Comparison of competitive radioimmunoassays and two-site sandwich assays for the measurement and interpretation of plasma ghrelin levels

Postprandial Increases in Liver-Gut Hormone LEAP2 Correlate with Attenuated Eating Behavior in Adults Without Obesity

Background

The novel liver-gut hormone liver-expressed antimicrobial peptide-2 (LEAP2) is a centrally acting inverse agonist, and competitive antagonist of orexigenic acyl ghrelin (AG), at the GH secretagogue receptor, reducing food intake in rodents. In humans, the effects of LEAP2 on eating behavior and mechanisms behind the postprandial increase in LEAP2 are unclear, though this is reciprocal to the postprandial decrease in plasma AG.

Methods

Plasma LEAP2 was measured in a secondary analysis of a previous study. Twenty-two adults without obesity attended after an overnight fast, consuming a 730-kcal meal without or with subcutaneous AG administration. Postprandial changes in plasma LEAP2 were correlated with postprandial changes in appetite, high-energy (HE) or low-energy (LE) food cue reactivity using functional magnetic resonance imaging, ad libitum food intake, and plasma/serum AG, glucose, insulin, and triglycerides.

Results

Postprandial plasma LEAP2 increased by 24.5% to 52.2% at 70 to 150 minutes, but was unchanged by exogenous AG administration. Postprandial increases in LEAP2 correlated positively with postprandial decreases in appetite, and cue reactivity to HE/LE and HE food in anteroposterior cingulate cortex, paracingulate cortex, frontal pole, and middle frontal gyrus, with similar trend for food intake. Postprandial increases in LEAP2 correlated negatively with body mass index, but did not correlate positively with increases in glucose, insulin, or triglycerides, nor decreases in AG.

Conclusions

These correlational findings are consistent with a role for postprandial increases in plasma LEAP2 in suppressing human eating behavior in adults without obesity. Postprandial increases in plasma LEAP2 are unrelated to changes in plasma AG and the mediator(s) remain uncertain.

Plasma Concentrations of Gut Hormones Acyl Ghrelin and Peptide YY and Subsequent Risk of Colorectal Cancer and Molecular Tumor Subtypes

Obesity and metabolic dysfunction are implicated in colorectal cancer development. Appetite-regulating gut hormones might have a role in colorectal cancer risk. We investigated whether circulating levels of the gut hormones ghrelin (analyzed as acyl ghrelin) and Peptide YY (PYY) were associated with subsequent colorectal cancer risk, including clinical and molecular tumor subtypes. We also provide descriptive data on these hormones in relation to background participant characteristics and metabolic biomarkers. This population-based study included 1,010 matched case-control pairs with a median of 12.3 years of follow-up. Acyl ghrelin and PYY were measured by multiplex immunoassay. Data on KRAS and BRAF mutations and microsatellite instability (MSI) status were available for 704 and 708 cases, respectively. Conditional logistic regression models estimated association to colorectal cancer risk. Partial correlation and linear regression were used to investigate relationships between background and metabolic variables and variation in plasma gut hormone concentrations. Acyl ghrelin was not clearly associated with colorectal cancer risk (multivariable OR per 1 SD increase: 1.11; 95% CI, 1.00-1.23). Positive associations were observed for specific subtypes, in particular BRAF-mutated colorectal cancer and right-sided colon cancer, although with nonsignificant heterogeneity. PYY was not related to colorectal cancer risk (multivariable OR per 1 SD: 1.04; 95% CI, 0.95-1.14) or any tumor subtype. In the control participants, ghrelin was inversely correlated with BMI, and PYY was positively correlated with C-peptide and insulin levels. These findings provide limited support for a possible role for ghrelin in colorectal cancer development, primarily in specific anatomical and molecular tumor subtypes.

PREVENTION RELEVANCE

The findings of this study do not support a major role for the metabolic gut hormones ghrelin and PYY in colorectal cancer development but suggest the possibility of an involvement for ghrelin in specific tumor subtypes. Elucidating subtype-specific risk factors and mechanisms of carcinogenesis may have implications for precision prevention.

Hormonal and metabolic profiles of obese and nonobese type 2 diabetes patients: implications of plasma insulin, ghrelin, and vitamin D levels

Type 2 diabetes (T2D) is associated with obesity whereas loss of weight is a feature of the disease; however, the two states are not mutually exclusive. Obesity is linked with changes in hormonal activity and overall body metabolism.

Pre-operative Predictors of Weight Loss and Weight Regain Following Roux-en-Y Gastric Bypass Surgery: a Prospective Human Study

BACKGROUND

There are currently few pre-operative predictors of initial and long-term weight loss following bariatric surgery.

OBJECTIVES

We evaluated the role of pre-operative patient characteristics and baseline gut and adipose-derived hormones in predicting maximal total body weight loss (WL_max) and risk of weight regain (WR) after Roux-en-Y gastric bypass (RYGB) surgery.

METHODS

One hundred five adult patients undergoing primary RYGB were prospectively recruited. Baseline demographics were recorded and fasting plasma glucose, glycosylated hemoglobin (A1C), insulin, glucagon, leptin, active ghrelin, glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) levels were measured on day of surgery.

RESULTS

Our cohort had a mean age of 44.4 ± 13.0 years, and initial BMI (body mass index) of 45.1 ± 6.7 kg/m² with mean post-operative follow-up of 40 months. Eighty patients were female and 26 had type 2 diabetes mellitus (T2D). Average WL_max was 35.3 ± 7.4%. On univariate analysis, higher baseline fasting ghrelin, lower age, lower CRP (C-reactive protein), lower A1C, and negative T2D status were associated with greater WL_max (p < 0.05). Controlling for these variables using stepwise multivariate regression, only higher fasting ghrelin and younger age were associated significantly with greater WL_max (p < 0.05). In subgroup multivariate regression analysis of T2D patients, higher ghrelin and glucagon were significantly associated with greater WL_max. Following stepwise multivariate regression, lower initial BMI and lower glucagon were associated with greater WR (p < 0.05).

CONCLUSIONS

Incorporation of baseline biological and hormonal markers may help in developing more accurate predictive models for weight loss following bariatric surgery that help inform patient counseling and decision-making.

Impact of assay format on miRNA sensing: Electrochemical microfluidic biosensor for miRNA-197 detection

MicroRNAs (miRNAs) are important biomarkers for the early detection of various diseases, especially cancer. Therefore, there is a continuing interest in different biosensing strategies that allow for the point-of-care measurement of miRNAs. Almost all miRNA sensors utilize cross-hybridization of the target miRNA with a capture probe for the recognition, which can be designed in either a sandwich or a competitive format. In this work, we present a low-cost microfluidic biosensor platform for the electrochemical measurement of miRNA-197 (a tumor biomarker candidate) in undiluted human serum samples, operating with very low sample volumes (580 nl) and a sample-to-result time of one hour. For this purpose, different on-chip miRNA bioassays based on sandwich and competitive formats are developed and compared in terms of their sensitivity, dynamic range, selectivity, precision, and simplicity. The obtained results show that, despite having a narrower dynamic range when compared to the competitive format, the sandwich assay has superior performance regarding its sensitivity and selectivity. The lowest limit of detection which can be achieved with the sandwich assay is 1.28 nM (0.74 fmole), while 4.05 nM (2.35 fmole) with the competitive format. Moreover, the sandwich assay proves to have a better distinction against single-base mismatch oligonucleotide sequences compared to the competitive one. Due to its versatility and easy handling, overcoming the issue with the sensitivity, the implemented electrochemical microfluidic biosensor could pave the way for rapid and low-cost on-site miRNA diagnostics.

Oral ghrelin receptor agonist MK-0677 increases serum insulin-like growth factor 1 in hemodialysis patients: a randomized blinded study

Background

Protein-energy wasting (PEW) in end-stage renal disease (ESRD) patients is associated with increased morbidity and mortality, but options for treatment are limited. Growth hormone (GH) increases insulin-like growth factor 1 (IGF-1), with improved nutritional parameters, but must be given subcutaneously and does not provide normal GH secretion patterns. MK-0677, an oral ghrelin receptor agonist (GRA), maintains normal GH secretion and increases lean body mass in normal subjects; it has not been studied in dialysis patients, an essential step in assessing efficacy and safety prior to clinical trials.

Methods

We performed a randomized crossover double-blind study in assessing the effect of MK-0677 versus placebo on IGF-1 levels, the primary outcome, in hemodialysis patients. In total, 26 subjects enrolled and 22 completed the 3-month crossover study.

Results

The geometric mean IGF-1 was 1.07-fold greater [95% confidence interval (CI) 0.89-1.27; P = 0.718] after placebo. In patients receiving MK-0677, the geometric mean IGF-1 were 1.76-fold greater (95% CI 1.48-2.10; P < 0.001) following MK-0677. When the data were adjusted for preintervention IGF-1 concentration, the ratio of geometric means (MK-0677 relative to placebo) for the pre- versus postintervention change in the IGF-1 was 1.65 (95% CI 1.33-2.04; P < 0.001). These data demonstrate a 65% greater increase (95% CI 33-104%) in IGF-1 in MK-0677-dosed subjects compared with placebo. There were no serious adverse effects attributable to MK-0677.

Conclusions

MK-0677 increased serum IGF-1 levels with minimal adverse effects in hemodialysis subjects. Studies are needed to evaluate whether long-term therapy with MK-0677 improves PEW, lean body mass, physical strength, quality of life and survival in CKD/ESRD patients.

Enteroendocrine Connections in Congenital Isolated GH Deficiency Due to a GHRH Receptor Gene Mutation

CONTEXT

GH and IGF-1 are crucial for attainment of normal body size and regulation of food intake, nutrient storage, and insulin sensitivity. Enteroendocrine connections exist between the GH-IGF-1 axis and insulin, ghrelin, and glucagon-like peptide 1 (GLP-1). The status of these connections in GH deficiency (GHD) is unknown.

OBJECTIVE

To study the enteroendocrine connections before and after a standard meal test in a homogeneous population of adults with congenital untreated isolated GHD (IGHD) due to a mutation in the GHRH receptor gene.

DESIGN

In a cross-sectional study of 20 individuals with IGHD and 20 control subjects, we measured glucose, insulin, ghrelin, and GLP-1 before and 30, 60, 120, and 180 minutes after a standardized test meal. Homeostasis model assessment index of insulin resistance (HOMA-IR) and homeostasis model assessment (HOMA)-β were calculated. Participants scored feelings of hunger, fullness, and prospective food consumption on a visual analog scale.

MAIN OUTCOME MEASURES

Area under the curve (AUC) values of glucose, insulin, ghrelin, GLP-1, hunger, fullness, and prospective food consumption.

RESULTS

Fasting HOMA-IR and HOMA-β were lower in individuals with IGHD than in control subjects (P = 0.002 and P = 0.023, respectively). AUC was higher for hunger (P < 0.0001), glucose (P = 0.0157), ghrelin (P < 0.0001), and GLP-1 (P < 0.0001) and smaller for fullness (P < 0.0001) in individuals with IGHD compared with control subjects. There was no difference in AUC for prospective food consumption or insulin.

CONCLUSIONS

Untreated IGHD is associated with increased GLP-1 secretion and reduced postprandial ghrelin and hunger attenuation in response to a mixed meal. These enteroendocrine connections can result in a favorable outcome in terms of environmental adaptation and guaranteeing appropriate food intake and can confer metabolic benefits.

Prokineticin-2 and ghrelin robustly influence the sexual and ingestive behaviors of female Syrian hamsters

Prokineticins are involved in many physiological processes including circadian rhythms, neurogenesis, angiogenesis, and cancer. Recently, they have been found to play a role in regulating food intake. Historically, proteins that increase feeding behavior in mammals decrease reproductive behavior to prevent pregnancy and lactation when food is scarce. In the current study, prokineticin-2 (PK2) had pronounced effects on reproductive and ingestive behaviors when given to female Syrian hamsters. Administration of PK2 prevented ingestive behaviors induced by food restriction, such as the amount of time spent with food and eating. Hamsters given PK2 preferred to engage in reproductive behaviors, including spending time with a male and lordosis. Furthermore, analysis of blood plasma revealed that changes to behavior persisted despite similar levels of des-acyl ghrelin (DAG) and reduced glucose concentrations in the blood. Additionally, administering 10 mg/kg of acyl ghrelin (AG) to a different cohort of animals significantly decreased the amount of time females spent with a potential mating partner, increased the amount of time females spent with food, decreased the duration of lordosis, and increased the duration of eating. Results from the current study support the need for further research investigating the reproductive and ingestive roles of PK2 and ghrelin.

Associations of breast milk adiponectin, leptin, insulin and ghrelin with maternal characteristics and early infant growth: a longitudinal study

Breast milk (BM) hormones have been hypothesised as a nutritional link between maternal and infant metabolic health. This study aimed to evaluate hormone concentrations in BM of women with and without gestational diabetes mellitus (GDM), and the relationship between maternal factors, BM hormones and infant growth. We studied ninety-six nulliparous women with (n 48) and without GDM and their exclusively breastfed term singletons. Women with GDM received dietary therapy or insulin injection for euglycaemia during pregnancy. Hormone concentrations in BM, maternal BMI and infant growth were longitudinally evaluated on postnatal days 3, 42 and 90. Mothers with GDM had decreased concentrations of adiponectin (P colostrum<0·001; P mature-milk=0·009) and ghrelin (P colostrum=0·011; P mature-milk<0·001) and increased concentration of insulin in BM (P colostrum=0·047; P mature-milk=0·021). Maternal BMI was positively associated with adiponectin (β=0·06; 95 % CI 0·02, 0·1; P=0·001), leptin (β=0·16; 95 % CI 0·12, 0·2; P<0·001) and insulin concentrations (β=0·06; 95 % CI 0·02, 0·1; P<0·001), and inversely associated with ghrelin concentration in BM (β=-0·08; 95 % CI -0·1, -0·06; P<0·001). Among the four hormones, adiponectin was inversely associated with infant growth in both the GDM (β weight-for-height=-2·49; 95 % CI -3·83, -1·15; P<0·001; β head-circumference=-0·39; 95 % CI -0·65, -0·13; P=0·003) and healthy groups (β weight-for-height=-1·42; 95 % CI -2·38, -0·46; P=0·003; β head-circumference=-0·15; 95 % CI -0·27, -0·03; P=0·007). Maternal BMI and GDM are important determinants of BM hormone concentrations. Milk-borne adiponectin is determined by maternal metabolic status and plays an independent down-regulating role in early infant growth.

Control of (pre)-analytical aspects in immunoassay measurements of metabolic hormones in rodents

The measurement of circulating hormones by immunoassay remains a cornerstone in preclinical endocrine research. For scientists conducting and interpreting immunoassay measurements of rodent samples, the paramount aim usually is to obtain reliable and meaningful measurement data in order to draw conclusions on biological processes. However, the biological variability between samples is not the only variable affecting the readout of an immunoassay measurement and a considerable amount of unwanted or unintended variability can be quickly introduced during the pre-analytical and analytical phase. This review aims to increase the awareness for the factors 'pre-analytical' and 'analytical' variability particularly in the context of immunoassay measurement of circulating metabolic hormones in rodent samples. In addition, guidance is provided how to gain control over these variables and how to avoid common pitfalls associated with sample collection, processing, storage and measurement. Furthermore, recommendations are given on how to perform a basic validation of novel single and multiplex immunoassays for the measurement of metabolic hormones in rodents. Finally, practical examples from immunoassay measurements of plasma insulin in mice address the factors 'sampling site and inhalation anesthesia' as frequent sources of introducing an unwanted variability during the pre-analytical phase. The knowledge about the influence of both types of variability on the immunoassay measurement of circulating hormones as well as strategies to control these variables are crucial, on the one hand, for planning and realization of metabolic rodent studies and, on the other hand, for the generation and interpretation of meaningful immunoassay data from rodent samples.

Elevated circulating ghrelin in patients with COPD: A meta-analysis

Ghrelin, an endogenous ligand for growth hormone secretagogue receptor, has been implicated in chronic obstructive pulmonary disease (COPD). Recently, several studies reported inconsistent levels of ghrelin in plasma/serum of COPD patients. This meta-analysis aims to determine the circulating level of ghrelin in COPD. Published case–control or cohort studies were retrieved from Pubmed and Embase databases. Pooled standardized mean difference (SMD) with 95% confidence interval (CI) was calculated in a random-effects model. Nine studies involving 515 subjects were included. Pooled effect size showed that circulating ghrelin levels were significantly enhanced in COPD patients compared with those in controls (SMD: 0.83, 95% CI: 0.04 to 1.62, p = 0.039). Noticeably, five studies stratified for body mass index in COPD group and we further found ghrelin levels were significantly higher in underweight COPD patients than those in normal weight cases (SMD: 1.52, 95% CI: 0.43 to 2.61, p = 0.006). However, no significant difference regarding ghrelin levels was indicated between normal weight COPD and controls (SMD: 0.64, 95% CI: −0.36 to 1.63, p = 0.210). In this meta-analysis, circulating level of ghrelin is significantly elevated in patients with COPD, especially in those underweight, indicating supplement with exogenous ghrelin could be a therapeutic choice for underweight COPD patients.

Leu72Met and Other Intronic Polymorphisms in the GHRL and GHSR Genes Are Not Associated with Type 2 Diabetes Mellitus, Insulin Resistance, or Serum Ghrelin Levels in a Saudi Population

BACKGROUND

Ghrelin (GHRL), a gastric peptide encoded by the GHRL gene, is known to be involved in energy homeostasis via its G protein receptor, encoded by the growth hormone secretagogue receptor (GHSR) gene. Some studies have shown associations between plasma GHRL levels and GHRL single-nucleotide polymorphisms (SNPs), namely the Leu72Met polymorphism (rs696217 TG), with type 2 diabetes mellitus (T2DM) and insulin resistance (IR), while others have not. The controversies in these associations raise the issue of 'which SNPs in which populations.' The aim of this study was to investigate whether SNPs in GHRL and/or GHSR genes were associated with T2DM, IR, or plasma GHRL levels among Arab Saudis.

METHODS

Blood was collected from 208 Saudi subjects with (n=107) and without (n=101) T2DM. DNA samples from these subjects were analyzed by real-time polymerase chain reaction to genotype five intronic SNPs in the GHRL (rs696217 TG, rs27647 CT, rs2075356 CT, and rs4684677 AT) and GHSR (rs509030 GC) genes. In addition, plasma GHRL levels were measured by a radioimmunoassay.

RESULTS

None of the SNPs were associated with T2DM, IR, or plasma GHRL levels. The frequencies of the alleles, genotypes, and haplotypes of the five SNPs were comparable between the T2DM patients and the non-diabetic subjects. A large number of the GHRL haplotypes indicates the molecular heterogeneity of the preproghrelin gene in this region.

CONCLUSION

Neither the Leu72Met polymorphism nor the other intronic GHRL and GHSR SNPs were associated with T2DM, IR, or GHRL levels. Further investigations should be carried out to explain the molecular basis of the association of the GHRL peptide with T2DM and IR.

The Acylated/Unacylated Ghrelin Ratio Is Similar in Patients With Acromegaly During Different Treatment Regimens

BACKGROUND

Data on plasma acylated ghrelin (AG) and unacylated ghrelin (UAG) levels in acromegaly are limited. High AG/UAG ratios are linked with type 2 diabetes, obesity, and hyperphagia (e.g., in Prader-Willi syndrome).

OBJECTIVE

To assess fasting plasma AG and UAG levels, and the AG/UAG ratio in acromegaly patients receiving combination treatment of long-acting somatostatin analogs (LA-SSAs) and pegvisomant (PEGV; n = 60). We used as controls acromegaly patients whose disease was controlled with PEGV monotherapy and medically naïve patients with active acromegaly.

METHODS

Fasting venous blood samples were collected and directly stabilized to inhibit deacylation of AG. Plasma AG and UAG levels were determined by double-antibody sandwich enzyme immunoassay, and the AG/UAG ratio was calculated.

RESULTS

Plasma AG and UAG levels were significantly lower in patients with acromegaly receiving combination treatment [median, interquartile range (IQR): AG: 8.5 pg/mL, 2.9 to 21.1 pg/mL; UAG: 26.9 pg/mL, 11.2 to 42.1 pg/mL] compared with patients using PEGV alone [AG: 60.5 pg/mL (IQR, 58.8 to 77.4 pg/mL); UAG: 153.7 pg/mL (IQR, 127.3 to 196.0 pg/mL)] and medically naïve patients with acromegaly [AG: 24.0 pg/mL (IQR, 12.6 to 49.7 pg/mL); UAG: 56.3 pg/mL (IQR, 43.4 to 61.5 pg/mL)]. However, AG/UAG ratios were similar in all groups.

CONCLUSIONS

Although plasma AG and UAG are suppressed during combination treatment with LA-SSAs and PEGV, the AG/UAG ratio remained similar. This shows that SSAs decrease both AG and UAG levels, which suggests that they do not alter metabolism significantly in acromegaly patients.

Association of Plasma Ghrelin Levels with Insulin Resistance in Type 2 Diabetes Mellitus among Saudi Subjects

BACKGROUND

Although the exact mechanism of insulin resistance (IR) has not yet been established, IR is the hallmark characteristic of type 2 diabetes mellitus (T2DM). The aim of this study was to examine the relationship between plasma ghrelin levels and IR in Saudi subjects with T2DM.

METHODS

Patients with T2DM (n=107, cases) and non-diabetic apparently healthy subjects (n=101, controls) from Saudi Arabia were included in this study. The biochemical profiles and plasma insulin levels of all subjects were analyzed, and IR was estimated using the homeostatic model assessment of insulin resistance (HOMA-IR) index. Active ghrelin levels in plasma were measured using the radioimmunoassay technique.

RESULTS

Only 46.7% (50 of 107) of the T2DM subjects had IR, including 26% (28 of 107) with severe IR (HOMA-IR ≥5), while 5.9% (six of 101) of the controls had moderate IR (3 ≤HOMA-IR <5). HOMA-IR values were not associated with age, disease duration, or gender. Importantly, T2DM itself and the co-occurrence of IR with T2DM were significantly associated with low plasma ghrelin levels. However, ghrelin levels were inversely correlated with the HOMA-IR index, body weight, and fasting plasma insulin levels, mainly in the control subjects, which was indicative of the breakdown of metabolic homeostasis in T2DM.

CONCLUSION

The prevalence of IR was relatively low, and IR may be inversely associated with plasma ghrelin levels among Saudi patients with T2DM.

Novel approach to determine ghrelin analogs by liquid chromatography with mass spectrometry using a monolithic column

In our project, ghrelin analogs possessing enhanced stability and potential to significantly increase food intake were used. Three newly synthesized ghrelin analogs with fatty acid residues consisting of 8, 10, and 14 carbon atoms were studied. The main goal of this work was to develop a suitable analytical method for the determination of the stability of the novel ghrelin analogs in plasma. An appropriate liquid chromatography-mass spectrometry method was developed and optimized. The results obtained were compared with the data measured by using a commercial enzyme-linked immunosorbent assay kit, and a good correlation was found. A preparation strategy for plasma samples was optimized and consisted of simple dilution of the plasma samples followed by direct injection onto a very short monolithic column in combination with mass spectrometric detection. The developed analytical method was utilized for the determination of the stability of the prepared lipopeptides in plasma and for the quantification of the lipopeptides in a preliminary pharmacokinetic study. The feasibility of the developed separation method was clearly demonstrated. Accuracy and precision were within 80-120% and ±20% limits, respectively. Calibration curves were constructed in the range of 1-250 μg/mL.

Ghrelin, CCK, GLP-1, and PYY(3-36): Secretory Controls and Physiological Roles in Eating and Glycemia in Health, Obesity, and After RYGB

The efficacy of Roux-en-Y gastric-bypass (RYGB) and other bariatric surgeries in the management of obesity and type 2 diabetes mellitus and novel developments in gastrointestinal (GI) endocrinology have renewed interest in the roles of GI hormones in the control of eating, meal-related glycemia, and obesity. Here we review the nutrient-sensing mechanisms that control the secretion of four of these hormones, ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine tyrosine [PYY(3-36)], and their contributions to the controls of GI motor function, food intake, and meal-related increases in glycemia in healthy-weight and obese persons, as well as in RYGB patients. Their physiological roles as classical endocrine and as locally acting signals are discussed. Gastric emptying, the detection of specific digestive products by small intestinal enteroendocrine cells, and synergistic interactions among different GI loci all contribute to the secretion of ghrelin, CCK, GLP-1, and PYY(3-36). While CCK has been fully established as an endogenous endocrine control of eating in healthy-weight persons, the roles of all four hormones in eating in obese persons and following RYGB are uncertain. Similarly, only GLP-1 clearly contributes to the endocrine control of meal-related glycemia. It is likely that local signaling is involved in these hormones' actions, but methods to determine the physiological status of local signaling effects are lacking. Further research and fresh approaches are required to better understand ghrelin, CCK, GLP-1, and PYY(3-36) physiology; their roles in obesity and bariatric surgery; and their therapeutic potentials.

Lipopeptides as therapeutics: applications and in vivo quantitative analysis

A number of novel lipopeptides have been studied for their possible therapeutic potential. These studies should be supported by the appropriate analytical tools not only for novel potential drugs but also for their metabolites, precursors and side products. Lipopeptides have specific physicochemical properties that make them successful in medical applications. However, there are some difficulties with their qualitative and quantitative analyses in biological samples. Therefore, reliable, sensitive and robust analytical methods are in high demand. The main interest of our review is to describe a selection of specific and important properties of lipopeptides, and the analytical methods currently utilized for their characterization and determination in biological samples. A comparison of the pros and cons of immunomethods versus LC-MS methods is discussed in detail.

Is there an effect of ghrelin/ghrelin analogs on cancer? A systematic review

Ghrelin is a hormone with multiple physiologic functions, including promotion of growth hormone release, stimulation of appetite and regulation of energy homeostasis. Treatment with ghrelin/ghrelin-receptor agonists is a prospective therapy for disease-related cachexia and malnutrition. In vitro studies have shown high expression of ghrelin in cancer tissue, although its role including its impact in cancer risk and progression has not been established. We performed a systematic literature review to identify peer-reviewed human or animal in vivo original research studies of ghrelin, ghrelin-receptor agonists, or ghrelin genetic variants and the risk, presence, or growth of cancer using structured searches in PubMed database as well as secondary searches of article reference lists, additional reviews and meta-analyses. Overall, 45 (73.8%) of the 61 studies reviewed, including all 11 involving exogenous ghrelin/ghrelin-receptor agonist treatment, reported either a null (no statistically significant difference) or inverse association of ghrelin/ghrelin-receptor agonists or ghrelin genetic variants with cancer risk, presence or growth; 10 (16.7%) studies reported positive associations; and 6 (10.0%) reported both negative or null and positive associations. Differences in serum ghrelin levels in cancer cases vs controls (typically lower) were reported for some but not all cancers. The majority of in vivo studies showed a null or inverse association of ghrelin with risk and progression of most cancers, suggesting that ghrelin/ghrelin-receptor agonist treatment may have a favorable safety profile to use for cancer cachexia. Additional large-scale prospective clinical trials as well as basic bioscientific research are warranted to further evaluate the safety and benefits of ghrelin treatment in patients with cancer.

The Effect of Casein Protein Prior to Sleep on Fat Metabolism in Obese Men

We have previously shown that ingesting protein at night before sleep is either beneficial or non-detrimental to metabolism, health, and body composition in obese women. However, the overnight protein-induced lipolytic actions and mechanism for improved metabolism and body composition have not been fully established. Therefore, in a crossover design, twelve obese men (age, 27.0 ± 2.2 years) were randomly assigned to ingest (within 30 min of sleep) casein protein (CAS, 120 kcal) or a non-nutritive placebo (PLA) before going to sleep. Markers of fat metabolism (lipolysis, substrate utilization, growth hormone), insulin, glucose, resting energy expenditure (REE), and appetite (questionnaire and ghrelin) were measured. During sleep and the next morning, interstitial glycerol from the subcutaneous abdominal adipose tissue (SCAAT) was measured using microdialysis. There were no differences in SCAAT glycerol (overnight: CAS, 177.4 ± 26.7; PLA, 183.8 ± 20.2 μmol/L; morning: CAS, 171.6 ± 19.1; PLA, 161.5 ± 18.6 μmol/L), substrate utilization, REE, or any blood markers between CAS and PLA. Desire to eat was greater for CAS compared to baseline (p = 0.03), but not different from PLA (baseline: 39 ± 6, CAS: 62 ± 8, PLA: 55 ± 5 mm). CAS consumption before sleep did not affect fat or glucose metabolism, REE, or suppress appetite in hyperinsulemic obese men. CAS may be consumed before sleep without impeding overnight or morning fat metabolism in young, obese men.

Circulating ghrelin level is higher in HNF1A-MODY and GCK-MODY than in polygenic forms of diabetes mellitus

Ghrelin is a hormone that regulates appetite. It is likely to be involved in the pathophysiology of varying forms of diabetes. In animal studies, the ghrelin expression was regulated by the hepatocyte nuclear factor 1 alpha (HNF1A). Mutations of the HNF1A gene cause maturity onset diabetes of the young (MODY). We aimed to assess the circulating ghrelin levels in HNF1A-MODY and in other types of diabetes and to evaluate its association with HNF1A mutation status. Our cohort included 46 diabetic HNF1A gene mutation carriers, 55 type 2 diabetes (T2DM) subjects, 42 type 1 diabetes (T1DM) patients, and 31 glucokinase (GCK) gene mutation carriers with diabetes as well as 51 healthy controls. Plasma ghrelin concentration was measured using the immunoenzymatic assay with polyclonal antibody against the C-terminal fragment of its acylated and desacylated forms. Ghrelin concentrations were 0.75 ± 0.32, 0.70 ± 0.21, 0.50 ± 0.20, and 0.40 ± 0.16 ng/ml in patients with HNF1A-MODY, GCK-MODY, T1DM, and T2DM, respectively. The ghrelin levels were higher in HNF1A-MODY and GCK-MODY than in T1DM and T2DM (p < 0.001 for all comparisons) but lower than in non-diabetic controls (1.02 ± 0.29 ng/ml, p < 0.001 for both comparisons). In the multivariate linear model, the differences between both MODY groups and common diabetes types remained significant. Analysis by a HNF1A mutation type indicated that ghrelin concentration is similar in patients with different types of sequence differences. Plasma ghrelin level is higher in HNF1A-MODY and GCK-MODY than in the common polygenic forms of diabetes.

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.

Ghrelin

BACKGROUND

The gastrointestinal peptide hormone ghrelin was discovered in 1999 as the endogenous ligand of the growth hormone secretagogue receptor. Increasing evidence supports more complicated and nuanced roles for the hormone, which go beyond the regulation of systemic energy metabolism.

SCOPE OF REVIEW

In this review, we discuss the diverse biological functions of ghrelin, the regulation of its secretion, and address questions that still remain 15 years after its discovery.

MAJOR CONCLUSIONS

In recent years, ghrelin has been found to have a plethora of central and peripheral actions in distinct areas including learning and memory, gut motility and gastric acid secretion, sleep/wake rhythm, reward seeking behavior, taste sensation and glucose metabolism.

Clinical protein mass spectrometry

Quantitative protein analysis is routinely performed in clinical chemistry laboratories for diagnosis, therapeutic monitoring, and prognosis. Today, protein assays are mostly performed either with non-specific detection methods or immunoassays. Mass spectrometry (MS) is a very specific analytical method potentially very well suited for clinical laboratories. Its unique advantage relies in the high specificity of the detection. Any protein sequence variant, the presence of a post-translational modification or degradation will differ in mass and structure, and these differences will appear in the mass spectrum of the protein. On the other hand, protein MS is a relatively young technique, demanding specialized personnel and expensive instrumentation. Many scientists and opinion leaders predict MS to replace immunoassays for routine protein analysis, but there are only few protein MS applications routinely used in clinical chemistry laboratories today. The present review consists of a didactical introduction summarizing the pros and cons of MS assays compared to immunoassays, the different instrumentations, and various MS protein assays that have been proposed and/or are used in clinical laboratories. An important distinction is made between full length protein analysis (top-down method) and peptide analysis after enzymatic digestion of the proteins (bottom-up method) and its implication for the protein assay. The document ends with an outlook on what type of analyses could be used in the future, and for what type of applications MS has a clear advantage compared to immunoassays.

The acylated (AG) to unacylated (UAG) ghrelin ratio in esterase inhibitor-treated blood is higher than previously described

CONTEXT

The acylated/unacylated ghrelin (AG/UAG) ratio has been reported to range from 0·02 to 0·3, suggesting biologically relevant independent regulation of each ghrelin isoform. However, AG is deacylated to UAG by esterases in blood samples, and esterase inhibition is critical for their accurate measurement. Our hypothesis is that at least part of the variation in reported AG and UAG values is due to inconsistent sample preparation.

DESIGN

A non-interventional study. Quantification with two different, commercially available, ELISA formats of AG and UAG in venous plasma stabilized or not with 4-(2-aminoethyl) benzenesulphonyl fluoride (AEBSF) and stored for 0-6 months at -20 or -80 °C.

PARTICIPANTS

Healthy, non-obese, adults (n = 8; 4 women), age 26-42 yrs, after an overnight fast.

MEASUREMENTS

AG and UAG stability following different methods of sample treatment and storage.

RESULTS

Non-AEBSF plasma contained low AG and high UAG (>270 pg/ml) indicating rapid conversion of AG to UAG. However, AEBSF plasma, stored at -80 °C and measured at 0, 1, 3 and 6 months contained AG and UAG ranges of 12-350 and 17-170 pg/ml, respectively. Mean (SEM) AG/UAG ratios were 1·7(0·3), 1·2(0·2), 1·5(0·3) and 1·8(0·5) at each time point with no significant effect of storage period.

CONCLUSIONS

AG and UAG levels measured in AEBSF-stabilized plasma indicate that the AG/UAG ratio is markedly higher than previously described and that UAG is a physiological component of the circulation. This highlights the importance of immediately stabilizing blood samples on collection for determination of both AG and UAG concentrations and provides a valuable tool for their measurement in physiological and interventional studies.

Recombinant human leptin does not alter gut hormone levels after gastric bypass but may attenuate sweet cravings

Bariatric surgery improves glucose homeostasis and alters gut hormones partly independent of weight loss. Leptin plays a role in these processes; levels are decreased following bariatric surgery, creating a relative leptin insufficiency. We previously showed that leptin administration in a weight-reduced state after Roux-en-Y gastric bypass (RYGB) caused no further weight loss. Here, we discuss the impact of leptin administration on gut hormones, glucostasis, and appetite. Weight stable women after RYGB were randomized to receive placebo or recombinant human metreleptin (0.05 mg/kg twice daily). At weeks 0 and 16, a liquid meal challenge was performed. Glucose, insulin, C-peptide, GLP-1, PYY, glucagon, and ghrelin (total, acyl, and desacyl) were measured fasting and postprandially. Appetite was assessed using a visual analog scale. Mean post-op period was 53 ± 2.3 months; mean BMI was 34.6 ± 0.2 kg/m(2). At 16 weeks, there was no significant change in weight within or between groups. Fasting PYY was significantly different between groups and the leptin group had lower sweets craving at week 16 than the placebo group (P < 0.05). No other differences were observed. Leptin replacement does not alter gut hormones or glucostasis but may diminish sweet cravings compared to placebo in this population of post-RYGB women.

Structure and physiological actions of ghrelin

Ghrelin is a gastric peptide hormone, discovered as being the endogenous ligand of growth hormone secretagogue receptor. Ghrelin is a 28 amino acid peptide presenting a unique n-octanoylation modification on its serine in position 3, catalyzed by ghrelin O-acyl transferase. Ghrelin is mainly produced by a subset of stomach cells and also by the hypothalamus, the pituitary, and other tissues. Transcriptional, translational, and posttranslational processes generate ghrelin and ghrelin-related peptides. Homo- and heterodimers of growth hormone secretagogue receptor, and as yet unidentified receptors, are assumed to mediate the biological effects of acyl ghrelin and desacyl ghrelin, respectively. Ghrelin exerts wide physiological actions throughout the body, including growth hormone secretion, appetite and food intake, gastric secretion and gastrointestinal motility, glucose homeostasis, cardiovascular functions, anti-inflammatory functions, reproductive functions, and bone formation. This review focuses on presenting the current understanding of ghrelin and growth hormone secretagogue receptor biology, as well as the main physiological effects of ghrelin.

Influence of pre-analytical conditions on the measurement of components of the GH/IGF axis in rats

Pre-analytical variability characterises effects which are introduced to an analysis by manipulation and storage of a biological sample after taking it ex-vivo, but before actually quantifying the respective analyte. In humans, recent studies demonstrated that pre-analytical factors can be an important confounder for immunoassay measurements of circulating hormones of the GH/IGF-system. In contrast, this topic has rarely been addressed in rodent studies. We therefore now systematically investigated if and how commonly used sample processing and pre-treatment protocols affect measured hormone concentrations of the GH/IGF system in rats. Furthermore, we explored if short term fasting, age and circadian rhythmicity have an impact upon the concentrations of IGF-I, IGFBP-2 and IGFBP-3 in rats.

RESULTS

On average, concentrations of IGF-I were lower by 9.2% (p < 0.01), while those of IGF-II and IGFBP-3 were lower by 24% (p < 0.01) in EDTA plasma when compared to plain serum from the same rats. In contrast, concentrations of GH were significantly higher in plain plasma samples compared with serum (+137.8%; p < 0.01). Repeated freeze/thaw cycles significantly influenced the measurements of serum IGF-II (+25.9%; p < 0.01) and IGFBP-3 (+19.3%; p < 0.01) when compared to native serum. Pre-treatment of EDTA plasma with protease inhibitors, or immediate storage of EDTA blood on ice, did not significantly affect the outcome of any measurement. Acidification of plasma samples with HCl led to significantly lower IGF-I in samples (-11.9%, p < 0.001) and detection of GH was completely hampered in these samples. With respect to biological variability, age (12-week-old vs. 1-year-old male Wistar rats), but not fasting (up to 18 h) or circadian rhythmicity affected circulating concentrations of IGF-I and IGFBP-3.

CONCLUSION

Pre-analytical variability is a potentially confounding factor which also must be considered in rodent studies when analysing and comparing hormones of the GH/IGF system. If and to what extent a specific pre-analytical procedure affects immunoassay measurements in rodent studies cannot be predicted in advance but rather needs to be tested for each analyte separately.

Association of plasma des-acyl ghrelin levels with CKD

BACKGROUND AND OBJECTIVES

There are no effective therapies for malnutrition in CKD/ESRD patients. This study hypothesized that ghrelin, an endogenous orexigenic hormone, would correlate with renal function and might suggest therapeutic interventions for CKD/ESRD malnutrition.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Fifty-one CKD and 15 hemodialysis patients were enrolled. Acyl ghrelin (AG) and des-acyl ghrelin (DG) were determined using separate two-site-specific assays. Leptin, insulin, growth hormone, insulin-link growth factor-1, C-reactive protein, TNF-α, and IL-6 were also measured.

RESULTS

Univariate correlation analyses showed that CKD stage was highly, positively correlated with the levels of preprandial and postprandial DG and positively correlated with TNF-α, IL-6, leptin, and age. Multivariate partial-correlation analyses showed that CKD was independently associated with the proportion of preprandial and postprandial DG, whereas TNF-α, IL-6, leptin, insulin, and age were not independently associated with either. Geometric mean (GM) preprandial and postprandial AG were comparable between CKD stages ≤2 and >2, whereas GM preprandial DG and postprandial DG were 1.95-fold and 2.17-fold greater, respectively, for CKD stage >2 versus stage ≤2. DG was the dominant form of ghrelin preprandially and postprandially for both CKD stages ≤2 and >2. Dialysis had no effect on AG, but reduced DG by 73% to levels even lower (GM 48.7 pg/ml) than those seen postprandially in CKD stage ≤2 patients (GM 77.0 pg/ml).

CONCLUSIONS

This study shows a strong and independent correlation of DG with CKD stage. Postprandial suppression of ghrelin is impaired with reduced renal function. Hemodialysis selectively removes DG but not AG.

High glycemic and insulinemic responses to meals affect plasma growth hormone secretory characteristics in Quarter Horse weanlings

Growth hormone is a key component of the somatotropic axis and is critical for the interplay between nutrition, regulation of metabolic functions, and subsequent processes of growth. The objective of this study was to investigate potential relations between meal feeding concentrates differing in the glycemic responses they elicit and GH secretory patterns in young growing horses. Twelve Quarter Horse weanlings (5.4 ± 0.4 mo of age) were used in a crossover design, consisting of two 21-d periods and two treatments, a high-glycemic (HG) or low-glycemic (LG) concentrate meal, fed twice daily. Horses were individually housed and fed hay ad libitum. On the final day of each period, quarter-hourly blood samples were drawn for 24 h to measure plasma glucose, insulin, non-esterified fatty acids, and GH. Growth hormone secretory characteristics were estimated with deconvolution analysis. After a meal, HG-fed horses exhibited a longer inhibition until the first pulse of GH secretion (P = 0.012). During late night hours (1:00 AM to 6:45 AM), HG horses secreted a greater amount of pulsatile GH than LG horses (P = 0.002). These differences highlight the potential relations between glycemic and insulinemic responses to meals and GH secretion. Dietary energy source and metabolic perturbations associated with feeding HG meals to young, growing horses have the potential to alter GH secretory patterns compared with LG meals. This may potentially affect the developmental pattern of various tissues in the young growing horse.

Ghrelin and eating disorders

There is growing evidence supporting a multifactorial etiology that includes genetic, neurochemical, and physiological components for eating disorders above and beyond the more conventional theories based on psychological and sociocultural factors. Ghrelin is one of the key gut signals associated with appetite, and the only known circulating hormone that triggers a positive energy balance by stimulating food intake. This review summarizes recent findings and several conflicting reports on ghrelin in eating disorders. Understanding these findings and inconsistencies may help in developing new methods to prevent and treat patients with these disorders.

Thr136Ile polymorphism of human vesicular monoamine transporter-1 (SLC18A1 gene) influences its transport activity in vitro

The hippocampus has the extraordinary capacity to process and store information. Consequently, there is an intense interest in the mechanisms that underline learning and memory. Synaptic plasticity has been hypothesized to be the neuronal substrate for learning. Ca²⁺ and Ca²⁺-activated kinases control cellular processes of most forms of hippocampal synapse plasticity. In this paper, I aim to integrate our current understanding of Ca²⁺-mediated synaptic plasticity and metaplasticity in motivational and reward-related learning in the hippocampus. I will introduce two representative neuromodulators that are widely studied in reward-related learning (e.g., ghrelin and endocannabinoids) and show how they might contribute to hippocampal neuron activities and Ca²⁺-mediated signaling processes in synaptic plasticity. Additionally, I will discuss functional significance of these two systems and their signaling pathways for its relevance to maladaptive reward learning leading to addiction.

Advantageous uses of mass spectrometry for the quantification of proteins

Quantitative protein measurements by mass spectrometry have gained wide acceptance in research settings. However, clinical uptake of mass spectrometric protein assays has not followed suit. In part, this is due to the long-standing acceptance by regulatory agencies of immunological assays such as ELISA assays. In most cases, ELISAs provide highly accurate, sensitive, relatively inexpensive, and simple assays for many analytes. The barrier to acceptance of mass spectrometry in these situations will remain high. However, mass spectrometry provides solutions to certain protein measurements that are difficult, if not impossible, to accomplish by immunological methods. Cases where mass spectrometry can provide solutions to difficult assay development include distinguishing between very closely related protein species and monitoring biological and analytical variability due to sample handling and very high multiplexing capacity. This paper will highlight several examples where mass spectrometry has made certain protein measurements possible where immunological techniques have had a great difficulty.

The ghrelin axis--does it have an appetite for cancer progression?

Ghrelin, the endogenous ligand for the GH secretagogue receptor (GHSR), is a peptide hormone with diverse physiological roles. Ghrelin regulates GH release, appetite and feeding, gut motility, and energy balance and also has roles in the cardiovascular, immune, and reproductive systems. Ghrelin and the GHSR are expressed in a wide range of normal and tumor tissues, and a fluorescein-labeled, truncated form of ghrelin is showing promise as a biomarker for prostate cancer. Plasma ghrelin levels are generally inversely related to body mass index and are unlikely to be useful as a biomarker for cancer, but may be useful as a marker for cancer cachexia. Some single nucleotide polymorphisms in the ghrelin and GHSR genes have shown associations with cancer risk; however, larger studies are required. Ghrelin regulates processes associated with cancer, including cell proliferation, apoptosis, cell migration, cell invasion, inflammation, and angiogenesis; however, the role of ghrelin in cancer is currently unclear. Ghrelin has predominantly antiinflammatory effects and may play a role in protecting against cancer-related inflammation. Ghrelin and its analogs show promise as treatments for cancer-related cachexia. Further studies using in vivo models are required to determine whether ghrelin has a role in cancer progression.

A guide for measurement of circulating metabolic hormones in rodents: Pitfalls during the pre-analytical phase

Researchers analyse hormones to draw conclusions from changes in hormone concentrations observed under specific physiological conditions and to elucidate mechanisms underlying their biological variability. It is, however, frequently overlooked that also circumstances occurring after collection of biological samples can significantly affect the hormone concentrations measured, owing to analytical and pre-analytical variability. Whereas the awareness for such potential confounders is increasing in human laboratory medicine, there is sometimes limited consensus about the control of these factors in rodent studies. In this guide, we demonstrate how such factors can affect reliability and consequent interpretation of the data from immunoassay measurements of circulating metabolic hormones in rodent studies. We also compare the knowledge about such factors in rodent studies to recent recommendations established for biomarker studies in humans and give specific practical recommendations for the control of pre-analytical conditions in metabolic studies in rodents.

Low-glycemic load decreases postprandial insulin and glucose and increases postprandial ghrelin in white but not black women

Alterations in appetite hormones favoring increased postprandial satiety have been implicated in both the glycemic control and potential weight-loss benefits of a low-glycemic diet. Racial differences exist in dietary glycemic load and appetite hormone concentrations. This study examined the impact of glycemic load on appetite hormones in 20 black women [10 normal weight, BMI = 22.8 ± 1.42 (mean ± SD); 10 obese, BMI = 35.1 ± 2.77] and 20 white women (10 normal weight, BMI = 22.9 ± 1.45; 10 obese, BMI = 34.3 ± 2.77). Each woman completed two 4.5-d weight-maintenance, mixed-macronutrient, high-glycemic vs. low-glycemic load diets that concluded with a test meal of identical composition. Blood samples collected before and serially for 3 h after each test meal were assayed for plasma ghrelin and serum insulin and glucose concentrations. Compared with the high-glycemic load meal, the low-glycemic load meal was associated with lower insulin(AUC) (P = 0.02), glucose(AUC) (P = 0.01), and urge to eat ratings (P = 0.05) but with higher ghrelin(AUC) (P = 0.008). These results suggest the satiating effect of a low-glycemic load meal is not directly linked to enhanced postprandial suppression of ghrelin. Notably, these effects were significant among white but not black women, suggesting that black women may be less sensitive than white women to the glucoregulatory effects of a low-glycemic load. These findings add to a growing literature demonstrating racial differences in postprandial appetite hormone responses. If reproducible, these findings have implications for individualized diet prescription for the purposes of glucose or weight control in women.

Acylated/unacylated ghrelin ratio in cord blood: correlation with anthropometric and metabolic parameters and pediatric lifespan comparison

CONTEXT

Ghrelin is a peptide with multiple functions that circulates in acylated (AG) and unacylated (UAG) forms. However, the role of ghrelin in neonates (NN) remains to be clarified.

OBJECTIVE

The aim of this study was to determine ghrelin concentrations of the two forms in NN to clarify their biological roles. As such, ghrelin levels at birth were compared with those in later life.

SETTING AND DESIGN

Tertiary Care Center. In this cross-sectional study, we evaluated AG, UAG, AG/UAG ratio, and insulin levels in venous cord blood from NN and in fasted normal weight (NW) and obese (OB) children, both prepubertal and pubertal.

SUBJECTS

We studied 82 NN, 82 NW, and 58 OB children.

RESULTS

AG levels were lower in NN than in NW and OB children (P<0.0001), more specifically the prepubertal NW and OB children (P<0.0001). UAG levels were higher in NN than in NW and OB children (P<0.0001). Therefore, the AG/UAG ratio was lower in NN than in NW and OB children (P<0.0001). NN showed insulin levels similar to NW and lower than OB children (P<0.0001). At birth UAG was positively correlated with AG (Pearson: 0.425; P<0.0001) and negatively with insulin (-0.253; P<0.02). In NW and OB, UAG and AG were positively correlated to each other and negatively correlated with insulin and body mass index (-0.566; P<0.0001).

CONCLUSIONS

NN compared with children, showed higher UAG and lower AG levels. The AG/UAG ratio showed a very different profile in NN, being lower than in NW and OB children, thus suggesting a different metabolic function for the two forms in NN. Further studies are needed to clarify the exact role of the different ghrelin forms in NN.

Meal anticipatory rise in acylated ghrelin at dark onset is blunted after long-term fasting in rats

Ghrelin is a 28 amino acid acylated peptide originally characterised for its capacity to stimulate growth hormone secretion. Ghrelin is also an orexigenic and adipogenic hormone and is thought to be a signal to increase locomotor activity in anticipation of a scheduled meal. Although ghrelin is considered to be up-regulated during fasting, there are still conflicting data regarding the impact of starvation on ghrelin secretion. To test whether the secretory pattern of acylated ghrelin is altered during fasting, plasma levels were monitored every 20 min for 6 h in freely-behaving rats at the light/dark cycle transition, when animals initiate feeding and activity and use preferentially free fatty acids (FFA) as a source of energy. Rats were fed ad lib. or fasted at dark onset for 24, 48 or 72 h, with or without refeeding rate. The anticipatory rise in ghrelin levels, as well as home-cage activity at the onset of darkness, was significantly reduced from 48 h of fasting compared to ad lib. conditions. A delayed ghrelin peak, sensitive to renutrition, was observed in fasted animals. Although their motivation to eat appeared to be intact, rats fasted for 72 h showed the smallest compensatory refeeding rate after fasting, possibly reflecting altered gut function. Expression of agouti-related protein and neuropeptide Y, was significantly increased in 48- and 72-h fasted animals. Thus, following fasting, a blunted acylated ghrelin secretion at dark onset (i.e. a period when animals depend on FFA as a source of energy) is associated with reduced locomotor activity and refeeding and an up-regulation of anabolic neuropeptides. Such changes could be interpreted as compensatory mechanisms for helping to conserve energy under conditions where food is not available.

The ghrelin axis in disease: potential therapeutic indications

Ghrelin, the natural ligand for the growth hormone (GH)-secretagogue receptor (GHS-R), is produced predominantly in the stomach. It is present in the circulation in two major forms, an acylated and an unacylated form, both of which have reported activities. Some of the best understood actions of acylated ghrelin administration are its orexigenic effects, and the stimulation of GH secretion. Ghrelin also seems to play a role in glucose homeostasis, lipid metabolism and immune function. Based on its orexigenic and metabolic effects, ghrelin and ghrelin mimetics have potential benefit in antagonizing protein breakdown and weight loss in catabolic conditions such as cancer cachexia, renal, cardiac and pulmonary disease, and age-related frailty. Ghrelin also has potentially useful positive effects on cardiac function and gastric motility. Ghrelin antagonists may be of benefit to increase insulin sensitivity and potentiate weight loss. The following chapter presents some background on ghrelin and ghrelin assays and discusses some of the potential therapeutic approaches for the use of ghrelin, ghrelin mimetic compounds and ghrelin antagonists in clinical disease.

Roux-en-Y gastric bypass and laparoscopic sleeve gastrectomy: understanding weight loss and improvements in type 2 diabetes after bariatric surgery

Obesity increases the likelihood of diseases like type 2 diabetes (T2D), heart disease, and cancer, and is one of the most serious public health problems of this century. In contrast to ineffectual prevention strategies, lifestyle modifications, and pharmacological therapies, bariatric surgery is a very effective treatment for morbid obesity and also markedly improves associated comorbidities like T2D. However, weight loss and resolution of T2D after bariatric surgery is heterogeneous and specific to type of bariatric procedure performed. Conventional mechanisms like intestinal malabsorption and gastric restriction do not fully explain this, and potent changes in appetite and the enteroinsular axis, as a result of anatomical reorganization and altered hormonal, neuronal, and nutrient signaling, are the portended cause. Uniquely these signaling changes appear to override vigorous homeostatic defenses of stable body weight and compelling self-gratifying motivations to eat and to reverse defects in beta-cell function and insulin sensitivity. Here we review mechanisms of weight loss and T2D resolution after Roux-en-Y gastric bypass and laparoscopic sleeve gastrectomy bariatric surgery, two markedly different procedures with robust clinical outcomes.

The central Sirtuin 1/p53 pathway is essential for the orexigenic action of ghrelin

OBJECTIVE

Ghrelin is a stomach-derived peptide that increases food intake through the activation of hypothalamic AMP-activated protein kinase (AMPK). However, the molecular mechanisms initiated by the activation of the ghrelin receptor, which in turn lead to AMPK activation, remain unclear. Sirtuin 1 (SIRT1) is a deacetylase activated in response to calorie restriction that acts through the tumor suppressor gene p53. We tested the hypothesis that the central SIRT1/p53 pathway might be mediating the orexigenic action of ghrelin.

RESEARCH DESIGN AND METHODS

SIRT1 inhibitors, such as Ex527 and sirtinol, and AMPK activators, such as AICAR, were administered alongside ghrelin in the brain of rats and mice (wild-type versus p53 knockout [KO]). Their hypothalamic effects on lipid metabolism and changes in transcription factors and neuropeptides were assessed by Western blot and in situ hybridization.

RESULTS

The central pretreatment with Ex527, a potent SIRT1 inhibitor, blunted the ghrelin-induced food intake in rats. Mice lacking p53, a target of SIRT1 action, failed to respond to ghrelin in feeding behavior. Ghrelin failed to phosphorylate hypothalamic AMPK when rats were pretreated with Ex527, as it did in p53 KO mice. It is noteworthy that the hypothalamic SIRT1/p53 pathway seems to be specific for mediating the orexigenic action of ghrelin, because central administration of AICAR, a potent AMPK activator, increased food intake in p53 KO mice. Finally, blockade of the central SIRT1 pathway did not modify ghrelin-induced growth hormone secretion.

CONCLUSIONS

Ghrelin specifically triggers a central SIRT1/p53 pathway that is essential for its orexigenic action, but not for the release of growth hormone.