Enterostatin inhibition of dietary fat intake is modulated through the melanocortin system

Relative contribution of foetal and post-natal nutritional periods on feeding regulation in adult rats

AIM

The aim of this study was to assess the contribution of both foetal and/or post-natal nutritional periods on feeding regulation in adult rats.

METHODS

Body weight gain, adipose tissue development, food preferences and feeding pattern under regular chow or Western diets were characterized on four experimental groups of rats: pups born from protein-restricted dams (R) and weaned by control (RC) or R dams (RR) and pups born from control dams weaned by C (CC) or R dams (CR).

RESULTS

Rats born with intrauterine growth restriction (IUGR) and fed a Western diet at adulthood appeared predisposed to body weight gain and more fat accretion, whereas CR rats, despite their preference for high-fat diet and their hyperphagia for Western diet, did not show significant increase in fat tissue. Daytime food intakes, as well as their speed of ingestion, were found modified in RC and RR. Alterations in the hypothalamic appetite regulatory mechanisms were investigated through neuropeptide expression analysis. IUGR rats showed altered expression of key elements of leptin and NPY signalling, while CR rats exhibited lesser expression of enterostatin, MC4r and HT-1Br mRNA.

CONCLUSION

Altogether, these results indicate that peri-natal nutrition has different lasting effects on feeding pattern and hypothalamic appetite regulation, depending on the time window insult.

Areias MF, Weissmann L, Quaresma PG, Katashima CK, Saad MJ, Prada PO. Diet-induced obesity induces endoplasmic reticulum stress and insulin resistance in the amygdala of rats

Insulin acts in the hypothalamus, decreasing food intake (FI) by the IR/PI3K/Akt pathway. This pathway is impaired in obese animals and endoplasmic reticulum (ER) stress and low-grade inflammation are possible mechanisms involved in this impairment. Here, we highlighted the amygdala as an important brain region for FI regulation in response to insulin. This regulation was dependent on PI3K/AKT pathway similar to the hypothalamus. Insulin was able to decrease neuropeptide Y (NPY) and increase oxytocin mRNA levels in the amygdala via PI3K, which may contribute to hypophagia. Additionally, obese rats did not reduce FI in response to insulin and AKT phosphorylation was decreased in the amygdala, suggesting insulin resistance. Insulin resistance was associated with ER stress and low-grade inflammation in this brain region. The inhibition of ER stress with PBA reverses insulin action/signaling, decreases NPY and increases oxytocin mRNA levels in the amygdala from obese rats, suggesting that ER stress is probably one of the mechanisms that induce insulin resistance in the amygdala.

Globular adiponectin regulates energy homeostasis through AMP-activated protein kinase-acetyl-CoA carboxylase (AMPK/ACC) pathway in the hypothalamus

Adiponectin is a newly researched adipokine which participates in the regulation of energy homeostasis. AMP-activated protein kinase (AMPK) represents an energy sensor that responds to hormone and nutrition status in vivo and exerts a regulatory effect in the hypothalamus and multiple peripheral tissues. We investigated the possible mechanisms involved in appetite regulation by adiponectin in vitro with GT1-7 cells, a mouse immortalized hypothalamic neuron. The results showed that adiponectin increased the phosphorylation of AMPK, activated AMPK phosphorylated and inactivated acetyl-CoA carboxylase (ACC), and subsequently increased expression of agouti-related peptide (AgRP) mRNA. Our results also indicated that adiponectin had no effect on signal transducer and activator of transcription (STAT3). Together these findings suggest that adiponectin regulated energy homeostasis through the AMPK/ACC pathway but not the JAK/STAT3 pathway in the hypothalamus.

Effects of dietary fat and enterostatin on dopamine and 5-hydroxytrytamine release from rat striatal slices

Studies have demonstrated defects of DA and 5HT neurotransmission in dietary fat induced obese animals. In the present study, we used a perfusion system to assay the release of DA and 5HT from striatal slices preloaded with [(3)H]-DA or [(3)H]-5HT. The release of both DA and 5HT from striatal slices of rats fed a high fat diet for 10 days, but not 3 days, was reduced when compared to striatal slices taken from rats fed a low fat diet. Enterostatin, an endogenous pentapeptide inhibits dietary fat intake when administered peripherally and centrally in animals. The central mechanism for the action of enterostatin is not yet determined even though several mechanisms have been suggested. We have shown that enterostatin enhanced [(3)H]-DA release, but not [(3)H]-5HT release from striatal slices of rats that had been adapted to high fat diet for 10 days. The enterostatin-induced increase in [(3)H]-DA release was blocked by nomifensine. Enterostatin did not alter [(3)H]-DA or [(3)H]-5HT release from striatal slices of rats adapted to high fat or low fat diet feeding for 3 days. These findings suggest that enterostatin may inhibit dietary fat intake by blocking dopamine reuptake transport to increase central striatal DA release from rats that have acquired diminished dopamine signal after an adaptive period of fat consumption.

Functions for pro-opiomelanocortin-derived peptides in obesity and diabetes

Melanocortin peptides, derived from POMC (pro-opiomelanocortin) are produced in the ARH (arcuate nucleus of the hypothalamus) neurons and the neurons in the commissural NTS (nucleus of the solitary tract) of the brainstem, in anterior and intermediate lobes of the pituitary, skin and a wide range of peripheral tissues, including reproductive organs. A hypothetical model for functional roles of melanocortin receptors in maintaining energy balance was proposed in 1997. Since this time, there has been an extraordinary amount of knowledge gained about POMC-derived peptides in relation to energy homoeostasis. Development of a Pomc-null mouse provided definitive proof that POMC-derived peptides are critical for the regulation of energy homoeostasis. The melanocortin system consists of endogenous agonists and antagonists, five melanocortin receptor subtypes and receptor accessory proteins. The melanocortin system, as is now known, is far more complex than most of us could have imagined in 1997, and, similarly, the importance of this system for regulating energy homoeostasis in the general human population is much greater than we would have predicted. Of the known factors that can cause human obesity, or protect against it, the melanocortin system is by far the most significant. The present review is a discussion of the current understanding of the roles and mechanism of action of POMC, melanocortin receptors and AgRP (agouti-related peptide) in obesity and Type 2 diabetes and how the central and/or peripheral melanocortin systems mediate nutrient, leptin, insulin, gut hormone and cytokine regulation of energy homoeostasis.

Melanocortin activity in the amygdala controls appetite for dietary fat

The amygdala is rich in melanocortin 4 receptors. Because the reduction in dietary fat intake after enterostatin is injected in the central nucleus of the amygdala (CeA) is blocked by a melanocortin 4 receptor antagonist, we investigated the role of melanocortin activity in the CeA in regulating food intake and macronutrient choice. Sprague-Dawley rats, fitted with CeA cannulas, were fed either chow, a high-fat (HF) diet, or adapted to a two-choice HF or low-fat (LF) diet. Injections of the MC4R agonist melanotan II (MTII) in the CeA had a dose-dependent inhibitory effect on food intake that lasted for at least 24 h. This response was greater in rats fed a HF diet. The inverse agonist agouti-related protein (AgRP) and antagonist SHU-9119 increased food intake in a dose-dependent manner, with the hyperphagia lasting for 60 h. In rats adapted to a two-choice HF/LF diet, MTII decreased HF consumption but had no effect on LF consumption, resulting in a long-lasting decrease in total calorie intake (−35.5% after 24 h, P < 0.05). Total calorie intake increased in both AgRP- and SHU-9119-treated rats (32 and 109% after 24 h, respectively) as the result of increased intake of HF diet. There was no modification of LF consumption with AgRP treatment and a transient nonsignificant decrease with SHU-9119 treatment. Amygdala brain-derived neurotrophic factor expression was increased by AgRP in fed rats. These results identify the amygdala as a site of action for the melanocortin system to control food intake and dietary preferences.

Regulatory effect of the AMPK-COX-2 signaling pathway in curcumin-induced apoptosis in HT-29 colon cancer cells

AMP-activated protein kinase (AMPK), a highly conserved protein in eukaryotes, functions as a major metabolic switch to maintain energy homeostasis. It also intrinsically regulates the mammalian cell cycle. Moreover, the AMPK cascade has emerged as an important pathway implicated in cancer control. In this study we investigated the effects of curcumin on apoptosis and the regulatory effect of the AMPK-cyclooxygenase-2 (COX-2) pathway in curcumin-induced apoptosis. Curcumin has shown promise as a chemopreventive agent because of its in vivo regression of various animal-model colon cancers. This study focused on exploiting curcumin to apply antitumorigenic effects through modulation of the AMPK-COX-2 cascade. Curcumin exhibited a potent apoptotic effect on HT-29 colon cancer cells at concentrations of 50 micromol/L and above. These apoptotic effects were correlated with the decrease in pAkt and COX-2, as well as the increase in p-AMPK. Cell cycle analysis showed that curcumin induced G(1)-phase arrest. Further study with AMPK synthetic inhibitor Compound C has shown that increased concentrations of Compound C would abolish AMPK expression, accompanied by a marked increase in COX-2 as well as pAkt expression in curcumin-treated HT-29 cells. By inhibiting AMPK with Compound C, we found that curcumin-treated colon cancer cells were no longer undergoing apoptosis; rather, they were proliferative. These results indicate that AMPK is crucial in apoptosis induced by curcumin and further that the pAkt-AMPK-COX-2 cascade or AMPK-pAkt-COX-2 pathway is important in cell proliferation and apoptosis in colon cancer cells.

High-fat diets induce a rapid loss of the insulin anorectic response in the amygdala

Intracerebroventricular insulin decreases food intake (FI). The central bed nucleus of the amygdala (CeA), as other regions of the brain regulating feeding behavior, expresses insulin receptors. Our objectives were to show an insulin anorectic response in the amygdala, study the effect of high-fat diets on this response, and map the neural network activated by CeA insulin using c-Fos immunohistochemistry. Sprague-Dawley (SD) rats fitted with unilateral CeA cannulas were adapted to a low-fat (LFD) diet before they were fed a high-fat diet (HFD). Their feeding response to CeA saline or insulin (8 mU) was tested after 24 h, 72 h, or 7 days of being on a HFD. In a second experiment, SD rats were fed the HFD for 3, 7, or 49 days and were then refed with the LFD. They were tested for their insulin response before and after an HFD and every 3 days for the following weeks. Insulin tolerance tests were performed in a parallel group of rats. The CeA insulin stimulation c-Fos expression was studied to identify the distribution of activated neuronal populations. Feeding an HFD for 72 h or more induced a CeA, but not peripheral, insulin resistance, which was slowly reversed by LFD refeeding. The duration of HFD feeding determined the time frame for reversal of the insulin resistance. CeA insulin increased c-Fos in multiple brain regions, including the arcuate nucleus/paraventricular nucleus region of the hypothalamus. We conclude that the amygdala may be an important site for insulin regulation of food intake and may have a significant role in determining susceptibility to HFD-induced obesity.

Hypothalamic cell lines to investigate neuroendocrine control mechanisms

The hypothalamus is the control center for most physiological processes; yet has been difficult to study due to the inherent heterogeneity of this brain region. For this reason, researchers have turned towards cell models. Primary hypothalamic cultures are difficult to maintain, are heterogeneous neuronal and glial cell populations and often contain a minimal number of viable peptide-secreting neurons. In contrast, immortalized, clonal cell lines represent an unlimited, homogeneous population of neurons that can be manipulated using a number of elegant molecular techniques. Cell line studies and in vivo experimentation are complementary and together provide a powerful tool to drive scientific discovery. This review focuses on three key neuroendocrine systems: energy homeostasis, reproduction, and circadian rhythms; and the use of hypothalamic cell lines to dissect the complex pathways utilized by individual neurons in these systems.

Enterostatin affects cyclic AMP and ERK signaling pathways to regulate Agouti-related protein (AgRP) expression

Enterostatin, a gut-brain peptide, inhibits dietary fat intake in rats. The purpose of this study was to identify the intracellular signaling pathways that are responsive to enterostatin and that modulate the effects of enterostatin on the expression of Agouti-related protein (AgRP). We used the hypothalamic GT1-7 neuronal cell line to identify the effects of enterostatin on cyclic AMP and ERK signaling using conventional immunoassays or Western blots to assay the activity of these pathways. Enterostatin enhanced the level of cyclic AMP, PKA(RIIbeta) and phospho-CREB and increased pERK levels in GT 1-7 cells. The effects on pERK were rapid (7.5 min) and dose-dependent. These signaling responses were blocked by an antibody to the enterostatin receptor (beta subunit of F1-ATPase), by the pERK inhibitor U0126 and by the P2Y receptor antagonist Suramin. Enterostatin showed a biphasic effect on AgRP mRNA, initially increasing but subsequently decreasing the levels. The cyclic AMP activator Sp-cAMP increased AgRP mRNA expression. Transfection of a wild type ERK construct reduced AgRP mRNA levels. Enterostatin inhibited expression of Krüppel-like factor 4 (KLF4), a transcriptional regulator of AgRP. KLF4 gene expression was increased by Sp-cAMP but decreased by wild-type ERK expression. U0126 blocked the effect of enterostatin on KLF4 expression. We conclude that enterostatin binding to its receptor activates the pERK pathway to inhibit AgRP gene expression but may enhance AgRP expression through activation of the cyclic AMP pathway. These pathways probably mediate the enterostatin inhibition of dietary fat intake.

Procolipase gene: no association with early-onset obesity or fat intake

BACKGROUND

Several lines of evidence in volvement of procolipase (CLPS) or its derivative enterostatin in dietary fat absorption, regulation of fat intake, and body weight in rodents. We explored the relationship between genetic variation in CLPS, early-onset obesity and fat intake in humans.

METHODS

We screened the CLPS in 93 extremely obese children and adolescents and 96 underweight young adults for sequence variations and genotyped single nucleotide polymorphisms (SNPs) in extremely obese children and adolescents, healthy normal-and underweight young adults and obesity trios. Case-control and family-based association analyses were performed.

RESULTS

Five sequence variations were identified: two non-synonymous SNPs: rs2766597 (Leu8Pro), rs41270082 (Arg109Cys); one SNP in the 5'UTR: rs3748050; one intronic SNP: rs3748051; and one infrequent novel non-synonymous variant: Arg55His. For rs2766597, rs3748050, and rs3748051 we obtained no evidence for an association with obesity in the case-control comparison. For rs41270082 there was a trend for association which could not be substantiated in the family-based association analysis. Additionally, we found no association in subgroup analyses pertaining to the extremely obese children and adolescents in the lowest and highest quartile of the percentage of energy consumed as fat.

CONCLUSIONS

We found no evidence for an association of CLPS SNPs rs2766597, rs41270082, rs3748050, and rs3748051 with obesity or percentage of dietary fat intake.

Enterostatin reduces serum cholesterol levels by way of a CCK(1) receptor-dependent mechanism

Enterostatin (APGPR), an anorectic pentapeptide derived from the amino terminus of procolipase, significantly reduced serum cholesterol levels after oral administration at a dose of 100 mg/kg for 3 days in mice fed a high-cholesterol-cholic acid diet. The hypocholesterolemic effect of APGPR was inhibited by pretreatment with lorglumide, an antagonist for cholecystokinin 1 (CCK(1)) receptor, even though APGPR does not have any affinity for CCK(1) receptors. Similarly, the hypocholesterolemic activity of VPDPR, an APGPR analogue, was blocked by lorglumide. These results suggest that the hypocholesterolemic effects of APGPR and VPDPR are mediated by a CCK(1) receptor-dependent mechanism.

Enterostatin (APGPR) suppresses the analgesic activity of morphine by a CCK-dependent mechanism

Enterostatin (APGPR) found in the gastrointestinal tract and brain is an anorectic pentapeptide. We found that APGPR inhibited morphine-induced analgesia after intracerebroventricular administration in mice at a dose of 10nmol/mouse. The anti-analgesic effect of APGPR was inhibited by pretreatment with lorglumide and LY225910, antagonists for cholecystokinin 1 (CCK1) and cholecystokinin 2 (CCK2) receptors, respectively. The anti-analgesic effect of APGPR may be mediated by CCK release, since APGPR does not have affinity for CCK receptors.