Exendin-4 Inhibits Hepatic Lipogenesis by Increasing β-Catenin Signaling

A model of hepatic steatosis with declined viability and function in a liver-organ-on-a-chip

Nonalcoholic fatty liver disease (NAFLD) begins with benign steatosis caused by ectopic storage of triacylglycerols in the liver. Persistent steatosis, in combination with other genetic and environmental factors, leads to nonalcoholic steatohepatitis (NASH) characterized by functional impairment, inflammation, and fibrosis. However, it remains unclear how persistent steatosis directly contributes to the progression of NAFLD, which may represent a therapeutic target. The organ-on-a-chip (OOC) has emerged as a new culture platform to recapitulate human pathological conditions under which drug candidates can be screened. Here, we developed a simple OOC steatosis model using the Mimetas OrganoPlate with a human liver cell line, HepG2. Treating the HepG2 OOCs with fatty acid overload induced steatosis within 24 h. Moreover, persistent steatosis for 6 days impaired OOC viability and hepatic function, as measured by a WST-8 assay and albumin production, respectively. Lastly, the HepG2 OOCs were exposed to drugs being tested in clinical trials for NAFLD/NASH during the 6-day period. Pioglitazone improved the OOC viability while elafibranor reduced the steatosis in association with reduced viability and albumin production. In conclusion, we show that the HepG2 steatosis OOC model is a useful tool on which the efficacy and toxicity of various therapeutic candidates can be tested.

Targeted MicroRNA Profiling Reveals That Exendin-4 Modulates the Expression of Several MicroRNAs to Reduce Steatosis in HepG2 Cells

Excess hepatic lipid accumulation is the hallmark of non-alcoholic fatty liver disease (NAFLD), for which no medication is currently approved. However, glucagon-like peptide-1 receptor agonists (GLP-1RAs), already approved for treating type 2 diabetes, have lately emerged as possible treatments. Herein we aim to investigate how the GLP-1RA exendin-4 (Ex-4) affects the microRNA (miRNAs) expression profile using an in vitro model of steatosis. Total RNA, including miRNAs, was isolated from control, steatotic, and Ex-4-treated steatotic cells and used for probing a panel of 799 highly curated miRNAs using NanoString technology. Enrichment pathway analysis was used to find the signaling pathways and cellular functions associated with the differentially expressed miRNAs. Our data shows that Ex-4 reversed the expression of a set of miRNAs. Functional enrichment analysis highlighted many relevant signaling pathways and cellular functions enriched in the differentially expressed miRNAs, including hepatic fibrosis, insulin receptor, PPAR, Wnt/β-Catenin, VEGF, and mTOR receptor signaling pathways, fibrosis of the liver, cirrhosis of the liver, proliferation of hepatic stellate cells, diabetes mellitus, glucose metabolism disorder and proliferation of liver cells. Our findings suggest that miRNAs may play essential roles in the processes driving steatosis reduction in response to GLP-1R agonists, which warrants further functional investigation.

GLP-1 Receptor Agonists in Non-Alcoholic Fatty Liver Disease: Current Evidence and Future Perspectives

To date, non-alcoholic fatty liver disease (NAFLD) is the most frequent liver disease, affecting up to 70% of patients with diabetes. Currently, there are no specific drugs available for its treatment. Beyond their anti-hyperglycemic effect and the surprising role of cardio- and nephroprotection, GLP-1 receptor agonists (GLP-1 RAs) have shown a significant impact on body weight and clinical, biochemical and histological markers of fatty liver and fibrosis in patients with NAFLD. Therefore, GLP-1 RAs could be a weapon for the treatment of both diabetes mellitus and NAFLD. The aim of this review is to summarize the evidence currently available on the role of GLP-1 RAs in the treatment of NAFLD and to hypothesize potential future scenarios.

Novel Therapeutic Potentials of Taxifolin for Obesity-Induced Hepatic Steatosis, Fibrogenesis, and Tumorigenesis

The molecular pathogenesis of nonalcoholic steatohepatitis (NASH) includes a complex interaction of metabolic stress and inflammatory stimuli. Considering the therapeutic goals of NASH, it is important to determine whether the treatment can prevent the progression from NASH to hepatocellular carcinoma. Taxifolin, also known as dihydroquercetin, is a natural bioactive flavonoid with antioxidant and anti-inflammatory properties commonly found in various foods and health supplement products. In this study, we demonstrated that Taxifolin treatment markedly prevented the development of hepatic steatosis, chronic inflammation, and liver fibrosis in a murine model of NASH. Its mechanisms include a direct action on hepatocytes to inhibit lipid accumulation. Taxifolin also increased brown adipose tissue activity and suppressed body weight gain through at least two distinct pathways: direct action on brown adipocytes and indirect action via fibroblast growth factor 21 production in the liver. Notably, the Taxifolin treatment after NASH development could effectively prevent the development of liver tumors. Collectively, this study provides evidence that Taxifolin shows pleiotropic effects for the treatment of the NASH continuum. Our data also provide insight into the novel mechanisms of action of Taxifolin, which has been widely used as a health supplement with high safety.

Mroue K, Mall R, Ullah E, S. Al-Akl N, Arredouani A. Investigation of the Effect of Exendin-4 on Oleic Acid-Induced Steatosis in HepG2 Cells Using Fourier Transform Infrared Spectroscopy

Non-alcoholic fatty liver disease (NAFLD) is a common liver lesion that is untreatable with medications. Glucagon-like peptide-1 receptor (GLP-1R) agonists have recently emerged as a potential NAFLD pharmacotherapy. However, the molecular mechanisms underlying these drugs’ beneficial effects are not fully understood. Using Fourier transform infrared (FTIR) spectroscopy, we sought to investigate the biochemical changes in a steatosis cell model treated or not with the GLP-1R agonist Exendin-4 (Ex-4). HepG2 cells were made steatotic with 400 µM of oleic acid and then treated with 200 nM Ex-4 in order to reduce lipid accumulation. We quantified steatosis using the Oil Red O staining method. We investigated the biochemical alterations induced by steatosis and Ex-4 treatment using Fourier transform infrared (FTIR) spectroscopy and chemometric analyses. Analysis of the Oil Red O staining showed that Ex-4 significantly reduces steatosis. This reduction was confirmed by FTIR analysis, as the phospholipid band (C=O) at 1740 cm⁻¹ in Ex-4 treated cells is significantly decreased compared to steatotic cells. The principal component analysis score plots for both the lipid and protein regions showed that the untreated and Ex-4-treated samples, while still separated, are clustered close to each other, far from the steatotic cells. The biochemical and structural changes induced by OA-induced lipotoxicity are at least partially reversed upon Ex-4 treatment. FTIR and chemometric analyses revealed that Ex-4 significantly reduces OA-induced lipid accumulation, and Ex-4 also restored the lipid and protein biochemical alterations caused by lipotoxicity-induced oxidative stress. In combination with chemometric analyses, FTIR spectroscopy may offer new approaches for investigating the mechanisms underpinning NAFLD.

Gryllus bimaculatus De Geer hydrolysates alleviate lipid accumulation, inflammation, and endoplasmic reticulum stress in palmitic acid-treated human hepatoma G2 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Nonalcoholic fatty liver disease (NAFLD) is one of the most common hepatic diseases closely intertwined with saturated fatty acids intake. Therefore, various studies are being conducted to find natural substances to prevent either the onset or progression of NAFLD. According to traditional medicinal literature, it has been reported that Gryllus bimaculatus De Geer (GB) has systemic detoxifying activity; however, the preventive effects of GB on NAFLD have not been elucidated to date.

AIM OF STUDY

To evaluate the potential of GB as a material for the mitigation of NAFLD, we investigated the effects of GB hydrolysates on the hepatic lipid accumulation, inflammation, and endoplasmic reticulum (ER) stress in human hepatoma G2 (Hep G2) cells treated with palmitic acid (PA).

METHODS

Steamed and dried GB was defatted, pulverized, and then lyophilized following hydrolyzation using Neutrase® (GB-N) or Flavourzyme® (GB-F). Hep G2 cells were incubated with GB-N or GB-F at various concentrations (0, 0.25, 0.5, and 1 mg/mL) for 24 h, and then PA was treated for another 24 h.

RESULTS

The GB-N and GB-F significantly prevented the PA-induced intracellular lipid accumulation in the human liver cells (p < 0.05). Moreover, the GB-N and GB-F increased the hepatic cellular viability against the PA-treatment (p < 0.05). In addition, the GB-N and GB-F significantly ameliorated the PA-inducible proinflammatory cytokines mRNA expression, such as tumor necrosis factor-α and interleukin-1β, compared to the PA-treated hepatic cells (p < 0.05). Furthermore, the GB-N and GB-F inhibited the PA-inducible lipogenic mRNA expression, such as fatty acid synthase, sterol regulatory element-binding protein 1c, and peroxisome proliferator-activated receptor-γ (p < 0.05). Moreover, the GB-N and GB-F alleviated the ER stress-related mRNA expression, such as glucose regulatory protein 78 and X-box binding protein increased in PA-treated cells (p < 0.05).

CONCLUSIONS

These results indicate that GB-N and GB-F could be used as materials to prevent the NAFLD onset or progression with alleviating hepatic lipid accumulation, inflammation, and ER stress.

Comparative Transcriptome Analysis Reveals That Exendin-4 Improves Steatosis in HepG2 Cells by Modulating Signaling Pathways Related to Lipid Metabolism

No therapy exists for non-alcoholic fatty liver disease (NAFLD). However, glucagon-like peptide receptor agonists (GLP-1RAs) showed a beneficial effect on NAFLD, although the underpinning mechanisms remain unclear due to their pleiotropic effects. We examined the implicated signaling pathways using comparative transcriptomics in a cell model of steatosis to overcome pleiotropy. We treated steatotic HepG2 cells with the GLP-1RA Exendin-4 (Ex-4). We compared the transcriptome profiles of untreated steatotic, and Ex-4-treated steatotic cells, and used Ingenuity Pathway Analysis (IPA) to identify the signaling pathways and associated genes involved in the protective effect of Ex-4. Ex-4 treatment significantly reduces steatosis. RNA-seq analysis revealed 209 differentially expressed genes (DEGs) between steatotic and untreated cells, with farnesoid X receptor/retinoid X receptor (FXR/RXR) (p = 8.9 × 10−7) activation being the top regulated canonical pathway identified by IPA. Furthermore, 1644 DEGs were identified between steatotic cells and Ex-4-treated cells, with liver X receptor/retinoid X receptor (LXR/RXR) (p = 2.02 × 10−7) and FXR/RXR (p = 3.28 × 10−7) activation being the two top canonical pathways. The top molecular and cellular functions between untreated and steatotic cells were lipid metabolism, molecular transport, and small molecular biochemistry, while organismal injury and abnormalities, endocrine system disorders, and gastrointestinal disease were the top three molecular and cellular functions between Ex-4-treated and steatotic cells. Genes overlapping steatotic cells and Ex-4-treated cells were associated with several lipid metabolism processes. Unique transcriptomic differences exist between steatotic cells and Ex-4-treated steatotic cells, providing an important resource for understanding the mechanisms that underpin the protective effect of GLP-1RAs on NAFLD and for the identification of novel therapeutic targets for NAFLD.

Exendin-4 alleviates steatosis in an in vitro cell model by lowering FABP1 and FOXA1 expression via the Wnt/-catenin signaling pathway

Non-alcoholic fatty liver disease (NAFLD) is the leading chronic liver disease worldwide. Agonists of the glucagon-like peptide-1 receptor (GLP-1R), currently approved to treat type 2 diabetes, hold promise to improve steatosis and even steatohepatitis. However, due to their pleiotropic effects, the mechanisms underlying their protective effect on NAFLD remain elusive. We aimed to investigate these mechanisms using an in vitro model of steatosis treated with the GLP-1R agonist Exendin-4 (Ex-4). We established steatotic HepG2 cells by incubating the cells with 400 µM oleic acid (OA) overnight. Further treatment with 200 nM Ex-4 for 3 h significantly reduced the OA-induced lipid accumulation (p < 0.05). Concomitantly, Ex-4 substantially reduced the expression levels of Fatty Acid-Binding Protein 1 (FABP1) and its primary activator, Forkhead box protein A1 (FOXA1). Interestingly, the silencing of β-catenin with siRNA abolished the effect of Ex-4 on these genes, suggesting dependency on the Wnt/β-catenin pathway. Additionally, after β-catenin silencing, OA treatment significantly increased the expression of nuclear transcription factors SREBP-1 and TCF4, whereas Ex-4 significantly decreased this upregulation. Our findings suggest that direct activation of GLP-1R by Ex-4 reduces OA-induced steatosis in HepG2 cells by reducing fatty acid uptake and transport via FABP1 downregulation.

TMEM88 Modulates Lipid Synthesis and Metabolism Cytokine by Regulating Wnt/β-Catenin Signaling Pathway in Non-Alcoholic Fatty Liver Disease

Objective: To clarify the molecular mechanism of TMEM88 regulating lipid synthesis and metabolism cytokine in NAFLD.

Methods:In vivo, NAFLD model mice were fed by a Methionine and Choline-Deficient (MCD) diet. H&E staining and immunohistochemistry experiments were used to analyze the mice liver tissue. RT-qPCR and Western blotting were used to detect the lipid synthesis and metabolism cytokine. In vitro, pEGFP-C1-TMEM88 and TMEM88 siRNA were transfected respectively in free fat acid (FFA) induced AML-12 cells, and the expression level of SREBP-1c, PPAR-α, FASN, and ACOX-1 were evaluated by RT-qPCR and Western blotting.

Results: The study found that the secretion of PPAR-α and its downstream target ACOX-1 were upregulated, and the secretion of SREBP-1c and its downstream target FASN were downregulated after transfecting with pEGFP-C1-TMEM88. But when TMEM88 was inhibited, the experimental results were opposite to the aforementioned conclusions. The data suggested that it may be related to the occurrence, development, and end of NAFLD. Additionally, the study proved that TMEM88 can inhibit Wnt/β-catenin signaling pathway. Meanwhile, TMEM88 can accelerate the apoptotic rate of FFA-induced AML-12 cells.

Conclusion: Overall, the study proved that TMEM88 takes part in regulating the secretion of lipid synthesis and metabolism cytokine through the Wnt/β-catenin signaling pathway in AML-12 cells. Therefore, TMEM88 may be involved in the progress of NAFLD. Further research will bring new ideas for the study of NAFLD.

Salt-inducible kinase 2 functions as a tumor suppressor in hepatocellular carcinoma

Salt-inducible kinase 2 (SIK2) has been reported to be involved in cancer progression in a dichotomous manner. However, the role and mechanism of action of SIK2 in hepatocellular carcinoma (HCC) progression remain elusive. SIK2 expression in HCC tissues in The Cancer Genome Atlas (TCGA) database was analyzed using the AIPuFu platform. SIK2 expression in HCC cells was examined by quantitative real-time PCR and western blot analysis. The expression of N-cadherin, E-cadherin, β-catenin, and c-Myc was detected by western blot analysis. SIK2 was downregulated in HCC tissues compared with normal patients, and low SIK2 expression was correlated with poor prognosis in HCC patients in TCGA database. SIK2 was lowly expressed in HCC cells than that in normal human liver epithelial cells. SIK2 overexpression inhibited cell proliferation and invasion and promoted apoptosis in HCC cells, while SIK2 silencing exerted the opposite effects. Additionally, SIK2 overexpression inactivated the Wnt/β-catenin pathway in HCC cells, as evidenced by the reduced expression of β-catenin and c-Myc. β-catenin overexpression rescued the inhibitory effects of SIK2 on the malignant properties of HCC cells. Xenograft tumor experiment confirmed that SIK2 suppressed the growth of HCC cells in vivo. In conclusion, SIK2 exerted anti-tumor activity in HCC via inactivating the Wnt/β-catenin signaling pathway.

Comprehensive analysis of LncRNAs expression profiles in an in vitro model of steatosis treated with Exendin-4

Background and aims

The hallmark of non-alcoholic fatty liver disease (NAFLD) is the excessive hepatic lipid accumulation. Currently, no pharmacotherapy exists for NAFLD. However, the glucagon-like peptide-1 receptor agonists have recently emerged as potential therapeutics. Here, we sought to identify the long non-coding RNAs (LncRNAs) associated with the steatosis improvement induced by the GLP-1R agonist Exendin-4 (Ex-4) in vitro.

Methods

Steatosis was induced in HepG2 cells with oleic acid. The transcriptomic profiling was performed using total RNA extracted from untreated, steatotic, and Ex-4-treated steatotic cells. We validated a subset of differentially expressed LncRNAs with qRT-PCR and identified the most significantly enriched cellular functions associated with the relevant LncRNAs.

Results

We confirm that Ex-4 improves steatosis in HepG2 cells. We found 379 and 180 differentially expressed LncRNAs between untreated and steatotic cells and between steatotic and Ex-4-treated steatotic cells, respectively. Interestingly, 22 upregulated LncRNAs in steatotic cells became downregulated with Ex-4 exposure, while 50 downregulated LncRNAs in steatotic cells became upregulated in the presence of Ex-4. Although some LncRNAs, such as MALAT1, H19, and NEAT1, were previously associated with NAFLD, the association of others with steatosis and the positive effect of Ex-4 is being reported for the first time. Functional enrichment analysis identified many critical pathways, including fatty acid and pyruvate metabolism, and insulin, PPAR, Wnt, TGF-β, mTOR, VEGF, NOD-like, and Toll-like receptors signaling pathways.

Conclusion

Our results suggest that LncRNAs may play essential roles in the mechanisms underlying steatosis improvement in response to GLP-1R agonists and warrant further functional studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02885-4.

The Heterogeneity of Lipid Metabolism in Cancer

The study of cancer cell metabolism has traditionally focused on glycolysis and glutaminolysis. However, lipidomic technologies have matured considerably over the last decade and broadened our understanding of how lipid metabolism is relevant to cancer biology [1-3]. Studies now suggest that the reprogramming of cellular lipid metabolism contributes directly to malignant transformation and progression [4, 5]. For example, de novo lipid synthesis can supply proliferating tumor cells with phospholipid components that comprise the plasma and organelle membranes of new daughter cells [6, 7]. Moreover, the upregulation of mitochondrial β-oxidation can support tumor cell energetics and redox homeostasis [8], while lipid-derived messengers can regulate major signaling pathways or coordinate immunosuppressive mechanisms [9-11]. Lipid metabolism has, therefore, become implicated in a variety of oncogenic processes, including metastatic colonization, drug resistance, and cell differentiation [10, 12-16]. However, whether we can safely and effectively modulate the underlying mechanisms of lipid metabolism for cancer therapy is still an open question.

Pyrvinium Treatment Confers Hepatic Metabolic Benefits via β-Catenin Downregulation and AMPK Activation

Genetic evidence has indicated that β-catenin plays a vital role in glucose and lipid metabolism. Here, we investigated whether pyrvinium, an anthelmintic agent previously reported as a down-regulator of cellular β-catenin levels, conferred any metabolic advantages in treatment of metabolic disorders. Glucose production and lipid accumulation were analyzed to assess metabolic response to pyrvinium in hepatocytes. The expression of key proteins and genes were assessed by immunoblotting and RT-PCR. The in vivo efficacy of pyrvinium against metabolic disorders was evaluated in the mice fed with a high fat diet (HFD). We found that pyrvinium inhibited glucose production and reduced lipogenesis by decreasing the expression of key genes in hepatocytes, which were partially elicited by the downregulation of β-catenin through AXIN stabilization. Interestingly, the AMPK pathway also played a role in the action of pyrvinium, dependent on AXIN stabilization but independent of β-catenin downregulation. In HFD-fed mice, pyrvinium treatment led to improvement in glucose tolerance, fatty liver disorder, and serum cholesterol levels along with a reduced body weight gain. Our results show that small molecule stabilization of AXIN using pyrvinium may lead to improved glucose and lipid metabolism, via β-catenin downregulation and AMPK activation.

β-catenin mediates the effect of GLP-1 receptor agonist on ameliorating hepatic steatosis induced by high fructose diet

The hypoglycemic drug GLP-1 receptor agonist can ameliorate hepatic steatosis but the mechanism is not clear. Intake of high fructose leads to non-alcoholic fatty liver disease by stimulating lipid synthesis, and β-catenin is the key molecule for realizing GLP-1 function in extrahepatic tissues; with the discovery of GLP-1 receptor in liver, we speculate that β-catenin might mediate GLP-1 receptor agonist on ameliorating hepatic steatosis induced by high fructose. Wistar rats were fed with high fructose diet for 8 weeks and then treated with GLP-1 receptor agonist exenatide for 4 weeks; the changes of lipid synthesis pathway factors, the expression and nuclear translocation of β-catenin, and the hepatic steatosis of the rats were observed. After the intervention of exenatide, the hepatic steatosis induced by high fructose was improved, the nuclear translocation and expression of β-catenin were facilitated, and the mRNA and protein expression of the upstream regulator SREBP-1 and the downstream key enzymes ACC, FAS and SCD-1 of de novo lipogenesis were down-regulated. GLP-1 receptor agonist may ameliorate hepatic steatosis induced by high fructose by β-catenin regulating de novo lipogenesis pathway. GLP-1 receptor agonist may be a potential new drug for the treatment of non-alcoholic fatty liver disease, and the β-catenin may be an important target for the drug therapy.

Long non-coding RNA HAGLROS regulates lipid metabolism reprogramming in intrahepatic cholangiocarcinoma via the mTOR signaling pathway

Alternation of long non-coding RNA (lncRNA) is implicated in intrahepatic cholangiocarcinoma (ICC) development. HAGLROS is a lncRNA with a length of 699 bp, which is involved in the progression of various cancers. But the mechanism of HAGLROS in ICC remains unknown. In this study, the sh-HAGLROS-1 or sh-HAGLROS-2 was transfected into QBC939 cells, and overexpressing HAGLROS vector was transfected into KMCH cells. HAGLROS expression in ICC tissues and cell lines was detected, and its association with ICC prognosis was further analyzed. Lipid accumulation and lipid-related indicators (TG, LDL-C, TC and HDLC) in QBC939 and KMCH cells were measured. ICC cell viability, invasion and migration were measured. Western blot analysis was used to detect levels of the mTOR axis-related proteins and autophagy-related proteins (LC3I, LC3II, Beclin and P62). The levels of serum lipids and SREBP1 positive expression in transplanted tumors of nude mice were detected. HAGLROS was highly expressed in ICC and negatively correlated with prognosis. QBC939 cells with knocking down HAGLROS exhibited reduced lipid-related protein levels, blocked ICC cellular processes, inactivated mTOR axis, and increased autophagy. QBC939 cells with overexpressing HAGLROS showed opposite trends. The lipid-related protein levels in serum of nude mice and SREBP1 positive expression in transplanted tumors were diminished. Taken together, sh-HAGLROS inactivated the mTOR axis and promoted autophagy, thereby improving lipid metabolism reprogramming in ICC. This study may offer novel ICC treatments.

Exendin‑4 promotes osteogenic differentiation of adipose‑derived stem cells and facilitates bone repair

Inflammation-related bone defects pose a heavy burden on patients and orthopedic surgeons. Although stem-cell-based bone repair has developed rapidly, it is of great significance to characterize bio-active molecules that facilitate bone regeneration. It is reported that a glucagon-like peptide 1 receptor agonist, exendin-4, promoted bone regeneration mediated by the transplantation of adipose-derived stem cells in a metaphyseal defect mouse model of femur injury. However, the underlying mechanism is unclear. Bone imaging, immunohistochemistry real-time PCR and western blot analysis were used in the present study, and the results revealed that exendin-4 increased the transcription of the osteogenic differentiation-related genes and induced osteogenic differentiation in situ. Furthermore, the present data obtained from sorted adipose-derived stem cells revealed that exendin-4 promoted osteogenic differentiation and inhibited adipogenic differentiation in vitro. These findings indicated that exendin-4 facilitates osteogenic differentiation of transplanted adipose-derived stem cells for bone repair and illuminated clinical prospects of both adipose-derived stem cells and exendin-4 in stem-cell-based bone defect repair.

Impact of exenatide on mitochondrial lipid metabolism in mice with nonalcoholic steatohepatitis

Exenatide (Exe) is a glucagon-like peptide (GLP)-1 receptor agonist that enhances insulin secretion and is associated with induction of satiety with weight loss. As mitochondrial dysfunction and lipotoxicity are central features of nonalcoholic steatohepatitis (NASH), we tested whether Exe improved mitochondrial function in this setting. We studied C57BL/6J mice fed for 24 weeks either a control- or high-fructose, high-trans-fat (TFD)-diet (i.e., a NASH model previously validated by our laboratory). For the final 8 weeks, mice were treated with Exe (30 µg/kg/day) or vehicle. Mitochondrial metabolism was assessed by infusion of [13C3]propionate, [3,4-13C2]glucose and NMR-based 13C-isotopomer analysis. Exenatide significantly decreased fasting plasma glucose, free fatty acids and triglycerides, as well as adipose tissue insulin resistance. Moreover, Exe reduced 23% hepatic glucose production, 15% tri-carboxylic acid (TCA) cycle flux, 20% anaplerosis and 17% pyruvate cycling resulting in a significant 31% decrease in intrahepatic triglyceride content (P = 0.02). Exenatide improved the lipidomic profile and decreased hepatic lipid byproducts associated with insulin resistance and lipotoxicity, such as diacylglycerols (TFD: 111 ± 13 vs Exe: 64 ± 13 µmol/g protein, P = 0.03) and ceramides (TFD: 1.6 ± 0.1 vs Exe: 1.3 ± 0.1 µmol/g protein, P = 0.03). Exenatide lowered expression of hepatic lipogenic genes (Srebp1C, Cd36) and genes involved in inflammation and fibrosis (Tnfa, Timp1). In conclusion, in a diet-induced mouse model of NASH, Exe ameliorates mitochondrial TCA cycle flux and significantly decreases insulin resistance, steatosis and hepatocyte lipotoxicity. This may have significant clinical implications to the potential mechanism of action of GLP-1 receptor agonists in patients with NASH. Future studies should elucidate the relative contribution of direct vs indirect mechanisms at play.

Jwa Kum Whan Attenuates Nonalcoholic Fatty Liver Disease by Modulating Glucose Metabolism and the Insulin Signaling Pathway

Over the last decade, the link between nonalcoholic fatty liver disease (NAFLD) and insulin resistance has attracted considerable attention. Caused by chronic hyperglycemic stress, insulin resistance (IR) impairs insulin signal transduction and leads to the development of NAFLD. Jwa Kum Whan (JKW), a herbal formula in Traditional Korean Medicine, consists of two medicinal herbs that possess notable effects against hyperglycemia and IR. In this study, we sought to determine the pharmacological effects of JKW, and the mechanisms responsible, on hepatic steatosis in free fatty acids (FFAs)-stimulated HepG2 cells and in high-fat diet (HFD)-fed obese mice. Treatment with JKW significantly decreased intracellular lipid accumulation in vitro. Furthermore, JKW significantly triggered the phosphorylation of insulin receptor substrate-1 (IRS-1) and phosphoinositide 3-kinase (PI3K) and modulated glucose and lipid metabolism via an AMP-activated protein kinase (AMPK) signaling pathway. Analysis of serum parameters in HFD-fed mice showed that JKW improved glucose levels and insulin resistance index (HOMA-IR). In addition, JKW successfully reduced hepatic triglyceride (TG) and cholesterol accumulation. Our results suggest that JKW alleviates NAFLD by modulating the insulin signaling pathway and glucose metabolism. These findings provide a scientific rationale for the potential use of JKW for the treatment and prevention of NAFLD.

Exendin-4 improves ER stress-induced lipid accumulation and regulates lipin-1 signaling in HepG2 cells

Lipin-1 performs dual function during lipid metabolism, i.e., it functions as a transcriptional coactivator and as a phosphatidate phosphatase during triglyceride biosynthesis. We investigated whether exendin-4 prevented endoplasmic reticulum (ER) stress-induced hepatic steatosis and whether the protective effects of exendin-4 were associated with lipin-1 signaling. Tunicamycin and thapsigargin, ER stress inducers, increased triglycerides (TG) content and expression of genes encoding lipid droplet surface proteins. Exendin-4 decreased the expression of ER stress markers phosphorylated PKR like ER kinase (PERK), phosphorylated inositol-requiring enzyme 1 alpha (IRE1α), and glucose-regulated protein 78 kDa (GRP78) proteins and spliced X-box binding protein 1 (XBP-1s) mRNA and increased the expression of genes encoding lipolytic enzymes hormone-sensitive lipase (HSL) and monoacylglycerol lipase (MGL) and VLDL assembly-associated proteins microsomal triglyceride transfer protein (MTP) and apolipoprotein B (APOB) in tunicamycin-pretreated cells. Moreover, exendin-4 significantly decreased lipin-1β/α ratio by increasing SFRP10 and increased lipin-1 nuclear localization. The decrease in lipin-1β/α ratio was also observed in SIRT1 and AMPK agonist-treated cells. These data suggest that exendin-4 improves ER stress-induced hepatic lipid accumulation by increasing lipolysis and VLDL assembly, which is partially mediated by the regulation of lipin-1 signaling.

Exendin-4 protects mice from D-galactose-induced hepatic and pancreatic dysfunction

Investigations into pharmaceutical intervention of pancreatic and hepatic dysfunction associated with metabolic disturbances have received relatively little attention. The aim of this study was to investigate the protective effects of exendin-4 in mice receiving D-galactose, a reducing sugar that triggers ROS production and inflammatory mediators affecting the pancreas and liver. Exendin-4 is an United States Food and Drug Administration (FDA) approved glucagon-like peptide that increases insulin dependent glycogen synthesis and glucose uptake. Male NMRI mice (20–25 g), 3 months of age, were randomly divided into 6 groups of 12 mice each: control, exendin-4 (1 nmol/kg), exendin-4 (10 nmol/kg), D-galactose, D-galactose + exendin-4 (1 nmol/kg) and D-galactose + exendin-4 (10 nmol/kg). D-galactose (500 mg/kg) was given daily by oral gavage for 6 weeks. During the last 10 days, exendin-4 (1 and 10 nmol/kg) was injected intraperitoneally daily. Glucose, insulin, insulin resistance, lipid profiles, and hepatic enzyme levels significantly increased in the D-galactose group (p < 0.05), along with a significant decrease in superoxide dismutase activity and pancreatic islet insulin secretion (p < 0.05). Exendin-4 decreased D-galactose-induced increases in serum glucose and insulin, insulin resistance, lipid profiles, and hepatic enzymes, and improved pancreatic islet insulin secretion and antioxidant defense status. The results show that exendin-4 can prevent complications in mice with compromised pancreatic and hepatic function. Long term administration of D-galactose in mice may be a useful model to study insulin resistance, metabolic syndrome, and aging.

The protective effects of Zhen-Wu-Tang against cisplatin-induced acute kidney injury in rats

Acute kidney injury (AKI) is a common clinical condition that confers a risk of progression of chronic kidney disease and a high risk of death. The purpose of the current study is to investigate the anti-apoptotic and anti-fibrotic effects of Zhen-Wu-Tang (ZWT) on cisplatin (CIS)-induced renal injury and elucidate the involvement of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), the PI3K/Akt signaling pathway, transforming growth factor (TGF)-β and the Wnt/β-catenin signaling pathway in the positive effects of Zhen-Wu-Tang on the kidneys. Wistar rats were randomly assigned into six groups of 6 rats each as follows: normal control 1; normal control 2; CIS 1 and CIS 2, which received single intraperitoneal injections of CIS (6 mg/kg); CIS+ZWT 4 and CIS+ZWT 10, which received ZWT (1 ml/100 g/day, ig) starting days after the CIS injection for 4 and 10 days, respectively. Hematoxylin-eosin (H&E) staining was performed to identify the amelioration of histopathological changes in the kidneys and apoptosis of the renal proximal tubular cells. Picrosirius red staining was used to evaluate renal fibrosis after ZWT treatment. The relationship between ZWT and the upregulation of Nrf2, phosphorylation of Akt, and the downregulation of TGF-β and WNT/β-catenin were determined by Western blotting. At the end of the experiment, serum was isolated from the orbital blood of rats, and blood urea nitrogen (BUN) and creatinine (Cr) levels were measured. The results showed that ZWT restored the histological alterations, aberrant collagen deposition in the kidneys and the BUN and Cr levels that were increased by CIS. Treatment with ZWT reduced the expression levels of TGF-β and Wnt and increased the expression levels of Nrf2, PI3K and Akt in the CIS-exposed kidney tissues. Furthermore, ZWT downregulated apoptosis and fibrosis by modulating the expression levels of caspase-3, Bax and alpha-smooth muscle actin (α-SMA). In conclusion, this study provides evidence for the anti-fibrotic and anti-apoptotic roles of ZWT in CIS-induced experimental kidney injury.