Inhibition Of Growth Hormone Secretion Research Articles

Acromegaly in humans and cats: Pathophysiological, clinical and management resemblances and differences

ObjectiveAcromegaly is a disorder associated with excessive levels of growth hormone (GH) and insulin-like growth factor-1 (IGF-1). In general, GH/IGF-1 excess leads to morphologic craniofacial and acral changes as well as cardiometabolic complications, but the phenotypic changes and clinical presentation of acromegaly differ across species. Here, we review the pathophysiology, clinical presentation and management of acromegaly in humans and cats, and we provide a systematic comparison between this disease across these different species. DesignA comprehensive literature review of pathophysiology, clinical features, diagnosis and management of acromegaly in humans and in cats was performed. ResultsAcromegaly is associated with prominent craniofacial changes in both species: frontal bossing, enlarged nose, ears and lips, and protuberant cheekbones are typically encountered in humans, whereas increased width of the head and skull enlargement are commonly found in cats. Malocclusion, prognathism, dental diastema and upper airway obstruction by soft tissue enlargement are reported in both species, as well as continuous growth and widening of extremities resulting in osteoarticular compromise. Increase of articular joint cartilage thickness, vertebral fractures and spine malalignment is more evident in humans, while arthropathy and spondylosis deformans may also occur in cats. Generalized organomegaly is equally observed in both species. Other similarities between humans and cats with acromegaly include heart failure, ventricular hypertrophy, diabetes mellitus, and an overall increased cardiometabolic risk. In GH-secreting pituitary tumours, local compressive effects and behavioral changes are mostly observed in humans, but also present in cats. Cutis verticis gyrata and skin tags are exclusively found in humans, while palmigrade/plantigrade stance may occur in some acromegalic cats.Serum IGF-1 is used for acromegaly diagnosis in both species, but an oral glucose tolerance test with GH measurement is only useful in humans, as glucose load does not inhibit GH secretion in cats. Imaging studies are regularly performed in both species after biochemical diagnosis of acromegaly. Hypophysectomy is the first line treatment for humans and cats, although not always available in veterinary medicine. ConclusionAcromegaly in humans and cats has substantial similarities, as a result of common pathophysiological mechanisms, however species-specific features may be found.

Clinical Pharmacology of Oral Octreotide Capsules for the Treatment of Acromegaly.

The primary goal of acromegaly treatment is to normalize biochemical parameters as it significantly reduces the risks of complications and comorbidities associated with the disease. First-line medical treatment is commonly represented by injectable somatostatin analogues (SRLs) after surgery. In June 2020, with the integration of Transient Permeation Enhancer® technology, oral octreotide capsules (OOCs) received regulatory approval from the US Food and Drug Administration for long-term maintenance treatment in patients with acromegaly who have responded to and tolerated treatment with octreotide or lanreotide. We reviewed the clinical pharmacological data on the development and clinical use of OOCs. The pharmacokinetic and pharmacodynamic data on OOCs showed a dose-dependent increase in octreotide levels and remarkable suppression of growth hormone secretion. The efficacy and safety of OOCs were investigated in four clinical trials conducted on patients with complete or partially controlled acromegaly. The trials resulted in the maintenance of biochemical control after switching from injectable SRLs to OOCs, with a comparable side-effect profile. Moreover, the acromegaly symptoms improved in patients on OOC. The data showed a patient preference to continue in the OOC arm for the extension phase of the trials. From the clinical pharmacological perspective, oral formulation of octreotide has the advantage of efficacy and safety with respect to injectable octreotide.

Dorsomedial Ventromedial Hypothalamic Nucleus Growth Hormone-Releasing Hormone Neuron Steroidogenic Factor-1 Gene Targets in Female Rat.

The prospect that the ventromedial hypothalamic nucleus (VMN) transcription factor steroidogenic factor-1/NR5A1 (SF-1) may exert sex-dimorphic control of glucose counterregulation is unresolved. Recent studies in male rats show that SF-1 regulates transcription of co-expressed hypoglycemia-sensitive neurochemicals in dorsomedial VMN growth hormone-releasing hormone (Ghrh) neurons. Gene knockdown and laser-catapult-microdissection/single-cell multiplex qPCR techniques were used here in a female rat model to determine if SF-1 control of Ghrh neuron transmitter marker, energy sensor, and estrogen receptor (ER) variant mRNAs varies according to sex. Data show that in females, hypoglycemia elicits a gain of SF-1 inhibitory control of VMNdm Ghrh neuron Ghrh and Ghrh-receptor gene profiles and loss of augmentation of glutaminase transcription; SF-1 gene silencing diminished eu- and hypoglycemic patterns of neuronal nitric oxide gene transcription. SF-1 imposes divergent control of baseline and hypoglycemic glutamate decarboxylase65 (GAD)-1 (stimulatory) versus GAD2 (inhibitory) mRNAs in that sex. SF-1 stimulates baseline VMNdm Ghrh neuron PRKAA1/AMPKα1 and PRKAA2/AMPKα2 gene expression, yet causes opposite changes in these gene profiles during hypoglycemia. SF-1 exerts glucose-dependent control of ER-alpha and G-protein-coupled ER-1 transcription, but blunts ER-beta gene profiles during eu- and hypoglycemia. In females, SF-1 knockdown did not affect hypercorticosteronemia or hyperglucagonemia, but blunted hypoglycemic suppression of growth hormone secretion. Results show that SF-1 expression is critical for female rat VMNdm Ghrh neuron counterregulatory neurochemical, AMPK catalytic subunit, and ER gene transcription responses to hypoglycemia. Sex differences in direction of SF-1 control of distinctive gene profiles may result in observed disparities in SF-1 regulation of counterregulatory hormone secretion between sexes.

The role of glucose and insulin in the metabolic regulation of growth hormone secretion

The exact physiological basis for the suppression of growth hormone secretion by oral glucose intake remains unknown, despite the widespread use of the oral glucose tolerance test in endocrinology. Lack of growth hormone suppression by glucose occurs in about a third of patients with acromegaly, as well as in other disorders. It is currently known that the secretion of growth hormone is affected by various factors, such as age, gender, body mass index, and the redistribution of adipose tissue. There is also evidence of the impact of overeating as well as being overweight on the secretion of growth hormone. It is known that both of these conditions are associated with hyperinsulinemia, which determines the possibility of its predominant role in suppressing the secretion of growth hormone. The purpose of this review is to discuss the accumulated data on the isolated effects of hyperglycemia and hyperinsulinemia on growth hormone secretion, as well as other metabolic regulators and conditions affecting its signaling. Understanding of the pathophysiological basis of these mechanisms is essential for further research of the role of glucose and insulin in the metabolic regulation of growth hormone secretion. However, the studies in animal models are complicated by interspecific differences in the response of growth hormone to glucose loading, and the only possible available model in healthy people may be the hyperinsulinemic euglycemic clamp.

Characterization of the ability of a, second-generation SST-DA chimeric molecule, TBR-065, to suppress GH secretion from human GH-secreting adenoma cells.

Somatostatin (SST) and dopamine (DA) inhibit growth hormone (GH) secretion and proliferation of GH-secreting pituitary adenomas (GHomas) through binding to SSTR2 and D2R receptors. Chimeric SST-DA compounds (Dopastatins) display increased potency in inhibiting GH secretion, as compared with individual SST or DA analogs (alone or combined). To assess the efficacy of a second-generation dopastatin, TBR-065, in suppressing GH secretion from human GH- and GH/prolactin(PRL)-omas. We compared the ability of TBR-065 to inhibit GH secretion from primary cultures of human GH- or GH/PRLoma cells to that of the first generation dopastatin, TBR-760 (formerly BIM-23A760), octreotide (OCT) and cabergoline (CAB), the later either alone or combined. We investigated whether there was any impact of BIM-133, the metabolite of TBR-065, on the ability of TBR-065 to inhibit GH in these cultures. 17 GH- and GH/PRLomas were included in this study. Inhibition of GH secretion by TBR-065, TBR-760, OCT and CAB (0.1pM to 0.1µM) was assessed over a period of 8h. All tumors expressed SSTR2 and D2R mRNAs. GH suppression was higher with TBR-065 as compared with TBR-760 (Emax = 57 ± 5.6% vs. 41.1 ± 12.5%, respectively, p < 0.001) or with OCT + CAB (Emax = 56.8 ± 7.2% vs. 44.4 ± 9.4%, p < 0.001). BIM-133 did not have any impact on the activity of TBR-065. TBR-065 has significantly improved efficacy in suppressing GH secretion as compared to current available therapies and may represent a new promising option for the treatment of acromegaly.

SAT-313 Synaptojanin 2 Binding Protein Is Required for Efficient Somatostatin Receptor 2A Phosphorylation by G Protein Coupled Receptor Kinases and Signaling to the ERK/MAPK Pathway

Somatostatin receptor 2A (Sst2A) agonists are the primary pharmacological treatment for growth hormone (GH) secreting pituitary tumors to inhibit GH secretion and limit the destructive effects of these tumors. Sst2A agonists are also widely used as imaging agents for neuroendocrine tumors, and are under investigation for treatment of these cancers. However, despite the clinical importance of Sst2A agonists, regulatory mechanisms controlling Sst2A internalization and signaling are not fully understood. Sst2A contains a C-terminal PDZ binding site that serves as a docking platform for PDZ domain containing proteins. In an unbiased screen for PDZ domain proteins that can interact with Sst2A, we identified Synaptojanin 2 binding protein (SYNJ2BP) / Outer mitochondrial protein 25 (OMP25). SYNJ2BP is an outer mitochondrial protein that has been shown previously to promote the internalization of the Activin Type II receptor. We find that SYNJ2BP interacts with Sst2A in a ligand-dependent manner. Importantly, we show that SYNJ2BP promotes interaction of Sst2A with the G protein couple receptor kinase 2 (GRK2), and that siRNA-mediated knockdown of SYNJ2BP dramatically inhibits Sst2A phosphorylation by endogenous GRKs. Moreover, overexpression of SYNJ2BP strongly potentiates Sst2A phosphorylation on the GRK phosphorylation sites. Modulation of SYNJ2BP expression also regulates somatostatin-stimulated β-arrestin recruitment to the plasma membrane. Interestingly, in contrast to the large effects on Sst2A phosphorylation and β-arrestin recruitment, modulation of SYNJ2BP expression only caused a small change in ligand-stimulated receptor internalization. When we assessed downstream signaling, we found that SYNJ2BP overexpression potently stimulated receptor-dependent activation of ERK1/2, but had little effect on the ability of Sst2A to repress forskolin-stimulated cAMP production. Taken together, these data demonstrate for the first time that interaction of Sst2A with a PDZ domain protein affects receptor regulation and signaling. Because multiple PDZ domain containing proteins have been shown to interact with Sst2A, these data also suggest that interaction of Sst2A with this class of proteins may be an important regulatory mechanism to bias its function within the cell.

Discovery and SAR Studies of Orally Active Somatostatin Receptor Subtype-2 (SSTR2) Agonists for the Treatment of Acromegaly.

Acromegaly is a disease caused by the oversecretion of growth hormone. It is currently treated by intravenous injection with cyclic peptide drugs that activate somatostatin receptor subtype 2 (SSTR2). Here, novel nonpeptidic, small-molecule, and orally active SSTR2 agonists were identified from a hit compound (13). Pharmacophore studies enabled scaffold hopping to obtain a unique 3,4,5-trisubstituted pyridine motif. Further optimization conferred potent SSTR2 agonistic activity and metabolic stability. Several compounds were evaluated and these showed good oral pharmacokinetic profiles in rats, and one representative compound (25) showed highly potent inhibition of growth hormone secretion induced by growth hormone-releasing hormone in rats. Based on these results, 25 was identified as a promising lead for further optimization. A structure-activity relationship (SAR) study and the metabolic stability data for this compound are also described.

Pharmacological Modulation of Ghrelin to Induce Weight Loss: Successes and Challenges.

Obesity is affecting over 600 million adults worldwide and has numerous negative effects on health. Since ghrelin positively regulates food intake and body weight, targeting its signaling to induce weight loss under conditions of obesity seems promising. Thus, the present work reviews and discusses different possibilities to alter ghrelin signaling. Ghrelin signaling can be altered by RNA Spiegelmers, GHSR/Fc, ghrelin-O-acyltransferase inhibitors as well as antagonists, and inverse agonists of the ghrelin receptor. PF-05190457 is the first inverse agonist of the ghrelin receptor tested in humans shown to inhibit growth hormone secretion, gastric emptying, and reduce postprandial glucose levels. Effects on body weight were not examined. Although various highly promising agents targeting ghrelin signaling exist, so far, they were mostly only tested in vitro or in animal models. Further research in humans is thus needed to further assess the effects of ghrelin antagonism on body weight especially under conditions of obesity.

P1.03: Intravenous glucose nocturnal infusion reduces growth hormone secretion in children on total parenteral nutrition

Introduction: Most children with intestinal failure (IF) benefit from home parenteral nutrition (HPN). It allows a familial life with normal children activities such as going to school, sports, and being at home. In order to do so, PN is provided with cyclic infusion at night. Children with IF on HPN should have normal growth. However, some children grow under their genetic target height and present with decreased height velocity. Methods: We report the case of two children on HPN who presented with decreased height velocity while their weight gain was normal. After ruling out usual etiology (insufficient protein intake, acidosis, sodium deficiency, IFALD…), growth hormone (GH) deficiency was considered. Extensive testings were performed such as IgF1 levels, GH secretion stimulation test and nocturnal GH secretion. PN dependency was assessed using the PN/REE index (parenteral nutrition non-protein energy intake divided by resting energy expenditure calculated using Schofield equation, expressed in percentage). Results: These two children needed extremely high PN caloric intake to achieve a normal weight gain with a PN dependency index of 163% and 150%. Table 1 shows their clinical characteristics. Table 2 shows the results of the biological testings. These two children showed a normal GH peak under stimulation, but a low nocturnal GH secretion meaning they were able to produce GH under stimulation, but their nocturnal physiological secretion was inhibited. Their mean glycemia during PN perfusion was high compared to fasting glycemia which should normally be observed at night in children. Hyperglycemia is a well known inhibitor of GH secretion. Conclusion: Children with very high PN dependency are at risk of developing reduced height. In some children, GH secretion seems to be inhibited by nocturnal high glucose infusion. A longer PN infusion time can be proposed and/or a decrease in glucose intake with an increase in lipid intake. Also, growth hormone supplementation might be discussed and should be evaluated in this setting.

Growth Hormone Increases Bone Toughness and Decreases Muscle Inflammation in Glucocorticoid-Treated Mdx Mice, Model of Duchenne Muscular Dystrophy.

The absence of functional dystrophin with mutations of the dystrophin-encoding gene in Duchenne muscular dystrophy (DMD) results in muscle inflammation and degeneration, as well as bone fragility. Long-term glucocorticoid therapy delays the muscular disease progression but suppresses growth hormone secretion, resulting in short stature and further deleterious effects on bone strength. This study evaluated the therapeutic potential of daily growth hormone therapy in growing mdx mice as a model of DMD. Growth hormone treatment on its own or in combination with glucocorticoids significantly improved muscle histology and function and decreased markers of inflammation in mdx mice. Glucocorticoid treatment thinned cortical bone and decreased bone strength and toughness. Despite the minimal effects of growth hormone on bone microarchitecture, it significantly improved biomechanical properties of femurs and vertebrae, even in the presence of glucocorticoid treatment. Together these studies suggest that the use of growth hormone in DMD should be considered for improvements to muscle and bone health. © 2019 American Society for Bone and Mineral Research.

Imatinib Inhibits GH Secretion From Somatotropinomas

Background: Imatinib, a tyrosine kinase inhibitor, causes growth failure in children with chronic myeloid leukemia probably by targeting the growth hormone (GH)/insulin like growth factor-1 (IGF-1) axis. We aim to explore the imatinib targets expression in pituitary adenomas and study the effect of imatinib on GH secretion in somatotropinoma cells and GH3 cell line.Materials and Methods: The expression pattern of imatinib's targets (c-kit, VEGF, and PDGFR-α/β) was studied using immunohistochemistry and immunoblotting 157 giant (≥4 cm) pituitary adenomas (121 non-functioning pituitary adenomas, 32 somatotropinomas, and four prolactinomas) and compared to normal pituitary (n = 4) obtained at autopsy. The effect imatinib on GH secretion, cell viability, immunohistochemistry, electron microscopy, and apoptosis was studied in primary culture of human somatotropinomas (n = 20) and in rat somato-mammotroph GH3 cell-line. A receptor tyrosine kinase array was applied to human samples to identify altered pathways.Results: Somatotropinomas showed significantly higher immunopositivity for c-kit and platelet-derived growth factor receptor-β (PDGFR-β; P < 0.009 and P < 0.001, respectively), while staining for platelet-derived growth factor receptor-α (PDGFR-α) and vascular endothelial growth factor (VEGF) revealed a weaker expression (P < 0.001) compared to normal pituitary. Imatinib inhibited GH secretion from both primary culture (P < 0.01) and GH3 cells (P < 0.001), while it did not affect cell viability and apoptosis. The receptor tyrosine kinase array showed that imatinib inhibits GH signaling via PDGFR-β pathway.Conclusion: Imatinib inhibits GH secretion in somatotropinoma cells without affecting cell viability and may be used as an adjunct therapy for treating GH secreting pituitary adenomas.

Stimulation of growth hormone by kisspeptin antagonists in ewes.

Kisspeptin signalling is indispensable for fertility, stimulating gonadotropin-releasing hormone (GnRH) secretion and mediating gonadal steroid feedback on GnRH neurons. Moreover, kisspeptin neurons have been implicated in other non-reproductive neuroendocrine roles. Kisspeptin appears to also regulate growth hormone secretion but much of the data appear contradictory. We sought to clarify a potential role of kisspeptin in growth hormone (GH) regulation by examining the effect of kisspeptin antagonists on GH secretion in ewes under various physiological conditions. Our data show clear and robust increases in GH secretion following lateral ventricle or third ventricle infusion of kisspeptin antagonists p-234 and p-271 in either ovariectomized or anestrous ewes. Central infusion of kisspeptin-10 had no effect on GH secretion. To determine the level at which kisspeptin may influence GH secretion, we examined expression of the cognate kisspeptin receptor, GPR54, in pituitary cells and showed by immunocytochemistry that the majority of somatotropes express GPR54 while expression was largely negative in other pituitary cells. Overall, we have demonstrated that blocking kisspeptin signalling by antagonists stimulates GH secretion in ewes and that this is likely mediated by inhibiting endogenous kisspeptin activation of GPR54 expressed on somatotropes. The findings suggest that endogenous kisspeptin inhibits GH secretion through GPR54 expressed on somatotropes.

The effects of l-DOPA and sulpiride on growth hormone secretion at different injection times in Holstein steers.

The effects of l-DOPA, a precursor of dopamine (DA), and sulpiride, a D2 -type DA receptor blocker, on growth hormone (GH) and prolactin (PRL) secretion were investigated in steers. Eight Holstein steers (212.8±7.8kg body weight) were used. Lighting conditions were 12:12 L:D (lights on: 06.00-18.00hours). Blood samplings were performed during the daytime (11.00-15.00hours) and nighttime (23.00-03.00hours). Intravenous injections of drugs or saline were performed at 12.00 hour for the daytime and 00.00hour for the nighttime, respectively. Plasma GH and PRL concentrations were determined by radioimmunoassay. l-DOPA did not alter the GH secretion when it was injected at 12.00hour (spontaneous GH level at its peak). On the other hand, l-DOPA increased GH secretion at 00.00hour (GH level at its trough). Injection of sulpiride suppressed GH secretion at 12.00hour but did not affect GH levels at 00.00hour. l-DOPA inhibited and sulpiride stimulated PRL release during both periods. These results suggest that dopaminergic neurons have stimulatory action on GH secretion and inhibitory action on PRL secretion in cattle. In addition, injection time should be considered to evaluate the exact effects on GH secretion due to its ultradian rhythm of GH secretion in cattle.

Irisin inhibition of growth hormone secretion in cultured tilapia pituitary cells

Irisin, the product of fibronectin type III domain-containing protein 5 (FNDC5) gene, is well-documented to be a regulator of energy metabolism. At present, not much is known about its biological function in non-mammalian species. In this study, a full-length tilapia FDNC5 was cloned and its tissue expression pattern has been confirmed. Based on the sequence obtained, we produced and purified recombinant irisin which could induce uncoupling protein 1 (UCP1) gene expression in tilapia hepatocytes. Further, the rabbit polyclonal irisin antiserum was produced and its specificity was confirmed by antiserum preabsorption. In tilapia pituitary cells, irisin inhibited growth hormone (GH) gene expression and secretion and triggered rapid phosphorylation of Akt, Erk1/2, and p38 MAPK. Furthermore, irisin-inhibited GH mRNA expression could be prevented by inhibiting PI3K/Akt, MEK1/2, and p38 MAPK, respectively. Apparently, fish irisin can act directly at the pituitary level to inhibit GH transcript expression via multiple signaling pathways.

A pilot study of the effects of niacin administration on free fatty acid and growth hormone concentrations in children with obesity

Children with obesity have low spontaneous growth hormone (GH) secretion. High circulating free fatty acid (FFA) concentration is believed to inhibit GH secretion in those with obesity. In adults, lipolytic inhibition with niacin lowers FFA and increases GH, but there are no prior studies in children with obesity. The objective of the study was to determine the dose and frequency of niacin administration required to lower FFA and stimulate GH in children with obesity. Dose-finding study of nondiabetic children ages 6-12 years with body mass index (BMI) ≥ 95th percentile given niacin 250 mg q2h × 3 doses (n = 2), 500 mg q2h × 3 doses (n = 5) or 500 mg q1h × 4 doses (n = 5). Eight boys and four girls (age 9.7 ± 1.8 years; BMI 26.4 ± 3.1 kg m-2 ; BMIz 2.2 ± .25) were studied. Percentage of serum FFA values that were below 0.2 mEq L-1 . GH, insulin and glucose were also measured serially. FFA decreased as the dose and frequency of niacin increased (p = .01). Niacin 500 mg q1h 4 doses suppressed FFA < 0.2 mEq L-1 and significantly increased GH (p = .04). Adverse effects were flushing/warmth (100%), tingling (60%) and GI complaints (20-40%). Niacin 500 mg q1h significantly lowered serum FFA and increased GH. These pilot data suggest that high FFA is an important suppressor of GH secretion in children with obesity.

Alteration of the miRNA expression profile in male porcine anterior pituitary cells in response to GHRH and CST and analysis of the potential roles for miRNAs in regulating GH

ObjectiveGrowth hormone releasing hormone (GHRH) is a major positive regulator of growth hormone (GH) in the anterior pituitary gland, while cortistatin's (CST) role is negative. miRNAs (microRNAs or miRs) are small RNA molecules modulating gene expression at the post-transcriptional level. However, little is known about the function of miRNAs in the regulation of GH synthesis and/or secretion. This study investigated potential functional miRNAs involved in GH secretion in the normal porcine pituitary. DesignPrimary porcine anterior pituitary cells were cultivated and then treated with 10nmol/L GHRH and 100nmol/L CST, respectively. The effects of GHRH and CST on GH secretion were determined using RIA. miRNA microarrays were employed to analyze miRNA expression after treatment and then differentially expressed miRNAs were screened. Bioinformatics analysis was used to analyze the potential targets in growth hormone regulation of altered miRNAs. Furthermore, functional experiments were conducted to study the function of ssc-let-7c. ResultsGHRH significantly promoted GH secretion, while CST suppressed GH secretion. 19 and 35 differentially expressed miRNAs were identified in response to GHRH and CST treatments respectively. Verification of 5 randomly selected miRNAs by quantitative real-time PCR (qRT-PCR) showed similar changes with microarray analysis. Target analysis showed that some miRNAs may be involved in GH secretion-related pathways. Importantly, ssc-let-7c was predicted to target GH1 and GHRHR mRNA 3′untranslated regions (3′UTRs), which was supported by luciferase reporter assay. Furthermore, functional experimental results showed that ssc-let-7c was involved in GH secretion regulation, and overexpression of ssc-let-7c inhibited GH secretion in porcine anterior pituitary cells. ConclusionsGHRH and CST modulated porcine pituitary cell miRNA expression. Bioinformatics analysis revealed a complicated network among differentially expressed miRNAs, GH regulation-related genes and hormones. More interestingly, ssc-let-7c inhibited both GH1 and GHRHR mRNA 3′UTR reporter vectors' luciferase activity and overexpression of ssc-let-7c led to a decrease of GH secretion.

Actions of NPY, and its Y1 and Y2 receptors on pulsatile growth hormone secretion during the fed and fasted state.

The hypothalamic NPY system plays an important role in regulating food intake and energy expenditure. Different biological actions of NPY are assigned to NPY receptor subtypes. Recent studies demonstrated a close relationship between food intake and growth hormone (GH) secretion; however, the mechanism through which endogenous NPY modulates GH release remains unknown. Moreover, conclusive evidence demonstrating a role for NPY and Y-receptors in regulating the endogenous pulsatile release of GH does not exist. We used genetically modified mice (germline Npy, Y1, and Y2 receptor knock-out mice) to assess pulsatile GH secretion under both fed and fasting conditions. Deletion of NPY did not impact fed GH release; however, it reversed the fasting-induced suppression of pulsatile GH secretion. The recovery of GH secretion was associated with a reduction in hypothalamic somatotropin release inhibiting factor (Srif; somatostatin) mRNA expression. Moreover, observations revealed a differential role for Y1 and Y2 receptors, wherein the postsynaptic Y1 receptor suppresses GH secretion in fasting. In contrast, the presynaptic Y2 receptor maintains normal GH output under long-term ad libitum-fed conditions. These data demonstrate an integrated neural circuit that modulates GH release relative to food intake, and provide essential information to address the differential roles of Y1 and Y2 receptors in regulating the release of GH under fed and fasting states.

The effect of albumin fusion structure on the production and bioactivity of the somatostatin-28 fusion protein in Pichia pastoris

Somatostatin, a natural inhibitor of growth hormone (GH), and its analogs have been used in clinical settings for the treatment of acromegaly, gigantism, thyrotropinoma, and other carcinoid syndromes. However, natural somatostatin is limited for clinical usage because of its short half-life in vivo. Albumin fusion technology was used to construct long-acting fusion proteins and Pichia pastoris was used as an expression system. Three fusion proteins (SS28)(2)-HSA, (SS28)(3)-HSA, and HSA-(SS28)(2), were constructed with different fusion copies of somatostatin-28 and fusion orientations. The expression level of (SS28)(3)-HSA was much lower than (SS28)(2)-HSA and HSA-(SS28)(2) due to the additional fusion of the somatostatin-28 molecule. MALDI-TOF mass spectrometry revealed that severe degradation occurred in the fermentation process. Similar to the standard, somatostatin-14, all three fusion proteins were able to inhibit GH secretion in blood, with (SS28)(2)-HSA being the most effective one. A pharmacokinetics study showed that (SS28)(2)-HSA had a prolonged half-life of 2 h. These results showed that increasing the number of small protein copies fused to HSA may not be a suitable method for improving protein bioactivity.

The Effect of Albumin Fusion Patterns on the Production and Bioactivity of the Somatostatin-14 Fusion Protein in Pichia pastoris

Somatostatin is a natural inhibitor of growth hormone, and its analogues are clinically used for the therapy of acromegaly, gigantism, thyrotropinoma, and other carcinoid syndrome. However, natural somatostatin is limited for clinical usage because of its short half-life in vivo. Albumin fusion technology was used to construct long-acting fusion proteins, and Pichia pastoris was used as an expression system. Three fusion proteins, (somatostatin (SS)14)2-human serum albumin (HSA), (SS14)3-HSA, and HSA-(SS14)3, were constructed with different fusion copies of somatostatin-14 and fusion orientations. The expression level of (SS14)3-HSA and HSA-(SS14)3 was much lower than (SS14)2-HSA due to the additional fusion of the somatostatin-14 molecule. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry revealed that severe degradation occurred in the fermentation process. Similar to the standard of somatostatin-14, all three fusion proteins were able to inhibit growth hormone secretion in the blood, with (SS14)2-HSA being the most effective one. On the whole, (SS14)2-HSA was the most effective protein in both production level and bioactivity, and increasing the number of small protein copies fused to HSA may not be a suitable method to improve the protein bioactivity.

Effect of immunization with a recombinant cholera toxin B subunit/somatostatin fusion protein on immune response and growth hormone levels in mice

Somatostatin (SS) is a hormone that inhibits growth hormone secretion. Cholera toxin B subunit (CTB) is a widely used adjuvant to improve the immunogenicity of co-administrated antigen. To block the growth hormone-inhibiting effect of SS, a fusion gene of CTB and SS was constructed and expressed in Escherichia coli. The purified CTB/SS fusion protein polymerized into a biologically active pentamer required for CTB binding to the GM1 ganglioside receptor. Immunization with the CTB/SS protein induced specific immunity against CTB and SS in mice. The serum growth hormone of the CTB/SS-treated mice increased by 29 % (P < 0.05) compared with the control. The results indicated that the CTB/SS fusion protein was effective in inducing immune response against SS as well as elevating the growth hormone level.