The effect of intrathecal injection of irisin on pain threshold and expression rate of GABAB receptors in peripheral neuropathic pain model

Does irisin has neuroprotective effect against diabetes induced neuropathy in male rats?

We aimed to investigate the contribution of irisin in the neuroprotective process of exercise training in diabetic rats. Serum irisin levels, thermal and mechanical pain thresholds and intracellular calcium ([Ca²⁺]_i) levels in sensory neurons were measured at different time intervals during the eight weeks of exercise sessions for the control, non-exercise diabetics (3 groups) and exercise performing (low and high intensity groups) diabetic rats (n = 7-10 for all groups). Non-exercise diabetic groups were treated with irisin in different doses (1, 10 and 20 µg/kg respectively). Recovered pain thresholds at the end of the exercise sessions (p < .05), higher serum irisin levels that compared to control and diabetics (p < .05) and insignificant mean [Ca2⁺]_i peak amplitudes in sensory neurons (p > .05) obtained from experiments. Furthermore, irisin injection decreased the thermal pain threshold of diabetics only at 60th minutes (p < .05). Irisin may have a role in the neuroprotective effect of exercise training.

Spinal Irisin Gene Delivery Attenuates Burn Injury-Induced Muscle Atrophy by Promoting Axonal Myelination and Innervation of Neuromuscular Junctions

Muscle loss and weakness after a burn injury are typically the consequences of neuronal dysregulation and metabolic change. Hypermetabolism has been noted to cause muscle atrophy. However, the mechanism underlying the development of burn-induced motor neuropathy and its contribution to muscle atrophy warrant elucidation. Current therapeutic interventions for burn-induced motor neuropathy demonstrate moderate efficacy and have side effects, which limit their usage. We previously used a third-degree burn injury rodent model and found that irisin-an exercise-induced myokine-exerts a protective effect against burn injury-induced sensory and motor neuropathy by attenuating neuronal damage in the spinal cord. In the current study, spinal irisin gene delivery was noted to attenuate burn injury-induced sciatic nerve demyelination and reduction of neuromuscular junction innervation. Spinal overexpression of irisin leads to myelination rehabilitation and muscular innervation through the modulation of brain-derived neurotrophic factor and glial-cell-line-derived neurotrophic factor expression along the sciatic nerve to the muscle tissues and thereby modulates the Akt/mTOR pathway and metabolic derangement and prevents muscle atrophy.

Irisin: A promising treatment for neurodegenerative diseases

The beneficial effects of exercise on human brain function have been demonstrated in previous studies. Myokines secreted by muscle have attracted increasing attention because of their bridging role between exercise and brain health. Regulated by PPARγ coactivator 1α, fibronectin type III domain-containing protein 5 releases irisin after proteolytic cleavage. Irisin, a type of myokine, is secreted during exercise, which induces white adipose tissue browning and relates to energy metabolism. Recently, irisin has been shown to exert a protective effect on the central nervous system. Irisin secretion triggers an increase in brain-derived neurotrophic factor levels in the hippocampus, contributing to the amelioration of cognition impairments. Irisin also plays an important role in the survival, differentiation, growth, and development of neurons. This review summarizes the role of irisin in neurodegenerative diseases and other neurological disorders. As a novel positive mediator of exercise in the brain, irisin may effectively prevent or decelerate the progress of neurodegenerative diseases in models and also improve cognitive functions. We place emphasis herein on the potential of irisin for prevention rather than treatment in neurodegenerative diseases. In ischemic diseases, irisin can alleviate the pathophysiological processes associated with stroke. Meanwhile, irisin has anxiolytic and antidepressant effects. The potential therapeutic effects of irisin in epilepsy and pain have been initially revealed. Due to the pleiotropic and beneficial properties of irisin, the possibility of irisin treating other neurological diseases could be gradually explored in the future.

Physiological Changes and Pathological Pain Associated with Sedentary Lifestyle-Induced Body Systems Fat Accumulation and Their Modulation by Physical Exercise

A sedentary lifestyle is associated with overweight/obesity, which involves excessive fat body accumulation, triggering structural and functional changes in tissues, organs, and body systems. Research shows that this fat accumulation is responsible for several comorbidities, including cardiovascular, gastrointestinal, and metabolic dysfunctions, as well as pathological pain behaviors. These health concerns are related to the crosstalk between adipose tissue and body systems, leading to pathophysiological changes to the latter. To deal with these health issues, it has been suggested that physical exercise may reverse part of these obesity-related pathologies by modulating the cross talk between the adipose tissue and body systems. In this context, this review was carried out to provide knowledge about (i) the structural and functional changes in tissues, organs, and body systems from accumulation of fat in obesity, emphasizing the crosstalk between fat and body tissues; (ii) the crosstalk between fat and body tissues triggering pain; and (iii) the effects of physical exercise on body tissues and organs in obese and non-obese subjects, and their impact on pathological pain. This information may help one to better understand this crosstalk and the factors involved, and it could be useful in designing more specific training interventions (according to the nature of the comorbidity).

Muscle-brain communication in pain: The key role of myokines

Pain is the most common reason for a physician visit, which accounts for a considerable proportion of the global burden of disease and greatly affects patients' quality of life. Therefore, there is an urgent need to identify new therapeutic targets involved in pain. Exercise-induced hypoalgesia (EIH) is a well known phenomenon observed worldwide. However, the available evidence demonstrates that the mechanisms of EIH remain unclear. One of the most accepted hypotheses has been the activation of several endogenous systems in the brain. Recently, the concept that the muscle acts as a secretory organ has attracted increasing attention. Proteins secreted by the muscle are called myokines, playing a critical role in communicating with other organs, such as the brain. This review will focus on several myokines and discuss their roles in EIH.

Upregulation of ubiquitin conjugating enzyme E2B (Ube2b) ameliorates neuropathic pain by regulating Kcna2 (potassium voltage-gated channel subfamily A member 2) in primary afferent neurons

Neuropathic pain is a kind of pain caused by damage to somatosensory nervous system. Currently, neuropathic pain is still a medical problem for clinicians. Ubiquitin conjugating enzyme E2B (Ube2b) is validated to be implicated with nerve function, but whether Ube2b can play a role in neuropathic pain is still elusive. In this work, we constructed chronic constriction injury (CCI) rat model by ligating the left sciatic nerve, Ube2b protein expression was confirmed to be decreased in spinal cord tissues of CCI rats via Western blot analysis and immunofluorescence (IF) staining. Moreover, Ube2b elevation alleviated the thermal hyperalgesia and mechanical hyperalgesia in CCI rats according to paw withdrawal thermal latency (PWTL) and paw withdrawal mechanic threshold (PWMT). In addition, Hematoxylin-eosin staining revealed that Ube2b elevation suppressed chronic sciatic nerve injury. All these data suggested that Ube2b could ameliorate neuropathic pain in CCI rats. Mechanically, Ube2b upregulation elevated the protein level of Kcna2 (potassium voltage-gated channel subfamily A member 2) and decreased the protein level of DNMT3a (DNA methyltransferase 3 alpha). Ube2b elevation could increase Kcna2 expression via suppressing DNMT3a. Rescue assays unveiled that Ube2b overexpression modulated-mechanical hyperalgesia and thermal hyperalgesia were reversed by Kcna2 depletion, indicating that Ube2b alleviated neuropathic pain via mediating Kcna2 via the regulation of DNMT3a. In summary, we found that Ube2b elevation ameliorated neuropathic pain through regulating Kcna2, which might offer a novel biomarker for the therapies of neuropathic pain.

FNDC5/Irisin System in Neuroinflammation and Neurodegenerative Diseases: Update and Novel Perspective

Irisin, the circulating peptide originating from fibronectin type III domain-containing protein 5 (FNDC5), is mainly expressed by muscle fibers under peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) control during exercise. In addition to several beneficial effects on health, physical activity positively affects nervous system functioning, particularly the hippocampus, resulting in amelioration of cognition impairments. Recently, FNDC5/irisin detection in hippocampal neurons and the presence of irisin in the cerebrospinal fluid opened a new intriguing chapter in irisin history. Interestingly, in the hippocampus of mice, exercise increases FNDC5 levels and upregulates brain-derived neurotrophic factor (BDNF) expression. BDNF, displaying neuroprotection and anti-inflammatory effects, is mainly produced by microglia and astrocytes. In this review, we discuss how these glial cells can morphologically and functionally switch during neuroinflammation by modulating the expression of a plethora of neuroprotective or neurotoxic factors. We also focus on studies investigating the irisin role in neurodegenerative diseases (ND). The emerging involvement of irisin as a mediator of the multiple positive effects of exercise on the brain needs further studies to better deepen this issue and the potential use in therapeutic approaches for neuroinflammation and ND.

Irisin Gene Delivery Ameliorates Burn-Induced Sensory and Motor Neuropathy

Burn-related neuropathy is common and often involves pain, paresthesia, or muscle weakness. Irisin, an exercise-induced myokine after cleavage from its membrane precursor fibronectin type III domain-containing 5 (FNDC5), exhibits neuroprotective and anti-inflammatory activities. A rat model of third-degree burn on the right hind paw was used to investigate the therapeutic role of irisin/FNDC5. Rats received burn injury and were treated with intrathecal recombinant adenovirus containing the irisin sequence (Ad-irisin) at 3 weeks postburn. One week later, mechanical allodynia was examined. The expression of irisin in cerebrospinal fluid (CSF) was detected. Ipsilateral gastrocnemius muscle and lumbar spinal cord were also obtained for further investigation. Furthermore, the anti-apoptotic effect of recombinant irisin in SH-SY5Y cells was evaluated through tumor necrosis factor alpha (TNFα) stimulus to mimic burn injury. We noted intrathecal Ad-irisin attenuated pain sensitization and gastrocnemius muscle atrophy by modulating the level of irisin in CSF, and the expression of neuronal FNDC5/irisin and TNFα in the spinal cord. Ad-irisin also ameliorated neuronal apoptosis in both dorsal and ventral horns. Furthermore, recombinant irisin attenuated TNFα-induced SH-SY5Y cell apoptosis. In summary, irisin attenuated allodynia and muscle wasting by ameliorating neuroinflammation-induced neuronal apoptosis.

The optimal therapeutic irisin dose intervention in animal model: A systematic review

Background and Aim:

Irisin, a novel myocyte-secreted hormone, was proposed to mediate some of the beneficial effects of exercise such as browning of adipocytes, thermogenesis, and metabolic homeostasis. Recently, several animals’ models’ studies have been performed to investigate the therapeutic impact of irisin in several disorders. Several interventional trials used different doses. However, optimum dose was not determined. This systematic review aims to identify the optimal dose of interventional irisin in mice and rat animal models.

Materials and Methods:

Online databases PubMed, Google Scholar, and Springer were systematically searched from 2012 to 2019. The words searched were irisin, irisin and animal model, physical activity, and irisin and irisin dosage. Non-irisin doses, in vitro studies, and factors influencing irisin levels were excluded.

Results:

Eleven of the total 391 qualifying studies were included. A daily injection of 500 μg/kg irisin may be the optimum dose of effect in mice and rats.

Conclusion:

More studies are required to determine the optimum dose of irisin to be used as a therapeutic intervention based on animal model.

Possible Neuroprotective Mechanisms of Physical Exercise in Neurodegeneration

Physical exercise (PE) improves physical performance, mental status, general health, and well-being. It does so by affecting many mechanisms at the cellular and molecular level. PE is beneficial for people suffering from neuro-degenerative diseases because it improves the production of neurotrophic factors, neurotransmitters, and hormones. PE promotes neuronal survival and neuroplasticity and also optimizes neuroendocrine and physiological responses to psychosocial and physical stress. PE sensitizes the parasympathetic nervous system (PNS), Autonomic Nervous System (ANS) and central nervous system (CNS) by promoting many processes such as synaptic plasticity, neurogenesis, angiogenesis, and autophagy. Overall, it carries out many protective and preventive activities such as improvements in memory, cognition, sleep and mood; growth of new blood vessels in nervous system; and the reduction of stress, anxiety, neuro-inflammation, and insulin resistance. In the present work, the protective effects of PE were overviewed. Suitable examples from the current research work in this context are also given in the article.

Effect of electroacupuncture on the expression of P2 × 4, GABAA γ 2 and long-term potentiation in spinal cord of rats with neuropathic pain

OBJECTIVE

To observe the impacts of electroacupuncture (EA) stimulation at "Zusanli and Kunlun Points" on spinal dorsal horn microglia activation in L5 spinal nerve ligation (SNL) rats and BNDF, P2 × 4 and GABAAγ2, and the changes in spinal dorsal horn synaptic plasticity in model rats.

METHODS

Adult male SD rats (180-220 g) were selected and randomly divided into 6 groups, including the sham group, the SNL group, the SNL + EA group, the SNL+5-BDBD group, the SNL + EA + 5-BDBD group and the SNL + FEA group. The changes in the Iba-1, BDNF, P2 × 4 and GABAAγ2 in the spinal cord of rats were observed by Western blotting, immunofluorescence, RT-PCR and other techniques; the long-term changes in the potential after the excitatory synapse of the spinal dorsal horn in rats were observed by in vivo electrophysiological technique.

RESULTS

After 7 days of intervention, the fluorescence intensity (FI) of P2 × 4 and Iba-1 in the SNL + EA group was lower than that in the SNL group and higher than that in the sham group(P < 0.01), but the FI of GABA_Aγ2 was higher than that in the SNL group(P < 0.01); the expression of Iba-1, BDNF and P2 × 4 proteins in the SNL + EA group, the SNL+5-BDBD group and the SNL + EA + 5-BDBD group was significantly lower than that in the SNL + FEA group(P < 0.05), but the expression of GABAAγ2 protein was higher (P < 0.05); after treatment with EA, the expression levels of Iba-1 mRNA and P2 × 4 mRNA in the SNL + EA group were lower than those in the SNL group(P < 0.01), but the expression levels of GABAAγ2 mRNA were higher (P < 0.01). Meanwhile, long-term potentiation changes could not be induced in the SNL + EA group.

CONCLUSION

The EA stimulation at "Zusanli" and "Kunlun" points can improve the pain threshold of rats with neuropathic pain (NP), inhibit the excitatory postsynaptic potential (EPSP), and weaken the excitatory transmission efficiency between synapses during NP.

Co-administration of human adipose-derived stem cells and low-level laser to alleviate neuropathic pain after experimental spinal cord injury

BACKGROUND

Evidence has suggested that human adipose-derived stem cells (hADSCs) and low-level laser has neuroprotective effects on spinal cord injury (SCI). Therefore, the combined effect of the hADSCs and laser on neuregeneration and neuropathic pain after SCI was investigated.

METHODS

Forty-eight adult male Wistar rats with 200-250 g weight were used. Thirty minutes after compression, injury with laser was irritated, and 1 week following SCI, about 1 × 106 cells were transplanted into the spinal cord. Motor function and neuropathic pain were assessed weekly. Molecular and histological studies were done at the end of the fourth week.

RESULTS

The combined application of hADSCs and laser has significantly improved motor function recovery (p = 0.0001), hyperalgesia (p < 0.05), and allodynia (p < 0.05). GDNF mRNA expression was significantly increased in hADSCs and laser+hADSC-treated animals (p < 0.001). Finally, co-administration of hADSCs and laser has enhanced the number of axons around cavity more than other treatments (p < 0.001).

CONCLUSIONS

The results showed that the combination of laser and ADSCs could significantly improve the motor function and alleviate SCI-induced allodynia and hyperalgesia. Therefore, using a combination of laser and hADSCs in future experimental and translational clinical studies is suggested.