Effect of diabetes type on long-term outcome of epidermal axon regeneration

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

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

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

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

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

Reversing painful and non-painful diabetic neuropathy with the capsaicin 8% patch: Clinical evidence for pain relief and restoration of function via nerve fiber regeneration

Introduction

Current oral treatments for pain in diabetic peripheral neuropathy (DPN) do not affect the progression of DPN i.e., "disease modification." We assessed whether Capsaicin 8% patch treatment can provide pain relief and also restore nerve density and function via nerve regeneration, in both painful (PDPN) and non-painful (NPDPN) diabetic peripheral neuropathy.

Methods

50 participants with PDPN were randomized to receive Capsaicin 8% patch Qutenza with Standard of Care (SOC) (PDPN Q+SOC group), or SOC alone (PDPN SOC group). Pain symptoms were assessed with a diary (Numerical Pain Rating Scale, NRPS) and questionnaires. Investigations included quantitative sensory testing (QST) and distal calf skin biopsies, at baseline and 3 months after baseline visit; subsequent options were 3-monthly visits over 1 year. 25 participants with NPDPN had tests at baseline, and 3 months after all received Capsaicin 8% patch treatment.

Results

At 3 months after baseline, PDPN Q+SOC group had reduction in NPRS score (p = 0.0001), but not PDPN SOC group. Short-Form McGill Pain Questionnaire (SF-MPQ) showed significant reductions in scores for overall and other pain descriptors only in the PDPN Q+SOC group. Warm perception thresholds were significantly improved only in the PDPN Q+SOC group (p = 0.02), and correlated with reduction in SF-MPQ overall pain score (p = 0.04). NPDPN Q+SOC group did not report pain during the entire study. Density of intra-epidermal nerve fibers (IENF) with PGP9.5 was increased at 3 months in PDPN Q+SOC (p = 0.0002) and NPDPN Q+SOC (p = 0.002) groups, but not in the PDPN SOC group. Increased sub-epidermal nerve fibers (SENF) were observed with GAP43 (marker of regenerating nerve fibers) only in PDPN Q+SOC (p = 0.003) and NPDPN Q+SOC (p = 0.0005) groups. Pain relief in the PDPN Q+SOC group was correlated with the increased PGP9.5 IENF (p = 0.0008) and GAP43 (p = 0.004), whereas those with lack of pain relief showed no such increase; in some subjects pain relief and increased nerve fibers persisted over months. PGP9.5 IENF increase correlated with axon-reflex vasodilatation in a NPDPN Q+SOC subset (p = 0.006).

Conclusions

Capsaicin 8% patch can provide pain relief via nerve regeneration and restoration of function in DPN (disease modification). It may thereby potentially prevent diabetic foot complications, including ulcers.

Cold sensitivity, functional disability and predicting factors after a repaired digital nerve injury

To investigate self-reported cold sensitivity and functional disability after a repaired digital nerve injury. We identified 3204 individuals operated with digital nerve repair in the Swedish national quality registry for hand surgery (HAKIR). Patient-reported symptoms, including cold sensitivity and perceived disability, were examined using two questionnaires (HQ-8 and QuickDASH), three and 12 months postoperatively. Patients with diabetes (n = 48; 3%) were identified in the Swedish National Diabetes Register (NDR). Cold sensitivity (scored 0–100) was the most prominent symptom among 1553 included individuals (998 men, 555 women; median age 41 [IQR 27–54] years). In the regression analysis, flexor tendon injury, hand fracture and injury to multiple structures predicted worsened cold sensitivity (6.9, 15.5 and 25.0 points; p = 0.005, 0.046 and < 0.001) at 12 months. Individuals with moderate (30–70) and severe (> 70) cold sensitivity had higher QuickDASH scores at three and 12 months postoperatively than individuals with mild cold sensitivity (6.0 and 5.5; 19.8 and 21.0 points; p = 0.001). Flexor tendon injury, injuries to multiple structures and diabetes had significant effect on QuickDASH scores at three, but not at 12, months postoperatively. Cold sensitivity is common after a digital nerve repair and impacts self-reported disability. A concomitant injury, particularly multiple injuries, predicts postoperative cold sensitivity.

Nonpermissive skin environment impairs nerve regeneration in diabetes via Sec31a

OBJECTIVE

Although the microenvironment for peripheral nerve regeneration is permissive, such a mechanism is defective in diabetes, and the molecular mediators remain elusive. This study aimed to (1) investigate the relationship between skin innervation and collagen pathology in diabetic neuropathy and to (2) clarify the molecular alterations that occur in response to hyperglycemia and their effects on axon regeneration.

METHODS

We addressed this issue using two complementary systems: (1) human skin from patients with diabetic neuropathy and to (2) a coculture model of human dermal fibroblasts (HDFs) with rat dorsal root ganglia neurons in the context of intrinsic neuronal factor and extrinsic microenvironmental collagen and its biosynthetic pathways.

RESULTS

In diabetic neuropathy, the skin innervation of intraepidermal nerve fiber density (IENFd), a measure of sensory nerve degeneration, was reduced with similar expression of a growth associated protein 43, a marker of nerve regeneration. In contrast, the content and packing of collagen in the diabetic skin became more rigid than the control skin. Sec31a, a protein that regulates the collagen biosynthetic pathway, was upregulated and inversely correlated with IENFd. In the cell model, activated HDFs exposed to high-glucose medium enhanced the expression of Sec31a and collagen I through the activation of transforming growth factor β, a profibrotic molecule. Sec31a upregulation impaired neurite outgrowth. This effect was reversed by silencing Sec31a expression and neurite outgrowth was resumed.

INTERPRETATION

The current study provides evidence that Sec31a plays a key role in inhibiting nerve regeneration in diabetic neuropathy. This article is protected by copyright. All rights reserved.

Temporal trend of small nerve fibre degeneration in people with and without type 2 diabetes mellitus

AIMS

We investigated the long-term temporal trend of intraepidermal nerve fibre density (IENFD) and the association between changes in IENFD and metabolic factors in individuals with and without type 2 diabetes.

METHODS

A total of 66 participants were enrolled in this longitudinal population-based study, at baseline consisting of 35 individuals (median 61 years) without diabetes and 31 individuals with type 2 diabetes mellitus. Participants underwent clinical and electrophysiological examinations, as well as a skin biopsy both at baseline and at the follow-up visit (mean 8.1 ± 0.5 years). IENFD was assessed in thin sections of 5 μm, stained with the protein gene product 9.5-antibody and compared between the groups.

RESULTS

IENFD decreased during the period in both groups, with a greater decline in the group without diabetes than in type 2 diabetes (-2.3 and -0.6 fibres/mm respectively; p < 0.001). While IENFD at baseline was significantly reduced in type 2 diabetes relative to people without (p < 0.001), no difference in IENFD was found between groups at the follow-up (p = 0.183). Linear mixed model analysis indicated that age, weight and HbA_1c were associated with decrease in IENFD in the total population (p < 0.007). IENFD also decreased with increasing age and weight, but not with HbA_1c , in the separate groups (p < 0.049).

CONCLUSIONS

Despite lower IENFD levels at baseline in type 2 diabetes, IENFD was equal between the groups at follow-up. A decrease in IENFD is to a limited extent affected by body weight, and HbA_1c , but age seems to be the long-term determinant of IENFD in an elderly population.

Redefining distal symmetrical polyneuropathy features in type 1 diabetes: a systematic review

Diabetic neuropathy is among the most frequent complications of both type 1 (T1DM) and type 2 diabetes (T2DM) and commonly manifests as a distal symmetrical polyneuropathy (DSPN). Despite evidence that T1DM- and T2DM-related DSPN are separate entities, most of our knowledge on diabetic DSPN derives from studies focused on type 2 diabetes. This systematic review provides an overview of current evidence on DSPN in T1DM, including its epidemiological, pathophysiological and clinical features, along with principal diagnostic tests findings. This review included 182 clinical and preclinical studies. The results indicate that DSPN is a less frequent complication in T1DM compared with T2DM and that distinctive pathophysiological mechanisms underlie T1DM-related DSPN development, with hyperglycemia as a major determinant. T1DM-related DSPN more frequently manifests with non-painful than painful symptoms, with lower neuropathic pain prevalence compared with T2DM-associated DSPN. The overt clinical picture seems characterized by a higher prevalence of large fiber-related clinical signs (e.g., ankle reflexes reduction and vibration hypoesthesia) and to a lesser extent small fiber damage (e.g., thermal or pinprick hypoesthesia). These findings as a whole suggest that large fibers impairment plays a dominant role in the clinical picture of symptomatic T1DM-related DSPN. Nevertheless, small fiber diagnostic testing shows high diagnostic accuracy in detecting early nerve damage and may be an appropriate diagnostic tool for disease monitoring and screening.

Failure to Upregulate the RNA Binding Protein ZBP After Injury Leads to Impaired Regeneration in a Rodent Model of Diabetic Peripheral Neuropathy

Most diabetes patients eventually suffer from peripheral nerve degeneration. Unfortunately, there is no treatment for the condition and its mechanisms are not well understood. There is, however, an emerging consensus that the inability of peripheral nerves to regenerate normally after injury contributes to the pathophysiology. We have previously shown that regeneration of peripheral axons requires local axonal translation of a pool of axonal mRNAs and that the levels and members of this axonal mRNA pool are altered in response to injury. Here, we show that following sciatic nerve injury in a streptozotocin rodent model of type I diabetes, this mobilization of RNAs into the injured axons is attenuated and correlates with decreased axonal regeneration. This failure of axonal RNA localization results from decreased levels of the RNA binding protein ZBP1. Over-expression of ZBP1 rescues the in vitro growth defect in injured dorsal root ganglion neurons from diabetic rodents. These results provide evidence that decreased neuronal responsiveness to injury in diabetes is due to a decreased ability to alter the pool of axonal mRNAs available for local translation, and may open new therapeutic opportunities for diabetic peripheral neuropathy.

Progression and regression of nerve fibre pathology and dysfunction early in diabetes over 5 years

It has been traditionally suggested that the early development of diabetic sensorimotor polyneuropathy (DSPN) is characterized by a predominant and progressive injury to small nerve fibres followed by large fibre impairment. We alternatively hypothesized that small and large fibre damage due to DSPN in type 1 and type 2 diabetes could develop in parallel and may not only be progressive but also reversible. Participants from the German Diabetes Study baseline cohort with recent-onset type 1/type 2 diabetes (n = 350/570) and age-matched glucose-tolerant control individuals (Control 1/Control 2: n = 114/190) were assessed by nerve conduction studies (NCS), thermal detection thresholds (TDT), vibration perception threshold (VPT), Neuropathy Symptom Score (NSS), Neuropathy Disability Score (NDS), and intraepidermal nerve fibre density (IENFD) in skin biopsies (type 1/type 2 diabetes: n = 102/226; Control 1/Control 2: n = 109/208). Subsets of participants with type 1/type 2 diabetes were followed for 5 years (n = 184/307; IENFD subset: n = 18/69). DSPN was defined by the Toronto Consensus criteria. At baseline, DSPN was present in 8.1 and 13.3% of the type 1 and type 2 diabetes groups, respectively. The most frequently abnormal tests in the lower limbs below or above the 2.5th and 97.5th centile of the controls were IENFD (13.7%) and individual NCS (up to 9.4%) in type 1 diabetes participants and IENFD (21.8%), malleolar VPT (17.5%), and individual NCS (up to 11.8%) in those with type 2 diabetes, whereas TDT abnormalities did not differ between the control and diabetes groups. After 5 years in type 2 diabetes participants, the highest progression rates from the normal to the abnormal range were found for IENFD (18.8%) by -4.1 ± 2.8 fibres/mm, malleolar VPT (18.6%) by 9.1 ± 20.2 µm, and NDS (15.0%) by 3.7 ± 1.5 points, while vice versa the highest regression rates were observed for NDS (11.2%) by -3.1 ± 1.3 points, sural nerve amplitude (9.1%) by 4.7 ± 3.0 µV, IENFD (8.7%) by 1.4 ± 1.3 fibres/mm, and NSS (8.2%) by -5.8 ± 1.6 points. In type 1 diabetes participants, no major progression was seen after 5 years, but subclinical DSPN regressed in 10.3%. These findings point to an early parallel damage to both small and large nerve fibres in well-controlled recent-onset type 2 and, to a lesser extent, type 1 diabetes. After 5 years peripheral nerve morphology and function and clinical measures progress to the abnormal range in type 2 diabetes, but initial nerve alterations are also reversible to a meaningful degree.

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

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

The Physiological Significance of A-Waves in Early Diabetic Neuropathy: Assessment of Motor Nerve Fibers by Neurophysiological Techniques

Objective: This study aimed to investigate how early A-waves could occur in type II diabetes, and what it implied functionally. Methods: We performed conduction velocity distribution (CVD) test in peroneal nerves of 37 type II diabetic patients with normal nerve conduction study (NCS) and 22 age-matched controls. The electrophysiological data and clinical information were analyzed. Results: A-waves were observed in 45.9% of diabetic patients and only in 1 person in healthy controls, all detected in the tibial nerves. The diabetic patients with A-waves showed faster conduction velocity in all quartiles in the motor peroneal nerves compared to the patients without A-waves, and their CVD histograms were shifted to the right side, consisting of a significantly larger percentage of fast conducting fibers. There was no significant difference in the CVD values of the upper extremity nerves among the patients with and without A-waves and the healthy controls. Conclusion: A-waves could occur in type II diabetes as early as when NCS showed normal, and represented as a sign of neuropathy as well as a sign of rescued motor nerve function.

Lost in Translation? Measuring Diabetic Neuropathy in Humans and Animals

The worldwide diabetes epidemic is estimated to currently afflict almost 500 million persons. Long-term diabetes damages multiple organ systems with the blood vessels, eyes, kidneys and nervous systems being particularly vulnerable. These complications of diabetes reduce lifespan, impede quality of life and impose a huge social and economic burden on both the individual and society. Peripheral neuropathy is a debilitating complication that will impact over half of all persons with diabetes. There is no treatment for diabetic neuropathy and a disturbingly long history of therapeutic approaches showing promise in preclinical studies but failing to translate to the clinic. These failures have prompted re-examination of both the animal models and clinical trial design. This review focuses on the functional and structural parameters used as indices of peripheral neuropathy in preclinical and clinical studies and the extent to which they share a common pathogenesis and presentation. Nerve conduction studies in large myelinated fibers have long been the mainstay of preclinical efficacy screening programs and clinical trials, supplemented by quantitative sensory tests. However, a more refined approach is emerging that incorporates measures of small fiber density in the skin and cornea alongside these traditional assays at both preclinical and clinical phases.

The Importance of Non-Coding RNAs in Neurodegenerative Processes of Diabetes-Related Molecular Pathways

Diabetes mellitus (DM) is a complex condition and serious health problem, with growing occurrence of DM-associated complications occurring globally. Persistent hyperglycemia is confirmed as promoting neurovascular dysfunction leading to irreversible endothelial cell dysfunction, increased neuronal cell apoptosis, oxidative stress and inflammation. These collaboratively and individually result in micro- and macroangiopathy as well as neuropathy demonstrated by progressive neuronal loss. Recently, major efforts have been pursued to select not only useful diagnostic and prognostic biomarkers, but also novel therapeutic approaches. Both microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) belong to a class of non-coding RNAs identified in most of the body fluids i.e., peripheral blood, cerebrospinal fluid, brain tissue and neurons. Numerous miRNAs, lncRNAs and their target genes are able to modulate signaling pathways known to play a role in the pathophysiology of progressive neuronal dysfunction. Therefore, they pose as promising biomarkers and treatment for the vast majority of neurodegenerative disorders. This review provides an overall assessment of both miRNAs’ and lncRNAs’ utility in decelerating progressive nervous system impairment, including neurodegeneration in diabetic pathways.