High Coexpression of the Ghrelin and LEAP2 Receptor GHSR With Pancreatic Polypeptide in Mouse and Human Islets

Intestinal expression profiles and hepatic expression of LEAP2, ghrelin and their common receptor, GHSR, in humans

Liver-expressed antimicrobial peptide 2 (LEAP2) and ghrelin have reciprocal effects on their common receptor, the growth hormone secretagogue receptor (GHSR). Ghrelin is considered a gastric hormone and LEAP2 a liver-derived hormone and both have been proposed to be involved in the pathophysiology of obesity and type 2 diabetes (T2D). We investigated the mRNA expression of LEAP2, ghrelin and GHSR along the intestinal tract of individuals with and without TD2, and in the liver of men with and without obesity. Mucosal biopsies retrieved with 30-cm intervals throughout the small intestine and from 7 well-defined locations along the large intestine from 12 individuals with T2D and 12 healthy controls together with liver biopsies from 15 men with obesity and 15 lean men were subjected to bulk transcriptomics analysis. Both in individuals with and without T2D, mRNA expression of LEAP2 increased through the small intestine until dropping at the ileocecal valve, with little LEAP2 mRNA expression in the large intestine. Pronounced LEAP2 expression was observed in the liver of men with and without obesity. Robust ghrelin mRNA expression was observed in the duodenum of individuals with and without T2D, gradually decreasing along the small intestine with little expression in the large intestine. Ghrelin mRNA expression was not detected in the liver biopsies, and GHSR mRNA expression was not. In conclusion, we provide unique mRNA expression profiles of LEAP2, ghrelin and GHSR along the human intestinal tract showing no T2D-associated changes, and in the liver showing no differences between men with and without obesity.

A long-acting LEAP2 analog reduces hepatic steatosis and inflammation and causes marked weight loss in mice

OBJECTIVE

The number of individuals affected by metabolic dysfunction associated fatty liver disease [1] is on the rise, yet hormonal contributors to the condition remain incompletely described and only a single FDA-approved treatment is available. Some studies suggest that the hormones ghrelin and LEAP2, which act as agonist and antagonist/inverse agonist, respectively, for the G protein coupled receptor GHSR, may influence the development of MAFLD. For instance, ghrelin increases hepatic fat whereas synthetic GHSR antagonists do the opposite. Also, hepatic steatosis is less prominent in standard chow-fed ghrelin-KO mice but more prominent in 42% high-fat diet-fed female LEAP2-KO mice.

METHODS

Here, we sought to determine the therapeutic potential of a long-acting LEAP2 analog (LA-LEAP2) to treat MAFLD in mice. LEAP2-KO and wild-type littermate mice were fed a Gubra-Amylin-NASH (GAN) diet for 10 or 40 wks, with some randomized to an additional 28 or 10 days of GAN diet, respectively, while treated with LA-LEAP2 vs Vehicle. Various metabolic parameters were followed and biochemical and histological assessments of MAFLD were made.

RESULTS

Among the most notable metabolic effects, daily LA-LEAP2 administration to both LEAP2-KO and wild-type littermates during the final 4 wks of a 14 wk-long GAN diet challenge markedly reduced liver weight, hepatic triglycerides, plasma ALT, hepatic microvesicular steatosis, hepatic lobular inflammation, NASH activity scores, and prevalence of higher-grade fibrosis. These changes were accompanied by prominent reductions in body weight, without effects on food intake, and reduced plasma total cholesterol. Daily LA-LEAP2 administration during the final 10 d of a 41.5 wk-long GAN diet challenge also reduced body weight, plasma ALT, and plasma total cholesterol in LEAP2-KO and wild-type littermates and prevalence of higher grade fibrosis in LEAP2-KO mice.

CONCLUSIONS

Administration of LA-LEAP2 to mice fed a MAFLD-prone diet markedly improves several facets of MAFLD, including hepatic steatosis, hepatic lobular inflammation, higher-grade hepatic fibrosis, and transaminitis. These changes are accompanied by prominent reductions in body weight and lowered plasma total cholesterol. Taken together, these data suggest that LEAP2 analogs such as LA-LEAP2 hold promise for the treatment of MAFLD and obesity.

GHSR Deletion in β-Cells of Male Mice: Ineffective in Obesity, but Effective in Protecting against Streptozotocin-Induced β-Cell Injury in Aging

Insulin secretion from pancreatic β cells is a key pillar of glucose homeostasis, which is impaired under obesity and aging. Growth hormone secretagogue receptor (GHSR) is the receptor of nutrient-sensing hormone ghrelin. Previously, we showed that β-cell GHSR regulated glucose-stimulated insulin secretion (GSIS) in young mice. In the current study, we further investigated the effects of GHSR on insulin secretion in male mice under diet-induced obesity (DIO) and streptozotocin (STZ)-induced β-cell injury in aging. β-cell-specific-Ghsr-deficient (Ghsr-βKO) mice exhibited no glycemic phenotype under DIO but showed significantly improved ex vivo GSIS in aging. We also detected reduced insulin sensitivity and impaired insulin secretion during aging both in vivo and ex vivo. Accordingly, there were age-related alterations in expression of glucose transporter, insulin signaling pathway, and inflammatory genes. To further determine whether GHSR deficiency affected β-cell susceptibility to acute injury, young, middle-aged, and old Ghsr-βKO mice were subjected to STZ. We found that middle-aged and old Ghsr-βKO mice were protected from STZ-induced hyperglycemia and impaired insulin secretion, correlated with increased expression of insulin signaling regulators but decreased pro-inflammatory cytokines in pancreatic islets. Collectively, our findings indicate that β-cell GHSR has a major impact on insulin secretion in aging but not obesity, and GHSR deficiency protects against STZ-induced β-cell injury in aging.

Impact of Ghrelin on Islet Size in Nonpregnant and Pregnant Female Mice

Reducing ghrelin by ghrelin gene knockout (GKO), ghrelin-cell ablation, or high-fat diet feeding increases islet size and β-cell mass in male mice. Here we determined if reducing ghrelin also enlarges islets in females and if pregnancy-associated changes in islet size are related to reduced ghrelin. Islet size and β-cell mass were larger (P = .057 for β-cell mass) in female GKO mice. Pregnancy was associated with reduced ghrelin and increased liver-expressed antimicrobial peptide-2 (LEAP2; a ghrelin receptor antagonist) in wild-type mice. Ghrelin deletion and pregnancy each increased islet size (by ∼19.9-30.2% and ∼34.9-46.4%, respectively), percentage of large islets (>25 µm2×103, by ∼21.8-42% and ∼21.2-41.2%, respectively), and β-cell mass (by ∼15.7-23.8% and ∼65.2-76.8%, respectively). Neither islet cross-sectional area, β-cell cross-sectional area, nor β-cell mass correlated with plasma ghrelin, although all positively correlated with LEAP2 (P = .081 for islet cross-sectional area). In ad lib-fed mice, there was an effect of pregnancy, but not ghrelin deletion, to change (raise) plasma insulin without impacting blood glucose. Similarly, there was an effect of pregnancy, but not ghrelin deletion, to change (lower) blood glucose area under the curve during a glucose tolerance test. Thus, genetic deletion of ghrelin increases islet size and β-cell cross-sectional area in female mice, similar to males. Yet, despite pregnancy-associated reductions in ghrelin, other factors appear to govern islet enlargement and changes to insulin sensitivity and glucose tolerance in the setting of pregnancy. In the case of islet size and β-cell mass, one of those factors may be the pregnancy-associated increase in LEAP2.

The Importance of Intra-Islet Communication in the Function and Plasticity of the Islets of Langerhans during Health and Diabetes

Islets of Langerhans are anatomically dispersed within the pancreas and exhibit regulatory coordination between islets in response to nutritional and inflammatory stimuli. However, within individual islets, there is also multi-faceted coordination of function between individual beta-cells, and between beta-cells and other endocrine and vascular cell types. This is mediated partly through circulatory feedback of the major secreted hormones, insulin and glucagon, but also by autocrine and paracrine actions within the islet by a range of other secreted products, including somatostatin, urocortin 3, serotonin, glucagon-like peptide-1, acetylcholine, and ghrelin. Their availability can be modulated within the islet by pericyte-mediated regulation of microvascular blood flow. Within the islet, both endocrine progenitor cells and the ability of endocrine cells to trans-differentiate between phenotypes can alter endocrine cell mass to adapt to changed metabolic circumstances, regulated by the within-islet trophic environment. Optimal islet function is precariously balanced due to the high metabolic rate required by beta-cells to synthesize and secrete insulin, and they are susceptible to oxidative and endoplasmic reticular stress in the face of high metabolic demand. Resulting changes in paracrine dynamics within the islets can contribute to the emergence of Types 1, 2 and gestational diabetes.

Ghrelin enhances tubular magnesium absorption in the kidney

Osteoporosis after bariatric surgery is an increasing health concern as the rate of bariatric surgery has risen. In animal studies mimicking bariatric procedures, bone disease, together with decreased serum levels of Ca2+, Mg2+ and the gastric hormone Ghrelin were described. Ghrelin regulates metabolism by binding to and activating the growth hormone secretagogue receptor (GHSR) which is also expressed in the kidney. As calcium and magnesium are key components of bone, we tested the hypothesis that Ghrelin-deficiency contributes to osteoporosis via reduced upregulation of the renal calcium channel TRPV5 and the heteromeric magnesium channel TRPM6/7. We expressed GHSR with TRPV5 or TRPM6/7 channel in HEK293 cells and treated them with purified Ghrelin. Whole-cell current density was analyzed by patch-clamp recording. Nephron-specific gene expression was performed by tubular microdissection followed by qPCR in wild-type (WT) mice, and immunofluorescent imaging of GHSR-eGFP mice. Tubular magnesium homeostasis was analyzed in GHSR-null and WT mice at baseline and after caloric restriction. After Ghrelin exposure, whole-cell current density did not change for TRPV5 but increased for TRPM6/7 in a dose-dependent fashion. Applying the Ghrelin-mimetic (D-Trp7, Ala8,D-Phe10)-α-MSH (6-11) amide without and with the GHSR antagonist (D-Lys3)-GHRP6, we confirmed the stimulatory role of Ghrelin towards TRPM6/7. As GHSR initiates downstream signaling via protein kinase A (PKA), we found that the PKA inhibitor H89 abrogated TRPM6/7 stimulation by Ghrelin. Similarly, transfected Gαs, but not the Gαs mutant Q227L, nor Gαi2, Gαq, or Gα13 upregulated TRPM6/7 current density. In microdissected TALs and DCTs similar levels of GHSR mRNA were detected. In contrast, TRPM6 mRNA was expressed in the DCT and also detected in the TAL at 25% expression compared to DCT. Immunofluorescent studies using reporter GHSR-eGFP mice showed a strong eGFP signal in the TAL but surprisingly displayed no eGFP signal in the DCT. In 3-, 6-, and 9-month-old GHSR-null and WT mice, baseline serum magnesium was not significantly different, but 24-h urinary magnesium excretion was elevated in 9-month-old GHSR-null mice. In calorically restricted GHSR-null mice, we detected excess urinary magnesium excretion and reduced serum magnesium levels compared to WT mice. The kidneys from calorically restricted WT mice showed upregulated gene expression of magnesiotropic genes Hnf1b, Cldn-16, Cldn-19, Fxyd-2b, and Parvalbumin compared to GHSR-null mice. Our in vitro studies show that Ghrelin stimulates TRPM6/7 via GHSR and Gαs-PKA signaling. The murine studies are consistent with Ghrelin-GHSR signaling inducing reduced urinary magnesium excretion, particularly in calorically restricted mice when Ghrelin levels are elevated. This effect may be mediated by Ghrelin-upregulation of TRPM6 in the TAL and/or upregulation of other magnesiotropic genes. We postulate that rising Ghrelin levels with hunger contribute to increased renal Mg2+ reabsorption to compensate for lack of enteral Mg2+ uptake.

Ghrelin-responsive mediobasal hypothalamic neurons mediate exercise-associated food intake and exercise endurance

Previous studies have implicated the orexigenic hormone ghrelin as a mediator of exercise endurance and the feeding response postexercise. Specifically, plasma ghrelin levels nearly double in mice when they are subjected to an hour-long bout of high-intensity interval exercise (HIIE) using treadmills. Also, growth hormone secretagogue receptor-null (GHSR-null) mice exhibit decreased food intake following HIIE and diminished running distance (time until exhaustion) during a longer, stepwise exercise endurance protocol. To investigate whether ghrelin-responsive mediobasal hypothalamus (MBH) neurons mediate these effects, we stereotaxically delivered the inhibitory designer receptor exclusively activated by designer drugs virus AAV2-hSyn-DIO-hM4(Gi)-mCherry to the MBH of Ghsr-IRES-Cre mice, which express Cre recombinase directed by the Ghsr promoter. We found that chemogenetic inhibition of GHSR-expressing MBH neurons (upon delivery of clozapine-N-oxide) 1) suppressed food intake following HIIE, 2) reduced maximum running distance and raised blood glucose and blood lactate levels during an exercise endurance protocol, 3) reduced food intake following ghrelin administration, and 4) did not affect glucose tolerance. Further, HIIE increased MBH Ghsr expression. These results indicate that activation of ghrelin-responsive MBH neurons is required for the normal feeding response to HIIE and the usual amount of running exhibited during an exercise endurance protocol.

Ghrelin deletion and conditional ghrelin cell ablation increase pancreatic islet size in mice

Ghrelin exerts key effects on islet hormone secretion to regulate blood glucose levels. Here, we sought to determine whether ghrelin's effects on islets extend to the alteration of islet size and β cell mass. We demonstrate that reducing ghrelin - by ghrelin gene knockout (GKO), conditional ghrelin cell ablation, or high-fat diet (HFD) feeding - was associated with increased mean islet size (up to 62%), percentage of large islets (up to 854%), and β cell cross-sectional area (up to 51%). In GKO mice, these effects were more apparent in 10- to 12-week-old mice than in 4-week-old mice. Higher β cell numbers from decreased β cell apoptosis drove the increase in β cell cross-sectional area. Conditional ghrelin cell ablation in adult mice increased the β cell number per islet by 40% within 4 weeks. A negative correlation between islet size and plasma ghrelin in HFD-fed plus chow-fed WT mice, together with even larger islet sizes in HFD-fed GKO mice than in HFD-fed WT mice, suggests that reduced ghrelin was not solely responsible for diet-induced obesity-associated islet enlargement. Single-cell transcriptomics revealed changes in gene expression in several GKO islet cell types, including upregulation of Manf, Dnajc3, and Gnas expression in β cells, which supports decreased β cell apoptosis and/or increased β cell proliferation. These effects of ghrelin reduction on islet morphology might prove useful when designing new therapies for diabetes.

Liver-expressed antimicrobial peptide 2 is associated with improved pancreatic insulin secretion in adults with overweight and obesity

AIMS

To examine association of liver-expressed antimicrobial peptide 2 (LEAP2), an endogenous ghrelin antagonist with anorexiant effects, to key cardiometabolic risk factors in people with overweight and obesity.

METHODS

In this cross-sectional study, we sought to identify associations between LEAP2 levels and cardiometabolic risk factors, including body composition (dual X-ray absorptiometry), insulin and glucose metabolism (oral and intravenous glucose tolerance tests and hyperinsulinaemic-euglycaemic clamps), plasma lipids and inflammation markers (ELISA and multiplex assays).

RESULTS

In 65 participants with overweight or obesity (63.1% male, mean age 31.3 ± 8.5 years), LEAP2 levels were associated with total body fat, but not with body mass index or waist-hip ratio in both univariable and age- and sex-adjusted models (P < 0.05). Higher LEAP2 level was also positively associated with higher insulin secretion in univariable (P = 0.047) and multivariable models adjusted for age, sex and body fat (P = 0.03), but not with fasting glucose levels (P ≥ 0.05). Higher LEAP2 levels were associated insulin resistance (P = 0.07) after adjustment for age and sex, but the association disappeared after an additional adjustment for body fat (P = 0.2). There was an inverse association between LEAP2 levels and nuclear factor kappa-B (NFκB) activity in the peripheral blood mononuclear cells in age-, sex- and body fat-adjusted models (P = 0.04). There were no associations with cardiovascular risk factors (lipids, blood pressure) or other inflammation markers.

CONCLUSIONS

These results provide important insights into the association between LEAP2 and cardiometabolic health in a high-risk population of individuals with overweight and obesity. This is a first report of an association between LEAP2 and insulin secretion, insulin sensitivity and NFκB activity. LEAP2 may represent an important potential therapeutic target to promote insulin secretion in people with type 2 diabetes and obesity.

Ghrelin receptor signaling in health and disease: a biased view

As allosteric complexes, G-protein-coupled receptors (GPCRs) respond to extracellular stimuli and pleiotropically couple to intracellular transducers to elicit signaling pathway-dependent effects in a process known as biased signaling or functional selectivity. One such GPCR, the ghrelin receptor (GHSR1a), has a crucial role in restoring and maintaining metabolic homeostasis during disrupted energy balance. Thus, pharmacological modulation of GHSR1a bias could offer a promising strategy to treat several metabolism-based disorders. Here, we summarize current evidence supporting GHSR1a functional selectivity in vivo and highlight recent structural data. We propose that precise determinations of GHSR1a molecular pharmacology and pathway-specific physiological effects will enable discovery of GHSR1a drugs with tailored signaling profiles, thereby providing safer and more effective treatments for metabolic diseases.

Feeding-induced hepatokines and crosstalk with multi-organ: A novel therapeutic target for Type 2 diabetes

Hyperglycemia, which can be caused by either an insulin deficit and/or insulin resistance, is the main symptom of Type 2 diabetes, a significant endocrine metabolic illness. Conventional medications, including insulin and oral antidiabetic medicines, can alleviate the signs of diabetes but cannot restore insulin release in a physiologically normal amount. The liver detects and reacts to shifts in the nutritional condition that occur under a wide variety of metabolic situations, making it an essential organ for maintaining energy homeostasis. It also performs a crucial function in glucolipid metabolism through the secretion of hepatokines. Emerging research shows that feeding induces hepatokines release, which regulates glucose and lipid metabolism. Notably, these feeding-induced hepatokines act on multiple organs to regulate glucolipotoxicity and thus influence the development of T2DM. In this review, we focus on describing how feeding-induced cross-talk between hepatokines, including Adropin, Manf, Leap2 and Pcsk9, and metabolic organs (e.g.brain, heart, pancreas, and adipose tissue) affects metabolic disorders, thus revealing a novel approach for both controlling and managing of Type 2 diabetes as a promising medication.

Beta-Hydroxybutyrate Suppresses Hepatic Production of the Ghrelin Receptor Antagonist LEAP2

INTRODUCTION

Liver-expressed antimicrobial peptide-2 (LEAP2) is an endogenous ghrelin receptor antagonist, which is upregulated in the fed state and downregulated during fasting. We hypothesized that the ketone body beta-hydroxybutyrate (BHB) is involved in the downregulation of LEAP2 during conditions with high circulating levels of BHB.

METHODS

Hepatic and intestinal Leap2 expression were determined in 3 groups of mice with increasing circulating levels of BHB: prolonged fasting, prolonged ketogenic diet, and oral BHB treatment. LEAP2 levels were measured in lean and obese individuals, in human individuals following endurance exercise, and in mice after BHB treatment. Lastly, we investigated Leap2 expression in isolated murine hepatocytes challenged with BHB.

RESULTS

We confirmed increased circulating LEAP2 levels in individuals with obesity compared to lean individuals. The recovery period after endurance exercise was associated with increased plasma levels of BHB levels and decreased LEAP2 levels in humans. Leap2 expression was selectively decreased in the liver after fasting and after exposure to a ketogenic diet for 3 weeks. Importantly, we found that oral administration of BHB increased circulating levels of BHB in mice and decreased Leap2 expression levels and circulating LEAP2 plasma levels, as did Leap2 expression after direct exposure to BHB in isolated murine hepatocytes.

CONCLUSION

From our data, we suggest that LEAP2 is downregulated during different states of energy deprivation in both humans and rodents. Furthermore, we here provide evidence that the ketone body, BHB, which is highly upregulated during fasting metabolism, directly downregulates LEAP2 levels. This may be relevant in ghrelin receptor-induced hunger signaling during energy deprivation.

LEAP2 reduces postprandial glucose excursions and ad libitum food intake in healthy men

The gastric hormone ghrelin stimulates food intake and increases plasma glucose through activation of the growth hormone secretagogue receptor (GHSR). Liver-expressed antimicrobial peptide 2 (LEAP2) has been proposed to inhibit actions of ghrelin through inverse effects on GHSR activity. Here, we investigate the effects of exogenous LEAP2 on postprandial glucose metabolism and ad libitum food intake in a randomized, double-blind, placebo-controlled, crossover trial of 20 healthy men. We report that LEAP2 infusion lowers postprandial plasma glucose and growth hormone concentrations and decreases food intake during an ad libitum meal test. In wild-type mice, plasma glucose and food intake are reduced by LEAP2 dosing, but not in GHSR-null mice, pointing to GHSR as a potential mediator of LEAP2’s glucoregulatory and appetite-suppressing effects in mice.

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Exogenous LEAP2 lowers postprandial plasma glucose excursions

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Exogenous LEAP2 suppresses ad libitum food intake

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During fasting, exogenous LEAP2 increases insulin secretion and suppresses lipolysis

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The GHSR is required for eliciting LEAP2 effects in mice

An insight into the multifunctional role of ghrelin and structure activity relationship studies of ghrelin receptor ligands with clinical trials

Ghrelin is a multifunctional gastrointestinal acylated peptide, primarily synthesized in the stomach and regulates the secretion of growth hormone and energy homeostasis. It plays a central role in modulating the diverse biological, physiological and pathological functions in vertebrates. The synthesis of ghrelin receptor ligands after the finding of growth hormone secretagogue developed from Met-enkephalin led to reveal the endogenous ligand ghrelin and the receptors. Subsequently, many peptides, small molecules and peptidomimetics focusing on the ghrelin receptor, GHS-R1a, were derived. In this review, the key features of ghrelin's structure, forms, its bio-physiological functions, pathological roles and therapeutic potential have been highlighted. A few peptidomimetics and pseudo peptide synthetic perspectives have also been discussed to make ghrelin receptor ligands, clinical trials and their success.

Mechanistic Investigation of GHS-R Mediated Glucose-Stimulated Insulin Secretion in Pancreatic Islets

Ghrelin receptor, a growth hormone secretagogue receptor (GHS-R), is expressed in the pancreas. Emerging evidence indicates that GHS-R is involved in the regulation of glucose-stimulated insulin secretion (GSIS), but the mechanism by which GHS-R regulates GSIS in the pancreas is unclear. In this study, we investigated the role of GHS-R on GSIS in detail using global Ghsr^−/− mice (in vivo) and Ghsr-ablated pancreatic islets (ex vivo). GSIS was attenuated in both Ghsr^−/− mice and Ghsr-ablated islets, while the islet morphology was similar between WT and Ghsr^−/− mice. To elucidate the mechanism underpinning Ghsr-mediated GSIS, we investigated the key steps of the GSIS signaling cascade. The gene expression of glucose transporter 2 (Glut2) and the glucose-metabolic intermediate—glucose-6-phosphate (G6P) were reduced in Ghsr-ablated islets, supporting decreased glucose uptake. There was no difference in mitochondrial DNA content in the islets of WT and Ghsr^−/− mice, but the ATP/ADP ratio in Ghsr^−/− islets was significantly lower than that of WT islets. Moreover, the expression of pancreatic and duodenal homeobox 1 (Pdx1), as well as insulin signaling genes of insulin receptor (IR) and insulin receptor substrates 1 and 2 (IRS1/IRS2), was downregulated in Ghsr^−/− islets. Akt is the key mediator of the insulin signaling cascade. Concurrently, Akt phosphorylation was reduced in the pancreas of Ghsr^−/− mice under both insulin-stimulated and homeostatic conditions. These findings demonstrate that GHS-R ablation affects key components of the insulin signaling pathway in the pancreas, suggesting the existence of a cross-talk between GHS-R and the insulin signaling pathway in pancreatic islets, and GHS-R likely regulates GSIS via the Akt-Pdx1-GLUT2 pathway.

Therapeutic effects of acylated ghrelin-specific receptor GHS-R1a antagonist in islet transplantation

Islet transplantation is a type of cellular replacement therapy for severe diabetes that is limited by compromising effect on engrafted islets. Trials aiming to improve the function of transplanted islets have also been challenging. This study attempted to elucidate whether regulation of growth hormone secretagogue receptor-1a (GHS-R1a), one of the ghrelin receptors, improve the therapeutic effects of islet transplantation using [D-Lys3]-GHRP-6 (DLS), a specific GHS-R1a antagonist. The therapeutic effects of DLS were assessed in terms of the expression/production of endocrine genes/proteins, insulin-releasing function under glucose stimulation of mouse islets, and outcomes of syngeneic murine islet transplantation with systemic DLS administration. DLS treatment promoted insulin production and suppressed somatostatin production, suggesting that cancelation of the binding between ghrelin and GHS-R1a on β or δ cells improved insulin expression. DLS also promoted the glucose-dependent insulin-releasing function of β cells. However, the therapeutic effect of DLS in islet transplantation was fractional. In conclusion, the GHS-R1a antagonist showed preferable effects in improving the therapeutic outcomes of islet transplantation, including the promotion of insulin-releasing function.