Des-acyl Ghrelin Research Articles

Fasting and postprandial acyl and desacyl ghrelin and the acyl/desacyl ratio in obese patients before and after different types of bariatric surgery.

IntroductionThe mechanism underlying beneficial outcomes of bariatric surgery still remains unclear. Especially little is known about hormonal and metabolic changes induced by the novel bariatric procedure mini gastric bypass (MGB).AimTo evaluate pre- and post-prandial changes in both ghrelin isoforms in obese patients without diabetes and cardiovascular complications treated with MGB, sleeve gastrectomy (SG) or Roux-en-Y gastric bypass (RYGB) surgery.Material and methodsFrom 45 patients initially enrolled in the study, 23 persons completed a one-year follow-up period. Venous blood for acyl and desacyl ghrelin (AG and DAG) as well as other metabolic assays was collected 3 months before and 6 and 12 months after bariatric surgery (MGB, RYGB, SG) – in the fasting state and 2 h after the consumption of a standard 300 kcal-mixed meal (Nutridrink standard, Nutricia).ResultsAG and DAG levels (both fasting and prandial) as well as AG/DAG ratio did not change after 6 and 12 months in MGB and RYGB groups. In the SG group we observed a significant decrease in fasting and postprandial DAG levels and consecutively an increase in the fasting AG/DAG ratio after 6 and 12 months. Six months after surgery we observed some differences between carbohydrate metabolism measures in the MGB group (lower HbA1c, HOMA-IR and fasting insulinaemia) in comparison to the rest of the participants, but 12 months after each type of surgery body mass index and indices of carbohydrate and lipid metabolism did not differ.ConclusionsThe results of our study demonstrate that all studied bariatric procedures can successfully reduce overall body weight and suggest also that the mechanisms of weight loss and improvement in carbohydrate and lipid metabolism after all three types of surgery are independent of ghrelin and the acyl/desacyl ghrelin ratio.

Effect of desacyl ghrelin on protein expression of GHS-R1 receptor in human placental cells

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Functional group and stereochemical requirements for substrate binding by ghrelin O-acyltransferase revealed by unnatural amino acid incorporation

Ghrelin is a small peptide hormone that undergoes a unique posttranslational modification, serine octanoylation, to play its physiological roles in processes including hunger signaling and glucose metabolism. Ghrelin O-acyltransferase (GOAT) catalyzes this posttranslational modification, which is essential for ghrelin to bind and activate its cognate GHS-R1a receptor. Inhibition of GOAT offers a potential avenue for modulating ghrelin signaling for therapeutic effect. Defining the molecular characteristics of ghrelin that lead to binding and recognition by GOAT will facilitate the development and optimization of GOAT inhibitors. We show that small peptide mimics of ghrelin substituted with 2,3-diaminopropanoic acid in place of the serine at the site of octanoylation act as submicromolar inhibitors of GOAT. Using these chemically modified analogs of desacyl ghrelin, we define key functional groups within the N-terminal sequence of ghrelin essential for binding to GOAT and determine GOAT’s tolerance to backbone methylations and altered amino acid stereochemistry within ghrelin. Our study provides a structure-activity analysis of ghrelin binding to GOAT that expands upon activity-based investigations of ghrelin recognition and establishes a new class of potent substrate-mimetic GOAT inhibitors for further investigation and therapeutic interventions targeting ghrelin signaling.

Decreased ghrelin and des-acyl ghrelin plasma levels in patients affected by pharmacoresistant epilepsy and maintained on the ketogenic diet

The gastric hormones ghrelin and des-acyl ghrelin have been found to be altered in patients treated with antiepileptic drugs. However, it is unknown if these hormones could be modified by other antiepileptic treatments, such as the ketogenic diet. Especially, a reduction in ghrelin levels could be relevant in view of the growth retardation observed under ketogenic diet treatment. For this reason we aimed to determine the changes in ghrelin and des-acyl ghrelin plasma levels in children affected by refractory epilepsy and treated with the ketogenic diet up to 90 days. Both peptides were measured by immunoassays in plasma obtained from 16 children. Ghrelin plasma levels were progressively reduced by the ketogenic diet, reaching a minimum corresponding to 42% of basal levels after 90 days of ketogenic diet (P<0.05, Duncan's test). Des-acyl ghrelin plasma levels were similarly affected, reaching minimal levels at 30 days (65% of basal levels), and maintaining a significant reduction until 90 days after the onset of ketogenic diet (P<0.01 for both time intervals). No significant changes in growth were observed during the monitored period of ketogenic diet administration. Ghrelin and des-acyl ghrelin are downregulated by the ketogenic diet in children affected by refractory epilepsy. Although no significant changes in growth were observed during the short time period of our investigation, the reduction in ghrelin availability may explain the reported growth retardation found in children treated with the ketogenic diet in the long-term.

The ghrelin paradox in the control of equine chondrocyte function: The good and the bad

Increasing evidence suggests a role for ghrelin in the control of articular inflammatory diseases like osteoarthritis (OA). In the present study we examined the ability of ghrelin to counteract LPS-induced necrosis and apoptosis of chondrocytes and the involvement of GH secretagogue receptor (GHS-R)1a in the protective action of ghrelin.The effects of ghrelin (10−7–10−11 mol/L) on equine primary cultured chondrocytes viability and necrosis in basal conditions and under LPS treatment (100 ng/ml) were detected by using both acridine orange/propidium iodide staining and annexin-5/propidium iodide staining. The presence of GHS-R1a on chondrocytes was detected by Western Blot. The involvement of the GHS-R1a in the ghrelin effect against LPS-induced cytotoxicity was examined by pretreating chondrocytes with D-Lys3-GHRP-6, a specific GHS-R1a antagonist, and by using des-acyl ghrelin (DAG, 10−7 and 10−9 mol/L) which did not recognize the GHS-R 1a.Low ghrelin concentrations reduced chondrocyte viability whereas 10−7 mol/L ghrelin protects against LPS-induced cellular damage. The protective effect of ghrelin depends on the interaction with the GHS-R1a since it is significantly reduced by D-Lys3-GHRP-6. The negative action of ghrelin involves caspase activation and could be due to an interaction with a GHS-R type different from the GHS-R1a recognized by both low ghrelin concentrations and DAG. DAG, in fact, induces a dose-dependent decrease in chondrocyte viability and exacerbates LPS-induced damage.These data indicate that ghrelin protects chondrocytes against LPS-induced damage via interaction with GHS-R1a and suggest the potential utility of local GHS-R1a agonist administration to treat articular inflammatory diseases such as OA.

DTPA-(PABn)-Leu5]-des-acyl ghrelin(1-5) as a new carrier of radionuclides and potential precursor of radiopharmaceuticals.

Ghrelin is a peptide consisting of 28 aminoacids and an octadecyl side chain (acyl group) binding to the growth hormone secretagogue receptor type 1a (GHS-R1a). Its des-acylated form, des-acyl ghrelin (DAG) binds to the corticotropin releasing factor receptor type 2a (CRF2a) located on endocrine cancer cells such as the prostate carcinoma cell line DU 145. The aim of this study is to develop a new DAG-based carrier of radionuclides with potential application in therapy. Trunctated C-terminal five aminoacids chain of the DAG peptide (H2N-Gly-Ser-Ser-Phe-Leu-COOH) was linked to DTPA to obtain [DTPA-(PABn)-Leu5]-DAG(1-5). For therapeutic application the lutetium-177 (177Lu) radionuclide was coordinated to the peptide. To determine biological and chemical properties of newly synthesized radiopharmaceutical, two iodine-131 (131I)-labelled compounds were used: [131I]-Tyr4-DAG(1-5) and full length [131I]-DAG(1-28) together with their nonradioactive forms: DAG(1-28) and DAG(1-5). Identical HPLC elution profiles of [177Lu-DTPA-(PABn)-Leu5]-DAG(1-5) before and after incubation with human serum proved its stability. The lipophilicity profile of [177Lu-DTPA-(PABn)-Leu5]-DAG(1-5) was log DO/W=-2.68±0.05, pH 7.4. Receptor affinity of the nonradioactive conjugate [Lu-DTPA-(PABn)-Leu5]-DAG(1-5) was IC50 (21.06 nmol/l), as shown against the [131I]-DAG(1-28) used as a competitor. The 3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyltetrazolium bromide assay indicated the significant cytotoxicity of the newly synthesized compounds, similar to that of [131I]-Tyr4-DAG(1-5). The results obtained suggest the potency of the [DTPA-(PABn)-Leu5]-DAG(1-5) as a new carrier of radionuclides in radiopharmacy.

Therapeutic Effects of Ghrelin and Des-Acyl Ghrelin on Doxorubicin-Induced Cardiotoxicity

Therapeutic Effects of Ghrelin and Des-Acyl Ghrelin on Doxorubicin-Induced Cardiotoxicity

Identification and Characterization of a New Series of Ghrelin O-Acyl Transferase Inhibitors

Ghrelin O-acyl transferase (GOAT; MBOAT4) catalyzes O-acylation at serine-3 of des-acyl ghrelin. Acyl ghrelin is secreted by stomach X/A-like cells and plays a role in appetite and metabolism. Therefore, GOAT has been expected to be a novel antiobesity target because it is responsible for acyl ghrelin production. Here, we report homogeneous time-resolved fluorescence (HTRF) and enzyme-linked immunosorbent assay (ELISA) methods utilizing human GOAT-expressing microsomes as a novel high-throughput assay system for the discovery of hit compounds and optimization of lead compounds. Hit compounds exemplified by compound A (2-[(2,4-dichlorobenzyl)sulfanyl]-1,3-benzoxazole-5-carboxylic acid) were identified by high-throughput screening using the HTRF assay and confirmed to have GOAT inhibitory activity using the ELISA. Based on the hit compound information, the novel lead compound (compound B, (4-chloro-6-{[2-methyl-6-(trifluoromethyl)pyridin-3-yl]methoxy}-1-benzothiophen-3-yl)acetic acid) was synthesized and exhibited potent GOAT inhibition with oral bioavailability. Both the hit compound and lead compound showed octanoyl-CoA competitive inhibitory activity. Moreover, these two compounds decreased acyl ghrelin production in the stomach of mice after their oral administration. These novel findings demonstrate that GOAT is a druggable target, and its inhibitors are promising antiobesity drugs.

Effects of Ipragliflozin on Postprandial Glucose Metabolism and Gut Peptides in Type 2 Diabetes: A Pilot Study.

IntroductionIpragliflozin is a novel antidiabetic drug that inhibits renal tubular sodium-glucose cotransporter-2 (SGLT2). The aim of this study was to evaluate the effects of ipragliflozin on glucose, insulin, glucagon, and gastrointestinal peptide responses to a meal tolerance test, as well as to investigate the glucose-lowering mechanisms of ipragliflozin.MethodsNine Japanese patients with obesity and type 2 diabetes mellitus were treated with ipragliflozin (50 mg/day) for 12 weeks. The postprandial profiles of glucose, insulin, glucagon, active glucagon-like peptide-1 (GLP-1), active glucose-dependent insulinotropic polypeptide (GIP), ghrelin, and des-acyl ghrelin were measured before and 12 weeks after ipragliflozin treatment.ResultsBody weight, body fat mass, systolic blood pressure, and HbA1c and serum uric acid levels were significantly decreased after the treatment. Postprandial glucose and insulin levels were also significantly decreased. Postprandial glucagon increased both before and after ipragliflozin treatment; however, the increment tended to be smaller after treatment. Active GLP-1, active GIP, ghrelin, and des-acyl ghrelin did not change after treatment.ConclusionIpragliflozin improved glycemic control by reducing body weight, postprandial inappropriate glucagon secretion, and the postprandial insulin requirement. Although this was a short-term study with a small sample size, ipragliflozin may offer benefits for patients with obesity and type 2 diabetes mellitus.Trial RegistrationUniversity Hospital Medical Information Network (UMIN No. 000017195).

GHRELIN ACTIVATION BY INGESTION OF MEDIUM-CHAIN TRIGLYCERIDES IN HEALTHY ADULTS: A PILOT TRIAL

Objective: To investigate the efficacy of dietary supplementation of medium-chain triglycerides (MCTs) and its effects on ghrelin activation in healthy adults. Methods: The present study examined two protocols with six healthy volunteers: 1) 12-hour profiles of the plasma levels of acylated and desacyl ghrelin without MCT ingestion, and 2) changes in serum ghrelin levels after oral ingestion of 45 g/day of MCTs for 1 week. Results: At baseline, serum acylated and desacyl ghrelin levels were 18.2±10.3 and 77.1±23.4 fmol/mL, respectively. The ratio of acylated/desacyl ghrelin was 19%. There were no significant differences in the 12-hour profiles of acylated and desacyl ghrelin. Significant increases were observed in all sampling times of serum acylated ghrelin after 1-week MCTs ingestion. The ratio of acylated/desacyl ghrelin increased to 37.7%. Conclusions: Oral ingestion of MCTs increased serum acylated ghrelin levels in healthy adults, suggesting that MCTs administration stimulates food intake.

Effect of clozapine dose and concentration on fasting concentration of appetite regulating peptides

The aim of this study is to analyze whether clozapine serum concentration may affect fasting serum levels of several appetite regulating peptides: CART, PYY(1-36), NPY, AgRP, des-acylated ghrelin, leptin and obestatin. Serum concentration of clozapine and fasting serum levels of des-acylated ghrelin, neuropeptide Y (NPY), agouti-related protein (AgRP), peptide YY (PYY(1-36)), cocaine- and amphetamine-regulated transcript (CART), leptin and obestatin were measured in 30 subjects with schizophrenia on clozapine monotherapy. Leptin concentration was negatively correlated with clozapine dose (r = −0.53, p = 0.002), while NPY concentration was negatively correlated with clozapine concentration (r = −0.55, p = 0.01). Correlations with other peptides were not significant. We cannot conclude that serum concentration of clozapine is directly associated with increased or decreased level of appetite-regulating peptides.

Evaluating the Levels of Nesfatin-1 and Ghrelin Hormones in Patients with Moderate and Severe Major Depressive Disorders.

Objective The goal of this study was to evaluate the importance of nesfatin-1, acylated and des-acylated ghrelin, which are known as energy regulatory hormones, in patients with moderate and severe major depression disorders (MDD). Methods Thirty patients with a moderate degree of MDD and, 30 with a severe degree of MDD were used as participants in this study. Thirty subjects without depression were enrolled as a control group. The Hamilton Depression Rating Scale was used to classify the patients with MDD. Blood samples were taken after overnight fasting. The plasma nesfatin-1, acylated ghrelin and des-acylated ghrelin levels were measured using a commercially available enzyme-linked immunosorbent assay kit. Results The nesfatin-1, the acylated ghrelin and the des-acylated ghrelin levels were found to be significantly higher in severe MDD (3.92±0.4 ng/mL; 88.56±4.1 pg/mL; 962.76±67 pg/mL) as compared to moderate MDD (2.91±0.5 ng/mL; 77.63±4.19 pg/mL; 631.16±35 pg/mL), or the control (1.01±0.3 ng/mL; 58.60±9.00 pg/mL; 543.13±62 pg/mL), respectively. Conclusion Although nesfatin-1 and ghrelin are known as adversely affecting the hormones involving the regulation of appetite and food intake, they all increase in depressive patients and are even associated with the severity of the disease. In clinical medicine, the evaluation of the role of nesfatin-1 and ghrelin in endocrine and neu-roendocrine regulation of major metabolic functions is an important key mechanism in solving numerous diseases associated with endocrine and neuroendocrine disturbance. Increased levels of nesfatin-1 and ghrelin may also be important criteria in describing the prognoses of the patients and the effectiveness of the treatments.

The Effects of Different Isocaloric Oral Nutrient Solutions on Psychophysical, Metabolic, Cognitive, and Olfactory Function in Young Male Subjects.

Food intake influences human cognition, olfaction, hunger, and food craving. However, little research has been done in this field to elucidate the effects of different nutrients. Thus, the goal of our study was to investigate the effects of oral ingestion of different nutrient solutions on olfactory, cognitive, metabolic and psychophysical function. Twenty healthy men participated in our study employing a double-blind, cross-over, repeated measurement design. Participants were tested on four different study days. Each day participants received, in randomized order, one of three isocaloric (protein, carbohydrate or fat 600 kcal, 1,500 mL) solutions or a placebo. Olfactory and cognitive tests (monitoring only) were conducted three times, i.e., 60 min before the beginning of nutrient intake, following oral ingestion of the solution and 60, and 240 min after. Psychophysical and metabolic function tests (active grehlin, desacyl ghrelin, insulin, glucagon, glucose, triglyceride, urea) were performed 7 times on each examination day (observation period: −60 min, 0 = solution intake, +60, +120, +180, +240, and +300 min). Ratings of hunger and food craving significantly differed over the observation period with lowest ratings following application of the protein solution. Highest ratings of craving were found following placebo intake. We further observed a significant positive correlation of active grehlin with hunger and fat, protein and sweets craving for each nutrient solution. Active grehlin significantly correlated with carbohydrate craving for carbohydrate and fat solution and with vegetable craving for fat solution only. Hunger hormone levels, hunger and food craving ratings demonstrated that the hierarchical order that appears in satiating efficiencies of isovolumetric-isocaloric ingested macronutrients is protein > fat > carbohydrate. Our study reveals that the type of nutrient exerts a significant influence on metabolic parameters, hunger and food craving.

Involvement of PPARγ in the Anticonvulsant Activity of EP-80317, a Ghrelin Receptor Antagonist.

Ghrelin, des-acyl ghrelin and other related peptides possess anticonvulsant activities. Although ghrelin and cognate peptides were shown to physiologically regulate only the ghrelin receptor, some of them were pharmacologically proved to activate the peroxisome proliferator-activated receptor gamma (PPARγ) through stimulation of the scavenger receptor CD36 in macrophages. In our study, we challenged the hypothesis that PPARγ could be involved in the anticonvulsant effects of EP-80317, a ghrelin receptor antagonist. For this purpose, we used the PPARγ antagonist GW9662 to evaluate the modulation of EP-80317 anticonvulsant properties in two different models. Firstly, the anticonvulsant effects of EP-80317 were studied in rats treated with pilocarpine to induce status epilepticus (SE). Secondly, the anticonvulsant activity of EP-80317 was ascertained in the repeated 6-Hz corneal stimulation model in mice. Behavioral and video electrocorticographic (ECoG) analyses were performed in both models. We also characterized levels of immunoreactivity for PPARγ in the hippocampus of 6-Hz corneally stimulated mice. EP-80317 predictably antagonized seizures in both models. Pretreatment with GW9662 counteracted almost all EP-80317 effects both in mice and rats. Only the effects of EP-80317 on power spectra of ECoGs recorded during repeated 6-Hz corneal stimulation were practically unaffected by GW9662 administration. Moreover, GW9662 alone produced a decrease in the latency of tonic-clonic seizures and accelerated the onset of SE in rats. Finally, in the hippocampus of mice treated with EP-80317 we found increased levels of PPARγ immunoreactivity. Overall, these results support the hypothesis that PPARγ is able to modulate seizures and mediates the anticonvulsant effects of EP-80317.

Effects of ghrelin agonist and antagonist on endogenous desacyl-ghrelin content in the brain limbical structures under psychoemotional stress in rats

Background. During last years it has been shown the ghrelin signaling system not only regulates energy balance and food intake. It also takes part in reinforcement mechanisms and addiction formation. So the ghrelin system may be considered as possible molecular target to study addiction treatment and post-stressor pharmacological modulation.&#x0D; The aim of this work was to study the effects of ghrelin agonist and antagonist administration on des-acyl ghrelin (DAG) content in the brain structures under stress exposure in Wistar rats.&#x0D; Methods. The acute psychoemotional stress was realized by means of exposure of experimental rats to predator, a tiger python. Ghrelin or ghrelin antagonist D-Lys3-GHRP-6 (Tocris, UK) 10 µg in 20 µl administered intranasally for 7 days after stress exposure. Then brain structures were obtained, homogenized with cryogenic system “Cryomill 200” (Retsch, Germany) and investigated with high-sensitive ELISA (SP-BIO, France). Results. DAG have been detected in every brain structures studied. That are amygdala, hippocampus and hypothalamus. In control group of animals the DAG concentration in hypothalamus was 3-fold more comparning to hippocampus and 2-fold more conparning to amygdala content. The acute stress have dramatically 8-12-fold decrease of DAG concentrations in every brain structures studied. The pharmacological actions on GHSR receptor by ghrelin agonist and antagonist have not affect significant changes in DAG concentrations in every brain structures.&#x0D; Conclusions. The different concentrations of DAG in brain structures in control gtoup supports the view about ghrelin releasing neurons in the hypothalamus. Intranasal administration of ghrelin agonist and antagonist changes the levels of DAG in the hippocampus and the hypothalamus but not in the amygdala nucleus. Our data confirm the opinion about ghrelin-releasing neurons in hypothalamus. The experiments showed the acute stress had caused great depression of ghrelin system in various brain structures. The response of ghrelin system to acute stress occur possibly besides GHSR receptor pathway. The last have been suggested by absence of significant response to ghrelin agonist and antagonist administration.

Comparison of the therapeutic effects of sildenafil citrate, heparin and neuropeptides in a rat model of acetic acid-induced gastric ulcer

AimsThe purpose of our investigative work has been to determine whether there can be therapeutic roles in the administration of sildenafil citrate, heparin and several neuropeptides on an animal model where gastric ulcers were induced with acetic acid, and to compare their efficacy. Materials and methodsThe animals were divided into 13 groups, with 4 animals in each. Gastric ulcers was induced in the animals of 12 groups with one untreated group being left as the control (Group I - control; given normal saline (NS)). The other groups were: Group II (ulcer+NS); Group III (5mg/kg sildenafil citrate, low dose); Group IV (10mg/kg sildenafil citrate, high dose); Group V (0.6mg/kg heparin, low dose); Group VI (6mg/kg heparin, high dose); Group VII (20nmol/kg des-acyl ghrelin); Group VIII (40nmol/kg des-acyl ghrelin); Group IX (4nmol/kg acyl ghrelin); Group X (8nmol/kg acly ghrelin); Group XI (20pmol/kg Nesfatin-1); Group XII (15nmol/kg Obestatin) and Group XIII (5nmol/kg Neuropeptide Y). Gastric neuropeptide expression was measured using an immunohistochemical method, and the amount in circulation was detected using ELISA. To compare with no treatment, the controls and other treatment groups, we recorded loss of the surface epithelium of the stomach, erosion, bleeding and inflammatory cell infiltration in the upper halves of the gastric glands. Key findingsThe muscularis and the layers beneath it were, however, apparently normal. The gastric mucosa healed with little or no inflammation when sildenafil citrate, low dose heparin, ghrelin, NUCB2/Nesfatin-1, obestatin, Neuropeptide Y were administered. SignificanceOverall the data indicate that low dose heparin, and especially sildenafil citrate and neuropeptides, can be used clinically as an alternative approach in the treatment of the gastric ulcer.

Changes in appetite, energy intake, body composition, and circulating ghrelin constituents during an incremental trekking ascent to high altitude

PurposeCirculating acylated ghrelin concentrations are associated with altitude-induced anorexia in laboratory environments, but have never been measured at terrestrial altitude. This study examined time course changes in appetite, energy intake, body composition, and ghrelin constituents during a high-altitude trek.MethodsTwelve participants [age: 28(4) years, BMI 23.0(2.1) kg m−2] completed a 14-day trek in the Himalayas. Energy intake, appetite perceptions, body composition, and circulating acylated, des-acylated, and total ghrelin concentrations were assessed at baseline (113 m, 12 days prior to departure) and at three fixed research camps during the trek (3619 m, day 7; 4600 m, day 10; 5140 m, day 12).ResultsRelative to baseline, energy intake was lower at 3619 m (P = 0.038) and 5140 m (P = 0.016) and tended to be lower at 4600 m (P = 0.056). Appetite perceptions were lower at 5140 m (P = 0.027) compared with baseline. Acylated ghrelin concentrations were lower at 3619 m (P = 0.046) and 4600 m (P = 0.038), and tended to be lower at 5140 m (P = 0.070), compared with baseline. Des-acylated ghrelin concentrations did not significantly change during the trek (P = 0.177). Total ghrelin concentrations decreased from baseline to 4600 m (P = 0.045). Skinfold thickness was lower at all points during the trek compared with baseline (P ≤ 0.001) and calf girth decreased incrementally during the trek (P = 0.010).ConclusionsChanges in plasma acylated and total ghrelin concentrations may contribute to the suppression of appetite and energy intake at altitude, but differences in the time course of these responses suggest that additional factors are also involved. Interventions are required to maintain appetite and energy balance during trekking at terrestrial altitudes.

Metabolic Syndrome is Associated with Lower Plasma Levels of Desacyl Ghrelin and Total Ghrelin in Asymptomatic Middle-aged Korean Men.

BackgroundDesacyl ghrelin is acylated by ghrelin O-acyltransferase (GOAT) and converted to acyl ghrelin. To date, little is known about the relationship among the levels of these two forms of ghrelin, GOAT level, and insulin resistance in Asian individuals. The purpose of this study was to determine the relationship between insulin resistance and the levels of plasma acyl ghrelin, desacyl ghrelin, and GOAT in asymptomatic middle-aged Korean men.MethodsThis cross-sectional study evaluated 78 asymptomatic middle-aged Korean men with metabolic syndrome (MS). We examined the correlation between the plasma levels of acyl ghrelin, desacyl ghrelin, and GOAT and sociodemographic, dietary, anthropometric, and metabolic parameters, as well as the association between insulin resistance and plasma levels of acyl ghrelin, desacyl ghrelin, and GOAT.ResultsThe levels of desacyl ghrelin and total ghrelin were significantly lower in the MS group than in the non-MS group (P<0.017, P=0.01, respectively). HOMA-IR values showed a significant negative correlation with desacyl ghrelin (r=−0.271, P=0.017) and total ghrelin (r=−0.271, P=0.016) levels. Acyl ghrelin and GOAT were not significantly correlated with HOMA-IR, and no correlation was found between the plasma levels of the two ghrelin types and GOAT.ConclusionThe plasma levels of desacyl ghrelin and total ghrelin in middle-aged Korean men with MS were lower than in those without MS. A significant negative correlation was observed between desacyl ghrelin level and HOMA-IR; however, no correlation was found between plasma levels of acyl ghrelin and GOAT and HOMA-IR.

Ghrelin receptors mediate ghrelin-induced excitation of agouti-related protein/neuropeptide Y but not pro-opiomelanocortin neurons.

Ghrelin increases food intake and body weight by stimulating orexigenic agouti-related protein (AgRP)/neuropeptide Y (NPY) neurons and inhibiting anorexic pro-opiomelanocortin (POMC) neurons in the hypothalamus. Growth hormone secretagogue receptor (Ghsr) mediates the effect of ghrelin on feeding behavior and energy homeostasis. However, the role of Ghsr in the ghrelin effect on these two populations of neurons is unclear. We hypothesized that Ghsr mediates the effect of ghrelin on AgRP and POMC neurons. In this study, we determined whether Ghsr similarly mediates the effects of ghrelin on AgRP/NPY and POMC neurons using cell type-specific Ghsr-knockout mice. Perforated whole-cell recordings were performed on green fluorescent protein-tagged AgRP/NPY and POMC neurons in the arcuate nucleus in hypothalamic slices. In Ghsr+/+ mice, ghrelin (100nM) significantly increased the firing activity of AgRP/NPY neurons but inhibited the firing activity of POMC neurons. In Ghsr-/- mice, the excitatory effect of ghrelin on AgRP/NPY neurons was abolished. Ablation of Ghsr also eliminated ghrelin-induced increases in the frequency of GABAergic inhibitory postsynaptic currents of POMC neurons. Strikingly, ablation of Ghsr converted the ghrelin effect on POMC neurons from inhibition to excitation. Des-acylated ghrelin had no such effect on POMC neurons in Ghsr-/- mice. In both Ghsr+/+ and Ghsr-/- mice, blocking GABAA receptors with gabazine increased the basal firing activity of POMC neurons, and ghrelin further increased the firing activity of POMC neurons in the presence of gabazine. Our findings provide unequivocal evidence that Ghsr is essential for ghrelin-induced excitation of AgRP/NPY neurons. However, ghrelin excites POMC neurons through an unidentified mechanism that is distinct from conventional Ghsr.

Role of aquaporin-7 in ghrelin- and GLP-1-induced improvement of pancreatic β-cell function after sleeve gastrectomy in obese rats.

Glycerol is a key metabolite for lipid accumulation in insulin-sensitive tissues as well as for pancreatic insulin secretion. We examined the role of aquaporin-7 (AQP7), the main glycerol channel in β-cells, and AQP12, an aquaporin related to pancreatic damage, in the improvement of pancreatic function and steatosis after sleeve gastrectomy in diet-induced obese rats. Male Wistar obese rats (n=125) were subjected to surgical (sham operation and sleeve gastrectomy) or dietary (pair-fed to the amount of food eaten by sleeve-gastrectomized animals) interventions. The tissue distribution and expression of AQPs in the rat pancreas were analyzed by real-time PCR, western blotting and immunohistochemistry. The effect of ghrelin isoforms and glucagon-like peptide 1 (GLP-1) on insulin secretion, triacylglycerol (TG) accumulation and AQP expression was determined in vitro in RIN-m5F β-cells. Sleeve gastrectomy reduced pancreatic β-cell apoptosis, steatosis and insulin secretion. Lower ghrelin and higher GLP-1 concentrations were also found after bariatric surgery. Acylated and desacyl ghrelin increased TG content, whereas GLP-1 increased insulin release in RIN-m5F β-cells. Sleeve gastrectomy was associated with an upregulation of AQP7 together with a normalization of the increased AQP12 levels in the rat pancreas. Interestingly, ghrelin and GLP-1 repressed AQP7 and AQP12 expression in RIN-m5F β-cells. AQP7 protein was negatively correlated with intracellular lipid accumulation in acylated ghrelin-treated cells and with insulin release in GLP-1-stimulated β-cells. AQP7 upregulation in β-cells after sleeve gastrectomy contributes, in part, to the improvement of pancreatic steatosis and insulin secretion by increasing intracellular glycerol used for insulin release triggered by GLP-1 rather than for ghrelin-induced TG biosynthesis.