Diabetic peripheral neuropathy: a clinicopathologic and immunohistochemical analysis of sural nerve biopsies

Targeting neuroinflammation in distal symmetrical polyneuropathy in diabetes

Diabetic distal symmetric polyneuropathy is the most common type of peripheral neuropathy complication of diabetes mellitus. Neuroinflammation is emerging as an important contributor to diabetes-induced neuropathy. Long-term hyperglycemia results in increased production of advanced glycation end products (AGEs). AGEs interact with their receptors to activate intracellular signaling, leading to the release of various inflammatory cytokines. Increased release of inflammatory cytokines is associated with diabetes, diabetic neuropathy, and neuropathic pain. Thus, anti-inflammatory intervention is a potential therapy for diabetic distal symmetric polyneuropathy. Further characterization of inflammatory mechanisms might identify novel therapeutic targets to mitigate diabetic neuropathy.

Novel strategy: Identifying new markers for demyelination in diabetic distal symmetrical polyneuropathy

Objective

To develop a novel strategy for identifying acquired demyelination in diabetic distal symmetrical polyneuropathy (DSP).

Background

Motor nerve conduction velocity (CV) slowing in diabetic DSP exceeds expectations for pure axonal loss thus implicating superimposed acquired demyelination.

Methods

After establishing demyelination confidence intervals by regression analysis of nerve conduction data from chronic inflammatory demyelinating polyneuropathy (CIDP), we prospectively studied CV slowing in 90 diabetic DSP patients with and without at least one motor nerve exhibiting CV slowing (groups A and B) into the demyelination range by American Academy of Neurology (AAN) criteria respectively and 95 amyotrophic lateral sclerosis (ALS) patients. Simultaneously, secretory phospholipase A2 (sPLA2) activity was assessed in both diabetic groups and 46 healthy controls.

Results

No ALS patient exhibited CV slowing in more than two motor nerves based on AAN criteria or the confidence intervals. Group A demonstrated a significantly higher percentage of patients as compared to group B fulfilling the above criteria, with an additional criterion of at least one motor nerve exhibiting CV slowing in the demyelinating range and a corresponding F response in the demyelinating range by AAN criteria (70.3 % vs. 1.9 %; p < 0.0001). Urine sPLA2 activity was increased significantly in diabetic groups as compared to healthy controls (942.9 ± 978.0 vs. 591.6 ± 390.2 pmol/min/ml, p < 0.05), and in group A compared to Group B (1328.3 ± 1274.2 vs. 673.8 ± 576.9 pmol/min/ml, p < 0.01). More patients with elevated sPLA2 activity and more than 2 motor nerves with CV slowing in the AAN or the confidence intervals were identified in group A as compared to group B (35.1 % vs. 5.7 %, p < 0.001). Furthermore, 13.5 % of patients in diabetic DSP Group A, and no patients in diabetic DSP Group B, fulfilled an additional criterion of more than one motor nerve with CV slowing into the demyelinating range with its corresponding F response into the demyelinating range by AAN criteria.

Conclusion

A combination of regression analysis of electrodiagnostic data and a urine biological marker of systemic inflammation identifies a subgroup of diabetic DSP with superimposed acquired demyelination that may respond favorably to immunomodulatory therapy.

Exploring the molecular mechanism of Xuebifang in the treatment of diabetic peripheral neuropathy based on bioinformatics and network pharmacology

Background

Xuebifang (XBF), a potent Chinese herbal formula, has been employed in managing diabetic peripheral neuropathy (DPN). Nevertheless, the precise mechanism of its action remains enigmatic.

Purpose

The primary objective of this investigation is to employ a bioinformatics-driven approach combined with network pharmacology to comprehensively explore the therapeutic mechanism of XBF in the context of DPN.

Study design and Methods

The active chemicals and their respective targets of XBF were sourced from the TCMSP and BATMAN databases. Differentially expressed genes (DEGs) related to DPN were obtained from the GEO database. The targets associated with DPN were compiled from the OMIM, GeneCards, and DrugBank databases. The analysis of GO, KEGG pathway enrichment, as well as immuno-infiltration analysis, was conducted using the R language. The investigation focused on the distribution of therapeutic targets of XBF within human organs or cells. Subsequently, molecular docking was employed to evaluate the interactions between potential targets and active compounds of XBF concerning the treatment of DPN.

Results

The study successfully identified a total of 122 active compounds and 272 targets associated with XBF. 5 core targets of XBF for DPN were discovered by building PPI network. According to GO and KEGG pathway enrichment analysis, the mechanisms of XBF for DPN could be related to inflammation, immune regulation, and pivotal signalling pathways such as the TNF, TLR, CLR, and NOD-like receptor signalling pathways. These findings were further supported by immune infiltration analysis and localization of immune organs and cells. Moreover, the molecular docking simulations demonstrated a strong binding affinity between the active chemicals and the carefully selected targets.

Conclusion

In summary, this study proposes a novel treatment model for XBF in DPN, and it also offers a new perspective for exploring the principles of traditional Chinese medicine (TCM) in the clinical management of DPN.

Dysregulation of Long Noncoding RNA NEAT1/miR-199a-5/BiP Axis in Patients with Diabetic Neuropathy

OBJECTIVE

Diabetic neuropathy (DN) is a type of nerve damage and the most common complication of diabetes. Regarding the association between endoplasmic reticulum (ER) stress with the pathogenesis of neuropathy, this study aims to examine binding immunoglobulin protein (BiP) gene expression and long noncoding RNA nuclear enriched abundant transcript 1 (NEAT1), miR-199a-5 as its regulator in the peripheral blood of DN patients compared to diabetic patients without neuropathy.

METHODS

Peripheral blood samples were obtained from DN (n = 20) patients and diabetic patients without neuropathy (non-DN) (n = 20). After RNA extraction from peripheral blood mononuclear cells, reverse transcription-quantitative polymerase chain reaction was performed to evaluate RNA expression.

RESULTS

The results showed that the expression level of NEAT1 and BiP genes in the DN group increased significantly compared to the non-DN group. Also, the expression level of miR-199a-5p in the DN group was significantly downregulated.

CONCLUSION

As a result, the axis of NEAT1, miR-199a-5p, and BiP may have a role in the DN pathogenesis.

Central and Peripheral Nervous System Complications of Vasculitis Syndromes from Pathology to Bedside: Part 2-Peripheral Nervous System

PURPOSE OF REVIEW

Peripheral nervous system vasculitides (PNSV) are a heterogeneous group of disorders with a clinical subset that may differ in prognosis and therapy. We provide a comprehensive update on the clinical assessment, diagnosis, complications, treatment, and follow-up of PNSV.

RECENT FINDINGS

Progress in neuroimaging, molecular testing, and peripheral nerve biopsy has improved clinical assessment and decision-making of PNSV, also providing novel insights on how to prevent misdiagnosis and increase diagnostic certainty. Advances in imaging techniques, allowing to clearly display the vessel walls, have also enhanced the possibility to differentiate inflammatory from non-inflammatory vascular lesions, while recent histopathology data have identified the main morphological criteria for more accurate diagnosis and differential diagnoses. Overall, the identification of peculiar morphological findings tends to improve diagnostic accuracy by defining a clearer boundary between systemic and non-systemic neuropathies. Therefore, the definition of epineurium vessel wall damage, type of vascular lesion, characterization of lymphocyte populations, antibodies, and inflammatory factors, as well as the identification of direct nerve damage or degeneration, are the common goals for pathologists and clinicians, who will both benefit for data integration and findings translation. Nevertheless, to date, treatment is still largely empiric and, in some cases, unsatisfactory, thus often precluding precise prognostic prediction. In this context, new diagnostic techniques and multidisciplinary management will be essential in the proper diagnosis and prompt management of PNSV, as highlighted in the present review. Thirty to fifty percent of all patients with vasculitis have signs of polyneuropathy. Neuropathies associated with systemic vasculitis are best managed according to the guidelines of the underlying disease because appropriate workup and initiation of treatment can reduce morbidity. Steroids, or in severe or progressive cases, cyclophosphamide pulse therapy is the standard therapy in non-systemic vasculitic neuropathies. Some patients need long-term immunosuppression. The use of novel technologies for high-throughput genotyping will permit to determine the genetic influence of related phenotypes in patients with PNSV.

Identification of Adipogenesis Subgroups and Immune Infiltration Characteristics in Diabetic Peripheral Neuropathy

Dysregulation of adipogenesis is related to diabetic peripheral neuropathy (DPN) pathogenesis, which may be mediated by immune infiltration. Nevertheless, the expression patterns of multiple adipogenesis-related genes and the differences of immune infiltration in different lipid metabolism levels remain unknown. GSE95849, a gene expression matrix containing DPN patients and healthy participants, was downloaded from Gene Expression Omnibus (GEO) database. Differentially expressed adipogenesis-related genes (DEARGs) were screened by overlapping the adipogenesis-related genes with differentially expressed genes (DEGs). DPN patients from GSE24290 and GSE148059 were divided into two adipogenesis subgroups according to the expression of DEARGs. The single-sample gene set enrichment analysis (ssGSEA) was used to estimate the abundance of the immune cells between two subgroups. The analysis of immune infiltration suggested that a variety of immune cells and immune processes were elevated in the high expression group of DEARGs. The differentially expressed genes of the two subgroups were mainly enriched in biological processes and signaling pathways related to lipid metabolism. PPARG, FABP4, LIPE, FASN, SCD, DGAT2, PNPLA2, ADIPOQ, LEP, and CEBPA were identified as the hub genes of the two subgroups, whose related transcription factors (TFs) and miRNAs were predicted. An immunohistochemical assay was used to verify the expression of hub genes in DPN nerve tissues. Our comprehensive analysis of adipogenesis subgroups in DPN illustrated that different expression patterns of DEARGs may lead to different immune and inflammatory states. The identification of DEARGs may help to further distinguish the different characteristics of DPN patients and lay the foundation for targeted treatment. Our findings may bring a novel perspective to the diagnosis and treatment of DPN patients.

Critical illness-associated weakness and related motor disorders

Weakness of limb and respiratory muscles that occurs in the course of critical illness has become an increasingly common and serious complication of adult and pediatric intensive care unit patients and a cause of prolonged ventilatory support, morbidity, and prolonged hospitalization. Two motor disorders that occur singly or together, namely critical illness polyneuropathy and critical illness myopathy, cause weakness of limb and of breathing muscles, making it difficult to be weaned from ventilatory support, commencing rehabilitation, and extending the length of stay in the intensive care unit, with higher rates of morbidity and mortality. Recovery can take weeks or months and in severe cases, and may be incomplete or absent. Recent findings suggest an improved prognosis of critical illness myopathy compared to polyneuropathy. Prevention and treatment are therefore very important. Its management requires an integrated team approach commencing with neurologic consultation, creatine kinase (CK) measurement, detailed electrodiagnostic, respiratory and neuroimaging studies, and potentially muscle biopsy to elucidate the etiopathogenesis of the weakness in the peripheral and/or central nervous system, for which there may be a variety of causes. These tenets of care are being applied to new cases and survivors of the coronavirus-2 disease pandemic of 2019. This chapter provides an update to the understanding and approach to critical illness motor disorders.

Adult and childhood vasculitis

Vasculitis refers to heterogeneous clinicopathologic disorders that share the histopathology of inflammation of blood vessels. Unrecognized and therefore untreated, vasculitis of the nervous system leads to pervasive injury and disability, making this a disorder of paramount importance to all clinicians. There has been remarkable progress in the pathogenesis, diagnosis, and treatment of primary CNS and PNS vasculitides, predicated on achievement in primary systemic forms. Primary neurological vasculitides can be diagnosed with assurance after intensive evaluation that incudes tissue confirmation whenever possible. Clinicians must choose from among the available immune modulating, suppressive, and targeted immunotherapies to induce and maintain remission status and prevent relapse, unfortunately without the benefit of RCTs, and tempered by the recognition of anticipated medication side effects. It may be said that efforts to define a disease are attempts to understand the very concept of the disease. This has been especially evident in systemic and neurological disorders associated with vasculitis. For the past 100 years, since the first description of granulomatous angiitis of the brain, the CNS vasculitides have captured the attention of generations of clinical investigators around the globe to reach a better understanding of vasculitides involving the central and peripheral nervous system. Since that time it has become increasingly evident that this will necessitate an international collaborative effort.

Anti-hyperalgesic effects of photobiomodulation therapy (904 nm) on streptozotocin-induced diabetic neuropathy imply MAPK pathway and calcium dynamics modulation

Several recent studies have established the efficacy of photobiomodulation therapy (PBMT) in painful clinical conditions. Diabetic neuropathy (DN) can be related to activating mitogen-activated protein kinases (MAPK), such as p38, in the peripheral nerve. MAPK pathway is activated in response to extracellular stimuli, including interleukins TNF-α and IL-1β. We verified the pain relief potential of PBMT in streptozotocin (STZ)-induced diabetic neuropathic rats and its influence on the MAPK pathway regulation and calcium (Ca²⁺) dynamics. We then observed that PBMT applied to the L4-L5 dorsal root ganglion (DRG) region reduced the intensity of hyperalgesia, decreased TNF-α and IL-1β levels, and p38-MAPK mRNA expression in DRG of diabetic neuropathic rats. DN induced the activation of phosphorylated p38 (p-38) MAPK co-localized with TRPV1⁺ neurons; PBMT partially prevented p-38 activation. DN was related to an increase of p38-MAPK expression due to proinflammatory interleukins, and the PBMT (904 nm) treatment counteracted this condition. Also, the sensitization of DRG neurons by the hyperglycemic condition demonstrated during the Ca²⁺ dynamics was reduced by PBMT, contributing to its anti-hyperalgesic effects.

Balance Analysis of Peripheral Neuropathy in Type 2 Diabetes Mellitus Based on Logistic Regression Equation

This paper analyzes the factors of peripheral neuropathy in type 2 diabetes mellitus and puts forward a balanced analysis of peripheral neuropathy in type 2 diabetes mellitus based on logistic regression equation. A total of 1192 eligible patients were selected as the study subjects. All selected patients underwent 75 g oral glucose tolerance test to measure fasting blood glucose and insulin and 2-hour postprandial blood glucose and 2-hour postprandial insulin, as well as neuroelectrophysiological examination. The results showed that the OR values of age, course of disease, fingertip blood glucose immediately after admission, and 2-hour blood glucose were greater than 1, and the P values were all less than 0.05, which were the risk factors of diabetic peripheral neuropathy. OR value of β cell function index (HBCI) is less than 1. P is less than 0.05, and it is a protective factor of diabetic peripheral neuropathy. Laboratory indicators are as follows: 75 g OGTT: 0-hour blood glucose, 2-hour blood glucose, and glycosylated hemoglobin; serum creatinine; glutamate transaminase; fibrinogen; ten items of hemoglobin; and indexes reflecting islet function: islet β is thin, and there are significant differences in cell function index, insulin resistance index, and insulin secretion index between the non-DPN group and DPN group. Age, course of disease, fingertip blood glucose immediately after admission, and blood glucose within 2 hours after admission were the risk factors for diabetic peripheral neuropathy. Islet β cell function index (HBCI) is a protective factor of diabetic peripheral neuropathy.

Interfascicular Gliding Dysfunction Relation with Focal Neuropathy in Diabetic Patients with Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS), a common neuropathy of the upper limb, is highly prevalent in diabetic patients. Recent findings indicate that changes in median nerve elasticity and its gliding characteristics may contribute to the development of CTS. Normally, each nerve should be able to adapt to the positional changes by passive movement relative to the surrounding tissues. This ability is provided by a gliding apparatus around the nerve trunk in the surrounding soft tissue. The fascicles of nerve trunks can also glide against each other (interfascicular gliding). Sonoelastography indicates that nerve elasticity is decreased in patients with CTS compared to healthy patients. Moreover, decreased nerve elasticity in diabetes mellitus type II is associated with increased neuropathy, especially in peripheral nerves. Biomechanical factors, oxidative stress, and microvascular defects are also observed in diabetic neuropathy and account for different complications. A reduction in the elasticity of peripheral nerves may be related to decreased interfascicular gliding because of the biomechanical changes that occur in neuropathy. Surgical treatments, including nerve release and reduction of carpal tunnel pressure, improve peripheral gliding but do not resolve disease symptoms completely. According to the evidence, interfascicular gliding dysfunction is the most important factor in the pathogenesis of CTS in diabetic patients. Available evidence suggests that biomechanical variations affect interfascicular gliding more than peripheral gliding in diabetic patients. Decreased nerve elasticity is strongly correlated with decreased interfascicular gliding. It is further hypothesized that the concurrent use of antioxidants and pharmacological treatment (neuroprotection) such as alpha lipoic acid with carpal tunnel release in diabetic patients may alleviate the interfascicular gliding dysfunction and improve median neve elasticity. Decreased nerve elasticity and interfascicular gliding dysfunction play significant roles in the pathogenesis of CTS in diabetic patients.

Diagnostic Tools, Biomarkers, and Treatments in Diabetic polyneuropathy and Cardiovascular Autonomic Neuropathy

The various manifestations of diabetic neuropathy, including distal symmetric sensorimotor polyneuropathy (DSPN) and cardiovascular autonomic neuropathy (CAN), are among the most prevalent chronic complications of diabetes. Major clinical complications of diabetic neuropathies, such as neuropathic pain, chronic foot ulcers, and orthostatic hypotension, are associated with considerable morbidity, increased mortality, and diminished quality of life. Despite the substantial individual and socioeconomic burden, the strategies to diagnose and treat diabetic neuropathies remain insufficient. This review provides an overview of the current clinical aspects and recent advances in exploring local and systemic biomarkers of both DSPN and CAN assessed in human studies (such as biomarkers of inflammation and oxidative stress) for better understanding of the underlying pathophysiology and for improving early detection. Current therapeutic options for DSPN are (I) causal treatment, including lifestyle modification, optimal glycemic control, and multifactorial risk intervention, (II) pharmacotherapy derived from pathogenetic concepts, and (III) analgesic treatment against neuropathic pain. Recent advances in each category are discussed, including non-pharmacological approaches, such as electrical stimulation. Finally, the current therapeutic options for cardiovascular autonomic complications are provided. These insights should contribute to a broader understanding of the various manifestations of diabetic neuropathies from both the research and clinical perspectives.

Immune mechanisms, the role of complement, and related therapies in autoimmune neuropathies

INTRODUCTION

Autoimmune neuropathies have diverse presentations and underlying immune mechanisms. Demonstration of efficacy of therapeutic agents that inhibit the complement cascade would confirm the role of complement activation.

AREAS COVERED

A review of the pathophysiology of the autoimmune neuropathies, to identify those that are likely to be complement mediated.

EXPERT OPINION

Complement mediated mechanisms are implicated in the acute and chronic neuropathies associated with IgG or IgM antibodies that target the Myelin Associated Glycoprotein (MAG) or gangliosides in the peripheral nerves. Antibody and complement mechanisms are also suspected in the Guillain-Barré syndrome and chronic inflammatory demyelinating neuropathy, given the therapeutic response to plasmapheresis or intravenous immunoglobulins, even in the absence of an identifiable target antigen. Complement is unlikely to play a role in paraneoplastic sensory neuropathy associated with antibodies to HU/ANNA-1 given its intracellular localization. In chronic demyelinating neuropathy with anti-nodal/paranodal CNTN1, NFS-155, and CASPR1 antibodies, myotonia with anti-VGKC LGI1 or CASPR2 antibodies, or autoimmune autonomic neuropathy with anti-gAChR antibodies, the response to complement inhibitory agents would depend on the extent to which the antibodies exert their effects through complement dependent or independent mechanisms. Complement is also likely to play a role in Sjogren's, vasculitic, and cryoglobulinemic neuropathies.

Advances About Immunoinflammatory Pathogenesis and Treatment in Diabetic Peripheral Neuropathy

Most diabetic patients develop diabetic peripheral neuropathy (DPN). DPN is related to the increase of inflammatory cells in peripheral nerves, abnormal cytokine expression, oxidative stress, ischemia ,and pro-inflammatory changes in bone marrow. We summarized the progress of immune-inflammatory mechanism and treatment of DPN in recent years. Immune inflammatory mechanisms include TNF-α, HSPs, PARP, other inflammatory factors, and the effect of immune cells on DPN. Treatment includes tricyclic antidepressants and other drug therapy, immune and molecular therapy, and non-drug therapy such as exercise therapy, electrotherapy, acupuncture, and moxibustion. The pathogenesis of DPN is complex. In addition to strictly controlling blood glucose, its treatment should also start from other ways, explore more effective and specific treatment schemes for various causes of DPN, and find new targets for treatment will be the direction of developing DPN therapeutic drugs in the future.

T lymphocyte and monocyte subsets are dysregulated in type 1 diabetes patients with peripheral neuropathic pain

Diabetic neuropathic pain is a common and devastating complication of type 1 diabetes, but the mechanism by which it develops and persists is yet to be fully elucidated. This study utilised high-dimensional suspension mass cytometry in a pilot cohort to investigate differences in peripheral blood immunophenotypes between type 1 diabetes patients with (n ​= ​9) and without (n ​= ​9) peripheral neuropathic pain. The abundance and activation of several leukocyte subsets were investigated with unsupervised clustering approaches FlowSOM and SPADE, as well as by manual gating. Major findings included a proportional increase in CD4+ central memory T cells and an absolute increase in classical monocytes, non-classical monocytes, and mature natural killer cells in type 1 diabetes patients with pain compared to those without pain. The expression of CD27, CD127, and CD39 was upregulated on select T cell populations, and the phosphorylated form of pro-inflammatory transcription factor MK2 was upregulated across most populations. These results provide evidence that distinct immunological signatures are associated with painful neuropathy in type 1 diabetes patients. Further research may link these changes to mechanisms by which pain in type 1 diabetes is initiated and maintained, paving the way for much needed targeted treatments.

Pathogenesis, diagnosis and clinical management of diabetic sensorimotor peripheral neuropathy

Diabetic sensorimotor peripheral neuropathy (DSPN) is a serious complication of diabetes mellitus and is associated with increased mortality, lower-limb amputations and distressing painful neuropathic symptoms (painful DSPN). Our understanding of the pathophysiology of the disease has largely been derived from animal models, which have identified key potential mechanisms. However, effective therapies in preclinical models have not translated into clinical trials and we have no universally accepted disease-modifying treatments. Moreover, the condition is generally diagnosed late when irreversible nerve damage has already taken place. Innovative point-of-care devices have great potential to enable the early diagnosis of DSPN when the condition might be more amenable to treatment. The management of painful DSPN remains less than optimal; however, studies suggest that a mechanism-based approach might offer an enhanced benefit in certain pain phenotypes. The management of patients with DSPN involves the control of individualized cardiometabolic targets, a multidisciplinary approach aimed at the prevention and management of foot complications, and the timely diagnosis and management of neuropathic pain. Here, we discuss the latest advances in the mechanisms of DSPN and painful DSPN, originating both from the periphery and the central nervous system, as well as the emerging diagnostics and treatments.

Skeletal Muscle and Peripheral Nerve Histopathology in COVID-19

OBJECTIVE

To explore the spectrum of skeletal muscle and nerve pathology of patients who died after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and to assess for direct viral invasion of these tissues.

METHODS

Psoas muscle and femoral nerve sampled from 35 consecutive autopsies of patients who died after SARS-CoV-2 infection and 10 SARS-CoV-2-negative controls were examined under light microscopy. Clinical and laboratory data were obtained by chart review.

RESULTS

In SARS-CoV-2-positive patients, mean age at death was 67.8 years (range 43-96 years), and the duration of symptom onset to death ranged from 1 to 49 days. Four patients had neuromuscular symptoms. Peak creatine kinase was elevated in 74% (mean 959 U/L, range 29-8,413 U/L). Muscle showed type 2 atrophy in 32 patients, necrotizing myopathy in 9, and myositis in 7. Neuritis was seen in 9. Major histocompatibility complex-1 (MHC-1) expression was observed in all cases of necrotizing myopathy and myositis and in 8 additional patients. Abnormal expression of myxovirus resistance protein A (MxA) was present on capillaries in muscle in 9 patients and in nerve in 7 patients. SARS-CoV-2 immunohistochemistry was negative in muscle and nerve in all patients. In the 10 controls, muscle showed type 2 atrophy in all patients, necrotic muscle fibers in 1, MHC-1 expression in nonnecrotic/nonregenerating fibers in 3, MxA expression on capillaries in 2, and inflammatory cells in none, and nerves showed no inflammatory cells or MxA expression.

CONCLUSIONS

Muscle and nerve tissue demonstrated inflammatory/immune-mediated damage likely related to release of cytokines. There was no evidence of direct SARS-CoV-2 invasion of these tissues.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that muscle and nerve biopsies document a variety of pathologic changes in patients dying of coronavirus disease 2019 (COVID-19).

Aging and the immune response in diabetic peripheral neuropathy

A large proportion of older individuals with diabetes go on to develop diabetic peripheral neuropathy (DPN). DPN is associated with an increase in inflammatory cells within the peripheral nerve, activation of nuclear factor kappa-light-chain-enhancer of activated B cells and receptors for advanced glycation end products/advanced glycation end products pathways, aberrant cytokine expression, oxidative stress, ischemia, as well as pro-inflammatory changes in the bone marrow; all processes that may be exacerbated with age. We review the immunological features of DPN and discuss whether age-related changes in relevant immunological areas may contribute to age being a risk factor for DPN.

Glucagon Prevents Cytotoxicity Induced by Methylglyoxal in a Rat Neuronal Cell Line Model

Although diabetic polyneuropathy (DPN) is a frequent diabetic complication, no effective therapeutic approach has been established. Glucagon is a crucial hormone for glucose homeostasis but has pleiotropic effects, including neuroprotective effects in the central nervous system. However, the importance of glucagon in the peripheral nervous system (PNS) has not been clarified. Here, we hypothesized that glucagon might have a neuroprotective function in the PNS. The immortalized rat dorsal root ganglion (DRG) neuronal cell line 50B11 was treated with methylglyoxal (MG) to mimic an in vitro DPN model. The cells were cultured with or without glucagon or MG. Neurotoxicity, survival, apoptosis, neurite projection, cyclic adenosine monophosphate (cAMP), and protein kinase A (PKA) were examined. Glucagon had no cytotoxicity and rescued the cells from neurotoxicity. Cell survival was increased by glucagon. The ratio of apoptotic cells, which was increased by MG, was reduced by glucagon. Neurite outgrowth was accelerated in glucagon-treated cells. Cyclic AMP and PKA accumulated in the cells after glucagon stimulation. In conclusion, glucagon protected the DRG neuronal cells from MG-induced cellular stress. The cAMP/PKA pathway may have significant roles in those protective effects of glucagon. Glucagon may be a potential target for the treatment of DPN.

High-Dose Intravenous Immunoglobulin Is Effective in Painful Diabetic Polyneuropathy Resistant to Conventional Treatments. Results of a Double-Blind, Randomized, Placebo-Controlled, Multicenter Trial

OBJECTIVES

The efficacy and safety of high-dose intravenous immunoglobulin (IVIG) in treatment-resistant diabetic painful polyneuropathy (DPN) were assessed.

DESIGN

This was a randomized, double-blind, placebo-controlled, multicenter trial (EudraCT 2010-023883-42).

SETTING

This trial was conducted at eight sites in Italy with a neurology specialist level of care.

SUBJECTS

Twenty-six diabetic patients with DPN who reported baseline severity of pain >60 units (mm) on a VAS scale at enrollment and were resistant to antidepressants and antiepileptic drugs were enrolled; 23 were randomized (11 in the IVIG arm and 12 in the placebo arm). All patients completed the study and were evaluated. All patients were Caucasian, 15 were male, and 21 had a diagnosis of type II diabetes.

METHODS

IVIG (0.4 g/kg/d) or placebo was given for five consecutive days. Pain intensity (visual analog scale, Neuropathic Pain Symptom Inventory) and quality of life (36-Item Short-Form Health Survey, Clinical/Patient Global Impression of Change questionnaires) assessments were performed at visits: baseline, start of therapy (one week later), end of therapy (five days later), and follow-up (four and eight weeks later).

RESULTS

The study achieved its prespecified primary end point of ≥50% pain reduction at four weeks after IVIG, achieved in seven of 11 patients (63.6%) in the IVIG group vs zero of 12 in the placebo group (P = 0.0013). Only two adverse events were reported during the study: one patient in the treatment arm reported a mild "dermatitis psoriasiform," whereas one patient from the placebo group reported a mild "influenza."

CONCLUSIONS

Treatment with IVIG at the dose given was efficacious and safe for patients with DPN resistant to standard therapies.

Associations of cells from both innate and adaptive immunity with lower nerve conduction velocity: the Maastricht Study

INTRODUCTION

Distal sensorimotor polyneuropathy (DSPN) is common in people with diabetes but is also found in pre-diabetes. Peripheral nerve myelin damage, which can be assessed by reduced nerve conduction velocity (NCV), is an essential feature of DSPN. Emerging evidence indicates that the development of DSPN may involve the activation of the immune system. However, available studies have mainly investigated circulating immune mediators, whereas the role of immune cells remains unclear. Therefore, we aimed to test whether leukocyte subsets are associated with NCV.

RESEARCH DESIGN AND METHODS

This cross-sectional study analyzed data from 850 individuals (of whom 252 and 118 had type 2 diabetes and pre-diabetes, respectively) of the Maastricht Study. NCV was measured in the peroneal and tibial motor nerves and the sural sensory nerve and summed to calculate a standardized NCV sum score. Associations between percentages of leukocyte subsets and NCV sum scores were estimated using linear regression models adjusted for demographic, lifestyle, metabolic and clinical covariates.

RESULTS

After adjustment for covariates, higher percentages of basophils and CD4⁺ T cells were associated with lower NCV (p=0.014 and p=0.005, respectively). The percentage of CD8⁺ T cells was positively associated with NCV (p=0.022). These associations were not modified by glucose metabolism status (all p_interaction >0.05). No associations were found for monocytes, eosinophils, neutrophils, lymphocytes, total T cells, Treg cells and B cells.

CONCLUSIONS

The associations of basophils, CD4⁺ and CD8⁺ T cells with NCV suggest that cell types from both innate and adaptive immunity may be implicated in the development of DSPN.

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.

Update on classification, epidemiology, clinical phenotype and imaging of the nonsystemic vasculitic neuropathies

PURPOSE OF REVIEW

Single-organ vasculitis of the peripheral nervous system (PNS) is often designated nonsystemic vasculitic neuropathy (NSVN). Several variants or subtypes have been distinguished, including migratory sensory neuropathy, postsurgical inflammatory neuropathy, diabetic radiculoplexus neuropathies, skin-nerve vasculitides, and, arguably, neuralgic amyotrophy. NSVN often presents as nondiabetic lumbosacral radiculoplexus neuropathy (LRPN). This review updates classification, clinical features, epidemiology, and imaging of these disorders.

RECENT FINDINGS

A recent study showed the annual incidence of LRPN in Olmstead County, Minnesota to be 4.16/100 000:2.79/100 000 diabetic and 1.27/100 000 nondiabetic. This study was the first to determine the incidence or prevalence of any vasculitic neuropathy. In NSVN, ultrasonography shows multifocal enlargement of proximal and distal nerves. In neuralgic amyotrophy, MRI and ultrasound reveal multifocal enlargements and focal constrictions in nerves derived from the brachial plexus. Histopathology of these chronic lesions shows inflammation and rare vasculitis. Diffusion tensor imaging of tibial nerves in NSVN revealed decreased fractional anisotropy in one study.

SUMMARY

Single-organ PNS vasculitides are the most common inflammatory neuropathies. Neuralgic amyotrophy might result from PNS vasculitis, but further study is necessary. The usefulness of focal nerve enlargements or constrictions in understanding pathological mechanisms, directing biopsies, and monitoring disease activity in NSVN should be further investigated.

MHCII-restricted T helper cells: an emerging trigger for chronic tactile allodynia after nerve injuries

Nerve injury-induced chronic pain has been an urgent problem for both public health and clinical practice. While transition to chronic pain is not an inevitable consequence of nerve injuries, the susceptibility/resilience factors and mechanisms for chronic neuropathic pain after nerve injuries still remain unknown. Current preclinical and clinical studies, with certain notable limitations, have shown that major histocompatibility complex class II–restricted T helper (Th) cells is an important trigger for nerve injury-induced chronic tactile allodynia, one of the most prevalent and intractable clinical symptoms of neuropathic pain. Moreover, the precise pathogenic neuroimmune interfaces for Th cells remain controversial, not to mention the detailed pathogenic mechanisms. In this review, depending on the biology of Th cells in a neuroimmunological perspective, we summarize what is currently known about Th cells as a trigger for chronic tactile allodynia after nerve injuries, with a focus on identifying what inconsistencies are evident. Then, we discuss how an interdisciplinary perspective would improve the understanding of Th cells as a trigger for chronic tactile allodynia after nerve injuries. Finally, we hope that the expected new findings in the near future would translate into new therapeutic strategies via targeting Th cells in the context of precision medicine to either prevent or reverse chronic neuropathic tactile allodynia.

T Cells as an Emerging Target for Chronic Pain Therapy

The immune system is critically involved in the development and maintenance of chronic pain. However, T cells, one of the main regulators of the immune response, have only recently become a focus of investigations on chronic pain pathophysiology. Emerging clinical data suggest that patients with chronic pain have a different phenotypic profile of circulating T cells compared to controls. At the preclinical level, findings on the function of T cells are mixed and differ between nerve injury, chemotherapy, and inflammatory models of persistent pain. Depending on the type of injury, the subset of T cells and the sex of the animal, T cells may contribute to the onset and/or the resolution of pain, underlining T cells as a major player in the transition from acute to chronic pain. Specific T cell subsets release mediators such as cytokines and endogenous opioid peptides that can promote, suppress, or even resolve pain. Inhibiting the pain-promoting functions of T cells and/or enhancing the beneficial effects of pro-resolution T cells may offer new disease-modifying strategies for the treatment of chronic pain, a critical need in view of the current opioid crisis.

Understanding the Signaling Pathways Related to the Mechanism and Treatment of Diabetic Peripheral Neuropathy

Worldwide, the most prevalent metabolic disorder is diabetes mellitus (DM), an important condition that has been widely studied. Diabetic peripheral neuropathy (DPN), a complication that can occur with DM, is associated with pain and can result in foot ulcers and even amputation. DPN treatments are limited and mainly focus on pain management. There is a clear need to develop treatments for DPN at all stages. To make this progress, it is necessary to understand the molecular signaling pathways related to DPN. For this review, we aimed to concentrate on the main signaling cascades that contribute to DPN. In addition, we provide information with regard to treatments that are being explored.

Overview of the Vasculitides

The systemic vasculitides are heterogeneous clinicopathologic disorders that share the common feature of vascular inflammation. The resulting disorder can vary depending on involvement of specific organs, caliber of blood vessels, the underlying inflammatory process, and individual host factors. The cumulative result is diminished blood flow, vascular alterations, and eventual occlusion with variable ischemia, necrosis, and tissue damage. An international revised nomenclature system provides the necessary nosology and findings relevant to classify each of the vasculitides. This article is an introduction and overview of the clinical presentation, differential diagnosis, laboratory evaluation, and treatment of systemic and nervous system vasculitides.

Treatment of Vasculitis of the Nervous System

The diagnosis of primary central and peripheral nerve vasculitides should be established with certainty if suspected before commencing potent immunosuppressive therapy. The aim of induction therapy is to rapidly control the underlying inflammatory response and stabilize the blood-brain and blood-nerve barriers, followed by maintenance immunosuppression tailored to the likeliest humoral and cell-mediated autoimmune inflammatory vasculitic processes.

Emerging Biomarkers, Tools, and Treatments for Diabetic Polyneuropathy

Diabetic neuropathy, with its major clinical sequels, notably neuropathic pain, foot ulcers, and autonomic dysfunction, is associated with substantial morbidity, increased risk of mortality, and reduced quality of life. Despite its major clinical impact, diabetic neuropathy remains underdiagnosed and undertreated. Moreover, the evidence supporting a benefit for causal treatment is weak at least in patients with type 2 diabetes, and current pharmacotherapy is largely limited to symptomatic treatment options. Thus, a better understanding of the underlying pathophysiology is mandatory for translation into new diagnostic and treatment approaches. Improved knowledge about pathogenic pathways implicated in the development of diabetic neuropathy could lead to novel diagnostic techniques that have the potential of improving the early detection of neuropathy in diabetes and prediabetes to eventually embark on new treatment strategies. In this review, we first provide an overview on the current clinical aspects and illustrate the pathogenetic concepts of (pre)diabetic neuropathy. We then describe the biomarkers emerging from these concepts and novel diagnostic tools and appraise their utility in the early detection and prediction of predominantly distal sensorimotor polyneuropathy. Finally, we discuss the evidence for and limitations of the current and novel therapy options with particular emphasis on lifestyle modification and pathogenesis-derived treatment approaches. Altogether, recent years have brought forth a multitude of emerging biomarkers reflecting different pathogenic pathways such as oxidative stress and inflammation and diagnostic tools for an early detection and prediction of (pre)diabetic neuropathy. Ultimately, these insights should culminate in improving our therapeutic armamentarium against this common and debilitating or even life-threatening condition.

Evoked hypoalgesia is accompanied by tonic pain and immune cell infiltration in the dorsal root ganglia at late stages of diabetic neuropathy in mice

Diabetic peripheral neuropathy is a major debilitating late complication of diabetes, which significantly reduces the quality of life in patients. Diabetic peripheral neuropathy is associated with a wide spectrum of sensory abnormalities, where in loss of sensation or hypoalgesia to applied external stimuli is paradoxically accompanied by debilitating tonic spontaneous pain. In numerous studies on animal models of diabetic peripheral neuropathy, behavioural measurements have been largely confined to analysis of evoked withdrawal to mechanical and thermal stimuli applied to dermatomes, whereas spontaneous, on-going pain has not been widely studied. In the Streptozotocin model of type 1 diabetes, we employed the Conditioned Place Preference test to assess tonic pain. Our results indicate that both phases, that is, early evoked hypersensitivity (i.e. 5–7 weeks post-Streptozotocin) as well as late stage hypoalgesia (i.e. 17–20 weeks post-Streptozotocin) are accompanied by significant tonic pain in mice with diabetic peripheral neuropathy. We also report on the temporal relation between on-going pain and neuropathological changes in the dorsal root ganglia of mice with diabetic peripheral neuropathy up to 6 months post-Streptozotocin. Neither early hypersensitivity nor late hypoalgesia were associated with markers of cellular stress in the dorsal root ganglia. Whereas significant neutrophil infiltration was observed in the dorsal root ganglia over both early and late stages post-Streptozotocin, T-cell infiltration in the dorsal root ganglia was prominent at late stages post-Streptozotocin. Thus, longitudinal analyses reveal that similar to patients with chronic diabetic peripheral neuropathy, mice show tonic pain despite sensory loss after several months in the Streptozotocin model, which is accompanied by neuroimmune interactions in the dorsal root ganglia.

Potential therapeutic role of melatonin on STZ-induced diabetic central neuropathy: A biochemical, histopathological, immunohistochemical and ultrastructural study

The aim of the present study was to assess the therapeutic potential of melatonin (Mel) in diabetic central neuropathy in a rat model of streptozotocin (STZ)-induced diabetes. The rats were injected with 60 mg/kg STZ and diabetes was confirmed by blood glucose levels (BGL) ≥ 250 mg/dL. Mel treatment (50 mg/kg) was started 72 h before the STZ injection and continued for 45 days. In addition, normal control, vehicle (5% ethanol) control, and Mel-treated non-diabetic control were also included. STZ induced a diabetic phenotype with persistent hyperglycemia and elevated oxidative stress in the brain, liver, and kidneys compared to the control groups. In addition, the diabetic rats showed severe β-cell necrosis with reduced insulin levels, cerebral neuronopathy, myelinopathy, axonopathy, microglial and astroglial activation, and vascular damage. While Mel treatment did not prevent the development of STZ-induced diabetes mellitus and had no significant effect on the BGLs of the diabetic rats, it significantly ameliorated the diabetes-induced oxidative stress and neurodegeneration. Taken together, Mel showed potent therapeutic effects against the neurological complications of hyperglycemia and therefore can be used to treat diabetic neuropathy.

Characterization of diabetic neuropathy progression in a mouse model of type 2 diabetes mellitus

Diabetes mellitus (DM) is one of most common chronic diseases with an increasing incidence in most countries. Diabetic neuropathy (DN) is one of the earliest and main complications of diabetic patients, which is characterized by progressive, distal-to-proximal degeneration of peripheral nerves. The cellular and molecular mechanisms that trigger DN are highly complex, heterogeneous and not completely known. Animal models have constituted a valuable tool for understanding diabetes pathophysiology; however, the temporal course of DN progression in animal models of type 2 diabetes (T2DM) is not completely understood. In this work, we characterized the onset and progression of DN in BKS diabetic (db/db) mice, including the main functional and histological features observed in the human disease. We demonstrated that diabetic animals display progressive sensory loss and electrophysiological impairments in the early-to-mid phases of the disease. Furthermore, we detected an early decrease in intraepidermal nerve fiber (IENF) density in 18-week-old diabetic mice, which is highly associated with sensory loss and constitutes a reliable marker of DN. Other common histological parameters of DN – like Schwann cells apoptosis and infiltration of CD3⁺ cells in the sciatic nerve – were altered in mid-to-late phases of the disease. Our results support the general consensus that DN evolves from initial functional to late structural changes. This work aimed to characterize the progression of DN in a reliable animal model sharing the main human disease features, which is necessary to assess new therapies for this complex disease. Finally, we also aimed to identify an effective temporal window where these potential treatments could be successfully applied.

Summary: We characterized the main functional and structural diabetic neuropathy features during early-to-late phases of type 2 diabetes mellitus. This study aimed to identify a therapeutic window for new treatments.

High frequency of MGUS in DSP

INTRODUCTION

Monoclonal gammopathy has been reported in several polyneuropathies. In this study, we sought to explore the frequency and characteristics of monoclonal gammopathy in patients with diabetic sensorimotor polyneuropathy (DSP).

METHODS

Patients with type 1 and type 2 diabetes mellitus (DM 1, DM 2) and controls without diabetes were evaluated between November 2008 and December 2013.

RESULTS

Fifty controls, 66 patients with DM 1, and 106 patients with DM 2 were included, with average ages of 43 ± 18, 45 ± 17, and 65 ± 10 years, respectively; the frequency of monoclonal gammopathy was 0%, 8%, and 15%, respectively. In patients with DSP, the frequency of monoclonal gammopathy increased to 14% in DM 1 and 21% in DM 2; the most common monoclonal proteins were immunoglobulin (Ig) M and IgG, respectively.

DISCUSSION

DSP might be associated with a high frequency of monoclonal gammopathy, with different characteristics in DM 1 and in DM 2. Muscle Nerve 57: 1018-1021, 2018.

I-Cubed (Infection, Immunity, and Inflammation) and the Human Microbiome

Medical science is just now realizing the full importance of the microbial world. Thanks to developments such as low-cost high-throughput sequencing of microbial communities comprising the human microbiome, the identity and function of unculturable microbes are being unveiled. Public health officials and neuroepidemiology researchers will be called on to guide the understanding of I-Cubed illnesses and the implications of the human microbiome for communicable and noncommunicable diseases, as the natural history is appreciated and the responsiveness of given medical and neurologic disorders to a variety of medical approaches, including strong antibiotics and immune-modulatory therapy is established.

Murine model and mechanisms of treatment-induced painful diabetic neuropathy

Diabetes mellitus represents a group of metabolic diseases that are characterized by hyperglycemia caused by either lack of insulin production or a reduced ability to respond to insulin. It is estimated that there were 347 million people worldwide who suffered from diabetes in 2008 and incidence is predicted to double by 2050. Neuropathy is the most common complication of long-term diabetes and approximately 30% of these subjects develop chronic neuropathic pain. A distinct acute, severe form of neuropathic pain, called insulin neuritis or treatment-induced painful neuropathy of diabetes (TIND), may also occur shortly after initiation of intensive glycemic control, with an incidence rate of up to 10.9%. The pathological mechanisms leading to TIND, which is mostly unresponsive to analgesics, are not yet understood, impeding the development of therapies. Studies to date have been clinical and with limited cohorts of patients. In the current study, we developed chronic and acute insulin-induced neuropathic pain in mice with type 2 insulin-resistant diabetes. Furthermore, we determined that insulin-induced acute allodynia is independent of glycemia levels, can also be induced with Insulin-like Growth Factor 1 (IGF1) and be prevented by inhibition of AKT, providing evidence of an insulin/IGF1 signaling pathway-based mechanism for TIND. This mouse model is useful for the elucidation of mechanisms contributing to TIND and for the testing of new therapeutic approaches to treat TIND.

The association of vitamin D with inflammatory cytokines in diabetic peripheral neuropathy

[Purpose] The effects of vitamin D on the circulating levels of IL-17 and IL-13 were investigated in patients with diabetic peripheral neuropathy, patients with diabetes mellitus type 2 without neuropathy, and healthy controls. [Subjects and Methods] A single-blind controlled clinical study was performed, including70 type 2 diabetic patients with or without diabetic peripheral neuropathy and 33 healthy volunteer controls. The 25(OH)D levels were evaluated using ultra-performance liquid chromatography, and IL-17 and IL-13 levels were assessed using enzyme-linked immunosorbent assays. [Results] The 25(OH) vitamin D concentration was lower in diabetic peripheral neuropathy patients than in diabetes mellitus patients without neuropathy and healthy controls. Similarly, 25(OH)D levels were lower in diabetes mellitus patients than healthy controls. IL-17 and IL-13 levels were higher in diabetes mellitus patients than in controls. Additionally, IL-13 levels were higher in diabetic peripheral neuropathy patients than in diabetes mellitus patients without neuropathy. These differences were statistically significant. There was a significant positive correlation between 25(OH)D and IL-13,and a negative correlation between 25(OH)D andIL-17 in the diabetic and diabetic neuropathy groups. [Conclusion] Vitamin D is a potential modifiable risk factor for diabetic peripheral neuropathy and may regulate inflammatory mediators, e.g., IL-17 and IL-13.

Mechanism of diabetic neuropathy: Where are we now and where to go?

Neuropathy is the most common complication of diabetes. As a consequence of longstanding hyperglycemia, a downstream metabolic cascade leads to peripheral nerve injury through an increased flux of the polyol pathway, enhanced advanced glycation end‐products formation, excessive release of cytokines, activation of protein kinase C and exaggerated oxidative stress, as well as other confounding factors. Although these metabolic aberrations are deemed as the main stream for the pathogenesis of diabetic microvascular complications, organ‐specific histological and biochemical characteristics constitute distinct mechanistic processes of neuropathy different from retinopathy or nephropathy. Extremely long axons originating in the small neuronal body are vulnerable on the most distal side as a result of malnutritional axonal support or environmental insults. Sparse vascular supply with impaired autoregulation is likely to cause hypoxic damage in the nerve. Such dual influences exerted by long‐term hyperglycemia are critical for peripheral nerve damage, resulting in distal‐predominant nerve fiber degeneration. More recently, cellular factors derived from the bone marrow also appear to have a strong impact on the development of peripheral nerve pathology. As evident from such complicated processes, inhibition of single metabolic factors might not be sufficient for the treatment of neuropathy, but a combination of several inhibitors might be a promising approach to overcome this serious disorder. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00070.x, 2010)

Reduced expression of Munc13-1 in human and porcine diabetic peripheral nerve

Peripheral neuropathy (PN) involves widespread peripheral nerve disorders affecting a large human population worldwide. In Europe and the United States, the first single most prominent cause of peripheral neuropathy is diabetes, affecting 60-70% patients with long-term diabetes followed by idiopathic neuropathy, peripheral nerve damage of unknown etiology, diagnosed in 10-40% of all patients admitted to hospitals with symptoms of peripheral nerve damage. The molecular mechanisms underlying the pathogenesis of this disorder are not yet fully understood, however a few potential molecular contributors, such as Munc13-1, have been recently suggested. Munc13-1 is a diacylglycerol (DAG) receptor and a multifunction active zone protein essential for synaptic vesicle priming and crucial for insulin release from pancreatic beta cells. Here, for the first time, we focused on the comparative expression of Munc13-1 in human and porcine peripheral nerves. Our results revealed significantly reduced number of Munc13-1 in human (64.26% ± 6.68%) and porcine (84.09% ± 2.21%) diabetic nerve fibers and lower number of the double stained, neuronal marker, Neurofilament (NF) and Munc13-1 positive, human (56.83% ± 3.77%) and porcine (65.87% ± 4.86%) nerve fibers. Optical density quantification of Western blots showed similar results. Our study indicates that Munc13-1, on account of its role in both insulin and neurotransmitter exocytosis and through its binding properties, may be an important factor contributing to the development or progression of diabetic neuropathy.

Increased expression of the receptor for advanced glycation end-products in human peripheral neuropathies

BACKGROUND

Diabetic neuropathy and idiopathic neuropathy are among the most prevalent neuropathies in human patients. The molecular mechanism underlying pathological changes observed in the affected nerve remains unclear but one candidate molecule, the receptor for advanced glycation end-products (RAGE), has recently gained attention as a potential contributor to neuropathy. Our previous studies revealed that RAGE expression is higher in porcine and murine diabetic nerve, contributing to the inflammatory mechanisms leading to diabetic neuropathy. Here, for the first time, we focused on the expression of RAGE in human peripheral nerve.

METHODS

Our study utilized de-identified human sural nerve surplus obtained from 5 non-neuropathic patients (control group), 6 patients with long-term mild-to-moderate diabetic neuropathy (diabetic group) and 5 patients with mild-to-moderate peripheral neuropathy of unknown etiology (idiopathic group). By using immunofluorescent staining and protein immunoblotting we studied the expression and colocalization patterns of RAGE and its ligands: carboxymethyllysine (CML), high mobility group box 1 (HMBG1) and mammalian Diaphanous 1 (mDia1) in control and neuropathic nerves.

RESULTS

We found that in a normal, healthy human nerve, RAGE is expressed in almost 30% of all nerve fibers and that number is higher in pathological states such as peripheral neuropathy. We established that the levels of RAGE and its pro-inflammatory ligands, CML and HMBG1, are higher in both idiopathic and diabetic nerve, while the expression of the RAGE cytoplasmic domain-binding partner, mDia1 is similar among control, diabetic, and idiopathic nerve. The highest number of double stained nerve fibers was noted for RAGE and CML: ∼76% (control), ∼91% (idiopathic) and ∼82% (diabetic) respectively.

CONCLUSIONS

Our data suggest roles for RAGE and its inflammatory ligands in human peripheral neuropathies and lay the foundation for further, more detailed and clinically oriented investigation involving these proteins and their roles in disorders of the human peripheral nerve.

Diabetic neuropathy part 2: proximal and asymmetric phenotypes

Diabetic neuropathies consist of a variety of syndromes resulting from different types of damage to peripheral or cranial nerves. Although distal symmetric polyneuropathy is the most common type of diabetic neuropathy, many other subtypes have been defined since the 1800s, including proximal diabetic, truncal, cranial, median, and ulnar neuropathies. Various theories have been proposed for the pathogenesis of these neuropathies. The treatment of most requires tight and stable glycemic control. Spontaneous recovery is seen in most of these conditions with diabetic control. Immunotherapies have been tried in some of these conditions however are controversial.

Diabetic neuropathy part 1: overview and symmetric phenotypes

Diabetes is the most common cause of neuropathy in United States and neuropathies are the most common complication of diabetes mellitus, affecting up to 50% of patients with type 1 and type 2 diabetes mellitus. Symptoms usually include numbness, tingling, pain, and weakness. Dizziness with postural changes can be seen with autonomic neuropathy. Metabolic, vascular, and immune theories have been proposed for the pathogenesis of diabetic neuropathy. Axonal damage and segmental demyelination can be seen with diabetic neuropathies. Management of diabetic neuropathy should begin at the initial diagnosis of diabetes and mainly requires tight and stable glycemic control.

Diabetic polyneuropathies: update on research definition, diagnostic criteria and estimation of severity

Prior to a joint meeting of the Neurodiab Association and International Symposium on Diabetic Neuropathy held in Toronto, Ontario, Canada, 13-18 October 2009, Solomon Tesfaye, Sheffield, UK, convened a panel of neuromuscular experts to provide an update on polyneuropathies associated with diabetes (Toronto Consensus Panels on DPNs, 2009). Herein, we provide definitions of typical and atypical diabetic polyneuropathies (DPNs), diagnostic criteria, and approaches to diagnose sensorimotor polyneuropathy as well as to estimate severity. Diabetic sensorimotor polyneuropathy (DSPN), or typical DPN, usually develops on long-standing hyperglycaemia, consequent metabolic derangements and microvessel alterations. It is frequently associated with microvessel retinal and kidney disease-but other causes must be excluded. By contrast, atypical DPNs are intercurrent painful and autonomic small-fibre polyneuropathies. Recognizing that there is a need to detect and estimate severity of DSPN validly and reproducibly, we define subclinical DSPN using nerve conduction criteria and define possible, probable, and confirmed clinical levels of DSPN. For conduct of epidemiologic surveys and randomized controlled trials, it is necessary to pre-specify which attributes of nerve conduction are to be used, the criterion for diagnosis, reference values, correction for applicable variables, and the specific criterion for DSPN. Herein, we provide the performance characteristics of several criteria for the diagnosis of sensorimotor polyneuropathy in healthy subject- and diabetic subject cohorts. Also outlined here are staged and continuous approaches to estimate severity of DSPN.

Diabetic neuropathy: a clinical and neuropathological study of 107 patients

One hundred seven patients were retrospectively studied from 1992 to 2002 with diabetic neuropathy that underwent peripheral nerve biopsy. Nerve biopsy revealed the underlying histopathology, including cell and humoral-mediated immunological lesions in the majority of patients. When combined with clinical and laboratory studies, nerve biopsy has the potential to assist in the selection of patients who may benefit from immunomodulatory therapy.

Differential gene expression in chronic inflammatory demyelinating polyneuropathy (CIDP) skin biopsies

Gene expression analysis previously identified molecular markers that are up-regulated in sural nerve biopsies from patients with chronic inflammatory demyelinating polyneuropathy (CIDP). To determine whether the same or additional genes are also up-regulated in skin, we applied gene microarray profiling and quantitative real-time PCR (qPCR) analysis to skin punch biopsies from patients with CIDP and controls. Five genes, allograft inflammatory factor 1 (AIF-1), lymphatic hyaluronan receptor (LYVE-1/XLKD1), FYN binding protein (FYB), P2RY1 (purinergic receptor P2Y, G-protein-coupled, 1), and MLLT3 (myeloid/lymphoid or mixed-lineage leukemia translocated to, 3), all associated with immune cells or inflammatory processes, were elevated in punch skin biopsies from patients with CIDP as compared to normal subjects or patients with Charcot-Marie-Tooth Type 1 (CMT1). The average fold change of the 5 genes over normal expression, as determined by qPCR, was significantly elevated in skin biopsies from patients with CIDP in comparison to CMT1 or diabetic neuropathy, and similar to that seen in Lyme disease. The findings indicate the presence of inflammatory changes in the skin of patients with CIDP.