Cintia Folgueira

The Gastric CB1 Receptor Modulates Ghrelin Production through the mTOR Pathway to Regulate Food Intake

Over the years, the knowledge regarding the relevance of the cannabinoid system to the regulation of metabolism has grown steadily. A central interaction between the cannabinoid system and ghrelin has been suggested to regulate food intake. Although the stomach is the main source of ghrelin and CB1 receptor expression in the stomach has been described, little information is available regarding the possible interaction between the gastric cannabinoid and ghrelin systems in the integrated control of energy homeostasis. The main objective of the present work was to assess the functional interaction between these two systems in terms of food intake using a combination of in vivo and in vitro approaches. The present work demonstrates that the peripheral blockade of the CB1 receptor by rimonabant treatment decreased food intake but only in food-deprived animals. This anorexigenic effect is likely a consequence of decreases in gastric ghrelin secretion induced by the activation of the mTOR/S6K1 intracellular pathway in the stomach following treatment with rimonabant. In support of this supposition, animals in which the mTOR/S6K1 intracellular pathway was blocked by chronic rapamycin treatment, rimonabant had no effect on ghrelin secretion. Vagal communication may also be involved because rimonabant treatment was no longer effective when administered to animals that had undergone surgical vagotomy. In conclusion, to the best of our knowledge, the present work is the first to describe a CB1 receptor-mediated mechanism that influences gastric ghrelin secretion and food intake through the mTOR pathway.

Circulating Betatrophin Levels Are Increased in Anorexia and Decreased in Morbidly Obese Women

CONTEXT Betatrophin is produced primarily by liver and adipose tissue and has been recently reported as a novel hormone promoting β-cell proliferation and β-cell mass and improving glucose tolerance. OBJECTIVE Because it is markedly regulated by nutritional status, we hypothesized that circulating betatrophin levels might be affected by pathophysiological conditions altering body weight. SETTING AND PATIENTS We analyzed circulating betatrophin levels in 149 female patients, including 99 with extreme body mass index (30 anorexia nervosa, 24 obese, 45 morbid obese, and 50 healthy eating/weight controls). OUTCOME MEASUREMENTS Serum betatrophin levels and its correlations with different anthropometric and biochemical parameters were measured. RESULTS Plasma betatrophin levels were significantly elevated in anorexic patients, whereas its levels were reduced in morbidly obese women when compared with normal-weight women. Plasma betatrophin correlated negatively with weight, body mass index, fat percentage, glucose, insulin, and homeostatic model assessment index and positively correlated with high-density lipoprotein. CONCLUSIONS These results suggest that metabolic status is an important regulator of circulating betatrophin levels.

Hypothalamic κ -Opioid Receptor Modulates the Orexigenic Effect of Ghrelin

The opioid system is well recognized as an important regulator of appetite and energy balance. We now hypothesized that the hypothalamic opioid system might modulate the orexigenic effect of ghrelin. Using pharmacological and gene silencing approaches, we demonstrate that ghrelin utilizes a hypothalamic κ-opioid receptor (KOR) pathway to increase food intake in rats. Pharmacological blockade of KOR decreases the acute orexigenic effect of ghrelin. Inhibition of KOR expression in the hypothalamic arcuate nucleus is sufficient to blunt ghrelin-induced food intake. By contrast, the specific inhibition of KOR expression in the ventral tegmental area does not affect central ghrelin-induced feeding. This new pathway is independent of ghrelin-induced AMP-activated protein kinase activation, but modulates the levels of the transcription factors and orexigenic neuropeptides triggered by ghrelin to finally stimulate feeding. Our novel data implicate hypothalamic KOR signaling in the orexigenic action of ghrelin.

Regulation of NUCB2/nesfatin-1 production in rat's stomach and adipose tissue is dependent on age, testosterone levels and lactating status

Nesfatin-1, which is derived from the NEFA/nucleobindin 2 (NUCB2) precursor, was recently identified as an anorexigenic peptide that is produced in several tissues including the hypothalamus. Currently, no data exist regarding the regulation of NUCB2/nesfatin-1 production in peripheral tissues, such as gastric mucosa and adipose tissue, through different periods of development. The aim of the present work was to study the variations on circulating levels, mRNA expression and tissue content in gastric mucosa and adipose tissue of NUCB2/nesfatin-1 with age and specially in two clue periods of maturation, weaning and puberty. The weaning period affected NUCB2/nesfatin-1 production in gastric tissue. The testosterone changes associated with the initiation of puberty regulated NUCB2/nesfatin-1 production via adipose tissue and gastric NUCB2/nesfatin-1 production. In conclusion, the production of NUCB2/nesfatin-1 by the stomach and adipose tissue fluctuates with age to regulate energy homeostasis during different states of development.

Peripheral Signals Mediate the Beneficial Effects of Gastric Surgery in Obesity

Obesity is nowadays a public health problem both in the industrialized world and developing countries. The different treatments to fight against obesity are not very successful with the exception of gastric surgery. The mechanism behind the achievement of this procedure remains unclear although the modifications in the pattern of gastrointestinal hormones production appear to be responsible for the beneficial effect. The gastrointestinal tract has emerged in the last time as an endocrine organ in charge of response to the different stimulus related to nutritional status by the modulation of more than 30 signals acting at central level to modulate food intake and body weight. The production of some of these gastric derived signals has been proved to be altered in obesity (ghrelin, CCK, and GLP-1). In fact, bariatric surgery modifies the production of both gastrointestinal and adipose tissue peripheral signals beyond the gut microbiota composition. Through this paper the main peripheral signals altered in obesity will be reviewed together with their modifications after bariatric surgery.

Circulating Irisin Levels Are Not Regulated by Nutritional Status, Obesity, or Leptin Levels in Rodents

Irisin is a cleaved and secreted fragment of fibronectin type III domain containing 5 (FNDC5) that is mainly released by skeletal muscle and was proposed to mediate the beneficial effects of exercise on metabolism. In the present study we aim to investigate the regulation of the circulating levels of irisin in obese animal models (diet-induced obese (DIO) rats and leptin-deficient (ob/ob) mice), as well as the influence of nutritional status and leptin. Irisin levels were measured by Enzyme-Linked Immunosorbent Assay (ELISA) and Radioimmunoassay (RIA). Serum irisin levels remained unaltered in DIO rats and ob/ob mice. Moreover, its circulating levels were also unaffected by fasting, leptin deficiency, and exogenous leptin administration in rodents. In spite of these negative results we find a negative correlation between irisin and insulin in DIO animals and a positive correlation between irisin and glucose under short-term changes in nutritional status. Our findings indicate that serum irisin levels are not modulated by different physiological settings associated to alterations in energy homeostasis. These results suggest that in rodents circulating levels of irisin are not involved in the pathophysiology of obesity and could be unrelated to metabolic status; however, further studies should clarify its precise role in states of glucose homeostasis imbalance.

Pharmacological inhibition of cannabinoid receptor 1 stimulates gastric release of nesfatin-1 via the mTOR pathway

AIM To determine whether Nucb2/nesfatin1 production is regulated by the cannabinoid system through the intracellular mTOR pathway in the stomach. METHODS Sprague Dawley rats were treated with vehicle, rimonabant, rapamycin or rapamycin+rimonabant. Gastric tissue obtained from the animals was used for biochemical assays: Nucb2 mRNA measurement by real time PCR, gastric Nucb2/nesfatin protein content by western blot, and gastric explants to obtain gastric secretomes. Nucb2/nesfatin levels were measured in gastric secretomes and plasma using enzyme-linked immunosorbent assay. RESULTS The inhibition of cannabinoid receptor 1 (CB1) by the peripheral injection of an inverse agonist, namely rimonabant, decreases food intake and increases the gastric secretion and circulating levels of Nucb2/nesfatin-1. In addition, rimonabant treatment activates mTOR pathway in the stomach as showed by the increase in pmTOR/mTOR expression in gastric tissue obtained from rimonabant treated animals. These effects were confirmed by the use of a CB1 antagonist, AM281. When the intracellular pathway mTOR/S6k was inactivated by chronic treatment with rapamycin, rimonabant treatment was no longer able to stimulate the gastric secretion of Nucb2/nesfatin-1. CONCLUSION The peripheral cannabinoid system regulates food intake through a mechanism that implies gastric production and release of Nucb2/Nesfatin-1, which is mediated by the mTOR/S6k pathway.

Regulation of Growth Hormone by the Splanchnic Area.

The regulation of growth hormone (GH) was traditionally thought to be under the control of two main hypothalamic neuropeptides; GH-releasing hormone and somatostatin. In 1999, with the isolation of ghrelin, as a gastric-derived peptide with potent GH-releasing activity, concept of regulation of the somatotropic axis completely changed. In addition to its GH-releasing activity, ghrelin exhibited the capacity to modulate food intake and body weight. The role of this splanchnic factor in regulating GH as a nexus of energy balance control and GH are explored in this chapter. From a physiological standpoint, a novel mechanism of GH regulation mediated by ghrelin exists, implicating the peripheral modulation of the cannabinoid receptor.

Plasma ANGPTL-4 is Associated With Obesity and Glucose Tolerance: Cross-Sectional and Longitudinal Findings

SCOPE Angiopoietin-like protein 4 (ANGPTL-4) regulates plasma lipoprotein levels, but its relevance in human obesity and type 2 diabetes (T2D) is largely unknown. We aim to investigate the regulation of circulating ANGPTL-4 levels in obesity, T2D, and after changes in body weight. METHODS AND RESULTS Circulating ANGPTL-4 levels were measured in two different cohorts. First, in a cross-sectional study, we evaluated ANGPTL-4 levels in lean and obese patients with normoglycemia or with altered glucose tolerance (AGT; n = 282). Second, in a longitudinal intervention study, 51 obese participants were evaluated. A hypocaloric diet was prescribed, with follow-up 2 years later. ANGPTL-4 levels were significantly increased in obese patients with AGT compared to lean participants. Moreover, ANGPTL-4 was positively correlated with BMI, waist circumference, fat mass, HbA1c, HOMA-IR, fasting triglycerides, and with inflammatory markers. Participants gaining weight after the follow-up showed increased ANGPTL-4 levels in parallel to increased BMI, fat mass, and fasting glucose, while ANGPTL-4 levels were reduced in participants losing weight. CONCLUSION Our data support a relevant role of ANGPTL-4 in human obesity and its involvement in long-term body weight changes.

Hypothalamic kappa opioid receptor mediates both diet- and MCH-induced liver damage through inflammation and ER stress

The opioid system is widely known to modulate the brain reward system and thus affect the behavior of humans and other animals, including feeding. We hypothesized that the hypothalamic opioid system might also control energy metabolism in peripheral tissues. Mice lacking the kappa opioid receptor (κOR) and adenoviral vectors overexpressing or silencing κOR were stereotaxically delivered in the lateral hypothalamic area (LHA) of rats. Vagal denervation was performed to assess its effect on liver metabolism. Endoplasmic reticulum (ER) stress was inhibited by pharmacological (tauroursodeoxycholic acid) and genetic (overexpression of the chaperone glucose‐regulated protein 78 kDa) approaches. The peripheral effects on lipid metabolism were assessed by histological techniques and western blot. We show that in the LHA κOR directly controls hepatic lipid metabolism through the parasympathetic nervous system, independent of changes in food intake and body weight. κOR colocalizes with melanin concentrating hormone receptor 1 (MCH‐R1) in the LHA, and genetic disruption of κOR reduced melanin concentrating hormone–induced liver steatosis. The functional relevance of these findings was given by the fact that silencing of κOR in the LHA attenuated both methionine choline–deficient, diet‐induced and choline‐deficient, high‐fat diet–induced ER stress, inflammation, steatohepatitis, and fibrosis, whereas overexpression of κOR in this area promoted liver steatosis. Overexpression of glucose‐regulated protein 78 kDa in the liver abolished hypothalamic κOR‐induced steatosis by reducing hepatic ER stress. Conclusions: This study reveals a novel hypothalamic–parasympathetic circuit modulating hepatic function through inflammation and ER stress independent of changes in food intake or body weight; these findings might have implications for the clinical use of opioid receptor antagonists. (Hepatology 2016;64:1086‐1104)The opioid system is widely known to modulate the brain reward system and thus affect human and animal behaviour, including feeding. We hypothesized that the hypothalamic opioid system might also control energy metabolism in peripheral tissues. Mice lacking the kappa opioid receptor (κOR) and adenoviral vectors over-expressing or silencing κOR were stereotaxically delivered in the lateral hypothalamic area (LHA) of rats. Vagal denervation was performed to assess its effect on liver metabolism. ER stress was inhibited by pharmacological (tauroursodeoxycholic acid - TUDCA) and genetic (over-expression of the chaperone glucose-regulated protein 78 kDa - GRP78) approaches. The peripheral effects on lipid metabolism were assessed by histological techniques and Western blot. We show that in the LHA, κOR directly controls hepatic lipid metabolism via the parasympathetic nervous system, independent of changes in food intake and body weight. κOR colocalizes with melanin concentrating hormone receptor (MCH-R1) in the LHA and genetic disruption of κOR reduced MCH-induced liver steatosis. The functional relevance of these findings was given by the fact that silencing of κOR in the LHA attenuated both methionine choline-deficient diet- and choline deficient-high fat diet-induced ER stress, inflammation, steatohepatitis and fibrosis, whereas over-expression of κOR in this area promoted liver steatosis. Over-expression of the GRP78 in the liver abolished hypothalamic κOR-induced steatosis by reducing hepatic ER stress. CONCLUSIONS: Overall, this study reveals a novel hypothalamic-parasympathetic circuit modulating hepatic function via inflammation and ER stress independent of changes in food intake or body weight. These findings might have implications for the clinical use of opioid receptor antagonists. This article is protected by copyright. All rights reserved.