Diabetic Mechanical Allodynia Research Articles

Skin keratinocyte-derived SIRT1 and BDNF modulate mechanical allodynia in mouse models of diabetic neuropathy.

Diabetic neuropathy is a debilitating disorder characterized by spontaneous and mechanical allodynia. The role of skin mechanoreceptors in the development of mechanical allodynia is unclear. We discovered that mice with diabetic neuropathy had decreased sirtuin 1 (SIRT1) deacetylase activity in foot skin, leading to reduced expression of brain-derived neurotrophic factor (BDNF) and subsequent loss of innervation in Meissner corpuscles, a mechanoreceptor expressing the BDNF receptor TrkB. When SIRT1 was depleted from skin, the mechanical allodynia worsened in diabetic neuropathy mice, likely due to retrograde degeneration of the Meissner-corpuscle innervating Aβ axons and aberrant formation of Meissner corpuscles which may have increased the mechanosensitivity. The same phenomenon was also noted in skin-keratinocyte specific BDNF knockout mice. Furthermore, overexpression of SIRT1 in skin induced Meissner corpuscle reinnervation and regeneration, resulting in significant improvement of diabetic mechanical allodynia. Overall, the findings suggested that skin-derived SIRT1 and BDNF function in the same pathway in skin sensory apparatus regeneration and highlighted the potential of developing topical SIRT1-activating compounds as a novel treatment for diabetic mechanical allodynia.

The Role of the Inflammatory and the Vascular Pathogenesis in a Model of Streptozotocin Induced Diabetic Neuropathy in Rats

Abstract Background Peripheral diabetic neuropathy (DN) is one of the major health problems facing the whole world. There is no treatment that could completely reverse or prevent progression of DN except for good glycemic control. The inflammatory and vascular pathways are two main domains that are incorporated in the pathogenesis of diabetic neuropathic pain (DNP) and DN. Thus, targeting both of them could be an appropriate way to delay progression of DN. Aim To investigate the role of the inflammatory and the vascular pathogenesis in diabetic mechanical allodynia. Method Twenty male Wistar rats were divided randomly into naïve and diabetic groups (n = 10). Diabetes was induced through i.p injection of single dose of streptozotocin (STZ) (50mg/kg), then 8 weeks after induction of diabetes, the sciatic content of tumor necrosis factor alpha (TNFα) and vascular endothelial growth factor (VEGF) was assessed using ELISA technique. Additionally, the number of intercellular adhesion molecule-1 (ICAM-1) as well as CD31, the most specific vascular marker, positively stained vessels was counted manually in sciatic nerves cross sections. Whereas, DNP was assessed weekly throughout the experiment using 60%mechanical threshold of paw withdrawal test. Results There was a significant increase in the sciatic content of TNFα, VEGF and ICAM-1 positively stained vessels and a significant decrease in CD31 positively stained vessels in the diabetic group as compared to the naïve group. There was a correlation between TNFα, VEGF, ICAM-1, CD31 positively stained vessels in one side and the 60% mechanical threshold on the other side (r=-0.8, -0.9, -0.8 and 0.7 respectively). Conclusion The diabetic mechanical allodynia is negatively correlated to the sciatic nerve content TNFα, VEGF, ICAM-1 and positively correlated to the CD31.

Metformin attenuates diabetic neuropathic pain via AMPK/NF-κB signaling pathway in dorsal root ganglion of diabetic rats

Neuropathic pain is a common complication of diabetes mellitus with poorly relieved by conventional analgesics. Metformin, a first-line drug for type 2 diabetes, reduces blood glucose by activating adenosine monophosphate protein kinase (AMPK) signalling system. However, the effect of Metformin on diabetic neuropathic pain is still unknown. In the present study, we showed that Metformin was capable of attenuating diabetes induced mechanical allodynia, and the analgesia effect could be blocked by Compound C (an AMPK inhibitor). Importantly, Metformin enhanced the phosphorylation level of AMPK in L4-6 DRGs of diabetic rats but not affect the expression of total AMPK. Intrathecal injection of AICAR (an AMPK agonist) could activate AMPK and alleviate the mechanical allodynia of diabetic rats. Additionally, phosphorylated AMPK and NF-κB was co-localized in small and medium neurons of L4-6 DRGs. Interestingly, the regulation of NF-κB in diabetic rats was obviously reduced when AMPK was activated by AICAR. Notably, Metformin could decrease NF-κB expression in L4-6 DRGs of diabetic rats, but the decrease was blocked by Compound C. In conclusion, Metformin alleviates diabetic mechanical allodynia via activation of AMPK signaling pathway in L4-6 DRGs of diabetic rats, which might be mediated by the downregulation of NF-κB, and this providing certain basis for Metformin to become a potential drug in the clinical treatment of diabetic neuropathic pain.

The ubiquitin E3 ligase Nedd4-2 relieves mechanical allodynia through the ubiquitination of TRPA1 channel in db/db mice.

Neural precursor cell-expressed developmentally downregulated protein 4-2 (Nedd4-2) is a member of the E3 ubiquitin ligase family that is highly expressed in sensory neurons and involved in pain modulation via downregulation of ion channels in excitable membranes. Ubiquitination involving Nedd4-2 is regulated by adenosine monophosphate-activated protein kinase (AMPK), which is impaired in the dorsal root ganglion (DRG) neurons of db/db mice. AMPK negatively regulates the expression of transient receptor potential ankyrin 1 (TRPA1), a recognised pain sensor expressed on the membrane of DRG neurons, consequently relieving mechanical allodynia in db/db mice. Herein, we studied the involvement of Nedd4-2 in painful diabetic neuropathy and observed that Nedd4-2 negatively regulated diabetic mechanical allodynia. Nedd4-2 was co-expressed with TRPA1 in mouse DRG neurons. Nedd4-2 was involved in TRPA1 ubiquitination, this ubiquitination, as well as Nedd4-2-TRPA1 interaction, was decreased in db/db mice. Moreover, Nedd4-2 levels were decreased in db/db mice, while an abnormal intracellular distribution was observed in short-term high glucose-cultured DRG neurons. AMPK activators not only restored Nedd4-2 distribution but also increased Nedd4-2 expression. These findings demonstrate that Nedd4-2 is a potent regulator of TRPA1 and that the abnormal expression of Nedd4-2 in DRG neurons contributes to diabetic neuropathic pain.

Expression and functional characterization of transient receptor potential vanilloid 4 in the dorsal root ganglion and spinal cord of diabetic rats with mechanical allodynia

Diabetic mechanical allodynia (DMA) is a common manifestation in patients with diabetes mellitus, and currently, no effective treatment is available. Transient receptor potential vanilloid 4 (TRPV4) is involved in mechanical hypersensitivity resulting from varying aetiologies in animal, but its expression pattern during DMA and whether it contributes to this condition are still unclear. We investigated the spatial and temporal expression patterns of TRPV4 in the dorsal root ganglion (DRG) and spinal dorsal horn (SDH) by qRT-PCR, Western blotting and immunofluorescence assays. The pathophysiological role of TRPV4 in DMA was also investigated by intrathecal application of the TRPV4 selective antagonist HC-067047 or the agonist GSK1016790A. The results showed that both the mRNA and protein levels of TRPV4 were strikingly upregulated on day 14 in the rats with DMA. The increase in TRPV4 was mainly observed in the soma and central processes of calcitonin gene-related peptide (CGRP)- or neurofilament 200 kDa (NF200)-containing DRG neurons. Both single and repetitive intrathecal applications of HC-067047 (400 ng/kg) significantly alleviated mechanical allodynia in the rats with DMA, whereas a single application of GSK1016790A (200 ng/kg) aggravated mechanical allodynia. The present data suggest that TRPV4 undergoes expression changes that are associated with mechanical hypersensitivity in diabetic rats. TRPV4 may be a new molecular target for developing a clinical strategy to treat this intractable neuropathic pain.

Resveratrol alleviates diabetic mechanical allodynia in rats by downregulating P2X3R.

Mechanical allodynia, which develops in patients of diabetes mellitus as a neuropathic manifestation, remains without an effective treatment. The aim of the present study was to investigate the effects and potential mechanisms underlying resveratrol (RES) in a rat model of streptozocin (STZ)-induced diabetic mechanical allodynia (DMA). The rat model of DMA was established by the administration of an intraperitoneal injection of STZ. From day 8 post-STZ injection, rats were administered with an intragastric injection of various doses of RES for 14 consecutive days. The von Frey filaments were applied to detect the paw withdrawal threshold and evaluate the analgesic effects of RES. Based on the dose-effect curve, the ED50 of RES was calculated. Immunofluorescence staining and western blotting were performed to detect the expression of purinergic receptor P2X3 (P2X3R) in the dorsal root ganglion (DRG) and spinal dorsal horn (SDH) following RESED50 treatment. The results indicated that RES significantly alleviated mechanical allodynia in DMA model rats in a dose-dependent manner. Compared with the control group, the expression of P2X3R in DRG neurons and SDH terminals was markedly decreased following the administration of RESED50 (P<0.05). Collectively, the results indicated that RES displayed a dose-dependent analgesic effect on DMA model rats. Furthermore, P2X3R expression downregulation in the DRG and SDH may be a mechanism underlying the analgesic effects of RES on DMA-related behaviors.

Astrocytic NDRG2 is involved in glucocorticoid-mediated diabetic mechanical allodynia

AimsThe present study aims to test whether astrocytes contribute to glucocorticoid-mediated diabetic mechanical allodynia. MethodsStreptozotocin (STZ)-induced diabetic rats were used in our study. The intrathecal operation was performed 21 days after the onset of diabetes. Diabetic mechanical allodynia was present 28 d after the onset of diabetes, and the mechanical threshold was tested using von Frey filaments. Immunohistochemistry, including immunofluorescent histochemical staining, was performed to observe the morphology of the spinal dorsal horn (SDH). Western blot analysis was employed as a semi-quantitative assay of the expression levels of GFAP and NDRG2 associated with diabetic mechanical allodynia. ResultsDiabetic rats displayed mechanical allodynia and activated astrocytes in the SDH 28 days after the onset of diabetes. This allodynia was attenuated by intrathecal administration of the astrocyte-specific inhibitor l-α-aminoadipate. In parallel, intrathecal injection of RU486, a glucocorticoid receptor antagonist, inhibited the activation of astrocytes in the SDH, alleviating the diabetes-induced mechanical allodynia. Furthermore, we found that dorsal horn astrocytes express abundant N-myc downstream-regulated gene 2 (NDRG2), which contributes to astrocyte reactivity. NDRG2 was over-expressed in activated astrocytes in diabetic rats with mechanical allodynia. Intrathecal injection of RU486 prevented the over-expression of NDRG2, which reversed the astrocyte reactivity and diabetic tactile allodynia. ConclusionsThese results suggest that glucocorticoid-mediated over-expression of NDRG2 may contribute to the activation of dorsal horn astrocytes, which play a crucial role in diabetic mechanical allodynia. Thus, inhibiting glucocorticoid receptors and/or astrocyte reactivity in the SDH may be a therapeutic strategy for treating diabetic tactile allodynia.

Correction: Spatio-Temporal Expression and Functional Involvement of Transient Receptor Potential Vanilloid 1 in Diabetic Mechanical Allodynia in Rats

Correction: Spatio-Temporal Expression and Functional Involvement of Transient Receptor Potential Vanilloid 1 in Diabetic Mechanical Allodynia in Rats

Spatio-temporal expression and functional involvement of transient receptor potential vanilloid 1 in diabetic mechanical allodynia in rats.

Diabetic neuropathic pain (DNP) is one of the most common clinical manifestations of diabetes mellitus (DM), which is characterized by prominent mechanical allodynia (DMA). However, the molecular mechanism underlying it has not fully been elucidated. In this study, we examined the spatio-temporal expression of a major nociceptive channel protein transient receptor potential vanilloid 1 (TRPV1) and analyzed its functional involvement by intrathecal (i.t.) application of TRPV1 antagonists in streptozocin (STZ)-induced DMA rat models. Western blot and immunofluorescent staining results showed that TRPV1 protein level was significantly increased in the soma of the dorsal root ganglion (DRG) neurons on 14 days after STZ treatment (DMA 14 d), whereas those in spinal cord and skin (mainly from the central and peripheral processes of DRG neurons) had already been enhanced on DMA 7 d to peak on DMA 14 d. qRT-PCR experiments confirmed that TRPV1 mRNA level was significantly up-regulated in the DRG on DMA 7 d, indicating a preceding translation of TRPV1 protein in the soma but preferential distribution of this protein to the processes under the DMA conditions. Cell counting assay based on double immunostaining suggested that increased TRPV1-immunoreactive neurons were likely to be small-sized and CGRP-ergic. Finally, single or multiple intrathecal applications of non-specific or specific TRPV1 antagonists, ruthenium red and capsazepine, at varying doses, effectively alleviated DMA, although the effect of the former was more prominent and long-lasting. These results collectively indicate that TRPV1 expression dynamically changes during the development of DMA and this protein may play important roles in mechanical nociception in DRG neurons, presumably through facilitating the release of CGRP.

The Dipeptide Phe-Phe Amide Attenuates Signs of Hyperalgesia, Allodynia and Nociception in Diabetic Mice Using a Mechanism Involving the Sigma Receptor System

BackgroundPrevious studies have demonstrated that intrathecal administration of the substance P amino-terminal metabolite substance P1-7 (SP1-7) and its C-terminal amidated congener induced antihyperalgesic effects in diabetic mice. In this study, we studied a small synthetic dipeptide related to SP1-7 and endomorphin-2, i.e. Phe-Phe amide, using the tail-flick test and von Frey filament test in diabetic and non-diabetic mice.ResultsIntrathecal treatment with the dipeptide increased the tail-flick latency in both diabetic and non-diabetic mice. This effect of Phe-Phe amide was significantly greater in diabetic mice than non-diabetic mice. The Phe-Phe amide-induced antinociceptive effect in both diabetic and non-diabetic mice was reversed by the σ1 receptor agonist (+)-pentazocine. Moreover, Phe-Phe amide attenuated mechanical allodynia in diabetic mice, which was reversible by (+)-pentazocine. The expression of spinal σ1 receptor mRNA and protein did not differ between diabetic mice and non-diabetic mice. On the other hand, the expression of phosphorylated extracellular signal-regulated protein kinase 1 (ERK1) and ERK2 proteins was enhanced in diabetic mice. (+)-Pentazocine caused phosphorylation of ERK1 and ERK2 proteins in non-diabetic mice, but not in diabetic mice.ConclusionsThese results suggest that the spinal σ1 receptor system might contribute to diabetic mechanical allodynia and thermal hyperalgesia, which could be potently attenuated by Phe-Phe amide.

Analgesic effect of TT-232, a heptapeptide somatostatin analogue, in acute pain models of the rat and the mouse and in streptozotocin-induced diabetic mechanical allodynia

Somatostatin released from capsaicin-sensitive sensory nerves exerts systemic anti-inflammatory and antinociceptive actions. TT-232 is a stable, peripherally acting heptapeptide (D-Phe-Cys-Tyr-D-Trp-Lys-Cys-Thr-NH 2) somatostatin analogue with highest binding affinity for somatostatin sst 4 receptors. It has been shown to inhibit acute and chronic inflammatory responses and sensory neuropeptide release from capsaicin-sensitive nociceptors. In the present study the antinociceptive effects of TT-232 were analysed using both acute and chronic models of nociception. Formalin-induced pain behaviour, noxious heat threshold and streptozotocin-induced diabetic neuropathic mechanical allodynia were examined in rats and phenylquinone-evoked abdominal constrictions were tested in mice. TT-232 (80 μg/kg i.p.) inhibited both early (0–5 min) and late phases (25–45 min) of formalin-induced nociception as revealed by determination of the composite pain score. The minimum effective dose to elevate the noxious heat threshold and diminish the heat threshold drop (heat allodynia) evoked by resiniferatoxin (0.05 nmol intraplantarly) was 20 and 10 μg/kg i.p., respectively, as measured by an increasing-temperature hot plate. TT-232 (10–200 μg/kg s.c.) significantly inhibited phenylquinone-evoked writhing movements in mice, but within this dose range no clear dose–response correlation was found. Five weeks after streptozotocin administration (50 mg/kg i.v.) the diabetes-induced decrease in the mechanonociceptive threshold was inhibited by 10–100 μg/kg i.p. TT-232. These findings show that TT-232 potently inhibits acute chemical somatic/visceral and thermal nociception and diminishes chronic mechanical allodynia associated with diabetic neuropathy, thereby it could open new perspectives in the treatment of various pain syndromes.