Nonalcoholic fatty liver disease (NAFLD) is a known outcome of hepatosteatosis. Free fatty acids (FFA) induce the unfolded protein response (UPR) or endoplasmic reticulum (ER) stress that may induce ...apoptosis. Recent data indicate ER stress to be a major player in the progression of fatty liver to more aggressive lesions. Autophagy on the other hand has been demonstrated to be protective against ER stress-induced cell death. We hypothesized that exendin-4 (GLP-1 analog) treatment of fat loaded hepatocytes can reduce steatosis by autophagy which leads to reduced ER stress-related hepatocyte apoptosis.
Primary human hepatocytes were loaded with saturated, cis- and trans-unsaturated fatty acids (palmitic, oleic and elaidic acid respectively). Steatosis, induced with all three fatty acids, was significantly resolved after exendin-4 treatment. Exendin-4 sustained levels of GRP78 expression in fat-loaded cells when compared to untreated fat-loaded cells alone. In contrast, CHOP (C/EBP homologous protein); the penultimate protein that leads to ER stress-related cell death was significantly decreased by exendin-4 in hepatocytes loaded with fatty acids. Finally, exendin-4 in fat loaded hepatocytes clearly promoted gene products associated with macroautophagy as measured by enhanced production of both Beclin-1 and LC3B-II, markers for autophagy; and visualized by transmission electron microscopy (TEM). Similar observations were made in mouse liver lysates after mice were fed with high fat high fructose diet and treated with a long acting GLP-1 receptor agonist, liraglutide.
GLP-1 proteins appear to protect hepatocytes from fatty acid-related death by prohibition of a dysfunctional ER stress response; and reduce fatty acid accumulation, by activation of both macro-and chaperone-mediated autophagy. These findings provide a novel role for GLP-1 proteins in halting the progression of more aggressive lesions from underlying steatosis in humans afflicted with NAFLD.
The aims of this study were designed to determine whether liraglutide, a long-acting glucagon-like peptide, could reverse the adverse effects of a diet high in fat that also contained trans-fat and ...high-fructose corn syrup (ALIOS diet). Specifically, we examined whether treatment with liraglutide could reduce hepatic insulin resistance and steatosis as well as improve cardiac function. Male C57BL/6J mice were pair fed or fed ad libitum either standard chow or the ALIOS diet. After 8 wk the mice were further subdivided and received daily injections of either liraglutide or saline for 4 wk. Hyperinsulinemic-euglycemic clamp studies were performed after 6 wk, revealing hepatic insulin resistance. Glucose tolerance and insulin resistance tests were performed at 8 and 12 wk prior to and following liraglutide treatment. Liver pathology, cardiac measurements, blood chemistry, and RNA and protein analyses were performed. Clamp studies revealed hepatic insulin resistance after 6 wk of ALIOS diet. Liraglutide reduced visceral adiposity and liver weight (P < 0.001). As expected, liraglutide improved glucose and insulin tolerance. Liraglutide improved hypertension (P < 0.05) and reduced cardiac hypertrophy. Surprisingly, liver from liraglutide-treated mice had significantly higher levels of fatty acid binding protein, acyl-CoA oxidase II, very long-chain acyl-CoA dehydrogenase, and microsomal triglyceride transfer protein. We conclude that liraglutide reduces the harmful effects of an ALIOS diet by improving insulin sensitivity and by reducing lipid accumulation in liver through multiple mechanisms including, transport, and increase β-oxidation.
Background & Aims Epidemiological studies have shown that obesity is a risk factor for hepatocellular carcinoma (HCC). Lower adiponectin levels are associated with poor prognosis in obese HCC ...patients, hence it is plausible that adiponectin acts as a negative regulator of HCC. We investigated the effects of adiponectin on HCC development and its molecular mechanisms. Methods Assays with Huh7 and HepG2 HCC cells were used to examine the signal transduction pathways involved in the protective functions of adiponectin in HCC. These studies were followed by in vivo approaches using HCC xenografts and tumor analysis. Results from in vitro and in vivo findings were corroborated using human HCC tissue microarray and analysis of clinicopathological characteristics. Results Adiponectin increased apoptosis of HCC cells through activation of caspase-3. Adiponectin increased phosphorylation of c-Jun-N-terminal kinase (JNK) and inhibition of c-Jun-N-terminal kinase−phosphorylation inhibited adiponectin-induced apoptosis and caspase-3 activation. Adiponectin increased phosphorylation of 5′-adenosine monophosphate−activated protein kinase and tumor suppressor tuberous sclerosis complex 2 and inhibited mammalian target of rapamycin phosphorylation. Inhibition of 5′-adenosine monophosphate−activated protein kinase phosphorylation not only inhibited adiponectin-induced c-Jun-N-terminal kinase phosphorylation, but also blocked biological effects of adiponectin. Adiponectin substantially reduced liver tumorigenesis in nude mice. Importantly, analysis of adiponectin expression levels in tissue microarray of human HCC patients revealed an inverse correlation of adiponectin expression with tumor size. Conclusions Adiponectin protects against liver tumorigenesis; its reduced expression is associated with poor prognosis in obese patients with HCC.
Obesity is rapidly becoming a pandemic and is associated with increased carcinogenesis. Obese populations have higher circulating levels of leptin in contrast to low concentrations of adiponectin. ...Hence, it is important to evaluate the dynamic role between adiponectin and leptin in obesity‐related carcinogenesis. Recently, we reported the oncogenic role of leptin including its potential to increase tumor invasiveness and migration of hepatocellular carcinoma (HCC) cells. In the present study we investigated whether adiponectin could antagonize the oncogenic actions of leptin in HCC. We employed HCC cell lines HepG2 and Huh7, the nude mice‐xenograft model of HCC, and immunohistochemistry data from tissue‐microarray to demonstrate the antagonistic role of adiponectin on the oncogenic actions of leptin. Adiponectin treatment inhibited leptin‐induced cell proliferation of HCC cells. Using scratch‐migration and electric cell‐substrate impedance‐sensing‐based migration assays, we found that adiponectin inhibited leptin‐induced migration of HCC cells. Adiponectin treatment effectively blocked leptin‐induced invasion of HCC cells in Matrigel invasion assays. Although leptin inhibited apoptosis in HCC cells, we found that adiponectin treatment induced apoptosis even in the presence of leptin. Analysis of the underlying molecular mechanisms revealed that adiponectin treatment reduced leptin‐induced Stat3 and Akt phosphorylation. Adiponectin also increased suppressor of cytokine signaling (SOCS3), a physiologic negative regulator of leptin signal transduction. Importantly, adiponectin significantly reduced leptin‐induced tumor burden in nude mice. In HCC samples, leptin expression significantly correlated with HCC proliferation as evaluated by Ki‐67, whereas adiponectin expression correlated significantly with increased disease‐free survival and inversely with tumor size and local recurrence. Conclusion: Collectively, these data demonstrate that adiponectin has the molecular potential to inhibit the oncogenic actions of leptin by blocking downstream effector molecules. (HEPATOLOGY 2010
Adiponectin is protective against hepatic fibrosis, whereas leptin promotes fibrosis. In HSCs (hepatic stellate cells), leptin signals via a JAK2 (Janus kinase 2)/STAT3 (signal transducer and ...activator of transcription 3) pathway, producing effects that enhance ECM (extracellular matrix) deposition. SOCS-3 (suppressor of cytokine signalling-3) and PTP1B (protein tyrosine phosphatase 1B) are both negative regulators of JAK/STAT signalling, and recent studies have demonstrated a role for adiponectin in regulating SOCS-3 expression. In the present study we investigate mechanisms whereby adiponectin dampens leptin signalling and prevents excess ECM production. We treated culture-activated rat HSCs with recombinant adiponectin, leptin, both or neither, and also treated adiponectin knockout (Ad-/-) and wild-type mice with leptin and/or carbon tetrachloride (CCl4) or saline. We analyse JAK2 and Ob-Rb (long form of the leptin receptor) phosphorylation, and PTP1B expression and activity. We also explore potential mechanisms through which adiponectin regulates SOCS-3-Ob-Rb association. Adiponectin inhibits leptin-stimulated JAK2 activation and Ob-Rb phosphorylation in HSCs, whereas both were increased in Ad-/- mice. Adiponectin stimulates PTP1B expression and activity in vitro, whereas PTP1B expression was lower in Ad-/-mice than in wild-type mice. Adiponectin also promotes SOCS-3-Ob-R association and blocks leptin-stimulated formation of extracellular TIMP-1 (tissue inhibitor of metalloproteinases-1)-MMP-1 (matrix metalloproteinase-1) complexes in vitro. These results suggest two novel mechanisms whereby adiponectin inhibits hepatic fibrosis: (i) by promoting binding of SOCS-3 to Ob-Rb, and (ii) by stimulating PTP1B expression and activity, thus inhibiting JAK2/STAT3 signalling at multiple points.
Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome (MetS). Up to a third of NAFLD subjects are at risk for developing nonalcoholic steatohepatitis (NASH). ...Many rodent models fail to replicate both MetS and NASH. The purpose of this study was to develop a reliable mouse model of NASH and MetS using a diet containing cholesterol, saturated fat and carbohydrate that is reflective of Western diets of North Americans. Experimental design: We used adult male C57BL/6 J 4- to 5-week-old mice and administered a solid diet containing 0.2% cholesterol, 45% of its calories from fat, with 30% of the fat in the form of partially hydrogenated vegetable oil. We also provided carbohydrate largely as high-fructose corn syrup equivalent in water. In a separate cohort, we gave the identical diet in the absence of cholesterol. Glucose and insulin tolerance testing was conducted throughout the feeding period. The feeding was conducted for 16 weeks, and the mice were sacrificed for histological analysis, markers of MetS, liver inflammation, circulating lipids, as well as liver staining for fibrosis and alpha smooth muscle actin (α-SMA). Results: We found that cholesterol significantly increased serum leptin, interleukin-6, liver weight and liver weight/body weight ratio, fibrosis and liver α-SMA. Conclusions: Mice administered a diet accurately reflecting patterns associated with humans afflicted with MetS can reliably replicate features of MetS, NASH and significant liver fibrosis. The model we describe significantly reduces the time by several months for development of stage 3 hepatic fibrosis.
Age related cognitive function (ARCF) is of increasing concern in an aging population. Few studies have examined the relationships between ARCF and antibody expression or blood pressure, particularly ...in older populations. Large sample sizes are needed to elucidate these relationships to inform better strategies for identification and prevention of cognitive decline. The present study was designed to investigate these relationships in Chinese oldest-old and centenarian adults.
A household survey was performed that included 436 centenarians and 520 oldest-old adults (80-99 years) residing in 16 cities and counties of Hainan province, China. ARCF was assessed using the mini-mental state examination.
The median age of participants in this study was 92 years, with a range of 80 to 116 years. Females accounted for 68.5% (655) of the participant pool. Multivariate linear regression analysis showed that age Exp(B): -0.220, 95% confidence interval (CI): -0.270--0.169, female gender Exp(B): -3.459, 95% CI:-4.458--2.460, Han ethnicity Exp(B): -1.732, 95% CI: -2.693--0.772, serum creatinine Exp(B): -0.019, 95% CI: -0.037--0.001, immunoglobulin light chain KAP Exp(B): -0.008, 95% CI: -0.015-0.000, and anti-ribonucleoprotein antibody Exp(B): -6.393, 95% CI: -10.898--1.887 were negatively associated with ARCF (P < 0.05). Coronary artery disease Exp(B): 1.957, 95% CI: 0.170-3.744 and diastolic pressure Exp(B): 0.041, 95% CI: 0.002-0.079 were positively associated with ARCF (P < 0.05).
ARCF was positively associated with diastolic pressure and negatively associated with antibody expression in Chinese oldest-old and centenarian adults.
Neuropeptides are ubiquitous intercellular signaling molecules in the CNS and play diverse roles in modulating physiological functions by acting on specific G-protein coupled receptors (GPCRs). Among ...them, the elevenin signaling system is now believed to be present primarily in protostomes. Although elevenin was first identified from the L11 neuron of the abdominal ganglion in mollusc Aplysia californica, no receptors have been described in Aplysia, nor in any other molluscs. Here, using two elevenin receptors in annelid Platynereis dumerilii, we found three putative elevenin GPCRs in Aplysia. We cloned the three receptors and tentatively named them apElevR1, apElevR2, and apElevR3. Using an inositol monophosphate (IP1) accumulation assay, we demonstrated that Aplysia elevenin with the disulfide bond activated the three putative receptors with low EC50 values (ranging from 1.2 to 25 nM), supporting that they are true receptors for elevenin. In contrast, elevenin without the disulfide bond could not activate the receptors, indicating that the disulfide bond is required for receptor activity. Using alanine substitution of individual conserved residues other than the two cysteines, we showed that these residues appear to be critical to receptor activity, and the three different receptors had different sensitivities to the single residue substitution. Finally, we examined the roles of those residues outside the disulfide bond ring by removing these residues and found that they also appeared to be important to receptor activity. Thus, our study provides an important basis for further study of the functions of elevenin and its receptors in Aplysia and other molluscs.
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•Mechanism between CO3∙- and a representative micropollutant was elucidated.•HAA pathway dominates the CO3∙--mediated degradation of IBU/IBU−.•Inclusion of hydration shell improves ...quality of reactivity evaluation of CO3∙-.•Contribution of CO3∙- to overall removal of micropollutants cannot be overlooked.
Carbonate radical (CO3∙-) is an abundant reactive oxygen species in sunlit surface waters and radical-based treatment systems. The roles of this kosmotropic radical in these aquatic systems have been often overlooked presumably due to its low redox potential and ambiguous solvation mechanism. In this study, CO3∙--mediated oxidation of a frequently detected micropollutant, ibuprofen, was investigated. The results showed that the H-atom abstraction (HAA) pathway dominated the degradation processes regardless of the protonation state. However, without explicitly considering the solvent molecules, the calculated reaction rate constant (k, 1.09 × 107 M−1 s−1) was overestimated by an order of magnitude. With the explicit inclusion of the hydration shell, the calculated k value (5.26 × 105 M−1 s−1) agreed well with the measured one (7.89 × 105 M−1 s−1). Considerable charge transfer was found from the CO3 center to the solvation shells. In addition, the contour plot of CO3∙- contribution to overall elimination of various micropollutants was also constructed. The surface with the contribution greater than 10% includes many micropollutants with electron-rich groups such as thioethers, anilines and phenolates, demonstrating that the role of CO3∙- cannot be overlooked in most sunlit surface waters. These results yield mechanistic insights to the CO3∙--mediated degradation of micropollutants, providing practical guidance for their removal in both natural water systems and engineered water treatment processes.
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