Apelin, a promising target for type 2 diabetes treatment?

Effects of exercise or metformin on myokine concentrations in patients with breast and colorectal cancer: A phase II multi-centre factorial randomized trial

BACKGROUND

Physical activity and metformin pharmacotherapy are associated with improved clinical outcomes in breast and colorectal cancer survivors. Myokines are cytokines secreted from skeletal muscle that may mediate these associations.

METHODS

This hypothesis-generating analysis used biospecimens collected from a multi-centre 2 × 2 factorial randomized design of 116 patients with stage I-III breast and colorectal cancer who were randomized to 12 weeks of (1) aerobic exercise (moderate intensity titrated to 220 min/week); (2) metformin (850 mg daily for 2 weeks and then titrated to 850 mg twice per day); (3) aerobic exercise and metformin; or (4) control. Fourteen myokines were quantified using a multiplex panel. Myokine concentrations were log-transformed, and main effects analyses were conducted using linear mixed-effects regression models. The type I error rate was controlled with the Holm sequential testing procedure.

RESULTS

Randomization to exercise increased leukaemia inhibitory factor (1.26 pg/mL, 95% confidence interval [CI]: 0.69, 1.84; adjusted P = 0.001) and interleukin-15 (2.23 pg/mL, 95% CI: 0.87, 3.60; adjusted P = 0.013) compared with randomization to no exercise. Randomization to metformin decreased apelin (-2.69 pg/mL, 95% CI: -4.31, -1.07; adjusted P = 0.014) and interleukin-15 (-1.74 pg/mL, 95% CI: -2.79, -0.69; adjusted P = 0.013) compared with randomization to no metformin. Metformin decreased myostatin, irisin, oncostatin M, fibroblast growth factor 21 and osteocrin; however, these changes were not statistically significant after correction for multiple comparisons.

CONCLUSIONS

This pilot study demonstrates that randomization to exercise and metformin elicit unique effects on myokine concentrations in cancer patients. This hypothesis-generating observation warrants further basic, translational and clinical investigation and replication.

Predicting cell-type specific disease genes of diabetes with the biological network

Type 2 diabetes (T2D) is a chronic condition that can lead to significant harm, such as heart disease, kidney disease, nerve damage, and blindness. Although T2D-related genes have been identified through Genome-wide association studies (GWAS) and various computational methods, the biological mechanism of T2D at the cell type level remains unclear. Exploring cell type-specific genes related to T2D is essential to understand the cellular mechanisms underlying the disease. To address this issue, we introduce DiGCellNet (predicting Disease Genes with Cell type specificity based on biological Networks), a model that integrates graph convolutional network (GCN) and multi-task learning (MTL) to predict T2D-associated cell type-specific genes based on the biological network. Our work represents the first attempt to predict cell type-specific disease genes using GCN and MTL. We evaluate our approach by predicting genes specific to four cell types and demonstrate that the proposed DiGCellNet outperforms other models that combine node embeddings with traditional machine learning algorithms. Moreover, DiGCellNet successfully identifies CALM1 as a gene specific to beta cell type in T2D cases, and this association is confirmed using an independent dataset. The code is available at https://github.com/23AIBox/23AIBox-DiGCellNet.

Serum apelin-12 and obesity-related markers in Egyptian children with Down syndrome

Children with Down syndrome (DS) exhibit higher overweight/obesity rates than their typically developing peers. Apelin-12 is a bioactive adipokine that exerts vital roles in obesity-related cardiometabolic comorbidities. To date, apelin-12 has not been investigated in obese-DS. This study aimed to explore the possible association between serum apelin-12 and obesity-related markers and to evaluate the efficiency of apelin-12 in the prediction of metabolic syndrome (MetS) in obese-DS compared to BMI Z-score matched obese-control. The cross-sectional study included 150 prepubertal children classified into three groups; obese-DS (n = 50), obese-control (n = 50), and normal-weight-control (n = 50). Anthropometric parameters, body adiposity, fasting serum levels of blood glucose (FBG), insulin, lipid profile, and apelin-12 were evaluated. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated from FBG and insulin. MetS was defined using Adult Treatment Panel III criteria modified for the pediatric age group. ROC curves were analyzed to evaluate the efficiency of apelin-12 in predicting MetS in obesity groups. Obese-DS exhibited higher body adiposity with marked central fat distribution, atherogenic lipid profile, and higher HOMA-IR compared to obese-control. Apelin-12 was significantly higher in obese-DS and obese-DS with MetS compared to obese-control and obese-control with MetS respectively (p < 0.001). The increase in apelin-12 with higher obesity grades was pronounced in obese-DS. Apelin-12 strongly correlated with body adiposity, several MetS risk factors, and HOMA-IR in obese-DS. Significantly higher AUC for apelin-12 in the diagnosis of MetS among obese-DS than obese-control (AUC = 0.948 vs. AUC = 0.807; p = 0.04).

CONCLUSIONS

 The current study supports the crucial role of apelin-12 in obesity-related clinical and biochemical markers and in MetS in obese-DS and obese-control. Serum apelin-12 is a potential diagnostic biomarker for MetS with greater performance in obese-DS than obese-control raising its potential for clinical and therapeutic applications.

WHAT IS KNOWN

• Obese-DS children displayed excess body adiposity, Pronounced central fat distribution, atherogenic lipid profile, higher HOMA-IR, and higher prevalence of MetS than obese-control.

WHAT IS NEW

• Higher serum apelin-12 was observed in obese-DS and obese-DS with MetS than obese-control and obese-control with MetS respectively. The increase in apelin-12 level with increasing obesity grades was more pronounced in obese-DS. • Apelin-12 strongly correlated with obesity-related markers and MetS components in obese-DS. Apelin-12 performed better as a diagnostic biomarker for MetS in obese-DS than obese-control.

Apelin C-Terminal Fragments: Biological Properties and Therapeutic Potential

Creation of bioactive molecules for treatment of cardiovascular diseases based on natural peptides is the focus of intensive experimental research. In the recent years, it has been established that 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 under normal and pathophysiological conditions in vitro and in vivo. It has been shown that the spectrum of action of apelin peptides on the damaged myocardium includes decrease in the death of cardiomyocytes from necrosis, reduction of damage to cardiomyocyte membranes, improvement in myocardial metabolic state, and decrease in formation of reactive oxygen species and lipid peroxidation products. The mechanisms of protective action of these peptides associated with activation of the APJ receptor and manifestation of antioxidant properties are discussed. The data presented in the review show promise of the molecular design of APJ receptor peptide agonists, which can serve as the basis for the development of cardioprotectors that affect the processes of free radical oxidation and metabolic adaptation.

Study of Serum Apelin and Insulin Resistance in Type 2 Diabetes Mellitus Patients With or Without Obesity

INTRODUCTION

Type 2 diabetes mellitus (T2DM) is a chronic disorder characterized by persistent hyperglycemia. Chronic hyperglycemia in diabetes mellitus can cause microvascular and macrovascular complications. Obesity is a major risk factor contributing to disease progression and complications of T2DM. Apelin is an adipokine having a compensatory role in reducing insulin resistance (IR) in morbidly obese individuals. This study was undertaken to find a correlation between Apelin, IR, and obesity.

METHODS

This case-control study included 180 participants, cases (n=90) having T2DM, and healthy controls (n=90). Further, the case and control groups were divided into group I (non-obese) and group II (obese) according to their body mass index (BMI) as per the Asia Pacific classification of BMI. Following obtaining consent, anthropometrical measurements and blood parameters like serum total lipid profile, fasting and postprandial glucose level, Apelin, and insulin were done, and results were analyzed statistically using Statistical Package for the Social Sciences (SPSS) version 21 (IBM Corp., Armonk, NY).

RESULTS

A significantly higher Apelin level was observed in diabetes patients with obesity (265.16±11.0 pg/mL) as compared to non-obese (206.44±83.0 pg/mL). A positive correlation between serum Apelin levels and BMI was found (r=0.367, p=0.003). Homeostasis Model Assessment of IR (HOMA-IR) is increased in obese patients in comparison to the control group. A significant positive correlation between BMI and HOMA-IR (r=0.429, p=0.001) and Apelin and IR (r=0.742, p=0.000) was found in this study.

CONCLUSION

On the basis of the finding of this study, we may conclude that Apelin has a role in improving insulin sensitivity in T2DM. Larger and multicentric studies are further required to discover the therapeutic role of Apelin in T2DM.

Exercise improves homeostasis of the intestinal epithelium by activation of apelin receptor-AMP-activated protein kinase signalling

Intestinal remodelling is dynamically regulated by energy metabolism. Exercise is beneficial for gut health, but the specific mechanisms remain poorly understood. Intestine-specific apelin receptor (APJ) knockdown (KD) and wild-type male mice were randomly divided into two subgroups, with/without exercise, to obtain four groups: WT, WT with exercise, APJ KD and APJ KD with exercise. Animals in the exercise groups were subjected to daily treadmill exercise for 3 weeks. Duodenum was collected at 48 h after the last bout of exercise. AMP-activated protein kinase (AMPK) α1 KD and wild-type mice were also utilized for investigating the mediatory role of AMPK on exercise-induced duodenal epithelial development. AMPK and peroxisome proliferator-activated receptor γ coactivator-1 α were upregulated by exercise via APJ activation in the intestinal duodenum. Correspondingly, exercise induced permissive histone modifications in the PR domain containing 16 (PRDM16) promoter to activate its expression, which was dependent on APJ activation. In agreement, exercise elevated the expression of mitochondrial oxidative markers. The expression of intestinal epithelial markers was downregulated due to AMPK deficiency, and AMPK signalling facilitated epithelial renewal. These data demonstrate that exercise-induced activation of the APJ-AMPK axis facilitates the homeostasis of the intestinal duodenal epithelium. KEY POINTS: Apelin receptor (APJ) signalling is required for improved epithelial homeostasis of the small intestine in response to exercise. Exercise intervention activates PRDM16 through inducing histone modifications, enhanced mitochondrial biogenesis and fatty acid metabolism in duodenum. The morphological development of duodenal villus and crypt is enhanced by the muscle-derived exerkine apelin through the APJ-AMP-activated protein kinase axis.

Eccentric and concentric exercises induce different adaptions in adipose tissue biology

Alterations in adipose tissue (AT) metabolism related to inflammation and adipokine's production lead to perturbations in its capacity to store lipids and release fatty acids (FA) during feeding/fasting transition or during exercise. Exercise has a beneficial effect on AT metabolism, but conventional trainings are not always suitable for patients with functional limitations. Dynamic eccentric (ECC) exercise prevents the accumulation of AT and may then overcome those limitations. Consequently, this study aimed at investigating AT's adaptations after ECC training. Nine-week-old male rats were randomly assigned to a control sedentary or three-trained groups for which treadmill slopes modulated exercise oxygen consumption (VO₂) and mechanical work (n = 15 per group): (1) + 15% uphill-concentric group (CONC), (2) - 15% downhill group (ECC15, same mechanical work as CONC) and (3) - 30% downhill group (ECC30, same VO₂, or oxygen cost as CONC). Body composition and energy expenditure (EE) were measured before and after 8 weeks of training. Subcutaneous AT was collected to study total FA profile and gene expression. Higher total EE was driven by lean mass gain in trained animals. In AT, there was a decrease in arachidonic acid with CONC or ECC15 training. Increased adiponectin, leptin, lipases, Glut4 and Igf1 mRNA levels in ECC15 group suggested major metabolic adaption in AT. In conclusion, ECC could induce beneficial modifications in AT fatty acid profile and the expression of key genes related to metabolism and insulin sensitivity.

Myokine, a key cytokine for physical exercise to alleviate sarcopenic obesity

Skeletal muscle has a robust endocrine function as a powerful organ and can secrete and release cytokines or polypeptides known as myokines. These myokines have significant regulatory effects on signal transduction in skeletal muscle and the metabolism of peripheral tissues and organs and exert biological effects via autocrine, paracrine, or endocrine forms. Obesity and aging cause myokine secretion dysregulation, and hastening sarcopenic obesity (SO) development. Exercise is currently an excellent intervention and prevention method for SO. Meanwhile, exercise impacts many organs and tissues. These organs and tissues will produce various myokines in response to movement and metabolism throughout the body to govern muscle differentiation, growth, and remodeling. According to accumulating data, exercise can increase the release of myokines from diverse tissues into the blood and postpone the SO onset and progression by influencing protein metabolism, inflammation, mitochondrial quality control, and other mechanisms.

The Interaction of Apelin and FGFR1 Ameliorated the Kidney Fibrosis through Suppression of TGFβ-Induced Endothelial-to-Mesenchymal Transition

Both epithelial-to-mesenchymal (EMT) and endothelial-to-mesenchymal (EndMT) transitions have shown to contribute to the development and progression of kidney fibrosis. It has been reported that apelin, a regulatory peptide, alleviates EMT by inhibiting the transforming growth factor β (TGFβ) pathway in renal diseases. Additionally, fibroblast growth factor receptor 1 (FGFR1) has been shown to be a key inhibitor of EndMT through suppression of the TGFβ/Smad pathway. In this study, we found that apelin and FGFR1 were spatially close to each other and that the apelin and FGFR1 complex displayed inhibitory effects on TGFβ/Smad signaling as well as associated EndMT in diabetic kidney fibrosis. In cultured human dermal microvascular endothelial cells (HMVECs), we found that the anti-EndMT and anti-TGFβ/Smad effects of apelin were dampened in FGFR1-deficient cells. Either siRNA- or an inhibitor-mediated deficiency of apelin induced the Smad3 phosphorylation and EndMT. Streptozotocin-induced CD-1 diabetic mice displayed EndMT and associated kidney fibrosis, which were restored by apelin treatment. The medium from apelin-deficient endothelial cells stimulated TGFβ/Smad-dependent EMT in cultured HK2 cells. In addition, depletion of apelin and the FGFR1 complex impaired CEBPA expression, and TGFβ-induced repression of CEBPA expression contributed to the initiation of EndMT in the endothelium. Collectively, these findings revealed that the interaction between apelin and FGFR1 displayed renoprotective potential through suppression of the TGFβ/Smad/CEBPA-mediated EndMT/EMT pathways.

Effect of Cow-Calf Supplementation on Gene Expression, Processes, and Pathways Related to Adipogenesis and Lipogenesis in Longissimus thoracis Muscle of F1 Angus × Nellore Cattle at Weaning

The aim of this study was to identify differentially expressed genes, biological processes, and metabolic pathways related to adipogenesis and lipogenesis in calves receiving different diets during the cow-calf phase. Forty-eight uncastrated F1 Angus × Nellore males were randomly assigned to two treatments from thirty days of age to weaning: no creep feeding (G1) or creep feeding (G2). The creep feed offered contained ground corn (44.8%), soybean meal (40.4%), and mineral core (14.8%), with 22% crude protein and 65% total digestible nutrients in dry matter. After weaning, the animals were feedlot finished for 180 days and fed a single diet containing 12.6% forage and 87.4% corn-based concentrate. Longissimus thoracis muscle samples were collected by biopsy at weaning for transcriptome analysis and at slaughter for the measurement of intramuscular fat content (IMF) and marbling score (MS). Animals of G2 had 17.2% and 14.0% higher IMF and MS, respectively (p < 0.05). We identified 947 differentially expressed genes (log₂ fold change 0.5, FDR 5%); of these, 504 were upregulated and 443 were downregulated in G2. Part of the genes upregulated in G2 were related to PPAR signaling (PPARA, SLC27A1, FABP3, and DBI), unsaturated fatty acid synthesis (FADS1, FADS2, SCD, and SCD5), and fatty acid metabolism (FASN, FADS1, FADS2, SCD, and SCD5). Regarding biological processes, the genes upregulated in G2 were related to cholesterol biosynthesis (EBP, CYP51A1, DHCR24, and LSS), unsaturated fatty acid biosynthesis (FADS2, SCD, SCD5, and FADS1), and insulin sensitivity (INSIG1 and LPIN2). Cow-calf supplementation G2 positively affected energy metabolism and lipid biosynthesis, and thus favored the deposition of marbling fat during the postweaning period, which was shown here in an unprecedented way, by analyzing the transcriptome, genes, pathways, and enriched processes due to the use of creep feeding.

Reactive Oxygen and Nitrogen Species (RONS) and Cytokines-Myokines Involved in Glucose Uptake and Insulin Resistance in Skeletal Muscle

Insulin resistance onset in skeletal muscle is characterized by the impairment of insulin signaling, which reduces the internalization of glucose, known as glucose uptake, into the cell. Therefore, there is a deficit of intracellular glucose, which is the main source for energy production in the cell. This may compromise cellular viability and functions, leading to pathological dysfunction. Skeletal muscle fibers continuously generate reactive oxygen and nitrogen species (RONS). An excess of RONS produces oxidative distress, which may evoke cellular damage and dysfunction. However, a moderate level of RONS, which is called oxidative eustress, is critical to maintain, modulate and regulate cellular functions through reversible interactions between RONS and the components of cellular signaling pathways that control those functions, such as the facilitation of glucose uptake. The skeletal muscle releases peptides called myokines that may have endocrine and paracrine effects. Some myokines bind to specific receptors in skeletal muscle fibers and might interact with cellular signaling pathways, such as PI3K/Akt and AMPK, and facilitate glucose uptake. In addition, there are cytokines, which are peptides produced by non-skeletal muscle cells, that bind to receptors at the plasma membrane of skeletal muscle cells and interact with the cellular signaling pathways, facilitating glucose uptake. RONS, myokines and cytokines might be acting on the same signaling pathways that facilitate glucose uptake in skeletal muscle. However, the experimental studies are limited and scarce. The aim of this review is to highlight the current knowledge regarding the role of RONS, myokines and cytokines as potential signals that facilitate glucose uptake in skeletal muscle. In addition, we encourage researchers in the field to lead and undertake investigations to uncover the fundamentals of glucose uptake evoked by RONS, myokines, and cytokines.

The emerging role of the apelinergic system in kidney physiology and disease

The apelinergic system (AS) is a novel pleiotropic system with an essential role in renal and cardiovascular physiology and disease, including water homeostasis and blood pressure regulation. It consists of two highly conserved peptide ligands, apelin and apela, and a G-protein-coupled apelin receptor. The two ligands have many isoforms and a short half-life and exert both similar and divergent effects. Vasopressin, apelin and their receptors colocalize in hypothalamic regions essential for body fluid homeostasis and interact at the central and renal levels to regulate water homeostasis and diuresis in inverse directions. In addition, the AS and renin-angiotensin system interact both systemically and in the kidney, with implications for the cardiovascular system. A role for the AS in diverse pathological states, including disorders of sodium and water balance, hypertension, heart failure, pre-eclampsia, acute kidney injury, sepsis and diabetic nephropathy, has recently been reported. Furthermore, several metabolically stable apelin analogues have been developed, with potential applications in diverse diseases. We review here what is currently known about the physiological functions of the AS, focusing on renal, cardiovascular and metabolic homeostasis, and the role of the AS in associated diseases. We also describe several hurdles and research opportunities worthy of the attention of the nephrology community.

(-)-Epicatechin Is a Biased Ligand of Apelin Receptor

(-)-Epicatechin (EC) is part of a large family of biomolecules called flavonoids and is widely distributed in the plant kingdom. Several studies have shown the beneficial effects of EC consumption. Many of these reported effects are exerted by activating the signaling pathways associated with the activation of two specific receptors: the G protein-coupled estrogen receptor (GPER), a transmembrane receptor, and the pregnane X receptor (PXR), which is a nuclear receptor. However, the effects of EC are so diverse that these two receptors cannot describe the complete phenomenon. The apelin receptor or APLNR is classified within the G protein-coupled receptor (GPCR) family, and is capable of activating the G protein canonical pathways and the β-arrestin transducer, which participates in the phenomenon of receptor desensitization and internalization. β-arrestin gained interest in selective pharmacology and mediators of the so-called "biased agonism". With molecular dynamics (MD) and in vitro assays, we demonstrate how EC can recruit the β-arrestin in the active conformation of the APLN receptor acting as a biased agonist.

A Tead1-Apelin axis directs paracrine communication from myogenic to endothelial cells in skeletal muscle

Apelin (Apln) is a myokine that regulates skeletal muscle plasticity and metabolism and declines during aging. Through a yeast one-hybrid transcription factor binding screen, we identified the TEA domain transcription factor 1 (Tead1) as a novel regulator of the Apln promoter. Single-cell analysis of regenerating muscle revealed that the apelin receptor (Aplnr) is enriched in endothelial cells, whereas Tead1 is enriched in myogenic cells. Knock-down of Tead1 stimulates Apln secretion from muscle cells in vitro and myofiber-specific overexpression of Tead1 suppresses Apln secretion in vivo. Apln secretion via Tead1 knock-down in muscle cells stimulates endothelial cell expansion via endothelial Aplnr. In vivo, Apln peptide supplementation enhances endothelial cell expansion while Tead1 muscle overexpression delays endothelial remodeling following muscle injury. Our work describes a novel paracrine crosstalk in which Apln secretion is controlled by Tead1 in myogenic cells and influences endothelial remodeling during muscle repair.

Association of serum omentin-1, apelin and chemerin concentrations with the presence and severity of diabetic retinopathy in type 2 diabetes mellitus patients

Omentin-1 is a novel adipokine with anti-inflammatory functions. Apelin is associated with hyperinsulinemia and pathological angiogenesis. Chemerin has both pro- and anti-inflammatory actions and implicated in insulin resistance and metabolic syndrome. The aim of this study was to assess serum omentin-1, apelin and chemerin concentrations and to investigate their association with the presence and severity of DR in T2DM patients. Serum omentin-1, apelin and chemerin were measured in 112 patients with DR and 56 patients without DR. Bivariate analysis showed omentin-1 correlated negatively with hsCRP and TyG index; while apelin correlated positively with chemerin. Linear regression data showed that apelin and chemerin were independent predictors of DR severity. ROC curve revealed that omentin-1 was the best discriminant for DR while apelin was the best discriminant for vision threatening retinopathy. Serum omentin-1 concentration correlates negatively, while serum apelin and chemerin concentrations correlate positively with DR presence and severity in T2DM patients.

Possible roles of exercise and apelin against pregnancy complications

The prevalence of maternal obesity during pregnancy is associated with the risk of gestational diabetes, preeclampsia, and cardiomyopathy. Environmental factors such as active lifestyles and apelin may lead to beneficial changes. In rats, apelin and exercise (45 to 65% VO_2max for 6 to 9 weeks) during pregnancy increase brown adipose tissue (BAT) proteins such as Cidea, Elovl3, UCP1, PRDM16, and PGC-1α in males and females fetuses, while white adipose tissue (WAT) is reduced. In humans and animals, apelin and exercise stimulate the expression of the glucose transporters (GLUT1/2/4) in the muscle and adipose tissue through the PI3K/Akt and AMPK pathways. Hence, exercise and apelin may are known as regulators of energy metabolism and be anti-obesity and anti-diabetic properties. In mice, exercise also creates a short-term hypoxic environment in the pregnant mother, activating HIF-1, VEGF, and VEGFR, and increasing angiogenesis. Exercise and apelin also increase vasodilation, angiogenesis, and suppression of inflammation through the L-arginine/eNOS/NO pathway in humans. Exercise can stimulate the ACE2-Ang-(1-7)-Mas axis in parallel with inhibiting the ACE-Ang II-AT1 pathway. Exercise and apelin seem to prevent preeclampsia through these processes. In rats, moderate-intensity exercise (60 to 70% VO_2max for 8 weeks) and apelin/APJ also may prevent pathological hypertrophy in pregnancy by activating the PI3K/Akt/mTOR/p70S6K pathway, PI3k-Akt-ERK1/2-p70S6K pathway, and the anti-inflammatory cytokine IL-10. Since pre-clinical studies have been more on animal models, future research with scientific guidelines should pay more attention to human specimens. In future research, time factors such as the first, second, and third trimesters of pregnancy and the intensity and duration of exercise are important variables that should be considered to determine the optimal intensity and duration of exercise.

Andrographolide, a novel inducer of apelin gene expression

ETHNOPHARMACOLOGICAL RELEVANCE

Andrographis paniculata (A. paniculata) has been used as a traditional medicine in Asia and Scandinavia for centuries to remedy several illnesses. It has since been shown to possess antibacterial, antifungal, antiviral, anti-neoplasm, hepatoprotective, hypoglycemic, hypocholesterolemic, and energetic effects.

AIMS OF THE STUDY

This study sought to investigate the effect of Andrographolide on apelin gene expression and serum levels of glucose.

MATERIALS AND METHODS

In this study, 18 male rats were used. They were divided into three groups of six, including i) negative control group, ii) 3.5 mg/kg Andrographolide group, and iii) 7 mg/kg Andrographolide group. Apelin gene expression was investigated by real-time PCR method. Serum levels of glucose were measured by the photometric method.

RESULTS

The results of this study revealed that 3.5 and 7 mg doses per kg of body weight of andrographolide, for six days, significantly increased hepatic expression of apelin gene in male Wistar rats, as compared with the control group (p < 0.05). Serum levels of glucose at doses of 3.5 and 7 mg/kg of andrographolide, and in the control group, were 71.5 ± 8.96, 51.5 ± 2.64, and 93.87 ± 14.27 mg/dl, respectively. Andrographolide induced a decrease in serum levels of HDL-c and an increase in LDL-c/HDL-c ratio.

CONCLUSIONS

Our results suggest that Andrographolide can elicit an increase of hepatic apelin gene expression and a decrease in serum levels of blood glucose.

Lychee Seed as a Potential Hypoglycemic Agent, and Exploration of its Underlying Mechanisms

Food is people's primal want. A reasonable diet and healthy food not only provide nutrients for human growth but also contribute to disease prevention and treatment, while following an unhealthy diet can lead to an increased risk of many diseases, especially metabolic disorders, such as diabetes. Nature is enriched with different food sources, and it seems that purely natural products are more in line with the current concept of health, which enhance the formation of the notion that "Food/Diet Supplements from Natural Sources as a Medicine." As a delicious fruit, the medicinal values such as anticancer, antibacterial, antioxidation, and antiglycating properties of lychee have been found. Lychee (Litchi in Chinese) is a subtropical fruit plant belonging to the family Sapindaceae. It has been widely cultivated in warm climates worldwide, particularly in China, for thousands of years. In recent years, various phytochemical components such as quercetin, procyanidin A2, and (2R)-naringenin-7-O-(3-O-αL-rhamnopyranosyl-β-D-glucopyranoside) have been identified in a lychee seed, which may lend a lychee seed as a relatively safe and inexpensive adjuvant treatment for diabetes and diabetic complications. In fact, accumulating evidence has shown that lychee seed, lychee seed extracts, and related compounds have promising antihyperglycemic activities, including improving insulin resistance, anti-inflammatory effect, lipid regulation, neuroprotection, antineurotoxic effect, and renoprotection effect. In this review, we summarized publications on antiglycemic effects and mechanisms of lychee seed, lychee seed extracts, and related compounds, which included their efficacies as a cure for diabetes and diabetic complications in cells, animals, and humans, attempting to obtain a robust evidence basis for the clinical application and value of lychee seed.

Prenatal exercise in fetal development: a placental perspective

Maternal obesity (MO) and gestational diabetes mellitus (GDM) are common in Western societies, which impair fetal development and predispose offspring to metabolic dysfunction. Placenta is the organ linking the mother to her fetus, and MO suppresses the development of vascular system and expression of nutrient transporters in placenta, thereby affecting fetal development. For maintaining its proper physiological function, placenta is energy demanding, which is met through extensive oxidative phosphorylation. However, the oxidative capacity of placenta is suppressed due to MO and GDM. Recently, several studies showed that physical activity during pregnancy enhances oxidative metabolism and improves placental function, which might be partially mediated by exerkines, referring to cytokines elicited by exercise. In addition, as an endocrine organ, placenta secretes cytokines, termed placentokines, including apelin, superoxide dismutase 3, irisin, and adiponectin, which mediate fetal development and maternal metabolism. Possible molecular mechanisms linking maternal exercise and placentokines to placental and fetal development are further discussed. As an emerging field, up to now, available studies are limited, mostly conducted in rodents. Given the epidemics of obesity and metabolic disorders, as well as the prevalence of maternal sedentary lifestyle, the effects of exercise of pregnant women on placental function and placentokine secretion, as well as their impacts on fetal development, need to be further examined.

The Role of the Skeletal Muscle Secretome in Mediating Endurance and Resistance Training Adaptations

Exercise, in the form of endurance or resistance training, leads to specific molecular and cellular adaptions not only in skeletal muscles, but also in many other organs such as the brain, liver, fat or bone. In addition to direct effects of exercise on these organs, the production and release of a plethora of different signaling molecules from skeletal muscle are a centerpiece of systemic plasticity. Most studies have so far focused on the regulation and function of such myokines in acute exercise bouts. In contrast, the secretome of long-term training adaptation remains less well understood, and the contribution of non-myokine factors, including metabolites, enzymes, microRNAs or mitochondrial DNA transported in extracellular vesicles or by other means, is underappreciated. In this review, we therefore provide an overview on the current knowledge of endurance and resistance exercise-induced factors of the skeletal muscle secretome that mediate muscular and systemic adaptations to long-term training. Targeting these factors and leveraging their functions could not only have broad implications for athletic performance, but also for the prevention and therapy in diseased and elderly populations.

In vitro antidiabetic, antioxidant activities and GC-MS analysis of Rhynchostylis Retusa and Euphorbia Neriifolia leaf extracts

This study aimed to assess the antidiabetic, and antioxidant potential of Rhynchostylis retusa and Euphorbia neriifolia, well known for traditional ethnomedicinal uses in North-east India. Leaf extracts prepared in water, methanol and petroleum ether were evaluated for in vitro antidiabetic and antioxidant assay using α-amylase inhibition, glucose diffusion method and DPPH radical scavenging activity. The α-amylase inhibition with E. neriifolia methanolic extract at 400 μg/ml (66.67%) and R. retusa aqueous extract at 300 μg/ml (58.15%) were stronger than in equivalent concentrations of acarbose, i.e., 62.17, and 51.52%, respectively. Aqueous extract R. retusa showed a maximum 67.65% inhibition of glucose diffusion at 180 min in comparison to control without leaf extract. The DPPH radical scavenging activity of E. neriifolia extract in methanol was significantly better than equivalent aqueous or ether extract. However, the solvent choice had little impact on antioxidant activity in R. retusa. GC-MS analysis revealed the presence of a large number of phytochemicals in methanol fraction of E. neriifolia aqueous extracts in comparison to R. retusa. Though the in vitro α-amylase inhibition or glucose diffusion retardation implied potential medicinal use of endangered orchid R. retusa and E. neriifolia, further investigation may be warranted for identification of relevant bio-active compounds and in vivo validation of their pharmacological properties.

A network map of apelin-mediated signaling

The apelin receptor (APLNR) is a class A (rhodopsin-like) G-protein coupled receptor with a wide distribution throughout the human body. Activation of the apelin/APLNR system regulates AMPK/PI3K/AKT/mTOR and RAF/ERK1/2 mediated signaling pathways. APLNR activation orchestrates several downstream signaling cascades, which play diverse roles in physiological effects, including effects upon vasoconstriction, heart muscle contractility, energy metabolism regulation, and fluid homeostasis angiogenesis. We consolidated a network map of the APLNR signaling map owing to its biomedical importance. The curation of literature data pertaining to the APLNR system was performed manually by the NetPath criteria. The described apelin receptor signaling map comprises 35 activation/inhibition events, 38 catalysis events, 4 molecular associations, 62 gene regulation events, 113 protein expression types, and 4 protein translocation events. The APLNR signaling pathway map data is made freely accessible through the WikiPathways Database ( https://www.wikipathways.org/index.php/Pathway:WP5067 ).

Relationship between Apelin/APJ Signaling, Oxidative Stress, and Diseases

Apelin, a peptide hormone, is an endogenous ligand for G protein-coupled receptor and has been shown to be widely expressed in human and animal tissues, such as the central nervous system and adipose tissue. Recent studies indicate that the apelin/APJ system is involved in the regulation of multiple physiological and pathological processes, and it is associated with cardiovascular diseases, metabolic disorders, neurological diseases, ischemia-reperfusion injury, aging, eclampsia, deafness, and tumors. The occurrence and development of these diseases are closely related to the local inflammatory response. Oxidative stress is that the balance between oxidation and antioxidant is broken, and reactive oxygen species are produced in large quantities, causing cell or molecular damage, which leads to vascular damage and a series of inflammatory reactions. Hence, this article reviewed recent advances in the relationship between apelin/APJ and oxidative stress, and inflammation-related diseases, and highlights them as potential therapeutic targets for oxidative stress-related inflammatory diseases.

The G Protein Biased Small Molecule Apelin Agonist CMF-019 is Disease Modifying in Endothelial Cell Apoptosis In Vitro and Induces Vasodilatation Without Desensitisation In Vivo

Signaling through the apelin receptor is beneficial for a number of diseases including pulmonary arterial hypertension. The endogenous small peptides, apelin and elabela/toddler, are downregulated in pulmonary arterial hypertension but are not suitable for exogenous administration owing to a lack of bioavailability, proteolytic instability and susceptibility to renal clearance. CMF-019, a small molecule apelin agonist that displays strong bias towards G protein signaling over β-arrestin (∼400 fold), may be more suitable. This study demonstrates that in addition to being a positive inotrope, CMF-019 caused dose-dependent vasodilatation in vivo (50 nmol 4.16 ± 1.18 mmHg, **p < 0.01; 500 nmol 6.62 ± 1.85 mmHg, **p < 0.01), without receptor desensitization. Furthermore, CMF-019 rescues human pulmonary artery endothelial cells from apoptosis induced by tumor necrosis factor α and cycloheximide (5.66 ± 0.97%, **p < 0.01) by approximately 50% of that observable with rhVEGF (11.59 ± 1.85%, **p < 0.01), suggesting it has disease-modifying potential in vitro. CMF-019 displays remarkable bias at the apelin receptor for a small molecule and importantly recapitulates all aspects of the cardiovascular responses to the endogenous ligand, [Pyr¹]apelin-13, in vivo. Additionally, it is able to protect human pulmonary artery endothelial cells from apoptosis, suggesting that the beneficial effects observed with apelin agonists extend beyond hemodynamic alleviation and address disease etiology itself. These findings support CMF-019 as a G protein biased small molecule apelin agonist in vitro and in vivo that could form the basis for the design of novel therapeutic agents in chronic diseases, such as, pulmonary arterial hypertension.

Association of Apelin Levels in Overweight-obese Children with Pubertal Development, but Not with Insulin Sensitivity: 6.5 Years Follow up Evaluation

BACKGROUND

Obesity in youth is associated with increased risk of metabolic disorders. Adipose tissue hormones are involved in body-weight regulation. Among these, apelin is recognized as an insulin-sensitizer adipokine. Data on apelin levels in obese children and its relation to insulin-sensitivity are limited.

OBJECTIVE

We aimed to evaluate apelin levels in relation to obesity and insulin sensitivity in a large cohort of overweight/obese children and adolescents. Furthermore, these youths were reevaluated after a median 6.5 years of follow-up, thus allowing assessing changes in apelin levels in relation to increasing age and weight changes.

METHODS

Clinical data in 909 children and adolescents were collected between 2007 and 2010. Two hundred and one were reexamined at a median 6.5 years of follow-up. All subjects at baseline and at follow-up underwent an OGTT. Apelin levels were measured on sera by ELISA method.

RESULTS

At baseline, lower apelin levels were associated with increasing age and puberty (Tanner ≥II 0.67 ± 0.96 ng/mL vs. Tanner I 0.89 ± 1.13 ng/mL, p < .002), but not with body-weight. At follow-up, apelin levels in the 201 subjects reexamined were significantly lower than at baseline (0.45 ± 0.77 ng/mL at follow-up, 0.68 ± 0.95 ng/mL baseline, p < .001), confirming the effects of age and puberty. Body-weight did not affect apelin levels. Multiple regression analysis confirmed that sex and puberty were associated with lower apelin levels, independently from age and insulin-sensitivity.

CONCLUSIONS

Apelin levels decrease significantly with pubertal development, whilst body-weight in children and adolescents did not determine changes in apelin. Reduced levels of apelin in children and adolescents may therefore represent a necessary response to maintain the "physiological" insulin resistance of puberty. Abbreviations: ALT: Alanine aminotransferase; AST: Aspartate aminotransferase; G: glucose; BMI: Body mass index; DBP: Diastolic blood pressure; ELISA: enzyme-linked immunosorbent assay; HDL-C: High-density lipoprotein-cholesterol; HOMA-B: Homeostatic model assessment for beta-cell function; HOMA-IR: Homeostatic model assessment of insulin-resistance; INS: Insulin; ISI: insulin-sensitivity index; LDL-C: Low-density lipoprotein cholesterol; NW: normal weight; OB: obese; OGTT: oral glucose tolerance test; OW: overweight; SBP: Systolic blood pressure; TC: Total cholesterol; TGs: Triglycerides.

Influence of a Novel Food-Grade Formulation of Red Chili Extract (Capsicum annum) on Overweight Subjects: Randomized, Double-Blinded, Placebo-Controlled Study

Capsaicinoids from pungent red chilies (Capsicum annum and Capsicum frutescens) have received significant attention as a natural supplement for the management of obesity. However, the consumption of chili extract at physiologically relevant dosage of capsaicinoids is a challenge owing to its pungency and gastrointestinal discomforts. The present study reports the systemic absorption, safety and influence of a novel, food-grade, and sustained-release formulation of capsaicinoids-rich red chili extract using fenugreek dietary fiber (Capsifen^®). Twenty-four healthy overweight subjects were randomized into placebo (n = 12) and Capsifen (n = 12) groups and supplemented with 200 mg × 1/day of Capsifen (4 mg capsaicinoids/day) for 28 days. Influence of Capsifen on eating behavior and appetite was followed by Three-Factor Eating Questionnaire (TFEQ) and Council of Nutrition Appetite Questionnaire (CNAQ), respectively. Consumption of Capsifen did not reveal any adverse events or deviations in hematology and biochemical parameters related to safety. However, a significant decrease in body weight (2.1%), w/h ratio (4%) and body mass index (BMI) (2.2%) were observed among Capsifen group when compared to placebo. The TFEQ and appetite analysis revealed a significant improvement in uncontrolled eating and reduction in appetite among Capsifen subjects. The UPLC-ESI-MS/MS analysis confirmed the absorption of capsaicinoids from CAP supplementation. The study further demonstrated the safety and tolerability of Capsifen at the investigational dosage. Thus, the significant reduction in anthropometric parameters such as body weight, w/h ratio, and BMI along with the improvement in eating behaviour as well as appetite, indicated the potential body weight management effect of Capsifen.

Fundamentals about onset and progressive disease character of type 2 diabetes mellitus

ResearchGate is a world wide web for scientists and researchers to share papers, ask and answer questions, and find collaborators. As one of the more than 15 million members, the author uploads research output and reads and responds to some of the questions raised, which are related to type 2 diabetes. In that way, he noticed a serious gap of knowledge of this disease among medical professionals over recent decades. The main aim of the current study is to remedy this situation through providing a comprehensive review on recent developments in biochemistry and molecular biology, which can be helpful for the scientific understanding of the molecular nature of type 2 diabetes. To fill up the shortcomings in the curricula of medical education, and to familiarize the medical community with a new concept of the onset of type 2 diabetes, items are discussed like: Insulin resistance, glucose effectiveness, insulin sensitivity, cell membranes, membrane flexibility, unsaturation index (UI; number of carbon-carbon double bonds per 100 acyl chains of membrane phospholipids), slow-down principle, effects of temperature acclimation on phospholipid membrane composition, free fatty acids, energy transport, onset of type 2 diabetes, metformin, and exercise. Based on the reviewed data, a new model is presented with proposed steps in the development of type 2 diabetes, a disease arising as a result of a hypothetical hereditary anomaly, which causes hyperthermia in and around the mitochondria. Hyperthermia is counterbalanced by the slow-down principle, which lowers the amount of carbon-carbon double bonds of membrane phospholipid acyl chains. The accompanying reduction in the UI lowers membrane flexibility, promotes a redistribution of the lateral pressure in cell membranes, and thereby reduces the glucose transporter protein pore diameter of the transmembrane glucose transport channel of all Class I GLUT proteins. These events will set up a reduction in transmembrane glucose transport. So, a new blood glucose regulation system, effective in type 2 diabetes and its prediabetic phase, is based on variations in the acyl composition of phospholipids and operates independent of changes in insulin and glucose concentration. UI assessment is currently arising as a promising analytical technology for a membrane flexibility analysis. An increase in mitochondrial heat production plays a pivotal role in the existence of this regulation system.

New Insights into Adipokines as Potential Biomarkers for Type-2 Diabetes Mellitus

A large number of studies have been focused on investigating serum biomarkers associated with risk or diagnosis of type-2 diabetes mellitus. In the last decade, promising studies have shown that circulating levels of adipokines could be used as a relevant biomarker for diabetes mellitus progression as well as therapeutic future targets. Here, we discuss the possible use of recently described adipokines, including apelin, omentin-1, resistin, FGF-21, neuregulin-4 and visfatin, as early biomarkers for diabetes. In addition, we also include recent findings of other well known adipokines such as leptin and adiponectin. In conclusion, further studies are needed to clarify the pathophysiological significance and clinical value of these biological factors as potential biomarkers in type-2 diabetes and related dysfunctions.

The Novel Perspectives of Adipokines on Brain Health

First seen as a fat-storage tissue, the adipose tissue is considered as a critical player in the endocrine system. Precisely, adipose tissue can produce an array of bioactive factors, including cytokines, lipids, and extracellular vesicles, which target various systemic organ systems to regulate metabolism, homeostasis, and immune response. The global effects of adipokines on metabolic events are well defined, but their impacts on brain function and pathology remain poorly defined. Receptors of adipokines are widely expressed in the brain. Mounting evidence has shown that leptin and adiponectin can cross the blood–brain barrier, while evidence for newly identified adipokines is limited. Significantly, adipocyte secretion is liable to nutritional and metabolic states, where defective circuitry, impaired neuroplasticity, and elevated neuroinflammation are symptomatic. Essentially, neurotrophic and anti-inflammatory properties of adipokines underlie their neuroprotective roles in neurodegenerative diseases. Besides, adipocyte-secreted lipids in the bloodstream can act endocrine on the distant organs. In this article, we have reviewed five adipokines (leptin, adiponectin, chemerin, apelin, visfatin) and two lipokines (palmitoleic acid and lysophosphatidic acid) on their roles involving in eating behavior, neurotrophic and neuroprotective factors in the brain. Understanding and regulating these adipokines can lead to novel therapeutic strategies to counteract metabolic associated eating disorders and neurodegenerative diseases, thus promote brain health.

Beyond adiponectin and leptin: adipose tissue-derived mediators of inter-organ communication

The breakthrough discoveries of leptin and adiponectin more than two decades ago led to a widespread recognition of adipose tissue as an endocrine organ. Many more adipose tissue-secreted signaling mediators (adipokines) have been identified since then, and much has been learned about how adipose tissue communicates with other organs of the body to maintain systemic homeostasis. Beyond proteins, additional factors, such as lipids, metabolites, noncoding RNAs, and extracellular vesicles (EVs), released by adipose tissue participate in this process. Here, we review the diverse signaling mediators and mechanisms adipose tissue utilizes to relay information to other organs. We discuss recently identified adipokines (proteins, lipids, and metabolites) and briefly outline the contributions of noncoding RNAs and EVs to the ever-increasing complexities of adipose tissue inter-organ communication. We conclude by reflecting on central aspects of adipokine biology, namely, the contribution of distinct adipose tissue depots and cell types to adipokine secretion, the phenomenon of adipokine resistance, and the capacity of adipose tissue to act both as a source and sink of signaling mediators.

International Union of Basic and Clinical Pharmacology. CVII. Structure and Pharmacology of the Apelin Receptor with a Recommendation that Elabela/Toddler Is a Second Endogenous Peptide Ligand

The predicted protein encoded by the APJ gene discovered in 1993 was originally classified as a class A G protein-coupled orphan receptor but was subsequently paired with a novel peptide ligand, apelin-36 in 1998. Substantial research identified a family of shorter peptides activating the apelin receptor, including apelin-17, apelin-13, and [Pyr1]apelin-13, with the latter peptide predominating in human plasma and cardiovascular system. A range of pharmacological tools have been developed, including radiolabeled ligands, analogs with improved plasma stability, peptides, and small molecules including biased agonists and antagonists, leading to the recommendation that the APJ gene be renamed APLNR and encode the apelin receptor protein. Recently, a second endogenous ligand has been identified and called Elabela/Toddler, a 54-amino acid peptide originally identified in the genomes of fish and humans but misclassified as noncoding. This precursor is also able to be cleaved to shorter sequences (32, 21, and 11 amino acids), and all are able to activate the apelin receptor and are blocked by apelin receptor antagonists. This review summarizes the pharmacology of these ligands and the apelin receptor, highlights the emerging physiologic and pathophysiological roles in a number of diseases, and recommends that Elabela/Toddler is a second endogenous peptide ligand of the apelin receptor protein.

The preprohormone expression profile of enteroendocrine cells following Roux-en-Y gastric bypass in rats

OBJECTIVE

Roux-en-Y gastric bypass (RYGB) leads to rapid remission of type 2 diabetes (T2D) and sustained body weight loss, but the underlying molecular mechanisms are still not fully understood. To further elucidate these mechanisms and identify potentially novel preprohormone encoding genes with anti-diabetic and/or anti-obesity properties, we performed a comprehensive analysis of gene expression changes in enteroendocrine cells after RYGB in diet-induced obese (DIO) rats.

METHODS

The mRNA expression profiles of enteroendocrine cell enriched samples were characterized at 9, 22 and 60 days after RYGB surgery in a DIO rat model. Enteroendocrine cells were identified by chromogranin A immunohistochemistry and isolated by laser capture microdissection (LCM) from five regions covering the full rostro-caudal extension of the gastrointestinal (GI) tract. RNA sequencing and bioinformatic analyses were subsequently applied to identify differentially expressed preprohormone encoding genes.

RESULTS

From the analysis of enteroendocrine cell mRNA expression profiles, a total of 54 preprohormones encoding genes were found to be differentially regulated at one or more time-points following RYGB. These included well-known RYGB associated preprohormone genes (e.g. Gcg, Cck, Gip, Pyy and Sct) and less characterized genes with putative metabolic effects (e.g. Nmu, Guca2a, Guca2b, Npw and Adm), but also 16 predicted novel preprohormone genes. Among the list of gene transcripts, Npw, Apln and Fam3d were further validated using in situ mRNA hybridization and corresponding peptides were characterized for acute effects on food intake and glucose tolerance in mice.

CONCLUSION

We present a comprehensive mRNA expression profile of chromogranin A positive enteroendocrine cells following RYGB in rats. The data provides a region-specific characterization of all regulated preprohormone encoding genes in the rat GI tract including 16 not hitherto known. The comprehensive catalogue of preprohormone expression changes may support our understanding of hormone mediated effects of RYGB on diabetes remission and body weight reduction.

Apelin affects the mouse aging urinary peptidome with minimal effects on kidney

Kidney function is altered by age together with a declined filtration capacity of 5–10% per decade after 35 years. Renal aging shares many characteristics with chronic kidney disease. Plasma levels of the bioactive peptide apelin also decline with age and apelin has been shown to be protective in chronic kidney disease. Therefore we evaluated whether apelin could also improve aging-induced renal lesions and function in mice. Since urine is for the major part composed of proteins and peptides originating from the kidney, we first studied apelin-induced changes, in the aging urinary peptidome. Despite the recently published age-associated plasma decrease of apelin, expression of the peptide and its receptor was increased in the kidneys of 24 months old mice. Twenty-eight days treatment with apelin significantly modified the urinary peptidome of 3 and 24 months old mice towards a signature suggesting more advanced age at 3 months, and a younger age at 24 months. The latter was accompanied by a decreased staining of collagen (Sirius red staining) in 24 months old apelin-treated mice, without changing aging-induced glomerular hypertrophy. In addition, apelin was without effect on aging-induced renal autophagy, apoptosis, inflammation and reduced renal function. In conclusion, treatment of aged mice with apelin had a limited effect on kidney lesions although modifying the urinary peptidome towards a younger signature. This supports evidence of apelin inducing more general beneficial effects on other aging organs, muscles in particular, as recently shown for sarcopenia, markers of which end up via the glomerular filtration in urine.

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.

Elevated blood apelin levels in type 2 diabetes mellitus: A systematic review and meta-analysis

AIMS

Apelin is a circulatory blood peptide acting as a ligand for the orphan G protein-coupled receptor known as APJ. Whether apelin blood levels can affect the pathogenesis of type 2 diabetes mellitus is an open question. In the present study, we aimed to assess the levels of circulatory apelin peptide in the type 2 diabetic subjects using systematic review and meta-analysis under random-effects model and standardized mean difference (SMD) as the effect size. For heterogeneity testing, Q and I²% statistic indices as well as meta-regression were applied.

METHODS

Using specialized biomedical online databases of Pubmed, Pubmed Central, Medline, Google scholar, Scopus and Embase databases without the beginning date restriction until July 2018, the systematic review retrieved nine studies for meta-analysis after fulfilling the inclusion and exclusion criteria.

RESULTS

Analysis of Q and I²% statistic indices as well as meta-regression showed a high heterogeneity in the 16 selected studies (737.578 and 96.475, respectively), thus, the random-effects model was chosen. The primary analysis for the main hypothesis on a total number of 1102 cases and 1078 healthy control subjects found that the weighted pooled SMD for the impact of apelin blood concentration in type 2 diabetes mellitus was as follows: SMD = 2.136 (95% confidence interval, 1.580-2.693). The P-value for the significance of the combined SMD examined by the z-test was 0.000 and thus, it was clearly significant.

CONCLUSIONS

This meta-analysis presents evidence that apelin circulatory levels are higher in type 2 diabetic subjects than normal controls.

Effects of aerobic and resistance exercises on circulating apelin-12 and apelin-36 concentrations in obese middle-aged women: a randomized controlled trial

BACKGROUND

The risk for obesity-related diseases increases with the prevalence of obesity. In obesity, adipokines secreted from adipose tissue induce inflammation, causing adverse effects. Recently, adipokines such as apelin, visfatin, and chemerin have been studied. Long-term resistance training improves health in middle-aged women by improving metabolic risk factors, body composition, and muscle strength. However, there is still a lack of evidence on the association of apelin concentration with different exercise types in middle-aged obese women This study aimed to investigate the effects of 8 weeks of aerobic and resistance exercises on apelin-12 and apelin-36 levels and thereby verify the effects of different exercise types in obese, middle-aged women.

METHODS

Participants were middle-aged women aged 50-61 years, with no experience of systematic exercise in the last 6 months, and met the WHO obesity criteria for the Asia-Pacific region of waist circumference ≥ 80 cm and body fat percentage ≥ 30%. Subjects were selected and allocated to the aerobic exercise, resistance exercise, or no exercise group by block randomization. Body weight, body fat, and body mass index were measured by bioelectrical impedance analysis. Analysis of variance, the t-test, and Tukey's post-hoc test were performed.

RESULTS

A total of 24 participants were selected with eight participants in each group. Both aerobic and resistance exercises were effective in altering the physical composition, showing significant decreases in weight, waist circumference, BMI, and body fat. The aerobic and resistance exercise group showed a significant, positive change in apelin-12 levels.

CONCLUSIONS

In obese individuals, aerobic and resistance exercise were effective in improving obesity and reducing blood apelin-12 concentration, which is closely correlated with indicators of metabolic syndrome. Future research should focus on comparing the response of apelin to exercise in obese subjects treated with only dietary control and the response in the obese subjects of different ages and sex.

TRIAL REGISTRATION

No. 1040917-201,506-BR-153-04 , Clinical Research Information Service (CRIS), Republic of Korea (05 October 2018, retrospectively registered).

Serum Apelin and Obesity-Related Complications in Egyptian Children

BACKGROUND

The rapidly increasing prevalence of childhood obesity became a major burden on health worldwide, giving an alarm to clinicians and researchers. Adipocytes act as an active endocrine organ by releasing plenty of bioactive mediators (adipokines) that play a major role in regulating metabolic processes. Apelin is a recently identified adipokine that is expressed in adipocytes.

AIM

The current work aimed to uncover the relation between serum apelin and childhood obesity and its related complications as hypertension and hyperglycemia.

METHOD

A group of 50 obese and 31 non-obese; sex- and age-matched children were enrolled in our study with a mean age of (9.5 ± 2.1) and (8.7 ± 1.3) respectively. Anthropometric measurements, blood pressure, were assessed in all studied participants, we also determined the lipid profile, serum insulin, fasting blood glucose (FBG) level, HOMA-IR and serum apelin.

RESULTS

Obese children had higher levels of HbA1c, FBG, serum insulin, HOMA-IR, total cholesterol, triglycerides, low-density lipoprotein (LDL) and diastolic blood pressure (DBP Z-score); compared to controls (all P < 0.05). Apelin was significantly higher in obese children versus controls and correlated positively with BMI Z-Score (P = 0.008), DBP Z-Score (P = 0.02), cholesterol, TG (both P = 0.02), serum insulin (P = 0.003), FBG and HOMA-IR (both P = 0.001). Linear regression analysis showed that FBG was the most effective factor in predicting the level of serum apelin (P = 0.04).

CONCLUSION

This work supports the hypothesis that apelin may have a crucial role in the pathogenesis of health hazards related to obesity in children including insulin resistance, hypertension and a higher risk of occurrence of metabolic syndrome.

Apelin and APJ orchestrate complex tissue-specific control of cardiomyocyte hypertrophy and contractility in the hypertrophy-heart failure transition

The G protein-coupled receptor APJ is a promising therapeutic target for heart failure. Constitutive deletion of APJ in the mouse is protective against the hypertrophy-heart failure transition via elimination of ligand-independent, β-arrestin-dependent stretch transduction. However, the cellular origin of this stretch transduction and the details of its interaction with apelin signaling remain unknown. We generated mice with conditional elimination of APJ in the endothelium (APJendo-/-) and myocardium (APJmyo-/-). No baseline difference was observed in left ventricular function in APJendo-/-, APJmyo-/-, or control (APJendo+/+, APJmyo+/+) mice. After exposure to transaortic constriction, APJendo-/- mice displayed decreased left ventricular systolic function and increased wall thickness, whereas APJmyo-/- mice were protected. At the cellular level, carbon fiber stretch of freshly isolated single cardiomyocytes demonstrated decreased contractile responses to stretch in APJ-/- cardiomyocytes compared with APJ+/+ cardiomyocytes. Ca2+ transients did not change with stretch in either APJ-/- or APJ+/+ cardiomyocytes. Application of apelin to APJ+/+ cardiomyocytes resulted in decreased Ca2+ transients. Furthermore, hearts of mice treated with apelin exhibited decreased phosphorylation in cardiac troponin I NH2-terminal residues (Ser22 and Ser23) consistent with increased Ca2+ sensitivity. These data establish that APJ stretch transduction is mediated specifically by myocardial APJ, that APJ is necessary for stretch-induced increases in contractility, and that apelin opposes APJ's stretch-mediated hypertrophy signaling by lowering Ca2+ transients while maintaining contractility through myofilament Ca2+ sensitization. These findings underscore apelin's unique potential as a therapeutic agent that can simultaneously support cardiac function and protect against the hypertrophy-heart failure transition. NEW & NOTEWORTHY These data address fundamental gaps in our understanding of apelin-APJ signaling in heart failure by localizing APJ's ligand-independent stretch sensing to the myocardium, identifying a novel mechanism of apelin-APJ inotropy via myofilament Ca2+ sensitization, and identifying potential mitigating effects of apelin in APJ stretch-induced hypertrophic signaling.

[Sport: A key element for myometrial contractility and regulation of adipokines in obese pregnant women?]

Obesity is a major public health problem. Pregnant women are also affected by this epidemic. In pregnant women, obesity increases obstetric and neonatal complications, and is associated with alterations in the quality of labor that could be explained by reduced myometrial contractility. This leads to an increase in the rate of caesarean sections and postpartum haemorrhages in this population at risk. Adipokines, hormones secreted by adipose tissue, may have a role in altering the myometrial contractility. Weight loss in these patients is based on dietary management and on physical activity, which could be a way to improve adipokines action and uterine contractility. The objective of this literature review was to review current knowledge about the role of adipokines on uterine contractility in obese pregnant women and to assess the interest of sport in improving contractility and in reducing obstetric complications in these women.

Downregulation of the Apelinergic Axis Accelerates Aging, whereas Its Systemic Restoration Improves the Mammalian Healthspan

Aging drives the occurrence of numerous diseases, including cardiovascular disease (CVD). Recent studies indicate that blood from young mice reduces age-associated pathologies. However, the "anti-aging" factors in juvenile circulation remain poorly identified. Here, we characterize the role of the apelinergic axis in mammalian aging and identify apelin as an anti-aging factor. The expression of apelin (apln) and its receptor (aplnr) exhibits an age-dependent decline in multiple organs. Reduced apln signaling perturbs organismal homeostasis; mice harboring genetic deficiency of aplnr or apln exhibit enhanced cardiovascular, renal, and reproductive aging. Genetic or pharmacological abrogation of apln signaling also induces cellular senescence mediated, in part, by the activation of senescence-promoting transcription factors. Conversely, restoration of apln in 15-month-old wild-type mice reduces cardiac hypertrophy and exercise-induced hypertensive response. Additionally, apln-restored mice exhibit enhanced vigor and rejuvenated behavioral and circadian phenotypes. Hence, a declining apelinergic axis promotes aging, whereas its restoration extends the murine healthspan.

Recognition of the polycistronic nature of human genes is critical to understanding the genotype-phenotype relationship

Technological advances promise unprecedented opportunities for whole exome sequencing and proteomic analyses of populations. Currently, data from genome and exome sequencing or proteomic studies are searched against reference genome annotations. This provides the foundation for research and clinical screening for genetic causes of pathologies. However, current genome annotations substantially underestimate the proteomic information encoded within a gene. Numerous studies have now demonstrated the expression and function of alternative (mainly small, sometimes overlapping) ORFs within mature gene transcripts. This has important consequences for the correlation of phenotypes and genotypes. Most alternative ORFs are not yet annotated because of a lack of evidence, and this absence from databases precludes their detection by standard proteomic methods, such as mass spectrometry. Here, we demonstrate how current approaches tend to overlook alternative ORFs, hindering the discovery of new genetic drivers and fundamental research. We discuss available tools and techniques to improve identification of proteins from alternative ORFs and finally suggest a novel annotation system to permit a more complete representation of the transcriptomic and proteomic information contained within a gene. Given the crucial challenge of distinguishing functional ORFs from random ones, the suggested pipeline emphasizes both experimental data and conservation signatures. The addition of alternative ORFs in databases will render identification less serendipitous and advance the pace of research and genomic knowledge. This review highlights the urgent medical and research need to incorporate alternative ORFs in current genome annotations and thus permit their inclusion in hypotheses and models, which relate phenotypes and genotypes.

A high-resolution genetic linkage map and QTL fine mapping for growth-related traits and sex in the Yangtze River common carp (Cyprinus carpio haematopterus)

Background

A high-density genetic linkage map is essential for QTL fine mapping, comparative genome analysis, identification of candidate genes and marker-assisted selection for economic traits in aquaculture species. The Yangtze River common carp (Cyprinus carpio haematopterus) is one of the most important aquacultured strains in China. However, quite limited genetics and genomics resources have been developed for genetic improvement of economic traits in such strain.

Results

A high-resolution genetic linkage map was constructed by using 7820 2b-RAD (2b-restriction site-associated DNA) and 295 microsatellite markers in a F2 family of the Yangtze River common carp (C. c. haematopterus). The length of the map was 4586.56 cM with an average marker interval of 0.57 cM. Comparative genome mapping revealed that a high proportion (70%) of markers with disagreed chromosome location was observed between C. c. haematopterus and another common carp strain (subspecies) C. c. carpio. A clear 2:1 relationship was observed between C. c. haematopterus linkage groups (LGs) and zebrafish (Danio rerio) chromosomes. Based on the genetic map, 21 QTLs for growth-related traits were detected on 12 LGs, and contributed values of phenotypic variance explained (PVE) ranging from 16.3 to 38.6%, with LOD scores ranging from 4.02 to 11.13. A genome-wide significant QTL (LOD = 10.83) and three chromosome-wide significant QTLs (mean LOD = 4.84) for sex were mapped on LG50 and LG24, respectively. A 1.4 cM confidence interval of QTL for all growth-related traits showed conserved synteny with a 2.06 M segment on chromosome 14 of D. rerio. Five potential candidate genes were identified by blast search in this genomic region, including a well-studied multi-functional growth related gene, Apelin.

Conclusions

We mapped a set of suggestive and significant QTLs for growth-related traits and sex based on a high-density genetic linkage map using SNP and microsatellite markers for Yangtze River common carp. Several candidate growth genes were also identified from the QTL regions by comparative mapping. This genetic map would provide a basis for genome assembly and comparative genomics studies, and those QTL-derived candidate genes and genetic markers are useful genomic resources for marker-assisted selection (MAS) of growth-related traits in the Yangtze River common carp.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4613-1) contains supplementary material, which is available to authorized users.

Efficacy of high-intensity, low-volume interval training compared to continuous aerobic training on insulin resistance, skeletal muscle structure and function in adults with metabolic syndrome: study protocol for a randomized controlled clinical trial (Intraining-MET)

Background

Evidence of the efficacy of high-intensity, low-volume interval training (HIIT-low volume) in treating insulin resistance (IR) in patients with metabolic disorders is contradictory. In addition, it is unknown whether this effect is mediated through muscle endocrine function, which in turn depends on muscle mass and fiber type composition. Our aims were to assess the efficacy of HIIT-low volume compared to continuous aerobic exercise (CAE) in treating IR in adults with metabolic syndrome (MS) and to establish whether musclin, apelin, muscle mass and muscle composition are mediators of the effect.

Methods

This is a controlled, randomized, clinical trial using the minimization method, with blinding of those who will evaluate the outcomes and two parallel groups for the purpose of showing superiority. Sixty patients with MS and IR with ages between 40 and 60 years will be included. A clinical evaluation will be carried out, along with laboratory tests to evaluate IR (homeostatic model assessment (HOMA)), muscle endocrine function (serum levels of musclin and apelin), thigh muscle mass (by dual energy x-ray absorptiometry (DXA) and thigh muscle composition (by carnosine measurement with proton magnetic resonance spectroscopy (¹H–MRS)), before and after 12 weeks of a treadmill exercise program three times a week. Participants assigned to the intervention (n = 30) will receive HIIT-low volume in 22-min sessions that will include six intervals at a load of 90% of maximum oxygen consumption (VO₂ max) for 1 min followed by 2 min at 50% of VO₂ max. The control group (n = 30) will receive CAE at an intensity of 60% of VO₂ max for 36 min. A theoretical model based on structural equations will be proposed to estimate the total, direct and indirect effects of training on IR and the proportion explained by the mediators.

Discussion

Compared with CAE, HIIT-low volume can be effective and efficient at improving physical capacity and decreasing cardiovascular risk factors, such as IR, in patients with metabolic disorders. Studies that evaluate mediating variables of the effect of HIIT-low volume on IR, such as endocrine function and skeletal muscle structure, are necessary to understand the role of skeletal muscle in the pathophysiology of MS and their regulation by exercise.

Trial registration

NCT03087721. High-intensity Interval, Low Volume Training in Metabolic Syndrome (Intraining-MET). Registered on 22 March 2017, retrospectively registered.

Electronic supplementary material

The online version of this article (10.1186/s13063-018-2541-7) contains supplementary material, which is available to authorized users.

Apelin Ameliorates High Glucose-Induced Downregulation of Connexin 43 via AMPK-Dependent Pathway in Neonatal Rat Cardiomyocytes

Diabetes Mellitus is a common disorder, with increasing risk of cardiac arrhythmias. Studies have shown that altered connexin expression and gap junction remodeling under hyperglycemia contribute to the high prevalence of cardiac arrhythmias and even sudden death. Connexin 43 (Cx43), a major protein that assembles to form cardiac gap junctions, has been found to be downregulated under high glucose conditions, along with inhibition of gap junctional intercellular communication (GJIC). While, apelin, a beneficial adipokine, increases Cx43 protein expression in mouse and human embryonic stem cells during cardiac differentiation. However, it remains unknown whether apelin influences GJIC capacity in cardiomyocytes. Here, using Western blotting and dye transfer assays, we found that Cx43 protein expression was reduced and GJIC was impaired after treatment with high glucose, which, however, could be abrogated after apelin treatment for 48 h. We also found that apelin increased Cx43 expression under normal glucose. Real-time PCR showed that the Cx43 mRNA was not significantly affected under high glucose conditions in the presence of apelin or high glucose and apelin. High glucose decreased the phosphorylation of AMPKα; however, apelin activated AMPKα. Interestingly, we found that Cx43 expression was increased after treatment with AICAR, an activator of AMPK signaling. AMPKα inhibition mediated with transfection of siRNA-AMPKα1 and siRNA-AMPKα2 abolished the protective effect of apelin on Cx43 expression. Our data suggest that apelin attenuates high glucose-induced Cx43 downregulation and improves the loss of functional gap junctions partly through the AMPK pathway.

Impact of Intestinal Peptides on the Enteric Nervous System: Novel Approaches to Control Glucose Metabolism and Food Intake

The gut is one of the most important sources of bioactive peptides in the body. In addition to their direct actions in the brain and/or peripheral tissues, the intestinal peptides can also have an impact on enteric nervous neurons. By modifying the endogenousproduction of these peptides, one may expect modify the "local" physiology such as glucose absorption, but also could have a "global" action via the gut-brain axis. Due to the various origins of gut peptides (i.e., nutrients, intestinal wall, gut microbiota) and the heterogeneity of enteric neurons population, the potential physiological parameters control by the interaction between the two partners are multiple. In this review, we will exclusively focus on the role of enteric nervous system as a potential target of gut peptides to control glucose metabolism and food intake. Potential therapeutic strategies based on per os administration of gut peptides to treat type 2 diabetes will be described.

Effects of exercise-induced apelin levels on skeletal muscle and their capillarization in type 2 diabetic rats

INTRODUCTION

Exercise-induced apelin as a myokine is believed to play a role in the improvement of type 2 diabetes mellitus (T2DM) and capillarization. In this study, we evaluated the association between exercise-induced apelin and muscle capillarization.

METHODS

Zucker rats underwent a treadmill exercise program. Body composition, muscle strength, muscle size, muscle capillarization, and insulin resistance (homeostatic model assessment [HOMA-IR]) were measured. Apelin levels of skeletal muscle and plasma were then analyzed.

RESULTS

Exercise improved body composition (P < 0.05), HOMA-IR (P < 0.05), and grip strength (P < 0.001). In the soleus, the fiber size of T2DM was decreased (P < 0.001), but it increased in fiber size and capillarization after exercise (P < 0.001) occurred. We identified an increase in plasma apelin (P < 0.05) and a decrease in soleus apelin (P < 0.01), as well as an association between soleus apelin and angiogenesis (P < 0.01).

DISCUSSION

A role for exercise-induced apelin in improving metabolism indicates the possibility of a new drug target for the treatment of metabolic diseases and repairing skeletal muscle damage. Muscle Nerve 56: 1155-1163, 2017.