A Spotlight on Appetite

Development of a mix-and-read assay for human asprosin using antibody-oligonucleotide probes and thermofluorimetric analysis

Adipose tissue, or fat tissue, can now be classified as an endocrine organ as it responds to stimuli by secreting a range of hormones, termed adipokines, which regulate the functions of various other tissues and organs. Because novel adipokines continue to be discovered and characterized by researchers, there is an enduring need for the development of new analytical assays that target these hormones. Discovered recently, asprosin is an adipokine hormone secreted by white adipose tissue (WAT) during fasting which has been implicated for its important effects on the liver, skeletal muscle, hypothalamus, pancreas, and possibly other tissues. While standard immunoassays have been developed, the continued surge in research on asprosin's function would greatly benefit from an assay with homogeneous, mix-and-read workflow, and the nanomolar clinical range makes this goal more feasible. In this work, we developed such an assay for asprosin using our thermofluorimetric analysis (TFA) methods with antibody-oligonucleotide conjugate probes. The assay, achievable in less than one hour, was successfully validated by quantifying native levels of asprosin in human serum collected from fasting, nonfasting, type II diabetic, and obese donors.

Asprosin, a novel glucogenic adipokine: a potential therapeutic implication in diabetes mellitus

OBJECTIVES

We aimed to investigate the effects of asprosin on diabetes with a focus on serum glucose, irisin, ghrelin, leptin levels and hepatic levels of triglycerides (TG), cholesterol, low-density lipoprotein (LDL).

METHODS

Asprosin (10 µg/kg) was administered intraperitoneally four times at 3-day intervals and then blood and hepatic parameters above mentioned were investigated in control and diabetic mice.

RESULTS

The administration of asprosin increased blood glucose level in healthy animals (p = .05) whereas it did not change blood glucose level in diabetic animals. In addition, while asprosin decreased irisin level and increased ghrelin level, it did not change leptin level in diabetic mice. Therewithal, asprosin decreased the increasing levels in hepatic TG, cholesterol, and LDL in diabetic mice.

CONCLUSIONS

Our novel findings implicate that asprosin may be a target molecule in preventing the development and complications of diabetes.

Fibrillin-1 and asprosin, novel players in metabolic syndrome

Fibrillin-1 is a major component of the extracellular microfibrils, where it interacts with other extracellular matrix proteins to provide elasticity to connective tissues, and regulates the bioavailability of TGFβ family members. A peptide consisting of the C-terminal 140 amino acids of fibrillin-1 has recently been identified as a glucogenic hormone, secreted from adipose tissue during fasting and targeting the liver to release glucose. This fragment, called asprosin, also signals in the hypothalamus to stimulate appetite. Asprosin levels are correlated with many of the pathologies indicative of metabolic syndrome, including insulin resistance and obesity. Previous studies and reviews have addressed the therapeutic potential of asprosin as a target in obesity, diabetes and related conditions without considering mechanisms underlying the relationship between generation of asprosin and expression of the much larger fibrillin-1 protein. Profibrillin-1 undergoes obligatory cleavage at the cell surface as part of its assembly into microfibrils, producing the asprosin peptide as well as mature fibrillin-1. Patterns of FBN1 mRNA expression are inconsistent with the necessity for regulated release of asprosin. The asprosin peptide may be protected from degradation in adipose tissue. We present evidence for an alternative possibility, that asprosin mRNA is generated independently from an internal promoter within the 3' end of the FBN1 gene, which would allow for regulation independent of fibrillin-synthesis and is more economical of cellular resources. The discovery of asprosin opened exciting possibilities for treatment of metabolic syndrome related conditions, but there is much to be understood before such therapies could be introduced into the clinic.

Apelin-13 and Asprosin in Adolescents with Anorexia Nervosa and Their Association with Psychometric and Metabolic Variables

Anorexia nervosa (AN) is a widespread, metabo-psychiatric disorder with high relapse rates, comorbidity, and mortality. Many regulatory proteins and neurohormones studied to date play essential roles in the etiopathogenesis of eating disorders and the maintenance of psychopathological symptoms. Nevertheless, the regulatory and pathophysiological mechanisms of AN are still poorly understood. In the presented study, the plasma levels of apelin-13 (APE-13) and asprosin (ASP), as well as carbohydrate metabolism parameters and psychometric parameters, were evaluated in low-weight adolescent female patients with AN (AN1), after partial weight normalization (AN2) and in an age-matched healthy control group (CG) were evaluated. APE-13 levels were higher in the AN1 group than in the post-realimentation and the CG group. APE-13 levels were independent of insulin and glucose levels. Plasma ASP levels increased with increasing body weight in patients with AN, correlating with the severity of eating disorder symptoms in emaciation. The presented data suggest that APE-13 and ASP may be AN’s biomarkers-regulation of eating behavior by APE-13 and ASP, the close relationship between them and emotional behavior, and changes in neurohormone levels in patients with eating and affective disorders seem to support these hypotheses. Moreover, their plasma levels seem to be related to the severity of psychopathological symptoms of eating disorders.

The modulatory effects of irisin on asprosin, leptin, glucose levels and lipid profile in healthy and obese male and female rats

OBJECTIVES

The main aim of this study was to investigate the effects of irisin on asprosin, leptin, glucose levels and lipid profile in healthy and obese male and female rats.

METHODS

Irisin was subcutaneously administered with osmotic minipumps at the dose of 100 ng/kg/day for 28 days and then, the serum levels of asprosin, leptin, glucose and lipid profile were investigated.

RESULTS

Irisin infusion increased asprosin levels in male rats (p = .02) but not in female rats. Irisin inhibited obesity-induced high glucose, low-density lipoprotein (LDL), triglyceride (TG) and leptin levels in all groups; however, it did not lead to any change in asprosin levels in both obese female and male rats.

CONCLUSIONS

It was determined that irisin increased serum asprosin levels and decreased LDL, TG, glucose and leptin levels, and this could indicate a protective role of irisin against obesity development.

Serum Asprosin Concentrations in Children with Prader-Willi Syndrome: Correlations with Metabolic Parameters

Children with Prader–Willi syndrome (PWS) are characterized by severe obesity. Asprosin is a newly discovered protein hormone produced by the white adipose tissue and is correlated with insulin resistance. The aim of our study was to describe the concentrations of serum asprosin in children with PWS compared to those with overweight/obesity and normal weight, and to explore the postprandial change in asprosin concentrations in participants with PWS and BMI-z matched controls. We enrolled 52 children, 23 with PWS, 8 with overweight/obesity, and 21 with normal weight. Fasting levels of asprosin, glucose, and insulin were collected in all children, and postprandial asprosin and fasting levels of acyl ghrelin (AG) and leptin were also determined in a subsample of participants. There were no significant differences among groups in fasting levels of asprosin, glucose, insulin, and HOMA-IR. Fasting serum asprosin and 1-h post-meal serum asprosin did not differ in children with PWS nor in BMI-z matched controls. Fasting asprosin showed an adjusted positive correlation with glucose in children with obesity (r = 0.93, p = 0.007) but not in children with PWS nor children with normal weight. Circulating asprosin might be a predictor of early alterations in glucose metabolism in children with obesity. More research is needed to further explain the association between asprosin, food intake, metabolism, and obesity in PWS.

Asprosin, a novel therapeutic candidate for painful neuropathy: an experimental study in mice

Recent studies indicate presence of a strong link between adipokines and neuropathic pain. However, the effects of asprosin, a novel adipokine, on neuropathic pain have not been studied in animal models.Mouse models were employed to investigate the antinociceptive effectiveness of asprosin in the treatment of three types of neuropathic pain, with metabolic (streptozocin/STZ), toxic (oxaliplatin/OXA), and traumatic (sciatic nerve ligation/CCI [chronic constriction nerve injury]) etiologies, respectively. Changes in nociceptive behaviors were assessed relative to controls using thermal (the hot plate and cold plate tests, at 50 °C and 4 °C respectively) and mechanical pain (von Frey test) tests after intraperitoneal (i.p.) administration of asprosin (10 µg/kg) and gabapentin (50 mg/kg) in several times intervals. Besides, possible effect of asprosin on the motor coordination of mice was assessed with a rotarod test. Serum level of asprosin was quantified by ELISA.In neuropathic pain models (STZ, OXA, and CCI), asprosin administration significantly reduced both mechanical and thermal hypersensitivity, indicating that it exhibits a clear-cut antihypersensitivity effect in the analyzed neuropathic pain models. The most effective time of asprosin on pain threshold was observed 60 min after its injection. Also, asprosin displayed no notable effect on the motor activity. Asprosin levels were significantly lower in neuropathic pain compared to healthy group (p < 0.05).The results yielded by the present study suggest that asprosin exhibits an analgesic effect in the neuropathic pain models and may have clinical utility in alleviating chronic pain associated with disease and injury originating from peripheral structures.

An investigation of the relationship between new fasting hormone asprosin, obesity and acute-chronic exercise: current systematic review

The purpose of this study was to reveal the relationship between new fasting hormone asprosin, obesity, and acute-chronic exercise. The prisma guidelines were followed in forming the methodological model of this review. The articles between 2016 and 2020 (including March) were identified by scanning Google Scholar, Pub Med, and Science Direct databases. Thirty-five articles were defined from 188 articles. Three cross-sectional, and 1 prospective cohort design studies in adults, and 3 cross-sectional studies in children were found. Three randomised-control group designed studies which examined the effect of acute exercise on serum asprosin levels in obese individuals. Asprosin may be a new therapeutic biomarker to be considered in the development, but long-term and deep-rooted researches are needed, and increasing the number of studies examining the effect of exercise on asprosin in the future might help us to identify the mechanisms underlying the decrease or increase in asprosin after exercise.

Asprosin-A Fasting-Induced, Glucogenic, and Orexigenic Adipokine as a New Promising Player. Will It Be a New Factor in the Treatment of Obesity, Diabetes, or Infertility? A Review of the Literature

Asprosin is a recently discovered protein released during fasting conditions mainly by adipocytes from white adipose tissue. As a glucogenic peptide, it stimulates the release of glucose from hepatic cells by binding to the OLFR734 receptor and leading to the activation of the G protein-cAMP-PKA pathway. As it crosses the blood–brain barrier, it also acts as an orexigenic peptide that stimulates food intake through activation of AgRP neurons in the hypothalamus; thus, asprosin participates in maintaining the body’s energy homeostasis. Moreover, studies have shown that asprosin levels are pathologically elevated in obesity and related diseases. However, the administration of anti-asprosin antibodies can both normalize its concentration and reduce food intake in obese mice, which makes it an interesting factor to combat obesity and related diseases. Current research also draws attention to the relationship between asprosin and fertility, especially in men. Asprosin improves age- and obesity-related decrease in fertility potential by improving sperm motility. It should also be mentioned that plasma asprosin levels can be differentially modulated by physical activity; intense anaerobic exercise increases asprosin level, while aerobic exercise decreases it. However, further research is necessary to confirm the exact mechanisms of asprosin activity and its potential as a therapeutic target.

Increased plasma asprosin levels in patients with drug-naive anorexia nervosa

PURPOSE

Asprosin is a centrally acting appetite-promoting hormone and promotes glucose production in the liver. This study is the first to investigate the difference in asprosin in the plasma between anorexia nervosa (AN) and healthy controls, and to explore the relationship between asprosin changes and plasma glucose levels and AN symptoms.

METHODS

Plasma asprosin and glucose concentrations were detected in AN patients (n = 46) and healthy control subjects (n = 47). Eating Disorder Inventory-2 (EDI-2) was used to assess subjects' eating disorder symptoms and related personality traits. The patient's concomitant levels of depression and anxiety were also measured using the beck depression inventory and beck anxiety inventory, respectively.

RESULTS

Results indicate that AN patients had a higher asprosin concentration in their plasma compared to healthy controls (p = 0.033). Among AN patients, plasma asprosin levels correlated positively with EDI-2 interoceptive awareness subscale score (p = 0.030) and negatively with duration of illness (p = 0.036). Multiple linear regression analyses showed that increases in asprosin levels (p = 0.029), glucose levels (p = 0.024) and body mass index (p = 0.003) were associated with an increase of the score of EDI-2 bulimia subscale.

CONCLUSIONS

Our findings suggest that the increase in plasma asprosin concentration in patients with AN may be a compensation for the body's energy shortage, and asprosin may be involved in the development of bulimia and lack of interoceptive awareness in AN patients.

LEVEL OF EVIDENCE

Level III, case-control analytic study.

GLP-1 and hunger modulate incentive motivation depending on insulin sensitivity in humans

OBJECTIVE

To regulate food intake, our brain constantly integrates external cues, such as the incentive value of a potential food reward, with internal state signals, such as hunger feelings. Incentive motivation refers to the processes that translate an expected reward into the effort spent to obtain the reward; the magnitude and probability of a reward involved in prompting motivated behaviour are encoded by the dopaminergic (DA) midbrain and its mesoaccumbens DA projections. This type of reward circuity is particularly sensitive to the metabolic state signalled by peripheral mediators, such as insulin or glucagon-like peptide 1 (GLP-1). While in rodents the modulatory effect of metabolic state signals on motivated behaviour is well documented, evidence of state-dependent modulation and the role of incentive motivation underlying overeating in humans is lacking.

METHODS

In a randomised, placebo-controlled, crossover design, 21 lean (body mass index [BMI] < 25 kg/m²) and 16 obese (BMI³ 30 kg/m²) volunteer participants received either liraglutide as a GLP-1 analogue or placebo on two separate testing days. Incentive motivation was measured using a behavioural task in which participants were required to exert physical effort using a handgrip to win different amounts of food and monetary rewards. Hunger levels were measured using visual analogue scales; insulin, glucose, and systemic insulin resistance as assessed by the homeostasis model assessment of insulin resistance (HOMA-IR) were quantified at baseline.

RESULTS

In this report, we demonstrate that incentive motivation increases with hunger in lean humans (F_(1,42) = 5.31, p = 0.026, β = 0.19) independently of incentive type (food and non-food reward). This effect of hunger is not evident in obese humans (F_(1,62) = 1.93, p = 0.17, β = -0.12). Motivational drive related to hunger is affected by peripheral insulin sensitivity (two-way interaction, F_{(1, 35)} = 6.23, p = 0.017, β = -0.281). In humans with higher insulin sensitivity, hunger increases motivation, while poorer insulin sensitivity dampens the motivational effect of hunger. The GLP-1 analogue application blunts the interaction effect of hunger on motivation depending on insulin sensitivity (three-way interaction, F_{(1, 127)} = 5.11, p = 0.026); no difference in motivated behaviour could be found between humans with normal or impaired insulin sensitivity under GLP-1 administration.

CONCLUSION

We report a differential effect of hunger on motivation depending on insulin sensitivity. We further revealed the modulatory role of GLP-1 in adaptive, motivated behaviour in humans and its interaction with peripheral insulin sensitivity and hunger. Our results suggest that GLP-1 might restore dysregulated processes of midbrain DA function and hence motivational behaviour in insulin-resistant humans.

Energy Regulation Mechanism and Therapeutic Potential of Asprosin

Genetic studies of patients with neonatal progeroid syndrome led to the discovery of the novel fasting-induced, glucogenic, and orexigenic hormone named asprosin, the C-terminal cleavage product of profibrillin. Upon secretion, asprosin travels to the liver, where it exerts a glucogenic effect through OR4M1, an olfactory G-protein-coupled receptor. It also crosses the blood-brain barrier to stimulate appetite-modulating neurons in the arcuate nucleus of the hypothalamus, exerting an orexigenic effect via an as yet unidentified receptor. Specifically, it stimulates appetite by activating orexigenic AgRP neurons and inhibiting anorexigenic POMC neurons. Studies have also focused on the therapeutic potential of inhibiting asprosin for treatment of obesity and type 2 diabetes, both of which are characterized by high levels of circulating asprosin. It has been shown that anti-asprosin monoclonal antibodies reduce blood glucose, appetite, and body weight, validating asprosin as a therapeutic target. Current work aims to uncover key features of the asprosin biology such as the identification of its neuronal receptor, identification of the secretion mechanism from adipose tissue, and development of anti-asprosin monoclonal antibodies as diabetes and obesity therapies.

Increased serum level and impaired response to glucose fluctuation of asprosin is associated with type 2 diabetes mellitus

AIMS/INTRODUCTION

Asprosin is a novel secreted adipokine that is induced by fasting and promotes hepatic glucose release. In healthy humans, circulating asprosin shows circadian oscillation with an acute drop coinciding with the onset of eating. The present study investigated whether this circadian oscillation still exists in patients with type 2 diabetes mellitus.

MATERIALS AND METHODS

We recruited 60 patients with type 2 diabetes mellitus and 60 individuals with normal glucose tolerance (NGT). All participants completed a 75-g oral glucose tolerance test. Fasting and 2-h postprandial serum asprosin concentrations were measured by the enzyme-linked immunosorbent assay method. Partial correlation coefficients were calculated to analyze the relationships between serum asprosin level and parameters of glucose metabolism. Multiple logistic regression analysis was used to determine the association of serum asprosin level with diabetes.

RESULTS

Both fasting and postprandial asprosin levels were significantly higher in patients with type 2 diabetes mellitus. The postprandial asprosin level was apparently lower than fasting asprosin level in individuals with NGT. The fasting asprosin level closely correlated with type 2 diabetes mellitus after multiple adjustment (odds ratio 2.329, P = 0.023). Asprosin correlated negatively with change in blood glucose (r = -0.502, P < 0.001) and change in C-peptide (r = -0.467, P < 0.001) in individuals with NGT, but not in type 2 diabetes mellitus patients.

CONCLUSIONS

Serum asprosin level decreased coinciding with the onset of the oral glucose tolerance test in individuals with NGT, whereas this circadian oscillation was disturbed in type 2 diabetes mellitus patients. The impaired response of asprosin to glucose fluctuation in type 2 diabetes mellitus patients might be one of the reasons for the onset of type 2 diabetes mellitus.

Decreased Circulating Levels of Asprosin in Obese Children

BACKGROUND

Circulating asprosin is a newly discovered adipokine that triggers the release of hepatic glucose stores and increases appetite. Asprosin levels are elevated in adult obese men as well as in mice, and reductions in asprosin protect against the hyperinsulinism associated with metabolic syndrome in mice with diet-induced obesity, which indicates a potential therapeutic role of asprosin in obesity and type 2 diabetes.

OBJECTIVES

Few data on asprosin in children are available, which is why this study aimed to assess concentrations of fasting asprosin, as well as its relationship to parameters of glucose and lipid metabolism, in children.

METHODS

Data on clinical and metabolic parameters were collected from 40 healthy normal-weight and 47 obese children. Circulating asprosin levels were measured using an ELISA.

RESULTS

The concentrations of fasting asprosin were lower in the obese children (9.24 ± 4.11 ng/mL) than in the normal-weight controls (12.33 ± 4.18 ng/mL, p < 0.001). When comparing the two groups by sex, both the boys and the girls showed similar trends. In within-group comparison, the asprosin levels were lower in boys than in girls only in the obese group (8.13 ± 4.10 vs. 10.61 ± 3.78 ng/mL, p = 0.013) but not in the control group. Interestingly, asprosin was correlated with ALT after adjusting for age and sex in all participants; in boys, asprosin was correlated with BMI, HOMA-IR, insulin, and HDL after adjusting for age.

CONCLUSIONS

Concentrations of asprosin were significantly lower in obese children than in normal-weight children, and there was a gender difference in asprosin concentration. Our results suggest a complex role for asprosin in energy metabolism.

Nutrient homeostasis - translating internal states to behavior

Behavioral neuroscience aims to describe a causal relationship between neuronal processes and behavior. Animals' ever-changing physiological needs alter their internal states. Internal states then alter neuronal processes to adapt the behavior of the animal enabling it to meet its needs. Here, we describe nutrient-specific appetites as an attractive framework to study how internal states shape complex neuronal processes and resulting behavioral outcomes. Understanding how neurons detect nutrient states and how these are integrated at the level of neuronal circuits will provide a multilevel description of the mechanisms underlying complex feeding and foraging decisions.

Eating disorder animal model

PURPOSE OF REVIEW

The aim of this review is to describe animal models that simulate the features of eating disorders. The literature pertaining to animal models that are of relevance for clinical eating disorders and the possible underpinning mechanisms was reviewed using PubMed, Ovid database and Google Scholar.

RECENT FINDINGS

New refinements of the circuits regulated by neurotransmitters and neuropeptides which instigate eating behaviours and the various feedback pathways which monitor acute and chronic nutrient status continue to be discovered. Moreover, work with the animal models that simulate the behavioural features and risk factors related to eating disorders is flourishing and providing new insights into possible causal mechanisms. For example, rodents develop binge-eating behaviours if they are intermittently exposed to processed, palatable foods and/or sugar adulterated drinks. This led to the controversial conceptualization of binge eating as a form of food addiction. Self-starvation taken to a fatal consequence such as occurs in anorexia nervosa can emerge in rodents exposed to triggers like social exclusion and/or the opportunity to exercise.

SUMMARY

There are plausible animal models for both anorexia nervosa and binge-eating disorders. These can be used to elaborate the theoretical models to explain the mechanisms underpinning eating disorders.