Ghrelin and glucose homeostasis

Ghrelin plays an important physiological role in modulating GH secretion, insulin secretion and glucose metabolism. Ghrelin has direct effects on pancreatic islet function. Also, ghrelin is part of a mechanism that integrates the physiological response to fasting. However, pharmacologic studies indicate the important obesogenic/diabetogenic properties of ghrelin. This is very likely of physiological relevance, deriving from a requirement to protect against seasonal periods of food scarcity by building energy reserves, predominantly in the form of fat. Available data indicate the potential of ghrelin blockade as a means to prevent its diabetogenic effects. Several studies indicate a negative correlation between ghrelin levels and the incidence of type 2 diabetes and insulin resistance. However, it is unclear if low ghrelin levels are a risk factor or a compensatory response. Direct antagonism of the receptor does not always have the desired effects, however, since it can cause increased body weight gain. Pharmacological suppression of the ghrelin/des-acyl ghrelin ratio by treatment with des-acyl ghrelin may also be a viable alternative approach which appears to improve insulin sensitivity. A promising recently developed approach appears to be through the blockade of GOAT activity, although the longer term effects of this treatment remain to be investigated.

Conversion of daily pegvisomant to weekly pegvisomant combined with long-acting somatostatin analogs, in controlled acromegaly patients

The efficacy of combined treatment in active acromegaly with both long-acting somatostatin analogs (SRIF) and pegvisomant (PEG-V) has been well established. The aim was to describe the PEG-V dose reductions after the conversion from daily PEG-V to combination treatment. To clarify the individual beneficial and adverse effects, in two acromegaly patients, who only normalized their insulin like growth factor (IGF-I) levels with high-dose pegvisomant therapy. We present two cases of a 31 and 44 years old male with gigantism and acromegaly that were controlled subsequently by surgery, radiotherapy, SRIF analogs and daily PEG-V treatment. They were converted to combined treatment of monthly SSA and (twice) weekly PEG-V. High dose SSA treatment was added while the PEG-V dose was decreased during carful monitoring of the IGF-I. After switching from PEG-V monotherapy to SRIF analogs plus pegvisomant combination therapy IGF-I remained normal. However, the necessary PEG-V dose, to normalize IGF-I differed significantly between these two patients. One patient needed twice weekly 100 mg, the second needed 60 mg once weekly on top of their monthly lanreotide Autosolution injections of 120 mg. The weekly dose reduction was 80 and 150 mg. After the introducing of lanreotide, fasting glucose and glycosylated haemoglobin concentrations increased. Diabetic medication had to be introduced or increased. No changes in liver tests or in pituitary adenoma size were observed. In these two patients, PEG-V in combination with long-acting SRIF analogs was as effective as PEG-V monotherapy in normalizing IGF-I levels, although significant dose-reductions in PEG-V could be achieved. However, there seems to be a wide variation in the reduction of PEG-V dose, which can be obtained after conversion to combined treatment.

Combination treatment with somatostatin analogues and pegvisomant in acromegaly

Mono-therapy using long-acting somatostatin analogues and surgery cannot provide optimal biochemical control in a large proportion of patients with acromegaly. This results in increased mortality, poor control of signs and symptoms of disease and decreased quality of life. Combined treatment with somatostatin analogues and pegvisomant (a growth-hormone-receptor antagonist) seems to be an attractive option. Combination treatment is highly effective at normalising the level of insulin-like growth factor 1 in over 90% of patients and has a favourable effect on quality of life in those with biochemically controlled acromegaly. Moreover, combination therapy with somatostatin analogues results in a clinically relevant decrease in tumour size in about 20% of patients, whereas pegvisomant (PEG-V) mono-therapy does not decrease pituitary tumour size. Transient elevations in the levels of transaminases are the main adverse effects of combination treatment, which occur in about 11-15% of patients.

Acute effects of acylated and unacylated ghrelin on total and high molecular weight adiponectin inmorbidly obese subjects

BACKGROUND

Energy homeostasis and body weight are regulated by a highly complex network involving the brain, the digestive tract, and white adipose tissue (WAT). Knowledge about signaling pathways connecting digestive tract and WAT is limited. Gut hormone ghrelin and adipokine adiponectin are both decreased in obesity and they share a potent effect on insulin sensitivity: both adiponectin and the combination of acylated (AG) and unacylated ghrelin (UAG) improve insulin sensitivity.

AIM

In the present study, we evaluated whether acute administration of UAG alone or combined with AG affects adiponectin concentrations.

SUBJECTS AND METHODS

Eight morbidly obese non-diabetic subjects were treated with either UAG 200 μg, UAG 100 μg + AG 100 μg (Comb), or placebo in 3 episodes in a double blind randomized cross-over design. Study medication was administered as single iv bolus injections at 09:00 h after an overnight fast. High molecular weight (HMW) and total adiponectin, glucose, insulin, and total ghrelin and AG were measured up to 1 h after administration.

RESULTS

HMW and total adiponectin concentrations did not change after administration of either UAG or Comb, nor were they different from placebo. Insulin concentrations decreased significantly after acute administration of Comb, reaching a minimum at 20 min: 58.2 ± 3.9% of baseline.

CONCLUSIONS

Acute iv administration of UAG and the combination of UAG and AG in morbidly obese non-diabetic subjects without overt diabetes does not affect total or HMW adiponectin concentrations, neither directly nor indirectly by changing insulin concentrations.

Unsaturated fatty acids prevent desensitization of the human growth hormone secretagogue receptor by blocking its internalization

The composition of the plasma membrane affects the responsiveness of cells to metabolically important hormones such as insulin and vasoactive intestinal peptide. Ghrelin is a metabolically regulated hormone that activates the G protein-coupled receptor GH secretagogue receptor type 1a (GHSR) not only in the pituitary gland but also in peripheral tissues such as the pancreas, stomach, and T cells in the circulation. We have investigated the effects of lipids and altered plasma membrane composition on GHSR activation. Oligounsaturated fatty acids (OFAs) disrupt the structure of membranes and make them more fluid. Prolonged (96 h), but not acute, treatment of the GHSR cells with the 18C OFAs oleic and linoleic acid caused a significant increase in sensitivity of the receptor to ghrelin (EC(50) reduced by a factor of 2.4 and 2.9 at 60 and 120 microM OFAs, respectively). OFAs were found to block the inhibitory effects of ghrelin pretreatment on subsequent ghrelin responsiveness, suggesting that OFAs suppress desensitization of GHSR. Radioligand displacement studies did not show a significant shift in receptor binding after incubation with OFAs. However, it was found that OFA treatment suppressed GHSR internalization, likely explaining OFA-induced refractoriness to ligand-induced desensitization. The involvement of lipid rafts in this process was indicated by the altered responsiveness of GHSR under conditions that alter membrane cholesterol. In conclusion, our findings demonstrate the importance of membrane composition for GHSR activation and desensitization and indicate at least part of the mechanism through which OFAs and cholesterol could affect ghrelin's activity in vivo.

Biochemical predictors of outcome of pituitary surgery for Cushing's disease

OBJECTIVE

Transsphenoidal surgery (TS) is the primary therapy for Cushing's disease (CD). The aims of this retrospective study were twofold: (i) investigate early and late results of TS for CD, and (ii) evaluate various postoperative tests in order to predict the outcome of TS.

METHODS

We reviewed the long-term outcome in 79 patients with CD who underwent TS (median follow-up 84 months, range 6-197). Within 2 weeks after surgery, morning serum cortisol concentrations were obtained (n = 78) and corticotropin-releasing hormone (CRH) (n = 53) and metyrapone tests (n = 72) were performed. Three groups of outcome were identified: sustained remission, early failure (persistent CD), and late relapse.

RESULTS

Immediate postoperative remission was achieved in 51 patients (65%), whereas 28 patients (35%) had persistent CD after TS. Ten patients developed recurrent CD after initial remission (20%). Morning cortisol: all relapses but one recorded serum cortisol >50 nmol/l. A cortisol threshold value of 200 nmol/l has a positive predictive value of 79% for immediate surgical failure (negative predictive failure [NPV] 97%). CRH test: CRH-stimulated peak cortisol > or =600 nmol/l predicted early failure in 78% (NPV 100%). All relapses recorded CRH-stimulated peak cortisol >or =485 nmol/l. Metyrapone test: 11-deoxycortisol >or =345 nmol/l predicted an early failure in 86% of cases (NPV 94%).

CONCLUSION

Predictive factors of surgical failure are morning cortisol >or =200 nmol/l, 11-deoxycortisol >or =345 nmol/l after metyrapone and CRH-stimulated cortisol >or =600 nmol/l. CRH and/or metyrapone testing are not superior to morning cortisol concentration in the prediction of outcome of TS. Careful long-term follow-up remains necessary independent of the outcome of biochemical testing.

Combined treatment for acromegaly with long-acting somatostatin analogs and pegvisomant: long-term safety for up to 4.5 years (median 2.2 years) of follow-up in 86 patients

BACKGROUND

We previously reported on the efficacy, safety, and quality of life (QoL) of long-acting somatostatin analogs (SSA) and (twice) weekly pegvisomant (PEG-V) in acromegaly and improvement after the addition of PEG-V to long-acting SSA.

OBJECTIVE

To assess the long-term safety in a larger group of acromegalic patients over a larger period of time: 29.2 (1.2-57.4) months (mean (range)).

DESIGN

Pegvisomant was added to SSA monotherapy in 86 subjects (37 females), to normalize serum IGF1 concentrations (n=63) or to increase the QoL. The median dosage was 60.0 (20-200) mg weekly.

RESULTS

After a mean treatment period of 29.2 months, 23 patients showed dose-independent PEG-V related transient liver enzyme elevations (TLEE). TLEE occurred only once during the continuation of combination therapy, but discontinuation and re-challenge induced a second episode of TLEE. Ten of these patients with TLEE also suffered from diabetes mellitus (DM). In our present series, DM had a 2.28 odds ratio (CI 1.16-9.22; p=0.03) higher risk for developing TLEE. During the combined therapy, a clinical significant decrease in tumor size by more than 20% was observed in 14 patients. Two of these patients were previously treated by pituitary surgery, 1 with additional radiotherapy and all other patients received primary medical treatment.

CONCLUSION

Long-term combined treatment with SSA and twice weekly PEG-V up to more than 4 years seems to be safe. Patients with both acromegaly and DM have a 2.28 higher risk of developing TLEE. Clinical significant tumor shrinkage was observed in 14 patients during combined treatment.

Effects of somatostatin analogs on a growth hormone-releasing hormone secreting bronchial carcinoid, in vivo and in vitro studies

CONTEXT

A 56-yr-old woman presented with acromegaly, a pulmonary mass, and elevated levels of GHRH, GH, and IGF-I. Histological examination revealed a bronchial carcinoid with positive staining for GHRH. Somatostatin analogs (SAs) can play an important role in the treatment of neuroendocrine tumors, dependent on the somatostatin receptor subtype (sst) expression pattern. The sst pattern in bronchial carcinoids and effects of SAs have not been extensively investigated, particularly not for the recently developed universal SA SOM230 (Pasireotide) that has high affinity for sst1, 2, 3, and 5.

OBJECTIVE

Our objective was to investigate the in vivo response of a GHRH-producing bronchial carcinoid to octreotide (OCT), its sst-expression profile, and in vitro responses to different SAs, including SOM230.

METHODS

In vivo, 50 microg OCT was administered, and plasma GH and GHRH responses were determined. In vitro, the expression of ssts was analyzed by quantitative PCR. Furthermore, the effects of SOM230 and OCT on GHRH secretion were evaluated in primary cell cultures of the carcinoid tissue.

RESULTS

In vivo, OCT administration fully suppressed GH and GHRH levels. In vitro, sst1 mRNA was most abundant, followed by sst2 and sst5. Both SOM230 and OCT inhibited GHRH production dose dependently (SOM230 100 nm vs. control, P = 0.01; OCT 110 nm vs. control, P = 0.05).

CONCLUSIONS

In this case of a GHRH-producing bronchial carcinoid, we demonstrated that SOM230 was a potent inhibitor of GHRH production in vitro and was at least equally potent compared with OCT. Therefore, SOM230 may be a potential therapeutic agent to control GHRH secretion in ectopic acromegaly.

Cushing's syndrome due to ectopic ACTH production by (neuroendocrine) prostate carcinoma

Ectopic adrenocorticotropin (ACTH) secretion accounts for less than 10% of all causes of endogenous Cushing's syndrome (CS) and is usually associated with neuroendocrine tumors and small cell carcinoma of the lung. We report the case of a 62-year-old man with CS due to ectopic ACTH production by small cell carcinoma of the prostate. He presented with severe hypercortisolism and associated symptoms. Plasma neuron specific enolase (NSE) was grossly elevated. Despite performing a laparoscopic bilateral adrenalectomy, the patient died as a result of sepsis with multi-organ failure. Post-mortem immunohistochemical staining of prostate tumor tissue showed ACTH expression. ACTH staining was also performed in four additional patients with small cell carcinoma of the urinary tract without CS. None of these additional cases showed a positive staining for ACTH. Although a rare cause of ectopic ACTH production, neuroendocrine prostate carcinoma should be considered in male patients with Cushing's syndrome, in particular in those with an occult source of ACTH overproduction.

Quality of life in acromegalic patients during long-term somatostatin analog treatment with and without pegvisomant

OBJECTIVE

The objective of the study was to assess whether weekly administration of 40 mg pegvisomant (PEG-V) improves quality of life (QoL) and metabolic parameters in acromegalic patients with normal age-adjusted IGF-I concentrations during long-acting somatostatin analog (SSA) treatment.

DESIGN

This was a prospective, investigator-initiated, double blind, placebo-controlled, crossover study. Twenty acromegalic subjects received either PEG-V or placebo for two consecutive treatment periods of 16 wk, separated by a washout period of 4 wk. Efficacy was assessed as change between baseline and end of each treatment period. QoL was assessed by the Acromegaly Quality of Life Questionnaire (AcroQoL) and the Patient-Assessed Acromegaly Symptom Questionnaire (PASQ).

RESULTS

The AcroQoL (P = 0.008) and AcroQoL physical (P = 0.002) improved significantly after PEG-V was added. The addition of PEG-V also significantly improved the PASQ (P = 0.038) and the single PASQ questions, perspiration (P = 0.024), soft tissue swelling (P = 0.036), and overall health status (P = 0.035). No significant change in Z-score of IGF-I (P = 0.34) was observed during addition of PEG-V. Transient liver enzyme elevations were observed in five subjects (25%).

CONCLUSION

Improvement in quality of life was observed without significant change in IGF-I after the addition of 40 mg pegvisomant weekly to monthly SSA therapy in acromegalic patients who had normalized IGF-I on SSA monotherapy. These data question the current recommendations in how to assess disease activity in acromegaly. Moreover, the findings question the validity of the current approach of medical treatment in which pegvisomant is used only when SSA therapy has failed to normalize IGF-I.

The continuous infusion of acylated ghrelin enhances growth hormone secretion and worsens glucose metabolism in humans

CONTEXT

Acylated ghrelin (AG) has been discovered as a natural ligand of the GH secretagogue receptor type 1a and is now recognized as an important orexigenic factor. Besides stimulation of GH secretion and appetite, it exerts other central and peripheral actions including modulation of insulin secretion, glucose and lipid metabolism.

OBJECTIVE

To define the effects of the continuous iv infusion of AG in humans with particular attention to metabolic parameters.

MATERIALS AND METHODS

We studied the effects of 16- h (from 21:00 to 13:00 h) infusion of AG (0.5 microg/kg/h) or saline in 8 young volunteers who were provided with isocaloric balanced meals. GH, cortisol, insulin, glucose, free fatty acid (FFA), and ghrelin levels were assayed every 20 min.

RESULTS

AG infusion increased circulating total ghrelin to a steady state that was maintained over 16 h infusion of the peptide. With respect to saline, AG infusion significantly modified GH, cortisol, insulin, and glucose profiles and decreased FFA area under the curve (p<0.01). AG increased GH pulse frequency and approximate entropy (p<0.05). AG enhanced the glucose response to both dinner (p<0.02) and breakfast (p<0.03). AG infusion blunted the early insulin response to dinner (p<0.03) but enhanced the second-phase insulin response to dinner and breakfast (p<0.05).

CONCLUSIONS

The continuous exposure to AG in humans enhances somatotroph secretion but also worsens glucose metabolism, although it inhibits lipolysis. These findings in normal young volunteers are consistent with data from studies in animals and suggest that acylated ghrelin is likely to play a negative role in glucose metabolism.

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.

Somatostatin receptors: clinical implications for endocrinology and oncology

Somatostatin receptors are present on most hormone-secreting tumours. They are the pathophysiological basis for the successful control of hormonal hypersecretion by pituitary adenomas, metastatic islet cell tumours and carcinoids during treatment with the long-acting somatostatin analogue octreotide. There is also evidence for inhibition of tumour growth in some of these patients. Visualization of somatostatin receptor-positive tumours is possible in vivo after the administration of ([111In]diethylenetriaminepentaacetic acid)octreotide. Primary tumours are detected and often metastases that were previously unrecognized. Tumours that secrete growth hormone or thyroid-stimulating hormone and non-functioning pituitary adenomas, islet cell tumours, carcinoids, paragangliomas, phaeochromocytomas, medullary thyroid carcinomas and small-cell lung cancers are visualized in 70-100% of cases. Meningiomas, renal cell cancers, breast cancers and malignant lymphomas are often somatostatin receptor positive, allowing their localization with this scanning procedure. In some of these tumours discrepancies have been noted between binding studies with somatostatin-14, somatostatin-28 and octreotide, which suggests the presence of somatostatin receptor subtypes on some tumours. Most hormone-secreting tumours react in vitro to octreotide with an inhibition of hormone release and growth. Cultured meningioma cells react to octreotide with a stimulation in growth, possibly by interference with the autocrine inhibitory growth control by interleukin 6. This suggests that the presence of somatostatin receptors on human tumours does not automatically imply a beneficial effect of somatostatin analogue therapy.

Unacylated ghrelin is not a functional antagonist but a full agonist of the type 1a growth hormone secretagogue receptor (GHS-R)

Recent findings demonstrate that the effects of ghrelin can be abrogated by co-administered unacylated ghrelin (UAG). Since the general consensus is that UAG does not interact with the type 1a growth hormone secretagogue receptor (GHS-R), a possible mechanism of action for this antagonistic effect is via another receptor. However, functional antagonism of the GHS-R by UAG has not been explored extensively. In this study we used human GHS-R and aequorin expressing CHO-K1 cells to measure [Ca(2+)](i) following treatment with UAG. UAG at up to 10(-5)M did not antagonize ghrelin induced [Ca(2+)](i). However, UAG was found to be a full agonist of the GHS-R with an EC(50) of between 1.6 and 2 microM using this in vitro system. Correspondingly, UAG displaced radio-labeled ghrelin from the GHS-R with an IC(50) of 13 microM. In addition, GHS-R antagonists were found to block UAG induced [Ca(2+)](i) with approximately similar potency to their effect on ghrelin activation of the GHS-R, suggesting a similar mode of action. These findings demonstrate in a defined system that UAG does not antagonize activation of the GHS-R by ghrelin. But our findings also emphasize the importance of assessing the concentration of UAG used in both in vitro and in vivo experimental systems that are aimed at examining GHS-R independent effects. Where local concentrations of UAG may reach the high nanomolar to micromolar range, assignment of GHS-R independent effects should be made with caution.

Ghrelin and its unacylated isoform stimulate the growth of adrenocortical tumor cells via an anti-apoptotic pathway

Ghrelin is expressed in normal human adrenocortical cells and induces their proliferation through growth hormone secretagogue receptor 1a (GHS-R1a). Consequently, it was of interest to us to determine whether acylated ghrelin and its predominant serum isoform, unacylated ghrelin, also act as factors for adrenocortical carcinoma cell growth. To examine a potential ghrelin-regulated system in adrenocortical tumors, we measured proliferative effects of acylated and unacylated ghrelin in the adrenocortical carcinoma cell lines SW-13 and NCI-H295R. We also examined the expression of ghrelin, GHS-R1a, and corticotrophin-releasing factor receptor 2 (CRF-R2). Acylated and unacylated ghrelin in the nanomolar range dose-dependently induced adrenocortical cell growth up to 200% of untreated controls, as measured by thymidine uptake and WST1 assay. The proliferative effects of acylated and unacylated ghrelin in SW-13 cells was blocked by [D-Lys(3)]growth hormone-releasing peptide 6 (GHRP6), but a CRF-R2 antagonist had no effect on unacylated ghrelin growth stimulation. Cell cycle analysis suggests that acylated and unacylated ghrelin suppress the sub-G(0)/apoptotic fraction by up to 50%. Measurement of DNA fragmentation and caspase-3 and -7 activity in SW-13 cells confirmed that acylated and unacylated ghrelin suppress apoptotic rate. SW-13 cells express preproghrelin mRNA and secrete ghrelin, and [D-Lys(3)]GHRP6 suppresses their basal proliferation rate, strongly suggesting that ghrelin could act as an auto/paracrine growth factor. Acylated and unacylated ghrelin are potential auto/paracrine factors acting through an antiapoptotic pathway to stimulate adrenocortical tumor cell growth. Unacylated ghrelin-stimulated growth is suppressed by an antagonist of GHS-R1a, suggesting either that unacylated ghrelin is acylated before its action or that ghrelin, unacylated ghrelin, and [D-Lys(3)]GHRP-6 bind to a novel receptor in these cells.

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.

[Cushing's syndrome. II. New forms of treatment]

Several new therapeutic options both medicinal and surgical, have emerged for the treatment of Cushing's syndrome. In Cushing's disease caused by an adrenocorticotropin (ACTH) secreting pituitary adenoma, the introduction ofendoscopic pituitary surgery offers better visualization of the sella than does the traditional explorative surgery. However, at present it is unclear whether this will result in a better outcome. New drugs under investigation include universal somatostatin analogues such as SOM230, and a combination of a somatostatin analogue and dopamine agonist known as dopastatin. These agents may also be effective for the medicinal treatment of ectopic ACTH-secretion. Treatment with radioactive-labelled somatostatin-analogues such as 177lutetium octreotate is another option for these patients. The primary treatment for ACTH-independent Cushing's syndrome is laparoscopic adrenalectomy. In rare cases of bilateral adrenal hyperplasia, medicinal treatment aimed at new regulatory pathways of cortisol secretion can be applied.

Chronic inflammation in psoriasis and obesity: implications for therapy

A recent study has shown an indisputable relationship between psoriasis and obesity. Obesity leads to a higher risk in developing psoriasis and a poorer long-term clinical outcome of psoriasis. Furthermore, loosing weight may improve the psoriasis. A network of pro-inflammatory cytokines (especially tumour necrosis factor alpha (TNF-alpha)) is believed to play an important role in the pathophysiology of both obesity and psoriasis. The chronic low-level inflammation- as seen in obesity--may contribute to the extent of psoriatic lesions in obese patients. TNF-alpha in obesity is presumed to be derived from inflammatory cells (macrophages) in the adipose tissue and in psoriasis from activated T cells. Several drugs, such as peroxisome proliferator activated receptor (PPAR)-gamma agonists and TNF-alpha blocking agents, that target the pro-inflammatory pathways involved in both psoriasis and obesity have proven their benefit in the treatment of these entities. Furthermore, changes in levels of metabolic hormones as ghrelin and leptin in obesity may also play a role in the pathogenesis of deterioration of psoriasis by their potency to release pro-inflammatory mediators (e.g. interleukin (IL) 6 and TNF-alpha). We hypothesize that the treatment of obese psoriasis patient could be focused on reducing the obesity-induced inflammation. Reducing this obesity-induced inflammation may finally lead to a better clinical outcome. Weight loss could lead to a less inflammatory state by reducing concentrations of TNF-alpha, IL-6, leptin and improving insulin sensitivity.

Drug-induced hepatitis in an acromegalic patient during combined treatment with pegvisomant and octreotide long-acting repeatable attributed to the use of pegvisomant

We report on a patient with acromegaly who developed severe drug-induced hepatitis during combined treatment with the long-acting somatostatin-analog octreotide and the GH receptor antagonist pegvisomant. The hepatic enzyme disturbances normalized after discontinuation of pegvisomant. After rechallenge with monotherapy pegvisomant, however, the hepatic enzyme disturbances reappeared within a few weeks, indicating that most likely pegvisomant alone and not the long-acting somatostatin analog or the combination of these two drugs was responsible for this case of drug-induced hepatitis. Clinicians should be aware of this potential severe adverse drug reaction and therefore frequent control of hepatic enzymes is mandatory during treatment with pegvisomant.

Growth hormone receptor antagonists

The currently available long-acting somatostatin analogs normalize serum growth hormone (GH) levels and insulin-like growth factor-I levels in approximately 60% of patients with acromegaly. The recently introduced GH receptor antagonist, pegvisomant, is able to normalize insulin-like growth factor-I levels in virtually all acromegalic subjects. Although no correlation between increased GH concentrations and tumor size has been found, long-term safety studies are still in progress. Also, pegvisomant monotherapy is administered once daily and is very costly. Combined treatment of a somatostatin analog with pegvisomant appears to be an effective and rational approach.

Ghrelin and unacylated ghrelin stimulate human osteoblast growth via mitogen-activated protein kinase (MAPK)/phosphoinositide 3-kinase (PI3K) pathways in the absence of GHS-R1a

Recent studies demonstrate widespread expression of ghrelin among tissues and have uncovered its pleiotropic nature. We have examined gene expression of ghrelin and its two receptor splice variants, growth hormone secretagogue receptors (GHS-R) 1a and 1b, in human bone biopsies and in the human pre-osteoblastic SV-HFO cell line during differentiation. Additionally, we examined proliferative effects of ghrelin and unacylated ghrelin (UAG) in differentiating and non-differentiating cells. We detected GHS-R1b mRNA in human bone and osteoblasts but not ghrelin's cognate receptor GHS-R1a, using two different real-time PCR assays and both total RNA and mRNA. In osteoblasts GHS-R1b mRNA expression remained low during the first 14 days of culture, but increased 300% in differentiating cells by day 21. Both human bone biopsies and osteoblasts expressed ghrelin mRNA, and osteoblasts were found to secrete ghrelin. Overall, ghrelin gene expression was greater in differentiating than non-differentiating osteoblasts, but was not increased during culture in either group. Ghrelin and UAG induced thymidine uptake dose-dependently, peaking at 1 and 10 nM respectively, at day 6 of culture in both non-differentiating and differentiating osteoblasts. The proliferative response to ghrelin and UAG declined with culture time and state of differentiation. The proliferative effects of ghrelin and UAG were suppressed by inhibitors of extracellular-signal-regulated kinase (ERK) and phosphoinositide-3 kinase, and both peptides rapidly induced ERK phosphorylation. Overall, our data suggest new roles for ghrelin and UAG in modulating human osteoblast proliferation via a novel signal transduction pathway.

Postoperative evaluation of patients with acromegaly: clinical significance and timing of oral glucose tolerance testing and measurement of (free) insulin-like growth factor I, acid-labile subunit, and growth hormone-binding protein levels

CONTEXT

It is not exactly known when patients with acromegaly should be evaluated for cure after transsphenoidal adenomectomy (TA).

OBJECTIVE

The objective of this study was to define the optimal time point of postoperative evaluation by serial measurements of glucose-suppressed GH levels [oral glucose tolerance test (OGTT)] and the GH-dependent parameters IGF-I, free IGF-I, acid labile subunit (ALS), and GH-binding protein (GHBP).

DESIGN

We describe a prospective study with 1-yr follow-up.

SETTING

The study was conducted at a university hospital.

PATIENTS

Seventeen patients with acromegaly were included in the study.

MAIN OUTCOME MEASURES

The main outcome measures were OGTT results at 1, 2, 3, 8, and 12 wk after TA; weekly measured GH, (free) IGF-I, ALS, and GHBP levels up to 12 wk; and total IGF-I levels measured at 52 wk.

RESULTS

Postoperatively, nine patients were in remission with an OGTT GH nadir of less than 0.5 microg/liter and normalized IGF-I levels, whereas eight patients had persistent acromegaly. In both cured and noncured patients, OGTT results at 1 wk after TA were highly reproducible over time. In contrast, early postoperative IGF-I levels fluctuated and only stabilized at 12 wk. In all cured patients, free IGF-I levels rapidly normalized within 2 wk after TA (specificity, 100%). Preoperative ALS levels were elevated in all patients and normalized only in the cured patients after TA (specificity, 89%). Preoperative GHBP levels were low and increased from 2 wk after surgery.

CONCLUSIONS

We show that in the postoperative evaluation of patients with acromegaly, already 1 wk after surgery, an OGTT using 0.5 microg as the GH nadir cutoff value has a high predictive value for cure, whereas early IGF-I levels show varying patterns toward stabilization. Therefore, IGF-I should be measured as a predictive parameter not within 3 months after surgery. Free IGF-I and ALS levels may have an additional value in the postoperative assessment of disease activity.

Combined therapy with somatostatin analogues and weekly pegvisomant in active acromegaly

Pegvisomant monotherapy once daily returns concentrations of insulin-like growth factor I (IGF-I) to normal in most patients with acromegaly, but is very costly. In a 42-week dose-finding study, we assessed the efficacy of the combination of long-acting somatostatin analogues once monthly and pegvisomant once weekly in 26 patients with active acromegaly. Dose of pegvisomant was increased until IGF-I concentration became normal or until a weekly dose of 80 mg was reached. IGF-I reached normal concentrations in 18 of 19 (95%) patients who completed 42 weeks of treatment, with a median weekly dose of 60 mg pegvisomant (range 40-80). No signs of pituitary tumour growth were noted, but mild increases in liver enzymes were observed in ten patients (38%). This combined treatment is effective, might increase compliance, and could greatly reduce the costs of medical treatment for acromegaly in some patients.

Ghrelin: a link between eating disorders, obesity and reproduction

Ghrelin, a 28-amino acid acylated peptide predominantly produced by the stomach, displays strong GH-releasing activity mediated by the hypothalamic-pituitary GH secretagogues (GHS) receptors (GHS-R) which had been shown specific for a family of synthetic, orally active molecules known as GHS. However, ghrelin and GHS, acting on central and peripheral receptors, also exert other actions. These include influence on pituitary functions, orexigenic action, influence on exocrine and endocrine gastro-entero-pancreatic functions, cardiovascular and anti-proliferative effects. In particular, the effect of ghrelin in promoting food intake and modulating energy metabolism strongly suggested that ghrelin has a key role in managing the neuroendocrine and metabolic response to starvation and that could be involved in the pathogenesis and/or in the metabolic and neuro-hormonal alterations of obesity and eating disorders. Although specific alterations in ghrelin secretion and/or action in obesity and anorexia nervosa (AN) have already been reported, the possibility that ghrelin analogues acting as agonists or antagonists has clinical perspectives for treatment of eating disorders presently remains a dream.