Plasma levels of agouti-related protein are increased in obese men

Appetite- and Weight-Regulating Neuroendocrine Circuitry in Hypothalamic Obesity

Since hypothalamic obesity (HyOb) was first described over 120 years ago by Joseph Babinski and Alfred Fröhlich, advances in molecular genetic laboratory techniques have allowed us to elucidate various components of the intricate neurocircuitry governing appetite and weight regulation connecting the hypothalamus, pituitary gland, brainstem, adipose tissue, pancreas, and gastrointestinal tract. On a background of an increasing prevalence of population-level common obesity, the number of survivors of congenital (eg, septo-optic dysplasia, Prader-Willi syndrome) and acquired (eg, central nervous system tumors) hypothalamic disorders is increasing, thanks to earlier diagnosis and management as well as better oncological therapies. Although to date the discovery of several appetite-regulating peptides has led to the development of a range of targeted molecular therapies for monogenic obesity syndromes, outside of these disorders these discoveries have not translated into the development of efficacious treatments for other forms of HyOb. This review aims to summarize our current understanding of the neuroendocrine physiology of appetite and weight regulation, and explore our current understanding of the pathophysiology of HyOb.

Serum proteomic profiling of carotid arteriopathy: A population outcome study

BACKGROUND AND AIMS

Circulating proteins reflecting subclinical vascular disease may improve prediction of atherosclerotic cardiovascular disease (ASCVD). We applied feature selection and unsupervised clustering on proteomic data to identify proteins associated with carotid arteriopathy and construct a protein-based classifier for ASCVD event prediction.

METHODS

491 community-dwelling participants (mean age, 58 ± 11 years; 51 % women) underwent carotid ultrasonography and proteomic profiling (CVD II panel, Olink Proteomics). ASCVD outcome was collected (median follow-up time: 10.2 years). We applied partial least squares (PLS) to identify proteins linked to carotid intima-media thickness (cIMT). Next, we assessed the association between future ASCVD events and protein-based phenogroups derived by unsupervised clustering (Gaussian Mixture modelling) based on proteins selected in PLS.

RESULTS

PLS identified 19 proteins as important, which were all associated with cIMT in multivariable-adjusted linear regression. 8 of the 19 proteins were excluded from the clustering analysis because of high collinearity. Based on the 11 remaining proteins, the clustering algorithm subdivided the cohort into two phenogroups. Compared to the first phenogroup (n = 177), participants in the second phenogroup (n = 314) presented: i) a more unfavorable lipid profile with higher total cholesterol and triglycerides and lower HDL cholesterol (p ≤ 0.014); ii) higher cIMT (p = 0.0020); and iii) a significantly higher risk for future ASCVD events (multivariable-adjusted hazard ratio (95 % CI) versus phenogroup 1: 2.05 (1.26-3.52); p = 0.0093). The protein-based phenogrouping supplemented ACC/AHA 10-year ASCVD risk scoring for prediction of a first ASCVD event.

CONCLUSIONS

Focused protein-based phenogrouping identified individuals at high risk for future ASCVD and may complement current risk stratification strategies.

Serum Levels of Hormones Regulating Appetite in Patients with Fetal Alcohol Spectrum Disorders

Prenatal alcohol exposure is the cause of impaired growth and a wide range of developmental and behavioral disorders in the child. Improper eating patterns are commonly associated with fetal alcohol spectrum disorders (FASD) and may contribute to poor nutrition and growth restriction. To date, there have been only a few studies investigating the hormonal regulation of appetite in patients with FASD. We analyzed the levels of neuropeptide Y (NPY), Agouti signaling protein (ASP), alpha-melanocyte-stimulating hormone (α-MSH), and kisspeptin (KISS1) in 57 patients with FASD and 23 healthy controls. A comparison of the hormone levels studied was also performed in subgroups of fetal alcohol syndrome (FAS) and neurobehavioral disorder associated with prenatal alcohol exposure (ND PAE), as well as in males and females. We have found no differences in hormone levels tested between affected individuals and the controls and between FASD subgroups. In addition, sex had no effect on hormone levels. However, we identified some associations between hormone concentrations and parameters describing the clinical status of patients with FASD. Most of them concerned ASP, which has shown a positive correlation with age and hormones involved in appetite and metabolism, such as proopiomelanocortin (POMC) and adrenocorticotropic hormone (ACTH). We have also found a negative correlation of α-MSH with age, BMI percentile, and glycated hemoglobin (HbA1c). Furthermore, we found a weak negative correlation of NPY with HbA1c. Although FASD has been associated with impaired child growth and development, including nutrition and puberty onset, we did not identify differences in the levels of the hormones studied, which may suggest that prenatal alcohol exposure does not affect the levels of these metabolites.

Evaluating the association between the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet, mental health, and cardio-metabolic risk factors among individuals with obesity

BACKGROUND

Several previous investigations have examined the brain-protective role of the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet. However, more knowledge is needed about the MIND diet's other favorable impacts. The purpose of this study was to examine the relationship between the MIND diet, mental health, and metabolic markers in individuals with obesity.

METHODS

In this cross-sectional study, we included 339 individuals with obesity (BMI ≥ 30 kg/m²) aged 20-50 years. We utilized a semi-quantitative Food Frequency Questionnaire (FFQ), we assessed dietary intake, including 168 food items, and calculated the value of MIND. Metabolic syndrome (MetS) was defined according to the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) guidelines. We assessed biochemical parameters using Enzymatic methods. Blood pressure and body composition were also determined.

RESULTS

Higher tertiles of the MIND diet score were associated with significantly higher energy intake, macronutrients, and brain-healthy food intakes (P < 0.001). Among the brain-unhealthy foods, only the intake of sweets and pastries was significantly lower in the highest versus lowest MIND tertiles. We also observed lower odds of stress (P < 0.05) and higher insulin sensitivity (P < 0.05) in the highest versus lowest MIND diet tertiles. We witnessed no significant changes in other parameters.

CONCLUSION

Lower stress levels and higher insulin sensitivity independent of some confounders like age, BMI, sex, and physical activity were associated with the highest tertile of MIND diet score.

Modeling the effects of genetic- and diet-induced obesity on melanoma progression in zebrafish

Obesity is a rising concern and associated with an increase in numerous cancers, often in a sex-specific manner. Preclinical models are needed to deconvolute the intersection between obesity, sex and melanoma. Here, we generated a zebrafish system that can be used as a platform for studying these factors. We studied how germline overexpression of Agrp along with a high-fat diet affects melanomas dependent on BRAFV600E and loss of p53. This revealed an increase in tumor incidence and area in male, but not female, obese fish, consistent with the clinical literature. We then determined whether this was further affected by additional somatic mutations in the clinically relevant genes rb1 or ptena/b. We found that the male obesogenic effect on melanoma was present with tumors generated with BRAF;p53;Rb1 but not BRAF;p53;Pten. These data indicate that both germline (Agrp) and somatic (BRAF, Rb1) mutations contribute to obesity-related effects in melanoma. Given the rapid genetic tools available in the zebrafish, this provides a high-throughput system to dissect the interactions of genetics, diet, sex and host factors in obesity-related cancers.

Rescue of obesity-induced infertility in female mice by silencing AgRP neurons

Obesity impacts multiple sites of the hypothalamus-pituitary gland-ovary axis (HPO axis) and has become a leading cause of female infertility. However, the critical hypothalamic neurons that participate in the development of obesity-induced infertility have not been well defined yet. Previous studies suggested that metabolic-sensing agouti-related peptide-expressing (AgRP) neurons in the arcuate nucleus (ARC) are hyperactive in diet-induced obesity (DIO) mice. We hypothesize that these neurons may convey metabolic dysfunction onto the HPO axis and contribute to obesity-induced infertility's pathophysiological process. To determine if AgRP neurons in obesity play a necessary role in the development of reproductive impairment in obesity, we used the chemogenetic method to normalize the neuronal activity of AgRP neurons in DIO female mice and test if their fertility can be restored. Our results indicated that chemogenetic inhibition of AgRP neurons could fully rescue the reproductive performance of DIO female mice, as manifested by recovered sex hormonal levels, ovulation, and fecundity. Moreover, we assayed serum AgRP levels in normal-weight and obese women and found elevated AgRP levels in obese subjects, suggesting the correlation between obesity and AgRP neuronal hyperactivity. Our results indicated that AgRP neurons constitute a central node connecting metabolism and reproduction, and dysfunctions of these neurons play a crucial role in reproductive impairment induced by metabolic abnormalities.

A gene-diet interaction controlling relative intake of dietary carbohydrates and fats

OBJECTIVE

Preference for dietary fat vs. carbohydrate varies markedly across free-living individuals. It is recognized that food choice is under genetic and physiological regulation, and that the central melanocortin system is involved. However, how genetic and dietary factors interact to regulate relative macronutrient intake is not well understood.

METHODS

We investigated how the choice for food rich in carbohydrate vs. fat is influenced by dietary cholesterol availability and agouti-related protein (AGRP), the orexigenic component of the central melanocortin system. We assessed how macronutrient intake and different metabolic parameters correlate with plasma AGRP in a cohort of obese humans. We also examined how both dietary cholesterol levels and inhibiting de novo cholesterol synthesis affect carbohydrate and fat intake in mice, and how dietary cholesterol deficiency during the postnatal period impacts macronutrient intake patterns in adulthood.

RESULTS

In obese human subjects, plasma levels of AGRP correlated inversely with consumption of carbohydrates over fats. Moreover, AgRP-deficient mice preferred to consume more calories from carbohydrates than fats, more so when each diet lacked cholesterol. Intriguingly, inhibiting cholesterol biosynthesis (simvastatin) promoted carbohydrate intake at the expense of fat without altering total caloric consumption, an effect that was remarkably absent in AgRP-deficient mice. Finally, feeding lactating C57BL/6 dams and pups a cholesterol-free diet prior to weaning led the offspring to prefer fats over carbohydrates as adults, indicating that altered cholesterol metabolism early in life programs adaptive changes to macronutrient intake.

CONCLUSIONS

Together, our study illustrates a specific gene-diet interaction in modulating food choice.

Association between Ag-RP, alpha-MSH and cardiovascular risk factors regarding adherence to diet quality index-international (DQI-I) among obese individuals

Introduction: Obesity is a strong promoter of cardiometabolic risk factors and is associated with several chronic comorbidities. Recently, the role of α-melanocyte stimulating hormone (α-MSH) and agouti related peptide (Ag-RP) in regulation of energy balance has attracted much attention. In current study, we evaluated the association between α-MSH and Ag-RP with cardiometabolic factors among obese individuals with different adherence to Diet Quality Index-International (DQI-I) values.

Methods: In this research, 188 obese adults aged between 20 and 50 years old and body mass index (BMI) between 30 and 40 kg/m² were recruited. Dietary intakes of participants and DQI-I calculation was performed using a semi-quantitative food frequency questionnaire (FFQ) with 132 food items. Serum glucose, lipids, insulin, and plasma α-MSH and Ag-RP levels were measured using ELISA kits. Homeostasis model assessment for insulin resistance index (HOMA-IR) and quantitative insulin sensitivity check index (QUICKI) were also calculated.

Results: Among those with the lowest adherence to DQI-I, Ag-RP was positively associated with systolic blood pressure (SBP) (P = 0.03) among males, which was associated with waist circumference (WC) (P = 0.01) and diastolic blood pressure (DBP) (P = 0.01). Moreover, among males with low and moderate adherence to DQI-I, α-MSH was positively associated with insulin (P = 0.04), weight (P = 0.03), WC (P < 0.01), SDP (P = 0.02) and DBP (P = 0.01). Also, Ag-RP showed a positive association with BMI values (R² = 0.03; P = 0.03).

Conclusion: According to our findings, in obese subjects with poor to moderate adherence to DQI-I, Ag-RP and α-MSH were in positive correlation with cardiometabolic risk factors. These findings further clarify the clinical importance of these parameters as prognostic factors of cardiometabolic abnormalities.

Pregnancy-specific Adaptations in Leptin and Melanocortin Neuropeptides in Early Human Gestation

INTRODUCTION

Pregnancy is characterized by increased appetitive drive beginning early in gestation, yet the central mechanisms underlying this adaptation are poorly understood in humans. To elucidate central mechanisms underlying appetite regulation in early pregnancy, we examine plasma and cerebrospinal fluid (CSF) leptin and Agouti-related peptide (AgRP) as well as CSF proopiomelanocortin (POMC) as surrogates for brain melanocortin activity.

METHODS

Plasma leptin, soluble leptin receptor, AgRP, and CSF leptin, POMC, and AgRP were collected from pregnant women before cerclage placement (16.6 ± 1.1 weeks; N = 24), scheduled cesarean section (39.2 ± 0.2 weeks; N = 24), and from nonpregnant controls (N = 24), matched for age and body mass index.

RESULTS

Plasma leptin was 1.5 times higher in pregnancy vs controls (P = 0.01), but CSF leptin did not differ. CSF/plasma leptin percentage was lower in early pregnancy vs controls (0.8 ± 0.1 vs 1.7 ± 0.2; P < 0.0001) and remained unchanged at term (0.9 ± 0.1), supporting a decrease in leptin transport into CSF in pregnancy. Plasma AgRP, a peripheral biomarker of the orexigenic hypothalamic neuropeptide, was higher in early pregnancy vs controls (95.0 ± 7.8 vs 67.5 ± 5.3; P = 0.005). In early gestation, CSF AgRP did not differ from controls, but CSF POMC was 25% lower (P = 0.006). In contrast, at term, CSF AgRP was 42% higher vs controls (P = 0.0001), but CSF POMC no longer differed. Overall, the CSF AgRP/POMC ratio was 1.5-fold higher in early pregnancy vs controls, reflecting a decrease in melanocortin tone favoring appetitive drive.

CONCLUSIONS

Pregnancy-specific adaptions in the central regulation of energy balance occur early in human gestation and are consistent with decreased leptin transport into brain and resistance to the effects of leptin on target melanocortin neuropeptides.

Melanocortin-4 receptor (MC4R) rs17782313 polymorphism interacts with Dietary Approach to Stop Hypertension (DASH) and Mediterranean Dietary Score (MDS) to affect hypothalamic hormones and cardio-metabolic risk factors among obese individuals

BACKGROUND AND AIM

The association with obesity of a common variant near the melanocortin-4 receptor (MC4R) gene (rs17782313) has been indicated in various studies. Adherence to dietary quality indices also have shown to have potential favorable effects on obesity-related health outcomes. However, no study has examined the interaction between rs17782313 and the Dietary Approach to Stop Hypertension (DASH) score and the Mediterranean Dietary Score (MDS) on cardio-metabolic risk factors and hypothalamic hormones. Therefore, the purpose of the current study was to examine whether adherence to these dietary quality indices modifies the association of the MC4R rs17782313 polymorphism with cardio-metabolic risk factors and hypothalamic hormones among obese adults.

METHOD

Two hundred eighty-eight healthy obese adults were recruited in this cross-sectional study. Diet quality indices, including DASH score and MDS, were calculated from a validated 147-item food frequency questionnaire (FFQ). MC4R s17782313 genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). An ANCOVA multivariate interaction model was used to assess the gene-diet interaction.

RESULTS

Significant interactions were detected between DASH score and MC4R rs17782313 genotypes on systolic blood pressure (SBP), atherogenic index of plasma (AIP), and serum glucose and triglyceride (TG) among the female group (p_Interaction < 0.05). In the male group, there were gene-DASH and gene-MDS interactions in relation to serum glucose concentration and plasma α-melanocyte stimulating hormone (MSH) levels, but these were found only in multi-adjusted interaction models (p_Interaction < 0.05). In addition, there was a significant interaction between MC4R rs17782313 polymorphism and DASH score on plasma agouti-related peptide (AgRP) concentrations in the female group in a multivariate interaction model (p_Interaction < 0.05). An inverse association between DASH score and chance of having the CC genotype in a multivariate-adjusted model among women was also revealed.

CONCLUSION

MC4R rs17782313 interacts with healthy dietary pattern (DASH score and MDS) to influence cardio-metabolic risk factors and hypothalamic hormones in obese individuals. Prospective cohort studies are needed to further assess these findings.

The Role of Leptin Levels in Adaptation to Cold Climates

Currently, adipose tissue is considered an endocrine organ that produces hormone-active substances, including leptin, which can play a key role in thermoregulation processes. Therefore, we performed a meta-analysis to investigate the influence of the climatic environment on leptin levels. A systematic literature search in the databases was carried out on 10 January 2020. Finally, 22 eligible articles were included in the current meta-analysis and a total of 13,320 participants were covered in the final analysis. It was shown that males of the “North” subgroup demonstrated significantly higher levels of leptin (10.02 ng/mL; CI: 7.92–12.13) than males of the “South” subgroup (4.9 ng/mL; CI: 3.71–6.25) (p = 0.0001). On the contrary, in the female group, a similar pattern was not detected (p = 0.91). Apparently, in order to maintain body temperature, higher leptin levels are required. The results of the study indicate that such effects are most pronounced in males and to a smaller extent in females, apparently due to a relatively high initial concentration of leptin in females. The correlation between leptin levels and climatic environment data support the hypothesis of leptin-mediated thermoregulation as an adaptive mechanism to cold climates.

Dietary quality indices modifies the effects of melanocortin-4 receptor (MC4R) rs17782313 polymorphism on cardio-metabolic risk factors and hypothalamic hormones in obese adults

BACKGROUND

Although the Melanocortin-4 Receptor (MC4R) gene rs17782313 C/T has been consistently related to obesity risk, the interaction between MC4R polymorphism and diet quality indices on cardio-metabolic risk factors has not yet investigated. Therefore we aimed to test this hypothesis.

METHODS

This cross-sectional study recruited 188 (96 males and 92 females) healthy obese adults aged 20-50 years. Diet quality indices including Healthy Eating Index-2015 (HEI-2015) and Diet Quality Index-International (DQI-I) were constructed using data from a validated food frequency questionnaire. MC4R s17782313 were genotyped by Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP). The interaction between MC4R polymorphism and diet quality indices was tested by Analysis of covariance (ANCOVA) multivariate interaction model.

RESULTS

There were significant gene-diet interactions between rs17782313 and HEI-2015 (P Interaction < 0.05) in modulating low-density lipoprotein cholesterol (LDL-C) levels among female group; rare allele heterozygotes of rs17782313 had highest mean of LDL-C concentration when placed in second tertile of HEI (P < 0.05). Moreover, rs17782313 and both indices (HEI and DQI-I) had significant interaction on serum glucose concentrations, systolic and diastolic blood pressure (SBP, DBP) in males (P Interaction < 0.05); when adherence to these indices was low, the obesity risk allele was associated with serum glucose concentrations, SBP and DBP. These gene-diet interactions remained significant even after adjustment for potential confounders.

CONCLUSION

Our study showed that MC4R rs17782313 interacts with adherence to the dietary quality indices (HEI and DQI-I) to influence several cardio-metabolic risk factors in obese male and females. Further large prospective studies are warranted to confirm our findings.

Cocaine and amphetamine-regulated transcript prepropeptide gene (CARTPT) polymorphism interacts with Diet Quality Index-International (DQI-I) and Healthy Eating Index (HEI) to affect hypothalamic hormones and cardio-metabolic risk factors among obese individuals

BACKGROUND

Epidemiologic studies show that cocaine- and amphetamine-regulated transcript prepropeptide (CARTPT) gene polymorphism modifies diet-obesity relationships. However, the interaction between CARTPT gene polymorphism and diet quality indices have not been investigated yet. The current study was aimed to evaluate the interaction between major dietary indices including Diet Quality Index-International (DQI-I) and Healthy Eating Index (HEI)-2015 and CARTPT gene rs2239670 variants among apparently healthy obese Iranians.

METHODS

This cross-sectional study was carried out by employing 288 apparently healthy obese adults aged 20-50 years with a BMI of 30-40 kg/m2. Diet quality was evaluated by Diet Quality Index-International (DQI-I) and Healthy Eating Index-2015 (HEI-2015) using a 132-items semi-quantitative validated food frequency questionnaire. The CARTPT gene rs2239670 polymorphism was genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. Blood concentrations of glycemic markers, lipid profile, α-melanocyte stimulating hormone (MSH) and agouti-related peptide (AgRP) were also measured. ANCOVA multivariate interaction model was used to analyze gene-diet interactions.

RESULTS

The significant interactions were identified between CARTPT gene polymorphism and HEI, affecting BMR (PInteraction = 0.003), serum glucose (PInteraction = 0.009) and high density lipoprotein cholesterol HDL concentrations (PInteraction = 0.03) after adjusting for the effects of sex and age. Also we found gene-diet interaction between CARTPT genotypes and DQI-I in terms of fat mass (FM; PInteraction = 0.02), waist circumference (WC; PInteraction < 0.001), body mass index (BMI; PInteraction < 0.001), basal metabolic rate (BMR, PInteraction < 0.001), serum fasting glucose (PInteraction < 0.01) and AgRP (PInteraction = 0.05) in individuals even after adjusting for potential confounders.

CONCLUSION

Current study showed the effects of interaction between CARTPT genotype with adherence to HEI and DQI-I scores on obesity-related anthropometric and metabolic risk-factors.

Plasma Agouti-Related Protein and Cortisol Levels in Cushing Disease: Evidence for the Regulation of Agouti-Related Protein by Glucocorticoids in Humans

CONTEXT

Glucocorticoids regulate energy balance, in part by stimulating the orexigenic neuropeptide agouti-related protein (AgRP). AgRP neurons express glucocorticoid receptors, and glucocorticoids have been shown to stimulate AgRP gene expression in rodents.

OBJECTIVE

We sought to determine whether there is a relationship between plasma AgRP and hypothalamic AgRP in rats and to evaluate the relationship between cortisol and plasma AgRP in humans.

METHODS

We retrospectively evaluated plasma AgRP levels prior to transsphenoidal surgery in 31 patients with Cushing disease (CD) vs 31 sex- and body mass index-matched controls from a separate study. We then prospectively measured plasma AgRP, before and 6 to 12 months after surgery, in a subgroup of 13 patients with CD. Plasma and hypothalamic AgRP were measured in adrenalectomized rats with and without corticosterone replacement.

RESULTS

Plasma AgRP was stimulated by corticosterone in rats and correlated with hypothalamic AgRP expression. Plasma AgRP levels were higher in patients with CD than in controls (139 ± 12.3 vs 54.2 ± 3.1 pg/mL; P < 0.0001). Among patients with CD, mean 24-hour urine free cortisol (UFC) levels were 257 ± 39 μg/24 hours. Strong positive correlations were observed between plasma AgRP and UFC (r = 0.76; P < 0.0001). In 11 of 13 patients demonstrating surgical cure, AgRP decreased from 126 ± 20.6 to 62.5 ± 8.0 pg/mL (P < 0.05) postoperatively, in parallel with a decline in UFC.

CONCLUSIONS

Plasma AgRP levels are elevated in CD, are tightly correlated with cortisol concentrations, and decline with surgical cure. These data support the regulation of AgRP by glucocorticoids in humans. AgRP's role as a potential biomarker and as a mediator of the adverse metabolic consequences of CD deserves further study.

Serum agouti-related protein (AgRP) levels in bipolar disorder: Could AgRP be a state marker for mania?

Orexigenic and anorexigenic peptides, especially agouti-related protein (AgRP) and leptin, play important roles in the regulation of energy homeostasis in bipolar disorder. AgRP regulates energy metabolism by increasing appetite and decreasing energy expenditure. The resting energy expenditures of patients with manic bipolar disorder are higher than those of controls. Due to the effects of AgRP on energy expenditure and the increased physical activity of manic patients, we hypothesised that serum AgRP levels may be lower in manic patients than in euthymic patients and controls. There was a total of 112 participants, including 47 patients in the manic group, 35 patients in the euthymic group and 30 healthy controls. For this study, serum AgRP, leptin, cholesterol, and cortisol levels were measured and compared between the groups. The serum AgRP, leptin, and cholesterol levels were significantly different between the groups. The serum AgRP levels of manic group were significantly lower than those of euthymic and control groups. The lower serum AgRP levels of manic patients could be indicators of impaired energy homeostasis during manic episodes. Since the serum AgRP levels of manic patients are lower than those of euthymic patients and controls, AgRP could be a state marker for manic episodes.

Regulation of plasma agouti-related protein and its relationship with hunger in lean and obese men

Agouti-related protein (AgRP) is an orexigenic (appetite stimulating) neuropeptide suggested to exert tonic control over long-term energy balance. While some have speculated AgRP is not involved in the episodic (i.e. meal to meal energy intake) control, acute decreases in plasma agouti-related protein (AgRP) following a meal have been observed in humans in a role consistent with episodic control for AgRP. Whether changes in plasma AgRP are associated with episodic, and/or tonic changes in appetite has yet to be directly examined. The present study examined the relationship between agouti-related protein (AgRP), leptin and the regulation of appetite following a 48-h fast and an acute meal challenge. Blood samples were obtained from young lean and obese men before and after a 48 h fast (lean n = 10; obese n = 7). Fasting resulted in an increase in AgRP and a decrease in leptin with these changes being greater in lean than obese. In addition, blood samples were obtained from lean men before and 1, 2, 3 and 4 h after a meal (n = 8). Following a meal, AgRP was reduced from 2 to 4 h, a change that was dissociated from both leptin and subjective measures of hunger and satiety. These results demonstrate that AgRP is not associated with changes in hunger or satiety, and can change without corresponding changes in leptin. This suggests that AgRP may not be involved in the episodic control of appetite and the release of AgRP may involve signals other than leptin.

Biased signaling initiated by agouti-related peptide through human melanocortin-3 and -4 receptors

The neural melanocortin receptors (MCRs), melanocortin-3 and -4 receptors (MC3R and MC4R), have been increasingly recognized as important regulators of energy homeostasis. The orexigenic agouti-related peptide (AgRP), initially identified as an endogenous antagonist for both neural MCRs, has been suggested to be a biased agonist of MC4R independent of its antagonizing effects. In the present study, we sought to determine the potential of AgRP to regulate the activation of intracellular kinases, including extracellular signal-regulated kinase 1 and 2 (ERK1/2), AKT and AMP-activated protein kinase (AMPK), through neural MCRs. We showed that AgRP acted as a biased agonist in human MC3R (hMC3R), decreasing cAMP activity of constitutively active mutant (F347A) hMC3R but stimulating ERK1/2 activation in both wide type and F347A hMC3Rs. AgRP-stimulated ERK1/2 phosphorylation through MC3R was abolished by protein kinase A (PKA) inhibitor H-89 but not Rp-cAMPS, whereas AgRP-initiated ERK1/2 activation through MC4R was inhibited by phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002. Both NDP-MSH and AgRP treatment induced significant AKT phosphorylation in GT1-7 cells but not in MC3R- or MC4R-transfected HEK293T cells. The phosphorylated AMPK levels in both GT1-7 cells and HERK293T cells transfected with neural MCRs were significantly decreased upon stimulation with NDP-MSH but not with AgRP. In summary, we provided novel data for AgRP-initiated multiple intracellular signaling pathways, demonstrating biased agonism of AgRP in both neural MCRs, leading to a better understanding of neural MCR pharmacology.

Alpha-Melanocyte-Stimulating Hormone and Agouti-Related Protein: Do They Play a Role in Appetite Regulation in Childhood Obesity?

OBJECTIVE

The hypothalamus plays a crucial role in the regulation of feeding behavior. The anorexigenic neuropeptide alpha-melanocyte-stimulating hormone (α-MSH) and the orexigenic neuropeptide agouti-related protein (AgRP) are among the major peptides produced in the hypothalamus. This study investigated the plasma concentrations of α-MSH and AgRP in underweight and obese children and their healthy peers. The associations between α-MSH and AgRP levels and anthropometric and nutritional markers of malnutrition and obesity were also assessed.

METHODS

Healthy sex-matched subjects aged 2 to 12 years were divided into 3 groups, as underweight (n=57), obese (n=61), and of normal weight (n=57). Plasma fasting concentrations of α-MSH and AgRP were measured by enzyme-linked immunosorbent assay. The differences between the three groups as to the relationships between plasma concentrations of α-MSH and AgRP and anthropometric data, serum biochemical parameters and homeostatic model assessment of insulin resistance were evaluated.

RESULTS

Obese children had significantly lower α-MSH levels than underweight (1194±865 vs. 1904±1312 ng/mL, p=0.006) and normal weight (1194±865 vs. 1762±1463 ng/mL, p=0.036) children; there were no significant differences in the α-MSH levels between the underweight and normal weight children (p=0.811). Also, no significant differences were observed between the underweight and obese children regarding the AgRP levels (742±352 vs. 828±417 ng/mL, p=0.125). We found a significant positive correlation between plasma α-MSH and AgRP levels across the entire sample.

CONCLUSION

This study is the first to demonstrate body weight-related differences in α-MSH and AgRP levels in children. Circulating plasma α-MSH levels in obese children were markedly lower than those of underweight and normal-weight children. This suggests that α-MSH could play a role in appetite regulation.

Serum levels of AgRP protein in patients with schizophrenia on clozapine monotherapy

AIM

Agouti-related peptide (AgRP) is one of the hypothalamic hormones that works by increasing appetite and decreasing metabolism, thus leading to weight gain. The aim of the study was to find out if AgRP level in subjects with schizophrenia on clozapine monotherapy is higher compared with healthy controls.

METHODOLOGY

We determined fasting serum AgRP levels in 24 subjects with schizophrenia on clozapine monotherapy and 24 healthy, age- and sex-matched controls. Biochemical and anthropometric measurements were combined with body composition analysis.

RESULTS

There was no difference for AgRP levels between patients taking clozapine and control group (15.00±8.65 vs. 15.33±6.82 pg/mL, p =0.37). We found negative correlations between AgRP levels and total body fat (r =-0.34 and -0.48 in the whole study group and clozapine group, respectively) and positive correlations with lean body mass (r =0.38 and 0.49 in the whole study group and clozapine group, respectively), body water (r =0.34 and 0.49 in the whole study group and clozapine group, respectively) and basal metabolic rate (r =0.42 both in the clozapine and control groups). There were no correlations with age, height, weight, body mass index, fat mass index, abdominal, waist or hip circumferences, waist-hip ratio, blood pressure, total cholesterol, HDL, LDL, triglycerides, uric acid, glucose, insulin, clozapine dose or treatment duration, duration of treatment with antipsychotics and markers for insulin resistance.

CONCLUSION

We cannot conclude that treatment with clozapine is associated with increased level of AgRP. We did not find previously described differences in AgRP levels between obese and non-obese subjects or associations between AgRP and various metabolic parameters.

Constitutive activity in melanocortin-4 receptor: biased signaling of inverse agonists

The melanocortin-4 receptor (MC4R) is a critical regulator of energy homeostasis, including both energy intake and energy expenditure. It mediates the actions of a number of hormones on energy balance. The endogenous ligands for MC4R include peptide agonists derived from processing of proopiomelanocortin and the antagonist Agouti-related peptide (AgRP). Wild-type MC4R has some basal (constitutive) activity. Naturally occurring and laboratory-generated mutations have been identified, which results in either increased or decreased basal activities. Impaired basal signaling has been suggested to be a cause of dysregulated energy homeostasis and early-onset obesity, although several constitutively active mutations have also been identified from obese patients. AgRP and several small-molecule antagonists have been shown to be inverse agonists in the Gs-cAMP pathway. However, in the extracellular signal-regulated kinase (ERK) 1/2 pathway, we showed that these inverse agonists are potent agonists, demonstrating convincingly that they are biased ligands. We also showed that some mutations that do not cause constitutive activation in the Gs-cAMP pathway cause constitutive activation in the ERK1/2 pathway, suggesting that they are biased receptors. The physiological and potential pathophysiological relevance of the biased constitutive signaling in MC4R and therapeutic potential remain to be investigated.

The brain–adipose axis: A review of involvement of molecules

Many molecules are involved in the regulation of feeding behavior, and they and their receptors are located in the brain hypothalamus and adipocytes. On the basis of evidence suggesting an association between the brain and adipose tissue, we propose the concept of the brain-adipose axis. This model consists of (l) the expression of endogenous molecules and/or their receptors in the hypothalamus and peripheral adipose tissue, (2) the function of these molecules as appetite regulators in the brain, (3) their existence in the general circulation as secreted proteins and (4) the physiological affects of these molecules on fat cell size and number. These molecules can be divided into two anorexigenic and orexigenic classes. In adipose tissue, all orexigenic molecules possess adipogenic activity, and almost all anorexigenic molecules suppress fat cell proliferation. Although the manner, in which they present in the circulating blood connect the brain and peripheral adipocytes, remains to be well-organized, these observations suggest the positive feedback axis affecting molecules in the hypothalamus and adipose tissue. Analysis of the disturbance and dysregulation of this axis might promote the development of new anti-obesity drugs useful in treating the metabolic syndrome.

Trajectories of agouti-related protein and leptin levels during antipsychotic-associated weight gain in patients with schizophrenia

OBJECTIVE

Some but not all second-generation antipsychotics can induce considerable weight gain and metabolic syndrome. Although the exact biochemical mechanisms for these adverse effects are unclear, appetite-regulating neuropeptides of the central nervous system are thought to be implicated in this process. The hypothalamic mediator Agouti-related protein (AGRP) is inhibited by leptin and was shown to increase food intake. The aim of the present study was to investigate the trajectory of AGRP levels during antipsychotic-induced weight gain.

METHODS

As part of a controlled prospective clinical study, we determined indicators of body fat mass, plasma AGRP, and leptin levels in 16 patients with schizophrenia treated with ziprasidone and 21 patients with schizophrenia treated with olanzapine. Measurements by enzyme-linked immunosorbent assay were obtained before treatment (T0), after 4 weeks (T1), and after 3 months (T2) of treatment.

RESULTS

Whereas body mass index and leptin levels increased in patients treated with olanzapine compared to patients treated with ziprasidone, plasma AGRP levels did not differ among the treatment groups and did not change over time. Associations between AGRP and fat mass as well as appetite were disrupted in the olanzapine-treated patients but not in the ziprasidone group.

CONCLUSION

Future studies are needed to test whether the lack of a decrease in AGRP levels during weight gain in patients treated with olanzapine could perpetuate adverse metabolic long-term effects.

AgRP and NPY expression in the human hypothalamic infundibular nucleus correlate with body mass index, whereas changes in αMSH are related to type 2 diabetes

CONTEXT

Rodent data show that altered hypothalamic signaling contributes to the development of obesity and insulin resistance.

OBJECTIVE

To determine differences in hypothalamic expression levels of neuropeptide Y (NPY), agouti-related peptide (AgRP), and αMSH in the infundibular nucleus, the human equivalent of the arcuate nucleus, in relation to body mass index (BMI). In addition, the expression in the infundibular nucleus of eight subjects diagnosed with type 2 diabetes was measured to determine possible interference of type 2 diabetes with the association observed between neuropeptides and BMI.

DESIGN

We studied AgRP, NPY, and αMSH expression by means of quantitative immunocytochemistry in postmortem hypothalami of 30 subjects with known BMI. In separate experiments, we compared neuropeptide expression in eight subjects with type 2 diabetes with eight matched controls.

RESULTS

We found that AgRP immunoreactivity showed a U-shaped correlation with BMI. No evidence was found for possible influences of corticosteroid treatment. NPY immunoreactivity was significantly lower in overweight and obese subjects. αMSH did not correlate with BMI but was significantly lower in subjects with type 2 diabetes compared with controls. By contrast, NPY and AgRP expression was not affected in type 2 diabetes.

CONCLUSION

Our results indicate that the expression of AgRP and NPY are correlated with body weight changes, rather than the presence of type 2 diabetes, whereas changes in αMSH immunoreactivity are related to the presence of type 2 diabetes, indicating separate hypothalamic mechanisms.

Daytime sleepiness in obesity: mechanisms beyond obstructive sleep apnea--a review

Increasing numbers of overweight children and adults are presenting to sleep medicine clinics for evaluation and treatment of sleepiness. Sleepiness negatively affects quality of life, mental health, productivity, and safety. Thus, it is essential to comprehensively address all potential causes of sleepiness. While many obese individuals presenting with hypersomnolence will be diagnosed with obstructive sleep apnea and their sleepiness will improve with effective therapy for sleep apnea, a significant proportion of patients will continue to have hypersomnolence. Clinical studies demonstrate that obesity without sleep apnea is also associated with a higher prevalence of hypersomnolence and that bariatric surgery can markedly improve hypersomnolence before resolution of obstructive sleep apnea. High fat diet in both humans and animals is associated with hypersomnolence. This review critically examines the relationships between sleepiness, feeding, obesity, and sleep apnea and then discusses the hormonal, metabolic, and inflammatory mechanisms potentially contributing to hypersomnolence in obesity, independent of sleep apnea and other established causes of excessive daytime sleepiness.

Agouti-related protein segments outside of the receptor binding core are required for enhanced short- and long-term feeding stimulation

The agouti-related protein (AgRP) plays a central role in energy balance by reducing signaling through the hypothalamic melanocortin receptors (McRs) 3 and 4, in turn stimulating feeding and decreasing energy expenditure. Mature AgRP(83-132), produced by endoproteolytic processing, contains a central region that folds as an inhibitor cystine knot (ICK) stabilized by a network of disulfide bonds; this domain alone carries the molecular features for high affinity McR binding and inverse agonism. Outside of the ICK domain are two polypeptide segments, an N-terminal extension and a C-terminal loop, both completely conserved but of unknown function. Here we examine the physiological roles of these non-ICK segments by developing a panel of modified AgRPs that were administered to rats through intracerebroventricular (ICV) injection. Analysis of food consumption demonstrates that basic (positively charged) residues are essential for potent short- and long-term AgRP stimulated feeding. Moreover, we demonstrate an approximate linear relationship between protein charge density and 24 h food intake. Next, we developed artificial AgRP(83-132) analogues with increased positive charge and found that these species were substantially more potent than wild type. A single dose of one protein, designated AgRP-4K, results in enhanced feeding for well over a week and weight gain that is nearly double that of AgRP(83-132). These studies suggest new strategies for the development of potent orexigenic species and may serve as leads for the development of therapeutics for treating wasting conditions such as cachexia.

Agouti-related protein in patients with acute and weight-restored anorexia nervosa

BACKGROUND

An imbalance in appetite-regulating neuropeptides of the central nervous system has been associated with anorexia nervosa (AN), but the mechanisms of action are poorly understood. Agouti-related protein (AGRP), an orexigenic mediator of the hypothalamus, increases food intake and decreases energy expenditure in times of negative energy balance. The aim of the present study was to investigate AGRP in acute and fully weight-restored patients with AN, as well as during weight gain.

METHOD

Plasma AGRP and leptin levels were assessed using an enzyme-linked immunosorbent assay kit in a total of 175 female participants, including 75 patients with acute AN, 37 weight-restored AN patients and 63 healthy controls. Of the patients with acute AN, 33 were reassessed after partial weight gain.

RESULTS

In weight-restored AN patients plasma AGRP levels were similar to those in healthy controls, whereas in patients with acute AN, AGRP was elevated. AGRP was inversely correlated with indicators of undernutrition such as body mass index and plasma leptin. In addition, AGRP levels normalized during weight gain of longitudinally assessed AN patients.

CONCLUSIONS

Our results underline the significance of undernutrition and hypoleptinemia for the interpretation of peripheral AGRP concentrations. This provides support for the hypothesis that abnormal AGRP plasma levels in AN patients reflect undernutrition, rather than disease-specific traits.

Comparison of agouti-related peptide levels in peripheral blood of postpartum pre-eclamptic and non pre-eclamptic women and in umbilical cord blood from their pregnancies

Plasma levels of agouti-related peptide (AgRP) were reported to continuously rise during ongoing pregnancy in rats. The aim of the study was to investigate the maternal pre-partum peripheral plasma levels of AgRP and levels in umbilical cord blood in pre-eclamptic and physiological pregnancies in humans.

Negative correlation between neuropeptide Y/agouti-related protein concentration and adiponectinemia in nonalcoholic fatty liver disease obese adolescents submitted to a long-term interdisciplinary therapy

The complexity pathogenesis in the nonalcoholic fatty liver disease (NAFLD) involves an interplay between adipokines and neuroendocrine regulation of energy balance, including the role of neuropeptide Y (NPY)/agouti-related protein (AgRP) system. The first aim of this study was to assess the effect of long-term interdisciplinary intervention on NAFLD in obese adolescents, and the second objective was to establish the relationship between NPY/AgRP ratio and adiponectinemia. Fifty-five postpuberty obese adolescents were submitted to interdisciplinary intervention. The group was divided between subjects with and without NAFLD (n = 19 and 36, respectively). Blood samples were collected to measure glycemia, hepatic transaminases, lipid profile, insulin resistance, and sensitivity. Adiponectin, NPY, and AgRP concentrations were measured by enzyme-linked immunosorbent assay. Food intake was measured using 3-day diet records. It was observed at baseline that important clinical parameters including body weight, body mass index, visceral fat, homeostasis model assessment of insulin resistance, quantitative insulin sensitivity check index, triglycerides, very low-density lipoprotein cholesterol, and hepatic transaminases were more altered in NAFLD patients. After the intervention, these parameters, total energy, and macronutrient intake were reduced significantly in both groups. The most important finding was the positive correlation between AgRP and visceral fat in all patients and the negative correlation between NPY/AgRP and adiponectinemia only in NAFLD obese adolescents. The NAFLD patients presented more altered clinical parameters than the non-NAFLD subjects, including the negative correlation between adiponectinemia and NPY/AgRP. These results suggested that NAFLD obese adolescents presented an inflammatory profile that can influence the neuroendocrine regulation of energy balance, suggesting an additional impairment in the weight loss therapy.

The role of nutritional profile in the orexigenic neuropeptide secretion in nonalcoholic fatty liver disease obese adolescents

BACKGROUND

Little progress has been made to identify the central neuroendocrine pathway involved in the energy intake control in nonalcoholic fatty liver disease (NAFLD) patients.

OBJECTIVE

To assess the influence of orexigenic neuropeptides in the nutritional aspects of NAFLD obese adolescents submitted to a long-term interdisciplinary approach.

METHODS

Fifty adolescents aged 15-19 years, with body mass index at least 95th percentile, consisting of 25 patients without NAFLD and 25 with NAFLD. The NAFLD diagnosis was determined by ultrasonography. Blood samples were collected to analyze glycemia, hepatic transaminases, and lipid profile. Insulin resistance was estimated by Homeostasis Model Assessment Insulin Resistance Index. Neuropeptide Y (NPY) and agouti related protein concentrations were measured by enzyme-linked immunosorbent assay. Analyses of food intake were made by 3 days recordatory inquiry.

RESULTS

At baseline conditions, the patients with NAFLD had significantly higher values of body mass, body mass index, visceral fat, triglycerides, VLDL-C, and hepatic transaminases. After the long-term intervention, they presented a significant reduction in these parameters. In both the groups, it was observed a significant decrease in energy intake, macronutrients and dietetic cholesterol. Only the patients with NAFLD presented a positive correlation between the saturated fatty acids intake and the orexigenic neuropeptides NPY and agouti related protein, and carbohydrate with NPY. Indeed, it was observed a positive correlation between energy intake, lipid (%) and saturated fatty acids with visceral fat accumulation.

CONCLUSION

Our findings showed an important influence of diet composition in the orexigenic system, being essential consider that the excessive saturated fatty acids intake could be a determinant factor to increase nonalcoholic fatty liver disease.

Association between a rare SNP in the second intron of human Agouti related protein gene and increased BMI

BACKGROUND

The agouti related protein (AGRP) is an endogenous antagonist of the melanocortin 4 receptor and is one of the most potent orexigenic factors. The aim of the present study was to assess the genetic variability of AGRP gene and investigate whether the previously reported SNP rs5030980 and the rs11575892, a SNP that so far has not been studied with respect to obesity is associated with increased body mass index (BMI).

METHODS

We determined the complete sequence of the AGRP gene and upstream promoter region in 95 patients with severe obesity (BMI > 35 kg/m2). Three polymorphisms were identified: silent mutation c.123G>A (rs34123523) in the second exon, non-synonymous mutation c.199G>A (rs5030980) and c.131-42C>T (rs11575892) located in the second intron. We further screened rs11575892 in a selected group of 1135 and rs5030980 in group of 789 participants from the Genome Database of Latvian Population and Latvian State Research Program Database.

RESULTS

The CT heterozygotes of rs11575892 had significantly higher mean BMI value (p = 0.027). After adjustment for age, gender and other significant non-genetic factors (presence of diseases), the BMI levels remained significantly higher in carriers of the rs11575892 T allele (p = 0.001). The adjusted mean BMI value of CC genotype was 27.92 +/- 1.01 kg/m2 (mean, SE) as compared to 30.97 +/- 1.03 kg/m2 for the CT genotype. No association was found between rs5030980 and BMI.

CONCLUSION

This study presents an association of rare allele of AGRP polymorphism in heterozygous state with increased BMI. The possible functional effects of this polymorphism are unclear but may relate to splicing defects.

Ranking candidate genes in rat models of type 2 diabetes

Background

Rat models are frequently used to find genomic regions that contribute to complex diseases, so called quantitative trait loci (QTLs). In general, the genomic regions found to be associated with a quantitative trait are rather large, covering hundreds of genes. To help selecting appropriate candidate genes from QTLs associated with type 2 diabetes models in rat, we have developed a web tool called Candidate Gene Capture (CGC), specifically adopted for this disorder.

Methods

CGC combines diabetes-related genomic regions in rat with rat/human homology data, textual descriptions of gene effects and an array of 789 keywords. Each keyword is assigned values that reflect its co-occurrence with 24 different reference terms describing sub-phenotypes of type 2 diabetes (for example "insulin resistance"). The genes are then ranked based on the occurrences of keywords in the describing texts.

Results

CGC includes QTLs from type 2 diabetes models in rat. When comparing gene rankings from CGC based on one sub-phenotype, with manual gene ratings for four QTLs, very similar results were obtained. In total, 24 different sub-phenotypes are available as reference terms in the application and based on differences in gene ranking, they fall into separate clusters.

Conclusion

The very good agreement between the CGC gene ranking and the manual rating confirms that CGC is as a reliable tool for interpreting textual information. This, together with the possibility to select many different sub-phenotypes, makes CGC a versatile tool for finding candidate genes. CGC is publicly available at .

Hormonal regulation of the mouse adrenal melanocortinergic system

Adrenocortical cells of several species have been reported to express significant levels of Agouti-related protein (Agrp) as well as melanocortin 4-receptor (MC4-R). In this study, we used the mouse tumoral adrenal cell line ATC7- L that secretes corticosterone in basal conditions with a 2- fold increase in response to ACTH treatment. We reported that these cells expressed functional MC4-R. They also expressed Agrp mRNA and secreted immunoreactive Agrp in the culture medium. Long-term treatment of ATC7-L with (Nle4,D-Phe7)-alpha MSH (NDP-alpha MSH) or forskolin as well as Agrp strongly reduced MC4-R level by more than 30%. On the contrary, leptin treatment did not modify this level although it significantly reduced MC2-R level. These results could be correlated to some data obtained in vivo on adrenal glands removed from diet-induced obese mice exhibiting a hyperleptinemia, where the level of both MC2-R and MC4-R appeared to be reduced as Agrp mRNA expression level was increased compared to Control mice. All these data would suggest the existence of a link between the metabolic status and the activation of the adrenal melanocortinergic system.

The role of the Agouti-Related Protein in energy balance regulation

The Agouti-Related Protein (AgRP) is a powerful orexigenic peptide that increases food intake when ubiquitously overexpressed or when administered centrally. AgRP-deficiency, on the other hand, leads to increased metabolic rate and a longer lifespan when mice consume a high fat diet. In humans, AgRP polymorphisms have been consistently associated with resistance to fatness in Blacks and Whites and resistance to the development of type-2 diabetes in African Blacks. Systemically administered AgRP accumulates in the liver, the adrenal gland and fat tissue while recent findings suggest that AgRP may also have inverse agonist effects, both centrally and peripherally. AgRP could thus modulate energy balance via different actions. Its absence or reduced functionality may offer a benefit both in terms of bringing about negative energy balance in obesigenic environments, as well as leading to an increased lifespan.

Neuroendocrine control of food intake

Appetite is regulated by a complex system of central and peripheral signals which interact in order to modulate the individual response to nutrient ingestion. Peripheral regulation includes satiety signals and adiposity signals, while central control is accomplished by several effectors, including the neuropeptidergic, monoaminergic and endocannabinoid systems. Satiety signals, including cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), originate from the gastrointestinal (GI) tract during a meal and, through the vagus nerve, reach the nucleus tractus solitarius (NTS) in the caudal brainstem. From NTS afferents fibers project to the arcuate nucleus (ARC), where satiety signals are integrated with adiposity signals, namely leptin and insulin, and with several hypothalamic and supra-hypothalamic inputs, thus creating a complex network of neural circuits which finally elaborate the individual response to a meal. As for the neuropeptidergic system, ARC neurons secrete orexigenic substances, such as neuropeptide Y (NPY) and agouti-related peptide (AGRP), and anorexigenic peptides such as pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART). Other brain areas involved in the control of food intake are located downstream the ARC: among these, the paraventricular nucleus (PVN), which produces anorexigenic peptides such as thyrotropin releasing hormone (TRH), corticotrophin releasing hormone (CRH) and oxytocin, the lateral hypothalamus (LHA) and perifornical area (PFA), secreting the orexigenic substances orexin-A (OXA) and melanin concentrating hormone (MCH). A great interest in endocannabinoids, important players in the regulation of food intake, has recently developed. In conclusion, the present work reviews the most recent insights into the complex and redundant molecular mechanisms regulating food intake, focusing on the most encouraging perspectives for the treatment of obesity.

Adrenocortical dysregulation as a major player in insulin resistance and onset of obesity

The aim of this review is to explore the dysregulation of adrenocortical secretions as a major contributor in the development of obesity and insulin resistance. Disturbance of adipose tissue physiology is one of the primary events in the development of pathologies associated with the metabolic syndrome, such as obesity and type 2 diabetes. Several studies indicate that alterations in metabolism of glucocorticoids (GC) and androgens, as well as aldosterone in excess, are involved in the emergence of metabolic syndrome. Cross talk among adipose tissue, the hypothalamo-pituitary complex, and adrenal gland activity plays a major role in the control of food intake, glucose metabolism, lipid storage, and energy balance. Perturbation of this cross talk induces alterations in the regulatory mechanisms of adrenocortical steroid synthesis, secretion, degradation, and/or recycling, at the level of the zonae glomerulosa (aldosterone), fasciculata (GC and GC metabolites), and reticularis (androgens and androgen precursors DHEA and DHEAS). As a whole, these adrenocortical perturbations contribute to the development of metabolic syndrome at both the paracrine and systemic level by favoring the physiological dysregulation of organs responsive to aldosterone, GC, and/or androgens, including adipose tissue.

Serum retinol-binding protein 4 is reduced after weight loss in morbidly obese subjects

CONTEXT

Administration of retinol-binding protein 4 (RBP-4) impairs insulin sensitivity in animals, and elevated serum concentrations have been associated with insulin resistance in humans.

OBJECTIVE

We have studied whether weight loss influences RBP-4.

PATIENTS AND METHODS

Fasting serum concentrations of RBP-4 were measured before and 6 months after gastric banding surgery in 33 morbidly obese patients aged 40 +/- 11 yr with a body mass index (BMI) of 46 +/- 5 kg/m(2). Fourteen healthy subjects aged 29 +/- 5 yr with a BMI less than 25 kg/m(2) served as controls. To characterize the association of weight loss with central and peripheral appetite regulation, the signaling protein agouti-related protein (AGRP), the orexigenic hormone ghrelin, and its recently identified antagonist obestatin were determined.

RESULTS

At baseline, RBP-4 levels were markedly higher in obese than in lean subjects (2.7 +/- 0.5 vs. 0.9 +/- 0.5 microg/ml; P < 0.001). In contrast, AGRP and obestatin were lower in obese subjects compared with lean controls (all P < 0.001). Six months after gastric banding, BMI was reduced to 40 +/- 5 kg/m(2), RBP-4 was reduced to 2.0 +/- 0.7 microg/ml, AGRP increased from 1.8 +/- 1.1 to 3.4 +/- 1.1 ng/ml, ghrelin increased from 93 +/- 58 to 131 +/- 70 pg/ml, and obestatin increased from 131 +/- 52 to 173 +/- 35 pg/ml (all P < 0.05). Individual changes of RBP-4 were associated with changes of BMI (r = 0.72), the homeostasis model assessment insulin resistance-index (r = 0.53), and total cholesterol (r = 0.42, for all P < 0.05).

CONCLUSION

Reductions in circulating RBP-4 may contribute to improved insulin resistance in morbidly obese subjects after weight loss. This is accompanied by favorable changes in appetite-regulating hormones, which might support the sustained weight loss after obesity surgery.

Role of Agouti-related protein in adrenal steroidogenesis

The levels of Agouti-related protein (AgRP) mRNA in the adrenal are second only to those in the hypothalamus, raising questions regarding its target binding sites and its specific role in adrenal steroidogenesis. We and others demonstrated the presence of a population of melanocortin receptor-4 (MC4R) positively coupled to steroidogenesis in adrenal cells. Moreover, AgRP inhibited both the acute and long-term steroidogenic responses of these cells to NDP-alphaMSH through its antagonistic properties towards MC4R. Although AgRP had no antagonistic properties towards the MC2R and did not modify the acute steroidogenic response to ACTH, it exerted a biphasic sustained inhibitory effect on the long-term response to ACTH through an undefined alternate mechanism. Since adrenal cells release a relatively large amount of AgRP, this protein likely exerts a local paracrine/autocrine control on adrenal steroidogenesis.

A rare mutation in AgRP, +79G>A, affects promoter activity

The agouti-related protein is a powerful orexigenic peptide. A rare mutation, +79G>A, was identified in its minimal promoter in two white carriers. Comparison of the 45-year-old male proband, who was also a carrier of the common Ala67Thr polymorphism, with an age- and weight-matching wild-type population showed marginal differences for resting metabolic rate (RMR) and body mass index. The second carrier however was an obese 57-year-old female with reduced RMR. Functional analysis in hypothalamus- and periphery-derived cell lines showed reduced promoter activity for the +79A allele in the adrenocortical cells only, suggesting that it could affect the peripheral expression levels of AgRP. The +79G>A mutation could predispose to body weight gain (as suggested by the phenotype of the second carrier), but it could only affect the proband at an older age as he may be protected by the Ala67Thr polymorphism that is associated with resistance to late-onset fatness.

Agouti-related protein promoter variant associated with leanness and decreased risk for diabetes in West Africans

OBJECTIVE

The role of the central melanocortin system in the development of obesity has been extensively studied. Single-nucleotide polymorphisms (SNPs) within several candidate genes have been associated with food intake and obesity-related phenotypes; however, few of these associations have been replicated. SNPs in the agouti-related protein (AGRP) gene coding (Ala67Thr, 199G/A) and promoter (-38C/T) have been reported to be associated with body mass index (BMI), fat mass (FM) and percent body fat, in populations of European and African descent. In this study, we evaluated the association between the functional AGRP -38C/T promoter SNP and weight-related traits, namely BMI, FM and fat-free mass (FFM), as well as diabetes status.

DESIGN

An association study of the AGRP -38C/T SNP and indices of obesity and diabetes status.

SUBJECTS

A well-characterized population of 538 West Africans from Ghana and Nigeria recruited in the AADM (Africa America Diabetes Mellitus) study (mean age 52 years, 41.3% males, 71% diabetic).

MEASUREMENTS

Genotyping of the AGRP -38C/T SNP, BMI, FM, FFM and fasting plasma glucose.

RESULTS

Women carrying two copies of the variant T allele had significantly lower BMI (OR=0.47; 95% CI, 0.25-0.87). Also, men with at least one copy of the variant T allele were over two times less likely to be diabetic than other men (OR=0.44; 95% CI, 0.22-0.89).

CONCLUSION

Our results replicate previous findings and implicate the AGRP -38C/T SNP in the regulation of body weight in West Africans.

Selective tissue uptake of agouti-related protein(82-131) and its modulation by fasting

The blood concentration of agouti-related protein (AgRP), a protein related to hyperphagia and obesity, is increased in obese human and fasted lean subjects. Because there is no saturable transport system at the blood-brain barrier for circulating AgRP to reach its central nervous system target, uptake of AgRP by peripheral organs might be physiologically meaningful. Using the biologically active fragment AgRP(82-131), we determined the pharmacokinetics of its radioactively labeled tracer after iv bolus injection and compared it with that of the vascular marker albumin. AgRP enters peripheral organs at different influx rates, all of which were higher than into brain and spinal cord. At 10 min after iv injection, the radioactivity recovered in the liver, which had the fastest influx rate for AgRP, represented intact (125)I-AgRP. The adrenal gland had a moderately fast uptake (but the highest initial volume of distribution), followed by the heart, lungs, and skeletal muscle. By comparison, epididymal fat, testis, and pancreas had low permeability to AgRP. Saturation of influx was determined by coadministration of excess unlabeled AgRP and was shown to be present in the liver and adrenal gland. The influx rate and initial volume of distribution did not show a linear correlation with vascular permeability or regional blood flow. AgRP uptake by the liver and epididymal fat was significantly increased by overnight fasting, whereas that by the adrenal gland was significantly decreased in fasted mice. Thus, the differential uptake of AgRP by peripheral organs could be a regulated process that is modulated by food deprivation.

Two ethnic-specific polymorphisms in the human Agouti-related protein gene are associated with macronutrient intake

BACKGROUND

The Agouti-related protein (AGRP), an appetite modulator, induces hyperphagia when administered intracerebroventricularly or when overexpressed in transgenic mice. Exogenous administration of AGRP in rodents predisposes to high fat and high sugar intakes.

OBJECTIVE

The objective was to examine the potential associations of 2 ethnic-specific polymorphisms in the AGRP gene (Ala67Thr in whites and -38C>T in blacks) in the Health, Risk Factors, Exercise Training, and Genetics (HERITAGE) Family Study.

DESIGN

We examined the effect of the 2 polymorphisms in the AGRP gene on self-reported macronutrient intakes in 478 white and 272 black participants in the HERITAGE Family Study.

RESULTS

Both AGRP polymorphisms showed a significant association with energy intake. In whites, a smaller proportion of total energy was derived from fat by the Ala67Thr heterozygotes (mean +/- SEM: 29.4 +/- 0.7%) than by the Ala67Ala homozygotes (31.5 +/- 0.5%; P = 0.009), mainly because of a lower intake of saturated (P = 0.06) and monounsaturated (P = 0.01) fats by the Ala67Thr heterozygotes. The percentage of energy from carbohydrates was 2.6% greater in the Ala67Thr heterozygotes (55.1 +/- 1.1%) than in the Ala67Ala homozygotes (52.5 +/- 0.6%; P = 0.03). In blacks, protein intake was associated with the -38C>T promoter polymorphism. T/T homozygotes had a significantly lower protein intake than did the C-allele carriers (C/C: 16.8 +/- 0.4%; C/T: 17.2 +/- 0.2%; T/T: 15.4 +/- 0.7%; P = 0.04). No significant differences in total energy and alcohol intakes existed between genotype groups in blacks or whites.

CONCLUSIONS

The present study suggests that 2 ethnic-specific AGRP variants, previously shown to be associated with leanness in the HERITAGE Family Study, are also associated with macronutrient intake.

Current concepts and future directions in the battle against obesity

Obesity is a significant unsolved public health problem. Future treatments of obesity will involve application of neuroendocrine concepts that are reviewed in this paper.

Agouti-related protein antagonizes glucocorticoid production induced through melanocortin 4 receptor activation in bovine adrenal cells: a possible autocrine control

Agouti-related protein (Agrp), primarily expressed in the hypothalamus, is an endogenous antagonist of alphaMSH at the level of melanocortin 3 receptor (MC3-R) and MC4-R, but the adrenal gland represents the second major Agrp-expressing tissue. In adrenal fasciculata cells, the glucocorticoid secretion is under the control of ACTH, which binds specifically MC2-R, the only functional melanocortin receptor described in these cells to date. Nevertheless, using cultured bovine fasciculata adrenal cells, we report that Agrp has no antagonistic properties against ACTH at the level of MC2-R. In our studies, (Nle4, d-Phe7)-alphaMSH (NDP-alphaMSH) stimulated the production of cortisol in a dose-dependent manner, and these effects were abolished by Agrp or SHU9119, a synthetic antagonist of MC3-R and MC4-R. Using a more specific antagonist (JKC-363) and RT-PCR analysis, we can postulate that the effects of NDP-alphaMSH were mediated via MC4-R. These results are suggestive that adrenal glucocorticoid production could be regulated through MC4-R that may have some relevance in the physiology of adrenal cells. Moreover, Agrp might exert an autocrine control on adrenal cells because a protein with biological Agrp-like activity is secreted by these cells. This peptide could then modulate locally the functions of some peripheral tissues such as adrenals.

Controle neuroendócrino do peso corporal: implicações na gênese da obesidade

O peso corporal é regulado por uma interação complexa entre hormônios e neuropeptídeos, sob o controle principal de núcleos hipotalâmicos. Mutações nos genes de hormônios e neuropeptídeos, de seus receptores ou de elementos regulatórios, têm sido descritas na espécie humana, mas são tidas como raras, não explicando as formas mais comuns de obesidade. No entanto, o estudo destas mutações tem propiciado um grande avanço nos conhecimentos sobre a base genética e a fisiopatologia da obesidade, possibilitando o estudo e abrindo perspectivas para o desenvolvimento de novas modalidades terapêuticas. Recentemente, demonstrou-se que mutações no receptor 4 da melanocortina podiam ser encontradas em até 5% dos casos de obesidade severa, representando até o presente momento a forma mais prevalente de obesidade monogênica na espécie humana. Nesta revisão, são discutidas as diversas mutações descritas nos seres humanos de elementos da rede neuroendócrina de controle do peso corporal, bem como as implicações dos mesmos na gênese da obesidade.

alpha -melanocyte-stimulating hormone is a novel regulator of bone

alpha-Melanocyte-stimulating hormone (alpha-MSH), a 13-amino acid peptide produced in the brain and pituitary gland, is a regulator of appetite and body weight, and its production is regulated by leptin, a factor that affects bone mass when administered centrally. alpha-MSH acts via melanocortin receptors. Humans deficient in melanocortin receptor 4 (MC4-R) have increased bone mass, and MC4-R has been identified in an osteoblast-like cell line. Thus alpha-MSH may act directly on the skeleton, a question addressed by the present studies. In primary cultures of osteoblasts and chondrocytes, alpha-MSH dose dependently (>or=10(-9) M) stimulated cell proliferation. In bone marrow cultures, alpha-MSH (>10(-9) M) stimulated osteoclastogenesis. Systemic administration of alpha-MSH to mice (20 injections of 4.5 microg/day) decreased the trabecular bone volume in the proximal tibiae from 19.5 +/- 1.8 to 15.2 +/- 1.4% (P = 0.03) and reduced trabecular number (P = 0.001). Radiographic indexes of trabecular bone, assessed by phase-contrast X-ray imaging, confirmed the bone loss. It is concluded that alpha-MSH acts directly on bone, increasing bone turnover, and, when administered systemically, it decreases bone volume. The latter result may also be contributed to by alpha-MSH effects elsewhere, such as the adipocyte, pancreatic beta-cell, or central nervous system.

The agouti-related protein and body fatness in humans

OBJECTIVE

The objective of this study was to examine the impact of a single nucleotide polymorphism (SNP) (-38C>T) in the promoter of the human agouti-related protein (hAgRP) gene on promoter affinity for transcription factors (TFs) and its possible association with body composition phenotypes.

DESIGN

Electrophoretic mobility shift assays for the functional studies and association analyses for the population studies.

SUBJECTS AND METHODS

Nuclear extracts were isolated from the mouse hypothalamus cell line GT1-7 and subjected to binding assays using oligonucleotide probes corresponding to the -38C>T region and an antibody for the E12/E47 TFs. Individuals (n = 259) from the HERITAGE Family Study were genotyped for the -38C>T SNP and used in the association studies.

RESULTS

Electrophoretic mobility shift and supershift assays confirmed binding of the E12/E47 TF to the -38C>T site in a genotype-dependent manner. The T allele was found exclusively in the black subjects while the genotype with the higher binding affinity, CC, was significantly associated with high BMI, fat mass, and percent body fat in the black subjects of the HERITAGE Family Study.

CONCLUSIONS

The E12/E47 TF could play a role in the regulation of hAgRP expression while the population studies suggest that the TT genotype of the -38C>T SNP could play a protective role against the development of obesity in the black population of the HERITAGE Family Study.