Somatostatin system: molecular mechanisms regulating anterior pituitary hormones

Efficacy and tolerability of somatostatin analogues according to gender in patients with neuroendocrine tumors

As the incidence of neuroendocrine tumors has been rising, gender differences in epidemiology and clinical behavior have emerged, and interest into a gender-driven management of these tumors has grown with the aim to improve survival and quality of life of these patients. Somatostatin Analogues represent the first line of systemic treatment of both functional and non-functional neuroendocrine tumors, through the expression of somatostatin receptors (SSTRs) in the tumor cells, and proved effective in controlling hormonal hypersecretion and inhibiting tumor growth, improving progression-free survival and overall survival of these patients. Aim of the present review is to investigate any differences by gender in efficacy and safety of SSTS-targeted therapies, that represent the mainstay treatment of neuroendocrine tumors, as they emerge from studies of varying design and intent. Although preclinical studies have provided evidence in favor of differences by gender in tumor expression of SSTR, as well as of the role of sex hormones and related receptors in modulating SSTRs expression and function, the clinical studies conducted so far have not shown substantial differences between males and females in either efficacy or toxicity of SSTR-targeted therapies, even if with sometimes inconsistent results. Moreover, in most studies gender was not a predictor of response to treatment. Studies specifically designed to address this issue are needed to develop gender-specific therapeutic algorithms, improving patients' prognosis and quality of life.

[68 Ga]-DOTATATE PET/MR-based evaluation of physiologic somatostatin receptor 2 expression in the adult pituitary gland as a function of age and sex in a prospective cohort

PURPOSE

The pituitary gland has the fourth highest physiologic avidity of [68 Ga]-DOTATATE. In order to guide our understanding of [68 Ga]-DOTATATE PET in clinical contexts, accurate characterization of the normal pituitary gland is first required. This study aimed to characterize the normal pituitary gland using dedicated brain [68 Ga]-DOTATATE PET/MRI as a function of age and sex.

METHODS

A total of 95 patients with a normal pituitary gland underwent brain [68 Ga]-DOTATATE PET examinations for the purpose of diagnosing CNS SSTR2 positive tumors (mean age: 58.9, 73% female). Maximum SUV of the pituitary gland was obtained in each patient. SUV of superior sagittal sinus was obtained to calculate normalized SUV score (SUVR) of the gland. The anatomic size of the gland was collected as maximum sagittal height (MSH). Correlations with age and sex were analyzed.

RESULTS

The mean SUV and SUVR of the pituitary gland were 17.6 (range: 7-59.5, SD = 7.1) and 13.8 (range: 3.3-52.6, SD = 7.2), respectively. Older females had significantly higher SUV of the pituitary gland compared to younger females. When stratified by age and sex, both older and younger females had significantly higher pituitary SUV than older males. SUVR did not differ significantly by age or sex. MSH of the pituitary gland in younger females was significantly greater than in younger males at all age cutoffs.

CONCLUSION

This study provides an empiric profiling of the physiological [68 Ga]-DOTATATE avidity of the pituitary gland. The findings suggest that SUV may vary by age and sex and can help guide the use of [68 Ga]-DOTATATE PET/MRI in clinical and research settings. Future studies can build on these findings to investigate further the relationship between pituitary biology and demographic factors.

The Spectrum of Familial Pituitary Neuroendocrine Tumors

Hereditary pituitary tumorigenesis is seen in a relatively small proportion (around 5%) of patients with pituitary neuroendocrine tumors (PitNETs). The aim of the current review is to describe the main clinical and molecular features of such pituitary tumors associated with hereditary or familial characteristics, many of which have now been genetically identified. The genetic patterns of inheritance are classified into isolated familial PitNETs and the syndromic tumors. In general, the established genetic causes of familial tumorigenesis tend to present at a younger age, often pursue a more aggressive course, and are more frequently associated with growth hormone hypersecretion compared to sporadic tumors. The mostly studied molecular pathways implicated are the protein kinase A and phosphatidyl-inositol pathways, which are in the main related to mutations in the syndromes of familial isolated pituitary adenoma (FIPA), Carney complex syndrome, and X-linked acrogigantism. Another well-documented mechanism consists of the regulation of p27 or p21 proteins, with further acceleration of the pituitary cell cycle through the check points G1/S and M/G1, mostly documented in multiple endocrine neoplasia type 4. In conclusion, PitNETs may occur in relation to well-established familial germline mutations which may determine the clinical phenotype and the response to treatment, and may require family screening.

NOVA1 acts on Impact to regulate hypothalamic function and translation in inhibitory neurons

We describe a patient haploinsufficient for the neuronal RNA binding protein NOVA1 who developed a behavioral motor hyperactivity disorder, suggesting a role of NOVA1 in postnatal motor inhibition. To investigate Nova1's action in adult Gad2+ inhibitory neurons, we generated a conditional Nova1-null mouse (Nova1-cKOGad2-cre). Strikingly, the phenotypes of these mice show many similarities to the NOVA1 haploinsufficient patient and identify a function of Nova1 in the hypothalamus. Molecularly, Nova1 loss in Gad2-positive neurons alters downstream expression of Impact mRNA, along with a subset of RNAs encoding electron transport chain-related factors and ribosomal proteins. NOVA1 stabilizes Impact mRNA by binding its 3' UTR, antagonizing the actions of miR-138 and miR-124. Together, these studies demonstrate actions of NOVA1 in adult hypothalamic neurons, mechanisms by which it functions in translation and metabolism, including through direct binding to Impact mRNA, and illuminate its role in human neurologic disease.

miR-383-5p, miR-181a-5p, and miR-181b-5p as Predictors of Response to First-Generation Somatostatin Receptor Ligands in Acromegaly

Acromegaly is a chronic systemic disease caused in the vast majority of cases by growth hormone (GH)-secreting adenoma, with surgery being the first-line treatment. When a cure is not attained with surgery, first-generation somatostatin receptor ligands (fg-SRLs) are the most common medication prescribed. Predictors of response to fg-SRLs have been studied; however, they cannot fully predict the response to fg-SRL. MicroRNAs are small RNAs, the main role of which is messenger RNA (mRNA) post-transcriptional regulation. This study aimed to identify the microRNAs involved in resistance to treatment with fg-SRLs in acromegaly. Ten patients with acromegaly undergoing treatment with fg-SRLs were selected to undergo miRNA sequencing: five controlled and five uncontrolled with treatment. Bioinformatic analysis was performed to detect differentially expressed miRNAs. Then, the same 10 samples were used for validation by qPCR and an additional 22 samples were analyzed, totaling 32 samples. e We found 59 differentially expressed miRNAs in the first analysis. miR-181a-5p and miR-181b-5p were downregulated, and miR-383-5p was upregulated in the uncontrolled group. Receiver operating characteristic (ROC) curve analysis of miR-383-5p showed an NPV of 84.3% and a PPV of 84.5%. In summary, miR-181a-5p, miR-181b-5p, and miR-383-5p are biomarkers of response to fg-SRLs, and they can be used individually or included in prediction models as tools to guide clinical decisions.

Transcriptome profile of the anterior pituitary gland in pigs during maternal recognition of pregnancy

The activity of the pituitary gland determines the success of female reproduction. The knowledge regarding the reproductive-status-related changes in the transcriptome of the porcine pituitary is limited. This study aimed to determine and compare the transcriptome profile of the pituitary gland collected from pigs during maternal recognition of pregnancy, i.e. on days 12-13 of pregnancy and during the respective days of the estrous cycle. Analysis indicated 482 differentially expressed genes (DEGs) with an FC > 1.5 (P < 0.05) in the pituitary of pregnant vs. estrous-cyclic pigs. Among them, 68 were up-regulated and 414 were down-regulated. The evaluated DEGs were annotated into 39 gene ontology (GO) biological process terms, 13 GO cellular component terms, and 10 GO molecular function terms. Among the evaluated DEGs were selected genes coding for proteins potentially involved in the regulation of early pregnancy in pigs and used for gene interaction analysis and validation of microarray results. An analysis of the relationships among DEGs in pituitaries collected during maternal recognition of pregnancy showed that some of them are connected with, for example, TGFβ signaling pathway, PRL synthesis, adipocytokines pathway and immune response during maternal recognition of pregnancy. These findings expand the knowledge regarding the molecular mechanisms appearing in the porcine pituitary during the maternal recognition period of pregnancy.

Development and Validation of an LC-MS/MS Method for Simultaneous Determination of Short Peptide-Based Drugs in Human Blood Plasma

A novel HPLC-ESI-MS/MS method for simultaneous gonadotropin-releasing hormone (GnRH) analogs and somatostatin analog quantitation was developed and validated. The developed method was successfully applied to pharmacokinetic studies. The sample preparation process included solid-phase extraction (SPE). Effective chromatographic separation of the analytes and internal standard (dalargin) was achieved with a C18 column, using a gradient elution with two mobile phases: 0.1% v/v formic acid (aqueous solution) and 0.1% v/v formic acid (acetonitrile solution). The linearity of the method was demonstrated within a concentration range of 0.5-20 ng/mL, with correlation coefficients between 0.998-0.999 for goserelin, buserelin, triptorelin, and octreotide, respectively. The relative standard deviation (RSD, %) values for method accuracy and precision did not exceed 20% at the lower level of quantitation (LLOQ) or 15% at other concentration levels.

Neurofibromatosis Type 1 Has a Wide Spectrum of Growth Hormone Excess

Overgrowth due to growth hormone (GH) excess affects approximately 10% of patients with neurofibromatosis type 1 (NF1) and optic pathway glioma (OPG). Our aim is to describe the clinical, biochemical, pathological, and genetic features of GH excess in a retrospective case series of 10 children and adults with NF1 referred to a tertiary care clinical research center. Six children (median age = 4 years, range of 3−5 years), one 14-year-old adolescent, and three adults (median age = 42 years, range of 29−52 years) were diagnosed with NF1 and GH excess. GH excess was confirmed by the failure to suppress GH (<1 ng/mL) on oral glucose tolerance test (OGTT, n = 9) and frequent overnight sampling of GH levels (n = 6). Genetic testing was ascertained through targeted or whole-exome sequencing (n = 9). Five patients (all children) had an OPG without any pituitary abnormality, three patients (one adolescent and two adults) had a pituitary lesion (two tumors, one suggestive hyperplasia) without an OPG, and two patients (one child and one adult) had a pituitary lesion (a pituitary tumor and suggestive hyperplasia, respectively) with a concomitant OPG. The serial overnight sampling of GH levels in six patients revealed abnormal overnight GH profiling. Two adult patients had a voluminous pituitary gland on pituitary imaging. One pituitary tumor from an adolescent patient who harbored a germline heterozygous p.Gln514Pro NF1 variant stained positive for GH and prolactin. One child who harbored a heterozygous truncating variant in exon 46 of NF1 had an OPG that, when compared to normal optic nerves, stained strongly for GPR101, an orphan G protein-coupled receptor causing GH excess in X-linked acrogigantism. We describe a series of patients with GH excess and NF1. Our findings show the variability in patterns of serial overnight GH secretion, somatotroph tumor or hyperplasia in some cases of NF1 and GH excess. Further studies are required to ascertain the link between NF1, GH excess and GPR101, which may aid in the characterization of the molecular underpinning of GH excess in NF1.

Pancreatic neuroendocrine tumor with ectopic adrenocorticotropic hormone syndrome: a case report and 5-year follow-up

Pancreatic neuroendocrine tumors (P-NETs) secreting ectopic adrenocorticotropic hormones (ACTH) are rare and often delayed in diagnosis due to their atypical clinical characteristics. Here, we describe a case of P-NET in the pancreatic tail. The tumor had metastasized to the liver and secreted gastrin and ACTH. A 60-year-old female patient was diagnosed with gastrinoma in the pancreatic tail with liver metastases in 2015. After 3 months, the patient presented refractory hypokalemia and thyroid dysfunction. The final diagnosis was P-NET with ectopic ACTH syndrome (EAS). After cytoreductive surgery and the use of long-acting somatostatin analogs, plasma potassium levels and thyroid function were effectively corrected. Although Sandostatin LAR^® Depot and proton pump inhibitors (PPIs) were used throughout the follow-up period, the tumor relapsed 4 years later. After aggressive treatment, including right hepatectomy, microwave coagulation of the left liver, and cholecystectomy, the tumor returned 4 months later. Finally, the patient underwent three hepatic artery embolizations and 12 courses of CAPTEM regimen chemotherapy. The markers of disease were almost maintained in the normal ranges until now. We have followed up on this case for more than 5 years. A timely and comprehensive examination of hormones and immunohistochemistry is essential. The prognosis of P-NET is poor. Regular long-term follow-up and the application of combined therapies are helpful to control the disease and improve the prognosis.

Site-Specific Hypermethylation of SST 1stExon as a Biomarker for Predicting the Risk of Gastrointestinal Tract Cancers

Background

DNA methylation is an important epigenetic modification in tumorigenesis, and similar epigenetic regulation mechanisms have been found in the gastrointestinal tract (GIT) cancers. Somatostatin (SST) has been confirmed to be expressed throughout the GIT. This study aimed to simultaneously explore the relationships between the SST methylation and the risks of three GIT cancers (esophageal cancer (EC), gastric cancer (GC), and colorectal cancer (CRC)) and to evaluate its diagnostic value.

Methods

Differentially methylated regions (DMRs) of the SST gene, including TSS200, 1stExon, and the gene body, were identified in GIT cancers by The Cancer Genome Atlas (TCGA) database analysis. Further analyses were conducted in tissue samples of EC (n = 50), GC (n = 99), and CRC (n = 80). The SST methylation was detected by bisulfite-sequencing PCR (BSP), and the SST expression was detected by quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR).

Results

In GIT cancers, DMR-related CpG islands were mainly located in the 1stExon. The methylation status of the SST 1stExon in the tumor tissues was significantly higher than that in the adjacent noncancerous tissues, and the methylation rates of the specific CpG sites were correlated with clinical phenotypes. The average methylation rate (AMR) of the SST 1stExon was negatively correlated with the SST gene expression in GC and CRC (both P < 0.001). For the diagnosis of GIT cancers, the combined detection of methylation at CpG sites +18 and +129 showed the highest area under the curve (AUC 0.698), with a sensitivity of 59.3% and a specificity of 72.8%.

Conclusions

The site-specific hypermethylation of the SST 1stExon increases the risk of GIT cancers and might be a potential predictive marker for pan-GIT cancers.

Progress in the Management of Pancreatic Neuroendocrine Tumors

Pancreatic neuroendocrine tumors (PNETs) are a heterogeneous and orphan group of neoplasms that vary in their histology, clinical features, prognosis, and management. The treatment of PNETs is highly dependent on the stage at presentation, tumor grade and differentiation, presence of symptoms from hormonal overproduction or from local growth, tumor burden, and rate of progression. The US Food and Drug Administration has recently approved many novel treatments, which have altered decision making and positively impacted the care and prognosis of these patients. In this review, we focus on the significant progress made in the management of PNETs over the past decade, as well as the active areas of research. Expected final online publication date for the Annual Review of Medicine, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Regulation of GH and GH Signaling by Nutrients

Growth hormone (GH) and insulin-like growth factor-1 (IGF-I) are pleiotropic hormones with important roles in lifespan. They promote growth, anabolic actions, and body maintenance, and in conditions of energy deprivation, favor catabolic feedback mechanisms switching from carbohydrate oxidation to lipolysis, with the aim to preserve protein storages and survival. IGF-I/insulin signaling was also the first one identified in the regulation of lifespan in relation to the nutrient-sensing. Indeed, nutrients are crucial modifiers of the GH/IGF-I axis, and these hormones also regulate the complex orchestration of utilization of nutrients in cell and tissues. The aim of this review is to summarize current knowledge on the reciprocal feedback among the GH/IGF-I axis, macro and micronutrients, and dietary regimens, including caloric restriction. Expanding the depth of information on this topic could open perspectives in nutrition management, prevention, and treatment of GH/IGF-I deficiency or excess during life.

Cushing's Syndrome Effects on the Thyroid

The most known effects of endogenous Cushing’s syndrome are the phenotypic changes and metabolic consequences. However, hypercortisolism can exert important effects on other endocrine axes. The hypothalamus–pituitary–thyroid axis activity can be impaired by the inappropriate cortisol secretion, which determinates the clinical and biochemical features of the “central hypothyroidism”. These findings have been confirmed by several clinical studies, which also showed that the cure of hypercortisolism can determine the recovery of normal hypothalamus–pituitary–thyroid axis activity. During active Cushing’s syndrome, the “immunological tolerance” guaranteed by the hypercortisolism can mask, in predisposed patients, the development of autoimmune thyroid diseases, which increases in prevalence after the resolution of hypercortisolism. However, the immunological mechanism is not the only factor that contributes to this phenomenon, which probably includes also deiodinase-impaired activity. Cushing’s syndrome can also have an indirect impact on thyroid function, considering that some drugs used for the medical control of hypercortisolism are associated with alterations in the thyroid function test. These considerations suggest the utility to check the thyroid function in Cushing’s syndrome patients, both during the active disease and after its remission.

Leptin Modulates the Response of Brown Adipose Tissue to Negative Energy Balance: Implication of the GH/IGF-I Axis

The growth hormone (GH)/insulin-like growth factor I (IGF-I) axis is involved in metabolic control. Malnutrition reduces IGF-I and modifies the thermogenic capacity of brown adipose tissue (BAT). Leptin has effects on the GH/IGF-I axis and the function of BAT, but its interaction with IGF-I and the mechanisms involved in the regulation of thermogenesis remains unknown. We studied the GH/IGF-I axis and activation of IGF-I-related signaling and metabolism related to BAT thermogenesis in chronic central leptin infused (L), pair-fed (PF), and control rats. Hypothalamic somatostatin mRNA levels were increased in PF and decreased in L, while pituitary GH mRNA was reduced in PF. Serum GH and IGF-I concentrations were decreased only in PF. In BAT, the association between suppressor of cytokine signaling 3 and the IGF-I receptor was reduced, and phosphorylation of the IGF-I receptor increased in the L group. Phosphorylation of Akt and cyclic AMP response element binding protein and glucose transporter 4 mRNA levels were increased in L and mRNA levels of uncoupling protein-1 (UCP-1) and enzymes involved in lipid anabolism reduced in PF. These results suggest that modifications in UCP-1 in BAT and changes in the GH/IGF-I axis induced by negative energy balance are dependent upon leptin levels.

Genomic Loci Affecting Milk Production in German Black Pied Cattle (DSN)

German Black Pied cattle (DSN) is an endangered population of about 2,550 dual-purpose cattle in Germany. Having a milk yield of about 2,500 kg less than the predominant dairy breed Holstein, the preservation of DSN is supported by the German government and the EU. The identification of the genomic loci affecting milk production in DSN can provide a basis for selection decisions for genetic improvement of DSN in order to increase market chances through the improvement of milk yield. A genome-wide association analysis of 30 milk traits was conducted in different lactation periods and numbers. Association using multiple linear regression models in R was performed on 1,490 DSN cattle genotyped with BovineSNP50 SNP-chip. 41 significant and 20 suggestive SNPs affecting milk production traits in DSN were identified, as well as 15 additional SNPs for protein content which are less reliable due to high inflation. The most significant effects on milk yield in DSN were detected on chromosomes 1, 6, and 20. The region on chromosome 6 was located nearby the casein gene cluster and the corresponding haplotype overlapped the CSN3 gene (casein kappa). Associations for fat and protein yield and content were also detected. High correlation between traits of the same lactation period or number led to some SNPs being significant for multiple investigated traits. Half of all identified SNPs have been reported in other studies, previously. 15 SNPs were associated with the same traits in other breeds. The other associated SNPs have been reported previously for traits such as exterior, health, meat and carcass, production, and reproduction traits. No association could be detected between DGAT1 and other known milk genes with milk production traits despite the close relationship between DSN and Holstein. The results of this study confirmed that many SNPs identified in other breeds as associated with milk traits also affect milk traits in dual-purpose DSN cattle and can be used for further genetic analysis to identify genes and causal variants that affect milk production in DSN cattle.

Differential effects of β-arrestin1 and β-arrestin2 on somatostatin receptors in murine AtT-20 corticotroph tumor cells

Autonomous production of adrenocorticotropic hormone (ACTH) from pituitary corticotroph adenomas is the primary cause of Cushing's disease. Somatostatin receptor, a G protein-coupled receptor (GPCR), types 2 (SSTR2) and 5 (SSTR5) mRNA expression is greater than that of other SSTR subtypes in human corticotroph adenomas. Further, the multiligand SOM230 shows potent effects in decreasing ACTH plasma levels and urinary free cortisol levels in patients with Cushing's disease. We previously showed that both Sstr2 and Sstr5 mRNA levels were unaffected by SOM230 treatment, suggesting that both receptors might not be downregulated by the agonist. Intracellular molecules, such as β-arrestins, modulate ligand activated-receptor responses. In the present study, we determined regulation of β-arrestin1 and β-arrestin2 by SOM230 and dexamethasone in murine AtT-20 corticotroph tumor cells. In addition, we examined the effects of β-arrestin1 and β-arrestin2 on Sstr mRNA and their protein levels. SOM230 treatment increased β-arrestin1 mRNA levels and did not alter β-arrestin2 mRNA levels. SOM230 treatment could induce β-arrestin1 production in corticotroph tumor cells. Dexamethasone treatment decreased β-arrestin2 mRNA levels. β-arrestin2 knockdown increased proopiomelanocortin, and both Sstr2 and Sstr5 mRNA and their protein levels. The β-arrestin2 knockdown-increased proopiomelanocortin mRNA levels were canceled by SOM230 treatment.

Three lactation-related hormones: Regulation of hypothalamus-pituitary axis and function on lactation

The endocrine system plays a central role in many aspects of lactation, including mammogenesis (mammary gland development), lactogenesis (onset of lactation), and galactopoiesis (maintenance of milk secretion). Many hormones of the endocrine system directly or indirectly regulate lactation process. The secretion of prolactin (PRL), one of the most important lactation-related hormones, is inhibited by hypothalamus-pituitary dopaminergic system and stimulated by hypothalamus-pituitary oxytocinergic system. This hormone is essential in all stages of lactation. The growth hormone (GH) regulates metabolism and the distribution of nutrients between tissues mammary glands, and stimulates the production of IGF-I from the liver which binds to IGF-IR of mammary epithelial cells (MECs) to indirectly promote lactation. The synthesis and secretion of estrogen (E) are affected by the hypothalamus-pituitary axis. The hormone regulates duct morphogenesis and MECs proliferation. It also modulates the synthesis and secretion of PRL and GH, which together regulate the lactation in female animals. In this article, we reviewed the three main lactation-related hormones (PRL, GH, and E), summarize their regulation by the hypothalamus-pituitary axis and how they influence lactation.

Turning the 'Tides on Neuropsychiatric Diseases: The Role of Peptides in the Prefrontal Cortex

Recent advancements in technology have enabled researchers to probe the brain with the greater region, cell, and receptor specificity. These developments have allowed for a more thorough understanding of how regulation of the neurophysiology within a region is essential for maintaining healthy brain function. Stress has been shown to alter the prefrontal cortex (PFC) functioning, and evidence links functional impairments in PFC brain activity with neuropsychiatric disorders. Moreover, a growing body of literature highlights the importance of neuropeptides in the PFC to modulate neural signaling and to influence behavior. The converging evidence outlined in this review indicates that neuropeptides in the PFC are specifically impacted by stress, and are found to be dysregulated in numerous stress-related neuropsychiatric disorders including substance use disorder, major depressive disorder (MDD), posttraumatic stress disorder, and schizophrenia. This review explores how neuropeptides in the PFC function to regulate the neural activity, and how genetic and environmental factors, such as stress, lead to dysregulation in neuropeptide systems, which may ultimately contribute to the pathology of neuropsychiatric diseases.

Insulin synthesized in the paraventricular nucleus of the hypothalamus regulates pituitary growth hormone production

Evidence has mounted that insulin can be synthesized in various brain regions, including the hypothalamus. However, the distribution and functions of insulin-expressing cells in the hypothalamus remain elusive. Herein, we show that in the mouse hypothalamus, the perikarya of insulin-positive neurons are located in the paraventricular nucleus (PVN) and their axons project to the median eminence; these findings define parvocellular neurosecretory PVN insulin neurons. Contrary to corticotropin-releasing hormone expression, insulin expression in the PVN was inhibited by restraint stress (RS) in both adult and young mice. Acute RS–induced inhibition of PVN insulin expression in adult mice decreased both pituitary growth hormone (Gh) mRNA level and serum GH concentration, which were attenuated by overexpression of PVN insulin. Notably, PVN insulin knockdown or chronic RS in young mice hindered normal growth via the downregulation of GH gene expression and secretion, whereas PVN insulin overexpression in young mice prevented chronic RS–induced growth retardation by elevating GH production. Our results suggest that in both normal and stressful conditions, insulin synthesized in the parvocellular PVN neurons plays an important role in the regulation of pituitary GH production and body length, unveiling a physiological function of brain-derived insulin.

Insulin produced in the paraventricular nucleus regulates body length by modulating pituitary growth hormone expression and secretion under both normal and stress conditions.

Regulated resurfacing of a somatostatin receptor storage compartment fine-tunes pituitary secretion

In pituitary cells, internalized somatostatin receptor is held in a GLUT4-like storage compartment. The receptor rapidly resurfaces in response to selective signaling pathways in a process that fine-tunes pituitary hormone release.

The surfacing of the glucose transporter GLUT4 driven by insulin receptor activation provides the prototypic example of a homeostasis response dependent on mobilization of an intracellular storage compartment. Here, we generalize this concept to a G protein–coupled receptor, somatostatin receptor subtype 2 (SSTR2), in pituitary cells. Following internalization in corticotropes, SSTR2 moves to a juxtanuclear syntaxin-6–positive compartment, where it remains until the corticotropes are stimulated with corticotropin releasing factor (CRF), whereupon SSTR2 exits the compartment on syntaxin-6–positive vesicular/tubular carriers that depend on Rab10 for their fusion with the plasma membrane. As SSTR2 activation antagonizes CRF-mediated hormone release, this storage/resurfacing mechanism may allow for a physiological homeostatic feedback system. In fact, we find that SSTR2 moves from an intracellular compartment to the cell surface in pituitary gland somatotropes, concomitant with increasing levels of serum growth hormone (GH) during natural GH cycles. Our data thus provide a mechanism by which signaling-mediated plasma membrane resurfacing of SSTR2 can fine-tune pituitary hormone release.

EGF-GH Axis in Rat Steatotic and Non-steatotic Liver Transplantation From Brain-dead Donors

BACKGROUND

We evaluated the potential dysfunction caused by changes in growth hormone (GH) levels after brain death (BD), and the effects of modulating GH through exogenous epidermal growth factor (EGF) in steatotic and nonsteatotic grafts.

METHODS

Steatotic and nonsteatotic grafts from non-BD and BD rat donors were cold stored for 6 hours and transplanted to live rats. Administration of GH and EGF and their underlying mechanisms were characterized in recipients of steatotic and nonsteatotic grafts from BD donors maintained normotensive during the 6 hours before donation. Circulating and hepatic GH and EGF levels, hepatic damage, and regeneration parameters were evaluated. Recipient survival was monitored for 14 days. Somatostatin, ghrelin, and GH-releasing hormones that regulate GH secretion from the anterior pituitary were determined. The survival signaling pathway phosphoinositide-3-kinase/protein kinase B that regulates inflammation (suppressors of cytokine signaling, high-mobility group protein B1, oxidative stress, and neutrophil accumulation) was evaluated.

RESULTS

BD reduced circulating GH and increased GH levels only in steatotic livers. GH administration exacerbated adverse BD-associated effects in both types of graft. Exogenous EGF reduced GH in steatotic livers, thus activating cell proliferation and survival signaling pathways, ultimately reducing injury and inflammation. However, EGF increased GH in nonsteatotic grafts, which exacerbated damage. The benefits of EGF for steatotic grafts were associated with increased levels of somatostatin, a GH inhibitor, whereas the deleterious effect on nonsteatotic grafts was exerted through increased amounts of ghrelin, a GH stimulator.

CONCLUSIONS

GH treatment is not appropriate in rat liver transplant from BD donors, whereas EGF (throughout GH inhibition) protects only in steatotic grafts.

Abundant expression of the membrane-anchored protease-regulator RECK in the anterior pituitary gland and its implication in the growth hormone/insulin-like growth factor 1 axis in mice

The tumor suppressor gene Reversion-inducing cysteine-rich protein with Kazal motifs (Reck) encodes a membrane-anchored protease regulator expressed in multiple tissues in mouse embryos and is essential for embryonic development. In postnatal mice, however, physiological roles for the RECK protein remain unclear. We found in this study that Reck is abundantly expressed in growth hormone (GH)-producing cells (somatotrophs) in the anterior pituitary gland (AP). We also found that two types of viable Reck mutant mice, one with reduced RECK expression (Hypo mice) and the other with induced Reck deficiency from 10 days after birth (iKO mice treated with tamoxifen), exhibit common phenotypes including decreases in body size and plasma levels of insulin-like growth factor-1 (IGF1). To gain insights into the function of RECK in the AP, we characterized several somatotroph-associated molecules in the AP of these mice. Immunoreactivity of GH was greatly reduced in tamoxifen-treated iKO mice; in these mice, two membrane receptors involved in the stimulation of GH secretion [growth hormone secretagogue receptor (GHSR) and growth hormone releasing hormone receptor (GHRHR)] were decreased, however, their mRNAs were increased. Decrease in GHSR immunoreactivity and concomitant increase in its mRNA were also found in the other mutant line, Hypo. Furthermore, reduced immunoreactivity of growth hormone receptor (GHR) and concomitant increase in its mRNA was also found in the liver of Hypo mice. These results raise the possibility that RECK supports proper functioning of the GH/IGF1 axis in mice, thereby affecting their growth and metabolism.

Peptide-Based Therapeutics for Oncology

The development of peptide-based drugs, which are usually synthetic analogues of endogenous peptides, is currently one of the most topical directions in drug development. Among them, antitumor peptide-based drugs are of great interest. Anticancer peptides can be classified into three main groups based on their mechanism of action: inhibitory, necrosis-inducing and pro-apoptotic peptides. As an antitumor therapy, peptides are considered to have at least the same efficacy as chemotherapy or surgical treatment, but offer advantages in terms of safety and tolerability, given that chemotherapy is usually characterized by severe adverse effects, and surgery carries additional risks for patients. Short peptides have a number of benefits over other molecules. First, compared with full-length proteins and antibodies, short peptides are less immunogenic, more stable ex-vivo (prolonged storage at room temperature), and have better tumor or organ permeability. Moreover, the production of such short peptide-based drugs is more cost effective. Second, in comparison with small organic molecules, peptides have higher efficacy and specificity. Finally, due to the fact that the main products of peptide metabolism are amino acids, these drugs are usually characterized by lower toxicity. Short peptides have a highly selective mechanism of action, thereby demonstrating low toxicity. Furthermore, with the addition of different stabilizing structural modifications, as well as novel drug delivery systems, the peptide-based drugs are proving to be promising therapeutics for cancer mono- or polytherapy. However, challenges remain including that endogenous and synthetic peptide molecules can be oncogenic. Therefore, it is important to investigate whether peptides contribute to tumor growth. In order to answer such questions, numerous preclinical and clinical studies of peptide-based therapeutics are currently being conducted.

Pharmacokinetics, radiation dosimetry, acute toxicity and automated synthesis of [18F]AmBF3-TATE

Introduction

[¹⁸F]AmBF₃-TATE is a somatostatin agonist that selectively binds to somatostatin receptor subtype 2 (SSTR2). For clinical translation, pharmacokinetics, radiation dosimetry, and acute toxicity of [¹⁸F]AmBF₃-TATE were assessed with good laboratory practice (GLP) standards.

Methods

ICR mice were intravenously administered 0.8–2.0 MBq of [¹⁸F]AmBF₃-TATE, with one group pre-injected with 100 μg of [¹⁹F]AmBF₃-TATE 30 min before radiopharmaceutical administration to assess uptake specificity. The mice were euthanized at 0.5, 1, 2, or 4 h post-injection (p.i.). Blood and tissues were collected, weighed, and counted on a gamma counter to determine percentage injected dose per gram (%ID/g). Dosimetry was calculated based on biodistribution data using the mouse and human phantoms included in OLINDA. Acute toxicity was assessed in Sprague-Dawley rats at the dose of 0.742 mg/kg [¹⁹F]AmBF₃-TATE, with a 14-day observation/recovery period. Blood chemistry parameters, gross, and histopathology were evaluated. Body weight change and food consumption were monitored. The production of [¹⁸F]AmBF₃-TATE was automated on a Trasis AllinOne synthesis module.

Results

[¹⁸F]AmBF₃-TATE was cleared through the renal and hepatobiliary pathway. At 1 h p.i., the pancreas (F, 15.7 ± 3.72 and M 14.3 ± 1.61 %ID/g), stomach (F, 15.3 ± 3.63 and M, 19.0 ± 3.49 %ID/g), and lungs (F, 9.26 ± 2.24 and M, 6.17 ± 6.04 %ID/g) were the organs with the highest specific uptake. Pre-injection with [¹⁹F]AmBF₃-TATE significantly reduced pancreatic uptake (F, 0.13 ± 0.03 and M, 0.18 ± 0.09 %ID/g) at 1 h p.i. For dosimetry extrapolated to the average adult human, the bladder (0.027–0.030 mGy/MBq), pancreas (0.018–0.028 mGy/MBq), and lungs (0.006–0.013 mGy/MBq) are expected to receive the highest doses. No test-item related effects were observed upon evaluation of clinical observations, body weights, food consumption, clinical pathology, gross pathology, and histopathology for acute toxicity. [¹⁸F]AmBF₃-TATE was produced at activity yields of 15.6 ± 4.59 GBq, average molar activity of 435 ± 162 GBq/μmol, and radiochemical purity of 98.0 ± 1.73% with the automated synthesizer.

Conclusion

[¹⁸F]AmBF₃-TATE binds specifically to SSTR2. At 1000× clinical dose, [¹⁹F]AmBF₃-TATE was well tolerated with no treatment-related adverse effects.

Thyrotropin-Releasing Hormone (TRH) and Somatostatin (SST), but not Growth Hormone-Releasing Hormone (GHRH) nor Ghrelin (GHRL), Regulate Expression and Release of Immune Growth Hormone (GH) from Chicken Bursal B-Lymphocyte Cultures

It is known that growth hormone (GH) is expressed in immune cells, where it exerts immunomodulatory effects. However, the mechanisms of expression and release of GH in the immune system remain unclear. We analyzed the effect of growth hormone-releasing hormone (GHRH), thyrotropin-releasing hormone (TRH), ghrelin (GHRL), and somatostatin (SST) upon GH mRNA expression, intracellular and released GH, Ser133-phosphorylation of CREB (pCREB^S133), intracellular Ca²⁺ levels, as well as B-cell activating factor (BAFF) mRNA expression in bursal B-lymphocytes (BBLs) cell cultures since several GH secretagogues, as well as their corresponding receptors (-R), are expressed in B-lymphocytes of several species. The expression of TRH/TRH-R, ghrelin/GHS-R1a, and SST/SST-Rs (Subtypes 1 to 5) was observed in BBLs by RT-PCR and immunocytochemistry (ICC), whereas GHRH/GHRH-R were absent in these cells. We found that TRH treatment significantly increased local GH mRNA expression and CREB phosphorylation. Conversely, SST decreased GH mRNA expression. Additionally, when added together, SST prevented TRH-induced GH mRNA expression, but no changes were observed in pCREB^S133 levels. Furthermore, TRH stimulated GH release to the culture media, while SST increased the intracellular content of this hormone. Interestingly, SST inhibited TRH-induced GH release in a dose-dependent manner. The coaddition of TRH and SST decreased the intracellular content of GH. After 10 min. of incubation with either TRH or SST, the intracellular calcium levels significantly decreased, but they were increased at 60 min. However, the combined treatment with both peptides maintained the Ca²⁺ levels reduced up to 60-min. of incubation. On the other hand, BAFF cytokine mRNA expression was significantly increased by TRH administration. Altogether, our results suggest that TRH and SST are implicated in the regulation of GH expression and release in BBL cultures, which also involve changes in pCREB^S133 and intracellular Ca²⁺ concentration. It is likely that TRH, SST, and GH exert autocrine/paracrine immunomodulatory actions and participate in the maturation of chicken BBLs.

The interoceptive hippocampus: Mouse brain endocrine receptor expression highlights a dentate gyrus (DG)-cornu ammonis (CA) challenge-sufficiency axis

The primeval function of the mammalian hippocampus (HPC) remains uncertain. Implicated in learning and memory, spatial navigation, and neuropsychological disorders, evolutionary theory suggests that the HPC evolved from a primeval chemosensory epithelium. Deficits in sensing of internal body status ('interoception') in patients with HPC lesions argue that internal sensing may be conserved in higher vertebrates. We studied the expression patterns in mouse brain of 250 endocrine receptors that respond to blood-borne ligands. Key findings are (i) the proportions and levels of endocrine receptor expression in the HPC are significantly higher than in all other comparable brain regions. (ii) Surprisingly, the distribution of endocrine receptor expression within mouse HPC was found to be highly structured: receptors signaling 'challenge' are segregated in dentate gyrus (DG), whereas those signaling 'sufficiency' are principally found in cornu ammonis (CA) regions. Selective expression of endocrine receptors in the HPC argues that interoception remains a core feature of hippocampal function. Further, we report that ligands of DG receptors predominantly inhibit both synaptic potentiation and neurogenesis, whereas CA receptor ligands conversely promote both synaptic potentiation and neurogenesis. These findings suggest that the hippocampus acts as an integrator of body status, extending its role in context-dependent memory encoding from 'where' and 'when' to 'how I feel'. Implications for anxiety and depression are discussed.

Diet-Induced Growth Is Regulated via Acquired Leptin Resistance and Engages a Pomc-Somatostatin-Growth Hormone Circuit

Anorexigenic pro-opiomelanocortin (Pomc)/alpha-melanocyte stimulating hormone (αMSH) neurons of the hypothalamic melanocortin system function as key regulators of energy homeostasis, also controlling somatic growth across different species. However, the mechanisms of melanocortin-dependent growth control still remain ill-defined. Here, we reveal a thus-far-unrecognized structural and functional connection between Pomc neurons and the somatotropic hypothalamo-pituitary axis. Excessive feeding of larval zebrafish causes leptin resistance and reduced levels of the hypothalamic satiety mediator pomca. In turn, this leads to reduced activation of hypophysiotropic somatostatin (Sst)-neurons that express the melanocortin receptor Mc4r, elevated growth hormone (GH) expression in the pituitary, and enhanced somatic growth. Mc4r expression and αMSH responsiveness are conserved in Sst-expressing hypothalamic neurons of mice. Thus, acquired leptin resistance and attenuation of pomca transcription in response to excessive caloric intake may represent an ancient mechanism to promote somatic growth when food resources are plentiful.

Somatostatin Analogues in the Treatment of Neuroendocrine Tumors: Past, Present and Future

In recent decades, the incidence of neuroendocrine tumors (NETs) has steadily increased. Due to the slow-growing nature of these tumors and the lack of early symptoms, most cases are diagnosed at advanced stages, when curative treatment options are no longer available. Prognosis and survival of patients with NETs are determined by the location of the primary lesion, biochemical functional status, differentiation, initial staging, and response to treatment. Somatostatin analogue (SSA) therapy has been a mainstay of antisecretory therapy in functioning neuroendocrine tumors, which cause various clinical symptoms depending on hormonal hypersecretion. Beyond symptomatic management, recent research demonstrates that SSAs exert antiproliferative effects and inhibit tumor growth via the somatostatin receptor 2 (SSTR2). Both the PROMID (placebo-controlled, prospective, randomized study in patients with metastatic neuroendocrine midgut tumors) and the CLARINET (controlled study of lanreotide antiproliferative response in neuroendocrine tumors) trial showed a statistically significant prolongation of time to progression/progression-free survival (TTP/PFS) upon SSA treatment, compared to placebo. Moreover, the combination of SSA with peptide receptor radionuclide therapy (PRRT) in small intestinal NETs has proven efficacy in the phase 3 neuroendocrine tumours therapy (NETTER 1) trial. PRRT is currently being tested for enteropancreatic NETs versus everolimus in the COMPETE trial, and the potential of SSTR-antagonists in PRRT is now being evaluated in early phase I/II clinical trials. This review provides a synopsis on the pharmacological development of SSAs and their use as antisecretory drugs. Moreover, this review highlights the clinical evidence of SSAs in monotherapy, and in combination with other treatment modalities, as applied to the antiproliferative management of neuroendocrine tumors with special attention to recent high-quality phase III trials.

Benzene affects the response to octreotide treatment of growth hormone secreting pituitary adenoma cells

Growth hormone (GH) secreting pituitary adenomas are the main cause of acromegaly. Somatostatin analogs are the gold standard of medical therapy; however, resistance represents a big drawback in acromegaly management. We recently demonstrated that benzene (BZ) modifies the aggressiveness of GH-secreting rat pituitary adenoma cells (GH3), increasing GH secretion and altering the synthesis of molecules involved in the somatostatin signaling pathway. Based on these pieces of evidence, this study aimed to evaluate the effects of BZ on octreotide (OCT) efficacy in GH-secreting adenoma cells. In GH3 cells, BZ counteracted the anti-proliferative action of OCT. GH gene expression, unmodified by OCT, remained high in BZ-treated cells as well as after treatment with the association of both. GH secretion, reduced by OCT, was increased after treatment with BZ alone or when the pollutant was used with OCT. The combination of BZ and OCT greatly reduced the gene expression of ZAC1 and SSTR2; and this reduction was also present at a protein level. BZ caused an increase in the protein level of the transcription factor STAT3 and in its phosphorylated form. In the presence of BZ, OCT lost the ability to reduce the phosphorylated protein levels. Finally, in primary cultures of human pituitary adenoma cells, BZ caused an increase in GH secretion. OCT decreased GH secretion, but the addition of BZ reversed the OCT effect. In conclusion, our results suggest that BZ may have an important role in the resistance of pituitary adenomas to the pharmacological treatment with somatostatin analogs.

International Union of Basic and Clinical Pharmacology. CV. Somatostatin Receptors: Structure, Function, Ligands, and New Nomenclature

Somatostatin, also known as somatotropin-release inhibitory factor, is a cyclopeptide that exerts potent inhibitory actions on hormone secretion and neuronal excitability. Its physiologic functions are mediated by five G protein-coupled receptors (GPCRs) called somatostatin receptor (SST)1-5. These five receptors share common structural features and signaling mechanisms but differ in their cellular and subcellular localization and mode of regulation. SST₂ and SST₅ receptors have evolved as primary targets for pharmacological treatment of pituitary adenomas and neuroendocrine tumors. In addition, SST₂ is a prototypical GPCR for the development of peptide-based radiopharmaceuticals for diagnostic and therapeutic interventions. This review article summarizes findings published in the last 25 years on the physiology, pharmacology, and clinical applications related to SSTs. We also discuss potential future developments and propose a new nomenclature.

Neuronostatin exerts actions on pituitary that are unique from its sibling peptide somatostatin

Neuronostatin, a somatostatin gene-encoded peptide, exerts important physiological and metabolic actions in diverse tissues. However, the direct biological effects of neuronostatin on pituitary function of humans and primates are still unknown. This study used baboon (Papio anubis) primary pituitary cell cultures, a species that closely models human physiology, to demonstrate that neuronostatin inhibits basal, but not ghrelin-/GnRH-stimulated, growth hormone (GH) and luteinizing hormone (LH) secretion in a dose- and time-dependent fashion, without affecting the secretion of other pituitary hormones (prolactin, ACTH, FSH, thyroid-stimulating hormone (TSH)) or changing mRNA levels. Actions of neuronostatin differs from somatostatin which in this study reduced GH/PRL/ACTH/LH/TSH secretion and GH/PRL/POMC/LH gene expression. Remarkably, we found that inhibitory actions of neuronostatin are likely mediated through: (1) the orphan receptor GPCR107 (found to be highly expressed in pituitary compared to somatostatin-receptors), (2) common (i.e. adenylyl cyclase/protein kinase A/MAPK/extra-/intracellular Ca²⁺ mobilization, but not phospholipase C/protein kinase C/mTOR) and distinct (i.e. PI3K) signaling pathways than somatostatin and; (3) dissimilar molecular mechanisms than somatostatin (i.e. upregulation of GPCR107 and downregulation of GHS-R/Kiss1-R expression by neuronostatin and, upregulation of sst1-5 expression by somatostatin). Altogether, the results of this study provide the first evidence that there is a functional neuronostatin signaling circuit, unique from somatostatin, which may work in concert with somatostatin to fine-tune hormone release from somatostropes and gonadotropes.

The progress of prophylactic treatment in retinopathy of prematurity

Retinopathy of prematurity (ROP) is a retinal vascular disorder frequently found in premature infants. Different therapeutic strategies have been developed to treat ROP. However, there are still many children with ROP suffering by severe limitations in vision or even blindness. Recently, ROP has been suggested to be caused by abnormal development of the retinal vasculature, but not simply resulted by retinal neovascularization which takes about 4 to 6wk after birth in premature infants. Thus, instead of focusing on how to reduce retinal neovascularization, understanding the pathological changes and mechanisms that occur prior to retinal neovascularization is meaningful, which may lead to identify novel target(s) for the development of novel strategy to promote the healthy growth of retinal blood vessels rather than passively waiting for the appearance of retinal neovascularization and removing it by force. In this review, we discussed recent studies about, 1) the pathogenesis prior to retinal neovascularization in oxygen-induced retinopathy (OIR; a ROP in animal model) and in premature infants with ROP; 2) the preclinical and clinical research on preventive treatment of early OIR and ROP. We will not only highlight the importance of the mechanisms and signalling pathways in regulating early stage of ROP but also will provide guidance for actively exploring novel mechanisms and discovering novel treatments for early phase OIR and ROP prior to retinal neovascularization in the future.

Malignant transformation in non-functioning pituitary adenomas (pituitary carcinoma)

Non-functioning pituitary carcinomas (NFPC) are defined as tumours of adenophyseal origin with craniospinal or systemic dissemination, with the absence of a hormonal hypersecretion syndrome. These are a histologically heterogenous group of tumours, comprising gonadotroph, null cell, "silent" tumours of corticotroph, somatotroph or lactotroph cell lineages as well as plurihormonal Pit-1 tumours. NFPC are exceedingly rare, and hence few cases have been described. This review has identified 38 patients with NFPC reported in the literature. Recurrent invasive non-functioning pituitary adenomas (NFPA) were observed in a majority of patients. Various factors have been identified as markers of the potential for aggressive behaviour, including rapid tumour growth, growth after radiotherapy, gain or shift of hormone secretion and raised proliferative markers. Typically, there is a latency of several years from the original presentation with an NFPA to identification of metastases and only 5 cases reported with rapidly progressive malignant disease within 1 month of presentation. Therapeutic options include debulking surgery, radiation therapy and chemotherapy with temozolomide recommended as first line systemic treatment. Although long-term survivors are described, prognosis remains generally very poor (median survival 8 months). Improvements in molecular tumour profiling may assist in predicting tumour behaviour, guide therapeutic choices and identify novel therapies.

Cellular effects of AP102, a somatostatin analog with balanced affinities for the hSSTR2 and hSSTR5 receptors

BACKGROUND

Somatostatin analogs (SSAs) are first-line medical therapy for the treatment of acromegaly and neuroendocrine tumors that express somatostatin receptors (SSTR). Somatostatin suppresses secretion of a large number of hormones through the stimulation of the five SSTR. However, unbalanced inhibition of secretion as observed with the highly potent SSAs pasireotide causes hyperglycaemia mainly by inhibiting insulin secretion. In contrast, AP102 a new SSAs has neutral effect on blood glucose while suppressing GH secretion. Our objective was to establish the cellular effects of AP102 on SSTR2 and SSTR5 that may explain the differences observed between AP102 and other SSAs.

METHODS

We compared the binding and agonist activity of AP102 with somatostatin-14, octreotide and pasireotide in HEK293 cells transfected with human SSTR2 and SSTR5 receptors. SSAs signal transduction effects (cAMP concentrations) were measured in forskolin-treated cells in the presence of SSAs. Proliferation and apoptotic effects were determined and binding assays were performed using ¹²⁵I- somatostatin-14.

RESULTS

AP102 has comparable affinity and agonist effect to octreotide at SSTR2 (IC50's of 112 pM and 244 pM, respectively; EC50's of 230 pM and 210 pM, respectively) in contrast to pasireotide that exhibits a 12-27 fold higher IC50 (3110 pM) and about 5-fold higher EC50 (1097 pM). At SSTR5, AP102 has much higher affinity and stimulating effect than octreotide (IC50's of 773 pM and 16,737 pM, respectively; EC50's of 8526 pM and 26,800 pM), and an intermediate affinity and agonist effect between octreotide and pasireotide. AP102, octreotide and pasireotide have variable anti-proliferative effects on HEK cells transfected with SSTR2 and SSTR5.

CONCLUSION

AP102 is a new SSA that better reduces signaling at SSTR2 than SSTR5 and prevents cell proliferation at both receptors. The euglycaemic effect of AP102 observed in preclinical studies may be related to this intermediate agonistic potency between pasireotide and octreotide at SSTR2 and SSTR5.

Management of NFAs: medical treatment

INTRODUCTION

Non-functioning pituitary adenomas (NFPAs) are in general large tumors that present with symptoms secondary to local pressure on adjacent structures. Transsphenoidal surgery is the first line of treatment but residual tumor mass is often detected post-operatively. Medical therapy, in any stage of tumor management, is not well established.

METHODS

A literature search was performed to review the available data on medical treatment of NFPAs.

RESULTS

Medications investigated for the treatment of NFPAs include dopamine receptor agonists (DA) and somatostatin receptor ligands. Randomized controlled trials are lacking, but available data suggest that DA have a positive effect on tumor remnant stabilization after surgery and could be considered in this setting. Temozolomide is reserved for aggressive tumors, although future studies are required.

CONCLUSIONS

NFPA are often not amenable to complete surgical resection. Conservative follow-up after surgery is associated with a high prevalence of tumor remnant progression. DA therapy may prevent residual tumor enlargement in over 85% of these patients, with a substantial consequent reduction in the need for repeat surgery or radiation therapy. It is our view that DA treatment should be routinely considered for the management of NFPA patients with incompletely resected tumors.

Neuroanatomical connections between kisspeptin neurones and somatostatin neurones in female and male rat hypothalamus: a possible involvement of SSTR1 in kisspeptin release

Somatostatin (SST) a neuropeptide involved in the central modulation of several physiological functions, is co-distributed in the same hypothalamic areas as kisspeptin (KP), the most potent secretagogue of the gonadotropin-releasing hormone (GnRH) secretion known to date. As SST infused intracerebroventricularly (icv) evoked a potent inhibition of GnRH release, we explored neuroanatomical relationships between KP and SST populations in male and female rats. For that, intact males and ovariectomised oestradiol-replaced females were killed and their brains processed in order to simultaneously detect KP, SST and synapsin, a marker for synapses. We observed numerous appositions of KP on SST neurones both in female and male arcuate nucleus (ARC) and ventromedial hypothalamus. A large association between SST terminals and KP neurones at the level of the pre-optic area (POA) was also observed in female rats and in a more limited frame in males. Finally, most KP neurones from the ARC showed SST appositions in both sexes. To determine whether SST could affect KP cell activity, we assessed whether SST receptors (SSTR) were present on KP neurones in the ARC. We also looked for the presence of SSTR1 and SSTR2A in the brain of male rats. Brains were processed through a sequential double immunocytochemistry in order to detect KP and SSTR1 or KP and SSTR2A. We observed overlapping distributions of immunoreactive neurones for SSTR1 and KP and counted approximately one third of KP neurones with SSTR1. In contrast, neurones labelled for SSTR2A or KP were often juxtaposed in the ARC and the occurrence of double-labelled neurones was sporadic (<5%). These results suggest that SST action on KP neurones would pass mainly through SSTR1 at the level of the ARC. This article is protected by copyright. All rights reserved.

Multiple signaling pathways convey central and peripheral signals to regulate pituitary function: Lessons from human and non-human primate models

The anterior pituitary gland is a key organ involved in the control of multiple physiological functions including growth, reproduction, metabolism and stress. These functions are controlled by five distinct hormone-producing pituitary cell types that produce growth hormone (somatotropes), prolactin (lactotropes), adrenocorticotropin (corticotropes), thyrotropin (thyrotropes) and follicle stimulating hormone/luteinizing hormone (gonadotropes). Classically, the synthesis and release of pituitary hormones was thought to be primarily regulated by central (neuroendocrine) signals. However, it is now becoming apparent that factors produced by pituitary hormone targets (endocrine and non-endocrine organs) can feedback directly to the pituitary to adjust pituitary hormone synthesis and release. Therefore, pituitary cells serve as sensors to integrate central and peripheral signals in order to fine-tune whole-body homeostasis, although it is clear that pituitary cell regulation is species-, age- and sex-dependent. The purpose of this review is to provide a comprehensive, general overview of our current knowledge of both central and peripheral regulators of pituitary cell function and associated intracellular mechanisms, focusing on human and non-human primates.

Neurotransmitter receptors as signaling platforms in anterior pituitary cells

The functions of anterior pituitary cells are controlled by two major groups of hypothalamic and intrapituitary ligands: one exclusively acts on G protein-coupled receptors and the other activates both G protein-coupled receptors and ligand-gated receptor channels. The second group of ligands operates as neurotransmitters in neuronal cells and their receptors are termed as neurotransmitter receptors. Most information about pituitary neurotransmitter receptors was obtained from secretory studies, RT-PCR analyses of mRNA expression and immunohistochemical and biochemical analyses, all of which were performed using a mixed population of pituitary cells. However, recent electrophysiological and imaging experiments have characterized γ-aminobutyric acid-, acetylcholine-, and ATP-activated receptors and channels in single pituitary cell types, expanding this picture and revealing surprising differences in their expression between subtypes of secretory cells and between native and immortalized pituitary cells. The main focus of this review is on the electrophysiological and pharmacological properties of these receptors and their roles in calcium signaling and calcium-controlled hormone secretion.

The influence of elevated hormone levels on physiologic accumulation of 68Ga-DOTATOC

OBJECTIVE

PET/CT imaging with ⁶⁸Ga-1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid-D-Phe¹-Tyr³-octreotide (DOTATOC) is useful in patients with neuroendocrine tumors (NETs). Functioning NETs by definition secrete abnormal levels of hormones, causing clinical symptoms. It is known that physiologic accumulation can be seen in some organs, but it remains unknown whether elevated hormone levels can affect the physiologic accumulation pattern of ⁶⁸Ga-DOTATOC. We aimed to investigate the influence of higher hormone levels on physiologic accumulation of ⁶⁸Ga-DOTATOC.

METHODS

A total of 167 patients with known or suspected NET lesions were enrolled in this study. The numbers of patients with elevations of ACTH, gastrin, insulin, and no elevation were 10, 25, 7, and 125, respectively. We compared the maximum standardized uptake value (SUVmax) in various organs of each group.

RESULTS

In the group with elevated ACTH levels, SUVmax in the pituitary gland, the uncinate process of the pancreas and adrenal glands was lower than those in the group with no elevation (5.7 ± 1.9 vs. 8.4 ± 3.1, P = 0.015; 4.7 ± 3.5 vs. 6.4 ± 2.8, P = 0.037; 10.8 ± 4.8 vs. 13.9 ± 4.7, P = 0.020, respectively). There were no differences in physiologic uptake of ⁶⁸Ga-DOTATOC in the thyroid gland, the pancreatic body, the liver, the spleen, the bowel, or the kidney.

CONCLUSIONS

In NET patients with elevated ACTH levels, physiologic uptake of ⁶⁸Ga-DOTATOC in the pituitary gland, the uncinate process of the pancreas and adrenal glands was significantly decreased. Other organs were unaffected.

Gene-Dairy Food Interactions and Health Outcomes: A Review of Nutrigenetic Studies

Each person differs from the next by an average of over 3 million genetic variations in their DNA. This genetic diversity is responsible for many of the interindividual differences in food preferences, nutritional needs, and dietary responses between humans. The field of nutrigenetics aims to utilize this type of genetic information in order to personalize diets for optimal health. One of the most well-studied genetic variants affecting human dietary patterns and health is the lactase persistence mutation, which enables an individual to digest milk sugar into adulthood. Lactase persistence is one of the most influential Mendelian factors affecting human dietary patterns to occur since the beginning of the Neolithic Revolution. However, the lactase persistence mutation is only one of many mutations that can influence the relationship between dairy intake and disease risk. The purpose of this review is to summarize the available nutrigenetic literature investigating the relationships between genetics, dairy intake, and health outcomes. Nonetheless, the understanding of an individual’s nutrigenetic responses is just one component of personalized nutrition. In addition to nutrigenetic responses, future studies should also take into account nutrigenomic responses (epigenomic, transcriptomic, proteomic, metabolomic), and phenotypic/characteristic traits (age, gender, activity level, disease status, etc.), as these factors all interact with diet to influence health.

BRD4 inhibitor IBET upregulates p27kip/cip protein stability in neuroendocrine tumor cells

The prevalence of neuroendocrine tumors (NETs) has recently been increasing. Although various drugs such as Octreotide and its analogs show certain efficacy, NETs in many patients progress and metastasize. It is desirable to develop new interventions to improve the therapy. Here we show that human neuroendocrine tumor BON cells are resistant to several drugs commonly used for NET therapy, including Octreotide that activates somatostatin receptor-induced anti-proliferation, and Capecitabine and Temozolimide that damage DNA. In contrast, an inhibitor (IBET) to an epigenetic regulator, Brd4 that binds acetylated histones and upregulates transcription of multiple genes including protooncogene c-Myc, potently inhibited the NET cells. We found that IBET increased the protein levels of cyclin-dependent kinase (CDK) inhibitor p27^kip/cip (or p27), but not its mRNA levels. Moreover, the p27 induction at protein level by IBET was at least partly through increasing the protein stability of p27. The increased protein stability of p27 likely resulted from IBET-mediated suppression of Skp2, an E3 ligase that can mediate p27 degradation by increasing its ubiquitinylation. These findings unravel a new mechanism whereby the IBET-induced repression of proliferation of neuroendocrine cells.

Somatostatin and dopamine receptor regulation of pituitary somatotroph adenomas

Somatostatin and dopamine receptors are expressed in normal and tumoral somatotroph cells. Upon receptor stimulation, somatostatin and the somatostatin receptor ligands octreotide, lanreotide, and pasireotide, and to a lesser extent, dopamine and the dopamine analogs bromocriptine and cabergoline, suppress growth hormone (GH) secretion from a GH-secreting pituitary somatotroph adenoma. Somatostatin and dopamine receptors are G_αi-protein coupled that inhibit adenylate cyclase activity and cAMP production and reduce intracellular calcium concentration and calcium flux oscillations. Although their main action on somatotroph cells is acute inhibition of GH secretion, they also may inhibit GH production and possibly somatotroph proliferation. These receptors have been reported to create complexes that exhibit functions distinct from that of receptor monomers. Somatostatin suppression of GH is mediated mainly by somatostatin receptor subtype 2 and to a lesser extent by SST5. Human somatostatin receptor subtype 5 has also been shown to harbor mutations associated with GH levels, somatotroph tumor behavior, and somatostatin receptor ligand (SRL) responsiveness. Reviewing current knowledge of somatostatin and dopamine receptor expression and signaling in normal and tumoral somatotroph cells offers insights into mechanisms underlying SRL and dopamine agonist effectiveness in patients with acromegaly.

Immunohistochemical Localization of Somatostatin in the Brain of Chinese Alligator Alligator sinensis

In this study, the regional distribution and histological localization of somatostatin (SS) immunoreactive (IR) perikarya and fibers was investigated for the first time in the brain of adult Chinese alligator by immunohistochemical method. The results showed SS-IR perikarya and fibers were widely distributed in various parts of the brain except for olfactory bulbs. In the telencephalon, SS-IR perikarya were predominantly located in the cellular layer and deep plexiform layer of dorsomedial and medial cortex, less in the dorsal and lateral cortex, while SS-IR fibers were found in all layers of the cerebral cortex. SS-IR perikarya and fibers were also detected in the dorsal ventricular ridge, hippocampus cortex, accessory olfactory bulb nuclearus, lenticular nucleus, and caudate nucleus. In the diencephalon, SS-IR perikarya and fibers were mainly present in supraoptic nucleus, paraventricular nucleus of hypothalamus, recessus infundibular nucleus, median eminence, the pineal gland and pituitary gland, in which the IR-fibers were abundant, appearing dot-shaped and varicosity-like. In the mesencephalon, they were present in tectum cortex, ependyma of cerebral aqueduct and the periaqueductal grey matter. Additionally, they were also detected in Purkinje's cellular layer of cerebellum, in the reticularis nucleus and raphe nucleus of medulla oblongata. The distribution pattern of SS-IR perikarya and fibers in the brain of Chinese alligator is generally similar to that reported in other reptiles, but also has some specific features. The wide distribution indicated that SS might be a neurotransmitter or neuromodulator which acts on many kinds of target cells with a wide range of physiological functions. Anat Rec, 300:507-519, 2017. © 2016 Wiley Periodicals, Inc.

Klotho and the Growth Hormone/Insulin-Like Growth Factor 1 Axis: Novel Insights into Complex Interactions

The growth hormone (GH)/insulin-like growth factor (IGF)-1 axis is pivotal for many metabolic functions, including proper development and growth of bones, skeletal muscles, and adipose tissue. Defects in the axis' activity during childhood result in growth abnormalities, while increased secretion of GH from the pituitary results in acromegaly. In order to keep narrow physiologic concentration, GH and IGF-1 secretion and activity are tightly regulated by hypothalamic, pituitary, endocrine, paracrine, and autocrine factors. Klotho was first discovered as an aging-suppressor gene. Mice that do not express klotho die prematurely with multiple symptoms of aging, several of them are also characteristic of decreased GH/IGF-1 axis activity. Klotho is highly expressed in the brain, the kidney, and parathyroid and pituitary glands, but can also serve as a circulating hormone by its shedding, forming soluble klotho that can be detected in blood, cerebrospinal fluid, and urine. Several lines of evidence suggest an association between klotho levels and activity of the GH/IGF-1 axis: the GH-secreting cells in the anterior pituitary of klotho-deficient mice are hypotrophic; klotho levels are altered in subjects with pathologies of the GH/IGF-1 axis; and accumulating data indicate that klotho is a direct regulator of GH secretion. Thus, klotho seems to be a new player in the intricate regulation of the GH/IGF-1 axis.