Nerve-growth promoting action of isaxonine in rat

Convection-enhanced delivery in intact and lesioned peripheral nerve

OBJECT

Although the use of multiple agents is efficacious in animal models of peripheral nerve injury, translation to clinical applications remains wanting. Previous agents used in trials in humans either engendered severe side effects or were ineffective. Because the blood-central nervous system barrier exists in nerves as it does in the brain, limited drug delivery poses a problem for translation of basic science advances into clinical applications. Convection-enhanced delivery (CED) is a promising adjunct to current therapies for peripheral nerve injury. In the present study the authors assessed the capacity of convection to ferry macromolecules across sites of nerve injury in rat and primate models, examined the functional effects of convection on the intact nerve, and investigated the possibility of delivering a macromolecule to the spinal cord via retrograde convection from a peripherally introduced catheter.

METHODS

The authors developed a rodent model of convective delivery to lesioned sciatic nerves (injury due to crush or laceration in 76 nerves) and compared the results to a smaller series of five primates with similar injuries. In the intact nerve, convective delivery of vehicle generated only a transient neurapraxic deficit. Early after injury (postinjury Days 1, 3, 7, and 10), infusion failed to cross the site of injury in crushed or lacerated nerves. Fourteen days after crush injury, CED of radioactively-labeled albumin resulted in perfusion through the site of injury to distal growing neurites. In primates, successful convection through the site of crush injury occurred by postinjury Day 28. In contrast, in laceration models there was complete occlusion of the extracellular space to convective distribution at the site of laceration and repair, and convective distribution in the extracellular space crossed the site of injury only after there was histological evidence of completion of nerve regeneration. Finally, in two primates, retrograde infusion into the spinal cord through a peripheral nerve was achieved.

CONCLUSIONS

Convection provides a safe and effective means to deliver macromolecules to regenerating neurites in crush-injured peripheral nerves. Convection block in lacerated and suture-repaired nerves indicates a significant intraneural obstruction of the extracellular space. a disruption that suggests an anatomical obstruction to extracellular and, possibly, intraaxonal flow, which may impair nerve regeneration. Through peripheral retrograde infusion, convection can be used for delivery to spinal cord gray matter. Convection-enhanced delivery provides a promising approach to distribute therapeutic agents to targeted sites for treatment of disorders of the nerve and spinal cord.

Increased axonal regrowth of lesioned rat sciatic nerve by veratrylguanidine methane sulfonate

Neurotrophic factors appear as essential factors for normal development and repair of the nervous tissue. Veratrylguanidine methane sulfonate, has been shown to induce important neurite outgrowth of cultured dorsal root ganglia isolated from newborn rats. Its action was similar to that of NGF and was found to be additive to that of NGF. In order to see if this compound was able to stimulate axonal growth in adult animals, we examined the effect of this substance on the regeneration of the lesioned sciatic nerve. Using histochemical, immunohistochemical and ultrastructural studies, it is shown that a single intraperitoneal injection of veratrylguanidine methane sulfonate significantly increases the axonal growth during repair of the adult rat sciatic nerve. The efficiency of this substance is explained by its good targeting and long life time in the sciatic nerve.

Melanocortins as factors in somatic neuromuscular growth and regrowth

Melanocortins, non-corticotropic fragments of adrenocorticotropic hormone, accelerate growth of the developing neuromuscular system and regrowth of damaged neurons, both in the adult and neonatal rat. Morphological, electrophysiological and behavioral characteristics are all improved by melanocortins, which, however, vary in potency, with alpha-MSH being the most effective. Tissue substrate, dosage, critical time periods and pattern of neuropeptide administration are all important variables. Melanocortins protect central neurons affecting motor behavior during development or following neuronal damage in the adult brain. Possible mechanisms of melanocortin action are discussed.

Neurite outgrowth of neurons of rat dorsal root ganglia induced by new neurotrophic substances with guanidine group

In order to search for compounds mimicking the neurotrophic activities, a series of substances possessing the guanidine group of isaxonine (2-isopropylamino-pyrimidine), were synthesized and tested for their ability to induce neurite outgrowth in cultures of explants of rat dorsal root ganglia. It is reported that several of these compounds, at concentrations ranging from 10(-5) to 10(-7) M, showed important effects on neurite outgrowth in vitro, similar to that obtained with the nerve growth factor NGF. These effects were found to be additive to that of NGF.

Putative neurotrophic factors and functional recovery from peripheral nerve damage in the rat

1. In rats, recovery of sensory-motor function following a crush lesion of the sciatic or tibial nerve was monitored by measuring foot reflex withdrawal from a local noxious stimulation of the foot sole. 2. Putative neurotrophic compounds were tested on this functional recovery model: melanocortins (peptides derived from ACTH (corticotropin) and alpha-MSH (melanotropin], gangliosides and nimodipine were effective whereas isaxonine and TRH (thyrotropin releasing hormone) were not. 3. Structure-activity studies with melanocortins revealed a similar effectiveness of alpha-MSH, [N-Leu4, D-Phe7]-alpha-MSH, desacetyl-alpha-MSH and the ACTH analogue ORG 2766, questioning the validity of the previously suggested notion that the melanotrophic properties of these peptides are responsible for their neurotrophic effect. 4. As recovery of function after peripheral nerve damage follows a similar time course in hypophysectomized (five days post operation) and sham-operated rats, effective melanocortin therapy does not mimic an endogenous peptide signal in the repair process from pituitary origin. 5. Subcutaneous treatment with ORG 2766 (7.5 micrograms kg-1 48 h-1) facilitates recovery of function following peripheral nerve damage in young (6-7 weeks old), mature (5 month old) and old (20 month old) rats. 6. In view of the diversity in structure of the effective neurotrophic factors and the complexity of nerve repair, the present data support the notion that peripheral nerve repair may be facilitated by different humoral factors likely to be active on different aspects of the recovery process.

Therapeutic trial of isaxonine in Duchenne muscular dystrophy

A randomized double-blind therapeutic trial of isaxonine was completed over a 2-year period for 20 ambulant boys with Duchenne muscular dystrophy aged 5 1/2-10 years. The effect of the drug was monitored by measurement of walking times over 28 and 150 ft, motor ability score, MRC score based on 32 muscle groups, and myometry of 7 muscle groups. The drug had no significant effect on the progression of the disease. The trial had statistical power comparable to previous larger-scale multicenter trials. This reflected the low variability in the patients in relation to the magnitude of the overall deterioration. Measurements of muscle force (myometry and MRC score) had much greater statistical power than measurements of function (motor ability score and walking times) as analyzed by our methods. These observations have important implications for the design of future trials.

Treatment of peripheral neuropathies

There are three general approaches to treatment of peripheral neuropathy. First, an attempt should be made to reverse the pathophysiological process if its nature can be elucidated. Second, nerve metabolism can be stimulated and regeneration encouraged. Third, even if the neuropathy itself cannot be improved, symptomatic therapy can be employed. This review outlines the options available for each approach.

A study of the effects of isaxonine on vincristine-induced peripheral neuropathy in man and regeneration following peripheral nerve crush in the rat

Administration of isaxonine (6 mg/kg powdered diet) had no effect on regeneration following sciatic nerve crush in the rat. In 10 patients undergoing treatment with vincristine (1.4 mg/m2 twice monthly) development of peripheral neuropathy was quantitated by neurological symptoms, signs and electrophysiological tests. Five also received isaxonine (1.5 g daily). All patients developed evidence of neuropathy, but in none was it severe. The three lowest disability scores were obtained in isaxonine treated patients, but the highest score was also in an isaxonine treated patient. The equivocal findings in this small study could not be amplified because the drug was withdrawn from clinical use on account of its hepatotoxicity.

Effects of isaxonine on skeletal muscle reinnervation in the rat: an electrophysiologic evaluation

Electrophysiologic detection of the first signs of gastrocnemius muscle reinnervation shows that after a single localized freezing of the rat sciatic nerve, isaxonine does not significantly increase the rate of axonal regeneration. However, this drug does significantly enhance axonal sprouting, as it induces an increase of 50% in the number of muscle fibers with multiple innervation 10-30 days after freezing. After 30 days, the proportion of multiinnervated fibers decreases in both the control and isaxonine-treated rats, and the differences between them gradually disappear.

The in vitro effect of some nitroimidazoles on microtubule formation

The in vitro effects of some nitroimidazoles (metronidazole, ornidazole) and their metabolites on microtubule formation have been tested. Cyclic metabolites are without effect. Metabolites proceeding from cleavage of the imidazole ring inhibit microtubule formation and reduce the polymerization rate of tubulin. This inhibitory effect might be correlated to some of the side-effects of these drugs. Isaxonine phosphate corrects this effect.