Treatment of acute spinal cord injuries: comparison of thyrotropin-releasing hormone and nimodipine

Translational potential of preclinical trials of neuroprotection through pharmacotherapy for spinal cord injury

There is a need to enhance the pipeline of discovery and evaluation of neuroprotective pharmacological agents for patients with spinal cord injury (SCI). Although much effort and money has been expended on discovering effective agents for acute and subacute SCI, no agents that produce major benefit have been proven to date. The deficiencies of all aspects of the pipeline, including the basic science input and the clinical testing output, require examination to determine remedial strategies. Where has the neuroprotective/pharmacotherapy preclinical process failed and what needs to be done to achieve success? These are the questions raised in the present review, which has 2 objectives: 1) identification of articles that address issues related to the translational readiness of preclinical SCI pharmacological therapies; and 2) examination of the preclinical studies of 5 selected agents evaluated in animal models of SCI (including blunt force trauma, penetrating trauma, or ischemia). The 5 agents were riluzole, glyburide, magnesium sulfate, nimodipine, and minocycline, and these were selected because of their promise of translational readiness as determined by the North American Clinical Trials Network Consortium.

The authors found that there are major deficiencies in the effort that has been extended to coordinate and conduct preclinical neuroprotection/pharmacotherapy trials in the SCI field. Apart from a few notable exceptions such as the NIH effort to replicate promising strategies, this field has been poorly coordinated. Only a small number of articles have even attempted an overall evaluation of the neuroprotective/pharmacotherapy agents used in preclinical SCI trials. There is no consensus about how to select the agents for translation to humans on the basis of their preclinical performance and according to agreed-upon preclinical performance criteria.

In the absence of such a system and to select the next agent for translation, the Consortium has developed a Treatment Strategy Selection Committee, and this committee selected the most promising 5 agents for potential translation. The results show that the preclinical work on these 5 agents has left numerous gaps in knowledge about their preclinical performance and confirm the need for significant changes in preclinical neuroprotection/pharmacotherapy trials in SCI. A recommendation is made for the development and validation of a preclinical scoring system involving worldwide experts in preclinical and clinical SCI.

Chemical priming for spinal cord injury: a review of the literature part II-potential therapeutics

INTRODUCTION

Spinal cord injury is a complex cascade of reactions secondary to the initial mechanical trauma that puts into action the innate properties of the injured cells, the circulatory, inflammatory, and chemical status around them, into a non-permissive and destructive environment for neuronal function and regeneration. Priming means putting a cell, in a state of "arousal" towards better function. Priming can be mechanical as trauma is known to enhance activity in cells.

MATERIALS AND METHODS

A comprehensive review of the literature was performed to better understand the possible chemical primers used for spinal cord injuries.

CONCLUSIONS

Taken together, many studies have shown various promising results using the substances outlined herein for treating SCI.

Identification of novel neuroprotective agents using pharmacophore modeling

In addition to its endocrine function, for which it was named, thyrotropin-releasing hormone (TRH) has substantial neuroprotective actions as well as other physiological effects. We have developed a number of modified TRH analogues as well as cyclic dipeptides structurally related to a major metabolic product of TRH, which have enhanced neuroprotective activity but none of the other major physiological effects of TRH. The extensive structure-activity data developed with these compounds were used to develop a pharmacophore model. Subsequently, a web-based pharmacophore searching program was used to query several large three-dimensional databases. Of the 219 compounds identified whose structures met the pharmacophore model, 15 were chosen for study in a classical model of neuronal cell death in vitro; five of these, 2-6, showed neuroprotective activity. Thus, pharmacophore modeling developed from neuroprotective small peptides can be used to identify novel lead compounds as neuroprotective agents.

Novel neuroprotective tripeptides and dipeptides

It has long been recognized that thyrotropin-releasing hormone (TRH) and certain TRH analogues are neuroprotective in a variety of animal models of CNS trauma. In addition to these neuroprotective actions, TRH and most TRH analogues have other physiological actions that may not be desirable for treatment of acute injury, such as analeptic, autonomic, and endocrine effects. We have developed a series of dual-substituted TRH analogues that have strong neuroprotective actions, but are largely devoid of these other physiological actions. In addition, we have developed a family of cyclized dipeptides (diketopiperazines), structurally somewhat related to a metabolic product of TRH, that appear even more effective as neuroprotective agents in vitro and in vivo, and may have nootropic properties. Here, we review these novel tripeptide and dipeptide compounds.

Neuroprotective and nootropic actions of a novel cyclized dipeptide after controlled cortical impact injury in mice

1-ARA-35b (35b) is a cyclized dipeptide that shows considerable neuroprotective activity in vitro and improves neurologic recovery after fluid percussion-induced traumatic brain injury in rats. The authors evaluated the effects of treatment with 35b in mice subjected to controlled cortical impact brain injury. Animals treated with intravenous 35b after traumatic injury showed significantly enhanced recovery of beam walking and place learning functions compared with vehicle-treated controls, in addition to reduced lesion volumes. Beneficial effects were dose related and showed an inverted U-shaped dose-response curve between 0.1 and 10 mg/kg. Protective actions were found when the drug was administered initially at 30 minutes or 1, 4, or 8 hours, but not at 24 hours, after trauma. In separate experiments, rats treated with 35b on days 7 through 10 after injury showed remarkably improved place learning in comparison with injured controls. These studies confirm and extend the neuroprotective effects of this diketopiperazine in traumatic brain injury. In addition, they show that 35b has a relatively wide therapeutic window and improves cognitive function after both acute and chronic injury.

Novel TRH analog improves motor and cognitive recovery after traumatic brain injury in rodents

Thyrotropin-releasing hormone (TRH) and certain TRH analogs show substantial neuroprotective effects in experimental brain or spinal cord trauma but also have other physiological actions (autonomic, analeptic, and endocrine) that may be undesirable for the treatment of neurotrauma in humans. We developed a novel TRH analog (2-ARA-53a), with substitutions at the NH(2)-terminus and imidazole ring, that preserves the neuroprotective action of TRH-like compounds while decreasing or eliminating their autonomic, analeptic, and endocrine effects. Rats administered 2-ARA-53a (1.0 mg/kg, n = 17) intravenously 30 min after lateral fluid percussion brain injury showed marked improvement in motor recovery compared with vehicle-treated controls (n = 14). Treatment of mice subjected to moderate controlled cortical impact brain injury, at the same dose and time after trauma (n = 8), improved both motor recovery and cognitive performance in a water maze place learning task compared with vehicle-treated controls (n = 8). In injured rats, no autonomic or analeptic effects were observed with this compound, and endocrine effects were significantly reduced with 2-ARA-53a, in contrast to those found with a typical NH(2)-terminal-substituted TRH analog (YM-14673). These findings demonstrate that the neuroprotective effects of TRH-related compounds can be dissociated from their other major physiological actions and suggest a potential role for dual-substituted TRH analogs in the treatment of clinical neurotrauma.

The effects of calcium channel blocker and thyrotropin releasing hormone on acute necrotizing pancreatitis in rats

The main purpose of this study was to investigate the influence of nimodipine, a calcium channel blocker (CCB) and thyroid-releasing hormone (TRH) on acute necrotizing pancreatitis (ANP) induced by glycodeoxycholic acid in rats. CCB decreased blood pressure in rats in the control and pancreatitis groups. TRH corrected this decrease. CCB alone had no effect on PO2 serum amylase activity, calcium concentration, liver transaminases, lactate dehydrogenase or the degree of pancreatic damage, except for the serum concentration of creatinine. CCB+TRH reduced the concentrations of serum urea and creatinine, the degree of pancreatic damage, and increased PO2 and serum calcium concentration. CCB and CCB+TRH had no effect on pancreatic myeloperoxidase activity. CCB alone had no effect on the course of ANP, but CCB+TRH had beneficial effects on the course of the ANP and various systems.

Beneficial effect of thyrotropin-releasing hormone on neuropathy in diabetic rats

Thyrotropin releasing hormone (TRH) is therapeutically effective in experimental and clinical spinal injury. The effects of TRH on diabetic neuropathy are not known. The aim of the present study was to investigate the electrophysiological effects of TRH in the streptozotocin diabetic rats. Three groups of rats were studied, non-diabetic control (n = 10), diabetic controls (n = 8), and TRH treated diabetic rats (n = 9). Administration of TRH or saline and electrophysiological measurements were performed 4 weeks after induction of diabetes. TRH was given intraperitoneally in a dose of 600 microg (3 ml). Nerve conduction velocity (NCV), measured in caudal nerve, and N1 latency of somatosensory evoked potentials (SEP) were measured 75 min after injection of TRH or serum saline. SEP latencies were 28.1 +/- 0.6, 29.4 +/- 0.8, 27.8 +/- 1.1 ms, in normal, diabetic and diabetic TRH-treated groups, and NCV values were 28.1 +/- 0.8, 23.8 +/- 0.4, and 27.9 +/- 0.7 m/s respectively. NCV was significantly reduced in the diabetic group compared to normals (P < 0.05). but then improved by TRH treatment (P < 0.05). Our findings suggest that TRH has an acute effect on peripheral neuropathy in experimental streptozotocin diabetes in the rat.

Influence of thyrotropin-releasing hormone on experimental pancreatitis in rats

The main purpose of this study was to investigate the influence of thyroid releasing hormone on acute sodium-taurocholate-induced pancreatitis in rats. Thyroid-releasing hormone did not change the survival rate, serum amylase, glucose calcium, liver transaminases levels or the degree of pancreatic damage, but reduced lactate dehydrogenase. Our findings suggest that the use of thyroid-releasing hormone has no beneficial effect on the course of acute experimental pancreatitis.

Treatment with thyrotropin-releasing hormone (TRH) in patients with traumatic spinal cord injuries

Numerous preclinical studies have demonstrated that posttraumatic treatment of spinal cord injury (SCI) with thyrotropin-releasing hormone (TRH) or TRH analogs improves long-term behavioral recovery. The purpose of the present study is to provide preliminary data regarding the safety and potential efficacy of TRH in patients with acute SCI. A total of 20 patients with SCI were classified by clinical examination into complete and incomplete injury groups within 12 h of trauma and randomly assigned in double-blinded fashion to treatment with either TRH (0.2 mg/kg intravenous bolus followed by 0.2 mg/kg/h infusion over 6 h) or vehicle (equal volume physiological saline) placebo. A variety of physiological variables were followed during treatment. Clinical examination included motor and sensory testing, as well as assigning a Sunnybrook score based upon level of function. Patients were examined at 24 h, 72 h, 1 week, 1 month, 4 months, and 12 months after injury. TRH infusions were well tolerated. There appeared to be no discernible treatment effect in patients with complete injuries although data were available from only six such patients at 4 months. For the incomplete injury group, a total of 6 treated and 5 placebo patients had 4-month evaluations. TRH treatment was associated with significantly higher motor, sensory, and Sunnybrook scores than placebo treatment. Because of patients lost to subsequent follow-up, 12-month data were not highly informative. These observations must be interpreted with considerable caution because of the small patient numbers, but together with extensive animal studies they support the need for a larger multicenter clinical trial of TRH.

Effects of TRH and high-dose corticosteroid therapy on evoked potentials, and tissue Na+,K+ and water content in experimental spinal injury

The therapeutic effects of continuous infusion of thyrotropin-releasing hormone (TRH) and methylprednisolone (MP) in experimental spinal cord injury were studied in Swiss albino rats. Thirty rats received a 53-g clip-compression injury on the cord at T1, then were allocated randomly and blindly to one of three treatment groups (ten animals in each): (1) control; received equal volumes of saline solution; (2) MP; received 30 mg/kg methylprednisolone i.v. 1h after trauma, followed by infusion of 5.4 mg/kg/per hour i.v. for 3h; (3) TRH; received 2 mg/kg TRH i.v. 1h after trauma, followed by infusion of 1 mg/kg/per hour i.v. for 3h. MP and TRH treatments significantly improved somatosensory-evoked potentials (SEPs; P < 0.001). Both treatments significantly reduced water content, decreased Na+ content and increased the K+ content of the cord segment that included the centre of the impact (P < 0.01). Our data provide evidence for the beneficial effects of high-dose corticosteroid and TRH in promoting electrophysiological recovery and preserving spinal cord tissue following experimental injury.