Abstract:The time course and intensity of brain hydroxyl radical ('OH) generation were examined in male CF-I mice during the first hour after moderate or severe concussive head injury. Hydroxyl radical production was measured using the salicylate trapping method in which the production of 2.3-and/or 2.5-dihydroxybenzoic acid (DHBA) in brain 15 min after salicylate administration was used as an index of 'OH formation. In mice injured with a concussion of moderate severity asdefined by the I-h posttraumatic neurologic recovery (grip score), a 60% increase in 2,5-DHBA formation was observed by 1 min after injury compared with that observed in uninjured mice. The peak in DHBA formation occurred at 15 min after injury (+67.5%; p < 0.02, compared with uninjured). At 30 min, the increase in DHBA lost significance, indicating that the posttraumatic increase in brain 'OH formation is a transient phenomenon. In severely injured mice, the peak increase in DHBA (both 2,3-and 2,5-) was observed at 30 min after injury, but also fell off thereafter as with the moderate injury severity. Preinjury dosing of the mice with SKF-525A (50 mg/kg i.p.), an inhibitor of microsomal drug oxidations, did not blunt the posttraumatic increase in salicylate-derived 2,5-DHBA, thus showing that it is not due to increased metabolic hydroxylation. Neither injury nor SKF-525A administration affected the DHBA plasma levels. However, saline perfusion of the injured mice to remove the intravascular blood before brain removal eliminated the injury-induced increase in 2,5-DHBA, but did not affect the baseline levels seen in uninjured mice. This implies that the source of the increased DHBA in the injured mice is the microvasculature, probably the endothelium. The administration of the 2 1 -aminosteroid lipid antioxidant, tirilazad mesylate, which possesses 'OH scavenging properties, also attenuated the posttraumatic increase in DHBA, further supporting that it reflects an increase in 'OH radical formation. These results are the first direct demonstration of the occurrence and time course of increased 'OH production in injured brain. Key Words: Hydroxyl radical-Concussion-Salicylate trapping-Brain. Hall E. D. et al. Brain hydroxyl radical generation in acute experimental head injury. J. Neurochem. 60, 588-594 (1 993).

The ability of the nonglucocorticoid 21-aminosteroid U74006F, a potent inhibitor of iron-dependent lipid peroxidation, to antagonize progressive brain hypoperfusion after a 5-minute episode of global brain ischemia was examined in a-chloralose-anesthetized cats. Immediately after a 5-minute episode of near-total tourniquet-induced brain ischemia, cortical blood flow returned to normal or above normal. Thereafter, cortical blood flow fell progressively to a level 71.7% below normal by 3 hours after ischemia. In contrast, in cats that received 1 mg/kg i.v. U74006F 15 minutes after the ischemlc episode, cortical blood flow remained significantly greater than that seen in vehicle-treated cats. At 3 hours, cortical blood flow had declined by only 45.7% (p < 0.04 compared with vehicle). In addition, U74006F treatment significantly improved postischemic maintenance of blood pressure and recovery of somatosensory evoked potentials and reduced postischemic arterial blood acidosis. U74006F had no effect on cortical blood flow, somatosensory evoked potentials, or blood pressure in nonischemic cats. Our results suggest that U74006F may be useful in the early treatment of global cerebral ischemia. (Stroke 1988;19:340-344) E xtensive studies have shown that temporary cerebral ischemia results in an initial period of postischemic brain hyperperfusion followed by a sustained and progressive hypoperfusion, the extent of which depends upon the severity and duration of the ischemic period. "6 Recent work has supported the concept that postischemic hypoperfusion can be a primary factor limiting recovery of cerebral energy metabolism.6 Furthermore, the delayed decrease in cerebral blood flow may, if of sufficient magnitude, produce a secondary ischemic brain insult.While the mechanism(s) of postischemic hypoperfusion are unknown, some investigators have postulated that oxygen-free-radical-induced microvascular lipid peroxidation (LP) may be a contributing factor. 7 Likewise, progressive microvascular LP has been convincingly implicated in relation to development of posttraumatic central nervous system (CNS) ischemia (i.e., hypoperfusion). 8 -9 Thus, considering the possible involvement of oxygen radicals and LP in delayed hypoperfusion, we have investigated the ability of the nonglucocorticoid 21-aminosteroid U74006F to attenuate cerebral hypoperfusion in cats after a brief episode of near-complete global brain ischemia. U74006F has been shown to be an extremely potent and effective inhibitor of irondependent LP in CNS tissue in vitro. 10 Other studies have demonstrated an action of U74006F to retard the development of posttraumatic spinal cord ischemia." Materials and Methods GeneralAdult female specific-pathogen-free cats from Liberty Laboratories (Liberty Corners, New Jersey) Received March 27, 1987; accepted August 21, 1987. weighing 2.5-3.5 kg were anesthetized with 50 mg/kg i.v. a-chloralose in 0.9% saline. A tracheostomy was performed, and femoral venous and arterial cannulas were inserted unilaterally. The cats were...

In the present study, the ability of U74006F, the 21-aminosteroid inhibitor of lipid peroxidation, to attenuate posttraumatic spinal cord ischemia has been examined in cats following a moderately severe compression injury. Moreover, in an attempt to assess whether U74006F is affecting in vivo posttraumatic lipid peroxidation, the effect of the compound on injury-induced spinal tissue vitamin E depletion was also studied. Following an initial 10 min postinjury hyperperfusion (+45%), spinal cord blood flow (SCBF) returned to the preinjury level at 30 min before entering a phase of progressive hypoperfusion, which reached -42.0 +/- 4.5% by 4 h postinjury in the vehicle-treated animals. In animals that received 30 min postinjury U74006F i.v. doses of 1.0, 3.0, or 10 mg/kg (plus 0.5, 1.5, and 5.0 mg/kg maintenance doses at 2.5 h.), the SCBF decline was reduced to -23.1%, -22.9%, and -26.1%, respectively (p less than 0.05 vs. vehicle at all three doses). A 0.3 mg/kg dose did not reduce the posttraumatic fall in SCBF. In vehicle-treated cats, the vitamin E content of the injured cord segment was reduced by 78.9% at 4 h postinjury in comparison to cord samples from uninjured vehicle-treated cats. In contrast, the same doses of U74006F (1.0, 3.0, and 10 mg/kg) that attenuated posttraumatic ischemia also significantly reduced the depletion of cord vitamin E. The lowest U74006F dosage (0.3 mg/kg), which failed to affect posttraumatic ischemia development, also had no effect on spinal cord vitamin E content.(ABSTRACT TRUNCATED AT 250 WORDS)

INTRODUCTIONOxygen-free radicals have been postulated to play a role in the acute pathophysiology of blunt head injury.14. Much of this work points to the cerebral microvasculature as a major target of oxygen radical-mediated damage. Moreover, free-radical scavengers such as superoxide dismutase' and lipid antioxidants, including methylprednisolone,h U-72099E,' U-74006F,X and U-78517F: which block free radical damage to membrane polyunsaturated fatty acids (i.e., lipid peroxidation), have been reported to attenuate posttraumatic pathophysiology and/or to promote survival and recovery in experimental head injury. However, a firm association of oxygen radicals and lipid peroxidation with pathophysiological events has been hindered by the lack of analytical methodology that will directly measure cerebral tissue levels of specific radicals or lipid hydroperoxides.In recent studies in both the mouse concussive and the rat controlled cortical impact head injury models, we have directly measured brain hydroxyl radical (.OH) levels via the salicylate trapping method in which the production of 2,3-and/or 2,5-dihydroxybenzoic acid (DHBA) in brain, 15 min after salicylate administration was used as an index of .Ou formation.'" In the mouse model, we have also examined the brain levels of enzymatically derived eicosanoids (e.g., PGFZa, PGE2, TXB2, 6-keto PGFI,, LTC.,). Additionally, in the rat model, we have employed the highpressure liquid chromatographic-chemiluminescence (HPLC-CL) method" to measure the lipid peroxidation product, phosphatidylcholine hydroperoxide (PCOOH), and its time course in relation to that of .OH generation. Finally, to provide a pathophysiological correlation, we have further compared the time course of bloodbrain barrier (BBB) disruption in both models as an index of microvascular damage by oxygen radical-induced lipid peroxidation. These studies have shown a clear association between posttraumatic -OH generation, membrane lipid peroxidation, and subsequent increases in cerebral microvascular permeability.

Methylprednisolone (MP) improves motor recovery in spinal cord-injured patients when administered in a 24 h intensive high dose regimen beginning within 8 h after spinal cord injury (SCI). The rationale for this regimen has been based upon the need for high doses (i.e., 30 mg/kg initial IV dose) to inhibit posttraumatic lipid peroxidation (LP) in the injured spinal segment. However, injury also triggers the immediate calcium-mediated activation of phospholipase A2 (PLA2), the release of arachidonic acid, and the enzymatic formation of potentially deleterious prostaglandins (PGE2 alpha, PGE2), thromboxane A2 (TXA2), and leukotrienes (LTs). Thus, in view of the glucocorticoid receptor-mediated inhibition of PLA2 that underlies much of MP's antiinflammatory actions, an additional neuroprotective mechanism may relate to an inhibition of eicosanoid formation. Using the cat spinal cord compression model (180g x 5 min at L3; Na pentobarbitol anesthesia), we examined whether 30 min postinjury dosing with MP (30 mg/kg IV) could attenuate spinal tissue eicosanoid levels measured by enzyme immunoassay at 1 h (Experiment 1). Pial blood flow was measured over the dorsal columns at the injury site using laser doppler flowmetry to monitor posttraumatic hyperperfusion as an index of the microvascular pathophysiology of acute SCI. In vehicle treated animals at 1 h postinjury, there was a significant increase in the tissue levels of PGF2 alpha (+290%), PGE2 (+260%), TXB2 (stable analog of TXA2, +126%), and LTB4 (+73%) in comparison to sham, uninjured animals. However, 6-keto-PGF1 alpha (stable analog of prostacyclin or PGI2) and LTC4 did not increase. Methylprednisolone did not reduce the increase in eicosanoid production. In the case of LTB4 and LTC4, MP actually increased the levels further. In addition, we examined the effects of a double dose MP regimen (30 mg/kg IV at 30 min plus 15 mg/kg IV at 2.5 h postinjury) on spinal cord eicosanoid levels at 4 h postinjury (Experiment 2). At 4 h postinjury, significant increases in PGF2 alpha, PGE2, TXB2, and 6-keto-PGF1 alpha were observed, and with the exception of PGE2, no MP attenuation of the increased eicosanoids was seen. These results fail to provide evidence that postinjury administration of high dose MP exerts a significant anti-PLA2 action. On the other hand, MP effectively inhibited secondary spinal cord pial hyperperfusion, which is believed to be largely mediated by free radical-lipid peroxidative mechanisms. Thus, it seems likely that the protective action of MP on the acute microvascular pathophysiology of SCI is mediated by its well-documented effects on posttraumatic LP.(ABSTRACT TRUNCATED AT 400 WORDS)