The Effect of Sitagliptin on Lipid Metabolism of Fatty Liver Mice and Related Mechanisms

Apolipoprotein A-IV restrains fat accumulation in skeletal and myocardial muscles by inhibiting lipogenesis and activating PI3K-AKT signalling

BACKGROUND

One of the pathological characteristics of obesity is fat accumulation of skeletal muscles (SKM) and the myocardium, involving mechanisms of insulin resistance and abnormal lipid metabolism. Apolipoprotein A-IV (ApoA-IV) is an essential gene in both glucose and lipid metabolisms.

MATERIALS AND METHODS

Using high-fat diet (HFD) induced obese apoA-IV-knockout mice and subsequent introduction of exogenous recombinant-ApoA-IV protein and adeno-associated virus (AAV)-transformed apoA-IV, we examined lipid metabolism indicators of SKM and the myocardium, which include triglyceride (TG) content, RT-PCR for lipogenic indicators and western blotting for AKT phosphorylation. Similarly, we used high-glucose-fed or palmitate (Pal)-induced C2C12 cells co-cultured with ApoA-IV protein to evaluate glucose uptake, the phosphoinositide 3-kinase (PI3K)-AKT pathway, and lipid metabolisms.

RESULTS

In stable obese animal models, we find ApoA-IV-knockout mice show elevated TG content, enhanced expression of lipogenic enzymes and diminished phosphorylated AKT in SKM and the myocardium, but both stable hepatic expression of AAV-apoA-IV and brief ApoA-IV protein administration suppress lipogenesis and promote AKT phosphorylation. In a myoblast cell line C2C12, ApoA-IV protein suppresses Pal-induced lipid accumulation and lipogenesis but enhances AKT activation and glucose uptake, and the effect is abolished by a PI3K inhibitor.

CONCLUSION

We find that ApoA-IV reduces fat accumulation by suppressing lipogenesis and improves glucose uptake in SKM and the myocardium by regulating the PI3K-AKT pathway.

Probiotic yogurt regulates gut microbiota homeostasis and alleviates hepatic steatosis and liver injury induced by high-fat diet in golden hamsters

This study aimed to investigate the beneficial effects of probiotic yogurt on lipid metabolism and gut microbiota in metabolic-related fatty liver disease (MAFLD) golden hamsters fed on a high-fat diet (HFD). The results demonstrated that probiotic yogurt significantly reversed the adverse effects caused by HFD, such as body and liver weight gain, liver steatosis and damage, sterol deposition, and oxidative stress after 8 weeks of intervention. qRT-PCR analysis showed that golden hamsters fed HFD had upregulated genes related to adipogenesis, increased free fatty acid infiltration, and downregulated genes related to lipolysis and very low-density lipoprotein secretion. Probiotic yogurt supplements significantly inhibited HFD-induced changes in the expression of lipid metabolism-related genes. Furthermore, 16S rRNA gene sequencing of the intestinal content microbiota suggested that probiotic yogurt changed the diversity and composition of the gut microbiota in HFD-fed hamsters. Probiotic yogurt decreased the ratio of the phyla Firmicutes/Bacteroidetes, the relative abundance of the LPS-producing genus Desulfovibrio, and bacteria involved in lipid metabolism, whereas it increased the relative abundance of short-chain fatty acids producing bacteria in HFD-fed hamsters. Predictive functional analysis of the microbial community showed that probiotic yogurt-modified genes involved in LPS biosynthesis and lipid metabolism. In summary, these findings support the possibility that probiotic yogurt significantly improves HFD-induced metabolic disorders through modulating intestinal microflora and lipid metabolism and effectively regulating the occurrence and development of MAFLD. Therefore, probiotic yogurt supplementation may serve as an effective nutrition strategy for the treatment of patients with MAFLD clinically.

Sitagliptin Reduces Endothelial Dysfunction and Apoptosis Induced by High-Fat Diet and Palmitate in Thoracic Aortas and Endothelial Cells via ROS-ER Stress-CHOP Pathway

Macrovascular disease is tightly associated with obesity-induced metabolic syndrome. Sitagliptin (SIT), an orally stable selective inhibitor of Dipeptidyl peptidase-4 (DPP-4), has protective effects on endothelium. However, the mechanisms enabling SIT to exhibit resistance to diet-induced obesity (DIO) related with reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress in the aorta and endothelial cells have not been reported yet. Therefore, the present study was conducted to determine if SIT exerts protective role in the thoracic aortas isolated from the high-fat diet (HFD)-treated rats and palmitate (PA)-treated endothelial cells by alleviating ROS and ER stress. Male Sprague Dawley rats were randomly divided into standard chow diet (SCD), HFD and HFD plus sitagliptin administration (HFD + SIT) groups. The rats of latter two groups were given HFD fodder for 12 weeks, then the HFD + SIT rats were treated with SIT (10 mg/kg/d) by intragastric administration for another 8 weeks. The body mass, vascular tension, serum oxidative stress indices and inflammatory parameters, pathological changes, protein expression of endothelial nitric oxide synthase (eNOS), the genes associated with ER stress and apoptosis in the thoracic aorta were measured. Furthermore, cell proliferation, ROS and the protein expression associated with ER stress (especially CHOP) and apoptosis were assessed in human umbilical vein endothelial cells (HUVECs) incubated with SIT and PA. Compared to the SCD rats, the HFD rats had higher serum lipid levels, decreased vascular tension, increased inflammation, oxidative and ER stress, and apoptosis of endothelial cells. PA promoted ROS generation, ER stress and apoptosis, inhibited cell proliferation in HUVECs. SIT treatment obviously ameliorated apoptosis via alleviating ROS and ER stress in the thoracic aortas isolated from HFD-fed rats and PA-treated HUVECs. The results suggest that SIT improved endothelial function via promoting cell proliferation and alleviating ROS-ER stress-CHOP pathway both in vivo and in vitro.

Resveratrol Protects SH-SY5Y Cells Against Oleic Acid-Induced Glucolipid Metabolic Dysfunction and Cell Injuries Via the Wnt/β-Catenin Signalling Pathway

Resveratrol (RES) is a polyphenol with diverse beneficial biological and pharmacological activities, and our previous results have demonstrated its neuroprotective effects in several metabolic diseases, including non-alcoholic fatty liver disease. The aim of the present study is to investigate the potential effect of RES against oleic acid (OA)-induced cell injuries in SH-SY5Y cells and explore the possible mechanism. Based on the dose- and time-dependent effects of OA on cell proliferation and LDH release, SH-SY5Y cells were challenged with OA and incubated with or without RES (10^-5-10^-9 mM) or sitagliptin (STG, 10^-7 mM). Lipid accumulation, SREBP1 and PPARα protein expression, glucose consumption and IRS1, AKT, ERK phosphorylation under insulin stimulation, and ROS production were detected. The protein expression of brain-derived neurotrophic factor (BDNF), Copine 6, and key molecules in the Wnt/β-catenin signalling pathway were measured via western blot. The expression of Wnt 1 was also measured via immunofluorescence staining. The results showed that RES treatment could alleviate the neurotoxicity induced by OA, as indicated by the increased cell proliferation and the decreased concentration of LDH in the supernatant. The increased lipid deposition and protein expression of SREBP1 and PPARα induced by OA was also reversed by treatment with RES. Moreover, RES could upregulate glucose consumption and the protein expression of phosphorylated IRS1, AKT, ERK and reduced ROS production in OA-induced SH-SY5Y cells. Furthermore, RES treatment reversed the imbalanced protein expression of BDNF, Copine 6, p-β-catenin, and Wnt 1 in SH-SY5Y cells induced by OA and decreased the hyperexpression of p-GSK3β. However, these effects were suppressed by DKK1, which is a specific antagonist of the Wnt signalling pathway. These results suggested that RES has a neuroprotective effect against OA-induced cell injury and dysfunctional glucolipid metabolism, and the mechanism might involve its ability to regulate oxidative stress and insulin resistance via the Wnt/β-catenin signalling pathway.

N-glycosylation of CREBH improves lipid metabolism and attenuates lipotoxicity in NAFLD by modulating PPARα and SCD-1

INTRODUCTION

Cyclic adenosine monophosphate (AMP)-responsive element-binding protein H (CREBH), an endoplasmic reticulum-anchored transcription factor essential for lipid metabolism and inflammation in nonalcoholic fatty liver disease (NAFLD), is covalently modified by N-acetylglucosamine. Glycosylation is a ubiquitous type of protein involved in posttranslational modifications, and plays a critical role in various biological processes. However, the mechanism of glycosylated CREBH remains poorly understood in NAFLD.

METHODS

CREBH glycosylation mutants were obtained by site-mutation methods. After transfection with plasmids, AML-12, LO2, or HepG2 cells were treated with palmitic acid (PA) proteolysis, tunicamycin (Tm), or their combination. Glycosyltransferase V (GnT-V) was used induce hyperglycosylation to further understand the effect of CREBH. In addition, glycosylation mutant mice and hyperglycosylated mice were generated by lentivirus injection to construct two kinds of NAFLD animal models. The expression of NAFLD-related factors was detected to further verify the role of N-linked glycosylation of CREBH in lipid and sterol metabolism, inflammation, and lipotoxicity.

RESULTS

N-glycosylation enhanced the ability of CREBH to activate transcription and modulated the production of peroxisome proliferator-activated receptor alpha (PPARα) and stearoyl-CoA desaturase-1 (SCD-1) activity by affecting their promoter-driven transcription activity and protein interactions, leading to reduce lipid deposition and attenuate lipotoxicity. Deglycosylation of CREBH induced by Tm could inhibit the proteolysis of CREBH induced by PA. The addition of unglycosylated CREBH to cells upregulates gene and protein expression of lipogenesis, lipotoxicity, and inflammation, and aggravates liver damage by preventing glycosylation in cells, as well as in mouse models of NAFLD. Furthermore, increased N-glycosylation of CREBH, as achieved by overexpressing GnT-V could significantly improve liver lesion caused by unglycosylation of CREBH.

CONCLUSION

These findings have important implications for the role of CREBH N-glycosylation in proteolytic activation, and they provide the first link between N-glycosylation of CREBH, lipid metabolism, and lipotoxicity processes in the liver by modulating PPARα and SCD-1. These results provide novel insights into the N-glycosylation of CREBH as a therapeutic target for NAFLD.

Mitigation of renal inflammation and endoplasmic reticulum stress by vildagliptin and statins in high-fat high-fructose diet-induced insulin resistance and renal injury in rats

Dyslipidemia and insulin resistance in obesity can lead to lipotoxicity and cellular damage. Renal lipotoxicity in association with an impairment of lipid metabolism induces renal damage through the activation of inflammation, ER stress, fibrosis and apoptosis. We investigated the effects of a combination treatment of the DPP-4 inhibitor vildagliptin and atorvastatin on renal lipotoxicity related to renal dysfunction and injury in a high-fat high-fructose diet (HFF)-induced insulin resistant condition. Male Wistar rats were fed on a high-fat diet and were given drinking water with 10% fructose for 16 weeks. After that, rats were divided into: no treatment (HFF), treatment with vildagliptin, atorvastatin and vildagliptin plus atorvastatin for 4 weeks. The results demonstrated that the combination treatment prominently improved insulin resistance, dyslipidemia and kidney morphological changes induced by HFF. These changes correlated well with the increased expression of nephrin and podocin and decreased urine protein. Notably, the combined treatment produced greater improvement in renal lipid metabolism through increasing fatty acid oxidation with the decreases in fatty acid transporters and fatty acid synthesis, thereby reducing renal lipid accumulation in HFF rats. The reduction in renal lipotoxicity via diminishing renal inflammation, ER stress, fibrosis and apoptosis was also more significant in the combined treatment group than in the other groups in which the drug was used as a monotherapy. In conclusion, the combination therapy produced synergistic beneficial effects on metabolic parameters, lipid metabolism and accumulation related to renal lipid accumulation-induced lipotoxicity and kidney injury in the HFF-induced insulin resistant model with improved outcomes.

Pharmacology of dipeptidyl peptidase-4 inhibitors and its use in the management of metabolic syndrome: a comprehensive review on drug repositioning

OBJECTIVES

Despite advances in our understanding of metabolic syndrome (MetS) and the treatment of each of its components separately, currently there is no single therapy approved to manage it as a single condition. Since multi-drug treatment increases drug interactions, decreases patient compliance and increases health costs, it is important to introduce single therapies that improve all of the MetS components.

EVIDENCE ACQUISITION

We conducted a PubMed, Scopus, Google Scholar, Web of Science, US FDA, utdo.ir and clinicaltrial.gov search, gathered the most relevant preclinical and clinical studies that have been published since 2010, and discussed the beneficial effects of dipeptidyl peptidase (DPP)-4 inhibitors to prevent and treat different constituent of the MetS as a single therapy. Furthermore, the pharmacology of DPP-4 inhibitors, focusing on pharmacodynamics, pharmacokinetics, drug interactions and their side effects are also reviewed.

RESULTS

DPP-4 inhibitors or gliptins are a new class of oral anti-diabetic drugs that seem safe drugs with no severe side effects, commonly GI disturbance, infection and inflammatory bowel disease. They increase mass and function of pancreatic β-cells, and insulin sensitivity in liver, muscle and adipose tissue. It has been noted that gliptin therapy decreases dyslipidemia. DPP-4 inhibitors increase fatty oxidation, and cholesterol efflux, and decrease hepatic triglyceride synthase and de novo lipogenesis. They delay gastric emptying time and lead to satiety. Besides, gliptin therapy has anti-inflammatory and anti-atherogenic impacts, and improves endothelial function and reduces vascular stiffness.

CONCLUSION

The gathered data prove the efficacy of DPP-4 inhibitors in managing MetS in some levels beyond anti-diabetic effects. This review could be a lead for designing new DPP-4 inhibitors with greatest effects on MetS in future. Introducing drugs with polypharmacologic effects could increase the patient's compliance and decrease the health cost that there is not in multi-drug therapy. Graphical abstract ᅟ.

Dendritic cells and Th17/Treg ratio play critical roles in pathogenic process of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common disorder of respiratory system. This study aimed to evaluate changes of mature dendritic cells (DCs) and regulatory T cells (Treg) in lung tissues and peripheral blood of COPD patients. For lung tissue analysis, patients were divided into no-smoking and no-COPD (CS-COPD-), smoking and no-COPD (CS + COPD-) and COPD group. For peripheral blood analysis, patients were divided into CS-COPD-, CS + COPD-, stable COPD (SCOPD) and acute exacerbation of COPD (AECOPD) group. Hematoxylin and eosin (HE) staining was used to evaluate inflammation of lung tissues. Immunohistochemistry assay was employed to examine CD80, CCR6, IL-17 A, FoxP3 in lung tissues. DCs and Treg cells were isolated from lung tissues and peripheral blood. Levels of CD80, FoxP3+ Treg, CCR6 and IL-17 A were detected by using flow cytometry. Results showed that FEV%, FVC% and FEV1/FVC were significantly reduced and Bosken scores were remarkably increased in COPD patients compared to non-COPD patients (p < 0.05). CD80 and FoxP3 levels were lower, and CCR6 and IL-17A levels were higher obviously in COPD compared to non-COPD patients (p < 0.05). COPD patients illustrated reduced mDCs levels and enhanced imDCs levels. COPD patients exhibited remarkably higher Th17 levels compared to no-smoking patients (p < 0.05). COPD patients illustrated obviously lower Treg levels and significantly higher Th17/Treg ratio compared to non-smoking patients (p < 0.05). Th17% (Th17/Treg) negatively and Treg% was positively correlated with FEV1%, FEVC%, FEV1/FEVC (p < 0.05). In conclusion, dendritic cells and Th17/Treg ratio play critical roles for pathogenic process of chronic obstructive pulmonary disease.

DPP-4 Inhibitor Sitagliptin Improves Cardiac Function and Glucose Homeostasis and Ameliorates β-Cell Dysfunction Together with Reducing S6K1 Activation and IRS-1 and IRS-2 Degradation in Obesity Female Mice

BACKGROUND

Chronic overnutrition leads to cardiac dysfunction and insulin (INS) resistance. Dipeptidyl peptidase-4 (DPP-4) improves glucose metabolism and insulin sensitivity in both human and animal models. In this study, we explored whether DPP-4 inhibitor sitagliptin (SIT) is involved in the protection of cardiac function and β-cell function using an obesity female mouse model.

METHODS

Six-week-old C57BL6/J mice were fed a high fat and fructose Western diet with DPP-4 inhibitor SIT for 12 weeks. Cardiac function was examined by echocardiography. Body weight, plasma glucose, and insulin concentrations were measured. The contents of total S6 kinase 1 (S6K1), phosphorylation of S6K1 activation, and INS docking proteins INS receptor substrates 1 and 2 (IRS-1, IRS-2) were assayed, and histology of heart tissue was performed.

RESULTS

Chronic Western diet consumption elevated plasma glucose and insulin and caused obesity, diastolic dysfunction, and β-cell dysfunction. DPP-4 inhibition with SIT resulted in reduction in body weight, fasting glucose, and plasma insulin, and improved cardiac diastolic dysfunction. SIT also decreased mTOR/S6K1 activation and prevented the degradation of IRS-1 and IRS-2.

CONCLUSIONS

This study revealed pleiotropic protective effects of DPP-4 inhibitor SIT on cardiac function, glycemia, and β-cell function together with reducing S6K1 activation and IRS-1 and IRS-2 degradation in the obesity female mouse model.