Reduction in spinal cord postischemic lactic acidosis and functional improvement with dichloroacetate

Effects of adenosine monophosphate-activated kinase in the ventral horn of rabbit spinal cord after transient ischemia

OBJECTIVE

To investigate the effect compound C, an adenosine monophosphate-activated kinase (AMPK) inhibitor, has on motor neurons of rabbit spinal cord after ischemia/reperfusion.

DESIGN

Compound C (30 mg/kg) was administered intraperitoneally to rabbits 30 minutes before ischemia and the animals were sacrificed at 15 minutes after ischemia/reperfusion to measure lactate levels and at 72 hours after ischemia/reperfusion for morphological study.

RESULTS

The administration of compound C did not produce any significant changes in physiological parameters such as pH, arterial blood gas (PaCO(2) and PaO(2)), and blood glucose in rabbit either at 10 minutes before ischemia or at 10 minutes after reperfusion. However, the administration of compound C did significantly ameliorate lactate acidosis at 15 minutes after reperfusion. In addition, the administration of compound C significantly improved the neurological scores of the rabbits and reduced the neuronal death seen in the ventral horn of their spinal cords at 72 hours after ischemia/reperfusion.

CONCLUSIONS

Inhibition of AMPK can ameliorate the ischemia-induced neuronal death in the spinal cord via the reduction of early lactate acidosis.

Effect of Temporary Visceral Ischemia on Spinal Cord Ischemic Damage in the Rabbit

BACKGROUND

Spinal cord ischemia and visceral ischemia may occur simultaneously during thoracoabdominal aortic aneurysm repair. The present rabbit study investigated the effect of a temporary interruption of the visceral perfusion on the development of ischemia-reperfusion injury of the spinal cord.

METHODS

Spinal cord ischemia was induced by occlusion of the infrarenal aorta for variable durations (6 to 20 minutes) in 32 rabbits. In the visceral ischemia group, 20-minute concurrent clamping of the celiac trunk and mesenteric arteries was performed. At 24, 48, and 72 hours after ischemia, neurologic outcome was assessed in the control and visceral ischemia group. The PD50 (the duration of ischemia that produces lower limb neurologic deficits in 50% of the animals) was determined by quantal bioassay analysis. At 72 hours, histologic evaluation of spinal cord infarct size was performed.

RESULTS

Compared with control animals, PD50 was significantly longer in the visceral ischemia group at 48 hours and 72 hours after ischemia. Neurologic and histologic outcomes correlated well (r = -0.90).

CONCLUSIONS

The results of the present rabbit study suggest that concurrent temporary visceral ischemia does not aggravate spinal cord ischemic injury in the rabbit. Moreover, the results suggest that concurrent visceral ischemia may increase the tolerance of the spinal cord to ischemic damage.

Dichloroacetate and cerebral ischaemia therapeutics

Brain ischaemia is a major medical problem which totally lacks meaningful therapeutic options. A drug that reduces morbidity and mortality associated with head injury and stroke would constitute a major medical breakthrough. Although many mechanistic approaches have been evaluated clinically for both stroke and head injury, none have yet to be proven successful. Dichloroacetate (DCA, Ceresine) is a small molecule that activates pyruvate dehydrogenase (PDH) and crosses the blood-brain barrier. PDH activation reduces neurotoxic lactic acidosis which always accompanies brain ischaemia. DCA shows substantial efficacy in a variety of models of stroke, pre-stroke, head or spinal cord injury. Agents that lower cerebral lactic acidosis have not yet been clinically evaluated in head injury and stroke, although DCA has been shown clinically to reduce ambient lactate concentrations in patients with such conditions. DCA has also been shown to be well-tolerated in these patients, and unlike many halogenated molecules, is not mutagenic. Since elevated brain lactate is correlated with poor outcome in both preclinical and clinical studies, an agent such as DCA may prove to reduce the brain injury associated with these disorders. Potential clinical applications of DCA include stroke, head injury, spinal cord injury, and chronic disorders such as congenital lactic acidosis (CLA) and mitochondrial lactic acidosis and stroke-like syndrome (MELAS).

Effect of mild hypothermia on brain dialysate lactate after fluid percussion brain injury in rodents

OBJECTIVE

To investigate the effects of mild hypothermia on brain microdialysate lactate after fluid percussion traumatic brain injury (TBI) in rats.

METHODS

Brain dialysate lactate before and after fluid percussion brain injury (2.1 +/- 0.2 atm) was measured in rats with preinjury mild hypothermia (32 degrees C), postinjury mild hypothermia (32 degrees C), injury normothermia (37 degrees C), and the sham control group. Mild hypothermia (32 degrees C) was induced by partial immersion in a water bath (0 degrees C) under general anesthesia and maintained for 2 hours.

RESULTS

In the normothermia TBI group, brain extracellular fluid lactate increased from 0.311 +/- 0.03 to 1.275 +/- 0.08 mmol/L within 30 minutes after TBI (P < 0.01) and remained at a high level (0.546 +/- 0.05 mmol/L) (P < 0.01) at 2 hours after injury. In the postinjury mild hypothermic group, brain extracellular fluid lactate increased from 0.303 +/- 0.03 to 0.875 +/- 0.05 mmol/L at 15 minutes after TBI (P < 0.01) and then gradually decreased to 0.316 +/- 0.04 mmol/L at 2 hours after TBI (P > 0.05). In the preinjury mild hypothermic group, brain extracellular fluid lactate remained at normal levels after injury (P > 0.05).

CONCLUSION

The cerebral extracellular fluid lactate level increases significantly after fluid percussion brain injury. Preinjury mild hypothermia completely inhibits the cerebral lactate accumulation, and early postinjury mild hypothermia significantly blunts the increase of cerebral lactate level after fluid percussion injury.

Perfusion-limited recovery of evoked potential function after spinal cord injury

STUDY DESIGN

The current study was designed to determine whether progressive spinal cord damage during residual compression is caused by low blood flow and ischemia.

OBJECTIVES

The purpose of this experiment was to determine the effects of sustained spinal cord compression on regional blood flow and evoked potential recovery after time-dependent decompression.

SUMMARY OF BACKGROUND DATA

Spinal cord injury after trauma is commonly associated with residual cord compression. Although decreased blood flow has been reported after spinal cord contusion, the effect of residual spinal cord displacement on reperfusion of blood flow or recovery of neurologic function remains unclear.

METHODS

Eighteen beagles were anesthetized, and the spinal cord at T13 was loaded dorsally under precision loading conditions until evoked potential amplitudes were reduced by 50%. At this function endpoint, spinal cord displacement was maintained for 90 minutes. Somatosensory-evoked potentials were measured at regular intervals until 3 hours after decompression. Regional spinal cord blood flow was measured with a fluorescent microsphere technique at regular time points during and after spinal cord decompression.

RESULTS

Within 5 minutes after dynamic cord compression was discontinued, evoked potential signals were absent in all dogs. Evoked potential recovery was observed after decompression in 7 of 18 dogs. Regional spinal cord blood flow at baseline, 21.8 +/- 1.9 mL/100 g. min (mean +/- SE), decreased to 3.9 +/- 0.9 mL/100 g. min after dynamic compression was discontinued. Although spinal cord-piston interface pressure dissipated by 87% of maximum interface pressure during sustained compression, mean blood flow recovered to only 34% of baseline flow. In the 7 dogs that recovered evoked potential function, blood flow increased to 11.3 +/- 2.7 mL/100g. min immediately before decompression (P < or = 0.05). In the 11 dogs that did not recover evoked potential function after decompression, regional blood flow did not improve during sustained compression.

CONCLUSIONS

Recovery of evoked potential function after decompression corresponded with a greater return of blood flow during sustained displacement and greater reperfusion of blood flow associated with decompression.

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.

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.

Lactate and excitatory amino acids measured by microdialysis are decreased by pentobarbital coma in head-injured patients

Primary traumatic brain injury and secondary ischemic/hypoxic injury are being increasingly characterized at the neurochemical level. Neurochemical monitoring using microdialysis has shown that these forms of tissue damage share many common features. In particular, anaerobic glycolysis with increased lactate production and release of excitatory amino acids into the extracellular space are seen in both conditions. Clinical microdialysis studies have heretofore focused on methodological issues, establishment of basal analyte values, and clinico-neurochemical correlation. Here we report the neurochemical consequences of therapeutic intervention in head injury. Specifically, induction of thiopental coma to manage severe increased intracranial pressure in seven patients was associated with a 37% reduction of lactate, 59% reduction of glutamate, and 66% reduction in aspartate in the extracellular space of the brain.

Lactic acid and amino acid fluctuations measured using microdialysis reflect physiological derangements in head injury

We examined the extracellular neurochemical milieu in 34 head injured patients using microdialysis while simultaneously monitoring intracranial pressure, cerebral perfusion pressure, and jugular venous oxygen saturation. Derangements of anaerobic metabolism reflected by increased lactate and lactate/pyruvate ratios, and release of amino acids were seen at the same time as physiological deterioration in the majority of instances. Clinical microdialysis may provide insights into the neurochemistry of head injury, and such information may lead to new methods of monitoring and treating head injured patients.

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)

Diffuse prolonged depression of cerebral oxidative metabolism following concussive brain injury in the rat: a cytochrome oxidase histochemistry study

Utilizing a lateral fluid percussion injury as a model of cerebral concussion, rats were studied histochemically measuring the degree of cytochrome oxidase activity present within different structures at different times following injury. After concussion, the cerebral cortex ipsilateral to the site of injury exhibited a diffuse decrease in its level of chromotome oxidase (CO) activity beginning at as soon as one day and lasting for up to 10 days after the insult. The ipsilateral dorsal hippocampus also exhibited an injury-induced decrease in CO activity, however, it was not as severe as in the cortex. These results indicate that oxidative metabolism is depressed primarily within the cerebral cortex and hippocampus for several days following a cerebral concussion. We propose that this period of metabolic depression may delineate a period of time during which the injured brain is unable to function normally and thus would be vulnerable to a second insult.