High-fructose diet stimulates hepatic de novo lipogenesis (DNL) and causes hypertriglyceridemia and insulin resistance in rodents. Fructose-induced insulin resistance may be secondary to alterations of lipid metabolism. In contrast, fish oil supplementation decreases triglycerides and may improve insulin resistance. Therefore, we studied the effect of high-fructose diet and fish oil on DNL and VLDL triglycerides and their impact on insulin resistance. Seven normal men were studied on four occasions: after fish oil (7.2 g/day) for 28 days; a 6-day high-fructose diet (corresponding to an extra 25% of total calories); fish oil plus high-fructose diet; and control conditions. Following each condition, fasting fractional DNL and endogenous glucose production (EGP) were evaluated using [1-13 C]sodium acetate and 6,6-2 H 2 glucose and a two-step hyperinsulinemic-euglycemic clamp was performed to assess insulin sensitivity. High-fructose diet significantly increased fasting glycemia (7 ؎ 2%), triglycerides (79 ؎ 22%), fractional DNL (sixfold), and EGP (14 ؎ 3%, all P < 0.05). It also impaired insulin-induced suppression of adipose tissue lipolysis and EGP (P < 0.05) but had no effect on wholebody insulin-mediated glucose disposal. Fish oil significantly decreased triglycerides (37%, P < 0.05) after high-fructose diet compared with high-fructose diet without fish oil and tended to reduce DNL but had no other significant effect. In conclusion, high-fructose diet induced dyslipidemia and hepatic and adipose tissue insulin resistance. Fish oil reversed dyslipidemia but not insulin resistance. Diabetes

The liver secretes triglyceride-rich VLDLs, and the triglycerides in these particles are taken up by peripheral tissues, mainly heart, skeletal muscle, and adipose tissue. Blocking hepatic VLDL secretion interferes with the delivery of liver-derived triglycerides to peripheral tissues and results in an accumulation of triglycerides in the liver. However, it is unclear how interfering with hepatic triglyceride secretion affects adiposity, muscle triglyceride stores, and insulin sensitivity. To explore these issues, we examined mice that cannot secrete VLDL [due to the absence of microsomal triglyceride transfer protein (Mttp) in the liver]. These mice exhibit markedly reduced levels of apolipoprotein B-100 in the plasma, along with reduced levels of triglycerides in the plasma. Despite the low plasma triglyceride levels, triglyceride levels in skeletal muscle were unaffected. Adiposity and adipose tissue triglyceride synthesis rates were also normal, and body weight curves were unaffected. Even though the blockade of VLDL secretion caused hepatic steatosis accompanied by increased ceramides and diacylglycerols in the liver, the mice exhibited normal glucose tolerance and were sensitive to insulin at the whole-body level, as judged by hyperinsulinemic euglycemic clamp studies. Normal hepatic glucose production and insulin signaling were also maintained in the fatty liver induced by Mttp deletion. Thus, blocking VLDL secretion causes hepatic steatosis without insulin resistance, and there is little effect on muscle triglyceride stores or adiposity.-Minehira, K., S. G. Most of the triglycerides in the plasma are carried by chylomicrons, which are secreted from the intestine, and by VLDLs, which are secreted by the liver (1). The triglycerides within chylomicrons and VLDL are hydrolyzed by lipoprotein lipase along the capillary endothelium, mainly in the heart, skeletal muscle, and adipose tissue (2). The lipids released from triglyceride-rich lipoproteins in capillaries are taken up by surrounding parenchymal cells and stored in triglyceride droplets or used for fuel within mitochondria.We have sought to better define the metabolic impact of the triglyceride secretion from the liver. We reasoned that the delivery of VLDL triglycerides to adipose tissue might have a significant impact on adiposity and on the metabolic activity of adipose tissue. We also suspected that the secretion of triglycerides by the liver might have a significant impact on the stores of triglycerides in skeletal muscle. In the current study, we have begun to address these issues by examining adipose tissue size and activity, as well as skeletal muscle triglyceride stores, in mice that cannot secrete VLDL. For these studies, we took advantage of mice that lack microsomal triglyceride transfer protein (Mttp) in the liver; these mice assemble and secrete chylomicrons normally but cannot assemble triglyceride-rich lipoproteins in the liver.The inability to secrete VLDL is accompanied by hepatic steatosis (3,4). In other settings, hepatic s...

Liver glucose metabolism plays a central role in glucose homeostasis and may also regulate feeding and energy expenditure. Here we assessed the impact of glucose transporter 2 (Glut2) gene inactivation in adult mouse liver (LG2KO mice). Loss of Glut2 suppressed hepatic glucose uptake but not glucose output. In the fasted state, expression of carbohydrate-responsive element-binding protein (ChREBP) and its glycolytic and lipogenic target genes was abnormally elevated. Feeding, energy expenditure, and insulin sensitivity were identical in LG2KO and control mice. Glucose tolerance was initially normal after Glut2 inactivation, but LG2KO mice exhibited progressive impairment of glucose-stimulated insulin secretion even though β cell mass and insulin content remained normal. Liver transcript profiling revealed a coordinated downregulation of cholesterol biosynthesis genes in LG2KO mice that was associated with reduced hepatic cholesterol in fasted mice and reduced bile acids (BAs) in feces, with a similar trend in plasma. We showed that chronic BAs or farnesoid X receptor (FXR) agonist treatment of primary islets increases glucose-stimulated insulin secretion, an effect not seen in islets from Fxr -/-mice. Collectively, our data show that glucose sensing by the liver controls β cell glucose competence and suggest BAs as a potential mechanistic link. IntroductionHepatic glucose metabolism is highly regulated during the fed-tofast transition by changes in plasma levels of insulin and glucagon, but also by the changes in blood glucose concentrations. In the fed state, the presence of high insulin concentrations in the portal circulation favors storage of glucose in the form of glycogen and the use of glucose through the glycolytic pathway for its conversion into fatty acids. Important regulatory events activated during the absorptive phase include the transcriptional induction of glucokinase by insulin and of L-pyruvate kinase by the carbohydrate-responsive element-binding protein (ChREBP), which translocates to the nucleus following its dephosphorylation by a glucose metabolite-activated phosphatase (1). At the same time, glucose inhibits glycogen phosphorylase through inhibition of glycogen phosphorylase phosphatase, whereas glucose-6-phosphate activates glycogen synthase (2), thus favoring glycogen biosynthesis. The combination of insulin-dependent Srebp-1c and glucose-dependent ChREBP activation then induces the expression of lipogenic genes, including Acc, Fas, and Scd1 (1, 3).In the fasted state, the decrease in glycemia reduces the intracellular levels of glucose and glucose-6-phosphate, thereby favoring glycogen degradation and reducing the activation of ChREBP and the expression of L-pyruvate kinase and lipogenic genes. Higher glucagon levels favor the gluconeogenic pathway by inducing the expression of PEPCK and G6Pase that catalyzes the hydrolysis of glucose-6-phosphate into glucose, a reaction that takes place in the lumen of the ER. The last steps of glucose output

Objective: To assess whether b-glucan (which is fermented in the colon) lowers postprandial glucose concentrations through mechanisms distinct from a delayed carbohydrate absorption and inhibits de novo lipogenesis. Design: Administration of frequent small meals each hour over 9 h allows a rate of intestinal absorption to be reached which is independent of a delayed absorption. A group of 10 healthy men received either an isoenergetic diet containing 8.9 gaday b-glucan or without b-glucan for 3 days. On the third day, the diet was administered as fractioned meals ingested every hour for 9 h. Setting: Laboratory for human metabolic investigations. Subjects: Ten healthy male volunteers. Main outcome measures: Plasma glucose and insulin concentrations, glucose kinetics, glucose oxidation, de novo lipogenesis. Results: On the third day, plasma glucose and free fatty acid concentrations, carbohydrate and lipid oxidation, and energy expenditure were identical with b-glucan and cellulose. Plasma insulin concentrations were, however, 26% lower with b-glucan during the last 2 h of the 9 h meal ingestion. Glucose rate of appearance at steady state was 12% lower with b-glucan. This corresponded to a 21% reduction in the systemic appearance rate of exogenous carbohydrate with b-glucan, while endogenous glucose production was similar with both diets. De novo lipogenesis was similar with and without b-glucan. Conclusion: Administration of frequent meals with or without b-glucan results in similar carbohydrate and lipid metabolism. This suggests that the lowered postprandial glucose concentrations which are observed after ingestion of a single meal containing b-glucan are essentially due to a delayed and somewhat reduced carbohydrate absorption from the gut and do not result from the effects of fermentation products in the colon. Descriptors: glucose production; de novo lipogenesis; substrate oxidation

OBJECTIVE: Lipids stored in adipose tissue can originate from dietary lipids or from de novo lipogenesis (DNL) from carbohydrates. Whether DNL is abnormal in adipose tissue of overweight individuals remains unknown. The present study was undertaken to assess the effect of carbohydrate overfeeding on glucose-induced whole body DNL and adipose tissue lipogenic gene expression in lean and overweight humans. DESIGN: Prospective, cross-over study. SUBJECTS AND METHODS: A total of 11 lean (five male, six female, mean BMI 21.070.5 kg/m 2 ) and eight overweight (four males, four females, mean BMI 30.170.6 kg/m 2 ) volunteers were studied on two occasions. On one occasion, they received an isoenergetic diet containing 50% carbohydrate for 4 days prior to testing; on the other, they received a hyperenergetic diet (175% energy requirements) containing 71% carbohydrates. After each period of 4 days of controlled diet, they were studied over 6 h after having received 3.25 g glucose/kg fat free mass. Whole body glucose oxidation and net DNL were monitored by means of indirect calorimetry. An adipose tissue biopsy was obtained at the end of this 6-h period and the levels of SREBP-1c, acetyl CoA carboxylase, and fatty acid synthase mRNA were measured by real-time PCR. RESULTS: After isocaloric feeding, whole body net DNL amounted to 3579 mg/kg fat free mass/5 h in lean subiects and to 4973 mg/kg fat free mass/5 h in overweight subjects over the 5 h following glucose ingestion. These figures increased (Po0.001) to 156721 mg/kg fat free mass/5 h in lean and 64711 mg/kg fat free mass/5 h (Po0.05 vs lean) in overweight subjects after carbohydrate overfeeding. Whole body DNL after overfeeding was lower (Po0.001) and glycogen synthesis was higher (Po0.001) in overweight than in normal subjects. Adipose tissue SREBP-1c mRNA increased by 25% in overweight and by 43% in lean subjects (Po0.05) after carbohydrate overfeeding, whereas fatty acid synthase mRNA increased by 66 and 84% (Po0.05). CONCLUSION: Whole body net DNL is not increased during carbohydrate overfeeding in overweight individuals. Stimulation of adipose lipogenic enzymes is also not higher in overweight subjects. Carbohydrate overfeeding does not stimulate whole body net DNL nor expression of lipogenic enzymes in adipose tissue to a larger extent in overweight than lean subjects.

Background--Reverse cholesterol transport from peripheral tissues is considered the principal atheroprotective mechanism of high-density lipoprotein, but quantifying reverse cholesterol transport in humans in vivo remains a challenge. We describe here a method for measuring flux of cholesterol though 3 primary components of the reverse cholesterol transport pathway in vivo in humans: tissue free cholesterol (FC) efflux, esterification of FC in plasma, and fecal sterol excretion of plasma-derived FC.Methods and Results--A constant infusion of [2,[3][4][5][6][7][8][9][10][11][12][13] C 2 ]-cholesterol was administered to healthy volunteers. Three-compartment SAAM II (Simulation, Analysis, and Modeling software; SAAM Institute, University of Washington, WA) fits were applied to plasma FC, red blood cell FC, and plasma cholesterol ester 13 C-enrichment profiles. Fecal sterol excretion of plasma-derived FC was quantified from fractional recovery of intravenous [2,[3][4][5][6][7][8][9][10][11][12][13] C 2 ]-cholesterol in feces over 7 days. We examined the key assumptions of the method and evaluated the optimal clinical protocol and approach to data analysis and modeling. A total of 17 subjects from 2 study sites (n=12 from first site, age 21 to 75 years, 2 women; n=5 from second site, age 18 to 70 years, 2 women) were studied. Tissue FC efflux was 3.79±0.88 mg/kg per hour (mean ± standard deviation), or %8 g/d. Red blood cell-derived flux into plasma FC was 3.38±1.10 mg/kg per hour. Esterification of plasma FC was %28% of tissue FC efflux (1.10±0.38 mg/kg per hour). Recoveries were 7% and 12% of administered [2,[3][4][5][6][7][8][9][10][11][12][13] C 2 ]-cholesterol in fecal bile acids and neutral sterols, respectively.Conclusions--Three components of systemic reverse cholesterol transport can be quantified, allowing dissection of this important function of high-density lipoprotein in vivo. Effects of lipoproteins, genetic mutations, lifestyle changes, and drugs on these components can be assessed in humans. ( J Am Heart Assoc. 2012;1:e001826 doi: 10.1161/JAHA.112.001826)Key Words: cholesterol efflux • esterification • reverse cholesterol transport • isotope labeling, stable • sterol excretion T he regulation of cellular cholesterol homeostasis is crucial for membrane function and cell survival and is maintained by multiple mechanisms, including control of uptake, synthesis, storage, and efflux. Compared to the pathways of cellular uptake and de novo synthesis of cholesterol, however, less information exists about the control of flux though pathways that remove cholesterol from cells and from the whole organism, 1,2 particularly in humans. [3][4][5] These pathways collectively have been termed reverse cholesterol transport (RCT). RCT is postulated to play a fundamental role in cholesterol homeostasis and distribution among tissues 5 and thereby in the development and reversal of atherosclerosis. 6,7 The atheroprotective effects of high-density lipoprotein cholesterol (HDL-C) in both human and animal studies often hav...

MINEHIRA, KAORI, VINCENT BETTSCHART, HUBERT VIDAL, NATHALIE VEGA, VÉ RONIQUE DI VETTA, VALENTINE REY, PHILIPPE SCHNEITER, AND LUC TAPPY. Effect of carbohydrate overfeeding on whole body and adipose tissue metabolism in humans. Obes Res. 2003;11:1096 -1103. Objective: To evaluate the effect of a 4-day carbohydrate overfeeding on whole body net de novo lipogenesis and on markers of de novo lipogenesis in subcutaneous adipose tissue of healthy lean humans. Research Methods and Procedures: Nine healthy lean volunteers (five men and four women) were studied after 4 days of either isocaloric feeding or carbohydrate overfeeding. On each occasion, they underwent a metabolic study during which their energy expenditure and net substrate oxidation rates (indirect calorimetry), and the fractional activity of the pentose-phosphate pathway in subcutaneous adipose tissue (subcutaneous microdialysis with 1,6 13 C 2 ,6,6 2 H 2 glucose) were assessed before and after administration of glucose. Adipose tissue biopsies were obtained at the end of the experiments to monitor mRNAs of key lipogenic enzymes. Results: Carbohydrate overfeeding increased basal and postglucose energy expenditure and net carbohydrate oxidation. Whole body net de novo lipogenesis after glucose loading was markedly increased at the expense of glycogen synthesis. Carbohydrate overfeeding also increased mRNA levels for the key lipogenic enzymes sterol regulatory element-binding protein-1c, acetyl-CoA carboxylase, and fatty acid synthase. The fractional activity of adipose tissue pentose-phosphate pathway was 17% to 22% and was not altered by carbohydrate overfeeding. Discussion: Carbohydrate overfeeding markedly increased net de novo lipogenesis at the expense of glycogen synthesis. An increase in mRNAs coding for key lipogenic enzymes suggests that de novo lipogenesis occurred, at least in part, in adipose tissue. The pentose-phosphate pathway is active in adipose tissue of healthy humans, consistent with an active role of this tissue in de novo lipogenesis.

In conjunction with the rise in rates of obesity, there has been an increase in the rate of nonalcoholic fatty liver disease (NAFLD). While NAFLD at least partially originates from poor diet, there is a lack of nutritional recommendations for patients with suspected or confirmed diagnosis of NAFLD, beyond eating a healthy diet, increasing physical activity, and emphasising weight loss. The limited current literature suggests that there may be opportunities to provide more tailored dietary advice for people diagnosed with or at risk of NAFLD. Epidemiological studies consistently find associations between whole grain intake and a reduced risk of obesity and related diseases, yet no work has been done on the potential of whole grains to prevent and/or be a part of the treatment for fatty liver diseases. In this review, we examine the potential and the current evidence for whole grains having an impact on NAFLD. Due to their nutrient and phytochemical composition, switching from consuming mainly refined grains to whole grains should be considered as part of the nutritional guidelines for patients diagnosed with or at risk for fatty liver disease.