Eugene D. Means

Spinal cord injury and protection

Subsequent to traumatic injury of the spinal cord, a series of pathophysiological events occurs in the injured tissue that leads to tissue destruction and paraplegia. These include hemorrhagic necrosis, ischemia, edema, inflammation, neuronophagia, loss of Ca2+ from the extracellular space, and loss of K+ from the intracellular space. In addition, there is trauma-initiated lipid peroxidation and hydrolysis in cellular membranes. Both lipid peroxidation and hydrolysis can damage cells directly; hydrolysis also results in the formation of the biologically active prostaglandins and leukotrienes (eicosanoids). The time course of membrane lipid alterations seen in studies of antioxidant interventions suggests that posttraumatic ischemia, edema, inflammation, and ionic fluxes are the result of extensive membrane peroxidative reactions and lipolysis that produce vasoactive and chemotactic eicosanoids. A diverse group of compounds has been shown to be effective in ameliorating spinal cord injury in experimental animals. These include the synthetic glucocorticoid methylprednisolone sodium succinate (MPSS); the antioxidants vitamin E, selenium, and dimethyl sulfoxide (DMSO); the opiate antagonist naloxone; and thyrotropin-releasing hormone (TRH). With the exception of TRH, all of these agents have demonstrable antioxidant and/or anti-lipid-hydrolysis properties. Thus the effectiveness of these substances may lie in their ability to quench membrane peroxidative reactions or to inhibit the release of fatty acids from membrane phospholipids, or both. Whatever the mode of action, early administration appears to be a requirement for maximum effectiveness.

Thrombin Interactions with Central Nervous System Tissue and Implications of These Interactionsa

A monospecific antibody was developed to human alpha-thrombin. This antibody stained neurons but not astrocytes in murine spinal cord cultures incubated with 1-10 nM alpha-thrombin using the avidin-biotin-peroxidase technique. Staining did not occur when the primary or linking antibodies were eliminated, and staining was blocked with hirudin. Preliminary studies showed release of arachidonic acid from the cultures when exposed to thrombin. It was proposed that arachidonate release from the membranes of neurons upon exposure to thrombin was similar to that observed in platelets, for example, by activation of phospholipases. Moreover, prostanoids were formed that could have a deleterious effect on cellular elements in the central nervous system. The potential role of thrombin receptors on neurons was discussed.

Methylprednisolone and membrane properties of primary cultures of mouse spinal cord

The present study attempts to define the capacity of methylprednisolone sodium succinate (MP) to protect neuronal membranes against a free radical challenge in primary cultures of fetal mouse spinal cord. Incubation of these cultures with MP significantly increased the Na+,K(+)-ATPase activity, an effect that was blocked by the RNA synthesis inhibitor, actinomysin D and the protein synthesis inhibitor, cycloheximide, suggesting an induction of protein synthesis by MP. In contrast, incubation with FeCl2 for 1 or 2 h significantly inhibited Na+,K(+)-ATPase activity and elevated the levels of thiobarbituric acid-reactive substances (TBARS). Pretreatment with MP prevented the rise in TBARS and partially prevented the decrease in Na+,K(+)-ATPase activity for the first hour of FeCl2 incubation, an effect that was lost during the second hour. A second dose of MP after the first hour of incubation with FeCl2 partially restored Na+,K(+)-ATPase activity and reduced TBARS levels after the second hour of exposure to FeCl2. Co-incubation of MP with cycloheximide completely prevented the decrease in Na+,K(+)-ATPase activity seen after a 2-h incubation with FeCl2 and eliminated the need for a second dose of MP after the first hour of incubation with FeCl2. These findings suggest a capacity for rapid protein induction and antioxidant activity for MP in vitro.

Early membrane lipid changes in laminectomized and traumatized cat spinal cord.

The effects of surgical exposure (laminectomy) and compression trauma on various aspects of membrane lipid metabolism in the feline spinal cord were determined in this study. Tissue samples were frozen in situ and grossly dissected into gray and white portions prior to lipid analyses. Laminectomy alone resulted in measurable changes in spinal cord lipid metabolism, including increases in gray matter free fatty acids, diacylglycerols, and eicosanoids. A 90-min recovery period greatly reduced the levels of these compounds. Compression of the spinal cord with a 170-g weight (following a 90-min recovery period) caused very large increases in gray matter free fatty acids, diacylglycerols, and eicosanoids, and decreases in cholesterol and ethanolamine plasmalogens. Similar, but time delayed changes in these compounds were also observed in white matter.

The kappa opioid-related anticonvulsants U-50488H and U-54494A attenuate N-methyl-D-aspartate induced brain injury in the neonatal rat

The neuroprotective effects of the kappa opioid-related anticonvulsants U-50488H and U-54494A were tested in a model of N-methyl-D-aspartate (NMDA)-induced brain injury in the neonatal rat. Seven-day-old rat pups were injected intracerebrally with 7.5 nmol NMDA. Five days later, the ensuing unilateral hemisphere weight reduction was measured and used to assess the severity of insult. Control animals (n = 85) exhibited a 21.7 +/- 0.5% hemisphere weight reduction. Animals treated with U-54494A in split doses before and after NMDA administration showed significant neuroprotection at 10, 15, and 20 mg/kg, with the maximum effect observed at 15 mg/kg (33.8% protection). Animals treated with U-50488H on a similar dosing schedule showed significant neuroprotection at all doses tested, with peak protection observed at 30 mg/kg (51.8% protection). Both compounds exhibited a neuroprotective effect when hemisphere cross-sectional area and hippocampal histology were assessed. Treatment with U-54494A after NMDA administration also afforded neuroprotection at various doses, as measured by hemisphere weight disparity, with peak protection occurring at a dose of 20 mg/kg (32.4% protection). These data show that both U-50488H and U-54494A afford neuroprotection against NMDA-induced neuronal injury in the neonatal rat brain.

Susceptibility of feline spinal cord energy metabolism to severe incomplete ischemia

Feline spinal cords were subjected to 10 to 30 minutes of severe incomplete ischemia (average reduction in blood flow of 92%) with and without 90 minutes of recirculation, and the L-2 segment was analyzed for high-energy phosphates and certain glycolytic metabolites. Spinal cord tissue lactic acid levels were stepwise elevated, and adenosine triphosphate (ATP), phosphocreatine (P-creatine), and glucose were progressively consumed by increasing durations of ischemia. However, upon restoration of blood flow, there was extensive recovery of energy metabolites and normalized lactic acid, demonstrating resumption of mitochondrial oxidative metabolism. These data indicate that the spinal cord can tolerate at least 30 minutes of severely reduced blood flow before recovery of energy metabolism is significantly impaired upon restitution of blood flow.

21-Aminosteroids ("lazaroids").

Acute central nervous system (CNS) injury, eg, ischemia, trauma, results in the almost immediate death of neurons. Surrounding tissue is at risk for further cell death. This circumjacent tissue has been labeled tissue-at-risk or the ischemic penumbra. A complex interrelated series of pathophysiological events occurs in this vulnerable tissue which, if not interrupted, will inexorably progress to tissue necrosis (secondary injury).1 A discussion of the various factors involved in this secondary injury cascade are beyond the scope of this chapter. However, one of the pathophysiological events believed to play a crucial role in this injury cascade is free radical-mediated lipid peroxidation.