Effect Of Tirilazad Mesylate Research Articles

Significance of Experimental Infarct Size as an Indicator of Therapeutic Efficacy in Humans

To the Editor: We would like to make a comment not in particular to the article by Shimamura et al1 but to the use of infarct size in animal experiments as a guide to human cerebrovascular research. Many human studies of treatments with neuroprotective agents for acute ischemic stroke, which had good experimental potential, had disappointing clinical results. This failure can be attributed to many factors.2 One of the main problems is that reliance on infarct size measurement alone in animals can be misleading as an indicator of therapeutic efficacy in humans.3 We know for example that nitric oxide synthase (NOS) inhibitors have provided significant neuroprotection in experimental animals subjected to focal ischemia.4,5 Tirilazad mesylate is a potent inhibitor of lipid peroxidation caused by …

Cyclophosphamide is neuroprotective in a gerbil model of transient severe focal cerebral ischemia: correlation with effects of tirilazad mesylate (U-74006F).

Using a gerbil model of severe, temporary focal ischemia (3 h unilateral carotid occlusion), preliminary experiments identified an involvement of neutrophils in the reperfusion injury to the ischemic hemisphere. The present experiments were designed to (1) quantitate the temporal accumulation of neutrophils in the gerbil model, (2) determine if cyclophosphamide-induced neutropenia provided cytoprotection to the ischemic hemisphere, and (3) attempt to correlate the cytoprotective efficacy of tirilazad mesylate with possible effects on postischemic neutrophil accumulation. Following 3 h of unilateral carotid occlusion, animals were collected at increasing times of reperfusion and the CA1 region of the hippocampus and the lateral cortex were assessed for postischemic neuronal damage using a semiquantitative index (N.D.I.) of 0 (no damage) to 4 (>75% neuronal loss). The extent of neutrophil accumulation was determined by counting intensely cytochrome oxidase-positive cells. Minimal neuronal death was evident after 2 h of reperfusion, mean N.D.I. = 0.36. However, between 2 and 4 h of reperfusion, neuronal death did not increase. By 6 h of reperfusion, the neuronal death began to proceed at an accelerated rate, N.D.I. = 0.78. By 12 h, the N.D.I. reached 3.20. The accelerated neuronal death coincided with parenchymal invasion of neutrophils. Cyclophosphamide administration delayed neuronal death in the hippocampus, but exhibited a more sustained protective effect in the lateral cortex. Administration of tirilazad mesylate also resulted in a significant reduction in neutrophil accumulation and significant neuronal protection in both brain areas. Thus, in this gerbil model of transient, but prolonged focal cerebral ischemia, neutrophils appear to play an active role in the reperfusion injury to brain tissue. Our experiments confirm the previously demonstrated neuroprotective efficacy of tirilazad mesylate in this model and provide evidence for a similar protective effect of cyclophosphamide. Although other effects of this antioxidant are also thought to contribute to the overall efficacy, the data are consistent with the hypothesis that one mechanism by which tirilazad acts involves limiting the ability of neutrophils to participate in the reperfusion phase of ischemic cerebral injury.

Effect of Tirilazad Mesylate on Middle Cerebral Artery Occlusion/Reperfusion in Nonhuman Primates

Agents with lipid membrane protective properties may theoretically reduce the zone of ischemic damage during cerebral arterial recanalization in the early hours of focal cerebral ischemia. The effect of the putative lipid peroxidation inhibitor tirilazad mesylate (U74006F) on infarction volume and neurological outcome following 3-hour middle cerebral artery occlusion and subsequent reperfusion in an awake baboon model was examined in a blinded, randomized placebo-controlled study. Awake subjects (8 each) were assigned randomly to receive either tirilazad mesylate (3 mg/kg) or matched vehicle given 15 min prior to reperfusion, and again at 2, 4, 12, and 24 h after reperfusion. Neurological status was serially assessed according to a quantitative scale and infarction volumes were computed on perfusion-fixed specimens at 14 days. A 40% reduction in mean total infarction volume index, normalized for basal ganglia volume, was seen in the tirilazad group. Persistent and increased improvement in mean neurological score with tirilazad infusion paralleled that of the placebo. Parallel studies on polymorphonuclear leukocyte responses indicated no significant changes in polymorphonuclear leukocyte reactivity. A reduction in infarction volume, predominantly in the cortex/subcortical white matter, and an improvement in neurological outcome were observed when tirilazad mesylate was given prior to reperfusion, but after the onset of focal cerebral ischemia.

Effect of tirilazad mesylate given after permanent middle cerebral artery occlusion in rat.

The effect of the antioxidant drug tirilazad mesylate (U-74006F) on histopathological and neurological outcome 3 days after permanent middle cerebral artery (MCA) occlusion was evaluated in rats. Several previous studies have demonstrated the efficacy of tirilazad in reducing infarct size when administered before and during MCA occlusion, whereas post-treatment may be less effective in permanent focal ischaemia. We sought to determine if a protective effect of tirilazad could be demonstrated when administered after the insult only. U-74006F (3 mg/kg, i.v.) or sterile vehicle, was randomly given to rats 10 minutes and 3 hours after permanent MCA occlusion produced by transcranial proximal electrocauterization. Infarct volume and hemisphere volumes were estimated blindly from histological sections of defined levels of the brain after 72 h of ischaemia. Neurological score was determined blindly 1, 2, and 3 days after insult. There was no significant difference in infarct volume, volume of non-infarcted tissue, or neurological score between the tirilazad and placebo-treated rats. In conclusion, our results support the conception that post-treatment with tirilazad mesylate is not efficacious in reducing infarct size in permanent focal ischaemia, while pre-treatment, as reported by other groups, appears to be effective in both permanent and temporary focal ischaemia models. In temporary focal ischaemia, the limited data available suggest that also post-treatment with tirilazad may prove to be neuroprotective.

Effects of tirilazad mesylate on postischemic brain lipid peroxidation and recovery of extracellular calcium in gerbils.

We describe the effects of the 21-aminosteroid tirilazad mesylate (U-74006F) on postischemic lipid peroxidation (depletion of brain vitamin E) and cortical extracellular calcium recovery in gerbils subjected to 3 hours of unilateral carotid artery occlusion. Male gerbils were treated with either 0.2 ml vehicle (0.05N HCl) or 10 mg/kg i.p. U-74006F 10 minutes before the induction of ischemia and again immediately after the initiation of reperfusion. In the first series of experiments, the brain concentration of vitamin E, which was unaffected by ischemia without reperfusion, was decreased after 2 hours of reperfusion by an average of 60% in vehicle-treated animals compared with sham-operated animals; in the U-74006F-treated gerbils, the 2-hour postischemic vitamin E loss was only 27% (p less than 0.002 different from vehicle-treated animals). In the second series, unilateral carotid artery occlusion produced a decrease in the cortical extracellular calcium concentration from 1.05 mM before ischemia to 0.11 mM by the end of the ischemic episode in both vehicle- and U-74006F-treated gerbils. After 2 hours of reperfusion, the calcium concentration had recovered to only 0.22 mM in the vehicle-treated animals compared with 0.56 mM in the U-74006F-treated group (p less than 0.01). Cortical blood flow, mean arterial blood pressure, and blood gases did not differ significantly between the two treatment groups. Administration of only the immediate postreperfusion dose (i.e., no pretreatment) also significantly improved the recovery of cortical extracellular calcium. The results indicate that U-74006F inhibits postischemic lipid peroxidation as assessed by the preservation of brain vitamin E and that, secondary to this membrane-protective effect, the processes responsible for the reversal of ischemia-triggered intracellular calcium accumulation are preserved.