Gambogic Acid Relieves Neuropathic Pain in Rats by Regulating CXCR4-TXNIP/NLRP3 Pathway

Neuropathic pain is caused by abnormal sensory processing in the central nervous system (CNS). The immune response of the CNS is related to the function of glial cells and is critical in neuropathic pain. Agents based on cytokines and glial cells in the CNS have potential for the treatment of neuropathic pain. Gambogic acid (GA) is one of the main components of Garcinia cambogia, which has anti-inflammatory, antitumor, and analgesic effects. However, the effect of GA on neuropathic pain and related mechanisms are still unclear. Previous studies indicated that GA could reduce CXCR4 expression in neuropathic pain. In this study, we found that GA could alleviate nerve pain behavior in rats by measuring the incubation period of heat shrinkage and mechanical pain threshold. Also, GA reduced inflammation in chronic constriction injury rats. We further found GA reduced the apoptosis of spinal cord nerve cells in chronic constriction injury rats. Mechanically, we noticed GA relieved neuropathic pain in rats via regulating CXCR4-TXNIP/NLRP3 pathway. Our data confirmed that GA could serve as a promising drug for the treatment of neuropathic pain.

Inhibitory Effects of Palmatine on P2X7 Receptor Expression in Trigeminal Ganglion and Facial Pain in Trigeminal Neuralgia Rats

Trigeminal Neuralgia (TN) refers to recurrent severe paroxysmal pain in the distribution area of the trigeminal nerve, which seriously affects the quality of life of patients. This research applied the chronic constriction injury of the infraorbital nerve (CCI—ION) approach to induce an animal model of TN in rats. The mechanical pain threshold of each group of rats was determined postoperatively; the expression of P2X7 receptor in trigeminal ganglion (TG) was assessed by qRT-PCR, immunofluorescence and Western blot; and the changes of the proinflammatory cytokines IL-1β and TNF-α in serum of rats were detected by ELISA. The results showed that the administration of palmatine in the TN rats could reduce the mechanical pain threshold, significantly decrease the expression of P2X7 receptor in TG, and lower the serum concentrations of IL-1β and TNF-α, compared to the sham group. In addition, the phosphorylation level of p38 in TG of TN rats was significantly decreased after treatment with palmatine. Likewise, inhibition of P2X7 expression by shRNA treatment could effectively counteract the adversary changes of pain sensitivity, IL-1β and TNF-α production, and p38 phosphorylation in TN rats. Our data suggest that palmatine may alleviate mechanical facial pain in TN rats possibly by reducing the expression of P2X7 receptor in TG of TN rats, which may be attributable to inhibiting p38 phosphorylation and reducing the release of IL-1β and TNF-α.

Minimally Invasive Embedding of Saturated MSU Induces Persistent Gouty Arthritis in Modified Rat Model

Introduction. Animal models are valid for in vivo research on the pathophysiological process and drug screening of gout arthritis. Intra-articular injection of monosodium urate (MSU) is the most common method, while stable MSU deposition enveloped by inflammatory cells was rarely reported. Objective. To develop a modified gouty arthritis rat model characterized by intra-articular MSU deposition and continuous joint pain with a minimally invasive method. Method. A total of twenty-four rats were randomly allocated into six groups. Three intervention groups of rats received intra-articular MSU embedment. Sham groups received pseudosurgeries with equal normal saline (NS). Gross parameters and pathological features of synovium harvested from anterior capsule were estimated. Mechanical pain threshold tests were conducted over a 96-hour period postoperatively. Moreover, quantitative immunofluorescence was conducted to assess tissue inflammation. Result. After MSU embedding, rats got more persistent arthritic symptoms as well as tissue MSU deposition. More significant synovial swelling was detected in the MSU group compared to sham groups ( P < 0.025 ). Behavioral tests showed that the embedding of MSU resulted in prolonged mechanical hyperalgesia during 2 hours to 96 hours postoperatively ( P < 0.05 ). MSU depositions enveloped by inflammatory cells that express IL-1β and TNF-α were detected in embedding groups. Quantitative immunofluorescence suggested that the frequencies of MSU interventions upregulated expression of proinflammatory factors including IL-1β and TNF-α ( P < 0.05 ). Conclusion. A minimally invasive method was developed to establish modified rat model of intra-articular MSU deposition. This model was proved to be a simple reproducible method to mimic the pathological characteristics of persistent gouty arthritis.

The Effect and Possible Mechanism of Intradiscal Injection of Simvastatin in the Treatment of Discogenic Pain in Rats

To study the effect of intradiscal injection of simvastatin on discogenic pain in rats and its possible mechanism, 30 adult female rats were used in this experiment. Twenty rats were randomly divided into sham operation group (Control group), intervertebral disk degeneration group (DDD group), intervertebral disk degeneration + hydrogel group (DDD + GEL group), and intervertebral disk degeneration + simvastatin group (DDD + SIM group). The mechanical pain threshold and cold sensation in rats were measured. The contents of NF-kappa B1, RelA, GAP43, SP, CGRP, TRPM 8, IL-1β, and TNF-α in the intervertebral disk (IVD), the corresponding contents of dorsal root ganglion (DRG) and plantar skin GAP43 and TRPM 8 were quantitatively detected by PCR. The corresponding IVDs were stained to detect their degeneration. There was no significant difference in the mechanical pain threshold between the groups at each time point. From the first day to the 8th week after surgery, the cold-sensing response of the DDD group was significantly higher than that of the Control group (P &lt; 0.05). At 7 and 8 weeks postoperatively, the cold-sensing response of the DDD + SIM group was significantly lower than that of the DDD + GEL group (P &lt; 0.05). The levels of NF-κB1, RelA, GAP43, SP, CGRP, TRPM8, IL-1β, and TNF-α in the IVD of DDD + SIM group were significantly lower than those in DDD group (P &lt; 0.05). The content of GAP43 and TRPM8 in rat plantar skin decreased significantly and TRPM8 in DRG decreased significantly (P &lt; 0.05).

Preliminary study of calcium homeostasis modulator 1 involved in trigeminal neuralgia

Background: The aim of this study was to observe the changes in the expression of calcium homeostasis modulator 1 (CALHM1) in the trigeminal nucleus of the trigeminal neuralgia (TN) rats with the infraorbital nerve-chronic constrictive nerve injury (ION-CCI) and to explore the role of CALHM1 in TN.Methods: Thirty SD rats were randomly assigned to 5 groups, namely normal control group (Control group), sham operation group (Sham group), TN model group (ION-CCI group), ruthenium red treatment group (RuR group) and control group of ruthenium red (NS group), with 6 rats in each group. An animal model was established by loosely ligating the rat's infraorbital nerve with a chrome gut in the ION-CCI group, while mice in the sham group were only exposed to the nerve and did not receive ligature. The rats in the RuR group were intraperitoneally injected with 0.5 mg/kg of CALHM1 inhibitor ruthenium red on the 9th day after the infraorbital nerve ligation, while the rats in NS group were intraperitoneally injected with an equal volume of normal saline on the 9th day after surgery. All experimental rats were tested for pain behavior 1 day before surgery, 1, 3, 5, 7, 9, 11 and 14 days after surgery, including the mechanical pain threshold of VonFrey filament in the trigeminal innervated skin area and number of faces captured in video recording. The expression of CALHM1 in the trigeminal spinal nucleus was detected on the 15th day after operation in all experimental groups.Results: The expression of CALHM1 in the trigeminal spinal nucleus of the ION-CCI group was significantly higher than that of control group and sham group on the 3rd and 15th day after modeling. The intraperitoneal injection of CALHM1 inhibitor ruthenium red increased the mechanical pain threshold of ION-CCI rats and significantly reduced the number of scratches, but did not change the expression of CALHM1 in the trigeminal spinal nucleus.Conclusion: The expression of CALHM1 protein in the trigeminal spinal nucleus is involved in the central sensitization of TN pain, which can be induced by elevated expression. Moreover, the hyperalgesia can be improved by using CALHM1 inhibitor.

Inhibition of Peripheral ERK Signaling Ameliorates Persistent Muscle Pain Around Trigger Points in Rats

The purpose of this study was to investigate whether the ERK signaling pathway was involved in ameliorating chronic myofascial hyperalgesia from contused gastrocnemius muscle in rats. We established an animal model associated with myofascial pain syndrome and described the mechanism of muscle pain in an animal model. Changes in the mechanical pain threshold were observed 0.5, 1, 2, 3, 4, 5, 8, 12, 18, and 24 h after ERK inhibitor injection around myofascial trigger points (MTrPs) of the gastrocnemius muscle in rats. Morphological changes in gastrocnemius muscle cells were observed by hematoxylin and eosin (H&E) staining. ERK signaling pathway activation was detected through immunohistochemistry and Western blotting. The main morphological characteristics of injured muscle fibers around MTrPs include gathered circular or elliptical shapes of different sizes in the cross-section and continuous inflated and tapering fibers in the longitudinal section. After intramuscular injection of U0126 (ERK inhibitor), the mechanical pain threshold significantly increased. The reduction in mechanical hyperalgesia was accompanied by reduced ERK protein phosphorylation, myosin light chain kinase (MLCK) protein, p-MLC protein expression, and the cross-sectional area of skeletal muscle cells around MTrPs. An ERK inhibitor contributed to the attenuation of mechanical hyperalgesia in the rat myofascial pain model, and the increase in pain threshold may be related to MLCK downregulation and other related contraction-associated proteins by ERK.

c-Abl-p38α signaling pathway mediates dopamine neuron loss in trigeminal neuralgia

Trigeminal neuralgia is a common neuropathic pain in the head and face. The pathogenesis of trigeminal neuralgia is complex, and so far, the pathogenesis of trigeminal neuralgia involving peripheral and central nervous inflammation theory has not been explained clearly. The loss of dopamine neurons in striatum may play an important role in the development of trigeminal nerve, but the reason is not clear. C-Abl is a nonreceptor tyrosine kinase, which can be activated abnormally in the environment of neuroinflammation and cause neuron death. We found that in the rat model of infraorbital nerve ligation trigeminal neuralgia, the pain threshold decreased, the expression of c-Abl increased significantly, the downstream activation product p38 was also activated abnormally and the loss of dopamine neurons in striatum increased. When treated with imatinib mesylate (STI571), a specific c-Abl family kinase inhibitor, the p38 expression was decreased and the loss of dopaminergic neurons was reduced. The mechanical pain threshold of rats was also improved. In conclusion, c-abl-p38 signaling pathway may play an important role in the pathogenesis of trigeminal neuralgia, and it is one of the potential targets for the treatment of trigeminal neuralgia.

Dextromethorphan Analgesia in a Human Experimental Model of Hyperalgesia

Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New Background Central pain sensitization is often refractory to drug treatment. Dextromethorphan, an N-methyl-d-aspartate receptor antagonist, is antihyperalgesic in preclinical pain models. The hypothesis is that dextromethorphan is also antihyperalgesic in humans. Methods This randomized, double-blind, placebo-controlled, crossover study explores the antihyperalgesic effect of single and repeated 30-mg dose of oral dextromethorphan in 20 volunteers, using the freeze-injury pain model. This model leads to development of primary and secondary hyperalgesia, which develops away from the site of injury and is associated with central sensitization and activation of N-methyl-d-aspartate receptor in the spinal cord. The primary outcome was antihyperalgesia calculated with the area under the curve of the percentage change in mechanical pain threshold (electronic von Frey) on the area of secondary hyperalgesia. The secondary outcomes were mechanical pain threshold on the area of primary hyperalgesia and cognitive (reaction time) effect. Results Single 30-mg results are reported. Antihyperalgesia (% · min) is significantly higher on the area of secondary hyperalgesia with dextromethorphan than placebo (median [interquartile range]: 3,029 [746; 6,195] vs. 710 [–3,248; 4,439], P = 0.009, Hedge’s g = 0.8, 95% CI [0.1; 1.4]). On primary hyperalgesia area, mechanical pain threshold 2 h after drug intake is significantly higher with dextromethorphan (P = 0.011, Hedge’s g = 0.63, 95% CI [0.01; 1.25]). No difference in antinociception is observed after thermal painful stimuli on healthy skin between groups. Reaction time (ms) is shorter with placebo than with dextromethorphan (median [interquartile range]: 21.6 [–37.4; 0.1] vs. –1.2 [–24.3; 15.4], P = 0.015, Hedge’s g = 0.75, 95% CI [0.12; 1.39]). Nonserious adverse events occurrence (15%, 3 of 20 volunteers) was similar in both groups. Conclusions This study shows that low-dose (30-mg) dextromethorphan is antihyperalgesic in humans on the areas of primary and secondary hyperalgesia and reverses peripheral and central neuronal sensitization. Because dextromethorphan had no intrinsic antinociceptive effect in acute pain on healthy skin, N-methyl-d-aspartate receptor may need to be sensitized by pain for dextromethorphan to be effective.

Nav1.7 via Promotion of ERK in the Trigeminal Ganglion Plays an Important Role in the Induction of Pulpitis Inflammatory Pain

The trigeminal ganglion (TG) refers to sensory neurons bodies that innervate the spinal cord and peripheral axons that innervate teeth. The tetrodotoxin-sensitive sodium (NA) channels (Nav1.7) play important roles in the pathophysiology of pain. In this study, we investigated the TG expression of Nav1.7 and extracellular signal-regulated kinase (ERK) in a rat model of pulpitis to explore the correlation between these channels and inflammatory pain. Pulpitis was confirmed by hematoxylin-eosin staining. In this study, we demonstrated that the reflex of rats to mechanical stimulation increases after pulp exposure and that the exposed rat molar pulp can upregulate the expression of Nav1.7 and ERK in the rat TG. Three days after rat pulp exposure, the expression levels of the two ion channels in the TG increased. TG target injection of PF04856264, a Nav1.7 inhibitor, dose-dependently increased the mechanical pain threshold and was able to inhibit ERK expression. TG target injection of PD98059, an ERK inhibitor, dose-dependently increased the mechanical pain threshold. These factors simultaneously resulted in the highest production. In this study, with the established link to inflammatory pain, we found that Nav1.7 and ERK both play important roles in the induction of inflammatory pain caused by pulpitis. We also found a correlation between the expression levels of Nav1.7 and ERK and the degree of inflammatory pain. Furthermore, ERK signaling pathways were promoted by the Nav1.7 in TG after pulpitis.