Diabetes and Peripheral Nerve Disease

Sortilin-Mediated Inhibition of TREK1/2 Channels in Primary Sensory Neurons Promotes Prediabetic Neuropathic Pain

Neuropathic pain can occur during the prediabetic stage, even in the absence of hyperglycemia. The presence of prediabetic neuropathic pain (PDNP) poses challenges to the management of individuals with prediabetes. However, the mechanisms underlying this pain remain unclear. This study aims to investigate the underlying mechanism and identify potential therapeutic targets of PDNP. A prediabetic animal model induced by a high-energy diet exhibits both mechanical allodynia and thermal hyperalgesia. Furthermore, hyperexcitability and decreased potassium currents are observed in the dorsal root ganglion (DRG) neurons of these rats. TREK1 and TREK2 channels, which belong to the two-pore-domain K+ channel (K2P) family and play an important role in controlling cellular excitability, are downregulated in DRG neurons. Moreover, this alteration is modulated by Sortilin, a molecular partner that modulates the expression of TREK1. The overexpression of Sortilin negatively affects the expression of TREK1 and TREK2, leading to increased neuronal excitability in the DRG and enhanced peripheral pain sensitivity in rats. Moreover, the downregulation of Sortilin or activation of TREK1 and TREK2 channels by genetic or pharmacological approaches can alleviate PDNP. Therefore, targeting the Sortilin-mediated TREK1/2 pathway may provide a therapeutic approach for ameliorating PDNP.

The Relationship Between UA/HDL and Diabetic Peripheral Neuropathy: A Cross-Sectional Analysis

Purpose

This study was designed to analyze correlations between the uric acid to high-density lipoprotein cholesterol ratio (UHR) and peripheral nerve conduction velocity (NCV) among type 2 diabetes mellitus (T2DM) patients.

Patients and Methods

This was a single-center cross-sectional analysis of 324 T2DM patients. All patients were separated into a group with normal NCV (NCVN) and a group with abnormal NCV (NCVA). Patients were also classified into groups with low and high UHR values based on the median UHR in this study cohort. Neurophysiological data including motor and sensory conduction velocity (MCV and SCV, respectively) were measured for all patients.

Results

Relative to patients with low UHR values, those in the high UHR group presented with greater NCVA prevalence (P = 0.002). UHR remained negatively correlated with bilateral superficial peroneal nerve SCV, bilateral common peroneal nerve MCV, bilateral ulnar nerve SCV, and bilateral right median nerve MCV even after adjustment for confounding factors. UHR was identified as an NCVA-related risk factor, with a 1.370-fold increase in NCVA prevalence for every unit rise in UHR (P < 0.001).

Conclusion

These results identify UHR as a risk factor associated with NCVA that was independently negatively associated with NCV among T2DM patients.

PnPP-15, a Synthetic Peptide Derived from a Toxin from Phoneutria nigriventer Spider Venom, Alleviates Diabetic Neuropathic Pain and Acts Synergistically with Pregabalin in Mice

Diabetic neuropathic pain is one of the complications that affect a wide variety of the diabetic population and is often difficult to treat. Only a small number of patients experience pain relief, which usually comes with onerous side effects and low levels of satisfaction. The search for new analgesic drugs is necessary, given the limitations that current drugs present. Combining drugs to treat neuropathic pain has been attracting interest to improve their efficacy compared to single-drug monotherapies while also reducing dose sizes to minimize side effects. The aim of our study was to verify the antinociceptive effect of a synthetic peptide, PnPP-15, alone and combined with pregabalin, in male Swiss diabetic mice using the von Frey method. PnPP-15 is a synthetic peptide derived from PnPP19, a peptide representing a discontinuous epitope of the primary structure of the toxin PnTx2-6 from the venom of the spider Phoneutria nigriventer. The antinociceptive activity of both compounds was dose-dependent and showed synergism, which was verified by isobolographic analysis. Treatment with PnPP-15 did not cause spontaneous or forced motor changes and did not cause any damage or signs of toxicity in the analyzed organs (pancreas, lung, heart, kidney, brain, or liver). In conclusion, PnPP-15 is a great candidate for an analgesic drug against neuropathic pain caused by diabetes and exerts a synergistic effect when combined with pregabalin, allowing for even more efficient treatment.

A Cross-Sectional Study Investigating Lumbar Proprioception Impairments in Individuals with Type 2 Diabetes Mellitus: Correlations with Glycated Hemoglobin Levels

Impaired proprioception is a recognized complication in individuals with type 2 diabetes mellitus (T2DM), contributing to balance deficits and increased risk of falls. However, limited research has focused on lumbar proprioception in this population. This study aimed to investigate lumbar proprioception in individuals with T2DM, as well as healthy individuals. Additionally, this study aimed to examine the correlation between lumbar proprioception and glycated hemoglobin (HbA1c) levels, which is a marker of long-term glycemic control in T2DM. A cross-sectional study was conducted, comparing lumbar joint reposition errors (JRE) between a T2DM group (n = 85) and a healthy group (n = 85). Lumbar JRE was assessed in flexion, extension, lateral bending left, and lateral bending right using a dual inclinometer device. HbA1c levels were measured as an indicator of glycemic control. Significant differences in lumbar JRE were found between the T2DM and healthy groups, with individuals with T2DM exhibiting larger JRE values, indicating impaired lumbar proprioception (p < 0.001). The correlation analysis revealed significant positive associations between HbA1c levels and lumbar JRE. Higher HbA1c levels were correlated with greater joint JRE in flexion (r = 0.49, p < 0.001), extension (r = 0.51, p < 0.001), left lateral bending (r = 0.45, p < 0.001), and right lateral bending (r = 0.48, p < 0.001) in the T2DM group. This study provides evidence of impaired lumbar proprioception in individuals with T2DM, as evidenced by larger lumbar JRE compared to the healthy group.

The prevalence of peripheral neuropathy among the patients with diabetes in Pakistan: a systematic review and meta-analysis

The most frequent complication of diabetes is peripheral neuropathy. The estimated prevalence of peripheral neuropathy in people with diabetes varies substantially between published studies in Pakistan. We conducted this meta-analysis to summarize the prevalence of peripheral neuropathy in people with diabetes. Different electronic databases were systematically searched using keywords and MeSH terms. Random-effects meta-analysis was conducted to pool the prevalence of peripheral neuropathy in people with diabetes in Pakistan. Heterogeneity was investigated by random-effects meta-regression and stratification. Two independent authors reviewed studies, extracted data, and conducted the risk of bias analysis. Nineteen studies with a total of 8487 diabetic patients were included. The overall pooled prevalence of diabetic peripheral neuropathy was 43.16% (95% CI 32.93-53.69%), with significant heterogeneity between estimates. The prevalence of peripheral neuropathy among those newly diagnosed with diabetes was 26.52% (95% CI 14.97-39.96%, n = 5). According to the subgroup meta-analysis, the pooled prevalence of diabetic peripheral neuropathy was highest in Khyber Pakhtunkhwa (55.29%; 95% CI 23.91-84.50%), followed by Sindh (40.04%; 95% CI 24.00-57.25%), and the lowest was found in Punjab (34.90%; 95% CI 15.05-57.95%). A significant association was found between the pooled prevalence estimate and the duration of diabetes. The results of this meta-analysis indicate a relatively high prevalence of peripheral neuropathy in people with diabetes in Pakistan. The study protocol has been registered in the PROSPERO, with the registration number CRD42022371617.

Exogenous Antioxidants in Remyelination and Skeletal Muscle Recovery

Inflammatory, oxidative, and autoimmune responses cause severe damage to the nervous system inducing loss of myelin layers or demyelination. Even though demyelination is not considered a direct cause of skeletal muscle disease there is extensive damage in skeletal muscles following demyelination and impaired innervation. In vitro and in vivo evidence using exogenous antioxidants in models of demyelination is showing improvements in myelin formation alongside skeletal muscle recovery. For instance, exogenous antioxidants such as EGCG stimulate nerve structure maintenance, activation of glial cells, and reduction of oxidative stress. Consequently, this evidence is also showing structural and functional recovery of impaired skeletal muscles due to demyelination. Exogenous antioxidants mostly target inflammatory pathways and stimulate remyelinating mechanisms that seem to induce skeletal muscle regeneration. Therefore, the aim of this review is to describe recent evidence related to the molecular mechanisms in nerve and skeletal muscle regeneration induced by exogenous antioxidants. This will be relevant to identifying further targets to improve treatments of neuromuscular demyelinating diseases.

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

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