The NMR structure of human obestatin in membrane-like environments: insights into the structure-bioactivity relationship of obestatin

Central obestatin administration affect the LH and FSH secretory activity in peripubertal sheep

Obestatin - a 23 amino acid peptide is synthesized as another product of the ghrl gene and its synthesis occurs mainly in gastric mucosa cells. This hormone is involved in complex gut-brain neurohormonal networks, thereby can participates in the modulation of gonadotrophic axis activity. The aim of this study was to investigate the consequence of intracerebroventricular infusions of obestatin on LH and FSH pituitary cells secretory activity in peripubertal female sheep. Animals were randomly divided into two groups: the control group (n = 14) received intracerebroventricular infusions of Ringer-Lock solution (120 μL h^-1), and the obestatin group (n = 14) was infused with obestatin (25 μg/120 μL h^-1) diluted in Ringer-Lock solution. A series of four infusions was performed on three consecutive days. Blood samples were collected on day 0 and day 3. The sheep were slaughtered immediately after the end of the experiment. For molecular biological analysis, pituitaries from 7 sheep from each group (n = 7 + 7) were prepared and frozen in liquid nitrogen immediately after collection and then stored at -80 °C until Real Time RT-qPCR and RIA analyzes. For immunohistochemical analysis, pituitary tissues from the remaining animals (n = 7 + 7) was fixed in situ for further examination. Real-Time qPCR and immunohistochemistry analyses revealed substantial changes in the LH and FSH pituitary cells secretory activity in obestatin-infused sheep. Exogenous obestatin administration reduced LHβ mRNA expression and increased the accumulation of immunoreactive LH in gonadotrophic cells of the adenohypophysis. These changes were accompanied by a decrease in the mean LH concentration in the peripheral blood resulting from the lower LH pulse amplitude. Moreover, an increase in both FSHβ mRNA expression and FSH immunoreactivity and amount in pituitary cells were noted, while mean blood FSH concentration remained unchanged after obestatin treatment. The obtained results showed that exogenous obestatin affected LH secretory activity at the level of protein synthesis, accumulation and release as well as obestatin increase FSHβ mRNA expression and accumulation of this hormone but at the same time have no effect on FSH release to blood. Thus, obestatin can participate in the neuroendocrine network, which modulates gonadotrophic axis activity in sheep.

Potential Therapeutic Effects of Gut Hormones, Ghrelin and Obestatin in Oral Mucositis

Chemotherapy and/or head and neck radiotherapy are frequently associated with oral mucositis. Oral pain, odynophagia and dysphagia, opioid use, weight loss, dehydration, systemic infection, hospitalization and introduction of a feeding tube should be mentioned as the main determinated effect of oral mucositis. Oral mucositis leads to a decreased quality of life and an increase in treatment costs. Moreover, oral mucositis is a life-threatening disease. In addition to its own direct life-threatening consequences, it can also lead to a reduced survival due to the discontinuation or dose reduction of anti-neoplasm therapy. There are numerous strategies for the prevention or treatment of oral mucositis; however, their effectiveness is limited and does not correspond to expectations. This review is focused on the ghrelin and obestatin as potentially useful candidates for the prevention and treatment of chemo- or/and radiotherapy-induced oral mucositis.

Biochemical properties and biological actions of obestatin and its relevence in type 2 diabetes

Obestatin was initially discovered in rat stomach extract, and although it is principally produced in the gastric mucosa, it can be found throughout the gastrointestinal tract. This 23-amino acid C-terminally amidated peptide is derived from preproghrelin and has been ascribed a wide range of metabolic effects relevant to type 2 diabetes. Obestatin reportedly inhibits gastrointestinal motility, reduces food intake and lowers body weight and improves lipid metabolism. Furthermore, it appears to exert actions on the pancreatic β-cell, most notably increasing β-cell mass and upregulating genes associated with insulin production and β-cell regeneration, with relevance to type 2 diabetes. It is becoming evident that obestatin also exerts pleiotropic effects on the cardiovascular system, possibly modulating blood pressure, endothelial function and triggering cardioprotective mechanisms, which may be important in determining cardiovascular outcomes in type 2 diabetes. Furthermore, it seems that like other gut peptides obestatin has neuroprotective properties. This review examines the biochemical properties of the obestatin peptide (its structure, sequence, stability and distribution) and the candidate receptors through which it may act. It provides a balanced examination of the reported pancreatic and extrapancreatic actions of obestatin and evaluates its potential relevance with respect to diabetes therapy, together with discussion of direct evidence linking alterations in obestatin signalling with obesity/diabetes and other diseases.

Obestatin Increases the Regenerative Capacity of Human Myoblasts Transplanted Intramuscularly in an Immunodeficient Mouse Model

Although cell-based therapy is considered a promising method aiming at treating different muscular disorders, little clinical benefit has been reported. One of major hurdles limiting the efficiency of myoblast transfer therapy is the poor survival of the transplanted cells. Any intervention upon the donor cells focused on enhancing in vivo survival, proliferation, and expansion is essential to improve the effectiveness of such therapies in regenerative medicine. In the present work, we investigated the potential role of obestatin, an autocrine peptide factor regulating skeletal muscle growth and repair, to improve the outcome of myoblast-based therapy by xenotransplanting primary human myoblasts into immunodeficient mice. The data proved that short in vivo obestatin treatment of primary human myoblasts not only enhances the efficiency of engraftment, but also facilitates an even distribution of myoblasts in the host muscle. Moreover, this treatment leads to a hypertrophic response of the human-derived regenerating myofibers. Taken together, the activation of the obestatin/GPR39 pathway resulted in an overall improvement of the efficacy of cell engraftment within the host's skeletal muscle. These data suggest considerable potential for future therapeutic applications and highlight the importance of combinatorial therapies.

Obestatin controls skeletal muscle fiber-type determination

Obestatin/GPR39 signaling stimulates skeletal muscle growth and repair by inducing both G-protein-dependent and -independent mechanisms linking the activated GPR39 receptor with distinct sets of accessory and effector proteins. In this work, we describe a new level of activity where obestatin signaling plays a role in the formation, contractile properties and metabolic profile of skeletal muscle through determination of oxidative fiber type. Our data indicate that obestatin regulates Mef2 activity and PGC-1α expression. Both mechanisms result in a shift in muscle metabolism and function. The increase in Mef2 and PGC-1α signaling activates oxidative capacity, whereas Akt/mTOR signaling positively regulates myofiber growth. Taken together, these data indicate that the obestatin signaling acts on muscle fiber-type program in skeletal muscle.

Obestatin as a key regulator of metabolism and cardiovascular function with emerging therapeutic potential for diabetes

Obestatin is a 23-amino acid C-terminally amidated gastrointestinal peptide derived from preproghrelin and which forms an α helix. Although obestatin has a short biological half-life and is rapidly degraded, it is proposed to exert wide-ranging pathophysiological actions. Whilst the precise nature of many of its effects is unclear, accumulating evidence supports positive actions on both metabolism and cardiovascular function. For example, obestatin has been reported to inhibit food and water intake, body weight gain and gastrointestinal motility and also to mediate promotion of cell survival and prevention of apoptosis. Obestatin-induced increases in beta cell mass, enhanced adipogenesis and improved lipid metabolism have been noted along with up-regulation of genes associated with beta cell regeneration, insulin production and adipogenesis. Furthermore, human circulating obestatin levels generally demonstrate an inverse association with obesity and diabetes, whilst the peptide has been shown to confer protective metabolic effects in experimental diabetes, suggesting that it may hold therapeutic potential in this setting. Obestatin also appears to be involved in blood pressure regulation and to exert beneficial effects on endothelial function, with experimental studies indicating that it may also promote cardioprotective actions against, for example, ischaemia-reperfusion injury. This review will present a critical appraisal of the expanding obestatin research area and discuss the emerging therapeutic potential of this peptide for both metabolic and cardiovascular complications of diabetes.

Action of obestatin in skeletal muscle repair: stem cell expansion, muscle growth, and microenvironment remodeling

The development of therapeutic strategies for skeletal muscle diseases, such as physical injuries and myopathies, depends on the knowledge of regulatory signals that control the myogenic process. The obestatin/GPR39 system operates as an autocrine signal in the regulation of skeletal myogenesis. Using a mouse model of skeletal muscle regeneration after injury and several cellular strategies, we explored the potential use of obestatin as a therapeutic agent for the treatment of trauma-induced muscle injuries. Our results evidenced that the overexpression of the preproghrelin, and thus obestatin, and GPR39 in skeletal muscle increased regeneration after muscle injury. More importantly, the intramuscular injection of obestatin significantly enhanced muscle regeneration by simulating satellite stem cell expansion as well as myofiber hypertrophy through a kinase hierarchy. Added to the myogenic action, the obestatin administration resulted in an increased expression of vascular endothelial growth factor (VEGF)/vascular endothelial growth factor receptor 2 (VEGFR2) and the consequent microvascularization, with no effect on collagen deposition in skeletal muscle. Furthermore, the potential inhibition of myostatin during obestatin treatment might contribute to its myogenic action improving muscle growth and regeneration. Overall, our data demonstrate successful improvement of muscle regeneration, indicating obestatin is a potential therapeutic agent for skeletal muscle injury and would benefit other myopathies related to muscle regeneration.

Ghrelin and obestatin plasma levels and ghrelin/obestatin prepropeptide gene polymorphisms in small for gestational age infants

OBJECTIVES

To investigate plasma ghrelin and obestatin levels, and ghrelin/obestatin prepropeptide gene polymorphisms, in sequentially enrolled small for gestational age (SGA) infants.

METHODS

Neonates were sequentially enrolled into this study and were then subdivided into different groups, according to different study aims and availability of study materials. Consequently, plasma ghrelin and obestatin levels were measured in term SGA, term appropriate for gestational age (AGA), term large for gestational age (LGA), preterm SGA and preterm AGA neonates. Levels of both peptides were also measured in AGA infants of different gestational ages, and in term AGA neonates at different days following birth. Three ghrelin/obestatin prepropeptide gene single nucleotide polymorphisms (SNPs), Arg51Gln, Leu72Met, and Gln90Leu, were measured in neonates.

RESULTS

The study involved a total cohort of 581 neonates. Out of 150 neonates (30 term AGA, 30 term SGA, 30 term LGA, 30 preterm AGA, and 30 preterm SGA), plasma obestatin levels were significantly higher in term SGA versus term LGA neonates (0.21 ± 0.02 ng/ml versus 0.17 ± 0.01 ng/ml, respectively). Out of a wider cohort, there were no significant differences in genotypes and allele frequencies of Arg51Gln, Leu72Met, and Gln90Leu SNPs between term SGA and AGA neonates, or between preterm SGA and AGA neonates.

CONCLUSIONS

Ghrelin/obestatin prepropeptide polymorphisms were not found to be associated with SGA status in neonates; however, ghrelin and obestatin levels may be involved in growth and development. Further studies are required to understand the relationship between ghrelin, obestatin and prenatal development.

Effect of TAT-obestatin on proliferation, differentiation, apoptosis and lipolysis in 3T3-L1 preadipocytes

It has been reported that obestatin regulates adipocyte metabolism via receptors on the cell surface. We wondered whether obestatin can interact with intracellular components that activated signalling pathways in adipocytes. Because obestatin (human) only presents one lysine (at position 10), which cannot penetrate the cell membrane, therefore, we used a cell-permeable peptide TAT (49-57) as a vector to carry obestatin across the cell membrane. The goal of this study was to further understand the function of obestatin after penetrating the cell membrane. Our results showed that TAT-obestatin could cross the 3T3-L1 cell membrane in the absence of cytotoxicity. TAT-obestatin showed no effect on the proliferation of 3T3-L1 preadipocytes. In contrast, obestatin significantly stimulated proliferation at a dose of 10(-11)  M and 10(-13)  M. In addition, TAT-obestatin demonstrated a more potent inhibitory effect on cell apoptosis induced by serum starvation than that of obestatin. During the progress of adipocyte differentiation, TAT-obestatin and obestatin had no effect on adipogenesis. In the lipolysis assay, TAT-obestatin significantly increased glycerol and free fatty acid release from 3T3-L1 adipocytes after 3 h treatment but showed no significant effect on lipolysis after 24 h and 48 h of treatment. In contrast, obestatin (10(-7)  M) had no effect on glycerol release after 3, 24 and 48 h of treatment. The difference between the effect of TAT-obestatin and obestatin on adipocytes metabolism indicated that TAT-obestatin may trigger intracellular signalling as well as signalling at the cell membrane.

Conformation propensities of des-acyl-ghrelin as probed by CD and NMR

Des-acyl-ghrelin is a 28 amino acid peptide secreted by both human and rat stomach. Together with ghrelin and obestatin, it is obtained by post-translational modification of a 117 aminoacid prepropeptide mainly expressed in distinct endocrine cell type in the stomach. Although its receptor has not been unambiguously identified so far, des-acyl-ghrelin is considered one of the strongest antagonists of ghrelin in activating the growth hormone secretagogue receptor (GHS-R). Here the secondary structure of des-acyl-ghrelin in different experimental conditions has been investigated and compared with that of obestatin, a bioactive peptide having similar biological functions. CD and NMR techniques have been combined for gaining the desired conformational features. The obtained structures support a steady alpha-helix structure spanning residues from 7 to 14, very similar to that observed for obestatin at the same experimental conditions, leading to suggest that a similar secondary structure can be associated with the similar biological role.