Current Status of Therapeutic Approaches against Peripheral Nerve Injuries: A Detailed Story from Injury to Recovery

Peripheral nerve injury is a complex condition with a variety of signs and symptoms such as numbness, tingling, jabbing, throbbing, burning or sharp pain. Peripheral nerves are fragile in nature and can easily get damaged due to acute compression or trauma which may lead to the sensory and motor functions deficits and even lifelong disability. After lesion, the neuronal cell body becomes disconnected from the axon's distal portion to the injury site leading to the axonal degeneration and dismantlement of neuromuscular junctions of targeted muscles. In spite of extensive research on this aspect, complete functional recovery still remains a challenge to be resolved. This review highlights detailed pathophysiological events after an injury to a peripheral nerve and the associated factors that can either hinder or promote the regenerative machinery. In addition, it throws light on the available therapeutic strategies including supporting therapies, surgical and non-surgical interventions to ameliorate the axonal regeneration, neuronal survival, and reinnervation of peripheral targets. Despite the availability of various treatment options, we are still lacking the optimal treatments for a perfect and complete functional regain. The need for the present age is to discover or design such potent compounds that would be able to execute the complete functional retrieval. In this regard, plant-derived compounds are getting more attention and several recent reports validate their remedial effects. A plethora of plants and plant-derived phytochemicals have been suggested with curative effects against a number of diseases in general and neuronal injury in particular. They can be a ray of hope for the suffering individuals.

Foeniculum vulgare (Fennel) promotes functional recovery and ameliorates oxidative stress following a lesion to the sciatic nerve in mouse model

Peripheral nerve injury is one of the major health concerns of the present era which can lead to the long-lasting disability and even demise. Currently, no effective and side effect free remedy exists and exploration of effective therapeutic strategies to regain functional outcome is a need of hour. In the present study, we used BALB/c mice (N = 14 age, 10-12 weeks & weight 32-34 g) that were divided into two groups: Normal chow (n = 7) and Fennel chow (n = 7) group. Here, we have explored the role of crude Foeniculum vulgare mill seeds in promoting functional recovery following a mechanical insult to the sciatic nerve by an oral administration of a crude dose of 500 mg/kg BW. The recovery of both sensory and motor functions was significantly (p > .05) accelerated in the treatment group, assessed by behavioral analyses alongside total antioxidant capacity increase. Conclusively, F. vulgare can be a potential therapeutic candidate for accelerating functional recovery after peripheral nerve injury. PRACTICAL APPLICATIONS: The outcomes of study have vital practical application both for scientists and consumers. The therapeutic role of phytochemicals on functional recovery has not been explored yet. This study will help figure out plant based regimen as booster for brain health and intervention against traumatic nerve injuries. Moreover, it may also attract the food and pharmaceutical industries to formulate cost effective therapeutic products. Likewise, it can prove instrumental for scientists for advance research on this aspect with more mechanistic targets.

Supplementation of Cannabis sativa L. leaf powder accelerates functional recovery and ameliorates haemoglobin level following an induced injury to sciatic nerve in mouse model

Peripheral nerve injury is a common condition with a multitude of signs and symptoms. The major consequence of injury is limited physical activity. Presently, we are lacking effective therapies for PNI and it is need of the hour is to explore potential remedies for the recovery of functional loss. Here, we have investigated the role of crude Cannabis sativa L. leaf powder in promoting functions recovery, in mouse model subjected to a traumatic sciatic nerve injury. A dose of 200mg/kg of the body weight per day was administered orally from the day of nerve crush till the end of the experiment. The motor functions were evaluated by measuring sciatic functional index, muscle grip strength and muscle mass; whereas the sensory functions were assessed by hotplate test. The haematology and serum analyses were carried out to estimate the effect of treatment on the systemic index and oxidative stress. The gain of motor functions was significantly improved and was early noticed in the treated mice. Restoration of muscle mass and elevated haemoglobin level were statistically significant in the treatment group. This study indicates that Cannabis sativa L. supplementation accelerates the motor functions recovery after nerve compression injury.

Fatting the brain: a brief of recent research

Fatty acids are of paramount importance to all cells, since they provide energy, function as signaling molecules, and sustain structural integrity of cellular membranes. In the nervous system, where fatty acids are found in huge amounts, they participate in its development and maintenance throughout life. Growing evidence strongly indicates that fatty acids in their own right are also implicated in pathological conditions, including neurodegenerative diseases, mental disorders, stroke, and trauma. In this review, we focus on recent studies that demonstrate the relationships between fatty acids and function and dysfunction of the nervous system. Fatty acids stimulate gene expression and neuronal activity, boost synaptogenesis and neurogenesis, and prevent neuroinflammation and apoptosis. By doing so, they promote brain development, ameliorate cognitive functions, serve as anti-depressants and anti-convulsants, bestow protection against traumatic insults, and enhance repairing processes. On the other hand, unbalance between different fatty acid families or excess of some of them generate deleterious side effects, which limit the translatability of successful results in experimental settings into effective therapeutic strategies for humans. Despite these constraints, there exists realistic evidence to consider that nutritional therapies based on fatty acids can be of benefit to several currently incurable nervous system diseases.

Degeneration of serotonergic neurons in amyotrophic lateral sclerosis: a link to spasticity

Spasticity is a common and disabling symptom observed in patients with central nervous system diseases, including amyotrophic lateral sclerosis, a disease affecting both upper and lower motor neurons. In amyotrophic lateral sclerosis, spasticity is traditionally thought to be the result of degeneration of the upper motor neurons in the cerebral cortex, although degeneration of other neuronal types, in particular serotonergic neurons, might also represent a cause of spasticity. We performed a pathology study in seven patients with amyotrophic lateral sclerosis and six control subjects and observed that central serotonergic neurons suffer from a degenerative process with prominent neuritic degeneration, and sometimes loss of cell bodies in patients with amyotrophic lateral sclerosis. Moreover, distal serotonergic projections to spinal cord motor neurons and hippocampus systematically degenerated in patients with amyotrophic lateral sclerosis. In SOD1 (G86R) mice, a transgenic model of amyotrophic lateral sclerosis, serotonin levels were decreased in brainstem and spinal cord before onset of motor symptoms. Furthermore, there was noticeable atrophy of serotonin neuronal cell bodies along with neuritic degeneration at disease onset. We hypothesized that degeneration of serotonergic neurons could underlie spasticity in amyotrophic lateral sclerosis and investigated this hypothesis in vivo using tail muscle spastic-like contractions in response to mechanical stimulation as a measure of spasticity. In SOD1 (G86R) mice, tail muscle spastic-like contractions were observed at end-stage. Importantly, they were abolished by 5-hydroxytryptamine-2b/c receptors inverse agonists. In line with this, 5-hydroxytryptamine-2b receptor expression was strongly increased at disease onset. In all, we show that serotonergic neurons degenerate during amyotrophic lateral sclerosis, and that this might underlie spasticity in mice. Further research is needed to determine whether inverse agonists of 5-hydroxytryptamine-2b/c receptors could be of interest in treating spasticity in patients with amyotrophic lateral sclerosis.

Mutations in cytoplasmic dynein lead to a Huntington's disease-like defect in energy metabolism of brown and white adipose tissues

The molecular motor dynein is regulated by the huntingtin protein, and Huntington's disease (HD) mutations of huntingtin disrupt dynein motor activity. Besides abnormalities in the central nervous system, HD animal models develop prominent peripheral pathology, with defective brown tissue thermogenesis and dysfunctional white adipocytes, but whether this peripheral phenotype is recapitulated by dynein dysfunction is unknown. Here, we observed prominently increased adiposity in mice harboring the legs at odd angles (Loa/+) or the Cramping mutations (Cra/+) in the dynein heavy chain gene. In Cra/+ mice, hyperadiposity occurred in the absence of energy imbalance and was the result of impaired norepinephrine-stimulated lipolysis. A similar phenotype was observed in 3T3L1 adipocytes upon chemical inhibition of dynein showing that loss of functional dynein leads to impairment of lipolysis. Ex vivo, dynein mutant adipose tissue displayed increased reactive oxygen species production that was, at least partially, responsible for the decreased cellular responses to norepinephrine and subsequent defect in stimulated lipolysis. Dynein mutation also affected norepinephrine efficacy to elicit a thermogenic response and led to morphological abnormalities in brown adipose tissue and cold intolerance in dynein mutant mice. Interestingly, protein levels of huntingtin were decreased in dynein mutant adipose tissue. Collectively, our results provide genetic evidence that dynein plays a key role in lipid metabolism and thermogenesis through a modulation of oxidative stress elicited by norepinephrine. This peripheral phenotype of dynein mutant mice is similar to that observed in various animal models of HD, lending further support for a functional link between huntingtin and dynein.

Nogo receptor antagonizes p75NTR-dependent motor neuron death

The Nogo-66 receptor (NgR) plays a critical role in restricting axon regeneration in the central nervous system. This inhibitory action is in part mediated by a neuronal receptor complex containing p75NTR, a multifunctional receptor also well known to trigger cell death upon binding to neurotrophins such as NGF. In the present study, we show that Pep4 and NEP1-40, which are two peptides derived from the Nogo-66 sequence that modulate NgR-mediated neurite outgrowth inhibition, prevent NGF-stimulated p75NTR-dependent death of cultured embryonic motor neurons. They also confer protection on spinal cord motor neurons after neonatal sciatic nerve axotomy. These findings demonstrate an as-yet-unknown function of NgR in maintaining neuronal survival that may be relevant for motor neuron development and degeneration.

Gene profiling of skeletal muscle in an amyotrophic lateral sclerosis mouse model

Muscle atrophy is a major hallmark of amyotrophic lateral sclerosis (ALS), the most frequent adult-onset motor neuron disease. To define the full set of alterations in gene expression in skeletal muscle during the course of the disease, we used the G86R superoxide dismutase-1 transgenic mouse model of ALS and performed high-density oligonucleotide microarrays. We compared these data to those obtained by axotomy-induced denervation. A major set of gene regulations in G86R muscles resembled those of surgically denervated muscles, but many others appeared specific to the ALS condition. The first significant transcriptional changes appeared in a subpopulation of mice before the onset of overt clinical symptoms and motor neuron death. These early changes affected genes involved in detoxification (e.g., ALDH3, metallothionein-2, and thioredoxin-1) and regeneration (e.g., BTG1, RB1, and RUNX1) but also tissue degradation (e.g., C/EBPdelta and DDIT4) and cell death (e.g., ankyrin repeat domain-1, CDKN1A, GADD45alpha, and PEG3). Of particular interest, metallothionein-1 and -2, ATF3, cathepsin-Z, and galectin-3 genes appeared, among others, commonly regulated in both skeletal muscle (our present data) and spinal motor neurons (as previously reported) of paralyzed ALS mice. The importance of these findings is twofold. First, they designate the distal part of the motor unit as a primary site of disease. Second, they identify specific gene regulations to be explored in the search for therapeutic strategies that could alleviate disease before motor neuron death manifests clinically.

Muscle Nogo-a expression is a prognostic marker in lower motor neuron syndromes

OBJECTIVE

A proportion of patients with pure lower motor neuron syndrome (LMNS) progress to amyotrophic lateral sclerosis (ALS). Early detection of this progression is impossible, which delays the patient's access to treatment. Muscle expression of Nogo-A is a new candidate marker of ALS. We tested whether detection of Nogo-A in a muscle biopsy from patients with LMNS predicts progression to ALS.

METHODS

Thirty-three patients who had undergone a muscle biopsy during the diagnostic workup of spinal LMNS were observed for 12 months. Nogo-A expression was measured by Western blot in muscle biopsy samples and compared with the final diagnosis.

RESULTS

Nogo-A expression was detected in 17 patients and was absent in 16 patients. The detection of Nogo-A in muscle biopsy samples from LMNS patients correctly identified patients who further progressed to ALS with 91% accuracy, 94% sensitivity, and 88% specificity. In patients who later developed typical ALS, Nogo-A may be detected as early as 3 months after the onset of symptoms.

INTERPRETATION

Nogo-A test is able to identify ALS early in the course of the disease when diagnosis is difficult, requiring further progression. Use of the test in clinical practice may shorten the delay before introduction of neuroprotective drugs or inclusion in clinical trials.

Sodium valproate exerts neuroprotective effects in vivo through CREB-binding protein-dependent mechanisms but does not improve survival in an amyotrophic lateral sclerosis mouse model

Amyotrophic lateral sclerosis (ALS) is characterized by motoneuron (MN) degeneration, generalized weakness, and muscle atrophy. The premature death of MNs is thought to be a determinant in the onset of this disease. In a transgenic mouse model of ALS expressing the G86R mutant superoxide dismutase 1 (mSOD1), we demonstrated previously that CREB (cAMP response element-binding protein)-binding protein (CBP) and histone acetylation levels were specifically decreased in nuclei of degenerating MNs. We show here that oxidative stress and mSOD1 overexpression can both impinge on CBP levels by transcriptional repression, in an MN-derived cell line. Histone deacetylase inhibitor (HDACi) treatment was able to reset proper acetylation levels and displayed an efficient neuroprotective capacity against oxidative stress in vitro. Interestingly, HDACi also upregulated CBP transcriptional expression in MNs. Moreover, when injected to G86R mice in vivo, the HDACi sodium valproate (VPA) maintained normal acetylation levels in the spinal cord, efficiently restored CBP levels in MNs, and significantly prevented MN death in these animals. However, despite neuroprotection, mean survival of treated animals was not significantly improved (<5%), and they died presenting the classical ALS symptoms. VPA was not able to prevent disruption of neuromuscular junctions, although it slightly delayed the onset of motor decline and retarded muscular atrophy to some extent. Together, these data show that neuroprotection can improve disease onset, but clearly provide evidence that one can uncouple MN survival from whole-animal survival and point to the neuromuscular junction perturbation as a primary event of ALS onset.

Amyotrophic lateral sclerosis: all roads lead to Rome

Amyotrophic lateral sclerosis (ALS) is the most frequent adult-onset motor neuron disease characterized by degeneration of upper and lower motor neurons, generalized weakness and muscle atrophy. Most cases of ALS appear sporadically but some forms of the disease result from mutations in the gene encoding the antioxidant enzyme Cu/Zn superoxide dismutase (SOD1). Several other mutated genes have also been found to predispose to ALS including, among others, one that encodes the regulator of axonal retrograde transport dynactin. As all roads lead to the proverbial Rome, we discuss here how distinct molecular pathways may converge to the same final result that is motor neuron death. We critically review the basic research on SOD1-linked ALS to propose a pioneering model of a 'systemic' form of the disease, causally involving multiple cell types, either neuronal or non-neuronal. Contrasting this, we also postulate that other neuron-specific defects, as those triggered by dynactin dysfunction, may account for a primary motor neuron disease that would represent 'pure' neuronal forms of ALS. Identifying different disease subtypes is an unavoidable step toward the understanding of the physiopathology of ALS and will hopefully help to design specific treatments for each subset of patients.

The neurite outgrowth inhibitor Nogo-A promotes denervation in an amyotrophic lateral sclerosis model

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by motor neuron loss and muscle wasting. In muscles of ALS patients, Nogo-A-a protein known to inhibit axon regeneration-is ectopically expressed at levels that correlate with the severity of the clinical symptoms. We now show that the genetic ablation of Nogo-A extends survival and reduces muscle denervation in a mouse model of ALS. In turn, overexpression of Nogo-A in wild-type muscle fibres leads to shrinkage of the postsynapse and retraction of the presynaptic motor ending. This suggests that the expression of Nogo-A occurring early in ALS skeletal muscle could cause repulsion and destabilization of the motor nerve terminals, and subsequent dying back of the axons and motor neurons.

Mitochondria in amyotrophic lateral sclerosis: a trigger and a target

Strong evidence shows that mitochondrial dysfunction is involved in amyotrophic lateral sclerosis (ALS), but despite the fact that mitochondria play a central role in excitotoxicity, oxidative stress and apoptosis, the intimate underlying mechanism linking mitochondrial defects to motor neuron degeneration in ALS still remains elusive. Morphological and functional abnormalities occur in mitochondria in ALS patients and related animal models, although their exact nature and extent are controversial. Recent studies postulate that the mislocalization in mitochondria of mutant forms of copper-zinc superoxide dismutase (SOD1), the only well-documented cause of familial ALS, may account for the toxic gain of function of the enzyme, and hence induce motor neuron death. On the other hand, mitochondrial dysfunction in ALS does not seem to be restricted only to motor neurons as it is also present in other tissues, particularly the skeletal muscle. The presence of this 'systemic' defect in energy metabolism associated with the disease is supported in skeletal muscle tissue by impaired mitochondrial respiration and overexpression of uncoupling protein 3. In addition, the lifespan of transgenic mutant SOD1 mice is increased by a highly energetic diet compensating both the metabolic defect and the motorneuronal function. In this review, we will focus on the mitochondrial dysfunction linked to ALS and the cause-and-effect relationships between mitochondria and the pathological mechanisms thought to be involved in the disease.

Reticulons as markers of neurological diseases: focus on amyotrophic lateral sclerosis

Reticulons (RTNs) are a family of proteins that are primarily associated with the endoplasmic reticulum. In mammals, four genes have been identified and referred as to rtn1, 2, 3 and the neurite outgrowth inhibitor rtn4/nogo. These genes generate multiple isoforms that contain a common C-terminal reticulon homology domain of 150-200 amino-acid residues. The N-terminal regions of RTNs are highly variable, and result from alternative splicing or differential promoter usage. Although widely distributed, the functions of RTNs are still poorly understood. Much interest has been focused on rtn4/nogo because of its activity as a potent inhibitor of axonal growth and repair. In the present study, we update recent knowledge on mammalian RTNs paying special attention to the involvement of these proteins as markers of neurological diseases. We also present recent data concerning RTN expression in amyotrophic lateral sclerosis, a fatal degenerative disorder characterized by loss of upper and lower motor neurons, and muscle atrophy. The rearrangement of RTN expression is regulated not only in suffering skeletal muscle but also preceding the onset of symptoms, and may relate to the disease process.

Effect of a cyclohexenonic long-chain fatty alcohol on calcium mobilization

Cyclohexenonic long-chain fatty alcohols constitute a family of synthetic compounds with trophic, secretagogue and antioxidant properties. Despite their multiple biological actions in neuronal and non-neuronal tissues, the intracellular mechanisms underlying CFA activity remain unknown. In the present study, we show that 3-(15-hydroxypentadecyl)-2,4,4-trimethyl-2-cyclohexen-1-one (tCFA15) directly mobilizes Ca(2+) in the pituitary neural lobe synaptosomes and in primary sensory neurons from dorsal root ganglia. This effect is dependent on the presence of extracellular Ca(2+), but does not involve transmembrane voltage-operated calcium channels. Using a combination of pharmacological agents that block or deplete intracellular Ca(2+) stores, our results suggest the implication of a calcium induced-calcium release mechanism evoked by tCFA15-induced Ca(2+) influx. To our knowledge, these findings constitute the first attempt towards the comprehension of the biological actions of cyclohexenonic long-chain fatty alcohols at a molecular level.

The metabolic hypothesis in amyotrophic lateral sclerosis: insights from mutant Cu/Zn-superoxide dismutase mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by selective loss of motor neurons and progressive muscle atrophy. A subset of patients harbors point mutations in the gene encoding Cu/Zn-superoxide dismutase (SOD1), which allowed the generation of transgenic mice that express different SOD1 mutations and develop an ALS-like pathology. Recently, we reported in these mice the occurrence of a characteristic defect in energy homeostasis and the beneficial effect on the course of the disease of a high-energy fat-enriched diet. In this review, we discuss the implication of these findings in the light of classical clinical observations concerning metabolic alterations in human ALS.

Nogo expression in muscle correlates with amyotrophic lateral sclerosis severity

Nogo, a protein inhibiting axonal regeneration, exhibits a characteristic isoform-specific pattern of expression in skeletal muscle of transgenic mice and patients with amyotrophic lateral sclerosis. Here, the increased levels of Nogo-A or Nogo-B in muscle biopsies of 15 amyotrophic lateral sclerosis patients significantly correlated with the severity of clinical disability and with the degree of muscle fiber atrophy. Nogo-A immunoreactivity was observed selectively in atrophic slow-twitch type I fibers. These results suggest that Nogo expression in muscle is a marker of amyotrophic lateral sclerosis severity.

Evidence for defective energy homeostasis in amyotrophic lateral sclerosis: benefit of a high-energy diet in a transgenic mouse model

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by selective loss of motor neurons and progressive muscle wasting. Growing evidence indicates that mitochondrial dysfunction, not only occurring in motor neurons but also in skeletal muscle, may play a crucial role in the pathogenesis. In this regard, the life expectancy of the ALS G93A mouse line is extended by creatine, an intracellular energy shuttle that ameliorates muscle function. Moreover, a population of patients with sporadic ALS exhibits a generalized hypermetabolic state of as yet unknown origin. Altogether, these findings led us to explore whether alterations in energy homeostasis may contribute to the disease process. Here, we show important variations in a number of metabolic indicators in transgenic ALS mice, which in all shows a metabolic deficit. These alterations were accompanied early in the asymptomatic phase of the disease by reduced adipose tissue accumulation, increased energy expenditure, and concomitant skeletal muscle hypermetabolism. Compensating this energetic imbalance with a highly energetic diet extended mean survival by 20%. In conclusion, we suggest that hypermetabolism, mainly of muscular origin, may represent by itself an additional driven force involved in increasing motor neuron vulnerability.

Nogo Provides a Molecular Marker for Diagnosis of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by the selective degeneration of upper and lower motor neurons. The lack of a molecular diagnostic marker is of increasing concern in view of the therapeutic strategies in development. Using an unbiased subtractive suppressive hybridization screen we have identified a clone encoding the neurite outgrowth inhibitor Nogo and shown that its isoforms display a characteristic altered expression in ALS. This was first confirmed by analyzing Nogo isoform expression in a transgenic ALS model at early asymptomatic stages where we found increased levels of Nogo-A and decreased Nogo-C and importantly, not following experimentally induced denervation. Furthermore, we confirmed these changes in both post-mortem and biopsy samples from diagnosed ALS patients but not control patients. Thus, the alteration in Nogo expression pattern, common to sporadic and familial ALS, represents a potential diagnosis tool and points strongly to Nogo having a central role in disease.