Ghrelin

Evidence for partial pharmaceutical reversal of the cancer anorexia-cachexia syndrome: the case of anamorelin

A major component of the cancer anorexia-cachexia syndrome is a decline in food intake. Up until now none of the drugs that improve appetite also improve skeletal muscle. Recent studies have suggested that the oral ghrelin-analog, anamorelin, increased food intake and muscle mass. Unfortunately, it does not increase muscle power. Its regulatory future is uncertain, although it has important clinical effects.

Insulin-Like Growth Factor-I is a Marker for the Nutritional State

Measurement of the serum concentration of insulin-like growth factor-I (IGF-l) is generally used as a screening investigation for disorders of the growth hormone (GH)/IGF-I axis in children and adolescents with short stature. IGF-I concentration is sensitive to short-term and chronic alterations in the nutritional state, and the interpretation of IGF-I measurements requires knowledge of the child's nutritional status. In this review, we summarize the effects of nutrition on the GH/IGF-I axis, and review the clinical implications of these interactions throughout childhood, both in under-nutrition and over-nutrition.

Fasting total ghrelin levels are increased in patients with adolescent idiopathic scoliosis

Background

A control study was designed to investigate circulating Ghrelin levels in adolescent girls with adolescent idiopathic scoliosis (AIS) and controls. Eating behavioral disorders, endocrine disorders, abnormal growth pattern and osteopenia have been well documented in AIS. Ghrelin is an orexigenic hormone produced by the stomach which reflects body weight changes and stimulates growth hormone secretion. Recently, it has been shown to be associated with bone metabolism and eating behavior. However, the circulating levels of ghrelin have never been evaluated in AIS patients.

Methods

Forty nine AIS girls and 15 controls were included. Anthropometric parameters and fasting circulating total ghrelin were measured. Curve severity was evaluated in AIS girls. The relationships between ghrelin and age, body weight, height, body mass index (BMI), BMI Z-score and corrected anthropometric parameters were analyzed in AIS girls and controls.

Results

There was no significant difference in body weight, height, BMI or BMI Z-score between AIS and controls. Serum ghrelin level was 1.8 fold higher in AIS girls than in controls. Elevation of ghrelin levels remained significant when corrected BMI or corrected BMI Z-score were considered. Unlike in controls, positive correlations were found between ghrelin and age in AIS girls with a gradual increase of circulating ghrelin with age.

Conclusions

We have observed significantly higher circulating ghrelin levels in AIS than in controls with a positive correlation with age. This pilot-study suggests that ghrelin signaling might play a role in the initiation or development of AIS. Further studies are needed to validate theses results.

Role of the clock gene Bmal1 and the gastric ghrelin-secreting cell in the circadian regulation of the ghrelin-GOAT system

As adequate food intake is crucial to survival, organisms have evolved endogenous circadian clocks to generate optimal temporal patterns of food-related behavior and physiology. The gastric ghrelin-secreting cell is thought to be part of this network of peripheral food-entrainable oscillators (FEOs), regulating the circadian release of this orexigenic peptide. This study aimed to determine the role of the core clock gene Bmal1 and the gastric ghrelin-secreting cell as an FEO in the circadian rhythmicity of ghrelin expression and secretion in vivo and in vitro. Bmal1-deficient mice not only lacked circadian rhythmicity in plasma ghrelin levels and food intake, but also showed decreased gastric mRNA expression of ghrelin and ghrelin O-acyltransferase (GOAT), the ghrelin activating enzyme. Furthermore, in the absence of the hypothalamic master clock, food-related stimuli entrained the molecular clock of gastric ghrelinoma cells to regulate the rhythmic release of ghrelin. Divergent responses in octanoyl and total ghrelin release towards different food cues were observed, suggesting that the FEO also regulates the circadian rhythmicity of GOAT. Collectively, these findings indicate that circadian rhythmicity of ghrelin signaling requires Bmal1 and is driven by a food-responsive clock in the gastric ghrelin-secreting cell that not only regulates ghrelin, but also GOAT activity.

Ghrelin regulates GLP-1 production through mTOR signaling in L cells

Glucagon-like peptide (GLP-1), an intestinal incretin produced in L-cells and released in response to meal intake, functions to promote insulin secretion and to decrease plasma glucose. Ghrelin is an orexigenic hormone critical for glucose homeostasis. The molecular mechanism by which ghrelin alters GLP-1 production remains largely unknown. Here we showed that ghrelin attenuates GLP-1 production through mTOR signaling. In GHSR1a null mice, ileal mTOR signaling, proglucagon and circulating GLP-1 were significantly increased. Antagonism of the GHSR1a by D-Lys-3-GHRP-6 increased GLP-1 synthesis and release in STC-1 cells. Treatment of STC-1 cells with ghrelin decreased the production of GLP-1. This effect was associated with a significant inhibition of mTOR signaling. Overexpression of ghrelin inhibited proglucagon promoter activity and GLP-1 production. Inhibition of mTOR activity by mTOR siRNA blocked D-Lys-3-GHRP-6 induced GLP-1 production in STC-1 cells. Our results suggest that mTOR signaling mediates the inhibitory effect of ghrelin on GLP-1 production.

Altered intestinal neuroendocrine gene expression in humans with obesity

OBJECTIVE

Gastrointestinal hormones are critically involved in the regulation of food intake and body weight. Previous studies support an interplay between gastrointestinal hormones and the serotonergic system. This study explored intestinal neuroendocrine expression patterns in humans with obesity versus nonobese humans.

METHODS

Jejunum samples were collected from 164 humans with obesity (120 women; BMI (mean ± SD): 43.5 ± 6.6 kg/m(2) ) while they underwent Roux-en-Y gastric bypass surgery and from 18 nonobese humans (7 women; BMI: 23.5 ± 3.0 kg/m(2) ) undergoing distinct intestinal surgeries. mRNA expression of cholecystokinin (CCK), peptide YY3-36 (PYY), nesfatin1, ghrelin, ghrelin O-acyltransferase (GOAT), leptin, leptin receptor (leptinR), glucagon-like-peptide 1 receptor (GLP1R), serotonin transporter (SERT), tryptophan hydroxylase 1 (TPH1), and serotonin receptor 3A (5HT3A R) was determined with qRT-PCR. Ghrelin and GOAT protein expression was quantified using immunohistological stainings. Statistical analyses were performed with SPSS.

RESULTS

Jejunum samples from humans with obesity showed a higher expression of GOAT (mRNA and protein), TPH1, and SERT mRNA compared with the nonobese humans (all P < 0.05). Positive correlations were observed between TPH1, CCK, PYY, and nesfatin1 in nonobese and GOAT, ghrelin, TPH1, SERT, CCK, and PYY in humans with obesity (all P < 0.01).

CONCLUSIONS

Our top-down approach substantiates the dysregulation of jejunal neuroendocrine hormones in obesity.

Chemosensory signalling pathways involved in sensing of amino acids by the ghrelin cell

Taste receptors on enteroendocrine cells sense nutrients and transmit signals that control gut hormone release. This study aimed to investigate the amino acid (AA) sensing mechanisms of the ghrelin cell in a gastric ghrelinoma cell line, tissue segments and mice. Peptone and specific classes of amino acids stimulate ghrelin secretion in the ghrelinoma cell line. Sensing of L-Phe occurs via the CaSR, monosodium glutamate via the TAS1R1-TAS1R3 while L-Ala and peptone act via 2 different amino acid taste receptors: CaSR &TAS1R1-TAS1R3 and CaSR &GPRC6A, respectively. The stimulatory effect of peptone on ghrelin release was mimicked ex vivo in gastric but not in jejunal tissue segments, where peptone inhibited ghrelin release. The latter effect could not be blocked by receptor antagonists for CCK, GLP-1 or somatostatin. In vivo, plasma ghrelin levels were reduced both upon intragastric (peptone or L-Phe) or intravenous (L-Phe) administration, indicating that AA- sensing is not polarized and is due to inhibition of ghrelin release from the stomach or duodenum respectively. In conclusion, functional AA taste receptors regulate AA-induced ghrelin release in vitro. The effects differ between stomach and jejunum but these local nutrient sensing mechanisms are overruled in vivo by indirect mechanisms inhibiting ghrelin release.

Altered gut and adipose tissue hormones in overweight and obese individuals: cause or consequence?

The aim of this article is to review the research into the main peripheral appetite signals altered in human obesity, together with their modifications after body weight loss with diet and exercise and after bariatric surgery, which may be relevant to strategies for obesity treatment. Body weight homeostasis involves the gut–brain axis, a complex and highly coordinated system of peripheral appetite hormones and centrally mediated neuronal regulation. The list of peripheral anorexigenic and orexigenic physiological factors in both animals and humans is intimidating and expanding, but anorexigenic glucagon-like peptide 1 (GLP-1), cholecystokinin (CCK), peptide YY (PYY) and orexigenic ghrelin from the gastrointestinal tract, pancreatic polypeptide (PP) from the pancreas and anorexigenic leptin from adiposites remain the most widely studied hormones. Homeostatic control of food intake occurs in humans, although its relative importance for eating behaviour is uncertain, compared with social and environmental influences. There are perturbations in the gut–brain axis in obese compared with lean individuals, as well as in weight-reduced obese individuals. Fasting and postprandial levels of gut hormones change when obese individuals lose weight, either with surgical or with dietary and/or exercise interventions. Diet-induced weight loss results in long-term changes in appetite gut hormones, postulated to favour increased appetite and weight regain while exercise programmes modify responses in a direction expected to enhance satiety and permit weight loss and/or maintenance. Sustained weight loss achieved by bariatric surgery may in part be mediated via favourable changes to gut hormones. Future work will be necessary to fully elucidate the role of each element of the axis, and whether modifying these signals can reduce the risk of obesity.

Cardiac cachexia: hic et nunc: "hic et nunc" - here and now

Cardiac cachexia (CC) is the clinical entity at the end of chronic natural course of heart failure (HF). Despite the efforts, even the most recent definition of cardiac cachexia has been challenged, more precisely the addition of new criteria on top of obligatory weight loss. The pathophysiology of CC is complex and multifactorial. Better understanding of pathophysiological pathways in body wasting will contribute to establish potentially novel treatment strategies. The complex biochemical network related with CC and HF pathophysiology underlines that a single biomarker cannot reflect all of the features of the disease. Biomarkers that could pick-up the changes in body composition before they convey into clinical manifestations of CC would be of great importance. The development of preventive and therapeutic strategies against cachexia, sarcopenia and wasting disorders is perceived as an urgent need by healthcare professionals. The treatment of body wasting remains an unresolved challenge to this day. As CC is a multifactorial disorder, it is unlikely that any single agent will be completely effective in treating this condition. Among all investigated therapeutic strategies, aerobic exercise training in HF patients is the most proved to counteract skeletal muscle wasting and is recommended by treatment guidelines for HF.

Octanoylated ghrelin attenuates angiogenesis induced by oxLDL in human coronary artery endothelial cells via the GHSR1a-mediated NF-κB pathway

OBJECTIVE

Low concentrations of oxidized low-density lipoprotein (oxLDL) promote the in vitro angiogenesis of endothelial cells and play an important role in plaque angiogenesis, which may cause plaque vulnerability and enhance the risk of intravascular thrombosis. The aim of this research was to investigate the effects of octanoylated ghrelin on oxLDL-induced angiogenesis and the underlying molecular mechanisms involved in this process.

MATERIALS/METHODS

Human coronary artery endothelial cells (HCAECs) were incubated with 5 μg/ml oxLDL and treated with various concentrations of octanoylated ghrelin (10(-9)-10(-6)M) with or without inhibitors for 24h. Cell proliferation, migration, and in vitro angiogenesis were analyzed by bromodeoxyuridine (BrdU) staining and BrdU enzyme-linked immunosorbent assay (ELISA), transwell assay, and tube formation on Matrigel, respectively. NF-κB (nuclear factor κB) expression was determined by Western-blot analysis.

RESULTS

Treatment with oxLDL at 5 μg/ml enhanced the proliferation, migration and tube formation of HCAECs. In contrast, pretreatment with octanoylated ghrelin significantly attenuated in vitro angiogenesis in oxLDL-induced HCAECs. In addition, Western blot analysis indicated that NF-κB expression was increased after oxLDL treatment, and that this effect was significantly reversed by pretreatment with octanoylated ghrelin. However, the NF-κB inhibitor PDTC or the GHSR1a inhibitor [D-Lys3]-GHRP-6 abolished the effects of octanoylated ghrelin on the inhibition of angiogenesis and NF-κB p65 expression induced by oxLDL.

CONCLUSIONS

These findings suggest that octanoylated ghrelin attenuates angiogenesis induced by oxLDL in HCAECs via the inhibition of GHSR1a-mediated NF-κB pathway. Furthermore, octanoylated ghrelin may promote the stability of vulnerable plaques by inhibiting plaque angiogenesis.

Ghrelin - Physiological Functions and Regulation

Ghrelin is an orexigenic peptide predominantly secreted from the stomach and stimulates appetite and growth hormone (GH) release. Studies have provided evidence that ghrelin exercises a wide range of functions, including regulation of food intake and energy metabolism, modulation of cardiovascular function, stimulation of osteoblast proliferation and bone formation and stimulation of neurogenesis and myogenesis. In the gastrointestinal system, ghrelin affects multiple functions, including secretion of gastric acid, gastric motility and pancreatic protein output. Most of these functions have been attributed to the actions of acylated ghrelin. The balance among its secretion rate, degradation rate and clearance rate determines the circulating level of ghrelin. This review explains what ghrelin is, its physiological functions and the factors that influence its level.

Neural Control of Energy Expenditure

The continuous rise in obesity is a major concern for future healthcare management. Many strategies to control body weight focus on a permanent modification of food intake with limited success in the long term. Metabolism or energy expenditure is the other side of the coin for the regulation of body weight, and strategies to enhance energy expenditure are a current focus for obesity treatment, especially since the (re)-discovery of the energy depleting brown adipose tissue in adult humans. Conversely, several human illnesses like neurodegenerative diseases, cancer, or autoimmune deficiency syndrome suffer from increased energy expenditure and severe weight loss. Thus, strategies to modulate energy expenditure to target weight gain or loss would improve life expectancies and quality of life in many human patients. The aim of this book chapter is to give an overview of our current understanding and recent progress in energy expenditure control with specific emphasis on central control mechanisms.