Chondroitinase improves anatomical and functional outcomes after primate spinal cord injury

Inhibitory extracellular matrices form around mature neurons as perineuronal nets containing chondroitin sulfate proteoglycans (CSPGs) that limit axonal sprouting after CNS injury. The enzyme chondroitinase (Chase) degrades the inhibitory CSPGs and improves axonal sprouting and functional recovery after spinal cord injury (SCI) in rodents. We evaluated the effects of Chase in Rhesus monkeys that had undergone C7 spinal cord hemisection. Four weeks after hemisection, multiple intraparenchymal Chase injections targeted spinal cord circuits controlling hand function below the lesion. Hand function improved significantly in Chase-treated monkeys relative to vehicle-injected controls. Moreover, Chase significantly increased corticospinal axon growth and the number of synapses formed by corticospinal terminals in gray matter caudal to the lesion. No detrimental effects were detected. This approach appears to merit clinical translation in SCI.

Transient Changes in Hepatic Physiology That Alter Bilirubin and Bile Acid Transport May Explain Elevations in Liver Chemistries Observed in Clinical Trials of GGF2 (Cimaglermin Alfa)

GGF2 is a recombinant human neuregulin-1β in development for chronic heart failure. Phase 1 clinical trials of GGF2 were put on hold when transient elevations in serum aminotransferases and total bilirubin were observed in 2 of 43 subjects who received single doses of GGF2 at 1.5 or 0.378 mg/kg. However, aminotransferase elevations were modest and not typical of liver injury sufficient to result in elevated serum bilirubin. Cynomolgus monkeys administered a single 15 mg/kg dose of GGF2 had similar transient elevations in serum aminotransferases and bilirubin as well as transient elevations in serum bile acids. However, no hepatocellular necrosis was observed in liver biopsies obtained during peak elevations. When sandwich-cultured human hepatocytes were treated with GGF2 for up to 72 h at concentrations approximately 0.8-fold average plasma Cmax for the 0.378 mg/kg dose, no cytotoxicity was observed. Gene expression profiling identified approximately 50% reductions in mRNAs coding for bilirubin transporters and bile acid conjugating enzymes, as well as changes in expression of additional genes mimicking the interleukin-6-mediated acute phase response. Similar gene expression changes were observed in GGF2-treated HepG2 cells and primary monkey hepatocytes. Additional studies conducted in sandwich-cultured human hepatocytes revealed a transient and GGF2 concentration-dependent decrease in hepatocyte bile acid content and biliary clearance of taurocholate without affecting biliary taurocholate efflux. Taken together, these data suggest that GGF2 does not cause significant hepatocellular death, but transiently modifies hepatic handling of bilirubin and bile acids, effects that may account for the elevations in serum bilirubin observed in the clinical trial subjects.

Abstract TMP33: TXA302 Promotes Permanent Functional Recovery With Delivery Initiated Up to 4 Weeks After Stroke in Multiple Rodent Models

Introduction: TXA302 is a proprietary analogue of angiotensin 1-7 (Ang1-7). Previous studies have shown that intracerebroventricular administration of Ang1-7 as a pre-treatment to experimental occlusive rodent stroke resulted in improved neurological function, decreased infarct volume, enhanced cerebral blood flow and decreased inflammation. Here, systemic administration of TXA302 was evaluated with treatment delayed up to 4 weeks to assess the potential of TXA302 to promote recovery in chronic stroke.

Methods and Results: Four independent studies were conducted in the rat transient (2 hour) and permanent middle cerebral artery occlusion (MCAO) models. Daily subcutaneous delivery of TXA302 or vehicle was started either 24 hours or 4 weeks after MCAO and continued for 4, 6 or 8 weeks. Treatment was started at 4 weeks to assess the ability of TXA302 to promote recovery independent of neuroprotection and to model the chronic phase of the injury. Two of the studies employed a dose range of TXA302 from 1 to 500 μg/kg and two studies had a washout period of 4 weeks after the completion of dosing to assess the permanence of the recovery effect. Sensorimotor recovery was measured by limb placing, stepping, and body swing tests along with composite neurological scoring. Cerebral blood flow (CBF) was evaluated by doppler ultrasonography. All studies were conducted in a blinded fashion and recovery of treated animals was compared to vehicle by repeated measures ANOVA with corrections for multiple comparisons. TXA302 treatment resulted in significant, robust and permanent dose-responsive improvements in neurological function and CBF compared to vehicle treated animals.

Conclusions: The ability to delay treatment for 4 weeks suggests the changes are not attributable to neuroprotection. Furthermore, this wide therapeutic window enhances translational potential as clinical trials can be conducted without confounding factors of treating, stabilizing and assessing baseline functional measures in acute stroke patients. Ongoing studies are exploring the potential of TXA302 to enhance endogenous remodeling through angiogenesis and neural plasticity. Non-clinical studies and manufacturing development are underway to enable an IND for stroke recovery.

Clinically Relevant Levels of 4-Aminopyridine Strengthen Physiological Responses in Intact Motor Circuits in Rats, Especially After Pyramidal Tract Injury

BACKGROUND

4-Aminopyridine (4-AP) is a Food and Drug Administration-approved drug to improve motor function in people with multiple sclerosis. Preliminary results suggest the drug may act on intact neural circuits and not just on demyelinated ones.

OBJECTIVE

To determine if 4-AP at clinically relevant levels alters the excitability of intact motor circuits.

METHODS

In anesthetized rats, electrodes were placed over motor cortex and the dorsal cervical spinal cord for electrical stimulation, and electromyogram electrodes were inserted into biceps muscle to measure responses. The motor responses to brain and spinal cord stimulation were measured before and for 5 hours after 4-AP administration both in uninjured rats and rats with a cut lesion of the pyramidal tract. Blood was collected at the same time as electrophysiology to determine drug plasma concentration with a goal of 20 to 100 ng/mL.

RESULTS

We first determined that a bolus infusion of 0.32 mg/kg 4-AP was optimal: it produced on average 61.5 ± 1.8 ng/mL over the 5 hours after infusion. This dose of 4-AP increased responses to spinal cord stimulation by 1.3-fold in uninjured rats and 3-fold in rats with pyramidal tract lesion. Responses to cortical stimulation also increased by 2-fold in uninjured rats and up to 4-fold in the injured.

CONCLUSION

Clinically relevant levels of 4-AP strongly augment physiological responses in intact circuits, an effect that was more robust after partial injury, demonstrating its broad potential in treating central nervous system injuries.

Effects of neuregulin GGF2 (cimaglermin alfa) dose and treatment frequency on left ventricular function in rats following myocardial infarction

Neuregulins are important growth factors involved in cardiac development and response to stress. Certain isoforms and fragments of neuregulin have been found to be cardioprotective. The effects of a full-length neuregulin-1β isoform, glial growth factor 2 (GGF2; USAN/INN; also called cimaglermin) were investigated in vitro. Various dosing regimens were then evaluated for their effects on left ventricular (LV) function in rats with surgically-induced myocardial infarction. In vitro, GGF2 bound with high affinity to erythroblastic leukemia viral oncogene (ErbB) 4 receptors, potently promoted Akt phosphorylation, as well as reduced cell death following doxorubicin exposure in HL1 cells. Daily GGF2 treatment beginning 7-14 days after left anterior descending coronary artery ligation produced improvements in LV ejection fraction and other measures of LV function and morphology. The improvements in LV function (e.g. 10% point increase in absolute LV ejection fraction) with GGF2 were dose-dependent. LV performance was substantially improved when GGF2 treatment was delivered infrequently, despite a serum half-life of less than 2h and could be maintained for more than 10 months with treatment once weekly or once every 2 weeks. These studies confirm previous findings that GGF2 may improve contractile performance in the failing rat heart and that infrequent exposure to GGF2 may improve LV function and impact remodeling in the failing myocardium. GGF2 is now being developed for the treatment of heart failure in humans.

AC105 Increases Extracellular Magnesium Delivery and Reduces Excitotoxic Glutamate Exposure within Injured Spinal Cords in Rats

Magnesium (Mg²⁺) homeostasis is impaired following spinal cord injury (SCI) and the loss of extracellular Mg²⁺ contributes to secondary injury by various mechanisms, including glutamate neurotoxicity. The neuroprotective effects of high dose Mg²⁺ supplementation have been reported in many animal models. Recent studies found that lower Mg²⁺ doses also improved neurologic outcomes when Mg²⁺ was formulated with polyethylene glycol (PEG), suggesting that a PEG/ Mg²⁺ formulation might increase Mg²⁺ delivery to the injured spinal cord, compared with that of MgSO₄ alone. Here, we assessed spinal extracellular Mg²⁺ and glutamate levels following SCI in rats using microdialysis. Basal levels of extracellular Mg²⁺ (∼0.5 mM) were significantly reduced to 0.15 mM in the core and 0.12 mM in the rostral peri-lesion area after SCI. A single intravenous infusion of saline or of MgSO₄ at 192 μmoL/kg did not significantly change extracellular Mg²⁺ concentrations. However, a single infusion of AC105 (a MgCl₂ in PEG) at an equimolar Mg²⁺ dose significantly increased the Mg²⁺ concentration to 0.3 mM (core area) and 0.25 mM (rostral peri-lesion area). Moreover, multiple AC105 treatments completely restored the depleted extracellular Mg²⁺ concentrations after SCI to levels in the uninjured spinal cord. Repeated MgSO₄ infusions slightly increased the Mg²⁺ concentrations while saline infusion had no effect. In addition, AC105 treatment significantly reduced extracellular glutamate levels in the lesion center after SCI. These results indicate that intravenous infusion of PEG-formulated Mg²⁺ normalized the Mg²⁺ homeostasis following SCI and reduced potentially neurotoxic glutamate levels, consistent with a neuroprotective mechanism of blocking excitotoxicity.

An optimized dosing regimen of cimaglermin (neuregulin 1β3, glial growth factor 2) enhances molecular markers of neuroplasticity and functional recovery after permanent ischemic stroke in rats

Cimaglermin (neuregulin 1β3, glial growth factor 2) is a neuregulin growth factor family member in clinical development for chronic heart failure. Previously, in a permanent middle cerebral artery occlusion (pMCAO) rat stroke model, systemic cimaglermin treatment initiated up to 7 days after ischemia onset promoted recovery without reduced lesion volume. Presented here to extend the evidence are two studies that use a rat stroke model to evaluate the effects of cimaglermin dose level and dose frequency initiated 24 hr after pMCAO. Forelimb‐ and hindlimb‐placing scores (proprioceptive behavioral tests), body‐swing symmetry, and infarct volume were compared between treatment groups (n = 12/group). Possible mechanisms underlying cimaglermin‐mediated neurologic recovery were examined through axonal growth and synapse formation histological markers. Cimaglermin was evaluated over a wider dose range (0.02, 0.1, or 1.0 mg/kg) than doses previously shown to be effective but used the same dosing regimen (2 weeks of daily intravenous administration, then 1 week without treatment). The dose‐frequency study used the dose‐ranging study's most effective dose (1.0 mg/kg) to compare daily, once per week, and twice per week dosing for 3 weeks (then 1 week without treatment). Dose‐ and frequency‐dependent functional improvements were observed with cimaglermin without reduced lesion volume. Cimaglermin treatment significantly increased growth‐associated protein 43 expression in both hemispheres (particularly somatosensory and motor cortices) and also increased synaptophysin expression. These data indicate that cimaglermin enhances recovery after stroke. Immunohistochemical changes were consistent with axonal sprouting and synapse formation but not acute neuroprotection. Cimaglermin represents a potential clinical development candidate for ischemic stroke treatment. © 2015 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Dalfampridine improves sensorimotor function in rats with chronic deficits after middle cerebral artery occlusion

BACKGROUND AND PURPOSE

Stroke survivors often have permanent deficits that are only partially addressed by physical therapy. This study evaluated the effects of dalfampridine, a potassium channel blocker, on persistent sensorimotor deficits in rats with treatment initiated 4 or 8 weeks after stroke.

METHODS

Rats underwent permanent middle cerebral artery occlusion. Sensorimotor function was measured using limb-placing and body-swing symmetry tests, which normally show a partial recovery from initial deficits that plateaus ≈4 weeks after permanent middle cerebral artery occlusion. Dalfampridine was administered starting at 4 or 8 weeks after permanent middle cerebral artery occlusion in 2 blinded, vehicle-controlled studies. Plasma samples were collected and brain tissue was processed for histologic assessment.

RESULTS

Dalfampridine treatment (0.5-2.0 mg/kg) improved forelimb- and hindlimb-placing responses and body-swing symmetry in a reversible and dose-dependent manner. Plasma dalfampridine concentrations correlated with dose. Brain infarct volumes showed no differences between treatment groups.

CONCLUSIONS

Dalfampridine improves sensorimotor function in the rat permanent middle cerebral artery occlusion model. Dalfampridine extended-release tablets (prolonged release fampridine outside the United States) are used to improve walking in patients with multiple sclerosis, and these preclinical data provide a strong rationale for examining the potential of dalfampridine to treat chronic stable deficits in stroke patients.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT01605825.

Glial growth factor 2 promotes functional recovery with treatment initiated up to 7 days after permanent focal ischemic stroke

Neuregulins are a family of growth factors essential for normal cardiac and nervous system development. The EGF-like domain of neuregulins contains the active site which binds and activates signaling cascades through ErbB receptors. A neuregulin-1 gene EGF-like fragment demonstrated neuroprotection in the transient middle cerebral artery occlusion (MCAO) stroke model and drastically reduced infarct volume (Xu et al., 2004). Here we use a permanent MCAO rat model to initially compare two products of the neuregulin-1 gene and also assess levels of recovery with acute versus delayed time to treatment. In the initial study full-length glial growth factor 2 (GGF2) and an EGF-like domain fragment were compared with acute intravenous delivery. In a second study GGF2 only was delivered starting at 24h, 3 days or 7 days after permanent ischemia was induced. In both studies daily intravenous administration continued for 10 days. Recovery of neurological function was assessed using limb placing and body swing tests. GGF2 had similar functional improvements compared to the EGF-like domain fragment at equimolar doses, and a higher dose of GGF2 demonstrated more robust functional improvements compared to a lower dose. GGF2 improved sensorimotor recovery with all treatment paradigms, even enhancing recovery of function with a delay of 7 days to treatment. Histological assessments did not show any associated reduction in infarct volume at either 48 h or 21 days post-ischemic event. Neurorestorative effects of this kind are of great potential clinical importance, given the difficulty of delivering neuroprotective therapies within a short time after an ischemic event in human patients. If confirmed by additional work including additional data on mechanism(s) of improved outcome with verification in other stroke models, one can make a compelling case to bring GGF2 to clinical trials as a neurorestorative approach to improving outcome following stroke injury.