Oxytocin Improves β-Cell Responsivity and Glucose Tolerance in Healthy Men

Extended kangaroo mother care - Examining the utility of skin-to-skin contact over the first year of life

OBJECTIVES

Kangaroo mother care which involves skin-to-skin contact (SSC) between mothers and newborns with support for exclusive breastfeeding, is an important innovation if practiced beyond the first week of life up to 1-year of age. We posit that extended SSC can benefit postpartum metabolic health.

STUDY DESIGN

Using a narrative literature review, we examine the interaction between hormones oxytocin and cortisol, which are either released or antagonized by the neural actions of skin-to-skin contact.

RESULTS

Oxytocin is released during SSC, which promotes attachment, improves parent-infant interactions and lowers levels of cortisol. No studies to date have reported SSC use beyond the first 5 to 7 weeks postpartum. Although no differences have been observed in infant body weight, increased head circumference has been noted among pre-term and low birth weight infants. Improved breastfeeding outcomes have also been observed. Oxytocin release is protective against type-2 diabetes and obesity in postpartum women, given its effects on β-cell function, improved insulin response and reduction of plasma glucose levels. Oxytocin has anti-inflammatory, analgesic and thermoregulatory effects. Hypothetical benefits due to oxytocin-cortisol dynamics, can be assumed for maternal posttraumatic stress, postpartum depression and anxiety. Sleep patterns, duration of crying and length of sleep are dose-dependent in effect. Postnatal skin-brain connection and thermoregulation via epidermal keratinocytes may mediate the relationship between SSC and autism spectrum disorder.

CONCLUSIONS

The extended use of SSC can lower dependence on pharmacotherapeutic options concerning postpartum mental health and galactagogue use while supporting maternal-infant psychosocial well-being and lowering stress via hormonal action and HPA-axis activation.

Oxytocin does not acutely improve glucose tolerance in men with type 2 diabetes

AIM

To assess oxytocin's acute glucoregulatory impact in men with type 2 diabetes in the context of our previous findings that oxytocin improves β-cell responsivity in healthy men.

METHODS

In a double-blind, crossover comparison, intranasal oxytocin (24 IU) and placebo, respectively, were administered to 25 fasted men with non-insulin-treated type 2 diabetes (age ± standard error of the mean, 63.40 ± 1.36 years; body mass index, 27.77 ± 0.66 kg/m2; HbA1c, 6.86% ± 0.08%; Homeostatic Model Assessment of Insulin Resistance (HOMA-IR, 3.44 ± 0.39) 60 minutes before an oral glucose tolerance test (oGTT). Key outcomes were compared with previous results in men with normal weight or obesity.

RESULTS

Oxytocin compared with placebo increased plasma oxytocin concentrations and reduced the heart rate, but did not alter glucose metabolism in the 3 hours after oGTT onset (area under the curve, glucose, 2240 ± 80.5 vs. 2190 ± 69.5 mmol/L × min; insulin, 45 663 ± 4538 vs. 44 343 ± 4269 pmol/L × min; C-peptide, 235 ± 5.1 vs. 231 ± 15.9 nmol/L × min).

CONCLUSIONS

This outcome contrasts with the oxytocin-induced attenuation of early postprandial glucose excursions in normal-weight individuals, but is in line with the absence of respective effects in men with obesity. We conclude that insulin resistance in type 2 diabetes is associated with decreased sensitivity to the acute glucoregulatory effect of oxytocin in male individuals.

Breastfeeding is associated with a delayed decrease in postprandial maternal glucose concentration

BACKGROUND

Breastfeeding has long-term benefits in reducing the risk of diabetes; however, information about the acute influence on maternal glucose profile is scarce. Thus, the aim of the study was to assess maternal glucose fluctuations associated with breastfeeding episodes in women with normal glucose status.

METHODS

We performed an observational study of glucose fluctuations with breastfeeding episodes in 26 women with normal glucose status in fasting and postprandial state. Continuous glucose monitoring was performed using CGMS MiniMed Gold®/iPro2® (Medtronic, Dublin, Ireland) three months after delivery under real-life conditions. We compared fasting and postprandial periods of 150 minutes affected or not by a breastfeeding episode.

RESULTS

Mean glucose concentration of postprandial periods affected by breastfeeding was lower than not affected (-6.31 mg/dL [95% CI: -11.17, -1.62] P<0.01). Glucose concentration was significantly lower between 50 and 105 minutes after meal initiation (maximum difference -9.19 mg/dL [95% CI: -16.03, -2.16] at 91-95 min). Mean glucose concentrations of fasting periods affected by breastfeeding were similar to those not affected (-0.18 mg/dL [95% CI: -2.7, 0] P=0.831).

CONCLUSIONS

In women with normal glucose status, breastfeeding episodes are associated with a lower glucose concentration in the postprandial but not in the fasting state.

Intranasal oxytocin as a treatment for obesity: safety and efficacy

INTRODUCTION

Known for its effect on labor and lactation and on emotional and social functions, oxytocin has recently emerged as a key modulator of feeding behavior and indeed suggested as a potential treatment for obesity. The potential positive effect of oxytocin on both metabolic and psychological-behavioral complications of hypothalamic lesions makes it a promising tool in the management of these conditions.

AREAS COVERED

The aim of the present review article is to provide an overview of the mechanism of action and clinical experience of the use of oxytocin in different forms of obesity.

EXPERT OPINION

Current evidence suggests a potential role of oxytocin in the treatment of obesity with different causes. Several challenges remain: an improved understanding of the physiological regulation, mechanisms of action of oxytocin, and interplay with other endocrine axes is fundamental to clarify its role. Further clinical trials are needed to determine the safety and efficacy of oxytocin for the treatment of different forms of obesity. Understanding the mechanism(s) of action of oxytocin on body weight regulation might also improve our understanding of obesity and reveal possible new therapeutic targets - as well as promoting advances in other fields in which oxytocin might be used.

Proteomic signatures for identification of impaired glucose tolerance

The implementation of recommendations for type 2 diabetes (T2D) screening and diagnosis focuses on the measurement of glycated hemoglobin (HbA1c) and fasting glucose. This approach leaves a large number of individuals with isolated impaired glucose tolerance (iIGT), who are only detectable through oral glucose tolerance tests (OGTTs), at risk of diabetes and its severe complications. We applied machine learning to the proteomic profiles of a single fasted sample from 11,546 participants of the Fenland study to test discrimination of iIGT defined using the gold-standard OGTTs. We observed significantly improved discriminative performance by adding only three proteins (RTN4R, CBPM and GHR) to the best clinical model (AUROC = 0.80 (95% confidence interval: 0.79-0.86), P = 0.004), which we validated in an external cohort. Increased plasma levels of these candidate proteins were associated with an increased risk for future T2D in an independent cohort and were also increased in individuals genetically susceptible to impaired glucose homeostasis and T2D. Assessment of a limited number of proteins can identify individuals likely to be missed by current diagnostic strategies and at high risk of T2D and its complications.

Oxytocin: A Multi-Functional Biomolecule with Potential Actions in Dysfunctional Conditions; From Animal Studies and Beyond

Oxytocin is a hormone secreted from definite neuroendocrine neurons located in specific nuclei in the hypothalamus (mainly from paraventricular and supraoptic nuclei), and its main known function is the contraction of uterine and/or mammary gland cells responsible for parturition and breastfeeding. Among the actions of the peripherally secreted oxytocin is the prevention of different degenerative disorders. These actions have been proven in cell culture and in animal models or have been tested in humans based on hypotheses from previous studies. This review presents the knowledge gained from the previous studies, displays the results from oxytocin intervention and/or treatment and proposes that the well described actions of oxytocin might be connected to other numerous, diverse actions of the biomolecule.

Crosstalk between Schizophrenia and Metabolic Syndrome: The Role of Oxytocinergic Dysfunction

The high prevalence of metabolic syndrome in persons with schizophrenia has spurred investigational efforts to study the mechanism beneath its pathophysiology. Early psychosis dysfunction is present across multiple organ systems. On this account, schizophrenia may be a multisystem disorder in which one organ system is predominantly affected and where other organ systems are also concurrently involved. Growing evidence of the overlapping neurobiological profiles of metabolic risk factors and psychiatric symptoms, such as an association with cognitive dysfunction, altered autonomic nervous system regulation, desynchrony in the resting-state default mode network, and shared genetic liability, suggest that metabolic syndrome and schizophrenia are connected via common pathways that are central to schizophrenia pathogenesis, which may be underpinned by oxytocin system dysfunction. Oxytocin, a hormone that involves in the mechanisms of food intake and metabolic homeostasis, may partly explain this piece of the puzzle in the mechanism underlying this association. Given its prosocial and anorexigenic properties, oxytocin has been administered intranasally to investigate its therapeutic potential in schizophrenia and obesity. Although the pathophysiology and mechanisms of oxytocinergic dysfunction in metabolic syndrome and schizophrenia are both complex and it is still too early to draw a conclusion upon, oxytocinergic dysfunction may yield a new mechanistic insight into schizophrenia pathogenesis and treatment.

Potential Therapeutic Targeting Neurotransmitter Receptors in Diabetes

Neurotransmitters are signaling molecules secreted by neurons to coordinate communication and proper function among different sections in the central neural system (CNS) by binding with different receptors. Some neurotransmitters as well as their receptors are found in pancreatic islets and are involved in the regulation of glucose homeostasis. Neurotransmitters can act with their receptors in pancreatic islets to stimulate or inhibit the secretion of insulin (β cell), glucagon (α cell) or somatostatin (δ cell). Neurotransmitter receptors are either G-protein coupled receptors or ligand-gated channels, their effects on blood glucose are mainly decided by the number and location of them in islets. Dysfunction of neurotransmitters receptors in islets is involved in the development of β cell dysfunction and type 2 diabetes (T2D).Therapies targeting different transmitter systems have great potential in the prevention and treatment of T2D and other metabolic diseases.

Ameliorative Effect of Oxytocin on FBN1 and PEPCK Gene Expression, and Behavioral Patterns in Rats' Obesity-Induced Diabetes

Amelioration of hyperinsulinemia and insulin resistance associated with obesity is a cardinal target for therapeutics. Therefore, we investigated the relation of Fibrilln-1 (FBN1) mRNA expression and hepatic phosphoenolpyruvate caboxykinase (PEPCK) enzyme to the ameliorative impact of oxytocin on obesity-induced diabetes, suggesting glycogenolysis markers in diabetic models. Four groups of forty male Wistar rats were formed (n = 10): a control group fed basal diet and intraperitoneal injections of saline; an oxytocin-injected group; a diet-induced obese group fed a high-fat/high-sugar diet and injected with saline; a diet-induced obese group injected with oxytocin. Depending on blood glucose levels, obese groups were further sub-grouped into prediabetic, and diabetic rats, with 5 rats each, at the ninth and the 16th week of the feeding period, respectively. FBN1 expression and PEPCK activity were determined using the qPCR technique and some biochemical parameters (glycemic, lipid profile, kidney, and liver functions) were determined using kits. Obese groups showed an elevation of brain FBN1 expression, high serum lipid profile, high glucose level, and a deleterious impact on liver and kidney functions. Obese groups showed the stimulator effect of the PEPCK enzyme and time-dependent pathological changes in renal and hepatic tissues. The motor activities were negatively correlated with FBN1 gene expression in prediabetic and diabetic rats. In addition to our previous review of the crucial role of asprosin, here we showed that oxytocin could ameliorate obesity-induced diabetes and decrease FBN1 gene expression centrally to block appetite. Oxytocin caused decreases in PEPCK enzyme activity as well as glycogenolysis in the liver. Therefore, oxytocin has a potential effect on FBN1 expression and PEPCK enzyme activity in the obesity-induced diabetic-rat model.

Basic mechanisms of SARS-CoV-2 infection. What endocrine systems could be implicated?

Although SARS-CoV-2 viral attacks starts by the interaction of spike protein (S Protein) to ACE2 receptor located at the cell surface of respiratory tract and digestive system cells, different endocrine targets, endocrine organs and metabolic conditions are of fundamental relevance for understanding disease progression and special outcomes, in particular those of fatal consequences for the patient. During pandemic, moreover, a specific phenotype of COVID-19 metabolic patient has been described, characterized by being at particular risk of worse outcomes. In the present paper we describe the mechanism of viral interaction with endocrine organs, emphasizing the specific endocrine molecules of particular relevance explaining COVID-19 disease evolution and outcomes.

The Effects of Oxytocin on Appetite Regulation, Food Intake and Metabolism in Humans

The hypothalamic peptide oxytocin and its receptor are involved in a range of physiological processes, including parturition, lactation, cell growth, wound healing, and social behavior. More recently, increasing evidence has established the effects of oxytocin on food intake, energy expenditure, and peripheral metabolism. In this review, we provide a comprehensive description of the central oxytocinergic system in which oxytocin acts to shape eating behavior and metabolism. Next, we discuss the peripheral beneficial effects oxytocin exerts on key metabolic organs, including suppression of visceral adipose tissue inflammation, skeletal muscle regeneration, and bone tissue mineralization. A brief summary of oxytocin actions learned from animal models is presented, showing that weight loss induced by chronic oxytocin treatment is related not only to its anorexigenic effects, but also to the resulting increase in energy expenditure and lipolysis. Following an in-depth discussion on the technical challenges related to endogenous oxytocin measurements in humans, we synthesize data related to the association between endogenous oxytocin levels, weight status, metabolic syndrome, and bone health. We then review clinical trials showing that in humans, acute oxytocin administration reduces food intake, attenuates fMRI activation of food motivation brain areas, and increases activation of self-control brain regions. Further strengthening the role of oxytocin in appetite regulation, we review conditions of hypothalamic insult and certain genetic pathologies associated with oxytocin depletion that present with hyperphagia, extreme weight gain, and poor metabolic profile. Intranasal oxytocin is currently being evaluated in human clinical trials to learn whether oxytocin-based therapeutics can be used to treat obesity and its associated sequela. At the end of this review, we address the fundamental challenges that remain in translating this line of research to clinical care.

Oxytocin Signaling Acts as a Marker for Environmental Stressors in Zebrafish

The oxytocin system plays a role in stress responses and behavior modulation. However, the effects of oxytocin signaling on stress adaptation remain unclear. Here, we demonstrated the roles of oxytocin signaling as a biomarker under stress conditions in the peripheral tissues (the gills) and central nervous system (the brain). All the environmental stressors downregulated the expression of oxytocin receptors in the gills, and the alteration of the expression of oxytocin receptors was also found in the brain after the acidic (AC) and high-ammonia (HA) treatments. The number of oxytocin neurons was increased after double-deionized (DI) treatment. By transgenic line, Tg(oxtl:EGFP), we also investigated the projections of oxytocin neurons and found oxytocin axon innervations in various nuclei that might regulate the anxiety levels and aggressiveness of adult zebrafish under different environmental stresses. The oxytocin system integrates physiological responses and behavioral outcomes to ensure environmental adaptation in adult zebrafish. Our study provides insight into oxytocin signaling as a stress indicator upon environmental stressors.

Oxytocin signal contributes to the adaptative growth of islets during gestation

BACKGROUND

Increased insulin production and secretion by pancreatic β-cells are important for ensuring the high insulin demand during gestation. However, the underlying mechanism of β-cell adaptation during gestation or gestational diabetes mellitus (GDM) remains unclear. Oxytocin is an important physiological hormone in gestation and delivery, and it also contributes to the maintenance of β-cell function. The aim of this study was to investigate the role of oxytocin in β-cell adaptation during pregnancy.

METHODS

The relationship between the blood oxytocin level and pancreatic β-cell function in patients with GDM and healthy pregnant women was investigated. Gestating and non-gestating mice were used to evaluate the in vivo effect of oxytocin signal on β-cells during pregnancy. In vitro experiments were performed on INS-1 insulinoma cells.

RESULTS

The blood oxytocin levels were lower in patients with GDM than in healthy pregnant women and were associated with impaired pancreatic β-cell function. Acute administration of oxytocin increased insulin secretion in both gestating and non-gestating mice. A 3-week oxytocin treatment promoted the proliferation of pancreatic β-cells and increased the β-cell mass in gestating but not non-gestating mice. Antagonism of oxytocin receptors by atosiban impaired insulin secretion and induced GDM in gestating but not non-gestating mice. Oxytocin enhanced glucose-stimulated insulin secretion, activated the mitogen-activated protein kinase pathway, and promoted cell proliferation in INS-1 cells.

CONCLUSIONS

These findings provide strong evidence that oxytocin is needed for β-cell adaptation during pregnancy to maintain β-cell function, and the lack of oxytocin could be associated with the risk of GDM.

Obesity-induced changes in human islet G protein-coupled receptor expression: Implications for metabolic regulation

G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that are the targets for many different classes of pharmacotherapy. The islets of Langerhans are central to appropriate glucose homeostasis through their secretion of insulin, and islet function can be modified by ligands acting at the large number of GPCRs that islets express. The human islet GPCRome is not a static entity, but one that is altered under pathophysiological conditions and, in this review, we have compared expression of GPCR mRNAs in human islets obtained from normal weight range donors, and those with a weight range classified as obese. We have also considered the likely outcomes on islet function that the altered GPCR expression status confers and the possible impact that adipokines, secreted from expanded fat depots, could have at those GPCRs showing altered expression in obesity.

Oxytocin: A Potential Therapeutic for Obesity

Oxytocin is a neuropeptide involved in the homeostasis of food consumption and energy; it affects hedonic eating. Studies in obese or binge-eating patients reported the hypophagic effect of oxytocin, which reduced caloric intake after administration. Several studies have demonstrated the effect of oxytocin’s increasing energy intake, decreasing food consumption, and contributing to weight loss. Oxytocin’s effects on food intake and metabolism suggest its therapeutic potential for treating obesity and binge eating.

An overview of obesity mechanisms in humans: Endocrine regulation of food intake, eating behaviour and common determinants of body weight

Obesity is one of the biggest health challenges of the 21st century, already affecting close to 700 million people worldwide, debilitating and shortening lives and costing billions of pounds in healthcare costs and loss of workability. Body weight homeostasis relies on complex biological mechanisms and the development of obesity occurs on a background of genetic susceptibility and an environment promoting increased caloric intake and reduced physical activity. The pathophysiology of common obesity links neuro-endocrine and metabolic disturbances with behavioural changes, genetics, epigenetics and cultural habits. Also, specific causes of obesity exist, including monogenetic diseases and iatrogenic causes. In this review, we provide an overview of obesity mechanisms in humans with a focus on energy homeostasis, endocrine regulation of food intake and eating behavior, as well as the most common specific causes of obesity.

Cardiovascular protective properties of oxytocin against COVID-19

SARS-CoV-2 infection or COVID-19 has become a worldwide pandemic; however, effective treatment for COVID-19 remains to be established. Along with acute respiratory distress syndrome (ARDS), new and old cardiovascular injuries are important causes of significant morbidity and mortality in COVID-19. Exploring new approaches managing cardiovascular complications is essential in controlling the disease progression and preventing long-term complications. Oxytocin (OXT), an immune-regulating neuropeptide, has recently emerged as a strong candidate for treatment and prevention of COVID-19 pandemic. OXT carries special functions in immunologic defense, homeostasis and surveillance. It suppresses neutrophil infiltration and inflammatory cytokine release, activates T-lymphocytes, and antagonizes negative effects of angiotensin II and other key pathological events of COVID-19. Additionally, OXT can promote γ-interferon expression to inhibit cathepsin L and increases superoxide dismutase expression to reduce heparin and heparan sulphate fragmentation. Through these mechanisms, OXT can block viral invasion, suppress cytokine storm, reverse lymphocytopenia, and prevent progression to ARDS and multiple organ failures. Importantly, besides prevention of metabolic disorders associated with atherosclerosis and diabetes mellitus, OXT can protect the heart and vasculature through suppressing hypertension and brain-heart syndrome, and promoting regeneration of injured cardiomyocytes. Unlike other therapeutic agents, exogenous OXT can be used safely without the side-effects seen in remdesivir and corticosteroid. Importantly, OXT can be mobilized endogenously to prevent pathogenesis of COVID-19. This article summarizes our current understandings of cardiovascular pathogenesis caused by COVID-19, explores the protective potentials of OXT against COVID-19-associated cardiovascular diseases, and discusses challenges in applying OXT in treatment and prevention of COVID-19.

Chemical compounds

Angiotensin-converting enzyme 2 (ACE2); atrial natriuretic peptide (ANP); cathepsin L; heparan sulphate proteoglycans (HSPGs); interferon; interleukin; oxytocin; superoxide dismutase; transmembrane serine protease isoform 2 (TMPRSS2).

Effect of oxytocin on lipid accumulation under inflammatory conditions in human macrophages

INTRODUCTION AND AIMS

Oxytocin (OT) is a neuropeptide hormone secreted by the posterior pituitary gland. Deficits in OT action have been observed in patients with behavioral and mood disorders, some of which correlate with an increased risk of cardiovascular disease (CVD). Recent research has revealed a wider systemic role that OT plays in inflammatory modulation and development of atherosclerotic plaques. This study investigated the role that OT plays in cholesterol transport and foam cell formation in LPS-stimulated THP-1 human macrophages.

METHODS

THP-1 differentiated macrophages were treated with media, LPS (100 ng/ml), LPS + OT (10 pM), or LPS + OT (100 pM). Changes in gene expression and protein levels of cholesterol transporters were analyzed by real time quantitative PCR (RT-qPCR) and Western blot, while oxLDL uptake and cholesterol efflux capacity were evaluated with fluorometric assays.

RESULTS

RT-qPCR analysis revealed a significant increase in ABCG1 gene expression upon OT + LPS treatment, compared to LPS alone (p = 0.0081), with Western blotting supporting the increase in expression of the ABCG1 protein. Analysis of oxLDL uptake showed a significantly lower fluorescent value in LPS + OT (100pM) -treated cells when compared to LPS alone (p < 0.0001). While not statistically significant (p = 0.06), cholesterol efflux capacity increased with LPS + OT treatment.

CONCLUSION

We demonstrate here that OT can attenuate LPS-mediated lipid accumulation in THP-1 macrophages. These findings support the hypothesis that OT could be used to reduce pro-inflammatory and potentially atherogenic changes observed in patients with heightened CVD risk. This study suggests further exploration of OT effects on monocyte and macrophage cholesterol handling in vivo.

Oxytocin, eating behavior, and metabolism in humans

The hypothalamic peptide oxytocin has been increasingly recognized as a hormone and neurotransmitter with important effects on energy intake, metabolism, and body weight and is under investigation as a potential novel therapeutic agent for obesity. The main neurons producing oxytocin and expressing the oxytocin receptor are strategically located in brain areas known to be critically involved in homeostatic energy balance as well as hedonic and motivational aspects of eating behavior. In this chapter, we will review the central and peripheral physiology of oxytocin and the interaction of oxytocin with key hormones and neural circuitries that affect food intake and metabolism. Next, we will synthesize the available data on endogenous oxytocin levels related to caloric intake, body weight, and metabolic status. We will then review the effects of exogenous oxytocin administration on eating behavior, body weight, and metabolism in humans, including in healthy individuals as well as specific populations with suspected perturbations involving oxytocin pathways. Finally, we will address the promise and fundamental challenges of translating this line of research to clinical care.

Intranasal oxytocin has sympathoexcitatory effects on vascular tone in healthy males

Oxytocin appears to be involved in the neuroendocrine regulation of sympathetic blood pressure (BP) homeostasis. In animals, intracerebral administration of oxytocin induces BP-relevant sympathetic activation. In humans, central nervous effects of oxytocin on BP regulation remain unclear. Intranasal administration supposedly delivers oligopeptides such as oxytocin directly to the brain. We investigated the effects of intranasal oxytocin on sympathetic vascular baroreflex function in humans using microneurographic techniques. In a balanced, double-blind crossover design, oxytocin or placebo was administered intranasally to 12 lean, healthy males (age 25 ± 4 yr). Muscle sympathetic nerve activity (MSNA) was assessed microneurographically before (presubstance), 30-45 min (postsubstance I), and 105-120 min (postsubstance II) after oxytocin administration. Baroreflex was challenged via graded infusions of vasoactive drugs, and correlation of BP with MSNA and heart rate (HR) defined baroreflex function. Experiments were conducted in the afternoon after a 5-h fasting period. After oxytocin, resting MSNA (burst rate and total activity) showed significant net increases from pre to postsubstance II compared with placebo [Δincrease = +4.3 ± 1.2 (oxytocin) vs. +2.2 ± 1.4 bursts/min (placebo), ANOVA; P < 0.05; total activity = 184 ± 11.5% (oxytocin) vs. 121 ± 14.3% (placebo), ANOVA; P = 0.01). This was combined with a small but significant net increase in resting diastolic BP, whereas systolic and mean arterial BP or HR as well as baroreflex sensitivity at vasoactive drug challenge were not altered. Intranasally administered oxytocin induced vasoconstrictory sympathoactivation in healthy male humans. The concomitant increase of diastolic BP was most likely attributable to increased vascular tone. This suggests oxytocin-mediated upward resetting of the vascular baroreflex set point at centers superordinate to the mere baroreflex-feedback loop.

Comprehensive Identification of Key Genes Involved in Development of Diabetes Mellitus-Related Atherogenesis Using Weighted Gene Correlation Network Analysis

Coronary heart disease (CHD) is common in patients with diabetes mellitus (DM), however, the relevant mechanism remains elusive. The whole blood gene expression profiles of healthy control, patients with DM, patients with DM and CHD (DMCHD) were used to performed weight gene correlation network analysis (WGCNA) to identify the gene modules associated with DM-related atherogenesis. The candidate module was significantly involved in immune- and T cell activity-related biological process. GSEA results suggested that lysosome and apoptosis were enriched in DM and DMCHD samples. The protein-protein-KEGG pathway network may reveal the potential transcriptional regulatory network involving in DM-related atherosclerosis. Nineteen genes (RTKN, DCP1B, PDZD4, CACNA2D2, TSEN54, PVRIG, PLEKHF1, NKG7, ZAP70, NUDCD3, SLAMF6, CCDC107, NAG6, ZDHHC14, EOMES, VIL2, WDR54, DMAP1, and PMPCA) were considered as DM-related atherogenesis genes (DRAGs). The Gene Set Variation Analysis (GSVA) score of the DRAG set gradually increased in the control, DM and DMCHD. ROC curve analysis showed that ZAP70, TSEN54, and PLEKHF1 may be potential blood circulation biomarkers for DMCHD in patients with DM. In conclusion, we identified nineteen hallmark genes involving in DM-related atherogenesis and constructed a potential transcriptional regulatory network involving in DM-related atherosclerosis.

The Role of Oxytocin in Cardiovascular Protection

The beneficial effects of oxytocin on infarct size and functional recovery of the ischemic reperfused heart are well documented. The mechanisms for this cardioprotection are not well defined. Evidence indicates that oxytocin treatment improves cardiac work, reduces apoptosis and inflammation, and increases scar vascularization. Oxytocin-mediated cytoprotection involves the production of cGMP stimulated by local release of atrial natriuretic peptide and synthesis of nitric oxide. Treatment with oxytocin reduces the expression of proinflammatory cytokines and reduces immune cell infiltration. Oxytocin also stimulates differentiation stem cells to cardiomyocyte lineages as well as generation of endothelial and smooth muscle cells, promoting angiogenesis. The beneficial actions of oxytocin may include the increase in glucose uptake by cardiomyocytes, reduction in cardiomyocyte hypertrophy, decrease in oxidative stress, and mitochondrial protection of several cell types. In cardiac and cellular models of ischemia and reperfusion, acute administration of oxytocin at the onset of reperfusion enhances cardiomyocyte viability and function by activating Pi3K and Akt phosphorylation and downstream cellular signaling. Reperfusion injury salvage kinase and signal transducer and activator of transcription proteins cardioprotective pathways are involved. Oxytocin is cardioprotective by reducing the inflammatory response and improving cardiovascular and metabolic function. Because of its pleiotropic nature, this peptide demonstrates a clear potential for the treatment of cardiovascular pathologies. In this review, we discuss the possible cellular mechanisms of action of oxytocin involved in cardioprotection.

Hypothalamic Neuropeptide Brain Protection: Focus on Oxytocin

Oxytocin (OXT) is hypothalamic neuropeptide synthetized in the brain by magnocellular and parvo cellular neurons of the paraventricular (PVN), supraoptic (SON) and accessory nuclei (AN) of the hypothalamus. OXT acts in the central and peripheral nervous systems via G-protein-coupled receptors. The classical physiological functions of OXT are uterine contractions, the milk ejection reflex during lactation, penile erection and sexual arousal, but recent studies have demonstrated that OXT may have anti-inflammatory and anti-oxidant properties and regulate immune and anti-inflammatory responses. In the pathogenesis of various neurodegenerative diseases, microglia are present in an active form and release high levels of pro-inflammatory cytokines and chemokines that are implicated in the process of neural injury. A promising treatment for neurodegenerative diseases involves new therapeutic approaches targeting activated microglia. Recent studies have reported that OXT exerts neuroprotective effects through the inhibition of production of pro-inflammatory mediators, and in the development of correct neural circuitry. The focus of this review is to attribute a new important role of OXT in neuroprotection through the microglia–OXT interaction of immature and adult brains. In addition, we analyzed the strategies that could enhance the delivery of OXT in the brain and amplify its positive effects.

Oxytocin in the neural control of eating: At the crossroad between homeostatic and non-homeostatic signals

The understanding of the biological substrates regulating feeding behavior is relevant to address the health problems related to food overconsumption. Several studies have expanded the conventional view of the homeostatic regulation of body weight mainly orchestrated by the hypothalamus, to include also the non-homeostatic control of appetite. Such processes include food reward and are mainly coordinated by the activation of the central mesolimbic dopaminergic pathway. The identification of endogenous systems acting as a bridge between homoeostatic and non-homeostatic pathways might represent a significant step toward the development of drugs for the treatment of aberrant eating patterns. Oxytocin is a hypothalamic hormone that is directly secreted into the brain and reaches the blood circulation through the neurohypophysis. Oxytocin regulates a variety of physiologic functions, including eating and metabolism. In the last years both preclinical and clinical studies well characterized oxytocin for its effects in reducing food intake and body weight. In the present review we summarize the role played by oxytocin in the control of both homeostatic and non-homeostatic eating, within cognitive, metabolic and reward mechanisms, to mostly highlight its potential therapeutic effects as a new pharmacological approach for the development of drugs for eating disorders. We conclude that the central oxytocinergic system is possibly one of the mechanisms that coordinate energy balance at the crossroads between homeostatic and non-homeostatic mechanisms. This concept should foster studies aimed at exploring the possible exploitation of oxytocin in the treatment of aberrant eating patterns. This article is part of the special issue on Neuropeptides.

Peripheral insulin administration enhances the electrical activity of oxytocin and vasopressin neurones in vivo

Oxytocin neurones are involved in the regulation of energy balance through diverse central and peripheral actions and, in rats, they are potently activated by gavage of sweet substances. Here, we test the hypothesis that this activation is mediated by the central actions of insulin. We show that, in urethane-anaesthetised rats, oxytocin cells in the supraoptic nucleus show prolonged activation after i.v. injections of insulin, and that this response is greater in fasted rats than in non-fasted rats. Vasopressin cells are also activated, although less consistently. We also show that this activation of oxytocin cells is independent of changes in plasma glucose concentration, and is completely blocked by central (i.c.v.) administration of an insulin receptor antagonist. Finally, we replicate the previously published finding that oxytocin cells are activated by gavage of sweetened condensed milk, and show that this response too is completely blocked by central administration of an insulin receptor antagonist. We conclude that the response of oxytocin cells to gavage of sweetened condensed milk is mediated by the central actions of insulin.

Metabolic Effects of Oxytocin

There is growing evidence that oxytocin (OXT), a hypothalamic hormone well recognized for its effects in inducing parturition and lactation, has important metabolic effects in both sexes. The purpose of this review is to summarize the physiologic effects of OXT on metabolism and to explore its therapeutic potential for metabolic disorders. In model systems, OXT promotes weight loss by decreasing energy intake. Pair-feeding studies suggest that OXT-induced weight loss may also be partly due to increased energy expenditure and/or lipolysis. In humans, OXT appears to modulate both homeostatic and reward-driven food intake, although the observed response depends on nutrient milieu (eg, obese vs. nonobese), clinical characteristics (eg, sex), and experimental paradigm. In animal models, OXT is anabolic to muscle and bone, which is consistent with OXT-induced weight loss occurring primarily via fat loss. In some human observational studies, circulating OXT concentrations are also positively associated with lean mass and bone mineral density. The impact of exogenous OXT on human obesity is the focus of ongoing investigation. Future randomized, placebo-controlled clinical trials in humans should include rigorous, standardized, and detailed assessments of adherence, adverse effects, pharmacokinetics/pharmacodynamics, and efficacy in the diverse populations that may benefit from OXT, in particular those in whom hypothalamic OXT signaling may be abnormal or impaired (eg, individuals with Sim1 deficiency, Prader-Willi syndrome, or craniopharyngioma). Future studies will also have the opportunity to investigate the characteristics of new OXT mimetic peptides and the obligation to consider long-term effects, especially when OXT is given to children and adolescents. (Endocrine Reviews XX: XX - XX, 2020).

The role of oxytocin in regulation of appetitive behaviour, body weight and glucose homeostasis

Obesity and its associated complications have reached epidemic proportions in the USA and also worldwide, highlighting the need for new and more effective treatments. Although the neuropeptide oxytocin (OXT) is well recognised for its peripheral effects on reproductive behaviour, the release of OXT from somatodendrites and axonal terminals within the central nervous system (CNS) is also implicated in the control of energy balance. In this review, we summarise historical data highlighting the effects of exogenous OXT as a short-term regulator of food intake in a context-specific manner and the receptor populations that may mediate these effects. We also describe what is known about the physiological role of endogenous OXT in the control of energy balance and whether serum and brain levels of OXT relate to obesity on a consistent basis across animal models and humans with obesity. We describe recent data on the effectiveness of chronic CNS administration of OXT to decrease food intake and weight gain or to elicit weight loss in diet-induced obese (DIO) and genetically obese mice and rats. Of clinical importance is the finding that chronic central and peripheral OXT treatments both evoke weight loss in obese animal models with impaired leptin signalling at doses that are not associated with visceral illness, tachyphylaxis or adverse cardiovascular effects. Moreover, these results have been largely recapitulated following chronic s.c. or intranasal treatment in DIO non-human primates (rhesus monkeys) and obese humans, respectively. We also identify plausible mechanisms that contribute to the effects of OXT on body weight and glucose homeostasis in rodents, non-human primates and humans. We conclude by describing the ongoing challenges that remain before OXT-based therapeutics can be used as a long-term strategy to treat obesity in humans.

Oxytocin and oxytocin receptor alterations, decreased survival, and increased chemoresistance in patients with pancreatic cancer

BACKGROUND

Oxytocin (OXT) and its receptor (OXTR) is associated with cancer. The present study was to investigate the correlation between the genetic expression alterations of OXT and OXTR and the outcomes in patients with pancreatic cancer (PC).

METHODS

Information regarding OXT and OXTR genetic alterations and changes in gene expression were retrieved from the Cancer Genome Atlas (TCGA) databases and analyzed using the cBioPortal online tool. We assessed the correlation of overall survival and disease/progression-free months to either OXT or OXTR genetic alterations and changes in gene expression using Kaplan-Meier and Cox regression analyses. Quantitative PCR (qPCR) was conducted to assess the mRNA expression levels of OXT and OXTR in human PC cell lines.

RESULTS

Five percent of PC cases showed mRNA upregulation in the OXT gene. These PC cases also showed genetic alterations and changes in gene expression of OXTR. The median months of survival and disease-free survival were lower for PC cases with genetic alterations and changes in gene expression in the OXT and OXTR genes as compared to those without such alterations. qPCR data showed that OXT and OXTR mRNA expression were 1-fold and 10-fold higher, respectively in PANC-1 cell lines as compared to L3.6pl cell lines in direct negative correlation with responsiveness to gemcitabine.

CONCLUSIONS

These data suggest that OXT and OXTR may potentially be important in PC progression, chemoresistance, and patient survival, and potentially could have prognostic and therapeutic implications in a subset of PC patients.

Engineering a Potent, Long-Acting, and Periphery-Restricted Oxytocin Receptor Agonist with Anorexigenic and Body Weight Reducing Effects

The effects of oxytocin on food intake and body weight reduction have been demonstrated in both animal models and human clinical studies. Despite being efficacious, oxytocin is enzymatically unstable and thus considered to be unsuitable for long-term use in patients with obesity. Herein, a series of oxytocin derivatives were engineered through conjugation with fatty acid moieties that are known to exhibit high binding affinities to serum albumin. One analog (OT-12) in particular was shown to be a potent full agonist at the oxytocin receptor (OTR) in vitro with good selectivity and long half-life (24 h) in mice. Furthermore, OT-12 is peripherally restricted, with very limited brain exposure (1/190 of the plasma level). In a diet-induced obesity mouse model, daily subcutaneous administration of OT-12 exhibited more potent anorexigenic and body weight reducing effects than carbetocin. Thus, our results suggest that the long-acting, peripherally restricted OTR agonist may offer potential therapeutic benefits for obesity.

New Molecular Insights into the Inhibition of Dipeptidyl Peptidase-4 by Natural Cyclic Peptide Oxytocin

Protease inhibition has led to treating many diseases and has been successful in producing many commercial drugs by pharmaceutical companies. Among many proteases, serine protease has been attractive in treating metabolic disorder diabetes mellitus (DM). Gliptins have been proven to inhibit dipeptidyl peptidase-4 (DPP4), a serine protease, and are an emerging therapeutic drug target to reduce blood glucose levels, but until now there is no natural cyclic peptide proven to inhibit serine protease DPP4. This study demonstrates the potential mechanism of natural cyclic peptide oxytocin (OXT) as a DPP4 inhibitor. To achieve this, initially, activity atlas and field-based models of DPP4 inhibitors were utilized to predict the possible features of positive and negative electrostatic, hydrophobic, and activity shapes of DPP4 inhibition. Oxytocin binding mode, flexibility, and interacting residues were studied using molecular docking simulations studies. 3D-RISM calculations studies revealed that the stability of water molecules at the binding site are favorable. Finally, an experimental study using fluorescence assay revealed OXT inhibits DPP4 in a concentration-dependent manner in a significant way (p < 0.05) and possess IC50 of 110.7 nM. These new findings significantly expand the pharmaceutical application of cyclic peptides, and in specific OXT, and implicate further optimization of OXT inhibition capacity to understand the effect of DPP4 inhibition. This work highlights the development of natural cyclic peptides as future therapeutic peptides to reduce glucose levels and treat diabetes mellitus.

Oxytocin and Vasopressin Systems in Obesity and Metabolic Health: Mechanisms and Perspectives

PURPOSE OF REVIEW

The neurohypophysial endocrine system is identified here as a potential target for therapeutic interventions toward improving obesity-related metabolic dysfunction, given its coinciding pleiotropic effects on psychological, neurological and metabolic systems that are disrupted in obesity.

RECENT FINDINGS

Copeptin, the C-terminal portion of the precursor of arginine-vasopressin, is positively associated with body mass index and risk of type 2 diabetes. Plasma oxytocin is decreased in obesity and several other conditions of abnormal glucose homeostasis. Recent data also show non-classical tissues, such as myocytes, hepatocytes and β-cells, exhibit responses to oxytocin and vasopressin receptor binding that may contribute to alterations in metabolic function. The modulation of anorexigenic and orexigenic pathways appears to be the dominant mechanism underlying the effects of oxytocin and vasopressin on body weight regulation; however, there are apparent limitations associated with their use in direct pharmacological applications. A clearer picture of their wider physiological effects is needed before either system can be considered for therapeutic use.

Association of oxytocin levels and oxytocin receptor gene polymorphism (rs2254298) with cardiovascular risk factors in Brazilian elderly from Primary Health Care

BACKGROUND

Morbidity and mortality from cardiovascular disease is a typical phenomenon in the elderly, and are related to unfavorable genetic, hormonal and environmental (lifestyle) interactions. In this context, oxytocin (OT) seems plays a key role in the development of CVD by performing important actions in metabolism energy and hemodynamic variables.

OBJECTIVE

To verify if there is an association between (OT) levels and the oxytocin receptor gene (OXTR) polymorphism (rs2254298) with cardiovascular risk factors (CRF) in the elderly.

METHODS

This was a cross-sectional study in community-dwelling elderly attending primary health care. The genotyping was done using the polymerase chain reaction technique. The CRF factors investigated included hypertension, diabetes mellitus, dyslipidemia, sedentary lifestyle, and obesity. Levels of triglycerides (TGC) postprandial and glucose were measured in capillary blood. OT and cortisol levels were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The sample comprised 177 elderly individuals. OT levels showed a significant negative correlation with postprandial triglycerides (p = 0.030) and BMI (p = 0.019). OT levels were also associated with leanness (p = 0.005). On Poisson regression analysis, OT remained a predictor for leanness (p = 0.010). No significant associations were observed between the OXTR polymorphism and CRF.

CONCLUSION

The results suggest that Postprandial TGC levels are increased, while OT levels are decreased, and this hormone was significantly elevated in lean elderly. Future studies are needed to confirm these findings, and the role of OT in metabolic parameters.

Long-Acting and Selective Oxytocin Peptide Analogs Show Antidiabetic and Antiobesity Effects in Male Mice

Oxytocin (OXT) has been shown to suppress appetite, induce weight loss, and improve glycemic control and lipid metabolism in several species, including humans, monkeys, and rodents. However, OXT's short half-life in circulation and lack of receptor selectivity limit its application and efficacy. In this study, we report an OXT peptide analog (OXTGly) that is potent and selective for the OXT receptor (OXTR). OXT, but not OXTGly, activated vasopressin receptors in vitro and acutely increased blood pressure in vivo when administered IP. OXT suppressed food intake in mice, whereas OXTGly had a moderate effect on food intake when administered IP or intracerebroventricularly. Both OXT (IP) and OXTGly (IP) improved glycemic control in glucose tolerance tests. Additionally, both OXT (IP) and OXTGly (IP) stimulated insulin, glucagon-like peptide 1, and glucagon secretion in mice. We generated lipid-conjugated OXT (acylated-OXT) and OXTGly (acylated-OXTGly) and demonstrated that these molecules have significantly extended half-lives in vivo. Compared with OXT, 2-week treatment of diet-induced obese mice with acylated-OXT [subcutaneous(ly) (SC)] resulted in enhanced body weight reduction, an improved lipid profile, and gene expression changes consistent with increased lipolysis and decreased gluconeogenesis. Treatment with acylated-OXTGly (SC) also resulted in a statistically significant weight loss, albeit to a lesser degree compared with acylated-OXT treatment. In conclusion, we demonstrate that selective activation of the OXTR pathway results in both acute and chronic metabolic benefits, whereas potential activation of vasopressin receptors by nonselective OXT analogs causes physiological stress that contributes to additional weight loss.

Oxytocin: Potential to mitigate cardiovascular risk

Cardiovascular disease (CVD) remains the leading cause of death worldwide, despite multiple treatment options. In addition to elevated lipid levels, oxidative stress and inflammation are key factors driving atherogenesis and CVD. New strategies are required to mitigate risk and most urgently for statin-intolerant patients. The neuropeptide hormone oxytocin, synthesized in the brain hypothalamus, is worthy of consideration as a CVD ancillary treatment because it moderates factors directly linked to atherosclerotic CVD such as inflammation, weight gain, food intake and insulin resistance. Though initially studied for its contribution to parturition and lactation, oxytocin participates in social attachment and bonding, associative learning, memory and stress responses. Oxytocin has shown promise in animal models of atherosclerosis and in some human studies as well. A number of properties of oxytocin make it a candidate CVD treatment. Oxytocin not only lowers fat mass and cytokine levels, but also improves glucose tolerance, lowers blood pressure and relieves anxiety. Further, it has an important role in communication in the gut-brain axis that makes it a promising treatment for obesity and type 2 diabetes. Oxytocin acts through its receptor which is a class I G-protein-coupled receptor present in cells of the vascular system including the heart and arteries. While oxytocin is not used for heart disease at present, residual CVD risk remains in a substantial portion of patients despite multidrug regimens, leaving open the possibility of using the endogenous nonapeptide as an adjunct therapy. This review discusses the possible role for oxytocin in human CVD prevention and treatment.

Therapeutic Potential of Oxytocin in Atherosclerotic Cardiovascular Disease: Mechanisms and Signaling Pathways

Coronary artery disease (CAD) is a major cardiovascular disease responsible for high morbidity and mortality worldwide. The major pathophysiological basis of CAD is atherosclerosis in association with varieties of immunometabolic disorders that can suppress oxytocin (OT) receptor (OTR) signaling in the cardiovascular system (CVS). By contrast, OT not only maintains cardiovascular integrity but also has the potential to suppress and even reverse atherosclerotic alterations and CAD. These protective effects of OT are associated with its protection of the heart and blood vessels from immunometabolic injuries and the resultant inflammation and apoptosis through both peripheral and central approaches. As a result, OT can decelerate the progression of atherosclerosis and facilitate the recovery of CVS from these injuries. At the cellular level, the protective effect of OT on CVS involves a broad array of OTR signaling events. These signals mainly belong to the reperfusion injury salvage kinase pathway that is composed of phosphatidylinositol 3-kinase-Akt-endothelial nitric oxide synthase cascades and extracellular signal-regulated protein kinase 1/2. Additionally, AMP-activated protein kinase, Ca²⁺/calmodulin-dependent protein kinase signaling and many others are also implicated in OTR signaling in the CVS protection. These signaling events interact coordinately at many levels to suppress the production of inflammatory cytokines and the activation of apoptotic pathways. A particular target of these signaling events is endoplasmic reticulum (ER) stress and mitochondrial oxidative stress that interact through mitochondria-associated ER membrane. In contrast to these protective effects and machineries, rare but serious cardiovascular disturbances were also reported in labor induction and animal studies including hypotension, reflexive tachycardia, coronary spasm or thrombosis and allergy. Here, we review our current understanding of the protective effect of OT against varieties of atherosclerotic etiologies as well as the approaches and underlying mechanisms of these effects. Moreover, potential cardiovascular disturbances following OT application are also discussed to avoid unwanted effects in clinical trials of OT usages.

New Metabolic Influencer on Oxytocin Release: The Ghrelin

Background: The hypothalamic–pituitary axis by secreting neuropeptides plays a key role in metabolic homeostasis. In light of the metabolic regulation, oxytocin is a potential neuropeptide for therapies against obesity and related disorders. The aim of our study is to measure ghrelin-induced oxytocin secretion in rats and to detect the changes after administration of ghrelin antagonist. Methods: Ghrelin was administrated centrally (intracerebroventricular, i.c.v., 1.0, 10.0, and 100.0 pmol) or systemically (intravenous, i.v., 1.0, and 10.0 nmol). [d-Lys³]-GHRP-6 ghrelin antagonist was injected 15 min before ghrelin injection in a dose of 10.0 pmol i.c.v. and 10.0 nmol i.v. Results: Either i.c.v. or i.v. administration of ghrelin dose-dependently increased the plasma oxytocin concentration. Following pretreatment with the ghrelin antagonist [d-Lys³]-GHRP-6, the high plasma oxytocin level induced by ghrelin was significantly reduced. Conclusion: The results indicate that the release of oxytocin is influenced directly by the ghrelin system. Examination of the mechanism of ghrelin-induced oxytocin secretion is a new horizon for potential therapeutic options.

Oxytocin therapy in hypopituitarism: Challenges and opportunities

Patients with hypopituitarism display impaired quality of life and excess morbidity and mortality, despite apparently optimal pituitary hormone replacement. Oxytocin is a neuropeptide synthesized in the anterior hypothalamus which plays an important role in controlling social and emotional behaviour, body weight and metabolism. Recent studies have suggested that a deficiency of oxytocin may be evident in patients with hypopituitarism and craniopharyngioma, and that this may be associated with deficits in cognitive empathy. Preliminary data hint at potential benefits of oxytocin therapy in improving these deficits and the accompanying metabolic disturbances that are common in these conditions. However, several challenges remain, including an incomplete understanding of the regulation and mechanisms of action of oxytocin, difficulties in accurately measuring oxytocin levels and in establishing a diagnosis of oxytocin deficiency, and a need to determine both the optimal mode of administration for oxytocin therapy and an acceptable safety profile with long-term use. This review considers the data linking oxytocin to the neuropsychological and metabolic disturbances evident in patients with craniopharyngioma and hypopituitarism, and describes the challenges that need to be overcome before replacement therapy can be considered as a therapeutic option in clinical practice.

Intranasal oxytocin fails to acutely improve glucose metabolism in obese men

The hypothalamic neuropeptide oxytocin not only modulates psychosocial function, but also contributes to metabolic regulation. We have recently shown that intranasal oxytocin acutely improves beta-cell responsivity and glucose tolerance in normal-weight men. In the present experiment, we investigated the acute glucoregulatory impact of oxytocin in obese men with impaired insulin sensitivity. Fifteen obese healthy men with an average body mass index of 35 kg/m² and an average body fat content of 33% received a single intranasal dose (24 IU) of oxytocin before undergoing an oral glucose tolerance test. Results were analysed according to the oral minimal model and compared with our findings in normal-weight participants. In contrast to the results in normal-weight subjects, oxytocin did not blunt postprandial glucose and insulin excursions in obese men, and moreover failed to enhance beta-cell responsivity and glucose tolerance. These results indicate that pronounced obesity may be associated with a certain degree of resistance to the glucoregulatory impact of exogenous oxytocin, and underlines the need for further investigations into the potential of oxytocin to improve glucose homeostasis in the clinical context.

The OXTR Polymorphism Stratified the Correlation of Oxytocin and Glucose Homeostasis in Non-Diabetic Subjects

OBJECTIVE

Previous animal studies have shown that the oxytocin system might affect glucose homeostasis through the hypothalamus-pituitary-adrenal (HPA) axis and peripheral organs. Moreover, whether the effect is stratified by the polymorphism of oxytocin receptor gene (OXTR) remains unclear.

METHODS

In this study, we recruited 89 non-diabetic participants. Their plasma oxytocin and serum insulin profiles were obtained, and the polymorphism of OXTR rs53576 was genotyped.

RESULTS

There were significant correlations between the oxytocin level and fasting glucose level (r = -0.29, P <0.01), insulin level (r = -0.26, P = 0.01), and homeostasis model assessment-estimated insulin resistance (HOMA-IR) (r = -0.25, P = 0.01), when adjusted for age, gender, and body mass index (BMI). When further considering the stratification effects of OXTR variation, we found that the oxytocin level was significantly correlated with the fasting glucose level (r = -0.25, P = 0.04), insulin level (r = -0.35, P = 0.03), and HOMA-IR (r = -0.35, P < 0.01) in subjects with the OXTR A allele (n = 75) after adjustment for age, gender, and BMI. In addition, the oxytocin level in those with the GG genotype of OXTR was significantly negatively correlated with the leptin level (n = 14, r = -0.66, P = 0.02).

CONCLUSION

The results demonstrated that the polymorphism of OXTR plays an important role in individual differences in the correlation of oxytocin and glucose homeostasis in non-diabetic subjects.

Oxytocin in metabolic homeostasis: implications for obesity and diabetes management

Oxytocin was once understood solely as a neuropeptide with a central role in social bonding, reproduction, parturition, lactation and appetite regulation. Recent evidence indicates that oxytocin enhances glucose uptake and lipid utilization in adipose tissue and skeletal muscle, suggesting that dysfunction of the oxytocin system could underlie the pathogenesis of insulin resistance and dyslipidaemia. Murine studies revealed that deficiencies in oxytocin signalling and oxytocin receptor expression lead to obesity despite normal food intake, motor activity and increased leptin levels. In addition, plasma oxytocin concentration is notably lower in obese individuals with diabetes, which may suggest an involvement of the oxytocin system in the pathogenesis of cardiometabolic disease. More recently, small scale studies demonstrated that intranasal administration of oxytocin was associated with significant weight loss as well as improvements in insulin sensitivity and pancreatic β-cell responsivity in human subjects. The multi-pronged effects of oxytocin signalling on improving peripheral insulin sensitivity, pancreatic function and lipid homeostasis strongly suggest a role for this system as a therapeutic target in obesity and diabetes management. The complexity of obesity aetiology and the pathogenesis of obesity-related metabolic complications underscore the need for a systems approach to better understand the role of oxytocin in metabolic function.

Brain-Derived Neurotrophic Factor and Oxytocin Signaling in Association With Clinical Symptoms in Adolescent Inpatients With Anorexia Nervosa-A Longitudinal Study

INTRODUCTION

Brain-derived neurotrophic factor (BDNF), as well as oxytocin (OXY), are centrally secreted neuropeptides regulating a range of physiological processes, including food intake and metabolism. Moreover, numerous reports suggest their role in affective and cognitive symptoms of various psychiatric disorders. Thus, the study aimed to measure the serum level of BDNF and its receptor-tropomyosin-related kinase B (TrkB) and OXY in the malnourished anorexia nervosa patients and following partial weight-recovery. The correlations between levels of these proteins with the primary symptoms of the anorexia nervosa (AN) were also analyzed.

METHODOLOGY

Eighty-four adolescent AN patients were recruited into the study, but only forty-two AN patients completed it. The control group comprises of thirty age- and height-matched girls (CG). Serum BDNF, TrkB, and OXY levels were measured in AN group in two time-points-at the beginning of the hospitalization in malnourished patients (AN-T1) and again after partial weight normalization, on the day of discharge (AN-T2). The severity of eating disorders, as well as depressive and obsessive-compulsive symptoms, were assessed at the same two-time points.

RESULTS

Body mass index (BMI) differed significantly between the AN-T1, AN-T2, and CG. BDNF levels for the AN-T2 increased significantly in comparison to the AN-T1, but at two-time points were significantly lower than in the CG. The OXY level did not change with weight gain and in both groups AN-T1 and AN-T2 were statistically significantly higher than in the CG. Statistically significant negative correlations between BDNF and the severity of eating disorders symptoms were found. Depressive and obsessive-compulsive symptoms did not show significant correlations with levels of studied proteins for either malnourished or partially weight recovered AN patients.

CONCLUSIONS

BDNF serum levels were decreased in the malnourished AN patients and tended to normalize with partial weight recovery. OXY serum levels were found to be increased in the malnourished AN patients and did not normalize with partial weight recovery, confirming previous reports about its role in the etiopathogenesis of AN. BDNF can be related to aberrant eating behaviors occurring in AN. Our results do not support the role of serum levels of BDNF, TrkB, or OXY in the modulation of depressive or obsessive-compulsive symptoms.

Intranasal oxytocin reduces weight gain in diet-induced obese prairie voles

Oxytocin (OT) elicits weight loss in diet-induced obese (DIO) rodents, nonhuman primates and humans by reducing food intake and increasing energy expenditure. In addition to being important in the regulation of energy balance, OT is involved in social behaviors including parent-infant bonds, friendships, and pair bonds. However, the impact of social context on susceptibility to diet-induced obesity (DIO) and feeding behavior (including food sharing) has not been investigated in a rodent model that forms strong social bonds (i.e. prairie vole). Our goals were to determine in Prairie voles (Microtus ochrogaster) whether i) social context impacts susceptibility to DIO and ii) chronic intranasal OT reverses DIO. Voles were housed in divided cages with holes in the divider and paired with a same-sex animal with either the same food [high fat diet (HFD)/HFD, [low fat diet (LFD; chow)/chow], or the opposite food (HFD/chow or chow/HFD) for 19 weeks. HFD-fed voles pair-housed with voles maintained on the HFD demonstrated increased weight relative to pair-housed voles that were both maintained on chow. The study was repeated to determine the impact of social context on DIO susceptibility and body composition when animals are maintained on purified sugar-sweetened HFD and LFD to enhance palatability. As before, we found that voles demonstrated higher weight gain on the HFD/HFD housing paradigm, in part, through increased energy intake and the weight gain was a consequence of an increase in fat mass. However, HFD-fed animals housed with LFD-fed animals (and vice versa) showed intermediate patterns of weight gain and evidence of food sharing. Of translational importance is the finding that chronic intranasal OT appeared to reduce weight gain in DIO voles through a decrease in fat mass with no reduction in lean body mass. These effects were associated with transient reductions in food intake and increased food sharing. These findings identify a role of social context in the pathogenesis of DIO and indicate that chronic intranasal OT treatment reduces weight gain and body fat mass in DIO prairie voles, in part, by reducing food intake.

Central insulin action induces activation of paraventricular oxytocin neurons to release oxytocin into circulation

Oxytocin neurons in the paraventricular nucleus (PVN) of hypothalamus regulate energy metabolism and reproduction. Plasma oxytocin concentration is reduced in obese subjects with insulin resistance. These findings prompted us to hypothesize that insulin serves to promote oxytocin release. This study examined whether insulin activates oxytocin neurons in the PVN, and explored the underlying signaling. We generated the mice deficient of 3-phosphoinositide-dependent protein kinase-1 (PDK1), a major signaling molecule particularly for insulin, specifically in oxytocin neurons (Oxy Pdk1 KO). Insulin increased cytosolic calcium concentration ([Ca²⁺]_i) in oxytocin neurons with larger (≧25 μm) and smaller (<25 μm) diameters isolated from PVN in C57BL/6 mice. In PDK1 Oxy Pdk1 KO mice, in contrast, this effect of insulin to increase [Ca²⁺]_i was markedly diminished in the larger-sized oxytocin neurons, while it was intact in the smaller-sized oxytocin neurons. Furthermore, intracerebroventricular insulin administration induced oxytocin release into plasma in Oxy Cre but not Oxy Pdk1 KO mice. These results demonstrate that insulin PDK1-dependently preferentially activates PVN magnocellular oxytocin neurons to release oxytocin into circulation, possibly serving as a mechanism for the interaction between metabolism and perinatal functions.

Oxytocin curbs calorie intake via food-specific increases in the activity of brain areas that process reward and establish cognitive control

The hypothalamic neurohormone oxytocin decreases food intake via largely unexplored mechanisms. We investigated the central nervous mediation of oxytocin's hypophagic effect in comparison to its impact on the processing of generalized rewards. Fifteen fasted normal-weight, young men received intranasal oxytocin (24 IU) or placebo before functional magnetic resonance imaging (fMRI) measurements of brain activity during exposure to food stimuli and a monetary incentive delay task (MID). Subsequently, ad-libitum breakfast intake was assessed. Oxytocin compared to placebo increased activity in the ventromedial prefrontal cortex, supplementary motor area, anterior cingulate, and ventrolateral prefrontal cortices in response to high- vs. low-calorie food images in the fasted state, and reduced calorie intake by 12%. During anticipation of monetary rewards, oxytocin compared to placebo augmented striatal, orbitofrontal and insular activity without altering MID performance. We conclude that during the anticipation of generalized rewards, oxytocin stimulates dopaminergic reward-processing circuits. In contrast, oxytocin restrains food intake by enhancing the activity of brain regions that exert cognitive control, while concomitantly increasing the activity of structures that process food reward value. This pattern points towards a specific role of oxytocin in the regulation of eating behaviour in humans that might be of relevance for potential clinical applications.

Oxytocin is present in islets and plays a role in beta-cell function and survival

Oxytocin is associated mainly with modulating reproductive function. However, studies suggest that oxytocin also plays a role in endocrine pancreatic function. In the present study, islet expression of oxytocin and its related receptor was confirmed in mouse islets as well as cultured rodent and human beta-cells. Oxytocin significantly stimulated glucose-induced insulin secretion from isolated mouse islets. Similar insulinotropic actions were also observed in rodent BRIN BD11 and human 1.1B4 beta-cells. Positive effects of oxytocin on insulin secretion were almost fully annulled by the oxytocin receptor antagonist, atosiban. In terms of mechanism of insulin secretory action, oxytocin had no effect on beta-cell membrane potential or cAMP generation, but did augment intracellular calcium concentrations. In vivo administration of oxytocin to mice significantly reduced overall blood glucose levels and increased plasma insulin concentrations in response to a glucose challenge. Oxytocin also had a modest, but significant, appetite suppressive effect. As expected, streptozotocin diabetic mice had marked loss of beta-cell area accompanied by increases in alpha-cell area, whilst hydrocortisone treatment increased beta-cell and overall islet areas. Both mouse models of diabetes presented with dramatically decreased percentage islet oxytocin co-localisation with insulin and increased co-localisation with glucagon. More detailed studies in cultured beta-cell lines revealed direct positive effects of oxytocin on beta-cell proliferation and protection against apoptosis. Together, these data highlight a potentially important role of islet-derived oxytocin and related receptor signalling pathways on the modulation of beta-cell function and survival.

Interactions Between the Neuroendocrine System and T Lymphocytes in Diabetes

It is well established that there is a fine-tuned bidirectional communication between the immune and neuroendocrine tissues in maintaining homeostasis. Several types of immune cells, hormones, and neurotransmitters of different chemical nature are involved as communicators between organs. Apart of being key players of the adaptive arm of the immune system, it has been recently described that T lymphocytes are involved in the modulation of metabolism of several tissues in health and disease. Diabetes may result mainly from lack of insulin production (type 1 diabetes) or insufficient insulin and insulin resistance (type 2 diabetes), both influenced by genetic and environmental components. Herein, we discuss accumulating data regarding the role of the adaptive arm of the immune system in the pathogenesis of diabetes; including the action of several hormones and neurotransmitters influencing on central and peripheral T lymphocytes development and maturation, particularly under the metabolic burden triggered by diabetes. In addition, we comment on the role of T-effector lymphocytes in adipose and liver tissues during diabetes, which together enhances pancreatic β-cell stress aggravating the disease.

Oxytocin and Eating Disorders: A Narrative Review on Emerging Findings and Perspectives

BACKGROUND

The hypothalamic neuropeptide oxytocin regulates reproductive behavior and mother-infant interaction, and conclusive studies in humans indicate that oxytocin is also a potent modulator of psychosocial function. Pilot experiments have yielded first evidence that this neuropeptide moreover influences eating behavior.

METHODS

We briefly summarize currently available studies on the involvement of the oxytocin system in the pathophysiology of eating disorders, as well as on the effects of oxytocin administration in patients with these disorders.

RESULTS

Brain administration of oxytocin in animals with normal weight, but also with diet-induced or genetically induced obesity, attenuates food intake and reduces body weight. In normal-weight and obese individuals, acute intranasal oxytocin delivery curbs calorie intake from main dishes and snacks. Such effects might converge with the poignant social and cognitive impact of oxytocin to also improve dysfunctional eating behavior in the therapeutic context. This assumption has received support in first studies showing that oxytocin might play a role in the disease process of anorexia nervosa. In contrast, respective experiments in patients with bulimia nervosa and binge eating disorder are still scarce.

CONCLUSIONS

We propose a framework of oxytocin's role and its therapeutic potential in eating disorders that aims at integrating social and metabolic aspects of its pharmacological profile, and ponder perspectives and limitations of oxytocin use in the clinical setting.

The effects of oxytocin on eating behaviour and metabolism in humans

Oxytocin, a hypothalamic hormone that is secreted directly into the brain and enters the peripheral circulation through the posterior pituitary gland, regulates a range of physiologic processes, including eating behaviour and metabolism. In rodents and nonhuman primates, chronic oxytocin administration leads to sustained weight reduction by reducing food intake, increasing energy expenditure and inducing lipolysis. Oxytocin might improve glucose homeostasis, independently of its effects on weight. Clinical studies are beginning to translate these important preclinical findings to humans. This Review describes key data linking oxytocin to eating behaviour and metabolism in humans. For example, a single intranasal dose of oxytocin can reduce caloric intake, increase fat oxidation and improve insulin sensitivity in men. Furthermore, a pilot study of 8 weeks of oxytocin treatment in adults with obesity or overweight led to substantial weight loss. Together, these data support further investigation of interventions that target pathways involving oxytocin as potential therapeutics in metabolic disorders, including obesity and diabetes mellitus. Therapeutic considerations and areas for further research are also discussed.

Oxytocin and potential benefits for obesity treatment

PURPOSE OF REVIEW

Laboratory animal experiments have consistently shown that oxytocin causes early termination of food intake, thereby promoting a decrease in body weight in a long term. Recent studies have also assessed some of oxytocin's effects on appetite and energy balance in humans. The present study examines the findings of the key basic research and of the few clinical studies published thus far in the context of potential benefits and challenges stemming from the use of oxytocin in obese patients.

RECENT FINDINGS

Basic research indicates the involvement of oxytocin in satiety, processing, in reducing a drive to eat for pleasure and because of psychosocial factors. Although the results of clinical studies are very scarce, they suggest that oxytocin administered intranasally in humans decreases energy-induced and reward-induced eating, supports cognitive control of food choices, and improves glucose homeostasis, and its effectiveness may be BMI dependent.

SUMMARY

Despite the wealth of basic research showing broad anorexigenic effects of oxytocin, clinical studies on oxytocin's therapeutic potential in obesity, are still in their infancy. Future implementation of oxytocin-based pharmacological strategies in controlling energy balance will likely depend on our ability to integrate diverse behavioral and metabolic effects of oxytocin in obesity treatment regimens.