Neurological protection by dichloroacetate depending on the severity of injury in the paraplegic rat

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.

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.

Role of glycemia in acute spinal cord injury. Data from a rat experimental model and clinical experience

While experimental and clinical evidence indicates that in brain injury blood glucose increases with injury severity and hyperglycemia worsens neurological outcome, the role of blood glucose in secondary mechanisms of neuronal damage after acute spinal cord injury has not yet been investigated. Data from spinal cord ischemia models suggests a deleterious effect of hyperglycemia, likely due to enhanced lactic acidosis, which is primarily dependent on the amount of glucose available to be metabolized. The purpose of this study is to summarize preliminary experimental and clinical observations on the role of blood glucose in acute spinal cord injury. Between 1995 and 1996 we used the New York University (NYU) rat spinal cord injury model to test the following hypotheses: 1) Blood glucose levels increase with injury severity. 2) Fasting protects from hyperglycemia and prevents secondary damage to the spinal cord. 3) Postinjury-induced hyperglycemia (dextrose 5% 2 gm/Kg) enhances spinal lesion volume. From a clinical perspective, we reviewed blood glucose records of 47 patients admitted to the Department of Neurosrgery in Verona, between 1991 and 1995, within 24 hours of acute spinal cord injury in order to determine: a) the incidence of hyperglycemia (> 140 mg/dl); b) the correlation between blood glucose and injury severity; and c) the role of methylprednisolone in affecting blood glucose. Results indicate that in a graded spinal cord injury model: 1) Early after injury, more severe contusions support significantly higher blood glucose levels. 2) Fasting overnight does not directly affect spinal cord lesion volume but influences blood gases, and we observed that a slightly systemic acidosis plays a minor neuroprotective role. Fasting also ensures more consistent normoglycemic baseline blood glucose values. 3) Postinjury-induced moderate hyperglycemia (160-190 mg/dl) does not significantly affect spinal cord injury. In the clinical study, we observed that during the first 24 hours after spinal cord injury: a) Glycemia ranges between 90 and 243 mg/dl (mean value 143 mg/dl), and close to 50% of the patients present blood glucose values higher than normal. b) Methylprednisolone administration is not associated to significantly higher blood glucose levels. c) There is a trend for larger glucose rises with more severe injury.

Spinal cord blood flow and pathophysiological changes after transient spinal cord ischemia in cats

OBJECTIVE

The goal was to study the hemodynamics and regional pathophysiological changes in the spinal cord after transient vascular occlusion in cats.

METHODS

We measured spinal cord blood flow (SCBF) continuously in the lumbar region with a laser-doppler flowmeter, before, during, and after spinal cord ischemia induced by balloon occlusion of the thoracic aorta, in 24 cats (divided into three groups) and simultaneously recorded the evoked spinal cord potentials (ESPs). In each group (n = 8), 10-, 20-, and 30-minute ischemic loading was performed. All animals were evaluated neurologically 36 hours later, and then their spinal cords were examined histologically.

RESULTS

The amplitude of ESPs decreased 10 minutes and disappeared 20 minutes after occlusion. SCBF increased to as much as 2 times the control values after reperfusion and decreased gradually in all groups. Then, in all animals in the 10-minute group and six animals in the 20-minute group, SCBF returned to the control values, which were subsequently maintained throughout the experiment, and ESPs returned to normal patterns within 1 hour. For all animals in the 30-minute group and two in the 20-minute group, hypoperfusion after recirculation, irreversible amplitude changes in ESPs, postischemic paraparesis, and pathological ischemic changes in the lower thoracic and lumbar spinal segments were recognized.

CONCLUSION

Our results showed that > 20-minute occlusion of the thoracic aorta in cats resulted in irreversible spinal perfusion disorders and that the monitoring of SCBF and ESPs could be useful for predicting potential neurological deficits. Furthermore, postischemic hypoperfusion may have an important role in the development of secondary spinal cord ischemia, resulting in severe neurological dysfunction. This observation suggested the possibility of therapeutic modification of the secondary processes inducing hypoperfusion after spinal ischemia.

Lactic acidosis and other mitochondrial disorders

The ability of mitochondria to oxidize substrates and generate energy is integral to normal homeostasis and to the ability of cells to survive in the face of impending energy failure. Lactic acidosis is a common and readily apparent biochemical marker for mitochondrial dysfunction. However, lactic acidosis represents only the most obvious example in which acquired or congenital abnormalities of mitochondrial oxidative phosphorylating capacity contribute to the pathobiology and phenotypic expression of a broad spectrum of clinical disorders. Consequently, interventions that improve mitochondrial function or prevent mitochondrial energy failure may have widespread therapeutic implications.

Dichloroacetate attenuates neuronal damage in a gerbil model of brain ischemia

Dichloroacetate facilitated a reduction in brain lactate following ischemia in the gerbil. This treatment also improved high-energy metabolite and pyruvate dehydrogenase enzyme recovery. The purpose of this study was to determine the effect of dichloroacetate on ischemia-induced neuronal damage in the hippocampus of the gerbil. In adult male gerbils, carotid arteries were clamped bilaterally for 5 min. After ischemia, each gerbil was graded neurologically and received an ip injection of dichloroacetate (75 or 225 mg/kg) or an equal volume (5 mL/kg) of sodium acetate (66 mg/kg). On the following morning, gerbils received a second injection, and 3 d later were anesthetized and perfused intracardially. Brains were processed, and stained sections were analyzed for neuronal damage. Gerbils treated with 225 mg/kg dichloroacetate exhibited significantly less damage than the untreated group (p = 0.05, Dunn's test). Gerbils with a normal neurologic score evidenced no neuronal damage. Abnormal neurologic scores immediately after ischemia did not correlate with degree of neuronal damage observed 4 d later. These results indicate that neuronal damage is less in gerbils treated after ischemia with an appropriate dose of dichloroacetate. The lack of any histological evidence for an adverse effect of dichloroacetate in the controls supports the safety of this drug in this protocol. Normal neurologic scores immediately after ischemia can be used to identify gerbils mimicking ischemia in this model.

Facilitating postischemic reduction of cerebral lactate in rats

BACKGROUND AND PURPOSE

Dichloroacetate facilitates a decrease in brain lactate during reperfusion after incomplete ischemia. This study examined the possible activation of pyruvate dehydrogenase enzyme by dichloroacetate to explain this effect. Because the duration of ischemia and hyperglycemia exacerbate ischemic brain damage, the effect of both of these factors on lactate reduction with and without dichloroacetate treatment after ischemia also was explored.

METHODS

The two-vessel occlusion and controlled blood loss model of stroke was applied to anesthetized rats. Samples of cerebral cortex were analyzed for lactate by enzyme fluorometry and for pyruvate dehydrogenase activity by radioassay.

RESULTS

Treatment with dichloroacetate produced no significant stimulation of pyruvate dehydrogenase after ischemia. When the duration of ischemia was increased or 50% glucose was infused before ischemia, brain lactate was significantly higher (p less than 0.01, Duncan's test). After 30 minutes of ischemia, treatment with a low dose of dichloroacetate (25 mg/kg) improved the reduction in lactate (p less than 0.01, Duncan's test).

CONCLUSIONS

These results indicate that although dichloroacetate reduces brain lactate after cerebral ischemia, the mechanism of action does not involve dichloroacetate's known ability to stimulate pyruvate dehydrogenase. However, these data support the use of dichloroacetate to lower cerebral lactate, especially in cases where ischemia is greater than or equal to 30 minutes in duration. They also suggest that early restoration and maintenance of perfusion after ischemia and discontinuing the use of 50% glucose before impending ischemia likewise would facilitate reduction of postischemic brain lactate.

Inhibition of lactate-induced swelling by dichloroacetate in human astrocytoma cells

High levels of tissue lactate exacerbate tissue damage that results from cerebral ischemia and reperfusion injury that follows. Post-ischemic treatment with dichloroacetate (DCA) facilitates a decrease in lactate in the central nervous system (CNS) of animals during reperfusion following experimental ischemia, thus it may help to ameliorate ischemic cell damage. It has been suggested that the lactate lowering effect is mediated through a stimulatory effect of DCA on pyruvate dehydrogenase (PDHC) activity. We have studied such a hypothesis in a human astrocytoma derived cell line, UC-11MG. Under conditions resembling those of the ischemic tissue (i.e. high lactate and low pH) these cells accumulate lactate, driven by the inwardly directed proton gradient, and swell as a consequence of the osmotic effect of intracellular lactate. We have demonstrated that DCA increases PDHC activity and also reduces lactate-induced swelling. However, we also found that these two effects could be uncoupled and that the ability of DCA to prevent swelling is still present in the absence of any stimulation of PDHC. We also demonstrated that DCA competitively inhibits the uptake of lactate (Ki = 1.9 mM) and increases the efflux of lactate in a trans-acting manner that suggests the presence of a lactate-DCA exchange. We present a mechanism by which reduction in the rate of lactate uptake could account for the observed inhibition of swelling. This effect of DCA on lactate transport indicates another possible mechanism of action for DCA in facilitating the decrease in lactate observed in vivo during reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)