Human Growth Hormone-releasing Research Articles

HGH release from directly compressed hGH-PLGA biodegradable implantable tablets: Influence of physicomechanical factors

The incidence of compression conditions, porosity and polymer degradation on human growth hormone (hGH) release from PLGA implantable tablets was evaluated with the aim of gaining insight in the mechanism involved in drug delivery from biodegradable matrices. Tablets elaborated by direct compression of hGH with PLGA, applying various compression forces for different times, kept the integrity and the stability of the hormone. Tablet dimensions, viscoelastic properties, glass to rubber transition temperature ( T g), PLGA degradation rate and water uptake were analyzed in the freshly prepared implantable tablets as well as at several times during release test in phosphate buffer pH 7.4. Placebo tablets were also prepared to evaluate the incidence of hGH on the physicomechanical properties of the device and PLGA degradation rate. Porosity remarkably determined the amount of hGH released, through an effect on the easiness of water penetration in the tablet and on the beginning of PLGA degradation. The decrease in PLGA molecular weight during the first days in the release medium, despite of being minor, significantly conditioned hGH release rate. The more dramatic changes in PLGA molecular weight observed after 20 days in the release medium notably reduced the T g and the viscous and elastic moduli of the tablets. The overall analysis of the events underwent by the tablets in contact with the aqueous medium was used to explain the drug release profile and may help to optimize the design of the PLGA-based implantable tablets as peptidic drug delivery systems.

Tesamorelin, a human growth hormone releasing factor analogue

Background: The combination of clinical effectiveness with a variety of adverse side effects from the use of recombinant human growth hormone (rhGH) in therapy for growth hormone (GH)-deficient disorders has led to the development of human growth hormone releasing factor (GFR) analogues, which may be better tolerated. Tesamorelin, a synthetic GFR, has been developed as a potential treatment for a variety of conditions that may be associated with a relative deficiency of GH including HIV-related lipodystrophy. Objective: This article reviews the development of tesamorelin and its purported role in HIV-related lipodystrophy and other potential indications. Methods: Relevant articles and abstracts were obtained from searches of the medical and chemical literature databases and the references from published articles. Results/conclusion: A multicenter, randomized, placebo-controlled, Phase III clinical trial suggested that tesamorelin might be a beneficial treatment strategy for HIV-related lipodystrophy with a good safety profile and a positive effect on reducing visceral fat. Other potential indications for tesamorelin appear less promising from the current data.

Varenicline, Appetite, and Weight Reduction

Varenicline, Appetite, and Weight Reduction

Varenicline, Appetite, and Weight Reduction

was normal (2.3 ng/ml), whereas serum prolactin level was suppressed to 1.3 ng/ml. His pathological hypersexuality completely disappeared 2 weeks after discontinuation of bromocriptine. After 4 weeks, pramipexole (0.125 mg b.i.d.), another dopamine receptor agonist, was added instead of bromocriptine since his motor performance deteriorated. After 1 week of pramipexole, all the hypersexual symptoms reemerged. At this point, his serum prolactin level was 2.2 ng/ml. His pathological hypersexuality completely disappeared again just by discontinuing pramipexole. Then we titrated madopar up to 125 mg t.i.d. instead of adding other dopamine receptor agonist. After 3 weeks, his motor performance improved with partial reemergence of hypersexual symptoms (penile erection, facial flushing, sexually suggestive remarks, touching). However, the severity of the reemerged symptoms was much more tolerable than those induced by dopamine receptor agonist. At this point, his serum prolactin level was not suppressed (13.3 ng/ml).

Knocking down gene expression for growth hormone-releasing hormone inhibits proliferation of human cancer cell lines

Splice Variant 1 (SV-1) of growth hormone-releasing hormone (GHRH) receptor, found in a wide range of human cancers and established human cancer cell lines, is a functional receptor with ligand-dependent and independent activity. In the present study, we demonstrated by western blots the presence of the SV1 of GHRH receptor and the production of GHRH in MDA-MB-468, MDA-MB-435S and T47D human breast cancer cell lines, LNCaP prostate cancer cell line as well as in NCI H838 non-small cell lung carcinoma. We have also shown that GHRH produced in the conditioned media of these cell lines is biologically active. We then inhibited the intrinsic production of GHRH in these cancer cell lines using si-RNA, specially designed for human GHRH. The knocking down of the GHRH gene expression suppressed the proliferation of T47D, MDA-MB-435S, MDA-MB-468 breast cancer, LNCaP prostate cancer and NCI H838 non-SCLC cell lines in vitro. However, the replacement of the knocked down GHRH expression by exogenous GHRH (1–29)NH2 re-established the proliferation of the silenced cancer cell lines. Furthermore, the proliferation rate of untransfected cancer cell lines could be stimulated by GHRH (1–29)NH2 and inhibited by GHRH antagonists MZ-5-156, MZ-4-71 and JMR-132. These results extend previous findings on the critical function of GHRH in tumorigenesis and support the role of GHRH as a tumour growth factor.

Sustained Release of Human Growth Hormone from Heparin-Based Hydrogel

Sustained Release of Human Growth Hormone from Heparin-Based Hydrogel

Associations between the human growth hormone-releasing hormone- and neuropeptide-Y-immunoreactive systems in the human diencephalon: A possible morphological substrate of the impact of stress on growth

Previous studies revealed that stress is a pivotal factor in the regulation of growth. Psychological harassment may result in psychosocial dwarfism with delayed puberty, short stature and depression. Growth hormone (GH) secretion is suppressed by stress, possibly via the attenuation of growth hormone-releasing hormone (GHRH) secretion. However, the morphological substrate of this phenomenon has not been elucidated yet.Since neuropeptide Y (NPY) levels in the plasma is increased by administration of various stressors, the common consensus is that NPY plays a crucial role in the stress response. In the present study, we examined the putative juxtapositions between the NPY- and GHRH-immunoreactive (IR) systems in the human hypothalamus using double-label immunohistochemistry. Our findings revealed that the majority of the GHRH-IR perikarya formed intimate associations with NPY-IR fiber varicosities. The majority of these juxtapositions were found in the infundibular nucleus/median eminence where NPY-IR fiber varicosities often covered a significant surface area of the GHRH neurons.Since the juxtapositions between the GHRH-IR perikarya and NPY-IR fiber varicosities may be functional synapses, they may represent the morphological substrate of stress-suppressed GH secretion. The large number of contacting elements indicates that NPY plays a pivotal role in GH release, and may be considered as a major factor in the attenuation of growth by stress in humans.

Endocrine and Antineoplastic Actions of Growth Hormone-Releasing Hormone Antagonists

Potent antagonists of growth hormone-releasing hormone (GHRH) have been developed for the treatment of disorders caused by excessive GHRH or growth hormone (GH) production and for therapy of cancers. GHRH antagonists suppressed the release of GH and insulin-like growth factor (IGF)-I in transgenic mice overexpressing human (h) GHRH gene, an animal model of human acromegaly. It was also shown in GH3 rat pituitary tumor cells overexpressing the human pituitary GHRH receptor (pGHRH-R) that GHRH antagonists can inhibit c-AMP production and GH secretion through the human receptor. These observations indicate that GHRH antagonists could be used clinically in disorders characterized by excessive GHRH/GH secretion. Many recent studies demonstrate that GHRH antagonists can inhibit tumor growth by several mechanisms. By indirect action through pGHRH-Rs these antagonists suppress circulating GH/IGF-I level, which results in the inhibition of cancers that depend on GH and/or IGF-I as growth factors. However, GHRH antagonists are also effective inhibitors of tumor IGF-II production, which is a potent mitogen but independent of GH. GHRH antagonists can inhibit tumor cell proliferation by direct action on tumor cell receptors, suppressing the IGF-II and other growth factor production of tumor cells. In addition, various human tumors and tumor cell lines secrete GHRH peptide and respond to GHRH with proliferation. This finding suggests that GHRH functions as an autocrine growth factor and that GHRH antagonists can block its effects on tumor growth. Recently, we demonstrated the expression of hGHRH-R and its splice variants in various human cancers. Antiproliferative action of GHRH antagonists on these cancers indicates that the direct inhibitory effects of GHRH antagonists are mediated by tumoral GHRH receptors.

Dynamin Is Functionally Coupled to Insulin Granule Exocytosis

The insulin granule integral membrane protein marker phogrin-green fluorescent protein was co-localized with insulin in Min6B1 beta-cell secretory granules but did not undergo plasma membrane translocation following glucose stimulation. Surprisingly, although expression of a dominant-interfering dynamin mutant (Dyn/K44A) inhibited transferrin receptor endocytosis, it had no effect on phogringreen fluorescent protein localization in the basal or secretagogue-stimulated state. By contrast, co-expression of Dyn/K44A with human growth hormone as an insulin secretory marker resulted in a marked inhibition of human growth hormone release by glucose, KCl, and a combination of multiple secretagogues. Moreover, serial pulse depolarization stimulated an increase in cell surface capacitance that was also blocked in cells expressing Dyn/K44A. Similarly, small interference RNA-mediated knockdown of dynamin resulted in marked inhibition of glucose-stimulated insulin secretion. Together, these data suggest the presence of a selective kiss and run mechanism of insulin release. Moreover, these data indicate a coupling between endocytosis and exocytosis in the regulation of beta-cell insulin secretion.

Efeito da suplementação de L-arginina sobre a secreção de hormônio do crescimento e fator de crescimento semelhante à insulina em adultos

Based on presumptions that the infusion of amino acids can augment the release of human growth hormone (hGH) and that this metabolism is related with secretion of insulin-like growth factor I (IGF-I), the purpose of this study was to verify the effect of L-arginine supplementation on GH and IGF-I in adults. Seventeen male individuals participated on the study and were randomized to receive L-arginine (n= 10) or placebo (n= 7), seven grams per day for seven days. Before and after the supplementation period, the volunteers realized blood collection in fasting to verify both GH and IGF-I levels, as well as urine collection to verify urea excretion. At the end of the experimental period, it was verified that the group that received L-arginine augmented the urea in urine excretion (to 2684.1 +/- 475.2 mg/dl from 2967.2 +/- 409.7 mg/dl, p= 0.002), therefore it did not alter significantly the release of hormones evaluated. The group which received placebo did not alter significantly any evaluated parameters. The L-arginine supplementation during seven days was ineffective to augment both GH and IGF-I release in individual male adults.

Effect of excipients on the encapsulation efficiency and release of human growth hormone from dextran microspheres

The possibility was investigated to modulate the encapsulation efficiency and release of human growth hormone (hGH) from hydroxyl ethyl methacrylated dextran (dex-HEMA) hydrogel microspheres by using excipients. Microspheres were prepared by polymerization of dex-HEMA in an aqueous two-phase system of this polymer and PEG with or without excipients (Tween 80, pluronic F68, sucrose, NaCl, urea or methionine). High hGH encapsulation efficiencies (50–70%) were obtained for microspheres prepared without excipients and with Tween 80, NaCl or methionine. Substantially lower encapsulation efficiencies (27% and 19%, respectively) were obtained for microspheres prepared in the presence of sucrose and urea, which was attributed to the more favoured partitioning of hGH over the PEG-phase due to higher hydrophobicity of the (partly) denatured hGH. Likely, differences in precipitate size of the encapsulated hGH resulted in different release profiles between microspheres prepared without excipients (biphasic release: 2 days delay time followed by 6 days release) and the release profile for microspheres prepared with Tween 80, pluronic F68, sucrose, NaCl and urea (release over a period of 6–8 days (without a delay time)). Microspheres prepared with methionine showed a concentration-dependent delay time varying from 0 to 2 days followed by almost zero-order release over 6 days, attributed to the effect of methionine on the polymerization of dex-HEMA. Especially, Tween 80 and methionine are attractive excipients since hGH was encapsulated in high yield (60–70%) and the protein was released from the microspheres mainly in its monomeric form without a delay time and with an almost zero-order release over 6–8 days.

Photo-cross-linkable and thermo-responsive hydrogels containing chitosan and Pluronic for sustained release of human growth hormone (hGH)

A Pluronic/chitosan hydrogel was prepared by employing di-acrylated Pluronic and acrylated chitosan for thermo-responsive and photo-cross-linkable in situ gelation. Mixtures of diacrylated Pluronic and acrylated chitosan were transformed to physical gels at elevated temperatures and the gelation temperature of the hydrogels gradually increased by increasing chitosan content in the hydrogels from 0% to 15%. Photo-cross-linked Pluronic/chitosan hydrogels were prepared by UV irradiation of the physical gels above their gelation temperatures. Hydrogels with a long photo-cross-linking time showed low degradation rates and chitosan contents in the hydrogels also impeded the degradation rates of the hydrogels, which was caused by a high degree of inter-connected polymer networks between acrylated Pluronic and acrylated chitosan. Human growth hormone (hGH), mixed with the mixture of Pluronic and chitosan, was photo-cross-linked to prepare biodegradable hGH hydrogels. The hydrogels containing hGH showed sustained release profiles for those with long photo-cross-linking times and high chitosan contents in the hydrogel. The hydrogels with a long cross-linking time showed impeded release of the protein and high content of chitosan in the hydrogels also decreased burst release of hGH from the hydrogels while hGH was rapidly released out for the hydrogels with low content of chitosan.

Acylated Ghrelin Secretion Is Acutely Suppressed by Oral Glucose Load or Insulin-Induced Hypoglycemia Independently of Basal Growth Hormone Secretion in Humans

Background: Ghrelin has been reported to be the natural ligand of growth hormone (GH) secretagogue receptor, and it is known that exogenous ghrelin administration strongly stimulates GH release in humans. However, the effects of endogenous ghrelin on GH secretion and changes in ghrelin levels during dynamic changes in GH levels are not well understood. Methods: Therefore, we measured circulating acylated ghrelin concentrations during oral glucose tolerance tests (OGTTs) in patients with active acromegaly (AA, n = 9) and in age/sex/BMI-matched group A controls (n = 12), and during insulin tolerance testing (ITT) in patients with GH deficiency (GHD, n = 10) and in group B controls (n = 10). Plasma acylated ghrelin, serum GH, insulin and glucose levels were measured during each test. Results: Fasting plasma ghrelin levels correlated negatively with serum insulin levels in both group A and B controls (r = –0.665; p < 0.05) but not in patients with AA or GHD. During OGTTs, circulating ghrelin levels decreased significantly with a nadir at 30 min in both patients with AA (p < 0.05) and group A controls (p < 0.01). Also, ITTs were followed by a significant decrease in circulating ghrelin levels with a nadir at 30 min in patients with GHD (p < 0.05) and in group B controls (p < 0.05). Conclusion: The results of the study show that at baseline acylated ghrelin levels do not differ with respect to the GH status (GH excess or GH deficiency) and, furthermore, the suppression of acylated ghrelin levels during OGTT or ITT is independent of the GH response to the tests.

Immunocytochemical localisation of plasma membrane GHRH receptors in human tumours using a novel anti-peptide antibody

Antagonists of growth hormone releasing hormone (GHRH) directly inhibit the growth of a variety of human neoplasms. However, the plasma membrane receptor mediating these effects has not been immunocytochemically visualised in primary tumour cells. Given that previous attempts using an antibody to the amino-terminal region did not result in the visualisation of plasma membrane receptors, we have developed and characterised an anti-peptide antibody to the carboxy-terminal region 403–422 of the human pituitary GHRH receptor. This sequence is identical to residues 339–358 of splice variant 1 (SV1) of tumoural GHRH receptors. Specificity of the antibody was demonstrated by (1) immunocytochemical staining of GHRH receptor-transfected cells, (2) detection of a broad glycosylated protein band migrating at Mr 50,000–60,000 in Western blots of membranes from human pituitary, and (3) abolition of tissue immunostaining by preadsorbtion of the antibody with its immunising peptide. The distribution of GHRH receptors was investigated in 69 formalin-fixed, paraffin-embedded human tumours showing that GHRH receptors were frequently expressed in breast, ovarian and prostate carcinomas. Immunoreactive GHRH receptors were clearly confined to the plasma membrane and uniformly present on nearly all tumour cells. In Western blots of membranes prepared from human tumours, the anti-GHRH receptor antibody detected a non-glycosylated protein band migrating at Mr 40,000, which corresponds to the expected molecular weight of splice variant 1 of tumoural GHRH receptors. Together, our findings provide direct evidence for the presence of GHRH receptor protein on the plasma membrane of primary human tumour cells. The GHRH receptor visualisation could be of value for a rapid immunohistochemical identification of those tumours which could be a target for diagnostic or therapeutic intervention using GHRH analogues.

Synthesis of stereoisomer analogs of the amino end sequence of human growth hormone releasing factor

A new method has been developed for the synthesis of previously unreported stereoisomer analogs of the amino end sequence of the human growth hormone releasing factor.

Biodegradable polymeric microspheres with “open/closed” pores for sustained release of human growth hormone

A new approach for attaining sustained release of protein is introduced, involving a pore-closing process of preformed porous PLGA microspheres. Highly porous biodegradable poly( d, l-lactic-co-glycolic acid) (PLGA) microspheres were fabricated by a single water-in-oil emulsion solvent evaporation technique using Pluronic F127 as an extractable porogen. Recombinant human growth hormone (rhGH) was incorporated into porous microspheres by a simple solution dipping method. For their controlled release, porous microspheres containing hGH were treated with water-miscible solvents in aqueous phase for production of pore-closed microspheres. These microspheres showed sustained release patterns over an extended period; however, the drug loading efficiency was extremely low. To overcome the drug loading problem, the pore-closing process was performed in an ethanol vapor phase using a fluidized bed reactor. The resultant pore-closed microspheres exhibited high protein loading amount as well as sustained rhGH release profiles. Also, the released rhGH exhibited structural integrity after the treatment.

The expression of the pituitary growth hormone-releasing hormone receptor and its splice variants in normal and neoplastic human tissues

Various attempts to detect human pituitary growth hormone-releasing hormone receptor (pGHRH-R) in neoplastic extrapituitary tissues have thus far failed. Recently, four splice variants (SVs) of GHRH-R have been described, of which SV1 has the highest structural homology to pGHRH-R and likely plays a role in tumor growth. The aim of this study was to reinvestigate whether human tumors and normal human extrapituitary tissues express the pGHRH-R and to corroborate our previous findings on its SVs. Thus, we developed a real-time PCR method for the detection of the mRNA for the pGHRH-R, its SVs, and the GHRH peptide. Using real-time PCR, Western blotting, and radioligand-binding assays, we detected the mRNA for pGHRH-R and pGHRH-R protein in various human cancer cell lines grown in nude mice and in surgical specimens of human lung cancers. The expression of mRNA for SVs of pGHRH-R and GHRH was likewise found in xenografts of human non-Hodgkin's lymphomas, pancreatic cancer, glioblastoma, small-cell lung carcinomas, and in human nonmalignant prostate, liver, lung, kidney, and pituitary. Western blots showed that these normal and malignant human tissues contain SV1 protein and immunoreactive GHRH. Our results demonstrate that some normal human tissues and tumors express mRNA and protein for the pGHRH-R and its splice variants. These findings confirm and extend the concept that GHRH and its receptors play an important role in the pathophysiology of human cancers.

Elevated plasma ghrelin levels in night eating syndrome

Night eating syndrome (NES) is a rare syndrome that includes disturbances of both eating and sleeping. It is characterized by awakening in the middle of the night, getting out of bed and consuming large quantities of food, then returning to sleep. The NES is associated with depression, elevated serum levels of cortisol, and blunting of the usual nighttime increase of the levels of melatonin and leptin. Ghrelin is an endogenous ligand of the growth hormone (GH) secretagogue (GHS) receptor, stimulates GH release, appetite, and weight gain in humans and rodents. We examined nocturnal secretion of plasma ghrelin and other hormones of a 27 year old female patient between 2200 and 0700 and polysomnographic recordings were obtained from 2300 to 0700. Ghrelin plasma concentrations and other hormornes were measured before treatment with a SSRI, during remission under a SSRI and after finishing treatment. Plasma ghrelin levels of our patient were about threefold higher compared to average ghrelin levels of healthy young women. No significant change of the elevated ghrelin plasma concentration was observed after successful treatment with the selective serotonin reuptake inhibitor citalopram. Other hormones tested like cortisol, ACTH, leptin and GH were in the normal range, during all stages of the illness and after remission. Ghrelin might be a keyplayer in the aetiology of this syndrome because of its known capacity to stimulate appetite.

Naturally-occurring missense mutations in the human growth hormone-releasing hormone receptor alter ligand binding

Growth hormone (GH) releasing hormone (GHRH) is a hypothalamic factor that stimulates GH secretion. It acts by activating a seven transmembrane domain G protein-coupled receptor of 423 amino acids expressed by the somatotroph cells of the pituitary gland (GHRH receptor, GHRH-R). Familial isolated growth hormone deficiency (IGHD) can be caused by mutations in the GHRH-R gene both in humans and mice. We have described six disease-causing missense mutations in this gene in IGHD patients (H137L, L144H, A176V, A222E, F242C, K329E). These mutations are inherited as autosomal recessive traits, and cause impairment of the receptor to transmit GHRH signalling. The aim of this study is to investigate the mechanisms through which these mutations cause receptor malfunction. To this end, we transiently expressed each mutated receptor into Chinese hamster ovary cells. Cells expressing each of the mutated receptors did not show an increase in intracellular cyclic AMP in response to GHRH. Immunoprecipitation and immunofluorescence studies indicated that the amino acid changes do not cause protein degradation, and do not alter the proper insertion of the receptor into the cell membrane. Binding studies with human 125I-GHRH showed that the lack of response to GHRH is due to inability of all the mutated receptors to bind the ligand. These studies demonstrate that abnormal ligand binding is a common mechanism by which naturally occurring missense mutation alter GHRH-R function.

Study of poly(lactic-co-glycolic acid) interactions with collagen

Poly(lactic-co-glycolic acid) (PLGA) is excellent to fabricate drug delivery systems that prolong the release of recombinant human growth hormone (rhGH), with current research focusing on their possible use for bone regeneration in odontological practice. Herein, we evaluate PLGA interactions with a component of the buccal cavity, as collagen, using monolayers and differential scanning calorimetry (DSC) techniques. Our results indicate that interactions in the PLGA–collagen mixtures showed no phase separation and attraction forces were detected irrespective of the concentration ratio.