Susceptible and Prognostic Genetic Factors Associated with Diabetic Peripheral Neuropathy: A Comprehensive Literature Review

Exploring the role of miRNA in diabetic neuropathy: from diagnostics to therapeutics

Diabetic neuropathy (DN) is one of the major microvascular complications of diabetes mellitus affecting 50% of the diabetic population marred by various unmet clinical needs. There is a need to explore newer pathological mechanisms for designing futuristic regimens for the management of DN. There is a need for post-transcriptional regulation of gene expression by non-coding RNAs (ncRNAs) to finetune different cellular mechanisms with significant biological relevance. MicroRNAs (miRNAs) are a class of small ncRNAs (~ 20 to 24 nucleotide length) that are known to regulate the activity of ~ 50% protein-coding genes through repression of their target mRNAs. Differential expression of these miRNAs is associated with the pathophysiology of diabetic neuropathy via regulating various pathways such as neuronal hyperexcitability, inflammation, axonal growth, regeneration, and oxidative stress. Of note, the circulating and extracellular vesicular miRNAs serve as potential biomarkers underscoring their diagnostic potential. Recent pieces of evidence highlight the potential of miRNAs in modulating the initiation and progression of DN and the possibility of developing miRNAs as treatment options for DN. In this review, we have elaborated on the role of different miRNAs as potential biomarkers and emphasized their druggable aspects for promising future therapies for the clinical management of DN.

Investigating the interplay between mitophagy and diabetic neuropathy: Uncovering the hidden secrets of the disease pathology

Mitophagy, the cellular process of selectively eliminating damaged mitochondria, plays a crucial role in maintaining metabolic balance and preventing insulin resistance, both key factors in type 2 diabetes mellitus (T2DM) development. When mitophagy malfunctions in diabetic neuropathy, it triggers a cascade of metabolic disruptions, including reduced energy production, increased oxidative stress, and cell death, ultimately leading to various complications. Thus, targeting mitophagy to enhance the process may have emerged as a promising therapeutic strategy for T2DM and its complications. Notably, plant-derived compounds with β-cell protective and mitophagy-stimulating properties offer potential as novel therapeutic agents. This review highlights the intricate mechanisms linking mitophagy dysfunction to T2DM and its complications, particularly neuropathy, elucidating potential therapeutic interventions for this debilitating disease.

Global hotspots and trends in diabetic peripheral neuropathy research from 2011 to 2023

Diabetic peripheral neuropathy (DPN) is a prevalent disease, and the relevant literature has been increasingly investigated over the past years. Consequently, it is imperative to conduct a scientific and comprehensive DPN research field bibliometric analysis. This study aims to summarize and visualize the literature distribution laws, the research hotspots, and the development trends in DPN using bibliometric methods. We searched all relevant documents published from 2011 to 2023 in the Web of Science Core Collection. Bibliometric analysis and network visualization were performed using VOSviewer, R-bibliometrix, and CiteSpace tools, focusing on countries, institutions, authors, journals, highly cited papers, references, and keywords. This study included a total of 2708 documents. The annual number of publications in the field has notably increased. China, the USA, and the UK take on critical significance in DPN research. The University of Manchester in the UK has the highest number of publications (109). Malik has the most publications (86). Tesfaye literature has been most frequently cited by scholars of DPN research. The Journal of Diabetes and its Complications and Frontiers in Endocrinology have the most publications (45 each). Diabetes Care stands out with the highest impact factor (16.200), number of citations (2516), and H-index (27) among the number of publications top 10 journals. The paper "Colloca, L. et al Neuropathic pain. Nature Reviews Disease Primers. 2017, 3 (1):1-19" has the highest number of citations (1224 times). The most critical co-cited reference is "Tesfaye S, 2010, DIABETES CARE, V33, P2285" (cited 408 times). Keywords like "type 2 diabetes," "diagnosis," "association," "retinopathy," "risk factors," "progression," "corneal confocal microscopy," "nephropathy," "balance," "microvascular complications," "inflammation," "disease," and "insulin resistance" represent the recent research hotspots. The development, research hotspots, and future trends of the global DPN domain from 2011 to 2023 were summarized and visualized in this study. This study can present more insights into the general situation of DPN research and provide a useful reference for clinical decision-making and directions of subsequent research.

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.

PPARγ and AKt gene modulation following pregabalin and duloxetine combination for painful diabetic polyneuropathy

Aim: Diabetic peripheral neuropathy (DPN) induces chronic neuropathic pain in diabetic patients. Current treatments like pregabalin and duloxetine offer limited efficacy. This study evaluates combining pregabalin and duloxetine versus pregabalin alone for DPN pain relief, and explores gene modulation (PPARγ and Akt) to understand neuropathic pain's molecular basis.Materials & methods: Diabetic patients with DPN were randomized into groups receiving combination therapy or pregabalin alone for 4 weeks. Pain intensity, gene expression and quality of life were assessed.Results: Combination therapy significantly reduced pain, improved quality of life and upregulated PPARγ and Akt genes compared with monotherapy.Conclusion: Pregabalin and duloxetine combination therapy in DPN led to PPARγ mRNA upregulation and negative correlation of Akt gene expression with pain scores. This combination therapy effectively reduced pain and improved quality of life.Clinical Trial Registration: CTRI/2021/02/031068.

Preclinical study of diabetic foot ulcers: From pathogenesis to vivo/vitro models and clinical therapeutic transformation

Diabetic foot ulcer (DFU), a common intractable chronic complication of diabetes mellitus (DM), has a prevalence of up to 25%, with more than 17% of the affected patients at risk of amputation or even death. Vascular risk factors, including vascular stenosis or occlusion, dyslipidemia, impaired neurosensory and motor function, and skin infection caused by trauma, all increase the risk of DFU in patients with diabetes. Therefore, diabetic foot is not a single pathogenesis. Preclinical studies have contributed greatly to the pathogenesis determination and efficacy evaluation of DFU. Many therapeutic tools are currently being investigated using DFU animal models for effective clinical translation. However, preclinical animal models that completely mimic the pathogenesis of DFU remain unexplored. Therefore, in this review, the preparation methods and evaluation criteria of DFU animal models with three major pathological mechanisms: neuropathy, angiopathy and DFU infection were discussed in detail. And the advantages and disadvantages of various DFU animal models for clinical sign simulation. Furthermore, the current status of vitro models of DFU and some preclinical studies have been transformed into clinical treatment programs, such as medical dressings, growth factor therapy, 3D bioprinting and pre-vascularization, Traditional Chinese Medicine treatment. However, because of the complexity of the pathological mechanism of DFU, the clinical transformation of DFU model still faces many challenges. We need to further optimize the existing preclinical studies of DFU to provide an effective animal platform for the future study of pathophysiology and clinical treatment of DFU.

Diabetic Peripheral Neuropathy Associated with Foot Ulcer: One of a Kind

Significance: Diabetic peripheral neuropathy (DPN) associated with a diabetic foot ulcer (DFU) is likely to be complicated with critical factors such as biofilm infection and compromised skin barrier function of the diabetic skin. Repaired skin with a history of biofilm infection is known to be compromised in barrier function. Loss of barrier function is also observed in the oxidative stress affected diabetic and aged skin. Recent Advances: Loss of barrier function makes the skin prone to biofilm infection and cellulitis, which contributes to chronic inflammation and vasculopathy. Hyperglycemia favors biofilm formation as glucose lowering led to reduction in biofilm development. While vasculopathy limits oxygen supply, the O2 cost of inflammation is high increasing hypoxia severity. Critical Issues: The host nervous system can be inhabited by bacteria. Because electrical impulses are a part of microbial physiology, polymicrobial colonization of the host's neural circuit is likely to influence transmission of action potential. The identification of perineural apatite in diabetic patients with peripheral neuropathy suggests bacterial involvement. DPN starts in both feet at the same time. Future Directions: Pair-matched studies of DPN in the foot affected with DFU (i.e., DFU-DPN) compared with DPN in the without ulcer, and intact skin barrier function, are likely to provide critical insight that would help inform effective care strategies. This review characterizes DFU-DPN from a translational science point of view presenting a new paradigm that recognizes the current literature in the context of factors that are unique to DFU-DPN.

Diabetic neuropathy: Past, present, and future

Background

A sedentary lifestyle and an unhealthy diet have considerably increased the incidence of diabetes mellitus worldwide in recent decades, which has generated a high rate of associated chronic complications.

Methods

A narrative review was performed in MEDLINE, EMBASES and SciELO databases, including 162 articles.

Results

Diabetic neuropathy (DN) is the most common of these complications, mainly producing two types of involvement: sensorimotor neuropathy, whose most common form is symmetric distal polyneuropathy, and autonomic neuropathies, affecting the cardiovascular, gastrointestinal, and urogenital system. Although hyperglycemia is the main metabolic alteration involved in its genesis, the presents of obesity, dyslipidemia, arterial hypertension, and smoking, play an additional role in its appearance. In the pathophysiology, three main phenomena stand out: oxidative stress, the formation of advanced glycosylation end-products, and microvasculature damage. Diagnosis is clinical, and it is recommended to use a 10 g monofilament and a 128 Hz tuning fork as screening tools. Glycemic control and non-pharmacological interventions constitute the mainstay of DN treatment, although there are currently investigations in antioxidant therapies, in addition to pain management.

Conclusions

Diabetes mellitus causes damage to peripheral nerves, being the most common form of this, distal symmetric polyneuropathy. Control of glycemia and comorbidities contribute to prevent, postpone, and reduce its severity. Pharmacological interventions are intended to relieve pain.

Blocking CXC Motif Chemokine Ligand 2 Ameliorates Diabetic Peripheral Neuropathy via Inhibiting Apoptosis and NLRP3 Inflammasome Activation

Evidence suggests that CXC motif chemokines are involved in neuronal injury and inflammatory processes. Bioinformatics analysis by using data from the Gene Expression Omnibus (GEO) database was performed and identified CXC motif chemokine ligands (CXCLs) as associated with diabetic peripheral neuropathy (DPN). The present study focused on CXC motif chemokine ligand 2 (CXCL2), and the role and potential mechanisms of CXCL2 in DPN were investigated. The DPN rat model was generated by streptozotocin (STZ) injection in vivo, and high-glucose (HG)-stimulated Schwann cell RSC96 was considered a cell model of DPN in vitro. Neuropathic symptoms of DPN were explored by neurological tests and histological examinations. DPN rats showed a decreased level of motor nerve conduction velocity (MNCV) along with typical histological changes. CXCL2 expression was significantly increased in STZ-induced DPN rat sciatic nerve and HG-induced RSC96 cells. Functionally, CXCL2 knockdown inhibited cell apoptosis and inflammation activation under diabetic conditions in vitro and in vivo. CXCL2 knockdown increased cell viability in HG-treated RSC96 cells and reduced apoptosis concerning the decreased expression of cleaved Caspase 3/9. In addition, CXCL2 knockdown protected against NOD-like receptor protein 3 (NLRP3) inflammasome activation and reduced levels of pro-inflammatory cytokines, interleukin (IL)-1β and IL-18. The repressive effects of CXCL2 knockdown on inflammasome activation under HG conditions were significantly abolished by treatment of the NLRP3 activator nigericin. In conclusion, these results indicated that CXCL2 knockdown exhibited amelioration of hyperglycemia-induced DPN by inhibiting cell apoptosis and NLRP3 inflammasome activation, suggesting that targeting CXCL2 might be a potential strategy for DPN treatment.

miRNA-130a-3p targets sphingosine-1-phosphate receptor 1 to activate the microglial and astrocytes and to promote neural injury under the high glucose condition

As a common complication of diabetes, diabetic pain neuropathy (DPN) is caused by neuron intrinsic and extrinsic factors. Neuron intrinsic factors include neuronal apoptosis and oxidative stress, while extrinsic factors are associated with glial activation. The present study was performed to reveal the functions of miR-130a-3p in apoptosis and oxidative stress of the high glucose (HG)-stimulated primary neurons as well as in the activation of microglial and astrocytes. Primary neurons, microglial, and astrocytes were isolated from newborn mice. Apoptosis was assessed by flow cytometry analysis and western blotting. Reactive oxygen species and glutathione levels were assessed to determine the oxidative stress. Markers of glial cells were detected by immunofluorescence staining. The results revealed that miR-130a-3p deficiency alleviated apoptosis and oxidative stress of HG-stimulated neurons as well as suppressed microglial and astrocyte activation. Moreover, sphingosine-1-phosphate receptor 1 (S1PR1) was found as a target downstream of miR-130a-3p. S1PR1 knockdown partially rescued the inhibitory effects of silenced miR-130a-3p on neuronal injury and glial activation. In conclusion, miR-130a-3p targets S1PR1 to activate the microglial and astrocytes and to promote apoptosis and oxidative stress of the HG-stimulated primary neurons. These findings may provide a novel insight into DPN treatment.

The Effect of Thymus vulgaris on Hepatic Enzymes Activity and Apoptosis-Related Gene Expression in Streptozotocin-Induced Diabetic Rats

Many diseases, including diabetes, are involved in the development of liver disorders through changes in the expression of genes such as apoptosis-related genes. In the present study, the effect of Thymus vulgaris (T. vulgaris) on hepatic enzyme activity and apoptosis-related gene expression in streptozotocin (STZ)-induced diabetic rats was examined. In this study, 50 adult male Wistar rats weighing approximately 200–220 g were divided into five groups. Diabetes was induced by an intraperitoneal injection of STZ (60 mg/kg). Following 18 days, all the animals in different groups were weighed and blood samples were taken from their cardiac veins. Gas chromatography-mass spectrometry (GC-MS) analysis revealed 45 different compounds in the T. vulgaris, including thymol (39.1%), p-cymene (20.63%), and γ-terpinene (14.85%). The results showed a significant increase in liver enzymes (aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP)) in diabetic or STZ mice compared to the control group (healthy mice) (P < 0.0001). The levels of AST, ALT, and ALP in rats treated with 200 mg/kg and 400 mg/kg of T. vulgaris extract showed a significant decrease in these enzymes in comparison with diabetic rats (P < 0.0001). The expression of caspase 3 and 9 genes in the groups treated with thyme significantly decreased compared to diabetic mice (P < 0.0001), and the expression of B-cell lymphoma-2 (Bcl-2) in the group receiving 400 mg/kg of thyme significantly increased compared to diabetic mice (P < 0.0001). Due to its antioxidant compounds, thyme improves the liver tissue cells in STZ-induced diabetic mice by reducing caspases 3 and 9 as well as increasing Bcl-2.

Involvement of Cdkal1 in the etiology of type 2 diabetes mellitus and microvascular diabetic complications: a review

Diabetes Mellitus, being a polygenic disorder, have a set of risk genes involved in the onset of the insulin resistance, obesity and impaired insulin synthesis. Recent genome wide association studies (GWAS) shows the intimacy of CDK5 regulatory subunit Associated protein 1-Like 1 (Cdkal1) with the pathophysiology of the diabetes mellitus and its complications, although the exact molecular relation is still unknown. In this short review, we have summarized all the diverse biological roles of Cdkal1 in relation to the onset of diabetes mellitus. Variations in the Cdkal1 transcript are responsible for the accumulation of misfolded insulin and thus generating oxidative and ER stress in the pancreatic β-cells, leading to their destruction. Recent studies have shown that Cdkal1 has an intrinsic thiomethyl transferase activity, which is essential for proper posttranslational processing of pre-proinsulin to produce mature insulin. Moreover, Cdkal1 has also been claimed as an endogenous inhibitor of cdk5, which prevents the cdk5-induced interruption in insulin synthesis through PDX1 translocation from nucleus to cytosol. Recent clinical studies have identified the risk single nucleotide polymorphisms (SNPs) of Cdkal1 as one of the root causes for the onset of diabetic complications. To the best of our knowledge, it is the first comprehensive review which elaborates most of the potential Cdkal1-dependent molecular mechanisms studied yet. In this review, we present a compiled and concise summary about all the diverse roles of Cdkal1 in the context of type 2 diabetes mellitus and its associated complications. This review will be helpful to target Cdkal1 as a potential option for the management of type 2 diabetes mellitus in future.

Graphical abstract

Association between serum Sestrin2 level and diabetic peripheral neuropathy in type 2 diabetic patients

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a chronic and serious microvascular complication of diabetes linked to redox imbalance. Sestrin2, a novel inducible stress protein, participates in glucose metabolic regulation and redox homeostasis. However, the association between serum Sestrin2 and DPN is unknown.

AIM

To explore the association between serum Sestrin2 and DPN in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 96 T2DM patients and 39 healthy volunteers, matched by age and sex, participated in this cross-sectional study. Clinical features and metabolic indices were identified. Serum Sestrin2 was measured by ELISA. The association between Sestrin2 and DPN was studied. Correlation and logistic regression analyses were used to evaluate the associations of different metabolic indices with Sestrin2 and DPN.

RESULTS

The 96 patients with T2DM were divided into DPN (n = 47) and patients without DPN (n = 49). Serum Sestrin2 was significantly lower in healthy volunteers than in all T2DM patients combined [9.10 (5.41-13.53) ng/mL vs 12.75 (7.44-23.80) ng/mL, P < 0.01]. T2DM patients without DPN also had significantly higher levels of Sestrin2 than healthy volunteers [14.58 (7.93-26.62) ng/mL vs 9.10 (5.41-13.53) ng/mL, P < 0.01]. However, T2DM patients with DPN had lower circulating Sestrin2 levels compared to T2DM patients without DPN [9.86 (6.72-21.71) ng/mL vs 14.58 (7.93-26.62) ng/mL, respectively, P < 0.01]. Bivariate correlation analysis revealed that serum Sestrin2 was positively correlated with body mass index (r = 0.672, P = 0.000), hemoglobin A1c (HbA1c) (r = 0.292, P = 0.000), serum creatinine (r = 0.206, P = 0.016), triglycerides (r = 0.731, P = 0.000), and fasting glucose (r = 0.202, P = 0.040), and negatively associated with estimated glomerular filtration rate (r = -0.230, P = 0.007). After adjustment for sex, age, HbA1c, and diabetes duration, multiple regression analysis revealed that Sestrin2 was independently correlated with body mass index and triglyceride levels (P = 0.000). Logistic regression analyses indicated that Sestrin2, diabetes duration, and high-density lipoprotein were strongly associated with DPN (odds ratio = 0.855, 1.411, and 0.041, respectively).

CONCLUSION

Our results show Sestrin2 is decreased in T2DM patients with DNP. As lower Sestrin2 is independently associated with DPN, Sestrin2 may contribute to progression of DPN in T2DM patients.

Characteristics of the intestinal flora in patients with peripheral neuropathy associated with type 2 diabetes

OBJECTIVE

To study the characteristics of the intestinal flora in patients with diabetic peripheral neuropathy (DPN) and analyze the association between the intestinal flora and clinical indicators.

METHODS

We classified 80 subjects into three groups: patients with DPN (n = 45), patients type 2 diabetes without DPN (n = 21), and healthy controls (n = 14). The intestinal flora composition was compared among the three groups, and the correlation between the intestinal flora and clinical indicators was analyzed.

RESULTS

At the phylum level, the richness of Firmicutes and Actinobacteria was elevated in the DN group, and that of Bacteroidetes was decreased. At the genus level, the richness of Bacteroides and Faecalibacterium was significantly decreased in the DPN group, whereas that of Escherichia-Shigella, Lachnoclostridium, Blautia, Megasphaera, and Ruminococcus torques group was increased. The homeostasis model assessment insulin resistance index was positively correlated with Megasphaera richness. Glycine ursodeoxycholic acid was positively correlated with Ruminococcus gnavus group and Phascolarctobacterium richness. Tauroursodeoxycholic acid was positively correlated with Ruminococcus gnavus group and Parabacteroides richness.

CONCLUSION

There was obvious intestinal microbiota disorder in patients with DPN, which may be related to insulin resistance. These changes may have important roles in the development of DPN.

Traditional Chinese medicine fumigation as auxiliary treatment of diabetic peripheral neuropathy: A protocol for systematic review and meta-analysis

BACKGROUND

Diabetic peripheral neuropathy (DPN) is 1 of the most common clinical complications of diabetes, which seriously affects the quality of life of patients and causes a substantial economic burden on diabetes care. The pathogenesis of DPN is complex. There is no targeted treatment method, and mainstream treatment methods have low efficacy and large side effects. Traditional Chinese medicine has rich clinical experience in the prevention and treatment of diabetic peripheral neuropathy, which has dramatically improved the quality of life of patients. It is clinically proven that traditional Chinese medicine fumigants (TCMF) have apparent effects in treating diabetic peripheral neuropathy. Therefore, we aim to systematically review the effectiveness and safety of TCMF for DPN.

METHODS

We will search the following databases: PubMed, Embase, Cochrane Library, MEDLINE, the China National Knowledge Infrastructure, the Chinese Biomedical Literature Database, Cqvip Database, and Wanfang Data. Besides, we will also search for clinical trial registrations, potential grey literature, relevant conference abstracts, and reference lists of established studies. The studies published from the inception of the database to November 2020 will be retrieved. The randomized controlled trials on TCMF for DPN will be included. Also, we will search for clinical trial registrations, potential grey literature, relevant conference abstracts, and reference lists of established studies. The main result is clinical efficacy and nerve conduction velocity. Fasting blood glucose, 2 hours postprandial blood glucose, blood lipid, glycosylated hemoglobin, and adverse events are secondary results. We will perform the analyses using RevMan V.5.3 software.

RESULTS

This study will provide a high-quality comprehensive evaluation of the efficacy and safety of TCMF in the treatment of DPN.

CONCLUSIONS

This systematic review will evaluate the effectiveness and safety of TCMF in the treatment of DPN, and provide the latest evidence for clinical application.

INPLASY REGISTRATION NUMBER

INPLASY2020110137.

SP6616 as a Kv2.1 inhibitor efficiently ameliorates peripheral neuropathy in diabetic mice

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes severely afflicting the patients, while there is yet no effective medication against this disease. As Kv2.1 channel functions potently in regulating neurological disorders, the present work was to investigate the regulation of Kv2.1 channel against DPN-like pathology of DPN model mice by using selective Kv2.1 inhibitor SP6616 (ethyl 5-(3-ethoxy-4-methoxyphenyl)-2-(4-hydroxy-3-methoxybenzylidene)-7-methyl-3-oxo-2,3-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidine-6-carboxylate) as a probe.

METHODS

STZ-induced type 1 diabetic mice with DPN (STZ mice) were defined at 12 weeks of age (4 weeks after STZ injection) through behavioral tests, and db/db (BKS Cg-m+/+Leprdb/J) type 2 diabetic mice with DPN (db/db mice) were at 18 weeks of age. SP6616 was administered daily via intraperitoneal injection for 4 weeks. The mechanisms underlying the amelioration of SP6616 on DPN-like pathology were investigated by RT-PCR, western blot and immunohistochemistry technical approaches against diabetic mice, and verified against the STZ mice with Kv2.1 knockdown in dorsal root ganglion (DRG) tissue by injection of adeno associated virus AAV9-Kv2.1-RNAi. Amelioration of SP6616 on the pathological behaviors of diabetic mice was assessed against tactile allodynia, thermal sensitivity and motor nerve conduction velocity (MNCV).

FINDINGS

SP6616 treatment effectively ameliorated the threshold of mechanical stimuli, thermal sensitivity and MNCV of diabetic mice. Mechanism research results indicated that SP6616 suppressed Kv2.1 expression, increased the number of intraepidermal nerve fibers (IENFs), improved peripheral nerve structure and vascular function in DRG tissue. In addition, SP6616 improved mitochondrial dysfunction through Kv2.1/CaMKKβ/AMPK/PGC-1α pathway, repressed inflammatory response by inhibiting Kv2.1/NF-κB signaling and alleviated apoptosis of DRG neuron through Kv2.1-mediated regulation of Bcl-2 family proteins and Caspase-3 in diabetic mice.

INTERPRETATION

Our work has highly supported the beneficial of Kv2.1 inhibition in ameliorating DPN-like pathology and highlighted the potential of SP6616 in the treatment of DPN.

FUNDING

Please see funding sources.

Aldose reductase (AC)n gene polymorphism in Iranian patients with type 2 diabetic microangiopathy; a case-control study

Aim

(AC)n promoter region of the aldose reductase (ALR) genes polymorphism has been associated with diabetic microvascular complications (MVCs). The aim of this study was to find the relationship between dinucleotide repeat (AC)n polymorphisms of the ALR gene and the occurrence of MVCs, such as diabetic retinopathy, neuropathy, and nephropathy in Iranian type 2 diabetic (T2D) patients.

Methods

This prospective case-control study was performed on T2D patients who were categorized into two groups based on the presence or absence of diabetic microangiopathy. All patients were provided informed consent. After extracting genomic DNA, the (AC)n of the ALR gene was determined using Polymerase chain reaction (PCR).

Results

Thirteen alleles of the (AC)n gene polymorphism were detected including Z + 16, Z + 14, Z + 8, Z + 6, Z + 4, Z + 2, Z, Z - 2, Z - 4, Z - 6, Z - 8, Z - 10, and Z - 12. The frequency of the Z - 4 allele was significantly higher in patients with retinopathy, nephropathy, and autonomic neuropathy compared with those with long-term uncomplicated diabetes (P < 0.001, P < 0.001, P = 0.031, respectively). After controlling for baseline risk factors, we found that the carrier of the Z - 4 allele of ALR (AC)n polymorphism had a higher risk of diabetic retinopathy and diabetic nephropathy (P < 0.001). The homozygosity for the Z - 4 allele was found to be associated with diabetic microangiopathy.

Conclusion

Our results showed that ALR (AC)n gene polymorphism in Iranian patients with type 2 diabetes independently, predispose retinal, renal and neural microvascular to diabetic complications.

Formononetin Ameliorates Diabetic Neuropathy by Increasing Expression of SIRT1 and NGF

Diabetic neuropathy is commonly observed complication in more than 50 % of type 2 diabetic patients. Histone deacetylases including SIRT1 have significant role to protect neuron from hyperglycemia induced damage. Formononetin (FMNT) is known for its effect to control hyperglycemia and also activate SIRT1. In present study, we evaluated effect of FMNT as SIRT1 activator in type 2 diabetic neuropathy. Type 2 diabetic neuropathy was induced in rats by modification of diet for 15 days using high fat diet and administration of streptozotocin (35 mg/kg/day, i. p.). FMNT treatment was initiated after confirmation of type 2 diabetes. Treatment was given for 16 weeks at 10, 20 and 40 mg/kg/day dose orally. FMNT treatment-controlled hypoglycemia and reduced insulin resistance significantly in diabetic animals. FMNT treatment reduced oxidative stress in sciatic nerve tissue. FMNT treatment also reduced thermal hyperalgesia and mechanical allodynia significantly. It improved conduction velocity in nerve and unregulated SIRT1 and NGF expression in sciatic nerve tissue. Results of present study indicate that continuous administration of FMNT protected diabetic animals from hyperglycemia induced neuronal damage by controlling hyperglycemia and increasing SIRT1 and NGF expression in nerve tissue. Thus, FMNT can be an effective candidate for treatment of type 2 diabetic neuropathy.

Challenges of neuropathic pain: focus on diabetic neuropathy

Neuropathic pain is a frequent condition caused by a lesion or disease of the central or peripheral somatosensory nervous system. A frequent cause of peripheral neuropathic pain is diabetic neuropathy. Its complex pathophysiology is not yet fully elucidated, which contributes to underassessment and undertreatment. A mechanism-based treatment of painful diabetic neuropathy is challenging but phenotype-based stratification might be a way to develop individualized therapeutic concepts. Our goal is to review current knowledge of the pathophysiology of peripheral neuropathic pain, particularly painful diabetic neuropathy. We discuss state-of-the-art clinical assessment, validity of diagnostic and screening tools, and recommendations for the management of diabetic neuropathic pain including approaches towards personalized pain management. We also propose a research agenda for translational research including patient stratification for clinical trials and improved preclinical models in relation to current knowledge of underlying mechanisms.

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.

Diabetic neuropathy

The global epidemic of prediabetes and diabetes has led to a corresponding epidemic of complications of these disorders. The most prevalent complication is neuropathy, of which distal symmetric polyneuropathy (for the purpose of this Primer, referred to as diabetic neuropathy) is very common. Diabetic neuropathy is a loss of sensory function beginning distally in the lower extremities that is also characterized by pain and substantial morbidity. Over time, at least 50% of individuals with diabetes develop diabetic neuropathy. Glucose control effectively halts the progression of diabetic neuropathy in patients with type 1 diabetes mellitus, but the effects are more modest in those with type 2 diabetes mellitus. These findings have led to new efforts to understand the aetiology of diabetic neuropathy, along with new 2017 recommendations on approaches to prevent and treat this disorder that are specific for each type of diabetes. In parallel, new guidelines for the treatment of painful diabetic neuropathy using distinct classes of drugs, with an emphasis on avoiding opioid use, have been issued. Although our understanding of the complexities of diabetic neuropathy has substantially evolved over the past decade, the distinct mechanisms underlying neuropathy in type 1 and type 2 diabetes remains unknown. Future discoveries on disease pathogenesis will be crucial to successfully address all aspects of diabetic neuropathy, from prevention to treatment.

Diabetic neuropathy

The global epidemic of prediabetes and diabetes has led to a corresponding epidemic of complications of these disorders. The most prevalent complication is neuropathy, of which distal symmetric polyneuropathy (for the purpose of this Primer, referred to as diabetic neuropathy) is very common. Diabetic neuropathy is a loss of sensory function beginning distally in the lower extremities that is also characterized by pain and substantial morbidity. Over time, at least 50% of individuals with diabetes develop diabetic neuropathy. Glucose control effectively halts the progression of diabetic neuropathy in patients with type 1 diabetes mellitus, but the effects are more modest in those with type 2 diabetes mellitus. These findings have led to new efforts to understand the aetiology of diabetic neuropathy, along with new 2017 recommendations on approaches to prevent and treat this disorder that are specific for each type of diabetes. In parallel, new guidelines for the treatment of painful diabetic neuropathy using distinct classes of drugs, with an emphasis on avoiding opioid use, have been issued. Although our understanding of the complexities of diabetic neuropathy has substantially evolved over the past decade, the distinct mechanisms underlying neuropathy in type 1 and type 2 diabetes remains unknown. Future discoveries on disease pathogenesis will be crucial to successfully address all aspects of diabetic neuropathy, from prevention to treatment.

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.

Neurons and Microglia; A Sickly-Sweet Duo in Diabetic Pain Neuropathy

Diabetes is a common condition characterized by persistent hyperglycemia. High blood sugar primarily affects cells that have a limited capacity to regulate their glucose intake. These cells include capillary endothelial cells in the retina, mesangial cells in the renal glomerulus, Schwann cells, and neurons of the peripheral and central nervous systems. As a result, hyperglycemia leads to largely intractable complications such as retinopathy, nephropathy, hypertension, and neuropathy. Diabetic pain neuropathy is a complex and multifactorial disease that has been associated with poor glycemic control, longer diabetes duration, hypertension, advanced age, smoking status, hypoinsulinemia, and dyslipidemia. While many of the driving factors involved in diabetic pain are still being investigated, they can be broadly classified as either neuron -intrinsic or -extrinsic. In neurons, hyperglycemia impairs the polyol pathway, leading to an overproduction of reactive oxygen species and reactive nitrogen species, an enhanced formation of advanced glycation end products, and a disruption in Na⁺/K⁺ ATPase pump function. In terms of the extrinsic pathway, hyperglycemia leads to the generation of both overactive microglia and microangiopathy. The former incites a feed-forward inflammatory loop that hypersensitizes nociceptor neurons, as observed at the onset of diabetic pain neuropathy. The latter reduces neurons' access to oxygen, glucose and nutrients, prompting reductions in nociceptor terminal expression and losses in sensation, as observed in the later stages of diabetic pain neuropathy. Overall, microglia can be seen as potent and long-lasting amplifiers of nociceptor neuron activity, and may therefore constitute a potential therapeutic target in the treatment of diabetic pain neuropathy.

System-specific neurodegeneration following glucotoxicity in the C. elegans model

Hyperglycemia-related neuropathy leads to the onset and exacerbation of several pathologies. The C. elegans model has been used to study this phenomenon and its underlying mechanisms using a broad evaluation for neurodegeneration. Here, we report a system-specific susceptibility for glucotoxicity, namely the dopaminergic, glutamatergic and cholinergic system. Under high-glucose conditions, these systems (and not the serotonergic or GABAergic) were impaired, as observed by evaluating the fluorescent signal in GFP-tagged worm strains. The significance and implications of unequal susceptibility for glucotoxicity in the nervous system is discussed.