Hyperglycemia magnifies Schwann cell dysfunction and cell death triggered by PA-induced lipotoxicity

Effective constituents and protective effect of Mudan granules against Schwann cell injury

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes. Mudan granules (MD) is a Chinese patent medicine for treating DPN, which is composed of nine Chinese medicinal herbs, including the radix of Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao or Astragalus membranaceus (Fisch.) Bge. (Huangqi in Chinese), rhizome of Corydalis yanhusuo W.T. Wang (Yanhusuo), radix and rhizome of Panax notoginseng (Burk.) F. H. Chen (Sanqi), radix of Paeonia lactiflora Pall. or Paeonia veitchii Lynch (Chishao), radix and rhizome of Salvia miltiorrhiza Bge. (Danshen), rhizome of Ligusticum chuanxiong Hort. (Chuanxiong), flowers of Carthamus tinctorius L. (Honghua), lignum of Caesalpinia sappan L. (Sumu), and caulis of Spatholobus suberectus Dunn (Jixueteng). MD was reported to have a protective effect on Schwann cell (SC) that is considered as an important therapeutic target of DPN. However, the constituents of MD have not been reported, and the effective constituents and protective pathways for MD against SC injury remain unclear.

AIM OF THE STUDY

This study aimed to identify the constituents in MD, and to investigate the effective constituents and protective pathways of MD against high-glucose/lipid injury in SC.

MATERIALS AND METHODS

The chemical constituents of MD were identified using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). Protective effect and effective constituents screening were performed in an in vitro SC injury model induced by high glucose and lipid levels. The protective pathways of MD and its effective constituents were investigated by western blotting assay of related proteins.

RESULTS

A total of 136 constituents were identified in MD. MD downregulated the phosphorylation of extracellular-regulated protein kinases 1/2 (ERK1/2) and expression of cyclooxygenase-2 (COX-2) and upregulated the expression of sirtuin 2 (SIRT2). Seven effective constituents were screened out, including three from Sanqi [20(R)-ginsenoside Rh2, 20(S)-ginsenoside Rh2, and ginsenoside Rk3], one from Huangqi (astragaloside II), one from Danshen (danshensu), and two from Chuanxiong (chlorogenic and cryptochlorogenic acid). Six of the seven compounds, excluding danshensu, inhibited the phosphorylation of ERK1/2. Both astragaloside II and chlorogenic acid upregulated the expression of SIRT2, and cryptochlorogenic acid and danshensu downregulated the expression of COX-2.

CONCLUSIONS

The constituents of MD were firstly identified, and seven effective constituents were found. MD can protect SC against high-glucose and -lipid injury by downregulating ERK1/2 phosphorylation and COX-2 expression and upregulating SIRT2 expression. Seven effective constituents regulated the expression of these proteins. This study presented an important advance toward elucidating the chemical constituents, and the effective constituents and protective pathways of MD against high-glucose/lipid injury in SC, which is very helpful for investigating the action mechanism of MD on treating DPN, and could ultimately inform the development of effective quality control procedures for MD production.

Study of the optic nerve in patients with type 2 diabetic retinopathy by shear-wave elastography

AIM

To investigate the clinical value of two-dimensional shear-wave elastography (2D-SWE) in detecting optic nerve elasticity and in-frame adipose tissue elasticity in patients with type 2 diabetic retinopathy (DR).

MATERIALS AND METHODS

2D-SWE was used to detect SWE values of the optic nerve and adipose tissue in adjacent optic nerve frames in 30 healthy participants, 30 patients with diabetic non-retinopathy (NDR), 35 patients with non-proliferative diabetic retinopathy (NPDR), and 30 patients with proliferative diabetic retinopathy (PDR). The correlation between SWE values and blood glucose, blood lipid, age, body mass index (BMI) was analysed. Receiver operating characteristic (ROC) curve analysis was performed for SWE values.

RESULTS

The SWE values of the optic nerve and in-frame adipose tissue increased with the progression of DR, and analysis of variance was compared with groups: the SWE values of the optic nerve and in-frame adipose tissue in each group were significantly different (all p<0.001). The SWE values of the optic nerve and in-frame adipose tissue correlated positively with BMI, age, triglyceride, and fasting blood glucose, and correlated negatively with high-density lipoprotein. The SWE values of the optic nerve and in-frame adipose tissue had higher diagnostic efficacy. The combination of the two had higher diagnostic accuracy.

CONCLUSION

The elastic modulus of optic nerve and in-frame adipose tissue can effectively predict and grade of DR, that is, 2D-SWE can be used as a non-invasive imaging diagnostic method for DR. The combined diagnostic efficacy of optic nerve SWE value and in-frame adipose tissue SWE value is significantly better than that of single use. This study found that increased BMI, age, triglyceride, and fasting blood glucose, and decreased high-density lipoprotein are risk factors for DR.

Biomarkers and signaling pathways of diabetic nephropathy and peripheral neuropathy: possible therapeutic intervention of rutin and quercetin

Diabetic nephropathy and peripheral neuropathy are the two main complications of chronic diabetes that contribute to high morbidity and mortality. These conditions are characterized by the dysregulation of multiple molecular signaling pathways and the presence of specific biomarkers such as inflammatory cytokines, indicators of oxidative stress, and components of the renin-angiotensin system. In this review, we systematically collected and collated the relevant information from MEDLINE, EMBASE, ELSEVIER, PUBMED, GOOGLE, WEB OF SCIENCE, and SCOPUS databases. This review was conceived with primary objective of revealing the functions of these biomarkers and signaling pathways in the initiation and progression of diabetic nephropathy and peripheral neuropathy. We also highlighted the potential therapeutic effectiveness of rutin and quercetin, two plant-derived flavonoids known for their antioxidant and anti-inflammatory properties. The findings of our study demonstrated that both flavonoids can regulate important disease-promoting systems, such as inflammation, oxidative stress, and dysregulation of the renin-angiotensin system. Importantly, rutin and quercetin have shown protective benefits against nephropathy and neuropathy in diabetic animal models, suggesting them as potential therapeutic agents. These findings provide a solid foundation for further comprehensive investigations and clinical trials to evaluate the potential of rutin and quercetin in the management of diabetic nephropathy and peripheral neuropathy. This may contribute to the development of more efficient and comprehensive treatment approaches for diabetes-associated complications.

How inflammation dictates diabetic peripheral neuropathy: An enlightening review

BACKGROUND

Diabetic peripheral neuropathy (DPN) constitutes a debilitating complication associated with diabetes. Although, the past decade has seen rapid developments in understanding the complex etiology of DPN, there are no approved therapies that can halt the development of DPN, or target the damaged nerve. Therefore, clarifying the pathogenesis of DPN and finding effective treatment are the crucial issues for the clinical management of DPN.

AIMS

This review is aiming to summary the current knowledge on the pathogenesis of DPN, especially the mechanism and application of inflammatory response.

METHODS

We systematically summarized the latest studies on the pathogenesis and therapeutic strategies of diabetic neuropathy in PubMed.

RESULTS

In this seminal review, the underappreciated role of immune activation in the progression of DPN is scrutinized. Novel insights into the inflammatory regulatory mechanisms of DPN have been unearthed, illuminating potential therapeutic strategies of notable clinical significance. Additionally, a nuanced examination of DPN's complex etiology, including aberrations in glycemic control and insulin signaling pathways, is presented. Crucially, an emphasis has been placed on translating these novel understandings into tangible clinical interventions to ameliorate patient outcomes.

CONCLUSIONS

This review is distinguished by synthesizing cutting-edge mechanisms linking inflammation to DPN and identifying innovative, inflammation-targeted therapeutic approaches.

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).

Effect of necrostatin-1 on sciatic nerve crush injury in rat models

BACKGROUND

Necrostatin-1 (Nec-1) is an inhibitor of the receptor interacting protein (RIP)1 kinase, which acts as an inhibitor of necroptosis, a special form of necrosis. In the present study, the effect of Nec-1 on peripheral nerve injury (PNI) was investigated.

METHODS

The PNI model was established by inducing sciatic nerve injury. Hematoxylin-eosin and immunofluorescence staining techniques were used to assess the extent of injury to nerve fibers and necrosis of Schwann cells (SCs). Western blotting was performed to detect the expression of necroptosis-related factors (RIP1 and RIP3). The concentrations of tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and the oxidative stress-related enzyme malondialdehyde (MDA) were determined to indicate the degree of inflammation and oxidative stress.

RESULTS

Nec-1 could decrease the degree of peripheral nerve lesions after PNI and protect SCs and axons by inhibiting necroptosis. Furthermore, Nec-1 could reduce necroptosis by inhibiting RIP1 and effectively reduce inflammation and reactive oxygen species production at the early stage of PNI.

CONCLUSIONS

Alleviation of necroptosis by Nec-1 may provide new insights into therapies for the early stages of peripheral nerve repair after PNI.

Identification of Adipogenesis Subgroups and Immune Infiltration Characteristics in Diabetic Peripheral Neuropathy

Dysregulation of adipogenesis is related to diabetic peripheral neuropathy (DPN) pathogenesis, which may be mediated by immune infiltration. Nevertheless, the expression patterns of multiple adipogenesis-related genes and the differences of immune infiltration in different lipid metabolism levels remain unknown. GSE95849, a gene expression matrix containing DPN patients and healthy participants, was downloaded from Gene Expression Omnibus (GEO) database. Differentially expressed adipogenesis-related genes (DEARGs) were screened by overlapping the adipogenesis-related genes with differentially expressed genes (DEGs). DPN patients from GSE24290 and GSE148059 were divided into two adipogenesis subgroups according to the expression of DEARGs. The single-sample gene set enrichment analysis (ssGSEA) was used to estimate the abundance of the immune cells between two subgroups. The analysis of immune infiltration suggested that a variety of immune cells and immune processes were elevated in the high expression group of DEARGs. The differentially expressed genes of the two subgroups were mainly enriched in biological processes and signaling pathways related to lipid metabolism. PPARG, FABP4, LIPE, FASN, SCD, DGAT2, PNPLA2, ADIPOQ, LEP, and CEBPA were identified as the hub genes of the two subgroups, whose related transcription factors (TFs) and miRNAs were predicted. An immunohistochemical assay was used to verify the expression of hub genes in DPN nerve tissues. Our comprehensive analysis of adipogenesis subgroups in DPN illustrated that different expression patterns of DEARGs may lead to different immune and inflammatory states. The identification of DEARGs may help to further distinguish the different characteristics of DPN patients and lay the foundation for targeted treatment. Our findings may bring a novel perspective to the diagnosis and treatment of DPN patients.

Diabetic neuropathy: Past, present, and future

Background

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

Methods

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

Results

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

Conclusions

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

Prevention and Management Strategies for Diabetic Neuropathy

Diabetic neuropathy (DN) is a common complication of diabetes that is becoming an increasing concern as the prevalence of diabetes rapidly rises. There are several types of DN, but the most prevalent and studied type is distal symmetrical polyneuropathy, which is the focus of this review and is simply referred to as DN. It can lead to a wide range of sensorimotor and psychosocial symptoms and is a major risk factor for diabetic foot ulceration and Charcot neuropathic osteoarthropathy, which are associated with high rates of lower limb amputation and mortality. The prevention and management of DN are thus critical, and clinical guidelines recommend several strategies for these based on the best available evidence. This article aims to provide a narrative review of DN prevention and management strategies by discussing these guidelines and the evidence that supports them. First, the epidemiology and diverse clinical manifestations of DN are summarized. Then, prevention strategies such as glycemic control, lifestyle modifications and footcare are discussed, as well as the importance of early diagnosis. Finally, neuropathic pain management strategies and promising novel therapies under investigation such as neuromodulation devices and nutraceuticals are reviewed.

Pathogenesis of Distal Symmetrical Polyneuropathy in Diabetes

Distal symmetrical polyneuropathy (DSPN) is a serious complication of diabetes associated with significant disability and mortality. Although more than 50% of people with diabetes develop DSPN, its pathogenesis is still relatively unknown. This lack of understanding has limited the development of novel disease-modifying therapies and left the reasons for failed therapies uncertain, which is critical given that current management strategies often fail to achieve long-term efficacy. In this article, the pathogenesis of DSPN is reviewed, covering pathogenic changes in the peripheral nervous system, microvasculature and central nervous system (CNS). Furthermore, the successes and limitations of current therapies are discussed, and potential therapeutic targets are proposed. Recent findings on its pathogenesis have called the definition of DSPN into question and transformed the disease model, paving the way for new research prospects.

Curcumin Ameliorates the Experimental Diabetic Peripheral Neuropathy through Promotion of NGF Expression in Rats

Increasing evidence suggested that inhibiting the apoptosis of Schwann cells (SCs) and promoting nerve growth factor (NGF) expression in sciatic nerves play key roles in preventing the onset of diabetic peripheral neuropathy (DPN). Curcumin, a primary bioactive substance in turmeric with multiple characteristics, has been shown to have many therapeutic effects in a variety of diseases. However, curcumin is poorly studied in the DPN models. We aimed to explore the therapeutic benefits and underlying mechanism of curcumin in high fat/sugar diets joint streptozotocin (STZ)-induced DPN rat models. Sprague-Dawley (SD) rats were divided into five groups (6 rats per group), control group, DPN group, Curcumin groups (50, 100, and 150 mg/kg). Curcumin was administered intragastrically once per day for 4 continuous weeks. Body weight (BW) and fasting blood glucose (FBG) were monitored in all groups. The mechanical withdraw threshold (MWT) was measured. We also assessed neuropathic change by testing nerve conductance velocity (NCV) in sciatic nerves. TEM was applied to observe the sciatic nerves ultrastructure. The SCs apoptosis in sciatic nerves was stained using TUNEL kit. NGF contents in sciatic nerves and serum were detected using western blotting and ELISA analysis. The results showed curcumin had no obvious effect on the BW and FBG change. Curcumin (100 and 150 mg/kg) attenuated the MWT, NCV, and sciatic nerves ultrastructure in DPN rats. Curcumin (50, 100 and 150 mg/kg) reduced SCs apoptosis in sciatic nerves. In addition, curcumin at 150 mg/kg had the best efficacy in increasing protein expression of NGF in sciatic nerves and serum NGF level. Our work demonstrated that curcumin has neuroprotective effects for the treatment of DPN.

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.

Thyroid Hormones, Peripheral White Blood Count, and Dose of Basal Insulin Are Associated with Changes in Nerve Conduction Studies in Adolescents with Type 1 Diabetes

Type 1 diabetes (T1D) in the child population is the third most common chronic disease. Diabetic peripheral neuropathy (DPN) is a very disabling and silently developing complication. This prospective, observational study enrolled 182 (93 girls) patients with T1D, aged 16.5-18 years. The aim of the study was to assess the correlation between factors of diabetes metabolic control, blood count, thyroid hormones, thyroid-stimulating hormone (TSH), level of cortisol, vitamin D3, metabolic factors, demographic data, and nerve conduction study (NCS) parameters. We revealed that in multivariate regression models for almost all NCS parameters, beside height and diabetes duration, significant factors were basal insulin dose per kilogram of weight (BID/kg), body mass index (BMI), and thyroid hormones. For conduction velocities of the motor nerves, mean HbA1c exists in models. In all models for all NCS parameters there exists at least one parameter of peripheral white blood cell counts (predominantly monocytes). There is a significant influence of thyroid hormones, peripheral blood white cells count, and BID per weight on parameters of NCS. It is essential to take care of the proper insulin dose per weight of patients and the adequate proportion of basal to prandial insulin.

Dehydrozingerone inhibits renal lipotoxicity in high-fat diet-induced obese mice

Ectopic fat accumulation in the kidneys causes oxidative stress, inflammation and cell death. Dehydrozingerone (DHZ) is a curcumin analog that exhibits antitumour, antioxidant and antidiabetic effects. However, the efficacy of DHZ in diabetic nephropathy (DN) is unknown. Here, we verified the efficacy of DHZ on DN. We divided the experimental animals into three groups: regular diet, 60% high‐fat diet (HFD) and HFD with DHZ for 12 weeks. We analysed levels of renal triglycerides and urinary albumin and albumin‐creatinine ratio, renal morphological changes and molecular changes via real‐time polymerase chain reaction and immunoblotting. Furthermore, high glucose (HG)‐ or palmitate (PA)‐stimulated mouse mesangial cells or mouse podocytes were treated with DHZ for 24 h. As a result, DHZ markedly reduced renal glycerol accumulation and albuminuria excretion through improvement of thickened glomerular basement membrane, podocyte loss and slit diaphragm reduction. In the renal cortex in the HFD group, phospho‐AMPK and nephrin expression reduced, whereas arginase 2 and CD68 expression increased; however, these changes were recovered after DHZ administration. Increased reactive oxygen species (ROS) stimulated by HG or PA in podocytes was inhibited by DHZ treatment. Collectively, these findings indicate that DHZ ameliorates DN via inhibits of lipotoxicity‐induced inflammation and ROS formation.

Pathogenesis, diagnosis and clinical management of diabetic sensorimotor peripheral neuropathy

Diabetic sensorimotor peripheral neuropathy (DSPN) is a serious complication of diabetes mellitus and is associated with increased mortality, lower-limb amputations and distressing painful neuropathic symptoms (painful DSPN). Our understanding of the pathophysiology of the disease has largely been derived from animal models, which have identified key potential mechanisms. However, effective therapies in preclinical models have not translated into clinical trials and we have no universally accepted disease-modifying treatments. Moreover, the condition is generally diagnosed late when irreversible nerve damage has already taken place. Innovative point-of-care devices have great potential to enable the early diagnosis of DSPN when the condition might be more amenable to treatment. The management of painful DSPN remains less than optimal; however, studies suggest that a mechanism-based approach might offer an enhanced benefit in certain pain phenotypes. The management of patients with DSPN involves the control of individualized cardiometabolic targets, a multidisciplinary approach aimed at the prevention and management of foot complications, and the timely diagnosis and management of neuropathic pain. Here, we discuss the latest advances in the mechanisms of DSPN and painful DSPN, originating both from the periphery and the central nervous system, as well as the emerging diagnostics and treatments.

Analysis of risk factors of diabetes peripheral neuropathy in type 2 diabetes mellitus and nursing intervention

The aim of the present study was to explore the risk factors of diabetes peripheral neuropathy (DPN) in type 2 diabetes mellitus, and to propose corresponding nursing intervention measures to provide the basis for early diagnosis, treatment and prevention of DPN. A retrospective analysis was performed on 130 patients with type 2 diabetes mellitus (T2DM) in the communities surrounding our hospital from January 2017 to June 2018. They were divided into a DPN group (62 cases) and non-DPN group (control group, 68 cases). First, a univariate analysis was performed. DPN or non-DPN were used as dependent variables, and statistically significant parameters in univariate analysis were used as independent variables. Multivariate logistic regression analysis was included to analyze the peripheral nerves in type 2 diabetes mellitus. At the same time, the patients with DPN were given individualized comprehensive nursing intervention. Univariate analysis showed that body mass index (BMI), diabetes duration, smoking history, drinking history, family history of diabetes, fasting blood glucose (FBG), postprandial blood glucose (PBG), glycosylated hemoglobin (HbA1c), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), systolic blood pressure, 24-h urine microalbumin excretion (24hmALB), glomerular filtration rate (GFR), serum creatinine in DPN group were significantly different from those in the control group (P<0.05). Logistic regression analysis showed that the duration of diabetes, PBG, glycosylated hemoglobin (HbA1c), HDL-C, 24hmALB, and GFR were independent risk factors for DPN. The quality of life [Physiological function (PF), Role-physical (RP), Role-emotional (RE), General health (GH), Social function (SF), Mental health (MH), Bodily pain (BP), Vitality (VT)] in the DPN group was significantly improved after six months of individualized nursing intervention compared with that before intervention (P<0.05). In conclusion, the high risk factors of DPN should be identified as early as possible, to prevent and delay the occurrence and development of diabetes peripheral neuropathy, so as to improve the quality of life of these patients.

The Multifunctionality of CD36 in Diabetes Mellitus and Its Complications-Update in Pathogenesis, Treatment and Monitoring

CD36 is a multiligand receptor contributing to glucose and lipid metabolism, immune response, inflammation, thrombosis, and fibrosis. A wide range of tissue expression includes cells sensitive to metabolic abnormalities associated with metabolic syndrome and diabetes mellitus (DM), such as monocytes and macrophages, epithelial cells, adipocytes, hepatocytes, skeletal and cardiac myocytes, pancreatic β-cells, kidney glomeruli and tubules cells, pericytes and pigment epithelium cells of the retina, and Schwann cells. These features make CD36 an important component of the pathogenesis of DM and its complications, but also a promising target in the treatment of these disorders. The detrimental effects of CD36 signaling are mediated by the uptake of fatty acids and modified lipoproteins, deposition of lipids and their lipotoxicity, alterations in insulin response and the utilization of energy substrates, oxidative stress, inflammation, apoptosis, and fibrosis leading to the progressive, often irreversible organ dysfunction. This review summarizes the extensive knowledge of the contribution of CD36 to DM and its complications, including nephropathy, retinopathy, peripheral neuropathy, and cardiomyopathy.

Docosahexaenoic acid protection against palmitic acid-induced lipotoxicity in NGF-differentiated PC12 cells involves enhancement of autophagy and inhibition of apoptosis and necroptosis

Lipotoxicity (LTx) leads to cellular dysfunction and cell death and has been proposed to be an underlying process during traumatic and hypoxic injuries and neurodegenerative conditions in the nervous system. This study examines cellular mechanisms responsible for docosahexaenoic acid (DHA 22:6 n‐3) protection in nerve growth factor‐differentiated pheochromocytoma (NGFDPC12) cells from palmitic acid (PAM)‐mediated lipotoxicity (PAM‐LTx). NGFDPC12 cells exposed to PAM show a significant lipotoxicity demonstrated by a robust loss of cell viability, apoptosis, and increased HIF‐1α and BCL2/adenovirus E1B 19 kDa protein‐interacting protein 3 gene expression. Treatment of NGFDPC12 cells undergoing PAM‐LTx with the pan‐caspase inhibitor ZVAD did not protect, but shifted the process from apoptosis to necroptosis. This shift in cell death mechanism was evident by the appearance of the signature necroptotic Topo I protein cleavage fragments, phosphorylation of mixed lineage kinase domain‐like, and inhibition with necrostatin‐1. Cultures exposed to PAM and co‐treated with necrostatin‐1 (necroptosis inhibitor) and rapamycin (autophagy promoter), showed a significant protection against PAM‐LTx compared to necrostatin‐1 alone. In addition, co‐treatment with DHA, as well as 20:5 n‐3, 20:4 n‐6, and 22:5 n‐3, in the presence of PAM protected NGFDPC12 cells against LTx. DHA‐induced neuroprotection includes restoring normal levels of HIF‐1α and BCL2/adenovirus E1B 19 kDa protein‐interacting protein 3 transcripts and caspase 8 and caspase 3 activity, phosphorylation of beclin‐1, de‐phosphorylation of mixed lineage kinase domain‐like, increase in LC3‐II, and up‐regulation of Atg7 and Atg12 genes, suggesting activation of autophagy and inhibition of necroptosis. Furthermore, DHA‐induced protection was suppressed by the lysosomotropic agent chloroquine, an inhibitor of autophagy. We conclude that DHA elicits neuroprotection by regulating multiple cell death pathways including enhancement of autophagy and inhibiting apoptosis and necroptosis.

Schwann cells apoptosis is induced by high glucose in diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes mellitus that affects approximately half of patients with diabetes. Current treatment regimens cannot treat DPN effectively. Schwann cells (SCs) are very sensitive to glucose concentration and insulin, and closely associated with the occurrence and development of type 1 diabetic mellitus (T1DM) and DPN. Apoptosis of SCs is induced by hyperglycemia and is involved in the pathogenesis of DPN. This review considers the pathological processes of SCs apoptosis under high glucose, which include the following: oxidative stress, inflammatory reactions, endoplasmic reticulum stress, autophagy, nitrification and signaling pathways (PI3K/AKT, ERK, PERK/Nrf2, and Wnt/β-catenin). The clarification of mechanisms underlying SCs apoptosis induced by high glucose will help us to understand and identify more effective strategies for the treatment of T1DM DPN.

Trolox prevents high glucose-induced apoptosis in rat myocardial H9c2 cells by regulating GLUT-4 and antioxidant defense mechanism

Redox imbalance due to hyperglycemia is a causative factor for an increased generation of reactive oxygen species (ROS) that leads to mitochondrial dysfunction and the release of cytochrome-c. The aim of the present study is to elucidate the functional role of oxidative stress (OS) in the induction of apoptosis in H9c2 cells in the hyperglycemic state through glucose transporter-4 (GLUT-4) regulation and antioxidant status. H9c2 cells were incubated with 15, 24, and 33 mM glucose for 24, 48, and 72 hr to induce hyperglycemic stress. Hyperglycemic episodes have significantly influenced GLUT-4 mRNA regulation, depleted glutathione (GSH) and its associated enzymes, reduced cellular antioxidant enzymes (AOEs), caused nuclear condensation, and induced apoptosis by activating caspase-9 and 3 and annexin V binding in a concentration and duration-dependent manner. Trolox pretreatment significantly enhanced the GLUT-4 mRNA and antioxidant defense mechanism, suppressed nuclear condensation, and prevented cytochrome-c release, thereby reducing mitochondrial-dependent apoptosis. The present study shows that the toxic effect of high glucose is significantly regulated and that OS induction can be prevented through a water-soluble vitamin E analog "Trolox" treatment.

Diabetic neuropathy

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

Diabetic neuropathy

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

Salvianolic Acid B Attenuates Apoptosis of HUVEC Cells Treated with High Glucose or High Fat via Sirt1 Activation

High glucose and high fat are important inducements for the development and progression of diabetic cardiopathy. Salvianolic acid B (SAB), which is the most abundant and bioactive compound in Danshen, attenuates oxidative stress-related disorders, such as cardiovascular diseases, cerebral ischemia, and diabetes. However, the effect of SAB on diabetic cardiopathy is not clear. The aim of study was to investigate the effect and the underlying molecular mechanisms of SAB on diabetic cardiopathy in vitro model. The human umbilical vein endothelial (HUVEC) cells were treated with high glucose (HG, 30 mM) or high fat (palmitic acid, PA, 0.75 mM) in the presence or absence of SAB (100, 200, and 400 mg/L) and incubated for 24 h. We found that HG or PA induced apoptosis of HUVEC cells, while treatment with SAB inhibited the apoptosis. We also found that SAB reversed HG- or PA-induced oxidative stress, apoptosis cell cytokines production, and expression of thioredoxin-interacting protein (TXNIP). Moreover, SAB increased HG- or PA-induced expression of Sirtuin 1 (Sirt1), a nicotinamide adenine dinucleotide- (NAD⁺-) dependent histone deacetylase. Exposure of HUVEC cells to Ex527 (Sirt1 inhibitor) suppressed the effect of SAB on acetyl-p53 and procaspase-3 expressions. In conclusion, the results suggested that SAB could attenuate HUVEC cells damage treated with HG or PA via Sirt1 and might be a potential therapy agent for the diabetic cardiopathy treatment.

1,25-(OH)2D3 protects Schwann cells against advanced glycation end products-induced apoptosis through PKA-NF-κB pathway

AIMS

To explore the effect and mechanism of 1, 25-(OH)₂D₃ on Schwann cell apoptosis induced by advanced glycation end products.

MAIN METHODS

Schwann cells, isolated from rodent sciatic nerve were incubated with AGE-modified bovine serum albumin(AGE) to mimic diabetic conditions and 1,25-(OH)₂D₃ was used as protector. Cell apoptosis was detected by PI/Annexin-V staining, caspase 3 activity assay and western blotting for caspase 3 and PARP. The activation of protein kinase A (PKA) and nuclear factor kappa-B (NF-κB) was evaluated by western blot. Immunofluorescent staining was used for intercellular location of NF-κB. Cytokine secretion was evaluated by enzyme-linked immunosorbent assay.

KEY FINDINGS

Schwann cell apoptosis accelerated after incubating with AGE. However, if combining 1,25-(OH)₂D₃ with AGE, apoptosis decreased significantly. 1,25-(OH)₂D₃ enhanced PKA activity, but inhibited AGE-induced nuclear translocation of NF-κB. Furthermore, PKA activator (8-bromoadenoside cyclic adenoside monophosphate, 8-Br-cAMP) or NF-κB inhibitor (caffeic acid phenethyl ester, CAPE) could reduce the apoptosis, decreased cleaved caspase 3 and cleaved PARP, suggesting the involvement of PKA and NF-κB pathways in the protection of 1,25-(OH)₂D₃ on Schwann cells. Moreover, 8-Br-cAMP and CAPE could inhibit AGE-induced secretion of interleukin(IL)-1β, prostaglandin E2(PEG2) and cyclooxygenase 2(COX2). Interestingly, 8-Br-cAMP decreased phospho-NF-κB and inhibited nucleus translocation of NF-κB. It hinted at the regulation of PKA to NF-κB. Finally, a pre-treatment of H-89 (an inhibitor of PKA) could block the protection of 1,25-(OH)₂D₃ on cell apoptosis. In conclusion, 1,25-(OH)₂D₃ could protect Schwann cell against AGE-induced apoptosis through PKA/NF-κB pathway.

SIGNIFICANCE

These findings provide experimental rationales for using vitamin D for diabetic neuropathy.

Gene expression profiling reveals candidate biomarkers and probable molecular mechanism in diabetic peripheral neuropathy

PURPOSE

To investigate the molecular mechanism and search for candidate biomarkers in the gene expression profile of patients with diabetic peripheral neuropathy (DPN).

METHODS

Differentially expressed genes (DEGs) of progressive vs non-progressive DPN patients in dataset GSE24290 were screened. Functional enrichment analysis was conducted, and hub genes were extracted from the protein-protein interaction network. The expression level of hub genes in serum samples in another dataset GSE95849 was obtained, followed by the ROC curve analysis.

RESULTS

A total of 352 DEGs were obtained from dataset GSE24290. They were involved in 14 gene ontology terms and 10 Kyoto Encyclopedia of Genes and Genomes pathways, mainly related to lipid metabolism. Eight hub genes (LEP, APOE, ADIPOQ, FABP4, CD36, GPAM, CIDEC, and PNPLA4) were revealed, and their expression level was obtained in dataset GSE95849. The receiver operating characteristic curve analysis indicated that CIDEC (AUC=1), APOE (AUC=0.833), CD36 (AUC=0.803), and PNPLA4 (AUC=0.861) might be candidate serum biomarkers of DPN.

CONCLUSION

Lipid metabolism of Schwann cells might be inhibited in progressive DPN. CIDEC, APOE, CD36, and PNPLA4 might be potential predictive biomarkers in the early DPN diagnosis of patients with DM.

Effects of omega-3 polyunsaturated fatty-acid supplementation on neuropathic pain symptoms and sphingosine levels in Mexican-Americans with type 2 diabetes

PURPOSE

To determine whether dietary supplementation with omega-3 polyunsaturated fatty acids (PUFAs) reduces neuropathic pain symptoms in Mexican-Americans with type 2 diabetes.

METHODS

Forty volunteers with type 2 diabetes enrolled in the "En Balance-PLUS" program, which provided weekly nutrition-diabetes education and daily supplementation with 1,000 mg docosahexaenoic acid (DHA)-200 mg eicosapentaenoic acid over 3 months. The study assessed self-reported neuropathic pain symptoms pre/postintervention using the short-form McGill Pain Questionnaire (SF-MPQ), monitored clinical laboratory values at baseline and 3 months, and performed baseline and 3-month metabolomic analysis of plasma samples.

RESULTS

A total of 26 participants self-reported neuropathic pain symptoms at baseline. After 3 months of omega-3 PUFA supplementation, participants reported significant improvement in SF-MPQ scores (sensory, affective, and visual analogue scale; P<0.001, P=0.012, and P<0.001, respectively). Untargeted metabolomic analysis revealed that participants in the moderate-high SF-MPQ group had the highest relative plasma sphingosine levels at baseline compared to the low SF-MPQ group (P=0.0127) and the nonpain group (P=0.0444). Omega-3 PUFA supplementation increased plasma DHA and reduced plasma sphingosine levels in participants reporting neuropathic pain symptoms (P<0.001 and P<0.001, respectively). Increased plasma DHA levels significantly correlated with improved SF-MPQ sensory scores (r=0.425, P=0.030). Improved SF-MPQ scores, however, did not correlate with clinical/laboratory parameters.

CONCLUSION

The data suggest that omega-3 PUFAs dietary supplementation may reduce neuropathic pain symptoms in individuals with type 2 diabetes and correlates with sphingosine levels in the plasma.

Protective effect of docosahexaenoic acid on lipotoxicity-mediated cell death in Schwann cells: Implication of PI3K/AKT and mTORC2 pathways

BACKGROUND AND AIM

Docosahexaenoic acid (DHA) exhibits neuroprotective properties and has been shown to preserve nerve cells following trauma and ischemic injury. Recently, we showed that DHA pretreatment improved locomotion and reduced neuropathic pain after acute spinal cord injury in adult rats. These improvements were associated with an increase in the levels of AKT in spinal cord injury neurons. In this study, we investigate the implication of PI3K/AKT and mTOR pathway in DHA-mediated protection of primary cultured Schwann cells (pSC) undergoing palmitic acid-induced lipotoxicity (PA-LTx).

METHODS

Primary cultured Schwann cells were treated with PA (PA:BSA, 2:1) in the presence or absence of DHA (1-200 µM) for 24-48 hr. Cell viability was determined by crystal violet staining and nuclear morphology was examined using Hoechst staining.

RESULTS

We found that pSC cultures exposed to palmitic acid (PA) overload showed chromatin condensation, a decrease in cell viability and an inhibition of AKT phosphorylation in a time-dependent manner. Next, pSC exposed to PA overload were treated with DHA. The data show that co-treatment with DHA inhibited the loss of cell viability and apoptosis caused by PA. Moreover, treatment with DHA inhibited chromatin condensation, significantly stimulated p-AKT phosphorylation under PA-LTx condition, and DHA alone increased AKT phosphorylation. Additionally, when these pSC cultures were treated with PI3K inhibitors LY294002 and, BKM120 and mTOR inhibitors Torin 1 (mTORC1/mTORC2), but not rapamycin (mTORC1), the protective effects of DHA were not observed.

CONCLUSION

These findings suggest PI3K/AKT and mTORC2 kinase pathways are involved in the protective function (s) of DHA in PA-induced Schwann cell death.

Palmitate induces lipoapoptosis in Schwann cells through ROS generation-mediated STAMP2 downregulation

Free fatty acids (FFAs) are considered the principal inducers of lipotoxicity, leading to cell dysfunction and/or cell death. Lipotoxicity in Schwann cells (SCs) damages neurons, which may be associated with peripheral neuropathies and axon degeneration. However, the molecular mechanism by which FFAs exert lipotoxicity in SCs remains to be established. In the present study, we demonstrate that palmitate exerts lipotoxicity in SCs through apoptosis and that palmitate-induced lipotoxicity in SCs is mediated through reactive oxygen species (ROS) generation. We observed that the six-transmembrane protein of prostate 2 (STAMP2), which plays a pivotal role in lipid homeostasis, is expressed in SCs. We further demonstrate that palmitate induces lipoapoptosis in SCs through ROS generation-mediated STAMP2 downregulation and that STAMP2 depletion accelerates the palmitate-exerted lipoapoptosis in SCs, indicating that STAMP2 confers on SCs the ability to resist palmitate-induced lipotoxicity. In conclusion, palmitate induces lipoapoptosis in SCs through ROS generation-mediated STAMP2 downregulation. Our findings indicate that ROS and STAMP2 may represent suitable targets for pharmacological interventions targeting lipotoxicity-associated peripheral neuropathies and axon degeneration.

Peripheral Glial Cells in the Development of Diabetic Neuropathy

The global prevalence of diabetes is rapidly increasing, affecting more than half a billion individuals within the next few years. As diabetes negatively affects several physiological systems, this dramatic increase represents not only impaired quality of life on the individual level but also a huge socioeconomic challenge. One of the physiological consequences affecting up to half of diabetic patients is the progressive deterioration of the peripheral nervous system, resulting in spontaneous pain and eventually loss of sensory function, motor weakness, and organ dysfunctions. Despite intense research on the consequences of hyperglycemia on nerve functions, the biological mechanisms underlying diabetic neuropathy are still largely unknown, and treatment options lacking. Research has mainly focused directly on the neuronal component, presumably from the perspective that this is the functional signal-transmitting unit of the nerve. However, it is noteworthy that each single peripheral sensory neuron is intimately associated with numerous glial cells; the neuronal soma is completely enclosed by satellite glial cells and the length of the longest axons covered by at least 1,000 Schwann cells. The glial cells are vital for the neuron, but very little is still known about these cells in general and especially how they respond to diabetes in terms of altered neuronal support. We will discuss current knowledge of peripheral glial cells and argue that increased research in these cells is imperative for a better understanding of the mechanisms underlying diabetic neuropathy.

Effects of acetyl-L-carnitine in diabetic neuropathy and other geriatric disorders

A long history of diabetes mellitus and increasing age are associated with the onset of diabetic neuropathy, a painful and highly disabling complication with a prevalence peaking at 50% among elderly diabetic patients. Acetyl-L-carnitine (ALC) is a molecule derived from the acetylation of carnitine in the mitochondria that has an essential role in energy production. It has recently been proposed as a therapy to improve the symptoms of diabetic neuropathy. ALC is widely distributed in mammalian tissues, including the brain, blood-brain barrier, brain neurons, and astrocytes. Aside from its metabolic activity, ALC has demonstrated cytoprotective, antioxidant, and antiapoptotic effects in the nervous system. It exerts an analgesic action by reducing the concentration of glutamate in the synapses. It facilitates nerve regeneration and damage repair after primary trauma: its positive effects on metabolism promote the synthesis, fluidity, and functionality of neuronal membranes, increase protein synthesis, and improve the axonal transport of neurofilament proteins and tubulin. It also amplifies nerve growth factor responsiveness, an effect that is believed to enhance overall neurite growth. ALC has been proposed for the treatment of various neurological and psychiatric diseases, such as mood disorders and depression, dementias, Alzheimer's disease, and Parkinson's disease, because synaptic energy states and mitochondrial dysfunction are core factors in their pathogenesis.

Mdivi-1 Protects Adult Rat Hippocampal Neural Stem Cells against Palmitate-Induced Oxidative Stress and Apoptosis

Palmitate concentrations in type 2 diabetic patients are higher than in healthy subjects. The prolonged elevation of plasma palmitate levels induces oxidative stress and mitochondrial dysfunction in neuronal cells. In this study, we examined the role of mdivi-1, a selective inhibitor of mitochondrial fission protein dynamin-regulated protein 1 (Drp1), on the survival of cultured hippocampal neural stem cells (NSCs) exposed to high palmitate. Treatment of hippocampal NSCs with mdivi-1 attenuated palmitate-induced increase in cell death and apoptosis. Palmitate exposure significantly increased Drp1 protein levels, which were prevented by pretreatment of cells with mdivi-1. We found that cytosolic Drp1 was translocated to the mitochondria when cells were exposed to palmitate. In contrast, palmitate-induced translocation of Drp1 was inhibited by mdivi-1 treatment. We also investigated mdivi-1 regulation of apoptosis at the mitochondrial level. Mdivi-1 rescued cells from palmitate-induced lipotoxicity by suppressing intracellular and mitochondrial reactive oxygen species production and stabilizing mitochondrial transmembrane potential. Mdivi-1-treated cells showed an increased Bcl-2/Bax ratio, prevention of cytochrome c release, and inhibition of caspase-3 activation. Our data suggest that mdivi-1 protects hippocampal NSCs against lipotoxicity-associated oxidative stress by preserving mitochondrial integrity and inhibiting mitochondrial apoptotic cascades.

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.

Palmitic acid is a toll-like receptor 4 ligand that induces human dendritic cell secretion of IL-1β

Palmitic acid (PA) and other saturated fatty acids are known to stimulate pro-inflammatory responses in human immune cells via Toll-like receptor 4 (TLR4). However, the molecular mechanism responsible for fatty acid stimulation of TLR4 remains unknown. Here, we demonstrate that PA functions as a ligand for TLR4 on human monocyte derived dendritic cells (MoDCs). Hydrophobicity protein modeling indicated PA can associate with the hydrophobic binding pocket of TLR4 adaptor protein MD-2. Isothermal titration calorimetry quantified heat absorption that occurred during PA titration into TLR4/MD2, indicating that PA binds to TLR4/MD2. Treatment of human MoDCs with PA resulted in endocytosis of TLR4, further supporting the function of PA as a TLR4 agonist. In addition, PA stimulated DC maturation and activation based on the upregulation of DC costimulatory factors CD86 and CD83. Further experiments showed that PA induced TLR4 dependent secretion of the pro-inflammatory cytokine IL-1β. Lastly, our experimental data show that PA stimulation of NF-κB canonical pathway activation is regulated by TLR4 signaling and that reactive oxygen species may be important in upregulating this pro-inflammatory response. Our experiments demonstrate for the first time that PA activation of TLR4 occurs in response to direct molecular interactions between PA and MD-2. In summary, our findings suggest a likely molecular mechanism for PA induction of pro-inflammatory immune responses in human dendritic cells expressing TLR4.

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.

Schwann cell interactions with axons and microvessels in diabetic neuropathy

The prevalence of diabetes worldwide is at pandemic levels, with the number of patients increasing by 5% annually. The most common complication of diabetes is peripheral neuropathy, which has a prevalence as high as 50% and is characterized by damage to neurons, Schwann cells and blood vessels within the nerve. The pathogenic mechanisms of diabetic neuropathy remain poorly understood, impeding the development of targeted therapies to treat nerve degeneration and its most disruptive consequences of sensory loss and neuropathic pain. Involvement of Schwann cells has long been proposed, and new research techniques are beginning to unravel a complex interplay between these cells, axons and microvessels that is compromised during the development of diabetic neuropathy. In this Review, we discuss the evolving concept of Schwannopathy as an integral factor in the pathogenesis of diabetic neuropathy, and how disruption of the interactions between Schwann cells, axons and microvessels contribute to the disease.

Protective Effect of Psoralea corylifolia L. Seed Extract against Palmitate-Induced Neuronal Apoptosis in PC12 Cells

The extract of Psoralea corylifolia seeds (PCE) has been widely used as a herbal medicine because of its beneficial effect on human health. In this study, we investigated the protective effects and molecular mechanisms of PCE on palmitate- (PA-) induced toxicity in PC12 cells, a neuron-like cell line. PCE significantly increased cell viability in PA-treated PC12 cells and showed antiapoptotic effects, as evidenced by decreased expression of cleaved caspase-3, cleaved poly(ADP-ribose) polymerase, and bax protein as well as increased expression of bcl-2 protein. In addition, PCE treatment reduced PA-induced reactive oxygen species production and upregulated mRNA levels of antioxidant genes such as nuclear factor (erythroid-derived 2)-like 2 and heme oxygenase 1. Moreover, PCE treatment recovered the expression of autophagy marker genes such as beclin-1 and p62, which was decreased by PA treatment. Treatment with isopsoralen, one of the major components of PCE extract, also recovered the expression of autophagy marker genes and reduced PA-induced apoptosis. In conclusion, PCE exerts protective effects against lipotoxicity via its antioxidant function, and this effect is mediated by activation of autophagy. PCE might be a potential pharmacological agent to protect against neuronal cell injury caused by oxidative stress or lipotoxicity.

Molecular Pathogenesis of NASH

Nonalcoholic steatohepatitis (NASH) is the main cause of chronic liver disease in the Western world and a major health problem, owing to its close association with obesity, diabetes, and the metabolic syndrome. NASH progression results from numerous events originating within the liver, as well as from signals derived from the adipose tissue and the gastrointestinal tract. In a fraction of NASH patients, disease may progress, eventually leading to advanced fibrosis, cirrhosis and hepatocellular carcinoma. Understanding the mechanisms leading to NASH and its evolution to cirrhosis is critical to identifying effective approaches for the treatment of this condition. In this review, we focus on some of the most recent data reported on the pathogenesis of NASH and its fibrogenic progression, highlighting potential targets for treatment or identification of biomarkers of disease progression.

Bioactive Compounds and Their Neuroprotective Effects in Diabetic Complications

Hyperglycemia, hyperlipidemia and impaired insulin signaling during the development of diabetes can cause diabetic complications, such as diabetic neuropathy, resulting in significant morbidity and mortality. Although various therapeutics are available for the treatment of diabetic neuropathy, no absolute cure exists, and additional research is necessary to comprehensively understand the underlying pathophysiological pathways. A number of studies have demonstrated the potential health benefits of bioactive compounds, i.e., flavonoids and vitamins, which may be effective as supplementary treatments for diabetes and its complications. In this review, we highlight the most recent reports about the mechanisms of action of bioactive compounds (flavonoids and vitamins) possessing potential neuroprotective properties in diabetic conditions. Additional clinical studies are required to determine the appropriate dose and duration of bioactive compound supplementation for neuroprotection in diabetic patients.

The Relationship between Dyslipidemia and Acute Axonal Function in Type 2 Diabetes Mellitus In Vivo

Objectives

Diabetic peripheral neuropathy (DPN) is a common and debilitating complication of diabetes mellitus. Treatment largely consists of symptom alleviation and there is a need to identify therapeutic targets for prevention and treatment of DPN. The objective of this study was to utilise novel neurophysiological techniques to investigate axonal function in patients with type 2 diabetes and to prospectively determine their relationship to serum lipids in type 2 diabetic patients.

Methods

Seventy-one patients with type 2 diabetes were consecutively recruited and tested. All patients underwent thorough clinical neurological assessments including nerve conduction studies, and median motor axonal excitability studies. Studies were also undertaken in age matched normal control subjects(n = 42). Biochemical studies, including serum lipid levels were obtained in all patients. Patient excitability data was compared to control data and linear regression analysis was performed to determine the relationship between serum triglycerides and low density lipoproteins and excitability parameters typically abnormal in type 2 diabetic patients.

Results

Patient mean age was 64.2±2.3 years, mean glycosylated haemoglobin (HbA1c%) was 7.8±0.3%, mean triglyceride concentration was 1.6±0.1 mmol/L and mean cholesterol concentration was 4.1±0.2mmol/L. Compared to age matched controls, median motor axonal excitability studies indicated axonal dysfunction in type 2 diabetic patients as a whole (T2DM) and in a subgroup of the patients without DPN (T2DM-NN). These included reduced percentage threshold change during threshold electrotonus at 10–20ms depolarising currents (TEd10–20ms)(controls 68.4±0.8, T2DM63.9±0.8, T2DM-NN64.8±1.6%,P<0.05) and superexcitability during the recovery cycle (controls-22.5±0.9, T2DM-17.5±0.8, T2DM-NN-17.3±1.6%,P<0.05). Linear regression analysis revealed no associations between changes in axonal function and either serum triglyceride or low density lipoprotein concentration when adjusted for renal function, a separate risk factor for neuropathy development. Our findings indicate that acutely, serum lipids do not exert an acute effect on axonal function in type 2 diabetic patients: TEd(10–20ms)(1.2(-1.4,3.8);P = 0.4) and superexcitability (2.4(-0.05, 4.8);P = 0.06).

Conclusions

These findings suggest that serum triglyceride levels are not related to axonal function in type 2 diabetic patients. Additional pathogenic mechanisms may play a more substantial role in axonal dysfunction prior to DPN development.

Oxidative, metabolic, and apoptotic responses of Schwann cells to high glucose levels

The specific response of murine Schwann cells IMS32 to acute and chronic hyperglycemia conditions was evaluated. The pathophysiological alterations were studied to deepening the role of Schwann cells in diabetes-related neurotoxicity and to assess a model to screen new protective molecules. IMS32 were incubated with 30 and 56 mM glucose for 48 h and 7 and 14 days, and markers of oxidative stress, apoptosis, and polyol pathway were evaluated. High glucose induced O(2) -production and lipid peroxidation at all time point whereas Caspase 3 activity was induced only after 14 days. Aldose reductase activity and expression were significantly increased after 48 h and 14 days, respectively. Our results describe the response of Schwann cells to high glucose conditions and suggest the use of IMS32 for the screening of protective molecules in diabetes-induced neuropathy.

Cardiovascular disease predicts diabetic peripheral polyneuropathy in subjects with type 2 diabetes: A 10-year prospective study

BACKGROUND

The relationship between cardiovascular disease and diabetic peripheral neuropathy is mainly sustained by data retrieved from cross-sectional studies focused on cardiovascular risk factors. We aimed to assess the presence of cardiovascular disease as a risk factor for developing diabetic peripheral neuropathy in a type 2 diabetes mellitus population.

METHOD

A 10-year prospective, primary care, multicentre study in a randomly selected cohort. Cardiovascular disease presence included stroke, coronary artery disease and/or peripheral ischaemia. Diabetic peripheral neuropathy diagnosis was based on clinical neurological examination as well as the neuropathy symptoms score and nerve conduction studies.

RESULTS

Three hundred and ten (N=310) patients were initially recruited. Two-hundred and sixty seven (N=267) patients were included in the study. Diabetic peripheral neuropathy cumulative incidence was 18.3% (95% confidence intervals 14.1-23.4; N=49). Diabetic peripheral neuropathy development was significantly more frequent in participants presenting with cardiovascular disease at baseline (P=0.01). In the final logistic regression analysis, the presence of cardiovascular disease remained associated with an increased risk for diabetic peripheral neuropathy (odds ratio 2.32, 95% confidence intervals 1.03-5.22) in addition to diabetes duration and low density lipoprotein-cholesterol levels.

CONCLUSIONS

In our series, type 2 diabetes mellitus patients with cardiovascular disease at baseline present with an increased risk of developing diabetic peripheral neuropathy at 10 years of follow-up. Our results suggest that measures aimed at the prevention, control and treatment of cardiovascular disease can also help prevent diabetic peripheral neuropathy development.

Puerarin prevents high glucose-induced apoptosis of Schwann cells by inhibiting oxidative stress

Oxidative stress may be the unifying factor for the injury caused by hyperglycemia in diabetic peripheral neuropathy. Puerarin is the major isoflavonoid derived from Radix puerariae and has been shown to be effective in increasing superoxide dismutase activity. This study sought to investigate the neuroprotective effect of puerarin on high glucose-induced oxidative stress and Schwann cell apoptosis in vitro. Intracellular reactive oxygen radicals and mitochondrial transmembrane potential were detected by flow cytometry analysis. Apoptosis was confirmed by TUNEL and oxidative stress was monitored using an enzyme-linked immunosorbent assay for the DNA marker 8-hydroxy-2-deoxyguanosine. The expression levels of bax and bcl-2 were analyzed by quantitative real-time reverse transcriptase-PCR, while protein expression of cleaved caspase-3 and -9 were analyzed by means of western blotting. Results suggested that puerarin treatment inhibited high glucose-induced oxidative stress, mitochondrial depolarization and apoptosis in a dose-dependent manner. Furthermore, puerarin treatment downregulated Bax expression, upregulated bcl-2 expression and attenuated the activation of caspase-3 and -9. Overall, our results indicated that puerarin antagonized high glucose-induced oxidative stress and apoptosis in Schwann cells.

Epidermal fatty acid-binding protein protects nerve growth factor-differentiated PC12 cells from lipotoxic injury

Epidermal fatty acid-binding protein (E-FABP/FABP5/DA11) binds and transport long-chain fatty acids in the cytoplasm and may play a protecting role during neuronal injury. We examined whether E-FABP protects nerve growth factor-differentiated PC12 cells (NGFDPC12 cells) from lipotoxic injury observed after palmitic acid (C16:0; PAM) overload. NGFDPC12 cells cultures treated with PAM/bovine serum albumin at 0.3 mM/0.15 mM show PAM-induced lipotoxicity (PAM-LTx) and apoptosis. The apoptosis was preceded by a cellular accumulation of reactive oxygen species (ROS) and higher levels of E-FABP. Antioxidants MCI-186 and N-acetyl cysteine prevented E-FABP's induction in expression by PAM-LTx, while tert-butyl hydroperoxide increased ROS and E-FABP expression. Non-metabolized methyl ester of PAM, methyl palmitic acid (mPAM), failed to increase cellular ROS, E-FABP gene expression, or trigger apoptosis. Treatment of NGFDPC12 cultures with siE-FABP showed reduced E-FABP levels correlating with higher accumulation of ROS and cell death after exposure to PAM. In contrast, increasing E-FABP cellular levels by pre-loading the cells with recombinant E-FABP diminished the PAM-induced ROS and cell death. Finally, agonists for PPARβ (GW0742) or PPARγ (GW1929) increased E-FABP expression and enhanced the resistance of NGFDPC12 cells to PAM-LTx. We conclude that E-FABP protects NGFDPC12 cells from lipotoxic injury through mechanisms that involve reduction of ROS.

Epidermal fatty acid-binding protein (E-FABP) may protect nerve cells from the damaging exposure to high levels of free fatty acids (FA). We show that E-FABP can neutralize the effects of reactive oxygen species (ROS) generated by the high levels of FA in the cell and protect PC12 cells from lipotoxic injuries common in Type 2 diabetes neuropathy. Potentially, E-FABP gene up-regulation may be mediated through the NFkB pathway and future studies are needed to further evaluate this proposition.

Long-chain acyl coenzyme A synthetase 1 overexpression in primary cultured Schwann cells prevents long chain fatty acid-induced oxidative stress and mitochondrial dysfunction

AIMS

High circulating long chain fatty acids (LCFAs) are implicated in diabetic neuropathy (DN) development. Expression of the long-chain acyl-CoA synthetase 1 (Acsl1) gene, a gene required for LCFA metabolic activation, is altered in human and mouse diabetic peripheral nerve. We assessed the significance of Acsl1 upregulation in primary cultured Schwann cells.

RESULTS

Acsl1 overexpression prevented oxidative stress (nitrotyrosine; hydroxyoctadecadienoic acids [HODEs]) and attenuated cellular injury (TUNEL) in Schwann cells following 12 h exposure to LCFAs (palmitate, linoleate, and oleate, 100 μM). Acsl1 overexpression potentiated the observed increase in medium to long-chain acyl-carnitines following 12 h LCFA exposure. Data are consistent with increased mitochondrial LCFA uptake, largely directed to incomplete beta-oxidation. LCFAs uncoupled mitochondrial oxygen consumption from ATP production. Acsl1 overexpression corrected mitochondrial dysfunction, increasing coupling efficiency and decreasing proton leak.

INNOVATION

Schwann cell mitochondrial function is critical for peripheral nerve function, but research on Schwann cell mitochondrial dysfunction in response to hyperlipidemia is minimal. We demonstrate that high levels of a physiologically relevant mixture of LCFAs induce Schwann cell injury, but that improved mitochondrial uptake and metabolism attenuate this lipotoxicity.

CONCLUSION

Acsl1 overexpression improves Schwann cell function and survival following high LCFA exposure in vitro; however, the observed endogenous Acsl1 upregulation in peripheral nerve in response to diabetes is not sufficient to prevent the development of DN in murine models of DN. Therefore, targeted improvement in Schwann cell metabolic disposal of LCFAs may improve DN phenotypes.

Iron homeostasis in peripheral nervous system, still a black box?

SIGNIFICANCE

Iron is the most abundant transition metal in biology and an essential cofactor for many cellular enzymes. Iron homeostasis impairment is also a component of peripheral neuropathies.

RECENT ADVANCES

During the past years, much effort has been paid to understand the molecular mechanism involved in maintaining systemic iron homeostasis in mammals. This has been stimulated by the evidence that iron dyshomeostasis is an initial cause of several disorders, including genetic and sporadic neurodegenerative disorders.

CRITICAL ISSUES

However, very little has been done to investigate the physiological role of iron in peripheral nervous system (PNS), despite the development of suitable cellular and animal models.

FUTURE DIRECTIONS

To stimulate research on iron metabolism and peripheral neuropathy, we provide a summary of the knowledge on iron homeostasis in the PNS, on its transport across the blood-nerve barrier, its involvement in myelination, and we identify unresolved questions. Furthermore, we comment on the role of iron in iron-related disorder with peripheral component, in demyelinating and metabolic peripheral neuropathies.