Injury severity and cell death mechanisms: effects of concomitant hypovolemic hypotension on spinal cord ischemia–reperfusion in rats

Predicting the Role of Preoperative Intramedullary Lesion Length and Early Decompressive Surgery in ASIA Impairment Scale Grade Improvement Following Subaxial Traumatic Cervical Spinal Cord Injury

BACKGROUND

 Traumatic cervical spinal cord injury (TCSCI) is a disabling condition with uncertain neurologic recovery. Clinical and preclinical studies have suggested early surgical decompression and other measures of neuroprotection improve neurologic outcome. We investigated the role of intramedullary lesion length (IMLL) on preoperative magnetic resonance imaging (MRI) and the effect of early cervical decompressive surgery on ASIA impairment scale (AIS) grade improvement following TCSCI.

METHODS

 In this retrospective study, we investigated 34 TCSCI patients who were admitted over a 12-year period, from January 1, 2008 to January 31, 2020. We studied the patient demographics, mode of injury, IMLL and timing of surgical decompression. The IMLL is defined as the total length of edema and contusion/hemorrhage within the cord. Short tau inversion recovery (STIR) sequences or T2-weighted MR imaging with fat saturation increases the clarity of edema and depicts abnormalities in the spinal cord. All patients included had confirmed adequate spinal cord decompression with cervical fixation and a follow-up of at least 6 months.

RESULTS

 Of the 34 patients, 16 patients were operated on within 24 hours (early surgery group) and 18 patients were operated on more than 24 hours after trauma (delayed surgery group). In the early surgery group, 13 (81.3%) patients had improvement of at least one AIS grade, whereas in the delayed surgery group, AIS grade improvement was seen in only in 8 (44.5%) patients (early vs. late surgery; odds ratio [OR] = 1.828; 95% confidence interval [CI]: 1.036-3.225). In multivariate regression analysis coefficients, the timing of surgery and intramedullary edema length on MRI were the most significant factors in improving the AIS grade following cervical SCI. Timing of surgery as a unique variance predicted AIS grade improvement significantly (p < 0.001). The mean IMLL was 41.47 mm (standard deviation [SD]: 18.35; range: 20-87 mm). IMLL was a predictor of AIS grade improvement on long-term outcome in bivariate analysis (p < 0.001). This study suggests that patients who had IMLL of less than 30 mm had a better chance of grade conversion irrespective of the timing of surgery. Patients with an IMLL of 31 to 60 mm had chances of better grade conversion after early surgery. A longer IMLL predicts lack of improvement (p < 0.05). If the IMLL is greater than 61 mm, the probability of nonconversion of AIS grade is higher, even if the patient is operated on within 24 hours of trauma.

CONCLUSION

 Surgical decompression within 24 hours of trauma and shorter preoperative IMLL are significantly associated with improved neurologic outcome, reflected by better AIS grade improvement at 6 months' follow-up. The IMLL on preoperative MRI can reliably predict outcome after 6 months. The present study suggests that patients have lesser chances of AIS grade improvement when the IMLL is ≥61 mm.

Therapeutic Effects of Risperidone against Spinal Cord Injury in a Rat Model of Asphyxial Cardiac Arrest: A Focus on Body Temperature, Paraplegia, Motor Neuron Damage, and Neuroinflammation

Cardiac arrest (CA) causes severe spinal cord injury and evokes spinal cord disorders including paraplegia. It has been reported that risperidone, an antipsychotic drug, effectively protects neuronal cell death from transient ischemia injury in gerbil brains. However, until now, studies on the effects of risperidone on spinal cord injury after asphyxial CA (ACA) and cardiopulmonary resuscitation (CPR) are not sufficient. Therefore, this study investigated the effect of risperidone on hind limb motor deficits and neuronal damage/death in the lumbar part of the spinal cord following ACA in rats. Mortality, severe motor deficits in the hind limbs, and the damage/death (loss) of motor neurons located in the anterior horn were observed two days after ACA/CPR. These symptoms were significantly alleviated by risperidone (an atypical antipsychotic) treatment after ACA. In vehicle-treated rats, the immunoreactivities of tumor necrosis factor-alpha (TNF-α) and interleukin 1-beta (IL-1β), as pro-inflammatory cytokines, were increased, and the immunoreactivities of IL-4 and IL-13, as anti-inflammatory cytokines, were reduced with time after ACA/CPR. In contrast, in risperidone-treated rats, the immunoreactivity of the pro-inflammatory cytokines was significantly decreased, and the anti-inflammatory cytokines were enhanced compared to vehicle-treated rats. In brief, risperidone treatment after ACA/CPR in rats significantly improved the survival rate and attenuated paralysis, the damage/death (loss) of motor neurons, and inflammation in the lumbar anterior horn. Thus, risperidone might be a therapeutic agent for paraplegia by attenuation of the damage/death (loss) of spinal motor neurons and neuroinflammation after ACA/CPR.

Therapeutic Hypothermia Improves Hind Limb Motor Outcome and Attenuates Oxidative Stress and Neuronal Damage in the Lumbar Spinal Cord Following Cardiac Arrest

Hypothermia enhances outcomes of patients after resuscitation after cardiac arrest (CA). However, the underlying mechanism is not fully understood. In this study, we investigated effects of hypothermic therapy on neuronal damage/death, microglial activation, and changes of endogenous antioxidants in the anterior horn in the lumbar spinal cord in a rat model of asphyxial CA (ACA). A total of 77 adult male Sprague–Dawley rats were randomized into five groups: normal, sham ACA plus (+) normothermia, ACA + normothermia, sham ACA + hypothermia, and ACA + hypothermia. ACA was induced for 5 min by injecting vecuronium bromide. Therapeutic hypothermia was applied after return of spontaneous circulation (ROSC) via rapid cooling with isopropyl alcohol wipes, which was maintained at 33 ± 0.5 °C for 4 h. Normothermia groups were maintained at 37 ± 0.2 °C for 4 h. Neuronal protection, microgliosis, oxidative stress, and changes of endogenous antioxidants were evaluated at 12 h, 1 day, and 2 days after ROSC following ACA. ACA resulted in neuronal damage from 12 h after ROSC and evoked obvious degeneration/loss of spinal neurons in the ventral horn at 1 day after ACA, showing motor deficit of the hind limb. In addition, ACA resulted in a gradual increase in microgliosis with time after ACA. Therapeutic hypothermia significantly reduced neuronal loss and attenuated hind limb dysfunction, showing that hypothermia significantly attenuated microgliosis. Furthermore, hypothermia significantly suppressed ACA-induced increases of superoxide anion production and 8-hydroxyguanine expression, and significantly increased superoxide dismutase 1 (SOD1), SOD2, catalase, and glutathione peroxidase. Taken together, hypothermic therapy was found to have a substantial impact on changes in ACA-induced microglia activation, oxidative stress factors, and antioxidant enzymes in the ventral horn of the lumbar spinal cord, which closely correlate with neuronal protection and neurological performance after ACA.

Therapeutic hypothermia attenuates paraplegia and neuronal damage in the lumbar spinal cord in a rat model of asphyxial cardiac arrest

Spinal cord ischemia can result from cardiac arrest. It is an important cause of severe spinal cord injury that can lead to serious spinal cord disorders such as paraplegia. Hypothermia is widely acknowledged as an effective neuroprotective intervention following cardiac arrest injury. However, studies on effects of hypothermia on spinal cord injury following asphyxial cardiac arrest and cardiopulmonary resuscitation (CA/CPR) are insufficient. The objective of this study was to examine effects of hypothermia on motor deficit of hind limbs of rats and vulnerability of their spinal cords following asphyxial CA/CPR. Experimental groups included a sham group, a group subjected to CA/CPR, and a therapeutic hypothermia group. Severe motor deficit of hind limbs was observed in the control group at 1 day after asphyxial CA/CPR. In the hypothermia group, motor deficit of hind limbs was significantly attenuated compared to that in the control group. Damage/death of motor neurons in the lumbar spinal cord was detected in the ventral horn at 1 day after asphyxial CA/CPR. Neuronal damage was significantly attenuated in the hypothermia group compared to that in the control group. These results indicated that therapeutic hypothermia after asphyxial CA/CPR significantly reduced hind limb motor dysfunction and motoneuronal damage/death in the ventral horn of the lumbar spinal cord following asphyxial CA/CPR. Thus, hypothermia might be a therapeutic strategy to decrease motor dysfunction by attenuating damage/death of spinal motor neurons following asphyxial CA/CPR.

Characterization of neural stem cells modified with hypoxia/neuron-specific VEGF expression system for spinal cord injury

Spinal cord injury (SCI) is an incurable disease causing an ischemic environment and functional defect, thus a new therapeutic approach is needed for SCI treatment. Vascular endothelial growth factor (VEGF) is a potent therapeutic gene to treat SCI via angiogenesis and neuroprotection, and both tissue-specific gene expression and high gene delivery efficiency are important for successful gene therapy. Here we design the hypoxia/neuron dual-specific gene expression system (pEpo-NSE) and efficient gene delivery platform can be achieved by the combination ex vivo gene therapy with erythropoietin (Epo) enhancer, neuron-specific enolase (NSE) promoter and neural stem cells (NSCs). An in vitro model, NSCs transfected with pEpo-NSE were consistently and selectively overexpressing therapeutic genes in response to neural differentiation and hypoxic conditions. Also, in SCI model, ex vivo gene therapy using pEpo-NSE system with NSCs significantly enhanced gene delivery efficiency compared with pEpo-NSE system gene therapy alone. However, microarray analysis reveals that introducing exogenous pEpo-NSE and VEGF triggers biological pathways in NSCs such as glycolysis and signaling pathways such as Ras and mitogen-activated protein kinase, leading to cell proliferation, differentiation and apoptosis. Collectively, it indicates that the pEpo-NSE gene expression system works stably in NSCs and ex vivo gene therapy using pEpo-NSE system with NSCs improves gene expression efficiency. However, exogenously introduced pEpo-NSE system has an influence on gene expression profiles in NSCs. Therefore, when we consider ex vivo gene therapy for SCI, the effects of changes in gene expression profiles in NSCs on safety should be investigated.

Spinal cord injury after thoracic endovascular aortic aneurysm repair

PURPOSE

Thoracic endovascular aortic aneurysm repair (TEVAR) has become a mainstay of therapy for aneurysms and other disorders of the thoracic aorta. The purpose of this narrative review article is to summarize the current literature on the risk factors for and pathophysiology of spinal cord injury (SCI) following TEVAR, and to discuss various intraoperative monitoring and treatment strategies.

SOURCE

The articles considered in this review were identified through PubMed using the following search terms: thoracic aortic aneurysm, TEVAR, paralysis+TEVAR, risk factors+TEVAR, spinal cord ischemia+TEVAR, neuromonitoring+thoracic aortic aneurysm, spinal drain, cerebrospinal fluid drainage, treatment of spinal cord ischemia.

PRINCIPAL FINDINGS

Spinal cord injury continues to be a challenging complication after TEVAR. Its incidence after TEVAR is not significantly reduced when compared with open thoracoabdominal aortic aneurysm repair. Nevertheless, compared with open procedures, delayed paralysis/paresis is the predominant presentation of SCI after TEVAR. The pathophysiology of SCI is complex and not fully understood, though the evolving concept of the importance of the spinal cord's collateral blood supply network and its imbalance after TEVAR is emerging as a leading factor in the development of SCI. Cerebrospinal fluid drainage, optimal blood pressure management, and newer surgical techniques are important components of the most up-to-date strategies for spinal cord protection.

CONCLUSION

Further experimental and clinical research is needed to aid in the discovery of novel neuroprotective strategies for the protection and treatment of SCI following TEVAR.

Effect of hypoxia-inducible factor-1/vascular endothelial growth factor signaling pathway on spinal cord injury in rats

The aim of the present study was to evaluate the expression of vascular endothelial growth factor (VEGF) and hypoxia inducible factor-1 (HIF-1), and to investigate the role of the HIF-1/VEGF signaling pathway following spinal cord injury (SCI). A total of 90 12-week-old Sprague Dawley rats were randomly divided into the following three groups: Sham group (operation without SCI); control group (SCI without ML228 treatment); and treatment group (SCI receiving ML228 treatment). ML228 was administered as it is an activator of HIF-1α. The control and treatment groups were subjected to spinal cord hemisection and motor activity was evaluated using the Basso, Beattie and Bresnahan (BBB) scoring system. Expression of HIF-1α and VEGF in each injured spinal cord section was assessed using immunohistochemistry. Prior to SCI, there were no significant differences in the BBB score among the three groups (P>0.05). However, one day after the operation, the BBB score of the sham group was significantly higher than that of the other two groups (P<0.05) and the BBB scores of the control and treatment groups did not differ significantly (P>0.05). BBB scores 3 and 7 days following surgery were significantly higher in the sham group than the other two groups (P<0.05) and the BBB scores of the treatment group were significantly higher than those of the control group (P<0.05). The expression of HIF-1α and VEGF proteins in all groups were measured 1, 3 and 7 days after the operation, and it was observed that their expression was higher in the treatment group than in the control group (P<0.05). Therefore, the results of the current study suggest that ML228 may effectively activate the HIF-1α/VEGF signaling pathway to promote the expression of HIF-1α and VEGF proteins within the injured segment of the spinal cord, which promotes neural functional recovery following SCI in rats. Therefore, treatment with ML228 may be developed as a novel therapeutic strategy to treat SCI.

TENS augments blood flow in somatotopically linked spinal cord segments and mitigates compressive ischemia

STUDY DESIGN

This was an acute basic physiological study in anesthetized adult male rats.

OBJECTIVES

The purpose of this study was to determine, in an animal model, whether innocuous somatic stimulation, in the form of transcutaneous electrical nerve stimulation (TENS), could produce a sustained augmentation of spinal cord blood flow, and whether this effect was robust in the face of relatively mild, non-destructive compression of the spinal cord.

SETTING

Neurophysiology laboratory, Canadian Memorial Chiropractic College, Toronto, Canada.

METHODS

In anesthetized adult male Wistar rats, spinal cord blood flow was measured with laser Doppler flowmetry during 5- and 15-min epochs of TENS stimulation in uncompressed and compressed lumbar spinal cord.

RESULTS

TENS applied to the L4/L5 dermatomes was associated with augmentation of blood flow in somatotopically linked spinal cord segments. This augmentation was robust in the face of non-destructive compression of the spinal cord, was sustained for periods of stimulation up to 15 min and occurred in the absence of any change in the mean arterial blood pressure.

CONCLUSIONS

TENS augments spinal cord blood flow in the uncompressed spinal cord and during acute, non-destructive spinal cord compression. It remains to be seen whether similar results can be achieved in chronically compressed spinal cord and spinal nerve roots, and whether these results have clinical implications in human syndromes of spinal cord compression.

Ischemic preconditioning ameliorates spinal cord ischemia-reperfusion injury by triggering autoregulation

OBJECTIVE

The mechanism underlying ischemic preconditioning (IPC) protection against spinal cord ischemia-reperfusion (I/R) injury is unclear. We investigated the role of spinal cord autoregulation in tolerance to spinal cord I/R injury induced by IPC in a rat model.

METHODS

Sprague-Dawley rats were randomly assigned to four groups. IPC (P) group animals received IPC by temporary thoracic aortic occlusion (AO) with a 2F Fogarty arterial embolectomy catheter (Baxter Healthcare, Irvine, Calif) for 3 minutes. The I/R injury (I/R) group animals were treated with blood withdrawal and temporary AO for 12 minutes, and shed blood reinfusion at the end of the procedures. The P+I/R animals received IPC, followed by 5 minutes reperfusion, and then I/R procedures for 12 minutes. Sham (S) group animals received anesthesia and underwent surgical preparation, but without preconditioning or I/R injury. Neurologic function on postprocedure days 1, 3, 5, and 7 was evaluated by Tarlov scoring. Lumbar segments were harvested for histopathologic examination on day 7. To evaluate the role of autoregulation in IPC, spinal cord blood flow and tissue oxygenation were continuously monitored throughout the procedure duration.

RESULTS

The Tarlov scores in the I/R group were significantly lower than those in the S, P, and P+I/R groups on days 1, 3, 5, and 7 (P < .001). No significant differences were noted between the S, P, and P+I/R groups. The numbers of surviving motor neurons in the S, P, and P+I/R groups were significantly higher than those in the I/R group (P < .001); however, the number of surviving motor neurons did not differ between the S, P, and P+I/R groups. The P group exhibited higher spinal cord blood flow (P = .001-.043) and tissue oxygenation (P = .032-.043) within the first 60 minutes after reperfusion than the S group. The P+I/R group exhibited higher spinal cord blood flow (P = .016-.045) and tissue oxygenation (P = .001-.038) within the first 60 minutes after reperfusion than the I/R group.

CONCLUSIONS

IPC ameliorates spinal cord I/R injury in rats, probably mediated by triggering spinal cord autoregulation and improving local spinal cord blood flow and tissue oxygenation. This concept may be the new therapeutic targets in patients requiring aortic surgery.

Preservation of mitochondrial integrity and energy metabolism during experimental status epilepticus leads to neuronal apoptotic cell death in the hippocampus of the rat

Status epilepticus results in mitochondrial damage or dysfunction and preferential neuronal cell loss in the hippocampus. Since a critical determinant of the eventual cell death fate resides in intracellular ATP concentration, we investigated whether mitochondrial integrity and level of energy metabolism are related with apoptotic cell death in specific hippocampal neuronal populations. A kainic acid (KA)-induced experimental temporal lobe status epilepticus model was used. Qualitative and quantitative analysis of DNA fragmentation, TUNEL immunohistochemistry, double immunofluorescence staining for activated caspase-3, electron microscopy or measurement of ATP level in the bilateral hippocampus was carried out 1, 3 or 7 days after microinjection unilaterally of a low dose of KA (0.5 nmol) into the CA3 hippocampal subfield. Characteristic biochemical (DNA fragmentation), histochemical (TUNEL or activated caspase-3 staining) or ultrastructural (electron microscopy) features of apoptotic cell death were presented bilaterally in the hippocampus 7 days after the elicitation of sustained hippocampal seizure activity by microinjection of KA into the unilateral CA3 subfield. At the same time, CA3 or CA1 subfield on either side manifested a maintained ATP level; alongside relatively intact mitochondria, rough endoplasmic reticulum, Golgi apparatus or cytoplasmic membrane in hippocampal neurons that exhibited ultrastructural features of apoptotic cell death. Our results demonstrated that preserved mitochondrial ultrastructural integrity and maintained energy metabolism during experimental temporal lobe status epilepticus is associated specifically with apoptotic, not necrotic, cell death in hippocampal CA3 or CA1 neurons.

Efficacy and vasodilatory benefit of magnesium prophylaxis for protection against spinal cord ischemia

Prevention of paraplegia remains an imperative issue in thoracoabdominal aortic surgery. The aim of this study was to assess the efficacy of a prophylactic magnesium infusion in a rat spinal cord ischemia model and to demonstrate spinal blood flow increase caused by the infusion. The study was conducted in two parts. Firstly, the neuroprotective effect of magnesium was assessed using a rat model with two different ischemic times: 10 min and 14 min. Spinal cord ischemia was induced by occlusion of the descending aorta. Rats in the treatment group were given a 100 mg/kg magnesium sulfate infusion before ischemia. Secondly, relative changes in spinal cord blood flow before and during ischemia were recorded using the laser Doppler flowmetry technique. Changes in blood flow were compared between the magnesium and control groups. Rats pretreated with magnesium showed good overall recovery after both 10 min (incidence of paraplegia 62.5% control vs. 37.5% Mg, n = 8 each) and 14 min (85.7% control vs. 57.1% Mg, n = 7 each) of ischemia, although the differences compared with controls were statistically insignificant. However, the magnesium group showed significantly better neurological performance during the early postischemic period. Comparison of changes in spinal circulation revealed less reduction in blood flow during ischemia in the magnesium-treated group. In conclusion, magnesium may have potential prophylactic benefits during ischemia by exerting a neuroprotective effect through vasodilation of the spinal cord vasculature. To our knowledge, this vasodilatory effect on the spinal cord has not previously been investigated. Optimization of the treatment regimen, however, is required.

Contribution of supraspinal and spinal structures to the responses of dorsal spinal cord blood flow to innocuous cutaneous brushing in rats

Responses of dorsal spinal cord blood flow (SCBF) to innocuous mechanical cutaneous stimulation were investigated in anesthetized central nervous system intact (CNS-intact) and C2 spinalized rats. SCBF was recorded at the L4-L6 level with a laser Doppler flowmeter. SCBF increased with brushing of the ipsilateral proximal hindlimb and hindpaw, and there were no significant differences in the magnitudes of the responses in CNS-intact and spinalized animals. Brushing of the lower back had no effect on SCBF at the L4-L6 level in either cohort. Brushing stimulation produced no significant changes in systemic arterial blood pressure. The responses of SCBF to brushing in CNS-intact animals were diminished by pretreatment with phenoxybenzamine, an alpha-adrenoceptor blocking agent, but no such effects were seen in spinalized animals. These results indicate that innocuous mechanical cutaneous input can produce a segmentally-organized increase in regional SCBF, and that the responses are modulated, in part at least, by alpha-adrenergic receptors via supraspinal structures.

Transcriptional and post-translational regulatory system for hypoxia specific gene expression using the erythropoietin enhancer and the oxygen-dependent degradation domain

Gene therapy with angiogenic factors is a promising strategy for the treatment of ischemic diseases. However, unregulated expression of an angiogenic factor may induce pathological angiogenesis. In this study, a hypoxia specific gene expression plasmid, pSV-Luc-ODD, was constructed with the oxygen-dependent degradation (ODD) domain for rapid degradation of a target protein under normoxia. In the transfection assay, luciferase activity in the pSV-Luc-ODD transfected cells was much lower under normoxia than that under hypoxia. However, the luciferase mRNA levels under hypoxia and normoxia were not significantly different. Therefore, decrease of luciferase activity under normoxia is not due to pre-translational events such as change of transcription rate or mRNA stability, but to post-translational degradation. For more hypoxia specific gene expression, pEpo-SV-Luc-ODD was constructed with the erythropoietin (Epo) enhancer and the ODD domain. pEpo-SV-Luc-ODD showed more than 1000 times increase of gene expression under hypoxia in Neuro2A cells, compared to normoxia. In addition, reoxygenation studies after hypoxia incubation showed that gene expression was decreased in response to increased oxygen concentration. This highly hypoxia specific gene expression system will be useful for development of targeting gene therapy for ischemic diseases.

Influence of Perioperative Hemodynamics on Spinal Cord Ischemia in Thoracoabdominal Aortic Repair

BACKGROUND

The purpose of this study is to investigate the influence of perioperative circulation on spinal cord during the repair of descending thoracic or thoracoabdominal aortic aneurysms.

METHODS

From October 1999, 92 patients (aged 66 +/- 13 years; 65 men) underwent the repair of descending thoracic (n = 30) or thoracoabdominal aortic aneurysm (Crawford I, 9; II, 14; III, 35; IV, 4). We measured the time duration of hypotension, defined as follows, and evaluated the relationship between the incidence of paraplegia and each duration: T1, systolic arterial pressure less than 80 mm Hg, or mean pressure less than 60 mm Hg during aortic cross-clamping; T2, distal aortic pressure less than 60 mm Hg during aortic cross-clamping; T3, systolic arterial pressure less than 80 mm Hg after coming off bypass; T4, systolic arterial pressure less than 80 mm Hg in the intensive care unit.

RESULTS

Hospital mortality was 8% (7 patients). Neurologic deficits occurred in 10 patients (10.9%). The T1 and T2 periods showed no difference between paraplegia cases (group P) and normal cases (group N). The T3 periods in both groups were 54 +/- 52 and 6.6 +/- 18, and the T4 periods were 62 +/- 89 and 2.3 +/- 14, respectively. The T3 and T4 periods in group P were significantly longer than in group N (p < 0.0001). Multivariate analysis demonstrated that T3 was an independent risk factor for paraplegia. When divided according to body temperature, the T2 period under mild hypothermia was significantly longer in group P than in group N, as well as the T3 and T4 periods.

CONCLUSIONS

Perioperative hemodynamics stability is of vital importance for spinal cord protection during thoracoabdominal aortic surgery. In particular, the duration of hypotension after coming off bypass was an independent risk factor for paraplegia.

Hypoxia-inducible expression of vascular endothelial growth factor for the treatment of spinal cord injury in a rat model

OBJECT

Vascular endothelial growth factor (VEGF) has been investigated as a therapy for many disorders and injuries involving ischemia. In this report, we constructed and evaluated a hypoxia-inducible VEGF expression system as a treatment for spinal cord injury (SCI).

METHODS

The hypoxia-inducible VEGF plasmid was constructed using the erythropoietin (Epo) enhancer with the Simian virus 40 (SV40) promoter (pEpo-SV-VEGF) or the RTP801 promoter (pRTP801-VEGF). The expression of VEGF in vitro was evaluated after transfection into N2A cells. The plasmids were then injected into rat spinal cords with contusion injuries. The expression of VEGF in vivo was measured using reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. Locomotor recovery in the rats was evaluated using the Basso, Beattie and Bresnahan (BBB) scale for locomotor analysis.

RESULTS

In vitro transfection showed that pEpo-SV-VEGF or pRTP801-VEGF induced VEGF expression under hypoxic conditions, whereas pSV-VEGF did not. The VEGF level was higher in the pEpo-SV-VEGF and pRTP801-VEGF groups than in the control group. The VEGF expression was detected in neurons and astrocytes of the spinal cord. Locomotor recovery was improved in the pEpo-SV-VEGF and pRTP801-VEGF groups, and BBB scores were higher than in the control group. Staining using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling showed that the number of apoptotic cells decreased in the plasmid-injected groups compared with the control group, and significant differences were observed between the hypoxia-responsive groups and the pSV-VEGF group.

CONCLUSIONS

These results suggest that the hypoxia-inducible VEGF expression system may be useful for gene therapy of SCI.

Inhibition of the MEK/ERK pathway reduces microglial activation and interleukin-1-beta expression in spinal cord ischemia/reperfusion injury in rats

OBJECTIVES

Ischemic spinal cord injury is a serious complication of aortic surgery. Although the extracellular signal-regulated kinases 1 and 2 are generally regarded as related to cell proliferation and survival, increasing evidence suggests that the role of the extracellular signal-regulated kinase pathway in ischemia/reperfusion injury is much more sophisticated.

METHODS

Spinal cord ischemia in rats was induced by occluding the thoracic descending aorta with a balloon catheter introduced through a femoral artery, accompanied by concomitant exsanguination. Rats in the control group were given dimethyl sulfoxide (vehicle) before undergoing spinal cord ischemia/reperfusion injury. In the U0126-treated group, rats were pretreated with a specific inhibitor of the mitogen-activated protein kinase/extracellular signal-regulated kinases 1 and 2, U0126, to inhibit extracellular signal-regulated kinases 1 and 2 phosphorylation. The sham-operated rats underwent aortic catheterization without occlusion. Parameters, including neurologic performance, neuronal survival, inflammatory cell infiltration, and interleukin-1beta production in the spinal cords, were compared between groups.

RESULTS

Early extracellular signal-regulated kinases 1 and 2 phosphorylation was observed after injury in the control group, followed by abundant microglial accumulation in the infarct area and increased interleukin-1beta expression. In the U0126 group, U0126 treatment completely blocked extracellular signal-regulated kinases 1 and 2 phosphorylation. Microglial activation and spinal cord interleukin-1beta levels were significantly reduced. Neuronal survival and functional performance were improved.

CONCLUSIONS

The mitogen-activated protein kinase/extracellular signal-regulated kinase pathway may play a noxious role in spinal cord ischemia/reperfusion injury by participating in inflammatory reactions and cytokine production. Targeting this pathway may be of potential value in terms of therapeutic intervention.

Activation of ASK1 during reperfusion of ischemic spinal cord

Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase kinase kinase (MAPKKK), which plays a pivotal role in cell apoptosis. To determine the mechanism of ASK1 induction during reperfusion of ischemic spinal tissue, we used a model of rabbit spinal cord ischemia and reperfusion. To assess the role of ASK1 in spinal cord ischemia-reperfusion injuries, we examined alterations in spinal tissue morphology, protein-protein interactions, and activation of key members of the ASK1-mediated signaling pathway. Changes in spinal cord morphology were observed with hematoxylin and eosin (H&E) staining and electron microscopy. The phosphorylation levels of ASK1, JNK, and p38 were assessed by immunoblotting proteins from animals that received 30 min of ischemia followed by 1 or 24h of reperfusion. We observed increased phosphorylation of ASK1, JNK, and p38 after reperfusing ischemic spinal cords. Immunohistochemical studies were performed to determine the cellular localization of phosphorylated ASK1 (pASK1) and 14-3-3. Following reperfusion for 24h, we observed increased cytoplasmic localization of pASK1 and decreased cytoplasmic localization of 14-3-3. Immunoprecipitation analyses suggested that 14-3-3 dissociates from ASK1 during reperfusion of ischemic spinal cords. These results indicate that activation of ASK1 may play an important role in the apoptotic signaling mechanisms that occur in reperfused spinal cord injuries.

A hypoxia-inducible gene expression system using erythropoietin 3′ untranslated region for the gene therapy of rat spinal cord injury

Many neurologic disorders are accompanied by ischemic injury during the pathologic process. To develop a controllable and injury-specific gene therapy system for the neurologic disorders, we constructed a hypoxia inducible plasmid with the erythropoietin (Epo) 3' untranslated region (UTR), which can enhance the stability of target mRNAs in response to hypoxia. The Epo 3' UTR was inserted at the 3' flanking region of luciferase gene in pSV-Luc, resulting in the construction of pSV-Luc-EpoUTR. In pEpo-SV-Luc-EpoUTR, the Epo enhancer was inserted into the upstream of the SV40 promoter to increase the hypoxia inducibility. The plasmids were evaluated in N2a mouse neuroblastoma cells under hypoxic conditions and in a rat spinal cord injury (SCI) model. The results showed that the Epo 3' UTR alone showed a three-fold increase in luciferase activity in hypoxic N2a cells as well as in the rat SCI model when compared to the sham control. In contrast, the Epo 3' UTR showed no effect on the luciferase activity in the presence of the Epo enhancer, probably because the Epo enhancer was more sensitive to hypoxia and showed a dominant effect. However, the Epo enhancer itself showed high level of luciferase activity even in normoxia (about five to eight-folds increase), while the Epo 3' UTR did not show enhanced background activity. Immunohistochemical staining showed expression of luciferase from pSV-Luc-EpoUTR both in neurons and astrocytes around the injured spinal cord of rat. These results suggest that the Epo 3' UTR could provide a specific and safe system for the hypoxia-inducible gene therapy of the neurologic disorders including SCI.

Neuronal damage in rat brain and spinal cord after cardiac arrest and massive hemorrhagic shock*

OBJECTIVE

Severe global ischemia often results in severe damage to the central nervous system of survivors. Hind-limb paralysis is a common deficit caused by global ischemia. Until recently, most studies of global ischemia of the central nervous system have examined either the brain or spinal cord, but not both. Spinal cord damage specifically after global ischemia has not been studied in detail. Because the exact nature of the neuronal damage to the spinal cord and the differences in neuronal damage between the brain and spinal cord after global ischemia are poorly understood, we developed a new global ischemia model in the rat and specifically studied spinal cord damage after global ischemia. Further, we compared the different forms of neuronal damage between the brain and spinal cord after global ischemia.

DESIGN

Randomized, controlled study using three different global ischemia models in the rat.

SETTING

University research laboratory.

SUBJECTS

Male, adult Sprague-Dawley rats (300 g).

INTERVENTIONS

Animals were divided into three experimental groups, group A (n = 6, survived for 7 days), 12 mins of hemorrhagic shock; group B (n = 6, survived for 7 days), 5 mins of cardiac arrest; or group C (n = 6, each for 6 hrs, 12 hrs, 1 day, 3 days, and 7 days), 7 mins of hemorrhagic shock and 5 mins of cardiac arrest. Motor deficit of the hind limbs was studied 6 hrs to 7 days after resuscitation. Also, nonoperated animals (n = 6) were used as the control. Histologic analysis (hematoxylin and eosin, Fluoro-Jade B, terminal deoxynucleotidyl transferase- mediated dUTP end-labeling [TUNEL], Klüver-Barrera) and ultrastructural analysis using electron microscopy were performed on samples from the CA1 region of the hippocampus and lumbar spinal cord. Demyelination of the white matter of the lumbar spinal cord was analyzed semiquantitatively using Scion Image software.

MAIN RESULTS

No paraplegic animals were observed in either group A or B. All group C animals showed severe hind-limb paralysis. Severe neuronal damage was found in the CA1 region of the hippocampus in all groups, and the state of delayed neuronal cell death was similar among the three groups. Neuronal damage in the lumbar spinal cord was detected only in group C animals, mainly in the dorsal horn and intermediate gray matter. Demyelination was prominent in the ventral and ventrolateral white matter in group C. A significant difference was observed between control and group C rats with Scion Image software. Ultrastructural analysis revealed extensive necrotic cell death in the intermediate gray matter in the lumbar spinal cord in group C rats.

CONCLUSION

The combination in the global ischemia model (i.e., hemorrhagic shock followed by cardiac arrest) caused severe neuronal damage in the central nervous system. Thereby, hind-limb paralysis after global ischemia might result from spinal cord damage. These results suggest that therapeutic strategies for preventing spinal cord injury are necessary when treating patients with severe global ischemia.

Critical ischemia time in a model of spinal cord section. A study performed on dogs

Vascular changes after acute spinal cord trauma are important factors that predispose quadriplegia, in most cases irreversible. Repair of the spinal blood flow helps the spinal cord recovery. The average time to arrive and perform surgery is 3 h in most cases. It is important to determine the critical ischemia time in order to offer better functional prognosis. A spinal cord section and vascular clamping of the spinal anterior artery at C5-C6 model was used to determine critical ischemia time. The objective was to establish a critical ischemia time in a model of acute spinal cord section. Four groups of dogs were used, anterior approach and vascular clamp of spinal anterior artery with 1, 2, 3, and 4 h of ischemia and posterior hemisection of spinal cord at C5-C6 was performed. Clinical evaluation was made during 12 weeks and morphological evaluation at the end of this period. We obtained a maximal neurological coordination at 23 days average. Two cases showed sequels of right upper limb paresis at 1 and 3 ischemia hours. There was nerve conduction delay of 56% at 3 h of ischemia. Morphological examination showed 25% of damaged area. The VIII and IX Rexed's laminae were the most affected. The critical ischemia time was 3 h. Dogs with 4 h did not exhibit any recovery.

Evolution of Spinal Cord Injury in a Porcine Model of Prolonged Aortic Occlusion

BACKGROUND

Spinal cord injury and subsequent paraplegia remains an unpredictable and devastating complication of thoracoabdominal aortic surgery. The aim of this study was to investigate spinal cord injury due to prolonged thoracoabdominal aortic occlusion.

MATERIALS AND METHODS

We used a highly reproducible porcine model of 45-min thoracoabdominal aortic occlusion, which was accomplished by two balloon occlusion catheters. Neurological evaluation after the end of experiment was performed by an independent observer according to the Tarlov scale. The lower thoracic and lumbar spinal cords were harvested at 10, 48, and 120 h (n = 6 animals per time point) and examined histologically with hematoxylin and eosin (H&E) stain and TUNEL method. Tarlov scores, number of neurons, and the grade of inflammation were analyzed.

RESULTS

H&E staining revealed reduction in the number of motor neurons which occurred in two phases (between 0 and 10 h and between 48 and 120 h of reperfusion), as well as development of inflammation in spinal cord sections during the reperfusion period, reaching a peak at 48 h. TUNEL reaction was negative for apoptotic neurons at any time point.

CONCLUSIONS

In this porcine model, we demonstrated that, after 45 min of thoracoabdominal aortic occlusion, motor neuron death seems to occur in two phases (immediate and delayed). Inflammation was a subsequent event of transient prolonged spinal cord ischemia and possibly a major contributor of delayed neuronal death. Using TUNEL straining we found no evidence of neuronal apoptosis at any time point of reperfusion.

Ischemic injury-specific gene expression in the rat spinal cord injury model using hypoxia-inducible system

STUDY DESIGN

A spinal cord injury and in vitro neural hypoxia models were used to evaluate the hypoxia responsive gene expression.

OBJECTIVES

To limit the risk of unwanted overexpression of therapeutic genes, we developed a hypoxia-inducible gene therapy system using the erythropoietin (Epo) enhancer and the RTP801 promoter.

SUMMARY OF BACKGROUND DATA

Gene therapy is an emerging therapeutic technique to treat spinal cord injury. However, uncontrolled overexpression of therapeutic genes in nondisease tissues during gene therapy raises a doubt about its safety. Post-traumatic ischemia is an important factor worsening the spinal cord damage, and hypoxia could regulate the gene expressions using a hypoxia-inducible promoter.

METHODS

The plasmids, pEpo-SV-Luc and pRTP801-Luc, were constructed. Mouse neuroblastoma cells (N2A) were used to evaluate the hypoxia-inducible gene expression in vitro.- Gene transfection and expression were allowed for 24 hours under normoxia (pO2, 152 mm Hg) or hypoxia (pO2, 7.6 mm Hg). Spinal cord injury was made using clip compression. Plasmids were injected directly into the injured spinal cord immediately following injury. The gene expression was assessed by luciferase assay.

RESULTS

pEpo-SV-Luc and pRTP801-Luc showed more than three times higher gene expression in N2A cells under hypoxia than normoxia. The expression level of luciferase in the injured spinal cord was higher than in the normal spinal cord. Immunostaining demonstrated that neurons, astrocytes, and capillary endothelial cells expressed luciferase in the cytoplasm.

CONCLUSIONS

The pEpo-SV-Luc and pRTP801-Luc systems are effective in that they induce gene expression specifically in neurons under the hypoxic condition and spinal cord injury.

Experimental spinal cord ischemia: Model characterization and improved outcome with arterial hypertension*

OBJECTIVE

Paraplegia from spinal cord ischemia is a devastating complication of thoracoabdominal aortic aneurysm repair. Perioperative hypoperfusion of the spinal cord is a critical determinant of residual neurologic deficits. We determined if functional and histologic outcome is dependent on systemic blood pressure in a rat model of spinal cord ischemia.

DESIGN

Randomized, controlled, prospective study.

SETTING

Research laboratory at a university teaching hospital.

SUBJECTS

Adult male Wistar rats.

INTERVENTIONS

Endotracheally intubated adult male Wistar rats (300-450 g) anesthetized with halothane underwent a thoracotomy and placement of a clip across the descending aorta for 27 mins. Mean proximal arterial blood pressure (MPABP) was monitored with a cannula placed in the left common carotid artery. Halothane was adjusted (1.25-1.5%) to maintain MPABP between 70 and 90 mm Hg (n = 20) or 140 and 150 mm Hg (n = 20). Shamoperated rats (n = 10) had a thoracotomy without aortic clamping at an MPABP of 70-90 mm Hg. Following 1, 24, 48, and 72 hrs of recovery from anesthesia, motor function of the hind paws was scored as follows: 0, no evidence of deficit; 1, toes flat under body when walking but with ataxia; 2, knuckle walks; 3, movements in hind limbs but unable to knuckle walk; 4, no movement, drags hind limbs. Body temperature was maintained between 37 and 38 degrees C throughout the experiment.

MEASUREMENTS AND MAIN RESULTS

All sham operated rats with MPABP 70-90 mm Hg recovered without neurologic deficits, whereas those that underwent aortic occlusion with MPABP between 70 and 90 mm Hg emerged from anesthesia with grade 3 and 4 deficits and remained in this condition without improvement at 72 hrs. Histopathology at 72 hrs demonstrated moderate to severe neuronal loss with involvement of dorsal, intermediate, and ventral horns. Only eight of 20 rats that underwent aortic occlusion with MPABP between 140 and 150 mm Hg had grade 1 and 2 deficits on emergence but had no neurologic deficit after 1 hr. Most of the surviving neurons in these animals appeared normal histologically, particularly motor neurons around the periphery of the ventral horn.

CONCLUSIONS

Systemic blood pressure is a critical determinant of outcome following spinal cord ischemia, and controlled peri-operative blood pressure augmentation may ameliorate neurologic deficits in patients who undergo thoracoabdominal vascular procedures and are at risk for spinal cord hypoperfusion.