Role of Lipid Peroxidation in Post-Traumatic Spinal Cord Degeneration: A Review

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Abstract
A large amount of biochemical, physiological, and pharmacological data has been obtained which supports a mechanistic role of oxygen free radical-induced lipid peroxidaton (LP) in post-traumatic spinal cord degeneration. Biochemical evidence of early and progressive lipid peroxidative reactions occurring in the injured spinal cord includes: 1) an increase in polyunsaturated fatty acid peroxidation products (e.g., malonyldialdehyde), 2) a decrease in cholesterol and the appearance of cholesterol oxidation products, 3) an increase in cyclic GMP presumably due to free radical activation of guanylate cyclase, 4) a decrease in tissue anti-oxidant levels (e.g., alpha tocopherol, reduced ascorbate), and 5) inhibition of membrane-bound enzymes such as Na+ K+-ATPase. In vitro CNS tissue studies have provided support for the possibility that LP may contribute to other early post-traumatic events including intracellular calcium accumulation and arachidonic acid release. Moreover, spinal tissue lactic acidosis, which occurs early after injury, can exacerbate LP reactions. The involvement of LP in the development of progressive post-traumatic spinal white matter ischemia has been strongly inferred from pharmacological studies in cats with known inhibitors of LP. For example, the dose-response curves for the ability of the glucocorticoid methylprednisolone (MP) to inhibit post-traumatic LP and to retard ischemia development are identical. This relationship between LP and post-traumatic ischemia is more directly implied from studies showing that pretreatment of cats with high doses of anti-oxidants (e.g., d-alpha tocopherol plus selenium p.o. or 1-ascorbic acid i.v.) can also significantly antagonize the progressive decrease in spinal cord blood flow that follows severe blunt injury. However, a similar efficacy of certain calcium and prostaglandin antagonists suggests an interrelationship between aberrant calcium fluxes, vasoconstrictor/platelet aggregating prostanoids, and LP in the post-traumatic ischemic phenomenon. In addition to a role of LP in ischemia development, the action of intensive d-alpha tocopherol and selenium pretreatment to retard anterograde cat motor nerve fiber degeneration after nerve section suggests that LP may also be a fundamental mechanism of "Wallerian" axonal degeneration after neural injury. Finally, a critical role of LP in the acute pathophysiology of CNS injury in general has been supported by the finding of an excellent correlation, in terms of efficacy and potency, between the action of glucocorticoid and nonglucocorticoid steroids to inhibit neural tissue LP in vitro and to promote early neurological recovery in severely head-injured mice. Key Words: Lipid peroxidation, Spinal cord injury, Ischemia, Degeneration, Steroids, Anti-oxidants.