Model Of Diabetic Neuropathy Research Articles

Involvement of TRPM2 in a wide range of inflammatory and neuropathic pain mouse models

Recent evidence suggests a role of transient receptor potential melastatin 2 (TRPM2) in immune and inflammatory responses. We previously reported that TRPM2 deficiency attenuated inflammatory and neuropathic pain in some pain mouse models, including formalin- or carrageenan-induced inflammatory pain, and peripheral nerve injury-induced neuropathic pain models, while it had no effect on the basal mechanical and thermal nociceptive sensitivities. In this study, we further explored the involvement of TRPM2 in various pain models using TRPM2-knockout mice. There were no differences in the chemonociceptive behaviors evoked by intraplantar injection of capsaicin or hydrogen peroxide between wildtype and TRPM2-knockout mice, while acetic acid-induced writhing behavior was significantly attenuated in TRPM2-knockout mice. In the postoperative incisional pain model, no difference in mechanical allodynia was observed between the two genotypes. By contrast, mechanical allodynia in the monosodium iodoacetate-induced osteoarthritis pain model and the experimental autoimmune encephalomyelitis model were significantly attenuated in TRPM2-knockout mice. Furthermore, mechanical allodynia in paclitaxel-induced peripheral neuropathy and streptozotocin-induced painful diabetic neuropathy models were significantly attenuated in TRPM2-knockout mice. Taken together, these results suggest that TRPM2 plays roles in a wide range of pathological pain models based on peripheral and central neuroinflammation, rather than physiological nociceptive pain.

Association of chronic diabetes and hypertension in sural nerve morphometry: an experimental study.

BackgroundProspective studies have shown incidence rates of hypertension in diabetes mellitus to be three times that of subjects without diabetes mellitus. The reverse also applies, with the incidence of diabetes two to three times higher in patients with hypertension. Despite this common clinical association, the contribution of each isolated entity in the development of a neuropathy is still not well understood. The aims of the present study were to investigate the presence of peripheral neuropathy in spontaneously hypertensive rats (SHR) and SHR with chronically induced diabetes, using a morphological and morphometric study of the sural nerves.MethodsFemale SHR and normotensive Wistar rats (WR), 8 weeks old, received a single intravenous injection of streptozotocin (STZ) through the tail vein. Controls from both strains received vehicle. Twelve weeks after the injection, sural nerves were dissected and prepared for light microscopy. Morphometry of sural nerve fascicles and myelinated fibers was performed with the aid of computer software.ResultsThe sural nerve myelinated fibers were highly affected by experimental diabetes in normotensive rats, causing mainly the reduction of the fiber size. Hypertensive rats showed characteristics of small fiber neuropathy and a severe reduction of the number and density or Schwann cells. The association between diabetes and hypertension caused an increase on the average size of the myelinated fibers, pointing to a small fiber loss, associated to axonal atrophy.ConclusionsOur study gives morphological support to the existence of a neuropathy due to hypertension, which is among one of the most common risk factors for diabetic neuropathy. The association between the two neuropathies showed to be a complex alteration, involving and including both, large and small fibers neuropathy. Hypertension caused, indeed, an exacerbation of the alterations already observed in experimental models of diabetic neuropathy.

The role of some chemokines from the CXC subfamily in a mouse model of diabetic neuropathy.

The mechanism involved in the development of diabetic neuropathy is complex. Currently, it is thought that chemokines play an important role in this process. The aim of this study was to determine how the level of some chemokines from the CXC subfamily varies in diabetic neuropathy and how the chemokines affect nociceptive transmission. A single intraperitoneal (i.p.) injection of streptozotocin (STZ; 200 mg/kg) resulted in an increased plasma glucose. The development of allodynia and hyperalgesia was measured at day 7 after STZ administration. Using Antibody Array techniques, the increases in CXCL1 (KC), CXCL5 (LIX), CXCL9 (MIG), and CXCL12 (SDF-1) protein levels were detected in STZ-injected mice. No changes in CXCL11 (I-TAC) or CXCL13 (BLC) protein levels were observed. The single intrathecal (i.t.) administration of CXCL1, CXCL5, CXCL9, and CXCL12 (each in doses of 10, 100, and 500 ng/5 μL) shows their pronociceptive properties as measured 1, 4, and 24 hours after injection using the tail-flick, von Frey, and cold plate tests. These findings indicate that the chemokines CXCL1, CXCL5, CXCL9, and CXCL12 are important in nociceptive transmission and may play a role in the development of diabetic neuropathy.

Comment on “The Combined Extract ofZingiber officinaleandZea mays(Purple Color) Improves Neuropathy, Oxidative Stress, and Axon Density in Streptozotocin Induced Diabetic Rats”

In a recent study, Wattanathorn et al. identified that the combined extract of purple waxy corn and ginger was effective in improving functional and structural changes in STZ-diabetic rats submitted to chronic constriction of the sciatic nerve, an effect that is potentially mediated by the antioxidant properties of these combined extracts. Although the results have been quite interesting, we would like to present a complementary conceptual perspective to improve the interpretation of the findings considering the disease model investigated. In the natural course of nontreated diabetes mellitus, diabetic neuropathy represents a chronic metabolic neuropathic disorder secondary to accumulated molecular and microvascular damage that impairs nerve structure and function [1, 2]. Fundamentally, diabetic neuropathy consists of a nontraumatic condition with prolonged time-course in which functional impairment overcomes the nerve structural damage, especially in the early stages of neuropathy [1–3]. Thus, even when applied to diabetic animals, the model of nerve constriction represents a traditional model of traumatic neuropathy and neuropathic pain [4, 5], which manifests a completely different pathophysiologic mechanism compared to diabetic neuropathy. In this trauma model, nerve ligation causes variable degrees of injury, which is difficult to measure directly and can range from neuropraxia (less severe functional nerve lesion) to neurotmesis (extensive and complex morphofunctional nerve lesion) [4, 5]. Furthermore, the injured nerve fibers cause chromatolysis and distal Wallerian degeneration, processes that are associated with intense focal inflammation and fibrosis, which limits axonal reparation [4, 5]. All of these structural changes are typical of traumatic lesions, but less frequent in diabetic neuropathy [1–3]. From this conceptual basis, the current interpretation of the findings reflects a construct bias since the results described cannot be used as an empirical basis to explain the improvements in diabetic neuropathy. Thus, a proper interpretation of the findings should consider the effect of treatments on healing/repair of traumatic nerve injury in diabetic animals, which recognizably presents an impaired healing process [1, 3]. When reviewing animal models of diabetic neuropathy, Klusakova and Dubový [5] indicated that rats with partial sciatic nerve ligation present minor pathogenesis of diabetic neuropathy, which is hardly representative of the human condition. This argument is reinforced by the short time course for neuropathy evolution, which showed a significant impairment of sciatic function index 24 hours after nerve ligation. This finding indicates a typical acute effect of mechanical nerve injuries [4, 5], which is not consistent with the chronic and progressive clinical course of diabetic neuropathy [1–3]. Although the relevance of the results is evident in traumatic nerve injury, it is wise to discuss the limitations of the model used and the interpretation of the findings. Whereas diabetic neuropathy is a condition of difficult clinical management that demands high cost to health care, we are looking forward to further studies by Wattanathorn et al. investigating whether the extracts tested can also bring similar benefits in specific and robust models, such as genetic or genetically modified models [3, 5, 6] of diabetic neuropathy.

Selective CB2 receptor agonists. Part 3: The optimization of a piperidine-based series that demonstrated efficacy in an in vivo neuropathic pain model

A novel class of potent cannabinoid receptor 2 (CB2) agonists based on a (S)-piperidine scaffold was identified using ligand-based pharmacophore models. Optimization of solubility and metabolic stability led to the identification of several potent CB2 agonists (e.g., 30) that displayed selectivity over cannabinoid receptor 1 (CB1) and acceptable drug like properties. In rats, compound 30 demonstrated a favorable pharmacokinetic profile and efficacy in a Streptozotocin-induced diabetic neuropathy model, with full reversal of mechanical hyperalgesia.

Selective CB2 receptor agonists. Part 2: Structure–activity relationship studies and optimization of proline-based compounds

Through a ligand-based pharmacophore model (S)-proline based compounds were identified as potent cannabinoid receptor 2 (CB2) agonists with high selectivity over the cannabinoid receptor 1 (CB1). Structure–activity relationship investigations for this compound class lead to oxo-proline compounds 21 and 22 which combine an impressive CB1 selectivity profile with good pharmacokinetic properties. In a streptozotocin induced diabetic neuropathy model, 22 demonstrated a dose-dependent reversal of mechanical hyperalgesia.

Comment on "short-term efficacy of ultramicronized palmitoylethanolamide in peripheral neuropathic pain".

In the recent paper published [1] in this journal, the efficacy and safety of a specific palmitoylethanolamide were reported: ultramicronized palmitoylethanolamide (PEA-um). This paper is one of recent series trying to convince readers that only a specific and patented formulation produced by the company Epitech Group S.r.L. in Italy is effective and has been explored sufficiently. This claim is not supported by the available evidence. We have discussed grave misrepresentations of data in a different paper [2]. We highlighted in that paper that the group of Professor Cuzzocrea repeatedly presented scientific facts related to unformulated palmitoylethanolamide (PEA) as if the data originated from experiments with ultramicronized PEA. The paper we discuss here is therefore not the first to wrongly attribute efficacy data gathered by pure, unmicronized palmitoylethanolamide to the so-called PEA-um formulation. For instance, the authors state on p. 1 the following: “PEA-um demonstrated a significant efficacy on pain in the murine model of diabetic neuropathy” and they refer to the data on palmitoylethanolamide published by the group of Professor Costa in 2008 [3]. These data however are not based on studies conducted with PEA-um. The PEA used in the Costa study is explicitly described as unmicronized, pure PEA. Costa et al. describe the PEA they tested as follows: “PEA was purchased from Cayman Chemical (Ann Arbor, MI, USA), dissolved in ethanol : saline (1 : 9), and used at a dose of 10 mg/kg.” Cayman only provides laboratories with pure, unformulated PEA (purity > 99%). Nowhere in the Costa (2008) paper do the authors refer to ultramicronized PEA. Secondly, the authors state the following: “However, the highly lipophilic PEA crystalline structure has a poor oral adsorption, thus requiring to be micronized and converted into particles with an elevated surface area to volume ratio, in order to enhance its assimilation.” This claim is not substantiated by any data in man. There are no pharmacokinetic data available of PEA to substantiate this claim, nor are there data available comparing plasma kinetics and dynamics of pure PEA versus ultramicronized PEA in man. Furthermore, all clinical double-blind placebo controlled studies published so far in more than 3000 patients have been conducted with simple PEA formulations. PEA was never tested as an ultramicronized or micronized formulation in such trials. It has recently come to our attention that the most impressive double-blind placebo controlled PEA study in 636 patients suffering from sciatic pain received ethics committee agreement in 1992 and was conducted with LG 2110/1, a code for pure PEA. Although the authors claim PEA has a poor oral absorption, the results of the clinical studies so far prove that, even if true, this is irrelevant as PEA does have significant and clinical relevant effects in simple, nonultramicronized formulations. As the study of Cocito et al. only reports the short-term follow-up data of a single center open-label study, in the absence of a placebo group, none of the conclusions of the authors are supported by the study. This study only supports the safety of PEA-um, and the safety of PEA in all known formulations has been documented already sufficiently. Therefore we need to conclude that the entire paper can only be seen as support for the market introduction of ultramicronized PEA, partly based on experiments conducted with unmicronized PEA. And as we pointed out elsewhere, never has there been any clinical trial conducted and published supporting superiority of any PEA formulation over another [4]. On the contrary, all double-blind placebo controlled trials to date have been conducted with unmicronized PEA and are supportive for such pharmaceutical formulation.

Central or peripheral delivery of an adenosine A1 receptor agonist improves mechanical allodynia in a mouse model of painful diabetic neuropathy

Diabetic peripheral neuropathy is a common complication of diabetes mellitus, and a significant proportion of individuals suffer debilitating pain that significantly affects their quality of life. Unfortunately, symptomatic treatment options have limited efficacy, and often carry significant risk of systemic adverse effects. Activation of the adenosine A1 receptor (A1R) by the analgesic small molecule adenosine has been shown to have antinociceptive benefits in models of inflammatory and neuropathic pain. The current study used a mouse model of painful diabetic neuropathy to determine the effect of diabetes on endogenous adenosine production, and if central or peripheral delivery of adenosine receptor agonists could alleviate signs of mechanical allodynia in diabetic mice. Diabetes was induced using streptozocin in male A/J mice. Mechanical withdrawal thresholds were measured weekly to characterize neuropathy phenotype. Hydrolysis of AMP into adenosine by ectonucleotidases was determined in the dorsal root ganglia (DRG) and spinal cord at 8 weeks post-induction of diabetes. AMP, adenosine and the specific A1R agonist, N6-cyclopentyladenosine (CPA), were administered both centrally (intrathecal) and peripherally (intraplantar) to determine the effect of activation of adenosine receptors on mechanical allodynia in diabetic mice. Eight weeks post-induction, diabetic mice displayed significantly decreased hydrolysis of extracellular AMP in the DRG; at this same time, diabetic mice displayed significantly decreased mechanical withdrawal thresholds compared to nondiabetic controls. Central delivery AMP, adenosine and CPA significantly improved mechanical withdrawal thresholds in diabetic mice. Surprisingly, peripheral delivery of CPA also improved mechanical allodynia in diabetic mice. This study provides new evidence that diabetes significantly affects endogenous AMP hydrolysis, suggesting that altered adenosine production could contribute to the development of painful diabetic neuropathy. Moreover, central and peripheral activation of A1R significantly improved mechanical sensitivity, warranting further investigation into this important antinociceptive pathway as a novel therapeutic option for the treatment of painful diabetic neuropathy.

BTBR ob/ob mice as a novel diabetic neuropathy model: Neurological characterization and gene expression analyses

Given the lack of treatments for diabetic neuropathy (DN), a common diabetic complication, accurate disease models are necessary. Characterization of the leptin-deficient BTBR ob/ob mouse, a type 2 diabetes model, demonstrated that the mice develop robust diabetes coincident with severe neuropathic features, including nerve conduction deficits and intraepidermal nerve fiber loss by 9 and 13weeks of age, respectively, supporting its use as a DN model. To gain insight into DN mechanisms, we performed microarray analysis on sciatic nerve from BTBR ob/ob mice, identifying 1503 and 642 differentially expressed genes associated with diabetes at 5 and 13weeks, respectively. Further analyses identified overrepresentation of inflammation and immune-related functions in BTBR ob/ob mice, which interestingly were more highly represented at 5weeks, an observation that may suggest a contributory role in DN onset. To complement the gene expression analysis, we demonstrated that protein levels of select cytokines were significantly upregulated at 13weeks in BTBR ob/ob mouse sciatic nerve. Furthermore, we compared our array data to that from an established DN model, the C57BKS db/db mouse, which reflected a common dysregulation of inflammatory and immune-related pathways. Together, our data demonstrate that BTBR ob/ob mice develop rapid and robust DN associated with dysregulated inflammation and immune-related processes.

Targeting apoptosis signalling kinase-1 (ASK-1) does not prevent the development of neuropathy in streptozotocin-induced diabetic mice.

Apoptosis signal-regulating kinase-1 (ASK1) is a mitogen-activated protein 3 kinase (MAPKKK/MAP3K) which lies upstream of the stress-activated MAPKs, JNK and p38. ASK1 may be activated by a variety of extracellular and intracellular stimuli. MAP kinase activation in the sensory nervous system as a result of diabetes has been shown in numerous preclinical and clinical studies. As a common upstream activator of both p38 and JNK, we hypothesised that activation of ASK1 contributes to nerve dysfunction in diabetic neuropathy. We therefore wanted to characterize the expression of ASK1 in sensory neurons, and determine whether the absence of functional ASK1 would protect against the development of neuropathy in a mouse model of experimental diabetes. ASK1 mRNA and protein is constitutively expressed by multiple populations of sensory neurons of the adult mouse lumbar DRG. Diabetes was induced in male C57BL/6 and transgenic ASK1 kinase-inactive (ASK1n) mice using streptozotocin. Levels of ASK1 do not change in the DRG, spinal cord, or sciatic nerve following induction of diabetes. However, levels of ASK2 mRNA increase in the spinal cord at 4 weeks of diabetes, which could represent a future target for this field. Neither motor nerve conduction velocity deficits, nor thermal or mechanical hypoalgesia were prevented or ameliorated in diabetic ASK1n mice. These results suggest that activation of ASK1 is not responsible for the nerve deficits observed in this mouse model of diabetic neuropathy.

Neutralization of schwann cell-secreted VEGF is protective to in vitro and in vivo experimental diabetic neuropathy.

The pathogenetic role of vascular endothelial growth factor (VEGF) in long-term retinal and kidney complications of diabetes has been demonstrated. Conversely, little is known in diabetic neuropathy. We examined the modulation of VEGF pathway at mRNA and protein level on dorsal root ganglion (DRG) neurons and Schwann cells (SC) induced by hyperglycaemia. Moreover, we studied the effects of VEGF neutralization on hyperglycemic DRG neurons and streptozotocin-induced diabetic neuropathy. Our findings demonstrated that DRG neurons were not affected by the direct exposition to hyperglycaemia, whereas showed an impairment of neurite outgrowth ability when exposed to the medium of SC cultured in hyperglycaemia. This was mediated by an altered regulation of VEGF and FLT-1 receptors. Hyperglycaemia increased VEGF and FLT-1 mRNA without changing their intracellular protein levels in DRG neurons, decreased intracellular and secreted protein levels without changing mRNA level in SC, while reduced the expression of the soluble receptor sFLT-1 both in DRG neurons and SC. Bevacizumab, a molecule that inhibits VEGF activity preventing the interaction with its receptors, restored neurite outgrowth and normalized FLT-1 mRNA and protein levels in co-cultures. In diabetic rats, it both prevented and restored nerve conduction velocity and nociceptive thresholds. We demonstrated that hyperglycaemia early affected neurite outgrowth through the impairment of SC-derived VEGF/FLT-1 signaling and that the neutralization of SC-secreted VEGF was protective both in vitro and in vivo models of diabetic neuropathy.

Preventive effect of Rubus fruticosus on learning and memory impairment in an experimental model of diabetic neuropathy in male rats

Diabetes mellitus is a common metabolic disorder that is associated with many complications such as learning and memory deficits. Rubus fruticosus (blackberry) has been extensively used in herbal medicine. In this study we evaluated the effect of R. fruticosus (RF) extract against memory dysfunction on streptozocin (STZ) induced diabetic neuropathy. Diabetes was induced by a single injection of STZ (60mg/kg i.p). Treatments were begun at the onset of hyperglycemia, followed by treatment with the RF extract (100, 200 and 400mg/kg p.o) for 4 weeks. Cognitive functions were evaluated using passive avoidance learning (PAL) task. Retention test was carried out 24h after training. At the end of experiment, animals were weighted and blood samples were taken for plasma glucose measurement. Diabetes caused impairment in acquisition and retrieval processes of PAL and memory in rats. RF treatment improved learning and memory in non-diabetic rats and reversed learning and memory deficits in diabetic rats. RF administration also partially improved the body weight loss and hyperglycemia of diabetics. These results show that RF administration to rats for 30 days from onset of diabetes alleviated the negative influence of diabetes on learning and memory.

The role of local renin-angiotensin system on high glucose-induced cell toxicity, apoptosis and reactive oxygen species production in PC12 cells.

Hyperglycemia, oxidative stress and apoptosis have key roles in pathogenesis of diabetic neuropathy. There are local renin-angiotensin systems (RASs) in different tissues such as neural tissue. Local RASs are involved in physiological and pathophysiological processes such as inflammation, proliferation and apoptosis. This study aimed to investigate the role of local renin-angiotensin system on high glucose-induced cell toxicity, apoptosis and reactive oxygen species (ROS) production in PC12 cells, as a cell model of diabetic neuropathy. PC12 cells were exposed to a high glucose concentration (27 mg/ml), captopril (ACE inhibitor), telmisartan and losartan (AT1 antagonists), and also PD123319 (AT2 antagonist) were administered before and after induction of high glucose toxicity. Then cell viability was assessed by MTT assay and apoptotic cells and intracellular ROS production were detected by annexin V-propidium iodide and DCFDA, respectively, using flow cytometry. High glucose concentration decreased cell viability, and increased apoptotic cells. Intracellular ROS production was also increased. In PC12 cells pretreatment and treatment by the drugs showed a significant improvement in cell viability and reduced apoptosis in captopril, telmisartan and PD123319 but only captopril and telmisartan were able to reduce ROS production. Losrtan significantly lowered ROS but didn't show any improvements in cell viability and apoptotic cells. The results of the present study showed that RAS inhibitors reduced cell toxicity and apoptosis and ROS production was induced by high glucose. It may be suggested that local RAS has a role in high glucose toxicity.

Investigating the protective effect of lithium against high glucose-induced neurotoxicity in PC12 cells: involvements of ROS, JNK and P38 MAPKs, and apoptotic mitochondria pathway.

Hyperglycemia that occurs under the diabetic condition is a major cause of diabetic complications such as diabetic neuropathy, one of the most common diabetes-related complications. It is well known that hyperglycemia could result in generation of reactive oxygen species (ROS). Over production of ROS recommended as an important mediator for apoptotic signaling pathway as well as a key early event in the development of diabetic neuropathy. Recently, many studies have indicated that lithium has robust neuroprotective effect in relation to several neurodegenerative diseases. The present study aimed to examine effects of lithium on high glucose (HG)-induced neurotoxicity and to determine some of the underlying molecular mechanisms involved in this response in PC12 cells as a neuronal culture model for diabetic neuropathy. PC12 cells were pretreated with different concentrations of lithium for 7days, exposed to HG for 24h. Cell viability was measured by MTT assay. ROS and lipid peroxidation levels as well as superoxide dismutase activity were measured. In order to examine the underlying molecular mechanisms, the expressions of Bax, Bcl-2, Caspase-3, total and phosphorylated JNK and P38 MAPK were also analyzed by Western blotting. The present results indicated that pretreatment with 1mM lithium has protected PC12 cells against HG-induced apoptotic cell death. It could reduce ROS generation, Bax/Bcl-2 ratio, Caspase-3 activation, and JNK and P38 MAPK phosphorylation. It may be concluded that in HG condition, lithium pretreatment could prevent mitochondrial apoptosis as well as JNK and P38 MAPK pathway in PC12 cells.

Effects of rosmarinic acid on an experimental model of painful diabetic neuropathy in rats

Context: Diabetic neuropathic (DN) pain is one of the diabetes complications. Rosmarinic acid (RA), a natural phenol antioxidant, shows some biological activities, including anti-inflammatory, analgesic, and anti-diabetic effects.Objectives: We investigated the efficacy of RA administration (10 and 30 mg/kg) on streptozotocin (STZ)-induced neuropathy in rats.Material and methods: The animals received saline or RA (10 and 30 mg/kg, p.o.; once daily) for 8 weeks. DN was evaluated by the tail flick (TF) method, formalin test, and tactile allodynia. At the end, all rats were weighed and underwent plasma glucose measurement.Results: There was an increase in licking time during both formalin test phases in diabetic animals (138.5 ± 10.7 and 448.7 ± 2.6 s) that was decreased by RA10 mg/kg (103.5 ± 7.5 and 284.4 ± 19 s) and RA 30 mg/kg (81.8 ± 11 and 192.7 ± 14 s). RA 30 mg/kg caused anti-nociception during the early phase in treated controls (52.1 ± 6 s) than untreated controls (99.4 ± 5.9 s). The TF latency in diabetics (2.9 ± 0.1 s) was increased in RA10 and 30 mg/kg treated diabetics (5.3 ± 0.4 and 6 ± 0.86 s). The paw withdrawal threshold (PWT) of the diabetics (3.6 ± 0.7 g) was increased after RA 10 and 30 mg/kg (13.8 ± 0.3 and 14 ± 0.4 g) treatment. RA did not induce a significant change in body weight and plasma glucose of rats.Conclusion: RA showed efficacy in amelioration of some aspects of DN. Therefore, RA makes a good candidate for DN treatment in clinical studies.

Soluble Epoxide Hydrolase Inhibition Is Antinociceptive in a Mouse Model of Diabetic Neuropathy

Neuropathic pain is currently an insufficiently treated clinical condition. There remains a critical need for efficacious therapies without severe side effects to treat the uniquely persistent and tonic pain of neuropathy. Inhibitors of the soluble epoxide hydrolase (sEH) enzyme that stabilize endogenous epoxy fatty acids have demonstrated antihyperalgesia in clinical chronic inflammatory pain and modeled neuropathic pain. Recently, the conditioned place preference assay has been used to evaluate the tonic nature of neuropathy in several animal models. The current experiments use the conditioned place preference assay alongside withdrawal thresholds to investigate the antihyperalgesic efficacy of sEH inhibitors in a murine model of diabetic neuropathy. Here, the sEH inhibitor trans-4-[4-(3-trifluoromethoxyphenyl-1-ureido)-cyclohexyloxy]-benzoic acid (t-TUCB) at 10 mg/kg induced a robust place preference in diabetic neuropathic mice representative of pain relief. Importantly, this effect was absent both in control mice and in sEH-knockout mice at the same dose, indicating that t-TUCB is not positively reinforcing or rewarding. When compared to gabapentin, t-TUCB elicited a similar degree of withdrawal threshold improvement without the same degree of spontaneous locomotion decline in neuropathic mice. Overall, these experiments show that inhibiting the sEH enzyme attenuates chronic pain and offers an alternative to current side-effect-limited therapies to meet this clinical need. PerspectiveThese experiments demonstrate antihyperalgesia in a murine chronic pain model mediated by inhibiting the sEH enzyme. The results of this study indicate that inhibiting the sEH is a promising alternative for blocking chronic pain.

Phenotyping animal models of diabetic neuropathy: a consensus statement of the diabetic neuropathy study group of the EASD (Neurodiab)

NIDDK, JDRF, and the Diabetic Neuropathy Study Group of EASD sponsored a meeting to explore the current status of animal models of diabetic peripheral neuropathy. The goal of the workshop was to develop a set of consensus criteria for the phenotyping of rodent models of diabetic neuropathy. The discussion was divided into five areas: (1) status of commonly used rodent models of diabetes, (2) nerve structure, (3) electrophysiological assessments of nerve function, (4) behavioral assessments of nerve function, and (5) the role of biomarkers in disease phenotyping. Participants discussed the current understanding of each area, gold standards (if applicable) for assessments of function, improvements of existing techniques, and utility of known and exploratory biomarkers. The research opportunities in each area were outlined, providing a possible roadmap for future studies. The meeting concluded with a discussion on the merits and limitations of a unified approach to phenotyping rodent models of diabetic neuropathy and a consensus formed on the definition of the minimum criteria required for establishing the presence of the disease. A neuropathy phenotype in rodents was defined as the presence of statistically different values between diabetic and control animals in 2 of 3 assessments (nocifensive behavior, nerve conduction velocities, or nerve structure). The participants propose that this framework would allow different research groups to compare and share data, with an emphasis on data targeted toward the therapeutic efficacy of drug interventions.

Allopregnanolone suppresses diabetes-induced neuropathic pain and motor deficit through inhibition of GABAA receptor down-regulation in the spinal cord of diabetic rats.

Painful diabetic neuropathy is associated with hyperexcitability and hyperactivity of spinal cord neurons. However, its underlying pathophysiological mechanisms have not been fully clarified. Induction of excitatory/inhibitory neurotransmission imbalance at the spinal cord seems to account for the abnormal neuronal activity in diabetes. Protective properties of neurosteroids have been demonstrated in numerous cellular and animal models of neurodegeneration. Here, the protective effects of allopregnanolone, a neurosteroid were investigated in an in vivo model of diabetic neuropathy. The tail-flick test was used to assess the nociceptive threshold. Diabetes was induced by injection of 50 mg/kg (IP) streptozotocin. Seven weeks after the induction of diabetes, the dorsal half of the lumbar spinal cord was assayed for the expression of γ2 subunit of GABAA receptor using semiquantitative RT-PCR. The data shows that allopregnanolone (5 and 20 mg/kg) markedly ameliorated diabetes-induced thermal hyperalgesia and motor deficit. The weights of diabetic rats that received 5 and 20 mg/kg allopregnanolone did not significantly reduce during the time course of study. Furthermore, this neurosteroid could inhibit GABAA receptor down-regulation induced by diabetes in the rat spinal cord. The data revealed that allopregnanolone has preventive effects against hyperglycemic-induced neuropathic pain and motor deficit which are related to the inhibition of GABAA receptor down-regulation.

Fentanyl produces an anti-hyperalgesic effect through the suppression of sodium channels in mice with painful diabetic neuropathy

Diabetic neuropathy is one of the most frequent complications of diabetes mellitus. Therefore, the present study was designed to investigate the anti-hyperalgesic mechanism of fentanyl in a mouse model of streptozotocin-induced diabetic neuropathy. The antinociceptive response was assessed by recording the latency in a tail-flick test. The tail-flick latency in diabetic mice was significantly shorter than that in non-diabetic mice. Fentanyl, at doses of 3 and 10μg/kg, s.c., produced a dose-dependent increase in the tail-flick latencies in diabetic mice. While fentanyl (3μg/kg, s.c.) did not produce a significant inhibition of the tail-flick response in non-diabetic mice, it significantly prolonged the tail-flick latency in diabetic mice to the same level as the baseline latency in non-diabetic mice. Although pretreatment with naloxone (3mg/kg, s.c.) completely antagonized fentanyl-induced antinociception in non-diabetic mice, it had no effect on the antinociceptive effect of fentanyl in diabetic mice. Pretreatment with either of the voltage-gated sodium channel openers fenvarelarte and veratridine practically abolished the antinociceptive effects of fentanyl in diabetic mice. However, neither fenvarelate nor veratridine affected the antinociceptive effect of fentanyl in non-diabetic mice. These results suggest that the anti-hyperalgesic effect of fentanyl is mediated through the blockade of sodium channels in diabetic mice, whereas opioid receptors mediate the antinociceptive effect of fentanyl in non-diabetic mice.

Inhibitory effect of Thymus caramanicus Jalas on hyperglycemia-induced apoptosis in in vitro and in vivo models of diabetic neuropathic pain

Ethnopharmacological relevanceSince Thymus caramanicus Jalas is used as a folk medicine for the treatment of rheumatism, skin disorders, bacterial infections and diabetes and it contain antioxidant agents, we decided to investigate the possible effects of Thymus caramanicus Jalas (TCJ) extract on in vitro and in vivo models of diabetic neuropathy. Materials and methodsThe high glucose-induced cell injury in Pheochromocytoma (PC12) cells and streptozotocin-induced diabetic rats were used. Tail-flick and rotarod treadmill assessments were used to determine nociceptive threshold and motor coordination. Cell viability was determined by MTT assay test. Western blotting was performed to measurement of apoptosis markers. ResultsThe data showed that elevation of glucose consecutively increases functional cell injury and apoptosis. Furthermore, diabetic rats developed thermal hyperalgesia and motor deficit. Activated caspase 3, cytochrome c release and Bax/Bcl-2 ratio were significantly increased in high glucose-treated PC12 cells and in spinal cord of diabetic animals. TCJ extract (60 and 80µg/ml) attenuates high glucose-induced PC12 cells damage and apoptosis. In diabetic animals, TCJ extract at daily doses of 100 and 150mg/kg ameliorated hyperalgesia and suppressed spinal apoptosis. ConclusionThe data indicate that TCJ extract has neuroprotective effects against high glucose-induced neural damage. These protective effects are mediated, at least in part, through attenuation of neural apoptosis and suggest therapeutic potential of TCJ extract in amelioration of diabetic neuropathy.