Effects Of Apelin-13 Research Articles

Apelin C-terminal fragments: biological properties and therapeutic potential

The creation of bioactive molecules for the treatment of cardiovascular diseases based on natural peptides stimulates intensive experimental research. In recent years, it has been established that the C-terminal fragments of apelin, an endogenous ligand of the APJ receptor, reduce metabolic and functional disorders in experimental heart damage. The review presents literature data and generalized results of our own experiments on the effect of apelin-13, [Pyr]apelin-13, apelin-12, and their chemically modified analogues on the heart in normal conditions and when modeling pathophysiological conditions in vitro and in vivo. It has been shown that the spectrum of action of apelin peptides on the damaged myocardium covers a decrease in the death of cardiomyocytes from necrosis, a decrease in cardiomyocyte membrane damage, an improvement in the metabolic state of the myocardium, and a decrease in the formation of reactive oxygen species and lipid peroxidation products. The mechanisms of the protective action of these peptides associated with the activation of the APJ receptor and the manifestation of antioxidant properties are discussed. The data presented in the review indicate the promise of molecular design of pharmacological APJ receptor agonists, which can serve as the basis for the development of cardioprotectors that affect the processes of free radical oxidation and metabolic adaptation.

Regulation of Apelin-13 on Bcl-2 and Caspase-3 and Its Effects on Adipocyte Apoptosis.

Objective The effects of apelin-13 on the expression of Bcl-2 and caspase-3 factors and the apoptosis of adipocytes were studied at the cellular and animal levels. Methods 3T3-L1 preadipocytes were cultured and grouped. The third-generation cells were added to the control DMSO solvent and amidation-modified apelin-13. The expression of Bcl-2 and caspase-3 were detected. The cell growth viability and cell apoptosis were detected. DOI model rats were established. The effects of apelin-13 on DOI rat biochemical indicators, the expression of Bcl-2, caspase-3, and cell apoptosis were investigated by injecting amidation-modified apelin-13 through the tail vein. Result In in vitro experiments, amidation-modified apelin-13 can significantly reduce the growth viability of adipocytes and the expression of Bcl-2, increase the expression of caspase-3, and promote the apoptosis of adipocytes. Animal experiments also show that apelin-13 modified by amidation can adjust the abnormal biochemical indicators of DOI rats, decrease the expression of Bcl-2 in adipose tissue, increase the expression of caspase-3, and promote the apoptosis of adipocytes. Conclusion Amidation of apelin-13 can promote fat cell apoptosis and reduce the incidence of obesity. The mechanism may be accomplished by inhibiting Bcl-2 and caspase-3 factors. This study helps us understand the effect of apelin-13 on fat cell apoptosis and hopes to provide a basis for the development of antiobesity drugs.

10-LB: The Apelinergic System Improves Angiogenesis and Blood Flow Reperfusion in Diabetic Mouse Model of Lower Limb Ischemia

Introduction: Peripheral vascular disease is a major risk factor for lower-extremity amputation in patients with diabetes due to an abnormal angiogenic response. The apelinergic system is known to improve cardiac function after ischemia by promoting angiogenesis. The objective: is to study the effects of Apelin-13 (Ape-13) and Elabela (Ela) on blood flow (BF) reperfusion following limb ischemia in diabetic mice as well as on endothelial cell (EC) function. Method: Primary EC were exposed to normal (5.6 mM; NG) or high (25 mM; HG) glucose concentrations for 24h and hypoxia (1% O2) for the last 16h. EC were stimulated or not with Ape-13 or Ela. Proliferation and migration assays were performed and apelin signaling pathway was evaluated by immunoblot and qPCR. In vivo, nondiabetic (NDM) and diabetic (DM) underwent femoral artery ligation to induce lower limb ischemia. DM mice received Ape-13 or Ela by subcutaneous osmotic pump. BF reperfusion was measured for 4 weeks post-surgery and exercise willingness was assessed in individual cages with voluntary wheel. The ischemic abductor muscles were collected for protein, genes and vascular density analyses. Results: Inhibitory effects of HG exposure on EC migration and proliferation were prevented with Ape-13 and Ela treatment under hypoxia condition through activation of Akt, AMPK and Rock2. In vivo, our results indicated that BF reperfusion was recovered at 75% in NDM as compared to 37% in DM whereas Ape-13 and Ela treatment in DM mice improved BF reperfusion by 65% and 69%, respectively. Similar results were observed using voluntary wheel as Ape-13 and Ela enhanced distance run as compared to untreated DM mice. Finally, the expression of proangiogenic factors (VEGF-A, PDGF-B) was increased in the ischemic muscle of DM+Ape-13 or Ela as compared to DM mice. Conclusion: We believe that stimulation of apelinergic system improved BF recovery in DM by increasing proangiogenic pathways and EC migration and proliferation. Disclosure S. Robillard: None. P. Geraldes: None. Funding Canadian Institutes of Health Research (PJT159627)

Apelin-13 Protects Corpus Cavernosum Against Fibrosis Induced by High-Fat Diet in an MMP-Dependent Mechanism

An increased fibrosis of the corpora cavernosa is a prevalent process that underlies most cases of erectile dysfunction. Apelin, an endogenous circulating peptide, has been documented as an important effector on cardiovascular homeostasis, controlling vascular function and reducing fibrosis in multiple pathological conditions. Recently, initial studies have shown that Apelin, acting through the APJ receptor, also modulates penile erection, however, the role of this system on penile structure and intracorporal collagen remodeling has not been investigated yet. Here we sought to investigate the effect of chronic Apelin treatment on the corpus cavernosum structure of hyperchOlesterolemic mice. Apolipoprotein gene-deleted (ApoE-/-) mice were fed with a Western diet for 11 weeks and received Apelin-13 (2 mg/kg/day) or vehicle during the last 3 weeks. Penile samples were obtained for histological and biochemical analyses to assess the intracorporal collagen content and key proteins expression. Furthermore, the effect of Apelin-13 was evaluated in cultured NIH3T3 mouse fibroblasts stimulated with TGF-β. Local expression of Apelin-13 in mouse corpus cavernosum and its protective effect against fibrosis. Apelin and APJ receptor were expressed (gene and protein) within the corpus cavernosum of ApoE-/- mice, indicating a local modulation of the Apelin system. Interestingly, 3 weeks of Apelin-13 treatment strongly reduced intracavernosal collagen content. In addition, Apelin-13 enhanced total matrix metalloproteinase (MMP) activity in the mice penis, which was associated with an increased protein expression of MMP-1, MMP-3, MMP-8, and MMP-9, while tissue inhibitor of metalloproteinase were unaltered. These beneficial actions were not associated with changes in nNOS or eNOS protein expression, intracavernosal reactive oxygen species content, or atherosclerotic plaque deposition. Additionally, in cultured fibroblast, Apelin-13 inhibited TGF-β-induced fibroblast to myofibroblast differentiation and collagen production, possibly through the activation of ERK1/2 kinase. These results point out Apelin/APJ system as a potential target to treat intracavernosal fibrosis-related disorders. These results provide the first evidence of the Apelin system's positive role on erectile tissue structure/remodeling. Nevertheless, additional functional study addressing erectile response would bring extended validation regarding the relevance of such effect. These results suggest a local modulation of the Apelin system within the corpus cavernosum. Remarkably, Apelin-13 reduced intracavernosal fibrosis in hypercholesterolemic mice by: (i) enhancing MMPs expression and activity; and (ii) inhibiting fibroblast differentiation into myofibroblast. Altogether, these results suggest an essential protective role of Apelin, indicating Apelin/APJ system as a promising candidate for the development of fibrosis-associated erectile dysfunction treatments. Sturny M, Anguenot L Costa-Fraga FP, etal. Apelin-13 Protects Corpus Cavernosum Against Fibrosis Induced by High-Fat Diet in an MMP-Dependent Mechanism. J Sex Med 2021;18:875-888.

Abstract P3060: Cardiovascular Regulatory Actions of Apelin in Normotensive Rats: Central versus Peripheral Effects

Apelin and its receptor APJ are expressed in both cardiovascular system (CVS) and central nervous system (CNS). Although the apelin/APJ system have already been shown to be involved in cardiovascular homeostasis, the mechanisms in the regulation of CVS are still not fully clear. Thus, this study was undertaken to compare central versus peripheral effect of apelin in the regulation of hemodynamic in SD rats. The chronic recording of blood pressure (BP) and heart rate (HR) were performed using radiotelemetry. Chronic infusion of apelin-13 (100 μg/kg/day) into the lateral cerebral ventricle using osmotic minipumps significantly elevated BP by 15.2±0.9 mmHg, The water intake was also increased from 38±2 to 51±3 ml/day before and after brain infusion of apelin-13. However, the HR was not significantly altered. Furthermore, this chronic pressor effect of apelin-13 was associated with a dramatic increase in the number of Fra-LI positive neurons within the paraventricular nucleus (PVN) and nucleus tractus solitarii (NTS), which were measured with immunohistochemistry using c-Fos antibodies, suggesting an elevated neuronal activity in the brain cardiovascular regulatory areas. Thus, apelin-13 was microinjected into the PVN to confirm the neuronal effect on the BP. The BP of rats was recorded using femoral arterial cannulation. The results demonstrated that acute microinjection of apelin-13 into the PVN significantly increased BP and HR. In peripheral CVS, acute intravenous injections of apelin-13 induced a transient reduction in BP by 25±3 mmHg as expected. Surprisingly, in the same group of rats, the cardiac contractility (dP/dt Max from 8131±512 to 7822±484 mmHg/s) was not significantly altered by apelin-13. In addition, chronic subcutaneous infusion of apelin-13 did not significantly alter either BP or cardiac contractility, which were detected with ratiotelemetry and echocardiography in rats. In conclusion, peripheral administration of apelin-13 only induced a transient decrease in BP without chronic BP regulatory and cardiotonic effects. In contrast, central application of apelin-13 leaded to a chronic elevation in the BP, suggesting that apelin-13 acting as an important neuropeptide in the CNS may contribute to the long-term control of BP.

The effect of apelin-13 on pancreatic islet beta cell mass and myocardial fatty acid and glucose metabolism of experimental type 2 diabetic rats

Apelin, a new identified adipokine, and its G protein–coupled receptor named APJ are widely expressed in various tissues. Apelin has been found to play important roles in the physiopathology of multiple diseases. Our aim is to assess the effect of long-term apelin treatment on serum insulin level and pancreatic islet beta-cell mass in the late stage of type 2 diabetes without hyperinsulinemia and to investigate the role of apelin in myocardial fatty acid and glucose metabolism. In the present study, the high-fat diet fed-streptozotocin-induced experimental type 2 diabetic rats were given once daily intraperitoneal injection of apelin-13 (0.1 μmol/kg) for 10 weeks. We observed that apelin significantly improved serum insulin reduction and reduced hyperglycemia. Histologic analysis showed that long-term apelin treatment significantly increased pancreatic islet beta cell mass. Exogenous apelin failed to change dyslipidaemia of type 2 diabetic rats. Apelin treatment markedly decreased elevated myocardial FFA and glycogen content. Treatment of type 2 diabetic rats with apelin markedly reduced increased gene expressions of the cardiac fatty acid transporter CD36, CPT-1, and Peroxisome proliferator-activated receptor (PPAR)-α. Whereas the gene levels of citrate synthase and peroxisome proliferator–activated receptor γ coactivator 1-α (PGC1-α), a transcriptional coactivator, mediating mitochondrial biogenesis in heart were unaltered in response to exogenous apelin. Taken together, longer-term apelin treatment prevented pancreatic beta-cell loss or failure in experimental type 2 diabetic rats. Apelin can regulate myocardial metabolism. Apelin reduced myocadial fatty acid uptake and oxidation through inhibiting PPAR-α but did not affect myocardial mitochondrial biogenesis in type 2 diabetic rats.

Effects of Apelin-13 on expression levels of glucose and lipid metabolism-related genes in the liver and skeletal muscle of diabetic rats

Objective To investigate the effects of exogenous Apelin-13 on the expression of glucose and fatty acid metabolism-related genes in the liver and skeletal muscle of diabetic rats. Methods Forty male Wister rats were randomly divided into a control group (n=8) and an experimental group (n=32). In the experimental group, a rat model of type 2 diabetes mellitus was established by a high-glucose and high-fat diet and intraperitoneal injection of streptozotocin (STZ). The diabetic rats were randomized into a diabetic model group and an Apelin-13 treatment group with 14 rats in each group.Rats in the Apelin-13 treatment group were intraperitoneally injected with 0.1 μmol·kg·d-1 Apelin-13 for 10 weeks, while the control group and the diabetic model group were injected with an equal volume of 0.9% NaCl solution for 10 weeks.At the end of the 10 week treatment, fasting blood glucose values in each group were measured.Levels of mRNA expression of glucose-6-phosphate (G-6-P), phosphoenolpyruvate carboxykinase (PEPCK), peroxisome proliferator-activated receptor alpha (PPAR-α), acy1-CoA synthetase long-chain family member1 (ACSL1), and carnitine palmitoyltransferase1 (CPT1) in the liver and levels of mRNA expression of PPAR-α and glucose transporter type 4 (GLUT4) in skeletal muscle were detected by real-time fluorescence quantitative polymerase chain reaction (PCR). Results Levels of mRNA expression of liver PPAR-α, liver ACSL1, liver CPT1, and GLUT4 in skeletal muscle were lower in the diabetic model group (0.309±0.073, 0.508±0.056, 0.389±0.118 and 0.289±0.066, respectively) than in the control group (0.971±0.028, 0.990±0.015, 0.987±0.015 and 0.994±0.009, respectively) (all P 0.05). Conclusions Apelin-13 increases the expression of the PPAR, ACSL1, and CPT1 genes in the liver and, to a certain extent, improves fatty acid oxidation metabolism in the liver in type 2 diabetic rats.It also increases the expression of the G-6-P and PEPCK genes, promotes gluconeogenesis in the liver, and may be related to the development of type 2 diabetes.In skeletal muscle, Apelin-13 increases GLUT4 gene expression, moderately improves skeletal muscle metabolism and may play a role in the regulation of oxidative stress. Key words: Diabetes mellitus; Carbohydrate metabolism; Lipid metabolism; Apelin-13

Protective Effect of Neuropeptide Apelin-13 on 6-Hydroxydopamine-Induced Neurotoxicity in SH-SY5Y Dopaminergic Cells: Involvement of Its Antioxidant and Antiapoptotic Properties.

Parkinson's disease (PD) is a severe neurodegenerative disorder characterized by the loss of brain dopaminergic neurons. Beside pharmacologic and symptomatic treatment of PD the neuroprotective therapy has recently attracted more attention. Apelin, a novel neuropeptide, and its receptors have numerous reported roles in regulating brain functions. In addition, this peptide has potent neuroprotective effects in some neurodegenerative situations. In this study, the effects of apelin-13 were investigated in a cell model of PD. Human neuroblastoma SH-SY5Y cell damage was induced by 150 μM 6-hydroxydopamine (6-OHDA) and the cells viability was examined by MTT assay. Intracellular reactive oxygen species (ROS) and mitochondrial membrane potential were determined by fluorescence spectrophotometry method. Immunoblotting analysis was also employed to evaluate cytochrome c release and caspase-3 activity. Data showed that 6-OHDA could decrease cell viability and mitochondrial membrane potential and increase intracellular ROS, cytochrome c, and cleaved caspase-3 levels. Pretreatment of SH-SY5Y cells with apelin-13 (5 and 10 nM) significantly prevented the mentioned biochemical and molecular markers of 6-OHDA-induced neurotoxicity. Furthermore, the results showed that apelin receptor and PI3K signaling contributed to the observed protective effects of apelin. The results suggest that apelin-13 has protective effects against dopaminergic neural toxicity and its antioxidant and antiapoptotic properties are involved, at least in part, in such protection.

Biochemical Interactions Between Angiotensin II and Apelin in Isolated Vascular Smooth Muscle Cells

Angiotensin II, angiotensin receptors, apelins and recently de-orphanized APJ receptors are important control factors of cardiovascular system. The present studies aimed the effects of apelin-13 and [Pyr1]-apelin-13 on apoptosis of cultured rat vascular smooth muscle cells, induced by enhanced concentrations of angiotensin II, in the presence of losartan, a specific inhibitor of AT1 angiotensin receptors type. The obtained data demonstrated that apelin-13 was less efficient in preventing the apoptosis of aortic smooth muscle cells in culture, induced by angiotensin II (in the presence of losartan), as compared to [Pyr1]-apelin-13. It could be concluded that the apoptotic effects induced by angiotensin II in rat aortic could be related to the involvement of AT2 angiotensin receptor type, other types of receptors or pathways unrelated to angiotensin receptors. Furthermore, the apoptotic effects induced by angiotensin II are counteracted by apelins in a structure-related manner.

Effects of apelin-13 on myocardium metabolism in diabetic rats

Objectives To investigate the effects of Apelin-13 on myocardial metabolism in diabetic rats. Methods A total of 40 male Wister rats were randomly divided into normal control group (NC, n=8) and experimental group (n=32). Diabetic rats model were induced by high-sugar and high-fat diet combined with low-dose intraperitoneal injection of streptozotocin (STZ). The well-established 28 diabetic model rats were randomly divided into diabetic model group (DM, n=14) and apelin-13 treated group (n=14). In the Apelin-13 group, diabetic rats were administered Apelin-13[0.1 μmol/(kg·d)]by intraperitoneal injection for 10 weeks, while the control group and diabetic model group were given an equal volume of 0.9% NaCl.At the end of the 10th week, all rats were sacrificed after fasting glucose measurement.Levels of serum free fatty acids (FFA) and myocardial FFA were measured by ELISA.Expression of myocardial glucose transporter member 4 (GLUT4) were detected by immunohistochemistry.The mRNA expressions of myocardial PPARα, CD36 and CPT-1 were detected by real-time fluorescence quantitative PCR. Results Fasting blood glucose, serum FFA and myocardial FFA were significantly higher in DM group than in NC group (all P 0.05) in Apelin-13 treated group than in DM group; but serum FFA was not significantly lower(Ρ<0.05). The mRNA expressions of PPARα, CD36, CPT-1 in cardiac myocyte were higher in DM group and Apelin-13 treated group than in control(P<0.05), and lower in Apelin-13 treated group than in DM group(P<0.05). The expression of myocardial GLUT4 was significantly lower in DM group(1.138±0.316)and in Apelin-13-treated group (4.631±1.832)than in NC group(9.132±2.156), (F=65.507, P<0.05), and higher in Apelin-13-treated group than in DM group(P<0.05). Conclusions Apelin-13 increases myocardial expression of GLUT4, improves utilization of FFA, and it can effectively reduce the expression of PPARα, CD36 and CPT-1.Therefore, it may play a vital role in the improvement of myocardial metabolism in diabetic rats. Key words: Apelin-13; Diabetes mellitus; Energy metabolism; Myocardium

Apelin-13 protects neurovascular unit against ischemic injuries through the effects of vascular endothelial growth factor

Apelin-13 has protective effects on many neurological diseases, including cerebral ischemia. Here, we aimed to test Apelin-13's effects on ischemic neurovascular unit (NVU) injuries and investigate whether the effects were dependent on vascular endothelial growth factor (VEGF). We detected the expression of VEGF and its receptors (VEGFRs) induced by Apelin-13 injection at 1d, 3d, 7d and 14d after middle cerebral artery occlusion (MCAO). Meanwhile, we examined the effects of Apelin-13 on NVU in both in vivo and in vitro experiments as well as whether the effects were VEGF dependent by using VEGF antibody. We also assessed the related signal transduction pathways via multiple inhibitors. We demonstrated Apelin-13 highly increased VEGF and VEGFR-2 expression, not VEGFR-1. Importantly, Apelin-13 led to neurological functions improvement by associating with promotion of angiogenesis as well as reduction of neuronal death and astrocyte activation, which was markedly blocked by VEGF antibody. In cell cultures, Apelin-13 protected neurons, astrocytes and endothelial cells against oxygen-glucose deprivation (OGD) injuries. Moreover, the effect of Apelin-13 to up-regulate VEGF was suppressed by extracellular signal-regulated kinase (ERK) inhibitor U0126 and phosphatidylinositol 3′-kinase (PI3K) inhibitor LY294002. Our data suggest protective effects of Apelin-13 on ischemic NVU injuries are highly associated with the increase of VEGF binding to VEGFR-2, possibly acting through activation of ERK and PI3K/Akt pathways.

Effect of apelin hormone on renal ischemia/reperfusion induced oxidative damage in rats

Apelin is a peptide hormone defined as a ligand for G-protein clamped receptor (APJ) receptor. It is indicated in the literature both apelin and APJ are synthesized on the peripheral tissues including the renal tissues. Which roles does the apelin play on the renal tissue has not been completely illuminated yet. This study is designed to determine the possible protective effect of apelin-13 on the kidney I/R injury. Adult male Sprague-Dawley rats were used in this study. In the sham group, right kidneys of the animals were dissected. In the I/R group, right kidney was dissected and ischemia of 45 min was performed, and then reperfusion was applied for 3 h. In the treatment groups, three different doses of apelin were injected at the beginning of the ischemia unlike the I/R group. BUN, Cre, Na, K, Cl, total protein and albumin from serum samples were determined and TNF-α, IL-1β, IL-6, TAS and TOS parameters were read with ELISA reader. MDA, SOD, CAT and GSH-Px enzyme activations from renal tissues were measured. In comparison with the sham and I/R groups, while the serum BUN, CRE, CI and TNF-α levels showed an increase in the groups on which the apelin-13 was applied, Na, total protein, albumin, TAS levels decreased. Serum TOS level of other groups showed an increase by comparison with the sham group. Our results showed that apelin-13 applied after I/R increased the antioxidant enzyme activity in a dose dependent manner, prevented the lipid oxidation and improved the renal functions.

Effect of apelin-13 on myocardium apoptosis in diabetic rats

Objective To investigate the effect of exogenous apelin-13 on oxidative stress, myocardial inflammatory cytokines and apoptosis in diabetic model rats. Methods A total of 40 male Wistar rats were randomly divided into 2 groups: normal control group (NC, n=8) and experimental group (EX, n=32). Diabetes was induced by feeding with high-sugary and high-fat diet for 8 weeks and a single intraperitoneal injection of streptozotocin (STZ) (30 mg/kg). The well-established 28 diabetic model rats were then randomly divided into 2 subgroups: model group (DM, n=14) and apelin-13 administration group (AP, n=14). The rats in AP group were given intraperitoneal administration of apelin-13 at a single dose of 0.1 μmol·kg-1·d-1 for 10 weeks, while NC group and DM group were given 0.9% NaCl in the same way. All rats were sacrificed at the end of the week 10. Blood hydrogen peroxide (H2O2), nitric oxide (NO) and malonaldehyde (MDA) were measured by colorimetry, and superoxide dismutase (SOD) was measured by enzyme-linked immunosorbent assay (ELISA). The expressions of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in rat myocardium were detected by immunohistochemistry.Masson staining was used to observe the myocardial fibrosis in rats of different groups. Cardiomyocyte apoptosis was determined by TUNEL. Results (1) Compared with NC groups, DM group showed that MDA, H2O2and NO were significantly increased, while SOD was significantly decreased (F=22.400, 6.230, 4.267 and 8.901, all P<0.0167). There was a statistically significant difference in the levels of MDA, H2O2,SOD between DM group and AP group. (2) The expression of TNF-α and IL-6 was significantly higher in DM group than in NC group (0.0599±0.0208 vs. 0.0076±0.0031, F=35.139; 0.0503±0.0243 vs. 0.0071±0.0024, F=15.946, both P<0.0167). After 10 weeks of apelin-13 administration, the levels of inflammatory cytokines were significantly decreased in AP group than in DM group. (3) The myocardial apoptosis and fibrosis were significantly increased in DM group than in NC group 〔0.0293±0.0061 vs. 0.0030±0.0013 and 0.0708±0.0420 vs. 0.0013±0.0003, F=84.930 and 19.420, both P<0.0167〕. The myocardial apoptosis and fibrosis were significantly decreased in AP group than in DM group (both P<0.0167). Conclusions To some extent, apelin-13 reduces the levels of oxidative stress and myocardial inflammation reaction in type 2 diabetes. Moreover, it may play a vital role in the improvement of myocardial apoptosis and fibrosis. Key words: Diabetes mellitus; Apoptosis; Myocytes, cardiac; Adipokines

Apelin-13 protects against apoptosis by activating AMP-activated protein kinase pathway in ischemia stroke

Apelin has been proved to be protective against apoptosis induced by ischemic reperfusion. However, mechanisms whereby apelin produces neuroprotection remain to be elucidated. AMP-activated protein kinase (AMPK) is a master energy sensor that monitors levels of key energy metabolites. It is activated via AMPKαThr172 phosphorylation during cerebral ischemia and appears to be neuroprotective. In this study, we investigated the effect of apelin on AMPKα and tested whether apelin protecting against apoptosis was associated with AMPK signals. Focal transient cerebral ischemia/reperfusion (I/R) model in male ICR mice was induced by 60min of ischemia followed by reperfusion. Apelin-13 was injected intracerebroventricularly 15min before reperfusion. AMPK inhibitor, compound C, was injected to mice intraperitoneally at the onset of ischemia. In experiment 1, the effect of apelin-13 on AMPKα was measured. In experiment 2, the relevance of AMPKα and apelin-13′ effect on apoptosis was measured. Data showed that apelin-13 significantly increased AMPKα phosphorylation level after cerebral I/R. Apelin-13, with the co-administration of saline, reduced apoptosis cells, down-regulated Bax and cleaved-caspase3 and up-regulated Bcl2. However, with the co-administration of compound C, apelin-13 was inefficient in affecting apoptosis and Bax, Bcl2 and cleaved-caspase3. The study provided the evidence that apelin-13 up-regulated AMPKα phosphorylation level in cerebral ischemia insults and AMPK signals participated in the mechanism of apelin-mediated neuroprotection.

Effects of apelin-13 in mice model of experimental pain and peripheral nociceptive signaling in rat sensory neurons

Objective: Apelin-13 is an endogenous peptide with potential analgesic action, although the sites of its analgesic effects remain uncertain and the results are even controversial with regard to its pain modulating action. This study evaluated the possible pain-modulating action of peripherally administered apelin-13 using heat-induced, withdrawal latency to the thermal stimuli, acute pain model in mice. Involvement of peripheral mechanisms was tested, by using the intracellular calcium concentrations as a key signal for nociceptive transmission, in cultured rat dorsal root ganglion (DRG) neurons. Methods: DRG neurons were cultured on glass coverslips following enzymatic digestion and mechanical agitation, and loaded with the calcium-sensitive dye Fura-2 acetoxymethyl ester (1 µM). Intracellular calcium responses in individual DRG neurons were quantified by ratiometric calcium imaging technique. Results: Peripheral injection of a single dose of apelin-13 (100 mg/kg and 300 mg/kg) significantly decreases the latency to painful stimuli in a dose and time-dependent manner (p < 0.01, p < 0.05, respectively, n = 8 each). Apelin-13 (0.1 µM and 1 µM) did not produce a significant effect on cytoplasmic Ca2+ ([Ca2+]i) responses, evoked by membrane depolarization, in cultured rat DRG neurons. Conclusion: Together these results indicate that apelin-13 can cause increased pain sensitivity after peripheral administration, but this effect does not involve calcium mediated signaling in primary sensory neurons.

Myocardial impact and cardioprotective effects of apelin-13 and a c-terminal-modified analog during lps and clp experimental sepsis

Apelin-13 (APL-13) is a member of an endogenous peptide's family (APLs) with powerful inotropic and cardioprotective properties. APLs bind to the dedicated receptor APJ-R, a member of the G protein-coupled receptor superfamily, all being widely expressed in the cardiovascular system. We have already shown that APL-13 infusion, was protective against LPS-induced myocardial dysfunction and death vs. dobutamine [1]. Furthermore, we have shown that, C-terminal Phe(13) modification of APL-13 by unnatural amino acids can change ligand binding and APJ-R signaling [2].

Apelin-13 protects the brain against ischemia/reperfusion injury through activating PI3K/Akt and ERK1/2 signaling pathways

Apelin has been proved to protect the heart against ischemia/reperfusion (I/R) injury via the activation of phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated kinase (ERK) signaling pathways. Whether this protective effect applies to brain I/R injury needed to be explored. We therefore investigated the potential neuroprotective role of Apelin-13 and the underlying mechanisms. Focal transient cerebral I/R model in male ICR mice was induced by 60min of ischemia followed by reperfusion. Apelin-13 intracerebroventricular injection was performed 15min before reperfusion. Neurological function, infarct volume, brain edema and apoptosis were measured at 24h after stroke. To further test the mechanism of Apelin-13, PI3K inhibitor LY294002 and ERK1/2 inhibitor PD98059 were injected into the lateral cerebral ventricle 15min before ischemia. Compared with the Vehicle group, Apelin-13 significantly ameliorated neurological deficit, infarct volume, brain edema and reduced TUNEL-positive cells. Bax, caspase-3 and cleaved caspase-3 were down-regulated and Bcl-2 up-regulated. While, the effect of Apelin-13 on Bax, Bcl-2, caspase-3 and cleaved caspase-3 was attenuated by LY294002 and PD98059. Apelin protected the brain against I/R insult injury, and this effect may be through activation of PI3K/Akt and ERK1/2 signaling pathways.

Effects of Apelin-13 on Human Prostate Cancer Lines (İnsan Prostat Kanseri Hücre Serilerinde Apelin-13'ün Etkileri)

Prostate cancer is one of the most prevalent type of cancer in men. The exact solution for the treatment of different types of cancers has not been fully elucideted. Apelin secreted from adipose tissue reveals its effects by binding to APJ receptor. Obesity develops together with increased adipose tissue, and the increase of obesity related-apelin secretion is known. Obesity is a risk factor in the development of cancer, and considering both apelin and its receptor widely localized in the tissues of testis and prostate and apelin may have significant effects on prostate cancer. In the present study, 0.1, 1 and 10 nM concentrations of apelin-13 and three different testosterone concentrations (1, 10 and 100 nM) were separately aplied to human prostate cancer cells with LNCaP (androgen receptor positive) and DU-145 (androgen receptor negative). Then 1, 10 and 100 nM concentrations of testosterone hormone and 10 nM dose of apelin-13 incubated for 24 h in the prostate cancer cells were administrated and were allowed to incubate for 24 h. Effects of apelin-13 and testosterone on prostate cancer cells were determined using 3-(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide (MTT) assay. At the end of the experiment, DU-145 did not affected cell viability while the treatment with apelin -13 and testosterone increased the viability of LNCaP cells (p<0.001). The proliferation effect was strongly occured when LNCaP cells were treated with together apelin-13 and testosterone (p<0.001) but, no effect was observed in DU-145 cells. In conclusion; apelin-13 had similar proliferative effects with testosterone on LNCaP cells, but had no effect on DU-145 cells. These results suggest that the effects of apelin-13 are similar to testosterone, and it realises their effects through an androgen receptor-dependent mechanism.

Effects of Apelin-13 on Human Prostate Cancer Lines [Insan Prostat Kanseri Hucre Serilerinde Apelin-13'un Etkileri

Prostate cancer is one of the most prevalent type of cancer in men. The exact solution for the treatment of different types of cancers has not been fully elucideted. Apelin secreted from adipose tissue reveals its effects by binding to APJ receptor. Obesity develops together with increased adipose tissue, and the increase of obesity related-apelin secretion is known. Obesity is a risk factor in the development of cancer, and considering both apelin and its receptor widely localized in the tissues of testis and prostate and apelin may have significant effects on prostate cancer. In the present study, 0.1, 1 and 10 nM concentrations of apelin-13 and three different testosterone concentrations (1, 10 and 100 nM) were separately aplied to human prostate cancer cells with LNCaP (androgen receptor positive) and DU-145 (androgen receptor negative). Then 1, 10 and 100 nM concentrations of testosterone hormone and 10 nM dose of apelin-13 incubated for 24 h in the prostate cancer cells were administrated and were allowed to incubate for 24 h. Effects of apelin-13 and testosterone on prostate cancer cells were determined using 3-(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide (MTT) assay. At the end of the experiment, DU-145 did not affected cell viability while the treatment with apelin -13 and testosterone increased the viability of LNCaP cells (p<0.001). The proliferation effect was strongly occured when LNCaP cells were treated with together apelin-13 and testosterone (p<0.001) but, no effect was observed in DU-145 cells. In conclusion; apelin-13 had similar proliferative effects with testosterone on LNCaP cells, but had no effect on DU-145 cells. These results suggest that the effects of apelin-13 are similar to testosterone, and it realises their effects through an androgen receptor-dependent mechanism.

Apelin-13 decreases lipid storage in hypertrophic adipocytes in vitro through the upregulation of AQP7 expression by the PI3K signaling pathway.

BackgroundAdipocyte-secreted apelin contributes to decreased adiposity and to improved insulin resistance, but the mechanisms remain unknown. The present study aimed to assess if apelin-13 is an upstream signal regulation factor of aquaporin 7 (AQP7), a water-glycerol transporter present in the plasma membrane of adipocytes that plays a key role in the regulation of lipid accumulation.Material/Methods3T3-L1 pre-adipocytes were induced to fully differentiated adipocytes; hypertrophic adipocytes were then induced using palmitate. The effects of apelin-13 on AQP7 expression in hypertrophic adipocytes were investigated before and after treatment with LY249002, a PI3K inhibitor. Accumulation of cytoplasmic triglycerides (TG) in hypertrophic adipocytes was also determined.ResultsWe found that 0.1 mM of palmitate induced a model of hypertrophic adipocytes with a lower AQP7 expression (0.26±0.07 vs. 0.46±0.04, P<0.05). Apelin-13 100 nM or 1000 nM upregulated AQP7 mRNA expression (100 nM: 0.54±0.06 and 1000 nM: 0.58±0.09 vs. control: 0.33±0.04, both P<0.05), and decreased accumulation of cytoplasmic triglycerides in hypertrophic adipocytes. Pretreatment using 10 μM LY294002 prevented the increase in AQP7 expression observed when using apelin-13 alone (apelin-13 + LY49002: 0.38±0.03 vs. apelin-13: 0.54±0.06, P<0.05), as well as the decreased cytoplasmic TG accumulation (apelin-13 + LY294002: 3.79±0.04 μM per μg/ml vs. apelin-13: 3.32±0.08 μM per μg/ml, P<0.05).ConclusionsApelin-13 decreases lipid storage in hypertrophic adipocytes in vitro, possibly through the upregulation of AQP7 expression by the PI3K signaling pathway. Treatment using apelin-13 and AQP modulators might represent novel treatment strategies against obesity and its related complications.