Mediators of diabetic neuropathy: is hyperglycemia the only culprit?

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.

Electrodiagnosis in the Patient with Metabolic Syndrome: Adding Value to Patient Care

Patients with metabolic syndrome are at increased risk of peripheral neuropathy; entrapment neuropathies, such as carpal tunnel syndrome; and spine disease that can lead to radiculopathy or spinal stenosis. Electrodiagnostic studies are a valuable part of patient care in this population. They can confirm suspected diagnoses, uncover additional conditions, and lead to the diagnosis of other causes of neuropathy that require treatment. By assessing the severity of neuropathy, patients at high risk for falls, functional decline, and foot ulcers are identified to guide prevention, treatment, and patient education.

Protection of insulin‑like growth factor 1 on experimental peripheral neuropathy in diabetic mice

The present study investigated whether insulin‑like growth factor‑1 (IGF‑1) exerts a protective effect against neuropathy in diabetic mice and its potential underlying mechanisms. Mice were divided into four groups: Db/m (control), db/db (diabetes), IGF‑1‑treated db/db and IGF‑1‑picropodophyllin (PPP)‑treated db/db. Behavioral studies were conducted using the hot plate and von Frey methods at 6 weeks of age prior to treatment. The motor nerve conduction velocity (NCV) of the sciatic nerve was measured using a neurophysiological method at 8 weeks of age. The alterations in the expression levels of IGF‑1 receptor (IGF‑1R), c‑Jun N‑terminal kinase (JNK), extracellular signal‑regulated kinase (ERK), p38 and effect of IGF‑1 on the sciatic nerve morphology were observed by western blotting and electron microscopy. Compared with the control group, the diabetes group developed hypoalgesia after 12 weeks, and neurological lesions improved following an intraperitoneal injection of recombinant (r)IGF‑1. The sciatic NCV in the diabetes group was significantly lower compared with the control group. The sciatic NCV improved following rIGF‑1 intervention; however, was impaired following administration of the IGF‑1 receptor antagonist, PPP. The myelin sheath in the sciatic nerve of the diabetes group was significantly more impaired compared with the control group. The myelin sheath in the sciatic nerves of the rIGF‑1‑treated group was significantly improved compared with the diabetes group; whereas, they were significantly impaired following administration of the IGF‑1R inhibitor. In addition, the expression of IGF‑1R, phosphorylated (p)‑JNK and p‑ERK of sciatic nerves in the db/db mice was significantly increased following treatment with IGF‑1. The expression levels of these proteins were significantly lower in the IGF‑1‑PPP group compared with the IGF‑1 group; however, no significant difference was observed in the expression levels of p‑p38 following treatment with IGF‑1. The results of the present study demonstrated that IGF‑1 may improve neuropathy in diabetic mice. This IGF‑1‑induced neurotrophic effect may be associated with the increased phosphorylation levels of JNK and ERK, not p38; however, it was attenuated by administration of an IGF‑1R antagonist.

Risk-Factor Trajectories Preceding Diabetic Polyneuropathy: ADDITION-Denmark

OBJECTIVE

To study cardiometabolic risk-factor trajectories (in terms of levels and changes over time) preceding diabetic polyneuropathy (DPN) 13 years after a screen-detected diagnosis of type 2 diabetes.

RESEARCH DESIGN AND METHODS

We clinically diagnosed DPN in a nested case-control study of 452 people in the Danish arm of the Anglo-Danish-Dutch Study of Intensive Treatment in People with Screen-Detected Diabetes in Primary Care (ADDITION). By linear regression models, we estimated preceding risk-factor trajectories during 13 years. Risk of DPN was estimated by multivariate logistic regression models of each individual's risk-factor trajectory intercept and slope adjusting for sex, age, diabetes duration, height, and trial randomization group.

RESULTS

Higher baseline levels of HbA_1c (odds ratio [OR] 1.76 [95% CI 1.37; 2.27] and OR 1.68 [95% CI 1.33; 2.12] per 1% and 10 mmol/mol, respectively) and steeper increases in HbA_1c over time (OR 1.66 [95% CI 1.21; 2.28] and OR 1.59 [95% CI 1.19; 2.12] per 1% and 10 mmol/mol increase during 10 years, respectively) were associated with DPN. Higher baseline levels of weight, waist circumference, and BMI were associated with DPN (OR 1.20 [95% CI 1.10; 1.31] per 5 kg, OR 1.27 [95% CI 1.13; 1.43] per 5 cm, and OR 1.24 [95% CI 1.12; 1.38] per 2 kg/m², respectively).

CONCLUSIONS

Both higher levels and slopes of HbA_1c trajectories were associated with DPN after 13 years. Our findings indicate that the rate of HbA_1c increase affects the development of DPN over and above the effect of the HbA_1c level. Furthermore, this study supports obesity as a risk factor for DPN.

The Potential Role of Fatty Acids in Treating Diabetic Neuropathy

PURPOSE OF REVIEW

This review will summarize recent findings of the effect of supplemental fatty acids, with an emphasis on omega-3 polyunsaturated fatty acids, as a treatment for diabetic peripheral neuropathy.

RECENT FINDINGS

Pre-clinical studies have provided evidence that treating diabetic rodents with δ linolenic acid (omega-6 18:3) and to a greater extent with eicosapentaenoic and docosahexaenoic acids (omega-3 20:5 and 22:6, respectively) improve and even reverse vascular and neural deficits. Additional studies have shown resolvins, metabolites of eicosapentaenoic and docosahexaenoic acids, can induce neurite outgrowth in neuron cultures and that treating type 1 or type 2 diabetic mice with resolvin D1 or E1 provides benefit for peripheral neuropathy similar to fish oil. Omega-3 polyunsaturated fatty acids derived from fish oil and their derivatives have anti-inflammatory properties and could provide benefit for diabetic peripheral neuropathy. However, clinical trials are needed to determine whether this statement is true.

Risk Factors for Incident Diabetic Polyneuropathy in a Cohort With Screen-Detected Type 2 Diabetes Followed for 13 Years: ADDITION-Denmark

OBJECTIVE

To study incident diabetic polyneuropathy (DPN) prospectively during the first 13 years after a screening-based diagnosis of type 2 diabetes and determine the associated risk factors for the development of DPN.

RESEARCH DESIGN AND METHODS

We assessed DPN longitudinally in the Danish arm of the Anglo-Danish-Dutch study of Intensive Treatment of Diabetes in Primary Care (ADDITION) using the Michigan Neuropathy Screening Instrument questionnaire (MNSIQ), defining DPN with scores ≥4. Risk factors present at the diabetes diagnosis associated with the risk of incident DPN were estimated using Cox proportional hazard models adjusted for trial randomization group, sex, and age.

RESULTS

Of the total cohort of 1,533 people, 1,445 completed the MNSIQ at baseline and 189 (13.1%) had DPN at baseline. The remaining 1,256 without DPN entered this study (median age 60.8 years [interquartile range 55.6; 65.6], 59% of whom were men). The cumulative incidence of DPN was 10% during 13 years of diabetes. Age (hazard ratio [HR] 1.03 [95% CI 1.00; 1.07]) (unit = 1 year), weight (HR 1.09 [95% CI 1.03; 1.16]) (unit = 5 kg), waist circumference (HR 1.14 [95% CI 1.05; 1.24]) (unit = 5 cm), BMI (HR 1.14 [95% CI 1.06; 1.23]) (unit = 2 kg/m²), log₂ methylglyoxal (HR 1.45 [95% CI 1.12; 1.89]) (unit = doubling), HDL cholesterol (HR 0.82 [95% CI 0.69; 0.99]) (unit = 0.25 mmol/L), and LDL cholesterol (HR 0.92 [95% CI 0.86; 0.98]) (unit = 0.25 mmol/L) at baseline were significantly associated with the risk of incident DPN.

CONCLUSIONS

This study provides further epidemiological evidence for obesity as a risk factor for DPN. Moreover, low HDL cholesterol levels and higher levels of methylglyoxal, a marker of dicarbonyl stress, are identified as risk factors for the development of DPN.

The relationship between diabetic risk factors, diabetic complications and salt intake

The relationship between salt and hypertension is the focus of a large amount of research, there are few reviews of the relationship between salt and diabetes, despite the increasing incidence of diabetes. By searching PubMed and the Cochrane Library, we summarized the relationships between diabetic risk factors, diabetic complications and salt intake. The pathophysiological mechanisms underlying the effects of salt on diabetes risk factors and diabetic complications are also discussed. Our findings should assist experts and scholars to understand the current research of salt intake and to pay more attention to the prevention and treatment of related diseases caused by excessive salt intake; guide treatment for patients with diabetes mellitus; and provide a reference for government departments to formulate a reasonable salt restriction policy. We also recommend future research directions.

Impact of Normoglycemia in Reducing Microvascular Complications in Patients with Type 2 Diabetes: A Follow-Up Study

AIMS

Hyperglycemia is associated with an increased risk of microvascular complications in patients with type 2 diabetes. The aim of the present study was to investigate whether the reduction of the levels of HbA1c by tight glycemic control (GC) decreases the rate of microvascular complications and improves the neurological measures in patients with type 2 diabetes.

METHODS

Detailed clinical and neurological examinations including corneal confocal microscopy (CCM) were performed in 141 Japanese patients with type 2 diabetes and 60 age-matched control subjects at baseline and follow-up with GC for 4 years. Patients were stratified according to the mean HbA1c level during follow-up into good (HbA1c < 53.0 mmol/mol, mean; 47.5 mmol/mol), fair (53.0 mmol/mol ≤HbA1c < 58.5 mmol/mol, mean; 55.6 mmol/mol), and poor (HbA1c ≥ 58.5 mmol/mol, mean; 68.9 mmol/mol) GC groups with similar HbA1c levels at baseline (84.5-88.2 mmol/mol).

RESULTS

At baseline, CCM revealed significant nerve fiber damage in all patients compared to that in controls. The interval changes in most corneal nerve fiber (CNF) parameters and neurophysiological functions were significantly related with the mean HbA1c levels during follow-up. Interestingly, the baseline HbA1c level did not impact on neurological functions at follow-up. Interval changes in neuropathy outcomes were associated with mean clinical factors during follow-up and hypoglycemic strategies. Good GC improved all nerve functions, including CNF branch density and bead, but not the length and main fiber density. Fair GC deteriorated some nerve functions. Poor GC compromised all neuropathy outcomes. Irrespective of GC levels, retinopathy increased after follow-up period, while nephropathy decreased.

CONCLUSION

This study showed that tight GC was beneficial just for nephropathy among microvascular complications. Despite strict GC, the retinopathy progressed in patients with type 2 diabetes. Glucose control did not improve neurophysiological and corneal nerve measurements unless near-normoglycemia was reached.

Correlation between serum uric acid and diabetic peripheral neuropathy in T2DM patients

AIM

To investigate the correlation between serum uric acid (SUA) and diabetic peripheral neuropathy (DPN) in type 2 diabetes mellitus (T2DM) patients.

METHODS

Two hundred T2DM patients were divided into four groups at the cut-off points of 5, 7, and 9mg/dL of SUA levels. Nerve conduction studies (NCS), Semmes-Weinstein monofilament testing (SWMT), and vibration perception threshold (VPT) tests were performed on these patients.

RESULTS

Significant differences in motor/sensory nerve amplitude and conduction velocity (CV) parameters among different SUA level groups were observed (all P<0.05). SUA levels were negatively correlated with the means of motor/sensory nerve amplitude and CV (all P<0.05). Duration of T2DM >10years, SUA >9mg/dL and total cholesterol (TC) >5.2mmol/L were found to be significantly associated with DPN (all P<0.05). Receiver-operating characteristic (ROC) analysis revealed that the cut-off points of T2DM duration combined with SUA and TC were 9years, 7.8mg/dL, and 4.97mmol/L, respectively (AUC=0.65; 95% CI: 0.53-0.77; sensitivity, 70.6%; specificity, 65.2%, P=0.009).

CONCLUSION

There is a significant association between elevated SUA levels and DPN, and T2DM duration, SUA, and TC may be valuable indicators to predict the occurrence of DPN in T2DM patients.