New perspectives on the management of diabetic peripheral neuropathic pain

Injectable, reversibly thermoresponsive captopril-laden hydrogel for the local treatment of sensory loss in diabetic neuropathy

A major and irreversible complication of diabetes is diabetic peripheral neuropathy (DPN), which can lead to significant disability and decreased quality of life. Prior work demonstrates the peptide hormone Angiotensin II (Ang II) is released locally in neuropathy and drives inflammation and impaired endoneurial blood flow. Therefore, we proposed that by utilizing a local thermoresponsive hydrogel injection, we could deliver inhibitors of angiotensin-converting enzyme (ACE) to suppress Ang II production and reduce nerve dysfunction in DPN through local drug release. The ACE inhibitor captopril was encapsulated into a micelle, which was then embedded into a reversibly thermoresponsive pluronics-based hydrogel matrix. Drug-free and captopril-loaded hydrogels demonstrated excellent product stability and sterility. Rheology testing confirmed sol properties with low viscosity at ambient temperature and increased viscosity and gelation at 37 °C. Captopril-loaded hydrogels significantly inhibited Ang II production in comparison to drug-free hydrogels. DPN mice treated with captopril-loaded hydrogels displayed normalized mechanical sensitivity and reduced inflammation, without side-effects associated with systemic exposure. Our data demonstrate the feasibility of repurposing ACE inhibitors as locally delivered anti-inflammatories for the treatment of sensory deficits in DPN. To the best of our knowledge, this is the first example of a locally delivered ACE inhibitor for the treatment of DPN.

Genetic Variants Influence the Development of Diabetic Neuropathy

The exact mechanism by which diabetic neuropathy develops is still not fully known, despite our advances in medical knowledge. Progressing neuropathy may occur with a persistently favorable metabolic status in some patients with diabetes mellitus, while, in others, though seldom, a persistently unfavorable metabolic status is not associated with significant neuropathy. This might be significantly due to genetic differences. While recent years have brought compelling progress in the understanding of the pathogenetic background-in particular, accelerated progress is being made in understanding molecular biological mechanisms-some aspects are still not fully understood. A comparatively small amount of information is accessible on this matter; therefore, by summarizing the available data, in this review, we aim to provide a clearer picture of the current state of knowledge, identify gaps in the previous studies, and possibly suggest directions for future studies. This could help in developing more personalized approaches to the prevention and treatment of diabetic neuropathy, while also taking into account individual genetic profiles.

How inflammation dictates diabetic peripheral neuropathy: An enlightening review

BACKGROUND

Diabetic peripheral neuropathy (DPN) constitutes a debilitating complication associated with diabetes. Although, the past decade has seen rapid developments in understanding the complex etiology of DPN, there are no approved therapies that can halt the development of DPN, or target the damaged nerve. Therefore, clarifying the pathogenesis of DPN and finding effective treatment are the crucial issues for the clinical management of DPN.

AIMS

This review is aiming to summary the current knowledge on the pathogenesis of DPN, especially the mechanism and application of inflammatory response.

METHODS

We systematically summarized the latest studies on the pathogenesis and therapeutic strategies of diabetic neuropathy in PubMed.

RESULTS

In this seminal review, the underappreciated role of immune activation in the progression of DPN is scrutinized. Novel insights into the inflammatory regulatory mechanisms of DPN have been unearthed, illuminating potential therapeutic strategies of notable clinical significance. Additionally, a nuanced examination of DPN's complex etiology, including aberrations in glycemic control and insulin signaling pathways, is presented. Crucially, an emphasis has been placed on translating these novel understandings into tangible clinical interventions to ameliorate patient outcomes.

CONCLUSIONS

This review is distinguished by synthesizing cutting-edge mechanisms linking inflammation to DPN and identifying innovative, inflammation-targeted therapeutic approaches.

4. Painful diabetic polyneuropathy

INTRODUCTION

Pain as a symptom of diabetic polyneuropathy (DPN) significantly lowers quality of life, increases mortality and is the main reason for patients with diabetes to seek medical attention. The number of people suffering from painful diabetic polyneuropathy (PDPN) has increased significantly over the past decades.

METHODS

The literature on the diagnosis and treatment of diabetic polyneuropathy was retrieved and summarized.

RESULTS

The etiology of PDPN is complex, with primary damage to peripheral nociceptors and altered spinal and supra-spinal modulation. To achieve better patient outcomes, the mode of diagnosis and treatment of PDPN evolves toward more precise pain-phenotyping and genotyping based on patient-specific characteristics, new diagnostic tools, and prior response to pharmacological treatments. According to the Toronto Diabetic Neuropathy Expert Group, a presumptive diagnosis of "probable PDPN" is sufficient to initiate treatment. Proper control of plasma glucose levels, and prevention of risk factors are essential in the treatment of PDPN. Mechanism-based pharmacological treatment should be initiated as early as possible. If symptomatic pharmacologic treatment fails, spinal cord stimulation (SCS) should be considered. In isolated cases, where symptomatic pharmacologic treatment and SCS are unsuccessful or cannot be used, sympathetic lumbar chain neurolysis and/or radiofrequency ablation (SLCN/SLCRF), dorsal root ganglion stimulation (DRGs) or posterior tibial nerve stimulation (PTNS) may be considered. However, it is recommended that these treatments be applied only in a study setting in a center of expertise.

CONCLUSIONS

The diagnosis of PDPN evolves toward pheno-and genotyping and treatment should be mechanism-based.

Arginine Biosynthesis Pathway Found to Play a Key Role in the Neuroprotective Effect of Liu-Wei-Luo-Bi (LWLB) Granules in Diabetic db/db Mice with Peripheral Neuropathy Using an Untargeted Metabolomics Strategy

Aim

Liu-Wei-Luo-Bi (LWLB) granules was a Chinese compound prescription for treating diabetic peripheral neuropathy (DPN). The aim of this study was to investigate the effect of LWLB granules on diabetic mice with peripheral neuropathy and to elucidate the potential mechanism based on an untargeted metabolomics approach.

Methods

One hundred forty db/db mice were randomly divided into seven groups: the Control group, DPN group, Mudan (MD) granules group, Epalrestat (Epa) group, and the LWLB low, medium, or high dose (LW-l, LW-m, or LW-h) group. After 12 weeks of treatment, body weight, blood glucose, mechanical pain threshold, motor conduction velocity (MCV), sensory conduction velocity (SCV), and Pathological Organization of the Sciatic and Caudal Nerves in mice were measured. Serum samples were collected for untargeted metabolomics analysis using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) and multivariate statistics. Disease-related pathways were screened out with function enrichment analyses of candidate biomarkers.

Results

LWLB granules can improve the peripheral neuropathy of type 2 diabetic mice with peripheral nerve conduction disorders, mainly through significantly improving the nerve conduction velocity (P < 0.05) and lowering the mechanical pain threshold (P < 0.05). A total of 43 metabolites were identified as potential biomarkers related to the therapeutic effect of LWLB granules. Fifty, 4, and 26; 23, 4, and 22; and 24, 1, and 16 biomarkers were discovered in the LW-l, LW-m, and LW-h groups at the 4th, 6th, and 12th weeks, respectively. Five, three, seven, five, and four metabolic pathways were found in MD, Epa, LW-l, LW-m, and LW-h groups, respectively. The arginine biosynthesis pathway is the overlapping pathway in LW-l, LW-m, and LW-h groups.

Conclusion

LWLB granules have an obvious neuroprotective effect on diabetic peripheral neuropathy, and the metabolism mechanism of LWLB is mainly related to the arginine biosynthesis pathway on diabetic db/db mice with peripheral neuropathy.

Efficacy of recurrent transcutaneous magnetic stimulation in the treatment of diabetic peripheral neuropathy: Multicenter randomized trial

AIMS

Transcutaneous magnetic stimulation (TCMS) is successful in decreasing pain in several neurologic conditions. This multicenter parallel double-blind phase II clinical trial is a follow-up to a pilot study that demonstrated pain relief in patients with diabetic peripheral neuropathy (DPN) treated with TCMS.

METHODS

Thirty-four participants with confirmed DPN and baseline pain score ≥ 5 were randomized to treatment at two sites. Participants were treated with either TCMS (n = 18) or sham (n = 16) applied to each foot once a week for four weeks. Pain scores using the Numeric Pain Rating Scale after 10 steps on a hard floor surface and answers to Patient-Reported Outcomes Measurement Information System pain questions were recorded by participants daily for 28 days.

RESULTS

Thirty-one participants completed the study and were analyzed. Average pain scores decreased from baseline in both the groups. The difference in pain scores between TCMS and sham treatments was -0.55 for morning, -0.13 for evening, and -0.34 overall, below the pre-determined clinically relevant difference of -2. Moderate adverse events that resolved spontaneously were experienced in both treatment arms.

CONCLUSION

In this two-arm trial, TCMS failed to demonstrate a significant benefit over sham in patient reported pain suggesting a substantial placebo effect in our previous pilot study.

TRIAL REGISTRATION

TCMS for the Treatment of Foot Pain Caused By Diabetic Neuropathy, https://clinicaltrials.gov/ct2/show/NCT03596203, ID-NCT03596203.

The hidden impact of neuropathic pain after surgical fixation of wrist, hip, and ankle fractures: A cross-sectional retrospective study evaluating its prevalence and risk factors

BACKGROUND

Dysesthesia, electrical and burning sensations, in addition to allodynia are frequent symptoms of neuropathic pain. Despite the high frequency, scientific data on the development of neuropathic pain after surgery for fracture fixation are scarce. The goal of the present study was to determine the prevalence, risk factors, and evaluate potential associations among neuropathic pain, pain intensity, sociodemographic, and clinical variables after wrist, hip, and ankle fracture fixation.

METHODS

A cross-sectional retrospective study involving a cohort of 166 patients who underwent surgery for distal radius, proximal femur, malleolar fracture fixation was performed. Neuropathic pain was assessed one year after fracture fixation using the Doleur Neuropathique Questionnaire (DN4).

RESULTS

The incidence of neuropathic pain in our sample was 49 (29.5%). Predictors for the development of neuropathic pain included patients with a high body mass index (BMI), female gender, diabetes mellitus, long-term use of analgesics (especially using pain-modulating medication), patients who presented some fracture-related complication during the course of the treatment, who had limitations for daily activity, and who were away from work due to chronic pain.

CONCLUSION

In our study, neuropathic pain after wrist, hip, and ankle fracture fixation was prevalent and associated with higher BMI values and amount of medication, in addition to higher proportions of female sex, absence from work, DM, limitation for daily activities, postoperative complications, and use of pain modulating medications.

Netrin-3 Suppresses Diabetic Neuropathic Pain by Gating the Intra-epidermal Sprouting of Sensory Axons

Diabetic neuropathic pain (DNP) is the most common disabling complication of diabetes. Emerging evidence has linked the pathogenesis of DNP to the aberrant sprouting of sensory axons into the epidermal area; however, the underlying molecular events remain poorly understood. Here we found that an axon guidance molecule, Netrin-3 (Ntn-3), was expressed in the sensory neurons of mouse dorsal root ganglia (DRGs), and downregulation of Ntn-3 expression was highly correlated with the severity of DNP in a diabetic mouse model. Genetic ablation of Ntn-3 increased the intra-epidermal sprouting of sensory axons and worsened the DNP in diabetic mice. In contrast, the elevation of Ntn-3 levels in DRGs significantly inhibited the intra-epidermal axon sprouting and alleviated DNP in diabetic mice. In conclusion, our studies identified Ntn-3 as an important regulator of DNP pathogenesis by gating the aberrant sprouting of sensory axons, indicating that Ntn-3 is a potential druggable target for DNP treatment.

The efficacy and safety of Chinese herbal medicine in the treatment of painful diabetic neuropathy: A systematic review and meta-analysis

Objective: The objective of this systematic review and meta-analysis is to assess the effectiveness and security of Chinese herbal medicine (CHM) in the therapy of painful diabetic neuropathy (PDN). Methods: We searched databases for randomized controlled trials (RCTs) of CHM in the treatment of PDN. Outcome indicators included nerve conduction velocity, clinical efficiency, pain score, TCM syndrome score, and adverse events. Stata 16.0 was used to carry out the Meta-analysis. Results: A total of 21 RCTs with 1,737 participants were included. This meta-analysis found that using CHM as adjuvant treatment or as monotherapy for PDN can improve SCV of median nerve [mean difference (MD) = 3.56, 95% Confidence interval (CI) (2.19, 4.92) ], MCV of median nerve [ MD = 3.82, 95% CI (2.51, 5.12) ], SCV of common peroneal nerve [ MD = 4.16, 95% CI (1.62, 6.70) ], MCV of common peroneal nerve [ MD = 4.37, 95% CI (1.82, 6.93) ], SCV of gastrocnemius nerve [ MD = 4.95, 95% CI (3.52, 6.37) ], SCV of tibial nerve [ MD = 3.17, 95% CI (-2.64, 8.99) ], MCV of tibial nerve [MD = 6.30, 95%CI (5.00, 7.60)] and clinical effective rate [ odds ratio (OR) = 4.00, 95% CI (2.89, 5.52) ] and reduce pain score [standardized mean difference (SMD) = -2.23, 95% CI (-3.04, -1.41) ], TCM syndrome score [ MD = -4.70, 95% CI (-6.61, -2.80) ]. In addition, compared to the control group, adverse events of Chinese medicine intervention occurred less. Conclusion: CHM as adjuvant therapy or single treatment has a good curative effect and is safe for patients with PDN, which is worthy of clinical promotion and use, however; higher quality clinical studies are still needed to prove. Systematic Review Registration: https://www.crd.york.ac.uk/, identifier CRD42022327967.

NRD.E1, an innovative non‐opioid therapy for painful diabetic peripheral neuropathy ‐ a randomised proof of concept study

Background

Painful diabetic peripheral neuropathy (PDPN) affects up to 26% of patients with diabetes mellitus, with major impacts on their general health and well‐being. Most available drugs fail to deliver acceptable pain reduction in the majority of patients and are often poorly tolerated. NRD.E1 is a novel product that has shown anti‐nociceptive preclinical effects and good tolerability in healthy volunteer studies.

Methods

This phase 2a, randomized, dose‐finding, Proof of Concept study enrolled patients with PDPN of ≥3 months duration. After at least one treatment‐free week (WO week), 88 patients entered a 1‐week single‐blind (SB)‐placebo run‐in period, followed by 3 weeks' double‐blind (DB) treatment, during which they received NRD.E1 at 10, 40 or 150 mg/day or placebo.

Results

The primary endpoint (change from SB‐placebo run‐in week to week 3 in weekly mean of daily average numerical rating scale [NRS] pain intensity) showed clinically relevant placebo‐corrected treatment effect pain reductions at 40 mg and 150 mg/day of 0.82 (95% CI: 0.07, 1.58, p = 0.034) and 0.66 (95% CI: −0.03, 1.35; p = 0.061) NRS points, respectively, though did not meet the pre‐specified value of p = 0.016 required due to multiplicity. An additional post hoc endpoint looking at the change from WO baseline to week 3 in weekly mean of daily average NRS showed the placebo‐corrected treatment effect was 1.46 (95% CI: 0.26, 2.66), and 1.20 (95% CI: 0.10, 2.29) NRS points, respectively. Secondary and post hoc analyses of NRS pain data (including 30 & 50% responder rate and NNT), sleep interference, Short‐form McGill pain questionnaire (especially pain intensity assessed on Visual Analogue Scale), Patient's and Clinician's Global Impression of Change showed effects consistent with the primary findings. NRD.E1 was well tolerated, with only headache reported in more than two patients and more frequently on NRD.E1 than placebo.

Conclusions

The data suggest that NRD.E1 potentially represents a novel non‐opioid therapeutic option for patients with PDPN, with at least similar efficacy and better tolerability than available therapies, justifying its further evaluation in larger‐scale confirmatory studies.

Significance

NRD.E1 is a novel non‐opioid therapeutic which is being developed for the treatment of PDPN. In this randomized, controlled, dose‐finding, Proof of Concept study, NRD.E1 induced a clinically relevant pain reduction and it was well tolerated. Available data suggest that NRD.E1 has at least similar efficacy and better tolerability than the currently available therapies, potentially offering a promising new therapeutic option to patients with PDPN and possibly other neuropathic pain indications.

Pharmacovigilance in hospice/palliative care: Net effect of amitriptyline or nortriptyline on neuropathic pain: UTS/IMPACCT Rapid programme international consecutive cohort

BACKGROUND

Real-world effectiveness of interventions in palliative care need to be systematically quantified to inform patient/clinical decisions. Neuropathic pain is prevalent and difficult to palliate. Tricyclic antidepressants have an established role for some neuropathic pain aetiologies, but this is less clear in palliative care.

AIM

To describe the real-world use and outcomes from amitriptyline or nortriptyline for neuropathic pain in palliative care.

DESIGN

An international, prospective, consecutive cohort post-marketing/phase IV/pharmacovigilance/quality improvement study of palliative care patients with neuropathic pain where the treating clinician had already made the decision to use a tricyclic antidepressant. Data were entered at set times: baseline, and days 7 and 14. Likert scales graded benefits and harms.

SETTING/PARTICIPANTS

Twenty-one sites (inpatient, outpatient, community) participated in six countries between June 2016 and March 2019. Patients had clinician-diagnosed neuropathic pain.

RESULTS

One hundred and fifty patients were prescribed amitriptyline (110) or nortriptyline (40) of whom: 85% had cancer; mean age 73.2 years (SD 12.3); mean 0-4 scores for neuropathic pain at baseline were 1.8 (SD 1.0). By day 14, doses of amitriptyline were 57 mg (SD 21) and nortriptyline (48 mg (SD 21). Fifty-two (34.7%) patients had pain improvement by day 14 (amitriptyline (45/110 (43.3%); nortriptyline (7/40 (18.9%)). Thirty-nine (27.7%) had new harms; (amitriptyline 29/104 (27.9%); nortriptyline 10/37 (27.0%); dizziness (n = 23), dry mouth (n = 20), constipation (n = 14), urinary retention (n = 10)). Benefits without harms occurred (amitriptyline (26/104 (25.0%); nortriptyline (4/37 (10.8%)).

CONCLUSIONS

Benefits favoured amitriptyline while harms were similar for both medications.

Randomized, double-blind, placebo-controlled trial of ISC 17536, an oral inhibitor of transient receptor potential ankyrin 1, in patients with painful diabetic peripheral neuropathy: impact of preserved small nerve fiber function

ABSTRACT

Patients with chronic pain syndromes, such as those with painful peripheral neuropathy due to diabetes mellitus, have limited treatment options and suffer ongoing attrition of their quality of life. Safer and more effective treatment options are needed. One therapeutic approach encompasses phenotypic characterization of the neuropathic pain subtype, combined with the selection of agents that act on relevant mechanisms. ISC 17536 is a novel, orally available inhibitor of the widely expressed pain receptor, transient receptor potential ankyrin 1, which mediates nociceptive signaling in peripheral small nerve fibers. In this randomized, placebo-controlled, proof-of-concept trial, we assessed the safety and efficacy of 28-day administration of ISC 17536 in 138 patients with chronic, painful diabetic peripheral neuropathy and used quantitative sensory testing to characterize the baseline phenotype of patients. The primary end point was the change from baseline to end of treatment in the mean 24-hour average pain intensity score based on an 11-point pain intensity numeric rating scale. The study did not meet the primary end point in the overall patient population. However, statistically significant and clinically meaningful improvement in pain were seen with ISC 17536 in an exploratory hypothesis-generating subpopulation of patients with preserved small nerve fiber function defined by quantitative sensory testing. These results may provide a mechanistic basis for targeted therapy in specific pain phenotypes in line with current approaches of "precision medicine" or personalized pain therapeutics. The hypothesis is planned to be tested in a larger phase 2 study.

Transcriptomic analysis of human sensory neurons in painful diabetic neuropathy reveals inflammation and neuronal loss

Pathological sensations caused by peripheral painful neuropathy occurring in Type 2 diabetes mellitus (T2DM) are often described as 'sharp' and 'burning' and are commonly spontaneous in origin. Proposed etiologies implicate dysfunction of nociceptive sensory neurons in dorsal root ganglia (DRG) induced by generation of reactive oxygen species, microvascular defects, and ongoing axonal degeneration and regeneration. To investigate the molecular mechanisms contributing to diabetic pain, DRGs were acquired postmortem from patients who had been experiencing painful diabetic peripheral neuropathy (DPN) and subjected to transcriptome analyses to identify genes contributing to pathological processes and neuropathic pain. DPN occurs in distal extremities resulting in the characteristic "glove and stocking" pattern. Accordingly, the L4 and L5 DRGs, which contain the perikarya of primary afferent neurons innervating the foot, were analyzed from five DPN patients and compared with seven controls. Transcriptome analyses identified 844 differentially expressed genes. We observed increases in levels of inflammation-associated transcripts from macrophages in DPN patients that may contribute to pain hypersensitivity and, conversely, there were frequent decreases in neuronally-related genes. The elevated inflammatory gene profile and the accompanying downregulation of multiple neuronal genes provide new insights into intraganglionic pathology and mechanisms causing neuropathic pain in DPN patients with T2DM.

Brain Mechanisms of Pain and Dysautonomia in Diabetic Neuropathy: Connectivity Changes in Thalamus and Hypothalamus

CONTEXT

About one-third of diabetic patients suffer from neuropathic pain, which is poorly responsive to analgesic therapy and associated with greater autonomic dysfunction. Previous research on diabetic neuropathy mainly links pain and autonomic dysfunction to peripheral nerve degeneration resulting from systemic metabolic disturbances, but maladaptive plasticity in the central pain and autonomic systems following peripheral nerve injury has been relatively ignored.

OBJECTIVE

This study aimed to investigate how the brain is affected in painful diabetic neuropathy (PDN), in terms of altered structural connectivity (SC) of the thalamus and hypothalamus that are key regions modulating nociceptive and autonomic responses.

METHODS

We recruited 25 PDN and 13 painless (PLDN) diabetic neuropathy patients, and 27 healthy adults as controls. The SC of the thalamus and hypothalamus with limbic regions mediating nociceptive and autonomic responses was assessed using diffusion tractography.

RESULTS

The PDN patients had significantly lower thalamic and hypothalamic SC of the right amygdala compared with the PLDN and control groups. In addition, lower thalamic SC of the insula was associated with more severe peripheral nerve degeneration, and lower hypothalamic SC of the anterior cingulate cortex was associated with greater autonomic dysfunction manifested by decreased heart rate variability.

CONCLUSION

Our findings indicate that alterations in brain structural connectivity could be a form of maladaptive plasticity after peripheral nerve injury, and also demonstrate a pathophysiological association between disconnection of the limbic circuitry and pain and autonomic dysfunction in diabetes.

Dietary Omega-3 Polyunsaturated Fatty-Acid Supplementation Upregulates Protective Cellular Pathways in Patients with Type 2 Diabetes Exhibiting Improvement in Painful Diabetic Neuropathy

Background: Omega-3 polyunsaturated fatty acids (PUFAs) have been proposed to improve chronic neuroinflammatory diseases in peripheral and central nervous systems. For instance, docosahexaenoic acid (DHA) protects nerve cells from noxious stimuli in vitro and in vivo. Recent reports link PUFA supplementation to improving painful diabetic neuropathy (pDN) symptoms, but cellular mechanisms responsible for this therapeutic effect are not well understood. The objective of this study is to identify distinct cellular pathways elicited by dietary omega-3 PUFA supplementation in patients with type 2 diabetes mellitus (T2DM) affected by pDN. Methods: Forty volunteers diagnosed with type 2 diabetes were enrolled in the “En Balance-PLUS” diabetes education study. The volunteers participated in weekly lifestyle/nutrition education and daily supplementation with 1000 mg DHA and 200 mg eicosapentaenoic acid. The Short-Form McGill Pain Questionnaire validated clinical determination of baseline and post-intervention pain complaints. Laboratory and untargeted metabolomics analyses were conducted using blood plasma collected at baseline and after three months of participation in the dietary regimen. The metabolomics data were analyzed using random forest, hierarchical clustering, ingenuity pathway analysis, and metabolic pathway mapping. Results: The data show that metabolites involved in oxidative stress and glutathione production shifted significantly to a more anti-inflammatory state post supplementation. Example of these metabolites include cystathionine (+90%), S-methylmethionine (+9%), glycine cysteine-glutathione disulfide (+157%) cysteinylglycine (+19%), glutamate (−11%), glycine (+11%), and arginine (+13.4%). In addition, the levels of phospholipids associated with improved membrane fluidity such as linoleoyl-docosahexaenoyl-glycerol (18:2/22:6) (+253%) were significantly increased. Ingenuity pathway analysis suggested several key bio functions associated with omega-3 PUFA supplementation such as formation of reactive oxygen species (p = 4.38 × 10−4, z-score = −1.96), peroxidation of lipids (p = 2.24 × 10−5, z-score = −1.944), Ca2+ transport (p = 1.55 × 10−4, z-score = −1.969), excitation of neurons (p = 1.07 ×10−4, z-score = −1.091), and concentration of glutathione (p = 3.06 × 10−4, z-score = 1.974). Conclusion: The reduction of pro-inflammatory and oxidative stress pathways following dietary omega-3 PUFA supplementation is consistent with the promising role of these fatty acids in reducing adverse symptoms associated with neuroinflammatory diseases and painful neuropathy.

Dorsal Root Ganglion Stimulation for Lower Extremity Neuropathic Pain Syndromes: An Evidence-Based Literature Review

Dorsal root ganglion stimulation (DRG-S) is a form of selective neuromodulation therapy that targets the dorsal root ganglion. DRG-S offers analgesia in a variety of chronic pain conditions and is approved for treatment of complex regional pain syndrome (CRPS) by the US Food and Drug Administration (FDA). There has been increasing utilization of DRG-S to treat various neuropathic pain syndromes of the lower extremity, although evidence remains limited to one randomized controlled trial and 39 observational studies. In this review, we appraised the current evidence for DRG-S in the treatment of lower extremity neuropathic pain using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) criteria. The primary outcome was change in pain intensity after DRG-S compared to baseline. We stratified presentation of results based of type of neuropathy (CRPS, painful diabetic neuropathy, mononeuropathy, polyneuropathy) as well as location of neuropathy (hip, knee, foot). Future powered randomized controlled trials with homogeneous participants are warranted.

Tracking macrophages in diabetic neuropathy with two-color nanoemulsions for near-infrared fluorescent imaging and microscopy

Background

The incidence of diabetes and diabetic peripheral neuropathy continues to rise, and studies have shown that macrophages play an important role in their pathogenesis. To date, macrophage tracking has largely been achieved using genetically-encoded fluorescent proteins. Here we present a novel two-color fluorescently labeled perfluorocarbon nanoemulsion (PFC-NE) designed to monitor phagocytic macrophages in diabetic neuropathy in vitro and in vivo using non-invasive near-infrared fluorescent (NIRF) imaging and fluorescence microscopy.

Methods

Presented PFC-NEs were formulated with perfluorocarbon oil surrounded by hydrocarbon shell carrying two fluorescent dyes and stabilized with non-ionic surfactants. In vitro assessment of nanoemulsions was performed by measuring fluorescent signal stability, colloidal stability, and macrophage uptake and subsequent viability. The two-color PFC-NE was administered to Lepr^db/db and wild-type mice by tail vein injection, and in vivo tracking of the nanoemulsion was performed using both NIRF imaging and confocal microscopy to assess its biodistribution within phagocytic macrophages along the peripheral sensory apparatus of the hindlimb.

Results

In vitro experiments show two-color PFC-NE demonstrated high fluorescent and colloidal stability, and that it was readily incorporated into RAW 264.7 macrophages. In vivo tracking revealed distribution of the two-color nanoemulsion to macrophages within most tissues of Lepr^db/db and wild-type mice which persisted for several weeks, however it did not cross the blood brain barrier. Reduced fluorescence was seen in sciatic nerves of both Lepr^db/db and wild-type mice, implying that the nanoemulsion may also have difficulty crossing an intact blood nerve barrier. Additionally, distribution of the nanoemulsion in Lepr^db/db mice was reduced in several tissues as compared to wild-type mice. This reduction in biodistribution appears to be caused by the increased number of adipose tissue macrophages in Lepr^db/db mice.

Conclusions

The nanoemulsion in this study has the ability to identify phagocytic macrophages in the Lepr^db/db model using both NIRF imaging and fluorescence microscopy. Presented nanoemulsions have the potential for carrying lipophilic drugs and/or fluorescent dyes, and target inflammatory macrophages in diabetes. Therefore, we foresee these agents becoming a useful tool in both imaging inflammation and providing potential treatment in diabetic peripheral neuropathy.

The Effects of Diabetic Polyneuropathy and Autonomic Neuropathy on Bone Turnover

Background: The effect of diabetic polyneuropathy (DPN) and autonomic neuropathy (AN) on bone turnover in type 2 diabetes mellitus (DM) is uncertain due to the lack of data. In this study, we tried to determine the effect of DPN and AN on bone metabolism. Materials and Methods: The study included patients with type 2 DM (aged 18-80 years) and age-matched healthy individuals who presented to the Departments of Metabolism and Diabetes, Geriatrics, and General Internal Medicine, Cerrahpaşa Medical School, Istanbul University. The patients were examined to find out whether they had AN, and neuropathy scores were recorded by exploring peripheral neuropathy. Bone mineral density was measured by dual-energy X-ray (DXA). Demographic characteristics, the presence of microvascular complications, and biochemical data were obtained from patients' files. Serum cross-linked C-telopeptide (Ctx), osteocalcin, and bone-specific alkaline phosphatase (B-ALP) were analyzed. Results: The study comprised a total of 64 patients: 23 had type 2 DM and osteoporosis (OP) (duration of diabetes 10.1 ± 7 years; mean age 63 ± 9.1 years; female/male 18/5; Group 1), 41 had type 2 DM and non-OP (duration of diabetes 10.3 ± 7.6 years; mean age 58 ± 7.4 years; female/male 30/11; Group 2), and 26 healthy volunteers made up the control group (mean age 62 ± 11.9 years; female/male 14/12; Group 3). The bone turnover parameters were lower in type 2 DM individuals. The levels of osteocalcin (13.3 ± 5.2 ng/mL) and B-ALP (44.7 ± 10.9 IU/L) in patients with type 2 DM were lower than those of healthy subjects: osteocalcin (20.6 ± 10 ng/mL) and B-ALP (111 ± 31.4 IU/L; P = 0.001 and P = 0.000, respectively). Ctx levels (193.5 ± 49.3; 207.6 ± 40 ng/mL) were recorded to be similar (P = 0.2). AN was also noted as a risk factor for OP. For patients without AN, the likelihood of developing OP (odds ratio) was 0.7. The corresponding ratio for patients with AN was 9.3. Conclusions: Among the independent variables, the neuropathy score was determined to have an impact on bone turnover. AN was identified to be a significant risk factor for OP.

Diabetic Peripheral Neuropathy Affects Pinch Strength and Hand Dexterity in Elderly Patients

Objective

Diabetic peripheral neuropathy (DPN) is one of the most common chronic complications of diabetes, leading to disability and decreased quality of life. In past research and clinical studies, the lower limb function of DPN patients was often the principal subject of research, with little attention given to the upper limb and hand. Our goal was to assess and compare hand function between elderly diabetic patients with DPN and without DPN.

Methods

A total of 52 diabetic patients were registered and underwent hand function assessments and electrodiagnostic tests. Dynamometer, pinch meter, Semmes Weinstein monofilaments, and the Purdue Pegboard Test (PPT) were used to assess the patients' grip strength, pinch strength, tactile sensory threshold, and hand dexterity.

Results

Compared with the non-DPN group, the elderly DPN group showed worse thumb-middle fingertip pinch strength and thumb-little fingertip pinch strength in the dominant hand (3.50 (2.50, 4.25) vs. 4.50 (3.00, 5.00), p = 0.019; 1.50 (1.00, 2.00) vs. 2.50 (2.00, 3.00), p < 0.001); the elderly DPN group displayed worse thumb-middle fingertip pinch strength, thumb-ring fingertip pinch strength, and thumb-little fingertip pinch strength in the nondominant hand (3.50 (2.00, 4.50) vs. 4.00 (3.00, 5.00), p = 0.013; 2.50 (1.25, 3.00) vs. 3.00 (2.50, 3.50), p = 0.033; 1.00 (0.75, 2.25) vs. 2.50 (2.00, 2.50), p < 0.001). The elderly DPN group scored lower than the non-DPN group on the PPT test of assembly (13.96 ± 5.18 vs. 16.96 ± 4.61, t = 2.212, p = 0.032).

Conclusion

Motor function limitation is the principal hand dysfunction in elderly patients with DPN, which is mainly manifested as a decline in fingertip pinch strength and a decrease in hand dexterity. This trial is registered with Clinical Trial Registry no. ChiCTR1900025358.

Effects of berberine on cholinesterases and monoamine oxidase activities, and antioxidant status in the brain of streptozotocin (STZ)-induced diabetic rats

OBJECTIVES

Several studies had been conducted to examine the link between diabetes and diabetes encephalopathy. This study was conducted to examine the potency of berberine (BER) on the restoration of impaired neurochemicals in the brain of streptozotocin (STZ)-induced diabetic Wistar rats.

METHODS

Fifty-six (56) adult rats weighing between 200 and 230 g were randomly divided into seven groups (n=8) as follows; Group I is normal control; Groups II and III were normal rats treated with 50 and 100 mg/kg respectively; Group IV-VII were STZ-induced rats, but Groups V-VII were treated with acarbose (25 mg/kg), 50 and 100 mg/kg of BER, respectively.

RESULTS

The result of the study showed that untreated STZ-induced diabetic rats have increased acetylcholinesterase (AChE), butyrylcholinesterase (BChE), monoamine oxidase (MAO) activities, and malonylaldehyde (MDA) level, with concomitant decrease of superoxide dismutase (SOD), glutathione peroxidase (GPx) activities, and glutathione (GSH) level. However, daily treatment with 50 and 100 mg/kg BER and ACA significantly reversed these effects.

CONCLUSIONS

The findings of this study clearly indicated that BER possesses neuro-protective and antioxidative potentials and normalize neurochemical impairment distort by diabetes.

N-Acetylcysteine causes analgesia in a mouse model of painful diabetic neuropathy

N-Acetylcysteine, one of the most prescribed antioxidant drugs, enhances pain threshold in rodents and humans by activating mGlu2 metabotropic glutamate receptors. Here, we assessed the analgesic activity of N-acetylcysteine in the streptozotocin model of painful diabetic neuropathy and examined the effect of N-acetylcysteine on proteins that are involved in mechanisms of nociceptive sensitization. Mice with blood glucose levels ≥250 mg/dl in response to a single intraperitoneal (i.p.) injection of streptozotocin (200 mg/kg) were used for the assessment of mechanical pain thresholds. Systemic treatment with N-acetylcysteine (100 mg/kg, i.p., either single injection or daily injections for seven days) caused analgesia in diabetic mice. N-acetylcysteine-induced analgesia was abrogated by the Sxc− inhibitors, sulfasalazine (8 mg/kg, i.p.), erastin (30 mg/kg, i.p.), and sorafenib (10 mg/kg, i.p.), or by the mGlu2/3 receptor antagonist, LY341495 (1 mg/kg, i.p.). Repeated administrations of N-acetylcysteine in diabetic mice reduced ERK1/2 phosphorylation in the dorsal region of the lumbar spinal cord. The analgesic activity of N-acetylcysteine was occluded by the MEK inhibitor, PD0325901 (25 mg/kg, i.p.), the TRPV1 channel blocker, capsazepine (40 mg/kg, i.p.), or by a cocktail of NMDA and mGlu5 metabotropic glutamate receptor antagonists (memantine, 25 mg/kg, plus MTEP, 5 mg/kg, both i.p.). These findings offer the first demonstration that N-acetylcysteine relieves pain associated with diabetic neuropathy and holds promise for the use of N-acetylcysteine as an add-on drug in diabetic patients.

Diabetic peripheral neuropathy in people with type 2 diabetes: too little too late

Diabetic peripheral neuropathy in people with type 2 diabetes is poorly managed because of its insidious onset, delayed diagnosis and more complex aetiology resulting from the contribution of not only hyperglycaemia, but also ageing, hyperlipidaemia, hypertension and obesity. Because there is no US Food and Drug Adminstration-approved disease-modifying therapy for diabetic peripheral neuropathy, the key to ameliorating it in type 2 diabetes has to be through earlier diagnosis and timely multi-factorial risk factor reduction. The management of painful diabetic peripheral neuropathy also requires a detailed appraisal of the choice of therapy, taking into account efficacy, patient wishes, comorbidities, side effect profile and potential for abuse.

The onset speed of hyperglycemia is important to the development of neuropathic hyperalgesia in streptozotocin-induced diabetic rats

Diabetic neuropathic hyperalgesia is one of the most common diabetes complications. The physiopathological mechanism of hyperalgesia and the reason by which this condition affects only part of the diabetic patients still unclear. We tested whether an adaptation of primary afferent neurons to hyperglycemia could prevent the development of hyperalgesia. Hyperglycemia was induced in male Wistar rats by a daily administration of a low dose of streptozotocin (STZ), during five consecutive days. Glycemia and mechanical nociceptive thresholds were measured at days 0, 3, 7 and 14 after starting the streptozotocin treatment. In parallel, dorsal root ganglia (DRG) neurons were collected from healthy male Wistar rats and cultured in different glucose concentrations (mimicking slow or fast increase of hyperglycemia), and used for calcium imaging and Western blot analyses. Rats with a slow increase of glycemia did not develop hyperalgesia, while rats with a fast increase of glycemia developed hyperalgesia. DRG neurons suddenly incubated in DMEM containing a high glucose concentration showed a significant increase of calcium influx. However, DRG neurons incubated in DMEM and receiving increasing doses of glucose had the same calcium influx observed in control neurons. The activation of AMPK (α1/α2) was greater in L5-L6 DRG of hyperglycemic and non-hyperalgesic rats, when compared with hyperglycemic and hyperalgesic rats. Our data suggest that the onset speed of hyperglycemia could be related to the development of diabetic neuropathic hyperalgesia, as a maladaptive consequence associated with low activation of AMPK (α1/α2) in peripheral nociceptive neurons when the glycemia suddenly increases.

Ameliorative Effects Of N-Acetylcysteine As Adjunct Therapy On Symptoms Of Painful Diabetic Neuropathy

Purpose

Painful diabetic neuropathy (PDN) is a variant of diabetic peripheral neuropathy which is highly prevalent and distressing in diabetic patients. Despite its high burden, the optimal treatment of PDN has remained a clinical challenge. To explain the emergence and maintenance of PDN, increasing attention has been focused on dimensions of inflammation and oxidative toxic stress (OTS). Accordingly, the aim of this study was to investigate the effects of oral N-acetylcysteine (NAC), an agent with known anti-oxidant and anti-inflammatory effects, as an adjunct therapy in patients suffering from PDN.

Patients and methods

113 eligible patients with type 2 diabetes suffering from PDN were randomly assigned to either the pregabalin + placebo or pregabalin + NAC group for 8 weeks (pregabalin at a dose of 150 mg per day, NAC and matched placebo at doses of 600 mg twice a day). Mean pain score was evaluated at baseline, week 1, 2, 4, 6, and 8 of the study based on the mean 24 hr average pain score, using an 11-point numeric rating scale (NRS). As secondary efficacy measures, mean sleep interference score (SIS) resulting from PDN, responder rates, Patient Global Impression of Change (PGIC), Clinical Global Impression of Change (CGIC), and safety were also assessed. Additionally, serum levels of total antioxidant capacity (TAC), total thiol groups (TTG), catalase activity (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), nitric oxide (NO), and malondialdehyde (MDA) were assessed at baseline and at the end of the study.

Results

Ninety patients completed the eight-week course of the study. The decrease in mean pain scores and mean sleep interference score in pregabalin + NAC group was greater in comparison with pregabalin + placebo group (p value<0.001 in both conditions). Moreover, more responders (defined as ≥50% reduction in mean pain score from baseline to end-point) were observed in the pregabalin + NAC group, in comparison with pregabalin + placebo group (72.1% vs 46.8%). More improvement in PGIC and CGIC from baseline to the end of the study was reported in pregabalin + NAC group. Oral NAC had minimal adverse effects and was well tolerated in almost all patients. Furthermore, in respect to OTS biomarkers, adjuvant NAC significantly decreased serum level of MDA and significantly increased serum levels of SOD, GPx, TAC, and TTG.

Conclusion

The pattern of results suggests that compared to placebo and over a time period of 8 weeks, adjuvant NAC is more efficacious in improving neuropathic pain associated with diabetic neuropathy than placebo. Ameliorative effects of NAC on OTS biomarkers demonstrated that NAC may alleviate painful symptoms of diabetic neuropathy, at least in part by its antioxidant effects.

Association of monocyte-to-high density lipoprotein-cholesterol ratio with peripheral neuropathy in patients with Type II diabetes mellitus

Aim: We assessed the association of monocyte count to high-density lipoprotein cholesterol ratio (MHR) with diabetic peripheral neuropathy (DPN) and its role as a marker for identification of high-risk patients for DPN. Methods: A total of 180 patients with Type II diabetes mellitus (T2DM) were enrolled in the study. MHR, erythrocyte sedimentation rate and serum CRP along with other tests for T2DM and DPN were measured. Results: Duration of T2DM (p = 0.013), insulin use (p = 0.006) and serum CRP levels (p = 0.008) were significantly higher in patients with DPN. MHR was similar between groups (p = 0.447). Duration of diabetes (OR: 1.048; p = 0.038) and the serum CRP levels (OR: 1.073; p = 0.026) were found as independent predictors for the presence of DPN, however, MHR was not. Conclusion: Higher MHR indicates an enhanced inflammation and oxidative stress which was not found to be associated with the presence of DPN.

Painful and Painless Diabetic Neuropathies: What Is the Difference?

PURPOSE OF REVIEW

The prevalence of diabetes mellitus and its chronic complications are increasing to epidemic proportions. This will unfortunately result in massive increases in diabetic distal symmetrical polyneuropathy (DPN) and its troublesome sequelae, including disabling neuropathic pain (painful-DPN), which affects around 25% of patients with diabetes. Why these patients develop neuropathic pain, while others with a similar degree of neuropathy do not, is not clearly understood. This review will look at recent advances that may shed some light on the differences between painful and painless-DPN.

RECENT FINDINGS

Gender, clinical pain phenotyping, serum biomarkers, brain imaging, genetics, and skin biopsy findings have been reported to differentiate painful- from painless-DPN. Painful-DPN seems to be associated with female gender and small fiber dysfunction. Moreover, recent brain imaging studies have found neuropathic pain signatures within the central nervous system; however, whether this is the cause or effect of the pain is yet to be determined. Further research is urgently required to develop our understanding of the pathogenesis of pain in DPN in order to develop new and effective mechanistic treatments for painful-DPN.

A Single-Blinded Trial Using Resting-State Functional Magnetic Resonance Imaging of Brain Activity in Patients with Type 2 Diabetes and Painful Neuropathy

About two-thirds of patients with painful diabetic neuropathy (PDN) suffer from anxiety and/or depression disorders. However, the pathogenesis of PDN is unclear, in particular with respect to the mechanism associated with the central nervous system. We used the neuroimaging techniques of fraction amplitude of low-frequency fluctuation (fALFF) and regional homogeneity of resting-state functional magnetic resonance imaging (fMRI) to explore the brain activity in patients with PDN. The symptoms, signs and mental conditions of 19 patients with PDN and of 18 patients with non-pain neuropathy were assessed separately and compared. Blood oxygenation level-dependent resting-state fMRI scans of the brain were performed in all 37 patients with neuropathy and in 15 gender- and age-matched healthy controls. Our data showed that patients with PDN had increased insulin resistance (p  = 0.03), increased depression (p  = 0.02) and increased anxiety (p  < 0.001) compared with the controls and that all of these conditions were associated with abnormal spontaneous activities in several regions of the brain, including the somatosensory, cognitive and emotional regions. The duration of diabetes, level of glycated hemoglobin, homeostasis model assessment of insulin resistance and estimated glomerular filtration rate were significantly correlated to abnormal spontaneous activity in patients' brains. These results lead to the conclusion that patients with PDN have abnormal brain activity, indicating that the central nervous system may contribute to painful diabetic neuropathy. TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT03700502.

Tricyclic Antidepressant and/or γ-Aminobutyric Acid-Analog Use Is Associated With Fall Risk in Diabetic Peripheral Neuropathy

BACKGROUND/OBJECTIVES

Peripheral neuropathy is a common diabetes complication that can increase fall risk. Regarding fall risk, the impact of pain management using tricyclic antidepressants (TCAs) or γ-aminobutyric acid (GABA) analogs is unclear because these medications can also cause falls. This study investigates the impact of these drugs on fall and fracture risk in older diabetic peripheral neuropathy (DPN) patients.

DESIGN

Historical cohort study with 1-to-1 propensity matching of TCA/GABA-analog users and nonusers.

SETTING

Nationally representative 5% Medicare sample between the years 2008 and 2010.

PARTICIPANTS

After applying all selection criteria, 5,550 patients with prescription and 22,200 patients without prescription of TCAs/GABA-analogs were identified. Both patient groups were then stratified for fall history and matched based on propensity of receiving TCAs/GABA-analogs within each group.

MEASUREMENTS

Patients were followed until the first incidence of fall or the first incidence of fracture during the follow-up period (for up to 5 years).

RESULTS

After matching, users and nonusers were largely similar. After covariate adjustment, TCA/GABA-analog use was associated with a statistically significant increase in fall risk (adjusted hazard ratio [HR] = 1.11; 95% confidence interval [CI] = 1.03-1.20), but was not associated with fracture risk (adjusted HR = 1.09; 95% CI = 0.99-1.19) in the conventional analysis. Treating TCA/GABA-analog use as a time-dependent covariate resulted in statistically significant associations of TCA/GABA-analog use with both fall and fracture risk (HR = 1.26 [95% CI = 1.17-1.36]; and HR = 1.12 [95% CI = 1.02-1.24], respectively).

CONCLUSION

Among older patients with DPN, GABA-analogs or TCAs increase fall risk and possibly fracture risk. Use of these medications is therefore a potentially modifiable risk factor for falls and fractures in this population.

The Effects of Substance Abuse on Blood Glucose Parameters in Patients with Diabetes: A Systematic Review and Meta-Analysis

Background: People who abuse substances are at increased risk of metabolic syndrome and diabetes resulting partly from increased cell damage and due to the effects of opioids on glucose homeostasis. Therefore, people with diabetes who abuse substances may carry greater health risks than the general population resulting from their effect on glucose metabolism. These substances may be in the form of cannabis, hallucinogens, opioids, and stimulants. Therefore, the aim of this review was to evaluate the effects of substance abuse on blood glucose parameters in patients with diabetes. Method: Databases including Embase, Psycho-Info, Google Scholar and PubMed were searched systematically for relevant articles from database inception to May 2018. Search terms including medical subject headings (MeSH) based on the Population, Intervention, Comparator and Outcomes (PICO) framework was used to access the databases. Eligible articles were selected based on set inclusion and exclusion criteria. The articles reviewed were evaluated for quality and meta-analysis and sensitivity analysis were carried out using the Review Manager (RevMan 5.3, The Cochrane Collaboration, Copenhagen, Denmark). The Random effects model was used for the data analysis. Results: Twelve studies which met the inclusion criteria were included in the systematic review, while nine articles were selected for the meta-analysis. The results of the meta-analysis showed that substance abuse does not have significant effects (p > 0.05) on postprandial blood glucose and glycated haemoglobin in patients with diabetes. With respect to the effect of substance abuse on fasting blood glucose, while this was significant (p < 0.05) following meta-analysis, the results of the sensitivity test did not demonstrate any significant difference (p > 0.05) between patients who abused substances compared with control. This would suggest that the effect of substance abuse on fasting blood glucose in these patients was not very reliable or not consistent. Conclusions: The effect of substance abuse on glycated haemoglobin and postprandial blood glucose in patients with diabetes was not significant. In the meta-analysis, while the value was slightly lower with respect to postprandial blood glucose, this was slightly higher in relation to HbA1c in the substance abuse group compared with control. On the other hand, the effect of substance abuse on fasting blood glucose was significant (p = 0.03) compared with control, but this was attenuated following a sensitivity test. A range of factors including eating habits, characteristics of drugs, erratic lifestyle of patients may explain the outcome of this review. There is the need for randomised controlled trials that will include diet and medication history in order to fully understand the effect of substance abuse on blood glucose parameters in patients with diabetes.

A new look at painful diabetic neuropathy

The prevalence of diabetes mellitus and its chronic complications continue to increase alarmingly. Consequently, the massive expenditure on diabetic distal symmetrical polyneuropathy (DSPN) and its sequelae, will also likely rise. Up to 50% of patients with diabetes develop DSPN, and about 20% develop neuropathic pain (painful-DSPN). Painful-DSPN can cast a huge burden on sufferers' lives with increased rates of unemployment, mental health disorders and physical co-morbidities. Unfortunately, due to limited understanding of the mechanisms leading to painful-DSPN, current treatments remain inadequate. Recent studies examining the pathophysiology of painful-DSPN have identified maladaptive alterations at the level of both the peripheral and central nervous systems. Additionally, genetic studies have suggested that patients with variants of voltage gated sodium channels may be more at risk of developing neuropathic pain in the presence of a disease trigger such as diabetes. We review the recent advances in genetics, skin biopsy immunohistochemistry and neuro-imaging, which have the potential to further our understanding of the condition, and identify targets for new mechanism based therapies.

Sigma 1 receptor mediated HMGB1 expression in spinal cord is involved in the development of diabetic neuropathic pain

No study has been conducted to examine the interactions of sigma-1 receptor (Sigma-1R) and high mobility group box 1 protein (HMGB1) in the development of diabetic peripheral neuropathy. Thus, we examined the effects of streptozotocin (STZ) treatment on expression of HMGB1 in subcellular levels in the dorsal root ganglion (DRG) in both wild-type and Sigma-1R-/- mice and evaluated the effects of repeated intrathecal administrations of selective Sigma-1R antagonists BD1047, agonist PRE-084, or HMGB1 inhibitor glycyrrhizin on peripheral neuropathy in wild-type mice. We found that STZ-induced tactile allodynia and thermal hyperalgesia was associated with increased total HMGB1 expression in DRG. STZ treatment promoted the distribution of HMGB1 into cytoplasm. Furthermore, STZ induced modest peripheral neuropathy and did not alter HMGB1 levels in DRG or the distribution of either cytoplasmic or nuclear HMGB1 in Sigma-1R-/- mice compared to sham control mice. Additionally, repeated stimulation of Sigma-1R in the spinal cord induced tactile allodynia and thermal hyperalgesia at 1 week. This phenomenon was associated with increased cytoplasmic HMGB1 translocation and HMGB1 expression in DRG. Finally, we found that repeated blockade of either Sigma-1R or HMGB1 in the spinal cord after STZ treatment prevent the development of tactile allodynia and thermal hyperalgesia at 1 week. These effects were associated with decreased cytoplasmic HMGB1 translocation and HMGB1 expression in DRG. Taken together, our results suggest that Sigma-1R-mediated enhancement of HMGB1 expression in the DRG is critical for the development of peripheral neuropathy in type 1 diabetes.

Severity of Neuropathy Is Associated With Long-term Spinal Cord Stimulation Outcome in Painful Diabetic Peripheral Neuropathy: Five-Year Follow-up of a Prospective Two-Center Clinical Trial

OBJECTIVE

Evidence from prospective studies for long-term treatment efficacy of spinal cord stimulation (SCS) in painful diabetic peripheral neuropathy (PDPN) is not available. We report prospective data on the effect of SCS on pain ratings, treatment success and failure, and complications during a 5-year follow-up in patients with PDPN.

RESEARCH DESIGN AND METHODS

Patients with PDPN (n = 48) were included in this prospective multicenter study. The Michigan Diabetic Neuropathy Score (MDNS) was used to assess the severity of neuropathy. Numerical rating scale (NRS) score for pain, Patient's Global Impression of Change (PGIC), and treatment success (50% reduction of NRS score or significant PGIC) during 5 years of follow-up were evaluated. Complications of SCS were reported, and associations between baseline characteristics and SCS trial success or failure during a 5-year follow-up were investigated by using survival analyses.

RESULTS

Treatment success was observed in 55% of patients after 5 years. Median duration of SCS treatment was 60 months (minimum 1 month, maximum 60 months), and 80% of patients with a permanent implant still used their SCS device after 5 years. Higher MDNS was associated with treatment failure during the 5-year follow-up (hazard ratio 3.9 [95% CI 1.3-11.6]; P = 0.014).

CONCLUSIONS

SCS is successful in reducing chronic pain symptoms in the lower extremities of patients with PDPN up to 5 years after initiation of treatment. Furthermore, 80% of patients with PDPN still use their SCS device after 5 years. Moreover, the severity of neuropathy is associated with a higher chance of long-term treatment failure during a 5-year follow-up.

Potential Therapeutic Benefits of Maintaining Mitochondrial Health in Peripheral Neuropathies

Background: Peripheral neuropathies are a group of diseases characterized by malfunctioning of peripheral nervous system. Neuropathic pain, one of the core manifestations of peripheral neuropathy remains as the most severe disabling condition affecting the social and daily routine life of patients suffering from peripheral neuropathy.

Method: The current review is aimed at unfolding the possible role of mitochondrial dysfunction in peripheral nerve damage and to discuss on the probable therapeutic strategies against neuronal mitotoxicity. The article also highlights the therapeutic significance of maintaining a healthy mitochondrial environment in neuronal cells via pharmacological management in context of peripheral neuropathies.

Results: Aberrant cellular signaling coupled with changes in neurotransmission, peripheral and central sensitization are found to be responsible for the pathogenesis of variant toxic neuropathies. Current research reports have indicated the possible involvement of mitochondria mediated redox imbalance as one of the principal causes of neuropathy aetiologies. In addition to imbalance in redox homeostasis, mitochondrial dysfunction is also responsible for alterations in physiological bioenergetic metabolism, apoptosis and autophagy pathways.

Conclusions: In spite of various etiological factors, mitochondrial dysfunction has been found to be a major pathomechanism underlying the neuronal dysfunction associated with peripheral neuropathies. Pharmacological modulation of mitochondria either directly or indirectly is expected to yield therapeutic relief from various primary and secondary mitochondrial diseases.

Substance Use Disorders among Patients with Type 2 Diabetes: a Dangerous but Understudied Combination

PURPOSE OF REVIEW

This paper reviews research on substance use and disorders (SUDs) among adults with diabetes. It describes epidemiological data on SUDs in persons with type 2 diabetes, overviews effects of substance use on diabetes outcomes, and discusses treatments for SUDs in patients with diabetes.

RECENT FINDINGS

Rates of current smoking range from 10 to 26% and alcohol use disorders are 0-5%. Rates of illicit SUDs are 3-4%, but there are no population-based studies using nationally representative samples. Smoking increases the risk for long-term diabetes complications and premature death. Alcohol and illicit drug use can also impact long-term diabetes complications by impairing glucose homeostasis and adversely influencing self-management behaviors. There is mixed evidence about psychosocial smoking cessation interventions in adults with diabetes and little on alcohol and illicit SUD interventions. Limited data exist on pharmacotherapies for SUDs in this population, but a recent study suggests that varenicline is safe and effective for treating smoking in patients with diabetes. Substance use is an understudied problem in type 2 diabetes, and addressing substance use holds potential for improving outcomes. Additional large population-based epidemiological studies in those with type 2 diabetes are needed, particularly for alcohol and illicit SUDs. Longitudinal studies should be conducted to better understand the time course of diabetes onset and outcomes in relation to SUDs. Randomized controlled trials are needed to assess safety and efficacy of promising psychosocial and pharmacological interventions.

Blockade of sigma 1 receptors alleviates sensory signs of diabetic neuropathy in rats

BACKGROUND

E-52862 (S1RA, 4-[2-[[5-methyl-1-(2-naphthalenyl)-1H-pyrazol-3-yl]oxy]ethyl]-morpholine), a novel selective sigma 1 receptor (σ1R) antagonist, has demonstrated efficacy in nociceptive and neuropathic pain models. Our aim was to test if σ1R blockade with E-52862 may modify the signs of neuropathy in Zucker diabetic fatty (ZDF) rats, a type 2 diabetes model.

METHODS

Mechanical and thermal response thresholds were tested on 7-, 13-, 14- and 15-week-old ZDF rats treated with saline or with E-52862 acutely administered on week 13, followed by sub-chronic administration (14 days). Axonal peripheral activity (skin-saphenous nerve preparation) and isolated aorta or mesenteric bed reactivity were analysed in 15-week-old ZDF rats treated with saline or E-52862 and in LEAN rats.

RESULTS

Zucker diabetic fatty rats showed significantly decreased thermal withdrawal latency and threshold to mechanical stimulation on week 13 compared to week 7 (prediabetes) and with LEAN animals; single-dose and sub-chronic E-52862 administration restored both parameters to those recorded on week 7. Regarding axonal peripheral activity, E-52862 treatment increased the mean mechanical threshold (77.3 ± 21 mN vs. 19.6 ± 1.5 mN, saline group) and reduced the response evoked by mechanical increasing stimulation (86.4 ± 36.5 vs. 352.8 ± 41.4 spikes) or by repeated mechanical supra-threshold steps (39.4 ± 1.4 vs. 83.5 ± 0.9). E-52862 treatment also restored contractile response to phenylephrine in aorta and mesenteric bed.

CONCLUSIONS

E-52862 administration reverses neuropathic (behavioural and electrophysiological) and vascular signs in the ZDF rat.

SIGNIFICANCE

Blockade of σ1R avoids the development of diabetic neuropathy in rats, and may represent a potentially useful therapeutic approach to peripheral neuropathies in diabetic patients. WHAT DOES THIS STUDY ADD?: This study presents evidences for the potential usefulness of sigma receptor blockade on diabetic neuropathy in rats. The methodology includes behavioural evidences, electrophysiological data and vascular-isolated models.

Capsaicin 8% patch repeat treatment plus standard of care (SOC) versus SOC alone in painful diabetic peripheral neuropathy: a randomised, 52-week, open-label, safety study

BACKGROUND

This 52-week study evaluated the long-term safety and tolerability of capsaicin 8% w/w (179 mg) patch repeat treatment plus standard of care (SOC) versus SOC alone in painful diabetic peripheral neuropathy (PDPN).

METHODS

Phase 3, multinational, open-label, randomised, controlled, 52-week safety study, conducted in Europe. Patients were randomised to capsaicin 8% patch repeat treatment (30 or 60 min; 1-7 treatments with ≥ 8-week intervals) to painful areas of the feet plus SOC, or SOC alone. The primary objective was the safety of capsaicin 8% patch repeat treatment (30 min and 60 min applications) plus SOC versus SOC alone over 52 weeks, assessed by changes in Norfolk Quality of Life-Diabetic Neuropathy (QOL-DN) total score from baseline to end of study (EOS). Secondary safety endpoints included Utah Early Neuropathy Scale (UENS) assessments and standardised testing of sensory perception and reflex function.

RESULTS

Overall, 468 patients were randomised (30 min plus SOC, n = 156; 60 min plus SOC, n = 157; SOC alone, n = 155). By EoS, mean changes in Norfolk QOL-DN total score from baseline [estimated mean difference versus SOC alone; 90% CI for difference] were: 30 min plus SOC, -27.6% [-20.9; -31.7, -10.1]; 60 min plus SOC, -32.8% [-26.1; -36.8, -15.4]; SOC alone, -6.7%. Mean changes [difference versus SOC alone] in UENS total score by EoS versus baseline were: 30 min plus SOC, -2.1 [-0.9; -1.8, 0.1]; 60 min plus SOC, -3.0 [-1.7; -2.7, -0.8]; SOC alone, -1.2. No detrimental deterioration was observed in any of the Norfolk or UENS subscales by EoS with capsaicin. Also, no worsening in sensory perception testing of sharp, warm, cold and vibration stimuli was found with capsaicin by EoS. Capsaicin treatment was well tolerated and the most frequent treatment-emergent adverse events were application site pain (30 min, 28.2%; 60 min, 29.3%), burning sensation (30 min, 9.0%; 60 min, 9.6%) and application site erythema (30 min, 7.7%; 60 min, 8.9%).

CONCLUSION

In patients with PDPN, capsaicin 8% patch repeat treatment plus SOC over 52 weeks was well tolerated with no negative functional or neurological effects compared with SOC alone.

TRIAL REGISTRATION

ClinicalTrials.gov registration: NCT01478607 . Date of registration November 21, 2011; retrospectively registered.

Spinal cord stimulation in experimental chronic painful diabetic polyneuropathy: Delayed effect of High-frequency stimulation

Background

Spinal cord stimulation (SCS) has been shown to provide pain relief in painful diabetic polyneuropathy (PDPN). As the vasculature system plays a great role in the pathophysiology of PDPN, a potential beneficial side‐effect of SCS is peripheral vasodilation, with high frequency (HF) SCS in particular. We hypothesize that HF‐SCS (500 Hz), compared with conventional (CON) or low frequency (LF)‐SCS will result in increased alleviation of mechanical hypersensitivity in chronic experimental PDPN.

Methods

Diabetes was induced in 8‐week‐old female Sprague–Dawley rats with an intraperitoneal injection of 65 mg/kg of streptozotocin (n = 44). Rats with a significant decrease in mechanical withdrawal response to von Frey filaments over a period of 20 weeks were implanted with SCS electrodes (n = 18). Rats were assigned to a cross‐over design with a random order of LF‐, CON‐, HF‐ and sham SCS and mechanical withdrawal thresholds were assessed with von Frey testing.

Results

Compared with sham treatment, the average 50% WT score for 5 Hz was 4.88 g higher during stimulation (p = 0.156), and 1.77 g higher post‐stimulation (p = 0.008). CON‐SCS resulted in 50% WT scores 5.7 g, and 2.51 g higher during (p = 0.064) and after stimulation (p < 0.004), respectively. HF‐SCS started out with an average difference in 50% WT score compared with sham of 1.87 g during stimulation (p = 0.279), and subsequently the steepest rise to a difference of 5.47 g post‐stimulation (p < 0.001).

Conclusions

We demonstrated a delayed effect of HF‐SCS on mechanical hypersensitivity in chronic PDPN animals compared with LF‐, or CON‐SCS.

Significance

This study evaluates the effect of SCS frequency (5–500 Hz) on mechanical hypersensitivity in the chronic phase of experimental PDPN. High frequency (500 Hz) – SCS resulted in a delayed effect‐ on pain‐related behavioural outcome in chronic PDPN.

Recognition and management of psychosocial issues in diabetic neuropathy

Although psychosocial aspects of diabetic neuropathy (DN) have received far less attention than biological aspects, research conducted over the last decade has begun to illuminate several important pathways between DN and psychosocial outcomes, including depression, anxiety, and self-management of diabetic foot ulcer (DFU)-risk. Growing body of evidence indicates that DN is a risk factor for depression predicting both the severity and increments in depression over time. Whereas painful DN contributes to depression, postural instability is the DN symptom with the strongest, cumulative effect on depression. Furthermore, depression and foot self-care, while having no impact on the development of recurrent diabetic foot ulcers (DFU), play a substantial role in incident first DFU. Patient common sense misconceptions about DFU risks and associated emotional responses play an important role in shaping foot self-care. Depression, and especially DFU-specific emotions, may be linked to DFU chronicity through biological and behavioral pathways that are at present under investigation in several ongoing trials. Integrative approaches that target psychological factors such as anxiety and depression while concurrently optimizing treatment and self-management may therefore be most powerful. Cognitive behavioral therapy-based techniques that are informed by these findings deserve investigation.

Neuropathic pain as part of chronic widespread pain: environmental and genetic influences

Chronic widespread pain (CWP) has complex aetiology and forms part of the fibromyalgia syndrome. Recent evidence suggests a higher frequency of neuropathic pain features in those with CWP than previously thought. The aim of this study was to determine the prevalence of neuropathic pain features in individuals with CWP and to estimate the influence of genetic and environmental factors on neuropathic pain in CWP. Validated questionnaires (the London Fibromyalgia Screening Study questionnaire and PainDETECT questionnaire) were used to classify twins as having CWP and neuropathic pain, respectively. The prevalence of CWP was 14.7% (n = 4324), and of the 1357 twins invited to complete neuropathic pain screening, 15.9% of those having CWP demonstrated features of neuropathic pain. Neuropathic pain was found to be heritable (A = 37%; 95% confidence interval [CI]: 23%-50%) with unique environmental factors accounting for 63% (95% CI: 49%-79%) of the variance. Heritability of neuropathic pain and CWP were found to be correlated, 0.54 (95% CI: 0.42-0.65). Increasing age, raised body mass index, female gender, and smoking were all risk factors for neuropathic pain (P < 0.05), and CWP (P < 0.05). High socioeconomic status showed negative correlation with neuropathic pain (P = 0.003) and CWP (P = 0.001). Bivariate analysis of the 2 pain traits revealed that genetic predisposition to neuropathic pain is shared with that for CWP. This is the first study to provide formal heritability estimates for neuropathic pain in CWP. The findings suggest that at least some of the genetic factors underlying the development of neuropathic pain and CWP are the same.

Could Spinal Canal Compression be a Cause of Polyneuropathy?

Causality between spinal cord compression and polyneuropathy is difficult to define, especially under the circumstances that polyneuropathy can have many causes.

Seven patients with spinal cord compression and electrophysiological signs of polyneuropathy were treated surgically on decompression of their spinal canal stenosis in the time from April 2010 to January 2013. Median follow up time was 9 months (2-23 months).

Causes of polyneuropathy were: 1 patient with methotrexate-induced polyneuropathy, 1 endocrine-dysfunction-induced, 2 with diabetic-polyneuropathy, and 3 patients had unknown reasons. The localization of the spinal canal stenosis was also varying: 2 patients suffered of cervical spinal canal stenosis and 5 of lumbar. Decompressive surgery led to pain relieve in all patients initially. Surprisingly, also symptoms of polyneuropathy seemed to regress in all 7 patients for the first 5 months after surgery, and in 5 patients for the time of 9 months after surgery.

There are two points we would like to emphasize in this short report. Since 5/7 patients with polyneuropathy and spinal canal stenosis improved clinically after surgery, surgery has a place in the treatment of such a combined pathology. Since it seems to be a possible causality between polyneuropathy of unknown origin and spinal cord stenosis, decompression of the spinal canal could also be a therapeutic step in a specific kind of polyneuropathy. Which patients could possibly have a spinal canal stenosis induced polyneuropathy remains a subject of further studies.

Sociodemographic and clinical characteristics of patients with diabetic foot ulcer

Summary Introduction: Diabetic foot is one of the most serious complications of diabetes affecting about 15% of all diabetes patients, and it is the leading cause of nontraumatic lower limb amputations. This study presents a sociodemographic and clinical characterization of patients with diabetic foot ulcer indicated for amputation surgery. Methods: A cross-sectional study with 206 patients with type 2 diabetes and a diabetic foot ulcer indicated for amputation surgery. Patients were assessed on sociodemographic and clinical characteristics, pain intensity and pain interference, after answering the Brief Pain Inventory, and on pain descriptors according to the Douleur Neuropathique 4. Results: Most patients were male, with little formal education and a mean age of 66 years. They had been diagnosed with type 2 diabetes for 18 years on average, and with diabetic foot ulcer on average 4 years prior to the assessment. About 59% of patients experienced pain in the lower limb that significantly affect all areas of their functioning. Conclusion: The social demographic variables play an important role in diabetic foot ulceration. Given that the neuropathic ulcers are more easily preventable, systematic monitoring of patients with neuropathy is important. In patients with neuroischemic foot, strategies to cope or manage more efficiently the pain are paramount. Intervention should be multidisciplinary and take into account sociodemographic and clinical factors, as well as the presence, intensity and interference of pain in the patient's daily life activities and whether the patient has family or caregiver support.

Adenosine Monophosphate-Activated Protein Kinase Abates Hyperglycaemia-Induced Neuronal Injury in Experimental Models of Diabetic Neuropathy: Effects on Mitochondrial Biogenesis, Autophagy and Neuroinflammation

Impaired adenosine monophosphate kinase (AMPK) signalling under hyperglycaemic conditions is known to cause mitochondrial dysfunction in diabetic sensory neurons. Facilitation of AMPK signalling is previously reported to ameliorate inflammation and induce autophagic response in various complications related to diabetes. The present study assesses the role of AMPK activation on mitochondrial biogenesis, autophagy and neuroinflammation in experimental diabetic neuropathy (DN) using an AMPK activator (A769662). A769662 (15 and 30 mg/kg, i.p) was administered to Sprague-Dawley rats (250-270 g) for 2 weeks after 6 weeks of streptozotocin (STZ) injection (55 mg/kg, i.p.). Behavioural parameters (mechanical/thermal hyperalgesia) and functional characteristics (motor/sensory nerve conduction velocities (MNCV and SNCV) and sciatic nerve blood flow (NBF)) were assessed. For in vitro studies, Neuro2a (N2A) cells were incubated with 25 mM glucose to simulate high glucose condition and then studied for mitochondrial dysfunction and protein expression changes. STZ administration resulted in significant hyperglycaemia (>250 mg/dl) in rats. A769662 treatment significantly improved mechanical/thermal hyperalgesia threshold and enhanced MNCV, SNCV and NBF in diabetic animals. A769662 exposure normalised the mitochondrial superoxide production, membrane depolarisation and markedly increased neurite outgrowth of N2A cells. Further, AMPK activation also abolished the NF-κB-mediated neuroinflammation. A769662 treatment increased Thr-172 phosphorylation of AMPK results in stimulated PGC-1α-directed mitochondrial biogenesis and autophagy induction. Our study supports that compromised AMPK signalling in hyperglycaemic conditions causes defective mitochondrial biogenesis ultimately leading to neuronal dysfunction and associated deficits in DN and activation of AMPK can be developed as an attractive therapeutic strategy for the management of DN.

A genome-wide association study suggests an association of Chr8p21.3 (GFRA2) with diabetic neuropathic pain

Background

Neuropathic pain, caused by a lesion or a disease affecting the somatosensory system, is one of the most common complications in diabetic patients. The purpose of this study is to identify genetic factors contributing to this type of pain in a general diabetic population.

Method

We accessed the Genetics of Diabetes Audit and Research Tayside (GoDARTS) datasets that contain prescription information and monofilament test results for 9439 diabetic patients, among which 6927 diabetic individuals were genotyped by Affymetrix SNP6.0 or Illumina OmniExpress chips. Cases of neuropathic pain were defined as diabetic patients with a prescription history of at least one of five drugs specifically indicated for the treatment of neuropathic pain and in whom monofilament test result was positive for sensory neuropathy in at least one foot. Controls were individuals who did not have a record of receiving any opioid analgesics. Imputation of non‐genotyped SNPs was performed by IMPUTE2, with reference files from 1000 Genomes Phase I datasets.

Results

After data cleaning and relevant exclusions, imputed genotypes of 572 diabetic neuropathic pain cases and 2491 diabetic controls were used in the Fisher's exact test. We identified a cluster in the Chr8p21.3, next to GFRA2 with a lowest p‐value of 1.77 × 10⁻⁷ at rs17428041. The narrow‐sense heritability of this phenotype was 11.00%.

Conclusion

This genome‐wide association study on diabetic neuropathic pain suggests new evidence for the involvement of variants near GFRA2 with the disorder, which needs to be verified in an independent cohort and at the molecular level.

A pooled analysis evaluating the efficacy and tolerability of tapentadol extended release for chronic, painful diabetic peripheral neuropathy

Background and Objective

Data from two similarly designed studies of tapentadol extended release (ER) for managing neuropathic pain associated with diabetic peripheral neuropathy (DPN; NCT00455520, NCT01041859) in adults were pooled for this analysis, allowing a detailed evaluation of efficacy in patient subgroups and secondary endpoints.

Methods

In each study, patients were titrated to their optimal dose of open-label tapentadol ER [100–250 mg twice daily (bid)] over 3 weeks. Patients with ≥1-point improvement in average pain intensity [11-point numerical rating scale (NRS)] were randomized (1:1) to receive placebo or tapentadol ER during a 12-week, double-blind maintenance period.

Results

Mean (standard deviation [SD]) changes in pain intensity from baseline to week 12 of maintenance in the placebo (n = 343) and tapentadol ER (n = 360) groups, respectively, were 1.28 (2.41) and 0.08 (1.87) [least squares mean difference (LSMD): −1.14 (95 % confidence interval [CI]: −1.435, −0.838); P < 0.001, in favour of tapentadol ER]. Significant between-group differences were also observed in changes from the start of the double-blind treatment period to the double-blind endpoint for the Short Form-36 physical functioning, role-physical, bodily pain, social functioning and role-emotional subscale and physical component summary scores, and the EuroQol 5-Dimension health status index (all P < 0.05, in favour of tapentadol ER). No clinically relevant differences were observed in the efficacy of tapentadol ER across patient subgroups divided by age, sex, race, opioid experience and pain intensity. Incidences of treatment-emergent adverse events were 56.0 % (192/343) with placebo and 74.7 % (269/360) with tapentadol ER during maintenance.

Conclusion

Results of this pooled analysis indicate that tapentadol ER was effective for managing DPN-related pain, and provided consistent analgesic efficacy across different patient subgroups.