Chronic Post-ischemia Pain Model Research Articles

Complex Regional Pain Syndrome Type I: Evidence for the CB1 and CB2 Receptors Immunocontent and Beneficial Effect of Local Administration of Cannabidiol in Mice.

Introduction: Complex regional pain syndrome type I (CRPS-I) is a debilitating neuropathic painful condition associated with allodynia, hyperalgesia, sudomotor and/or vasomotor dysfunctions, turning investigation of its pathophysiology and new therapeutic strategies into an essential topic. We aim to investigate the impact of ischemia/reperfusion injury on the immunocontent of CB1 and CB2 cannabinoid receptor isoforms in the paws of mice submitted to a chronic postischemia pain (CPIP) model and the effects of local administration of cannabidiol (CBD) on mechanical hyperalgesia. Methods: Female Swiss mice, 30-35 g, were submitted to the CPIP model on the right hind paw. Skin and muscle samples were removed at different periods for western blot analysis. Results: No changes in the immunocontent of CB1 and CB2 receptors in paw muscle tissues after ischemia-reperfusion were observed. CBD promoted an antihyperalgesic effect in both phases. AM281 reversed the effect of CBD, whereas ruthenium red abolished the late phase. Conclusion: Our results point to the possible beneficial effects of local administration of CBD in modulating CRPS-I in humans. As possible targets for CBD antihyperalgesia in this model, the contribution of cannabinoid receptor CB1, in addition to TRPM8 is suggested.

Immunoregulatory Effect of Preventive Supplementation of Omega-3 Fatty Acid in a Complex Regional Pain Syndrome Type I Model in Mice.

ObjectiveComplex regional pain syndrome (CRPS) is usually triggered by trauma or a surgical procedure, and it typically becomes an established one after an intense inflammatory process with chronic pain and edema as the main symptoms. Available treatments for CRPS have low efficacy. This study aimed to evaluate the clinical and immunoregulatory effects of omega-3 polyunsaturated fatty acid (PUFA) supplementation on paw edema and anti- and pro-inflammatory cytokines and macrophage phenotypes in the chronic post-ischemia pain (CPIP) preclinical model of CRPS-Type I.MethodsFemale Swiss mice were supplemented with omega-3, corn oil, or saline and then submitted to the CPIP model of ischemia/reperfusion (I/R) injury. Supplementation was carried out for 30 days prior to and up to 2 or 15 days after the induction of CPIP, according to experimental protocols. The supplementation protocol included 1,500 mg/kg of omega-3 or corn oil through an intragastric route (gavage). Paw edema, interleukin- (IL-) 4, IL-10, transforming growth factor-β1 (TGF-β1), monocyte chemotactic protein-1 (MCP-1), and tumor necrosis factor (TNF) were then measured in the paw skin and muscle by enzyme-linked immunosorbent assay (ELISA), and macrophage phenotypes (M1 and M2) assessed in the paw muscle by Western blotting.ResultsThe CPIP model induced an increase in paw thickness up to 72 h post-I/R. Mice supplemented with omega-3 compared to the saline group displayed reduced edema but neither altered skin IL-4 or skin and muscle TGF-β1, TNF, and MCP-1 concentrations, nor did they exhibit significantly altered muscle macrophage phenotype on the 2nd-day post-CPIP. However, omega-3 supplementation reversed the I/R-related reduction in IL-4 in the paw muscle compared to groups supplemented with saline and corn oil. Furthermore, omega-3 promoted the reduction of IL-10 levels in the paw skin, compared to animals with lesions supplemented with saline, until the 2nd-day post-CPIP. On the 15th day post-CPIP, IL-10 was significantly increased in the muscle of animals supplemented with omega-3 compared to the saline group.ConclusionThe results suggest that omega-3 PUFA supplementation has anti-inflammatory effects in the CPIP model of CRPS-Type I, significantly reducing paw edema and regulating concentrations of anti-inflammatory cytokines, including IL-4 and IL-10.

Effect of Pregabalin Combined with Duloxetine and Tramadol on Allodynia in Chronic Postischemic Pain and Spinal Nerve Ligation Mouse Models.

Although there are various drugs for Neuropathic pain (NP), the effects of single drugs are often not very satisfactory. The analgesic effects of different combinations of pregabalin, duloxetine, and tramadol or the combination of all three are still unclear. Mixtures of two or three drugs at low and high concentrations (7.5, 10, 15, and 20 mg/kg pregabalin; 7.5, 10, 15, and 30 mg/kg duloxetine; 5 and 10 mg/kg tramadol) were administered to chronic postischemic pain (CPIP) and spinal nerve ligation (SNL) model mice. The effects of these combinations of drugs on mechanical allodynia were investigated. The expression of the glial fibrillary acidic protein (GFAP) in the spinal cord and dorsal root ganglia (DRGs) was measured. The combination of pregabalin, duloxetine, and tramadol significantly alleviated mechanical hyperalgesia in mice with CPIP and SNL. After the administration of this drug combination, the expression of GFAP in the spinal cord and DRGs was lower in the CPIP and SNL model mice than in control mice. This result suggests that the combination of these three drugs may be advantageous for the treatment of NP because it can reduce side effects by preventing the overuse of a single drug class and exert increased analgesic effects via synergism.

Nrf2 Activation Mediates Antiallodynic Effect of Electroacupuncture on a Rat Model of Complex Regional Pain Syndrome Type-I through Reducing Local Oxidative Stress and Inflammation.

Complex regional pain syndrome type-I (CRPS-I) represents a type of neurovascular condition featured by severe pain in affected extremities. Few treatments have proven effective for CRPS-I. Electroacupuncture (EA) is an effective therapy for pain relief. We explored the mechanism through which EA ameliorates pain in a rat CRPS-I model. The chronic postischemic pain (CPIP) model was established using Sprague-Dawley rats to mimic CRPS-I. We found that oxidative stress-related biological process was among the predominant biological processes in affected hindpaw of CPIP rats. Oxidative stress occurred primarily in local hindpaw but not in the spinal cord or serum of model rats. Antioxidant N-acetyl cysteine (NAC) attenuated mechanical allodynia and spinal glia overactivation in CPIP model rats, whereas locally increasing oxidative stress is sufficient to induce chronic pain and spinal glia overactivation in naive rats. EA exerted remarkable antiallodynia on CPIP rats by reducing local oxidative stress via enhancing nuclear factor erythroid 2-related factor 2 (Nrf2) expression. Pharmacological blocking Nrf2 abolished antioxidative and antiallodynic effects of EA. EA reduced spinal glia overactivation, attenuated the upregulation of inflammatory cytokines, reduced the enhanced TRPA1 channel activity in dorsal root ganglion neurons innervating the hindpaws, and improved blood flow dysfunction in hindpaws of CPIP rats, all of which were mimicked by NAC treatment. Thus, we identified local oxidative injury as an important contributor to pathogenesis of animal CRPS-I model. EA targets local oxidative injury by enhancing endogenous Nrf2-mediated antioxidative mechanism to relieve pain and inflammation. Our study indicates EA can be an alternative option for CRPS-I management.

Gene Expression Profiling of Contralateral Dorsal Root Ganglia Associated with Mirror-Image Pain in a Rat Model of Complex Regional Pain Syndrome Type-I.

BackgroundMirror-image pain (MIP), which develops from the healthy body region contralateral to the actual injured site, is a mysterious pain phenomenon accompanying many chronic pain conditions, such as complex regional pain syndrome (CRPS). However, the pathogenesis of MIP still remains largely unknown. The purpose of this study is to perform an expression profiling to identify genes related to MIP in an animal model of CRPS-I.MethodsWe established a rat chronic post-ischemic pain (CPIP) model to mimic human CRPS-I. RNA-sequencing (RNA-Seq), bioinformatics, qPCR, immunostaining, and animal behavioral assays were used to screen potential genes in the contralateral dorsal root ganglia (DRG) that may be involved in MIP.ResultsThe CPIP model rats developed robust and persistent MIP in contralateral hind paws. Bilateral DRG neurons did not exhibit obvious neuronal damage. RNA-Seq of contralateral DRG from CPIP model rats identified a total 527 differentially expressed genes (DEGs) vs sham rats. The expression changes of several representative DEGs were further verified by qPCR. Bioinformatics analysis indicated that the immune system process, innate immune response, and cell adhesion were among the mostly enriched biological processes, which are important processes involved in pain sensitization, neuroinflammation, and chronic pain. We further identified DEGs potentially involved in pain mechanisms or enriched in small- to medium-sized sensory neurons or TRPV1-lineage nociceptors. By comparing with published datasets summarizing genes enriched in pain mechanisms, we sorted out a core set of genes which might contribute to nociception and the pain mechanism in MIP.ConclusionWe provided by far the first study to profile gene expression changes and pathway analysis of contralateral DRG for the studying of MIP mechanisms. This work may provide novel insights into understanding the mysterious mechanisms underlying MIP.

Electroacupuncture Alleviates Mechanical Allodynia of a Rat Model of CRPS-I and Modulates Gene Expression Profiles in Dorsal Root Ganglia.

Complex regional pain syndrome type-I (CRPS-I) is chronic neurological disorder accompanied with devastating pain. Most conventional medical treatments lack effectiveness, making CRPS-I a challenging clinical condition. Electroacupuncture (EA) showed effectiveness in alleviating the pain symptoms of CRPS-I patients. However, the molecular mechanisms underlying EA's therapeutic effect are still not well-understood. Here, we established the rat chronic post-ischemic pain (CPIP) model to mimic CRPS-I and performed repetitive EA on bilateral hind limbs of the CPIP model rats. We then performed RNA-sequencing (RNA-Seq) to study the differences in gene expression, gene networks, and molecular pathways in ipsilateral DRGs innervating the hind limb of the CPIP model rats with and without repetitive EA treatment. Our results found that repetitive EA treatment significantly alleviated mechanical allodynia in bilateral hind limbs of CPIP model rats. RNA-Seq analysis indicated that EA modulated the expression of multiple genes and gene networks in the DRGs of CPIP model rats. Further bioinformatics analysis identified the up-regulation of an array of genes involved in biological process such as neutrophil chemotaxis and immune response in the DRGs of CPIP model rats after EA treatment. Thus, these results suggest that EA may alleviate pain response in CPIP model rats via regulating multiple genes. Our work may help to further advance the understandings of the molecular mechanisms underlying EA's therapeutic effects on CRPS-I and help to identify novel targets for CRPS-I treatment.

Electroacupuncture Alleviates Mechanical Allodynia in a Rat Model of Complex Regional Pain Syndrome Type-I via Suppressing Spinal CXCL12/CXCR4 Signaling

Complex regional pain syndrome (CRPS) results in chronic and excruciating pain in patients. Conventional therapies lack effectiveness, rendering it one of the most difficult to treat neurological conditions.. Electroacupuncture (EA) is an effective alternative therapy for pain relief. Here, we investigated whether EA exerts analgesic effect on a rat model of CRPS type-I (CRPS-I) and related mechanisms. The rat chronic postischemic pain (CPIP) model was established to mimic CRPS-I. 100Hz EA exerted robust and persistent antiallodynic effect on CPIP model compared with 2 Hz EA or sham EA. EA markedly suppressed the overexpression of CXCL12/CXCR4 in spinal cord dorsal horn (SCDH) of CPIP model, leading to substantial decrease in neuronal and glial cell activities in SCDH. Pharmacological blocking CXCR4 mimicked EA-induced antiallodynic effect and related cellular events in SCDH, whereas exogenous CXCL12 abolished EA's effect. CXCR4 signaling resulted in ERK activation in SCDH, contributing to mechanical allodynia of CPIP model rats, whereas EA markedly reduced ERK activation. Therefore, we demonstrated that EA interferes with CXCL12/CXCR4 signaling in SCDH and downstream ERK pathway to exert robust antiallodynic effect on an animal model of CRPS-I. Our work suggests that EA may be a potential therapeutic option for CRPS-I in clinic. PerspectiveOur work identified that EA exerts robust antiallodynic effect on an animal model of CRPS-I, via mechanisms involving inhibition of CXCL12/CXCR4 signaling. EA further attenuates downstream neuronal and glial cell activation and ERK pathway in SCDH. This work suggests that EA may be a potential therapeutic option for CRPS-I management in clinic.

Expression profiling of spinal cord dorsal horn in a rat model of complex regional pain syndrome type-I uncovers potential mechanisms mediating pain and neuroinflammation responses

BackgroundComplex regional pain syndrome type-I (CRPS-I) is a progressive and devastating pain condition. The mechanisms of CRPS-I still remain poorly understood. We aim to explore expression profiles of genes relevant to pain and neuroinflammation mechanisms involved in CRPS-I.MethodsThe rat chronic post-ischemic pain (CPIP) model that mimics human CRPS-I was established. RNA-sequencing (RNA-Seq), qPCR, Western blot, immunostaining, and pharmacological studies were used for profiling gene changes in ipsilateral spinal cord dorsal horn (SCDH) of CPIP model rat and further validation.ResultsCPIP rats developed persistent mechanical allodynia in bilateral hind paws, accompanied with obvious glial activation in SCDH. RNA-Seq identified a total of 435 differentially expressed genes (DEGs) in ipsilateral SCDH of CPIP rats. qPCR confirmed the expression of several representative genes. Functional analysis of DEGs identified that the most significantly enriched biological processes of upregulated genes include inflammatory and innate immune response. We further identified NLRP3 inflammasome expression to be significantly upregulated in SCDH of CPIP rats. Pharmacological blocking NLRP3 inflammasome reduced IL-1β overproduction, glial activation in SCDH as well as mechanical allodynia of CPIP rats.ConclusionOur study revealed that immune and inflammatory responses are predominant biological events in SCDH of CPIP rats. We further identified NLRP3 inflammasome in SCDH as a key contributor to the pain and inflammation responses in CPIP rats. Thus, our study provided putative novel targets that may help to develop effective therapeutics against CRPS-I.

Increased calcium-mediated cerebral processes after peripheral injury: possible role of the brain in complex regional pain syndrome.

BackgroundAmong various diseases that accompany pain, complex regional pain syndrome (CRPS) is one of the most frustrating for patients and physicians. Recently, many studies have shown functional and anatomical abnormalities in the brains of patients with CRPS. The calcium-related signaling pathway is important in various physiologic processes via calmodulin (CaM) and calcium-calmodulin kinase 2 (CaMK2). To investigate the cerebral mechanism of CRPS, we measured changes in CaM and CaMK2 expression in the cerebrum in CRPS animal models.MethodsThe chronic post-ischemia pain model was employed for CRPS model generation. After generation of the animal models, the animals were categorized into three groups based on changes in the withdrawal threshold for the affected limb: CRPS-positive (P), CRPS-negative (N), and control (C) groups. Western blot analysis was performed to measure CaM and CaMK2 expression in the rat cerebrum.ResultsAnimals with a decreased withdrawal threshold (group P) showed a significant increment in cerebral CaM and CaMK2 expression (P = 0.013 and P = 0.021, respectively). However, groups N and C showed no difference in CaM and CaMK2 expression.ConclusionsThe calcium-mediated cerebral process occurs after peripheral injury in CRPS, and there can be a relationship between the cerebrum and the pathogenesis of CRPS.

Chronic Post-Ischemia Pain Model for Complex Regional Pain Syndrome Type-I in Rats

Complex regional pain syndrome type-I (CRPS-I) is a neurological disease that causes severe pain among patients and remains an unresolved medical condition. However, the underlying mechanisms of CRPS-I have yet to be revealed. It is known that ischemia/reperfusion is one of the leading factors that causes CRPS-I. By means of prolonged ischemia and reperfusion of the hind limb, the rat chronic post-ischemia pain (CPIP) model has been established to mimic CRPS-I. The CPIP model has become a well-recognized animal model for studying the mechanisms of CRPS-I. This protocol describes the detailed procedures involved in the establishment of the rat model of CPIP, including anesthesia, followed by ischemia/reperfusion of the hind limb. Characteristics of the rat CPIP model are further evaluated by measuring the mechanical and thermal hypersensitivities of the hind limb as well as the nocifensive responses to acute capsaicin injection. The rat CPIP model exhibits several CRPS-I-like manifestations, including hind limb edema and hyperemia in the early stage after establishment, persistent thermal and mechanical hypersensitivities, and increased nocifensive responses to acute capsaicin injection. These characteristics render it a suitable animal model for further investigation of the mechanisms involved in CRPS-I.

Comparative Study of Chronic Postischemic Pain Models in Mice: O-Ring Versus Tie Method

The success rate for the production of animal models of chronic postischemia pain (CPIP) using an O-ring has yet to be improved in the study of complex regional pain syndrome-type I (CRPS-I), and producing a CPIP model is challenging, especially for mice. We devised a new CPIP model with a higher success rate that induces ischemia for 3 hours by tying the hind limbs of mice with a rubber band, followed by reperfusion. A randomized, controlled animal trial. Twenty-two male C57BL/6 mice were divided into a sham (n = 6), a ring (n = 8), and a tie group (n = 8). Anesthesia was induced using isoflurane. A precut O-ring was mounted on the upper left ankle in the sham group. A tight-fitting O-ring and a push-pull gauge manometer were mounted at the same location in the ring and tie groups, respectively. Reperfusion was induced 3 hours later. The thickness and circumference of the hind paws were measured before ischemia induction. Measurements were repeated 10 days after reperfusion. Mechanical allodynia was measured with a von Frey filament until 12 weeks after reperfusion. The new tie model required 5 additional days until the onset of allodynia compared with the existing CPIP O-ring model. However, the successful induction rate of CPIP was higher in the tie group than in the ring group, and allodynia was maintained for over 30 days in the tie group. The ring and tie groups exhibited significantly high levels of tumor necrosis factor-alpha than those in the sham group. First, we did not evaluate hyperalgesia, cold or heat allodynia. Second, we did not measure blood levels of inflammatory or antiinflammatory cytokines, and research on oxidative stress biomarkers such as isoprostane, 8-hydroxy-2'-deoxyguanosine (a marker of DNA oxidative damage), and malondialdehyde was not performed. The new CPIP tie model has a higher rate of successful induction than existing O-ring models for mice, with longer duration of mechanical allodynia. The model may reduce the number of animals sacrificed in CRPS-I research and could be useful for studying long-term effects of drugs. CPIP, mouse, O-ring, rubber band, reperfusion, allodynia, hyperalgesia.

The effect of human mesenchymal stem cell injection on pain behavior in chronic post-ischemia pain mice.

BackgroundNeuropathic pain (NP) is considered a clinically incurable condition despite various treatment options due to its diverse causes and complicated disease mechanisms. Since the early 2000s, multipotent human mesenchymal stem cells (hMSCs) have been used in the treatment of NP in animal models. However, the effects of hMSC injections have not been studied in chronic post-ischemia pain (CPIP) mice models. Here, we investigated whether intrathecal (IT) and intrapaw (IP) injections of hMSCs can reduce mechanical allodynia in CPIP model mice.MethodsSeventeen CPIP C57/BL6 mice were selected and randomized into four groups: IT sham (n = 4), IT stem (n = 5), IP sham (n = 4), and IP stem (n = 4). Mice in the IT sham and IT stem groups received an injection of 5 μL saline and 2 × 104 hMSCs, respectively, while mice in the IP sham and IP stem groups received an injection of 5 μL saline and 2 × 105 hMSCs, respectively. Mechanical allodynia was assessed using von Frey filaments from pre-injection to 30 days post-injection. Glial fibrillary acidic protein (GFAP) expression in the spinal cord and dorsal root ganglia were also evaluated.ResultsIT and IP injections of hMSCs improved mechanical allodynia. GFAP expression was decreased on day 25 post-injection compared with the sham group. Injections of hMSCs improved allodynia and GFAP expression was decreased compared with the sham group.ConclusionsThese results suggested that hMSCs may be also another treatment modality in NP model by ischemia-reperfusion.

Anti-Allodynic Effects of Polydeoxyribonucleotide in an Animal Model of Neuropathic Pain and Complex Regional Pain Syndrome.

BackgroundSpinal nerve ligation (SNL) model is one of the representative models of the neuropathic pain model. Neuropathic pain in a chronic post-ischemic pain (CPIP) mimics the symptoms of complex regional pain syndrome (CRPS). The administration of polydeoxyribonucleotide (PDRN), which has regenerative and anti-inflammatory effects, has been studied and is used in clinical practice treating various diseases. However, the analgesic effect of PDRN in a neuropathic pain or CRPS model remains unknown.MethodsPDRN (3.3, 10, and 20 mg/kg) was administered into the subcutaneous (SC) layer of the hind paws of SNL and CPIP models. Mechanical anti-allodynic effects were then investigated using the von Frey test. In the immunohistochemical examination, dorsal root ganglia (DRG) and the spinal cord were harvested and examined for the expression of glial fibrillary acidic protein (GFAP) after the 20 mg PDRN injection.ResultsMechanical allodynia was significantly alleviated by administration of PDRN in SNL and CPIP mice at all of the time point. As the dose of PDRN increased, the effect was greater. The 20 mg PDRN injection was found to have the most effective anti-allodynic effect. The increased expression of GFAP in DRG and the spinal cord of SNL and CPIP model decreased following the administration of PDRN than vehicle.ConclusionSC administration of PDRN results in the attenuation of allodynia and activation of astrocytes in neuropathic pain or CRPS models. We propose that PDRN can have significant potential advantages in neuropathic pain treatment.

The analgesic effect of propofol associated with the inhibition of hypoxia inducible factor and inflammasome in complex regional pain syndrome

BackgroundComplex regional pain syndrome (CRPS) is related to microcirculation impairment caused by tissue hypoxia and peripheral cytokine overproduction in the affected human limb and chronic post-ischemic pain (CPIP) is considered as an animal model for this intractable disease. Previous studies suggest that the pathogenesis of CPIP involves the hypoxia inducible factor-1α (HIF-1α) and an exaggerated regional inflammatory and free radical response. The inhibition of HIF-1α is known to relieve CPIP. So, propofol, as a free radical scavenger, is very likely to be beneficial in terms of relieving CPIP.MethodsWe set up a CPIP model using the hindpaw of mice. We administered propofol (10 mg/kg) just after the reperfusion period (early stage) and also on the second day (late stage), as treatment. The analysis evaluated the expression of HIF-1α, free radicals, and inflammasome.ResultsPropofol administration produced obvious analgesia in both mechanical and thermal evaluation in the early stage of CPIP (2 h after reperfusion). Only a mild analgesic effect was found in the late stage (48 h later after reperfusion). In the early stage, the expression of HIF-1α and the inflammasome marker (NALP1) along with caspase-1 were suppressed by propofol. The free radical level also decreased in the propofol group. But those molecular changes were not founded in the late stage of CPIP.ConclusionOur data demonstrated that propofol produces mice analgesia in the early stage of CPIP and this effect is associated with inhibition of free radical, hypoxia inducible factor and inflammasome.

Transcriptome profiling of dorsal root ganglia in a rat model of complex regional pain syndrome type-I reveals potential mechanisms involved in pain.

Purpose: Complex regional pain syndrome type-I (CRPS-I) is a progressive and devastating pain condition, which remains clinically challenging. The mechanisms of CRPS-I still remain largely unknown. We aim to identify transcriptome profiles of genes relevant to pain mechanisms and major pathways involved in CRPS-I.Methods: A rat model of chronic post-ischemia pain (CPIP) was established to mimic CRPS-I. RNA-sequencing (RNA-Seq) was used to profile transcriptome of L4-6 dorsal root ganglia (DRGs) of a rat model of CRPS-I.Results: CPIP model rats developed persistent mechanical/thermal hyperalgesia in ipsilateral hind paw. RNA-Seq identified a total of 295 differentially expressed genes (DEGs), including 195 up- and 100 downregulated, in ipsilateral DRGs of CPIP rats compared with sham rats. The expression of several representative genes was confirmed by qPCR. Functional analysis of DEGs revealed that the most significant enriched biological processes of upregulated genes include response to lipopolysaccharide, inflammatory response and cytokine activity, which are all important mechanisms mediating pain. We further screened DEGs implicated in pain progress, genes enriched in small- to medium-sized sensory neurons and enriched in TRPV1-lineage nociceptors. By comparing our dataset with other published datasets of neuropathic or inflammatory pain models, we identified a core set of genes and pathways that extensively participate in CPIP and other neuropathic pain states.Conclusion: Our study identified transcriptome gene changes in DRGs of an animal model of CRPS-I and could provide insights into identifying promising genes or pathways that can be potentially targeted to ameliorate CRPS-I.

Linagliptin attenuates chronic post-ischemia pain: Possible anti-inflammatory and anti-oxidant mechanisms

Complex regional pain syndrome (CRPS) is a debilitating neurologic disorder with an interlinked and yet incompletely defined pathogenesis. Treatment options remain a therapeutic challenge. Linagliptin is one of the dipeptidyl peptidase-4 (DPP-4) inhibitors which are used for the treatment of diabetes mellitus. Apart from the improvement of glycemic control, accumulating evidence points to the beneficial effects of DPP-4 inhibitors in a wide array of conditions. Herein, the present study was outlined to investigate the antinociceptive effect of linagliptin in acute pain conditions, and in an animal model of CRPS.A prolonged hind paw ischemia reperfusion (I/R) injury to the left hind paw was done to induce chronic post-ischemia pain (CPIP) in rats. Allodynia and hyperalgesia were assessed in both ipsilateral and contralateral hind paws at different time points. At the end of the experiment, markers of oxidative stress and inflammatory cytokines were assayed in paw skin samples.The results showed that linagliptin had no effect on acute nociception. On the other hand, linagliptin treatment, for seven days, ameliorated hyperalgesia, mechanical and cold allodynia, and attenuated oxidative and inflammatory markers in CPIP rats.In conclusion, linagliptin was able to ameliorate aberrant pain behavior induced by prolonged hind paw ischemia. These effects can be attributed, at least partially, to the reduction of inflammatory cytokine levels and restore oxidant/antioxidant balance in the CPIP model. Hence, linagliptin pleiotropic effects open a new horizon to further investigate its role in the treatment of inflammatory and chronic painful conditions, especially in diabetic patients.

Interaction between astrocytic colony stimulating factor and its receptor on microglia mediates central sensitization and behavioral hypersensitivity in chronic post ischemic pain model

Accumulation of microglia occurs in the dorsal horn in the rodent model of chronic post ischemic pain (CPIP), while the mechanism how microglia affects the development of persistent pain largely remains unknown. Here, using a rodent model of CPIP induced by ischemia–reperfusion (IR) injury in the hindpaw, we observed that microglial accumulation occurred in the ipsilateral dorsal horn after ischemia 3h, and in ipsilateral and contralateral dorsal horn in the rats with ischemia 6h. The accumulated microglia released BDNF, increased neuronal excitability in dorsal horn, and produced pain behaviors in the modeled rodents. We also found significantly increased signaling mediated by astrocytic colony-stimulating factor-1 (CSF1) and microglial CSF1 receptor (CSF1R) in dorsal horn in the ischemia 6h modeled rats. While exogenous M-CSF induced microglial activation and proliferation, BDNF production, neuronal hyperactivity in dorsal horn and behavioral hypersensitivity in the naïve rats, inhibition of astrocytic CSF1/microglial CSF1R signaling by fluorocitric or PLX3397 significantly suppressed microglial activation and proliferation, BDNF upregulation, and neuronal activity in dorsal horn, as well as the mechanical allodynia and thermal hyperalgesia, in the rats with ischemia 6h. Collectively, these results demonstrated that glial CSF1/CSF1R pathway mediated the microglial activation and proliferation, which facilitated the nociceptive output and contributed to the chronic pain induced by IR injury.

Effects of Simvastatin Beyond Dyslipidemia: Exploring Its Antinociceptive Action in an Animal Model of Complex Regional Pain Syndrome-Type I.

Simvastatin is a lipid-lowering agent that blocks the production of cholesterol through inhibition of 3-hydroxy-methyl-glutaryl coenzyme A (HMG-CoA) reductase. In addition, recent evidence has suggested its anti-inflammatory and antinociceptive actions during inflammatory and pain disorders. Herein, we investigated the effects of simvastatin in an animal model of complex regional pain syndrome-type I, and its underlying mechanisms. Chronic post-ischemia pain (CPIP) was induced by ischemia and reperfusion (IR) injury of the left hind paw. Our findings showed that simvastatin inhibited mechanical hyperalgesia induced by CPIP model in single and repeated treatment schedules, respectively; however simvastatin did not alter inflammatory signs during CPIP model. The mechanisms underlying those actions are related to modulation of transient receptor potential (TRP) channels, especially TRMP8. Moreover, simvastatin oral treatment was able to reduce the nociception induced by acidified saline [an acid-sensing ion channels (ASICs) activator] and bradykinin (BK) stimulus, but not by TRPA1, TRPV1 or prostaglandin-E2 (PGE2). Relevantly, the antinociceptive effects of simvastatin did not seem to be associated with modulation of the descending pain circuits, especially noradrenergic, serotoninergic and dopaminergic systems. These results indicate that simvastatin consistently inhibits mechanical hyperalgesia during neuropathic and inflammatory disorders, possibly by modulating the ascending pain signaling (TRPM8/ASIC/BK pathways expressed in the primary sensory neuron). Thus, simvastatin open-up new standpoint in the development of innovative analgesic drugs for treatment of persistent pain, including CRPS-I.

The Therapeutic Effect of Vitamin C in an Animal Model of Complex Regional Pain Syndrome Produced by Prolonged Hindpaw Ischemia-Reperfusion in Rats.

Objectives: It is known that increased free radicals from oxidative stress are one of the major causes of complex regional pain syndrome (CRPS). In this study, we tested the hypothesis that vitamin C has a dose-related treatment effect in a chronic post-ischemic pain (CPIP) model.Methods: A total of 49 male rats weighing 250 to 350 g were used. The 4 treatment groups were control (no medication), group 1.0 (administration of 1 mg/day for vitamin C for 5 days), group 2.5 (administration of 2.5 mg/day vitamin C for 5 days), and group 7.5 (administration of 7.5 mg/day vitamin C for 5 days). The 50% mechanical withdrawal threshold and total blood antioxidant status (TAS) were measured before and after administration of vitamin C.Results: Twenty-eight CPIP model rats were generated from 49 rats. Seven rats were randomly allocated to each group. The 50% mechanical withdrawal threshold of group 2.5 (after the administration of vitamin C) was higher than that of the control group and group 1.0 (P < 0.05). At 1 day of the administration of vitamin C, the 50% mechanical withdrawal threshold of group 1.0 was higher than that of the control group and the blood levels of TAS in groups 2.5 and 7.5 were higher than that in control group (P < 0.05). Twelve days after the administration of vitamin C, the blood levels of TAS in groups 2.5 and 7.5 were lower than that of the control group (P < 0.05).Discussion: The administration of a proper dose of vitamin C can reduce oxidative stress, increase antioxidants, and recover the threshold for mechanical allodynia in the CPIP model.

Astrocyte contributes to pain development via MMP2-JNK1/2 signaling in a mouse model of complex regional pain syndrome

BackgroundThe activation of spinal glial cells (astrocyte and microglia) is reported in patient with complex regional pain syndrome (CRPS). However, the roles of spinal glial activities in the pathophysiology of CRPS are unclear. Here, we explored the roles of spinal astrocyte and microglia and the molecular mechanisms underlying CRPS using a mouse model of chronic post-ischemia pain (CPIP). ResultsCPIP injury increased the level of glial fibrillary acidic protein (GFAP, reactive astrocyte biomarker), but had no significant impact on ionized calcium binding adaptor molecule 1 (IBA1, reactive microglia biomarker), in the ipsilateral dorsal horn on post-injury day (PID) 3 when the pain threshold started to reduce significantly. Astrocytic inhibition with fluorocitrate but not microglial inhibition with minocycline attenuated the development of allodynia in CPIP-injured mice, which was concomitant with increased spinal levels of phosphorylated c-jun N-terminal kinase 1/2 (pJNK1/2) on PID 3. Furthermore, the intrathecal administration of SP600125 (JNK inhibitor) prevented the development of allodynia in CPIP-injured mice. Double immunofluorescence staining showed that pJNK1/2 was mainly co-localized with GFAP. Subsequently, increased levels of pJNK1/2 were reversed by intrathecal fluorocitrate. Furthermore, the level of spinal matrix metalloproteinase-2 (MMP2) was increased and mainly expressed in NeuN (neuron biomarker) on PID 3 in the CPIP-injured mice, while intrathecal APR 100 (MMP2 inhibitor) delayed the development of allodynia and decreased spinal levels of GFAP and pJNK1/2 on PID 3. ConclusionThis study shows that activation of astrocyte MMP2/JNK1/2 signaling pathway contributes to the pathogenesis of pain hypersensitivity in the CPIP model.