Pathogenesis Of Diabetic Peripheral Neuropathy Research Articles

Satellite glia as a critical component of diabetic neuropathy: Role of lipocalin-2 and pyruvate dehydrogenase kinase-2 axis in the dorsal root ganglion.

Diabetic peripheral neuropathy (DPN) is a common complication of uncontrolled diabetes. The pathogenesis of DPN is associated with chronic inflammation in dorsal root ganglion (DRG), eventually causing structural and functional changes. Studies on DPN have primarily focused on neuronal component, and there is limited knowledge about the role of satellite glial cells (SGCs), although they completely enclose neuronal soma in DRG. Lipocalin-2 (LCN2) is a pro-inflammatory acute-phase protein found in high levels in diverse neuroinflammatory and metabolic disorders. In diabetic DRG, the expression of LCN2 was increased exclusively in the SGCs. This upregulation of LCN2 in SGCs correlated with increased inflammatory responses in DRG and sciatic nerve. Furthermore, diabetes-induced inflammation and morphological changes in DRG, as well as sciatic nerve, were attenuated in Lcn2 knockout (KO) mice. Lcn2 gene ablation also ameliorated neuropathy phenotype as determined by nerve conduction velocity and intraepidermal nerve fiber density. Mechanistically, studies using specific gene KO mice, adenovirus-mediated gene overexpression strategy, and primary cultures of DRG SGCs and neurons have demonstrated that LCN2 enhances the expression of mitochondrial gate-keeping regulator pyruvate dehydrogenase kinase-2 (PDK2) through PPARβ/δ, thereby inhibiting pyruvate dehydrogenase activity and increasing production of glycolytic end product lactic acid in DRG SGCs and neurons of diabetic mice. Collectively, our findings reveal a crucial role of glial LCN2-PPARβ/δ-PDK2-lactic acid axis in progression of DPN. Our results establish a link between pro-inflammatory LCN2 and glycolytic PDK2 in DRG SGCs and neurons and propose a novel glia-based mechanism and drug target for therapy of DPN. MAIN POINTS: Diabetes upregulates LCN2 in satellite glia, which in turn increases pyruvate dehydrogenase kinase-2 (PDK2) expression and lactic acid production in dorsal root ganglia (DRG). Glial LCN2-PDK2-lactic acid axis in DRG plays a crucial role in the pathogenesis of diabetic neuropathy.

Proinflammatory Cytokines Predict the Incidence of Diabetic Peripheral Neuropathy Over 5 Years in Chinese Type 2 Diabetes Patients: A Prospective Cohort Study

Aims: Inflammation has been implicated in the pathogenesis of diabetic peripheral neuropathy (DPN) as suggested in various cross-sectional studies. However, more convincing prospective studies in diabetes patients are scarce. Therefore, we aimed to evaluate whether proinflammatory cytokines could predict the incidence of DPN through a prospective study with a five-year follow-up. Methods: We followed up 315 patients with diabetes who did not have DPN, recruited from five community health centers in Shanghai in 2014, for an average of 5.06 years. Based on the integrity of blood samples, 106 patients were selected to obtain the proinflammatory cytokines. Plasma markers of proinflammatory cytokines at baseline included interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), vascular endothelial growth factor (VEGF), and intercellular adhesion molecule 1 (ICAM-1). Neuropathy was assessed by MSNI at baseline and during follow-up. Results: Among the 106 randomly chosen patients, 63 developed DPN after 5.06±1.14 years of follow-up. The baseline plasma levels of TNF-α, IL-6, and ICAM-1 were higher in the neuropathic group (P<0.05). In multivariate models, increased plasma levels of TNF-α (hazard ratio, HR: 8.74 [95% confidence interval, CI: 1.05-72.68]; p <0.05) and ICAM-1 (HR 23.74 [95% CI 1.47-383.81]; p <0.05) were both associated with incident DPN, after adjusting for known DPN risk factors. Conclusions: Increased plasma levels of proinflammatory factors, especially TNF-α and ICAM-1, predicted the incidence of DPN over 5 years in Chinese diabetes patients, but larger longitudinal studies are required for confirmation. Funding Statement: The present study was supported by grants from the National Natural Science Foundation of China (81770807, to B Lu and 81800692, to LJ Ji), Shanghai Talent Development Fund Program (2018054, to B Lu), Shanghai Shenkang Hospital Developing Center Clinical Scientific and Technological Innovation Program (SHDC12016210, to B Lu), Shanghai Science and Technology Committee Program (17411961500, to S Zhang), Shanghai General Hospital Program of Chinese traditional and Western medicine combination (ZY(2018-2020)-FWTX-1002, to YM Li) and Shanghai Municipal Commission of Health and Family Planning Clinical Research Project (20184Y0318, to LJ Ji). Declaration of Interests: The authors declare that there is no conflict of interest. Ethics Approval Statement: The study was approved by the Human Investigation Ethics Committee of Huashan Hospital.

Diphenyl diselenide alleviates diabetic peripheral neuropathy in rats with streptozotocin-induced diabetes by modulating oxidative stress

Diabetic peripheral neuropathy (DPN) is one of the most common microvascular complications occurring in both type 1 and type 2 diabetes mellitus patients. Oxidative stress (OS) plays a key role in the pathogenesis of DPN; thus, antioxidant therapy is considered a promising strategy for treating DPN. Diphenyl diselenide (DPDs) is an organic selenium compound with antioxidant pharmacological activities. This study aimed to evaluate its preventive and therapeutic effects on DPN in rats with streptozotocin (STZ)-induced diabetes and explore the underlying mechanisms. In vitro, RSC96 cells were exposed to high glucose (100 mM) and then treated with different concentrations of DPDs (1, 10, 25 and 50 μM). Notably, DPDs markedly suppressed high glucose-induced cytotoxicity and oxidative stress in Schwann cells by decreasing reactive oxygen species (ROS) and malondialdehyde (MDA) levels. Furthermore, the DPDs treatment effectively activated Nrf2 signaling and inhibited Keap1 expression. An in vivo DPN model was established in Sprague-Dawley (SD) rats injected with STZ (60 mg·kg−1, ip) and orally administered either different doses of DPDs (5 and 15 mg· kg−1· d−1) for 12 weeks or alpha lipoic acid (ALA, 100 mg kg−1·d−1) as a positive control. The administration of DPDs significantly increased the motor nerve conduction velocity (MNCV), improved thermal and mechanical hyperalgesia and the sciatic nerve morphology, and ameliorated oxidative stress in the serum and the sciatic nerve of rats with DPN. Mechanistically, DPDs reduced the level of Keap1 and stimulated Nrf2 signaling in the sciatic nerve. Taken together, the results of this study indicate that DPDs ameliorates experimental DPN as an antioxidant by activating the Nrf2/Keap1 signaling pathway. DPDs may represent a new alternative treatment for DPN.

A Review on Mechanistic and Pharmacological Findings of Diabetic Peripheral Neuropathy including Pharmacotherapy.

Chronic hyperglycemia and related complications involving peripheral nerves in diabetes are one of the most severe microvascular complications with an average prevalence of 50-60%. Diabetic neuropathy is among the vascular disorders of diabetes, the most debilitating and crippled, lethal condition impacting patients's quality of life. In the present review article, several hypotheses associated with the pathogenesis of Diabetic Peripheral Neuropathy (DPN) have been introduced, among them metabolic pathways associated with polyol pathway, oxidative stress, production of reactive oxygen species (ROS) amplified under chronic hyperglycemic conditions and activation of transcription factor Nuclear factor-κB (NF- κB). The review article also possesses pathogenetic and pharmacologic treatments along with others, including acupressure, lidocaine, and capsaicin for DPN. It may be concluded that we can combat the pathogenesis of DPN with different suggested treatments.

Non-glucose risk factors in the pathogenesis of diabetic peripheral neuropathy.

In this review, we consider the diverse risk factors in diabetes patients beyond hyperglycemia that are being recognized as contributors to diabetic peripheral neuropathy (DPN). Interest in such alternative mechanisms has been encouraged by the recognition that neuropathy occurs in subjects with metabolic syndrome and pre-diabetes and by the reporting of several large clinical studies that failed to show reduced prevalence of neuropathy after intensive glucose control in patients with type 2 diabetes. Animal models of obesity, dyslipidemia, hypertension, and other disorders common to both pre-diabetes and diabetes have been used to highlight a number of plausible pathogenic mechanisms that may either damage the nerve independent of hyperglycemia or augment the toxic potential of hyperglycemia. While pathogenic mechanisms stemming from hyperglycemia are likely to be significant contributors to DPN, future therapeutic strategies will require a more nuanced approach that considers a range of concurrent insults derived from the complex pathophysiology of diabetes beyond direct hyperglycemia.

Pim1 kinase provides protection against high glucose-induced stress and apoptosis in cultured dorsal root ganglion neurons

The pathogenesis of diabetic peripheral neuropathy (DPN) is complex and not well understood. Recently, oxidative stress and endoplasmic reticulum (ER) stress induced by hyperglycemia have been demonstrated to play a critical role in neuronal apoptosis, which then contributing to DPN. However, the specific molecular mechanism that underlies the hyperglycemia-induced neuronal stresses and apoptosis remains largely unknown. In this study, we demonstrated for the first time that Pim1 kinase is a positive modulator of dorsal root ganglion (DRG) neuron survival in vitro. Hyperglycemia causes compensatory upregulation of Pim1 kinase in the DRG neurons, which provides protection against high glucose-induced oxidative stress and ER stress. Pharmacological inhibition of Pim1 not only sensitizes the stress response to high glucose in the DRG neurons, but also accelerates the apoptosis of DRG neurons in vitro. Therefore, our work provides experimental evidence for the prevention of high glucose-induced neuronal stress and apoptosis by targeting Pim1 kinase.

The Construction and Analysis of lncRNA-miRNA-mRNA Competing Endogenous RNA Network of Schwann Cells in Diabetic Peripheral Neuropathy.

BackgroundDiabetes mellitus is a worldwide disease with high incidence. Diabetic peripheral neuropathy (DPN) is one of the most common but often ignored complications of diabetes mellitus that cause numbness and pain, even paralysis. Recent studies demonstrate that Schwann cells (SCs) in the peripheral nervous system play an essential role in the pathogenesis of DPN. Furthermore, various transcriptome analyses constructed by RNA-seq or microarray have provided a comprehensive understanding of molecular mechanisms and regulatory interaction networks involved in many diseases. However, the detailed mechanisms and competing endogenous RNA (ceRNA) network of SCs in DPN remain largely unknown.MethodsWhole-transcriptome sequencing technology was applied to systematically analyze the differentially expressed mRNAs, lncRNAs and miRNAs in SCs from DPN rats and control rats. Gene ontology (GO) and KEGG pathway enrichment analyses were used to investigate the potential functions of the differentially expressed genes. Following this, lncRNA-mRNA co-expression network and ceRNA regulatory network were constructed by bioinformatics analysis methods.ResultsThe results showed that 2925 mRNAs, 164 lncRNAs and 49 miRNAs were significantly differently expressed in SCs from DPN rats compared with control rats. 13 mRNAs, 7 lncRNAs and 7 miRNAs were validated by qRT-PCR and consistent with the RNA-seq data. Functional and pathway analyses revealed that many enriched biological processes of GO terms and pathways were highly correlated with the function of SCs and the pathogenesis of DPN. Furthermore, a global lncRNA–miRNA–mRNA ceRNA regulatory network in DPN model was constructed and miR-212-5p and the significantly correlated lncRNAs with high degree were identified as key mediators in the pathophysiological processes of SCs in DPN. These RNAs would contribute to the diagnosis and treatment of DPN.ConclusionOur study has shown that differentially expressed RNAs have complex interactions among them. They also play critical roles in regulating functions of SCs involved in the pathogenesis of DPN. The novel competitive endogenous RNA network provides new insight for exploring the underlying molecular mechanism of DPN and further investigation may have clinical application value.

Targeting the NADPH Oxidase-4 and Liver X Receptor Pathway Preserves Schwann Cell Integrity in Diabetic Mice.

Diabetes triggers peripheral nerve alterations at a structural and functional level, collectively referred to as diabetic peripheral neuropathy (DPN). This work highlights the role of the liver X receptor (LXR) signaling pathway and the cross talk with the reactive oxygen species (ROS)-producing enzyme NADPH oxidase-4 (Nox4) in the pathogenesis of DPN. Using type 1 diabetic (T1DM) mouse models together with cultured Schwann cells (SCs) and skin biopsies from patients with type 2 diabetes (T2DM), we revealed the implication of LXR and Nox4 in the pathophysiology of DPN. T1DM animals exhibit neurophysiological defects and sensorimotor abnormalities paralleled by defective peripheral myelin gene expression. These alterations were concomitant with a significant reduction in LXR expression and increase in Nox4 expression and activity in SCs and peripheral nerves, which were further verified in skin biopsies of patients with T2DM. Moreover, targeted activation of LXR or specific inhibition of Nox4 in vivo and in vitro to attenuate diabetes-induced ROS production in SCs and peripheral nerves reverses functional alteration of the peripheral nerves and restores the homeostatic profiles of MPZ and PMP22. Taken together, our findings are the first to identify novel, key mediators in the pathogenesis of DPN and suggest that targeting LXR/Nox4 axis is a promising therapeutic approach.

Identification of Key Genes Involved in Diabetic Peripheral Neuropathy Progression and Associated with Pancreatic Cancer.

IntroductionDiabetes mellitus (DM) patients suffer from high morbidity and premature mortality due to various diabetic complications and even cancers. Therefore, this study aimed to identify key genes involved in the pathogenesis of diabetic peripheral neuropathy (DPN) and pancreatic cancer (PC).MethodsWe analyzed three gene expression profiles (GSE95849, GSE28735 and GSE59953) to obtain differentially expressed genes (DEGs). Then, Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed by using the Database for Annotation, Visualization, and Integrated Discovery (DAVID). The Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database was then used to establish a protein–protein interaction (PPI) network. The MCODE and cytoHubba plug-ins of Cytoscape were used to select hub genes. Finally, survival analysis of the hub genes was performed using the Kaplan–Meier plotter and GEPIA online tool.ResultsWe first analyzed GSE95849 to obtain DPN-related genes. DEGs were obtained from three groups in GSE95849. The DEGs were enriched in the Toll-like receptor signaling pathway, hematopoietic cell lineage and chemokine signaling pathway. Importantly, we identified three shared genes as hub genes, including TLR4, CCR2 and MMP9. We then analyzed and integrated GSE95849 and GSE28735 to obtain genes common in DM and PC. A total of 58 mutual DEGs were identified, and these DEGs were enriched in the ECM-receptor interaction, focal adhesion and pathways in cancer. Five hub genes (including PLAU, MET, CLU, APOL1 and MMP9) were associated with the overall survival of PC patients. However, the results from the analysis of GSE59953 showed that hyperglycemia or TGF-β1 treatment did not affect the expression level of these hub genes, but the DEGs based on hyperglycemia or TGF-β1 treatment were mostly enriched in the ECM-receptor interaction, focal adhesion and pathways in cancer. Finally, functional enrichment analysis of MMP9 showed that significant genes correlated with MMP9 were associated with the tumorigenicity of cancers, insulin resistance, development of DM and inflammation.ConclusionIn summary, inflammation and immunity-related pathways may play an important role in DM and DPN, while the ECM-receptor interaction, focal adhesion and pathways in cancer pathways may play significant roles in DM and PC. MMP9 may be used as a prognostic marker for PC and may be helpful for the treatment of DM, DPN and PC.

Long Non‑Coding RNAs Regulate Inflammation in Diabetic Peripheral Neuropathy by Acting as ceRNAs Targeting miR-146a-5p.

BackgroundLong non-coding RNAs (lncRNAs), as competing endogenous RNAs (ceRNAs), can regulate various pathophysiological processes by binding competitively to microRNAs at the post-transcription level. Our previous work demonstrated that miR-146a-5p was lowly expressed in diabetic peripheral neuropathy (DPN) rats. However, the ceRNA network in DPN mediated by lncRNAs and miR-146a-5p remains to be explored.MethodsTwo groups of rats (n=4 per group), a type 2 diabetes (T2DM) group and a DPN group, were used in this study. Sciatic nerve conduction velocity (NCV) of each rat was determined at the 6th and the 12th week. LncRNA microarray analysis was performed in the sciatic nerve of DPN and T2DM rats. Based on the TargetScan algorithm and the miRanda database, we determined the differentially expressed (DE) lncRNAs bound to miR-146a-5p. Furthermore, we verified the DE lncRNAs potentially bound to miR-146a-5p by qRT-PCR. The genes targeted by miR-146a-5p were identified by bioinformatics prediction and experimental techniques.ResultsWe found 413 DE lncRNAs between DPN and T2DM rats (|log2FC| ≥ 2 and adjust P ≤ 0.05). Eight DE lncRNAs were predicted to bind to miR-146a-5p by both algorithms, of which four were verified by qRT-PCR. TRAF6, IRAK1, and SMAD4 were identified as miR-146a-5p targeted genes and were predominantly enriched in the inflammatory signaling pathway.ConclusionLncRNAs may contribute to the pathogenesis of DPN by regulating inflammation through functioning as ceRNAs of miR-146a-5p.

The Association between Mn-SOD Gene Polymorphism and Peripheral Neuropathy in Type2 Diabetic Patients of Babylon Province-Iraq

Background: Oxidative stress has been known to be implicated in the onset and development of impaired insulin secretion and insulin resistance and both are involved in diabetes. The mechanisms involved in oxidative stress-induced diabetic peripheral neuropathy include the generation of reactive oxygen species ROS, excesses reactive nitrogen species RNS, lipid peroxidation, DNA damage, and reduction in cellular antioxidants. Polymorphisms in genes responsible for encoding these antioxidant enzymes causes the development of diabetic peripheral neuropathy (DPN). Aim: this study was aimed to indicated the role of genes encoding manganese (Mn-SOD) superoxide dismutase in the pathogenesis of DPN in a type2 diabetic patients of Babylon province. Ala(-9)Val polymorphism of Mn-SOD gene polymorphism were studied in type2 diabetic patients with (n=30) and without DPN (n=30).Results: Polymerase chain reaction (PCR) technique were used for detection Mn-SOD polymorphisms. This technique included the use of PCR primers (Forward and Reverse) to produce a restriction site in the amplified Mn-SOD gene product just with the polymorphic base. Then, the product of (PCR) was digested with Bsh TI restriction enzyme to detect Ala(-9) polymorphic position. The results of Ala(-9)Val polymorphism showed that the frequency of Ala/Ala, Ala/Val, and Val/Val were 63.3%, 20%, and 13.3% in healthy control subject and 36.6%, 33.3%, and 30% in diabetic without neuropathy countered by 23.3%, 20%, and 56.6% in diabetic with neuropathy. This proposed that the Ala(-9)Val polymorphism in the Mn-SOD gene is significantly associated with a risk for progression of diabetic peripheral neuropathy.Conclusions: Homozygote pattern Ala/Ala were more frequent in control groups compared with homozygote pattern Val/Val were significantly more frequent in diabetic peripheral neuropathy patients.

IFN-γ/mTORC1 decreased Rab11 in Schwann cells of diabetic peripheral neuropathy, inhibiting cell proliferation via GLUT1 downregulation.

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes mellitus. Rab11 is conserved gene-regulating vesicle traffic and reported to be involved in the pathogenesis of diabetes mellitus by affecting insulin sensitivity. We aimed to investigate the role of Rab11 in the pathogenesis of DPN. In this study, Rab11 expression decreased in the sciatic nerves of diabetic mice with impaired conduction function versus those of normal mice. In vitro experiment revealed interferon-γ (IFN-γ), not high glucose and interleukin 1β was the main factor to lead to Rab11 downregulation in RSC96 cells. Again, both Rab11 knockdown and IFN-γ treatment caused cell viability inhibition and the decrease in BrdU-positive cells. In contrast, overexpression of Rab11 reversed IFN-γ-reduced cell proliferation. Furthermore, mTORC1 not mTORC2 was proven to be suppressed by IFN-γ treatment in RSC96 cells, indicated in decreased phospho-p70S6K. Inhibition of the mTORC1 pathway resulted in Rab11 expression downregulation in RSC96 cells. Activation of the mTORC1 pathway effectively prevented IFN-γ-reduced Rab11 expression in RSC96 cells. Also, glucose transporter 1 (GLUT1) was found to be downregulated in RSC96 cells with Rab11 silence and overexpression of GLUT1 reversed Rab11 blocking-caused proliferation inhibition. Taken together, our findings suggest that IFN-γ decreases Rab11 expression via the inhibition of the mTORC1 signaling pathway, causing reduced cell proliferation in Schwann cells of DPN by GLUT1 downregulation.

The effect of vitamin D therapy on inflammatory markers in patients with type 2 diabetes mellitus and diabetic peripheral polyneuropathy

BACKGROUND: The pathogenesis of diabetic peripheral neuropathy (DPN) in patients with type 2 diabetes mellitus (T2DM) is multifactorial, and includes increased inflammation. In recent years, the effect of vitamin D therapy on improving the profile of inflammatory parameters has been actively studied.&#x0D; AIMS: The aim of this study was to assess inflammation markers before and after various doses of cholecalciferol therapy in T2DM with DPN.&#x0D; MATERIALS AND METHODS: Single-center open randomized study included T2DM patients with PDN. Sixty-seven patients were randomized into 2 groups. For 24 weeks Group I have been taking a dosage of cholecalciferol 5,000 IU/week, and Group II a dosage of 40,000 IU/week. At the baseline and in the end of the research there have been studied body mass index (BMI), glycated hemoglobin (HbA1c), 25-hydroxyvitamin D (25(OH)D), PTH, interleukin-1, -6, -10 (IL), C-reactive protein (CRP), tumor necrosis factor - (TNF).&#x0D; RESULTS: Sixty-two patients completed the study. Group I (n=31, F16), Group II (n=31, F15) were initially compared by age, sex, BMI and НbA1clevel. Vitamin D deficiency/insufficiency was detected in 78% of patients with T2DM. After 24 weeks of therapy with cholecalciferol in Group II there was a significant decrease in BMI, HbA1c, IL-6 levels and an increase in IL-10 levels while no changes were found in Group I. There has been established a correlation between the final level of 25(OH)D and IL-6 (r=-0.378, p=0.036), IL-10 (r=0.483, p=0.006), BMI (r=-0.388, p=0.031) and НbA1c(r=-0.388, p=0.031).&#x0D; CONCLUSION: The intake of cholecalciferol at a dosage of 40,000 IU/week for 24 weeks is associated with a decrease in BMI, improvement of glycemic control and pro-inflammatory markers profile in patients with T2DM with DPN. Study results showed that the normalization of serum 25(OH)D level can be one of the modifying factors for the development and progression of DPN in patients with T2DM.

Clinical Features and Rules of Chinese Herbal Medicine in Diabetic Peripheral Neuropathy Patients.

Objective To analyse the clinical features of diabetic peripheral neuropathy (DPN) and employ data mining technology to explore the rules of Chinese herbal medicine (CHM) therapy. Methods The clinical data of 216 patients with DPN and qi-yin deficiency syndrome were obtained, and the clinical features of the patients were assessed by cluster analysis. Relevant information was entered into the clinical diagnosis and treatment collection system, and data mining techniques were used to analyse the drug frequency, core CHM, CHM pair, and so on. Results In this study, glycated haemoglobin (HbA1c) and homocysteine (HCY) were closely related to the pathogenesis of DPN. Overall, 162 patients had typical DPN syndrome characteristics, and we analysed 216 prescriptions, including 182 CHM. The frequencies of prescription of Astragalus membranaceus, Ligusticum wallichii, Poria cocos, and Radix Rehmanniae were greater than 45%. A Bayesian network analysis diagram showed that the 9 most common core CHM included Astragalus membranaceus, Ligusticum wallichii, Poria cocos, atractylodes rhizome, and Salvia miltiorrhiza Bge. According to the association rules of CHM, Radix Ophiopogon is used for Codonopsis pilosula; Astragalus membranaceus and atractylodes rhizome for Rehmannia are also frequently used. Astragalus membranaceus and Cinnamomi Ramulus or Ligusticum wallichii and Moutan bark were highly related to a decreased Michigan Diabetic Neuropathy Score. Conclusion HbA1c and HCY are related risk factors for DPN. Numbness is a typical syndrome characteristic. Astragalus membranaceus is a monarch CHM and is used most frequently.

Expressions of Thioredoxin Interacting Protein/Nucleotide-binding Oligomerization Domain-like Receptor Protein 3 Inflammasome in the Sciatic Nerve of Streptozotocin-induced Diabetic Rats

Objective To investigate the role of thioredoxin interacting protein(TXNIP)/ nucleotides-binding oligomerization domain-like receptor protein(NLRP)3 inflammasome in the sciatic nerve of streptozotocin(STZ)-induced diabetic rats. Methods The diabetic rat model was established by single intraperitoneal injection of STZ.The rats with matched sex and age were taken as normal control group.The blood glucose and body weight were monitored.The mechanical withdrawal threshold was measured by von Frey filaments at 12 weeks after the model was established.At 12 weeks,the rats were sacrificed and the sciatic nerves were separated for Luxol fast blue staining,the expressions of TXNIP,NLRP3,caspase-1,and interleukin(IL)-1β were detected by immunohistochemistry and Western blot method,and the levels of IL-1β and IL-18 in serum were measured by enzyme-linked immunosorbent assay(ELISA). Results The expression of TXNIP protein in the sciatic nerve of diabetic rats was 3.78±0.08,which significantly increased than that in the normal control group(0.99±0.06)(t=26.980,P<0.0001).Compared with the normal control group(0.97±0.05),the expression of NLRP3 protein in the diabetic group(2.44±0.16)was significantly higher(t=8.885,P<0.0001).The expression of cleaved caspase-1 was 4.45±0.19 in the diabetic group and 1.08±0.06 in the normal control group,and the difference was significant(t=16.900,P<0.0001).The expression of IL-1β protein in the diabetic group(4.50±0.16)was significantly higher than that(1.19±0.08)in the normal control group(t=18.630,P<0.0001).Compared with the normal control group,the levels of IL-1β [(110.50±8.80)pg/ml vs.(17.97±3.18)pg/ml,t=9.892,P<0.0001] and IL-18 [(591.70±8.78)pg/ml vs.(160.70±8.33)pg/ml,t=35.620,P<0.0001] in the serum of diabetic rats significantly increased. Conclusion The pathogenesis of diabetic peripheral neuropathy may be related to increased expression of TXNIP,activation of NLRP3 inflammasome,and downstream inflammation,which may provide a new target for diabetic peripheral neuropathy therapy.

Role of Inflammation in the Pathogenesis of Diabetic Peripheral Neuropathy.

BACKGROUND:Diabetic peripheral neuropathy (DPN) means the presence of symptoms and/or signs of peripheral nerve damage that occur to people with diabetes, excluding all other causes of neuropathy. Chronic hyperglycaemia leads to increased secretion of tumour necrotic factor-alpha (TNF-α), with the development of micro and macroangiopathy, damage to nerve fibres and local demyelination.AIM:To determine the role of inflammation in the peripheral nerve damage process concerning people suffering from type II diabetes mellitus.MATERIAL AND METHODS:The study included a total of 80 subjects, men and women, divided into two groups: an examined group (n = 50) consisting of subjects with DPN at the age from 30 to 80 years and a control group (n = 30) of healthy subjects aged from 18 to 45. In the investigated group, a neurological examination was performed using the Diabetic Neuropathy Symptoms (DNS) Score and Electroneurography. All the subjects had the blood plasma concentration of TNF-α by ELISA technique.RESULTS:The average value of TNF-α in the test group was 8.24 ± 2.899 pg/ml, while the control group was 4.36 ± 2.622 pg/ml (p < 0.0001). The average value of TNF-α was correlated with the achieved DNS score in the investigated group (p = 0.005). Concerning the linear association of the concentration of TNF-α with the peripheral nerve velocity in the investigated group, no statistical significance was detected.CONCLUSION:Inflammation can play a role in the pathogenesis of diabetic autonomic neuropathy and cranial neuritis.

The Akt/mTOR cascade mediates high glucose-induced reductions in BDNF via DNMT1 in Schwann cells in diabetic peripheral neuropathy

Brain-derived neurotropic factor (BDNF) deficiency in Schwann cells plays an important role in the pathogenesis of diabetic peripheral neuropathy (DPN). Little is known about the mechanism involved in BDNF downregulation in Schwann cells in DPN. In this study, we first confirmed downregulation of BDNF and neurotrophin 3 expression in the sciatic nerves of diabetic mice, which was accompanied by myelin sheath abnormalities. Moreover, in vitro, high glucose was revealed to cause downregulation of BDNF, but not neurotrophin 3, expression in RSC96 cells, which was accompanied by DNA hypermethylation of BDNF promoters I and II. DNMT1 was subsequently revealed to be enhanced at the mRNA and protein levels in high glucose-stimulated RSC96 cells, and inhibition of DNMT1 with 5-Aza treatment or shRNA vector transfection reversed high glucose-induced reductions in BDNF expression. Furthermore, the mTOR and upstream Akt pathways were indicated to mediate high glucose-induced DNMT1 and BDNF expression in RSC96 cells. Taken together, our results suggest that the Akt/mTOR cascade mediates high glucose-induced reductions in BDNF via DNMT1 in Schwann cells in DPN.

Tumor necrosis factor alpha in peripheral neuropathy in type 2 diabetes mellitus

ObjectiveTo compare serum levels of tumor necrosis factor alpha (TNF-α) between type 2 diabetes mellitus patients with and without peripheral neuropathy (PN). Also, to study the relation between peripheral nerves conduction velocity and serum level of TNF-α in those patients.Patients and methodsThis study included three groups with 40 patients in each group. Diabetic PN patients (groups I and II) were compared with diabetic patients without PN (group III). Groups I and II differed in the duration of clinical neuropathy with less than 5 years in group I and more than 5 years in group II.All patients were subjected to general and neurological examination, neuropathy symptom score (NSS), neuropathy disability score (NDS), glycosylated hemoglobin (HbA1c), serum level of TNF-α and both sensory and motor nerve conduction study.ResultsThis study showed raised serum levels of TNF-α in diabetic patients with PN, more with increased duration of neuropathy. TNF-α levels showed statistically significant negative correlation with nerve conduction velocity but positive correlations with each of neuropathy disability score, neuropathy symptom score, and glycosylated hemoglobin.ConclusionTNF-α might be involved in the pathogenesis of diabetic PN, and its serum level might be used as a biomarker for the severity of diabetic PN.

A Genetic Locus on Chromosome 2q24 Predicting Peripheral Neuropathy Risk in Type 2 Diabetes: Results From the ACCORD and BARI 2D Studies.

Genetic factors have been postulated to be involved in the etiology of diabetic peripheral neuropathy (DPN), but their identity remains mostly unknown. The aim of this study was to conduct a systematic search for genetic variants influencing DPN risk using two well-characterized cohorts. A genome-wide association study (GWAS) testing 6.8 million single nucleotide polymorphisms was conducted among participants of the Action to Control Cardiovascular Risk in Diabetes (ACCORD) clinical trial. Included were 4,384 white case patients with type 2 diabetes (T2D) and prevalent or incident DPN (defined as a Michigan Neuropathy Screening Instrument clinical examination score >2.0) and 784 white control subjects with T2D and no evidence of DPN at baseline or during follow-up. Replication of significant loci was sought among white subjects with T2D (791 DPN-positive case subjects and 158 DPN-negative control subjects) from the Bypass Angioplasty Revascularization Investigation in Type 2 Diabetes (BARI 2D) trial. Association between significant variants and gene expression in peripheral nerves was evaluated in the Genotype-Tissue Expression (GTEx) database. A cluster of 28 SNPs on chromosome 2q24 reached GWAS significance (P < 5 × 10−8) in ACCORD. The minor allele of the lead SNP (rs13417783, minor allele frequency = 0.14) decreased DPN odds by 36% (odds ratio [OR] 0.64, 95% CI 0.55–0.74, P = 1.9 × 10−9). This effect was not influenced by ACCORD treatment assignments (P for interaction = 0.6) or mediated by an association with known DPN risk factors. This locus was successfully validated in BARI 2D (OR 0.57, 95% CI 0.42–0.80, P = 9 × 10−4; summary P = 7.9 × 10−12). In GTEx, the minor, protective allele at this locus was associated with higher tibial nerve expression of an adjacent gene (SCN2A) coding for human voltage-gated sodium channel NaV1.2 (P = 9 × 10−4). To conclude, we have identified and successfully validated a previously unknown locus with a powerful protective effect on the development of DPN in T2D. These results may provide novel insights into DPN pathogenesis and point to a potential target for novel interventions.

Nanoparticle–microRNA-146a-5p polyplexes ameliorate diabetic peripheral neuropathy by modulating inflammation and apoptosis

Nontoxic and nonimmunogenic nanoparticles play an increasingly important role in the application of pharmaceutical nanocarriers. The pathogenesis of diabetic peripheral neuropathy (DPN) has been extensively studied. However, the role of microRNAs in DPN remains to be clarified. We verified in vitro that miR-146a-5p mimics inhibited the expression of proinflammatory cytokines and apoptosis. Then, we explored the protective effect of nanoparticle–miRNA-146a-5p polyplexes (nano-miR-146a-5p) on DPN rats. We demonstrated that nano-miR-146a-5p improved nerve conduction velocity and alleviated the morphological damage and demyelination of the sciatic nerve of DPN rats. The expression of the inflammatory cytokines, caspase-3, and cleaved caspase-3 in the sciatic nerve was inhibited by nano-miR-146a-5p. Additionally, nano-miR-146a-5p increased the expression of myelin basic protein. These results all indicated that nano-miR-146a-5p had a protective effect on peripheral nerves in the DPN rat model, which may occur through the regulation of the inflammatory response and apoptosis.