The spinal antinociceptive mechanism determined by systemic administration of BD1047 in zymosan-induced hyperalgesia in rats

Effects of Sigma-1 Receptor Ligands on Peripheral Nerve Regeneration

Peripheral nerve injuries lead to the loss of motor, sensory and autonomic functions in the territories supplied by the injured nerve. Currently, nerve injuries are managed by surgical repair procedures, and there are no effective drugs in the clinic for improving the capacity of axonal regeneration. Sigma-1 receptor (Sig-1R) is an endoplasmic reticulum chaperon protein involved in many functions, including neuroprotection and neuroplasticity. A few previous studies using Sig-1R ligands reported results that suggest this receptor as a putative target to enhance regeneration. The aim of this study was to evaluate the possible effects of Sig-1R ligands on axonal regeneration in a sciatic nerve section and repair model in mice. To this end, mice were treated either with the Sig-1R agonist PRE-084 or the antagonist BD1063, and a Sig-1R knock-out (KO) mice group was also studied. The electrophysiological and histological data showed that treatment with Sig-1R ligands, or the lack of this protein, did not markedly modify the process of axonal regeneration and target reinnervation after sciatic nerve injury. Nevertheless, the nociceptive tests provided results indicating a role of Sig-1R in sensory perception after nerve injury, and immunohistochemical labeling indicated a regulatory role in inflammatory cell infiltration in the injured nerve.

Sigma-1 receptor increases intracellular calcium in cultured astrocytes and contributes to mechanical allodynia in a model of neuropathic pain

Recent studies have revealed that glial sigma-1 receptor (Sig-1R) in the spinal cord may be a critical factor to mediate sensory function. However, the functional role of Sig-1R in astrocyte has not been clearly elucidated. Here, we determined whether Sig-1Rs modulate calcium responses in primary cultured astrocytes and pathological changes in spinal astrocytes, and whether they contribute to pain hypersensitivity in naïve mice and neuropathic pain following chronic constriction injury (CCI) of the sciatic nerve in mice. Sig-1R was expressed in glial fibrillary acidic protein (GFAP)-positive cultured astrocytes. Treatment with the Sig-1R agonist, PRE-084 or neurosteroid dehydroepiandrosterone (DHEA) increased intracellular calcium responses in cultured astrocytes, and this increase was blocked by the pretreatment with the Sig-1R antagonist, BD-1047 or neurosteroid progesterone. Intrathecal administration of PRE-084 or DHEA for 10 days induced mechanical and thermal hypersensitivity and increased the number of Sig-1R-immunostained GFAP-positive cells in the superficial dorsal horn (SDH) region of the spinal cord in naïve mice, and these changes were inhibited by administration with BD-1047 or progesterone. In CCI mice, intrathecal administration of BD-1047 or progesterone at post-operative day 14 suppressed the developed mechanical allodynia and the number of Sig-1R-immunostained GFAP-positive cells that were increased in the SDH region of the spinal cord following CCI of the sciatic nerve. These results demonstrate that Sig-1Rs play an important role in the modulation of intracellular calcium responses in cultured astrocytes and pathological changes in spinal astrocytes and that administration of BD-1047 or progesterone alleviates the Sig-1R-induced pain hypersensitivity and the peripheral nerve injury-induced mechanical allodynia.

The Peripheral Role of CCL2 in the Anti-Nociceptive Effect of Sigma-1 Receptor Antagonist BD1047 on Inflammatory Hyperalgesia in Rats

Our recent study demonstrated that the CC-chemokine ligand 2 (CCL2) present in primary afferent fibers (PAFs) plays an important role in the microglia-dependent neuronal activation associated with zymosan-induced inflammatory pain. The present study was aimed to evaluate whether BD1047 (a prototypical sigma-1 receptor (Sig-1R) antagonist) is capable of modifying elevated levels of inflammation-evoked CCL2 as a peripheral antinociceptive mechanism. In DRG primary culture, zymosan dose-dependently increased CCL2 release from isolectin B4 (IB4)-positive DRG neurons, a process that was inhibited by co-culture with BD1047. Single treatment of BD1047 before intraplantar injection of zymosan in rats significantly reduced thermal hyperalgesia and mechanical hyperalgesia, as well as CCL2 expression in DRG neurons and microglia activation in the spinal dorsal horn. In the Complete Freund's adjuvant (CFA)-induced inflammation model, repeated administration of BD1047 dramatically attenuated thermal hyperalgesia and mechanical hyperalgesia, and significantly diminished CCL2 immunoreactivity and microglia activation. Notably, CFA-induced inflammation significantly increased Sig-1R immunoreactivity in DRG neurons, which was co-localized with CCL2 and IB4, respectively. Taken together, our results suggest that BD1047's anti-nociceptive property was substantially mediated by the inhibition of CCL2 release in unmyelinated PAFs and that this may, in turn, have attenuated the spinal microglia activation that is associated with inflammatory pain.

Sigma-1 receptor: A drug target for the modulation of neuroimmune and neuroglial interactions during chronic pain

Immune and glial cells play a pivotal role in chronic pain. Therefore, it is possible that the pharmacological modulation of neurotransmission from an exclusively neuronal perspective may not be enough for adequate pain management, and the modulation of complex interactions between neurons and other cell types might be needed for successful pain relief. In this article, we review the current scientific evidence for the modulatory effects of sigma-1 receptors on communication between the immune and nervous systems during inflammation, as well as the influence of this receptor on peripheral and central neuroinflammation. Several experimental models of pathological pain are considered, including peripheral and central neuropathic pain, osteoarthritic, and cancer pain. Sigma-1 receptor inhibition prevents peripheral (macrophage infiltration into the dorsal root ganglion) and central (activation of microglia and astrocytes) neuroinflammation in several pain models, and enhances immune-driven peripheral opioid analgesia during painful inflammation, maximizing the analgesic potential of peripheral immune cells. Therefore, sigma-1 antagonists may constitute a new class of analgesics with an unprecedented mechanism of action and potential utility in several painful disorders.

p38 mitogen-activated protein kinase and pain

Inflammatory and neuropathic pain is initiated by tissue inflammation and nerve injury, respectively. Both are characterized by increased activity in the peripheral and central nervous system, where multiple inflammatory cytokines and other active molecules activate different signaling pathways that involve in the development and/or maintenance of pain. P38 mitogen-activated protein kinase (MAPK) is one member of the MAPK family, which is activated in neurons and glia and contributes importantly to inflammatory and neuropathic pain. The aim of this review is to summarize the latest advances made about the implication of p38 MAPK signaling cascade in pain. It can deepen our understanding of the molecular mechanisms of pain and may help to offer new targets for pain treatment.

Sigma-1 receptors control neuropathic pain and macrophage infiltration into the dorsal root ganglion after peripheral nerve injury

Neuron-immune interaction in the dorsal root ganglia (DRG) plays a pivotal role in the neuropathic pain development after nerve injury. Sigma-1 receptor (Sig-1R) is expressed by DRG neurons but its role in neuropathic pain is not fully understood. We investigated the effect of peripheral Sig-1R on neuroinflammation in the DRG after spared (sciatic) nerve injury (SNI) in mice. Nerve injury induced a decrease in NeuN staining along with the nuclear eccentricity and ATF3 expression in the injured DRG. Sig-1R was present in all DRG neurons examined, and after SNI this receptor translocated to the periphery of the soma and the vicinity of the nucleus, especially in injured ATF3 + neurons. In WT mice, injured DRG produced the chemokine CCL2, and this was followed by massive infiltration of macrophages/monocytes, which clustered mainly around sensory neurons with translocated Sig-1R, accompanied by robust IL-6 increase and mechanical allodynia. In contrast, Sig-1R knockout (Sig-1R-KO) mice showed reduced levels of CCL2, decreased macrophage/monocyte infiltration into DRG, and less IL-6 and neuropathic mechanical allodynia after SNI. Our findings point to an important role of peripheral Sig-1R in sensory neuron-macrophage/monocyte communication in the DRG after peripheral nerve injury; thus, these receptors may contribute to the neuropathic pain phenotype.

Tetrahydroxystilbene glucoside relieves the chronic inflammatory pain by inhibiting neuronal apoptosis, microglia activation, and GluN2B overexpression in anterior cingulate cortex

Tetrahydroxystilbene glucoside (THSG) is one of the active ingredients of Polygonum multiflorum. It has been shown to exert a variety of pharmacological effects, including antioxidant, anti-aging, and anti-atherosclerosis. Because of its prominent anti-inflammatory effect, we explored whether THSG had analgesic effect. In this study, we used a model of chronic inflammatory pain caused by injecting complete Freund's adjuvant into the hind paw of mice. We found THSG relieved swelling and pain in the hind paw of mice on a dose-dependent manner. In the anterior cingulate cortex, THSG suppressed the upregulation of GluN2B-containing N-methyl-D-aspartate receptors and the downregulation of GluN2A-containing N-methyl-D-aspartate receptors caused by chronic inflammation. In addition, THSG increased Bcl-2 and decreased Bax and Caspase-3 expression by protecting neuronal survival. Furthermore, THSG inhibited the phosphorylation of p38 and the increase of nuclear factor κB (NF-κB) and tumor necrosis factor α (TNF-α). Immunohistochemical staining revealed that THSG blocked the activation of microglia and reduced the release of proinflammatory cytokines TNF-α, interleukin 1β (IL-1β), and interleukin 6 (IL-6). In conclusion, this study demonstrated that THSG had a certain effect on alleviating complete Freund's adjuvant-induced chronic inflammatory pain.

Pharmacological Modulation of the Sigma 1 Receptor and the Treatment of Pain

There is a critical need for new analgesics acting through new mechanisms of action, which could increase the efficacy with respect to existing therapies and reduce their unwanted effects. Current preclinical evidence supports the modulatory role of sigma-1 receptors (σ1R) in nociception, mainly based on the pain-attenuated phenotype of σ1R knockout mice and on the antinociceptive effect exerted by σ1R antagonists on pains of different etiologies. σ1R is highly expressed in different pain areas of the CNS and the periphery (particularly dorsal root ganglia), and interacts and modulates the functionality of different receptors and ion channels . The antagonism of σ1R leads to decreased amplification of pain signaling within the spinal cord (central sensitization), but recent data also support a role at the periphery. σ1R antagonists have consistently demonstrated efficacy in neuropathic pain , but also in other types of pain including inflammatory, orofacial, visceral, and post-operative pain. Apart from acting alone, when combined with opioids, σ1R antagonists enhance opioid analgesia but not opioid-induced unwanted effects. Interestingly, unlike opioids, σ1R antagonists do not modify normal sensory mechanical and thermal sensitivity thresholds but they exert antihypersensitive effects in sensitizing conditions, enabling the reversal of nociceptive thresholds back to normal values. Accordingly, σ1R antagonists are not strictly analgesics; they are antiallodynic and antihyperalgesic drugs acting when the system is sensitized following prolonged noxious stimulation or persistent abnormal afferent input (e.g., secondary to nerve injury). These are distinctive features allowing σ1R antagonists to exert a modulatory effect specifically in pathophysiological conditions such as chronic pain .

Sigma-1 Receptor Antagonists: A New Class of Neuromodulatory Analgesics

The sigma-1 receptor is a unique ligand-operated chaperone present in key areas for pain control, in both the peripheral and central nervous system. Sigma-1 receptors interact with a variety of protein targets to modify their function. These targets include several G-protein-coupled receptors such as the μ-opioid receptor, and ion channels such as the N-methyl-D-aspartate receptor (NMDAR). Sigma-1 antagonists modify the chaperoning activity of sigma-1 receptor by increasing opioid signaling and decreasing NMDAR responses, consequently enhancing opioid antinociception and decreasing the sensory hypersensitivity that characterizes pathological pain conditions. However, the participation in pain relief of other protein partners of sigma-1 receptors in addition to opioid receptors and NMDARs cannot be ruled out. The enhanced opioid antinociception by sigma-1 antagonism is not accompanied by an increase in opioid side effects , including tolerance, dependence or constipation, so the use of sigma-1 antagonists may increase the therapeutic index of opioids. Furthermore, sigma-1 antagonists (in the absence of opioids) have been shown to exert antinociceptive effects in preclinical models of neuropathic pain induced by nerve trauma or chemical injury (the antineoplastic paclitaxel), and more recently in inflammatory and ischemic pain. Although most studies attributed the analgesic properties of sigma-1 antagonists to their central actions, it is now known that peripheral sigma-1 receptors also participate in their effects. Overwhelming preclinical evidence of the role of sigma-1 receptors in pain has led to the development of the first selective sigma-1 antagonist with an intended indication for pain treatment, which is currently in Phase II clinical trials.

The effects of Qi Teng Xiao Zhuo granules, traditional Chinese medicine, on the expression of genes in chronic glomerulonephritis rats

BACKGROUND AND AIM

Chronic glomerulonephritis (CGN) is a primary glomerular disease that is related to immune-mediated inflammatory diseases. Qi Teng Xiao Zhuo granules have been proposed as a prescription of traditional Chinese medicine for treatment of CGN, but the comprehensive molecular mechanism underlying this therapeutic effect is not clear to date. The aim of this study was to evaluate and analyze the possible roles and molecular mechanisms of Qi Teng Xiao Zhuo granule-mediated treatment of CGN induced by adriamycin in rats.

METHODS

For gene expression analysis, four samples of glomerular tissue from rats in the Qi Teng Xiao Zhuo granule group and four samples each from the adriamycin treated and control groups were hybridized with Agilent Rat 4×44K whole genome microarrays. KEGG and Gene Ontology (GO) analyses and LIMMA, String and Cytoscape software were used to analyze the functional microarray data and screen differentially expressed genes. Hub genes were identified using Pathway Studio software. Real-time PCR was performed to verify the selected genes.

RESULTS

Microarray gene expression analysis showed that Pnoc, Cacfd1, Fos, Igll1, Lcn2, and Syk were among the most downregulated genes in the Qi Teng Xiao Zhuo granule group compared with the adriamycin treated group, whereas Cyp2c7, Hsd3b6, Acsm5, and Ugt2b15 were significantly upregulated. Functional analysis demonstrated that metabolism of xenobiotics by cytochrome P450, the B cell receptor signaling pathway, and cytokine-cytokine receptor interaction pathways were significantly downregulated in the Qi Teng Xiao Zhuo granule group and that GO terms related to positive regulation of immune response, immune response-activating signal transduction, cell differentiation, cell cycle, proliferation, and adhesion were significantly affected. Fos and Syk were considered to be potential hub genes.

CONCLUSIONS

In the adriamycin-induced CGN rat model, comprehensive molecular mechanisms were involved with complex gene expression alterations containing many altered pathways and GO terms. However, how Qi Teng Xiao Zhuo granules regulate these events warrants further investigation.

Modulation of nociception by medial pre-optic area orexin a receptors and its relation with morphine in male rats

INTRODUCTION

Recent studies have shown that medial pre-optic area (MPOA) of hypothalamus are involved in nociception. Orexin A (hypocretin 1) has been found to have numerous applications including pain modulation. However, the role of orexin A receptors in the MPOA on the nociception has not been yet studied. Therefore, the aim of the present study is to investigate the effect of orexin A microinjection on MPOA on the nociception transmission and morphine induced analgesia in adult male rats.

METHODS

Using stereotaxic surgery, a cannula was implanted at a site 1mm above the MPOA in the anesthetized rats. After the recovery period, tail-flick (TF) latency was measured as 0, 15, 30, 45 and 60min following the onset of two experimental protocols. Two experiments were carried out. Experiment 1: The male rats received intra-MPOA of 25, 100, 1000, 10000pmol/0.5μl orexin A or 0.5μl of aCSF (control, just 5min before the TF assay. Experiment 2: The aim of this experiment was to examine the effect of orexin microinjection into MPOA on morphine analgesia (3mg/kg,s.c). Morphine was administered 30min before orexin A intra-MPOA microinjection (four doses similar to experiment 1) or aCSF, then TF latency was measured.

RESULTS

The results indicated that microinjection of orexin A into the MPOA showed anti-nociceptive effect in a time-dependent manner. Dose response curve results also revealed that the maximum effective dose of orexin A injection into MPOA for pain inhibition is 1000pmol/0.5μl. Co-administration of systemic morphine and orexin into the MPOA has additive analgesia with different time course compared morphine or orexin alone.

CONCLUSION

It can be concluded that MPOA OrexinA receptors play an important role in the modulation of pain in normal and morphine treated male rats.