Diabetic peripheral neuropathy: should a chaperone accompany our therapeutic approach?

Integrating plasma metabolomics and gut microbiome to reveal the mechanisms of Huangqi Guizhi Wuwu Decoction intervene diabetic peripheral neuropathy

ETHNOPHARMACOLOGICAL RELEVANCE

Huangqi Guizhi Wuwu Decoction (HGWD) is a classic traditional Chinese herbal formula from "Synopsis of Golden Chamber," which is used to treat blood stagnation and has been used for alleviating diabetic peripheral neuropathy (DPN) in the clinic. However, the mechanisms of HGWD intervention DPN are still to be discovered.

AIM OF THE STUDY

This study aims to explore the mechanism of HGWD intervention DPN by integrating plasma metabolomics and gut microbiome.

MATERIALS AND METHODS

BKS Cg-m+/+Leprdb/J (db/db) mice with DPN were at 16 weeks of age. The indices of DPN phenotypes in db/db mice, pathomorphology of the sciatic nerve, intraepithelial nerve fibers (IENF) of the foot pad, levels of blood lipids and oxidative stress, and inflammatory reaction were used to appraise the HGWD efficacy. Finally, the pharmacological mechanisms of HGWD intervening DPN were explored by metabolomics and 16S rRNA gene sequencing.

RESULTS

HGWD reversed DPN phenotypes in db/db mice, improved peripheral nerve structure, ameliorated the level of blood lipids and nerve growth factor in plasma, enhanced antioxidant capacity, and alleviated inflammatory responses. Plasma metabolomics disclosed that HGWD remarkably regulated the unusual levels of thirty-seven metabolites involved in sphingolipid metabolism, biosynthesis of unsaturated fatty acids, arachidonic acid metabolism, and amino acid biosynthesis pathways. The gut microbiome showed that nine bacteria were highly correlated with the efficacy of HGWD in DPN. Integrating analysis of microbiome and metabolomics demonstrated that the interaction of four bacteria with four metabolic pathways might be the significant mechanism of HGWD intervention in DPN.

CONCLUSIONS

The mediation of gut microbiota and plasma metabolism may be the potential mechanism of HGWD ameliorating DPN in db/db mice. The interaction of Lactobacillus, Alloprevotella, Bacteroides, and Desulfovibio with four metabolic pathways might be the critical mechanism for HGWD treating DPN.

A Mitochondrial Nanoguard Modulates Redox Homeostasis and Bioenergy Metabolism in Diabetic Peripheral Neuropathy

As a major late complication of diabetes, diabetic peripheral neuropathy (DPN) is the primary reason for amputation. Nevertheless, there are no wonder drugs available. Regulating dysfunctional mitochondria is a key therapeutic target for DPN. Resveratrol (RSV) is widely proven to guard mitochondria, yet the unsatisfactory bioavailability restricts its clinical application. Tetrahedral framework nucleic acids (tFNAs) are promising carriers due to their excellent cell entrance efficiency, biological safety, and structure editability. Here, RSV was intercalated into tFNAs to form the tFNAs-RSV complexes. tFNAs-RSV achieved enhanced stability, bioavailability, and biocompatibility compared with tFNAs and RSV alone. With its treatment, reactive oxygen species (ROS) production was minimized and reductases were activated in an in vitro model of DPN. Besides, respiratory function and adenosine triphosphate (ATP) production were enhanced. tFNAs-RSV also exhibited favorable therapeutic effects on sensory dysfunction, neurovascular deterioration, demyelination, and neuroapoptosis in DPN mice. Metabolomics analysis revealed that redox regulation and energy metabolism were two principal mechanisms that were impacted during the process. Comprehensive inspections indicated that tFNAs-RSV inhibited nitrosation and oxidation and activated reductase and respiratory chain. In sum, tFNAs-RSV served as a mitochondrial nanoguard (mito-guard), representing a viable drilling target for clinical drug development of DPN.

Quantification of heat shock proteins in the posterior interosseous nerve among subjects with type 1 and type 2 diabetes compared to healthy controls

Introduction

Diabetic peripheral neuropathy (DPN) is a common complication of both type 1 (T1D) and type 2 diabetes (T2D). No cure for DPN is available, but several potential targets have been proposed for treatment. Heat shock proteins (HSPs) are known to respond to both hyper- and hypoglycemia. DPN can be diagnosed using electrophysiology and studied using peripheral nerve biopsies.

Aim

This study aimed to analyze the presence and patterns of HSPs in peripheral nerve biopsies from subjects with T1D, T2D, and healthy controls.

Methods

Posterior interosseous nerves (PIN) from a total of 56 subjects with T1D (n = 9), with T2D (n = 24), and without diabetes (i.e., healthy controls, n = 23) were harvested under local anesthesia and prepared for quantitative mass spectrometry analysis. Protein intensities were associated with electrophysiology data of the ulnar nerve and morphometry of the same PIN, and differences in protein intensities between groups were analyzed.

Results

In total, 32 different HSPs were identified and quantified in the nerve specimens. No statistically significant differences were observed regarding protein intensities between groups. Furthermore, protein intensities did not correlate with amplitude or conduction velocity in the ulnar nerve or with the myelinated nerve fiber density of PIN.

Conclusion

Quantitative proteomics can be used to study HSPs in nerve biopsies, but no clear differences in protein quantities were observed between groups in this cohort.

The circ_0002538/miR-138-5p/plasmolipin axis regulates Schwann cell migration and myelination in diabetic peripheral neuropathy

Circular RNAs (circRNAs) play a vital role in diabetic peripheral neuropathy. However, their expression and function in Schwann cells in individuals with diabetic peripheral neuropathy remain poorly understood. Here, we performed protein profiling and circRNA sequencing of sural nerves in patients with diabetic peripheral neuropathy and controls. Protein profiling revealed 265 differentially expressed proteins in the diabetic peripheral neuropathy group. Gene Ontology indicated that differentially expressed proteins were mainly enriched in myelination and mitochondrial oxidative phosphorylation. A real-time polymerase chain reaction assay performed to validate the circRNA sequencing results yielded 11 differentially expressed circRNAs. circ_0002538 was markedly downregulated in patients with diabetic peripheral neuropathy. Further in vitro experiments showed that overexpression of circ_0002538 promoted the migration of Schwann cells by upregulating plasmolipin (PLLP) expression. Moreover, overexpression of circ_0002538 in the sciatic nerve in a streptozotocin-induced mouse model of diabetic peripheral neuropathy alleviated demyelination and improved sciatic nerve function. The results of a mechanistic experiment showed that circ_0002538 promotes PLLP expression by sponging miR-138-5p, while a lack of circ_0002538 led to a PLLP deficiency that further suppressed Schwann cell migration. These findings suggest that the circ_0002538/miR-138-5p/PLLP axis can promote the migration of Schwann cells in diabetic peripheral neuropathy patients, improving myelin sheath structure and nerve function. Thus, this axis is a potential target for therapeutic treatment of diabetic peripheral neuropathy.

Axonal transport deficits in the pathogenesis of diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is a chronic and prevalent metabolic disease that gravely endangers human health and seriously affects the quality of life of hyperglycemic patients. More seriously, it can lead to amputation and neuropathic pain, imposing a severe financial burden on patients and the healthcare system. Even with strict glycemic control or pancreas transplantation, peripheral nerve damage is difficult to reverse. Most current treatment options for DPN can only treat the symptoms but not the underlying mechanism. Patients with long-term diabetes mellitus (DM) develop axonal transport dysfunction, which could be an important factor in causing or exacerbating DPN. This review explores the underlying mechanisms that may be related to axonal transport impairment and cytoskeletal changes caused by DM, and the relevance of the latter with the occurrence and progression of DPN, including nerve fiber loss, diminished nerve conduction velocity, and impaired nerve regeneration, and also predicts possible therapeutic strategies. Understanding the mechanisms of diabetic neuronal injury is essential to prevent the deterioration of DPN and to develop new therapeutic strategies. Timely and effective improvement of axonal transport impairment is particularly critical for the treatment of peripheral neuropathies.

The protective effects of flavonoids and carotenoids against diabetic complications-A review of in vivo evidence

Diabetes mellitus is a chronic metabolic disorder caused either by inadequate insulin secretion, impaired insulin function, or both. Uncontrolled diabetes is characterized by hyperglycemia which over time leads to fatal damage to both macro-and microvascular systems, causing complications such as cardiovascular diseases, retinopathy and nephropathy. Diabetes management is conventionally delivered through modifications of diet and lifestyle and pharmacological treatment, using antidiabetic drugs, and ultimately insulin injections. However, the side effects and financial cost of medications often reduce patient compliance to treatment, negatively affecting their health outcomes. Natural phytochemicals from edible plants such as fruits and vegetables (F&V) and medicinal herbs have drawn a growing interest as potential therapeutic agents for treating diabetes and preventing the onset and progression of diabetic complications. Flavonoids, the most abundant polyphenols in the human diet, have shown antidiabetic effects in numerous in vitro and preclinical studies. The underlying mechanisms have been linked to their antioxidant, anti-inflammatory and immunomodulatory activities. Carotenoids, another major group of dietary phytochemicals, have also shown antidiabetic potential in recent in vitro and in vivo experimental models, possibly through a mechanism of action similar to that of flavonoids. However, scientific evidence on the efficacy of these phytochemicals in treating diabetes or preventing the onset and progression of its complications in clinical settings is scarce, which delays the translation of animal study evidence to human applications and also limits the knowledge on their modes of actions in diabetes management. This review is aimed to highlight the potential roles of flavonoids and carotenoids in preventing or ameliorating diabetes-related complications based on in vivo study evidence, i.e., an array of preclinical animal studies and human intervention trials. The current general consensus of the underlying mechanisms of action exerted by both groups of phytochemicals is that their anti-inflammatory action is key. However, other potential mechanisms of action are considered. In total, 50 in vivo studies were selected for a review after a comprehensive database search via PubMed and ScienceDirect from January 2002 to August 2022. The key words used for analysis are type-2 diabetes (T2DM), diabetic complications, flavonoids, carotenoids, antioxidant, anti-inflammatory, mechanisms of prevention and amelioration, animal studies and human interventions.

A moisturizing chitosan-silk fibroin dressing with silver nanoparticles-adsorbed exosomes for repairing infected wounds

Refractory wounds caused by microbial infection impede wound healing, vascular regeneration, nerve system repair and the regeneration of other skin appendages. In addition, large-area infected wounds cause the appearance of multidrug-resistant (MDR) bacterial strains, which pose a major challenge both in clinical and scientific research. Although many stem cell-derived exosomes have been demonstrated to promote skin repair and regeneration, exosomes are seldom applied in the treatment of infective wounds due to the lack of antimicrobial function. In this study, we fabricated an asymmetric wettable dressing with a composite of exosomes and silver nanoparticles (CTS-SF/SA/Ag-Exo dressing) for promoting angiogenesis, nerve repair and infected wound healing. The CTS-SF/SA/Ag-Exo dressing possesses multifunctional properties including broad-spectrum antimicrobial activity, promoting wound healing, retaining moisture and maintaining electrolyte balance. It can effectively inhibit the growth of bacterial and promote the proliferation of human fibroblasts in vitro. Moreover, the in vivo results show that the CTS-SF/SA/Ag-Exo dressing enhanced wound healing by accelerating collagen deposition, angiogenesis and nerve repair in a P. aeruginosa infected mouse skin wound defect model. We hope that this dressing will provide a solution for the repair of infected wounds for treatments in the clinic.

Compound XiongShao Capsule ameliorates streptozotocin-induced diabetic peripheral neuropathy in rats via inhibiting apoptosis, oxidative - nitrosative stress and advanced glycation end products

ETHNOPHARMACOLOGICAL RELEVANCE

Compound XiongShao Capsule (CXSC), a traditional herb formula, has been approved for using to treat diabetic peripheral neuropathy (DPN) by the Shanghai Food and Drug Administration, with significant efficacy in clinic.

AIM OF THE STUDY

This study aimed to investigate the multidimensional pharmacological mechanisms and synergism of CXSC against DPN in rats.

METHODS

The quality analysis of CXSC was performed by high-performance liquid chromatography (HPLC) and thin-layer chromatography. Rats with DPNinduced by streptozotocin/high-fat diet for 4 weeks were treated with CXSC at three doses (1.2 g/kg, 0.36 g/kg, and 0.12 g/kg), or epalrestat (15 mg/kg) daily for 8 weeks continuously. During the treatment period, body weight, serum glucose levels, and nerve function, including nerve conduction velocity (NCV), and mechanical and thermal hyperalgesia were tested and assessed every 4 weeks. In the 13th week, the histopathological examination in the sciatic nerve was performed using a transmission electron microscope. The expression of apoptosis-related proteins of BAX, BCL2, and caspase-3 in the sciatic nerve was examined using hematoxylin and eosin staining. The serum levels of advanced glycation end products (AGEs), oxidative-nitrosative stress biomarkers of superoxide dismutase (SOD), and nitric oxide synthase (NOS) were measured using a rat-specific ELISA kit.

RESULTS

CXSC had no significant effect on body weight or serum glucose levels (P > 0.05), but it significantly improved mechanical hyperalgesia (F_5,36 = 18.24, P < 0.0001), thermal hyperalgesia (F_5,36 = 8.45, P < 0.0001), and NCV (motor NCV: F_5,36 = 7.644, P < 0.0001, sensory NCV: F_5,36 = 12.83, P < 0.0001). Besides, it maintained myelin and axonal structure integrity, downregulated the expression of apoptosis-related proteins in the sciatic nerve tissue, reduced AGEs and NOS levels, and enhanced antioxidant enzyme SOD activities in the serum.

CONCLUSION

CXSC exerted neuroprotective effects against rats with DPN through multidimensional pharmacological mechanisms including antiapoptotic activity in the sciatic nerve and downregulation of the level of serum NOS, SOD and AGEs.

Quercetin Attenuates Diabetic Peripheral Neuropathy by Correcting Mitochondrial Abnormality via Activation of AMPK/PGC-1α Pathway in vivo and in vitro

The AMPK/PGC-1α pathway-mediated mitochondrial dysfunction has been supposed to play a crucial role in pathogenesis of diabetic peripheral neuropathy (DPN). The present study investigated the neuroprotective potential of quercetin, a natural AMPK activator. Streptozotocin (STZ)-induced diabetic rats that developed DPN phenotype were orally administrated with quercetin (30 and 60 mg/kg per day) for 6 weeks. The morphologic changes in the sciatic nerves (SN), the pathological structure of neurons in dorsal root ganglion (DRG), and the expressions of myelin proteins were assessed. The ATP content and the mitochondrial ultrastructure were measured. Furthermore, key proteins in the AMPK/PGC-1α pathway were determined. As a result, quercetin administration at both doses improved the paw withdrawal threshold, nerve conduction velocity, and the pathologic changes in SN and DRG of DPN rats. The expressions of myelin basic protein and myelin protein zero were also increased by quercetin. The oxidative stress, decreased ATP generation, and morphological changes of mitochondria were corrected by quercetin. In vitro study found that quercetin treatment significantly decreased the high-glucose-induced generation of reactive oxygen species, as well as attenuated the mitochondrial morphologic injuries and oxidative DNA damages of RSC96 cells. Quercetin treatment promoted the expressions of phosphorylated AMPK, PGC-1α, SIRT1, NRF1, and TFAM under hyperglycemic state in vivo and in vitro. This study revealed that the neuroprotective effect of quercetin was mainly related to mitochondrial protection by activation of the AMPK/PGC-1α pathway for the first time and proved quercetin as a potential therapeutic agent in the management of diabetic neuropathy.

The role and therapeutic potential of Hsp90, Hsp70, and smaller heat shock proteins in peripheral and central neuropathies

Heat shock proteins (Hsps) are molecular chaperones that also play important roles in the activation of the heat shock response (HSR). The HSR is an evolutionary conserved and protective mechanism that is used to counter abnormal physiological conditions, stressors, and disease states, such as those exemplified in cancer and/or neurodegeneration. In normal cells, heat shock factor-1 (HSF-1), the transcription factor that regulates the HSR, remains in a dormant multiprotein complex that is formed upon association with chaperones (Hsp90, Hsp70, etc.), co-chaperones, and client proteins. However, under cellular stress, HSF-1 dissociates from Hsp90 and induces the transcriptional upregulation of Hsp70 to afford protection against the encountered cellular stress. As a consequence of both peripheral and central neuropathies, cellular stress occurs and results in the accumulation of unfolded and/or misfolded proteins, which can be counterbalanced by activation of the HSR. Since Hsp90 is the primary regulator of the HSR, modulation of Hsp90 by small molecules represents an attractive therapeutic approach against both peripheral and central neuropathies.

SMTP-44D improves diabetic neuropathy symptoms in mice through its antioxidant and anti-inflammatory activities

Diabetic neuropathy (DN) is one of the major complications of diabetes. However, there are few approved effective therapies for painful or insensate DN. Recent studies have implicated oxidative stress and inflammation in the pathogenesis of DN, and suppressing these could be an important therapeutic strategy. We previously reported that Stachybotrys microspora triprenyl phenol-44D (SMTP-44D) exhibits both antioxidant and anti-inflammatory activities. The aim of this study was to evaluate the effects of SMTP-44D in a mouse model of streptozotocin-induced DN. SMTP-44D was administered for 3 weeks after the disease induction, and its effects were evaluated on the basis of mechanical and thermal thresholds, blood flow in the bilateral hind paw, and blood flow and conduction velocity in the sciatic nerve. Furthermore, the levels of inflammatory factors, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and malondialdehyde (MDA), in the sciatic nerve were assessed. Neurological degeneration was assessed by measuring myelin thickness and g-ratio in the sciatic nerve. SMTP-44D treatment significantly improved allodynia, hyperalgesia, blood flow, and conduction velocity in DN model mice in a dose-dependent manner. Neurological degeneration was also significantly improved, accompanied by decreased levels of inflammatory factors (TNF-α, 57.8%; IL-1β, 51.4%; IL-6, 62.8%; and MDA, 40.7% reduction rate against the diabetes mellitus + normal saline group). Thus, SMTP-44D can improve allodynia and hyperalgesia in DN without affecting the body weight and blood glucose levels, which may be due to its antioxidant and anti-inflammatory properties. In conclusion, SMTP-44D could be a potential therapeutic agent for the treatment of DN.

Circulating human anti nucleolus antibody (ANCAb) and biochemical parameters in type 2 diabetic patients with and without complications

Introduction

There is no evidence on the role of Human Anti Nucleolus Antibody (ANCAb) in type 2 diabetes mellitus (T2DM). We compared prevalence and concentration of ANCAb between age and a gender-matched sample of T2DM with and without diabetes-related complications.

Methods

In this study, the reaction to ANCAb was compared quantitatively between 38 T2DM patients complicated with microvascular conditions and 43 T2DM without complications as controls.

Results

The patients in complicated and non-complicated groups were comparable in diabetes duration (9.0 vs. 5.0 years; P = 0.065), respectively. The study found that 27 cases (71.1%) of the complicated group reacted to ANCAb test compared to 25 (58.1%) in non-complicated patients (P = 0.226; 3.53 vs. 2.72 ng/mL; P = 0.413). The reaction response to ANCAb in patients with neuropathy and cardiovascular complications was 80.0%, 76.2% in patients with neuropathy compared to 58.1% in the control group (P = 0.398). The reaction response to ANCAb in patients with mono-complication was 72.7% compared 68.8% in patients with multi-complication (P = 0.466). Similarly, 76.2% of patients with T2DM and complicated with neuropathy (n = 21 patients) reacted to ANCAb compared to 58.1% in control patients with (P = 0.158).

Conclusions

Reaction to ANCAb was not statistically different between the T2DM patients with and without complications.

The Preventive Effect of IL-1beta Antagonist on Diabetic Peripheral Neuropathy

Objective:

To investigate the relationship between Interleukin-1beta (IL-1beta) and diabetic peripheral neuropathy (DPN) using animal models.

Materials:

The rat model of diabetic neuropathy was induced by intraperitoneal injection of a single dose of streptozotocin (STZ) at 65mg/kg. Diabetic rats were randomly divided into two groups (10 each), one treated with 0.9% saline (DMS group) and the other with interleukin-1 receptor antagonist (IL-1RA) at 50mg/kg (DMI group) twice a day for 5 weeks. Ten normal rats matched for weight, age and sex served as normal controls (Con group) and were treated with saline. Morphologic studies of sciatic nerves were achieved using light and transmission electron microscopy.

Results:

Transmission electron microscopy of the sciatic nerve showed the ultrastructure of myelin and the axon in the IL-1RA group was highly protected compared to diabetic controls.

Conclusions:

High levels of circulating IL-1beta may be associated with the risk of DPN and anti-IL-1 treatment may provide a potential strategy for the prevention of diabetic neuropathy.

Protective effect of quercetin on streptozotocin-induced diabetic peripheral neuropathy rats through modulating gut microbiota and reactive oxygen species level

OBJECTIVE

Diabetic peripheral neuropathy (DPN) is a prevalent complication of diabetes with no effective drug currently. As a powerful antioxidant, the flavonoid quercetin has been demonstrated to have potential neuroprotective and prebiotic capacity. But the mechanism of its neuroprotective function and the link to the gut microbiota remains to be elucidated.

METHODS

The neuroprotective effect of quercetin was evaluated on streptozotocin(STZ)-induced DPN rats through electrophysiology, behavioristic, and pathomorphology studies. Serum and urine reactive oxygen species (ROS) production levels and fecal gut microbiota compositions were detected, and the relationship between them was analyzed by Spearman's correlation.

RESULTS

Quercetin not only reversed the decreased mechanical withdraw thresholds and intraepidermal nerve fiber densities in DPN rats, but also improved neurological morphology of sciatic nerves, accompanied with up-regulated percentage of paranodes at paranodal junctions, and down-regulated amyloid precursor protein and ionized calcium-binding adaptor molecule 1 in DPN rats. More importantly, quercetin rescued gut dysbiosis in DPN rats by decreasing four potential pathogenic species and enriching two prebiotic species associated with DPN phenotypes and ROS production levels.

CONCLUSIONS

Quercetin exerts neuroprotective effect and modulates gut microbiota associated with DPN phenotypes and ROS production levels in STZ-induced DPN rats, suggesting the therapeutic application of quercetin for DPN prevention and treatment.

A Metabolic Insight Into the Neuroprotective Effect of Jin-Mai-Tong (JMT) Decoction on Diabetic Rats With Peripheral Neuropathy Using Untargeted Metabolomics Strategy

Jin-Mai-Tong (JMT) decoction is a traditional Chinese compound prescription for treating diabetic peripheral neuropathy (DPN). The aim of this study is to investigate the neuroprotective effect of JMT decoction on diabetic rats with peripheral neuropathy and to elucidate the potential mechanism based on a metabolomics approach. Sprague-Dawley (SD) rats were randomly divided into four groups: control group, Streptozotocin (STZ) induced model group, JMT low dose (JMT-L) treated group and JMT high dose (JMT-H) treated group. After 12 weeks of treatment, behavioral changes, small fiber loss, and histopathological damages of sciatic nerves were estimated. Serum samples were collected for untargeted metabolomics analysis based on UPLC/QTOF-MS and multivariate statistics. As a result, JMT treatment at two dosages (13.9 and 27.8 g/kg⋅d) evidently improved the mechanical pain threshold (P < 0.05), increased the intraepidermal nerve fiber density (IENFD) and subepidermal nerve fiber density (SNFD) (P < 0.05), and renovated the demyelination and axonal atrophy of sciatic nerves on DPN rats. Furthermore, metabolomics study revealed that the serum metabolic profiles altered significantly among the control group and the STZ-induced model group. A total of 21 metabolites were identified as potential biomarkers related to the therapeutic effect of JMT decoction. Among them, 16 biomarkers were found in both JMT-H and JMT-L treated groups, while the five others were specific to JMT-H group. These metabolites mainly involved in lipid metabolism, tricarboxylic acid (TCA) cycle, amino acid metabolism, and so on. Besides, correlation analysis indicated that both mechanical pain threshold and distal nerve fiber density were negatively correlated with the serum levels of metabolites from lipid metabolism and TCA cycle. In conclusion, the results demonstrated that JMT decoction has an obvious protective effect against DPN, which could be mediated via ameliorating the metabolic disorders in diabetic rats with peripheral neuropathy.

Protective effect of hydrogen sulfide on oxidative stress-induced neurodegenerative diseases

Hydrogen sulfide is an antioxidant molecule that has a wide range of biological effects against oxidative stress. Balanced oxidative stress is also vital for maintaining cellular function in biological system, where reactive oxygen species are the main source of oxidative stress. When the normal redox balance is disturbed, deoxyribonucleic acid, lipid, and protein molecules are oxidized under pathological conditions, like diabetes mellitus that leads to diabetic peripheral neuropathy. In diabetes mellitus-induced diabetic peripheral neuropathy, due to hyperglycemia, pancreatic beta cell (β cell) shows resistance to insulin secretion. As a consequence, glucose metabolism is disturbed in neuronal cells which are distracted from providing proper cell signaling pathway. Not only diabetic peripheral neuropathy but also other central damages occur in brain neuropathy. Neurological studies regarding type 1 diabetes mellitus patients with Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis have shown changes in the central nervous system because high blood glucose levels (HbA1c) appeared with poor cognitive function. Oxidative stress plays a role in inhibiting insulin signaling that is necessary for brain function. Hydrogen sulfide exhibits antioxidant effects against oxidative stress, where cystathionine β synthase, cystathionine γ lyase, and 3-mercaptopyruvate sulfurtransferase are the endogenous sources of hydrogen sulfide. This review is to explore the pathogenesis of diabetes mellitus-induced diabetic peripheral neuropathy and other neurological comorbid disorders under the oxidative stress condition and the anti-oxidative effects of hydrogen sulfide.

Sarm1 Gene Deficiency Attenuates Diabetic Peripheral Neuropathy in Mice

Diabetic peripheral neuropathy (DPN) is the most common complication in both type 1 and type 2 diabetes, but any treatment toward the development of DPN is not yet available. Axon degeneration is an early feature of many peripheral neuropathies, including DPN. Delay of axon degeneration has beneficial effects on various neurodegenerative diseases, but its effect on DPN is yet to be elucidated. Deficiency of Sarm1 significantly attenuates axon degeneration in several models, but the effect of Sarm1 deficiency on DPN is still unclear. In this study, we show that Sarm1 knockout mice exhibit normal glucose metabolism and pain sensitivity, and deletion of the Sarm1 gene alleviates hypoalgesia in streptozotocin-induced diabetic mice. Moreover, Sarm1 gene deficiency attenuates intraepidermal nerve fiber loss in footpad skin; alleviates axon degeneration, the change of g-ratio in sciatic nerves, and NAD⁺ decrease; and relieves axonal outgrowth retardation of dorsal root ganglia from diabetic mice. In addition, Sarm1 gene deficiency markedly diminishes the changes of gene expression profile induced by streptozotocin in the sciatic nerve, especially some abundant genes involved in neurodegenerative diseases. These findings demonstrate that Sarm1 gene deficiency attenuates DPN in mice and suggest that slowing down axon degeneration is a potential promising strategy to combat DPN.

Increased Circulating Chemerin in Relation to Chronic Microvascular Complications in Patients with Type 2 Diabetes

OBJECTIVE

Type 2 diabetes (T2DM) is a global epidemic and increases mortality due to its vascular complications. Chemerin has been found to exert a major role in glucose and lipid metabolism. The aim of this study was to explore the correlation between plasma chemerin levels and microangiopathy in patients with T2DM.

METHODS

A total of 598 T2DM patients were classified into two groups: with and without microvascular complications. Anthropometric parameters and blood pressure were taken. The amounts of glycosylated hemoglobin, glucose, lipid profiles, creatinine, and chemerin concentrations in the blood were determined. The presence and severity of nephropathy, retinopathy, and neuropathy were also evaluated by specific tests.

RESULTS

Plasma levels of chemerin in diabetic subjects with microvascular complications were markedly elevated compared to those without. The number of microvascular complications increased with high plasma chemerin levels. Patients with high chemerin levels had an increased incidence of nephropathy and retinopathy. Furthermore, the chemerin plasma concentrations increased with the progression of diabetic nephropathy with highest values in macroalbuminuria groups. In contrast, no significant difference was observed in plasma chemerin levels between subjects with and without peripheral neuropathy. Pearson correlation analysis showed that plasma chemerin levels were positively related to duration of diabetes, serum creatinine, and 24-hour urine albumin excretion, even after multiple adjustments. Using logistic regression analysis, plasma chemerin concentrations were independently associated with the presence of nephropathy and retinopathy, not neuropathy.

CONCLUSION

This study elucidated a positive correlation between increased chemerin levels and the development of some subtypes of diabetic microangiopathy.

Melatonin Prevents Oxidative Stress-Induced Mitochondrial Dysfunction and Apoptosis in High Glucose-Treated Schwann Cells via Upregulation of Bcl2, NF-κB, mTOR, Wnt Signalling Pathways

Neuropathy is a complication that affects more than 50% of long-standing diabetic patients. One of the causes of diabetes neuropathy (DN) is the apoptosis of Schwann cells due to prolonged exposure to high glucose and build-up of oxidative stress. Melatonin is a hormone that has a known antioxidant property. In this study, we investigated the protective effect of melatonin on high glucose-induced Schwann cells' apoptosis. Our results revealed that high glucose promoted apoptosis via mitochondrial-related oxidative stress and downregulated Bcl-2 family proteins in Schwann cells. In this signalling pathway, Bcl-2, Bcl-XL and Mcl-1 proteins were down-regulated while p-BAD and Puma proteins were up-regulated by high glucose treatment. Besides, we also proved that high glucose promoted apoptosis in Schwann cells through decreasing the p-NF-κB in the NF-κB signalling pathway. Key regulators of mTOR signalling pathway such as p-mTOR, Rictor and Raptor were also down-regulated after high glucose treatment. Additionally, high glucose treatment also decreased the Wnt signalling pathway downstream proteins (Wnt 5a/b, p-Lrp6 and Axin). Our results showed that melatonin treatment significantly inhibited high glucose-induced ROS generation, restored mitochondrial membrane potential and inhibited high glucose-induced apoptosis in Schwann cells. Furthermore, melatonin reversed the alterations of protein expression caused by high glucose treatment. Our results concluded that melatonin alleviates high glucose-induced apoptosis in Schwann cells through mitigating mitochondrial-related oxidative stress and the alterations of Bcl-2, NF-κB, mTOR and Wnt signalling pathways.

The Relationship between Plasma Taurine Levels and Diabetic Complications in Patients with Type 2 Diabetes Mellitus

Background: Taurine has an active role in providing glucose homeostasis and diabetes causes a decline in taurine levels. This paper investigates the relationship between taurine and diabetic complications, patients' demographic features, and biochemical parameters. Methods: Fifty-nine patients with type 2 diabetes mellitus (T2DM), and 28 healthy control subjects between the ages of 32 and 82 were included in the study. The mean age of subjects was 55.6 ± 10.3 and mean diabetes duration was 10.2 ± 6.0 years. The most commonly accompanying comorbidity was hypertension (HT) (64.5%, n = 38), and the most frequent diabetic complication was neuropathy (50.8%, n = 30). Plasma taurine concentrations were measured by an enzyme-linked immunoassay (ELISA) kit. Results: Plasma taurine concentrations were significantly lower in diabetic patients (0.6 ± 0.1 mmol/L) than controls (0.8 ± 0.2 mmol/L) and in hypertensive (0. 6 ± 0.1 mmol/L) patients (p = 0.000, p = 0.027 respectively). Conclusion: Plasma taurine levels were decreased in patients with T2DM and this was not related to FBG, HbA1c, and microalbuminuria. With regard to complications, we only found a correlation with neuropathy. We suggest that taurine levels may be more important in the development of diabetes; however, it may also have importance for the progression of the disease and the subsequent complications. We further assert that taurine measurement at different times may highlight whether there is a causal relationship in the development of complications.

Topical treatments for diabetic neuropathic pain

Diabetic neuropathic pain (DNP) has a huge impact on quality of life and can be difficult to treat. Oral treatment is the most frequently used method for DNP, but its use is often limited by systemic side effects. Topical use of drugs as an alternative option for DNP treatment is currently gaining interest. In the present review, a summary is provided of the available agents for topical use in patients with DNP, including lidocaine plasters or patches, capsaicin cream, gel or patches, amitriptyline cream, clonidine gel, ketamine cream, extracts from medicinal plants including nutmeg extracts and Citrullus colocynthis extract oil, and certain compounded topical analgesics. Furthermore, the potential efficacy of these treatments is addressed according to the available clinical research literature. It has been indicated that these topical drugs have the potential to be valuable additional options for the management of DNP, with adequate safety and continuous long-term treatment efficacy. Compounded topical agents are also effective and safe for patients with DNP and could be another area worthy of further investigation based on the strategy of using low-dose, complementary therapies for DNP. The findings indicate that developing topical drugs acting on different targets in the process of DNP is a valuable area of future research.

Synthesis and evaluation of a ring-constrained Hsp90 C-terminal inhibitor that exhibits neuroprotective activity

KU-596 is a second-generation C-terminal heat shock protein 90 KDa (Hsp90) modulator based on the natural product, novobiocin. KU-596 has been shown to induce Hsp70 levels and manifest neuroprotective activity through induction of the heat shock response. A ring-constrained analog of KU-596 was designed and synthesized to probe its binding orientation and ability to induce Hsp70 levels. Compound 2 was found to exhibit comparable or increased activity compared to KU-596, which is under clinical investigation for the treatment of neuropathy.

Proanthocyanidin B2 attenuates high-glucose-induced neurotoxicity of dorsal root ganglion neurons through the PI3K/Akt signaling pathway

High glucose affects primary afferent neurons in dorsal root ganglia by inhibiting neurite elongation, causing oxidative stress, and inducing neuronal apoptosis and mitochondrial dysfunction, which finally result in neuronal damage. Proanthocyanidin, a potent antioxidant, has been shown to have neuroprotective effects. Proanthocyanidin B2 is a common dimer of oligomeric proanthocyanidins. To date, no studies have reported the neuroprotective effects of proanthocyanidin B2 against high-glucose-related neurotoxicity in dorsal root ganglion neurons. In this study, 10 µg/mL proanthocyanidin B2 was used to investigate its effect on 45 mM high-glucose-cultured dorsal root ganglion neurons. We observed that challenge with high levels of glucose increased neuronal reactive oxygen species and promoted apoptosis, decreased cell viability, inhibited outgrowth of neurites, and decreased growth-associated protein 43 protein and mRNA levels. Proanthocyanidin B2 administration reversed the neurotoxic effects caused by glucose challenge. Blockage of the phosphatidylinositol 3 kinase/Akt signaling pathway with 10 µM LY294002 eliminated the protective effects of proanthocyanidin B2. Therefore, proanthocyanidin B2 might be a potential novel agent for the treatment of peripheral diabetic neuropathy.

Gene Expression Profiling Identifies Downregulation of the Neurotrophin-MAPK Signaling Pathway in Female Diabetic Peripheral Neuropathy Patients

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes mellitus (DM). It is not diagnosed or managed properly in the majority of patients because its pathogenesis remains controversial. In this study, human whole genome microarrays identified 2898 and 4493 differentially expressed genes (DEGs) in DM and DPN patients, respectively. A further KEGG pathway analysis indicated that DPN and DM share four pathways, including apoptosis, B cell receptor signaling pathway, endocytosis, and Toll-like receptor signaling pathway. The DEGs identified through comparison of DPN and DM were significantly enriched in MAPK signaling pathway, NOD-like receptor signaling pathway, and neurotrophin signaling pathway, while the "neurotrophin-MAPK signaling pathway" was notably downregulated. Seven DEGs from the neurotrophin-MAPK signaling pathway were validated in additional 78 samples, and the results confirmed the initial microarray findings. These findings demonstrated that downregulation of the neurotrophin-MAPK signaling pathway may be the major mechanism of DPN pathogenesis, thus providing a potential approach for DPN treatment.

Physical Training and Activity in People With Diabetic Peripheral Neuropathy: Paradigm Shift

Diabetic peripheral neuropathy (DPN) occurs in more than 50% of people with diabetes and is an important risk factor for skin breakdown, amputation, and reduced physical mobility (ie, walking and stair climbing). Although many beneficial effects of exercise for people with diabetes have been well established, few studies have examined whether exercise provides comparable benefits to people with DPN. Until recently, DPN was considered to be a contraindication for walking or any weight-bearing exercise because of concerns about injuring a person's insensitive feet. These guidelines were recently adjusted, however, after research demonstrated that weight-bearing activities do not increase the risk of foot ulcers in people who have DPN but do not have severe foot deformity. Emerging research has revealed positive adaptations in response to overload stress in these people, including evidence for peripheral neuroplasticity in animal models and early clinical trials. This perspective article reviews the evidence for peripheral neuroplasticity in animal models and early clinical trials, as well as adaptations of the integumentary system and the musculoskeletal system in response to overload stress. These positive adaptations are proposed to promote improved function in people with DPN and to foster the paradigm shift to including weight-bearing exercise for people with DPN. This perspective article also provides specific assessment and treatment recommendations for this important, high-risk group.

Sugar Composition Analysis of Fuzi Polysaccharides by HPLC-MSn and Their Protective Effects on Schwann Cells Exposed to High Glucose

Fuzi has been used to treat diabetic complications for many years in china. In a previous study, we have shown that Fuzi aqueous extract can attenuate Diabetic peripheral neuropathy (DPN) in rats and protect Schwann cells from injury. Thus, the protective effect of Fuzi polysaccharides (FPS) on high glucose-induced SCs and the preliminary mechanism were investigated. Firstly, the FPS were obtained and their monose composition was analyzed by the combination of pre-column derivatization and high performance liquid chromatography coupled with electrospray ionization multi-tandem mass spectrometry (HPLC/ESI-MSⁿ). The results witnessed the efficiency of this method and seven monosaccharides were tentatively identified, among which fucose was first reported. Simultaneously, m/z 215 can be considered as diagnostic ions to confirm the number of monosaccharides. Next, high glucose-induced SC model was applied and divided into model group, treated group of FPS, normal and osmotic control group. After treatment for 48 h, the data showed FPS could significantly decrease the intracellular ROS and apoptosis, which were determined by the corresponding fluorescent probes. Then, the expression of oxidative stress-related proteins in SCs were measured by Western blot. Furthermore, the protein tests found that FPS markedly up-regulated superoxide dismutase (SOD), catalase (CAT) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) protein level, but down-regulated NADPH oxidase-1 (Nox1) protein level. Moreover, FPS could also increase AMP-activated protein kinase (AMPK) activation significantly. Hence, we preliminary deduced that AMPK-PGC-1α pathway may play an important role in the protective effect of FPS against high glucose-induced cell damage.

Tissue resident macrophages: Key players in the pathogenesis of type 2 diabetes and its complications

There is increasing evidence showing that chronic inflammation is an important pathogenic mediator of the development of type 2 diabetes (T2D). It is now generally accepted that tissue-resident macrophages play a major role in regulation of tissue inflammation. T2D-associated inflammation is characterized by an increased abundance of macrophages in different tissues along with production of inflammatory cytokines. The complexity of macrophage phenotypes has been reported from different human tissues. Macrophages exhibit a phenotypic range that is intermediate between two extremes, M1 (pro-inflammatory) and M2 (anti-inflammatory). Cytokines and chemokines produced by macrophages generate local and systemic inflammation and this condition leads to pancreatic β-cell dysfunction and insulin resistance in liver, adipose and skeletal muscle tissues. Data from human and animal studies also suggest that macrophages contribute to T2D complications such as nephropathy, neuropathy, retinopathy and cardiovascular diseases through cell-cell interactions and the release of pro-inflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. In this review we focus on the functions of macrophages and the importance of these cells in the pathogenesis of T2D. In addition, the contribution of macrophages to diabetes complications such as nephropathy, neuropathy, retinopathy and cardiovascular diseases is discussed.

Multifunctional Magnetoliposomes for Sequential Controlled Release

The simultaneous or sequential delivery of multiple therapeutic active principles to a specific target is one of the main challenges of nanomedicine. This goal requires the construction of complex devices often extremely time and cost consuming. Supramolecular self-assemblies, with building blocks of different nature, each providing a specific function to the final construct, can combine a facile synthetic route with a high tunability and structural control. In this study we provide the proof-of-principle of a drug delivery system, DDS, constituted of (i) liposomes, providing a fully biocompatible lipid scaffold suitable to host both hydrophobic and hydrophilic drugs; (ii) a double-stranded DNA conjugated with a cholesteryl unit that spontaneously inserts into the lipid membrane; and (iii) hydrophobic and hydrophilic superparamagnetic iron oxide nanoparticles (SPIONs) embedded inside the lipid membrane of liposomes or connected to the DNA, respectively. Upon application of an alternating magnetic field, the SPIONs can trigger, through thermal activation, the release of a DNA strand or of the liposomal payload, depending on the frequency and the application time of the field, as proved by both steady-state and time-resolved fluorescence studies. This feature is due to the different localization of the two kinds of SPIONS within the construct and demonstrates the feasibility of a multifunctional DDS, built up from self-assembly of biocompatible building blocks.

Thymoquinone Alleviates the Experimental Diabetic Peripheral Neuropathy by Modulation of Inflammation

Thymoquinone has been reported to exhibit antioxidant and anti-inflammatory effects. Inflammation plays an important role in pathogenesis of diabetic peripheral neuropathy. This study investigated the effects of TQ on proliferation and apoptosis of Schwann cells exposed to high glucose conditions and electrophysiological and morphological changes of the sciatic nerve in a DPN rat model as well as relevant inflammatory mechanism. Cell proliferation and apoptosis of Schwann cells were measured using the Cell Counting Kit-8 and flow cytometry. DPN model was established in streptozotocin-induced diabetic rats. Nerve conduction velocity was measured before and after treatment. Morphologic changes were observed by H&E staining and transmission electron microscopy. COX-2, IL-1β, IL-6, and Caspase-3 expression was investigated by western blotting and Bio-Plex Pro^TM Assays. Finally, TQ alleviated the inhibition of Schwann cell proliferation and protected against Schwann cell apoptosis. It improved nerve conduction velocity, and alleviated the DPN-induced morphological changes and demyelination of the sciatic nerve. COX-2, IL-1β, IL-6 and Caspase-3 expression in sciatic nerve or isolated cultured Schwann cells, were also decreased by TQ. These results indicate TQ has a protective effect on peripheral nerves in a DPN rat model. The mechanism may be mediated partly by the modulation of the inflammatory reaction.

Targeting the Diabetic Chaperome to Improve Peripheral Neuropathy

The chaperome constitutes a broad family of molecular chaperones and co-chaperones that facilitate the folding, refolding, and degradation of the proteome. Heat shock protein 90 (Hsp90) promotes the folding of numerous oncoproteins to aid survival of malignant phenotypes, and small molecule inhibitors of the Hsp90 chaperone complex offer a viable approach to treat certain cancers. One therapeutic attribute of this approach is the selectivity of these molecules to target high affinity oncogenic Hsp90 complexes present in tumor cells, which are absent in nontransformed cells. This selectivity has given rise to the idea that disease may contribute to forming a stress chaperome that is functionally distinct in its ability to interact with small molecule Hsp90 modulators. Consistent with this premise, modulating Hsp90 improves clinically relevant endpoints of diabetic peripheral neuropathy but has little impact in nondiabetic nerve. The concept of targeting the "diabetic chaperome" to treat diabetes and its complications is discussed.

Mesenchymal stem cells to treat diabetic neuropathy: a long and strenuous way from bench to the clinic

As one of the most common complications of diabetes, diabetic neuropathy often causes foot ulcers and even limb amputations. Inspite of continuous development in antidiabetic drugs, there is still no efficient therapy to cure diabetic neuropathy. Diabetic neuropathy shows declined vascularity in peripheral nerves and lack of angiogenic and neurotrophic factors. Mesenchymal stem cells (MSCs) have been indicated as a novel emerging regenerative therapy for diabetic neuropathy because of their multipotency. We will briefly review the pathogenesis of diabetic neuropathy, characteristic of MSCs, effects of MSC therapies for diabetic neuropathy and its related mechanisms. In order to treat diabetic neuropathy, neurotrophic or angiogenic factors in the form of protein or gene therapy are delivered to diabetic neuropathy, but therapeutic efficiencies are very modest if not ineffective. MSC treatment reverses manifestations of diabetic neuropathy. MSCs have an important role to repair tissue and to lower blood glucose level. MSCs even paracrinely secrete neurotrophic factors, angiogenic factors, cytokines, and immunomodulatory substances to ameliorate diabetic neuropathy. There are still several challenges in the clinical translation of MSC therapy, such as safety, optimal dose of administration, optimal mode of cell delivery, issues of MSC heterogeneity, clinically meaningful engraftment, autologous or allogeneic approach, challenges with cell manufacture, and further mechanisms.

Promoting Neuronal Tolerance of Diabetic Stress: Modulating Molecular Chaperones

The etiology of diabetic peripheral neuropathy (DPN) involves an interrelated series of metabolic and vascular insults that ultimately contribute to sensory neuron degeneration. In the quest to pharmacologically manage DPN, small-molecule inhibitors have targeted proteins and pathways regarded as "diabetes specific" as well as others whose activity are altered in numerous disease states. These efforts have not yielded any significant therapies, due in part to the complicating issue that the biochemical contribution of these targets/pathways to the progression of DPN does not occur with temporal and/or biochemical uniformity between individuals. In a complex, chronic neurodegenerative disease such as DPN, it is increasingly appreciated that effective disease management may not necessarily require targeting a pathway or protein considered to contribute to disease progression. Alternatively, it may prove sufficiently beneficial to pharmacologically enhance the activity of endogenous cytoprotective pathways to aid neuronal tolerance to and recovery from glucotoxic stress. In pursuing this paradigm shift, we have shown that modulating the activity and expression of molecular chaperones such as heat shock protein 70 (Hsp70) may provide translational potential for the effective medical management of insensate DPN. Considerable evidence supports that modulating Hsp70 has beneficial effects in improving inflammation, oxidative stress, and glucose sensitivity. Given the emerging potential of modulating Hsp70 to manage DPN, the current review discusses efforts to characterize the cytoprotective effects of this protein and the benefits and limitations that may arise in drug development efforts that exploit its cytoprotective activity.

Modulating Molecular Chaperones Improves Mitochondrial Bioenergetics and Decreases the Inflammatory Transcriptome in Diabetic Sensory Neurons

We have previously demonstrated that modulating molecular chaperones with KU-32, a novobiocin derivative, ameliorates physiologic and bioenergetic deficits of diabetic peripheral neuropathy (DPN). Replacing the coumarin core of KU-32 with a meta-fluorinated biphenyl ring system created KU-596, a novobiocin analogue (novologue) that showed neuroprotective activity in a cell-based assay. The current study sought to determine whether KU-596 offers similar therapeutic potential for treating DPN. Administration of 2-20 mg/kg of KU-596 improved diabetes induced hypoalgesia and sensory neuron bioenergetic deficits in a dose-dependent manner. However, the drug could not improve these neuropathic deficits in diabetic heat shock protein 70 knockout (Hsp70 KO) mice. To gain further insight into the mechanisms by which KU-596 improved DPN, we performed transcriptomic analysis of sensory neuron RNA obtained from diabetic wild-type and Hsp70 KO mice using RNA sequencing. Bioinformatic analysis of the differentially expressed genes indicated that diabetes strongly increased inflammatory pathways and that KU-596 therapy effectively reversed these increases independent of Hsp70. In contrast, the effects of KU-596 on decreasing the expression of genes regulating the production of reactive oxygen species were more Hsp70-dependent. These data indicate that modulation of molecular chaperones by novologue therapy offers an effective approach toward correcting nerve dysfunction in DPN but that normalization of inflammatory pathways alone by novologue therapy seems to be insufficient to reverse sensory deficits associated with insensate DPN.

Levetiracetam synergises with common analgesics in producing antinociception in a mouse model of painful diabetic neuropathy

Painful diabetic neuropathy is difficult to treat. Single analgesics often have insufficient efficacy and poor tolerability. Combination therapy may therefore be of particular benefit, because it might provide optimal analgesia with fewer adverse effects. This study aimed to examine the type of interaction between levetiracetam, a novel anticonvulsant with analgesic properties, and commonly used analgesics (ibuprofen, aspirin and paracetamol) in a mouse model of painful diabetic neuropathy. Diabetes was induced in C57BL/6 mice with a single high dose of streptozotocin, applied intraperitoneally (150 mg/kg). Thermal (tail-flick test) and mechanical (electronic von Frey test) nociceptive thresholds were measured before and three weeks after diabetes induction. The antinociceptive effects of orally administered levetiracetam, analgesics, and their combinations were examined in diabetic mice that developed thermal/mechanical hypersensitivity. In combination experiments, the drugs were co-administered in fixed-dose fractions of single drug ED50 and the type of interaction was determined by isobolographic analysis. Levetiracetam (10-100 mg/kg), ibuprofen (2-50 mg/kg), aspirin (5-75 mg/kg), paracetamol (5-100 mg/kg), and levetiracetam-analgesic combinations produced significant, dose-dependent antinociceptive effects in diabetic mice in both tests. In the tail-flick test, isobolographic analysis revealed 15-, and 19-fold reduction of doses of both drugs in the combination of levetiracetam with aspirin/ibuprofen, and paracetamol, respectively. In the von Frey test, approximately 7- and 9-fold reduction of doses of both drugs was detected in levetiracetam-ibuprofen and levetiracetam-aspirin/levetiracetam-paracetamol combinations, respectively. These results show synergism between levetiracetam and ibuprofen/aspirin/paracetamol in a model of painful diabetic neuropathy and might provide a useful approach to the treatment of patients suffering from painful diabetic neuropathy.

Antioxidation and anti-inflammatory activity of Tang Bi Kang in rats with diabetic peripheral neuropathy

Background

Tang Bi Kang (TBK) is a traditional Chinese medicine granule. It has been shown to have effects on nerve conduction velocity deficits, blood-related factors and oxidative stress. This study was undertaken to evaluate proposed antioxidative and anti-inflammatory activity of Tang Bi Kang in rats with diabetic peripheral neuropathy (DPN).

Methods

DPN was induced in male Wistar rats by intraperitoneal administration of streptozocin (STZ) (60 mg/kg.b.w) for 8 weeks. Fasting blood glucose (FBG) levels were measured in the blood obtained by clipping the tails of the rats. Tail-flick tests were conducted with a tail-flick analgesic meter. Motor and sensory nerve conduction velocities (MNCV and SNCV) of sciatic nerve were measured directly at two sites using a Functional Experiment System. Oxidative stress makers such as malondialdehyde (MDA), superoxide-dismutase (SOD) and glutathione peroxidase (GSH-Px), inflammatory cytokines such as interleukin (IL)-6, and tumour necrosis factor (TNF)-α were estimated. The statistical analysis of results was carried out using Student t-test and one-way analysis of variance (ANOVA), followed by least-significant difference post hoc with SPSS.

Results

The administration of TBK for 4 weeks in DPN rats resulted in a significant decrease in FBG levels compared to untreated DPN rats. There was a significant increase in MNCV and SNCV in the DPN rats compared to untreated DPN rats. Serum level of MDA was significantly reduced while the activities of SOD and GSH-pX were significantly increased in the TBK treated DPN rats. TBK prevented DPN-induced increase in the serum levels of IL-6 and TNF-α.

Conclusion

The results of this study demonstrate that the therapeutic effect of TBK on DPN rats may be associated with the antioxidative and anti-inflammatory responses.

Protective and therapeutic effectiveness of taurine in diabetes mellitus: a rationale for antioxidant supplementation

Taurine, 2-amino ethanesulfonic acid, is a conditionally essential β amino acid which is not utilized in protein synthesis. Taurine is one of the most abundant free amino acids in mammals tissues and is one of the three well-known sulfur-containing amino acids; the others are methionine and cysteine which are considered as the precursors for taurine synthesis. Different scientific studies emphasize on the cytoprotective properties of taurine which included antioxidation, antiapoptosis, membrane stabilization, osmoregulation, and neurotransmission. Protective and therapeutic ameliorations of oxidative stress-induced pathologies were also attributed to taurine both in experimental and human models. Data demonstrating the beneficial effectiveness of taurine against type 1 and type 2 diabetes mellitus and their complications are growing and providing a better understanding of the underlying molecular mechanisms. Although the clinical studies are limited compared to the experimental ones, the present updated systematic review of the literature is set up to provide experimental and clinical evidences regarding the effectiveness of taurine in the context of diabetes mellitus and its complications. Gathering these scientific effects of taurine on diabetes mellitus could provide the physicians and specially the endocrinologists with a comprehensive overview on possible trends in the prevention and management of the disease and its complications through antioxidant supplementation.

Angiogenin gene polymorphism: A risk factor for diabetic peripheral neuropathy in the northern Chinese Han population

Angiogenin is associated with the pathogenesis of diabetic peripheral neuropathy. Here, we quenced the coding region of the angiogenin gene in genomic DNA from 207 patients with type 2 diabetes mellitus (129 diabetic peripheral neuropathy patients and 78 diabetic non-neuropathy patients) and 268 healthy controls. All subjects were from the Han population of northern China. No mutations were found. We then compared the genotype and allele frequencies of the angiogenin synonymous single nucleotide polymorphism rs11701 between the diabetic peripheral neuropathy patients and controls, and between the diabetic neuropathy and non-neuropathy patients, using a case-control design. We detected no statistically significant genetic associations. Angiogenin may not be associated with genetic susceptibility to diabetic peripheral neuropathy in the Han population of northern China.

Neurotoxic effects of iron overload under high glucose concentration

Iron overload can lead to cytotoxicity, and it is a risk factor for diabetic peripheral neuropathy. However, the underlying mechanism remains unclear. We conjectured that iron overload-induced neurotoxicity might be associated with oxidative stress and the NF-E2-related factor 2 (Nrf2)/ARE signaling pathway. As an in vitro cellular model of diabetic peripheral neuropathy, PC12 cells exposed to high glucose concentration were used in this study. PC12 cells were cultured with ferric ammonium citrate at different concentrations to create iron overload. PC12 cells cultured in ferric ammonium citrate under high glucose concentration had significantly low cell viability, a high rate of apoptosis, and elevated reactive oxygen species and malondialdehyde levels. These changes were dependent on ferric ammonium citrate concentration. Nrf2 mRNA and protein expression in the ferric ammonium citrate groups were inhibited markedly in a dose-dependent manner. All changes could be inhibited by addition of deferoxamine. These results indicate that iron overload aggravates oxidative stress injury in neural cells under high glucose concentration and that the Nrf2/ARE signaling pathway might play an important role in this process.

Mesenchymal stem cell-based treatment for microvascular and secondary complications of diabetes mellitus

The worldwide increase in the prevalence of Diabetes mellitus (DM) has highlighted the need for increased research efforts into treatment options for both the disease itself and its associated complications. In recent years, mesenchymal stromal cells (MSCs) have been highlighted as a new emerging regenerative therapy due to their multipotency but also due to their paracrine secretion of angiogenic factors, cytokines, and immunomodulatory substances. This review focuses on the potential use of MSCs as a regenerative medicine in microvascular and secondary complications of DM and will discuss the challenges and future prospects of MSCs as a regenerative therapy in this field. MSCs are believed to have an important role in tissue repair. Evidence in recent years has demonstrated that MSCs have potent immunomodulatory functions resulting in active suppression of various components of the host immune response. MSCs may also have glucose lowering properties providing another attractive and unique feature of this therapeutic approach. Through a combination of the above characteristics, MSCs have been shown to exert beneficial effects in pre-clinical models of diabetic complications prompting initial clinical studies in diabetic wound healing and nephropathy. Challenges that remain in the clinical translation of MSC therapy include issues of MSC heterogeneity, optimal mode of cell delivery, homing of these cells to tissues of interest with high efficiency, clinically meaningful engraftment, and challenges with cell manufacture. An issue of added importance is whether an autologous or allogeneic approach will be used. In summary, MSC administration has significant potential in the treatment of diabetic microvascular and secondary complications but challenges remain in terms of engraftment, persistence, tissue targeting, and cell manufacture.

Neuroinflammation and oxidative stress in diabetic neuropathy: futuristic strategies based on these targets

In Diabetes, the chronic hyperglycemia and associated complications affecting peripheral nerves are one of the most commonly occurring microvascular complications with an overall prevalence of 50-60%. Among the vascular complications of diabetes, diabetic neuropathy is the most painful and disabling, fatal complication affecting the quality of life in patients. Several theories of etiologies surfaced down the lane, amongst which the oxidative stress mediated damage in neurons and surrounding glial cell has gained attention as one of the vital mechanisms in the pathogenesis of neuropathy. Mitochondria induced ROS and other oxidants are responsible for altering the balance between oxidants and innate antioxidant defence of the body. Oxidative-nitrosative stress not only activates the major pathways namely, polyol pathway flux, advanced glycation end products formation, activation of protein kinase C, and overactivity of the hexosamine pathway, but also initiates and amplifies neuroinflammation. The cross talk between oxidative stress and inflammation is due to the activation of NF- κ B and AP-1 and inhibition of Nrf2, peroxynitrite mediate endothelial dysfunction, altered NO levels, and macrophage migration. These all culminate in the production of proinflammatory cytokines which are responsible for nerve tissue damage and debilitating neuropathies. This review focuses on the relationship between oxidative stress and neuroinflammation in the development and progression of diabetic neuropathy.

Heat shock protein 70 is necessary to improve mitochondrial bioenergetics and reverse diabetic sensory neuropathy following KU-32 therapy

Impaired neuronal mitochondrial bioenergetics contributes to the pathophysiologic progression of diabetic peripheral neuropathy (DPN) and may be a focal point for disease management. We have demonstrated that modulating heat shock protein (Hsp) 90 and Hsp70 with the small-molecule drug KU-32 ameliorates psychosensory, electrophysiologic, morphologic, and bioenergetic deficits of DPN in animal models of type 1 diabetes. The current study used mouse models of type 1 and type 2 diabetes to determine the relationship of changes in sensory neuron mitochondrial bioenergetics to the onset of and recovery from DPN. The onset of DPN showed a tight temporal correlation with a decrease in mitochondrial bioenergetics in a genetic model of type 2 diabetes. In contrast, sensory hypoalgesia developed 10 weeks before the occurrence of significant declines in sensory neuron mitochondrial bioenergetics in the type 1 model. KU-32 therapy improved mitochondrial bioenergetics in both the type 1 and type 2 models, and this tightly correlated with a decrease in DPN. Mechanistically, improved mitochondrial function following KU-32 therapy required Hsp70, since the drug was ineffective in diabetic Hsp70 knockout mice. Our data indicate that changes in mitochondrial bioenergetics may rapidly contribute to nerve dysfunction in type 2 diabetes, but not type 1 diabetes, and that modulating Hsp70 offers an effective approach toward correcting sensory neuron bioenergetic deficits and DPN in both type 1 and type 2 diabetes.