Feeding behavior during long-term hexarelin administration in young and old rats

Hypothalamic Glucose Hypersensitivity-Induced Insulin Secretion in the Obese Zücker Rat Is Reversed by Central Ghrelin Treatment

Aims: Part of hypothalamic (mediobasal hypothalamus [MBH]) neurons detect changes in blood glucose levels that in turn coordinate the vagal control of insulin secretion. This control cascade requires the production of mitochondrial reactive oxygen species (mROS), which is altered in models of obesity and insulin resistance. Obese, insulin-resistant Zücker rats are characterized by hypothalamic hypersensitivity to glucose. This initiates an abnormal vagus-induced insulin secretion, associated with an overproduction of mROS in response to a low glucose dose. Here, we hypothesized that ghrelin, known to buffer reactive oxygen species (ROS) via mitochondrial function, may be a major component of the hypothalamic glucose hypersensitivity in the hypoghrelinemic obese Zücker rat. Results: Hypothalamic glucose hypersensitivity-induced insulin secretion of Zücker obese rats was reversed by ghrelin pretreatment. The overproduction of MBH mROS in response to a low glucose load no longer occurred in obese rats that had previously received the cerebral ghrelin infusion. This decrease in mROS production was accompanied by a normalization of oxidative phosphorylation (OXPHOS). Conversely, blocking the action of ghrelin with a growth hormone secretagogue receptor antagonist in a model of hyperghrelinemia (fasted rats) completely restored hypothalamic glucose sensing-induced insulin secretion that was almost absent in this physiological situation. Accordingly, ROS signaling and mitochondrial activity were increased by the ghrelin receptor antagonist. Innovation: These results demonstrate for the first time that ghrelin addressed only to the brain could have a protective effect on the defective control of insulin secretion in the insulin-resistant, hypoghrelinemic obese subject. Conclusions: Ghrelin, through its action on OXPHOS, modulates mROS signaling in response to cerebral hyperglycemia and the consequent vagal control of insulin secretion. In insulin-resistant obese states, brain hypoghrelinemia could be responsible for the nervous defect in insulin secretion.

Hexarelin modulates lung mechanics, inflammation, and fibrosis in acute lung injury

Introduction:

Acute respiratory distress syndrome (ARDS) is an acute form of diffuse lung injury characterized by (i) an intense inflammatory response, (ii) increased pulmonary vascular permeability, and (iii) the loss of respiratory pulmonary tissue. In this article we explore the therapeutic potential of hexarelin, a synthetic hexapeptide growth hormone secretagogue (GHS), in an experimental model of ARDS. Hexarelin has anti-inflammatory properties and demonstrates cardiovascular-protective activities including the inhibition of cardiomyocyte apoptosis and cardiac fibrosis, both of which may involve the angiotensin-converting enzyme (ACE) system.

Methods:

In our experimental model, ARDS was induced by the instillation of 100 mM HCl into the right bronchus; these mice were treated with hexarelin (320 μg/kg, ip) before (Pre) or after (Post) HCl challenge, or with vehicle. Respiratory system compliance, blood gas analysis, and differential cell counts in a selective bronchoalveolar lavage (BAL) were determined 6 or 24 hours after HCl instillation. In an extended study, mice were observed for a subsequent 14 days in order to assess lung fibrosis.

Results:

Hexarelin induced a significant improvement in lung compliance and a reduction of the number of total immune cells in BAL 24 hours after HCl instillation, accompanied with a lower recruitment of neutrophils compared with the vehicle group. At day 14, hexarelin-treated mice presented with less pulmonary collagen deposition compared with vehicle-treated controls.

Conclusions:

Our data suggest that hexarelin can inhibit the early phase of the inflammatory response in a murine model of HCl-induced ARDS, thereby blunting lung remodeling processes and fibrotic development.

JMV2894, a novel growth hormone secretagogue, accelerates body mass recovery in an experimental model of cachexia

Oncologic patients subjected to chemotherapy frequently present aphagia, malnutrition, and cachexia. The purpose of this study was to investigate whether selected growth hormone secretagogues including hexarelin, JMV2894 and JMV2951 could antagonize body weight loss and wasting induced by cisplatin administration in rats. The three growth hormone secretagogues behaved as full agonists of the growth hormone secretagogues receptor both in terms of ability to stimulate calcium mobilization in Chinese hamster ovary cells and stimulation of growth hormone release in neonatal rats. Adult rats were (i) treated with vehicle throughout (controls), or (ii) treated with cisplatin (days 1-3) and a growth hormone secretagogues or vehicle, (days 1-12). Body weight and food consumption were measured daily. Although all growth hormone secretagogues caused initial transient acute increases in food intake, the total amount of food eaten by controls and growth hormone secretagogues treated groups over the 12 experimental days was not significantly different. All groups pre-treated with cisplatin lost up to 5-10 % body weight in the first 4 days; they subsequently gained weight at a rate comparable with controls. Interestingly, rats which received JMV2894 demonstrated a faster gain in body weight than any other growth hormone secretagogues treated group and at the end of the protocol reached a weight similar to that of controls. JMV2894 did not stimulate perirenal and epididymal fat accumulation but reduced MuRF mRNA levels in skeletal muscles. In conclusion, our findings demonstrate that JMV2894 antagonizes cisplatin induced weight loss in rats and may prove useful in antagonizing cachexia associated with cancer and chemotherapy in humans.

Hexarelin, a Growth Hormone Secretagogue, Improves Lipid Metabolic Aberrations in Nonobese Insulin-Resistant Male MKR Mice

Despite the occurrence of dyslipidemia and its contribution to the development of insulin resistance in obese subjects, a growing number of studies have described abnormal lipid profiles among leaner persons. For example, individuals with an abnormal paucity or distribution of fat (lipodystrophy) develop severe insulin resistance, dyslipidemia, and hepatic steatosis. Deranged adipocyte metabolism and differentiation contribute to ectopic fat deposition and consequent development of insulin resistance. Growth hormone (GH) therapy has been shown to correct body composition abnormalities in some lipodystrophy patients. However, little is known about the effects of GH-releasing peptides in this regard. Hexarelin, a GH secretagogue, has recently been shown to have beneficial effects on fat metabolism via the CD36 receptor. In this study, the effects of twice daily intraperitoneal injections of hexarelin (200 μg/kg body weight) were examined in nonobese insulin-resistant MKR mice and corresponding wild-type FVB mice for 12 days. Hexarelin treatment significantly improved glucose and insulin intolerance and decreased plasma and liver triglycerides in MKR mice. These beneficial metabolic effects could be due to the improved lipid metabolism and enhanced adipocyte differentiation of white adipose tissue with hexarelin treatment. Interestingly, although food intake of hexarelin-treated MKR mice was significantly increased, this did not change total body weight. Moreover, hexarelin treatment corrected the abnormal body composition of MKR mice, as demonstrated by a decrease in fat mass and an increase in lean mass. Our results suggest a possible application of hexarelin in treatment of lipid disorders associated with the metabolic syndrome.

Reproductive performance and fertility in male and female adult mice chronically treated with hexarelin

Hexarelin (HEXr), a synthetic ghrelin analogue, has been associated with modifications of reproductive physiology. In previous studies of adult mice, we detected that HEXr induced significantly reduced ovulation rate and significant correlation coefficients between sexual maturation and corporal weight in offspring. In this study, we investigated the effects of chronic HEXr administration on sperm concentration and functional activity, oestrous cyclicity and pregnancy index, in addition to the number of fetuses and its correlation with the number of corpora lutea. Adult Albino swiss mice were injected (sc) daily with HEXr: 100 μg kg–1 day–1 (HEXr D1) or 200 μg kg–1 day–1 (HEXr D2) for 53 days in males and 30 days in females. We detected a significantly decreased ratio in the number of fetuses per corpora lutea in females treated with HEXr D2 for 30 days before mating and during the first 6 days of pregnancy, in addition to a downward trend in the pregnancy index and percentage of females impregnated by each male treated with both doses of the analogue. Although we did not find any significant effect on additional parameters evaluated in both genders, we propose certain effects of HEXr on the implantation process and/or early development of embryos and over the in vivo reproductive capability of males.

Integrating GHS into the Ghrelin System

Oligopeptide derivatives of metenkephalin were found to stimulate growth-hormone (GH) release directly by pituitary somatotrope cells in vitro in 1977. Members of this class of peptides and nonpeptidyl mimetics are referred to as GH secretagogues (GHSs). A specific guanosine triphosphatate-binding protein-associated heptahelical transmembrane receptor for GHS was cloned in 1996. An endogenous ligand for the GHS receptor, acylghrelin, was identified in 1999. Expression of ghrelin and homonymous receptor occurs in the brain, pituitary gland, stomach, endothelium/vascular smooth muscle, pancreas, placenta, intestine, heart, bone, and other tissues. Principal actions of this peptidergic system include stimulation of GH release via combined hypothalamopituitary mechanisms, orexigenesis (appetitive enhancement), insulinostasis (inhibition of insulin secretion), cardiovascular effects (decreased mean arterial pressure and vasodilation), stimulation of gastric motility and acid secretion, adipogenesis with repression of fat oxidation, and antiapoptosis (antagonism of endothelial, neuronal, and cardiomyocyte death). The array of known and proposed interactions of ghrelin with key metabolic signals makes ghrelin and its receptor prime targets for drug development.

Effects of hexarelin (a ghrelin analogue) on fertilisation and the pre- and postnatal development of mice

Ghrelin (Ghr) has been associated with reproductive physiology and pre- and postnatal development. The objectives of the present study were to evaluate the effects of hexarelin (HEX; 100 or 200 µg kg−1 day−1), a therapeutic Ghr analogue, on: (1) embryo development 60 h post ovulation, induced pharmacologically, in pregnant mice; (2) the physical, neurobiological and sexual development of offspring of female mice injected with HEX during the first, second or third week of pregnancy or throughout the entire pregnancy; and (3) adult memory acquisition in these offspring. We also evaluated the effects of chronic HEX administration on memory acquisition in adult mice. Treatment of non-pregnant female mice with HEX decreased ovulation rate. However, treatment of pregnant mice with HEX at any time during pregnancy tended to accelerate offspring maturation, regardless of bodyweight. This effect was only significant on neurobiological parameters following treatment during the first week. HEX treatment during the first week and/or throughout the entire pregnancy resulted in impaired memory acquisition in the offspring, with female mice being more susceptible to these effects. Similar results were observed for the effects of chronic HEX treatment on memory acquisition in adult mice. In conclusion, HEX seems to exert differential effects depending on when it is administered. Because HEX has started to be used therapeutically, its deleterious effects on ovulation and memory acquisition must be further evaluated.