Further studies on free-radical pathology in the major central nervous system disorders: effect of very high doses of methylprednisolone on the functional outcome, morphology, and chemistry of experimental spinal cord impact injury.

The hypothesis that pathologic free-radical reactions are initiated and catalyzed in the major central nervous system (CNS) disorders has been further supported by the current acute spinal cord injury work that has demonstrated the appearance of specific, cholesterol free-radical oxidation products. The significance of these products is suggested by the fact that: (i) they increase with time after injury; (ii) their production is curtailed with a steroidal antioxidant; (iii) high antioxidant doses of the steroidal antioxidant which curtail the development of free-radical product prevent tissue degeneration and permit functional restoration. The role of pathologic free-radical reactions is also inferred from the loss of ascorbic acid, a principal CNS antioxidant, and of extractable cholesterol. These losses are also prevented by the steroidal antioxidant. This model system is among others in the CNS which offer distinctive opportunities to study, in vivo, the onset and progression of membrane damaging free-radical reactions within well-defined parameters of time, extent of tissue injury, correlation with changes in membrane enzymes, and correlation with readily measurable in vivo functions.

The effect of dihydroergotoxine on lipid peroxidation in vitro.

Dihydroergotoxine mesylate (DHET), an ergot alkaloid derivative, is widely used to treat senile cerebral vascular insufficiency. Aspects of this age-related phenomenon may be due to deterioration by lipid oxidation of cellular membranes. DHET stabilizes EEG alpha frequencies, increases cerebral blood flow and oxygen uptake and accumulates in lipid-rich structures of the brain. The effect of DHET was studied on iron-catalyzed peroxidation of liposomes as measured by the thiobarbituric acid assay. It was found that DHET inhibits peroxidation in vitro in a dose-dependent manner. These results suggest that DHET acts in part as a lipid antioxidant when used to treat senile cerebral vascular insufficiency.

Loss of essential membrane lipids and ascorbic acid from rat brain following cryogenic injury and protection by methylprednisolone.

Previous work has shown that unsaturated fatty acid components of model membrane phospholipids in vitro, damaged via a free radical mechanism, are protected by the presence of cholesterol in these membranes. The participation of these membrane lipids in the pathogenesis of traumatic injury to brain was studied in vivo using the Klatzo method of cryogenic injury in rats. Increased edema 4 hr after cryogenic injury was noted on the lesioned side. Total cerebral cholesterol was decreased significantly in the lesioned hemispheres 10 hr following injury. In lesioned animals pretreated and post-treated with methylprednisolone, there were no significant differences in the cholesterol levels. Arachidonic acid isolated from total membrane phospholipids was significantly reduced on the injured side 24 hr after injury, but not before. Other fatty acids were not significantly affected. Methylprednisolone treatment prevented the decrease in arachidonic acid. Animals that had received a cold injury had significant decreases in ascorbic acid levels after 4 hr on the lesioned side of the brain. This decrease was significantly ameliorated by corticosteroid administration. These results support the hypothesis that the protective effect of corticosteroids in cryogenic cerebral trauma may be due to antioxidant protection of major cell membrane lipid components such as cholesterol and phospholipids.

Spontaneous generation of adriamycin semiquinone radicals at physiologic pH.

Adriamycin semiquinone radicals are spontaneously generated by adriamycin solutions at physiologic pH. Rate of radical formation and equilibrium-state radical yield increase with increasing pH from 7.4 to 8.85. The radicals are oxygen sensitive, but the mechanism of radical formation is oxygen independent and associated with proton removal from the dihydroquinone of adriamycin. The less cardiotoxic and non-mutagenic (Ames test) anthracycline 5-iminodaunorubicin does not form semiquinone radicals spontaneously at physiologic pH.

Free radicals in cerebral ischemia.

The possibility that cerebral ischemia may initiate a series of pathological free radical reactions within the membrane components of the CNS was investigated in the cat. The normally occurring electron transport radicals require adequate molecular oxygen for orderly transport of electrons and protons. A decrease in tissue oxygen removes the controls over the electron transport radicals, and allows them to initiate pathologic radical reactions among cell membranes such as mitochondria. Pathologic radical reactions result in multiple products, each of which may be present in too small a concentration to permit their detection at early time periods. It is possible to follow the time course, however, by the decrease of a major antioxidant as it is consumed by the pathologic radical reactions. For this reason, ascorbic acid was measured in ischemic and control brain following middle cerebral artery occlusion. There was a progressive decrease in the amount of detectable ascorbic acid ranging from 25% at 1 hour to 65% at 24 hours after occlusion. The reduction of this normally occurring antioxidant and free radical scavenger may indicate consumption of ascorbic acid in an attempt to quench pathologic free radical reactions occurring within the components of cytomembranes.

Ethanol potentiation of central nervous system trauma.

Two models have been used to study the effects of ethanol on injuries of the central nervous system. The spinal cords of cats were injured by delivering a 200 gm-cm impact to the exposed dura mater. A second group of animals received a similar injury to the exposed dura mater overlying the cerebral hemispheres. The animals were divided into two groups, those that received an infusion of ethanol before injury, and control animals that received no ethanol. The parameters of injury used in this model produced small and insignificant lesions in those animals that received no ethanol; however, when the animals were pretreated with ethanol, a considerable increase in the extent of the injury was noted. These include alterations in membranes-bound enzymes and clotting mechanisms, and alteration of cell membranes through abnormal free radical reactions.

Retarding effects of DNA on the autoxidation of liposomal suspensions.

Deoxyribonucleic acid (DNA) is associated with the cell membrane of prokaryotes and the inner nuclear membrane of eukaryotes. The unsaturated fatty acids of phospholipids, which constitute the bilaminar structure of membranes, undergo autoxidation in the presence of O2. Calf thymus DNA was incuabted with methyl archidonate-enriched phosphatidyl choline liposomes in order to study the effect of DNA upon the oxidation of phospholipids while present in their natural in vivo bilayer configuration. DNA retarded the rate of lipid oxidation as monitored by both diene conjugation and the TBA test, but it did not alter the induction period. These results suggest that DNA is scavenging free radicals produced within the phospholipid bilayer.