Nerve growth factor and expression of its receptors in patients with diabetic neuropathy

Lost in Translation: Neurotrophins Biology and Function in the Neurovascular Unit

The neurovascular unit (NVU) refers to the functional building unit of the brain and the retina, where neurons, glia, and microvasculature orchestrate to meet the demand of the retina's and brain's function. Neurotrophins (NTs) are structural families of secreted proteins and are known for exerting neurotrophic effects on neuronal differentiation, survival, neurite outgrowth, synaptic formation, and plasticity. NTs include several molecules, such as nerve growth factor, brain-derived neurotrophic factor, NT-3, NT-4, and their precursors. Furthermore, NTs are involved in signaling pathways such as inflammation, apoptosis, and angiogenesis in a nonneuronal cell type. Interestingly, NTs and the precursors can bind and activate the p75 neurotrophin receptor (p75NTR) at low and high affinity. Mature NTs bind their cognate tropomyosin/tyrosine-regulated kinase receptors, crucial for maintenance and neuronal development in the brain and retina axis. Activation of p75NTR results in neuronal apoptosis and cell death, while tropomysin receptor kinase upregulation contributes to differentiation and cell growth. Recent findings indicate that modulation of NTs and their receptors contribute to neurovascular dysfunction in the NVU. Several chronic metabolic and acute ischemic diseases affect the NVU, including diabetic and ischemic retinopathy for the retina, as well as stroke, acute encephalitis, and traumatic brain injury for the brain. This work aims to review the current evidence through published literature studying the impact of NTs and their receptors, including the p75NTR receptor, on the injured and healthy brain-retina axis.

Ocular surface microbiota dysbiosis contributes to the high prevalence of dry eye disease in diabetic patients

People with diabetes mellitus (DM) are at an increased risk for developing dry eye disease (DED). However, the mechanisms underlying this phenomenon remain unclear. Recent studies have found that the ocular surface microbiota (OSM) differs significantly between patients with DED and healthy people, suggesting that OSM dysbiosis may contribute to the pathogenesis of DED. This hypothesis provides a new possible explanation for why diabetic patients have a higher prevalence of DED than healthy people. The high-glucose environment and the subsequent pathological changes on the ocular surface can cause OSM dysbiosis. The unbalanced microbiota then promotes ocular surface inflammation and alters tear composition, which disturbs the homeostasis of the ocular surface. This "high glucose-OSM dysbiosis" pathway in the pathogenesis of DED with DM (DM-DED) is discussed in this review.

Modulation of neurotrophic factors in the treatment of dementia, stroke and TBI: Effects of Cerebrolysin

Neurotrophic factors (NTFs) are involved in the pathophysiology of neurological disorders such as dementia, stroke and traumatic brain injury (TBI), and constitute molecular targets of high interest for the therapy of these pathologies. In this review we provide an overview of current knowledge of the definition, discovery and mode of action of five NTFs, nerve growth factor, insulin-like growth factor 1, brain derived NTF, vascular endothelial growth factor and tumor necrosis factor alpha; as well as on their contribution to brain pathology and potential therapeutic use in dementia, stroke and TBI. Within the concept of NTFs in the treatment of these pathologies, we also review the neuropeptide preparation Cerebrolysin, which has been shown to resemble the activities of NTFs and to modulate the expression level of endogenous NTFs. Cerebrolysin has demonstrated beneficial treatment capabilities in vitro and in clinical studies, which are discussed within the context of the biochemistry of NTFs. The review focuses on the interactions of different NTFs, rather than addressing a single NTF, by outlining their signaling network and by reviewing their effect on clinical outcome in prevalent brain pathologies. The effects of the interactions of these NTFs and Cerebrolysin on neuroplasticity, neurogenesis, angiogenesis and inflammation, and their relevance for the treatment of dementia, stroke and TBI are summarized.

Selected Serum Markers Associated with Pathogenesis and Clinical Course of Type 1 Diabetes in Pediatric Patients—The Effect of Disease Duration

Biochemical abnormalities in the course of type 1 diabetes (T1D) may cause the production/activation of various proteins and peptides influencing treatment and causing a risk of complications. The aim of this study was to assess concentrations of selected serum substances involved in the pathogenesis and course of T1D and to correlate their concentrations with the duration of T1D. The study included patients with T1D (n = 156) at the age of 3–17, who were divided according to the duration of the disease into those newly diagnosed (n = 30), diagnosed after 3–5 (n = 77), 6–7 (n = 25), and over 7 (n = 24) years from the onset of T1D, and age-matched healthy controls (n = 30). Concentrations of amylin (IAPP), proamylin (proIAPP), catestatin (CST), chromogranin A (ChgA), nerve growth factor (NFG), platelet-activating factor (PAF), uromodulin (UMOD), and intestinal fatty acid binding protein (I-FABP) were measured in sera using immunoenzymatic tests. There were significant differences in concentrations of all the substances except UMOD and NGF between T1D patients and healthy children. The duration of the disease affected concentrations of CST, ChgA, PAF, and NGF, i.e., proteins/peptides which could have an impact on the course of T1D and the development of complications. In long-term patients, a decrease in concentrations of CST and ChgA, and an increase in PAF concentrations were found. In the case of NGF, a decrease was observed after the initial high values, followed by an increase over 7 years after T1D diagnosis. Concluding, the results show that concentrations of selected serum indicators may change in the course of T1D. Further studies are needed to establish whether these indicators could be used in the context of predicting long-term complications.

Microbiological Characteristics of Ocular Surface Associated With Dry Eye in Children and Adolescents With Diabetes Mellitus

Purpose

To analyze the characteristics of ocular surface microbial composition in children and adolescents with diabetes mellitus and dry eye (DE) by tear analysis.

Methods

We selected 65 children and adolescents aged 8 to 16 years with DE and non-DE diabetes mellitus and 33 healthy children in the same age group from the Shanghai Children and Adolescent Diabetes Eye Study. Tears were collected for high-throughput sequencing of the V3 and V4 region of 16S rRNA. The ocular surface microbiota in diabetic DE (DM-DE; n = 31), diabetic with non-DE (DM-NDE; n = 34), and healthy (NDM; n = 33) groups were studied. QIIME2 software was used to analyze the microbiota of each group.

Results

The DM-DE group had the highest amplicon sequence variants, and the differences in α-diversity and β-diversity of micro-organisms in the ocular surfaces of DM-DE, diabetic with non-DE, and healthy eyes were statistically significant (P < 0.05). Bacteroidetes (15.6%), Tenericutes (9.3%), Firmicutes (21.8%), and Lactococcus (7.9%), Bacteroides (7.8%), Acinetobacter (3.9%), Clostridium (0.8%), Lactobacillus (0.8%) and Streptococcus (0.2%) were the specific phyla and genera, respectively, in the DM-DE group.

Conclusions

Compared with the patients with non-DE and healthy children, the microbial diversity of the ocular surface in children and adolescents with diabetes mellitus and DE was higher with unique bacterial phyla and genera composition.

Diabetic corneal neuropathy as a surrogate marker for diabetic peripheral neuropathy

Diabetic neuropathy is a prevalent microvascular complication of diabetes mellitus, affecting nerves in all parts of the body including corneal nerves and peripheral nervous system, leading to diabetic corneal neuropathy and diabetic peripheral neuropathy, respectively. Diabetic peripheral neuropathy is diagnosed in clinical practice using electrophysiological nerve conduction studies, clinical scoring, and skin biopsies. However, these diagnostic methods have limited sensitivity in detecting small-fiber disease, hence they do not accurately reflect the status of diabetic neuropathy. More recently, analysis of alterations in the corneal nerves has emerged as a promising surrogate marker for diabetic peripheral neuropathy. In this review, we will discuss the relationship between diabetic corneal neuropathy and diabetic peripheral neuropathy, elaborating on the foundational aspects of each: pathogenesis, clinical presentation, evaluation, and management. We will further discuss the relevance of diabetic corneal neuropathy in detecting the presence of diabetic peripheral neuropathy, particularly early diabetic peripheral neuropathy; the correlation between the severity of diabetic corneal neuropathy and that of diabetic peripheral neuropathy; and the role of diabetic corneal neuropathy in the stratification of complications of diabetic peripheral neuropathy.

Traditional chinese medicine to prevent and treat diabetic erectile dysfunction

Diabetic erectile dysfunction (DED) is one of the most common complications of diabetes mellitus. However, current therapeutics have no satisfactory effect on DED. In recent years, traditional Chinese medicine (TCM) has shown good effects against DED. By now, several clinical trials have been conducted to study the effect of TCM in treating DED; yet, the underlying mechanism is not fully investigated. Therefore, in this review, we briefly summarized the pathophysiological mechanism of DED and reviewed the published clinical trials on the treatment of DED by TCM. Then, the therapeutic potential of TCM and the underlying mechanisms whereby TCM exerts protective effects were summarized. We concluded that TCM is more effective than chemical drugs in treating DED by targeting multiple signaling pathways, including those involved in oxidation, apoptosis, atherosclerosis, and endothelial function. However, the major limitation in the application of TCM against DED is the lack of a large-scale, multicenter, randomized, and controlled clinical trial on the therapeutic effect, and the underlying pharmaceutical mechanisms also need further investigation. Despite these limitations, clinical trials and further experimental studies will enhance our understanding of the mechanisms modulated by TCM and promote the widespread application of TCM to treat DED.

Fluid Biomarkers for Monitoring Structural Changes in Polyneuropathies: Their Use in Clinical Practice and Trials

Reliable and responsive tools for monitoring disease activity and treatment outcomes in patients with neuropathies are lacking. With the emergence of ultrasensitive blood bioassays, proteins released with nerve damage are potentially useful response biomarkers for many neurological disorders, including polyneuropathies. In this review, we provide an overview of the existing literature focusing on potential applications in polyneuropathy clinical care and trials. Whilst several promising candidates have been identified, no studies have investigated if any of these proteins can serve as response biomarkers of longitudinal disease activity, except for neurofilament light (NfL). For NfL, limited evidence exists supporting a role as a response biomarker in Guillain-Barré syndrome, vasculitic neuropathy, and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Most evidence exists for NfL as a response biomarker in hereditary transthyretin-related amyloidosis (hATTR). At the present time, the role of NfL is therefore limited to a supporting clinical tool or exploratory endpoint in trials. Future developments will need to focus on the discovery of additional biomarkers for anatomically specific and other forms of nerve damage using high-throughput technologies and highly sensitive analytical platforms in adequality powered studies of appropriate design. For NfL, a better understanding of cut-off values, the relation to clinical symptoms and long-term disability as well as dynamics in serum on and off treatment is needed to further expand and proceed towards implementation.

Alteration of intrapancreatic serotonin, homocysteine, TNF-α, and NGF levels as predisposing factors for diabetes following exposure to 900-MHz waves

Exposure to mobile phone radiation causes deleterious health effects on biological systems. The objects of this study were to investigate the effect of 900-MHz radiofrequency waves (RFW) emitted from base transceiver station antenna on intrapancreatic homocysteine (Hcy), tumor necrosis factor-α (TNF-α), and nerve growth factor (NGF) as predisposing factors involved in pancreatic beta cell damage. Thirty male rats (Sprague-Dawley, 200 ± 10 g) were randomly divided into the control (without any exposure) and exposed groups: short time (2 h/day), long time (4 h/day), and exposed to 900-MHz RFW for 30 consecutive days. On the last days of the experiment, animals were killed and pancreas tissue was dissected out for evaluation of serotonin, Hcy, TNF-α, and NGF. There was a significant decrease in the serotonin and NGF levels in the pancreatic tissue of exposed groups compared to the control group (p < 0.05). Also, the levels of serotonin and NGF in the long-time exposure were significantly lower than the short-time exposure (p < 0.05). However, levels of Hcy and TNF-α were significantly increased in the pancreas of exposed groups compared to the control groups (p < 0.05). Exposure to 900-MHz RFW decreased pancreatic NGF and serotonin levels and increased the proinflammatory markers (Hcy and TNF-α), which can be a predisposing factor for type 2 diabetes.

Is diabetic neuropathy associated with vitamin D status? A meta-analysis

Several studies have been conducted to investigate the relation between 25-hydroxyvitamin D [25(OH)D] level and diabetic neuropathy (DN). However, there is still no clear conclusion due to differences in study design and cut-off values used in the published work, in addition to the absence of a comprehensive meta-analysis (MA) on the topic. The present systematic review and MA therefore aims at clarifying the association between vitamin D level and peripheral DN in patients with type 2 diabetes mellitus. Primary research studies that explored the association between 25(OH)D level and diabetic peripheral neuropathy in type 2 diabetes were located from Medline, EMBASE, Web of Science, Cochrane Library, CINHAL and Google Scholar. Twenty-six studies met the inclusion criteria with 6277 participants where 2218 were diabetic with DN, 2959 were diabetic without DN and 406 were healthy. Diabetic patients with DN showed significantly lower serum 25(OH)D compared with patients without DN (standardised mean difference (SMD) of -0·92 (95 % CI -1·18, -0·65, I2 = 93·3 %, P < 0·0001). The pooled OR value of vitamin D deficiency was higher in patients with DN, 1·84 (95 % CI 1·46, 2·33, P < 0·0001) and 2·87 (95 % CI 1·10, 7·52, P = 0·03) when using fixed-effects and random-effects models, respectively. Vitamin D deficiency has been found to be highly prevalent among diabetic patients with neuropathy. Since 25(OH)D has been implicated in glucose haemostasis and showed benefit in reducing neuropathy symptoms, its supplementation is warranted for this population of patients.

Recent Advances in Biomarkers and Regenerative Medicine for Diabetic Neuropathy

Diabetic neuropathy is one of the most common complications of diabetes. This complication is peripheral neuropathy with predominant sensory impairment, and its symptoms begin with hyperesthesia and pain and gradually become hypoesthesia with the loss of nerve fibers. In some cases, lower limb amputation occurs when hypoalgesia makes it impossible to be aware of trauma or mechanical stimuli. On the other hand, up to 50% of these complications are asymptomatic and tend to delay early detection. Therefore, sensitive and reliable biomarkers for diabetic neuropathy are needed for an early diagnosis of this condition. This review focuses on systemic biomarkers that may be useful at this time. It also describes research on the relationship between target gene polymorphisms and pathological conditions. Finally, we also introduce current information on regenerative therapy, which is expected to be a therapeutic approach when the pathological condition has progressed and nerve degeneration has been completed.

The Role of Vascular Cells in Pancreatic Beta-Cell Function

Insulin-producing β-cells constitute the majority of the cells in the pancreatic islets. Dysfunction of these cells is a key factor in the loss of glucose regulation that characterizes type 2 diabetes. The regulation of many of the functions of β-cells relies on their close interaction with the intra-islet microvasculature, comprised of endothelial cells and pericytes. In addition to providing islet blood supply, cells of the islet vasculature directly regulate β-cell activity through the secretion of growth factors and other molecules. These factors come from capillary mural pericytes and endothelial cells, and have been shown to promote insulin gene expression, insulin secretion, and β-cell proliferation. This review focuses on the intimate crosstalk of the vascular cells and β-cells and its role in glucose homeostasis and diabetes.

Early Biomarkers of Neurodegenerative and Neurovascular Disorders in Diabetes

Diabetes mellitus (DM) is a common disease worldwide. There is a strong association between DM and neurovascular and neurodegenerative disorders. The first group mainly consists of diabetic retinopathy, diabetic neuropathy and stroke, whereas, the second group includes Alzheimer's disease, Parkinson's disease, mild cognitive impairment and dementia. The aforementioned diseases have a common pathophysiological background including insulin resistance, oxidative stress, atherosclerosis and vascular injury. The increasing prevalence of neurovascular and neurodegenerative disorders among diabetic patients has resulted in an urgent need to develop biomarkers for their prediction and/or early detection. The aim of this review is to present the potential application of the most promising biomarkers of diabetes-related neurodegenerative and neurovascular disorders, including amylin, β-amyloid, C-reactive protein (CRP), dopamine, gamma-glutamyl transferase (GGT), glycogen synthase kinase 3β, homocysteine, microRNAs (mi-RNAs), paraoxonase 1, phosphoinositide 3-kinases, tau protein and various growth factors. The most clinically promising biomarkers of neurovascular and neurodegenerative complications in DM are hsCRP, GGT, homocysteine and miRNAs. However, all biomarkers discussed in this review could become a part of the potential multi-biomarker screening panel for diabetic patients at risk of neurovascular and neurodegenerative complications.

Nerve growth factor in metabolic complications and Alzheimer's disease: Physiology and therapeutic potential

As the population ages, obesity and metabolic complications as well as neurological disorders are becoming more prevalent, with huge economic burdens on both societies and families. New therapeutics are urgently needed. Nerve growth factor (NGF), first discovered in 1950s, is a neurotrophic factor involved in regulating cell proliferation, growth, survival, and apoptosis in both central and peripheral nervous systems. NGF and its precursor, proNGF, bind to TrkA and p75 receptors and initiate protein phosphorylation cascades, resulting in changes of cellular functions, and are associated with obesity, diabetes and its complications, and Alzheimer's disease. In this article, we summarize changes in NGF levels in metabolic and neuronal disorders, the signal transduction initiated by NGF and proNGF, the physiological and pathophysiological relevance, and therapeutic potential in treating chronic metabolic diseases and cognitive decline.

Early nerve fibre regeneration in individuals with type 1 diabetes after simultaneous pancreas and kidney transplantation

AIMS/HYPOTHESIS

The study aimed to assess the impact on neuropathy of simultaneous pancreas and kidney transplantation (SPK) in individuals with type 1 diabetes.

METHODS

This longitudinal observational study examined neuropathic symptoms, deficits, quantitative sensory testing, neurophysiology, corneal confocal microscopy and skin biopsy results in 32 healthy (non-diabetic) control participants, 29 individuals with type 1 diabetes and severe diabetic peripheral neuropathy [DPN] and 36 individuals with type 1 diabetes after SPK.

RESULTS

Following SPK, HbA_1c, eGFR, triacylglycerols and HDL improved significantly (all p < 0.05). Compared with the DPN group, which remained unchanged over the 36 month study period, corneal confocal microscopy assessments improved over 36 months following SPK, with increasing corneal nerve fibre density of 5/mm² (95% CI 1.8, 8.2; p = 0.003) and corneal nerve fibre length of 3.2 mm/mm² (95% CI 0.9, 5.5; p = 0.006). The Neuropathy Symptom Profile and peroneal nerve conduction velocity also improved significantly by 36 months compared with DPN (2.5; 95% CI 0.7, 4.3; p = 0.008 and 4.7 m/s; 95% CI 2.2, 7.4; p = 0.0004, respectively), but with a temporal delay compared with the corneal confocal microscopy assessments. Intraepidermal nerve fibre density did not change following SPK; however, mean dendritic length improved significantly at 12 (p = 0.020) and 36 (p = 0.019) months. In contrast, there were no changes in the Neuropathy Disability Score, quantitative sensory testing or cardiac autonomic function assessments. Except for a small decrease in corneal nerve fibre density in the healthy control group, there were no changes in any other neuropathy measure in the healthy control or DPN groups over 36 months.

CONCLUSIONS/INTERPRETATION

SPK is associated with early and maintained small nerve fibre regeneration in the cornea and skin, followed by an improvement in neuropathic symptoms and peroneal nerve conduction velocity.

Emerging Biomarkers, Tools, and Treatments for Diabetic Polyneuropathy

Diabetic neuropathy, with its major clinical sequels, notably neuropathic pain, foot ulcers, and autonomic dysfunction, is associated with substantial morbidity, increased risk of mortality, and reduced quality of life. Despite its major clinical impact, diabetic neuropathy remains underdiagnosed and undertreated. Moreover, the evidence supporting a benefit for causal treatment is weak at least in patients with type 2 diabetes, and current pharmacotherapy is largely limited to symptomatic treatment options. Thus, a better understanding of the underlying pathophysiology is mandatory for translation into new diagnostic and treatment approaches. Improved knowledge about pathogenic pathways implicated in the development of diabetic neuropathy could lead to novel diagnostic techniques that have the potential of improving the early detection of neuropathy in diabetes and prediabetes to eventually embark on new treatment strategies. In this review, we first provide an overview on the current clinical aspects and illustrate the pathogenetic concepts of (pre)diabetic neuropathy. We then describe the biomarkers emerging from these concepts and novel diagnostic tools and appraise their utility in the early detection and prediction of predominantly distal sensorimotor polyneuropathy. Finally, we discuss the evidence for and limitations of the current and novel therapy options with particular emphasis on lifestyle modification and pathogenesis-derived treatment approaches. Altogether, recent years have brought forth a multitude of emerging biomarkers reflecting different pathogenic pathways such as oxidative stress and inflammation and diagnostic tools for an early detection and prediction of (pre)diabetic neuropathy. Ultimately, these insights should culminate in improving our therapeutic armamentarium against this common and debilitating or even life-threatening condition.

Deficits in systemic biomarkers of neuroinflammation and growth factors promoting nerve regeneration in patients with type 2 diabetes and polyneuropathy

INTRODUCTION

The determinants and mechanisms contributing to diabetic sensorimotor polyneuropathy (DSPN) remain unclear. Since neuroinflammation and altered nerve regeneration have been implicated in the pathogenesis of both DSPN and neuropathic pain, we hypothesized that the corresponding biomarkers could be associated with DSPN in general and could have the potential to discriminate between the painful and painless DSPN entities.

METHODS

In a cross-sectional study using multimarker proximity extension assay technology we assessed 71 serum biomarkers including cytokines, chemokines, growth factors, receptors, and others in patients with type 2 diabetes with DSPN (DSPN+) (n=304) or without DSPN (DSPN-) (n=158) and persons with normal glucose tolerance (NGT) without polyneuropathy (n=354).

RESULTS

After adjustment for multiple testing and sex, age, body mass index, HbA1c, and smoking, the serum levels of 17 biomarkers (four cytokines, five chemokines, four growth factors, two receptors, two miscellaneous) were lower in DSPN+ than in DSPN- and NGT. In DSPN+, six of these biomarkers were associated with peripheral nerve function. The concentrations of 15 other biomarkers differed between NGT and both DSPN+ and DSPN-, but not between DSPN+ and DSPN-. No differences in biomarker levels were found between patients with painful (n=164) and painless DSPN (n=140).

CONCLUSIONS

Deficits in systemic cytokines, chemokines, and growth factors promoting nerve regeneration in patients with type 2 diabetes are linked to polyneuropathy in general but not specifically to the painful or painless entity.

TRIAL REGISTRATION NUMBER

NCT02243475.

Diagnostic Significance of Serum Levels of Nerve Growth Factor and Brain Derived Neurotrophic Factor in Diabetic Peripheral Neuropathy

Background

Our study aimed to explore the levels of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) in healthy participants, type 2 diabetes mellitus (T2DM) patients, and diabetic peripheral neuropathy (DPN) patients in order to find their effects on DPN.

Material/Methods

The clinical data of 110 healthy participants (age: 57.3±8.2 year, height: 165.4±5.5 cm, weight: 64.1±7.5 kg), 83 T2DM patients (age: 56.5±7.9 year, height: 164.8±6.2 cm, and weight: 63.6±6.6 kg), and 65 DPN patients (age: 58.2±7.3 year, height: 166.7±6.7 cm, weight: 63.1±5.8 kg) were observed. ELISA was applied to detect serum NGF and BDNF levels. Receiver operating characteristic (ROC) curve analysis was performed to evaluate diagnostic value of serum NGF and BDNF levels in DPN. Logistic regression analysis was performed to analyze risk factors for DPN.

Results

Serum NGF and BDNF levels decreased most in DPN patients. Subsequently, we determined that serum NGF and BDNF levels were correlated with: the course of disease for patients, fasting C-peptide (FCP), 2-hour postprandial C-peptide level (2-h PCP), glycosylated hemoglobin level (HbAlc), and 24-hour urinary microalbumin excretion (24-h UME). ROC curve analysis identified high sensitivity, specificity, and accuracy of NGF and BDNF levels on DPN. Serum levels of NGF and BDNF, course of disease, 2-h PCP level, and postprandial blood glucose level were determined to be risk factors for DPN.

Conclusions

Our study highlights that serum levels of NGF and BDNF might be associated with the occurrence and development of DPN.

Safflower Extract and Aceglutamide Injection Promoting Recovery of Peripheral Innervations via Vascular Endothelial Growth Factor-B Signaling in Diabetic Mice

Background:

Safflower extract and aceglutamide (SA) has been used clinically for the treatment of cerebrovascular diseases such as cerebral embolism, hemorrhage, and mental deterioration. This study aimed to investigate the effect and mechanism of SA injection in the recovery of peripheral innervations of diabetic mice.

Methods:

The C57BL/6 male mice were divided into four groups: normal control group (n = 44), diabetic group (n = 44), diabetic + SA group (diabetic mice treated with SA injection, n = 44), and diabetic + SA + vascular endothelial growth factor receptor (VEGFR)1-BL group (diabetic mice treated with SA injection and VEGFR 1 blocking antibody n = 24). The streptozotocin-induced diabetic mice model and injured peripheral nerve mice model were built. The mice with injured peripheral nerves were intraperitonealy administered with SA injection for successive 21 days. The corneal sensitivity, number of corneal nerve fibers, and contents of vascular endothelial growth factor (VEGF)-B and various neurotrophic factors such as nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF) in corneal tissue of four groups were observed.

Results:

The diabetic group showed decreased number of corneal nerve fibers, compared with the control group (P = 0.002). And compared with the diabetic group, the diabetic + SA group showed a significant increase in the number of nerve fibers (P = 0.024) and the contents of VEGF-B, NGF, and GDNF in the cornea (all P < 0.05). However, when the diabetic mice were treated with the blocking antibodies specialized for VEGF-B receptor, the neutralization of VEGFR-1 completely abolished the increased expression of NGF and GDNF stimulated by SA injection.

Conclusions:

SA injection could reduce the nerve injury caused by diabetic peripheral neuropathy, and its protective effect might be associated with the promotion of the expressions of VEGF-B, NGF, and GDNF.

Neuropathic Pain and Nerve Growth Factor in Chemotherapy-Induced Peripheral Neuropathy: Prospective Clinical-Pathological Study

CONTEXT

Neuropathic pain can be present in patients developing chemotherapy-induced peripheral neuropathy (CIPN). Nerve growth factor (NGF) is trophic to small sensory fibers and regulates nociception.

OBJECTIVES

We investigated the changes in serum NGF and intraepidermal nerve fiber density in skin biopsies of cancer patients receiving neurotoxic chemotherapy in a single-center prospective observational study.

METHODS

Patients were evaluated before and after chemotherapy administration. CIPN was graded with Total Neuropathy Score^©, nerve conduction studies, and National Common Institute-Common Toxicity Criteria for Adverse Events scale. Neuropathic pain was defined according to the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-CIPN20 questionnaire.

RESULTS

Neuropathic pain was present in 13 of 60 patients (21%), who reported shooting or burning pain in the hands (n = 9) and the feet (n = 12). Patients displaying painful CIPN presented higher NGF after treatment compared with patients with painless or absent CIPN (8.7 ± 11.9 vs. 2.5 ± 1.4 pg/mL, P = 0.016). The change of NGF significantly correlated with neuropathic pain. Patients with painful CIPN did not show significant loss of IEFND compared with patients with painless or absent CIPN (6.16 ± 3.86 vs. 8.37 ± 4.82, P = 0.12). No correlation between IEFND and NGF was observed.

CONCLUSION

Serum NGF increases in cancer patients receiving taxane or platinum with painful CIPN, suggesting that it might be a potential biomarker of the presence and severity of neuropathic pain in this population. Long-term comprehensive studies to better define the course of NGF in relation with neurological outcomes would be helpful in the further design of therapies for CIPN-related neuropathic pain.

Neuropathy-specific alterations in a Mexican population of diabetic patients

Background

Neuropathy is one of the major complications of type 2 diabetes mellitus. Our first aim was to determine the clinical characteristics of a population of diabetic patients with different types of neuropathy. Our next goal was to characterize the cytokine profile (IL-6 and IL-10), nerve growth factor (NGF) and circulating cell-adhesion molecules in these patients. Finally, we aimed to compare the renal function among the groups of neuropathic patients.

Methods

In a cross-sectional study, we included 217 diabetic patients classified in three groups: sensory polyneuropathy with hypoesthesia (DS_hP) or hyperesthesia (DS_HP), and motor neuropathy (DMN). Two control groups were included: one of 26 diabetic non-neuropathic patients (DNN), and the other of 375 non-diabetic (ND) healthy subjects. The participants were attending to the Mexican Institute of Social Security.

Results

The circulating levels of NGF were significantly lower in diabetic patients, compared to healthy subjects. The range of IL-6 and IL-10 levels in neuropathic patients was higher than the control groups; however, several samples yielded null measurements. Neuropathic patients also showed increased circulating levels of the adhesion molecules ICAM, VCAM, and E-Selectin, compared to the ND group. Moreover, neuropathic patients showed reduced glomerular filtration rates compared to healthy subjects (82–103 ml/min per 1.73 m², data as range from 25th–75th percentiles), especially in the group with DMN (45–76 ml/min per 1.73 m²).

Conclusions

Some particular alterations in neuropathic patients included -but were not limited to- changes in circulating NGF, cell adhesion molecules, inflammation, and the worsening of the renal function. This study supports the need for further clinical surveillance and interventions considering a neuropathy-related basis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-017-0939-6) contains supplementary material, which is available to authorized users.

Neurotrophin Signaling Is Required for Glucose-Induced Insulin Secretion

Insulin secretion by pancreatic islet β cells is critical for glucose homeostasis, and a blunted β cell secretory response is an early deficit in type 2 diabetes. Here, we uncover a regulatory mechanism by which glucose recruits vascular-derived neurotrophins to control insulin secretion. Nerve growth factor (NGF), a classical trophic factor for nerve cells, is expressed in pancreatic vasculature while its TrkA receptor is localized to islet β cells. High glucose rapidly enhances NGF secretion and increases TrkA phosphorylation in mouse and human islets. Tissue-specific deletion of NGF or TrkA, or acute disruption of TrkA signaling, impairs glucose tolerance and insulin secretion in mice. We show that internalized TrkA receptors promote insulin granule exocytosis via F-actin reorganization. Furthermore, NGF treatment augments glucose-induced insulin secretion in human islets. These findings reveal a non-neuronal role for neurotrophins and identify a new regulatory pathway in insulin secretion that can be targeted to ameliorate β cell dysfunction.

A systematic review on the impact of diabetes mellitus on the ocular surface

Diabetes mellitus is associated with extensive morbidity and mortality in any human community. It is well understood that the burden of diabetes is attributed to chronic progressive damage in major end-organs, but it is underappreciated that the most superficial and transparent organ affected by diabetes is the cornea. Different corneal components (epithelium, nerves, immune cells and endothelium) underpin specific systemic complications of diabetes. Just as diabetic retinopathy is a marker of more generalized microvascular disease, corneal nerve changes can predict peripheral and autonomic neuropathy, providing a window of opportunity for early treatment. In addition, alterations of immune cells in corneas suggest an inflammatory component in diabetic complications. Furthermore, impaired corneal epithelial wound healing may also imply more widespread disease. The non-invasiveness and improvement in imaging technology facilitates the emergence of new screening tools. Systemic control of diabetes can improve ocular surface health, possibly aided by anti-inflammatory and vasoprotective agents.

Fine tuning of insulin secretion by release of nerve growth factor from mouse and human islet β-cells

Nerve growth factor (NGF) is a protein required for neuronal development that also has regulatory functions in non-neuronal cells. Both NGF and its membrane receptors trkA and p75(NTR) are expressed by islet β-cells. In this study we dynamically profiled NGF secretion from islets and used selective trkA and p75(NTR) inhibitors to identify the role of endogenous NGF in β-cell stimulus-secretion coupling. NGF secretion from mouse islets was transient and did not accompany the sustained second phase of glucose-induced insulin secretion. Despite being present in human islets, NGF was not released at sufficient levels to be quantified. Inhibition of NGF signaling through trkA and p75(NTR) increased basal insulin secretion from both human and mouse islets, but impaired glucose-stimulated insulin secretion. These data support a role for islet NGF in fine-tuning insulin secretion, to both maintain a low basal level of insulin output and contribute to the biphasic secretory response to glucose.

Therapeutic targeting of diabetic retinal neuropathy as a strategy in preventing diabetic retinopathy

Diabetes causes a panretinal neurodegeneration herein termed diabetic retinal neuropathy, which manifests in the retina early and progresses throughout the disease. Clinical manifestations include changes in the ERG, perimetry, dark adaptation, contrast sensitivity and colour vision which correlate with laboratory findings of thinning of the retinal neuronal layers, increased apoptosis in neurons and activation of glial cells. Possible mechanisms include oxidative stress, neuronal AGE accumulation, altered balance of neurotrophic factors and loss of mitohormesis. Retinal neural damage precedes and is a biologically plausible cause of retinal vasculopathy later in diabetes, and this review suggests that strategies to target it directly could prevent diabetes induced blindness. The efficacy of fenofibrate in reducing retinopathy progression provides a possible proof of concept for this approach. Strategies which may target diabetic retinal neuropathy include reducing retinal metabolic demand, improving mitochondrial function with AMPK and Sirt1 activators or providing neurotrophic support with neurotrophic supplementation.

Imbalance of the Nerve Growth Factor and Its Precursor: Implication in Diabetic Retinopathy

Diabetic retinopathy is the leading cause of blindness in working age in US and worldwide. Neurotrophins including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) are known to be essential for growth, differentiation and survival of neurons in the developing and mature retina. Nevertheless, a growing body of evidence supports an emerging role of neurotrophins in retinal diseases and in particular, diabetic retinopathy. Neurotrophins are initially synthesized in a pro-form and undergo proteolytic cleavage to produce the mature form that activates two distinctive receptors, the tyrosine kinase tropomycin receptor (Trk) and, to lesser extent, the common low affinity p75 neurotrophin receptor (p75^NTR). Despite tight glycemic and metabolic control, many diabetic patients continue to experience progressive retinal damage. Understanding the molecular events involved in diabetic retinopathy is extremely important to identify novel therapeutic strategies to halt the disease progression. Diabetes induces imbalance in neurotrophins by increasing its proform, which is associated with upregulation of the p75^NTR receptor in the retina. A growing body of evidence supports a link between the imbalance of pro-neurotrophins and early retinal inflammation, neuro-and microvascular degeneration. Therefore, examining changes in the levels of neurotrophins and its receptors might provide a therapeutically beneficial target to combat disease progression in diabetic patients. This commentary aims to highlight the impact of diabetes-impaired balance of neurotrophins and in particular, the NGF and its receptors; TrkA and p75^NTR in the pathology of DR.

Molecular mechanisms of diabetic retinopathy: potential therapeutic targets

Diabetic retinopathy (DR) is the leading cause of blindness in working-age adults in United States. Research indicates an association between oxidative stress and the development of diabetes complications. However, clinical trials with general antioxidants have failed to prove effective in diabetic patients. Mounting evidence from experimental studies that continue to elucidate the damaging effects of oxidative stress and inflammation in both vascular and neural retina suggest its critical role in the pathogenesis of DR. This review will outline the current management of DR as well as present potential experimental therapeutic interventions, focusing on molecules that link oxidative stress to inflammation to provide potential therapeutic targets for treatment or prevention of DR. Understanding the biochemical changes and the molecular events under diabetic conditions could provide new effective therapeutic tools to combat the disease.

Nerve growth factor rescues diabetic mice heart after ischemia/reperfusion injury via up-regulation of the TRPV1 receptor

AIMS

Nerve growth factor (NGF), a member of the neurotrophin family, plays an essential role in diabetic neuropathy and ischemic heart disease. In the present study, we explored the potential role of NGF and the involvement of TRPV1 receptor in isolated diabetic mouse hearts following ischemia/reperfusion (I/R) injury.

METHODS

Adenovirus-mediated NGF gene delivery was performed on diabetic and sham hearts 8weeks after streptozotocin treatment. The sciatic nerve conduction velocity was recorded using a biological signal acquisition system. Forty-eight hours after heart surgery, mice were subjected to I/R injury using a Langendorff system. Several cardiac parameters and the expression of associated molecules were analyzed during the experiment.

RESULTS

The sciatic nerve conduction velocity was reduced in diabetic mice compared with that in control mice. Decreased expression of NGF, TRPV1, and the downstream neurotransmitters CGRP and SP was observed in the diabetic hearts. Adenovirus-mediated NGF overexpression reversed the reduction in TRPV1 and downstream neuropeptides, resulting in improved cardiac recovery post-I/R injury in diabetic hearts. The protective effect of NGF was abolished by CGRP8-37 (a selective CGRP antagonist), while it was preserved by low-dose capsaicin.

CONCLUSIONS

The NGF-induced up-regulation of TRPV1 via the increased synthesis and release of endogenous CGRP leads to improved cardiac performance in I/R-injured diabetic heart.

Imbalance of the nerve growth factor and its precursor as a potential biomarker for diabetic retinopathy

Our previous studies have demonstrated that diabetes-induced oxidative stress alters homeostasis of retinal nerve growth factor (NGF) resulting in accumulation of its precursor, proNGF, at the expense of NGF which plays a critical role in preserving neuronal and retinal function. This imbalance coincided with retinal damage in experimental diabetes. Here we test the hypothesis that alteration of proNGF and NGF levels observed in retina and vitreous will be mirrored in serum of diabetic patients. Blood and vitreous samples were collected from patients (diabetic and nondiabetic) undergoing vitrectomy at Georgia Regents University under approved IRB. Levels of proNGF, NGF, and p75^NTR shedding were detected using Western blot analysis. MMP-7 activity was also assayed. Diabetes-induced proNGF expression and impaired NGF expression were observed in vitreous and serum. Vitreous and sera from diabetic patients (n = 11) showed significant 40.8-fold and 3.6-fold increases, respectively, compared to nondiabetics (n = 9). In contrast, vitreous and sera from diabetic patients showed significant 44% and 64% reductions in NGF levels, respectively, compared to nondiabetics. ProNGF to NGF ratios showed significant correlation between vitreous and serum. Further characterization of diabetes-induced imbalance in the proNGF to NGF ratio will facilitate its utility as an early biomarker for diabetic complications.

Exploring the role of tanezumab as a novel treatment for the relief of neuropathic pain

OBJECTIVE

Evaluate efficacy and safety of tanezumab, a humanized monoclonal antibody against nerve growth factor, in neuropathic pain.

DESIGN

Two randomized controlled trials.

SUBJECTS

Patients with pain due to diabetic peripheral neuropathy (DPN) or postherpetic neuralgia (PHN).

METHODS

In the DPN study, patients received subcutaneous tanezumab 20 mg or placebo on Day 1 and Week 8. Evaluations included change from baseline in average DPN pain (primary endpoint), Patient's Global Assessment of DPN, and safety (including neuropathy assessments). Due to a partial clinical hold limiting enrollment and treatment duration, the prespecified landmark analysis was modified post hoc from Week 16 to Week 8. In the PHN study, patients received intravenous tanezumab 50 μg/kg, tanezumab 200 μg/kg, or placebo on Day 1. Evaluations included change from baseline in average daily pain (primary endpoint), Brief Pain Inventory-short form, Patient's Global Assessment of pain from PHN, and safety.

RESULTS

Mean DPN pain reduction from baseline to Week 8 was greater with tanezumab vs placebo (P = 0.009); differences in Patient's Global Assessment of DPN were not significant (P > 0.05). Neither tanezumab dose resulted in significant differences vs placebo in efficacy in PHN (P > 0.05), although tanezumab 200 μg/kg provided some benefit. Neuropathy assessments showed no meaningful changes.

CONCLUSIONS

Tanezumab provided effective pain reduction in DPN. In PHN, only the highest tanezumab dose reduced pain; treatment differences were not significant. No new safety concerns were observed despite preexisting neuropathy.

Corneal nerves in health and disease

Corneal nerves are responsible for the sensations of touch, pain, and temperature and play an important role in the blink reflex, wound healing, and tear production and secretion. Corneal nerve dysfunction is a frequent feature of diseases that cause opacities and result in corneal blindness. Corneal opacities rank as the second most frequent cause of blindness. Technological advances in in vivo corneal nerve imaging, such as optical coherence tomography and confocal scanning, have generated new knowledge regarding the phenomenological events that occur during reinnervation of the cornea following disease, injury, or surgery. The recent availability of transgenic neurofluorescent murine models has stimulated the search for molecular modulators of corneal nerve regeneration. New evidence suggests that neuroregenerative and inflammatory pathways in the cornea are intertwined. Evidence-based treatment of neurotrophic corneal diseases includes using neuroregenerative (blood component-based and neurotrophic factors), neuroprotective, and ensconcing (bandage contact lens and amniotic membrane) strategies and avoiding anti-inflammatory therapies, such as cyclosporine and corticosteroids.

Mechanisms of disease: role of neurotrophins in diabetes and diabetic neuropathy

Neuropathy is an insidious and devastating consequence of diabetes. Early studies provided a strong rationale for deficient neurotrophin support in the pathogenesis of diabetic neuropathy in a number of critical tissues and organs. It has now been over a decade since the first failed human neurotrophin supplementation clinical trials, but mounting evidence still implicates these trophic factors in diabetic neuropathy. Since then, tremendous advances have been made in our understanding of the complexities of neurotrophin signaling and processing and how the diabetic milieu might impact this. This in turn changes both our perception of how the altered trophic environment contributes to the etiology of diabetic neuropathy and the design of future neurotrophin therapeutic interventions. This chapter summarizes some of these findings and attempts to integrate neurotrophin actions on the nervous system with an increasing appreciation of their role in the regulation of metabolic processes in diabetes that impact the diabetic neuropathic state.

Assessing corneal nerve structure and function in diabetic neuropathy

The accurate detection and quantification of human diabetic peripheral neuropathy are important to define at-risk patients, anticipate deterioration and assess new therapies. Two emerging ophthalmic techniques, namely, corneal confocal microscopy and corneal aesthesiometry, demonstrate the ability to diagnose, quantify severity and assess therapeutic benefit in diabetic peripheral neuropathy. Corneal confocal microscopy allows quantification of corneal nerve morphology and non-contact corneal aesthesiometry assesses corneal sensitivity. The present review provides a detailed critique of the rationale, practical application in terms of the instruments used to capture images and the basis on which images are interpreted and analysed. We also critically evaluate how these two new non-invasive ophthalmic tests can be deployed to diagnose diabetic and other peripheral neuropathies.

The effect of ubiquinone in diabetic polyneuropathy: a randomized double-blind placebo-controlled study

INTRODUCTION

Diabetic polyneuropathy aetiology is based on oxidative stress generation due to production of reactive oxygen species. Ubiquinone is reduced to ubiquinol and redistributed into lipoproteins, possibly to protect them from oxidation.

AIMS

To evaluate the impact of oral ubiquinone in diabetic polyneuropathy, and the role of lipid peroxidation (LPO) and nerve growth factor (NGF-β).

METHODS

We conducted a double-blind, placebo-controlled clinical trial, patients were randomized to ubiquinone (400 mg) or placebo daily for 12 weeks. Main outcomes were clinical scores, nerve conduction studies, LPO, NGF-β and safety.

RESULTS

Twenty four patients on experimental group and twenty five on control group met the inclusion criteria (mean age 56 years, 22% male and 78% female, mean evolution of type 2 diabetes mellitus 10.7 years). Significant improvement on experimental vs control group was found in neuropathy symptoms score (from 2.5 ± 0.7 to 1 ± 0.8, p<0.001), neuropathy impairment score (5.5 ± 4 to 3.1 ± 2.6, p<0.001), sural sensory nerve amplitude (13.0 ± 6.1 to 15.8 ± 5.1 μV, p=0.049), peroneal motor nerve conduction velocity (39.7 ± 5.0 to 47.8 ± 4.9 m/s, p=0.047), and ulnar motor nerve conduction velocity (48.8 ± 6.8 to 54.5 ± 6.1m/s, p=0.046). There was a significant reduction of LPO in subjects treated with ubiquinone vs placebo (16.7 ± 8.6 and 23.2 ± 15.8 nmol/mL, respectively) with p<0.05, and NGF-β did not change (control 66.5 ± 26.7 vs. experimental 66.8 ± 28.4 pg/mL, p=0.856). No drug-related adverse reactions were reported.

CONCLUSIONS

Twelve weeks treatment with ubiquinone improves clinical outcomes and nerve conduction parameters of diabetic polyneuropathy; furthermore, it reduces oxidative stress without significant adverse events.

COMP-angiopoietin-1 recovers molecular biomarkers of neuropathy and improves vascularisation in sciatic nerve of ob/ob mice

BACKGROUND

Leptin-deficient ob/ob mice are a model of type 2 diabetes induced peripheral neuropathy. Ob/ob mice exhibit obesity, insulin resistance, hyperglycaemia, and alterations of peripheral nerve fibres and endoneural microvessels. Here we test the hypothesis that cartilage oligomeric matrix protein (COMP)-Ang-1, a soluble and stabile form of Ang-1 which promotes angiogenesis and nerve growth, improves regeneration of nerve fibres and endoneural microvessels in ob/ob mice.

METHODS AND FINDINGS

COMP-Ang-1 (100 ng/ml) or NaCl were intraperitoneally (i.p.) injected into male (N = 184), 3-month old, ob/ob or ob/+ mice for 7 and 21 days. We measured expression of Nf68, GAP43, Cx32, Cx26, Cx43, and TNFα in sciatic nerves using Western blot analysis. To investigate the inflammation in sciatic nerves, numbers of macrophages and T-cells were counted after immunofluorescence staining. In ultrathin section, number of myelinated/non-mylinated nerve fibers, g-ratio, the thickness of Schwann cell basal lamina and microvessel endothelium were investigated. Endoneural microvessels were reconstructed with intracardial FITC injection. Treatment with COMP-Ang-1 over 21 days significantly reduced fasting blood glucose and plasma cholesterol concentrations compared to saline treated ob/ob mice. In addition, COMP-Ang-1 treatment: 1) up-regulated expression of Nf68 and GAP43; 2) improved expression of gap junction proteins including connexin 32 and 26; 3) suppressed the expression of TNFα and Cx43 and 4) led to decreased macrophage and T-cell infiltration in sciatic nerve of ob/ob mice. The significant changes of sciatic nerve ultrastructure were not observed after 21-day long COMP-Ang-1 treatment. COMP-Ang-1 treated ob/ob mice displayed regeneration of small-diameter endoneural microvessels. Effects of COMP-Ang-1 corresponded to increased phosphorylation of Akt and p38 MAPK upon Tie-2 receptor.

CONCLUSIONS

COMP-Ang-1 recovers molecular biomarkers of neuropathy, promotes angiogenesis and suppresses inflammation in sciatic nerves of ob/ob mice suggesting COMP-Ang-1 as novel treatment option to improve morphologic and protein expression changes associated with diabetic neuropathy.

Small fibre neuropathy: role in the diagnosis of diabetic sensorimotor polyneuropathy

Small fibres constitute 70-90% of peripheral nerve fibres and regulate several key functions such as tissue blood flow, temperature and pain perception as well as sweating, all of which are highly relevant to the clinical presentation and adverse outcomes associated with foot ulcerations in patients with diabetes. Recent studies demonstrated significant abnormalities in the small fibres in subjects with impaired glucose tolerance and diabetes, despite normal electrophysiology, suggesting that the earliest nerve fibre damage is to the small fibres. Unfortunately, guidelines and consensus statements focus on large fibres and continue to advocate electrophysiology as a diagnostic modality and as a primary end point for the assessment of therapeutic benefit. (In part, this reflects the difficulties in quantifying small fibre dysfunction and damage.) We have therefore critically assessed currently available techniques that measure small fibre dysfunction in diabetic neuropathy, using quantitative sensory and sudomotor testing. We have assessed the role of identifying structural damage by quantifying intraepidermal nerve fibre density in skin biopsies and corneal nerve morphology using corneal confocal microscopy. Finally, we propose a definition for diabetic neuropathy that incorporates small fibre damage.

Impaired nerve growth factor homeostasis in patients with bipolar disorder

OBJECTIVE

Neuro-trophins are critically involved in neuro-plasticity, the impairment of which is a major role-player in bipolar disorder (BD), and their altered levels have been recently advocated in the patho-physiology of this affective malady. The aim of this study, therefore, was to evaluate the plasma levels of nerve growth factor (NGF) in BD patients in comparison with control subjects.

METHODS

Forty-nine BD type-I individuals (30 in mania and 19 in euthymia) and 36 healthy controls were assessed by Mini-plus, Young mania and Hamilton depression rating scales. NGF levels were detected by ELISA.

RESULTS

Plasma NGF concentrations were decreased in BD patients when compared to that seen with controls. BD individuals in mania had lower NGF levels than euthymic patients or controls. NGF levels were negatively correlated with the severity of mania.

CONCLUSIONS

This is the first study to evaluate NGF levels in BD patients, providing further support to the hypothesis of impaired neuro-plasticity in BD. These data also suggest that NGF measurement could be used for the biological marker for manic state.