Resveratrol, a polyphenolic phytoalexin attenuates thermal hyperalgesia and cold allodynia in STZ-induced diabetic rats

The effects of resveratrol, a polyphenolic phytoalexin present in red wine have been investigated on hyperalgesia and cold allodynia in streptozotocin (STZ) induced diabetic rats. Diabetes was induced by a single intraperitoneal injection of streptozotocin (65mg/kg). After 4-weeks of STZ injection, diabetic rats exhibited a significant thermal hyperalgesia and cold allodynia along with increased plasma glucose and decreased body weights as compared with controls rats. Chronic treatment with resveratrol (10mg/kg orally) from week 4 to week 6 significantly attenuated the cold allodynia and thermal hyperalgesia. The results emphasize the role of oxidative stress in development of hyperalgesia and cold allodynia in diabetic animals and point towards the potential of resveratrol as an adjuvant therapy for the prevention and treatment of diabetic neuropathy.     

Quercetin attenuates thermal hyperalgesia and cold allodynia in STZ-induced diabetic rats

Neuropathic pain is one of the important microvascular complications of diabetes. Oxidative stress and superoxide play a critical role in the development of neurovascular complications in diabetes. Aim of the present study was to evaluate the effect of quercetin, a bioflavonoid on thermal nociceptive responses in streptozotocin (STZ)-induced diabetic rats assessed by tail-immersion and hot plate methods. After 4-weeks of a single intravenous STZ injection (45 mg/kg body weight), diabetic rats exhibited a significant thermal hyperalgesia and cold allodynia along with increased plasma glucose and decreased body weights as compared with control rats. Chronic treatment with quercetin (10 mg/kg body weight; p.o) for 4-weeks starting from the 4th week of STZ-injection significantly attenuated the cold allodynia as well as hyperalgesia. Results indicate that quercetin, a natural antioxidant, may be helpful in diabetic neuropathy.     

Transplantation of bone marrow-derived mononuclear cells improves mechanical hyperalgesia, cold allodynia and nerve function in diabetic neuropathy

Relief from painful diabetic neuropathy is an important clinical issue. We have previously shown that the transplantation of cultured endothelial progenitor cells or mesenchymal stem cells ameliorated diabetic neuropathy in rats. In this study, we investigated whether transplantation of freshly isolated bone marrow-derived mononuclear cells (BM-MNCs) alleviates neuropathic pain in the early stage of streptozotocin-induced diabetic rats. Two weeks after STZ injection, BM-MNCs or vehicle saline were injected into the unilateral hind limb muscles. Mechanical hyperalgesia and cold allodynia in SD rats were measured as the number of foot withdrawals to von Frey hair stimulation and acetone application, respectively. Two weeks after the BM-MNC transplantation, sciatic motor nerve conduction velocity (MNCV), sensory nerve conduction velocity (SNCV), sciatic nerve blood flow (SNBF), mRNA expressions and histology were assessed. The BM-MNC transplantation significantly ameliorated mechanical hyperalgesia and cold allodynia in the BM-MNC-injected side. Furthermore, the slowed MNCV/SNCV and decreased SNBF in diabetic rats were improved in the BM-MNC-injected side. BM-MNC transplantation improved the decreased mRNA expression of NT-3 and number of microvessels in the hind limb muscles. There was no distinct effect of BM-MNC transplantation on the intraepidermal nerve fiber density. These results suggest that autologous transplantation of BM-MNCs could be a novel strategy for the treatment of painful diabetic neuropathy.     

Neurobiological effects of pulsed magnetic field on diabetes‐induced neuropathy

In the clinic, although several pharmacological agents or surgical procedures are used to treat diabetes and diabetes‐induced neuropathic pain, their success has been limited. Therefore, development of different alternatives in treatments is very important. The purpose of this study was to determine the efficacy of pulsed magnetic field (PMF) in improving signs and symptoms of diabetic neuropathy. In this study, the effects of PMF treatment were investigated in Streptozotocin (STZ)‐induced acute and chronic diabetic rats by measuring the thermal latencies, mechanical thresholds, whole blood glucose levels and body weights. After STZ administration to rats, blood glucose level elevated and body weight decreased. Although PMF treatment did not affect changes in body weight, the blood glucose levels of PMF‐treated diabetic rats exhibited a decrease during the treatments. Diabetic animals displayed marked decrease in mechanical thresholds and thermal latencies. While treatment of PMF partially restored the mechanical thresholds and thermal latency in acute diabetic rats, PMF caused a corrective effect on only mechanical threshold of chronic diabetic rats. These results suggested that treatment of PMF can potentially ameliorate the painful symptoms of diabetes, such as hyperalgesia and allodynia, by partially preventing the hyperglycemia. Bioelectromagnetics 31:39–47, 2010. © 2009 Wiley‐Liss, Inc.     

MiR-214-3p plays a protective role in diabetic neuropathic rats by regulating Nav1.3 and TLR4

This study aimed to investigate the functions of miR-214-3p in diabetic neuropathic rodents. The diabetic neuropathy was induced by intraperitoneal injection of streptozotocin (STZ) in rats, and miR-214-3p was delivered via tail vein injection of lentivirus. Hot or cold stimulus tests demonstrated that STZ induced thermal hyperalgesia. Neurophysiological measurements revealed that motor and sensory nerve conduction velocity and nerve blood flow were decreased in diabetic neuropathic rats. However, the STZ-induced hyperalgesia, and reduced nerve conduction velocity and nerve blood flow were all significantly reversed by miR-214-3p administration. HE staining, TUNEL, ELISA, and immunoblotting demonstrated that STZ led to obvious pathological lesion, cell apoptosis, and inflammation in dorsal root ganglion (DRG), evidenced by altered levels of apoptosis-related protein molecules and inflammatory factors, and activation of Toll-like receptor 4 (TLR4)/myeloid differentiation primary response gene 88/nuclear factor kappa B signaling. The pathological alterations in diabetic neuropathic rats in DRG were significantly ameliorated by miR-214-3p application. In addition, sodium channel protein type 3 subunit alpha isoform 1 (Nav1.3) and TLR4 were identified as targets of miR-214-3p via dual-luciferase reporter assay. MiR-214-3p may play its roles by downregulating Nav1.3 and TLR4. In summary, miR-214-3p alleviated diabetes-induced nerve injury, and pathological lesion, cell apoptosis, and inflammation in DRG by regulating Nav1.3 and TLR4 in STZ-induced rats. These findings may provide novel therapeutic targets for clinical treatment of diabetic neuropathy.     

Effects of U83836E on nerve functions, hyperalgesia and oxidative stress in experimental diabetic neuropathy

Oxidative stress has been implicated to play an important role in the pathogenesis of diabetic neuropathy, which is the most common complication of diabetes mellitus affecting more than 50% of diabetic patients. In the present study, we have investigated the effect of U83836E [(-)-2-((4-(2,6-Di-1-pyrrolidinyl-4-pyrimidinyl)-1-piperazinyl)methyl)-3,4-dihydro-2,3,7,8-tetramethyl-2H-1-benzopyran-6-ol, 2HCl], a potent free radical scavenger in streptozotocin (STZ)-induced diabetic neuropathy in rats. STZ-induced diabetic rats showed significant deficit in motor nerve conduction velocity (MNCV), nerve blood flow (NBF) and thermal hyperalgesia after 8 weeks of diabetes induction, indicating development of diabetic neuropathy. Antioxidant enzyme (superoxide dismutase and catalase) levels were reduced and malondialdehyde (MDA) levels were significantly increased in diabetic rats as compared to the age-matched control rats, this indicates the involvement of oxidative stress in diabetic neuropathy. The 2-week treatment with U83836E (3 and 9 mg/kg, i.p.) started 6 weeks after diabetes induction significantly ameliorated the alterations in MNCV, NBF, hyperalgesia, MDA levels and antioxidant enzymes in diabetic rats. Results of the present study suggest the potential of U83836E in treatment of diabetic neuropathy.     

Pain modality and spinal glia expression by streptozotocin induced diabetic peripheral neuropathy in rats

Pain symptoms are a common complication of diabetic peripheral neuropathy or an inflammatory condition. In the most experiments, only one or two evident pain modalities are observed at diabetic peripheral neuropathy according to experimental conditions. Following diabetic peripheral neuropathy or inflammation, spinal glial activation may be considered as an important mediator in the development of pain. For this reason, the present study was aimed to address the induction of pain modalities and spinal glial expression after streptozotocin injection as compared with that of zymosan inflammation in the rat. Evaluation of pain behavior by either thermal or mechanical stimuli was performed at 3 weeks or 5 hours after either intravenous streptozotocin or zymosan. Degrees of pain were divided into 4 groups: severe, moderate, mild, and non-pain induction. On the mechanical allodynia test, zymosan evoked predominantly a severe type of pain, whereas streptozotocin induced a weak degree of pain (severe+moderate: 57.1%). Although zymosan did not evoke cold allodynia, streptozotocin evoked stronger pain behavior, compared with zymosan (severe+moderate: 50.0%). On the other hand, the high incidence of thermal hyperalgesia (severe+moderate: 90.0%) and mechanical hyperalgesia (severe+moderate: 85.7%) by streptozotocin was observed, as similar to that of zymosan. In the spinal cord, the increase of microglia and astrocyte was evident by streptozotocin, only microglia was activated by zymosan. Therefore, it is recommended that the selection of mechanical and thermal hyperalgesia is suitable for the evaluation of streptozotocin induced diabetic peripheral neuropathy. Moreover, spinal glial activation may be considered an important factor.     

The cytochrome P450 inhibitor, ketoconazole, inhibits oxidized linoleic acid metabolite-mediated peripheral inflammatory pain

Background

Painful neuropathy is a common complication of diabetes. Previous studies have identified significant increases in the amount of voltage gated sodium channel isoforms Na_V1.7 and Na_V1.3 protein in the dorsal root ganglia (DRG) of rats with streptozotocin (STZ)-induced diabetes. We found that gene transfer-mediated release of the inhibitory neurotransmitters enkephalin or gamma amino butyric acid (GABA) from DRG neurons in diabetic animals reduced pain-related behaviors coincident with a reduction in Na_V1.7 protein levels in DRG in vivo. To further evaluate the role of Na_V?? subunit levels in DRG in the pathogenesis of pain in diabetic neuropathy, we constructed a non-replicating herpes simplex virus (HSV)-based vector expressing a microRNA (miRNA) against Na_V?? subunits.

Results

Subcutaneous inoculation of the miRNA-expressing HSV vector into the feet of diabetic rats to transduce DRG resulted in a reduction in Na_V?? subunit levels in DRG neurons, coincident with a reduction in cold allodynia, thermal hyperalgesia and mechanical hyperalgesia.

Conclusions

These data support the role of increased Na_V?? protein in DRG in the pathogenesis of pain in diabetic neuropathy, and provide a proof-of-principle demonstration for the development of a novel therapy that could be used to treat intractable pain in patients with diabetic neuropathy.     

Early painful diabetic neuropathy is associated with differential changes in tetrodotoxin-sensitive and -resistant sodium channels in dorsal root ganglion neurons in the rat

Diabetic neuropathy is a common form of peripheral neuropathy, yet the mechanisms responsible for pain in this disease are poorly understood. Alterations in the expression and function of voltage-gated tetrodotoxin-resistant (TTX-R) sodium channels have been implicated in animal models of neuropathic pain, including models of diabetic neuropathy. We investigated the expression and function of TTX-sensitive (TTX-S) and TTX-R sodium channels in dorsal root ganglion (DRG) neurons and the responses to thermal hyperalgesia and mechanical allodynia in streptozotocin-treated rats between 4-8 weeks after onset of diabetes. Diabetic rats demonstrated a significant reduction in the threshold for escape from innocuous mechanical pressure (allodynia) and a reduction in the latency to withdrawal from a noxious thermal stimulus (hyperalgesia). Both TTX-S and TTX-R sodium currents increased significantly in small DRG neurons isolated from diabetic rats. The voltage-dependent activation and steady-state inactivation curves for these currents were shifted negatively. TTX-S currents induced by fast or slow voltage ramps increased markedly in neurons from diabetic rats. Immunoblots and immunofluorescence staining demonstrated significant increases in the expression of Na(v)1.3 (TTX-S) and Na(v) 1.7 (TTX-S) and decreases in the expression of Na(v) 1.6 (TTX-S) and Na(v)1.8 (TTX-R) in diabetic rats. The level of serine/threonine phosphorylation of Na(v) 1.6 and In Na(v)1.8 increased in response to diabetes. addition, increased tyrosine phosphorylation of Na(v)1.6 and Na(v)1.7 was observed in DRGs from diabetic rats. These results suggest that both TTX-S and TTX-R sodium channels play important roles and that differential phosphorylation of sodium channels involving both serine/threonine and tyrosine sites contributes to painful diabetic neuropathy.     

A Novel and Selective Poly (ADP-Ribose) Polymerase Inhibitor Ameliorates Chemotherapy-Induced Painful Neuropathy

Background

Chemotherapy-induced neuropathy is the principle dose limiting factor requiring discontinuation of many chemotherapeutic agents, including cisplatin and oxaliplatin. About 30 to 40% of patients receiving chemotherapy develop pain and sensory changes. Given that poly (ADP-ribose) polymerase (PARP) inhibition has been shown to provide neuroprotection, the current study was developed to test whether the novel PARP inhibitor compound 4a (analog of ABT-888) would attenuate pain in cisplatin and oxaliplatin-induced neuropathy in mice.

Results

An established chemotherapy-induced painful neuropathy model of two weekly cycles of 10 intraperitoneal (i.p.) injections separated by 5 days rest was used to examine the therapeutic potential of the PARP inhibitor compound 4a. Behavioral testing using von Frey, paw radiant heat, cold plate, and exploratory behaviors were taken at baseline, and followed by testing at 3, 6, and 8 weeks from the beginning of drug treatment.

Conclusion

Cisplatin-treated mice developed heat hyperalgesia and mechanical allodynia while oxaliplatin-treated mice exhibited cold hyperalgesia and mechanical allodynia. Co-administration of 50 mg/kg or 25 mg/kg compound 4a with platinum regimen, attenuated cisplatin-induced heat hyperalgesia and mechanical allodynia in a dose dependent manner. Similarly, co-administration of 50 mg/kg compound 4a attenuated oxaliplatin-induced cold hyperalgesia and mechanical allodynia. These data indicate that administration of a novel PARP inhibitor may have important applications as a therapeutic agent for human chemotherapy-induced painful neuropathy.     

Formononetin Ameliorates Diabetic Neuropathy by Increasing Expression of SIRT1 and NGF

Diabetic neuropathy is commonly observed complication in more than 50 % of type 2 diabetic patients. Histone deacetylases including SIRT1 have significant role to protect neuron from hyperglycemia induced damage. Formononetin (FMNT) is known for its effect to control hyperglycemia and also activate SIRT1. In present study, we evaluated effect of FMNT as SIRT1 activator in type 2 diabetic neuropathy. Type 2 diabetic neuropathy was induced in rats by modification of diet for 15 days using high fat diet and administration of streptozotocin (35 mg/kg/day, i. p.). FMNT treatment was initiated after confirmation of type 2 diabetes. Treatment was given for 16 weeks at 10, 20 and 40 mg/kg/day dose orally. FMNT treatment‐controlled hypoglycemia and reduced insulin resistance significantly in diabetic animals. FMNT treatment reduced oxidative stress in sciatic nerve tissue. FMNT treatment also reduced thermal hyperalgesia and mechanical allodynia significantly. It improved conduction velocity in nerve and unregulated SIRT1 and NGF expression in sciatic nerve tissue. Results of present study indicate that continuous administration of FMNT protected diabetic animals from hyperglycemia induced neuronal damage by controlling hyperglycemia and increasing SIRT1 and NGF expression in nerve tissue. Thus, FMNT can be an effective candidate for treatment of type 2 diabetic neuropathy.     

Paclitaxel-induced neuropathic hypersensitivity in mice: responses in 10 inbred mouse strains

Mechanical allodynia, or hypersensitivity to tactile stimuli, is a frequent clinical symptom of neuropathy. Large interindividual differences have been observed in neuropathic pain, both in susceptibility to its development and in its severity. Identification of genetic factors relevant to this variability would be of obvious utility. Although many animal models of neuropathic pain following peripheral nerve injury have been developed, most involve intricate surgeries and are thus poorly suited for large-scale linkage mapping investigations in the mouse. Recently, a schedule of intraperitoneal injections of the chemotherapeutic agent, paclitaxel (Taxol(R)), has been shown to produce a long-lasting, bilateral neuropathy in the rat, featuring hypersensitivity to mechanical, thermal and cold stimuli. We present here a survey of the responses of 10 inbred mouse strains to paclitaxel injections. Virtually all strains developed statistically significant mechanical allodynia, with one strain, DBA/2J, exhibiting especially robust changes. Strain sensitivities to paclitaxel-induced mechanical allodynia were similar to those obtained previously using a surgical model of neuropathic pain, supporting our contention that genetic sensitivity to mechanical allodynia is independent of the precise mode of induction. Using sensitive DBA/2 mice and a resistant strain, C57BL/6J, for comparison, we further characterized the paclitaxel model in mice by examining cold allodynia and thermal hyperalgesia. Both strains displayed equivalent cold allodynia but neither strain developed thermal hyperalgesia. The present data confirm a genetic component in mechanical allodynia using this model, while dissociating mechanical hypersensitivity from other pain modalities.     

PARP inhibition or gene deficiency counteracts intraepidermal nerve fiber loss and neuropathic pain in advanced diabetic neuropathy

Evidence that poly(ADP-ribose) polymerase (PARP) activation plays an important role in diabetic complications is emerging. This study evaluated the role of PARP in rat and mouse models of advanced diabetic neuropathy. The orally active PARP inhibitor 10-(4-methylpiperazin-1-ylmethyl)-2H-7-oxa-1,2-diaza-benzo[de]anthracen-3-one (GPI-15427; formulated as a mesilate salt, 30 mg kg(-1) day(-1) in the drinking water for 10 weeks after the first 2 weeks without treatment) at least partially prevented PARP activation in peripheral nerve and DRG neurons, as well as thermal hypoalgesia, mechanical hyperalgesia, tactile allodynia, exaggerated response to formalin, and, most importantly, intraepidermal nerve fiber degeneration in streptozotocin-diabetic rats. These findings are consistent with the lack of small sensory nerve fiber dysfunction in diabetic PARP -/- mice. Furthermore, whereas diabetic PARP +/+ mice displayed approximately 46% intraepidermal nerve fiber loss, diabetic PARP -/- mice retained completely normal intraepidermal nerve fiber density. In conclusion, PARP activation is an important contributor to intraepidermal nerve fiber degeneration and functional changes associated with advanced Type 1 diabetic neuropathy. The results support a rationale for the development of potent and low-toxicity PARP inhibitors and PARP inhibitor-containing combination therapies.     

Repeated Administration of Mirtazapine Attenuates Oxaliplatin-Induced Mechanical Allodynia and Spinal NR2B Up-Regulation in Rats

Chemotherapic drugs may elicit acute or chronic peripheral neuropathies. Mirtazapine, as an antidepressant, is also used for the treatment of neuropathic pain. The current study aimed to investigate the effect of mirtazapine on the oxaliplatin-induced neuropathy in rats as well as the underlying mechanism. A neuropathy model was established in Sprague–Dawley rats by intraperitoneal (i.p.) injection of oxaliplatin 4 mg/kg twice a week for 4 weeks. The therapeutic potential of mirtazapine 10, 20, and 30 mg/kg/day per-orally for 28 consecutive days was evaluated. Subsequently, a dose of 1 mg/kg of WAY100635 i.p., a selective antagonist of 5-HT_1A receptor, was preadministrated before mirtazapine 20 mg/kg/day per-orally in oxaliplatin-induced neuropathy. The behavioral tests and the expression of NMDA receptor subunit NR2B were determined. The results displayed that repeated administration of mirtazapine 20 or 30 mg/kg/day for 28 consecutive days significantly attenuated the mechanical allodynia and the up-regulation of spinal cord NR2B but not the cold hyperalgesia in rats with oxaliplatin-induced neuropathy, which was reversed by WAY100635 preadministration. Our findings suggest that oxaliplatin-induced mechanical allodynia is associated with spinal NR2B up-regulation, which may be attenuated by mirtazapine administration.     

Beneficial effects of n-hexane bark extract of Onosma echioides L. on diabetic peripheral neuropathy

Onosma echioides Linn (Boraginaceae) is the most frequently used curative herb widely used for kidney obstruction, sciatic pain, and gout. The present study was designed to investigate the therapeutic effects of n-hexane bark extract of O. echioides (OE) L. root in vivo against Streptozotocin-induced diabetic neuropathy in SD rats. For in vivo activity, the experiment was categorized into five different groups (n = 5). Group-I was considered as nondiabetic/normal control (NC) treated with 0.5% carboxymethyl cellulose (CMC), Group II as diabetic control, Group-III, IV, and V served as diabetic treated with OE 50, OE 100, and pregabalin at a dose of 50, 100, and 10 mg/kg body weight, orally, respectively. Body weight, blood glucose, oral glucose tolerance test, behavioral studies (motor coordination test, thermal hyperalgesia, cold allodynia, locomotor activity, oxidative biomarkers (thio barbituric acid reactive substances [TBARS], superoxide dismutase [SOD], glutathione [GSH], and catalase), and histopathology of the sciatic nerve were performed. Treatment with OE showed a dose-dependent increase in neuroprotective activity by improving the myelination and decreasing the axonal swelling of nerve fibers. The verdicts of behavioral activities showed a remarkable effect on animals after the treatment of extract and standard drug pregabalin. In conclusion, our findings supported the traditional application of OE and explored its importance in the management of diabetic neuropathy. Additional clinical experiments may provide novel therapeutic drugs for diabetes and its complications.     

An Early Diagnostic Tool for Diabetic Peripheral Neuropathy in Rats

The skin’s rewarming rate of diabetic patients is used as a diagnostic tool for early diagnosis of diabetic neuropathy. At present, the relationship between microvascular changes in the skin and diabetic neuropathy is unclear in streptozotocin (STZ) diabetic rats. The aim of this study was to investigate whether the skin rewarming rate in diabetic rats is related to microvascular changes and whether this is accompanied by changes observed in classical diagnostic methods for diabetic peripheral neuropathy. Computer-assisted infrared thermography was used to assess the rewarming rate after cold exposure on the plantar skin of STZ diabetic rats’ hind paws. Peripheral neuropathy was determined by the density of intra-epidermal nerve fibers (IENFs), mechanical sensitivity, and electrophysiological recordings. Data were obtained in diabetic rats at four, six, and eight weeks after the induction of diabetes and in controls. Four weeks after the induction of diabetes, a delayed rewarming rate, decreased skin blood flow and decreased density of IENFs were observed. However, the mechanical hyposensitivity and decreased motor nerve conduction velocity (MNCV) developed 6 and 8 weeks after the induction of diabetes. Our study shows that the skin rewarming rate is related to microvascular changes in diabetic rats. Moreover, the skin rewarming rate is a non-invasive method that provides more information for an earlier diagnosis of peripheral neuropathy than the classical monofilament test and MNCV in STZ induced diabetic rats.     

Neurotropin® relieves oxaliplatin-induced neuropathy via Gi protein-coupled receptors in the monoaminergic descending pain inhibitory system

Aims

Oxaliplatin is a key drug in the treatment of colorectal cancer, but it causes acute and chronic peripheral neuropathies. We previously reported that repeated administration of neurotropin prevents oxaliplatin-induced mechanical allodynia by inhibiting axonal degeneration in rats. In the present study, we investigated the analgesic effect of a single administration of neurotropin on oxaliplatin-induced neuropathy in rats.

Main methods

Oxaliplatin (4 mg/kg) was administered intraperitoneally twice a week for 4 weeks. Cold hyperalgesia was assessed using the acetone test and mechanical allodynia was evaluated using the von Frey test.

Key findings

Repeated injection of oxaliplatin induced cold hyperalgesia on day 5 and mechanical allodynia on day 28. A single administration of neurotropin transiently relieved both pain behaviors. The analgesic effect of neurotropin was inhibited by pretreatment with 5-HT_1A, 5-HT₂, 5-HT₃, and α2 receptor antagonists and by monoamine depletion. Moreover, the analgesic effect of neurotropin was abolished by intrathecal injection of pertussis toxin, a G_i protein inhibitor.

Significance

These results suggest that neurotropin is effective in relieving oxaliplatin-induced neuropathy, and that G_i protein-coupled receptors in the monoaminergic descending pain inhibitory system may be involved in the analgesic effect of neurotropin. Neurotropin may have clinical potential for the treatment of oxaliplatin-induced neuropathies.     

The Induction of Heme Oxygenase 1 Decreases Painful Diabetic Neuropathy and Enhances the Antinociceptive Effects of Morphine in Diabetic Mice

Painful diabetic neuropathy is a common complication of diabetes mellitus which is poorly controlled by conventional analgesics. This study investigates if treatment with an heme oxygenase 1 (HO-1) inducer, cobalt protoporphyrin IX (CoPP), could modulate the allodynia and hyperalgesia induced by diabetes and enhanced the antinociceptive effects of morphine. In a diabetic mice model induced by the injection of streptozotocin (STZ), we evaluated the antiallodynic and antihyperalgesic effects produced by the intraperitoneal administration of 5 and 10 mg/kg of CoPP at several days after its administration. The antinociceptive actions produced by the systemic administration of morphine alone or combined with CoPP were also evaluated. In addition, the effects of CoPP treatment on the expression of HO-1, the microglial activation marker (CD11b/c), the inducible nitric oxide synthase (NOS2) and μ-opioid receptors (MOR), were also assessed. Our results showed that the administration of 10 mg/kg of CoPP during 5 consecutive days completely blocked the mechanical and thermal hypersensitivity induced by diabetes. These effects are accompanied by the increased spinal cord, dorsal root ganglia and sciatic nerve protein levels of HO-1. In addition, the STZ-induced activation of microglia and overexpression of NOS2 in the spinal cord were inhibited by CoPP treatment. Furthermore, the antinociceptive effects of morphine were enhanced by CoPP treatment and reversed by the administration of an HO-1 inhibitor, tin protoporphyrin IX (SnPP). The spinal cord expression of MOR was also increased by CoPP treatment in diabetic mice. In conclusion, our data provide the first evidence that the induction of HO-1 attenuated STZ-induced painful diabetic neuropathy and enhanced the antinociceptive effects of morphine via inhibition of microglia activation and NOS2 overexpression as well as by increasing the spinal cord levels of MOR. This study proposes the administration of CoPP alone or combined with morphine as an interesting therapeutic approach for the treatment of painful diabetic neuropathy.     

Gastrodin inhibits allodynia and hyperalgesia in painful diabetic neuropathy rats by decreasing excitability of nociceptive primary sensory neurons

Painful diabetic neuropathy (PDN) is a common complication of diabetes mellitus and adversely affects the patients' quality of life. Evidence has accumulated that PDN is associated with hyperexcitability of peripheral nociceptive primary sensory neurons. However, the precise cellular mechanism underlying PDN remains elusive. This may result in the lacking of effective therapies for the treatment of PDN. The phenolic glucoside, gastrodin, which is a main constituent of the Chinese herbal medicine Gastrodia elata Blume, has been widely used as an anticonvulsant, sedative, and analgesic since ancient times. However, the cellular mechanisms underlying its analgesic actions are not well understood. By utilizing a combination of behavioral surveys and electrophysiological recordings, the present study investigated the role of gastrodin in an experimental rat model of STZ-induced PDN and to further explore the underlying cellular mechanisms. Intraperitoneal administration of gastrodin effectively attenuated both the mechanical allodynia and thermal hyperalgesia induced by STZ injection. Whole-cell patch clamp recordings were obtained from nociceptive, capsaicin-sensitive small diameter neurons of the intact dorsal root ganglion (DRG). Recordings from diabetic rats revealed that the abnormal hyperexcitability of neurons was greatly abolished by application of GAS. To determine which currents were involved in the antinociceptive action of gastrodin, we examined the effects of gastrodin on transient sodium currents (I(NaT)) and potassium currents in diabetic small DRG neurons. Diabetes caused a prominent enhancement of I(NaT) and a decrease of potassium currents, especially slowly inactivating potassium currents (I(AS)); these effects were completely reversed by GAS in a dose-dependent manner. Furthermore, changes in activation and inactivation kinetics of I(NaT) and total potassium current as well as I(AS) currents induced by STZ were normalized by GAS. This study provides a clear cellular basis for the peripheral analgesic action of gastrodin for the treatment of chronic pain, including PDN.     

鞘内注射γ-氨基丁酸转运体抑制剂NO-711抑制坐骨神经慢性挤压伤大鼠神经病理性痛觉过敏

为研究γ-氨基丁酸转运体在神经病理性痛中的作用,实验用坐骨神经慢性挤压伤致神经病理性痛模型大鼠,以清醒大鼠分别对辐射热刺激和机械性触觉刺激的缩腿潜伏期和机械阈值为指标,分为NS组、N5组、N10组、N20组、N40组5组,分别在坐骨神经结扎前和结扎后第三天鞘内给予生理盐水或不同剂量的γ-氨基丁酸转运体特异性抑制剂NO-711(5、10、20、40μg),观察鞘内注射NO-711对大鼠热痛敏和触诱发痛的影响.结果表明,NO-711可显著抑制神经病理性痛大鼠的热痛觉过敏和触诱发痛(P＜0.05,P＜0.01),其抑制作用持续时间最长分别可达2 h(N40组)和4 h(N20组),其抗热痛敏作用呈剂量依赖性.坐骨神经结扎前鞘内给予不同剂量的NO-711可不同程度地延迟坐骨神经结扎所致的热痛觉过敏的发生,但不能延迟结扎所致的触诱发痛的发生.结果表明γ-氨基丁酸转运体抑制剂在神经病理性痛大鼠具有抗热痛敏和抗触诱发痛的作用.