Improved functional outcome after chronic stroke with delayed anti-Nogo-A therapy: A clinically relevant intention-to-treat analysis

Anti-Nogo-A Antibody Therapy Improves Functional Outcome Following Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) can cause sensorimotor deficits, and recovery is slow and incomplete. There are no effective pharmacological treatments for recovery from TBI, but research indicates potential for anti-Nogo-A antibody (Ab) therapy. This Ab neutralizes Nogo-A, an endogenous transmembrane protein that inhibits neuronal plasticity and regeneration.

OBJECTIVE

We hypothesized that anti-Nogo-A Ab treatment following TBI results in disinhibited axonal growth from the contralesional cortex, the establishment of new compensatory neuronal connections, and improved function.

METHODS

We modeled TBI in rats using the controlled cortical impact method, resulting in focal brain damage and motor deficits like those observed in humans with a moderate cortical TBI. Rats were trained on the skilled forelimb reaching task and the horizontal ladder rung walking task. They were then given a TBI, targeting the caudal forelimb motor cortex, and randomly divided into 3 groups: TBI-only, TBI + Anti-Nogo-A Ab, and TBI + Control Ab. Testing resumed 3 days after TBI and continued for 8 weeks, when rats received an injection of the anterograde neuronal tracer, biotinylated dextran amine (BDA), into the corresponding area contralateral to the TBI.

RESULTS

We observed significant improvement in rats that received anti-Nogo-A Ab treatment post-TBI compared to controls. Analysis of BDA-positive axons revealed that anti-Nogo-A Ab treatment resulted in cortico-rubral plasticity to the deafferented red nucleus. Conclusions. Anti-Nogo-A Ab treatment may improve functional recovery via neuronal plasticity to brain areas important for skilled movements, and this treatment shows promise to improve outcomes in humans who have suffered a TBI.

Neurofunctional and neuroimaging readouts for designing a preclinical stem-cell therapy trial in experimental stroke

With the aim of designing a preclinical study evaluating an intracerebral cell-based therapy for stroke, an observational study was performed in the rat suture model of ischemic stroke. Objectives were threefold: (i) to characterize neurofunctional and imaging readouts in the first weeks following transient ischemic stroke, according to lesion subtype (hypothalamic, striatal, corticostriatal); (ii) to confirm that intracerebral administration does not negatively impact these readouts; and (iii) to calculate sample sizes for a future therapeutic trial using these readouts as endpoints. Our results suggested that the most relevant endpoints were side bias (staircase test) and axial diffusivity (AD) (diffusion tensor imaging). Hypothalamic-only lesions did not affect those parameters, which were close to normal. Side bias in striatal lesions reached near-normal levels within 2 weeks, while rats with corticostriatal lesions remained impaired until week 14. AD values were decreased at 4 days and increased at 5 weeks post-surgery, with a subtype gradient: hypothalamic < striatal < corticostriatal. Intracerebral administration did not impact these readouts. After sample size calculation (18-147 rats per group according to the endpoint considered), we conclude that a therapeutic trial based on both readouts would be feasible only in the framework of a multicenter trial.

A Potent Inhibitor of Aminopeptidase P2 Reduces Reperfusion Injury in Models of Myocardial Infarction and Stroke

During a myocardial infarction or ischemic stroke, blood flow to the heart or brain is partially blocked. This results in reduced delivery of oxygen and nutrients and, ultimately, tissue damage. Initial treatment involves removing the clot and restoring blood flow (reperfusion). However, this treatment is not as effective as one would hope because the reperfusion process itself can cause a different type of damage (reperfusion injury) that contributes up to 50% of the total damage. Bradykinin is an autocoid that is released from blood vessel endothelial cells during ischemia and reperfusion and has the potential to prevent reperfusion injury. However, bradykinin is rapidly inactivated by enzymes on endothelial cells, limiting its beneficial effects. One of these enzymes is aminopeptidase P2. We designed a potent and specific inhibitor of aminopeptidase P2 called ST-115, [(S)-2-mercapto-4-methylpentanoyl]-4(S)-fluoro-Pro-Pro-3(R)-beta-Pro. When ST-115 is administered intravenously at the start of reperfusion, it reduces bradykinin degradation. This increases bradykinin's concentration in the capillaries and enhances its protective effects. We tested ST-115 in a mouse model of myocardial infarction and found that the damaged area of the heart was reduced by 58% compared with mice given saline. In a rat model of ischemic stroke, ST-115 reduced functional deficits in a skilled walking test by 60% and reduced brain edema by 51%. It reduced brain infarct size by 48% in a major subset of rats with small strokes. The results indicate that ST-115 can ameliorate reperfusion injury and can ultimately serve as a therapeutic for acute myocardial infarction and ischemic stroke. SIGNIFICANCE STATEMENT: We have shown that our aminopeptidase P2 inhibitor, ST-115, can reduce tissue injury caused by episodes of ischemia followed by reperfusion. It was successful in rodent models of myocardial infarction and stroke. The clinical use would involve the intravenous administration of ST-115 at the induction of reperfusion. In the case of stroke, the successful technique of thrombectomy could be combined with ST-115 administration to simultaneously reduce both ischemic and reperfusion injury.

Improved Functional Outcome After Peripheral Nerve Stimulation of the Impaired Forelimb Post-stroke

Lack of blood flow to the brain, i.e., ischemic stroke, results in loss of nerve cells and therefore loss of function in the effected brain regions. There is no effective treatment to improve lost function except restoring blood flow within the first several hours. Rehabilitation strategies are widely used with limited success. The purpose of this study was to examine the effect of electrical stimulation on the impaired upper extremity to improve functional recovery after stroke. We developed a rodent model using an electrode cuff implant onto a single peripheral nerve (median nerve) of the paretic forelimb and applied daily electrical stimulation. The skilled forelimb reaching test was used to evaluate functional outcome after stroke and electrical stimulation. Anterograde axonal tracing from layer V pyramidal neurons with biotinylated dextran amine was done to evaluate the formation of new neuronal connections from the contralesional cortex to the deafferented spinal cord. Rats receiving electrical stimulation on the median nerve showed significant improvement in the skilled forelimb reaching test in comparison with stroke only and stroke with sham stimulation. Rats that received electrical stimulation also exhibited significant improvement in the latency to initiate adhesive removal from the impaired forelimb, indicating better sensory recovery. Furthermore, axonal tracing analysis showed a significant higher midline fiber crossing index in the cervical spinal cord of rats receiving electrical stimulation. Our results indicate that direct peripheral nerve stimulation leads to improved sensorimotor recovery in the stroke-impaired forelimb, and may be a useful approach to improve post-stroke deficits in human patients.

Constraint-induced movement therapy improves functional recovery after ischemic stroke and its impacts on synaptic plasticity in sensorimotor cortex and hippocampus

Constraint-induced movement therapy (CIMT) has proven to be an effective way to restore functional deficits following stroke in human and animal studies, but its underlying neural plasticity mechanism remains unknown. Accumulating evidence indicates that rehabilitation after stroke is closely associated with synaptic plasticity. We therefore investigated the impact of CIMT on synaptic plasticity in ipsilateral and contralateral brain of rats following stroke. Rats were subjected to 90 minutes of transient middle cerebral artery occlusion (MCAO). CIMT was performed from 7 days after stroke and lasted for two weeks. Modified Neurology Severity Score (mNSS) and the ladder rung walking task tests were conducted at 7,14 and 21 days after stroke. Golgi-Cox staining was used to observe the plasticity changes of dendrites and dendritic spines. The expression of glutamate receptors (GluR1, GluR2 and NR1) were examined by western blot. Our data suggest that the dendrites and dendritic spines are damaged to varying degrees in bilateral sensorimotor cortex and hippocampus after acute stroke. CIMT treatment enhances the plasticity of dendrites and dendritic spines in the ipsilateral and contralateral sensorimotor cortex, increases the expression of synaptic GluR2 in ipsilateral sensorimotor cortex, which may be mechanisms for CIMT to improve functional recovery after ischemic stroke.

Experimental pediatric stroke shows age-specific recovery of cognition and role of hippocampal Nogo-A receptor signaling

Ischemic stroke is a leading cause of death worldwide and clinical data suggest that children may recover from stroke better than adults; however, supporting experimental data are lacking. We used our novel mouse model of experimental juvenile ischemic stroke (MCAO) to characterize age-specific cognitive dysfunction following ischemia. Juvenile and adult mice subjected to 45-min MCAO, and extracellular field recordings of CA1 neurons were performed to assess hippocampal synaptic plasticity changes after MCAO, and contextual fear conditioning was performed to evaluate memory and biochemistry used to analyze Nogo-A expression. Juvenile mice showed impaired synaptic plasticity seven days after MCAO, followed by full recovery by 30 days. Memory behavior was consistent with synaptic impairments and recovery after juvenile MCAO. Nogo-A expression increased in ipsilateral hippocampus seven days after MCAO compared to contralateral and sham hippocampus. Further, inhibition of Nogo-A receptors reversed MCAO-induced synaptic impairment in slices obtained seven days after juvenile MCAO. Adult MCAO-induced impairment of LTP was not associated with increased Nogo-A. This study demonstrates that stroke causes functional impairment in the hippocampus and recovery of behavioral and synaptic function is more robust in the young brain. Nogo-A receptor activity may account for the impairments seen following juvenile ischemic injury.

Influencing neuroplasticity in stroke treatment with advanced biomaterials-based approaches

Since the early 1990s, we have known that the adult brain is not static and has the capacity to repair itself. The delivery of various therapeutic factors and cells have resulted in some exciting pre-clinical and clinical outcomes in stroke models by targeting post-injury plasticity to enhance recovery. Developing a deeper understanding of the pathways that modulate plasticity will enable us to optimize delivery strategies for therapeutics and achieve more robust effects. Biomaterials are a key tool for the optimization of these potential treatments, owing to their biocompatibility and tunability. In this review, we identify factors and targets that impact plastic processes known to contribute to recovery, discuss the role of biomaterials in enhancing the efficacy of treatment strategies, and suggest combinatorial approaches based on the stage of injury progression.

Early constraint-induced movement therapy affects behavior and neuronal plasticity in ischemia-injured rat brains

Constraint-induced movement therapy is an effective rehabilitative training technique used to improve the restoration of impaired upper extremity movement after stroke. However, whether constraint-induced movement therapy is more effective than conventional rehabilitation in acute or sub-acute stroke remains controversial. The aim of the present study was to identify the optimal time to start constraint-induced movement therapy after ischemic stroke and to explore the mechanisms by which constraint-induced movement therapy leads to post-stroke recovery. Sixty-four adult male Sprague-Dawley rats were randomly divided into four groups: sham-surgery group, cerebral ischemia/reperfusion group, early constraint-induced movement therapy group, and late constraint-induced movement therapy group. Rat models of left middle cerebral artery occlusion were established according to the Zea Longa line embolism method. Constraint-induced movement therapy was conducted starting on day 1 or day 14 in the early constraint-induced movement therapy and late constraint-induced movement therapy groups, respectively. To explore the effect of each intervention time on neuromotor function, behavioral function was assessed using a balance beam walking test before surgery and at 8 and 21 days after surgery. The expression levels of brain-derived neurotrophic factor, nerve growth factor and Nogo receptor were evaluated using real time-polymerase chain reaction and western blot assay to assess the effect of each intervention time. The results showed that the behavioral score was significantly lower in the early constraint-induced movement therapy group than in the cerebral ischemia/reperfusion and late constraint-induced movement therapy groups at 8 days. At 21 days, the scores had significantly decreased in the early constraint-induced movement therapy and late constraint-induced movement therapy groups. At 8 days, only mild pyknosis appeared in neurons of the ischemic penumbra in the early constraint-induced movement therapy group, which was distinctly better than in the cerebral ischemia/reperfusion group. At 21 days, only a few vacuolated cells were observed and no obvious inflammatory cells were visible in late constraint-induced movement therapy group, which was much better than at 8 days. The mRNA and protein expression levels of brain-derived neurotrophic factor and nerve growth factor were significantly higher, but expression levels of Nogo receptor were significantly lower in the early constraint-induced movement therapy group compared with the cerebral ischemia/reperfusion and late constraint-induced movement therapy groups at 8 days. The changes in expression levels at 21 days were larger but similar in both the early constraint-induced movement therapy and late constraint-induced movement therapy groups. Besides, the protein nerve growth factor level was higher in the late constraint-induced movement therapy group than in the early constraint-induced movement therapy group at 21 days. These results suggest that both early (1 day) and late (14 days) constraint-induced movement therapy induces molecular plasticity and facilitates functional recovery after ischemic stroke, as illustrated by the histology. The mechanism may be associated with downregulation of Nogo receptor expression and upregulation of brain-derived neurotrophic factor and nerve growth factor expression.