1)) was given intravenously for 3 hours at reperfusion. At 24 hours, motor function was assessed using the Tarlov scale. Tissue was analyzed for neuronal viability, microtubule-associated protein-2 expression, and neutrophil sequestration (myeloperoxidase activity).

RESULTS

Four pigs received retrograde barium showing both radiographic and histologic spinal cord perfusion. Tarlov scores at 24 hours were significantly improved versus both control groups in all ATL groups except the combined ATL-146e group (all p < 0.05). Neuronal viability by hematoxylin and eosin stain was significantly preserved in systemic ATL groups compared with both control groups (all p < 0.05). Microtubule-associated protein-2 expression was significantly preserved compared with both control groups in all systemic ATL groups. Systemic ATL significantly lowered myeloperoxidase activity versus both control groups (p < 0.01).

CONCLUSIONS

Both retrograde and systemic ATL-146e therapies attenuate ischemic spinal cord injury, but combining the two routes was less effective. Given comparable results between the two routes and the simplicity of systemic delivery, peripheral venous ATL-146e at reperfusion should be preferred for spinal cord protection in thoracic aortic surgery.

Onlay Patch for Complete Intercostal Artery Preservation During Thoracic and Thoracoabdominal Aortic Aneurysm Repair

BACKGROUND

Replacement of the thoracic aorta is associated with a potential for interruption of the blood supply to the spinal cord leading to paralysis. Techniques have been proposed to ameliorate this risk, including reimplantation of the intercostal arteries. We present a technique to simplify this approach.

METHODS

In patients with extensive aneurysmal disease, a standard approach to the thoracic aorta via a left thoracotomy is performed. The patient is placed on full cardiopulmonary bypass with moderate hypothermia. The proximal anastomosis is performed unclamped with circulatory arrest. After completing the proximal and distal anastomosis separately, an onlay patch of Dacron is created and placed along the entire back wall of the aorta to cover all of the intercostal arteries. A side-to-side anastomosis between the patch and the distal graft is then performed and subsequently the anastomosis tested by retrograde flow.

RESULTS

The technique allows direct inspection of all suture lines, tested to an adequate pressure, so that postoperative bleeding is minimal.

CONCLUSION

Techniques to lessen the risk of paraplegia associated with aortic surgery include reimplantation of the intercostal arteries. This technique allows each suture line to be tested and easily visually inspected prior to closure of the chest.

Superiority of early relative to late ischemic preconditioning in spinal cord protection after descending thoracic aortic occlusion

OBJECTIVE

We previously showed that ischemic preconditioning significantly reduced spinal cord injury caused by 35-minute aortic occlusion. In this study we investigated the effect of ischemic preconditioning on spinal cord injury after 45-minute aortic occlusion.

METHODS

Thirty-two pigs were divided as follows: group 1 (n = 6) underwent sham operation, group 2 (n = 6) underwent 20 minutes of aortic occlusion, group 3 (n = 6) underwent 45 minutes of occlusion, group 4 (n = 6) underwent 20 minutes of occlusion and 48 hours later underwent an additional 45 minutes, and group 5 (n = 8) underwent 20 minutes of occlusion and 80 minutes later underwent an additional 45 minutes. Aortic occlusion was accomplished with two balloon occlusion catheters placed fluoroscopically after the origin of the left subclavian artery and at the aortic bifurcation. Neurologic evaluation was by Tarlov score. The lower thoracic and lumbar spinal cords were harvested at 120 hours and examined histologically with hematoxylin-eosin staining. The number of neurons was counted, and the inflammation was scored (0-4). Statistical analysis was by Kruskal-Wallis and 1-way analysis of variance tests.

RESULTS

Group 5 (early ischemic preconditioning) had better Tarlov scores than group 3 ( P < .001) and group 4 (late ischemic preconditioning, P < .001). The histologic changes were proportional to the Tarlov scores, with the least histologic damage in the animals of group 5 relative to group 3 (number of neurons P < .001, inflammation P = .004) and group 4 (number of neurons P < .001, inflammation P = .006).

CONCLUSION

Early ischemic preconditioning is superior to late ischemic preconditioning in reducing spinal cord injury caused by the extreme ischemia of 45 minutes of descending thoracic aortic occlusion.

Neuroprotection of adult rat dorsal root ganglion neurons by combined hypothermia and alkalinization against prolonged ischemia

Ischemia and ischemia-induced secondary events, such as acidosis and excessive activation of receptors by amino acids, trigger neuron death. The isolation and dissociation of dorsal root ganglion (DRG) involves time during which the neurons are ischemic due to being densely packed within the intact DRG and surrounded by a connective tissue coat. Thus, the longer the time between killing the host animal and when the DRG are dissociated, the longer the neurons are ischemic and exposed to ischemia-induced secondary causes of neuron death. It is well established that hypothermia and alkalinization each separately protect neurons from ischemia and ischemia-induced secondary causes of neuron death, but there are no data on the neuroprotection provided by simultaneous hypothermia and alkalinization. The present experiments were designed to determine the combination of hypothermic and alkaline conditions that yield the largest number of viable neurons dissociated from intact DRG maintained ischemic for up to 4 h. Hypothermia (20 degrees C>15 degrees C>37 degrees C) and alkalinization (pH 9.3>pH 8.3>pH 7.4) increased the yield of viable neurons compared with the yield from DRG maintained under physiological conditions. Hypothermia and alkalinization combined (20 degrees C/pH 9.3) provided the greatest neuroprotection with a yield of viable neurons after 1 h of ischemia 2.5-fold larger than that from DRG maintained under physiological conditions (37 degrees C/pH 7.6). Over 4 h of ischemia, the yield of viable neurons from DRG maintained under both hypothermic/alkaline and physiological conditions decreased in a linear manner, but those at 20 degrees C/pH 9.3 had a 4.5-fold greater yield of viable neurons than those at 37 degrees C/pH 7.6. Thus, combined hypothermia and alkalinization provide significantly greater protection against ischemia and ischemia-induced secondary causes of neuron death than either alone.

The evolution of ischemic spinal cord injury in function, cytoarchitecture, and inflammation and the effects of adenosine A2A receptor activation

OBJECTIVE

Spinal cord ischemia/reperfusion injury involves multiple factors that may be modulated by adenosine A 2A receptor activation. This study defines injury progression in terms of function, cytoarchitecture, and inflammation and assesses whether adenosine A 2A receptor activation by ATL-146e limits injury progression.

METHODS

Mature swine were divided into 3 groups: sham thoracotomy, IR (30 minutes of ischemia followed by reperfusion), and ATL (ischemia/reperfusion with ATL-146e administration for the first 3 hours of reperfusion). Subgroups were killed at 0, 3, 6, 12, 24, and 48 hours after reperfusion. Function was followed up with Tarlov scores. Spinal cord tissue was evaluated for neuronal viability, microtubule-associated protein-2 immunohistochemistry, and neutrophil sequestration (myeloperoxidase assay). Spinal cord tissue, cerebrospinal fluid, and serum were evaluated for tumor necrosis factor-alpha by enzyme-linked immunosorbent assay.

RESULTS

Function was significantly impaired at 24, 36, and 48 hours in the IR group compared with the sham and ATL groups ( P < .05). Neuronal viability and microtubule-associated protein-2 staining were significantly preserved in the sham and ATL groups compared with the IR group at 24 and 48 hours ( P < .05). Spinal cord myeloperoxidase levels were significantly higher in the IR group than in the sham and ATL groups at 24 and 48 hours. Although negligible in serum and cerebrospinal fluid, tumor necrosis factor-alpha levels in the spinal cord peaked significantly higher in the IR group compared with the sham and ATL groups at 6 and 24 hours ( P < .05).

CONCLUSIONS

Spinal cord ischemia/reperfusion induced changes in neutrophil sequestration, microtubule-associated protein-2 expression, and neuronal viability within 24 hours of reperfusion. Spinal cord tumor necrosis factor-alpha increased significantly by 6 to 12 hours after reperfusion. Adenosine A 2A receptor activation attenuates spinal cord inflammation, which may be critical for the preservation of neuronal function and cytoarchitecture after ischemia/reperfusion.

Prevention of Postischemic Spinal Cord Injury by Means of Regional Infusion of Adenosine and l-carnitine Dissolved in Normothermic Saline

Spinal cord ischemia still remains an unsolved problem in modern aortic surgery. In this study, we investigated the effectiveness of combined agents such as adenosine and L-carnitine infused to the isolated segment of abdominal aorta in a rabbit model. Twenty-eight rabbits divided into four groups underwent 40 min of isolated infrarenal aortic occlusion. Group I animals received no medication. Group II received an infusion of 100 mg/kg L-carnitine in normothermic saline over the first 10 min of ischemia. Group III received 50 mg adenosine, and group IV received a combination of the two agents in the same fashion. Spinal cord function was evaluated at 24 and 72 hr after operation on the basis of Tarlov scale and similar results were obtained. After a second evaluation, spinal cords were harvested for histological examination. Group I animals were all paraplegics. Spinal cord function was partially intact in two of the group II animals with Tarlov scores of 5 in two and 4 in two whereas one of the rabbits could not hop with a score of 3, and the remaining two could not sit with scores of 1 and 0. The spinal cord function of group III animals was intact with Tarlov scores of 5 in three, 4 in two, and 3 and 1 in remaining ones. In the group IV animals, it was fully intact with Tarlov scores of 5. Histological examination in group I revealed marked enlargement of the vacuoles of glial cells in the white matter of spinal cord. Glial cells were deteriorated in some locations in group II whereas they were mostly protected in the third group. In group IV, histological examination revealed no evidence of spinal cord injury. In conclusion, combined infusion of adenosine and L-carnitine provided better protection against postischemic spinal cord injury than individual infusion of these agents.

Complications of coarctation repair

Surgery's role in the treatment of coarctation has been established, and the benefit to life expectancy and quality of life is undeniable. Three postaortic coarctation repair complications are discussed, with review of existing literature: recurrent or residual aortic coarctation, postrepair aneurysm formation, and spinal cord ischemia. Incidence, potential causative factors, and outcome of surgical or transcatheter treatment for recurrent and residual aortic coarctation are reviewed. A literature review of postrepair aneurysm formation focuses on etiologic factors such as use of patch aortoplasty repair techniques, aortic arch hypoplasia, congenital abnormality of the aortic wall, and persistent hypertension after repair. The spectrum, onset, incidence, and potential risk factors for postcoarctation repair spinal cord ischemia are reviewed. Use of adenosine receptor agonists to achieve a state of ischemic resistance is under investigation to address this potential hazard of coarctation repair. Complications after surgery do occur in certain subsets of patients, but the risk of subsequent intervention is still lower than the hazards associated with the natural course of the defect.

The role of pharmacology in spinal cord protection during thoracic aortic reconstruction

Surgery of the thoracic aorta continues to have a significant risk of neurologic complication. Several strategies to minimize this risk are emerging. Pharmacologic protection from these complications continues to be researched, but at this point few medications are being used clinically. This article reviews the pathophysiology of ischemic spinal cord injury and summarizes the investigational pharmacology that may prevent these serious complications.

Left atrial-inferior vena cava bypass achieves retroperfusion of the porcine spinal cord: morphologic and preliminary physiologic studies

BACKGROUND

Spinal cord injury remains a devastating complication after procedures on the descending thoracic aorta. A new model for retrograde perfusion of the spinal cord during aortic cross-clamping was evaluated for its potential role in preventing spinal cord injury after thoraco-abdominal aortic surgery.

METHODS

Retrograde perfusion of the spinal cord was established in juvenile pigs using partial bypass from the left atrium to the isolated inferior vena cava. Flow was maintained for a 60-min period of aortic occlusion. Morphologic studies of spinal cord blood flow were obtained using injection of a dilute barium-gelatin-chromatin dye solution. Physiologic cooling of the spinal cord was achieved using varying degrees of hypothermic retroperfusion.

RESULTS

Five animals underwent a 30-min period of retroperfusion followed by dye injection. Dye was identified in spinal cord venules and capillaries, most heavily concentrated in the lumbar and lower thoracic cord. Thirteen animals underwent a 60-min period of normothermic (37 degrees C), mild hypothermic (27 degrees C), moderate hypothermic (17 degrees C), or deep hypothermic (7 degrees C) retroperfusion; mean spinal cord temperatures were 35.2, 32.2, 28.0, and 24.4 degrees C, respectively.

CONCLUSIONS

Retrograde perfusion of the porcine spinal cord using a left atrial to inferior vena cava partial bypass circuit can be accomplished and can be used with hypothermic perfusate to produce cooling of the spinal cord. This new technique warrants further investigation into spinal cord protection and potential application for operations on the descending thoracic aorta.

Systemic adenosine A2A agonist ameliorates ischemic reperfusion injury in the rabbit spinal cord

BACKGROUND

The adenosine A2A agonist ATL-146e (4-[3-[6-Amino-9-(5-ethylcarbamoyl-3,4-dihydroxytetrahydro-furan-2-yl)-9H-purin-2-yl]-prop-2-ynyl]-cyclohexanecarboxylic acid methyl ester) has been shown to prevent reperfusion injury in multiple organ systems through inhibition of activated leukocyte-endothelial interaction. We hypothesized that systemic ATL-146e could reduce spinal cord reperfusion injury after aortic clamping.

METHODS

Twenty-six rabbits underwent cross-clamping of the infrarenal aorta for 45 minutes. One group received intravenous ATL-146e for 3 hours during reperfusion. A second cohort received only vehicle and served as controls. Animals were assessed at 24 and 48 hours using the Tarlov (0 to 5) scoring system for hind limb function. To evaluate neuronal attrition, immunostaining of lumbar spinal cord sections was performed using anti-SMI 33 antibody against neurofilament.

RESULTS

Systemic ATL-146e was tolerated without hemodynamic lability. Animals that received ATL-146e had significantly improved neurologic outcomes 24 and 48 hours after spinal cord ischemia (p < 0.001). There was preservation of neuronal architecture in the ventral horn of spinal cord sections from animals receiving ATL-146e compared with control animals.

CONCLUSIONS

Intravenous ATL-146e given during reperfusion is tolerated without hemodynamic lability, and results in substantially improved spinal cord function after ischemia by preservation of ventral horn neurons.

An adenosine A2A agonist, ATL-146e, reduces paralysis and apoptosis during rabbit spinal cord reperfusion

BACKGROUND

We hypothesized that systemic ATL-146e, an adenosine A(2A) agonist, would decrease spinal cord reperfusion inflammatory stress and inhibit apoptosis and that these effects would correlate with improved neurologic functional outcome.

METHODS

Thirty rabbits underwent cross-clamping of the infrarenal aorta for 45 minutes. One group of animals (n = 14) received 0.06 microg/kg per minute of ATL-146e infused intravenously for 3 hours, beginning 15 minutes before reperfusion. A second group of animals (n = 16) underwent spinal cord ischemia with saline vehicle alone and served as ischemic controls. Animals (n = 9, 11) from each group survived for 48 hours and assessed for neurologic impairment with the Tarlov (0-5) scoring system. Four animals from each group were humanely killed at the end of the 3-hour treatment period, and the remainder killed after 48 hours' survival. In all animals, lumbar spinal cord tissue specimens were frozen for subsequent Western blot analysis of heat shock protein 70 (HSP 70), and for the p85 fragment of poly (ADP-ribose) polymerase (PARP). Neuronal viability indices were determined at 48 hours with hematoxylin and eosin staining.

RESULTS

There was improvement in neurologic function in rabbits receiving ATL-146e (P <.001) compared with ischemic controls. At the end of the 3-hour treatment period there was a 46% (P <.05) decrease in HSP 70 expression in the ATL-146e group compared with the control group, but no difference in PARP expression. At 48 hours, there was no difference between control and ATL-146e groups in HSP 70 expression, but there was a 65% (P <.05) reduction in PARP in the spinal cords of animals that had received ATL-146e. There was a significant improvement in neuronal viability indices in animals receiving ATL-146e compared with ischemic controls (P <.05).

CONCLUSIONS

Systemic ATL-146e infusion during reperfusion after spinal cord ischemia results in preservation of hindlimb motor function. There is evidence of decreased spinal cord inflammatory stress immediately after treatment with ATL-146e as indicated by reduced HSP 70 induction. Treatment with ATL-146e is associated with a reduction in neuronal apoptosis as suggested by a substantial decrease in the fragmentation of PARP at 48 hours. These results suggest that inflammation during reperfusion and subsequent apoptosis contribute to paralysis after restoration of blood flow to the ischemic spinal cord.

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.