Development Of Diabetic Neuropathic Pain Research Articles

Suppression of HCN channels in the spinal dorsal horn restores KCC2 expression and attenuates diabetic neuropathic pain

Previous studies have shown that the hyperpolarized cyclic nucleotide gated (HCN) ion channels in the spinal dorsal horn (SDH) might be involved in the development of diabetic neuropathic pain (DNP). Additionally, other studies have shown that the decreased potassium-chloride cotransporter 2 (KCC2) expression in the SDH promotes pain hypersensitivity. Both HCN channels and KCC2 were highly expressed in spinal substantia gelatinosa neurons. However, whether the K+ efflux induced by the activation of HCN channels in DNP modulate KCC2 function and subsequently affect the role of γ-aminobutyric acid (GABA)/GABA-A receptors of neurons in the SDH remains to be clarified. The purpose of this work was to investigate the underlying mechanisms of KCC2 participating in HCN channels to promote DNP. Here, we found that the analgesic role of HCN channels blocker ZD7288 was associated with the up-regulated KCC2 expression and could be prevented by DIOA, a KCC2 blocker. Furthermore, the level of GABA in DNP rats significantly increased, which was decreased by ZD72288. Moreover, DIOA pretreatment could partly block the inhibitory effect of ZD7288 on the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) signaling activation of DNP rats. Finally, inhibition of cAMP-PKA signaling alleviated allodynia and elevated KCC2 expression in DNP rats. Altogether, this study reveals that the role of cAMP-PKA signaling-regulated HCN channels in DNP associated with decreased KCC2 expression in the spinal cord and altered GABA nature.

Effect of Aerobic Training and Melatonin Consumption on TNF-α Expression in the Spinal Cord Tissue of Male Rats with Type 1 Diabetes

Background: Neuroinflammation plays a central role in the onset and development of diabetic neuropathic pain. Objectives: This study aims to thoroughly investigate the effects of aerobic training and melatonin on TNF-α expression in rats suffering from diabetic neuropathic pain. Methods: Twenty-five male Wistar rats, aged 8 weeks and weighing 204 ± 11.3 g, were randomly assigned to one of five groups: Diabetic, melatonin-treated diabetic, exercise-trained diabetic, melatonin and exercise-trained diabetic, and control. Diabetes was induced by injecting streptozotocin (STZ) at a dose of 50 mg/kg. After verifying the development of diabetes through a pain perception test, the training group underwent six weeks of continuous aerobic training on a treadmill with an average intensity of 15 meters per minute for 30 minutes. The melatonin groups received a daily dose of 10 mg per kilogram of body weight for 6 weeks. TNF-α expression levels were measured using real-time PCR. Results: The combination of aerobic training and melatonin supplementation significantly decreased TNF-α expression levels (P < 0.05). Additionally, the levels of TNF-α expression were found to be lower in the diabetic group compared to the control group (P < 0.05). Conclusions: It appears that combining aerobic training with melatonin supplementation can regulate TNF-α expression levels and enhance the sensitivity of nociceptors to nociceptive factors resulting from the gradual deterioration of sensory neurons caused by diabetes.

Effects of 1-methyl-1, 2, 3, 4-tetrahydroisoquinoline on a diabetic neuropathic pain model.

Background: Neuropathy is a prevalent and debilitating complication of poorly managed diabetes, contributing towards poor quality of life, amputation risk, and increased mortality. The available therapies for diabetic neuropathic pain (DPN) have limitations in terms of efficacy, tolerability and patient compliance. Dysfunction in the peripheral and central monoaminergic system has been evidenced in various types of neuropathic and acute pain. The objective of the present study was to investigate 1-methyl 1, 2, 3, 4-tetrahydroisoquinoline (1MeTIQ), an endogenous amine found in human brain with a known neuroprotective profile, in a model of streptozotocin (STZ) induced neuropathic pain. Methods: Diabetic neuropathy in male BALB/c mice was induced by intraperitoneal injection of a single dose of STZ (200mg/kg). Upon development of DPN after 4weeks, mice were investigated for mechanical allodynia (von Frey filament pressure test) and thermal hyperalgesia (tail immersion test). Ondansetron (1.0mg/kg i.p.), naloxone (3.0mg/kg i.p.) and yohimbine (2.0mg/kg i.p.) were used to elucidate the possible mechanism involved. Postmortem frontal cortical, striatal and hippocampal tissues were dissected and evaluated for changes in levels of dopamine, noradrenaline and serotonin using High-Performance Liquid Chromatography (HPLC) with UV detection. Results: Acute administration of 1MeTIQ (15-45mg/kg i.p.) reversed streptozotocin-induced diabetic neuropathic static mechanical allodynia (von Frey filament pressure test) and thermal hyperalgesia (tail immersion test), these outcomes being comparable to standard gabapentin. Furthermore, HPLC analysis revealed that STZ-diabetic mice expressed lower concentrations of serotonin in all three brain regions examined, while dopamine was diminished in the striatum and 1MeTIQ reversed all these neurotransmitter modifications. These findings suggest that the antihyperalgesic/antiallodynic activity of 1MeTIQ may be mediated in part via supraspinal opioidergic and monoaminergic modulation since they were naloxone, yohimbine and ondansetron reversible. Conclusion: It was also concluded that acute treatment with 1MeTIQ ameliorated STZ-induced mechanical allodynia and thermal hyperalgesia and restored brain regionally altered serotonin and dopamine concentrations which signify a potential for 1MeTIQ in the management of DPN.

BHF177 Suppresses Diabetic Neuropathic Pain by Blocking PKC/CaMKII/ERK1/2/CREB Signaling Pathway through Activating GABAB Receptor

The gamma-aminobutyric acid type B (GABAB) receptor may participate in the development of diabetic neuropathic pain (DNP). BHF177 serves as a positive allosteric modulator of the GABAB receptor. In the current study, we sought to study the role of the BHF177-GABAB receptor in DNP and its underlying mechanism. Streptozotocin was adopted to induce a rat model of DNP, followed by determination of the paw withdrawal threshold (PWT), paw withdrawal latency (PWL), and glucose level. The effect of BHF177 on DNP by regulating the GABAB receptor in vivo was determined by the injection of BHF177 and/or CGP46381 (a GABAB receptor antagonist) into rat models of DNP. Hippocampal neuronal cells were isolated and cultured, and the neurons and DNP model rats were treated with activators of PKC (PMA), CaMKII (CaCl2), or ERK1/2 (EGF) to study the role of GABAB receptors in DNP via regulation of the NR2B-PKC-CaMKII-ERK-CREB pathway. BHF177 suppressed DNP symptoms by activating the GABAB receptors, as evidenced by increased PWT and PWL of DNP rats and the increased number of neurons expressing the GABAB receptor, but this effect was reversed by CGP46381 treatment. BHF177 treatment markedly repressed PKC, CaMKII, p-ERK1/2, and p-CREB expressions in the rat DNP model, but these suppressive effects were abrogated by treatments with PMA, CaCl2, or EGF treatment, respectively. To sum up, BHF177 suppresses DNP symptoms by blocking the PKC/CaMKII/ERK1/2/CREB signaling pathway to activate the GABAB receptors.

LncRNA-UC.25 + shRNA Alleviates P2Y14 Receptor-Mediated Diabetic Neuropathic Pain via STAT1.

Diabetic neuropathic pain (DNP) is a common complication of diabetes, and its complicated pathogenesis, as well as clinical manifestations, has brought great trouble to clinical treatment. The spinal cord is an important part of regulating the occurrence and development of DNP. Spinal microglia can regulate the activity of spinal cord neurons and have a regulatory effect on chronic pain. P2Y12 receptor is involved in DNP. P2Y14 and P2Y12 receptors belong to the Gi subtype of P2Y receptors, but there is no report that the P2Y14 receptor is involved in DNP. Closely related to many human diseases, the dysregulation of long noncoding RNA (lncRNA) has the effect of promoting or inhibiting the occurrence and development of diseases. The aim of this research is to investigate the function of the spinal cord P2Y14 receptor in type 2 DNP and to understand the function as well as the possible mechanism of lncRNA-UC.25 + (UC.25 +) in rat spinal cord P2Y14 receptor-mediated DNP. Our results showed that P2Y14 shRNA can reduce the expression of P2Y14 in DNP rats, thereby restraining the activation of microglia, decreasing the expression of inflammatory factors and the level of p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation. At the same time, UC.25 + shRNA can downregulate the expression of the P2Y14 receptor, reduce the release of inflammatory factors, and diminish the p38 MAPK phosphorylation, indicating that UC.25 + can alleviate spinal cord P2Y14 receptor-mediated DNP. The RNA immunoprecipitation result showed that UC.25 + enriched signal transducers and activators of transcription1 (STAT1) and positively regulated its expression. The chromatin immunoprecipitation result indicated that STAT1 combined with the promoter region of the P2Y14 receptor and positively regulated the expression of the P2Y14 receptor. Therefore, we infer that UC.25 + may alleviate DNP in rats by regulating the expression of the P2Y14 receptor in spinal microglia via STAT1.

Decreased amino acids in the brain might contribute to the progression of diabetic neuropathic pain

AimsThe pathophysiological alteration of diabetic neuropathic pain (DNP) in brain is unclear. Here we aimed to explore the metabolomic characteristics of brain in rats over the progression of DNP through metabolomic analysis. MethodsAdult rats were randomly divided into control group and DNP group. Body weight, blood glucose and behavioral assessment of neuropathic pain were measured every week after streptozotocin (STZ) injection. Finally, the brains of 2 rats from control group and 6 rats from DNP group were removed every 4 weeks after STZ injection for metabolomics analysis. ResultsAfter 4 weeks of STZ-injection, the rats with diabetes developed DNP, which was characterized as mechanical allodynia and thermal nociception. As for metabolomic analysis, differentially expressed metabolites (DE metabolites) showed a dynamic alteration over the development of DNP and affected several KEGG pathways associated with amino acid metabolism. Furthermore, the expression of l-Threonine, l-Methionine, d-Proline, l-Lysine and N-Acetyl-l-alanine were significantly decreased at all time points of DNP group. The amino acids which were precursor of analgesic neurotransmitters were downregulated over the progression of DNP, including l-tryptophan, l-histidine and l-tyrosine. ConclusionsThe impairment of amino acid metabolism in brain might contribute to the progression of DNP through decreasing analgesic neurotransmitters.

N-Acetylcysteine Attenuates Hyperalgesia in Rats with Diabetic Neuropathic Pain: Role of Oxidative Stress and Inflammatory Mediators and CXCR4

Objectives. CXCR4 plays critical roles in the development of diabetic neuropathic pain (DNP) in rats, and its mechanism is unknown. This study was aimed at evaluating the potential therapeutic value of the antioxidant N-acetylcysteine (NAC) against DNP in rats and how CXCR4 participates in the formation of DNP. Methods. Control or streptozotocin- (STZ-) induced diabetic Sprague-Dawley rats received vehicle or NAC for four weeks starting one week after STZ injection. Von Frey and Hargreaves Apparatus were used to analyze the behavioral changes of mechanical allodynia and heat hyperalgesia. CXCR4, p-CXCR4, interleukin- (IL-) 6, and tumor necrosis factor- (TNF-) α in the spinal cord and the prefrontal cortex were detected by western blotting. Plasma IL-6, TNF-α, superoxide dismutase- (SOD-) 1, SOD-2, and lipid peroxidation products malondialdehyde (MDA) and 15-F2t-Isoprostane were detected by ELISA. Results. The values of paw withdrawal threshold (PWT) and paw withdrawal latencies (PWL) were reduced in diabetic rats compared to control rats that were concomitant with significant increases of CXCR4, p-CXCR4, IL-6, and TNF-α protein expressions in the spinal cord and prefrontal cortex. The treatment with NAC decreased the IL-6 and TNF-α protein expression and further increased CXCR4 and p-CXCR4 in the spinal cord and the cortex of diabetic rats that were accompanied with enhancement of PWT and PWL. NAC also significantly attenuated or reverted the increases of plasma IL-6, TNF-α, SOD-1, SOD-2, MDA, and 15-F2t-Isoprostane in diabetic rats. Conclusion. It is concluded that NAC treatment could effectively alleviate DNP and that induction of CXCR4 and p-CXCR4 may represent a mechanism whereby NAC attenuates DNP.

Increased number of activated microglia in rat spinal cord during early stage of diabetic induction.

Diabetic neuropathy is a common chronic complication in diabetes mellitus. Such neuropathy associates with chronic inflammation and immune system activation. Microglia, a type of neuroglia, are involved in the immune system and are found in grey and white matter of the central nervous system, such as the brain and spinal cord. The spinal cord connects the peripheral nervous system and the higher brain centre. Hyperglycaemia during diabetes mellitus has been found to activate and increase number of microglia in the dorsal grey horn or column of the lumbar segments in spinal cord, which release several cytokines in the development of hypersensitivity in diabetic neuropathic pain. Therefore, in this study, anatomical alterations of rat spinal microglia in all areas (dorsal, intermediate and ventral columns of grey matter and dorsal, lateral and ventral funiculi of white matter) in cervical enlargement, thoracic level and lumbosacral enlargement were observed in early stage of diabetic conditions by using light and transmission electron microscopies. The numbers of microglia in all parts of grey and white matter of all spinal levels significantly increased in the diabetic group. The structures and ultrastructures of microglia in grey and white matter at cervical enlargement, thoracic level and lumbosacral enlargement similarly changed in diabetes. In diabetic rats, microglia became hypertrophied with a pale nucleus. Moreover, short fragments of rough endoplasmic reticulum, elevated numbers of lysosomes and numerous actin filaments in the cytoplasm were examined. Microglial phagocytosis of myelin and axonal debris were also observed. In this investigation, the morphology of spinal microglia during short-term diabetes became activated during hyperglycaemia. It is suggested that these changes may be involved in the development of diabetic neuropathic pain in the spinal cord.

Spinal cannabinoid CB1 or CB2 receptors activation attenuates mechanical allodynia in streptozotocin-induced diabetic rats.

Diabetes is a chronic disease associated with a high number of complications such as peripheral neuropathy, which causes sensorial disturbances and may lead to the development of diabetic neuropathic pain (DNP). The current treatment for DNP is just palliative and the drugs may cause severe adverse effects, leading to discontinuation of treatment. Thus, new therapeutic targets need to be urgently investigated. Studies have shown that cannabinoids have promising effects in the treatment of several pathological conditions, including chronic pain. Thus, we aimed to investigate the acute effect of the intrathecal injection of CB1 or CB2 cannabinoid receptor agonists N-(2-chloroethyl)-5Z, 8Z, 11Z, 14Z-eicosatetraenamide (ACEA) or JWH 133, respectively (10, 30 or 100 μg/rat) on the mechanical allodynia associated with experimental diabetes induced by streptozotocin (60 mg/kg; intraperitoneal) in rats. Cannabinoid receptor antagonists CB1 AM251 or CB2 AM630 (1 mg/kg) were given before treatment with respective agonists to confirm the involvement of cannabinoid CB1 or CB2 receptors. Rats with diabetes exhibited a significant reduction on the paw mechanical threshold 2 weeks after diabetes induction, having the maximum effect observed 4 weeks after the streptozotocin injection. This mechanical allodynia was significantly improved by intrathecal treatment with ACEA or JWH 133 (only at the higher dose of 100 μg). Pre-treatment with AM251 or AM630 significantly reverted the anti-allodynic effect of the ACEA or JWH 133, respectively. Considering the clinical challenge that the treatment of DPN represents, this study showed for the first time, that the intrathecal cannabinoid receptors agonists may represent an alternative for the treatment of DNP.

IL-35 alleviates inflammation progression in a rat model of diabetic neuropathic pain via inhibition of JNK signaling

BackgroundEmerging evidence has demonstrated that inflammation is involved in the occurrence and development of diabetic neuropathic pain (DNP). The anti-inflammatory property of interleukin (IL)-35 makes it a promising candidate to block the pain perception. The present study was undertaken to investigate whether IL-35 could attenuate DNP in streptozotocin (STZ)-induced rat model and its potential mechanism.MethodsThe rat model of DNP was established by a single STZ injection followed by measurements of fasting blood glucose and insulin. Fourteen days after STZ injection, DNP rats were intrathecally injected with IL-35, c-Jun N-terminal kinase (JNK) inhibitor or activator or dimethylsulfoxide (DMSO) as vehicle control, respectively. The mechanical allodynia was assayed to evaluate the therapeutic effect of IL-35. In mechanism study, the serum and protein levels of inflammatory cytokines using ELISA and western blotting and the activation of JNK signaling were further evaluated by quantitative reverse transcription PCR (qRT-PCR). Histopathologic changes were evaluated by Nissl staining. Apoptosis was examined using TUNEL staining.ResultsDNP rats exhibited increased fasting blood glucose and insulin levels and reduced insulin sensitivity index (ISI). Intrathecal injection of IL-35 reduced accumulation of pro-inflammatory cytokines in the spinal cord of DNP rats. Furthermore, IL-35 displayed anti-inflammatory and anti-apoptotic effects via inhibition of JNK pathway.ConclusionIL-35 treatment mitigated DNP via downregulating JNK signaling pathway.

Progressive Increase of Inflammatory CXCR4 and TNF-Alpha in the Dorsal Root Ganglia and Spinal Cord Maintains Peripheral and Central Sensitization to Diabetic Neuropathic Pain in Rats.

Diabetic neuropathic pain (DNP) is a common and serious complication of diabetic patients. The pathogenesis of DNP is largely unclear. The proinflammation proteins, CXCR4, and TNF-α play critical roles in the development of pain, while their relative roles in the development of DNP and especially its progression is unknown. We proposed that establishment of diabetic pain models in rodents and evaluating the stability of behavioral tests are necessary approaches to better understand the mechanism of DNP. In this study, Von Frey and Hargreaves Apparatus was used to analyze the behavioral changes of mechanical allodynia and heat hyperalgesia in streptozotocin-induced diabetic rats at different phases of diabetes. Moreover, CXCR4 and TNF-α of spinal cord dorsal and dorsal root ganglia (DRG) were detected by western blotting and immunostaining over time. The values of paw withdrawal threshold (PWT) and paw withdrawal latencies (PWL) were reduced as early as 1 week in diabetic rats and persistently maintained at lower levels during the progression of diabetes as compared to control rats that were concomitant with significant increases of both CXCR4 and TNF-α protein expressions in the DRG at 2 weeks and 5 weeks (the end of the experiments) of diabetes. By contrast, CXCR4 and TNF-α in the spinal cord dorsal horn did not significantly increase at 2 weeks of diabetes while both were significantly upregulated at 5 weeks of diabetes. The results indicate that central sensitization of spinal cord dorsal may result from persistent peripheral sensitization and suggest a potential reference for further treatment of DNP.

Role of spinal cord TRAF6/NF-κB signaling pathway in development of diabetic neuropathic pain in rats

Objective To evaluate the role of spinal cord tumor necrosis factor receptor-associated factor 6 (TRAF6)/nuclear factor kappa B(NF-κB)signaling pathway in the development of diabetic neuropathic pain(DNP)in rats. Methods Clean-grade healthy adult male Sprague-Dawley rats, aged 2 months, weighing 180-230 g, in which IT catheters were implanted, were used in this study.Streptozotocin 60 mg/kg was intraperitoneally injected after IT catheterization to establish the model of DNP.Twelve DNP rats were divided into 2 groups (n=6 each) by a random number table method: DNP group and DNP plus TRAF6 inhibitor group (group DTR). Another 6 age-matched Sprague-Dawley rats were used as normal control group(group NC). The rats in group DC and group DTR received IT injection of dimethyl sulfoxide 10 μl and TRAF6 inhibition 10 μg, respectively, once a day for 7 consecutive days starting from day 21 after establishing the model.The mechanical paw withdrawal threshold (MWT) was determined before establishing the model(T1), on 7, 14 and 21 days after establishing the model(T2-4), and on 1, 4 and 7 days after IT injection (T5-7). The rats were sacrificed after the last MWT measurement, and the L3-5 segments of the spinal cord were removed for determination of the expression of TRAF6 and NF-κB p65 by Western blot. Results Compared with group NC, the MWT at T3-7 in group DC and at T3-6 in group DTR was significantly decreased, and the expression of spinal TRAF6 and NF-κB p65 was up-regulated in DC and DTR groups (P<0.05). Compared with group DC, the MWT was significantly increased at T6-7, and the expression of spinal TRAF6 and NF-κB p65 was down-regulated in group DTR (P<0.05). Conclusion Spinal cord TRAF6/NF-κB signaling pathway is involved in the development of DNP in rats. Key words: Spinal cord; Tumor necrosis factor receptor-associated peptides and proteins; NF-kappa B; Diabetes mellitus; Neuralgia

Diabetes-induced microvascular complications at the level of the spinal cord: a contributing factor in diabetic neuropathic pain.

Key points Diabetes is thought to induce neuropathic pain through activation of dorsal horn sensory neurons in the spinal cord.Here we explore the impact of hyperglycaemia on the blood supply supporting the spinal cord and chronic pain development.In streptozotocin‐induced diabetic rats, neuropathic pain is accompanied by a decline in microvascular integrity in the dorsal horn. Hyperglycaemia‐induced degeneration of the endothelium in the dorsal horn was associated with a loss in vascular endothelial growth factor (VEGF)‐A165b expression. VEGF‐A165b treatment prevented diabetic neuropathic pain and degeneration of the endothelium in the spinal cord.Using an endothelial‐specific VEGFR2 knockout transgenic mouse model, the loss of endothelial VEGFR2 signalling led to a decline in vascular integrity in the dorsal horn and the development of hyperalgesia in VEGFR2 knockout mice.This highlights that vascular degeneration in the spinal cord could be a previously unidentified factor in the development of diabetic neuropathic pain. Abnormalities of neurovascular interactions within the CNS of diabetic patients is associated with the onset of many neurological disease states. However, to date, the link between the neurovascular network within the spinal cord and regulation of nociception has not been investigated despite neuropathic pain being common in diabetes. We hypothesised that hyperglycaemia‐induced endothelial degeneration in the spinal cord, due to suppression of vascular endothelial growth factor (VEGF)‐A/VEGFR2 signalling, induces diabetic neuropathic pain. Nociceptive pain behaviour was investigated in a chemically induced model of type 1 diabetes (streptozotocin induced, insulin supplemented; either vehicle or VEGF‐A165b treated) and an inducible endothelial knockdown of VEGFR2 (tamoxifen induced). Diabetic animals developed mechanical allodynia and heat hyperalgesia. This was associated with a reduction in the number of blood vessels and reduction in Evans blue extravasation in the lumbar spinal cord of diabetic animals versus age‐matched controls. Endothelial markers occludin, CD31 and VE‐cadherin were downregulated in the spinal cord of the diabetic group versus controls, and there was a concurrent reduction of VEGF‐A165b expression. In diabetic animals, VEGF‐A165b treatment (biweekly i.p., 20 ng g−1) restored normal Evans blue extravasation and prevented vascular degeneration, diabetes‐induced central neuron activation and neuropathic pain. Inducible knockdown of VEGFR2 (tamoxifen treated Tie2CreERT2‐vegfr2flfl mice) led to a reduction in blood vessel network volume in the lumbar spinal cord and development of heat hyperalgesia. These findings indicate that hyperglycaemia leads to a reduction in the VEGF‐A/VEGFR2 signalling cascade, resulting in endothelial dysfunction in the spinal cord, which could be an undiscovered contributing factor to diabetic neuropathic pain.

Inhibition of protein tyrosine phosphatase 1B in spinal cord dorsal horn of rats attenuated diabetic neuropathic pain

Protein tyrosine phosphatase 1B (PTP1B) has been shown to dephosphorylate and inactivate insulin receptors, which contributes to the pathogenesis of diabetes. Neuropathic pain is one of the severe complications that results from diabetic neuropathy. However, whether PTP1B was involved in the development of diabetic neuropathic pain is largely unknown. The current study illustrated that PTP1B was located in spinal cord dorsal horn neurons of Sprague-Dawley rats. Western blot analysis demonstrated that the diabetic neuropathic pain induced by intraperitoneal injection of streptozotocin was associated with an increased protein expression and a dynamic redistribution of spinal PTP1B into excitatory glutamatergic synapses. We found that PTP1B operated to stimulate Src kinase and enhance the tyrosine phosphorylation of N-methyl-D-aspartate (NMDA) subtype of glutamate receptors. The siRNA-mediated knockdown of PTP1B in streptozotocin-injected rats repressed Src activity, decreased NMDA receptor phosphorylation and alleviated the thermal hyperalgesia and mechanical allodynia. A similar analgesia against diabetic neuropathic pain was also achieved when PTP1B activity was manipulated by a chemical PTP Inhibitor or PTP1B(C215S) mutant. These data revealed a regulated expression of PTP1B in spinal cord dorsal horn of rats after diabetic neuropathy, and demonstrated that inhibition of PTP1B was beneficial for the treatment of pain hypersensitivity related to diabetes.

Sigma 1 receptor mediated HMGB1 expression in spinal cord is involved in the development of diabetic neuropathic pain

No study has been conducted to examine the interactions of sigma-1 receptor (Sigma-1R) and high mobility group box 1 protein (HMGB1) in the development of diabetic peripheral neuropathy. Thus, we examined the effects of streptozotocin (STZ) treatment on expression of HMGB1 in subcellular levels in the dorsal root ganglion (DRG) in both wild-type and Sigma-1R−/− mice and evaluated the effects of repeated intrathecal administrations of selective Sigma-1R antagonists BD1047, agonist PRE-084, or HMGB1 inhibitor glycyrrhizin on peripheral neuropathy in wild-type mice. We found that STZ-induced tactile allodynia and thermal hyperalgesia was associated with increased total HMGB1 expression in DRG. STZ treatment promoted the distribution of HMGB1 into cytoplasm. Furthermore, STZ induced modest peripheral neuropathy and did not alter HMGB1 levels in DRG or the distribution of either cytoplasmic or nuclear HMGB1 in Sigma-1R−/− mice compared to sham control mice. Additionally, repeated stimulation of Sigma-1R in the spinal cord induced tactile allodynia and thermal hyperalgesia at 1 week. This phenomenon was associated with increased cytoplasmic HMGB1 translocation and HMGB1 expression in DRG. Finally, we found that repeated blockade of either Sigma-1R or HMGB1 in the spinal cord after STZ treatment prevent the development of tactile allodynia and thermal hyperalgesia at 1 week. These effects were associated with decreased cytoplasmic HMGB1 translocation and HMGB1 expression in DRG. Taken together, our results suggest that Sigma-1R-mediated enhancement of HMGB1 expression in the DRG is critical for the development of peripheral neuropathy in type 1 diabetes.

Activation of ephrinB-EphB receptor signalling in rat spinal cord contributes to maintenance of diabetic neuropathic pain.

Diabetic neuropathic pain (DNP) is severe and intractable in clinic. The specific cellular and molecular mechanisms underlying DNP remain elusive and its treatment are limited. We investigated roles of EphB1 receptor in the development of DNP. Diabetic neuropathic pain was produced in male, adult, Sprague-Dawley rats by a single i.p. streptozotocin (STZ) or alloxan. Western blot analysis and immunohistochemistry were used to analyse expression of EphB1 receptor as well as the activation of the glial cells and the pro-inflammatory cytokines in the spinal cord. DNP manifested as mechanical allodynia, which was determined by measuring incidence of foot withdrawal in response to mechanical indentation of the hind paw by an electro von Frey filament. Diabetic neuropathic pain and high blood glucose were exhibited simultaneously in around 70% of animals that received i.p. STZ or alloxan. Phosphorylation of EphB1, activation of the astrocytes and microglial cells, and level of tumour necrosis factor (TNF)-α and interleukin (IL)-1β in the spinal cord were significantly increased in rats with DNP. Spinal blocking EphB1 receptor activation in the late phase after STZ injection significantly suppressed the established mechanical allodynia as well as activation of the astrocytes and microglial cells and activity of TNF-α and IL-1β. However, spinal treatment of EphB1-Fc in the early phase after STZ injection did not prevent the induction of DNP. EphB1 receptor activation in the spinal cord is critical to the maintenance, but not induction of diabetic pain. EphB1 receptor may be a potential target for relieving the established diabetic pain. Activation of EphB1 receptor in the spinal cord is critical to maintaining the established diabetic neuropathic pain, but not to diabetic pain induction. Spinal blocking EphB1 receptor activation suppresses ongoing diabetic neuropathic pain.

A preliminary study on the role of the complement regulatory protein, cluster of differentiation 55, in mice with diabetic neuropathic pain.

The aim of this study was to investigate the role of the complement regulatory protein cluster of differentiation 55 (CD55) in the pathogenesis of diabetic neuropathic pain (DNP). Healthy adult male C57BL/6J mice were intraperitoneally injected with streptozotocin (STZ) in order to induce DNP. Peripheral blood glucose and protein, and the mRNA expression levels of C3 and CD55 in the spinal cord were determined. In addition, the behaviors of these mice were observed. The results showed that STZ‑treated mice displayed the clinical manifestations of diabetes mellitus, and that their peripheral blood glucose was markedly increased. On the 21st and 28th days following the STZ injection, the mechanical pain threshold and thermal pain threshold of the mice were dramatically reduced (P<0.05). |Additionally, 14 days post‑STZ injection, the mRNA expression of C3 in the spinal cord was significantly increased, which continued for 28 days. On the 21st and 28th days, the number of C3 positive cells in the spinal cord was markedly increased. Seven days after the STZ injection, the number of cells positive for CD55 was markedly reduced in the spinal dorsal horn and subsequently remained at a low level. The mRNA expression of CD55 also was significantly reduced (P<0.05) and remained so for 28 days. The reduction in the expression levels of CD55 occurred earlier than the changes in the expression of C3, suggesting that the downregulation of CD55 expression precedes, and has an important role regarding, the activation of C3 in the occurrence and development of DNP.

Role of transient receptor potential ankyrin 1 in dorsal root ganglion neurons in development of diabetic neuropathic pain in rats

Objective To evaluate the role of transient receptor potential ankyrin 1 (TRPA1) in the dorsal root ganglion neurons in the development of diabetic neuropathic pain (DNP) in rats.Methods Twenty-four Sprague-Dawley rats with DNP were randomly divided into 3 groups (n-=8 each) using a random number table:DNP group,TRPA1-specific siRNA group (siRNA group) and TRPA1-negative siRNA group (NC group).Another 8 Sprague-Dawley rats with normal blood glucose served as control group (C group).In siRNA group,TRPA1-specific siRNA 45 μl was injected intrathecally.In NC group,TRPA1-negative siRNA 45 μl was injected intrathecally.In DNP and C groups,normal saline 45 μl was injected intrathecally.On 2nd day after intrathecal administration,the lumbar segment (L4-6) of the dorsal root ganglions was removed for determination of the expression of TRPA1 mRNA.On 7,14,21 and 28 days after intrathecal administration (T1-4),MWT was measured.Results Compared with DNP group,TRPA1 mRNA expression was down-regulated in siRNA and C groups.Compared with DNP group,and MWT was significantly decreased at T1.2 in siRNA group,MWT was decreased at T1-3 in NC group,MWT was increased at T1-4 in group C.Compared with siRNA group,MWT was significantly increased at T1-4 in group C.MWT was significantly higher at T1~ in group C than in NC group.Conclusion TRPA1 in the dorsal root ganglion neurons is involved in the development of DNP in rats. Key words: Transient receptor potential channels; Posterior horn cells; Diabetic neuropathies

Kaempferol Attenuates the Development of Diabetic Neuropathic Pain in Mice: Possible Anti-Inflammatory and Anti-Oxidant Mechanisms

BACKGROUND: Diabetic neuropathic pain (DNP) is one of the most difficult types of pain to treat. Many studies emphasized on the role of microglial cells, oxidative stress (OS) and inflammatory cytokines (IC) in the development of diabetic neuropathy (DN).AIM: Present study was designed to evaluate the effect of kaempferol in attenuation of DN in mice. METHODS: Diabetes was induced in mice by i.p. injection of a single dose of streptozotocin (STZ) (200 mg/kg). Cold allodynia, thermal hyperalgesia and chemical hyperalgesia were assessed, as well as markers of inflammation and OS.RESULTS: Diabetic mice (DM) showed an increased pain sensation, IC and OS accompanied with reduced body weigh gain. Treatment of DM with kaempferol (25, 50 and 100 mg/kg/day/orally) attenuated the development of DN and reduced pain sensation. Moreover, it reduced interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), lipid peroxidation and nitrite, concomitant with the improvement of antioxidant defense and body weight gain. In contrast, kaempferol (100 mg/kg) had no effects on the behavioral and biochemical parameters. Our results strongly suggest that activated microglia, IC and OS are involved in the development of DN.CONCLUSIONS: Kaempferol attenuates the development of DNP in mice probably by inhibition of neuroimmune activation of microglia and, partly mediated by reducing IC and OS.

Kaempferol Attenuates the Development of Diabetic Neuropathic Pain in Mice: Possible Anti-Inflammatory and Anti-Oxidant Mechanisms

Macedonian Journal of Medical Sciences (MJMS) is an international peer reviewed journal published four times per year by the ID Design 2012/DOOEL Skopje on behalf of Foundation Macedonian Donor Registry (MKDR), Skopje, Republic of Macedonia.