Effects of estradiol on cerebrospinal fluid levels of agouti-related protein in ovariectomized rhesus monkeys

Defining Predictors of Weight Loss Response to Lorcaserin

CONTEXT

Individual responses to weight loss (WL) medications vary widely and prediction of response remains elusive.

OBJECTIVE

We investigated biomarkers associated with use of lorcaserin (LOR), a 5HT2cR agonist that targets proopiomelanocortin (POMC) neurons that regulate energy and glucose homeostasis, to identify predictors of clinical efficacy.

METHODS

Thirty individuals with obesity were treated with 7 days of placebo and LOR in a randomized crossover study. Nineteen participants continued on LOR for 6 months. Cerebrospinal fluid (CSF) POMC peptide measurements were used to identify potential biomarkers that predict WL. Insulin, leptin, and food intake during a meal were also studied.

RESULTS

LOR induced a significant decrease in CSF levels of the POMC prohormone and an increase in its processed peptide β-endorphin after 7 days; β-endorphin/POMC increased by 30% (P < .001). This was accompanied by a substantial decrease in insulin, glucose, and homeostasis model assessment of insulin resistance before WL. Changes in CSF POMC peptides persisted after WL (6.9%) at 6 months that were distinct from prior reports after diet alone. Changes in POMC, food intake, or other hormones did not predict WL. However, baseline CSF POMC correlated negatively with WL (P = .07) and a cutoff level of CSF POMC was identified that predicted more than 10% WL.

CONCLUSION

Our results provide evidence that LOR affects the brain melanocortin system in humans and that effectiveness is increased in individuals with lower melanocortin activity. Furthermore, early changes in CSF POMC parallel WL-independent improvements in glycemic indexes. Thus, assessment of melanocortin activity could provide a way to personalize pharmacotherapy of obesity with 5HT2cR agonists.

The gut signals to AGRP-expressing cells of the pituitary to control glucose homeostasis

Glucose homeostasis can be improved after bariatric surgery, which alters bile flow and stimulates gut hormone secretion, particularly FGF15/19. FGFR1 expression in AGRP-expressing cells is required for bile acids' ability to improve glucose control. We show that the mouse Agrp gene has 3 promoter/enhancer regions that direct transcription of each of their own AGRP transcripts. One of these Agrp promoters/enhancers, Agrp-B, is regulated by bile acids. We generated an Agrp-B knockin FLP/knockout allele. AGRP-B-expressing cells are found in endocrine cells of the pars tuberalis and coexpress diacylglycerol lipase B - an endocannabinoid biosynthetic enzyme - distinct from pars tuberalis thyrotropes. AGRP-B expression is also found in the folliculostellate cells of the pituitary's anterior lobe. Mice without AGRP-B were protected from glucose intolerance induced by high-fat feeding but not from excess weight gain. Chemogenetic inhibition of AGRP-B cells improved glucose tolerance by enhancing glucose-stimulated insulin secretion. Inhibition of the AGRP-B cells also caused weight loss. The improved glucose tolerance and reduced body weight persisted up to 6 weeks after cessation of the DREADD-mediated inhibition, suggesting the presence of a biological switch for glucose homeostasis that is regulated by long-term stability of food availability.

Effects of Opioid Antagonism on Cerebrospinal Fluid Melanocortin Peptides and Cortisol Levels in Humans

CONTEXT

Hypothalamic proopiomelanocortin (POMC) is processed to α-melanocyte-stimulating hormone, which interacts with the melanocortin antagonist agouti-related protein (AgRP), to regulate energy balance. The POMC-derived opioid peptide β-endorphin (β-EP) also affects feeding behavior via interactions with brain µ-opioid receptors (MORs), including autoinhibitory interactions with MOR expressed by POMC neurons. The opioid antagonist naltrexone (NTX) stimulates POMC neurons in rodents and decreases food intake.

OBJECTIVE AND DESIGN

The effect of NTX on brain POMC in humans was assessed by measuring POMC peptide concentrations in lumbar cerebrospinal fluid (CSF). AgRP and cortisol levels were also measured because both are inhibited by opioids. In a double-blinded crossover study, 14 healthy subjects were given NTX (50 mg daily) or placebo for either 2 or 7 days.

RESULTS

CSF β-EP levels increased after 2 and 7 days of NTX treatment; CSF POMC levels did not change, but the β-EP-to-POMC ratio increased. CSF AgRP levels did not change, but plasma AgRP levels tended to increase after NTX (P = 0.06). Cortisol increased in plasma and CSF after NTX treatment; these changes correlated positively with changes in AgRP levels.

CONCLUSION

Opioid antagonism stimulates POMC peptide release into CSF in humans. The increase in the CSF β-EP-to-POMC ratio could indicate selective release of processed peptides or an effect on POMC processing. Furthermore, AgRP and cortisol stimulation by NTX may mitigate POMC-induced decrease in food intake. It remains to be determined if biomarkers in CSF and plasma could be used to predict responses to pharmacotherapy targeting the melanocortin system.

Evaluation of CSF and plasma biomarkers of brain melanocortin activity in response to caloric restriction in humans

The melanocortin neuronal system, which consists of hypothalamic proopiomelanocortin (POMC) and agouti-related protein (AgRP) neurons, is a leptin target that regulates energy balance and metabolism, but studies in humans are limited by a lack of reliable biomarkers to assess brain melanocortin activity. The objective of this study was to measure the POMC prohormone and its processed peptide, β-endorphin (β-EP), in cerebrospinal fluid (CSF) and AgRP in CSF and plasma after calorie restriction to validate their utility as biomarkers of brain melanocortin activity. CSF and plasma were obtained from 10 lean and obese subjects after fasting (40 h) and refeeding (24 h), and from 8 obese subjects before and after 6 wk of dieting (800 kcal/day) to assess changes in neuropeptide and hormone levels. After fasting, plasma leptin decreased to 35%, and AgRP increased to 153% of baseline. During refeeding, AgRP declined as leptin increased; CSF β-EP increased, but POMC did not change. Relative changes in plasma and CSF leptin were blunted in obese subjects. After dieting, plasma and CSF leptin decreased to 46% and 70% of baseline, CSF POMC and β-EP decreased, and plasma AgRP increased. At baseline, AgRP correlated negatively with insulin and homeostasis model assessment (HOMA-IR), and positively with the Matsuda index. Thus, following chronic calorie restriction, POMC and β-EP declined in CSF, whereas acutely, only β-EP changed. Plasma AgRP, however, increased after both acute and chronic calorie restriction. These results support the use of CSF POMC and plasma AgRP as biomarkers of hypothalamic melanocortin activity and provide evidence linking AgRP to insulin sensitivity.

Proopiomelanocortin, agouti-related protein, and leptin in human cerebrospinal fluid: correlations with body weight and adiposity

Leptin and its neuronal targets, which produce proopiomelanocortin (POMC) and agouti-related protein (AgRP), regulate energy balance. This study characterized leptin, POMC, and AgRP in the cerebrospinal fluid (CSF) of 47 healthy human subjects, 23 lean and 24 overweight/obese (OW/OB), as related to BMI, adiposity, plasma leptin, soluble leptin receptor (s-OB-R), and insulin. POMC was measured since the POMC prohormone is the predominant POMC peptide in CSF and correlates with hypothalamic POMC in rodents. Plasma AgRP was similarly characterized. CSF leptin was 83-fold lower than in plasma and correlated strongly with BMI, body fat, and insulin. The relative amount of leptin transported into CSF declined with increasing BMI, ranging from 4.5 to 0.52%, consistent with a saturable transport mechanism. CSF sOB-R was 78-fold lower than in plasma and correlated negatively with plasma and CSF leptin. CSF POMC was higher in lean vs. OW/OB subjects (P < 0.001) and correlated negatively with CSF leptin (r = -0.60, P < 0.001) and with plasma leptin, insulin, BMI, and adiposity. CSF AgRP was not different in lean vs. OW/OB; however, plasma AgRP was higher in lean subjects (P = 0.001) and correlated negatively with BMI, adiposity, leptin, insulin, and HOMA (P < 0.005). Thus, CSF measurements may provide useful biomarkers for brain leptin and POMC activity. The striking negative correlation between CSF leptin and POMC could be secondary to leptin resistance and/or neuronal changes associated with obesity but may also indicate that POMC plays a primary role in regulating body weight and adiposity. The role of plasma AgRP as a neuroendocrine biomarker deserves further study.

Estradiol prevents fat accumulation and overcomes leptin resistance in female high-fat diet mice

In premenopausal and menopausal women in particular, suboptimal estrogens have been linked to the development of the metabolic syndrome as major contributors to fat accumulation. At the same time, estrogens have been described to have a role in regulating body metabolic status. We evaluated how endogenous or administered estrogens impact on the changes associated with high-fat diet (HFD) consumption in 2 different paradigms; ovarian-intact and in ovariectomized mice. When estradiol (E2) was cyclically administered to ovarian-intact HFD-fed mice for 12 weeks, animals gained significantly less weight than ovarian-intact vehicle controls (P < .01). This difference was mainly due to a reduced caloric intake but not to an increase in energy expenditure or locomotor activity. This E2 treatment regime to mice exposed to HFD was overall able to avoid the increase of visceral fat content to levels of those found in mice fed a regular chow diet. In the ovariectomized model, the main body weight and fat content reducing action of E2 was not only through decreasing food intake but also by increasing the whole-body energy expenditure, locomotor activity, and by inducing fat oxidation. Importantly, these animals became responsive to the anorexigenic effects of leptin in contrast to the vehicle-treated and the pair-fed control groups (P < .01). Further, in vitro hypothalamic secretion experiments revealed that treatment of obese mice with E2 is able to modulate the secretion of appetite-regulating neuropeptides; namely, E2 increased the secretion of the anorectic neuropeptide α-melanocyte-stimulating hormone and decreased the secretion of the orexigenic neuropetides neuropeptide Y and Agouti-related peptide. In conclusion, differences in response to E2 treatment of HFD-fed animals depend on their endogenous estrogenic status. Overall, E2 administration overcomes arcuate leptin resistance and partially prevents fat accumulation on these mice.

Clinical utility of plasma POMC and AgRP measurements in the differential diagnosis of ACTH-dependent Cushing's syndrome

CONTEXT

Distinguishing between pituitary [Cushing's disease (CD)] and ectopic causes [ectopic ACTH syndrome (EAS)] of ACTH-dependent Cushing's syndrome can be challenging. Inferior petrosal sinus sampling (IPSS) best discriminates between CD and occult EAS but is a specialized procedure that is not widely available. Identifying adjunctive diagnostic tests may prove useful. In EAS, abnormal processing of the ACTH precursor proopiomelanocortin (POMC) and the accumulation of POMC-derived peptides might be expected and abnormal levels of other neuropeptides may be detected.

OBJECTIVE

The objective of the study was to evaluate the diagnostic utility of POMC measurements for distinguishing between CD and occult EAS in patients referred for IPSS. Another objective of the study was to evaluate in parallel the diagnostic utility of another neuropeptide, agouti-related protein (AgRP), because we have observed a 10-fold elevation of AgRP in plasma in a patient with EAS from small-cell lung cancer.

DESIGN AND PARTICIPANTS

Plasma POMC and AgRP were measured in 38 Cushing's syndrome patients presenting for IPSS, with either no pituitary lesion or a microadenoma on magnetic resonance imaging, and in 38 healthy controls.

RESULTS

Twenty-seven of 38 patients had CD; 11 of 38 had EAS. The mean POMC was higher in EAS vs CD [54.5 ± 13.0 (SEM) vs 17.2 ± 1.5 fmol/mL; P < .05]. Mean AgRP was higher in EAS vs CD (280 ± 76 vs 120 ± 16 pg/mL; P = .01). Although there was an overlap in POMC and AgRP levels between the groups, the POMC levels greater than 36 fmol/mL (n = 7) and AgRP levels greater than 280 pg/mL (n = 3) were specific for EAS. When used together, POMC greater than 36 fmol/mL and/or AgRP greater than 280 pg/mL detected 9 of 11 cases of EAS, indicating that elevations in these peptides have a high positive predictive value for occult EAS.

CONCLUSIONS

Expanding upon previous observations of high POMC in EAS, this study specifically demonstrates elevated POMC levels can identify occult ectopic tumors. Elevations in AgRP also favor the diagnosis of EAS, suggesting AgRP should be further evaluated as a potential neuroendocrine tumor marker.

Continuous 24-hour leptin, proopiomelanocortin, and amino acid measurements in human cerebrospinal fluid: correlations with plasma leptin, soluble leptin receptor, and amino acid levels

CONTEXT

In order to characterize diurnal changes in central leptin and its target neuropeptide, proopiomelanocortin (POMC), we measured leptin and POMC in cerebrospinal fluid (CSF) as related to changes in plasma leptin and soluble leptin receptor (sOB-R) levels. CSF and plasma levels of 20 amino acids (AA) were also measured because AA can affect brain POMC.

DESIGN AND PARTICIPANTS

Stored CSF and plasma samples obtained from eight healthy subjects who served as controls for a previous study were evaluated. CSF was collected hourly over 33 h via indwelling subarachnoid catheter. Leptin, sOB-R, and POMC were measured by sensitive ELISA and AA by gas chromatography-mass spectrometry.

RESULTS

There was a diurnal rhythm for plasma leptin with a peak at 2200 h (144% of baseline) and there was a similar diurnal rhythm for CSF leptin with a peak (117%) 3-5 h after the plasma peak. Plasma sOB-R was lowest at 0300 h and correlated negatively with plasma and CSF leptin. A diurnal rhythm for POMC in CSF was also detected with a peak (125%) at 0100 h. A positive correlation existed between CSF POMC and leptin in individual subjects over time. CSF levels of many AA increased at night. There was a significant correlation between CSF POMC and 10 AA, including leucine, isoleucine, tryptophan, and tyrosine.

CONCLUSIONS

Diurnal changes occur in leptin and POMC in human CSF that likely reflect changes in central leptin and melanocortin activity. Our results suggest that nocturnal elevations in leptin, AA, and POMC may help to suppress appetite and feeding at night.

Understanding the control of ingestive behavior in primates

This article is part of a Special Issue "Energy Balance". Ingestive behavior in free-ranging populations of nonhuman primates is influenced by resource availability and social group organization and provides valuable insight on the evolution of ecologically adaptive behaviors and physiological systems. As captive populations were established, questions regarding proximate mechanisms that regulate food intake in these animals could be more easily addressed. The availability of these captive populations has led to the use of selected species to understand appetite control or metabolic physiology in humans. Recognizing the difficulty of quantitating food intake in free-ranging groups, the use of captive, singly-housed animals provided a distinct advantage though, at the same time, produced a different social ecology from the animals' natural habitat. However, the recent application of novel technologies to quantitate caloric intake and energy expenditure in free-feeding, socially housed monkeys permits prospective studies that can accurately define how food intake changes in response to any number of interventions in the context of a social environment. This review provides an overview of studies examining food intake using captive nonhuman primates organized into three areas: a) neurochemical regulation of food intake in nonhuman primates; b) whether exposure to specific diets during key developmental periods programs differences in diet preferences or changes the expression of feeding related neuropeptides; and c) how psychosocial factors influence appetite regulation. Because feeding patterns are driven by more than just satiety and orexigenic signals, appreciating how the social context influences pattern of feeding in nonhuman primates may be quite informative for understanding the biological complexity of feeding in humans.

Sex differences in the physiology of eating

Hypothalamic-pituitary-gonadal (HPG) axis function fundamentally affects the physiology of eating. We review sex differences in the physiological and pathophysiological controls of amounts eaten in rats, mice, monkeys, and humans. These controls result from interactions among genetic effects, organizational effects of reproductive hormones (i.e., permanent early developmental effects), and activational effects of these hormones (i.e., effects dependent on hormone levels). Male-female sex differences in the physiology of eating involve both organizational and activational effects of androgens and estrogens. An activational effect of estrogens decreases eating 1) during the periovulatory period of the ovarian cycle in rats, mice, monkeys, and women and 2) tonically between puberty and reproductive senescence or ovariectomy in rats and monkeys, sometimes in mice, and possibly in women. Estrogens acting on estrogen receptor-α (ERα) in the caudal medial nucleus of the solitary tract appear to mediate these effects in rats. Androgens, prolactin, and other reproductive hormones also affect eating in rats. Sex differences in eating are mediated by alterations in orosensory capacity and hedonics, gastric mechanoreception, ghrelin, CCK, glucagon-like peptide-1 (GLP-1), glucagon, insulin, amylin, apolipoprotein A-IV, fatty-acid oxidation, and leptin. The control of eating by central neurochemical signaling via serotonin, MSH, neuropeptide Y, Agouti-related peptide (AgRP), melanin-concentrating hormone, and dopamine is modulated by HPG function. Finally, sex differences in the physiology of eating may contribute to human obesity, anorexia nervosa, and binge eating. The variety and physiological importance of what has been learned so far warrant intensifying basic, translational, and clinical research on sex differences in eating.

Cerebrospinal fluid levels of leptin, proopiomelanocortin, and agouti-related protein in human pregnancy: evidence for leptin resistance

CONTEXT

Leptin suppresses appetite by modulating the expression of hypothalamic neuropeptides including proopiomelanocortin (POMC) and agouti-related peptide (AgRP). Yet during pregnancy, caloric consumption increases despite elevated plasma leptin levels.

DESIGN AND PARTICIPANTS

To investigate this paradox, we measured leptin and soluble leptin receptor in plasma and leptin, POMC, and AgRP in cerebrospinal fluid (CSF) from 21 fasting pregnant women before delivery by cesarean section at a university hospital and from 14 fasting nonpregnant women.

RESULTS

Prepregnancy body mass index was 24.6 ± 1.1 (SE) vs. 31.3 ± 1.3 at term vs. 26.5 ± 1.6 kg/m(2) in controls. Plasma leptin (32.9 ± 4.6 vs. 16.7 ± 3.0 ng/ml) and soluble leptin receptor (30.9 ± 2.3 vs. 22.1 ± 1.4 ng/ml) levels were significantly higher in pregnant women. However, mean CSF leptin did not differ between the two groups (283 ± 34 vs. 311 ± 32 pg/ml), consistent with a relative decrease in leptin transport into CSF during pregnancy. Accordingly, the CSF/plasma leptin percentage was 1.0 ± 0.01% in pregnant subjects vs. 2.1 ± 0.2% in controls (P < 0.0001). Mean CSF AgRP was significantly higher in pregnant subjects (32.3 ± 2.7 vs. 23.5 ± 2.5 pg/ml; P = 0.03). Mean CSF POMC was not significantly different in pregnant subjects (200 ± 13.6 vs. 229 ± 17.3 fmol/ml; P = 0.190). However, the mean AgRP/POMC ratio was significantly higher among pregnant women (P = 0.003), consistent with an overall decrease in melanocortin tone favoring increased food intake during pregnancy.

CONCLUSIONS

These data demonstrate that despite peripheral hyperleptinemia, positive energy balance is achieved during pregnancy by a relative decrease in central leptin concentrations and resistance to leptin's effects on target neuropeptides that regulate energy balance.

Genomics of estradiol-3-sulfate action in the ovine fetal hypothalamus

In fetal sheep during late gestation sulfoconjugated estrogens in plasma reach a concentration 40-100 times greater than unconjugated estrogens. The objective of the present study was to determine the genomics of estradiol-3-sulfate (E(2)S) action in the ovine fetal brain. The hypothesis was that E(2)S stimulates genes involved in the neuroendocrine pathways that direct or facilitate fetal development at the end of gestation. Four sets of chronically catheterized ovine twin fetuses were studied (gestational age: 120-127 days gestation) with one infused with E(2)S intracerebroventricularly (1 mg/day) and the other remaining untreated (control). After euthanasia, mRNA samples were extracted from fetal brains. Only hypothalamic samples were employed for this study given the important function of this brain region in the control of the hypothalamus-pituitary-adrenal axis. Microarray analysis was performed following the Agilent protocol for one-color 8 × 15 microarrays, designed for Ovis aries. A total of 363 known genes were significantly upregulated by the E(2)S treatment (P < 0.05). Network and enrichment analyses were performed using the Cytoscape/Bingo software, and the results validated by quantitative real-time PCR. The main overrepresented biological processes resulting from this analysis were feeding behavior, hypoxia response, and transforming growth factor signaling. Notably, the genes involved in the feeding behavior (neuropeptide Y and agouti-related protein) were the most strongly induced by the E(2)S treatment. In conclusion, E(2)S may be an important component of the mechanism for activating orexigenic, hypoxia responsiveness and neuroprotective pathways in the lamb as it approaches postnatal life.

Hypothalamic proopiomelanocortin processing and the regulation of energy balance

Hypothalamic proopiomelanocortin (POMC) neurons play a key role in regulating energy balance and neuroendocrine function. Much attention has been focused on the regulation of POMC gene expression with less emphasis on regulated peptide processing. This is particularly important given the complexity of posttranslational POMC processing which is essential for the generation of biologically active MSH peptides. Mutations that impair POMC sorting and processing are associated with obesity in humans and in animals. Specifically, mutations in the POMC processing enzymes prohormone convertase 1/3 (PC1/3) and in carboxypeptidase E (CPE) and in the α-MSH degrading enzyme, PRCP, are associated with changes in energy balance. There is increasing evidence that POMC processing is regulated with respect to energy balance. Studies have implicated both the leptin and insulin signaling pathways in the regulation of POMC at various steps in the processing pathway. This article will review the role of hypothalamic POMC in regulating energy balance with a focus on POMC processing.