Sigal Fishman

Glucagon-like peptide-1 reduces hepatic lipogenesis via activation of AMP-activated protein kinase

BACKGROUND & AIMS Glucagon-like peptide-1 (GLP-1), a gut-derived peptide degraded by dipeptidyl peptidase-4 (DPP4), stimulates insulin secretion in response to nutrients, yet its direct effect on the liver is controversial. We investigated the effects of GLP-1 on hepatic fat and glucose metabolism and elucidated its mechanism of action. METHODS Hepatic fat metabolism, including lipogenic enzymes and signal transduction regulators, was assessed in livers of DPP4-deficient rats (DPP4-) with chronically elevated GLP-1 and in GLP-1-treated primary hepatocytes. The effect of chronic elevated GLP-1 on insulin sensitivity was measured using the hyperinsulinemic-euglycemic clamp. RESULTS Normal and high fat diet fed DPP4-rats displayed reduced hepatic triglycerides, accompanied by down-regulation of lipogenesis enzymes and parallel up-regulation of carnitine palmitoyltransferase-1, a key enzyme in fatty acid β-oxidation. In vitro studies demonstrated that these effects were directly induced by GLP-1. Mechanistically, GLP-1 increased cAMP in hepatocytes, resulting in the phosphorylation of cAMP-activated protein kinase (AMPK), a suppressor of lipogenesis. Indeed, hepatocytes expressing a dominant negative Ad-DN-AMPK displayed attenuated GLP-1 effects on AMPK phosphorylation and its downstream lipogenic targets. Importantly, normoglycemic DPP4-rats did not display improved hepatic insulin sensitivity in vivo, suggesting a direct effect of GLP-1 on fat metabolism. Finally, DPP4-rats expressed lower levels of hepatic proinflammatory and profibrotic cytokines in response to nutrient stimuli. CONCLUSIONS GLP-1 suppresses hepatic lipogenesis via activation of the AMPK pathway. GLP-1 inhibitory effects on hepatic fat accumulation and nutrient-induced hepatic proinflammatory response suggest GLP-1 analogs as novel therapies for non-alcoholic fatty liver diseases.

Interleukin-1β May Mediate Insulin Resistance in Liver-Derived Cells in Response to Adipocyte Inflammation

Central obesity is frequently associated with adipose tissue inflammation and hepatic insulin resistance. To identify potential individual mediators in this process, we used in vitro systems and assessed if insulin resistance in liver cells could be induced by secreted products from adipocytes preexposed to an inflammatory stimulus. Conditioned medium from 3T3-L1 adipocytes pretreated without (CM) or with TNFalpha (CM-TNFalpha) was used to treat Fao hepatoma cells. ELISAs were used to assess the concentration of several inflammatory mediators in CM-TNFalpha. CM-TNFalpha-treated Fao cells exhibited about 45% diminution in insulin-stimulated phosphorylation of insulin receptor, insulin receptor substrate proteins, protein kinase B, and glycogen synthase kinase-3 as compared with CM-treated cells, without changes in the total abundance of these protein. Insulin increased glycogenesis by 2-fold in CM-treated Fao cells but not in cells exposed to CM-TNFalpha. Expression of IL-1beta mRNA was elevated 3-fold in TNFalpha-treated adipocytes, and CM-TNFalpha had 10-fold higher concentrations of IL-1beta but not TNFalpha or IL-1alpha. IL-1beta directly induced insulin resistance in Fao, HepG2, and in primary rat hepatocytes. Moreover, when TNFalpha-induced secretion/production of IL-1beta from adipocytes was inhibited by the IL-1 converting enzyme (ICE-1) inhibitor II (Ac-YVAD-CMK), insulin resistance was prevented. Furthermore, liver-derived cells treated with IL-1 receptor antagonist were protected against insulin resistance induced by CM-TNFalpha. Finally, IL-1beta secretion from human omental fat explants correlated with body mass index (R(2) = 0.639, P < 0.01), and the resulting CM induced insulin resistance in HepG2 cells, inhibitable by IL-1 receptor antagonist. Our results suggest that adipocyte-derived IL-1beta may constitute a mediator in the perturbed cross talk between adipocytes and liver cells in response to adipose tissue inflammation.

Curcumin inhibits hepatitis B virus via down-regulation of the metabolic coactivator PGC-1α

Hepatitis B virus (HBV) infects the liver and uses its cell host for gene expression and propagation. Therefore, targeting host factors essential for HBV gene expression is a potential anti‐viral strategy. Here we show that treating HBV expressing cells with the natural phenolic compound curcumin inhibits HBV gene expression and replication. This inhibition is mediated via down‐regulation of PGC‐1α, a starvation‐induced protein that initiates the gluconeogenesis cascade and that has been shown to robustly coactivate HBV transcription. We suggest curcumin as a host targeted therapy for HBV infection that may complement current virus‐specific therapies.

Sequential capsule endoscopy of the small bowel for follow-up of patients with known Crohn's disease

BACKGROUND AND AIMS The aim of this study was to perform sequential small bowel (SB) capsule endoscopy (CE) studies in patients with known active Crohns disease (CD) during different treatments, to characterize the changes in the SB mucosa over time, and to correlate the CE findings with clinical and laboratory parameters of inflammation. METHODS Consecutive patients with known moderately active CD were prospectively recruited. After proven patency with Agile capsule, CE studies were performed at baseline and after 4, 12 and 24 weeks. CE parameters and a Lewis score were calculated. Clinical and laboratory parameters were correlated. A control group of 178 non-CD patients was used for comparisons. RESULTS Thirty-one CD patients were recruited and 19 met the inclusion criteria. A total of 43 CE studies were performed over the time. There was no capsule retention despite a high rate of previous SB surgery. The mean baseline CDAI, IBDQ and Lewis scores were 306±56, 135±26.6 and 1730±1780, respectively. There was no correlation at the baseline between clinical and laboratory parameters (CDAI, CRP, IBDQ) and mucosal disease (Lewis scores). CDAI and IBDQ changes over a period of 4 and 12 weeks did not correlate with the Lewis score. The cecum arrival rate of the CD patients was significantly lower (p=0.0047) and the SB transit time was significantly longer (p=0.005) compared to those of the controls. CONCLUSIONS Sequential CE studies are feasible and safe in CD patients. In patients with complete CE studies, they provide reliable information on mucosal changes in CD and should be considered as an independent and objective follow-up tool in known CD patients.

Balloon dilatation for symptomatic gastric sleeve stricture

During recent years, laparoscopic sleeve gastrectomy (LSG) for morbidly obese patients has been gaining popularity. Several studies have reported that it yields a percentage of weight loss similar to that of Roux-en-Y gastric bypass (RYGB). Moreover, LSG has demonstrated a good safety profile and is not as technically demanding as RYGB. In addition, LSG has fewer late adverse events, such as nutrient and vitamin deficiencies, marginal ulceration, and internal hernia. Last, it leaves the gut in continuity and allows future ERCP without difficulty. Nevertheless, because of a long staple line and altered intragastric pressures, sleeve gastrectomy is prone to some serious adverse events, such as staple line leakage in 1% to 20% of patients, bleeding, and sleeve stricture. The reported prevalence of sleeve stricture is between 0.7% and 4% in different studies. Early strictures are symptomatic in the first 6 weeks after surgery. Strictures may be caused by imbrications of the staple line, overretraction of the greater curvature during stapling, progressive rotation of the staple line, and scarring of the sleeve in a kinked rotation. Whether the size of the bougie is related to the incidence of strictures remains controversial. The incisura angularis is the site most prone to stricture development. Typical symptoms of sleeve stenosis include dysphagia, vomiting, and rapid weight loss. Different therapeutic approaches have been suggested including conservative

Artificial Neural Networks Based Controller for Glucose Monitoring during Clamp Test

Insulin resistance (IR) is one of the most widespread health problems in modern times. The gold standard for quantification of IR is the hyperinsulinemic-euglycemic glucose clamp technique. During the test, a regulated glucose infusion is delivered intravenously to maintain a constant blood glucose concentration. Current control algorithms for regulating this glucose infusion are based on feedback control. These models require frequent sampling of blood, and can only partly capture the complexity associated with regulation of glucose. Here we present an improved clamp control algorithm which is motivated by the stochastic nature of glucose kinetics, while using the minimal need in blood samples required for evaluation of IR. A glucose pump control algorithm, based on artificial neural networks model was developed. The system was trained with a data base collected from 62 rat model experiments, using a back-propagation Levenberg-Marquardt optimization. Genetic algorithm was used to optimize network topology and learning features. The predictive value of the proposed algorithm during the temporal period of interest was significantly improved relative to a feedback control applied at an equivalent low sampling interval. Robustness to noise analysis demonstrates the applicability of the algorithm in realistic situations.

Sortilin deficiency improves the metabolic phenotype and reduces hepatic steatosis of mice subjected to diet-induced obesity

BACKGROUND & AIMS Sortilin traffics newly synthesized molecules from the trans-Golgi apparatus along secretory pathways to endosomes, lysosomes or to the cell surface. Sortilin trafficking of acid sphingomyelinase (aSMase) may regulate ceramide levels, a major modulator of insulin signalling. We therefore tested whether sortilin deficiency reduces hepatic and adipose tissue aSMase activity, improving insulin sensitivity in diet-induced obesity (DIO). METHODS DIO in C57BL/6 (WT) and sortilin(-/-) mice was induced by high-fat diet feeding for 10 weeks. RESULTS Sortilin(-/-) mice gained less body weight and less visceral fat, despite similar food intake compared to WT type mice and had enhanced glucose uptake in insulin tolerance tests, which was further corroborated by enhanced hepatic pAkt expression. Sortilin deficiency led to attenuated hepatic steatosis, reduced expression of genes involved in lipogenesis, ceramide synthesis and inflammatory cytokine production and reduced activity of ceramide synthase 5/6 (CerS5/6). Sortilin(-/-) mice had reduced hepatic aSMase activity under both steady-state and DIO. Likewise, sortilin(-/-) hepatocytes displayed hypersensitivity to insulin, due to enhanced insulin receptor downstream signalling. In adipose tissue, sortilin(-/-) mice exhibited lower expression of inflammatory cytokines and lower expression and activity of CerS5/6. As in liver, adipose tissue displayed increased insulin signalling, accompanied by attenuated aSMase activity. CONCLUSIONS Sortilin deficiency induces a beneficial metabolic phenotype in liver and adipose tissue upon DIO, mediated in part by reduced aSMase activity.

Long-Acting Glucose-Dependent Insulinotropic Polypeptide Ameliorates Obesity-Induced Adipose Tissue Inflammation

Obesity induces low-grade chronic inflammation, manifested by proinflammatory polarization of adipose tissue innate and adaptive resident and recruited immune cells that contribute to insulin resistance (IR). The glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone that mediates postprandial insulin secretion and has anabolic effects on the adipose tissue. Importantly, recent evidence suggested that GIP is a potential suppressor of inflammation in several metabolic models. In this study, we aimed to investigate the immunoregulatory role of GIP in a murine model of diet-induced obesity (DIO) using the long-acting GIP analog [d-Ala2]GIP. Administration of [d-Ala2]GIP resulted in adipocytes of increased size, increased levels of adipose tissue lipid droplet proteins, indicating better lipid storage capacity, and reduced adipose tissue inflammation. Flow cytometry analysis revealed reduced numbers of inflammatory Ly6Chi monocytes and F4/80hiCD11c+ macrophages, associated with IR. In addition, [d-Ala2]GIP reduced adipose tissue infiltration of IFN-γ–producing CD8+ and CD4+ T cells. Furthermore, [d-Ala2]GIP treatment induced a favorable adipose tissue adipokine profile, manifested by a prominent reduction in key inflammatory cytokines (TNF-α, IL-1β, IFN-γ) and chemokines (CCL2, CCL8, and CCL5) and an increase in adiponectin. Notably, [d-Ala2]GIP also reduced the numbers of circulating neutrophils and proinflammatory Ly6Chi monocytes in mice fed regular chow or a high-fat diet. Finally, the beneficial immune-associated effects were accompanied by amelioration of IR and improved insulin signaling in liver and adipose tissue. Collectively, our results describe key beneficial immunoregulatory properties for GIP in DIO and reveal that its augmentation ameliorates adipose tissue inflammation and improves IR.

The metabolic regulator PGC-1α links hepatitis C virus infection to hepatic insulin resistance

BACKGROUND & AIMS Chronic hepatitis C virus (HCV) infection is strongly associated with insulin resistance and diabetes mellitus. Peroxisome proliferator-activated receptor-gamma co-activator 1α (PGC-1α) is a transcriptional co-activator involved in the initiation of gluconeogenesis in the liver. Increased hepatic expression of PGC-1α has been implicated in insulin resistance. We investigated whether modulation of PGC-1α levels following HCV infection underlies HCV-associated hepatic insulin resistance. METHODS HCV genomes were expressed in hepatoma cells followed by analysis of PGC-1α and gluconeogenesis levels. RESULTS PGC-1α was robustly induced in HCV infected cells. PGC-1α induction was accompanied by an elevated expression of the gluconeogenic gene glucose-6 phosphatase (G6Pase) and increased glucose production. The induction of gluconeogenesis is HCV dependent, since interferon treatment abolishes PGC-1α and G6Pase elevation and decreases glucose output. Moreover, PGC-1α knockdown resulted in a significant reduction of G6Pase levels in HCV full length replicon cells, emphasizing the central role of PGC-1α in the exaggerated gluconeogenic response observed in HCV patients. Treatment of HCV replicon cells with the antioxidant N-acetylcysteine resulted in reduction of PGC-1α levels, suggesting that HCV-induced oxidative stress promoted PGC-1α upregulation. Finally, both PGC-1α and G6Pase RNA levels were significantly elevated in liver samples of HCV infected patients, highlighting the clinical relevance of these results. CONCLUSIONS PGC-1α is robustly induced following HCV infection, resulting in an upregulated gluconeogenic response, thereby linking HCV infection to hepatic insulin resistance. Our results suggest that PGC-1α is a potential molecular target for the treatment of HCV-associated insulin resistance.

Heparin-derived disaccharides modulate proliferation and Erb-B2–mediated signal transduction in colon cancer cell lines

Organ‐specific extracellular matrix (ECM) determines metastasis formation by regulating tumor cell proliferation. Hepatocyte‐derived ECM enhances proliferation of colon cancer cell lines by increasing expression of tyrosine kinase receptors of the erb‐B family. The active components in the ECM are the heparan sulfates, which are highly heterogenous in their chemistry and size. We determined the effect of heparan sulfate disaccharides, of defined chemistry and present in high amounts in the liver heparan sulfate chains, on the proliferation of colon cancer cell lines and investigated the mechanism involved. The low‐metastatic cell line KM12 was stimulated to proliferate by a highly sulfated disaccharide, found in the highest amounts in hepatocyte‐derived heparan sulfate. Growth of the highly metastatic cell line KM12SM was inhibited by the second most common disaccharide in hepatocyte‐derived heparan sulfate. The effect of both disaccharides was not accompanied by changes in the expression of erb‐B1, erb‐B2, erb‐B3 or heregulin‐α. We determined whether the disaccharides modified the signal‐transduction pathways mediated by the erb‐B receptors. The erb‐B2‐specific tyrosine kinase inhibitor AG825 abolished the enhancement of KM12 cell proliferation by the stimulatory disaccharide. This disaccharide increased tyrosine phosphorylation of erb‐B1 and erb‐B2 receptors, effects that were abolished by AG825. Moreover, the disaccharide caused increased expression of cyclin D1 and of activated MAP kinase, again reduced in the presence of the inhibitor AG825. The growth‐inhibitory disaccharide reduced phosphorylation of erb‐B1, but not of erb‐B2, receptors in KM12SM cells. In conclusion, not only hepatocyte‐derived heparan sulfate but also disaccharide molecules derived from heparan sulfate can affect colon cancer cell proliferation. Their effect is mediated by modulation of the erb‐B signal transduction.