Chronic treatment with a stable obestatin analog significantly alters plasma triglyceride levels but fails to influence food intake; fluid intake; body weight; or body composition in rats

Development of a sensitive and quantitative HPLC-FLD method for the determination of obestatin in human plasma

Obestatin is a gastrointestinal system peptide. The quantification of this peptide is conventionally performed using immunological techniques. In this study, a selective and sensitive HPLC method coupled with fluorescence detection for the quantitation of obestatin in human plasma was developed and validated. The separation was obtained on a C18 (4.6 × 100 mm, 3.5-μm particles) column using a mobile phase composed of acetonitrile and water, both including 0.1% trifluoroacetic acid. The developed method was found to be linear in the concentration range of 20 to 1000 ng/mL, with a coefficient of determination of 0.9982. The precision results were less than 10%, and the accuracy results were between 92% and 107%. The detection and quantification limit values were obtained as 2.8 and 9.4 ng/mL, respectively. Analyte solutions were found stable for 24 h at room temperature, three freeze-thaw cycles, and 2 weeks at -20°C. The developed method was successfully used for the quantification of obestatin in human plasma samples. In conclusion, the developed method is sensitive and specific for measuring the plasma concentrations of obestatin.

Crucial Regulatory Role of Organokines in Relation to Metabolic Changes in Non-Diabetic Obesity

Obesity is characterized by an excessive accumulation of fat leading to a plethora of medical complications, including coronary artery disease, hypertension, type 2 diabetes mellitus or impaired glucose tolerance and dyslipidemia. Formerly, several physiological roles of organokines, including adipokines, hepatokines, myokines and gut hormones have been described in obesity, especially in the regulation of glucose and lipid metabolism, insulin sensitivity, oxidative stress, and low-grade inflammation. The canonical effect of these biologically active peptides and proteins may serve as an intermediate regulatory level that connects the central nervous system and the endocrine, autocrine, and paracrine actions of organs responsible for metabolic and inflammatory processes. Better understanding of the function of this delicately tuned network may provide an explanation for the wide range of obesity phenotypes with remarkable inter-individual differences regarding comorbidities and therapeutic responses. The aim of this review is to demonstrate the role of organokines in the lipid and glucose metabolism focusing on the obese non-diabetic subgroup. We also discuss the latest findings about sarcopenic obesity, which has recently become one of the most relevant metabolic disturbances in the aging population.

Investigation of the association between cardio-metabolic risk factors, neurotrophins and gastric hormones among apparently healthy women: A cross-sectional analysis

Introduction: Although, some evidence has shown that obestatin, ghrelin, and neurotrophic factors can be involved in the development of cardio-metabolic risk factors, there are some contradictions in this regard. We aimed to investigate the association of serum neurotrophic factors and some gastric hormones with cardio-metabolic risk factors among apparently healthy women.

Methods: In the present study, 90 apparently healthy women were recruited by a convenient sampling method from the nutrition counseling clinic in Tabriz, Iran. All participants need dietary counseling for weight loss and were recruited before receiving any dietary interventions. Anthropometric, biochemical, physical activity, and blood pressure (BP) measurements, as well as dietary assessment, were done in all participants.

Results: Women who were in the highest tertile of serum obestatin levels (OR=0.118, 95% CI:0.035-0.396) had a significantly lower risk for development of hypertriglyceridemia compared to the reference group (P_trend < 0.001). Participants in the highest tertile of serum ghrelin had a significant lower risk of hypertriglyceridemia, hyperglycemia, low HDL-C, and MetS (P_trend < 0.05). Women who were in the higher tertile of serum NGF levels had a significantly lower risk for development of hypertriglyceridemia after adjustment for potential confounding variables (OR=0.091, 95% CI: 0.023-0.361 and OR=0.193, 95% CI: 0.057-0.649 respectively).

Conclusion: In the current study serum levels of obestatin, NGF, and ghrelin were associated with some cardio-metabolic risk factors such as hypertriglyceridemia and MetS. It seems that these factors are associated with metabolic regulation. However, further studies are needed to substantiate this claim.

Protective role of melatonin against adipose-hepatic metabolic comorbidities in experimentally induced obese rat model

Background

Adipose and hepatic metabolic dysfunctions are critical comorbidities that also aggravate insulin resistance in obese individuals. Melatonin is a low-cost agent and previous studies suggest that its use may promote metabolic health. However, its effects on some comorbidities associated with obesity are unknown. Herein, we investigated the hypothesis that melatonin supplementation would attenuate adipose-hepatic metabolic dysfunction in high fat diet (HFD)-induced obesity in male Wistar rats.

Materials and methods

Twenty-four adult male Wistar rats (n = 6/group) were used: Control group received vehicle (normal saline), obese group received 40% high fat diet, melatonin-treated group received 4 mg/kg of melatonin, and obese plus melatonin group received 40% HFD and melatonin. The treatment lasted for 12 weeks.

Results

HFD caused increased food intake, body weight, insulin level, insulin resistance and plasma and liver lipid but decreased adipose lipid. In addition, HFD also increased plasma, adipose and liver malondialdehyde, IL-6, uric acid and decreased Glucose-6-phosphate dehydrogenase, glutathione, nitric oxide and circulating obestatin concentration. However, these deleterious effects except food intake were attenuated when supplemented with melatonin.

Conclusion

Taken together, the present results indicate that HFD exposure causes adipose-hepatic metabolic disturbance in obese animals, which are accompanied by oxidative stress and inflammation. In addition, the present results suggest that melatonin supplementation attenuates adipose-hepatic metabolic dysfunction, accompanying obesity by suppression of oxidative stress/inflammation-dependent mechanism and increasing circulating obestatin.

Serum obestatin level strongly correlates with lipoprotein subfractions in non-diabetic obese patients

BACKGROUND

Obestatin is a ghrelin-associated peptide, derived from preproghrelin. Although many of its effects are unclear, accumulating evidence supports positive actions on both metabolism and cardiovascular function. To date, level of obestatin and its correlations to the lipid subfractions in non-diabetic obese (NDO) patients have not been investigated.

METHODS

Fifty NDO patients (BMI: 41.96 ± 8.6 kg/m²) and thirty-two normal-weight, age- and gender-matched healthy controls (BMI: 24.16 ± 3.3 kg/m²) were enrolled into our study. Obestatin level was measured by ELISA. Low-density lipoprotein (LDL) and high-density lipoprotein (HDL) subfractions, intermediate density lipoprotein (IDL) and very low-density lipoprotein (VLDL) levels and mean LDL size were detected by nongradient polyacrylamide gel electrophoresis (Lipoprint).

RESULTS

Serum level of obestatin was significantly lower in NDO patients compared to controls (3.01 ± 0.5 vs. 3.29 ± 0.6 μg/ml, p < 0.05). We found significant negative correlations between the level of obestatin and BMI (r = - 0.33; p < 0.001), level of serum glucose (r = - 0.27, p < 0.05), HbA1c (r = - 0.38; p < 0.001) and insulin (r = - 0.34; p < 0.05). Significant positive correlation was found between obestatin level and the levels of ApoA1 (r = 0.25; p < 0.05), large HDL subfraction ratio and level (r = 0.23; p < 0.05 and r = 0.24; p < 0.05), IDL (r = 0.25 p < 0.05) and mean LDL size (r = 0.25; p < 0.05). Serum VLDL ratio and level negatively correlated with obestatin (r = - 0.32; p < 0.01 and r = - 0.21; p = 0.05). In multiple regression analysis obestatin was predicted only by VLDL level.

CONCLUSIONS

Based on our data, measurement of obestatin level in obesity may contribute to understand the interplay between gastrointestinal hormone secretion and metabolic alterations in obesity.

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.

Combination of Obestatin and Bone Marrow Mesenchymal Stem Cells Prevents Aggravation of Endocrine Pancreatic Damage in Type II Diabetic Rats

One of the new promising therapies in treatment of diabetes mellitus is mesenchymal stem cells (MSCs) which have an interesting therapeutic potentiality based on their paracrine effect and transdifferentiation potentiality. Also obestatin improves the generation of functional β cells/islet-like cell clusters in vitro, suggesting implications for cell-based replacement therapy in diabetes. So the aim of this study was to evaluate the effect of combination of both MSCs and obestatin on an experimental model of type II diabetes mellitus (T2DM). Sixty male rats were divided into; group I (control group), group II (T2DM group) induced by administration of high fat diet (HFD) and injection of streptozotocin (STZ) in low dose, group III (T2DM treated with MSCs), group IV (T2DM treated with obestatin), group V (T2DM treated with MSCs and obestatin). Fasting blood glucose, C-peptide, insulin and lipid profile were measured. HOMA-IR and HOMA-β were calculated. Pancreatic expression of insulin, glucagon like peptide -1 (GLP-1) and pancreatic duodenal homeobox 1 (Pdx1) mRNA levels were measured. In addition pancreatic histological changes, insulin and Bax were analyzed by immunohistochemical examination of islets of Langerhans. Diabetic rats showed significant increase in HOMA-IR, serum glucose and lipid profile levels with significant decrease in insulin, HOMA-β, GLP-1 and Pdx1 levels. MSCs and obestatin caused significant improvement in all parameters with more significant improvement in combined therapy. The protective effects afforded by MSCs and obestatin may derive from improvement of the metabolic profile, antiapoptosis and by increase in pancreatic GLP-1and Pdx1 gene expression.

Serum ghrelin, but not obestatin, is a potential predictor of acute pancreatitis severity

The roles of ghrelin and obestatin in AP remain controversial.This study investigates the effects and the predictive value of serum ghrelin and obestatin levels in the early stage of AP.A total of 193 consecutive patients with AP and 24 healthy controls were included. Patients were divided into mild acute pancreatitis (MAP), moderately severe acute pancreatitis (MSAP), and severe acute pancreatitis (SAP) groups. Serum levels of ghrelin and obestatin were measured on the first, third, and fifth days of hospitalization. The predictive value of serum ghrelin and obestatin levels on the first day in AP was examined using receiver-operating characteristic (ROC) curves.On the first day of hospitalization, the mean serum ghrelin level was significantly lower in patients with AP than in controls (P < .01). The serum ghrelin concentration decreased with increasing AP severity and was lower in patients with SAP than in those with MAP and MSAP (P < .05). It increased gradually from the first to the fifth day after treatment. ROC curves demonstrated that the serum ghrelin level on the first day had some predictive value for AP severity (area under the ROC curve = 0.646), with an optimal cut-off value of 87.83 pg/mL. Logistic regression showed that the serum ghrelin level had independent predictive value for non-MAP (odds ratio = 10.94; 95% confidence interval, 5.08-23.55; P < .01). The serum obestatin level did not differ significantly between patients with AP and controls and had the limited predictive value for non-MAP (area under the ROC curve = 0.564). However, the serum obestatin concentration showed a "warning" effect regarding AP etiology; on the first day of treatment, it was significantly lower in patients with AP of hypertriglyceridemic etiology than in those with AP of biliary, alcohol-related, and other etiologies (P = .05, P = .031, and P = .029, respectively).Serum ghrelin and obestatin levels may be related to the progression of AP in the early stage. Only the serum ghrelin level is a potential predictor of AP severity in the early stage. Obestatin may be involved in the pathogenesis of AP caused by hypertriglyceridemia.

Long-term obestatin treatment of mice type 2 diabetes increases insulin sensitivity and improves liver function

PURPOSE

Obestatin and ghrelin are peptides encoded by the preproghrelin gene. Obestatin inhibits food intake, in addition to regulation of glucose and lipid metabolism. Here, we test the ability of obestatin at improving metabolic control and liver function in type 2 diabetic animals (type 2 diabetes mellitus).

METHODS

The effects of chronic obestatin treatment of mice with experimentally induced type 2 diabetes mellitus on serum levels of glucose and lipids, and insulin sensitivity are characterized. In addition, alterations of hepatic lipid and glycogen contents are evaluated.

RESULTS

Obestatin reduced body weight and decreased serum glucose, fructosamine, and β-hydroxybutyrate levels, as well as total and low-density lipoprotein fractions of cholesterol. In addition, obestatin increased high-density lipoproteins cholesterol levels and enhanced insulin sensitivity in mice with type 2 diabetes mellitus. Moreover, obestatin diminished liver mass, hepatic triglycerides and cholesterol contents, while glycogen content was higher in livers of healthy and mice with type 2 diabetes mellitus treated with obestatin. These changes were accompanied by reduction of increased alanine aminotransferase, aspartate aminotransferase, and gamma glutamyl transpeptidase in T2DM mice with type 2 diabetes mellitus. Obestatin increased adiponectin levels and reduced leptin concentration. Obestatin influenced the expression of genes involved in lipid and carbohydrate metabolism by increasing Fabp5 and decreasing G6pc, Pepck, Fgf21 mRNA in the liver. Obestatin increased both, AKT and AMPK phosphorylation, and sirtuin 1 (SIRT1) protein levels as well as mRNA expression in the liver.

CONCLUSION

Obestatin improves metabolic abnormalities in type 2 diabetes mellitus, restores hepatic lipid contents and decreases hepatic enzymes. Therefore, obestatin could potentially have a therapeutic relevance in treating of insulin resistance and metabolic dysfunctions in type 2 diabetes mellitus.

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.

Treatment of lean and diet-induced obesity (DIO) mice with a novel stable obestatin analogue alters plasma metabolite levels as detected by untargeted LC-MS metabolomics

INTRODUCTION

Obestatin is a controversial gastrointestinal peptide purported to have metabolic actions.

OBJECTIVES

This study investigated whether treatment with a stable obestatin analogue (PEG-OB(Cys¹⁰, Cys¹³)) changed plasma metabolite levels firstly in lean and subsequently in diet-induced obesity (DIO) C57BL6/J mice.

METHODS

Untargeted LC-HRMS metabolomics experiments were carried out in ESI + mode with plasma extracts from both groups of animals. Data were normalised, multivariate and univariate statistical analysis performed and metabolites of interest putatively identified.

RESULTS

In lean mice, 39 metabolites were significantly changed by obestatin treatment and the majority of these were increased, including various C16 and C18 moieties of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and monoacylglycerol, along with vitamin A, vitamin D3, tyrosine, acetylcarnitine and 2α-(hydroxymethyl)-5α-androstane-3β,17β-diol. Decreased concentrations of glycolithocholic acid, 3-dehydroteasterone and various phospholipids were observed. In DIO mice, 25 metabolites were significantly affected and strikingly, the magnitudes of changes here were generally much greater in DIO mice than in lean mice, and in contrast, the majority of metabolite changes were decreases. Four metabolites affected in both groups included glycolithocholic acid, and three different long-chain (C18) phospholipid molecules (phosphatidylethanolamine, platelet activating factor (PAF), and monoacylglycerol). Metabolites exclusively affected in DIO mice included various phosphatidylcholines, lysophosphatidylcholines and fatty acyls, as well as creatine and oxidised glutathione.

CONCLUSION

This investigation demonstrates that obestatin treatment affects phospholipid turnover and influences lipid homeostasis, whilst providing convincing evidence that obestatin may be acting to ameliorate diet-induced impairments in lipid metabolism, and it may influence steroid, bile acid, PAF and glutathione metabolism.

Peripheral administration of TAT-obestatin can influence the expression of liporegulatory genes but fails to affect food intake in mice

Obestatin is a 23-amino-acid peptide originally regarded as an anorexigenic factor. However, most of the subsequent studies failed to confirm the initially reported anorexigenic properties of obestatin. Obestatin is incapable of crossing the blood brain barrier (BBB), which may affect its biological function. Here, we report the physiological effects of obestatin in mice after intraperitoneal administration of obestatin conjugated to the cell-permeable peptide TAT, which is capable of delivering different types of proteins through the BBB. Acute peripheral administration of 1 μmol/kg of TAT-obestatin did not influence the 24 h cumulative food intake and body weight gain of mice that were fasted for 18 h. Fed mice were injected intraperitoneally with 100 nmol/kg of TAT-obestatin daily for 25 d. Compared with control groups, on day 3, the gain in body weight was significantly altered; on day 7, abdominal fat mass was remarkably reduced; however, on day 25, there was a surprisingly notable increase in abdominal and epididymal fat mass. In comparison with control groups, on day 25, the expression levels of adiponectin, ADD1, C/EBPα, PPARG and GLUT4 were significantly up-regulated in liver tissues; in white adipose tissue, the expression level of C/EBPα was significantly up-regulated, but adiponectin and GLUT4 were significantly down-regulated. In addition, GPR39, the suspected receptor of obestatin, was up-regulated in white adipose tissue on day 25. These findings suggest that TAT-obestatin might play a role in white adipose tissue metabolism, but its physiological effects on food intake and body weight gain regulation remain unclear.

Obestatin receptor in energy homeostasis and obesity pathogenesis

Based on the bioinformatic prediction, Zhang and colleagues discovered obestatin, a new 23-amino acid hormone from rat stomach extract encoded by the ghrelin gene. Obestatin is present not only in the gastrointestinal tract, but also in the spleen, mammary gland, breast milk, and plasma. Obestatin appears to function as part of a complex gut-brain network whereby hormones and substances from the stomach, intestine and the brain about satiety or hunger. Given the current research regarding the effects of obestatin and its possible cognate receptor(s), this chapter provides the latest review of the physiological and pathological characteristics of this hormone and its possible receptor(s) in energy homeostasis and obesity.

The gastrointestinal peptide obestatin induces vascular relaxation via specific activation of endothelium-dependent NO signalling

BACKGROUND AND PURPOSE

Obestatin is a recently discovered gastrointestinal peptide with established metabolic actions, which is linked to diabetes and may exert cardiovascular benefits. Here we aimed to investigate the specific effects of obestatin on vascular relaxation.

EXPERIMENTAL APPROACH

Cumulative relaxation responses to obestatin peptides were assessed in rat isolated aorta and mesenteric artery (n≥ 8) in the presence and absence of selective inhibitors. Complementary studies were performed in cultured bovine aortic endothelial cells (BAEC).

KEY RESULTS

Obestatin peptides elicited concentration-dependent relaxation in both aorta and mesenteric artery. Responses to full-length obestatin(1-23) were greater than those to obestatin(1-10) and obestatin(11-23). Obestatin(1-23)-induced relaxation was attenuated by endothelial denudation, l-NAME (NOS inhibitor), high extracellular K(+) , GDP-β-S (G-protein inhibitor), MDL-12,330A (adenylate cyclase inhibitor), wortmannin (PI3K inhibitor), KN-93 (CaMKII inhibitor), ODQ (guanylate cyclase inhibitor) and iberiotoxin (BK(Ca) blocker), suggesting that it is mediated by an endothelium-dependent NO signalling cascade involving an adenylate cyclase-linked GPCR, PI3K/PKB, Ca(2+) -dependent eNOS activation, soluble guanylate cyclase and modulation of vascular smooth muscle K(+) . Supporting data from BAEC indicated that nitrite production, intracellular Ca(2+) and PKB phosphorylation were increased after exposure to obestatin(1-23). Relaxations to obestatin(1-23) were unaltered by inhibitors of candidate endothelium-derived hyperpolarizing factors (EDHFs) and combined SK(Ca) /IK(Ca) blockade, suggesting that EDHF-mediated pathways were not involved.

CONCLUSIONS AND IMPLICATIONS

Obestatin produces significant vascular relaxation via specific activation of endothelium-dependent NO signalling. These actions may be important in normal regulation of vascular function and are clearly relevant to diabetes, a condition characterized by endothelial dysfunction and cardiovascular complications.

In vitro metabolic stability of iodinated obestatin peptides

Different iodinated mouse obestatin peptides have been characterized toward their in vitro stability in the main metabolic compartments plasma, liver and kidney. Using HPLC-UV for quantification, significant differences in the degradation kinetics of the iodinated peptides, arising from both enzymatic proteolysis and dehalogenation, were found when compared to the native, unmodified peptide. HPLC-MS/MS analysis demonstrated that the cleavage sites were dependent upon the biological matrix and the location of the amino acid residue incorporating the iodine atom(s). The degrading proteases were found to target peptide bonds further away from the iodine incorporation, while proteolytic cleavages of nearby peptide bonds were more limited. Diiodinated amino acid residue containing peptides were found to be more susceptible to deiodination than the mono-iodinated derivative. In plasma, the percentage of peptide degradation solely attributed to deiodinase activity after 20 min incubation reached up to 25% for 2,5-diiodo-H(19)-obestatin compared to 20% and only 3% for (3,5-diiodo-Y(16))- and (3-iodo-Y(16)) obestatin, respectively. Hence, our results demonstrate that the different iodinated peptides pose significantly different metabolization properties and thus, also different biological activities are expected for peptides upon iodination.