Elena Gramaglia

Metabolic effects of overnight continuous infusion of unacylated ghrelin in humans

OBJECTIVE To clarify the metabolic effects of an overnight i.v. infusion of unacylated ghrelin (UAG) in humans. UAG exerts relevant metabolic actions, likely mediated by a still unknown ghrelin receptor subtype, including effects on β-cell viability and function, insulin secretion and sensitivity, and glucose and lipid metabolism. DESIGN We studied the effects of a 16-h infusion (from 2100 to 1300  h) of UAG (1.0  μg/kg per h) or saline in eight normal subjects (age (mean±s.e.m.), 29.6±2.4 years; body mass index (BMI), 22.4±1.7  kg/m(2)), who were served, at 2100 and 0800  h respectively, with isocaloric balanced dinner and breakfast. Glucose, insulin, and free fatty acid (FFA) levels were measured every 20  min. RESULTS In comparison with saline, UAG induced significant (P<0.05) changes in glucose, insulin, and FFA profiles. UAG infusion decreased glucose area under the curve (AUC) values by 10% (UAG(0 - 960  min): 79.0±1.7×10(3)  mg/dl per min vs saline(0- 960  min): 87.5±3.8×10(3)  mg/dl per min) and the AUC at night by 14% (UAG(180)(-)(660  min): 28.4±0.5×10(3)  mg/dl per min vs saline(180 - 660  min): 33.2±1.1×10(3)  mg/dl per min). The overall insulin AUC was not significantly modified by UAG infusion; however, insulin AUC observed after meals was significantly increased under the exposure to UAG with respect to saline at either dinner or breakfast. The FFA AUC values were decreased by 52% under the exposure to UAG in comparison with saline (UAG(0 - 960  min): 0.3±0.02×10(3)  mEq/l per min vs saline(0 - 960  min): 0.6±0.05×10(3)  mEq/l per min). CONCLUSIONS Exposure to the i.v. administration of UAG improves glucose metabolism and inhibits lipolysis in healthy volunteers. Thus, in contrast to the diabetogenic action of AG, UAG displays hypoglycemic properties.

d-Lys-GHRP-6 does not modify the endocrine response to acylated ghrelin or hexarelin in humans

Acylated ghrelin exerts numerous endocrine and non-endocrine activities via the GH Secretagogue receptor type 1a (GHS-R1a). D-Lys-GHRP-6 has been widely studied in vitro and in vivo in animal studies as GHS-R1a antagonist; its action in humans has, however, never been tested so far. Aim of our study was to verify the antagonistic action of D-Lys-GHRP-6 on the endocrine responses to acylated ghrelin and hexarelin, a peptidyl synthetic GHS, in humans. The effects of different doses of D-Lys-GHRP-6 (2.0microg/kg iv as bolus or 2.0microg/kg/h iv as infusion) on both spontaneous and acylated ghrelin- or hexarelin (1.0microg/kg iv as bolus) -stimulated GH, PRL, ACTH and cortisol levels were studied in six normal volunteers (age [mean+/-SEM]: 25.4+/-1.2yr; BMI: 22.3+/-1.0kg/m(2)). The effects of D-Lys-GHRP-6 (2.0microg/kg iv as bolus+4.0microg/kg/h iv) on the GH response to 0.25microg/kg iv as bolus acylated ghrelin was also studied. During saline, spontaneous ACTH and cortisol decrease was observed while non changes occurred in GH and PRL levels. Acylated ghrelin and hexarelin stimulated (p<0.05) GH, PRL, ACTH and cortisol secretions. D-Lys-GHRP-6 administered either as bolus or a continuous infusion did not modify both spontaneous and acylated ghrelin- or hexarelin-stimulated GH, PRL, ACTH and cortisol secretion. D-Lys-GHRP-6 did not modify even the GH response to 0.25microg/kg iv acylated ghrelin. In conclusion, D-Lys-GHRP-6 does not affect the neuroendocrine response to both ghrelin and hexarelin. These findings question D-Lys-GHRP-6 as an effective GHS-R1a antagonist for human studies.

Other than Growth Hormone Neuroendocrine Actions of Ghrelin

Besides its growth hormone-releasing effect, ghrelin has been demonstrated to influence other hormonal systems, such as the hypothalamo-pituitary-adrenal axis, prolactin secretion, the thyroid axis as well as the gonadal axis. Ghrelin and its analogues stimulate the hypothalamo-pituitary-adrenal axis independent of the pituitary, via the hypothalamus, involving both corticotrophin-releasing hormone, arginine-vasopressin and neuropeptide Y stimulation. In adrenocortocotropic hormone (ACTH)-secreting tumors, the ghrelin receptor is pathologically expressed, thus accounting for especially high ACTH and cortisol responses to ghrelin and GH secretagogues in patients with Cushings disease. Ghrelin stimulates prolactin release most probably from the somatomammotroph cells of the pituitary gland. The effect of ghrelin on the pituitary regulation of the thyroid axis is controversial and its role in the physiological control of thyroid function is still matter of investigation. On the other hand, ghrelin has been reported to exert an inhibitory effect on follicle-stimulating hormone and, in particular, on luteinizing hormone, probably via an inhibitory effect exerted at the hypothalamic level on gonadotropin-releasing hormone secretion.

Circulating obestatin levels in normal and Type 2 diabetic subjects.

Background: Obestatin has been discovered as a new product of the ghrelin gene. Its physiological actions are still a matter of debate, but it seems that this peptide is likely to be involved in the control of insulin secretion and action as well as of adipocyte function. It has been already shown that obestatin secretion in humans is negatively modulated by food intake. Aim: To clarify obestatin secretion in normal subjects and in patients with Type 2 diabetes (T2D) in basal conditions and after a standardized meal. Subjects/methods: Five normal subjects and 5 T2D patients were studied during infusion of saline (iv for over 5 h from −120 to +180 min). A standardized lunch was served at 0 min. Obestatin, glucose, and insulin levels were assayed at −120, −90, −60, −45, −30, −15, 0, 15, 30, 45, 60, 90, 120, 150, and 180 min. Results: From −120 to 0 min, obestatin levels in normal and T2D subjects were similar (area under the curve: 32.3±5.6 pg/ml/min vs 31.1 ±1.0 pg/ml/min). After the meal, circulating obestatin levels underwent a clear decrease in normal subjects (0 min: 300.6±34.7 pg/ml vs nadir at 60 min: 161.8±29.4 pg/ml; p=0.002) but not in diabetic patients (0 min: 267.2±16.5 pg/ml vs nadir at 180 min: 226.0±10.5 pg/ml). Conclusion: This study shows that normal and diabetic subjects display similar levels of circulating obestatin in fasting condition. However patients with T2D look refractory to the inhibitory effect of meal on obestatin secretion.

Cortistatin-8, a synthetic cortistatin-derived ghrelin receptor ligand, does not modify the endocrine responses to acylated ghrelin or hexarelin in humans

Cortistatin (CST), a neuropeptide with high structural homology with somatostatin (SST), binds all SST receptor (SST-R) subtypes but, unlike SST, also shows high binding affinity to ghrelin receptor (GHS-R1a). CST exerts the same endocrine activities of SST in humans, suggesting that the activation of the SST-R might mask the potential interaction with ghrelin system. CST-8, a synthetic CST-analogue devoid of any binding affinity to SST-R but capable to bind the GHS-R1a, has been reported able to exert antagonistic effects on ghrelin actions either in vitro or in vivo in animals. We studied the effects of CST-8 (2.0 microg/kg i.v. as a bolus or 2.0 microg/kg/h i.v. as infusion) on both spontaneous and ghrelin- or hexarelin- (1.0 microg/kg i.v. as bolus) stimulated GH, PRL, ACTH and cortisol secretion in 6 normal volunteers. During saline, no change occurred in GH and PRL levels while a spontaneous ACTH and cortisol decrease was observed. As expected, both ghrelin and hexarelin stimulated GH, PRL, ACTH and cortisol secretion (p<0.05). CST-8, administered either as bolus or as continuous infusion, did not modify both spontaneous and ghrelin- or hexarelin-stimulated GH, PRL, ACTH and cortisol secretion. In conclusion, CST-8 seems devoid of any modulatory action on either spontaneous or ghrelin-stimulated somatotroph, lactotroph and corticotroph secretion in humans in vivo. These negative results do not per se exclude that, even at these doses, CST-8 might have some neuroendocrine effects after prolonged treatment or that, at higher doses, may be able to effectively antagonize ghrelin action in humans. However, these data strongly suggest that CST-8 is not a promising candidate as GHS-R1a antagonist for human studies to explore the functional interaction between ghrelin and cortistatin systems.

The metabolic response to the activation of the β- adrenergic receptor by salbutamol is amplified by acylated ghrelin

Background: It is well recognized that β-adrenergic receptors mediate important endocrine and metabolic actions. In fact, β-adrenergic receptor activation negatively influences GH secretion while exerting relevant metabolic actions such as the stimulation of insulin secretion, glycogenosis, and lipolysis. Aim: We have already shown that the activation of the GH secretagogue receptor (GHS-R)-1a by acylated ghrelin (AG) counteracts the inhibitory effect of salbutamol (SALB), a β2-adrenergic agonist, on GH release. The aim of the present study in humans was to clarify whether the metabolic response to SALB is affected by the infusion of AG, also known to exert significant metabolic actions. Methods: Six healthy young male volunteers underwent the following testing sessions in random order at least 5 days apart: a) SALB (0.06 μg/kg/min iv from 0 to 60 min) alone; b) SALB in combination with AG (1.0 μg/kg/min iv from −60 to 60 min); c) isotonic saline. Insulin, glucose, and free fatty acids (FFA) levels were evaluated every 15 min. Results: As expected, with respect to saline, SALB administration tended to increase both insulin secretion [Δ area under the curve (ΔAUC): 0.16±0.09 vs 0.003±0.077 × 103 μU/ml/min; p>0.05] and FFA levels (ΔAUC: 8.0±7.3 vs ∼-4.0±4.0 mEq/l/min; p>0.05), while glucose levels did not change. The metabolic response to SALB was significantly modified under the exposure of AG. In fact, under AG infusion, SALB elicited a more marked increase of FFA (ΔAUC: 22.3±3.2 vs 8.0±7.3 mEq/l/min; p<0.05) as well as a slight elevation in insulin (ΔAUC: 0.37±0.11 vs 0.16±0.09 × 103 μU/ml/min; p>0.05). Under AG, the baseline glucose levels were more elevated but, again, in combination with AG, SALB did not significantly modify glucose levels. Conclusions: β-adrenergic receptors and AG are likely to interact at the metabolic level. In humans, the lypolitic response to a β2-adrenergic agonist such as SALB is amplified by AG. Meanwhile, during the co-treatment, the marginal insulinotropic effect was not associated with an increase in glycemia.

The GH-releasing effect of acylated ghrelin in normal subjects is refractory to GH acute auto-feedback but is inhibited after short-term GH administration inducing IGF1 increase.

OBJECTIVE GH secretion is regulated by an interplay between GH-releasing hormone (GHRH), somatostatin (SST), and other central and peripheral signals. Acylated ghrelin (AG) amplifies GH pulsatility acting, at least partially, independently from GHRH and SST. The GH response to GHRH is inhibited by recombinant human GH (rhGH), likely due to a SST-mediated negative GH auto-feedback. The effect of exogenous rhGH on the GH-releasing effect of AG has never been tested. DESIGN AND METHODS In six healthy volunteers, we studied the GH response to acute AG administration (1.0 μg/kg i.v.) during saline or rhGH infusion (4.0 μg/kg per h i.v.) or after 4-day rhGH (10.0 μg/kg s.c.) administration. RESULTS Compared with saline, rhGH infusion increased GH levels (P<0.01). During saline, acute i.v. AG induced a marked increase (P<0.01) in GH levels similar to those observed after AG administration during rhGH infusion. During s.c. rhGH, IGF1 levels rose from day 0 to day 5 (P<0.01). After 4-day s.c. rhGH, i.v. AG increased (P<0.01) GH levels, though significantly (P<0.05) less than on day 0. CONCLUSIONS The marked somatotroph-releasing effect of AG is refractory to a direct GH auto-feedback whereas is markedly inhibited after 4-day rhGH administration, suggesting the possibility of a selective IGF1-mediated inhibitory feedback.

Beta‐adrenergic agonism does not impair the GH response to acylated ghrelin in humans

Background  Acylated ghrelin (AG) is a physiological GH secretion amplifier, in part stimulating GHRH neurones and antagonizing somatostatin activity. In humans, AG is one of the most potent pharmacological stimuli of GH secretion and, unlike GHRH, is refractory to the inhibitory effect of glucose, free fatty acids (FFA) and somatostatin. Somatotroph secretion is also profoundly modulated by the adrenergic system. Indeed, beta‐adrenergic agonists abolish spontaneous and GHRH‐stimulated GH secretion. Based on these data, the aim of the present study was to investigate the effects of beta adrenergic agonism on the GH response to AG.

Disturbi del sonno e sindrome metabolica: quali relazioni eziopatogenetiche?

RiassuntoNelle ultime decadi si è assistito a un incremento dell’incidenza dei disturbi quali-quantitativi del sonno. Parallelamente è aumentata l’incidenza della sindrome metabolica. Quest’ultimo fenomeno è certamente imputabile in primo luogo a fattori ambientali (iper-alimentazione e sedentarietà) ma numerose evidenze epidemiologiche e sperimentali suggeriscono che i disturbi del sonno possano agire come concausa. Del resto un sonno quantitativamente e qualitativamente adeguato è fondamentale per il mantenimento di un ottimale metabolismo glicidico, dell’integrità dei meccanismi di regolazione dell’appetito e di un normale pattern pressorio. La consapevolezza di una possibile associazione tra i disturbi del sonno e le diverse componenti della sindrome metabolica offre importanti spunti nel campo della prevenzione e del trattamento di queste ultime.