Endoplasmic reticulum stress contributes to prediabetic peripheral neuropathy

HDAC1 Promotes Mitochondrial Pathway Apoptosis and Inhibits the Endoplasmic Reticulum Stress Response in High Glucose-Treated Schwann Cells via Decreased U4 Spliceosomal RNA

Dysfunction of Schwann cells, including cell apoptosis, autophagy inhibition, dedifferentiation, and pyroptosis, is a pivotal pathogenic factor in induced diabetic peripheral neuropathy (DPN). Histone deacetylases (HDACs) are an important family of proteins that epigenetically regulate gene transcription by affecting chromatin dynamics. Here, we explored the effect of HDAC1 on high glucose-cultured Schwann cells. HDAC1 expression was increased in diabetic mice and high glucose-cultured RSC96 cells, accompanied by cell apoptosis. High glucose also increased the mitochondrial pathway apoptosis-related Bax/Bcl-2 and cleaved caspase-9/caspase-9 ratios and decreased endoplasmic reticulum response-related GRP78, CHOP, and ATF4 expression in RSC96 cells (P < 0.05). Furthermore, overexpression of HDAC1 increased the ratios of Bax/Bcl-2, cleaved caspase-9/caspase-9, and cleaved caspase-3 and reduced the levels of GRP78, CHOP, and ATF4 in RSC96 cells (P < 0.05). In contrast, knockdown of HDAC1 inhibited high glucose-promoted mitochondrial pathway apoptosis and suppressed the endoplasmic reticulum response. Moreover, RNA sequencing revealed that U4 spliceosomal RNA was significantly reduced in HDAC1-overexpressing RSC96 cells. Silencing of U4 spliceosomal RNA led to an increase in Bax/Bcl-2 and cleaved caspase-9 and a decrease in CHOP and ATF4. Conversely, overexpression of U4 spliceosomal RNA blocked HDAC1-promoted mitochondrial pathway apoptosis and inhibited the endoplasmic reticulum response. In addition, alternative splicing analysis of HDAC1-overexpressing RSC96 cells showed that significantly differential intron retention (IR) of Rpl21, Cdc34, and Mtmr11 might be dominant downstream targets that mediate U4 deficiency-induced Schwann cell dysfunction. Taken together, these findings indicate that HDAC1 promotes mitochondrial pathway-mediated apoptosis and inhibits the endoplasmic reticulum stress response in high glucose-cultured Schwann cells by decreasing the U4 spliceosomal RNA/IR of Rpl21, Cdc34, and Mtmr11.

Endoplasmic reticular stress as an emerging therapeutic target for chronic pain: a narrative review

Chronic pain is a severely debilitating condition with enormous socioeconomic costs. Current treatment regimens with nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, or opioids have been largely unsatisfactory with uncertain benefits or severe long-term side effects. This is mainly because chronic pain has a multifactorial aetiology. Although conventional pain medications can alleviate pain by keeping several dysfunctional pathways under control, they can mask other underlying pathological causes, ultimately worsening nerve pathologies and pain outcome. Recent preclinical studies have shown that endoplasmic reticulum (ER) stress could be a central hub for triggering multiple molecular cascades involved in the development of chronic pain. Several ER stress inhibitors and unfolded protein response modulators, which have been tested in randomised clinical trials or apprpoved by the US Food and Drug Administration for other chronic diseases, significantly alleviated hyperalgesia in multiple preclinical pain models. Although the role of ER stress in neurodegenerative disorders, metabolic disorders, and cancer has been well established, research on ER stress and chronic pain is still in its infancy. Here, we critically analyse preclinical studies and explore how ER stress can mechanistically act as a central node to drive development and progression of chronic pain. We also discuss therapeutic prospects, benefits, and pitfalls of using ER stress inhibitors and unfolded protein response modulators for managing intractable chronic pain. In the future, targeting ER stress to impact multiple molecular networks might be an attractive therapeutic strategy against chronic pain refractory to steroids, NSAIDs, or opioids. This novel therapeutic strategy could provide solutions for the opioid crisis and public health challenge.

Therapeutic potential of endoplasmic reticulum stress inhibitors in the treatment of diabetic peripheral neuropathy

Endoplasmic stress response, the unfolded protein response (UPR), is a homeostatic signaling pathway comprising transmembrane sensors that get activated upon alterations in ER luminal environment. Studies suggest a relation between activated UPR pathways and several disease states such as Parkinson, Alzheimer, inflammatory bowel disease, tumor growth, and metabolic syndrome. Diabetic peripheral neuropathy (DPN), a common microvascular complication of diabetes-related chronic hyperglycemia, causes chronic pain, loss of sensation, foot ulcers, amputations, allodynia, hyperalgesia, paresthesia, and spontaneous pain. Factors like disrupted calcium signaling, dyslipidemia, hyperglycemia, inflammation, insulin signaling, and oxidative stress disturb the UPR sensor levels manifesting as DPN. We discuss new effective therapeutic alternatives for DPN that can be developed by targeting UPR pathways like synthetic ER stress inhibitors like 4-PhenylButyric acid (4-PBA), Sephin 1, Salubrinal and natural ER stress inhibitors like Tauroursodeoxycholic acid (TUDCA), Cordycepin, Proanthocyanidins, Crocin, Purple Rice extract and cyanidin and Caffeic Acid Phenethyl Ester (CAPE).

Cardiac Autonomic Neuropathy in Prediabetes: A Case-Control Study

Introduction

Early detection and diagnosis of diabetic autonomic neuropathy, especially cardiac autonomic neuropathy (CAN), have gained attention recently because of their elevated cardiovascular mortality risk. Although the connection between type 2 diabetes mellitus and autonomic neuropathy is well established, evidence is emerging that the association might predate the stage of prediabetes.

Objective

The present study was undertaken to compare the prevalence of CAN in prediabetes versus that in normoglycemic controls.

Materials and Methods

The study population was selected by purposive sampling from individuals attending a tertiary care hospital from January 2018 to June 2019. Fifty individuals with prediabetes diagnosed by the American Diabetes Association's glycated haemoglobin criteria and 50 age- and gender-matched healthy controls were recruited. CAN was assessed by standard cardiovascular reflex tests, as described by Ewing and Clarke. Changes in R-R with deep breathing, Valsalva manoeuver, and changes in blood pressure (BP) in response to standing and sustained handgrip were evaluated. Three-time domains [standard deviation of normal-to-normal intervals (SDNN), root mean square of successive RR intervals (rMSSD) and percentage of successive normal to normal R-R (NN) intervals that differ by more than 50 ms (pNN50)] and four frequency domain indices [very low-frequency band (VLF), low-frequency band (LF), high-frequency band (HF), LF/HF ratio) of heart rate variability (HRV)] were examined.

Results

The mean heart rate was 71.37 ± 7.94 and 65.59 ± 8.73 beats/min in patients with prediabetes and controls, respectively (P < 0.05). All three-time-domain indices of HRV were significantly lower in persons with prediabetes compared to controls. The peak frequency of LF, peak power of LF, normalised unit of LF, and LF/HF ratio was significantly lower in subjects with prediabetes than in controls. There was no difference in the traditional cardiovascular autonomic reflex testing.

Conclusion

Our study demonstrates the presence of subclinical autonomic dysfunction in persons with prediabetes. Early detection of CAN in prediabetes can have future implications for cardiovascular risk reduction.

Role of ferroptosis inhibitors in the management of diabetes

Ferroptosis, the iron-dependent, lipid peroxide-mediated cell death, has garnered attention due to its critical involvement in crucial physiological and pathological cellular processes. Indeed, several studies have attributed its role in developing a range of disorders, including diabetes. As accumulating evidence further the understanding of ferroptotic mechanisms, the impact this specialized mode of cell death has on diabetic pathogenesis is still unclear. Several in vivo and in vitro studies have highlighted the association of ferroptosis with beta-cell death and insulin resistance, supported by observations of marked alterations in ferroptotic markers in experimental diabetes models. The constant improvement in understanding ferroptosis in diabetes has demonstrated it as a potential therapeutic target in diabetic management. In this regard, ferroptosis inhibitors promise to rescue pancreatic beta-cell function and alleviate diabetes and its complications. This review article elucidates the key ferroptotic pathways that mediate beta-cell death in diabetes, and its complications. In particular, we share our insight into the cross talk between ferroptosis and other hallmark pathogenic mediators such as oxidative and endoplasmic reticulum stress regulators relevant to diabetes progression. Further, we extensively summarize the recent developments on the role of ferroptosis inhibitors and their therapeutic action in alleviating diabetes and its complications.

Characterization of a novel variant in the HR1 domain of MFN2 in a patient with ataxia, optic atrophy and sensorineural hearing loss

Background: Pathogenic variants in MFN2 cause Charcot-Marie-Tooth disease (CMT) type 2A (CMT2A) and are the leading cause of the axonal subtypes of CMT. CMT2A is characterized by predominantly distal motor weakness and muscle atrophy, with highly variable severity and onset age. Notably, some MFN2 variants can also lead to other phenotypes such as optic atrophy, hearing loss and lipodystrophy. Despite the clear link between MFN2 and CMT2A, our mechanistic understanding of how dysfunction of the MFN2 protein causes human disease pathologies remains incomplete. This lack of understanding is due in part to the multiple cellular roles of MFN2. Though initially characterized for its role in mediating mitochondrial fusion, MFN2 also plays important roles in mediating interactions between mitochondria and other organelles, such as the endoplasmic reticulum and lipid droplets. Additionally, MFN2 is also important for mitochondrial transport, mitochondrial autophagy, and has even been implicated in lipid transfer. Though over 100 pathogenic MFN2 variants have been described to date, only a few have been characterized functionally, and even then, often only for one or two functions. Method: Several MFN2-mediated functions were characterized in fibroblast cells from a patient presenting with cerebellar ataxia, deafness, blindness, and diffuse cerebral and cerebellar atrophy, who harbours a novel homozygous MFN2 variant, D414V, which is found in a region of the HR1 domain of MFN2 where few pathogenic variants occur. Results: We found evidence for impairment of several MFN2-mediated functions. Consistent with reduced mitochondrial fusion, patient fibroblasts exhibited more fragmented mitochondrial networks and had reduced mtDNA copy number. Additionally, patient fibroblasts had reduced oxygen consumption, fewer mitochondrial-ER contacts, and altered lipid droplets that displayed an unusual perinuclear distribution. Conclusion: Overall, this work characterizes D414V as a novel variant in MFN2 and expands the phenotypic presentation of MFN2 variants to include cerebellar ataxia.

Soluble Epoxide Hydrolase and Diabetes Complications

Type 2 diabetes mellitus (T2DM) can result in microvascular complications such as neuropathy, retinopathy, nephropathy, and cerebral small vessel disease, and contribute to macrovascular complications, such as heart failure, peripheral arterial disease, and large vessel stroke. T2DM also increases the risks of depression and dementia for reasons that remain largely unclear. Perturbations in the cytochrome P450-soluble epoxide hydrolase (CYP-sEH) pathway have been implicated in each of these diabetes complications. Here we review evidence from the clinical and animal literature suggesting the involvement of the CYP-sEH pathway in T2DM complications across organ systems, and highlight possible mechanisms (e.g., inflammation, fibrosis, mitochondrial function, endoplasmic reticulum stress, the unfolded protein response and autophagy) that may be relevant to the therapeutic potential of the pathway. These mechanisms may be broadly relevant to understanding, preventing and treating microvascular complications affecting the brain and other organ systems in T2DM.

Endoplasmic Reticulum Stress and Its Role in Homeostasis and Immunity of Central and Peripheral Neurons

Neuronal cells are specialists for rapid transfer and translation of information. Their electrical properties relay on a precise regulation of ion levels while their communication via neurotransmitters and neuropeptides depends on a high protein and lipid turnover. The endoplasmic Reticulum (ER) is fundamental to provide these necessary requirements for optimal neuronal function. Accumulation of misfolded proteins in the ER lumen, reactive oxygen species and exogenous stimulants like infections, chemical irritants and mechanical harm can induce ER stress, often followed by an ER stress response to reinstate cellular homeostasis. Imbedded between glial-, endothelial-, stromal-, and immune cells neurons are constantly in communication and influenced by their local environment. In this review, we discuss concepts of tissue homeostasis and innate immunity in the central and peripheral nervous system with a focus on its influence on ER stress, the unfolded protein response, and implications for health and disease.

Ferroptosis and Ferritinophagy in Diabetes Complications

With long-term metabolic malfunction, diabetes can cause more serious damage to the whole body tissue and organs, resulting in a variety of complications. Therefore, it is particularly important to further explore the pathogenesis of diabetes complications and develop drugs for prevention and treatment. In recent years, ferroptosis has been recognized as a new regulatory mode of cell death different from apoptosis and necrosis, which involves the regulation of nuclear receptor coactivator 4 (NCOA4)-mediated ferritinophagy. Evidence shows that ferroptosis and ferritinophagy provide a significant role in the occurrence and development of diabetes complications. This article systematically reviews the current understanding of ferroptosis and ferritinophagy, focusing on their potential mechanisms, connection, and regulation. We discuss their involvement in diabetes complications and consider emerging therapeutic opportunities and the associated challenges with future prospects.

Association of Obesity and Incidence of Third, Fourth, and Sixth Cranial Nerve Palsies

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To assess the association between obesity and the development of third, fourth, and sixth cranial nerve palsy (CNP).

METHODS

We analyzed a cohort of 4,067,842 adults aged between 20 and 90 years who underwent health checkups within the National Health Insurance Service between January 1 and December 31, 2009. The participants were followed until December 31, 2017. Cox proportional hazards regression analysis was used to determine the adjusted hazard ratios (HRs) for CNP. Model 3 (the main analysis model) was adjusted for age, sex, smoking status, alcohol consumption, and physical activity. Model 4 was additionally adjusted for hypertension, dyslipidemia, and diabetes mellitus in the setting of model 3.

RESULTS

A total of 5,835 individuals were diagnosed with CNP during the follow-up period (7.3 years). General obesity (body mass index [BMI] ≥25 kg/m²) was associated with an increased risk of CNP compared to individuals without general obesity (model 3, HR 1.248, 95% CI 1.184-1.315; model 4, HR 1.162, 95% CI 1.102-1.227). Abdominal obesity (waist circumference [WC] ≥90 cm in men and ≥85 cm in women) also showed an increased HR compared to individuals without abdominal obesity (model 3, 1.239, 95% CI 1.170-1.313; model 4, HR 1.127, 95% CI 1.062-1.196). Compared to the group without either type of obesity, the group with only abdominal obesity (model 3, HR 1.167, 95% CI 1.035-1.317), the group with only general obesity (HR 1.19, 95% CI 1.14-1.24), and the group with both obesity types (HR 1.317, 95% CI 1.236-1.404) showed increased HRs for CNP.

CONCLUSION

Based on our population-based cohort study, both general and abdominal obesity increased the risk of CNP. Also, the combination of general and abdominal obesity may further increase the risk of CNP.

Proteomic quantitative study of dorsal root ganglia and sciatic nerve in type 2 diabetic mice

OBJECTIVE

Peripheral neuropathy is the most common and debilitating complication of type 2 diabetes, leading to sensory loss, dysautonomia, hyperalgesia, and spontaneous noxious sensations. Despite the clinical and economic burden of diabetic neuropathy, no effective treatment is available. More preclinical research must be conducted in order to gain further understanding of the aetiology of the disease and elucidate new therapeutic targets.

METHODS

The proteome of lumbar dorsal root ganglia and sciatic nerve of BKS-db/db mice, which contain a mutation of the leptin receptor and are an established type 2 diabetes model, was characterized for the first time by tandem mass tag labelling and mass spectrometry analysis.

RESULTS

Proteomic analysis showed differentially expressed proteins grouped into functional clusters in db/db peripheral nerves compared to control mice, underlining reduced glycolytic and TCA cycle metabolism, higher lipid catabolism, upregulation of muscle-like proteins in DRG and downregulation in SCN, increased cytoskeleton-related proteins, a mild dysregulation of folding chaperones, activation of acute-phase and inflammatory response, and alterations in glutathione metabolism and oxidative stress related proteins.

CONCLUSIONS

Our data validate previous transcriptomic and metabolomic results and uncover new pathways altered in diabetic neuropathy. Our results point out that energetic deficiency could represent the main mechanism of neurodegeneration observed in diabetic neuropathy. These findings may provide important information to select appropriate targets to develop new therapeutic strategies.

The protective effects of hesperidin against paclitaxel-induced peripheral neuropathy in rats

Paclitaxel (PTX), which is widely used in the treatment of solid tumors, leads to dose limitation because it causes peripheral neuropathy. This study was conducted to evaluate the potential effects of hesperidin (HES), which has various biological and pharmacological properties, against PTX-induced sciatic nerve damage. For this purpose, Sprague Dawley rats were given PTX 2 mg/kg/b.w for 5 days, then 100 or 200 mg/kg/b.w HES for 10 days, and behavioral tests were conducted at the end of the experiment. The data obtained show that PTX-induced MDA, NF-κB, IL-1β, TNF-α, COX-2, nNOS, JAK2, STAT3, and GFAP levels decreased with HES administration. Moreover, it was observed that SOD, CAT, and GPx activities inhibited by PTX increased with HES administration. It was determined that PTX caused apoptosis in the sciatic nerve by increasing Caspase-3 and Bax levels and suppressing Bcl-2 levels. HES, on the other hand, showed an anti-apoptotic effect, increasing Bcl-2 levels and decreasing Caspase-3 and Bax levels. Also, it was observed that PTX could cause endoplasmic reticulum stress (ERS) by increasing PERK, IRE1, ATF-6, GRP78 and CHOP mRNA transcript levels, while HES could alleviate ERS by suppressing them. The results indicate that neuropathic pain associated with PTX-induced peripheral neuropathy can be alleviated by HES administration and that it is a promising compound for cancer patients. In addition, it is thought that the results of the present study contain information that will shed light for researchers regarding further studies to be conducted with HES.

Characterization of a novel variant in the HR1 domain of MFN2 in a patient with ataxia, optic atrophy and sensorineural hearing loss

Background: Pathogenic variants in MFN2 cause Charcot-Marie-Tooth disease (CMT) type 2A (CMT2A) and are the leading cause of the axonal subtypes of CMT. CMT2A is characterized by predominantly distal motor weakness and muscle atrophy, with highly variable severity and onset age. Notably, some MFN2 variants can also lead to other phenotypes such as optic atrophy, hearing loss and lipodystrophy. Despite the clear link between MFN2 and CMT2A, our mechanistic understanding of how dysfunction of the MFN2 protein causes human disease pathologies remains incomplete. This lack of understanding is due in part to the multiple cellular roles of MFN2. Though initially characterized for its role in mediating mitochondrial fusion, MFN2 also plays important roles in mediating interactions between mitochondria and other organelles, such as the endoplasmic reticulum and lipid droplets. Additionally, MFN2 is also important for mitochondrial transport, mitochondrial autophagy, and has even been implicated in lipid transfer. Though over 100 pathogenic MFN2 variants have been described to date, only a few have been characterized functionally, and even then, often only for one or two functions. Method: Several MFN2-mediated functions were characterized in fibroblast cells from a patient presenting with cerebellar ataxia, deafness, blindness, and diffuse cerebral and cerebellar atrophy, who harbours a novel homozygous MFN2 variant, D414V, which is found in a region of the HR1 domain of MFN2 where few pathogenic variants occur. Results: We found evidence for impairment of several MFN2-mediated functions. Consistent with reduced mitochondrial fusion, patient fibroblasts exhibited more fragmented mitochondrial networks and had reduced mtDNA copy number. Additionally, patient fibroblasts had reduced oxygen consumption, fewer mitochondrial-ER contacts, and altered lipid droplets that displayed an unusual perinuclear distribution. Conclusion: Overall, this work characterizes D414V as a novel variant in MFN2 and expands the phenotypic presentation of MFN2 variants to include cerebellar ataxia.

Direct and Indirect Effect of Honey as a Functional Food Against Metabolic Syndrome and Its Skeletal Complications

Metabolic syndrome (MetS) refers to the simultaneous presence of hypertension, hyperglycemia, dyslipidemia and/or visceral obesity, which predisposes a person to cardiovascular diseases and diabetes. Evidence suggesting the presence of direct and indirect associations between MetS and osteoporosis is growing. Many studies have reported the beneficial effects of polyphenols in alleviating MetS in in vivo and in vitro models through their antioxidant and anti-inflammation actions. This review aims to summarize the effects of honey (based on unifloral and multi-floral nectar sources) on bone metabolism and each component of MetS. A literature search was performed using the PubMed and Scopus databases using specific search strings. Original studies related to components of MetS and bone, and the effects of honey on components of MetS and bone were included. Honey polyphenols could act synergistically in alleviating MetS by preventing oxidative damage and inflammation. Honey intake is shown to reduce blood glucose levels and prevent excessive weight gain. It also improves lipid metabolism by reducing total cholesterol, triglycerides and low-density lipoprotein, as well as increasing high-density lipoprotein. Honey can prevent bone loss by reducing the adverse effects of MetS on bone homeostasis, apart from its direct action on the skeletal system. In conclusion, honey supplementation could be integrated into the management of MetS and MetS-induced bone loss as a preventive and adjunct therapeutic agent.

Metformin: A Prospective Alternative for the Treatment of Chronic Pain

Metformin (biguanide) is a drug widely used for the treatment of type 2 diabetes. This drug has been used for 60 years as a highly effective antihyperglycemic agent. The search for the mechanism of action of metformin has produced an enormous amount of research to explain its effects on gluconeogenesis, protein metabolism, fatty acid oxidation, oxidative stress, glucose uptake, autophagy and pain, among others. It was only up the end of the 1990s and beginning of this century that some of its mechanisms were revealed. Metformin induces its beneficial effects in diabetes through the activation of a master switch kinase named AMP-activated protein kinase (AMPK). Two upstream kinases account for the physiological activation of AMPK: liver kinase B1 and calcium/calmodulin-dependent protein kinase kinase 2. Once activated, AMPK inhibits the mechanistic target of rapamycin complex 1 (mTORC1), which in turn avoids the phosphorylation of p70 ribosomal protein S6 kinase 1 and phosphatidylinositol 3-kinase/protein kinase B signaling pathways and reduces cap-dependent translation initiation. Since metformin is a disease-modifying drug in type 2 diabetes, which reduces the mTORC1 signaling to induce its effects on neuronal plasticity, it was proposed that these mechanisms could also explain the antinociceptive effect of this drug in several models of chronic pain. These studies have highlighted the efficacy of this drug in chronic pain, such as that from neuropathy, insulin resistance, diabetic neuropathy, and fibromyalgia-type pain. Mounting evidence indicates that chronic pain may induce anxiety, depression and cognitive impairment in rodents and humans. Interestingly, metformin is able to reverse some of these consequences of pathological pain in rodents. The purpose of this review was to analyze the current evidence about the effects of metformin in chronic pain and three of its comorbidities (anxiety, depression and cognitive impairment).

Is there cardiac autonomic neuropathy in prediabetes?

Although there is considerably more data showing an association between type 2 diabetes mellitus (T2DM) and autonomic neuropathy, accumulating evidence indicates that cardiovascular autonomic neuropathy (CAN) is common in persons with impaired glucose tolerance (IGT). Furthermore, CAN may occur early after a metabolic insult and obesity, especially among mean, and seems to play an important role in the early pathogenesis of CAN. Autonomic symptoms are common in subjects with IGT. In addition to defects in CAN, in subjects with IGT, there is impaired sudomotor function and abnormalities of endothelial peripheral vasoreactivity. At the present time, the only interventions that may be effective in preventing or reversing IGT associated autonomic neuropathy are lifestyle improvement. These include a tailored diet and exercise program. Other approaches that may be beneficial include modulation of oxidative stress and improvement of metabolic regulation in subjects with IGT. Interventions are most likely to be effective early in the course of disease and therefore it is extremely important to have early diagnosis of IGT and autonomic neuropathy.

Prediabetes Deserves More Attention: A Review

Evidence increasingly demonstrates that prediabetes is a toxic state, as well as a risk factor for diabetes, and is associated with pathophysiological changes in several tissues and organs. Unfortunately, use of available evidence-based treatments for prediabetes is low. This review seeks to explain why prediabetes must be viewed and treated as a serious pathological entity in its own right. It offers an overview of the pathophysiology and complications of prediabetes and describes how this condition can be reversed if all treatment avenues are deployed early in its course.

Evidence of Altered Peripheral Nerve Function in a Rodent Model of Diet-Induced Prediabetes

Peripheral neuropathy (PN) is a debilitating complication of diabetes that affects >50% of patients. Recent evidence suggests that obesity and metabolic disease, which often precede diabetes diagnosis, may influence PN onset and severity. We examined this in a translationally relevant model of prediabetes induced by a cafeteria (CAF) diet in Sprague–Dawley rats (n = 15 CAF versus n = 15 control). Neuropathy phenotyping included nerve conduction, tactile sensitivity, intraepidermal nerve fiber density (IENFD) and nerve excitability testing, an in vivo measure of ion channel function and membrane potential. Metabolic phenotyping included body composition, blood glucose and lipids, plasma hormones and inflammatory cytokines. After 13 weeks diet, CAF-fed rats demonstrated prediabetes with significantly elevated fasting blood glucose, insulin and impaired glucose tolerance as well as obesity and dyslipidemia. Nerve conduction, tactile sensitivity and IENFD did not differ; however, superexcitability was significantly increased in CAF-fed rats. Mathematical modeling demonstrated this was consistent with a reduction in sodium–potassium pump current. Moreover, superexcitability correlated positively with insulin resistance and adiposity, and negatively with fasting high-density lipoprotein cholesterol. In conclusion, prediabetic rats over-consuming processed, palatable foods demonstrated altered nerve function that preceded overt PN. This work provides a relevant model for pathophysiological investigation of diabetic complications.

Amyloid Proteins and Peripheral Neuropathy

Painful peripheral neuropathy affects millions of people worldwide. Peripheral neuropathy develops in patients with various diseases, including rare familial or acquired amyloid polyneuropathies, as well as some common diseases, including type 2 diabetes mellitus and several chronic inflammatory diseases. Intriguingly, these diseases share a histopathological feature-deposits of amyloid-forming proteins in tissues. Amyloid-forming proteins may cause tissue dysregulation and damage, including damage to nerves, and may be a common cause of neuropathy in these, and potentially other, diseases. Here, we will discuss how amyloid proteins contribute to peripheral neuropathy by reviewing the current understanding of pathogenic mechanisms in known inherited and acquired (usually rare) amyloid neuropathies. In addition, we will discuss the potential role of amyloid proteins in peripheral neuropathy in some common diseases, which are not (yet) considered as amyloid neuropathies. We conclude that there are many similarities in the molecular and cell biological defects caused by aggregation of the various amyloid proteins in these different diseases and propose a common pathogenic pathway for "peripheral amyloid neuropathies".

Pim1 kinase provides protection against high glucose-induced stress and apoptosis in cultured dorsal root ganglion neurons

The pathogenesis of diabetic peripheral neuropathy (DPN) is complex and not well understood. Recently, oxidative stress and endoplasmic reticulum (ER) stress induced by hyperglycemia have been demonstrated to play a critical role in neuronal apoptosis, which then contributing to DPN. However, the specific molecular mechanism that underlies the hyperglycemia-induced neuronal stresses and apoptosis remains largely unknown. In this study, we demonstrated for the first time that Pim1 kinase is a positive modulator of dorsal root ganglion (DRG) neuron survival in vitro. Hyperglycemia causes compensatory upregulation of Pim1 kinase in the DRG neurons, which provides protection against high glucose-induced oxidative stress and ER stress. Pharmacological inhibition of Pim1 not only sensitizes the stress response to high glucose in the DRG neurons, but also accelerates the apoptosis of DRG neurons in vitro. Therefore, our work provides experimental evidence for the prevention of high glucose-induced neuronal stress and apoptosis by targeting Pim1 kinase.

High fat diet consumption results in mitochondrial dysfunction, oxidative stress, and oligodendrocyte loss in the central nervous system

Metabolic syndrome is a key risk factor and co-morbidity in multiple sclerosis (MS) and other neurological conditions, such that a better understanding of how a high fat diet contributes to oligodendrocyte loss and the capacity for myelin regeneration has the potential to highlight new treatment targets. Results demonstrate that modeling metabolic dysfunction in mice with chronic high fat diet (HFD) consumption promotes loss of oligodendrocyte progenitors across the brain and spinal cord. A number of transcriptomic and metabolomic changes in ER stress, mitochondrial dysfunction, and oxidative stress pathways in HFD-fed mouse spinal cords were also identified. Moreover, deficits in TCA cycle intermediates and mitochondrial respiration were observed in the chronic HFD spinal cord tissue. Oligodendrocytes are known to be particularly vulnerable to oxidative damage, and we observed increased markers of oxidative stress in both the brain and spinal cord of HFD-fed mice. We additionally identified that increased apoptotic cell death signaling is underway in oligodendrocytes from mice chronically fed a HFD. When cultured under high saturated fat conditions, oligodendrocytes decreased both mitochondrial function and differentiation. Overall, our findings show that HFD-related changes in metabolic regulators, decreased mitochondrial function, and oxidative stress contribute to a loss of myelinating cells. These studies identify HFD consumption as a key modifiable lifestyle factor for improved myelin integrity in the adult central nervous system and in addition new tractable metabolic targets for myelin protection and repair strategies.

Dexmedetomidine Alleviated Endoplasmic Reticulum Stress via Inducing ER-phagy in the Spinal Cord of Neuropathic Pain Model

Studies demonstrated that spinal autophagy was impaired in spinal nerve ligation (SNL) rats. However, the relationship of endoplasmic reticulum (ER) stress and ER-phagy and whether dexmedetomidine (DEX) modulates ER-phagy remain unclear. In this study, male Sprague-Dawley (SD) rats and the SNL animal model were used. 4-Phenylbutyric acid (4-PBA), tunicamycin (TM), rapamycin (RAP), and 3-methyladenine (3-MA) were intrathecally administered, respectively to demonstrate the relationship of ER stress and ER-phagy. Dexmedetomidine (30 μg/kg) was administered as treatment. Mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) tests were performed to evaluate nociceptive hypersensitivity. Protein expressions were examined by Western blot, and the location of glucose-regulated protein 78 (Grp78) was examined by immunofluorescence staining. SNL induced ER stress and ER-phagy impairment. ER stress was altered in rostral ventromedial medulla (RVM); 4-phenylbutyric acid induced analgesic effect via inhibiting ER stress and unfolded protein response (UPR) pathways to induce ER-phagy; tunicamycin led to worsening pain through enhancing ER stress and UPR pathways to further impair ER-phagy. Rapamycin provided analgesic effect through enhancing ER-phagy to relieve SNL-induced ER stress and UPR pathway activation; 3-methyladenine deteriorated pain via further impairing ER-phagy to aggravate ER stress. Dexmedetomidine provided analgesic effect through elevating ER-phagy. In conclusion, ER stress led to ER-phagy impairment in the spinal cord of SNL rats and participated in the nociceptive descending system. ER-phagy impairment was both a trigger and an effector of ER stress via UPR pathways in SNL rats. Dexmedetomidine targeted ER-phagy to provide analgesic effect.

"Adjusting internal organs and dredging channel" electroacupuncture treatment prevents the development of diabetic peripheral neuropathy by downregulating glucose-related protein 78 (GRP78) and caspase-12 in streptozotocin-diabetic rats

BACKGROUND

The clinical efficacy of electroacupuncture in treating diabetic peripheral neuropathy (DPN) is significant, but the underlying mechanism of action is not clear. Considering that glucose-regulated protein 78 (GRP78) and caspase-12 are major proteins participating in cell apoptosis, we investigated the effects of "adjusting internal organs and dredging channel" electroacupuncture therapy on GRP78 and caspase-12 levels in streptozotocin (STZ)-diabetic rats to elucidate the mechanism of action.

METHODS

Rats were first divided into two groups: one group was rendered diabetic with a single injection of 50 mg/kg STZ, whereas the other normal control group was injected with an equivalent volume of citrate buffer. The STZ-diabetic rats were randomly divided into three groups: model control and electroacupuncture- and mecobalamin-treated groups. After 12 weeks treatment, the therapeutic efficacy of electroacupuncture was assessed using sciatic nerves isolated from rats. In the electroacupuncture group, rats were treated by electroacupuncture for 20 minutes once daily for 6 days each week, with 1 day off, for 12 consecutive weeks. The selected acupressure points include bilateral acupressure points of BL13 (Fehu), BL20 (Pishu), BL23 (Shenshu), LI4 (Hegu), LR3 (faichong), ST36 (Zusanli), and SP6 (Sanyiniiao). Acupressure points were stimulated using a HuaTuo SDZ-V Electric Acupuncture Therapy Apparatus. The acupressure points of BL13 and BL23, as well as SP6 and LR3, were connected on the same side with a dilatational wave of 3 Hz (frequency ratio of 1 : 5) to stimulate the parts of the body to the extent that could be tolerated by the rat. As for the mecobalamin-treated groups, mecobalamin was administrated to rats intragastrically at a dose of 20 mg/kg once daily for 12 consecutive weeks. Immunofluorescence and western blot analysis were used to determine GRP78 and caspase-12 levels in sciatic nerves. In addition, cell apoptosis in sciatic nerves was determined using the terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labeling (TUNEL) assay.

RESULTS

Electroacupuncture markedly reduced the pathological injury to sciatic nerves in STZ-diabetic rats. Moreover, electroacupuncture significantly downregulated GRP78 and caspase-12 and reduced cell apoptosis of sciatic nerves in DPN rats.

CONCLUSIONS

Electroacupuncture improved DPN by downregulating GRP78 and caspase-12 and reducing cell apoptosis of sciatic nerves in STZ-diabetic rats, and further inhibited the occurrence of endoplasmic reticulum stress, thus preventing sciatic nerve injuries.

Activation of the integrated stress response in nociceptors drives methylglyoxal-induced pain

Methylglyoxal (MGO) is a reactive glycolytic metabolite associated with painful diabetic neuropathy at plasma concentrations between 500 nM and 5 μM. The mechanisms through which MGO causes neuropathic pain at these pathological concentrations are not known. Because MGO has been linked to diabetic neuropathic pain, which is prevalent and poorly treated, insight into this unsolved biomedical problem could lead to much needed therapeutics. Our experiments provide compelling evidence that ∼1-μM concentrations of MGO activate the integrated stress response (ISR) in IB4-positive nociceptors in the dorsal root ganglion (DRG) of mice in vivo and in vitro. Blocking the integrated stress response with a specific inhibitor (ISRIB) strongly attenuates and reverses MGO-evoked pain. Moreover, ISRIB reduces neuropathic pain induced by diabetes in both mice and rats. Our work elucidates the mechanism of action of MGO in the production of pain at pathophysiologically relevant concentrations and suggests a new pharmacological avenue for the treatment of diabetic and other types of MGO-driven neuropathic pain.

Activation of Nrf2 signaling by natural products-can it alleviate diabetes?

Type 2 diabetes mellitus (DM) has reached pandemic proportions and effective prevention strategies are wanted. Its onset is accompanied by cellular distress, the nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor boosting cytoprotective responses, and many phytochemicals activate Nrf2 signaling. Thus, Nrf2 activation by natural products could presumably alleviate DM. We summarize function, regulation and exogenous activation of Nrf2, as well as diabetes-linked and Nrf2-susceptible forms of cellular stress. The reported amelioration of insulin resistance, β-cell dysfunction and diabetic complications by activated Nrf2 as well as the status quo of Nrf2 in precision medicine for DM are reviewed.

The leptin receptor mutation of the obese Zucker rat causes sciatic nerve demyelination with a centripetal pattern defect

Young male Zucker rats with a leptin receptor mutation are obese, have a non-insulin-dependent diabetes mellitus (NIDDM), and other endocrinopathies. Tibial branches of the sciatic nerve reveal a progressive demyelination that progresses out of the Schwann cells (SCs) where electron-contrast deposits are accumulated while the minor lines or intermembranous SC contacts display exaggerated spacings. Cajal bands contain diversely contrasted vesicles adjacent to the abaxonal myelin layer with blemishes; they appear dispatched centripetally out of many narrow electron densities, regularly spaced around the myelin annulus. These anomalies widen and yield into sectors across the stacked myelin layers. Throughout the worse degradations, the adaxonal membrane remains along the axonal neuroplasm. This peripheral neuropathy with irresponsive leptin cannot modulate hypothalamic-pituitary-adrenal axis and SC neurosteroids, thus exacerbates NIDDM condition. Additionally, the ultrastructure of the progressive myelin alterations may have unraveled a peculiar, centripetal mode of trafficking maintenance of the peripheral nervous system myelin, while some adhesive glycoproteins remain between myelin layers, somewhat hindering the axon mutilation. Heading title: Peripheral neuropathy and myelin.

Pepsin Egg White Hydrolysate Improves Glucose Metabolism Complications Related to Metabolic Syndrome in Zucker Fatty Rats

The purpose of this study was to evaluate the effect of the administration of two egg white hydrolysates on glucose metabolism complications related to Metabolic Syndrome (MS) in Zucker fatty rats (ZFR). ZFR were given 750 mg/kg/day of egg white hydrolyzed with pepsin (HEW1) or with aminopeptidase (HEW2) for 12 weeks in their drinking water or just water. Zucker lean rats (ZLR), which received water, were used as a control. The presence of tactile allodynia, which is a sign of peripheral neuropathy, was assessed. Blood samples and pancreas were collected to determine the effect of the hydrolysates on glucose metabolism. The intake of HEW1 significantly lowered plasma insulin levels and improved the quantitative indexes of insulin resistance, insulin sensitivity, and pancreatic β-cell functionality (HOMA-IR, HOMA-β, and QUICKI, respectively), but non-significant changes were observed in group treated with HEW2. Compared to ZLR, ZFR showed tactile allodynia, but the consumption of both hydrolysates significantly increased mechanical sensitivity in ZFR. In conclusion, HEW1 pepsin could improve the glucose metabolism abnormalities associated with MS in obese Zucker rats.

Trimethylamine N-oxide: breathe new life

Association between elevated levels of systemic trimethylamine N-oxide (TMAO) and increased risk for adverse cardiovascular events have been proposed in recent years. Increasing experimental and clinical evidence in the last decade has implicated TMAO as an important contributor to the pathogenesis of cardiovascular diseases. TMAO, the oxygenated product of trimethylamine (TMA), belongs to the class of amine oxides. Most of the TMA derived from the metabolism of choline and L-carnitine by gut bacteria is absorbed into the bloodstream and gets rapidly oxidized to TMAO by the hepatic enzyme, flavin-containing monooxgenase-3. Here, we discussed the biosynthesis of TMAO and clinical studies that have assessed TMAO as a biomarker for various cardiovascular and other diseases such as kidney failure, thrombosis, atherosclerosis, obesity, diabetes and cancer. We also summarized the interaction of TMAO with synthetic and traditional molecules that together affect circulating TMAO levels.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Herbal Remedies: A Boon for Diabetic Neuropathy

Diabetic neuropathy is a chronic complication of diabetes mellitus affecting about 50% of patients. Its symptoms include decreased motility and severe pain in peripheral parts. The pathogenesis involved is an abnormality in blood vessels that supply the peripheral nerves, metabolic disorders such as myo-inositol depletion, and increased nonenzymatic glycation. Moreover, oxidative stress in neurons results in activation of multiple biochemical pathways, which results in the generation of free radicals. Apart from available marketed formulations, extensive research is being carried out on herbal-based natural products to control hyperglycemia and its associated complications. This review is focused to provide a summary on diabetic neuropathy covering its etiology, types, and existing work on herbal-based therapies, which include pure compounds isolated from plant materials, plant extracts, and Ayurvedic preparations.

Tang-Luo-Ning, a Traditional Chinese Medicine, Inhibits Endoplasmic Reticulum Stress-Induced Apoptosis of Schwann Cells under High Glucose Environment

Tang-Luo-Ning (TLN) has a definite effect in the clinical treatment of diabetic peripheral neuropathy (DPN). Schwann cells (SCs) apoptosis induced by endoplasmic reticulum stress (ER stress) is one of the main pathogeneses of DPN. This study investigates whether TLN can inhibit SCs apoptosis by inhibiting ER stress-induced apoptosis. Our previous researches have demonstrated that TLN could increase the expression of ER stress marker protein GRP78 and inhibited the expression of apoptosis marker protein CHOP in ER stress. In this study, the results showed that TLN attenuated apoptosis by decreasing Ca²⁺ level in SCs and maintaining ER morphology. TLN could decrease downstream proteins of CHOP including GADD34 and Ero1α, while it increased P-eIF2α and decreased the upstream proteins of CHOP including P-IRE1α/IRE1α and XBP-1, thereby reducing ER stress-induced apoptosis.

Neurological consequences of obesity

The high prevalence of obesity is associated with an enormous medical, social, and economic burden. The metabolic dysfunction, dyslipidaemia, and inflammation caused by obesity contribute to the development of a wide variety of disorders and effects on the nervous system. In the CNS, mild cognitive impairment can be attributed to obesity-induced alterations in hippocampal structure and function in some patients. Likewise, compromised hypothalamic function and subsequent defects in maintaining whole-body energy balance might be early events that contribute to weight gain and obesity development. In the peripheral nervous system, obesity-driven alterations in the autonomic nervous system prompt imbalances in sympathetic-parasympathetic activity, while alterations in the sensory-somatic nervous system underlie peripheral polyneuropathy, a common complication of diabetes. Pharmacotherapy and bariatric surgery are promising interventions for people with obesity that can improve neurological function. However, lifestyle interventions via dietary changes and exercise are the preferred approach to combat obesity and reduce its associated health risks.

Intraventricular administration of Tenebrio molitor larvae extract regulates food intake and body weight in mice with high-fat diet-induced obesity

We recently reported the in vitro and in vivo antiobesity effects of Tenebrio molitor larvae, a traditional food in many countries, but it remains unknown how the larvae affect appetite regulation in mice with diet-induced obesity. We hypothesized that the extract of T molitor larvae mediates appetite by regulating neuropeptide expression. We investigated T molitor larvae extract's (TME's) effects on anorexigenesis and endoplasmic reticulum (ER) stress-induced orexigenic neuropeptide expression in the hypothalami of obese mice. Intracerebroventricular TME administration suppressed feeding by down-regulating the expression of the orexigenic neuropeptides neuropeptide Y and agouti-related protein. T molitor larvae extract significantly reduced the expression of ER stress response genes. These results suggest that TME and its bioactive components are potential therapeutics for obesity and ER stress-driven disease states.

Dual Delivery of NGF and bFGF Coacervater Ameliorates Diabetic Peripheral Neuropathy via Inhibiting Schwann Cells Apoptosis

Diabetic neuropathy is a kind of insidious complications that impairs neural and vascular function and ultimately leads to somatic and visceral denervation. Basic fibroblast growth factor (bFGF) and nerve growth factor (NGF) are important neurotrophic factors for stimulating angiogenesis and improving peripheral nerve function. Administrating a single factor has good therapeutic effect on diabetic peripheral neuropathy (DPN). However, the short half-life and rapid diffusion of growth factors under physiological conditions limits its clinical applications. Here, we used a biodegradable coacervate, composed of heparin and polycation, to dominate the combined release of bFGF and NGF in a steady fashion. We found this combined growth factors (GFs) coacervate, administered as a single injection, improved motor and sensory functions, restored morphometric structure and decreased apoptosis of Schwann cells in a rat model of prolonged DPN. Similarly the GFs coacervate, as compared with free bFGF and NGF combination, markedly reduced the apoptosis level of a rat Schwann cell line, RSC 96 cells in vitro. We also demonstrated that neuroprotective effects of the GFs coacervate in both rat DPN model and hyperglycemia-induced RSC 96 cell model is likely due to suppression of endocytoplasmic reticulum stress (ERS).

Tangluoning, a traditional Chinese medicine, attenuates in vivo and in vitro diabetic peripheral neuropathy through modulation of PERK/Nrf2 pathway

Prolonged hyperglycemia-induced oxidative stress and endoplasmic reticulum stress have been demonstrated to play a key role in progression of diabetic peripheral neuropathy (DPN). PERK/ Nrf2 pathway plays a predominant role in oxidative and endoplasmic reticulum (ER) stress which is associated with cell survival. This study examined the modulation of the PERK/Nrf2 pathway and apoptosis by a traditional Chinese medicine Tangluoning (TLN) in streptozotocin-induced DPN rat models and the effects of serum TLN on the PERK/Nrf2 pathway, apoptosis, intracellular reactive oxygen species and mitochondrial membrane potential in Schwann cells cultured in 150 mM glucose. It is found that TLN attenuated oxidative and ER stress and apoptosis through the PERK/Nrf2 pathway by upregulating p-PERK, Nrf2/ARE pathways and downregulating the CHOP-related apoptosis pathways in the experimental DPN models both in vivo and in vitro.

TNF-Alpha in Peripheral Neuropathy Patients with Impaired Glucose Regulation

Impaired glucose regulation (IGR) is the prestate of diabetes; about 1/3 of IGR patients will develop to diabetes finally. In this study, we investigated the serum tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) levels in peripheral neuropathy impaired patients with impaired glucose regulation (IGR). A total of 70 IGR patients received the conventional nerve conduction test, including 30 patients with peripheral neuropathy (PN) and 40 patients without peripheral neuropathy (NPN). The other 40 healthy individuals were recruited as controls. The serum TNF-α and IL-6 in IGR patients were higher than in control group, and serum TNF-α and IL-6 levels in IGR-PN group were higher than in IGR-NPN group (27.7 ± 17.8 versus 13.1 ± 6.7 pg/mL and 18.1 ± 17.7 versus 6.4 ± 3.7 pg/mL, resp., both p < 0.05). Multifactors logistic regression analysis showed that TNF-α (OR = 0.893; p = 0.009) was an independent factor affecting whether IGR could combine with peripheral neuropathy. TNF-α and IL-6 could aggregate peripheral neuropathy in impaired glucose regulation patients; TNF-α might be independent risk factor for peripheral neuropathy in glucose regulation impaired patients.

Diastolic dysfunction in prediabetic male rats: Role of mitochondrial oxidative stress

Although incidence and prevalence of prediabetes are increasing, little is known about its cardiac effects. Therefore, our aim was to investigate the effect of prediabetes on cardiac function and to characterize parameters and pathways associated with deteriorated cardiac performance. Long-Evans rats were fed with either control or high-fat chow for 21 wk and treated with a single low dose (20 mg/kg) of streptozotocin at week 4 High-fat and streptozotocin treatment induced prediabetes as characterized by slightly elevated fasting blood glucose, impaired glucose and insulin tolerance, increased visceral adipose tissue and plasma leptin levels, as well as sensory neuropathy. In prediabetic animals, a mild diastolic dysfunction was observed, the number of myocardial lipid droplets increased, and left ventricular mass and wall thickness were elevated; however, no molecular sign of fibrosis or cardiac hypertrophy was shown. In prediabetes, production of reactive oxygen species was elevated in subsarcolemmal mitochondria. Expression of mitofusin-2 was increased, while the phosphorylation of phospholamban and expression of Bcl-2/adenovirus E1B 19-kDa protein-interacting protein 3 (BNIP3, a marker of mitophagy) decreased. However, expression of other markers of cardiac auto- and mitophagy, mitochondrial dynamics, inflammation, heat shock proteins, Ca²⁺/calmodulin-dependent protein kinase II, mammalian target of rapamycin, or apoptotic pathways were unchanged in prediabetes. This is the first comprehensive analysis of cardiac effects of prediabetes indicating that mild diastolic dysfunction and cardiac hypertrophy are multifactorial phenomena that are associated with early changes in mitophagy, cardiac lipid accumulation, and elevated oxidative stress and that prediabetes-induced oxidative stress originates from the subsarcolemmal mitochondria.

Compromised Wound Healing in Ischemic Type 2 Diabetic Rats

Ischemia is one of the main epidemic factors and characteristics of diabetic chronic wounds, and exerts a profound effect on wound healing. To explore the mechanism of and the cure for diabetic impaired wound healing, we established a type 2 diabetic rat model. We used an 8weeks high fat diet (HFD) feeding regimen followed by multiple injections of streptozotocin (STZ) at a dose of 10mg/kg to induce Wister rat to develop type 2 diabetes. Metabolic characteristics were assessed at the 5th week after the STZ injections to confirm the establishment of diabetes mellitus on the rodent model. A bipedicle flap, with length to width ratio 1.5, was performed on the back of the rat to make the flap area ischemic. Closure of excisional wounds on this bipedicle flap and related physiological and pathological changes were studied using histological, immunohistochemical, real time PCR and protein immunoblot approaches. Our results demonstrated that a combination of HFD feeding and a low dose of STZ is capable of inducing the rats to develop type 2 diabetes with noticeable insulin resistance, persistent hyperglycemia, moderate degree of insulinemia, as well as high serum cholesterol and high triglyceride levels. The excision wounds on the ischemic double pedicle flap showed deteriorative healing features comparing with non-ischemic diabetic wounds, including: delayed healing, exorbitant wound inflammatory response, excessive and prolonged ROS production and excessive production of MMPs. Our study suggested that HFD feeding combined with STZ injection could induce type 2 diabetes in rat. Our ischemic diabetic wound model is suitable for the investigation of human diabetic related wound repair; especically for diabetic chronic wounds.

Alternatives to the Streptozotocin-Diabetic Rodent

The study of diabetic neuropathy has relied primarily on the use of streptozotocin-treated rat and mouse models of type 1 diabetes. This chapter will review the creation and use of other rodent models that have been developed in order to investigate the contribution of factors besides insulin deficiency to the development and progression of diabetic neuropathy as it occurs in obesity, type 1 or type 2 diabetes. Diabetic peripheral neuropathy is a complex disorder with multiple mechanisms contributing to its development and progression. Even though many animal models have been developed and investigated, no single model can mimic diabetic peripheral neuropathy as it occurs in humans. Nonetheless, animal models can play an important role in improving our understanding of the etiology of diabetic peripheral neuropathy and in performing preclinical screening of potential new treatments. To date treatments found to be effective for diabetic peripheral neuropathy in rodent models have failed in clinical trials. However, with the identification of new endpoints for the early detection of diabetic peripheral neuropathy and the understanding that a successful treatment may require a combination therapeutic approach there is hope that an effective treatment will be found.

Allomyrina Dichotoma Larvae Regulate Food Intake and Body Weight in High Fat Diet-Induced Obese Mice Through mTOR and Mapk Signaling Pathways

Recent evidence has suggested that the Korean horn beetle (Allomyrina dichotoma) has anti-hepatofibrotic, anti-neoplastic, and antibiotic effects and is recognized as a traditional medicine. In our previous works, Allomyrina dichotoma larvae (ADL) inhibited differentiation of adipocytes both in vitro and in vivo. However, the anorexigenic and endoplasmic reticulum(ER) stress-reducing effects of ADL in obesity has not been examined. In this study, we investigated the anorexigenic and ER stress-reducing effects of ADL in the hypothalamus of diet-induced obese (DIO) mice. Intracerebroventricular (ICV) administration of ethanol extract of ADL (ADE) suggested that an antagonizing effect on ghrelin-induced feeding behavior through the mTOR and MAPK signaling pathways. Especially, ADE resulted in strong reduction of ER stress both in vitro and in vivo. These findings strongly suggest that ADE and its constituent bioactive compounds are available and valuable to use for treatment of various diseases driven by prolonged ER stress.

Algae Undaria pinnatifida Protects Hypothalamic Neurons against Endoplasmic Reticulum Stress through Akt/mTOR Signaling

Increased endoplasmic reticulum (ER) stress is known to be one of the causes of hypothalamic neuronal damage, as well as a cause of metabolic disorders such as obesity and diabetes. Recent evidence has suggested that Undaria pinnatifida (UP), an edible brown algae, has antioxidant activity. However, the neuroprotective effect of UP has yet to be examined. In this study, to investigate the neuroprotective effect of UP on ER stress-induced neuronal damage in mouse hypothalamic neurons, mice immortal hypothalamic neurons (GT1-7) were incubated with extract of UP. ER stress was induced by treating with tunicamycin. Tunicamycin induced apoptotic cell death was compared with the vehicle treatment through excessive ER stress. However UP protected GT1-7 cells from cell death, occurring after treatment with tunicamycin by reducing ER stress. Treatment with UP resulted in reduced increment of ATF6 and CHOP, and recovered the decrease of phosphorylation of Akt/mTOR by tunicamycin and the increment of autophagy. These results show that UP protects GT1-7 cells from ER stress induced cell death through the Akt/mTOR pathway. The current study suggests that UP may have a beneficial effect on cerebral neuronal degeneration in metabolic diseases with elevated ER stress.

An association of large-fibre peripheral nerve dysfunction with non-invasive measures of liver fibrosis secondary to non-alcoholic fatty liver disease in diabetes

AIM

To examine for an association of elevated lower-limb vibration perception threshold (VPT) with NAFLD fibrosis.

METHODS

Two cohorts from a tertiary diabetes centre were studied - Cohort 1, n=456 with type 1 or 2 diabetes, and Cohort 2, n=106 with type 2 diabetes mellitus. All underwent a detailed assessment, including VPT measurement. Cohort 2 also had liver ultrasound and transient elastography (TE). NAFLD Fibrosis Score (NFS) was calculated for all with available data. Follow-up VPT measurements on participants in Cohort 1 to 2014 were also collected if available.

RESULTS

Adjusted risk of higher VPT category (≥25V but <50V, or ≥50V, c.f. < 25V) was greater for high-risk NFS in both cohorts (Cohort 1, OR 2.22 [95% CI 1.24-3.98, p=0.007] and Cohort 2, OR 4.51 [95% CI 1.08-18.87], p=0.039) and higher liver stiffness measurement (LSM) by TE in Cohort 2 (OR for each unit natural log increase in LSM of 2.42 (95% CI 1.13-5.19), p=0.023). In Cohort 1, in those with VPT<50V and complete data, those with higher NFS had greater odds of increasing VPT category after 2.2 (IQR 1.5-2.9) years.

CONCLUSIONS

Higher VPT associates with markers of liver fibrosis due to NAFLD in diabetes mellitus.

Musculoskeletal manifestations in diabetic versus prediabetic patients

AIM

This study was carried out to evaluate the prevalence of musculoskeletal manifestations in a sample of patients with diabetes mellitus (DM) and those with prediabetes and compare the findings between the two groups.

METHODS

One hundred and eighty-eight patients with DM and 125 prediabetic subjects were randomly enrolled in this cross-sectional study. Demographic data and past history were recorded. Musculoskeletal physical examinations were done by a single rheumatologist. Regression analyses were employed to assess the crude and adjusted effects of determinants on DM musculoskeletal manifestations (DMMMs).

RESULTS

Female/male ratio was not significantly different between diabetic and prediabetic patients (4.4 vs. 4.7, respectively, P = 0.9). However, diabetic patients were significantly older than the prediabetic ones (56.6 vs. 52 years, respectively, P = 0.0001); 83.5% of diabetic patients and 52.8% of prediabetic ones had at least one musculoskeletal manifestation (P = 0.0001). The prevalence of knee osteoarthritis and shoulder involvement were almost two times more common (P = 0.0001 and P = 0.015) in diabetic patients than in prediabetic ones (73.4% vs. 38% and 21.2% vs. 9.5%, respectively). Prevalence of carpal tunnel syndrome (CTS) was 48% and 36.5% in patients with diabetes and prediabetes, respectively (P = 0.053). Multivariate backward regression analysis showed age, sex, BMI (body mass index) and DM as the significant determinants in development of musculoskeletal manifestations in all subjects. Age and BMI were the only significant factors associated with musculoskeletal manifestations in both diabetic and prediabetic patients.

CONCLUSION

Diabetic and prediabetic patients may show high prevalence of musculoskeletal manifestations. In non-diabetic patients diagnosed with CTS, prediabetes might be ruled out.

Endoplasmic reticulum stress in the peripheral nervous system is a significant driver of neuropathic pain

Despite intensive effort and resulting gains in understanding the mechanisms underlying neuropathic pain, limited success in therapeutic approaches have been attained. A recently identified, nonchannel, nonneurotransmitter therapeutic target for pain is the enzyme soluble epoxide hydrolase (sEH). The sEH degrades natural analgesic lipid mediators, epoxy fatty acids (EpFAs), therefore its inhibition stabilizes these bioactive mediators. Here we demonstrate the effects of EpFAs on diabetes induced neuropathic pain and define a previously unknown mechanism of pain, regulated by endoplasmic reticulum (ER) stress. The activation of ER stress is first quantified in the peripheral nervous system of type I diabetic rats. We demonstrate that both pain and markers of ER stress are reversed by a chemical chaperone. Next, we identify the EpFAs as upstream modulators of ER stress pathways. Chemical inducers of ER stress invariably lead to pain behavior that is reversed by a chemical chaperone and an inhibitor of sEH. The rapid occurrence of pain behavior with inducers, equally rapid reversal by blockers and natural incidence of ER stress in diabetic peripheral nervous system (PNS) argue for a major role of the ER stress pathways in regulating the excitability of the nociceptive system. Understanding the role of ER stress in generation and maintenance of pain opens routes to exploit this system for therapeutic purposes.

Significance of functional GRP78 polymorphisms in predicting the onset of type 2 diabetic peripheral neuropathy in Chinese population

OBJECTIVE

The objective of this study is to investigate the significance of functional GRP78 polymorphisms in predicting the risk of type 2 diabetic peripheral neuropathy in Chinese population.

METHODS

Between the years of 2006 and 2010, a total of 295 definitely diagnosed type 2 diabetes mellitus (T2DM) patients were included into our study cohort and followed for 3 years. At baseline and annual re-examinations, the patients underwent physical examinations, laboratory tests and evaluation of Michigan diabetic neuropathy score (MDNS). Age, gender, disease course, waist-hip circumference ratio (WHR), body mass index (BMI), triglycerine (TG), total cholesterol (Tch), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), glycosylated haemoglobin (HbA1c), uric acid elimination rate (UAER) and uric acid (UA) were recorded and GRP78 polymorphisms were tested by direct sequencing. The prognostic significance of GRP78 polymorphisms were analysed using monovariate and multivariate logistic regression.

RESULTS

Three years after baseline, 32.9% (97/295) of the T2DM patients had suffered the development of diabetic peripheral neuropathy and GRP78 rs391957 promoter polymorphism is a significant risk factor for the onset of type 2 diabetic peripheral neuropathy. In monovariate regression model, the OR values of GRP78 rs391957 promoter polymorphism were 2.233 (C/T) and 2.734 (T/T). As for the model calibrated with demographic and laboratory indexes, the OR values were, respectively, 2.124 (C/T) and 2.423 (T/T).

CONCLUSION

Our study suggested that the GRP78 rs391957 promoter polymorphism is a potential risk factor for type 2 diabetic peripheral neuropathy.

Myelin abnormalities in the optic and sciatic nerves in mice with GM1-gangliosidosis

GM1-gangliosidosis is a glycosphingolipid lysosomal storage disease involving accumulation of GM1 and its asialo form (GA1) primarily in the brain. Thin-layer chromatography and X-ray diffraction were used to analyze the lipid content/composition and the myelin structure of the optic and sciatic nerves from 7- and 10-month old β-galactosidase (β-gal) +/? and β-gal −/− mice, a model of GM1gangliosidosis. Optic nerve weight was lower in the β-gal −/− mice than in unaffected β-gal +/? mice, but no difference was seen in sciatic nerve weight. The levels of GM1 and GA1 were significantly increased in both the optic nerve and sciatic nerve of the β-gal −/− mice. The content of myelin-enriched cerebrosides, sulfatides, and plasmalogen ethanolamines was significantly lower in optic nerve of β-gal −/− mice than in β-gal +/? mice; however, cholesteryl esters were enriched in the β-gal −/− mice. No major abnormalities in these lipids were detected in the sciatic nerve of the β-gal −/− mice. The abnormalities in GM1 and myelin lipids in optic nerve of β-gal −/− mice correlated with a reduction in the relative amount of myelin and periodicity in fresh nerve. By contrast, the relative amount of myelin and periodicity in the sciatic nerves from control and β-gal −/− mice were indistinguishable, suggesting minimal pathological involvement in sciatic nerve. Our results indicate that the greater neurochemical pathology observed in the optic nerve than in the sciatic nerve of β-gal −/− mice is likely due to the greater glycolipid storage in optic nerve.

Mouse models of diabetic neuropathy

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes and is associated with significant morbidity and mortality. DPN is characterized by progressive, distal-to-proximal degeneration of peripheral nerves that leads to pain, weakness, and eventual loss of sensation. The mechanisms underlying DPN pathogenesis are uncertain, and other than tight glycemic control in type 1 patients, there is no effective treatment. Mouse models of type 1 (T1DM) and type 2 diabetes (T2DM) are critical to improving our understanding of DPN pathophysiology and developing novel treatment strategies. In this review, we discuss the most widely used T1DM and T2DM mouse models for DPN research, with emphasis on the main neurologic phenotype of each model. We also discuss important considerations for selecting appropriate models for T1DM and T2DM DPN studies and describe the promise of novel emerging diabetic mouse models for DPN research. The development, characterization, and comprehensive neurologic phenotyping of clinically relevant mouse models for T1DM and T2DM will provide valuable resources for future studies examining DPN pathogenesis and novel therapeutic strategies.

Endoplasmic reticulum stress in insulin resistance and diabetes

The endoplasmic reticulum is the main intracellular Ca(2+) store for Ca(2+) release during cell signaling. There are different strategies to avoid ER Ca(2+) depletion. Release channels utilize first Ca(2+)-bound to proteins and this minimizes the reduction of the free luminal [Ca(2+)]. However, if release channels stay open after exhaustion of Ca(2+)-bound to proteins, then the reduction of the free luminal ER [Ca(2+)] (via STIM proteins) activates Ca(2+) entry at the plasma membrane to restore the ER Ca(2+) load, which will work provided that SERCA pump is active. Nevertheless, there are several noxious conditions that result in decreased activity of the SERCA pump such as oxidative stress, inflammatory cytokines, and saturated fatty acids, among others. These conditions result in a deficient restoration of the ER [Ca(2+)] and lead to the ER stress response that should facilitate recovery of the ER. However, if the stressful condition persists then ER stress ends up triggering cell death and the ensuing degenerative process leads to diverse pathologies; particularly insulin resistance, diabetes and several of the complications associated with diabetes. This scenario suggests that limiting ER stress should decrease the incidence of diabetes and the mobility and mortality associated with this illness.

ER stress in diabetic peripheral neuropathy: A new therapeutic target

SIGNIFICANCE

Diabetes and other diseases that comprise the metabolic syndrome have reached epidemic proportions. Diabetic peripheral neuropathy (DPN) is the most prevalent complication of diabetes, affecting ~50% of diabetic patients. Characterized by chronic pain or loss of sensation, recurrent foot ulcerations, and risk for amputation, DPN is associated with significant morbidity and mortality. Mechanisms underlying DPN pathogenesis are complex and not well understood, and no effective treatments are available. Thus, an improved understanding of DPN pathogenesis is critical for the development of successful therapeutic options.

RECENT ADVANCES

Recent research implicates endoplasmic reticulum (ER) stress as a novel mechanism in the onset and progression of DPN. ER stress activates the unfolded protein response (UPR), a well-orchestrated signaling cascade responsible for relieving stress and restoring normal ER function.

CRITICAL ISSUES

During times of extreme or chronic stress, such as that associated with diabetes, the UPR may be insufficient to alleviate ER stress, resulting in apoptosis. Here, we discuss the potential role of ER stress in DPN, as well as evidence demonstrating how ER stress intersects with pathways involved in DPN development and progression. An improved understanding of how ER stress contributes to peripheral nerve dysfunction in diabetes will provide important insight into DPN pathogenesis.

FUTURE DIRECTIONS

Future studies aimed at gaining the necessary insight into ER stress in DPN pathogenesis will ultimately facilitate the development of novel therapies.

Calcium signalling in sensory neurones and peripheral glia in the context of diabetic neuropathies

Peripheral sensory nervous system is comprised of neurones with their axons and neuroglia that includes satellite glial cells in sensory ganglia, myelinating, non-myelinating and perisynaptic Schwann cells. Pathogenesis of peripheral diabetic polyneuropathies is associated with aberrant function of both neurones and glia. Deregulated Ca(2+) homoeostasis and aberrant Ca(2+) signalling in neuronal and glial elements contributes to many forms of neuropathology and is fundamental to neurodegenerative diseases. In diabetes both neurones and glia experience metabolic stress and mitochondrial dysfunction which lead to deregulation of Ca(2+) homeostasis and Ca(2+) signalling, which in their turn lead to pathological cellular reactions contributing to development of diabetic neuropathies. Molecular cascades responsible for Ca(2+) homeostasis and signalling, therefore, can be regarded as potential therapeutic targets.

Experimental diabetes in neonatal mice induces early peripheral sensorimotor neuropathy

Animal models of diabetes do not reach the severity of human diabetic neuropathy but relatively mild neurophysiological deficits and minor morphometric changes. The lack of degenerative neuropathy in diabetic rodent models seems to be a consequence of the shorter length of the axons or the shorter animal life span. Diabetes-induced demyelination needs many weeks or even months before it can be evident by morphometrical analysis. In mice myelination of the peripheral nervous system starts at the prenatal period and it is complete several days after birth. Here we induced experimental diabetes to neonatal mice and we evaluated its effect on the peripheral nerve 4 and 8 weeks after diabetes induction. Neurophysiological values showed a decline in sensory nerve conduction velocity at both time-points. Morphometrical analysis of the tibial nerve demonstrated a decrease in the number of myelinated fibers, fiber size and myelin thickness at both time-points studied. Moreover, aldose reductase and poly(ADP-ribose) polymerase activities were increased even if the amount of the enzyme was not affected. Thus, type 1 diabetes in newborn mice induces early peripheral neuropathy and may be a good model to assay pharmacological or gene therapy strategies to treat diabetic neuropathy.