Liraglutide reduces lipid accumulation in steatotic L‑02 cells by enhancing autophagy

Liraglutide reduces bone marrow adipogenesis by miR-150-5p/ GDF11 axis in diabetic rats

In recent years, a common-used antidiabetic drug, liraglutide, was identified with extra effects on lipid metabolism. Its effects against excessive lipid deposition in bone marrow were gained much attention but not well established. Our aim in the present study is to explore the interaction of miRNAs-mRNAs altered by liraglutide administration during bone marrow adipogenesis in diabetes. To establish the diabetic animal model, rats were treated with high fat diet (HFD) and STZ injection. We then identified the lowering effect of liraglutide on lipids metabolism in the diabetes. During this process, high-throughput sequencing and bioinformatics analyses on miRNAs extracted from bone marrow mesenchymal stem cells (BMSCs) were conducted after liraglutide administration. We then identified five differentially expressed miRNAs (miRNA-150-5p, miRNA-129-5p, miRNA-201-3p, miRNA-201-5p, and miRNA-214-5p). The expressions of the DE miRNAs were verified as temporal specific expression patterns in Day 3 and in Day 7. Among them, miRNA-150-5p expression was more stable and consistent with the sequencing data. Of interest, miR-150-5p overexpression facilitated adipogenesis of BMSCs. But this promotion was alleviated by liraglutide. The predicted target gene of miR-150-5p, GDF11, was validated to be involved in liraglutide alleviated BMSCs' lipid accumulation in diabetes. In vitro, liraglutide increased the GDF11 expression, rescued its down-expression by siGDF11 and inhibit the adipogenesis of BMSCs cultured in high glucose medium. In vivo, liraglutide reversed the HFD-STZ induced excessive lipid droplets by up-regulation of GDF11 expression, which was discounted by agomiR-150-5p injection. Above all, liraglutide might alleviate bone marrow fat accumulation via inactivating miR-150-5p/GDF11 axis in diabetes.

Glycyrrhizic acid attenuates the malignant biological properties of nonalcoholic fatty liver disease-related hepatocellular carcinoma

Glycyrrhizic acid (GA) has effects on anti-hepatic fibrosis, anti-tumor and prevention from hepatocellular carcinoma (HCC) progression. Yet, the capacity of GA to ameliorate the advance of HCC pertinent to nonalcoholic fatty liver disease (NAFLD) remains to be clarified. We used the CCK-8 method to detect the optimal treatment concentration and time for L-02 cells, palmitic acid (PA)-induced L-02 cells and HepG2 cells, and selected 40 μM and 48 h to treat PA-induced L-02 cells and 60 μM for 24 h to treat HepG2 cells. Moreover, functional associations of HepG2 cells were elucidated through various assays. The results showed that GA demonstrated enhances lipid deposition and alleviates the inflammatory response in L-02 cells induced by palmitic acid. Simultaneously, we found that GA inhibits the proliferation, migration, and invasion while promoting apoptosis in HepG2 cells. In pursuit of constructing of HCC model rats, a combination of high-fat diets and diethylnitrosamine was utilized. The results showed that GA significantly decreased the liver index, body weight, liver weight, and the number of nodules in HCC model rats. Moreover, GA mitigated infiltration and heightened apoptosis in these rats. Mechanistically, GA notably attenuated the KKβ/NF-κB pathway in both HepG2 cells and the HCC model rats. In conclusion, GA functions as an inhibitor in the progression of NAFLD-related HCC cells, which might be relevant to the KKβ/NF-κB pathway. Therefore, GA is a potential drug for NAFLD-related HCC treatment.

Harmine ameliorates CCl4-induced acute liver injury through suppression of autophagy and inflammation

CCl4-induced acute liver injury (ALI) is characterized by heightened autophagy, inflammation, and oxidative damage. Accumulating evidence suggests that harmine exerts beneficial effects in countering CCl4-induced ALI by mitigating inflammation and oxidative stress. However, the impact of autophagy on CCl4-induced ALI and the protective role of harmine remain unclear. This study aimed to investigate the potential protective effects of harmine against CCl4-induced ALI in mice by suppressing autophagy and inflammation. Male Kunming mice were orally administered harmine or bifendate for seven days. Subsequently, one hour after the final administration, the model group and treatment groups were intraperitoneally injected with CCl4 to induce ALI. The findings revealed that harmine significantly reduced the levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in serum, and ameliorated the liver histopathological changes induced by CCl4. Furthermore, harmine diminished the levels of TNF-α and IL-6, restored the levels of glutathione (GSH) and superoxide dismutase (SOD), and suppressed the production of nitric oxide (NO) and malondialdehyde (MDA) in the liver. Mechanistically, harmine down-regulated LC3B II/I, p38 MAPK, TLR4, and NF-κB levels, while upregulating p62, Bcl-2, Beclin1, ULK1, and p-mTOR expression. In conclusion, harmine mitigated CCl4-induced ALI by inhibiting autophagy and inflammation through the p38 MAPK/mTOR autophagy pathway, the Bcl-2/Beclin1 pathway, and the TLR4/NF-κB pathway.

SIRT1/mTOR pathway-mediated autophagy dysregulation promotes Pb-induced hepatic lipid accumulation in HepG2 cells

Lead (Pb) is a common and toxic metal pollutant in the ecological environment and has drawn significant attention due to its presence in various channels, including the use of lead-based paint, mineral extraction and smelting, exhaust gas from gasoline combustion. Autophagy is an essential catabolic pathway and blocked autophagy may result in abnormal lipid metabolism in liver. A body of evidence demonstrates that Pb exposure causes abnormal lipid droplet (LDs) accumulation in the liver, but the mechanism remains unknown. Here, we investigated whether Pb induced lipid accumulation by regulating autophagy in HepG2 cells. In this study, we found that Pb (50 μM) blocked the autophagy flux mainly by transcription factor EB (TFEB)-mediated impairment of lysosome formation and activity. Then we demonstrated that the dense lipid accumulation was observed upon Pb exposure, and induction of autophagy by the autophagy activator rapamycin (Rap) alleviated Pb-induced lipid accumulation, while suppression of autophagy by chloroquine (CQ) exacerbated Pb-induced lipid accumulation, suggested that Pb-induced autophagy blockage might be responsible for lipid accumulation. Moreover, we demonstrated that the SIRT1/mTOR pathway participated in Pb-induced autophagy dysregulation, leading to Pb-induced hepatic lipid accumulation. In summary, these results revealed a new insight into the relationship between Pb-caused autophagy dysregulation and lipid accumulation for the first time and highlight autophagy as a novel therapeutic target against Pb-induced hepatic lipid accumulation which supplying the theoretical basis and potential strategies for the intervention and treatment of Pb-related disease.

Role of fatty liver in coronavirus disease 2019 patients' disease severity and hospitalization length: a case-control study

Background and purpose

Fatty liver is one of the most common pre-existing illnesses; it can cause liver injury, leading to further complications in coronavirus disease 2019 patients. Our goal is to determine if pre-existing fatty liver is more prevalent in hospitalized COVID-19 patients compared to patients admitted before the SARS-CoV-2 pandemic and determine the disease severity among fatty liver patients.

Experimental approach

This retrospective study involves a case and a control group consisting of 1162 patients; the case group contains hospitalized COVID-19 patients with positive PCR tests and available chest CT-scan; the control group contains patients with available chest CT-scan previous to the COVID-19 pandemic. Patients’ data such as liver Hounsfield unit, hospitalization length, number of affected lobes, and total lungs involvement score were extracted and compared between the patients.

Results

The findings indicate that 37.9% of hospitalized COVID-19 patients have a pre-existing fatty liver, which is significantly higher (P < 0.001) than the prevalence of pre-existing fatty liver in control group patients (9.02%). In comparison to hospitalized non-fatty liver COVID-19 patients, data from hospitalized COVID-19 patients with fatty liver indicate a longer hospitalization length (6.81 ± 4.76 P = 0.02), a higher total lungs involvement score (8.73 ± 5.28 P < 0.001), and an increased number of affected lobes (4.42 ± 1.2 P < 0.001).

Conclusion

The statistical analysis shows fatty liver is significantly more prevalent among COVID-19 against non-COVID-19 patients, and they develop more severe disease and tend to be hospitalized for more extended periods.

Kun-Dan Decoction Ameliorates Insulin Resistance by Activating AMPK/mTOR-Mediated Autophagy in High-Fat Diet-Fed Rats

Background: Metabolic syndrome is characterized by central obesity, hyperglycemia and hyperlipidemia. Insulin resistance is the leading risk factor for metabolic syndrome. Kun-Dan decoction (KD), a traditional Chinese medicine, has been applied to treat patients with metabolic syndrome for over ten years. It is increasingly recognized that autophagy deficiency is the key cause of metabolic syndrome. Therefore, we aimed to explore whether KD can activate autophagy to improve metabolic syndrome.

Methods: Network pharmacology was used to explore the underlying mechanism of KD in the treatment of metabolic syndrome. The high-fat diet-fed rats and oleic acid-induced LO2 cells were employed in our study. Oral glucose tolerance test and insulin tolerance test, obesity and histological examination, serum cholesterol, triglyceride, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), homeostasis model assessment of insulin resistance (HOMA-IR) and insulin sensitivity in high-fat diet-fed rats were analyzed. Furthermore, the protein expressions of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), phospho-AMPK, mammalian target of rapamycin (mTOR), phospho-mTOR, p62, autophagy related protein (Atg) 5, Atg7, Atg12, Atg13, Atg16L1 and microtubule-associated protein 1A/1B-light chain 3 (LC3)-Ⅱ/Ⅰ were examined in rats and LO2 cells. Moreover, autophagy activator rapamycin and inhibitor 3-methyladenine, and small interfering RNA against Atg7 were utilized to verify the role of autophagy in the treatment of metabolic syndrome by KD in oleic acid-induced LO2 cells.

Results: Results from network pharmacology indicated that targeted insulin resistance might be the critical mechanism of KD in the treatment of metabolic syndrome. We found that KD significantly suppressed obesity, serum cholesterol, triglyceride and LDL-C levels and increased serum HDL-C level in high-fat diet-fed rats. Furthermore, KD enhanced insulin sensitivity and attenuated HOMA-IR in high-fat diet-fed rats. Western blot showed that KD could enhance autophagy to increase the insulin sensitivity of high-fat diet-fed rats and oleic acid-induced LO2 cells. Furthermore, 3-methyladenine and small interfering RNA against Atg7 could reverse the protective effect of KD on LO2 cells. However, rapamycin could cooperate with KD to enhance autophagic activation to increase insulin sensitivity in LO2 cells.

Conclusion: The induction of autophagy may be the major mechanism for KD to improve insulin resistance and metabolic syndrome.

The preventive effect of liraglutide on the lipotoxic liver injury via increasing autophagy

INTRODUCTION AND OBJECTIVES

The incidence of non-alcoholic fatty liver disease (NAFLD) is increasing. Previous studies indicated that Liraglutide, glucagon-like peptide-1 analogue, could regulate glucose homeostasis as a valuable treatment for Type 2 Diabetes. However, the precise effect of Liraglutide on NAFLD model in rats and the mechanism remains unknown. In this study, we investigated the molecular mechanism by which Liraglutide ameliorates hepatic steatosis in a high-fat diet (HFD)-induced rat model of NAFLD in vivo and in vitro.

MATERIALS AND METHODS

NALFD rat models and hepatocyte steatosis in HepG2 cells were induced by HFD and palmitate fatty acid treatment, respectively. AMPK inhibitor, Compound C was added in HepG2 cells. Autophagy-related proteins LC3, Beclin1 and Atg7, and AMPK pathway-associated proteins were evaluated by Western blot and RT-PCR.

RESULTS

Liraglutide enhanced autophagy as showed by the increased expression of the autophagy markers LC3, Beclin1 and Atg7 in HFD rats and HepG2 cells treated with palmitate fatty acid. In vitro, The AMPK inhibitor exhibited an inhibitory effect on Liraglutide-induced autophagy enhancement with the deceased expression of LC3, Beclin1 and Atg7. Additionally, Liraglutide treatment elevated AMPK levels and TSC1, decreased p-mTOR expression.

CONCLUSIONS

Liraglutide could upregulate autophagy to decrease lipid over-accumulation via the AMPK/mTOR pathway.

Melatonin Orchestrates Lipid Homeostasis through the Hepatointestinal Circadian Clock and Microbiota during Constant Light Exposure

Misalignment between natural light rhythm and modern life activities induces disruption of the circadian rhythm. It is mainly evident that light at night (LAN) interferes with the human endocrine system and contributes to the increasing rates of obesity and lipid metabolic disease. Maintaining hepatointestinal circadian homeostasis is vital for improving lipid homeostasis. Melatonin is a chronobiotic substance that plays a main role in stabilizing bodily rhythm and has shown beneficial effects in protecting against obesity. Based on the dual effect of circadian rhythm regulation and antiobesity, we tested the effect of melatonin in mice under constant light exposure. Exposure to 24-h constant light (LL) increased weight and insulin resistance compared with those of the control group (12-h light–12-h dark cycle, LD), and simultaneous supplementation in the melatonin group (LLM) ameliorated this phenotype. Constant light exposure disturbed the expression pattern of a series of transcripts, including lipid metabolism, circadian regulation and nuclear receptors in the liver. Melatonin also showed beneficial effects in improving lipid metabolism and circadian rhythm homeostasis. Furthermore, the LL group had increased absorption and digestion of lipids in the intestine as evidenced by the elevated influx of lipids in the duodenum and decrease in the efflux of lipids in the jejunum. More interestingly, melatonin ameliorated the gut microbiota dysbiosis and improved lipid efflux from the intestine. Thus, these findings offer a novel clue regarding the obesity-promoting effect attributed to LAN and suggest a possibility for obesity therapy by melatonin in which melatonin could ameliorate rhythm disorder and intestinal dysbiosis.

Hypericin attenuates nonalcoholic fatty liver disease and abnormal lipid metabolism via the PKA-mediated AMPK signaling pathway in vitro and in vivo

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide and constitutes a major risk factor for progression to cirrhosis, liver failure and hepatocellular carcinoma (HCC). The occurrence of NAFLD is closely associated with abnormal lipid metabolism and implies a high risk of type 2 diabetes and cardiovascular disease. Therefore, specific and effective drugs for the prevention and treatment of NAFLD are necessary. Hypericin (HP) is one of the main active ingredients of Hypericum perforatum L., and we previously revealed its protective role in islet β-cells and its effects against type 2 diabetes. In this study, we aimed to explore the preventive and therapeutic effects of HP against NAFLD and the underlying mechanisms in vitro and in vivo. Here, we demonstrated that HP improved cell viability by reducing apoptosis and attenuated lipid accumulation in hepatocytes both in vitro and in vivovia attenuating oxidative stress, inhibiting lipogenesis and enhancing lipid oxidization. Thus, HP exhibited significant preventive and therapeutic effects against HFHS-induced NAFLD and dyslipidemia in mice. Furthermore, we demonstrated that HP directly bound to PKACα and activated PKA/AMPK signaling to elicit its effects against NAFLD, suggesting that PKACα is one of the drug targets of HP. In addition, the enhancing effect of HP on lipolysis in adipocytes through the activation of PKACα was also elucidated. Together, the conclusions indicated that HP, of which one of the targets is PKACα, has the potential to be used as a preventive or therapeutic drug against NAFLD or abnormal lipid metabolism in the future.

Inhibited Lipophagy Suppresses Lipid Metabolism in Zebrafish Liver Cells

Lipophagy degrades lipid droplets (LDs) through the lysosomal degradative pathway, thus plays important roles in regulating lipid metabolism in mammals. However, information on the existence and functions of lipophagy in fish lipid metabolism is still limited. In the present study, we confirmed the existence of lipophagy by observing the structures of LDs sequestered in autophagic vacuoles in the zebrafish liver cell line (ZFL) via electronic microscopy. Moreover, starved cells increased the mRNA expression of the microtubule-associated protein 1A/1B light chain 3 beta (LC3), which is a marker protein for autophagy and protein conversion from LC3-I to LC3-II. Inhibiting autophagy with chloroquine increased significantly the LDs content and decreased fatty acid β-oxidation and esterification activities in the ZFL cells cultured in the fed state. Furthermore, inhibiting autophagy function downregulated the mRNA expression of the genes and their proteins related to lipid metabolism. Altogether, the present study verified the existence of lipophagy and its essential regulatory roles in lipid metabolism in fish cells.

Effects of GLP-1 Receptor Activation on a Pentylenetetrazole-Kindling Rat Model

Objectives: To study the possible anti-seizure and neuroprotective effect of glucagon like peptide 1 (GLP1) analogue (liraglutide) in a pentylenetetrazole (PTZ) induced kindled rat model and its underlying mechanisms. Methods: Thirty Sprague Dawley rats were allocated into 3 equal groups; i) Normal group: normal rats received normal saline, ii) PTZ (kindling) group: received PTZ (50 mg/Kg intraperitoneally (i.p.)) every other day for 2 weeks and iii) PTZ + GLP1 group: same as the PTZ group but rats received liraglutide (75 µg/kg i.p. daily) for 2 weeks before PTZ injection. Seizure severity score, seizure latency and duration were assessed. Also, the expression of caspase-3 (apoptotic marker) and β-catenin (Wnt pathway) by western blotting, markers of oxidative stress (GSH, CAT and MDA) by biochemical assay and the expression of LC3 (marker of autophagy) and heat shock protein 70 (Hsp70) by immunostaining were assessed in hippocampal regions of brain tissues. Results: PTZ caused a significant increase in Racine score and seizure duration with a significant decrease in seizure latency. These effects were associated with a significant increase in MDA, β-catenin, caspase-3, Hsp70 and LC3 in brain tissues (p < 0.05). Meanwhile, liraglutide treatment caused significant attenuation in PTZ-induced seizures, which were associated with significant improvement in markers of oxidative stress, reduction in LC3, caspase-3 and β-catenin and marked increase in Hsp70 in hippocampal regions (p < 0.05). Conclusion: Activation of GLP1R might have anticonvulsant and neuroprotective effects against PTZ-induced epilepsy. These effects could be due to suppression of oxidative stress, apoptosis and autophagy and upregulation of Hsp70.

Alogliptin improves survival and health of mice on a high-fat diet

Alogliptin is a commonly prescribed drug treating patients with type 2 diabetes. Here, we show that long‐term intervention with alogliptin (0.03% w/w in diet) improves survival and health of mice on a high‐fat diet. Alogliptin intervention takes beneficial effects associated with longevity, including increased insulin sensitivity, attenuated functionality decline, decreased organ pathology, preserved mitochondrial function, and reduced oxidative stress. Autophagy activation is proposed as an underlying mechanism of these beneficial effects. We conclude that alogliptin intervention could be considered as a potential strategy for extending lifespan and healthspan in obesity and overweight.

Alogliptin improves endothelial function by promoting autophagy in perivascular adipose tissue of obese mice through a GLP-1-dependent mechanism

OBJECTIVE

Perivascular adipose tissue (PVAT) regulates vascular function in a paracrine manner and the vasodilatory effect of PVAT on vessels is completely abolished in obesity. In addition, autophagy is required for maintaining biological function of PVAT and has been shown to be inhibited in obesity. The aim of this study was to explore whether alogliptin improves endothelial function by promoting autophagy in PVAT in obese mice.

METHODS

C57BL/6 mice were maintained on high fat diet with or without alogliptin intervention for 3 months. Vasorelaxation function of thoracic aorta with or without PVAT was determined. Autophagy related protein level of p62 and LC3B, along with phosphorylated mTOR (p-mTOR) were evaluated. In addition, the effects of alogliptin on autophagy were also investigated in cultured adipocytes.

RESULTS

The presence of PVAT significantly impaired endothelium-dependent vasodilation in obese mice and alogliptin intervention corrected this defect. Autophagy in PVAT was decreased in obese mice and alogliptin intervention activated autophagy. Activating autophagy in PVAT improved endothelium-dependent vasodilation while blocking it in PVAT impaired vasodilation function. Further, addition of glucagon-like peptide-1 (GLP-1) but not alogliptin alone activated autophagy. Moreover, GLP-1 and alogliptin co-treatment did not show additive effect on activating autophagy.

CONCLUSIONS

These results revealed that promoting autophagy in PVAT improved endothelial function in response to alogliptin intervention. Additionally, the beneficial effect of alogliptin intervention on PVAT was GLP-1 dependent.

Neuroprotective effects of the novel GLP-1 long acting analogue semaglutide in the MPTP Parkinson's disease mouse model

Parkinson's disease (PD) is the second most common neurodegenerative disease, and there is no recognised therapy to cure it. Recently, it has been shown that treatments to improve insulin resistance in type 2 diabetes (T2DM) may be useful for PD patients. In previous studies, the glucagon-like peptide-1 (GLP-1) receptor agonist liraglutide showed good neuroprotective effects in animal models of PD. In addition, the GLP-1 mimetic exendin-4 has shown good protective effects in PD patients in a phase II clinical trial. Here, we report the protective effects of semaglutide (25 nmol/kg ip. once-daily for 7 days), a new long-acting GLP-1 analogue, in the MPTP mouse model of PD. Moreover, we compared the neuroprotective effect of semaglutide with liraglutide given at the same dose. Our work shows that both semaglutide and liraglutide improved 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced motor impairments. In addition, both GLP-1 analogues rescued the decrease of tyrosine hydroxylase (TH) levels, alleviated the inflammation response, reduced lipid peroxidation, inhibited the apoptosis pathway, and also increased autophagy- related protein expression, to protect dopaminergic neurons in the substantia nigra and striatum. Moreover, the long-acting GLP-1 analogue semaglutide was superior to liraglutide in most parameters measured in this study. Our results demonstrate that the new long- acting GLP-1 analogue semaglutide may be a promising treatment for PD.

Methyl ferulic acid attenuates ethanol-induced hepatic steatosis by regulating AMPK and FoxO1 Pathways in Rats and L-02 cells

Methyl ferulic acid (MFA) is a biologically active monomer extracted and purified from the Chinese herbal medicine Securidaca inappendiculata hasskarl. The previously studies showed that MFA improved acute liver injury induced by ethanol. However, the effect of MFA on ethanol-induced hepatic steatosis in alcoholic liver disease (ALD) still remains unclear. The current study was aimed at elucidating the effect of MFA on alcohol-induced hepatic steatosis and the underlying mechanisms. Human hepatocyte L-02 cells exposed to 200 mM ethanol for 24 h to simulate alcoholic steatosis in vitro. SD rats were fed a Lieber-DeCarli diet containing 5% (w/v) alcohol for 16 weeks to induce alcoholic liver disease in vivo. We examined the effect of MFA on ethanol-induced lipid deposition in L-02 cells and SD rats. The results showed that MFA reduced the accumulation of lipid in L-02 cells, improved alcoholic liver injury in rats, alleviated hepatic pathological lesions, and reduced lipid deposition in rat serum and liver. Further studies suggest that MFA reduces lipid synthesis by activating AMPK-ACC/MAPK-FoxO1 pathway. In addition, MFA also promotes lipid oxidation by up-regulating the expression of SIRT1, PPAR-α, and CPT-1α. Taken together, MFA ameliorates ethanol-induced hepatic steatosis by activating AMPK-ACC/MAPK-FoxO1 pathway and up-regulating the expression levels of SIRT1, PPAR-α, and CPT-1α.

Liraglutide Enhances Autophagy and Promotes Pancreatic β Cell Proliferation to Ameliorate Type 2 Diabetes in High-Fat-Fed and Streptozotocin-Treated Mice

Background

Clinical and experimental studies have revealed that liraglutide has multiple anti-diabetes biological effects. However, little is known about its role in autophagy and pancreatic β cell proliferation. This study aimed to assessed the effects of liraglutide on pancreatic β cell proliferation and autophagy in a mouse model of type 2 diabetes.

Material/Methods

The effect of liraglutide on autophagy and proliferation in pancreatic β cells was investigated using a high-fat-fed and streptozotocin-induced mouse model of type 2 diabetes.

Results

Liraglutide significantly improved the symptoms of high-fat-fed (HFD) and streptozotocin (STZ)-induced type 2 diabetic mice, as indicated by body weight gain, reduction of blood glucose and plasma insulin, and enhanced sensitivity to insulin. The results of quantitative real-time polymerase chain reaction and Western blot analysis showed that liraglutide upregulated AGT5 expression and promoted the conversion of LC3-I to LC3-II, thus improving the defective autophagy. In addition, we observed that both mRNA and protein expressions of PCNA and Ki-67 were upregulated by liraglutide treatment. Immunocytochemical staining results showed that the number of PCNA- or Ki-67-positive cells in pancreatic islet tissues in the HFD + STZ + liraglutide group were increased compared with the HFD + STZ group.

Conclusions

These results strongly suggest that liraglutide is able to enhance autophagy and promote pancreatic β cell proliferation. This study improves our insights into the mechanism by which liraglutide treatment relieves diabetes, and provides experimental evidence for clinical utilization of liraglutide in type 2 diabetes treatment.

Exenatide Delays the Progression of Nonalcoholic Fatty Liver Disease in C57BL/6 Mice, Which May Involve Inhibition of the NLRP3 Inflammasome through the Mitophagy Pathway

Objective

This study is aimed at investigating whether exenatide (Exe) delays the progression of nonalcoholic fatty liver disease (NAFLD) in C57BL/6 mice by targeting the NLRP3 inflammasome through the autophagy/mitophagy pathway.

Methods

Thirty male C57BL/6 mice were randomly divided into three groups: control group (n = 10), model group (n = 10), and Exe (exenatide) group (n = 10). Mouse models of NAFLD and diabetes were established using a high-fat diet and streptozocin.

Results

The levels of fasting blood glucose (FBG), total cholesterol (TC), and triglyceride (TG) in the serum were significantly reduced after Exe treatment. The body weight, liver weight/body weight, and number of lipid droplets in the liver significantly decreased in Exe-treated mice. Treatment with Exe markedly reduced the levels of liver lipids, malondialdehyde (MDA), and alanine aminotransferase (ALT) in serum and livers. The number of autophagosomes increased significantly in the Exe group. The expression of LC3A/B-II/I, Beclin-1, Parkin, and BNIP3L increased significantly, whereas NLRP3 and IL-1β proteins were suppressed after Exe treatment.

Conclusion

We successfully established a mouse model of NAFLD and diabetes. Exe may reduce oxidative stress injury and inhibit the NLRP3 inflammasome by enhancing the autophagy/mitophagy pathway in liver, which has a protective effect on the liver in NAFLD and diabetes in C57BL/6 mice.

Therapeutic potential of spinal GLP-1 receptor signaling

GLP-1 signaling pathway has been well studied for its role in regulating glucose homeostasis, as well as its beneficial effects in energy and nutrient metabolism. A number of drugs based on GLP-1 have been used to treat type 2 diabetes mellitus. GLP-1R is expressed in multiple organs and numerous experimental studies have demonstrated that GLP-1 signaling pathway exhibits pro-survival functions in various disorders. In the central nervous system, stimulation of GLP-1R produces neuroprotective effects in specific neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease. The preproglucagon neurons located in the brainstem can also produce GLP-1. GLP-1 analogs have a long-acting effect and are able to pass the blood-brain barrier, which probably extends the therapeutic efficacy of GLP-1R activation. Neurodegenerative or traumatic conditions can damage the spinal cord and result in motor and sensory dysfunction. Evidence supports that GLP-1R activation in the spinal cord possesses beneficial effects and significant therapeutic potential. Herein, we review studies that have focused on GLP-1 and the spinal cord, and summarize the expression of GLP-1R and the innervation of PPG neurons in the spinal cord, as well as the potential therapeutic benefits of GLP-1R activation.

A role for Glucagon-Like Peptide-1 in the regulation of β-cell autophagy

Autophagy is a highly conserved intracellular recycling pathway that serves to recycle damaged organelles/proteins or superfluous nutrients during times of nutritional stress to provide energy to maintain intracellular homeostasis and sustain core metabolic functions. Under these conditions, autophagy functions as a cell survival mechanism but impairment of this pathway can lead to pro-death stimuli. Due to their role in synthesising and secreting insulin, pancreatic β-cells have a high requirement for robust degradation pathways. Recent research suggests that functional autophagy is required to maintain β-cell survival and function in response to high fat diet suggesting a pro-survival role. However, a role for autophagy has also been implicated in the pathogenesis of type 2 diabetes. Thus, the pro-survival vs pro-death role of autophagy in regulating β-cell mass requires discussion. Emerging evidence suggests that Glucagon-Like Peptide-1 (GLP-1) may exert beneficial effects on glucose homeostasis via autophagy-dependent pathways both in pancreatic β-cells and in other cell types. The aim of the current review is to: i) summarise the literature surrounding β-cell autophagy and its pro-death vs pro-survival role in regulating β-cell mass; ii) review the literature describing the impact of GLP-1 on β-cell autophagy and in other cell types; iii) discuss the potential underlying mechanisms.

Liraglutide restores chronic ER stress, autophagy impairments and apoptotic signalling in SH-SY5Y cells

Growing evidence suggests that agonists of glucagon-like peptide (GLP-1) receptor exert neuroprotective and neurorestorative effects across a range of experimental models of neuronal degeneration, and, recently, a pilot clinical trial of Liraglutide in Alzheimer’s disease patients showed improvements in cerebral glucose consumption that signifies disease progression. However, the exact underlying mechanism of action remains unclear. Chronic endoplasmic reticulum (ER) stress has recently emerged as a mechanism for neuronal injury, rendering it a potent therapeutic target for acute and chronic neurodegenerative disorders. Here, we investigate the neuroprotective effects of Liraglutide along with the signalling network against prolong ER stress and autophagy impairments induced by the non-competitive inhibitor of sarco/ER Ca²⁺-ATPase, thapsigargin. We show that Liraglutide modulates the ER stress response and elicits ER proteostasis and autophagy machinery homeostasis in human SH-SY5Y neuroblastoma cell line. These effects correlate with resolution of hyper-activity of the antioxidant Nrf2 factor and restoration of the impaired cell viability and proliferation. Mechanistically, Liraglutide engages Akt and signal transducer and activator of transcription 3 (STAT3) signalling to favour adaptive responses and shift cell fate from apoptosis to survival under chronic stress conditions in SH-SY5Y cells.

Liraglutide alleviates H2O2-induced retinal ganglion cells injury by inhibiting autophagy through mitochondrial pathways

Retinal ganglion cells (RGCs), which exist in the inner retina, are the retinal neurons which can be damaged in the early stage of diabetic retinopathy (DR). Liraglutide, a glucagon-like peptide-1 (GLP-1) analog, exerts biological functions by binding the receptor (GLP-1R), the expression of which in RGC-5 cells was first shown by our team in 2012. It was reported that liraglutide prevented retinal neurodegeneration in diabetic subjects. However, the involvement of mechanisms such as autophagy and mitochondrial balance in liraglutide-induced retinal protection is unknown. Here, we aimed to investigate the protective effects of liraglutide and explore the potential mechanisms of liraglutide-induced retinal RGC protection. RGC-5 cells were treated with H₂O₂ and/or liraglutide. Cell viability was detected with the CCK-8 kit. The axon marker GAP43, autophagy and mitophagy indicators LC3A/B, Beclin-1, p62, Parkin, BCL2/Adenovirus E1B 19kDa protein-interacting protein 3-like (BNIP3L) and the key regulator of mitochondrial biogenesis PGC-1α were examined via western blot analysis. Autophagy was also evaluated using the ImageXpress Micro XLS system and transmission electron microscopy (TEM). Reactive oxygen species (ROS), mitochondrial membrane potential and fluorescent staining for mitochondria were also measured using the ImageXpress Micro XLS system. Our results showed that pretreatment with liraglutide significantly prevented H₂O₂-induced cell viability decline, mitochondrial morphological deterioration and induction of autophagy, which appeared as increased expression of LC3 II/I and Beclin-1, along with p62 degradation. Moreover, liraglutide suppressed the H₂O₂-induced decline in GAP43 expression, thus protecting cells. However, rapamycin induced autophagy and blocked the protective process. Liraglutide also provided mitochondrial protection and appeared to alleviate H₂O₂-induced ROS overproduction and a decline in mitochondrial membrane potential, partially by promoting mitochondrial generation and attenuating mitophagy. In conclusion, liraglutide attenuates H₂O₂ induced RGC-5 cell injury by inhibiting autophagy through maintaining a balance between mitochondrial biogenesis and mitophagy.

Microbiome Remodeling via the Montmorillonite Adsorption-Excretion Axis Prevents Obesity-related Metabolic Disorders

Obesity and its related metabolic disorders are closely correlated with gut dysbiosis. Montmorillonite is a common medicine used to treat diarrhea. We have previously found that dietary lipid adsorbent-montmorillonite (DLA-M) has an unexpected role in preventing obesity. The aim of this study was to further investigate whether DLA-M regulates intestinal absorption and gut microbiota to prevent obesity-related metabolic disorders. Here, we show that DLA-M absorbs free fatty acids (FFA) and endotoxins in vitro and in vivo. Moreover, the combination of fluorescent tracer technique and polarized light microscopy showed that DLA-M crystals immobilized BODIPY® FL C16 and FITC-LPS, respectively, in the digestive tract in situ. HFD-fed mice treated with DLA-M showed mild changes in the composition of the gut microbiota, particularly increases in short-chain fatty acids (SCFA)-producing Blautia bacteria and decreases in endotoxin-producing Desulfovibrio bacteria, these changes were positively correlated with obesity and inflammation. Our results indicated that DLA-M immobilizes FFA and endotoxins in the digestive tract via the adsorption-excretion axis and DLA-M may potentially be used as a prebiotic to prevent intestinal dysbiosis and obesity-associated metabolic disorders in obese individuals.

Fatty Liver and Chronic Kidney Disease: Novel Mechanistic Insights and Therapeutic Opportunities

Chronic kidney disease (CKD) is a risk factor for end-stage renal disease (ESRD) and cardiovascular disease (CVD). ESRD or CVD develop in a substantial proportion of patients with CKD receiving standard-of-care therapy, and mortality in CKD remains unchanged. These data suggest that key pathogenetic mechanisms underlying CKD progression go unaffected by current treatments. Growing evidence suggests that nonalcoholic fatty liver disease (NAFLD) and CKD share common pathogenetic mechanisms and potential therapeutic targets. Common nutritional conditions predisposing to both NAFLD and CKD include excessive fructose intake and vitamin D deficiency. Modulation of nuclear transcription factors regulating key pathways of lipid metabolism, inflammation, and fibrosis, including peroxisome proliferator-activated receptors and farnesoid X receptor, is advancing to stage III clinical development. The relevance of epigenetic regulation in the pathogenesis of NAFLD and CKD is also emerging, and modulation of microRNA21 is a promising therapeutic target. Although single antioxidant supplementation has yielded variable results, modulation of key effectors of redox regulation and molecular sensors of intracellular energy, nutrient, or oxygen status show promising preclinical results. Other emerging therapeutic approaches target key mediators of inflammation, such as chemokines; fibrogenesis, such as galectin-3; or gut dysfunction through gut microbiota manipulation and incretin-based therapies. Furthermore, NAFLD per se affects CKD through lipoprotein metabolism and hepatokine secretion, and conversely, targeting the renal tubule by sodium-glucose cotransporter 2 inhibitors can improve both CKD and NAFLD. Implications for the treatment of NAFLD and CKD are discussed in light of this new therapeutic armamentarium.

Inhibition of caspase-9 aggravates acute liver injury through suppression of cytoprotective autophagy

Acute liver disease is characterized by inflammation, oxidative stress and necrosis, which can greatly influence the long term clinical outcome and lead to liver failure or cancer. Here, we initially demonstrated the beneficial role of caspase-9-dependent autophagy in acute liver injury. Treatment with caspase-9 inhibitor z-LEHD-FMK in HepG2 cells, AML12 cells and C57BL/b6N mice exacerbated CCl₄-induced acute hepatocellular damage, and also down-regulated autophagy markers expression levels, indicating that caspase-9 inhibition may aggravate acute liver damage by suppressing cytoprotective autophagy. CCl₄ was used as an acute liver injury inducer which caused oxidative stress and apoptosis through up-regulation of HIF-1α, as well as triggered hepatic inflammation and necroptosis via TLR4/NF-κB pathway. Caspase-9 Thr125 site was firstly phosphorylated by ERK1/2 which subsequently activated the cytoprotective autophagy process to attenuate acute CCl₄ injury. Caspase-9 inhibition further aggravated hepatic necroptosis through NF-κB expression, leading to increased pro-inflammatory mediators levels, suggesting a protective role of caspase-9-dependent autophagy in the inflammatory process as well as its possibility being a new therapeutic target for the treatment of acute liver injury.

Long-term treatment with nicotinamide induces glucose intolerance and skeletal muscle lipotoxicity in normal chow-fed mice: compared to diet-induced obesity

Nicotinamide (NAM), or vitamin B3, is an essential coenzyme for ATP synthesis and an inhibitor of sirtuin 1. Recently, conflicting results were reported regarding the treatment of NAM in type 2 diabetes and obesity. The aim of this study was to determine whether and how long-term treatment with NAM at lower dose would affect insulin sensitivity in mice fed chow diet. We treated mice with NAM (100 mg/kg/day) and normal chow for 8 weeks. Strikingly, NAM induced glucose intolerance and skeletal muscle lipid accumulation in nonobese mice. NAM impaired mitochondrial respiration capacity and energy production in skeletal muscle, in combination with increased expression of the mediators for mitophagy (p62, PINK1, PARK2 and NIX) and autophagy (FOXO3, Bnip3, CTSL, Beclin1 and LC-3b). Next, we treated mice with high-fat diet (HFD) and resveratrol (RSV; 100 mg/kg/day) for 8 weeks. RSV protected against HFD-induced insulin resistance and obesity. HFD increased skeletal muscle lipid content as well as NAM, but this increase was attenuated by RSV. In contrast to NAM, HFD enhanced fatty acid oxidative capacity. Muscle transcript levels of genes for mitophagy and autophagy were largely suppressed by HFD, whereas RSV did not rescue these effects. These differences suggest that skeletal muscle autophagy may represent adaptive response to NAM-induced lipotoxicity, whereas reduced autophagy in skeletal muscle may promote HFD-induced lipotoxicity. Our results demonstrate that chronic NAM supplementation in healthy individuals, although at lower dose than previously reported, is still detrimental to glucose homeostasis and skeletal muscle lipid metabolism.

Liraglutide ameliorates non-alcoholic fatty liver disease by enhancing mitochondrial architecture and promoting autophagy through the SIRT1/SIRT3-FOXO3a pathway

AIM

Overwhelming oxidative stress is implicated as crucial in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Liraglutide, a well-established antidiabetes drug, was recently reported to ameliorate NAFLD with an elusive mechanism. We used a mouse model to examine whether liraglutide could ameliorate NAFLD and explored the possible mechanisms.

METHODS

Twenty C57BL/6J mice were randomly treated with a normal-fat diet or high-fat diet for 16 weeks, then further distributed into four groups and subjected to s.c. injection of liraglutide or saline for 4 weeks. The growth/metabolism, oxidative stress, mitochondrial architecture and autophagy were assessed prospectively at the 20th week.

RESULTS

High-fat diet inducement resulted in severe NAFLD while liraglutide treatment significantly reversed the trend, marked by reduced bodyweight, improved glucose tolerance and liver triglyceride composition. Reduced hepatic malondialdehyde level, increased mRNA and protein levels of CATALASE and MNSOD indicated liraglutide affected both the oxidative and antioxidative process to ameliorate oxidative stress. After liraglutide administration, the upregulated mRNA and protein levels of mitochondrial fission and fusion-related DRP1, OPA1 and respiratory chain-related COMPLEX1, UCP2 demonstrated the enhancement of mitochondrial architecture which may attenuate the generation of reactive oxygen species (ROS), while the diminished mRNA and protein level of P62 and increased levels of Beclin1 and LC3II/I ratio indicated the promoting autophagy, which probably contribute to the ROS elimination. Further, restored protein levels of Sirtuin1/Sirtuin3 and the downstream p-FOXO3a reveal the probable pathways of liraglutide acting on autophagy.

CONCLUSION

Liraglutide diminishes oxidative stress by enhancing mitochondrial architecture and promoting autophagy through the SIRT1/SIRT3-FOXO3a-LC3 pathway to ameliorate diet-induced NAFLD.

Dipeptidyl peptidase-4 inhibitor MK-626 restores insulin secretion through enhancing autophagy in high fat diet-induced mice

Autophagy is cellular machinery for maintenance of β-cell function and mass. The current study aimed to investigate the regulatory effects of MK-626, a dipeptidyl peptidase-4 inhibitor, on insulin secretion through the activation of autophagy in high fat diet-induced obese mice. C57BL/6 mice were fed with a rodent diet containing 45 kcal% fat for 16 weeks to induce obesity and then were received either vehicle or MK-626 (3 mg/kg/day) orally during the final 4 weeks. Mouse islets were isolated. Phosphorylation of serine/threonine-protein kinase mTOR and levels of light chain 3B I (LC3B I), LC3B II, sequestosome-1 (SQSTM1/p62) and autophagy-related protein-7 (Atg7) were examined by Western blotting. Glucagon like-peptide-1 (GLP-1) level and insulin secretion were measured by ELISA. GLP-1 level in plasma was decreased in obese mice, which was elevated by dipeptidyl peptidase-4 inhibitor MK-626. In the islets of obese mice, phosphorylation of mTOR, ratio of LC3B I and LC3B II, and level of p62 were elevated and the expression of Atg7 and insulin secretion were reduced compared to those of C57BL/6 mice. However, such effects were reversed by MK-626. Autophagy activator rapamycin stimulated insulin secretion in obese mice but autophagy inhibitor chloroquine treatment inhibited insulin secretion in obese mice administrated by MK-626. Furthermore, the beneficial effects of MK-626 were inhibited by GLP-1 receptor antagonist exendin 9-39. The present study reveals the activation of autophagy to mediate the anti-diabetic effect of GLP-1.

Liraglutide reduces oxidized LDL-induced oxidative stress and fatty degeneration in Raw 264.7 cells involving the AMPK/SREBP1 pathway

Backgound

Recent studies have suggested a potential role for liraglutide in the prevention and stabilization of atherosclerotic vascular disease. However, the molecular mechanisms underlying the effect of liraglutide on atherosclerosis have not been well elucidated. The purpose of this study was to examine whether liraglutide protects against oxidative stress and fatty degeneration via modulation of AMP-activated protein kinase (AMPK)/sterol regulatory element binding transcription factor 1 (SREBP1) signaling pathway in foam cells.

Methods

Mouse macrophages Raw264.7 cells were exposed to oxidized low density lipoprotein (oxLDL) to induce the formation of foam cells. The cells were incubated with oxLDL (50 µg/mL), liraglutide (0.1, 0.5, 1 and 2 nmol/L) or exendin-3 (9-39) (1, 10 and 100 nmol/L) alone, or in combination. Oil Red O staining was used to detect intracellular lipid droplets. The levels of TG and cholesterol were measured using the commercial kits. Oxidative stress was determined by measuring intracellular reactive oxygen species (ROS), malondialdehyde (MDA) and superoxide dismutase 1 (SOD). Western blot analysis was used to examine the expression of AMPKα1, SREBP1, phosphorylated AMPKα1, phosphorylated SREBP1, glucagon-like peptide-1 (GLP-1) and GLP-1 receptor (GLP-1R).

Results

Oil Red O staining showed that the cytoplasmic lipid droplet accumulation was visibly decreased in foam cells by treatment with liraglutide. The TG and cholesterol content in the liraglutide-treated foam cells was significantly decreased. In addition, foam cells manifested an impaired oxidative stress following liraglutide treatment, as evidenced by increased SOD, and decreased ROS and MDA. However, these effects of liraglutide on foam cells were attenuated by the use of GLP-1R antagonist exendin-3 (9-39). Furthermore, we found that the expression level of AMPKα1 and phosphorylated AMPKα1 was significantly increased while the expression level of SREBP1 and phosphorylated SREBP1 was significantly decreased in foam cells following treatment with liraglutide.

Conclusions

This study for the first time demonstrated that the effect of liraglutide on reducing oxidative stress and fatty degeneration in oxLDL-induced Raw264.7 cells is accompanied by the alteration of AMPK/SREBP1 pathway. This study provided a potential molecular mechanism for the effect of liraglutide on reducing oxidative stress and fatty degeneration.

(Pro)renin receptor regulates autophagy and apoptosis in podocytes exposed to high glucose

High glucose reduces autophagy and enhances apoptosis of podocytes. Previously, we reported that high glucose induced podocyte injury through upregulation of the (pro)renin receptor (PRR). We hypothesized that increasing PRR reduces autophagy and increases apoptosis of mouse podocytes exposed to high glucose via activation of the PI3K/Akt/mTOR signaling pathway. Mouse podocytes were cultured in normal (5 mmol/l) or high (25 mmol/l) d-glucose for 48 h. High glucose significantly increased mRNA and protein levels of PRR, phosphorylation of PI3K/Akt/mTOR, and p62. In contrast, high glucose decreased activation of UNC-51-like kinase-1 (ULK1) by phosphorylating Ser⁷⁵⁷ and protein levels of microtubule-associated protein-1 light chain 3B (LC3B)-II and Lamp-2. Bafilomycin A1 increased LC3BII and p62 accumulation in high-glucose-treated cells. High glucose reduced the autophagic flux. Confocal microscopy studies showed significant reduction in the protein level of LC3B in response to high glucose. Cyto-ID autophagy staining showed a significant decrease in autophagosome formation with high glucose. In the absence of PRR, activation of Akt with sc-79 or mTOR with MHY-1485 increased p62 accumulation. Caspase-3/7 activity and apoptosis monitored by TUNEL assay were significantly increased in podocytes treated with high glucose. PRR siRNA significantly reversed the effects of high glucose. Based on these data, we conclude that high glucose decreases autophagy and increases apoptosis in mouse podocytes through the PRR/PI3K/Akt/mTOR signaling pathway.