Effects of anti-rVEGF on the expression of VEGF receptor-2 and P2X2/3 receptors of the spinal dorsal horn in neuropathic pain rats

Targeting Vascular endothelial growth factor A with soluble vascular endothelial growth factor receptor 1 ameliorates nerve injury-induced neuropathic pain

Neuropathic pain is a distressing medical condition with few effective treatments. The role of Vascular endothelial growth factor A (VEGFA) in inflammation pain has been confirmed in many researches. However, the mechanism of VEGFA affects neuropathic pain remains unclear. In this study, we demonstrated that VEGFA plays an important role in spare nerve injury (SNI)-induced neuropathic pain, which is mediated by enhanced expression and colocalized of VEGFA, p-AKT and TRPV1 in SNI-induced neuropathic pain model. Soluble VEGFR1 (sFlt1) not only relieved mechanical hyperalgesia and the expression of inflammatory markers, but ameliorated the expression of VEGFA, VEGFR2, p-AKT, and TRPV1 in spinal cord. However, these effects of sFlt1 can be blocked by rpVEGFA and by 740 Y-P. Therefore, our study indication that targeting VEGFA with sFlt1 reduces neuropathic pain development via the AKT/TRPV1 pathway in SNI-induced nerve injury. This study elucidates a new therapeutic target for neuropathic pain.

Toxicogenomic study to identify potential signaling alterations related to nasal inflammatory damages induced by diesel exhaust particles in primary human nasal epithelial cells

In this study, we aimed to identify signaling alteration caused by exposure to diesel exhaust particles (DEPs) using primary human nasal epithelial cells (PHNECs). Global gene expression profiles in PHNECs following 50 and 200 μg/ml of DEP exposure were identified using microarray analysis. To cover the limitation of array-based mRNA expression analysis, text-mining-based software was used to analyze the integrative biological networks and relevant disease-focused functions among identified DEP-responsive genes. The confidence was valued based on the connectivity between the analyzed pathway and marker candidates. Through a literature-based pathway analysis, the stimulation of inflammation- and immune response-related processes mediated by TNF were predicted as major signaling alterations in PHNECs caused by DEP exposure. CSF3, CXCL8, MMP1, and VEGFA were identified as key hub genes in the predicted pathway. Significant expression level changes in the five key genes following DEP exposure were validated in terms of protein and mRNA expression. Although further studies are required, our toxicogenomic investigation provides key clues to the exact mechanism underlying DEP-induced nasal inflammatory damage. It also suggests an efficient approach for other research on adverse effects occurring in the upper respiratory tract following DEP exposure.

Central VEGF-A pathway plays a key role in the development of trigeminal neuropathic pain in rats

The study reported here investigated the role of the central vascular endothelial growth factor-A (VEGF-A) pathway in the development of trigeminal neuropathic pain following nerve injury. A Sprague-Dawley rat model of trigeminal neuropathic pain was produced using malpositioned dental implants. The left mandibular second molar was extracted under anesthesia and replaced with a miniature dental implant to induce injury to the inferior alveolar nerve. The inferior alveolar nerve injury produced a significant upregulation of astrocytic VEGF-A expression in the medullary dorsal horn. The nerve injury-induced mechanical allodynia was inhibited by an intracisternal infusion of VEGF-A₁₆₄ antibody. Although both VEGF-A Receptor 1 (VEGF-A R1; colocalized with the blood–brain barrier) and VEGF-A Receptor 2 (VEGF-A R2; colocalized with astrocytes) participated in the development of trigeminal neuropathic pain following nerve injury, only the intracisternal infusion of a VEGF-A R1 antibody, and not that of a VEGF-A R2 antibody, inhibited the increased blood–brain barrier permeability produced by nerve injury. Finally, we confirmed the participation of the central VEGF-A pathway in the development of trigeminal neuropathic pain by reducing VEGF-A expression using VEGF-A₁₆₄ siRNA. This suppression of VEGF-A produced significant prolonged anti-allodynic effects. These results suggest that the central VEGF-A pathway plays a key role in the development of trigeminal neuropathic pain following nerve injury through two separate pathways: VEGF-A R1 and VEGF-A R2. Hence, a blockade of the central VEGF-A pathway provides a new therapeutic avenue for the treatment of trigeminal neuropathic pain.

Role of hesperidin in P2X3 receptor-mediated neuropathic pain in the dorsal root ganglia

Aim: This study investigated whether the neuronal P2X3 receptor in rat dorsal root ganglia (DRG) mediated the effects of hesperidin on neuropathic pain. Materials and methods: The chronic constriction injury (CCI) model was used as a model of neuropathic pain. The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were measured. The mRNA and protein expression levels were assayed by real-time RT-PCR and Western blotting. Results: The results showed that mechanical and thermal hyperalgesia in the CCI rats were increased as compared to those in the sham group. The expression levels of P2X3 mRNA and protein in CCI rats were higher than those in the sham group. Dual-labelling immunofluorescence showed that the elevated P2X3 receptor was co-expressed with the neuronal marker NeuN in the DRG of CCI rats. Hesperidin treatment decreased both the mechanical and thermal hyperalgesia, and upregulated P2X3 expression in the CCI rats. Hesperidin treatment also reduced the ERK1/2 phosphorylation in the DRG of CCI rats. Moreover, hesperidin inhibited the P2X3 agonist ATP-induced currents in HEK293 cells transfected with the P2X3 plasmid. Therefore, hesperidin treatment could reverse the elevated expression of neuronal P2X3 receptor and reduce the activation of ERK1/2 in the DRG of CCI rats. Conclusions: Our findings suggested that hesperidin inhibited the nociceptive transmission mediated by the P2X3 receptor in neurons of DRG, and thus, relieved the mechanical and thermal hyperalgesia in CCI rats.

Nanoparticle-Encapsulated Curcumin Inhibits Diabetic Neuropathic Pain Involving the P2Y12 Receptor in the Dorsal Root Ganglia

Diabetic peripheral neuropathy results in diabetic neuropathic pain (DNP). Satellite glial cells (SGCs) enwrap the neuronal soma in the dorsal root ganglia (DRG). The purinergic 2 (P2) Y12 receptor is expressed on SGCs in the DRG. SGC activation plays an important role in the pathogenesis of DNP. Curcumin has anti-inflammatory and antioxidant properties. Because curcumin has poor metabolic stability in vivo and low bioavailability, nanoparticle-encapsulated curcumin was used to improve its targeting and bioavailability. In the present study, our aim was to investigate the effects of nanoparticle-encapsulated curcumin on DNP mediated by the P2Y12 receptor on SGCs in the rat DRG. Diabetic peripheral neuropathy increased the expression levels of the P2Y12 receptor on SGCs in the DRG and enhanced mechanical and thermal hyperalgesia in rats with diabetes mellitus (DM). Up-regulation of the P2Y12 receptor in SGCs in the DRG increased the production of pro-inflammatory cytokines. Up-regulation of interleukin-1β (IL-1β) and connexin43 (Cx43) resulted in mechanical and thermal hyperalgesia in rats with DM. The nanoparticle-encapsulated curcumin decreased up-regulated IL-1β and Cx43 expression and reduced levels of phosphorylated-Akt (p-Akt) in the DRG of rats with DM. The up-regulation of P2Y12 on SGCs and the up-regulation of the IL-1β and Cx43 in the DRG indicated the activation of SGCs in the DRG. The nano-curcumin treatment inhibited the activation of SGCs accompanied by its anti-inflammatory effect to decrease the up-regulated CGRP expression in the DRG neurons. Therefore, the nanoparticle-encapsulated curcumin treatment decreased the up-regulation of the P2Y12 receptor on SGCs in the DRG and decreased mechanical and thermal hyperalgesia in rats with DM.

Effect of artemisinin on neuropathic pain mediated by P2X4 receptor in dorsal root ganglia

Neuropathic pain is a type of chronic pain caused by nervous system damage and dysfunction. The pathogenesis of chronic pain is complicated, and there are no effective therapies for neuropathic pain. Studies show that the P2X₄ receptor expressed in the satellite glial cells (SGCs) of dorsal root ganglia (DRG) is related to neuropathic pain. Artemisinin is a monomeric component extracted from traditional Chinese medicine and has a variety of important pharmacological effects and potential applications. This study observed the effect of artemisinin on neuropathic pain and delineated its possible mechanism. The chronic constriction injury (CCI) rat model was used in this study. The results demonstrated that artemisinin relieved pain behaviors in the CCI rats, inhibited the expression of P2X₄ receptor in the DRG, and decreased the ATP-activated currents in HEK293 cells transfected with P2X₄ plasmid. Dual-labeling immunofluorescence showed that the coexpression of P2X₄ receptor and glial fibrillary acidic protein (GFAP) in the DRG of CCI rats was increased compared to control rats. After CCI rats were treated with artemisinin, the coexpression of P2X₄ receptor and GFAP in the DRG was significantly decreased compared to the CCI group. This finding suggested that artemisinin could inhibit the nociceptive transmission mediated by P2X₄ receptor in the DRG SGCs and thus relieve pain behaviors in the CCI rats.

Bevacizumab for Treatment-Refractory Pain Control in Neurofibromatosis Patients

OBJECTIVE

Chronic pain is a well-known morbidity associated with neurofibromatosis (NF) for which better therapies are needed. Surgery, radiation, and pain medications have been utilized, but often fail to relieve debilitating pain. One patient at our institution was noted to have near complete resolution of pain after treatment with bevacizumab for progressive neurologic deficit associated with NF2, suggesting its potential as an effective pain control method. We aim to better characterize the use of bevacizumab for pain control in this subset of patients.  Patients and Methods: We retrospectively reviewed 38 NF patients treated at our institution.   Results: Of the 38 total NF patients, we found that 63% reported chronic pain, with 18% reporting chronic opiate usage. Nine patients with chronic pain were considered for bevacizumab treatment and five went on to receive infusions. Of these patients, four out of five had previous surgical debulking and two out of five had previous radiation for attempted pain control. One patient had a lesion not amenable to surgery or radiation. Patients received a median of 13 cycles of bevacizumab, and four out of five patients reported a decrease in subjective pain. All patients that had pain relief had a relapse of pain symptoms when the dose was reduced or infusions were paused. Seventy-five percent were able to decrease opiate use. No major complications were noted. All five patients have elected to continue infusions for pain control.  Conclusion: Bevacizumab was, in general, well tolerated and should be considered as a treatment option in NF patients with chronic pain refractory or not amenable to surgical decompression and debulking, radiation, and pain medication.

Delayed Imatinib Treatment for Acute Spinal Cord Injury: Functional Recovery and Serum Biomarkers

With no currently available drug treatment for spinal cord injury, there is a need for additional therapeutic candidates. We took the approach of repositioning existing pharmacological agents to serve as acute treatments for spinal cord injury and previously found imatinib to have positive effects on locomotor and bladder function in experimental spinal cord injury when administered immediately after the injury. However, for imatinib to have translational value, it needs to have sustained beneficial effects with delayed initiation of treatment, as well. Here, we show that imatinib improves hind limb locomotion and bladder recovery when initiation of treatment was delayed until 4 h after injury and that bladder function was improved with a delay of up to 24 h. The treatment did not induce hypersensitivity. Instead, imatinib-treated animals were generally less hypersensitive to either thermal or mechanical stimuli, compared with controls. In an effort to provide potential biomarkers, we found serum levels of three cytokines/chemokines--monocyte chemoattractant protein-1, macrophage inflammatory protein (MIP)-3α, and keratinocyte chemoattractant/growth-regulated oncogene (interleukin 8)--to increase over time with imatinib treatment and to be significantly higher in injured imatinib-treated animals than in controls during the early treatment period. This correlated to macrophage activation and autofluorescence in lymphoid organs. At the site of injury in the spinal cord, macrophage activation was instead reduced by imatinib treatment. Our data strengthen the case for clinical trials of imatinib by showing that initiation of treatment can be delayed and by identifying serum cytokines that may serve as candidate markers of effective imatinib doses.

SRPK1 inhibition in vivo: modulation of VEGF splicing and potential treatment for multiple diseases

SRPK1 (serine-arginine protein kinase 1) is a protein kinase that specifically phosphorylates proteins containing serine-arginine-rich domains. Its substrates include a family of SR proteins that are key regulators of mRNA AS (alternative splicing). VEGF (vascular endothelial growth factor), a principal angiogenesis factor contains an alternative 3' splice site in the terminal exon that defines a family of isoforms with a different amino acid sequence at the C-terminal end, resulting in anti-angiogenic activity in the context of VEGF165-driven neovascularization. It has been shown recently in our laboratories that SRPK1 regulates the choice of this splice site through phosphorylation of the splicing factor SRSF1 (serine/arginine-rich splicing factor 1). The present review summarizes progress that has been made to understand how SRPK1 inhibition may be used to manipulate the balance of pro- and anti-angiogenic VEGF isoforms in animal models in vivo and therefore control abnormal angiogenesis and other pathophysiological processes in multiple disease states.

The role of glutamate release mediated by extrasynaptic P2X7 receptors in animal models of neuropathic pain

Purinergic signaling represents a major non-synaptic signaling mechanism in the normal and pathological nervous system. The expression of the purinergic ligand gated ion channel P2X7 receptor (P2rx7) has been described on nerve terminals as well as in non-neuronal cells, such as astrocytes and microglia. The activation of P2rx7s results in Ca(2+) influx and increased transmitter release in the brain. P2rx7s previously suggested having a pivotal role in different pain modalities, including neuropathic pain. Here we investigated whether the activation of P2rx7 leads to increased glutamate release from the spinal cord in an experimental model of neuropathic pain (partial nerve ligation of the sciatic nerve, PNL). One week after surgery, we studied the effects of PNL on tactile allodynia using aesthesiometry, in parallel with the in vitro release of [(3)H]glutamate from lumbar spinal cord slices. The observed allodynia in wild-type (P2rx7+/+) mice one week after PNL surgery was lower that was observed in P2rx7 deficient (P2rx7-/-) animals. Perfusion of spinal cord slices with ATP (10mM) elicited [(3)H]glutamate release in both sham operated and neuropathic P2rx7+/+ animals. The ATP-induced [(3)H]glutamate release was absent in P2rx7-/- mice. Electrically evoked release of [(3)H]glutamate from spinal cord slices was not significantly altered in PNL animals and in P2rx7-/- mice. The results suggest that activation of P2rx7 by ATP releases glutamate in the spinal cord, which might contribute to mechanical allodynia following PNL. On the other hand, this release does not contribute to glutamate efflux evoked by conventional neuronal activity, which is consistent with the idea that P2X7 receptors are either extrasynaptic or expressed on non-neuronal cells. This article is part of a Special Issue entitled 'Extrasynaptic ionotropic receptors'.