Apelin stimulates glucose uptake through the PI3K/Akt pathway and improves insulin resistance in 3T3-L1 adipocytes

The PI3K/Akt signaling axis and type 2 diabetes mellitus (T2DM): From mechanistic insights into possible therapeutic targets

Type 2 diabetes mellitus (T2DM) is an immensely debilitating chronic disease that progressively undermines the well-being of various bodily organs and, indeed, most patients succumb to the disease due to post-T2DM complications. Although there is evidence supporting the activation of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway by insulin, which is essential in regulating glucose metabolism and insulin resistance, the significance of this pathway in T2DM has only been explored in a few studies. The current review aims to unravel the mechanisms by which different classes of PI3Ks control the metabolism of glucose; and also to discuss the original data obtained from international research laboratories on this topic. We also summarized the role of the PI3K/Akt signaling axis in target tissues spanning from the skeletal muscle to the adipose tissue and liver. Furthermore, inquiries regarding the impact of disrupting this axis on insulin function and the development of insulin resistance have been addressed. We also provide a general overview of the association of impaired PI3K/Akt signaling pathways in the pathogenesis of the most prevalent diabetes-related complications. The last section provides a special focus on the therapeutic potential of this axis by outlining the latest advances in active compounds that alleviate diabetes via modulation of the PI3K/Akt pathway. Finally, we comment on the future research aspects in which the field of T2DM therapies using PI3K modulators might be developed.

From fasting to fat reshaping: exploring the molecular pathways of intermittent fasting-induced adipose tissue remodeling

Obesity, characterised by excessive fat accumulation, is a complex chronic condition that results from dysfunctional adipose tissue expansion due to prolonged calorie surplus. This leads to rapid adipocyte enlargement that exceeds the support capacity of the surrounding neurovascular network, resulting in increased hypoxia, inflammation, and insulin resistance. Intermittent fasting (IF), a dietary regimen that cycles between periods of fasting and eating, has emerged as an effective strategy to combat obesity and improve metabolic homeostasis by promoting healthy adipose tissue remodeling. However, the precise molecular and cellular mechanisms behind the metabolic improvements and remodeling of white adipose tissue (WAT) driven by IF remain elusive. This review aims to summarise and discuss the relationship between IF and adipose tissue remodeling and explore the potential mechanisms through which IF induces alterations in WAT. This includes several key structural changes, including angiogenesis and sympathetic innervation of WAT. We will also discuss the involvement of key signalling pathways, such as PI3K, SIRT, mTOR, and AMPK, which potentially play a crucial role in IF-mediated metabolic adaptations.

APLN promotes the proliferation, migration, and glycolysis of cervical cancer through the PI3K/AKT/mTOR pathway

Apelin (APLN) is an endogenous ligand of the G protein-coupled receptor APJ (APLNR). APLN has been implicated in the development of multiple tumours. Herein, we determined the effect of APLN on the biological behaviour and underlying mechanisms of cervical cancer. The expression and survival curves of APLN were determined using Gene Expression Profiling Interactive Analysis. The cellular functions of APLN were detected using CCK-8, clone formation, EdU, Transwell assays, flow cytometry, and seahorse metabolic analysis. The underlying mechanisms were elucidated using gene set enrichment analysis and Western blotting. APLN was upregulated in the samples of patients with cervical cancer and is associated with poor prognosis. APLN knockdown decreased the proliferation, migration, and glycolysis of cervical cancer cells. The opposite results were observed when APLN was overexpressed. Mechanistically, we determined that APLN was critical for activating the PI3K/AKT/mTOR pathway via APLNR. APLN receptor inhibitor ML221 reversed the effect of APLN overexpression on cervical cancer cells. Treatment with LY294002, the PI3K inhibitor, drastically reversed the oncological behaviour of APLN-overexpressing C-33A cells. APLN promoted the proliferation, migration, and glycolysis of cervical cancer cells via the PI3K/AKT/mTOR pathway.

Localized apelin-17 analogue-bicelle interactions as a facilitator of membrane-catalyzed receptor recognition and binding

The apelinergic system encompasses two peptide ligand families, apelin and apela, along with the apelin receptor (AR or APJ), a class A G-protein-coupled receptor. This system has diverse physiological effects, including modulating heart contraction, vasodilation/constriction, glucose regulation, and vascular development, with involvement in a variety of pathological conditions. Apelin peptides have been previously shown to interact with and become structured upon binding to anionic micelles, consistent with a membrane-catalyzed mechanism of ligand-receptor binding. To overcome the challenges of observing nuclear magnetic resonance (NMR) spectroscopy signals of a dilute peptide in biological environments, 19F NMR spectroscopy, including diffusion ordered spectroscopy (DOSY) and saturation transfer difference (STD) experiments, was used herein to explore the membrane-interactive behaviour of apelin. NMR-optimized apelin-17 analogues with 4-trifluoromethyl-phenylalanine at various positions were designed and tested for bioactivity through ERK activation in stably-AR transfected HEK 293 T cells. Far-UV circular dichroism (CD) spectropolarimetry and 19F NMR spectroscopy were used to compare the membrane interactions of these analogues with unlabelled apelin-17 in both zwitterionic/neutral and net-negative bicelle conditions. Each analogue binds to bicelles with relatively weak affinity (i.e., in fast exchange on the NMR timescale), with preferential interactions observed at the cationic residue-rich N-terminal and mid-length regions of the peptide leaving the C-terminal end unencumbered for receptor recognition, enabling a membrane-anchored fly-casting mechanism of peptide search for the receptor. In all, this study provides further insight into the membrane-interactive behaviour of an important bioactive peptide, demonstrating interactions and biophysical behaviour that cannot be neglected in therapeutic design.

The role of apelinergic system in metabolism and reproductive system in normal and pathological conditions: an overview

Lifestyle changes have made metabolic disorders as one of the major threats to life. Growing evidence demonstrates that obesity and diabetes disrupt the reproductive system by affecting the gonads and the hypothalamus-pituitary-gonadal (HPG) axis. Apelin, an adipocytokine, and its receptor (APJ) are broadly expressed in the hypothalamus nuclei, such as paraventricular and supraoptic, where gonadotropin-releasing hormone (GnRH) is released, and all three lobes of the pituitary, indicating that apelin is involved in the control of reproductive function. Moreover, apelin affects food intake, insulin sensitivity, fluid homeostasis, and glucose and lipid metabolisms. This review outlined the physiological effects of the apelinergic system, the relationship between apelin and metabolic disorders such as diabetes and obesity, as well as the effect of apelin on the reproductive system in both gender. The apelin-APJ system can be considered a potential therapeutic target in the management of obesity-associated metabolic dysfunction and reproductive disorders.

Natural activators of AMPK signaling: potential role in the management of type-2 diabetes

Adenosine 5'-monophosphate-activated protein kinase (AMPK) is an evolutionarily conserved serine/threonine kinase involved in the homeostasis of cellular energy. AMPK has developed as an appealing clinical target for the diagnosis of multiple metabolic diseases such as diabetes mellitus, obesity, inflammation, and cancer. Genetic and pharmacological studies indicate that AMPK is needed in response to glucose deficiency, dietary restriction, and increased physical activity for preserving glucose homeostasis. After activation, AMPK influences metabolic mechanisms contributing to enhanced ATP production, thus growing processes that absorb ATP simultaneously. In this review, several natural products have been discussed which enhance the sensitivity of AMPK and alleviate sub complications or different pathways by which such AMPK triggers can be addressed. AMPK Natural products as potential AMPK activators can be developed as alternate pharmacological intervention to reverse metabolic disorders including type 2 diabetes.

The molecular link between obesity and genomic instability in cancer development

Obesity has been known to be a major risk factor for various types of cancers for several decades. More recently, the relationship between dysregulated adipokines and cancer development has been the focus of much research. Adipose tissue is an important endocrine organ that secretes adipokines that affect both autocrine and paracrine signaling. These adipokines modulate inflammation, induce insulin resistance, and regulate their own behavior and production. Adipokine-production dysregulation is due to physiological changes in adipose tissue that prompt molecular modifications, including low-grade inflammation and the stimulatory production of reactive oxygen species. Additionally, studies have linked DNA damage response, genomic instability, and the innate immune response to tumorigenesis. Further investigation of adipokines and their role in the promotion of genomic instability may clarify the link between obesity and cancer, as well as elucidate potential pharmaceutical targets. In this review, we discuss the progress of recent literature, focusing on the impact of adipokines, genomic instability, and the innate immune response on increasing the risk of cancer.

Pancreas-Liver-Adipose Axis: Target of Environmental Cadmium Exposure Linked to Metabolic Diseases

Cadmium has been well recognized as a critical toxic agent in acute and chronic poisoning cases in occupational and nonoccupational settings and environmental exposure situations. Cadmium is released into the environment after natural and anthropogenic activities, particularly in contaminated and industrial areas, causing food pollution. In the body, cadmium has no biological activity, but it accumulates primarily in the liver and kidney, which are considered the main targets of its toxicity, through oxidative stress and inflammation. However, in the last few years, this metal has been linked to metabolic diseases. The pancreas-liver-adipose axis is largely affected by cadmium accumulation. Therefore, this review aims to collect bibliographic information that establishes the basis for understanding the molecular and cellular mechanisms linked to cadmium with carbohydrate, lipids, and endocrine impairments that contribute to developing insulin resistance, metabolic syndrome, prediabetes, and diabetes.

Extracellular vesicles regulate the transmission of insulin resistance and redefine noncommunicable diseases

Noncommunicable diseases (NCDs), such as diabetes and related neurological disorders, are considered to not be directly transmissible from one person to another. However, NCDs may be transmissible in vivo through extracellular vesicles (EVs). A long-term high-fat diet (HFD) can induce a series of health issues like hyperlipidemia, type 2 diabetes mellitus (T2DM), and diabetic peripheral neuropathy (DPN) due to insulin resistance. Multiple molecular signaling changes can stimulate insulin resistance, especially blocking insulin signaling by increased insulin resistance inducer (phosphorylation of negative regulatory sites of insulin receptor substrate (IRS) proteins) and decreased tyrosine phosphorylation of insulin receptor substrate (phosphorylation of positive regulatory sites of IRS), thus leading to reduced phosphorylation of AKT enzymes. Current efforts to treat T2DM and prevent its complications mainly focus on improving insulin sensitivity, enhancing insulin secretion, or supplementing exogenous insulin based on a common assumption that insulin resistance is noncommunicable. However, insulin resistance is transmissible within multiple tissues or organs throughout the body. Exploring the regulatory roles of EVs in developing insulin resistance may provide novel and effective preventive and therapeutic strategies.

Olive Leaves Extract and Oleuropein Improve Insulin Sensitivity in 3T3-L1 Cells and in High-Fat Diet-Treated Rats via PI3K/AkT Signaling Pathway

Olive leaves extracts are known to exert potential pharmacological activities especially, antidiabetic and antiobesity. This study explores the anti-insulin resistant effect of olive leaves extracts and oleuropein in 3 T3-L1 cells and in high-fat diet fed rats. Our results showed that ethanol extract (EE) suppressed significantly (P < 0.01) triacylglycerol accumulation. In preadipocytes cells, EE 1/100 decreased cell viability and induced apoptosis. Real-time PCR analysis showed that EE reduced the mRNA levels of adipogenesis (CEBP-α, PPARγ, SREBP-1c, and FAS) and proinflammatory (TNF-α and IL-6) genes. Moreover, the cotreatment of EE 1/1000 or oleuropein with insulin increased considerably the expression of p-IRS, p85-pI3K, and p-AKT. In vivo model, the oral administration of oleuropein at 50 mg/kg in rats fed with high fat diet for 8 weeks reduced inflammation in liver and adipose tissues (WAT), improved glucose intolerance, and decreased hyperinsulinemia. Furthermore, the immunohistochemistry revealed that the expression level of p-Akt, IRS1, and Glut-4 were significantly enhanced in liver and WAT tissues after oleuropein supplementation comparing with that in HFD group. Additionally, the expression of IRS1 was markedly ameliorated in pancreas. Our obtained results can be adopted as an approach to used olive leaves as complement to prevent insulin-resistance disease.

Systematic review and meta-analysis regarding maternal apelin in pregnant women with and without preeclampsia

Aims: To investigate maternal circulating apelin levels in pregnancies with and without preeclampsia.Design and Method: Systematic review and meta-analysis of observational studies reporting circulating apelin in women who develop preeclampsia. We searched databases for appropriate studies published through December 2021, without language restriction. The quality of studies was evaluated using the Newcastle-Ottawa-Scale. Data were pooled as mean difference (MDs) or standardized MDs (SMDs) and 95% confidence interval (95% CI). A random-effects model enabled reporting of differences between groups, minimizing the effects of uncertainty associated with inter-study variability on the effects of different endpoints.Results: We identified a total of 122 studies, and ten of them reported circulating apelin in women with and without preeclampsia. Maternal apelin did not show a difference in preeclamptic compared to normotensive women (SMD: -0.38, 95%CI -0.91 to 0.15), although there was high heterogeneity between the included studies (I² = 95%). Participants with preeclampsia had higher body mass index, lower gestational age at delivery, and birth weight. Preeclamptic pregnant women with higher BMI showed significantly lower apelin levels in the subgroup analysis. There was no significant apelin difference in the preeclampsia severity sub-analysis.Conclusion: There was no significant difference in apelin levels in pregnant women with and without preeclampsia.

Oral Subacute Exposure to Cadmium LOAEL Dose Induces Insulin Resistance and Impairment of the Hormonal and Metabolic Liver-Adipose Axis in Wistar Rats

Cadmium is a nonessential transition metal considered one of the more hazardous environmental contaminants. The population is chronically exposed to this metal at low concentrations, designated as the LOAEL (lowest observable adverse effect level) dose. We aimed to investigate whether oral subacute exposure to cadmium LOAEL disrupts hormonal and metabolic effects of the liver-adipose axis in Wistar rats. Fifty male Wistar rats were separated into two groups: control (standard normocalorie diet + water free of cadmium) and cadmium (standard normocalorie diet + drinking water with 32.5 ppm CdCl2). After 1 month, zoometry, a serum lipid panel, adipokines, and proinflammatory cytokines were evaluated. Tests of glucose and insulin tolerance (ITT) and insulin resistance were performed. Histological studies on structure, triglyceride distribution, and protein expression of the insulin pathway were performed in the liver and retroperitoneal adipose tissue. In both tissues, the cadmium, triglyceride, glycogen, and proinflammatory cytokine contents were also quantified. The cadmium group developed dyslipidemia, glucose intolerance, hyperinsulinemia, hyperleptinemia, inflammation, and selective insulin resistance in the liver and adipose tissue. In the liver, glycogen synthesis was diminished, while de novo lipogenesis increased, which was associated with low GSK3β-pS9 and strong expression of SREBP-1c. Dysfunctional adipose tissue was observed with hypertrophy and lipolysis, without changes in SREBP-1c expression and low glycogen synthesis. Both tissues accumulated cadmium and developed inflammation. In conclusion, oral subacute cadmium LOAEL dose exposure induces inflammation, insulin signaling modifications, an early insulin resistance stage (insensibility), and impairment of the hormonal and metabolic liver-adipose axis in Wistar rats.

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% VO2max 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% VO2max 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.

Kutkin, iridoid glycosides enriched fraction of Picrorrhiza kurroa promotes insulin sensitivity and enhances glucose uptake by activating PI3K/Akt signaling in 3T3-L1 adipocytes

BACKGROUND

Therapeutic failure and drug resistance are common sequelae to insulin resistance associated with type 2 diabetes mellitus (T2DM). Consequently, there is an unmet need of alternative strategies to overcome insulin resistance associated complications.

PURPOSE

To demonstrate whether Kutkin (KT), iridoid glycoside enriched fraction of Picrorhiza kurroa extract (PKE) has potential to increase the insulin sensitivity vis à vis glucose uptake in differentiated adipocytes.

METHODS

Molecular interaction of KT phytoconstituents, picroside-I (P-I) & picroside- II (P-II) with peroxisome proliferator-activated receptor gamma (PPARγ), phosphatidylinositol 3-kinase (PI3K) and protein kinase B (Akt) were analyzed in silico. Cellular viability and adipogenesis were determined by following 3-(4, 5-Dimethylthiazol-2-Yl)-2, 5-Diphenyltetrazolium bromide (MTT) assay and Oil Red-O staining. Further, ELISA kit based triglycerides and diacylglycerol-O-Acyltransferase-1 (DGAT1) were assessed in differentiated adipocytes. ELISA based determination were performed to check the levels of adiponectin and tumor necrosis factor alpha (TNF-α). However, Flow cytometry and immunofluorescence based assays were employed to measure the glucose uptake and glucose transporter 4 (glut4) expression in differentiated adipocytes, respectively. Further to explore the targeted signaling axis, mRNA expression levels of PPARγ, CCAAT/enhancer binding protein α (CEBPα), and glut4 were determined using qRT-PCR and insulin receptor substrate-1 (IRS-1), Insulin receptor substrate-2 (IRS-2), PI3K/Akt, AS160, glut4 followed by protein validation using immunoblotting in differentiated adipocytes.

RESULTS

In silico analysis revealed the binding affinities of major constituents of KT (P-I& P-II) with PPARγ/PI3K/Akt. The enhanced intracellular accumulation of triglycerides with concomitant activation of PPARγ and C/EBPα in KT treated differentiated adipocytes indicates augmentation of adipogenesis in a concentration-dependent manner. Additionally, at cellular level, KT upregulated the expression of DAGT1, and decreases fatty acid synthase (FAS), and lipoprotein lipase (LPL), further affirmed improvement in lipid milieu. It was also observed that KT upregulated the levels of adiponectin and reduced TNFα expression, thus improving the secretory functions of adipocytes along with enhanced insulin sensitivity. Furthermore, KT significantly promoted insulin mediated glucose uptake by increasing glut4 translocation to the membrane via PI3/Akt signaling cascade. The results were further validated using PI3K specific inhibitor, wortmannin and findings revealed that KT treatment significantly enhanced the expression and activation of p-PI3K/PI3K and p-Akt/Akt even in case of treatment with PI3K inhibitor wortmannin alone and co-treatment with KT in differentiated adipocytes and affirmed that KT as activator of PI3K/Akt axis in the presence of inhibitor as well.

CONCLUSION

Collectively, KT fraction of PKE showed anti-diabetic effects by enhancing glucose uptake in differentiated adipocytes via activation of PI3K/Akt signaling cascade. Therefore, KT may be used as a promising novel natural therapeutic agent for managing T2DMand to the best of our knowledge, this is the first report, showing the efficacy and potential molecular mechanism of KT in enhancing insulin sensitivity and glucose uptake in differentiated adipocytes.

Mechanisms by Which Skeletal Muscle Myokines Ameliorate Insulin Resistance

The skeletal muscle is the largest organ in the body and secretes circulating factors, including myokines, which are involved in various cellular signaling processes. Skeletal muscle is vital for metabolism and physiology and plays a crucial role in insulin-mediated glucose disposal. Myokines have autocrine, paracrine, and endocrine functions, serving as critical regulators of myogenic differentiation, fiber-type switching, and maintaining muscle mass. Myokines have profound effects on energy metabolism and inflammation, contributing to the pathophysiology of type 2 diabetes (T2D) and other metabolic diseases. Myokines have been shown to increase insulin sensitivity, thereby improving glucose disposal and regulating glucose and lipid metabolism. Many myokines have now been identified, and research on myokine signaling mechanisms and functions is rapidly emerging. This review summarizes the current state of the field regarding the role of myokines in tissue cross-talk, including their molecular mechanisms, and their potential as therapeutic targets for T2D.

Exercise training modulates adipokine dysregulations in metabolic syndrome

Metabolic syndrome (MetS) is a cluster of risk factors for various metabolic diseases, and it is characterized by central obesity, dyslipidemia, hypertension, and insulin resistance. The core component for MetS is adipose tissue, which releases adipokines and influences physical health. Adipokines consist of pro and anti-inflammatory cytokines and contribute to various physiological functions. Generally, a sedentary lifestyle promotes fat accumulation and secretion of pro-inflammatory adipokines. However, regular exercise has been known to exert various beneficial effects on metabolic and cognitive disorders. Although the mechanisms underlying exercise beneficial effects in MetS are not fully understood, changes in energy expenditure, fat accumulation, circulatory level of myokines, and adipokines might be involved. This review article focuses on some of the selected adipokines in MetS, and their responses to exercise training considering possible mechanisms.

Apelin pathway in cardiovascular, kidney, and metabolic diseases: Therapeutic role of apelin analogs and apelin receptor agonists

The apelin/apelin receptor (ApelinR) signal transduction pathway exerts essential biological roles, particularly in the cardiovascular system. Disturbances in the apelin/ApelinR axis are linked to vascular, heart, kidney, and metabolic disorders. Therefore, the apelinergic system has surfaced as a critical therapeutic strategy for cardiovascular diseases (including pulmonary arterial hypertension), kidney disease, insulin resistance, hyponatremia, preeclampsia, and erectile dysfunction. However, apelin peptides are susceptible to rapid degradation through endogenous peptidases, limiting their use as therapeutic tools and translational potential. These proteases include angiotensin converting enzyme 2, neutral endopeptidase, and kallikrein thereby linking the apelin pathway with other peptide systems. In this context, apelin analogs with enhanced proteolytic stability and synthetic ApelinR agonists emerged as promising pharmacological alternatives. In this review, we focus on discussing the putative roles of the apelin pathway in various physiological systems from function to dysfunction, and emphasizing the therapeutic potential of newly generated metabolically stable apelin analogs and non-peptide ApelinR agonists.

Identification of a Hydroxypyrimidinone Compound () as a Potent APJ Receptor Agonist for the Potential Treatment of Heart Failure

This paper describes our continued efforts in the area of small-molecule apelin receptor agonists. Recently disclosed compound 2 showed an acceptable metabolic stability but demonstrated monodemethylation of the dimethoxyphenyl group to generate atropisomer metabolites in vitro. In this article, we extended the structure-activity relationship at the C2 position that led to the identification of potent pyrazole analogues with excellent metabolic stability. Due to the increased polarity at C2, the permeability for these compounds decreased. Further adjustment of the polarity by replacing the N1 2,6-dimethoxyphenyl group with a 2,6-diethylphenyl group and reoptimization for the potency of the C5 pyrroloamides resulted in potent compounds with improved permeability. Compound 21 displayed excellent pharmacokinetic profiles in rat, monkey, and dog models and robust pharmacodynamic efficacy in the rodent heart failure model. Compound 21 also showed an acceptable safety profile in preclinical toxicology studies and was selected as a backup development candidate for the program.

Impact of Incretin-Based Therapies on Adipokines and Adiponectin

Adipokines are a family of hormones and cytokines with both pro- and anti-inflammatory effects released into the circulation to exert their hormonal effects. Adipokines are closely involved in most metabolic pathways and play an important modulatory role in lipid and carbohydrate homeostasis as they are involved in the pathophysiology of most metabolic disorders. Incretin-based therapy is a newly introduced class of antidiabetic drugs that restores euglycemia through several cellular processes; however, its effect on adipokines expression/secretion is not fully understood. In this review, we propose that incretin-based therapy may function through adipokine modulation that may result in pharmacologic properties beyond their direct antidiabetic effects, resulting in better management of diabetes and diabetes-related complications.

Adipokine levels and carbohydrate metabolism in patients diagnosed de novo with polycystic ovary syndrome

INTRODUCTION

Central obesity appears to play a major role in the pathogenesis of metabolic disorders in polycystic ovary syndrome. Insulin resistance and carbohydrate disorders are associated with dysfunctional secretion of various adipokines by the adipose tissue.

OBJECTIVES

This study aimed to evaluate leptin, apelin, and visfatin against a background of carbohydrate metabolism parameters in patients diagnosed de novo with polycystic ovary syndrome (PCOS).

MATERIAL AND METHODS

The study group consisted of 40 patients with PCOS (mean age, 29 years) diagnosed in accordance with the American Society for Reproductive Medicine criteria from 2003. The control group consisted of 37 clinically healthy women (mean age, 26 years). All controls had regular menses and no clinical or biochemical signs of hyperandrogenism. Concentrations of leptin, apelin, visfatin, and insulin were measured by immunoenzymatic methods. Glucose concentrations were determined using spectrophotometry.

RESULTS

Significantly higher concentrations of leptin, insulin, homeostatic model assessment for insulin resistance (HOMA-IR) index, and the immunoreactive insulin (IRI)/glucose index were found in the PCOS group than in the control group. Notably, the concentration of apelin was over five times lower in the PCOS group than in the control group. In patients with PCOS, a positive correlation was found between the concentrations of insulin and leptin and concentrations of leptin and IRI/glucose. Patients of the PCOS group with body mass index (BMI) ≥  25 had significantly higher values of leptin, insulin, HOMA-IR index, and IRI/glucose index than patients of the PCOS group with normal BMI. In the PCOS group, a positive correlation was found between BMI and leptin concentration (r = 0.7176; p < 0.0001) and carbohydrate metabolism, such as insulin (r = 0.5524; p = 0.0003), glucose (r = 0.3843; p = 0.0157), HOMA-IR (r = 0.5895; p < 0.0001), and IRI/glucose (r = 0.3872; p = 0.0163). These findings were not observed in the control group.

CONCLUSIONS

(1) Increased leptin concentration observed in women diagnosed de novo with PCOS as well as positive correlations between leptin and HOMA-IR, and IRI/glucose and BMI may indicate a potential role of leptin in the reduction of tissue sensitivity to insulin. (2) Significantly lower apelin concentration in the PCOS group (>5 fold) than in the control group, associated with a concomitant increase in leptin, may also contribute to carbohydrate metabolism disorders occurring in the course of PCOS.

Universal concept signature analysis: genome-wide quantification of new biological and pathological functions of genes and pathways

Identifying new gene functions and pathways underlying diseases and biological processes are major challenges in genomics research. Particularly, most methods for interpreting the pathways characteristic of an experimental gene list defined by genomic data are limited by their dependence on assessing the overlapping genes or their interactome topology, which cannot account for the variety of functional relations. This is particularly problematic for pathway discovery from single-cell genomics with low gene coverage or interpreting complex pathway changes such as during change of cell states. Here, we exploited the comprehensive sets of molecular concepts that combine ontologies, pathways, interactions and domains to help inform the functional relations. We first developed a universal concept signature (uniConSig) analysis for genome-wide quantification of new gene functions underlying biological or pathological processes based on the signature molecular concepts computed from known functional gene lists. We then further developed a novel concept signature enrichment analysis (CSEA) for deep functional assessment of the pathways enriched in an experimental gene list. This method is grounded on the framework of shared concept signatures between gene sets at multiple functional levels, thus overcoming the limitations of the current methods. Through meta-analysis of transcriptomic data sets of cancer cell line models and single hematopoietic stem cells, we demonstrate the broad applications of CSEA on pathway discovery from gene expression and single-cell transcriptomic data sets for genetic perturbations and change of cell states, which complements the current modalities. The R modules for uniConSig analysis and CSEA are available through https://github.com/wangxlab/uniConSig.

Role of Brown and Beige Adipose Tissues in Seasonal Adaptation in the Raccoon Dog (Nyctereutes procyonoides)

Brown adipose tissue (BAT) expresses uncoupling protein-1 (UCP1), which enables energy to be exerted towards needed thermogenesis. Beige adipocytes are precursor cells interspersed among white adipose tissue (WAT) that possess similar UCP1 activity and capacity for thermogenesis. The raccoon dog (Nyctereutes procyonoides) is a canid species that utilizes seasonal obesity to survive periods of food shortage in climate zones with cold winters. The potential to recruit a part of the abundant WAT storages as beige adipocytes for UCP1-dependent thermogenesis was investigated in vitro by treating raccoon dog adipocytes with different browning inducing factors. In vivo positron emission tomography/computed tomography (PET/CT) imaging with the glucose analog ¹⁸F-FDG showed that BAT was not detected in the adult raccoon dog during the winter season. In addition, UCP1 expression was not changed in response to chronic treatments with browning inducing factors in adipocyte cultures. Our results demonstrated that most likely the raccoon dog endures cold weather without the induction of BAT or recruitment of beige adipocytes for heat production. Its thick fur coat, insulating fat, and muscle shivering seem to provide the adequate heat needed for surviving the winter.

Obesity-induced changes in human islet G protein-coupled receptor expression: Implications for metabolic regulation

G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that are the targets for many different classes of pharmacotherapy. The islets of Langerhans are central to appropriate glucose homeostasis through their secretion of insulin, and islet function can be modified by ligands acting at the large number of GPCRs that islets express. The human islet GPCRome is not a static entity, but one that is altered under pathophysiological conditions and, in this review, we have compared expression of GPCR mRNAs in human islets obtained from normal weight range donors, and those with a weight range classified as obese. We have also considered the likely outcomes on islet function that the altered GPCR expression status confers and the possible impact that adipokines, secreted from expanded fat depots, could have at those GPCRs showing altered expression in obesity.

Polysaccharide Derived from Nelumbo nucifera Lotus Plumule Shows Potential Prebiotic Activity and Ameliorates Insulin Resistance in HepG2 Cells

Polysaccharides are key bioactive compounds in lotus plumule tea, but their anti-diabetes activities remain unclear. The purpose of this study was to investigate the prebiotic activities of a novel polysaccharide fraction from the Nelumbo nucifera lotus plumule, and to examine its regulation of glucose metabolism in insulin-resistant HepG2 cells. The N. nucifera polysaccharide (NNP) was purified after discoloration, hot water extraction, ethanol precipitation, and DEAE-cellulose chromatography to obtain purified polysaccharide fractions (NNP-2). Fourier transform infrared spectroscopy was used to analyze the main structural characteristics and functional group of NNP-2. Physicochemical characterization indicated that NNP-2 had a molecular weight of 110.47 kDa and consisted of xylose, glucose, fructose, galactose, and fucose in a molar ratio of 33.4:25.7:22.0:10.5:8.1. The prebiotic activity of NNP-2 was demonstrated in vitro using Lactobacillus and Bifidobacterium. Furthermore, NNP-2 showed bioactivity against α-glucosidase (IC₅₀ = 97.32 µg/mL). High glucose-induced insulin-resistant HepG2 cells were used to study the effect of NNP-2 on glucose consumption, and the molecular mechanism of the insulin transduction pathway was studied using RT-qPCR. NNP-2 could improve insulin resistance by modulating the IRS1/PI3K/Akt pathway in insulin-resistant HepG2 cells. Our data demonstrated that the Nelumbo nucifera polysaccharides are potential sources for nutraceuticals, and we propose functional food developments from the bioactive polysaccharides of N. nucifera for the management of diabetes.

The Role of Peptide Hormones Discovered in the 21st Century in the Regulation of Adipose Tissue Functions

Peptide hormones play a prominent role in controlling energy homeostasis and metabolism. They have been implicated in controlling appetite, the function of the gastrointestinal and cardiovascular systems, energy expenditure, and reproduction. Furthermore, there is growing evidence indicating that peptide hormones and their receptors contribute to energy homeostasis regulation by interacting with white and brown adipose tissue. In this article, we review and discuss the literature addressing the role of selected peptide hormones discovered in the 21st century (adropin, apelin, elabela, irisin, kisspeptin, MOTS-c, phoenixin, spexin, and neuropeptides B and W) in controlling white and brown adipogenesis. Furthermore, we elaborate how these hormones control adipose tissue functions in vitro and in vivo.

Clinical significance of apelin in the treatment of type 2 diabetic peripheral neuropathy

BACKGROUND

Diabetic peripheral neuropathy (DPN) is one of the most common chronic complications of diabetes. As apelin is an adipocytokine closely associated with diabetes, this study explored the clinical significance of serum apelin levels in patients with type 2 DPN before and after treatment.

METHODS

In total, 44 patients with T2DM without DPN (non-DPN group), 41 patients with DPN who received antihyperglycemic treatment (DPN-A group), 44 patients with DPN who received antihyperglycemic treatment combined with nutritional neurotherapy (DPN-B group), and 40 healthy control individuals (NC group) were selected continuously enrolled in the present study. Enzyme-linked immunosorbent assays (ELISA) were performed to determine serum levels of apelin and tumor necrosis factor-α (TNF-α). Related apelin, fasting blood glucose (FBG), glycosylated hemoglobin A1c, TNF-α, body mass index, fasting C peptide, and nerve conduction velocity (NCV) were recorded in each group before and after treatment.

RESULTS

Serum levels of apelin and TNF-α were higher in patients with diabetes than those in the NC group, as well as in the DPN group as compared to the non-DPN group; furthermore, some NCV values were significantly reduced in the DPN group. After treatment, the serum levels of apelin, TNF-α, and FBG reduced in patients with diabetes; moreover, apelin levels were found significantly lower in the DPN-B group as compared to the DPN-A group, while some NCV values significantly increased in the DPN-B group. Apelin was negatively correlated with part of NCV values and positively correlated with TNF-α and FBG (P < .01).

CONCLUSION

Our results show that the increase in serum apelin levels is an important clinical reference index for DPN, while a decrease indicates that the DPN treatment is effective.

Integrative Analysis of Whole-genome Expression Profiling and Regulatory Network Identifies Novel Biomarkers for Insulin Resistance in Leptin Receptor-deficient Mice

BACKGROUND

Molecular characterization of insulin resistance, a growing health issue worldwide, will help to develop novel strategies and accurate biomarkers for disease diagnosis and treatment.

OBJECTIVE

Integrative analysis of gene expression profiling and gene regulatory network was exploited to identify potential biomarkers early in the development of insulin resistance.

METHODS

RNA was isolated from livers of animals at three weeks of age, and whole-genome expression profiling was performed and analyzed with Agilent mouse 4×44K microarrays. Differentially expressed genes were subsequently validated by qRT-PCR. Functional characterizations of genes and their interactions were performed by Gene Ontology (GO) analysis and gene regulatory network (GRN) analysis.

RESULTS

A total of 197 genes were found to be differentially expressed by fold change ≥2 and P < 0.05 in BKS-db +/+ mice relative to sex and age-matched controls. Functional analysis suggested that these differentially expressed genes were enriched in the regulation of phosphorylation and generation of precursor metabolites which are closely associated with insulin resistance. Then a gene regulatory network associated with insulin resistance (IRGRN) was constructed by integration of these differentially expressed genes and known human protein-protein interaction network. The principal component analysis demonstrated that 67 genes in IRGRN could clearly distinguish insulin resistance from the non-disease state. Some of these candidate genes were further experimentally validated by qRT-PCR, highlighting the predictive role as biomarkers in insulin resistance.

CONCLUSION

Our study provides new insight into the pathogenesis and treatment of insulin resistance and also reveals potential novel molecular targets and diagnostic biomarkers for insulin resistance.

The Role of Apelin/Apelin Receptor in Energy Metabolism and Water Homeostasis: A Comprehensive Narrative Review

The apelin receptor (APJ) is a member of the family A of G-protein-coupled receptors (GPCRs) and is involved in range of physiological and pathological functions, including fluid homeostasis, anxiety, and depression, as well as cardiovascular and metabolic disorders. APJ was classically described as a monomeric transmembrane receptor that forms a ternary complex together with its ligand and associated G proteins. More recently, increasing evidence indicates that APJ may interact with other GPCRs to form heterodimers, which may selectively modulate distinct intracellular signal transduction pathways. Besides, the apelin/APJ system plays important roles in the physiology and pathophysiology of several organs, including regulation of blood pressure, cardiac contractility, angiogenesis, metabolic balance, and cell proliferation, apoptosis, or inflammation. Additionally, the apelin/APJ system is widely expressed in the central nervous system, especially in neurons and oligodendrocytes. This article reviews the role of apelin/APJ in energy metabolism and water homeostasis. Compared with the traditional diuretics, apelin exerts a positive inotropic effect on the heart, while increases water excretion. Therefore, drugs targeting apelin/APJ system undoubtedly provide more therapeutic options for patients with congestive heart failure accompanied with hyponatremia. To provide more precise guidance for the development of clinical drugs, further in-depth studies are warranted on the metabolism and signaling pathways associated with apelin/APJ system.

The APLNR gene polymorphism rs7119375 is associated with an increased risk of development of essential hypertension in the Chinese population: A meta-analysis

Hypertension (HT) has recently been defined as a systolic blood pressure (BP) of ≥130 mm Hg and/or a diastolic BP of ≥80 mm Hg. It is important to further understand the pathophysiology of essential HT as its proportion is larger among most of the diagnosed HT cases. The apelin and apelin receptor (APLNR) are known to play roles in regulating BP, but the putative associations of single nucleotide polymorphisms in the APLNR gene with the risk of development of essential HT have not yet been fully investigated. Herein, we conducted a meta-analysis to investigate the relationship between single nucleotide polymorphisms in the APLNR gene and the risk of essential HT.We conducted a search in the PubMed and Web of Science databases for eligible studies. The pooled odds ratios (ORs) with their 95% confidence intervals (CI) were calculated using random-effects models when heterogeneity was expected across the studies. Otherwise, fixed-effect models were used.Regarding the SNP rs7119375, 5 studies were analyzed, which included a total of 3567 essential HT patients and 3256 healthy controls. Four of the 5 studies were from China and 1 was from Mexico. The meta-analysis showed the existence of a significant association between the AA genotype of rs7119375 and the risk of developing essential HT in the Chinese population, as determined using additive and recessive models (OR, 2.11; 95% CI, 1.12-3.96; I = 86% for AA vs GG. OR, 1.53; 95% CI, 1.21-1.94; I = 28% for AA vs AG. OR, 1.88; 95% CI, 1.13-3.12; I = 79% for AA vs AG + GG).Our study showed, for the first time, the existence of an association between rs7119375 and the risk of development of essential HT in the Chinese population, although the sample size was small and there was considerable population heterogeneity. The apelin/APLNR system could be a novel therapeutic target for the treatment of essential HT, and more studies are warranted to further investigate the association.

FoxO1 signaling as a therapeutic target for type 2 diabetes and obesity

Glucose production and the consumption of high levels of carbohydrate increase the chance of insulin resistance, especially in cases of obesity. Therefore, maintaining a balanced glucose homeostasis might form a strategy to prevent or cure diabetes and obesity. The activation and inhibition of glucose production is complicated due to the presence of many interfering pathways. These pathways can be viewed at the downstream level because they activate certain transcription factors, which include the Forkhead-O1 (FoxO1). This has been identified as a significant agent in the pancreas, liver, and adipose tissue, which is significant in the regulation of lipids and glucose. The objective of this review is to discuss the intersecting portrayal of FoxO1 and its parallel cross-talk which highlights obesity-induced insulin susceptibility in the discovery of a targeted remedy. The review also analyses current progress and provides a blueprint on therapeutics, small molecules, and extracts/phytochemicals which are explored at the pre-clinical level.

Maresin 1 regulates insulin signaling in human adipocytes as well as in adipose tissue and muscle of lean and obese mice

Maresin 1 (MaR1) is a DHA-derived pro-resolving lipid mediator. The present study aimed to characterize the ability of MaR1 to prevent the alterations induced by TNF-α on insulin actions in glucose uptake and Akt phosphorylation in cultured human adipocytes from overweight/obese subjects, as well as to investigate the effects of MaR1 acute and chronic administration on Akt phosphorylation in absence/presence of insulin in white adipose tissue (WAT) and skeletal muscle from lean and diet-induced obese (DIO) mice. MaR1 (0.1 nM) prevented the inhibitory effect of TNF-α on insulin-stimulated 2-Deoxy-D-glucose uptake and Akt phosphorylation in human adipocytes. Acute treatment with MaR1 (50 μg/kg, 3 h, i.p.) induced Akt phosphorylation in WAT and skeletal muscle of lean mice. However, MaR1 did not further increase the stimulatory effect of insulin on Akt activation. Interestingly, intragastric chronic treatment with MaR1 (50 μg/kg, 10 days) in DIO mice reduced the hyperglycemia induced by the high fat diet (HFD) and improved systemic insulin sensitivity. In parallel, MaR1 partially restored the impaired insulin response in skeletal muscle of DIO mice and reversed HFD-induced lower Akt phosphorylation in WAT in non-insulin-stimulated DIO mice while did not restore the defective Akt activation in response to acute insulin observed in DIO mice. Our results suggest that MaR1 attenuates the impaired insulin signaling and glucose uptake induced by proinflammatory cytokines. Moreover, the current data support that MaR1 treatment could be useful to reduce the hyperglycemia and the insulin resistance associated to obesity, at least in part by improving Akt signaling.

Angiotensin AT1 receptor antagonism by losartan stimulates adipocyte browning via induction of apelin

Adipocyte browning appears to be a potential therapeutic strategy to combat obesity and related metabolic disorders. Recent studies have shown that apelin, an adipokine, stimulates adipocyte browning and has negative cross-talk with angiotensin II receptor type 1 (AT₁ receptor) signaling. Here, we report that losartan, a selective AT₁ receptor antagonist, induces browning, as evidenced by an increase in browning marker expression, mitochondrial biogenesis, and oxygen consumption in murine adipocytes. In parallel, losartan up-regulated apelin expression, concomitant with increased phosphorylation of protein kinase B and AMP-activated protein kinase. However, the siRNA-mediated knockdown of apelin expression attenuated losartan-induced browning. Angiotensin II cotreatment also inhibited losartan-induced browning, suggesting that AT₁ receptor antagonism-induced activation of apelin signaling may be responsible for adipocyte browning induced by losartan. The in vivo browning effects of losartan were confirmed using both C57BL/6J and ob/ob mice. Furthermore, in vivo apelin knockdown by adeno-associated virus carrying-apelin shRNA significantly inhibited losartan-induced adipocyte browning. In summary, these data suggested that AT₁ receptor antagonism by losartan promotes the browning of white adipocytes via the induction of apelin expression. Therefore, apelin modulation may be an effective strategy for the treatment of obesity and its related metabolic disorders.

Butaphosphan Effects on Glucose Metabolism Involve Insulin Signaling and Depends on Nutritional Plan

Butaphosphan is an organic phosphorus compound used in several species for the prevention of rapid catabolic states, however, the mechanism of action remains unclear. This study aimed at determining the effects of butaphosphan on energy metabolism of mice receiving a normal or hypercaloric diet (HCD) and submitted or not to food restriction. Two experiments were conducted: (1) during nine weeks, animals were fed with HCD (n = 28) ad libitum, and at the 10th week, were submitted to food restriction and received butaphosphan (n = 14) or saline injections (n = 14) (twice a day, for seven days) and; (2) during nine weeks, animals were fed with a control diet (n = 14) or HCD (n = 14) ad libitum, and at the 10th week, all animals were submitted to food restriction and received butaphosphan or saline injections (twice a day, for seven days). In food restriction, butaphosphan preserved epididymal white adipose tissue (WAT) mass, increased glucose, NEFA, and the HOMA index. In mice fed HCD and submitted to food restriction, the butaphosphan preserved epididymal WAT mass. Control diet influences on PI3K, GCK, and Irs1 mRNA expression. In conclusion, butaphosphan increased blood glucose and reduced fat mobilization in overweight mice submitted to caloric restriction, and these effects are influenced by diet.

Semaphorin 3 C is a Novel Adipokine Representing Exercise-Induced Improvements of Metabolism in Metabolically Healthy Obese Young Males

This study investigated the endurance exercise-induced changes in lesser known adipokines (visfatin, chemerin, apelin, semaphorin 3 C) related to obesity and metabolism, and their correlations with the changes in the parameters of obesity and glucose homeostasis. Forty metabolically healthy obese young males were randomly assigned to control group (C, n = 12) or exercise group (Ex, n = 28). The subjects in Ex participated in a 8-week supervised endurance exercise training program, comprised of four sessions of treadmill running at 65–70% of VO_2max per week. Serum levels of visfatin, chemerin, apelin, and semaphorin 3 C were significantly decreased in Ex. At baseline, apelin and semaphorin 3 C appeared to be correlated with obesity measures, including body mass index, % total fat and trunk fat, and waist circumference. Exercise-induced changes in these obesity measures significantly correlated with the changes in chemerin and semaphorin 3 C. Basal chemerin, apelin and semaphorin 3 C correlated with glucose homeostasis parameters, including fasting plasma glucose, fasting plasma insulin, homeostasis model assessment of insulin resistance and β-cell function, and quantitative insulin-sensitivity check index to different extents. Furthermore, the changes in apelin and semaphorin 3 C well predicted the improvements in glycemic parameters. We suggest that semaphorin 3 C is a novel adipokine involved in pathophysiology of obesity and metabolism, and that it is a biomarker representing an exercise-induced improvement in metabolically healthy obese young males.

Review: the Roles and Mechanisms of Glycoprotein 130 Cytokines in the Regulation of Adipocyte Biological Function

Chronic low-grade inflammation is now widely accepted as one of the most important contributors to metabolic disorders. Glycoprotein 130 (gp130) cytokines are involved in the regulation of metabolic activity. Studies have shown that several gp130 cytokines, such as interleukin-6 (IL-6), leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor (CNTF), and cardiotrophin-1 (CT-1), have divergent effects on adipogenesis, lipolysis, and insulin sensitivity as well as food intake. In this review, we will summarize the present knowledge about gp130 cytokines, including IL-6, LIF, CNTF, CT-1, and OSM, in adipocyte biology and metabolic activities in conditions such as obesity, cachexia, and type 2 diabetes. It is valuable to explore the diverse actions of these gp130 cytokines on the regulation of the biological functions of adipocytes, which will provide potential therapeutic targets for the treatment of obesity and cachexia.

Scopoletin increases glucose uptake through activation of PI3K and AMPK signaling pathway and improves insulin sensitivity in 3T3-L1 cells

Coumarins have been shown to reduce blood glucose levels and improve insulin sensitivity in other studies. The purpose of this study was to investigate the effects of scopoletin, which is a type of coumarin family, on glucose uptake in 3T3-L1 cells to test the hypothesis that scopoletin exerts an antidiabetic function on adipocytes. Scopoletin significantly increased glucose uptake, which was associated with increased expression of the plasma membrane glucose transporter type 4 (PM-GLUT4) in 3T3-L1 adipocytes. This increase in PM-GLUT4 expression was promoted by phosphorylation of protein kinase B, activation of phosphatidylinositol-3-kinase (PI3K), and enhanced intracellular glucose uptake. Scopoletin also promoted phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and enhanced PM-GLUT4 expression. Scopoletin-induced glucose uptake in 3T3-L1 adipocytes was inhibited by treatment with the PI3K inhibitor wortmannin and the AMPK inhibitor compound C. These results suggest that scopoletin has an antidiabetic effect by stimulating GLUT4 translocation to the PM through activation of the PI3K and AMPK pathways in 3T3-L1 adipocytes, thereby upregulating glucose uptake.

Apelin and stem cells: the role played in the cardiovascular system and energy metabolism

Apelin, a member of the adipokine family, is widely distributed in the body and exerts cytoprotective effects on many organs. Apelin isoforms are involved in different physiological processes, including regulation of the cardiovascular system, cardiac contractility, angiogenesis, and energy metabolism. Several investigations have been performed to study the effect of apelin on stem cell therapy. This review aims to summarize the literature representing the effects of apelin on stem cell properties. Furthermore, this review discusses the therapeutic potential of apelin-treated stem cells for cardiovascular diseases and demonstrates the effect of stem cells overexpressing apelin on energy metabolism. Stem cells with their unique characteristics play a crucial role in the maintenance of tissue integrity. These cells participate in tissue regeneration via multiple mechanisms. Although preclinical and clinical studies have demonstrated the therapeutic potential of stem cells in various diseases, their application in regenerative medicine has not been efficient. A number of strategies such as genetic modification or treatment of stem cells with different factors have been used to improve the efficacy of cell therapy and to increase their survival after transplantation. This article reviews the effect of apelin treatment on the efficacy of cell therapy.

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.

MiR-27a promotes insulin resistance and mediates glucose metabolism by targeting PPAR-γ-mediated PI3K/AKT signaling

This study aimed to establish a high-fat diet (HFD)-fed obese mouse model and a cell culture model of insulin resistance (IR) in mature 3T3-L1 adipocytes. A dual-luciferase reporter assay (DLRA) was confirmed interaction between miR-27a and the 3'-untranslated region (UTR) of Peroxisome proliferator-activated receptor (PPAR)-γ. The inhibition of PPAR-γ expression by microRNA (miR)-27a in IR cells at both the protein and mRNA levels was confirmed by a mechanistic investigation. Moreover, the 3'-UTR of PPAR-γ was found to be a direct target of miR-27a, based on the DLRA. Furthermore, antagomiR-27a upregulated the activation of PI3K/Akt signaling and glucose transporter type 4 (GLUT4) expression at the protein and mRNA levels. Additionally, the PPAR inhibitor T0070907 repressed the insulin sensitivity upregulated by antagomiR-27a, which was accompanied by the inhibition of PPAR-γ expression and increased levels of AKT phosphorylation and GLUT4. The PI3K inhibitor wortmannin reduced miR-27a-induced increases in AKT phosphorylation, glucose uptake, and GLUT4. miR-27a is considered to be involved in the PPAR-γ-PI3K/AKT-GLUT4 signaling axis, thus leading to increased glucose uptake and decreased IR in HFD-fed mice and 3T3-L1 adipocytes. Therefore, miR-27a is a novel target for the treatment of IR in obesity and diabetes.

The Mechanism of Phillyrin from the Leaves of Forsythia suspensa for Improving Insulin Resistance

Three lignans, phillyrin, forsythia ester A, and rosin-β-D-furan glucose, were isolated from Forsythia suspensa which is a famous Traditional Chinese Medicine used for clearing heat and detoxifying, reducing swelling and dispersing knot, and dispersing wind heat. In this study, the effects of phillyrin, forsythia ester A, and rosin-β-D-furan glucose on insulin resistance of 3T3-L1 adipocytes were investigated by the method of glucose oxidase-peroxidase (GOD-POD) and the mechanism was assayed by the method of western blot. The results indicated that phillyrin, forsythia ester A, and rosin-β-D-furan glucose could improve the glucose uptake in 3T3-L1 adipocytes under insulin resistance (IR). Among them, phillyrin showed significant activity in increasing glucose consumption at the concentrations of 100 μM and 200 μM (P < 0.001). The mechanism of improving insulin resistance may be that phillyrin could raise the protein phosphorylation of IRS-1 and Akt and the expression levels of GLUT4 protein.

Association of a genetic variant in AKT1 gene with features of the metabolic syndrome

Metabolic syndrome (MetS) is a clustering of metabolic abnormalities that is associated with increased risk of developing cardiovascular disease and type 2 diabetes. There is growing body of data showing the associations of genetic variants of the genes involved in the PI3K/AKT/mTOR pathway with diabetes and obesity. We aimed to investigate the association between MetS and its components with the genetic polymorphism in AKT1, rs1130233 (T > C). Total of 618 participants, recruited from Mashhad stroke and heart atherosclerosis disorder cohort (MASHAD study). Patients with MetS were defined by using international diabetes federation (IDF) criteria (n = 326) and those without MetS (n = 261) were recruited. Anthropometric and biochemical parameters were measured in all subjects. Genetic analysis for the rs1130233 polymorphism was performed, using the ABI-StepOne instruments with SDS version-2.0 software. Individuals with MetS had a significantly higher levels of BMI, waist-circumference, total cholesterol, triglyceride, high sensitivity-c reactive protein (hs-CRP) and blood-pressure, and lower concentrations of high density lipoprotein (HDL-C), compared to non-MetS individuals (P < 0.05). The association between the rs1130233 and MetS was not significant. Subjects with a CC or CT genotypes had a significantly higher serum hs-CRP-level (OR: 1.5; 95% CI (1.05–2.1), P = 0.02). Additionally, subjects who carried the TC genotype had a higher BMI compared to the CC genotype (p value = 0.045). Our findings demonstrated that AKT1, rs1130233 (T > C) polymorphism was associated with major components of MetS such as hs-CRP, and BMI, indicating further investigation in a multi-center setting to explore its value as an emerging biomarker of risk stratification marker.

SIRT6 as a potential target for treating insulin resistance

AIMS

We aimed to explore the role of SIRT6 in Insulin resistance (IR). We are the first to investigate on this crucial relationship in an obese mouse model fed on a high-fat diet (HFD) and an IR model based on the mature 3T3-L1-derived adipocytes.

MAIN METHODS

Western blotting (WB) and qPCR analysis were performed to evaluate the SIRT6 protein and mRNA expressions in HFD mice as well as IR cells. Injection of adenovirus encoding SIRT6 gene in HFD mice and transfection of pcDNA3-SIRT6 in IR cells increased the glucose uptake levels and insulin sensitivity.

KEY FINDINGS

The positive regulatory effects of SIRT6 on transient receptor potential vallinoid 1 (TRPV1) in IR cells were confirmed by a mechanistic investigation at both protein and mRNA levels. Further, the overexpression of SIRT6 was found to activate the TRPV1/Calcitonin gene-related peptide (CGRP) signaling and upregulate the glucose transporter (GLUT) expression at protein and mRNA levels. Additionally, administration of the TRPV1 antagonist, SB-705498 repressed the insulin sensitivity upregulated by SIRT6 overexpression accompanied with the inhibition of CGRP and decrease in GLUT proportions. The results also showed that TRPV1 agonist, Capsaicin boosted the SIRT6-induced glucose uptake, CGRP production, and GLUT4 levels.

SIGNIFICANCE

Overall, SIRT6 was concluded to be involved in the TRPV1-CGRP-GLUT4 signaling axis thus leading to increased glucose uptake and decreased IR in HFD mice and 3T3-L1 adipocytes. Therefore, in terms of obesity and diabetes, SIRT6 is a novel candidate for treating IR.

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.

Alizarin increase glucose uptake through PI3K/Akt signaling and improve alloxan-induced diabetic mice

Aim: Alizarin (AZ), that can be isolated from Rubia cordifolia, has biological activities such as antioxidation and anti-inflammatory. This study aimed to investigate the effect of AZ on glucose and lipid metabolism disorders in alloxan-induced diabetic mice and also explored the effect of AZ on insulin resistance in 3T3-L1 adipocytes. Results: The research showed that AZ could decrease fasting and postprandial blood glucose, TG, TC and MDA, and it could also increase liver glycogen levels and SOD activity in diabetic mice. AZ could significantly improve the glucose uptake of 3T3-L1 adipocytes under insulin resistance, and could also increase GLUT4 protein expression levels, IRS-1 and Akt protein phosphorylation. Conclusion: These results showed that AZ has the potential to reduce blood sugar and improve insulin resistance.

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).

The apelin/APJ system as a therapeutic target in metabolic diseases

INTRODUCTION

Apelin, a bioactive peptide, is the endogenous ligand of APJ, a G protein-coupled receptor which is widely expressed in peripheral tissues and in the central nervous system. The apelin/APJ system is involved in the regulation of various physiological functions and is a therapeutic target in different pathologies; the development of APJ agonists and antagonists has thus increased. Area covered: This review focuses on the in vitro and in vivo metabolic effects of apelin in physiological conditions and in the context of metabolic diseases. Expert opinion: In experimental models, novel APJ agonists are efficient in vivo, to treat metabolic diseases and associated complications. However, more clinical trials are necessary to determine whether molecules that target APJ could become an alternative therapeutic strategy in the treatment of metabolic diseases and associated complications.