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 ß 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 ß 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 ß cell numbers from decreased ß cell apoptosis drove the increase in ß cell cross-sectional area. Conditional ghrelin cell ablation in adult mice increased the ß 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 ß cells, which supports decreased ß cell apoptosis and/or increased ß cell proliferation. These effects of ghrelin reduction on islet morphology might prove useful when designing new therapies for diabetes.

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.

Effects of thermoneutrality on food intake, body weight, and body composition in a Prader-Willi syndrome mouse model.

OBJECTIVE: Prader-Willi syndrome (PWS) is a multisystem genetic disorder. Unfortunately, none of several mouse models carrying PWS mutations emulates the entirety of the human PWS phenotype, including hyperphagia plus obesity. METHODS: To determine whether housing at thermoneutrality (TN, 30 °C) permits the development of hyperphagia and obesity in the Snord116del PWS mouse model, the effects of housing three different ages of Snord116del and wild-type (WT) littermates at TN versus room temperature (RT, 22-24 °C) for 8 weeks were compared. RESULTS: Snord116del mice born and maintained at TN exhibited lower body weight curves, lower percentage fat mass, and lower food intake than WT mice at RT. In 4- to 6-month-old high-fat diet-fed female mice, TN raised the Snord116del body weight curve closer to that of RT-housed WT mice although the TN-housed Snord116del mice did not gain more adiposity or exhibit greater food intake. In 6- to 8-month-old high-fat diet-fed male mice, body weight, adiposity, and food intake of TN-housed Snord116del mice remained far below levels in RT-housed WT mice. TN elicited hypotonia in Snord116del adults and exacerbated mortality of Snord116del newborns. CONCLUSIONS: In none of three tested TN protocols were greater food intake, body weight, or adiposity induced in Snord116del mice compared with RT-housed WT mice.

LEAP2 deletion in mice enhances ghrelin's actions as an orexigen and growth hormone secretagogue.

OBJECTIVE: The hormone liver-expressed antimicrobial peptide-2 (LEAP2) is a recently identified antagonist and an inverse agonist of the growth hormone secretagogue receptor (GHSR). GHSR's other well-known endogenous ligand, acyl-ghrelin, increases food intake, body weight, and GH secretion and is lowered in obesity but elevated upon fasting. In contrast, LEAP2 reduces acyl-ghrelin-induced food intake and GH secretion and is found elevated in obesity but lowered upon fasting. Thus, the plasma LEAP2/acyl-ghrelin molar ratio could be a key determinant modulating GHSR signaling in response to changes in body mass and feeding status. In particular, LEAP2 may serve to dampen acyl-ghrelin action in the setting of obesity, which is associated with ghrelin resistance. Here, we sought to determine the metabolic effects of genetic LEAP2 deletion. METHODS: We generated the first known LEAP2-KO mouse line. Food intake, GH secretion, and cellular activation (c-fos induction) in different brain regions following s.c. acyl-ghrelin administration in LEAP2-KO mice and wild-type littermates were determined. LEAP2-KO mice and wild-type littermates were submitted to a battery of tests (such as measurements of body weight, food intake, and body composition; indirect calorimetry, determination of locomotor activity, and meal patterning while housed in metabolic cages) over the course of 16 weeks of high-fat diet and/or standard chow feeding. Fat accumulation was assessed in hematoxylin & eosin-stained and oil red O-stained liver sections from these mice. RESULTS: LEAP2-KO mice were more sensitive to s.c. ghrelin. In particular, acyl-ghrelin acutely stimulated food intake at a dose of 0.5 mg/kg BW in standard chow-fed LEAP2-KO mice while a 2× higher dose was required by wild-type littermates. Also, acyl-ghrelin stimulated food intake at a dose of 1 mg/kg BW in high-fat diet-fed LEAP2-KO mice while not even a 10× higher dose was effective in wild-type littermates. Acyl-ghrelin induced a 90.9% higher plasma GH level and 77.2-119.7% higher numbers of c-fos-immunoreactive cells in the arcuate nucleus and olfactory bulb, respectively, in LEAP2-KO mice than in wild-type littermates. LEAP2 deletion raised body weight (by 15.0%), food intake (by 18.4%), lean mass (by 6.1%), hepatic fat (by 42.1%), and body length (by 1.7%) in females on long-term high-fat diet as compared to wild-type littermates. After only 4 weeks on the high-fat diet, female LEAP2-KO mice exhibited lower O2 consumption (by 13%), heat production (by 9.5%), and locomotor activity (by 49%) than by wild-type littermates during the first part of the dark period. These genotype-dependent differences were not observed in high-fat diet-exposed males or female and male mice exposed for long term to standard chow diet. CONCLUSIONS: LEAP2 deletion sensitizes lean and obese mice to the acute effects of administered acyl-ghrelin on food intake and GH secretion. LEAP2 deletion increases body weight in females chronically fed a high-fat diet as a result of lowered energy expenditure, reduced locomotor activity, and increased food intake. Furthermore, in female mice, LEAP2 deletion increases body length and exaggerates the hepatic fat accumulation normally associated with chronic high-fat diet feeding.

"A LEAP 2 conclusions? Targeting the ghrelin system to treat obesity and diabetes".

BACKGROUND: The hormone ghrelin stimulates food intake, promotes adiposity, increases body weight, and elevates blood glucose. Consequently, alterations in plasma ghrelin levels and the functioning of other components of the broader ghrelin system have been proposed as potential contributors to obesity and diabetes. Furthermore, targeting the ghrelin system has been proposed as a novel therapeutic strategy for obesity and diabetes. SCOPE OF REVIEW: The current review focuses on the potential for targeting ghrelin and other proteins comprising the ghrelin system as a treatment for obesity and diabetes. The main components of the ghrelin system are introduced. Data supporting a role for the endogenous ghrelin system in the development of obesity and diabetes along with data that seemingly refute such a role are outlined. An argument for further research into the development of ghrelin system-targeted therapeutic agents is delineated. Also, an evidence-based discussion of potential factors and contexts that might influence the efficacy of this class of therapeutics is provided. MAJOR CONCLUSIONS: It would not be a "leap to" conclusions to suggest that agents which target the ghrelin system - including those that lower acyl-ghrelin levels, raise LEAP2 levels, block GHSR activity, and/or raise desacyl-ghrelin signaling - could represent efficacious novel treatments for obesity and diabetes.

The novel cannabinoid CB1 receptor agonist AM11101 increases food intake in female rats.

BACKGROUND AND PURPOSE: Δ9 -tetrahydrocannabinol (THC) acts via cannabinoid CB1 receptors to increase feeding. Here, we assessed the orexigenic effect of AM11101, a novel CB1 receptor agonist designed to have a more favourable pharmacodynamic profile than THC. EXPERIMENTAL APPROACH: The acute, orexigenic effects of AM11101 and THC were compared in female rats. Food intake and meal patterns were also examined following once daily treatment with AM11101 and THC for 7 days. KEY RESULTS: AM11101 (0.01-0.1 mg·kg-1 ) increased food intake during the first hour following both acute and chronic treatments in pre-fed and freely feeding animals. This orexigenic effect persisted for up to 4 hr, with no compensatory decrease in feeding during the subsequent 4-22 hr. THC (1 mg·kg-1 ) increased 1-hr food intake in pre-fed animals, but was less reliable than AM11101 in increasing 1-hr food intake in freely feeding animals following both acute and chronic administration. The orexigenic effect of both compounds was due to an increase in meal size, not meal number. CONCLUSIONS AND IMPLICATIONS: Our study provides the first demonstration that AM11101 increases short-term food intake via a selective increase in meal size. AM11101 promotes a more reliable orexigenic effect than THC in freely feeding animals, with no subsequent compensatory decrease in feeding. AM11101 may offer a greater efficacy than THC and its congeners in stimulating food intake in underweight clinical populations.

Saccharin pre-exposure enhances appetitive flavor learning in pre-weanling rats.

In adult rats, data suggest that consumption of sweet tastes that do not deliver anticipated caloric consequences using high-intensity, non-caloric sweeteners, such as saccharin, interferes with learned relations that may contribute to energy balance. The goal of the present study was to assess the development of learning about sweet taste and calories by assessing whether pre-exposure to saccharin solutions reduces cue competition in pre-weanling rats. The results demonstrated that rats pre-exposed to saccharin and then trained with a novel grape flavor paired with a glucose-sweetened solution consumed more of the novel grape flavor presented alone than rats that had been pre-exposed to saccharin and given the grape flavor paired with water alone. No differences in intake of the novel grape flavor were observed in groups given pre-exposure to water or glucose solutions. Thus, by 15 days of age, rats appear to have established an association between sweet tastes and calories, and this association can be weakened by exposure to saccharin.

Fat substitutes promote weight gain in rats consuming high-fat diets.

The use of food products designed to mimic the sensory properties of sweet and fat while providing fewer calories has been promoted as a method for reducing food intake and body weight. However, such products may interfere with a learned relationship between the sensory properties of food and the caloric consequences of consuming those foods. In the present experiment, we examined whether use of the fat substitute, olestra, affect energy balance by comparing the effects of consuming high-fat, high-calorie potato chips to the effects of consuming potato chips that sometimes signaled high calories (using high-fat potato chips) and that sometimes signaled lower calories (using nonfat potato chips manufactured with the fat substitute olestra). Food intake, body weight gain and adiposity were greater for rats that consumed both the high-calorie chips and the low-calorie chips with olestra compared to rats that consumed consuming only the high-calorie chips, but only if animals were also consuming a chow diet that was high in fat and calories. However, rats previously exposed to both the high- and low-calorie chips exhibited increased body weight gain, food intake and adiposity when they were subsequently provided with a high fat, high calorie chow diet suggesting that experience with the chips containing olestra affected the ability to predict high calories based on the sensory properties of fat. These results extend the generality of previous findings that interfering with a predictive relationship between sensory properties of foods and calories may contribute to dysregulation of energy balance, overweight and obesity.