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

The interplay of oxytocin and sex hormones

The neuropeptide oxytocin has historically been associated with reproduction and maternal behavior. However, more recent research has uncovered that oxytocin has a much wider range of roles in physiology and behavior. Despite the excitement surrounding potential therapeutical applications of intranasally administered oxytocin, the results of these intervention studies have been inconsistent. Various reasons for these mixed results have been proposed, which tend to focus on methodological issues, such as study design. While methodological issues are certainly important, emerging evidence suggests that the interaction between oxytocin and sex hormones may also account for these varied findings. To better understand the purpose and function of the interaction of oxytocin with sex hormones, with a focus on estrogens, progesterone, and testosterone, we conducted a comprehensive thematic review via four perspectives: evolutionary, developmental, mechanistic, and survival. Altogether, this synergistic approach highlights the critical function of sex hormone activity for accomplishing the diverse roles of oxytocin via the modulation of oxytocin release and oxytocin receptor activity, which is also likely to contribute to the heterogeneity of outcomes after oxytocin administration.

Autophagy and inflammation an intricate affair in the management of obesity and metabolic disorders: evidence for novel pharmacological strategies?

Unhealthy lifestyle habits including a sedentary life, the lack of physical activity, and wrong dietary habits are the major ones responsible for the constant increase of obesity and metabolic disorders prevalence worldwide; therefore, the scientific community pays significant attention to the pharmacotherapy of such diseases, beyond lifestyle interventions, the use of medical devices, and surgical approaches. The intricate interplay between autophagy and inflammation appears crucial to orchestrate fundamental aspects of cellular and organismal responses to challenging stimuli, including metabolic insults; hence, when these two processes are dysregulated (enhanced or suppressed) they produce pathologic effects. The present review summarizes the existing literature reporting the intricate affair between autophagy and inflammation in the context of metabolic disorders, including obesity, diabetes, and liver metabolic diseases (non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH)). The evidence collected so far suggests that an alteration of autophagy might lead to maladaptive metabolic and inflammatory responses thus exacerbating the severity of the disease, and the most prominent conclusion underlies that autophagy might exert a protective function by contributing to balance inflammation. However, the complex nature of obesity and metabolic disorders might represent a limit of the studies; indeed, although many pharmacological treatments, producing positive metabolic effects, are also able to modulate autophagic flux and inflammation, it is not clear if the final beneficial effect might occur only by their mechanism of action, rather than because of additionally involved pathways. Finally, although future studies are needed, the observation that anti-obesity and antidiabetic drugs already on the market, including incretin mimetic agents, facilitate autophagy by dampening inflammation, strongly contributes to the idea that autophagy might represent a druggable system for the development of novel pharmacological tools that might represent an attractive strategy for the treatment of obesity and metabolic disorders.

Oxytocin as neuro-hormone and neuro-regulator exert neuroprotective properties: A mechanistic graphical review

BACKGROUND

Neurodegeneration is progressive cell loss in specific neuronal populations, often resulting in clinical consequences with significant medical, societal, and economic implications. Because of its antioxidant, anti-inflammatory, and anti-apoptotic properties, oxytocin has been proposed as a potential neuroprotective and neurobehavioral therapeutic agent, including modulating mood disturbances and cognitive enchantment.

METHODS

Literature searches were conducted using the following databases Web of Science, PubMed, Elsevier Science Direct, Google Scholar, the Core Collection, and Cochrane from January 2000 to February 2023 for articles dealing with oxytocin neuroprotective properties in preventing or treating neurodegenerative disorders and diseases with a focus on oxidative stress, inflammation, and apoptosis/cell death.

RESULTS

The neuroprotective effects of oxytocin appears to be mediated by its anti-inflammatory properties, inhibition of neuro inflammation, activation of several antioxidant enzymes, inhibition of oxidative stress and free radical formation, activation of free radical scavengers, prevent of mitochondrial dysfunction, and inhibition of apoptosis.

CONCLUSION

Oxytocin acts as a neuroprotective agent by preventing neuro-apoptosis, neuro-inflammation, and neuronal oxidative stress, and by restoring mitochondrial function.

Microbes, oxytocin and stress: Converging players regulating eating behavior

Oxytocin is a peptide-hormone extensively studied for its multifaceted biological functions and has recently gained attention for its role in eating behavior, through its action as an anorexigenic neuropeptide. Moreover, the gut microbiota is involved in oxytocinergic signaling through the brain-gut axis, specifically in the regulation of social behavior. The gut microbiota is also implicated in appetite regulation and is postulated to play a role in central regulation of hedonic eating. In this review, we provide an overview on oxytocin and its individual links with the microbiome, the homeostatic and non-homeostatic regulation of eating behavior as well as social behavior and stress.

"To brain or not to brain": evaluating the possible direct effects of the satiety factor oleoylethanolamide in the central nervous system

Introduction

Oleoylethanolamide (OEA), an endogenous N-acylethanolamine acting as a gut-to-brain signal to control food intake and metabolism, has been attracting attention as a target for novel therapies against obesity and eating disorders. Numerous observations suggested that the OEA effects might be peripherally mediated, although they involve central pathways including noradrenergic, histaminergic and oxytocinergic systems of the brainstem and the hypothalamus. Whether these pathways are activated directly by OEA or whether they are downstream of afferent nerves is still highly debated. Some early studies suggested vagal afferent fibers as the main route, but our previous observations have contradicted this idea and led us to consider the blood circulation as an alternative way for OEA's central actions.

Methods

To test this hypothesis, we first investigated the impact of subdiaphragmatic vagal deafferentation (SDA) on the OEA-induced activation of selected brain nuclei. Then, we analyzed the pattern of OEA distribution in plasma and brain at different time points after intraperitoneal administration in addition to measuring food intake.

Results

Confirming and extending our previous findings that subdiaphragmatic vagal afferents are not necessary for the eating-inhibitory effect of exogenous OEA, our present results demonstrate that vagal sensory fibers are also not necessary for the neurochemical effects of OEA. Rather, within a few minutes after intraperitoneal administration, we found an increased concentration of intact OEA in different brain areas, associated with the inhibition of food intake.

Conclusion

Our results support that systemic OEA rapidly reaches the brain via the circulation and inhibits eating by acting directly on selected brain nuclei.

Modulatory Effect of Gut Microbiota on the Gut-Brain, Gut-Bone Axes, and the Impact of Cannabinoids

The gut microbiome is a collection of microorganisms and parasites in the gastrointestinal tract. Many factors can affect this community's composition, such as age, sex, diet, medications, and environmental triggers. The relationship between the human host and the gut microbiota is crucial for the organism's survival and development, whereas the disruption of this relationship can lead to various inflammatory diseases. Cannabidiol (CBD) and tetrahydrocannabinol (THC) are used to treat muscle spasticity associated with multiple sclerosis. It is now clear that these compounds also benefit patients with neuroinflammation. CBD and THC are used in the treatment of inflammation. The gut is a significant source of nutrients, including vitamins B and K, which are gut microbiota products. While these vitamins play a crucial role in brain and bone development and function, the influence of gut microbiota on the gut-brain and gut-bone axes extends further and continues to receive increasing scientific scrutiny. The gut microbiota has been demonstrated to be vital for optimal brain functions and stress suppression. Additionally, several studies have revealed the role of gut microbiota in developing and maintaining skeletal integrity and bone mineral density. It can also influence the development and maintenance of bone matrix. The presence of the gut microbiota can influence the actions of specific T regulatory cells, which can lead to the development of bone formation and proliferation. In addition, its metabolites can prevent bone loss. The gut microbiota can help maintain the bone's equilibrium and prevent the development of metabolic diseases, such as osteoporosis. In this review, the dual functions gut microbiota plays in regulating the gut-bone axis and gut-brain axis and the impact of CBD on these roles are discussed.

Do the diverse phenotypes of Prader-Willi syndrome reflect extremes of covariation in typical populations?

The phenotypes of human imprinted neurogenetic disorders can be hypothesized as extreme alterations of typical human phenotypes. The imprinted neurogenetic disorder Prader-Willi syndrome (PWS) features covarying phenotypes that centrally involve altered social behaviors, attachment, mood, circadian rhythms, and eating habits, that can be traced to altered functioning of the hypothalamus. Here, we conducted analyses to investigate the extent to which the behavioral variation shown in typical human populations for a set of PWAS-associated traits including autism spectrum cognition, schizotypal cognition, mood, eating, and sleeping phenotypes shows covariability that recapitulates the covariation observed in individuals with PWS. To this end, we collected data from 296 typical individuals for this set of phenotypes, and showed, using principal components analysis, evidence of a major axis reflecting key covarying PWS traits. We also reviewed the literature regarding neurogenetic syndromes that overlap in their affected traits with PWS, to determine their prevalence and properties. These findings demonstrate that a notable suite of syndromes shows phenotypic overlap with PWS, implicating a large set of imprinted and non-imprinted genes, some of which interact, in the phenotypes of this disorder. Considered together, these findings link variation in and among neurogenetic disorders with variation in typical populations, especially with regard to pleiotropic effects mediated by the hypothalamus. This work also implicates effects of imprinted gene variation on cognition and behavior in typical human populations.

Oxytocin: An Old Hormone, A Novel Psychotropic Drug And Possible Use In Treating Psychiatric Disorders

BACKGROUND

Oxytocin is a nonapeptide synthesized in the paraventricular and supraoptic nuclei of the hypothalamus. Historically, this molecule has been involved as a key factor in the formation of infant attachment, maternal behavior and pair bonding and, more generally, in linking social signals with cognition, behaviors and reward. In the last decades, the whole oxytocin system has gained a growing interest as it was proposed to be implicated in etiopathogenesis of several neurodevelopmental and neuropsychiatric disorders.

METHODS

With the main goal of an in-depth understanding of the oxytocin role in the regulation of different functions and complex behaviors as well as its intriguing implications in different neuropsychiatric disorders, we performed a critical review of the current state of art. We carried out this work through PubMed database up to June 2021 with the search terms: 1) "oxytocin and neuropsychiatric disorders"; 2) "oxytocin and neurodevelopmental disorders"; 3) "oxytocin and anorexia"; 4) "oxytocin and eating disorders"; 5) "oxytocin and obsessive-compulsive disorder"; 6) "oxytocin and schizophrenia"; 7) "oxytocin and depression"; 8) "oxytocin and bipolar disorder"; 9) "oxytocin and psychosis"; 10) "oxytocin and anxiety"; 11) "oxytocin and personality disorder"; 12) "oxytocin and PTSD".

RESULTS

Biological, genetic, and epigenetic studies highlighted quality and quantity modifications in the expression of oxytocin peptide or in oxytocin receptor isoforms. These alterations would seem to be correlated with a higher risk of presenting several neuropsychiatric disorders belonging to different psychopathological spectra. Collaterally, the exogenous oxytocin administration has shown to ameliorate many neuropsychiatric clinical conditions.

CONCLUSION

Finally, we briefly analyzed the potential pharmacological use of oxytocin in patient with severe symptomatic SARS-CoV-2 infection due to its anti-inflammatory, anti-oxidative and immunoregulatory properties.

Sucrose intake by rats affected by both intraperitoneal oxytocin administration and time of day

RATIONALE

Daily limited access to palatable food or drink at a fixed time is commonly used in rodent models of bingeing. Under these conditions, entrainment may modulate intake patterns. Oxytocin is involved in circadian patterns of intake and, when administered peripherally, reduces sucrose intake. However, oxytocin's effects on intake under limited-access conditions and its potential interaction with entrainment have not been explored.

OBJECTIVES

This study examined the role of entrainment on intake patterns, oxytocin's effects on sucrose intakes and locomotor activity and whether oxytocin's effects were mediated by its actions at the oxytocin receptor.

METHODS

Sated rats received daily 1-h access to 10% sucrose solution either at a fixed or varied time of day. Rats received intraperitoneal oxytocin (0 mg/kg, 0.3 mg/kg, 1 mg/kg, 3 mg/kg) prior to sucrose access, and spontaneous locomotor activity was assessed in an open-field test. Rats were then pre-treated with an oxytocin receptor antagonist, L368,899, prior to oxytocin before sucrose access.

RESULTS

Intake patterns did not differ between fixed- or varied-time presentations; rats consumed more sucrose solution in the middle as opposed to the early-dark phase. Oxytocin dose-dependently reduced sucrose intakes, but also reduced locomotor activity. There was some evidence of partial blockade of oxytocin-induced sucrose intake reductions by L368,899, but the results were unclear.

CONCLUSIONS

Time of day and oxytocin impact sucrose solution intake under daily limited access in rats and the sedative-like effects of oxytocin should be considered in future studies on oxytocin and food intake.

Targeting the Oxytocinergic System: A Possible Pharmacological Strategy for the Treatment of Inflammation Occurring in Different Chronic Diseases

Unresolved inflammation represents a central feature of different human pathologies including neuropsychiatric, cardiovascular, and metabolic diseases. The epidemiologic relevance of such disorders justifies the increasing interest in further understanding the mechanisms underpinning the inflammatory process occurring in such chronic diseases to provide potential novel pharmacological approaches. The most common and effective therapies for controlling inflammation are glucocorticoids; however, a variety of other molecules have been demonstrated to have an anti-inflammatory potential, including neuropeptides. In recent years, the oxytocinergic system has seen an explosion of scientific studies, demonstrating its potential to contribute to a variety of physiological processes including inflammation. Therefore, the aim of the present review was to understand the role of oxytocin in the modulation of inflammation occurring in different chronic diseases. The criterion we used to select the diseases was based on the emerging literature showing a putative involvement of the oxytocinergic system in inflammatory processes in a variety of pathologies including neurological, gastrointestinal and cardiovascular disorders, diabetes and obesity. The evidence reviewed here supports a beneficial role of oxytocin in the control of both peripheral and central inflammatory response happening in the aforementioned pathologies. Although future studies are necessary to elucidate the mechanistic details underlying such regulation, this review supports the idea that the modulation of the endogenous oxytocinergic system might represent a new potential pharmacological approach for the treatment of inflammation.

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.

Reappraising the role of the vagus nerve in GLP-1-mediated regulation of eating

Here, we provide a focused review of the evidence for the roles of the vagus nerve in mediating the regulatory effects of peripherally and centrally produced GLP-1 on eating behaviour and energy balance. We particularly focus on recent studies which have used selective genetic, viral, and transcriptomic approaches to provide important insights into the anatomical and functional organisation of GLP-1-mediated gut-brain signalling pathways. A number of these studies have challenged canonical ideas of how GLP-1 acts in the periphery and the brain to regulate eating behaviour, with important implications for the development of pharmacological treatments for obesity.

The potential role of oxytocin in addiction: What is the target process?

Oxytocin regulates a variety of centrally-mediated functions, ranging from socio-sexual behavior, maternal care, and affiliation to fear, stress, anxiety. In the past years, both clinical and preclinical studies characterized oxytocin for its modulatory role on reward-related neural substrates mainly involving the interplay with the mesolimbic and mesocortical dopaminergic pathways. This suggests a role of this nonapeptide on the neurobiology of addiction raising the possibility of its therapeutic use. Although far from a precise knowledge of the underlying mechanisms, the putative role of the bed nucleus of the stria terminalis as a key structure where oxytocin may rebalance altered neurochemical processes and neuroplasticity involved in dependence and relapse has been highlighted. This view opens new opportunities to address the health problems related to drug misuse.

Understanding the appetite modulation pathways: The role of the FFA1 and FFA4 receptors

Pharmaconutrition is an area of current interest, especially concerning the advances in the pharmacology of nutrient-sensing receptors, as have been accomplished in the last 20 years. The family of free fatty acid (FFA) receptors is composed of four members, sequentially named as FFA1 to FFA4, which are activated by the short to long-chain fatty acids. The affinity of the FFA1 and FFA4 receptors for the omega-3 polyunsaturated fatty acids prompted pre-clinical and clinical investigations regarding their involvement in metabolic diseases. The main studies have been focused on the receptors' expression analyses, the featuring of knockout mice, and the assessment of selective synthetic ligands. These clearly have indicated a relevant role for FFA1 and FFA4 in the peripheral and central circuits for the regulation of energetic metabolism. This review article aimed to discuss the relevance of the FFA1 and FFA4 receptors in appetite-related complications, mainly related to obesity, cancer cachexia, and anorexia in the elderly, emphasizing whether their pharmacological modulation might be useful for the management of these disorders.

Oleoylethanolamide decreases frustration stress-induced binge-like eating in female rats: a novel potential treatment for binge eating disorder

Binge eating disorder (BED) is the most frequent eating disorder, for which current pharmacotherapies show poor response rates and safety concerns, thus highlighting the need for novel treatment options. The lipid-derived messenger oleoylethanolamide (OEA) acts as a satiety signal inhibiting food intake through the involvement of central noradrenergic and oxytocinergic neurons. We investigated the anti-binge effects of OEA in a rat model of binge-like eating, in which, after cycles of intermittent food restrictions/refeeding and palatable food consumptions, female rats show a binge-like intake of palatable food, following a 15-min exposure to their sight and smell ("frustration stress"). Systemically administered OEA dose-dependently (2.5, 5, and 10 mg kg^-1) prevented binge-like eating. This behavioral effect was associated with a decreased activation (measured by mapping the expression of c-fos, an early gene widely used as a marker of cellular activation) of brain areas responding to stress (such as the nucleus accumbens and amygdala) and to a stimulation of areas involved in the control of food intake, such as the VTA and the PVN. These effects were paralleled, also, to the modulation of monoamine transmission in key brain areas involved in both homeostatic and hedonic control of eating. In particular, a decreased dopaminergic response to stress was observed by measuring dopamine extracellular concentrations in microdialysates from the nucleus accumbens shell, whereas an increased serotonergic and noradrenergic tone was detected in tissue homogenates of selected brain areas. Finally, a decrease in corticotropin-releasing factor (CRF) mRNA levels was induced by OEA in the central amygdala, while an increase in oxytocin mRNA levels was induced in the PVN. The restoration of a normal oxytocin receptor density in the striatum paralleled the oxytocinergic stimulation produced by OEA. In conclusion, we provide evidence suggesting that OEA might represent a novel potential pharmacological target for the treatment of binge-like eating behavior.