Diabetic neuropathy and the sensory neuron: New aspects of pathogenesis and their treatment implications

Therapeutic Effect of Schwann Cell-Like Cells Differentiated from Human Tonsil-Derived Mesenchymal Stem Cells on Diabetic Neuropathy in db/db Mice

BACKGROUND

Diabetic neuropathy (DN) is the most common complication of diabetes, and approximately 50% of patients with this disease suffer from peripheral neuropathy. Nerve fiber loss in DN occurs due to myelin defects and is characterized by symptoms of impaired nerve function. Schwann cells (SCs) are the main support cells of the peripheral nervous system and play important roles in several pathways contributing to the pathogenesis and development of DN. We previously reported that human tonsil-derived mesenchymal stem cells differentiated into SCs (TMSC-SCs), named neuronal regeneration-promoting cells (NRPCs), which cells promoted nerve regeneration in animal models with peripheral nerve injury or hereditary peripheral neuropathy.

METHODS

In this study, NRPCs were injected into the thigh muscles of BKS-db/db mice, a commonly used type 2 diabetes model, and monitored for 26 weeks. Von Frey test, sensory nerve conduction study, and staining of sural nerve, hind foot pad, dorsal root ganglia (DRG) were performed after NRPCs treatment.

RESULTS

Von Frey test results showed that the NRPC treatment group (NRPC group) showed faster responses to less force than the vehicle group. Additionally, remyelination of sural nerve fibers also increased in the NRPC group. After NRPCs treatment, an improvement in response to external stimuli and pain sensation was expected through increased expression of PGP9.5 in the sole and TRPV1 in the DRG.

CONCLUSION

The NRPCs treatment may alleviate DN through the remyelination and the recovery of sensory neurons, could provide a better life for patients suffering from complications of this disease.

Effect and Safety of Herbal Medicine Foot Baths in Patients with Diabetic Peripheral Neuropathy: A Multicenter Double-Blind Randomized Controlled Trial

OBJECTIVE

To evaluate the effect and safety of foot baths with Tangbi Waixi Decoction (TW) in treating patients with diabetic peripheral neuropathy (DPN).

METHODS

It is a multicenter double-blinded randomized controlled trial. Participants with DPN were recruited between November 18, 2016 and May 30, 2018 from 8 hospitals in China. All patients received basic treatments for glycemic management. Patients received foot baths with TW herbal granules either 66.9 g (intervention group) or 6.69 g (control group) for 30 min once a day for 2 weeks and followed by a 2-week rest, as a therapeutic course. If the Toronto Clinical Scoring System total score (TCSS-TS) ⩾6 points, the patients received a total of 3 therapeutic courses (for 12 weeks) and were followed up for 12 weeks. The primary outcome was change in TCSS-TS score at 12 and 24 weeks. Secondary outcomes included changes in bilateral motor nerve conduction velocity (MNCV) and sensory nerve conduction velocity (SNCV) of the median and common peroneal nerve. Safety was also assessed.

RESULTS

Totally 632 patients were enrolled, and 317 and 315 were randomized to the intervention and control groups, respectively. After the 12-week intervention, patients in both groups showed significant declines in TCSSTS scores, and significant increases in MNCV and SNCV of the median and common peroneal nerves compared with pre-treatment (P<0.05). The reduction of TCSS-TS score at 12 weeks and the increase of SNCV of median nerve at 24 weeks in the control group were greater than those in the intervention group (P<0.05). The number of adverse events did not differ significantly between groups (P>0.05), and no serious adverse event was related with treatment.

CONCLUSION

Treatment of TW foot baths was safe and significantly benefitted patients with DPN. A low dose of TW appeared to be more effective than a high dose. (Registry No. ChiCTR-IOR-16009331).

Identification and validation of NAD+ metabolism-related biomarkers in patients with diabetic peripheral neuropathy

Background

The mechanism of Nicotinamide Adenine Dinucleotide (NAD+) metabolism-related genes (NMRGs) in diabetic peripheral neuropathy (DPN) is unclear. This study aimed to find new NMRGs biomarkers in DPN.

Methods

DPN related datasets GSE95849 and GSE185011 were acquired from the Gene Expression Omnibus (GEO) database. 51 NMRGs were collected from a previous article. To explore NMRGs expression in DPN and control samples, differential expression analysis was completed in GSE95849 to obtain differentially expressed genes (DEGs), and the intersection of DEGs and NMRGs was regarded as DE-NMRGs. Next, a protein-protein interaction (PPI) network based on DE-NMRGs was constructed and biomarkers were screened by eight algorithms. Additionally, Gene Set Enrichment Analysis (GSEA) enrichment analysis was completed, biomarker-based column line graphs were constructed, lncRNA-miRNA-mRNA and competing endogenouse (ce) RNA networks were constructed, and drug prediction was completed. Finally, biomarkers expression validation was completed in GSE95849 and GSE185011.

Results

5217 DEGs were obtained from GSE95849 and 21 overlapping genes of DEGs and NMRGs were DE-NMRGs. Functional enrichment analysis revealed that DE-NMRGs were associated with glycosyl compound metabolic process. The PPI network contained 93 protein-interaction pairs and 21 nodes, with strong interactions between NMNAT1 and NAMPT, NADK and NMNAT3, ENPP3 and NUDT12 as biomarkers based on 8 algorithms. Expression validation suggested that ENPP3 and NUDT12 were upregulated in DPN samples (P < 0.05). Moreover, an alignment diagram with good diagnostic efficacy based on ENPP3 and NUDT12 were identified was constructed. GSEA suggested that ENPP3 was enriched in Toll like receptor (TLR) pathway, NUDT12 was enriched in maturity onset diabetes of the young and insulin pathway. Furthermore, 18 potential miRNAs and 36 Transcription factors (TFs) were predicted and the miRNA-mRNA-TF networks were constructed, suggesting that ENPP3 might regulate hsa-miR-34a-5p by affecting MYNN. The ceRNA network suggested that XLOC_013024 might regulate hsa-let-7b-5p by affecting NUDT12. 15 drugs were predicted, with 8 drugs affecting NUDT12 such as resveratrol, and 13 drugs affecting ENPP3 such as troglitazone.

Conclusion

ENPP3 and NUDT12 might play key roles in DPN, which provides reference for further research on DPN.

SUMOylation Modulates Reactive Oxygen Species (ROS) Levels and Acts as a Protective Mechanism in the Type 2 Model of Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) is the prevalent type of peripheral neuropathy; it primarily impacts extremity nerves. Its multifaceted nature makes the molecular mechanisms of diabetic neuropathy intricate and incompletely elucidated. Several types of post-translational modifications (PTMs) have been implicated in the development and progression of DPN, including phosphorylation, glycation, acetylation and SUMOylation. SUMOylation involves the covalent attachment of small ubiquitin-like modifier (SUMO) proteins to target proteins, and it plays a role in various cellular processes, including protein localization, stability, and function. While the specific relationship between high blood glucose and SUMOylation is not extensively studied, recent evidence implies its involvement in the development of DPN in type 1 diabetes. In this study, we investigated the impact of SUMOylation on the onset and progression of DPN in a type 2 diabetes model using genetically modified mutant mice lacking SUMOylation, specifically in peripheral sensory neurons (SNS-Ubc9-/-). Behavioural measurement for evoked pain, morphological analyses of nerve fibre loss in the epidermis, measurement of reactive oxygen species (ROS) levels, and antioxidant molecules were analysed over several months in SUMOylation-deficient and control mice. Our longitudinal analysis at 30 weeks post-high-fat diet revealed that SNS-Ubc9-/- mice exhibited earlier and more pronounced thermal and mechanical sensation loss and accelerated intraepidermal nerve fibre loss compared to control mice. Mechanistically, these changes are associated with increased levels of ROS both in sensory neuronal soma and in peripheral axonal nerve endings in SNS-Ubc9-/- mice. In addition, we observed compromised detoxifying potential, impaired respiratory chain complexes, and reduced levels of protective lipids in sensory neurons upon deletion of SUMOylation in diabetic mice. Importantly, we also identified mitochondrial malate dehydrogenase (MDH2) as a SUMOylation target, the activity of which is negatively regulated by SUMOylation. Our results indicate that SUMOylation is an essential neuroprotective mechanism in sensory neurons in type 2 diabetes, the deletion of which causes oxidative stress and an impaired respiratory chain, resulting in energy depletion and subsequent damage to sensory neurons.

New perspectives in diabetic neuropathy

Diabetes prevalence continues to climb with the aging population. Type 2 diabetes (T2D), which constitutes most cases, is metabolically acquired. Diabetic peripheral neuropathy (DPN), the most common microvascular complication, is length-dependent damage to peripheral nerves. DPN pathogenesis is complex, but, at its core, it can be viewed as a state of impaired metabolism and bioenergetics failure operating against the backdrop of long peripheral nerve axons supported by glia. This unique peripheral nerve anatomy and the injury consequent to T2D underpins the distal-to-proximal symptomatology of DPN. Earlier work focused on the impact of hyperglycemia on nerve damage and bioenergetics failure, but recent evidence additionally implicates contributions from obesity and dyslipidemia. This review will cover peripheral nerve anatomy, bioenergetics, and glia-axon interactions, building the framework for understanding how hyperglycemia and dyslipidemia induce bioenergetics failure in DPN. DPN and painful DPN still lack disease-modifying therapies, and research on novel mechanism-based approaches is also covered.

Corneal Confocal Microscopy Abnormalities in Children and Adolescents With Type 1 Diabetes

OBJECTIVE

Utility of corneal confocal microscopy (CCM) in children and adolescents with type 1 diabetes mellitus (T1DM) without neuropathic symptoms or signs and minimal abnormality in large and small nerve fiber function tests remains largely undetermined. This study aimed to evaluate the performance of CCM in comparison to thermal detection thresholds (TDT) testing and nerve conduction studies (NCS) for detecting neuropathy in children with T1DM.

METHODS

A cohort of children and adolescents with T1DM (n = 51) and healthy controls (n = 50) underwent evaluation for symptoms and signs of neurological deficits, including warm detection threshold, cold detection threshold, vibration perception threshold, NCS, and CCM.

RESULTS

Children with T1DM had no or very minimal neuropathic symptoms and deficits based on the Toronto Clinical Neuropathy Score, yet NCS abnormalities were present in 18 (35%), small fiber dysfunction defined by an abnormal TDT was found in 13 (25.5%) and CCM abnormalities were present in 25 (49%). CCM was abnormal in a majority of T1DM children with abnormal TDT (12/13, 92%) and abnormal NCS (16/18, 88%). CCM additionally was able to detect small fiber abnormalities in 13/38 (34%) in T1DM with a normal TDT and in 9/33 (27%) with normal NCS.

CONCLUSION

CCM was able to detect corneal nerve loss in children with and without abnormalities in TDT and NCS.

Slow or fast: Implications of myofibre type and associated differences for manifestation of neuromuscular disorders

Many neuromuscular disorders can have a differential impact on a specific myofibre type, forming the central premise of this review. The many different skeletal muscles in mammals contain a spectrum of slow- to fast-twitch myofibres with varying levels of protein isoforms that determine their distinctive contractile, metabolic, and other properties. The variations in functional properties across the range of classic 'slow' to 'fast' myofibres are outlined, combined with exemplars of the predominantly slow-twitch soleus and fast-twitch extensor digitorum longus muscles, species comparisons, and techniques used to study these properties. Other intrinsic and extrinsic differences are discussed in the context of slow and fast myofibres. These include inherent susceptibility to damage, myonecrosis, and regeneration, plus extrinsic nerves, extracellular matrix, and vasculature, examined in the context of growth, ageing, metabolic syndrome, and sexual dimorphism. These many differences emphasise the importance of carefully considering the influence of myofibre-type composition on manifestation of various neuromuscular disorders across the lifespan for both sexes. Equally, understanding the different responses of slow and fast myofibres due to intrinsic and extrinsic factors can provide deep insight into the precise molecular mechanisms that initiate and exacerbate various neuromuscular disorders. This focus on the influence of different myofibre types is of fundamental importance to enhance translation for clinical management and therapies for many skeletal muscle disorders.

Neurologic Complications of Endocrine Disorders

OBJECTIVE

This article provides an overview of the neurologic complications of the most prevalent endocrine disorders in adults with an emphasis on relevant neurologic symptoms, signs, and laboratory and neuroimaging findings.

LATEST DEVELOPMENTS

Although the mechanisms of many of the neurologic complications discussed here remain unclear, our understanding of the impacts of diabetes and hypothyroidism on the nervous system and muscle, including complications of rapid correction of chronic hyperglycemia, has advanced in recent years. Recent large studies have not demonstrated a convincing association between subclinical or overt hypothyroidism and cognitive decline.

ESSENTIAL POINTS

Neurologists must become familiar with the neurologic complications of endocrine disorders not only because they are common and treatable (and often reversible) but also because they may be iatrogenic, as is the case with adrenal insufficiency in the setting of long-term corticosteroid therapy.

Vascular endothelial growth factor levels in diabetic peripheral neuropathy: a systematic review and meta-analysis

Objective

Vascular endothelial growth factors (VEGFs, including VEGF-A, VEGF-B, VEGF-C, VEGF-D and PLGF) have important roles in the development and function of the peripheral nervous system. Studies have confirmed that VEGFs, especially VEGF-A (so called VEGF) may be associated with the diabetic peripheral neuropathy (DPN) process. However, different studies have shown inconsistent levels of VEGFs in DPN patients. Therefore, we conducted this meta-analysis to evaluate the relationship between cycling levels of VEGFs and DPN.

Methods

This study searched 7 databases, including PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure (CNKI), VIP Database, WanFang Database, and Chinese Biomedical Literature (CBM), to find the target researches. The random effects model was used to calculate the overall effect.

Results

14 studies with 1983 participants were included, among which 13 studies were about VEGF and 1 was VEGF-B, so only the effects of VEGF were pooled. The result showed that there were obviously increased VEGF levels in DPN patients compared with diabetic patients without DPN (SMD:2.12[1.34, 2.90], p<0.00001) and healthy people (SMD:3.50[2.24, 4.75], p<0.00001). In addition, increased circulating VEGF levels were not associated with an increased risk of DPN (OR:1.02[0.99, 1.05], p<0.00001).

Conclusion

Compared with healthy people and diabetic patients without DPN, VEGF content in the peripheral blood of DPN patients is increased, but current evidence does not support the correlation between VEGF levels and the risk of DPN. This suggests that VEGF may play a role in the pathogenesis and repairment of DPN.

Diabetic Polyneuropathy: New Strategies to Target Sensory Neurons in Dorsal Root Ganglia

Diabetic polyneuropathy (DPN) is the most common type of diabetic neuropathy, rendering a slowly progressive, symmetrical, and length-dependent dying-back axonopathy with preferential sensory involvement. Although the pathogenesis of DPN is complex, this review emphasizes the concept that hyperglycemia and metabolic stressors directly target sensory neurons in the dorsal root ganglia (DRG), leading to distal axonal degeneration. In this context, we discuss the role for DRG-targeting gene delivery, specifically oligonucleotide therapeutics for DPN. Molecules including insulin, GLP-1, PTEN, HSP27, RAGE, CWC22, and DUSP1 that impact neurotrophic signal transduction (for example, phosphatidylinositol-3 kinase/phosphorylated protein kinase B [PI3/pAkt] signaling) and other cellular networks may promote regeneration. Regenerative strategies may be essential in maintaining axon integrity during ongoing degeneration in diabetes mellitus (DM). We discuss specific new findings that relate to sensory neuron function in DM associated with abnormal dynamics of nuclear bodies such as Cajal bodies and nuclear speckles in which mRNA transcription and post-transcriptional processing occur. Manipulating noncoding RNAs such as microRNA and long-noncoding RNA (specifically MALAT1) that regulate gene expression through post-transcriptional modification are interesting avenues to consider in supporting neurons during DM. Finally, we present therapeutic possibilities around the use of a novel DNA/RNA heteroduplex oligonucleotide that provides more efficient gene knockdown in DRG than the single-stranded antisense oligonucleotide.

Diabetic Foot Considerations Related to Plantar Pressures and Shear

Diabetic foot ulcers are a complex, multifaceted, and widespread complication of diabetes mellitus. Although there are a multitude of risk factors contributing to diabetic foot ulcer development, pressure and (more recently) shear stresses are two biomechanical metrics that are gaining popularity for monitoring risk factors predisposing skin breakdown. Other areas of diabetic foot ulcers under research include plantar temperature measuring, as well as monitoring wear-time compliance and machine learning/AI algorithms. Charcot arthropathy is another diabetes complication that has a relationship with diabetic foot ulcer development, which should be monitored for development alongside ulcer development. The ability to monitor and prevent diabetic foot ulcer development and Charcot neuroarthropathy will lead to increased patient outcomes and patient quality of life.

Role of tubulin post-translational modifications in peripheral neuropathy

Peripheral neuropathy is a common disorder that results from nerve damage in the periphery. The degeneration of sensory axon terminals leads to changes or loss of sensory functions, often manifesting as debilitating pain, weakness, numbness, tingling, and disability. The pathogenesis of most peripheral neuropathies remains to be fully elucidated. Cumulative evidence from both early and recent studies indicates that tubulin damage may provide a common underlying mechanism of axonal injury in various peripheral neuropathies. In particular, tubulin post-translational modifications have been recently implicated in both toxic and inherited forms of peripheral neuropathy through regulation of axonal transport and mitochondria dynamics. This knowledge forms a new area of investigation with the potential for developing therapeutic strategies to prevent or delay peripheral neuropathy by restoring tubulin homeostasis.

Best Practices for Dorsal Root Ganglion Stimulation for Chronic Pain: Guidelines from the American Society of Pain and Neuroscience

With continued innovations in neuromodulation comes the need for evolving reviews of best practices. Dorsal root ganglion stimulation (DRG-S) has significantly improved the treatment of complex regional pain syndrome (CRPS), and it has broad applicability across a wide range of other conditions. Through funding and organizational leadership by the American Society for Pain and Neuroscience (ASPN), this best practices consensus document has been developed for the selection, implantation, and use of DRG stimulation for the treatment of chronic pain syndromes. This document is composed of a comprehensive narrative literature review that has been performed regarding the role of the DRG in chronic pain and the clinical evidence for DRG-S as a treatment for multiple pain etiologies. Best practice recommendations encompass safety management, implantation techniques, and mitigation of the potential complications reported in the literature. Looking to the future of neuromodulation, DRG-S holds promise as a robust intervention for otherwise intractable pain.

A Novel Technique Restores Function while Eliminating Intractable Neuropathic Pain in a 71-Year-Old Diabetic Patient under Challenging Injury Conditions

Background The extent of functional recovery induced in healthy patients by sensory nerve grafts, the clinical “gold standard” technique for repairing peripheral nerves with a gap, is significantly limited by increasing gap length, time between trauma and repair, and patient age. When the values of any two, or all three, variables increase simultaneously, there is little to no recovery. For diabetic patients, even under the best of conditions and without any large variables, the extent of axon regeneration and functional recovery is significantly less, but generally none. Therefore, novel techniques are required that enhance recovery in diabetic patients.

Methods A 12-cm long median nerve gap in the wrist/palm of a 71-year-old male long-term diabetic patient was bridged 1.3 years post nerve injury with a sural nerve graft within a platelet-rich plasma-filled collagen tube.

Results By 2 months post-repair, the patient's level 6 chronic neuropathic pain was permanently eliminated. By 6.75 months, the palm had recovered good sensitivity to stimuli of all sensory modalities, including 4.56 g pressure and less than 15 mm two-point discrimination. Each finger had good motor function of M3–5, with partial to complete sensitivity to stimuli of all sensory modalities and an overall recovery of S3.

Conclusion This technique permanently eliminates severe chronic neuropathic pain while simultaneously inducing good motor and sensory recovery in a long-term diabetic patient, under conditions where recovery is rarely, if ever, seen, even in non-diabetic patients. This technique holds great promise of restoring function to diabetic patients, for whom it is otherwise not possible.

Axonal transport deficits in the pathogenesis of diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is a chronic and prevalent metabolic disease that gravely endangers human health and seriously affects the quality of life of hyperglycemic patients. More seriously, it can lead to amputation and neuropathic pain, imposing a severe financial burden on patients and the healthcare system. Even with strict glycemic control or pancreas transplantation, peripheral nerve damage is difficult to reverse. Most current treatment options for DPN can only treat the symptoms but not the underlying mechanism. Patients with long-term diabetes mellitus (DM) develop axonal transport dysfunction, which could be an important factor in causing or exacerbating DPN. This review explores the underlying mechanisms that may be related to axonal transport impairment and cytoskeletal changes caused by DM, and the relevance of the latter with the occurrence and progression of DPN, including nerve fiber loss, diminished nerve conduction velocity, and impaired nerve regeneration, and also predicts possible therapeutic strategies. Understanding the mechanisms of diabetic neuronal injury is essential to prevent the deterioration of DPN and to develop new therapeutic strategies. Timely and effective improvement of axonal transport impairment is particularly critical for the treatment of peripheral neuropathies.

Ameliorative effect of the oil components derived from sweet potato shochu on impaired short-term memory in mice after amyloid β25-35 injection

Sweet potato shochu oil is a by-product of shochu production and usually discarded although some physiological functions are considered. In this study, we investigated the effects of shochu oil on short-term memory using a murine model of spontaneous alternating behavior induced by the intracerebroventricular (ICV) administration of amyloid β_25-35 (Aβ_25-35). Mice were orally administered shochu oil for 15 days. Experiments with a Y-maze model revealed that the Aβ_25-35 caused a significant decrease in spontaneous alternation behavior, and supplementation with shochu oil significantly improved this behavior. DNA microarray analysis revealed that the administration of shochu oil downregulated the expression of S100a9 and Ptgs2, which reportedly exacerbate amyloid β deposition in Alzheimer's disease. The administration of shochu oil upregulated the expression of Dnaja1 and PP2A, which is typically downregulated in Alzheimer's disease. These data suggest that shochu oil possible ameliorates on impaired short-term memory in mice after amyloid β_25-35 injection, as indicated by its effects on improving spontaneous alternation behavior and modulating the expressions of related genes.

Corneal dendritic cells in diabetes mellitus: A narrative review

Diabetes mellitus is a global public health problem with both macrovascular and microvascular complications, such as diabetic corneal neuropathy (DCN). Using in-vivo confocal microscopy, corneal nerve changes in DCN patients can be examined. Additionally, changes in the morphology and quantity of corneal dendritic cells (DCs) in diabetic corneas have also been observed. DCs are bone marrow-derived antigen-presenting cells that serve both immunological and non-immunological roles in human corneas. However, the role and pathogenesis of corneal DC in diabetic corneas have not been well understood. In this article, we provide a comprehensive review of both animal and clinical studies that report changes in DCs, including the DC density, maturation stages, as well as relationships between the corneal DCs, corneal nerves, and corneal epithelium, in diabetic corneas. We have also discussed the associations between the changes in corneal DCs and various clinical or imaging parameters, including age, corneal nerve status, and blood metabolic parameters. Such information would provide valuable insight into the development of diagnostic, preventive, and therapeutic strategies for DM-associated ocular surface complications.

Mechanisms behind diffuse idiopathic peripheral neuropathy in humans - a systematic review

Introduction: Diffuse peripheral neuropathy is a well-known complication of several conditions, whereas many patients have peripheral neuropathy of unknown etiology and pathophyisology. Increased knowledge of mechanisms may provide insight into enteric neuropathy with gastrointestinal dysmotility. The aim of the present systematic review was to identify mechanisms behind diffuse idiopathic peripheral neuropathies in humans.Methods: Searches were performed in PubMed, Embase, and Web of Science. Human original and review articles, written in English, describing mechanisms behind diffuse peripheral neuropathy verified by objective examinations were intended to be studied. Articles that described animal models, well-described hereditary diseases, drug-induced neuropathy, pain syndromes, malnutrition, and local neuropathy were excluded.Results: In total, 4712 articles were identified. After scrutinizing titles and abstracts, 633 remained and were studied in full text. After the removal of articles not fulfilling inclusion or exclusion criteria, 52 were finally included in this review. The most frequently described neuropathy was diabetic neuropathy, with a wide range of mechanisms involving mitochondrial dysfunction such as oxidative stress and inflammation. Microvascular changes in diabetes and vasculitis lead to ischemia and secondary oxidative stress with inflammation. Structural changes in neurons and glial cells are observed, with abnormalities in different neurotrophic factors. Neuropathy induced by autoantibodies or immunological mechanisms is described in infectious and systemic inflammatory diseases. Several ion channels may be involved in painful neuropathy. No study identified why some patients mainly develop large fiber neuropathy and others small fiber neuropathy.Conclusion: Metabolic and immunological factors and channelopathy may be considered in diffuse idiopathic peripheral neuropathy.

An induced pluripotent stem cell-based model identifies molecular targets of vincristine neurotoxicity

To model peripheral nerve degeneration and investigate molecular mechanisms of neurodegeneration, we established a cell system of induced pluripotent stem cell (iPSC)-derived sensory neurons exposed to vincristine, a drug that frequently causes chemotherapy-induced peripheral neuropathy. Sensory neurons differentiated from iPSCs exhibit distinct neurochemical patterns according to the immunocytochemical phenotypes, and gene expression of peripherin (PRPH, hereafter referred to as Peri) and neurofilament heavy chain (NEFH, hereafter referred to as NF). The majority of iPSC-derived sensory neurons were PRPH positive/NEFH negative, i.e. Peri(+)/NF(-) neurons, whose somata were smaller than those of Peri(+)/NF(+) neurons. On exposure to vincristine, projections from the cell body of a neuron, i.e. neurites, were degenerated quicker than somata, the lethal concentration to kill 50% (LC50) of neurites being below the LC50 for somata, consistent with the clinical pattern of length-dependent neuropathy. We then examined the molecular expression in the MAP kinase signaling pathways of, extracellular signal-regulated kinases 1/2 (MAPK1/3, hereafter referred to as ERK), p38 mitogen-activated protein kinases (MAPK11/12/13/14, hereafter referred to as p38) and c-Jun N-terminal kinases (MAPK8/9/10, hereafter referred to as JNK). Regarding these three cascades, only phosphorylation of JNK was upregulated but not that of p38 or ERK1/2. Furthermore, vincristine-treatment resulted in impaired autophagy and reduced autophagic flux. Rapamycin-treatment reversed the effect of impaired autophagy and JNK activation. These results not only established a platform to study peripheral degeneration of human neurons but also provide molecular mechanisms for neurodegeneration with the potential for therapeutic targets.

Voltage-gated sodium channels in diabetic sensory neuropathy: Function, modulation, and therapeutic potential

Voltage-gated sodium channels (Na V ) are the main contributors to action potential generation and essential players in establishing neuronal excitability. Na V channels have been widely studied in pain pathologies, including those that develop during diabetes. Diabetic sensory neuropathy (DSN) is one of the most common complications of the disease. DSN is the result of sensory nerve damage by the hyperglycemic state, resulting in a number of debilitating symptoms that have a significant negative impact in the quality of life of diabetic patients. Among those symptoms are tingling and numbness of hands and feet, as well as exacerbated pain responses to noxious and non-noxious stimuli. DSN is also a major contributor to the development of diabetic foot, which may lead to lower limb amputations in long-term diabetic patients. Unfortunately, current treatments fail to reverse or successfully manage DSN. In the current review we provide an updated report on Na V channels including structure/function and contribution to DSN. Furthermore, we summarize current research on the therapeutic potential of targeting Na V channels in pain pathologies, including DSN.

Unleashing Intrinsic Growth Pathways in Regenerating Peripheral Neurons

Common mechanisms of peripheral axon regeneration are recruited following diverse forms of damage to peripheral nerve axons. Whether the injury is traumatic or disease related neuropathy, reconnection of axons to their targets is required to restore function. Supporting peripheral axon regrowth, while not yet available in clinics, might be accomplished from several directions focusing on one or more of the complex stages of regrowth. Direct axon support, with follow on participation of supporting Schwann cells is one approach, emphasized in this review. However alternative approaches might include direct support of Schwann cells that instruct axons to regrow, manipulation of the inflammatory milieu to prevent ongoing bystander axon damage, or use of inflammatory cytokines as growth factors. Axons may be supported by a growing list of growth factors, extending well beyond the classical neurotrophin family. The understanding of growth factor roles continues to expand but their impact experimentally and in humans has faced serious limitations. The downstream signaling pathways that impact neuron growth have been exploited less frequently in regeneration models and rarely in human work, despite their promise and potency. Here we review the major regenerative signaling cascades that are known to influence adult peripheral axon regeneration. Within these pathways there are major checkpoints or roadblocks that normally check unwanted growth, but are an impediment to robust growth after injury. Several molecular roadblocks, overlapping with tumour suppressor systems in oncology, operate at the level of the perikarya. They have impacts on overall neuron plasticity and growth. A second approach targets proteins that largely operate at growth cones. Addressing both sites might offer synergistic benefits to regrowing neurons. This review emphasizes intrinsic aspects of adult peripheral axon regeneration, emphasizing several molecular barriers to regrowth that have been studied in our laboratory.

Recent updates in the treatment of diabetic polyneuropathy

Distal symmetric diabetic peripheral polyneuropathy (DPN) is the most common form of neuropathy in the world, affecting 30 to 50% of diabetic individuals and resulting in significant morbidity and socioeconomic costs. This review summarizes updates in the diagnosis and management of DPN. Recently updated clinical criteria facilitate bedside diagnosis, and a number of new technologies are being explored for diagnostic confirmation in specific settings and for use as surrogate measures in clinical trials. Evolving literature indicates that distinct but overlapping mechanisms underlie neuropathy in type 1 versus type 2 diabetes, and there is a growing focus on the role of metabolic factors in the development and progression of DPN. Exercise-based lifestyle interventions have shown therapeutic promise. A variety of potential disease-modifying and symptomatic therapies are in development. Innovations in clinical trial design include the incorporation of detailed pain phenotyping and biomarkers for central sensitization.

Impaired wound healing in diabetes

Impaired wound healing for patients with diabetes is due to a constellation of structural, biochemical, cellular and microbial factors. Hyperglycaemia and its associated inflammation contribute to immune dysfunction, vascular damage, neuropathy, cellular senescence, impaired transition beyond the inflammatory stage, microbiome disruptions, failed extracellular matrix formation, growth factor and cytokine imbalance, limited re-epithelialisation, and alterations in fibroblast migration and proliferation. Optimising glycaemic control remains the primary intervention to prevent continual dysfunction and comorbid disease progression.

Protein pyrrole adducts are associated with elevated glucose indices and clinical features of diabetic diffuse neuropathies

INTRODUCTION

Diabetic neuropathy is the most prevalent complication of diabetes mellitus. Although the precise etiology of this neurological disorder has yet to be defined, elevated blood glucose promotes anerobic glycolysis; this produces excess advanced glycation end-products, many of which have a pyrrole structure. Here, we test the hypothesis that protein pyrrole adducts are associated with elevated glucose indices and some clinical features of diabetic diffuse neuropathies.

METHOD

We investigated the levels of plasma pyrrole adducts and adjusted urinary pyrrole adducts in a group of elderly persons (n = 516, age 60-79) residing in the District of Luohu, Shenzhen, China between 2017 and 2018. Symptoms of distal symmetric polyneuropathy (DSPN) and resting heart rate, a measure of autonomic nervous system function, were collected from participants (n = 258) with elevated glucose indices.

RESULT

Protein pyrrole adducts showed a strong correlation with glucose indices before and after adjustment for age and estimated glomerular filtration rates. Stratified analysis showed that the medians and interquartile values of pyrrole adducts grew as glucose indices of the subgroups increased. Participants with symptoms of DSPN and sinus tachycardia presented elevated levels of plasma pyrrole adducts.

CONCLUSION

This study provides a novel link between glucose indices and the etiology of diabetic diffuse neuropathies.

Liraglutide Attenuates Glucolipotoxicity-Induced RSC96 Schwann Cells’ Inflammation and Dysfunction

Diabetic neuropathy (DN) is a type of sensory nerve damage that can occur in patients with diabetes. Although the understanding of pathophysiology is incomplete, DN is often associated with structural and functional alterations of the affected neurons. Among all possible causes of nerve damage, Schwann cells (SCs) are thought to play a key role in repairing peripheral nerve injury, suggesting that functional deficits occurring in SCs may potentially exhibit their pathogenic roles in DN. Therefore, elucidating the mechanisms that underlie this pathology can be used to develop novel therapeutic targets. In this regard, glucagon-like peptide-1 receptor agonists (GLP-1 RAs) have recently attracted great attention in ameliorating SCs’ dysfunction. However, the detailed mechanisms remain uncertain. In the present study, we investigated how GLP-1 RA Liraglutide protects against RSC96 SCs dysfunction through a diabetic condition mimicked by high glucose and high free fatty acid (FFA). Our results showed that high glucose and high FFAs reduced the viability of RSC96 SCs by up to 51%, whereas Liraglutide reduced oxidative stress by upregulating antioxidant enzymes, and thus protected cells from apoptosis. Liraglutide also inhibited NFκB-mediated inflammation, inducing SCs to switch from pro-inflammatory cytokine production to anti-inflammatory cytokine production. Moreover, Liraglutide upregulated the production of neurotrophic factors and myelination-related proteins, and these protective effects appear to be synergistically linked to insulin signaling. Taken together, our findings demonstrate that Liraglutide ameliorates diabetes-related SC dysfunction through the above-mentioned mechanisms, and suggest that modulating GLP-1 signaling in SCs may be a promising strategy against DN.

Adipose mTORC2 is essential for sensory innervation in white adipose tissue and whole-body energy homeostasis

OBJECTIVE

Adipose tissue, via sympathetic and possibly sensory neurons, communicates with the central nervous system (CNS) to mediate energy homeostasis. In contrast to the sympathetic nervous system, the morphology, role and regulation of the sensory nervous system in adipose tissue are poorly characterized.

METHODS AND RESULTS

Taking advantage of recent progress in whole-mount three-dimensional imaging, we identified a network of calcitonin gene-related protein (CGRP)-positive sensory neurons in murine white adipose tissue (WAT). We found that adipose mammalian target of rapamycin complex 2 (mTORC2), a major component of the insulin signaling pathway, is required for arborization of sensory neurons, but not of sympathetic neurons. Time course experiments revealed that adipose mTORC2 is required for maintenance of sensory neurons. Furthermore, loss of sensory innervation in WAT coincided with systemic insulin resistance. Finally, we established that neuronal protein growth-associated protein 43 (GAP43) is a marker for sensory neurons in adipose tissue.

CONCLUSION

Our findings indicate that adipose mTORC2 is necessary for sensory innervation in WAT. In addition, our results suggest that WAT may affect whole-body energy homeostasis via sensory neurons.

The Role of Long Noncoding RNA MALAT1 in Diabetic Polyneuropathy and the Impact of Its Silencing in the Dorsal Root Ganglion by a DNA/RNA Heteroduplex Oligonucleotide

Diabetic polyneuropathy (DPN) is the most common complication of diabetes, yet its pathophysiology has not been established. Accumulating evidence suggests that long noncoding RNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) plays pivotal roles in the regulation of cell growth and survival during diabetic complications. This study aimed to investigate the impact of MALAT1 silencing in dorsal root ganglion (DRG) sensory neurons, using an α-tocopherol-conjugated DNA/RNA heteroduplex oligonucleotide (Toc-HDO), on the peripheral nervous system of diabetic mice. We identified MALAT1 upregulation in the DRG of chronic diabetic mice that suggested either a pathological change or one that might be protective, and systemic intravenous injection of Toc-HDO effectively inhibited its gene expression. However, we unexpectedly noted that this intervention paradoxically exacerbated disease with increased thermal and mechanical nociceptive thresholds, indicating further sensory loss, greater sciatic-tibial nerve conduction slowing, and additional declines of intraepidermal nerve fiber density in the hind paw footpads. Serine/arginine-rich splicing factors, which are involved in pre-mRNA splicing by interacting with MALAT1, reside in nuclear speckles in wild-type and diabetic DRG neurons; MALAT1 silencing was associated with their disruption. The findings provide evidence for an important role that MALAT1 plays in DPN, suggesting neuroprotection and regulation of pre-mRNA splicing in nuclear speckles. This is also the first example in which a systemically delivered nucleotide therapy had a direct impact on DRG diabetic neurons and their axons.

Increased serum levels of advanced glycation end products are negatively associated with relative muscle strength in patients with type 2 diabetes mellitus

BACKGROUND

In this study, we investigated whether serum levels of advanced glycation end products (AGEs) independently correlated with relative muscle strength after adjustment for clinical variables including diabetic peripheral neuropathy in patients with type 2 diabetes. Relative muscle strength was defined as muscle strength (in decinewtons, dN) divided by total muscle mass (in kg).

METHODS

We enrolled 152 ambulatory patients with type 2 diabetes. Each participant underwent measurements of muscle strength and total muscle mass. Serum levels of AGEs were determined. The Michigan Neuropathy Screening Instrument Physical Examination (MNSI-PE) was performed to assess diabetic peripheral neuropathy.

RESULTS

The participants were divided into three groups on the basis of tertiles of serum AGEs levels. Significant differences were observed among the three groups in relative handgrip strength (71.03 ± 18.22, 63.17 ± 13.82, and 61.47 ± 13.95 dN/kg in the low-tertile, mid-tertile, and high-tertile groups, respectively, P = 0.005). The relative muscle strength of the ankle plantar flexors was higher in the low-tertile group than in the mid-tertile and high-tertile groups (107.60 ± 26.53, 94.97 ± 19.72, and 94.18 ± 16.09 dN/kg in the low-tertile, mid-tertile, and high-tertile groups, respectively, P = 0.002). After adjustment for MNSI-PE score and other clinical variables in partial correlation analysis, the correlations between serum levels of AGEs and the relative muscle strength of handgrip, ankle dorsiflexor, and ankle plantar flexor remained significant. Serum AGEs level was the only variable that remained significantly related to the relative muscle strength of handgrip, ankle dorsiflexor, and ankle plantar flexor when AGEs level, fasting plasma glucose, and glycated hemoglobin (HbA_1c) were entered into multiple regression models simultaneously.

CONCLUSIONS

After adjustment for multiple factors including diabetic peripheral neuropathy, this study demonstrated that increased serum levels of AGEs were independently associated with decreased relative muscle strength in patients with type 2 diabetes. Compared with fasting plasma glucose and HbA_1c, serum level of AGEs is more strongly associated with relative muscle strength.

Kir6.2-deficient mice develop somatosensory dysfunction and axonal loss in the peripheral nerves

Glucose-responsive ATP-sensitive potassium channels (K_ATP) are expressed in a variety of tissues including nervous systems. The depolarization of the membrane potential induced by glucose may lead to hyperexcitability of neurons and induce excitotoxicity. However, the roles of K_ATP in the peripheral nervous system (PNS) are poorly understood. Here, we determine the roles of K_ATP in the PNS using K_ATP-deficient (Kir6.2-deficient) mice. We demonstrate that neurite outgrowth of dorsal root ganglion (DRG) neurons was reduced by channel closers sulfonylureas. However, a channel opener diazoxide elongated the neurite. K_ATP subunits were expressed in mouse DRG, and expression of certain subunits including Kir6.2 was increased in diabetic mice. In Kir6.2-deficient mice, the current perception threshold, thermal perception threshold, and sensory nerve conduction velocity were impaired. Electron microscopy revealed a reduction of unmyelinated and small myelinated fibers in the sural nerves. In conclusion, K_ATP may contribute to the development of peripheral neuropathy.

Treatment for Diabetic Peripheral Neuropathy: What have we Learned from Animal Models?

INTRODUCTION

Animal models have been widely used to investigate the etiology and potential treatments for diabetic peripheral neuropathy. What we have learned from these studies and the extent to which this information has been adapted for the human condition will be the subject of this review article.

METHODS

A comprehensive search of the PubMed database was performed, and relevant articles on the topic were included in this review.

RESULTS

Extensive study of diabetic animal models has shown that the etiology of diabetic peripheral neuropathy is complex, with multiple mechanisms affecting neurons, Schwann cells, and the microvasculature, which contribute to the phenotypic nature of this most common complication of diabetes. Moreover, animal studies have demonstrated that the mechanisms related to peripheral neuropathy occurring in type 1 and type 2 diabetes are likely different, with hyperglycemia being the primary factor for neuropathology in type 1 diabetes, which contributes to a lesser extent in type 2 diabetes, whereas insulin resistance, hyperlipidemia, and other factors may have a greater role. Two of the earliest mechanisms described from animal studies as a cause for diabetic peripheral neuropathy were the activation of the aldose reductase pathway and increased non-enzymatic glycation. However, continuing research has identified numerous other potential factors that may contribute to diabetic peripheral neuropathy, including oxidative and inflammatory stress, dysregulation of protein kinase C and hexosamine pathways, and decreased neurotrophic support. In addition, recent studies have demonstrated that peripheral neuropathy-like symptoms are present in animal models, representing pre-diabetes in the absence of hyperglycemia.

CONCLUSION

This complexity complicates the successful treatment of diabetic peripheral neuropathy, and results in the poor outcome of translating successful treatments from animal studies to human clinical trials.

Exercise as Treatment for Neuropathy in the Setting of Diabetes and Prediabetic Metabolic Syndrome: A Review of Animal Models and Human Trials

BACKGROUND

Peripheral neuropathy is among the most common complications of diabetes, but a phenotypically identical distal sensory predominant, painful axonopathy afflicts patients with prediabetic metabolic syndrome, exemplifying a spectrum of risk and continuity of pathogenesis. No pharmacological treatment convincingly improves neuropathy in the setting of metabolic syndrome, but evolving data suggest that exercise may be a promising alternative.

OBJECTIVE

The aim of the study was to review in depth the current literature regarding exercise treatment of metabolic syndrome neuropathy in humans and animal models, highlight the diverse mechanisms by which exercise exerts beneficial effects, and examine adherence limitations, safety aspects, modes and dose of exercise.

RESULTS

Rodent models that recapitulate the organismal milieu of prediabetic metabolic syndrome and the phenotype of its neuropathy provide a strong platform to dissect exercise effects on neuropathy pathogenesis. In these models, exercise reverses hyperglycemia and consequent oxidative and nitrosative stress, improves microvascular vasoreactivity, enhances axonal transport, ameliorates the lipotoxicity and inflammatory effects of hyperlipidemia and obesity, supports neuronal survival and regeneration following injury, and enhances mitochondrial bioenergetics at the distal axon. Prospective human studies are limited in scale but suggest exercise to improve cutaneous nerve regenerative capacity, neuropathic pain, and task-specific functional performance measures of gait and balance. Like other heath behavioral interventions, the benefits of exercise are limited by patient adherence.

CONCLUSION

Exercise is an integrative therapy that potently reduces cellular inflammatory state and improves distal axonal oxidative metabolism to ameliorate features of neuropathy in metabolic syndrome. The intensity of exercise need not improve cardinal features of metabolic syndrome, including weight, glucose control, to exert beneficial effects.

Changes in and the association of retinal blood perfusion and retinal nerves in diabetic patients without retinopathy

OBJECTIVE

To explore intraretinal blood flow perfusion and nerve changes, as well as the correlation between them, in diabetic patients without diabetic retinopathy (NDR).

METHOD

Eighty-six NDR patients (86 eyes) who attended the ophthalmology clinic between December 2019 and December 2021 were included. Sixty-four eyes of 64 healthy examined controls in the same period were selected as the control group. The patients underwent routine ophthalmological examination, optical coherence tomography (OCT) and OCT angiography.

RESULTS

The average thickness, minimum thickness and thickness of each quadrant except for the superior temporal quadrant of the ganglion cell-inner plexiform layer (GCIPL) in the macular area of the affected eyes in the NDR group were lower than that of the tested eyes in the control group (P < 0.05). The average retinal nerve fibre layer (RNFL) thickness of the NDR group and the superior, inferior and nasal quadrants around the optic disc of the affected eyes in the NDR group were lower compared with the tested eyes in the control group (P < 0.001, P = 0.003, P = 0.001, P = 0.009). The mean vessel length density in the parafoveal and perifoveal areas in the NDR group was positively associated with the mean GCIPL thickness in the macular area (ρ = 0.265, ρ = 0.257 and P < 0.001). No blood flow perfusion parameters in the NDR group were correlated with the RNFL thickness of the corresponding quadrant around the optic disc (P > 0.05).

CONCLUSION

In diabetic patients without diabetic retinopathy, the superficial retinal vessel density in the macular area positively correlated with GCIPL thickness, and the superficial retinal vessel density around the optic disc was not correlated with RNFL thickness.

Diabetic Gastroenteropathy: Soothe the Symptoms or Unravel a Cure?

Autonomic neuropathy in patients with diabetes mellitus, and especially complications related to gastrointestinal neuropathy, are often overlooked in the clinic. Diabetic gastroenteropathy affects every segment of the gastrointestinal tract and generates symptoms that may include nausea, early satiety, vomiting, abdominal pain, constipation, and diarrhea. Severe cases can be complicated by weight loss, dehydration, and electrolyte disturbances. The pathophysiology is complex, the diagnostics and treatment options are multidisciplinary, and there is generally a lack of evidence for the treatment options. The aims for this review are first to summarize the pathophysiology and describe possible and expected symptoms and complications.Further, we will try to supply the clinician with a straightforward tool for diagnostics, and then, we shall summarize established treatment options, including diet recommendations, pharmacological and non-pharmacological options. Finally, we will explore the multiple possibilities of novel treatment, looking at medications related to the pathophysiology of neuropathy, other manifestations of autonomic neuropathies, and symptomatic treatment for other gastrointestinal disorders, also including new knowledge of endosurgical and neuromodulatory treatment. The overall goal is to increase awareness and knowledge on this frequent diabetic complication and to provide better tools for diagnosis and treatment. Ultimately, we hope to encourage further research in this field, as there are clear shortcomings in terms of biomarkers, pathophysiology, as well as treatment possibilities. In conclusion, diagnosis and management of diabetic gastroenteropathy are challenging and often require multidisciplinary teams and multimodal therapies. Treatment options are sparse, but new pharmacological, endoscopic, and neuromodulatory techniques have shown promising results in initial studies.

Recent updates in the treatment of diabetic polyneuropathy

Distal symmetric diabetic peripheral polyneuropathy (DPN) is the most common form of neuropathy in the world, affecting 30 to 50% of diabetic individuals and resulting in significant morbidity and socioeconomic costs. This review summarizes updates in the diagnosis and management of DPN. Recently updated clinical criteria facilitate bedside diagnosis, and a number of new technologies are being explored for diagnostic confirmation in specific settings and for use as surrogate measures in clinical trials. Evolving literature indicates that distinct but overlapping mechanisms underlie neuropathy in type 1 versus type 2 diabetes, and there is a growing focus on the role of metabolic factors in the development and progression of DPN. Exercise-based lifestyle interventions have shown therapeutic promise. A variety of potential disease-modifying and symptomatic therapies are in development. Innovations in clinical trial design include the incorporation of detailed pain phenotyping and biomarkers for central sensitization.

Covering the Role of PGC-1α in the Nervous System

The peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) is a well-known transcriptional coactivator involved in mitochondrial biogenesis. PGC-1α is implicated in the pathophysiology of many neurodegenerative disorders; therefore, a deep understanding of its functioning in the nervous system may lead to the development of new therapeutic strategies. The central nervous system (CNS)-specific isoforms of PGC-1α have been recently identified, and many functions of PGC-1α are assigned to the particular cell types of the central nervous system. In the mice CNS, deficiency of PGC-1α disturbed viability and functioning of interneurons and dopaminergic neurons, followed by alterations in inhibitory signaling and behavioral dysfunction. Furthermore, in the ALS rodent model, PGC-1α protects upper motoneurons from neurodegeneration. PGC-1α is engaged in the generation of neuromuscular junctions by lower motoneurons, protection of photoreceptors, and reduction in oxidative stress in sensory neurons. Furthermore, in the glial cells, PGC-1α is essential for the maturation and proliferation of astrocytes, myelination by oligodendrocytes, and mitophagy and autophagy of microglia. PGC-1α is also necessary for synaptogenesis in the developing brain and the generation and maintenance of synapses in postnatal life. This review provides an outlook of recent studies on the role of PGC-1α in various cells in the central nervous system.

Exercise and Neuropathy: Systematic Review with Meta-Analysis

INTRODUCTION

Peripheral neuropathies are a prevalent, heterogeneous group of diseases of the peripheral nervous system. Symptoms are often debilitating, difficult to treat, and usually become chronic. Not only do they diminish patients' quality of life, but they can also affect medical therapy and lead to complications. To date, for most conditions there are no evidence-based causal treatment options available. Research has increased considerably since the last review in 2014 regarding the therapeutic potential of exercise interventions for patients with polyneuropathy.

OBJECTIVE

Our objective in this systematic review with meta-analysis was to analyze exercise interventions for neuropathic patients in order to update a systematic review from 2014 and to evaluate the potential benefits of exercise on neuropathies of different origin that can then be translated into practice.

METHODS

Two independent reviewers performed a systematic review with meta-analysis according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Inclusion criteria according to the PICOS approach were: neuropathic patients, exercise interventions only, an inactive or non-exercising control group, and solely randomized controlled trials with the following outcome parameters: neuropathic symptoms, balance parameters, functional mobility, gait, health-related quality of life, and HbA1c (glycated hemoglobin).

RESULTS

A total of 41 randomized, controlled trials met all inclusion criteria, 20 of which could be included in the quantitative analysis. Study quality varied from moderate to high. Current data further support the hypothesis that exercise is beneficial for neuropathic patients. This is best documented for patients with diabetic peripheral neuropathy (DPN) (27 studies) as well as for chemotherapy-induced peripheral neuropathy (CIPN) (nine studies), while there are only few studies (five) on all other causes of neuropathy. We found standardized mean differences in favor of the exercise group of 0.27-2.00 for static balance, Berg Balance Scale, Timed-up-and-go-test, nerve conduction velocity of peroneal and sural nerve as well as for HbA1c in patients with DPN, and standardized mean differences of 0.43-0.75 for static balance, quality of life, and neuropathy-induced symptoms in patients with CIPN.

CONCLUSION

For DPN, evidence-based recommendations can now be made, suggesting a combination of endurance and sensorimotor training to be most beneficial. For patients with CIPN, sensorimotor training remains the most crucial component. For all other neuropathies, more high-quality research is needed to derive evidence-based recommendations. Overall, it seems that sensorimotor training has great potential to target most neuropathies and combined with endurance training is therefore currently the best treatment option for neuropathies. REGISTRATION NUMBER: (PROSPERO 2019 CRD42019124583)/16.04.2019.

Ablation of transient receptor potential vanilloid subtype 1-expressing neurons in rat trigeminal ganglia aggravated bone resorption in periodontitis with diabetes

OBJECTIVES

We aimed to investigate the contribution of neurons expressing transient receptor potential vanilloid subtype 1 (TRPV1) to alveolar bone homeostasis in periodontitis with diabetes.

DESIGN

Diabetes was induced by streptozotocin injection in Sprague-Dawley rats. Resiniferatoxin was injected into left trigeminal ganglia to ablate TRPV1-expressing neurons. 3-0 silks were tied around left maxillary second molars to induce experimental periodontitis. Alveolar bone was assessed by micro-computed tomography and tartrate-resistant acid phosphatase staining. Macrophages were detected by immunohistochemistry staining.

RESULTS

TRPV1 expression in trigeminal ganglia was increased in diabetic rats compared to non-diabetic counterparts. Local ablation of TRPV1 eliminated facial heat hyperalgesia but aggravated alveolar bone damage and osteoclastogenesis in experimental periodontitis in both diabetic and non-diabetic rats. Immunohistochemistry staining presented enhanced macrophage infiltration and M1 macrophage polarization in periodontal lesions in TRPV1-ablated groups.

CONCLUSIONS

These findings demonstrated that TRPV1 expression in trigeminal ganglia could be enhanced in diabetic condition, and the integrity of TRPV1-expressing neurons in trigeminal ganglia exerted a neuroprotective effect against alveolar bone resorption and inflammation in diabetic periodontitis.

Paeoniflorin Effect of Schwann Cell-Derived Exosomes Ameliorates Dorsal Root Ganglion Neurons Apoptosis through IRE1α Pathway

Background

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes but its pathogenesis is not fully clarified. Endoplasmic reticulum (ER) stress has been confirmed to be involved in the development of DPN. Dorsal root ganglion neuron (DRGn) is the target cell of DPN injure in the peripheral neurons system. Schwann cell (SCs)-derived exosomes (SC-EXOs) can carry IRE1α signal transduction factors in ER stress to DRGn. The aim of this study is to investigate the effect of SC-EXOs treated with paeoniflorin (PF) on DRGn stimulated by high glucose.

Methods

SCs were divided into Control group (Control), 150 mM glucose group (HG), high osmotic pressure group (HOP), and low, middle, and high dose PF group (PF1, PF10, and PF100). Exosomes were obtained from SCs by ultracentrifugation and identified according to marker proteins, including CD63, Alix, Hsp70, and TSG101. ER stress initiating factor GRP78, the IRE1α pathway information transmission factor IRE1α, and the phosphorylation level of IRE1α were detected by Western blot, DRGn is divided into Control group (Control), 50 mM glucose group + Control exosomes group (HG + EXOs Control), 50 mM glucose group (HG), and 50 mM glucose group + administration exosomes group (HG + EXOs PF1, HG + EXOs PF10, and HG + EXOs PF100); ER morphology of primary DRGn was observed by using the transmission electron microscope, the level of DRGn apoptosis was analyzed by TUNEL, and the downstream proteins of ER stress including CHOP, XBP1S, JNK, and p-JNK in DRG and the expression of apoptosis-related proteins Bcl-2, Bax, Caspase-3, and Caspase-12 were measured by Western blot.

Results

Compared with the exosomes in the HG group, the exosomes after the intervention of PF can significantly reduce the expression of GRP78, IRE1α, and the phosphorylation level of IRE1α(P < 0.05); compared with the DRGn in the HG group, the SC-EXOs treated with PF could regulate the expression of proteins downstream of IRE1α pathway in ER stress (P < 0.05 or P < 0.01), improve the morphological integrity of ER, and reduce apoptosis in DRGn (P < 0.05 or P < 0.01).

Conclusion

PF regulates the information of ER stress carried by SC-EXOs and further affects downstream of IRE1α pathway in DRGn, thus reducing ER stress-induced apoptosis. PF can interfere with DPN through affecting information communication carried by EXOs between SCs and DRGn.

Systemic inflammatory biomarkers in painful diabetic neuropathy

OBJECTIVES

We conducted a systematic review of the literature with meta-analysis to determine whether painful diabetic neuropathy is associated with a specific inflammatory profile.

METHODS

The study is based on the PRISMA statement for systematic reviews. We performed a search of published studies up until January 2021 in MEDLINE and Web of Science based on heading and free text terms. The search strategy included the phrases: diabetic peripheral neuropathy, painful peripheral neuropathy individually and in combination with the terms: inflammation and inflammatory biomarkers. We screened titles and abstracts and performed data extraction. We also manually searched the article titles in the reference lists of key studies and reviews published in the last 20 years.

DATA EXTRACTION

Data extracted from the studies included study design, inclusion and exclusion criteria, sample type including serum and plasma, source of the sample including patients with peripheral diabetic neuropathy or patients with painful and painless neuropathy of any etiology. Blood concentrations of all measured cytokines were recorded. Whenever possible we calculated the effect size and confidence interval. Non-human studies were excluded from the meta-analysis.

RESULTS

Thirteen studies were included in this meta-analysis. The study design was cross-sectional, case control or cohort type studies. Specific inflammatory mediators are significantly higher in painful than in painless diabetic neuropathy as well as in painful neuropathies of any etiology. Markers of inflammation are also increased in those patients with diabetes mellitus, who suffer from peripheral neuropathy in comparison to patients with diabetes mellitus but no signs of peripheral neuropathy. A proinflammatory state may be the common denominator of pain and peripheral neuropathy in patients with diabetes mellitus but the inflammatory profiles seem to differ.

Magnetic Resonance Neurography: Improved Diagnosis of Peripheral Neuropathies

Peripheral neuropathies account for the most frequent disorders seen by neurologists, and causes are manifold. The traditional diagnostic gold-standard consists of clinical neurologic examinations supplemented by nerve conduction studies. Due to well-known limitations of standard diagnostics and atypical clinical presentations, establishing the correct diagnosis can be challenging but is critical for appropriate therapies. Magnetic resonance neurography (MRN) is a relatively novel technique that was developed for the high-resolution imaging of the peripheral nervous system. In focal neuropathies, whether traumatic or due to nerve entrapment, MRN has improved the diagnostic accuracy by directly visualizing underlying nerve lesions and providing information on the exact lesion localization, extension, and spatial distribution, thereby assisting surgical planning. Notably, the differentiation between distally located, complete cross-sectional nerve lesions, and more proximally located lesions involving only certain fascicles within a nerve can hold difficulties that MRN can overcome, when basic technical requirements to achieve sufficient spatial resolution are implemented. Typical MRN-specific pitfalls are essential to understand in order to prevent overdiagnosing neuropathies. Heavily T2-weighted sequences with fat saturation are the most established sequences for MRN. Newer techniques, such as T2-relaxometry, magnetization transfer contrast imaging, and diffusion tensor imaging, allow the quantification of nerve lesions and have become increasingly important, especially when evaluating diffuse, non-focal neuropathies. Innovative studies in hereditary, metabolic or inflammatory polyneuropathies, and motor neuron diseases have contributed to a better understanding of the underlying pathomechanism. New imaging biomarkers might be used for an earlier diagnosis and monitoring of structural nerve injury under causative treatments in the future.

Management of diabetic neuropathy

Diabetic neuropathy is a neurodegenerative disorder that may alter both the somatic and autonomic peripheral nervous systems in the context of diabetes mellitus (DM). It is a prevalent and burdensome chronic complication of DM, that requires timely management. Optimized glycemic control (mainly for type 1 DM), multifactorial intervention (mainly for type 2 DM), with lifestyle intervention/physical exercise, and weight loss represent the basis of management for diabetic distal symmetrical polyneuropathy, and should be implemented early in the disease course. Despite better understanding of the pathogenetic mechanisms of diabetic peripheral neuropathy, there is still a stringent need for more pathogenetic-based agents that would significantly modify the natural history of the disease. The paper reviews the available drugs and current recommendations for the management of distal symmetrical polyneuropathy, including pain management, and for diabetic autonomic neuropathy. Evaluation of drug combinations that would perhaps be more efficient in slowing the progression of the disease or even reversing it, and that would provide a better pain management is still needed.

Efficacy, Pharmacokinetics, Biodistribution and Excretion of a Novel Acylated Long-Acting Insulin Analogue INS061 in Rats

Purpose

Long-acting insulin analogues are known to be a major player in the management of glucose levels in type I diabetic patients. However, highly frequent hypo- and hyperglycemic incidences of current long-acting insulins are the important factor to limit stable management of glucose level for clinical benefits. To further optimize the properties for steadily controlling glucose level, a novel long-acting insulin INS061 was designed and its efficacy, pharmacokinetics, biodistribution and excretion profiles were investigated in rats.

Methods

The glucose-lowering effects were evaluated in a streptozocin-induced diabetic rats compared to commercial insulins via subcutaneous administration. The pharmacokinetics, biodistribution, and excretion were examined by validated analytical methods including radioactivity assay and radioactivity assay after the precipitation with TCA and the separation by HPLC.

Results

INS061 exhibited favorable blood glucose lowering effects up to 24 h compared to Degludec. Pharmacokinetic study revealed that the concentration-time curves of INS061 between two administration routes were remarkably different. Following intravenous administration, INS061 was quickly distributed to various organs and tissues and slowly eliminated over time with urinary excretion being the major route for elimination, and the maximum plasma concentrations (Cmax) and systemic exposures (AUC) increased in a linear manner.

Conclusion

The present structural modifications of human insulin possessed a long-acting profile and glucose-lowering function along with favorable in vivo properties in rats, which establish a foundation for further preclinical and clinical evaluation.

TRPM8 Channels: Advances in Structural Studies and Pharmacological Modulation

The transient receptor potential melastatin subtype 8 (TRPM8) is a cold sensor in humans, activated by low temperatures (>10, <28 °C), but also a polymodal ion channel, stimulated by voltage, pressure, cooling compounds (menthol, icilin), and hyperosmolarity. An increased number of experimental results indicate the implication of TRPM8 channels in cold thermal transduction and pain detection, transmission, and maintenance in different tissues and organs. These channels also have a repercussion on different kinds of life-threatening tumors and other pathologies, which include urinary and respiratory tract dysfunctions, dry eye disease, and obesity. This compendium firstly covers newly described papers on the expression of TRPM8 channels and their correlation with pathological states. An overview on the structural knowledge, after cryo-electron microscopy success in solving different TRPM8 structures, as well as some insights obtained from mutagenesis studies, will follow. Most recently described families of TRPM8 modulators are also covered, along with a section of molecules that have reached clinical trials. To finalize, authors provide an outline of the potential prospects in the TRPM8 field.

Peripheral blood levels of CXCL10 are a useful marker for diabetic polyneuropathy in subjects with type 2 diabetes

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a chronic complication of diabetes mellitus associated with high morbidity and mortality. Major risk factors for DPN include metabolic changes, duration of diabetes, nerve ischaemia and derangements in regeneration and nerve repair programmes. Chemokines have been previously implicated in the pathogenesis of various neuropathies and neuropathic pain processes. The aim of this pilot study was to evaluate the association between the plasma levels of chemokines (CXCL9, CXCL10 and CXCL11) in the presence of DPN in a cohort of type 2 diabetes (T2D) patients.

MATERIALS AND METHODS

We studied 73 patients with T2D: 36 with DPN and 37 without DPN. DPN was established through the Semmes-Weinstein test (SW). Plasma levels of circulating chemokines CXCL9, CXCL10 and CXCL11 were determined using DuoSet ELISA kits (Abingdon, UK).

RESULTS

We found that levels of CXCL10 were significantly higher in patients with DPN than amongst patients without DPN (57.6 ± 38.3 vs 38.1 ± 33.4 pg/mL, respectively; P = .034). Serum levels of chemokine CXCL9 were also higher amongst patients with DPN but did not reach a statistical significance (188.1 ± 72.7 and 150.4 ± 83.6 pg/mL, respectively, P = .06).

CONCLUSIONS

Increased circulating levels of CXCL10 were associated with DPN in T2D patients, suggesting a role of this chemokine in the DPN. Determination of CXCL10 levels could be used as a marker for the early detection and implementation of therapeutic strategies in order to reverse and prevent the DPN.

Electrophysiological characteristics of patients with nitrous oxide abuse

Objective: In the young generations with nitrous oxide abuse (N₂O), featured electrophysiological response of the peripheral neuropathy caused by nitrous oxide remains to be defined.Methods: Patients with nitrous oxide abuse (20 cases), two variants of Guillain-Barré syndrome (GBS), that is, acute inflammatory demyelinating polyradiculoneuropathy (GBS-AIDP, 19 cases) and acute motor axonal neuropathy (GBS-AMAN, 18 cases), as well as diabetic peripheral neuropathy (DPN, 20 cases) were enrolled into this study. Electrophysiological parameters including distal motor latency (DML), motor nerve conduction velocity (MNCV), sensory nerve conduction velocity (SNCV), amplitudes of compound muscle action potential (CMAP), and sensory nerve action potential (SNAP) were measured and analyzed by comparing the parameters between the aforementioned patients groups as well as normal control group (20 subjects).Results: Compared to normal control subjects, patients with nitrous oxide abuse showed prolonged DML, slower MNCV and SNCV in the limbs, lower amplitudes of CMAP in the median, tibial and peroneal nerves, and lower SNAP in median and ulnar nerves. Abnormalities of MNCV and amplitudes of CMAP in the lower limbs were significantly higher than that in the upper limbs . Abnormal electrophysiological features of patients with nitrous oxide abuse were dramatically different from those in GBS-AIDP or DPN patients, but similar to those in GBS-AMAN patients.Conclusions: Nitrous oxide abuse could cause abnormal electrophysiological response in the limbs. Some of the parameters (DML, MNCV, SNCV, CMAP and SNAP) appeared significantly different between the patients with nitrous oxide abuse, GBS with AIDP or AMAN, and DPN patients.Significance: Electrophysiological examination could be considered as an important supporting factor in differential diagnosis for nitrous oxide abuse, GBS with AIDP or AMAN, and DPN.

Diabetic polyneuropathy: Bridging the translational gap

Clinical trials for diabetic polyneuropathy (DPN) have failed to identify therapeutic impacts that have arrested or reversed the disorder, despite a long history. This review considers DPN in the context of a unique neurodegenerative disorder that targets peripheral neurons and their companion glial cells. The approach is to examine what cells, cell substructures, and pathways are implicated in causing DPN and how they might be addressed therapeutically. These include axonopathy, neuronopathy, hyperglycemia, polyol flux, advanced glycation endproduct (AGE)-receptor AGE signaling, growth factor disruption, abnormal insulin signaling, and abnormalities of other intrinsic neuron pathways. Mitochondrial dysfunction and lipid toxicity are largely delegated to the companion review in this issue by Stino and Feldman. Finally, the linkage between axon plasticity of cutaneous nerves, peripheral neuroregenerative pathways, and diabetes are discussed.

Deciphering the Neuroprotective Role of Glucagon-like Peptide-1 Agonists in Diabetic Neuropathy: Current Perspective and Future Directions

Diabetic neuropathy is referred to as a subsequential and debilitating complication belonging to type 1 and type 2 diabetes mellitus. It is a heterogeneous group of disorders with a particularly complex pathophysiology and also includes multiple forms, ranging from normal discomfort to death. The evaluation of diabetic neuropathy is associated with hyperglycemic responses, resulting in an alteration in various metabolic pathways, including protein kinase C pathway, polyol pathway and hexosamine pathway in Schwann and glial cells of neurons. The essential source of neuronal destruction is analogous to these respective metabolic pathways, thus identified as potential therapeutic targets. These pathways regulating therapeutic medications may be used for diabetic neuropathy, however, only target specific drugs could have partial therapeutic activity. Various antidiabetic medications have been approved and marketed, which possess the therapeutic ability to control hyperglycemia and ameliorate the prevalence of diabetic neuropathy. Among all antidiabetic medications, incretin therapy, including Glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors, are the most favorable medications for the management of diabetes mellitus and associated peripheral neuropathic complications. Besides enhancing glucose-evoked insulin release from pancreatic β-cells, these therapeutic agents also play a vital role to facilitate neurite outgrowth and nerve conduction velocity in dorsal root ganglion. Furthermore, incretin therapy also activates cAMP and ERK signalling pathways, resulting in nerve regeneration and repairing. These effects are evidently supported by a series of preclinical data and investigations associated with these medications. However, the literature lacks adequate clinical trial outcomes related to these novel antidiabetic medications. The manuscript emphasizes the pathogenesis, current pharmacological approaches and vivid description of preclinical and clinical data for the effective management of diabetic neuropathy.

The Role of microRNAs in the Development of Type 2 Diabetes Complications

MicroRNAs represent a class of small (19-25 nucleotides) single-strand pieces of RNA that are noncoding ones. They are synthesized by RNA polymerase II from transcripts that fold back on themselves. They mostly act as gene regulatory agents that pair with complementary sequences on mRNA and produce silencing complexes, which, in turn, suppress coding genes at a post-transcriptional level. There is now evidence that microRNAs may affect insulin secretion or insulin action, as they can alter pancreatic beta cells development, insulin production, as well as insulin signaling. Any molecular disorder that affects these pathways can deteriorate insulin resistance and lead to type 2 diabetes mellitus (T2DM) onset. Furthermore, the expression of several microRNAs is up- or down-regulated in the presence of diabetic microvascular complications (i.e., peripheral neuropathy, nephropathy, retinopathy, foot ulcers), as well as in patients with coronary heart disease, stroke, and peripheral artery disease. However, more evidence is needed, specifically regarding T2DM patients, to establish the use of such microRNAs as diagnostical biomarkers or therapeutic targets in daily practice.