Ghrelin inhibits ovarian epithelial carcinoma cell proliferation in vitro

A survey of stapling methods to increase affinity, activity, and stability of ghrelin analogues

The growth hormone secretagogue receptor (GHSR) is a G protein-coupled receptor which regulates various important physiological and pathophysiological processes in the body such as energy homeostasis, growth hormone secretion and regulation of appetite. As a result, it has been postulated as a potential therapeutic target for the treatment of cancer cachexia and other metabolic disorders, as well as a potential imaging agent target for cancers and cardiovascular diseases. Ghrelin is the primary high affinity endogenous ligand for GHSR and has limited secondary structure in solution, which makes it proteolytically unstable. This inherent instability in ghrelin can be overcome by incorporating helix-inducing staples that stabilize its structure and improve affinity and activity. We present an analysis of different stapling methods at positions 12 and 16 of ghrelin(1-20) analogues with the goal of increasing proteolytic stability and to retain or improve affinity and activity towards the GHSR. Ghrelin(1-20) analogues were modified with a wide range of chemical staples, including a lactam staple, triazole staple, hydrocarbon staple, Glaser staple, and xylene-thioether staple. Once synthesized, the receptor affinity and α-helicity were measured using competitive binding assays and circular dichroism spectroscopy, respectively. Generally, an increase in alpha-helicity using a flexible staple linker led to improved affinity towards GHSR. Ghrelin(1-20) analogues with a lactam, triazole, and hydrocarbon staple resulted in helical analogues with stronger affinity towards GHSR than unstapled ghrelin(1-20), a compound that lacks helical character. Compounds were also investigated for their agonist activity through β-arrestin 1 & 2 recruitment BRET assays and for their metabolic stability through serum stability analysis.

Ghrelin enhances cisplatin sensitivity in HO-8910 PM human ovarian cancer cells

BACKGROUND

Resistance to platinum-based chemotherapy is one of the crucial problems in ovarian cancer treatment. Ghrelin, a widely distributed peptide hormone, participates in a series of cancer progression. The aim of this study is to determine whether ghrelin influences the sensitivity of ovarian cancer to cisplatin, and to demonstrate the underlying mechanism.

METHODS

The anti-tumor effects of ghrelin and cisplatin were evaluated with human ovarian cancer cells HO-8910 PM in vitro or in vivo. Cell apoptosis and cell cycle were analyzed via flow cytometry assay. The signaling pathway and the expression of cell cycle protein were analyzed with Western Blot.

RESULTS

Our results showed that treatment with ghrelin specifically inhibited cell proliferation of HO-8910 PM and sensitized these cells to cisplatin via S phase cell cycle arrest, and enhanced the inhibitory effect of cisplatin on tumor growth of HO-8910 PM derived xenografts in vivo. Treatment with ghrelin inhibited the expression of p-Erk1/2 and p-p38, which was opposite the effect of cisplatin. However, under the treatment of ghrelin, cisplatin treatment exhibited a stronger effect on inhibiting P21 expression, upregulating p-CDK1 and cyclin B1 expression, and blocking cell cycle progression. Mechanistically, ghrelin promoted S phase cell cycle arrest and upregulated p-CDK1 and cyclin B1 expression induced by cisplatin via inhibition of p38.

CONCLUSION

This study revealed a specifically inhibitory effect of ghrelin on platinum-resistance via suppressing p-P38 and subsequently promoting p-CDK1 mediated cell cycle arrest in HO-8910 PM.

Protective and Healing Effects of Ghrelin and Risk of Cancer in the Digestive System

Ghrelin is an endogenous ligand for the ghrelin receptor, previously known as the growth hormone secretagogue receptor. This hormone is mainly produced by endocrine cells present in the gastric mucosa. The ghrelin-producing cells are also present in other organs of the body, mainly in the digestive system, but in much smaller amount. Ghrelin exhibits a broad spectrum of physiological effects, such as stimulation of growth hormone secretion, gastric secretion, gastrointestinal motility, and food intake, as well as regulation of glucose homeostasis and bone formation, and inhibition of inflammatory processes. This review summarizes the recent findings concerning animal and human data showing protective and therapeutic effects of ghrelin in the gut, and also presents the role of growth hormone and insulin-like growth factor-1 in these effects. In addition, the current data on the possible influence of ghrelin on the carcinogenesis, its importance in predicting the risk of developing gastrointestinal malignances, as well as the potential usefulness of ghrelin in the treatment of cancer, have been presented.

Ghrelin Affects Gastric Cancer Progression by Activating AMPK Signaling Pathway

As the endogenous ligand for the GH secretagogue receptor (GHSR), Ghrelin is aberrant expressed in multiple malignant carcinoma, and involved in regulating a number of progression of cancer, especially in metastasis and proliferation. However, the precise role of Ghrelin in tumorigenesis of gastric cancer (GC) is still poorly understood. In this study, we extensively investigated the roles and mechanisms of Ghrelin in human gastric cancer. Ghrelin levels in cancer tissues and cell lines were analyzed by immunohistochemistry, qRT-PCR, and Western blot. Functional studies were performed after Ghrelin overexpressed or knockdown in AGS cell line. Cell proliferation was evaluated in by MTT and clone formation assays. The wound healing and Transwell system were used to assess the cell migration and invasive ability of GC cells. Cell apoptosis was detected by flow cytometry, and metabolic assays were performed to reveal the function of Warburg effect in the process. Ghrelin was lowly expressed in gastric cancer tissues and cell lines. Overexpression of Ghrelin inhibited gastric cancer cell proliferation, migration, invasion, and promoted apoptosis by activating the AMPK pathway, while D-[lys3]-GHRP-6 (a GHSR agonist) treatment relieved the effect, promoting tumorigenesis. Ghrelin knockdown increased the glucose uptake and lactic acid release, suggesting that Ghrelin elicited an anti-Warburg effect via AMPK pathway to inhibit gastric tumorigenesis. Ghrelin inhibits cell proliferation, migration, and invasion by eliciting an anti-Warburg effect via AMPK signaling pathway in gastric cancer cells.

Can Estradiol and Ghrelin Play a Protective Role in Epithelial Ovarian Cancer Incidence in Postmenopausal Women?

OBJECTIVE

The present study aimed to investigate the association between estradiol, n-octanoylated, des-octanoylated, total ghrelin, and ghrelin/des-octanoylated ghrelin ratio levels along with pathological parameters and epithelial ovarian cancer (EOC) odds in postmenopausal women.

MATERIALS AND METHODS

A case-control study was carried out on 45 patients with EOC and 33 age-matched postmenopausal women as the control group. Plasma levels of estradiol, n-octanoylated, des-octanoylated, and total ghrelin were measured by ELISA method.

RESULTS

Estradiol's plasma levels were significantly higher in patients with EOC than in control women (p <0.001). Although the ratio levels of n-octanoylated, des-octanoylated, total ghrelin, and ghrelin/des-octanoylated ghrelin were not associated with EOC in logistic regression models, estradiol levels were significantly related to the increase in EOC odds (OR: 1.083, 95% CI: 1.037-1.13, p <0.001). However, estradiol levels in the two first quartiles (Q₁, Q₂) were associated with decreased odds of EOC (OR: 0.011, 95% CI: 0.001-0.118, p <0.001, and OR: 0.030, 95% CI: 0.003-0.284, p = 0.002, respectively). For those patients in the third quartile of plasma des-octanoylated and total ghrelin compared to those in the highest (Q4), the multivariate odds ratios of EOC were respectively 0.192 and 0.25.

CONCLUSION

In conclusion, higher concentrations of des-octanoylated and total ghrelin might be associated with the decreased EOC odds. Furthermore, the findings suggest that high levels of estradiol might be a potential odds factor in EOC, however, lower estradiol levels may have a protective effect on EOC development.

Rikkunshito attenuates induction of epithelial-mesenchymal switch via activation of Sirtuin1 in ovarian cancer cells

Rikkunshito, a traditional Japanese herbal medicine, improves appetite via activation of gastrointestinal hormone ghrelin pathway. The function of ghrelin is mediated by growth hormone secretagogue receptor (GHSR1a), and ghrelin has been known to possess diverse physiological functions including growth suppression of some cancer cells. Considering that increased ghrelin signaling by Rikkunshito could enhance sirtuin1 (SIRT1) activity in nervous system, we aimed to investigate the effect of Rikkunshito in ovarian cancer cells. Ovarian cancer cell lines were treated with Rikkunshito, and cellular viability, gene expressions and epithelial-mesenchymal transition (EMT) status were investigated. To investigate the involvement of SIRT1 by Rikkunshito in SKOV3 cancer cells, endogenous expression of SIRT1 was depleted using small interfering RNA (siRNA). Treatment with Rikkunshito elevated ghrelin, GHSR1a and SIRT1, while cellular viability was decreased. The treatment of Rikkunshito also inhibited cellular migration and invasion status in a dose-dependent manner, and these effects were translated to the enhanced EMT status, although the role of SIRT1 was not determined. Our study revealed a novel function of Rikkunshito in enhancing EMT status of ovarian cancer cells. Therefore, we would like to propose that Rikkunshito may be used as a novel adjunctive therapy in chemotherapy of ovarian cancer because platinum-based chemotherapy frequently used for the treatment of ovarian cancer inevitably impairs appetite.

The new mechanism of Ghrelin/GHSR-1a on autophagy regulation

Autophagy is associated with several diseases. In recent years, accumulating evidence has suggested that ghrelin pathway exerts a protective effect by regulating autophagy. This review aims to assess the potential role and use of ghrelin as a new treatment for obesity, cardiovascular diseases, nonalcoholic fatty liver disease (NFALD), neurodegenerative diseases, and tissue damage associated with autophagy. Ghrelin reduces the basal expression of autophagy-related genes in obesity-associated type 2 diabetes and ghrelin level changes in obesity, heart failure, and NFALD as well as altered autophagy. Ghrelin and its receptor GHSR-1 activation induce the phosphorylation of ERK1/2 and the induction of PI-3 kinase (PI3 K) and phosphorylation of Akt. In the myocardium and hypothalamic NPY/AgRP neurons, ghrelin increases levels of the intracellular energy sensor AMPK and enhances autophagy, protecting cardiac ischemia and inducing neural stem cells. Nonetheless, ghrelin activates the PI3 K/Akt/Bcl-2 pathway and inhibits the activation of autophagy, such as tissues injured by sepsis or doxorubicin. In conclusion, endogenous ghrelin system could be considered as a new target or treatment for metabolism disorders, cardiac diseases, neurodegenerative diseases, and tissue injuries.

Exendin-4 Induces Cytotoxic Autophagy in Two Ovarian Cancer Cell Lines through Inhibition of Mtorc1 Mediated by Activation of AMPK and Suppression of Akt

Activation of autophagy suppresses ovarian cancer (OC). This in vitro study investigated whether the anti-tumour effect of exendin-4 against OC involves modulation of autophagy and figured out the possible mechanisms of action. SKOV-3 and OVCAR-3 cells (1 × 105/ml) were cultured in DMEM medium and treated with exendin-4 in the presence or absence of chloroquine (CQ), an autophagy inhibitor. In some cases, cells were also treated with exendin- 4 with or without pre-treatment with compound C (CC), an AMPK inhibitor, or insulin-like growth factor (IGF-1), a PI3K/Akt activator. Exendin-4 increased expression of beclin-1 and LC3I/II, suppressed expression of p62, reduced cell survival, migration, and invasion, and increased cell apoptosis and LDH release in both SKOV-3 and OVCAR-3 cells. Besides, exendin-4 reduced phosphorylation of mTORC1, 6SK, 4E-BP1, and Akt but increased phosphorylation of AMPK in both cell lines. These effects were associated with down-regulation of Bcl-2, suppression of nuclear phosphorylation of NF-κB p65, and increased expression of Bax and cleaved caspases 3/8. Chloroquine completely prevented the inhibitory effects of exendin-4 on the cell survival, Bcl-2, NF-κB, and cell invasiveness and abolished its stimulation of cell apoptosis and LDH release. Moreover, only the combined treatment with IGF-1 and CC completely abolished the observed effect of exendin-4 on the expression of beclin-1, LC3I/II, p62, as well as on cell survival, apoptosis, and LDH release. Exendin-4 exhibits a potent anti-tumour cytotoxic effect in SKOV-3 and OVCAR-3 cells by activating the markers of autophagy, mediated by activation of AMPK and inhibition of Akt.

Single Amino Acid Replacement in G-7039 Leads to a 70-fold Increase in Binding toward GHS-R1a

The growth hormone secretagogue receptor type 1a (GHS-R1a) is a class A rhodopsin-like G protein coupled receptor (GPCR) that is expressed in a variety of human tissues and is differentially expressed in benign and malignant prostate cancer. Previously, the peptidomimetic [1-Nal⁴ ,Lys⁵ (4-fluorobenzoyl)]G-7039 was designed as a molecular imaging tool for positron emission tomography (PET). However, this candidate was a poor binder (IC₅₀ =69 nm), required a lengthy four-step radiosynthesis, and had a cLogP above 8. To address these challenges, we now report on changes targeted at the 4^th position of G-7039. A 2-fluoropropionic acid (2-FPA) group was added on to Lys⁵ to determine the potential binding affinity of the [¹⁸ F]-2-FP radiolabeled analogue, which could be prepared by simplified radiochemistry. Lead candidate [Tyr⁴ ,Lys⁵ (2-fluoropropionyl)]G-7039 exhibited an IC₅₀ of 0.28 nm and low picomolar activity toward GHS-R1a. Molecular docking revealed a molecular basis for this picomolar affinity.

Ghrelin promotes human non-small cell lung cancer A549 cell proliferation through PI3K/Akt/mTOR/P70S6K and ERK signaling pathways

Ghrelin is a gastric acyl-peptide that plays an important role in cell proliferation. In the present study, we explored the role of ghrelin in A549 cell proliferation and the possible molecular mechanisms. We found that ghrelin promotes A549 cell proliferation, knockdown of the growth hormone secretagogue receptor (GHSR) attenuated A549 cell proliferation caused by ghrelin. Ghrelin induced the rapid phosphorylation of phosphatidylinositol 3-kinase (PI3K), Akt, ERK, mammalian target of rapamycin (mTOR) and P70S6K. PI3K inhibitor (LY 294002), ERK inhibitor (PD98059) and mTOR inhibitor (Rapamycin) inhibited ghrelin-induced A549 cell proliferation. Moreover, GHSR siRNA inhibited phosphorylation of PI3K, Akt, ERK, mTOR and P70S6K induced by ghrelin. Akt and mTOR/P70S6K phosphorylation was inhibited by LY 294002 but not by PD98059. These results indicate that ghrelin promotes A549 cell proliferation via GHSR-dependent PI3K/Akt/mTOR/P70S6K and ERK signaling pathways.

Autophagy as an emerging therapy target for ovarian carcinoma

Autophagy is a conserved cellular self-digestion pathway for maintenance of homeostasis under basal and stressed conditions. Autophagy plays pivotal roles in the pathogenesis of many diseases, such as aging-related diseases, autoimmune diseases, cardiovascular diseases, and cancers. Of special note is that accumulating data suggest an intimate relationship between autophagy and ovarian carcinoma. Autophagy is well identified to act as either as a tumor-suppressor or as a tumor-promoter in ovarian carcinoma. The exact function of autophagy in ovarian carcinoma is highly dependent on the circumstances of cancer including hypoxic, nutrient-deficient, chemotherapy and so on. However, the mechanism underlying autophagy associated with ovarian carcinoma remains elusive, the precise role of autophagy in ovarian carcinoma also remains undetermined. In this review, we tried to sum up and discuss recent research achievements of autophagy in ovarian cancer. Moreover, waves of novel therapies ways for ovarian carcinoma based on the functions of autophagy were collected.

Current Evidence for a Role of Neuropeptides in the Regulation of Autophagy

Neuropeptides drive a wide diversity of biological actions and mediate multiple regulatory functions involving all organ systems. They modulate intercellular signalling in the central and peripheral nervous systems as well as the cross talk among nervous and endocrine systems. Indeed, neuropeptides can function as peptide hormones regulating physiological homeostasis (e.g., cognition, blood pressure, feeding behaviour, water balance, glucose metabolism, pain, and response to stress), neuroprotection, and immunomodulation. We aim here to describe the recent advances on the role exerted by neuropeptides in the control of autophagy and its molecular mechanisms since increasing evidence indicates that dysregulation of autophagic process is related to different pathological conditions, including neurodegeneration, metabolic disorders, and cancer.

Reciprocal Crosstalk Between Autophagic and Endocrine Signaling in Metabolic Homeostasis

Autophagy is a cellular quality control and energy-providing process that is under strict control by intra- and extracellular stimuli. Recently, there has been an exponential increase in autophagy research and its implications for mammalian physiology. Autophagy deregulation is now being implicated in many human diseases, and its modulation has shown promising results in several preclinical studies. However, despite the initial discovery of autophagy as a hormone-regulated process by De Duve in the early 1960s, endocrine regulation of autophagy still remains poorly understood. In this review, we provide a critical summary of our present understanding of the basic mechanism of autophagy, its regulation by endocrine hormones, and its contribution to endocrine and metabolic homeostasis under physiological and pathological settings. Understanding the cross-regulation of hormones and autophagy on endocrine cell signaling and function will provide new insight into mammalian physiology as well as promote the development of new therapeutic strategies involving modulation of autophagy in endocrine and metabolic disorders.

Cytotoxic Tirucallane and Apotirucallane Triterpenoids from the Stems of Picrasma quassioides

Phytochemical investigation on the stems of Picrasma quassioides led to the isolation of a novel compound, picraquassin A (1), with an unprecedented 21,24-cycloapotirucallane skeleton, and four new apotirucallane-type triterpenoids (2-5), together with 15 new tirucallane-type triterpenoids (6-20) and 10 known tirucallane-type triterpenoids (21-30). To our knowledge, this is the first report demonstrating the presence of apotirucallane-type triterpenoids in the genus Picrasma. The structures of the new compounds were determined based on spectroscopic data interpretation. Cytotoxicities of the isolated compounds were evaluated using three human cancer cell lines, MKN-28, A-549, and MCF-7. Compound 2 exhibited the most potent activity against MKN-28 cells with an IC50 value of 2.5 μM. Flow cytometry and Western blot analysis revealed that 2 induces the apoptosis of MKN-28 cells via activating caspase-3/-9, while increasing Bax and Bad and decreasing Bcl-2 expression levels.

Ghrelin attenuates the growth of HO-8910 ovarian cancer cells through the ERK pathway

Ovarian cancer is one of the most common causes of death from gynecologic tumors and is an important public health issue. Ghrelin is a recently discovered bioactive peptide that acts as a natural endogenous ligand of the growth hormone secretagogue receptor (GHSR). Several studies have identified the protective effects of ghrelin on the mammalian reproductive system. However, little research has been done on the effects of ghrelin on ovarian cancer cells, and the underlying mechanisms of these effects. We sought to understand the potential involvement of mitogen-activated protein kinases (MAPKs) in ghrelin-mediated inhibition of growth of the ovarian line HO-8910. We applied different concentrations of ghrelin and an inhibitor of the ghrelin receptor (D-Lys3-GHRP-6) to HO-8910 cells and observed the growth rate of cells and changes in phosphorylation of the MAPKs ERK1/2, JNK and p38. We discovered that ghrelin-induced apoptosis of HO-8910 cells was though phosphorylated ERK1/2, and that this phosphorylation (as well as p90rsk phosphorylation) was mediated by the GHSR. The ERK1/2 pathway is known to play an essential part in the ghrelin-mediated apoptosis of HO-8910 cells. Hence, our study suggests that ghrelin inhibits the growth of HO-8910 cells primarily through the GHSR/ERK pathway.

Effects of Ghrelin on the Proteolytic Pathways of Alzheimer's Disease Neuronal Cells

Ghrelin is an orexigenic hormone with a role in the onset and progression of neurodegenerative disorders. It has been recently associated to Alzheimer's disease (AD) for its neuroprotective and anti-apoptotic activity. In the present study, we dissected the effect of ghrelin treatment on the two major intracellular proteolytic pathways, the ubiquitin-proteasome system (UPS) and autophagy, in cellular models of AD (namely SH-SY5Y neuroblastoma cells stably transfected with either the wild-type AβPP gene or the 717 valine-to-glycine AβPP-mutated gene). Ghrelin showed a growth-promoting effect on neuronal cells inducing also time-dependent modifications of the growth hormone secretagogue receptor type 1 (GHS-R1) expression. Interestingly, we demonstrated for the first time that ghrelin was able to activate the proteasome in neural cells playing also a role in the interplay between the UPS and autophagy. Our data provide a novel mechanism by which circulating hormones control neural homeostasis through the regulation of proteolytic pathways implicated in AD.

Correlation of ghrelin and growth hormone secretagogue receptor expression with clinical features in human pituitary adenomas

Ghrelin, as a brain-gut peptide, has growth hormone (GH)-releasing and appetite-inducing activities and a widespread tissue distribution. Furthermore, ghrelin is an endogenous ligand of the GH secretagogue receptor (GHSR), and both ghrelin and GHSR are expressed in the pituitary; however, the data regarding the expression of ghrelin and GHSR in pituitary adenomas are divergent and conflicting. In the present study, therefore, the expression of ghrelin and GHSR was examined in the full spectrum of human pituitary adenoma subtypes (n=34) and in normal pituitary tissue (n=3). The mRNA and protein expression levels were quantified using a competitive reverse transcription-polymerase chain reaction and western blotting and the correlation of the results with the clinical parameters was assessed. mRNA and protein expression of ghrelin and GHSR was detected in all samples with the highest mean level in GH adenomas, a moderate level in clinically non-functioning adenomas and the lowest level in adrenocorticotropin adenomas. A significant correlation between the ghrelin and GHSR mRNA expression levels was observed in the GH adenomas (n=12) (r=0.8435, P=0.0006). The ghrelin mRNA expression level in the GH adenomas correlated positively with the basic serum GH level (n=12) (r=0.6488, P=0.0225). Furthermore, the mean level of ghrelin mRNA expression was significantly higher in invasive adenomas than in noninvasive adenomas (P<0.01). Collectively, the results of the study provided evidence that ghrelin and GHSR are expressed in the various subtypes of pituitary adenoma, with specific overexpression in GH adenomas. The study suggests that the binding of ghrelin to GHSR promotes the secretion of GH and plays an important role in the development of GH adenomas via autocrine and/or paracrine effects.