Des-acyl ghrelin prevents heatstroke-like symptoms in rats exposed to high temperature and high humidity

Ghrelin-LEAP2 interactions along the stomach-liver axis

Ghrelin produced in the stomach promotes food intake and GH secretion, and acts as an anabolic peptide during starvation. Ghrelin binds to the growth hormone secretagogue receptor, a G protein-coupled receptor (GPCR), whose high-resolution complex structures have been determined in the apo state and when bound to an antagonist. Anamorelin, a low-molecular-weight ghrelin agonist, has been launched in Japan for the treatment of cancer cachexia, and its therapeutic potential has attracted attention due to the various biological activities of ghrelin. In 2019, liver-expressed antimicrobial peptide (LEAP2), initially discovered as an antimicrobial peptide produced in the liver, was identified to be upregulated in the stomach of diet-induced obese mice after vertical sleeve gastrectomy. LEAP2 binds to the GHSR and antagonizes ghrelin's activities. The serum concentrations of human LEAP2 are positively correlated with body mass index, body fat accumulation, and fasting serum concentrations of glucose and triglyceride. Serum LEAP2 elevated and ghrelin reduced in obesity. Ghrelin and LEAP2 regulate body weight, food intake, and GH and blood glucose concentrations, and other physiological phenomena through their interactions with the same receptor, GHSR.

Desacyl-ghrelin, not just an inactive form of ghrelin?-A review of current knowledge on the biological actions of desacyl-ghrelin

Desacyl-ghrelin is a form of ghrelin which lacks acyl-modification of the third serine residue of ghrelin. Originally, desacyl-ghrelin was considered to be just an inactive form of ghrelin. More recently, however, it has been suggested to have various biological activities, including control of food intake, growth hormone, glucose metabolism, and gastric movement, and is involved in cell survival. In this review, we summarize the current knowledge of the biological actions of desacyl-ghrelin and the proposed mechanisms by which it exerts the effects.

Modulation of acyl and des-acyl ghrelin on autonomic and behavioral thermoregulation in various ambient temperatures

Maintenance of body temperature (T_b) at various ambient temperatures (T_a) during fasting is important for homeotherms. Fasting decreases T_b in thermoneutral and cold conditions and facilitates thermoregulatory behavior in the cold in rats; however, the mechanism is unknown. We focused on ghrelin, a hormone secreted by the stomach during fasting, in two circulatory forms: acyl ghrelin (AG) and des-acyl ghrelin (DAG). AG is called active ghrelin, while DAG, the non-active ghrelin, was unknown for a long time before its many functions were recently clarified. In the present review, we present the modulation of AG and DAG on autonomic and behavioral thermoregulation at various T_a and discuss the differences between their modulation on thermoregulation. AG decreases T_b in thermoneutral and cold conditions but does not affect the thermoregulatory behavior of rodents in cold conditions. The DAG decreases T_b in thermoneutral and hot conditions, but it does not affect T_b and facilitates the thermoregulatory behavior of rodents in the cold. These findings indicate that the actions of AG and DAG on thermoregulation are similar in thermoneutral conditions but are different in cold conditions.

Exendin-4 antagonizes the metabolic action of acylated ghrelinergic signaling in the hypothalamic paraventricular nucleus

In the current study we investigated the interaction of hypothalamic paraventricular nucleus (PVN) glucagon-like peptide-1 (GLP-1) and ghrelin signaling in the control of metabolic function. We first demonstrated that acylated ghrelin injected directly into the PVN reliably altered the respiratory exchange ratio (RER) of adult male Sprague Dawley rats. All testing was carried out during the initial 2 h of the nocturnal cycle using an indirect open circuit calorimeter. Results indicated that acylated ghrelin induced a robust increase in RER representing a shift toward enhanced carbohydrate oxidation and reduced lipid utilization. In contrast, treatment with comparable dosing of des-acyl ghrelin failed to significantly impact metabolic activity. In separate groups of rats we subsequently investigated the ability of exendin-4 (Ex-4), a GLP-1 analogue, to alter acylated ghrelin's metabolic effects. Rodents were treated with either systemic or direct PVN Ex-4 followed by acyl ghrelin microinjection. While our results showed that both systemic and PVN administration of Ex-4 significantly reduced RER, importantly, Ex-4 pretreatment itself reliably inhibited the impact of ghrelin on RER. Overall, these findings provide increasingly compelling evidence that GLP-1 and ghrelin signaling interact in the neural control of metabolic function within the PVN.

Fasting or systemic des-acyl ghrelin administration to rats facilitates thermoregulatory behavior in a cold environment

Fasted rats place their tails underneath their body trunks in the cold (tail-hiding behavior), which is a thermoregulatory behavior. The aim of the present study was to investigate the effect of fasting and des-acyl ghrelin, a hormone related to fasting, on tail-hiding behavior and neural activity in the cold. Wistar rats were divided into 'fed', '42-h fasting' and des-acyl ghrelin groups. The rats received an intraperitoneal saline or 30-μg des-acyl ghrelin injection, and were then exposed to 27 °C or 15 °C for 2-h with continuous body temperature (T_b), tail skin temperature (T_tail), and tail-hiding behavior measurements. cFos immunoreactive (cFos-IR) cells in the insula, secondary somatosensory cortex, medial preoptic nucleus, parastrial nucleus, amygdala, and lateral parabrachial nucleus were counted in four segments: seg1, 2, 3, and 4 (bregma -0.36, -1.44, -2.64, and -9.00 mm), respectively. At 15 °C, T_b and T_tail were lower in the 42-h fasting group than in the fed and des-acyl ghrelin groups, and the duration of tail-hiding behavior was longer in the 42-h fasting and des-acyl ghrelin groups than in the fed group. The onset of tail-hiding behavior more advanced in the des-acyl ghrelin group than in the fed group at 15 °C. Only at the insula in seg3 at 15 °C, the number of cFos-IR cells was greater in the 42-h fasting group than in the fed group. Both the 42-h fasting and des-acyl ghrelin groups might modulate the tail-hiding behavior of rats in a cold, and a part of the insula might be involved this response during fasting.