Brain-derived neurotrophic factor modulates glucagon secretion from pancreatic alpha cells: its contribution to glucose metabolism

Immunolocalization of Two Neurotrophins, NGF and BDNF, in the Pancreas of the South American Sea Lion Otaria flavescens and Bottlenose Dolphin Tursiops truncatus

In this study, we have investigated the immunolocalization of NGF (Nerve Growth Factor) and BDNF (Brain-Derived Neurotrophic Factor) in the pancreas of two species of marine mammals: Tursiops truncatus (common bottlenose dolphin), belonging to the order of the Artiodactyla, and Otaria flavescens (South American sea lion), belonging to the order of the Carnivora. Our results demonstrated a significant presence of NGF and BDNF in the pancreas of both species with a wide distribution pattern observed in the exocrine and endocrine components. We identified some differences that can be attributed to the different feeding habits of the two species, which possess a different morphological organization of the digestive system. Altogether, these preliminary observations open new perspectives on the function of neurotrophins and the adaptive mechanisms of marine mammals in the aquatic environment, suggesting potential parallels between the physiology of marine and terrestrial mammals.

Metabolomics in Depression: What We Learn from Preclinical and Clinical Evidences

Depression is one of the predominant common mental illnesses that affects millions of people of all ages worldwide. Random mood changes, loss of interest in routine activities, and prevalent unpleasant senses often characterize this common depreciated mental illness. Subjects with depressive disorders have a likelihood of developing cardiovascular complications, diabesity, and stroke. The exact genesis and pathogenesis of this disease are still questionable. A significant proportion of subjects with clinical depression display inadequate response to antidepressant therapies. Hence, clinicians often face challenges in predicting the treatment response. Emerging reports have indicated the association of depression with metabolic alterations. Metabolomics is one of the promising approaches that can offer fresh perspectives into the diagnosis, treatment, and prognosis of depression at the metabolic level. Despite numerous studies exploring metabolite profiles post-pharmacological interventions, a quantitative understanding of consistently altered metabolites is not yet established. The article gives a brief discussion on different biomarkers in depression and the degree to which biomarkers can improve treatment outcomes. In this review article, we have systemically reviewed the role of metabolomics in depression along with current challenges and future perspectives.

Targeting BDNF with acupuncture: A novel integrated strategy for diabetes and depression comorbidity

Diabetes and depression are common comorbid conditions that impose a substantial health burden. Acupuncture may effectively improve symptoms in patients with diabetes and depression, but the underlying mechanism remains unclear. Brain-derived neurotrophic factor (BDNF) may play a vital role in the effects of acupuncture on diabetes and depression comorbidity. This review summarizes the potential role of BDNF in acupuncture for diabetes and depression comorbidity. BDNF appears to exert its effects via the BDNF-TrkB-ERK-CREB signaling pathway. BDNF levels are reduced in diabetes and depression, and acupuncture may increase BDNF expression, improving symptoms and glycemic control. High-quality research is needed to validate the efficacy of acupuncture for diabetes and depression comorbidity. Randomized controlled trials and mechanistic studies should investigate the BDNF pathway and other potential mechanisms. Improved understanding of the links between diabetes, depression and acupuncture may enable targeted and individualized patient care. Earlier diagnosis and management of diabetes and depression comorbidity should also be a priority.

A Supportive Role of Mesenchymal Stem Cells on Insulin-Producing Langerhans Islets with a Specific Emphasis on The Secretome

Type 1 Diabetes (T1D) is a chronic autoimmune disease characterized by a gradual destruction of insulin-producing β-cells in the endocrine pancreas due to innate and specific immune responses, leading to impaired glucose homeostasis. T1D patients usually require regular insulin injections after meals to maintain normal serum glucose levels. In severe cases, pancreas or Langerhans islet transplantation can assist in reaching a sufficient β-mass to normalize glucose homeostasis. The latter procedure is limited because of low donor availability, high islet loss, and immune rejection. There is still a need to develop new technologies to improve islet survival and implantation and to keep the islets functional. Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells with high plasticity that can support human pancreatic islet function both in vitro and in vivo and islet co-transplantation with MSCs is more effective than islet transplantation alone in attenuating diabetes progression. The beneficial effect of MSCs on islet function is due to a combined effect on angiogenesis, suppression of immune responses, and secretion of growth factors essential for islet survival and function. In this review, various aspects of MSCs related to islet function and diabetes are described.

Optic Nerve Regeneration in Diabetic Retinopathy: Potentials and Challenges Ahead

Diabetic retinopathy (DR), the most common microvascular compilation of diabetes, is the leading cause of vision loss and blindness worldwide. Recent studies indicate that retinal neuron impairment occurs before any noticeable vascular changes in DR, and retinal ganglion cell (RGC) degeneration is one of the earliest signs. Axons of RGCs have little capacity to regenerate after injury, clinically leading the visual functional defects to become irreversible. In the past two decades, tremendous progress has been achieved to enable RGC axon regeneration in animal models of optic nerve injury, which holds promise for neural repair and visual restoration in DR. This review summarizes these advances and discusses the potential and challenges for developing optic nerve regeneration strategies treating DR.

DeepVelo: Single-cell transcriptomic deep velocity field learning with neural ordinary differential equations

Recent advances in single-cell sequencing technologies have provided unprecedented opportunities to measure the gene expression profile and RNA velocity of individual cells. However, modeling transcriptional dynamics is computationally challenging because of the high-dimensional, sparse nature of the single-cell gene expression measurements and the nonlinear regulatory relationships. Here, we present DeepVelo, a neural network-based ordinary differential equation that can model complex transcriptome dynamics by describing continuous-time gene expression changes within individual cells. We apply DeepVelo to public datasets from different sequencing platforms to (i) formulate transcriptome dynamics on different time scales, (ii) measure the instability of cell states, and (iii) identify developmental driver genes via perturbation analysis. Benchmarking against the state-of-the-art methods shows that DeepVelo can learn a more accurate representation of the velocity field. Furthermore, our perturbation studies reveal that single-cell dynamical systems could exhibit chaotic properties. In summary, DeepVelo allows data-driven discoveries of differential equations that delineate single-cell transcriptome dynamics.

Network Pharmacology and ­Experimental Analyses of the Mechanism of Analgesic and Glucose Intolerance Through Glucocorticoid Signaling in C57 Mice Treated with Water Extract of Prunella vulgaris L. Spica

The aim of this study was to confirm the anti-inflammatory effect and explore the adverse effects and underlying mechanisms of Prunella vulgaris L., which has been extensively used for hundreds of years in East Asia. Network pharmacology studies predicted that glucocorticoids (GCs), GC-targeting molecules, and brain-derived neurotrophic factor (BDNF) were intensively involved in the anti-inflammation and glucose intolerance. To attest the effects and underlying mechanisms, C57 male mice were randomly divided into 5 groups, control (C), dexamethasone (Dex), water extract of P. vulgaris (PE 35 or 70 mg), and PE (70 mg) + mifepristone (PEM). After a 3-week treatment, acetic acid-induced writhing and hot plate tests confirmed the peripheral and central analgesic effects, respectively. Plasma GCs and BDNF were significantly increased. Coincidently, plasma pro-inflammatory cytokines, including IL1β, IL6, and IL10, were decreased by PE treatment, which were blocked by the application of mifepristone ( P < 0.5). Western blots confirmed GC receptor (GR) translocation, and decreased cyclooxygenase 2 in the lumber spine by PE treatment. Food intake was impeded after a 4-week PE treatment, but the ratio of bodyweight gain to food intake was increased in a time-dependent manner. An intraperitoneal glucose tolerance test disclosed that PE treatment impaired glucose disposal in mice. Quantitative polymerase chain reaction (PCR) showed that hepatic GC-responsive genes such as GC-induced leucine zipper protein and glucose-6-phosphatase catalytic subunit 1 were up-regulated, and hypothalamic neuropeptide Y and agouti-related protein expressions were decreased by PE treatment. Hypothalamic BDNF was up-regulated, whereas hepatic BDNF was down-regulated. The regulation of these genes by PE was reversed by mifepristone administration. In conclusion, PE treatment plays analgesic and glucose regulation roles simultaneously through GC-induced signaling pathways, and P. vulgaris may provide a natural ligand of GR for the treatment of inflammation with glucose dysregulation.

Methylation Status of Exon IV of the Brain-Derived Neurotrophic Factor (BDNF)-Encoding Gene in Patients with Non-Diabetic Hyperglycaemia (NDH) before and after a Lifestyle Intervention

BDNF signalling in hypothalamic neuronal circuits is thought to regulate mammalian food intake. In light of this, we investigated how a lifestyle intervention influenced serum levels and DNA methylation of BDNF gene in fat tissue and buffy coat of NDH individuals. In total, 20 participants underwent anthropometric measurements/fasting blood tests and adipose tissue biopsy pre-/post-lifestyle (6 months) intervention. DNA was extracted from adipose tissue and buffy coat, bisulphite converted, and pyrosequencing was used to determine methylation levels in exon IV of the BDNF gene. RNA was extracted from buffy coat for gene expression analysis and serum BDNF levels were measured by ELISA. No differences were found in BDNF serum levels, but buffy coat mean BDNF gene methylation decreased post-intervention. There were correlations between BDNF serum levels and/or methylation and cardiometabolic markers. (i) Pre-intervention: for BDNF methylation, we found positive correlations between mean methylation in fat tissue and waist-hip ratio, and negative correlations between mean methylation in buffy coat and weight. (ii) Post-intervention: we found correlations between BDNF mean methylation in buffy coat and HbA1c, BDNF methylation in buffy coat and circulating IGFBP-2, and BDNF serum and insulin. Higher BDNF % methylation levels are known to reduce BNDF expression. The fall in buffy coat mean BDNF methylation plus the association between lower BDNF methylation (so potentially higher BDNF) and higher HbA1c and serum IGFBP-2 (as a marker of insulin sensitivity) and between lower serum BDNF and higher circulating insulin are evidence for the degree of BDNF gene methylation being implicated in insulinisation and glucose homeostasis, particularly after lifestyle change in NDH individuals.

The Pleiotropic Potential of BDNF beyond Neurons: Implication for a Healthy Mind in a Healthy Body

Brain-derived neurotrophic factor (BDNF) represents one of the most widely studied neurotrophins because of the many mechanisms in which it is involved. Among these, a growing body of evidence indicates BDNF as a pleiotropic signaling molecule and unveils non-negligible implications in the regulation of energy balance. BDNF and its receptor are extensively expressed in the hypothalamus, regions where peripheral signals, associated with feeding control and metabolism activation, and are integrated to elaborate anorexigenic and orexigenic effects. Thus, BDNF coordinates adaptive responses to fluctuations in energy intake and expenditure, connecting the central nervous system with peripheral tissues, including muscle, liver, and the adipose tissue in a complex operational network. This review discusses the latest literature dealing with the involvement of BDNF in the maintenance of energy balance. We have focused on the physiological and molecular mechanisms by which BDNF: (I) controls the mitochondrial function and dynamics; (II) influences thermogenesis and tissue differentiation; (III) mediates the effects of exercise on cognitive functions; and (IV) modulates insulin sensitivity and glucose transport at the cellular level. Deepening the understanding of the mechanisms exploited to maintain energy homeostasis will lay the groundwork for the development of novel therapeutical approaches to help people to maintain a healthy mind in a healthy body.

A systematic review and meta-analysis of association between brain-derived neurotrophic factor and type 2 diabetes and glycemic profile

Several epidemiologic studies have evaluated the relation between serum/plasma brain-derived neurotrophic factor (BDNF) levels and glycemic parameters, but the findings were conflicting. We performed a systematic review and meta-analysis to compare circulating BDNF levels in individuals with type 2 diabetes (T2D) or other glycemic disorders with healthy controls and to evaluate correlation between BDNF concentrations with glycemic profile. A systematic search up to July 2020 was conducted in reliable electronic databases (MEDLINE (Pubmed), EMBASE, Scopus) and Google scholar. Sixteen observational studies compared serum/plasma BDNF levels in diabetic patients (or individuals with glycemic disorders) vs. healthy controls or reported correlations between serum BDNF levels and glycemic parameters in adults were included in the review. Overall weighted mean difference (WMD) of circulating BDNF levels in 1306 patients with T2D (or other glycemic disorders) was 1.12 ng/mL lower than 1250 healthy subjects (WMD: − 1.12; 95%CI − 1.37, − 0.88, I² = 98.7%, P < 0.001). Subgroup analysis revealed that both diabetic patients and subjects with other glycemic disorders had lower serum/plasma BDNF levels than healthy controls (WMD: − 1.74; 95%CI − 2.15, − 1.33 and WMD: − 0.49; 95%CI − 0.82, − 0.16, respectively). No significant correlation was found between BDNF levels and glycemic parameters [fasting blood glucose (FBG) (Fisher’s Z = 0.05; 95%CI − 0.21, 0.11; n = 1400), homeostatic model assessment for insulin resistance (HOMA-IR) (Fisher’s Z = 0.12; 95%CI − 0.20, 0.44; n = 732) and glycosylated hemoglobin (HbA1c) (Fisher’s Z = 0.04; 95%CI − 0.05, 0.12; n = 2222)]. We found that diabetic patients and subjects with glycemic disorders had lower circulating BDNF levels than healthy controls. However, there was no significant correlation between BDNF concentrations and glycemic parameters including FBG, HOMA-IR and HbA1c. Further prospective investigations are required to confirm these findings.

Neurotrophins as Key Regulators of Cell Metabolism: Implications for Cholesterol Homeostasis

Neurotrophins constitute a family of growth factors initially characterized as predominant mediators of nervous system development, neuronal survival, regeneration and plasticity. Their biological activity is promoted by the binding of two different types of receptors, leading to the generation of multiple and variegated signaling cascades in the target cells. Increasing evidence indicates that neurotrophins are also emerging as crucial regulators of metabolic processes in both neuronal and non-neuronal cells. In this context, it has been reported that neurotrophins affect redox balance, autophagy, glucose homeostasis and energy expenditure. Additionally, the trophic support provided by these secreted factors may involve the regulation of cholesterol metabolism. In this review, we examine the neurotrophins' signaling pathways and their effects on metabolism by critically discussing the most up-to-date information. In particular, we gather experimental evidence demonstrating the impact of these growth factors on cholesterol metabolism.

Drug delivery platforms for neonatal brain injury

Hypoxic-ischemic encephalopathy (HIE), initiated by the interruption of oxygenated blood supply to the brain, is a leading cause of death and lifelong disability in newborns. The pathogenesis of HIE involves a complex interplay of excitotoxicity, inflammation, and oxidative stress that results in acute to long term brain damage and functional impairments. Therapeutic hypothermia is the only approved treatment for HIE but has limited effectiveness for moderate to severe brain damage; thus, pharmacological intervention is explored as an adjunct therapy to hypothermia to further promote recovery. However, the limited bioavailability and the side-effects of systemic administration are factors that hinder the use of the candidate pharmacological agents. To overcome these barriers, therapeutic molecules may be packaged into nanoscale constructs to enable their delivery. Yet, the application of nanotechnology in infants is not well examined, and the neonatal brain presents unique challenges. Novel drug delivery platforms have the potential to magnify therapeutic effects in the damaged brain, mitigate side-effects associated with high systemic doses, and evade mechanisms that remove the drugs from circulation. Encouraging pre-clinical data demonstrates an attenuation of brain damage and increased structural and functional recovery. This review surveys the current progress in drug delivery for treating neonatal brain injury.

Acute Systemic Response Of BDNF, Lactate and Cortisol to Strenuous Exercise Modalities in Healthy Untrained Women

Acute bouts of intense exercise increase lactate concentration, which in turn stimulates brain-derived neurotrophic factor (BDNF) production. Cortisol released during intense exercise might inhibit BDNF synthesis. This study examined the acute effects of 2 protocols of strenuous exercise on serum BDNF. Seventeen physically-active healthy females (Age = 20.0 ± 0.9 yr., BMI = 23.0 ± 2.6 kg/m²) performed a strenuous cycle-ergometer graded exercise test (GXT) and a high-intensity interval training session (HIIT). Serum BDNF, serum cortisol, cortisol: BDNF ratio and blood lactate (BLa) were recorded at baseline and immediately following exercise. Although non-statistically significant, the HIIT session elicited a higher magnitude of change from baseline for BDNF (d = 0.17) and cortisol (d = 1.18) than after the GXT (d = -0.26, and d = 0.82, respectively). An interaction was found between GXT and HIIT trials and measurements on BLa levels, with higher post-exertion values after HIIT than after GXT (p < 0.0001, η² = 0.650, 95%CI = 2.2, 5.2). The higher BLa levels did not raise circulating BDNF. The elevated cortisol levels may have overcome the effects of lactate on BDNF. However, the higher BLa induced by HIIT suggest that interval exercise modality on the long-term could be a feasible intervention to increase circulating peripheral BDNF, at least in untrained healthy women.

Transcriptomic and Quantitative Proteomic Profiling Reveals Signaling Pathways Critical for Pancreatic Islet Maturation

Pancreatic β-cell dysfunction and reduced insulin secretion play a key role in the pathogenesis of diabetes. Fetal and neonatal islets are functionally immature and have blunted glucose responsiveness and decreased insulin secretion in response to stimuli and are far more proliferative. However, the mechanisms underlying functional immaturity are not well understood. Pancreatic islets are composed of a mixture of different cell types, and the microenvironment of islets and interactions between these cell types are critical for β-cell development and maturation. RNA sequencing and quantitative proteomic data from intact islets isolated from fetal (embryonic day 19) and 2-week-old Sprague-Dawley rats were integrated to compare their gene and protein expression profiles. Ingenuity Pathway Analysis (IPA) was also applied to elucidate pathways and upstream regulators modulating functional maturation of islets. By integrating transcriptome and proteomic data, 917 differentially expressed genes/proteins were identified with a false discovery rate of less than 0.05. A total of 411 and 506 of them were upregulated and downregulated in the 2-week-old islets, respectively. IPA revealed novel critical pathways associated with functional maturation of islets, such as AMPK (adenosine monophosphate-activated protein kinase) and aryl hydrocarbon receptor signaling, as well as the importance of lipid homeostasis/signaling and neuronal function. Furthermore, we also identified many proteins enriched either in fetal or 2-week-old islets related to extracellular matrix and cell communication, suggesting that these pathways play critical roles in islet maturation. Our present study identified novel pathways for mature islet function in addition to confirming previously reported mechanisms, and provided new mechanistic insights for future research on diabetes prevention and treatment.

α2-Adrenergic Disruption of β Cell BDNF-TrkB Receptor Tyrosine Kinase Signaling

Adrenergic signaling is a well-known input into pancreatic islet function. Specifically, the insulin-secreting islet β cell expresses the Gi/o-linked α2-adrenergic receptor, which upon activation suppresses insulin secretion. The use of the adrenergic agonist epinephrine at micromolar doses may have supraphysiological effects. We found that pretreating β cells with micromolar concentrations of epinephrine differentially inhibited activation of receptor tyrosine kinases. We chose TrkB as an example because of its relative sensitivity to the effects of epinephrine and due to its potential regulatory role in the β cell. Our characterization of brain-derived neurotrophic factor (BDNF)-TrkB signaling in MIN6 β cells showed that TrkB is activated by BDNF as expected, leading to canonical TrkB autophosphorylation and subsequent downstream signaling, as well as chronic effects on β cell growth. Micromolar, but not nanomolar, concentrations of epinephrine blocked BDNF-induced TrkB autophosphorylation and downstream mitogen-activated protein kinase pathway activation, suggesting an inhibitory phenomenon at the receptor level. We determined epinephrine-mediated inhibition of TrkB activation to be Gi/o-dependent using pertussis toxin, arguing against an off-target effect of high-dose epinephrine. Published data suggested that inhibition of potassium channels or phosphoinositide-3-kinase signaling may abrogate the negative effects of epinephrine; however, these did not rescue TrkB signaling in our experiments. Taken together, these results show that (1) TrkB kinase signaling occurs in β cells and (2) use of epinephrine in studies of insulin secretion requires careful consideration of concentration-dependent effects. BDNF-TrkB signaling in β cells may underlie pro-survival or growth signaling and warrants further study.

Novel metabolic role for BDNF in pancreatic β-cell insulin secretion

BDNF signaling in hypothalamic circuitries regulates mammalian food intake. However, whether BDNF exerts metabolic effects on peripheral organs is currently unknown. Here, we show that the BDNF receptor TrkB.T1 is expressed by pancreatic β-cells where it regulates insulin release. Mice lacking TrkB.T1 show impaired glucose tolerance and insulin secretion. β-cell BDNF-TrkB.T1 signaling triggers calcium release from intracellular stores, increasing glucose-induced insulin secretion. Additionally, BDNF is secreted by skeletal muscle and muscle-specific BDNF knockout phenocopies the β-cell TrkB.T1 deletion metabolic impairments. The finding that BDNF is also secreted by differentiated human muscle cells and induces insulin secretion in human islets via TrkB.T1 identifies a new regulatory function of BDNF on metabolism that is independent of CNS activity. Our data suggest that muscle-derived BDNF may be a key factor mediating increased glucose metabolism in response to exercise, with implications for the treatment of diabetes and related metabolic diseases.

Glucose metabolism is regulated by hypothalamic brain functions and factors produced by peripheral tissues. Here, the authors show that the regulator of food intake Brain-derived neurotrophic factor is also produced and secreted by muscle and stimulates pancreas insulin release.

Mechanisms behind Retinal Ganglion Cell Loss in Diabetes and Therapeutic Approach

Diabetes produces several changes in the body triggered by high glycemia. Some of these changes include altered metabolism, structural changes in blood vessels and chronic inflammation. The eye and particularly the retinal ganglion cells (RGCs) are not spared, and the changes eventually lead to cell loss and visual function impairment. Understanding the mechanisms resulting in RGC damage and loss from diabetic retinopathy is essential to find an effective treatment. This review focuses mainly on the signaling pathways and molecules involved in RGC loss and the potential therapeutic approaches for the prevention of this cell death. Throughout the manuscript it became evident that multiple factors of different kind are responsible for RGC damage. This shows that new therapeutic agents targeting several factors at the same time are needed. Alpha-1 antitrypsin as an anti-inflammatory agent may become a suitable option for the treatment of RGC loss because of its beneficial interaction with several signaling pathways involved in RGC injury and inflammation. In conclusion, alpha-1 antitrypsin may become a potential therapeutic agent for the treatment of RGC loss and processes behind diabetic retinopathy.

The protective role of musk on salivary glands of mice exposed to chronic unpredictable mild stress

This study assessed the impact of chronic unpredictable mild stress (CUMS) on the structure of mouse salivary glands and the role of musk in alleviating this impact. Forty male albino mice were distributed equally into four groups; control (untreated), CUMS (exposed to CUMS for 4 weeks), CUMS+fluoxetine (FLU) (exposed to CUMS then treated with FLU, CUMS+musk (exposed to CUMS then treated with musk). Behavioral changes and serum corticosterone levels were assessed at the end of the experiment. The submandibular and parotid glands were dissected out and processed for histopathological and immunohistochemical examination using antibodies against alpha smooth muscle actin (ASMA) and brain-derived neurotropic factor (BDNF). Exposure to CUMS significantly (P < 0.001) increased the serum corticosterone level and induced depression. CUMS also induced vacuolation in acinar cells along with a significant (P < 0.001) reduction of ASMA immunoexpression, indicating an effect on myoepithelial cells, and a significant (P < 0.001) increase of BDNF expression in the gland ductal system. Both FLU and musk alleviated the CUMS-induced behavioral, biochemical and histopathological changes in the salivary glands. In conclusion, musk ameliorates stress-induced structural changes in mouse salivary glands. This effect might be mediated through up-regulation of BDNF secretion by the glands.

Short-term high-Intensity interval training increases systemic brain-derived neurotrophic factor (BDNF) in healthy women

BACKGROUND

Brain-derived neurotrophic factor (BDNF) increases neuronal viability and cognitive function, peripheral lipid metabolism and skeletal muscle repair. The primary purpose of this study was to determine the effect of short-term high-intensity interval training (HIIT) on serum BDNF concentrations in healthy young women.

METHODS

Seventeen women (age:22 ± 1 years); body mass index (BMI:24.2 ± 2.2 kg/m²), body fat percentage (% fat:25.8 ± 4.7) participated in the study. Participants were randomly assigned to a control (n = 8) or HIIT group (n = 9). All participants performed a graded exercise test (GXT) on an electronically-braked cycle ergometer to determine maximal aerobic power (MAP, Watts). HIIT was performed three days per week for four weeks. Each HIIT session consisted of three to five cycling bouts of 30 s each at 80% MAP, followed by four-minutes of recovery at 40% MAP. Forty-eight hours after the last bout of exercise, both groups performed a follow-up GXT. Non-fasting blood samples were collected before and immediately after each GXT. Mixed factorial (2 groups x 4 measures, and 2 groups x 2 measures) ANOVA was used to assess BDNF concentrations, performance and anthropometric variables.

RESULTS

Serum BDNF concentrations in the HIIT group (21.9 ± 1.3 ng/mL) increased compared to control (19.2 ± 2.8 ng/mL) (∼12%, P < 0.05) following HIIT. In contrast, circulating BDNF concentrations were reduced following the GXT (P < 0.05). The MAP and % Fat did not change with HIIT.

CONCLUSIONS

Twelve sessions of HIIT increases circulating BDNF concentrations in healthy young women despite no change in physical performance or % fat.

Influencing neuroplasticity in stroke treatment with advanced biomaterials-based approaches

Since the early 1990s, we have known that the adult brain is not static and has the capacity to repair itself. The delivery of various therapeutic factors and cells have resulted in some exciting pre-clinical and clinical outcomes in stroke models by targeting post-injury plasticity to enhance recovery. Developing a deeper understanding of the pathways that modulate plasticity will enable us to optimize delivery strategies for therapeutics and achieve more robust effects. Biomaterials are a key tool for the optimization of these potential treatments, owing to their biocompatibility and tunability. In this review, we identify factors and targets that impact plastic processes known to contribute to recovery, discuss the role of biomaterials in enhancing the efficacy of treatment strategies, and suggest combinatorial approaches based on the stage of injury progression.

Intracerebral Delivery of Brain-Derived Neurotrophic Factor Using HyStem®-C Hydrogel Implants Improves Functional Recovery and Reduces Neuroinflammation in a Rat Model of Ischemic Stroke

Ischemic stroke is a leading cause of death and disability worldwide. Potential therapeutics aimed at neural repair and functional recovery are limited in their blood-brain barrier permeability and may exert systemic or off-target effects. We examined the effects of brain-derived neurotrophic factor (BDNF), delivered via an extended release HyStem^®-C hydrogel implant or vehicle, on sensorimotor function, infarct volume, and neuroinflammation, following permanent distal middle cerebral artery occlusion (dMCAo) in rats. Eight days following dMCAo or sham surgery, treatments were implanted directly into the infarction site. Rats received either vehicle, BDNF-only (0.167 µg/µL), hydrogel-only, hydrogel impregnated with 0.057 µg/µL of BDNF (hydrogel + BDNF_LOW), or hydrogel impregnated with 0.167 µg/µL of BDNF (hydrogel + BDNF_HIGH). The adhesive removal test (ART) and 28-point Neuroscore (28-PN) were used to evaluate sensorimotor function up to two months post-ischemia. The hydrogel + BDNF_HIGH group showed significant improvements on the ART six to eight weeks following treatment and their behavioral performance was consistently greater on the 28-PN. Infarct volume was reduced in rats treated with hydrogel + BDNF_HIGH as were levels of microglial, phagocyte, and astrocyte marker immunoexpression in the corpus striatum. These data suggest that targeted intracerebral delivery of BDNF using hydrogels may mitigate ischemic brain injury and restore functional deficits by reducing neuroinflammation.

The Impact of High-Intensity Interval Training on Brain Derived Neurotrophic Factor in Brain: A Mini-Review

The brain-derived neurotrophic factor (BDNF) is a protein mainly synthetized in the neurons. Early evidence showed that BDNF participates in cognitive processes as measured at the hippocampus. This neurotrophin is as a reliable marker of brain function; moreover, recent studies have demonstrated that BDNF participates in physiological processes such as glucose homeostasis and lipid metabolism. The BDNF has been also studied using the exercise paradigm to determine its response to different exercise modalities; therefore, BDNF is considered a new member of the exercise-related molecules. The high-intensity interval training (HIIT) is an exercise protocol characterized by low work volume performed at a high intensity [i.e., ≥80% of maximal heart rate (HRmax)]. Recent evidence supports the contention that HIIT elicits higher fat oxidation in skeletal muscle than other forms of exercise. Similarly, HIIT is a good stimulus to increase maximal oxygen uptake (VO₂max). Few studies have investigated the impact of HIIT on the BDNF response. The present work summarizes the effects of acute and long-term HIIT on BDNF.

Developmental origins of adult health and disease: The metabolic role of BDNF from early life to adulthood

Accumulating evidence suggests that the origins of adult disease may occur during fetal life. Thus, the concept of "developmental programming" has been introduced and supported by epidemiological and experimental data. This concept supports the idea that the nutritional and hormonal status during pregnancy could interfere in metabolism control. The mechanisms responsible for this "developmental programming" remain poorly documented. Current research indicates that neurotrophins and particularly brain-derived neurotrophic factor (BDNF) may play a crucial role in this process. Although mainly expressed in the nervous system, BDNF and its receptor, tropomyosin-related kinase B (TrkB), are immunolocalized in several regions of the human placenta and have important functions during pregnancy. BDNF serves widespread roles in regulating energy homeostasis in both fetuses and adults, by controlling patterns of fetal growth, adult feeding and physical activity, and by regulating glucose metabolism in peripheral tissues. Impaired BDNF signaling may be implicated in the etiopathogenesis of the metabolic syndrome. Novel BDNF-focused interventions are being developed for obesity, diabetes and neurological disorders. The aim of this article is to provide a brief comprehensive literary review regarding the potential implications of BDNF in "developmental programming", through regulation of metabolism and energy balance from early life to adulthood.

Glucagon-like peptide-1 reduces pancreatic β-cell mass through hypothalamic neural pathways in high-fat diet-induced obese rats

We examined whether glucagon-like peptide-1 (GLP-1) affects β-cell mass and proliferation through neural pathways, from hepatic afferent nerves to pancreatic efferent nerves via the central nervous system, in high-fat diet (HFD)-induced obese rats. The effects of chronic administration of GLP-1 (7–36) and liraglutide, a GLP-1 receptor agonist, on pancreatic morphological alterations, c-fos expression and brain-derived neurotrophic factor (BDNF) content in the hypothalamus, and glucose metabolism were investigated in HFD-induced obese rats that underwent hepatic afferent vagotomy (VgX) and/or pancreatic efferent sympathectomy (SpX). Chronic GLP-1 (7–36) administration to HFD-induced obese rats elevated c-fos expression and BDNF content in the hypothalamus, followed by a reduction in pancreatic β-cell hyperplasia and insulin content, thus resulting in improved glucose tolerance. These responses were abolished by VgX and SpX. Moreover, administration of liraglutide similarly activated the hypothalamic neural pathways, thus resulting in a more profound amelioration of glucose tolerance than native GLP-1 (7–36). These data suggest that GLP-1 normalizes the obesity-induced compensatory increase in β-cell mass and glucose intolerance through a neuronal relay system consisting of hepatic afferent nerves, the hypothalamus, and pancreatic efferent nerves.

Hydrogel-delivered brain-derived neurotrophic factor promotes tissue repair and recovery after stroke

Stroke is the leading cause of adult disability. Systemic delivery of candidate neural repair therapies is limited by the blood-brain barrier and off-target effects. We tested a bioengineering approach for local depot release of BDNF from the infarct cavity for neural repair in chronic periods after stroke. The brain release levels of a hyaluronic acid hydrogel + BDNF were tested in several stroke models in mouse (strains C57Bl/6, DBA) and non-human primate ( Macaca fascicularis) and tracked with MRI. The behavioral recovery effects of hydrogel + BDNF and the effects on tissue repair outcomes were determined. Hydrogel-delivered BDNF diffuses from the stroke cavity into peri-infarct tissue over 3 weeks in two mouse stroke models, compared with 1 week for direct BDNF injection. Hydrogel delivery of BDNF promotes recovery of motor function. Mapping of motor system connections indicates that hydrogel-BDNF induces axonal sprouting within existing cortical and cortico-striatal systems. Pharmacogenetic studies show that hydrogel-BDNF induces the initial migration of immature neurons into the peri-infarct cortex and their long-term survival. In chronic stroke in the non-human primate, hydrogel-released BDNF can be detected up to 2 cm from the infarct, a distance relevant to human functional recovery in stroke. The hydrogel can be tracked by MRI in mouse and primate.

Advanced glycation end products induce brain-derived neurotrophic factor release from human platelets through the Src-family kinase activation

Background

Brain-derived neurotrophic factor (BDNF) exerts beneficial effects not only on diabetic neuropathies but also on cardiovascular injury. There is argument regarding the levels of serum BDNF in patients with diabetes mellitus (DM). Because BDNF in peripheral blood is rich in platelets, this may represent dysregulation of BDNF release from platelets. Here we focused on advanced glycation end products (AGEs), which are elevated in patients with DM and have adverse effects on cardiovascular functions. The aim of this study is to elucidate the role of AGEs in the regulation of BDNF release from human platelets.

Methods

Platelets collected from peripheral blood of healthy volunteers were incubated with various concentrations of AGE (glycated-BSA) at 37 °C for 5 min with or without BAPTA-AM, a cell permeable Ca²⁺ chelator, or PP2, a potent inhibitor of Src family kinases (SFKs). Released and cellular BDNF were measured by ELISA and calculated. Phosphorylation of Src and Syk, a downstream kinase of SFKs, in stimulated platelets was examined by Western blotting and immunoprecipitation.

Results

AGE induced BDNF release from human platelets in a dose-dependent manner, which was dependent on intracellular Ca²⁺ and SFKs. We found that AGE induced phosphorylation of Src and Syk.

Conclusions

AGE induces BDNF release from human platelets through the activation of the Src-Syk-(possibly phospholipase C)-Ca²⁺ pathway. Considering the toxic action of AGEs and the protective roles of BDNF, it can be hypothesized that AGE-induced BDNF release is a biological defense system in the early phase of diabetes. Chronic elevation of AGEs may induce depletion or downregulation of BDNF in platelets during the progression of DM.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-017-0505-y) contains supplementary material, which is available to authorized users.

Serum brain-derived neurotrophic factor levels and sleep disorders in Chinese healthy and newly diagnosed type 2 diabetic subjects

BACKGROUND

The aims of the present study were to detect serum brain-derived neurotrophic factor (BDNF) protein concentrations in healthy and diabetic subjects with sleep disorders and to explore correlations among serum BDNF concentrations, metabolic parameters and inflammation.

METHODS

In all, 377 eligible subjects were recruited to the study and underwent a 75-g oral glucose tolerance test. Various clinical parameters of metabolic disorders and cytokines were measured. Sleep disorders were assessed using the Pittsburgh Sleep Quality Index (PSQI). Subjects were grouped into those with normal glucose tolerance (NGT), those with NGT and sleep disorders (NGT-SDi), those with newly diagnosed type 2 diabetes mellitus (T2DM), and those with newly diagnosed T2DM and sleep disorders (T2DM-SDi).

RESULTS

Serum BDNF levels were higher in the NGT-SDi and T2DM-SDi subgroups than in the NGT and T2DM groups, respectively. Multiple linear regression analysis revealed that serum BDNF concentrations were independently correlated with PSQI scores, homeostasis model assessment of insulin resistance, and HbA1c, interleukin 6 and tumor necrosis factor-α concentrations (P < 0.05 for all). Binary logistic regression analysis revealed that significant associations remained between serum BDNF concentrations and sleep disorders after adjustment for glucose- and metabolic-related factors in both the NGT-SDi and T2DM-SDi subgroups.

CONCLUSIONS

Serum BDNF concentrations were higher in patients with sleep disorders and were associated with various metabolic parameters and inflammatory cytokines.

Antidiabetic Effect of Brain-Derived Neurotrophic Factor and Its Association with Inflammation in Type 2 Diabetes Mellitus

Brain-derived neurotrophic factor (BDNF) is a neurotrophin, which plays an important role in the central nervous system, and systemic or peripheral inflammatory conditions, such as acute coronary syndrome and type 2 diabetes mellitus (T2DM). BDNF is also expressed in several nonneuronal tissues, and platelets are the major source of peripheral BDNF. Here, we reviewed the potential role of BDNF in platelet reactivity in T2DM and its association with selected inflammatory and platelet activation mediators. Besides that, we focused on adipocytokines such as leptin, resistin, and adiponectin which are considered to take part in inflammation and both lipid and glucose metabolism in diabetic patients as previous studies showed the relation between adipocytokines and BDNF. We also reviewed the evidences of the antidiabetic effect of BDNF and the association with circulating inflammatory cytokines in T2DM.

Submandibular Glands Contribute to Increases in Plasma BDNF Levels

Brain-derived neurotrophic factor (BDNF) promotes survival and differentiation of neural cells in the central and peripheral nervous systems. BDNF has been detected in plasma, but its source has not yet been established. Expression of BDNF mRNA has been identified in the submandibular glands when male rats are exposed to acute immobilization stress. In the present study, we investigated whether plasma BDNF is influenced by the submandibular glands in this model. Acute immobilization stress for 60 min significantly increased the level of plasma BDNF. However, plasma BDNF elevation was markedly suppressed in bilaterally sialoadenectomized rats. There were no significant differences between stressed (60 min) and non-stressed rats with respect to the BDNF mRNA expression in the hippocampus, heart, lung, liver, pancreas, or spleen, as determined by real-time polymerase chain-reaction. These findings suggest that the submandibular glands may be the primary source of plasma BDNF in conditions of acute immobilization stress.

Pancreatic regulation of glucose homeostasis

In order to ensure normal body function, the human body is dependent on a tight control of its blood glucose levels. This is accomplished by a highly sophisticated network of various hormones and neuropeptides released mainly from the brain, pancreas, liver, intestine as well as adipose and muscle tissue. Within this network, the pancreas represents a key player by secreting the blood sugar-lowering hormone insulin and its opponent glucagon. However, disturbances in the interplay of the hormones and peptides involved may lead to metabolic disorders such as type 2 diabetes mellitus (T2DM) whose prevalence, comorbidities and medical costs take on a dramatic scale. Therefore, it is of utmost importance to uncover and understand the mechanisms underlying the various interactions to improve existing anti-diabetic therapies and drugs on the one hand and to develop new therapeutic approaches on the other. This review summarizes the interplay of the pancreas with various other organs and tissues that maintain glucose homeostasis. Furthermore, anti-diabetic drugs and their impact on signaling pathways underlying the network will be discussed.

Role of the central nervous system and adipose tissue BDNF/TrkB axes in metabolic regulation

Background/Objectives:

Brain-derived neurotrophic factor (BDNF) and its receptor (tropomyosin-related kinase B: TrkB, also known as Ntrk2) have a key role in central regulation of the energy balance. BDNF and TrkB are also expressed in the peripheral tissues, including adipose tissue, but their peripheral role has been unclear. Here we report on the functional significance of the adipose tissue BDNF/TrkB axis in metabolic homeostasis.

Materials and Methods:

To examine the role of the BDNF/TrkB axis in the central nervous system and in adipose tissue, we generated adipocyte-specific or neuron-specific BDNF/TrkB conditional knockout (CKO) mice. Then we compared the feeding behavior and metabolic profile between each type of CKO mouse and their littermates.

Results:

Bdnf expression was significantly increased in the adipose tissue of mice receiving a high-calorie diet, whereas Ntrk2 expression was decreased. The Bdnf/Ntrk2 expression ratio of adipose tissue was higher in female mice than male mice. Fabp4-Cre mice are widely used to establish adipocyte-specific CKO mice. However, we found that Fabp4-Cre-induced deletion of Bdnf or Ntrk2 led to hyperphagia, obesity, and aggressiveness, presumably due to ectopic Fabp4-Cre mediated gene recombination in the brain. Next, we attempted to more specifically delete Bdnf or Ntrk2 in adipocytes using Adipoq-Cre mice. Expression of Ntrk2, but not Bdnf, in the adipose tissue was reduced by Adipoq-Cre mediated gene recombination, indicating that adipocytes only expressed TrkB. No phenotypic changes were detected when Adipoq-Cre TrkB CKO mice were fed a normal diet, whereas female CKO mice receiving a high-calorie diet showed a decrease in food intake and resistance to obesity.

Conclusions:

The adipose tissue BDNF/TrkB axis has a substantial influence on the feeding behavior and obesity in female mice.

Serum Levels of Brain-Derived Neurotrophic Factor Are Associated with Diabetes Risk, Complications, and Obesity: a Cohort Study from Chinese Patients with Type 2 Diabetes

Brain-derived neurotrophic factor (BDNF) is associated with systemic inflammatory conditions, such as diabetes. The aim of this study was to assess the serum BDNF levels in Chinese patients with type 2 diabetes (T2DM). From the outpatient clinic at the endocrinology department of our hospital, all patients with long-standing T2DM were recruited for this study between August 2014 and December 2014. Serum levels of BDNF were assayed with solid-phase sandwich ELISA, and the demographical and clinical data were evaluated on admission. Median serum BDNF levels were significantly lower in patients with T2DM compared to control subjects (15.9 ng/mL (interquartile range (IQR), 12.6-19.8) VS. 24.6 ng/mL (IQR, 17.2-27.8); P < 0.0001). Serum BDNF levels were inversely correlated with fasting glucose (r = -0.394, P < 0.0001) and duration of illness (r = -0.272, P < 0.0001) in T2DM patients. Based on the receiver operating characteristic (ROC) curve, the optimal cutoff value of serum BDNF levels as an indicator for diagnosis of T2DM was projected to be 23.0 ng/mL, which yielded a sensitivity of 89.0 % and a specificity of 60.9 %, with the area under the curve at 0.794 (95 % confidence interval (CI), 0.747-0.841; P < 0.001). In multivariate logistic regression analysis, after adjusting for other significant factors, BDNF can be seen as an indicator of independent diabetes complications with an odds ratio (OR) of 0.84 (95 % CI, 0.75-0.89; P < 0.001) and obesity with an OR of 0.88 (95 % CI, 0.80-0.92; P < 0.001). Our study suggested that low levels of BDNF accompany impaired glucose metabolism. Importantly, we found that decreased BDNF were correlated with obesity and diabetes complications.

Chronic exercise increases plasma brain-derived neurotrophic factor levels, pancreatic islet size, and insulin tolerance in a TrkB-dependent manner

BACKGROUND

Physical exercise improves glucose metabolism and insulin sensitivity. Brain-derived neurotrophic factor (BDNF) enhances insulin activity in diabetic rodents. Because physical exercise modifies BDNF production, this study aimed to investigate the effects of chronic exercise on plasma BDNF levels and the possible effects on insulin tolerance modification in healthy rats.

METHODS

Wistar rats were divided into five groups: control (sedentary, C); moderate- intensity training (MIT); MIT plus K252A TrkB blocker (MITK); high-intensity training (HIT); and HIT plus K252a (HITK). Training comprised 8 weeks of treadmill running. Plasma BDNF levels (ELISA assay), glucose tolerance, insulin tolerance, and immunohistochemistry for insulin and the pancreatic islet area were evaluated in all groups. In addition, Bdnf mRNA expression in the skeletal muscle was measured.

PRINCIPAL FINDINGS

Chronic treadmill exercise significantly increased plasma BDNF levels and insulin tolerance, and both effects were attenuated by TrkB blocking. In the MIT and HIT groups, a significant TrkB-dependent pancreatic islet enlargement was observed. MIT rats exhibited increased liver glycogen levels following insulin administration in a TrkB-independent manner.

CONCLUSIONS/SIGNIFICANCE

Chronic physical exercise exerted remarkable effects on insulin regulation by inducing significant increases in the pancreatic islet size and insulin sensitivity in a TrkB-dependent manner. A threshold for the induction of BNDF in response to physical exercise exists in certain muscle groups. To the best of our knowledge, these are the first results to reveal a role for TrkB in the chronic exercise-mediated insulin regulation in healthy rats.

A possible link between BDNF and mTOR in control of food intake

Food intake is intricately regulated by glucose, amino acids, hormones, neuropeptides, and trophic factors through a neural circuit in the hypothalamus. Brain-derived neurotrophic factor (BDNF), the most prominent neurotrophic factor in the brain, regulates differentiation, maturation, and synaptic plasticity throughout life. Among its many roles, BDNF exerts an anorexigenic function in the brain. However, the intracellular signaling induced by BDNF to control food intake is not fully understood. One candidate for the molecule involved in transducing the anorexigenic activity of BDNF is the mammalian target of rapamycin (mTOR). mTOR senses extracellular amino acids, glucose, growth factors, and neurotransmitters, and regulates anabolic reactions response to these signals. Activated mTOR increases protein and lipid synthesis and inhibits protein degradation. In the hypothalamus, mTOR activation is thought to reduce food intake. Here we summarize recent findings regarding BDNF- and mTOR-mediated feeding control, and propose a link between these molecules in eating behavior.

Brain-derived neurotrophic factor inhibits glucose intolerance after cerebral ischemia

Brain-derived neurotrophic factor is associated with the insulin signaling pathway and glucose tabolism. We hypothesized that expression of brain-derived neurotrophic factor and its receptor may be involved in glucose intolerance following ischemic stress. To verify this hypothesis, this study aimed to observe the changes in brain-derived neurotrophic factor and tyrosine kinase B receptor expression in glucose metabolism-associated regions following cerebral ischemic stress in mice. At day 1 after middle cerebral artery occlusion, the expression levels of brain-derived neurotrophic factor were significantly decreased in the ischemic cortex, hypothalamus, liver, skeletal muscle, and pancreas. The expression levels of tyrosine kinase B receptor were decreased in the hypothalamus and liver, and increased in the skeletal muscle and pancreas, but remained unchanged in the cortex. Intrahypothalamic administration of brain-derived neurotrophic factor (40 ng) suppressed the decrease in insulin receptor and tyrosine-phosphorylated insulin receptor expression in the liver and skeletal muscle, and inhibited the overexpression of gluconeogenesis-associated phosphoenolpyruvate carboxykinase and glucose-6-phosphatase in the liver of cerebral ischemic mice. However, serum insulin levels remained unchanged. Our experimental findings indicate that brain-derived neurotrophic factor can promote glucose metabolism, reduce gluconeogenesis, and decrease blood glucose levels after cerebral ischemic stress. The low expression of brain-derived neurotrophic factor following cerebral ischemia may be involved in the development of glucose intolerance.

Modulation of neurotrophin signaling by monoclonal antibodies

The neurotrophin family is comprised of the structurally related secreted proteins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophine-4 (NT-4). They bind and activate the tyrosine kinase receptors Trk A, B, and C in a ligand-specific manner and additionally bind a shared p75NTR receptor. The neurotrophins were originally defined by their ability to support the survival and maturation of embryonic neurons. However, they also control important physiological functions of the adult nervous system including learning and memory, sensation, and energy homeostasis. For example, NGF/trkA signaling is critical for normal and pathological sensation of pain. Likewise, the BDNF/trkB pathway controls feeding and metabolism, and its dysfunction leads to severe obesity. Antibodies can modulate neurotrophin signaling. Thus, NGF blocking agents can attenuate pain in several animal models, and a recombinant humanized NGF blocking antibody (Tanezumab) has shown promising results in human clinical trials for osteoarthritic pain. On the other hand trkB agonist antibodies can modulate food intake and body weight in rodents and nonhuman primates. The power of monoclonal antibodies to modulate neurotrophin signaling promises to turn the rich biological insights into novel human medicines.

Hypothalamic brain-derived neurotrophic factor regulates glucagon secretion mediated by pancreatic efferent nerves

Understanding the molecular mechanism of the regulation of glucagon secretion is critical for treating the dysfunction of α cells observed in diabetes. Glucagon-like peptide (GLP)-1 analogues reduce plasma glucagon and are assumed to contribute to their action to lower blood glucose. It has previously been demonstrated that the central administration of brain-derived neurotrophic factor (BDNF) improves glucose metabolism by a mechanism independent of feeding behaviour in obese subjects. Using male rats, we examined whether BDNF influences glucagon secretion from α cells via the the central nervous system. We investigate whether: (i) the central infusion of BDNF stimulates glucagon and/or insulin secretion via the pancreatic efferent nerve from the hypothalamus; (ii) the intraportal infusion of GLP-1 regulates glucose metabolism via the central and peripheral nervous system; and (iii) BDNF receptor and/or BDNF-positive fibres are localised near α cells of islets. The portal glucagon level decreased with the central administration of BDNF (n = 6, in each; P < 0.05); in contrast, there was no significant change in portal insulin, peripheral glucagon and insulin levels with the same treatment. This reduction of glucagon secretion was abolished by pancreatic efferent denervation (n = 6, in each; P < 0.05). In an immunohistochemical study, pancreatic α cells were stained specifically with BDNF and tyrosine-related kinase B, a specific receptor for BDNF, and α cells were also co-localised with BDNF. Moreover, intraportal administration of GLP-1 decreased glucagon secretion, as well as blood glucose, whereas it increased the BDNF content in the pancreas; these effects were inhibited with the central infusion of BDNF antibody (n = 6, in each; P < 0.05). BDNF and GLP-1 affect glucose metabolism and modulate glucagon secretion from pancreatic α cells via the central and peripheral nervous systems.

Role of stress-related brain-derived neurotrophic factor (BDNF) in the rat submandibular gland

The nerve growth factor (NGF) family comprises NGF, brain-derived neurotrophic factor (BDNF) and neurotrophins (NTs)-3, -4/5, -6 and -7, all of which are collectively referred to as neurotrophins. However, the expression of neurotrophins other than NGF in the salivary gland has not been described in detail. Through interaction with the TrkB receptor, BDNF plays an important role in long-term potentiation. We found that BDNF expression increased within submandibular gland tissue in response to stress, suggesting that the salivary glands are sensitive to stress. In addition, stress caused increases in plasma BDNF derived from the submandibular gland and in TrkB receptor mRNA in the adrenal medulla. Plasma BDNF might activate TrkB receptors in the adrenal medulla during acute stress. The salivary glands are likely to influence not only oral health, but also systemic organs. This review addressed the relationship between hormone-like effects and stress-related BDNF expression in the rat submandibular gland.

The impact of dietary energy intake on cognitive aging

Rodents that are insulin resistant and obese as the result of genetic factors, overeating and/or a sedentary lifestyle, exhibit cognitive deficits that worsen with advancing age compared to their more svelte counterparts. Data from epidemiological and clinical studies suggest similar adverse effects of excessive dietary energy intake and insulin resistance on cognition in humans. Our findings from studies of animal models suggest that dietary energy restriction can enhance neural plasticity and reduce the vulnerability of the brain to age-related dysfunction and disease. Dietary energy restriction may exert beneficial effects on the brain by engaging adaptive cellular stress response pathways resulting in the up-regulation of genes that encode proteins that promote neural plasticity and cell survival (e.g., neurotrophic factors, protein chaperones and redox enzymes). Two energy state-sensitive factors that are proving particularly important in regulating energy balance and improving/preserving cognitive function are brain-derived neurotrophic factor and glucagon-like peptide 1. Alternate day calorie restriction, novel insulin-sensitizing and neuroprotective agents, and drugs that activate adaptive stress response pathways, are examples of approaches for preserving cognitive function that show promise in preclinical studies.

Chronic administration of brain-derived neurotrophic factor in the hypothalamic paraventricular nucleus reverses obesity induced by high-fat diet

An acute injection of brain-derived neurotrophic factor (BDNF) in the hypothalamic paraventricular nucleus (PVN) reduces body weight by decreasing feeding and increasing energy expenditure (EE), in animals on standard laboratory chow. Animals have divergent responses to a high-fat diet (HFD) exposure, with some developing obesity and others remaining lean. In the current study, we tested two hypotheses: 1) BDNF in the PVN reverses HFD-induced obesity, and 2) animals with higher body fat have a greater physiological response to BDNF than those with less body fat. Eighty-four 10-wk old rats were allowed HFD ad libitum for 9 wk and then prepared with bilateral PVN cannulas. Animals were then divided into tertiles based on their body fat rank: high, intermediate, and low (H, I, and L). Each group was further divided into 2 subgroups and then PVN injected with BDNF or control (artificial cerebrospinal fluid, aCSF) every other day for 3 wk. Energy intake (EI), body weight, and body composition were measured. At study's end, rats were killed to allow measurement of other metabolic indices. In parallel, another 12 rats were fed control diet (CD), PVN-cannulated and injected with aCSF. HFD exposure induced obesity, particularly in the H body fat group, with a significant increase in EI, body weight, fat mass, liver size, and serum glucose, triglycerides, insulin, and leptin. BDNF significantly reduced EI, body weight, body fat, lean mass, and serum metabolic indices. These BDNF effects were greatest in the H body fat group. These data indicate that BDNF reduced HFD-induced obesity and metabolic syndrome-like measures, and the animals with the most body fat had the most significant response to BDNF.

Chronic stress affects the expression of brain-derived neurotrophic factor in rat salivary glands

Plasma brain-derived neurotrophic factor (BDNF) levels are associated with several neural disorders. Previously, we reported that BDNF is produced from salivary glands under acute immobilization stress. Additionally, salivary glands are the origin of plasma BDNF during stress; however, the association between the expression of BDNF by the salivary glands under chronic stress conditions is not known. In the present study, we investigated whether plasma BDNF levels in chronic stress depend on the salivary glands. Expression of BDNF mRNA and protein were identified in the submandibular glands when male rats were exposed to chronic restraint stress (12 h daily for 22 days). Chronic stress significantly increased plasma BDNF concentration, as well as adrenocorticotropic hormone and corticosterone levels, but was not altered under chronic stress in bilaterally sialoadenectomized rats. Since chronic stress increases plasma BDNF levels in the sialoadenectomized rat model, the plasma BDNF level was not dependent on BDNF from the salivary glands. Although the salivary glands were the source of plasma BDNF in acute stress conditions in our previous study, it seems that that the increased BDNF expression in the salivary glands in chronic stress does not contribute importantly to the increased circulating BDNF level. The increased plasma BDNF levels may play important roles in homeostasis under stress conditions.

Brain-derived neurotrophic factor in infants <32 weeks gestational age: correlation with antenatal factors and postnatal outcomes

Neurotrophins (NTs) play important roles in brain growth and development. Cord blood (CB) brain-derived neurotrophic factor (BDNF) concentrations increase with gestational age but data regarding postnatal changes are limited. We measured BDNF concentrations after birth in 33 preterm infants <32-wk gestation. Serum was collected at birth (CB), at day 2, between day 6 and 10 (D6), at day 30 (D30), and at day 60 (D60). BDNF concentrations fell on D2 (p = 0.03), recovered by D6 (p = 0.10), and continued to rise thereafter at D30 (p = 0.06) and D60 (p = 0.01) compared with CB. CB BDNF concentrations positively correlated with duration of rupture of membranes (r = 0.43, p = 0.04). Antenatal steroids (ANS, p = 0.02), postnatal steroids (PNS, p = 0.04), and retinopathy of prematurity (ROP, p = 0.02) were identified as significant factors in multivariate analyses. The median (25-75th interquartile range) CB BDNF concentrations were higher in infants who received a complete course ANS compared with those who received a partial course [1461 (553-2064) versus 281 (171-536) pg/mL, p = 0.04]. BDNF concentrations negatively correlated with the use of PNS at D30 (r = -0.53, p = 0.002) and at D60 (r = -0.55, p = 0.009). PNS use was associated with reduced concentrations of BDNF at D30 [733 (101-1983) versus 2224 (1677- 4400) pg/mL, p = 0.004] and at D60 [1149 (288-2270) versus 2560 (1337-5166) pg/mL, p = 0.01]. BDNF concentrations on D60 in infants who developed ROP (n = 16) were lower than those who did not develop ROP (n = 7) [1417 (553-2540) versus 3593 (2620-7433) pg/mL, respectively, p = 0.005]. Our data suggests that BDNF concentrations rise beyond the first week of age. BDNF concentrations correlate with factors that influence neurodevelopment outcomes.

Intermittent administration of brain-derived neurotrophic factor (BDNF) ameliorates glucose metabolism and prevents pancreatic exhaustion in diabetic mice

We previously demonstrated that repetitive administration of brain-derived neurotrophic factor (BDNF) ameliorates glucose metabolism and energy expenditure in obese diabetic db/db mice. However, we have not evaluated in detail the effect of single or intermittent BDNF administration on glucose metabolism in a diabetic animal model. The objectives of this study were to examine the dose-response effect and dosing interval of BDNF administration in db/db mice and to evaluate the effect of intermittent BDNF administration on pancreatic function in db/db mice. We evaluated the dose-response effect of BDNF by single administration in db/db mice. First, single administration of BDNF greater than 70 mg/kg significantly reduced blood glucose concentration one day after administered, and the BDNF effect was maintained for 6 d. Next, the effects of BDNF administered twice a week at 4, 10, 25, and 62.5 mg/kg on blood glucose concentration, and the effects of BDNF administered once a week at 10, 20, 30, 50, and 70 mg/kg on blood glucose concentration were examined in db/db mice. In the intermittent treatment studies, BDNF dose-dependently ameliorated glucose metabolism by not only the twice-a-week administration but also the once-a-week administration. Lastly, because BDNF reduces the food intake of obese hyperphagic diabetic mice, the effects of BDNF administered once or twice a week on the blood glucose concentration and plasma and pancreatic insulin concentrations in db/db mice were compared with those of the vehicle under pair-fed conditions. Under pair-fed conditions, the intermittent administration of BDNF (25 mg/kg, twice a week, or 50 mg/kg, once a week) significantly reduced the blood glucose concentration and increased the plasma and pancreatic insulin concentrations compared with those in the pair-fed vehicle-treated db/db mice. This indicates that the prolonged hypoglycemic effect of BDNF is not simply due to the reduction of food intake. In conclusion, we demonstrated that the intermittent administration of BDNF ameliorates glucose metabolism and prevents pancreatic exhaustion in obese diabetic mice. These findings indicate that BDNF may have potential as a unique hypoglycemic agent for the treatment of diabetes at a fundamental level with good patient compliance.

Comparison of the antidiabetic effects of brain-derived neurotrophic factor and thiazolidinediones in obese diabetic mice

AIMS

Brain-derived neurotrophic factor (BDNF) ameliorates glucose metabolism in obese diabetic db/db mice. The antidiabetic effect of BDNF is dependent on plasma insulin levels, and BDNF enhances insulin action by modulating insulin signalling in peripheral tissues. The aim of the study was to compare the antidiabetic effects of BDNF with those of thiazolidinediones (TZDs), which are insulin-sensitizing agents, through evaluation of the effects of BDNF and TZDs on glucose metabolism, energy expenditure, pancreatic function and hepatic steatosis in db/db mice.

METHODS

The effects of BDNF, pioglitazone and rosiglitazone on blood glucose concentration, body weight and pancreatic insulin and glucagon contents and the effects of BDNF and troglitazone treatment for 3 weeks on blood glucose concentration, body and liver weights and histological liver images were examined in db/db mice. Furthermore, since BDNF reduces food intake in obese hyperphagic diabetic mice, the effects of BDNF treatment for 3 weeks on blood glucose concentration, body weight, fat pad and liver weights and rectal temparature in db/db mice were compared with those of troglitazone under pair-fed conditions.

RESULTS

BDNF, pioglitazone and rosiglitazone all ameliorated hyperglycaemia in db/db mice, but BDNF increased the pancreatic insulin content more effectively than pioglitazone and rosiglitazone. The pancreatic glucagon content decreased with BDNF, but increased with pioglitazone and rosiglitazone compared with vehicle, and body weight and liver weight increased with troglitazone, but decreased with BDNF compared with vehicle. Histological analysis of the liver showed that BDNF treatment reduced the massive vacuolization observed with vehicle, whereas troglitazone worsened the vacuolization. Body weight, fat pad and liver weights in BDNF-treated mice were significantly lower than those in pair-fed troglitazone-treated db/db mice, and rectal temperature in BDNF-treated mice was significantly higher than that in pair-fed troglitazone-treated mice, suggesting that BDNF enhances energy expenditure.

CONCLUSIONS

These data suggest that compared with TZDs, BDNF potently ameliorates pancreatic dysfunction, fatty liver and energy expenditure, thereby exerting favourable antidiabetic effects in type 2 diabetic mice.

Protective effect of brain-derived neurotrophic factor on pancreatic islets in obese diabetic mice

We have previously demonstrated that brain-derived neurotrophic factor (BDNF) ameliorates glucose metabolism and energy expenditure in obese diabetic db/db mice. In the present study, the effect of BDNF treatment on pancreatic islets of db/db mice was examined, using vehicle-treated pair-fed db/db mice as controls. Brain-derived neurotrophic factor (10 mg/kg) or vehicle was subcutaneously administered to male db/db mice for 4 weeks. The food intake of vehicle-treated db/db mice was restricted and precisely synchronized with that of BDNF-treated db/db mice using a pellet pair-feeding apparatus because BDNF decreases food intake in hyperphagic mice. Repetitive administration of BDNF significantly lowered the blood glucose concentration compared with pair-fed vehicle-treated db/db mice. The pancreatic insulin and glucagon concentrations were measured in db/db mice to evaluate the effect of BDNF on the pancreas. Although the insulin concentration in the pancreas of pair-fed vehicle-treated db/db mice was lower than in nondiabetic control +m/+m mice, it was higher in BDNF-treated db/db mice than in vehicle-treated pair-fed db/db mice and comparable to the concentration in +m/+m mice. The glucagon concentration in the pancreas of vehicle-treated pair-fed db/db mice was higher than in +m/+m mice, and BDNF partially decreased the glucagon concentration in the pancreas of db/db mice compared with vehicle. Histologic analyses of pancreatic sections were performed to characterize the mechanism through which BDNF modulates the hormonal concentration in the pancreas of db/db mice. Although there were no significant differences in the number and total area of islets between the BDNF- and vehicle-treated groups, immunostaining with an anti-insulin antibody indicated that the islet beta-cell area in BDNF-treated db/db mice was larger than that in vehicle-treated pair-fed db/db mice. Furthermore, immunostaining with an antiglucagon antibody indicated that BDNF normalized the delocalization of non-beta cells in islets of db/db mice. Electron microscopic images of beta cells indicated a decrease in secretory granules in vehicle-treated pair-fed db/db mice; this change was reversed in BDNF-treated db/db mice and reached a level comparable to that found in +m/+m mice. These findings suggest that BDNF prevents exhaustion of the pancreas in diabetic mice by maintaining the histologic cellular organization of beta cells and non-beta cells in pancreatic islets and restoring the level of insulin-secreting granules in beta cells.

Serum brain-derived neurotrophic factor level is increased and associated with obesity in newly diagnosed female patients with type 2 diabetes mellitus

Previous studies have demonstrated that brain-derived neurotrophic factor (BDNF) played a role in the eating behavior and glucose and lipid metabolism. In this study we measured the serum BDNF levels in newly diagnosed female patients with type 2 diabetes mellitus (n = 24, aged 34-59 years) and female subjects with normal glucose tolerance (n = 7, aged 34-56 years). The serum BDNF level was found to significantly increase in diabetic patients in comparison to that in healthy subjects (P < .05). In these patients, the serum BDNF level showed positive correlation with the body mass index (r = 0.535, P < .01), the percentage of body fat (r = 0.552, P < .01), the subcutaneous fat area based on computed tomography scan (r = 0.480, P < .05), the triglyceride level (r = 0.470, P < .05), the fasting blood glucose level (r = 0.437, P < .05), and the homeostasis model assessment of insulin resistance score (r = 0.506, P < .05), whereas it showed a negative correlation with age (r = -0.486, P < .05). The partial correlation coefficients adjusted by age showed significant differences regarding the body mass index (r = 0.423, P < .05), percentage of body fat (r = 0.504, P < .05), and triglyceride level (r = 0.426, P < .05). These results provide the first evidence that an increased BDNF is associated with a prevalence of type 2 diabetes mellitus. In addition, the BDNF is related to the total and abdominal subcutaneous fat mass and energy metabolism in the newly diagnosed female patients with type 2 diabetes mellitus.

Association between endocrine pancreas and ductal system. More than an epiphenomenon of endocrine differentiation and development?

Traditional histological descriptions of the pancreas distinguish between the exocrine and the endocrine pancreas, as if they were two functionally distinct glands. This view has been proven incorrect and can be considered obsolete. Interactions between acinar and islet tissues have been well established through numerous studies that reveal the existence of anatomical and functional relationships between these compartments of the gland. Less attention, however, has traditionally been paid to the relationships occurring between the endocrine pancreas and the ductal system. Associations between islet tissue and ducts are considered by most researchers as only a transient epiphenomenon of endocrine development. This article reviews the evidence that has emerged in the last 10 years demonstrating the existence of stable, close, and systematic relationships between these two pancreatic compartments. Functional and pathophysiological implications are considered, and the existence of an "acinar-duct-islet" axis is put forward. The pancreas appears at present to be an integrated organ composed of three functionally related components of well-orchestrated endocrine and exocrine physiological responses.

Neurotrophins in clinical diagnostics: pathophysiology and laboratory investigation

There is now growing evidence that a number of multifunctional signaling molecules, originally discovered as signal molecules in specific cells, exert their effects in various other tissue compartments. Neurotrophins, a class of homologues growth factors initially discovered to promote neuronal growth and survival, display such a dual activity and contribute to the development of a variety of non-neuronal tissues. Nowadays, several examples of essential non-neuronal functions played by neurotrophins and of variations of neurotrophin expression that accompany these processes can be presented. As will be shown, neurotrophins are found in many body tissues produced by a variety of non-neuronal cell types such as immune cells, adipocytes, endothelia, epithelia, fibroblasts, keratinocytes and endocrine cells. Assuming a general role as growth and survival factors, changes in neurotrophin expression may reflect physiological or pathological processes, such as activation, proliferation or repair followed by injury in the tissues. Neurotrophins were also present in the systemic blood circulation and variations in blood concentrations indicate vascular as well as peripheral production. In this review, we will discuss changes in local and systemic neurotrophin concentrations as well as their known pathophysiological relationship in various inflammatory and non-inflammatory disorders. Beside the nervous system, these will include diseases of the airways, skin and joints as well as systemic autoimmune diseases. Furthermore, new aspects of neurotrophin actions in maintenance of body energy balance and in reproductive endocrinology will be presented.

Remodeling of the innervation of pancreatic islets accompanies insulitis preceding onset of diabetes in the NOD mouse

The innervation of the islets of Langerhans may constitute a first target for the autoimmunity that develops in type 1 diabetes. Here, we report the occurrence of a decrease in general innervation within the islets in the nonobese diabetic (NOD) mouse, and the establishment of strands of Schwann cells, as detected via p75 and S-100 immunoreactivity (IR), and varicose nerve fibers expressing tyrosine kinase A (TrkA) in association with the immune cells. The findings suggest that there are marked attempts for neurotrophins to promote nerve ingrowth and survival for islet tissue and that remodeling of innervation occurs in the continuation of the insulitis process preceding the onset of type 1 diabetes.