Preservation of motor nerve function during early degeneration by the 21-aminosteroid anti-oxidant U74006F

Limiting spinal cord injury by pharmacological intervention

The direct primary mechanical trauma to neurons, glia and blood vessels that occurs with spinal cord injury (SCI) is followed by a complex cascade of biochemical and cellular changes which serve to increase the size of the injury site and the extent of cellular and axonal loss. The aim of neuroprotective strategies in SCI is to limit the extent of this secondary cell loss by inhibiting key components of the evolving injury cascade. In this review we will briefly outline the pathophysiological events that occur in SCI, and then review the wide range of neuroprotective agents that have been evaluated in preclinical SCI models. Agents will be considered under the following categories: antioxidants, erythropoietin and derivatives, lipids, riluzole, opioid antagonists, hormones, anti-inflammatory agents, statins, calpain inhibitors, hypothermia, and emerging strategies. Several clinical trials of neuroprotective agents have already taken place and have generally had disappointing results. In attempting to identify promising new treatments, we will therefore highlight agents with (1) low known risks or established clinical use, (2) behavioral data gained in clinically relevant animal models, (3) efficacy when administered after the injury, and (4) robust effects seen in more than one laboratory and/or more than one model of SCI.

Attenuation of motor nerve terminal repetitive discharge by the 21-aminosteroid tirilazad: evidence of a neural calcium antagonist action

Pretreatment with the 21-aminosteroid antioxidant compound tirilazad mesylate has been previously shown to retard the axotomy-induced anterograde degeneration of soleus motor nerve terminals in the cat. In the present study, we examined tirilazad's effects (7.7, 13.0 or 30.0 mg/kg twice daily P.O. for 6 days) on the excitability of normal cat soleus motor nerve terminals. Low frequency (0.4 Hz) neuromuscular transmission was measured as well as the occurrence of muscle contractile potentiation in response to either a 400 Hz/10 s episode of tetanic conditioning stimulation of the soleus nerve or the administration of a 200 microg/kg i.v. dose of the neuromuscular facilitatory drug edrophonium. The mechanism of the post-tetanic potentiation (PTP) or edrophonium-induced facilitatory response involves the occurrence of a stimulus-dependent repetitive discharge of the soleus motor nerve terminals due to an exaggeration of the nerve terminal Ca2+-mediated after-depolarization. Tirilazad pretreatment caused a dose-related suppression of PTP and the edrophonium response indicative of a suppression of motor nerve terminal repetitive discharge. These effects were not shared by 6 days of oral pretreatment of cats with a high dose combination of the antioxidants vitamin E (200 I.U./day) and selenium (50 microg/day). Thus, it is unlikely that the antioxidant properties of tirilazad are involved in the suppression of motor nerve terminal excitability. Rather, it is proposed that tirilazad suppresses delayed motor nerve terminal Ca2+ conductances secondary to its ability to decrease membrane phospholipid fluidity, and that this action might in some circumstances contribute to its neuroprotective activity.

Lazaroids: Mechanisms of Action and Implications for Disorders of the CNS

Oxygen radical-induced lipid peroxidation to cerebrovascular or brain parenchymal cell membranes has been implicated as a pathophysiological mechanism in both acute and chronic neurodegenerative disorders, including brain and spinal cord trauma, ischemic and hemorrhagic stroke, Alzheimer's and Parkinson's diseases, and amyotrophic lateral sclerosis. As a result, pharmacological strategies have been aimed at antagonizing lipid peroxidative damage in a safe and effective manner. Perhaps the first successful antioxidant neuroprotective approach is high dose treatment with the glucocorticoid steroid methylprednisolone, which has been reported to be effective in improving neurological recovery after blunt spinal cord injury in animals and humans. After a determination that these effects were based upon inhibition of posttraumatic lipid peroxidative reactions rather than steroid receptor interactions, a new class of 21-aminosteroids (“lazaroids”) was discovered. The lazaroids are more effective inhibitors of lipid peroxidation and, at the same time, devoid of glucocorticoid side effect potential. One of them, tirilazad (U-74006F), was found protective in a variety of preclinical neuroprotection models and is currently the subject of Phase III clinical trials. Thus far, the compound has been demonstrated to significantly improve 3-month survival and neurological recovery after subarachnoid hemorrhage in humans. Although tirilazad does penetrate the injured CNS, much of its protective activity is mediated by an action on vascular endothelium. Recently, the 21-aminosteroids have been followed up with a newer series of non-steroidal compounds, the pyrrolopyrimidines, which possess even greater antioxidant efficacy and brain penetration that may be useful for the treatment of chronic neurodegenerative disorders.

Protective effect of 21-aminosteroid pretreatment in peripheral nerve low-load crush injury in mature and immature rats

The effects of U-74006F (tirilazad mesylate), a 21-aminosteroid antioxidant, on injured peripheral nerve were studied. Twenty-two immature and 44 mature rats were divided equally into two groups. The experimental group received two injections of 3 mg/kg of U-74006F at a 2 hour interval. The control group received the same volumes of a citrate buffer. A 5 mm segment of the sciatic nerve was subjected to a crush load of 100 g for 2 hours. Motor function (sciatic functional index) was assessed to day 48 postoperatively. There was total paralysis of the crushed limb in all rats the first week after crushing. The experimental group had a statistically significant improvement in motor function compared with the controls on days 14, 21, 25, and 28 for the mature rats and on days 11 and 14 for the immature rats. The mature controls attained complete recovery on day 42 and had a significantly slower recovery rate than the immature controls, which had recovered fully by day 25. The recovery rates were almost similar among mature and immature groups pretreated with U-74006F, both of which had fully recovered motor function by day 28. The results indicate that pretreatment with U-74006F can significantly promote peripheral nerve function after low-load crush injury and that the age of the animal influences the rate of peripheral nerve recovery.

Inhibition of lipid peroxidation attenuates axotomy-induced apoptotic degeneration of facial motor neurons in neonatal rats

The purpose of this study was to investigate the role of oxygen radical-induced lipid peroxidative mechanisms in trophic deprivation-induced apoptotic motor neuronal degeneration by testing the ability of the 21-aminosteroid lipid peroxidation inhibitor tirilazad mesylate (U-74006F) to attenuate the retrograde degeneration of facial motor neurons following axotomy in 14-day-old rat pups. On day 0, the right facial nerve of each rat was transected at its point of exit from the stylomastoid foramen. Pups were treated orally with either 10 or 30 mg/kg U-74006F or cyclodextrin vehicle 10 min before axotomy, and post-treated once a day from days 1 to 6, and then once every other day from days 8 to 21. The rats were sacrificed 3 weeks post-transection and the surviving motor neurons, identified through choline acetyltransferase immunocytochemistry, were counted in three regions (planes) in the facial nucleus. In vehicle-treated rats, 56.2% (region A), 50.6% (region B), and 57.4% (region C) of the motor neurons in the ipsilateral facial nucleus survived 21 days following facial nerve axotomy in comparison to the non-axotomized contralateral nucleus (P < 0.0001). Treatment with 10 mg/kg U-74006F significantly enhanced motor neuron survival in regions B and C to 72.8% (P < 0.01) and 66.7% (P < 0.02%), respectively. The 30 mg/kg dose level also increased survival rates to 64.2% (P < 0.02) and 67.9% (P < 0.01), respectively. A second experiment demonstrated that oral dosing with U-74006F (30 mg/kg), when limited to the first 5 days after axotomy, also significantly blunted retrograde degeneration measured at 21 days post-axotomy. The efficacy of the lipid peroxidation inhibitor U-74006F in protecting a portion of the facial motor neuron pool from post-axotomy degeneration suggests that lipid peroxidation may play a mechanistic role in trophic deprivation-induced apoptotic neuronal death.

Antioxidants in peripheral nerve

Oxidative stress and antioxidants have been related in a wide variety of ways with nervous tissue. This review attempts to gather the most relevant information related to a) the antioxidant status in non pathologic nervous tissue; b) the hypothesis and evidence for oxidative stress (considered as the disequilibrium between prooxidants and antioxidants in the cell) as the responsible mechanism of diverse neurological diseases; and c) the correlation between antioxidant alterations and neural function, in different experimental neuropathies. Decreased antioxidant availability has been observed in different neurological disorders in the central nervous system, for example, Parkinson's disease, Alzheimer's disease, epilepsy, amyotrophic lateral sclerosis, cerebral ischaemia, etc. Moreover, the experimental manipulation of the antioxidant defense has led in some cases to interesting experimental models in which electrophysiological alterations are associated with the metabolic modifications induced. In view of the electrophysiological and biochemical effects of some protein kinase C inhibitors on different neural experimental models, special attention is dedicated to the role of this kinase in peripheral nervous tissue. The nervous tissue, central as well as peripheral, has two main special features that are certainly related to its antioxidant metabolism: the lipid-enriched membrane and myelin sheaths, and cellular excitability. The former explains the importance of the glutathione (GSH)-conjugating activity towards 4-hydroxy-nonenal, a biologically active product of lipid peroxidation, present in nervous tissue and in charge of its inactivation. The impairment of the latter by oxidative damage or experimental manipulation of antioxidant metabolism is discussed. Work on different experimental neuropathies from author's laboratory has been primarily used to provide information about the involvement of free radical damage and antioxidants in peripheral nerve metabolic and functional impairment.

Lewis rat EAN is suppressed by the 21-aminosteroid tirilazad mesylate (U-74006F)

Lewis rat experimental allergic neuritis (EAN) was treated with the 21-aminosteroid, tirilazad mesylate (U-74006F). High doses of tirilazad mesylate, begun just before the onset of clinical signs, reduced the clinical and pathological severity of the disease. In rats immunized with a high dose of myelin, axonal degeneration was a major pathological feature. Tirilazad mesylate reduced the amount of axonal degeneration but had little effect on the other pathological features of EAN, such as inflammation and demyelination. Tirilazad mesylate may block axonal degeneration by inhibiting lipid peroxidation of axonal membranes. Inhibition of axonal degeneration is an important goal in the treatment of human neuropathies.

Neuroprotective actions of glucocorticoid and nonglucocorticoid steroids in acute neuronal injury

1. The glucocorticoid steroid methylprednisolone (MP) has been shown to enhance chronic recovery after human spinal cord injury when administered in a 24-hr high-dose regimen beginning within 8 hr. The doses of MP that affect this improved recovery have been demonstrated to inhibit posttraumatic spinal cord lipid peroxidation (LP), which has been postulated to be a key event in the secondary injury-induced degenerative cascade. 2. The molecular mechanism of action of the steroid appears to involve intercalation into the cell membrane and blockade of the propagation of peroxidative reactions. At a physiological level, the inhibition of injury-induced LP has been found to result in an attenuation of progressive posttraumatic ischemia and energy failure together with an augmented reversal of intracellular calcium accumulation. However, MP also acts directly to retard secondary neuronal degeneration as observed in studies showing the steroid's ability to slow the anterograde degeneration of experimentally injured cat soleus motor nerves. 3. The duplication of this effect by the nonsteroidal lipid antioxidant alpha-tocopherol supports the notion that is indeed a manifestation of the inhibition of posttraumatic LP. Moreover, the efficacy of MP in limiting lipid peroxidation and secondary spinal cord or motor nerve degeneration has also been duplicated by a nonglucocorticoid 21-aminosteroid tirilazad mesylate (U-74006F), which suggests the independence of the antioxidant and glucocorticoid effects of MP.

Severe axonal degeneration in acute Guillain-Barré syndrome: evidence of two different mechanisms?

Four cases of severe acute Guillain-Barré syndrome (GBS) characterized by severe axonal degeneration are presented. All had electrically inexcitable motor nerves as early as 4 days after onset. The disease was rapid in onset and the residual disability was severe. Two different types of pathology were seen. Nerve biopsies in 3 cases showed severe axonal degeneration without inflammation or demyelination. Autopsy in one of these cases showed that the dorsal and ventral roots were also significantly affected. These cases illustrate the primary axonal form of GBS. Nerve biopsy in the fourth case at day 15 showed marked inflammation and demyelination with axonal degeneration. Contralateral nerve biopsy at day 75 showed almost complete loss of axons. This case illustrates another type of axonal degeneration, that which occurs secondary to inflammation and demyelination.

Novel pharmacologic therapies in the treatment of experimental traumatic brain injury: a review

Delayed or secondary neuronal damage following traumatic injury to the central nervous system (CNS) may result from pathologic changes in the brain's endogenous neurochemical systems. Although the precise mechanisms mediating secondary damage are poorly understood, posttraumatic neurochemical changes may include overactivation of neurotransmitter release or re-uptake, changes in presynaptic or postsynaptic receptor binding, or the pathologic release or synthesis of endogenous "autodestructive" factors. The identification and characterization of these factors and the timing of the neurochemical cascade after CNS injury provides a window of opportunity for treatment with pharmacologic agents that modify synthesis, release, receptor binding, or physiologic activity with subsequent attenuation of neuronal damage and improvement in outcome. Over the past decade, a number of studies have suggested that modification of postinjury events through pharmacologic intervention can promote functional recovery in both a variety of animal models and clinical CNS injury. This article summarizes recent work suggesting that pharmacologic manipulation of endogenous systems by such diverse pharmacologic agents as anticholinergics, excitatory amino acid antagonists, endogenous opioid antagonists, catecholamines, serotonin antagonists, modulators of arachidonic acid, antioxidants and free radical scavengers, steroid and lipid peroxidation inhibitors, platelet activating factor antagonists, anion exchange inhibitors, magnesium, gangliosides, and calcium channel antagonists may improve functional outcome after brain injury.

Forelimb motor performance following cervical spinal cord contusion injury in the rat

The purpose of this study was to examine the degree, persistence, and nature of forelimb behavioral deficits following cervical spinal cord contusion injury in the rat. Forelimb reaching and pellet retrieval, forehead adhesive sticker removal, and vibrissae-induced forelimb placing were examined for 16 weeks following a weight-drop injury (10.0 g-2.5 cm) at the C4-C5 spinal level. Nine of 13 rats studied were unable to perform the pellet retrieval task due to pronounced forelimb extension hypometria. However, these animals did carry out the forehead sticker removal and vibrissae-induced placing tasks. Therefore, the loss of reaching ability related to pellet retrieval was not due to generalized paralysis. This interpretation was further supported by evaluation of the rostrocaudal extent of relative motoneuron loss from 1-mm divisions through the lesion zone. The extent of motoneuron pathology ranged from 2 to 6 mm but was largely confined to the C4-C5 spinal segments. Morphometric assessments of axonal sparing revealed that pellet retrieval performance during the last month of observation was significantly correlated with fiber sparing in the dorsal columns and ventral white matter, whereas no significant correlation could be demonstrated with regard to dorsolateral white matter. While there were no conspicuous differences in qualitative assessments of damage to interneuron pools (i.e., laminae V to VII) between the nonreaching and retrieval-recovered rats, the possibility of combined white and gray matter pathology contributing to this deficit still exists. These initial findings thus demonstrate that the weight-drop contusion injury model can be adopted to studies of cervical spinal cord trauma in the rat. Such lesions yield permanent deficits in forelimb function lending to future studies of possible therapeutic interventions. Furthermore, performance deficits observed at 1 week postinjury in the placing and forehead sticker removal tasks can be predictive of any potential for long-range spontaneous recovery in pellet retrieval ability.

Novel inhibitors of iron-dependent lipid peroxidation for neurodegenerative disorders

A considerable body of information supports the occurrence and pathophysiological importance of oxygen radical-mediated lipid peroxidation in acute cerebral damage secondary to traumatic or ischemic injury. Moreover, peroxidative mechanisms have been implicated in chronic neurodegenerative (e.g., Alzheimer's and Parkinson's diseases) and demyelinating (e.g., multiple sclerosis) disorders. Consequently, there has been interest in identification of pharmacological agents with potent ability to interrupt oxygen radical formation or cell membrane lipid peroxidative mechanisms. Our laboratories have developed a novel series of potent lipid peroxidation inhibitors known as the 21-aminosteroids or "lazaroids." One of these compounds, U-74006F or tirilazad mesylate, has shown efficacy in animal models of brain injury and focal cerebral ischemia. In addition, the compound has been found to attenuate the increased lipid peroxidation observed in Alzheimer's brain tissue, to retard anterograde degeneration of motor nerve fibers, and to be effective in decreasing the clinical disease severity and blood-brain barrier disruption observed in the multiple sclerosis model of experimental allergic encephalomyelitis. Another series of antioxidants, the 2-methylaminochromans typified by the compound U-78517F, have been discovered that are even more potent and effective inhibitors of lipid peroxidation than the 21-aminosteroids.

Effect of delayed administration of U74006F (tirilazad mesylate) on recovery of locomotor function after experimental spinal cord injury

Beginning at either 30 minutes, 2 hours, 4 hours, or 8 hours after 180 g compression of the cat L2 spinal cord for 5 minutes, infusion of U74006F was initiated. In this series, the cats received a total U74006F dose of 5 mg/kg/48 hours. An additional group of injured cats was treated at 8 hours postinjury with a three-fold higher dose of U74006F (i.e., a total 48-hour dose of 15 mg/kg). Controls received an equal volume of vehicle (citrate-buffered saline) delivered over 48 hours. The cats were evaluated weekly for 4 weeks for recovery of overground locomotion based on an 11-point scale by an investigator blinded to the time and type (i.e., vehicle or drug) of material administered. By 4 weeks postinjury, there was no significant difference in the locomotor recovery of cats that received U74006F at either 30 minutes, 2 hours, 4 hours, or 8 hours after injury. However, only recovery in the groups treated at 30 minutes, 2 hours, or 4 hours after injury was significantly greater than vehicle-treated controls. Locomotor function in cats receiving either 5 mg/kg/48 hours or 15 mg/kg/48 hours of U74006F at 8 hours postinjury was not significantly different from that of the vehicle-treated animals. Mean (+/- SEM) 4-week recovery scores were 6.8 +/- 0.9, 5.9 +/- 1.0, 7.2 +/- 1.1, and 4.7 +/- 2.9 out of 11 for cats treated at 30 minutes, 2 hours, 4 hours, or 8 hours postinjury, respectively, with the 5 mg/kg/48 hour dose. The mean recovery score for cats treated at 8 hours after injury with the 15 mg/kg/48 hour dose was 3.4 +/- 1.8. The average score for the vehicle-treated controls was 1.8 +/- 0.8. These findings demonstrate that U74006F can significantly protect locomotor function in our model of compression spinal cord injury if administered as late as 4 hours postinjury. Delaying administration of the compound to 8 hours after injury results in considerable loss of its protective capabilities even if the dose is increased threefold.