Mediators of diabetic neuropathy: is hyperglycemia the only culprit?

The Experience of Peripheral Neuropathy Symptoms in Breast Cancer Survivors With Diabetes

BACKGROUND

Diabetes (type 2) is a risk factor for developing peripheral neuropathy (PN) symptoms in breast cancer survivors (BCS). Because PN symptoms are associated with deficits in physical functioning and quality of life, more information is needed about the effects of PN symptoms on the lives of BCS with diabetes.

OBJECTIVE

The aim of this study was to describe the experiences of PN among BCS with diabetes from their own perspectives.

INTERVENTIONS/METHODS

This substudy is part of a larger investigation examining factors associated with cancer-related cognitive impairment in cancer survivors. Female early-stage (stage I-III) BCS with diabetes and PN symptoms were eligible to participate. A qualitative descriptive approach using purposive sampling and semistructured interviews was used. Participant narratives were summarized using standard content analytic techniques.

RESULTS

Eleven BCS with diabetes and PN symptoms were interviewed. Participants described PN symptoms that were varied, were often persistent, and had troublesome effects on their physical functioning and quality of life. Participants used a variety of self-management strategies and prescription and over-the-counter medications to manage their PN symptoms. Some said that having both cancer and diabetes exacerbated the PN symptoms and complicated symptom management.

CONCLUSION

Peripheral neuropathy symptoms can have a profound effect on the lives of BCS with diabetes and should be addressed by healthcare providers.

IMPLICATIONS FOR PRACTICE

Clinical care for this population should include ongoing assessment of PN symptoms, conversations about the effects of these symptoms on everyday life, evidence-based treatment for the symptoms, and support for symptom self-management.

Humanin's impact on pain markers and neuronal viability in diabetic neuropathy model

OBJECTIVE

This study investigates the impact of chronic humanin (HN) treatment on pain-related markers (NMDA, substance P, TRPV1, and IL-1β) in diabetic mice's dorsal root ganglia (DRG). Additionally, we assess the effects of HN on cellular viability in DRG neurons.

METHODS

In vivo experiments involved 15 days of HN administration (4 mg/kg) to diabetic mice (n = 10). Protein levels of NMDA, IL-1β, TRPV1, and substance P were measured in diabetic DRG. In vitro experiments explored HN's impact on apoptosis and cellular viability, focusing on the JAK2/STAT3 pathway.

RESULTS

Humanin significantly reduced the elevated expression of NMDA, IL-1β, TRPV1, and substance P induced by diabetes (p < .05). Furthermore, HN treatment increased cellular viability in DRG neurons through JAK2/STAT3 pathway activation (p < .05).

CONCLUSION

These findings highlight the significance of understanding mitochondrial function and pain markers, as well as apoptosis in diabetes. The study provides insights for managing the condition and its complications.

Research progress of the effective active ingredients of Astragalus mongholicus in the treatment of diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is one of the most prevalent consequences of diabetes, with a high incidence and disability rate. The DPN's pathogenesis is extremely complex and yet to be fully understood. Persistent high glucose metabolism, nerve growth factor deficiency, microvascular disease, oxidative stress, peripheral nerve cell apoptosis, immune factors, and other factors have been implicated in the pathogenesis of DPN. Astragalus mongholicus is a commonly used plant used to treat DPN in clinical settings. Its rich chemical components mainly include Astragalus polysaccharide, Astragalus saponins, Astragalus flavones, etc., which play a vital role in the treatment of DPN. This review aimed to summarize the pathogenesis of DPN and the studies on the mechanism of the effective components of Astragalus mongholicus in treating DPN. This is of great significance for the effective use of Chinese herbal medicine and the promotion of its status and influence on the world.

AMPK and Beyond: The Signaling Network Controlling RabGAPs and Contraction-Mediated Glucose Uptake in Skeletal Muscle

Impaired skeletal muscle glucose uptake is a key feature in the development of insulin resistance and type 2 diabetes. Skeletal muscle glucose uptake can be enhanced by a variety of different stimuli, including insulin and contraction as the most prominent. In contrast to the clearance of glucose from the bloodstream in response to insulin stimulation, exercise-induced glucose uptake into skeletal muscle is unaffected during the progression of insulin resistance, placing physical activity at the center of prevention and treatment of metabolic diseases. The two Rab GTPase-activating proteins (RabGAPs), TBC1D1 and TBC1D4, represent critical nodes at the convergence of insulin- and exercise-stimulated signaling pathways, as phosphorylation of the two closely related signaling factors leads to enhanced translocation of glucose transporter 4 (GLUT4) to the plasma membrane, resulting in increased cellular glucose uptake. However, the full network of intracellular signaling pathways that control exercise-induced glucose uptake and that overlap with the insulin-stimulated pathway upstream of the RabGAPs is not fully understood. In this review, we discuss the current state of knowledge on exercise- and insulin-regulated kinases as well as hypoxia as stimulus that may be involved in the regulation of skeletal muscle glucose uptake.

Biomarkers in diabetic neuropathy

CONTEXT

The prevalence of diabetic neuropathy is drastically increasing in the world. To halt the progression of diabetic neuropathy, there is an unmet need to have potential biomarkers for the diagnosis and new drug discovery.

OBJECTIVE

To study various biomarkers involved in the pathogenesis of diabetic neuropathy.

METHODS

The literature was searched with the help of various scientific databases and resources like PubMed, ProQuest, Scopus, and Google scholar from the year 1976 to 2020.

RESULTS

Biomarkers of diabetic neuropathy are categorised as inflammatory biomarkers such as MCP-1, VEGF, TRPV1, NF-κB; oxidative biomarkers such as adiponectin, NFE2L2; enzyme biomarkers like NADPH, ceruloplasmin, HO-1, DPP-4, PARP α; miscellaneous biomarkers such as SIRT1, caveolin 1, MALAT1, and microRNA. All biomarkers have a significant role in the pathogenesis of diabetic neuropathy.

CONCLUSION

These biomarkers have a potential role in the progression of diabetic neuropathy and can be considered as potential targets for new drug discovery.

Schwann cells-derived exosomal miR-21 participates in high glucose regulation of neurite outgrowth

As a common complication of diabetes, the pathogenesis of diabetic peripheral neuropathy (DPN) is closely related to high glucose but has not been clarified. Exosomes can mediate crosstalk between Schwann cells (SC) and neurons in the peripheral nerve. Herein, we found that miR-21 in serum exosomes from DPN rats was decreased. SC proliferation was inhibited, cell apoptosis was increased, and the expression of miR-21 in cells and exosomes was downregulated when cultured in high glucose. Increasing miR-21 expression reversed these changes, while knockdown of miR-21 led to the opposite results. When co-cultured with exosomes derived from SC exposed to high glucose, neurite outgrowth was inhibited. On the contrary, neurite outgrowth was accelerated when incubated with exosomes rich in miR-21. We further demonstrated that the SC-derived exosomal miR-21 participates in neurite outgrowth probably through the AKT signaling pathway. Thus, SC-derived exosomal miR-21 contributes to high glucose regulation of neurite outgrowth.

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The miR-21 was decreased in serum exosomes and sciatic nerve of DPN rats

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High glucose inhibited SC viability and downregulated the expression of miR-21

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Exosomes derived from SC cultured in high glucose inhibited the neurite outgrowth

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SC-derived exosomes rich in miR-21 accelerated the neurite outgrowth of neuron

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.

Obesity-Associated Neuropathy: Recent Preclinical Studies and Proposed Mechanisms

Significance: The prevalence of metabolic syndrome (MetS) and associated obesity has increased in recent years, affecting millions worldwide. One of the most common complications of obesity is damage to the peripheral nerve system, referred to as neuropathy. The lack of disease-modifying therapy for this complication is largely due to a poor understanding of the complex neurobiology underlying neuropathy. Recent preclinical studies suggest that in addition to glucotoxic events, other mechanisms, including lipid signaling, microbiome, or inflammation, may be viable targets to prevent nerve damage and neuropathic pain in obesity. Recent Advances: Clinical and preclinical studies using diet-induced obesity rodent models have identified novel interventions that improve neuropathy. Notably, mechanistic studies suggest that lipid, calcium signaling, and inflammation are converging pathways. Critical Issues: In this review, we focus on interventions and their mechanisms that are shown to ameliorate neuropathy in MetS obese models, including: (i) inhibition of a sensory neuron population, (ii), modification of dietary components, (iii) activation of nuclear and mitochondrial lipid pathways, (iv) exercise, and (v) modulation of gut microbiome composition and their metabolites. Future Directions: These past years, novel research increased our knowledge about neuropathy in obesity and discovered the involvement of nonglucose signaling. More studies are necessary to uncover the interplay between complex metabolic pathways in the peripheral nerve system of obese individuals. Further mechanistic studies in preclinical models and humans are crucial to create single- or multitarget interventions for this complex disease implying complex metabolic phenotyping. Antioxid. Redox Signal. 37, 597-612.

Influence of intermittent fasting on prediabetes-induced neuropathy: Insights on a novel mechanistic pathway

Aims

Peripheral neuropathy (PN) is correlated with obesity and metabolic syndrome. Intermittent fasting (IF) has been described as the cornerstone in the management of obesity; however, its role in prediabetic complications is not well elucidated. Cytochromes P450 Monooxygenases (CYP450) are major sources of Reactive Oxygen Species (ROS) that orchestrate the onset and development of diabetic complications. One of the CYP-metabolites, Expoxyecosatetraenoic Acids (EETs), are considered to be negative regulators of ROS production. In this study, we elucidated the role of IF on ROS production and investigated its influence on prediabetes-induced PN.

Methods

C57/BL6 control mice, prediabetic, prediabetic that underwent alternate day fasting with different diet composition, and prediabetic mice treated with EET-metabolizing sEH-inhibitor, AUDA. Body mass composition, metabolic, behavioral, and molecular tests were performed.

Results

High-fat diet (HFD) led to an increase in NADPH-induced ROS production; that was due to an alteration in the epoxygenase pathway assessed by the decrease in CYP1a1/1a2 expression. IF reinstated the homeostatic levels of EETs in HFD-fed mice. Moreover, treatment with AUDA mimicked the beneficial effect observed with IF.

Conclusion

IF and EETs bioavailability have a protective role in prediabetes-induced PN, suggesting a novel interventional strategy in the management of prediabetes and its associated complications.

Median Nerve Affection in Hypertensive Patients with and without Diabetes High-Resolution Ultrasound Assessment

PURPOSE

Diabetes is a documented risk factor for peripheral neuropathy. It was reported that associated hypertension could increase this risk. The present study aimed to assess the effect of hypertension and diabetes on median nerve using high-resolution ultrasound.

METHODS

The study includes 50 hypertensive patients (HTN group), 50 diabetic patients (DM group), 50 patients with coexisting diabetes and hypertension (HTN + DM group) and 50 healthy controls. Median nerve affection in the studied groups was studied by vibration perception thresholds (VPT). The median nerve cross-sectional area was determined at the nerve cross-sectional area of the median nerve at the carpal tunnel by high-resolution ultrasound. Clinical symptoms were assessed using Toronto Clinical Severity Score (TCSS).

RESULTS

There was significantly higher median nerve CSA in all patient groups in comparison to controls. HTN + DM group had significantly higher median nerve CSA when compared with DM group. Patients with peripheral neuropathy in HTN + DM and DM groups had significantly higher median nerve CSA than patients without. Using ROC curve analysis, it was shown that median CSA could successfully distinguish patients with peripheral neuropathy from patients without in HTN + DM group [AUC (95% CI): 0.71 (0.54-0.89)] and in DM group [AUC (95% CI): 0.86 (0.72-0.99)].

CONCLUSION

Hypertensive patients with and without diabetes have significantly higher median nerve CSA when compared with controls.

Sodium Glucose Cotransporter-2 Inhibitor Protects Against Diabetic Neuropathy and Nephropathy in Modestly Controlled Type 2 Diabetes: Follow-Up Study

AIMS

This three-year follow-up study aimed to elucidate whether sodium-glucose cotransporter-2 inhibitors (SGLT2is) have any protection against diabetic neuropathy and nephropathy in patients with type 2 diabetes via reducing variability in glycemia and extraglycemic factors or their averages.

METHODS

Two type 2 diabetic cohorts of 40 and 73 patients treated with or without SGLT2i along with 60 control subjects were recruited. Two diabetic cohorts matched for HbA1c levels and oral hypoglycemic agents other than SGLT2is underwent glycemic control with or without SGLT2is more than two years. The urinary albumin to creatinine ratio (ACR), estimated glomerular filtration rate (eGFR) every 3 months and neuropathy outcome measures and mean Z-score of 8 neurophysiological tests were determined at the baseline and endpoint. Glycemic variability, evaluated by the coefficient of variation of monthly measured HbA1c levels and casual postprandial plasma glucose (CPPG), and coefficient of variation and average of extraglycemic parameters in diabetic cohorts were determined.

RESULTS

The glycemic variability and variability of some extraglycemic factors in SGLT2i cohort were smaller than those in non-SGLT2i cohort. However, only smaller coefficient of variation of HbA1c improved some neuropathy outcome measures, and ameliorated eGFR decline. SGLT2i improved the Z-score of neurophysiological tests. The optimized changes in the blood pressure, HDL-cholesterol and uric acid by SGLT2i led to neurological and renal protection. SGLT2i decreased the prevalence of nephropathy significantly and the prevalence of neuropathy insignificantly.

CONCLUSION

Over 3 years period, SGLT2i significantly improved some neuropathy outcome measures, mean Z-score of 8 neurophysiological tests, and attenuated nephropathy in modestly controlled type 2 diabetes by reducing glycemic variability and mean nonglycemic factors of diabetic microvascular complication.

Systems Biology to Address Unmet Medical Needs in Neurological Disorders

Neurological diseases are highly prevalent and constitute a significant cause of mortality and disability. Neurological disorders encompass a heterogeneous group of neurodegenerative conditions, broadly characterized by injury to the peripheral and/or central nervous system. Although the etiology of neurological diseases varies greatly, they share several characteristics, such as heterogeneity of clinical presentation, non-cell autonomous nature, and diversity of cellular, subcellular, and molecular pathways. Systems biology has emerged as a valuable platform for addressing the challenges of studying heterogeneous neurological diseases. Systems biology has manifold applications to address unmet medical needs for neurological illness, including integrating and correlating different large datasets covering the transcriptome, epigenome, proteome, and metabolome associated with a specific condition. This is particularly useful for disentangling the heterogeneity and complexity of neurological conditions. Hence, systems biology can help in uncovering pathophysiology to develop novel therapeutic targets and assessing the impact of known treatments on disease progression. Additionally, systems biology can identify early diagnostic biomarkers, to help diagnose neurological disease preceded by a long subclinical phase, as well as define the exposome, the collection of environmental toxicants that increase risk of certain neurological diseases. In addition to these current applications, there are numerous potential emergent uses, such as precision medicine.

Postoperative management and rehabilitation after the supercharged end-to-side anterior interosseous nerve to ulnar motor nerve transfer: A report of 3 cases

INTRODUCTION

Compressive ulnar neuropathy at the elbow is the second most common compressive neuropathy. Nerve transfers are used for severe ulnar neuropathies as a means of facilitating recovery. Hand therapy and rehabilitation after nerve transfers have not been extensively explored.

PURPOSE OF THE STUDY

The aim of this repeated case study was to describe the responses, functional outcome, and neuromuscular health of three participants after the supercharged end-to-side (SETS) anterior interosseous nerve (AIN) to ulnar motor nerve transfer do describe the hand therapy and recovery of 3 cases reflecting different recovery potential mediators, trajectories, and outcomes.

STUDY DESIGN

Repeated case study.

METHODS

Three participants of similar age (76-80 years) that had severe ulnar neuropathy who underwent surgical treatment including a SETS AIN to ulnar motor nerve surgery were purposively selected from an ongoing clinical trial, based on their response to the surgical and the rehabilitation intervention (large, moderate, and small improvements). Clinical evaluations included measuring range of motion, strength testing, and clinical tests (ie, Egawa's sign) and, subjective assessment of rehabilitation adherence., Quick Disability of Arm, Shoulder and Hand and decomposition-based quantitative electromyography were performed at >23 months to evaluate patients.

RESULTS

All the three participants completed the surgical and hand therapy interventions, demonstrating a variable course of recovery and functional outcomes. The Quick Disability of Arm, Shoulder and Hand scores (>23 months) for participants A, B, and C were 68, 30, and 18, respectively. The person with the least improvement had idiopathic Parkinson's disease, dyslipidemia, history of depression, and gout. Comparison across cases suggested that the comorbidities, longer time from neuropathy to the surgical intervention, and psychosocial barriers to exercise and rehabilitation adherence influenced the recovery process. The participants with the best outcomes demonstrated improvements in his lower motor neurons or motor unit counts (109 and 18 motor units in the abductor digiti minimi (ADM) and first dorsal interosseous, respectively) and motor unit stability (39.5% and 37.6% near-fiber jiggle in the ADM and first dorsal interosseous, respectively). The participant with moderate response to the interventions had a motor unit count of 93 for the ADM muscle. We were unable to determine motor unit counts and measurements from the participant with the poorest outcomes due to his physical limitations.

CONCLUSIONS

SETS AIN to ulnar motor nerve followed by multimodal hand therapy provides measurable improvements in neurophysiology and function, although engagement in hand therapy and outcomes appear to be mediated by comorbid physical and psychosocial health.

Prevalence and Clinical Significance of Subclinical Hypothyroidism in Diabetic Peripheral Neuropathy

Background and Aim

Diabetic peripheral neuropathy (DPN) is one of the most common and disabling complications of DM. Many studies documented the prevalence of clinical and subclinical hypothyroidism (SCH) in diabetic patients but not in the particular group of patients with DPN. The present study aimed to determine the prevalence of SCH in DPN patients and to evaluate its association with severity of DPN.

Patients and Methods

The present cross-sectional study was conducted on 300 consecutive patients with DPN. The clinical manifestations of DPN were documented according to the validated Arabic version of the Michigan Neuropathy Screening Instrument. Severity of DPN was categorized into mild (6–8 points), moderate (9–11 points) or severe (12+ points) according to the Toronto Clinical Scoring System. All patients were submitted to careful history-taking and full clinical and neurological examination. Patients were diagnosed with SCH if they had TSH level above the upper limit of the normal reference range in association with normal free thyroxine (FT4) level.

Results

SCH was prevalent in 53 patients (17.7%, 95% CI: 13.5%–22.5%). Patients with SCH had significantly higher frequency of severe DPN (52.8% versus 28.3%, p=0.003). It was also shown that patients with SCH had significantly higher HbA1c (8.4 ± 1.0 versus 7.3 ± 1.2%, p<0.001) and HOMA-IR (3.7 ± 0.8 versus 2.7 ± 0.9, p<0.001) when compared with patients without SCH. Logistic regression analysis identified patients’ age [OR (95% CI): 1.06 (1.03–1.08), p<0.001], HbA1c [OR (95% CI): 2.2 (1.7–2.9), p<0.001] and SCH [OR (95% CI): 7.7 (3.6–15.5), p<0.001] as independent predictors of DPN severity.

Conclusion

The present study showed that SCH is highly prevalent in DPN patients and is independently related to its severity.

Burning sensation in the feet and glycosylated haemoglobin levels in Swedish- and non-Swedish-born primary healthcare patients

BACKGROUND

A painful burning sensation in the feet is a common problem. The most common cause is small fibre neuropathy, a type of peripheral neuropathy that is often a consequence of diabetes and prediabetes.

AIM

To examine the association between a self-reported burning sensation in the feet and HbA1c levels in primary healthcare patients.

METHODS

This study used data from patients in the 4D diabetes project in Swedish primary healthcare. The study population included 824 patients. Logistic regression was performed to study the association between the outcome and explanatory variables.

RESULTS

A total of 24% of patients reported a burning sensation in the feet. This sensation was not associated with HbA1c levels. However, the probability of reporting a burning sensation was two times higher in non-Swedish-born than Swedish-born patients (OR, 2.31; 95% CI, 1.55-3.44) and higher in smokers than those who had never smoked, regardless of region of birth (OR, 1.69; 95% CI, 1.07-2.65).

CONCLUSIONS

Our results do not support the hypothesis that a self-reported burning sensation in the feet is associated with HbA1c levels. Rather, they indicate a strong relationship between a burning sensation and region of birth, as well as between a burning sensation and smoking.

Differences and Similarities in Neuropathy in Type 1 and 2 Diabetes: A Systematic Review

Background: Diabetic neuropathy is defined as the dysfunction of the peripheral nervous system in diabetic patients. It is considered a microvascular complication of diabetes mellitus. Its presence is associated with increased morbidity and mortality. Although several studies have found alterations at somatic motor, sensory levels and at the level of autonomic nervous system in diabetic patients, there is not a systematic approach regarding the differences in neuropathy between the major variants of diabetes, e.g., type 1 and 2 diabetes at both neurological and molecular level. Data sources: we systematically (Medline, Scopus, and Cochrane databases) evaluated the literature related to the difference of neuropathy in type 1 and 2 diabetes, differences in molecular biomarkers. Study characteristics: seventeen articles were selected based on pre-defined eligibility criteria. Conclusions: both superficial sensitivity (primarily thermal sensitivity to cold) and deep sensitivity (such as vibratory sensitivity), have been reported mainly in type 2 diabetes. Cardiac autonomic neuropathy is one of the diabetic complications with the greatest impact at a clinical level but is nevertheless one of the most underdiagnosed. While for type 1 diabetes patients most neuropathy alterations have been reported for the Valsalva maneuver and for the lying-to-standing test, for type 2 diabetes patients, alterations have been reported for deep-breathing test and the Valsalva test. In addition, there is a greater sympathetic than parasympathetic impairment, as indicated by the screening tests for autonomic cardiac neuropathy. Regarding subclinical inflammation markers, patients with type 2 diabetes showed higher blood levels of inflammatory markers such as high-sensitivity C-reactive protein, proinflammatory cytokines IL-6, IL-18, soluble cell adhesion molecules and E-selectin and ICAM-1, than in type 1 diabetes patients. By contrast, the blood levels of adiponectin, an adipocyte-derived protein with multiple paracrine and endocrine activities (anti-inflammatory, insulin-sensitizing and proangiogenic effects) are higher in type 1 than in type 2 diabetic patients. This review provides new insights into the clinical differences in type 1 and 2 diabetes and provide future directions in this research field.

Diabetic neuropathy and neuropathic pain: a (con)fusion of pathogenic mechanisms?

Neuropathy is a common complication of long-term diabetes that impairs quality of life by producing pain, sensory loss and limb amputation. The presence of neuropathy in both insulin-deficient (type 1) and insulin resistant (type 2) diabetes along with the slowing of progression of neuropathy by improved glycemic control in type 1 diabetes has caused the majority of preclinical and clinical investigations to focus on hyperglycemia as the initiating pathogenic lesion. Studies in animal models of diabetes have identified multiple plausible mechanisms of glucotoxicity to the nervous system including post-translational modification of proteins by glucose and increased glucose metabolism by aldose reductase, glycolysis and other catabolic pathways. However, it is becoming increasingly apparent that factors not necessarily downstream of hyperglycemia can also contribute to the incidence, progression and severity of neuropathy and neuropathic pain. For example, peripheral nerve contains insulin receptors that transduce the neurotrophic and neurosupportive properties of insulin, independent of systemic glucose regulation, while the detection of neuropathy and neuropathic pain in patients with metabolic syndrome and failure of improved glycemic control to protect against neuropathy in cohorts of type 2 diabetic patients has placed a focus on the pathogenic role of dyslipidemia. This review provides an overview of current understanding of potential initiating lesions for diabetic neuropathy and the multiple downstream mechanisms identified in cell and animal models of diabetes that may contribute to the pathogenesis of diabetic neuropathy and neuropathic pain.

Diagnosis of Neuropathy and Risk Factors for Corneal Nerve Loss in Type 1 and Type 2 Diabetes: A Corneal Confocal Microscopy Study

OBJECTIVE

To assess the diagnostic utility of corneal confocal microscopy (CCM) for diabetic peripheral neuropathy (DPN) and the risk factors for corneal nerve loss.

RESEARCH DESIGN AND METHODS

A total of 490 participants, including 72 healthy control subjects, 149 with type 1 diabetes, and 269 with type 2 diabetes, underwent detailed assessment of peripheral neuropathy and CCM in relation to risk factors.

RESULTS

Corneal nerve fiber density (CNFD) (P < 0.0001 and P < 0.0001), corneal nerve fiber branch density (CNBD) (P < 0.0001 and P < 0.0001), and corneal nerve fiber length (CNFL) (P < 0.0001 and P = 0.02) were significantly lower in patients with type 1 and type 2 diabetes compared with control subjects. CNFD (P < 0.0001), CNBD (P < 0.0001), and CNFL (P < 0.0001) were lower in type 1 diabetes compared with type 2 diabetes. Receiver operating characteristic curve analysis for the diagnosis of DPN demonstrated a good area under the curve for CNFD of 0.81, CNBD of 0.74, and CNFL of 0.73. Multivariable regression analysis showed a significant association among reduced CNFL with age (β = -0.27, P = 0.007), HbA_1c (β = -1.1; P = 0.01), and weight (β = -0.14; P = 0.03) in patients with type 2 diabetes and with duration of diabetes (β = -0.13; P = 0.02), LDL cholesterol (β = 1.8, P = 0.04), and triglycerides (β = -2.87; P = 0.009) in patients with type 1 diabetes.

CONCLUSIONS

CCM identifies more severe corneal nerve loss in patients with type 1 diabetes compared with type 2 diabetes and shows good diagnostic accuracy for DPN. Furthermore, the risk factors for a reduction in corneal nerve fiber length differ between type 1 and type 2 diabetes.

The Impact of Glycemic Control on Retinal Photoreceptor Layers and Retinal Pigment Epithelium in Patients With Type 2 Diabetes Without Diabetic Retinopathy: A Follow-Up Study

AIMS

To establish the sequential changes by glycemic control in the mean thickness, volume and reflectance of the macular photoreceptor layers (MPRLs) and retinal pigment epithelium in patients with type 2 diabetes without diabetic retinopathy.

METHODS

Thirty-one poorly controlled (HbA1c > 8.0%) patients with type 2 diabetes without diabetic retinopathy undergoing glycemic control and 39 control subjects with normal HbA1c levels (< 5.9%) underwent periodical full medical, neurological and ophthalmological examinations over 2 years. Glycemic variability was evaluated by standard deviation and coefficient of variation of monthly measured HbA1c levels and casual plasma glucose. 3D swept source-optical coherence tomography (OCT) and OCT-Explorer-generated enface thickness, volume and reflectance images for 9 subfields defined by Early Treatment Diabetic Retinopathy Study of 4 MPRLs {outer nuclear layer, ellipsoid zone, photoreceptor outer segment (PROS) and interdigitation zone} and retinal pigment epithelium were acquired every 3 months.

RESULTS

Glycemic control sequentially restored the thickness and volume at 6, 4 and 5 subfields of outer nuclear layer, ellipsoid zone and PROS, respectively. The thickness and volume of outer nuclear layer were restored related to the decrease in HbA1c and casual plasma glucose levels, but not related to glycemic variability and neurological tests. The reflectance of MPRLs and retinal pigment epithelium in patients was marginally weaker than controls, and further decreased at 6 or 15 months during glycemic control. The reduction at 6 months coincided with high HbA1c levels.

CONCLUSION

Glycemic control sequentially restored the some MPRL thickness, especially of outer nuclear layer. In contrast, high glucose during glycemic control decreased reflectance and may lead to the development of diabetic retinopathy induced by glycemic control. The repeated OCT examinations can clarify the benefit and hazard of glycemic control to the diabetic retinopathy.

Long-term metformin treatment and risk of peripheral neuropathy in older Veterans

AIM

Our objective was to assess whether increased duration of metformin therapy is associated with incident peripheral neuropathy (PN) in older Veterans with diabetes.

METHODS

Using national Veterans Affairs registry data from 2002 to 2015, we examined Veterans (50 + years) with diabetes. Long-term metformin therapy was defined as prescription ≥ 500 mg/day, filled for ≥ 6 consecutive months. Metformin therapy duration was examined both as continuous and categorical measures. Incident PN was defined by medical chart review. We estimated unadjusted and adjusted (variables selecteda priori)odds ratios (OR) and 95% confidence intervals (CI) using logistic regression.

RESULTS

The study included n = 210,004 individuals (mean ± SD: age: 66.2 ± 8.4 yrs, 96% male) prescribed metformin for 47.0 ± 34.0 months. Nineteen percent developed PN during follow-up. After adjusting for age, body mass index, duration of time receiving health care within the VA, smoking status, alcohol abuse, and vitamin B12 testing and treatment, the number of months of metformin treatment was associated with elevated odds for incident PN (aOR (metformin treatment - continuous) = 1.009 (95% CI = 1.009, 1.010); aOR (metformin treatment - categorical (ref: 6-<18 months): 18-<44.1 months = 1.57 (1.51-1.63), 44.1-<61 months = 2.05 (1.97-2.14), 61 + months = 2.69 (2.58-2.79), all p-values < 0.0001).

CONCLUSION

Our study suggests that Veterans treated for at least 18 months with metformin are approximately 2-3 times more likely to develop PN than those treated at least six, but<18 months. Future studies are needed to determine whether the association we found may be due to a decline in vitamin B12 status following metformin initiation.

Statin Therapy and Risk of Polyneuropathy in Type 2 Diabetes: A Danish Cohort Study

OBJECTIVE

Statins may reduce the risk of diabetic polyneuropathy (DPN) as a result of lipid-lowering and anti-inflammatory effects, but statins have also been associated with neurotoxicity. We examined whether statin therapy affects the risk of DPN.

RESEARCH DESIGN AND METHODS

We identified all Danish patients with incident type 2 diabetes during 2002-2016. New users initiated statins between 180 days before and 180 days after their first diabetes record, while prevalent users had initiated statins before that period. Patients were followed for incident DPN using validated hospital diagnosis codes, starting 180 days after their first diabetes record. Cox proportional hazard analysis was used to compute adjusted hazard ratios (aHRs) for DPN.

RESULTS

The study cohort comprised 59,255 (23%) new users, 75,528 (29%) prevalent users, and 124,842 (48%) nonusers; median follow-up time was 6.2 years (interquartile range 3.4-9.6). The incidence rate of DPN events per 1,000 person-years was similar in new users (4.0 [95% CI 3.8-4.2]), prevalent users (3.8 [3.6-3.9]), and nonusers (3.8 [3.7-4.0]). The aHR for DPN was 1.05 (0.98-1.11) in new users and 0.97 (0.91-1.04) in prevalent users compared with statin nonusers. New users had a slightly increased DPN risk during the first year (1.31 [1.12-1.53]), which vanished after >2 years of follow-up. Findings were similar in on-treatment and propensity score-matched analyses and with additional adjustment for pretreatment blood lipid levels.

CONCLUSIONS

Statin therapy is unlikely to increase or mitigate DPN risk in patients with type 2 diabetes, although a small acute risk of harm cannot be excluded.

Protection from neuropathy in extreme duration type 1 diabetes

A proportion of individuals with type 1 diabetes mellitus for more than 50 years (medallists) may be protected from developing nephropathy, retinopathy and neuropathy. Detailed neuropathy phenotyping was undertaken in a cohort of 33 medallists aged 63.7 ± 1.4 years with diabetes for 58.5 ± 0.8 years and HbA1c of 65.9 ± 2.1 mmol/mmol. Medallists had a significantly higher HbA1c (P < .001), lower estimated glomerular filtration rate (eGFR) (P = .005) and higher albumin creatinine excretion ratio (ACR) (P = .01), but a lower total cholesterol (P < .001), triacylglycerols (P = .001), low density lipoprotein‐cholesterol (P < .001) and higher high density lipoprotein‐cholesterol (P = .03), compared to controls. Twenty‐four percent of participants were identified as “escapers” without confirmed diabetic neuropathy. They had a lower neuropathy symptom profile (P = .002), vibration perception threshold (P = .02), warm threshold (P = .05), higher peroneal amplitude (P = .005), nerve conduction velocity (P = .03), heart rate variability (P = .001), corneal nerve fibre density (P = 0.001), branch density (P < .001) and length (P = .001), compared to medallists with diabetic neuropathy. Escapers had a shorter duration of diabetes (P = .006), lower alcohol consumption (P = .04), lower total cholesterol (P = .04) and LDL (P = .02), higher eGFR (P = .001) and lower ACR (P < .001). Patients with extreme duration diabetes without diabetic neuropathy have a comparable HbA1c, blood pressure and body mass index, but a more favourable lipid profile and consume less alcohol compared to those with diabetic neuropathy.

Early disruption of nerve mitochondrial and myelin lipid homeostasis in obesity-induced diabetes

Diabetic neuropathy is a major complication of diabetes. Current treatment options alleviate pain but do not stop the progression of the disease. At present, there are no approved disease-modifying therapies. Thus, developing more effective therapies remains a major unmet medical need. Seeking to better understand the molecular mechanisms driving peripheral neuropathy, as well as other neurological complications associated with diabetes, we performed spatiotemporal lipidomics, biochemical, ultrastructural, and physiological studies on PNS and CNS tissue from multiple diabetic preclinical models. We unraveled potentially novel molecular fingerprints underlying nerve damage in obesity-induced diabetes, including an early loss of nerve mitochondrial (cardiolipin) and myelin signature (galactosylceramide, sulfatide, and plasmalogen phosphatidylethanolamine) lipids that preceded mitochondrial, myelin, and axonal structural/functional defects; started in the PNS; and progressed to the CNS at advanced diabetic stages. Mechanistically, we provided substantial evidence indicating that these nerve mitochondrial/myelin lipid abnormalities are (surprisingly) not driven by hyperglycemia, dysinsulinemia, or insulin resistance, but rather associate with obesity/hyperlipidemia. Importantly, our findings have major clinical implications as they open the door to novel lipid-based biomarkers to diagnose and distinguish different subtypes of diabetic neuropathy (obese vs. nonobese diabetics), as well as to lipid-lowering therapeutic strategies for treatment of obesity/diabetes-associated neurological complications and for glycemic control.

Prevalence of people at risk of developing type 2 diabetes mellitus and the involvement of community pharmacies in a national screening campaign: a pioneer action in Brazil

BACKGROUND

Brazil is one of top 10 countries with the highest number of people with diabetes mellitus (DM), affecting 16.8 million peoples. It is estimated that 7.7 million people (20-79 years) in the country have not yet been diagnosed, representing an under-diagnosis rate of 46.0%. Herein we aimed to screen people for high blood glucose or risk for developing type 2 DM (T2DM) through community pharmacies in Brazil.

METHODS

A cross-sectional study was carried out in November 2018, involving 977 pharmacists from 345 municipalities in Brazil. The study evaluated people between 20 and 79 years old without a previous diagnosis of DM. Glycemia was considered high when its value was ≥ 100 mg/dL fasting and ≥ 140 mg/dL in a casual feeding state. The FINDRISC (Finnish Diabetes Risk Score) was used to estimate the risk for developing T2DM. The prevalence of high blood glucose was estimated and the associated factors were obtained using Poisson's multivariate analysis with robust variance.

RESULTS

During the national screening campaign, 17,580 people were tested with the majority of the consultations (78.2%) being carried out in private pharmacies. The population was composed mainly of women (59.5%) and people aged between 20 and 45 years (47.9%). The frequency of participants with high blood glucose was 18.4% (95% CI 17.9-19.0). Considering the FINDRISC, 22.7% of people had a high or very high risk for T2DM. The risk factors associated with high blood glucose were: Body Mass Index > 25 kg/m2, abdominal circumference > 94 cm for men and > 80 cm for women; education level below 15 years of study, no daily intake of vegetables and fruits; previous diagnosis of arterial hypertension; history of high blood glucose and family history of DM.

CONCLUSIONS

This is the largest screening study that evaluated the frequency of high blood glucose and its associated factors in a population without a previous diagnosis ever performed in community pharmacies in Brazil. These results may help to improve public health policies and reinforce the role of pharmacists in screening and education actions aimed at this undiagnosed population in a continent-size country such as Brazil.

The bone marrow-derived mesenchymal stem cells (BMSCs) alleviate diabetic peripheral neuropathy induced by STZ via activating GSK-3β/β-catenin signaling pathway

BACKGROUND

Diabetic peripheral neuropathy, a common complication of diabetic mellitus, has brought a threaten on patients' health. The bone marrow-derived mesenchymal stem cells (BMSCs) were reported to play an important role in diverse diseases. Nevertheless, the specific function of BMSCs in diabetic peripheral neuropathy remained uncharacterized.

METHODS

A wide range of experiments including RT-qPCR, western blot, H&E staining, oxidative stress assessment, measurement of thermal sensitivity, ELISA, urine protein and CCK-8 assays were implemented to explore the function and mechanism of BMSCs in vivo and vitro.

RESULTS

The experimental results displayed that BMSCs improve STZ-induced diabetes symptoms in rats by decreasing blood glucose and urinary protein. Functionally, BMSCs ameliorate oxidative stress, painful diabetic neuropathy, neurotrophic status and angiogenesis in STZ-induced rats. Moreover, BMSCs participate in the regulation of sciatic neuro morphology in diabetic neuropathy rat model. In mechanism, BMSCs alleviate diabetic peripheral neuropathy via activating GSK-3β/β-catenin signaling pathway in rats and improve Schwann's cells viability by activating GSK-3β/β-catenin signaling pathway under high glucose.

CONCLUSIONS

We verified that BMSCs alleviate diabetic peripheral neuropathy of rats induced by STZ via activating GSK-3β/β-catenin signaling pathway, which implied a novel biomarker for diabetic peripheral neuropathy treatment.

Schwann cell p75 neurotrophin receptor modulates small fiber degeneration in diabetic neuropathy

Diabetic neuropathy has an incidence as high as 50% of diabetic patients and is characterized by damage to neurons, Schwann cells and blood vessels within the peripheral nervous system. The low-affinity neurotrophin receptor p75 (p75^NTR ), particularly expressed by the Schwann cells in the peripheral nerve, has previously been reported to play a role in developmental myelination and cell survival/death. Increased levels of p75^NTR , in the endoneurium and plasma from diabetic patients and rodent models of disease, have been observed, proposing that this receptor might be involved in the pathogenesis of diabetic neuropathy. Therefore, in this study, we addressed this hypothesis by utilizing a mouse model of selective nerve growth factor receptor (Ngfr) deletion in Schwann cells (SC-p75^NTR -KO). Electron microscopy of sciatic nerves from mice with high fat diet induced obesity demonstrated how loss of Schwann cell-p75^NTR aggravated axonal atrophy and loss of C-fibers. RNA sequencing disclosed several pre-clinical signaling alterations in the diabetic peripheral nerves, dependent on Schwann cell p75^NTR signaling, specially related with lysosome, phagosome, and immune pathways. Morphological and biochemical analyses identified abundant lysosomes and autophagosomes in the C-fiber axoplasm of the diabetic SC-p75^NTR -KO nerves, which together with increased Cathepsin B protein levels corroborates gene upregulation from the phagolysosomal pathways. Altogether, this study demonstrates that Schwann cell p75^NTR deficiency amplifies diabetic neuropathy disease by triggering overactivation of immune-related pathways and increased lysosomal stress.

Amyloid Proteins and Peripheral Neuropathy

Painful peripheral neuropathy affects millions of people worldwide. Peripheral neuropathy develops in patients with various diseases, including rare familial or acquired amyloid polyneuropathies, as well as some common diseases, including type 2 diabetes mellitus and several chronic inflammatory diseases. Intriguingly, these diseases share a histopathological feature-deposits of amyloid-forming proteins in tissues. Amyloid-forming proteins may cause tissue dysregulation and damage, including damage to nerves, and may be a common cause of neuropathy in these, and potentially other, diseases. Here, we will discuss how amyloid proteins contribute to peripheral neuropathy by reviewing the current understanding of pathogenic mechanisms in known inherited and acquired (usually rare) amyloid neuropathies. In addition, we will discuss the potential role of amyloid proteins in peripheral neuropathy in some common diseases, which are not (yet) considered as amyloid neuropathies. We conclude that there are many similarities in the molecular and cell biological defects caused by aggregation of the various amyloid proteins in these different diseases and propose a common pathogenic pathway for "peripheral amyloid neuropathies".

Metabolic Factors, Lifestyle Habits, and Possible Polyneuropathy in Early Type 2 Diabetes: A Nationwide Study of 5,249 Patients in the Danish Centre for Strategic Research in Type 2 Diabetes (DD2) Cohort

OBJECTIVE

To investigate the association of metabolic and lifestyle factors with possible diabetic polyneuropathy (DPN) and neuropathic pain in patients with early type 2 diabetes.

RESEARCH DESIGN AND METHODS

We thoroughly characterized 6,726 patients with recently diagnosed diabetes. After a median of 2.8 years, we sent a detailed questionnaire on neuropathy, including the Michigan Neuropathy Screening Instrument questionnaire (MNSIq), to identify possible DPN (score ≥4) and the Douleur Neuropathique en 4 Questions (DN4) questionnaire for possible associated neuropathic pain (MNSIq ≥4 + pain in both feet + DN4 score ≥3).

RESULTS

Among 5,249 patients with data on both DPN and pain, 17.9% (n = 938) had possible DPN, including 7.4% (n = 386) with possible neuropathic pain. In regression analyses, central obesity (waist circumference, waist-to-hip ratio, and waist-to-height ratio) was markedly associated with DPN. Other important metabolic factors associated with DPN included hypertriglyceridemia ≥1.7 mmol/L, adjusted prevalence ratio (aPR) 1.36 (95% CI 1.17; 1.59); decreased HDL cholesterol <1.0/1.2 mmol/L (male/female), aPR 1.35 (95% CI 1.12; 1.62); hs-CRP ≥3.0 mg/L, aPR 1.66 (95% CI 1.42; 1.94); C-peptide ≥1,550 pmol/L, aPR 1.72 (95% CI 1.43; 2.07); HbA_1c ≥78 mmol/mol, aPR 1.42 (95% CI 1.06; 1.88); and antihypertensive drug use, aPR 1.34 (95% CI 1.16; 1.55). Smoking, aPR 1.50 (95% CI 1.24; 1.81), and lack of physical activity (0 vs. ≥3 days/week), aPR 1.61 (95% CI 1.39; 1.85), were also associated with DPN. Smoking, high alcohol intake, and failure to increase activity after diabetes diagnosis associated with neuropathic pain.

CONCLUSIONS

Possible DPN was associated with metabolic syndrome factors, insulin resistance, inflammation, and modifiable lifestyle habits in early type 2 diabetes.

Superimposition of hypertension on diabetic peripheral neuropathy affects small unmyelinated sensory nerves in the skin and myelinated tibial and sural nerves in rats with alloxan-induced type 1 diabetes

Diabetic peripheral neuropathy (DPN) is a major complication of diabetes mellitus, and hypertension is considered to be a risk factor for DPN in patients with type 1 diabetes (T1DM). However, the morphological effects of hypertension on DPN are unclear. In this study, we investigated the effect of hypertension on DPN by investigating the changes in unmyelinated and myelinated nerve fibers in hypertensive rats with alloxan (AL)-induced T1DM. Thirteen-week-old WBN/Kob rats with AL-induced diabetes were allocated to receive tap water only (AL group), tap water containing 0.5% saline (0.5AN group), or tap water containing 0.75% saline (0.75AN group) for 15 weeks. Hyperglycemia was maintained for 15 weeks, and the animals were euthanized at 28 weeks. By 23 weeks of age, the systolic blood pressure was significantly higher in the 0.75AN and 0.5AN groups than in the AL group and was unchanged in all groups at 28 weeks. The number of intraepidermal sensory unmyelinated nerve fibers was significantly smaller in the 0.75AN and 0.5AN groups than in the AL group. The axonal size in the myelinated tibial and sural nerve fibers was significantly smaller in the 0.75AN group than in the AL group. Furthermore, luminal narrowing and endothelial hypertrophy were observed in the endoneurial tibial nerve vessels in the 0.75AN group. These findings suggest that superimposing hypertension on hyperglycemia may accelerate a reduction in the number of small unmyelinated sensory nerve fibers in the skin and induce mild axonal atrophy in myelinated tibial and sural nerve fibers in rats with AL-induced T1DM.

Spectrum of diabetic neuropathies

The diabetic state results in neuropathy. The main causative mechanism is hyperglycemia, although microvascular involvement, hypertriglyceridemia, as well as genetic and immune mechanisms may be contributory. There is a growing spectrum of types of diabetic neuropathies that differ based on the type of fibers involved (e.g. myelinated, unmyelinated, autonomic, somatic), distribution of nerves involved, and mechanisms of neuropathy. The most common type is distal sensory neuropathy (DSN), which affects the distal ends of large myelinated fibers, more often sensory than motor, and is often asymptomatic. The next-most common is distal small fiber neuropathy (DSFN), which largely affects the unmyelinated fibers and carries the phenotype of burning feet syndrome. Diabetic autonomic neuropathy (DAN) occurs when widespread involvement of autonomic unmyelinated fibers occurs, and patients can be incapacitated with orthostatic hypotension as well as neurogenic bladder and bowel involvement. Radiculoplexus diabetic neuropathy causes proximal weakness and pain, usually in the lower extremity, and has a combination of immune, inflammatory, and vascular mechanisms. The nerve roots and plexus are involved. These patients present with proximal weakness of a subacute onset, often with severe pain and some autonomic failure. Finally, rapid and sustained reduction of blood glucose can result in treatment-induced diabetic neuropathy (TIND), which largely affects the sensory and autonomic fibers. This occurs if HbA1c is rapidly reduced within 3 months, and the likelihood is proportional to the original A1c and the size of the reduction.

The emerging role of dyslipidemia in diabetic microvascular complications

PURPOSE OF REVIEW

To summarize recent advancements in our understanding of the impact of dyslipidemia on microvascular complications in type 2 diabetes (T2D), with an emphasis on peripheral neuropathy and nephropathy.

RECENT FINDINGS

Mounting evidence suggests that rigorous glycemic control only mitigates certain microvascular complications in T2D patients. Particularly, well regulated blood glucose levels only marginally improve peripheral neuropathy in the T2D setting. Dyslipidemia, an abnormal lipid profile, is emerging as a key factor in peripheral neuropathy. Furthermore, although glycemic control may prevent or slow nephropathy, recent developments demonstrate that dyslipidemia can also affect kidney outcomes in normoglycemic patients. Transcriptomic, epigenomic, and lipidomic investigations, as well as integrative approaches, are shedding light on potential pathomechanisms. These molecular studies are identifying possible targets for therapeutic intervention. Complementing molecular research, lifestyle interventions are on-going to assess whether dietary choices and/or exercise, weight-loss, or surgical interventions, such as bariatric surgery, can ameliorate peripheral neuropathy and nephropathy in T2D patients.

SUMMARY

Dyslipidemia is an emerging mechanism in microvascular complications in T2D. Elucidating the molecular pathomechanisms may pinpoint potential lipid-centric treatments. Interventional studies of dietary changes, exercise, or weight-loss surgery may also positively impact these highly prevalent and morbid complications.

Obesity, Metabolic Syndrome and the Risk of Microvascular Complications in Patients with Diabetes mellitus

BACKGROUND

Obesity frequently co-exists with type 2 diabetes mellitus (T2DM), leading to the socalled "diabesity epidemic". The metabolic syndrome (MetS), a cluster of central obesity, hypertension, dysglycemia, insulin resistance and/or atherogenic dyslipidemia, as well as non-alcoholic fatty liver disease (NAFLD), a hepatic manifestation of MetS, has been associated with increased cardiovascular disease (CVD), T2DM and chronic kidney disease (CKD) incidence. However, the association between obesity, MetS (including NAFLD) and diabetic microvascular complications is less evident.

METHODS

The present narrative review discusses the associations of obesity, MetS and NAFLD with diabetic kidney disease (DKD), diabetic retinopathy (DR) and diabetic peripheral neuropathy (DPN) as well as cardiac autonomic neuropathy (CAN). The available data on the effects of lifestyle measures and bariatric surgery on these diabetic complications are also briefly discussed.

RESULTS

Overall, both obesity and MetS have been related to DKD, DR and DPN, although conflicting results exist. Links between NAFLD and diabetic microvascular complications have also been reported but data are still limited. Lifestyle intervention and bariatric surgery may prevent the development and/or progression of these microvascular complications but more evidence is needed.

CONCLUSION

Clinicians should be aware of the frequent co-existence of MetS and/or NAFLD in T2DM patients to prevent or treat these metabolic disorders, thus potentially minimizing the risk for both CVD and diabetic microvascular complications.

The impact of demographic and clinical characteristics on diabetic painful neuropathy

INTRODUCTION

Diabetic neuropathy (DN) is one of the most devastating complications of diabetes mellitus; however, in contrast to other countries, there are no scientific studies in Portugal evaluating the impact of demographic and clinical characteristics of this pathological entity. The aim of this study was to evaluate the impact of gender, metabolic control, age of diabetic patients, as well as time of disease progression, the appearance of complaints related to neuropathic pain.

MATERIAL AND METHODS

A multicentre study with a non-probabilistic, convenience sample of 359 patients was performed employing the quantitative method, using the Statistical Package for Social Science 24 software. The p-value of p < 0.05 was defined to consider a result statistically significant. The Spearman correlation coefficient (r) was determined to determine the relationship between categorical variables.

RESULTS

There was no statistically significant difference in the prevalence of DN between genders (p = 0.633 and r = 0.025). There was a statistically significant relationship between the value of HbA1c and DN, with p = 0.010 and r = 0.136. There is a relationship between age and complaints of neuropathic pain, with p = 0.034 and r = 0.112. The variable, time of disease progression, is also correlated with the appearance of complaints of neuropathic pain with p = 0.020 and r = 0.112.

CONCLUSION

The prevalence of neuropathic pain in subjects with diabetes is not negligible and is associated with modifiable risk factors that can be identified, possibly modified and prevented. The correct approach for these patients, which involves screening and early treatment, is decisive improving functionality and quality of life.

Dunaliella salina Attenuates Diabetic Neuropathy Induced by STZ in Rats: Involvement of Thioredoxin

Diabetic neuropathy (DN) is a widespread disabling disorder including peripheral nerves' damage. The aim of the current study was to estimate the potential ameliorative effect of Dunaliella salina (D. salina) on DN and the involvement of the thioredoxin. Diabetes was induced by streptozotocin (STZ; 50 mg/kg; i.p). Glimepiride (0.5 mg/kg) or D. salina powder (100 or 200 mg/kg) were given orally, after 2 days of STZ injection for 4 weeks. Glucose, total antioxidant capacity (TAC), superoxide dismutase (SOD), and catalase (CAT) serum levels as well as brain contents of thioredoxin (Trx), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6) were measured with the histopathological study. STZ-induced DN resulted in a significant (P < 0.05) rise in glucose blood level and brain contents of TNF-α and IL-6 and produced a reduction in serum TAC, SOD, CAT, and brain Trx levels with irregular islets of Langerhans cells and loss of brain Purkinje cells. Treatment with glimepiride or both doses of D. salina alleviated these biochemical and histological parameters as compared to the STZ group. D. salina has a neurotherapeutic effect against DN via its inhibitory effect on inflammatory mediators and oxidative stress molecules with its upregulation of Trx activity.

Diabetic peripheral neuropathy: advances in diagnosis and strategies for screening and early intervention

Diabetic peripheral neuropathy (DPN) is a common complication of both type 1 and 2 diabetes. It is a leading cause of lower-limb amputation and disabling neuropathic pain. Amputations in patients with diabetes have a devastating effect on quality of life and are associated with an alarmingly low life expectancy (on average only 2 years from the amputation). Amputation also places a substantial financial burden on health-care systems and society in general. With the introduction of national diabetes eye screening programmes, the prevalence of blindness in working-age adults is falling. This is not the case, however, with diabetes related amputations. In this Review, we appraise innovative point-of-care devices that enable the early diagnosis of DPN and assess the evidence for early risk factor-based management strategies to reduce the incidence and slow the progression of DPN. We also propose a framework for screening and early multifactorial interventions as the best prospect for preventing or halting DPN and its devastating sequelae.

Associations between metformin use and vitamin B12 levels, anemia, and neuropathy in patients with diabetes: a meta-analysis

BACKGROUND

Metformin is first-line therapy for patients with diabetes. However, it may lower vitamin B₁₂ concentrations, which could have hematological or neurological implications. This meta-analyses reviewed all available studies on associations between metformin use and vitamin B₁₂ levels, anemia, and neuropathy in diabetic patients.

METHODS

PubMed, Web of Knowledge, Cochrane Library, and Embase were searched to identify all relevant studies published in English prior to March 2018. Pooled risk ratios (RRs) and 95% confidence intervals (CIs) were calculated for dichotomous outcomes and pooled mean differences (MDs) and 95% CIs were calculated for continuous outcomes.

RESULTS

Thirty-one studies were included in the meta-analyses. Compared with diabetic patients not taking metformin, patients taking metformin had a significantly higher risk of vitamin B₁₂ deficiency (RR 2.09; 95% CI 1.49, 2.93; P < 0.0001; I²  = 64%) and significantly lower serum vitamin B₁₂ concentrations (MD -63.70; 95% CI -74.35, -53.05] pM; P < 0.00001; I²  = 87%), which depended on dose and duration of treatment. Metformin use was also associated with significantly greater percentage decrease in serum vitamin B₁₂ concentrations from baseline in diabetic patients (MD -14.68%; 95% CI -17.98%, -11.39%; P < 0.00001; I²  = 33%). Analyses revealed no significant association between metformin use and the prevalence of anemia or neuropathy.

CONCLUSIONS

Metformin use led to significantly lowered vitamin B₁₂ concentrations and significantly higher risk of vitamin B₁₂ deficiency in diabetic patients. More quality studies are needed to explore the associations between metformin use and anemia and neuropathy in these patients. Annual vitamin B₁₂ assessment in diabetic patients taking metformin is recommended.

ER stress response mediates diabetic microvascular complications

Endoplasmic reticulum (ER) homeostasis orchestrates the folding, modification, and trafficking of secretory and membrane proteins to the Golgi compartment, thus governing cellular functions. Alterations in ER homeostasis result in the activation of signaling pathways, such as the unfolded protein response (UPR), to regain ER homeostasis. Nevertheless, failure of UPR leads to activation of autophagy-mediated cell death. Several recent studies emphasized the association of the ER stress (ERS) response with the initiation and progression of diabetes. In this review, we highlight the contribution of the ERS response, such as UPR and autophagy, in the initiation and progression of diabetes and associated microvascular complications, including diabetic nephropathy (DN), retinopathy, and neuropathy, in various experimental models, as well as in humans. We highlight the ERS as a putative therapeutic target for the treatment of diabetic microvascular complications and, thus, the urgent need for the development of improved synthetic and natural inhibitors of ERS.

The Effects of Diabetes and High-Fat Diet on Polymodal Nociceptor and Cold Thermoreceptor Nerve Terminal Endings in the Corneal Epithelium

Purpose

There is a substantial body of evidence indicating that corneal sensory innervation is affected by pathology in a range of diseases. However, there are no published studies that have directly assessed whether the nerve fiber density of the different subpopulations of corneal sensory neurons are differentially affected. The present study explored the possibility that the intraepithelial nerve fiber density of corneal polymodal nociceptors and cold thermoreceptors are differentially affected in mice fed with a high-fat high cholesterol (HFHC; 21% fat, 2% cholesterol) diet and in those that also have diabetes.

Methods

The mice were fed the HFHC diet for the duration of the experiment (up to 40 weeks). Mice in the diabetes group had hyperglycaemia induced with streptozotocin after 15 weeks on the HFHC diet. Age-matched control animals were fed a standard diet. All corneal nerve fibers were labeled with a pan neuronal antibody (antiprotein gene product 9.5), and polymodal nociceptors and cold thermoreceptors were labeled with antibodies directed against transient receptor potential cation channel, subfamily V, member 1 and transient receptor potential cation channel subfamily M member 8, respectively.

Results

The mice fed a HFHC diet and those that in addition have hyperglycemia have similar reductions in corneal nerve fiber density consistent with small fiber neuropathy. Importantly, both treatments more markedly affected the intraepithelial axons of cold thermoreceptors than those of polymodal nociceptors.

Conclusions

The results provide evidence that distinct subpopulations of corneal sensory neurons can be differentially affected by pathology.

TOTAL BODY ADIPOSITY, TRIGLYCERIDES, AND LEG FAT ARE INDEPENDENT RISK FACTORS FOR DIABETIC PERIPHERAL NEUROPATHY IN CHINESE PATIENTS WITH TYPE 2 DIABETES MELLITUS

OBJECTIVE

To evaluate the risk factors associated with diabetic peripheral neuropathy (DPN) in Chinese patients with type 2 diabetes mellitus (T2DM).

METHODS

Between January 2014 and December 2017, 107 participants who had obesity with T2DM and 349 participants who had normal weight with T2DM, matched for age, sex, and duration of diabetes, were recruited. The clinical and biochemical parameters were measured in each patient. DPN was diagnosed based on neuropathy symptom score and neuropathy deficit score. Motor and sensory nerve conduction velocities were measured by electromyography. Body fat mass was estimated by dual-energy X-ray absorptiometry, while hepatic steatosis was evaluated by ultrasonography.

RESULTS

The group with obesity had a significant higher prevalence of DPN (66.62%) than that (46.99%) of the group with normal weight. Compared to the patients with normal weight, the sural sensory nerve in the right lower limbs of the patients with obesity was more susceptible to damage. Hypertriglyceridemia in the patients with obesity was a significant independent risk factor for DPN (odds ratio [OR], 3.90 [95% confidence interval (CI), 1.01 to 15.02]; P = .04), while the duration of diabetes (OR, 1.33 [95% CI, 1.07 to 1.65]; P<.01) and leg subcutaneous fat mass (OR, 0.72 [95% CI, 0.57 to 0.90]; P<.01) in the patients with normal weight were independent risk factors for DPN. The presence of obesity alone in patients with T2DM could predict high DPN risk (OR, 3.09 [95% CI, 1.11 to 8.65]; P = .04).

CONCLUSION

Reducing total body adiposity and triglyceride levels, as well as avoiding leg subcutaneous fat atrophy, could be new prevention strategies for DPN in Chinese patients with T2DM.

ABBREVIATIONS

ALB = albumin; ALT = alanine transaminase; AST = aspartate transaminase; AUC = area under the curve; AUCc-p/AUCglu = AUC of C-peptide/AUC of glucose; BMI = body mass index; BP = blood pressure; CI = confidence interval; Cr = creatinine; DBP = diastolic blood pressure; DPN = diabetic peripheral neuropathy; FC-P = fasting C-peptide; FPG = fasting plasma glucose; FFA = free fatty acid; γ-GGT = γ-glutamyl transferase; HbA1c = glycated hemoglobin A1c; HDL-C = high-density-lipoprotein cholesterol; ISI = insulin sensitivity index; ISSI-2 = insulin secretion-sensitivity index-2; LDL-C = low-density-lipoprotein cholesterol; MNCS = motor nerve conduction velocity; OGTT = oral glucose tolerance test; PG = plasma glucose; SAT = subcutaneous adipose tissue; SBP = systolic blood pressure; SNCS = sensory nerve conduction velocity; T2DM = type 2 diabetes mellitus; TC = total cholesterol; TG = triglyceride; UA = uric acid; VAT = visceral adipose tissue; WC = waist circumference.

Peripheral nervous system involvement in systemic lupus erythematosus: a retrospective study on prevalence, associated factors and outcome

Background

Despite its potentially significant impact on disease outcome, peripheral nervous system involvement in systemic lupus erythematosus has received little attention.

Objective

The objective of this study was to assess the prevalence and clinical features of peripheral nervous system involvement in a large cohort of systemic lupus erythematosus patients.

Methods

The records of systemic lupus erythematosus patients examined at two tertiary referral centres over a period of 14 years (from 2000 to 2014) were analyzed. Peripheral nervous system events were ascertained according to the 1999 American College of Rheumatology case definitions and by using an attribution algorithm for neuropsychiatric events. Prevalence of peripheral nervous system in systemic lupus erythematosus and demographic, clinical and laboratory features were assessed. Patients with peripheral nervous system events were compared with a control group of systemic lupus erythematosus patients without peripheral nervous system involvement.

Results

In a retrospective cohort of 1224 patients, the overall prevalence of peripheral nervous system involvement was 6.9% (85 patients, 95% confidence interval 0.06–0.08), with 68% of peripheral nervous system events attributable to systemic lupus erythematosus. Polyneuropathy was the most common manifestation observed (38 events, 39.2%), followed by cranial neuropathy in 30 cases (30.9%) and 12 cases of single (12.4%) or multiple (eight events, 8.2%) mononeuritis. The average age of systemic lupus erythematosus onset was significantly higher in patients with peripheral nervous system events than in controls (mean ± standard deviation: 45.9 ± 14.8 vs. 37.1 ± 14.0) and they were more likely to have higher SLEDAI-2K and SLICC/ACR Damage Index scores, as well as hypertension and livedo reticularis. A subgroup analysis of events deemed to be systemic lupus erythematosus-related provided similar results.

Conclusion

Peripheral nervous system manifestations are a potential complication of systemic lupus erythematosus. Careful neurological assessment should therefore be included in the diagnostic workup of patients with systemic lupus erythematosus, especially in those with later onset and greater damage and disease activity.

Effect of Early and Late Interventions with Dietary Oils on Vascular and Neural Complications in a Type 2 Diabetic Rat Model

AIMS

Determine the effect of dietary oils enriched in different mono- or polyunsaturated fatty acids, i.e., olive oil (18 : 1, oleic acid), safflower oil (18 : 2 n-6, linoleic acid), flaxseed oil (18 : 3 n-3, alpha linolenic acid), evening primrose oil (18 : 3 n-6, gamma linolenic acid), or menhaden oil (20:5/22 : 6 n-3 eicosapentaenoic/docosahexaenoic acids), on vascular and neural complications in high-fat-fed low-dose streptozotocin-treated Sprague-Dawley rats, an animal model for late-stage type 2 diabetes.

MATERIALS AND METHODS

Rats were fed a high-fat diet (45% kcal as fat primarily derived from lard) for 8 weeks and then treated with a low dose of streptozotocin (30 mg/kg) in order to induce hyperglycemia. After an additional 8 (early intervention) or 20 (late intervention) weeks, the different groups of rats were fed diets with 1/2 of the kcal of fat derived from lard replaced by the different dietary oils. In addition, a control group fed a standard diet (4.25% kcal as fat) and a diabetic group maintained on the high-fat diet were maintained. The treatment period was approximately 16 weeks. The endpoints evaluated included vascular reactivity of epineurial arterioles, motor and sensory nerve conduction velocity, thermal and corneal sensitivity, and innervation of sensory nerves in the cornea and skin.

RESULTS

Our findings show that menhaden and flaxseed oil provided the greatest benefit for correcting peripheral nerve damage caused by diabetes, whereas enriching the high-fat diet with menhaden oil provided the most benefit to acetylcholine-mediated vascular relaxation of epineurial arterioles of the sciatic nerve. Enriching the diets with fatty acids derived from the other oils provided none to partial improvements.

CONCLUSIONS

These studies imply that long-chain n-6 and n-3 polyunsaturated fatty acids could be an effective treatment for diabetic peripheral neuropathy with n-3 polyunsaturated fatty acids derived from fish oil being the most effective.

Improvement in Neuropathy Outcomes With Normalizing HbA1c in Patients With Type 2 Diabetes

OBJECTIVE

To investigate the impact of normalizing HbA_1c by extensive HbA_1c control (EHC) on neuropathy outcome measures (NOMs), nephropathy, and retinopathy in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Detailed clinical and neurological examinations were performed in two cohorts of 38 patients with uncontrolled type 2 diabetes (HbA_1c 9.6% [81.4 mmol/mol]) at baseline and after glycemic control (GC) with or without EHC by diet restriction and hypoglycemic agents over 4 years along with 48 control subjects with normal glucose tolerance (NGT) and 34 subjects with impaired glucose tolerance (IGT) only at baseline. EHC patients, control subjects, and subjects with IGT underwent oral glucose tolerance tests. Glycemic variability (GV) was evaluated by SD and coefficient of variation of monthly measured HbA_1c levels and casual plasma glucose.

RESULTS

In the EHC cohort, HbA_1c levels over 4.3 years and the last 2 years improved to 6.1% (43.2 mmol/mol) and 5.8% (39.9 mmol/mol) with 7.3 kg body wt reduction, and 50% and 28.9% of patients returned to IGT and NGT, respectively, at end point. Baseline neurophysiological and corneal nerve fiber (CNF) measures were impaired in patients. Normalized HbA_1c with EHC improved neurophysiological and CNF measures to be similar for those for IGT, while GC without EHC (mean HbA_1c level 7.0% [53.5 mmol/mol]) improved only vibration perception. The mean normalized HbA_1c levels by EHC determined NOM improvements. The high GV and baseline HbA_1c levels compromised NOMs. Albumin excretion rate significantly decreased, while retinopathy severity and frequency insignificantly worsened on EHC.

CONCLUSIONS

Normalizing HbA_1c in type 2 diabetes of short duration improves microvascular complications including neuropathy and nephropathy more effectively than standard GC but not retinopathy.

Observational clinical and nerve conduction study on effects of a nutraceutical combination on painful diabetic distal symmetric sensory-motor neuropathy in patients with diabetes type 1 and type 2

BACKGROUND

Painful distal symmetric polyneuropathy (pDSPN) is one of the most common and invalidating complications of diabetes mellitus, both of type 1 and type 2. Mechanisms responsible for the occurrence of the pDSPN are multifactorial and involve metabolic pathways regulating inflammation, microvessel circulation, axonal degeneration and so on. Several therapeutic approaches have been proposed to treat pain and each of them showed positive effects associated to drug-related side effects.

METHODS

Twenty-five consecutive patients with diagnosis of diabetes mellitus and pDSPN and tried to manage pain with a dietary supplement composed of a mixture of natural extracts (β-caryophyllene, myrrh, carnosic acid) and PEA. This is a nutraceutical with potential multiple effects on metabolic, pain and vascular compartments, a profile considered useful in pDSPN. Patients were enrolled and polyneuropathy evaluated by means of nerve conduction study. Pain was assessed using VAS score scale and MNSI. Each patient was evaluated at T0 (time of enrollment) and at T1 (after 16 weeks of treatment).

RESULTS

Supplement administration was well tolerated and induced unexpectedly significant amelioration of polyneuropathy with increase amplitude and reduction of pain. No side effects were reported.

CONCLUSIONS

This fixed combination could well be considered as a potential nutraceutical option to manage pDSPN in diabetic patients.

Activation of Nrf2 signaling by natural products-can it alleviate diabetes?

Type 2 diabetes mellitus (DM) has reached pandemic proportions and effective prevention strategies are wanted. Its onset is accompanied by cellular distress, the nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor boosting cytoprotective responses, and many phytochemicals activate Nrf2 signaling. Thus, Nrf2 activation by natural products could presumably alleviate DM. We summarize function, regulation and exogenous activation of Nrf2, as well as diabetes-linked and Nrf2-susceptible forms of cellular stress. The reported amelioration of insulin resistance, β-cell dysfunction and diabetic complications by activated Nrf2 as well as the status quo of Nrf2 in precision medicine for DM are reviewed.

Variations in adrenal gland medulla and dopamine effects induced by the lack of Irs2

The adrenomedullary chromaffin cells' hormonal pathway has been related to the pathophysiology of diabetes mellitus. In mice, the deletion of insulin receptor substrate type 2 (Irs2) causes peripheral insulin resistance and reduction in β-cell mass, leading to overt diabetes, with gender differences on adrenergic signaling. To further unravel the relevance of Irs2 on glycemic control, we analyzed in adult Irs2 deficient (Irs2^-/-) mice, of both sexes but still normoglycemic, dopamine effects on insulin secretion and glycerol release, as well as their adrenal medulla by an immunohistochemical and morphologic approach. In isolated islets, 10 μM dopamine significantly inhibited insulin release in wild-type (WT) and female Irs2^-/- mice; however, male Irs2^-/- islets were insensitive to that catecholamine. Similarly, on isolated adipocytes, gender differences were observed between WT and Irs2^-/- mice in basal and evoked glycerol release with crescent concentrations of dopamine. By immunohistochemistry, reactivity to tyrosine hydroxylase (TH) in female mice was significantly higher in the adrenal medulla of Irs2^-/- compared to WT; although no differences for TH-immunopositivity were observed between the male groups of mice. However, compared to their corresponding WT animals, adrenomedullary chromaffin cells of Irs2^-/- mice showed a significant decrease in the cellular and nuclear areas, and even in their percentage of apoptosis. Therefore, our observations suggest that, together with gender differences on dopamine responses in Irs2^-/- mice, disturbances in adrenomedullary chromaffin cells could be related to deficiency of Irs2. Accordingly, Irs2 could be necessary for adequate glucose homeostasis and maintenance of the population of the adrenomedullary chromaffin cells.

Nociceptin/orphanin FQ opioid peptide-receptor expression in pachyonychia congenita

Nociceptin/orphanin FQ opioid peptide (NOP)-receptor (NOP-R) is a member of the opioid receptor family. NOP-R activation has demonstrated analgesic effects in preclinical pain models without the addiction risks associated with other opiate targets. Pachyonychia congenita (PC) is a palmoplantar keratoderma characterized by neuropathic pain in affected skin. A cohort of KRT6A gene mutation PC patients with no other explanation for their neuropathic pain offered a unique opportunity to assess potential of NOP-R as a therapeutic target. Plantar biopsies from 10 PC patients and 10 age/gender matched controls were performed at the ball (PC-affected) and the arch (PC-unaffected) of the foot. NOP-R expression was assessed by immunohistochemistry. Localization of NOP-R in subsets of epidermal nerve fibers was investigated using the pan-neuronal marker PGP9.5, markers for unmyelinated peptidergic fibers (calcitonin gene-related peptide [CGRP] and substance P [SP]), as well as for myelinated Aδ and Aβ fibers (neurofilament H [NFH]). Robust NOP-R expression was detected in epidermal keratinocytes and in a subset of PGP9.5+ fibers in both epidermis and dermis, confirmed by western blot and absorption experiments with NOP-R peptide. NOP-R expression in keratinocytes was significantly reduced in PC-affected plantar skin compared with PC-unaffected skin. In addition, NOP-R expression occurred in dermal NFH+ myelinated fibers in all groups, although few CGRP+ fibers co-expressed NOP-R. Furthermore, most SP+ fibers also co-expressed NOP-R. These findings indicate that NOP-R is expressed on epidermal keratinocytes, as well as on epidermal and dermal nerve fibers and has potential as a promising target to treat neuropathic pain in PC.