Analgesic Effect of Recombinant GABAergic Cells in a Model of Peripheral Neuropathic Pain

Attenuation of SCI-Induced Hypersensitivity by Intensive Locomotor Training and Recombinant GABAergic Cells

The underlying mechanisms of spinal cord injury (SCI)-induced chronic pain involve dysfunctional GABAergic signaling and enhanced NMDA signaling. Our previous studies showed that SCI hypersensitivity in rats can be attenuated by recombinant rat GABAergic cells releasing NMDA blocker serine-histogranin (SHG) and by intensive locomotor training (ILT). The current study combines these approaches and evaluates their analgesic effects on a model of SCI pain in rats. Cells were grafted into the spinal cord at 4 weeks post-SCI to target the chronic pain, and ILT was initiated 5 weeks post-SCI. The hypersensitivity was evaluated weekly, which was followed by histological and biochemical assays. Prolonged effects of the treatment were evaluated in subgroups of animals after we discontinued ILT. The results show attenuation of tactile, heat and cold hypersensitivity in all of the treated animals and reduced levels of proinflammatory cytokines IL1β and TNFα in the spinal tissue and CSF. Animals with recombinant grafts and ILT showed the preservation of analgesic effects even during sedentary periods when the ILT was discontinued. Retraining helped to re-establish the effect of long-term training in all of the groups, with the greatest impact being in animals with recombinant grafts. These findings suggest that intermittent training in combination with cell therapy might be an efficient approach to manage chronic pain in SCI patients.

Analgesic effect of recombinant GABAergic precursors releasing MVIIA in a model of peripheral nerve injury in rats

Development of chronic pain has been attributed to dysfunctional GABA signaling in the spinal cord. Direct pharmacological interventions on GABA signaling are usually not very efficient and often accompanied by side effects due to the widespread distribution of GABA receptors in CNS. Transplantation of GABAergic neuronal cells may restore the inhibitory potential in the spinal cord. Grafted cells may also release additional analgesic peptides by means of genetic engineering to further enhance the benefits of this approach. Conopeptides are ideal candidates for recombinant expression using cell-based strategies. The omega-conopeptide MVIIA is in clinical use for severe pain marketed as FDA approved Prialt in the form of intrathecal injections. The goal of this study was to develop transplantable recombinant GABAergic cells releasing conopeptide MVIIA and to evaluate the analgesic effect of the grafts in a model of peripheral nerve injury-induced pain. We have engineered and characterized the GABAergic progenitors expressing MVIIA. Recombinant and nonrecombinant cells were intraspinally injected into animals after the nerve injury. Animals were tested weekly up to 12 weeks for the presence of hypersensitivity, followed by histochemical and biochemical analysis of the tissue. We observed beneficial effects of the grafted cells in reducing hypersensitivity in all grafted animals, especially potent in the recombinant group. The level of pain-related cytokines was reduced in the grafted animals and correlation between these pain markers and actual behavior was indicated. This study demonstrated the feasibility of recombinant cell transplantation in the management of chronic pain.

The Effect of GABAergic Cells Transplantation on Allodynia and Hyperalgesia in Neuropathic Animals: A Systematic Review With Meta-Analysis

The role of GABAergic cell transplantation in improving neuropathic pain is controversial. We comprehensively searched the relevant literature to identify animal studies of GABAergic cell transplantation that recorded pain behaviors as an outcome according to the Cochrane Handbook 5.0.2. Controlled studies assessing the administration of GABAergic neurons or GABAergic neuronal progenitor cells to rat or mouse neuropathic pain animal models were included. Basic design information and mechanical allodynia thresholds and heat hyperalgesia thresholds data were collected. The risk of bias for the animal experiments was assessed according to the SYRCLE's tool. This study included 10 full-text articles. GABAergic cells transplantation leads to a statistically significant improvement of allodynia (SMD = 5.26; 95% confidence interval: 3.02–7.51; P < 0.001) and hyperalgesia (SMD: 4.10; 95% confidence interval: 1.84–6.35; P < 0.001). Differentiated GABAergic cells and without antibiotics using may have a better effect for improving neuropathic pain. GABAergic cell transplantation is a promising treatment for improving neuropathic pain. This systematic review and meta-analysis evaluated the effects of GABAergic cell transplantation on neuropathic pain, which can guide future clinical trials and possible clinical treatments, and better attenuate neuropathic pain caused by abnormal circuit hyperexcitability.

The efficacy of GABAergic precursor cells transplantation in alleviating neuropathic pain in animal models: a systematic review and meta-analysis

Background

Current therapies are quite unsuccessful in the management of neuropathic pain. Therefore, considering the inhibitory characteristics of GABA mediators, the present systematic review and meta-analysis aimed to determine the efficacy of GABAergic neural precursor cells on neuropathic pain management.

Methods

Search was conducted on Medline, Embase, Scopus, and Web of Science databases. A search strategy was designed based on the keywords related to GABAergic cells combined with neuropathic pain. The outcomes were allodynia and hyperalgesia. The results were reported as a pooled standardized mean difference (SMD) with a 95% confidence interval (95% CI).

Results

Data of 13 studies were analyzed in the present meta-analysis. The results showed that administration of GABAergic cells improved allodynia (SMD = 1.79; 95% CI 0.87, 271; P < 0.001) and hyperalgesia (SMD = 1.29; 95% CI 0.26, 2.32; P = 0.019). Moreover, the analyses demonstrated that the efficacy of GABAergic cells in the management of allodynia and hyperalgesia is only observed in rats. Also, only genetically modified cells are effective in improving both of allodynia, and hyperalgesia.

Conclusions

A moderate level of pre-clinical evidence showed that transplantation of genetically-modified GABAergic cells is effective in the management of neuropathic pain. However, it seems that the transplantation efficacy of these cells is only statistically significant in improving pain symptoms in rats. Hence, caution should be exercised regarding the generalizability and the translation of the findings from rats and mice studies to large animal studies and clinical trials.

Intensive Locomotor Training Provides Sustained Alleviation of Chronic Spinal Cord Injury-Associated Neuropathic Pain: A Two-Year Pre-Clinical Study

Neuropathic pain often accompanies the functional deficits associated with spinal cord injury (SCI) and further reduces a patient's quality of life. Clinical and pre-clinical research is beginning to highlight the beneficial role that rehabilitative therapies such as locomotor training can have not only on functional recovery but also on chronic pain management. Our group has previously developed an intensive locomotor training (ILT) treadmill protocol on rats that reduced SCI neuropathic pain symptoms for at least 3 months. We have extended these findings in the current study to evaluate the ability of regular ILT regimen over a 2 year period post-SCI to maintain neuropathic pain reduction. To assess this, the rat clip compression SCI model (T7/8) was used and treadmill training was initiated starting 4 weeks after SCI and continuing through the duration of the study. Results showed continued suppression of SCI neuropathic pain responses (reduced mechanical, heat, and cold hypersensitivity throughout the entire time course of the study). In contrast, non-exercised rats showed consistent and sustained neuropathic pain responses during this period. In addition, prolonged survival and improved locomotor outcomes were observed in rats undergoing ILT as the study longevity progressed. Potential contributory mechanisms underlying beneficial effects of ILT include reduced inflammation and restoration of anti-nociceptive inhibitory processes as indicated by neurochemical assays in spinal tissue of remaining rats at 2 years post-SCI. The benefits of chronic ILT suggest that long-term physical exercise therapy can produce powerful and prolonged management of neuropathic pain, partly through sustained reduction of spinal pathological processes.

Mutually beneficial effects of intensive exercise and GABAergic neural progenitor cell transplants in reducing neuropathic pain and spinal pathology in rats with spinal cord injury

Spinal cord injury (SCI) produces both locomotor deficits and sensory dysfunction that greatly reduce the overall quality of life. Mechanisms underlying chronic pain include increased neuro-inflammation and changes in spinal processing of sensory signals, with reduced inhibitory GABAergic signaling a likely key player. Our previous research demonstrated that spinal transplantation of GABAergic neural progenitor cells (NPCs) reduced neuropathic pain while intensive locomotor training (ILT) could reduce development of pain and partially reverse already established pain behaviors. Therefore, we evaluate the potential mutually beneficial anti-hypersensitivity effects of NPC transplants cells in combination with early or delayed ILT. NPC transplants were done at 4 weeks post-SCI. ILT, using a progressive ramping treadmill protocol, was initiated either 5 days post-SCI (early: pain prevention group) or at 5 weeks post-SCI (delayed: to reverse established pain) in male Sprague Dawley rats. Results showed that either ILT alone or NPCs alone could partially attenuate SCI neuropathic pain behaviors in both prevention and reversal paradigms. However, the combination of ILT with NPC transplants significantly enhanced neuropathic pain reduction on most of the outcome measures including tests for allodynia, hyperalgesia, and ongoing pain. Immunocytochemical and neurochemical analyses showed decreased pro-inflammatory markers and spinal pathology with individual treatments; these measures were further improved by the combination of either early or delayed ILT and GABAergic cellular transplantation. Lumbar dorsal horn GABAergic neuronal and process density were nearly restored to normal levels by the combination treatment. Together, these interventions may provide a less hostile and more supportive environment for promoting functional restoration in the spinal dorsal horn and attenuation of neuropathic pain following SCI. These findings suggest mutually beneficial effects of ILT and NPC transplants for reducing SCI neuropathic pain.

Calcium Signaling in Vertebrate Development and Its Role in Disease

Accumulating evidence over the past three decades suggests that altered calcium signaling during development may be a major driving force for adult pathophysiological events. Well over a hundred human genes encode proteins that are specifically dedicated to calcium homeostasis and calcium signaling, and the majority of these are expressed during embryonic development. Recent advances in molecular techniques have identified impaired calcium signaling during development due to either mutations or dysregulation of these proteins. This impaired signaling has been implicated in various human diseases ranging from cardiac malformations to epilepsy. Although the molecular basis of these and other diseases have been well studied in adult systems, the potential developmental origins of such diseases are less well characterized. In this review, we will discuss the recent evidence that examines different patterns of calcium activity during early development, as well as potential medical conditions associated with its dysregulation. Studies performed using various model organisms, including zebrafish, Xenopus, and mouse, have underscored the critical role of calcium activity in infertility, abortive pregnancy, developmental defects, and a range of diseases which manifest later in life. Understanding the underlying mechanisms by which calcium regulates these diverse developmental processes remains a challenge; however, this knowledge will potentially enable calcium signaling to be used as a therapeutic target in regenerative and personalized medicine.

Microencapsulated Schwann cell transplantation inhibits P2X3 receptor expression in dorsal root ganglia and neuropathic pain

Schwann cell transplantation is a promising method to promote neural repair, and can be used for peripheral nerve protection and myelination. Microcapsule technology largely mitigates immune rejection of transplanted cells. We previously showed that microencapsulated olfactory ensheathing cells can reduce neuropathic pain and we hypothesized that microencapsulated Schwann cells can also inhibit neuropathic pain. Rat Schwann cells were cultured by subculture and then microencapsulated and were tested using a rat chronic constriction injury (CCI) neuropathic pain model. CCI rats were treated with Schwann cells or microencapsulated Schwann cells and were compared with sham and CCI groups. Mechanical withdrawal threshold and thermal withdrawal latency were assessed preoperatively and at 1, 3, 5, 7, 9, 11 and 14 days postoperatively. The expression of P2X3 receptors in L4-5 dorsal root ganglia of the different groups was detected by double-label immunofluorescence on day 14 after surgery. Compared with the chronic constriction injury group, mechanical withdrawal threshold and thermal withdrawal latency were higher, but the expression of P2X3 receptors was remarkably decreased in rats treated with Schwann cells and microencapsulated Schwann cells, especially in the rats transplanted with microencapsulated Schwann cells. The above data show that microencapsulated Schwann cell transplantation inhibits P2X3 receptor expression in L4-5 dorsal root ganglia and neuropathic pain.

Experimental Gene Therapy with Serine-Histogranin and Endomorphin 1 for the Treatment of Chronic Neuropathic Pain

The insufficient pain relief provided by current pharmacotherapy for chronic neuropathic pain is a serious medical problem. The enhanced glutamate signaling via NMDA receptors appears to be one of the key events in the development of chronic pain. Although effective, clinical use of systemic NMDA antagonists is limited by adverse effects such as hallucinations and motor dysfunction. Opioids are also potent analgesics but their chronic use is accompanied by tolerance and risk of addiction. However, combination of NMDA antagonists and opioids seems to provide a stable pain relieve at subthreshold doses of both substances, eliminating development of side effects. Our previous research showed that combined delivery of NMDA antagonist Serine histrogranin (SHG) and endomorphin1 (EM1) leads to attenuation of acute and chronic pain. The aim of this study was to design and evaluate an analgesic potency of the gene construct encoding SHG and EM1. Constructs with 1SHG copy in combination with EM1, 1SHG/EM1, and 6SHG/EM1 were intraspinally injected to animals with peripheral nerve injury-induced pain (chronic constriction injury, CCI) or spinal cord injury induced pain (clip compression model, SCI) and tactile and cold allodynia were evaluated. AAV2/8 particles were used for gene delivery. The results demonstrated 6SHG/EM1 as the most efficient for alleviation of pain-related behavior. The effect was observed up to 8 weeks in SCI animals, suggesting the lack of tolerance of possible synergistic effect between SHG and EM1. Intrathecal injection of SHG antibody or naloxone attenuated the analgesic effect in treated animals. Biochemical and histochemical evaluation confirmed the presence of both peptides in the spinal tissue. The results of this study showed that the injection of AAV vectors encoding combined SHG/EM constructs can provide long term attenuation of pain without overt adverse side effects. This approach may provide better treatment options for patients suffering from chronic pain.

Hyperbaric oxygenation alleviates chronic constriction injury (CCI)-induced neuropathic pain and inhibits GABAergic neuron apoptosis in the spinal cord

BACKGROUND AND AIMS

Dysfunction of GABAergic inhibitory controls contributes to the development of neuropathic pain. We examined our hypotheses that (1) chronic constriction injury (CCI)-induced neuropathic pain is associated with increased spinal GABAergic neuron apoptosis, and (2) hyperbaric oxygen therapy (HBO) alleviates CCI-induced neuropathic pain by inhibiting GABAergic neuron apoptosis.

METHODS

Male rats were randomized into 3 groups: CCI, CCI+HBO and the control group (SHAM). Mechanical allodynia was tested daily following CCI procedure. HBO rats were treated at 2.4 atmospheres absolute (ATA) for 60min once per day. The rats were euthanized and the spinal cord harvested on day 8 and 14 post-CCI. Detection of GABAergic cells and apoptosis was performed. The percentages of double positive stained cells (NeuN/GABA), cleaved caspase-3 or Cytochrome C in total GABAergic cells or in total NeuN positive cells were calculated.

RESULTS

HBO significantly alleviated mechanical allodynia. CCI-induced neuropathic pain was associated with significantly increased spinal apoptotic GABA-positive neurons. HBO considerably decreased these spinal apoptotic cells. Cytochrome-C-positive neurons and cleaved caspase-3-positive neurons were also significantly higher in CCI rats. HBO significantly decreased these positive cells. Caspase-3 mRNA was also significantly higher in CCI rats. HBO reduced mRNA expression of caspase-3.

CONCLUSIONS

CCI-induced neuropathic pain was associated with increased apoptotic GABAergic neurons induced by activation of key proteins of mitochondrial apoptotic pathways in the dorsal horn of the spinal cord. HBO alleviated CCI-induced neuropathic pain and reduced GABAergic neuron apoptosis. The beneficial effect of HBO may be via its inhibitory role in CCI-induced GABAergic neuron apoptosis by suppressing mitochondrial apoptotic pathways in the spinal cord.

IMPLICATIONS

Increased apoptotic GABAergic neurons induced by activation of key proteins of mitochondrial apoptotic pathways in the dorsal horn of the spinal cord is critical in CCI-induced neuropathic pain. The inhibitory role of HBO in GABAergic neuron apoptosis suppresses ongoing neuropathic pain.